The optical properties and applications of AlN thin films prepared by a helicon sputtering system

AlN thin films were grown on SiO2/Si and quartz substrates using a helicon sputtering system. The dependence of film quality on growth parameters, such as total sputtering pressure, substrate temperature, and nitrogen concentration has been studied. There is a good correlation of thin film crystallinity addressed by x-ray diffraction (XRD) and spectroscopic ellipsometer. The optimized films exhibit highly oriented, with only (002) peak shown in a θ–2θ scan XRD pattern, and extremely smooth surface with rms roughness of 2 Å. The extinction coefficient of the film was 4×10−4, which is lower than that of AlN films grown by conventional sputtering. Double-layer antireflection (DLAR) coating using AlN and Al3O3 grown on quartz has been demonstrated. The transmittance of DLAR was high as 96% compared to 93% of bare substrates with the measurement error less than 0.2%. AlN films prepared by Helicon sputtering thus are potential for optical application.