Constant voltage electromigration for advanced BEOL copper interconnects

© 2015 IEEE. 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 Ea and n values.status: publishe

In-situ scanning electron microscope observation of electromigration-induced void growth in 30 nm 1/2 pitch Cu interconnect structures

In-situ electromigration tests have been performed inside a scanning electron microscope on 30 nm wide single damascene interconnects without vias, where a good resolution was obtained and drift velocities during void growth could be measured at 300 C. These tests showed direct evidence that the cathode end of the line, where a polycrystalline grain cluster encounters a bigger grain, can act as a flux divergent point of Cu diffusion. Moreover, it was found that a thicker barrier suppresses barrier/interface diffusivity of Cu atoms, thereby slowing down electromigration-induced void growth. It was also demonstrated that Cobalt based metal caps are beneficial to electromigration for advanced interconnects where thinner barriers are required.status: publishe