Apparatus for inspecting defects in a periodic pattern
First Claim
1. An apparatus for inspecting defects in a periodic pattern comprising:
- a light source for producing a coherent light directed to the periodic pattern to be inspected;
a fourier transformer for Fourier-transforming a light including the information of the periodic pattern and defects; and
filtering means positioned at the backward focal point of the Fourier transformer and having a light block areas for blocking mainly the periodic pattern information component of the light passed the Fourier transformer and a ring-like light transmission area allowing mainly the defects information component of the light to pass therethrough, the light block area including a first light block area of spot like shape which prevents a transmission of the zeroth order diffraction light transmitted through the Fourier transformer and a second light block area which is disposed around the first area and prevents a transmission of the first and higher order diffraction light transmitted through the Fourier transformer.
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Accused Products
Abstract
An apparatus for inspecting a defect in a periodic pattern on an object is provided with a laser device for projecting a laser beam toward the object. A mechanism further included in the defect inspecting apparatus rotates the object in a plane orthogonal to an optical path of the laser beam while moving in the same plane. A spatial band-pass filter is located at the backward focal plane of a lens for Fourier-transforming the laser beam including the information of the periodic pattern and a defect, the laser beam coming from the object. The band-pass filter has a spot-like area for blocking the zeroth order diffraction light transmitted through the periodic pattern a peripheral light blocking area for blocking the first and higher order diffracted light beams, and a ring-like light transmission area permitting the light beam component including the information of a defect to pass therethrough, the light transmission area being located between the spot-like area and the peripheral area. A photo-electric converter for picking up the light beam component including the defect information transmitted through the filter is located on an image forming plane where an image of the object is formed by a lens.
83 Citations
11 Claims
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1. An apparatus for inspecting defects in a periodic pattern comprising:
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a light source for producing a coherent light directed to the periodic pattern to be inspected; a fourier transformer for Fourier-transforming a light including the information of the periodic pattern and defects; and filtering means positioned at the backward focal point of the Fourier transformer and having a light block areas for blocking mainly the periodic pattern information component of the light passed the Fourier transformer and a ring-like light transmission area allowing mainly the defects information component of the light to pass therethrough, the light block area including a first light block area of spot like shape which prevents a transmission of the zeroth order diffraction light transmitted through the Fourier transformer and a second light block area which is disposed around the first area and prevents a transmission of the first and higher order diffraction light transmitted through the Fourier transformer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus for inspecting defects in a periodic pattern, comprising:
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means for converting an image of a periodic pattern to be inspected into digital signals including defect signals and periodic pattern signals; means for fourier-transforming the digital signals from said converting means; filter means having a memory storing pattern data for processing the digital signals according to the pattern data, thus filtering only the defect signals included in the digital signals, said pattern data each consisting of a block area data for blocking periodic pattern information and a ring-like area data for transmitting defect information, said block area data containing a first area corresponding to a first-order diffraction image formed by fourier-transforming the image of the periodic pattern and a second area data corresponding to a higher-order diffraction image; means for inversely fourier-transforming the defect signals from the filter means; and means for displaying defects according to the defect signals from said inverse fourier-transforming means.
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Specification