This article describes a study of chemical vapor deposition (CVD) copper thin films deposited on TaNx substrates using Cu(TMVS)(hfac) as a precursor. We have characterized the deposition rate, resistivity, surface roughness, and reflectivity of the films as functions of substrate temperature, precursor and carrier gas flow rates, and the presence or absence of water vapor as a coreactant. We have also examined the nucleation process for these films as functions of substrate temperature and the presence or absence of water vapor. We observed an activation energy for nucleation of 39 kcal/mol and an activation energy for film growth of 14 kcal/mol. Introducing water vapor during nucleation reduces the activation energy for nucleation to 6.1 kcal/mol. We found that water vapor helps to reduce the incubation time and activation energy of the nucleation stage and enhances nuclei formation, uniformity, and adhesion. In our reactor, the highest quality films were obtained using a process protocol for Cu CVD in which small amounts of water vapor were introduced before or during the initial stage of deposition at 473 K substrate temperature.