ISO/TR 16268:2009

TECHNICAL ISO/TR
REPORT 16268
First edition
2009-10-01
Surface chemical analysis — Proposed
procedure for certifying the retained areic
dose in a working reference material
produced by ion implantation
Analyse chimique des surfaces — Mode opératoire proposé pour
certifier la dose aréique retenue dans un matériau de référence de
travail produit par implantation d'ions

Reference number
©
ISO 2009
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ii © ISO 2009 – 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 .5
5 Concept and procedure .6
5.1 General information .6
5.2 Preparation of the working and transfer reference materials.8
5.3 Measurement of retained areic dose in the transfer reference material.8
5.4 Compatibility of the working reference material and the surface-analytical method .8
6 Requirements.9
6.1 Reference materials .9
6.2 Instrumentation requirements.9
6.2.1 Ion implanter .9
6.2.2 Wavelength-dispersive X-ray fluorescence spectrometer.9
6.2.3 Electron microprobe .10
6.3 Ion-implantation requirements.10
6.4 Uniformity requirement.10
7 Certification.10
7.1 Working reference material against the transfer reference material .10
7.2 Transfer reference material against the secondary reference material.10
7.3 Retained areic dose of the working reference material.11
Annex A (informative) Ion implantation .12
Annex B (informative) Ion-implantation dosimetry.13
Annex C (informative) X-ray fluorescence spectrometry.14
Annex D (informative) Non-certified secondary reference materials and substitutes.15
Annex E (informative) Uncertainties in measurements of areic dose .16
Bibliography.19

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
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.
ISO/TR 16268 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee
SC 2, General procedures.
iv © ISO 2009 – All rights reserved

Introduction
This Technical Report brings together experience to provide a proposed procedure, untested as a full
procedure, to address the general problem of how to obtain a certified working reference material (WoRM) for
the quantitative surface chemical analysis of a given solid material available in wafer (disc) form. The WoRM
discussed here is essentially an ion-implanted wafer, where the virgin wafer — chosen or prepared by the
analyst — has been ion-implanted with, typically, one isotope of a chemical element (henceforth referred to as
the analyte) of an atomic number larger than that of silicon. This WoRM is certified by the proposed procedure
for the areic dose of the analyte retained.
The retained areic dose of the ion-implanted analyte in the WoRM wafer is certified by comparative
measurement against the retained areic dose of the same analyte in an ion-implanted silicon wafer having the
status of a (preferably certified) secondary reference material (SeRM). The comparative measurement is
performed in a two-step process in which an intermediary third reference material and two measurement
techniques [wavelength-dispersive X-ray fluorescence spectrometry (WD/XFS) and ion-implantation
dosimetry] are used. The intermediary reference material, referred to as a transfer reference material (TrRM),
is also an ion-implanted silicon wafer and is a (non-identical) implantation twin of the WoRM (i.e. it is
co-produced with the WoRM but differs in wafer type and retained areic dose). Its function is, firstly, to avoid
possible secondary-excitation effects in a direct WD/XFS measurement on the WoRM and, secondly, to allow
the WoRM to be certified also for retained areic dose levels far below the measuring range of WD/XFS.
This certification of the WoRM is part of a new concept and procedure for characterization of reference
materials. In this concept, the WoRM, TrRM and SeRM have their places in a chain of reference materials and
a sequence of certifications. The SeRM is at the interface between the area of responsibility of the analyst and
that of a commercial supplier of reference materials. This Technical Report describes the part of the
procedure within the area of responsibility of the analyst and is based on the assumption that a suitable SeRM
is obtainable. When an SeRM is available, the analyst must also have access to a suitable ion implanter and
to a suitable wavelength-dispersive X-ray fluorescence spectrometer for comparative measurement of
retained areic doses.
The wafer format requirement of the WoRMs implies a particular suitability for the analysis of semiconductor
materials, although it is by no means restricted to this application. A restriction exists, however, in the choice
of surface-analytical technique. Although specimen and WoRM may be identical in analyte and host matrix,
the analyte may be present in a different chemical state and a different depth distribution. Meaningful results
from referencing to the WoRM can then be obtained only if the chosen surface-analytical technique is
insensitive to the chemical state of the analyte and if the technique allows corrections for different depth
distributions. This problem is addressed with special reference to analysis by secondary-ion mass
spectrometry. With an appropriate choice of surface-analytical technique, the WoRMs can be used for
quantitative measurement of homogeneous, ion-implanted, diffused and layered depth distributions of the
analyte.
This Technical Report is essentially based on Reference [1]. This work has also been a project (Technical
Working Area 2/Project 5) within the international Versailles Project on Advanced Materials and Standards
[2]
(VAMAS) .
TECHNICAL REPORT ISO/TR 16268:2009(E)

Surface chemical analysis — Proposed procedure for certifying
the retained areic dose in a working reference material
produced by ion implantation
1 Scope
This Technical Report specifies a procedure for the certification of the areic dose of an ion-implanted analyte
element of atomic number larger than that of silicon retained in a working reference material (WoRM) intended
for surface-analytical use. The WoRM is in the form of a polished (or similarly smooth-faced) wafer (also
referred to as the host), of uniform composition and nominal diameter 50 mm or more, that has been ion-
implanted with nominally one isotope of a chemical element (also referred to as the analyte), not already
16 2 13 2
present in the host, to a nominal areic dose normally within the range 10 atoms/cm to 10 atoms/cm (i.e.
the range of primary interest in semiconductor technology). The areic dose of the ion-implanted analyte
retained in the WoRM wafer is certified against the areic dose of the same analyte retained in an ion-
implanted silicon wafer having the status of a (preferably certified) secondary reference material (SeRM).
Information is provided on the concept and the procedure for certification of the WoRM. There is also a
description of the requirements for the reference materials, the comparative measurements and the actual
certification. Supporting information on ion implantation, ion-implantation dosimetry, wavelength-dispersive
X-ray fluorescence spectroscopy and non-certified substitutes for unobtainable SeRMs is provided in
Annexes A to D. Sources and magnitudes of uncertainties arising in the certification process are detailed in
Annex E.
2 Normative references
The following referenced documents are indispensable for the application 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.
3.1
certification
〈of a reference material, by a procedure〉 act of establishing the traceability of a property value to an accurate
realization of the unit in which the property value is expressed, where the certified value is accompanied by an
uncertainty value at a stated level of confidence
NOTE The term is used for both “the action of making certain” (i.e. certification by a procedure) and “the issuing of a
certificate” stating what has been certified by the procedure.
3.2
lower critical energy
kinetic energy of an ion beam below which the backscattering of perpendicularly incident ions exceeds a
specified percentage of the received areic dose
3.3
definitive method
〈of referencing〉 method based on a valid, well-described theoretical foundation ensuring negligible systematic
errors relative to end-user requirements, allowing a property to be measured either directly in terms of basic
units of measurement or in terms closely related to the base units through physical or chemical theory
expressed in exact mathematical equations
[9]
NOTE A definitive method is a special method of reference (see ISO Guide 30 ) particularly suitable for the
certification of primary reference materials by “allowing the property in question to be either measured directly in terms of
basic units of measurement or in terms closely related to the base units”. An example thereof would be the vapour
deposition of a high-purity element on a wafer and the measurement of the deposit by direct weighing.
3.4
areic dose
dose density (deprecated)
quotient of dN by dA, where dN is the number of particles of a specified type from a mono-energetic,
mass-analysed, quasi-parallel particle beam incident on a solid and suffering a specified fate on or after
passing through a geometric surface area dA
NOTE 1 The particles may be monoatomic or multiatomic. The chemical type, isotopic type and charge state of the
particles before incidence on the solid have to be specified.
NOTE 2 The geometric surface area refers to the areal measure of the projection of the usually micro-rough surface
onto an ideal plane parallel to that surface of the solid.
NOTE 3 Areic dose is a generic term requiring further specification concerning the temporary or permanent fate of the
particles before numeric values can be assigned. The fate of the particles refers to states of the particles prior to, during or
after encounter with the solid, such as incidence on, transmission through, backscattering from, stopping within,
re-emission by sputtering from, or retention in the solid.
3.5
implanted areic dose
imp
D
imp imp
quotient of dN by dA, where dN is the number of particles of a specified type from a mono-energetic,
mass-analysed, quasi-parallel particle beam incident on a solid within a geometric surface area dA and
captured within the solid
imp imp
D = dN /dA
NOTE 1 The particles may be monoatomic or multiatomic. The chemical type, isotopic type and charge state of the
particles before incidence on the solid have to be specified.
NOTE 2 The geometric surface area refers to the areal measure of the projection of the usually micro-rough surface
onto an ideal plane parallel to that surface of the solid.
NOTE 3 The implanted areic dose is smaller than the received areic dose if some of the particles incident on the solid
are transmitted through or backscattered from the solid.
3.6
lower critical value of areic dose
〈for referencing one reference material with respect to another by means of wavelength-dispersive X-ray
fluorescence spectrometry〉 minimum value of the retained areic dose necessary for the repeatability of a
specified measurement of this dose by this method to meet a given requirement
2 © ISO 2009 – All rights reserved

3.7
nominal areic dose
nom
D
nominal (approximate and averaged) value of the received areic dose, obtained from the quotient of the
particle equivalent of the beam current integral over time and the surface area over which the beam is
scanned with the best lateral uniformity possible in a given ion implanter
NOTE An analyte ion beam is always contaminated to some, although sometimes negligible, extent by analyte
neutrals as well as by non-analyte charged particles. Also, ion dosimetry may be flawed. Therefore, the beam current
integral over time is normally only an approximate measure of the number of analyte particles received. Also, the beam
scanning may not be entirely uniform and thus the nominal areic dose is an approximate average measure of the received
areic dose.
3.8
received areic dose
dose density (deprecated)
rec
D
rec rec
quotient of dN by dA, where dN is the number of particles of a specified type from a mono-energetic,
mass-analysed, quasi-parallel particle beam incident on a solid within a geometric surface area dA
rec rec
D = dN /dA
NOTE 1 The particles may be monoatomic or multiatomic. The chemical type, isotopic type and charge state of the
particles before incidence on the solid have to be specified.
NOTE 2 The geometric surface area refers to the areal measure of the projection of the usually micro-rough surface
onto an ideal plane parallel to that surface of the solid.
NOTE 3 The nominal areic dose is often wrongly substituted for the received areic dose and even for the retained areic
dose.
3.9
retained areic dose
ret
D
ret ret
quotient of dN by dA, where dN is the number of particles of a specified type from a mono-energetic,
mass-analysed, quasi-parallel particle beam incident on a solid within a geometric surface area dA and
permanently retained within the solid
ret ret
D = dN /dA
NOTE 1 The particles may be monoatomic or multiatomic. The chemical type, isotopic type, and charge state of the
particles before incidence on the solid have to be specified.
NOTE 2 The geometric surface area refers to the areal measure of the projection of the usually micro-rough surface
onto an ideal plane parallel to that surface of the solid.
NOTE 3 The retained areic dose is smaller than the implanted areic dose if some of the implanted particles are
re-emitted by sputtering from the solid. The amount by which the retained areic dose is less than the implanted areic dose
increases with increasing implanted areic dose.
3.10
upper critical value of areic dose
〈for referencing one reference material with respect to another by means of ion-implanter dosimetry〉 value of
the implanted areic dose at which the deviation of the retained areic dose from the implanted areic dose
reaches a given small percentage
NOTE The upper critical value of the areic dose is the highest value of the implanted areic dose at which the
conditions of quantitative ion implantation are still met.
3.11
implantation conditions
energy, composition (inclusive of charge states), current, diameter, angle of incidence and scanning
parameters of the ion beam at the target station, in addition to the target wafer, implanted area and nominal
areic dose (and, by implication, implantation time)
3.12
lower critical implantation time
time required to complete one hundred identical ion-beam scan patterns
3.13
implanter operating conditions
ion-implanter settings that influence the energy, composition (inclusive of charge states), current, diameter,
angle of incidence and scanning parameters of the ion beam at the target station on the implantation end of
the ion implanter
NOTE The residual pressure in the ion implanter can have a significant influence on the ion-beam composition.
3.14
ion implantation
process whereby, in a vacuum environment, a beam of ions of a specified type and of sufficient kinetic energy
is caused to penetrate a solid for the purpose of being retained therein
3.15
quantitative ion implantation
dose-limited ion implantation under conditions where, within experimental error, the implanted areic dose
equals the received areic dose, and the deviation of the retained areic dose from the implanted areic dose
remains below a given small percentage
3.16
overscan arrangement
target station design in an ion implanter in which one or more Faraday cups are situated at the perimeter of
the target wafer such that the aperture of each cup is in the same plane as the surface of the target wafer, and
the ion beam is scanned in a laterally uniform mode at right angles across the target wafer and the Faraday
cup(s)
3.17
reference material
material or substance one or more of whose properties are sufficiently well established to be used for the
calibration of an apparatus, for the assessment of a measurement method or for assigning values to materials
[9]
NOTE This definition deviates from that in ISO Guide 30:1992 by omission of the words “homogeneous and” after
“sufficiently” since the ISO Guide 30 definition omitted to consider ion-implanted materials which, by nature, are
inhomogeneous in the depth dimension.
3.18
certified reference material
reference material (as defined in 3.17), accompanied by a certificate, one or more of whose property values
are certified by a procedure which establishes its traceability to an accurate realization of the unit in which the
property units are expressed, and for which each certified value is accompanied by an uncertainty value at a
stated level of confidence
NOTE For ion-implanted reference materials, the certified property values must include the retained areic dose
averaged over the area of implantation, the point-to-point variation of the retained areic dose, the size and exact location
of the area of implantation, the kinetic energy of implantation, and preferably also a graphical or mathematical
representation of the depth distribution.
4 © ISO 2009 – All rights reserved

3.19
primary (ion-implanted) reference material
certified reference material, consisting of a high-purity silicon wafer ion-implanted with the analyte, that all
other ion-implanted reference materials are referenced against (directly or indirectly), the certified property
being the retained areic dose (inclusive of the lateral uniformity thereof) determined by a definitive method (as
defined in 3.3)
NOTE The primary reference material is used solely for purposes of certification of secondary reference materials
that are to be issued to analysts.
3.20
secondary (ion-implanted) reference material
ion-implanted certified reference material, nominally identical to the primary reference material in material and
areic dose, serving as an intermediary between a primary reference material and a working reference material,
the certified property being the retained areic dose (inclusive of the lateral uniformity thereof) determined by a
comparative measurement against the primary reference material
3.21
transfer (ion-implanted) reference material
ion-implanted certified reference material, nominally identical to the secondary reference material in material
and areic dose, co-produced with the working reference material and serving as an intermediary between a
secondary reference material and a working reference material, the certified property being the retained areic
dose (inclusive of the lateral uniformity thereof) determined by a comparative measurement against a
secondary reference material
NOTE Each working reference material is paired with a transfer reference material that is ion-implanted in the same
implanter under invariant (and hence identical) implanter operating conditions.
3.22
working (ion-implanted) reference material
certified reference material, consisting of a wafer of a composition specified by the analyst, ion-implanted with
the analyte for direct use in a surface analysis, the certified property being the retained areic dose (inclusive of
the lateral uniformity thereof) determined by a comparative measurement against a secondary reference
material via a transfer reference material
3.23
target wafer
host wafer
virgin wafer subjected to ion implantation
4 Symbols and abbreviated terms
CRM certified reference material
D areic dose
imp
D implanted areic dose
nom
D nominal areic dose
nom
D nominal areic dose for the transfer reference material
T
nom
D nominal areic dose for the working reference material
W
rec
D received areic dose
ret
D retained areic dose
ret
D retained areic dose for the secondary reference material
S
ret
D retained areic dose for the transfer reference material
T
ret
D retained areic dose for the working reference material
W
PrRM primary reference material, ion-implanted
Q X-ray fluorescence signal for the analyte in the secondary reference material
S
Q X-ray fluorescence signal for the analyte in the transfer reference material
T
RM reference material
SeRM secondary reference material
SIMS secondary-ion mass spectrometry
TrRM transfer reference material
WD/XFS wavelength-dispersive X-ray fluorescence spectrometry
WoRM working reference material
5 Concept and procedure
5.1 General information
A fundamental problem in surface chemical analysis of a given material is the calculation of the local
concentration of the analyte from the intensity of the signal registered by the measuring instrument. Generally
preferred is a calculation based on a modelling of the signal excitation and measuring processes. For the
powerful and widely used surface-analytical technique of secondary-ion mass spectrometry (SIMS),
quantification via modelling has, hitherto, proved to be impossible. Instead, reference materials of similar and
known composition are used for establishing a quantitative relationship between signal intensity and analyte
concentration, based on the similarity principle and the rule of proportionality.
There are problems associated with this analysis approach that have not as yet been satisfactorily solved. A
major problem is that no commercial supplier is prepared to prepare and stock certified reference materials
(CRMs) for the great variety of multi-component materials in use. The cost of certifying potential CRMs can
only be justified if some minimum number can be sold at an affordable price. This market can be estimated
with some certainty only for CRMs used in the routine quality control of industrially established processes. The
materials developer, experimenting with ever-new compositions and requiring a one-off CRM for every
composition, cannot be catered for under this practice.
A solution to this problem is described in this Technical Report that addresses both the need of the analyst
and the commercial reality of the reference material business. The solution is based on a new concept and
[1]
procedure that is not based on the current practice in which all reference materials, including working
reference materials (WoRMs), are prepared, certified, certificated and sold by a commercial supplier. Instead,
the analyst is given the opportunity to accept responsibility for the preparation and certification of special
WoRMs, and the commercial supplier is merely expected to stock a small range of generic primary reference
materials (PrRMs) and to certify and sell secondary reference materials (SeRMs) in response to market
demand (i.e. just-in-time). The analyst, in turn, certifies the WoRM against the SeRM. Service providers are
expected to assist in the preparation and certification of the reference materials.
The complete scheme is outlined in Table 1.
6 © ISO 2009 – All rights reserved

Table 1 — Referencing scheme for measurement of a chemical element (analyte) in a host matrix
(The specimen and the two reference materials WoRM and TrRM are within the area of responsibility of the
analyst. This Technical Report is concerned with the certification of the TrRM and the WoRM.)
Host Host Analyte quantity Referenced Referencing
Analyte
material format measured against method
1.
Chemical element Areic dose
Surface-analytical
of atomic number As given As given or WoRM
Specimen to
technique
larger than silicon local concentration
be analysed
2.
Areic dose < upper
Wafer or Ion-implantation
Isotope thereof As specimen critical areic dose TrRM
WoRM
disc dosimetry
value
working
Areic dose between
3. WD/XFS
lower and upper
As WoRM Silicon Wafer SeRM
critical areic dose
TrRM transfer
comparative
values
Areic dose between
4.
WD/XFS
lower and upper
As WoRM Silicon Wafer PrRM
SeRM
critical areic dose
comparative
secondary
values
Areic dose between
5.
Definitive method
lower and upper
As WoRM Silicon Wafer Not applicable
critical areic dose
PrRM primary (see 3.3)
values
Interpretation of table
Row 5: The specified PrRM is kept by a commercial supplier of reference materials.
Row 4: The SeRM is sold by this supplier as a certified copy of the PrRM, after being referenced by the referencing method in row 4.
Row 1: The given analyte in a given specimen is quantified by comparative measurement against a WoRM by the referencing method in
row 1.
Row 2: The WoRM is referenced against the SeRM in a two-step process via a TrRM and a combination of the referencing methods in
rows 2 and 3. In the first step, the WoRM is referenced against the TrRM by the referencing method in row 2.
Row 3: The TrRM is then referenced against the SeRM by the referencing method in row 3 (i.e. the second step of the two-step process
of referencing of the WoRM against the SeRM).

As shown in Table 1, all four reference materials in the chain PrRM → SeRM → TrRM → WoRM are of wafer
or disc format into which the analyte has been introduced by ion implantation. For reasons explained in
Annex C, the analyte is a chemical element of atomic number larger than that of silicon. The reason for the
choice of ion implantation for the manufacture of reference materials is that, in general, the process is fast,
cheap, versatile and well controlled. The quantity of analyte is measured during implantation and can be
uniformly spread over the wafer surface. The analyte is safely stored inside the wafer and the depth
distribution is sufficiently well known. Further, the commercial supplier benefits from the fact that the
expenditure for the certification of the PrRM is a once-only expenditure because the PrRM is neither sold to
the analyst nor is it consumed in the certification of the SeRMs against the PrRMs. This situation is made
possible by the use of wavelength-dispersive X-ray fluorescence spectrometry (WD/XFS) for certification. This
non-invasive analytical technique leaves the PrRM undamaged and reusable.
This Technical Report describes the certification of the two reference materials WoRM and TrRM, which fall
within the area of responsibility of the analyst. The role of the supplier is beyond the scope of this Technical
Report.
The analyst starts with the acquisition of a suitable SeRM from a commercial supplier. At the time of
preparation of this Technical Report, only four suitable PrRMs or SeRMs were available from two suppliers:
[4]
three CRMs from the US National Institute of Standards and Technology (NIST) and one from the European
[5]
Institute for Reference Materials and Measurements (IRMM) . A suitable CRM for this application is one for
which a certified areic dose is provided that is appropriate for comparative measurement by WD/XFS. If a
suitable CRM is not available, the analyst must either fall back on non-certified SeRMs (if commercially
available) or follow the suggestion made in Annex D on how to prepare a substitute SeRM that is linked to a
CRM.
The analyst then proceeds with the following two steps, explained in 5.2 and 5.3, respectively.
5.2 Preparation of the working and transfer reference materials
The analyst should contact a service provider for the preparation by ion implantation of the WoRM and the
associated TrRM. The service provider is given a host wafer for the WoRM and a silicon wafer for the TrRM,
together with instructions on the implantation energy and the respective nominal areic doses of the desired
analyte. These nominal areic doses are not to exceed the respective upper critical areic doses. At the same
time, the nominal areic dose of the TrRM must be larger than the lower critical areic dose in order to remain
within the measurement range of WD/XFS. There is no such restriction on the nominal areic dose of the
WoRM; this dose can, if required for the analytical task, be several orders of magnitude lower than that of the
TrRM. The implantation energy must be at least as high as the critical energy for the wafer material with the
lowest atomic number (most often silicon). This condition is essential for keeping ion backscattering from the
wafer at a negligible value, such that the received and the retained areic doses are practically equal within the
quantitative ion-implantation regime.
The analyst monitors adherence to these specifications and, most importantly, records the nominal areic
doses actually measured. The ratio of the nominal areic doses for the WoRM and TrRM is taken to be equal to
the ratio of the retained areic doses.
5.3 Measurement of retained areic dose in the transfer reference material
The retained areic dose in the TrRM is measured by comparative analytical measurements using WD/XFS
against the known retained areic dose in the SeRM. A qualified service provider could make this
measurement.
NOTE The use of WD/XFS as a near-surface analytical technique (inclusive of the use of ion-implanted reference
materials for certification) requires computational correction for different depth distributions of the analyte. This topic is
discussed in Annex C.
The retained areic dose of the ion-implanted analyte in the WoRM is then obtained from the measurement of
the retained areic dose of the TrRM and the ratio of the nominal areic doses of the WoRM and TrRM obtained
in 5.2.
5.4 Compatibility of the working reference material and the surface-analytical method
Considered here is the use of SIMS as the surface-analytical method in which the WoRM is to be used. For
analysis by SIMS, only the analyte in the freshly sputtered surface is measured at any particular time. In other
words, the analyte signal is generated not in the undisturbed material but in a so-called altered layer at the
instantaneous surface where any pre-existing physical and chemical structure has been largely destroyed by
the incident energetic ions. Hence, provided that the matrices of the specimen and the WoRM are as similar
as they are expected (by design) to be, analysis by SIMS converts the analyte in either of the two matrices
into quasi-identical states, and the proportionality of signal to concentration is transferable between them. It is
then not necessary to specify or determine the physical and chemical states of the matrices during the SIMS
measurements.
The working reference material and the specimen material should be handled in the same way during the time
from ion implantation to the SIMS measurements in order to minimize the possibility that different amounts or
types of surface contamination on the wafers might affect the SIMS measurements.
8 © ISO 2009 – All rights reserved

An analysis similar to that given here for SIMS needs to be made if another surface-analysis technique is
utilized for the comparative measurements.
6 Requirements
6.1 Reference materials
The PrRM, SeRM and TrRM are high-purity silicon wafers (host wafers) of nominally 50 mm diameter (or
more), ion-implanted under non-channelling conditions to a lateral uniformity of uncertainty u ±1 % (95 %
confidence level) with nominally one isotope of a chemical element (the analyte) with an atomic number larger
than that of silicon to a retained areic dose (the certified property) between the lower and upper critical areic
15 2 16 2
dose values (typically in the range from a low 10 atoms/cm value to a high 10 atoms/cm value).
The WoRM is a wafer of the material required by the analyst of nominally 50 mm diameter (or more), ion-
implanted under non-channelling conditions to a lateral uniformity of uncertainty u ± 1 % (95 % confidence
level) with nominally one isotope of a chemical element as the analyte to a retained areic dose below the
13 2
upper critical areic dose value (typically in the range from a low 10 atoms/cm value to a high
16 2
10 atoms/cm value).
6.2 Instrumentation requirements
6.2.1 Ion implanter
For preparation of the WoRM and the TrRM, an ion implanter of implantation energy W 300 keV and,
[3]
preferably, high mass resolution (ideally M/∆M W 500 ) with the following features is required:
a) stability of current, composition and energy of the ion beam such that the uncertainty of each does not
exceed ± 1 % (95 % confidence level);
b) the ability to separate neutrals from the ion beam or to operate at a target-station pressure at the low
−5
10 Pa level;
c) lateral uniformity of the areic dose in compliance with the intended application of the WoRM (see 6.2.3,
6.4 and Annex B);
d) wafer mounting with tilt (to avoid axial channelling) and twist (to avoid planar channelling) [for Si(100)
wafers, 7° tilt and 30° twist is recommended];
e) overscan arrangement of Faraday cup(s) at the target station;
f) Faraday cup(s) designed to reject externally generated secondary charged particles (electrons and ions).
6.2.2 Wavelength-dispersive X-ray fluorescence spectrometer
For comparative measurements of the TrRM against the SeRM, a wavelength-dispersive X-ray fluorescence
spectrometer with the following features is required:
a) an X-ray tube (preferably with a rhodium anode) operating at a power W 3 kW;
b) specimen rotation;
c) a mask for defining identical exposure windows on different RMs.
The mask should be free of the analyte and should not give rise to spectral interference or a high background
at the signal X-ray line.
6.2.3 Electron microprobe
Scanning-pattern generators in commercial ion implanters are designed to minimize the non-uniformity of the
retained areic dose to an extent given in the generator specifications. This is generally satisfactory for all
broad-beam analytical applications of the WoRM. Only if narrow-beam analytical application is intended may it
be necessary to check the lateral uniformity of the retained areic dose by means of an electron microprobe
with a wavelength-dispersive X-ray spectrometer, either on the TrRM or another suitable test specimen.
6.3 Ion-implantation requirements
The WoRM and TrRM are prepared sequentially in the same ion implanter under identical implanter operating
conditions meeting the following requirements:
a) the critical energy is exceeded for each RM;
b) the ion beam current is set so that the lower critical implantation time is exceeded for each RM while
ensuring that the maximum implantation time remains acceptable;
c) the upper critical areic dose value for 99 % retention is not exceeded for each RM.
NOTE 1 The critical energy is taken from literature sources (such as Reference [6]).
NOTE 2 The lower critical implantation time is the minimum time required to ensure a uniform areic dose across the
target wafer and Faraday cup(s). This time is about 15 s (varying with the scan frequency) and is usually the minimum
implantation time for the WoRM. The implantation time for the TrRM is related to the implantation time for the WoRM in the
same ratio as the nominal areic doses of the two. For example, if the nominal areic dose of the TrRM is larger than that of
the WoRM by a factor of 1 000, then the minimum implantation time for the TrRM is 15 000 s (i.e. just over 4 h).
6.4 Uniformity requirement
As explained in 6.2.3, scanning-pattern generators in commercial ion implanters are designed to minimize
non-uniformity of the retained areic dose to an extent given in the generator specifications. This is generally
satisfactory for all broad-beam analytical applications of the WoRM. Only if narrow-beam analytical application
is intended may it be necessary to check the point-to-point variation by means of an electron microprobe,
either on the TrRM or another suitable test specimen. The electron beam is applied in the point mode at
randomly chosen positions on the surface of the TrRM or test specimen, and measurements are made of
X-rays emitted from the analyte with a wavelength-dispersive X-ray spectrometer. Sufficient X-ray photon
counts must be collected for the uncertainty to be reduced to the desired level (see Annex E).
7 Certification
7.1 Working reference material against the transfer reference material
Under conditions of quantitative ion implantation, when the received areic dose is, for all practical purposes,
ret ret
equal to the retained areic dose, the retained areic doses of the WoRM and TrRM, D and D ,
W T
nom nom
respectively, are related to the corresponding measured nominal areic dose values, D and D , as
W T
follows:
ret ret nom nom
DD//=D D (1)
WT W T
7.2 Transfer reference material against the secondary reference material
WD/XFS is used for comparative measurement of the TrRM against the SeRM. X-ray fluorescence signals of
identical signal type from the analyte are produced by identical X-ray exposures from identical surface areas
on the two RMs. Covering each RM with the same mask ensures the exposure of and emission from identical
surface areas.
10 © ISO 2009 – All rights reserved

If the TrRM and the SeRM have been ion-implanted at the same implantation energy and at the same angle of
incidence, the analyte depth distributions will be identical and no attenuation correction is required. If either
th
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