ASTM F1593-97

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 1593 – 97
Standard Test Method for
Trace Metallic Impurities in Electronic Grade Aluminum by
High Mass-Resolution Glow-Discharge Mass Spectrometer
This standard is issued under the fixed designation F 1593; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2 campaign—a series of analyses of similar specimens
performed in the same manner in one working session, using
1.1 This test method covers measuring the concentrations of
one GDMS setup. As a practical matter, cleaning of the ion
trace metallic impurities in high purity aluminum.
source specimen cell is often the boundary event separating
1.2 This test method pertains to analysis by magnetic-sector
one analysis campaign from the next.
glow discharge mass spectrometer (GDMS).
3.3 reference sample— material accepted as suitable for use
1.3 The aluminum matrix must be 99.9 weight % (3N-
as a calibration/sensitivity reference standard by all parties
grade) pure, or purer, with respect to metallic impurities. There
concerned with the analyses.
must be no major alloy constituent, for example, silicon or
3.4 specimen—a suitably sized piece cut from a reference or
copper, greater than 1000 weight ppm in concentration.
test sample, prepared for installation in the GDMS ion source,
1.4 This test method does not include all the information
and analyzed.
needed to complete GDMS analyses. Sophisticated computer-
3.5 test sample— material (aluminum) to be analyzed for
controlled laboratory equipment skillfully used by an experi-
trace metallic impurities by this GDMS test method. Generally
enced operator is required to achieve the required sensitivity.
the test sample is extracted from a larger batch (lot, casting) of
This test method does cover the particular factors (for example,
product and is intended to be representative of the batch.
specimen preparation, setting of relative sensitivity factors,
determination of sensitivity limits, etc.) known by the respon-
4. Summary of the Test Method
sible technical committee to affect the reliability of high purity
4.1 A specimen is mounted as the cathode in a plasma
aluminum analyses.
discharge cell. Atoms subsequently sputtered from the speci-
2. Referenced Documents men surface are ionized, and then focused as an ion beam
through a double-focusing magnetic-sector mass separation
2.1 ASTM Standards:
apparatus. The mass spectrum, that is, the ion current, is
E 135 Terminology Relating to Analytical Atomic Spectros-
collected as magnetic field, or acceleration voltage is scanned,
copy
or both.
E 177 Practice for Use of the Terms Precision and Bias in
4.2 The ion current of an isotope at mass M is the total
i
ASTM Test Methods
measured current, less contributions from all other interfering
E 691 Practice for Conducting an Interlaboratory Study to
sources. Portions of the measured current may originate from
Determine the Precision of a Test Method
the ion detector alone (detector noise). Portions may be due to
E 1257 Guide for Evaluating Grinding Materials Used for
incompletely mass resolved ions of an isotope or molecule with
Surface Preparation in Spectrochemical Analysis
mass close to, but not identical with, M . In all such instances
i
3. Terminology
the interfering contributions must be estimated and subtracted
from the measured signal.
3.1 Terminology in this test method is consistent with
4.2.1 If the source of interfering contributions to the mea-
Terminology E 135. Required terminology specific to this test
sured ion current at M cannot be determined unambiguously,
method and not covered in Terminology E 135 is indicated i
the measured current less the interfering contributions from
below.
identified sources constitutes an upper bound of the detection
limit for the current due to the isotope.
This test method is under the jurisdiction of ASTM Committee F-1 on
4.3 The composition of the test specimen is calculated from
Electronics and is the direct responsibility of Subcommittee F01.17 on Sputter
the mass spectrum by applying a relative sensitivity factor
Metallization.
(RSF(X/M)) for each contaminant element, X, compared to the
Current edition approved June 10, 1997. Published November 1997. Originally
e1
published as F 1593 – 95. Last previous edition F 1593 – 96 .
matrix element, M. RSFs are determined in a separate analysis
Annual Book of ASTM Standards, Vol 03.05.
Annual Book of ASTM Standards, Vol 14.02.
Annual Book of ASTM Standards, Vol 03.06.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 1593 – 97
of a reference material performed under the same analytical 7.2 Demineralized Water.
conditions, source configuration, and operating protocol as for
7.3 Tantalum Reference Sample.
the test specimen.
7.4 Aluminum Reference Sample.
4.4 The relative concentrations of elements X and Y are
7.4.1 To the extent available, Aluminum reference materials
calculated from the relative isotopic ion currents I(X ) and I(Y )
shall be used to produce the GDMS relative sensitivity factors
i j
in the mass spectrum, adjusted for the appropriate isotopic
for the various elements being determined (see Table 1).
abundance factors (A(X ), A(Y )) and RSFs. I(X ) and I(Y ) refer
i j i j 7.4.2 As necessary, non-aluminum reference materials may
to the measured ion current from isotopes X and Y , respec-
i j be used to produce the GDMS relative sensitivity factors for
tively, of atomic species X and Y.
the various elements being determined.
~X!/~Y!5 RSF~X/M!/RSF~Y/M!3 A~Y !/A~X!3 I~X !/I~Y ! (1) 7.4.3 Reference materials should be homogeneous and free
j i i i
of cracks or porosity.
where (X)/(Y) is the concentration ratio of atomic species X
7.4.4 At least two reference materials are required to estab-
to species Y. If species Y is taken to be the aluminum matrix
lish the relative sensitivity factors, including one nominally
(RSF(M/M) = 1.0), (X) is (with only very small error for pure
99.9999 % pure (6N-grade) aluminum metal to establish the
metal matrices) the absolute impurity concentration of X.
background contribution in analyses.
5. Significance and Use
7.4.5 The concentration of each analyte for relative sensi-
tivity factor determination should be a factor of 100 greater
5.1 This test method is intended for application in the
than the detection limit determined using a nominally
semiconductor industry for evaluating the purity of materials
99.9999 % pure (6N-grade) aluminum specimen, but less than
(for example, sputtering targets, evaporation sources) used in
100 ppmw.
thin film metallization processes. This test method may be
useful in additional applications, not envisioned by the respon- 7.4.6 To meet expected analysis precision, it is necessary
that specimens of reference and test material present the same
sible technical committee, as agreed upon by the parties
concerned. size and configuration (shape and exposed length) in the glow
discharge ion source, with a tolerance of 0.2 mm in diameter
5.2 This test method is intended for use by GDMS analysts
in various laboratories for unifying the protocol and parameters and 0.5 mm in the distance of specimen to cell ion exit slit.
for determining trace impurities in pure aluminum. The objec-
tive is to improve laboratory to laboratory agreement of 8. Preparation of Reference Standards and Test
analysis data. This test method is also directed to the users of Specimens
GDMS analyses as an aid to understanding the determination
8.1 The surface of the parent material must not be included
method, and the significance and reliability of reported GDMS
in the specimen.
data.
8.2 The machined surface of the specimen must be cleaned
5.3 For most metallic species the detection limit for routine
by electropolishing or etching immediately prior to mounting
analysis is on the order of 0.01 weight ppm. With special
the specimen and inserting it into the glow discharge ion
precautions detection limits to sub-ppb levels are possible.
source.
5.4 This test method may be used as a referee method for
8.2.1 In order to obtain a representative bulk composition in
producers and users of electronic-grade aluminum materials.
a reasonable analysis time, surface cleaning must remove all
contaminants without altering the composition of the specimen
6. Apparatus
surface.
6.1 Glow Discharge Mass Spectrometer, with mass resolu-
8.2.2 To minimize the possibility of contamination, clean
tion greater than 3500, and associated equipment and supplies.
each specimen separately immediately prior to mounting in the
The GDMS must be fitted with a liquid nitrogen cooled ion
glow discharge ion source.
source specimen cell.
8.2.3 Prepare and use electropolishing or etching solutions
6.2 Machining Apparatus, capable of preparing specimens
in a clean container insoluble in the contained solution.
and reference samples in the required geometry and with
8.2.4 Electropolishing— perform electropolishing in a so-
smooth surfaces.
lution of methanol and HNO mixed in the ratio 7:5 by volume.
6.3 Electropolishing Apparatus, capable of removing the 3
Apply 5–15 volts (dc) across the cell, with the specimen as
contaminants from the surfaces of specimens.
anode. Electropolish for up to 4 min, as sufficient to expose
7. Reagents and Materials
smooth, clean metal over the entire polished surface.
7.1 Reagent and High Purity Grade Reagents, as required 8.2.5 Etching—perform etching by immersing the specimen
(MeOH, HNO , HCl). in aqua regia (HNO and HF, mixed in the ratio 3:1 by
3 3
A
TABLE 1 Suite of Impurity Elements to Be Analyzed
NOTE 1—Establish RSFs for the following suite of elements.
silver arsenic gold boron beryllium calcium cerium chromium cesium copper iron
potassium lithium magnesium manganese sodium nickel phosphorus antimony silicon tin thorium
titanium uranium vanadium zinc zirconium
A
Additional species may be determined and reported, as agreed upon between all parties concerned with the analyses.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 1593 – 97
volume). Etch for several minutes, until smooth, clean metal is 10. Instrument Quality Control
exposed over the entire surface.
10.1 A well-characterized specimen must be run on a
8.2.6 Immediately after cleaning, wash the specimen with regular basis to demonstrate the capability of the GDMS
several rinses of high purity methanol or other high purity system as a whole for the required analyses.
10.2 A recommended procedure is the measurement of the
reagent to remove water from the specimen surface, and dry
the specimen in the laboratory environment. relative ion currents of selected analytes and the matrix
element in aluminum or tantalum reference samples.
8.3 Immediately mount and insert the specimen into the
10.3 Plot validation analysis data from at least five elements
glow discharge ion source, minimizing exposure of the
with historic values in statistical process control (SPC) chart
cleaned, rinsed specimen surface to the laboratory environ-
format to demonstrate that the analysis process is in statistical
ment.
control. The equipment is suitable for use if the analysis data
8.3.1 As necessary, use a non-contacting gage when mount-
group is within the 3-sigma control limits and shows no
ing specimens in the analysis cell specimen holder to ensure
non-random trends.
the proper sample configuration in the glow discharge cell (see
10.4 Upper and lower control limits for SPC must be within
7.4.6).
at least 20 % of the mean of previously determined values of
8.4 Sputter etch the specimen surface in the glow discharge
the relative ion currents.
plasma for a period of time before data acquisition (see 12.3)
to ensure the cleanliness of the surface. Pre-analysis sputtering
11. Standardization
conditions are limited by the need to maintain sample integrity.
11.1 The GDMS instrument should be standardized using
Pre-analysis sputtering at twice the power used for the analysis
National Institute of Standards Technology (NIST) traceable
should be adequate for sputter etch cleaning.
reference materials, preferably aluminum, to the extent such
reference samples are available.
9. Preparation of the GDMS Apparatus
11.2 Relative sensitivity factor (RSF) values should, in the
best case, be determined from the ion beam ratio measurements
9.1 The ultimate background pressure in the ion source
−6
of four randomly selected specimens from each standard
chamber should be less than 1 3 10 Torr before operation.
required, with four independent measurements of each pin.
The background pressure in the mass analyzer should be less
−7
11.3 RSF values must be determined for the suite of
than 5 3 10 Torr during operation.
impurity elements for which specimens are to be analyzed (see
9.2 The glow discharge ion source must be cooled to near
Table 1) using the selected isotopes (see Table 2) for measure-
liquid nitrogen temperature.
ment and RSF calculation.
9.3 The GDMS instrument must be accurately mass cali-
brated prior to measurements.
12. Procedure
9.4 The GDMS instrument must be adjusted to the appro-
12.1 Establish a suitable data acquisition protocol (DAP)
priate mass peak shape and mass resolving power for the
appropriate for the GDMS instrument used for the analysis.
required analysis.
12.1.1 The DAP must include, but is not limited to, the
9.5 If the instrument uses different ion collectors to measure
measurement of elements tabulated in Table 1 and the isotopes
ion currents during the same analysis, the measurement effi-
tabulated in Table 2.
ciency of each detector relative to the others should be
12.1.2 Instrumental parameters selected for isotope mea-
determined at least weekly.
surements must be appropriate for the analysis requirements:
12.1.2.1 Ion current integration times to achieve desired
9.5.1 If both Faraday cup collector for ion current measure-
precision and detection limits; and,
ment and ion counting detectors are used during the same
12.1.2.2 Mass ranges about the analyte mass peak over
analysis, the ion counting efficiency (ICE) must be determined
which measurements are acquired to clarify mass interferences.
prior to each campaign of specimen analyses using the fol
...