Detection of wafer-edge defects

1. Apparatus for inspection of a disk, which includes a crystalline material and has first and second sides, the apparatus comprising:

an X-ray source, which is configured to direct a beam of X-rays to impinge on an area of the first side of the disk;

an X-ray detector, which is positioned to receive and form input images of the X-rays that are diffracted from the area of the first side of the disk in a reflective mode;

a motion assembly, which is configured to rotate the disk relative to the X-ray source and detector so that the area scans over a circumferential path in proximity to an edge of the disk; and

a processor, which is configured to process the input images formed by the X-ray detector along the circumferential path so as to generate a composite output image indicative of defects along the edge of the disk.

2. The apparatus according to claim 1 , wherein the defects comprise cracks in the disk.

3. The apparatus according to claim 1 , wherein the processor is configured to form the composite image in a coordinate system defined by a radial distance and an azimuth relative to a center of the disk.

4. The apparatus according to claim 1 , wherein the X-ray source and X-ray detector respectively comprise a first X-ray source and a first X-ray detector positioned opposite the first side of the disk, and the first X-ray detector forms first input images of a first area on the first side of the disk, and

wherein the apparatus comprises a second X-ray source, which is configured to direct X-rays to impinge on a second area on the second side of the disk, and a second X-ray detector, which is positioned to receive and form second input images of the X-rays that are diffracted from the second area.

5. The apparatus according to claim 4 , wherein a projection of the first area onto the second side of the disk overlaps the second area, and wherein the processor is configured to jointly process the first and second input images of the overlapping first and second areas.

6. The apparatus according to claim 5 , wherein the processor is configured to compare the first and second input images so as to detect cracks passing through the disk.

7. The apparatus according to claim 1 , wherein the X-ray source and the X-ray detector are positioned so that the X-ray detector receives Bragg reflections from a crystal plane that is parallel to within ±2° to the first side of the disk.

8. The apparatus according to claim 7 , wherein the X-ray source and the X-ray detector are symmetrically positioned at equal elevations angles relative to the disk.

9. The apparatus according to claim 7 , wherein the X-ray source and the X-ray detector are non-symmetrically positioned at different, respective elevations angles relative to the disk.

10. The apparatus according to claim 1 , wherein the disk comprises a semiconductor wafer.

11. A method for inspection of a disk, which includes a crystalline material and has first and second sides, the method comprising:

directing a beam of X-rays to impinge on an area of the first side of the disk;

forming input images of the X-rays that are diffracted from the area of the first side of the disk in a reflective mode;

rotating the disk so that the area on which the beam of X-rays impinges scans over a circumferential path in proximity to an edge of the disk; and

processing the input images formed along the circumferential path so as to generate a composite output image indicative of defects along the edge of the disk.

12. The method according to claim 11 , wherein the defects comprise cracks in the disk.

13. The method according to claim 11 , wherein processing the input images comprises forming the composite image in a coordinate system defined by a radial distance and an azimuth relative to a center of the disk.

14. The method according to claim 11 , wherein directing the beam of X-rays comprises directing first and second beams of the X-rays to impinge respectively on first and second areas on the first and second sides of the disk, and

wherein forming the input images comprises capturing, in the reflective mode, first input images of the X-rays that are diffracted from the first area and second input images of the X-rays that are diffracted from the second area.

15. The method according to claim 14 , wherein a projection of the first area onto the second side of the disk overlaps the second area, and wherein processing the input images comprises jointly processing the first and second input images of the overlapping first and second areas.

16. The method according to claim 15 , wherein jointly processing the first and second input images comprises comparing the first and second input images so as to detect cracks passing through the disk.

17. The method according to claim 11 , wherein directing the beam of X-rays and forming the X-ray images comprise irradiating the area and detecting the diffracted X-rays using a source and detector positioned so as to detect Bragg reflections from a crystal plane that is parallel to within ±2° to the first side of the disk.

18. The method according to claim 17 , wherein the source and the detector are symmetrically positioned at equal elevations angles relative to the disk.

19. The method according to claim 17 , wherein the source and the detector are non-symmetrically positioned at different, respective elevations angles relative to the disk.

20. The method according to claim 11 , wherein the disk comprises a semiconductor wafer.