Suppression of Electromigration Early Failure of Cu/Porous Low-k Interconnects Using Dummy Metal

The electromigration (EM) lifetime of Cu/porous low-k interconnects was evaluated by EM experiments in which the effect of back-flow stress was negligible. The EM lifetime of the downstream mode was reduced using a porous low-k film (SiOCH) as an intermetal dielectric (IMD) in comparison with using a SiO₂ dielectric. The reduction in EM lifetime was observed only at low cumulative failure probability, considered as "early failure". The early failure was caused by the formation of a slit void under a via. It was found that the early failure was suppressed by placing a dummy metal near the metal/via contact that inhibited the formation of a slit void. The EM degradation of Cu/porous low-k interconnects is likely to be caused by the mechanical properties of porous low-k film. The dummy metal supports the porous low-k film near the metal/via contact, which leads to improved EM.