A framework for combined simulations of electromigration induced stress evolution, void nucleation, and its dynamics: Application to nano-interconnect reliability

Abstract

A comprehensive physics-based modeling framework for electromigration (EM) in copper nano-interconnects is presented. It combines the three stages of stress evolution, void nucleation, and void dynamics in a single fully coupled and consolidated platform. Mechanical stress evolution, pre- and post-void nucleation, and its impact on void dynamics are deciphered, which enables accurate predictions of EM aging processes as validated by dedicated EM experiments. Subsequently, the experimentally validated model is utilized to shed light on the impact of a number of manufacturing variables, namely, line extension, via taper angle, and the effectiveness of the via bottom flux divergence point. A linear correlation between the ion leakage through the via bottom barrier and the peak tensile stress at the cathode was observed in long lines. In short lines, a blocked cathode end with atomic leakage through the anode end weakens the back-stress effect and threatens the Blech effect induced interconnect immortality. Increasing the line extension length was shown to increase the EM lifetime by about 40%. This impact was saturated beyond 1 critical dimension of line extension. On the other hand, the via taper angle increased the upstream EM lifetime by about twofold when the taper angle was increased from 0° to 30°, which indicates that the change of via taper angle has a stronger impact on EM lifetime compared to the line extension.