Qinghuang Lin IBM T. J. Watson Research Center
Wen-li Wu National Institute of Standards and Technology
E. Todd Ryan Advanced Micro Devices
IBM - Albany NanoTech
Do Yeung Yoon Seoul National University
B1: Dielectric Materials I
Tuesday AM, April 10, 2007
Room 3002 (Moscone West)
9:15 AM -
9:30 AM - **B1.1
Vapor Deposition of Pore-Sealing, Barrier, Adhesion and Seed Layers for Interconnects.
Roy Gordon 1 , Huazhi Li 1 , Zhengwen Li 1 , Daewon Hong 1 , Damon Farmer 2 , Youbo Lin 2 , Joost Vlassak 2 , Daniel Josell 3 , Thomas Moffat 3 , Christian Witt 4 Show Abstract
1 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 2 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 Metallurgy Division, National Institute of Standards and Technology, Gaithersberg, Maryland, United States, 4 TJ Watson Research Center, IBM, Yorktown Heights, New York, United States
An integrated process has been developed for vapor deposition of all the layers needed to prepare a damascene structure in porous low-k dielectric for electroplating with copper. As a first step, the open pores were sealed with one atomic layer deposition (ALD) cycle that closes the pores with about 6 nm of smooth silica. At the same time, less than 0.4 nm of silica (less than 2 mono-layers) deposited on the copper at via bottoms that had been protected by a self-assembled monolayer (SAM). This residual silica and SAM can be removed from the copper by ion etching methods normally used to clean the copper at via bottoms. Next a diffusion barrier of amorphous tungsten nitride (WN) ~ 2 nm thick was deposited by ALD or by CVD. An adhesion-promoting layer of ruthenium ~ 2 nm thick was formed by ALD or CVD on the WN. Electron microscopy and chemical etch tests demonstrated complete coverage by the ruthenium film. Finally copper seed layers were made by ALD or CVD with a non-fluorine-containing precursor. Quantitative 4-point bend tests showed very strong adhesion (> 20 J m-2) when the metal layers were deposited without an air break. The resulting completely conformal structure (aspect ratio 4:1) had a sheet resistance less than 50 ohms per square for a copper seed layer thickness of less than 4 nm. Electroplating copper on this structure showed complete trench-filling without voids. The structure also survived chemical-mechanical planarization, forming electrically continuous copper in serpentine trenches.
10:00 AM - **B1.2
Interface with High Adhesive and Cohesive Strength Between SiCOH Dielectrics and SiCHN Caps.
Alfred Grill 1 , Dan Edelstein 1 , Michael Lane 1 , Vishnubhai Patel 1 , Stephen Gates 1 , Darryl Restaino 2 , Steven Molis 2 , Nancy Klymko 2 , Kang Yim 3 , V. Nguyen 3 , Alex Demos 3 , Steven Reiter 3 , Hichem M'Saad 3 Show Abstract
1 , IBM - T.J.Watson Res.Ctr., Yorktown Heights, New York, United States, 2 , IBM SRDC, Hopewell Junction, New York, United States, 3 , Applied Materials, Santa Clara, California, United States
The integration of low and ultralow-k SiCOH dielectrics in the interconnect structures of VLSI chips involves complex stacks with multiple interfaces. Successful fabrication of reliable chips requires, among other, strong adhesion between the different layers of the stacks. A critical interface in the dielectric stack is the interface between the SiCH(N) diffusion cap and the SiCOH intra- and interlevel dielectric (ILD). It was observed that, due to the original deposition conditions, the interface layer was weakened both by a low adhesion strength between SiCHN and SiCOH and by the formation of an initial layer of SiCOH with reduced cohesive strength. The manufacturing process has been modified to engineer this interface and obtain adhesion strength close to the cohesive strength of the bulk ILD. The talk will discuss the reasons for the original low adhesion strength and will present the approach for engineering the interface to the cap for both the dense SiCOH and porous SiCOH ILDs.
10:30 AM - **B1.3
Interfacial Organic Layers: Tailored Surface Chemistry for Nucleation and Growth of Inorganic Barrier Layer Materials.
James Engstrom 1 Show Abstract
1 Chemical Engineering, Cornell University, Ithaca, New York, United States
Interfacial organic layers, including self-assembled monolayers, have long been recognized for their potential to modify the chemical and physical properties of surfaces. One particularly exciting concept is to use interfacial organic layers to promote thin film deposition of inorganic materials, particularly in situations where nucleation is problematic. One problem that falls into this class is that of the growth of barrier layer materials on low-κ dielectrics. Nucleation on low-κ dielectrics is difficult due to two basic reasons: the chemical termination of the surface is unreactive, and the void space represented by the pores, of course, is by definition unreactive. In the work we describe here we propose the use of interfacial organic layers to promote nucleation and growth of barrier materials on low-κ dielectrics. In a series of studies we have been investigating a variety of phenomena associated with this concept, from studies of the organic layers themselves, to thin film growth via atomic layer deposition (ALD) on these layers. We have demonstrated controlled growth of organic interfacial layers with reactive terminal organic functional (–OH and –NH2) groups, and both linear (straight chain) and branched microstructures. The structure and reactivity of these layers with precursors for ALD, such as Ti[N(CH3)2]4 and Ta[N(CH3)2]5, has also been evaluated. Nucleation and growth of barrier layer materials (TiNxCy) on these organic interfacial layers via ALD has been investigated via the use of molecular beam techniques. We have found that the interfacial layers with reactive terminations give the most uniform films, and thus they should be best suited for ultrathin barrier layer applications.
11:30 AM - **B1.4
Formation of Porous Organosilicate Glasses Produced by PECVD and UV Curing
Mark O'Neill 1 , Patrick Hurley 1 , Scott Weigel 1 , Mary Haas 1 , Brian Peterson 1 , Raymond Vrtis 1 , Dingjun Wu 1 , Steven Mayorga 1 Show Abstract
1 Electronics Technology, Air Products and Chemicals, Inc., Allentown, Pennsylvania, United States
The need of the semiconductor industry for improved dielectric insulators has resulted in the choice of organosilicate glass materials for the manufacture of devices beyond the 130nm node. The inherent limitations of these materials (e.g. inferior mechanical strength, reduced thermal/chemical stability versus silicate glass) have been overcome through modifications to back-end-of-line (BEOL) integration processes. For 45nm generation IC manufacturing and beyond porous organosilicate glasses (OSGs) produced by plasma enhanced chemical vapor deposition will be employed. The introduction of porosity to OSG materials enables improvements in the insulating property while retaining the basic structure and materials character of the previous generations. These porous materials inherently suffer from further reductions in mechanical properties relative to their non-porous predecessors; post-treatment processes such as UV and e-beam are used to improve the material integrity. The final structure and composition of the porous film will impact the processes used for back-end-of-line integration for integrated circuit manufacturing.Previously we have studied the process involved in the production of dense and porous OSGs produced by PECVD and UV processing [1-3] and its potential impact upon integration . The PDEMS™ ILD process involves the co-deposition of an organosilicate glass network with an organic porogen . The deposition is followed by a post-treatment process to liberate the labile organic material and mechanically fortify the porous structure . The impact of deposition and curing has been the subject of much study, however attention has focused most significantly on final material properties. Analysis of the evolution of the materials produced from of OSGs by a plasma-enhanced CVD process with a UV post-treatment process will aid in the understanding of the critical mechanisms involved in the production of a porous OSG network and provide essential information for the optimization and extendibility of these materials.
12:00 PM - B1.5
Remote Plasma Assisted Atomic Layer Deposition of Ultra-thin Pore-sealing for Self-assembled Porous Low-k Materials
Ying-Bing Jiang 1 , George Xomeritakes 2 , Zhu Chen 2 , Darren Dunphy 1 , Jiebin Pang 2 , Eric Branson 1 , Joseph L. Cecchi 2 , C. Jeffrey Brinker 1 2 Show Abstract
1 , Sandia National Labs, Albuquerque, New Mexico, United States, 2 , Univ. of New Mexico, Albuquerque, New Mexico, United States
With ordered pore structure and mono-dispersed pore sizes as small as 2 nm, mesoporous silica thin films made by evaporation-induced self-assembly (EISA) are of great interest for low-k applications. These spin-on films exhibit excellent mechanical strength and thermal stability, along with an isotropic k and low surface roughness, important for etching or chemical mechanical polishing. To seal the open pores at the surface, atomic layer deposition was employed for its capability of obtaining ultra-thin and conformal coatings. However, on a porous substrate, regular ALD takes place not only on the top of the substrate, but also penetrates into the internal porosity, filling pores and drastically increasing the effective ILD k value. Here we report using remote plasma to prevent this internal deposition and confine ALD only to the very top of a porous low-k material. The ALD process is such designed that ALD deposition will not proceed unless triggered by a plasma. Although ALD precursors will be incident on all exposed surfaces, including the internal pores, they are not reactive to each other unless triggered by active plasma radicals. Since the radicals in the plasma do not penetrate into the nanoporous matrix, no ALD will take place in the internal pores, thus the pores will be sealed without losing the original porosity. TEOS (or the related silanes) and O2 were used as the precursors for SiO2 ALD. The substrate was self-assembled mesoporous silica directed by Brij 56 molecules, patterned by interferometric lithography and etched with a CHF3/Ar plasma to create trenched surface. The samples before and after the remote-plasma ALD (PA-ALD) process have been investigated with gas permeability test, pore surface adsorption measurement by surface acoustic wave, Fourier Transform Infrared Spectroscopy (FT-IR), and transmission electron microscope (TEM) / scanning TEM / elemental TEM mapping by electron energy loss spectrum (EELS). It was found that that the PA-ALD pore-sealing was conformal to the patterned surface, and gas-tight although a few nanometers thick. In addition, no internal deposition and no pronounced impairment to the underlying low-k silica was observed. The k-value changed little after PA-ALD pore-sealing (from 2.42 to 2.49).
12:15 PM - B1.6
Ash-free Porogen for Ultralow Spin-On-Dielectrics
Kun Woo Park 1 , Tae Hoon Lee 1 , Gun Woo An 1 , Sung Kyu Min 2 , Bong Jin Moon 3 , Do Young Yoon 4 , Hee Woo Rhee 1 Show Abstract
1 Chemical & Biomolecular Engineering, Sogang University, Seoul Korea (the Republic of), 2 Thin Film Team, Hynix Semiconductor Inc., Icheon, Kyunggido, Korea (the Republic of), 3 Chemistry, Sogang University, Seoul Korea (the Republic of), 4 Chemistry, Seoul National University, Seoul Korea (the Republic of)
According to ITRS 2005 devices with feature size of 50 nm or less would require new interlayer dielectrics whose dielectric constant (k) is less than 2.2. The general method to reduce the dielectric constant is to incorporate nano-scaled air voids in the SOD upon decomposition of thermally labile organic materials called porogen. We prepared the nanoporous ultra-low dielectrics with desirable pore morphologies and remarkably high mechanical strength using β-cyclodextrin (CD)- and glucose (GC)-based porogens, which had reactivity with organosilicate matrices through allylation and hydrosilylation reactions. However, these reactive porogens left a small amount of carbon residue after calcination so that it was needed to develop a new reactive porogen without leaving any carbon residue. Therefore, we used new reactive porogens based on organic noncyclic-polyols and reducing sugars. TGA result indicated that the new porogens completely decomposed without any carbon residue. When the organosilicate matrix (k = 2.9) was combined with the new porogens, we could obtain nanoporous SOD which had much lower dielectric constant (k = 2.12) and higher mechanical properties (E = 9.1 GPa) at the porosity of 60%.
12:30 PM - **B1.7
Robust Ultra-Low K and Directly Patterned Interlayer Dielectrics Prepared by Templating Processes.
James Watkins 1 Show Abstract
1 Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Device scaling below the 45 nm node will place greater demands on interlayer dielectrics, requiring the development of robust, porous films that can be extended to dielectric constants well below 2.4. Our approach to mesoporous silicates for ULKs involves the infusion and selective condensation of organosilicate precursors within one phase domain of a highly ordered, preformed block copolymer template dilated with supercritical carbon dioxide. The template is then removed to produce the mesoporous oxide. Advantages of this approach include rapid and high degrees of network condensation, low film stress, rapid cycle times, stable templates and precursors and opportunities for direct patterning strategies. The first-generation of templates yielded films dielectric constants as low as 1.8. A film with k = 2.2 was selected for further evaluation and found to survive CMP in a planar test stack. In this talk we describe three recent extensions to the technique that significantly enhance film properties and integration strategies. A second generation of templates yield highly ordered films with pore sizes on the order of 2 nm. The use of selected bridged silsesquioxane precursors, the inclusion of porous silica-based nanoparticles within the template system, and new catalyst systems, yield further enhancement in mechanical properties. We also discuss direct pattering of interlayer dielectric films using optical lithography for selective area exposure of templates containing photoacid generators prior to precursor infusion. Removal of the template then yields a directly patterned mesoporous film, eliminating the need for etching and substantially compressing the number of processing steps. Efforts in this last area are initially targeted towards wide lines, with promising results indicating good potential for scaling.
B2: Dielectric Materials II
Tuesday PM, April 10, 2007
Room 3002 (Moscone West)
2:30 PM - **B2.1
Requirements and Constraints on Optimizing UV Processing of Low-k Dielectrics.
Ivan Berry 1 , Carlo Waldfried 1 , Kevin Durr 1 Show Abstract
1 , Axcelis Technologies, Beverly, Massachusetts, United States
UV curing of low-k dielectrics presents a unique challenge in that the cure process is expected to do the impossible – increase hardness, modulus, cohesive strength, adhesion and reliability, decrease water absorbtion and dielectric constant, remove porogens (for porogen containing films), improve dielectric breakdown and chemical stability, all while minimizing shrinkage and contributions to film stress. Achieving this, in general, requires optimization of all of the cure parameters, such as UV spectral intensity, temperature, time, pressure, background gas, and process sequence, as well as the formulation of the low-k material itself. The spectral dependence of many of these important parameters will be discussed. A good figure of merit for modulus and k-value is the ratio of modulus/k-value. If one plots the spectral response of this ratio, one finds it peaks at a specific wavelength range. In principle it is possible to measure the UV spectral response of all of the critical parameters (not just modulus and k-value) and by overlaying these responses together determine what the proper UV exposure wavelength ranges should be. An example of this will be shown for an idealized porogen containing low-k material, for modulus, k-value, porogen removal and porogen crosslinking. An actual low-k dielectric system has many more wavelength parameters to consider and the problem of bulb spectral intensity optimization is deemed even more complex. It is also found that the relative intensity of the critical wavelength bands also plays a significant role in the curing process and requires a great deal of experimentation to optimize depending on the approach taken.UV cure performance is also dependent on cure temperature, time, background gases and ironically, the deposition or post-deposition bake temperature. Most cure parameters such as modulus, hardness, leakage, adhesion, etc, have a strong and generally exponential dependence on cure temperature. As a result, most UV cures are performed at the highest temperature allowable as defined by thermal budget constraints and copper voiding thresholds. The background ambient can also play a critical role in the UV cure, especially for porous low-k materials and those containing porogens. The ultimate in performance is obtained when the low-k material formulation itself is included as a key parameter in the cure optimization. By optimizing the material, UV spectrum, and cure parameters collectively, significant improvements can be made.In conclusion, UV curing cannot be implemented without serious consideration to the wavelength dependence on many critical process factors. The interdependence of all components that makeup the optical system such as the wavelengths employed, light source technology, chamber design and ironically, the dielectric film itself must be considered. Only with these factors in mind, can the full benefit of UV curing be realized.
3:00 PM - B2.2
Understanding the Role of UV Cure on Enhancing Glass Structure and Mechanical Reliability of Porous Low-k Thin Films.
David Gage 1 , Jonathan Stebbins 2 , Zhenjiang Cui 3 , Amir Al-Bayati 3 , Alex Demos 3 , Kenneth MacWilliams 3 , Reinhold Dauskardt 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Geological and Environmental Sciences, Stanford University, Stanford, California, United States, 3 , Applied Materials, Inc., Santa Clara, California, United States
UV radiation curing has emerged as a promising post-deposition processing strategy for significantly improving the mechanical properties of low and ultra low-k dielectric films while still preserving the films targeted dielectric properties. These include improvements in hardness, elastic modulus and adhesive fracture energy. This study examined the detailed effects of UV curing on the structure and mechanical properties of porous carbon doped oxide thin films (k ~2.5). The effects of UV cure exposure time on glass structure were examined through the use of nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy (FTIR). Detailed 29Si and 13C magic angle spinning NMR spectra revealed a significant alteration in the glass structure with UV curing. Most notably, the UV curing process led to a progressive removal of certain terminal, non-bridging bonds (for example, Si-OH and Si-CH3) and a subsequent formation of bridged network Si-O-Si bonds. FTIR data confirmed skeleton network formation and the loss of methyl groups during the initial UV curing and relatively little change of the glass structure with extended curing. Fracture mechanics based testing methods, including the four-point bend (FPB) and double cantilever beam (DCB) testing geometries were used to analyze cohesive and adhesive fracture properties. Interfacial fracture energies increased significantly (~300% increase) between the shortest and longest UV exposure times. However, while the cohesive fracture energy increased with initial UV curing, subsequent increases with additional UV exposure were less pronounced compared to the interfacial fracture energies on either side of the CDO films. Additionally, UV curing was found to have little effect on the films resistance to environmentally assisted cohesive cracking in humid environments. Based on the detailed understanding of UV cure mechanisms gained through the NMR and FTIR data, we are able to explain the significant increases in adhesive fracture energy, as well as the insensitivity of cohesive fracture properties to longer UV curing times. The role of UV curing and implications for reliable integration will be discussed.
3:15 PM - B2.3
The Effect of Ultraviolet Light Curing on the Fracture Properties of a k~2.5 Low-k Dielectric.
Ryan Smith 1 , Ting Tsui 2 , Paul Ho 1 Show Abstract
1 Material Science and Engineering, University of Texas at Austin, Austin, Texas, United States, 2 Silicon Technology Development, Texas Instruments, Inc., Dallas, Texas, United States
Ultra-violet light curing has been shown to improve the mechanical properties of low-k dielectrics, e.g. modulus and density. Yet, a paucity of literature exists on the effects of UV curing on the fracture properties of ultra low-k films. In this paper, we investigated the role of UV curing on critical and sub-critical fracture of a k~2.5 low-k material. The fracture toughness was correlated with the molecular structure of the material using Fourier Transform IR (FTIR) Spectroscopy. The prinicipal structure elements were network, cage, and sub-oxide. Furthermore, changes in the molecular structure with UV exposure were demonstrated by subtractive FTIR. Density and k-values had a direct correlation with the sub-oxide content. Additionally, UV exposure significantly influenced the critical fracture toughness by increasing the density; yet, sub-critical fracture was insensitive to UV exposure. The surface bond density of the fracture surfaces was roughly independent of UV cure. The threshold and bond rupture energies had a linear dependence on relative humidity.
3:30 PM - B2.4
Structural Transformation During Porogen Removal Under Ultraviolet Assisted Thermal Curing on PECVD Porous Ultra low-k Material.
Aziz Zenasni 1 , Laurent Favennec 2 , Vincent Jousseaume 1 , Olivier Gourhant 2 , Julien Fort 3 , Patrick Maury 2 , Lucile Mage 1 , Samphy Hong 3 , Gerard Passemard 2 Show Abstract
1 LETI-D2NT-LBE, CEA, Grenoble France, 2 , STMicroelectronics, Crolles France, 3 , Applied Materials, Meylan France
3:45 PM - B2.5
Self-organized Nanostructures by Atmospheric Microplasma Processing.
Davide Mariotti 1 , Yoshiki Shimizu 1 , Vladimir Svrcek 1 , Dae-Gun Kim 1 , Takeshi Sasaki 1 , Naoto Koshizaki 1 Show Abstract
1 NARC, AIST, Tsukuba, Ibaraki, Japan
The importance of plasmas in the next generation of material processing is evident. At the same time plasma technology needs to progress in order to meet future requirements of nanoscale processing. Our general scope is to achieve an evolutionary and deterministic material synthesis through plasma processing. In this contribution we present the results of our initial attempt to use microplasma processing to promote self-organized growth of nanostructures. Our technique exploits novel microplasma configurations (D. Mariotti et al., J. Appl. Phys. in press, 2006); in this particular case the treated surface is in contact with the plasma and at the same time subjected to strong electromagnetic fields due to the microscale nature of the plasma itself.A description of the microplasma system is provided together with some important plasma parameters measured by optical emission spectroscopy (D. Mariotti et al., Appl. Phys. Lett. 89, in press 2006). The microplasma is ignited by a high voltage pulse and then sustained by power at 450 MHz. The microplasma is formed between a metal wire (or tubing) and a substrate placed on top of the powered copper electrode. Processing occurs in atmospheric pressure argon mixed to other gases such as oxygen or methane.Our original microplasma system shows a high degree of flexibility in the fabrication of nanostructures and more importantly it can induce the formation of self-organized carbon-based interconnects (e.g. nanotubes, nanowires etc.) between nanoparticles. Here we will present results showing evidence of self-organization, in particular we have produced self-aligned molybdenum-oxides nanostructures and we will report on promising self-organized carbon-based structures connecting silicon nanoscrystals, gold nanoparticles or silver nanoparticles onto a silicon substrate. Influence of catalyst and nanoparticle size on interconnections will be discussed in details. In order to characterize such interconnects and nanostructure products SEM, XPS and HRTEM are used.The mechanisms that are responsible for these self-organized nanosctructures are not fully identified nevertheless it is believed that the peculiar microplasma properties and the electromagnetic fields generated in our system are of fundamental importance. Our future work is aimed to achieve complete processing control and contribute to the understanding and a better exploitation of self-organization.
4:30 PM - **B2.6
The Role of Pore Characterization in the Challenge to Integrate Porous low-k Dielectrics
David Gidley 1 , Richard Vallery 1 , Ming Liu 1 Show Abstract
1 Physics, University of Michigan, Ann Arbor, Michigan, United States
Beam-based positron annihilation lifetime spectroscopy (PALS) is a powerful porosimetry technique with broad applicability in characterizing nanoporous thin film dielectrics. Pore sizes and distributions in the 0.3 – 30 nm range are non-destructively determined with only the implantation of low energy positrons from a table-top beam. Depth-profiling with PALS has proven to be an ideal way to measure the interconnection length of pores, search for depth-dependent inhomogeneities or damage in the pore structure, and to explore porosity hidden beneath dense layers or diffusion barriers. The capability of PALS is rapidly maturing as new intense positron beams around the globe spawn more accessible positron facilities. After a brief introduction this talk will focus on recent efforts to address the challenge of integrating porous low-k dielectrics. PALS can detect and profile plasma-induced damage especially when pore-collapse is involved. Pore sealing strategies can be tested for sealing efficacy and profiled for pore filling or film densification. Nano-imprinting of trenches in porous dielectrics is being explored and PALS is helping to characterize the effects on pore structure of the imprint process.
5:00 PM - B2.7
Mechanical Impacts of Templating Polystyrene Porogen in Methylsilsesquioxane.
Markus Ong 1 , Geraud Dubois 2 , Willi Volksen 2 , Robert Miller 2 , Reinhold Dauskardt 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Almaden Research Center, IBM, San Jose, California, United States
Templating porosity in low-k materials such as methylsilsesquioxane (MSSQ) using polymer porogen particles is a way to achieve well-controlled pore size. The pore architecture of these films plays a significant role in the mechanical and fracture properties and ultimately the practical reliability of these ultra-low-k films. The effects of these templating particles on the mechanical and fracture properties of these low-k films were investigated in this study. Polystyrene particles (~10 nm) were used to template porosity in an MSSQ matrix, and the porogen loading was varied from 0 to 50%. Fracture energies were measured using four-point bend tests to quantify the adhesion of the porous MSSQ to adjacent SiC or metal layers. It was found that the porogen was attracted to the MSSQ/SiC interface, leaving behind disproportionately high porosity near this interface during the burnout process. The fracture energies for these films were less than 0.5 J/m2, far below the expected value for films of comparable densities. However, when a dense layer of MSSQ was used to “prime” the substrate before creating the porous film, the porogen had no preference to segregate from the MSSQ matrix toward the dense MSSQ underlayer. Corresponding fracture energies were much higher compared to the films without the priming underlayer and were comparable to measurements made during previous studies of porous MSSQ. Clearly, the chemistry of porogen/matrix systems is a critical factor in the pore structure and mechanical properties of these films.
5:15 PM - B2.8
Atomic-Scale Analysis of Structural and Mechanical Properties of Amorphous Microporous and Mesoporous Silica Thin Films.
M. Rauf Gungor 1 , James Watkins 2 1 , Dimitrios Maroudas 1 Show Abstract
1 Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts, United States, 2 Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Porous amorphous silica films have important technological applications in sensor and detection arrays, separation processes, and, more recently, in microelectronic devices as ultra-low-dielectric-constant materials. In microelectronics, the structure of “mesoporous” amorphous silica films (pore diameters of 5-10 nm) creates challenging materials reliability problems due to inferior mechanical strength compared to that of the more traditionally used dense amorphous silica films. Toward fundamental understanding of the nano-scale mechanisms that control the mechanical behavior of microporous and mesoporous structures of dielectric materials and toward predictions of the response of such structures to various mechanical loading conditions, we have performed molecular-dynamics (MD) simulations using a realistic classical potential that includes two-body and three-body interatomic interactions.The normal-density amorphous silica structures are prepared through MD, starting from crystalline beta-cristobalite structures and following a thermal processing protocol. We have generated the microporous amorphous structures by volume expansion of the originally dense amorphous structure and “regular” mesoporous structures through introduction of a regular array of spherical pores by removal of atoms from the amorphous silica matrices. The MD-generated structures are annealed at the temperature of interest to ensure proper structural relaxation. In this presentation, we report results for the mechanical behavior of the microporous and regular mesoporous amorphous silica structures under applied strains within the elastic strain range at temperatures over a range of a few hundred degrees above room temperature obtained through nanosecond-scale MD simulation using large-size computational supercells. The elastic moduli and the hardness of the amorphous microporous and regular mesoporous silica structures are calculated as a function of their density. For the mesoporous structures, the analysis is carried out over a range of pore sizes and pore separation distances. Furthermore, a detailed analysis of the atomistic mechanisms of pore morphological evolution is reported in response to both compressive and tensile strains.
5:30 PM - B2.9
Organic-Functionalized Pure-Silica-Zeolite MFI and MEL Films for Low-Dielectric Constant Applications.
Christopher Lew 1 , Zijian Li 1 , Shuang Li 1 , Sonjong Hwang 2 , Dora Medina 1 , Minwei Sun 1 , Mark Davis 2 , Yushan Yan 1 Show Abstract
1 Chemical and Environmental Engineering, University of California, Riverside, Riverside, California, United States, 2 Chemical Engineering, California Institute of Technology, Pasadena, California, United States
As the feature size of next-generation microprocessors decreases, the need for low-dielectric constant (low-k) materials with high mechanical strength is an increasing concern. Many potential porous materials take advantage of the low-k value of air, which is about 1, but they are often amorphous in nature and thus lack mechanical strength. Porous zeolites, however, are highly crystalline and have a high elastic modulus but still retain the low-k values of amorphous porous silica materials. Since water has a high k value, moisture adsorption is a serious concern for all porous low-k materials. Consequently, along with low-k and high elastic modulus values, hydrophobicity is becoming an increasingly important parameter. To combat this problem, post-spin-on silylation treatments with chlorotrimethylsilane and hexamethyldisilazane have been performed, and pure-silica-zeolite (PSZ) MFI has been functionalized with methyltrimethoxysilane. Here, we report organic-functionalized PSZs with MFI- and MEL-type structures prepared through a direct-synthesis method by adding a fluorinated silane to the synthesis solution, and the added fluorine functionality increased the hydrophobicity of the zeolites. The zeolite was characterized by x-ray diffraction, scanning electron microscopy, 29Si solid-state nuclear magnetic resonance spectroscopy, nitrogen adsorption-desorption measurements, and thermogravimetric analysis. Spin-on films prepared from the nanoparticle suspension exhibited higher water contact angles than non-functionalized PSZ films, and the zeolite powders had low water content. k-values were as low as 1.8 and increases due to moisture adsorption were limited to below 15%. Mechanical strength tests were also performed by nanoindentation.
5:45 PM - B2.10
Damage-free Etching Processes of Low Dielectric (Low-k) Films Using the Neutral Beam
Butsurin Jinnai 1 , Seiji Samukawa 1 Show Abstract
1 Institute of Fluid Science, Tohoku University, Sendai, Miyagi, Japan
For 90 nm and beyond ULSI devices, Al/SiO2 interconnects have been substituted by Cu/low-k film interconnects in order to reduce the RC delay time and the power consumption. Plasma etching processes are extensively used for the etching of low-k films. However, severe damages of low-k films are induced during plasma etching processes. These damages are mainly caused by irradiating UV/VUV photons from the plasma to the low-k surfaces, resulting in the increasing of dielectric constant of low-k films. In order to overcome these problems, we propose novel low-k film etching processes by using our newly developed neutral beam, which enables no UV/VUV irradiation from the plasma. In this paper, we investigated radiation damages of low-k films etched in the conventional inductively coupled plasma (ICP) process and the neutral beam process, and could accomplish damage-free low-k film etching by the neutral beam.Our neutral beam source consists of an ICP and parallel carbon plates. The process chamber is separated from the plasma chamber by a carbon plate fitted at the bottom. Numerous apertures in the bottom carbon plate extract neutral beams from the plasma into the process chamber. The accelerated ions are effectively neutralized by a charge transfer when they pass through the apertures. Additionally, the photons generated in the plasma chamber are almost completely eliminated by passing through the apertures because UV lights are effectively absorbed and/or shaded in the apertures of the carbon plate.SiOC films (film thickness: 200 nm) on silicon substrates were etched to 150 nm depth with SF6 gas chemistries in both the neutral beam process and the conventional ICP process. The in-depth composition of SiOC films after irradiating the plasma and the neutral beam were evaluated by using X-ray photoelectron spectroscopy (XPS). Additionally, thermal desorption spectroscopy (TDS) was used to observe desorption gases (H2O and F) from SiOC films. The change of in-depth composition of SiOC film corresponds to the amount of damages.SiOC films before the processes have the uniform in-depth composition (Si, O, C), and F atom was not observed at all. After irradiating the neutral beam, just at the SiOC film surface, the concentrations of O and C atom were slightly changed. A small amount of F atom was also observed. However, after irradiating the plasma, the structure of the SiOC film was drastically changed even at more than 100 nm in depth. We believe that the change of SiOC film structure is mainly caused by UV/VUV photon irradiation. UV/VUV photons in the conventional ICP process could deeply penetrate into the SiOC film and could break the chemical bonding in the SiOC. On the other hand, in the neutral beam process, because of the elimination of UV/VUV photons, only the slight surface of the SiOC film was influenced. This result suggests that our developed neutral beam process could realize damage-free etching of low-k films.
B3: Poster Session: Dielectric Materials
Tuesday PM, April 10, 2007
Salon Level (Marriott)
9:00 PM - B3.1
Mechanical Properties and Fracture of Ultra-low-k (ULK) Nanoporous Organosilicate Glass Coatings with Varied Porosities.
Youbo Lin 1 , Han Li 1 , Joost Vlassak 1 Show Abstract
1 , Harvard University, Cambridge, Massachusetts, United States
Nanoporous organosilicate glass coatings with relative dielectric constant less than 2.5 are widely considered for use as inter-metal dielectric in future generations of advanced integrated circuits. Their ultra low dielectric constant is achieved by incorporating a significant fraction of nanometer-sized pores in a hybrid organic-inorganic matrix, which resembles an amorphous silicon dioxide network with some bridging oxygen atoms replaced by organic groups such as methyl, hydrogen and methylene. While this results in improved dielectric performance, the mechanical response of these coatings is degraded. In order to be successfully integrated in a process flow, it is desired to optimize the mechanical properties while retaining a low dielectric permittivity. This may be done by engineering the pore size and morphology, and tuning the composition and structure of the matrix. Thus, a good understanding of the respective impacts of matrix structure and porosity on the mechanical and fracture properties of these low-k films is critical. In this paper, we will report experimental results on the mechanical properties of nanoporous ULK films, including stiffness, hardness and intrinsic fracture toughness over a range of porosities. The evolution of the mechanical and fracture properties will be rationalized in terms of the structure and porosity changes in the ULK films.
9:00 PM - B3.10
Effect of He, Ar, O2 Plasma Treatments on the Electrical and Chemical Properties low-k SiCOH Film Deposited by PECVD.
Sungwoo Lee 1 , Jaeyoung Yang 1 , Changrok Choi 1 , Sangmin Do 1 , Heeyeop Chae 2 , Donggeun Jung 1 , Jim-hyo Boo 3 , Hyoungsub Kim 4 Show Abstract
1 Physics, sungkyunkwan University, Suwon, Gyunggi, Korea (the Republic of), 2 Chemical engnieering, Sungkyunkwan University, Suwon, Gyunggi, Korea (the Republic of), 3 Chemistry, sungkyunkwan University, Suwon, Gyunggi, Korea (the Republic of), 4 Materials Engineering, Ssungkyunkwan University, Suwon, Gyunggi, Korea (the Republic of)
We investigated the effect of various plasma treatments (helium, argon and oxygen plasma) of the low-k SiCOH films deposited by PECVD. The relative dielectric constants, k, of the SiOCH films may be changed during the interconnect integration process, during which the He and Ar plasma treatment are used for the adhesion enhancement and the surface cleaning, respectively. The O2 plasma treatment is used to remove photoresist. As-deposited and 450oC annealed SiCOH films with k=3.0 and k=2.5, respectively, were used. Ar and O2 plasma treated samples showed increased k-values and decreased breakdown voltages. The plasma treatment is thought to cause modification of the bonding structure of the film, chemical degradation, moisture adsorption and/or O-H bond formation. However, the He plasma treatment of the SiCOH films did not show any notable degradation of SiCOH films. The He plasma treated sample showed decreased k-value from 3.0 to 2.9 for the as-deposited film and from 2.5 to 2.4 for the 450oC annealed film. Suppression of O-H group formation and more decrease of Si-O related groups than C-Hx groups in the SiCOH film were thought to contribute to the reduction of the k values. In terms of the dielectric constant, the largest damage to the film was caused by the O2 plasma treatment, and the lowest damage by the He plasma treatment. The leakage current density of ~10-8A/cm2 at 1MV/cm is obtained for all the SiCOH films.
9:00 PM - B3.11
Optical Absorption and Characteristics of Low-k Films and Barrier Layers in the Ultra-Violet Range
Salvador Eslava 1 2 , Guillaume Eymery 1 , Mikhail Baklanov 1 , Francesca Iacopi 1 , Francesca Clemente 1 , Carlo Carbonaro 3 , Philippe Foubert 1 , Karen Maex 1 2 Show Abstract
1 , IMEC, Leuven Belgium, 2 ESAT, Katholieke Univ. Leuven, Leuven Belgium, 3 Dept. of Physics, Cagliari Univ., Monserrato Italy
The ultraviolet irradiation combined with thermal activation (UV-cure) not only enhances the mechanical properties of low-k materials but also removes more efficiently the porogens. The UV-cure mechanism is assumed to depend on the UV wavelengths used, but so far, no characterization has been reported on the absorption of low-k materials in the ultraviolet range. Moreover, many uncertainties appear when UV-cure is applied to multiple layers, as there is no information of the transmission across a whole stack.Since the absorption characterization might be key for the integration of UV-cure in Microelectronics, we studied the optical characteristics, focusing on the absorption, of low-k materials and barrier layers measured by ellipsometry (UV and visible range) and VacuumUltraViolet absorption (VUV range). In the used ellipsometry setup, the refractive index and the extinction coefficient at every wavelength (150 - 700 nm) are extracted by applying regression analysis of a model that approximates the measured angles Ψ and Δ. In the VUV absorption experiments, measurements have been performed in transmission in the 150 - 300 nm range with synchronous detection.First, the accuracy of the ellipsometry results was assessed. This was done by comparing the results of different incident angles; correlating the regression with direct calculations; and, characterizing thermal oxide, whose absorption can be compared to that of amorphous silica reported in literature. VUV absorption is combined to this study for obtaining direct measurements of the absorption spectra of the thin films. The different organosilica low-k films show a shift in the absorption edge to lower energies as compared to thermal oxide. Moreover, absorption bands appear in the UV range that could be attributed to the C concentration. The absorption bands decrease or shift upon the UV-cure. Finally, the absorption of different barrier layers show marked differences depending on their composition, being TaN the one with the highest absorption. Combining both the extracted refractive indices and the extinction coefficients we simulated the total transmission and absorption for different stacks of low-k and barrier. Due to the multiple internal reflections, the transmission and the absorption strongly oscillate along the spectrum. This simulation provides the intensity spectrum that underneath layers will be exposed to, necessary for the architecture of interconnects.In conclusion, we present the absorption of organosilica low-k films, barrier layers, and combinations of them in multiple layers. This study is of critical importance for a correct implementation of UV-cure processes in Microelectronics manufacturing.
9:00 PM - B3.12
Effects of CH4 Plasma Treatment on Porous Organosilicate Low-k Dielectrics
Hualiang Shi 1 , Junjing Bao 1 , Junjun Liu 2 , Huai Huang 1 , Paul S. Ho 2 Show Abstract
1 Physics, The University of Texas at Austin, Austin, Texas, United States, 2 Material Science, The University of Texas at Austin, Austin, Texas, United States
To investigate plasma induced damage on porous low k dielectrics and possible pre-treatment and post-treatment remedies, effects of direct CH4 plasma and downstream CH4 plasma treatments on porous Organosilicate low-k dielectrics were evaluated. Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Residual Gas Analyzer (RGA), Spectroscopic Ellipsometry (S.E.), Fourier Transform Infrared Spectroscopy (FTIR), and Contact Angle Goniometer were employed to study the damage related to plasma energy, dose, and Ar balance gas, and how CH4 plasma pretreatment and postashing treatment can affect the O2 plasma induced damage. For CH4 plasma pre-treatment of pristine low k films, XRR and XPS depth profiling confirmed the formation of a carbon-rich densified polymer layer (~3 nm) on top of the low-k dielectric. Treatments by mixing Ar to CH4 direct plasma led to negligible additional damages, suggesting that the plasma process was dominated by surface chemical reactions. For post O2-ashing CH4 plasma treatments, the surface carbon concentration and hydrophobicity were partially recovered. A broad absorption peak from 1300cm-1 to 1500cm-1appeared in the FTIR spectra, suggesting the formation of methylene groups. The mechanism of interaction between CH4 plasma and low-k surface will be discussed.
9:00 PM - B3.13
Spin-on Barrier-dielectric/CMP-cap for Cu/low-k Interconnect.
Shin-ya Arase 1 , Nobuhide Maeda 1 , Yoshio Takimoto 1 , Hiroshi Kawakami 1 , Kouji Sumiya 3 , Yoshio Homma 1 , Hidenori Saito 2 , Masahiro Tada 2 , Terukazu Kokubo 3 Show Abstract
1 , Consortium for Advanced Semiconductor Materials and Related Technologies (CASMAT), Kokubunji, Tokyo, Japan, 3 , JSR Corporation, Ltd., Tsukuba, Ibaraki, Japan, 2 , Sumitomo Bakelite Co., Ltd., Yokohama, Kanagawa, Japan
In order to reduce of RC delay in interconnect, various low-k dielectrics have been investigated as ILDs of Cu interconnect. In conventional Cu/low-k interconnect structures, however, p-SiO and p-SiCN films used as CMP-cap and Cu diffusion barrier layer have prevented inter-line capacitance from effective reduction due to their large k-values. Therefore, k-value reduction of CMP cap and Cu diffusion barrier layer is necessary to reduce the effective k-value (k_eff) of interconnect. We have developed Cu/low-k interconnect with spin-on diffusion barrier, and CMP cap. Since k-values of these SODs could be made significantly lower than that of CVD films, incorporation of SODs with lower k-value will result in significant reduction of effective k-value of interconnect. It is estimated that Spin-on-Barrier/Cap (SBC) interconnect shows k_eff reduction of 13% than that of conventional interconnect, in which p-SiO and p-SiCN are used as cap and Cu diffusion barrier layer respectively. In order to evaluate the barrier performance of the new organic barrier SOD (CRC-5200), TDDB measurements are carried out It is seen that CRC-5200 can guarantee 10-year life time against Cu diffusion (0.2 MV/cm @200 degC). In the fabrication process of interconnects, due to spin-on stuck structure, multiple layers could be cured simultaneously. This simultaneous curing enhanced adhesion strength between layers and shortens its process time. In addition, the spin-on type CMP cap (LKD-2055) showed sufficient immunity against SOD dry-etching and subsequent Cu/barrier metal CMP by exhibiting no de-lamination. Since SODs have self planarization property, the Cu diffusion barrier SOD layer shows an excellent planarity regardless of underlying metal line undulations. To suppress chemical interaction between Cu and CRC-5200 varnish components, we also prepared a sample in which Cu lines were covered with CoWP metal cap. I-V characteristics using comb structure of metal-1 layer shows that SBC interconnects with metal cap exhibit similar profile to that of the conventional CVD/SOD structure (CVD cap and barrier). Electrical characteristics of fabricated via chain structures based on SBC indicate good distributions of resistance for 180-nm and 130-nm vias.
9:00 PM - B3.15
Effect of Environment on the Modulus of low-k Porous ILD Films Used in the BEOL.
Eva Simonyi 1 , Christos Dimitrakopoulos 1 , Stephen Gates 1 , Michael Lane 1 , Eric Liniger 1 Show Abstract
1 , IBM, Yorktown Heights, New York, United States
Reliability is an important requirement for the newly developed porous low-k ILD materials that are being introduced into (BEOL). Dependence of Young’s moduli, as measured by nanoindentation technique, on the environment [such as high relative humidity, water immersion and recovery] is presented along with FT-IR spectra for a number of films with different k values. Effect of the moduli changes on cracking behavior is also discussed.
9:00 PM - B3.16
Dry Etching of SiC with CF4/Ar Inductively Coupled Plasmawith a Photoresist Mask.
Jie Lu 1 , Chris Thomas 1 , Mvs Chandrashekhar 1 , Michael Spencer 1 Show Abstract
1 Electrical and Computer Engineering, Cornell University, Ithaca, New York, United States
9:00 PM - B3.17
The Impact of Dielectric Films and Post-Metal Etch Wet Treatment on Charge-Induced Corrosion of Tungsten Vias.
Szetsen Lee 1 , Chi-Jung Ni 2 Show Abstract
1 Chemistry, Chung Yuan Christian University, Chungli Taiwan, 2 Module Technology Development, Winbond Electronics, Hsinchu Taiwan
The prevention of charge-induced corrosion of tungsten vias after metal etch has been studied with several types of commonly used wet chemical solutions and two kinds of dielectric film materials, silicon dioxide and silicon oxynitride. It is found that one of the solutions, leaving essentially no polymer residue on metal lines, can effectively prevent corrosion of tungsten vias. Other solutions either produce minor residues or severe sidewall erosion on metal lines. In our study, it also shows that the combination of wet treatment with oxynitride as the dielectric charge shielding film is as effective as other conventional methods for preventing tungsten vias corrosion. However, significant metal sidewall erosion and surface roughness and residue were observed on metal lines capped with silicon dioxide. Chemical reaction mechanisms are proposed for the preservation of tungsten vias after metal etch.
9:00 PM - B3.18
Synthesis and Characterization of Porogen-bridged Silsesquioxane Monomers and Their Application to Ultralow-k Films
Woojin Lee 1 , Jae Hwan Sim 1 , David Gidley 2 , Do Y. Yoon 1 Show Abstract
1 Department of Chemistry, Seoul National University, Seoul Korea (the Republic of), 2 Department of Physics, University of Michigan, Ann Arbor, Michigan, United States
For advanced microelectronic devices, it is expected that an insulating material should have ultralow-dielectric constant (ultralow-k) lower than 2.2 for feature sizes smaller than 40 nm. This goal can be achieved only through incorporation of nano-sized pores over 30 % porosity in the insulator. However, it is difficult to obtain isolated nanopore structures without pore interconnection by the conventional porogen blending approach at high porosities above 20%. In order to prevent pore interconnectivity, two kinds of porogens can be used simultaneously, such that separate nanopores are obtained in the thin film by repulsion between different porogens. We synthesized porogen-bridged silsesquioxane comonomers and synthesized silsesquioxane polymers containing two different porogens for ultralow-k films. Detaile