Method and apparatus for visual inspection

• US 8,131,058 B2
• Filed: 07/20/2006
• Issued: 03/06/2012
• Est. Priority Date: 07/22/2005
• Status: Expired due to Fees

• Current Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Inventors: Shimura, Kei
• Primary Examiner(s): LEE, JOHN W
• Application Number:
  US11/489,472
• Publication Number:
  US 20070019858A1
• Time in Patent Office: 2,056 Days
• Field of Search: 382/149
• US Class Current: 382/149
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

In the case of die-to-die comparison, threshold processing units process the differential image between the image of a sample chip and the images of left and right adjacent chips using a second threshold value lower than a first threshold value thereby to determine a defect candidate for the sample chip. Further, threshold processing units process the differential image using the first threshold value. The defect candidates which develops a signal not smaller than the first threshold is detected as a defect. Also in the cell-to-cell comparison, the differential image is first processed by the second threshold value to determine a defect candidate, and the differential image is further processed by the first threshold value. The defect candidates which develops a signal not smaller than the first threshold value is detected as a defect.

Claims

1. A defect inspection method comprising steps of:

acquiring first, second and third images of an object, which is a semiconductor wafer having a plurality of chips formed with the same wiring pattern, to be inspected using an image acquisition unit;

receiving the first, second and third images from the image acquisition unit at an image input unit;

sending the first image and the second image to a first image comparator at the image input unit;

sending the second image and the third image to a second image comparator at the image input unit;

obtaining a first differential image from an absolute value of difference which is calculated by subtracting said second image from said first image at the first image comparator;

obtaining a second differential image from an absolute value of difference that is calculated by subtracting said third image from said second image at the second image comparator;

a first processing step, at a first threshold processing unit, processing the first differential image with a first threshold value to determine whether a pixel value of each pixel of the first differential image exceeds the first threshold value or not;

a second processing step, at a second threshold processing unit, processing the first differential image with a second threshold value to determine whether a pixel value of each pixel of the first differential image exceeds the second threshold value or not, wherein said second threshold value is lower than the first threshold value and set to a level exceeded by a pixel value which can be a potential defect even when the pixel value is reduced by at least one of a noise of an imaging device and a vibration of a stage;

a third processing step, at a third threshold processing unit, processing the second differential image with the first threshold value to determine whether a pixel value of each pixel of the second differential image exceeds said first threshold value or not;

a fourth processing step, at a fourth threshold processing unit, processing the second differential image with the second threshold value to determine whether a pixel value of each pixel of the second differential image exceeds said second threshold value or not;

determining, at a defect candidate determining unit, pixels exceeding the second threshold value in both the second and the fourth processing steps as defect candidates; and

determining a presence or absence of a defect based on the defect candidates, sent from the defect candidate determining unit, by determining the defect candidates, which is higher than the first threshold value in at least one of the first and third processing steps, as the defect.

2. An inspection apparatus comprising:

an image data acquisition unit acquiring first, second and third images of an object, which is a semiconductor wafer having a plurality of chips formed with the same wiring pattern, to be inspected;

an image input unit receiving the first, second and third images from the image acquisition unit at an image input unit, sending the first image and the second image to a first image comparator and sending the second image and the third image to a second image comparator;

the first image comparator to obtain a first differential image from an absolute value of difference which is calculated by subtracting said second image from said first image obtained from the image data acquisition unit;

the second image comparator to obtain a second differential image from an absolute value of difference which is calculated by subtracting said third image from said second image obtained from the image data acquisition unit;

a first threshold processing unit processing the first differential image using a first threshold value to determine whether a pixel value of each pixel of the first differential image exceeds the first threshold value or not;

a second threshold processing unit processing the first differential image using a second threshold value to determine whether a pixel value of each pixel of the first differential image exceeds the second threshold value or not, wherein said second threshold value is lower than the first threshold value and set to a level exceeded by a pixel value which can be a potential defect even when the pixel value is reduced by at least one of a noise of an imaging device and a vibration of a stage;

a third threshold processing unit processing the second differential image using the first threshold value to determine whether a pixel value of each pixel of the second differential image exceeds said first threshold value or not;

a fourth threshold processing unit processing the second differential image using the second threshold value to determine whether a pixel value of each pixel of the second differential image exceeds said second threshold value or not;

a defect candidate determining unit determining pixels exceeding the second threshold value in both the second and fourth processing units as defect candidates; and

a defect detection unit determining a presence or absence of a defect based on the defect candidates, sent from the defect candidate determining unit, by determining the defect candidates, which is higher than the first threshold value in at least one of the first and third processing steps, as the defect.