Understanding Electromigration Failure Modes in Cu Interconnects with Different Line Widths

This paper investigated the electromigration (EM) of Cu interconnects with different line widths. It was found that EM performance of wide lines was worse than narrow lines due to bimodal failures, where the early failure mode is void under via. Comprehensive testing and failure analyses (FA) were carried out to understand the mechanisms. Slit voids between Cu and capping layer in line ends adjacent to vias prior to EM stress and via bottom to Cu line interface cleanness were identified as the two root causes of the early fails. Modulation of failure modes by different processes was achieved. The early failure mode was suppressed after process optimization.