Stress evolution during stress migration and electromigration in passivated interconnect lines

Differences between the coefficients of thermal expansion of a narrow metal line and surrounding chip and passivation lead to the establishment of very large tensile stresses, which can only be effectively relaxed through the formation and growth of voids when the passivation remains intact. Furthermore, an electromigration induced atomic flux will lead to simultaneous void growth and accumulation of atoms at appropriate flux divergences. For a given current and microstructures (including void locations) a unique relationship can be established between the time, stress distributions and the corresponding void volumes. We model the stress evolution in passivated near‐bamboo lines to account for the synergistic effects of stress migration and electromigration on void growth and open failure under various combinations of temperature, current, microstructure, and the presence of W‐studs/vias.