Electromigration-Induced Plastic Deformation in Cu Interconnects: Effects on Current Density Exponent, n, and Implications for EM Reliability Assessment

While Black’s equation for electromigration (EM) in interconnects with n = 1 is rigorously based on the principles of electrotransport, n > 1 is more commonly observed empirically. This deviation is usually attributed to Joule heating. An alternative explanation is suggested by the recent discovery of EM plasticity. To examine this possibility, we have retested samples that had been previously subjected to a predamaging phase of high temperature and current densities to determine whether the loss of median time to failure (MTF) is retained. We find that the predamaged samples exhibit MTFs that are permanently reduced, which is a characteristic of EM plasticity.