# US 10,767,978 B2 · Transmission small-angle X-ray scattering metrology system

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- Number: US 10,767,978 B2
- Document ID: US10767978B2
- Status: Granted
- Kind: B2
- Application number: 15/950,823
- Filed: 2018-04-11
- Published: 2018-10-18
- Granted: 2020-09-08
- Earliest claimed: 2017-04-14
- Assignees: KLA-Tencor Corporation
- Applicants: KLA-Tencor Corporation
- Inventors: Andrei V. Shchegrov; Antonio Arion Gellineau; Sergey Zalubovsky
- Web page: https://patentgrep.com/patent/US10767978B2

## CPC

- G01B 11/14: for measuring distance or clearance between spaced objects or spaced apertures (G01B11/26 takes precedence; rangefinders G01C3/00)
- G01N 23/02: by transmitting the radiation through the material
- G01B 11/0616: {of coating}
- G01B 11/26: for measuring angles or tapers; for testing the alignment of axes
- G01B 15/00: Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons (characterised by the use of optical techniques G01B9/00, G01B11/00)
- G01N 21/211: {Ellipsometry (optical thickness measurement G01B11/06)}
- G01N 21/4785: {Standardising light scatter apparatus; Standards therefor}
- G01N 21/9501: {Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)}
- G01N 23/201: by measuring small-angle scattering
- G03F 7/70616: {Monitoring the printed patterns}
- 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}
- H01J 37/28: with scanning beams {(H01J37/268, H01J37/292, H01J37/2955 take precedence)}
- H10P 74/203: {Structural properties, e.g. testing or measuring thicknesses, line widths, warpage, bond strengths or physical defects}
- G01N 23/20: by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials
- G01N 2223/03: by transmission
- G01N 2223/6116: semiconductor wafer
- G01N 2223/645: quality control
- G01N 2223/6462: microdefects
- G21K 2201/06: using diffractive, refractive or reflecting elements
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- 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)
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- G21K: HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES

## Abstract

Methods and systems for characterizing dimensions and material properties of semiconductor devices by transmission small angle x-ray scatterometry (TSAXS) systems having relatively small tool footprint are described herein. The methods and systems described herein enable Q space resolution adequate for metrology of semiconductor structures with reduced optical path length. In general, the x-ray beam is focused closer to the wafer surface for relatively small targets and closer to the detector for relatively large targets. In some embodiments, a high resolution detector with small point spread function (PSF) is employed to mitigate detector PSF limits on achievable Q resolution. In some embodiments, the detector locates an incident photon with sub-pixel accuracy by determining the centroid of a cloud of electrons stimulated by the photon conversion event. In some embodiments, the detector resolves one or more x-ray photon energies in addition to location of incidence.

## Claims

### Claim 1

A metrology system comprising:
an x-ray illumination source configured to generate an amount of x-ray radiation;
an x-ray illumination optics subsystem configured to illuminate a measurement target formed on a wafer surface with an incident focused beam of the amount of x-ray radiation;
a specimen positioning system that positions the measurement target at a plurality of orientations with respect to the incident focused beam;
an x-ray detector configured to detect an intensity associated with each of a plurality of diffraction orders of an amount of radiation scattered from the measurement target in response to the incident focused beam at each orientation, wherein an optical path length between the illumination source and the detector is less than three meters; and
a computing system configured to
determine a value of a parameter of interest associated with the measurement target based on the detected intensities of the plurality of diffraction orders at the plurality of different orientations.

### Claim 2 (depends on 1)

The metrology system of claim 1, wherein the x-ray illumination optics subsystem focuses the focused beam less than 200 millimeters before the wafer surface, at the measurement target, at the detector, or any location in the optical path between the measurement target and the detector.

### Claim 3 (depends on 1)

The metrology system of claim 1, wherein the x-ray illumination optics subsystem includes one or more beam shaping slits located within 100 millimeters of the measurement target.

### Claim 4 (depends on 1)

The metrology system of claim 1, wherein a portion of an optical path from the measurement target to the x-ray detector is maintained in a vacuum.

### Claim 5 (depends on 1)

The metrology system of claim 1, wherein the x-ray detector is maintained in a vacuum.

### Claim 6 (depends on 1)

The metrology system of claim 1, wherein the x-ray detector includes a plurality of pixels each having a size less than 100 micrometers and a point spread function smaller than a first pixel of the plurality of pixels such that a portion of a diffracted beam incident on a second pixel adjacent to the first pixel is less than 0.1% of a portion of the diffracted beam incident on the first pixel.

### Claim 7 (depends on 1)

The metrology system of claim 1, wherein a photo-sensitive volume of the x-ray detector includes Cadmium Telluride, Germanium, Gallium Arsenide, or any combination thereof.

### Claim 8 (depends on 7)

The metrology system of claim 7, wherein the photosensitive volume is at least 500 micrometers thick.

### Claim 9 (depends on 1)

The metrology system of claim 1, wherein the x-ray detector interpolates between a plurality of energy levels at each pixel of the x-ray detector.

### Claim 10 (depends on 1)

The metrology system of claim 1, wherein the x-ray detector determines a location of a centroid of a photon interaction with the detector with sub-pixel resolution.

### Claim 11 (depends on 1)

The metrology system of claim 1, wherein the focused beam propagates in a direction that is substantially parallel to a gravity vector.

### Claim 12 (depends on 1)

The metrology system of claim 1, wherein two or more of the diffracted orders spatially overlap on the detector, and wherein the computing system is further configured to:
determine an intensity of each of the overlapping diffraction orders based on a beam shape of zeroth diffraction order.

### Claim 13 (depends on 1)

The metrology system of claim 1, wherein the measurement target includes one or more high aspect ratio structures.

### Claim 14 (depends on 13)

The metrology system of claim 13, wherein the one or more high aspect ratio structures is any of a spin transfer torque random access memory (STT-RAM), a three dimensional NAND memory (3D-NAND), a dynamic random access memory (DRAM), a three dimensional FLASH memory (3D-FLASH), resistive random access memory (Re-RAMPC), and a phase change random access memory (PC-RAM).

### Claim 15

A method comprising:
illuminating a measurement target formed on a wafer surface with a beam of x-ray radiation generated by an illumination source at an energy level of 15 kiloelectronvolts or higher;
detecting an intensity associated with a plurality of diffraction orders of an amount of radiation scattered from the measurement target in response to the incident beam, wherein two or more of the plurality of diffraction orders spatially overlap on a surface of a detector that detects the intensities, and wherein an optical path length between the illumination source and the detector is less than three meters;
determining an intensity of each of the overlapping diffraction orders based on a beam shape of a zeroth diffraction order; and
determining a value of a parameter of interest associated with the measurement target based on the intensities of the plurality of diffraction orders.

### Claim 16 (depends on 15)

The method of claim 15, wherein the beam of x-ray radiation is focused less than 200 millimeters before the wafer surface, at the measurement target, at the detector, or any location in an optical path between the measurement target and the detector.

### Claim 17 (depends on 15)

The method of claim 15, wherein the detector includes a plurality of pixels each having a size less than 100 micrometers and a point spread function smaller than a first pixel of the plurality of pixels such that a portion of a diffracted beam incident on a second pixel adjacent to the first pixel is less than 0.1% of a portion of the diffracted beam incident on the first pixel.

### Claim 18 (depends on 15)

The method of claim 15, further comprising:
interpolating between a plurality of energy levels at each pixel of the x-ray detector.

### Claim 19

A metrology system comprising:
an x-ray illumination source configured to generate an amount of x-ray radiation;
an x-ray illumination optics subsystem configured to illuminate a measurement target formed on a wafer surface with an incident focused beam of the amount of x-ray radiation;
an x-ray detector configured to detect an intensity associated with each of a plurality of diffraction orders of an amount of radiation scattered from the measurement target in response to the incident focused beam, wherein an optical path length between the illumination source and the detector is less than three meters, and wherein two or more of the plurality of diffraction orders spatially overlap on a surface of the x-ray detector; and
a non-transitory, computer-readable medium, comprising:
code for causing a computing system to determine an intensity of each of the overlapping diffraction orders based on a beam shape of a zeroth diffraction order; and
code for causing the computing system to determine a value of a parameter of interest associated with the measurement target based on the determined intensities of the plurality of diffraction orders.

### Claim 20 (depends on 19)

The metrology system of claim 19, wherein the x-ray illumination optics subsystem focuses the focused beam at the measurement target, at the detector, or any location in the optical path between the measurement target and the detector.