Electromigration Study of the Al-Cu/Ti/Al-Cu System

We have investigated unpassivated Al-Cu(4.5%)/Ti/Al-Cu laminated structures for their electromigration behavior for linewidths between 5 ¿ and 1.5 ¿ We find that although line opens are not the dominant failure mode, significant mass accumulation occurs all along the line leading to the real possibility of extrusion induced shorts. In our experiments laminated structures had lifetimes in excess of conventional Al-Cu lines by at least a factor of 10. Cu migration takes place in the early part of the stripe life. Al migration occurs preferentially from the top layer. Furthermore, a decrease of the line resistance, unlike in conventional structures, is observed during current stress. The Ti intermetallic layer does not show any motion.