Constant voltage electromigration for advanced BEOL copper interconnects

For characterizing the electromigration (EM) reliability of advanced interconnects, we propose a constant voltage approach (CV-EM) as an alternative method to traditional constant current tests (CI-EM). As extremely scaled interconnects require very thin barriers, their current shunting capabilities will be reduced. When close to full void formation, we show that this lack of current shunting capability leads to unrealistically high stress conditions during CI-EM while more realistic stresses are induced during CV-EM. We also demonstrate that the void detection capability is highly improved after CV-EM. We use simulations and experiments to compare CV-EM with CI-EM where we obtain a) slightly longer lifetimes for CV-EM, b) the same failure mechanisms and c) similar E_a and n values.