Mass Transport of Aluminum by Momentum Exchange with Conducting Electrons

A failure mode commonly found in high power devices and integrated circuits appears when aluminum conductors carry current densities in excess of 105 amperes per square centimeter at temperatures above 100°C. The mode of failure is an open circuit which often is observed as a "crack" in the aluminum and is commonly referred to as "cracked stripe" or "disappearing aluminum." This paper presents a study of this failure mode which has been identified with the mass transport of aluminum by momentum exchange between activated aluminum ions and conducting electrons. The activation energy for the reaction has been obtained and equations relating temperature, current density and film structure to conductor life are presented. The activation energy appears to be identical to that for the lattice self-diffusion of aluminum modified by factors involving both surface diffusion and grain-boundary diffusion. These latter two factors are important in films formed by the condensation of aluminum vapor.