Impact of post via Etch cleans on mechanical reliability of W Plug vias

Tungsten-plug via failure is one of the key interconnect reliability issues, due to electromigration and stress migration concerns. Electromigration (EM) failure is usually accerelated after thermal anneals due to stress voiding. In this study, we show that the via electromigration lifetime can be significantly improved after thermal anneal by careful selection of post via etch clean. The via profile, contact resistance and Auger chemical analysis near the via from various via cleans will be presented. We propose that modified W/Al interface may slow down the Al diffusion under the via, leading to increased EM lifetimes.