Method for repairing a mask

1. A method of repairing a mask, the method comprising:

inspecting the mask using a mask inspection tool to identify a defect on a circuit pattern of the mask;

repairing the defect using a mask repair tool to form a repaired pattern;

forming, using a point source, a first group of diffraction images of the repaired pattern and a second group of diffraction images of a reference feature; and

validating the mask by comparing the first group of diffraction images with the second group of diffraction images.

2. The method of claim 1 , wherein the first group of diffraction images includes a first diffraction image from the point source; and

the second group of diffraction images includes a second diffraction image from the point source.

3. The method of claim 2 , wherein

the first diffraction image includes a first plurality of diffraction order images;

the second diffraction image includes a second plurality of diffraction order images; and

the validating the mask includes comparing first intensities and numerical apertures of the first plurality of diffraction order images to second intensities and numerical apertures of the second plurality of diffraction order images, respectively.

4. The method of claim 3 , wherein the first plurality of diffraction order images includes zero order, first order, and second order diffraction images.

5. The method of claim 3 , wherein the validating the mask includes evaluating differences between the first intensities and numerical apertures of the first plurality of diffraction order images and the second intensities and numerical apertures of the second plurality of diffraction order images, respectively according to predefined criteria.

6. The method of claim 1 , wherein the forming the first group of diffraction images of the repaired pattern and the second group of diffraction images of the reference feature includes:

forming first two diffraction images of the repaired pattern using a first point source and a second point source, respectively; and

forming second two diffraction images of the reference feature using the first point source and the second point source, respectively.

7. The method of claim 6 , wherein the first and second point sources are a pair of symmetric point sources.

8. The method of claim 6 , wherein the validating the mask includes comparing first respective intensities and numerical apertures of the first two diffraction images to second respective intensities and numerical apertures of the second two diffraction images.

9. The method of claim 1 , wherein the reference feature is a defect-free pattern on the mask.

10. The method of claim 9 , wherein the circuit pattern and the reference feature are the same by design.

11. The method of claim 9 , wherein

the circuit pattern includes a first feature where the defect is located;

the reference feature includes a second feature; and

the first feature and the second feature have a same dimension by design.

12. The method of claim 1 , wherein the mask includes a mask selected from the group consisting of a binary mask, a phase shift mask, and a reflective mask.

13. A method, comprising:

receiving a mask having a first feature with a defect and a second feature;

inspecting the mask using a mask inspection tool to locate the defect;

repairing the defect using a mask repair tool, resulting in a repaired first feature;

forming a first diffraction image of the repaired first feature using a first point source;

forming a second diffraction image of the second feature using the first point source; and

validating the repaired first feature by comparing the first diffraction image with the second diffraction image.

14. The method of claim 13 , wherein

the first diffraction image includes a first plurality of diffraction order images;

the second diffraction image includes a second plurality of diffraction order images; and

the validating the repaired first feature includes comparing first intensities and numerical apertures of the first plurality of diffraction order images to second intensities and numerical apertures of the second plurality of diffraction order images, respectively.

15. The method of claim 14 , wherein the validating the repaired first feature includes evaluating differences between the first intensities and numerical apertures of the first plurality of diffraction order images and the second intensities and numerical apertures of the second plurality of diffraction order images, respectively according to predefined criteria, and wherein the repaired first feature is validated if the differences are within the predefined criteria.

16. The method of claim 13 , further comprising:

forming a third diffraction image of the repaired first feature using a second point source; and

forming a fourth diffraction image of the second feature using the second point source,

wherein the validating the repaired first feature further includes comparing the third diffraction image to the fourth diffraction image.

17. The method of claim 13 , wherein the first feature and the second feature have the same dimension by design.

18. The method of claim 13 , further comprising patterning a semiconductor wafer using the mask in a lithography process.

19. A method of repairing a mask, the method comprising:

identifying a defect on a circuit pattern of the mask;

repairing the defect to form a repaired pattern;

forming, using a point source, a first group of diffraction images of the repaired pattern and a second group of diffraction images of a reference feature; and

validating the mask by comparing the first group of diffraction images with the second group of diffraction images.

20. The method of claim 19 , wherein the first group of diffraction images includes a first diffraction image from the point source; and

the second group of diffraction images includes a second diffraction image from the point source.