Dynamic interferometer controlling direction of input beam

• US 20030043384A1
• Filed: 08/23/2002
• Published: 03/06/2003
• Est. Priority Date: 08/23/2001
• Status: Active Grant

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A.
• Granted Patent: US 6,987,569 B2
• Time in Patent Office: Days
• US Class Current: 356/510
• 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 9/02068 Auto-alignment of optical elements
• CPC Class Codes: G03F 7/70775 Position control, e.g. interferometers or encoders for determining the stage position

Abstract

Interferometers can be configured to maintain a measurement beam substantially orthogonal to a plane measurement mirror and to minimize the lateral beam shear between the measurement and reference beam components of the output beam to a detector. These interferometers use a dynamic beam steering element to redirect the input beam in response to changes in the orientation of the measurement plane mirror. These interferometers may be further configured to measure displacement and change in orientation of the plane mirror or configured in a combination of single pass interferometers fed by the input beam for measuring displacement and change in orientation of the plane mirror.

Claims

1. An interferometry system, comprising:

an interferometer which during operation receives an input beam, separates the input beam into a measurement beam and another beam, directs the measurement beam to contact a measurement object, and overlaps the measurement beam after it reflects from the measurement object with the other beam to form an output beam;

a beam steering assembly having a beam steering element positioned to direct the input beam into the interferometer and to not contact the output beam, and an electronic positioning system to selectively orient the beam steering element relative to the interferometer; and

a control circuit coupled to the positioning system which during operation causes the positioning system to reorient the beam steering element based on information derived from the output beam.

2. The system of claim 1, wherein the control circuit comprises a signal processor which during operation calculates a change in angular orientation of the measurement object based on the information derived from the output beam.

3. The system of claim 1, wherein during operation the control circuit causes the positioning system to reorient the beam steering element in response to a change in the angular orientation of the measurement object.

4. The system of claim 1, wherein the control circuit causes the positioning system to reorient the beam steering element based on a change in direction or position of the measurement beam.

5. The system of claim 1, wherein the interferometer directs the measurement beam to contact the measurement object multiple times.

6. The interferometry system of claim 1, wherein the measurement object comprises a plane mirror.

7. The interferometry system of claim 6, wherein during operation the beam steering assembly causes the measurement beam to be orthogonal to the plane mirror for a range of orientations of the plane mirror.

8. The system of claim 1, wherein the beam steering assembly changes a propagation direction of the input beam in response to changes in the output beam in order to minimize a difference in propagation directions between the measurement beam and the other beam in the output beam.

9. The system of claim 1, wherein the control circuit further comprises a differential angle displacement interferometer, which during operation generates an interference signal related to a difference in propagation directions between the measurement beam and the other beam in the output beam.

10. The system of claim 9, wherein the interference signal is related to a difference in propagation directions in a first plane between the measurement beam and the other beam in the output beam.

11. The system of claim 10, further comprising a second differential angle displacement interferometer, which during operation generates an interference signal related to a difference in propagation directions between the measurement beam and the at least one other beam in the output beam in a second plane perpendicular to the first plane.

12. The system of claim 9, further comprising a beam splitter, which during operation derives a secondary output beam from the output beam and directs the secondary output beam towards the differential angle displacement interferometer.

13. The interferometry system of claim 12, wherein during operation the differential angle displacement interferometer splits the secondary output beam into first and second components, directs the first and second components along first and second paths, and overlaps the first and second components at a detector.

14. The interferometry system of claim 13, wherein during operation the overlapping first and second components cause the detector to generate an interference signal related to a propagation direction of the output beam.

15. The interferometry system of claim 9, wherein the interference signal is related to the orientation of the measurement object.

16. The interferometry system of claim 9, wherein the differential angle displacement interferometer comprises an etalon, and transmission of the secondary output beam through the etalon is related to a propagation direction of the output beam.

17. The system of claim 1, wherein the control circuit further comprises an angle displacement interferometer, which during operation generates an interference signal related to a propagation direction of the output beam.

18. The interferometry system of claim 1, wherein the interferometer is a single pass interferometer.

19. The interferometry system of claim 1, further comprising a light source positioned relative to the beam steering assembly so that during operation the light source directs the input beam toward the beam steering assembly.

20. The interferometry system of claim 1, further comprising a detector positioned to receive the output beam from the interferometer.

21. 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 1 for monitoring the position of the wafer relative to the imaged radiation.

22. 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 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.

23. A lithography system for fabricating integrated circuits, comprising:

first and second components, the first and second components being movable relative to one another; and

the interferometry system of claim 1 secured to the second component, wherein the measurement object is rigidly secured to the first component and during operation the interferometry system measures the position of the first component relative to the second component.

24. 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 inteferometry system of claim 1, for monitoring the position of the stage relative to the beam directing assembly.

25. A method, comprising:

directing an input beam to contact a beam steering element prior to entering an interferometer;

splitting the directed input beam into a measurement beam and at least one other beam;

directing the measurement beam to reflect from the measurement object at least once;

overlapping the reflected measurement beam and the at least one other beam to form an output beam which does not contact the beam steering element; and

electronically reorienting the beam steering element based on information derived from the output beam.

26. A lithography method, comprising:

positioning a first component of a lithography system relative to a second component of a lithography system to expose a wafer to spatially patterned radiation; and

measuring the position of the first component relative to the second component using the method of claim 25 wherein the first component includes the measurement object.

27. A beam writing method for use in 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

measuring the position of the substrate relative to the write beam using the interferometry method of claim 25.