# US 11,029,258 B2 · Optical phase measurement method and system

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- Number: US 11,029,258 B2
- Document ID: US11029258B2
- Status: Granted
- Kind: B2
- Application number: 16/231,718
- Filed: 2018-12-24
- Published: 2019-05-23
- Granted: 2021-06-08
- Earliest claimed: 2014-04-07
- Assignees: Nova Measuring Instruments Ltd.
- Applicants: Nova Measuring Instruments Ltd.
- Inventors: Gilad Barak; Danny Grossman; Dror Shafir; Yoav Berlatzky; Yanir Hainick
- Web page: https://patentgrep.com/patent/US11029258B2

## CPC

- G01N 21/956: Inspecting patterns on the surface of objects {(contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)}
- G01B 9/02007: {Two or more frequencies or sources used for interferometric measurement (using only beat G01B9/02003)}
- G01B 9/02032: {generating a spatial carrier frequency, e.g. by creating lateral or angular offset between reference and object beam (shearing interferometers G01B9/02098)}
- G01B 9/02072: {by calibration or testing of interferometer}
- G01B 9/0209: Low-coherence interferometers
- G01B 11/0675: {using interferometry}
- G01J 3/4535: {Devices with moving mirror (G01J3/4532 takes precedence)}
- G01N 21/8806: {Specially adapted optical and illumination features}
- G01B 2210/56: Measuring geometric parameters of semiconductor structures, e.g. profile, critical dimensions or trench depth
- G01B 2290/70: Using polarization in the interferometer
- G01N 2021/8848: {Polarisation of light}
- 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)
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)

## Abstract

A measurement system for use in measuring parameters of a patterned sample, the system including a broadband light source, an optical system configured as an interferometric system, a detection unit, and a control unit, where the interferometric system defines illumination and detection channels having a sample arm and a reference arm having a reference reflector, and is configured for inducing an optical path difference between the sample and reference arms, the detection unit for detecting a combined light beam formed by a light beam reflected from the reflector and a light beam propagating from a sample's support, and generating measured data indicative of spectral interference pattern formed by spectral interference signatures, and the control unit for receiving the measured data and applying a model-based processing to the spectral interference pattern for determining one or more parameters of the pattern in the sample.

## Claims

### Claim 1

A measurement system for use in measuring parameters of a patterned sample, the system comprising:
a broadband light source;
an optical system including an objective lens and configured as an interferometric system;
a detection unit;
a control unit; and
a beam-splitter-and-combiner positioned along an optical path between the objective lens and the patterned sample,
wherein the interferometric system
defines an illumination channel, and detection channels having a sample arm and a reference arm comprising a reference reflector, wherein the sample arm is not parallel with the reference arm, the detection channels comprise a first detection channel and a second detection channel that share at least the objective lens; and
is configured and operable to induce an optical path difference between the sample arm and reference arm, and to combine output of the sample arm and reference arm into the detection channels for propagation of a combined light beam formed by a light beam reflected from said reference reflector and a light beam propagating from the patterned sample, the light beams derived from light originating from the broadband light source,
wherein the detection unit comprises an imaging sensor and a spectral sensor, the spectral sensor is configured and operable to detect a first portion of the combined light beam from the first detection channel and generate measurement data indicative of each wavelength of the first portion of the combined light separately, the imaging sensor is configured to detect a second portion of the combined light beam;
wherein said control unit is configured and operable to receive the measurement data for determining one or more parameters of a pattern in the patterned sample, and
wherein the beam-splitter-and-combiner is configured to:
split the light originating from the broadband light source into a probe light beam and a reference light beam,
direct the probe light beam along the sample arm towards the patterned sample, and
direct the reference light beam along the reference arm towards the reference reflector.

### Claim 2 (depends on 1)

The measurement system of claim 1, wherein said interferometric system comprises polarizers, wherein the polarizers consist of a first polarizer in the illumination channel and outside the collection channels a second polarizer in the detection channels and outside the illumination channel.

### Claim 3 (depends on 2)

The measurement system of claim 2, wherein said interferometric system comprises a driving mechanism, associated with either one or both of said reference reflector and a sample support supporting the patterned sample, and configured and operable to controllably move at least one of said reference reflector and the sample support along an optical axis of the interferometric system, to induce the optical path difference between the sample arm and the reference arm.

### Claim 4 (depends on 1)

The measurement system of claim 1, wherein at least one of said reference reflector and a sample support supporting the patterned sample is oriented with a fixed tilted position with respect to an optical axis of the interferometric system, providing the optical path difference between the sample arm and the reference arm.

### Claim 5 (depends on 4)

The measurement system of claim 4, wherein said reflector is located in a plane parallel to and spaced-apart from a focal plane of an objective lens unit of said interferometric system.

### Claim 6 (depends on 4)

The measurement system of claim 4, wherein said reflector is configured as a retro-reflector assembly.

### Claim 7 (depends on 1)

The measurement system of claim 1, wherein said interferometric system is configured and operable to induce defocusing effect on an illuminating light beam propagating along the reference arm towards said reference reflector, providing the optical path difference between the sample arm and the reference arm.

### Claim 8 (depends on 1)

The measurement system of claim 1, wherein the broadband light source is configured and operable to produce illumination in the form of ultra-short pulses.

### Claim 9 (depends on 1)

The measurement system of claim 1, comprising an additional beam-splitter-and-combiner that is configured to split the combined light beam to the first portion of the combined light beam and to the second portion of the combined light beam.

### Claim 10 (depends on 9)

The measurement system of claim 9, wherein the imaging sensor is a CCD.

### Claim 11 (depends on 1)

The measurement system of claim 1, wherein the reference reflector is a MEMS reference mirror that is movable for controlling at least one of tilt and the optical path difference.

### Claim 12 (depends on 11)

The measurement system of claim 11, wherein the imaging sensor is in communication with the control unit.

### Claim 13

A method for use in measuring parameters of a patterned sample, the method comprising:
directing broadband light through an interferometric optical system, the interferometric optical system including an objective lens and defining an illumination channel and detection channels having a sample arm not parallel to a reference arm comprising a reference reflector;
the detection channels comprise a first detection channel and a second detection channel that share at least the objective lens;
splitting the broadband light into a probe light beam and a reference light beam, wherein the splitting is performed along an optical path between the objective lens and the patterned sample;
directing the probe light beam along the sample arm towards the patterned sample;
directing the reference light beam along the reference arm towards the reference reflector;
inducing an optical path difference between the sample arm and the reference arm;
combining output of the sample arm and reference arm into the detection channel for propagation of a combined light beam formed by a light beam reflected from said reference reflector and a light beam propagating from a patterned sample, the light beams derived from the broadband light;
detecting an intensity of every wavelength separately of a first portion of the combined light beam using a spectral sensor and generating measurement data,
detecting, by an imaging sensor that differs from the spectral sensor, a second portion of the combined light sensor; and
determining from the measurement data one or more parameters of a pattern in the patterned sample.

### Claim 14 (depends on 13)

The method of claim 13, wherein the reference reflector is a MEMS reference mirror, the method further comprising moving the MEMS reference mirror.

### Claim 15 (depends on 13)

The method of claim 13, and further comprising controllably moving, along an optical axis of the interferometric system, at least one of said reference reflector and a sample support supporting the patterned sample, thereby inducing the optical path difference between the sample arm and the reference arm.

### Claim 16 (depends on 13)

The method of claim 13, and further comprising orienting, with a fixed tilted position with respect to an optical axis of the interferometric system, at least one of said reference reflector and a sample support supporting the patterned sample, thereby providing the optical path difference between the sample arm and the reference arm.

### Claim 17 (depends on 16)

The method of claim 16, and further comprising positioning said reflector in a plane parallel to and spaced-apart from a focal plane of an objective lens unit of said interferometric system.

### Claim 18 (depends on 16)

The method of claim 16, and further comprising configuring said reflector as a retro-reflector assembly.

### Claim 19 (depends on 13)

The method of claim 13, and further comprising inducing a defocusing effect on an illuminating light beam propagating along the reference arm towards said reference reflector, thereby providing the optical path difference between the sample arm and the reference arm.

### Claim 20 (depends on 13)

The method of claim 13, and further comprising producing illumination of the broadband light in the form of ultra-short pulses.