Adaptive Nonlinearity Compensation of Heterodyne Laser Interferometer
With its outstanding ultra-precise resolution, the heterodyne laser interferometer systems are commonly used in semiconductor manufacturing industry. However, the periodical nonlinearity error caused from frequency-mixed cross talks limits the accuracy in nanometer scale. In this paper to improve the accuracy of laser interferometer system, we propose an adaptive nonlinearity compensation algorithm using RLS (recursive least square) method. As a reference signal, the capacitance displacement sensor mounted on a linear piezo-electric transducer gives a feedback information on how to transform the elliptical phase into a circular one.
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