Copper was electrodeposited directly onto a 5 nm thick physical vapor deposited tantalum (Ta) diffusion barrier layer in a copper-ammonium-citrate (Cu-NH3-Cit) bath. An anodic potential was applied to Ta in a saturated KOH solution to remove native Ta oxide before seedless copper deposition on Ta. The dense growth of copper films with sufficient wetting and adhesion on Ta was made possible by a two-step potentiostatic deposition at -1.26 V vs saturated calomel electrode (SCE) for Cu-2(Cit)(2)OH3- ion reduction and then at -0.58 V vs SCE for cupric ion reduction. (C) 2010 The Electrochemical Society. [D01: 10.1149/1.3485026] All rights reserved.