Study of Conduction Modes of Time to Dielectric Breakdown Reliability in Cu Damascene Structures

Low k time-dependent dielectric breakdown is increasingly becoming a major issue at the 45 nm technology node and beyond. Although TDDB models, such as the E model, the E model and the 1/E model, have been extensively explored, determining the back end of line processing direction for TDDB warrants further study. This study attempts to determine whether the thickness of the etching stop layer film influences the electron conduction mechanism. Cu damascene structures were designed following three approaches with various thickness of the etching stop layer : Co/ESL = 0 A-550 A (low-k: SiCO k = 3.1), Cu/ESL = 0 A-275 A (low-k: SiCO k = 2.5) and Co/ESL = 0 A-275 A (low-k: SiCO k = 2.5). The application of capping material Co is warranted for electron emission suppression, but the oxygen attacking from subsequent low-k deposition is a concern. In addition, greater ESL thickness offers paths for electron conduction which worsens TDDB; i.e., less ESL thickness is better. Therefore, the combination of Co with SiH 4 treatment addresses optimized conditions to achieve an ESL-less application for TDDB enhancement.