Accelerating Sustainable Manufacturing

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ISMI/SIA Stack Testing Technical 

Presentation

ISMI/SIA Stack Test Sub-team 

November 30, 2011
Contents

• Proposal & Key Supporting Information

• Supplemental Information: Summary of Stack Testing:

– Company Z: March vs. August 2011, and minute by minute for 2 gases

– Company A: 5 consecutive days and a Fab over a 10 year time scale

– Company Y: 1 day each at 3 stacks

– Company B: 1 day each at 3 stacks

• EPA Feedback on Proposal

November 30, 2011 2
Summary of the Proposed Stack 

Test Method

• Submit initial test plans, prepared in accordance with EPA Guideline 

GD-042, one month prior to start of testing to regulatory agencies .

– Advance notice provides agencies the opportunity to witness 

testing and/or split sample. 

• Validate the analytical method using EPA Method 320 or alternate 

validation method.

• Identify fab stacks that exhaust GHG emissions above threshold 

quantities

• Measure total gas flow rate of stack on the test day using EPA 

Method 1 or 2.

• Measure designated process GHG emissions from relevant stacks.

• Sample stack for a period of 8 hours.

• Sample each stack sequentially.

• Document test results using GD-043.

November 30, 2011 3
Summary of the Proposed Stack 

Test Method – continued

• Measure gas usage on day of stack testing.

• For each gas determine emission factor (EF) by correlating emissions to 

gas usage.

• Adjust EF for gases that fall below detection limits due to small quantity 

usage by process.

• Adjust EF for gases not used in process, but formed as by-products and 

detected. 

• Determine annual usage of each gas from inventory or purchase 

records. 

• Calculate annual emissions for each GHG by multiplying EF by annual 

gas usage.

• Track abatement units downtime and adjust annual emissions of each 

gas accordingly.

• Report annual emissions. 

November 30, 2011 4
F-gas Emissions Can be Accurately Measured 

and are Consistent Over Time

• Method 320 validation performed at Company Z and 

Company Y.

• Detection limits are adequate to detect compounds at 

relevant emissions levels.

• Stack testing at multiple fabs demonstrates tight 

Confidence Intervals (CI) on emission concentrations.

• Stack flow rates are constant over the test period.

• Data indicates an 8-hour sampling period is appropriate.

November 30, 2011 5
Detection Limits Adequate to Detect 

GHGs at Relevant Emissions Levels

Results from stack test at Company Y using FTIR

6

cfm : 50,000

(m3/d) : 2,038,813

MW GWP100 ppb conversion

F-gas (g/g-mole) (gCO2e/g) (ug/m3) per ppbv ppbv (ug/m3) (kg/yr) (mtCO2e/yr)

CF4 88.00 7,390 3.599 0.889 3.20 2.38 17.60

NF3 71.00 17,200 2.904 0.886 2.57 1.91 32.93

SF6 146.06 22,800 5.973 0.802 4.79 3.57 81.28

N2O 44.00 298 1.799 1,716 3,087.08 2,297.31 684.60

c-C4F8 200.02 10,300 8.180 1.249 10.22 7.60 78.31

C2F6 138.01 12,200 5.644 0.962 5.43 4.04 49.29

CHF3 70.01 14,800 2.863 1.060 3.03 2.26 33.43

Emissions at the LOD for a given stack flow

 Field LOD Emissions

Conclusion: Detection limits are more than sufficient to 

accurately measure relevant quantities of GHG emissions

November 30, 2011
Detection Limits

Conclusion: Influence of detection limits on fab emissions during this 

test are insignificant.

Example:

• 3 ppbv CF4

• 45,000 cfm

DL= 3MTCO2e/yr

3

3

12

88

28

144

33

26

MDL, ppb

Delta, mtCO2e

15

1212 14

2180

5

474

1

294

26

0

4421

7

MTCO2e/year

From 2011 Company A Stack Testing

November 30, 2011
Measured Emissions Are Constant 

Over Test Period

• At the 95% confidence interval, the difference between the 

upper and lower concentrations over the duration of the test 

is quite small; this shows that fab emissions are very 

constant over time.

• Stack flow, as shown on the next chart, is also constant.

November 30, 2011 8

Material Company A Stack1 

(5 days, Aug 2011)

Company Y Stack A 

(1 day, Oct 2011)

Company B 

(1 day, May 2011)

Company Z Stack 1 

(1 day, Aug 2011)

CF4 89.8 – 93.0 81.6 - 91.4 120.0 - 132.6 181.3 - 193.3

CHF3 43.9 – 44.4 3.2 - 3.9 46.2 - 49.9 35.4 - 38.3

CH2F2 <28 NA NA ND

CH3F <35 NA NA NA

C2F6 3.1 – 3.6 3.4 - 3.6 9.8 - 10.4 3.7 - 4.4

C4F8 24.6 – 25.2 5.4 - 5.8 11.9 - 12.7 nd

NF3 28.0 – 31.6 6.5 - 9.0 8.6 - 13.3 208.2 - 247.8

SF6 34.4 – 35.8 17.2 - 20.2 3.5 - 5.0 7.0 - 9.5

N2O 3,576 – 3,681 2,537 - 2,886 639 - 1,058 9,644 - 10,754

Upper and lower 95 % CI in ppbv
Stack Flow Rates are Consistent 

over Time

9

Measured flow rate over 4-5 days during 2011 Company A stack testing.

• Flow only varies by a few percent.

Flow Difference 

from Avg.

Difference 

from Avg.

Difference 

from Avg.

Difference 

from Avg.

Difference 

from Avg.

Run 1 Run 2 Run 3 Run 4 Run 5 Average

Scrubber (DSCFM) % (DSCFM) % (DSCFM) % (DSCFM) % (DSCFM) % (DSCFM)

OCF3 SC-133-5-100 44,496 1.03 43,625 0.99 43,576 0.99 43,899

OCF3 SC-133-4-100 44,829 0.98 46,142 0.99 46,768 1.02 45,542 0.99 45,820

OCF3 SC-133-3-100 43,314 0.98 44,171 1.00 44,877 1.02 44,120

OCF3 SC-133-2-100 40,957 0.94 43,888 1.00 43,530 1.00 44,127 1.01 45,261 1.04 43,553

OCF3 SC-133-1-100 37,481 1.00 36,824 0.99 39,018 1.05 35,117 0.95 37,110

Flow Difference 

from Avg.

Difference 

from Avg.

Difference 

from Avg.

Difference 

from Avg.

Difference 

from Avg.

Run 1 Run 2 Run 3 Run 4 Run 5 Average

Scrubber (DSCFM) % (DSCFM) % (DSCFM) % (DSCFM) % (DSCFM) % (DSCFM)

OCF3 SC-133-5-100 44,496 1.03 43,625 0.99 43,576 0.99 43,899

OCF3 SC-133-4-100 44,829 0.98 46,142 0.99 46,768 1.02 45,542 0.99 45,820

OCF3 SC-133-3-100 43,314 0.98 44,171 1.00 44,877 1.02 44,120

OCF3 SC-133-2-100 40,957 0.94 43,888 1.00 43,530 1.00 44,127 1.01 45,261 1.04 43,553

OCF3 SC-133-1-100 37,481 1.00 36,824 0.99 39,018 1.05 35,117 0.95 37,110 November 30, 2011
60

64

68

72

76

80

8/1/2011 0:00 8/2/2011 0:00 8/3/2011 0:00

Fan Speed (%)

Acid Fan 1

Fan Speed (%)

Acid Fan 2

Fan Speed (%)

Acid Fan 3

Fan Speed (%)

Acid Fan 5

Fan Speed (%)

Acid Fan 6

Fan Speed (%)

Acid Fan 7

0.00

1.00

2.00

3.00

4.00

5.00

8/1/2011 0:00 8/2/2011 0:00 8/3/2011 0:00

System Header

Exhaust Pressure

(psig)

Exhaust Fan Speed is Constant 

During Stack Test

• Exhaust flow rate and 

pressure are very 

tightly controlled to 

maintain process 

control.

• During stack test, fan 

speed and exhaust 

pressure were 

constant.

• Supports testing 

stacks sequentially.

10

From 2011 Company Z Stack Testing – Fab 1.

November 30, 2011 10
F-Gas Emissions Are Correlated to 

F-Gas Usage

• Correlations demonstrated over multiple time 

scales from minutes to years.

• Data demonstrates testing for 8 hours is 

representative of fab emissions. 

• Historical data demonstrates annual stack testing 

can be used to accurately estimate annual 

emissions.

November 30, 2011 11
The Relation Between Gas Usage and 

Emissions has been Evaluated over Multiple 

Time Scales

9 consecutive years

Correlations Consistent Mar vs. Aug 2011

5 consecutive days – 24 hour period

• Consistent emission factors have 

been demonstrated at several 

different time scales – all data shows 

good correlation.

.

November 30, 2011 12
Emissions Track Gas Usage

(15 min. Data Points) 

• Unique opportunity at Company Z to track CF4 pressure drop (a high use Fgas) over short intervals. 

• Data demonstrates that usage and emissions are correlated over short time 

intervals. 

November 30, 2011 13

CF4: Mar 2011, Stack S1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 10 20 30 40 50 60 70 80 90 100

Time (qtr hour increments)

CF4 emissions

0.0

0.5

1.0

1.5

2.0

2.5

3.0

CF4 usage (gas P delta)

CF4_FTIR PressDelta
CF4 emissions vs CF4 use

R

2

 = 0.94

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

CF4 use

CF4 emissions (lbs/hr)

• Top chart shows measured CF4 

stack emissions and recorded CF4 

usage (normalized) from 2001 thru 

2010.

• Lower chart shows plot of 

measured CF4 emissions vs. 

recorded CF4 usage from 2001 thru 

2010; data shows a high degree of 

correlation (R2=0.94). 

• Over the period from 2001 thru 

2010, Company A fab transitioned 

from the 180 nm to 45 nm 

technology node which required 

several process conversions.

 Emissions as a function of gas 

usage is very linear.

 The relation is robust through 

multiple technology nodes. 

Relationship Between Use and Emissions is 

Steady Over Time

November 30, 2011 14

Company A: Normalized CF4 use, and CF4 emissions

0.0

0.2

0.4

0.6

0.8

1.0

1.2

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

CF4 emissions (lb/hr)

0.0

0.5

1.0

1.5

2.0

2.5

Normalized CF4 use

Normalized CF4 usage CF4 emissions (lb/hr)
Relationship Between Use and Emissions is Steady Over Time

• Top chart shows measured SF6

stack emissions vs recorded SF6

usage (normalized) from 2003 thru 

2011; it shows a high degree of 

correlation (R2=0.89).

• Lower chart shows the same for 

years 2004 thru 2011; during these 

years the site had no SF6 

abatement. Data shows a higher 

degree of correlation (R2=0.94).

• With consistent levels of abatement 

correlation improves. 

• Change in number of abatement 

devices is a key variable to track.

 Historical testing demonstrates that 

stack testing can be used to 

accurately estimate annual 

emissions.

SF6 2003-2011

SF6 2004-2011

Emissions, lbs./hr

Emissions, lbs./hr

15

SF6 Usage (Normalized)

SF6 Usage (Normalized)

November 30, 2011
8-Hour Sample is Representative

Company A tested each stack for 5 days (120 hours).

Emissions calculated using 8 hr. of data per stack to develop average lbs./hr. emissions

Conclusion: 8 hrs. of testing per stack is representative; results very similar to 

120 hr. averages

MTCO2e/yr.

16

From 2011 

Company A 

Stack Testing

November 30, 2011
8-Hour Sample is Representative

17

CF4 vs time with 8 hour running average

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0.180

0.200

0.220

0.240

0.260

10:04 AM 12:28 PM 2:52 PM 5:16 PM 7:40 PM 10:04 PM 12:28 AM 2:52 AM 5:16 AM 7:40 AM 10:04 AM

time [CF4] ppmv

CF4 CF4 8 hr avg

• CF4 emissions measured continuously over 24-hour period in 300mm stack 

• The mean CF4 conc. is 167 ppbv, with upper and lower 95 % CI of 162 – 172 ppbv

• The 8-hour running average ranged between 144 and 186 ppbv

 An 8-hour sample time yields substantially the same result as a 24-hour sample 

time.

From 2011 Company Z Stack Testing

November 30, 2011
Use of Stack Emission Factors to 

Determine Annual Emissions

• Conduct stack test to measure the emissions rate of each gas (i) over the test period

• Measure the total average gas usage rate over the corresponding period

• Calculate Fab specific emissions factors 

Example:

A) Measure the CF4 emission rate and gas usage rate to determine an emission factor 

(EF) for the Fab:

0.5 (kg/day) of CF4emission @ Stack1, 0.3 (kg/day) @ Stack 2, 0.2 (kg/day) @ Stack 3

4.0 (kg/day) of CF4used across the fab, over the corresponding period

B) Compute the annual CF4emissions: 

Total annual CF4usage = 400 (kg)

year

k g

k g

k g

y r

k g

E

C F emissions

100

used

emitted

0.2 5

used

400 4

i

s s

S

s

i

E Q C

1

18

used

emitted 0.25

4

1

1

0.5 0.3 0.2

k g

k g

k g

day

day

k g

e

i

November 30, 2011
Stack Testing Frequency

Changes in POU abatement and F-gas use as a percentage of total are 

parameters which will result in emissions changes and should trigger retesting.

Proposal: 

• Fabs which use the stack test option will test major F-gas emitting 

stacks in the first year. 

• Thereafter, testing in the subsequent year is required whenever:

– The weight % makeup of an individual F-gas changes by more than 10 

percentage points from one year to the next year, or

– If the fraction of abated tools decreases by greater than 10 %. 

• If no significant changes occur, the EF determined from the initial 

testing may be used for 5 years. 

• As a minimum, stacks would be re-tested every 5 years.

November 30, 2011 19
Re-Testing Upon Major Process Change as 

Signaled by Change in Gas Mix

• The Company A site transitioned from both 200 and 300 mm wafer processing to strictly 

300mm processing in 2008 with switch from remaining C2F6 chamber cleans to NF3 

• The production change is clearly signaled by the NF3 and C2F6 wt % 

– The CF4 emission vs. gas use correlation remained unchanged by the production line change

– The C2F6 emission vs. use correlation was good until the change

– The SF6 emission vs. use correlation was affected by the change in abatement, not the production 

line change

 Conclusion: Changes in the wt. % and abatement provide a clear indicator of the need to 

retest stacks and determine emission factors

20

% of Total F-Gas Usage by Year for Company A Site

F-Gas 2003 2004 2005 2006 2007 2008 2009 2010

NF3 44 51 45 45 54 85 79 82

SF6 5 7 7 5 5 5 3 2

CF4 14 12 9 8 6 1 9 8

CH2F2 0 0 1 0 1 1 0 1

CHF3 1 1 1 1 1 0 3 3

C2F6 33 19 23 29 26 0 0 0

C4F6 0 0 0 0 0 1 1 0

C4F8 1 2 4 3 2 6 5 4

C4F8O 2 8 10 8 5 0 0 0

November 30, 2011
Minimum Threshold Quantities

At what emission level can stack emissions be calculated rather than 

measured? 

• Proposal:

– Ensure coverage of the vast majority of process gas emissions (e.g., all process GHG stacks 

with emissions in excess of 10,000 MT CO2e/year or 15% of total emissions).

– Develop options for reasonable engineering estimates for the emissions of stacks not tested

• Example:

– The site shown below has 14 stacks from which F-GHG are emitted.

– The total GHG emissions are 20,739 (MTCO2e/yr.)

– Under the above proposal, stack testing would be performed on 10 of 14 stacks.

November 30, 2011 21
Analytical Methods for Subpart I

Proposal: 

• Measure stack process GHG concentrations using EPA Method 320 for FTIR, or any other 

method that is capable of detecting the analytes of interest at the concentrations of interest; 

which has been validated using EPA Method 301 or an alternate scientifically sound 

validation protocol.

– Allow use of quality assured analytical methods for all analyses required by Subpart I.

• Measure stack flow rates using EPA Method 1 or 2.

Similar flexibility provisions are contained in Subpart L:

“Analytical methods. Use a quality assured analytical measurement technology capable of detecting the 

analyte of interest at the concentration of interest and use a sampling and analytical procedure validated with 

the analyte of interest at the concentration of interest. 

Where calibration standards for the analyte are not available, a chemically similar surrogate may be used.

Acceptable analytical measurement technologies include but are not limited to gas chromatography (GC) with 

an appropriate detector, infrared (IR), fourier transform infrared (FTIR), and nuclear magnetic resonance 

(NMR). Acceptable methods for determining fluorinated GHGs include EPA Method 18 in appendix A–1 of 40 

CFR part 60, EPA Method 320 in appendix A of 40 CFR part 63, EPA 430–R–10–003 (incorporated by 

reference, see § 98.7), ASTM D6348–03 (incorporated by reference, see § 98.7), or other analytical methods 

validated using EPA Method 301 at 40 CFR part 63, appendix A or some other scientifically sound validation 

protocol.”

November 30, 2011 22
Key Takeaways

• SIA is proposing a stack testing model as an alternative method under Subpart I

– Stack testing is a well-accepted method for quantifying emissions

• Testing and data collected by SIA companies demonstrates:

– Established methods can accurately measure process GHG emissions at 

semiconductor fabs.

– Emissions from one 8 hour test period are representative of emissions at the fab

over an extended period of time.

– Results of testing combined with chemical use can be scaled to estimate annual 

emissions.

• The data and analysis developed by ISMI/SIA establishes a solid foundation for 

future action by EPA

– Testing was conducted at multiple 200 mm and 300 mm fabs which manufacture a variety 

of semiconductor devices.

– Stack testing provides a direct measure of a fab’s emissions. 

• Numerous benefits of the SIA proposal – both to EPA and the industry

– Improved accuracy over current methods, minimizes cost and CBI concerns, potential for 

expeditious resolution of this matter.

November 30, 2011 23