Compensation for effects of beam misalignments in interferometer metrology systems

• US 7,327,465 B2
• Filed: 10/13/2005
• Issued: 02/05/2008
• Est. Priority Date: 06/19/2003
• Status: Expired due to Fees

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A.
• Primary Examiner(s): CONNOLLY, PATRICK J
• Application Number:
  US11/250,116
• Publication Number:
  US 20060061771A1
• Time in Patent Office: 845 Days
• Field of Search: 356/486, 356/487, 356/498, 356/500, 356/508, 356/510, 356/493
• US Class Current: 356/498
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02007 Two or more frequencies or sources used for interferometric measurement using only beat G01B9/02003
• 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: G01B 9/02074 of the detector
• CPC Class Codes: G01B 9/02098 Shearing interferometers
• 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 general, in a first aspect, the invention features methods that include deriving a first beam and a second beam from an input beam and directing the first and second beams along different paths, where the path of the first beam contacts a measurement object, producing an output beam comprising a phase related to an optical path difference between the different beam paths, determining a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam, monitoring variations in a direction of the input beam, and using the monitored variations in the direction of the input beam to reduce errors in the determined position associated with deviations of the path of the input beam from a nominal input beam path.

Claims

1. A method, comprising:

deriving a first beam and a second beam from an input beam and directing the first and second beams along different paths, where the path of the first beam contacts a measurement object;

producing an output beam comprising a phase related to an optical path difference between the different beam paths;

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

monitoring variations in a direction of the input beam; and

using the monitored variations in the direction of the input beam to reduce errors in the determined position associated with deviations of the path of the input beam from a nominal input beam path.

2. The method of claim 1, wherein the variations in the input beam direction are monitored using an angle interferometer.

3. The method of claim 1, wherein variations in the input beam direction are monitored in a first plane.

4. The method of claim 3, wherein variations in the input beam direction are also monitored in a second plane orthogonal to the first plane.

5. The method claim 1, wherein the errors in the determined position of the measurement object are reduced based on precalibrated information that accounts for contributions to the optical path difference caused by a deviation of the path of the input beam from the nominal input beam path.

6. The method of claim 5, wherein the precalibrated information comprises a set of correction data values and reducing the errors includes selecting one of the values from the set of correction data values based on the monitored variation.

7. The method of claim 6, wherein the precalibrated information comprises a lookup table including the set of correction data values.

8. The method of claim 5, wherein reducing the errors includes determining a correction value using the precalibrated information and the monitored variation.

9. The method of claim 8, wherein the precalibrated information comprises information describing a functional relationship between the input beam path and corrections to the position of the measurement object.

10. The method of claim 1, wherein the input beam is directed to the interferometer via a beam steering assembly.

11. The method of claim 10, wherein the errors are reduced by adjusting the beam steering assembly to reduce a deviation of the path of the input beam from the nominal input beam path based on the monitored variations.

12. The method of claim 11, wherein the beam steering assembly is adjusted using a servo controller that receives information about the monitored variations in the input beam direction.

13. The interferometry system of claim 10, wherein the measurement object comprises a plane mirror.

14. The interferometry system of claim 13, wherein the beam steering assembly causes the measurement beam to be orthogonal to the plane mirror for a range of orientations of the plane mirror.

15. The method of claim 1, further comprising directing a preconditioned input beam to reflect from the measurement object and deriving the input beam from the preconditioned input beam after it reflects from the measurement object.

16. The method of claim 15, wherein the variations in the input beam direction are monitored by monitoring variations in the direction of the preconditioned input beam.

31. 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.

32. 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.

33. 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.

34. A method for fabricating integrated circuits, the method comprising the lithography method of claim 31.

35. A method for fabricating integrated circuits, the method comprising the lithography method of claim 32.

36. A method for fabricating integrated circuits, the method comprising the lithography method of claim 33.

39. 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 method of claim 1.

17. A system, comprising:

an interferometer configured to derive a first beam and a second beam from an input beam, to direct the first and second beams along different paths, where the path of the first beam contacts a measurement object, and to produce an output beam comprising a phase related to an optical path difference between the different beam paths;

an angle interferometer configured to monitor variations in a direction of the input beam; and

an electronic controller configured to determine a position of the measurement object with respect to at least one degree of freedom based on information derived from the output beam and to use the monitored variations in the direction of the input beam to reduce errors in the determined position associated with deviations of the path of the input beam from a nominal input beam path.

18. The system of claim 17, wherein the interferometer is a multiple pass interferometer.

19. The system of claim 17, wherein the angle interferometer comprises a beam shearing assembly configured to introduce a shear between two orthogonally polarized components of a secondary beam related to the input beam, the amount of the shear being related to a direction of the secondary beam.

20. The system of claim 17, further comprising a beam steering assembly having a beam steering element configured to direct the input beam to the interferometer and an electronic positioning system to selectively orient the beam steering element relative to the interferometer.

21. The system of claim 20, further comprising a control circuit coupled to the electronic positioning system and configured to cause the electronic positioning system to reorient the beam steering element based on information derived from the output beam or based on the monitored variations in the direction of the input beam.

22. The system of claim 17, further comprising a beam conditioning assembly configured to direct an initial beam to reflect from the measurement object and derive the input beam from the initial beam after it reflects from the measurement object.

23. The system of claim 22, wherein the beam conditioning assembly comprises an optical system configured to direct the initial beam to reflect from the measurement object to cause a change in propagating direction of the input beam in response to a change in the angular orientation of the measurement object with respect to the initial beam.

24. The system of claim 23, wherein the optical system comprises a single pass interferometer.

25. The system of claim 23, wherein the beam conditioning assembly further comprises an afocal system that scales the change in propagation direction of the conditioned beam by an amount related to a magnification of the afocal system.

26. The system of claim 25, wherein the factor is 2.

27. The system of claim 22, further comprising a beam splitter configured to derive a secondary beam from the initial beam and to direct the secondary beam to the angle interferometer, and wherein the angle interferometer is configured to monitor variations in the direction of the input beam by monitoring a direction of the secondary beam.

28. 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 interferometry system of claim 17 for monitoring the position of the wafer relative to the imaged radiation.

29. 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 interferometry system of claim 17,

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.

30. 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 interferometry system of claim 17 for monitoring the position of the stage relative to the beam directing assembly.

37. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 28.

38. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 29.