Mechanisms of Electromigration Damage in Cu Interconnects

Mechanisms of electromigration (EM) damage in Cu interconnects through various CMOS nodes are reviewed. Pure Cu and Cu alloy interconnects that were used down to 14 nm node can no longer satisfy the electrical current used for 10 nm node and beyond in high-performance ICs. Cu interconnects with a metal cap should be used. Cu interface diffusivity with EM activation energy of 1.6 eV was found to be the dominate EM factor in Cu lines with a Co liner and cap. The median lifetime of 7 or 10 nm node Cu with TaN/Co liner and Co cap is predicted to be over ten thousand years at 140°C with $1.5\times 10^{7}\mathrm{A}/\text{cm}^{2}$. However, the resistivity size effect and the difficulty of scaling barrier/liner layer without defects can limit the Cu BEOL roadmap below the 7 nm node.