Methods for analyzing defect artifacts to precisely locate corresponding defects

• US 20030222220A1
• Filed: 02/18/2003
• Published: 12/04/2003
• Est. Priority Date: 01/23/2002
• Status: Active Grant

• Current Assignee: Marena Systems Corporation
• Original Assignee: Marena Systems Corporation
• Inventors: Belikov, Sergey, Enachescu, Marian
• Granted Patent: US 7,149,343 B2
• Time in Patent Office: Days
• US Class Current: 250/341.6
• CPC Class Codes: G01R 31/308 using non-ionising electromagnetic radiation, e.g. optical radiation investigating or analysing materials by the use of optical means G01N21/00; image analysis G06T7/00

Abstract

Described are methods and systems for providing improved defect detection and analysis using infrared thermography. Test vectors heat features of a device under test to produce thermal characteristics useful in identifying defects. The test vectors are timed to enhance the thermal contrast between defects and the surrounding features, enabling IR imaging equipment to acquire improved thermographic images. In some embodiments, a combination of AC and DC test vectors maximize power transfer to expedite heating, and therefore testing. Mathematical transformations applied to the improved images further enhance defect detection and analysis. Some defects produce image artifacts, or “defect artifacts,” that obscure the defects, rendering difficult the task of defect location. Some embodiments employ defect-location algorithms that analyze defect artifacts to precisely locate corresponding defects.

Claims

1. An automated method of locating at least one defect on an object of interest, wherein the object includes at least one defect region corresponding to the defect and a defect-free region absent the defect, the method comprising:

a. acquiring an image of the object, the image including image data spatially correlated to the object, the image data including;

i. defect data spatially correlated to the defect region; and

ii. defect-artifact data spatially correlated to portions of the defect-free region; and

b. analyzing the defect-artifact data.

2. The method of claim 1, further comprising classifying the defect-artifact data as a member of one of a plurality of artifact types.

3. The method of claim 2, wherein the artifact types include at least one of point-type, line-type, and corner-type.

4. The method of claim 1, further comprising filtering the image data to remove at least one type of defect, thereby creating a type-specific image.

5. The method of claim 1, further comprising:

a. applying a first threshold value to the image data to create a first thresholded image, the first thresholded image depicting a first defect area in the defect region and a first defect-artifact area encompassing the first defect area and extending into the defect-free region; and

b. applying a second threshold value to the image data to create a second thresholded image, the second thresholded image depicting a second defect area in the defect region and a second defect-artifact area encompassing the second defect area and extending into the defect-free region.

6. The method of claim 5, further comprising selecting a first peak within the first defect-artifact area, selecting a second peak within the second defect-artifact area, and calculating a gradient extending between the first and second peaks.

7. The method of claim 6, further comprising calculating the defect coordinates using the gradient.

8. The method of claim 5, wherein the first and second defect areas correspond spatially to the defect region.

9. An imaging systems for localizing a defect on an object under test, the imaging system comprising:

a. a excitation source applying a test vector to the defect, wherein the defect exhibits a response to the applied test vector;

b. an image detector positioned to observe the response of the defect, thereby producing an image including defect data and defect-artifact data encompassing the defect data; and

c. an image processor analyzing the defect-artifact data and the defect data to locate the defect data within the defect-artifact data.

10. The imaging system of claim 9, wherein the response is a thermal response.

11. The imaging system of claim 9, wherein analyzing the defect-artifact data comprises:

a. applying a plurality of threshold values to the image to produce a plurality of thresholded images;

b. wherein a number of the thresholded images include respective defect artifacts corresponding to the defect region.

12. The imaging system of claim 11, further comprising a type-specific filter sorting the defect artifacts in each thresholded image by type to produce type-specific images having type-specific defect artifacts.

13. The imaging system of claim 12, wherein the image processor includes a data structure associating type-specific defect artifacts from different type-specific images.

14. The imaging system of claim 13, wherein the image processor establishes a gradient between peak values of the type-specific defect artifacts.

15. The imaging system of claim 14, wherein the image processor calculates the location of the defect using the gradient.

16. An inspection system comprising:

a. an object under test, including at least one defect;

b. a means for heating the defect and related resources;

c. an infrared imaging device capturing a thermal image heated object, the thermal image including defect data representative of the defect and defect-artifact data representative of the related resources; and

d. image-processing means for locating the defect data within the defect-artifact data.