Effects of Ti and TiN underlayers on electromigration reliability of Al–Cu interconnects

The effects of Al underlayer between Ti and TiN on the electromigration (EM) reliability of Al stack film were compared. And both package-level and conventional wafer-level EM tests were performed. Microstructures of underlayer and Al films were characterized to understand the EM results. The surface roughness of the underlayer was related to the grain size distribution and surface roughness of Al film. The higher EM resistance of the Al stacks prepared with Ti underlayer can be best explained by their better Al (111) texture and grain size distribution than those with TiN underlayer.