ISO 13424:2013
(Main)Surface chemical analysis — X-ray photoelectron spectroscopy — Reporting of results of thin-film analysis
Surface chemical analysis — X-ray photoelectron spectroscopy — Reporting of results of thin-film analysis
ISO 13424:2013 specifies the minimum amount of information required in reports of analyses of thin films on a substrate by XPS. These analyses involve measurement of the chemical composition and thickness of homogeneous thin films, and measurement of the chemical composition as a function of depth of inhomogeneous thin films by angle-resolved XPS, XPS sputter-depth profiling, peak-shape analysis, and variable photon energy XPS.
Analyse chimique des surfaces — Spectroscopie de photoélectrons X — Rapport des résultats de l'analyse de films minces
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 13424
First edition
2013-10-01
Surface chemical analysis — X-ray
photoelectron spectroscopy —
Reporting of results of thin-film analysis
Analyse chimique des surfaces — Spectroscopie de photoélectrons X
— Rapport des résultats de l’analyse de films minces
Reference number
ISO 13424:2013(E)
©
ISO 2013
---------------------- Page: 1 ----------------------
ISO 13424:2013(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2013
All rights reserved. Unless otherwise specified, 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
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2013 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 13424:2013(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 1
5 Overview of thin-film analysis by XPS . 1
5.1 Introduction . 1
5.2 General XPS . 3
5.3 Angle-resolved XPS . 3
5.4 Peak-shape analysis . 3
5.5 Variable photon energy XPS . 3
5.6 XPS with sputter-depth profiling . 3
6 Specimen handling . 4
7 Instrument and operating conditions . 4
7.1 Instrument calibration . 4
7.2 Operating conditions . 4
8 Reporting XPS method, experimental conditions, analysis parameters, and
analytical results . 5
8.1 XPS method for thin-film analysis . 5
8.2 Experimental conditions . 5
8.3 Analysis parameters . 6
8.4 Examples of summary tables . 7
8.5 Analytical Results. 9
Annex A (informative) General XPS .10
Annex B (informative) Angle-resolved XPS .18
Annex C (informative) Peak-shape analysis .24
Annex D (informative) XPS with sputter-depth profiling .37
Bibliography .40
© ISO 2013 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 13424:2013(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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 201, Surface chemical analysis, Subcommittee
SC 7, Electron spectroscopies.
iv © ISO 2013 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 13424:2013(E)
Introduction
X-ray photoelectron spectroscopy (XPS) is widely used for the characterization of surfaces of materials,
especially for overlayer thin films on a substrate. The chemical composition of the near-surface region
of a thin film can be determined by XPS. If the film has a uniform thickness and the thickness is less than
about three times the mean escape depth (MED) for the measured photoelectrons, the film thickness and
the depth distribution of elements or chemical states of elements in the film can be determined by angle-
resolved XPS or peak-shape analysis . For thicker films, the depth distributions of elements in the film
can be obtained by sputter-depth profiling. Possible lateral inhomogeneities in film thicknesses or depth
profiles can be determined if the XPS system has sufficient lateral resolution. These XPS applications are
particularly valuable for characterizing thin-film nanostructures since the MED is typically less than
5 nm for many materials and common XPS measurement conditions.
Clauses 6 and 7 of this International Standard provide guidance to the operator of an XPS instrument in
making efficient measurements for determining meaningful chemical compositions and film thicknesses
for overlayer films on a substrate. Clause 8 of this International Standard shows the information to be
included in reports of the measurements and the analyses of the XPS data. Annex A, Annex B, Annex C,
and Annex D provide supplementary information on methods of data analysis for different types of XPS
measurements on thin-film samples.
© ISO 2013 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 13424:2013(E)
Surface chemical analysis — X-ray photoelectron
spectroscopy — Reporting of results of thin-film analysis
1 Scope
This International Standard specifies the minimum amount of information required in reports of
analyses of thin films on a substrate by XPS. These analyses involve measurement of the chemical
composition and thickness of homogeneous thin films, and measurement of the chemical composition
as a function of depth of inhomogeneous thin films by angle-resolved XPS, XPS sputter-depth profiling,
peak-shape analysis, and variable photon energy XPS.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 18115-1:2010, Surface chemical analysis — Vocabulary — Part 1: General terms and terms used in
spectroscopy
3 Terms and definitions
For the purposes of this document, the terms and definitions in ISO 18115-1:2010 apply.
4 Abbreviated terms
AES Auger electron spectroscopy
ARXPS Angle-resolved X-ray photoelectron spectroscopy
IMFP Inelastic mean free path
MED Mean escape depth
RSF Relative sensitivity factor
TRMFP Transport mean free path
XPS X-ray photoelectron spectroscopy
5 Overview of thin-film analysis by XPS
5.1 Introduction
XPS analyses of thin films on substrate can provide information on the variation of chemical composition
with depth and on film thicknesses. Several XPS methods can be used if the total film thickness is less than
three times the largest MED for the detected photoelectrons. The MED for particular photoelectrons is
a function of the IMFP and the emission angle of the photoelectrons with respect to the surface normal.
The IMFP depends on the photoelectron energy and the material. MED values can be obtained from a
[1]
database. A simple analytical formula for estimating MEDs has been published for emission angles
[2]
≤50°. For such emission angles, the MED is less than the product of the IMFP and the cosine of the
© ISO 2013 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 13424:2013(E)
emission angle by an amount that depends on the strength of the elastic scattering of the photoelectrons
[2]
in the film. Both the IMFP and the strength versus depend on the chemical composition of the film.
The MED is typically less than 5 nm for many materials and common XPS instruments and measurement
conditions. If the effects of elastic scattering are neglected, the MED is given approximately by the
product of the IMFP and the cosine of the emission angle. The latter estimates of the MED can be
sufficient for emission angles larger than 50° although better estimates can be obtained, e.g. from the
[1]
database. If the total film thickness is greater than three times the largest MED, XPS can be used under
certain conditions (see Annex D) together with ion sputtering to determine the variation of chemical
composition with depth.
Table 1 provides a summary of the XPS methods which can be used for determining chemical composition
and/or film thickness. Some methods can be utilized for the characterization of single-layer or multiple-
layer thin films on a substrate and some methods can be used to determine the composition-depth
profile of a sample for which the composition is a function of depth measured from the surface (i.e.
where there is not necessarily an interface between two or more phases). The choice of method typically
depends on the type of sample and the analyst’s knowledge of the likely or expected morphology of
the sample (i.e. whether the sample can consist of a single overlayer film on a flat substrate, multiple
films on a flat substrate, or a sample with composition varying continuously with depth), whether the
total film thickness is less than or greater than the largest MED for the detected photoelectrons, and
the desired information (i.e. film composition or film thickness). The first three methods in Table 1 are
non-destructive while the final method is destructive (i.e. the composition of the exposed surface is
determined by XPS as the sample is etched by ion bombardment). Brief descriptions of these methods
are given in the following clauses and additional information is provided in the indicated annexes.
Table 1 — XPS methods for the characterization of thin films on substrates and for samples
with composition varying with depth
Film thickness
Sample Information Additional
Clause Method less than three
morphology obtained information
times MED?
Single and multiple Layer order, film
5.2 General XPS films on a flat Yes thickness, and film Annex A
substrate composition
Multiple films on a
Film thickness and
flat substrate
film composition
Angle-resolved
5.3 Yes Annex B
Sample with com-
XPS
Composition as a
position varying
function of depth
with depth
Multiple films on a
Film thickness and
flat substrate
film composition
Peak-shape
5.4 Yes Annex C
Sample with com-
analysis
Composition as a
position varying
function of depth
with depth
Multiple films on a
Film thickness and
flat substrate
film composition
Variable pho-
5.5 No
Sample with com-
ton energy XPS
Composition as a
position varying
function of depth
with depth
Multiple films on a
Film thickness and
flat substrate
XPS with
film composition
5.6 sputter-depth No Annex D
Sample with com-
Composition as a
profiling
position varying
function of depth
with depth
2 © ISO 2013 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 13424:2013(E)
XPS is typically performed with laboratory instruments that are often equipped with monochromated
Al Kα or non-monochromated Al or Mg Kα X-ray sources. For some applications, XPS with X-rays from
synchrotron-radiation sources is valuable because the energy of the X-ray exciting the sample can be
varied. XPS with Ag X-rays is also used to observe deeper regions compared to excitation with Al X-rays.
In some cases, X-ray energies less than the Mg or Al Kα X-ray energies can be selected to gain enhanced
surface sensitivity while in other cases, higher energies are chosen to gain greater bulk sensitivity and
to avoid artefacts associated with the use of sputter-depth profiling.
Analysts should be aware of possible artefacts in XPS analyses. These artefacts include sample
degradation during X-ray irradiation, reactions of the sample with gases in the ambient vacuum, and
[3]
many effects that can occur during sputtering-depth profiling.
5.2 General XPS
For a uniform thin film on a flat substrate, the film thickness can be determined from a ratio of a photoelectron
peak intensity of an element in the substrate for a particular emission angle when an overlayer film is
present to the corresponding intensity when the film is absent. Alternatively, the thickness can be obtained
from a ratio of photoelectron peak intensity for an element in the film to the corresponding intensity for a
thick film (i.e. a film with a thickness much greater than three times the MED). The composition of the film
can be determined by the RSF method. Additional information is in Annex A.
For multiple thin-film analysis, it is important to determine the relative order of the layers above the
substrate. We can estimate the layer order, thicknesses, and compositions by measuring the changes of peak-
intensity ratios of components at two widely separated emission angles. Further details are in Annex A.
5.3 Angle-resolved XPS
[4]
Angle-resolved XPS (ARXPS) can be utilized to determine composition as a function of depth for depths
up to three times the largest MED of the detected electrons. The composition can be found for each film
of a multilayer film on a substrate or the distribution of composition with depth can be determined for
samples with no phase boundaries. For the former type of sample, film thicknesses can be estimated.
Further details are in Annex B.
5.4 Peak-shape analysis
[5]
Peak-shape analysis, the analysis of a photoelectron peak and its associated region of inelastically
scattered electrons, can be utilized to determine composition as a function of depth for depths up to
three times the largest MED of the detected electrons. The analyst can know the expected morphology
of the sample (i.e. the distribution of composition with depth) or can often deduce the likely morphology
from peak-shape analysis. Further details are in Annex C.
5.5 Variable photon energy XPS
Variable photon energy XPS can be employed to determine composition as a function of depth for depths
[6]
up to three times the largest MED of the detected electrons. XPS measurements of this type are
typically performed with synchrotron radiation over a sufficiently wide photon energy range to give a
useful range of MEDs of the detected photoelectrons.
5.6 XPS with sputter-depth profiling
Since 1985, “small-spot” XPS systems have been developed with lateral resolutions of commercial
instruments less than 10 μm. Ion guns with focused beams have also become available so that faster
sputtering of smaller regions on a sample became possible. Recent materials developments (e.g. the
development of new gate oxides for semiconductor devices and the development of many types of
nanostructures) have stimulated the growing use of XPS with sputter-depth profiling. It has also
become necessary to obtain composition-depth profiles for inorganic and organic thin films without
causing significant damage. XPS with sputter-depth profiling of such materials has now become possible
with the development of buckminsterfullerene (C ), argon cluster, water cluster, and other cluster-
60
© ISO 2013 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 13424:2013(E)
ion sources. Low damage and low contamination by residual carbon have been reported in XPS depth
[7] [8] [9]
profiling of several polymers using an Ar cluster-ion beam and a C ion beam. Further details
60
are in Annex D.
6 Specimen handling
Various types of thin-film specimens of metals, semiconductors, inorganic compounds, and polymers
can be analysed by XPS. Guidelines for the preparation and mounting of specimens for analysis are given
[10] [11]
in ISO 18116 and ISO 18117.
7 Instrument and operating conditions
7.1 Instrument calibration
The following ISO procedures should be performed to calibrate or check the performance of the XPS
instrument or the analyst should check the instrument’s performance by following the manufacturer’s
instructions or equivalent documentation.
[12]
a) calibration and checks of the binding-energy scale with ISO 15472
[13]
b) checks of the repeatability and constancy of the intensity scale with ISO 24237
[14]
c) checks of the linearity of the intensity scale with ISO 21270
7.2 Operating conditions
7.2.1 Energy resolution
The main purpose of a wide scan is qualitative analysis. A full width at half maximum (FWHM) for the
Ag 3d photoelectron peak of 2 eV is recommended for a wide scan. Narrow-scan spectra will provide
5/2
quantitative information and chemical-state information and an energy resolution of less than 1 eV
FWHM for the Ag 3d peak is recommended.
5/2
7.2.2 Energy range and step size
The energy range for a wide-scan spectrum shall be large enough to include the C KLL Auger peak and
other potentially valuable peaks for the planned XPS analysis. The energy range should be 1 200 eV for Mg
Kα X-rays and 1 400 eV for Al Kα X-rays. A step size of 1,0 eV is adequate when the energy resolution for a
wide scan described in 7.2.1 is about 2 eV. For narrow scans (i.e. for chemical state analysis, quantification,
or other mathematical manipulations of the XPS data), the step size should be 0,05 eV or 0,1 eV.
7.2.3 Multiple scans
Multiple scans are recommended for the acquisition of both wide scans and narrow scans to allow
checks to be made of any changes in the XPS spectrum with time (e.g. can occur due to changes in X-ray
intensity or to sample damage under X-ray irradiation).
7.2.4 Charge control and charge correction
Surface charging is likely for insulating samples. Techniques for charge control and charge correction
[15]
are described in ISO 19318. It is often convenient to use a reference C 1s binding energy between
[16]
284,6 eV and 285 eV for an observed peak due to carbonaceous contamination. It is often very difficult
to control the surface potential of a rough surface.
4 © ISO 2013 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 13424:2013(E)
8 Reporting XPS method, experimental conditions, analysis parameters, and
analytical results
8.1 XPS method for thin-film analysis
The method chosen for XPS thin-film analysis (as summarized in Clause 5 and described in Annexes A,
B, C, and D) shall be reported.
EXAMPLE 1 Angle-resolved XPS.
EXAMPLE 2 Peak-shape analysis.
EXAMPLE 3 XPS with sputter-depth profiling.
8.2 Experimental conditions
8.2.1 Introduction
The experimental conditions for the XPS measurements shall be reported. Values of the parameters
described in 8.2 shall be reported. In addition, information on the XPS instrument and the experimental
conditions described here shall be reported. Examples of experimental parameters and their descriptions
are given in Table 2.
8.2.2 XPS instrument
The name and model of the instrument used for the XPS measurements shall be reported. If any
components on the instrument are not standard for the particular model, information shall be provided
on the manufacturer or on the relevant design characteristics.
EXAMPLE The instrument used for the XPS experiments was a PHI Quantera SXM.
8.2.3 XPS analyser
Analyser conditions including the electron energy analyser, the acceptance angle of the input lens, the
analysed area on the sample from which signals are detected, the pass energy in eV, the energy resolution
in eV, the measured binding energy ranges for each peak in eV, and the energy step in eV shall be reported.
2
EXAMPLE The acceptance angle of the analyser was ±20°, the acceptance area was 1 × 0,5 mm , the pass
energy was 55 eV, the energy resolution for the XPS measurements with the X-ray source of 8.2.4 was 0,6 eV, the
measured binding energy range for the Si 2p peak was 115 eV to 95 eV, and the energy step was 0,1 eV.
8.2.4 X-ray source
The type of X-ray source (e.g. Mg Kα, Al Kα, monochromatic Al Kα, use of other anodes in the X-ray
source, or synchrotron radiation), the photon energy in eV, the irradiation area on the sample, and the
power dissipated in the X-ray anode shall be reported. The X-ray spot size should be described together
with its measurement method, if known.
EXAMPLE 1 Monochromatic Al Kα X-rays were used, the photon energy was 1 486,6 eV, the power in the X-ray
2
anode was 50 W, and the irradiation area on the sample was 1,5 × 0,4 mm . The X-ray spot was circular with a
diameter estimated using the knife-edge method of 100 μm. The spot diameter was measured from a line scan and
corresponded to the distance between the points where the photoelectron intensity was 50 % of the difference in
the intensities in the plateau regions away from each edge in the direction of the scan.
EXAMPLE 2 Conventional Mg Kα X-rays were used, the photon energy was 1 253,6 eV, and the irradiation area
2
on the sample was approximately 10 × 20 mm at 300 W.
© ISO 2013 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO 13424:2013(E)
8.2.5 XPS configuration
The XPS configuration including the angle between the X-ray direction on the sample and the average
analyser acceptance direction, the angle of X-ray incidence on the sample with respect to the surface
normal, the photoelectron emission angles with respect to the surface normal, and the analyser azimuth
angle with respect to the plane of X-ray incidence shall be reported.
EXAMPLE The angle between the X-ray direction and the analyser axis was 45°, the X-rays were incident
normally on the sample surface, the emission angles of the photoelectrons were 0°, 25°, 37°, 45°, 53°, and 58° with
respect to the surface normal, and the analyser azimuth was 22,5° with respect to the plane of X-ray incidence.
8.2.6 Charge control
The particular instrumental component(s) used for charge control shall be reported. The particular
experimental conditions for charge control (such as the beam voltage in V and the total beam current in
μA for the electron beam from a flood gun) shall be reported.
EXAMPLE For the flood gun, the beam voltage was −1,4 V (with respect to instrumental ground) and the total
beam current was 10 μA measured on clean silver.
8.2.7 Ion gun parameters for sputter-depth profiling
Ion gun parameters for sputter-depth profiling such as ion species, beam voltage, beam current, spot
size, raster size, incidence angle, sputter rate, and mass filter (if used) shall be reported.
+
EXAMPLE 1 The ion species was Ar , the beam voltage was 1 kV, the beam current was 500 nA, the spot size was
2
300 μm, the raster size was 2 × 2 mm , the incidence angle was 45°, and the sputter rate for SiO was 3 nm/min.
2
+
EXAMPLE 2 The ion species was C , the beam voltage was 10 kV, the beam current was 10 nA, the spot size
60
2
was 100 μm, the raster size was 2 × 2 mm , the incidence angle was 20°, the sputter rate for SiO was 3 nm/min,
2
and a mass filter was used to choose a 10 keV C ion beam.
60
8.3 Analysis parameters
8.3.1 Introduction
All methods and parameters used in the data analysis shall be reported. Some methods and parameters
such as the transmission-function correction for the analyser, the method used for peak-intensity
calculation (such as peak area or peak height), and the method used for background subtraction (and
the starting and ending energies) are common to all XPS methods described here. If film compositions
are reported, the type of relative sensitivity factor and the values of these factors shall be reported for
each peak. Examples of analysis parameters and their descriptions are given in Table 3.
EXAMPLE The transmission-function correction was made from measurements of peak area/pass energy
versus retarding ratio, peak areas were used for intensity calculations, the iterated Shirley background was used,
the starting and ending binding energies for the Si 2p peak were 107 eV and 97 eV, respectively, and the average
matrix relative sensitivity factors for the Si 2p was 0,368.
8.3.2 IMFP
Values of the IMFPs used in film-thickness calculations by general XPS, peak-shape analysis, and XPS
with sputter-depth profiling shall be reported together with the source of the data.
[17]
EXAMPLE The IMFP for the Si 2p peak with Al Kα X-rays of 3,2 nm was obtained from the TPP-2M equation.
6 © ISO 2013 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 13424:2013(E)
8.3.3 Single-scattering albedo
Values of the single-scattering albedo, if used in film-thickness calculations as described in Annex A,
should be reported.
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.