Fluorine Face-Off In Electronics Market

For over a decade the accepted standard for gas-cleaning in the electronics market has been NF₃. But recent findings about levels of emissions have paved the way for the more environmentally friendly fluorine gas (F₂) to enter the arena.

Fluorine generator installed at a Schüco facility in Germany by Linde electronics. Image Credit: Linde

In addition to reducing climate change potential, the savings promised from using this gas are generous. But are these benefits enough for electronics manufacturers to move their bets away from firmly established NF₃ processes?

Where It Began

Gas cleaning is part of a small but crucial step in the fabrication of semiconductors, liquid-crystal displays, and certain photovoltaic modules. This step occurs after the application of silicon-containing materials via chemical vapor deposition (CVD), when the CVD chamber starts to become clogged with stray silicon. Although this silicon could be removed by physical scrubbing or scraping, it is more effective to react the silicon with fluorine radicals from a fluorine containing gas. This forms silicon tetrafluoride gas, which is easily vented away from the chamber.

Initially, manufacturers used perfluorinated compounds (PFCs) such as hexafluoroethane for this process, but eventually scientists realized that these compounds contributed significantly to trapping heat in the atmosphere. Consequently, the reduction of these PFCs was targeted under the 1997 Kyoto protocol on climate change, as well as in agreements between the U.S. semiconductor industry and the EPA.

The Current Choice

In 1998, IBM researchers developed a chamber process using NF₃ in place of hexafluoroethane. While this greenhouse gas has a potential some 17,000 times that of carbon dioxide (compared to 12,000 for hexafluoroethane), the cleaning process was believed to consume almost all of the gas, resulting in negligible emission levels.

Within a few years of IBM's new development, the production of NF₃ grew from a few hundred tons per year to about 12,000 metric tons (global estimates for this year).

The image on the left shows visually the industrial growth of the NF₃ market. (Source: Techcet)

In 2008, however, researchers at Scripps Institution of Oceanography reported much higher atmospheric levels of NF₃ than industry had been estimating. These levels, translating to as much as 16% of total production, were in contrast to studies from some companies such as Air Products, whose own NF₃ emissions are only about 1.7% of total output.

The Coming Contender

As calls for regulation begin to surface for NF₃, some manufacturers have begun implementing fluorine gas processes as a replacement in order to stay ahead of regulatory requirements. While F₂ has been competing with NF₃ for years, it has only recently been getting increased attention.

There are potentially large economic benefits to installing on-site fluorine gas generators to replace NF3. "If you use 2,000 metric tons of NF₃, you could save approximately $24 million per year with on-site fluorine," says Tim Maykut, product manager for NF₃ and fluorine at Air Products. Malibu, a photovoltaic module manufacturer, has already converted its operations to using solely F₂, boasting that it not only is environmentally friendly but also speeds up the processing and uses less energy.

An Uphill Battle

Despite the promise of savings and fear of regulation, many companies are still hard-pressed to make the switch away from NF₃, which has become entrenched in the complex manufacturing schemes that electronics companies don't want to tamper with. "The electronics industry is extremely resistant to change, particularly when introducing a new material - no matter how large the benefits," says Carl Jackson, head of the fluorine business as Linde Electronics.

The old adage of 'if it ain't broke, don't fix it' seems to be the resounding theme among many current technologies seeing increased pressure from environmental regulation, and it will be interesting to see how much 'fixing' is done in years to come.

Source: ACS - C&EN