Patent Number: 
Section: claims

1. An imaging optical unit for EUV projection lithography for imaging an object field in an object plane into an image field in an image plane, the imaging optical unit comprising:a plurality of mirrors for guiding imaging light from the object field to the image field;an aperture stop, which is tilted by at least 1° relative to a normal plane which is perpendicular to an optical axis,wherein the aperture stop is configured with a circular stop contour,wherein the aperture stop is arranged in such a way that the following applies to mutually perpendicular planes: a deviation of a numerical aperture NAx measured in one of these planes from a numerical aperture NAy measured in the other one of these two planes is less than 0.003, averaged over the field points of the image field. 2. The imaging optical unit of claim 1, wherein the stop is arranged at a distance from, or tilted relative to, a plane, in which coma rays of the imaging light from spaced apart field points intersect. 3. The imaging optical unit of claim 1, wherein the aperture stop is arranged at a distance from, or tilted relative to, a plane, in which chief rays of the imaging light from spaced apart field points intersect. 4. The imaging optical unit of claim 1, wherein a centre of the aperture stop is at a distance from a reference axis of the imaging optical unit. 5. The imaging optical unit of claim 1, wherein the aperture stop is tilted about a tilt axis which is perpendicular to a tilt normal plane,which contains an object displacement direction for an object arrangeable in the object plane andwith at least one field plane being perpendicular thereto. 6. The imaging optical unit of claim 1, wherein the tilt angle is less than 20°. 7. The imaging optical unit of claim 1, wherein the aperture stop is tilted in such a way that an angle of a stop normal relative to a chief ray of a central field point becomes smaller in comparison with an angle of the optical axis relative to the chief ray of the central field point. 8. The imaging optical unit of claim 1, wherein the aperture stop is tilted in such a way that an angle of a stop normal relative to a chief ray of a central field point becomes larger in comparison with an angle of the optical axis relative to the chief ray of the central field point. 9. The imaging optical unit of claim 1, wherein the aperture stop is configured as a planar stop. 10. The imaging optical unit of claim 1, wherein at least one of the mirrors has a reflection surface embodied as a free-form surface. 11. The imaging optical unit of claim 1, further comprising a tilt drive, to which the aperture stop is connected for the purposes of tilting. 12. An optical system, comprising:the imaging optical unit of claim 1; andan illumination optical unit for illuminating the object field with illumination light or imaging light. 13. A projection exposure apparatus, comprising:the optical system of claim 12; anda light source for generating EUV illumination light or imaging light;an object holder with an object displacement drive; anda substrate holder for holding a wafer, arrangeable in the image field, with a wafer displacement drive. 14. A method for producing a structured component, comprising:providing a reticle and a wafer;projecting a structure on the reticle onto a light-sensitive layer of the wafer with the aid of the projection exposure apparatus of claim 13; andgenerating a structure on the wafer.