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The design and operational features are described for a computer-assisted ellipsometer (called ETA for Ellipsometric Thickness Analyzer), developed to provide reliable, real-time measurement of field-effect transistor gate insulator thickness in a manufacturing environment. ETA illuminates the sample with light of fixed polarization and uses a rotating analyzer to measure the polarization of the reflected light. Sample alignment is done automatically by ETA, so that usually no operator adjustments are required. Fourier analysis of the light transmitted by the analyzer is used to reduce noise and enhance measurement precision. In its normal mode of operation (incident light linearly polarized at 45°), ETA can measure single and double-layer films of SiO
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