Silicon wafer thickness measurement using terahertz time domain spectroscopy main

When measuring optical material parameters with terahertz spectroscopy the accuracy of the material parameters measured depends strongly on knowing and supplying the precise sample thickness when processing the raw terahertz data. It turns out that the terahertz data itself typically does contain accurate information as to the sample thickness. In this study we determine the accuracy with which the exact thickness of nominally 500 μm silicon wafers can be measured using terahertz time domain spectroscopy (THz-TDS). We analyze and compare the resolution of 5 different approaches for determining sample thickness using THz-TDS data including three methods previously proposed in the literature, one novel approach and a refined implementation of an existing approach. The quantitative results and analyses of methods we present will be useful in developing far-infrared optical metrology. Conversely the quantitative results presented in this study can be used to relate uncertainty in sample thickness to uncertainty in the measured terahertz data both in the time domain and frequency domain (phase and amplitude).