Nitrous oxide no laughing matter

By Pete Singer, Editor-in-Chief

N2O, or Nitrous Oxide, also known as laughing gas, is a weak anesthetic gas that has been in use since the late 18th century. Most people have experienced nitrous in the context of dentistry, but it’s also used to make whipped cream, in auto racing, deep sea diving, or – in the semiconductor industry — as the oxygen source for chemical vapor deposition (CVD) of silicon oxy-nitride (doped or undoped) or silicon dioxide, where it is used in conjunction with deposition gases such as silane. It’s also used in diffusion, rapid thermal processing and for process chamber treatments.

The problem – and why it’s no laughing matter – is that after CO2 and CH4, N2O is the 3rd most impactful man-induced greenhouse gas (GHG), accounting for 7% of emissions. According to the U.S. Environmental Protection Agency, 5% of U.S. N2O originates from industrial manufacturing, largely semiconductor manufacturing. “It’s very much of interest because of its high global warming potential, combined with its long atmospheric lifetime of over 100 years,” said Mike Czerniak Environmental Solutions Business Development Manager, Edwards. “After PFCs, this is one of the most impactful gases from semiconductor manufacturing.” With a TLV of 50ppm, N20 is also poses a health risk.

There are two ways to get rid of N2O: reducing and oxidizing. “Reducing means getting rid of the oxygen in it so you just drive it down to be nitrogen, or you can oxidize it and add additional oxygen to it,” Czerniak explained.

Oxidizing is the easier approach in that it involves putting the gas through an ordinary flame. “The problem with doing this is you then make nitrogen oxides, NOx, and that generally is very bad because that’s the gas that’s the acid rain contributor and it also does nasty things to people,” Czerniak said. When NOx and volatile organic compounds (VOCs) react in the presence of sunlight, they form photochemical smog, a significant form of air pollution, especially in the summer. “If you do make NOx, then you probably want to do some additional treatment to try and get rid of the NOx that you’ve generated,” Czerniak said.

Reduction, therefore, is preferable. N2O can be catalytically reduced to H20 + N2. A reducing flame can be used in a combustor; this requires the presence of a reducing agent, such as methane (a commonly used fuel gas) or even a hydrogen-containing process gas such as silane. “You can avoid forming NOx if you use low temperatures, moderate amounts of oxygen, and you add a reducing agent like methane,” Czerniak said.

Edwards presently offers the Atlas series of inward-fired combustion gas abatement solutions. Atlas systems have low fuel consumption compared with previous-generation gas abatement devices and utilize proven Alzeta inward-fired combustor technology to achieve significantly reduced costs of ownership. With one to six inlets with a number of options, including a temperature management system (TMS), they can reach a flow capacity of up to 600 slm and they offer enhanced ease-of-use and more efficient maintenance.

After CO2 and CH4, N2O is the 3rd most impactful man-induced greenhouse gas (GHG). Source: Climate Analysis Indicators Tool, World Resources Institute.

After CO2 and CH4, N2O is the 3rd most impactful man-induced greenhouse gas (GHG). Source: Climate Analysis Indicators Tool, World Resources Institute.

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