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

• Published in: Physica status solidi. A, Applications and materials science Vol. 218; no. 22
• Main Authors: Haque, S. Maidul, De, Rajnarayan, Prathap, C., Srivastava, S. K., Rao, K. Divakar
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.11.2021
• Subjects: antireflection coating; bandgap; Deposition; e-beam evaporation; Electron beams; Evaporation; Microscopes; Optical materials; Optical properties; Optics; Oxidation; oxidation of silicon; Photoelectrons; Refractivity; Silicon; Spectroellipsometry; Spectrophotometry; Stoichiometry; Substrates; Thin films; tunability in optical constants; X-ray photoelectron spectroscopy
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.202100299

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. The native oxidation of Si without inflow of oxygen gas from external supply during e‐beam evaporation shows e‐beam current‐dependent oxidation and hence quasicontinuous tunability of refractory properties of deposited SiOx thin films. This is utilized to experimentally demonstrate antireflection coating on silicon wafer yielding ≈2.7% average reflectance loss in wavelength range of 400–900 nm.