Solute Effects on Grain Boundary Electromigration and Diffusion

The grain boundary transport of aluminum chromium, and copper resulting from electromigration at 175°C in aluminum-chromium and aluminum-copper thin film conductors has been measured. The forces acting on the various types of atoms are estimated from other experiments or from theoretical derivations. It is then possible to calculate the diffusion constants of the different atomic species. The values obtained for aluminum grain boundary diffusion in aluminum-chromium correspond well to values which have been found through different means in the grain boundary of pure silver. It is concluded that chromium does not reduce the rate of grain boundary diffusion of aluminum, but copper reduces this rate by a factor of about 80. The results of a series of electromigration experiments in aluminum-copper thin films are interpreted in terms of the information they yield on the diffusion of adsorbed copper atoms in aluminum-copper grain boundaries. The conclusions reached are compared to the previously reported results on the effect of alloy additions on grain boundary diffusion in a variety of different elements.