# US 12,001,148 B2 · Enhancing performance of overlay metrology

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- Number: US 12,001,148 B2
- Document ID: US12001148B2
- Status: Granted
- Kind: B2
- Application number: 18/114,451
- Filed: 2023-02-27
- Published: 2023-12-14
- Granted: 2024-06-04
- Earliest claimed: 2021-03-31
- Assignees: KLA Corporation
- Applicants: KLA Corporation
- Inventors: Amnon Manassen; Andrew V. Hill; Yonatan Vaknin; Yossi Simon; Daria Negri; Vladimir Levinski; Yuri Paskover; Anna Golotsvan; Nachshon Rothman; Nireekshan K. Reddy; Nir BenDavid; Avi Abramov; Dror Yaacov; Yoram Uziel; Nadav Gutman
- Web page: https://patentgrep.com/patent/US12001148B2

## CPC

- 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}
- G02B 21/241: {Devices for focusing (focusing in general G02B7/28)}
- G02B 21/361: {Optical details, e.g. image relay to the camera or image sensor (G02B21/364 takes precedence; illumination details G02B21/06 and subgroups)}
- G02B 27/283: {used for beam splitting or combining}
- G03F 7/70641: {Focus}
- G06T 7/33: using feature-based methods
- G06T 7/68: of symmetry
- H04N 23/56: provided with illuminating means
- G06T 2207/10016: Video; Image sequence
- G06T 2207/10152: Varying illumination
- H04N 23/45: for generating image signals from two or more image sensors being of different type or operating in different modes, e.g. with a CMOS sensor for moving images in combination with a charge-coupled device [CCD] for still images
- 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
- G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A method includes generating a sequence of images of a semiconductor wafer from first and second detectors. The first detector images the wafer with first imaging parameters and the second detector images the wafer with second imaging parameters. The first or second imaging parameters are varied across the sequence of images to provide variation at sites across the wafer. The method includes providing a metric indicative of center-of-symmetry variations of first and second target features as a function of the varied imaging parameters based on the sequence of images. The method includes identifying a landscape of values of the varied image parameters for which the metric are below a predefined limit. The method includes generating a recipe for metrology measurements in which the varied imaging parameters are set to values within the landscape. The method includes generating metrology measurements from a production wafer based on the recipe.

## Claims

### Claim 1

An optical apparatus comprising:
an illumination assembly configured to direct one or more illumination beams to a semiconductor wafer, wherein the first and second target features at least partially overlap;
an imaging assembly comprising:
a first detector configured to image the semiconductor wafer with first imaging parameters; and
a second detector configured to image the semiconductor wafer with second imaging parameters different than the first imaging parameters; and
a controller including one or more processors configured to:
receive a sequence of images from the first and second detectors, wherein at least one of the first imaging parameters or the second imaging parameters are varied across the sequence of images to provide varied image parameters at one or more sites on the semiconductor wafer;
provide a metric indicative of center of symmetry (COS) variations of first and second target features as a function of the varied imaging parameters based on the sequence of images;
identify a landscape of values of the varied image parameters for which the metric are below one or more predefined limits;
generate a recipe for metrology measurements in which the varied imaging parameters are set to values within the landscape; and
generate one or more metrology measurements associated of one or more production wafers based on the recipe.

### Claim 2 (depends on 1)

The optical apparatus of claim 1, wherein the one or more processors of the controller are further configured to:
at least one of calibrate or correct the one or more metrology measurements based on the COS variations.

### Claim 3 (depends on 1)

The optical apparatus of claim 1, wherein the one or more metrology measurements comprise:
one or more overlay measurements.

### Claim 4 (depends on 1)

The optical apparatus of claim 1, further comprising:
a grating projector configured to project grating images onto the first and second detectors, wherein the one or more processors of the controller are further configured to register the sequence of images based on the projected grating images.

### Claim 5 (depends on 1)

The optical apparatus of claim 1, wherein the varied imaging parameters comprise:
at least one of focal position of the semiconductor wafer, wavelength, polarization, an angular offset of an aperture in the imaging assembly, or an angular position of at least one of the first or second detectors.

### Claim 6 (depends on 1)

The optical apparatus of claim 1, wherein the varied imaging parameters comprise a focal position of the semiconductor wafer, wherein the first and second detectors are configured to simultaneously image the semiconductor wafer at different values of the focal position separated by a fixed value of, wherein the sequence of images are generated by consecutively steps in which the values of the focal position associated with the first and second detectors are shifted by the fixed value of ΔZ.

### Claim 7 (depends on 6)

The optical apparatus of claim 6, further comprising:
a grating projector configured to project grating images onto the first and second detectors, wherein the one or more processors of the controller are further configured to:
register the images from the first and second detectors at each of the consecutive steps; and
register the images from the first detector associated with a current one of the consecutive steps with the images from the second detector associated with a previous one of the consecutive steps at a common value of the focal position.

### Claim 8 (depends on 1)

The optical apparatus of claim 1, wherein the varied imaging parameters comprise a wavelength of at least one of the one or more illumination beams, wherein the first and second detectors are configured to simultaneously image the semiconductor wafer based on different values of the wavelength, wherein the sequence of images comprise:
a first sequence of images in which the value of the wavelength associated with the first detector is held constant and the value of the wavelength associated with the second detector is consecutively varied in a first series of consecutive steps; and
a second sequence of images in which the value of the wavelength associated with the second detector is held constant and the value of the wavelength associated with the first detector is consecutively varied in a second series of consecutive steps.

### Claim 9 (depends on 8)

The optical apparatus of claim 8, further comprising:
a grating projector configured to project grating images onto the first and second detectors, wherein the one or more processors of the controller are further configured to:
register the first sequence of images from the first and second detectors at each of the first series of consecutive steps;
register the images from the first detector associated with a current one of the first series of consecutive steps with the images from the second detector associated with a previous one of the first series of consecutive steps;
register the second sequence of images from the first and second detectors at each of the second series of consecutive steps; and
register the images from the first detector associated with a current one of the second series of consecutive steps with the images from the second detector associated with a previous one of the second series of consecutive steps.

### Claim 10 (depends on 1)

The optical apparatus of claim 1, wherein the sequence of images from the first and second detectors comprises:
a first sequence of images from the first and second detectors with the semiconductor wafer in a first orientation in which the varied imaging parameters are varied; and
a second sequence of images from the first and second detectors with the semiconductor wafer in a second orientation in which the varied imaging parameters are varied;
wherein the second orientation is rotated 180 degrees relative to the first orientation, wherein the varied imaging parameters comprise:
at least one of focal position of the semiconductor wafer, wavelength, or polarization;
wherein the metric is based on COS variations from the first and second sequences of images associated with the first and second orientations of the semiconductor wafer.

### Claim 11 (depends on 10)

The optical apparatus of claim 10, wherein the COS as a function of the varied imaging parameters from the first sequence of images is COS0, wherein the COS as a function of the varied imaging parameters from the first sequence of images is COS180, wherein the metric is based on at least one of COS_TIS=(COS0+COS180)/2, a second derivative of COS_TIS with respect to at least one of the varied imaging parameters, COS_COR=(COS0−COS180)/2, or a second derivative of COS_COR with respect to at least one of the varied imaging parameters.

### Claim 12 (depends on 10)

The optical apparatus of claim 10, wherein the metric is further based on a precision metric associated with a precision of the COS based on multiple measurements.

### Claim 13 (depends on 10)

The optical apparatus of claim 10, wherein the metric is based on a measurement of asymmetry of one or more features on the semiconductor wafer based on the sequence of images.

### Claim 14

A method comprising:
generating a sequence of images of a semiconductor wafer from first and second detectors of an imaging assembly, wherein the first detector is configured to image the semiconductor wafer with first imaging parameters, wherein the second detector is configured to image the semiconductor wafer with second imaging parameters different than the first imaging parameters, wherein at least one of the first imaging parameters or the second imaging parameters are varied across the sequence of images to provide varied image parameters at one or more sites on the semiconductor wafer;
providing a metric indicative of center of symmetry (COS) variations of first and second target features as a function of the varied imaging parameters based on the sequence of images;
identifying a landscape of values of the varied image parameters for which the metric are below one or more predefined limits;
generating a recipe for metrology measurements in which the varied imaging parameters are set to values within the landscape; and
generating one or more metrology measurements associated of one or more production wafers based on the recipe.

### Claim 15 (depends on 14)

The method of claim 14, further comprising:
at least one of calibrating or correcting the one or more metrology measurements based on the COS variations.

### Claim 16 (depends on 14)

The method of claim 14, wherein the one or more metrology measurements comprise:
one or more overlay measurements.

### Claim 17 (depends on 14)

The method of claim 14, further comprising:
projecting grating images onto the first and second detectors, wherein the one or more processors of the controller are further configured to register the sequence of images based on the projected grating images.

### Claim 18 (depends on 14)

The method of claim 14, wherein the varied imaging parameters comprise:
at least one of focal position of the semiconductor wafer, wavelength, polarization, an angular offset of an aperture in the imaging assembly, or an angular position of at least one of the first or second detectors.

### Claim 19 (depends on 14)

The method of claim 14, wherein the varied imaging parameters comprise a focal position of the semiconductor wafer, wherein the first and second detectors are configured to simultaneously image the semiconductor wafer at different values of the focal position separated by a fixed value of, wherein the sequence of images are generated by consecutively steps in which the values of the focal position associated with the first and second detectors are shifted by the fixed value of ΔZ.

### Claim 20 (depends on 19)

The method of claim 19, further comprising:
projecting grating images onto the first and second detectors;
registering the images from the first and second detectors at each of the consecutive steps; and
registering the images from the first detector associated with a current one of the consecutive steps with the images from the second detector associated with a previous one of the consecutive steps at a common value of the focal position.

### Claim 21 (depends on 14)

The method of claim 14, wherein the varied imaging parameters comprise a wavelength of at least one of the one or more illumination beams, wherein the first and second detectors are configured to simultaneously image the semiconductor wafer based on different values of the wavelength, wherein the sequence of images comprise:
a first sequence of images in which the value of the wavelength associated with the first detector is held constant and the value of the wavelength associated with the second detector is consecutively varied in a first series of consecutive steps; and
a second sequence of images in which the value of the wavelength associated with the second detector is held constant and the value of the wavelength associated with the first detector is consecutively varied in a second series of consecutive steps.

### Claim 22 (depends on 21)

The method of claim 21, further comprising:
projecting grating images onto the first and second detectors;
registering the first sequence of images from the first and second detectors at each of the first series of consecutive steps;
registering the images from the first detector associated with a current one of the first series of consecutive steps with the images from the second detector associated with a previous one of the first series of consecutive steps;
registering the second sequence of images from the first and second detectors at each of the second series of consecutive steps; and
registering the images from the first detector associated with a current one of the second series of consecutive steps with the images from the second detector associated with a previous one of the second series of consecutive steps.

### Claim 23 (depends on 14)

The method of claim 14, wherein the sequence of images from the first and second detectors comprises:
a first sequence of images from the first and second detectors with the semiconductor wafer in a first orientation in which the varied imaging parameters are varied; and
a second sequence of images from the first and second detectors with the semiconductor wafer in a second orientation in which the varied imaging parameters are varied;
wherein the second orientation is rotated 180 degrees relative to the first orientation, wherein the varied imaging parameters comprise:
at least one of focal position of the semiconductor wafer, wavelength, or polarization;
wherein the metric is based on COS variations from the first and second sequences of images associated with the first and second orientations of the semiconductor wafer.

### Claim 24 (depends on 14)

The method of claim 14, wherein the COS as a function of the varied imaging parameters from the first sequence of images is COS0, wherein the COS as a function of the varied imaging parameters from the first sequence of images is COS180, wherein the metric is based on at least one of COS_TIS=(COS0+COS180)/2, a second derivative of COS_TIS with respect to at least one of the varied imaging parameters, COS_COR=(COS0−COS180)/2, or a second derivative of COS_COR with respect to at least one of the varied imaging parameters.

### Claim 25 (depends on 14)

The method of claim 14, wherein the metric is further based on a precision metric associated with a precision of the COS based on multiple measurements.

### Claim 26 (depends on 14)

The method of claim 14, wherein the metric is based on a measurement of asymmetry of one or more features on the semiconductor wafer based on the sequence of images.