Effect of Post-Annealing on Reliability of Cu/Low-k Interconnects

Abstract

Due to the continuous increase of multilevel Cu/low-k interconnects, the total thermal budget has been increasing. As a result, the effects of post-annealing on the time-dependent-dielectric-breakdown (TDDB) and electromigration (EM) reliability of Cu/low-k interconnects were investigated in this study. Dense and porous low-k SiCOH dielectric films without or with an SiCNH capping layer were used for comparison. Post-annealing reduced TDDB lifetimes for dense and porous SiCOH dielectric films without a capping layer. With an SiCNH capping layer, annealing at 400 °C had no impact on TDDB lifetime due to the suppression of Cu migration induced breakdown. However, as the annealing temperature increased to 600 °C, both dense and porous SiCOH dielectric films displayed a significant reduction in TDDB lifetimes. The SiCNH capping layer is crucial for EM lifetime improvement due to the reduction of Cu surface migration. With an SiCNH capping layer, the post-annealing influencing EM lifetimes depended on the flow direction of electron. In the case of electron up-flow, EM lifetimes remained unchanged for both dense and porous low-k dielectrics upon annealing at 400 °C. While for electron down-flow case, annealing at 400 °C degraded EM lifetime and the reduction was pronounced for porous dielectric films.