Method and apparatus for surface inspection

• US 4,975,972 A
• Filed: 10/18/1988
• Issued: 12/04/1990
• Est. Priority Date: 10/18/1988
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.), Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: AT&T, Inc.
• Inventors: Ray, Rajarshi, Bose, Chinmoy B.
• Primary Examiner(s): Moore, David K.
• Assistant Examiner(s): Razavi, Michael
• Application Number:
  US07/259,640
• Time in Patent Office: 777 Days
• Field of Search: 382/1, 382/8, 382/51, 382/55, 382/49, 382/27, 356/237, 358/106
• US Class Current: 382/149
• CPC Class Codes: G01N 2021/8887 based on image processing techniques
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 5/30 Erosion or dilatation, e.g. thinning
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/136 involving thresholding

Abstract

Detection of a defect (18) on the surface (15) of an article (10), such as a semiconductor chip, is accomplished by illuminating the chip in a bright field and then capturing the image thereof with a television camera (30) coupled to a machine vision processor (32). To detect the defect 18, the vision processor first adaptively thresholds the captured image to effectively eliminate areas in the image brighter than those associated with the defect (18) which are usually dark. Thereafter, the vision processor (32) erodes and then dilates the dark areas within the image remaining after binarization to isolate those dark areas associated with the defect. The existence of a defect can then be established by the existence of a now-isolated dark area.

Claims

1. A method for inspecting a surface of an article, having at least one feature thereon, to detect defects, if any, which are either smaller or larger than the linewidth of the feature, the method comprising the steps of:

illuminating the surface of the article with light which is directed to strike the surface substantially normal to the plane thereof so that upon illumination of the surface, each defect appears dark;

capturing the image of the surface of the article with an image-acquisition device whose optical axis is substantially normal to the axis of the surface;

binarizing the captured image to cause those areas within the image having an intensity below a threshold value to appear dark, and those areas having an intensity above the threshold value to appear bright;

processing the binarized image to produce a first image in which those defects, if any, which are larger than the linewidth of the feature, are isolated;

processing the binarized image to produce a second image in which those defects, if any, which are smaller than the linewidth of the feature, are isolated;

logically ANDing the first and second images to yield a third image; and

establishing the presence of a defect by the existence in the third image of a dark area.

3. The apparatus according to claim 1 wherein the image-acquisition means comprises a television camera.

2. A method for processing an image containing both regularly occurring features and at least one defect which may be smaller or larger than the linewidth of the feature, to isolate the feature from the defect, the method comprising the steps of:

binarizing the image to cause those areas within the image having an intensity below a threshold value to appear dark, and those areas having an intensity above the threshold value to appear bright;

processing the binarized image by eroding and dilating each dark area therein to yield a first image containing only the defects, if any, larger than the feature;

processing the binarized image by eroding and dilating each dark area to yield a second image in which each defect, if any, which is smaller than the linewidth of the feature, is effectively eliminated, while the feature, and the defects, if any, larger than the feature remain; and

subtracting the second image from the first image and then inverting the resultant image, the inverted resultant image now containing only the regularly occurring feature.

4. The apparatus according to claim 2 wherein the means for binarizing the image, the means for processing the image, and the means for establishing the size of the defects comprise a machine vision processor coupled to the television camera.