Formation process of Al2O3 thin film by reactive sputtering

Reactive sputtering is one of the widely used techniques to prepare compound thin films. In this study, Al and Al2O3 films were deposited by RF magnetron sputtering using mixed gas of Ar and O2. The formation process of the Al2O3films was studied by plasma emission spectroscopy and target voltage measurements. Al2O3films with transmittance above 95% and refractive index of 1.50-1.66 were found to be formed at O2 flow ratios above 8%. Plasma emission peaks of O atoms (777nm) were clearly seen at oxygen flow ratios above 8%, and target voltage decreased drastically at O2 flow ratios above 8%. It is thought that the surface of Al target was changed from metallic mode into oxide mode at the O2 flow ratios of 8%. The relationship between the amount of sputtered Al atoms and the amount of supplied O2molecules was studied, and the atomic ratio of sputtered Al atoms to supplied oxygen atoms was found to be approximately 2:3 at the critical O2flow ratio of 8%