Abstract: A method of determining materials of lenses contained in an optical system of a projection exposure apparatus is described. First, for each lens of a plurality of the lenses, a susceptibility factor KLT/LH is determined. This factor is a measure of the susceptibility of the respective lens to deteriorations caused by at least one of lifetime effects and lens heating effects. Then a birefringent fluoride crystal is selected as a material for each lens for which the susceptibility factor KLT/LH is above a predetermined threshold. Theses lenses are assigned to a first set of lenses. For these lenses, measures are determined for reducing adverse effects caused by birefringence inherent to the fluoride crystals.

Abstract: In a method for improving the imaging properties of a projection objective of a microlithographic projection exposure apparatus, an appropriate illumination angle distribution adapted to a mask (24; 224) to be projected is selected. Then locations (40a, 40b; 60a, 60b; 80a, 80b, 80c) in an exit pupil of the projection objective (20), which are illuminated under these conditions by projection light during a projection of the mask, are determined. For at least one image point, an actual value of an imaging quantity, e.g. a wavefront profile or a polarization state, is determined that influences the imaging properties of the projection objective. Finally, corrective measures are calculated such that the actual value of the imaging quantity approximates a desired value at these locations. In this last step, however, deviations of the actual value from the desired value are taken into account exclusively at said locations illuminated in the exit pupil.

Abstract: An optical system, for example a lens for a photolithography tool, includes a group of optical elements (L1, L2) that each comprise a birefringent cubic crystal such as CaF2. The crystal lattices of the crystals have different orientations, e.g. for reducing the overall retardance of the group by mutual compensation. The [110] crystal axis of at least one optical element (L1, L2) is tilted with respect to an optical axis (34) of the system (10) by a predefined tilting angle (?1, ?2) having an absolute value between 1° and 20°. This reduces the magnitude, but not significantly changes the orientation of intrinsic birefringence. By selecting an appropriate tilting angle it is possible to achieve a better performance of the optical system. For example, the overall retardance of the optical system may be reduced, or the angular retardance distribution may be symmetrized.

Abstract: A catadioptric projection lens for use in microlithographic projection-exposure apparatus includes a plurality of refractive optical elements having intrinsic birefringence both in a catadioptric part and in a dioptric part adjacent to the image plane. Because these refractive optical elements in the catadioptric part and in the dioptric part are decoupled from one another with respect to polarisation by a polarisation-sensitive reflective layer, the catadioptric part and the dioptric part are compensated separately from one another with respect to intrinsic birefringence.

Abstract: A catadioptric projection objective for projecting a pattern, which is located in the object plane of the projection objective, into the image plane of the projection objective has, between the object plane and the image plane, a catadioptric objective part provided with a concave mirror (17), with a first deviating mirror (16) and with at least one second deviating mirror (19). A polarization rotating device (26) rotates the preferred polarization direction of the light approximately 90° inside the light path between the deviating mirrors. This permits an at least partial compensation for polarization-dependent reflectivity differences and phase effect differences of the deviating mirrors thereby enabling a projection with a largely identical contrast for all structural directions.

Abstract: A numerical optimizing method serves to reduce harmful effects caused by intrinsic birefringence in lenses of a fluoride crystal material of cubic crystal structure in an objective, particularly a projection objective for a microlithography system. Under the optimizing method, an optimizing function which takes at least one birefringence-related image aberration into account is minimized. The birefringence-related image aberration is determined from a calculation for a light ray passing through the fluoride crystal lenses. To the extent that the birefringence-related image aberration is a function of parameters of the light ray, it depends only on geometric parameters of the light ray. The numerical optimizing method is used to produce objectives in which an optical retardation as well as an asymmetry of the optical retardation are corrected. The lenses are arranged in homogeneous groups, where each homogeneous group is corrected for the optical retardation asymmetry.

Abstract: A catadioptric projection lens (1) which is designed in particular for use in microlithographic projection-exposure apparatus includes a plurality of refractive optical elements having intrinsic birefringence both in a catadioptric part (5) and in a dioptric part (18) adjacent to the image plane (3). Because these refractive optical elements in the catadioptric part (5) and in the dioptric part (18) are decoupled from one another with respect to polarisation by a polarisation-sensitive reflective layer (10), the catadioptric part (5) and the dioptric part (18) are compensated separately from one another with respect to intrinsic birefringence.

Abstract: Centimeter thick plates or lenses made from calcium fluoride or barium fluoride with beam propagation in the direction of the <110> crystal direction or of a main axis equivalent thereto are provided as retardation elements for the deep ultraviolet. They can be installed in an unstressed fashion. In a particular embodiment a retardation plate comprises a birefringent crystal plate which has an entry face and an exit face for incident and emerging light, respectively. A form-birefringent dielectric layer structure is applied to the entry and/or exit face. It may, for example, be a periodic sequence of at least two layers with alternating refractive indices. The retardation plate is suitable for ultraviolet light, and permits a large range of angles of incidence. Retardation elements according to the invention are particularly suitable for microlithography at 157 nm.