ISO 14237:2000

Surface chemical analysis — Secondary-ion mass spectrometry — Determination of boron atomic concentration in silicon using uniformly doped materials

Analyse chimique des surfaces — Méthode par spectrométrie de masse des ions secondaires — Dosage des atomes de bore dans le silicium à l'aide de matériaux dopés uniformément

General Information

• Status: Withdrawn
• Publication Date: 02-Feb-2000
• Withdrawal Date: 02-Feb-2000
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: ISO/TC 201/SC 6 - Secondary ion mass spectrometry
• Drafting Committee: ISO/TC 201/SC 6 - Secondary ion mass spectrometry
• Current Stage: 9599 - Withdrawal of International Standard
• Completion Date: 09-Jul-2010

Relations

• Revised: ISO 14237:2010 - Surface chemical analysis — Secondary-ion mass spectrometry — Determination of boron atomic concentration in silicon using uniformly doped materials
• Effective Date: 15-Apr-2008

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 14237
First edition
2000-02-01
Surface chemical analysis — Secondary-
ion mass spectrometry — Determination of
boron atomic concentration in silicon using
uniformly doped materials
Analyse chimique des surfaces — Méthode par spectrométrie de masse
des ions secondaires — Dosage des atomes de bore dans le silicium à
l'aide de matériaux dopés uniformément
Reference number
ISO 14237:2000(E)
©
ISO 2000

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ISO 14237:2000(E)
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ii © ISO 2000 – All rights reserved

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ISO 14237:2000(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative reference .1
3 Principle.1
4 Reference materials.1
5 Apparatus .2
6 Specimen.3
7 Procedure .3
8 Expression of results .6
9 Test report .8
Annex A (informative) Determination of carrier density in silicon wafers .9
Annex B (informative) Boron isotope ratio measured by SIMS.12
Annex C (normative) Procedures for evaluation of apparatus performance.15
Annex D (normative) Procedures for the depth profiling of NIST SRM 2137.17
Annex E (informative) Statistical report on interlaboratory test programme.20
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ISO 14237:2000(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
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.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 14237 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 6, Secondary ion mass spectrometry.
Annexes C and D form a normative part of this International Standard. Annexes A, B and E are for information only.
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ISO 14237:2000(E)
Introduction
This International Standard was prepared for the determination by secondary-ion mass spectrometry (SIMS) of
boron atomic concentrations in uniformly doped silicon wafers.
SIMS needs reference materials to perform quantitative analyses. Certified reference materials are only available
for limited matrix-impurity combinations, and they are costly. SIMS inevitably consumes these reference materials
at every measurement. Thus, secondary reference materials which can be prepared by each laboratory and
calibrated using a certified reference material are useful for daily analyses.
In this International Standard, a standard procedure is described for quantitative boron analysis in single-crystalline
silicon using secondary reference materials calibrated by a certified reference material implanted with boron.
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INTERNATIONAL STANDARD ISO 14237:2000(E)
Surface chemical analysis — Secondary-ion mass spectrometry —
Determination of boron atomic concentration in silicon using
uniformly doped materials
1 Scope
This International Standard specifies a secondary-ion mass spectrometric method for the determination of boron
atomic concentration in single-crystalline silicon using uniformly doped materials calibrated by a certified reference
material implanted with boron. This method is applicable to uniformly doped boron in the concentration range from
16 3 20 3
1� 10 atoms/cm to 1� 10 atoms/cm .
2 Normative reference
The following normative document contains provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, this publication do
not apply. However, parties to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent edition of the normative document indicated below. For undated references,
the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of
currently valid International Standards.
ISO 5725-2:1994, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method
for the determination of repeatability and reproducibility of a standard measurement method.
3Principle
An oxygen-ion beam or a caesium-ion beam is impinged onto the sample surface and the emitted secondary ions
of boron and silicon are mass-analysed and detected.
Uniformly doped secondary reference materials are calibrated by using an ion-implanted primary reference material
and are used as working reference materials.
4 Reference materials
4.1 Primary reference material
A primary reference material is used for the determination of the boron atomic concentration of the secondary
reference materials. The primary reference material shall be a certified reference material (CRM) of silicon
implanted with boron.
NOTE NIST Standard Reference Material 2137 (referred to hereinafter as NIST SRM) is the only CRM of boron in silicon at
this moment.
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ISO 14237:2000(E)
4.2 Secondary reference materials
4.2.1 Secondary reference materials are used for the determination of boron atomic concentrations in test
specimens. At least one boron-doped reference material together with one non-boron-doped reference material
shall be used for daily analysis. Two other different boron-doping levels are recommended to be used to confirm
the performance of the apparatus (see annex C).
4.2.2 The secondary reference materials (referred to hereinafter as bulk RMs) shall be single-crystal silicon
wafers or epitaxial silicon wafers with a ca. 100�m thick epitaxial layer, and shall be uniformly doped with natural-
isotopic boron.
16 3 20
4.2.3 Boron-doped wafers with boron atomic concentrations between 1� 10 atoms/cm and 1� 10
3
atoms/cm shall be obtained. It is recommended that the three doping levels given in Table 1 are used. When only
one level is used, RM-B or RM-C should be chosen. A non-boron-doped wafer shall be obtained for background
checking.
Wafers with small boron concentration gradients shall be selected. The boron concentration gradient shall be less
than 5 % per cm.
NOTE Approximate boron atomic concentrations can be determined as carrier densities from the resistivity of the wafers.
The resistivity measurement procedures and the procedure for converting between resistivity and carrier density are presented
in annex A.
Table 1 — Bulk reference materials
Boron doping level
Name
3
atoms/cm
16 17
RM-A
low 1� 10 to 1� 10
17 18
RM-B
middle 5� 10 to 5� 10
19 20
RM-C
high 1� 10 to 1� 10
14
RM-BG
none � 1� 10
11 10
4.2.4 Theisotope ratioof Bto B in the bulk RM chosen in 4.2.2 shall be determined by one of following
methods.
–
a) The isotope ratio shall be evaluated by a magnetic-sector SIMS instrument detecting BSi ions. The
measurement procedure stipulated in 7.5.2 shall be used for this purpose.
b) The bulk RM shall be assumed to have the accepted nominal natural isotopic composition of 19,9 atomic
10 11 11 10
percent B and 80,1 atomic percent B, i.e. a ratio of B atoms to B atoms of 4,025. The boron isotope
ratio in a specific material, however, can have� 5 % deviation from the natural isotope ratio.
NOTE SIMS will generally measure a deviated isotope ratio depending on type of instrument and detected ions. The
10 28 – 11 28 � 10 � 11 �
deviation is smaller between B Si and B Si than between B and B in a magnetic-sector mass spectrometer (see
annex B).
5 Apparatus
Secondary-ion mass spectrometry apparatus equipped with an oxygen-ion source and/or a caesium-ion source
shall be used.
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ISO 14237:2000(E)
Whenever the apparatus performance is required to be confirmed, the procedures stipulated in annex C shall be
carried out. The procedures for linearity of measurement stipulated in C.6 can be replaced by local documented
procedures.
6 Specimen
The analysed specimen shall have a mirror-polished surface. The specimen shall be cut into an appropriate size for
analysis and further degreased and washed if necessary.
7 Procedure
7.1 Adjustment of secondary-ion mass spectrometer
For oxygen-ion beam use, see Table 2. For caesium-ion beam use, see Table 3. Other conditions not shown here
shall be set in accordance with the manufacturer’s instructions or a local documented procedure.
Table 2 — Measurement conditions for oxygen-ion beam
Element Characteristic
�
Primary-ion species
O
2
Secondary-ion polarity Positive
2
Analysed area
� 100 �m
Primary-ion scan area 4 times the analysed area or larger
Table 3 — Measurement conditions for caesium-ion beam
Element Characteristic
�
Primary-ion species
Cs
Secondary-ion polarity Negative
2
Analysed area
>100 �m
Primary-ion scan area 4 times the analysed area or larger
7.2 Optimizing the secondary-ion mass spectrometer settings
7.2.1 Set the required instrument parameters and align the ion optics in accordance with the manufacturer's
instructions or a local documented procedure.
7.2.2 Ensure the stability of the primary-ion current and the mass spectrometer in accordance with the
manufacturer's instructions or a local documented procedure.
7.3 Specimen introduction
Immediately prior to introducing the specimens into the SIMS apparatus, dust particles shall be removed from the
surfaces with a pressurized duster. After introducing the specimens into the analysis chamber, analysis shall not
start until the pressure has recovered to the normal value recommended by the manufacturer or a local
documented procedure.
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ISO 14237:2000(E)
10 28 1 � 11 28 �
NOTE Residual gases in the analysis chamber can produce a B Si H background signal which interferes in B Si
detection, so care should be taken to obtain a better vacuum condition when a caesium-ion beam is used.
7.4 Detected ions
10 + 11 +
7.4.1 When an oxygen-ion beam is used, both B and B shall be detected as secondary-ion species of
10 28 � 11 28 �
boron. When a caesium-ion beam is used, both B Si and B Si shall be detected as secondary-ion species
of boron.
7.4.2 The ion species of silicon which has an appropriate ion intensity shall be detected, following the
manufacturer's instructions or a local documented procedure.
28 �
NOTE If the instrument has an electrometer detection mode, it is recommended that Si be detected as the reference ion
� 5
of B using the electrometer. For the pulse-counting mode, the silicon-ion intensity should be less than 1 � 10 counts/s. For
� �
BSi detection, Si is preferable as the reference ion.
2
7.5 Calibration
7.5.1 Measurement procedure for CRM
10 11
7.5.1.1 The depth profile of boron (either Bor B) in the CRM shall be measured using the same conditions
as those for the bulk RMs on the same day as the bulk RM measurements, following the procedures stipulated in
imp
annex D. The mean integrated ion intensity ratio of the CRM, A , shall be calculated following the procedures
stipulated in clause D.7.
7.5.1.2 The relative sensitivity factor of the CRM shall be obtained from the following formula:
�
imp
RSF �
imp
A
where
imp
RSF is the isotopic relative sensitivity factor obtained from the CRM;
10 11
� is the implanted boron (either Bor B) dose of the CRM.
7.5.2 Measurement procedure for bulk RMs
7.5.2.1 Measurements shall be made from the central region of the specimen holder window. When the boron-
ion intensity of the bulk RM is high, care shall be taken so as not to saturate the detector. If the boron-ion intensity
5
is higher than 1� 10 counts/s, the primary-ion intensity shall be reduced.
7.5.2.2 Depth profiles of boron and silicon shall be measured for all the bulk RMs. The data sampling
described below shall start after any surface contamination is removed and the secondary-ion intensities reach
stationary values, but shall be concluded before a change in secondary-ion intensity occurs due to surface
roughening induced by ion bombardment.
7.5.2.3 The secondary-ion intensities of boron and silicon shall be measured for at least 10 cycles alternately,
for at least 1 s for each boron isotope per cycle, at the same analysis position. This procedure shall be repeated
three times at different positions on the same specimen surface. Then another specimen shall be measured.
If the variation of silicon-ion intensity for one measurement point is less than the value guaranteed by the
manufacturer or that determined to be acceptable by local documented procedures, it can be regarded as constant.
In this case, it is not necessary to measure the silicon-ion intensity cycle by cycle. It can be measured at any one
cycle for each analysis position.
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ISO 14237:2000(E)
7.5.2.4 The detected secondary-ion intensity of boron in RM-BG shall be used as the background level of the
analysis.
7.5.2.5 Ion intensity ratios of boron to silicon for each bulk RM shall be determined for each measurement cycle
by cycle at one measurement position, and then a mean value for all the measurement cycles shall be calculated,
and the mean value obtained further averaged for three measurement positions, using the following formulae:
11
I
ij,
11
J �
ij,
Si
I
ij,
3 n
F I
1 1
11 11
J � J
G J
� � ij,
3 n
H K
j�1 i�1
where
11 Si
11
I and I are the B-ion intensity and the silicon-ion intensity in each RM, respectively, at measurement
ij, ij,
cycle i and measurement position j;
11 11
J is the mean ion intensity ratio for Bineachbulk RM;
n is the total number of measurement cycles for each bulk RM.
10 10
The same procedure shall be used to determine the mean intensity ratio, J ,for B.
7.5.2.6 The experimental boron isotope ratio for the SIMS instrument shall be determined using one of the
10 � 30 3+
bulk RMs. Since there is a possible mass spectral interference between B and Si that may be significant for
lower boron atomic concentration specimens, it is recommended that a bulk RM be used which has a boron atomic
17 3
concentration greater than 1� 10 atoms/cm with a known isotope ratio. The measured isotope ratio shall be
calculated using the following formula:
11 11
JJ�
BG
� �
10 10
JJ�
BG
where
11 10
� is the measured isotope ratio of Bto B;
11 10
11 10
J and J are the mean background ion intensity ratios for Band B, respectively, derived from RM-BG.
BG
BG
A correction factor for the measured isotope ratio shall be determined using the following formula:
�
0
� �
�
where � is the actual isotope ratio in the bulk RM.
0
If � is not known, the natural isotope ratio,� = 4,025 (see 4.2.3), shall be used.
0 0
10 11
� shall be used to correct the experimental mass discrimination between Band B.
7.5.3 Calibration of bulk RMs
imp 11
The value of RSF obtained in 7.5.1 shall be used as the calibration relative-sensitivity factor. The Batomic
concentration in each bulk RM shall be calibrated using the calibration relative-sensitivity factor.
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ISO 14237:2000(E)
10
If the CRM is implanted with B, the mass discrimination correction factor obtained in 7.5.2 shall be used:
11cal imp 11 11
CJ��RSF �J
ej
kk BG
where
11cal
11
C is the calibrated B atomic concentration in each bulk RM;
k
11
11
J is the mean ion intensity ratio for Bineachbulk RM.
k
11
If the CRM is implanted with B, mass discrimination correction is not necessary:
11cal imp 11 11
CJ��RSF J
ej
kk BG
7.6 Measurement of test specimen
7.6.1 Measurement procedure
Test specimens shall be measured under the same conditions as stipulated in 7.5.2.
Ion intensity ratios of boron to silicon shall be determined for each measurement cycle by cycle at one
measurement position, and then a mean value for all the measurement cycles shall be calculated. The mean value
obtained shall be further averaged for three measurement positions.
7.6.2 Determination of working relative-sensitivity factor
7.6.2.1 Use one of the previously calibrated bulk RMs to determine the working relative-sensitivity factor and
the mass discrimination correction factor for the test specimen measurement. It is recommended that the bulk RM
be selected whose boron-ion intensity is as close to those in the test specimens as possible. Use the calibrated
boron atomic concentration determined in 7.5.3 as the reference value.
2
NOTE Use of RM-A is not recommended when boron-ion intensities for the sample are lower than 1 � 10 counts/s.
7.6.2.2 The bulk RM chosen and the RM-BG shall be measured under the same conditions as the test
specimens on the same day, following the procedures stipulated in 7.5.2.
Ion intensity ratios of each boron isotope to silicon shall be determined for each measurement cycle by cycle at one
measurement position, and then a mean value for all the measurement cycles shall be calculated. The mean value
obtained shall be further averaged for three measurement positions.
8 Expression of results
8.1 Method of calculation
8.1.1 The working relative-sensitivity factor shall be obtained from the following formula:
11cal
C
work
m
RSF �
11 11
JJ�
m
BG
where
work
RSF is the working relative sensitivity factor obtained from the bulk RM chosen;
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ISO 14237:2000(E)
11cal
C
11
m
is the calibrated B atomic concentration in the bulk RM chosen;
11
11
J is the mean ion intensity ratio for B in the bulk RM chosen;
m
11
11
J is the mean background ion intensity ratio for B derived from the RM-BG.
BG
8.1.2 The mass discrimination correction factor for the test specimen measurement, � , shall be determined
m
using the following formula:
10 10
JJ�
�
m
0m BG
����
m 0m
11 11
�
JJ�
m
m BG
where
� is the actual isotope ratio in the bulk RM chosen;
0m
10
10
J is the mean ion intensity ratio for B in the bulk RM chosen;
m
10
10
J is the mean background ion intensity ratio for B derived from the RM-BG.
BG
8.1.3 Th
...