Electromigration in single-crystal aluminum lines with fast diffusion paths made by nanoindentation

Abstract

Segments containing a continuous region of plastic deformation were made in single-crystal aluminum conductor lines having widths near 2 μm using nanoindentation techniques. These segments act as fast diffusion paths similar to the polygranular clusters in a line having a near-bamboo grain structure. Segments of various lengths were created in lines having (111) and (110) planes parallel to the substrate, and these lines were subjected to accelerated electromigration testing with in-situ observations. A critical segment length below which no electromigration damage occurs at a given current density was found which is comparable to that seen in experiments using rectangular aluminum stripes (“Blech experiments”). Subcritical segments placed near one another were observed to interact to generate electromigration damage and failure. Results suggest that defects play a significant role in damage nucleation in near-bamboo lines. Single-crystal lines with (111) orientation have electromigration lifetimes an order of magnitude longer than those having (110) orientation. This difference is attributed to void motion, shape change, and growth processes.