# 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 m ethods used to develop emission factors reported in Chapter 6, “Electronics Industry Emissio ns” of 2006 IPCC Guidelines for

Greenhouse Gas Inventories (2006 GL) for the semiconductor industry. The report a lso compares the 2006 GL emission factors with the correspond ing factors provided in the inaugural

2000 GL.

Peer-reviewed articles about PFC-emission factors for comm ercially relevant semiconductor manufacturing processes are rare and dated (when avail able)—the circumstance that motivates this report. 1 

### This circumstance may be explained by the protections affo rded 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 forma l non-disclosure agreements (NDAs), which restrict the public disclosure of information covere d by the NDA (including the owner) yet permit appropriate use. Through NDAs and other establi shed and evolving mechanisms, the semiconductor industry collaboratively establishes near- a nd 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 fa ctors for semiconductor manufacturing is globally distributed and proprietary. That informatio n encompasses the full panoply of gases, thin-film etching and deposition processes, and wafer si zes.

1 A simple Google search might help convince a skeptical r eader. 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 i ndustry (see http://www.siaonline.org/pre_facts.cfm ). See also Schmitz, J. “R&D in the Microelectronics Indu stry—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 compar ison 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 inti mate knowledge of the dominant and emerging PFC-using processes as well as the emerging meth ods of reliable measurement. Since then, the industry has established protocols for eq uipment and material suppliers to follow for measuring and characterizing PFC emissions from comme rcial-ready etching and cleaning processes. Device manufacturers may base equipment and gas -purchase decisions on the availability of properly measured data for estimating em ission factors as well as the magnitude of emissions during operation, among other things. Th is information then becomes part of the competitive profile of vendors and, consequently, closely guarded.

In preparing the 2006 GL participation broadened. Th is 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 an d accurate methodology for estimating emissions—affords use of undisclosed factors. Secon dly, industry vendors voluntarily provided centerline, process-specific emission factor data t o the author of this report through NDAs or other means to afford IP protection. This inf ormation 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. Fr om these Tier 2b factors, Tier 2a emissions factors (that are averages of the Tier 2b et ching and chamber-cleaning factors) for each gas could also be formed. This report documents th e process for developing the Tier 2b factors by describing the sources, nature and quantity of i nformation 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/checki ng and storing/maintaining emissionsrelevant data as well as the methods for developing emi ssions factors. It concludes with tables of results for Tier 2b and 2a factors. Section 3 compar es 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 m anufacture 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 em ission factors

4. Estimate emission factors 5. Estimate variability in emission factors, and 6. Tabulate results and incorporate into Chapter 6 o f 2006 GL

2.1 Information collection—Steps 1 and 2

The authors of Chapter 6 (Breakout Group [BOG]} devise d 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 provid ed forms to national trade associations with the request that they facilitate complet ion. Recipients were requested to complete the forms and return them to the authors wit hin three months, by October 2004. By the end of October 2004, it was evident that, while th e form seemed appropriate, an alternative method for obtaining the data was needed.4Figure 1. Data Collection Form for Tier 2a and 2b Documentation of Emission Factor DevelopmentIPCC 2006 Guidelines Data Documentation – Semiconductor Manufacturing EmissionsAuthor1Date of studyLocation of studyProcess Type/Name2Equipment (Manufacturername/model number)Substrate size (Si wafer)Measurement methodProcess Gases (i)3CF4C2F6C3F8c-C4F8CHF3SF6NF3C4F6C5F8C4F8OCH2F2F2COF2Measured Emissions4:1-CiMeasured FC ByproductEmissions5: Bi,pUnit of measurement:Number of wafers measured instudy (minimum of 5)Standard DeviationSource of data (choose one) Measurement – Scientific LiteratureOther MeasurementNational Inventory ReportCalculatedBased on Fuel QualityExpert JudgmentReference5Supplemental Information (Optional)Film thickness deposited betweencleaning1)The author is the LA/CA/CLA who writes the relevantsection 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 the process step.5)Fraction of gas i transformed into other FC gases such as CF4.6)As references to document, report, calculation or if expert judgment to those involved(Names or group e.g., “Waste BOG on Solid Waste Disposal Sites”).

### 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 w ould be used as well as how it would be protected.

The approach that satisfied these concerns was to have t he 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 informa tion-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 a ggregate, gas- and process-specific emission factors, i.e., Tier 2b emission factors. These agr eements 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 confidentia l data-collection process had produced information that spanned approximately 190 dist inct etching and chamber-cleaning processes for all gases (and gas combinations) except C 5 

### F 8 

### (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 w ith 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 * (CF 4 , CHF 3 , CH 2 F 2 , C 2 F 6 , C 3 F 8 , C 4 F 6 , cC 4 F 8 , C 4 F 8 O, C 5 F 8 , NF 3 and SF 6 ) Process name (e.g. SiNx, oxide etch, etc.) Film-thickness Product formation rates * for CF 4 , CHF 3 , C 2 F 6 and C 3 F 8 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 Ch apter 6 adopted the convention that product yields would be expressed as a mass-fraction of that gas wi th the highest mass-flow. The experiments required to decide the precise relationship of product to precu rsor 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 reliab ility and representativeness of the data (particularly the reliability of measurements of emission s). As evident in Figure 1, emissions estimates are an average of measured results over a min imum of five processed silicon wafers. In addition, measurements were made following the pr otocol 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 estima ting gas utilization and product yields. While a complete analysis was not performed for this repo rt, a sample comprising approximately 20 percent of the submittals indicated the standard d eviations to fall between 3 – 15 percent, with the majority being 5 – 6 percent. As will be evid ent later the variability of the emissions between processes exceeded the variability in the measure ments themselves.

While every effort within the available resources was d irected at acquiring a dataset representative of current and projected PFC-using pro cesses, assuring and measuring such

### 7

representativeness was outside the report’s scope. Nevert heless, 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 statist ics that help to gauge its representativeness of current industry PFC usage and em issions. As the following statistics indicate, the database would appear representative o f current PFC-using manufacturing practices.

PFC-using equipment manufacturers and gas suppliers pro vided all of the information used for preparing this report. Device manufacturers provided co nfirmation of the results through their participation in writing and reviewing Chapter 6 of t he 2006 GL. Equipment manufacturers provided 90 percent of the records in the database. Th ese equipment manufacturers accounted for approximately 80 percent of global PFC-using film-d eposition 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 equipmen t 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 su ppliers. Collectively these suppliers account for approximately 70 percent of gas sales and ha ve been leaders in PFC emissions measurement and process-optimization studies to reduce PF C emissions. Semiconductor manufacturers, while not directly providing emissions info rmation, did participate by reviewing the final results (via their anonymous reviews of the Fir st Order Draft (FOD and Second Order Draft (SOD) and by confirming the reasonableness of a ny 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. Mu ltiple 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 distr ibution 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.

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2.3 Estimation of Emission Factors—Step 4

Gas utilizations were estimated for each of the gases ide ntified in Table 1. Using features of Excel, the database was segmented into etch and clean po rtions. Then Excel functions were used to calculate, for each gas, the average utilizatio n over all etch processes for that gas, including the instances where the gas is used in multi-g as processes. 3 

### The same was done for each gas used in chamber-cleaning processes. In the case of NF 3 

### , however, two average

estimates of NF 3 

### utilizations were developed: (1) the in-situ process, an d (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 wei ghts was unavailable.

Similarly, after segregating the database into etch and chamber-cleaning parts, average product-formation yields of CF 4 

### , C 2 

### F 6 

### , CHF 3 

### and C 3 

### F 8 

### were estimated for each precursor gas. In the case of multi-gas mixtures, averages were taken ove r 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 CF 4 

### was observed, then the product yield of

CF 4 

### would be expressed as the fraction of CF 4 

### 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 weig hts were used that correspond to estimates of the global proportion of gas usages for et ch 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: CF 4 

### (0.8:0.2), C 2 

### F 6 

### (0.8:0.2), cC 4 

### F 8 

### (0.7:0.3), NF 3 

### (0.9:0.1) and C 5 

### F 8 

### (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: SF 6 

### , CH 2 

### F 2 

### , CHF 3 

### and C 4 

### F 6 

### . Finally, the remaining four gases (C 3 

### F 8 

### , NF 3 

### -Remote,

C 4 

### F 8 

### O, F 2 

### and COF 2 

### ) are used only for chamber cleaning.

3 For example when estimating the average utilization of CF 4 , where an etch process might employ a mixture of CF 4 , CHF 3 and C 4 F 6 , the average utilization of CF 4 over all CF 4 processes would include the utilization of CF 4 in this multi-gas process even if it were not the do minant constituent. The same procedure would apply when estimating the average uti lization of CHF 3 and C 4 F 6 in etch processes.

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2.5 Variability in Emission Factors—Step 5

The variability in reported gas utilizations and produ ct formations yields were estimated as the standard deviations in the simple averages. As was descri bed in the previous section, the standard deviations were estimated for each gas, includi ng those used in multi-gas processes.

These estimates of the standard deviations were convert ed 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 yie lds.10Table 2. Tier 2 Default emission factors for FC emissionsfrom semiconductor manufacturingGreenhouse Gases with TAR GWPGreenhouse Gases withoutTAR GWPNon-GHGsProducing FCBy-products‡Process Gas (i) CF4C2F6CHF3CH2F2C3F8c-C4F8NF3RemoteNF3SF6C4F6C5F8C4F8O F2COF2Tier 2a1-Ui0.9 0.6 0.4 0.1 0.4 0.1 0.02 0.2 0.2 0.1 0.1 0.1 NA NABCF4NA 0.2 0.07 0.08 0.1 0.1 0.02†0.09 NA 0.3 0.1 0.1 0.02†0.02†BC2F6NA NA NA NA NA 0.1 NA NA NA 0.2 0.04 NA NA NABC3F8NA NA NA NA NA NA NA NA NA NA NA 0.04 NA NATier 2bEtch 1-Ui0.7*0.4*0.4*0.06*NA 0.2*NA 0.2 0.2 0.1 0.2 NA NA NACVD 1-Ui0.9 0.6 NA NA 0.4 0.1 0.02 0.2 NA NA 0.1 0.1 NA NAEtch BCF4NA 0.4*0.07*0.08*NA 0.2 NA NA NA 0.3*0.2 NA NA NAEtch BC2F6NA NA NA NA NA 0.2 NA NA NA 0.2*0.2 NA NA NACVD BCF4NA 0.1 NA NA 0.1 0.1 0.02†0.1†NA NA 0.1 0.1 0.02†0.02†CVD BC2F6NA NA NA NA NA NA NA NA NA NA NA NA NA NACVD BC3F8NA NA NA NA NA NA NA NA NA NA NA 0.04 NA NANotes: NA denotes not applicable based on currentlyavailable information‡The default emission factors for F2and COF2may be applied to cleaning low-k CVD reactors withClF3.*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 additive11Table 3. Tier 2 Default Estimates of Relative Errors (%) for emission factor for FC emissions from semiconductor manufacturing, 95%Confidence Intervals*Greenhouse Gases with TAR GWPGreenhouse Gases withoutTAR GWPNon-GHGsProducing FCBy-productsProcess Gas (i) CF4C2F6CHF3CH2F2C3F8c-C4F8NF3RemoteNF3SF6C4F6C5F8C4F8O F2COF2Tier 2a1-Ui15 30 100 400 20 80 400 70 300 300 80†40 NA NABCF4NA 90 300 200 60 100 200 200 NA 200 100†80 200 200BC2F6NA NA NA NA NA 200 NA NA NA 200 200 NA NA NABC3F8NA NA NA NA NA NA NA NA NA NA NA 40 NA NATier 2bEtch 1-Ui60100100700NA 200 NA 300 300 300 200†NA NA NACVD 1-Ui10 30 NA NA 0.4 30 400 70 NA NA 30†40 NA NAEtch BCF4NA 200 300200NA 200 NA NA NA 200200†NA NA NAEtch BC2F6NA NA NA NA NA 200 NA NA NA 200200†NA NA NACVD BCF4NA 80 NA NA 60 60 200200 NA NA 60†80 200 200CVD BC2F6NA NA NA NA NA NA NA NA NA NA NA NA NA NACVD BC3F8NA NA NA NA NA NA NA NA NA NA NA 40 NA NANotes: NA denotes not applicable based on currentlyavailable information*Values that exceed 100% do not imply negative emissions are possible, but rather a distribution thatis skewed towards values close to zero, for which an appropriate analysis of uncertainty willaccount.†Estimate relies on an analogy to c-C4F8as the data for C5F8were insufficient to estimate a confidence interval.

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### 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 2 b 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 SF 6 

### usage it appears etch mass emissions using the 2006 GL co uld be lower than the corresponding emissions that use the 2000 GL f actors. 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-U2000 GL, 1-U

NF 3 C 3 F 8 C 2 F

6 CF 4 "Error" bars represent one standard deviation about 2006 GL estimate.

1:1 Line

Figure 2. Comparison of chamber cleaning factors: 200 0 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-U2000 GL, 1-U

CHF 3 NF3 & c-C4F8 C 2 F 6 SF 6 CF 4 "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

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Finally, the Tier 2a emissions factors for the 2006 GL ar e 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 lo wer 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-U2000 GL, 1-U

NF3 CHF3 c-C 4 F 8 SF6

C3F8 C 2 F

6 CF4 "Error" bars represent one standard deviation about the

1:1

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

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### References

Cowles, D. (1999) “Oxide Etch Tool Emissions Comparison fo r 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 S emiconductors” available at http://public.itrs.net/report.htm

WFW (2004) “World Fab Watch” global database of manu facturing 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