The electromigration diffusion mechanisms of electroplated Cu with Ta barrier/dielectric diffusion barrier SiCxNy and cold/hot 2-step sputter-deposited Al–0.5wt%Cu damascene interconnects with Nb liner were examined and compared using the via-electromigration testing pattern with different line-widths. The interface between Cu and SiCxNy was the dominant diffusion path for the Cu damascene interconnects regardless of the Cu microstructure. An activation energy (Ea) of approximately 0.9eV was obtained for the width range of 0.1–6µm. Therefore, the diffusion mechanism was independent of the Cu microstructure. Regarding the cold/hot two-step sputter-deposited Al–0.5-wt%Cu damascene interconnects with Nb liner, the electromigration median time-to-failure increased with increasing the line-width for the Al bamboo-like microstructure, indicating that the interface between the Al and Nb liners was the dominant diffusion path. This was probably because a rapid diffusion path along the NbAlx reaction product was formed during the 2-step cold/hot sputter deposition at 400C. The electromigration median time-to-failure did not increase for more than 4µm. It was also found that the Ea was approximately 0.9eV for the Al bamboo-like microstructure and that it decreased with increasing line-width for the Al polycrystalline microstructure, meaning that the grain-boundary diffusion was also included and that ratio of the interfacial diffusion and grain-boundary diffusion depends upon the line-width. This was because the Ea of the grain-boundary diffusion was smaller than that of the interfacial diffusion for Al–0.5-wt%Cu damascene interconnects. The electromigration diffusion mechanism of the Cu damascene interconnects with Ta barrier/dielectric diffusion barrier SiCxNy was completely different from that of the Al damascene interconnects with Nb liner.

Electromigration Diffusion Mechanism of Electroplated Copper and Cold/Hot Two-Step Sputter-Deposited Aluminum-0.5wt.% Copper Damascene Interconnects. T.Usui, H.Nasu, T.Watanabe, H.Shibata, T.Oki, M.Hatano: Journal of Applied Physics, 2005, 98[6], 063509 (6pp)