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

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 degrees C had no impact on TDDB lifetime due to the suppression of Cu migration induced breakdown. However, as the annealing temperature increased to 600 degrees 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 degrees C. While for electron down-flow case, annealing at 400 degrees C degraded EM lifetime and the reduction was pronounced for porous dielectric films. (C) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.