Fig. 1. Schematic diagram of multi wavelength spectral reconstruction and film thickness fitting experiment

Fig. 2. （a）Comparison chart of measured reflectance and transmittance spectra before and after program calibration processing of Si₃N₄（283.2 nm）sample；（b）thickness fitting error between fitting thickness and SEM thickness of different samples before and after spectral calibration（using full spectrum data points）

Fig. 3. Spectral fitting images using 10 different wavelength information of coating samples with different material compositions：（a）reflectance spectrum；（b）transmittance spectrum；（c）thickness fitting error between fitting thickness and SEM thickness of different samples when using different numbers of data points for fitting