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System and method for compensating instability in an autofocus system

  • US 9,097,851 B2
  • Filed: 02/18/2014
  • Issued: 08/04/2015
  • Est. Priority Date: 03/31/2009
  • Status: Active Grant
First Claim
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1. A method for compensating instability in an optical autofocus system, which optical autofocus system uses light directed at and reflected from a substrate to determine changes in a height position of the substrate, the method comprising:

  • a. deflecting a reference beam component of said light by a beam-deflecting optic located a predetermined distance from the substrate to form a deflected reference beam, said predetermined distance defining a first space;

    b. providing a reflector, spaced from the beam-deflecting optic by said predetermined distance, to define a second space between the reflector and the beam-deflecting optic;

    c. directing a measurement beam component of said light at the substrate to form a reflected measurement beam that is directed from the substrate through the first space between the substrate and the beam-deflecting optic, while directing the deflected reference beam at the reflector to form a reflected reference beam that is directed from the reflector through the second space;

    d. returning the reflected reference beam and the reflected measurement beam such that the reference beam and the reflected measurement beam emerge substantially collinearly from the beam-deflecting optic;

    e. detecting the reflected reference beam and the reflected measurement beam and producing from said beams information enabling compensation for changes in the height position of the substrate, said changes defined by instabilities in at least one of the optical autofocus system and environmental factors; and

    f. propagating the deflected reference beam formed by the beam-deflecting optic and the reflected reference beam formed by the reflector along a first plane, which first plane crosses a second plane, said second plane defined by the measurement beam component incident onto the substrate and the reflected measurement beam formed at the substrate.

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