Electromigration Testing of Ti/Al-Si Metallization for Integrated Circuits

Electromigration tests have been performed on a two layer metal system consisting of a thin Ti barrier (0.1-0.175¿m) underlying a 1.0-1.25 ¿m conductor of Al-Si. The titanium not only acts as a diffusion barrier against contact spiking, but also maintains electrical continuity in the event of void formation in the Al-Si layer. It is shown that large resistance transients can occur during electromigration stressing. The characteristics of these transients including their dependence on temperature and current density have been studied experimentally. Theoretical estimates of the resistance increase caused by creating a gap in an aluminum line are made. The self heating in the surrounding area, due to current diversion into the Ti underlayer is also calculated. Finally, a new failure criteria is defined for Ti/Al-Si.