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SEMI C2.27-1102 © SEMI 1984, 2002 6 and compared to a curve pre p ared from standard sulfate solutions. 8.5.1 Method Capabilities — The range of the method is 7-70 ppm . NOTE 3: Color or suspended matter in large amounts…

SEMI C3.27-1102 © SEMI 1984, 2002 5

(NH

)

O, in water and dilute to 500 mL.

Store in a plastic bottle. Prepare fresh weekly.

8.4.3.4 Sulfuric acid, 5N, H

— Carefully pour 35

mL of concentrated sulfuric acid into about 150 mL of

water in an ice bath. Cool to room temperature, dilute to

250 mL and mix. Store in a plastic bottle.

8.4.3.5 Tartaric acid solution, 40% — Dissolve 80 g of

tartaric acid in 140 mL of water. Dilute to 200 mL and

mix. Store in a plastic bottle. Prepare fresh weekly.

8.4.3.6 l-Amino-2-naphthol-4 sulfonic acid solution,

2.5 g/L — Dissolve 30 g of sodium bisulfite in 100 mL

of water in a 250-mL beaker. In a 100-mL beaker,

dissolve 1 g of sodium sulfite in 25 mL of water and

add 0.5 g of 1-amino-2-naphthol-4-sulfonic acid. Mix

the two solutions and dilute to 200 mL. Store in a

plastic bottle and filter before using. Prepare fresh

weekly.

8.4.3.7 Sodium silicate standard solution, 1 mL = 10

micrograms Si — Dissolve 1.012 g sodium silicate

(meta), Na

SiO

O, in water in a 100-mL plastic

volumetric flask and dilute to volume. Pipet 10.00 mL

of this solution, using a polyethylene pipet, into a 1-liter

plastic volumetric flask and dilute to volume. One mL

of this dilution contains the equivalent of 10

micrograms Si.

8.4.4 Calibration

8.4.4.1 To a series of nine 150-mL plastic beakers,

pipet 0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, and 10.0 mL of

sodium silicate standard solution. These additions

correspond to 0, 10, 20, 30, 40, 50, 60, 80, and 100

micrograms of Si.

8.4.4.2 Into each beaker, pipet 25.0 mL of boric acid

solution. Dilute to about 60 mL with water and mix.

8.4.4.3 Continue with Procedure Sections 8.4.5.3–

8.4.5.9. Measure the absorption of each standard and

then return to Calibration, Section 8.4.4.4.

8.4.4.4 Subtract the absorbance of the 0 microgram

standard from each of the other standard absorbances

and plot the net absorbance versus the corresponding

micrograms of Si. Draw the best smooth line fitting the

points and passing through the origin.

8.4.5 Procedure (To be run in triplicate)

8.4.5.1 Calculate the amount of sample prepared in

Section 8.1.4 that contains about 0.5 g of BF

gas.

Transfer this amount to a polyethylene bottle and weigh

to the nearest 0.0001 g.

8.4.5.2 Wash this solution into a 150-mL plastic

beaker. Add 25 mL of boric acid solution. Dilute to

about 60 mL and mix.

8.4.5.3 Add 5 mL of ammonium molybdate solution

and mix.

8.4.5.4 Adjust the pH to 1.1-1.5 with 5N sulfuric acid.

Allow to stand 10 minutes.

8.4.5.5 Transfer the solution to a 100-mL plastic

volumetric flask and add 10 mL of tartaric acid

solution. Mix well.

8.4.5.6 Add 1 mL of 1-amino-2-naphthol-4-sulfonic

acid solution. Dilute to 100 mL and mix. Allow to stand

30 minutes.

8.4.5.7 Prepare a reagent blank by treating a 50-mL

aliquot of water as directed in Sections 8.4.5.2-8.4.5.6.

8.4.5.8 Set the wavelength of the spectrophotometer to

650 nm.

a. Single Beam Spectrophotometer — Rinse and then

fill a 1-cm absorption cell with water. Place the cell

into the cell holder and adjust the instrument to zero

absorbance.

b. Double Beam Spectrophotometer — Rinse and then

fill two matched 1-cm absorption cells with water

and zero the instrument with water in both beams.

Keep water in the reference beam and use the other

matched cell for the blank, standards and samples.

8.4.5.9 Rinse a second matched 1-cm absorption cell

with the blank solution and measure its absorbance.

Then, using the same cell, measure the absorbance of

each sample solution. Be sure to rinse the cell

completely with the solution to be measured before

each measurement. Recheck the instrument zero before

each measurement.

8.4.5.10 Subtract the blank absorbance from the

absorbance of the sample. Determine the corresponding

micrograms of Si from the standard curve.

8.4.6 Calculations

ppm SiF

Micrograms of Si× 3.706 × 1,000, 000

Weight of sample × 1, 000, 000

where :

3.706 converts Si to SiF

1,000, 000 converts ug to g

1,000, 000 converts to ppm.

8.5 Sulfate — This procedure describes the

determination of sulfate in boron trifluoride gas. Sulfate

ion is converted to a barium sulfate suspension under

controlled conditions in such a manner as to form

barium sulfate crystals of uniform size. Solutions are

added to stabilize the suspension and minimize

interferences. The resulting turbidity is determined by a

turbidimeter, filter photometer or spectrophotometer

SEMI C2.27-1102 © SEMI 1984, 2002 6

and compared to a curve prepared from standard sulfate

solutions.

8.5.1 Method Capabilities — The range of the method

is 7-70 ppm.

NOTE 3: Color or suspended matter in large amounts may

interfere with this procedure.

8.5.2 Apparatus

8.5.2.1 Platinum dish, 100-mL capacity.

8.5.2.2 Steam bath (or Argand burner, if available).

8.5.2.3 Photometer: One of the following is required,

with preference in the order given:

a. Turbidimeter

b. Spectrophotometer, for use at 420 nm, providing a

light path of 4 to 5 centimeters.

c. Filter photometer, equipped with a violet filter

having a maximum transmittance near 420 nm and

providing a light path of 4 to 5 centimeters.

d. Fisher Electrophotometer, using a #525 Green Filter

and 23-mm cells.

8.5.2.4 Stopwatch.

8.5.3 Reagents — All reagents used are reagent grade

unless otherwise specified.

8.5.3.1 Water — All water used in the preparation of

reagents and in the procedure is either distilled or

deionized.

8.5.3.2 Sodium carbonate, Na

8.5.3.3 Hydrochloric acid, concentrated, HC

8.5.3.4 Barium chloride, BaCl

8.5.3.5 Sodium chloride solution, 10% in water —

Dissolve 10 grams sodium chloride in 100 mL water.

8.5.3.6 Gum Arabic Solution — Dissolve 0.5 gram gum

arabic (acacia) in 100 mL of water, heat if necessary to

dissolve, filter before using. Conditioning Reagent (may

be used in place of gum arabic solution): Mix 50 mL

glycerol with a solution containing 30 mL concentrated

hydrochloric acid, 300 mL water, 100 mL 95% ethyl

alcohol or isopropyl alcohol and 75 grams sodium

chloride.

8.5.3.7 Standard sulfate solution, 1.00 mL = 0.100 mg

-2

— Dissolve 0.1479 grams anhydrous sodium

sulfate in 4 water and dilute to 1 L.

8.5.3.8 Sodium hydroxide, 1N, NaOH; dissolve 40 g of

sodium hydroxide pellets in water and dilute to 1 L.

8.5.3.9 Nitric acid, concentrated, HNO

8.5.4 Calibration

8.5.4.1 Calibrate the photometer according to the

manufacturer’s instructions.

8.5.4.2 Pipet 0, 1.0, 3.0, 3.0, 4.0, 5.0, 10.0 and 20.0 mL

of the 0.100 mg SO

-2

standard into each of eight

separate 150-mL beakers. These additions correspond to

0, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, and 2.0 mg SO

-2

8.5.4.3 Follow the Procedure described in Sections

8.5.5.5-8.5.5.7.

8.5.4.4 Plot, on linear graph paper, the sulfate ion in

grams against the corresponding photometer reading

and draw the best smooth line through the points.

NOTE 4: A specific calibration curve must be prepared for

each photometer. A new curve must be prepared if the

instruments cell, lamp, or filter are changed, or if any other

significant change in instrument or reagents is made.

8.5.5 Procedure

8.5.5.1 Weigh a clean platinum dish to 0.0001 g;

weight = A.

8.5.5.2 Calculate the amount of sample prepared in

Section 8.1.4 that contains about 50 grams of BF

gas;

transfer this amount to the platinum dish, then weigh

the dish to the nearest 0.0001 g; weight = B.

8.5.5.3 Add about 0.1 gram of sodium carbonate and

10 mL of hydrochloric acid to the dish. Evaporate to

dryness over a steam bath or an Argand burner. Repeat

the evaporation 4 more times with 10-mL portions of

hydrochloric acid.

8.5.5.4 Add 1 mL of hydrochloric acid and 5 mL of

water to the dish; warm to dissolve any residue. Filter

through Fisher G4 or equivalent filter paper in a 55-mm

Buchner funnel, then transfer the filtrate to a 150-mL

beaker. Wash the filter with water and transfer washings

to the same 150-mL beaker.

8.5.5.5 Dilute to approximately 90 mL. Add 1 mL of

10% sodium chloride solution, 1.5 mL of freshly

filtered gum arabic solution and mix. Adjust the pH to

1.75 with 1:10 hydrochloric acid or sodium hydroxide

(1N). Dilute to 100 mL.

NOTE 5: The conditioning reagent may be substituted for the

gum arabic solution. In this case Procedure, Step 8.5.5.5

reads: Add 5.0 mL of conditioning reagent, then dilute to 100

mL with water. Proceed to Step 8.5.5.6.

8.5.5.6 Place the beaker on a magnetic stirrer and while

the solution is being stirred add 1 gram of barium

chloride (BaCl

O) crystals. Begin timing

immediately and stir for exactly 1 minute at a constant

speed.

NOTE 6: It is recommended that a timer be used to permit the

magnetic stirrer to operate exactly one minute with a constant

stirring speed. The important point is the speed of stirring and

time should be constant for the standards and the samples.

8.5.5.7 Immediately after the stirring is completed,

pour some of the solution into the absorption cell of the

photometer. Record the measured turbidity after 4

minutes.

NOTE 7: If the reading is off the calibration curve, prepare a

new curve with standards in the required range, or take a

smaller portion of sample.

8.5.5.8 Prepare a sample blank using the same

quantities of all reagents except the barium chloride,

which is withheld. Read the blank and obtain the

correction.

8.5.5.9 After proper correction for the blank, determine

the mg of sulfate from the calibration curve.

8.5.6 Calculations

mg SO

−

1000

ppm SO

−

where

F is from Section 8.1.4.8

1/8" Steel Pipe

1/8" Steel

Sleeve

1/8" Brass

Needle Valve

Stainless

Steel Needle

1/4" Steel

Coupling

Gas Cylinder

Connection

1/8" to 1/4"

Steel

Bushing

1/4" Steel Pipe

1/4" Tygon Tubing

Figure 1

Preparation of Sample Solution in Ice

Figure 2

Modified Gas Collecting Tube

NOTICE: SEMI makes no warranties or

representations as to the suitability of the standards set

forth herein for any particular application. The

determination of the suitability of the standard is solely

the responsibility of the user. Users are cautioned to

refer to manufacturer’s instructions, product labels,

product data sheets, and other relevant literature

respecting any materials mentioned herein. These

standards are subject to change without notice.

The user’s attention is called to the possibility that

compliance with this standard may require use of

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patent rights. By publication of this standard, SEMI

takes no position respecting the validity of any patent

rights or copyrights asserted in connection with any

item mentioned in this standard. Users of this standard

are expressly advised that determination of any such

patent rights or copyrights, and the risk of infringement

of such rights, are entirely their own responsibility.

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