Mirror for the EUV wavelength range, substrate for such a mirror, projection objective for microlithography comprising such a mirror or such a substrate, and projection exposure apparatus for microlithography comprising such a projection objective

• US 9,494,718 B2
• Filed: 06/15/2012
• Issued: 11/15/2016
• Est. Priority Date: 12/15/2009
• Status: Active Grant

• Current Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Inventors: Muellender, Stephan, Weber, Joern, Clauss, Wilfried, Paul, Hans-Jochen, Braun, Gerhard, Migura, Sascha, Dodoc, Aurelian, Zaczek, Christoph, Von Blanckenhagen, Gisela, Loercher, Roland
• Primary Examiner(s): Won, Bumsuk
• Assistant Examiner(s): Gagnon, Grant
• Application Number:
  US13/525,233
• Publication Number:
  US 20130038929A1
• Time in Patent Office: 1,614 Days
• Field of Search: 359590-590
• US Class Current: 1/1
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: G02B 1/10 Optical coatings produced by application to, or surface treatment of, optical elements G02B1/08 takes precedence
• CPC Class Codes: G02B 1/14 Protective coatings, e.g. hard coatings
• CPC Class Codes: G02B 5/0816 Multilayer mirrors, i.e. having two or more reflecting layers G02B5/0883, G02B5/0891 take precedence
• CPC Class Codes: G02B 5/0891 Ultraviolet [UV] mirrors apparatus for microlithography exposure G03F7/70; X-ray multilayer structures G21K1/06
• CPC Class Codes: G03F 7/70233 Optical aspects of catoptric systems, i.e. comprising only reflective elements, e.g. extreme ultraviolet [EUV] projection systems
• CPC Class Codes: G03F 7/70316 Details of optical elements, e.g. of Bragg reflectors, extreme ultraviolet [EUV] multilayer or bilayer mirrors or diffractive optical elements
• CPC Class Codes: G03F 7/70958 Optical materials or coatings, e.g. with particular transmittance, reflectance or anti-reflection properties

Abstract

A mirror (1a; 1a′; 1b; 1b′; 1c; 1c′) for the EUV wavelength range and having a substrate (S) and a layer arrangement, wherein the layer arrangement includes at least one surface layer system (P′″) consisting of a periodic sequence of at least two periods (P₃) of individual layers, wherein the periods (P₃) include two individual layers composed of different materials for a high refractive index layer (H′″) and a low refractive index layer (L′″), wherein the layer arrangement includes at least one surface protecting layer (SPL, L_p) or at least one surface protecting layer system (SPLS) having a thickness of greater than 20 nm, and preferably greater than 50 nm.

Claims

1. A mirror configured to reflect radiation in an extreme-ultraviolet (EUV) wavelength range, comprising:

a substrate (S) and a layer arrangement, wherein the layer arrangement comprises a reflective portion and a surface protecting layer portion,

wherein the reflective portion comprises at least one surface layer system (P′

″

) consisting of a periodic sequence of at least two periods (P₃) of individual layers, wherein the periods (P₃) each comprise two individual layers composed of different materials for a high refractive index layer (H′

″

) and a low refractive index layer (L′

″

) such that the reflectivity of the reflective portion varies according to an angle of incidence of the EUV radiation, and

wherein the surface protective layer portion is arranged between the reflective portion and substrate and comprises at least one surface protecting layer (SPL, L_p) or at least one surface protecting layer system (SPLS) having a thickness of greater than 20 nm, configured to absorb radiation in the EUV wavelength range such that the transmission of the EUV radiation through the layer arrangement amounts to less than 2%.

2. The mirror according to claim 1, wherein the layer arrangement comprises at least one layer which is formed from or as a compound is composed of an alloy from the group nickel-boron, nickel-silicon, nickel-molybdenum, nickel-vanadium, and nickel-silicon-boron.

3. The mirror according to claim 1, wherein the layer arrangement comprises at least three surface layer systems (SPL, P′

, P″

, P′

″

) and the number (N_p;

N₁) of periods (P_p;

P₁) of the surface layer system (SPL, P′

) that is situated closest to the substrate (S) is greater than for the surface layer system (P′

″

) that is most distant from the substrate (S) and/or is greater than for the surface layer system (P″

) that is second most distant from the substrate (S).

4. The mirror according to claim 1, wherein the materials of the two individual layers (L″

, H″

, L′

″

, H′

″

) forming the periods (P₂, P₃) are either molybdenum and silicon or ruthenium and silicon, and wherein a covering layer system (C) comprises at least one layer (M) composed of a chemically inert material and terminates the layer arrangement of the mirror.

5. The mirror according to claim 1, wherein a thickness factor of the layer arrangement along the mirror surface assumes values of between 0.9 and 1.05, and at a location of the mirror surface correlates with the maximum angle of incidence that is to be ensured there.

6. The mirror according to claim 1, wherein the thickness of the at least one surface protecting layer (SPL, L_p) or of the at least one surface protecting layer system (SPLS) is greater than 50 nm, and wherein the transmission of the EUV radiation through the layer arrangement amounts to less than 0.2%.

7. The mirror according to claim 1, wherein the layer arrangement comprises at least one layer which is formed from or as a compound is composed of a material from the group consisting of nickel, carbon, boron carbide, cobalt, beryllium, silicon, and silicon oxides.

8. The mirror according to claim 1, wherein the at least one surface protecting layer (SPL, Lp) or at the least one surface protecting layer system (SPLS) is adjacent to the substrate.

9. The mirror according to claim 1, wherein the layer arrangement comprises an amorphous layer comprising at least quartz or silicon having a thickness of greater than 100 nm, deposited by a CVD method.

10. The mirror according to claim 9, wherein the amorphous layer has a surface roughness of less than 0.5 nm rms HSFR.

11. The mirror according to claim 1, wherein the layer arrangement comprises at least one surface protecting layer system (SPLS) consisting of a periodic sequence of at least two periods (P_p) of individual layers, wherein the periods (P_p) comprise two individual layers composed of different materials for a low refractive index layer (L_p) and a barrier layer (B).

12. The mirror according to claim 11, wherein the material for the low refractive index layer (L_p) consists of nickel and the material for the barrier layer (B) is selected from or as a compound is composed of the group of materials:

B₄C, C, Si nitride, Si carbide, Si boride, Mo nitride, Mo carbide, Mo boride, Ru nitride, Ru carbide and Ru boride.

13. A projection objective for microlithography comprising a mirror according to claim 1.

14. A projection exposure apparatus for microlithography comprising a projection objective according to claim 13.

15. The mirror according to claim 1, wherein the layer arrangement comprises at least one surface protecting layer system (SPLS) consisting of a periodic sequence of at least two periods (P_p) of individual layers, where the periods (P_p) comprise two individual layers composed of different materials for a high refractive index layer (H_p) and a low refractive index layer (L_p), wherein the materials of the two individual layers (L_p, H_p) forming the periods (P_p) are either nickel and silicon or cobalt and beryllium.

16. The mirror according to claim 15, wherein the individual layers are separated by at least one barrier layer (B) and the barrier layer (B) consists of a material which is selected from or as a compound is composed of the group of materials:

B₄C, C, Si nitride, Si carbide, Si boride, Mo nitride, Mo carbide, Mo boride, Ru nitride, Ru carbide and Ru boride.

17. The mirror according to claim 15, wherein the at least one surface protecting layer system (SPLS) has layers having a surface roughness of less than 0.5 nm HSFR rms.

18. A mirror configured to reflect radiation in an extreme-ultraviolet (EUV) wavelength range, comprising:

a substrate (S) and a layer arrangement, wherein the layer arrangement comprises at least one surface layer system (P′

″

) consisting of a periodic sequence of at least two periods (P₃) of individual layers, wherein the periods (P₃) each comprise two individual layers composed of different materials for a high refractive index layer (H′

″

) and a low refractive index layer (L′

″

),

wherein the layer arrangement comprises at least one surface protecting layer (SPL, L_p) or at least one surface protecting layer system (SPLS) having a thickness of greater than 20 nm, wherein the surface protecting layer (SPL, L_p) or the surface protecting layer system (SPLS) is configured to absorb radiation in the EUV wavelength range and experiences an irreversible change in volume of less than 1% under EUV radiation.

19. The mirror according to claim 18, wherein the thickness of the at least one surface protecting layer (SPL, L_p) or of the at least one surface protecting layer system (SPLS) is greater than 50 nm, and wherein the surface protecting layer (SPL, L_p) or the surface protecting layer system (SPLS) experiences an irreversible change in volume of less than 0.2% under the EUV radiation.

20. The mirror according to claim 18, wherein the layer arrangement comprises at least one layer which is formed from or as a compound is composed of an alloy from the group nickel-boron, nickel-silicon, nickel-molybdenum, nickel-vanadium, and nickel-silicon-boron.

21. The mirror according to claim 18, wherein the layer arrangement comprises at least one layer which is formed from or as a compound is composed of a material from the group consisting of nickel, carbon, boron carbide, cobalt, beryllium, silicon, and silicon oxides.

22. The mirror according to claim 18, wherein the at least one surface protecting layer (SPL, Lp) or at the least one surface protecting layer system (SPLS) is adjacent to the substrate.

23. A mirror configured to reflect radiation in an extreme-ultraviolet (EUV) wavelength range, comprising:

a substrate (S) and a layer arrangement, wherein the layer arrangement comprises at least one surface layer system (P′

″

) consisting of a periodic sequence of at least two periods (P₃) of individual layers, wherein the periods (P₃) each comprise two individual layers composed of different materials for a high refractive index layer (H′

″

) and a low refractive index layer (L′

″

),

wherein the layer arrangement comprises at least one surface protecting layer (SPL, L_p) or at least one surface protecting layer system (SPLS) having a thickness of greater than 20 nm, wherein the surface protecting layer (SPL, L_p) or the surface protecting layer system (SPLS) is configured to absorb radiation in the EUV wavelength range and prevents an irreversible alteration of the surface of the substrate (S) under the EUV radiation of more than 0.1 nm measured in the normal direction at a location within the irradiated region of the substrate (S) relative to the surface of the substrate (S) at a location outside the irradiated region measured in the same direction and exerts a tensile stress at least partly compensating layer stresses in the layer arrangement.

24. The mirror according to claim 23, wherein the thickness of the at least one surface protecting layer (SPL, L_p) or of the at least one surface protecting layer system (SPLS) is greater than 50 nm.

25. The mirror according to claim 23, wherein the layer arrangement comprises at least one layer which is formed from or as a compound is composed of an alloy from the group nickel-boron, nickel-silicon, nickel-molybdenum, nickel-vanadium, and nickel-silicon-boron.

26. The mirror according to claim 23, wherein the layer arrangement comprises at least one layer which is formed from or as a compound is composed of a material from the group consisting of nickel, carbon, boron carbide, cobalt, beryllium, silicon, and silicon oxides.

27. The mirror according to claim 23, wherein the at least one surface protecting layer (SPL, Lp) or at the least one surface protecting layer system (SPLS) is adjacent to the substrate.