Nucleation and growth of Cu by chemical vapor deposition (CVD) using hexafluoracetylacetonato-Cu(I)-trimethylvinylsilane [hfac(Cu)tmvs] on different physical vapor deposition (PVD) diffusion barriers, namely, tantalum (Ta) and tantalum nitride (TaNx with x < 0.5). were studied by means of scanning and transmission electron microscopy to understand the dependence of morphology and microstructure on deposition parameters. X-ray diffraction measurements were carried out to study the orientation of the polycrystalline films. Atomic force microscopy was used to investigate the surface roughness. The results were compared to sheet resistance and reflectivity measurements. Nucleation on ban Ta and TaNx surfaces is significantly more difficult than on Ta with a 200 Angstrom PVD Cu "flash" layer. The films directly deposited on Ta or TaNx show a random orientation and an amorphous interlayer between the CVD Cu film and the barrier. CVD Cu films grown on a PVD Cu ''flash" layer expose a highly preferred [111] orientation of the grains and no amorphous interlayer.