Thickness effect on microstructure and residual stress of annealed copper thin films

In this work, coupled effects of thickness and annealing temperature on both microstructure and residual stress of electroplated copper thin films are studied. Microstructure is investigated by Electron Backscattered Diffraction (EBSD) and residual stress is estimated from samples curvature. All films exhibit highly twinned grains. Except for several microns films, median crystallite size grows with both film thickness and annealing temperature. Concerning residual stress, it decreases, first as the increase of film thickness, and secondly as the decrease of annealing temperature. The comparison between experiments and stress models demonstrates that the root mechanisms of residual stress generation change with annealing temperature. As well as annealing temperature, film thickness determines the level of residual stress through control of microstructure. Furthermore, EBSD investigations confirmed that the relevant microstructural length to define mechanical properties of thin copper films is the median crystallite size.