Method and apparatus for visual inspection

• US 20070019858A1
• Filed: 07/20/2006
• Published: 01/25/2007
• Est. Priority Date: 07/22/2005
• Status: Active Grant

• Current Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Original Assignee: Hitachi High-Technologies Corporation (Hitachi, Ltd.)
• Inventors: Shimura, Kei
• Granted Patent: US 8,131,058 B2
• Time in Patent Office: Days
• 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 the steps of:

acquiring plurality of images of an object to be inspected, a first processing step for processing difference between a first image and a second image with a first threshold value,

a second processing step for processing difference between a first image and a second image with a second threshold value lower than the first threshold value,

a third processing step for processing difference between a second image and a third image with the first threshold value,

a fourth processing step for processing difference between a second image and a third image with the second threshold value,

a step of determining pixels exceeding the second threshold value in both the second and the fourth processing steps as defect candidates,

and a step of determining as a defect any of the defect candidates which exceeds the first threshold value in at least one of the first and the third processing steps.

2. An inspection apparatus comprising:

an image data acquisition unit for acquiring the image data of an object to be inspected;

a first processing unit for processing the difference between first and second images from the image data acquisition unit using a first threshold value;

a second processing unit for processing the difference between the first and second images using a second threshold value lower than the first threshold value;

a third processing unit for processing the difference between the second and third images from the image data acquisition unit using the first threshold value;

a fourth processing unit for processing the difference between the second and third images using the second threshold value;

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

a defect detection unit for determining as a defect any of the pixels determined as defect candidates in the defect candidate determining unit which exceeds the first threshold value in at least one of the first and third processing units.

3. An inspection apparatus comprising:

an image data acquisition unit for acquiring the image data of an object to be inspected;

an image generating unit for generating a second image displaced from the first image of the object acquired by the image data acquisition unit, by an amount equal to an integer multiple of the period of the periodical structure of the object to be inspected;

a processing unit for processing the differential image between the first and second images using a second threshold value;

a defect candidate determining unit for determining a defect candidate in the case where the differential image develops a peak exceeding the second threshold value at two points at the same interval as the distance of the displacement; and

a defect detection unit for detecting the pixel of the first image corresponding to the defect candidate as a defect, when at least one of the two peaks associated with the defect candidate exceeds the first threshold value higher than the second threshold value.