Optimized spatial filter for defect detection
First Claim
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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Abstract
An apparatus for detecting the defects composed of non-linear components of a subject pattern, includes a laser source for illuminating the subject pattern by a laser beam, a Fourier-transform lens for projecting an information light from the pattern through a spatial filter onto a screen. The filter is placed on the Fourier-transform plane of the Fourier-transformed information light for intercepting the coherent light having information of the linear components, the filter having arm sections extending correspondingly to the linear components of said normal pattern, the outer periphery of said arm sections including curved sections protruding toward the intersecting point of the arms.
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Citations
10 Claims
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1. An apparatus for detecting defects in a pattern having linear straight line features and nonlinear defects comprising:
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(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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification