Study on Epitaxial Layer Thickness Measurement Based on Infrared Interferometry Combined with Machine Algorithm

Abstract

This study focuses on accurate measurement of epitaxial layer thickness for silicon carbide (SiC) and silicon crystals using infrared interferometry combined with machine algorithms, while addressing beam interference effects. Theoretically, it builds a mathematical model based on optical interference theory, Snell's law, and Fresnel reflection formula, incorporating a half-wave loss correction to minimize phase difference errors. Reflection spectrum data are gathered via Fourier transform infrared spectrometry, and a linear fitting model is derived for calculations. Algorithmically, a two-step inversion method is developed: first, a simulated annealing-like algorithm optimizes wavenumber intervals with Monte Carlo sampling to enhance spectral data use; then, thickness and refractive index are calculated within a physically valid range. Results show low error and high robustness. Additionally, the study examines multi-beam interference, proposing a model with high-order reflections (Airy distribution) and spectral fitting to eliminate errors from multiple reflections in SiC wafers, achieving accurate thickness measurements.