System and method to form unpolarized light

• US 7,649,676 B2
• Filed: 06/14/2006
• Issued: 01/19/2010
• Est. Priority Date: 06/14/2006
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Baselmans, Johannes Jacobus Matheus, Visser, Huibert
• Primary Examiner(s): MARTINEZ, JOSEPH P
• Application Number:
  US11/452,435
• Publication Number:
  US 20070291372A1
• Time in Patent Office: 1,315 Days
• Field of Search: 359301-303, 359/629, 359/831, 359/832, 359/834, 372/27, 372/106, 355/71
• US Class Current: 359/301
• CPC Class Codes: G02B 27/123 The splitting element being a lens or a system of lenses, including arrays and surfaces with refractive power
• CPC Class Codes: G03F 7/70566 Polarisation control

Abstract

A system and method are used to form an unpolarized light beam from a polarized light beam. A system comprises a source of radiation and a unpolarizing system. The source of radiation produces a linear polarized beam. The unpolarizing system has first and second optical paths and splits the linear polarized beam. A first portion of the split beam travels along the first optical path having a first path length. A second portion of the split beam travels along the second optical path having a second, different path length. The first and second portions of the split beam are combined to form the unpolarized beam.

Claims

1. A system, comprising:

a source of radiation that produces a linearly polarized beam; and

an unpolarizing system comprising,

a splitter configured to split the linearly polarized beam into first and second portions,

first and second optical paths, the first portion of the split beam travels along the first optical path that has a first path length and the second portion of the split beam travels along the second optical path that has a second path length, the second path length being different than the first path length,

a combiner configured to combine the first and second portions to form an unpolarized beam, and

a rotatable half wave plate located before the splitter configured to tune an intensity of at least one of the first or second portions of the split beam,

wherein the tuning produces a uniform intensity of the first and second portions.

2. The system of claim 1, wherein:

the splitter is a polarizing beam splitting system that is configured to perform the splitting of the linearly polarized beam based on respective polarization directions within the linearly polarized beam; and

the combiner is a polarizing beam combining system that is configured to perform the combining of the first and second portions of the split beam based on their respective polarization directions.

3. The system of claim 2, wherein:

the polarizing beam splitting system is a beam splitting cube; and

the polarizing beam combining system is a beam combining cube.

4. The system of claim 2, wherein:

the polarizing beam splitting system comprises a beam splitter and a reflecting device; and

the polarizing beam combining system comprises a beam combiner and a reflecting device.

5. The system of claim 1, wherein the unpolarizing system further comprises:

an optical element configured to form the first optical path; and

a gaseous area configured to form the second optical path.

6. The system of claim 5, wherein the gaseous area comprises vacuum or air.

7. The system of claim 1, wherein a length of at least one of the first and second optical paths is longer than a temporal coherence length of the linearly polarized beam.

8. The system of claim 1, wherein the first and second optical paths include portions having different indices of refraction, which results in the difference between the first and second optical path lengths.

9. The system of claim 1, further comprising:

a patterning device that patterns the unpolarized beam; and

a projection system that projects the patterned beam onto a target portion of a substrate.

10. The system of claim 9, further comprising:

an illumination system that processes the unpolarized beam and directs the unpolarized beam onto the patterning device.

11. The system of claim 10, wherein the illumination system comprises the radiation source and the unpolarizing system.

12. A lithography system, comprising:

an illumination system that generates an illumination beam of radiation, comprising,

a source of radiation, and

an unpolarizing system comprising,

a splitter,

first and second optical paths,

a combiner, and

a rotatable half wave plate located before the splitter configured to tune a uniform intensity of the illumination beam;

a patterning device that patterns the illumination beam of radiation; and

a projection system that projects the patterned beam onto a target portion of a substrate.

13. The lithography system of claim 12, wherein:

the splitter is a polarizing beam splitting system that is configured to perform splitting of a linearly polarized beam produced by the source of radiation into first and second portions based on respective polarization directions within the linearly polarized beam; and

the combiner is a polarizing beam combining system that is configured to perform combining of the first and second portions of the split beam based on their respective polarization directions.

14. The lithography system of claim 12, wherein the unpolarizing system further comprises:

an optical element configured to form the first optical path; and

a gaseous area configured to form the second optical path.

15. The lithography system of claim 12, wherein a path length of at least one of the first and second optical paths is longer than a temporal coherence length of the linearly polarized beam.

16. The lithography system of claim 12, wherein the first and second optical paths include portions having different indices of refraction, which results in the difference between the first and second optical path lengths.

17. A method, comprising:

(a) splitting a linearly polarized beam into first and second beams;

(b) directing the first beam along a first optical path having a first optical path length;

(c) directing the second beam along a second optical path having a second optical path length, the second path length being different than the first path length;

(d) combining the first beam from the first optical path with the second beam from the second optical path to form an unpolarized beam, and

(e) tuning of an intensity of at least one of the first beam or the second beam based on respective polarization directions of the first beam and the second beam, wherein the tuning produces a uniform intensity of the first and second beams.

18. The method of claim 17, further comprising:

basing step (b) on polarizations directions of light within the linearly polarized beam; and

basing step (d) on respective polarization directions of the first and second beams.

19. The method of claim 17, wherein a path length of at least one of the first and second optical paths is longer than a temporal coherence length of the linearly polarized beam.

20. The method of claim 17, wherein the first and second optical paths include portions having different indices of refraction, which results in the difference between the first and second optical path lengths.

21. The method of claim 17, further comprising:

patterning the unpolarized beam; and

projecting the patterned beam on a target portion of a substrate.

22. Forming an integrated circuit on a wafer using the method of claim 21.

23. Forming a flat panel device on a flat panel glass substrate using the method of claim 21.

24. A laser that outputs an unpolarized beam, comprising:

a source of radiation that produces a linearly polarized beam; and

an unpolarizing system comprising,

a splitter configured to split the linearly polarized beam into first and second portions,

first and second optical paths, the first portion of the split beam travels along the first optical path that has a first path length and the second portion of the split beam travels along the second optical path that has a second path length, the second path length being different than the first path length,

a combiner configured to combine the first and second portions to form an unpolarized beam, and

a rotatable half wave plate located before the splitter configured to tune an intensity of at least one of the first or second portions of the split beam,

wherein the tuning produces a uniform intensity of the first and second portions.

25. The laser of claim 24, wherein:

the splitter is a polarizing beam splitting system that is configured to perform the splitting of the linearly polarized beam based on respective polarization directions within the linearly polarized beam; and

the combiner is a polarizing beam combining system that is configured to perform the combining of the first and second portions of the split beam based on their respective polarization directions.

26. The laser of claim 24, wherein the unpolarizing system further comprises:

an optical element configured to form the first optical path; and

a gaseous area configured to form the second optical path.

27. The laser of claim 24, wherein a path length of at least one of the first and second optical paths is longer than a temporal coherence length of the linearly polarized beam.

28. The laser of claim 24, wherein the first and second optical paths include portions having different indices of refraction, which results in the difference between the first and second optical path lengths.

29. An illuminator that outputs an unpolarized beam, comprising:

a source of radiation that produces a linearly polarized beam; and

an unpolarizing system comprising,

a splitter configured to split the linearly polarized beam into first and second portions,

first and second optical paths, the first portion of the split beam travels along the first optical path that has a first path length and the second portion of the split beam travels along the second optical path that has a second path length, the second path length being different than the first path length,

a combiner configured to combine the first and second portions to form an unpolarized beam, and

a rotatable half wave plate located before the splitter configured to tune an intensity of at least one of the first or second portions of the split beam,

wherein the tuning produces a uniform intensity of the first and second portions.

30. The illuminator of claim 29, wherein:

the splitter is a polarizing beam splitting system that is configured to perform the splitting of the linearly polarized beam based on respective polarization directions within the linearly polarized beam; and

the combiner is a polarizing beam combining system that is configured to perform the combining of the first and second portions of the split beam based on their respective polarization directions.

31. The illuminator of claim 29, wherein the unpolarizing system further comprises:

an optical element configured to form the first optical path; and

a gaseous area configured to form the second optical path.

32. The illuminator of claim 29, wherein a path length of at least one of the first and second optical paths is longer than a temporal coherence length of the linearly polarized beam.

33. The illuminator of claim 29, wherein the first and second optical paths include portions having different indices of refraction, which results in the difference between the first and second optical path lengths.