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SEMI C3.27-1102 © SEMI 1984, 2002 3 8.2.2 Apparat us 8.2.2.1 The modified gas collecti ng tube shown i n Section 8.1.1. 7, Figure 2. 8.2.2.2 Separatory fun n el, 2000-m L Pyrex (with 61 -cm Tygon R tubing and pinch clamp…

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SEMI C2.27-1102 © SEMI 1984, 2002 2
8.1.1.3 Tygon
R
tubing, 6 mm (1/4 in).
8.1.1.4 PTFE tubing, 6 mm (1/4 in).
8.1.1.5 Valve assembly consisting of a needle valve
with a stainless steel needle, a steel bushing and steel
coupling with a steel gas cylinder connection; a gas
take-off consisting of a steel sleeve from the valve with
steel pipe leading to a 61 cm Tygon delivery tube. The
delivery tube is a temporary connection and is replaced
as needed (see Figure 1).
8.1.1.6 Trap: 1-liter polyethylene bottle fitted with a 2-
hole Neoprene stopper and two 4-inch pieces of 1/4"
PTFE tubing which do not extend below the stopper by
more than 1 inch. The Tygon delivery tube is attached
to one of the PTFE tubes in the stopper (Inlet to Trap).
A 61 cm length of Tygon tubing is attached to the
second piece of PTFE tubing in the stopper (Outlet from
Trap). The trap is supported with a clamp and ring
stand.
8.1.1.7 Modified gas collecting tube (see Figure 2);
250-mL Pyrex sampling tube (modified with a
graduated scale on one end).
8.1.2 Reagents
8.1.2.1 Distilled-water ice, cracked.
8.1.2.2 Nitrogen, dry; 35 ppm water, or less.
8.1.3 Operating Procedure - Water-Insoluble
Components
CAUTION: Perform all work in a hood.
8.1.3.1 Prepare the gas-collecting tube by washing with
distilled water, rinsing with acetone, then drying in an
air oven at 100–125°C. Flush with dry nitrogen for
about one minute. Leave filled with dry nitrogen; close
the stopcocks.
8.1.3.2 Connect the needle valve assembly apparatus to
the cylinder to be tested.
8.1.3.3 Attach the gas-collecting tube to the valve
nipple with a short piece of dry Tygon tubing.
8.1.3.4 Open the cylinder valve, open the gas collecting
tube stopcocks, and very carefully crack open the
needle valve.
8.1.3.5 Purge the tube for 5 minutes with a slow stream
of BF
3
gas.
8.1.3.6 Close the needle valve, close the gas-collecting
tube stopcocks, and then close the cylinder valve.
8.1.3.7 Proceed with the analysis, after removing the
gas-collecting tube from the valve nipple.
8.1.4 Operating Procedure - Water Soluble
Components
CAUTION: Perform all work in a hood.
8.1.4.1 Before attaching the Tygon delivery tube, purge
the sampling valve system for 1 minute with a slow
stream of boron trifluoride from the cylinder. Use a
separate piece of tubing when purging.
8.1.4.2 Weigh an empty 1-L polyethylene bottle with
cap to the nearest 0.01 g. Record this weight as A.
8.1.4.3 Fill the bottle with about 400 g of cracked,
distilled-water ice. Re-weigh the bottle with cap to the
nearest 0.01 g; record as weight B.
8.1.4.4 A sampling line is used to transfer BF
3
gas from
the cylinder to the sample bottle.
8.1.4.5 Connect the Tygon delivery tube from the
sampling valve apparatus to the trap. Support the Tygon
tubing from the trap outlet; then open the needle valve
and adjust until a steady flow of BF
3
is obtained. Insert
this Tygon tubing (from the trap outlet) into the
polyethylene sample bottle, extending down to the
bottom of the bottle. Carefully introduce the BF
3
into
the ice until most of the ice is melted, then close the
needle valve and remove the Tygon tubing. Remove the
sample bottle and cap it. Re-weigh the bottle, cap and
contents to the nearest 0.01 g. Record this weight as C.
8.1.4.6 Mix thoroughly by careful inversion until all of
the ice melts, being certain to keep the plastic bottle
tightly capped so that none of the liquid is lost.
8.1.4.7 Proceed with the determination of water-soluble
components, being sure to do the sulfur dioxide first,
since opening the bottle repeatedly may result in a
considerable loss of sulfur dioxide.
8.1.4.8 Calculations for sample size:
B - A = Grams of Ice (H
2
O)
C - A = Weight of Solution (BF
3
Solution)
C - B = Weight of Water-soluble Material (grams of
BF
3
gas)
Grams of BF
3
Gas
Grams of Solution
=
C-B
C-A
= F
Grams BF
3
needed for Method
F
=
Grams Solution
Needed for Method
8.2 Air — This procedure describes the determination
of insoluble gases in boron trifluoride gas. A known
volume of boron trifluoride gas is absorbed in sodium
chloride solution, then any undissolved gases remaining
are measured and calculated as % air.
8.2.1 Method Capabilities — The range of this method
is 0.05% to 2.3%.
SEMI C3.27-1102 © SEMI 1984, 2002 3
8.2.2 Apparatus
8.2.2.1 The modified gas collecting tube shown in
Section 8.1.1.7, Figure 2.
8.2.2.2 Separatory funnel, 2000-mL Pyrex (with 61-cm
Tygon
R
tubing and pinch clamp attached to stopcock
end).
8.2.2.3 Tygon tubing, 1/4 inch.
8.2.2.4 Balance, capable of weighing 1000 grams to
0.01 gram.
8.2.3 Reagents — All reagents used are reagent grade
unless otherwise indicated.
8.2.3.1 Water — All water used in the preparation of
reagents and in the procedure is either distilled or
deionized.
8.2.3.2 Sodium chloride solution — Dissolve 300 g of
sodium chloride in 1 liter of water.
8.2.4 Calibration - Gas Collecting Tube
8.2.4.1 Weigh the gas collecting tube to the nearest 0.1
g; weight = A, then clamp the tube securely on a
ringstand with the calibrated stem up.
8.2.4.2 Fill the tube with distilled water and allow it to
stand with the top stopcock open until it has reached
room temperature.
8.2.4.3 Record the room temperature to the nearest
0.01°C; temperature = °C.
8.2.4.4 Close the top stopcock. Drain and dry both of
the outer stems. Weigh the water-filled collecting tube
to the nearest 0.1 g; weight = B.
8.2.4.5 The net weight of the water in the tube (B - A)
in grams is equal to the volume of the tube in milliliters,
corrected for the density of water at temperature °C.
Determine this volume as follows:
V
olume in mL =
(B - A)
D - E
w
here D = Density (g/mL) of water
a
t temperature
°
C (from Table 1).
Table 1 Density vs T°C for Water
Temp. °C Density g/mL
20 0.99823
21 0.99802
22 780
23 756
24 732
25 0.99707
Temp. °C Density g/mL
26 681
27 654
28 626
29 597
30 567
8.2.5 Procedure
8.2.5.1 Obtain the sample of BF
3
gas in the gas
collecting tube. See Section 8.1.3 for sampling details.
8.2.5.2 Fill the separatory funnel with sodium chloride
solution. Attach Tygon tubing and a pinch clamp to the
funnel.
8.2.5.3 With a small dropper, fill the glass tubing
leading to the stopcock opposite the calibrated end of
the gas collecting tube with the salt solution. (Note: the
gas collecting tube is inverted at this point.)
8.2.5.4 Open the separatory funnel stopcock and the
pinch clamp on the Tygon tubing. Hold the tubing
upright and when it completely fills with NaCl solution,
slip the tubing onto the end of the gas collecting tube
which was previously filled in step 8.2.5.3.
NOTE 1: There should be no air bubbles in the connections
between the gas collecting tube and the separatory funnel. A
trace of a wetting agent such as Ultrawet (Atlantic Refining
Co.) in the salt solution assists in freeing small air bubbles
from the walls of connecting tubes.
8.2.5.5 Hold the gas collecting tube vertical, with the
calibrated end up and the entire collecting tube below
the liquid level of the separatory funnel.
8.2.5.6 Open the lower stopcock of the gas collecting
tube carefully and shake the tube to aid in dissolving of
the BF
3
gas in the salt solution.
8.2.5.7 Bring the liquid level in the gas collecting tube
equal to the liquid level in the separatory funnel.
8.2.5.8 Read and record the volume of undissolved gas
in the upper calibrated end of the gas collecting tube
and record this volume, to the nearest one-tenth of a
milliliter; mL = F. Record the room temperature.
8.2.6 Calculations
8.2.6.1 F = Total milliliters of undissolved gas (from
Section 8.2.5.8).
8.2.6.2 E = Total volume of gas collecting tube in mL;
see Calibration - Gas Collecting Tube.
SEMI C2.27-1102 © SEMI 1984, 2002 4
8.2.6.3
F
E
×100 = %air
Re
p
ort to the nearest 0.01%
.
8.3 Sulfur Dioxide — This procedure describes the
determination of sulfur dioxide in boron trifluoride gas.
A sample of the solution prepared in Section 8.1.4 is
titrated with standard iodine solution to a starch end-
point (blue). The sulfur dioxide is determined from the
equivalents of iodine used in the titration.
8.3.1 Method Capabilities: The range of this method is
5 ppm to 1500 ppm.
8.3.2 Apparatus
8.3.2.1 Burette, 10 mL, graduated in units of 0.05 mL.
8.3.2.2 Beaker, 250-mL.
8.3.3 Reagents — All reagents used are reagent grade
unless otherwise specified.
8.3.3.1 Water — All water used in the preparation of
reagents and in the procedure is either distilled or
deionized.
8.3.3.2 Iodine solution, 0.01 N — Prepare fresh daily
and standardize.
8.3.3.3 Starch indicator solution, 10 g/L — Prepare a
thin paste of 1 g of soluble starch with water. Pour the
paste with constant stirring, into 100 mL of boiling
water. Boil for one minute. Allow the solution to cool
and add 2.5 g of potassium iodide. Keep the solution in
a glass-stoppered bottle. Prepare fresh when the color
obtained for end points is violet or red instead of blue.
Alternatively, Thyodene dry indicator powder may be
used.
8.3.4 Operating Procedure
8.3.4.1 Calculate the amount of sample (prepared in
Section 8.1.4 that contains about 20 grams of BF
3
gas,
rounding off to the nearest milliliter. Calculate the
grams of BF
3
gas in this volume to the nearest 0.01 g,
using the “F” factor in Section 8.1.4.8. Transfer this
amount to a 250-mL beaker and add 5 drops of starch
indicator.
8.3.4.2 Using a 10-mL burette graduated in 0.05 mL,
titrate with iodine to a starch end-point (blue). Stir
constantly with a Teflon stir-bar or equivalent. Record
the volume of the iodine solution to the nearest 0.01
mL.
8.3.5 Calculations
mL I
2
×
Normality of I
2
×
0.032 × 1× 10
6
Grams of Water - Soluble Material
= ppm SO
2
where : 0.032 the milliequivalent weight of SO
2
;
1
×
10
6
is factor for conversion to
pp
m.
8.4 Silicon Tetrafluoride — This procedure describes
the determination of silicon tetrafluoride in boron
trifluoride gas. This method is based on the reaction of
soluble silica with molybdate ion to form a greenish-
yellow complex, B-silicomolybdic acid. This complex
is then reduced to a blue complex by 1-amino-2-
naphthol-4-sulfonic acid. The absorbance is measured at
650 nm and the amount of silicon tetrafluoride present
is obtained from a calibration curve.
8.4.1 Method Capabilities — The range of this method
is 45–450 ppm.
8.4.2 Apparatus
8.4.2.1 Photometer: One of the following is required,
with preference in the order given.
a. Spectrophotometer, suitable for measurements at
650 nm.
b. Filter photometer, for measurements from 640-700
nm, if less sensitivity is preferred.
c. Fisher Electrophotometer, with a red filter and 23-
mm cells.
NOTE 2: If the photometer being used measures in units other
than absorbance, the appropriate conversion to absorbance
must be made before calculating any results.
8.4.2.2 Absorption cells, 1.0-cm light path (for use with
a or b above).
8.4.2.3 Plastic beakers, 150-mL capacity.
8.4.2.4 Polyethylene weighing bottle with cap, 250-
mL.
8.4.2.5 Plastic volumetric flasks, 100-mL.
8.4.2.6 Plastic pipets, 0, 1.0, 2.0, 3.0, 4.0, 6.0, 8.0 and
10.0-mL sizes.
8.4.3 Reagents — All reagents are reagent grade unless
otherwise specified.
8.4.3.1 Water — All water used in this method is either
distilled or deionized and must be silica-free.
8.4.3.2 Boric acid solution, saturated — Dissolve 70 g
of boric acid, H
3
BO
3
, in 800 mL of hot water. Dilute to
1000 mL and mix. Store in a plastic bottle.
8.4.3.3 Ammonium molybdate solution, 10% —
Dissolve 50 g of ammonium molybdate,