Design And Implementation Of Laser Interferometric Signal Processing Algorithm

As the core of the information technology industry,the integrated circuit industry is a leading industry supporting economic and social development.Laser interferometry is one of the most accurate measurement methods.Because the heterodyne grating interferometer has the characteristics of high resolution and high stability,it is widely used in the positioning of the moving stage in the lithography system.Signal processing of the reference and measurement signals generated by the grating interferometer is crucial to improving the resolution of the grating interferometer and reducing nonlinear errors.Starting from the measurement principle of the grating interferometer,this paper analyzes the characteristics of the reference and measurement signals of the grating interferometer,and designs and implements a processing algorithm for the laser interference signal.The pre-processing module is designed for the noise in the reference and measurement signals.In the pre-processing module,a dynamic filter composed of a real-time frequency measurement module and a variable coefficient filter is designed to solve the problems of large noise and large frequency range of the measurement signal.After the measurement signal is input,the frequency of the signal is measured in real time and accurately by the frequency measurement module.According to the frequency of the signal,the coefficients of the variable filter are changed dynamically in real time,so that the signal is in the passband of the filter.When designing filter coefficients,the sampling frequency approximation method and windowing method will not cause sudden changes in signal amplitude and phase when the coefficients change,so as to realize the filtering under the premise of ensuring that the measurement signal in a large frequency range can pass through the filter The passband of the device is narrow and the suppression effect on noise is better.Aiming at the problem of nonlinear error in grating interferometer,the model of nonlinear error is established and the algorithm of nonlinear error separation and compensation is proposed.The main error sources of the nonlinear error are analyzed,and the influence of the three errors on the measurement signal,including the laser x,y axis angle error and the dual-frequency laser non-orthogonal error,the polarization beam splitter light leakage error and the ghost reflection,is analyzed through simulation.The influence of the z-axis angle error of the laser on the high-order nonlinear error caused by ghost reflection is analyzed when the grating is not parallel to the polarization beam splitter and there are two relative motions in x and z directions.The mechanism of the above four sources of error is summarized and the parameter value ranges of the four sources of nonlinear error are given.A nonlinear error compensation method based on cross-correlation coefficient is proposed.By the maximum value of the cross-correlation coefficient,the frequency multiplication and phase modulation of the phase signal generate structural errors.The nonlinear error is finally suppressed by subtracting the phase signal from the construction error.In the actual measurement environment,combined with a high-precision motion table equipped with a quadruple-pass dual-frequency grating interferometer,the performance tests of the signal processing algorithms are completed.The maximum deviation of the phase increment of the algorithm is not greater than 6mrad,and the 1024 subdivision of the singlecycle phase is achieved,and the system resolution reaches 0.15 nm.After nonlinear error compensation,one standard deviation of nonlinear error is reduced to 2.36 nm.