Surface Morphological Evolution of Thin Films Under Stress and Capillary Forces

Holes and hillocks can commonly be observed on the surface of thin films after thermal processing. For films deposited on a substrate with a different coefficient of thermal expansion, strains due to thermal expansion mismatch can produce very large stresses. While capillary forces tend to produce a thermal groove at a grain boundary (GB), compressive and tensile stresses can form, respectively, a ridge or a canal at the GB. These phenomena can strongly influence mobility of a GB. The formation of a canal enhances the potential for pinning the GB, whereas the formation of a ridge tends to repel the GB.After a short overview of the theory, analytical and numerical solutions for surface profiles of static and travelling GBs under stress are presented. The results of the computed profiles are compared to experimental surface morphologies in aluminum thin film.