Optical interferometric approach for measuring the geometrical dimension and refractive index profiles of a double-sided polished undoped Si wafer

Abstract

In this investigation, we propose a technique to obtain not only the dimensional profile of an undoped double-side polished silicon (Si) wafer but also its refractive index profile simultaneously. This technique is based on low coherence scanning interferometry using a near-infrared light around 1 µm wavelength, for which transmission is non-zero for undoped silicon and also detectable by the typical visible CCD camera. As the experimental results show, the profiles of optical thicknesses, geometrical thicknesses, group refractive indices and phase refractive indices were successfully obtained by the proposed technique, and the mean values were 1869.6 µm, 490.45 µm, 3.8121 and 3.516, respectively. Compared to the reference values of the group refractive index and the phase refractive index of the Si wafer given by the previous researches, the deviations were 0.055 and 0.04, respectively. The deviations were attributed to the position error of the scanning stage. In addition, the combined technique with spectrally-resolved interferometry was also discussed to improve the measurement accuracy of the system.