Determination of impurities in germanium tetrafluoride by IR spectroscopy and gas chromatography

Article abstract of DOI:10.1134/S0020168510100225

Using high-resolution Fourier-transform IR spectroscopy and gas chromatography, we have identified more than 20 impurity species, in concentrations from 10^-1 to 10^-5 vol %, in GeF₄ samples of different isotopic composition

Full text of DOI:10.1134/S0020168510100225

ISSN 0020ꢀ1685, Inorganic Materials, 2010, Vol. 46, No. 10, pp. 1147–1150. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © P.G. Sennikov, A.D. Bulanov, V.A. Krylov, T.G. Sorochkina, 2010, published in Neorganicheskie Materialy, 2010, Vol. 46, No. 10, pp. 1267–1271.
Determination of Impurities in Germanium Tetrafluoride
by IR Spectroscopy and Gas Chromatography
P. G. Sennikov, A. D. Bulanov, V. A. Krylov, and T. G. Sorochkina
Institute of Chemistry of HighꢀPurity Substances, Russian Academy of Sciences,
ul. Tropinina 49, Nizhni Novgorod, 603950 Russia
eꢀmail: bulanov@ihps.nnov.ru
Received September 10, 2009
Abstract—Using highꢀresolution Fourierꢀtransform IR spectroscopy and gas chromatography, we have idenꢀ
–1
–5
tified more than 20 impurity species, in concentrations from 10 to 10 vol %, in GeF samples of different
4
isotopic compositions. The germanium tetrafluoride samples are shown to contain C –C hydrocarbons;
1
4
hydrogen, carbon, silicon, and sulfur fluorides; fluorogermanes; fluorosilanes; and carbon and nitrogen
oxides.
DOI: 10.1134/S0020168510100225
–1
INTRODUCTION
0.5 cm , respectively, as described in detail elsewhere
[
4]. The optical pathlength was 20 cm, and the presꢀ
× ×
Since GeF4 is rather widely used in the production
of silicon–germanium thinꢀfilm structures and isotoꢀ
pically enriched germanium, including that enriched
3
3
sure in the cell was 12
10 and 78
10 Pa, respecꢀ
tively. The concentrations of some impurities were
determined using the integrated absorption coeffiꢀ
cients of analytical lines available in the literature.
Gasꢀchromatographic analyses of germanium tetꢀ
rafluoride were performed as described by Krylov and
Sorochkina [5], using a setup built around a Tswettꢀ100
chromatograph. We determined hydrocarbon impuriꢀ
ties using a flame ionization detector and SF6 using an
electron capture detector. The detection limit was (2–
76
in Ge for doubleꢀbeta decay detectors [1, 2], there is
high current interest in the ultrapurification and analꢀ
ysis of germanium tetrafluoride. There is, however, litꢀ
tle or no information about the impurity composition
and analysis of GeF4. Using a simplified mass spectroꢀ
metric approach, Ferreiro et al. [3] compared the
properties of GeF4 and GeН4 for germanium implanꢀ
tation into silicon layers. The few manufacturers of
–
6
6
of
)
×
10 vol % for С –С4 hydrocarbons and at a level
1
×
germanium tetrafluoride indicate О , N2, Ar, CO,
2
8
10–8 vol % for sulfur hexafluoride. Concentraꢀ
CO , SO , CF4, and HF among regulated impurities
2
2
tions exceeding the detection limit by an order of magꢀ
nitude were determined with an uncertainty of 10–
2
but do not specify the analytical techniques employed.
The objective of this work was to determine the
impurity composition of germanium tetrafluoride and
the concentrations of a number of impurities using
highꢀresolution Fourierꢀtransform IR spectroscopy
and gas chromatography.
5%.
RESULTS AND DISCUSSION
Highꢀresolution Fourierꢀtransform IR spectrosꢀ
copy. Determination of impurity composition by IR
spectroscopy requires detailed information about the
absorption spectrum of the host substance. IR spectra
of germanium tetrafluoride have not yet been studied
in sufficient detail, in contrast to those of silicon tetꢀ
rafluoride. Caunt et al. [6] and Woltz et al. [7] reported
wideꢀscan spectra and specified only the peak posiꢀ
EXPERIMENTAL
We studied germanium tetrafluoride of natural isoꢀ
70
72
topic composition (20.51% Ge, 27.43% Ge, 7.76%
7
3
74
76
Ge, 36.54% Ge, and 7.76% Ge) prepared by
direct fluorination of 6N metallic germanium (sample 1)
74
and samples enriched in Ge (85.12%) (sample 2) and
tions of the absorption bands. A highꢀresolution specꢀ
1
70
72Ge (>50%) (sample 3) by centrifugation.
trum of GeF4 in the
ν
to
ν
stretching region was
3
4
reported by Boudon et al. [8].
The positions of the intrinsic bands in the spectra of
our samples on the whole agree with those reported in
Their spectra were measured in the range 500 to
200 cm on Bruker IFSꢀ120 HR and VERTEX 80
vacuum spectrometers with a resolution of 0.1 and
–1
4
the literature. We identified bands at 1600 (2
535.5 ( ), 1072 ( ) (?), 1008.6 ( +
4
ν
3),
or
1
1
ν
+
ν
ν
+
ν
ν
ν
The samples were obtained from OAO PO Electrochemical
Plant, Zelenogorsk, Russia.
1
3
3
4
1
−1
ν
+
ν
3), ~800 ( 3
ν
), and 738.1 cm (
ν
+ 2 4) (?).
ν
2
2
1147

1148
SENNIKOV et al.
Table 1. Impurity composition of the GeF samples according to highꢀresolution Fourierꢀtransform IR spectroscopy data
4
Sample no.
Wavenumber, cm–1
Impurity
Detection limit, mol %
1
2
3
4
200–3700
HF
1
1
n
8
1
1
1
1
×
×
×
×
×
×
×
×
10–4
10–3
10–3
10–5
10–3
10–3
10–3
10–3
+
+
+
+
+
+
+
+
–
+
–
+
+
+
+
+
+
–
+
+
+
+
–
+
+
+
+
+
+
+
–
+
+
–
+
+
–
+
+
+
+
+
+
–
+
+
–
_
3100–3040
CH4
2967, 2957, 2952, 2917, 2892, 2880, 1458, 1446 C hydrocarbons
4
3
613, 3617, 2349, 667
224
315, 846
75
251.6
110
186, 1283, 631
876
829
943, 1243, 1241, 1239
743
454
417
261
116
031
39
59, 874
CO2
2
N O
2
2
SiF H
3
8
SiFH3
–
–
–
+
–
–
–
+
–
–
–
+
+
–
–
2
SiF H2
2
2
?
2
CF4
5
1
×
×
10–4
10–3
1
NO
1
?
1
COF2
1
×
10–3
1
?
1
?
1
?
1
?
1
C2F6
SiF4
?
1
5
×
×
10–3
10–4
1
9
8
GeH3F
n
n
×
10–2
10–2
7
20, 596
GeH2F2
?
×
+
+
+
+
–
–
6
91
Note: The symbols + and – denote that the impurity was present or not (its content was below the detection limit) in the sample under our
experimental conditions. The symbol ? denotes that the chemical species responsible for the absorption was not identified.
These frequencies correspond to the natural isotopic 10–1 mol % SiF4). Also noteworthy is the high CF4
–2
composition. The frequencies in the isotopically modꢀ concentration in this sample (up to 10 mol %).
ified samples were slightly lower.
There are also СОF and N O impurities. In the range
2
2
–1
Table 1 lists the impurities identified in samples 1– 2850–2950 cm , we observe a broad band with maxꢀ
by IR spectroscopy and the absorption bands that ima at 2973 (very weak), 2967 (very strong), 2952,
3
–1
have not been identified.
2917, 2892, and 2880 cm (all with a medium
Consider in greater detail the nature of the impuriꢀ strength). According to earlier data [9], this composite
–1
ties in our samples. Note that all of the samples conꢀ band may be due to a mixture of propane (2973 cm ),
–
2
–3
–1
tain hydrogen fluoride (
n
×
10 to
10 mol %), and SiF4 (
10–5 mol %). Sample 1 has the highest HF, CO2
n
×
10 mol %), isobutane (2967 and 2880 cm ), and butane (2952
–1
×
–2
–4
–1
CO (
n
×
10 to
n
×
n
10
and 2892 cm ), with the isobutane content being
probably the highest. Near 3100 cm , we observe a
weak absorption due to methane.
2
–1
to
n
×
,
–
2
and SiF4 concentrations (
n
×
10 mol % СО2 and
n
×
INORGANIC MATERIALS Vol. 46
No. 10
2010

DETERMINATION OF IMPURITIES IN GERMANIUM TETRAFLUORIDE
1149
Table 2. Verification of analytical accuracy in the determinaꢀ one order of magnitude. This is inconsistent with the
tion of hydrocarbons and sulfur hexafluoride in germanium
tetrafluoride (pressure variation method)
assignment of this band to solely the
ν
+ 2 4 mode of
ν
2
the GeF4 molecule [6, 7]. Moreover, the spectrum of
sample 2 shows a broad, weak band with a rather well
defined maximum at 3687 cm . By analogy with
Impurity
p1 = 27.7
С , vol %
С , vol %
–1
1
2
spectra of SiF4 of various origins [4], it is reasonable to
×
103 Pa
,
p2 = 40.6
×
103 Pa
(
n1
=
n2 = 4,
P
= 0.95)
–1
assume that the band at 738 cm is due to Ge F O and
2
6
–1
10–5
10–5
that at 3687 cm , to GeF OH. This assignment, howꢀ
3
СН4
(4.1
(2.3
(1.0
(2.5
±
±
±
±
1.0)
0.6)
0.2)
0.4)
×
×
×
×
(4.5
(2.0
(1.1
(2.3
±
±
±
±
1.0)
×
ever, requires thorough verification.
С Н
2
10–5
0.5)
0.2)
0.4)
×
×
×
10–5
The samples were analyzed by their vendor using
direct mass spectrometry (samples 1 and 2) and gas
chromatography (sample 3). The results for СО2 and
SiF4 in the first two samples agree well with the present
data, whereas the SO2 content is below the detection
limits of gas chromatography and IR spectroscopy.
Thus, we are led to conclude that, on the whole,
among the samples studied sample 3 contains the
smallest number of impurity species, which is probaꢀ
4
С Н
3
10–4
10–4
6
10–4
10–4
IsoꢀС Н
4
10
p1 = 31.6
×
103 Pa
,
p2 = 42.6
×
103 Pa
(n1
=
n2 = 4,
P
= 0.95)
10–4
(1.0
±
0.2)
×
10–4
(1.2
±
0.2)
×
SF6
72
bly related to the specific features of the Ge enrichꢀ
The IR spectra of the isotopically enriched samples 2 ment process, accompanied by germanium tetrafluoꢀ
and 3 indicate that they differ in quantitative and qualꢀ ride purification. Sample 2 differs insignificantly in
itative impurity compositions. In particular, the CO
qualitative impurity composition from sample 1 (natꢀ
2
74
and SiF contents of sample 2 (enriched in Ge) are ural isotopic composition), but the concentrations of
4
about one order of magnitude higher than those in regulated impurities in sample 2 are also substantially
sample 3. In addition, sample 2 has high NO concenꢀ lower.
–
2
tration (
enriched in 72Ge) contains
contrast to sample 2. Moreover, sample 3 shows a sigꢀ
3
×
10 mol %). At the same time, sample 3
Gas chromatography. As mentioned above, this
method is used mainly to identify hydrocarbon impuꢀ
rities in germanium tetrafluoride. Analytical accuracy
was verified by varying the sample pressure. The verifiꢀ
cation results for germanium tetrafluoride are preꢀ
sented in Table 2. Raising the pressure by a factor of
–4
(
n
×
10 mol % CF , in
4
–1
nificant absorption in the range 2850–2950 cm , due
to С4 hydrocarbons. Note also that the spectrum of
sample 3 contains a rather strong band at 1250 cm ,
which remains unidentified. The spectrum of sample 2
like that of sample 1) contains bands at 859 and
91 cm , assignable to GeH3F [10, 11]. The weak feaꢀ
ture at 720 cm seems to arise from GeH2F [12].
Both samples contain the fluorosilanes SiHF , SiH F2,
–1
1
.5 is seen to produce no statistically significant
(
6
changes, which points to sufficient accuracy in impuꢀ
rity determination.
–1
–
1
2
The impurity determination results for our samples
are presented in Table 3. As seen, seven hydrocarbon
impurities were detected in the germanium tetrafluoꢀ
3
2
–2
–3
and SiH F (
n
×
10 to
n 10 mol %).
×
3
Comparison of spectra measured under identical ride samples. In the three samples, the major hydroꢀ
–
3
conditions demonstrates that samples 2 and 3 differ in carbon impurities are C and C : at a level of
6 × 10
3
4
–1
the strength of the 738ꢀcm absorption by more than vol % in sample 1 (natural isotopic composition) and
Table 3. Concentrations of hydrocarbon and sulfur hexafluoride impurities in the germanium tetrafluoride samples according
to gas chromatography data
Сi, vol %
Impurity
Cmin(i), vol %
sample 1
sample 2
sample 3
СН4
С Н
(3.4
(9.0
(2.6
(2.4
(9.7
(5.9
(5.0
(1.0
±
0.3)
1.6)
0.7)
0.4)
1.6)
0.5)
0.8)
0.1)
×
×
×
×
×
×
×
×
10–3
10–5
10–5
10–4
10–5
10–3
10–4
10–4
(9.2
±
1.6)
<2
×
×
×
×
×
×
×
×
10–5
10–6
10–5
10–5
10–4
10–4
10–5
10–5
(6
±
1)
< 2
< 2
×
×
×
×
×
×
×
10–5
10–6
10–6
10–5
10–6
10–4
10–5
2
2
2
2
3
4
6
8
×
×
×
×
×
×
×
×
10–6
10–6
10–6
10–6
10–6
10–6
10–6
10–8
±
2
6
4
8
6
С Н
±
±
±
±
±
±
(7.9
(2.5
(8.2
(3.5
(4.8
(4.0
±
±
±
±
±
±
1.6)
0.4)
1.3)
0.6)
1.0)
0.6)
2
С Н
(1.2
±
0.3)
< 3
3
С Н
3
IsoꢀС Н
4
(6.2
±
0.8)
10
nꢀС Н
4
(6
±
1)
–
10
SF6
INORGANIC MATERIALS Vol. 46
No. 10 2010

1150
SENNIKOV et al.
8
×
10–4 vol % in samples 2 and 3 (isotopically
This work was supported by the RF President’s
enriched). The total hydrocarbon content of the isotoꢀ Grants Council (Support to RF’s Leading Scientific
pically enriched samples is seven times lower than that Schools Program, grant no. NShꢀ4701.2008.03) and
of the sample of natural isotopic composition. Isotopic the Presidium of the Russian Academy of Sciences
(
program no. 20, theme 2).
enrichment reduces the content of saturated hydroꢀ
carbons in germanium tetrafluoride by a factor of 10–
5
0. The content of unsaturated hydrocarbons in the
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4
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tetrafluoride samples, at a level of 10 to 10 vol %.
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concentration by a factor of 2.5.
3
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CONCLUSIONS
Using highꢀresolution Fourierꢀtransform IR specꢀ
troscopy and gas chromatography, we identified more
–
1
than 20 impurity species, in concentrations from 10
–5
5. Krylov, V.A. and Sorochkina, T.G., GasꢀChromatoꢀ
graphic Determination of C –C Hydrocarbons and
to 10 vol %, in GeF samples of different isotopic
4
1
4
compositions. The germanium tetrafluoride samples
were shown to contain C –C hydrocarbons; hydroꢀ
gen, carbon, silicon, and sulfur fluorides; fluorogerꢀ
manes; fluorosilanes; and carbon and nitrogen oxides.
Sulfur Hexafluoride in HighꢀPurity Germanium Tetꢀ
rafluoride of Natural and Isotopically Enriched Comꢀ
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1
4
The likely sources of these impurities in GeF are
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background) gases in the process equipment. The
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Raman and Infrared Spectra of Germanium Tetrafluoꢀ
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4
(
preparation of GeF by direct fluorination of germaꢀ
4
7
. Woltz, P.J.H. and Nielsen, A.H., The Infrared Spectra
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4
4
of CF and GeF , J. Chem. Phys., 1952, vol. 20, no. 2,
4
4
cially in the sample of natural isotopic composition. At
the same time, it follows from IR spectroscopy and,
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derivatives does not reach completion.
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8
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ν
4
3
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4
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the whole, accompanied by a reduction in the concenꢀ
tration of a number of impurities. The smallest numꢀ
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9
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,
1
ACKNOWLEDGMENTS
1
2. Ebsworth, E.A.V. and Robiette, A.S., The Infrared
Spectra of Dihalogermanes, Spectrochim. Acta, 1964,
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for their assistance in taking the IR spectra.
INORGANIC MATERIALS Vol. 46
No. 10
2010