The effect of a threshold failure time and bimodal behavior on the electromigration lifetime of copper interconnects

Electromigration results are described for a dual damascene structure with copper metallization and a low-k dielectric material. The failure times follow a bimodal lognormal behavior with early and late failures. Moreover, there is evidence of a threshold failure time such that each failure mode is represented by a 3-parameter lognormal distribution. It is found that the threshold failure time scales differently with current density from the median time to failure, which can be explained by considering two components of the electromigration lifetime: one controlled by void nucleation and the other controlled by void growth.