ISO 14606:2015

Surface chemical analysis — Sputter depth profiling — Optimization using layered systems as reference materials

ISO 14606:2015 gives guidance on the optimization of sputter-depth profiling parameters using appropriate single-layered and multilayered reference materials in order to achieve optimum depth resolution as a function of instrument settings in Auger electron spectroscopy, X-ray photoelectron spectroscopy and secondary ion mass spectrometry. ISO 14606:2015 is not intended to cover the use of special multilayered systems such as delta doped layers.

Analyse chimique des surfaces — Profilage d'épaisseur par bombardement — Optimisation à l'aide de systèmes mono- ou multicouches comme matériaux de référence

General Information

• Status: Withdrawn
• Publication Date: 30-Nov-2015
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: ISO/TC 201/SC 4 - Depth profiling
• Drafting Committee: ISO/TC 201/SC 4 - Depth profiling
• Current Stage: 9599 - Withdrawal of International Standard
• Completion Date: 21-Nov-2022

Relations

• Revised: ISO 14606:2022 - Surface chemical analysis — Sputter depth profiling — Optimization using layered systems as reference materials
• Effective Date: 18-Dec-2021
• Revises: ISO 14606:2000 - Surface chemical analysis — Sputter depth profiling — Optimization using layered systems as reference materials
• Effective Date: 15-Dec-2012

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 14606
Second edition
2015-12-01
Surface chemical analysis — Sputter
depth profiling — Optimization using
layered systems as reference materials
Analyse chimique des surfaces — Profilage d’épaisseur par
bombardement — Optimisation à l’aide de systèmes mono- ou
multicouches comme matériaux de référence
Reference number
ISO 14606:2015(E)
©
ISO 2015

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ISO 14606:2015(E)

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ISO 14606:2015(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Symbols and abbreviated terms . 2
4 Setting parameters for sputter depth profiling . 2
4.1 General . 2
4.2 Auger electron spectroscopy . 3
4.3 X-ray photoelectron spectroscopy . 4
4.4 Secondary ion mass spectrometry . 4
5 Depth resolution at an ideally sharp interface in sputter depth profiles .4
5.1 Measurement of depth resolution . 4
5.2 Average sputtering rate . 5
5.3 Depth resolution ∆z .5
6 Procedures for optimization of parameter settings . 6
6.1 Alignment of sputtered area with a smaller analysis area . 6
6.1.1 General. 6
6.1.2 AES . 7
6.1.3 XPS with a small probe (for example monochromator) . 7
6.1.4 XPS with a large area source (for example without monochromator) . 7
6.1.5 SIMS . 7
6.2 Optimization of parameter settings . 8
Annex A (informative) Factors influencing the depth resolution . 9
Annex B (informative) Typical single-layered systems as reference materials .11
Annex C (informative) Typical multilayered systems used as reference materials .12
Annex D (informative) Uses of multilayered systems .13
Bibliography .14
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ISO 14606:2015(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 4, Depth profiling.
This second edition cancels and replaces the first edition (ISO 14606:2000), of which it constitutes a
minor revision to update the content of Table C.1
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Introduction
Reference materials are useful in optimizing the depth resolution of sputter profiling methods in
materials such as silicon wafers, multilayered devices (for example AlGaAs double-hetero lasers, high
electron mobility transistors) and alloy-galvanized steel for corrosion-resistant car bodies.
The specific applications of this International Standard are as follows:
a) Single-layered and multilayered systems on a substrate as reference materials are useful for
the optimization of depth resolution as a function of instrument settings in Auger electron
spectroscopy, X-ray photoelectron spectroscopy and secondary ion mass spectrometry.
b) These systems are useful for illustrating the effects of the evenness of the sputter crater, the
inclination of the crater bottom, the sample drift, the drift of sputter conditions (for example ion
beam current density) on depth resolution.
c) These systems are useful for illustrating the effects of sputter-induced surface roughening and
sputter-induced atomic mixing on depth resolution.
d) These systems are useful for the evaluation of instrument performance for instrument
suppliers and users.
e) This International Standard is timely and topical, and can be used for a basis of future development
of sputter depth profiling.
[1][2][3][4][5]
A list of ISO Guides related to this International Standard is given in the Bibliography.
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INTERNATIONAL STANDARD ISO 14606:2015(E)
Surface chemical analysis — Sputter depth profiling —
Optimization using layered systems as reference materials
1 Scope
This International Standard gives guidance on the optimization of sputter-depth profiling parameters
using appropriate single-layered and multilayered reference materials in order to achieve optimum
depth resolution as a function of instrument settings in Auger electron spectroscopy, X-ray
photoelectron spectroscopy and secondary ion mass spectrometry.
This International Standard is not intended to cover the use of special multilayered systems such as
delta doped layers.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
[6]
NOTE The terms used in this International Standard follow basically ASTM E 673–97 . The definitions of
the terms used are to be modified to conform to those being developed by ISO/TC 201/SC 1, Terminology.
2.1
analysis area
two-dimensional region of a sample surface measured in the plane of that surface from which the full
signal or a specified percentage of that signal is detected
2.2
angle of incidence
angle between the incident beam and the local or average surface normal
2.3
crater edge effect
signals from the crater edge which often originate from depths shallower than the central region of the
crater formed in depth profiling
2.4
depth resolution
depth range over which a signal intensity increases or decreases by a specified amount when profiling
an ideally sharp interface between two media
Note 1 to entry: By convention, a measure of the depth resolution is often taken to be the distance over which
the signal intensity changes from 16 % to 84 % of the full change between the respective plateau values of the
[7]
two media.
2.5
gated area
defined area within a larger area from which the signal may be obtained
2.6
image depth profile
three-dimensional representation of the spatial distribution of a particular elemental or molecular
species (as indicated by emitted secondary ions or electrons) as a function of depth or material removed
by sputtering
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2.7
plateau region
region in which the signal remains constant or without significant variation with sputtering time
2.8
signal intensity
strength of a signal at the spectrometer output or after some defined data processing
Note 1 to entry: Examples of signal intensity are the height of the peak above the background or the peak-to-peak
heights in AES or the peak areas in XPS.
2.9
sputter depth profile
compositional depth profile obtained when the surface composition is measured as material is removed
by sputtering
2.10
sputtering rate
quotient of amount of sample material removed as a result of particle bombardment by time
Note 1 to entry: The rate may be measured as a velocity, a mass per unit area per unit time, or some other measure
of quantity per unit time.
3 Symbols and abbreviated terms
∆z depth resolution
I signal intensity
sputtering rate
z
AES Auger electron spectroscopy
SEM scanning electron microscopy
SIMS secondary ion mass spectrometry
XPS X-ray photoelectron spectroscopy
4 Setting parameters for sputter depth profiling
4.1 General
For the purposes of this International Standard, typical probing and sputtering parameters for
sputter depth profiling in AES, XPS and SIMS are given in Table 1 and Table 2. These parameters
represent a range which covers many different types of instrumentation. Recommended conditions
for a particular instrument may be available from the respective instrument manufacturers and
optimized by experimentation on the laboratory instrument using the information included in this
International Standard.
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Table 1 — Typical probing parameters for sputter depth profiling
AES XPS SIMS
+ – +
Probing species Electrons Photons: Primary ions: Cs , O , O ,
2
+
Ga
Mg Kα, Al Kα
Energy 1 keV to 25 keV 1,253 keV, 1,486 keV 0,1 keV to 25 keV
3 4 4
Current or power 1 nA to 10 nA (Faraday cup) 1 W to 10 W (Source 1 nA to 10 nA (Faraday
power) cup)
Angle of incidence 0° ≤ θ < 90° 0° ≤ θ < 90° 0° ≤ θ < 90°
Analysed species Auger electrons in eV (ki- Photoelectrons in eV (kinet- Secondary ions in AMU
netic energy) ic or binding energy) (mass or mass/charge)
Energy range 0 keV to 3 keV 0 keV to 1,5 keV 0 keV to 0,125 keV
Angle of emission 0° ≤ θ ≤ 90° 0° ≤ θ ≤ 90° 0° ≤ θ ≤ 90°
−8 2 −2 2 −4 2 2 −6 2 −2 2
Analysis area 10 mm to 10 mm 10 mm to 10 mm 10 mm to 10 mm
Table 2 — Typical sputtering parameters for sputter depth profiling
     Typical operating parameters Remarks
+ + + – + + +
Ion species Ar , Kr , Xe , O , O , Ga , Cs Inert or reactive gas ions or metal ions
2
Ion energy 0,1 keV to 25 keV
4
Ion beam current 1 nA to 10 nA Faraday cup
Angle of incidence 0° ≤ θ < 90°
−2 2 2 2
Sputtered area 10 mm to 10 mm Raster scan of focused ion beam
NOTE The ion gun parameters and vacuum conditions may also affect the depth resolution. For example, the
gas pressure in the ion source may change during the course of the analysis.
4.2 Auger electron spectroscopy
Important parameters for a depth profile measurement of a single layered or an A/B/A/B/. multilayered
[8]
system by AES with ion sputtering are the following.
a) Probing parameters (important for analysis): Electron energy, electron beam current, angle of
incidence, analysis area (i.e. beam diameter or raster area).
[9]
b) Sputtering parameters (important for depth resolution): Ion species, ion energy, ion beam current ,
angle of incidence, sputtered or raster area. Sample stage is in a stationary or rotational mode.
c) Measurement parameters:
1) Kinetic energies of Auger electrons from both overlayer and substrate elements, or from
elements A and B (important for both analysis and depth resolution).
2) Direct mode, N (E) or EN (E), or differential mode, dN (E)/dE or dEN (E)/dE (important for
1)
analysis).
NOTE Usually with ion sputtering, data may be collected in either an alternating mode or continuous mode. If
the continuous mode is used, it is preferable to ensure that the ion-induced Auger electron signals are negligible.
[10][11]
The problem of ion-induced Auger electrons seems only significant for Auger electron peaks below 100 eV.
1) N(E), EN(E), dN(E)/dE and dEN(E)/dE refer to different kinds of Auger spectra where the Auger electron
intensity, N, is plotted as a function of the electron kinetic energy, E. In N(E) spectra, signal intensities are measured
as the heights of the Auger peaks above background. In dN(E)/dE spectra, signal intensities are measured as the
peak-to-peak heights of the Auger signals or the differential spectra of N(E). With certain types of analyser (for
example, the cylindrical mirror analyser), Auger electron intensities are presented in EN(E) and dEN(E)/dE formats,
in which the spectrum approximates E times the true spectrum.
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4.3 X-ray photoelectron spectroscopy
Important parameters for a depth profile measurement of a single layered or an A/B/A/B/. multilayered
system by XPS with ion sputtering are the following.
a) Probing parameters (important for analysis): Photon energy (X-ray source), X-ray source power
(i.e. voltage and current), angle of incidence, analysis area (i.e. beam diameter or selected area).
b) Sputtering parameters (important for depth resolution): Ion species, ion energy, ion beam
current, angle of incidence, sputtered or raster area. The sample stage can be in a stationary or
rotational mode.
c) Measurement parameters (important for both analysis and depth resolution):
1) Kinetic energies of photoelectrons and/or the respective electron binding energies of both
overlayer and substrate elements or both elements A and B.
2) Area of measurement for selected area XPS.
NOTE Usually, XPS signal intensities are measured as a function of sputtering time in an alternating mode
with ion sputtering.
4.4 Secondary ion mass spectrometry
Important parameters for a depth profile measurement of a single layered or an A/B/A/B/. multilayered
system by SIMS are the following.
a) Probing and simultaneously sputtering parameters (important for both analysis and depth
resolution): Primary ion species, ion impact energy, ion beam current, angle of incidence, analysis
area (i.e. gated area), sputtered area. The sample stage can be a stationary or rotational mode.
NOTE 1 In some SIMS systems the beam energy is given for the source potential with respect to the
ground but the sample potential is not at ground. The impact energy takes account of the sample potential.
NOTE 2 Some time of flight SIMS instruments use dual beams. In this case, all parameters for both beams
may be noted.
b) Measurement parameters (important for both analysis and depth resolution):
1) Positive or negative secondary ion species (atomic or molecular) of both overlayer and
substrate elements or both elements A and B.
2) Settings of gates (i.e. electronic, optical, etc.).
NOTE 3 Usually, secondary ion signal intensities are measured as a function of sputtering time in a
continuous mode with primary ion sputtering. In some SIMS instruments an interrupted mode (primary ion
gating) is used where different ion beams are used for sputtering and analysis.
5 Depth resolution at an ideally sharp interface in sputter depth profiles
5.1 Measurement of depth resolution
For the purposes of this International Standard, the measurement of the depth resolution ∆z of sputter
[7][12][13]
depth profiles of a single layered or an A/B/A/B/. multilayered system is as follows.
NOTE 1 The definition of depth resolution ∆z in this clause applies only for optimization of setting parameters
in depth profiling. The definition and measurement procedures of depth resolution will be described in
International Standards to be developed by ISO/TC 201/SC 1 and SC 4, respectively, in the future.
NOTE 2 For SIMS, where matrix effects are significantly different between the two layers, ∆z may still be used
for optimization but may not relate closely to the real depth resolution of the underlying chemical composition.
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5.2 Average sputtering rate
z is given by the following expression:
av
z = z /t (1)
tot tot
av
where
z is the total thickness of a single overlayer or multilayered system on a substrate;
tot
t is the total sputtering time required to sputter from the topmost surface until the overlayer/
tot
substrate interface at which the signal intensity of the element reaches 50 % of its value in
the adjacent overlayer on a substrate.
5.3 Depth resolution ∆z
∆z is given by the following expression:
∆z = z × ∆t (2)
av
where ∆t is the sputtering time interval in which the signal intensities change from 16 % to 84 % (or
84 % to 16 %) of the intensity corresponding to 100 % of each of the overlayer and the substrate of a
single-layered system or each of the adjacent layers of a multilayer system.
The measurement of ∆t is only applicable where plateau regions have been obtained for both maximum
and minimum intensities (see Figure 1).
Figure 1 — Diagram of the measurement of ∆t at an ideally sharp interface in a sputter
depth profile
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6 Procedures for optimization of parameter settings
6.1 Alignment of sputtered area with a smaller analysis area
6.1.1 General
The centre of a sputtered area shall be aligned with a smaller analysis area using an appropriate
method. A number of different situations exist, as discussed below (see Figure 2 and the Note).
Key
1 sample
2 probe
3 sputtered area
4 direction of ions
5 spectrometer analysis area
6 electronic gate
Figure 2 — Methods for aligning the sputtered area with a smaller analysis area
NOTE In some cases a third area, a broader area at the sample surface is used in alignment. For each example,
the smaller area is given as a black shaded area in Figure 2 and by “X” in Table 3 whereas the third area is given
by “Y” in Table 3.
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Table 3 — Description of sputtering alignment methods
Figure Smaller area Larger area Example
X Y
2 a) Focused probe beam Spectrometer analysis AES, or XPS with focused monochromator, or time
area of flight SIMS
2 b) Spectrometer analysis Broad probe beam XPS without monochromator
area
2 c) Electronic gate Spectrometer analysis Dynamic SIMS with electronic gate
area
2 d) Optical aperture Not appropriate Dynamic SIMS with optical aperture
6.1.2 AES
6.1.2.1 The centre of the sputtered area shall be aligned with the analysis area as defined by the
focused electron beam, which may be rastered as shown in Figure 2a).
6.1.2.2 Correct alignment may be checked by either post-profile crater observation or by measurement
[14]
to ensure that the sputtered area lies centred over the analysis area [see Figure 2a) ]. If necessary,
alignment and post-profile crater observation may be repeated.
6.1.2.3 If an instrument is available with SEM imaging, post-profile crater observation may be
[14]
performed using a monitor display.
6.1.3 XPS with a small probe (for example monochromator)
6.1.3.1 The centre of the sputtered area shall be aligned with the analysis area as defined by the
focused X-ray beam [(see Figure 2a)].
6.1.3.2 Correct alignment may be checked by either post-profile crater observation or by measurement
[14]
to ensure that the sputtered area lies centred over the analysis area [see Figure 2a) ]. If necessary,
alignment and post-profile crater observation may be repeated.
6.1.4 XPS with a large area source (for example without monochromator)
6.1.4.1 The centre of the sputtered area shall be aligned with the analysis area as defined by the
electron spectrometer [see Figure 2b)].
6.1.4.2 Correct alignment may be checked by either post-profile crater observation or by measurement
[14]
to ensure that the sputtered area lies centred over the analysis area [see Figure 2b) ]. If necessary,
alignment and post-profile crater observation may be repeated.
6.1.5 SIMS
6.1.5.1 If an electronic gate is used in dynamic SIMS, the centre of the sputtered area shall be aligned
[15]
with the analysis area as defined by the electronic gate [(see Figure 2c) ].
6.1.5.2 If an ion optical aperture is used in dynamic SIMS, the centre of the sputtered area shall be
aligned with the analysis area as defined by the ion optical aperture [see Figure 2d)], and this is carried
out in a test area as near as possible to the analysis area. For some instruments with an optical aperture
and a scanning ion image display, alignment may be carried out during the profile.
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6.1.5.3 If different ion beams are used for sputtering and analysis, in a time-of-flight SIMS instrument,
the centre of the sputtered area shall be aligned with the analysis area as defined by the focused ion
beam [see Figure 2a)].
6.1.5.4 If the post-profile realignment of each column of pixels is used to provide an image depth
profile alignment shall not be necessary.
6.2 Optimization of parameter settings
6.2.1 See Table 1 and Table 2 for probing and sputtering parameters which shall be optimized as follows.
6.2.2 Perform the measurements of sputter depth profiles on a single-layered or multilayered system
using the appropriate parameter settings, in particular, those important for depth resolution (see Table 1
and Table 2).
6.2.3 Determine the depth resolution ∆z from the data sets of depth profiles using Formulae (1)
and (2) (see Clause 5).
6.2.4 Choose the parameter settings so as to obtain the minimum depth resolution ∆z.
NOTE 1 Useful information for a number of important parameters is given in Annex A.
NOTE 2 In general, the ratio of the analysis area to the sputtered area is chosen to be as small as possible so as
[15]
to reduce effects resulting in the depth resolution due to the proximity to the crater edge.
NOTE 3 If the analysis area is too small, the measured resolution may be decreased. For example, in AES, a
small analysis area gives rise to sputter enhancement on the area irradiated by the electron beam and leads to
poor depth resolution. This effect is best known to occur with SiO but also occurs with many compounds. In
2
SIMS, as the measured signal intensity depends on the analysis area, sputtering rate and integration time, the
experimental conditions need to be chosen with care to ensure that the signal is sufficiently high so as to obtain a
good signal-to-noise ratio but at the same time having sufficient data points obtained for the interface regions so
as to allow the depth resolution to be measured.
NOTE 4 If a sample consisting of a single-layered or multilayered structure on a substrate is to be measured,
then a similar reference material system should be used for optimization. Some single-layered and multilayered
reference materials are listed in Annex B and Annex C.
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Annex A
(informative)

Factors influencing the depth resolution
A.1 General
Usually, probing and sputtering parameters are taken into account in order to optimize parameter
[12][16][17][18][19][20][21][22]
settings for enhancing the depth resolution ∆z .
A.2 Sputtering parameters
A.2.1 Ion species
The ion species should be considered in order to reduce the sputter-induced roughness, or cone
[23][24]
formation, or extent of atomic mixing. Typical ion species used for sputtering are inert gas ions
+ + + – + + +
(e.g. Ar , Kr , Xe ), reactive gas ions (e.g. O , O ) or metal ions (e.g. Ga , Cs ).
2
A.2.2 Ion energy
In general, a lower ion energy is preferable in order to reduce the atomic mixing effect and/or the sputter-
[25][26][27]
induced roughness. But this should be balanced against the reduced sputtering yield and lower
sputtering rates where contamination from adsorption of residual gas species may be a problem.
A.2.3 Angle of incidence
Often, a high angle of incidence (i.e. glancing incidence) may be used to reduce the atomic mixing effect
[26][28][29]
and/or the sputter-induced roughness. In some cases, a higher angle of incidence may lead
to increased sputter-induced roughness, for example when using reactive primary ions and stationary
[29][30][31][32]
sample stage .
A.2.4 Sample stage
The rotational mode is generally preferable, in particular, for polycrystalline metallic materials so as
[28][29][33][34][35][36]
to reduce sputter-induced roughness. The speed of rotation is generally chosen to
be greater than a critical value so as to ensure an improvement of ∆z when compared to stationary
[29]
conditions.
A.3 Measurement parameters
A.3.1 Kinetic energy (E ) of signal used in AES and XPS
k
[37][38]
A signal with a lower kinetic energy is preferable in order to reduce the information depth
(E > 30 eV).
k
NOTE “Information depth” is the maximum depth, normal to the surface, from which useful information is
obtained. The information depth can be identified with the sample thickness from which a specified percentage
(e.g. 95 % or 99 %) of the detected signal originates. In addition, the information depth may be determined from
a measured, calculated or estimated emission-depth distribution function for the signal of interest.
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A.3.2 Angle of emission
More grazing emission reduces the sampling de
...