Compensation for geometric effects of beam misalignments in plane mirror interferometer metrology systems

• US 20050018206A1
• Filed: 06/18/2004
• Published: 01/27/2005
• Est. Priority Date: 06/19/2003
• Status: Active Grant

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A.
• Granted Patent: US 7,286,240 B2
• Time in Patent Office: Days
• US Class Current: 356/498
• 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 9/02061 Reduction or prevention of effects of tilts or misalignment
• CPC Class Codes: G01B 9/02072 by calibration or testing of interferometer
• CPC Class Codes: G03F 7/70516 Calibration of components of the microlithographic apparatus, e.g. light sources, addressable masks or detectors
• CPC Class Codes: G03F 7/70775 Position control, e.g. interferometers or encoders for determining the stage position

Abstract

In one aspect, the invention features a method, including using an interferometer in an interferometry system to produce an output beam comprising a phase related to an optical path difference between a path of a first beam and a path of a second beam, wherein the first beam contacts a measurement object at a first location and the first or second beam contacts the measurement object at a second location, and wherein the first and second locations are different, providing precalibrated information that accounts for contributions to the optical path difference caused by a deviation of the path of the first or second beam from a nominal beam path due to an imperfection of the measurement object at the first location and due to an imperfection of the measurement object at the second location, and determining a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam and the precalibrated information.

Claims

1. A method, comprising:

using an interferometer in an interferometry system to produce an output beam comprising a phase related to an optical path difference between a path of a first beam and a path of a second beam, wherein the first beam contacts a measurement object at a first location and the first or second beam contacts the measurement object at a second location, and wherein the first and second locations are different;

providing precalibrated information that accounts for contributions to the optical path difference caused by a deviation of the path of the first or second beam from a nominal beam path due to an imperfection of the measurement object at the first location and due to an imperfection of the measurement object at the second location; and

determining a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam and the precalibrated information.

2. The method of claim 1, wherein the precalibrated information accounts for contributions to the optical path difference caused by a deviation of the path of the first or second beam within a plane defined by the nominal beam path due to the imperfection of the measurement object at the first or second location.

3. The method of claim 2, wherein the precalibrated information accounts for contributions to the optical path difference caused by a deviation of the path of the first or second beam out of a plane defined by a nominal beam path due to the imperfection of the measurement object at the first or second location.

4. The method of claim 1, wherein the precalibrated information further accounts for contributions to the optical path difference caused by a deviation of the path of the first or second beam from the nominal beam path due to an imperfection in at least one optic of the interferometer.

5. The method of claim 4, wherein the imperfection in at least one optic of the interferometer comprises an imperfection in a surface of the optic.

6. The method of claim 4, wherein the imperfection in at least one optic of the interferometer comprises a bulk imperfection in the optic.

7. The method of claim 1, wherein the precalibrated information further accounts for contributions to the optical path difference caused by a deviation of the path of the first or second beam from the nominal beam path due to an imperfection in a light source that causes an input beam derived from the light source to deviate from an input beam path to the interferometer.

8. The method of claim 1, wherein the first or second beam contacts the measurement object at one or more additional locations different from the first and second locations and the precalibrated information accounts for contributions to the optical path difference caused by a deviation of the path of the first or second beam from the nominal beam path due to an imperfection of the measurement object at one or more additional locations.

9. The method of claim 1, wherein the precalibrated information is parameterized in terms of at least one of an angular orientation of the measurement object relative to the interferometer, a distance between the measurement object and the interferometer, and a direction of an input beam to the interferometer.

10. The method of claim 9, wherein the precalibrated information is parameterized in terms of at least two of an angular orientation of the measurement object relative to the interferometer, a distance between the measurement object and the interferometer, and a direction of an input beam to the interferometer.

11. The method of claim 10, wherein the precalibrated information is parameterized in terms of an angular orientation of the measurement object relative to the interferometer, a distance between the measurement object and the interferometer, and a direction of an input beam to the interferometer.

12. The method of claim 9, wherein the precalibrated information is stored as a representation in an electronic storage medium.

13. The method of claim 12, wherein the representation comprises a lookup table.

14. The method of claim 12, wherein the representation comprises a functional representation.

15. The method of claim 1, wherein the determined position of the measurement object with respect to at least one degree of freedom is related to a displacement of the measurement object relative to the interferometer.

16. The method of claim 15, wherein the determined position of the measurement object with respect to at least one degree of freedom is the displacement of the measurement object relative to the interferometer.

17. The method of claim 1, wherein the determined position of the measurement object with respect to at least one degree of freedom is related to an angular orientation of the measurement object.

18. The method of claim 17, wherein the determined position of the measurement object with respect to at least one degree of freedom is the angular orientation of the measurement object.

19. The method of claim 1, wherein determining the position of the measurement object comprises measuring the phase of the output beam and relating the phase to the position of the measurement object based on one or more values derived from the predetermined information.

20. The method of claim 19, wherein the values derived from the predetermined information are selected based on the phase.

21. The method of claim 19, wherein the values derived from the predetermined information are selected based on an angular orientation of the measurement object.

22. The method of claim 19, wherein the values derived from the predetermined information are selected based on a path of an input beam derived from the light source to the interferometer relative to the nominal path.

23. The method of claim 22, further comprising monitoring deviations of the input beam path from the nominal path.

24. The method of claim 19, wherein a relationship between the phase, Φ

, and the optical path difference can be expressed by the equation

Φ

=2pkLζ

(1−

(θ

₁−

η

₁)²−

(θ

₂−

η

₂)²+2k(X₁+X₂),

wherein p is an integer, k is a wavenumber, L is a relative distance between the interferometer and the measurement object, θ

₁ and θ

₂ are angular orientation of the measurement object with respect to the interferometer along orthogonal coordinates, and ζ and

η

₁ and η

₂ are terms that depend on the deviation of at least one of the beam paths from the nominal beam path, and X₁ and X₂ is are local displacements of a surface of the measurement object from a nominal plane surface at the first and second locations, respectively.

25. The method of claim 1, wherein using the interferometer to produce the output beam comprises producing the output beam as the measurement object is moved relative to the interferometer, and wherein determining the position of the measurement object comprises monitoring the position of the measurement object during the relative movement.

26. The method of claim 1, wherein using the interferometer to produce the output beam comprises separating an input beam into at least the first and second beams, directing the first and second beams along their respective paths, and recombining the two beams after one or both of the beams contacts the measurement object.

27. The method of claim 26, wherein the second beam contacts the measurement object at the second location and the optical path difference is related to an angular orientation of the measurement object with respect to the interferometer.

44. 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.

45. 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.

46. 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.

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

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

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

52. 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.

28. A method, comprising:

using an interferometer to produce an output beam comprising a phase related to an optical path difference between a path of a first beam and a path of a second beam, wherein the first beam contacts a measurement object at a first location;

providing precalibrated information that accounts for contributions to the optical path difference caused by a deviation of the path of the first beam out of a plane defined by a nominal beam path due to an imperfection of the measurement object at the first location; and

determining a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam and the precalibrated information.

29. The method of claim 28, wherein the precalibrated information accounts for contributions to the optical path difference caused by a deviation of a path of the first beam out within the plane defined by the nominal beam path due to the imperfection of the measurement object at the first location.

30. The method of claim 28, wherein the precalibrated information accounts for contributions to the optical path difference caused by a local displacement of a surface of the measurement object from a nominal plane surface at the first location.

31. The method of claim 28, wherein the first or second beam contacts the measurement object at a second location, wherein the first and second locations are different.

32. The method of claim 31, wherein the precalibrated information accounts for contributions to the optical path difference caused by a deviation of the path of the first or second beam from a nominal beam path due to an imperfection of the measurement object at the second location.

33. A method, comprising:

using an interferometer to produce an output beam comprising a phase related to an optical path difference between a first beam path and a second beam path, wherein the first or second beam contacts a measurement object;

providing precalibrated information that accounts for contributions to the optical path difference caused by a deviation of a path of the first beam from a nominal beam path due to an imperfection of the measurement object, and accounts for contributions to the optical path difference caused by a deviation of the path of the first beam from the nominal beam path due to an imperfection in one or more optics of the interferometer or in a light source used to produce the output beam; and

determining a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam and the precalibrated information.

34. A method, comprising:

using a first interferometer and a second interferometer in an interferometry system to produce a first output beam and a second output beam, respectively, wherein each output beam comprises a phase related to an optical path difference between two beam paths, at least one of which contacts a measurement object;

providing precalibrated information that accounts for a misalignment of an axis of the first interferometer relative to an axis of the second interferometer; and

determining a position of the measurement object with respect to at least one degree of freedom based on information derived from the first and second output beams and the precalibrated information.

35. The method of claim 34, wherein the degree of freedom corresponds to an angular orientation of the measurement object.

36. The method of claim 34, wherein for each interferometer, the precalibrated information accounts for contributions to the optical path difference caused by a deviation of at least one of the beam paths from a nominal beam path due to other imperfections in the interferometry system.

37. The method of claim 36, wherein other imperfections comprise an imperfection in at least one optic of the interferometer, an imperfection in the measurement object, or an imperfection in a light source that causes an input beam derived from the light source to deviate from an input beam path for the interferometer.

38. An apparatus comprising:

an interferometer configured to produce an output beam comprising a phase related to an optical path difference between a path of a first beam and a path of a second beam, wherein the first beam contacts a measurement object at a first location and the first or second beam contacts the interferometer at a second location, and wherein the first and second locations are different; and

an electronic controller coupled to the interferometer, wherein during operation the electronic controller determines a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam and precalibrated information that accounts for contributions to the optical path difference caused by a deviation of at least one of the beam paths from a nominal beam path due to an imperfection of the measurement object at the first location and due to an imperfection of the measurement object at the second location.

41. 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 38 for monitoring the position of the wafer relative to the imaged radiation.

42. 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 38,

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.

43. 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 38 for monitoring the position of the stage relative to the beam directing assembly.

50. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 41.

51. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 42.

39. An apparatus, comprising:

an interferometer configured to produce an output beam comprising a phase related to an optical path difference between a path of a first beam and a path of a second beam, wherein the first beam contacts a measurement object at a first location; and

an electronic controller coupled to the interferometer, wherein during operation the electronic controller determines a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam and precalibrated information that accounts for contributions to the optical path difference caused by a deviation of the path of the first beam out of a plane defined by a nominal beam path due to an imperfection of the measurement object at the first location.

40. An interferometry system, comprising:

a measurement object;

a first interferometer and a second interferometer, the first and second interferometers respectively being configured to produce an output beam comprising a phase related to an optical path difference between a path of a first beam and a path of a second beam, wherein the first beam contacts the measurement object at a first location; and

an electronic controller coupled to the interferometer, wherein during operation the electronic controller determines a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam and precalibrated information that accounts for a misalignment of an axis of the first interferometer relative to an axis of the second interferometer.