Tuning the structure and preferred orientation in reactively sputtered copper oxide thin films

Binary copper oxide (Cu2O, Cu4O3 and CuO) thin films have been selectively deposited on glass and silicon substrates by magnetron sputtering at room temperature from a metallic copper target in various Ar-O2 reactive mixtures. The influence of oxygen flow rate and total pressure on the film structure and its preferred orientation has been studied. A schematic deposition diagram, which describes the film structure as a function of O2 flow rate and total pressure, is depicted by combining X-ray diffraction and Raman spectrometry. The oxygen flow rate process windows for Cu2O or Cu4O3 single phase synthesis are narrow, while that for CuO is wider. Between two single phase domains, biphase films are systematically deposited. It is found that the deposition total pressure is a relevant parameter to control the texture and the morphology of pure Cu2O and Cu4O3 films. Low total pressure favors the growth of planes with high surface energy ((1 0 0) for Cu2O and (1 0 1) for Cu4O3) parallel to the substrate. On the other hand, high total pressure facilitates the growth of planes with low surface energy ((1 1 1) for Cu2O and (1 0 0) for Cu4O3). The oxygen flow rate is effective to control the preferred orientation of CuO thin films that evolves from 〈1 1 1〉 to 1¯11 with the increase of oxygen flow rate. These results are supported by transmission electron microscopy observation in cross section.