Effects of capillary forces on copper∕dielectric interfacial void evolution

The shape evolution of interface voids in copper metallization systems under electromigration stress is modeled including instabilities driven by both capillary and electron wind forces. The model employs a three-dimensional, axisymmetric, finite-difference method combined with a boundary-element electrical potential. With zero electric field or with small fields applied, a large void experiences a capillary instability which leads to open circuit failure. As the electric field becomes larger, the growth of this instability is suppressed and the void shape stabilizes. Thus, for a typical electromigration stress condition, a large copper void elongates its shape along the interface parallel to the electric field, suggesting a mechanism for the delayed open circuit failure observed in copper integrated circuit metallization system.