Graphene spectral purity filter

1. A spectral purity filter comprising a graphene structure having uniform thickness and homogeneous composition wherein the graphene has an EUV transmittance of greater than 85%.

2. The spectral purity filter according to claim 1 , comprising a graphene layer.

3. The spectral purity filter according to claim 1 , comprising a graphene sheet.

4. The spectral purity filter according to claim 3 , wherein the graphene sheet is disposed on a spectral purity filter frame.

5. The spectral purity filter according to claim 4 , wherein the graphene sheet is supported by the spectral purity frame without a supporting grid.

6. The spectral purity filter according to claim 3 , wherein the graphene sheet supports an out-of-band radiation suppression structure.

7. The spectral purity filter according to claim 6 , wherein the graphene sheet is configured to prevent oxidation of the out-of-band radiation suppression structure.

8. The spectral purity filter according to claim 6 or 7 , wherein both sides of the out-of-band radiation suppression structure are covered with graphene.

9. The spectral purity filter according to claim 6 , wherein the suppression structure comprises a suppression layer comprising a material selected from the group consisting of: Mo, W, Si, and Zr.

10. The spectral purity filter according to claim 1 , comprising graphene flakes.

11. The spectral purity filter according to claim 10 , wherein the graphene flakes support an out-of-band radiation suppression structure.

12. The spectral purity filter according to claim 11 , wherein the graphene flakes are configured to prevent oxidation of the out-of-band radiation suppression structure.

13. The spectral purity filter according to claim 11 , wherein the suppression structure comprises a suppression layer comprising a material selected from the group consisting of: Mo, W, Si, and Zr.

14. The spectral purity filter according claim 1 , further comprising a material which blocks out-of-band radiation and wherein the graphene is configured to protect the material from oxidation and/or outgassing.

15. The spectral purity filter according to claim 14 , comprising a grid of the material to block the out-of-band radiation.

16. The spectral purity filter according to claim 15 , wherein the grid is a tungsten grid.

17. The spectral purity filter according to claim 16 , wherein the graphene is applied such that none of the tungsten grid is exposed.

18. The spectral purity filter according to claim 16 , wherein the graphene is applied as graphene layers on either side of the tungsten grid.

19. The spectral purity filter according to any of the claims 14 to 18 , wherein the graphene is provided as a layer, a sheet or as flakes.

20. The spectral purity filter according to claim 15 , wherein the grid comprises a support structure and a reflective coating, reflective to the out-of-band radiation.

21. The spectral purity filter according to claim 20 , wherein the reflective coating comprises molybdenum to reflect the out-of-band radiation.

22. The spectral purity filter according to claim 1 , further comprising a grid, the graphene being disposed on the grid.

23. The spectral purity filter according to claim 22 , wherein the grid is configured to block out-of-band radiation, a pitch of the grid being smaller than wavelengths of the to be blocked out-of-band radiation.

24. The spectral purity filter according to claim 1 , further comprising a filter constructed and arranged to pass a selected band of radiation and to suppress out of band radiation.

25. The spectral purity filter according to claim 24 , wherein the out of band radiation is selected from the group consisting of: DUV radiation and infrared radiation.

26. The spectral purity filter according to claim 1 , wherein the graphene comprises between 1 and 100 layers of graphene.

27. The spectral purity filter according to claim 26 , wherein the graphene comprises between 10 and 100 layers of graphene.