It was recalled that voids formed in interconnects due to severe thermal stresses and high current densities in the lines. Typical interconnect lines contained large numbers of voids which grew gradually and changed their shape during the lifetime of a line. It was observed that many open circuits occurred when a round void collapsed into a slit that was perpendicular to the direction of current flow. It had been shown that these slits could be caused by electromigration-induced surface diffusion. Anisotropy of surface diffusivity played a key role in the formation of slit voids. The object here was to present a detailed parametric study of electromigration-induced void evolution in interconnects. The interconnect was idealized as being a 2-dimensional electrically conducting strip which contained an initially semi-circular void. Stresses were neglected for simplicity, and a finite-element method was used to predict the evolution of the void when an electric field was applied to the strip. It was shown that the void could either evolve into a stable shape as it migrated down the line, break up into several smaller voids or separate from the boundary, or form a slit which severed the strip.

Influence of Anisotropic Surface Diffusivity on Electromigration-Induced Void Migration and Evolution. D.R.Fridline, A.F.Bower: Journal of Applied Physics, 1999, 85[6], 3168-74