Direct measurement of nucleation times and growth rates of electromigration induced voids

Abstract

Electromigration failure is a complex process of void nucleation, growth, motion and shape evolution. A technique has been developed that allows the measurement of these individual stages of electromigration failure in a statistically meaningful way. Void nucleation times, growth rates and velocities have been measured in ten or more lines at each of 4 different accelerated test conditions. These stages scale as expected with temperature, however, the current scaling was more complex. Many models predict lifetimes to scale with the inverse square of the current density. In such models, the nucleation stage is often assumed to be dominant and to scale as j−2. In this work, lifetimes were found to scale with the inverse square of the current density, but the nucleation times of the voids that cause failure scaled with the inverse of the current. At the lowest current density, instead of increasing linearly with time to failure, void growth often saturated and led to an extension of the lifetime.