Rotating compensator spectroscopic ellipsometry based on frequency division multiplexing with retardation calibration

Spectroscopic ellipsometry (SE) is widely used to obtain valuable information about materials such as optical constants or film thickness in a non-destructive way. Various types of SE, each possessing distinct characteristics, have been studied for specific applications. Here, we theoretically and experimentally demonstrate Frequency Division Multiplexing Rotating Compensator Spectroscopic Ellipsometry (FDM-RCSE) by using the frequency division multiplexing (FDM) technique and a rotating compensator with retardation calibration. By utilizing lasers with multiple wavelengths and a spectrally integrating detector, FDM-RCSE enables the simultaneous measurement of three ellipsometry transfer quantities (ETQ) of materials at multiple wavelengths without the need for spectroscopy or switching between wavelengths. This method provides more comprehensive optical material properties such as depolarization and the rotation direction of the elliptical polarization of the measured beam compared to a conventional rotating polarizer ellipsometer. To evaluate the performance of the novel FDM-RCSE technique, the thicknesses of SiO₂ films on a Si wafer were measured by determining the ETQ values via FDM-RCSE and compared to a commercially available SE instrument, resulting in a measured thickness difference between both ellipsometers of less than 2 Å on average and high measurement reproducibility. Consequently, it is demonstrated that the FDM technique can be effectively applied to ellipsometry employing compensators with retardation calibration, providing a versatile alternative measurement method in the field of SE.