Molecular dynamics study of diffusion and atomic configuration in layered structures for Al circuit interconnects

Abstract

Diffusion at Al(1 1 1)/underlay-metal interfaces, which is a dominant factor of electromigration-induced open-circuit failures in Al interconnects, was investigated by molecular dynamics simulation. The author focused on interfaces between the (1 1 1) plane in Al and the plane of greatest atomic density in five kinds of metals that have high melting temperatures: Ti, Cr, Mo, W, and Ta. The calculated self-diffusion coefficients of Al atoms near the Al/Ti and Al/Cr interfaces were smaller than those near the other three interfaces. This result is consistent with experimental results by other works that showed that Ti and Cr are effective underlay metals for suppressing the diffusion in Al interconnects. This result on the self-diffusion coefficient was linked to the result on the atomic configurations. The configurations of Al atoms at Al/Ti and Al/Cr interfaces were close to that for bulk Al, while the configurations at the other three interfaces were significantly different from that for bulk Al. It was found that diffusion as well as atomic configuration at the Al/underlay-metal interface is determined by the lattice mismatch between the (1 1 1) plane in Al and the plane of greatest atomic density in the underlay metal.