Method and apparatus for semiconductor wafer alignment

• US 20080050006A1
• Filed: 08/23/2006
• Published: 02/28/2008
• Est. Priority Date: 08/23/2006
• Status: Active Grant

• Current Assignee: Cognex Corporation
• Original Assignee: Cognex Corporation
• Inventors: Clark, James, Michael, David J., Liu, Gang
• Granted Patent: US 8,162,584 B2
• Time in Patent Office: Days
• US Class Current: 382/144
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: H01L 21/681 using optical controlling means

Abstract

The invention provides, in some aspects, a wafer alignment system comprising an image acquisition device, an illumination source, a rotatable wafer platform, and an image processor that includes functionality for mapping coordinates in an image of an article (such as a wafer) on the platform to a “world” frame of reference at each of a plurality of angles of rotation of the platform.

Claims

1. A wafer alignment system, comprising

A. a rotatable platform,

B. an image acquisition device having a field of view that includes at least a portion of a wafer on the platform,

C. an illumination source that illuminates at least a portion of the wafer,

D. an image processor that is coupled to the image acquisition device and that processes an image showing one or more characteristics of the wafer in a first frame of reference, the image processor determining therefrom a position and/or orientation of the wafer, or a portion thereof, in a second frame of reference, and

E. the image processor including a mapping element that maps coordinates in the first frame of reference to coordinates in the second frame of reference at each of a plurality of angles of rotation of the platform.

2. The wafer alignment system of claim 1, wherein the platform holds the wafer on a plane having a normal that precesses as the platform rotates.

3. The wafer alignment system of claim 2, wherein the platform is disposed on and rotationally coupled to a chuck, the axis of rotation of which is not normal to the holding plane of the platform.

4. The wafer alignment system of claim 3, wherein the platform rotates as the chuck rotates and the normal to the platform'"'"'s holding plane precesses during the course of that rotation.

5. The wafer alignment system of claim 1, wherein the second frame of reference is independent of one or more frames of reference defined by the platform at one or more angles of rotation thereof.

6. The wafer alignment system of claim 1, wherein the second frame of reference is a planar.

7. The wafer alignment system of claim 1, wherein the mapping element comprises a discrete function that maps coordinates in an image of the wafer on the platform to the second frame of reference for each of two or more discrete angles of the platform.

8. The wafer alignment system of claim 1, wherein the mapping element comprises a continuous function that maps coordinates in an image of the wafer on the platform to the second frame of reference as a continuous function of the angle of the platform.

9. The wafer alignment system of claim 1, wherein the illumination source provides backlighting for the wafer on the platform.

10. The wafer alignment system of claim 9, wherein the illumination source provides that backlighting at an angle parallel to the normal to the holding plane of the platform.

11. The wafer alignment system of claim 9, wherein the illumination source is disposed in the holding plane of the platform.

12. The wafer alignment system of claim 11, wherein the illumination source comprises a planar source that is disposed between the wafer and the platform.

13. The wafer alignment system of claim 9, wherein the illumination source comprises an electroluminescent light source.

14. The wafer alignment system of claim 1, wherein the image acquisition device is arranged to acquire an image of the entire wafer in a single field of view.

15. The wafer alignment system of claim 1, wherein the image processor further comprises functionality that determines the position and/or orientation of the wafer, or a portion thereof, in any of the first and second frames of reference as a function of one or more features shown in the image.

16. A method of wafer alignment comprising

A. acquiring an image of a wafer that is disposed on a rotatable platform, the image showing one or more characteristics of the wafer in a first frame of reference,

B. processing the image to determine therefrom a position and/or orientation of the wafer, or a portion thereof, in a second frame of reference,

C. the processing step including determining the position and/or orientation by using a mapping element that maps coordinates in the first frame of reference to coordinates in the second frame of reference at each of a plurality of angles of rotation of the platform, and

D. using the position and/or orientation determined in step (B) to position the wafer for any of processing and inspection.

17. The method of claim 16, wherein the platform holds the wafer on a plane having a normal that precesses as the platform rotates.

18. The method of claim 16, wherein the second frame of reference is independent of one or more frames of reference defined by the platform at one or more angles of rotation thereof.

19. The method of claim 16, comprising backlighting the wafer during acquisition of the image in step (A).

20. The method of claim 19, comprising disposing an illumination source between the wafer and the platform.

21. The method of claim 19, comprising backlighting the wafer with a planar, electroluminescent light source.