Effects of overlayers on electromigration reliability improvement for Cu/low K interconnects

Electromigration in Cu Damascene lines capped with either a CoWP, Ta/TaN, SiNx, or SiC xN yH z layer was reviewed. A thin CoWP or Ta/TaN cap on top of the Cu line surface significantly reduced interface diffusion and improved the electromigration lifetime when compared with lines capped with SiN x or SiC xN yH z. Activation energies for electromigration were found to be 2.0 eV, 1.4 eV, and 0.85-1.1 eV for the Cu lines capped with CoWP, Ta/TaN, and SiN x or SiC xN yH z, respectively.