Projection objective of a microlithographic projection exposure apparatus and method for its production

A microlithographic projection exposure apparatus, comprising:

• a) an illumination system;
• b) a projection objective of a microlithographic projection exposure apparatus for imaging a reticle that can be arranged in an object plane of the projection objective onto an image plane, said projection objective comprising:
• a first lens which is the penultimate curved optical element on the image side, has a concave surface on the image side and contains a first intrinsically birefringent crystal which has a first orientation of the crystal axes, and
• a second lens which is the last curved optical element on the image side, has a convex surface on the object side and contains a second intrinsically birefringent crystal, which has a second orientation of the crystal axes that can be described by rotating the first orientation of the crystal axes about a symmetry axis of the first lens,
• wherein the first and second orientations of the crystal axes are selected so that an intrinsic birefringence due to the first crystal, together with an intrinsic birefringence due to the second crystal, leads in total to at least approximately axisymmetric distribution of the overall birefringence, and
• wherein the first lens is contact bonded to the second lens.

A method for the production of a projection objective of a microlithographic projection exposure apparatus, which is intended for imaging a reticle that can be arranged in an object plane of the projection objective onto an image plane, said method comprising the following steps:

• a) providing a housing of the projection objective,
• b) providing a crystal which is optically birefringent for the wavelength used in the projection exposure apparatus;
• c) splitting the crystal into a first lens and a second lens along a curved bowl-shaped separating surface, which is axisymmetric with respect to a symmetry axis, so that the first lens is provided with a concave surface;
• d) mutually rotating the two lenses about the symmetry axis;
• e) fitting the first and second rotated lenses into the housing so that the first lens is the penultimate curved lens on the image side and the second lens is the last curved lens on the image side of the projection objective.