IEC/TR 63258:2021

IEC TR 63258
Edition 1.0 2021-03
TECHNICAL
REPORT
colour
inside
Nanotechnologies – A guideline for ellipsometry application to evaluate the
thickness of nanoscale films


IEC TR 63258:2021-03(en)

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IEC TR 63258


Edition 1.0 2021-03




TECHNICAL



REPORT








colour

inside










Nanotechnologies – A guideline for ellipsometry application to evaluate the

thickness of nanoscale films


























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 07.120 ISBN 978-2-8322-9584-7




  Warning! Make sure that you obtained this publication from an authorized distributor.

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– 2 – IEC TR 63258:2021 © IEC 2021
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
3.1 General terms . 6
3.2 Terms specific to this document . 7
4 Measurement of ellipsometry . 8
4.1 General . 8
4.2 Measurement procedure . 9
4.2.1 Sample preparation for system check . 9
4.2.2 Experimental procedure for system check . 9
4.2.3 Sample handling . 9
4.2.4 Experimental procedures . 9
5 Reporting data . 10
6 Data analysis / interpretation of results . 10
6.1 General . 10
6.2 Setting analysis model . 11
6.3 Data fitting and validation of analysis result . 12
6.3.1 General . 12
6.3.2 Data analysis method 1 – Dispersion law (Cauchy model) [6] . 13
6.3.3 Data analysis method 2 – Sellmeier equation model (transparent
material) [7] . 13
6.3.4 Data analysis method 3 – Drude dispersion model (conductive material)
[8], [9] . 13
6.3.5 Data analysis method 4 – Dispersion law (classical model / Lorentz
model) [8], [9] . 14
6.3.6 Data analysis method 5 – Forouhi-Bloomer dispersion model [10], [11]. 15
6.3.7 Data analysis method 6 – Tauc-Lorentz dispersion model (amorphous
materials) [12], [13]. 15
Annex A (informative) Case study: Interlaboratory comparison by using SiO /Si
2
samples . 17
Annex B (informative) Case study: Ellipsometry measurement of other materials . 19
Bibliography . 20

Figure 1 – Primary structure of ellipsometry measurement . 8
Figure 2 – Flow chart of the ellipsometry data analysis . 11
Figure A.1 – An example of the report form of ellipsometry measurements . 17
Figure A.2 – An example of the results of the interlaboratory comparison . 18
Figure A.3 – The wafer-shaped sample used for the interlaboratory comparison . 18

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IEC TR 63258:2021 © IEC 2021 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

NANOTECHNOLOGIES – A GUIDELINE FOR ELLIPSOMETRY
APPLICATION TO EVALUATE THE THICKNESS OF NANOSCALE FILMS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a Technical Report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC TR 63258, which is a Technical Report, has been prepared by IEC technical committee
113: Nanotechnology for electrotechnical products and systems, in collaboration with
ISO technical committee 229: Nanotechnologies.
It is published as a double logo document.
The text of this Technical Report is based on the following documents:
DTR Report on voting
113/548/DTR 113/563/RVDTR

Full information on the voting for the approval of this Technical Report can be found in the
report on voting indicated in the above table.

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– 4 – IEC TR 63258:2021 © IEC 2021
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

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IEC TR 63258:2021 © IEC 2021 – 5 –
INTRODUCTION
Ellipsometry is a powerful optical technique to evaluate the dielectric properties of thin films.
Ellipsometry can be used to characterize thickness, roughness, composition, crystalline nature,
and other properties of nanomaterials, and is frequently used to warrant the quality and the
performance of thin-film growth equipment. The signal depends on the change in the optical
response of incident light that interacts with the nanomaterial being investigated.
Many current and emerging electrotechnical devices employ nanomaterials in the form of thin
films. Therefore, it is important to develop a measurement protocol to evaluate the thickness of
such films with sufficient accuracy. This document describes the practical considerations that
need to be taken into account in using ellipsometry to evaluate the thickness of nanoscale films.

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– 6 – IEC TR 63258:2021 © IEC 2021
NANOTECHNOLOGIES – A GUIDELINE FOR ELLIPSOMETRY
APPLICATION TO EVALUATE THE THICKNESS OF NANOSCALE FILMS



1 Scope
This document, which is a Technical Report, is focused on the practical protocol of ellipsometry
to evaluate the thickness of nanoscale films. This document does not include any specification
of the ellipsometers, but suggests how to minimize the data variation to improve data
reproducibility.
This document includes
– outlines of the ellipsometry procedures,
– methods of interpretation of results and discussion of data analysis, and
– case studies.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
ISO/TS 80004-1, Nanotechnologies –Vocabulary – Part 1: Core terms
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TS 80004-1 and the
following 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 General terms
3.1.1
interlaboratory comparison
organization, performance and evaluation of measurements or tests on the same or similar
items by two or more laboratories in accordance with predetermined conditions
[SOURCE: ISO/IEC 17043:2010, 3.4]

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IEC TR 63258:2021 © IEC 2021 – 7 –
3.2 Terms specific to this document
3.2.1
polarization
direction of the electric field vector of an optical beam
Note 1 to entry: The plane of polarization is the plane containing the electric field vector and the direction of
propagation of the beam.
[SOURCE: ISO/IEC 30193:2020, 3.28]
3.2.2
optical constant
refractive index n(λ) and extinction coefficient k(λ), as functions of wavelength λ
3.2.3
refractive index
n
ratio of the speed of electromagnetic wave in vacuum c to that in another medium ν
c
n=
v
Note 1 to entry: The refractive index shows how the speed of light is changing depending on media.
3.2.4
complex refractive index
N
index that determines the propagation of a plane electromagnetic wave in an isotropic absorbing
medium expressed as
N(λ) = n(λ) + ik(λ)
where n and k are the real and imaginary parts, respectively
Note 1 to entry: The real n and imaginary k parts are called the refractive index and the extinction coefficient,
respectively.
Note 2 to entry: Optics field convention is used for the definition of complex refractive index [1].
3.2.5
absorption coefficient
α
coefficient that describes the attenuation of electromagnetic wave intensity I during
0
propagation in absorbing media
Note 1 to entry: The electromagnetic wave intensity attenuates according to the following equation:
II exp(−αx) .
0
where I is the initial electromagnetic wave intensity and x is the propagation distance.
0
Note 2 to entry: Absorption coefficient α is related to extinction coefficient at a wavelength:
4πk
α= .
λ
3.2.6
complex dielectric constant
ε
value that indicates how atoms in a material respond when an outside electric field is applied
to the material
=

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Note 1 to entry: Complex dielectric constant is given by the equation
ε(λ) = ε (λ) + iε (λ)
r i
where ԑ , ԑ are the real and imaginary parts of complex dielectric function, respectively.
r i
Note 2 to entry: Relationship between the complex dielectric constant and the complex refractive index obtained
from Maxwell's equation is:
2
ε(λ) = N(λ) .
Note 3 to entry: Optics field convention is used for the definition of the complex dielectric constant [1].
Note 4 to entry: The terms complex dielectric function and dielectric function are used for the complex dielectric
constant and dielectric constant when focusing on their wavelength or angular frequency dependence.
3.2.7
film thickness
d
distance between the top and bottom boundaries of the laminar film, where each boundary is
determined as the interface at which the refractive index changes
3.2.8
Brewster's angle
angle of incidence at which there is no reflection of p-polarized light at an uncoated optical
surface
4 Measurement of ellipsometry
4.1 General
The practical protocol of ellipsometry is well-established.


Figure 1 – Primary structure of ellipsometry measurement
Ellipsometry measures a change in polarization as light reflects from a sample. The polarization
change is represented as an amplitude ratio, Ψ, and the phase difference, Δ. The basic
components of the ellipsometry measurement are a light source, a polarizer, a polarization
1
analyser and a detector, as shown in Figure 1. See references [2] and [3] for principles of
ellipsometry.
__________
1
 Numbers in square brackets refer to the Bibliography.

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IEC TR 63258:2021 © IEC 2021 – 9 –
4.2 Measurement procedure
4.2.1 Sample preparation for system check
Before the actual sample measurement is performed, it is necessary to check the system’s
accuracy. To make it possible, a reference sample with known thickness and/or refractive index
should be used. The reference samples such as thermally oxidized SiO on Si are available.
2
Ellipsometry is very sensitive to physical and chemical properties of the thin film material, its
surface and the properties at the film–substrate interface.
4.2.2 Experimental procedure for system check
The general protocol of ellipsometry measurement is standardized to evaluate thin films.
– Step 1: Positioning of the reference sample on the stage.
– Step 2: Adjustment of the height and tilt.
– Step 3: Measurement of the reference sample.
– Step 4: Data analysis.
– Step 5: Result of thickness or refractive index should be within 1 % of the guaranteed values.
– Step 6: If the obtained result fulfils the condition of step 5, start to measure the test sample.
If not, the system needs additional check.
It is advisable to check the system at the required angle of incidence.
4.2.3 Sample handling
Ellipsometry is very sensitive to physical and chemical properties of the sample’s surface, so it
is advisable to keep the sample in a clean and dry place after the preparation. Touching and
scratching the surface should be avoided, because non-professional cleaning might affect the
surface state and therefore change the result.
4.2.4 Experimental procedures
The general protocol of ellipsometry measurement is as follows.
– Step 1: Positioning of the sample on the stage.
– Step 2: Adjustment of the angle of incidence, height and tilt.
– Step 3: Measurement of the sample.
– Step 4: Data analysis.
– Step 5: Validation of analysis result.
NOTE This protocol is valid for non scattering and isotropic sample planes.
In order to minimize the data variation, the following practical recommendations apply.
1) The ellipsometry measurement should be done at an angle of incidence close to the
Brewster's angle of the substrate.
2) The ellipsometry measurement should be done over a measurement wavelength range as
wide as possible. For example, if there is absorption in the visible range, it needs to be
measured including the near-infrared range.
3) The fitting analysis should be performed by changing the initial value of the film thickness
and the type of dispersion formula at the time of analysis. The comparison should be done
to confirm that equivalent results can be o
...