Pattern inspection method and its apparatus

Abstract

A pattern inspection technique using compared images is improved in that the amount of displacement between compared images can be detected precisely and with high speed, thereby making it possible to detect in high-speed and inspect particles with high sensitivity. To achieve this technique, each of an inspected image and a reference image is divided into a plurality of small regions, and the amount of displacement between the whole inspected image and the whole reference image is determined by using reliable information of displacement between the divided images of both images. In addition, the displacement-computed regions, the computation order and the image search range are previously scheduled.

What is claimed is:  
     
         1 . A pattern inspection method comprising the steps of: 
 storing an image to be inspected corresponding to a pattern-formed region of an object to be inspected;    storing a reference image corresponding to a pattern-formed reference region that is used for comparison;    dividing each of said stored inspected image and reference image into a plurality of regions;    computing displacements between some divided images of said inspected image subjected to said division and those of said reference image corresponding to said divided images;    computing a displacement between said whole inspected image and said whole reference image from the results of said computation of said displacements between said divided images;    aligning said whole inspected image and said whole reference image on the basis of said computed displacement between both images thereof;    comparing said whole inspected image and said whole reference image aligned with each other to detect the difference between them; and    displaying the results of having detected said difference on a screen.    
     
     
         2 . A pattern inspection method according to  claim 1 , wherein said some divided images of said inspected image and said corresponding divided images of said reference image from which said amounts of displacement are computed are those of previously selected regions.  
     
     
         3 . A pattern inspection method according to  claim 1 , wherein said some divided images of said inspected image and said corresponding divided images of said reference image from which said amounts of displacement are computed are those selected on the basis of the pattern information of the divided images of said image divided into said plurality of regions.  
     
     
         4 . A pattern inspection method according to  claim 1 , wherein said some divided images of said inspected image and said corresponding divided images of said reference image from which said amounts of displacement are computed are those selected from said divided images of said plurality of regions on the basis of the shape, density and direction of said pattern information.  
     
     
         5 . A pattern inspection method according to  claim 1 , wherein said some divided images of said inspected image and said corresponding divided images of said reference image from which said amounts of displacement are computed are those of said regions having a relatively large number of patterns.  
     
     
         6 . A pattern inspection apparatus comprising: 
 storage means for storing an inspected image corresponding to a pattern-formed region of an object to be inspected, and a reference image corresponding to a pattern-formed reference region to be used for comparison;    image-dividing means for dividing each of said inspected image and said reference image stored in said storage means into a plurality of regions;    divided-image displacement-detecting means for computing the amounts of displacement between some divided images of said inspected image divided into said plurality of regions by said image-dividing means and the corresponding ones of said divided images of said reference image;    whole-image displacement-detecting means for computing the amount of displacement between said whole inspected image and said whole reference image from the results of having computed the amounts of displacement between said divided images of said both inspected and reference images by said divided-image displacement-detecting means;    alignment means for aligning said whole inspected image and said whole reference image on the basis of said amount of displacement detected between both whole images by said whole-image displacement-detecting means;    detection means for comparing said whole inspected image and said whole reference image aligned by said alignment means to detect the difference between both images; and    display means for displaying on a screen said results of having detected said difference by said detection means.    
     
     
         7 . A pattern inspection apparatus according to  claim 6 , wherein said some divided images of said inspected image and said corresponding divided images of said reference image from which said amounts of displacement are computed by said divided-image displacement-detecting means are those of previously selected regions.  
     
     
         8 . A pattern inspection apparatus according to  claim 6 , wherein said some divided images of said inspected image and said corresponding divided images of said reference image from which said amounts of displacement are computed by said divided-image displacement-detecting means are those selected on the basis of the pattern information of the divided images of said image divided into said plurality of regions by said image-dividing means.  
     
     
         9 . A pattern inspection apparatus according to  claim 6 , wherein said some divided images of said inspected image and said corresponding divided images of said reference image from which said amounts of displacement are computed by said divided-image displacement-detecting means are those selected from said divided images of said plurality of regions on the basis of the shape, density and direction of said pattern information.  
     
     
         10 . A pattern inspection apparatus according to  claim 6 , wherein said some divided images of said inspected image and said corresponding divided images of said reference image from which said amounts of displacement are computed by said divided-image displacement-detecting means are those of regions having a relatively large number of patterns.  
     
     
         11 . A pattern inspection method, comprising the steps of: 
 storing images to be inspected of each region in an object on which a plurality of patterns are formed;    storing images to be compared which correspond to said images to be inspected;    calculating a displacement between said images to be inspected and said images to be compared in the order according to an amplitude of a pattern density in each region;    aligning said image to be inspected and said image to be compared on the basis of said calculated displacement between said both images; and    detecting a difference between said both aligned images.    
     
     
         12 . A pattern inspection method according to the  claim 11 , wherein in the step of calculating, at least one of the order of calculation and the limit of calculation is determined before the calculation.  
     
     
         13 . A pattern inspection method according to the  claim 11 , wherein in the step of calculating, a data of a displacement between said images to be inspected and said images to be compared in a region with a relatively low pattern density is substituted with a data of displacement in a region with a relatively high pattern density.  
     
     
         14 . A pattern inspection method, comprising the steps of: 
 storing images to be inspected of each region in an object on which a plurality of patterns are formed;    storing images to be compared which correspond to said images to be inspected;    calculating a displacement between said images to be inspected and said image to be compared;    aligning said image to be inspected and said image to be compared on the basis of said calculated displacement between said both images; and    detecting a difference between said both aligned images, wherein in the step of calculating, in an area where a pattern density is relatively low, the limit of search for displacement is around a matching portion to be aligned which is calculated from an area where the pattern density is relatively high.    
     
     
         15 . A pattern inspection method according to the  claim 14 , in the step of calculating, at least one of the order of calculation and the limit of calculation is determined before the calculation.  
     
     
         16 . A pattern inspection apparatus comprising: 
 a memory which stores images to be inspected and images to be compared;    a image dividing means which divides said images to be inspected and said images to be compared which correspond to said images to be inspected into a plurality of divided images;    a first calculating means for calculating to provide pattern information of said plurality of divided images;    a selecting unit which selects divided image from said plurality of divided image to calculate a displacement between said divided images to be inspected and said divided images to be compared by using pattern information calculated by said first calculating means;    a search limit determining means for determining a search limit for calculating the displacement between said divided images to be inspected and said divided images to be compared by using said calculated pattern information;    a second calculating means for calculating a displacement within said determined search limit between said divided images to be inspected and said divided images to be compared selected by said selecting unit; and    a third calculating means for calculating displacement between said stored images to be inspected and said stored images to be compared by using information obtained from said second calculation means.    
     
     
         17 . A pattern inspection apparatus comprising: 
 storing means for storing images to be inspected of each region in an object on which a plurality of patterns are formed and images to be compared which correspond to said images to be inspected;    calculating means for calculating a displacement between said images to be inspected and said images to be compared in the order according to an amplitude of a pattern density in each image;    aligning means for aligning said image to be inspected and said image to be compared on the basis of said calculated displacement between said both images; and    detecting means for detecting a difference between both aligned images.    
     
     
         18 . A pattern inspection apparatus according to the  claim 17 , wherein in the calculating means, the displacement between said images to be inspected and said images to be compared is calculated in a region having a relatively high pattern density and a displacement between said images to be inspected and said images to be compared in a region having a relatively low pattern density is substituted with said calculated data of displacement in said region having relatively high pattern density.  
     
     
         19 . A pattern inspection apparatus comprising: 
 storing means for storing images to be inspected of each region in an object on which a plurality of patterns are formed and images to be compared;    a image dividing means which divides said images to be inspected and said images to be compared which correspond to said images to be inspected into a plurality of divided images;    calculating means for calculating a displacement between said divided images to be inspected and said divided images to be compared and said both divided images being selected from a predetermined area;    aligning means for aligning said image to be inspected and said image to be compared on the basis of said calculated displacement between said both divided images; and    detecting means for detecting a difference between said both aligned images.    
     
     
         20 . A pattern inspection apparatus comprising: 
 storing means for storing images to be inspected of each region in an object on which a plurality of patterns are formed and images to be compared which correspond to said images to be inspected;    calculating means for calculating a displacement between said images to be inspected and said image to be compared;    aligning means for aligning said image to be inspected and said image to be compared on the basis of said calculated displacement between said images to be inspected and said image to be compared; and    detecting means for detecting a difference between said images to be inspected and said image to be compared aligned by said aligning means, wherein in the calculating means, in an area where the pattern density is relatively low, the limit of search for displacement is around a matching portion to be aligned calculated from an are where the pattern density is relatively high.