Comprehensive investigations of CoWP metal-cap impacts on low-k TDDB for 32nm technology application

As the current-carrying capability of a copper line is reduced due to interconnect dimension shrinkage, self-aligned CoWP metal-cap has been reported to be helpful to improve degraded electromigration (EM) reliability. However, adoption of the metal cap in general further exacerbates the already problematic low-k dielectric TDDB reliability at 32nm and beyond. This paper provides a comprehensive study of CoWP metal-cap impacts on low-k TDDB for 32nm technology application. It was found that CoWP could induce a severe degradation of low-k TDDB if its process is not optimized, and its impacts on dense low-k and porous ultra low-k (ULK) dielectrics were different. An optimized CoWP process with the least defect density could lead to an acceptable TDDB performance as compared to the control for both dense low-k and porous ULK dielectrics, while showing substantial improvements in EM and stress migration (SM).