Chairs
Eduard Arzt, Max-Planck-Inst
Theodore Kamins, Hewlett Packard
Carl Thompson, MIT
* Invited paper
SESSION A1: MICROSTRUCTURAL EVOLUTION I
Chairs:
Michael Hirscher and Carl V. Thompson
Tuesday Morning, December 1,
1998
Salon A/B (M)
8:30 AM
A1.1
EVOLUTION OF STRESS AND MICROSTRUCTURE DURING DEPOSITION OF THIN METAL FILMS. S.
Hearne 1, E. Chason2, J. Floro2, J. Hunter2, I. Tsong
1; 1Arizona State University, Tempe, AZ; 2 Sandia National
Laboratories, Albuquerque, NM.
Understanding the
evolution of microstructure is critical for control of the electrical
and mechanical properties of thin films. We have developed a
capacity for studying simultaneous evolution of film microstructure
and stress in real-time during deposition of Ag on SiO2. In situ
X-ray reflectivity has been combined with a Multiple Optical beam
Stress Sensor (MOSS) to provide real-time measurements of the film's
surface roughness, thickness, and stress. In situ X-ray diffraction
provides measurements of film texture. We have used this new
capability to investigate the dependence of nucleation rate, film
coalescence, and film stress as functions of deposition rate, and
temperature. A simple analytical model has been developed to
simulate the microstructural evolution during deposition. In
combination with kinetic Monte Carlo simulations these studies are
being used to increase the understanding of film microstructural
evolution from nucleation, through coalescence, to continuous film
growth.
Sandia is a multiprogram laboratory operated by Sandia Corporation, A
Lockheed Martin Company, for the United States Department of Energy
under Contract DE-AC04-94AL85000.
8:45 AM
A1.2
POLYCRYSTALLINE GROWTH REGIMES IN
HOT WIRE CHEMICAL VAPOR DEPOSITION. R.E.I. Schropp and
J.K. Rath, Utrecht University, Debye Institute, Utrecht, THE
NETHERLANDS.
Hot Wire Chemical Vapor Deposition has
recently advanded to a stage where it yields high quality
fine-grained polycrystalline silicon thin films at low temperature
(< 500C). Films grown with highly hydrogen-diluted silane
show immediate nucleation of crystals. The crystals have random
orientation. XTEM and HREM show interconnected voids throughout the
thickness of the films leading to severe post-oxidation. Instead,
films grown with low hydrogen dilution have a compact bulk structure
which eliminates oxygen incorporation (5 x^18cm^-3; SIMS) and result in a low defect density (8 x
1016 cm-3; ESR). The complete coalescence of grains is
evident from the fact that the SiH stretching mode only absorbs at
2000 cm-1, and from the high temperature evolution (
600C). The crystals have purely (220) orientation, but the
initial growth shows an incubation phase of amorphous material. For
devices such as TFTs and thin film crystalline solar cells, entirely
crystalline film growth as well as high quality are desirable. In
this paper we discuss the successful integration of the two
differently hydrogen-diluted growth regimes into a profiled growth
sequence to yield an entirely polycrystalline thin film. The thin
film grows selectively along the (220) direction even though the seed
layer has random orientation.
Thin film solar cells have been made on stainless steel foil. Only
solar cells incorporating a profiled growth sequence have low
recombination losses and good power conversion characteristics. The
devices further benefit from the optical enhancement due to the
surface texture, leading to high generated current densities (> 20
mA/cm2) despite a small total thickness (< 2
m).
9:00 AM
A1.3
NUCLEATION OF CVD ALUMINUM ON
TITANIUM NITRIDE, TANTALUM NITRIDE, AND TITANIUM-TUNGSTEN SURFACES.
B.R. Rogers , Motorola, Inc., Mesa, AZ; T.S. Cale, Dept.
of Chemical Engineering, Rensselaer Polytechnic Institute, Troy, NY.
The rough surface of chemical vapor deposited (CVD)
aluminum thin film is one technological problem that needs to be
resolved before CVD aluminum can be used in microelectronic device
processing. The surface roughness of CVD aluminum thin films is at
least partially determined by the material on which it is deposited.
This work demonstrates that the nucleation of dimethylaluminum
hydride-sourced CVD aluminum is distinctly different on TiN, Ti-W and
TaN surfaces. High magnification scanning electron micrographs of
TiN, Ti-W and TaN surfaces exposed to identical process conditions
were used to determine the aluminum island shape, island size
distributions, the fraction of surface covered by islands and island
density on each surface.
Islands formed on both TaN and Ti-W surfaces were faceted, while
those formed on TiN had smooth surfaces. Surface coverages and
densities of islands formed on TiN were an order of magnitude higher
that those formed on TaN and Ti-W under similar processing
conditions. Arrhenius plots of deposition rate show that CVD of Al
onto TaN and Ti-W surfaces is much more thermally activated than onto
TiN surfaces.
Possible causes of these differences include both physical and
electronic characteristics of the metal surfaces. The possible
correlation of barrier metal surface roughness to nucleation is
examined. Also, the role of the surfaces' electronic
characteristics, such as interstitial electron density and number of
partially filled d electron-orbitals on the nucleation of CVD
aluminum from DMAH is discussed.
9:15 AM A1.4
MONOMER
DIFFUSION AND NUCLEATION OF ISLANDS ON POLYCRYSTALLINE SUBSTRATES.
C. Eisenmenger-Sittner , A. Bergauer, Institut fuer
Angewandte und Technische Physik, Technische Universitaet Wien,
Vienna, AUSTRIA.
For Physical Vapor Deposition (PVD)
processes considerable experimental and theoretical work has been
done concerning monomer diffusion as well as nucleation and growth of
islands on atomically flat substrates. These elementary steps of film
formation can be modeled by Kinetic Monte Carlo (KMC) simulations.
Work on island nucleation and growth on polycrystalline substrates,
however, is sparse.
In this paper we present the results of Kinetic Monte Carlo
simulations of monomer diffusion on polycrystalline substrates. The
simulations consist of two steps: first a polycrystalline surface is
generated by a Potts model of grain coarsening. Then different
diffusion barriers for monomer diffusion are assigned to the
different grains. The diffusion length of monomers is monitored as a
function of the crystallinity of the substrate. Higher crystallinity
(i. e. the existence of large monocrystalline grains) leads to higher
diffusion lengths.
In thin film growth the crystallinity of a surface can be influenced
by the thickness of the film. The higher the film thickness the more
large grains exist due to coarsening effects. Therefore, if a highly
mobile, island forming material is deposited on underlayers of
varying crystallinity the island density should be lowered with
increasing underlayer thickness due to the existence of large
monocrystalline grains. This effect was in fact observed for tin (Sn)
deposited on aluminum (Al) underlayers. Because the island density is
related to the monomer diffusion length the experimental results can
be compared to the simulations. Good qualitative agreement of
simulation and experiment is found.
9:30 AM
A1.5
DEVELOPMENT OF FINE
MICROSTRUCTURES IN THIN FILMS. C. L. Bauer , Department
of Materials Science & Engineering, Carnegie Mellon University,
Pittsburgh, PA.
Development of fine microstructures
in thin films usually involves (1) nucleation of separate islands on
a suitable substrate, (2) island growth and coarsening to form a
continuous polycrystalline film, and (3) subsequent grain evolution
to produce a thicker film, characterized by unique distributions of
grain size, shape, crystallographic orientation (macrotexture) and
boundary misorientation (microtexture). Each of these processes is
analyzed sequentially through application of fundamental principles,
incorporating deposition flux, surface diffusion and capillarity, as
well as other thermodynamic and kinetic phenomena. First, a
fundamental expression for island density (consequent grain size) is
derived and analyzed; then, minimum thickness of a continuous film
(island coalescence) is considered; finally, dynamic evolution of
grain size, shape and distribution (texture), based on assumed
thermodynamic equilibrium at the growing surface, is developed.
Thereafter, results stemming from each process are compared with
existing experimental observations in order to achieve a broader
fundamental appreciation for development of fine microstructures in
thin films.
Research supported, in part, by the National Science Foundation under
Award DMR-9319896 and DMR-9632556 (MRSEC Program).
9:45 AM A1.6
ROLE OF
GRAIN GROWTH ON MICROSTRUCTURAL DEVELOPMENT DURING DEPOSITION OF THIN
FILMS. John Sanchez, Jr. , Adtiana Lita, University of
Michigan, Dept. of Materials Science and Engineering, Ann Arbor, MI.
The development of deposited film microstructure has
considerable importance for many technologies such as microelectronic
and thin film magnetic data storage devices. We describe the effects
of grain growth during the sputter deposition of 0.1m to 1.0
m thick Al films on the crystallographic texture and surface
structure. The Al columnar grain size varied with thickness (h) d
h0.9, determined by plan view transmission electron
microscopy. The Al (111) fiber texture, determined by quantitative
x-ray pole figure analysis, evolved from an initially random film
(below 0.2 m thickness) to above 90% Al (111) volume fraction at
1.0 m thickness. In addition the root-mean-square surface
height variation (ÏRMSÓ roughness) initially decreased with thickness
below 0.3 µm, and thereafter increased monotonically as the film
thickness reached 1.0 µm. The transition from random to (111) fiber
textured and initial smoothing of the film surface are described in
terms of the grain growth kinetics which are shown to dramatically
alter film structure early in the film formation process. A model
for film structural evolution based on processing and substrate
effects will be discussed.
10:00 AM
A1.7
SIMULATION OF GRAIN GROWTH DURING
DEPOSITION OF POLYCRYSTALLINE THIN FILMS. S.C. Seel and
C.V. Thompson* Dept. of Materials Science and Engineering M.I.T.,
Cambridge, MA (*on leave, Max-Plank Institut fur Metallforschung,
Stuttgart, GERMANY).
A computer simulation of grain
growth in two dimensions has been used to model microstructural
evolution during deposition of thin films. When thin films are
deposited under conditions which allow grain boundary motion, grain
size coarsening will occur during film thickening, with grain
boundaries that traverse the film thickness. We have included the
effects of grain boundary grooving at the film surface by imposing a
film thickness dependent stagnation condition on grain boundary
motion. By varying the deposition rate for a given grain boundary
mobility, we were able to simulate the dynamic effects of grain
growth during deposition. We find that the median grain size scales
with the film thickness to a power equal to or less than one,
depending on the relative values of the deposition rate and the
boundary mobilities. We also find that the grain sizes are
lognormally distributed except for the smallest grains. Both results
are similar to experimentally observed microstructural features of
as-deposited films of high atomic mobility materials. By comparing
simulated grain-size-to-film-thickness scaling with scaling observed
in experiments carried out at different deposition rates, the average
grain boundary mobility can be extracted.
10:45 AM
*A1.8
TEXTURE EVOLUTION IN ALUMINUM
AND COPPER FILMS. Walter L. Brown , Bell Labs/Lucent
Technologies, Murray Hill, NJ.
The texture of
aluminum and copper thin films that are of primary interest for
multilevel metal interconnects on ULSI chips is thought to be
important for the reliability of the sub-micron interconnect
structures that are fabricated. Aluminum conducting lines are usually
formed through a subtractive process of reactive ion etching from
blanket deposited films. The texture of the lines is thus intimately
related to the texture of the blanket films which, in turn, is
strongly dependent on the texture of the refractory metal barrier
film on which the aluminum is deposited. The ``inheritance'' of
sputter deposited Al(111) texture from the texture of underlying Ti
or Ti/TiN has been clearly established. The case of copper is
different. The metal architecture is now typically damascene rather
than subtractive, the metal being deposited into trenches which have
been fabricated by reactive ion etching into a blanket insulator
(typically SiO2). The trenches are coated with a barrier layer
(Ta or TaN, for example) and with a seed layer of Cu and are then
filled with Cu by electroplating. The evolution of texture in this
case is much more complex since the walls of the trenches as well as
their bottoms and the top of the insulator surrounding the trenches
are all involved in texture development. The current state of
experiments and their interpretation for Cu damascene will be
discussed and compared with the case of subtractive Al.
11:15 AM
A1.9
EFFECTS OF SEED LAYER TEXTURE AND
SURFACE ROUGHNESS ON THE MICROSTRUCTURE OF ELECTROPLATED COPPER
FILM. Haebum Lee 1, Sergey D. Lopatin2, Takeshi
Nogami, and S. Simon Wong1, 1Stanford University, Center for
Integrated Systems, Stanford, CA; 2Advanced Micro Devices,
Sunnyvale, CA.
The electromigration lifetime of
polycrystalline Cu metal line is known to be highly dependent on the
microstructure of the film; the lifetime increases with larger median
grain size and a stronger texture. Therefore, microstructure control
of Cu film is critical to the optimization of Cu metallization
process. Recently, electroplating has been considered as the most
promising technique for Cu metallization mainly due to the advantages
of low cost, high manufacturability, good via/trench filling
capability, and formation of copper films of high quality including
very large grain size and a strong (111) texture. This paper focuses
on understanding the microstructure of electroplated Cu films, and
the correlation with the texture and surface condition of the various
Cu seed layers.
100nm thick thermal oxide was grown on n-type (100) Si wafers and
25-50nm thick barrier layers and Cu seed layers were deposited on
SiO2. In order to determine the effects of seed thickness and
surface condition on the properties of plated films, the seed layers
were deposited with different thickness by both PVD and CVD. 1m
thick electroplated Cu was then deposited at a current density of
10mA/cm2, with no additives in the plating solution. Current
distribution was optimized to obtain <3% variation of electrical
uniformity across the electroplated films.
TEM(Transmission Electron Microscopy), AFM(Atomic Force Microscopy)
and X-Ray Bragg-Brentano scan experiments demonstrate that the grain
size and texture of plated top layer is highly dependent on the
roughness and texture of the underlying seed layer, and the surface
roughness of the seed layer is related to the texture of the layer
itself, which greatly affects the texture of the plated film. The
films plated on smooth and strongly textured seed layers achieve a
median grain size larger than 1m and a strong (111) texture in
as-deposited films, and the grain size extends to 20 m for some
samples. The films on rough and weakly textured seed layers have
grains of 0.08-0.15 m and weak (111) texture. Some films show
bimodal grain size distributions, which is possibly an indication of
secondary grain growth occurring during the deposition.
The effects of the seed layer thickness on the texture of the plated
film were also examined. Seed layers with thickness of 200, 500, and
1000 were investigated. PVD seed layers all show a very strong
(111) texture with no traceable existence of (200) texture while CVD
seeds show far more random orientation of grain textures. Although no
noticeable variation of texture with varying seed thickness is
observed in both cases, AFM roughness measurements reveal that the
surface becomes rougher as the thickness is increased for both PVD
and CVD seed layers. Furthermore, the CVD seeds have much rougher
surface than the PVD ones. X-ray analysis of electroplated films
demonstrates that the films plated on smooth and strongly textured
PVD seeds have very strong (111) texture, while the films on rough
and weakly-textured CVD seeds form much more random texture.
Noticeably, the ratio of (111) to (200) X-ray peaks reduces greatly
as the seed thickness increases despite the minor variation of the
seed texture. This indicates that surface roughness is a dominant
factor affecting the plated film texture. The degradation of
texture in films plated on a rough seed surface is believed to be due
to the film growth on more randomly oriented faces of the surface
layer.
11:30 AM
A1.10
CHARACTERIZATION OF THE
MICROSTRUCTURE AND CHEMISTRY OF A Ti/Cu/Ti THIN-FILM DEPOSITED ON A
SILICON WAFER BY ELECTRON BEAM EVAPORATION. John M.
Phelps , David T. Read, National Institute of Standards and
Technology, Materials Reliability Division, Boulder, CO.
A 3 layer thin-film consisting of 0.05m Ti,
1.0m Cu, and 0.05m Ti was deposited onto a silicon wafer.
This sample is the type ultimately used to perform thin-film tensile
tests to determine the stress Ò strain behavior for the thin-film
(Read, 1998). These tests have shown that the thin-films typically
have yielding strengths greater than that you would expect for the
bulk material. Characterization of the thin-film microstructure and
chemistry by the Analytical Electron Microscope (AEM) required
modifications and improvements to existing sample preparation
techniques (Phelps, 1998). Suitable samples for analysis were made,
and the analysis shows that the average grain diameter is less than
that of the film thickness, and the grain structure is something
between zone 1 and zone T as described by Smith, 1995. Energy
Dispersive Spectrometery (EDS) of grains in the cross section of the
sample shows that trace amounts of Ti are present. The Ti is thought
to have diffused into the Cu during the deposition process. The
trace amounts of Ti in the grains in conjunction with a grain
diameter that is less than the total film thickness may inhibit
dislocation motion that would help to explain the increase in yield
strength we observe.
11:45 AM
A1.11
IMPROVED MICROSTRUCTURE BY
PROGRAMMED RATE CHEMICAL VAPOR DEPOSITION PROCESSES.
Daewon Yang , Raj Jonnalagadda, Arizona State Univ, Center
for Solid State Electronics Research, Tempe, AZ; Bridget R. Rogers,
Motorola, Materials Characterization Lab, Mesa, AZ; Joseph T.
Hillman, Robert F. Foster, Tokyo Electron Arizona, Gilbert, AZ;
Timothy S. Cale, Rensselaer Polytechnic Institute, Dept of Chemical
Engineering, Troy, NY.
As device sizes shrink to
deep sub-micron scales, interconnect reliability (e.g.,
electromigration) and interconnect resistance become increasingly
important. The grain sizes of chemical vapor deposited (CVD) films
can be large enough that high aspect ratio contact/via holes are not
filled well. It is important to tailor the grain sizes of the as
deposited films such that these holes are reliably filled. The
microstructure of the initial film deposited has a significant effect
on grain growth and overall film properties. As an alternative to
conventional constant rate CVD (CRCVD) process, we have investigated
programmed rate CVD (PRCVD) processes to improve microstructure.
We studied the effects of process conditions on the nucleation and
growth stages of tri-isobutyl-aluminum (TIBA) sourced aluminum
deposition on TiN coated Si substrates in a LPCVD reactor. The
initial stages of deposition were studied using films deposited for
short times. Films deposited for 5 seconds as the substrate
temperature was ramped at -200 K/min from 673 K, followed by 25
seconds of deposition at 573 K resulted in enhanced nucleation
density, and preferred Al(111) crystal orientation compared to films
deposited for 30 seconds at 573 K. For growth stage depositions,
films deposited for 10 seconds as the substrate temperature was
ramped at -200 K/min from 673 K, then for 10 minutes at 573 K,
resulted in films with strong Al(111) crystal orientation compared to
the films deposited for 10 min at a constant substrate temperature of
573 K. AES analyses showed the deposited films to be free of carbon
and oxygen. A designed experiment was performed to statistically
determine the effects of the main process variables and their
interactions. Our PRCVD work shows that film microstructure and
properties can be controlled.
SESSION A2: MICROSTRUCTURAL EVOLUTION II
Chairs:
Walter L. Brown and Carl V. Thompson
Tuesday Afternoon, December
1, 1998
Salon A/B (M)
1:30 PM A2.1
2-D
SIMULATION OF MICROSTRUCTURE, TEXTURE AND MORPHOLOGY EVOLUTION DURING
THE CVD OF DIAMOND. Paritosh , Dept. of Chemical Eng.,
University of Michigan, Ann Arbor, MI; D.J. Srolovitz, Dept. of
Materials Science & Eng., University of Michigan, Ann Arbor, MI; C.C.
Battaile, Sandia National Laboratories, Albuquerque, NM; J.E. Butler,
Naval Research Laboratory, Washington, DC.
We
simulate the growth of faceted, polycrystalline diamond films during
chemical vapor deposition using a front tracking method in two
spatial dimensions. The resulting microstructures are shown to be in
excellent correspondance with experimental observations. The grain
size and surface roughness both increase as the square root of film
thickness. The films form a pronounced crystallographic texture that
sharpens with increasing film thickness as a result of growth
competition. The distribution of grain orientations is shown to be
Gaussian, in agreement with theory. This simulation method is applied
to the problems of minimizing surface roughness, choosing the desired
crystallographic texture and minimizing the concentrations of defects
incorporated during growth.
1:45 PM
A2.2
SIMULATION OF EVOLUTION OF GRAIN
SIZE AND ORIENTATION DISTRIBUTION IN CVD DIAMOND FILMS.
Ge Yu and S.T. Lee, Dept of Physics and Materials
Science, City University of Hong Kong, Kewloon, HONG KONG.
Abstract:
The evolution of the microstructure of CVD diamond films during
prolonged deposition is studied by computer simulation. In
particular, the average grain size on a plane parallel to the
substrate surface is determined as a function of the height of the
plane. From a model system composed of 104 grains, reliable results
can be evaluated for [111] and [001] growth of diamond films under
different initial conditions and with varying growth parameters. It
is demonstrated that grains of the maximal misorientation , of both
the largest tilt and the largest twist angle, are most capable of
surviving elimination in the selected growth. The rate of evolution
is sensitively influenced by the aspect ratio of diamond crystal,
but doesn't depend on the absolute deviation of the misorientation.
In the range investigated in this work, a proportionality between the
average grain size and the thickness of films can be approximately
yielded. The proportionality constant varies from 0.035 to 0.43 and
can be controlled by changing the aspect ratio. Furthermore, the
orientational distribution is drastically narrowed down so that the
probability of coalescence of grains with a slight orientational
difference is considerably increased. These facts indicate that the
selected growth is a possible way for fabricating single crystal
diamond film on a large scale area.
2:00 PM A2.3
KINETIC
LATTICE MONTE CARLO SIMULATION OF FACET GROWTH RATE.
Zhiyong Wang , Science and Engineering of Materials
Program, Arizona State University, Tempe, AZ; Youhong Li, James B.
Adams, Dept of Chemical, Bio and Materials Engineering, Arizona State
University, Tempe, AZ.
We present a fast
micron-scale Kinetic Lattice Monte Carlo simulation model which
describes deposition, nucleation, surface diffusion (including
adatom, dimer and ledge adatom diffusion) and film growth on fcc
metal substrates. The activation energies for diffusion are
calculated using embedded-atom method (EAM). Using this model, we
determine the relative growth rates of (100), (110) and (111) facets
as a function of substrate temperature, deposition rate and facet
size.
2:15 PM
A2.4
MICROSTRUCTURED MONOLITHS IN THIN
FILMS FABRICATED BY GLANCING ANGLE DEPOSITION (GLAD).
M.W. Seto , K. Robbie, M.J. Brett, Department of
Electrical and Computer Engineering, University of Alberta, Edmonton,
CANADA, and Alberta Microelectronic Corporation, Edmonton, CANADA.
Thin films grown by physical vapour deposition with
the Glancing Angle Deposition (GLAD) technique have been engineered
with a diverse range of columnar microstructures. These porous films
consist of isolated columns of material which are created by
orienting the substrate at a highly oblique angle to the evaporant
source, and utilizing computer controlled substrate motion during
deposition. Governing the growth process at these high angles is
enhanced self-shadowing, where variations in the developing
topography result in areas which become shadowed during the growth of
the film. A porous, columnar film then results as the film further
evolves. Through careful control of substrate motion and incident
flux angle, an assortment of structures can be fabricated including
beds of post, ``zig-zagular'', periodically bent nematic, and helical
[1] monoliths on the micrometer scale. The microstructure parameters
and porosities can be tailored to affect the properties of these
films, and further capabilities of the GLAD control system can
produce a dense capping layer atop the structured film. A
presentation of the GLAD process will show how an extensive number of
materials have been used to fabricate these films using thermal or
electron beam evaporation and long-throw sputtering techniques.
Results of the unique structural, crystal, and mechanical properties
of these films will also be reported.
References
[1] K. Robbie, M. J. Brett, A. Lakhtakia, Nature 384, 616
(1996).
2:30 PM A2.5
ZONES
OF SURFACE TEXTURE GROWTH AND MICROSTRUCTURAL EVALUATION OF ZnO
POLYCRYSTALLINE THIN FILMS BY REACTIVE SPUTTERING AND CHEMICAL VAPOUR
DEPOSITION. J.A. Anna Selvan , H. Keppner and A. Shah,
Institute of Microtechnology, University of Neuchatel, Neuchatel,
SWITZERLAND.
Surface texture growth of thin films
are highly preferred in some specific applications. For application
in thin film solar cells ZnO films are expected to have simultaneous
transparency, high electrical conductivity and surface texture.
Different ways to obtain surface texture growth using physical vapour
deposition and chemical vapour deposition were analysed in detail for
couple of years by the authors. The evaluation of surface roughness,
crystallographic texture, microstructure evaluation and the resulting
changes in the electrical, optical and surface properties of ZnO
films grown by sputtering as well as CVD techniques under different
experimental conditions will be presented in detail. By sputtering,
the influence of atmosphere of mixture of Ar and water vapour, RF
power, and substrate temperature and by CVD the influence of ratio of
reacting gases (Diethyl Zinc and water vapour), substrate temperature
and the dopants on the growth were studied in detail. In CVD, we have
identified three general regimes of growth; namely, 1)
normal growth 2) low surface mobility growth and 3) intensified
growth. As a general solution we come to the following conclusions.
For applications where one needs a smooth surface, a normal growth
regime should be selected. For a surface textured growth with
superior structural properties one can go for a intensified growth.
And for a granular growth with voids as well as poor mechanical
properties a low surface mobility growth can be selected. During
sputtering, we have classified three regimes; namely, columnar,
granular and smooth regimes. In the case of reactive sputtering, one
may not expect a transition regime (that results in a smooth surface
morphology) as is seen in the classical J. A. Thronton's model [1]
for normal sputtering. These results give certain general rules of
growth which can be applied to any thin film growth to a certain
extent and one can tune required microstructure of thin films and a
better interface for devices.
[1] J.A. Thronton, J. Vac. Sci. Tech, 11 (1974), 666
2:45 PM A2.6
BIAXIAL
TEXTURE EVOLUTION IN THIN-SPUTTERED FILMS. J.F.
Whitacre , B.A. Rainey, J.C. Bilello and S.M. Yalisove, University of
Michigan, Department of Materials Science and Engineering, Ann Arbor,
MI.
The evolution of both out-of-plane and in-plane
texture was examined in sputtered Mo and Cr films. Depositions were
carried out at different sputter gas (Ar) pressures and sputter
cathode heights to determine the importance of arriving adatom
kinetic energies and subsequent surface diffusion on texture
development. All depositions used a geometry where substrates rested
on a platen which swept them beneath the sputter cathode at 20 RPM.
Scanning electron microscopy, transmission electron microscopy,
transmission electron diffraction, and x-ray pole figure analyses
were used to characterize microstructure and texturing. It was found
in all films that a strong out-of-plane texture developed initially
(within the first 100 nm of growth), followed by a gradual increase
in the degree of in-plane texture in some cases. Different
out-of-plane crystallographic orientations formed depending on
deposition conditions. In Mo, a (111) out-of plane texture was
observed when the cathode height was less than 9.5 cm, while a (110)
orientation developed if the cathode-to-substrate distance was
larger. Similar results were observed for Cr films. The rate of
texturing in the plane of growth was found to be more rapid for films
deposited at lower Ar pressures. All films were found to have heavily
faceted surface morphologies. A revised mathematical model which
describes the evolution of texture and surface morphology is
introduced. The dependence of shadowing on the scale of single atoms
is removed. The model, instead, relies on the interaction between
film surface morphology and deposition chamber geometry and has a
diffusion parameter as an independent variable. Once out-of-plane
texture evolves, those grains whose surface facets are oriented in a
particular in-plane direction compete favorably during further growth
because they have relatively higher adatom capture efficiencies.
Mathematical simulations are fit to actual data and show that the
model may be favorably compared with experimental results.
Work supported by the U.S. Air Force.
3:00 PM A2.7
KINETIC
MONTE CARLO SIMULATIONS OF POLYCRYSTALLINE-LIKE MATERIALS. Steven W.
Levine, Exxon Research and Engineering, Florham Park, NJ;
Paulette Clancy , School of Chemical Engineering, Cornell
University, Ithaca, NY.
An adaptation of the Kinetic
Monte Carlo method was used to emulate thin film growth of a system
reminiscent of polycrystalline silicon. The deposition process was
constructed to produce a polycrystalline material composed of distinct
grains (albeit with identical orientation). For the deposition of
poly-Si on a substrate of poly-Si, columnar grains were observed that
grew into the direction of the incident beam, in agreement with
experiment. The angle made by the columns is measurable at all angles
of the incident beam, in contrast to results for single crystal Si for
which needles rather than columns are produced, and for which porous
films are only observed when the incident beam is greater than about
60 from normal. Existing theories, such as the tangent rule,
fail to explain the observed relationship between angle of incidence
and angle of the grown film. As they grew, some of the grains
initially present in the film became extinct. The initial number of
grains was not an important factor in determining the morphology of
the film. Other properties of the film, such as its density, mirror
the results for single-crystal Si. Deposition of poly-Si onto an
immobile heterogeneous substrate with a sticking coefficient much
lower than the deposited film (like Si on silicon dioxide, say)
produced qualitatively different behavior. As the angle of incidence
is increased (from normal incidence), fewer grains are nucleated than
in the previous isotropic case due to non-local shadowing. Increasing
the substrate temperature, which increases the diffusion of deposited
atoms, produces fewer, larger grains.
3:30 PM A2.8
REAL-TIME STRAIN MONITORING IN
THIN FILM GROWTH: CUBIC BORON NITRIDE ON Si(100). Dmitri
Litvinov , and Roy Clarke, Randall Laboratory of Physics, University
of Michigan, Ann Arbor, MI; Charles A. Taylor II and Darryl Barlett,
k-Space Associates, Inc., Ann Arbor, MI.
We
demonstrate the application of real-time film-stress monitoring and
control using a multi-beam optical sensor (MOS). In-situ
measurements on cubic boron nitride (c-BN) films grown by
ECR-assisted sputtering reveal a critical stress beyond which defects
are injected into the silicon substrate. This is marked by a rapid
onset of wafer curvature. The calculated stress in the silicon
substrate corresponding to the onset of defect injection coinsides
with the yield strength of the material at the given temperature. Our
measurements suggest a possible route to mediate such effects by
utilitzing the compliant nature of the hexagonal (h-BN) buffer
layers. The ability to perform in-situ, real-time wafer
curvature measurements using the MOS technique will greatly aid this
task. The method should also be very useful for monitoring stress
build-up in other wide-bandgap nitride films where no appropriate
lattice-matched substrates are presently available. The real-time
nature of the technique should allow also to shed a light on the
effect of stress in the formation of metastable phases.
3:45 PM A2.9
MICROSTRUCTURAL CHARACTERIZATION
OF POLYCRYSTALLINE Ni3Al/Ni FILMS. X.D. Zhang , G.
Thompson, R. Banerjee, P. Anderson, and H.L. Fraser.
Monolithic Ni3Al and multilayered Ni3Al/Ni films were deposited using
a magnetron sputtering technique. The films were deposited on
various substrates, including amorphous SiO2 and varous single
crystals* at substrate temperatures between 25 and 400 degrees C.
Low and high angle X-ray diffraction shows strong (111) and (002)
texturing that depends upon substrate features and deposition
temperature. TEM and HREM of cross section and plan view specimens
of monolithic Ni3Al films shows an equiaxed grain structure, with a
typical grain size of 20nm. Samples deposited at higher temperatures
showed no obvious macroscopic grain growth. Samples deposited at
lower temperatures had a large density of planar defects.
Microstructual features, including the planar defects and texturing,
will be discussed in terms of the processing conditions used.
*Thanks to Tim Foecke and Tom Moffit at NIST for substrates and
surface preparation assistance.
4:00 PM
A2.10
HYDROGEN ENHANCED ABNORMAL GRAIN
GROWTH OF MAGNETRON SPUTTERED NICKEL FILMS. Dietmar Mueller, Jens
Greiser, Thomas Wagner , Eduard Arzt.
Thin Ni films have been deposited by magnetron sputtering on oxidized
Si wafers using either argon or an argon-hydrogen sputter-gas mixture
in order to study the influence of hydrogen on grain growth. In
addition, post deposition annealing (800C) was performed
either in high vacuum (HV) or in a defined hydrogen atmosphere. The
microstructural evolution of the films was investigated by X-ray
diffraction, focused ion beam and scanning electron microscopy. After
deposition, the typical grain size was between 100 - 200 nm and the
Ni films showed a (111) texture with a small volume fraction of (100)
Ni grains. During annealing the (111) grains underwent normal grain
growth whereas the (100) grains showed abnormal grain growth (grain
size 500 m). For films either sputtered or annealed in the
presence of hydrogen, abnormal grain growth of the (100) grains was
much stronger . The appearence of abnormal grain growth in Ni films
as a function of hydrogen treatment is discussed in
detail.
4:15 PM A2.11
MICROSTRUCTURE AND PROPERTIES OF
Cu-C AND Cu-Mo PSEUDOALLOY FILMS PREPARED BY SPUTTER DEPOSITION.
J.P. Chu , C.H. Chung and T.N. Lin, Institute of Materials
Engineering, National Taiwan Ocean University, Keelung, Taiwan,
REPUBLIC OF CHINA.
The microstructure and properties
of Cu-C and Cu-Mo pseudoalloy films prepared by R. F. magnetron
sputtering have been investigated. As Cu is mutually immiscible with
C or Mo, non-equilibrium supersaturated solid solutions of C or Mo in
Cu with nanocrystalline microstructures were observed in as-deposited
films. Upon heating of the films, three major transition events took
place. Recovery occurred at 280-300C while at
400C crystallites started to growth and coalescence, due
to the release of strain energies stored during deposition. Annealing
at above 600C led to occurrence of grain growth and altered
the microstructure considerably. Although attempts have been made in
this study, a possible annealing-induced phase separation could not
be unambiguously identified. Yet, the fact of low twin densities and
fine grain structures observed in the annealed films suggests that
the extensive grain growth was impeded by the presence of carbon.
Resistivity and hardness properties correlated well with the film
microstructure and were governed by the impurity effect of carbon.
Low carbon Cu-C films yielded relatively low resistivity,
attributable to the improved film microstructure. Hardness results
indicated the strengthening of films was mainly due to fine
structure, presence of carbon, and grain refinement by annealing
twins.
4:30 PM A2.12
LIMITING CONDITIONS FOR GIANT
GRAINS IN SILVER THIN FILMS. J. Greiser , J. Ankele,
E.Arzt, Max-Planck-Institut fuer Metallforschung, Stuttgart, GERMANY;
P. Muellner, Institut fuer Angewandte Physik, ETH-Hoenggerberg,
Zuerich, SWITZERLAND; C. V. Thompson, Department of Materials Science
and Engineering, MIT, Cambridge, MA.
The performance
and reliability of thin metal films depend strongly on their
microstructure, which develops during deposition and / or during
post-deposition annealing processes. A large grain size is desired
for many applications. However, normal grain growth stagnates at 2-3
times the film thickness. Abnormal grain growth can lead to
considerably larger grain sizes.
The present work focuses on a new type of abnormal grain growth or
recrystallization, where <001> oriented grains grow to an enormous
extent, from about 160 nm to the millimeter size range. These grains
are called giant grains (GGs). GGs have first been observed in
undoped 2 m thick PVD silver films. The microstructure of the
films was analysed by focused ion beam imaging (FIB). The grain
orientation was determined by electron backscatter diffraction (EBSD)
and by X-ray texture analysis. Systematic variation of the film
thickness and the deposition temperature has shown that the
as-deposited state of the silver film is decisive for the growth of
the giant grains. The limiting conditions for GGs, e.g. with regard
to film thickness, have been determined and will be reported. Even
though the as deposited films have a strong <111> fiber texture,
only giant <001> oriented grains grow until the whole film is fully
recrystallized. These results demonstrate the possibility of
transforming small grained single-phase polycrystalline thin films
into pseudo-monocrystalline films.
4:45 PM A2.13
THE EFFECT OF SURFACE ROUGHNESS ON GRAIN GROWTH IN THIN FILMS.
H.J. Frost , E.E.K. Cooper, Dartmouth College, Thayer
School of Engineering, Hanover, NH; C.V. Thompson, W. Fayad, M.I.T.,
Dept. of Materials Science and Engineering, Cambridge, MA.
We have modeled grain growth in polycrystalline thin
films for the case in which grain boundary migration becomes impeded
by the roughness of either the free surface or the film-substrate
interface. For this we used a two-dimensional simulation of
capillarity-driven grain growth in which grain boundaries migrate at
velocities proportional to a driving force given by the local
boundary curvature minus a constant frictional drag. In this model,
the grain growth eventually stagnates in a manner very similar to the
behavior observed for grain boundary pinning by surface grooving.
These simulations produce lognormally distributed grain sizes, which
match typical experimental observations in thin films. These
lognormal size distributions are also similar to those produced by
simulations of the effects of solute drag.
SESSION A3: POLYCRYSTALLINE SILICON I
Chairs: Theodore
I. Kamins and Timothy D. Sands
Wednesday Morning, December 2,
1998
Salon A/B (M)
8:00 AM
*A3.1
POLY-Si - SUBSTRATE
INTERACTIONS. D.G. Ast , Cornell Univ, Dept of Material
Science and Eng, Ithaca, NY; J.G. Couillard, Corning Inc, Sullivan
Park, Corning, NY.
Important properties of poly-Si
Thin Film Transistors (TFTs), such as leakage current and lifetime
under stress are strongly (< order of magnitude) influenced by the
chemical composition of the substrate - even when the poly-Si and
substrate are separated by a 100 nm thick LPCVD or APCVD Si(O)2
'buffer' layer. These interactions were studied for a variety of
glass substrates as a function of the SiO(2) layer thickness, with
oxidized Si wafers serving as a control. Results obtained indicate
that the glass substrate acts both as a source for impurities and as
a sink. The former dominates the lifetime and the latter the leakage
current which is lower in certain glass substrates than in oxidized
Si wafers. These studies are being extended to glass ceramic
substrates, using a high temperature process to fabricate the TFTs.
Preliminary experiments indicate that SiN diffusion barriers are
required in this case.
8:30 AM A3.2
THE
EFFECT OF SURFACE NUCLEATION BY HYDROGEN PLASMA SURFACE PRETREATMENT
OF SILICON DIOXIDE PREPARED BY ELECTRON CYCLOTRON RESONANCE CHEMICAL
VAPOR DEPOSITION. Eun-Chel Cho , Yo-Sep Min, Young-Hyun
Cho, and In-Yong Song, Electronic Materials Lab., Samsung Advaced
Institute of Technology, Sunwon, KOREA.
We will
report the growth properties of polycrystalline silicon (poly-Si)
films grown at low temperature ( < 300 C) using a hydrogen
plasma surface pretreatment of silicon dioxide. The silicon dioxide
surfaces pretreated by a low energy hydrogen ion beam act as a
nucleation site for the poly-Si deposition. The poly-Si films were
deposited by means of reactive plasma beam deposition technique using
argon/hydrogen/silane gas mixture. The microstructures of the
deposited poly-Si films are determined by analysis of Raman
spectroscopy, X-ray diffractometer, ex-situ spectroscopic
ellipsometry and atomic force microscopy (AFM) measurements. The
orientation and crystallinity of the as-deposited poly-Si films had
the growth with strongly preferential (100) orientation and more
than 92% respectively. The rms roughness of the poly-Si was decreased
with increasing the reactive ion beam density. In our experiments the
rms roughness was less than 50 .
8:45 AM A3.3
GROWTH
MECHANSIM OF CAT-CVD POLY-Si FILMS AND GRAIN CONTROL BY TWO-STEP
DEPOSITION. Akira Heya , Akira Izumi, Atsushi Masuda,
Hideki Matsumura, JAIST (Japan Advanced Institute of Science and
Technology), Tatsunokuchi, Ishikawa , JAPAN.
Catalytic chemical vapor deposition (Cat-CVD) method (often called
Hot-Wire CVD method) is a new low temperature deposition method.
Poly-Si films obtained at temperatures lower than 400 C by
Cat-CVD method have unique structural properties, that is,
crystalline grains with a few-tens-nm diameter are columnarly grown
and the grains are surrounded with a few-nm thick amorphous layer. In
the present work, growth mechanism of poly-Si films is studied by
TEM, AFM and RHEED observation. Poly-Si films deposited by two-step
deposition (TSD) method are also examined. In the method, the
deposition is started at low temperatures in the first step and then
continued at elevated temperatures in the second step.
It is found that 1) the surface morphology of a-Si films is smooth
(RMS roughness < 0.1 nm) and that of poly-Si films is rough (RMS
roughness > 0.5 nm), 2) the behaviors of both nucleation and grain
growth change at substrate temperatures around 350 C, 3)
RMS roughness of initial deposition stage, obtained by AFM images, is
related with grain size estimated by plan-view TEM images, 4) the
a-Si incubation layer is sometimes incorporated between substrate and
growing poly-Si layer. The microstructure of such a incubation layer
itself appears to vary from the initial atomic layer toward growth
direction and 5) the control of the a-Si incubation layer is
effective to control the whole poly-Si structure. Thus the grain size
of poly-Si films can be controlled ranging from 15 to 20 nm by
controlling incubation layer by the TSD method.
9:00 AM A3.4
AND STRUCTURAL
CHARACTERIZATION OF LOW TEMPERATURE HEAVILY DOPED POLYCRYSTALLINE
SILICON THIN FILMS PREPARED BY ECR PLASMA CVD. Hsi-Lien
Hsiao , Y-Y Hsieh, Huey-Liang Hwang, Department of Electrical
Engineering, National Tsing Hua University, Hsinchu, TAIWAN; An-Ban
Yang, Department of Physics, Tunghai University, Taichung, TAIWAN,
ROC.
Boron-doped and Phosphine-doped polycrystalline
silicon thin films were deposited on glass substrates at
250C by using electron cyclotron resonance
SiH4/Ar/H2/B2H6 and SiH4/Ar/H2/PH3
downstream plasma chemical vapor deposition (ECR-CVD) technique. The
effects of in-situ doping on the structural and electrical properties
of heavily doped polycrystalline silicon thin films have been
investigated. These films were characterized by conductivity, Hall
effect, Raman spectra, X-ray diffraction (XRD), transmission electron
microscopy (TEM), atomic force microscopy (AFM), Fourier-transform
infrared (FTIR) spectra and secondary ion mass spectroscopy (SIMS).
The crystalline fraction of the films was calculated to be larger
than 90% by deconvoluting the Raman spectra. The largest grain size
of heavily doped poly-Si films with 700 nm thickness (growth rate
20 nm/min) is approximately 500 nm, and the surface roughness is
about 60 nm. The hydrogen contents was estimated to be below 0.8%.
With increasing doping concentration, the conductivity rapidly
increases and the maximum values of 26 Scm-1 at
[B2H6]/[SiH4] 2x10^-2for p-type poly-Si
films and 50 Scm^-1at
[PH_3]/[SiH_4] 1x10-2 for p-type poly-Si films
were achieved, while it decreases at larger doing ratios. Hall
measurement revealed that the change is mainly caused by the change
in the carrier density. X-ray diffraction and transmission electron
microscopy indicated that this electronic change is associated with
the change in the preferred orientation of grains from <110> to
<111>
with a decrease in grain size. The peculiar change in structure and
electrical properties with doping concentration was attributed to the
solid solubility limitation and impurity coverage effect. Because the
solid solubility of P and B atoms in the silicon crystal were
estimated to be about 1x10^-20cm^-3at 300^, H2, Ar)
were the varied parameters. XRD profiles were measured to establish
orientation, estimate grain size and lattice strain. SIMS
measurements were performed to determine impurities depth profiles
and FE-SEM, FT-IR, Raman scattering and spectroscopic ellipsometry
were used to observe surface morphology, short/medium range ordering
and so on. Dark and photoconductivity and Hall effects were also
measured. All experimental were performed for both (220) and (400)
oriented films to compare their structural and transport properties.
So far, (220) preferential growth was obtained with Ar/H2/SiF4
gas flow rates of 60/15/30sccm and (400) one with those of
60/10/90sccm. SIMS measurements showed that the content of
impurities such as hydrogen and fluorine were rather small for the
(400) cases compared with the (220) cases. These results correspond
to the sharpness of Raman spectra and ellipsometry spectra. Lattice
parameters of the (400) oriented films also indicates the lower
content of impurities in the crystal lattice.
Hall mobility of electrons increases with thickness from 6 to
13cm2/V/s for the (220) oriented films. On the contrary, the
(400) oriented films which exhibit highly ordered structures and
small impurities compared with the (220) films show smaller mobility
up to 7cm2/V/s. This is due to larger fluctuation of the
orientation, that is, the structure of the grain boundary has not
been optimized yet at the present stage. We will discuss on the
recombination of photo-excited carrier related to the structures as
well.
10:00 AM *A3.6
LASER-CRYSTALLIZED
POLYCRYSTALLINE Si FILMS FOR MICROELECTRONIC AND PHOTOVOLTAIC
DEVICES. James S. Im , Robert S. Sposili, M.A. Crowder,
H. Cho, S.H. Christiansen and K. Adib, Program in Materials Science
and Engineering, School of Engineering and Applied Science, Columbia
University, New York, NY.
Thin crystalline Si films
are becoming increasingly recognized as a technologically versatile
material that can potentially enable effective realization of
important new microelectronic and photovoltaic devices. For many of
these applications, it is imperative that the process by which
crystalline Si is produced not involve extended exposure to high
temperatures. As well, it is generally desired--being that the
crystalline Si films are used for electronic applications--that the
material be free from structural defects, such as high-angle grain
boundaries and microtwins, that can lead to high densities of carrier
trapping states.
In this paper we review the details of a particular form of
pulsed-laser-based thin-film crystallization method, referred to as
sequential lateral solidification (SLS), that permits realization of
low-defect-density crystalline Si films with controlled
microstructures on amorphous and high-temperature-intolerant
substrates. By systematically manipulating and controlling the
locations, shapes, and extent of melting induced by the incident
laser pulses, the SLS approach can lead to both efficient
(i.e., high throughput rates) and effective (i.e., large
energy-density processing windows) production of a variety of
microstructurally designed crystalline Si films with low structural
defect densities, including (1) large-grained and
grain-boundary-location-controlled polycrystalline films, (2)
directionally solidified microstructures, or (3) location-controlled
single-crystal regions.
In this paper, we elaborate on salient materials-, process-, and
device-related results that are relevant in determining the
applicability of the SLS method to the production of crystalline
Si-based thin-film transistors (TFTs) and thin-film-based solar cells
on low-cost/large-area substrates.
10:30 AM A3.7
FORMATION OF ADJACENT GRAINS AT
PREDETERMINED POSITION ON GLASS SUBSTRATE BY DUAL-BEAM EXCIMER-LASER
MELTING OF Si THIN-FILMS. Ryoichi Ishihara , Delft Univ.
of Technol., DIMES-ECTM, Delft, THE NETHERLANDS.
We
have proposed a method to control the position of the large grain by
excimer-laser irradiation to both sides of a-Si / SiO2 with a bump
/ metal structure on glass substrate, and demonstrated that the
crystal-Si grain with a diameter of 3.5 m was located exactly
on top of the SiO2 bump. [Jpn. J. Appl. Phys. 37 3B (1998)
1071]
In this paper, we have investigated the effect of the thickness and
separation of the SiO2 bumps on the location-control
characteristics and the diameter of the Si grain. The thickness of
the SiO2 bumps was varied from 190 nm to 630 nm, while the height
of the SiO2 bump, thickness of a-Si and TiW were fixed at 30 nm,
100 nm and 550 nm, respectively.
By SEM observation of Secco-etched Si film, it was found that the
diameter of the location-controlled Si grain was increased from 3.5
m to 6.0 m with increasing the thickness of the SiO2
bumps. It was also found that the separation between the bumps should
be increased 3.5 m to 4.5 m as increasing the grain size
from 3.5 m to 6 m in order to locate the Si grain on the
SiO2 bump. Finally the adjacent grains were successfully formed at
the predetermined positions on the glass substrate.
10:45 AM A3.8
GRAIN
ENLARGEMENT OF POLYCRYSTALLINE Si FILMS THROUGH MULTIPLE-PULSE
EXCIMER LASER IRRADIATION. Robert S. Sposili and James S.
Im, Program in Materials Science, Columbia University, New York, NY.
Under certain conditions, repeated excimer-laser
irradiation of thin polycrystalline Si films can lead to an increase
in the grain size. This phenomenon is not only of fundamental
interest, but is also technologically significant as it is
responsible for the large grain sizes that are sometimes obtained
using the conventional excimer-laser annealing (ELA) process, and
which translate into high-performance thin-film transistors (TFTs).
Two distinct models have been suggested to account for the
phenomenon: (1) a solid-phase model based on surface energy-driven
secondary grain growth (SEDSGG), and (2) a melting/ solidification
model that invokes near-complete melting [and the associated
super-lateral growth (SLG)] of the films, where localized complete
melting occurs predominantly at the grain boundaries.
In this paper, we report on a set of experiments that was conducted
in order to better characterize the phenomenon and thereby evaluate
the validity of the respective models. Silicon films with
thicknesses ranging from 500 to 2,000 â were irradiated with a 308-nm
excimer laser at a series of schedules of fluence and number of
pulses (1Ò100). Subsequent to irradiation, the samples were examined
using optical microscopy, SEM, and TEM in order to characterize the
average grain size as well as the grain size distribution. Grain
enlargement was observed only when the energy density was slightly
below the complete-melting threshold (and not under partial or
complete melting conditions).
We will discuss how these results are not consistent with the SEDSGG
model, but are in agreement with the basic tenets of the SLG model.
Also, the results refute a SiÒSiO2 interface-roughening model that
has previously been suggested in order to account for the
creation/destruction of large grains. An important technological
implication of this work is that the conventional ELA process will
not be able to achieve a uniform, large-grained microstructure at
high throughput rates.
11:00 AM A3.9
A
MODEL FOR AMORPHOUS Si1-xGex THIN FILMS CRYSTALLIZATION.
Mario Castro1, J. Olivares2, A. Rodriguez 2, J.
Sangrador2, T. Rodriguez2, A. Sanchez3, C. Ballesteros3,
F. Dominguez-Adame1 1Fisica de Materiales, UCM, Madrid, SPAIN.
2E.T.S.I.T.-U.P.M., Madrid, SPAIN. 3E.P.S.-U. Carlos III,
Madrid, SPAIN.
We study crystallization behavior of
amorphous Si1-xGex thin films by means of computer
simulations of a specific model introduced to this end. The model we
propose assumes nuclei are generated at each time step according to
an Arrhenius distribution. Initial nuclei are generated with radii
smaller than or equal to the critical radius. Nuclei with radii
smaller than the critical radius decrease in size, whereas those with
radii larger than the critical radius grow at constant rate. Along
the process, subsequent nuclei are generated with the same
distribution but only within the remaining amorphous area. As
measurable quantities, we focus on grain size distribution and Avrami
plots, the reference parameters for the simulations being the mean
grain size and the crystallization time. In addition, temperature and
fraction x of Ge are introduced in the model by a interpolation
between the activation energies for growth and nucleation of pure Si
and pure Ge. In order to test the model we have introduced above,
specific experiments were carried out. Amorphous SiGe layers were
deposited by LPCVD at 450 on oxidized Si wafers and 7059
Corning glasses using Si2H6 and GeH4 as gas sources. The
films were 100 nm thick and the Ge fraction was in the 0-0.42 range.
The samples were annealed at 550 for times up to 450 hours
at low pressure (below 100 mTorr) to crystallize the amorphous
layers. The crystallization behavior and film microstructure was
analyzed by X-ray diffraction and transmission electron microscopy.
We find a quite satisfactory agreement between the model predictions
and the experimental results. Thus validated, the model can be useful
to search for optimal preparation conditions in view of the required
properties.
11:15 AM
A3.10
DEPENDENCE OF MAXIMUM GRAIN SIZE
IN Si SELECTIVE NUCLEATION AND SOLID PHASE EPITAXY ON B DOPING
CONCENTRATION. Hiroshi Tanabe and Harry A. Atwater,
Thomas J. Watson Laboratory of Applied Physics, California Institute
of Technology, Pasadena, CA.
Selective nucleation
and solid phase epitaxy (SNSPE) is a process that employs patterned
selective nucleation to enable larger grain size than that is
achievable by conventional solid phase crystallization. The maximum
grain size is dependent on the product of the incubation time for
random nucleation and the lateral solid phase epitaxy rate, and is
estimated to be in the range of 1-5 micron. Thus the maximum grain
size is also a function of doping concentration. The incubation time
of undoped silicon is about 20 hours at the annealing temperature of
580oC. Doping with boron in the concentration range between 4.8
x 1018 /cm3 and 1.6 x 1021 /cm3 decreases the
incubation time for boron concentration exceeding 1.6 x 1019
/cm3. The lateral solid phase epitaxy rate of undoped silicon
at 580oC is about 0.02 nm/second and is increased by a factor of
5 at the concentration of 5 x 1020 /cm3 relative to the
undoped silicon. The lateral solid phase epitaxy rate decreases for
boron concentration exceeding 5 x 1020 /cm3, possibly due
to loss of electrically active boron concentration at high doping.
Variation of annealed tempe rature in the range between 580oC
and 620oC indicates the best nucleation selectivity, and largest
potential grain size, at the lowest temperatures. Possible
mechanisms for the onset of decreased incubation time and decreased
so lid phase epitaxy rate at very high boron concentrations will be
discussed.
11:30 AM A3.11
TEMPERATURE EFFECT ON
MICROSTRUCTURE OF POLYCRYSTALLINE SILICON THIN FILMS PREPARED BY
SILICIDE-MEDIATED CRYSTALLIZATION WITH RAPID THERMAL ANNEALING.
Yo-Sep Min , Eun-Chul Cho, Electronic Materials
Laboratory, Samsung Advanced Institute of Technology, Suwon, KOREA.
The silicide-mediated crystallization of
nanocrystalline silicon thin films on the nickel-coated glass
substrates was investigated. Nickel thin films with the thickness of
150 were coated on Corning 1737 glasses by sputtering and then
nanocrystalline silicon thin films were deposited on Ni/glass
substrates at 200C by ECR-CVD (electron cyclotron resonance
chemical vapor deposition) using SiH4/H2/Ar gas mixtures.
Preferrentially (111)-oriented nickel disilicides were formed between
silicon and nickel thin films above 700C by rapid thermal
annealing, which enhanced the crystallinity of the nanocrystalline
silicon thin films. However, under 600 C nickel disilicides
were not formed and especially, the crystallinity of the silicon thin
films annealed at 400C by RTA was degraded on the contrary.
The microstructure of polycrystalline silicon thin films was
characterized by Raman spectroscopy, X-ray diffraction, spectroscopic
ellipsometry.
11:45 AM
A3.12
IN-SITU MICRORAMAN
CHARACTERIZATION ON THE CRYSTALLIZATION KINETICS OF LPCVD SILICON
FILMS. Josep-Lluis Alay, Joan Ramon Morante , Departament
d'Electronica, Universitat de Barcelona, Barcelona, SPAIN; T.
Mohammed-Brahim, M. Sarret and O. Bonnaud, Groupe de
Microelectronique et Visualisation, Universite de Rennes I, Rennes,
FRANCE.
A powerful in-situ technique has been
developed to study the solid phase crystallization of low pressure
chemical vapor deposition (LPCVD) silicon thin films that are
attractive for applications in matrix liquid displays and
photovoltaic solar energy converters. This characterization technique
is based on microraman measurements performed in a heating chamber
wherein the annealing temperature can be maintained at a selected
temperature up to 600C. By monitoring the position, intensity and
full width at half maximum for the TO Raman peaks, it is possible to
characterize the kinetics of the crystallization process. Another
advantage provided by this new in-situ microraman based
characterization technique is the possibility of enhancing the
crystallization kinetics by increasing the incident laser power. If
the thin films are deposited on glass substrates, measurements can be
performed either on the silicon surface or at the Si/glass interface.
On the other hand, transmission electron microscopy (TEM) and x-ray
diffraction (XRD) analysis performed on silicon films annealed for
various periods of time give additional information on the structural
changes undergone by those films. By using glass substrates, the
crystallization process can be monitored and its kinetics determined.
It starts with the formation of crystalline seeds at the interface
Si/glass and proceeds towards the film surface until the entire film
becomes crystalline.
SESSION A4: POLYCRYSTALLINE SILICON II
Chairs: Dieter
G. Ast and James S. Im
Wednesday Afternoon, December 2, 1998
Salon A/B (M)
1:30 PM A4.1
STRESS
DISTRIBUTION IN POLYCRYSTALLINE SILICON MEMBRANES BY MICRO-RAMAN
SPECTROSCOPY. H. Talaat1, S. Negm 1, H.
Schaffer2, F. Adar2, G. Kaltsas3 and A.G. Nassiopoulou3;
1Faculty of Science, Ain Shams University, Cairo, EGYPT;
2Instruments SA, Edison, NJ; 3Institute of Microelectronics,
NCSR Demokritos, Aghia Paraskevi Attikis, Athens, GREECE.
The determination of the local stresses in
Polycrystalline silicon (poly-Si) thin layers used in IC devices and
MOS technology is of vital importance due to their detrimental effect
on the reliability of these devices. Micro-Raman spectroscopy with
spatial resolution of 1um, offers a powerful non-destructive
method for the measurements of local stresses in these poly-Si
membranes, in particular for complex structured ones as bridges. In
this work we present our micro-Raman study of local stresses in
poly-Si membranes of relatively large dimensions (570 x 380 um2)
deposited over tunnels as deep as (120 um) micromachined in Si
wafers. The membranes (or bridges) of various thicknesses (1-3um)
are either free standing or lying on sacrificial porous silicon. The
effect of the thickness of the bridges as well as conditions of
growth and annealing process are studied to determine the parameters
needed to obtain bridges of least stresses. The features of the
poly-Si Raman line (position of maximum and FWHM) are analyzed and
compared to reference c-Si , where it is shown that the FWHM for the
Raman lines gives as much information as the shift in the position of
the maximum to characterize the stresses in the
membranes.
1:45 PM A4.2
RAMAN
STUDY OF AMORPHOUS AND POLYCRYSTALLINE SiGe FILMS. J. Olivares, A.
Rodríguez, J. Sangrador, T. Rodríguez, E.T.S.I.T.-U.P.M., Madrid,
SPAIN; P. Martín, J. Jiménez , U. Valladolid,
Vallodolid, SPAIN.
Polycrystalline SiGe films are of
interest for the fabrication of thin film transistors for flat panel
displays. In this work, Raman spectroscopy has been used to
characterize: a) the amorphous SiGe deposited by LPCVD on oxidized Si
and glass, b) the solid phase crystallization kinetics of this
material and c) the resulting polycrystalline film microstructure.
Amorphous SiGe layers were deposited by LPCVD at 450C on
oxidized Si wafers and 7059 Corning glasses using Si2H6 and
GeH4 as gas sources. The Ge fraction of the films was in the
0-0.38 range. The samples were crystallized at 550C: for
times up to 450 h at Iow pressure (below 100 mTorr). The frequency
shifts of the Si-Si and Si-Ge peaks of the spectra of the amorphous
layers have been analyzed as a function of the Ge content. The
crystallization of the films has been studied using the dependence of
the peak areas on the annealing time. The data have been fit using
the Avrami's model and the characteristic parameters have been
extracted. The frequency shifts, shape and intensity of the Si-Si,
Si-Ge and Ge-Ge peaks of the spectra of the polycrystalline layers
depend on the Ge content, the grain size and the residual stress in
the films. Characterization of the samples using several spot sizes
and film thicknesses have been used to separate the different
contributions. The evolution of the Raman spectra with the
temperature was also studied in order to evaluate the contribution of
the crystallinity and residual stress to the
anharmonicity.
2:00 PM A4.3
EFFECT
OF INCORPORATING GERMANIUM IN THE POLYCRYSTALLINE SILICON FILM.
D. Guillet , T. Mohammed-Brahim, M. Sarret, L. Haji, F. Le
Bihan, B. Fortin and O. Bonnaud, GMV, Université de Rennes, FRANCE.
The study of electrical and physical properties of
the polycrystalline SiGe films is necessary as this alloy is a
potential material for active channel of thin film transistor or
photovoltaic applications. The Low Pressure Chemical Vapor Deposition
technique is used to in-situ control high incorporation of
germanium in Si1-xGex films by varying the magnitude x from
0.1 to 0.5 (and making an alloy). The film composition is determined
by Secondary Ion Mass Spectroscopy (SIMS), X-Ray Diffraction (XRD)
and Transmission Electron Microscopy (TEM) for studying respectively
incorporation of germanium and grain structure of polycrystalline
thin films. In-situ measurements of the film conductance during
annealing (around 600C) under vacuum in classical furnace are
used to determine the crystallization kinetics. The increase of
incorporated germanium content leads to a high decrease of
crystallization time of amorphous Si1-xGex. Electrical
properties of the film are studied by Hall effect measurements. The
rise of Ge content in silicon matrix induces a decrease of electrical
resistivity due to a high increase of the carrier mobility.
2:15 PM A4.4
PROPERTIES OF POLYCRYSTALLINE
SILICON THIN FILMS GROWN FROM METALLIC SOLUTIONS BY TEMPERATURE
DIFFERENCE METHOD (TDM). B. Thomas , G. Müller, P.-M.
Wilde, H. Wawra, Institute of Crystal Growth, Berlin, GERMANY.
Thin film polycrystalline solar cells offer
significant potential for the reduction of cost and improvement of
conversion efficiency of photovoltaic power. Thin film solar cells
reduce the mass of feedstock silicon required. Second, low cost
substrates enable large-area solar cells. Finally, an established
silicon technology already exists. Thin film silicon solar cells have
been demonstrated a capability to exceed the 15 efficiency mark.
LPE layers on highly doped multicrystalline silicon substrates showed
efficiencies up to 15,4 .The temperature difference method (TDM) has the following advantages
in comparison with the conventional LPE: The thickness of the grown
layer is independent of the element solubility in the melt and the
melt height. Because of the constant temperature at the phase
boundary it is possible to grow layers with homogeneous distribution
of dopants. The TDM possesses the capability to grow thin films in a
quasi-continuous process. The steady state process allows saving of
energy and time.
We describe the TDM as a promising technology for the continuous
growth of thin film silicon from the solution on polycrystalline
silicon substrates (10 x10 cm^2) as well as on silicon
seeded graphite substrates. The thermodynamic driving force of the
layer growth by TDM is generated by a temperature gradient
perpendicular to the substrate surface. Silicon thin films have been
grown from Indium solutions at 980^C and a gradient of 10
K/cm.
The layer structure and morphology were determined by SEM and XRD. By
using spreading resistance (SR) measurements p-doping concentrations
from 10^16to 2 x 1018 cm-3 have been detected
in dependence of the Ga concentration in the In/Si solution. SR depth
profiles show a homogeneous distribution of charge carriers
perpendicular to the substrate surface due to the constant growth
temperature. Minority charge carrier life times of 5-10 s were
determined in 30 m thick layers by TRMC (time resolved microwave
conductivity) measurements. The influence of the microstructure
(grain size, grain boundaries) on the electrical and photoelectrical
properties of silicon TDM layers will be discussed.
SESSION A5: CERAMIC FILMS
Chairs: Dieter G. Ast and
James S. Im
Wednesday Afternoon, December 2, 1998
Salon A/B (M)
3:00 PM
*A5.1
CRYSTALLOGRAPHIC TEXTURE IN
ELECTROCERAMIC THIN FILMS ON SILICON. Tim Sands and
Loucas Tsakalakos, Dept. of Materials Science and Mineral
Engineering, University of California, Berkeley, CA.
The macroscopic piezoelectric, pyroelectric and ferroelectric
properties of bulk polycrystalline perovskite ceramics such as
Pb(Zr,Ti)O3 (PZT) are dependent on crystallographic anisotropy as
achieved by uniaxial electric-field poling at temperatures below the
Curie temperature (Tc). Electric-field-driven poling mechanisms
involve the motion of ferroelectric (180o) domain walls,
ferroelastic/ferroelectric twin boundaries and interphase boundaries
(e.g., rhombohedral-tetragonal phase boundaries in
morphotropic-phase-boundary PZT). In thin films, however,
electric-field poling at room temperature is generally believed to
mobilize only 180o domain boundaries while the ferroelastic twin and
phase boundaries remain pinned by the fine-grain microstructure and
the mechanical clamping effect of the substrate. Thus, optimal poling
of thin films demands control of the crystallographic texture of the
cubic phase during deposition, combined with control of the biaxial
stresses that influence domain selection during cooling through Tc.
In this talk, we describe templates (e.g., layered compounds such as
bismuth titanate) and processing conditions that yield strong uniaxial
texture in PZT thin films on Si substrates. We argue that such
texture will be essential to achieving both optimal properties (e.g.,
> 1% strain via the converse piezoelectric effect, without
microcracking) and performance (resistance to fatigue and aging). A
novel laser liftoff process for separating nominally monocrystalline
films from their single-crystal oxide growth substrate and
transferring them to a Si, glass or polymer substrate is described.
3:30 PM
A5.2
STRUCTURE AND PROPERTIES OF
MAGNETRON-SPUTTERED CHROMIUM NITRIDE FILMS. Xiao-Ming
He , Neil Baker, Stephan Grigull, Kevin C. Walter, and Michael A.
Nastasi, Materials Science and Technology Division, Los Alamos
National Laboratory, Los Alamos, NM.
Chromium
nitride (CrN) films were prepared on low temperature substrates by
d.c. reactive magnetron sputtering with Ar as the sputtering gas and
N2 as the reactive gas. The influence of experimental parameters,
such as the substrate bias, power density, and gas flow ratio of
N2 to Ar (or FN2/FAr), on the structure and properties
of the resultant films were studied. It was found that stoichiometric
or near-stoichiometric CrN films were easily obtained in the
crystalline form depending on gas flow ratio FN2/FAr and
bias voltages applied to the substrate. The morphology, hardness and
residual stress were substantially affected by the bias voltage and
the sputtering power. The experimental results confirmed that the
thick CrN films can be prepared with a fine and compact
nano-crystalline structure, an extreme hardness of 30 GPa, and a
compressive stress of -(2-3.8) GPa. The prepared CrN films exhibit a
strong enhancement on the tribological properties.
3:45 PM A5.3
EFFECT
OF DEPOSITION PARAMETERS, SURFACE SPUTTER, AND POST-DEPOSITION
ANNEALING ON THE MICROSTRUCTURE, CHEMICAL COMPOSITION, AND ELECTRICAL
CHARACTERISTICS OF ZnO THIN FILMS. B. J. Kim, J. H. Choi,
N.-H. Cho , Inha University, Dept. of Ceramic Engineering,
Incheon, KOREA.
ZnO thin films were prepared by
rf-magnetron sputter techniques at various conditions. The
microstructure, surface morphology, chemical composition, and
electrical characteristics of the films were investigated as
functions of substrate temperature (R.T. - 500oC), sputter gas
(O-2/Ar = 0 50), post-deposition annealing
atmospheres, and surface sputter conditions.
ZnO thin films grown at 500oC with sputter gas of pure argon as
well as at R.T. with sputter gas of a mixture of argon and oxygen
(O-2/Ar = 2) exhibit a strong tendency of 002 preferred
orientation, compared with a considerable random orientation at the
other conditions. The thin films with 002 preferred orientation has a
chemical stoichiometry of Zn/O=1.01, a band gap of 3.3 eV, and a
packing density of 98, respectively.
The films, which were annealed at various atmospheres, exhibit sheet
resistances ranging from a few G to a few k, charge
carrier concentration of 1015 1018/cm3, and
mobility of a few 10 cm2/Vsec. When the surface of the films was
sputtered at particular conditions, the surface area was increased,
making the films more sensitive to heat-treatments at particular
atmospheres.
4:00 PM
A5.4
STRUCTURE AND PROPERTIES OF
NANO-CERAMIC THIN LAYERS. J.Th.M. De Hosson , J.
Hooijmans, R. Popma, Department of Applied Physics, University of
Groningen, Groningen, THE NETHERLANDS.
The research
presented in this contribution focuses on the densification of sol
gel derived thin nano-ceramic layers by laser radiation. In our work
the sol-gel concept is combined with inkjet technology and laser
treatment of surfaces. Afterwards the drops are exposed to an intense
laser beam that gives rise to drying and densification of the drops,
thereby forming a sintered polycrystalline thin ceramic layer.
Arbitrary patterns can be generated and foil thickness of 0.1 - 0.5
mm can be obtained. The research concentrates on the densification
mechanisms, the residual stress formation and crack patterns in the
layers after laser radiation. The thin layers investigated are mainly
SiO2, Al2O3 , TiO2 and to a minor extent ZrO2. Morphologies of the
materials are studied using a dedicated low voltage scanning electron
microscope. The advantage of this low voltage microscope over
conventional microscopes is that a non- conducting specimen may be
studied directly, since charging effects are suppressed by balancing
the amount of inserted and emitted electrons at low accelerating
voltages. For highly porous layers a model is described for the
crack patterns expected for layers of various thickness. Thick
layers, for example Al2O3 layer thickness exceeding 500 nm, are
expected to delaminate. Layers with lower thickness will exhibit
channeling crack like behavior. For layers of low thickness, e.g.
below 200 nm, only sub-micron sized surface cracks are expected and
observed in the layers.
4:15 PM A5.5
LOW
TEMPERATURE PREPARATION OF THIN FILM INDIUM TIN OXIDE VIA CONTROLLED
CRYSTALLIZATION OF AS-DEPOSITED AMORPHOUS THIN FILMS.
David C. Paine , Trevor Whitson, Derek Janiac and Cleva Ow
Yang, Brown University, Division of Engineering, Providence RI.
Polycrystalline tin-doped indium oxide (ITO) is a
degenerate semiconductor that is used as
a transparent conductor in flat panel display applications. Films
with both low resistivity
(1-2x10-4 ohmcm) and good transmissivity (>90%) are typically
deposited on heated substrates (approx. 200 C) and often
possess a distinct ricefield morphology consisting of highly textured
polycrystalline grains (500 nm diameter) which contain 10 nm diameter
subgrain regions. The deposition of ITO on heat intolerant polymer
substrates or polymer-based color filters requires the use of low
substrate temperatures (i.e. RT) and low
kinetic energy deposition methods. These deposition conditions favor
the formation of amorphous ITO thin films. The transformation of the
amorphous phase to polycrystalline ITO occurs at remarkably low
temperatures; for example, at 190C, the
transformation of In 9.8wt%SnO2 is complete after 1 hour. The details
of the kinetics of this transformation are important both as a
potential process step for manipulating thin film ITO
microstructure/properties and in understanding the formation of the
ricefield structure that forms during deposition on heated
substrates. We have usedin situ monitoring the electrical
(resistivity, Hall mobility) and optical (time resolved reflectivity)
properties in combination with glancing incidence angle x-ray and TEM
to establish the kinetics of transformation of e-beam deposited
indium oxide containing 0, 1, 2.5, 5.5, and 9.8 wt% SnO2 over the
temperature range 100 to 200 C in reducing and oxidizing
environments. We report that
the rate of transformation increases with decreasing Sn content and,
based on this, have demonstrated a multilayer scheme to control the
final microstructure of crystallized ITO which optimizes resistivity
and optical transmissivity. Detailed x-ray and resistivity analysis
reveals that amorphous ITO undergoes crystallization in a two stage
process in which the amorphous structure undergoes relaxation (with
an Avrami growth mode parameter of unity) which is followed by
two-dimensional nucleation and growth (growth mode parameter of 3).
The activation energy for both processes as a function of composition
has been established and, based on TEM and x-ray analysis, we have
developed a model that describes microstructure development in this
system as a function of film deposition parameters, annealing
temperature and gas ambient.
4:30 PM
A5.6
MICROSTRUCTURE-PROPERTY
RELATIONSHIPS OF TIN OXIDE THIN FILMS GROWN ON DIFFERENT SUBSTRATES.
L. Fu and X.Q. Pan, Dept. of Materials Sci. & Eng.,
University of Michigan, Ann Arbor, MI; M. Bastea and C. Uher, Dept.
of Physics, University of Michigan, Ann Arbor, MI.
Tin oxide thin films were deposited on SiO2/Si-(100) and
sapphire (with various cuts) substrates by electron beam evaporation
under controlled deposition conditions. The effects of substrate
temperatures and post-deposition annealing conditions on the
microstructure and electrical properties of the films were studied.
X-ray diffraction studies showed that films deposited at lower
temperatures are amorphous, whereas those deposited above
300C are polycrystalline with the -SnO structure.
All -SnO films on different substrates have a strong fiber
texture with -SnO (001) parallel to the substrate surface.
The rutile SnO2 films were obtained by annealing as-deposited
films at temperature above 550C. Scanning electron
microscopy and atomic force microscopy studies showed that a larger
grain size exists in SnO2 films obtained by annealing the
-SnO films which were deposited at 600C.
Transmission electron microscopy studies revealed that the
microstructures of the rutile SnO2 films are determined by the
substrate structure and annealing conditions (temperature, time, and
oxygen pressure). Electrical properties and the responses to reducing
gases such as CO strongly depend on the microstructures of films. The
structure-property relationships of these films will be
discussed.
4:45 PM
A5.7
PREPARATION, COMPOSITION,
MICROSTRUCTURE, AND ELECTRICAL PROPERTIES OF Y2O3 DOPED CEO2
THIN FILMS. Chunyan Tian , Siu-Wai Chan, School of
Engineering & Applied Science, Materials Science Division, Columbia
University, New York, NY.
Polycrystalline and high
quality textured Y2O3 doped CeO2 thin films were prepared on
various substrates using electron beam evaporation. The
microstructures of the films are largely dependent on the substrates.
Polycrystalline films formed on oxide substrates with metallic films
in between, while single crystal-like [001] textured films evolved on
(001)LaAlO3, [110] textured films grew on amorphous silica, and
[001]&[111] dual textured films formed on r-cut sapphire. The oxygen
partial pressures during and post film depositions are found to have
a significant effect on the film microstructures and electrical
properties. Low oxygen partial pressure promotes [111] textured films
which exhibit electronically conducting mechanism; while the films
grown in high oxygen partial pressure behave ionically conducting.
The composition and stoichiometry of the films were verified by
Rutherford backscattering spectroscopy analysis. Both x-ray
diffraction and transmission electron microscopy analyses gave
consistent microstructural information. Complex impedance
spectroscopy was used to study the electrical properties of the
films.
SESSION A6: POSTER SESSION
Chairs: Eduard Arzt,
Theodore I. Kamins and Carl V. Thompson
Wednesday Evening,
December 2, 1998
8:00 P.M.
Grand Ballroom (S)
A6.1
AUTOMATED
MICROSTRUCTURAL ANALYSIS OF POLYCRYSTALLINE THIN FILMS.
D.T. Carpenter , J.M. Rickman, K. Barmak, and J.R. Codner,
Lehigh Univ, Dept of Materials Science and Engineering, Bethlehem,
PA.
The grain size distribution of a thin film can
have a profound effect on its performance, for instance the
reliability of metallization in microelectronic applications, or the
signal to noise ratio of a magnetic thin film. The grain size
distribution is typically measured manually from TEM micrographs of
the film, over a population of a few hundred grains. However, this
limited sampling may result in significant errors, making measurement
over larger populations desirable. Automated grain size analysis
should improve statistics, but simple image processing techniques
give unacceptable results when applied to TEM images due to complex
contrast including bend contours and grain boundary fringes. A robust
image analysis algorithm has been developed and applied to TEM images
of an Al thin film to measure the grain size distribution from a
population of over 8000 grains. This novel algorithm will be
summarized and its results will be quantitatively compared to those
of conventional manual analysis. In addition, the results of manual
analyses performed by different people will be treated in a similar
fashion as a reference. Results of the automated analysis applied to
different materials and microscopies will also be
presented.
A6.2
ATOM PROBE
FIELD-ION MICROSCOPY CHARACTERIZATION OF MULTILAYER THIN-FILM
STRUCTURES. D.J. Larson , M.K. Miller, Oak Ridge National
Laboratory, Metals and Ceramics Division, Oak Ridge, TN; A.K.
Petford-Long, A. Cerezo and G.D.W. Smith, University of Oxford,
Department of Materials, Oxford, ENGLAND.
Multilayer
thin film structures, which are formed by alternate deposition of two
or more different elements or compounds, have a range of applications
including magnetic recording media. The nature of the interfaces
between the films and between grains is very important in determining
the properties of these films. Atom probe field ion microscopy has
sufficiently high spatial resolution to characterize local structure
and composition of multilayer thin film devices at the atomic scale.
However, a major difficulty is specimen preparation, which requires
fabrication of a sharply pointed needle (radius of the order of 50 nm)
containing the layers of interest in the apex region. Focused ion
beam milling has been used to fabricate field-ion specimens from a
multilayer film structure containing 100 repetitions of a
(Cu2nm/Co2nm) bilayer deposited directly onto a planar substrate. The
use of a focused ion-beam allows a suitable specimen to be cut out of
the film and to concurrently monitor the fabrication process by
imaging with secondary electrons. This specimen fabrication method
has allowed the observation of the structure of these devices,
including individual film thickness and curvature as well as grain
boundary properties, by field-ion imaging and three-dimensional atom
probe compositional analysis. In addition, the correlation of
structural and chemical observations with magnetic property data from
the same thin film structure has been accomplished.
This
research was sponsored by the Division of Materials Sciences, U. S.
Department of Energy, under contract DE-AC05-96OR22464 with Lockheed
Martin Energy Research Corp. This research was conducted utilizing
the Shared Research Equipment (SHaRE) User Program facilities at Oak
Ridge National Laboratory.
A6.3
THIN FILM
TEXTURE DETERMINATION FROM RHEED. Dmitri Litvinov ,
Thomas O'Donnell, and Roy Clarke, Randall Laboratory of Physics,
University of Michigan, Ann Arbor, MI.
A kinematic
theory of reflection high energy electron diffraction (RHEED) is
presented for textured polycrystalline thin films. RHEED patterns are
calculated for arbitrary texture situations and for any general
crystallographic orientation that may be encountered in thin-film
growth. It is shown that the RHEED pattern can be used as a fast and
convenient tool for in-situ texture characterization. The
approach also permits quantitative extraction of angular dispersion
parameters which are useful for optimizing thin-film growth
conditions.
The application of the technique is demonstrated for texture
identification and optimization of growth parameters of cubic boron
nitride (c-BN) thin films. We find that decreasing the energy of
nitrogen ions used to stabilize the cubic phase in ion assisted
sputtering, significantly reduces the amount of angular distpersion
in the texture direction.
A6.4
COMPREHENSIVE
CHARACTERIZATION OF THIN FILMS USING X-RAY REFLECTOMETRY AND
FLUORESCENCE. R. Wilson, G. Hamill , Rigaku USA Inc.,
Danvers, MA; M. Funahashi, M. Kuraoka, S. Fujimura and H. Kohno,
Rigaku International Corporation, Osaka, JAPAN.
Critical issues in the characterization of thin films include
thickness, elemental composition and stoichiometry, surface and
interface roughness, and density. This paper will present data from
two complementary techniques that completely characterize single
layer and multi-layer thin films. X-ray Reflectometry (XRR) provides
data on the thickness, density and surface roughness, while X-ray
Fluorescence (XRF) provides corresponding data on thickness and
elemental composition. In the semiconductor industry, XRF has been
widely used as the standard characterization tool for film thickness
and composition. As the direction of current and future generation
films is toward ultra-thin layers, surface roughness is becoming a
more significant factor in the device properties. The comprehensive
characterization of these films by XRR and XRF, therefore, is
necessary for improved process control. As an example, thin film
ferro-electric materials, BaxSr1-xTiO3 (BST) on Si wafers will be
discussed. These films are known to play an important role not only
for non-volatile memory but also for next generation memory
processes. The results of the analyses of these materials by the
combination of XRR and XRF give a better understanding of the quality
of the deposited films.
A6.5
QUANTITATIVE
RHEED ANALYSIS OF POLYCRYSTALLINE FILM TEXTURE AND ORIENTATION.
J.W. Hartman and H.A. Atwater, California Institute of
Technology, Dept of Applied Physics, Pasadena, CA.
Reflection High Energy Diffraction (RHEED) is a tool for analysis of
crystalline texture and surface roughness which is compatible with
many growth chamber geometries. However, because solving the
equations of motion for electrons diffracting from an imperfect
crystalline surface is difficult, quantitative evaluation of RHEED
patterns to determine crystalline quality is prohibitively
time-consuming. We are developing efficient algorithms able to
predict the effects of grain size, surface roughness, and crystalline
texture distribution on RHEED patterns in the limit of kinematic
electron scattering, and will present predictions and comparisons to
RHEED from biaxially textured ion beam assisted deposited (IBAD)
MgO. In the limit of kinematic RHEED from mosaic crystals of MgO,
the shapes of the high order (n 3,4,5) diffraction spots are strongly
dependent on the grain texture distributions. By studying these
higher order diffraction spots, we find that we can discern
distributions of grain misalignment in mosaic MgO about the three
principle crystal axes to within 1 degree.
A6.6
ESTIMATION OF
ENERGY DISSIPATED RATIO FOR MULTI-LAYERED FILMS BY NANOINDENTATION.
Naoto Kikuchi , Yoshihiro Sawahira, Akishige Sato, Eiji
Kusano, Akira Kinbara, Kanazawa Inst. Tech., Adv.Mater. Sci. Res. and
Develop. Center, Kanazawa, JAPAN.
Hardness is an
ambiguous concept in physical meaning. In this presentation, we
propose the dissipated energy and the energy dissipation ratio. The
former is the energy to deform a material plastically and can be
obtained from the area surrounded by loading and unloading curves in
load-displacement data of nanoindentation. The latter is the ratio of
the dissipated energy to the total energy applied to a material.
Large value of the ratio suggests that large plastic deformation take
place in a material relative to the elastic deformation. The ratio
gives us significant information about the mechanical properties in
complex system such as a multilayered film with different, dominant
process for deformation.
We examined the hardness, the dissipated energy and the energy
dissipated ratio to the total energy applied to films of TiN/Al
multilayered films selected as typical film with hard/soft
combination using the nanoindentation. The effects of thickness for
TiN or Al layer on the mechanical properties were discussed. The
films were prepared by dc magnetron sputtering process on silicate
glass substrates in their order of TiN/Al/glass. Thickness of each
layer was 100 and 500 nm for Al and 300, 500 and 700 nm for TiN.
Dynamic hardness of all films estimated from the maximum load and
displacement was about 14 GPa with the indentation load of 0.98 mN.
The energy dissipated ratio of the films with thickness of 100 nm Al
layer showed about 48 % and increased to 65 % with 500 nm thickness
of Al. In both cases, the ratio was independent to the thickness of
TiN layer. It was concluded that the energy dissipated ratio is
effective indicator to discuss a detail behavior of deformation.
A6.7
EFFECT OF
THERMAL TREATMENT ON THE INDENTATION FRACTURE BEHAVIOR OF SPUTTER
DEPOSITED MUTLI-LAYERED THIN FILMS ON SILICON. M.
Manoharan *, Su Dan* and G.Muralidharan**, * Division of Materials
Engineering, School of Applied Science, Nanyang Technological
University, SINGAPORE; ** Failure Analysis and Reliability Department
Institute of Microelectronics, Science Park II, SINGAPORE.
Indentation cracking has been extensively used for
the measurement of fracture toughness of brittle materials due to its
small sample size requirements as well as a relatively good
correlation with values obtained from traditional fracture mechanics
tests. Different types of cracks can be generated on the surface of
brittle materials by indentation loading. Loading by sharp indenters
such as the Vickers indenter leads to the generation of a remnant
plastic impression in the surface and such contacts are often termed
elastic-plastic. In these cases radial as well as lateral cracks may
be generated. In the present study, microhardness testing has been
used to follow the evolution of the mechanical properties of a Ti -
Ni(V) - Al(Cu) thin film deposited on a Si substrate. Composite
hardness and fracture toughness have been followed as a function of
heat treatment temperatures and times and were found to be dependent
on both variables. The roles of residual stresses, interdiffusion,
and intermediate phase formation in the observed variation in
hardness and fracture toughness are discussed.
A6.8
EXCIMER-LASER
CRYSTALLIZATION OF SI THIN FILMS ON TUNGSTEN. H. Jin
Song , J. H. Glownia, and S. M. Gates, IBM Thomas J. Watson Research
Center, Yorktown Heights, NY.
Crystallization of
amorphous Si thin films in contact with a metal is often accompanied
by silicide formation and metal diffusion into Si. Depending on the
application of the crystallized film, these phenomena can be
detrimental.
The excimer-laser crystallization technique is well suited to
circumvent these side effects due to its rapid surface processing
capability. Additionally, tungsten acts as a relatively stable
substrate because tungsten silicide forms at higher temperatures,
compared to other metal/silicide systems.
In this presentation, excimer-laser crystallization of Si thin films
on tungsten will be discussed. The characteristics of irradiated Si
thin films depend mainly on the energy densities with which the films
are irradiated. The energy density dependence of microstructure,
silicide formation, and tungsten diffusion will be
presented.
A6.9
OF
THE SUBSTRATE TEMPERATURE ON THE PROPERTIES OF LASER CRYSTALLIZED
POLYCRYSTALLINE SILICON. N.H. Nickel ,
Hahn-Meitner-Institut Berlin, Berlin, GERMANY; G.B. Anderson and R.I.
Johnson, Xerox Palo Alto Research Center, Palo Alto, CA.
Polycrystalline silicon films were prepared by laser
crystallization of amorphous silicon at various temperatures. At 300K
and at a laser fluence of 540 mJ/cm2 an average grain size of
1.5 was obtained. With increasing substrate temperature the
maximum grain size decreases. This is accompanied by a decrease of
the laser fluence required to maximize the grain size. An increase of
the grain size results in a decrease of the spin density due to a
reduction of the grain-boundary volume. In addition, the increase in
substrate temperature resulted in a pronounced decrease of the spin
density independent of the laser energy density. The grain-boundary
defects are passivated by exposing the poly-Si films to a hydrogen
plasma at elevated temperatures. This causes the spin density to
decrease to a residual value of 9 x10^16cm^-3m to greater than 100 m). In addition to these
microstructural results, we will also discuss additional less
well-recognized attributes of the SLS process, such as (1) wide
energy-density processing windows, (2) high throughput rates, and (3)
insensitivity to the particular method and details of deposition,
which are of importance in the actual implementation of the method.
This work was supported by DARPA under project N61331-94-K-0033.
A6.11
Withdrawn.
A6.12
CHARACTERISTICS
OF BORON-DOPED SiGe FILMS FOR LOW-VOLTAGE MOS GATE.
Takashi Noguchi , Dharam Pal Gosain and Setsuo Usui,
Research Center, Sony Corporation, Yokohama-shi, JAPAN.
Precise control of the threshold voltage is
important for the CMOS transistor in low-voltage driving. In order to
keep current drivability without modifying the channel concentration,
new gate materials with a controllable work function within the
bandgap of polysilicon is required for CMOS and SOI beyond the 0.18
m channel size. SiGe is a candidate for the gate material, as
capped Si/SiGe structure.
After preparing solid targets from Si and Ge powder, SiGe thin films
were deposited without using dangerous CVD gases like SiH4 or GeH4.
After thermally annealing B-doped films or annealing by UV pulse
beam, the films were characterized. As the content of Ge increases,
the refractive index increases and the band edge narrows. The higher
the annealing temperature, the lower the resistivity and the higher
the degree of crystallization. For films with a high Ge content
(x0.5), the Vfb value, which was calculated using the CV
characteristics, was adjusted to the middle point between p+ and n+
poly-Si deposited by CVD. We found that Vfb can be controlled without
a significant shift in the B profile by using UV pulse beam annealing.
The B-doped SiGe films are expected to be a promising gate material
for MOS and SOI transistor in low-voltage driving.
A6.13
STUDY OF
NICKEL SILICIDE IN POLYCRYSTALLINE SILICON FILM. C.H.
Ho , M.C. Poon and J.K.O. Sin Department of Electrical and Electronic
Engineering, The Hong Kong University of Science and Technology,
Clearwater Bay, HONG KONG.
Nickel silicide (NiSi) is
one of the most promising silicides for future novel devices. Effects
of Ni silicides in polycrystalline Si (poly-Si) and amorphous Si
(a-Si) films have been studied. 180nm CVD a-Si was deposited at
475C onto thermal oxide. 260nm poly-Si was CVD-deposited at
550C, implanted with arsenic at 50keV and 1x1016/cm2, and
annealed at 950C/30min. Ni film was e-beam evaporated in
vacuum<2E-7 torr. NiSi (70nm) has been found to have low
resistivity of 25/15/30 micro-ohm-cm after
300/700/800C/30min annealing. On a-Si, however, NiSi is very
unstable and has 60/25/18/45/45/ 60/60 micro-ohm-cm after
200/300/400/500/600/700C annealing. NiSi/Si layer structures
are confirmed for poly-Si. Nevertheless, for a-Si, the film is a
mixture of NiSi, NiSi2 and a-Si. The better thermal stability of
silicides on poly-Si might be correlated to the larger poly grains
formed after dopant anneal, as confirmed by SEM. Moreover, Ni also
causes a-Si to form poly-Si at 1 micron/hour and with mobility
>100 cm2/Vs after 500C annealing, probably due to the
diffused Ni (NiSi2) in a-Si. Furthermore, pure NiSi gate
(120nm) formed from 54nm of Ni and 100nm of a-Si (or poly-Si)
on 100nm thermal oxide is found to have low resistivity of 13
micro-ohm-cm and stable structures after 400-1000C/30min
annealing. Threshold voltages (VT) are around 0.5V for both p- and
n-Si substrates (doping 1E15/cm3). The new NiSi midgap gate can
help to achieve symmetrical VT and substantially impact the CMOS and
TFT technologies.
A6.14
UNIFORM Co
SALICIDE FORMATION FOR SUB-QUARTER-MICRON DUAL-GATE CMOS DEVICES.
Hirofumi Sumi , Jun Suenaga and Yutaka Okamoto, Process
Development Dept., System LSI Division, Semiconductor Company, Sony
Corporation, Kanagawa, JAPAN.
For dual-gate CMOS
application, a low depletion condition of the gate electrode is
necessary by the high content of the dopant. However, it is difficult
to uniformly reduce the sheet resistance of Co salicide by
non-optimized pretreatment process. Applying the salicide process
with an optimized pretreatment method, low sheet resistance and low
depletion condition of the gate were obtained.
Before salicidation, the surface morphology of the poly-Si with a
high concentration of doped arsenic (5x1015/cm2) was rough
after pH7.2 HF pretreatment. In the case of a relatively low
concentration of arsenic (less than 3x1015/cm2) doped into
the Si or p-type poly-Si, smooth surface morphology of poly-Si was
maintained after the pH 7.2 HF treatment. By using the salicide
process with pH3.0 HF pretreatment method, superior uniformity in the
sheet resistance and a reduced depletion condition of the gate with
also high concentration of doped As at the narrow regions were
obtained. The Si crystal surface with arsenic was selectively etched
off by the pH7.2 HF treatment as determined by TEM analysis. The
surface morphology was rougher in the narrow region of poly-Si than
in the wide region of the gate according to AFM analysis. It seems
that oxygen is easily diffused from sidewall oxide layer (the
structure is SiO2/SiN on the gate) at the narrow gate regions and
the roughness of the surface with the pretreatment process was
affected by the diffused oxide. As a result, nonuniformly
salicidation occurred at the narrow regions with pH7.2 HF
pretreatment salicide process.
In the mechanism of the degradation of morphology, after the native
oxide on the poly Si is etched off by HF2- in the HF treatment,
the polycrystal that is highly damaged by arsenic ion implantation
and in which a damage layer is remained in spite of activation
annealing at 1000C for 10s, is easily etched off by the
NH4+ in the pH7. 2 HF. The grains on the Si surface are eroded
by NH4+ or HF2- component in the pH7. 2 HF solution. The
HF solution without NH4+ (pH3. 0) prevents the corrosion of Si.
As a result, smooth morphology of the poly-Si is obtained by
pretreatment using pH3.0 HF treatment
A6.15
EFFECT OF
ANNEALING TEMPERATURE AND THICKNESS ON SILICIDATION PROCESS OF
TiN/TiSi2/Si STRUCTURES. S. Santucci , A.R. Phani,
Department of Physics University of L'Aquila, Via Vetoio, Coppito,
L'Aquila, ITALY; R. Alfonsetti, M. De Biase, Texas Instruments,
Avezzano, ITALY.
One of the most promising
metallization schemes on silicon is the TiN/TiSi2/Si structure,
since it takes advantage of good electrical contact between Si and
TiSi2 and the property as a diffusion barrier of TiN. Initial
stage of the C49-TiSi2 formation has been investigated at
590C and complete formation of C54-TiSi2 phase has been
observed at 850C by using Transmission Electron Microscopy
(TEM) as well as Grazing Angle X-ray Diffraction (GAXRD). The results
of TiN/TiSi2/Si structures with different thickness and annealed
at different temperatures with and without N2/H2gases have been
studied. we demonstrate that as the thickness of TiN and Ti is
increased from 30(TiN)and 170(Ti)respectively to
500(TiN) and 500(Ti) there is a dramitic change in the
formation of silicide layer at an annealing temperature of
850C. This is explained by the dissociation of TiSi2, in
which the dissociated Ti is consumed in the formation of TiN (since
it has been annealed in N2 atmosphere)which has been further
observed in grazing angle XRD where the intensity of the TiN peak is
increased. Similar behviour is not observed in the case of higher
thickness sample.
A6.16
STRUCTURAL
TRANSFORMATIONS IN THERMAL-IONIC TiN FILMS ON THE (111) Si
SUBSTRATE. M.S.Boltovets, G.M. Veremeychenko, Research Institute
ORION, Kyiv, UKRAINE; T.D. Kotikova , V.A. Makara, O.V.
Rudenko , National Kiev Taras Shevchenko University, Kyiv, UKRAINE.
Methods of electronography and roentgenology were
used to study the structure and phase composition of TiN films of
different thickness obtained by the thermal-ionic synthesis on the
single crystal (111)Si substrate.
It is shown that TiN films on the TiN substrate at the initial growth
stages have amorphous structure (L<30Å). The existence of X-ray
amorphous constituent (70%) and the appearance of the textured
<111> polycrystalline phase (30%) are observed in it if the film
thickness grows up to 1 m. Further growth of the film thickness
up to 6 m results in a decrease of the fraction of the TiN
amorphous constituent phase down to (35%) and in an increase of the
polycrystalline phase (up to 65%). The size of polycrystalline phase
grains makes up 16OÅ.
To determine the thermal stability of films the samples were annealed
in vacuum within the temperature range up to 800C. It is
shown that annealing at 600C leads to the appearance of the
TiN polycrystalline phase and for thicker films (>1m) to the
redistribution between fractions of both phases. Annealing at
800C almost completes the amorphous phase. The formed TiN
layers due to annealing have thermodynamic texture [111], the
disorientation angle being several degrees. Annealing leads to a
significant decrease of micro- and macrostresses in films, at
800C stresses fall to zero. The parameter of TiN film lattice
on annealing decreases and on annealing at 800C becomes close
to standard values (4.2416(4)Å). The specific resistance of TiN
films is 3050 cm. After annealing the
electrical conductivity of films is within the same
ranges.
A6.17
LARGE AREA
DEPOSITION OF CADMIUM SULFIDE BY CHEMICAL BATH DEPOSITION FOR
PHOTOVOLTAIC APPLICATIONS. David S. Boyle and Paul
O'Brien, Department of Chemistry, Imperial College of Science,
Technology and Medicine, South Kensington, London, UK.
One of our research interests at Imperial College
concern solar cell materials, specifically polycrystalline
n-CdS/p-CdTe heterojunction devices. The main advantage of thin film
solar cells is their promise of large area, low cost photovoltaic
energy conversion for a variety of applications.
Chemical Bath Deposition (CBD) of compound semiconductors has
recently gained the attention of workers in the field of photovoltaic
technology. The technique offers many advantages over the more
established synthetic routes to semiconductor materials such as CVD,
MBE and spray pyrolysis. The main aim of the project is to develop a
recyclable chemical bath deposition (CBD) process, for the production
of the CdS window of the devices on TO-glass substrates, in which
99% of the cadmium is recycled or recovered. The present commercial
process utilises only around 2% of the initial materials in a batch
process The work is in collaboration with BP Solar Ltd (who are the
world leaders in this technology with their Apollo cells). Initial
efforts at Imperial College have utilised chemical modelling and
speciation studies to generate an improved process efficiency of ca.
90% w.r.t. total cadmium.
It has been established that solar cell parameters are sensitive to
the nature of the CdS/CdTe interface. Understanding the mechanisms in
detail would accelerate device optimization. Electrical behaviour,
structure and impurity distributions have been investigated. Our
results from quantitatative SIMS have indicated that high
concentrations of chloride and oxygen at the CdS-CdTe interface
region are necessary for high device efficiencies.
A6.18
PHASE
SEGREGATION AND GRAIN BOUNDARIES IN POLYCRYSTALLINE CU(GA,IN)SE2
FILMS - A PHOTOELECTRIC AND OPTICAL STUDY ON THE MICRO-SCALE.
Gerd Lippold , Universitaet Leipzig, Fakultaet fuer Physik
und Geowissenschaften, Leipzig, GERMANY; Volker Nadenau, Hans-Werner
Schock, Universitaet Stuttgart, Institut fuer Physikalische
Elektronik.
Polycrystalline semiconducting
chalcopyrite films are successful candidates for a new generation of
commercial high-efficiency, low-cost thin film solar cells. The
Cu(In,Ga)Se2 absorber layers are not only polycrystalline, but
often also multiphase systems. The influence of some aspects of this
complicated microstructure on the macroscopic photoelectric
properties is still object of controversial discussions. Examples are
the microscopic origin of structural and electrical improvements by
isoelectronic dopants such as sodium or the processing-dependent
influence of grain boundaries and interfaces on solar cell
properties. A typical size of grains and segregations is one
micrometer. The three-dimensional spatial resolution of confocal
laser microscopy can be used to obtain valuable spectroscopic
information on this scale even within the complete multilayer
structure of a solar cell. In the present work we study binary and
ternary phase segregations and local defect density variations in
polycrystalline Cu(Ga,In)Se2 thin films grown with deviations from
stoichiometry. Raman scattering is analyzed in order to get
information about chemical binding and structure, necessary to
identify various phases. Smaller compositional variations can be
tolerated within chalcopyrite phase homogeneity but give rise to
local variations of the intrinsic defect density.
Micro-photoluminescence at various temperatures down to 10 K is used
to characterize this type of inhomogeneities. This information is
correlated with the spectral photoresponse of the solar cell, studied
by LBIC (Light Beam Induced Current) measurements with variable
excitation energy on the same sub-micrometer scale. The LBIC
relaxation after short-pulse excitation is used to obtain the local
lifetime of the photo-excited carriers. In summary, this study
enables us to identify Cu- and (In,Ga)- rich secondary phase
segregations on the microscale, to study defect characteristics in
their vicinity and to correlate these data with the local
photoelectric and charge carrier transport properties. Especially in
cells based on Cu-rich absorber layers and in cells without sodium
content we found a significant increase in recombination velocity at
grain boundaries. Details of this behavior and its modification due
to doping/alloying with sodium and hydrogen will be discussed in the
paper.
A6.19
ABNORMAL
TEMPERATURE DEPENDENCE OF CONDUCTIVITY DUE TO THE STRUCTURAL CHANGES
IN DOPED ZINC TELLURIDE POLYCRYSTALLINE FILMS. Yaping
Cai , Wei Cai, Jiagui Zheng, Sichuan Univ., Dept of Materials
Science, Chengdu, CHINA; Lianghuan Feng, Jian Tang, Don.L.Williamson,
John.U.Trefny, Colorado School of Mines, Dept of Physics, Golden, CO.
The temperature dependence of dark conductivity of
un-doped and Cu-doped ZnTe polycrystalline films have been
systematically studied as a function of Cu concentration. The curves
of log 1/T are linear for un-doped films, but exhibit a
maximum and a minimum, then steeply raise for heavily doped films.
The temperatures at the extrema depend on Cu concentrations.
In order to understand the abnormal conductance behavior, the effects
of temperature on the structural and electronic properties of the
films have been investigated.It has been found that after annealing,
the log 1/T of doped films become linear below the
annealing temperature, which implies that the changes resulted from
annealing have been frozen when cooling. The structures in un-doped
ZnTe films only display a cubic phase, and do not show any other
phase after annealing. While, their activation energies of
conductivity and mobility do not alter. The as-deposited ZnTe:Cu
films exhibit both the cubic and hexagonal phases. The latter
increases with Cu concentration, and with temperature. However, it
has vanished above 230 C. In heavily doped films, the cubic phasres
with non-preferred orientations obviously increase with temperatures,
and a new Cu1.44Te orthogonal phase appears and increases when
increasing temperature beyond 160 C. Considering the phase
transitions, some changes in construction and ionization of Cu atoms,
together with the data of carrier concentration are analyzed. The
relationship between the activation energy of mobility, i.e. grain
boundary barrier, and structural changes is observed and discussed.
An improvement in applying ZnTe:Cu films to the back contact of CdTe
solar cells is presented. It is much valuable to add a buffer layer
of un-doped ZnTe between p-CdTe and ZnTe:Cu layers. Using our
structural design, deposition and annealing technologies based on the
above studies, the increases in efficiency by 30 - 40 % were
recorded for the spray pyrolysis and electrodeposited CdTe cells.
A6.20
STRUCTURE AND
PHASE EVOLUTION DURING RAPID THERMAL PROCESSING FOR CuInSe2 THIN
FILM FORMATION FROM A MULTILAYER PRECURSOR. Chih-hung
Chang , Billy Stanbery, Min Huang, Tim Anderson, Dept of Chemical
Engineering, Univ of Florida, Gainesville, FL; Qing Zhai, Jeremy
Thompson, Paul Holloway, Dept of Materials Science and Engineering,
Univ of Florida, Gainesville, FL.
Rapid Thermal
Processing (RTP) is an attractive technique for developing low cost
polycrystalline CuInSe2-based solar cells. It has been applied
successfully to form device quality CuInSe2 thin film based on a
stacked elemental layer process.
Based on our assessment of the thermochemistry and phase diagram of
the Cu-In-Se ternary system a binary precursor combination should
lead to a lower temperature reaction pathway for CuInSe2 thin
film formation . This novel binary In-Se/Cu-Se precursor was
deposited in a migration enhanced physical vapor deposition system at
a low temperature (200C).
Ex-situ RTP was performed in a customized RTP furnace with a quartz
susceptor. The process parameters (ramp rate, maximum annealing
temperature, and soak time) were explored to study the reaction
pathways and phase evolution. The precursors and the annealed films
were characterized by TEM, SEM, XRD, WDS, Raman, Auger and
thermoelectric probe. The relationships between precursor structures,
annealing parameters and the resulted microstructure were studied.
The results showed single phase CuInSe2 thin films could be
synthesized by this novel process at low temperature.
A6.21
STUDY OF
RESIDUAL STRESS IN VARIOUS METALLIZATIONS ON GLASS SUBSTRATES.
Chen Zhou , Nan Jiang1, Matt Korhonen, and Che-Yu Li,
Dept of Materials Science and Engineering, Cornell University,
Ithaca, NY; 1 Materials Science Center, Cornell University,
Ithaca, NY.
Thin metal coatings on glass surfaces
are widely used in various micro- and optoelectronic devices.
Because of the nature of the deposition process and differences in
thermal expansion during fabrication and use, very large residual
stress can arise in the thin metallic films and lead to interfacial
debonding. Effects of deposition conditions, thermal anneal and film
thickness on the grain structures and residual stresses are studied.
It has been found that sputtering could generate columnar grain
structures under certain conditions, but by changing the chamber
pressure, totally different stress state was found. TEM and SEM are
used to study the grain structures in the film and debonding at the
interface.
A6.22
STUDY OF
INDENTATION CRACK INTERACTION EFFECTS AND ASSOCIATED ACOUSTIC
EMISSIONS ON METALLIZED SILICON. M. Manoharan and Su
Dan, Division of Materials Engineering, School of Applied Science,
Nanyang Technological University, SINGAPORE.
The
metallization of Si represents a important industrial process and
produces a bi-layered composite of a ductile metal film on a brittle
substrate. The mechanical properties of such a composite are
determined by the properties of the two layers and the interface and
influenced by the fact that the metallized layer, being a very thin
film, possesses properties different from those of a bulk material.
The fracture toughness is also influenced by the nature and
distribution of defects which may be generated during use of these
materials, even if the manufacturing process produces a reasonably
defect free material. Indentation cracking has been extensively used
for the measurement of fracture toughness due to its small sample
size requirements as well as a relatively good correlation with
values obtained from traditional fracture mechanics tests. The
indentation process, with its associated cracks, produces permanent
plastic deformation, introduces a residual stress field and generates
acoustic emissions. The residual stress field influences the crack
pattern generated in an adjacent indent and can be used as a
methodology to model the influence of multiple defect sources. The
present study was aimed at understanding the effect of a thin Al
alloy metallization layer sputtered on a Si wafer on the sizes of the
cracks associated with the indents. It was also aimed at studying the
interaction between cracks emanating from sequentially placed
indentations. The distance between the indents which generated these
cracks was varied from a level comparable to the crack size to a
level where interaction could be ignored. This paper discusses the
changes in the nature as well as the sizes of cracks due to the
presence of the metallization layer as well as the interaction
between the stress fields of the indents in this ductile thin film -
brittle substrate composite and possible methodologies for
delineating these effects. The crack initiation and propagation
process was also followed using an acoustic emission system and
these results are also discussed.
A6.23
TRANSMISSION
ELECTRON MICROSCOPE (TEM) MICROSTRUCTURES OF Al FILMS FOR ENHANCED
REFLECTANCE IN COLOR DISPLAY TUBES. S.J. Lee, E.S. Hwang, Technology
Division of Samsung Display Devices Co., Suwon, Kyungki-Do, SOUTH
KOREA; C. Sung , T. Dolukhanyan, Center for Advanced
Materials, Dept. of Chemical Engineering, University of
Massachusetts, Lowell, MA.
Al films have been
deposited on the inside of the Color Display Tube (CDT) panel on which
black matrix carbon and RGB phosphors were coated to improve
brightness with the prevention of voltage down and less ion impact to
phosphors. The characteristics of Al films have a close relationship
with the deposition variables such as base pressure and deposition
rate causing changes in Al film microstructures and differences in the
reflectance. It is generally known that the reflectance is affected
by the thickness, grain size, and surface roughness of the Al film:
The grain size of the Al film tends to decrease when base pressure is
poor due to the presence of residual gas. The reflectance of Al
alloys was reported to be increased with the larger grain size. The
purpose of this study is to understand the relationship between the
reflectance and the microstructures of Al films as a function of base
pressure in a CDT manufacturing to optimize deposition conditions for
improved reflection properties. TEM has been employed to examine
grain size changes and surface roughness of the films under four
different base pressure conditions in both cross- sectional and
plan-view. Plan-view TEM results reveal that grain size of the Al
film tends to be larger at lowest base pressure while the thickness of
the Al film seems to be independent of vacuum status. In summary,
centered dark field images of Al films along with electron diffraction
patterns have been employed to investigate the relationship between
grain microstructures and deposition processing conditions.
Cross-sectional view of the film has shown clear characteristics of
both surface roughness and grain growth at a short processing time
such as 15 seconds which help optimization of manufacturing process
for improved reflectance and probably better brightness of
CDT.
A6.24
SIZE EFFECT OF
OPTICAL CONSTANTS OF ULTRATHIN ALUMINUM FILMS. X.D. Bai, Institute
of Metal Research, Academia Sinica, Shenyang, CHINA; R.F. Huang, City
University of Hong Kong, Department of Physics and Materials Science,
Hong Kong, CHINA; L.S. Wen , Institute of Metal Research,
Academia Sinica, Shenyang, CHINA.
Optical and
electromagnetic characteristic constants of ultrathin films, such as
n, k, , , , etc., are the fundamentals for
evaluating and designing nanocomposite multilayer films with desired
optical and electromagnetic properties. In this paper, ultrathin
aluminum film samples with thickness d in range of 2-60 nm have been
deposited on glass substrate by d.c. magnetron sputtering.
Reflectance and transparency of the samples were measured by a
WFZ900-D4 UV-Visible spectrophotometer. Optical constants n and k for
a series of wavelength in frequency band of visible light were
obtained by applying Newton-Sympson recurrent substitution method to
the calculation formulae of reflectivity and transmittivity from n
and k, using our experimental data of reflectance and transparency of
the films. Then, the real part of permittivity
and the imaginary part of permittivity
of the films were determined based on
the n and k values above-mentioned. The relationship of
and to d for
ultrathin aluminum films revealed maximum peaks of
and at d in
range of 5-20nm, corresponding to the maximum peaks of absorptance
curves in the same thickness range on the films.
A6.25
KINETICS OF
SILICON PRECIPITATION IN Al-5Cu-1Si THIN FILM DEPOSITION.
Chi-Fung Lo , Materials Research Corporation, Orangeburg,
NY.
Al-.5Cu-1Si alloy has been used as a conducting
material in semiconductor devices for years. During the
metallization process, the silicon will be reprecipitated in the
aluminum matrix to some extent depending on the deposition
temperature or post-annealing temperature. Due to the requirement of
smaller device geometries, the reprecipitated silicon may cause a
particle problem. To effectively inhibit the reprecipitation in the
deposited film without affecting the aluminum filling requirement,
the influence of the silicon precipitates in the target must be
considered. This is in addition to any effects of deposition
temperature. The quantitative link between silicon precipitation in
sputter targets and in deposited films indicates that the
precipitation size in the films increases with the precipitation size
in the targets1. In addition, at the deposition temperature range
from 300C to 450C, a transition of silicon growth as
a function of deposition temperature occurs at about 400C.
Based on these results together with the Lifshitz-Slyozov-Wagner
relationship of particle growth as a function of diffusion
coefficient and the solubility of silicon in aluminum as a function
of temperature, a formula for the precipitation size of silicon in
aluminum thin films as a function of silicon size in sputter targets
and deposition temperature is derived. By taking into account the
diffusion-controlled mechanism of particle growth and the dissolution
of silicon in aluminum at elevated temperatures, a good agreement
between measurement and calculation of the silicon precipitation
behavior in the Al-.5Cu-1Si thin film deposition is obtained.
Ref. 1 Lo et al., VLSI Multilevel Interconnection Conference,
June15-19, 1998, Santa Clara, CA.
A6.26
ROUGHNESS
EVOLUTION AND CRYSTALLINITY OF THICK SPUTTERED ALUMINUM-COATINGS. A.
Bergauer, C. Eisenmenger-Sittner , Institut fuer
Angewandte und Technische Physik, Technische Universitaet Wien,
Wiedner Hauptstrasse, Vienna, AUSTRIA.
Understanding
the growth mechanisms of physical vapor deposited metallic coatings
is of considerable importance for a wide range of applications from
microelectronics to micromagnetism.
The present work investigates the microstructural evolution of
magnetron sputtered Aluminum coatings deposited on glass substrates
(roughness smaller than 10 nm). The deposition temperatures were
varied from -100ÉC to 280ÉC, the film thickness ranged from 10 nm to
5 µm. The film surface was characterized by Atomic Force Microscopy
(AFM) in respect to roughness and power spectral density.
From the evolution of the surface roughness and of the power spectral
density with increasing film thickness the dominant growth mechanisms
are identified for the different deposition temperatures. At low
temperatures the low mobility of ad-atoms leads to the formation of
surfaces similar to those of ballistically deposited aggregates. An
increase in deposition temperature leads to the formation of rough,
polycrystalline surfaces by surface relaxation due to the activation
of surface diffusion.
A6.27
CONTROLLING
AMORPHOUS CONTENT AND STRESS STATE IN ULTRATHIN Ta FILMS.
J.F. Whitacre , University of Michigan, Dept of Materials
Science & Engineering Ann Arbor MI; Z.U. Rek, Stanford Synchrotron
Radiation Laboratory Stanford University, Stanford, CA; S.M. Yalisove
and J.C. Bilello, University of Michigan, Department of Materials
Science & Engineering, Ann Arbor, MI.
The
relationship between deposition conditions, residual stress, and
amorphous content for extremely thin Ta films was studied. Films
2.5 nm to 20 nm in thickness were sputter-deposited using different
sputter gas (Ar) pressures and cathode power settings. The average
in-plane residual stresses for all films were determined using double
crystal diffraction topography (DCDT). X-ray analysis, using the
grazing incidence x-ray scattering (GIXS) geometry, was performed
using a synchrotron light source. Transmission electron microscopy
(TEM) and transmission electron diffraction (TED) were used to gain
further information concerning microstructure and phase content. The
DCDT stress data, electron diffraction patterns, and GIXS data were
self-consistent with one another. The diffraction patterns observed
were indicative of films which possessed a combination of amorphous
and beta (tetragonal) Ta phases. The ratio of amorphous to
crystalline volume fraction was found to be dependent upon the
deposition conditions during growth. The highest amorphous fraction
was found in films deposited using 2mTorr Ar pressure and 460 W
cathode power. Similar films grown using 10mTorr Ar sputter gas
pressure and 100 W displayed a much lower amorphous content. An
inverse relationship between stress state and phase content was
observed; those films under higher residual stresses (-3.5 +/- 0.3
GPa) displayed a lower amorphous fraction as compared to films
possessing lower residual stresses (-1.5 +/- 0.4 GPa). These results
will be discussed in terms of a model which describes the
relationship between film phase content, stress state, and film
growth rate.
This work funded by ARO contract number DAAH 04-95-1-0120.
Diffraction data collected at SSRL beam line 7-2, funded by the US
DoE.
A6.28
INPUT POWER
AND BACKGROUND PRESSURE EFFECT ON SURFACE MORPHOLOGY OF SPUTTERED
COPPER FILM. W. Zou , H. N.G. Wadley, Department of
Materials Science and Engineering, University of
Virginia,Charlottesville, VA; D. Wang, Nonvolatile Electronics, Inc.
Eden Prairie, MN.
RF diode sputtering is widely used
for depositing microelectronic interconnects, giant magneto resistive
devices, and other metal films. The growth conditions (i.e. input
power, background pressure, deposition rate, bias voltage,
source-substrate distance, etc) have a large effect on the surface
morphology of the sputtered films. Using a Randex 2400-6J RF Diode
sputtering system, the deposition rate of copper and bias voltage
have been measured as a function of input power and background
pressure. To establish links with the resulting surface morphology,
surface images and grain size have been experimentally obtained.
Using Atomic Forced Microscopy (AFM), relationships between input
power, background pressure with grain size have been established.
Results indicate that grain size increases with the increasing input
power and decrease with increasing background pressure. These
observations are related to changes in the energy spectrum of the
atomic and ionic fluxes incident upon the substrate.
A6.29
LOW ENERGY
MECHANICAL INTERMIXING OF Cu-ALLOYS WITH POSITIVE AND NEGATIVE HEATS
OF MIXING. G. Wilde , H. Sieber* and J.H. Perepezko
University of Wisconsin-Madison, Department of Material Science and
Engineering, Madison, WI; *University of Erlangen-Nuernberg,
Department of Material Science (III) Glass and Ceramics, Erlangen,
GERMANY.
Cold rolling - a low strain rate mechanical
alloying procedure - was used to produce multilayer samples with
various intermixing levels. A series of binary Cu-alloys was chosen
which differ considerably with respect to their thermochemical
behavior. Cu-Ag, Cu-Co and Cu-Fe alloys show positive, Cu-Zr negative
and Cu-Ni nearly vanishing values for the enthalpy of formation. For
alloys of these systems, the late and the very early stages of the
intermixing process including the formation of stable and metastable
phases were studied in detail by the application of DSC, XRD, SEM and
TEM techniques on as rolled and pre-annealed samples. The comparative
results of the experiments were analyzed in order to examine the
effects due to mechanical mixing and effects which are related to the
thermodynamic properties of the respective alloy systems. It turns
out, that the initial alloying at ambient temperature is governed by
the deformation characteristics of the elemental components, but that
the phase formation sequence is strongly influenced by the enthalpy
of formation of the alloys. The support of the Alexander von
Humboldt-Foundation via the Feodor-Lynen-Program (V-3-FLF-1052606),
ARO (DAAG 55-97-1-0261) and ONR (N00014-92-J-1554) is gratefully
acknowledged.
A6.30
THE INFLUENCE
OF THE GLASSY CARBON SURFACE ELECTROCHEMICAL PRETREATMENT ON THE
STRUCTURE OF POLYCRYSTALLINE THIN COPPER FILMS. Tatyana
Arzhanova , Inst of Chemistry, Far-Eastern Div, Russian Academy of
Sciences, Vladivostok, RUSSIA.
The most prospective
technique of polycrystalline thin film formation is the method of
electrocrystallization which allows to control saturation in the
process of a new phase formation and growth. The crystal density and
orientation, spatial distribution of crystals and their features of
formation and growth with time directly determine the structure and,
thus, the properties of polycrystalline thin films. These variables
can be strongly influenced not only by thin film formation conditions
on substrates but also by their electrochemical surface treatment
which, at the same respect, can undergo significant evolution during
its preliminary preparation.
This paper discusses the
results of the influence of the glassy carbon surface electrochemical
pretreatment and the conditions of polycrystalline thin copper film
electrodeposition on their structure on the example of researching the
process of copper electrocrystallization on glassy carbon from
solutions of copper sulfate with sulfuric acid. The specific
conditions of the quality polycrystalline thin copper film formation
on glassy carbon were found.
A6.31
HYDROGEN
PENETRATION AND CORROSION RESISTANCE AND MICROSTRUCTURE OF
ELECTROPLATED FILMS. W. Sha and C.J. Murphy, Department
of Civil Engineering, The Queen's University of Belfast, Belfast,
UNITED KINGDOM.
The present work involves
preparation of electroplated thin coatings on mild steel samples and
investigation of their microstructure and corrosion and hydrogen
penetration properties. The types of coatings made are Zn, Ni,
Zn-Ni, Zn-Co, Zn-Fe and Cd. Chemical and microstructural
characterisation was carried out using scanning electron microscope.
The corrosion protection performance was tested using weight loss
measurements after immersion in nitric, sulphuric and hydrochloric
acids, and salty water, all representing accelerated corrosion
conditions. The results were compared to those of bare steel
substrates. Resistance to heat was also investigated, by heat
treating at 300C for 24 hours and carrying out corrosion
tests after the treatment. It has been found that Zn-Ni coating
provided the best corrosion protection for steel.
Hydrogen permeating experiments were carried out in a solution of
sulphuric acid, at a designated current density. The quantity of
hydrogen released after permeation was measured and regarded as the
quantity of hydrogen absorbed during permeation. It has been found
that all coatings reduced hydrogen permeating to some extent, but Ni
had the best effect.
A6.32
Withdrawn.
A6.33
CORRELATIONS
BETWEEN THE ELECTRICAL AND MECHANICAL PROPERTIES OF PHYSICALLY
VAPOR-DEPOSITED IRIDIUM AND RHODIUM THIN FILMS AND THE DEPOSITION
PARAMETERS. Ilan Golecki and Margaret Eagan,
AlliedSignal, Inc., Morristown, NJ.
Iridium and
rhodium are attractive candidates for use in metallizations for
electronic devices. These elements are chemically inert, possess
relatively high intrinsic electrical conductivities, have high values
of Young's moduli and tensile strengths and acceptable thermal
expansion coefficients. The actual values of these properties,
especially in thin films, depend, however, on the microstructure and
purity levels, which in turn, are functions of the method of
preparation and processing conditions. In this study, iridium and
rhodium thin films have been deposited on chromium-coated,
thermally-oxidized silicon substrates by means of physical vapor
deposition. We will describe the variation of the physical
properties of the films, such as the electrical sheet resistance,
film stress and microstructure as functions of the substrate
temperature, deposition rate and film thickness.
A6.34
EFFECTS OF
HELIUM ION IMPLANTATION ON THE STRUCTURE OF NANOPHASE TITANIUM
FILMS. Yuzun Gao , Yonghong Li, Taisong Zhang, General
Research Institute for Non-Ferrous Metals, Beijing, P.R. CHINA.
Helium can't dissolve in metals. Due to its high
flow rate, behavior of Helium becomes very important for the
structural materials used in fusion device. Diffusion and
accumulation of Helium atoms lead to the formation of bubbles and
cause the brittleness for the structural materials. In the present
work, ion implantation of Helium in Ti films was used to simulate the
behavior of Helium in Ti films. 100KeV He ions were implanted into
both nanophase Ti films and coarse grain Ti films with the same dose.
After implantation, Enhanced Proton Back Scattering (EPBS) was used to
detect the Helium in both kind of films. X-ray Diffraction and
Transmission Electron Microscopy(TEM) were used to characterize the
structure of Ti films. Vertical cross-section TEM specimens were
prepared for study of the depth distribution profile of the bubbles in
Ti films. It was observed that bubbles occurred in the coarse grain
of Ti films. The size of bubbles is between 1 to 10nm. Its numerical
density is 10 to the power of 22 per cubic meter. No bubble was
observed in the nanophase Ti films.
A6.35
ION BEAM
ASSISTED DEPOSITION AND CHARACTERIZATION OF ULTRATHIN NICKEL FILMS
VIA A MULTI-SAMPLE ELLIPSOMETRIC TECHNIQUE. Jhon F.
Londono and Richard J. Gambino, Department of Materials Science and
Engineering, State University of New York at Stony Brook, Stony
Brook, NY; Kurt E. Williams, Veeco Instruments Inc., Plainview, NY.
Deposition of ultrathin nickel films using a dual
Radio Frequency Inductively Coupled Plasma (RF-ICP) Ion Beam System
is discussed. Nickel films ranging in thickness from 30 to 350
Angstroms were deposited onto Si substrates, which have approximately
1 micron of thermally grown oxide on the surface, using an ion beam
deposition system with a nominal background pressure of 10-7 Torr.
Thickness and optical properties of films were determined via a
multi-sample, Variable Angle Spectroscopic Ellipsometric (VASE)
technique. Determination of thickness and optical constants of the
films is accomplished simultaneously by coupling the thickness and
optical properties of the films during analysis. Optical properties
and thickness of individual films are also obtained using the VASE
technique. Comparison and analysis of properties obtained via both
techniques are made, and the merits and/or benifits of both methods
are discussed.
A6.36
Withdrawn.
A6.37
PHASE
TRANSFORMATIONS IN TITANIUM / ALUMINUM MULTILAYERS. R.
Banerjee , X.D. Zhang, S.A. Dregia and H.L. Fraser, Department of
Materials Science and Engineering, The Ohio State University,
Columbus, OH.
Recently, there have been reports of
interesting phase transformations in polycrystalline Titanium /
Aluminum multilayered thin films with a columnar growth morphology.
Titanium has been reported to undergo a transition from its bulk
stable hcp crystal structure to fcc in cross-section TEM specimens of
Ti / Al multilayers. Similarly, Al is also reported to transform
from fcc to hcp at small layer thicknesses, on the basis of
cross-section TEM examination. These results have been qualitatively
rationalized based on a classical thermodynamic model of multilayer
phase stability and a biphase diagram for Ti / Al multilayers has
been proposed. However, there is a certain amount of controversy
surrounding the issue of structural transitions in Ti especially due
to the inconsistencies between results obtained by cross-section TEM
and x-ray diffraction. These discrepancies can possibly be accounted
for on the basis of increased susceptibility of cross-section TEM
specimens of Ti / Al multilayers to hydrogen contamination
affecting the phase stabilities. The corresponding effect on the
biphase stability diagram has been qualitatively demonstrated. In
order to reduce the influence of hydrogen on the phase stability, the
multilayers have been studied in a plan-view geometry. Furthermore,
the formation of fcc Ti in as-deposited multilayers with very small
volume fractions of Ti has been studied by fabricating new
multilayers. These results will be discussed and the biphase diagram
for this system correspondingly modified.
A6.38
EVOLUTION OF
GROWTH STRESS IN TiCux-ALLOY FILMS. Stephan Bertel ,
Reinhard Abermann, Inst of Physical Chemistry, Univ of Innsbruck,
AUSTRIA.
The growth stress (i. e. film forces
normalized to substrate width) of TiCux-alloy films on alumina
substrates was measured in situ under UHV-conditions with a cantilever
beam technique. The alloy components were evaporated from separate
evaporation sources. Both the effect of substrate temperature and
stoichiometry on the growth stress of the respective alloy-film were
investigated. Pure Cu- as well as pure Ti-films are polycrystalline
(island growth) with compressive forces in the continuous film. In
the alloy-films, deposited at TS<200C these compressive
stress contributions are reduced with increasing Cu-content. For
films of composition between TiCu and TiCu2 the differences in the
stress curves are marginal. Growth stress as well as stress changes
after deposition indicate the formation of amorphous alloy films.
This is confirmed by electron microscopy (TEM) and diffraction (TED)
results. A significant compressive stress is again found in TiCu3
films which in view of the TEM microstructure is interpreted to
indicate Cu segregation in these films. Annealing experiments of low
temperature alloy-films will also be presented. With high temperature
alloy-films (TS>200C) a transition from amorphous to
the formation of polycrystalline films is seen in the TEM and TED.
The respective stress vs. thickness curves of these alloy-films show
an irregular sequence of tensile as well as compressive film forces of
comparable magnitude for all alloy compositions. This indicates
strong recrystallization and segregation of different alloy phases
already during alloy depositon. This transition in the growth mode
was investigated in detail for TiCu-films. The results of these
experiments show that the growth mode of these films and the stress
changes after deposition are very sensitive to minute changes in the
stoichiometry and substrate temperature between 300C and
350C.
A6.39
EVOLUTION OF
PHASE COMPOSITION AND ASSOCIATED PROPERTIES IN THE PROCESS OF GROWTH
OF THIN FILMS. S.A. Kukushkin , Institute of Mechanical
Engineering, Russian Academy of Sciences, Bolshoy, RUSSIA.
A complete set of equations describing the evolution
of phase composition of an island ensemble at the stage of the Ostwald
ripening in the process of thin film growth is derived and its
solution is found. The size distribution function of islands in solid
solutions is obtained for different types of the growth mechanisms.
The general approach to control phase composition and associated
properties ( electric, optical, mechanical and others ) in the formed
multicomponent systems is elaborated. It is shown that the most
favourable conditions to control these properties are discovered at
the Ostwald ripenning stage and also during non-linear phenomena, such
as, self-excited oscillations or self-organization. The relationship
between size and composition of new phase nuclei formed in the course
of condensation of solid solution films is revealed. A set of
equations describing evolution of the size distribution function of
properties in island films of solid solutions during changes in
external parameters of the system is derived and solved. For island
type films of stoichiometric composition the diagram for co-existence
of appropriate properties is plotted in the concentration-temperature
coordinates that allows to determine conditions required to gain the
properties. Probable periodic changes in time and space of various
properties on multicomponent systems undergo the first order of phase
transition are predicted.
A6.40
Abstract
Withdrawn.
A6.41
,
MICROSTRUCTURE AND MAGNETIC PROPERTIES OF Fe-Si ALLOY FILMS.
Tie-Jun Zhou , W. Yang, J.H. Yin, Z. Yu and Y.W. Du,
National Laboratory of Solid State Microstructure and Department of
Physics, Nanjing University, Nanjing, P.R. CHINA.
The polycrystalline and amorphous Fe100-xSix alloy films can be prepared by co-sputtering Fe and Si on
the common glass substrates at room temperature. Asx25, the
films have b.c.c. structure with<110>texture and asx20the
films appear some amorphous phases, whenx=28, they become
completely amorphous. The crystallization temperature of the
amorphous films increases with increasingx. The saturation
magnetization of these films decreases with increasingx, and a
plateau of constant magnetization occurs as22x28. Their
coercive force shows some fluctuation asxis increased: a minimal
value aroundx=12and a maximum one aroundx=28. Their polar Kerr
rotation_kdecreases with increasingxasx16.2, but
increases with increasingxas20x28, reach a maximum
value of0.36degree (=770nm and applied field=1T) aroundx=28and decreases quickly with increasingxagain asx30 of NiFe.
Magnetic, transport and structural properties of these films were
studied. The results show that the change in resistance is increased
by approximately 10% when sandwiching a 5 to 35
thin layer of Co or CoFe between the NiFe layers. Compared to the
Co containing structures, CoFe structure preserved the soft magnetic
properties. The easy axis coercivity, hard axis coercivity and
anisotropy field increased with increasing (CoFe, Co) thickness. The
rate of increase is a factor of 2 lower for the CoFe film series.
Rocking curves and scans show no significant
structural differences between these two types of sandwiched
structures.
A6.43
EFFECT OF
DEPOSITION AND POST HEAT TREATMENT TEMPERATURE ON NiTi SHAPE MEMORY
ALLOY THIN FILMS. Chen Zhang , Ralph H. Zee, Dept of
Mechanical Engineering, MTL program, Auburn University, Auburn, AL;
Paul E. Thoma, Johnson Controls Inc., Central Research, Milwaukee,
WI.
Polycrystalline Ti-rich NiTi thin films were
deposited from a single NiTi target using DC magnetron sputtering
system. Free standing films were obtained by using silicon substrate.
The thickness of the films was around 10-15 microns. In this
investigation, the effect of different substrate temperatures during
sputtering on the thin films' microstructure and transformation
temperatures was examined. The influence of post heat treatment at
different temperatures on the thin films' properties was also
investigated. Transformation temperatures of the thin films were
measured using differential scanning calorimetry (DSC). The surface
microstructure and cross sectional microstructure of the thin films
were studied using a scanning electron microscope (SEM), and the
crystallinity of the films was determined by X-ray diffractometry.
Results show that films deposited on a hot substrate are crystalline
even when the substrate temperature is as low as 300 degree C, while
the normal crystallization temperature for an amorphous thin film is
above 500 degree C. The microstructure of the above film has very
fine grain size. The grain size increases with increasing post heat
treatment temperature and increasing substrate temperature. The
transformation characteristics of the films are correlated with the
deposition conditions and post deposition treatment.
A6.44
PULSED LASER
DEPOSITION OF HIGH TEMPERATURE NiTi AND NiTiHf SHAPE MEMORY ALLOY
THIN FILMS. Jonathan C.Y. Chung , L. You, City University
of Hong Kong, Department of Physics and Materials Science, Hong Kong,
CHINA.
Near equiatomic NiTi and NiTiHf shape memory
alloys thin films were deposited by Pulsed Laser Depositions (PLD)
techniques. The SMA thin films are amorphous with crystallisation
temperature higher than those obtained from sputtering. Near
congruent transfer of alloy can be achieved by PLD using an
equiatomic NiTi target through optimising the target-substrate
distance and the laser pulse energy. The average deposition rate of
0.09nm per pulse was obtained. A 10 mm NiTi film can be formed in 3
hours, which is comparable to sputtering deposition. Addition of Hf
(upto 30at% Hf) to replace Ti has increased the transformation
temperature to 300ÉC. However, such NiTiHf is of little practical
use because they are extremely brittle. The amorphous NiTiHf thin
film crystallised upon annealing to 0.1-0.4mm fine crystallites.
R-phase transformation, which is absent in NiTiHf bulk materials, was
observed. The transformation temperatures of NiTiHf SMA are much
higher than that of the NiTi SMA. The NiTiHf would be a prospective
candidate for MEMS application if the brittle problem can be
solved.
A6.45
MICROSTRUCTURE
AND OPTICAL PROPERTIES OF Cu-CaF2 GRANULAR FILMS. Hao
Wang , Wuyi Univ, Dept of Mathematics & Physics, Jiangmen, Guangdong,
PR CHINA; Ziqiang Zhao, Peking Univ, Dept of Technique Physics,
Beijing, PR CHINA.
The Cu-CaF2 granular films
have been prepared at room temperature by Sputter-Gas-Aggregation
co-deposition technique. TEM morphology show that nanoscale Cu
clusters being in triangle shape are well encapsulated in CaF2
matrix. TEM structure characterization reveal that the Cu-CaF2
granular films are polycrystalline. Compared with that of the bulk
Cu, the lattice constant of Cu clusters in as-prepared samples are
expanding at different degree depending on clusters size. The
expanding amount is about 15 with Cu clusters being 15nm in
average size, respectively. From the optical absorption spectra, the
resonance absorption peak exhibits a redshift and broadening with the
decreasing of the size of the Cu clusters, which are contrast to the
results of the quantum confinement. The observed optical properties
of the thin films originate from the variations of the lattice
constant of the Cu clusters.
A6.46
EFFECTS OF
ADDING THIRD TRANSITION METAL ELEMENTS ON MICROSTRUCTURES AND
RESISTIVITIES OF Al-Nd(OR Gd) BINARY ALLOY FILMS. Shinji
Takayama , Hosei University, Dept of System and Control Engineering,
Tokyo, JAPAN.
Microelectronic conductor lines with
high thermal stability have received much high attention recently
because of their potential use in advanced TFT-LCD and VLSI devices.
For this purpose, we had currently investigated sputtered Al-RE-TM
ternary alloy films (RE=rare-earth-elements,TM = transition metal
elements) to obtain very low resistivities without growth of hillocks
or whiskers on the film surfaces at high temperatures (350-
450C)(1). In this report, subsequent works were conducted by
adding transition metals such as Fe or Ni with 1 - 4 at % contents,
to Al-Nd (or Gd) binary alloy fiims. Note that the elements Fe and Ni
have an attractive chemical interaction with the constituent Nd or Gd.
Al ternary alloy films about 400 nm thick were deposited on a 7059
glass substrate by using a DC magnetron sputtering apparatus. Their
isochronal annealing revealed that compared with Al-RE binary alloy
films, the addition of Fe or Ni increased resistivities and largely
delayed the temperatures at which resistivitie:s started to drop
significantly on annealing. It is worth to know that the growth of
hillocks is not observed on the film surfaces after annealing at
350C for samples added Fe or Ni., like those added Cu or Co
reported previously (1). X-ray diffraction analysis showed that the
fine metallic compounds of Al-RE and RE-Fe(or Ni) were segregated in
Al matrix for samples annealed more than 300C. These results
can be also explained by employing a theory of grain boundary
segregation taking account of a solute atom interaction.
(1) S. Takayama, abstract of 1998 MRS spring meeting, symposium B,
B9.7 (1998).
A6.47
PHASE
TRANSFORMATION OF RF SPUTTERED ZnS:Mn THIN FILMS USING PULSED KrF
LASER ANNEALING. E.A.Mastio , The Nottingham Trent
University, Department of Electrical and Electronic Engineering,
Nottingham, ENGLAND; M. Robino, IPCMS-GONLO, Strasbourg; E.
Fogarassy, S. de Unamuno, Laboratoire PHASE (UPR du CNRS no. 292)
Strasbourg, FRANCE; M.R. Craven, W.M. Cranton, C.B. Thomas, The
Nottingham Trent University, Department of Electrical and Electronic
Engineering, Nottingham, ENGLAND.
Thin films of
ZnS:Mn (800nm) have been deposited by r.f. magnetron sputtering onto
100mm diameter n-type single-crystal <100> Si wafers. Specifically
for use as active layers in thin film electroluminescent devices
(TFEL), the films need a post-deposition annealing treatment which
facilitates the effective incorporation of the Mn2+ ions within the
host lattice.
Reported is the microstructural modification induced by thermal and
laser annealing using XRD analysis. Pulsed KrF laser treated samples
were annealed at fluences from 217mJ/cm2 to 533mJ/cm2 under 13.6 bars
of argon pressure. Demonstrated is that at the fluences used, a
gradual phase transition cubic to hexagonal is occurring. A
one-dimensional thermal model of the pulsed laser annealing process
shows that a surface temperature equal to the metallurgic
transformation temperature should be reached at a fluence of 340
mJ/cm2, significantly below the numerically evaluated melting
threshold of ZnS:Mn.
Thermal treatment of the same layers, in the 400ÉC to 700ÉC range,
were performed and compared to the laser processed samples.
A6.48
SYNTHESIS OF
CUBIC AlN ON Si (100) AT ROOM TEMPERATURE BY PULSED LASER
DEPOSITION. V. Gopal , R. Kalyanaraman, A.K. Sharma, K.
Dovidenko, S. Oktyabrsky, J. Narayan, Dept of Materials Science and
Engineering, North Carolina State University, Raleigh, NC.
We have synthesized cubic Aluminum Nitride (AlN)
films at room temperature on Si (100) by pulsed laser ablation of
sintered AlN target in nitrogen atmosphere. Systematic studies have
been carried out on the nature of phases formed as a function of
nitrogen partial pressure. We have found that hexagonal to cubic
phase transformation occurs as the partial pressure increases.
Detailed structural characterization has been carried out using TEM,
EDX and XPS. Using selected area diffraction (SAD) and high
resolution TEM techniques, we have analyzed that the cubic AlN
possesses the NaCl (sodium chloride) structure with space group Fm3m
225. These films have been found to be (111) textured. Statistical
analysis of grains from bright and dark field images has been used
for grain size measurements. These films have grain sizes of the
order of 10-15 nm. Implications of these microstructures on the
mechanical and electrical properties is also
discussed.
A6.49
ALUMINUM
NITRIDE (AlN) THIN FILMS FOR SAW SENSORS. Thomas Daley ,
Martin Burkhart, Greg Auner, EMIT Laboratory, Wayne State Unversity,
Department of Electrical Engineering, Detroit, MI.
Surface acoustic wave (SAW) technology has been applied to the field
of microelectronic sensors quite successfully. The high sensitivity
of these sensors make them efficient devices for measuring gaseous
analytes in extremely low
concentrations. Gas sensitivity is typically achieved by
coating the device with a thin film stationary phase
which will selectively adsorb the gaseous analyte. The prospect of
using aluminum nitride (AlN) thin films as a piezoelectric substrate
for SAW devices is highly promising. AlN thin films possess very high
phase velocity which is responsible for less SAW dispersion, a high
chemical and thermal resistance, and is mechanically durable. Thin
films of AlN were grown using plasma source molecular beam epitaxy
(PSMBE). The films were grown on Al2O3(1-102) and Al2O3(0001)
substrates. Structural characterization includes x-ray diffraction
(XRD) and high resolution electron microscopy (HREM). The XRD
pattern indicates complete film texture. Cross-sectional TEM reveals
epitaxy of AlN on these substrates. The Al2O3(0001) plane is
latticed matched to the c-plane growth of AlN. Thermal conductivity
of these films was investigated by thermal mirage technique which
revealed a high value of 25 W/(mK) for the r-plane AlN film growth on
Al2O3(1-102) as compared to that on Al2O3(0001). A gas sensor using
delay line configuration has been designed on the basis of these
material properties which indicate a higher SAW velocity on the
r-plane then on the c-plane. The SAW velocity and related thermal
conductivity are compared for a-plane versus c-plane growth of AlN
films.
A6.50
PREPARATION
AND CHARACTERIZATION OF POLYCRYSTALLINE AlN LAYER BY A NEW ION
IMPLANTATION METHOD. Mu Sun , Si-ze Yang, State Key
Laboratory of Surface Physics, Institute of Physics, Chinese Academy
of Sciences, Beijing, CHINA.
The inner surface of an
aluminum alloy cylindrical target was successfully implanted with
nitrogen ion using a new plasma source ion implantation method. By
means of x-ray photoelectron spectroscopy(XPS), x-ray
diffraction(XRD) and transmitting electron microscope(TEM), the
reactive phase, chemical state and microstructure of the implanted
layer were investigated. In order to characterize the dose uniformity
and the surface modification caused by the nitrogen ion implantation,
the Auger depth profile of nitrogen ions and the microhardness at
different positions on the inner surface of the target were measured
respectively. The experimental results show that a uniform
polycrystalline AIN reactive phase was formed in the implanted layer,
which contributed to the improvement of inner surface microhardness.
The measured root-mean-square variations of retained dose and
microhardness along the axis of the target are less than 9% and 4%
respectively, which is well within the acceptable tolerance range for
metallic applications of ion implantation.
A6.51
STRUCTURAL
STUDIES OF POLYCRYSTALLINE NANOSCALE FILMS OF NICKEL ALUMINIDE.
Stephen C. McGuire , Jarvis D. Sulcer, Cornell University,
Ward Center for Nuclear Sciences, Ithaca, NY.
We
present results from our use of high resolution STEM imaging of
boron-doped (500 ppm) Ni3Al films having thicknesses in
the range of 300 - 600 angstroms. Interest in this intermetallic
rests in its potential use as a surface coating in high temperature
and corrosive environments. The films were grown on single crystal
NaCl and Si substrates by Ar ion beam sputttering of boron-doped
compound targets. STEM bright and annular dark field images show
the films to have a fine grain microstructure with an average cluster
size of 30 + 3 angstroms. Films produced in this
thickness range also show clustering indicative of Volmer-Weber (VW),
or island growth, mode of film formation. Energy dispersive X-ray
(EDX) and electron energy loss (EELS) spectroscopy measurements
reveal the local composition of the cluster regions to be Ni-rich.
Complementary neutron depth profiling measurements are being used to
determine post-fabrication boron content. It is found using
instrumental neutron activation analysis (INAA) and RBS that the bulk
atomic ratio of Ni to Al in the target is replicated in the films.
Minor impurities such as C, O, Si, Fe and W are interpreted in terms
of their reduction of the surface mobility of adatoms and clusters.
A6.52
THE
INVESTIGATION OF THE STRUCTURE OF SiO2 FILMS ON Si WITH LOCAL
CATHODOLUMINESCENCE. M.V. Zamoryanskay , V.I. Sokolov,
Ioffe Physico-Technical Institute, St. Petersburg, RUSSIA.
The interface Si-SiO2 has an essential influence
on the parameters of planar devices. That's why the investigation of
SiO2 properties and their relation with electrical characteristics
of interface is an actual problem. One of more factual methods is
local cathodoluminescence (CL). CL spectra excited by electron beam
give information about structure defects and their distribution in
thin films. In SiO2 films such defects as non-bridging oxygen
states, twofold-coordinated silicon have characteristic bands. Using
special method to prepare the sample it is possible to study defect
distribution at different depths in layers with resolution 40-100A.
At the same time CL spectra are very sensitive to the density of
excitation. There is an energy threshold of excitation for every
SiO2 material (film and bulk). For high-density excitation CL
spectra change very much. A band at 2,2eV appears in CL spectra and
grow very quickly. This energy threshold depends on the sample of
SiO2.
Thermal oxides (6000A thick) were grown in wet oxygen on Chochralski
silicon (both p-and n-type simultaneously) at 1050C. We investigate
the CL spectra of these oxides and the evolution of C/V
(volt-pharade) characteristics (dark measurements on - 1mm diameter
MOS capacitors, the gates being InGa evtecticum) during radiation of
-Co60.
The electrical measurements and CL study demonstrate that the fixed
oxide charge defects have very different defect distribution in
oxides grown on p- and n-type silicon. The energy threshold for
SiO2 films on interface has lower range that in film. This energy
threshold is lower on the defects which introduce the interface all
along internal mechanical
stresses on the interface.
A6.53
THE DEPOSITION
OF TiO2 THIN FILMS FOR DYNAMIC RANDOM ACCESS MEMORY.
Xuping Zhang , Qing Li, Hongli Luo, Dept of Electronic
Engineering, Southeast University, Nanjing, CHINA.
In order to meet the needs of memory density increasing while each
cell area shrinking in the same time of the storage capacitor in
dynamic random access mcmory (DRAM), an insulator with a
high-dielectric constant is required. Titanium dioxide films is one
of the most promising candidates due to its high dielectric constant
in rutile phase. Besides, the TiO2 also has several advantages
for use as dielectric films in storage capacitors such as thermal
stability in high temperatures (up to 1000c), good adhesion
to Si substrate etc.
The TiO2 thin films were deposited by DC reactive magnetron
sputtering from a 120 x 250 mm2 titanium target of 99.99%
purity. The preparing technique of rutile phase TiO2 thin films
and the interrelation of the preparing conditions, structures,
composition and properties of TiO2 films were studied. AES
analysis indicates that the ratio of O to Ti in TiO2 films
deposited is less than 2 and increases with the increasing of oxygen
partial pressure when the oxygen gas content in sputtering gases is
less than 30% and a stoichiometric TiO2 film can be obtained with
higher oxygen gas content in sputtering gases (greater than 30%) or
heat-treated in air at temperatures higher than 600c. The
XRD results of TiO2 thin films heat-treated at different
temperatures show that the film consists mainly of anatase phase when
the heat-treating temperature is lower than 600c and it
changes gradually into rutile phase with the increasing of
temperature. The l-V characteristics, dielectric constant, leaking
current of TiO2 thin films deposited were measured. And a optimum
preparing condition of TiO2 films with good properties is
given.
A6.54
SECOND
HARMONIC GENERATION IN BaTiO3 FILM PREPARED VIA
SURFACE-CRYSTALLIZATION OF BaO-TiO2-TeO2 GLASS.
Aiko Narazaki , Katsuhisa Tanaka, Kazuyuki Hirao, Naohiro
Soga, Kyoto Univ, Dept of Material Chemistry, Kyoto, JAPAN.
BaTiO3 polycrystalline thin films have been
fabricated via surface crystallization of
15BaO15TiO270TeO2 (in mol) glasses. The
X-ray patterns indicate (101)- and (110)-oriented crystal growth of
BaTiO3 with an average particle size of around 1m.
Thickness of the surface crystallized layers of BaTiO3 increases
from a few to about 30m with an increase in heat treatment
temperature. Second harmonic generation (SHG) from these
glass-ceramics containing BaTiO3 surface layers has been
observed, variation of second harmonic intensity with incident angle
of light, namely Maker fringe pattern, changes drastically with an
increase in heat treatment temperature. The glass-ceramic
heat-treated at 415C exhibits zero second harmonic
intensity at the incident angle of 0. In contrast, Maker
fringe pattern for the glass-ceramic heat-treated at 422.5C
shows a maximum intensity at 0. We also found that
application of a dc voltage during heat treatment facilitates the
surface crystallization of BaTiO3 at lower temperature. X-ray
diffraction measurements suggest that the BaTiO3 phase
precipitated when the heat treatment with high dc voltage is carried
out is likely to be tetragonal. Thus, it is considered that the
application of high voltage enhances the ferroelectricity of
surface-crystallized BaTiO3. Moreover, the second harmonic
intensity is larger than that for the glass-ceramics heat-treated
with no voltage applied.
A6.55
INFLUENCE OF
PROCESSING CONDITIONS ON THE MICROSTRUCTURE AND DIELECTRIC PROPERTIES
OF HYDROTHERMALLY DERIVED BaTiO3 AND BaxSr(1-x)TiO3
THIN FILMS. Mark A. McCormick , Elliott B. Slamovich,
Purdue University, School of Materials Engineering, West Lafayette,
IN.
Polycrystalline BaTiO3 and
BaxSr(1-x)TiO3 thin films were processed on Ag-coated
quartz substrates at temperatures ranging from 80C to
200C by hydrolyzing a metallo-organic precursor (titanium
dimethoxy dineodecanoate) in alkaline solutions containing
Ba2+. The effects of processing time, reaction temperature, and
solution pH on film microstructural evolution were examined. The
submicrometer thickness thin films were continuous and crack free,
with grain sizes ranging from 40 to 100 nm. Capacitors were
assembled using photolithography to apply top electrodes, and
dielectric properties were examined in the context of film
microstructure and thickness. Dielectric constants ranged from 5 to
25 depending on the specific processing conditions. Heat treatments
up to 800C were used to assess the effects of absorbed
hydroxyl groups and thin film porosity on dielectric
properties.
A6.56
GROWTH OF
BaTiO3 FILMS UNDER MILD HYDROTHERMAL CONDITIONS: TIME DEPENDENCE.
M. Gueltzow, T. Hoffmann, C. Sotomayor-Torres, Universitaet
Wuppertal; T. Doll, Universitaet der Bundeswehr, GERMANY,
C. Silva , Chilean Nuclear Energy Commission; Judit G.
Lisoni, T. Vargs and M. Fuenzalida, U. de Chile, CHILE.
The time dependence of the growth of BaTiO3 thin
films under mild hydrothermal conditions was investigated. The
substrates were silicon wafers coated on both sides with a W-Ti
adhesion layer and a protective platinum layer, with 50 nm titanium
sputtered on the polished side. The hydrothermal experiments were
carried out at 80C, under atmospheric pressure and during
times ranging from 2 to 240 minutes. During growth oxygen was bubbled
through the Ba(OH)2 solution. After growth the samples were
characterized by SEM, XRD and surface profilometry. These methods
consistently showed that cubic BaTiO3 films nucleated rapidly on the
substrate surface. After 4 minutes the surface was almost completely
covered. The thickness of the films increased rapidly and reached a
maximum at 15 minutes decreasing with larger treatments.
A6.57
GROWTH AND
MICROSTRUCTURE OF SrBi2Ta2O9 THIN FILMS.
S. Srinivas , Estevao R. Fachini, S.B. Majumdar, S.
Bhaskar and R.S. Katiyar University of Puerto Rico, Rio Piedras
Campus, San Juan, PR.
Layered perovskite materials
such as SrBi2(Ta/Nb)2O9 present excellent
ferroelectric properties. Work on these materials has been less
extensive than the work on the PT/PZT based technology. In this
paper, we are going to present a systematic study about the growth
conditions influence on the microstructure of RF magnetron sputter
deposited SrBi2Ta2O9 (SBT) thin films. A single
stoichiometric SBT target of 2 inch dia has been used for
depositing the films. SBT films of 200nm thick were grown using
both in-situ/ex-situ methods. Films were deposited at room
temperature, 400, 500, 600, 700, and 800 oC on single crystal
Si, LaAlO3 SrTiO3, YSZ, and MgO substrates. All the
films were post annealed at around 800 oC in oxygen. These
films were characterized using XRD SEM, EDAX, AFM, and XPS
techniques. We found that 800 oC is good for the growth of
00l oriented SBT films. In order to understand how the sputtering
gas pressure and nature is effecting the microstructure of the SBT
films we have studied the Ar /Ar+O2 gas partial pressures. We
have observed that 9:1 of Ar:O2 mixture gas is good for
depositing polycrystalline SBT films. When oxygen gas content is
beyond 20, we noticed that back-sputtering occurs due to oxygen
negative ions. These back-sputtered films were non-stoichiometric
and contains intermediate phases. A strong tendency for columnar
growth has been observed in the films deposited at 700 and 800
oC substrate temperatures with high gas pressures. However,
AFM studies of SBT films deposited at 800oC have shown a
relatively smooth microstructure with surface roughness of <1nm
and free from columnar structure. However, post-annealed films were
having surface roughness of 4nm. Studies on the
microstructure-ferroelectric property relationship are in progress. A
detail AFM and XPS studies of these films will be presented during
the conference.
This research work was supported inpart by DAAG55-98-1-0012 and DE
-FGO2- 91ER75764 grants.
A6.58
STRUCTURES AND
PROPERTIES OF SOL-GEL DERIVED BARIUM TITANATE FILMS ON BARE AND
BUFFERED SILICON SUBSTRATES. Zhang Hongxi , Zhou Yan, Kam
Chan Hin, Lam Yee Loy, Microelectronics Division, School of Electric
and Electronic Engineering, Nanyang Technological University,
SINGAPORE.
Barium titanate films have been deposited
on bare and silicon oxide buffered silicon substrates by sol-gel
method. The crystallization, structures, surface morphology, and
interfacial diffusion were characterized and analyzed by X-ray
diffraction, atomic force microscopy, scanning electron microscopy,
and Auger electron spectroscopy. It has been found that the buffer
layer not only decreases interfacial diffusion but also has severe
influence on the crystalline orentation and the grain size of the
films. The dependence of dielectric constant of the film was measured
and fitted by the space charge relaxation model. The effective
dielectric constant and dissipation factor were determined from the
capacitance-voltage measurement results. The leakage current density
at different applied electric field was also measured for the films
calcined at different temperature and the results showed that the
films deposited on buffered substrates have lower leakage current.
The dielectric properties of the films were analysed with respect to
their structures and a comprison study has been
given.
A6.59
SYNTHESIS AND
CHARACTERIZATION OF Bi4Ti3O12 THIN FILMS FROM OXIDE
PRECURSORS. E.B. Arajo and J.A. Eiras , Universidade
Federal de Sao Carlos, Departamento de Fisica, Sao Carlos, SP,
BRAZIL.
In recent years, considerable attention has
been devoted to the development of thin film technology of
ferroelectric materials with a view toward applications in many
electronic and optical devices. Large-scale processing of
high-quality thin films requires low-temperature synthesis, high
reproducibility and simplicity in all processing steps with low cost.
Very recently, was proposed by Arajo and Eiras [1] a hybrid chemical
method for preparation of ferroelectric thin films based on oxide
precursors. The method was initially applied to prepare lead
zirconate titanate ( or PZT) thin films of good quality. This work
reports the synthesis and electrical characterization of
Bi4Ti3O12 (BIT) thin films produced from oxide precursor
method [1]. The structure of these films was characterized using
x-ray diffraction (XRD). At a temperature of 500-800C,
Bi4Ti3O12 films were successfully crystallized on Pt/Si
and Si substrates. Some electrical and ferroelectric properties of
the films were also determined. The electrical properties reported
include dielectric and capacitance-voltage (C-V). The measured
dielectric constant and dissipation factor at a frequency of 100 KHz
were 146 and 0.04, respectively for films annealed at 700C
for 2 hours. Ferroelectricity was confirmed by C-V measurements in
metal-ferroelectric-metal configuration, which presented two peaks,
associated to ferroelectric domain switching, and P-E hysteresis
loops with remanent coercive field of 1.7 mC/cm2 and 31.3 kV/cm,
respectively.
A6.60
ELECTRICAL
PROPERTIES OF (Ba,Sr)RuO3 THIN FILM. Chiou-Chu Lai,
Hsin-Cheng Lai and Shang-Lin Chung, Materials Reserach
Laboratories, Hsinchu, TAIWAN.
It was reported that
the electric conductivity of a bulk BaRuO3 ranges from metallic
to semiconducting after different thermal histories (1). It was also
found that SrRuO3 is a metallic material and both of BaRuO3
and SrRuO3 are hexagonal and orthorhombic structures
respectively (2). It is of interest to adjust the structure from
hexagonal to orthorhombic by changing the atomic ratio of Ba : Sr in
these ruthenates and find out the relationship of the transition of
electric property and structure. We carry out a systematic study that
correlates structure, processing and electrical properties of (Ba,
Sr)RuO3 thin films. We may concern the interdiffusion between
substrate and film interferes with the electric properties, Si (110)
and Al2O3 polycrystalline substrates have been chosen for
comparison. Films are prepared by rf-magnetron sputtering technique
and followed by ex-situ annealing process under various ambient.
X-ray diffraction (XRD) and R/T measurement are used to identify
phase purity and electric properties. Scanning electron microscopy
(SEM) equipped with EDS (energy dispersive spectroscopy) is used to
analyze film composition and surface morphology. Auger electron
microscopy (AES) will be used for observation of the variation of the
composition near both the film surface and the interface between the
films and the substrates. Discussion on possible mechanisms will also
be included. (1) B. Szymanik and A. Edgar, Solid State Communications
Vol. 79, No. 4, 355(1991)
(2) P.R. Van Loan, Ceram. Bull. Am. Ceram. Soc. 51(3), 231(1991)
A6.61
ZIRCONIA FILMS
ON SAPPHIRE SUBSTRATES FROM LIQUID PRECURSOR. Alain
Dauger , René Guinebretiére, Francine Dherbey, Claire Mary,
André Lecomte, Bernard Soulestin, Laboratoire de Matériaux
Céramiques et Traitements de Surface, ENSCI, URA CNRS, Limoges,
FRANCE.
Thin films of undoped zirconia have been
deposited by dip-coating on sapphire substrates starting with a
sol-gel process. The zirconium n-propoxide solution was chelated with
acetylacetone and the precursor was hydrolyzed in air after coating.
Precursor films decompose to tetragonal zirconia and continuous
polycrystalline layers, 50 nm thick, were obtained after annealing at
600ÉC. Nanometer grains , about 5 nm in size, were randomly oriented
throughout the film. The film quality and thickness were checked by
X-ray reflectometry, the grain size and orientation were determined
by X-ray diffractometry and transmission electron microscopy on cross
sectional samples.
Whatever the crystallographic orientation of the sapphire substrate,
islanding and epitaxy phenomena arose from competitive grain growth
during high temperature further heat treatments. The alumina -
zirconia system displays non reactive interactions and the physical
bonding at the interface is related to crystallographic features.
Several substrate orientations were used, namely c-planes, a-planes
and R-planes sapphire. Abnormal growth of grains with two or three
preferred orientations was observed depending on the sapphire
substrate orientation. In all cases film breakup and islanding
resulted from preferential out of plane growth of sugar loaf shaped
(hhh) or (hh0) oriented zirconia grains while in plane growth of flat
(00h) oriented crystals was favored by controlling film thickness.
The morphological features and in plane island orientations were
studied by scanning electron microscopy and electron backscattering
pattern experiments, while the heteroepitaxial relations and
interface structure were determined through X-ray diffraction
experiments (phi-scan, omega-rocking curves) and TEM
observations.
A6.62
STRUCTURE AND
PROPERTY RELATIONSHIPS IN DISPERSION-STRENGTHENED FILMS OF
NICKEL-SILIKA (ZIRCONIA). Alexandr Ilinsky , Alexandr
Terletsky, Alexandr Stetsenko, Svetlana Lyabuk, Kharkov State
Polytechnic Univ, Kharkov, UKRAINE.
There is much
current interest in novel methods for producing
ultrafine-grained materials. Therefore, the goal of this report is to
review the peculiarities of structure and tensile strength of binary
Ni-base films, made of insoluble components (Ni-SiO and Ni-ZrO2).
There dispersion-strengthening films of thickness 20-40 m - were
prepared by e-beam evaporation of materials from two sources
(PVD-method) and their deposition onto a metal and sital substrates
preheated to the desired temperature. The content of strengthening
oxides is not exceeding approximately 2 vol. . Films were studied
byTEM and X-ray diffraction techniques. The individual films were
controlled by autoion microscopy. Tensile tests were performed using
micromechanical testing machine. The films as coatings were studied
also by abrasion wear.
The as-deposited composite films have the two-phase structure -
ultrafine-grained nickel matrix with typical face-centered lattice and
grain size of 0,2-0,5 m and nanoscale amorphous silica (zirconia)
particles (10-30 nm) homogeneously distributed in the matrix. Such
structure ensures an extremely high level of mechanical properties.
For instance, the films of the system Ni-SiO ( 2 vol. ) have
the
yield strength 1.2 GPa. Finally, a comparison between the
wearability of PVD and electroplated Ni base films will be considered.
The correlations between the structural and mechanical characteristics
of composite films are discussed.
A6.63
PROCESSING-STRUCTURE-PROPERTY
RELATIONSHIPS OF TIN OXIDE THIN FILMS. Xiaoqing Pan , Li
Fu, and Jiechao Jiang, Dept. of Materials Science and Engineering,
The University of Michigan, Ann Arbor, MI.
Tin oxide
thin films were grown on the R-cut sapphire substrates by electron
beam evaporation at different temperatures. Films deposited below
300C are amorphous, while those deposited at temperatures
above 350C have the -SnO structure. Epitaxial
films with the -SnO structure were obtained by deposition at
600C. SnO2 films with the rutile-type structure were
obtained by post-deposition annealing of as-deposited films at
700C for 2 h in air. Both TEM and AFM studies showed that
the surfaces of rutile-type SnO2 films are very rough in
comparison to the as-deposited films, a result of the nucleation and
growth of the rutile SnO2 structure during the high-temperature
anneal. X-ray diffraction and TEM studies showed that the
rutile-type SnO2 films are polycrystalline with final
microstructures that depend on both the microstructures of the
as-deposited films and the annealing conditions. SnO2 films
obtained by annealing the amorphous SnO thin films have columnar
microstructure, while those obtained by annealing the crystalline
-SnO films show a laminar microstructure. The influence of
film microstructures on electrical and gas sensing properties will be
addressed. The film with a laminar structure shows a low electrical
conductivity and a higher sensitivity to carbon monoxide than the
film with a columnar structure. The processing-structure-property
relationships of the tin oxide thin films will be
presented.
A6.64
EFFECT OF
LONG-TERM ANNEALING ON MICROSTRUCUTRES AND ELECTRICAL PROPERTIES OF
INDIUM TIN OXIDE FILMS DEPOSITED ON PET SUBSTRATE. J.G. Kwon, S.C.
Moon, Samsung Display Devices, Suwon Plant, SOUTH KOREA; M.G. Kang,
Samsung Display Devices, Chonan Plant, SOUTH KOREA; T. Dolukhanyan,
C.M. Sung , Dept. of Chemical Engineering, Center for
Advanced Materials, Univ. of Massachusetts, Lowell, MA.
Indium tin oxide films of 60 nm thick have been
deposited on PET substrate by radio-frequency (RF) magnetron
sputtering. The effect of heat-treatment for many days on both
chemical/microstructural changes and electrical properties of indium
tin oxide (ITO) films are investigated by transmission electron
microscope (TEM), high resolution scanning electron microscope (SEM),
glancing angle x-ray diffractometer (XRD), x-ray photoelectron
spectroscopy (XPS), and secondary ion mass spectroscopy (SIMS).
Annealing of ITO-coated PET substrate at 60C for 55 days
under humidity condition causes the ITO layers to crystallize and
grains to grow as well as chemistry changes, e.g., non-stoichiometric
ITO, formation of In islands, etc. The electrical resistivity of ITO
has also increased as a function of annealing time. The relationship
between microstructures and electrical properties will be discussed in
order to understand reaction mechanism in this study and possible
solutions for the improvement of microstructures and electrical
properties will be suggested in
A6.65
KINETIC
CHARACTERISTICS OF TIN DIOXIDE POLYCRYSTAL LAYERS.
Vyacheslav I. Kukuev , Anna V. Raskhozheva, Voronezh State
Univ, Dept of Solid State Physics, Voronezh, RUSSIA; Stanislav I.
Rembeza, Tamara V. Svistova, Voronezh State Technical Univ, Dept of
Microelectronics, Voronezh, RUSSIA.
Tin dioxide thin
films are well known as sesing layers.
Response activity depends on crystal structure and elements
distribution (local non-stoichiometry) percularities which
determine electrical conductivity (resistance) of the film
specimen.
We analized the temperature dependence R(T), carriers
mobility and carriers concentration n(T) (Hall effect by Van
der Pawn method) as well as the optical density of the
polycrystalline SnO2 films (dc-magnetron sputtering and spray
techniques) with wide range of grain size 10-500 nm. There is a
wide maximum on the , n(T) curves at the temperatures of
1800 C.
The comparison of Debye length with grain size and , n(T)
dependences shape correlate with conductivity model for ultrafine
particles system. Optical absorption measurements allow to resume
the direct transitions and confirm the presence in the films of
additional phase with tin in a low oxidation state.
By plasma etching we modified the structure of preliminary
deposited SnO2 film decreasing their thickness up to one
monolayer
of grains (SEM) and increasing, at the same time, the film resistance
by four orders of magnitude up to 0,5-1,0 MOhm. As-prepared films
can be approximated by planar network having incommensurable
resistance between separate parts: grains with low resistance and
intergrain region with high resistance. According to percolation
model the estimated intergrain barriers height 0,6-1,1 eV and
their energy dispersion 0,2-0,4 eV differ from those ones of
untreated films (current-voltage measurements).
A6.66
OPTICAL,
ELECTRICAL AND THERMAL CHARACTERIZATION OF STRUCTURE AND DEFECTS IN
POLYCRYSTALLINE DIAMOND FILMS. A.V. Khomich , V.I.
Polyakov, A.I. Rukovishnikov, Institute of Radio Engineering and
Electronics, Moscow, RUSSIA; V.G. Ralchenko, I.I. Vlasov, A.V.
Vlasov, General Physics Institute, Moscow, RUSSIA.
Optical, electrical and thermal data for a representative set of
diamond films are obtained in order to establish growth-property
relationships. Polycrystalline diamond films were grown on silicon
substrates in MW plasma reactor using methane/hydrogen/oxygen mixtures
and in a DC plasma system using methane/hydrogen gas mixture. The
optical measurements were carried out on free-standing films formed by
selective removal of the silicon substrates. The impurity and defect
contents were deduced from UV-IR optical absorption. Thermal
conductivity (up to 18 W/cm K) along growth direction of columnar
grains was measured by laser flash technique. The concentration and
activation energy of trapping centers were determined using a
deep-level transient spectroscopy. The presence of nondiamond phases
and intrinsic stress were analyzed by micro-Raman spectroscopy. The
relation between electrical, optical and photoelectrical properties in
the different spectral regions, and thermal conductivity has been
investigated. The influence of remnants amorphous carbon phases
located at the grain boundaries and defects in the bulk material on
the CVD diamond properties was discussed. A correlation between
concentrations of impurities (nitrogen (1-15 ppm) and hydrogen (30-400
ppm) in different carbon-hydrogen groups), diamond film's growth
regimes and grain structure was discussed. It is shown that defective
fine-grained layer at substrate side of free-standing films can be
removed by laser ablation and subsequent oxidation of graphitized
layer. It is found that the quality of best samples approach to that
of IIa type natural diamonds. This work was partly supported by
grants No 98-02-16679 and No 98-03-332117a of the Russian Fund of
Fundamental Research.
A6.67
THEORETICAL
STUDIES OF NANOCRYSTALLINE DIAMOND NUCLEATION AND GRAIN BOUNDARY
STRUCTURE AND BONDING. D. Gruen , L. Curtiss, P. Redfern,
D. Horner, and P. Zapol, Argonne National Laboratory, Materials
Science and Chemistry Divisions, Argonne, IL.
The
many extraordinary properties of diamond can be optimized for
particular applications only through controlling the microstructure,
since neither the molecular structure nor the composition (except for
doping) can be altered. One can now transform microcrystalline into
nanocrystalline diamond continuously by stepwise addition of argon to
methane-hydrogen mixtures. Films grown from microwave plasmas
containing more than 95% argon consist of crystallites with an
average size of 3-5 nm. Such films have 3% of the carbon at
two-atom-wide grain boundaries.
The complex structure and bonding of the carbon at the high angle,
high-energy grain boundaries typical of the nanocrystalline diamond
films impart unique electrical, mechanical, and tribological
properties to this material.
A secondary nucleation mechanism based on density functional
calculations involving direct carbon dimer insertion into the
-bonds of the reconstructed (100) surface will be presented. The
mechanism accounts for the 1010 cm-2 sec-1
heterogeneous nucleation rates required to account for the
preservation of nanocrystallinity independent of film thickness. The
reaction of singlet C2 with the double bond of the C9H12
cluster leads to either carbene structures or a cyclobutynelike
structure. At the HF/6-31G* level, the carbene product has a C2v
structure, while at the B3LYP/6-31G* level of theory, it has a Cs
structure with the inserted C2 tilted. No barrier for insertion
into the C=C double bond of the C9H12 cluster was found at
the HF/6-31G* and B3LYP/6-31G* levels of theory. Thus, calculations
including correlation energy and geometry optimization indicate that
insertion of C2 into a C=C double bond leads to a large energy
lowering, 120 kcal/mol for a C9H12 cluster, and there
is no barrier for insertion.
*Work supported by the U.S. Department of Energy, BES-Materials
Sciences, under Contract W-31-109-ENG-38.
A6.68
CRYSTALLIZATION
BEHAVIOUR OF SILICON CARBIDE THIN FILMS PRODUCED BY SOLUTION
PRECURSOR METHOD. Christof Rau , Joachim Bill, Thomas
Wagner, Fritz Aldinger, Max-Planck-Institut f. Metallforschung,
Stuttgart, GERMANY; Fred Lange, Materials Department, Univ. of
California, Santa Barbara, CA.
Polymethylvinylsilane
precursors with varying chemical compositions were used for the
growth of SiC thin films by pyrolysis at different temperatures. The
films were grown on single crystalline 6H-SiC, sapphire and Si
substrates by the solution precursor method. Thin amorphous films
with a thickness less than 0.5 m were obtained by dip- or
spin-coating and subsequent thermal treatment at 1100 degree Celsius
in an inert atmosphere. XPS and AES analysis revealed that the films
mainly consisted of C and Si. The crystallization behaviour of films
heat treated at T>1200 degree Celsius was investigated in detail.
As revealed by XRD and TEM, growth of polycrystalline beta-SiC was
observed on the 6H-SiC and Si substrates with increasing temperature.
The annealing time and the purity of the inert gas atmosphere during
pyrolysis and heat treatment was critical for the formation of SiC.
By controlling these parameters films of reproducible quality can be
obtained.
A6.69
PREPARATION OF
CRYSTALLINE CARBON THIN FILMS BY DC MAGNETRON SPUTTERING WITH A HOT
FILAMENT. Myo Than Oo , Yuji Matsumoto, Masato Nakao,
Kiichi Kamimura, Yoshiharu Onuma, Shinshu University, Department of
Electric and Electronic Engineering, Faculty of Engineering, Nagano,
JAPAN.
Generally, carbon thin films produced by
sputtering method are amorphous in crystallinity. But, using a newly
developed DC magnetron sputtering system with a tungsten hot filament
yields crystalline carbon thin films at relatively low substrate
temperature. The crystal structure of the carbon films was
investigated by X-ray diffraction, TEM and TED analysis. X-ray
diffraction analysis of the films prepared at substrate temperatures
600‰È and with the filament temperature up to 2000‰È showed
diffraction peaks around 2Šê= 47.56, 35.16 and 30.37 degrees. From
TEM images of the sample, the needle shaped microcrystallites were
observed. They were several hundred nanometer in length and from 10
to 20 nanometer in width. According to the TED analysis of the carbon
thin films, it was found to be net patterns. And also, the electrical
properties of the films was examined to observe it's expected
superconductivity.
A6.70
CHARACTERIZATION
AND PROPERTIES INVESTIGATION OF MOCVD LEAD GERMANATE THIN FILM.
Fengyan Zhang , Tingkai Li, Doug Tweet, Sheng Teng Hsu,
Sharp Microelectronics Technology, Inc., Camas, WA.
Lead germanate (Pb5Ge3O11) thin film has many applications
because of its piezoelectric, dielectric, electro-optical and its
ferroelectric properties. But in the complex PbO-GeO2 system the
stability range for the Pb5Ge3O11 phase is very limited
and that even relatively small deviation in composition or in growth
temperature could lead to the formation of other lead germanate
compounds, such as Pb3GeO5, PbGeO3 compounds. Therefore when
growing single phase lead germanate thin film by advance MOCVD
technique it has been a big challenge on optimizing the processing
parameters and on characterizing and controlling the secondary
phases' formations in order to achieve good film properties. This
paper will emphasize on the characterization of the lead germanate
phase and other secondary phases and on their forming conditions. The
microstructures, compositions and crystal orientations of each phase
have been investigated by SEM, EDS, XRD, OIM, XRF, etc. The
influence of the crystal orientation and secondary phases on the
ferroelectric properties of the Pb5Ge3O11 thin film will
also be discussed. It has been confirmed that the lead rich phase
Pb3GeO5 is very easily to be formed during the MOCVD process
and it exhibit a ferroelastic property. The c-axis oriented
Pb5Ge3O11 thin film and random oriented polycrystalline
Pb5Ge3O11 with small amount of Pb3GeO5 secondary
phase will be presented with well saturated hysteresis loop and 2Pr
about 4 C/cm2 and dielectric constant about 45.
A6.71
GROWTH OF
HIGHLY <200>- OR <111>-TEXTURED POLYCRYSTALLINE MgO FILMS ON
AMORPHOUS SUBSTRATE BY AEROSOL-ASSISTED MOCVD ON AMORPHOUS
SUBSTRATE. Olivier Renault , Michel Labeau, Laboratoire
des Matériaux et du Génie Physique, CNRS UMR 5628, ENSPG-INPG,
St Martin d'Héres, FRANCE.
Polycristalline
magnesium oxide (MgO) thin films have been grown on large-area glass
substrates using the aerosol-assisted MOCVD method with a high
frequency ultrasonic spraying of the liquid source. At a deposition
temperature of 400C, the maximum deposition rate can be
varied by using different kinds of liquid sources allowing to
transport variable raw material quantity and thus to achieve very low
(10-20/min) or somewhat higher (120/min) growth rates. This
induces major changes in the preferrential orientation of the film,
which exhibit extremely strong <200> or <111> texture at
respectively very low and very high deposition rate. Columnar
microstructure is obtained for highly textured films and nodular-like
one for non oriented films, as deduced by high-resolution SEM. The
grain sizes along the texturing direction are in the range of
200-1000 in agreement with the growth rates and the X-Ray
Diffraction measurements. The early stages of the growth of one film
has been studied by Atomic Force Microscopy and evidence a 3D
(Volmer-Weber) growth mechanism with a periodic variation of the
surface roughness (Rms) as the film thickness increases.
Doping the film with small quantities of aluminium (0.2at.)
enhances the MgO grain growth. Further addition of aluminium strongly
reduces the grain size and decreases the MgO lattice parameter from
4,21 to 4,18 at 15at.
A6.72
PTCRS WITH
La(Ni,Co)O3 THIN-FILM ELECTRODES: PREPARATION AND
CHARACTERIZATION OF THE INTERFACE. Bernd Trummer , Otto
Fruhwirth, Klaus Reichmann, SFB Elektroaktive Stoffe, TU Graz,
AUSTRIA.
A series of different ceramic thin-film
electrodes of the La(Ni, Co)O3 system ranging in composition
from LaNiO3 (n-conducting) to LaCoO3 (p-conducting) was
prepared by spincoating of precursor solutions and subsequent thermal
treatment onto n-conducting BaTiO3 (donor doped) PTCR ceramic
pellets.
Thereafter, the different interfaces were characterized by structural
and electrical methods. Structure and chemical composition of the
interfaces were investigated by SEM and XRD. Electrical
characterization was carried out by using conductivity measurements
(van der Pauw geometry) and impedance spectroscopy in a temperature
range from 20C to 400C.
RESULTS: A close contact of dense, polycrystalline thin-film
electrodes onto the polycrystalline PTCR ceramic was obtained. The
thickness of the electrodes was ranging from 200 to 500 nm, depending
on the parameters of the preparation process. The electrodes
themselves consisted of nanosized particles. The electrical
conductivity of the PTCR ceramic was about 0.1 Scm-1 at room
temperature with an exponential decrease of the conductivity to
higher temperatures. The conductivities of the thin-film electrodes
were between 300 Scm-1 (LaNiO3) and 60 Scm-1
(LaCoO3) at room temperature and exhibited varying temperature
dependences. Overall electrical behavior of the interface was
compared to Ag and InGa metal electrodes and the behavior of the
ceramic electrodes was placed between noble metal and base metal
electrodes. An equivalent circuit, explaining frequency and voltage
behavior of the interface, was modeled. Good agreement between
measured and calculated data was obtained.
A6.73
SYNTHETIC
CONDITION EFFECT ON Li1-xNi1+xO2 AND LiCoO2 FILM
PROPERTIES IN SOFT SOLUTION PROCESSING. Kyoo-Seung Han ,
Seung-Wan Song, Itsuro Sasagawa, Masahiro Yoshimura, Center for
Materials Design, Materials and Structures Laboratory, Tokyo
Institute of Technology, Yokohama, JAPAN.
A process
called ``Soft Solution Processing'' was used to prepare lithiated
thin-film electrodes as a cathode for lithium rechargeable
microbatteries in a single synthetic step.
Li1-xNi1+xO2 and LiCoO2 films were fabricated
using the Soft Solution Processing in a concentrated LiOH solution at
fixed temperatures between 20 and 200C with a fixed current
density between 0.1 and 5.0mA/cm2 without any post-synthesis
annealing. The prepared films exhibit prospective electrochemical
activity, however, it is dependent on the synthetic conditions.
Similarly, the synthetic condition effect on the surface morphology
and film thickness was also detected. In order to determine the
optimal synthetic conditions, the effect of various synthetic
conditions such as fabrication temperature, applied current density,
concentration of LiOH solution, and reaction time was investigated.
The synthetic condition effect study shows that Soft Solution
Processing is capable of preparing advanced inorganic materials with
planned properties through the active control of synthetic
conditions.
A6.74
SPUTTERED CHROMIUM NITRIDE FILMS STUDIED BY IN SITU X-RAY
DIFFRACTION AND SYNCHROTRON GRAZING INCIDENCE SCATTERING.
Z.B. Zhao , Z.U. Rek*, S.M. Yalisove and J.C. Bilello
Center for Nanomaterials Science, Department of Materials Science and
Engineering, The University of Michigan, Ann Arbor, MI *Stanford
Synchrotron Radiation Laboratory, Stanford University, CA.
The films of chromium nitrides have been deposited
in a magnetron sputter equipped with an in situ X-ray characterizing
system, which allows the growth of films to be studied in a
quasi-real time fashion. The objective of the paper is to investigate
the effect of deposition conditions on phase formations,
crystallographic characteristics, and their evolving nature as a
function of film thickness. In addition to the in situ X-ray
diffraction, grazing incidence x-ray scattering with synchrotron
radiation and scanning electron microscopy were also used to
characterize the post-deposited films. The phases in the sputtered
films can be either bcc Cr, or Cr2N, or CrN or their mixtures,
depending on the deposition conditions (mainly the nitrogen flow).
Small amount of nitrogen typically leads to the mixture of Cr and
Cr2N phases. Sufficient nitrogen flow is observed to be crucial for
formation of single phase CrN. As abundant nitrogen is supplied,
strong (111) out-of -plane crystallographic texture develops,
regardless of the variation of other deposition conditions. The
transition from N-deficient CrN to fully ordered CrN has been
observed. The out-of-plane texture is found to be 111) type and the
in-plane texture is correlated to the deposition
geometry.
A6.75
C-AXIS
ORIENTED STRONTIUM BISMUTH NIOBIUM OXIDE FILMS PREPARED BY SOL-GEL
DIP-COATING. Yun Wu and G.Z. Cao, University of
Washington, Department of Materials Science and Engineering, Seattle,
WA.
We report the (00l) oriented SrBi2Nb2O9 (SBN)
films dip-coated on (100) single crystal strontium titanate, SrTiO3
(STO) substrates. A multiple step hydrolysis-condensation process was
applied to the synthesis of strontium bismuth niobium oxide sol using
inorganic salts as precursors with citric acid as a complexing
regent. Uniform thin SBN films were formed by dip-coating the sol
onto (100) single crystal STO and (100) silicon substrates. Single
crystalline SBN phase was obtained after a heat-treatment at 650 C.
The phase evolution, crystallinity and orientation of the SNB films
on both STO and silicon substrates under various heat-treatments were
studied by means of X-ray diffraction and Rocking curves. Highly
c-axis oriented SBN films were obtained on single crystal STO
substrates and well aligned microstructure was observed by SEM with
the average grain size of approximate 200 nm after a heat-treatment
at 800 C for 1 hour.
A6.76
CHARACTERIZATION
OF POST ION IMPLANTED c-BN FILM BY HIGH RESOLUTION TRANSMISSION
ELECTRON MICROSCOPY. E.S. Byon, S.W.Lee, S.R. Lee, Korea Institute
of Metal and Machinery, Changwon, KOREA; Sandhya
Gunasekara, Changmo Sung , Center for Advanced Materials,
Dept. of Chemical Eng., University of Massachusetts, Lowell, MA.
Boron nitride thin films have been deposited on
(100) oriented Si substrate by Magnetically Enhanced Evaporation
Technique.The build up of c-BN is normally accompanied by strong
compressive stresses. When these stresses exceeds the strength of the
adhesion forces at the interface, adhesion fails causing the
destruction of the c-BN film. This has been one of the major limiting
factors of using the c-BN films for many important industrial
applications such as cutting tools and semiconductor devices.
In this experiment, the plasma immersion ion implantation
has been applied to improve the adhesion of the film. The post ion
implantation was conducted at several implantation energies and
constant dose. The effect of ion implantation on the microstructures
was investigated by Fourier Transform Infrared Spectroscopy (FTIR)
and High Resolution Transmission Electron Microscopy (HRTEM).
Cross-sectional TEM images show three distinct layers on the
deposited film: an initial layer of amorphous BN at the interface, a
layer of h-BN and a layer of c-BN at top. The Fast Fourier Transform
(FFT) performed on HRTEM images matched these results and also showed
that the c-BN layer continues to grow as a single phase. HRTEM images
also show sharp interface between the ion implanted film and the
substrate, which indicates a better adhesion of the film to the
substrate.It is concluded that the post ion implantation proved to be
an effective technique which reduces the compressive stresses build
up on the film improving the adhesion between the film and the
substrate.
A6.77
THE USE OF
DOPANT ADDITIONS TO FORM NANOCRYSTALLINE BERYLLIUM COATINGS.
Alan Jankowski , University of California, Lawrence
Livermore National Laboratory, Livermore, CA.
We are
developing a process to sputter deposit Be-rich, thick coatings that
must be both strong and gas permeable. Both material properties are
sensitive to the growth morphology and microstructure of the
deposit. For example, it appears advantageous to form a coating that
is dense in order to control gas permeation and that has as small a
grain size for enhanced strength. We have shown that a dense
columnar growth can be induced using ion-assisted processing as in
application of a substrate bias. Additionally, it is known from
prior studies of evaporative and sputter deposition processes that
the grain size of nominally pure (>99.8 atomic percent) Be films
can be dramatically refined through the incorporation of specific
metal impurities. Presently, we examine the feasibility of Fe and B
as dopants to the sputter deposition of Be to form a dense,
nanocrystalline microstructure.
This work was performed under the auspices of the United States
Department of Energy by Lawrence Livermore National Laboratory under
contract #W-7405-Eng-48.
A6.78
STRUCTURAL
CHARACTERIZATION OF BARIUM-FERRITE THIN FILMS ON SAPPHIRE BY
SYNCHROTRON X-RAY SCATTERING. Tae Sik Cho , Seok Ju Doh,
Jung Ho Je, Pohang Univ of Science and Technology, Dept of Materials
Science and Engineering, Pohang, KOREA; Do Young Noh, Kwangju Inst of
Science and Technology, Dept of Materials Science and Engineering and
Center for Electronic Materials, Kwangju, KOREA.
The
structural nature of Ba-ferrite thin films was investigated using
synchrotron x-ray scattering. Ba-ferrite films were grown on
sapphire(0001) substrate at room temperature by RF magnetron
sputtering. We found that a very thin ( 40 thickness)
interlayer of magnetite Fe3O4 was, in initial stage, grown
epitaxially on sapphire inside amorphous Ba-ferrite film. As
Ba-ferrite films were post-annealed at 750 C for 5 hrs in
air, the magnetite interlayer was disappeared. In addition, not only
hexagonal Ba-ferrite but also hematite -Fe22O3
were grown epitaxially on sapphire as a surprise. The epitaxial
relationship was Ba-ferrite (000l) [-Fe2O3
(0006)]// sapphire (0001), Ba-ferrite (107)// sapphire
(113), and -Fe2O3
(104)]//sapphire (102). The domain size of both
phases that is estimated from the broadening of the scattering
profile was almost the same as 200 in the normal
direction to the substrate. These results indicate that Ba-ferrite
and -Fe2O3 are presumably formed as hexagonal
pillar-shape. The structural change of the as-deposited Ba-ferrite
films during in-situ annealing will be presented as well.
A6.79
STRUCTURE AND
COMPOSITION OF GRAIN BOUNDARIES IN Fe1-xO POLYCRYSTALLINE THIN
FILMS BY MOLECULAR-DYNAMICS SIMULATION*. S.R.
Phillpot a, D. Wolfa and P. Keblinskia,b; aMaterials
Science Division, Argonne National Laboratory, Argonne, IL;
bForschungszentrum Karlsruhe, Karlsruhe, GERMANY.
W½stite, Fe1-xO, is a prototypical system for the study of
off-stoichiometry in ceramic oxides. We have used molecular-dynamics
simulations to grow highly-textured, small-grain sized (4nm)
polycrystalline thin films of Fe1-xO and its hypothetical
stoichiometric analog, FeO. To grow the thin film, a layer of liquid
was placed on top of a previously grown polycrystalline substrate.
On cooling below the melting point, the thin film grew on the
substrate with highly ordered grains and rather narrow grain
boundaries (GBs). We compare the structures of crystallographically
identical GBs in the Fe1-xO and FeO thin films with particular
reference to deviations from bulk composition in the GBs in
Fe1-xO and the presence of a compensating space-charge region
around the GBs. To elucidate the effects of the small grain size on
interface structure, the structures of GBs in the films are compared
with those of crystallographically identical bicrystalline GBs.
* This work was supported by the U.S. Department of Energy
BES-Materials Science under Contract No. W-31-109-Eng-38. P. K.
gratefully acknowledges support from the Alexander von Humboldt
Foundation.
A6.80
MAGNETIC AND
STRUCTURAL PROPERTY OF Fe-O FILMS AND Fe-O/MgO MULTILAYERS GROWN ON
<111> POLYCRYSTALLINE MgO BUFFER LAYER. D.V. Dimitrov ,
Y. Ding, G. C. Hadjipanayis, Dept. of Physics and Astronomy,
University of Delaware, Newark, DE; A. Simopoulos, NCSR Demokritos,
Athens, GREECE.
Fe-O films (350 nm) and (Fe-O 10 nm
/MgO 10 nm) multilayers with 500 nm <111> MgO buffer layer were
grown on glass and Kapton substrates. Reactive sputtering in a
mixture of oxygen and argon with fixed dc power for MgO and variable
dc power for Fe- O was used to deposit the films. Samples were
characterized by, low and high angle X- ray diffraction,
cross-sectional transmission microscopy, SQUID magnetometry, and
Mossbauer spectroscopy. Sputtering conditions (dc sputtering power)
for deposition of thick films of non-stoichiometric wustite,
magnetite, and mixtures of magnetite and maghemite phases were
identified. The saturation magnetization of the best magnetite films
was 430 emu/cc and the Verwey transition was clearly observed in the
temperature dependence of the low field magnetization and coercivity.
The transformation from magnetite to a mixture of magnetite and
maghemite was identified by both magnetic and lattice parameter
determination. Studies of Fe-O/MgO multilayers showed that the MgO
layers stabilize the spinel structure and the formation of magnetite
phase for the whole range of dc power used. The lattice parameter was
practically constant for all samples (0.842 nm) and exactly twice that
of MgO (0.421 nm). The saturation magnetization consistently
decreased from 340 emu/cc to 117 emu/cc with the decrease of the
sputtering power. Mossbauer spectroscopy studies showed that the Fe
ion occupation of A and B sites in the spinel structure systematically
changes and correlates with the sputtering power. The isomer shifts
of the A and B sites suggests that there is a transfer of electron
density from A to B sites as the dc power decreases. The decrease of
the saturation magnetization is consistent with the change in the site
occupation and electron density transfer between A and B
crystallographic sites. This work was supported by NSF DMR
9307676
A6.81
MICROSTRUCTURE
OF ALKALINE EARTH AND RARE EARTH FLUORIDE THIN FILMS PREPARED BY
CHEMICAL PROCESS. Munehiro Tada , Shinobu Fujihara,
Toshio Kimura, Keio Univ, Dept of Applied Chemistry, Yokohama, JAPAN.
Fluoride thin films are of great importance in the
field of optics because they exhibit low refractive indices, wide
range of transmittance and fine insulation. A chemical route to
prepare the fluoride films is interesting as a viable and low-costing
method, which can extend research in the optical thin films. In the
present work, alkaline earth and rare earth fluoride thin films have
been prepared by a sol-gel process using trifluoroacetic acid as a
fluorine source.
Metal acetates were dissolved in a mixture of isopropanol, TFA and
water. The solution was stirred for 2 h at a room temperature, and
spin-coated on silica glass substrates. Then the films were heated at
a constant temperature between 300 and 800C for 10 min in
air followed by quenching. Surface morphology and roughness of the
films were evaluated with FE-SEM and AFM.
The fluoride phases were formed by heating the coated films below
500C. On the contrary, oxide or oxyfluoride phases were
formed above 600C. The surface morphology and roughness of
the films depended strongly on the heat-treatment temperature. The
fluoride films exhibited high optical transmittance more than 90
in the UV-visible region. The film thickness was calculated to be
about 200 nm from interference fringes of the transmittance spectra.
The refractive indices of the films were lower than the theoretical
values because the films were porous. These results indicate that the
refractive index of the fluoride films can be controlled by the
heat-treatment process through the chemical route.
A6.82
Abstract
Withdrawn.
A6.83
PROPERTIES OF
IRON OXIDE FILMS PREPARED BY THE SOL-GEL TECHNIQUE. Brigida Allieri,
Laura E. Depero, Luigi Sangaletti , INFM and Dipartimento
di Chimica e Fisica per l'Ingegneria e per i Materiali, University di
Brescia, ITALY; Sandro Santucci, A.R. Phani, INFM and Dipartimento di
Fisica, University dell'Aquila, ITALY; Guglielmina Gnappi, Co.R.I.Ve,
University di Parma, ITALY; Angelo Montenero, Dipartimento di
Chimica, Universita' di Parma, ITALY; Gualtiero Gusmano, Enrico
Traversa, Dipartimento di Scienze e Tecnologie Chimiche, University
di Roma Tor Vergata, ITALY.
Iron oxide thin films
have been deposited onto amorphous SiO2 by the sol-gel technique.
The structural and vibrational properties of the thin films as
function of the annealing temperature have been investigated with
X-ray diffraction, optical absorption, and microraman techniques.
Four annealing treatments have been performed in air at C,
C, C, and C. The results of the
experimental studies show that above C the thin films are
mainly composed of Fe2O3 hematite. A smaller amount of
magnetite is also detected, but the hematite/magnetite ratio does not
change with temperature. Both vibrational bands and diffraction peaks
get narrower with the annealing temperature, which indicates an
increase of the crystallite size. A microraman mapping of the thin
film surface did not show inhomogeneity on a micrometer scale. Below
C an amorphous phase is observed both by X-ray diffraction
and Raman spectroscopy. This finding is related with a change in the
optical absorption spectrum in the region below the absortion edge.
The results are compared to those already obtained for iron-oxide
powders grown by the same sol-gel method. In particular, the effect
of the SiO2 substrate on the evolution of the structural
properties with temperature is discussed.
A6.84
CHARACTERIZATION
OF Ti1-xSixN FILMS BY SURFACE ACOUSTIC WAVES. S.
Carvalho 1, F. Vaz1, L. Rebouta1, D. Schneider2, M.Z.
Silva1; 1Dept Física, Universidade do Minho, Azurém,
Guimarães, PORTUGAL; 2Fraunhofer Institut für Werkstoffphysik
und Schichttechnologie, Dresden, GERMANY.
The aim of
this work is to present the results regarding a non-destructive
Young's modulus evaluation of thin films using Surface Acoustic Waves
(SAW). This technique allows the correlation between composition
changes, bias voltage and working gas flow, with the Young's modulus
of hard TiN based coatings. These Ti1-xSixN coatings, with 0
x 0.37 and thickness ranging from 1.2 to 3.5 m, were
deposited onto polished high-speed steel substrates by r.f. reactive
magnetron sputtering. The atomic composition of the samples was
obtained by Rutherford Backscattering Spectrometry (RBS) and the
structure and grain size were determined by X-ray diffraction (XRD).
The results reveal an increase in the Young's modulus for samples
with low Si content (0.05 x 0.15) when compared with TiN.
For higher Si contents a decrease in Young¼s modulus was observed,
which becomes smaller than the corresponding value of TiN. The
dependency of Young's modulus as a function of x, bias voltage and
working gas (Ar) flow and its correlation with the developed texture
will be discussed in some detail. Also, a comparison between these
results and those obtained from ultramicrohardness tests will be
presented.
A6.85
MICROSTRUCTURE
AND ELECTRICAL RESPONSE TO NO2 OF In2O3 THIN FILMS GAS
SENSORS PREPARED BY VACUUM THERMAL EVAPORATION. C.
Cantalina , M. Pelino, University of L'Aquila, Dept. of Chemistry and
Materials, L'Aquila, ITALY; S. Santucci, University of L'Aquila,
Dept. of Physics, L'Aquila, ITALY.
Microstructures
of thermally evaporated In2O3 thin films have been investigated
by wide angle X-ray diffraction, atomic force microscopy and X-ray
photoelectron spectroscopy. The films have been prepared by
evaporating commercially pure In2O3 powders on sapphire and
Si/SiO2 substrates provided with Pt interdigital electrodes. The
as-deposited films have been annealed in static air at different
temperatures ranging from 300 to 500C and for different times
ranging from 5 to 96 hours. All the films have resulted to be
crystalline after annealing with the formation of cubic In2O3
(JCPDS card 6-0416). Detailed XPS scan have confirmed the formation
of nearly stoichiometric In2O3 (58% O and 42 % In). The
increasing of the annealing temperature have shown a positive effect
on the surface roughness, surface area, grain size and fractal
dimension, as computed by Atomic force microscopy measurements.
The H2O, C2H5OH, CO, CH4, NO and SO2 cross sensitivity
to NO2 ``target'' gas, as well as preliminary long term stability
of the electrical response, have been discussed in the light of
different preparation conditions and different working temperatures.
All the films have shown high sensitivity to NO2 gas (0.7-7 ppm in
Air) at 250C working temperature. The highest sensitivity of
the 500C annealed for 96 hours is explained in terms of the
annealing temperature effect on the geometrical (surface area and
crystallites size) and chemical (oxygen vacancies and grain
boundaries) heterogeneities.
A6.86
THE EFFECTS OF
HIGH TEMPERATURE ON CERAMIC THIN-FILMS GROWN ON SAPPHIRE AND SILICON
BASED SUBSTRATES. Michael Post , Dongfang Yang and Jim
Tunney, National Research Council of Canada, Ottawa, Ontario, CANADA.
The present work reports a study of the effects of
temperature on the morphology and chemical composition of ceramic
type, perovskite thin-films which have been deposited by pulsed laser
ablation onto silicon oxide, silicon nitride and sapphire as
substrates. The technological issues related to this combination of
materials are important because of proposed integration of this type
of functional ceramic film with various substrate platforms to
provide multiple array, thin-film gas sensor devices. In sensor
devices which exploit the electronic properties of the films, the
morphology becomes a key factor in determining sensor properties.
For experimental work, an excimer laser (Kr/F, =248nm,
E=2J.cm-2, t25ns) was used to deposit the films from
targets of SrRuO3 and non-stoichiometric perovskites of the family
SrFeO2.5+x (0<x<0.5). The substrates were cut from thermally
oxidised Si wafers (SiO2 thickness 500nm) or Si upon which
had been grown silicon nitride by CVD (SiNy thickness
500nm). The thickness of the ceramic films was between 100nm
and 300nm. After deposition, the samples were given thermal
treatments in different gas atmospheres for various time periods at
temperatures up to T=600C. Both oxidising and reducing
conditions were used. At set time intervals the sample films were
characterised by techniques including XRD, XPS (with depth
profiling), SEM, AFM and optical microscopy. Results from this study
will be presented which indicate morphological and chemical
composition changes which occur in the evolution of film texture,
grain growth and diffusion at the ceramic film interface with the
SiO2 (or SiNy) coating. The consequent changes which are
observed in the electrical conductivity of the films when used as
oxygen sensors are correlated with these physical
changes.
A6.87
STRENGTHENING
EFFECT OF NANOCOMPOSITE MULTILAYER FILMS. R.F. Huang, City
University of Hong Kong, Department of Physics and Materials Science,
Hong Kong, CHINA; L.P. Guo, State University of New York at Buffalo,
Dept of Materials Science, Buffalo, NY; J. Gong, L.S.
Wen , Institute of Metal Research, Academia Sinica, Shenyang, CHINA.
The idea of strengthening by nanocomposite
multilayer structure could be stemmed from Koehler in 1970. Recently,
more and more nanocomposite multilayer films have been used as
commercial coating series. However, the strengthening mechanism has
not yet been enough studied. To reveal the origin of strengthening,
Ti/TiN nanocomposite multilayer films with single layer thickness in
range of 10-500 nm have been prepared by ion plating. Microstructure
of the films was studied by X-ray diffraction and transmission
electron microscopy. The single layer thickness of the multilayer
films were measured using cross-sectional sample electron microscopy,
while grain size of the multilayer films was obtained by planar
sample electron microscopy. Composition modulation wavelengths
of the films are twofold single layer thickness.
Relationship of grain size with reveals a grain refining
effect of multilayer film with decreasing . Microhardness of
the films was measured by using super-hardness tester. The
relationship of microhardness with of the multilayer film
shows hardness strengthening with decreasing , approximately
similar to Hall Petch relation. On the other side, electron
microscopy of cross sectionally fractured sample shows toughening
effect of multilayer films. Therefore, the results on Ti/TiN suggests
a grain refining mechanism of hardness strengthening and toughening
of nanocomposite multilayer films.
A6.88
FIRST STAGES
OF THE INTERMETALLIC PHASE FORMATION IN COLD ROLLED
ALUMINUM-TANTALUM MULTILAYERS. H. Sieber , University of
Erlangen-Nuernberg, Department of Material Science (III) Glass and
Ceramics, Erlangen, GERMANY; G. Wilde, J.H. Perepezko, University of
Wisconsin-Madison, Department of Material Science and Engineering,
Madison, WI.
The reaction kinetics of the first
stages of the intermetallic phase formation in Al-25Ta multilayer
samples was investigated by XRD, SEM, TEM/SAED, DSC and DTA
measurements. Multilayered structures with elemental layer thickness
between 100-1000 nm were prepared by cold rolling of elemental Al and
Ta foils. XRD and TEM investigations indicate no phase formation
during the cold rolling process. DSC annealing shows a first phase
formation reaction to the TaAl3 phase starts at around 570K. The
phase formation kinetics exhibits a double exothermic peak, related
to nucleation and 2-dimensional lateral growth at lower temperatures
and a 3-dimensional phase thickening at higher temperatures that is
known for the formation of the first phase in different other
multilayer systems. The as-rolled multilayer microstructure and the
reaction product morphology are characterized by detailed SEM and TEM
investigations in plan view and cross section geometry. The kinetics
and thermodynamics of the reactive phase formation are examined by
isothermal and isochronal DSC and DTA investigations. The support of
ONR (N00014-92-J-1554) is gratefully acknowledged.
A6.89
X-RAY
DIFFRACTION INTERNAL STRESS STUDY OF TANTALUM CARBIDE.
Sucharitha Alagudu , Robert Catchings, Howard Univ, Dept
of Physics, Washington, DC.
The phenomenon of
residual stress occuring in materials such as metals, polymers and
thin film composites is important since it can cause material
degradation which alters significantly the performance and physical
properties of the material. The high residual stress generally
observed can result in debonding, film rupture and substrate
cracking. However, the effects of residual stress is more prounced
in thin film samples compared to the bulk material. The stresses
developed in the deposited film is related to the internal
arrangement of the atoms comprising the film and due to the thermal
expansion and the lattice mismatch between the substrate and the
deposited film.
In this work, we report on the variation of residual stress as a
function of temperature performed on hot pressed and thin film
samples of Tac in the temperature range of 25-350K. Our results
indicate that residual stresses developed in Tac thin film are more
predominant at lower temperatures compared to measurement performed
on hot pressed pellet under identical conditions and vice versa. The
lattice spacing versus temperature for (200) reflection of X-ray beam
shows decrease in d spacings with increase in sample temperature.
Further results of stress mesurement analysis will be presented.
A6.90
GROWTH,
STRUCTURE AND MECHANICAL PROPERTIES OF PULSED LASER DEPOSITED
MICROLAMINATES COATINGS. Ashok Kumar and R. Bahl, Dept.
of Electrical Engineering, University of South Alabama, Mobile, AL.
Hard coatings of TiN and TiB2 have many
interesting properties such as high thermal and electrical
conductivity, high melting point, good thermodynamic stability and
combination of these properties make them an interesting prospect for
a wide range of tribological and electronic applications. It is
understood that artificial multilayer structures have shown
anamolously high hardness and modulii making them likely candidate
for future protective coatings. Single layer of TiN, TiB2, and
TiB2/TiN microlaminates coatings with varying thicknesses have
been deposited on Si (100) by in-situ pulsed laser deposition method.
These films are deposited at 10 Hz repetition rate of excimer laser
( = 248 nm). Our preliminary results show that elastic
modulii and hardness values of multilayered coatings are superior
than monolithic coatings of either of the two constituent materials.
The coatings will be characterized by X-ray diffractometer, scanning
and transmission electron microscopic techniques. Detailed results
will be presented to correlate thc effect of microlaminate thickness
on the mechanical properties.
A6.91
INTERMETALLIC
PHASE FORMATION SEQUENCE IN COLD ROLLED ALUMINUM-NICKEL MULTILAYERS.
H. Sieber , University of Erlangen-Nuernberg, Department
of Material Science (III) Glass and Ceramics, Erlangen, GERMANY; J.H.
Perepezko, University of Wisconsin-Madison, Department of Material
Science and Engineering, Madison, WI.
During the
reactive phase formation in thin bi- and multilayer structures the
reaction kinetics is determined mainly by the very small diffusion
distances for the atomic species. The reactive phase formation
follows a sequential reaction pathway that allows only one phase to
form at a given temperature and time. A systematic investigation of
the of the phase formations sequence was conducted in `massive
samples' of multilayered structures of different Al-Ni (Al-20Ni,
Al-25Ni, Al-40Ni, Al-50Ni and Al-75Ni) composites. The multilayered
samples were prepared by cold rolling of elemental foils at ambient
temperature. The as-rolled microstructure and phase development
during alloying were characterized by XRD, SEM and TEM/SAED and the
reactive phase formation kinetics was examined by DSC and DTA
measurements in multilayer foils rolled for different deformation
levels. The cold rolling procedure results not only in a decrease of
the layer thickness of the elemental foils (down to below 100 nm in
average) but also in the decrease of the individual grains size (down
to below 50 nm in average). No intermetallic phase formation is
observed during cold rolling. The reactive phase formation occurred
upon annealing and was then studied in multilayer foils for different
compositions. The first phase formed is the Al3Ni phase starting at
temperatures below 470K. The phase formation shows a double exotherm
in DSC measurements related to a 2-dimensional nucleation and lateral
growth and a 3-dimensional phase thickening. In Ni-rich samples
further annealing yield the formations of the Al3Ni2 phase at about
620KC and the AlNi and AlNi3 phases at about 670K. The support of ORN
(N00014-92-J-1554) is gratefully acknowledged.
A6.92
METAL BORIDE
THIN FILMS FABRICATED BY LASER-INDUCED DEPOSITION FROM SOLUTION.
Z.C. Zhong , P.A. Dowben and D.J. Sellmyer, Center for
Materials Research and Analysis and Department of Physics and
Astronomy, University of Nebraska, Lincoln NE.
We
have explored a new deposition technique called laser-induced
solution deposition (LISD). This technique is both simple and
efficient. Unlike gas phase deposition (e.g. CVD and PECVD),
deposition from solution is compatible with thin film formation on
thermally sensitive substrates while allowing for recovery of the
unused metals. The results of LISD deposition indicate the formation
of polycrystalline thin films of rare earth hexaborides such as
gadolinium hexaboride and lanthanide hexaboride through the chemical
photolysis of nido-decaborane and rare earth chloride in liquid
solution is possible. Deposition were carried out on a variety of
substrates including glass and silicon. The X-ray diffraction (XRD)
and scanning electron microscopy (SEM) have been used to characterize
the formed thin film materials. In addition, the possibility for
applying these rare-earth boride thin films as cathode materials in
plasma display technology will be discussed.
*) Supported by Dale Electronics and the National Science Foundation
through grant OSR-92-55225
A6.93
DISLOCATIONS
AND TWINNING IN MBE Al THIN FILMS GROWN ON SAPPHIRE. B.J.
Inkson , Dept. of Materials, University of Oxford, Oxford, U.K.; Th.
Wagner, Max-Planck-Institut fuer Metallforschung, Stuttgart, GERMANY.
Metal films on ceramic substrates are widely used
for electronic applications. Al thin films have been grown on basal
plane sapphire by MBE with no subsequent annealing. The
microstructure of the films was examined by cross-sectional electron
microscopy, and by surface studies using a focussed ion beam
microscope (FIB).
Under the MBE conditions used, the Al grew with the orientation
relationship <-110>Al// Al2O3 and {111}Al //(0001) Al2O3. The two
variants of this relationship are observed, that is Al twins [1-10]Al
and [-110]Al // Al2O3. In the examined as-grown samples, one twin
variant was observed by FIB to have a higher area density than the
second. The Al-Al twin boundaries predominantly lay parallel to the
foil normal in the Al //[0001] Al2O3 zone. {1-21}Al twin
interfaces were atomically flat, with a rigid body shear component in
the foil normal direction causing deviation from mirror symmetry.
In addition to extensive twinning, dislocation loops were also
observed in the TEM foils. These loops were mobile, migrating in-situ
within the Al film under the influence of the electron beam. The
Al-sapphire surface itself was observed to have a atomically rough
interface by HREM.
SESSION A7: MECHANICAL PROPERTIES
Chairs: Eduard Arzt
and Caroline A. Ross
Thursday Morning, December 3, 1998
Salon
A/B (M)
8:00 AM
*A7.1
MECHANISMS OF PLASTICITY IN
POLYCRYSTALLINE THIN FILMS ON SUBSTRATES. W.D. Nix ,
Department of Materials Science and Engineering, Stanford University,
Stanford, CA.
Mechanisms of plasticity in
polycrystalline thin films are reviewed with particular reference to
understanding the softening and hardening effects of grain boundaries
in thin metal films on substrates. It is shown that diffusional
deformation involving mass transport between the free surface of the
film and the grain boundaries is constrained by kinetic processes at
the film/substrate interface and that classical Coble or
Herring-Nabarro creep relations do not apply unless the
film/substrate is free to slide. For the case of no sliding at the
film/substrate interface, diffusional deformation alone cannot relax
the stresses completely at high temperatures, with the consequence
that dislocation plasticity must be active when full relaxation is
observed.
The hardening effects of grain boundaries are also explored and
compared with the hardening processes that occur in single crystal
films. ThompsonÌs mechanism of dislocation storage at grain
boundaries is reviewed and compared with experiment. An attempt is
made to extend ThompsonÌs model to account for the propagation of
slip from one grain to another by focusing on the energy of the
defect structure left at the grain boundary by the process of slip
transmission. This approach to grain size hardening leads naturally
to a recovery process for plastic deformation at elevated
temperatures. These mechanisms will be explored and compared with
experiment.
8:30 AM
*A7.2
STIFFNESS, YIELD STRENGTH AND
CREEP RATE OF FREE-STANDING METALLIC THIN FILMS AND MULTILAYERS.
Frans Spaepen , Division of Engineering and Applied
Sciences, Harvard University, Cambridge, MA.
Methods
for tensile testing of free standing thin films to large strains are
reviewed. Differences have been observed between the quasistatic
moduli of thin films and the bulk stiffnesses; possible
microstructural origins will be discussed. The yield stress of
mulitlayers increases with decreasing individual layer thickness. The
formal dependence and microscopic interpretation (Hall-Petch) will be
presented. Power law creep has been observed, and was found to be
considerably faster than creep in bulk at low stresses. Deviations
from bulk behavior start to occur when the dislocation cell size
becomes on the order of the film thickness. Comparisons will be made
with the plastic behavior of free-standing and supported thin
films.
9:00 AM A7.3
THE
THICKNESS DEPENDENCE OF THE FLOW STRESS OF CAPPED AND UNCAPPED
POLYCRYSTALLINE AG THIN FILMS. Mauro J. Kobrinsky and
Carl V. Thompson, Massachusetts Institute of Technology, Dept of
Materials Science and Engineering, Cambridge, MA.
The flow stress of capped and uncapped polycrystalline silver films
on oxidized silicon wafers is reported as a function of Ag film
thickness (in the range 0.2-1.2 m) and temperature (in the
range -50 to 500C). Capping layers, when present, were
sputtered SiOx films. As expected, the flow stress was found to
continuously increase with decreasing film thickness in capped films.
However, in uncapped films, while the flow stress at low temperature
(below 150C) was found to increase with decreasing film
thickness in the film thickness range 0.5-1.2 m, the flow
stress at low temperature was found to decrease with decreasing film
thickness in the thickness range 0.2-0.5 m. The flow stress at
low temperature increases with decreasing temperature in all cases.
When uncapped films were cooled from 500C, we found two
different inelastic regimes. In the high temperature regime
(150-500C), the flow stress is independent of temperature
and the Ag film thickness. In the low temperature regime (T <
150C), the flow stress is strongly dependent on
temperature and film thickness. In uncapped films, the temperature at
which the transition between regimes occurs, Tp, decreases with
decreasing film thickness with an Arrhenius dependence characterized
by an activation energy of 0.4 eV. These results suggest a role of
surface diffusion in the higher temperature regime in uncapped films.
Because the average grain size of the Ag films scales with the film
thickness, diffusion distances decrease so that stress relaxation
becomes more rapid with decreasing film thickness, leading to the
observed decrease in the flow stress with decreasing film thickness
in the thinnest uncapped films. Surface diffusion is suppressed in
capped films, so that the flow stress continuously increases with
decreasing film thickness.
9:15 AM A7.4
EFFECTS
OF PROCESSING PARAMETERS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES
OF ELECTRODEPOSITED NICKEL. F. Ebrahimi , G. R. Bourne,
M. S. Kelly, and T. E. Mathews, Materials Science and Engineering
Dept., University of Florida, Gainesville, FL.
Recently, attention has been given to the electroforming of nickel,
which has diverse applications from printing or embossing to compact
disc manufacturing. In this study thin polycrystalline foils
(30 micrometer thick) have been produced by electrodeposition
on polycrystalline copper substrates with a strong <100> texture.
Nickel was deposited galvanostatically using a sulfumate solution.
The copper substrate was removed after the deposition. The effects of
pH, current density, and pulse plating on the microstructure and
mechanical properties were evaluated using XRD, SEM, and tensile
testing. It has been shown that the processing parameters affect the
crystallite size, grain morphology, and the defect structure of the
deposits. For example, inceasing the pH decreases the crystallite
size without a modification of texture or grain morphology. The
results of this study show that high quality (very low pore density),
high strength (>1000 MPa) nanocrystalline (<100 nm) nickel foils
can be produced by optimizing the processing parameters.
9:30 AM
A7.5
MICROSCOPIC AND BULK BEHAVIOR OF
THE ELASTIC MODULI IN PLASMA SPRAYED COATINGS. Thomas
Gnupel-Herold , University of Maryland, Department of Materials and
Nuclear Engineering, College Park, MD and National Institute of
Standards and Technology, Center for Neutron Research, Gaithersburg,
MD; Paul C. Brand, Henry J. Prask, National Institute of Standards
and Technology, Center for Neutron Research, Gaithersburg, MD; Jiri
Matejicek, State University of New York, Stony Brook, NY.
The elastic properties of Yttrium Stabilized
Zirconia and Alumina plasma sprayed coatings are examined. Free
standing pieces of sprayed deposits have been used to perform
uniaxial load tests both normal and parallel to the deposit surface.
In situ neutron diffraction under load has been used for the
determination of the diffraction elastic constants (DEC) which probes
directly the average elastic behavior on a microscopic scale. On the
macroscopic scale, the bulk deformation behavior has been measured by
examining the total specimen strain under load. Both deposits exhibit
a strong anisotropy both in their microscopic and bulk behavior in
the directions normal and parallel to the deposit surface. Although
crystallographically random, these coatings possess a grain shape
anisotropy that is caused by pancake shaped grains all having the
same orientation. Based on recent results which relate the DEC and
single crystal elastic constants, and allowing for the influence of
the grain shape, the isotropic elastic constants have been
calculated. Due to porosity, there are strong deviations of the bulk
elastic constants compared to the microscopic ones so that the bulk
moduli are only a fraction of the elastic constants that have been
determined from the DEC. The influence of shape and arrangement of
the pores on the bulk behavior is discussed.
10:15 AM
A7.6
RESIDUAL STRESSES IN
POLYCRYSTALLINE Cu/Cr MULTILAYERED THIN FILMS. A. Misra ,
H. Kung, T.E. Mitchell and M. Nastasi, Materials Science and
Technology Division, Los Alamos National Laboratory, Los Alamos, NM.
Residual stresses in sputter deposited Cu/Cr
multilayers, and Cu and Cr single layered polycrystalline thin films
are evaluated by substrate curvature method. The stresses in the
multilayers are found to be tensile and to increase in magnitude with
increasing layer thickness (h) to a peak value of 1 GPa for h =
50 nm. For h > 50 nm, residual stress decreased with increasing h
but remained tensile. Same trends are observed in single layered Cu
and Cr thin films. While the maximum tensile stress in Cr films is
1.7 GPa, the maximum stress in Cu films is an order of
magnitude lower. The residual stresses in multilayers are attributed
primarily to the growth stresses in the Cr layers with secondary
contributions from the interface stress. The contribution of Cu layer
growth stresses to the total stress of the multilayers is
insignificant. Substrate curvature measurements on bilayer films of
different thicknesses are used to determine the interface stress.
Transmission electron microscopy is used to relate the stress
evolution to the microstructures. Cu films exhibit defects such as
dislocations and twins which may serve to relax the growth stresses.
Cr films exhibit columnar porosity independent of the film thickness.
The generation of tensile stresses as a function of Cr film thickness
is explained using a grain growth model. For h 50 nm, the model
predictions fit the experimental data but for h 50 nm, the
model overestimates the residual stress. We have used a model for the
yield stress of polycrystalline films proposed by Thompson
(J.Mater.Res., vol.8, p.237, 1993) to show that the maximum value of
the residual stress is set by the film yield strength and hence, the
decrease in residual stress with increasing h for h 50 nm
reflects a decrease in the film yield stress with increasing
thickness. The effects of processing parameters on the
microstructure and the corresponding residual stresses is also
discussed.
10:30 AM
A7.7
SUBSTRATE EFFECTS ON
DETERMINATION OF INTERFACIAL FRACTURE PROPERTIES. N. R.
Moody , D. Medlin, J. Schneider, Sandia National Laboratories,
Livermore, CA; A. Strojny, W. W. Gerberich, University of Minnesota,
Minneapolis, MN; A. Talin, Motorola, Tempe, AZ; D. Feiler, Rockwell
International, Newport Beach, CA.
Thin tantalum
nitride films are often used in microelectronic applications because
of their long term stability and low thermal coefficients of
resistance. However, they are high heat generators that when combined
with a high structural defect content and high compressive residual
stresses can alter properties over long service lives. This has
motivated replacing aluminum oxide substrates currently in use with
aluminum nitride. However, recent results characterizing interface
structure and fracture properties of these films on aluminum oxide
and aluminum nitride substrates lead to contradictory conclusions. We
have therefore combined continuous nanoscratch testing with a
multi-layer aluminum oxide and aluminum nitride single substrate
system to eliminate sample-to-sample variations. The results show
that the difference between fracture property results on individual
substrates arises primarily from differences in substrate properties.
In this presentation, the results will be used to show how substrate
properties and interface structure affect measurement and analysis of
film fracture.
This work supported by U.S. DOE Contract DE-AC04-94AL85000.
10:45 AM
A7.8
INTERCONNECT LINES ON SILICON
WAFERS: THERMOMECHANICAL ANALYSIS AND EXPERIMENTS. Adam
Wikstrom , Peter Gudmundson, Dept of Solid Mechanics, Royal Institute
of Technology, Stockholm, SWEDEN; Subra Suresh, Dept of Materials
Science and Engineering, MIT, Cambridge, MA.
Stresses and curvatures arising from patterned thin lines on
initially flat isotropic substrates are analyzed. Approximate
analytical expressions are derived for volume-averaged stresses as
well as curvatures along and normal to the lines, for any thickness,
width and spacing of the lines. The predictions of the analysis are
shown to compare favorably with finite element simulations of
stresses and curvatures for Si substrates with Al, Cu or SiO2 lines.
The predictions also match prior experimental measurements of
curvatures along and normal to patterned SiO2 lines on Si wafers, and
further capture the general experimental trends reported previously
for curvature evolutions in Si wafers with Al lines. The model
presented here thus provides a very convenient and simple analytical
tool for extracting stresses in thin lines on substrates from a
knowledge of experimentally determined film stress, thereby
circumventing the need for detailed computations for a wide range of
unpassivated line geometries of interest in microelectronic
applications. This constitutes a new extension of the well known
Stoney formula to thin lines on substrates. Possible extensions to
analyze the onset of plastic deformation are also explored.
11:00 AM
A7.9
EXPERIMENTS AND ANALYSIS OF
PLASTIC DEFORMATION OF ALUMINUM LINES ON SILICON SUBSTRATES.
A. Gouldstone , V.T. Srikar, S. Suresh and C.V. Thompson,
Massachusetts Institute of Technology, Dept of Materials Science and
Engineering, Cambridge, MA.
The inelastic
deformation of periodic Al thin lines on Si substrates has been
investigated by recourse to theory, computations and experiments.
The onset and progression of plastic yielding are examined as a
function of the line thickness, width and spacing, and are compared
to those of continuous aluminum films of comparable thicknesses on Si
substrates. By employing wafer curvature and nanoindentation
experiments along with finite element simulations and theoretical
analysis of curvatures and stresses, the dependence of line yield
strength on line geometry has been identified. A theoretical model
which facilitates direct interpretations of line yield strength from
routine wafer curvature measurements is suggested. The predicted
volume-averaged stresses are compared with x-ray measurements.
Possible extensions of the present results to passivated Al lines on
Si substrates are also considered.
11:15 AM A7.10
ON
THE NATURE OF GRAIN BOUNDARIES IN NANOCRYSTALLINE DIAMOND.
P. Keblinski a,b, D. Wolfa and S.R Phillpota
and H. Gleiterb, aMaterials Science Division, Argonne National
Laboratory, Argonne, IL, bForschungszentrum Karlsruhe, Karlsruhe,
GERMANY.
Recent molecular dynamics simulations of
nanocrystalline silicon microstructures have shown that, provided the
grain orientations are random, all the grain boundaries are
incommensurate and have a relatively high energy. Based on these
insights, we have used Monte Carlo simulations to determine the
atomic structures of a few representative large-unit-cell grain
boundaries thought to dominate the behavior of nanocrystalline
diamond. In these highly disordered grain boundaries up to 80 of
the C atoms exhibit local sp2 bonding. However, because the
three-coordinated C atoms are poorly connected amongst each-other,
graphite-like electrical conduction through the grain boundaries is
unlikely. Surprisingly, based on their fracture energies, the
high-energy, large-unit-cell boundaries are more stable against
brittle decohesion into free surfaces than low-energy ones and
perhaps even the perfect crystal. The presence of only high-energy
GBs thus appears to be the main reason for the excellent mechanical
performance of nanocrystalline diamond films.
This work was supported by the U.S. Department of Energy
BES-Materials Science under Contract No. W-31-109-Eng-38. P. K.
gratefully acknowledges support from the Alexander von Humboldt
Foundation.
11:30 AM
A7.11
STRESS ANISOTROPY, IN-PLANE
TEXTURING AND THEIR THICKNESS DEPENDENCE IN MAGNETRON SPUTTERED Cr
FILMS. Z.B. Zhao , Z.U. Rek*, S.M. Yalisove and J.C.
Bilello, Department of Materials Science & Engineering, University of
Michigan, Ann Arbor, MI. *Stanford Synchrotron Radiation
Laboratory, Stanford University, CA.
Cr films
deposited onto the moving substrates have been investigated by means
of synchrotron grazing incidence x-ray scattering (GIXS) and double
crystal diffraction topography (DCDT). For films at certain
thicknesses, the lattice curvatures of the (100) Si substrates have
been observed to be significantly non-spherical. This indicates that
the biaxial in-plane stresses are highly anisotropic in these Cr
films deposited under the given conditions. The anisotropic in-plane
stresses in Cr films are quantified using a modified Stoney equation.
The maximum in-plane stress (tensile) is always in the direction
perpendicular to the direction of motion of the substrates. In
addition to the (111) out-of-plane texture for these thin films, the
remarkable in-plane crystallographic anisotropy (texturing) has also
been revealed by means of the azimuthal (f) x-ray scans at a grazing
incidence angle. The f scans have also established the correlation
between the in-plane texturing directions and the deposition
geometry. The [110] and [200] crystallographic orientations of the Cr
films align preferentially parallel and perpendicular to the
direction of motion of the substrates, respectively. Furthermore,
such in-plane texturing appears to have connections with the stress
anisotropy: the directions of the principal stresses (i.e. maximum
and minimum) coincide with the [110] and [200] preferred
orientations. This viewpoint is further supported by the observations
of their similar thickness dependence.
11:45 AM
A7.12
EFFECT OF GRAIN ORIENTATION AND
GRAIN-BOUNDARY MISORIENTATION ON ELECTROMIGRATION FAILURE IN
SUB-MICROMETER ALUMINUM INTERCONNECTS. X. Chu , C.L.
Bauer, W.W. Mullins, Department of Materials Science & Engineering,
Carnegie Mellon University, Pittsburgh, PA; J.A. Prybyla, S.K.
Theiss, M.A. Marcus, Bell Laboratories, Lucent Technologies, Murray
Hill, NJ.
Although void formation, growth and
movement represent important electromigration-induced failure modes
in fine line interconnects, corresponding mechanisms for nucleation
and mass transport, in general, have not been identified.
Electromigration-induced (open-circuit) failures for <111> textured
sub-micrometer (bamboo) Al interconnects were recorded as a function
of failure time at 215C, line width (300, 500 and 800 nm) and
Cu concentration (0, 0.5 and 0.9 wt.%). Subsequently, (fatal) void
shape and surrounding grain structure were observed by focused ion
beam microscopy, whereas grain orientation was measured both
sequentially along the interconnect length (several hundred grains)
and locally by electron back-scattered diffraction. Measured
orientations were then processed in order to obtain global and local
(adjacent-to-void) distributions of grain orientation and
grain-boundary misorientation. These distributions are presented,
compared with existing models, and analyzed further in order to
identify likely electromigration-induced failure mechanisms in
fine-line interconnects. Research supported, in part, by Lucent
Technologies and the National Science Foundation under Award
DMR-9319896.
SESSION A8: MAGNETIC PROPERTIES
Chairs: Theodore I.
Kamins and Frans Spaepen
Thursday Afternoon, December 3, 1998
Salon A/B (M)
1:30 PM
*A8.1
IN-PLANE MAGNETIC ANISOTROPY IN
POLYCRYSTALLINE COBALT ALLOY FILMS. C.A. Ross , D.J.
Twisselmann, Department of Materials Science and Engineering, M.
Farhoud, Henry I. Smith, Department of Electrical Engineering and
Computer Science, Massachusetts Institute of Technology, Cambridge
MA.
Sputtered cobalt-alloy polycrystalline thin
films, on a chromium underlayer, are commonly used to store data in
magnetic hard disks. The hard-disk substrate is often roughened by
mechanical abrasion to form shallow circumferential scratches, prior
to sputtering the Cr/Co-alloy bilayer. It is found that the in-plane
magnetic properties of the cobalt-alloy film depend on the substrate
topography. The coercivity, remanence, squareness and S* are higher
parallel to the scratches compared to their values perpendicular to
the scratches, and this affects the recording performance of the
disk. The origin of this topographically-induced in-plane anisotropy
has been debated. It could be a result of in-plane stress
differences, of the preferential alignment of the cobalt c-axes
parallel to the scratches, or to differences in magnetic interactions
between the grains in different in-plane directions. We have
investigated in-plane anisotropy by making oxidised silicon
substrates with controlled, periodic grooves using interferometric
lithography. Grooves with periods of 100 - 300 nm and depths in the
range of 10 - 50 nm have been made over areas of several square cm.
The profile of the grooves can be varied from square-wave to
sinusoidal by appropriate etching. Cr/CoCrPt films were deposited on
the substrates by both d.c.- and r.f.-magnetron sputtering, and the
in-plane magnetic properties were measured using vibrating sample
magnetometry. Deposition conditions were established under which
films grown on silica have similar microstructure and preferred Co
(11.0) orientation compared to those grown on standard NiP hard disk
substrates. Films deposited on grooved silica show an increase in
anisotropy with amplitude of the grooves. The influence of groove
period, amplitude, and profile on the magnitude of the magnetic
anisotropy will be described, and related to the models for the
origin of topographically-induced anisotropy.
2:00 PM
*A8.2
INFLUENCE OF THE MICROSTRUCTURE
ON THE MAGNETIC PROPERTIES OF GIANT MAGNETOSTRICTIVE TbDyFe FILMS.
Michael Hirscher , Bernhard Winzek, Saskia F. Fischer,
Helmut Kronmüller, Max-Planck-Institut für Metallforschung
Stuttgart, GERMANY.
Amorphous TbDyFe films show
excellent soft-magnetic properties combined with giant
magnetostriction. However, for technical applications the major
drawback is the low Curie temperature which is typically around 400 K.
To increase the Curie temperature and simultaneously achieve good
soft-magnetic properties as well as giant magnetostriction the
preparation of crystalline films with nanometer-sized grains is
necessary. Terfenol-D-like films with additives of Zr, Nb, Mo were
prepared by ion beam sputtering and different heat treatments were
applied to investigate the crystallization behaviour. These additives
enhance the nucleation of REFe2 grains and hinder the formation of
REFe3 which is assumed to be responsible for high coercivity
values. Furthermore, nanometer-scaled multilayers with Nb interlayers
were prepared. This multilayer structure is suitable to inhibit grain
growth and hence further decreases the average grain size. The
resulting nanocrystalline microstructure leads to small coercive
fields and high Curie temperatures. In addition, protective layers
were investigated in order to avoid oxidation during the heat
treatments for crystallization.
The results will be
discussed with respect to possible applications in micro system
technology.
2:30 PM
A8.3
MICROSTRUCTURE AND MAGNETIC
PROPERTIES OF ANNEALED CoPt/C FILMS PREPARED BY LASER ABLATION.
I. Panagiotopoulos , S. Stavroyiannis, D. Niarchos, IMS,
NCSR ``Demokritos'', Ag. Paraskevi Attikis, GREECE; J.
Christodoulides and G.C. Hadjipanayis, Department of Physics and
Astronomy, University of Delaware, Newark, DE.
Bulk
Co-Pt alloys around the equiatomic composition have a disordered fcc
structure at high temperatures which transforms to an ordered face
centered tertagonal (fct) upon annealing below 800C. The
high anisotropy of the tetragonal phase makes these materials
attractive for high density magnetic recording media. We have
recently studied the formation of nanoscale isolated CoPt phases in
annealed CoPt/C pseudomultilayers obtained by laser ablation From
CoPt and C targets using an KrF excimer laser with fluence of 4
J/cm2. The as-made films have been found to have a disordered fcc
structure and are magnetically soft. Upon annealing at temperatures
in the range of 500-700C a two phase microstructure
consisting of CoPt particles in a C matrix is obtained. The type of
Co-Pt phases formed depends on the amount of Pt and the
microstructure morphology on the C content in the sample. For films
with Pt content below 40%, the microstructure consists of fcc CoPt
nanoparticles embedded in a C matrix and the magnetic properties are
still soft. For higher Pt content samples the anisotropic fct phase
is formed leading to an increase in coercivity to several kOe.
However, the formation of this phase is rather slow as compared to
CoPt/Ag films with similar composition. By varying the annealing
conditions, microstructures with dfferent particle size have been
obtained and will be correlated with the magnetic properties of the
sample.
SESSION A9: ELECTRICAL AND OPTICAL PROPERTIES
Chairs:
Theodore I. Kamins and Frans Spaepen
Thursday Afternoon, December
3, 1998
Salon A/B (M)
3:00 PM
A9.1
ELECTRICAL PROPERTIES OF GRANULAR
THIN FILMS FORMED BY METAL IMPLANTATION INTO SILICON. C.P. Li, K.Y.
Lai, Qicai Peng, W.Y. Cheung, S.P. Wong , Dept of
Electronic Engineering, The Chinese University of Hong Kong, Shatin,
N.T., Hong Kong, CHINA.
Granular thin films consist
of metal silicide nanocrystals embedded in silicon substrates have
been prepared by high dose Co or Ti ion implantation using a metal
vapor vacuum arc (MEVVA) ion source. The MEVVA implantation was
performed at extraction voltages ranging from 30 to 70 kV to doses
ranging from 5x1016 to 4x1017 cm-2. Characterization
of the implanted samples was performed using x-ray diffraction,
Rutherford backscattering spectrometry, transmission electron
microscopy and electrical measurements. It is found that nanocrystals
of CoSi2 or TiSi2 with various sizes dependent on the
implantation conditions have been formed in the as-implanted samples.
For samples prepared under appropriate conditions, the electrical
resistance was found to exhibit a nearly-temperature-independent (NTI)
behavior from 20K to 300K. Such an NTI behavior is believed to be a
common phenomenon for metallic nanocrystals embedded in a
semiconducting matrix. The detailed temperature dependence of the
electrical properties of these implanted granular thin films will be
presented and discussed in conjunction with the results of the other
characterization techniques. This work is supported in part by the
Research Grants Council of Hong Kong (Ref. No.: CUHK 374/96E).
One of us (QP) is supported by a Postdoctoral Fellowship of CUHK.
3:15 PM
A9.2
COMPOSITE CVD DIAMOND FILMS WITH
UNUSUAL ELECTRICAL PROPERTIES. Maria L. Terranova ,
Susanna Piccirillo, Vito Sessa, Dip. Scienze e Tecnologie Chimiche,
Univ. Tor Vergata, Roma, ITALY; Marco Rossi, Dip. Energetica, Univ.
La Sapienza, Roma, ITALY; Giovanni Micocci, Antonio Serra, Antonio
Tepore, Dip. Scienza dei Materiali, Lecce, ITALY.
A
new technique utilizing a powder-flowing apparatus coupled with a
CVD reactor is being used to produce a novel class of diamond-based
composite materials. This methodology, which allows to incorporate
a variety of elements and compounds in form of aggregates ,
clusters or dispersions of nanosized grains inside a polycrystalline
diamond matrix, has been used in the present study for depositing
composite Nd-containing diamond films on Si(100) plates. To produce
the mixed phases, flowing Ar streams containing either Nd-oxide or
Nd-acetylacetonate (fine-grained powders) were mixed in the CVD
chamber with CH4/H2 diamond feeding mixtures.
Hall effect measurements performed by the van der Pauw method on
deposits containing 5-10% Nd evidenced very surprising
electrical transport properties. The p-type conductivity measured
at room temperature (of the order of 220 Ohm-1 cm-1) is that of a
conducting material, the hole density is as high as 10exp18 cm-3,
whereas the Hall mobility is about 1500 cm2/V s , value typical
of diamond single crystal.
Overall , the alteration of the electronic properties of the host
diamond matrix by randomly dispersed conducting domains gives rise
to an unexpected electrical behaviour of the composite system, which
exhibits a doped-semiconducting behaviour, with very high
conductivity values.
3:30 PM A9.3
HIGH
TEMPERATURE ELECTRICAL PROPERTIES OF REACTIVELY SPUTTERED INDIUM TIN
OXIDE. Otto J. Gregory , Joseph M. Bienkiewicz, Brian M.
Erwin, Univ. of Rhode Island, Sensor and Surface Technology
Partnership, Chemical Engineering Dept., Kingston, RI.
The high temperature electrical properties of oxygen
deficient indium-tin oxide (ITO) thin films prepared by rf reactive
sputtering were investigated. These films were prepared in various
argon:oxygen mixtures from a high density ITO target (90 wt% indium
oxide and 10 wt% tin oxide). The resulting ITO films were
transparent in the visible spectrum, tested n type by hot probe, and
exhibited room temperature resistivities in the range 1x10-2 to 2x102
ohm cm after annealing in nitrogen. Mobilities and charge carrier
concentrations in the as-deposited and annealed ITO thin films were
determined from Hall measurements. In addition, the films were
characterized by glancing angle X-ray diffraction, UV-Vis
spectroscopy and XPS to determine crystallinity and composition. The
piezoresistive response and electrical resistivity of the ITO films
at elevated temperature were dependent on the oxygen content in the
plasma. In particular, the ITO films prepared in high oxygen content
plasmas produced a large, negative piezoresistive response, with
little or no hysteresis when strained in either tension or
compression (up to 700 in/in) at temperatures up to
1250C. The temperature coefficient of resistance (TCR) of
the nitrogen annealed ITO films was also dependent on the oxygen
content in the plasma. The electrical behavior of films prepared in
low oxygen partial pressures showed a relativley large, negative TCR
(-1560 ppm/C) over the temperature range
150C<T<1100 C, whereas films produced in high
oxygen partial pressures exhibited very different behavior; i.e. a
relativley small, negative TCR (-430 ppm/C) in the
temperature range 100C<T<800C and a relatively
large TCR (-1760 ppm/C) in the temperature range
800<T<1250C. This implies that two different thermally
activated charge carriers were responsible for the observed
electrical behavior. The relationship between processing parameters,
electrical properties, and piezoresistive properties of these ITO
films is reviewed and the prospects of using these films as high
temperature strain sensors is discussed.
3:45 PM
A9.4
OF LARGE GRAIN
POLYCRYSTALLINE LEAD IODIDE FILMS FOR DIGITAL IMAGING APPLICATIONS.
K.C. Mandal , L.P. Moy, L. Cirignano, K.S. Shah, M.S.
Squillante, Radiation Monitoring Devices, Inc., Watertown, MA; O.
Savadogo, Department of Materials Engineering, Ecole Polytechnique,
Montreal, CANADA; R.N. Bhattacharya, National Renewable Energy
Laboratory, Golden, CO.
In this paper, we report our
recent research in developing large grain polycrystalline PbI2
(Eg 2.3 eV at 300 K) films for digital medical imaging
applications. The grown films have shown high promise for this
application due to their high dark resistivity (5 x10^12
_e= 8 x 10-7 cm2/V), low cost and
easy scale-up. Lead iodide films (up to 7.5 x5 cm^2, D.E. Jonsen, J.J. Hren and J.J. Cuomo Department
of Materials Science and Engineering, North Carolina State
University, Raleigh, NC; *Institute of Crystallography, Moscow,
RUSSIA.
AlN has excellent properties for use in
Field Emission Displays such as good thermal conductivity and high
chemical stability. Previous study show AlN can be used as a coating
material on metal and silicon tips. In general, it is known that
electron emission characteristics of wide band gap materials depend
on the crystal quality, structure and thickness of deposited
materials. However, few studies have examined the relationship
between these deposition parameters and I-V characteristics.
In this study, AlN was deposited on metal tips under a variety of
deposition temperatures and gas mixture ratios. Thickness effects of
AlN on metal tips were observed by measuring I-V characteristics
immediately after every 20 sec AlN deposition. All I-V data was
obtained by measurement in situ, which was set up inside of a typical
magnetron sputtering chamber at pressures of 10-7 Torr.
TEM is used to examine crystal structure and thickness of AlN on the
metal tips. Preliminary results show that a critical thickness
exists, at which the emission characteristics of the coating are
optimized.
4:15 PM
A9.6
INFLUENCE OF MICROSTRUCTURE ON
THE DIELECTRIC PROPERTIES OF HYDROTHERMALLY DERIVED
BaTiO3/POLYMER THIN FILMS. David E. Collins ,
Elliott B. Slamovich, Purdue University, School of Materials
Engineering, West Lafayette, IN.
Nanocomposite
BaTiO3/polymer films (<1m in thickness) for dielectric
applications were prepared below 100C by hydrothermal
processing. This method involves the formation of crystalline
materials from metallo-organic precursors, in this case a titanium
alkoxide, under strongly alkaline conditions to form nanocrystalline
particles. Films were prepared by dissolving the polymer and a
titanium metallo-organic precursor in a mutual solvent to facilitate
spin casting. Subsequent hydrothermal treatment (<100C)
of precursor films in alkaline solutions of Ba(OH)2 or BaCl2
produced BaTiO3 within the polymer matrix. Films fabricated in
this manner consisted of a continuous BaTiO3 layer on the surface
and a subsurface composite layer of dispersed BaTiO3 particles.
These films were investigated to determine the influence of
processing conditions and precursor composition on the ensuant
composite microstructure and dielectric properties.
4:30 PM A9.7
GROWTH
AND CHARACTERIZATION OF ZnGa2O4: Mn THIN FILM PHOSPHORS
USING PULSED LASER ABLATION. Yong Eui Lee *, David P.
Norton, J.D. Budai, S.J. Pennycook, C. Rouleau, and G.E. Jellison,
Jr., *ORISE Postdoctoral Research Program, Solid State Division,
Oak Ridge National Laboratory, Oak Ridge, TN.
Polycrystalline ZnGa2O4:Mn thin films have received
considerable attention as green light emitting phosphors for use in
field emission displays and thin-film electroluminescent devices
because of their excellent chemical stability and good luminescence
characteristics. Unfortunately, as-deposited ZnGa2O4:Mn
thin films often do not exhibit good luminescent properties,
requiring post-annealing at 1,000C in order to achieve high
performance luminescent characteristics. Correlating the structural
and optical properties of these materials is essential in further
improving these materials. We will report on the synthesis and
properties of ZnGa2O4:Mn thin film phosphors deposited on
various substrates using pulsed laser deposition. The focus of this
work is to investigate the relationship between processing
conditions, structure, and luminescence in ZnGa2O4:Mn
films. The structural and optical properties of as-deposited
luminescent films will be described, comparing epitaxial single
crystal and polycrystalline films, in an attempt to delineate the
role of specific defects detemining photo- and electroluminescent
properties. The effect of post-annealing on structural and optical
properties of the films will be also discussed.
This research was sponsored by the Oak Ridge National Laboratory,
managed by Lockheed Martin Energy Research Corp., for the U.S.
Department of Energy, under contract DE-AC05-96OR22464.
newline
``The submitted manuscript has been authored by a contractor of the
U.S. Government under contract DE-AC05-96OR22464. Accordingly, the
U.S. Government retains a nonexclusive, royalty-free license to
publish or reproduce the published form of this contribution, or
allow others to do so, for U.S. Government purposes.''
4:45 PM A9.8
TEM
MICROSTRUCTURAL STUDIES ON YHx FILM. M.A. Verheijen ,
Philips Centre for Manufacturing Technology, Eindhoven, THE
NETHERLANDS; F.J.A. den Broeder, P.A. Duine, Philips Research
Laboratories, Eindhoven, THE NETHERLANDS.
Thin films
of yttrium and certain rare-earth (RE) metal hydrides can reversibly
be switched between a metallic opaque and a transparant semiconducting
state when the hydrogen concentration is varied in the film [1]. This
concentration can be controlled by varying the pressure of the
surrounding hydrogen gas. Upon loading an Y film with hydrogen two
phase transitions occur:
The first step is
unidirectional, the second step is a reversible transition between the
opaque and transparant states. The crystal structure of the YHx
film changes from h.c.p. via f.c.c. towards a distorted h.c.p.
structure. In this paper we present studies on the microstructure of
the different YHx phases and the mechanism of the phase
transitions.
The sample geometry of the yttrium hydride
films studied consist of a 150 - 300 nm thick Y film, deposited on a
substrate by evaporation or sputtering. Normally, a cap layer of
palladium (5 to 10 nm thick) is used to protect the hydride film
against oxidation.
In order to study the hydrogen diffusion
and the consecutive phase transitions within one sample, on our
samples only a small strip of Pd has been deposited, thereby
localising the area in which the hydrogen can enter the Y film. As a
result a lateral H concentration profile is obtained and thus a
lateral sequence of phases [2].
Cross-sectional as well as
plan-view samples show that the first phase transition involves a
total recrystallisation of the Y layer from fine to coarse
crystalline. Growth of the YH2 phase proceeds by stimulated
nucleation and results in a layer with a very small spread in
orientation of the individual crystals. In the transition towards the
YH3 phase the YH2 microstructure is conserved. The effects of
deposition conditions on the microstructure of the Y film and the role
of oxidation of the Y will be treated in more detail.
[1]
J.N. Huiberts et al., Nature 380 (1996) 231.
[2]
F.J.A. den Broeder et al., Nature (1998), to be published.