Cu diffusion in the spin-on hydrogen silsesquioxane (HSQ) is a major obstacle in the low-k plus Cu technology for future ULSI devices. We have optimized the process conditions for the spin-on HSQ low-k films. Subsequent metallization with Al and Cu shows a higher leakage current for Cu contact. We have employed Cat-CVD to deposit a-SiC:H films of different thickness on HSQ and studied their effect on the leakage current with both Al and Cir electrodes. The films were deposited using silane (SiH4) and acetylene (C2H2) gases. Also, an independent determination of the dielectric constant of the Cat-CVD a-SiC:H layer has been carried out from the C-V measurements on Al/c-Si/a-SiC:H/Al structure. The electrical characteristics of the Al/c-Si/HSQ+a-SiC:H/Cu structures show almost two orders of magnitude lower leakage current compared with Al/c-Si/HSQ/Cu, indicating very good barrier properties of the a-SiC:H material. Moreover, the low dielectric value observed for a-SiC:H compares favorably to other diffusion barrier materials. (c) 2005 Elsevier B.V. All rights reserved.