Tunability of CuOx properties by gas flow rate control in the reactive DC magnetron sputtering

The reactive magnetron sputtering process of Cu target in Ar/O₂ atmosphere is described in a wide interval of reactive gas flow rate fractions, ranging from 0 to 70 %. The experiments took place in the constant pressure mode, at 0.67 Pa constant pressure. The gas flow ratios were calculated to take into account the differences in the pumping speeds for different gases. This approach makes possible the distinct evaluation of the oxygen gas losses due to the reactive processes inside the plasma chamber. The pressure and voltage variations, along with optical emission intensity variations of the selected lines during the hysteresis experiments are used to describe and identify the process windows. Considering a selected number of critical points on the process window, thin films of CuOx were deposited and characterized. The transition from Cu₂O to CuO structure was assessed by XRD analysis, and confirmed by the optical properties of the films. The films with higher Cu content were identified as Cu₂O, with direct optical band gap values in the range of 2.53 to 2.41 eV, whereas lower Cu content films were identified as CuO with indirect band gap values in the range of 1.13 to 1.09 eV. Moreover, a reliable concordance between the variations of process parameters and thin film properties was obtained.