On the propensity of electromigration void growth from preexisting stress-voids in metal interconnects

摘要

Thermomechanical and electrical finite element analyses of voided metal interconnects were undertaken. The resulting information was used in modeling the stress buildup and atomic flux divergence during electromigration using the finite difference method. A simple correlation between the preexisting stress-void and electromigration void growth was identified. A large preexisting-stress void in the metal line is more prone to growth during electromigration than small voids. This is a consequence of the stress gradient along the line generated by the stress-induced voiding. Controlling stress-induced voiding is thus seen to be important in preventing electromigration failure. The present modeling provides a mechanistic rationale for previous experimental observations. It also serves to illustrate that, in electromigration modeling, simply using a critical stress as the failure criterion may be insufficient. Material: Al line in a silicon dioxide dielectric.