This article provides a detailed introduction to the method of inversion of thin film pa-rameters based on spectral fitting,obtaining a simplified transmittance formula for the thin film sub-strate optical system.With the help of the Cauchy model,a spectral fitting evaluation function is estab-lished.The simplified transmittance formula of the thin film substrate optical system is obtained,and a spectral fitting evaluation function is established using the Cauchy model.The improved genetic algo-rithm was used to obtain the optical constants and thickness of Si thin films in the wavelength range of 500～800 nm.The results showed that the calculation accuracy of the refractive index and thickness of the films was high,with average errors of only 0.1％and 0.2％,and the error of extinction coefficient could also be controlled around 10％.This method has the characteristics of simple operation,fast cal-culation speed,and accurate results.
维普
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