Defect inspection method and apparatus

Abstract

An inspection method, including: illuminating a light on a wafer on which plural chips having identical patterns are formed; imaging corresponding areas of two chips formed on the wafer to obtain inspection images and reference images with an image sensor; and processing the obtained inspection image and the reference image to produce a difference image which indicates a difference between the inspection image and the reference image and detect a defect by comparing the difference image with a threshold, wherein a threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging peripheral portion of the wafer is different from a threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging central portion of the wafer.

1 . An inspection method, comprising:
 illuminating a light on a wafer on which plural chips having identical patterns are formed;   imaging corresponding areas of two chips formed on the wafer to obtain inspection images and reference images with an image sensor; and   processing the obtained inspection image and the reference image to produce a difference image which indicates a difference between the inspection image and the reference image and detect a defect by comparing the difference image with a threshold,   wherein a threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging peripheral portion of the wafer is different from a threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging central portion of the wafer.   
     
     
         2 . An inspection method according to  claim 1 , wherein said threshold applied to a difference image which is produced by comparing the reference image obtained by imaging peripheral portion of the wafer is higher than said threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging central portion of the wafer. 
     
     
         3 . An apparatus for inspecting a pattern, comprising:
 a stage on which a wafer to be inspected is mounted, and movable at least in one direction;   an illuminator which illuminates a light on the wafer on which plural chips having identical patterns are formed;   an imaging unit which forms and captures an image of corresponding areas of two chips formed on the wafer to obtain inspection images and reference images; and   a processing unit which processes the obtained inspection image and the reference image to produce a difference image which indicates a difference between the inspection image and the reference image and detect a defect by comparing the difference image with a threshold,   wherein said processing unit further including a threshold value estimator to estimate a value of said threshold, and   wherein a threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging peripheral portion of the wafer is different from a threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging central portion of the wafer.   
     
     
         4 . An apparatus for inspecting a pattern according to  claim 3 , wherein said threshold value estimator estimates a value of said threshold so that a threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging peripheral portion of the wafer is higher than a threshold applied to a difference image which is produced by comparing the inspection image and the reference image obtained by imaging central portion of the wafer. 
     
     
         5 . An inspection method according to  claim 1 , wherein the threshold applied to a difference image which is produced by comparing to the inspection image and the reference image obtained by imaging a first area of the chip is different from a threshold applied to a difference image which is produced by comparing the inspection image and the reference image by imaging a second area of the chip.