Optical element, lithographic apparatus comprising such optical element and device manufacturing method

摘要

An optical element includes a top layer which is transmissive for EUV radiation with wavelength in the range of 5-20 nm, and a structure of the top layer is a structure having an rms roughness value equal to or larger than lambda/10 for spatial periods equal to or smaller than lambda/2. The structure promotes transmission through the top layer to the optical element.