Understanding the physical mechanisms controlling thin film growth is of vital importance to obtain the desired microstructures and related specific properties. Subtle structural changes may occur in the early growth stages, driven by surface/interface effects, epitaxy, chemical driving forces or energetic conditions intrinsic to PVD techniques like sputtering. Atomic-scale sensitive and real-time diagnostics are therefore required to address such issues.
In the present work, we demonstrate the unique potential offered by real-time stress diagnostics, combined with structural investigation, to understand not only the stress development during thin film growth but more generally to study dynamic microstructural evolution processes. It is shown that stress measurements using a multiple-beam optical stress sensor (MOSS) implemented in the deposition chamber offer an efficacious and accurate way to identify structural changes with sub-monolayer sensitivity.
The presentation will focus on case studies of low-mobility materials, including sputter-deposition of single metals (Mo, W, Ta) and binary alloys (Mo-Si). The importance of i) the surface stress variation in the first monolayers regime and ii) interface energy minimisation in governing nucleation conditions will be demonstrated. In particular, for the Mo-Si system, the amorphous-to-crystalline phase transition is accompanied by a stress signature at a critical thickness . The differences in film stress evolution during polycrystalline and epitaxial growth will be also addressed. Finally, the role of grain size on the mechanism of atoms incorporation due to energetic bombardment, at the origin of compressive stress often encountered in low-mobility materials, will be discussed.
 A. Fillon, G. Abadias, A. Michel, C. Joauen, P. Villechaise, PRL 104, 096101 (2010)