Optical monitoring of DC/RF plasma sputtering for copper oxide film growth at low temperature

DC/RF plasma sputtering process for the growth of copper oxide thin film was studied by optical emission spectroscopy. The films were produced by a balanced magnetron sputtering system nearly at room temperature. The influence of applied power in DC and RF mode and Ar/O2 flow ratio on the film properties was investigated as well as their relationship to the plasma species and the main chemical reactions during the film growth. It was found that the concentration of active species in the plasma and their abundance ratio is very effective in the reactions related to the film growth process and the properties of the deposited film. It was shown that copper oxide film with CuO phase owing low energy band gap can be synthesized at low temperatures by controlling the ionization rate, the energy of the active species, the film growth rate, and finally the relative concentration of copper to oxygen species in the plasma. CuO thin films (Eg=1.28 eV) were achieved in DC mode at the lowest applied power (50 W) and in the lowest Ar/O2 flow ratio (2/1). This oxide phase was also observed for two both the synthesized films in RF mode, at 50 W (Eg=1.39 eV) and 100 W (Eg=1.23 eV) in an Ar/O2 flow ratio of 2/1.