Separated beam multiple degree of freedom interferometer

• US 20030186136A1
• Filed: 02/11/2003
• Published: 10/02/2003
• Est. Priority Date: 02/12/2002
• Status: Active Grant

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A.
• Granted Patent: US 7,057,739 B2
• Time in Patent Office: Days
• US Class Current: 430/5
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02003 using beat frequencies
• CPC Class Codes: G01B 9/02019 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 interferometric apparatus includes: a polarizing beam-splitting interface positioned to separate an input beam into two orthogonally polarized beams; and interferometer optics positioned to receive a first set of beams derived from one of the orthogonally polarized beams and a second set of beams derived from the other of the orthogonally polarized beams. The interferometer optics are configured to direct each beam in the first set to contact different locations of a measurement object at least once, and subsequently combine each beam in the first set with a corresponding beam from the second set of beams to produce a corresponding output beam comprising information about changes in the position of the measurement object with respect to a different degree of freedom.

Claims

1. Interferometric apparatus comprising:

a polarizing beam-splitting interface positioned to separate an input beam into two orthogonally polarized beams; and

interferometer optics positioned to receive a first set of beams derived from one of the orthogonally polarized beams and a second set of beams derived from the other of the orthogonally polarized beams,

wherein the interferometer optics are configured to direct each beam in the first set to contact different locations of a measurement object at least once, and subsequently combine each beam in the first set with a corresponding beam from the second set of beams to produce a corresponding output beam comprising information about changes in the position of the measurement object with respect to a different degree of freedom.

2. The apparatus of claim 1, further comprising a light source for producing the input beam and directing it to the polarizing beam-splitting interface, wherein the light source is configured to generate a frequency splitting suitable for heterodyne detection between the orthogonal polarized components of the input beam.

3. The apparatus of claim 1, wherein each beam from the first set of beams is spatially separated from the corresponding beam from the second set upon entering the interferometer optics.

4. The system of claim 1, wherein the beams in the first and second sets have the same polarization upon entering the interferometer optics.

5. The apparatus of claim 1, wherein one of the output beams comprises information about changes in distance to a first location on the measurement object.

6. The apparatus of claim 1, wherein another of the output beams comprises information about changes in distance to a second location on the measurement object, wherein the second location different from the first location.

7. The apparatus of claim 1, wherein the interferometer optics direct at least one of the beams from the first set to contact the measurement object at least twice before it is combined with the corresponding beam from the second set.

8. The apparatus of claim 1, wherein at least one of the output beams comprises information about changes in an angular orientation of the measurement object with respect to a first rotation axis.

9. The apparatus of claim 1, wherein the interferometer optics direct at least one of the beams from the first set to contact the measurement object only once and direct the corresponding beam from the second set to likewise contact the measurement object only once, but at a location different from that of the one beam in the first set, and prior to combining it with the one beam in the first set.

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

11. The apparatus of claim 1, wherein the interferometer optics are configured to produce more than two output beams, each of which provides information about changes in the position of the measurement object with respect to a different degree of freedom.

12. The apparatus of claim 11, further comprising a non-polarizing, input beam-splitting assembly configured to separate a progenitor input beam into the first-mentioned input beam and a parallel propagating second input beam spatially separated from the first input beam, and wherein the input beam-splitting assembly is further configured to direct the spatially separated first and second input beams to the polarizing beam-splitter interface,

wherein the polarizing beam-splitting interface is positioned to separate the second input beam into a second set of two orthogonally polarized beams, and

wherein interferometer optics are positioned to receive a third set of beams derived from one of the second set of orthogonally polarized beams and a fourth set of beams derived from the other of the second set of othogonally polarized beams,

wherein the interferometer optics are configured to direct each beam in the third set of beams to contact different locations of a measurement object at least once, and subsequently combine each beam from the third set of beams with a corresponding beam from the fourth set of beams to produce a corresponding output beam comprising information about changes in the position of the measurement object with respect to a different degree of freedom.

13. The apparatus of claim 1, further comprising polarization modification optics positioned to receive a first one of the orthogonally polarized beams and produce a modified polarized beam having a polarization orthogonal to that of the first polarized beam.

14. The apparatus of claim 13, wherein the polarization modification optics comprise a retarder and at least one reflector.

15. The apparatus of claim 14, wherein the retarder and the reflector are in sequence, and the reflector is positioned to direct the first polarized beam beam back through the retarder to the polarizing beam splitter to define the modified polarized beam.

16. The apparatus of claim 15, wherein the retarder is a quarter wave retarder.

17. The apparatus of claim 14, wherein the retarder is a half-wave retarder positioned to receive the first polarized beam and produce the modified polarized beam, and wherein the at least one reflector comprises a pair of reflectors.

18. The apparatus of claim 13, wherein the first set of beams are derived from the modified polarized beam.

19. The apparatus of claim 13, wherein the second set of beams are derived from the modified polarized beam.

20. The apparatus of claim 1, further comprising non-polarizing beam-splitting optics positioned to generate the first and second sets of beams from the two orthogonally polarized beams.

21. The apparatus of claim 20, wherein the non-polarizing beam-splitting optics comprises a first non-polarizing beams splitting interface positioned to generate at least two of the first set of beams and a second non-polarizing beam-splitting interface positioned to generate at least two of the second set of beams.

22. The apparatus of claim 21, wherein the non-polarizing beam-splitting optics further comprise at least one reflector for causing the beams from the first set to be parallel to one another upon entering the interferometer optics.

23. The apparatus of claim 22, wherein the non-polarizing beam-splitting optics further comprise at least one reflector for causing the beams from the second set to be parallel to one another upon entering the interferometer optics.

24. The apparatus of claim 1, further comprising a second polarizing beam-splitting interface positioned in the interferometer optics.

25. The apparatus of claim 24, further comprising a first polarizing beam-splitter optic defining the first-mentioned polarizing beam-splitter interface, and a second polarizing beam splitter optic in the interferometer optics defining the second polarizing beam-splitter interface.

26. The apparatus of claim 24, further comprising a common polarizing beam-splitter optic defining the first-mentioned polarizing beam-splitting interface and the second polarizing beam-splitting interface.

27. The apparatus of claim 24, wherein the interferometer optics further comprise a quarter wave retarder positioned between the second polarizing beam-splitting interface and the measurement object.

28. The apparatus of claim 27, wherein the interferometer optics further comprises a reference mirror and a quarter wave retarder positioned between the second polarizing beam-splitting interface and the reference mirror, and wherein the second polarizing beam-splitting interface is positioned to direct each beam in the second set to contact the reference mirror at least once.

29. The apparatus of claim 28, wherein the interferometer optics further comprise fold optics positioned to receive from the second polarizing beam-splitting interface the first set of beams after they contact the measurement object for a first time and the second set of beams after they contact the reference mirror for a first time and subsequently direct the first and second sets of beams back to the second polarizing beam-splitting interface.

30. The apparatus of claim 29, wherein upon receiving the first and second sets of beams from the fold optics, the second polarizing beam-splitting interface is configured to direct each beam in the first set of beams to contact the measurement object for a second time and each beam in the second set of beams to contact the reference mirror for a second time.

31. The apparatus of claim 29, wherein the fold optics comprise a retarder positioned to receive a first one of the beams in the first set and the corresponding beam from the second set and rotate their respective polarizations by about 90 degrees before they return to the second polarizing beam-splitting interface.

32. The apparatus of claim 31, wherein upon receiving the first and second sets of beams from the fold optics including the retarder, the second polarizing beam-splitting interface is configured to direct the first beam from the first set of beams to contact the reference mirror and direct the corresponding beam in the second set to contact the measurement object.

33. The apparatus of claim 31, wherein the retarder is a half-wave retarder.

34. The apparatus of claim 31, wherein the fold optics are configured to reflect the first beam from the first set and the corresponding beam from the second set an odd number of times from surfaces that have normal directions in a common plane when directing them back to the second polarizing beam-splitting interface.

36. 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 for monitoring the position of the wafer relative to the imaged radiation.

37. 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,

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.

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

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

46. A method for fabricating integrated circuits, the method comprising using the lithography apparatus of claim 37.

35. An interferometric method comprising:

separating an input beam into two orthogonally polarized beams;

directing each beam from a first set of beams derived from one of the orthogonally polarized beams to contact different locations of a measurement object at least once; and

subsequently combining each beam in the first set with a corresponding beam from a second set of beams derived from the other one of the orthogonally polarized beams to produce a corresponding output beam comprising information about changes in the position of the measurement object with respect to a different degree of freedom.

39. 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 35.

40. 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 35;

and

imaging the spatially patterned radiation onto a wafer.

41. 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 35.

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.

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

47. 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 35.