# US 9,518,916 B1 · Compressive sensing for metrology

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- Number: US 9,518,916 B1
- Document ID: US9518916B1
- Status: Granted
- Kind: B1
- Application number: 14/511,810
- Filed: 2014-10-10
- Granted: 2016-12-13
- Earliest claimed: 2013-10-18
- Assignees: KLA-Tencor Corporation
- Applicants: KLA-Tencor Corporation
- Inventors: Stilian Ivanov Pandev; Alexander Kuznetsov; Gregory R. Brady; Andrei V. Shchegrov; Noam Sapiens; John J. Hench
- Web page: https://patentgrep.com/patent/US9518916B1

## CPC

- G06T 7/0004: {Industrial image inspection}
- G01N 21/211: {Ellipsometry (optical thickness measurement G01B11/06)}
- G01N 21/255: {Details, e.g. use of specially adapted sources, lighting or optical systems}
- G01N 21/84: Systems specially adapted for particular applications
- G01N 21/8422: {Investigating thin films, e.g. matrix isolation method}
- G03F 7/70625: {Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness}
- G03F 7/70633: {Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching}
- G06T 7/60: Analysis of geometric attributes
- G01B 2210/56: Measuring geometric parameters of semiconductor structures, e.g. profile, critical dimensions or trench depth
- G01N 2201/06113: Coherent sources; lasers
- G06T 2207/10004: Still image; Photographic image
- G06T 2207/30148: Semiconductor; IC; Wafer
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- 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

Disclosed are apparatus and methods for determining a structure or process parameter value of a target of interest on a semiconductor wafer. A plurality of collection patterns are defined for a spatial light beam controller positioned at a pupil image plane of a metrology tool. For each collection pattern, a signal is collected from a sensor of the metrology tool, and each collected signal represents a combination of a plurality of signals that the spatial light beam controller samples, using each collection pattern, from a pupil image of the target of interest. The collection patterns are selected so that the pupil image is reconstructable based on the collection patterns and their corresponding collection signals. The collected signal for each of the collection patterns is analyzed to determine a structure or process parameter value for the target of interest.

## Claims

### Claim 1

A method of determining a structure or process parameter value of a target of interest on a semiconductor wafer, the method comprising:
defining a plurality of collection patterns for a spatial light beam controller positioned at a pupil image plane of a metrology tool;
for each collection pattern, collecting a signal from a sensor of the metrology tool, wherein each collected signal represents a combination of a plurality of signals that the spatial light beam controller samples, using each collection pattern, from a pupil image of the target of interest, wherein the collection patterns are selected so that the pupil image is reconstructable based on the collection patterns and their corresponding collection signals;
analyzing the collected signal for each of the collection patterns to determine a structure or process parameter value for the target of interest;
obtaining a representative set of pupil images from a plurality of test structures that were fabricated or simulated with known process variations;
extracting basis images for a plurality of possible collection patterns that are most related to the known process variations from a large set, of basis images that are generated for the representative set of pupil images; and
using the extracted basis images to define the collection patterns for the spatial light beam controller.

### Claim 2 (depends on 1)

The method of claim 1, wherein the signal collected for each of the collection patterns is collected from a single point or pixel detector.

### Claim 3 (depends on 2)

The method of claim 2, wherein each signal collected from the single point or pixel detector is a sum or average of a plurality of intensities that the spatial light beam controller samples from the pupil image.

### Claim 4 (depends on 1)

The method of claim 1, further comprising:
reconstructing the pupil image based on the collection patterns and their corresponding collection signals,
wherein the pupil image of the target of interest is sparse when transformed to a particular domain of transformation elements Ψ, and
wherein the pupil image can be represented by Ψα, with α being weights, and the pupil image is reconstructed by an l1 optimization.

### Claim 5 (depends on 4)

The method of claim 4, wherein the particular domain corresponds to a transform to a plurality of Zernike polynomial basis images.

### Claim 6 (depends on 4)

The method of claim 4, wherein the particular domain corresponds to a MT (discrete Fourier transform), DCT (discrete cosine transform), or a Wavelet transform.

### Claim 7 (depends on 1)

The method of claim 1, wherein the spatial light beam controller includes a plurality of pixels that are turned on or off for spatially sampling the pupil image to form each collection pattern.

### Claim 8 (depends on 1)

The method of claim 1, wherein the spatial light beam controller includes a plurality of pixels that have a plurality of analog values for spatially sampling the pupil image to form each collection pattern.

### Claim 9 (depends on 1)

The method of claim 1, further comprising:
defining a plurality of illumination patterns for a second spatial light beam controller positioned at an illumination plane of the metrology tool.

### Claim 10 (depends on 9)

The method of claim 9, further comprising:
repeating the operations for defining, collecting, and reconstructing for each of a plurality of combinations of wavelength ranges, polarization states, and illumination patterns.

### Claim 11 (depends on 1)

The method of claim 1, further comprising:
repeating the operations for defining, collecting, and reconstructing for each of a plurality of combinations of wavelength ranges and polarization states.

### Claim 12 (depends on 1)

The method of claim 1, wherein the structure or process parameter value is determined by a model for predicting a structure or process parameter value based on a plurality of collected signal values.

### Claim 13 (depends on 1)

The method of claim 1, wherein the structure or process parameter value for the target of interest is determined without reconstructing the pupil image.

### Claim 14

A semiconductor metrology system, comprising:
an illuminator for generating illumination;
illumination optics for directing the illumination towards a target of interest on a semiconductor wafer;
collection optics for directing a plurality of signals from the particular structure to a sensor in response to the illumination, wherein the collection optics comprise a spatial light beam controller for controlling a spatial profile of a pupil image of the metrology system;
the sensor for collecting the plurality of signals from the target of interest; and
a controller configured for performing the following operations:
defining a plurality of collection patterns for the spatial light beam controller;
for each collection pattern, collecting a signal from the sensor of the metrology tool, wherein each collected signal represents a combination of a plurality of signals that the spatial light beam controller samples, using each collection pattern, from a pupil image of the target of interest, wherein the collection patterns are selected so that the pupil image is reconstructable based on the collection patterns and their corresponding collection signals; and
analyzing the collected signal for each of the collection patterns to determine a structure or process parameter value for the target of interest;
obtaining a representative set of pupil images from a plurality of test structures that were fabricated or simulated with known process variations;
extracting basis images for a plurality of possible collection patterns that are most related to the known process variations from a large set of basis images that are generated for the representative set of pupil images; and
using the extracted basis images to define the collection patterns for the spatial light beam controller.

### Claim 15 (depends on 14)

The metrology system of claim 14, wherein the sensor is a single point or pixel detector.

### Claim 16 (depends on 15)

The metrology system of claim 15, wherein each signal collected from the single point or pixel detector is a sum or average of a plurality of intensities that the spatial light beam controller samples from the pupil image.

### Claim 17 (depends on 14)

The method of claim 14, wherein the controller is further configured for:
reconstructing the pupil image based on the collection patterns and their corresponding collection signals,
wherein the pupil image of the target of interest is sparse when transformed to a particular domain of transformation elements Ψ, and
wherein the pupil image can be represented by Ψα, with α being weights, and the pupil image is reconstructed by an l1 optimization.

### Claim 18 (depends on 17)

The metrology system of claim 17, wherein the particular domain corresponds to a transform to a plurality of Zernike polynomial basis images.

### Claim 19 (depends on 17)

The metrology system of claim 17, wherein the particular domain corresponds to a DFT (discrete Fourier transform), DCT (discrete cosine transform), or a Wavelet transform.

### Claim 20 (depends on 14)

The metrology system of claim 14, wherein the spatial light beam controller includes a plurality of pixels that are turned on or off for spatially sampling the pupil image to form each collection pattern.

### Claim 21 (depends on 14)

The metrology system of claim 14, wherein the spatial light beam controller includes a plurality of pixels that have a plurality of analog values for spatially sampling the pupil image to form each collection pattern.

### Claim 22 (depends on 14)

The metrology system of claim 14, further comprising:
a second spatial light beam controller positioned at an illumination plane of the metrology,
wherein the controller is further configured for defining a plurality of illumination patterns for the second spatial light beam controller.

### Claim 23 (depends on 22)

The metrology system of claim 22, wherein the controller is further configured for:
repeating the operations for defining, collecting, and reconstructing for each of a plurality of combinations of wavelength ranges, polarization states, and illumination patterns.

### Claim 24 (depends on 14)

The metrology system of claim 14, wherein the controller is further configured for:
repeating the operations for defining, collecting, and reconstructing for each of a plurality of combinations of wavelength ranges and polarization states.

### Claim 25 (depends on 14)

The metrology system of claim 14, wherein the structure or process parameter value is determined by a model for predicting a structure or process parameter value based on a plurality of collected signal values.

### Claim 26 (depends on 14)

The metrology system of claim 14, wherein the structure or process parameter value for the target of interest is determined without reconstructing the pupil image.

### Claim 27 (depends on 14)

The metrology system of claim 14, further comprises a monochromator to filter input wavelengths onto the target of interest.

### Claim 28 (depends on 14)

The metrology system of claim 14, wherein the spatial light beam controller is a spatial light modulator, a liquid crystal device, a liquid crystal on Si (LCOS) device), and/or a set of masks.

### Claim 29

A method of determining a structure or process parameter value of a target of interest on a semiconductor water, the method comprising:
defining one or more collection patterns for a spatial light beam controller positioned at a pupil image plane of a metrology tool, wherein each collection pattern is defined based on a plurality of coefficients of a model for predicting a corresponding structure or process parameter value for a target of interest;
for each collection pattern, collecting a signal from a sensor of the metrology tool, wherein each collected signal represents a combination of a plurality of signals that the spatial light beam controller samples, using each collection pattern, from a pupil image of the target of interest;
reporting a value of each collected signal for each of the collection patterns as a corresponding structure or process parameter value for the target of interest;
obtaining a representative set of pupil images from a plurality of test structures that were fabricated or simulated with known process variations;
extracting basis images for a plurality of possible collection patterns that are most related to the known process variations from a large set of basis images that are generated for the representative set of pupil images; and
using the extracted basis images to define the collection patterns for the spatial light beam controller.