The electromigration performance of multi-level interconnect vias was investigated by using a 3-dimensional computer model. The model used the finite-element method to obtain self-consistent temperature and current density distributions, in order to calculate the electromigration fluxes. The model took account of the polycrystalline grain structure of the tracks as well as of stress-migration and concentration-gradient back-fluxes. It was noted that, whereas in single-level systems failure could be analyzed by using 2-dimensional models because the fluxes were homogeneous, the inclusion of a third dimension along the track thickness was necessary for multi-level systems. In addition to the effects of hot-spots, current-crowding and microstructure, it was found that anisotropy of the grain-boundary diffusion played an important role in determining the positions of voids.

A.Ghiti, A.G.O’Neill: Journal of Applied Physics, 1997, 81[7], 3064-8