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 this new metal cap in general further exacerbates the already problematic low-k dielectric TDDB reliability at 32nm and beyond. This paper provides a comparative study of ULK conduction mechanisms over a wide range of temperature (30°C to 295°C) and TDDB acceleration kinetics at 125°C for Cu interconnects with and without CoWP metal cap at 32nm technology. It was found that adding CoWP didn't change the fundamental ULK leakage conduction mechanism and TDDB kinetics if its process was optimized. Comparable leakage and TDDB performance were achieved with an optimized CoWP process. ©2010 IEEE.