Strain evolution in Al conductor lines during electromigration

Abstract

Monochromatic and white beam synchrotron x rays were used to study the deviatoric strains and full elastic strains in passivated Al conductor lines with near-bamboo structures during electromigration (EM) at 190 °C. A strong strain gradient formed in the upstream part of the Al lines. Strains along the downstream part of the lines were smaller and more scattered. Numerical analysis using the Eshelby model and finite element method (FEM) calculations suggest that the moving of atoms during EM in these near-bamboo Al lines is dominated by top and/or bottom interface diffusion, which differs from the reported results for nonbamboo, polycrystalline Al conductor lines, where EM is mainly along the grain boundaries. Local strain measurements and FEM calculations indicate that the EM flux is also nonuniform across the width of the conductor line because of stronger mechanical constraint by the passivation layer near the edges of the line. Plastic deformation is observed during EM by changes in the Laue diffraction patterns. The effective valence |Z∗|=1.8±0.4 is determined from the measured strain gradient.