Hybridization of ellipsometry and energy loss spectra from XPS for bandgap and optical constants determination in SiON thin films

Abstract

In this study, we first compare the bandgap determination methods in SiON thin films using two established techniques: Ellipsometry and the Energy Loss Spectrum from X-ray Photoelectron Spectroscopy. In the ellipsometry case, we modelled the optical properties using a single Tauc-Lorentz oscillator model, in a range from 1.5 to 6 eV, while for the XPS case, we used the threshold energy of the Energy Loss Spectrum from the O1s and N1s main core levels to determine the bandgap. We observed a consistent difference of the energy bandgap values obtained between the two methods, reaching up to 1.6 eV. Therefore, we combined the ellipsometry and Energy Loss Spectrum from XPS measurements, creating a hybrid metrology method using a triple Tauc-Lorentz oscillator model. This methodology respected the optical relations of each technique and the complex dielectric constant of the material, creating an overlap of the two measurements between 3.5 and 6 eV. The combination method brings the advantage of a more robust determination of the bandgap in the SiO 2 –Si 3 N 4 system, while creating a way to measure the refractive index and coefficient of extinction for intermixed thin films of SiON, from 1.5 up to 30 eV. • Comparison of bandgap determination using ellipsometry and ELS-XPS. • Large energy bandgap difference between the two methods, up to 1.6 eV. • Combination of the two techniques, using a triple Tauc-Lorentz oscillator model. • Robust determination of the bandgap in the SiO 2 –Si 3 N 4 system. • Method to measure n and k in a large energy range, from 1.5 up to 30 eV.