Effects of length scaling on electromigration in dual-damascene copper interconnects

Abstract

The electromigration short-length effect in dual-damascene Cu interconnects has been investigated through experiments on lines of various lengths (L), being stressed at a variety of current densities (j), and using a technologically realistic three-level structure. This investigation represents a complete study of the short-length effect after a well-developed dual-damascene Cu process. Lifetime measurement and resistance degradation as a function of time were used to describe this phenomenon. It has been found that the sigma of log-normal distribution increased as the current density-length product decreased. The statistical distribution of the critical volume fits the sigma curve well. Lower jL(2) values show large sigma values because of back-stress-induced TTF (time-to-fail) dispersion. A simplified equation is proposed to analyze the experimental data from various combinations of current density and line length at a certain temperature. The resulting threshold-length product (jL)(C) value appears to be temperature dependent, decreasing with an increase in temperature in a range of 250-300 degrees C. (c) 2007 Elsevier Ltd. All rights reserved.