Questioning NF₃

INCREASING DEMAND for electronic products, including flat-panel displays, has triggered concern among atmospheric scientists over emissions of nitrogen trifluoride, a potent greenhouse gas.

In electronics manufacturing, NF₃ is used to clean chambers used for chemical vapor deposition of key materials onto glass or a silicon wafer. Most, but not all, of the gas is destroyed in the process.

In a new paper, Michael J. Prather and Juno Hsu of the University of California, Irvine, write that "it is urgent to document NF₃ emissions through atmospheric observations" because the gas has a life span of 550 years and its greenhouse effect is roughly 17,000 times as potent as CO₂ (J. Geophys. Res. Lett. 2008, 35, L12810). The gas is not monitored under the Kyoto protocol but is included in the 2001 Intergovernmental Panel on Climate Change assessment. Prather, an atmospheric chemistry researcher, was the lead author of the IPCC assessment.

The gas was little used in 1996, when the Kyoto protocol was written, but demand for NF₃ began to increase in 1999, when the semiconductor industry vowed to cut greenhouse gas emissions 10% by 2010. The NF₃ process has been replacing older perfluorocarbon systems, commonly based on C₂F₆.

Although the greenhouse gas profiles of NF₃ and C₂F₆ are similar, NF₃ is significantly more efficient as a cleaning agent. With the ₂F₆ process, which is only 20–30% efficient, large quantities of the gas are released to the atmosphere.

Air Products & Chemicals, the leading manufacturer of NF₃, is in the process of expanding global capacity to 3,000 metric tons per year to meet rising demand. Corning Painter, the firm's vice president of global electronics, agrees that atmospheric measurements should be taken but says "more than 20 years of research and work with our customers find that less than 2% of NF₃ is released to the atmosphere." According to Painter, more than 98% of the gas is destroyed in the cleaning process and most of the rest by emission-control equipment.

Prather and Hsu estimate that 2008 production of NF₃ will be about 4,000 metric tons. There are currently no measurements of how much NF₃ is in the atmosphere.