Method and apparatus for macro defect detection using scattered light
First Claim
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1. A method for detecting macro defects on a sample surface comprising the steps of:
- forming a first edge enhanced image of a reference;
directing light from a light source onto said sample surface at an oblique angle wherein said sample surface corresponds to said reference;
detecting light from said light source scattered by said sample surface;
forming a test image of said sample surface from the scattered light;
performing an edge enhancement of said image to form a second edge enhanced image;
forming a difference image by subtracting said first edge enhanced image from said second enhanced image;
forming a thresholded difference image by applying a pre-selected threshold method to said difference image, wherein said thresholded difference image further comprises an array of pixels; and
determining a presence or absence of macro defects wherein each pixel or contiguous group of pixels, of said thresholded difference image having a gray scale value in excess of a value determined by said threshold method is defined as a macro defect.
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Abstract
Macro defects in a processed or partly processed semiconductor wafer, liquid crystal display element, disk drive element or the like, are detected using scattered light. By use of automated image processing techniques, a reference image and a sample image are formed from the scattered light and edge enhanced. A difference image is formed by comparing the edge enhanced reference and sample images. The difference image is evaluated using one or more automated image processing techniques such as thresholding, morphological transformations and blob analysis to identify macro defects.
134 Citations
20 Claims
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1. A method for detecting macro defects on a sample surface comprising the steps of:
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forming a first edge enhanced image of a reference; directing light from a light source onto said sample surface at an oblique angle wherein said sample surface corresponds to said reference; detecting light from said light source scattered by said sample surface; forming a test image of said sample surface from the scattered light; performing an edge enhancement of said image to form a second edge enhanced image; forming a difference image by subtracting said first edge enhanced image from said second enhanced image; forming a thresholded difference image by applying a pre-selected threshold method to said difference image, wherein said thresholded difference image further comprises an array of pixels; and determining a presence or absence of macro defects wherein each pixel or contiguous group of pixels, of said thresholded difference image having a gray scale value in excess of a value determined by said threshold method is defined as a macro defect. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of scattered light macro defect detection comprising the steps of:
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training a macro defect detection apparatus, wherein said training comprises forming a reference template image; acquiring a sample image of a sample surface from scattered light with a camera; forming an edge enhanced image of said sample image; normalizing said edge enhanced image to said reference template image; forming a difference image of said normalized edge enhanced image and said reference template; forming a thresholded difference image of said difference image; performing a direct blob analysis of said thresholded difference image or a differential blob analysis of said difference image and said thresholded difference image; and determining a presence or absence of macro defects using said direct or differential Blob analysis and thresholded difference image; wherein forming said edge enhanced image, normalizing said edge enhanced image, forming said difference image, forming said thresholded difference image, performing said direct or differential blob analysis and said determining a presence or absence of macro defects is performed by said macro defect detection apparatus. - View Dependent Claims (12, 13, 14, 15)
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16. An apparatus to inspect for macro defects on a substrate comprising:
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a support for holding said substrate; a light source for directing light onto a surface of said substrate when said substrate is on said support; a detector located to receive light scattered from said surface of said substrate; and an automated processor coupled to said detector for comparing an edge enhanced image of said surface to an edge enhanced reference template, thereby to determine a presence or absence of macro defects on the surface of the substrate. - View Dependent Claims (17, 18, 19, 20)
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Specification