# US 12,111,578 B2 · Mirror for an illumination optical unit of a projection exposure apparatus comprising a spectral filter in the form of a grating structure and method for producing a spectral filter in the form of a grating structure on a mirror

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- Number: US 12,111,578 B2
- Document ID: US12111578B2
- Status: Granted
- Kind: B2
- Application number: 17/317,417
- Filed: 2021-05-11
- Published: 2021-08-26
- Granted: 2024-10-08
- Earliest claimed: 2018-11-29
- Assignees: Carl Zeiss SMT GmbH
- Applicants: Carl Zeiss SMT GmbH
- Inventors: Christof Jalics; Fabian Schuster; Holger Kierey; Andreas Sandner; Tobias Meisch
- Web page: https://patentgrep.com/patent/US12111578B2

## CPC

- G03F 7/70166: {Capillary or channel elements, e.g. nested extreme ultraviolet [EUV] mirrors or shells, optical fibers or light guides}
- G02B 5/0891: {Ultraviolet [UV] mirrors (apparatus for microlithography exposure G03F7/70; X-ray multilayer structures G21K1/06)}
- 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 27/425: {in illumination systems (mask illumination systems in photolithographic systems G03F7/70158)}
- G03F 7/70158: {Diffractive optical elements}
- G03F 7/70191: {Optical correction elements, filters or phase plates for controlling intensity, wavelength, polarisation, phase or the like}
- G03F 7/702: {Reflective illumination, i.e. reflective optical elements other than folding mirrors, e.g. extreme ultraviolet [EUV] illumination systems}
- G03F 7/70575: {Wavelength control, e.g. control of bandwidth, multiple wavelength, selection of wavelength or matching of optical components to wavelength}
- 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

## Abstract

A mirror for an illumination optical unit of a projection exposure apparatus comprises a spectral filter in the form of a grating structure, wherein the grating structure has a maximum edge steepness in the range of 15° to 60°.

## Claims

### Claim 1

A mirror, comprising:
a reflection surface comprising a spectral filter which comprises a grating structure,
wherein:
the grating structure comprises a plurality of grating ridges;
for each grating ridge, the grating ridges comprises a front side and sidewalls;
for each of at least some pairs of adjacent grating ridges:
a groove comprising a bottom is between the adjacent grating ridges;
a depth of the groove is a distance between the bottom and the adjacent grating ridges; and
the depth is configured to mask out infrared radiation;
the grating structure has a maximum edge steepness in the range of 15° to 60°; and
the mirror is selected from the group consisting of a condenser mirror and a collector mirror.

### Claim 2 (depends on 1)

The mirror of claim 1, further comprising a closed protective layer covering the grating structure.

### Claim 3 (depends on 2)

The mirror of claim 2, wherein:
the protective layer comprises a plurality of double plies; and
each double plie comprises molybdenum and silicon.

### Claim 4 (depends on 3)

The mirror of claim 3, wherein the protective layer comprises at least 10 double plies.

### Claim 5 (depends on 3)

The mirror of claim 3, wherein the double plies are in the form of a stack without interruptions between the double plies.

### Claim 6 (depends on 3)

The mirror of claim 3, further comprising a substrate, wherein:
the substrate has the grating structure; and
the substrate comprises at least one member selected from the group consisting of amorphous silicon, nickel-phosphorus, silicon dioxide, titanium, platinum, gold, aluminium, titanium oxide, nickel, copper, silver, tantalum and aluminium oxide.

### Claim 7 (depends on 6)

The mirror of claim 6, wherein, for each of the at least some pairs of adjacent ridges, the depth of the groove is from one micron to 10 microns.

### Claim 8 (depends on 6)

The mirror of claim 6, wherein, for each of at least some of the grating ridges, the grating ridge has a cross section having a trapezoid-shaped smallest convex envelope.

### Claim 9 (depends on 1)

The mirror of claim 1, further comprising a substrate, wherein:
the substrate has the grating structure; and
the substrate comprises at least one member selected from the group consisting of amorphous silicon, nickel-phosphorus, silicon dioxide, titanium, platinum, gold, aluminium, titanium oxide, nickel, copper, silver, tantalum and aluminium oxide.

### Claim 10 (depends on 1)

An optical unit, comprising:
a mirror according to claim 1,
wherein the optical unit is a projection lithography illumination optical unit.

### Claim 11 (depends on 1)

A system, comprising:
a projection lithography illumination optical unit which comprises a mirror according to claim 1; and
a radiation source configured to generate illumination radiation.

### Claim 12 (depends on 1)

An apparatus, comprising:
an illumination optical unit comprising a mirror according to claim 1; and
a projection optical unit configured to image an object field into an image field,
wherein the apparatus is a microlithographic projection exposure apparatus.

### Claim 13 (depends on 1)

A method of using a projection exposure system comprising an illumination optical system and an imaging optical system, the method comprising:
using the illumination optical system to illuminate a region of a reticle in an object field of the imaging optical system; and
using the imaging optical to project at least a part of the illuminated reticle onto a region of a light-sensitive material in an object field of the imaging optical system,
wherein the illumination optical system comprises a mirror according to claim 1.

### Claim 14 (depends on 1)

The mirror of claim 1, wherein the mirror is a condenser mirror.

### Claim 15 (depends on 1)

The mirror of claim 1, wherein the mirror is a collector mirror.

### Claim 16 (depends on 1)

The mirror of claim 1, further comprising a substrate, wherein the substrate comprises at least one member selected from the group consisting of amorphous silicon, nickel-phosphorus, silicon dioxide, titanium, platinum, gold, aluminium, titanium oxide, nickel, copper, silver, tantalum and aluminium oxide.

### Claim 17

A method, comprising:
structuring a structuring layer applied on a substrate of a mirror body; and
structuring the substrate of the mirror body,
wherein structuring the substrate of the mirror body comprises at least one member selected from the group consisting of:
etching with an etching angle in the range of 0° to 60°;
etching, wherein the structuring layer and the substrate of the mirror body have different etching rates; and
etching, wherein the structuring layer is provided with a sidewall steepness in the range of 10° to 90° during the structuring; and
applying a closed protective layer on the substrate,
wherein:
the grating structure comprises a plurality of grating ridges;
for each grating ridge, the grating ridges comprises a front side and sidewalls;
for each of at least some pairs of adjacent grating ridges:
a groove comprising a bottom is between the adjacent grating ridges;
a depth of the groove is a distance between the bottom and the adjacent grating ridges; and
the depth of the groove is configured to mask out infrared radiation; and
the grating structure has a maximum edge steepness in the range of 15° to 60°.

### Claim 18 (depends on 17)

The method of claim 17, wherein structuring the substrate of the mirror body comprises at least one member selected from the group consisting of:
inert dry etching with an etching angle in the range of 0° to 60°;
inert dry etching, wherein the structuring layer and the substrate of the mirror body have different etching rates;
inert dry etching, wherein the structuring layer is provided with a sidewall steepness in the range of 0° to 60° during structuring;
reactive dry etching comprising controlling a composition of an etching gas to set a ratio of the etching rates of substrate of the mirror body and structuring layer; and
wet chemical etching comprising controlling a composition of an etching medium to set a ratio of the etching rates of substrate of the mirror body and the structuring layer.

### Claim 19 (depends on 17)

The method of claim 17, wherein structuring the substrate of the mirror body comprises using a combination of inert etching and reactive etching.

### Claim 20 (depends on 17)

The method of claim 17, wherein structuring the substrate of the mirror body comprises etching method with a longitudinal etching angle in the range of 0° to 60°.

### Claim 21 (depends on 17)

The method of claim 17, wherein structuring the substrate of the mirror body comprises etching method with a transverse etching angle in the range of 0° to 60°.

### Claim 22 (depends on 17)

The method of claim 17, further comprising setting a sidewall steepness of the structuring layer by controlling at least one parameter in a targeted manner, wherein the at least one parameter comprises at least one member selected from the group consisting of a focusing a laser beam for structuring the structuring layer, an intensity of the exposure in a lithography process for structuring the structuring layer, a duration of the development of a lithography process for structuring the structuring layer, a hard bake of the structuring layer after a structuring thereof, a re-flow of the structuring layer after a structuring thereof, and a temperature of the structuring layer after a structuring thereof.

### Claim 23 (depends on 17)

The method of claim 17, further comprising setting a sidewall steepness of the structuring layer.

### Claim 24 (depends on 17)

The method of claim 17, wherein, for each of the at least some pairs of adjacent ridges, the depth of the groove is from one micron to 10 microns.