Reflective optical element and EUV lithography appliance

Abstract

The invention relates to a reflective optical element and an EUV lithography appliance containing one such element, said appliance displaying a low propensity to contamination. According to the invention, the reflective optical element has a protective layer system consisting of at least one layer. The optical characteristics of the protective layer system are between those of a spacer and an absorber or correspond to those of a spacer. The selection of a material with the smallest possible imaginary part and a real part which is as close to 1 as possible in terms of the refractive index leads to a plateau-type reflectivity course according to the thickness of the protective layer system between two thicknesses d 1 and d 2 . The thickness of the protective layer system is selected in such a way that it is less than d 2 .

1 . A reflective optical element for the EUV and soft X-ray wavelength region, comprising: a multilayer system and a protective layer system, wherein a side of the multilayer system facing the protective layer system terminates in an absorber layer, wherein the protective layer system has at least 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, so that the reflectivity plotted as a function of the thickness of the protective layer system at first drops, until a thickness d 1  is reached, the reflectivity remains essentially constant between thickness d 1  and another thickness, d 2 , d 2 >d 1 , and the reflectivity further drops for a thickness>d 2 , and the thickness of the protective layer system is smaller than d 2 .  
     
     
         2 . The reflective optical element according to  claim 1 , wherein the imaginary part is between 0 and 0.015 and the real part is between 0.95 and 1.02.  
     
     
         3 . The reflective optical element according to  claim 1 , wherein the protective layer system consists of one or more materials from the group Ce, Be, SiO, SiC, SiO 2 , Si 3 N 4 , C, Y, MoSi 2 , B, Y 2 O 3 , MoS 2 , B 4 C, BN, Ru x Si y , Zr, Nb, MoC, ZrO 2 , Ru x Mo y , Rh x Mo y , or Rh x Si y .  
     
     
         4 . The reflective optical element according to  claim 1 , wherein the multilayer system is a system that consists of molybdenum and silicon layers, ending with a molybdenum layer on the side facing the protective layer system.  
     
     
         5 . The reflective optical element according to  claim 1 , wherein the protective layer system ends on a side of a vacuum with a layer of a material for which the build-up of carbon is suppressed.  
     
     
         6 . The reflective optical element according to  claim 1 , wherein the protective layer system ends toward a side of a vacuum with a layer of a material that is inert to energy injection.  
     
     
         7 . The reflective optical element according to  claim 1 , wherein the protective layer system consists of two layers.  
     
     
         8 . The reflective optical element according to  claim 1 , wherein the protective layer system consists of three layers.  
     
     
         9 . The reflective optical element according to  claim 1 , wherein the thickness d 1  of the protective layer system is such that a standing wave formed by reflection at operating wavelength λ B  has a minimum at a distance from the surface of the reflective optical element of 0.1 λ B  or less.  
     
     
         10 . The reflective optical element according to  claim 1 , wherein the reflectivity curve as a function of the thickness of the protective layer system is constant in the context of a reflectivity decrease of 1% of the maximum reflectivity in the protective layer thickness region between d 1  and d 2 .  
     
     
         11 . The reflective optical element according to  claim 1 , wherein the reflectivity curve as a function of the protective layer thickness between d 1  and d 2  goes through at least one inflection point at the protective layer thickness d w  and the thickness of the protective layer system is less than d w .  
     
     
         12 . The reflective optical element according to  claim 1 , wherein the thickness of the protective layer system is equal to d 1 .  
     
     
         13 . A EUV lithography appliance with at least one reflective optical element according to  claim 1 .  
     
     
         14 . A reflective optical element for the EUV and soft X-ray wavelength region, comprising a multilayer system and a protective layer system, having at least one layer of a material with a refractive index whose real part at an operating wavelength λB between 12.5 nm and 15 nm is between 0.90 and 1.03, and whose imaginary part at an operating wavelength of 12.5 nm to 15 nm is between 0 and 0.025, so that the reflectivity plotted as a function of the thickness of the protective layer system at first drops, until a thickness d 1  is reached, the reflectivity remains essentially constant between thickness d 1  and another thickness d 2 , d 2 >d 1 , and the reflectivity further drops for a thickness>d 2 , wherein a side of the multilayer system facing the protective layer system ends in an absorber layer, wherein the thickness of the protective layer system is smaller than d 2 , and wherein the thickness d 1  is chosen such that a standing wave formed upon reflection at operating wavelength λB has a minimum at a distance from the surface of the reflective optical element of 0.1 λB or less, and the minimum lies in the vacuum.  
     
     
         15 . The reflective optical element according to  claim 2 , wherein the protective layer system consists of one or more materials from the group Ce, Be, SiO, SiC, SiO 2 , Si 3 N 4 , C, Y, MoSi 2 , B, Y 2 O 3 , MoS 2 , B 4 C, BN, Ru x Si y , Zr, Nb, MoC, ZrO 2 , Ru x Mo y , Rh x Mo y , or Rh x Si y .  
     
     
         16 . The reflective optical element according to  claim 15 , wherein the multilayer system is a system that consists of molybdenum and silicon layers, ending with a molybdenum layer on the side facing the protective layer system.  
     
     
         17 . The reflective optical element according to  claim 16 , wherein the protective layer system ends on a side of a vacuum with a layer of a material for which the build-up of carbon is suppressed.  
     
     
         18 . The reflective optical element according to  claim 17 , wherein the protective layer system ends toward the a side of a vacuum with a layer of a material that is inert to energy injection.  
     
     
         19 . The reflective optical element according to  claim 18 , wherein the protective layer system consists of two layers.  
     
     
         20 . The reflective optical element according to  claim 18 , wherein the protective layer system consists of three layers.  
     
     
         21 . The reflective optical element according to  claim 20 , wherein the thickness d 1  of the protective layer system is such that a standing wave formed by reflection at operating wavelength λ B  has a minimum at a distance from the surface of the reflective optical element of 0.1 λ B  or less.  
     
     
         22 . The reflective optical element according to  claim 21 , wherein the reflectivity curve as a function of the thickness of the protective layer system is constant in the context of a reflectivity decrease of 1% of the maximum reflectivity in the protective layer thickness region between d 1  and d 2 .  
     
     
         23 . The reflective optical element according to  claim 22 , wherein the reflectivity curve as a function of the protective layer thickness between d 1  and d 2  goes through at least one inflection point at the protective layer thickness d w  and the thickness of the protective layer system is less than d w .  
     
     
         24 . The reflective optical element according to  claim 23 , wherein the thickness of the protective layer system is equal to d 1 .  
     
     
         25 . A EUV lithography appliance with at least one reflective optical element according to  claim 20.