Method of and apparatus for detecting pattern defects
First Claim
1. A method of detecting pattern defects by comparing a unit area of a two-dimensional object pattern, said unit area having a prescribed size and formed by digitized picture signals obtained sequentially along scanning lines, with a plurality of areas of a digitized two-dimensional master pattern, said method comprising the steps of:
- defining a reference area by expanding the periphery of an area of said master pattern to positionally correspond to an area of said object pattern expanded by a predetermined number of pixels for defining said plurality of said master pattern areas, each of said master pattern areas being two-dimensionally misregistered pixel-by-pixel by prescribed different amounts over the expanded area; and
comparing the digitized signals of said master pattern areas with the digitized signals of said unit area of said object pattern corresponding to said master pattern areas to perform defect detection by;
(a) while scanning defect inspection windows, sized to contain a plurality of pixels, over said unit area of said object pattern and said master pattern areas, comparing each one of said plurality of master pattern areas with said unit area of said object pattern to determine for each pair-wise comparison that said patterns are mismatched when all digitized signals representing corresponding pixels included in said windows are mismatched in any scanning position;
(b) determining that said object pattern is defective when said object pattern area is determined to be mismatched with respect to each one of said plurality of master pattern areas; and
(c) determining that said object pattern is not defective when said object pattern area is determined not to be mismatched with respect to at least one of said master pattern areas.
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Accused Products
Abstract
The periphery of an area of a master pattern is expanded by a required number of pixels to define a plurality of master pattern areas two-dimensionally misregistered pixel by pixel, for performing pattern comparison of the respective master pattern areas with an area of an object pattern. The object pattern is deemed defective when all of the comparisons indicate pattern mismatches. The pattern is deemed not defective when at least one comparison indicates a pattern match. Thus, even if an inspected object includes misregistration errors, pattern defects can be detected with high accuracy.
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Citations
14 Claims
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1. A method of detecting pattern defects by comparing a unit area of a two-dimensional object pattern, said unit area having a prescribed size and formed by digitized picture signals obtained sequentially along scanning lines, with a plurality of areas of a digitized two-dimensional master pattern, said method comprising the steps of:
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defining a reference area by expanding the periphery of an area of said master pattern to positionally correspond to an area of said object pattern expanded by a predetermined number of pixels for defining said plurality of said master pattern areas, each of said master pattern areas being two-dimensionally misregistered pixel-by-pixel by prescribed different amounts over the expanded area; and comparing the digitized signals of said master pattern areas with the digitized signals of said unit area of said object pattern corresponding to said master pattern areas to perform defect detection by; (a) while scanning defect inspection windows, sized to contain a plurality of pixels, over said unit area of said object pattern and said master pattern areas, comparing each one of said plurality of master pattern areas with said unit area of said object pattern to determine for each pair-wise comparison that said patterns are mismatched when all digitized signals representing corresponding pixels included in said windows are mismatched in any scanning position; (b) determining that said object pattern is defective when said object pattern area is determined to be mismatched with respect to each one of said plurality of master pattern areas; and (c) determining that said object pattern is not defective when said object pattern area is determined not to be mismatched with respect to at least one of said master pattern areas. - View Dependent Claims (2)
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3. An apparatus for detecting pattern defects by comparing a two-dimensional object pattern with a two-dimensional master pattern for each unit area of a prescribed size, said apparatus comprising:
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means for inputting digitized signals of said object pattern in a sequential manner; means for reading digitized signals of said master pattern in a sequential manner from a memory synchronously with said inputted digitized signals of said object pattern; first extraction means for extracting digitized signals in a specific area of said object pattern in a sequential manner along the scanning direction synchronously with said inputted digitized signals of said object pattern; second extraction means for defining an expanded area by expanding the periphery of a specific area of said master pattern by a required number of pixels to positionally correspond to said specific area whose digitized signals are extracted by said first extraction means and extracting from said memory, in a sequential manner along the scanning direction, digitized signals in a plurality of specific areas of said master pattern which are two-dimensionally misregistered pixel by pixel by prescribed different amounts over said expanded area; a plurality of comparison/decision means for sequentially pair-wise comparing said digitized signals from prescribed size window areas in said specific area of said object pattern extracted by said first extraction means with said digitized signals from corresponding window areas of said prescribed size in each of said specific areas of said master pattern extracted by said second extraction means to provide and store a mismatch result when all of said digitized signals of corresponding pixels in said pair of specific areas are mismatched in at least one portion in any scanning position; and first decision means for determining that said prescribed size area of said object pattern is defective when all of said comparison/decision means hold mismatch results and for determining that said prescribed size area of said object pattern is not defective when at least one of said comparison/decision means does not hold a mismatch result. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification