A Comparison of Bottom-up Global Emission Estimates of PFCs from the Electronics Industry and Atmospheric Measurements
Stephanie Bogle
(US Environmental Protection Agency)
Electronics manufacturing and primary aluminum production have been recognized as the primary industrial sources of PFC emissions globally. Efforts to reconcile the PFC emissions inferred from atmospheric measurements (“top-down” estimates) and those reported by countries and/or industries using inventory methods (“bottom-up” estimates) have therefore focused on these industries. One method that has been used to attribute inferred emissions to one or the other of these industries is to apply characteristic ratios of emissions of CF4 and C2F6 from either industry. The ratio of C2F6 to CF4 emissions from aluminum production is typically in the neighborhood of 0.1 while the ratio of C2F6 to CF4 emissions from electronics production has historically been estimated to be near 1.1 using the 2006 IPPC Guidelines. Previous research has attributed changes in the global C2F6/CF4 emissions ratio to changes in the share of total PFC emissions contributed by each industry. For example, because the C2F6/CF4 ratio in inferred emissions in Asia has decreased, some researchers have concluded that Asian emissions from aluminum production have increased compared to emissions from electronics production. However, underlying trends in the electronics industry are currently changing the typical ratio of C2F6 to CF4 emissions in that industry, complicating attribution efforts. Emission profiles from the semiconductor industry have changed over time due to changes in technology, especially the transition to production of devices using 300 mm wafers from smaller wafer sizes. The semiconductor industry has also been moving gradually to replace C2F6 with NF3 as the preferred gas for chamber cleaning, decreasing emissions of C2F6. In this paper, the authors will show that the ratio of C2F6 to CF4 reported under the U.S. EPA’s Greenhouse Gas Reporting Program, and, in earlier years, under the EPA’s PFC Reduction/Climate Partnership for the Semiconductor Industry, has in fact declined steadily over the past 15 years, from a ratio greater than 1 to a current ratio 0.5, which is supported by recent regional atmospheric measurements available in the literature . Thus, for the electronics industry, applying a C2F6 to CF4 ratio that varies over time is necessary to correctly interpret atmospheric trends demonstrating the need for a comprehensive understanding of the key technology and emission trends for each industry. In addition, the authors will show that global and regional emissions estimates using wafer size specific emission factors applied to publicly available capacity data show similar trends to estimates derived from using a year-specific ratio method for allocating atmospheric measurements to the two industries.