# US 11,079,604 B2 · Device for determining the exposure energy during the exposure of an element in an optical system, in particular for microlithography

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- Number: US 11,079,604 B2
- Document ID: US11079604B2
- Status: Granted
- Kind: B2
- Application number: 16/589,278
- Filed: 2019-10-01
- Published: 2020-04-02
- Granted: 2021-08-03
- Earliest claimed: 2018-10-02
- Assignees: Carl Zeiss SMT GmbH
- Applicants: Carl Zeiss SMT GmbH
- Inventors: Thomas Frank
- Web page: https://patentgrep.com/patent/US11079604B2

## CPC

- G02B 27/0961: {Lens arrays (lens arrays per se G02B3/0006)}
- G03F 7/7085: {Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load}
- G02B 27/0905: {Dividing and/or superposing multiple light beams}
- G02B 27/108: {for sampling a portion of a beam or combining a small beam in a larger one, e.g. wherein the area ratio or power ratio of the divided beams significantly differs from unity, without spectral selectivity}
- G02B 27/1086: {operating by diffraction only}
- G03F 1/84: Inspecting
- G03F 7/70158: {Diffractive optical elements}
- G03F 7/70316: {Details of optical elements, e.g. of Bragg reflectors, extreme ultraviolet [EUV] multilayer or bilayer mirrors or diffractive optical elements}
- G03F 7/70558: {Dose control, i.e. achievement of a desired dose}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- 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)

## Abstract

The invention relates to a device for determining the exposure energy during the exposure of an element in an optical system, in particular for microlithography, comprising an optical element, a diffractive structure which has a locally varying grating period, and an intensity sensor arrangement, wherein electromagnetic radiation diffracted at the diffractive structure during operation of the optical system, in at least one order of diffraction, is directed to the intensity sensor arrangement by way of total internal reflection effected in the optical element.

## Claims

### Claim 1

A system comprising:
a light source;
an illumination optical unit configured to project light from the light source towards a first element;
a first detector unit;
an imaging optical unit configured to project light from the first element towards the first detector unit;
an exposure determining device disposed between the illumination optical unit and the first element, the exposure determining device comprising:
a first optical element;
a diffractive structure; and
a second detector unit;
wherein the exposure determining device is configured such that light diffracted at the diffractive structure during operation of the system, in at least one order of diffraction, is directed to the second detector unit by total internal reflection in the first optical element.

### Claim 2 (depends on 1)

The system of claim 1 in which the first element comprises a photomask, the system comprises a mask inspection system, and the exposure determining device is configured to estimate an exposure energy applied to the photomask during inspection of the photomask.

### Claim 3 (depends on 1)

The system of claim 1, wherein the diffractive structure has a locally varying grating period; and
the second detector unit comprises an intensity sensor arrangement;
wherein electromagnetic radiation diffracted at the diffractive structure during operation of the system, in at least one order of diffraction, is directed to the intensity sensor arrangement by way of total internal reflection effected in the first optical element.

### Claim 4 (depends on 3)

The system according to claim 3, wherein the system has an optical system axis (OA), and the grating period decreases with increasing distance from said optical system axis (OA).

### Claim 5 (depends on 3)

The system according to claim 3, wherein the diffractive structure is embodied on a light entrance surface of the first optical element.

### Claim 6 (depends on 5)

The system according to claim 5, wherein the diffractive structure is embodied only on a partial region of said light entrance surface.

### Claim 7 (depends on 3)

The system according to claim 3, wherein the diffractive structure has a plurality of diffraction gratings which differ from one another with regard to the direction in which one and the same order of diffraction is directed by the relevant diffraction grating.

### Claim 8 (depends on 3)

The system according to claim 3, wherein the intensity sensor arrangement has a plurality of intensity sensors.

### Claim 9 (depends on 3)

The system according to claim 3, wherein the intensity sensor arrangement has at least one spatially resolving intensity sensor.

### Claim 10 (depends on 3)

The system according to claim 3, wherein the diffractive structure has at least one phase grating.

### Claim 11 (depends on 1)

The system according to claim 1, wherein the system comprises a mask inspection apparatus.

### Claim 12 (depends on 1)

The system according to claim 1, wherein the system comprises a microlithographic projection exposure apparatus.

### Claim 13 (depends on 12)

The system of claim 12 in which the microlithographic projection exposure apparatus is configured to expose the mask to project a pattern on the mask onto a second element to form the pattern on the second element, and the exposure determining device is configured to estimate the exposure energy applied to the mask during the exposure of the mask.

### Claim 14 (depends on 3)

The system of claim 3 in which the diffractive structure is disposed on the first optical element.

### Claim 15 (depends on 3)

The system of claim 3 in which the diffractive structure is disposed on a second optical element that is positioned upstream of the first optical element in a path of electromagnetic radiation used to expose the first element.

### Claim 16 (depends on 15)

The system of claim 15 in which the diffractive structure is disposed on a radiation exit surface of the second optical element.

### Claim 17 (depends on 3)

The system of claim 3 in which the system is configured to expose the first element using electromagnetic radiation, and the diffractive structure is configured to diffract a first portion of the electromagnetic radiation toward the intensity sensor arrangement and allow a second portion of the electromagnetic radiation to pass the diffractive structure and travel toward the first element to expose the first element.

### Claim 18 (depends on 1)

The system of claim 1, in which the system is configured to perform:
projecting electromagnetic radiation along a propagation path toward the first element;
disposing the first optical element and the diffractive structure upstream of the first element in the propagation path, wherein the diffractive structure has a locally varying grating period; and
estimating an exposure energy applied to the first element due to the electromagnetic radiation, including:
diffracting a fraction of the electromagnetic radiation in at least one order of diffraction, and
directing the diffracted electromagnetic radiation to the second detector unit by total internal reflection effected in the optical element, wherein the second detector unit comprises an intensity sensor arrangement.

### Claim 19 (depends on 18)

The system of claim 18, wherein the system is configured to perform directing multiple portions of diffracted electromagnetic radiation that are associated with a same order of diffraction toward multiple directions.

### Claim 20 (depends on 18)

The system of claim 18, wherein the system is configured to perform:
projecting a portion of the electromagnetic radiation that has not been diffracted toward the first element;
exposing the first element using the electromagnetic radiation; and
performing at least one of (i) collecting data representing the exposed first element, and inspecting the first element based on the collected data; or (ii) projecting a pattern on the first element onto a second element, and forming the pattern on the second element.

### Claim 21 (depends on 18)

The system of claim 18 in which the first element comprises a photolithography mask.