INFERENCE OF ELECTRON CONFIGURATION AND ACTIVATION ENERGY OF SOLUTE ATOMS IN COPPER AND SILVER CONDUCTORS ON ELECTROMIGRATION VOID FORMATION

Abstract

It is shown that the kinetics of vacancy coagulation to macroscopic erosion voids in dilute crystalline metallic alloys depends strongly on the chemical nature of the solute element. In numerous published and the author's own electromigration data, it was found that the formation of erosion voids is suppressed if valence electrons of the matrix metal atom and the alloying (or impurity) atom sum up to an odd number. This is due to the formation and electronic charging state of vacancy-impurity pairs. Provided that activation energies of the solute elements are low compared to those of matrix atoms, stable vacancy-impurity pairs dominate and resist coagulation. At higher temperatures the number of pairs diminishes, weakening the mechanism of mutual Coulomb repulsion. Dilute copper and silver alloys are compared in the framework of the mentioned properties, giving copper a better chance for electromigration resistance than silver.