| 摘要 |
A method and system for predicting a signal fluctuation due to a flow of gaseous fluid approximately transverse to an optical path between a stage and an interferometric measuring apparatus for determining a position of the stage in a direction of a stage movement. The method includes acquiring three interferometric signals of three parallel optical beams, lying within the flow of the gaseous fluid, reflected from predetermined portions of the stage, extracting a mutual signal fluctuation caused by fluctuations of the gaseous fluid properties from the three interferometric signals, and predicting a future fluctuation of the interferometric signals using a linear adaptive filter acting on the extracted mutual signal fluctuation. Prior to the processing with the adaptive filter, a low-pass filter removes high frequency stage motions, and an adaptive moving average algorithm removes low frequency stage motions. When applied to a two-moving axis configuration, it is possible to use only two interferometers in each direction because of the redundancy of measuring stage yaw.
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