A free-space method for measurement of complex permittivity of silicon wafers at microwave frequencies

A non-destructive, non-contact technique has been developed to characterize p-type and n-type silicon semiconductor wafers at microwave frequencies. The measurement system consists of a pair of spot-focusing horn lens antennas, mode transitions, coaxial cables and a vector network analyser (VNA). In this paper, the free-space reflection and transmission coefficients, S₁₁ and S₂₁, for a normally incident plane wave, are measured for a silicon wafer sandwiched between two teflon plates which are quarter-wavelength at midband. The actual reflection and transmission coefficient, S₁₁ and S₂₁, of the silicon wafers are calculated from the measured S₁₁ and S₂₁ of the teflon plate-silicon wafer-teflon plate assembly in which the complex permittivity and thickness of the teflon plates are known. From the complex permittivity, the resistivity and conductivity can be obtained. Results are reported in the frequency range of 11-12.5 GHz. The values of the dielectric constant obtained were close to published values for silicon wafers.