Patent ID: 7952797
Filing Date: 2011-05-31
Classification: B82Y,G02B,G03F,G21K

Abstract:
1. A reflective optical element for the extreme ultraviolet and soft X-ray wavelength regions, the reflective optical element comprising a multilayer system and a protective layer system, wherein: the multilayer system is a system that consists of molybdenum and silicon layers, ending with a molybdenum layer on a side facing the protective layer system, the side of the multilayer system facing the protective layer system terminates in an absorber layer, the protective layer system comprises at least two layers, the protective layer system terminates at a vacuum side in one layer of a material with a refractive index whose real part at an operating wavelength between 12.5 nm and 15 nm is between 0.90 and 1.03, and whose imaginary part at an operating wavelength between 12.5 nm and 15 nm is between 0 and 0.025, the reflectivity plotted as a function of a thickness of the protective layer system by varying a thickness of the layer terminating the protective system at the vacuum side at first drops, until a first thickness value d the thickness of the protective layer system is smaller than d