Plasma emission control of reactive sputtering process in mid-frequency mode with dual cathodes to deposit photocatalytic TiO2 films

Titanium dioxide (TiO2) films were deposited on unheated non-alkali glass substrates by reactive mid-frequency (mf) magnetron sputtering using dual cathodes with two Ti metal targets. In order to achieve a very high deposition rate, the depositions were carried out in the `transition region' between the metallic and the reactive (oxide) sputter mode where the target surface was metallic and oxidized, respectively. Stable deposition was successfully carried out in the whole transition region at both total pressures of 1 Pa and 3 Pa, using the plasma control unit (PCU). The highest deposition rate in this study for the photocatalytic TiO2 films deposited in the transition region was over 30 nm/min, which was larger than that for the conventional sputter deposition by one order of magnitude. These films could be crystallized by post-annealing in air at 200 °C. Photoinduced decomposition of acetaldehyde and photoinduced hydrophilicity was successfully demonstrated.