Optical element with low surface figure deformation
A reflective optical element includes a body with a first reflective surface of a high precision geometrical form, which can be used for reflecting light in a wavelength range less than 50 nm in an EUV-lithographic projection exposure system. The body includes first and a second non-reflecting surfaces. Further, the body includes a single connection area formed on the first non-reflecting surface with at least one fixation surface inside the connection area for fixing the entire optical element directly or indirectly to at least one bearing surface of a bearing element. The second non-reflecting surface is different from the single connection area formed on the first non-reflective surface. The second non-reflecting surface at least partly surrounds the single connection area. At least one stress relief recess is formed into the body. The stress relief recess at least partly separates the first non-reflective surface from the second non-reflecting surface.
1. An optical element, comprising:
a body, comprising:
a first reflective surface configured to reflect EUV light in a wavelength range less than 50 nm;
a first non-reflective surface;
a single connection area, the single connection area being on the first non-reflective surface, the single connection area having a fixation surface configured to fix the body to a bearing surface of a bearing element;
a second non-reflective surface, the second non-reflective surface being different from the single connection area, and the second non-reflective surface at least partially surrounding the single connection area; and
a stress relief feature at least partially separating the first non-reflective surface from the second non-reflective surface.
2. The optical element according to claim 1 , wherein the stress relief feature includes a recess or a curved surface.
3. The optical element according to claim 1 , wherein the single connection area is on a side of the body about opposite the first reflective surface.
4. The optical element according to claim 1 , wherein the second non-reflective surface completely surrounds the single connection area.
5. The optical element according to claim 1 , wherein the stress relief feature separates the single connection area from the second non-reflective surface.
6. The optical element according to claim 1 , further comprising the bearing element, wherein the body is fixed to the bearing element, and a line of force of gravitational force of the optical element, which is effective on the centre center of gravity of the optical element, intersects the single connection area.
7. The optical element according to claim 6 , wherein the single connection area is a planar area, and the planar area is arranged perpendicular to the line of force.
8. The optical element according to claim 6 , wherein the single connection area is symmetrically arranged relative to the line of force.
9. The optical element according to claim 6 , wherein the body is rigidly fixed to the bearing element.
10. The optical element according to claim 9 , wherein the body is fixed to the bearing element by at least one bond selected from the group consisting of an adhesive bond, a metallic continuity bond and a form fit bond.
11. The optical element according to claim 6 , wherein the fixation surface and the bearing surface at least partly contact each other to fix the optical element with a resultant bearing force which generates no moments with respect to the centre center of gravity of the optical element.
12. The optical element according to claim 1 , further comprising the bearing element, wherein the bearing element comprises an actuation device configured to actuate the bearing element in at least one degree of freedom and/or to deform the bearing element.
13. The optical element according to claim 1 , comprising a connection element including the connection area, wherein the connection element is an integral element of the body.
14. The optical element according to claim 1 , further comprising the bearing element, wherein the bearing element comprises a connection element, and the bearing surface is on the connection element.
15. The optical element according to claim 14 , wherein the bearing element comprises a reflective surface and/or a reflective grating.
16. The optical element according to claim 1 , further comprising the bearing element, wherein the body and the bearing element are a monolithic element.
17. The optical element according to claim 1 , wherein the first reflective surface includes an area which is curved along at least one direction.
18. The optical element according to claim 1 , wherein the body comprises a second reflective surface and/or a reflective grating.
19. A system, comprising:
an optical element according to claim 1 ,
wherein the system is an EUV-lithographic projection exposure system.
20. An objective, comprising:
an optical element according to claim 1 ,
wherein the objective is an EUV-lithographic projection objective.
21. The optical element according to claim 1 , wherein the first and second non-reflective surface extend in the same plane.
22. The optical element according to claim 1 , wherein the stress relief extends from the first non-reflective surface toward the first reflective surface.
23. The optical element according to claim 1 , wherein the second non-reflective surface surrounds the first non-reflective surface.
24. The optical element according to claim 1 , wherein the stress relief is between the first and second non-reflective surfaces.
25. The optical element according to claim 24 , wherein the stress relief extends in a direction perpendicular to the first and second non-reflective surfaces.
26. The optical element according to claim 24 , wherein the stress relief extends from the first non-reflective surface toward the first reflective surface.
27. The optical element according to claim 1 , wherein the EUV light has a wavelength of at least five nanometers.
28. The optical element according to claim 1 , wherein the EUV light has a wavelength of from five nanometers to 15 nanometers.
29. An optical element, comprising:
a body, comprising:
a reflective surface configured to reflect EUV light in a wavelength range less than 50 nm;
a non-reflective surface;
a single connection area, the single connection area being on the non-reflective surface, the single connection area having a fixation surface configured to fix the body to a bearing surface of a bearing element; and
a stress relief feature at least partially separating the reflective surface from the non-reflective surface.
30. The optical element according to claim 29 , wherein the EUV light has a wavelength of at least five nanometers.
31. The optical element according to claim 29 , wherein the EUV light has a wavelength of from five nanometers to 15 nanometers.
32. An optical element, comprising:
a bearing element; and
a body, comprising:
a reflective surface configured to reflect EUV light in a wavelength range less than 50 nm;
a single connection element defining a first non-reflective surface, the single connection element connecting the body and the bearing element;
a second non-reflective surface different from the first non-reflective surface, the second non-reflective surface at least partially surrounding the single connection element; and
a stress relief feature at least partially separating the reflective surface from the non-reflective surface.
33. The reflective optical element according to claim 32 , wherein the body and the bearing element are a monolithic element.
34. The optical element according to claim 32 , wherein the EUV light has a wavelength of at least five nanometers.
35. The optical element according to claim 32 , wherein the EUV light has a wavelength of from five nanometers to 15 nanometers.