Optimized spatial filter for defect detection

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 (|X|-A)(|Y|-A)≦B.sup.2 where 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 A×B≃1/64 L where L is the side length of an effective pupil or the diameter of an effective pupil of said spatial filter.

Claim 2

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 (|X|-A)(|Y|-A)≦B.sup.2 where 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 A×B≃1/64 L where L is the side length of an effective pupil or the diameter of an effective pupil of said spatial filter.