Process Monitoring and Near-Surface Control Using In-Situ Characterizations in Microelectronics Applications

In advanced electronic devices in particular field effect transistors (FETs), thin films materials are commonly processed at atomic scale. The thickness control and uniformity over large surface are reaching atomic limits where the surface properties become dominant on bulk or volume counterpart. As example, we use to process 2nm-thick materials, such as HfO₂-dielectric as gate-material in transistor production, with a control below σ&lt;1% in thickness deviation on 300mm silicon wafer. Moreover, the control in thickness is now close to the atomic roughness, not only at the surface but also between layers at interfaces. Another good example is the sputtered depositions of advanced Al or La angstrom-scale encapsulated layers in metal nitrides to adjusted transistors threshold voltages using dipoles formation. In such technology, very thin 5-10A layers are sandwiched in the metal gate, and one must insures that the thin doping layer is continuous at angstrom scale. The geometric inspection of such layered materials has becoming a challenge, in particular when a “reactive” surface is exposed to air-break between processes. This in turn may affect device performance and yield. For example, trace of organic contaminants and water potentially absorbing on the surface of wafers have become an increasingly critical issue, such in equivalent oxide regrowth in MOS gates. <i>In-situ</i> or <i>quasi-insitu</i> characterizations solutions have been developed to limit these adverse effects, and to help the process engineers to monitor their processes.<br/><br/>In this presentation, we will illustrate the status regarding <i>in-situ</i> deposition processes monitoring, by showing three practical examples. The first one will address <i>in-situ</i> process monitoring using optical emission spectroscopy (OES) used to monitor plasma properties in plasma enhanced atomic layer deposition (PEALD) of tantalum nitride gate materials for FETs. In this first example, the beneficial effect of adding a weak low frequency (LF) power to the RF power was correlated to a modification of the precursor fragmentation as observed by OES monitoring of the plasma during deposition. Then, we will introduce the concept of quasi <i>in-situ</i> transfer, using a specific substrate carrier keeping high quality static vacuum between process and/or analyses tools. We will illustrate this concept by a study we performed on metal nitride and 2D-sulphides growth by ALD, and where we followed the surface modifications half-cycle by half-cycle during atomic growth by X-ray photospectrometry. In the third example, we will show some examples of <i>in-situ</i> residual gas analysis (RGA) to monitor reactive gas flow rate in vacuum chambers and to evaluate the amount of water in a liquid thiol-based chemical precursor. We will explain the limits of such RGA in reactor’s technical implementation, and give some insight for future improvements.<br/><br/>Finally, we will conclude and give some perspectives and future trends, where we adapted current <i>in-situ</i> solutions to monitor doping of Al and La in nitride layer for advanced sub-10nm node FETs<br/><br/><i>This work has been partially supported by the program EquipEx IMPACT (ANR-10-EQPX-33)</i>