Characterization of SiO2 and TiO2 films prepared using rf magnetron sputtering and their application to anti-reflection coating

Abstract

Preparation of TiO2 and SiO2 films for optical applications was attempted using conventional rf magnetron sputtering in the sputtering ambient with various O2/Ar+O2 ratios and at substrate temperatures between room temperature and 400°C. X-ray photoelectron spectroscopy (XPS) and optical spectroscopy investigations indicated that oxygen addition in the sputtering ambient was essential for growing TiO2 films with stoichiometric compositions and good transmittance, while SiO2 films had a stoichiometric composition of O/Si ratio=2.1–2.2 and were highly transparent in the visible wavelength region, independent of gas composition in the growing ambient. It was also identified from scanning electron microscope (SEM), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) measurements that the structural characteristics of both TiO2 and SiO2 films were significantly improved with O2 addition in the sputtering ambient, showing smoother surface morphologies and higher resistances to water absorption when compared with films grown without O2 addition. Heating of the substrate between 200 and 400°C considerably increased the refractive index of TiO2 layers, resulting in dense structures along with an improvement of crystallinity. For optical applications, AR coatings composed of 2–4 multi-layers on glass were designed and manufactured by stacking in turn the SiO2 and TiO2 films at room temperature and O2/Ar+O2=10%, and the performance of the produced coatings was compared with simulation results.