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SEMI C3.26-03 01 © SEMI 1984 , 2001 1 SEMI C3.26-0301 SPECIFICA TION FOR TUNGSTEN HEX A FLUORIDE (WF 6 ) IN CYLINDERS, 99. 8% QU ALITY This specif ication was technic ally approved by the Global Ga ses Committee and is t…
SEMI C3.24-0301 © SEMI 1984, 20013
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SEMI C3.26-0301 © SEMI 1984, 20011
SEMI C3.26-0301
SPECIFICATION FOR TUNGSTEN HEXAFLUORIDE (WF
6
) IN
CYLINDERS, 99.8% QUALITY
This specification was technically approved by the Global Gases Committee and is the direct responsibility of
the North American Gases Committee. Current edition approved by the North American Regional Standards
Committee on November 22, 2000. Initially available at www.semi.org January 2001; to be published March
2001. Originally published in 1984; previously published in 1994.
1 Description
1.1 Tungsten hexafluoride is a colorless gas or
colorless liquid. It is shipped as a liquefied gas under
its own vapor pressure.
2 Specifications
QUALITY: 99.8%
Impurities
Maximum Acceptable
Level (ppm) (See NOTE 1.)
Carbon Tetrafluoride (CF
4
)10
Hydrogen Fluoride (HF) 1000
Nitrogen (N
2
)50
Oxygen (O
2
) + Argon (Ar) 50
Sulfur Hexafluoride 10
Silicon Tetrafluoride 10
TOTAL LISTED IMPURITIES 1130
NOTE 1: An analysis of significant figures has not been considered.
The number of significant figures will be based on analytical
accuracy and the precision of the provided procedure.
3 Physical Constants (for in formation only)
Metric Units US Units
Molecular weight 297.85 297.85
Boiling point at 1 atm 17.1°C 62.8°F
Density of gas at 22.8°C
(73°F) and 1 atm
12.9 kg/m
3
0.805 lb/ft
3
Specific gravity of gas 10.8 10.8
Density of liquid at boiling
point
3440 kg/m
3
214.8 lb/ft
3
4 Analytical Procedures (Se e Notes 1, 2, 3, 4,
5, 6, 7)
4.1 Nitrogen and Oxygen + Argon — This procedure
is for the determination of nitrogen and oxygen + argon
in tungsten hexafluoride using a gas chromatograph
with a thermal conductivity detector.
4.1.1 Detection Limits — 10 ppm (mol/mol) nitrogen,
and 10 ppm (mol/mol) oxygen + argon.
4.1.2 Instrument Parameters
4.1.2.1 Columns: (See Figures 1, 2)
Column 1: Porapak S, 80/100 mesh, 1.5 m (5 ft) by
6.4 mm (1/4 in) OD, 5.1 mm (0.2 in) ID, ss
or equivalent.
Column 2: Molecular sieve 5A, 80/100 mesh, 1.8 m
(6 ft) by 4.8 mm (3/16 in) OD, 3.7 mm
(0.147 in) ID, ss or equivalent.
4.1.2.2 Column Flow: 30 mL/min helium.
4.1.2.3 Sample Volume: 2 mL
4.1.2.4 Temperatures
Detector 70°C
Column 40°C
4.1.3 Calibration Standard — 50 ppm (mol/mol)
nitrogen, 50 ppm (mol/mol) oxygen, balance helium.
4.1.4 Operating Procedures
4.1.4.1 Determine the times for valve switching and
signal changes, and enter into the run table. An example
of a run table follows.
Time Position Function
0 min. 1 Purge sample through loop. Backflush
Porapak column. Connect MS column
to the TCD.
1 min. 2 Inject sample onto Porapak column.
Allow oxygen + argon and nitrogen to
elute from the Porapak column to the
MS column. Sequentially elute the
oxygen + argon and nitrogen from the
MS column to the TCD.
4 min. 1 Backflush Porapak column to vent for
8 minutes.
4.1.4.2 Set the valves in Position 1 (Figure 1).
4.1.4.3 Flow the calibration standard through the 10-
port valve. Analyze standard using the conditions
described above. Record retention times and peak areas.
SEMI C3.26-0301 © SEMI 1984, 2001 2
4.1.4.4 Flow the sample to be tested through the 10-
port valve for 1 minute. Analyze in the same manner as
in 4.1.4.3.
4.1.4.5 The standard is again run as in 4.1.4.3.
4.1.4.6 Calculate the concentrations of nitrogen and
oxygen + argon in the sample, using the formula below.
The result may not exceed the specifications in Section
2 of this Standard.
Sample Peak Area
Standard Peak Area
×
Concentratio
n
of Standard
=
Concentratio
n
of Sample
4.2 Carbon Tetrafluoride, Hydrogen Fluoride, Silicon
Tetrafluoride, and Sulfur Hexafluoride — This
procedure is for the determination of these gases in
tungsten hexafluoride using infrared
spectrophotometry. (See Note 2.)
4.2.1
Detection Limits — 10 ppm (mol/mol) carbon
tetrafluoride, 1000 ppm (mol/mol) hydrogen fluoride,
10 ppm (mol/mol) silicon tetrafluoride and 10 ppm
(mol/mol) sulfur hexafluoride.
4.2.2
Instrument Parameters
4.2.2.1 Cell path length: 10 cm
4.2.2.2 Sample Cell Pressure: 1 atmosphere
4.2.2.3 Wavenumbers:
Component Wavenumber (cm
-1
)
Carbon Tetraflouride (CF
4
) 1283
Hydrogen Fluoride (HF) 4076
Silicon Tetrafluoride (SiF
4
) 1029
Sulfur Hexafluoride (SF
6
) 948
4.2.3 Calibration Standards — 1% (mol/mol)
hydrogen fluoride in tungsten hexafluoride, 100 ppm
(mol/mol) silicon tetrafluoride in nitrogen, 25 ppm
(mol/mol) each carbon tetrafluoride and sulfur
hexafluoride in nitrogen.
4.2.4
Operating Procedures
4.2.4.1 Flow each calibration gas through the system
for 1 minute. Pressurize the cell to 1 atmosphere.
Record the absorbance of each calibration standard at
the wavenumber listed in 4.2.2.3.
4.2.4.2
Flow the sample gas through the system for 1
minute. Pressurize the cell to 1 atmosphere. Record the
absorbance at each of the appropriate wavenumbers.
Calculate (See Note 1) the concentration of each gas,
using the formula below. The results may not exceed
the specification in Section 2 of this standard.
Sample of
ionConcentrat
Standard of
ionConcentrat
Standard theof
Absorbance Measured
Sample theof
Absorbance Measured
=×
4.3 Notes
NOTE 1: Tungsten hexafluoride interferes with the direct
absorbance reading for silicon tetrafluoride. The absorbance
for silicon tetrafluoride is determined by compensating for the
interfering absorbance from the tungsten hexafluoride.
Compensation is made by subtracting the absorbance
contributed to this band by tungsten hexafluoride band at 930
cm
-1
. This absorbance is halved and subtracted from the total
peak absorbance at 1040 cm
-1
, resulting in the peak
absorbance for silicon tetrafluoride.
NOTE 2: Actual detection limits will be determined by the
noise level and the resolution of the spectrometer. One way is
to reduce the noise level is to use a Fourier Transform
Infrared Spectrometer.
NOTE 3: All gases used in the analysis of the sample should
not contain more than 10% of the specified value of the
component of interest, unless otherwise stated.
NOTE 4: As tungsten hexafluoride has a low vapor pressure,
the cylinder should be kept at room temperature (20°C) for at
least 8 hours prior to analysis.
NOTE 5: Observe proper safety procedures for handling and
disposing of tungsten hexafluoride.
NOTE 6: Prior to introducing tungsten hexafluoride purge the
sample lines and instrument tubing with helium to remove
moisture.
NOTE 7: Upon completing the analysis, cap off the manifold
and instrument lines or purge the system with helium.
Figure 1