Quantitative analysis of electromigration damage in Al-based conductor lines

Electromigration damage in Al-based interconnects with three compositions (pure Al, Al-1%Si-0.5%Cu, and Al-2%Cu) was studied quantitatively. Using scanning electron microscopy, the spacings between more than 1000 voids and hillocks were measured. The distribution of the spacings was found to be a function of the composition, the applied current density, and the linewidth. The measurements confirm the existence of a threshold product of current density and diffusion length. In particular, a dependence of this threshold product on the Cu content was found. The results of the analysis show that there are clear correlations between the details of the microscopic damage processes and the lifetime of the conductor lines.