Interaction of a void and a grain boundary under a high electric current stress employing three-dimensional molecular dynamics simulation

Molecular dynamics simulation of the behavior of a void in an Al interconnect with a bamboo grain boundary under a high DC current stress has been accomplished. It is shown that when the current density is higher than some threshold value, a void can move across the grain boundary transversely without being trapped in it, and a disordered region is formed between a void and a grain boundary after the transverse process. Annihilation and reformation of the void is also simulated when the void comes close to the grain boundary, which was experimentally observed before. It should be noted that a backflow of a void is simulated after the current is turned-off at this situation. Analysis using local stress distribution reveals that a large compressive stress is built up near the grain boundary, and an enormous stress gradient is formed between the grain boundary and the void, and it is strongly suggested that this stress gradient is the driving force of the backflow of the void. The present computational work strongly suggest an existence of the backflow of a void, which has not yet been observed experimentally.