The dependence of W-plug via EM performance on via size

The electromigration (EM) performance of W-plug vias of different sizes, different capping layer types and electron flow directions in a multilevel metallization system was investigated. When the electron flow direction was from metal 2 to metal 1, with a TiN-capped metallization system, the time-to-failure dispersion (sigma) was greatly influenced by via size. However, when the electron flow direction was from metal 1 to metal 2, there was little dependence on via size. Similarly, the via EM performance of a metallization system with titanium as a part of the capping layer exhibited no dependence on via size.