Effects of annealing temperature on electromigration performance of multilayer metallization systems

The electromigration (EM) performance for the Ti:W/Al-1%Si two-layer and the Ti/W/Al-1%Si three-layer metallizations annealed at elevated temperatures was investigated. The formation of the Al₁₂ W intermetallic compound, which transforms to Al₅W as the annealing temperature increases, was observed at the Al-alloy/refractory-metal interface. An increase in activation energy and sheet resistance was observed for both the two-layer and three-layer systems for annealing above 450°C and 500°C, respectively. The operating lifetimes of the conductors, for 1% failures, were projected to 80°C and 2×10⁵ A/cm². The three-layer system shows a 2× increase in lifetime, relative to the other system, for the standard 30-min, 450°C anneal and an enhancement in film integrity at higher annealing temperatures, near 550°C. However, the two-layer system shows a 2× increase in lifetime near 475°C, due to an increase in activation energy for a lower temperature anneal