Projection objective, in particular for microlithography, as well as a method for tuning a projection objective

摘要

A process for the tuning of a projection objective makes it possible, the projection objective with intervention in the system between an increasingly ion configuration and a dry configuration and thus to be adapted to selectively as immersion objective or to use as a dark field beam. The projection lens has a plurality of optical elements, the along an optical axis of the projection objective are arranged, wherein the optical elements one of the object plane the following first group of optical elements and a of the first group of the following, the image plane of the next last optical element, the one outlet surface of the projection objective defined, which is in a working distance to the image plane is arranged. The last optical element is essentially no refracting power and has no or only a slight sag. The method comprises a change in the thickness of the last optical element, a change in the refractive index of the space between the outlet area and the image plane by introduction or removal of an immersion medium and preferably has an axial displacement of the last optical element to the setting of a suitable working distance.