The effect of the microstructure upon the electromigration behavior was studied by using 3 nominally 1-thick films of the pure metal. These were tested at temperatures ranging from 423 to 523K. The 3 films had essentially the same grain structure, but differing variants of a <111> texture. It was found that the texture had a marked effect upon the electromigration behavior in 2-wide polycrystalline lines; in that a reduced fraction of randomly oriented grains and a tighter <111> distribution increased the electromigration lifetime. The apparent activation energy for electromigration decreased as the texture was strengthened. The near-bamboo microstructure of 0.5 lines exhibited extensive orientation clustering, with an unusually high proportion of low-angle boundaries in the most strongly <111>-textured film. The electromigration damage in both 2- and 0.5-wide lines was related to the type of flux divergence site in each film. The texture governed the nature of the grain boundaries and of the interfaces which controlled mass transport during electromigration. Thus, a weaker texture had more juxtaposed so-called fast- and slow-diffusion grain boundaries and interfaces. This resulted in faster mass transport, more flux divergence sites, and in the more rapid accumulation of damage.

D.B.Knorr, K.P.Rodbell: Journal of Applied Physics, 1996, 79[5], 2409-17