It was recalled that Cu-doping suppressed the Al electromigration which was caused by high-density electric currents. The mechanism of this suppression was investigated here by performing quantum mechanical calculations. A periodic surface model was assumed which comprised three Al layers with a Cu or Al atom approaching the surface. The calculations showed that adhering Cu atoms drew electrons out of the Al atoms, and that they acquired more negative charge than that on the adhering Al atoms. It was also found that the Cu atoms adhered closer to the surface than did Al atoms, and that the energy barrier which impeded Cu atom motion on the surface was higher than that which impeded Al. It was expected that these features of Cu atoms in Al crystals played an important role in the suppression of Al electromigration by Cu. The barrier to motion along the surface, and the stable location of the adhering atom, were highly dependent upon the orientation of the surface.

Static Electronic Properties of Various Surface Orientations of Al Crystal Undergoing Electromigration. K.Iguchi, A.Tachibana: Applied Surface Science, 2000, 159-160, 167-73