Attenuation filter for projection objective, projection objective with attenuation filter for projection exposure apparatus and projection exposure apparatus with projection objective

摘要

An attenuation filter (AF, AF ', AF1, AF2, AF3) is for the defined attenuation of the intensity of ultraviolet radiation (LR1I, LR2I) with a predetermined operating wavelength from a wavelength range of 150 nm to 370 nm according to a predeterminable spatial distribution in a projection objective (PO , PO ') of a projection exposure apparatus (WSC) for microlithography. The attenuation filter has a substrate (SU, SU ') and an absorption layer (AL). The substrate is sufficiently transparent at the operating wavelength. The absorption layer is arranged on the substrate and absorbs incident ultraviolet radiation of the operating wavelength according to the predeterminable local distribution at different locations (Z1, Z2) of a useful area (UA) to different degrees. The attenuation filter is designed to reduce or avoid a thermally induced wavefront variation error in the ultraviolet radiation (LR10, LR2O) passed through the attenuation filter due to locally varying heating of the substrate caused by the absorption of ultraviolet radiation spatially varying across the substrate.