Compensation of refractivity perturbations in an interferometer path

• US 20040141185A1
• Filed: 11/04/2003
• Published: 07/22/2004
• Est. Priority Date: 11/04/2002
• Status: Active Grant

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A.
• Granted Patent: US 7,268,888 B2
• Time in Patent Office: Days
• US Class Current: 356/500
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02019 contacting different points on same face of object
• CPC Class Codes: G01B 9/02021 contacting different faces of object, e.g. opposite faces
• CPC Class Codes: G01B 9/02027 Two or more interferometric channels or interferometers
• CPC Class Codes: G01B 9/02075 of particular errors
• CPC Class Codes: G01B 9/02083 characterised by particular signal processing and presentation
• CPC Class Codes: G03F 7/70775 Position control, e.g. interferometers or encoders for determining the stage position

Abstract

In general, in one aspect, the invention features a method that includes directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object, directing a second measurement beam along a second path contacting the measurement object to determine an second interferometric phase related to the position of the measurement object, and determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase.

Claims

1. A method, comprising:

directing a first measurement beam along a first path contacting a measurement object to determine a first interferometric phase related to a position of a measurement object;

directing a second measurement beam along a second path contacting the measurement object to determine an second interferometric phase related to the position of the measurement object; and

determining a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase.

2. The method of claim 1, wherein the contribution to the first interferometric phase due to perturbations in refractivity at a first time is related to a contribution to the second interferometric phase due to perturbations in refractivity at a second time different from the first time.

3. The method of claim 2, wherein a difference between the first time and the second time is related to a velocity of a gas in the first path.

4. The method of claim 2, wherein the position of the measurement object changes from the first time to the second time.

5. The method of claim 1, wherein the first path and second path are non-parallel to a direction of gas flow in the first path.

6. The method of claim 5, wherein the first path and second path are substantially parallel.

7. The method of claim 6, wherein the first path and second path are substantially orthogonal to the direction of gas flow in the first path.

8. The method of claim 1, wherein determining the contribution to the first interferometric phase due to perturbations in refractivity comprises determining a difference between the first interferometric phase and the second interferometric phase.

9. The method of claim 8, wherein determining the contribution to the first interferometric phase due to perturbations in refractivity further comprises correcting the difference between the first interferometric phase and the second interferometric phase for variations in an angular orientation of the measurement object.

10. The method of claim 8, wherein determining the contribution to the first interferometric phase due to perturbations in refractivity further comprises summing the differences of first and second interferometric phases determined for different times.

11. The method of claim 10, wherein the different times are related to a velocity of a gas in the first path.

12. The method of claim 10, wherein the different times are related to a separation between the first path and the second path.

13. The method of claim 8, wherein a difference between the contribution to the first interferometric phase due to perturbations in refractivity and a contribution to the second interferometric phase due to perturbations in refractivity is proportional to the difference between the first interferometric phase and the second interferometric phase.

14. The method of claim 8, wherein determining the contribution to the first interferometric phase further comprises determining a parameter related to the difference between the contribution to the first interferometric phase and a contribution to the second interferometric phase due to perturbations in refractivity based on the difference between the first interferometric phase and the second interferometric phase.

15. The method of claim 14, wherein the contribution to the first interferometric phase is determined based on an integral relationship between the parameter and the contribution.

16. The method of claim 15, wherein the integral relationship is based on a Fredholm integral relationship.

17. The method of claim 8, wherein the contribution to the first interferometric phase due to perturbations in refractivity is determined based on variations in the angular orientation of the measurement object.

18. The method of claim 17, wherein variations in the angular orientation of the measurement object are measured simultaneously to determining the first and second interferometric phases.

19. The method of claim 17, wherein variations in the angular orientation of the measurement object are measured using one or more interferometers.

20. The method of claim 19, wherein the one or more interferometers direct respective measurement beams along measurement paths substantially non-orthogonal to a gas flow direction.

21. The method of claim 20, wherein the measurement paths are substantially parallel to the gas flow direction.

22. The method of claim 18, wherein the one or more interferometers include a multi-axis interferometer.

23. The method of claim 1, further comprising compensating the first interferometric phase for contributions due to non-perturbative variations in refractivity.

24. The method of claim 1, wherein the contribution to the first interferometric phase due to perturbations in refractivity is determined contemporaneously to determining the first interferometric phase.

25. The method of claim 1, wherein the contribution to the first interferometric phase due to perturbations in refractivity is determined non-contemporaneously to determining the first interferometric phase.

41. A lithography method for use in fabricating integrated circuits on a wafer, the method comprising:

supporting the wafer on a moveable stage;

imaging spatially patterned radiation onto the wafer;

adjusting the position of the stage; and

monitoring the position of the stage using the method of claim 1.

42. A lithography method for use in the fabrication of integrated circuits comprising:

directing input radiation through a mask to produce spatially patterned radiation;

positioning the mask relative to the input radiation;

monitoring the position of the mask relative to the input radiation using the method of claim 1;

and

imaging the spatially patterned radiation onto a wafer.

43. A lithography method for fabricating integrated circuits on a wafer comprising:

positioning a first component of a lithography system relative to a second component of a lithography system to expose the wafer to spatially patterned radiation; and

monitoring the position of the first component relative to the second component using the method of claim 1.

44. A method for fabricating integrated circuits, the method comprising the lithography method of claim 41.

45. A method for fabricating integrated circuits, the method comprising the lithography method of claim 42.

46. A method for fabricating integrated circuits, the method comprising the lithography method of claim 43.

49. A method for fabricating a lithography mask, the method comprising:

directing a write beam to a substrate to pattern the substrate;

positioning the substrate relative to the write beam; and

monitoring the position of the substrate relative to the write beam using the interferometry method of claim 1.

26. An apparatus, comprising:

an interferometry system which during operation directs a first measurement beam along a first path contacting a measurement object and directs a second measurement beam along a second path contacting the measurement object; and

an electronic controller which during operation determines a first and second interferometric phase related to a position of the measurement object based on the first and second measurement beams, respectively, and determines a contribution to the first interferometric phase due to perturbations in refractivity along the first path based on the second interferometric phase.

27. The apparatus of claim 26, wherein the interferometry system comprises a multi-axis interferometer which during operation directs the first and second measurement beams along the first and second measurement paths.

28. The apparatus of claim 26, wherein the first path is substantially parallel to the second path.

29. The apparatus of claim 26, further comprises a gas source which during operation causes gas to flow through the first and second measurement paths.

30. The apparatus of claim 29, wherein the direction of gas flow is substantially non-parallel to the first and second measurement paths.

31. The apparatus of claim 30, wherein the direction of gas flow is substantially orthogonal to the first and second measurement paths.

32. The apparatus of claim 26, wherein during operation the interferometry system directs a third measurement beam along a third path to contact a second measurement object and the electronic controller determines a third phase related to a position of the second measurement object and monitors variations in an angular orientation of the measurement object based on the third interferometric phase.

33. The apparatus of claim 32, wherein the third path is substantially non-parallel to the first path.

34. The apparatus of claim 33, wherein the third path is substantially orthogonal to the first path.

35. The apparatus of claim 26, wherein the measurement object is mounted on a stage which is moveable relative to the interferometry system.

36. The apparatus of claim 26, wherein the measurement object comprises a plane mirror.

37. The apparatus of claim 26, wherein the measurement object comprises a retroreflector.

38. A lithography system for use in fabricating integrated circuits on a wafer, the system comprising:

a stage for supporting the wafer;

an illumination system for imaging spatially patterned radiation onto the wafer;

a positioning system for adjusting the position of the stage relative to the imaged radiation; and

the apparatus of claim 26 for monitoring the position of the wafer relative to the imaged radiation.

39. A lithography system for use in fabricating integrated circuits on a wafer, the system comprising:

a stage for supporting the wafer; and

an illumination system including a radiation source, a mask, a positioning system, a lens assembly, and the apparatus of claim 26,

wherein during operation the source directs radiation through the mask to produce spatially patterned radiation, the positioning system adjusts the position of the mask relative to the radiation from the source, the lens assembly images the spatially patterned radiation onto the wafer, and the apparatus monitors the position of the mask relative to the radiation from the source.

40. A beam writing system for use in fabricating a lithography mask, the system comprising:

a source providing a write beam to pattern a substrate;

a stage supporting the substrate;

a beam directing assembly for delivering the write beam to the substrate;

a positioning system for positioning the stage and beam directing assembly relative one another; and

the apparatus of claim 26 for monitoring the position of the stage relative to the beam directing assembly.

47. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 38.

48. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 39.