Technique for repairing an EUV photo-mask

1. A computer-implemented method for calculating a modification to a reflective photo-mask, comprising:

receiving information specifying a defect associated with a recessed area on a top surface of the reflective photo-mask;

using the computer, calculating the modification to the reflective photo-mask, wherein the modification includes a negative feature in which one or more pairs of layers in a multilayer stack in the reflective photo-mask are removed using a subtractive fabrication process, and wherein the modification is proximate to the recessed area; and

performing the modification on the reflective photo-mask.

2. A computer-program product for use in conjunction with a computer system, the computer-program product comprising a non-transitory computer-readable storage medium and a computer-program mechanism embedded therein to calculate a modification to a reflective photo-mask, the computer-program mechanism including:

instructions for receiving information specifying a defect associated with a recessed area on a top surface of the reflective photo-mask;

instructions for calculating the modification to the reflective photo-mask, wherein the modification includes a negative feature in which one or more pairs of layers in a multilayer stack in the reflective photo-mask are removed using a subtractive fabrication process, and wherein the modification is proximate to the recessed area; and

instructions for performing the modification on the reflective photo-mask.

3. The computer-program product of claim 2 , wherein the calculating involves an inverse optical calculation in which a difference between a pattern associated with the reflective photo-mask at an image plane in a photo-lithographic process and a reference pattern at the image plane in the photo-lithographic process is used to determine the modification at an object plane in the photo-lithographic process.

4. The computer-program product of claim 2 , wherein the defect includes a phase error.

5. The computer-program product of claim 2 , wherein proximity to the recessed area includes within the recessed area.

6. The computer-program product of claim 2 , wherein proximity to the recessed area includes at least partially surrounding a periphery of the recessed area.

7. The computer-program product of claim 2 , wherein the modification further includes defining a pattern in an absorption layer in the reflective photo-mask using a subtractive fabrication process.

8. The computer-program product of claim 2 , wherein the modification further includes depositing a positive feature that includes a layer of an additional material proximate to the recessed area using an additive fabrication process.

9. A computer system, comprising:

at least one processor;

at least one memory; and

at least one program module, the program module stored in the memory and configured to be executed by the processor to calculate a modification to a reflective photo-mask, the program module including:

instructions for receiving information specifying a defect associated with a recessed area on a top surface of the reflective photo-mask;

instructions for calculating the modification to the reflective photo-mask, wherein the modification includes a negative feature in which one or more pairs of layers in a multilayer stack in the reflective photo-mask are removed using a subtractive fabrication process, and wherein the modification is proximate to the recessed area; and

instructions for performing the modification on the reflective photo-mask.

10. The computer system of claim 9 , wherein the calculating involves an inverse optical calculation in which a difference between a pattern associated with the reflective photo-mask at an image plane in a photo-lithographic process and a reference pattern at the image plane in the photo-lithographic process is used to determine the modification at an object plane in the photo-lithographic process.

11. The computer system of claim 9 , wherein proximity to the recessed area includes one of: within the recessed area; and at least partially surrounding a periphery of the recessed area.

12. The computer system of claim 9 , wherein the defect includes a phase error.

13. The computer system of claim 9 , wherein the receiving involves identifying the defect.

14. The computer system of claim 9 , wherein the modification further includes defining a pattern in an absorption layer in the reflective photo-mask using a subtractive fabrication process.

15. The computer system of claim 9 , wherein the modification further includes depositing a positive feature that includes a layer of an additional material proximate to the recessed area using an additive fabrication process.

16. A reflective photo-mask, comprising:

a substrate;

a multilayer stack disposed on the substrate;

an absorption layer disposed on a top surface of the multilayer stack; and

a fabricated negative feature in which one or more pairs of layers in a multilayer stack in the reflective photo-mask are removed, wherein the fabricated negative feature is proximate to a recessed area on a top surface of the reflective photo-mask that is associated with a defect in the reflective photo-mask.

17. A computer-implemented method for calculating a modification to a reflective photo-mask, comprising:

receiving information specifying a defect associated with a recessed area on a top surface of the reflective photo-mask;

using the computer, calculating the modification to the reflective photo-mask, wherein the modification includes a negative feature in which one or more pairs of layers in a multilayer stack in the reflective photo-mask are removed using a subtractive fabrication process, and wherein the modification is proximate to the recessed area;

displaying a directive to perform the modification on the reflective photo-mask; performing the modification on the reflective photo-mask.

18. The method of claim 17 , wherein the calculating involves an inverse optical calculation in which a difference between a pattern associated with the reflective photo-mask at an image plane in a photo-lithographic process and a reference pattern at the image plane in the photo-lithographic process is used to calculate the modification at an object plane in the photo-lithographic process.

19. The method of claim 17 , wherein the defect includes a phase error.

20. The method of claim 17 , wherein the receiving involves identifying the defect.

21. The method of claim 17 , wherein proximity to the recessed area includes within the recessed area.

22. The method of claim 17 , wherein proximity to the recessed area includes at least partially surrounding a periphery of the recessed area.

23. The method of claim 17 , wherein the modification further includes defining a pattern in an absorption layer in the reflective photo-mask using a subtractive fabrication process.

24. The method of claim 17 , wherein the modification further includes depositing a positive feature that includes a layer of an additional material proximate to the recessed area using an additive fabrication process.

25. The method of claim 17 , wherein the modification increases a margin in a photo-lithographic process that uses the reflective photo-mask.