Mechanical stress induced void and hillock formations in thin films

Abstract

In an effort to enhance our understanding of stress induced void formations in thin films voids were created in initially stress-free lead films at room temperature through a direct application of mechanical tensile stresses instead of a thermally-induced stress. Application of mechanical compressive stresses resulted in the formation of hillocks. In-situ observation inside an SEM indicates that the effect of the mechanical stresses on the hillock and void formations in lead films at room temperature is similar to that of thermally induced stresses in lead and aluminum films at higher temperatures. Grain boundary sliding and diffusion creep processes appear to play a significant role in the growth of hillocks and voids, respectively. Evaluation of the observations indicates that restriction of grain boundary sliding during stress relaxation leads to void formation and growth by diffusion creep processes in which transportation of materials occurs mainly through high diffusivity paths, such as, grain boundaries. >