Diode r.f. sputtering in oxygen-argon mixtures has been used to produce thin copper oxide films with a controlled amount of oxygen. The stoichiometry of the films was monitored in situ during the deposition by kinetic ellipsometry and was characterized ex situ by grazing X-ray reflection and Rutherford backscattering. Phases from copper to CuO were obtained with a good reproducibility by varying only the partial pressure of oxygen in the plasma. The reactivity of the films with silicon and float glass substrates was evaluated. Cu/CuO multilayers exhibited well-defined Bragg peaks at 1.54 Å. Kinetic ellipsometry trajectories and grazing X-ray reflectivities have been interpreted assuming sharp Cu---CuO interfaces and diffused CuO---Cu interfaces.