Electromigration anisotropy and mechanical stress in modern copper interconnect

Modern interconnect structures are exposed to high mechanical stresses during their operation. These stresses have their sources in interconnect process technology and electromigration. The mechanical properties of passivating films and the choice of process technology influence electromigration reliability. In this paper we analyze the interplay between electromigration and mechanical stress on an atomistic level. A stress-dependent diffusion tensor has been derived and implemented in a continuum electromigration model. Since the vacancy dynamics at grain boundaries also contributes to the stress distribution, the electromigration model has been extended by a grain boundary model. The plausibility of the compound model is demonstrated with an example of stress dependent electromigration in a three-dimensional, dual-damascene interconnect structure.