Microlithography optical system

1. An optical system having an optical axis, the optical system comprising:

at least one optical element comprising an optically uniaxial material having, for an operating wavelength of the optical system, an ordinary refractive index n o and an extraordinary refractive index n e , the extraordinary refractive index n e being larger than the ordinary refractive index n o ;

wherein the optical element absorbs, at least for light rays of the operating wavelength entering the optical element with respect to the optical axis under an angle of incidence that lies within a certain angle region, a p-polarized component of the light rays significantly stronger than a s-polarized component of the light rays, and

wherein the optical system is a microlithography optical system.

2. The optical system according to claim 1 , wherein a difference between the extraordinary refractive index and the ordinary refractive index at the operating wavelength is at least 0.15.

3. The optical system according to claim 1 , wherein an optical crystal axis of the optical element is at least substantially parallel to the optical axis of the optical system.

4. The optical system according to claim 1 , wherein the optical element is an at least substantially plan-parallel plate.

5. The optical system according to claim 1 , wherein the optical element is arranged at a position along the optical axis where an optical path of the optical system is at least substantially telecentric.

6. The optical system according to claim 1 , further comprising at least one correction element that provides for an at least substantially telecentric light path within the optical element.

7. The optical system according to claim 6 , wherein the at least one correction element is a refractive lens element.

8. The optical system according to claim 6 , wherein the at least one correction element has at least one optically effective surface that is aspheric.

9. The optical system according to claim 6 , wherein the at least one correction element is in direct contact with the optical element.

10. The optical system according to claim 1 , wherein the optical element is arranged in an image plane or an intermediate image plane of the optical system.

11. The optical system according to claim 1 , wherein the angle region comprises at least all incident angles with respect to the optical axis being larger than 60°.

12. The optical system according to claim 1 , wherein the optical element absorbs at least 90% of the intensity of the p-polarized component.

13. The optical system according to claim 1 , wherein the optical element transmits at least 90% of the s-polarized component.

14. The optical system according to claim 1 , wherein the uniaxial material comprises an alkali earth metal or alkali metal as a first component and a chemical N 3 -compound, a chemical NCN-compound or a chemical OCN-compound as a second component.

15. The optical system according to claim 1 , wherein the uniaxial material is selected from the group consisting of Potassium Azid (KN 3 ), Calcium Cyanamide (CaCN 2 ) and Sodium Cyanate (NaOCN).

16. The optical system according to claim 1 , wherein the uniaxial material is selected from the group consisting of Henotim (Y[PO 4 ]), Bastnäsite ((Ce,La,Nd)[CO 3 F]), Synchisite (CeCa[(CO 3 ) 2 F], Parisite ((Ce,La) 2 Ca[(CO 3 ) 3 F 2 ] 3 ), Röntgenite (Ce 3 Ca 2 [(CO 3 ) 5 F 3 ], [Pt(CN) 4 ]Mg.7H 2 O, AgCN, AgK(CN) 2 , [NH 4 ] 2 CO and BBO.

17. The optical system according to claim 1 , wherein the operating wavelength is less than 250 nm.

18. The optical system according to claim 1 , wherein at least two of the optical elements are provided at different predetermined positions in the optical system.

19. The optical system according to claim 18 , wherein at least some of the predetermined positions are positions at which an optical path of the optical system is at least substantially telecentric.

20. The optical system according to claim 1 , wherein the light passing the optical system has, at the light entrance side of the optical element, an at least approximate tangential polarization distribution.

21. The optical system according to claim 1 , wherein the optical element is rotatably mounted around the optical axis.

22. The optical system according to claim 1 , wherein a space between a last optical element of the optical system and an image plane of the optical system includes an immersion medium having a refractive index n larger than 1.

23. The optical system according to claim 1 , wherein an image-side numerical aperture NA of the optical system has a value of at least 0.8.

24. The optical system according to claim 1 , wherein the optical system is an illumination system for a microlithographic projection exposure apparatus comprising a light source and a plurality of optical elements through which a reticle plane is illuminated with light being emitted from the light source, wherein the optical element is the element that is most proximate to the reticle plane.

25. The optical system according to claim 1 , wherein the optical system is an illumination system for a microlithographic projection exposure apparatus comprising along the optical axis a light source, a light mixing device and a REMA-projection lens projecting a variable masking onto a reticle plane, and wherein the optical element is arranged between the REMA-projection lens and the reticle plane.

26. The optical system according to claim 1 , wherein the optical system is a microlithographic projection exposure apparatus comprising an illumination system and a projection lens, wherein the illumination system illuminates a reticle being arranged in an object plane of the projection lens with light, and wherein the projection lens images the reticle onto an image plane of the projection lens.

27. The optical system according to claim 26 , wherein the optical element is arranged between the reticle and the projection lens.

28. A method, comprising:

using the system of claim 1 for microlithographic projection exposure.

29. A method of microlithographic structuring a substrate, comprising: illuminating a mask with light and projecting an image of the mask onto the substrate, wherein the illuminating the mask with light and/or the step of projecting an image of the mask onto the substrate uses an optical system according to claim 1 .