ISO/TS 22933:2022
(Main)Surface chemical analysis — Secondary ion mass spectrometry — Method for the measurement of mass resolution in SIMS
Surface chemical analysis — Secondary ion mass spectrometry — Method for the measurement of mass resolution in SIMS
This document specifies a method for measuring the mass resolution in SIMS, and how to compare the mass resolution between different instruments (e.g. TOF-SIMS, Magnetic SIMS, Quadrupole SIMS, Fourier Transform SIMS, etc.) by considering the peak shapes.
Analyse chimique des surfaces — Spectrométrie de masse des ions secondaires — Méthode pour le mesurage de la résolution en masse dans la SIMS
General Information
Standards Content (Sample)
TECHNICAL ISO/TS
SPECIFICATION 22933
First edition
2022-04
Surface chemical analysis —
Secondary ion mass spectrometry —
Method for the measurement of mass
resolution in SIMS
Reference number
ISO/TS 22933:2022(E)
© ISO 2022
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ISO/TS 22933:2022(E)
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ISO/TS 22933:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.2
5 Definitions of mass resolution based on peak separations of two mass peaks.2
5.1 General . 2
5.2 X% valley . 2
5.3 X% peak width ΔM (X%) or R (X%)=M/ΔM (X%). 3
5.4 X% peak tail interference . 4
5.5 Summary . 4
6 Procedure to determine the mass resolution . 5
6.1 General . 5
6.2 Removing contamination on sample surface . 5
6.3 Obtaining spectrum peak . 5
6.4 Determination of mass resolution. 5
7 Mass resolution comparison between different type of SIMS . 5
7.1 Mass resolution comparison between M-SIMS and TOF-SIMS . 5
7.2 Mass resolution comparison between TOF-SIMS and FTICR-SIMS . 7
7.3 Mass resolution of flat top mass peak . 8
8 Conclusion . 9
Annex A (informative) Examples of mass resolution measured by Q-SIMS, TOF-SIMS,
Magnetic-SIMS, Orbitrap-SIMS and FTICR-SIMS .10
Bibliography .15
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ISO/TS 22933:2022(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
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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
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on the ISO list of patent declarations received (see www.iso.org/patents).
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 6, Secondary ion mass spectrometry.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/TS 22933:2022(E)
Introduction
Mass resolution is one of the most important instrumental parameters in mass spectrometry (MS). For
any MS experiments, an unambiguous result can only be acquired if sufficient mass resolution is reached
to separate the target analytes from any possible interference. If the mass resolution of the instrument
is insufficient, it can result in a false positive or negative signal. Therefore, the mass resolution is the
primary consideration for determining whether an instrument is adequate for the intended purpose.
For routine applications, the mass resolution should be adjusted based on the analytical requirements of
the sample. Mass resolution is important not only for the instrument acceptance tests and fundamental
studies, but also for almost all routine applications.
This document gives guidance for the measurement of mass resolution in SIMS. Various definitions
of mass resolution have been summarized and common problems with popular definitions have been
[18]
discussed elsewhere . To compare mass resolution between different instrument or/and different
types of instruments (e.g. TOF-SIMS, Magnetic SIMS, Quadrupole SIMS, Fourier Transform SIMS and
Orbitrap-SIMS, etc.), it is necessary to show the measured peak shape and define mass resolution
correctly.
After introducing a reasonable new definition for mass resolution and a method considering the peak
shape to compare the mass resolution between TOF-SIMS, Magnetic SIMS, Quadrupole SIMS and Fourier
Transform SIMS, this document specifies a method to measure the mass resolution in SIMS.
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TECHNICAL SPECIFICATION ISO/TS 22933:2022(E)
Surface chemical analysis — Secondary ion mass
spectrometry — Method for the measurement of mass
resolution in SIMS
1 Scope
This document specifies a method for measuring the mass resolution in SIMS, and how to compare
the mass resolution between different instruments (e.g. TOF-SIMS, Magnetic SIMS, Quadrupole SIMS,
Fourier Transform SIMS, etc.) by considering the peak shapes.
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, 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 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
mass resolution
measurement of the ability of a mass spectrometer to separate mass peaks in a mass spectrum
Note 1 to entry: For a mass peak at position M and a mass peak at position M+ΔM which can be separated in a
mass spectrum then ΔM is the mass resolution of the mass spectrometer at M under these conditions. The peak
shape as well as the method of measurement of ΔM should be reported.
Note 2 to entry: If M and M+ΔM can be separated, ΔM, M/ΔM or ΔM/M are defined as mass resolution, mass
resolving power or relative mass resolution respectively. Designs of mass spectrometer generally maintain the
resolution either to be constant throughout the mass spectrum or to be proportional to mass being scanned. For
the former, the mass resolution is a useful term whereas, for the latter, the relative mass resolution and resolving
power are more useful.
Note 3 to entry: The sensitivity required to detect the presence of a peak at a position M+ΔM depends upon the
shape of the peak at M and the degree to which peak tails place limits on the magnitude of a peak at M+ΔM which
can be detected. Simple measures of resolution may not represent the actual or practical resolution needed for
particular applications.
Note 4 to entry: Usually, normalized output signal distribution from an instrument is a function of variable input
measurand values which arises from a feature with a single measurand value. However, in mass spectrometry
community, because “mass” is a single measurand value, the peak shape is normally used for the resolution
function.
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ISO/TS 22933:2022(E)
4 Symbols and abbreviated terms
-1
I Measured intensity at mass peak (cts or cts·s or arbitrary unit)
M
I Current of primary ion beam (nA)
p
I Current of electron beam for charge compensation (µA)
g
E Energy of primary ion beam (keV)
p
ΔM Mass resolution (m/z)
ΔM/M Relative mass resolution
M/ΔM Mass resolving power
TOF-SIMS Time-of-flight secondary ion mass spectrometer
M-SIMS Magnetic-sector secondary ion mass spectrometer
Q-SIMS Quadrupole secondary ion mass spectrometer
Orbitrap-SIMS Orbitrap secondary ion mass spectrometer
FT-SIMS Fourier transform secondary ion mass spectrometer
FTICR-SIMS Fourier transform ion cyclotron resonance secondary ion mass spectrometer
SHRIMP Sensitive high-resolution ion microprobe
X% valley Valley between the two adjacent and equal peaks is X% of the peak height
X% peak width Peak width ΔM shall be measured at X% of the peak height (m/z)
X% peak tail interference Contribution of the M peak tail to its ΔM adjacent peak is X%
R Mass resolving power (M/ΔM)
5 Definitions of mass resolution based on peak separations of two mass peaks
5.1 General
There are three different kinds of mass peak separations commonly used for definition of mass
resolution, which are summarized as follows.
5.2 X% valley
When the valley between two adjacent and equal peaks is X% h, the peak separations of the two mass
peaks is ΔM.
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ISO/TS 22933:2022(E)
a
Valley ≤ 0,1 h for two adjacent, equal peaks.
Figure 1 — 0,1 h valley between two adjacent and equal peaks
There are rarely standard samples that satisfies the X% valley definition. The following describes how
to obtain X% valley for usual standard samples which have only one mass peak. First, select a peak
shape without any interference or clean the surface of standard sample to remove any interference of
other peaks, then make a second mass peak by copying first peak and compose the two peaks. From the
composed peak shape, obtain X% valley. Figure 2 shows how to compose two peaks to obtain X% valley.
a) b)
Key
measured peak
measured peak after shift ΔM
sum of the two peaks
NOTE Here, x=10, 10 % valley, the measured peak is measured by TOF-SIMS on Si wafer
Figure 2 — Two peaks composed from one peak shape to obtain x % valley (x=10, 10 % valley)
As shown in Figure 2 a) another peak is obtained by copying the measured peak with shift ΔM. The two
peaks add up so that the intensity of the valley between them is x%h, namely x% valley (here, x=10,
10 % valley) as shown in Figure 2 b).
5.3 X% peak width ΔM (X%) or R (X%)=M/ΔM (X%)
When the peak width measured at X% of the peak height is ΔM, the peak separations for two mass
peaks is ΔM.
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ISO/TS 22933:2022(E)
a
AT 0,1 h.
Figure 3 — Peak width ΔM measured at a point equal to 10 % of the peak height
5.4 X% peak tail interference
When the contribution of the M peak tail to its ΔM adjacent peak is X%, the peak separations for two
mass peaks is ΔM.
a
1 % contribution adjacent peaks.
Figure 4 — 1 % contribution of the M peak tail to its ΔM adjacent peak
NOTE For M-SIMS, abundance sensitivity has been used to describe the peak tail interference. For example,
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the ratio of the signal intensity can be examined at Al ± 27/250 m/z [27,089 6 or 26,873 6 m/z, next to the mass
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peak of Al (26,981 6 m/z)] to the signal intensity of Al. The smaller the ratio, the better, generally 0,1 ppm is
required for analysing the isotope ratio in geological samples.
5.5 Summary
The physical concept of the valley definition for peak separation is quite clear but it is often difficult to
find two adjacent and equal peaks. Therefore, peak fitting or peak composing should normally be used,
making the whole process inconvenient.
The peak width is the most popular definition to be used in the field of mass spectrometry. However,
there are different X values used in 5.2 to 5.4, which can be selected as 50 %, 20 %, 10 %, 5 %, 1 %,
or near 0 %, etc. The 50 % peak width definition is often simplified as full width at half maximum
(FWHM) definition. In SIMS analysis, the R=M/ΔM (10 %, 1 % or even 0 %) definitions are used for high
performance magnetic sector SIMS, and ΔM (10 %, 5 %) definitions are used for quadrupole SIMS, but
only R=M/ΔM (50 %) definition is normally used for TOF-SIMS and FT-SIMS.
In order to perform quantitative analysis, it is necessary to avoid the interference due to contribution
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of the adjacent peak tail. For example, to analyse the trace Al at Si wafer by SIMS, it is necessary to
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avoid the possible interference from the strong Si peak tail. In this case, X% peak tail interference
definition is commonly used for quantitative analysis.
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ISO/TS 22933:2022(E)
6 Procedure to determine the mass resolution
6.1 General
For adjusting and optimizing the setting of a SIMS spectrometer, the parameters of analysis (e.g. energy
of primary ion, ion species, polarity of secondary ion, scan area of primary ion beam, analysis area,
stability of primary ion current, species of secondary ion, etc.) should be set following the procedure
given by the maker or industry standard or national standard or international standard.
6.2 Removing contamination on sample surface
The contamination on sample surface should be removed by sputtering or other ways. The
contamination layer usually is about 1 nm to 3 nm.
6.3 Obtaining spectrum peak
1) The measured location should be in the area with no or less contamination in the centre of the
sample, and at least 0,2 mm away from the edge of the sample.
2) Adjust the current I of a beam current and making the maximum of mass spectrum pea
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