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Method of and apparatus for detecting foreign substances

  • US 5,225,886 A
  • Filed: 09/18/1990
  • Issued: 07/06/1993
  • Est. Priority Date: 09/18/1989
  • Status: Expired due to Term
First Claim
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1. A method of detecting a foreign substance on a patterned object having a plane surface and a raised pattern formed on said plane surface by illuminating said patterned object and detecting via an optical system light reflected by said patterned object to detect said foreign substance in distinction from said raised pattern, comprising the steps of:

  • applying oblique illumination onto an oblong area of the plane surface of said patterned object having said raised pattern formed thereon in an oblique direction relative to an optical axis of said optical system, and applying vertical illumination vertically onto the oblong area of the plane surface of said patterned object along the optical axis of said optical system;

    receiving, via said optical system, light from said oblique illumination reflected and scattered from the oblong area and light from said vertical illumination reflected and scattered from the oblong area, separating the received scattered lights from the received reflected lights by shutting off the received reflected lights, and independently detecting the separated scattered lights with one-dimensional photodetecting means to obtain a first detection signal based on the scattered light from the oblique illumination and a second detection signal based on the scattered light from the vertical illumination, wherein the oblong area is large enough to contain an image of an entire photodetecting area of said one-dimensional photodetecting means projected onto the plane surface of said patterned object through said optical system; and

    non-additively processing said first detection signal and said second detection signal to cancel a component of said first detection signal and said second detection signal due to light scattered from said raised pattern and detect said foreign substance.

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