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Optimized spatial filter for defect detection

  • US 4,153,336 A
  • Filed: 12/21/1976
  • Issued: 05/08/1979
  • Est. Priority Date: 12/22/1975
  • Status: Expired due to Term
First Claim
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1. An apparatus for detecting defects in a pattern having linear straight line features and nonlinear defects comprising:

  • (a) a coherent light source for radiating a coherent light;

    (b) a collimator for collimating the coherent light radiated from said coherent light source into a light beam with a predetermined diameter and leading it to said pattern;

    (c) a transform lens for transforming the intensity distribution of transmitted or reflected light from said pattern into a Fourier-transformed pattern; and

    (d) a spatial filter placed on the Fourier-transform plane of said transform lens and preventing transmission of the coherent light having information of said linear straight line features of said pattern, said filter having a light intercepting area defined by a plurality of arm sections extending in the horizontal and vertical directions from a common point of intersection correspondingly to the linear straight line features of said subject pattern, a portion lying between two adjacent arms being of a hyperbola-shape protruding toward the center of said filter wherein the coherent light intercepting area of said spatial filter is defined according to
    
    
    space="preserve" listing-type="equation">(|X|-A)(|Y|-A)≦

    B.sup.2where X and Y indicate the X-axis and Y-axis of said filter respectively, said X- and Y-axes corresponding to the respective axes of the arms of said filter extending in the horizontal and vertical directions, X=Y=0 is indicative of the center of said filter, and both A and B are positive constants, wherein said constants A and B are given as values complying with
    
    
    space="preserve" listing-type="equation">A×

    B≃

    1/64 Lwhere L is the side length of an effective pupil or the diameter of an effective pupil of said spatial filter.

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