Electromigration-induced stress in aluminum conductor lines measured by x-ray microdiffraction

Abstract

Electromigration-induced stress distributions in 200 μm long, 10 μm wide aluminum conductor lines in 1.5 μm ${\mathrm{SiO}}_{\mathrm{2}}$ passivation layers have been investigated in real time using synchrotron-based white-beam x-ray microdiffraction. The results show that a steady-state linear stress gradient along the length of the line developed within the first few hours of electromigration and that the stress gradient could be manipulated by controlling the magnitude and the direction of the current flow. From the current density dependence of the steady-state stress gradient, the effective valence $Z^{*}$ was determined to be 1.6 at 260 °C. From the time dependence of the transient-state stress gradient, the effective grain boundary diffusion coefficient $D_{\mathrm{eff}}$ was estimated to be ${\text{8.2×10}}^{\text{−11}}\hspace{0.17em}{\mathrm{cm}}^{\mathrm{2}}\mathrm{/s}$ at 260 °C using Korhonen’s stress evolution model [M. A. Korhonen, P. Bo/rgesen, K. N. Tu, and C.-Y. Li, J. Appl. Phys. 73, 3790 (1993)]. Both $Z^{*}$ and $D_{\mathrm{eff}}$ values are in good agreement with the previously reported values.