Cu was electrodeposited directly on a 3-nm-thick atomic-layer-deposited (ALD) Ru diffusion barrier layer in Cucitrate-based electrolytes for Cu interconnect. The nucleation and growth behavior of Cu thin films on the ALD Ru was compared between an additive-free electrolyte and a polyethylene glycol (PEG)/janus green B (JGB)-added electrolyte. The suppression effect of additives in the PEG/JGB-added electrolyte led to lower Cu deposition rate. It was accordingly responsible for the growth of thin and uniform Cu films from smaller Cu nuclei of higher area density. In consequence, Cu filling of 30-nm-wide and 120-nm-deep trenches coated by the 3-nm-thick ALD Ru layer was much improved in the PEG/JGB-added electrolyte compared with the additive-free electrolyte. (C) 2017 Elsevier B.V. All rights reserved.