In this paper, we describe an experimental study of the nucleation and growth stages during Cu(TMVS)(hfac) sourced Cu CVD on TaN substrates. In particular, we have investigated the effects of water vapor as a co-reactant on evolving surface morphology. The results of short (less than 10 s) depositions without/with water vapor indicate that water vapor helps to reduce the incubation time and to enhance the nuclei formation, uniformity, and adhesion (based on AFM analysis). Introducing water vapor during only the initial stage of deposition results in lower roughnesses, larger grain sizes, and lower short-range roughnesses as compared to the films deposited without water vapor. From this study, we conclude that water vapor enhances Cu nucleation and that a relatively small amount of water vapor before or during the initial stage of deposition improves surface morphology in terms of roughness and grain size.