E‐Beam Evaporation of Silicon: Native Oxidation and Quasicontinuous Tailoring of Optical Properties

Abstract

An experimental study of native oxidation of silicon during electron beam evaporation is carried out. A set of SiOx thin films is prepared at varying e‐beam current (50–300 mA) without inflow of oxygen gas from external supply. The O:Si stoichiometry ratio of grown SiOx films, as estimated through X‐ray photoelectron spectroscopy (XPS) measurement, is found to be mainly governed by the deposition rate. Optical analysis using transmission spectrophotometry and spectroscopic ellipsometry measurements reveal gradual variation of refractive index (1.58–4.09@650 nm) and bandgap (3.65–1.90 eV) of grown films with the increase in e‐beam current. Such high contrast changes in Si‐based optical materials just by variations of e‐beam current are not reported previously. Deposition rate‐dependent oxidation and optical constants are confirmed by investigating two separate films at lower substrate heights. Finally, utilizing the quasicontinuous variation of optical constants of SiOx films, antireflection (AR) coating is designed and experimentally demonstrated on Si wafer and achieved reflectance loss of ≈2.7% in wavelength range of 400–900 nm. The native oxidation under varying e‐beam current is envisaged to be an effective and a facile method for preparing quasicontinuously tunable silicon‐based optical materials.