REFLECTIVE OPTICAL ELEMENT, AND OPTICAL SYSTEM OF A MICROLITHOGRAPHIC PROJECTION EXPOSURE SYSTEM

摘要

The invention relates to a reflective optical element, and to an optical system of a microlithographic projection exposure system. A reflective optical element comprises a substrate (52) and a multi-layer system (51) arranged on said substrate, wherein the multi-layer system (51) has a plurality of partial stacks each comprising a first layer (54) of a first material and at least one second layer (55) of a second material, wherein the first material and the second material differ from each other in the value of the real part of the index of refraction at a working wavelength of the reflective optical element (50), wherein each of said partial stacks (53) has a partial stack thickness (Di) and a layer thickness ratio (Γi), wherein the layer thickness ratio (Γi) is defined as the quotient of the thickness of the particular first layer (54) and the partial stack thickness (Di), wherein for at least one of the two values of partial stack thickness (Di) and layer thickness ratio (Γi), the mean squared deviation from the particular mean is at least 10% less in a first section of the multi-layer system (51) than in a second section of the multi-layer system (51); and wherein the reflective optical element (50) has a reflectivity (R), the wavelength dependence of which in a wavelength interval of Δλ = 0.5 nm has a PV value less than 0.25, wherein the PV value is defined as PV = (Rmax_rel - Rmin_rel)/Rmax_abs, wherein Rmax_rel indicates the maximum reflectivity value in said wavelength interval Δλ, Rmin_rel indicates the minimum reflectivity value in said wavelength interval Δλ, and Rmax_abs indicates the absolute maximum reflectivity value.