Electromigration Lifetime Improvement of Copper Interconnect by Cap/Dielectric Interface Treatment and Geometrical Design

A significant improvement of electromigration (EM) lifetime is achieved by modification of the preclean step before cap-layer deposition and by changing Cu cap/dielectric materials. A possible mechanism for EM lifetime enhancement was proposed. Cu-silicide formation prior to cap-layer deposition and adhesion of Cu/cap interface were found to be the critical factors in controlling Cu electromigration reliability. The adhesion of the Cu/cap interface can be directly correlated to electromigration median-time-to-failure and activation energy. Effects of layout geometrical variation and stress current direction were also investigated.