The effect of Al3Ti capping layers on electromigration in single-crystal aluminum interconnects

Studies of accelerated electromigration were conducted on passivated Al single-crystal interconnects fabricated on oxidized Si, and capped with Al3Ti overlayers. The capping layers were formed by the reaction of the single-crystal Al films with Ti overlayers. The activation energy for electromigration-induced failure was determined to be 0.94 +/- 0.05 eV. Previous work on Al single-crystal interconnects without Al3Ti overlayers gave an activation energy of 0.98 +/- 0.2 eV and lifetimes of similar magnitude [Y.-C. Joo and C. V. Thompson, J. Appl. Phys. 81, 6062 (1997)]. The similarity of these results suggests that either the rate-limiting mechanism for electromigration-induced failure of single-crystal. Al interconnects is not diffusion along the interface of the Al with the surrounding oxide and overlayer, or that, surprisingly, the diffusivity of Al along the Al/Al3Ti interface is approximately the same as, or lower than, the diffusivity of Al along the Al/AlOx, interface. (C) 1998 American Institute of Physics.