A three-dimensional model of electromigration and stress induced void nucleation in interconnect structures

A three-dimensional finite element method is developed to predict the critical conditions necessary to nucleate electromigration or stress induced voids in interconnects. Our approach is to model interfaces using a modified cohesive zone, which permits the interfaces to separate at a critical stress, and also accounts for mass transport along the interfaces. A simple boundary value problem is solved to verify the numerical procedure. The method is then used to simulate the nucleation and initial growth of voids in a realistic interconnect test structure. Predicted void nucleation sites are in good agreement with experimental observations. In addition, modeling analysis is also consistent with qualitative effects of geometric and material parameters such as the line length, cap layer and passivation material on critical times to nucleate voids