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