ISO 22415:2019

INTERNATIONAL ISO
STANDARD 22415
First edition
2019-05
Surface chemical analysis —
Secondary ion mass spectrometry
— Method for determining yield
volume in argon cluster sputter depth
profiling of organic materials
Analyse chimique des surfaces — Spectrométrie de masse des ions
secondaires — Méthode de détermination du rendement volumique
dans le cadre du profilage en profondeur de matériaux organiques
par pulvérisation d'argon en grappe
Reference number
©
ISO 2019
© ISO 2019
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Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols (and abbreviated terms) . 1
5 Requirements . 3
5.1 Test samples . 3
5.2 Sputtering ion source . 3
5.3 Analysis conditions . 4
6 Data Acquisition . 5
6.1 Analysis. 5
6.2 Minimum data requirements . 6
6.3 Data quality . 6
7 Calculation of sputtering yield volume . 6
7.1 Introduction . 6
7.2 Determination of sputtering yield volume for a single layer profile . 7
7.2.1 Introduction . 7
7.2.2 First interface position . 7
7.2.3 Interface position between two materials . 7
7.2.4 Sputtering time. 7
7.2.5 Calculation of sputtering yield volume using a single layer thickness . 8
7.3 Determination of sputtering yield volume from profiles of layers of more than one
thickness . 9
7.3.1 Introduction . 9
7.3.2 First interface . 9
7.3.3 Interface between two materials . 9
7.3.4 Areic dose of ions used for sputtering . .10
7.3.5 Calculation of sputtering yield volume using more than one-layer thickness .11
8 Reporting of sputtering yield volume .11
8.1 Required information .11
Annex A (informative) Sputtered area and sputtering beam width.13
Annex B (informative) Examples of depth profile data .18
Annex C (informative) Estimation of sputtering yield volumes for argon clusters .28
Bibliography .30
Foreword
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This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 6, Secondary ion mass spectrometry.
A list of all parts in the ISO 22415 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv © ISO 2019 – All rights reserved

Introduction
In many technological and biological samples, it is necessary to understand the distribution of organic
chemical species as a function of depth and to combine this with laterally resolved surface chemistry
to provide three-dimensional representations. Secondary ion mass spectrometry is a method capable
of determining depth distribution combined with lateral information. Argon cluster ion beams can
provide sputter depth profiles through most organic materials without causing significant damage and
molecular species may be detected and located by mass spectrometry. This approach can provide depth
resolutions better than 10 nm and depth profiles which extend over many micrometres in thickness. In
order to reconstruct a depth profile or three-dimensional image, it is important to establish the depth
scale in the depth profiling experiment. For this purpose, the sputtering yield volume is required.
The sputtering yield volume defines the ratio between the areic dose of sputtering ions and the
sputtered depth. Knowledge of the sputtering yield volume enables the depth of features of interest to be
determined from the sputtering ion current, the sputtered area and the sputtering time. The sputtering
yield volume depends upon the specific experimental conditions such as the sample temperature, the
material being sputtered, the cluster source identity, kinetic energy and angle of incidence. However, the
prediction of sputtering yield volumes for a particular material is possible using measurements made
from the same material under different experimental conditions. Therefore, reliable measurements of
sputtering yield volumes are required for accurate measurement of depth, to provide comparability
between laboratories and to enable analysts to implement and use sputtering yield volumes reported
by others.
This document provides methods to measure sputtering yield volumes of organic test materials using
argon cluster ions. The test materials should consist of thin films of known thicknesses between 50 nm
and 1 000 nm. The format of the test materials, the measurement of sputtering ion dose, sputtered depth
and reporting requirements for sputtering yield volumes are described. Annex A provides informative
definitions of sputtered area and sputtering beam width and an example of their measurement. Annex B
provides informative examples of typical depth profiles and an example calculation of sputtering yield
volume. Annex C provides informative methods to estimate sputtering yield volumes under different
sputtering conditions.
INTERNATIONAL STANDARD ISO 22415:2019(E)
Surface chemical analysis — Secondary ion mass
spectrometry — Method for determining yield volume in
argon cluster sputter depth profiling of organic materials
1 Scope
This document specifies a method for measuring and reporting argon cluster sputtering yield volumes
of a specific organic material. The method requires one or more test samples of the specified material
as a thin, uniform film of known thickness between 50 and 1 000 nanometres on a flat substrate
which has a different chemical composition to the specified material. This document is applicable to
test samples in which the specified material layer has homogeneous composition in depth and is not
applicable if the depth distribution of compounds in the specified material is inhomogeneous. This
document is applicable to instruments in which the sputtering ion beam irradiates the sample using a
raster to ensure a constant ion dose over the analysis area.
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 18115-1:2013, 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 given in ISO 18115-1:2013 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/
4 Symbols (and abbreviated terms)
a number of secondary ions used to determine Y
b number of layers of different thicknesses used to determine Y
A area of the raster pattern of the sputtering beam on the sample
d known thickness of material for which the sputtering yield volume is to be measured
D areic dose of ions used for sputtering
δ relative standard uncertainty in A
A
δ relative standard uncertainty in d for a specified layer
d
δ relative standard uncertainty in the current during a specified profile
J
δ relative standard uncertainty in average cluster size during a specified profile
n
δ relative standard uncertainty in sputtering time in a specified profile
τ
δ relative standard uncertainty in the sputtering yield volume for a specified profile
y
δ relative standard uncertainty in the sputtering yield volume
Y
Δt absolute difference in time between t(16) and t(84)
Δt width of the first interface in sputtering time
Δt width of the second interface in sputtering time
−19
e elementary charge, 1,602 × 10 Coulombs
E kinetic energy of primary argon cluster ions used for sputtering in eV
FWHM full width at half maximum
i identifier for the secondary ions monitored in experiments
J current of ions used for sputtering measured before analysis in Amperes
J current of ions used for sputtering measured after analysis in Amperes
J current of primary ions used for analysis in Amperes
a
k identifier for the different layers of the test material
l side length of the analysed area on the sample
L minimum side length of sputtering area on the sample
n average number of argon atoms per ion in the primary cluster
n average number of argon atoms per ion in the primary argon cluster measured before analysis
n average number of argon atoms per ion in the primary argon cluster measured after analysis
N number of lines in sputtering beam raster pattern
q number of elementary charges on a primary ion
σ standard uncertainty in d for a specified layer
d
σ standard uncertainty in Y
Y
t sputtering time to reach the first interface of the organic material in seconds
t sputtering time to reach the second interface of the organic material in seconds
t(x) sputtering time for secondary ion intensity to reach x % of that in the pure material in seconds
τ sputtering time through a layer of thickness d in a specified profile in seconds
τ’ gradient in a graph of τ plotted against d
2 © ISO 2019 – All rights reserved

W maximum FWHM of sputtering ion beam spot on the sample
y sputtering yield volume determined for a specified ion from the slope of a graph of dose, D, on
the x-axis and thickness, d, on the y-axis
Y sputtering yield volume
5 Requirements
5.1 Test samples
The test sample(s) shall consist of one or more layers of organic materials of uniform thicknesses on a
flat substrate. The chemical composition of the organic materials and substrate used to construct the
test sample(s) shall be known. The thickness of each layer of material for which the sputtering yield
volume is to be measured shall be known for each sample. The standard uncertainty in thickness from
both the measurement method and variability in thickness shall be known or estimated. If the test
sample consists of more than one layer of organic material, the order in which those layers are formed
shall be known. The test sample(s) shall be classified according to the sample construction as either:
a) A surface layer: if the first interface of the material is the surface of the test sample.
b) A buried layer: if the first interface of the material is not at the surface of the test sample.
c) A series of layers: if there is more than one layer of the material, with thicknesses spanning at
least a factor of 1,5 and having the same first and second interfaces for all layers.
The first interface is the initial boundary of the material encountered in a sputter depth profile. The
second interface is the final boundary of the material encountered in a sputter depth profile. The series
of layers is the more accurate method for determination of the sputtering yield volume but requires
most effort.
NOTE 1 Typical methods used to prepare reference samples are vapour deposition, spin casting from
appropriate solvents, Langmuir-Blodgett or Langmuir-Schaefer deposition.
NOTE 2 In the case of single layers of organic materials on inorganic substrates, the most appropriate methods
[1]
to directly measure layer thickness are atomic force microscopy (AFM), ellipsometry and X-ray reflectometry .
For multiple layers, these methods typically provide insufficient contrast between different organic materials
and other approaches, such as in situ measurements using a quartz crystal microbalance or analysis after each
deposition step, are appropriate.
5.2 Sputtering ion source
To ensure that the data required to calculate sputtering yield volumes are useful and that the reporting
requirements are met, the following information and conditions are required.
a) The number weighted mean size of the argon clusters, n , used for sputtering shall be measured
before analysis and the number weighted mean size of the argon clusters, n , shall be measured
after analysis.
b) The sputtering ion kinetic energy, E, shall be known.
c) The sputtering ion charge, q, shall be known.
d) The incidence angle between the sputtering ion beam and the reference sample surface normal
shall be known.
e) The sputtering ion current, J , shall be measured using a Faraday cup before analysis of the reference
sample and the sputtering ion current, J , shall be measured after analysis of the reference sample
in the same manner as J . See 6.1.
f) The minimum side length, L, and the area, A, of the raster pattern of the primary ion source on the
sample shall be measured.
g) The maximum full width at half maximum (FWHM) of the sputtering ion beam spot on the sample,
W, shall be measured.
h) The number of lines in the raster pattern, N, shall be known.
i) The sputtering and analysis cycle shall be set to ensure that raster frames of the sputtering source
are complete and without gaps.
j) The ambient sample temperature shall be measured.
The FWHM of the sputtering ion beam spot shall be greater than twice the distance between adjacent
lines in the raster pattern, this condition is expressed in Formula (1). If this condition is not met then,
either the ion beam shall be defocussed to increase W, or the raster area changed to decrease L until
this condition is satisfied.
LN<05, W (1)
where
L is the minimum side length of sputtering area on the sample;
N is the number of lines in the sputtering beam raster pattern;
W is the maximum FWHM of the sputtering ion beam spot on the sample.
The minimum side length of the sputtering source raster, L, shall be larger than the maximum FWHM of
the sputtering ion spot, W, by at least a factor of 8. This condition is expressed in Formula (2).
LW> 8 (2)
If this condition is not met then either the ion beam shall be focussed to decrease W, or the raster size
changed to increase L until this condition is satisfied and does not violate the condition described by
Formula (1).
NOTE 1 A diagram is provided for information in A.1.1. The area of the raster pattern can be measured by
imaging a reference grid positioned at the same height as the test sample. A method is provided in A.1.2 and an
example in A.1.3.
NOTE 2 The condition expressed in Formula (1) ensures a constant ion beam dose in the analysed area both
[2]
on and between raster lines .
NOTE 3 The condition expressed in Formula (2) ensures that the central part of the sputtered area on the
sample, which has a constant ion beam dose, is large enough to be analysed.
5.3 Analysis conditions
The size and position of the area for analysis shall be within the area irradiated by the sputtering
source. The centre of the analysis area shall be aligned with the centre of the sputtered area and have
side length, l, meeting the condition expressed in Formula (3). If the sputtering ion beam is used for
4 © ISO 2019 – All rights reserved

analysis, then the gating conditions to select the signal as a function of raster position shall be selected
to meet this criterion.
lL<−6W (3)
where l is the side length of the analysed area on sample.
NOTE The condition expressed in Formula (3) is to ensure that the area analysed receives a laterally
invariant dose of sputtering ions and that the analysis beam does not sample areas that, due to edge effects, have
received a lower dose than the centre. A diagram is provided in A.1.1.
If a different primary ion beam is used for analysis the alignment of the two ion beams on the sample
shall be within a distance W/2. In this case, the primary ion source used for analysis shall have a dose
rate much smaller than the sputtering source. The time-averaged current of the analytical primary ion
beam on the sample shall meet the criterion expressed in Formula (4) see also NOTE 1 below.
l
JJ<00, 5 (4)
a 1
A
where
J is the time averaged current of primary ions used for analysis;
a
J is the current of primary ions used for sputtering measured before analysis;
l is the side length of the analysed area on sample;
A is the area of the raster pattern of the sputtering beam on sample.
If this condition is not met then J or A shall be reduced or J or l increased until the condition is met,
a 1
whilst also meeting the conditions expressed in Formulae (1), (2) and (3). The ratio of J to J can be
a 1
altered by changing the ratio of sputtering cycles to analysis cycles, or the duty cycle of the analytical
primary ion beam in time-of-flight systems.
Charge compensation using an electron flood gun is usually required. If it is necessary to use electrons
for charge compensation the electron beam current should be kept as low as possible to avoid
unintended damage to the sample.
It is usually necessary to use an area of the test sample to optimise the analysis conditions. If this is the
case, the position of the area used for optimisation shall be selected to be as far as possible from areas
that will be used for the determination of sputtering yield volume.
If it is suspected that the primary ions used for analysis have a significantly higher sputtering yield
volume than that of the sputtering ions then the factor 0,05 in Formula (4) shall be replaced by the
product of 0,05 and the ratio of the expected sputtering yield volume of the sputtering ion to that of the
analysis ion.
NOTE 1 The condition expressed in Formula (4) is derived from reference [3] where the sputtering and
analysis ions have similar sputtering yield volumes in the test material.
6 Data Acquisition
6.1 Analysis
The analysis position on the sample shall be chosen to maintain a suitable distance from the edge of
the sample and other areas where non-homogeneous thickness or surface damage is suspected. If an
electron flood source is used, the separation of areas used for instrument set up and analysis shall be
as large as possible to avoid areas previously irradiated by the electron flood gun. The sputtering ion
current J shall be recorded using a Faraday cup prior to the start of each profile. Then the depth profile
is performed at the selected analysis position, see 6.2. Finally, the sputtering ion current J shall be
recorded using a Faraday cup immediately after the profile is complete. If the ratio of J and J is greater
1 2
than 1,1 or less than 0,9 then the data from the depth profile shall not be used to calculate a sputtering
yield volume.
NOTE 1 The effect of electron-induced surface damage on sputtering yields is described in reference [4].
6.2 Minimum data requirements
The intensities of secondary ions which display visibly and identifiably greater intensity for the
material of interest in the sample, compared to the other materials, shall be measured as a function of
sputtering time. More than one secondary ion from the material for which the sputtering yield volume
is to be determined shall have their intensities measured. This condition applies even in the case of a
surface or buried layer, where only one secondary ion is employed for the measurement of sputtering
yield volume, because selected secondary ions may be rejected in the data quality check in 6.3.
By preference, one of the secondary ions unique to the material for which the sputtering yield volume is
to be determined should be atomic or diatomic.
NOTE 1 Atomic or diatomic secondary ions are likely to exhibit smaller matrix effects than molecular
secondary ions as demonstrated in reference [5].
6.3 Data quality
After the depth profiles are complete, the intensities of the selected secondary ions shall be plotted as
a function of sputtering time and inspected visually. The secondary ion intensities shall have plateaus
of relatively constant (±10 %) intensity before and after each interface for a longer sputtering time than
the transition in intensity at the interfaces.
If there is an increase in secondary ion intensity at the interface above the plateau value for the pure
material and only one layer is being used to determine sputter yield volume, then the secondary ion
shall not be used to determine the sputtering yield volume: a different secondary ion shall be chosen.
NOTE 1 An increase in secondary ion intensity above the plateau for interfaces between two organic materials
[6]
indicates that significant matrix effects are occurring , whereas for a second interface between an organic
material and an inorganic material such effects are usually caused by an enhancement in sputtering yield close
to the interface. For secondary ions which are not specific to the material, interfacial contaminants can also
produce such features.
NOTE 2 If there is a decline in secondary ion intensity in the plateau region of all profiles and the absolute
intensities in the repeated profiles are similar then this strongly indicates that the sputtering yield volume is
[7]
not constant . If there is a decline in secondary ion intensity in the plateau region of all profiles and a decline
in absolute intensities in subsequent experiments, then this indicates that there is a decline in the primary ion
current used for analysis.
7 Calculation of sputtering yield volume
7.1 Introduction
In the case that only one thickness of material (b = 1) has been analysed, the procedure to locate
interfaces in sputtering time is to measure the sputtering time, through the layer of interest, τ and
calculate the sputtering yield volume, Y, as described in 7.2. In this case only one secondary ion is
required because the uncertainty in sputtering time is dominated by matrix effects. Without additional
knowledge, the uncertainty is not reduced by including more than one secondary ion in the analysis.
In the case that more than one thickness of material (b > 1) has been analysed, the procedure to locate
interfaces in sputtering time, measure sputtering time, τ, and calculate sputtering yield volume, Y, is
described in 7.3.
6 © ISO 2019 – All rights reserved

If the test samples a) or b) are used (a surface layer or a buried layer), follow the procedure in 7.2. If test
sample c) is used (a series of layers), follow the procedure in 7.3.
7.2 Determination of sputtering yield volume for a single layer profile
7.2.1 Introduction
For the depth profile of the selected secondary ion using known thickness of material, d, there will be
two interfaces, these are defined as the first interface and the second interface in order of sputtering
time. If the layer of interest is a surface layer, then the first interface is defined as that between the test
material and the vacuum.
7.2.2 First interface position
In the case that the test sample is a surface layer then the sputtering time to the first interface, t , and
the width of the first interface, Δt , shall both be set to zero. If the test sample is a buried layer, then the
procedure described in 7.2.3 shall be followed to determine t and Δt .
1 1
For surface layers, transient behaviour in secondary ion intensity can occur at the first interface. A
sharp exponential decay in intensity indicates either that damage occurs during the depth profile,
or if the material is a mixture, that one of the components has segregated to the surface. A sharp
rise in intensity of the form of an inverted exponential decay, indicates that some surface damage,
contamination or segregation from a mixture has occurred. If the initial intensity is less than 10 % of
the plateau intensity in the pure material, then the first interface shall be treated as a buried layer and
the values of t and Δt shall be determined using 7.2.3.
1 1
7.2.3 Interface position between two materials
For the selected secondary ion, the time positions at the interface where the intensity is 16 %, 50 % and
84 % of the difference between the plateau values before and after the interface shall be recorded as
t(16), t(50) and t(84). The value of Δt shall be calculated as the absolute difference between t(16) and
t(84). If the interface is the first interface in a buried layer then the sputtering time to the first interface,
t , and the width of the first interface, Δt , shall be equal to t(50) and Δt respectively. If the interface is
1 1
the second interface then the sputtering time to the second interface, t , and the width of the second
interface, Δt , shall be equal to t(50) and Δt respectively.
NOTE 1 The measurement of Δt is described in reference [8]. It is often convenient to fit the data with an
appropriate sigmoidal curve to determine t(16), t(50) and t(84). Examples are provided in Annex B.
NOTE 2 t(50) will, in general, not coincide with the position of the physical interface in the sputter depth
profile. The depth of production and origin of secondary ions causes interfaces to appear in different places for
[9]
different secondary ions with a range typically of the order of 3 nm and matrix effects cause significant shifts,
[6]
which can be as large as 0,5Δt . The bias is not necessarily reduced by analysing more secondary ions and the
uncertainty in sputtering time is provided in 7.2.4.
7.2.4 Sputtering time
The sputtering time through the layer of interest, τ, shall be calculated using Formula (5) and the
relative standard uncertainty in sputtering time, δ , estimated using Formula (6).
τ
τ =−tt (5)
δτ=+05,(ΔΔtt )/ (6)
τ 12
where
t is the sputtering time to the first interface;
t is the sputtering time to the second interface;
Δt is the width in sputtering time of the first interface;
Δt is the width in sputtering time of the second interface.
NOTE This estimation of δ accounts for matrix effects at the interface which are the primary source of
τ
[6]
uncertainty in the position of interfaces. The shift in the position measured as t(50) are as high as 0,5Δt and
are typically correlated, an example is shown in Annex B. Hence the interface widths are not added in quadrature.
7.2.5 Calculation of sputtering yield volume using a single layer thickness
The sputtering yield volume, Y, shall be calculated using Formula (7).
2qeAd
Y = (7)
()JJ+ τ
where
q is the number of elementary charges on a primary sputtering ion;
−19
e is the elementary charge, 1,602 × 10 Coulombs;
A is the area of the raster pattern of the sputtering beam on the sample;
d is the thickness of the layer for which the sputtering yield volume is to be measured;
J is the current of primary sputtering ions measured before analysis in amperes;
J is the current of primary sputtering ions measured after analysis in amperes;
τ is the sputtering time through the specified layer.
3 2
NOTE It is usual to express Y in nm and therefore it is convenient to convert A to nm and d to nm prior to
the calculation.
The relative standard uncertainty in Y, δ , shall be estimated using Formula (8).
Y
 
 
 
22 22 2 2
δδ=+δδ+++δδ (8)
Yd AJ τ n
 
 E 
 
1+
 
 
3n
 
 
where
δ is the relative standard uncertainty in thickness of the layer, σ / d;
d d
δ is the relative standard uncertainty in raster area of the sputtering ion beam;
A
δ is the relative standard uncertainty in the primary ion beam current;
J
δ is the relative standard uncertainty in τ;
τ
δ is the relative standard uncertainty in n;
n
E is the kinetic energy of primary argon cluster ions used for sputtering;
n is the average number of argon atoms per ion in the primary cluster (n + n )/2.
2 1
8 © ISO 2019 – All rights reserved

NOTE The factor in Formula (8) prior to the δ term is obtained by differentiation of Formula (C.1) given in
n
C.1 and using the typical values for parameters therein. This is described in C.2.
If the first interface of the organic material is the surface of the test sample or the second interface is
between the organic material and an inorganic material, then σ shall be set no smaller than 5 nm prior
d
to the calculation of δ . This accounts for secondary ion information depths and increased sputtering
d
yields at inorganic interfaces.
NOTE In the case of a first interface between two materials the secondary ion information depth does not
[6]
need to be accounted for because a similar information depth is expected at both the first and second interface .
2 2 2
The value of (δ ) shall be estimated as 2(J – J ) / (J + J ) .
J 2 1 2 1
NOTE This estimation of δ does not account for uncertainty in the current measurement and only accounts
J
for drift in current from the start to the end of the profile. It is assumed that uncertainty due to the accuracy of
the current measurement method is negligible compared to other sources of uncertainty. If (δ ) is greater than
J
0,002 5, the requirement on beam current drift can be checked as per 6.1.
2 2 2
The value of (δ ) shall be estimated as 2(n – n ) / (n + n ) .
n 2 1 2 1
NOTE This estimation of δ does not account for uncertainty in the average number of atoms per ion and
n
only accounts for drift in cluster size from the start to the end of the profile.
Reporting the results of these calculations is specified in Clause 8.
7.3 Determination of sputtering yield volume from profiles of layers of more than one
thickness
7.3.1 Introduction
For each depth profile of known thickness of material, d , and selected secondary ion, i , there will be two
k k
interfaces, these are defined as the first interface and the second interface in order of sputtering time.
The determination of interface positions does not require accuracy in this case, because the difference
in sputtering times for different thicknesses permits bias in the measurement to be eliminated. In 7.3.2
to 7.3.4, the calculation of areic doses, D , for each layer, k, and secondary ion, i, is described. Subscripts
ik
are dropped for convenience until the data are combined in 7.3.5.
7.3.2 First interface
In the case that the first interface is the surface of the material, then the method in 7.2.2 shall be applied
to obtain t .
7.3.3 Interface between two materials
If the intensity at the interface does not exceed the plateau regions, the time position at the interface
where the intensity is 50 % of the difference between the plateau values before and after the interface
shall be recorded as t(50). If the interface is the first interface then the sputtering time to the first
interface, t , shall be equal to t(50). If the interface is the second interface then the sputtering time to
the second interface, t , shall be equal to t(50). See 7.2.3.
If the intensity in the interface region exceeds the plateau region for the material, the sputtering time
position of the maximum intensity in the interface region shall be recorded as the interface position. If
the interface is the first interface this shall be t . If the interface is the second interface this shall be t .
1 2
7.3.4 Areic dose of ions used for sputtering
For each layer and ion, the areic dose through the layer of interest, D, shall be calculated using
Formula (9).
JJ+ tt−
()()
12 21
D= (9)
2qeA
where
q is the number of elementary charges on a primary sputtering ion;
−19
e is the elementary charge, 1,602 × 10 Coulombs;
A is the area of the raster pattern of the sputtering beam on the sample;
J is the current of primary sputtering ions measured before analysis in Amperes;
J is the current of primary sputtering ions measured after analysis in Amperes;
t is the sputtering time to the first interface;
t is the sputtering time to the second interface;
2 2
NOTE It is useful to express D in ions per nm and therefore to convert A to nm prior to the calculation.
For each layer, the relative standard uncertainty in areic dose, δ , shall be estimated using Formula (10).
D


 
 
22 2 2
δδ=+δδ+ (10)
DA Jn
 
 E 
 
1+
 
 
3n
 
 
where
δ is the relative standard uncertainty in raster area of the sputtering ion beam;
A
δ is the relative standard uncertainty in the primary ion beam current;
J
δ is the relative standard uncertainty in n;
n
E is the kinetic energy of primary argon cluster ions used for sputtering;
n is the average number of argon atoms per ion in the primary cluster (n + n )/2.
2 1
NOTE The factor in Formula (8) prior to the δ term is obtained by differentiation of Formula (C.1) given in
n
C.1 and using the typical values for parameters therein. This is described in C.2.
2 2 2
The value of (δ ) shall be estimated as 2(J – J ) / (J + J ) .
J 2 1 2 1
NOTE 1 This estimation of δ does not account for uncertainty in the current measurement and only accounts
J
for drift in current from the start to the end of the profile. It is assumed that uncertainty due to the accuracy of
the current measurement method is negligible compared to other sources of uncertainty. If (δ ) is greater than
J
0,002 5, then the requirement on beam current drift can be checked as per 6.1.
NOTE 2 This estimation of uncertainty does not include inaccuracy in the position of the interfaces, because
these biases are eliminated through the comparison of more than one layer of the same material. The remaining
major uncertainties are the measurement of sputtered areas, the uncertainty in the thicknesses of the layers and
the variation in areic dose during the experiments.
10 © ISO 2019 – All rights reserved

2 2 2
The value of (δ ) shall be estimated as 2(n – n ) / (n + n ) .
n 2 1 2 1
NOTE This estimation of δ does not account for uncertainty in the average number of atoms per ion and
n
only accounts for drift in cluster size from the start to the end of the profile.
7.3.5 Calculation of sputtering yield volume using more than one-layer thickness
For each secondary ion, i, the thickness of each layer, d , shall be plotted as a dependent variable against
k
the areic dose of ions used for sputtering for that secondary ion and layer, D . A linear fit to the graph
ik
shall be performed to find the slope, which is the sputtering yield volume, y , for that secondary ion.
i
The mean sputtering yield volume, Y, for all selected secondary ions shall be calculated using
Formula (11).
a
y
∑ i
il=
Y = (11)
a
where
y is the sputtering yield volume determined using secondary ion i;
i
a is the number of different secondary ions used.
The relative standard uncertainty in Y, δ , shall be estimated using Formula (12).
Y
a
  b
 
 
δ ()j
 
δ (k)
∑ d
∑ D
 
 
jl=
kl=
δ =  + (12)
 
Y
bb
 
 
 
 
 
 
 
 
where
δ ( j) is the relative standard uncertainty in thickness for layer j;
d
δ (k) is the relative standard uncertainty in areic dose to remove layer k;
D
b is the number of different layer thicknesses used to determine Y.
NOTE The uncertainty using this method is dominated by the uncertainty in dose and thickness, this is
reflected in Formula (12). These uncertainties are usually correlated; hence they are not combined in quadrature.
Other uncertainties from the linear fit and the variation between ions are neglected because with the conditions
on data quality in this standard, these are negligible.
8 Reporting of sputtering yield volume
8.1 Required information
The following information shall be reported.
a) The sputtering ion source species, n, which shall be the mean value of all n and n values measured.
1 2
b) The sputtering ion kinetic energy, E.
c) The sputtering ion charge, q.
d) The incidence angle between the sputtering ion beam and the reference sample surface normal.
e) The sputtering yield volume, Y.
f) The standard uncertainty in the sputtering yield volume, ΔY (=Yδ ).
Y
g) The identity of the material, including molecular weight if it is a polymer, and the source of the
material.
h) The preparation method for the material layer, or layers if 7.3 was used.
i) The method by which the thickness of the layer was measured.
j) The thickness of the layer used or the range of thicknesses if 7.3 is used.
12 © ISO 2019 – All rights reserved

Annex A
(informative)
...