Method and apparatus for visual inspection

• US 8,126,259 B2
• Filed: 04/07/2010
• Issued: 02/28/2012
• 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
• Application Number:
  US12/755,596
• Publication Number:
  US 20100194876A1
• Time in Patent Office: 692 Days
• Field of Search: None
• 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. An inspection apparatus comprising:

an image data acquisition unit acquiring a first image of an object, which has a repetitive pattern structure, to be inspected;

an image input unit inputting the first image of the object acquired by the image data acquisition unit to an image comparator, generating a second image shifted from the first image of the object acquired by the image data acquisition unit by an amount equal to an integer multiple of a period of the repetitive pattern structure of the object to be inspected and inputting the second image to the image comparator;

the image comparator to generate a differential image from an absolute value of a difference between the first image and the second image, wherein said difference is obtained by subtracting the second image from the first image;

a first threshold processing unit processing the differential image generated from the image comparator using a first threshold value;

a second threshold processing unit processing the differential image generated from the image comparator using a second threshold value, wherein the second threshold value being lower than the first threshold value and in a case where a defect exists, the differential image develops two peaks separated from each other by a distance equal to an image displacement;

a defect candidate determining unit determining a corresponding pixel as a defect candidate in the differential image in a case where the two peaks separated from each other by the distance equal to the image displacement are both higher than the second threshold value; and

a defect detection unit determining a presence or absence of the defect based on the defect candidate sent from the defect candidate determining unit and the processed differential image from the first threshold processing, so that the corresponding pixel is determined as the defect where any one of the two peaks sent from the defect candidate determining unit exceeds the first threshold value.

2. A defect inspection method comprising steps of:

acquiring a first image of an object, which has a repetitive pattern structure, to be inspected at an image data acquisition unit;

inputting the first image of the object acquired by the image data acquisition unit to an image comparator at an image input unit;

generating a second image shifted from the first image of the object acquired by the image data acquisition unit by an amount equal to an integer multiple of a period of the repetitive pattern structure of the object to be inspected at the image input unit;

inputting the second image to the image comparator at the image input unit;

generating a differential image from an absolute value of a difference between the first image and the second image, wherein said difference is obtained by subtracting the second image from the first image at the image comparator;

processing the differential image generated from the image comparator using a first threshold value at a first threshold processing unit;

processing the differential image generated from the image comparator using a second threshold value at a second threshold processing unit, wherein the second threshold value being lower than the first threshold value and in a case where a defect exists, the differential image develops two peaks separated from each other by a distance equal to an image displacement;

determining a corresponding pixel as a defect candidate in the differential image in a case where the two peaks separated from each other by the distance equal to the image displacement are both higher than the second threshold value at a defect candidate determining unit; and

determining a presence or absence of the defect based on the defect candidate sent from the defect candidate determining unit and the processed differential image from the first threshold processing at a defect detection unit, so that the corresponding pixel is determined as the defect where any one of the two peaks sent from the defect candidate determining unit exceeds the first threshold value.