Questions for SIA Response from April 19, 2012 SIA/EPA Call 

With April 25, 2012 SIA Response 

The following are questions raised during the SIA/EPA conference call on 4/19/12. They cover 

questions on SIA feedback / responses related to apportioning model verification and the DRE 

summary paper. 

Apportioning model verification: 

1. Please provide a suggested definition of "representative of normal operation". 

Response in progress. 

DRE summary paper: 

• Please provide an outline / bullet points that describe what content from the ISMI 

guidelines SIA is proposing to include in subpart I with regard to measurement of sitespecific DRE values. Please also provide the purpose / use of each guideline method in 

the context of subpart I. 

SIA is requesting that EPA allow for use of the 2009 ISMI guideline or most recent 

version1 for process emissions and abatement DRE characterization in place of the 2006 

ISMI guideline currently specified in 98.7 (n) (1). The 98.7 references are detailed on 

pages 74816 and 74817 of the December 1, 2010 Federal Register. This will apply to 

the current references for Subpart I. References should also be added to 98.7(n)(1) for 

98.94(f)(4)(i); 98.94(g)(3); 98.97(d)(4), and 98.98 to incorporate the Appendix B; Section 

B.1.5 “POU Abatement Device Dilution Factor Determination” procedure into the DRE 

testing and certification requirements. 

In order to incorporate the 2009 ISMI guideline and the complete mixing demonstration 

protocol into 98.7(m)(3),the “Protocol for Measuring the Destruction or Removal 

Efficiency (DRE) of Fluorinated Gas Abatement Equipment in Electronics Manufacturing 

Version 1”, two subsections need to be added. 

1. 98.7(m)(3)(i) should indicate that the 2009 ISMI guideline referenced in 98.96(n)(1) 

can be used in place of the 2006 guideline where the 2006 guideline is referenced in 

the “Protocol for Measuring the Destruction or Removal Efficiency (DRE) of 

Fluorinated Gas Abatement Equipment in Electronics Manufacturing Version 1. 

2. 98.7(m)(3)(ii) should state the EPA reference method 7E should be used to 

demonstrate that the gases are well mixed in the duct downstream of the POU 

device at the sampling point. The specific language that SIA recommend be 

referenced is “ Measure at three points on a line passing through the centroidal area. 

Space the three points at 16.7, 50.0, and 83.3 percent of the measurement line. 

Sample for a minimum of twice the system response time (see Section 8.2.6) at each 

traverse point. Calculate the individual point and mean F-GHG concentrations. If the 

 

1

 Over time, the industry has revised the ISMI guideline to incorporate improved analytical methods. SIA requests 

that EPA allow use of the most recent version of the ISMI guideline. 
concentration at each traverse point differs from the mean concentration for all 

traverse points by no more than: (a) ± 10.0 percent of the mean concentration; or (b) 

± 0.5 ppm (whichever is less restrictive) the gas stream is considered unstratified and 

you may collect samples from a single point that most closely matches the mean.” 

This is the language that SIA proposed in the 4/18/202 comments to EPA’s DRE 

summary document. 

Incorporating these references into 98.7 will enable companies to use the most recent 

ISMI guideline and incorporate the revised Dilution Factor Determination methodology 

and QA/QC requirements in both the abatement and emissions factor testing protocols. 

SIA wants to incorporate the 2009 ISMI guidelines updates to section 6 and Appendices 

A and B into the emissions factor and DRE testing protocols for Subpart I. 

A. The 98.7 references to the 2009 ISMI guideline would include the following important 

updates from the 2006 guideline: 

1. Appendix B, Section B.1.5 “POU Abatement Device Dilution Factor 

Determination” which is not in the 2006 ISMI guideline and which enables dilution 

determination using FTIR. This is the critical addition in the 2009 ISMI Guideline 

for Environmental Characterization of Semiconductor Process Equipment – 

Revision 2. 

2. Updates to Chapter 6 which clarifies and updates the “Test for Air Emissions” 

procedures. The updates do not materially change the testing protocols and 

approach for emissions factor and abatement systems testing, but reflect new 

knowledge learned from applying the protocol from 2006 to 2008. 

3. Updates to Appendix A, specifically A.1 Mass Spectrometry Protocol and A.2: 

Fourier Transform Infrared (FTIR) Spectroscopy Protocol, which clarifies and 

updates the instructions for the analytical and sampling processes. The updates 

do not materially change the testing protocols and approach for emissions factor 

and abatement systems testing, but reflect new knowledge learned from applying 

the guideline from 2006 to 2008. 

B. Inclusion of the EPA reference method 7E: This reference provides the transverse 

sampling method to validate that the concentration measurement is being taken in a 

completed mix zone of the ductwork downstream of the POU abatement device. This 

is the addition requested by EPA in their 4/12/2012 comments to the DRE proposal. 

The other option to include this would be for ISMI to update Appendix B, Section B.1.5, 

“POU Abatement Device Dilution Factor Determination”, Section titled "Using a Gas at 

POU Abatement Device Outlet" Item 5 of the Guideline for Environmental 

Characterization of Semiconductor Process Equipment – Revision 2 to specifically 

reference the transverse sampling method detailed in EPA reference method 7E and 

providing the text that SIA provided in the response to the EPA 4/12/2012 comments to 
the DRE proposal. EPA could then reference the third revision in 98.7, simplifying the 

reference and clarifying the requirements. 

• Can SIA provide, for the chamber clean NF3 DRE tests, which abatement system tests 

operated outside of the manufacturer's recommendations and which ones did not? 

Please also provide information on what caused the unit to operate outside of allowed 

parameters (i.e. high flow) for the cases where manufacturer's recommendations were 

not observed. 

There were three chamber clean abatement units which tested with DREs lower than the 

manufacturer’s specifications for the abatement of NF3. Two of the units abated in-situ 

plasma chamber clean processes and one unit abated a remote plasma clean chamber. 

Two of the units, Tool #1 and Tool #2 had low DREs due to high output flows, outside 

the range of the manufacturer’s specifications. The flows were adjusted to both units and 

a retest of Tool #1 validated that reducing the output flow improved the DRE above the 

expected DRE for the unit. 

On Tool #3 adjustments were made to the combustion blower to increase the flow of air 

and DRE improved to within 10% of the expected DRE, but was still slightly below the 

expected DRE. Because of this low DRE, further work was done on this unit in March of 

2012. The combustion liner was replaced, adjustments were made to the pump purge 

flow to slightly reduce flows in the individual chamber lines, and combustion gas flow 

was further adjusted to improve the residual oxygen. This unit has been retested and 

preliminary indications are that the unit is performing above the expected DRE. Per the 

results of this work, the maintenance procedures have been modified to include flow 

checks of the Volume In and Volume Out. 

TOOL# Test Date 

Total 

Vol in 

SLPM 

Total 

Vol out 

SLPM 

Dilution 

Factor 

DRE 

NF3 

Process 

Type Comments

Expected 

DRE 

1 

Sept 27 

2012 142.171 1226.663 8.628 35.832 

In-situ 

Plasma 70% 

1 

Sept 28 

2012 136.17 1031.208 7.573 82.019 

In-situ 

Plasma Retest 70% 

2 

July 27 

2012 124.944 1300.149 10.406 50.51 

In-situ 

Plasma 70% 

3 

May 12 

2012 188.1 628.2 3.34 49.55 

Remote 

Plasma 70% 

3 Sept 7 2012 174.718 721.771 4.131 63.355 

Remote 

Plasma Retest 70% 

Removing a total of four tests for the three devices that had low DREs, the statistical 

analysis yields the results shown in Revised Table B-1 (next page). The average DRE for 

NF3 in chamber cleaning (the last line of the table) is raised by 3.5 percentage points from 

88.7% to 92.2%. There is no change in the data for etch processes and the etch DRE 

results are therefore unchanged. 
The substantial issue is the large effect that EPA’s discounting of the average has on the 

default DRE value to be used in reporting. EPA’s method is to discount the DRE 2 standard 

deviations below the mean, which would result in a value of 75% for NF3 in chamber 

cleaning using the revised data. At this low level, 43 of the 45 MfrZ devices tested actually 

outperform the 75% average. In a fab using 60 MfrZ devices to abate NF3 in chamber 

cleaning (the smallest number of devices reported by SIA members), the odds of the actual 

average DRE being as low as 75% are vanishingly small (less than 1 in 1 million). Even if 

the fab uses some non-MfrZ devices, it is still highly unlikely that the actual average DRE 

would be as low as 75%, as long as the performance of the non-MfrZ equipment is 

reasonably similar to the MfrZ equipment. 

We discussed two other approaches for calculating a discounted default DRE on the April 

19th call. One approach applied a log transform to the DRE data before discounting 2 

standard deviations below the mean. With the change to remove the four low DRE test 

results, the remaining data now pass the tests for skewness and kurtosis, and there is no 

need to consider this approach. 

A second approach discounts 2 standard errors (of the mean) below the mean value, 

without transforming the data, which results in placing confidence limits on the mean. We 

believe there is considerable merit in this approach, because it is the mean DRE for a fab 

that influences emissions and placing confidence limits on the mean would be the usual 

statistical approach for controlling the risk of understating or overstating the mean value. As 

the table shows, when applied to the revised data this approach yields 90% as the 

discounted value that would be used in reporting. This is still a conservative estimate. 

Two-thirds of the MfrZ devices that have been tested outperform the 90% value and onethird perform below the 90% value. This approach introduces a substantial, but reasonable, 

degree of conservatism to the default DRE. 

Considering a fab that uses 60 MfrZ devices to abate NF3 in chamber cleaning, if the 

default DRE is set at 90%, then we can be 97.5% confident that the actual average DRE is 

at least 90%. If some non-MfrZ devices were used in the fab, the confidence level could 

vary depending on the number of such devices and their performance in comparison to 

MfrZ devices. But, there is a margin of safety in this approach to help it meet a 95% 

confidence level, even if the presence of non-MfrZ devices proves to have an adverse effect 

on DRE. Whenever MfrZ equipment is the large majority of devices in a fab, the actual 

average DRE and the statistical confidence level will largely be determined by the MfrZ 

devices.
Revised Table B-1. Summary of Average DREs in Abatement Testing

Original Dataset 

(Feb 29, 2012) 

Dataset Revised to Remo

in Chamber Cle

Process Gas 

N 

(Tests)

Average DRE (%) 

(± standard error) 

EPA 

Proposed 

Defaults 1/

N 

(Tests) 

Average DRE (%) 

(± standard error) 

Dis

2 S

Be

Plasma Etch 

Etch (CF4) CF4 23 54.5 ± 7.5 60% 

Not changed by revision 

Etch (Other Gases) NF3 14 99.27 ± 0.13 98% 

SF6 4 99.14 ± 0.31 98% 

C2F6 1 99.0 60% 

C2F8, C5F8, CH3F 0 60% 

C4F6 5 99.06 ± 0.28 98% C4F8 14 98.85 ± 0.18 98% 

CHF3 19 99.18 ± 0.36 98% 

CH2F2 16 98.94 ± 0.19 98% 

 All Etch (Excluding CF4) NF3/Other 73 99.07 ± 0.13 Chamber Cleaning 

In-situ Plasma NF3 22 88.7 ± 3.7 20 93.2 ± 1.8

Remote Plasma NF3 26 88.4 ± 2.6 24 91.0 ± 1.9Thermal Clean NF3 1 98.9 1 98.9 

All Chamber Cleaning NF3 49 88.7 ± 2.1 60% 45 92.2 ± 1.3 1/ Discounted 2 standard deviations below the mean (assuming normal distribution for DRE values)
SIA v. EPA, (D.C. Cir. No. 1024) Privileged and Confidential, For Settlement Purposes Only - Do Not Cite or Quote

At this point, SIA is not in a position to provide additional data on abatement system DREs. 

As SIA has noted in earlier submittals, we are working to collect additional DRE testing data 

for several process gas/combinations from several abated fabs. The plan is to include test 

data from multiple abatement device manufacturers where available. 

SIA requests that EPA specifically make a request in the preamble to the reproposed rule 

for the submittal of additional DRE data and statistical analysis during the comment period 

to support the creation of more representative default DREs for additional process/gas 

combinations. This will give SIA and ISMI sufficient time to collect additional testing data 

and perform the statistical analysis necessary to justify the use of more representative 

industry wide default DREs. 

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