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Response to EPA’s Stack Test Question 1

Frequency of stack testing (emission factor variability): The answers to these questions will 

help EPA to determine the appropriate frequency of stack testing.

1. Please provide the per-gas emission factors (EFs) and by-product emission factors (BEFs) 

across fabs (kg emissions/kg input) that you have collectively measured. Please provide 

each EF and BEF for each measurement campaign at each fab (i.e., not averages over 

multiple months or years). Please identify the fabs, line widths, product mixes, and dates 

from which the emission factors come. If Company D measured N2O emissions during the 

March and August runs, what were these emissions and emission factors? 

Response: Listed below are fab-wide emissions factors computed for the following: 

 Company D Fab 1: March and August 2011 

 Company D Fab 2: March and August 2011

 Company E: May 2011 

 Company F: Fab 1, 2001 thru 2011

 Company F: Fab 2, 2011

Table 1-1 provides information for each fab requested by EPA.

Table 1-1. Description of Stack Test Fabs showing Test Dates, and Line Widths & Product Mixes

As stated in Company G’s test plan, Company G tested a subset of acid and base stacks at its 

300mm fab. Data from Company G stack tests are being provided to EPA under separate cover. 

Because all greenhouse gas emitting stacks were not tested, Company G is unable to provide 

fab-wide emission factors.

Emission factors listed in subsequent tables were calculated using the following methods:

 If an fluorinated greenhouse gas (F-gas) is used in a fab, mass emissions are divided by 

the mass of that F-gas used;

 If an F-gas is not used but emissions are measured, the mass of emissions are divided by 

the total mass of all F-gases used.

Company D Emission Factors 

COMPANY D conducted stack emissions tests on Fabs 1, 2 and 3 in March and August of 2011. A 

comparison of the March and August emissions factors produced by the Fab 1 test is listed in 

Facility Wafer size 

(mm) Tests Production Technology 

Company D Fab 1 300 Mar & Aug 2011 Primarily digital signal processors, 130 - 65 nm 

Company D Fab 2 200 Mar & Aug 2011 Analog devices, 90 nm 

Company E Fab 200 May 2011 Logic for automotive and networking, 250 to 90nm

Company F Fab1 200/300 to 300 Annually,

2003 - 2011

Logic, 250 to 45 nm, over time

Company F Fab2 300 Aug - Sept 2011 Logic, 45 nm
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Table 1-2 and a comparison of the March and August emission factors produced by the Fab 2 

test is listed in Table 1-3. In Fab 3, two of three process GHG emitting stacks were tested and 

limited gas usage data was collected; therefore, it was not possible to calculate fab-wide 

emission factors. 

COMPANY D Fab 1:

Seven principal fluorinated gases, NF3, CF4, CHF3, SF6, CH2F2, C4F8, and C5F8 are used in Fab 1, 

and comprise over 95 % of the fab’s F-gas emissions. As listed in Table 1-2, the emission factors 

that were determined for these gases from the March and August stack testing agree closely, 

with a maximum difference of 20.6 %. 

Table 1-2. COMPANY D Fab 1 Stack Emissions and Emission Factors for March and August 

2011. 

a. C2F6 and C3F8 were not used by COMPANY D Fab 1, and are byproducts. 

b. The totals include N2O. 

Although we believe that the 20.6 % difference between the March and August emission factors 

for SF6 is quite good, we note that the relatively higher difference between the March and 

August tests for SF6 may likely be attributable to the resolution of the gas usage metrology that 

was available at the time of the test. Figure 1-1 shows the SF6 measurements data that is 

available from the time of the March test, and it can be seen that recorded weight from one of 

the gas cylinders experienced a small, but distinctly anomalous amount of drift. In order to 

correct for this drift, a regression analysis was performed over a one month period of SF6 data 

that bracketed the test period, and used to compute the emission factors. 

The F-gas with the next highest divergence between the March and August emission factors was 

c-C4F8 (18.1%). The March c-C4F8 usage rate is only <0.02 kg/hr., and the emissions only 0.0008 

kg/hr., which is equivalent to 65 mTCO2e/yr. In the particular case of c-C4F8, all of the measured 

stack concentrations were less than the 0.8 ppbv field detection limit (FDL); therefore, the 

emission calculation is based upon an assigned concentration of 1⁄2 the FDL as per the standard 

practice used in this effort. Likewise, because of the very low gas usage rate, the measured gas 

usage for c-C4F8 is based upon the 5 day period bracketing the stack test period. Notably, the 

measured usage rate for this 5 day period was less than 0.3 % different than the average usage 

rate for the entire month of March. 

Gas Units NF3 CF4 CHF3 SF6 CH2F2 C4F8 C5F8 C2F6aC3F8aTotalb

EF (kg emit / kg use) 0.0673 0.8669 0.0591 0.3126 0.1108 0.0572 0.0247

bpEF (kg emit / tot F use) 0.0069 0.0004

GWP CO2e 17,200 6,500 11,700 23,900 650 8,700 100 9,200 7,000

Emissions Kg/hr 0.2288 0.2776 0.0502 0.0059 0.0010 0.0008 0.0009 0.0322 0.0021 3.1024

Emissions (mTCO2e/mo) 2,873 1,317 428 103 0 5 0 216 11 5,521

Emissions % of total CO2e 52.03% 23.86% 7.76% 1.87% 0.01% 0.10% 0.00% 3.92% 0.19%

Gas Units NF3 CF4 CHF3 SF6 CH2F2 C4F8 C5F8 C2F6aC3F8aTotalb

EF Emissions/Usage 0.0576 0.8321 0.0569 0.3768 0.1129 0.0676 0.0252

bpEF (kg emit / tot F use) 0.0050 0.0039

GWP CO2e 17,200 6,500 11,700 23,900 650 8,700 100 9,200 7,000

Emissions Kg/hr 0.1453 0.2591 0.0426 0.0071 0.0009 0.0008 0.0008 0.0183 0.0142 4.9066

Emissions (mTCO2e/mo) 1,824 1,229 364 125 0 5 0 123 73 4,743

Emissions % of total 38.46% 25.92% 7.67% 2.63% 0.01% 0.10% 0.00% 2.60% 1.53%

EF Agreement % Mar - Aug EF  14.38% 4.01% 3.73% -20.56% -1.90% -18.10% -1.98% 27.55%

Fluorinated Gases Used in Fab 1 Byproducts

Fab 1 - August 2011 Fluorinated Gases Used in Fab 1 Byproducts

Fab 1 - March 2011
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There are a number of relatively straight forward options for increasing the resolution of gas 

usage measurements during future tests. For instance, under fab normal operation it is a 

common practice to gang several gas cylinders together as a means of minimizing the risk of the 

fab running out of a gas. For some fabs, one very simple means of increasing the gas usage 

measurement resolution is therefore to adjust the system so that only a single cylinder is used to 

supply gas over the duration of the stack test. 

C2F6 and C3F8 are not used in Fab 1 but are generated as process byproducts. The byproduct 

emission factors (bpEF) for C2F6 as listed in Table 1-2 for March (0.0069) and August (0.0050) 

differ by 27.6%. Overall, the absolute C2F6 emissions are very small. The C3F8 byproduct 

emission factors for March (0.0004) and August (0.0039) did not agree well, but with less than 

130 (mTCO2e/yr) emissions in March, the emissions are exceptionally low (approaching the 

resolution limits of the metrology) and of questionable relevance to the total GHG emissions 

statement for the fab. We note that, whereas the byproduct emission factors are calculated on 

the basis of the total F-gas usage, it seems likely that C2F6 and C3F8 byproducts would 

predominately be generated from higher fluorocarbon homologues; however, when we tried 

calculating bpEF for C2F6 and C3F8 solely on the basis of the COMPANY D Fab 1 usage of higher 

homologues, there was no significant change in the bpEF values for March and August. 

Figure 1-1. SF6 weight scale measurements during the March 2011 Stack test at COMPANY D

Fab 1. 

COMPANY D Fab 2:

Two principal F-gases CHF3 and C2F6 were used in Fab 2 during the March and August stack 

testing periods. These 2 gases account for 97% of the total CO2e emissions. C4F8 and SF6 are 

used in small quantity in Fab 2; the usage rate is estimated to be less than 0.2 lb./day and is 

below the ability of the fab to measure with the metrology in use today. COMPANY D was thus 

not able to calculate emission factors. For low usage gases, the industry recommends estimating 

emissions using Tier 2a emission factors as discussed below. As listed in Table 1-3, the March 

and August emission factors for CF4 in Fab 2 agree within 17.7 %; whereas the emission factor 

for C2F6 agrees within 21 %. Although the agreement is not quite as good as obtained for the 

SF6, Fab 1, Mar 2011

20

30

40

50

60

70

80

90

100

110

0 400 800 1,200 1,600 2,000 2,400 2,800 3,200 3,600 4,000 4,400 4,800 5,200 5,600 6,000 6,400 6,800 7,200

Elap min from 00:00 Mar 11 lbs SF6

1L 1R 2L 2R 4L 4R 5L 5R
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Fab 1 gases, we believe that this data also represents an exceptionally good and robust 

demonstration of the utility of the SIA’s proposed stack testing method for F-gas. 

Table 1-3. COMPANY D Fab 2 Stack Emissions and Emission Factors for March and August 

2011.

COMPANY D N2O Emissions:

Table 1-4 lists the emissions for N2O as measured at both Fab 1 and Fab 2, during the March and 

August 2011 stack testing. The reported ambient atmospheric concentration of ~320 ppbv N2O 

was subtracted from the measured stack N2O concentration values in order to calculate 

emissions. Emission factors were determined using the March and August data for Fab 1, but not 

for Fab 2. The Fab 2 N2O gas usage rates could not be determined because data were missing 

from two of the N2O gas cylinder weight sensors. For Fab 1, the N2O emission factors for March 

(0.34) and August (0.66) differ by a factor of almost 2. N2O is the only gas in the COMPANY D

data for which a large difference in the March and August emission factors was determined, and 

we do not know the reason for the large difference. Accordingly we believe it is appropriate to 

structure a Subpart I reproposal such that N2O emissions are estimated by applying a default 

emission factor to usage as currently required by the rule instead of through stack monitoring.

Table 1-4. COMPANY D Fab 1 and 2 Stack Emissions and Emission Factors for N2O.

Gas Units NF3 CF4 CHF3 SF6 C2F6 C3F8 CH2F2 C4F8 C5F8 Total

EF (kg emit / kg use) 6.408 0.422

GWP CO2e 17,200 6,500 11,700 23,900 9,200 7,000 650 8,700

Emissions Kg/hr 0.000 0.186 0.018 0.001 0.888 0.000 0.000 0.000 0.000

Emissions MTCO2e/month 0 884 157 17 5,965 0 0 0 0 7,023

Emissions % of total 0.00% 12.59% 2.23% 0.25% 84.94% 0.00% 0.00% 0.00% 0.00% 100.00%

Gas Units NF3 CF4 CHF3 SF6 C2F6 C3F8 CH2F2 C4F8 C5F8 Total

EF

Emissions/Usag

e 5.273 0.511

GWP CO2e 17,200 6,500 11,700 23,900 9,200 7,000 650 8,700

Emissions Kg/hr 0.000 0.211 0.029 0.001 1.049 0.000 0.000 0.000 0.000

Emissions MTCO2e/month 0 1,003 252 11 7,044 0 0 0 0 8,310

Emissions % of total 0.00% 12.07% 3.03% 0.13% 84.77% 0.00% 0.00% 0.00% 0.00% 100.00%

EF Agreement % Mar - Aug EF  17.71% -20.91%

Fab 2 - August 2011

Fab 2 - March 2011

Quantity Units Mar N2O Mar N2O

EF (kg emit / kg use) 0.3417 NA

GWP CO2e 310 310

Emissions Kg/hr 2.5029 1.6247

Emissions (mTCO2e/mo) 566 368

Emissions % of total CO2e 10.26% 4.97%

Quantity Units Aug N2O Aug N2O

EF Emissions/Usage 0.6558 NA

GWP CO2e 310 310

Emissions Kg/hr 4.4176 2.3878

Emissions (mTCO2e/mo) 1,000 540

Emissions % of total 21.08% 6.11%

March 2011 Fab 1 Fab 2

August 2011 Fab 1 Fab 2
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Company E Emission Factors

Company E conducted emissions testing at a 200mm fab in May 2011. FTIR sampling was 

conducted on the three exhaust headers through which GHG using processes are exhausted. The 

fab has primarily NF3-based CVD chamber cleans using remote plasma devices, but it does still 

have some CVD tools that run C2F6 and CF4 cleans – such that C2F6 and CF4 are the primary 

emissions overall. There are more than 100 tools using GHGs (F-gases and N2O) in the fab. The 

CVD and etch tools have up to four individual process chambers per tool. The fab uses 10 

different process greenhouse gases: CF4, C2F6, C4F8, CHF3, NF3, SF6, N2O and very small 

amounts of C4F6, CH2F2, and CH3F. 

 Table 1-5. Emission Factors and Annual Emissions from Company E Fab

Six process greenhouse gases were measured in the exhaust and emission factors are listed in 

Table 1-5. C4F6, CH2F2 and CH3F emissions were not detected. As previously discussed, 

emissions of these low use gases can be estimated using Tier 2a emission factors. N2O emissions 

were only detected in a single header which is the lowest using zone; concentrations were below 

measurement sensitivities. Detection limits for N2O were high during this testing (several ppm), 

because the enhanced FTIR system is optimized for F-gas detection. N2O is not included in this 

analysis. It is recommended that N2O emissions be estimated using default factors separate 

from F-gas emissions. 

Company F Emission Factors

This section describes the emission factors that have been determined at two Company F Fabs: 

one in Fab 1 and the other in Fab 2. 

Fab 1:

Company F has conducted annual stack level emissions testing at their Fab 1 since 2003, and the 

results from this testing, as presented in Table 1-6 , present an excellent record for the 

evaluation of stack testing, and stack testing emission factors. Following is a discussion of 

several key aspects of the Fab 1 stack testing data that are important to consider in addressing 

this data. 

 There are 3 times over the 9 year sequence of data at which the change in gas mix would 

have signaled a need to retest the stacks and determine new emission factors. Recall 

from our November 2011 presentation to EPA in Washington DC, as well as from our 

prior letters that we believe that a change in the proportion of gases used at a Fab 

serves as a direct indicator of when production conditions have changed significantly, 
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and stack retesting is warranted. The bottom row in Table 1-6 indicates that retesting 

would have been warranted in 2007, 2008, and 2009. 

 The fraction of the Company F Fab plasma tool fleet which has POU abatement installed 

has evolved over the nine year period. Since the presence of POU abatement influences 

the emissions from a stack, we have configured Table 1-6 to show the pre-POU 

abatement EF for NF3, CF4 and SF6. These gases were all partially abated at this fab in 

recent years, with the % mix abated changing year by year. The listing of both a preabated EFs as well as the measured abated EF serves to factor out the difference caused 

by the changing abatement mix. Thus, for instance the measured EF for CF4 in 2010 and 

2011 were 1.03 and 0.93 as listed in the first row of Table 1-6; however, factoring out 

the influence of the change in abatement, the effective emissions factors were 1.05 and 

1.07, as listed in the second row of the table. The net effect is that there is a 9.7 % 

difference between the raw CF4 emission factors for 2010 and 2011; but only a 1.9% 

difference when the influence of the change in abatement is factored out. Likewise, by 

factoring out the influence of the changing mix in abatement the difference between the 

2010 and 2011 EF for SF6 reduces from a 28.4 % to a 7.1 % difference; and the NF3 

reduces from a 41.2 % to a 21.1 % difference. As we had noted previously for the period 

to period comparisons of the Company D emission factors, the Company F data likewise 

shows an exceptional degree of agreement that is highly supportive of our stack 

emission factor proposal. The influence of abatement affects NF3 from 2008-‘11, and 

SF6 & CF4 in 2010 and ‘11. NF3 had no abatement prior to 2008 and SF6 and CF4 had 

none prior to 2010. 

 C2F6 was not used at the fab after 2007. Although C2F6 is a known byproduct of some 

other F-gases, it has never been detected in the exhaust stacks in Fab 1 since it ceased 

being used as a process gas after 2007; therefore, no conclusions can be reached about 

byproduct C2F6 emission factors from this data. 

 The CHF3 emission factors are listed as ranges because the concentrations were typically 

quite low, and influenced by the manner in which values below the limit of detection 

were treated. The lower value listed in the table was obtained by treating non-detects as 

if they were equal to zero, and the higher value is based upon treating the non-detects 

as if they were equal to the detection limit. 

 CH2F2 was never detected in the Fab 1 stack tests although it is used at that facility. 

Because its use is small, it would still have been non-detectable even if all use had been 

emitted. Accordingly, we have listed the EF for CH2F2 as 1.0. This simply signifies that 

due to the low usage rate, and corresponding low emission rate, no conclusions about 

CH2F2 emission rates could be reached from this data. As discussed in the section

below, SIA recommends that emissions of low use F-gases be estimated using Tier 2a 

emission factors.
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Table 1-6. F-Gas Emission Factors for Years 2003 -2011 at Company F’s Fab 1 Site 

2003 2004 2005 2006 2007 2008 2009 2010 2011

CF4 0.84 0.70 0.82 0.66 0.78 1.39 0.86 1.03 .93

Pre-abated EF 1.05 1.07

SF6 0.79 0.53 0.64 0.59 0.39 0.69 0.51 0.67 0.48

Pre-abated EF 0.70 0.65

CHF3 .33 - .96 <1 0.58 - 1 .63 - .83 0.52 - 1 <1 0.13 - 1 0.54 - 1 .35 - .98

NF3 0.05 0.05 0.12 0.06 0.11 0.125 0.093 0.085 0.050

Pre-abated EF 0.14 0.23 0.19 0.23

C4F8 No data No data No data No data No data No data No data No data <1

CH2F2 <1 <1 <1 <1 <1 <1 <1 <1 <1

C2F6 0.58 0.60 0.48 0.37 0.38 Not used Not used Not used Not used

C4F6 No data No data No data No data No data No data No data No data No data

product microprocessors, flash memory microprocessors

linewidth 90 -

180nm

90 -

180nm

90 ,180nm 90 

,180nm

90 

,180nm

90nm 45nm 45, 

32nm

32nm

Retesting 

required?1

yes yes yes

The N2O emissions factors for Company F’s Fab 1 site are listed in Table 1-7. Ambient 

atmospheric concentrations of N2O are reported to be on the order of 320 ppb and, therefore,

this value was subtracted from the measured stack value of N20 to develop the N2O emission 

factors. As indicated previously, the N2O emission factors represent an anomaly relative to the 

predictable and consistent behavior that has been observed in the F-gases. It is recommended

that N2O emissions be estimated using default factors.

Table 1-7. N2O Emission Factors for Years 2003 -2011 at Company F’s Fab 1 Site

Averages of the emissions factors from 2009 -2011 were applied to estimated 2011 chemical use 

for the Fab 1 site to determine the emissions that would have been calculated using this data. 

The results are shown in Table 1-8. Current emission factors would only be based on 2009 and 

later data under the SIA stack re-testing proposal; earlier emission factors would have been 

updated under the SIA proposal due to changes in the F-gas usage mix. As Table 1-8 shows, 

when we apply these emission factors to 2011 usage, only 4 gases make significant contributions 

to annual F-gas emissions. 

2003 2004 2005 2006 2007 2008 2009 2010 2011

N2O 0.51 0.52 4.18 0.87 1.7 1.89 0.77 1.15 0.54

Retesting required Yes Yes Yes
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Table 1-8. 2011 Emissions for the Fab 1 Site Based on 2011 Gas Usage and 2009-2011 Average 

Emission Factors

GWP Avg. EF Avg. Emissions 

(MTCO2e/yr) % of total 

CF4 6500 0.94 36,029 26.3%

SF6 23900 0.55 26,831 19.6%

CHF3 11700 0.67 17,779 13.0%

NF3 17200 0.08(1) 56,174 41.0%

C4F8 8700 Not Detected 0.0%

CH2F2 650 1 132 0.1%

C2F6 9200 Not Detected 0.0%

Total F-gases 136,945

N2O 310 0.88 1,856

Total GHGs 138,801

Fab 2:

Table 1-9 lists the emission factors for Company F’s Fab 2 site. The 2011 testing at the Fab 2

facility was specifically targeted at measuring F-gases and was able to achieve lower limits of 

detection for those materials than the previous testing at the Fab 1 facility. As a result, the 

errors introduced by non-detect values are considerably less. The table illustrates the 

uncertainty introduced by non-detect readings for each compound. It does this by showing total 

emissions calculated as if all non-detect readings were equal to zero, then recalculates the totals 

setting non-detect readings equal to the detection limit, and one half the detection limit. In this 

case, the total error introduced by non-detect readings across all gases is about 4,000 

MTCO2e/yr. Whereas the gases that are emitted at higher levels are not strongly influenced by 

the MDL, the gases that are emitted at lower concentrations, and therefore which have 

measured values that are closer to the MDL, are in fact influenced by the choice of how the MDL 

is handled. 

Table 1-9. Emission Factors for Company F’s Fab 2 Site based on 2011 Testing and Different 

Non-Detect (ND) Value Assumptions

ND=0 1/2 MDL ND = MDL ND=0 ND=1/2MDL

CF4 25,488 25,490 25,492 0.825 0.825 31.88%

CHF3 11,692 11,732 11,772 0.648 0.650 14.67%

CH2F2 0 65 130 0.000 1.000 0.08%

C2F6* 7291 7837 8382 0.021 0.023 9.80%

C4F8 4,801 5,789 6,778 0.446 0.538 7.24%

C4F6 0 no GWP 0.000 0.791 0.00%

NF3 5,049 5,264 5,479 0.011 0.011 6.58%

SF6 10,282 10,414 10,548 0.360 0.365 13.02%

N2O 13,372 13,372 13,371 1.760 1.760 16.72%

Total 77,975 79,963 81,952 100.00%

F-Gases 64,603 66,591 68,581

Emissions (MTCO2e/yr) EF % tot CO2e 

@ 1/2 MDL
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* C2F6 is not used in this fab; the EF calculation uses total F-gas used in the denominator.

SIA Proposal for Estimating Emissions of Low Use Gases:

The ability to develop an accurate emission factor is highly dependent on the ability to monitor 

gas usage during the test period. For low usage gases, it is difficult to accurately measure gas 

usage over a brief period of time with currently available pressure or weight based monitoring. 

In the document “EPA Etch Question Responses 02032012”, SIA provided justification for our 

proposal that Tier 2a be used as the basis for calculating annual manufacturing capacity and 

determining whether reporting is required. Under the Stack Test Alternative, SIA recommends 

that Tier 2a be used as a screening tool to determine what gases must be addressed via stack 

testing. If estimated emissions of an F-gas exceed a minimum threshold (to be determined) or if 

estimated emissions for that gas are greater than 15% of total F-gas emissions, SIA recommends 

that stacks be monitored for emissions of that gas and that a fab specific emission factor be 

developed. If emissions are less than the threshold or 15% of total estimated F-gas emissions, 

SIA recommends estimating emissions using Tier 2a emission factors.