PROJECTION OBJECTIVE FOR MICROLITHOGRAPHY

摘要

An assembly 11 of a projection objective for microlithography comprises a number of optical elements and an aperture 14. The optical element of the assembly 11 before the last optical element oriented towards the image is a planar convex lens 12, whose convex surface 2b is oriented towards the object, and whose planar surface 2a is oriented towards the image. As a last optical element of the assembly 11 oriented towards the image, an optical terminal element 17 is provided which comprises a planar plate 19. Between the planar surface 2b of the lens 12 and the planar plate 19 of the optical terminal element 17, thus at the object oriented surface of the planar plate, and also on the image oriented surface of the planar plate of the terminal element 17 a respective immersion liquid 13b or 13a is provided. The planar plate is thus in contact with the immersion liquids 13a and 13b on both sides. By this configuration it is assured that contaminations within the immersion liquid 13a disposed on the image oriented side do not impair the planar convex lens 12. Replacing the terminal element 17 or the planar plate 19 of the terminal element 17, however, is easily possible, as soon as their imaging properties become insufficient through contamination or other impairments.