Optical modeling of SiOx thin films for physicochemical property measurement by spectroscopic ellipsometry

Abstract

Spectroscopic ellipsometry (SE) is widely recognized for measuring the optical parameters of thin films, and its potential for in-depth analysis attracts attention from both scientific and technological aspects. Here, an advanced optical modeling approach was proposed to extend SE to investigate the physicochemical properties of SiO_x thin films. Amorphous silicon oxide thin films (SiO_x, 0 ≤ x ≤ 2) were deposited via mid-frequency magnetron sputtering under varying oxygen partial pressures and sputtering powers. The Tauc-Lorentz model was first developed to extract the optical properties of amorphous silicon (a-Si) and SiO₂, then the Bruggeman Effective Medium Approximation (BEMA) model based on the derived optical constants (n, k) of a-Si and SiO₂ was further employed to reveal the structure and optical properties of SiO_x thin films. The SE results were simultaneously verified through profilometer, UV–vis–NIR spectrophotometer, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, ensuring the accuracy and reliability of the modeling. Our work provides a theoretical and methodological foundation for advancing SE as a non-destructive in-situ technique, which is not only suitable for amorphous silicon oxide films but also for other non-stoichiometric thin films.