Electromigration proximity effects of two neighboring fast-diffusion segments in single-crystal aluminum lines

In near-bamboo lines, electromigration-induced damage initiates at polygranular clusters which are longer than a critical length and which act as fast-diffusion segments. It has been proposed that two neighboring subcritical clusters can also lead to damage through the interaction of their stress fields. In order to prove the existence of, and to study, such proximity effects, artificial clusters were generated by creating continuous segments of plastic deformation in single-crystal aluminum lines using nanoindentation. Pairs of segments having different separation distances and lengths were made. In situ electromigration tests showed that these segments generated damage in the form of voids and hillocks even when the individual segments were shorter than the critical length. The void growth rate was found to be a function of the separation distance and segment length. A simple analytical model for the electromigration flux in these structures is shown to be consistent with the measured void growth rates. Electromigration characteristics such as the diffusivity, the effective charge, and the critical stress for void formation can be extracted from a comparison between experimental results and model predictions.