Co-doped Ru liners for highly reliable Cu interconnects with selective Co cap

It has been confirmed that Co diffusion from the cap into a Ru liner (resulting in Co depletion at the top of Cu lines) is the root cause of EM degradation for Cu interconnects in the case of using a combination of Ru liner and selective Co cap. Increasing the Co cap thickness is an effective EM degradation remedy, but at the expense of Vbd degradation (breakdown voltage between lines) due to lateral growth of Co. Alternatively, replacing the Co cap with a Ru cap showed marginal EM improvement. Here we report a novel Co-doped Ru liner, which demonstrates a significant EM performance boost by addressing the Co diffusion issue. This Co-doped Ru liner is shown to be a promising liner of choice for Cu interconnects in advanced nodes.