The use of an ultrathin Ru-Ta-C film as a barrier for copper metallization in sub-32-nm ultra-large-scale integration (ULSI) has been evaluated. The films, fixed at 5 nm, were deposited by magnetron sputtering using Ru and TaC targets, and the film composition and structure were adjusted by tuning the respective deposition power. The structure of the Ru-Ta-C films gradually changed from Ru4Ta(C) to nanocrystalline or nearly amorphous when optimizing TaC. For a sandwiched scheme of Cu/Ru82Ta12C5/Si or Cu/Ru77Ta15C7/Si, the failure temperature was at least 750 degrees C. We also electroplated Cu directly onto a Ru-Ta-C film without Cu seeding. Because of their low resistivity (< 100 mu Omega cm) and high thermal stability, Ru-Ta-C films are promising as a Cu barrier. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3518411] All rights reserved.