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

Abstract

We propose a high-accuracy spectral interferometer that uses multi-Fabry–Perot Etalon to measure the thickness of silicon wafer. Three Fabry–Perot etalons (f1=14.5 GHz, f2=14.9 GHz and f3=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 μm.