Method and apparatus for surface inspection

• US 5,311,598 A
• Filed: 06/13/1990
• Issued: 05/10/1994
• Est. Priority Date: 10/18/1988
• Status: Expired due to Term

• Current Assignee: AT&T, Inc.
• Original Assignee: AT&T, Inc.
• Inventors: Ray, Rajarshi, Bose, Chinmoy B.
• Primary Examiner(s): Moore, David K.
• Application Number:
  US07/537,846
• Time in Patent Office: 1,427 Days
• Field of Search: 382/1, 382/8, 382/51, 382/55, 382/49, 382/27, 356/237, 358/106, 358/461, 358/465
• 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 patterned surface on an article, having at least one feature therein, to detect defects, if any, which are smaller than the linewidth of a dark-appearing feature on the surface, independently of any other pattern, 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, if any thereon, 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 these areas within the image, which are associated with features in the patterned surface that have an intensity below a threshold value to appear dark, and those ares which are associated with regularly occurring features that have an intensity above the threshold value to appear bright;

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

substracting the binarized image from the first image to yield a second image;

inverting the second image to yield a third image; and

establishing the existence of a defect smaller than the linewidth of the feature on the surface by the presence of a dark area within the third image.