We describe a polarizer–compensator–sample–analyzer (PCSA) null ellipsometer in which a variable retarder is used as the compensator and either the polarizer or the analyzer is held at a fixed azimuthal angle. Ellipsometric angles ψ and Δ are determined directly from the azimuth of the rotating component and the compensator delay, respectively. A Soleil–Babinet compensator with quartz plates is used as the variable delay element and the delay at any wavelength is calculated from the independently measured delay at and a knowledge of the dispersion of quartz. The thicknesses of thin silicon di oxide films on a silicon wafer were determined both spectroscopically and at a single wavelength and show excellent agreement with those determined using a traditional single wavelength PCSA null ellipsometer.
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