High-accuracy spectral interferometer with multi-Fabry–Perot Etalon for thickness measurement of the silicon wafer

We propose a high-accuracy spectral interferometer that uses multi-Fabry–Perot Etalon to measure the thickness of silicon wafer. Three Fabry–Perot etalons ( f 1 = 14 . 5 GHz, f 2 = 14 . 9 GHz and f 3 = 15 . 0 GHz) are used to measure the wafer thickness, and the measurement accuracy of the spectral interferometer is improved by taking the average value of the thickness measurements corresponding to the three Fabry–Perot etalons. An effective peak extraction algorithm is developed to extract the effective peak frequencies. The proposed algorithm uses the crest width threshold and average crest height to improve the measurement accuracy of the spectral interferometer. We design a calibration method for the optical system, which uses the free spectral range (FSR) characteristics of the Fabry–Perot Etalon to calculate the calibration distances to reduce the errors. We build an experimental setup and use a high-precision laser hologage for reference. The experimental results show that the errors between the measured values and the reference values are between 0.00037% and 0.00046%, and the standard deviation is 0.06 μ m. • A high-accuracy spectral interferometer for thickness measurement of the silicon wafer is proposed. • Multi-Fabry–Perot Etalon is developed to improve the measurement accuracy of the spectral interferometer. • An effective peak extraction algorithm is designed to extract peak frequencies by crest width threshold and average crest height. • A calibration method for the optical system is proposed to use the free spectral range characteristics of the Fabry–Perot Etalon. • The proposed scheme has high precision, which the measurement errors are within 0.1%.