Pattern inspection method and its apparatus

Abstract

In a pattern inspection apparatus for comparing images of corresponding areas of two patterns, which are formed so as to be identical, so as to judge that a non-coincident part of the images is a defect, the influence of unevenness in brightness of patterns caused by a difference of thickness or the like is reduced, whereby highly sensitive pattern inspection is realized. In addition, high-speed pattern inspection can be carried out without changing the image comparison algorithm. For this purpose, the pattern inspection apparatus operates to perform comparison processing of images in parallel in plural areas. Further, the pattern inspection apparatus operates to convert gradation of an image signal among compared images using different plural processing units such that, even in the case in which a difference of brightness occurs in an identical pattern among images, a defect can be detected correctly.

1 . An inspection method, comprising the steps of:
 illuminating a specimen with light, said specimen being placed on a continuously moving table and on which plural chips having identical patterns are formed;   capturing images of the specimen by imaging the specimen with an image sensor while said specimen is continuously moving in one direction and obtaining an inspection image and a reference image; and   processing said inspection image and said reference image obtained at the step of capturing to detect defects,   wherein in the step of processing, said inspection image and said reference image are periodically divided into plural reference sub-images and inspection sub-images and each of the divided reference sub-images and inspection sub-images are input into one of plural processors to detect defects in parallel.   
   
   
       2 . An inspection method according to  claim 1 , wherein in the step of capturing, said image sensor includes plural taps and said image sensor outputs said obtained inspection image and reference image from said plural taps in parallel. 
   
   
       3 . An inspection method according to  claim 1 , wherein the processing step includes the sub-steps of:
 correcting a brightness difference between the reference sub-images and the inspection image sub-images, and   detecting a defect on the specimen by using the brightness difference corrected reference sub-images and the inspection image sub-images.   
   
   
       4 . An inspection method according to  claim 3 , wherein the step of correcting a brightness difference includes correcting a first brightness difference which occurs as characteristics inherent in the inspection apparatus and a second brightness difference which occurs at random depending upon the pattern formed on the specimen. 
   
   
       5 . An inspection method, comprising the steps of:
 illuminating a specimen with light, said specimen being placed on a continuously moving table and on which plural chips having identical patterns are formed;   capturing images of the specimen by imaging the specimen with an image sensor while said specimen is continuously moving in one direction and obtaining an inspection image and a reference image; and   processing said inspection image and reference image obtained at the step of capturing to detect defects,   wherein in the step of processing, said inspection image and reference image are divided into plural inspection sub-images and reference sub-images by movement of the specimen and each of the divided inspection sub-images and reference sub-images are input into one of plural processors to detect defects in parallel.   
   
   
       6 . An inspection method according to  claim 5 , wherein in the step of capturing, said image sensor includes plural taps and said image sensor outputs said obtained inspection image and reference image from said plural taps in parallel. 
   
   
       7 . An inspection method according to  claim 5 , wherein the processing step includes the sub-steps of:
 correcting a brightness difference between the inspection sub-images and the reference sub-images, and   detecting a defect on the specimen by using the brightness difference corrected inspection sub-images and the reference image sub-images.   
   
   
       8 . An inspection method according to  claim 7 , wherein the step of correcting a brightness difference includes correcting a first brightness difference which occurs as characteristics inherent in the inspection apparatus and a second brightness difference occurs at random depending upon the pattern formed on the specimen. 
   
   
       9 . An inspection apparatus, comprising:
 a table for mounting a specimen, said table being continuously movable in at least one direction;   an illuminating unit which illuminates the specimen mounted on the table with a light;   an image capturing unit which forms an image of the specimen on which plural chips having identical patterns are formed and placed on a continuously moving table, and captures the formed image with a sensor having plural pixels to obtain inspection image and reference image; and   a processing unit having plural processors to process the obtained inspection image and reference image to detect defects,   wherein the processing unit periodically divides the inspection image and the reference image into plural inspection sub-images and reference sub-images and each of the divided inspection sub-images and reference sub-images are input into one of the plural processors to detect defects in parallel.   
   
   
       10 . An inspecting apparatus according to  claim 9 , wherein said sensor is a TDI image sensor having plural taps to output signals in parallel. 
   
   
       11 . An inspecting apparatus according to  claim 9 , wherein each of said plural processors installs a first brightness difference corrector which corrects a first brightness difference caused by at least one of a difference in a sensitivity of each pixel of the image sensor, a difference in the amount of accumulated light due to unevenness of the speed of movement of the stage and fluctuation in an illumination light, and a second brightness difference corrector which corrects a second brightness difference caused by a slight difference in the thickness of thin film among chips formed on the specimen. 
   
   
       12 . An inspection apparatus, comprising:
 a table for mounting a specimen, said table being movable at least in one direction;   an illuminating unit which illuminates the specimen mounted on the table with a light, said specimen being placed on a continuously moving table and on which plural chips having identical patterns are formed;   an image capturing unit which forms an image of the specimen and captures the formed image with a sensor having plural pixels to obtain an inspection image and a reference image; and   a processing unit having plural processors to process the obtained inspection image and reference image to detect defects,   wherein the processing unit divides the reference image and the inspection image into plural inspection sub-images and reference sub-images by the movement of the table and each of the divided inspection sub-images and reference sub-images are input into one of the plural processors to detect defects in parallel.   
   
   
       13 . An inspecting apparatus according to  claim 10 , wherein said sensor is a TDI image sensor having plural taps to output signals in parallel. 
   
   
       14 . An inspecting apparatus according to  claim 10 , wherein each of said plural processors installs a first brightness difference corrector which corrects a first brightness difference caused by at least one of a difference in a sensitivity of each pixel of the image sensor, a difference in the amount of accumulated light due to unevenness of the speed of movement of the stage and fluctuation in an illumination light, and a second brightness difference corrector which corrects a second brightness difference caused by a slight difference in the thickness of thin film among chips formed on the specimen.