# US 11,442,368 B2 · Inspection tool, inspection method and computer program product

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- Number: US 11,442,368 B2
- Document ID: US11442368B2
- Status: Granted
- Kind: B2
- Application number: 17/051,287
- Filed: 2019-04-05
- Published: 2021-07-29
- Granted: 2022-09-13
- Earliest claimed: 2018-04-30
- Assignees: ASML Netherlands B.V.
- Applicants: Asml Netherlands B.V.
- Inventors: Richard Quintanilha; Scott Anderson Middlebrooks; Adrianus Cornelis Matheus Koopman; Albertus Victor Gerardus Mangnus
- Web page: https://patentgrep.com/patent/US11442368B2

## CPC

- G03F 7/70616: {Monitoring the printed patterns}
- G01B 11/24: for measuring contours or curvatures
- G01B 15/04: for measuring contours or curvatures
- 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: 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)
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS

## Abstract

A method of determining a measurement sequence for an inspection tool inspecting a structure generated by a lithographic process performed by a lithographic system is presented, the method including deriving a model for the lithographic process as performed by the lithographic system, the model including a relationship between a set of system variables describing the lithographic system and an output variable representing the structure resulting of the lithographic process, determining an observability of one or more system variables in the output variable, and determining the measurement sequence for the inspection tool, based on the observability.

## Claims

### Claim 1

A method of determining a measurement sequence for an inspection tool inspecting a structure generated by a lithographic process performed by a lithographic system, the method comprising:
deriving a model for the lithographic process as performed by the lithographic system, the model including a relationship between a set of system variables describing the lithographic system and an output variable representing the structure resulting of the lithographic process,
determining an observability of one or more system variables in the output variable, and
determining, by a hardware computer system and based on the observability, the measurement sequence for the inspection tool.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the set of system variables comprises one or more input variables of the lithographic process.

### Claim 3 (depends on 1)

The method according to claim 1, wherein the output variable comprises an image of an area of interest comprising the structure, obtained by an inspection tool.

### Claim 4 (depends on 3)

The method according to claim 3, wherein the image comprises a two-dimensional digital image of the structure, obtained by an electron beam inspection tool.

### Claim 5 (depends on 3)

The method according to claim 3, wherein determining an observability of one or more system variables in the output variable comprises determining which part of the image is affected by a change or modification of the one or more system variables.

### Claim 6 (depends on 5)

The method according to claim 5, wherein determining the measurement sequence for the inspection tool comprises selecting a part of the area of interest corresponding to the part of the image as an area that is to be measured.

### Claim 7 (depends on 1)

The method according to claim 1, wherein the model is a steady state mathematical model.

### Claim 8 (depends on 1)

The method according to claim 1, wherein the model comprises a state-space model of the lithographic system.

### Claim 9

An inspection tool comprising:
an object table configured to hold a sample, the sample comprising a structure;
a probing device configured to inspect the sample;
a detector configured to detect a response signal of the sample caused by interaction of the probing device with the sample;
a processing unit configured to:
receive the response signal from the detector;
generate an image of the structure based on the response signal; and
receive a measurement sequence for inspecting the structure, the measurement sequence being obtained by:
derivation of a model for a lithographic process as performed by a lithographic system, the model including a relationship between a set of system variables describing the lithographic system and an output variable representing the structure resulting from the lithographic process,
determination of an observability of one or more system variables in the output variable, and
determination, based on the observability, of a measurement sequence for the inspection tool;
inspect the sample according to the received measurement sequence.

### Claim 10 (depends on 9)

The inspection tool according to claim 9, wherein the probing device comprises:
an electron beam source configured to generate an electron beam; and
a beam manipulator configured to direct the electron beam onto the sample, and
wherein the detector is configured to detect a response signal of the sample caused by interaction of the electron beam with the sample.

### Claim 11 (depends on 9)

The inspection tool according to claim 9, wherein the probing device comprises an electron beam source, an X-ray beam source, an optical inspection beam source or an atomic force probe.

### Claim 12 (depends on 9)

The inspection tool of claim 9, wherein the set of system variables comprises one or more input variables of the lithographic process.

### Claim 13

A computer program product comprising a non-transitory computer-readable medium having a set of instructions which, when executed by a computer system, cause the computer system to at least:
derive a model for a lithographic process as performed by a lithographic system, the model including a relationship between a set of system variables describing the lithographic system and an output variable representing a structure resulting from the lithographic process,
determine an observability of one or more system variables in the output variable, and
determine, based on the observability, a measurement sequence for the inspection tool.

### Claim 14 (depends on 13)

The computer program product of claim 13, wherein the set of system variables comprises one or more input variables of the lithographic process.

### Claim 15 (depends on 13)

The computer program product of claim 13, wherein the output variable comprises an image of an area of interest comprising the structure, obtained by an inspection tool.

### Claim 16 (depends on 15)

The computer program product of claim 15, wherein the image comprises a two-dimensional digital image of the structure, obtained by an electron beam inspection tool.

### Claim 17 (depends on 15)

The computer program product of claim 15, wherein the instructions configured to cause the computer system to determine an observability of one or more system variables in the output variable is further configured to determine which part of the image is affected by a change or modification of the one or more system variables.

### Claim 18 (depends on 17)

The computer program product of claim 17, wherein the instructions configured to cause the computer system to determine the measurement sequence for the inspection tool is further configured to select a part of the area of interest corresponding to the part of the image as an area that is to be measured.

### Claim 19 (depends on 13)

The computer program product of claim 13, wherein the model is a steady state mathematical model.

### Claim 20 (depends on 13)

The computer program product of claim 13, wherein the model comprises a state-space model of the lithographic system.