Patent ID: 9733580
Date: 2017-08-15
CPC Classifications: B82Y,C23C,G02B,G03F,G21K

Claim:
1. A method of producing a reflective optical element for extreme ultraviolet (EUV) lithography, which element has a maximum reflectivity at an operating wavelength in a range of 5 nm to 20 nm, comprising: applying to a substrate a first multilayer system composed of thirty to sixty stacks arranged one above another, wherein each stack has a layer having a thickness dMLs composed of a material having a higher real part of the refractive index at the operating wavelength and a layer having a thickness dMLa composed of a material having a lower real part of the refractive index at the operating wavelength, wherein the thickness ratio is d applying a second multilayer system comprising at least two but no more than five further stacks to the first multilayer system, said further stacks each having a layer having a thickness ds composed of a material having a higher real part of the refractive index at the operating wavelength and a layer having a thickness da composed of a material having a lower real part of the refractive index at the operating wavelength, wherein the thickness ratio is d applying a further layer composed of the material from the group consisting of ruthenium, cerium, yttrium, molybdenum silicide, ytttrium oxide, molybdenum sulfide, zirconium, niobium, molybdenum carbide, zirconium oxide, rhenium, and rhodium directly to the at least two but no more than five further stacks, wherein the first multilayer system is arranged between the second multilayer system and the substrate, and wherein the first multilayer system is configured to reflect EUV radiation at the operating wavelength, and the second multilayer system reduces reflectivity of the optical element at the operating wavelength to less than that of the first multilayer layer system.