Measurement Of Silicon Carbide Epitaxial Layer Thickness Based on Infrared Interferometry and Fourier Transform Analysis

Abstract

To meet the demand for high-accuracy, non-destructive measurement of silicon carbide (SiC) epitaxial layer thickness, this paper presents a progressively refined infrared interferometry methodology. Starting from fundamental physical principles, this approach systematically addresses two major error sources in practical measurements—dynamic refractive index changes and multi-beam interference—by constructing increasingly sophisticated mathematical models. The main innovations of this work are: 1) To overcome the noise sensitivity of traditional extremum-based methods, a robust "Global Interference Order Alignment" algorithm is proposed, which utilizes the entire spectrum to achieve a reliable initial thickness estimation. 2) To resolve the systematic errors caused by multi-beam interference, a high-precision model based on the Fast Fourier Transform (FFT) is further developed. This advanced model extracts the optical path difference from the signal's global frequency characteristics, proving insensitive to non-sinusoidal fringe shape distortions. A Drude-Sellmeier hybrid model is integrated to accurately describe the material's optical properties, accounting for both lattice vibrations and free carriers. Experimental results show that while the initial global alignment algorithm demonstrates strong noise resistance (yielding a thickness of 9.9005 µm), it exhibits a notable discrepancy between measurements at different angles. The advanced FFT model, after confirming the presence of multi-beam interference via kurtosis analysis, effectively eliminates the associated systematic errors. It yields a revised and more accurate thickness of 11.0616 µm for the SiC epitaxial layer, with significantly enhanced consistency and stability across different incident angles. This study not only provides a high-accuracy and highly stable measurement solution for industrial quality control of SiC epitaxial layers but also offers a valuable reference for other spectral metrology fields with its systematic, multi-stage approach to solving complex physical problems.