Emission Factors for Semiconductor Manufacturing: 

Sources, Methods and Results 

February 2006 

Prepared for

Scott C. Bartos 

U.S. Environmental Protection Agency 

Climate Change Division 

1200 Pennsylvania Ave., NW (6207J) 

Washington, D.C. 20460 

Prepared by

C. Shepherd Burton, Ph. D. 

Consultant 

2047 Huckleberry Road 

San Rafael, CA 94903 

Draft Report 
1

1.0 INTRODUCTION 

This report documents the sources of information and methods used to develop emission 

factors reported in Chapter 6, “Electronics Industry Emissions” of 2006 IPCC Guidelines for 

Greenhouse Gas Inventories (2006 GL) for the semiconductor industry. The report also 

compares the 2006 GL emission factors with the corresponding factors provided in the inaugural 

2000 GL. 

Peer-reviewed articles about PFC-emission factors for commercially relevant semiconductor 

manufacturing processes are rare and dated (when available)—the circumstance that motivates 

this report.1 This circumstance may be explained by the protections afforded intellectual 

property (IP) across this global technologically driven and highly competitive industry. IP is 

viewed as the lifeblood of the semiconductor industry; it invests unusually high percentages of 

sales in research and development.2

Yet, the semiconductor industry is also collaborative. For example, while securing its IP it 

shares certain technological information through formal non-disclosure agreements (NDAs), 

which restrict the public disclosure of information covered by the NDA (including the owner) yet 

permit appropriate use. Through NDAs and other established and evolving mechanisms, the 

semiconductor industry collaboratively establishes near- and long-term technological direction 

and performance targets (ITRS, 2004), reports its PFC emissions to national governments 

(WSC, 2000), and fosters sharing environmental, safety and health practices, among others. 

All of the information required to develop emissions factors for semiconductor manufacturing is 

globally distributed and proprietary. That information encompasses the full panoply of gases, 

thin-film etching and deposition processes, and wafer sizes. 

 

1A simple Google search might help convince a skeptical reader. 

2

 According to the Semiconductor Association, in 2003, 17% of sales were invested in R&D for its US 

member companies, which represents 85% of the total industry (see http://www.siaonline.org/pre_facts.cfm). See also Schmitz, J. “R&D in the Microelectronics Industry—A Cautionary 

Assessment”, Future Fab International, June 21, 2004. Available at www.futurefab.com/documents.asp?grID=208&d_ID=2594# .Schmitz (Figure 2) shows global average long-term 

R&D expenditure rates at 20% of revenues. For comparison the automotive industry invests 

approximately 4% of its sales in R&D. 
2

Preparation of the 2000 GL relied (without disclosing process details) on consensus judgments 

of a relatively small number of industry experts with intimate knowledge of the dominant and 

emerging PFC-using processes as well as the emerging methods of reliable measurement. 

Since then, the industry has established protocols for equipment and material suppliers to follow 

for measuring and characterizing PFC emissions from commercial-ready etching and cleaning 

processes. Device manufacturers may base equipment and gas-purchase decisions on the 

availability of properly measured data for estimating emission factors as well as the magnitude 

of emissions during operation, among other things. This information then becomes part of the 

competitive profile of vendors and, consequently, closely guarded. 

In preparing the 2006 GL participation broadened. This change from the preparation of the 2000 

GL increased the potential quantity of information as well as concern about IP protection. IP 

protection was afforded in two ways. Firstly, the tiered methodology provides a way for 

manufacturers (at their discretion) to use IP-protected, process-specific emissions factors. For 

example, the Tier 3 methodology—the most comprehensive and accurate methodology for 

estimating emissions—affords use of undisclosed factors. Secondly, industry vendors voluntarily 

provided centerline, process-specific emission factor data to the author of this report through 

NDAs or other means to afford IP protection. This information was then used to form average 

Tier 2b etching and chamber-cleaning emissions factors for specific FC gases as well as other 

gases that might lead to the formation of FC gases. From these Tier 2b factors, Tier 2a 

emissions factors (that are averages of the Tier 2b etching and chamber-cleaning factors) for 

each gas could also be formed. This report documents the process for developing the Tier 2b 

factors by describing the sources, nature and quantity of information that was obtained as well 

as how it was used to form the emission factors. 

The remainder of this report consists of two additional sections. The next section, Section 2, 

describes the methodology for collecting, handling/checking and storing/maintaining emissionsrelevant data as well as the methods for developing emissions factors. It concludes with tables 

of results for Tier 2b and 2a factors. Section 3 compares the Tier 2b and Tier 2a factors 

obtained here with those presented in the 2000 GL. 
3

2.0 METHODOLOGY 

The methodology for forming emission factors for device manufacture consisted of six steps: 

1. Develop a data/information collection form 

2. Collect data/information by disseminating the form to equipment manufacturers, gas 

suppliers and device manufacturers 

3. Assemble and organize data for the task of forming emission factors 

4. Estimate emission factors 

5. Estimate variability in emission factors, and 

6. Tabulate results and incorporate into Chapter 6 of 2006 GL 

2.1 Information collection—Steps 1 and 2

The authors of Chapter 6 (Breakout Group [BOG]} devised a standard form for requesting and 

gathering the information needed for developing and documenting emission factors (Step 1). 

Figure 1 is that form, which was provided (Step 2) to equipment and gas-supplier vendors and 

to semiconductor device manufacturers. Authors also provided forms to national trade 

associations with the request that they facilitate completion. Recipients were requested to 

complete the forms and return them to the authors within three months, by October 2004. By 

the end of October 2004, it was evident that, while the form seemed appropriate, an alternative 

method for obtaining the data was needed. 
4

Figure 1. Data Collection Form for Tier 2a and 2b Documentation of Emission Factor Development IPCC 2006 Guidelines Data Documentation – Semiconductor Manufacturing Emissions Author1Date of study Location of study Process Type/Name2Equipment (Manufacturer name/model number) Substrate size (Si wafer) Measurement method Process Gases (i)3 CF4 C2F6 C3F8 c-C4F8 CHF3 SF6 NF3 C4F6 C5F8 C4F8O Measured Emissions4: 1-CiMeasured FC Byproduct Emissions5: Bi,p Unit of measurement: Number of wafers measured in study (minimum of 5) Standard Deviation Source of data (choose one) Measurement – Scientific Literature 

Other Measurement National Inventory Report Calculated Based on Fuel Quality Expert Judgment

Reference5

Supplemental Information (Optional) 

Film thickness deposited between cleaning 

1) The author is the LA/CA/CLA who writes the relevant section and proposes the data. 2) For example, CVD chamber cleaning, plasma etching – please state material cleaned or etched. 3) Add additional gases as required. 

4) Fraction of gas i not destroyed or transformed during th5) Fraction of gas i transformed into other FC gases such 6) As references to document, report, calculation or if exp

(Names or group e.g., “Waste BOG on Solid Waste Dis
5

It also became evident that companies were reluctant to provide the requested information in 

any manner that would also be available to competitors. Further, those companies wanted more 

information about how the information they provided would be used as well as how it would be 

protected. 

The approach that satisfied these concerns was to have the author of this report collect the 

requested information, as required, under the terms of formal non-disclosure agreements. 

Under such agreements the information for the information-request forms (or any other 

information provided by a company that was not otherwise publicly available) could be entered 

into a database only for the purpose of developing aggregate, gas- and process-specific 

emission factors, i.e., Tier 2b emission factors. These agreements also had terms that did not 

expire. 

Under these terms, the information required to develop emission factors accumulated. 

Approximately 20 percent of the required data came via completed forms, the remainder via 

company-provided databases. By March 2005, the confidential data-collection process had 

produced information that spanned approximately 190 distinct etching and chamber-cleaning 

processes for all gases (and gas combinations) except C5F8 (which was eventually taken from 

1999-vintage publicly available data. (Crowles, 1999) 

2.2 Data assembly and organization—Step 3

 

An Microsoft® Excel database designed to form emission factors from the information was 

devised. That database provided for 18 fields for each record. Table 1 provides the fields that 

define each record. Each entry in Table 1 is associated with a separate field except 
6

Table 1. Identification and description of fields that define each record in database used to 

develop emissions factors for semiconductor manufacturing

Company and process Film and wafer Gas utilization and product 

formation rates 

Company name Film-type (e.g., low-k) Utilization for dominant gas and 

any gas used in mixtures*(CF4, 

CHF3, CH2F2, C2F6, C3F8, C4F6, cC4F8, C4F8O, C5F8, NF3 and SF6)

Process name (e.g. SiNx, oxide 

etch, etc.) 

Film-thickness Product formation rates*

 for CF4, 

CHF3, C2F6 and C3F8

Process type (e.g. PECVD clean, 

dielectric etch, etc.) 

Wafer size (150 mm, 200 mm, 

300 mm) 

Dominant gas (e.g. c-C4F8) 

Number of gases, varies by 

process type (1, 2 or 3) 

*

 In the case of multi-gas mixtures the authors of Chapter 6 adopted the convention that product yields 

would be expressed as a mass-fraction of that gas with the highest mass-flow. The experiments required 

to decide the precise relationship of product to precursor were unavailable. 

for column three, gas utilization and product formation rates. Column three accounts for 10 of 

the 18 fields for each records. 

The quality of the database may be judged by the reliability and representativeness of the data 

(particularly the reliability of measurements of emissions). As evident in Figure 1, emissions 

estimates are an average of measured results over a minimum of five processed silicon wafers. 

In addition, measurements were made following the protocol provided in “Guidelines for 

Environmental Characterization Semiconductor Equipment”, which is available 

www.sematech.org/docubase/document/4197axfr.pdf. Finally, many submissions included the 

standard deviation of the measurements used for estimating gas utilization and product yields. 

While a complete analysis was not performed for this report, a sample comprising approximately 

20 percent of the submittals indicated the standard deviations to fall between 3 – 15 percent, 

with the majority being 5 – 6 percent. As will be evident later the variability of the emissions 

between processes exceeded the variability in the measurements themselves. 

While every effort within the available resources was directed at acquiring a dataset 

representative of current and projected PFC-using processes, assuring and measuring such 
7

representativeness was outside the report’s scope. Nevertheless, even though the NDAs 

prevent the author from disclosing the company names that supplied information (and much 

more), the database may be characterized by some statistics that help to gauge its 

representativeness of current industry PFC usage and emissions. As the following statistics 

indicate, the database would appear representative of current PFC-using manufacturing 

practices. 

PFC-using equipment manufacturers and gas suppliers provided all of the information used for 

preparing this report. Device manufacturers provided confirmation of the results through their 

participation in writing and reviewing Chapter 6 of the 2006 GL. Equipment manufacturers 

provided 90 percent of the records in the database. These equipment manufacturers accounted 

for approximately 80 percent of global PFC-using film-deposition equipment sales in 2004. 

Those same manufacturers account for 30-35 percent of global PFC-using etch sales in 2004. 

In addition, these manufacturers are major equipment suppliers in all geographical markets 

(Europe, Japan, Taiwan, Republic of Korea and China). The remaining 10 percent of the 

records that comprise the database was provided by gas suppliers. Collectively these suppliers 

account for approximately 70 percent of gas sales and have been leaders in PFC emissions 

measurement and process-optimization studies to reduce PFC emissions. Semiconductor 

manufacturers, while not directly providing emissions information, did participate by reviewing 

the final results (via their anonymous reviews of the First Order Draft (FOD and Second Order 

Draft (SOD) and by confirming the reasonableness of any results considered suspicious (as did 

equipment manufacturers). 

Additional statistics provide further characterization of the database. Approximately 70 percent 

of the records describe PFC emissions from chamber cleaning, which account for approximately 

60-70 percent of global PFC usage and up to 80 percent of global uncontrolled emissions. The 

remaining records describe emissions from etch processes. Multiple PFC-gas processes, which 

are used almost exclusively in etch processes to achieve an appropriate C:F ratio, account for 

roughly one-third of all etch records. Finally, the distribution of 150 mm: 200 mm: 300 mm wafer 

sizes is 1:60:39, respectively, which roughly corresponds to the distribution of PFC-using global 

manufacturing capacity (on an area of silicon-layer basis) in 2005 (WFW, 2004). The records 

span processes for depositing/etching more than 15 films with thickness >0.001 mm and <4 

mm. 
8

2.3 Estimation of Emission Factors—Step 4

Gas utilizations were estimated for each of the gases identified in Table 1. Using features of 

Excel, the database was segmented into etch and clean portions. Then Excel functions were 

used to calculate, for each gas, the average utilization over all etch processes for that gas, 

including the instances where the gas is used in multi-gas processes.3 The same was done for 

each gas used in chamber-cleaning processes. In the case of NF3, however, two average 

estimates of NF3 utilizations were developed: (1) the in-situ process, and (2) the remote clean 

process. Simple (i.e., unweighted) averaging was used in all cases because reliable information 

from which to estimate global process-specific usage weights was unavailable. 

Similarly, after segregating the database into etch and chamber-cleaning parts, average 

product-formation yields of CF4, C2F6, CHF3 and C3F8 were estimated for each precursor gas. In 

the case of multi-gas mixtures, averages were taken over all processes. As noted previously, for 

multi-gas mixtures, the BOG for Chapter 6 adopted the convention that product yields be 

expressed as the mass-fraction of the dominant gas (on a mass flow basis). In other words, if a 

mixture consisted of the two gases A and B, and CF4 was observed, then the product yield of 

CF4 would be expressed as the fraction of CF4 formed relative to B provided the flow rate of B 

exceeded the flow rate of A. 

Tier 2a emission factors were developed by averaging, for each gas, the Tier 2b etch and 

chamber cleaning factors. In forming these averages weights were used that correspond to 

estimates of the global proportion of gas usages for etch and chamber cleaning. These weights 

were developed by members of the BOG. Five of the 14 gases for which emission factors were 

developed are used in etching and chamber-cleaning processes: CF4(0.8:0.2), C2F6(0.8:0.2), cC4F8 (0.7:0.3), NF3(0.9:0.1) and C5F8 (0.8:0.2), where the proportion (i.e., weights) of cleaning 

and etching usages are given parenthetically for each gas. Another five gases are used only in 

etching: SF6, CH2F2, CHF3 and C4F6. Finally, the remaining four gases (C3F8, NF3-Remote, 

C4F8O, F2 and COF2) are used only for chamber cleaning. 

 

 

3

 For example when estimating the average utilization of CF4, where an etch process might employ a 

mixture of CF4, CHF3 and C4F6, the average utilization of CF4 over all CF4 processes would include the 

utilization of CF4 in this multi-gas process even if it were not the dominant constituent. The same 

procedure would apply when estimating the average utilization of CHF3 and C4F6 in etch processes. 
9

2.5 Variability in Emission Factors—Step 5

The variability in reported gas utilizations and product formations yields were estimated as the 

standard deviations in the simple averages. As was described in the previous section, the 

standard deviations were estimated for each gas, including those used in multi-gas processes. 

These estimates of the standard deviations were converted to 95 percent confidence intervals 

by multiplying them by two, as specified by IPCC guidance. 

2.6 Tabulation of Results—Step 6

The results for Steps 4 and 5 are presented in Tables 2 and 3 for emissions factors (i.e., the 

complement of utilization) and product formation yields. 
10

Table 2. Tier 2 Default emission factors for FC emissions from semiconductor manufacturing 

Greenhouse Gases with TAR GWP Greenhouse Gases with

TAR GWP 

Process Gas (i) CF4 C2F6 CHF3 CH2F2 C3F8 c-C4F8 NF3

Remote 

NF3 SF6 C4F6 C5F8 C4

Tier 2a 1-Ui 0.9 0.6 0.4 0.1 0.4 0.1 0.02 0.2 0.2 0.1 0.1 0BCF4 NA 0.2 0.07 0.08 0.1 0.1 0.02† 0.09 NA 0.3 0.1 0BC2F6 NA NA NA NA NA 0.1 NA NA NA 0.2 0.04 NBC3F8 NA NA NA NA NA NA NA NA NA NA NA 0Tier 2b Etch 1-Ui 0.7* 0.4* 0.4* 0.06* NA 0.2* NA 0.2 0.2 0.1 0.2 NCVD 1-Ui 0.9 0.6 NA NA 0.4 0.1 0.02 0.2 NA NA 0.1 0Etch BCF4 NA 0.4* 0.07* 0.08* NA 0.2 NA NA NA 0.3* 0.2 NEtch BC2F6 NA NA NA NA NA 0.2 NA NA NA 0.2* 0.2 NCVD BCF4 NA 0.1 NA NA 0.1 0.1 0.02† 0.1† NA NA 0.1 0CVD BC2F6 NA NA NA NA NA NA NA NA NA NA NA NCVD BC3F8 NA NA NA NA NA NA NA NA NA NA NA 0.

Notes: NA denotes not applicable based on currently available information ‡ The default emission factors for F2 and COF2 may be applied to cleaning low-k CVD reactors with ClF3. 

* Estimate includes multi-gas etch processes † Estimate reflects presence of low-k, carbide and multi-gas etch processes that may contain a C-containing FC additive 
11

Table 3. Tier 2 Default Estimates of Relative Errors (%) for emission factor for FC emissions from semiconductoConfidence Intervals* 

Greenhouse Gases with TAR GWP Greenhouse Gases wi

TAR GWP 

Process Gas (i) CF4 C2F6 CHF3 CH2F2 C3F8 c-C4F8 NF3

Remote 

NF3 SF6 C4F6 C5F8 C

Tier 2a 1-Ui 15 30 100 400 20 80 400 70 300 300 80† BCF4 NA 90 300 200 60 100 200 200 NA 200 100† BC2F6 NA NA NA NA NA 200 NA NA NA 200 200 BC3F8 NA NA NA NA NA NA NA NA NA NA NA Tier 2b Etch 1-Ui 60 100 100 700 NA 200 NA 300 300 300 200† CVD 1-Ui 10 30 NA NA 0.4 30 400 70 NA NA 30† Etch BCF4 NA 200 300 200 NA 200 NA NA NA 200 200† Etch BC2F6 NA NA NA NA NA 200 NA NA NA 200 200† CVD BCF4 NA 80 NA NA 60 60 200 200 NA NA 60† CVD BC2F6 NA NA NA NA NA NA NA NA NA NA NA CVD BC3F8 NA NA NA NA NA NA NA NA NA NA NA 

Notes: NA denotes not applicable based on currently available information * Values that exceed 100% do not imply negative emissions are possible, but rather a distribution that is skewed towards values close to zero, for which an appropriate anaccount. † Estimate relies on an analogy to c-C4F8 as the data for C5F8 were insufficient to estimate a confidence interval. 
12

3.0 Comparison with 2000 GL Emissions Factors 

The emission factors in Table 2 may be compared with the corresponding factors in Table 3.5 of 

the 2000 GL (p. 3.74). Figure 2 compares the Tier 2b factors for chamber cleaning: the 2000 

GL estimates with the 

corresponding estimates 

developed herein (2006 GL). 

The comparison indicates that, 

that, for the same mass 

distribution of emissions, 

estimates of mass emissions 

from chamber cleaning using 

the 2006 GL factors should be 

reasonably close to those 

using the 2000 GL. 

Figure 3 compares the 2000 

GL emission factors for etch 

processes with the 2006 GL 

estimates. The variability of 

these factors exceeds the 

variability for chamber 

cleaning, which is reported 

without explanation except to 

note that the variability in etch 

process conditions present in 

the database is considerably 

greater than the corresponding 

conditions for chamber 

cleaning. In addition, 

depending on SF6 usage it appears etch mass emissions using the 2006 GL could be lower 

than the corresponding emissions that use the 2000 GL factors. 

Comparison of Tier 2b Chamber Clean Factors (1-U), 2006 GL vs. 2000 GL

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

2006 GL, 1-U

2000 GL, 1-U

NF3

C3F8

C2F6 CF4

"Error" bars represent one 

standard deviation about 

2006 GL estimate.

1:1 Line

Figure 2. Comparison of chamber cleaning factors: 2000 GL vs. 2006 GL 

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

2006 GL, 1-U

2000 GL, 1-U

NF3 & c-C4F8 CHF3

C2F6

SF6

CF4

"Error" bars represent one 

standard deviation about 

2006 GL estimate.

1:1 Line

Comparison of Tier 2b Etch Emission Factors (1-U): 2006 GL vs. 2000 GL

Figure 3. Comparison of etch emission factors: 2000 GL vs. 2006 GL 
13

Finally, the Tier 2a emissions factors for the 2006 GL are compared with the corresponding 

factors provided in the 2000 

GL (see Figure 4). As 

expected the Tier 2a 

results illustrate the effect of 

averaging the Tier 2b etch 

and chamber cleaning 

factors. This is evident in both 

the average and in the 

variability about the 

average for each gas. In 

addition, it appears that, for 

the same distribution of 

mass emissions, emissions 

estimated using the 2006 GL Tier 2a factors might be lower than those estimated using the 

2000 GL factors. 

Comparison of Tier 2a Emission Factors (1-U): 2006 GL vs. 

2000 GL

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1 1.2

2006 GL, 1-U

2000 GL, 1-U

NF3

c-C4F8 CHF3

SF6

C3F8

C2F6

CF4

"Error" bars represent one 

standard deviation about the 

1:1 

Figure 4. Comparison of Tier 2a emissions factors: 2000 GL vs. 2006 GL 
14

References 

Cowles, D. (1999) “Oxide Etch Tool Emissions Comparison for C5F8 and C4F8 Process 

Recipes”, presented at A Partnership for PFC Emissions Reductions, SEMICON Southwest 

99, Austin, TX. October 1999. 

ITRS (2004), “International Technology Roadmap for Semiconductors” available at 

http://public.itrs.net/report.htm

WFW (2004) “World Fab Watch” global database of manufacturing facilities, available at 

http://dom.semi.org/webcatalog.nsf/itemList?OpenForm&group=110

WSC (2000) “World Semiconductor Council”, purpose and principles of WSC available at 

http://www.semiconductorcouncil.org/about/purpose.html