Preparation of indium tin oxide films by radio frequency magnetron sputtering under low vacuum level

Indium tin oxide (ITO) thin films were prepared by radio frequency (RF) magnetron sputtering and under a quite low vacuum level of 2.3 × 10 ^-3 Pa. The sputtering was done in an Ar and O₂ gas mixture at a temperature of 200°C. A ceramic In₂O₃:SnO ₂ target (10 wt% SnO₂) was used. The microstructures of the films were investigated by a field emission scanning electron microscope (FESEM) and an X-ray diffractometer (XRD). X-ray photoelectron spectroscopy (XPS) was performed to characterize the composition of the films. ITO films with a high transparency in the visible wavelength range (80-95%) were obtained. The dependency of the electrical, optical and structural properties of ITO films on both the O₂ flow ratio (O₂/(O₂ + Ar)) and the working pressure was investigated. In the case of low working pressure (1Pa), the more highly transparent and conducting films were produced at the lower O₂ flow ratio. High working pressure (2 Pa) gave rise to low quality, low transparency and amorphous films. Under RF sputtering at low vacuum level, the main contribution to the chamber atmosphere is due to water vapor. Oxygen originating from water vapor dissociation induced by plasma, plays the same role as an oxygen or water vapor flux usually intentionally introduced in the system in order to have good quality films.