Micro-texture dependence of stress-induced migration of electroplated copper thin film interconnections used for 3D integration

Effect of the micro texture of electroplated copper thin film interconnections on stress-induced migration was investigated experimentally and theoretically. The micro texture of electroplated copper thin films changed drastically as a function of the annealing temperature after the electroplating. However, stress-induced migration was activated even though the thin film interconnection was kept at room temperature after annealing. As a result, voids and hillocks appeared on the thin film interconnection. This is because high residual stress was caused by shrinkage of the thin film interconnection due to the densification caused by recrystallization. Molecular dynamics simulations showed that the diffusivity of copper atoms along grain boundaries with low crystallinity was enhanced significantly by high tensile residual stress. Therefore, the grain boundary diffusion accelerated by tensile residual stress is the main reason for the formation of hillocks and voids in the thin film interconnection after annealing.