Electrical leakage and breakdown of low-dielectric constant (low-k) dielectrics are increasingly becoming major reliability issues as inter-metal spacings in interconnects scale towards the 0.1 μm technology node. In Cu damascene structures, these issues are greatly alleviated by the retention of a thin layer of hardmask, which is also known as buried capping layer (BCL), after chemical-mechanical polishing. It is found that a BCL of 100 Å thickness in Cu/SiOC interdigitated comb structures effectively reduces the leakage current by one order of magnitude and improves breakdown strength by a factor of 1.5–2. In addition, the BCL is able to prevent the formation of process-induced traps in the low-k dielectric. These findings can have important and positive reliability considerations for Cu/low-k integration schemes.