Electroplasticity and Electromigration

Abstract

AbstractIt is known that an electric current can interact with dislocations in metals. Recent studies suggest that these interactions include current-induced dislocation motion and multiplication (electroplasticity) through both glide and climb mechanisms. Such interactions might be expected to effect both the mechanical properties and the electromigration behavior of the thin metal conductor lines used in integrated circuits. The mechanical properties would be directly modified through changes in dislocation density and mobility. Changes in microstructure and strength could affect electromigration lifetime and failure morphology. In order to investigate the effects of current-dislocation interactions, we conducted three sets of experiments in unpassivated aluminum conductor lines: First, a nanoindentation device was used to measure the mechanical properties of the lines during application of current densities up to 6 MA/cm2. Second, the mechanical properties of the lines were measured ex situ as a function of time in accelerated electromigration testing conditions. Third, the nanoindentation device was used to damage the lines at specific sites and damage morphology was examined during subsequent electromigration experiments by means of in situ scanning electron microscopy. To date we observe no direct effect of electric current on the mechanical properties of conductor lines and no clear correlation between mechanical damage and electromigration failure characteristics. Based on theoretical calculations and previous experiments on bulk samples, these results were not expected.