ISO 13424:2013

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 2013
© ISO 2013
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ii © ISO 2013 – All rights reserved

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
Foreword
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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

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.
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
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

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-
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
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

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.
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
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
on the sample was approximately 10 × 20 mm at 300 W.
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
300 μm, the raster size was 2 × 2 mm , the incidence angle was 45°, and the sputter rate for SiO was 3 nm/min.
+
EXAMPLE 2 The ion species was C , the beam voltage was 10 kV, the beam current was 10 nA, the spot size
was 100 μm, the raster size was 2 × 2 mm , the incidence angle was 20°, the sputter rate for SiO was 3 nm/min,
and a mass filter was used to choose a 10 keV C ion beam.
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

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.
EXAMPLE The single-scattering albedo for the Si 2p peak with Al Kα X-rays was 0,111. This value was
[18]
calculated from the ratio of the IMFP to the sum of the IMFP and TRMFP, as described in Annex A.
8.3.4 Parameters for peak-shape analysis
The chosen structure model (e.g. buried thin film, exponential depth profile, homogeneous depth profile,
substrate with overlayer) and values of the parameters B, C, and D in the selected Tougaard inelastic-
[83]
scattering cross-section formula (e.g. for metals and oxides, polymers, SiO , Si, Ge, and Al ) shall be
reported. Information on the structure models and the various parameters is given in Annex C.
EXAMPLE A substrate with an overlayer was the chosen morphology model and recommended values of the
2 2
parameters B and C for metals and oxides of 2 866 eV and 1 643 eV , respectively, were used (the parameter D
was not used).
8.3.5 Parameters for angle-resolved XPS
The type of algorithm used for depth profile reconstruction shall be reported. If the maximum entropy
algorithm is used, the value of the regularizing constant for the final results shall be reported. Any
corrections applied in the calculation of the depth profiles (e.g. for the asymmetry parameter, sample
crystallinity, surface roughness, and elastic scattering) shall be reported. Information on analysis
algorithms and corrections is given in Annex B.
EXAMPLE The maximum entropy method was used. The value of the regularizing constant α was fixed at
−4 [19]
5 × 10 during the calculation.
8.3.6 Special methods
Any special methods used for data analysis (e.g. curve fits to extract chemical states, linear least-square
fitting, target factor analysis) shall be reported.
EXAMPLE A curve fit was applied to the Si 2p spectrum to determine the intensities of the metal and oxide
chemical states.
8.4 Examples of summary tables
Summary tables for methods, acquisition parameters, and analysis parameters, as shown in Tables 2
and 3, can be convenient and useful for day-to-day use.
Table 2 — Examples of experimental conditions to be reported, as described in 8.2
Parameters Description
Date 2010–04–01
Sample description SiO (2,0 nm)/Si(100) (substrate)
XPS method Film thickness analysis
Peak-shape analysis
XPS instrument PHI Quantera SXM
XPS configuration
Angle between analyser and X-ray source 45°
Emission angle 45°
Analyser azimuth 22,5° with respect to the plane of X-ray incidence
Analyser condition
Table 2 (continued)
Parameters Description
Type of electron energy analyser Concentric hemispherical analyser (CHA)
Acceptance angle ±20°
Acceptance area 1 × 0,5 mm
Photoelectron peak 1 Si 2p
Energy range 112 ~ 92 eV
Energy step 0,1 eV
Pass energy 55,0 eV
Photoelectron peak 2 O 1 s
Energy range 542 ~ 522 eV
Energy step 0,1 eV
Pass energy 55,0 eV
Photoelectron peak 1 C 1s
Energy range 298 ~ 278 eV
Energy step 0,1 eV
Pass energy 55,0 eV
X-ray source condition
Type of X-ray source, energy, and power Monochromatized Al Kα, 1 486,6 eV, 25 W
Expected spot size 100 μm in diameter
Charge control 1,4 eV 10 μΑ electron and 7 eV 35 nA Ar ion beam irradiation
Sputter on beam Not used for this analysis but typical value for sputter clean-
ing is described below
Gas species Ar
Beam voltage and current 1 kV, 500 nA
Spot size 300 μm in diameter
Raster size 2 × 2 mm
Incident angle 40°
Sputter rate for SiO 3 nm/min
Mass filter None
8 © ISO 2013 – All rights reserved

Table 3 — Examples of analysis parameters to be reported, as described in 8.3
Parameters Description
Analysis mode Film thickness
General parameter The transmission-function correction was made from meas-
urements 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 bind-
ing energies for the Si 2p peak were 107 eV and 97 eV, respec-
tively, and the average matrix relative sensitivity factors for
the Si 2p peak was 0,368
Inelastic mean free path 3,2 nm for Si 2p peak with Al Kα X-rays
Single-scattering albedo ω = 0,111 for Si 2p peak with Al Kα X-rays
Parameters for peak-shape analysis Not applicable
Parameters for angle-resolved XPS Not applicable
Special method Curve fit to extract elemental Si and Si oxide peaks
8.5 Analytical Results
Depending on the detail requested by a customer, the following analytical results shall be reported
together with the chosen analysis method (as listed in Table 1).
a) film layer order
b) film thickness and composition
c) composition as a function of depth
[20]
The recording and reporting of these information should follow ISO 16243.
Details and examples of the XPS analysis methods described are shown in Annexes A, B, C, and D. Table 1
can be used to select an analysis method that is suitable for the desired information.
Annex A
(informative)
General XPS
A.1 Introduction
Methods to obtain thin-film thickness, thin-film composition, and the structure of a multilayer film
are described. In structure analysis, the relative order of the layers above the substrate or the relative
depths of different functional groups can be obtained.
A.2 Symbols and abbreviated terms
AMRSF Average matrix relative sensitivity factor
ARSF Atomic relative sensitivity factor
EAL Effective attenuation length
E Energy of the photoelectron emitted from the overlayer
f
E Energy of the photoelectron emitted from the substrate
s
ERSF Elemental relative sensitivity factor
θ
L
Intensity of component “A” at lower emission angle
I
A
θ
H Intensity of component “A” at higher emission angle
I
A
θ
L Intensity of component “B” at lower emission angle
I
B
θ
H
Intensity of component “B” at higher emission angle
I
B
I Intensity of photoelectrons emitted from the overlayer (“overlayer signal”)
f
I Intensity of photoelectrons emitted from nth layer from the top
n
I Intensity of photoelectrons emitted from n+1th layer from the top
n+1
I Intensity of photoelectrons emitted from the substrate and transmitted through the thin-film over-
s
layers
f
Intensity of photoelectrons emitted from the semi-infinite overlayer material
I
s
Intensity of photoelectrons emitted from the semi-infinite substrate
I
L Effective attenuation length of the photoelectron in the nth layer
n
L Effective attenuation length of the photoelectron in the n+1th layer
n+1
L(E) Effective attenuation length at kinetic energy E
10 © ISO 2013 – All rights reserved

N Atomic density of the oxide overlayer
N Atomic density of the substrate
e
Q Elastic-scattering correction factor in the overlayer
o
Q Elastic-scattering correction factor in the substrate
e
R Ratio of intensities at high emission angles of component A to B and low emission angles of component
A/B
A to B
R Ratio of intensities for photoelectrons emitted from the oxide-overlayer and the substrate
expt
RSF Relative sensitivity factor
R Ratio of intensities of photoelectrons emitted from the bulk oxide and the bulk substrate material
o
s Relative sensitivity factor of the component in the nth layer
n
s Relative sensitivity factor of the component in the n+1th layer
n+1
t Thickness of the thin-film overlayer
t Thickness of the nth layer
n
t Thickness of the n+1th layer
n+1
W(β,γ) Angular distribution of photoemission from an atom as a function of β and γ
W Angular distribution of photoelectrons emitted from the overlayer
o
W Angular distribution of photoelectrons emitted from the substrate
e
x Atomic fraction of the target element of the substrate
e
x Atomic fraction of the target element of the overlayer
x Atomic fraction of the element i
i
Z Atomic number of an element
Z Average atomic number
av
α Angle of photoelectron emission with respect to the surface normal of the sample
β Effective asymmetry parameter, accounting for effects of elastic scattering on the photoelectron
eff
angular distribution in a solid
Γ Angle between the direction of X-rays and the mean direction towards the analyser
Γ Calculated, averaged, and interpolated coefficients for determining ζ
i
ζ Ratio of the transport mean free path to the inelastic mean free path
λ Inelastic mean free path
i
λ Inelastic mean free path in the bulk substrate
e
λ Inelastic mean free path in the bulk overlayer
λ Transport mean free path
tr
ω Single-scattering albedo
A.3 Film thickness analysis
The thickness of overlayer thin films can be measured by XPS when the overlayer film is homogeneous
and uniform.
When the film thickness is less than about three times the MED for the target photoelectron peak and
[21]
α ≤ 58°, the overlayer film thickness t can be determined from Formula (A.1).
 
I
s
tL= ()E cosαln (A.1)
s  
s
I
 0 
or
 I 
f
tL= E coslα n 1− (A.2)
()
 
f f
I
 0 
where
α is the angle of photoelectron emission (with respect to the surface normal);
L(E ) and are effective attenuation lengths (EALs) in the overlayer film at the substrate photo-
s
L(E ) electron energy E and the overlayer film energy E , respectively;
f s f
s
I and I are photoelectron intensities measured from the substrate with the overlayer film and
s 0
the bare substrate, respectively;
f
I and I are measured intensities from the film and a thick layer of that film, respectively.
f 0
[22]
For peak intensity measurements, ISO 20903 should be utilized.
12 © ISO 2013 – All rights reserved

[2] [21]
The EAL can be estimated from Formula (A.3) when α ≤ 50° or from Formula (A.4) when α ≤ 58°
L(E) = λ (1 – 0,735ω)
i
(A.3)
or
L(E) = 0,979 λ [ 1 – ω (0,955 – 0,077 ln Z)]
i
(A.4)
where
λ 1
i
ω= = (A.5)
λλ+ 1+ζ
itr
[18]
The value of ζ for element i can be estimated from Formula (A.6).
3 2
ζ = exp[Γ ln E + Γ ln E +Γ lnE +Γ ]
i i,3 i i,2 i i,1 i i,0
(A.6)
where the values of Γ , Γ , Γ andΓ for element i can be obtained from a table in Reference [32]. For
i,3 i,2 i,1, i,0
compounds or alloys, the Γ values for a material m can be estimated from the average atomic number
m
Z for that material.
av
Zx= Z (A.7)
av ∑ ii
Values of Γ for Z can then be selected from the table in Reference [32]. If Z is not an integer, one can
m av av
[18]
interpolate using Γ values for neighbouring elements.
m
[17][32] [23]
Values of λ can be obtained from the predictive TPP-2M equation and a database. Values of λ
i tr
[24][25] [26] [27]
can be obtained from two databases, the computer code ELSEPA, and a predictive equation.
For a metal substrate with its oxide as an overlayer, the film thickness can be calculated using
[28]
Formula (A.8).
R
 
expt
tL=+()E cosα 1 (A.8)
 
R
o
 
where
R is the ratio of photoelectron intensities from the oxide overlayer and the elemental
expt
substrate;
R is the corresponding ratio for the bulk solids (or sufficiently thick films).
o
It is recommended that R be measured experimentally using the same peak-fitting algorithm as that
o
used for the analysis of the spectrum for the oxide sample to obtain an accurate measurement of the film
[19]
thickness. The value R can also be calculated from References [21], [29], and [30].
xN QW(,αω) λ
oo oo o
R = (A.9)
o
xN QW(,αω) λ
ee ee e
 
W(,βγ)c=−13βγos −14 (A.10)
()
{}
effeff
 
4π
where
N is the atomic density in the oxide;
o
Q (α,ω) is the elastic-scattering correction factor in the oxide;
o
W is the angular distribution of photoelectrons from the oxide;
o
λ is the inelastic mean free path in the oxide;
o
N , Q (α,ω), W , and λ are the corresponding quantities in the substrate.
e e e e
[31]
Guidelines for background subtraction from the obtained spectra are given in ISO/TR 18392 and
[22]
ISO 20903.
A.4 Chemical composition
RSFs are commonly used for quantification of unknown samples. The use of AMRSFs is recommended
[32]
for photoelectron energies larger than 200 eV. Guidelines for the quantitative surface analysis by XPS
[32]
are given in ISO 18118.
NOTE The use of RSFs is only recommended when the thin film is homogeneous and its surface is flat.
A.5 Structure analysis
In practical thin-film analysis, it is important to determine the relative order of the layers above the
substrate or the relative position (depth) of different functional groups such as C = O, NO within a
particular layer. Seah et al. proposed a simple method to estimate the layer order by measuring the
change of peak-intensity ratios of components at two-emission-angles (that were recommended to be
[33]
0° and more than 70° relative to the sample normal). This method is called structure analysis and is
utilized to determine the relative depths (from the surface) of layers in the sample. The larger the ratio
of the photoelectron signal at the high emission angle to the low emission angle, the closer is the layer to
the surface. Figure A.1 shows an example of spectra measured at low and high emission angles and Table
A.1 shows the layer order established from the intensity ratios.
The same approach can also be used to estimate layer thicknesses and compositions. We designate the
θ θ
L H
intensities of component “A” at lower and higher emission angles as I and I , respectively. Similarly,
A A
θ θ
L H
the intensities of component “B” at lower and higher emission angles are I and I , respectively. The
B B
ratio is then calculated as:
θ θ
H L
I I
A B
R =�� (A.11)
AB/ θ θ
L H
I I
A B
If R is larger than 1, component “A” is located above component “B” if the EALs of each component
A/B
are almost the same. The relative depths of all components can be estimated by this procedure. If R
A/B
is close to 1, these components would be in the same layer. If R is smaller than 1, component “A” is
A/B
located under component “B”.
14 © ISO 2013 – All rights reserved

After determination of layer order, iterated calculations can be performed for the intensity ratios using
Formula (A12) to minimize the differences between calculated and measured intensities by changing
[34]
the compositions and thicknesses of each layer.
 
I st L 1 tt+⋅⋅⋅+ tt+⋅⋅⋅+ 
n nn n+1 n 1 n−1 11
=×exp − (A.12)
 
 
I st L cosα L L
n+1 nn++11 n  n+1 n 
 
[35]
The ratio of EALs in Formula (A.12) can be estimated from Formula (A.13).
07, 5
Ln++11 En 
= (A.13)
   
Ln En
   
Formula (A.13) neglects any change in the atomic relative sensitivity factors for pa
...