ISO 22278:2020
(Main)Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for crystalline quality of single-crystal thin film (wafer) using XRD method with parallel X-ray beam
Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for crystalline quality of single-crystal thin film (wafer) using XRD method with parallel X-ray beam
This document specifies the test method for measuring the crystalline quality of single-crystal thin film (wafer) using the XRD method with parallel X-ray beam. This document is applicable to all of the single-crystal thin film (wafer) as bulk or epitaxial layer structure.
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INTERNATIONAL ISO
STANDARD 22278
First edition
2020-08
Fine ceramics (advanced ceramics,
advanced technical ceramics) — Test
method for crystalline quality of
single-crystal thin film (wafer) using
XRD method with parallel X-ray beam
Reference number
ISO 22278:2020(E)
©
ISO 2020
---------------------- Page: 1 ----------------------
ISO 22278:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 22278:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Fundamentals . 3
5 Devices and instruments. 3
5.1 Schematic diagrams . 3
5.2 X-ray generator . 4
5.3 X-ray mirror . 5
5.4 Monochromator . 5
5.5 Sample attachment . 5
5.6 Goniometer. 5
5.7 Detector . 5
5.8 Instrument calibration . 5
6 Preparation of sample . 6
7 Test method and procedure . 6
7.1 Optics alignment . 6
7.2 Sample alignment . 6
7.3 Adjusting the initial position of goniometer . 7
7.3.1 Symmetric diffraction . 7
7.3.2 Asymmetric diffraction . 9
7.4 Microscopic position adjustment of goniometer (Φ and χ axes) and ω scan . 9
7.4.1 Symmetric diffraction . 9
7.4.2 Asymmetric diffraction .12
7.5 Crystalline quality measurement method of single-crystal wafer .16
7.5.1 General.16
7.5.2 Selecting the flat zone position of wafer .16
7.5.3 Arranging the fixed size of the square .17
7.5.4 Measuring the FWHM value of RC .17
7.5.5 Interference effect by the wafer's curvature .17
7.5.6 Doped epitaxy film on a single-crystal thin film substrate .17
8 Data analysis .18
9 Test report .18
Annex A (informative) Example of d-spacing, 2θ, χ value (tilt angle) and relative ideal
intensity of the symmetric and asymmetric diffraction on the SiC single-crystal thin
film (wafer) .20
Annex B (informative) Determination of d-spacing, 2θ, χ value (tilt angle) and relative ideal
intensity for the symmetric and asymmetric diffraction on the single-crystal thin
film (wafer) .22
Annex C (informative) Results of interlaboratory test .27
Bibliography .29
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ISO 22278:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
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ISO 22278:2020(E)
Introduction
Single crystals are important in many applications ranging from synthetic gemstones for jewellery to
hosts for solid-state lasers. For some applications, ceramic materials are prepared as single crystals.
When used as substrates for thin film growth (such as gallium-on-sapphire technology or the growth
of superconductor thin films) it is the crystalline perfection of a single crystal that is important. Wide
bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) have drawn a lot of
attention in power applications due to their superior material properties such as high critical electric
field resulting in a minimum of 10 times higher breakdown voltage or a 100 times smaller on-resistance
than Si. These unique properties of SiC and GaN materials have made them promising candidates for
future high-power, high-frequency semiconductor devices. In optical applications, such as the use
of ruby and yttrium–aluminium–garnet (YAG) for laser hosts and quartz and sapphire for optical
windows, single crystals are used to minimize scattering or absorption of energy. In piezoelectric
materials, such as quartz, the optimum properties are obtained in single-domain single crystals. In
addition, there are many other applications that require the optical, electrical, magnetic or mechanical
properties of ceramic single crystals.
Substrate diameters for the single crystal have been steadily increasing since the commercial
introduction of substrates in 1990 and crystal defects have been greatly reduced in the past 15 years.
Commercial devices are available, but their widespread use will depend on the ability of growers to
make large, inexpensive, defect-free materials available.
While various methods for measuring the defect of single-crystal thin films have been presented until
now, the most typical method for measuring the crystalline quality (degree of average defect) of single-
crystal thin films that have a wide area (e.g. 2 inches, 4 inches, 6 inches) is the X-ray diffraction (XRD)
method with parallel X-ray beam. However, this method can easily create a great error margin as the
result value is analysed to be very different depending on the measuring process and conditions of the
user or the pre-treatment of samples, for example. A standard on universal measurement methods and
conditions, therefore, is absolutely necessary.
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INTERNATIONAL STANDARD ISO 22278:2020(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for crystalline quality of single-
crystal thin film (wafer) using XRD method with parallel
X-ray beam
1 Scope
This document specifies the test method for measuring the crystalline quality of single-crystal thin
film (wafer) using the XRD method with parallel X-ray beam. This document is applicable to all of the
single-crystal thin film (wafer) as bulk or epitaxial layer structure.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
single crystal
crystalline material having identical atomic arrangement on all areas of the material
3.2
off-cut angle
angle that a specific crystallographic orientation forms with surface in a single-crystal thin film (wafer)
Note 1 to entry: Off-cut angle is a key condition determining the growth behaviour of thin film during epitaxial
growth on a single-crystal thin film (wafer).
3.3
chemical mechanical polishing
CMP
process to planarize the thin film surface using a combination of chemical action by a slurry composed
of chemical liquid or abrasive particles and the mechanical action of a grinder
3.4
Bragg diffraction
width between the wavelength of light and the width of crystal structure, or relationship between the
reflecting surface and the angle formed by the ray
Note 1 to entry: The formula is 2d·sinθ = n·λ
where
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ISO 22278:2020(E)
d is the width of periodic structure;
θ is the angle between the crystal plane and incident light;
λ is the wavelength of light;
n is the constant.
3.5
parallel X-ray beam
X-ray beam obtained by collimating an incident X-ray beam or diffracted X-ray beam by using a solar
slit, an analyser crystal or an x-ray mirror
Note 1 to entry: In comparison with the focused beam, the parallel X-ray beam does not suffer the sample
condition (such as surface roughness) and geometrical limitations of the optical system (such as mechanical
focal-circle deviation).
3.6
slit
device for controlling the size and photon flux amount of X-ray beam
3.7
symmetric diffraction
state where the surface of sample and the Bragg diffraction are parallel
3.8
asymmetric diffraction
state where the surface of sample and the Bragg diffraction are not parallel
3.9
2 theta
2θ
angle of the detected X-ray beam with respect to the incident X-ray beam direction
3.10
omega
ω
angle between the incident X-ray beam and the sample surface
3.11
chi
χ
angle of tilt of sample about an axis in the plane of the sample and in the plane of the incident X-ray
beam, X-ray source and detector
Note 1 to entry: It can also be defined as psi (ψ) depending on the equipment manufacturer.
3.12
phi
Φ
angle of rotation about the normal to the nominal surface of the sample
3.13
X, Y, Z coordinate system
orthogonal coordinate system in which X is the direction in the plane of the sample, parallel to the
incident beam when Φ = 0; Y is the direction in the plane of the sample, perpendicular to the incident
beam when Φ = 0; and Z is the direction normal to the plane of the sample
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ISO 22278:2020(E)
3.14
flat zone
flat section in order to distinguish the structure of thin film (wafer)
Note 1 to entry: Since crystal structure in the thin film (wafer) cannot be visually identified with the human eye,
the location is classified by making one section flat.
3.15
rocking curve
RC
ω rocking
ω scan
intensity of peak and change of FWHM (full width at half maximum) on the incident angle ω as the
optimum Bragg diffraction condition on a specific crystal plane of a single crystal
Note 1 to entry: It is normally an indicator showing crystalline quality of the sample.
3.16
crystalline quality
FWHM value of a rocking curve based on various degrees of defects (such as dislocation density, mosaic
spread, curvature, misorientation and inhomogeneity) in the sample
3.17
arc second
FWHM unit of rocking curve as 1/3 600 of a degree of an angle
4 Fundamentals
The purpose of this document is to provide information to minimize the measuring error on the
crystalline quality evaluation of a single crystal. An X-ray beam shall be investigated in order to satisfy
the Bragg diffraction conditions on a single-crystal thin film (wafer) that has grown into a specific
crystal plane. Information on the internal defects of single crystal (such as dislocation density, mosaic
spread, curvature, misorientation and inhomogeneity) can be gained using the microscopic angle
change of X-ray beam (or microscopic change in the position of sample) investigated at this time. Since
the crystal plane interval and the arrangement of the crystal plane are very consistent in an almost
perfect crystal, most diffraction conditions are gained from one angle (2θ) in all crystal planes so that a
very sharp peak can be gained. In contrast, the single crystals with more defects show a broader peak.
5 Devices and instruments
5.1 Schematic diagrams
Figure 1 shows an example configuration for XRD with parallel X-ray beam system.
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ISO 22278:2020(E)
Key
1 X-ray source
2 X-ray mirror
3 incident X-ray beam
4 sample
5 diffracted X-ray beam
6 X-ray mirror
7 slit
8 detector
9 roland circle
2θ angle between the detected beam and the extension of the incident X-ray beam
ω angle between the specimen surface and the incident X-ray beam 2θ angle between the detected beam and the
extension of the incident X-ray beam
ϕ angle of rotation about the normal to the nominal surface of the sample
χ angle of tilt of sample about an axis in the plane of the sample and in the plane of the incident X-ray beam, X-ray
source and detector
Figure 1 — Example schematic layout of an XRD experimental configuration with parallel X-ray
beam system, projected into the plane of the source, detector, incident and diffracted X-ray beams
5.2 X-ray generator
Device which generates an X-ray beam of fixed intensity.
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ISO 22278:2020(E)
5.3 X-ray mirror
Device which makes the dispersed beam generated from an X-ray generator parallel or one that can
control the amount of X-ray beam that reaches the monochromator by passing through the slit.
NOTE Since the X-ray mirror is related only to the intensity of the peak (regardless of the beam's resolution),
it might not be used.
5.4 Monochromator
Device which monochromatizes the parallel beam generated from the X-ray mirror to have a specific
resolution. Selecting an appropriate monochromator is critical in the XRD analysis. In cases where
the crystalline quality [FWHM of rocking curve (RC)] of the sample is similar to the resolution of a
monochromator, the monochromator shall be replaced with a new one having higher resolution for
measurement purposes. This is because the resolution of the monochromator is likely to be lower than
the crystalline quality (FWHM of RC) of the single crystal.
NOTE X-rays (coming from the X-ray tube) have various wavelengths such as K , K and K . For instance, if
ɑ1 ɑ2 β
the target is Cu, Cu K (λ = 0,154 056 nm), Cu K (λ = 0,154 439 nm) and Cu K (λ = 0,139 221 nm) are emitted in
ɑ1 ɑ2 β
the ratio of 10:5:2. Because of a large gap between the wavelength of K ray and the rest (K K ), K ray can be
β ɑ1, ɑ2 β
easily filtered using a thin Ni filter. However, as the wavelengths of K and K are quite similar, they cannot be
ɑ1 ɑ2
filtered through a general Ni filter. Likewise, with the incident X-rays on a specimen having diverse wavelengths,
a diffraction peak broadening occurs, disrupting interpretation of the diffraction peak. This causes a problem in
measuring the accurate angle of diffraction (2θ). For this reason, a monochromator that takes only K ray from
ɑ1
incident X-rays to make a single wavelength must be used for accurate diffraction tests with high resolution.
5.5 Sample attachment
Plate where the measured sample gets placed to become parallel.
5.6 Goniometer
Device designed for the sample to move in the x-axis, y-axis and z-axis (X, Y, Z coordinate system), in
Φ and χ directions. A mechanically well-aligned and stable X-ray goniometer is required. The sample
height (z-axis) shall be capable of being set accurately on the centre of rotation of the ω and 2θ axes, and
the sample stage angle of tilt (χ) shall enable setting the sample parallel to the incident beam slits.
NOTE A goniometer can have different moving fundamentals and structure depending on the equipment
manufacturer.
5.7 Detector
Device which changes into a form of peak on the software by receiving the X-ray beam that has passed
through the slit of the analyser crystal. The detector response shall be stable within the time frame of
the experiment. It is usual and recommended that the acceptance slits at the detector be set to match
the incident beam width and divergence.
NOTE An analyser crystal works only for zero-dimensional detector (scintillation detector). A
multidimensional X-ray detector can drastically reduce total measurement time and can observe detailed
information of the sample very quickly. Moreover, the X-ray sensitivity and angular resolution of modern
multidimensional X-ray detector devices are comparable to scintillation systems.
5.8 Instrument calibration
The aligned state of devices mentioned in these subclauses is critical in the single-crystal thin film
(wafer) analysis. As even a minor misalignment makes it different to get a precise FWHM of the RC,
calibration on a regular basis shall be conducted in accordance with the procedures and methods in the
manual provided by the XRD manufacturer.
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ISO 22278:2020(E)
6 Preparation of sample
Process the single crystal under a state of ingot into a form of wafer with a specific size by cutting
with a multi-wire saw. Polish using a chemical mechanical polishing (CMP) for the planarized surface of
processed single-crystal thin film (wafer).
7 Test method and procedure
7.1 Optics alignment
The X-ray generated from the X-ray generator shall be made to reach the detector by passing through
the monochromator after going through the X-ray mirror as shown in Figure 2. Alignment checks might
be part of automated (or manual mode) routines available on particular equipment. The following basic
requirements shall be met:
a) Make sure that nothing unwanted obstructs the beam between the source and detector. The sample
attachment shall be out of the beam.
b) The incident X-ray beam shall be accurately centred on the centre of the sample attachment and
detector axes.
c) The incident X-ray beam shall be made to become parallel with the surface of the sample attachment.
NOTE 1 It is possible with modern control software that corrections to axes motions can take into account
a non-ideal instrument alignment.
NOTE 2 To perform accurate evaluation on a high-quality single-crystal thin film (wafer), the resolution
of the monochromator must not be lower than the crystalline quality of the single crystal sample (refer to
the resolution data of the monochromator provided by the supplier).
Key
1 X-ray generator
2 X-ray mirror
3 monochromator
4 sample attachment
5 detector
Figure 2 — Schematic diagram of optics alignment
7.2 Sample alignment
After placing the single-crystal thin film (wafer) to be measured on the sample attachment above
the sample plate, make the incident X-ray beam become parallel with the sample surface as shown
in Figure 3. The sample surface also coincides with the centre of rotation of the goniometer axes.
Equipment and its controls can include automatic sample alignment, data collection and analysis
6 © ISO 2020 – All rights reserved
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ISO 22278:2020(E)
routines, and can make use of other methods of alignment, such as range finders or position monitors.
The following basic requirements shall be met:
a) The instrument shall be aligned correctly, with appropriate slit widths, with the incident beam
accurately over the centre of rotation. Set the X-ray source slit width to minimize spill off (typically
1 mm in a laboratory system) and set the detector slits significantly wider than the source slits
(many times wider).
b) The angle, ω, between sample surface and incident beam shall be calibrated so that zero sets the
sample surface approximately parallel to the incident beam.
c) Where applicable, set the X-ray generator power to the manufacturer’s recommended operating
level. Ensure stable operation.
d) Make sure that no obstructions (such as magnet or tape to attach the sample firmly on the sample
plate) can interfere with the incident or diffracted beams. In the case of a wafer sample, make sure
that the direction of the flat zone faces the bottom when it is placed above the sample plate.
If there is no high-quality single-crystal thin film or wafer available for XRD machine checking
and calibration, the certified internationally standard single-crystal wafer [e.g. silicon (Si) single-
crystal wafer for crystalline orientation] should be used.
e) If required, insert an attenuator in the beam so that the detected intensity is well within the linear
or linearized regime of the detector.
Key
1 X-ray generator
2 X-ray mirror
3 monochromator
4 incident beam
5 sample
6 sample attachment
7 detector
Figure 3 — Schematic diagram of sample alignment
7.3 Adjusting the initial position of goniometer
7.3.1 Symmetric diffraction
Single-crystal thin film (wafer) has several specific crystal planes depending on the growing method.
Examples for d, 2θ, ω and relative ideal intensity values of symmetric diffraction of the grown crystal
plane are shown in Annex A, Table A.1, using the method given in Annex B. Once 7.2 is completed, adjust
the X-ray generator (mirror), detector (analyser) and the position of the sample plate by as much as
© ISO 2020 – All rights reserved 7
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ISO 22278:2020(E)
an angle equivalent to ω (an angle equivalent to half of 2θ) and 2θ value on the corresponding crystal
plane (see Figure 4).
When cutting the single crystal at a specific angle (off-cut angle), the cutting angle shall be added to or
subtracted from the 2θ and ω values. For instance, for a 4 off-cut on a 6H-SiC single-crystal thin film
(wafer) that has the crystal growth face of (006), ω = 29,548 7° −4° = 25,548 7°, 2θ = 59,097 5° and
−8° = 51,097 5° (see Annex A, Table A.1, and Figure 5)
Key
1 X-ray generator
2 X-ray mirror
3 monochromator
4 sample
5 sample attachment
6 detector
ω angle between the sample surface and the incident X-ray beam 2θ angle between the detected beam and the
extension of the incident X-ray beam
2θ angle between the detected beam and the extension of the incident X-ray beam
Figure 4 — Schematic diagram of the initial position adjustment of goniometer (symmetric
diffraction observation)
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ISO 22278:2020(E)
Key
X omega angle (°)
Y arbitrary unit (au)
1 RC with off-cut angle 4°
2 RC with off-cut angle 0°
Figure 5 — Change of ω value depending on off-cut angle
7.3.2 Asymmetric diffraction
Examples for d, 2θ, ω and χ values of asymmetric diffraction of the grown crystal plane are shown in
Annex A, Table A.2, using the method given in Annex B. Once 7.2 is completed, adjust the X-ray generator
(mirror), detector (analyser) and the position of the sample plate by as much as an angle equivalent to
ω, 2θ and χ values on the corresponding growing faces.
Moving fundamentals and st
...
DRAFT INTERNATIONAL STANDARD
ISO/DIS 22278
ISO/TC 206 Secretariat: JISC
Voting begins on: Voting terminates on:
2020-01-07 2020-03-31
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for crystalline quality of single-
crystal thin film (wafer) using XRD method with parallel
X-ray beam
ICS: 81.060.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
This document is circulated as received from the committee secretariat.
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 22278:2020(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
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ISO/DIS 22278:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/DIS 22278:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Symbols and abbreviated terms. 3
4 Fundamentals . 3
5 Devices and instruments. 3
5.1 Schematic diagrams . 3
5.2 X-ray generator . 4
5.3 X-ray mirror . 4
5.4 Monochromator . 5
5.5 Sample attachment . 5
5.6 Goniometer. 5
5.7 Detector . 5
5.8 Instrument calibration . 5
6 Preparation of sample . 5
7 Test method and procedure . 6
7.1 Optics alignment . 6
7.2 Sample alignment . 6
7.3 Adjusting the initial position of goniometer . 7
7.3.1 In case of symmetric diffraction . 7
7.3.2 In case of asymmetric diffraction . 9
7.4 Microscopic position adjustment of goniometer (Φ and χ axes) and ω scan . 9
7.4.1 In case of symmetric diffraction . 9
7.4.2 In case of asymmetric diffraction .12
7.5 Crystalline quality measurement method of single-crystal wafer .16
8 Data analysis .18
9 Test report .18
Annex A (normative) Example for d-spacing, 2 theta, χ value (tilt angle), and relative ideal
intensity of the symmetric and asymmetric diffraction on the silicon carbide (SiC)
single-crystal thin film (wafer) .20
Annex B (normative) Determination of d-spacing, 2 theta, χ value (tilt angle), and relative
ideal intensity for the symmetric and asymmetric diffraction on the single-crystal
thin film (wafer) .22
Annex C (informative) Results of round-robin test.25
Bibliography .27
© ISO 2020 – All rights reserved iii
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ISO/DIS 22278:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/DIS 22278:2020(E)
Introduction
Single-crystals are important in many applications ranging from synthetic gemstones for jewelry
to hosts for solid-state lasers. For some applications, ceramic materials must be prepared as single-
crystals. When used as substrates for thin film growth (e.g. gallium-on-sapphire technology or the
growth of superconductor thin films) it is the crystalline perfection of a single-crystal that is important.
Wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) have drawn a lot
of attention in power applications due to their superior material properties such as high critical electric
field resulting in a minimum of 10 times higher breakdown voltage or a 100 times smaller on-resistance
than Si. These unique properties of SiC and GaN materials have made them promising candidates for
future high power, high frequency semiconductor devices. In optical applications, e.g. the use of ruby
and yttrium–aluminum–garnet (YAG) for laser hosts and quartz and sapphire for optical windows,
single-crystals are used to minimize scattering or absorption of energy. In piezoelectric materials, e.g.
quartz, the optimum properties are obtained in single-domain single-crystals. Some of the applications
that utilize the desirable optical, electrical, magnetic, or mechanical properties of ceramic single-
crystals.
Substrate diameters for the single-crystal have been steadily increasing since the commercial
introduction of substrates in 1990 and crystal defects have been greatly reduced in the past 15 years.
Commercial devices are available, but their widespread use will depend on the ability of growers to
make large, inexpensive, defect free materials available.
While various methods for measuring the defect of single-crystal thin films have been presented until
now, the most typical method for measuring the crystalline quality (degree of average defect) of single-
crystal thin films that have wide area (2 inch, 4 inch and 6 inch, etc.) is X-ray diffraction (XRD) method
with parallel X-ray beam. However, this method can easily create a great error margin as the result
value is analysed to be very different depending on the measuring process and conditions of the user or
the pre-treatment of sample, etc.
Therefore, a standard on universal measurement methods and conditions is absolutely necessary.
Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for crystalline quality
of single-crystal thin film (wafer) using XRD method with parallel X-ray beam
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DRAFT INTERNATIONAL STANDARD ISO/DIS 22278:2020(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for crystalline quality of single-
crystal thin film (wafer) using XRD method with parallel
X-ray beam
1 Scope
This standard is the one for measuring the crystalline quality of single-crystal thin film (wafer) XRD
method with parallel X-ray beam. All of the single-crystal thin film (wafer) as bulk or epitaxial layer
structure is included in the scope of this standard.
2 Normative references
There are no normative references in this document.
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 Terms and definitions
3.1.1
Single-crystal
While all atoms that exist in one crystal form a fixed regular arrangement in a three dimensional space,
a single-crystal at this time stands for a crystalline material having identical atomic arrangement on all
areas of the material
3.1.2
Off-cut angle
Angle that a specific crystallographic orientation forms with surface in a single-crystal thin film
(wafer). Off-cut angle is a key condition determining the growth behaviour of thin film during epitaxial
growth on a single-crystal thin film (wafer)
3.1.3
CMP (chemical mechanical polishing)
A process to planarize the thin film surface using the combination of chemical action by a slurry
composed of chemical liquid / abrasive particles and mechanical action of a grinder
3.1.4
Bragg diffraction
Shows the width between the wavelength of light and the width of crystal structure, or relationship
between the reflecting surface and the angle formed by the ray. The formula is 2d·sinθ = n·λ.
Here, d is the width of periodic structure, θ is the angle between crystal plane and incident light, λ is
the wavelength of light and n is the constant
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ISO/DIS 22278:2020(E)
3.1.5
Parallel X-ray beam
Refers to X-ray beam obtained by collimating incident and/or diffracted X-ray beam by using solar slit,
analyser crystal and/or x-ray mirror. As comparison with the focused beam, parallel X-rays, it does not
suffer the sample condition (e.g. surface roughness) and geometrical limitations of the optical system
(e.g. mechanical focal-circle deviation)
3.1.6
Slit
Device for controlling the size and photon flux amount of X-ray beam
3.1.7
Symmetric diffraction
State where the surface of sample and the Bragg diffraction are parallel
3.1.8
Asymmetric diffraction
State where the surface of sample and the Bragg diffraction are not parallel
3.1.9
2-theta
2θ
Angle of the detected X-ray beam with respect to the incident X-ray beam direction
3.1.10
omega
ω
Angle between the incident X-ray beam and the sample surface
3.1.11
chi
χ
Angle of tilt of sample about an axis in the plane of the sample and in the plane of the incident X-ray
beam, X-ray source and detector
Note 1 to entry: It is also may define as psi (ψ) depending on equipment companies
3.1.12
phi
Φ
Angle of rotation about the normal to the nominal surface of the sample
3.1.13
X, Y, Z coordinate system
Orthogonal coordinate system in which X is the direction in the plane of the sample, parallel to the
incident beam when Φ = 0; Y is the direction in the plane of the sample, perpendicular to the incident
beam when Φ = 0; and Z is the direction normal to the plane of the sample
3.1.14
Flat zone wafer
Since crystal structure in the thin film (wafer) cannot be visually identified with human eye, the
location is classified by making one section flat in order to distinguish the structure of thin film (wafer)
3.1.15
Rocking curve
ω rocking
ω scan
A term which indicates the intensity of peak and the change of FWHM (Full Width at Half Maximum) on
the incident angle ω as the optimum Bragg diffraction condition on a specific crystal plane of a single-
crystal. It is normally an indicator showing crystalline quality of the sample.NOTE Rocking curve is
normally called an RC by abbreviation.
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ISO/DIS 22278:2020(E)
3.1.16
Crystalline quality
The "crystalline quality" used in this standard shall mean the FWHM value of a rocking curve based
on various degrees of defects (dislocation density, mosaic spread, curvature, misorientation, and
inhomogeneity etc.) in the sample.
3.1.17
Arc seconds
FWHM unit of rocking curve as 1/3600 of a degree of an angle
3.2 Symbols and abbreviated terms
2θ 2Theta, the angle of the detected X-ray beam with respect to the incident X-ray beam
ω Omega, the angle between the incident X-ray beam and the sample surface
ϕ Phi, the angle of rotation about the normal to the nominal surface of the sample
χ Chi, the angle of tilt of sample about an axis in the plane of the sample and in the plane of the
incident X-ray beam, X-ray source and detector (may define as psi (ψ))
λ Wavelength of the incident X-ray beam
4 Fundamentals
The purpose of this standard is to provide an information to minimize the measuring error on the
crystalline quality evaluation of a single-crystal. An X-ray beam shall be investigated in order to satisfy
the Bragg diffraction conditions on a single-crystal thin film (wafer) that has grown into a specific
crystal plane. Information on the internal defects of single-crystal (dislocation density, mosaic spread,
curvature, misorientation and inhomogeneity, etc.) can be gained using the microscopic angle change of
X-ray beam (or microscopic change in the position of sample) investigated at this time. Since the crystal
plane interval and the arrangement of crystal plane are very consistent in an almost perfect crystal,
most diffraction conditions are gained from one angle (2 theta) in all crystal planes so that a very sharp
peak can be gained. On the contrary, the single-crystals with more defects show a broader peak.
5 Devices and instruments
5.1 Schematic diagrams
Figure 1 shows a diagram of an example configuration for XRD with parallel X-ray beam system.
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ISO/DIS 22278:2020(E)
Key
1 X-ray source
2 X-ray mirror
3 incident X-ray beam
4 sample
5 diffracted X-ray beam
6 X-ray mirror
7 slit
8 detector
9 roland circle
ω angle between the specimen surface and the incident X-ray beam 2θ angle between the detected beam and the
extension of the incident X-ray beam
Φ angle of rotation about the normal to the nominal surface of the sample
χ angle of tilt of sample about an axis in the plane of the sample and in the plane of the incident X-ray beam, X-ray
source and detector
Figure 1 — Example schematic layout of an XRD experimental configuration with parallel X-ray
beam system, projected into the plane of the source, detector, incident and diffracted X-ray beams
5.2 X-ray generator
Device which generates an X-ray beam of fixed intensity
5.3 X-ray mirror
Device which makes the dispersed beam generated from an X-ray generator parallel or the one that can
control the amount of X-ray beam that reaches monochromator by passing through the slit
NOTE Since the X-ray mirror is related only to the intensity of the peak (regardless of the beam's
resolution), it may not be used as the case may be.
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ISO/DIS 22278:2020(E)
5.4 Monochromator
Device which monochromatizes the parallel beam generated from X-ray mirror to have a specific
resolution. Selecting an appropriate monochromator is critical in the XRD analysis. In the case
where the crystalline quality (FWHM of rocking curve) of the sample is similar to the resolution of a
monochromator, the monochromator needs to be replaced with a new one having higher resolution for
measurement purposes. This is because the resolution of the monochromator is likely to be lower than
the crystalline quality (FWHM of rocking curve) of the single-crystal.
NOTE X-rays (coming from the X-ray tube) have various wavelengths such as K , K , and K . For instance, if
ɑ1 ɑ2 β
the target is Cu, Cu K (λ = 0,154056 nm), Cu K (λ = 0,154439 nm), and Cu K (λ = 0,139221 nm) are emitted in
ɑ1 ɑ2 β
the ratio of 10:5:2. Because of a large gap between the wavelength of K ray and the rest (K K ), K ray can be
β ɑ1, ɑ2 β
easily filtered using a thin Ni filter. However, as the wavelengths of K and K are quite similar, they cannot be
ɑ1 ɑ2
filtered through a general Ni filter. Likewise, with the incident X-rays on a specimen having diverse wavelengths,
a diffraction peak broadening occurs, disrupting interpretation of the diffraction peak. Therefore, it causes a
problem in measuring the accurate angle of diffraction (2θ). For this reason, using a monochromator that takes
only K ray from incident X-rays to make a single wavelength is required for accurate diffraction tests with high
ɑ1
resolution.
5.5 Sample attachment
Plate where the measured sample gets placed to become parallel
5.6 Goniometer
Device designed for the sample to move in x-axis, y-axis, z-axis, Φ and χ directions. A mechanically well
aligned and stable X-ray goniometer is required. The sample height (z-axis) shall be capable of being set
accurately on the centre of rotation of ω and 2θ axes, and the sample stage angle of tilt (χ) shall enable
setting the sample parallel to the incident beam slits.
NOTE A goniometer may have different moving fundamentals and structure depending on the equipment
company.
5.7 Detector
Device which changes into a form of peak on the software by receiving the X-ray beam that has passed
through the slit of analyser crystal. The detector response shall be stable within the time-frame of the
experiment. It is usual and recommended that the acceptance slits at the detector be set to match the
incident beam width and divergence.
NOTE Analyser crystal works only for zero-dimensional detector (Scintillation detector). Multidimensional
X-ray detector can be drastically reduced total measurement time and can be observed detail information of
the sample very quick. Moreover, X-ray sensitivity and angular resolution, of modern multidimensional X-ray
detector devices, are comparable to scintillation systems.
5.8 Instrument calibration
The aligned state of devices mentioned above is critical in the single-crystal thin film (wafer) analysis.
As even a minor misalignment makes it different to get a precise FWHM of the rocking curve, calibration
on a regular basis shall be conducted in accordance with the procedures and methods in the manual
provided by the XRD manufacturer.
6 Preparation of sample
Process the single-crystal under a state of ingot into a form of wafer with specific size by cutting with
a multi-wire saw, etc. Polish using a chemical mechanical polishing (CMP) for the planarized surface of
processed single-crystal thin film (wafer).
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ISO/DIS 22278:2020(E)
7 Test method and procedure
7.1 Optics alignment
X-ray generated from the X-ray generator shall be made to reach the detector by passing through the
monochromator after going through the X-ray Mirror as shown in Fig. 2. Alignment checks may be
part of automated (or manual mode) routines available on particular equipment. The following basic
requirements shall be verified.
a) Make sure that nothing unwanted obstructs the beam between the source and detector. The sample
attachment shall be out of the beam.
b) The incident X-ray beam shall be accurately centred on the centre of the sample attachment and
detector axes.
c) The incident X-ray beam shall be made to become parallel with the surface of sample attachment.
Note 1 It is possible, with modern control software, that corrections to axes motions may take into account a
non-ideal instrument alignment.
NOTE 2 To perform accurate evaluation on a high quality single-crystal thin film (wafer), the resolution of the
monochromator shall not be lower than crystalline quality of the single-crystal sample (refer to the resolution
data of the monochromator provided by the supplier).
Key
1 X-ray generator
2 X-ray Mirror
3 monochromator
4 sample attachament
5 detector
Figure 2 — Schematic diagram of optics alignment
7.2 Sample alignment
After placing the single-crystal thin film (wafer) to be measured on sample attachment above the
sample plate, make the incident X-ray beam become parallel with the sample surface as shown in Fig.
3. The sample surface also coincides with the center of rotation of the goniometer axes. Equipment and
its controls may include automatic sample alignment, data collection and analysis routines, and may
make use of other methods of alignment, e.g. range finders or position monitors. The following basic
requirements shall be verified.
a) The instrument shall be aligned correctly, with appropriate slit widths, with the incident beam
accurately over the center of rotation.
NOTE Set the X-ray source slit width to minimize spill off (typically 1 mm in a laboratory system), and
set the detector slits significantly wider than the source slits (many times wider).
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b) The angle, ω, between sample surface and incident beam shall be calibrated so that zero sets the
sample surface approximately parallel to the incident beam.
c) Where applicable, set the X-ray generator power to the manufacturer’s recommended operating
level. Ensure stable operation.
d) Make sure that nothing unwanted obstructs (such as magnet or tape to attach the sample firmly on
the sample plate) can interfere with the incident or diffracted beams.
NOTE 2 In case of a wafer sample, make sure that the direction of wafer flat zone faces the bottom when
it is placed above the sample plate.
Note 2 If there are no high-quality single-crystal thin film or wafer available for XRD machine checking
and calibration, the certified internationally standard Si single-crystal wafer (e.g. SRM 1994 - Standard
Silicon (Si) Single-Crystal Wafer for Crystalline Orientation (https:// www -s .nist .gov/ srmors/ view _detail
.cfm ?srm = 1994) should be used.
e) If required, insert an attenuator in the beam so that the detected intensity is well within the linear
or linearized regime of the detector.
Key
1 X-ray generator
2 X-ray Mirror
3 monochromator
4 incident beam
5 sample
6 sample attachament
7 detector
Figure 3 — Schematic diagram of sample alignment
7.3 Adjusting the initial position of goniometer
7.3.1 In case of symmetric diffraction
Single-crystal thin film (wafer) has several specific crystal planes depending on the growing method.
An example for d, 2θ, ω, and relative ideal intensity values of symmetric diffraction of the grown crystal
plane are shown in Table A.1 using the method given in Annex B. Once 7.2 gets completed, adjust the
X-ray generator (mirror), detector (analyzer) and the position of sample plate by as much as an angle
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ISO/DIS 22278:2020(E)
equivalent to ω (an angle equivalent to half of 2θ) and 2θ value on the corresponding crystal plane
(refer to Fig. 4).
NOTE In case of cutting as specific angle (off-cut angle) while cutting the single-crystal, the cutting angle
must be added to or subtracted from the 2θ and ω values. For instance, in case of 4° off-cut on a 6H-SiC single-
crystal thin film (wafer) that has the crystal growth face of (006), ω = 29,5487° - 4° = 25,5487°, 2θ = 59,0975° and
- 8° = 51,0975° (refer to Table A.1 and Fig. 5)
Key
1 X-ray generator
2 X-ray Mirror
3 monochromator
4 sample
5 sample attachament
6 detector
ω angle betw
...
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