A kinetic analysis of residual stress evolution in polycrystalline thin films

Residual stress is a longstanding problem in thin film growth that affects film performance and limits the range of applicability. A better understanding of why this stress develops and how it depends on the growth conditions and material properties would improve our ability to predict it and control it. We describe a kinetic model we have developed that explains stress evolution in terms of a dynamic competition between tensile and compressive stress generation mechanisms. The balance between them changes as the microstructure evolves from isolated islands, through coalescence and into a uniform film, leading to the sequence of stress states observed during growth. The model further predicts that the stress in the steady-state depends on the dimensionless parameter D/LR where D is the diffusivity, R is the growth rate and L is the grain size. Calculations from the model in both the high and low mobility regime are compared with real-time measurements of stress using wafer curvature in different systems The discussion addresses limitations of the model and other issues that are not covered such as surface roughness and energetic particle deposition.