Electromigration damage in fine Al alloy lines due to interfacial diffusion

Abstract

Both electromigration lifetime experiments and experiments of the drift velocity type have been conducted with the alloys: Al(2% Cu), Al(0.5% Cu, 0.3% Zr), and Al(0.3% Pd, 0.3% Nb) also with structures with two wiring levels of Ti/Al (0.5 - 4 % Cu)/Ti interconnected with W studs. The latter structure and these structures in general, are representative of present applications, which contain Al alloy/W interfaces. In all cases it was found that the mass transport along the line's edges played a role in their damage formation, which was at least as great as grain boundary diffusion. It is postulated that the results obtained using the traditional test structure, which has reservoirs of metal alloy at each electrode and is conducted at a single level, have been misinterpreted as indicating that flux divergence at triple junctions were critical failure sites for on-chip interconnections. These present results show that the material in the electrode pads of the conventional structure can resupply material to the lines. A direct experimental comparison of the two structural types is made to demonstrate the point.