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Automatic focusing apparatus

  • US 20050052634A1
  • Filed: 07/23/2004
  • Published: 03/10/2005
  • Est. Priority Date: 07/25/2003
  • Status: Active Grant
First Claim
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1. An automatic focusing apparatus comprising:

  • a stage which holds a substrate and which is movable in a horizontal direction and a vertical direction;

    an objective lens disposed facing a surface of the substrate;

    a first illumination optics which illuminates the surface of the substrate with at least one spotted light beam from an oblique direction;

    a first photodetector which detects reflected light from the surface of the substrate to output a first electrical signal;

    a first position detection circuit which detects a vertical position of the surface of the substrate from the first electric signal to output a first position detection signal;

    a correction circuit which monitors the first position detection signal in real time and which subtracts a surplus exceeding a signal change corresponding to a surface shape change of the substrate from the first position detection signal, when a change amount per unit time of the first position detection signal exceeds a first predetermined level, to output a corrected position signal; and

    a stage control circuit which controls the vertical position of the stage based on the corrected position signal.

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