Angle interferometers

• US 20070064240A1
• Filed: 08/15/2006
• Published: 03/22/2007
• Est. Priority Date: 08/16/2005
• Status: Active Grant

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry
• Granted Patent: US 7,532,330 B2
• Time in Patent Office: Days
• US Class Current: 356/487
• CPC Class Codes: G01B 11/272 using photoelectric detection means
• CPC Class Codes: G01B 2290/45 Multiple detectors for detecting interferometer signals
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02003 using beat frequencies
• CPC Class Codes: G01B 9/02027 Two or more interferometric channels or interferometers
• CPC Class Codes: G03F 7/70775 Position control, e.g. interferometers or encoders for determining the stage position

Abstract

Methods and systems for determining information about the incident angle of a beam are disclosed, the method including directing a beam having an s-polarized component and a p-polarized component to reflect from an interface at a non-normal angle, where the non-normal reflection introduces for each component a phase change upon reflection that is different for each component, and measuring an optical interference signal related to the phase change between the components of the reflected beam.

Claims

1. A method, comprising:

directing a beam to reflect from an interface at a non-normal angle, the beam having an s-polarized component and a p-polarized component at the interface, wherein the non-normal reflection introduces a phase change upon reflection for each component that differs from one another according to the incident angle of the beam; and

measuring an optical interference signal related to the phase change between the components of the reflected beam to determine information about the incident angle of the beam.

2. The method of claim 1, wherein the information is determined based on a phase of the optical interference signal.

3. The method of claim 2, wherein the beam reflects from the interface more than once and the phase of the optical interference signal is related to a number of times the beam reflects from the interface.

4. The method of claim 2, wherein the phase of the optical interference signal varies depending on a deviation, dθ

_s, of the s-polarized component and a deviation, dθ

_p, of the p-polarized polarized component from a nominal beam path.

5. The method of claim 4, wherein the phase of the optical interference signal is proportional to a difference between dθ

_s and dθ

_p.

6. The method of claim 1, wherein the beam is directed to the interface at an angle near the angle for total internal reflection.

7. The method of claim 1, wherein the beam experiences total internal reflection at the interface.

8. The method of claim 1, wherein the beam reflects from the interface multiple times.

9. The method of claim 1, wherein the interface is a first surface of a prism.

10. The method of claim 9, wherein the beam reflects from a second surface of the prism at a non-normal angle.

11. The method of claim 10, wherein the second surface is substantially parallel to the first surface.

12. The method of claim 1, wherein the s- and p-polarized beam components have different frequencies.

13. The method of claim 1, wherein the interface is a surface of a first optical element and the method further comprises directing the beam to reflect from a surface of a second optical element at a non-normal angle.

14. The method of claim 13, wherein the surface of the first optical element is substantially parallel to the surface of the second optical element.

15. The method of claim 13, further comprising rotating the polarization of the beam after the beam exits the first optical element prior to directing the beam to reflect from the surface of the second optical element.

16. The method of claim 15, wherein the polarization of the beam is rotated so that the s-polarized component of the beam at the surface of the first optical element corresponds to the p-polarized component of the beam at the surface of the second optical element.

17. The method of claim 13, wherein an optical path length of the beam in the first optical element is substantially equal to an optical path length of the beam in the second optical element.

18. The method of claim 1, further comprising reducing a width of the beam in at least one dimension prior to directing the beam to reflect from the interface.

19. The method of claim 1, wherein a path of the s-polarized component deviates from a path of the p-polarized component.

20. The method of claim 1, further comprising deriving the beam from an output beam of a displacement measuring interferometer used to monitor the position of a measurement object.

21. The method of claim 20, further comprising using the determined information about the incident angle of the beam to reduce errors in the monitored position of the measurement object.

22. The method of claim 21, wherein the displacement measuring interferometer monitors the position of the measurement object by directing a measurement beam to reflect from a measurement object and combining the measurement beam with another beam to form the output beam, and wherein either the s-polarized component or the p-polarized component corresponds to the measurement beam.

23. A system, comprising:

an optical element having an interface positioned relative to a beam path so that a beam propagating along the path reflects from the interface at a non-normal angle, the beam having an s-polarized component and a p-polarized component at the interface, wherein the non-normal reflection introduces a phase change upon reflection for the s-polarized and p-polarized components that differ from one another according to the incident angle of the beam;

a detector positioned to receive the beam after it reflects from the interface; and

an electronic processor coupled to the detector and configured to measure an optical interference signal related to the phase change between the components of the reflected beam to determine information about the incident angle of the beam.

24. The system of claim 23, wherein the optical element is a prism and the interface is a first surface of the prism.

25. The system of claim 24, wherein the first surface is oriented so that the beam experiences total internal reflection at the first surface.

26. The system of claim 24, wherein the prism comprises a second surface opposite the first surface and the beam reflects from the second surface at a non-normal angle.

27. The system of claim 26, wherein the second surface is substantially parallel to the first surface.

28. The system of claim 23, further comprising a second optical element having an interface positioned relative to the beam path after the first optical element, wherein the interface of the second optical element is substantially parallel to the interface of the first optical element.

29. The system of claim 28, wherein the first and second optical elements are a pair of prisms.

30. The system of claim 29, wherein the prisms are substantially the same size and shape.

31. The system of claim 28, further comprising a wave plate positioned in the path of the beam between the first and second optical elements.

32. The system of claim 31, wherein the beam has a wavelength λ

and the wave plate is a half wave plate at λ

.

33. The system of claim 31, wherein the wave plate is configured to transform the polarization of the beam so that the s-polarized component of the beam at the first interface corresponds to the p-polarized component of the beam at the second interface.

34. The system of claim 23, further comprising an afocal system positioned in the path of the beam prior to the optical element, the afocal system being configured to reduce a width of the beam in at least one dimension.

35. The system of claim 23, wherein the electronic processor coupled to the detector is configured to determine information about the incident angle of the beam in a first plane.

36. The system of claim 35, further comprising an assembly positioned in the path of the beam prior to the optical element, the assembly being configured to derive a secondary beam from the beam and to direct the secondary beam to an angle interferometer configured to determine information about the incident angle of the beam in a second plane orthogonal to the first plane.

37. The system of claim 36, wherein the angle interferometer comprises the optical element.

38. The system of claim 23, further comprising a light source configured to provide the beam where the s-polarized and p-polarized components have different frequencies.

39. The system of claim 23, further comprising a interferometry system configured to monitor a position of a measurement object, the interferometry system comprising an interferometer configured to direct a measurement beam to reflect from the measurement object and to combine the reflected measurement beam with another beam to form an output beam, the system further configured to direct a beam related to the output beam along the beam path to reflect from the interface at the non-normal angle.

40. The system of claim 39, wherein the measurement beam corresponds to either the s-polarized component or the p-polarized component of the beam at the interface.

41. The system of claim 39, wherein the electronic processor is further configured to use the determined information about the incident angle of the beam to reduce errors in the monitored position of the measurement object.

42. 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 system of claim 39 wherein the interferometry system is configured to monitor the position of the wafer relative to the imaged radiation.

43. 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 system of claim 39,

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.

44. 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 system of claim 39 wherein the interferometry system is configured to monitor the position of the stage relative to the beam directing assembly.

45. 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 system of claim 39.

46. 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 system of claim 39;

and

imaging the spatially patterned radiation onto a wafer.

47. 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 system of claim 39.

48. 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 system of claim 39.