Calculation and Reliability Analysis of Epitaxial Layer Thickness Using Infrared Interferometry Based on the Constant Refractive Index Assumption

This study focuses on applying infrared interferometry to calculate the precise thickness of silicon carbide epitaxial layers and conducting reliability analysis of the results. Addressing the complexity of epitaxial layer refractive index variation across infrared spectral wavelengths, this research proposes a key assumption: the refractive index can be treated as constant within specific wavenumber ranges outside the vicinity of the vibrational absorption peak near 1000 . To validate this hypothesis, experimental data from two incident angles were visualized. Within the specified wavenumber range, minimal reflectance fluctuations and stable interference fringes were observed. The hypothesis's applicability was further confirmed by verifying the proportional relationship between wavenumber increments and order increments through a proof by contradiction approach. Based on literature review, the refractive index was set to 2.55. Subsequently, using the epitaxial layer thickness calculation formula, eight thickness values were selected and computed using the interference order. Calculations revealed average thicknesses of 8.0381 μm and 7.9797 μm for the 10° and 15° incidence angles, respectively. The final determined epitaxial layer thickness was 8.0089 μm. Reliability analysis indicated that the relative error of all calculated results was controlled below 0.4%, and the maximum relative errors under both incidence conditions were extremely close, fully demonstrating the high consistency and reliability of the calculation results.