Effect of CoWP Capping Layers on Dielectric Breakdown of SiO2

Leakage and dielectric breakdown of SiO2 are studied for Cu interconnect structures with either stand-alone CoWP or two-layer CoWP+SiN caps. Without a post-CoWP plasma clean, there are many early fails and the dielectric breakdown exhibits bimodal behavior. By adding a plasma clean after CoWP deposition, the early fails can be eliminated and high dielectric breakdown is achieved. The improvement in dielectric breakdown with the plasma clean is greater for the two-layer cap compared to the stand-alone cap, probably due to the extra plasma clean associated with SiN deposition.