Imaging optical unit for EUV projection lithography

摘要

An imaging optical unit for EUV projection lithography serves to image an object field into an image field. Mirrors guide imaging light from the object field to the image field. An aperture stop is tilted by at least 1° in relation to a normal plane which is perpendicular to an optical axis. The aperture stop has a circular stop contour. In mutually perpendicular planes, a deviation of a numerical aperture NAx measured in one plane from a numerical aperture NAy measured in the other plane is less than 0.003, averaged over the field points of the image field. What emerges is an imaging optical unit, in which homogenization of an image-side numerical aperture is ensured so that an unchanging high structure resolution in the image plane is made possible, independently of an orientation of a plane of incidence of the imaging light in the image field.

主权项

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.