REFLECTIVE OPTICAL ELEMENT FOR EUV LITHOGRAPHY AND METHOD OF MANUFACTURING A REFLECTIVE OPTICAL ELEMENT

摘要

The invention relates to a reflective optical element of an optical system for EUV lithography as well as to a method of manufacturing a reflective optical element of an optical system for EUV lithography, said reflective optical element (20) comprising a multilayer system (23, 83) for reflecting an incident electromagnetic wave having an operating wavelength in the EUV range, the reflected wave having a phase &phgr;, and a capping layer (25, 85) made from a capping layer material, wherein the method comprises the following steps: determining, for said capping layer material, a dependency according to which the phase of the reflected wave varies with the thickness of the capping layer, determining a linearity-region in said dependency in which the phase of the reflected wave varies substantially linearly with the thickness of the capping layer (25, 85), and creating a thickness profile in said capping layer (25, 85) such that both the maximum thickness and the minimum thickness in said thickness profile are in said linearity-region.