Patent Number: 
Section: claims

1. A reflective mirror for reflecting incident light comprising:a base having a base surface that includes a first surface portion and a second surface portion associated with a first base height and a second base height, respectively; anda multilayer film having a first surface situated on the base surface and a second surface opposite the first surface, wherein the second surface has a constant height, wherein the multilayer film is configured to reflect at least a portion of the incident light and includes a first layer and a second layer that are laminated alternately on the base, the multilayer film including a first portion having a first thickness situated at the first surface portion of the base that is associated with the first base height and a second portion having a second thickness different from the first thickness situated at the second surface portion of the base that is associated with the second base height, the second portion being provided at a position rotationally symmetric to a position of the first portion about an optical axis of the reflective mirror. 2. The reflective mirror according to claim 1, wherein, in the multilayer film, the first thickness and the second thickness are each determined such that light incident at a first angle on the first portion is reflected, light incident at a second angle on the second portion is reflected, and a difference in reflectance of the incident light between the first portion and the second portion is reduced. 3. The reflective mirror according to claim 1, wherein the multilayer film has a thickness distribution, the thickness distribution changing in an azimuthal direction of the optical axis of the reflective mirror. 4. The reflective mirror according to claim 1, wherein the multilayer film has a thickness distribution, the thickness distribution not being rotationally symmetric about the optical axis of the reflective mirror. 5. The reflective mirror according to claim 1, wherein the multilayer film is line symmetric with respect to a line passing through a center of a region to which the light is incident on a surface of the multilayer film and the optical axis of the reflective mirror. 6. The reflective mirror according to claim 1, wherein the multilayer film has a thickness distribution, the thickness distribution having a finite order of rotational symmetry on the surface of the multilayer film. 7. The reflective mirror according to claim 1, wherein the base has a first surface where the first portion is formed and a second surface where the second portion is formed, the second surface being provided to be separated with respect to the first surface in a direction of lamination of the multilayer film. 8. A projection optical system comprising a plurality of optical elements, the projection optical system projecting an image of a first surface onto a second surface, and at least one of the optical elements being the reflective mirror recited in claim 1. 9. The projection optical system according to claim 8, wherein light from the first surface is irradiated onto the second surface via the plurality of optical elements, and at least an optical element where an incident angle range of the light is largest out of the plurality of optical elements is the reflective mirror. 10. An exposure apparatus for exposing a substrate to exposure light comprising the reflective mirror recited in claim 1. 11. A device manufacturing method comprising steps of:exposing a substrate using the exposure apparatus recited in claim 10; anddeveloping the exposed substrate. 12. A reflective mirror for reflecting incident light, comprising:a base; anda multilayer film configured to reflect at least a portion of the incident light and including a first layer and a second layer that are laminated alternately on the base, the multilayer film including a first portion having a first thickness and a second portion having a second thickness different from the first thickness, the second portion being provided at a position rotationally symmetric to a position of the first portion about an optical axis of the reflective mirror, wherein a shape of a surface of the base at which the multilayer film is situated is determined such that an aberration associated with a thickness distribution of the multilayer film is reduced. 13. The reflective mirror according to claim 12, wherein the base has a first surface where the first portion is formed and a second surface where the second portion is formed, the second surface being provided to be separated with respect to the first surface in a direction of lamination of the multilayer film. 14. A projection optical system, comprising a plurality of optical elements, the projection optical system projecting an image of a first surface onto a second surface, and at least one of the optical elements being the reflective mirror recited in claim 12. 15. An exposure apparatus for exposing a substrate to exposure light, comprising the reflective mirror recited in claim 12. 16. A method comprising:defining a mirror base having at least a first surface portion and second surface portion having different surface heights;providing a multilayer film configured to reflect at least a portion of light incident to the multilayer film, the multilayer film including a first layer and a second layer that are laminated alternately on the mirror base, the multilayer film including a first portion having a first thickness situated at the first surface portion of the mirror base and a second portion situated at the second surface portion of the mirror base, wherein the different surface heights are selected based on an optical aberration associated with a thickness distribution of the multilayer film. 17. The method of claim 16, wherein the multilayer film includes a first surface situated at the mirror base and an opposing surface, wherein the opposing surface has a constant height. 18. The method of claim 17, wherein the multilayer film includes a first portion situated at the first surface portion of the base and a second portion situated at the second surface portion of the base, wherein at least some layers of the first portion of the multilayer film and the second portion of the multilayer film have different layer periods. 19. A reflective mirror, comprising:a mirror base having a mirror base surface that includes a first surface portion and a second surface portion associated with a first mirror base height and a second mirror base height, respectively; anda multilayer film having a first surface situated on the mirror base surface and a second surface opposite the first surface, wherein the multilayer film is configured to reflect at least a portion of the incident light and includes a first layer and a second layer that are laminated alternately on the base, the multilayer film including a first portion having a first thickness situated at the first surface portion of the mirror base that is associated with the first mirror base height and a second portion having a second thickness different from the first thickness situated at the second surface portion of the mirror base that is associated with the second mirror base height,wherein the second portion of the multilayer film is situated at a position rotationally symmetric to a position of the first portion of the multilayer film about an optical axis of the reflective mirror. 20. A reflective mirror, comprising:a mirror base having a mirror base surface that includes a first surface portion and a second surface portion associated with a first mirror base height and a second mirror base height, respectively; anda multilayer film having a first surface situated on the mirror base surface and a second surface opposite the first surface, wherein the multilayer film is configured to reflect at least a portion of the incident light and includes a first layer and a second layer that are laminated alternately on the base, the multilayer film including a first portion having a first thickness situated at the first surface portion of the mirror base that is associated with the first mirror base height and a second portion having a second thickness different from the first thickness situated at the second surface portion of the mirror base that is associated with the second mirror base height,wherein a height of the first surface portion of the multilayer film is based on the height of the first mirror base portion and the thickness of the first surface portion of the multilayer film, and a height of the second surface portion of the multilayer film is based on the height of the second mirror base portion and the thickness of the second surface portion of the multilayer film, and wherein the height of the first surface portion of the multilayer film corresponds to the height of the second surface portion of the multilayer film. 21. A reflective mirror, comprising:a mirror base having a mirror base surface that includes a first surface portion and a second surface portion associated with a first mirror base height and a second mirror base height, respectively; anda multilayer film having a first surface situated on the mirror base surface and a second surface opposite the first surface, wherein the multilayer film is configured to reflect at least a portion of the incident light and includes a first layer and a second layer that are laminated alternately on the base, the multilayer film including a first portion having a first thickness situated at the first surface portion of the mirror base that is associated with the first mirror base height and a second portion having a second thickness different from the first thickness situated at the second surface portion of the mirror base that is associated with the second mirror base height,wherein the multilayer film has a thickness distribution that varies so as to compensate a height difference between the first surface portion of the mirror base and the second surface portion of the mirror base. 22. A projection optical system comprising a plurality of optical elements, the projection optical system projecting an image of a first surface onto a second surface, and at least one of the optical elements being the reflective mirror recited in claim 19. 23. An exposure apparatus for exposing a substrate to exposure light comprising the reflective mirror recited in claim 19. 24. A device manufacturing method comprising steps of:exposing a substrate using the exposure apparatus recited in claim 23; anddeveloping the exposed substrate. 25. A projection optical system comprising a plurality of optical elements, the projection optical system projecting an image of a first surface onto a second surface, and at least one of the optical elements being the reflective mirror recited in claim 20. 26. An exposure apparatus for exposing a substrate to exposure light comprising the reflective mirror recited in claim 20. 27. A device manufacturing method comprising steps of:exposing a substrate using the exposure apparatus recited in claim 26; anddeveloping the exposed substrate. 28. A projection optical system comprising a plurality of optical elements, the projection optical system projecting an image of a first surface onto a second surface, and at least one of the optical elements being the reflective mirror recited in claim 21. 29. An exposure apparatus for exposing a substrate to exposure light comprising the reflective mirror recited in claim 21. 30. A device manufacturing method comprising steps of:exposing a substrate using the exposure apparatus recited in claim 29; anddeveloping the exposed substrate.