Characteristics of TiO2 Surfaces Etched by Capacitively Coupled Radio Frequency N2 and He Plasmas

Abstract

We have investigated characteristics of anatase TiO2 thin film surfaces etched by a capacitively coupled radio frequency N2 plasma from the viewpoint of both an experiment and a simulation. The result obtained with use of the N2 plasma is compared with that obtained with use of the He plasma. The experimental O/Ti ratio at the surface etched by the N2 plasma increases as a function of etching time. The increase in the experimental O/Ti ratio is independent of a change in gas pressure. The above-mentioned experimental results agree with the simulation result that the Ti atoms at the surface are preferentially removed by N2+ ions. The experimental O/Ti ratio at the surface etched by the He plasma also increases, which does not agree with the simulation result that the O atoms are preferentially removed by He+ ions. The O-1s XPS spectra of the surface etched by the He plasma show the peak associated with oxygen and water adsorbed by the surface. In the case where the component of the adsorbed oxygen and water in each spectrum is subtracted, the experimental O/Ti ratio at the surface etched by the He plasma shows a decrease. This is consistent with the simulation result. The adsorption of oxygen and water seems to be caused by ambient air. Morphology of the surface etched by the N2 plasma is almost similar to that of the as-grown surface regardless of the changes both in etching time and in gas pressure. In contrast, morphology of the surface etched by the He plasma changes as the etching time increases. This result is independent of the gas pressure.