Comparative Study of Statistical Distributions in Electromigration-Induced Failures of Al/Cu Thin-Film Interconnects

In electromigration failure studies, it is in general assumed that electromigration-induced failures maybe adequately modelled by a log-normal distribution. Further to this, it has been argued that a lognormaldistribution of failure times is indicative of electromigration mechanisms. We have combinedpost processing of existing life-data from Al/Cu + TiW bilayer interconnects with our own results fromAl/Cu interconnects to show that the Log Extreme Value distribution is an equally good statisticalmodel for electromigration failures, even in cases where grain size exceeds the linewidth. The significanceof such a modelling is particularly apparent in electromigration failure rate prediction