Athermal zero-shear interferometer

• US 20040004722A1
• Filed: 04/24/2003
• Published: 01/08/2004
• Est. Priority Date: 04/24/2002
• Status: Active Grant

• Current Assignee: Zygo Corporation (Ametek Incorporated)
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Carlson, Andrew Eric
• Granted Patent: US 7,030,993 B2
• Time in Patent Office: Days
• US Class Current: 356/493
• CPC Class Codes: G01B 2290/15 Cat eye, i.e. reflection always parallel to incoming beam
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• 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

An interferometer for receiving a measurement beam from a target location on a stage of a semiconductor lithography machine and a reference beam from a reference location separated from the target location by a separation distance. The interferometer has a reference path to be traversed by the reference beam within the interferometer and a measurement path to be traversed by the measurement beam within the interferometer. Both the measurement path and the reference path are at least as long as the separation distance between the reference location and the target location.

Claims

1. An interferometer comprising:

a first polarizing beam splitter configured to direct an input beam in a direction that depends on a polarization state of the input beam; and

a second polarizing beam splitter configured to receive an output beam from the first polarizing beam splitter and to direct the received output beam in a direction that depends on a polarization state thereof.

2. The interferometer of claim 1, further comprising a polarization rotator on an optical path between the first and second polarizing beam splitters for rotating the polarization of the output beam received from the first polarizing beam splitter.

3. The interferometer of claim 1, further comprising

a first retroreflector in optical communication with the first polarizing beam splitter;

and

a second retroreflector in optical communication with the second polarizing beam splitter.

4. The interferometer of claim 1, wherein the polarization rotator comprises a half-wave plate.

5. The interferometer of claim 1, further comprising a steering wedge disposed on an optical path between the first and second polarizing beam splitters.

6. The interferometer of claim 3, further comprising:

a first reflective polarization-rotator in optical communication with the first retroreflector;

a second reflective polarization-rotator in optical communication with the second retroreflector.

7. The interferometer of claim 6, wherein at least one of the first and second reflective polarization-rotators comprises a mirror in optical communication with a quarter-wave plate.

8. A semiconductor lithography system comprising:

an interferometer as recited in claim 1;

and

a semiconductor lithography machine having

a base in optical communication with the second polarizing beam splitter of the interferometer, and

a stage moveable relative to the base, the stage being in optical communication with the first polarizing beam splitter of the interferometer.

9. An interferometer comprising:

a first polarizing beam splitter in optical communication with a first retroreflector;

a first reflective polarization-rotator on an optical path between the first polarizing beam-splitter and the first retroreflector;

a second polarizing beam-splitter in optical communication with a second retroreflector;

a second reflective polarization-rotator on an optical path between the second polarizing beam-splitter and the second retroreflector; and

a third polarization rotator on an optical path between the first and second polarizing beam-splitters.

10. The interferometer of claim 9, wherein the first polarizing beam-splitter comprises:

a first beam-splitting plane oriented to reflect light having a first polarization toward the third polarization rotator, and

a second beam-splitting plane in optical communication with the first beam-splitting plane, the second beam-splitting plane being

oriented to transmit light having a second polarization received from the first beam-splitting plane to the first retroreflector, and

oriented to reflect light received from the first retroreflector and having the first polarization toward the third polarization rotator.

11. The interferometer of claim 9, wherein the second polarizing beam-splitter comprises

a mirror plane oriented to redirect light received from the first polarizing beam-splitter;

and

a third beam-splitting plane in optical communication

with the mirror plane,

with the second retroreflector, and

with the first polarizing beam-splitter,

the third beam-splitting plane being

oriented to transmit light received from the mirror plane toward the second retroreflector,

oriented to transmit, toward a detector, light received from the second retroreflector and having the first polarization, and

oriented to transmit, toward the detector, light received from the first polarizing beam-splitter and having the second polarization.

12. The interferometer of claim 9, further comprising a steering wedge on the optical path between the first polarizing beam splitter and the second polarizing beam splitter.

13. The interferometer of claim 9, wherein the third polarization-rotator comprises a half-wave plate.

14. The interferometer of claim 9, wherein at least one of the first and second reflective polarization-rotators comprises a mirror in optical communication with a quarter-wave plate.

15. The interferometer of claim 9, wherein the first and second mirror are integral with each other.

16. A semiconductor lithography system comprising:

an interferometer as recited in claim 9;

and

a semiconductor lithography machine having

a base on which is mounted the second retroreflector;

a stage on which is mounted the first retroreflector, the stage being moveable relative to the base;

17. An interferometer for receiving a measurement beam from a target location and a reference beam from a reference location separated from the target location by a separation distance, the interferometer comprising:

a reference path to be traversed by the reference beam within the interferometer the reference path having a reference-path length at least as long as the separation distance, and

a measurement path to be traversed by the measurement beam within the interferometer, the measurement path having a measurement-path length at least as long as the separation distance.

18. The interferometer of claim 17, further comprising:

a first polarizing beam-splitter disposed to intersect the reference path and the measurement path; and

a second polarizing beam splitter disposed to intersect the measurement path and the reference path.

19. The interferometer of claim 17, further comprising a polarization rotator disposed to intersect at least one of the reference path and the measurement path.

20. The interferometer of claim 19, wherein the polarization rotator comprises a reflective-polarization rotator.

21. The interferometer of claim 20, wherein the reflective polarization-rotator comprises a quarter-wave plate in optical communication with a mirror.

22. The interferometer of claim 18, further comprising a polarization rotator disposed to intersect the reference path and the measurement path between the first and second polarizing beam-splitters.

23. The interferometer of claim 22, wherein the polarization rotator comprises a half-wave plate.

24. A semiconductor lithography system comprising:

an interferometer as recited in claim 17;

and

a semiconductor lithography machine having

a base defining the reference location;

a stage defining the target location, the stage being moveable relative to the base.

25. The semiconductor lithography system of claim 24, further comprising

a reference retroreflector mounted on the base at the reference location;

and

a measurement retroreflector mounted on the stage at the target location.

26. A method for determining the location of a moveable stage of a semiconductor lithography machine relative to a base separated from the stage by a separation distance, the method comprising:

directing a measurement beam along a measurement path that intersects the stage;

directing a reference beam along a reference path that intersects the base;

causing the reference beam to traverse a path length within an interferometer that is at least as long as the separation distance; and

causing the measurement beam to traverse a path length within the interferometer that is at least as long as the separation distance.