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 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 or SiCNH. 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 or SiCNH, respectively.