| 摘要 |
An automatic focusing apparatus comprises a stage holding a substrate, an objective lens disposed facing the substrate surface, an illumination optics illuminating the substrate surface with a spotted light beam from an oblique direction, a photodetector detecting reflected light from the substrate surface, a position detection circuit detecting a vertical position of the substrate surface from an electric signal obtained from the photodetector to output a position signal, a correction circuit monitoring the position signal in real time and subtracting a surplus exceeding a signal change corresponding to a surface shape change of the substrate from the position signal, when a change amount per unit time of the position signal exceeds a predetermined level and outputting a corrected position signal, and a stage control circuit controlling the vertical position of the stage based on the corrected position signal.
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