It was noted that one of the most serious failure mechanisms in thin films having a bamboo grain structure was the propagation of transgranular voids. A comprehensive theoretical analysis was presented here of the complex non-linear dynamics of transgranular voids in metallic thin films, as determined by capillarity-driven surface diffusion; coupled with a drift that was induced by electromigration. The analysis was based upon self-consistent dynamical simulations of void-morphology evolution, and was supported by an approximate linear stability theory. The simulations emphasized that the strong dependence of surface diffusivity upon void surface orientation, the strength of the applied electric field, and the void size played important roles in void dynamics. The simulations predicted the occurrence of void faceting, the formation of wedge-shaped voids due to facet selection, the propagation of slit-like features which emanated from void surfaces, open-circuit failure due to slit propagation, and the appearance and disappearance of soliton-like features at void surfaces before failure. The predictions were in very good agreement with experimental observations of accelerated electromigration in non-passivated metallic films. The simulation results were used to establish conditions for the formation of various void-morphology features.

Theoretical Analysis of Electromigration-Induced Failure of Metallic Thin Films due to Transgranular Void Propagation. M.R.Gungor, D.Maroudas: Journal of Applied Physics, 1999, 85[4], 2233-46