Comparison of Al electromigration in conventional Al alloy and W-plug contacts to silicon

Abstract

We examine the impact of the presence of a W plug on electromigration-induced voiding of the Al alloy layer of contacts to silicon. By comparing conventional Al alloy and W-plug contacts we show that the presence of the plug does not significantly improve the intrinsic susceptibility of contacts to Al voiding despite the elimination of the Al step coverage problem. Both the conventional Al alloy and W-plug contacts degrade by drift of the Al layer with a velocity that is not influenced by the contact structure. The sheet resistance of the underlayer material of multilayer conductors plays an important role in influencing failure times since it determines the rate of resistance increase due to electromigration.