Compensation for geometric effects of beam misalignments in plane mirror interferometers

• US 20030223077A1
• Filed: 05/13/2003
• Published: 12/04/2003
• Est. Priority Date: 05/13/2002
• Status: Active Grant

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A.
• Granted Patent: US 7,330,274 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 9/02019 contacting different points on same face of object
• CPC Class Codes: G01B 9/02061 Reduction or prevention of effects of tilts or misalignment
• CPC Class Codes: G03F 7/70775 Position control, e.g. interferometers or encoders for determining the stage position

Abstract

Techniques for compensating for geometric effects of beam misalignment in plane mirror interferometers are disclosed.

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 two beam paths, at least one of which contacts a measurement object in the interferometry system;

providing 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 in the interferometry system; 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 imperfection comprises an imperfection in at least one optic of the interferometer.

3. The method of claim 2, wherein the imperfection in at least one optic of the interferometer comprises an imperfection in a surface of the optic.

4. The method of claim 2, wherein the imperfection in at least one optic of the interferometer comprises a bulk imperfection in the optic.

5. The method of claim 1, wherein the imperfection comprises an imperfection in an optic of the measurement object.

6. The method of claim 1, wherein the imperfection comprises 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.

7. 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.

8. The method of claim 7, 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.

9. The method of claim 8, 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.

10. The method of claim 7, wherein the precalibrated information is stored as a representation in an electronic storage medium.

11. The method of claim 10, wherein the representation comprises a lookup table.

12. The method of claim 10, wherein the representation comprises a functional representation.

13. 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.

14. The method of claim 13, 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.

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 an angular orientation of the measurement object.

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 angular orientation of the measurement object.

17. The method of claim 1, wherein determining the position of the measurement object comprises measuring a 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.

18. The method of claim 17, wherein the values derived from the predetermined information are selected based on the phase.

19. The method of claim 17, wherein the values derived from the predetermined information are selected based on an angular orientation of the measurement object.

20. The method of claim 17, 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.

21. The method of claim 20, further comprising monitoring deviations of the input beam path from the nominal path.

22. The method of claim 17, wherein a relationship between the phase, d), and the optical path difference can be expressed by the equation

Φ

=2pkLζ

(1−

(θ

−

η

)²),

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

is an angular orientation of the measurement object with respect to the interferometer, and ζ and

η

are terms that depend on the deviation of at least one of the beam paths from the nominal beam path.

23. 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.

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

25. The method of claim 24, wherein both beam paths contact the measurement object.

26. The method of claim 25, wherein the optical path difference is related to an angular orientation of the measurement object with respect to the interferometer.

27. A method comprising:

using an interferometer to produce an output beam comprising 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 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 in at least one of a light source for the interferometer, the interferometer, or the measurement object; and

determining a displacement of the measurement object relative to the interferometer based on the precalibrated information and information derived from the output beam.

28. A method comprising:

correcting interferometric measurements made by an interferometry system based on precalibrated information that accounts for contributions to an optical path difference caused by a deviation of at least one beam path from a nominal beam path due to an imperfection in the interferometry system.

38. 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 28.

39. 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 28;

and

imaging the spatially patterned radiation onto a wafer.

40. 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 28.

41. A method for fabricating integrated circuits, the method comprising the lithography method of claim 38.

42. A method for fabricating integrated circuits, the method comprising the lithography method of claim 39.

43. A method for fabricating integrated circuits, the method comprising the lithography method of claim 40.

46. 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 28.

29. A method comprising:

calibrating an interferometry system by determining information that accounts for contributions to an optical path difference caused by a deviation of at least one beam path from a nominal beam path due to an imperfection in the interferometry system.

30. The method of claim 29, wherein the calibrating comprises monitoring changes in a direction of one or more intermediate beams in the interferometry system while varying the optical path difference.

31. The method of claim 30, wherein the varying of the optical path difference comprises displacing a measurement object relative to an interferometer in the interferometry system.

32. The method of claim 30, wherein the varying of the optical path difference comprises changing an angular orientation of a measurement object relative to an interferometer in the interferometry system.

33. An apparatus comprising:

an interferometer configured to produce an output beam comprising a phase related to an optical path difference between two beam paths, at least one of which contacts a measurement object; 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 in at least one of a light source for the interferometer, the interferometer, or the measurement object.

35. 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 33 for monitoring the position of the wafer relative to the imaged radiation.

36. 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 33,

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.

37. 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 33 for monitoring the position of the stage relative to the beam directing assembly.

44. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 35.

45. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 36.

34. An apparatus comprising an electronic storage medium storing 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 in at least one of a light source for the interferometer, the interferometer, or the measurement object.