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

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 jL2 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 °C.