Electromigration reliability improvement of W-plug vias by titanium layering

The electromigration (Er) performance of layered Al-0.5%Cu and Al-1%Si-0.5%Cu metallization systems was investigated, including leads with refractory barrier and capping layers, and tungsten-filled via holes. While the W-plugs exhibited a lifetime shorter than the leads, a dramatic improvement in EM performance of the vias was achieved by incorporating a thin layer of titanium between the aluminum and its cap. Among the most likely explanations for this observation is that the aluminum is protected from physical damage during via etch by the continuous TiAl/sub 3/ layer which forms by reaction between the titanium and the aluminum. Current flow simulations show complex crowding effects at the bottom of the vias. The role of grain boundaries and the effects of dopants on early via failure modes are also discussed.<>