ISO 23170:2022

INTERNATIONAL ISO
STANDARD 23170
First edition
2022-06
Surface chemical analysis — Depth
profiling — Non-destructive depth
profiling of nanoscale heavy metal
oxide thin films on Si substrates with
medium energy ion scattering
Analyse chimique des surfaces — Profilage d'épaisseur — Profilage
d'épaisseur non destructif de films minces d'oxydes de métaux lourds
à l'échelle nanométrique sur des substrats de Si par diffusion d'ions de
moyenne énergie
Reference number
© ISO 2022
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle and recommendations of MEIS analysis . 1
5 MEIS analysis .2
6 MEIS spectra simulation .2
7 Reporting MEIS analysis results .5
Annex A (informative) Interlaboratory test report . 6
Annex B (informative) List of MEIS spectra simulation program sources and a procedure of
MEIS spectra simulation using PowerMeis .19
Annex C (informative) Reliability of the IAEA electronic stopping power data .22
Annex D (informative) Fitting parameters A, B, C, D from the IAEA database .24
Bibliography .29
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 4, Depth profiling.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
Introduction
Medium energy ion scattering (MEIS) has been considered to be a quantitative surface and interface
composition analysis method with single atomic depth resolution since its invention in the early of
1980s. MEIS has been widely used for ultrathin films, especially nm gate oxides analysis to determine
its composition, thickness, and the interface. Recently, MEIS has been used for nanoparticle analysis
to determine the size and the composition with the core and shell structure information. In addition
to the toroidal electrostatic energy analyser used in the early stage, different types of energy analyser
such as magnetic energy analyser and time-of-flight (TOF) energy analyser have been used. With the
continued scaling down of electronic devices, demands on accurate and reliable depth profiling have
reached beyond the limit of sputter depth profiling which provides deteriorated depth profiles due
to the sputter damage. Needs have been risen to investigate the consistency between the three types
of energy analyser, ion species, and the different energy range of incident ions used for MEIS analysis
and to set up a procedure for quantitative MEIS analysis. Two international interlaboratory tests were
performed to develop this document which is reported in Annex A.
v
INTERNATIONAL STANDARD ISO 23170:2022(E)
Surface chemical analysis — Depth profiling — Non-
destructive depth profiling of nanoscale heavy metal
oxide thin films on Si substrates with medium energy ion
scattering
1 Scope
This document specifies a method for the quantitative depth profiling of amorphous heavy metal oxide
ultrathin films on Si substrates using medium energy ion scattering (MEIS).
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, Surface chemical analysis — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18115 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
electronic stopping power
retarding force acting on charged particles, typically alpha and proton particles, due to interaction with
electrons, resulting in loss of particle energy
4 Principle and recommendations of MEIS analysis
+
4.1 Ultrathin films of thickness less than 10 nm can be analysed with MEIS. (100 to 500) keV H or
+
He ions are used for MEIS analysis. Scattered ion energy and angle are measured precisely so that
measured MEIS spectra be compared with simulated MEIS spectra. MEIS spectra can be simulated with
1 2
various programs from free codes such as PowerMeis and SIMNRA in public websites, MEIS expert
laboratories, and MEIS manufacturers. Simulation programs calculate scattering cross-sections and
electronic stopping powers. Quite often, calculated electronic stopping powers are subject to significant
errors so that tabulated electronic stopping power values in the IAEA website are recommended to
use.
4.2 If not tabulated, it is recommended to measure electronic stopping power by users for more
reliable results. Various types of energy analyzers can be used such as toroidal electrostatic analyser
(TEA), magnetic energy analyser (magnetic), and TOF energy analyser. With MEIS analysis procedures
specified in this document, less than 10 % uncertainty can be expected for ultrathin films under the
guidelines describe in this document. This document is written for amorphous or polycrystalline thin
films but not for crystalline thin films. To reduce the uncertainty of MEIS analysis, additional standards
for calibration of scattering geometry, ion energy, energy resolution, detector efficiency, sample
alignment, are required.
5 MEIS analysis
5.1 Set the ion scattering conditions such as ion energy, scattering angle, incidence angle from the
surface normal, ion species, and ion dose for MEIS analysis. The ion dose is recommended to be in the
15 2
static condition (<10 /cm ) but the static requirement for MEIS analysis is not strict compared to
surface analysis such as XPS and static SIMS.
5.2 For MEIS analysis, specimen should be flat. Slight contamination due to air oxidation and ambient
water and hydrocarbon adsorption does not disturb the MEIS analysis badly. However, if the surface
contamination layer is thicker than 1 nm it shall be cleaned by appropriate methods such as solvent
washing or ion milling.
5.3 Measure a MEIS spectrum of a specimen and generate a MEIS spectrum file with intensity
(counts) vs energy (keV) at a specific angle. Specify all the ion scattering conditions such as ion beam
energy, ion species, incidence angle from the surface normal, scattering angle, ion dose or ion current
with analysis time, beam radius, and the type of energy analyser.
5.4 For MEIS analysis of ultrathin films of approximately 1 nm thickness, a clear plateau does not
appear so that it may have poor reproducibility. It is recommended to express MEIS analysis result in
surface areal density rather than in thickness or concentration for MEIS analysis of ultrathin films of
approximately 1 nm thickness.
5.5 If the primary ion beam current is too high, it can cause multi-hit problems of detector. Under
each MEIS analysis condition, it shall be checked whether the data is affected by the multi-hit problem
by comparing MEIS results from high ion beam current and low ion beam current available from each
MEIS system.
6 MEIS spectra simulation
1)
6.1 MEIS spectra can be simulated with various programs from free codes such as PowerMeis and
2)
SIMNRA in public websites and simulation programs from MEIS laboratories and manufacturers as
listed in Annex B. Detailed procedures for PowerMeis is also given in Annex B as an example. In this
document, general procedures for MEIS spectra simulation are given as a guidance.
Most of MEIS spectra simulation programs are based on Monte Carlo simulation or analytical
calculation of binary scatterings and electronic stopping between binary scatterings. Multiple
scattering is suggested to be included in all MEIS simulations. Thin films thicker than 5 nm are strongly
recommended to be analysed including multiple scattering for the MEIS data obtained by He ions of ion
energy lower than 500 keV. SIMNRA provides multiple scattering simulation so that users can choose
whether including it or not.
Generally, the integration step, and the slab thickness or atom density in MEIS simulations are 0,1 nm,
15 2
and 0,1 nm or 1 x10 atoms/cm , respectively.
In simulation, line shape, cross-section, electronic stopping power, charge neutralization, and energy
straggling shall be selected by users as described below. Electronic stopping power is described in
detail in 6.2
1) http:// tars .if .ufrgs .br
2) https:// home .mpcdf .mpg .de/ ~mam/
Generally, simple Gaussian can be used as basic line shape for the first approximation. For MEIS systems
−4
with high resolution of δE/E approximately 8x10 with proton as a projectile, exponentially modified
Gaussian is recommended for ultrathin films. However, other options can be chosen, if needed. Line
3)
shape parameters for each element, σ (additional parameter), is calculated by Casp version 5.2
o
program for each projectile, projectile energy, and target element. Follow the instructions in Casp
version 5.2.
To calculate cross-sections, interatomic potentials can be chosen from Anderson, L’Ecuyer, Moliere
[1]
potential, or ZBL potential . For MEIS analysis, Moliere potential is widely used. For energy straggling,
[2]
Chu or Yang can be usually chosen. For charge neutralization, Marion and Young’s equation is used f
...