# US 10,503,075 B2 · EUV Collector

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- Number: US 10,503,075 B2
- Document ID: US10503075B2
- Status: Granted
- Kind: B2
- Application number: 16/199,946
- Filed: 2018-11-26
- Published: 2019-03-28
- Granted: 2019-12-10
- Earliest claimed: 2016-05-31
- Assignees: Carl Zeiss SMT GmbH
- Applicants: Carl Zeiss SMT GmbH
- Inventors: Ingrid Schuster; Wolfgang Merkel; Georgo Metalidis; Holger Kierey
- Web page: https://patentgrep.com/patent/US10503075B2

## CPC

- G03F 7/702: {Reflective illumination, i.e. reflective optical elements other than folding mirrors, e.g. extreme ultraviolet [EUV] illumination systems}
- G02B 5/0833: {comprising inorganic materials only}
- G02B 5/0891: {Ultraviolet [UV] mirrors (apparatus for microlithography exposure G03F7/70; X-ray multilayer structures G21K1/06)}
- G02B 5/09: Multifaceted or polygonal mirrors {, e.g. polygonal scanning mirrors; Fresnel mirrors}
- G02B 5/1838: {for use with ultraviolet radiation or X-rays}
- G02B 5/1861: {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)}
- G02B 19/0047: {for use with a light source (G02B19/009, G02B19/0095 take precedence; details of lighting devices in general F21V; non-semiconductor lasers having optical devices external to the laser cavity H01S3/005)}
- G02B 19/0095: {for use with ultraviolet radiation}
- G03F 7/70033: {by plasma extreme ultraviolet [EUV] sources}
- G03F 7/70175: {Lamphouse reflector arrangements or collector mirrors, i.e. collecting light from solid angle upstream of the light source}
- G03F 7/70316: {Details of optical elements, e.g. of Bragg reflectors, extreme ultraviolet [EUV] multilayer or bilayer mirrors or diffractive optical elements}
- G21K 1/062: {Devices having a multilayer structure}
- G21K 2201/064: having a curved surface
- G21K 2201/067: Construction details
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G21K: HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES

## 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.

## Claims

### Claim 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.

### Claim 2 (depends on 1)

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

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 1)

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

### Claim 5 (depends on 1)

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.

### Claim 6 (depends on 1)

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.

### Claim 7 (depends on 6)

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

### Claim 8 (depends on 1)

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.

### Claim 9 (depends on 8)

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.

### Claim 10 (depends on 8)

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

### Claim 11 (depends on 1)

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

### Claim 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.

### Claim 13 (depends on 12)

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.

### Claim 14 (depends on 12)

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.

### Claim 15 (depends on 12)

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.

### Claim 16 (depends on 15)

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.

### Claim 17 (depends on 15)

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

### Claim 18 (depends on 12)

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

### Claim 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.

### Claim 20 (depends on 19)

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