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SIA Revised Proposal to Amend the Apportionment Model Validation Criteria in 40 CFR 98.94(c)

SIA has several concerns with the current language.

1. Most U.S. fabs have no way to measure the use of fluorinated gas exclusively for etch or chamber clean as req uired in 98.94(c)(2) unless it is only used in etch or clean , in which case apportionment may not be relevant. SIA and its members requested the ability to model gas use to eliminate the need to perform direct measurements in a complex system.

2. Some fabs m ay be configured such that they can apportion gas use based on gas delivery system
connections and flow values rather than engineering models and, therefore, we would like to
create this option under the rule . Where supply systems serve only one process ty pe, gas use can be applied directly to a process type . Where supply system s serve multiple processes, gas

use might be apportioned based on flowmeter readings rather than an apportioning model . This is not allowed for under the current language in 98.94(c)

. 3. T he criteria used to determine which time period to assess use against the model are unnecessarily complex and uncertain . As specified in 98.94(c)(2)(i)

, data to assess the maximum 30 day period will not be available until sometime in January of the ne xt year. Then the facility has to determine the assessment period, complete the modeling and gas use measurement analysis, perform the comparison and make corrections, and complete the emissions estimates prior to the March deadline making it difficult to complete the validation in a timely manner so that any issue with the model can be addressed.

4. Lastly, the closure standard in the rule ( between modeled use and actual gas use ) is unrealistically tight and not necessary for several reasons.

a. First , with the use of a 2

- factor approach to etch and the process of combining wafer cleaning with etch as a n emissions factor category, the level of apportioning is greatly
reduced.
b. Second, SIA has demonstrated, in its recent analysis of the Etch Factor Proposal, that even a relatively high level of error in apportionment does not compromise the

emissions method precisions because all actual gas use is accounted for

, and any error
that is introduced is due only to any difference in the emission factor for the diffe rent uses of the gas.

c. There are a limited number of gases that require apportioning. Generally, f or 300 mm facilities, only NF3 requires apportioning (where the etch and wafer clean categories are combined) and for 200 mm fabs 3 to 5 gases have to be app ortioned over the 4 categories. If wafer cleans and etch are combined, greater accuracy can be achieved.

With this background, SIA is proposing the following approach to validation of the apportioning model: Allow fabs to apportion F

- gas either through a modeling method or direct measurements

, such
as flow and scale values

, to create the apportioning factors. The comparison of actual gas use to modeled /measured gas use will be for use in the entire fab
and it will be done for the F

- gas with the greatest u se that will need to be apportioned. The time period for the comparison will be selected by the reporting party as representative of normal operation during the reporting period and can be no smaller than a month and no greater than a year.
The model will be deemed acceptable for apportioning actual gas use if the model ed/measured

use and the actual use in the selected time period match within 20% of actual use. If the match is not within 20%, the reporting party is required to review and correct the model
or measurement method until the 20% criterion is met. Once the 20% criterion is met, the2

model ed or measured apportionment fractions can be used to apportion gas use for purposes of determining and reporting emissions.

Here are suggested amendments to t he language of 40 CFR 98.94(c)

(c) You must develop apportioning factors for fluorinated GHG and N 2 O consumption to use in Equation I

– 13 of this subpart for each input gas i, as appropriate, using a facility

- specific engineering model that is
documented in your site GHG Monitoring Plan as required under §98.3(g)(5). This model must be based on a quantifiable metric, such as wafer passes

, or wafer starts , or measured gas use data . To verify your model, you must demonstrate its precision and accuracy by adhe ring to the requirements in paragraphs (c)(1) and (c)(2) of this section.

(1) You must demonstrate that the fluorinated GHG and N 2 O apportioning factors are developed using calculations that are repeatable, as defined in §98.98.

(2) You must demonstrate th e accuracy of your facility

- specific model by comparing the actual amount of input gas i consumed and the modeled amount of input gas i consumed in the facility for the plasma etching and chamber cleaning process types , as follows:

(i) You must analyze at l east a 30

- day period of operation but no more than one year of operation that is representative of normal operation. during which the capacity utilization equals or exceeds 60 percent of its design capacity. In the event your facility operates below 60 per cent of its design capacity during the reporting year, you must use the period during which the facility experiences its highest 30

- day average
utilization for model verification.

(ii) You must compare the actual gas consumed of input gas i to the modeled gas consumed of input gas i for one fluorinated GHG reported under this subpart under the plasma etching process type and the chamber cleaning process type . You must certify that the fluorinated GHG s selected for comparison correspond s to the largest quant it ies y , on a mass basis, of fluorinated GHGs used at your facility during the reporting year of the fluorinated GHGs that will be apportioned in the determination of emissions under this subpart. If there are two gases which may meet th ese criteri a , that is the ir use is similar in quantity and both are apportioned, you may do this comparison for bot h and demonstrate conformance on aggregate use basis for both fluorinated GHGs

. for the plasma etching process type and the chamber cleaning process type.

(iii) You must demonstrate that the comparison performed for the largest quantity of gas, on a mass basis, that is apportioned for reporting under this s ubpart consumed under the plasma etching process type in paragraph (c)(2)(ii) of this section , does not result in a difference between the actual and
modeled /measured gas consumption that exceeds five 20 percent relative to actual gas consumption, reported to one two significant figure s using standard rounding conventions. If the comparison shows a difference great er than 20%

, you are required to review and correct the facility specific engineering
model or measurements until the 20% criterion is met. Once the 20% criterion is met, the
model ed/measured fractions are to be used to apportion gas use for purposes of determining and reporting emissions under this s ubpart.