Stress-induced surface damage and grain boundary characteristics of sputtered and electroplated copper thin films

The morphology of the stress-induced surface damage and its relationship with the microstructure in electroplated and sputtered copper thin films is discussed. After annealing at 435 °C for 1 h, two types of surface damage were observed. In some films, grooves along the grain boundaries were formed, whereas in other films, voids at the grain boundary triple junctions were observed. In films of similar thickness, the triple junction voids were deeper than the grain boundary grooves. It was found that the high energy grain boundaries (HEGBs) or their triple junctions are the sites where damages are generated by thermal stress. The area ratio of the HEGBs to the surface area per grain, which is a function of both the grain size ( d) and the film thickness ( h), as well as the fraction of HEGB ( f), determines the morphological equilibrium between the two types of damage. It is suggested that, in general, a microstructural parameter, d/ hf, can be used to predict the damage morphology in Cu films.