'ICF
Market Characterization of the U.S.
Semiconductor Industry
Prepared for:
Stratospheric Protection Division
Office of Air and Radiation
U.S. Environmental Protection Agency
Washington, D.C. 20460
Prepared by:
ICF
2550 S Clark St.
Suite 1200
Arlington, VA 22202
February 2021
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Table of Contents
1. Summary 3
2. Introduction 3
3. Market Characterization 3
3.1. Overview of Semiconductor Devices 4
3.2. Major Manufacturers 5
4. Subsector Background and Use 5
4.1. Current Gases Used in Semiconductor Production 5
4.2. Projected Use of HFCs in Semiconductor Manufacturing 9
4.3. Imports and Exports of Semiconductors in the United States 11
12
5. References 12
Appendix A: Uncertainties in this Analysis 14
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1 Summary
Semiconductor devices are critical to the functioning of electronic equipment. Semiconductor
manufacture uses three hydrofluorocarbons (HFCs), HFC-23, HFC-32, and HFC-41, primarily in
etching processes, but also minimally in chemical vapor deposition (CVD) chamber cleaning
processes. HFC use in semiconductor manufacturing began in the mid-1980s, along with use of
other fluorinated greenhouse gases (GHGs) such as perfluorocarbons and sulfur hexafluoride
(EPA 2020).
In 2019, an estimated 35 metric tons (MT) of HFC-23, 4.2 MT of HFC-32, and 0.23 MT of HFC-
41 were used in semiconductor fabrication facilities in the United States. The use of HFCs in
semiconductor manufacture is expected to continue as HFCs have physical properties that
make them well suited for semiconductor manufacturing.
In this analysis, HFC use is projected to grow proportionally with GDP growth in the United
States; this approach is based on the assumption that the semiconductor industry is a mature
industry that will not experience rapid and sudden growth in the coming years. In 2040,
approximately 52 MT of HFC-23, 6.1 MT of HFC-32, and 0.33 MT of HFC-41 is expected to be
used in semiconductor manufacturing in the United States.
2. Introduction
Semiconductor devices are used to provide logic and memory functions in many electronic
appliances as well as social infrastructure (e.g., cellphones, computers, data servers) that
support everyday life.
Semiconductor manufacturers use a variety of high-global-warming-potential (GWP) fluorinated
gases, including hydrofluorocarbons (HFCs), in two critical processes: to create intricate
circuitry patterns upon silicon wafers (etching, also known as plasma etching) and to clean
chemical vapor deposition (CVD) chambers (EPA 2020). Depending on the complexity of the
product, the manufacturing process may require upwards of 100 steps utilizing high-GWP gases
(EPA 2020). HFC-23 (CHF3) is the primary HFC used in the manufacturing process, along with
HFC-32 (CH2F2) and HFC-41 (CH3F) (EPA 2020).
The remainder of this report characterizes HFC use by the U.S. semiconductor industry,
including key market players and historical and current use of HFCs and other high GWP gases
in the semiconductor industry.
3. Market Characterization
This section provides an overview of the semiconductor market, as well as the current market
segments and key manufacturers.
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3.1. Overview of Sem iconductor Devices
Since the 1990s, the U.S. semiconductor industry has accounted for a substantial share of
global semiconductor production (SIA 2020b). Semiconductors can be classified into four major
product groups, primarily based on their function. Some semiconductors have broad
functionality, while others are designed for specific use.
• Microprocessors and logic devices are used for the interchange and manipulation of
data in computers, communication devices, and consumer electronics (CRS 2020).
Microprocessors and logic boards account for 42% of total semiconductor sales
worldwide (SIA 2020a).
• Memory devices are used to store information. This segment includes dynamic
random-access memory (RAM or DRAM) that stores temporary bits of information and is
found in smartphones, computers, and flash drives. Memory devices accounted for 25%
of global semiconductor sales (SIA 2020a).
• Analog devices are used to translate analog signals, such as light, touch, and voice,
into digital signals. For example, they are used to convert the analog sound of musical
performances into a digital recording stored online or on a compact disc (CRS 2020).
Analog devices account for 13% of global semiconductor sales.
• Optoelectronics, sensors, and discrete (commonly referred to as O-S-D).
Optoelectronics and sensors are used for generating or sensing light while discrete are
designed to perform a single electrical function (SIA 2020a). O-S-D account for 20% of
total semiconductor sales worldwide.
The semiconductor industry uses a variety of fluorinated gases during manufacturing, including
perfluorocarbons (e.g., CF4, C2F6, C3F8, and C4F8), sulfur hexafluoride (SFe), nitrogen trifluoride
(NF3), HFCs, and fluorinated heat transfer fluids (EPA 2020).1 HFCs are used in two main
stems of the semiconductor manufacture process: etching (the primary use of HFCs), but also in
CVD chamber cleaning. The etching process uses plasma-generated fluorine atoms and other
reactive fluorine-containing fragments, including HFCs, which chemically react with exposed
thin-films or substrates to selectively remove the desired proportions of the material and make
the desired etching pattern (IPCC 2019).
Deposition is a vital step in the fabrication of a variety of electronic devices. During deposition,
layers of dielectric, barrier, or electrically conductive films are deposited or grown on a wafer or
other substrate. CVD enables the deposition of dielectric or metal films. During the CVD
process, gases that contain atoms of the material to be deposited react on the wafer surface to
form a thin film of solid material (EPA 2010). These deposition tool chambers are cleaned
periodically using fluorinated and other gases. During the cleaning cycle the gas is converted to
fluorine atoms in plasma, which etches away residual material from chamber walls, electrodes,
and chamber hardware, maintaining the effectiveness of the tools.
Emissions from both etching and chamber cleaning processes consist of (1) a fraction of each
fluorinated GHG that is fed into the process ("input gas") that is not broken down (or is
1 Perfluorocarbons, sulfur hexafluoride, nitrogen trifluoride, HFC-23 account for 62.5 percent, 16.6
percent, 12.5 percent, and 8.3 percent of GWP-weighted emissions, respectively (EPA 2020).
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reformed) during the process, and (2) by-product fluorinated GHGs that are formed during the
process from the input gas(es). The fraction of the input gas that survives, as well as the identity
and quantity of the by-product fluorinated GHGs that are formed, vary depending on the input
gas, process, and the size of the wafer on which the semiconductor devices are manufactured.2
Certain fabrication facilities (fabs) within the United States have implemented a variety of
emissions control technologies that significantly reduce emissions of HFCs and other fluorinated
GHGs during semiconductor manufacturing.
The physical and chemical characteristics of the single-carbon HFCs make them well suited for
use in semiconductor manufacturing processes. Specific HFC compounds are employed in
precise quantities and under carefully controlled process conditions to achieve the desired
results (e.g., etching a certain type of feature on a semiconductor device). Because HFCs are
used only during the manufacture of semiconductors, the finished product does not contain
HFCs.
3.2. Major Manufacturers
A number of U.S.-headquartered or foreign-owned semiconductor companies currently operate
over 70 fabs in the United States (SIA 2020b, CRS 2020b). The manufacturing output has
remained stable for many years (SIA 2020b). Table 1 lists some of the major manufacturers of
semiconductors in the U.S. Semiconductor fabs are classified as either 300-millimeter (mm)
diameter wafer production facilities or 200-mm diameter wafer production facilities (CRS 2020).
Currently, there are more 200-mm fabs than 300-mm fabs within the United States (WFF 2020).
Table 1. Some Major Manufactures of Semiconductors in the United States3
Company
Number of Fabs
Products
GlobalFoundries
3
Foundry/Dedicated
Intel Corporation
8
Logic/Microprocessor Unit
Micron Technology
4
Memory/Flash/DRAM
Samsung
2
Foundry/IDM
Texas Instruments
2
Analog/Linear
Source: CSR 2020
a The companies in this table do not represent an exhaustive list of all semiconductor manufacturing companies
within the United States.
HFC producers, including 3M (3M 2021), Chemours (Semi 2021), Air Liquide (EPW2020a), and
lofina Chemicals (EPW 2020b), supply some semiconductor manufacturers with HFC
compounds (i.e., HFC-23, HFC-32, and HFC-41). Further research would need to be conducted
to identify all HFC suppliers to semiconductor manufacturers.
4. Subsector Background and Use
4.1. Current Gases Used in Semiconductor Production
The etching and CVD chamber cleaning processes have both historically utilized HFCs and
other fluorinated gases. Table 2 summarizes the environmental characteristics, including ozone
2 For this reason, most methods for calculating emissions from semiconductor manufacturing multiply the
consumption of the input gas by measured or default input-gas and by-product-gas emission factors that
vary by input gas, process type or subtype, and wafer size. This includes the calculation method specified
for semiconductor manufacturers in the Greenhouse Gas Reporting Program (GHGRP).
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depletion potential (ODP) and global warming potential (GWP), for HFCs used in semiconductor
production.
Table 2. Environmental Characteristics of HFCs used in Semiconductor Production
Production Gas
ODPa
GWPa
HFC-23
0
14,800
HFC-32
0
675
HFC-41
0
92
Note: GWPs are aligned with the exchange values used in the AIM act.
a Ozone Secretariat
Fabs are required to report their emissions of fluorinated gases and nitrous oxide, as well as the
extent to which they abate or control these emissions, under subpart I of EPA's GHGRP.3
Specifically, fabs report their emissions of each fluorinated GHG and nitrous oxide, indicate
whether or not emissions of specific fluorinated GHGs or nitrous oxide from specific processes
are abated, and report their fab-wide destruction and removal efficiency (DRE), which is
calculated as 1 minus the ratio of controlled, GWP-weighted emissions of nitrous oxide and all
fluorinated GHGs to hypothetical uncontrolled, GWP-weighted emissions of nitrous oxide and all
fluorinated GHGs.
Fabs that report a fab-wide DRE to the GHGRP are referred to as "abated fabs" for the purpose
of this analysis. Fabs that do not implement abatement technology are referred to as "unabated
fabs." In addition, there are at least ten fabs that do not report under the GHGRP as they do not
meet the reporting threshold (i.e., non-reporters).
Historical HFC use in semiconductor manufacturing was estimated using emissions and
abatement data from the GHGRP and production capacity information (silicon area) from the
World Fab Forecast (WFF). (The WFF data is used to estimate HFC use by fabs not reporting to
GHGRP.)
The sum of HFC use across the three fab categories described above (i.e., abated fabs,
unabated fabs, and non-reporting fabs) is the estimated overall HFC use of the semiconductor
industry. Historical estimates for each fab category were calculated for 2013 and 2017 to 2019.
Historical estimates for 2015 to 2016 were interpolated based on 2013 and 2017 data.
Estimates of HFC use for 2013 were calculated using GHGRP data in an approach similar to
that described below for calculating the estimates of HFC use for 2017 to 2019.
Estimates of HFC use for 2017-19 were calculated as follows. HFC use estimates for unabated
fabs were calculated using reported GHGRP emissions data and default emission factors for
subpart I. Because HFCs are generated as by-products as well as used as input gases, both
input gas emission factors and by-product gas emission factors were factored into this
3 GHGRP requires fabs that calculate emissions of 25,000 metric tons (MT) or more of carbon dioxide
equivalent (CO2 eq.) per year in the United States to report emissions annually. A small percentage of
fabs ("non-reporters") are not required to report emissions to GHGRP as these fabs do not meet the
25,000 MT threshold. Emissions data reported under subpart I are not considered to be confidential
business information.
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calculation.4 Following the calculation, the estimated consumption of each HFC was divided by
the reported emissions of each HFC to develop a "consumption factor" for each wafer size. This
consumption factor was used to estimate HFC consumption by abated fabs, as described
further below.
To estimate consumption for fabs that abated HFCs and reported through the GHGRP (i.e.,
abated fabs), the first step was to estimate what emissions from these fabs would have been in
the absence of abatement ("hypothetical uncontrolled emissions"). This step was completed
using the following approach:
1. Calculate total hypothetical fab-wide uncontrolled CCbeq emissions from the abated fab
by dividing the total reported GWP-weighted sum of fluorinated GHG and nitrous oxide
emissions by (1 minus fab-wide DRE).
2. Sum carbon dioxide equivalent (CCbeq) emissions of all fluorinated GHGs and nitrous
oxide that come from abated processes at that fab.
3. Sum CCbeq emissions of all fluorinated GHGs and nitrous oxide that come from
unabated processes at that fab.
4. For each HFC, break out emissions from abated vs. unabated processes.
5. Calculate the hypothetical uncontrolled emissions from abated processes at the fab by
subtracting the emissions of unabated processes from the total hypothetical fab-wide
uncontrolled CC>2eq emissions.
6. Divide the hypothetical uncontrolled emissions from abated processes by the actual
emissions from abated processes. Multiply the abated emissions of each HFC by this
scale-up factor to calculate hypothetical uncontrolled emissions of each HFC from
abated processes.
After the hypothetical uncontrolled emissions of each HFC were calculated, the consumption
factors developed based on the analysis of the unabated fabs were applied to estimate
consumption for the abated fabs. These consumption factors are shown in Table 3.
Table 3. Consumption Factors by Wafer Size, HFC, and Year
200 mm Wafer Size
300 mm Wafer Size
2017
2018
2019
2017
2018
2019
HFC-23
1.27
1.28
1.26
1.84
1.90
1.88
HFC-32
7.69
7.69
7.69
4.30
4.04
4.21
HFC-41
1.43
1.43
1.43
0.00
0.00
0.00
HFC use by non-reporters was estimated using the emission estimates prepared for this group
for the U.S. Greenhouse Gas Inventory. As described in the Inventory, those estimates are
based on the estimated production in total manufactured layer-area (TMLA) of non-reporting
4 For each wafer size, a system of simultaneous linear equations, including input gas emission factors
and by-product emission factors as coefficients, was used to back-calculate the consumption of each
fluorinated GHG from the emissions of each fluorinated GHG. The system for each wafer size was tested
by using a set of known consumption values by wafer size and process type to calculate emissions, and
then successfully back-calculating the same consumption values by using the system.
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fabs along with emission factors (emissions per TMLA) developed for each wafer size based on
GHGRP-reported emissions from unabated fabs. These estimated uncontrolled emissions were
multiplied by the consumption factors per wafer size used to calculate HFC consumption by
abated fabs (based on the unabated fab data).
In all calculations, differences for wafer sizes (i.e., 200 mm or 300 mm) were accounted for.
Table 3 and Figures 1 and 2 show the estimated HFC use in the semiconductor industry from
2015 to 2019.
There is a steady increase in HFC use in semiconductor manufacturing from 2015 to 2017,
which is reflected in the steady increase in wafer manufacturing capacity within U.S. fabs (SIA
2020a). The decline in estimated HFC use between 2018 and 2019 mirrors declines in
emissions seen for HFCs and for most other fluorinated GHGs used in semiconductor
manufacturing in the U.S. during those years (U.S. Census 2021). These declines are likely
attributable to a drop in semiconductor manufacturing capacity utilization in 2019 that was
reported by the U.S. Census Bureau (see Table 4).
Table 4. Estimated Historical HFC Use in the Semiconductor Industry
2015
2016
2017
2018
2019
Historical Use (MT)
HFC-23
33
37
41
45
35
HFC-32
5.1
4.9
4.8
3.5
4.2
HFC-41
1.0
0.60
0.23
1.0
0.23
Total HFC
39
43
46
49
40
Historical Use (MMT C02 eq)
HFC-23
0.49
0.55
0.61
0.66
0.52
HFC-32
3.4x10-3
3.3x10-3
3.3x10-3
2.3x10-3
2.8x10-3
HFC-41
8.9x10-5
5.5x10-5
2.1x10-5
9.7x10-5
2.1x10-5
Total HFC
0.50
0.56
0.61
0.66
0.52
Totals may not sum due to independent rounding.
Source: GHGRP (2020), WFF (2020)
Table 5. Semiconductor Manufacturing Capacity Utilization
Year
2017
2018
2019
Average Semiconductor Manufacturing
Capacity Utilization (%)
83.8
81.8
75.7
Source: U.S. Census (2020)
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Figure 1. Historic Estimated HFC Use in Semiconductor Manufacturing the United States
from 2015-2019 (MT)
Source: GHGRP (2020), WFF (2020)
Figure 2. Historic Estimated HFC Use in Semiconductor Manufacturing the United States
from 2015-2019 (MMTC02 Eq.)
Source: GHGRP (2020), WFF (2020)
4.2. Projected Use of HFCs in Semiconductor Manufacturing
As discussed above, HFC use in semiconductor manufacturing is projected to continue. Future
HFC use in the United States was therefore projected by growing the U.S. semiconductor
manufacturing capacity at a rate equivalent to the growth of annual U.S. gross domestic product
(GDP) over the same time period.5 Because HFC use in 2019 was anomalously low compared
to the previous three years, HFC use in 2020 was estimated by multiplying the average use of
5 This assumption is also applied to the Global Non-CC>2 Greenhouse Gas Emission Projections &
Mitigation Potential: 2015-2050 (EPA 2019). The introduction of 450mm wafers has been under
consideration by the industry for many years, which could change the industry's current patterns of
fluorinated GHG use. However, due to its significantly higher costs and need for specialized equipment, it
is not anticipated that wide-spread manufacturing of 450mm will occur in the near future (Hruska 2017).
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each HFC between 2017 and 2019 by projected U.S. GDP growth. Table 5 shows the projected
GDP growth and the estimated use of HFCs in the semiconductor industry from 2020 to 2040.
Table 4. Projected HFC Use in the Semiconductor Industry
2020
2025
2030
2035
2040
Projected Use (MT)
HFC-23
38
43
48
53
59
HFC-32
3.9
4.5
5.0
5.5
6.1
HFC-41
0.5
0.5
0.6
0.7
0.7
Total
42
48
54
60
66
Projected Use (MMT CC>2eq)
HFC-23
0.56
0.64
0.71
0.79
0.88
HFC-32
2.6x10"3
3.0x10"3
3.3x10"3
3.7x10"3
4.1x10 3
HFC-41
4.3x10"5
5.0x10"5
5.5x10"5
6.1 x10"5
6.8x10"5
Total
0.57
0.65
0.72
0.79
0.88
GDP Growth
(%)
-5.8
2.1
2.1
2.1
2.1
Totals may not sum due to independent rounding.
Figure 3 and Figure 4 shows the projected future use of HFCs in U.S. semiconductor
manfacturing.
Figure 3. Projected HFC Use in Semiconductor Manufacturing in the United States from
2020-2040 (MT)
Source: GHGRP (2020), WFF (2020), COB (2020)
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Figure 4. Projected HFC Use in Semiconductor Manufacturing in the United States from
2020-2040 (MMTCO2eg)
1.00
0.90
LU
g 0.80
u
H 0.70
5. 0-60
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5. References
3M. 2021. Semiconductor Industry Solutions. Available online at:
https://www.3m.com/3M/en US/semiconductor-us/.
Congressional Budget Office (CBO). 2020. An Update to the Economic Outlook: 2020 to 2030.
July 2020. Available online at: https://www.cbo.gov/svstem/files/2020-07/56442-CBQ-update-
economic-outlook.pdf.
Congressional Research Service (CRS). 2020. Semiconductors: U.S. Industry, Global
Competition, and Federal Policy. October 26, 2020. Available online at:
https://fas.org/sgp/crs/misc/R46581.pdf.
Hruska, Joel. 2017. 450mm silicon wafers aren't happening any time soon as major consortium
collapses. Extreme Tech. January 13, 2017. Available online at:
https://www.extremetech.com/computing/242699-450mm-silicon-wafers-arent-happening-time-
soon-maior-consortium-collapses.
Intergovernmental Panel on Climate Change (IPCC). 2019. 2019 Refinement to the 2006 IPCC
Guidelines for National Greenhouse Gas Inventories. May 2019. Available online at:
https://www.ipcc.ch/report/2019-refinement-to-the-2006-ipcc-guidelines-for-national-
greenhouse-gas-inventories/
Ozone Secretariat. The Montreal Protocol on Substances that Deplete the Ozone Layer. United
National Environment Programme (UNEP). Available Online at:
https://ozone.unep.org/treaties/montreal-protocol/articles/annex-f-controlled-substances.
Semiconductor Industry Association (SIA). 2020a. 2020 Factbook. Available online at:
https://www.semiconductors.org/wp-content/uploads/2020/04/202Q-SIA-Factbook-
FINAL reduced-size.pdf.
Semiconductor Industry Association (SIA). 2020b. 2020 State of the U.S. Semiconductor
Industry. Available online at: https://www.semiconductors.org/wp-
content/uploads/2020/06/2020-SIA-State-of-the-lndustrv-Report.pdf.
Semi. 2021. The Chemours Company. Available online at:
https://www.semi.org/en/members/chemours-company.
Senate Environmental and Public Works Committee (EPW). 2020a. S.2754, American
Innovation and Manufacturing Act of 2019 Senate Testimony for Air Liquide. Available online at:
https://www.epw.senate.gov/public/ cache/files/a/e/ae7f200d-7643-4572-867e-
f4f3f1d7bebc/0879EDAF597CF17D7843C2DC7D62D46A.04.08.2020-air-liguide.pdf.
Senate Environmental and Public Works Committee (EPW). 2020b. S.2754, American
Innovation and Manufacturing Act of 2019 Senate Testimony for lofina Chemicals. Available
online at: https://www.epw.senate.gov/public/ cache/files/9/5/9528c7b7-468a-47cd-83d8-
7de9790c830e/B61940783FECDC3399B2848492EE00C7.04.08.2020-iofina-.pdf.
U.S. Environmental Protection Agency (EPA). 2010. Technical Support Document for Process
Emissions from Electronics Manufacture: Proposed Rule for Mandatory Reporting of
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Greenhouse Gases. Office of Air and Radiation. November 2010. Available online at:
https://19ianuarv2017snapshot.epa.gov/sites/production/files/2015-02/documents/subpart-
i techsupportdoc.pdf.
U.S. Census Bureau. 2021. Quarterly Survey of Plant Capacity Utilization. January 5, 2021.
Available online at: https://www.census.gov/programs-surveys/qpc.html
U.S. Environmental Protection Agency (EPA). 2019. Global Non-C02 Greenhouse Gas
Emission Projections & Mitigation Potential: 2015-2050. October 2019. Available online at:
https://www.epa.gov/global-mitigation-non-co2-greenhouse-gases/global-non-co2-greenhouse-
gas-emission-proiections.
U.S. Environmental Protection Agency (EPA). 2020. Inventory of U.S. Greenhouse Gas
Emissions and Sinks: 1990-2018. . Available online at:
https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks-1990-
2018
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Appendix A: Uncertainties in this Analysis
There are three significant sources of uncertainty in this analysis: (1) the extent to which HFC
emissions are abated by semiconductor fabs, (2) the correct consumption-to-emissions ratio
("consumption factor") to apply to hypothetical uncontrolled HFC emissions from abated fabs
and non-reporting fabs, and (3) the likely growth rate of HFC consumption over the next two
decades.
The extent to which HFC emissions are abated by semiconductor fabs is uncertain because
facilities do not report the fraction of each HFC abated to the GHGRP. Instead, they report their
overall abatement levels across fluorinated GHGs and process types (fab-wide DREs) and
whether or not specific HFCs used in specific process types are abated at all. Because each
process type emitting HFCs is likely to involve multiple manufacturing tools, each of which must
be abated separately, some tools emitting a particular HFC may be abated while others are not.
In this analysis, hypothetical uncontrolled emissions of abated HFCs are calculated by
assuming that HFCs are abated to the same level as all other abated fluorinated GHGs in each
fab. This approach is expected to yield an unbiased estimate across the full population of
abated fabs unless there are systematic differences between HFCs and other abated fluorinated
GHGs in the extent to which they are abated. For example, fabs may abate relatively high
fractions of fluorinated GHGs with large GWPs, such as SF6 (whose GWP is 22,800), while they
abate lower fractions of fluorinated GHGs with relatively small GWPs, such as HFC-41 (whose
GWP is 92). Since the GWP of the most highly used HFC, HFC-23, is in the middle of the range
of GWPs of the fluorinated GHGs used in semiconductor manufacturing, concerns about GWPs
may not create large systematic differences in the extent to which HFC-23 is abated compared
to other fluorinated GHGs. Nevertheless, such systematic differences cannot be ruled out.
The consumption-to-emissions ratio ("consumption factor") that is applied to the calculated
uncontrolled emissions of abated fabs to estimate their consumption is uncertain for two
reasons. First, because emissions of HFCs (especially HFC-23) result both from the use of
HFCs as input gases and from the formation of HFCs as by-products from the use of other input
gases, the consumption factor that is calculated depends on the relative quantities of the
different fluorinated GHGs that are used as input gases in each fab. These quantities vary from
fab to fab depending on the types of devices manufactured and the processes used to
manufacture them. In this analysis, various methods of calculating consumption factors were
evaluated, including weighted averages, straight averages, and regressions of consumption
against emissions. For HFC-23, straight averages yielded the lowest consumption factors while
regressions yielded the highest, spanning a difference of approximately 20% for both wafer
sizes. (The regression analyses showed R2 values between 87 and 97 percent, depending on
the wafer size and whether or not the regression was forced through the origin.) For each wafer
size, weighted averages fell approximately in the middle of these two extremes and were used
for this analysis. These calculated consumption factors were quite stable across the three years,
and when inverted, the resulting implied emission factors were either identical to the subpart I
default input gas emission factors for the same HFC and wafer size (e.g., for HFC-32 and HFC-
41 used in 200-mm manufacturing) or were somewhat higher than the subpart I default input
gas emission factors, as is expected when the HFC is formed as a by-product in addition to
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being used as an input gas (e.g., for HFC-23 for both wafer sizes). This outcome indicates that
the calculated consumption factors are within the expected range.
Second, assuming that the HFC consumption factors calculated for each wafer size are
representative of unabated fabs, there may be differences between unabated fabs and abated
fabs that make the factors less representative of consumption of abated fabs. Such differences
may arise, for example, if abated fabs were built more recently than unabated fabs or if abated
fabs make more advanced devices than unabated fabs, both of which could result in use of a
different mix of input gases.
Finally, the likely future growth rate of HFC use by semiconductor manufacturers in the U.S. is
uncertain because it depends both on the future growth rate of semiconductor manufacturing in
the U.S. and on the evolving use of HFCs for this manufacturing. The use of HFCs in turn
depends on the number of steps that use fluorinated GHGs in the manufacturing process and
on manufacturer's preferences for HFCs compared to other fluorinated GHGs as input gases for
their processes. Both of these parameters have changed over time.
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