System and method for selection of a reference die

• US 6,252,981 B1
• Filed: 03/17/1999
• Issued: 06/26/2001
• Est. Priority Date: 03/17/1999
• Status: Expired due to Term

• Current Assignee: Rudolph Technologies Incorporated (Onto Innovation Inc.)
• Original Assignee: Semiconductor Technologies & Instruments Incorporated (Onto Innovation Inc.)
• Inventors: Harris, Charles Kenneth, Guest, Clyde Maxwell, Roy, Rajiv
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Werner, Brian P.
• Application Number:
  US09/270,607
• Time in Patent Office: 832 Days
• Field of Search: 382/145, 382/148, 382/149, 382/144, 382/168, 382/170, 382/146, 382/147, 382/150, 382/151, 382/152, 356/237.5, 356/237.4, 356/601, 356/613, 356/390, 438/16, 348/87, 348/126, 250/559.2, 250/559.39, 250/559.46, 700/110, 702/40, 702/159
• US Class Current: 382/149
• CPC Class Codes: G03F 7/7065 Defects, e.g. optical inspection of patterned layer for defects
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

A system for selecting reference die images, such as for use with a visual die inspection system, is provided. The system includes a die image comparator, which compares a first die image to a second die image in order to create a difference image that contains only the differences between the two die images. The system also includes a difference image analysis system that receives data from the die image comparator. The difference image analysis system analyzes the difference image and determines whether there are any features of the difference image that indicate that either the first die image or the second die image should not be used as a reference die image.

Claims

1. A system for selection of a reference die image comprising:

a die image comparator operable to create a difference image based upon a first die image and a second die image; and

a difference image analysis system coupled to the die image comparator, the difference image analysis system generating histogram data from the difference image and analyzing the slope of the histogram data to determine the length of a region over which the slope of the histogram data increases and then decreases, wherein the length of the anomalous region is then used to determine whether the first die image and the second die image may each be used as the reference die image for subsequent comparison with other dies on a wafer.

2. The system of claim 1 further comprising a die imaging system coupled to the die image comparator, the die imaging system operable to create a digital representation of a die.

3. The system of claim 1 further comprising a die image storage system coupled to the die image comparator, the die image storage system operable to store data representative of the first die image and the second die image.

4. The system of claim 1 wherein the difference image analysis system further comprises a slope detector, the slope detector operable to determine whether the slope of a histogram changes from negative to positive.

5. The system of claim 1 wherein the difference image analysis system further comprises a size detector, the size detector operable to determine whether a size of the anomalous region exceeds a predetermined allowable size.

6. The system of claim 1 wherein the difference image analysis system further comprises a density detector, the density detector operable to determine whether a number of anomalous regions per unit area exceeds a predetermined allowable number of anomalous regions per unit area.

7. A system for inspecting dies comprising:

a camera configured to obtain an image of two or more dies; and

a reference die detection system coupled to the camera, the reference die detection system operable to analyze slope changes in histogram data a difference between a first die image and a second die image to determine the length of a region over which the slope of the histogram data increases and then decreases, wherein the length of the anomalous region is then used to determine whether the first die image and the second die image can be used as reference images for subsequent comparison with other dies on a wafer.

8. The system of claim 7 wherein the reference die detection system further comprises an image comparator operable to produce a difference image from the first die image and the second die image.

9. The system of claim 8 wherein the reference die detection system further comprises a difference analyzer coupled to the image comparator, the difference analyzer operable to determine whether the difference image contains unacceptable features.

10. The system of claim 9 wherein the difference analyzer further comprises a data sorter that is operable to receive brightness data associated with a plurality of pixels of the difference image and to create a histogram from the brightness data.

11. The system of claim 10 wherein the difference analyzer further comprises a slope detector coupled to the data sorter, the slope detector operable to determine whether a slope of the brightness data histogram changes from negative to positive as a brightness magnitude increases.

12. The system of claim 10 wherein the difference analyzer further comprises a dimension analyzer that is operable to determine (a) one or more dimensions for a group of pixels, where each pixel has a brightness magnitude that exceeds a predetermined allowable magnitude, and (b) whether one or more dimensions of the group of pixels exceeds one or more predetermined allowable dimensions.

13. The system of claim 10 wherein the difference analyzer further comprises a density analyzer that is operable to determine (a) one or more dimensions of two or more groups of pixels, where each group of pixels has a brightness magnitude that exceeds a predetermined allowable magnitude, and (b) whether a density of the two or more groups of pixels per unit area exceeds a predetermined allowable density.

14. The system of claim 9 wherein the difference analyzer further comprises a data sorter that is operable to receive image data associated with a plurality of pixels of the difference image and to create a histogram from the image data.

15. The system of claim 14 wherein the difference analyzer further comprises a slope detector coupled to the data sorter, the slope detector operable to determine whether a slope of the image data histogram changes from negative to positive as an image data magnitude increases.

16. The system of claim 14 wherein the difference analyzer further comprises a dimension analyzer that is operable to determine (a) one or more dimensions of a group of pixels, where each group of pixels has an image data magnitude that exceeds a predetermined allowable magnitude, and (b) whether the dimensions of the group of pixels per unit area exceeds one or more predetermined allowable dimensions.

17. The system of claim 14 wherein the difference analyzer further comprises a density analyzer that is operable to determine (a) one or more dimensions of two or more groups of pixels, where each group of pixels has an image data magnitude that exceeds a predetermined allowable magnitude, and (b) whether a density of the two or more groups of pixels per unit area exceeds a predetermined allowable density.

18. A method for selecting a reference die image comprising:

subtracting a first die image from a second die image to create a difference image;

generating histogram data from the difference image;

determining the length of a region over which a slope of the histogram data increases and then decreases;

determining whether the difference image contains unacceptable data based on whether the length of the region exceeds predetermined allowable criteria; and

determining whether the first die image and the second die image can be used as reference images for subsequent comparison with other dies on the wafer.

19. The method of claim 18 wherein subtracting the first die image from the second die image comprises subtracting brightness data for each pixel of the first die image from brightness data for a corresponding pixel of the second die image.

20. The method of claim 18 wherein subtracting the first die image from the second die image comprises subtracting image data other than brightness data for each pixel of the first die image from image data other than brightness data for a corresponding pixel of the second die image.

21. The method of claim 18 wherein determining whether the difference image contains unacceptable data comprises:

forming a histogram from difference image data; and

determining whether a slope of the histogram changes from negative to positive.

22. The method of claim 18 wherein determining whether the difference image contains unacceptable data comprises determining whether a size of an area having a brightness deviation exceeds a predetermined allowable size.

23. The method of claim 18 wherein determining whether the difference image contains unacceptable data comprises determining whether a size of an area having an image data deviation for image data other than brightness data that exceeds a predetermined allowable size.

24. The method of claim 18 wherein determining whether the difference image contains unacceptable data comprises determining whether a number of areas having brightness deviations exceeds a predetermined allowable number of areas having brightness deviations per unit area.

25. The method of claim 18 wherein determining whether the difference image contains unacceptable data comprises determining whether a number of areas having other image data deviations exceeds a predetermined allowable number of areas having image data deviations per unit area for image data other than brightness data.

26. The method of claim 18 further comprising:

selecting two or more difference images that do not contain unacceptable data, where each difference image is selected from a different predetermined region of the silicon wafer; and

combining the die images used to create the two or more difference images to form a reference image for use in comparing with each die of the silicon wafer.