Scientific Development Research

When measuring epitaxial layer thickness using infrared interferometry, the multi-beam effect can lead to systematic deviations in the two-beam model. To address the computational complexity of existing model validity verification methods, this study proposes a rapid judgment approach based on residual analysis. Taking the infrared reflectance spectra of SiC epitaxial layers at incident angles of 10°and 15°as the research object, nonlinear fitting is performed using the two-beam model. By analyzing the periodicity, sign pattern, and amplitude characteristics of the fitting residuals, criteria for identifying the multi-beam effect are established. The results indicate that at a 10° incident angle, the residual ranges from -0.6 to +0.2 with an RMS of 0.32; at a 15° incident angle, the residual ranges from -0.55 to +0.18 with an RMS of 0.30. The residuals exhibit periodic oscillations at the same frequency as the interference fringes, with a spectral correlation coefficient exceeding 0.95. At all peak positions, the residuals are negative, while at all valley positions, they are positive, with both the negative-at-peak and positive-at-valley proportions reaching 100%. The criteria for the multi-beam effect are summarized as follows: the residuals oscillate at the same frequency as the interference fringes, residuals are negative at peaks and positive at valleys, and the RMS of residuals exceeds 0.2. This method requires only the model fitting results for analysis, without the need for additional material parameters, providing a basis for assessing the applicability of the two-beam model.

Residual analysis; Infrared interferometry; Dual-beam model; Multi-beam effects