Spectral purity filter for multi-layer mirror, lithographic apparatus including such multi-layer mirror, method for enlarging the ratio of desired radiation and undesired radiation, and device manufacturing method

Abstract

A multi-layer mirror includes a multi-layer stack. The multi-layer stack includes a plurality of alternating layers with a multi-layer stack top layer and a spectral filter top layer arranged on the multi-layer stack. The spectral filter top layer includes a first spectral purity enhancement layer that includes a first material m 1 and has a first layer thickness d 1 , an intermediate layer that includes a second material m 2 and has a second layer thickness d 2 . The intermediate layer is arranged on the multi-layer stack top layer. The first material is selected from SiN, Si 3 N 4 , SiO 2 , ZnS, Te, diamond, CsI, Se, SiC, amorphous carbon, MgF 2 , CaF 2 , TiO 2 , Ge, PbF 2 , ZrO 2 , BaTiO 3 , LiF or NaF. The second material includes a material different from the first material, and d 1 +d 2 has a thickness between 1.5 and 40 nm.

1 . A multi-layer mirror, comprising:
 a multi-layer stack, the multi-layer stack comprising a plurality of alternating layers with a multi-layer stack top layer and a spectral filter top layer arranged on the multi-layer stack, the spectral filter top layer comprising
 a first spectral purity enhancement layer comprising a first material m 1  and having a first layer thickness d 1 ; 
 an intermediate layer comprising a second material m 2  and having a second layer thickness d 2 , the intermediate layer being arranged on the multi-layer stack top layer, wherein the first material is selected from SiN, Si 3 N 4 , SiO 2 , ZnS, Te, diamond, CsI, Se, SiC, amorphous carbon, MgF 2 , CaF 2 , TiO 2 , Ge, PbF 2 , ZrO 2 , BaTiO 3 , LiF or NaF, the second material comprises a material different from the first material, and d 1 +d 2  has a thickness between 1.5 and 40 nm. 
   
     
     
         2 . A multi-layer mirror according to  claim 1 , wherein the spectral filter top layer further comprises a cap layer on top of the first spectral purity enhancement layer, the cap layer comprising a third material selected from Ru, BN, B 4 C, B, C, TiN, Pd, Rh, Au, C 2 F 4 , SiN, Si 3 N 4 , SiC, MgF 2  or LiF. 
     
     
         3 . A multi-layer mirror according to  claim 1 , wherein the spectral filter top layer further comprises a cap layer on top of the first spectral purity enhancement layer, comprising Ru and having a layer thickness d 4  between 0.5 and 2.5 nm. 
     
     
         4 . A multi-layer mirror according to  claim 1 , wherein the intermediate layer comprises a metal. 
     
     
         5 . A multi-layer mirror according to  claim 1 , wherein the second material is selected from Be, B, C, Si, P, S, K, Ca, Sc, Br, Rb, Sr, Y, Zr, Nb, Mo, Ba, La, Ce, Pr, Pa or U. 
     
     
         6 . A multi-layer mirror according to  claim 1 , wherein the first spectral purity enhancement layer has an imaginary part of the complex index of refraction k≦0.25*n+1.07, wherein n is the real part of the complex index of refraction. 
     
     
         7 . A multi-layer mirror according to  claim 1 , wherein the first spectral purity enhancement layer has a real part of the complex index of refraction equal or larger than 2 and an imaginary part of the complex index of refraction equal or smaller than 1.6. 
     
     
         8 . A multi-layer mirror according to  claim 1 , wherein the first and second materials and the first and second layer thicknesses are configured to minimize absorption and/or destructive interference of radiation having a wavelength selected from a first wavelength range of 5-20 inn, and maximize absorption and/or destructive interference of radiation having a wavelength selected from a second wavelength range of 100-400 nm. 
     
     
         9 . A multi-layer mirror according to  claim 1 , wherein the multi-layer mirror is a normal incidence mirror. 
     
     
         10 . A multi-layer mirror according to  claim 1 , wherein the multi-layer mirror is a normal incidence mirror configured to reflect radiation having a wavelength selected from a first wavelength range of 5-20 nm. 
     
     
         11 . A multi-layer mirror according to  claim 1 , wherein the multi-layer mirror is a normal incidence Si/Mo multi-layer mirror configured to reflect radiation having a wavelength selected from the wavelength range of 12-15 nm. 
     
     
         12 . A multi-layer mirror according to  claim 1 , wherein the first spectral purity enhancement layer comprises Si 3 N 4 , having a layer thickness between 4 and 11 nm, and wherein the intermediate layer comprises Mo having a layer thickness between 1 and 3 nm. 
     
     
         13 . A multi-layer mirror according to  claim 1 , wherein the multi-layer stack top layer comprises a cap layer, the top layer comprising a material m 5  selected from Ru, BN, B 4 C, B, C, TiN, Pd, Rh, Au, C 2 F 4 , SiN, Si 3 N 4 , SiC, MgF 2  or LiF. 
     
     
         14 . A multi-layer mirror according to  claim 1 , wherein the multi-layer stack top layer comprises a cap layer, the multi-layer stack top layer comprising Ru and having a layer thickness d 5  between 0.5 and 2.5 nm. 
     
     
         15 . A lithographic apparatus comprising a multi-layer mirror comprising a multi-layer stack, the multi-layer stack comprising a plurality of alternating layers with a multi-layer stack top layer and a spectral filter top layer arranged on the multi-layer stack, the spectral filter top layer comprising a first spectral purity enhancement layer comprising a first material m 1  and having a first layer thickness d 1 ; an intermediate layer comprising a second material m 2  and having a second layer thickness d 2 , the intermediate layer being arranged on the multi-layer stack top layer, wherein the first material is selected from SiN, Si 3 N 4 , SiO 2 , ZnS, Te, diamond, CsI, Se, SiC, amorphous carbon, MgF 2 , CaF 2 , TiO 2 , Ge, PbF 2 , ZrO 2 , BaTiO 3 , LiF or NaF, the second material comprises a material different from the first material, and d 1 +d 2  has a thickness between 1.5 and 40 nm. 
     
     
         16 . A lithographic apparatus according to  claim 15 , further comprising a plurality of multi-layer mirrors, wherein the first and second material materials and the first and second layer thicknesses are configured to minimize absorption and/or destructive interference of radiation having a wavelength selected from a first wavelength range of 5-20 nm, and maximize absorption and/or destructive interference of radiation having a wavelength selected from a substantial part of the wavelength range of 100-400 nm. 
     
     
         17 . A method for enlarging the ratio of radiation having a wavelength selected from a first wavelength range of 5-20 nm and radiation having a wavelength selected from a second wavelength range of 100-400 nm in a beam of radiation of a source emitting radiation in both wavelength ranges, the method comprising reflecting at least part of the beam of radiation on a multi-layer mirror comprising a multi-layer stack, the multi-layer stack comprising a plurality of alternating layers with a multi-layer stack top layer and a spectral filter top layer arranged on the multi-layer stack, the spectral filter top layer comprising a first spectral purity enhancement layer comprising a first material m 1  and having a first layer thickness d 1 ; an intermediate layer comprising a second material m 2  and having a second layer thickness d 2 , the intermediate layer being arranged on the multi-layer stack top layer, wherein the first material is selected from SIN, Si 3 N 4 , SiO 2 , ZnS, Te, diamond, CsI, Se, SiC, amorphous carbon, MgF 2 , CaF 2 , TiO 2 , Ge, PbF 2 , ZrO 2 , BaTiO 3 , LiF or NaF, the second material comprises a material different from the first material, and d 1 +d 2  has a thickness between 1.5 and 40 nm. 
     
     
         18 . A method according to  claim 17 , wherein reflecting the at least part of the beam of radiation comprises reflecting the at least part of the beam on a plurality of multi-layer mirrors. 
     
     
         19 . A method according to  claim 17 , wherein the first and second materials and the first and second layer thicknesses are configured to minimize absorption and/or destructive interference of radiation having a wavelength selected from the first wavelength range, and maximize absorption and/or destructive interference of radiation having a wavelength selected from the second wavelength range of 100-400 nm. 
     
     
         20 . A device manufacturing method, comprising:
 providing a beam of radiation;   patterning the beam of radiation;   projecting the patterned beam of radiation onto a target portion of a substrate;   enlarging the ratio of radiation having a wavelength selected from a first wavelength range of 5-20 nm and radiation having a wavelength selected from a second wavelength range of 100-400 nm by reflecting at least part of the beam of radiation on a multi-layer mirror comprising a multi-layer stack, the multi-layer stack comprising a plurality of alternating layers with a multi-layer stack top layer and a spectral filter top layer arranged on the multi-layer stack, the spectral filter top layer comprising a first spectral purity enhancement layer comprising a first material m 1  and having a first layer thickness d 1 ; an intermediate layer comprising a second material m 2  and having a second layer thickness d 2 , the intermediate layer being arranged on the multi-layer stack top layer, wherein the first material is selected from SiN, Si 3 N 4 , SiO 2 , ZnS, Te, diamond, CsI, Se, SiC, amorphous carbon, MgF 2 , CaF 2 , TiO 2 , Ge, PbF 2 , ZrO 2 , BaTiO 3 , LiF or NaF, the second material comprises a material different from the first material, and d 1 +d 2  has a thickness between 1.5 and 40 nm.