Implications of a threshold failure time and void nucleation on electromigration of copper interconnects

Abstract

Electromigration results are described for a dual damascene structure with copper metallization and a low-k dielectric material. The failure times follow a 3-parameter lognormal behavior, with a threshold failure time needed to represent the entire failure distribution. We found that the threshold failure time scales differently with current density from the median time to failure, which has significant implications for making reliability predictions. It is shown that the threshold failure time corresponds to damage (presumably voids) nucleation of the electromigration process. The observed current density dependency, along with scanning electron microscopy cross sections of stressed samples and Monte Carlo simulations of failure distributions, suggests that both void nucleation and void growth should be considered for accurate modeling of the electromigration lifetime.