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 most commonly used by the industry and the environmental impact of these gases if released into the atmosphere.
Table 1. Electronic Gas Applications and Climate Impact
|Global Warming Potential
Source: IPCC, 2007.
Semiconductor manufacturing processes use high GWP fluorinated compounds including perfluorocarbons (e.g., CF4, C2F6, C3F8), hydrofluorocarbons (CHF3, CH3F, CH2F2), nitrogen trifluoride (NF3), and sulfur hexafluoride (SF6), collectively referred to as perfluorocompounds (PFCs) or fluorinated greenhouse gases (F-GHGs). Semiconductor manufacturing processes also use fluorinated heat transfer fluids and N2O. Although F-GHGs use did not begin until the late 1980s, their application facilitated the development of significantly more complex and faster processing semiconductors. The continued availability and use of all of these gases is considered to be critical to the future success of the industry.
Estimating F-GHG 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 known that under normal operating conditions, anywhere from 10 to upwards of 80 percent of the F-GHGs pass through the manufacturing tool chambers unreacted and are released into the air. In addition F-GHG emissions vary depending on a number of factors: gas used, type/brand of equipment used, company-specific process parameters, number of F-GHG-using steps in a production process, generation of F-GHG 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.
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. Also see, subpart I (Electronics Manufacturing) of EPA’s Greenhouse Gas Reporting Program for information about calculation methodologies for those electronics manufacturing facilities in the United States that are required to report their GHG emissions.
Fluorinated GHG emissions from semiconductor manufacturing can be and have been successfully reduced as part of EPA’s PFC Reduction/Climate Partnership. EPA’s Partners identified, evaluated, and implemented a variety of technologies that not only protect the climate but also improve production efficiencies. Following the pollution prevention hierarchal approach, the industry 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.
Partners' individual F-GHG emission reduction strategies varied greatly depending on the companies’ product and equipment mix as well as future business plans.