# US 2025/0147435 A1 · Method for focus metrology and associated apparatuses

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- Number: US 2025/0147435 A1
- Document ID: US20250147435A1
- Status: Published application
- Kind: A1
- Application number: 18/690,979
- Filed: 2022-08-26
- Published: 2025-05-08
- Earliest claimed: 2021-09-27
- Assignees: ASML Netherlands B.V.
- Applicants: ASML Netherlands B.V.
- Inventors: Marie-Claire VAN LARE; Wilhelmus Patrick Elisabeth Maria OP T ROOT
- Web page: https://patentgrep.com/patent/US20250147435A1

## CPC

- G03F 7/706841: {Machine learning}
- G03F 7/705: {Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions}
- G03F 7/70625: {Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness}
- G03F 7/70641: {Focus}
- G03F 7/70683: {Mark designs}
- 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

Disclosed is a method for determining a focus parameter from a target on a substrate. The target comprises an isofocal first sub-target and a second non-isofocal sub-target. The method comprises obtaining a first measurement signal relating to measurement of the first sub-target, a second measurement signal relating to measurement of the second sub-target and at least one trained relationship and/or model which relates at least said second measurement signal to said focus parameter. A value for said focus parameter is determined from said first measurement signal, second measurement signal and said at least one trained relationship and/or model.

## Claims

### Claim at position 1

-15. (canceled)

### Claim 16

A method comprising:
obtaining a first measurement signal relating to measurement of a first sub-target of a target on a substrate, the first sub-target comprising an isofocal structure;
obtaining a second measurement signal relating to measurement of a second sub-target of the target, the second sub-target comprising a non-isofocal structure;
obtaining at least one trained relationship and/or model that relates at least the second measurement signal to the focus parameter; and
determining a value for a focus parameter relating to a focus setting of a lithographic exposure process in which the target was exposed, the determining being based on the first measurement signal, second measurement signal and the at least one trained relationship and/or model.

### Claim 17 (depends on 16)

The method of claim 16, wherein the determining a value comprises determining the value for the focus parameter corrected for the effect of variation of a dose parameter on the second measurement signal.

### Claim 18 (depends on 17)

The method of claim 17, wherein a correction for the effect of variation of a dose parameter on the second measurement signal is determined from the first measurement signal and the at least one trained relationship and/or model.

### Claim 19 (depends on 17)

The method of claim 17, wherein the at least one trained relationship and/or model comprises:
a first relationship between the second measurement signal and the focus parameter, the first relationship including a dependence on the dose parameter, and
a second relationship between the first measurement signal and the dose parameter; or
a combination of the first relationship and second relationship.

### Claim 20 (depends on 17)

The method of claim 17, wherein the at least one trained relationship and/or model comprises:
at least one trained machine learning model operable to infer a value for the focus parameter from the second measurement signal using the first measurement signal to correct the focus inference for the dose parameter.

### Claim 21 (depends on 17)

The method of claim 17, further comprising determining a value for the dose parameter from at least the first measurement signal and the at least one trained relationship and/or model.

### Claim 22 (depends on 17)

The method of claim 17, further comprising an initial calibration phase to train the at least one trained relationship and/or model, the initial calibration phase comprising:
exposing multiple repetitions of the target on one or more substrates, the multiple repetitions being exposed with deliberate variation in the focus parameter and dose parameter;
measuring the multiple repetitions of the target to obtain calibration measurement signals; and
training the at least one trained relationship and/or model using the calibration measurement signals and known focus parameter and dose parameter settings.

### Claim 23 (depends on 22)

The method of claim 22, wherein:
the calibration measurement signals comprise first calibration measurement signals relating to the first sub-structure of each target and second calibration measurement signals relating to the the second sub-structure of each target; and
any variation in the second calibration measurement signals is assumed to be dependent only on the dose parameter.

### Claim 24 (depends on 16)

The method of claim 16, wherein the first sub-target and the second sub-target each comprise a different best focus setting and/or a different pitch and/or critical dimension.

### Claim 25 (depends on 16)

The method of claim 16, wherein the determining a value for the focus parameter comprises determining a value for the focus parameter directly from the first measurement signal, second measurement signal and the at least one trained relationship and/or model.

### Claim 26 (depends on 16)

The method of claim 16, wherein the determining a value for the focus parameter comprises determining a value for critical dimension of at least the second sub-target from the first measurement signal, second measurement signal and the at least one trained relationship and/or model, and determining the focus parameter from the value for critical dimension of at least the second sub-target.

### Claim 27 (depends on 16)

The method of claim 16, further comprising:
performing the lithographic exposure process to expose the target on the substrate using a patterning device;
exposing the first sub-target from isofocal patterning features on the patterning device; and
exposing the second sub-target from non-isofocal patterning features on the patterning device,
wherein the isofocal patterning features and the non-isofocal patterning features differ in terms of one or more of pitch, critical dimension and mask absorber type.

### Claim 28 (depends on 16)

A metrology device comprising:
a processor; and
a storage device, the storage device comprising a computer program product, the computer program product comprising instructions operable to perform the method of claim 16.

### Claim 29

A patterning device comprising:
target patterning features configured to form a target, the target patterning features comprising:
isofocal patterning features configured to form a first sub-target such that it comprises an isofocal structure; and
non-isofocal patterning features configured to form a second sub-target such that it comprises a non-isofocal structure.

### Claim 30 (depends on 29)

A substrate comprising:
at least a target formed using the patterning device of claim 29.