Sputter Deposition of Cuprous and Cupric Oxide Thin Films Monitored by Optical Emission Spectroscopy for Gas Sensing Applications

Cuprous oxide and cupric oxide thin films were deposited on silicon wafer with additional substrate bias voltage using radio-frequency magnetron sputtering of a Cu target with Ar+O2 discharge plasma. Optical emission spectroscopy was employed to monitor the intensity of atomic Cu and O emission lines at various substrate bias voltages and oxygen flow ratios. Thin film transition from cuprous oxide to cupric oxide phase was observed by X-ray diffraction analysis when the oxygen flow ratio increased. This transition was not influenced by the substrate bias voltage. Optical emission spectroscopy showed a real time monitoring results of the transition from cuprous to cupric oxide thin films. The transition was observed at a critical O2 flow ratio of 7%. The results proposed a tightly control of reactive Cu sputtering through a closed loop and real-time monitoring system for precise copper oxide thin films deposition.