Reflective optical element for ultraviolet radiation, projection optical system and projection exposure system therewith, and method for forming the same

• US 20060262389A1
• Filed: 05/15/2006
• Published: 11/23/2006
• Est. Priority Date: 05/23/2005
• Status: Abandoned Application

• Current Assignee: Carl Zeiss AG (Carl-Zeiss-Stiftung)
• Original Assignee: Carl Zeiss AG (Carl-Zeiss-Stiftung)
• Inventors: Zaczek, Christoph
• Application Number:
  US11/434,439
• Publication Number:
  US 20060262389A1
• Time in Patent Office: Days
• US Class Current: 359/359
• CPC Class Codes: G02B 5/0825 the reflecting layers comprising dielectric materials only
• CPC Class Codes: G02B 5/0875 the reflecting layers comprising two or more metallic layers
• CPC Class Codes: G02B 5/0891 Ultraviolet [UV] mirrors apparatus for microlithography exposure G03F7/70; X-ray multilayer structures G21K1/06

Abstract

A reflective optical element for radiation with a wavelength A in the ultraviolet wavelength range comprises a reflective surface, and a dielectric multilayer system formed on said reflective surface, said dielectric multilayer system comprising at least two successive pairs of layers, each pair of layers consisting of a high refractive index layer alternating with a low refractive index layer, wherein optical thicknesses of said high refractive index layers and optical thicknesses of said low refractive index layers of each adjacent pair of layers are different from each other.

Claims

1. Reflective optical element for radiation with a wavelength A in the ultraviolet wavelength range comprising:

a reflective surface, and

a dielectric multilayer system formed on said reflective surface,

said dielectric multilayer system comprising at least two successive pairs of layers, each of said pairs of layers consisting of a high refractive index layer alternating with a low refractive index layer,

wherein optical thicknesses of said high refractive index layers and optical thicknesses of said low refractive index layers of each adjacent pair of layers are different from each other.

2. Reflective optical element according to claim 1, wherein said optical thicknesses of all of said high and low refractive index layers of said dielectric multilayer system are different from each other.

3. Reflective optical element according to claim 1, wherein said optical thickness of said high and low refractive index layers is between 0.1 λ

and 0.35 λ

.

4. Reflective optical element according to claim 1, wherein said dielectric multilayer system further comprises a first low refractive index layer formed contiguous to said reflective surface having an optical thickness between 0.1 λ

and 0.2 λ

.

5. Reflective optical element according to claim 1, wherein said optical thickness of said high refractive index layers decreases with increasing distance from said reflective surface.

6. Reflective optical element according to claim 5, wherein said optical thickness of said low refractive index layers increases at least on average with increasing distance from said reflective surface.

7. Reflective optical element according to claim 1, wherein said optical thickness of said low refractive index layers decreases with increasing distance from said reflective surface.

8. Reflective optical element according to claim 7, wherein said optical thickness of said high refractive index layers increases at least on average with increasing distance from said reflective surface.

9. Reflective optical element according to claim 1, wherein said reflective surface is a surface of a metal film, in particular an aluminium film being formed contiguous to a substrate, said metal film preferably having a thickness smaller than 100 nm, in particular between 55 nm and 100 nm.

10. Reflective optical element according to claim 1, wherein each of said high refractive index layers is composed of one or more materials selected from the group consisting of:

lanthanum fluoride (LaF₃), gadolinium fluoride (GdF₃), aluminium oxide (Al₂O₃), neodymium fluoride (NdF₃), dysprosium fluoride (DyF₃), lead fluoride (PbF₂), hafnium oxide (HfO₂), and zirconium oxide (ZrO₂).

11. Reflective optical element according to claim 1, wherein each of said low refractive index layers is composed of one or more materials selected from the group consisting of:

aluminium fluoride (AlF₃), magnesium fluoride (MgF₂), sodium fluoride (NaF), lithium fluoride (LiF), thiolithe (Na₅Al₃Fl₄), cryolite (Na₃AlF₆), silicon oxide (SiO₂), calcium fluoride (CaF₂), barium fluoride (BaF₂), and strontium fluoride (SrF₂).

12. Projection optical system for forming an image of a pattern arranged on a mask on a photosensitive substrate, comprising at least one reflective optical element according to claim 1.

13. Projection optical system according to claim 12, wherein said reflective optical element is a concave reflector.

14. Projection optical system according to claim 12, wherein said reflective optical element is a deflecting mirror arranged in an optical path before a concave reflector.

15. Projection optical system according to claim 12, wherein said reflective optical element is a deflecting mirror arranged in an optical path after a concave reflector.

16. Projection exposure apparatus for radiation in the ultraviolet wavelength range, comprising:

an illuminating system for illuminating a mask, and

a projection optical system for forming an image of a pattern arranged on said mask on a photosensitive substrate, said projection exposure apparatus further comprising at least one reflective optical element according to claim 1.

17. Projection exposure apparatus according to claim 16, wherein said at least one reflective optical element is arranged in said illumination system.

18. Projection exposure apparatus according to claim 16, wherein said at least one reflective optical element is arranged in said projection optical system.

19. Method for forming a reflective optical element for radiation with a wavelength λ

in the ultraviolet wavelength range, said method comprising the steps of;

forming a metal film, in particular an aluminium film, on a substrate with a thickness preferably below 100 nm, in particular between 55 nm and 100 nm, a surface of the metal film forming a reflective surface,

forming a dielectric multilayer system on said reflective surface starting with a first low refractive index layer with an optical thickness between 0.1 λ and

0.2 λ

,

superimposing over said first layer at least two successive pairs of layers, each pair of layers consisting of a high refractive index layer alternating with a low refractive index layer, wherein

optical thicknesses of said high refractive index layers and optical thicknesses of said low refractive index layers of each adjacent pair of layers are different from each other.

20. Method according to claim 19, wherein said high and low refractive index layers are formed on said substrate by a deposition method selected from the group consisting of thermal evaporation, ion assisted deposition, and sputtering.