Subpart I; Recipe-Specific Emission Factors
Greenhouse Gas Reporting Program
This fact sheet is designed to provide clarification on how to implement provisions related to the
development and use of recipe-specific utilization and by-product formation rates (emission
factors) under Subpart I: Electronics Manufacturing.
How should a facility handle multi-step etch recipes where different steps use process
parameters that fluctuate by more than 10 percent? Should each step be treated as if it is an
individual recipe?
EPA does not require facilities to treat each step of an etch recipe as an "individual recipe" as
defined in Subpart I. EPA recognizes that etch recipes may consist of multiple steps, and in
some cases may consist of as many as 10-30 distinct steps (e.g., stabilization step, RF power
ramp step, plasma ON step...), each with varying process parameters. Some of these
parameters, including reactor pressure, individual gas flow rates, and applied radio frequency
(RF) power, may vary by more than 10 percent from one step to another.
As a means to reduce burden for facilities that are required or elect to develop and use recipe-
specific emission factors, EPA is permitting a facility to apply the same emission factors to a set
of "similar recipes." To assist facilities in comparing recipes for similarity, EPA is providing the
following guidance on how a facility could perform the comparison using a time-weighted
average (TWA) approach. This guidance is not intended to preclude facilities from using other
approaches permissible under the rule, such as a consumption-weighted average approach.
To compare two individual recipes and determine whether they are "similar," a facility can take
into account the differences between TWAs of reactor pressure, individual fluorinated GHG (F-
GHG) gas flow rates, and (total) applied radio frequency (RF) power over multi-step recipes.
The time-weighted average approach (as opposed to a simple average approach), would
account for the fact that longer steps will have a larger impact on the overall emission factors
than shorter steps. This approach is consistent with the 2006 International SEMATECH
Manufacturing Initiative's Guideline for Environmental Characterization of Semiconductor
Process Equipment (2006 ISMI Guidelines) and industry common practices where emission
factors are averaged over the entire recipe (not measured for each distinct step).
To determine the TWA value for a particular parameter (X=gas flow, pressure or total power), a
facility would multiply the value for that parameter for a given step ']' by the duration of that
step, sum up the results of the multiplication over all steps, and divide the result of the
summation by the total recipe time. This weighted-averaging method is represented
mathematically in the equation below:
United Slates
Environmental Protection
Agency
April 2011 1 40CFR98
-------
X
TWA
d
Where:
XTWA = time-weighted average of pressure or total RF power or gas flow for a particular
recipe (Torrs or W or seem)
Xj = pressure or total RF power or gas flow during step j (Torrs or W or seem)
dj = duration of step j (min)
d = total duration of recipe (min)
n = total number of steps using F-GHGs during etch recipe
To compare recipes with respect to similarity, a facility would then compare the TWA values of
pressure, total RF power, or gas flow to determine if they deviate by more than +/-10%
between recipes. If not, the two recipes would be considered "similar." An example calculation
is provided below for two recipes with three steps each.
Duration (min)
CF4 flow (seem)
C2F6 flow (seem)
Pressure (Torrs)
RF Power 1(W)
RFpower2(W)
Total RF power (W)
RECIPE A
Stepl
0.25
100
20
2
150
1000
1150
Step 2
2
150
30
4
200
1000
1200
StepS
0.25
120
20
2
150
1000
1150
TWA
142
28.0
3.60
190
1000
1190
RECIPE B
Stepl
0.25
110
10
2
120
1500
1620
Step 2
1.83
140
33
4
180
1000
1180
StepS
0.25
120
20
2
120
1000
1120
TWA
135
29.1
3.57
167
1054
1221
Similarity
between
A&B
-5.2%
4.1%
-0.8%
-12%
5.4%
2.58%
In this example, recipes A and B are considered "similar" for the following reasons. First,
recipes A and B are similar with respect to the CF4 and C2F6 TWA flows because the differences
in these values are 5.2% and +4.1% respectively. Recipes A and B are also similar with respect
to pressure because the difference between the TWA values for pressure is -0.8%. Finally,
recipes A and B are similar with respect to total RF power because the difference between the
TWA totals is only +2.58%. This is so even though the difference between RF power 1 for
recipes A and B is -12%, because it is total power that is taken into account. Because RF power
2 has a stronger impact on the utilization efficiency of the gas (higher power) and because RF
power 2 varies by +5.4%, the change in RF power 2 compensates for the diminution in RF power
1.
How can a facility obtain recipe-specific emission factors?
A facility may develop (or obtain) recipe-specific emission factors in multiple ways. Some
examples are presented below:
• Make direct measurements on-site at the facility.
April 2011
40 CFR 98
-------
• Obtain measurement information, and hence emission factors, from tests performed by
a third party, such as a tool supplier. Any measurements made by a third party are
required to have been made for recipes that are similar recipes (as defined in §98.98) to
those used at the facility.
• Use factors from another facility that uses similar recipes. (For example, there are
instances where a company operating multiple facilities will use the same or similar
recipes in more than one facility; in this instance, measured recipe-specific emission
factors for a recipe used at one facility may also be used for estimating emissions from
the use of the same or a similar recipe at another facility.)
• Work collaboratively with other facilities, companies, or research organizations in the
industry to obtain recipe-specific emission factors. An emission factor may be shared
for all similar recipes, regardless of where the factor was measured.
Note, in a given reporting year, a facility must develop new recipe-specific emission factors only
for recipes that are not similar to any recipe whose emission factors have already been
measured in a previous reporting year.
All recipe-specific emission factors must be measured using the 2006 International SEMATECH
Manufacturing Initiative's Guideline for Environmental Characterization of Semiconductor
Process Equipment (International SEMATECH #06124825A-ENG). Alternatively, a facility may
use recipe-specific emission factors that were developed prior to January 1, 2007, provided
they were measured using the 2001 International SEMATECH's Guidelines for Environmental
Characterization of Semiconductor Equipment (International SEMATECH #01104197A-XFR).
Can a third party take part in collaborative work to obtain recipe-specific emission factors?
Yes, Subpart I does not prohibit involvement of third parties in collaborative efforts to develop
and obtain recipe-specific emission factors. For example, multiple facilities may work together
to develop and obtain recipe-specific emission factors by working through a third party. In this
instance, facilities may submit blinded recipe information to a third party, and then work with
the third party to collaborate on a single study to identify similar recipes and develop recipe-
specific emission factors that could be used by multiple facilities. Facilities must comply with all
applicable recordkeeping and reporting requirements. In particular, facilities must maintain
documentation that the emission factors were measured for recipes that are similar to the
recipes used at their facility, as required by §98.97(b)(2). Facilities must also comply with the
certification requirement at §98.96(f).
For More Information
This document is provided solely for informational purposes. It does not provide legal advice,
have legally binding effect, or expressly or implicitly create, expand, or limit any legal rights,
obligations, responsibilities, expectations, or benefits in regard to any person. The series of
April 2011 3 40CFR98
-------
information sheets is intended to assist reporting facilities/owners in understanding key
provisions of the final rule.
Visit EPA's Web site (www.epa.gov/climatechange/emissions/ghgrulemaking.html) for more
information, including the final preamble and rule, additional information sheets on specific
industries, the schedule for training sessions, and other documents and tools. For questions
that cannot be answered through the Web site, please contact us at: ghgmrr@epa.gov.
April 2011 4 40CFR98
------- |