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Basic Information
Introduction
The semiconductor industry is responding to the challenge of climate change by collaborating with EPA to measure, record, and reduce emissions of high global warming potential (high GWP) gases and by working aggressively to identify and install environmentally friendly technologies. Semiconductor manufacturers use a variety of high GWP gases to create intricate circuitry patterns upon silicon wafers and to rapidly clean chemical vapor deposition (CVD) tool chambers. Table 1 presents some of the process chemicals used by the industry and the environmental impact of these gases if released to the atmosphere.
Table 1. Electronic Gas Applications and Climate Impact
| Compound | Application | Atmospheric Lifetime (years) |
Global Warming Potential (100 year) |
|
|---|---|---|---|---|
| CVD Chamber Cleaning |
Plasma Etching | |||
| CO2 | N/A | N/A | variable | 1 |
| C2F6 | √ | √ | 10,000 | 12,200 |
| CF4 | √ | 50,000 | 7,390 | |
| SF6 | √ | 3,200 | 22,800 | |
| NF3 | √ | √ | 740 | 17,200 |
| CHF3 | √ | 270 | 11,700 | |
| C3F8 | √ | 2,600 | 8,830 | |
| c-C4F8 | √ | √ | 3,200 | 10,300 |
Source: IPCC, 2007 (PDF) (106 pp, 7.7MB). 
Emissions
Current semiconductor manufacturing processes require the use of high GWP fluorinated compounds including perfluorocarbons (e.g., CF4, C2F6, C3F8), trifluoromethane (CHF3), nitrogen trifluoride (NF3), and sulfur hexafluoride (SF6), collectively termed perfluorocompounds (PFCs). PFCs are unsurpassed in their process performance and vital to etching intricate circuitry features on silicon wafers and for cleaning chemical vapor deposition (CVD) tool chambers. The continued availability and use of these chemicals is considered critical to the future success of the semiconductor industry. Although PFC use did not begin until the late 1980s, their application facilitated the development of significantly more complex and faster processing semiconductors.
Estimating PFC emissions from semiconductor manufacture is complicated and has required a significant and coordinated effort by the industry and governments. Before launching the partnership, it was assumed that the majority of these chemicals were consumed or transformed in the manufacturing process. It is now recognized that under normal operating conditions, anywhere from 10 to 80 percent of the PFC gases pass through the manufacturing tool chambers unreacted and are released into the air. In addition PFC emissions vary depending on a number of factors: gas used, type/brand of equipment used, company-specific process parameters, number of PFC-using steps in a production process, generation of PFC by-product chemicals, and whether appropriate abatement equipment has been installed. Companies’ product types and manufacturing processes and, consequently, emissions also vary widely across semiconductor fabs. All semiconductor manufacturers participating in EPA’s voluntary partnership as well emissions were equivalent to 4.6 million metric tons of carbon dioxide in 2002, a 37 percent improvement since 1999.
See the 2006 IPCC Guidelines for National Greenhouse Gas Inventories,
Volume 3, Chapter 6 for a description of fluorinated compound (FC) greenhouse
gas emissions estimating guidelines for electronics manufacturing,
including semiconductors.
Mitigation Options
The semiconductor industry, with strong support from its equipment and materials suppliers, has identified, evaluated, and implemented a variety of new technologies that not only protect the climate but also improve production efficiencies. Following the pollution prevention hierarchal approach, the industry has investigated and successfully developed solutions to this environmental challenge in all four key technological areas:
- process improvements/source reduction,
- alternative chemicals,
- capture and beneficial reuse, and
- destruction technologies.
While the industry has made significant advances in controlling emissions from CVD processes, there is still considerable work needed to economically reduce PFC emissions from delicate plasma etching processes. More detailed information on the costs of reducing PFC emissions from semiconductor manufacturing is available at EPA’s High GWP Home Page.
Climate Protection Goal
Since the U.S. partnership’s launch in 1996, EPA’s program has served as a catalyst for semiconductor companies in Europe, Japan, Korea, and Taiwan to organize similar voluntary programs and join with the United States to establish the first global industry climate protection goal. In April 1999, the World Semiconductor Council (WSC) announced its intention to reduce PFC emissions by at least 10 percent below the industry’s 1995 baseline level by year-end 2010. The U.S. Partners were recognized for their environmental stewardship and leadership as participants in President Bush’s Climate VISION initiative in February 2003. The semiconductor industry’s aggressive goal setting assures governments, industry suppliers, and the public of their commitment to protect the environment.
The technical optimism represented by the WSC’s climate protection goal of 10% below the 1995 baseline by 2010 is obvious when one models future emissions assuming no action by the industry. Figure 1 is derived from a top-down model of average PFC emissions from semiconductor manufacturing that accounts for the evolution of more complex devices. This chart illustrates an estimate of the U.S. industry’s rapidly expanding use and emission of the high GWP gases under a “business without action” scenario. By achieving the WSC’s “business with action” reduction goal (10% below 1995 baseline), the U.S. would prevent greenhouse gas (GHG) emissions equivalent to 10 million metric tons of carbon (MMTCE) in 2010 alone, achieving climate protection equivalent to eliminating GHG emissions from more than 8 million cars.
Figure 1. Business as Usual — Annual U.S. PFC Emissions (MMTCE) by Linewidth PVM v3.1.0306.0304
