Multiple degree of freedom interferometer

• US 6,757,066 B2
• Filed: 01/27/2003
• Issued: 06/29/2004
• Est. Priority Date: 01/28/2002
• Status: Expired due to Fees

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A.
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): CONNOLLY, PATRICK J
• Application Number:
  US10/351,707
• Publication Number:
  US 20030164948A1
• Time in Patent Office: 519 Days
• Field of Search: 356/487, 356/486, 356/493, 356/500, 356/498
• US Class Current: 356/493
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02003 using beat frequencies
• CPC Class Codes: G01B 9/02018 Multipass interferometers, e.g. double-pass
• CPC Class Codes: G01B 9/02019 contacting different points on same face of object
• CPC Class Codes: G01B 9/02059 Reducing effect of parasitic reflections, e.g. cyclic errors
• CPC Class Codes: G03F 7/70775 Position control, e.g. interferometers or encoders for determining the stage position

Abstract

An apparatus includes a multi-axis interferometer for measuring a relative position of a reflective measurement object along multiple degrees of freedom, wherein the interferometer is configured to produce multiple output beams each comprising information about the relative position of the measurement object with respect to a different one of the degrees of freedom. Each output beam includes a beam component that contacts the measurement object at least one time along a common path, and at least one of the beam components further contacts the measurement object at least a second time along a first path different from the common path.

Claims

1. An apparatus comprising:

a multi-axis interferometer for measuring a relative position of a reflective measurement object along multiple degrees of freedom, wherein the interferometer is configured to produce multiple output beams each comprising information about the relative position of the measurement object with respect to a different one of the degrees of freedom, and

wherein each output beam includes a beam component that contacts the measurement object at least one time along a common path, and

wherein at least one of the beam components further contacts the measurement object at least a second time along a first path different from the common path.

2. The apparatus of claim 1, wherein the output beam comprising the beam component that contacts the measurement object along the common path and along the first path further comprises a second beam component that does not contact the measurement object.

3. The apparatus of claim 1, wherein one of the degrees of freedom is distance to the measurement object along a first measurement axis.

4. The apparatus of claim 3, wherein the output beam comprising information about the distance to the measurement object along the first measurement axis comprises the beam component that contacts the measurement object along the common path and along the first path.

5. The apparatus of claim 4, wherein the first measurement axis is defined by the common path and the first path.

6. The apparatus of claim 5, wherein each point on the first measurement axis is equidistant to corresponding points on the common path and the first path.

7. The apparatus of claim 4, wherein another of the beam components further contacts the measurement object at least a second time along a second path different from the common path.

8. The apparatus of claim 7, wherein the output beam comprising the beam component that contacts the measurement object along the common path and along the second path comprises information about distance to the measurement object along a second measurement axis defined by the common path and the second path, the second measurement axis being different from the first measurement axis.

9. The apparatus of claim 8, wherein a third of the beam components further contacts the measurement object at least a second time along a third path different from the common path.

10. The apparatus of claim 9, wherein the output beam comprising the beam component that contacts the measurement object along the common path and the third path comprises information about distance to the measurement object along a third measurement axis defined by the common path and the third path, the third measurement axes being different from the first and second measurement axes.

11. The apparatus of claim 10, wherein the first and second measurement axes define a first plane, and the second and third measurement axes define a second plane different from the first plane.

12. The apparatus of claim 4, wherein a second one of the output beams comprises information about an angular orientation of the measurement object with respect to a first rotation axis.

13. The apparatus of claim 12, wherein the second output beam comprises the first-mentioned beam component that contacts the measurement object along the common path and another beam component different from the first beam component, wherein the other beam component contacts the measurement object along a second path different from the common path.

14. The apparatus of claim 13, wherein the first path is different from the second path.

15. The apparatus of claim 14, wherein the first rotation axis is normal to a plane defined by the common path and the second path.

16. The apparatus of claim 13, wherein a third one of the output beams comprises information about an angular orientation of the measurement object with respect to a second rotation axis different from the first rotation axis, and wherein the third output beam comprises the first-mentioned beam component that contacts the measurement object along the common path and another beam component different from the first beam component, wherein the other beam component in the third output beam contacts the measurement object along a third path different from the common path.

17. The apparatus of claim 16, wherein the second rotation axis is normal to the first rotation axis.

18. The apparatus of claim 1, wherein the multi-axis interferometer produces at least four output beams each comprising information about a different one of the multiple degrees of freedom.

19. The apparatus of claim 1, wherein the multi-axis interferometer provides information with respect to at least five degrees of freedom.

20. The apparatus of claim 1, wherein the multi-axis interferometer provides information with respect to at least seven degrees of freedom.

21. The apparatus of claim 1, wherein the measurement object comprises a plane mirror.

22. The apparatus of claim 1, further comprising a light source configured to direct an input beam into the multi-axis interferometer, the input beam comprising two components having an heterodyne frequency splitting,

wherein each output beam component that contacts the measurement object along the common path is derived from one of the components in the input beam, and

wherein each output beam further comprises a second component derived from the other one of the components in the input beam.

23. The apparatus of claim 22, wherein the components of the input beam have orthogonal polarizations.

24. The apparatus of claim 1, further comprising detectors configured to receive the output beams and generate electrical signals indicative of the information about the relative position of the measurement object with respect to the different degrees of freedom.

25. The apparatus of claim 24, further comprising a polarization analyzer positioned prior to each detector and configured to pass an intermediate polarization to those of the components in each of the output beams.

26. The apparatus of claim 25, further comprising a fiber-optic pick-up for coupling each output beam to a corresponding detector after it passes through the corresponding polarization analyzer.

27. The apparatus of claim 1, wherein the interferometer is configured to direct a first beam derived from an input beam to contact the measurement object along the common path and separate the first beam into multiple sub-beams after it contacts the measurement object, wherein the sub-beams correspond to the beam components in the output beams that contact the measurement object along the common path.

28. The apparatus of claim 27, wherein the interferometer is configured to further direct at least one of the sub-beams to contact the measurement object at least a second time along the first path to define the beam component that contacts the measurement object along the common path and along the first path.

29. The apparatus of claim 28, wherein the interferometer is configured to derive another sub-beam from the input beam and combine the sub-beam that contacts the measurement object at least twice with the other sub-beam to produce a first one of the output beams, wherein the first output beam comprises information about distance to the measurement object along a measurement axis defined by the common path and the first path.

30. The apparatus of claim 28, wherein the interferometer is configured to further direct at least another one of the sub-beams to contact the measurement object at least a second time along a second path different from the common path and different from the first path.

31. The apparatus of claim 30, wherein the interferometer is configured to derive another set of sub-beams from the input beam and combine each of the sub-beams that contacts the measurement object at least twice with a corresponding sub-beam from the other set to produce a corresponding one of the output beams.

32. The apparatus of claim 28, wherein the interferometer is configured to derive another set of sub-beams from the input beam, combine the sub-beam that contacts the measurement object at least twice with one of the sub-beams from the other set to produce one of the output beams, direct another one of the sub-beams from the other set to contact the measurement object along a second path different from the common path, and combine another one of the sub-beams that contact the measurement object along the common path with the sub-beam that contacts the measurement object along the second path to produce another one of the output beams.

33. The apparatus of claim 27, wherein the interferometer is further configured to:

i) combine the first beam after it contacts the measurement object with a primary reference beam to define an intermediate beam;

ii) separate the intermediate beam into a set of secondary measurement beams and a set of secondary reference beams;

iii) direct each of the secondary measurement beams to contact the measurement object; and

iv) recombine each secondary measurement beam after it contacts the measurement object with a one of corresponding secondary reference beams to produce a corresponding one of the output beams, wherein each of the sub-beams corresponds to a different one of the secondary measurement and reference beams.

34. The apparatus of claim 1, wherein the interferometer comprises:

a common polarizing beam-splitter positioned to direct a primary measurement beam derived from an incident input beam to contact the measurement object along the common path; and

a return beam assembly configured to receive an intermediate beam comprising the primary measurement beam from the polarizing beam-splitter, separate the intermediate beam into multiple beams, and direct the multiple beams back to the polarizing beam-splitter.

35. The apparatus of claim 34, wherein the polarizing beam-splitter is further positioned to direct a primary reference beam derived from the incident input beam to contact a reflective reference object, wherein the primary measurement beam and primary reference beam correspond to orthogonal polarization components of the incident input beam.

36. The apparatus of claim 35, wherein the polarizing beam-splitter is further positioned to recombine the primary measurement and reference beams to form the intermediate beam after they contact the measurement and reference objects, respectively.

37. The apparatus of claim 36, wherein the polarizing beam-splitter is positioned to:

i) separate the multiple beams into a set of secondary measurement beams and a set of secondary reference beams;

ii) direct each of the secondary measurement beams to contact the measurement object;

iii) direct each of the secondary reference beams to contact the reference object; and

iv) recombine each secondary measurement beam with a corresponding one of the secondary reference beams after they contact the measurement and reference objects, respectively, to form a corresponding one of the output beams.

38. The apparatus of claim 37, wherein the each secondary measurement beam contacts the measurement object along a path different from the common the path.

39. The apparatus of claim 37, wherein the interferometer further comprises the reference object.

40. The apparatus of claim 39, wherein the reference object comprises a plane mirror.

41. The apparatus of claim 37, wherein the interferometer further comprises a measurement quarter-wave retarder positioned between the polarizing beam-splitter and the measurement object.

42. The apparatus of claim 41, wherein the interferometer further comprises a reference quarter-wave retarder positioned between the polarizing beam-splitter and the reference object.

43. The apparatus of claim 34, wherein the return beam assembly comprises at least one set of fold optics and at least one non-polarizing beam-splitter positioned to separate the intermediate beam into the multiple beams.

44. The apparatus of claim 43, wherein the at least one set of fold optics comprises a retroreflector positioned to receive the intermediate beam prior to any of the non-polarizing beam-splitters.

45. The apparatus of claim 44, wherein the return beam assembly further comprises a beam-splitting assembly comprising the at least one non-polarizing beam-splitter, wherein the beam-splitting assembly receives the intermediate beam from the retroreflector, generates the multiple beams, and directs the multiple beams back to the polarizing beam splitter along directions parallel to that of the intermediate beam.

46. The apparatus of claim 45, wherein the beam-splitting assembly comprises multiple non-polarizing beam-splitters.

47. The apparatus of claim 46, wherein the return beam assembly further comprises a retardation plate positioned between the retroreflector and the beam-splitting assembly, wherein the retardation plate is oriented to reduce polarization rotation of the intermediate beam caused by the retroreflector.

48. The apparatus of claim 34, wherein the interferometer further comprises an input beam optical assembly comprising a non-polarizing beam-splitter, wherein the input beam optical assembly is configured to separate a progenitor input beam into the first-mentioned input beam and a second input beam propagating parallel to the first input beam and direct the first and second input beams to the polarizing beam-splitter.

49. The apparatus of claim 43, wherein the at least one set of fold optics comprises angle-measuring fold optics and distance-measuring fold optics, wherein the angle-measuring fold optics comprises a half-wave retarder positioned to rotate the polarization of at least one of the multiple beams.

50. The apparatus of claim 49, wherein the angle-measuring fold optics further comprise a penta-prism and the distance-measuring optics comprise a retroreflector.

51. The apparatus of claim 43, wherein non-polarizing beam-splitter is positioned to receive the intermediate beam prior to any of the fold optics.

59. 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 1 or claim 53 for monitoring the position of the wafer relative to the imaged radiation.

60. 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 1 or claim 53,

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 interferometry system monitors the position of the mask relative to the radiation from the source.

61. 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 1 or claim 53 for monitoring the position of the stage relative to the beam directing assembly.

66. A method for fabricating integrated circuits, the method comprising using the lithography apparatus of claim 59.

70. A method for fabricating integrated circuits, the method comprising using the lithography apparatus of claim 60.

52. A method comprising:

interferometrically producing multiple output beams each comprising information about a relative position of a measurement object with respect to a different degree of freedom,

wherein each output beam includes a beam component that contacts the measurement object at least one time along a common path, and

wherein at least one of the beam components further contacts the measurement object at least a second time along a first path different from the common path.

62. 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 52 or claim 58.

63. 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 52 or claim 58; and

imaging the spatially patterned radiation onto a wafer.

64. 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 52 or claim 58.

65. A method for fabricating integrated circuits, the method comprising the lithography method of claim 62.

68. A method for fabricating integrated circuits, the method comprising the lithography method of claim 63.

69. A method for fabricating integrated circuits, the method comprising the lithography method of claim 64.

53. An apparatus comprising:

a multi-axis interferometer for measuring a relative position of a reflective measurement object along multiple degrees of freedom, wherein the interferometer is configured to produce multiple output beams each comprising information about the relative position of the measurement object with respect to a different one of the degrees of freedom, and

wherein each output beam includes a beam component that contacts the measurement object at least one time along a common path,

wherein at least one of the output beams comprises another beam component different from the first-mentioned beam component, and

wherein the other beam component contacts the measurement object at least one time along a first path different from the common path.

54. The apparatus of claim 53, wherein the output beam comprising the first beam component that contacts the measurement object along the common path and the other beam component that contacts the measurement object along the first path comprises information about the angular orientation of the measurement object with respect to a first rotation axis.

55. The apparatus of claim 54, wherein the first rotation axis is normal to a plane defined by the common path and the first path.

56. The apparatus of claim 54, wherein a second one of the output beams comprises information about an angular orientation of the measurement object with respect to a second rotation axis different from the first rotation axis, and wherein the second output beam comprises the first-mentioned beam component that contacts the measurement object along the common path and another beam component different from the first beam component, wherein the other beam component in the second output beam contacts the measurement object along a second path different from the common path.

57. The apparatus of claim 56, wherein the second rotation axis is normal to the first rotation axis.

67. 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 53 or claim 58.

58. A method comprising:

interferometrically producing multiple output beams each comprising information about a relative position of a measurement object with respect to a different degree of freedom,

wherein each output beam includes a beam component that contacts the measurement object at least one time along a common path,

wherein at least one of the output beams comprises another beam component different from the first-mentioned beam component, and

wherein the other beam component contacts the measurement object at least one time along a first path different from the common path.

71. An apparatus comprising:

a multi-axis interferometer for measuring a relative position of a reflective measurement object along multiple degrees of freedom, wherein the interferometer is configured to produce at least three output beams each comprising information about the relative position of the measurement object with respect to a different one of the degrees of freedom, and

wherein each output beam includes a beam component that contacts the measurement object at least one time along a common path, and

wherein at least one of the beam components further contacts the measurement object at least a second time along a first path different from the common path.

72. An apparatus comprising:

a multi-axis interferometer for measuring a relative position of a reflective measurement object along multiple degrees of freedom, wherein the interferometer is configured to produce multiple output beams each comprising information about the relative position of the measurement object with respect to a different one of the degrees of freedom, and

wherein each output beam includes a beam component that contacts the measurement object at least one time along a common path,

wherein one of the beam components further contacts the measurement object at least a second time along a first path different from the common path, and

wherein another of the beam components further contacts the measurement object at least a second time along a second path different from the common path and the first path.

73. An apparatus comprising:

a multi-axis interferometer for measuring a relative position of a reflective measurement object along multiple degrees of freedom, wherein the interferometer is configured to produce multiple output beams each comprising information about the relative position of the measurement object with respect to a different one of the degrees of freedom, and

wherein each output beam includes a beam component that contacts the measurement object at least one time along a common path,

wherein at least one of the output beams comprises another beam component different from the first-mentioned beam component,

wherein the other beam component contacts the measurement object at least one time along a first path different from the common path, and

wherein the two beam components in the at least one output beam each make pass to a common, reflective reference object.