EUV Collector

Patent metadata

Field	Value
Publication number	US-10503075-B2
Application number	US-201816199946-A
Country	US
Kind code	B2
Filing date	Nov 26, 2018
Priority date	May 31, 2016
Publication date	Dec 10, 2019
Grant date	Dec 10, 2019

Abstract

An EUV collector for use in an EUV projection exposure apparatus includes at least one mirror surface having surface structures for scattering a used EUV wavelength (λ) of used EUV light. The mirror surface has a surface height with a spatial wavelength distribution between a lower limit spatial wavelength and an upper limit spatial wavelength. An effective roughness (rmsG) below the lower limit spatial wavelength (PG) satisfies the following relation: (4π rmsG cos(θ)/λ)2<0.1. θ denotes an angle of incidence of the used EUV light at the mirror surface. The following applies to an effective roughness (rmsGG′) between the lower limit spatial wavelength (PG) and the upper limit spatial wavelength (PG′): 1.5 rmsG<rmsGG′<6 rmsG.

First claim

What is claimed is:

1. An EUV collector, comprising:
a mirror surface which comprises surface structures configured to scatter a wavelength (λ) of EUV light,
wherein:
the mirror surface has a surface height with a spatial wavelength distribution between a lower limit spatial wavelength and an upper limit spatial wavelength;
the lower limit spatial wavelength lies in the range between 1 μm and 100 μm;
the upper limit spatial wavelength is at least ten times larger than the lower limit spatial wavelength;
an effective roughness (rmsG) below the lower limit spatial wavelength satisfies the following relation:
(4π rmsG cos(θ)/λ) 2 <0.1;

where θ denotes an angle of incidence of the EUV light at the mirror surface;
the following applies to an effective roughness (rmsGG′) between the lower limit spatial wavelength (PG) and the upper limit spatial wavelength (PG′):
1.5 rmsG<rmsGG′<6 rmsG;

the collector has a mirror center; and
the spatial wavelength distribution is such that a mirror surface element has a radial scattering angle distribution in relation to the mirror center that deviates from an azimuthal scattering angle distribution in relation to the mirror center.

2. The EUV collector of claim 1 , wherein the lower limit spatial wavelength is greater than 5 μm.

3. The EUV collector of claim 1 , wherein the radial scattering angle distribution covers a greater scattering angle range than the azimuthal scattering angle distribution.

4. The EUV collector of claim 1 , wherein the azimuthal scattering angle distribution covers a greater scattering angle range than the radial scattering angle distribution.

5. The EUV collector of claim 1 , wherein a portion of the mirror surface comprises a grating structure configured to diffract extraneous light having a wavelength that deviates from λ.

6. A method, comprising:
providing an EUV collector according to claim 1 by a method that comprises:
providing a raw collector substrate having an initial roughness over all spatial wavelengths; and
processing a surface of the raw collector substrate so that an effective roughness is reduced only below the lower limit spatial wavelength by more than a factor of 1.5.

7. The method of claim 6 , wherein processing the surface of the raw collector comprises polishing the surface of the raw collector.

8. An illumination system, comprising:
an EUV collector according to claim 1 ; and
an illumination optical unit configured to guide EUV light from the EUV collector toward an object field in an object plane.

9. The illumination system of claim 8 , wherein the EUV collector is arranged in a near-field fashion in relation to a field plane that is conjugate to the object plane.

10. The illumination system of claim 8 , further comprising a projection optical unit configured to image the object field into an image field.

11. A projection exposure apparatus, comprising:
an EUV light source; and
an illumination system according to claim 1 .

12. An EUV collector, comprising:
a mirror surface which comprises surface structures configured to scatter a wavelength (λ) of EUV light,
wherein:
the mirror surface has a surface height with a spatial wavelength distribution between a lower limit spatial wavelength (PG) and an upper limit spatial wavelength;
the lower limit spatial wavelength (PG) lies in the range between 1 μm and 100 μm;
the upper limit spatial wavelength is at least ten times larger the lower limit spatial wavelength (PG);
an effective roughness (rmsG) below the lower limit spatial wavelength (PG) satisfies the following relation:
(4π rmsG cos(θ)/λ) 2 <0.1;

where θ denotes an angle of incidence of the EUV light at the mirror surface;
the following applies to an effective roughness (rmsGG′) between the lower limit spatial wavelength (PG) and the upper limit spatial wavelength (PG′):
1.5 rmsG<rmsGG′<6 rmsG;

for the lower limit spatial wavelength (PG) of the spatial wavelength distribution the following relationship applies: PG≈(2 L/dIF)λ1/cos θ;
where L is a distance between a mirror surface element carrying the surface structures and an intermediate focus into which a source region is transferred by the EUV collector during use; and
dIF denotes a permissible diameter of the intermediate focus.

13. The EUV collector of claim 12 , wherein the collector has a mirror center, and the spatial wavelength distribution is such that a mirror surface element has a radial scattering angle distribution in relation to the mirror center that deviates from an azimuthal scattering angle distribution in relation to the mirror center.

14. A method, comprising:
providing an EUV collector according to claim 12 by a method that comprises:
providing a raw collector substrate having an initial roughness over all spatial wavelengths; and
processing a surface of the raw collector substrate so that an effective roughness is reduced only below the lower limit spatial wavelength by more than a factor of 1.5.

15. An illumination system, comprising:
an EUV collector according to claim 12 ; and
an illumination optical unit configured to guide EUV light from the EUV collector toward an object field in an object plane.

16. The illumination system of claim 15 , wherein the EUV collector is arranged in a near-field fashion in relation to a field plane that is conjugate to the object plane.

17. The illumination system of claim 15 , further comprising a projection optical unit configured to image the object field into an image field.

18. A projection exposure apparatus, comprising:
an EUV light source; and
an illumination system according to claim 12 .

19. An illumination system, comprising:
an EUV collector comprising a mirror surface which comprises surface structures configured to scatter a wavelength (λ) of EUV light; and
an illumination optical unit configured to guide the EUV light from the EUV collector toward an object field in an object plane,
wherein:
the mirror surface has a surface height with a spatial wavelength distribution between a lower limit spatial wavelength and an upper limit spatial wavelength;
the lower limit spatial wavelength lies in the range between 1 μm and 100 μm;
the upper limit spatial wavelength is at least ten times larger than the lower limit spatial wavelength;
an effective roughness (rmsG) below the lower limit spatial wavelength satisfies the following relation:
(4π rmsG cos(θ)/λ) 2 <0.1;

where θ denotes an angle of incidence of the EUV light at the mirror surface;
the following applies to an effective roughness (rmsGG′) between the lower limit spatial wavelength (PG) and the upper limit spatial wavelength (PG′):
1.5 rmsG<rmsGG′<6 rmsG; and

the EUV collector is arranged in near-field fashion in relation to a field plane that is conjugate to the object plane.

20. The illumination system of claim 19 , further comprising a projection optical unit configured to image the object field into an image field.

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Schuster Ingrid
• Merkel Wolfgang
• Metalidis Georgo
• Kierey Holger

Classifications

• G03F7/70033

  by plasma extreme ultraviolet [EUV] sources · CPC title

• G02B5/1861

  Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials (G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence) · CPC title

• G02B5/0891

  Ultraviolet [UV] mirrors (apparatus for microlithography exposure G03F7/70; X-ray multilayer structures G21K1/06) · CPC title

• G03F7/702 Primary

  Reflective illumination, i.e. reflective optical elements other than folding mirrors, e.g. extreme ultraviolet [EUV] illumination systems · CPC title

• G03F7/70316

  Details of optical elements, e.g. of Bragg reflectors, extreme ultraviolet [EUV] multilayer or bilayer mirrors or diffractive optical elements · CPC title