Broad band DUV, VUV long-working distance catadioptric imaging system

• US 6,842,298 B1
• Filed: 02/28/2001
• Issued: 01/11/2005
• Est. Priority Date: 09/12/2000
• Status: Expired due to Term

• Current Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Original Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Inventors: Chuang, Yung-Ho, Shafer, David R.
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): Raizen, Deborah A.
• Application Number:
  US09/796,117
• Time in Patent Office: 1,413 Days
• Field of Search: 359726-736, 359364-366, 359656-661
• US Class Current: 359/730
• CPC Class Codes: G02B 13/143 for use with ultraviolet radiation
• CPC Class Codes: G02B 17/0804 using two curved mirrors G02B17/0864, G02B17/0896 takes precedence
• CPC Class Codes: G02B 17/0808 on-axis systems with at least one of the mirrors having a central aperture
• CPC Class Codes: G02B 17/0856 comprising a refractive element with a reflective surface, the reflection taking place inside the element, e.g. Mangin mirrors
• CPC Class Codes: G02B 17/0892 specially adapted for the UV
• CPC Class Codes: G02B 21/04 involving mirrors
• CPC Class Codes: G03F 7/70225 Optical aspects of catadioptric systems, i.e. comprising reflective and refractive elements

Abstract

A high performance objective having very small central obscuration, an external pupil for apertureing and Fourier filtering, loose manufacturing tolerances, large numerical aperture, long working distance, and a large field of view is presented. The objective is preferably telecentric. The design is ideally suited for both broad-band bright-field and laser dark field imaging and inspection at wavelengths in the UV to VUV spectral range.

Claims

1. A method of imaging an object, comprising:

collecting light from said object with a focussing lens group;

correcting chromatic aberration by use of a catadioptric group; and

passing said light through a field lens group located between said focussing lens group and said catadioptric group;

wherein said catadioptric group comprises a plurality of Mangin reflective elements and said light collecting occurs at a numerical aperture of in excess of 0.8.

2. The method of claim 1, wherein said focussing lens group is separated from said object by at least 2 mm.

3. The method of claim 1, wherein said object is a reticle, and a pellicle is located between said reticle and said focussing lens group.

4. The method of claim 1, wherein said focussing lens group, said catadioptric group, and said field lens group are arranged along a common optical axis.

5. The method of claim 1, wherein said focussing lens group is located between said object and said field lens group.

6. The method of claim 1 where the catadioptric group at least partially corrects for spherical aberration.

7. A catadioptric optical system comprising:

a focusing lens group at a high numerical aperture end of said system;

a catadioptric group for at least partially correcting chromatic aberration, said catadioptric group comprising a plurality of Mangin reflective elements; and

a field lens group located along an optical path between said focusing lens group and said catadioptric group.

8. The system of claim 7, wherein at least one of said lens groups comprises a lens made of silica.

9. The system of claim 7, wherein said system has a designed center wavelength of 193 mm.

10. The system of claim 7, wherein at least one of said lens groups comprises a lens made of calcium fluoride.

11. The system of claim 7, wherein said system has a designed center wavelength of 157 nm.

12. The system of claim 7, wherein said light has at least a 1 pm bandwidth.

13. The system of claim 7, wherein said light has at least a 2 pm bandwidth.

14. The system of claim 7, wherein said catadioptric group comprises a pair of curved reflective elements.

15. The system of claim 14, wherein said catadioptric group further comprises a transmissive element located between said reflective elements.

16. The system of claim 7, wherein substantially all of the optical elements comprise spherical optics.

17. The system of claim 7, wherein said system is free of aspherical optical elements.

18. The system of claim 7, wherein said system is used to image an object maintained in a moisture and oxygen free ambient environment.

19. The system of claim 18, wherein said ambient environment comprises a vacuum.

20. The system of claim 7 where the catadioptric group at least partially corrects for spherical aberration.

21. A catadioptric optical system having a working distance between optical components and a specimen, comprising:

a catadioptric group comprising a plurality of Mangin elements and having a relatively high degree of chromatic correction; and

image forming optics producing an image of a surface being examined;

wherein said working distance is at least 2 mm, and further wherein said catadioptric optical system exhibits a numerical aperture in excess of 0.8.

22. The system of claim 21, wherein said chromatic correction is provided over a range of wavelengths in the DUV or VUV range.

23. The system of claim 22, wherein said range of wavelengths is at least 1 pm in width.

24. The system of claim 22, wherein said range of wavelengths is at least 2 pm in width.

25. The system of claim 22, wherein said chromatic correction is provided for higher order chromatic aberration.

26. The system of claim 22, wherein said system additionally corrects for spherical aberration, coma and astigmatism.

27. The system of claim 26, wherein said spherical aberration, coma and astigmatism are at least partially corrected by said image forming optics.

28. The system of claim 22, wherein said system corrects for at least secondary longitudinal color and primary and secondary lateral color.

29. The system of claim 28, wherein said correction is performed in the DUV or VUV range over a bandwidth of at least 1 pm.

30. The system of claim 28, wherein said secondary longitudinal color and primary and secondary lateral color are at least partially corrected by said image forming optics.

31. The system of claim 22, wherein a working distance is used to separate a photomask from said system, and wherein there is a pellicle between said photomask and said system.

32. The system of claim 22, wherein said system is designed with loose manufacturing tolerances.

33. The system of claim 32, wherein said manufacturing tolerances permit elements within the system to be decentered to within 5 microns.

34. The system of claim 33, wherein said decentering produces less than 0.07 waves r.m.s of on-axis coma.

35. The system of claim 32 wherein said manufacturing tolerances permit all elements within the system to be decentered to within 5 microns.

36. An apparatus for photolithographically imaging a semiconductor wafer, comprising:

a focusing lens group at a high numerical aperture end of said apparatus;

a catadioptric group for at least partially correcting chromatic aberration; and

a field lens group located along an optical path between said focusing lens group and said catadioptric group;

wherein said catadioptric group comprises a plurality of Mangin elements and said apparatus is configured to have a numerical aperture in excess of 0.8.

37. The apparatus of claim 36, wherein said wafer is separated from said apparatus by a distance sufficient to purge oxygen and moisture from a region separated from said wafer.

38. The apparatus of claim 37, wherein said region is maintained in a vacuum.