ISO 17331:2004
(Main)Surface chemical analysis — Chemical methods for the collection of elements from the surface of silicon-wafer working reference materials and their determination by total-reflection X-ray fluorescence (TXRF) spectroscopy
Surface chemical analysis — Chemical methods for the collection of elements from the surface of silicon-wafer working reference materials and their determination by total-reflection X-ray fluorescence (TXRF) spectroscopy
ISO 17331:2004 specifies chemical methods for the collection of iron and/or nickel from the surface of silicon-wafer working reference materials by the vapour-phase decomposition method or the direct acid droplet decomposition method. It applies to iron and/or nickel atomic surface densities from 6 times 10 to the power 9 atoms per square centimetre to 5 times 10 to the power 11 atoms per square centimetre.
Analyse chimique des surfaces — Méthodes chimiques pour collecter les éléments analysés de tranches de silicium comme matériaux de référence pour l'analyse par spectroscopie de fluorescence X en réflexion totale (TXRF)
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INTERNATIONAL ISO
STANDARD 17331
First edition
2004-05-15
Surface chemical analysis — Chemical
methods for the collection of elements
from the surface of silicon-wafer working
reference materials and their
determination by total-reflection X-ray
fluorescence (TXRF) spectroscopy
Analyse chimique des surfaces — Méthodes chimiques pour collecter
les éléments analysés de tranches de silicium comme matériaux de
référence pour l'analyse par spectroscopie de fluorescence X en
réflexion totale (TXRF)
Reference number
©
ISO 2004
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ii © ISO 2004 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 Abbreviations. 2
5 Reagents. 2
6 Apparatus. 6
7 Specimen preparation and measurement environments. 6
8 Preparation of calibration specimen. 6
9 Making calibration curve. 8
10 Collection of iron and/or nickel from working reference material . 10
11 Determination of iron and/or nickel of working reference material. 11
12 Precision. 11
13 Test report. 12
Annex A (informative) International inter-laboratory test results. 13
Annex B (informative) International inter-laboratory test results of GF-AAS and ICP-MS . 16
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.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights (see Note to 10.1). ISO shall not be held responsible for identifying any or all such patent rights.
ISO 17331 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis.
iv © ISO 2004 – All rights reserved
Introduction
The measurement of metal impurities on the surface of silicon wafers by total-reflection X-ray fluorescence
spectroscopy (TXRF) is commonly accepted by the semiconductor industry.
ISO 14706 specifies a TXRF method for the measurement of metal impurities on a silicon-wafer surface with
10 2 14 2
atomic surface densities from 1 × 10 atoms/cm to 1 × 10 atoms/cm , also a vapour-phase decomposition
8 2 12 2
(VPD) method for atomic surface densities from 5 × 10 atoms/cm to 5 × 10 atoms/cm .
In ultra-large-scale integrated circuit (ULSI) manufacturing, the measurement of very-low-level metal
10 2
impurities on the surface of a silicon wafer, less than 10 atoms/cm , is currently required.
Reference materials with low-level metal impurities are important in TXRF analysis (see ISO 14706), but the
reference materials have a limited shelf life, especially as regards surface contamination. As a result,
preparation methods for working reference materials need to be standardized.
This test method allows the calculation of metal impurities on the surface of reference and test wafers.
Interlaboratory trials in nine laboratories in different countries indicated that this method has good
reproducibility and repeatability.
INTERNATIONAL STANDARD ISO 17331:2004(E)
Surface chemical analysis — Chemical methods for the
collection of elements from the surface of silicon-wafer working
reference materials and their determination by total-reflection
X-ray fluorescence (TXRF) spectroscopy
1 Scope
This International Standard specifies chemical methods for the collection of iron and/or nickel from the surface
of silicon-wafer working reference materials by the vapour-phase decomposition method or the direct acid
droplet decomposition method.
NOTE The determination of the elements collected may be carried out by graphite-furnace atomic-absorption
spectroscopy or inductively coupled plasma mass spectrometry instead of by total-reflection X-ray fluorescence
spectroscopy.
9 2
This International Standard applies to iron and/or nickel atomic surface densities from 6 × 10 atoms/cm to
11 2
5 × 10 atoms/cm .
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 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
ISO 14644-1:1999, Cleanrooms and associated controlled environments — Part 1: Classification of air
cleanliness
ISO 14706:2000, Surface chemical analysis — Determination of surface elemental contamination on silicon
wafers by total-reflection X-ray fluorescence (TXRF) spectroscopy
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
working reference material
silicon wafer used for the calibration specified in ISO 14706
3.2
calibration specimen
silicon wafer with a known amount of iron and/or nickel in a dried residue, used for calibration purposes
3.3
calibration solution
solution used to make a calibration specimen
3.4
internal standard
known amount of vanadium or scandium used to normalize the variation in the fluorescence X-ray intensities
of iron and/or nickel in a residue
3.5
internal-standard solution
solution used to make an internal standard
3.6
scanning
rolling a VPD or DADD microdroplet on a hydrophobic silicon surface in a reproducible pattern to cover the
entire surface of the wafer
4 Abbreviations
For the purposes of this document, the following abbreviations apply:
TXRF total-reflection X-ray fluorescence spectroscopy
VPD vapour-phase decomposition
DADD direct acid droplet decomposition
PE polyethylene
PFA polyfluoroalkoxyethylene
PP polypropylene
PTFE polytetrafluoroethylene
GF-AAS graphite furnace atomic absorption spectroscopy
ICP-MS inductively coupled plasma mass spectroscopy
5 Reagents
WARNING — Hydrofluoric acid is a highly corrosive liquid which attacks glass and has a great affinity
for water. Its vapour is irritant and toxic. Its action on the skin and eyes is strongly corrosive,
producing severe and painful burns which may not be immediately evident and which respond slowly
to treatment.
All specimens shall be handled in a well-ventilated area. Rubber gloves, rubber boots and a gown of a
suitable size to give adequate protection to the individual, as well as full head and face protection,
shall be worn when handling materials.
In an event of contact or suspected contact with hydrofluoric acid, wash the affected area with
copious quantities of water and seek immediate medical attention. Consult the manufacture’s
literature for further information.
2 © ISO 2004 – All rights reserved
5.1 Ultra-pure water, containing less than 1 pg/ml of each of the impurities iron, nickel, vanadium and
scandium.
5.2 Ultra-pure hydrofluoric acid, concentration ca. 21 mol/l to ca. 29 mol/l and containing less than
10 pg/ml of each of the impurities iron, nickel, vanadium and scandium.
NOTE The concentration of commercially available ultra-pure hydrofluoric acid is expressed as a percentage.
21 mol/l hydrofluoric acid corresponds to ca. 38 % and 29 mol/l to ca. 50 %.
5.3 Ultra-pure hydrogen peroxide, concentration ca. 10 mol/l to ca. 12 mol/l and containing less than
10 pg/ml of each of the impurities iron, nickel, vanadium and scandium.
NOTE The concentration of commercially available ultra-pure hydrogen peroxide is expressed as a percentage.
10 mol/l hydrogen peroxide corresponds to ca. 30 % and 12 mol/l to ca. 35 %.
5.4 Ultra-pure nitric acid, concentration ca. 11 mol/l to ca. 15 mol/l and containing less than 100 pg/ml of
each of the impurities iron, nickel, vanadium and scandium.
NOTE The concentration of commercially available ultra-pure nitric acid is expressed as a percentage. 11 mol/l nitric
acid corresponds to ca. 55 % and 15 mol/l to ca. 68 %.
5.5 Hydrofluoric acid, concentration ca. 29 mol/l and containing less than 100 pg/ml of each of the
impurities iron, nickel, vanadium and scandium.
NOTE The concentration of commercially available hydrofluoric acid is expressed as a percentage. 29 mol/l
hydrofluoric acid corresponds to ca. 50 %. The hydrofluoric acid specified in 5.5 is available commercially as
“semiconductor” grade.
5.6 Hydrogen peroxide, concentration ca. 10 mol/l and containing less than 100 pg/ml of each of the
impurities iron, nickel, vanadium and scandium.
NOTE The concentration of commercially available hydrogen peroxide is expressed as a percentage. 10 mol/l
hydrogen peroxide corresponds to ca. 30 %. The hydrogen peroxide specified in 5.6 is available commercially as
“semiconductor” grade.
5.7 Standard solutions
5.7.1 Iron standard solution: Use a commercially available 1 000 µg/ml iron standard solution specified for
AAS.
5.7.2 Nickel standard solution: Use a commercially available 1 000 µg/ml nickel standard solution
specified for AAS.
5.7.3 Vanadium standard solution: Use a commercially available 1 000 µg/ml vanadium standard solution
specified for AAS.
5.7.4 Scandium standard solution: Use a commercially available 1 000 µg/ml scandium standard solution
specified for AAS.
5.8 Diluted calibration solutions
5.8.1 Diluted iron calibration solution 1: A 10 µg/ml iron calibration solution in nitric acid.
Prepare diluted iron calibration solution 1 by either method a) or b) below:
a) Transfer 1 000 µl of iron standard solution (5.7.1) to a plastic 100 ml one-mark volumetric flask (6.1) with
a plastic micropipette (6.2), add ca. 90 ml of ultra-pure water (5.1), then add ca.1 ml of ultra-pure nitric
acid (5.4) and finally make up to the mark with ultra-pure water (5.1) and mix.
b) Weigh a 100 ml plastic beaker (6.3) to the nearest 0,1 g. Transfer 1 000 µl of iron standard solution
(5.7.1) to the beaker with a plastic micropipette (6.2), add ca. 90 ml of ultra-pure water (5.1), then add ca.
1 ml of ultra-pure nitric acid (5.4) and finally add ultra-pure water (5.1) to make the mass up to 100 g (plus
the mass of th
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