Glancing angle deposition of SiO2 thin films using a novel collimated magnetron sputtering technique

Abstract

A novel deposition flux collimation technique has been explored in combination with glancing angle deposition geometry in radio frequency magnetron sputtering deposition technique with a motive to tailor the refractive index of silicon di-oxide thin film. In this technique, a collimating plate has been placed in parallel to the substrate at variable substrate to collimator distances (DSC=4mm, 6mm and 9mm) and the effect of DSC on various properties of the deposited film at different spatial locations on the substrate has been investigated. The use of such collimator was found to be highly effective in reducing the refractive index of the deposited film. A lowest refractive index of ~1.31 @ 550nm of SiO2 was achieved by using this novel collimation technique in combination with glancing angle deposition geometry which is not possible by glancing angle deposition geometry alone in the framework of non-directional deposition flux in magnetron sputtering technique. Variable angle spectroscopic ellipsometry (VASE) has been employed to accurately determine thickness and refractive index of the deposited films at various spatial locations of the sample. Ellipsometry data fitting model at different spatial locations has been verified by simulating the transmission spectrum based on the layer structure model obtained from ellipsometry modeling and then comparing it with that of the experimentally measured transmission spectra. For a given DSC an optimum location on the substrate surface was obtained to exhibit lowest refractive index. FTIR measurement showed no significant difference in bonding behavior of SiO among different representative spots of the deposited SiO2 samples. AFM measurement on various spatial locations indicates a possible strong correlation between variation of refractive index and the grain size which is again affected by the degree of collimation and ad atom kinetic energy at various spatial locations.