Electromigration Failure Mechanisms of Cu-Cu Joints at Low Stressing Temperatures

Electromigration-induced failures and behaviors in Cu-Cu joints under low stressing temperature (130 ℃) were examined in this investigation. The Cu-Cu joints were bonded successfully at 200 ℃ with initial contact resistance as low as 1.81 × 10 ⁻⁸ Ω∙cm ² . Mean-time-to-failure (MTTF) of the low stressing condition (130 ℃ and 10 ⁵ A/cm ² ) reached 7900 h. We discovered various failure mechanisms under low temperature EM. Once the bonding interface was robust enough, failures tended to occur at the Cu traces where current density was the highest in the stressing circuits. Furthermore, resistance reduction was observed in the joints of which bonding interfaces vanished due to recrystallization and grain growth, leading to a prolonged lifetime up to 10000 h. However, tensile-stress-induced failures were prone to occur at the weak bonding interface rather than at the Cu traces. As a consequence, we can predicate that the qualities of the bonding interface are crucial to the EM reliabilities and thus affect the failure mechanisms.