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SEMI C3.40-10 00 © SEMI 1989 , 2000 5 C: Measu red hy drol y zable fluoride con ce ntration (M) determin ed i n sect ion 5.6.5.11 Vs: Volume of CF 4 sampled (liters at ST P) 5.6.5.13 The HF con centration of the se c o n…
SEMI C3.40-1000 © SEMI 1989, 2000 4
5.6.2.3 Fluoride ion selective electrode
5.6.2.4 Magnetic stir bars (PTFE coated)
5.6.2.5 Magnetic stirrer
5.6.2.6 Plastic beakers (See note 5)
5.6.2.7 PTFE bubblers
5.6.2.8 1000 ml and 100 ml plastic volumetric flasks
(See note 5)
5.6.2.9 0.2 ml and 1 ml plastic volumetric pipettes
(See note 5)
5.6.2.10 Flow controller or flowmeter (0-1000 sccm
CF
4
)
5.6.3 Reagents
5.6.3.1 Distilled or deionized water
5.6.3.2 5 N sodium hydroxide
5.6.3.3 0.2 N sodium hydroxide
5.6.3.4 Glacial acetic acid
5.6.3.5 Buffer Solution — To 500 ml distilled or
deionized water in a 1000 ml volumetric flask, add 57
ml glacial acetic acid and 58 g of sodium chloride.
Adjust the pH to between 5.0–5.5 with 5 M sodium
hydroxide. Cool to room temperature. Dilute to one
liter with distilled or deionized water.
5.6.4 Calibration Standard — Sodium fluoride
standard (10
-3
M F
-
in water, freshly prepared)
5.6.5 Operating Procedure
5.6.5.1 Prepare working standard by adding 100 ml
10
-3
M F
-
to 100 ml buffer solution.
5.6.5.2 Prepare a blank containing 50.0 ml 0.2 N
NaOH and 50.0 ml buffer solution in a plastic beaker.
5.6.5.3 While stirring blank gently, record mV reading
from the blank once reading is stable.
5.6.5.4 Successively add increments of working
standard to the blank to generate a calibration curve.
Record stable mV reading after each addition. Table 1
shows recommended increments and resultant
concentrations.
Table 1 Calibration Concentrations
Added volume of
Working Standard
(ml)
Total Volume
(ml)
Resulting F-
Concentration
(M)
0.2 100.2 1.0 x10
-6
0.2 100.4 2.0 x10
-6
0.4 100.8 4.0 x10
-6
0.4 101.2 5.9 x10
-6
0.8 102.0 9.8 x10
-6
1.0 103.0 1.5 x 10
-5
2.0 105.0 2.4 x 10
-5
5.6.5.5 Put 50 ml 0.2 N NaOH into each of two
bubblers connected in series
5.6.5.6 Establish a flow of < 1000 sccm of CF
4
through the bubblers using a suitable flow controller or
flowmeter.
5.6.5.7 Sample approximately 15 liters of CF
4
.
Record flowrate and time of sampling to determine total
volume sampled (flowrate x time). A wet test meter
can also be used to measure total volume. The amount
of gas sample must be the volume at STP. If the
flowmeter or wet test meter is not reference to 0º and
760 torr, use the formula below to correct sample
volume.
K 273
273 T
P
Torr 760
Liters Measured STPat Liters
+
××=
P: Pressure of sampled gas (mm Hg)
T: Temperature of sampled gas or reference
temperature of the flow controller or meter in ºC.
5.6.5.8 Transfer contents of each bubbler to individual
100 ml volumetric flasks and add 50 ml Buffer solution
to each. Then, if necessary, add deionized or distilled
water to bring the volume up to 100 ml.
5.6.5.9
Transfer contents to a plastic beaker
5.6.5.10 While stirring, measure and record mV
readings for each sample.
5.6.5.11 Determine F
-
concentration in solution using
calibration curve generated in section 5.6.5.4.
5.6.5.12 Calculate gas phase hydrolyzable fluoride
concentration using the equation below. Note: the
equation assumes the hydrolyzable fluoride is hydrogen
fluoride.
6
y
10
Vs
l/mole 22.4
0.11 C )(ppm HF Phase Gas ×××=
SEMI C3.40-1000 © SEMI 1989, 20005
C: Measured hydrolyzable fluoride concentration (M)
determined in section 5.6.5.11
Vs: Volume of CF
4
sampled (liters at STP)
5.6.5.13 The HF concentration of the second bubbler
should be insignificant compared to the first bubbler. If
significant HF levels are found in the second bubbler,
resample with a lower flowrate.
5.7
Notes
Note 1: Introduce the calibration standard as many
times as necessary to achieve the desired precision.
Note 2: 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 3: A passivation procedure is described in the
Metals Handbook, 10th ed., Vol. 2, American Society
for Metals, Metals Park, OH.
Note 4: The sampling system and hygrometer must be
designed to operate at the sample pressure, or the
sample pressure must be reduced, by a regulator with a
diaphragm of stainless steel or other suitable material,
to accommodate the pressure restrictions of the
hygrometer.
Note 5: Polytetrafluoroethlyene, polymethylpentene
and polypropylene are suitable plastic materials.
Figure 1
Configuration for the Analysis of CO
2
, O
2
, N
2
, and CO in CF
4
SEMI C3.40-1000 © SEMI 1989, 2000 6
Figure 2
Configuration for the Analysis of SF
6
in CF
4
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