Constant voltage electromigration for advanced BEOL copper interconnects

Abstract

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.

Plasma-Based Copper Etch Process and Reliability

“…EM tests were carried out with a constant voltage of 7 V. Cu lines with widths of 10, 20, or 40 µm and the same length of 800 µm were used in the EM study. The change of the current density with time was recorded (13).…”