Large-scale statistical analysis of early failures in Cu electromigration, Part I: Dominating mechanisms

With continuing scaling of Cu-based metallization, the electromigration (EM) failure risk has remained one of the most important reliability concerns for advanced process technologies. The main factors requiring attention are the activation energy related to the dominating diffusion mechanism, the current exponent as well as the median lifetimes and lognormal standard deviation values of experimentally acquired failure time distributions. In general, the origin and scaling behavior of these parameters are relatively well understood. However, the observation of strong bimodality for the electron up-flow direction in dual-inlaid Cu interconnects has added complexity. The failure voids can occur both within the via (“early” mode) or within the trench (“late” mode). Over the last few years, bimodality has been reported also in down-flow EM, leading to very short lifetimes due to small, slit-shaped voids under vias. These voids, requiring only a very limited amount of mass movement, are generally causing conce...