MEASURED GAS USAGE RATES DURING STACK TESTING 

Table of Contents 

1.0 Introduction................................................................................................................... 1 

2.0 IBM 300mm Fab.......................................................................................................... 2 

2.1 CF4............................................................................................................................ 2 

2.2 NF3 ........................................................................................................................... 3 

2.3 SF6 ............................................................................................................................ 4 

2.4 CHF3......................................................................................................................... 5 

3.0 TI FAB 1...................................................................................................................... 6 

3.1 NF3 ........................................................................................................................... 6 

3.2 CF4............................................................................................................................ 8 

3.3 CHF3......................................................................................................................... 9 

3.4 SF6 .......................................................................................................................... 10 

4.0 TI Fab 2....................................................................................................................... 11 

4.1 C2F6........................................................................................................................ 11 

4.2 CF4.......................................................................................................................... 12 

4.3 CHF3....................................................................................................................... 13 

5.0 INTEL Fab 32............................................................................................................. 15

5.1 C4F6........................................................................................................................ 16 

5.2 C4F8........................................................................................................................ 17 

5.3 CF4.......................................................................................................................... 17 

5.4 CH2F2..................................................................................................................... 18 

5.5 CHF3....................................................................................................................... 20 

5.6 NF3 ......................................................................................................................... 21 

5.7 SF6 .......................................................................................................................... 21 

1.0 Introduction 

This letter presents gas usage data that was recorded at four semiconductor Fabs during stack 

testing conducted in 2011, and is intended to answer EPA’s questions regarding the “steadiness” 

of gas usage rates. A large cross section of gas usage data is provided in order to assure a 

representative combination of different gas metrology methods and usage rates. Additionally we 

provide several comparisons of gas usage data collected over long and short periods of time. 

Due to the fact that gas usage data is confidential business information, certain portions of 

this document have been redacted or modified from the original document, so as to remove 

gas usage data, and quantitative comparisons using actual gas usage rates. At EPA’s 

request, we can send the complete memo, in the form of separate, company specific CBI 

documents. 

GasUsageREV7.doc Page 1 of 22 
We believe that several conclusions can be drawn from the data sets described below: 

 The rate at which a particular F-gas is used at a Fab tends to be steady1

 over long periods. 

 The steadiness demonstrates that although the individual F-gas using tools operate as 

batch processes; the composite effect of dozens to hundreds of batch tools operating in 

unison, is that the gas usage rate resembles that of a continuous process. It follows that 

the composite emissions from these tools, as measured in aggregate at the Fab stack level, 

likewise emulates a continuous process. 

 Some gases have a continuous, but low gas usage rate relative to the size of the gas 

supply cylinder(s), such that there is a high signal to noise ratio, and it is difficult to 

obtain a usage rate over the relatively short duration of the stack test. For those situations, 

we believe that it is appropriate to determine the gas usage rate from a longer period of 

data that brackets the period of the test. 

 Gas usage rate determinations that are made using data obtained from 2 different types of 

gas usage measurement methods over the same period, are very similar, and therefore 

demonstrate the viability of the alternative methods with which gas usage can be 

determined for creating emissions factors under the Stack Testing alternative.. 

These points, in conjunction with the successful validation of the stack emissions measurement 

capability provide the basis for concluding that the Stack Testing method is a valid and useful 

approach. 

2.0 IBM 300mm Fab 

F-gas usage was determined at IBM’s 300mm Fab using a combination of pressure and weight 

scale data, collected manually over the duration of the October 2011 stack test. The gas usage 

data from the period of the stack test is compared to long term gas usage rates, as determined 

from recorded dates and times on which depleted gas cylinders were replaced with full gas 

cylinders on the manufacturing line. This provides us with the basis for comparing short and long 

term gas usage rates, where the short and long term period data also represent completely 

different metrology methods. 

2.1 CF4 

Figure 2-1 shows the CF4 usage as determined over the period of the IBM 300mm stack tests by 

measuring the gas cylinder pressure, and converting to a mass rate of change using a real gas 

conversion. Figure 2-2 shows the CF4 usage as determined from long term cylinder change log. 

This log records the time and date that each cylinder is changed out on the manufacturing line. A 

10 % heel factor was subtracted from the mass of gas in each cylinder, unless a known gas 

specific heel value was available. The CF4 rate measured during the October stack test was 

within 1 % of the annual average. 

 

1 We anticipate that the rates at which different gases are used will transition over time, and for that reason the SIA has 

proposed to use the relative proportions at which gases are used as a bellweather for when stack re-testing is required

GasUsageREV7.doc Page 2 of 22 
Figure 2-1. CF4 usage rate over the duration of the IBM 300mm Stack Test. 

CF4 usage: Oct 3 - 6, 2011 - Determined from P measurements

CF4 (lbs) = (lbs/hr) x (hrs) + 585.61

R2

 = 0.96

400

0 10 20 30 40 50 60 70

elapsed hrs

CF4 cylinder wt (lbs)

80

Figure 2-2. CF4 long term. 

CF4 usage rate 2011 based upon cylinder change log

CF4 (lbs) = (lbs/day) * days - 1E+06

R2

 = 0.9963

0

Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11

date

CF4 lbs

2.2 NF3 

Figure 2-3 shows the NF3 usage as determined over the period of the IBM 300mm stack tests by 

measuring the gas cylinder pressure, and converting to a mass rate of change using a real gas 

conversion. Figure 2-4 shows the NF3 usage as determined from long term cylinder change log. 

This log records the time and date that each cylinder is changed out on the manufacturing line. A 

10 % heel factor was subtracted from the mass of gas in each cylinder, unless a known gas 

specific heel value was available. The short and long term NF3 gas usage rates are within 1 %. 

GasUsageREV7.doc Page 3 of 22 
Figure 2-3. NF3 usage rate measured during the Oct 2011 stack test. 

Oct 2011 IBM 300mm Stack Test: NF3 use measued w/ RKS vs Ideal

RKS(P,T) NF3 (lbs) = + 718.64

R2 = 0.9969

0

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00

elapsed hrs

mass of NF3 in cylinder (lbs)

Lbs in cylinder RKS Linear (Lbs in cylinder RKS )

Figure 2-4. NF3 usage rate for 2011, based upon the cylinder change log. 

NF3 tube trailers 2011

NF3 (lbs) = ( (lbs/day) * days) - 3945.6

R2

 = 0.9974

100 150 200 250 300 350 400 450 500

elapsed days

NF3 (lbs)

2.3 SF6 

Figure 2-5 shows the SF6 usage as determined over the period of the IBM 300mm stack tests by 

measuring the gas cylinder weight. Figure 2-6 shows the SF6 usage as determined from long term 

cylinder change log. This log records the time and date that each cylinder is changed out on the 

manufacturing line. A 10 % heel factor was subtracted from the mass of gas in each cylinder, 

unless a known gas specific heel value was available. 

GasUsageREV7.doc Page 4 of 22 
Figure 2-5. SF6 usage rate measured over the duration of the Oct 2011 stack test. 

SF6 B323: Oct 3 - 6, 2011

y = - + 550

R2

 = 0.9948

528

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00

Elap hrs

SF6 mass (lbs)

Figure 2-6. SF6 usage rate in 2011. 

SF6 in 2011

SF6 (lbs) = (Lbs/day) * days

R2

 = 0.9961

Jan-11 Feb-11 Mar-11 Apr-11 May-11 Jun-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11

SF6 (lbs)

2.4 CHF3 

Figure 2-7 shows the CHF3 usage as determined over the period of the IBM 300mm 

stack tests by measuring the gas cylinder weight. Figure 2-8 shows the CHF3 usage as 

determined from long term cylinder change log. This log records the time and date that 

each cylinder is changed out on the manufacturing line. A 10 % heel factor was 

subtracted from the mass of gas in each cylinder, unless a known gas specific heel value 

was available. The short and long term CHF3 gas usage rates agree within 5%. 

GasUsageREV7.doc Page 5 of 22 
Figure 2-7. CHF3 usage rate during the stack test. 

CHF3 Usage in B323: Oct 4 - 6, 2011

CHF3 (lbs) = ( (lbs/hr) * hrs ) + 1131

R2 = 0.9418

1100

0 10 20 30 40 50

elapsed time (hrs)

total cylinder wt (lbs)

60

Figure 2-8. CHF3 usage rate based upon the cylinder change log. 

CHF3 usage 2010 - 2012

y = - 137803

R2

 = 0.998

29/2010 11/18/2010 1/7/2011 2/26/2011 4/17/2011 6/6/2011 7/26/2011 9/14/2011 11/3/2011 12/23/2011 2/11/2012 4/1/2012

date

lbs CHF3 

3.0 TI FAB 1 

The TI Fabs have a sophisticated data acquisition system that provides a data record of time 

stamped values for the pressure or weight of the Fgas gas cylinders supplying the Fabs. Although 

the primary design intent of this system was to ensure that the Fabs do not run out of gas, it 

provides a basis for determining gas usage rates. The following sections are arranged by gas, and 

illustrate that the gas usage rates are generally quite consistent over long durations. 

For a few gases, notably, CHF3, the gas usage rates are less than can be measured over the 

duration of a single 24 hour period with the existing metrology. The weight scales have a 

resolution of approximately 1 lb, and so for changes of that magnitude the signal is difficult to 

separate from the noise level. However, when the same data is plotted over a longer period that 

brackets the period of the stack test, it can be observed that the data follows a uniform linear trend. 

3.1 NF3 

GasUsageREV7.doc Page 6 of 22 
Figures 3-1 and 3-2 show the NF3 cylinder pressure data for TI Fab 1 for March and August. A 

real gas law relation2

 was used to convert the cylinder pressure to the mass of NF3 in the cylinder, 

and from that the NF3 usage rate was determined. Since the relation between gas density and 

pressure is nonlinear, these pressure versus time data are not quite as linear as the converted data 

for the mass of gas within the cylinder as a function of time. 

The March data shows that a single cylinder is in use over the duration of the test. The pressure 

drops by over 300 psi over the duration of the day long test, providing good resolution. The 

August data reflects the use of 2 cylinders, both of which show more than 100 psi of drop, and 

therefore likewise provide a good signal to noise ratio. 

Figure 3-1. NF3 cylinder pressure measured over the duration of the March 2011 stack test. 

Mar 14 NF3 cylinder pressures, Fab 1

600

0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 1140 1200 1260 1320 1380 1440

elap mn from Mar 14 17:45

NF3 (psi) Cylinder f

0

NF3 (psi) cyinders a,b,c,d,e

f a b c d e

Figure 3-2. NF3 cylinder pressure measured in August 2011. 

NF3 Aug 1, Fab 1

80

0 200 400 600 800 1000 1200 1400 1600

Elap min from Aug 1, 13:00

NF3 cylinder f pressure (psi)

1,290

NF3 cylinder e pressure (psi)

 

2

 Redlich, Kwong, Soave (RKS) method. 

GasUsageREV7.doc Page 7 of 22 
3.2 CF4 

Figure 3-3 show the CF4 gas pressure data for TI Fab 1 in March 2011; where it can be seen that 

two cylinders were in service, and that both dropped by more than 1,000 psi. The cylinder 

pressure data was converted to the mass of CF4 contained within the cylinder as a function of 

time, using the Redlich, Kwong, Soave (RKS) method for real gases, and a usage rate determined 

accordingly. 

In May 2011, TI converted the CF4 cylinder pressure measurements to a cylinder weight 

measurement. Figure 3-4 shows the cylinder weight over the entire month of August 2011. The 

data forms a series of parallel stripes, which correspond to the alternating use, and replacement of 

the left and right cylinders. The average usage rate that corresponds to each curve segment is 

posted on the figure, and it can be seen that the usage rate is very consistent. 

Figure 3-3. CF4 cylinder pressure for Fab 1 during the March 2011 stack test. 

CF4 P, March 2011

0

0 200 400 600 800 1000 1200 1400 1600

Elap time from 00:00 Mar 11, 2011

psi

L_Press R_Press

Figure 3-4. CF4, Fab 1, August 2011. 

CF4 Cylinder weight, TI Fab 1 , August 2011

0 100 200 300 400 500 600 800

Elap hrs from Aug 1, 2011

lbs CF4

1L 1R

Cylinder (kg/hr)

kg/hr)

GasUsageREV7.doc Page 8 of 22 
3.3 CHF3 

Figure 3-5shows the CHF3 cylinder weight over the period of the March stack test. Although the 

CHF3 usage rate is discernable, the usage rate is low, and a single 1 (lb) increment constitutes a 

large proportion of the total signal. In comparison, Figure 3-6 shows the CHF3 usage rate for the 

entire month of March, wherein uniform slopes of the curves demonstrate a steady and consistent 

rate of gas usage. Figure 3-7, shows that the CHF3 usage rate during the month of August is 

likewise steady and consistent. 

Figure 3-5. CHF3 usage during the March 2011 Stack test. 

CHF3, Fab 1, 00:00 Mar 11 thru Mar 16

0 1000 2000 3000 4000 5000 6000 7000 8000

Elap min from 00:00 Mar 11

Lbs CHF3

1L 1R 2L 2R 3L 3R

Figure 3-6. CHF3, TI Fab 1, March 2011. 

CHF3 Fab 1, March 2011

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

elap days from 00:00 Mar 1, 2011

(lbs) CHF3 CHF3-1 Left Scale CHF3-1 Right Scale CHF3-2 Left Scale CHF3-2 Right Scale CHF3-3 Left Scale CHF3-3 Right Scale

GasUsageREV7.doc Page 9 of 22 
Figure 3-7. CHF3, TI Fab 1, August 2011. 

CHF3, Fab 1, August 2011

0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Elap days from 00:00 Aug 1, 

lbs CHF3 in cylinders

1L 1R 2L 2R 3L 3R

3.4 SF6 

Figure 3-8 shows the SF6 usage for March. Whereas one of the two gas cylinders that is in use 

(4L) shows a steady and consistent rate of gas usage, the signal from the other cylinder (5L) is 

observed to be experiencing a transducer problem. However, as shown in Figure 2-8, an average 

usage rate could be recovered from the data via linear regression. The SF6 data for August is 

shown in Figure 3-9, where it can be seen that the transducer has been repaired, and that the usage 

rate is steady and consistent. 

Figure 3-8. SF6 usage data for TI Fab 1 for the month of Mar 2011. 

SF6 Fab 1, Mar 2011

5L = + 67.787

R2

 = 0.8374

4R = + 34.936

R2

 = 0.9928

1440

28804320576072008640

1008011520129601440015840172801872020160216002304024480259202736028800302403168033120345603600037440388804032041760

Elap min from 00:00 Mar 1

lbs

1L 1R 2L 2R 4L 4R 5L 5R Linear (5L) Linear (4R)

GasUsageREV7.doc Page 10 of 22 
Figure 3-9. SF6 usage data at TI Fab 1, for the month of August 2011. 

SF6, Fab 1, August 2011

5R = + 77.229

R2

 = 0.993

4L = x + 63.859

R2

 = 0.9908

1440

28804320576072008640

10080115201296014400158401728018720201602160023040244802592027360288003024031680331203456036000374403888040320417604320044640

Elap min from 00:00 Aug 1, 2011

lbs

1L 1R 2L 2R 4L 4R 5L 5R Linear (5R) Linear (4L)

4.0 TI Fab 2 

This section presents gas usage data from TI Fab 2. 

4.1 C2F6 

Figure 4-1 shows the weight record for the C2F6 cylinders during the March 2011 stack test. It 

can be seen from this data 10 cylinders are ganged together, and that 4 of them are active during 

the test. Two different methods for determining the rate of usage were employed. The first 

method is based upon a linear regression, such that the slope of the regression curve represents 

the usage rate. The 2nd method is based upon an evaluation of the beginning and ending weight of 

each cylinder over the duration of the test. The usage rate as determined using the two different 

methods, agree with less than a 0.5% difference. 

Figure 4-1. C2F6 cylinder weight in TI Fab 2, March 2011 

DMOS 5N (Fab 2) Mar C2F6 cylinder weight

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Elap min from Mar 17 13:20

lbs C2F6

1L 1R 2L 2R 3L 3R 4L 4R 5L 5R

GasUsageREV7.doc Page 11 of 22 
4.2 CF4 

Figure 4-2 shows the pressure for 12 CF4 cylinders over the duration of the March stack test. 

Very little pressure drop occurs over the duration of the test. In comparison, Figure 4-3 shows the 

CF4 cylinder pressure for the entire month of March, where it can be seen that 6 cylinders are 

active and provide a good signal for the determination of the average gas usage rate. Figures 4-4 

and 4-5 show the short and long term data for August, and demonstrate a similar consistency in 

the long term data. 

Figure 4-2. CF4 cylinder pressure over the duration of the March Stack test. 

CF4 DMOS 5N Mar 2011

0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 1140 1200 1260 1320 1380 1440

elap min from 13:00 Mar 17

psi

1L 1R 3L 3R 4L 4R 5L 5R 6L 6R 8L 8R

Fab 4-3. CF4 cylinder pressures, March 2011, Fab 2. 

CF4, March 2011, Fab 2

0

0 50 100 150 200 250 300 350 400

elap hrs from Mar 1

PSI

3R 4L 4R 5L 5R 6L 6R 8L 8R

GasUsageREV7.doc Page 12 of 22 
Figure 4-4. CF4 cylinder pressures, Stack test period during Aug 2011, Fab 2. 

CF4 Aug 2011 DMOS 5N

0

0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200

elap min from 00:00 Aug 4

psi

1L 1R 3L 3R 4L 4R 5L 5R 6L 6R 8L 8R

Figure 4-5. CF4 cylinder pressures, Stack test period during Aug 2011, Fab 2. 

CF4 cylinder P, Month of Aug 2011, TI Fab 2

0

0 50 100 150 200 250 300 350 400

elap time

PSI

4.3 CHF3 

Figures 4-6 and 4-7 show the CHF3 usage data for the duration of the test, and over the entire 

month, respectively. The CHF3 usage rate is low, and as shown on Figure 4-6, the data over the 

duration of the stack test period has a “blocky” character that illustrates the digital resolution of 

the data acquisition system, and which is sometimes known as “digital flipping”. The data for 

cylinder 3L, for instance, can be seen to flip back and forth between a value of 41 and 42 (lbs). 

However, when the CHF3 data, is plotted over the entire month of March 2011, as shown in 

Figure 4-7, CHF3 usage is uniform, continuous, and can be readily determined. 

GasUsageREV7.doc Page 13 of 22 
Figure 4-6. CHF3 Fab 2, over the duration of the March 2011 stack test. 

CHF3, Fab 2, Mar 2011

0

2

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Elap min from 13:00 Mar 17, 2011

Lbs 

1L 1R 2L 2R 3L 3R 4L 4R 5L 5R

Figure 4-7. CHF3 Fab 2, for the month of March 2011. 

Fab 2, CHF3 Mar 2011

0

0 100 200 300 400 500 600 700 800

elap hrs from Mar 1

lbs CHF3

1L 1R 2L 2R 3L 3R 4L 4R 5L 5R

GasUsageREV7.doc Page 14 of 22 
Figure 4-8. CHF3 Fab 2, over the duration of the August 2011stack test. 

CHF3, Fab 2, Aug 2011

9

0 500 1000 1500 2000 2500

elap min from 00:00 Aug 4

lbs

A B C D E F G I J K

Figure 4-9. CHF3 Fab 2, for the month of August 2011. 

Fab 2, CHF3, August 2011

0

0 100 200 300 400 500 600 700 800

Elap hrs from Aug 1

lbs CHF3

1L 1R 2L 2R 3L 3R 4L 4R 5L 5R

5.0 INTEL Fab 32 

Gas usage was determined at Intel’s Fab 32 facility using a combination of pressure and weight 

scale data. The figures in this section represent graphs of the readings from the pressure gauges 

and scales on fluorinated gas cylinders/containers. The graphs show continuous readings from 

each container during the 3 week period from July 26- August 19, 2011 when Intel performed 

emissions testing on the scrubbed exhaust stacks. 

There are some cases where a reading is near zero, then the next reading is much higher. That 

situation shows a container change, where a container that is nearly empty is taken off line and 

replaced with a full one. 

GasUsageREV7.doc Page 15 of 22 
5.1 C4F6 

Figures 5-1 and 5-2 show uniform usage rates over the duration of the stack test period. Note that 

2 cylinders are in use, and that there is a separate graph for each cylinder. 

Figure 5-1. C4F6 at Intel Fab 32. 

lbs 

Figure 5-2. C4F6 at Intel Fab 32. 

lbs 

GasUsageREV7.doc Page 16 of 22 
5.2 C4F8 

The constant linear slope for C4F8 reflects a uniform usage rate as shown in Figures 5-3 and 5-4. 

A separate figure is used for each of the two cylinders that were in use. 

Figure 5-3. C4F8 at Intel Fab 32. 

lbs 

Figure 5-4. C4F8 at Intel Fab 32

lbs 

5.3 CF4 

CF4 usage was determined from continuous pressure readings which were used in conjunction 

with a real gas relation to calculate the mass of gas in each cylinder as a function of time. 

GasUsageREV7.doc Page 17 of 22 
Figure 5-5. CF4 at Intel Fab 32

psi 

Figure 5-6. CF4 at Intel Fab 32

psi 

5.4 CH2F2 

The CH2F2 usage was determined from the graphs as shown below, which reflect a low 

but consistent usage rate. A separate figure is used for each of the three cylinders that 

were in use at the time of the Intel stack test. 

GasUsageREV7.doc Page 18 of 22 
Figure 5-7. CH2F2 at Intel Fab 32

lbs 

Figure 5-8. CH2F2 at Intel Fab 32

lbs 

Figure 5-9. CH2F2 at Intel Fab 32

lbs 

GasUsageREV7.doc Page 19 of 22 
5.5 CHF3 

The CHF3 usage was determined from the graphs as shown below. As with the other 

gases, the graphs demonstrate a consistent rate of usage over the test period. 

Figure 5-10. CHF3. 

lbs 

Figure 5-11. CHF3 at Intel Fab 32

lbs 

GasUsageREV7.doc Page 20 of 22 
5.6 NF3 

The NF3 usage rate was determined from the time versus pressure graphs shown below. A real 

gas relation was subsequently used to convert the pressure readings to mass. 

Figure 5-12. NF3 

psi 

Figure 5-13. NF3. 

psi 

5.7 SF6 

The SF6 usage rate was determined from the graphs shown below, which reflect a 

consistent usage rate. 

GasUsageREV7.doc Page 21 of 22 
Figure 5-14. SF6. 

lbs 

Figure 5-15. SF6. 

lbs 

GasUsageREV7.doc Page 22 of 22