Nitrogen trifluoride
From Wikipedia, the free encyclopedia
| Nitrogen trifluoride | |
|---|---|
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| IUPAC name |
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| Other names | Nitrogen fluoride Trifluoramine Trifluorammonia |
| Identifiers | |
| CAS number | [] |
| PubChem | |
| UN number | 2451 |
| RTECS number | QX1925000 |
| Properties | |
| Molecular formula | NF3 |
| Molar mass | 71.0019 g/mol |
| Appearance | colorless gas |
| Density | 3.003 kg/m3 (1 atm, 15 °C) 1.885 g/cm3 (liquid at b.p.) |
| Melting point |
−207.15 °C, 66 K, -341 °F |
| Boiling point |
−129.1 °C, 144 K, -200 °F |
| Solubility in water | 0.021 vol/vol (20 °C, 1 bar) |
| Structure | |
| Molecular shape | trigonal pyramidal |
| Dipole moment | 0.234 D |
| Hazards | |
| MSDS | Air Liquide MSDS |
| EU Index | Not listed |
| NFPA 704 |
 3
3
0
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| Flash point | Non-flammable |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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Nitrogen trifluoride is the inorganic compound with the formula NF3. This nitrogen-fluorine compound is a colorless, toxic, odourless, nonflammable gas. It finds increasing use as an etchant in microelectronics.
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[edit] Applications
Nitrogen trifluoride is used in the plasma etching of silicon wafers. Today nitrogen trifluoride is predominantly employed in the cleaning of the PECVD chambers in the high volume production of liquid crystal displays and silicon-based thin film solar cells. In these applications NF3 is initially broken down in situ, by a plasma. The resulting fluorine atoms are the active cleaning agents that attack the polysilicon,silicon nitride and silicon oxide. Nitrogen trifluoride can be used as well with tungsten silicide, and tungsten produced by CVD. NF3 has been promoted as a a safe and environmentally preferable substitute for perfluorocarbons such as hexafluoroethane,sulfur hexafluoride etc..[1] The process utilization of the chemicals applied in plasma processes is typically below 20 %. Therefore the PFCs and also NF3 may escape into the atmosphere. Modern gas abatement systems can decrease such emissions.
Recently elemental fluorine has been introduced as an environmentally friendly replacement for nitrogen trifluoride in state-of-the-art high volume manufacturing of flat panel displays and solar cell manufacturing.[2]
Nitrogen trifluoride is also used in hydrogen fluoride and deuterium fluoride lasers, which are types of chemical lasers. It is preferred to fluorine gas due to its convenient handling properties, reflecting its considerable stability.
It is compatible with steel and Monel, as well as several plastics.
[edit] Synthesis and reactivity
NF3 is a rare example of a binary fluoride that cannot be prepared directly from the elements (i.e., N2 does not react with F2). Almost all other elements in the periodic table react directly, often violently, with fluorine.
After first attempting the synthesis in 1903, Otto Ruff prepared nitrogen trifluoride 25 years later by the electrolysis of a molten mixture of ammonium fluoride and hydrogen fluoride.[3] It proved to be far less reactive than nitrogen trichloride. Today, it is prepared both by direct reaction of ammonia and fluorine and by a variation of Ruff's method.[4]
It is supplied in pressurized cylinders.
[edit] Reactions
NF3 is slightly soluble in water without undergoing chemical reaction. It is nonbasic with a low dipole moment of 0.2340 D. By contrast, ammonia is basic and highly polar (1.47 D).[5] NF3 is a potent yet sluggish oxidizer. It converts to tetrafluorohydrazine upon contact with metals, but only at high temperatures:
- 2 NF3 + Cu → N2F4 + CuF2
NF3 reacts with fluorine and antimony pentafluoride to give the tetrafluoroammonium salt:
- NF3 + F2 + SbF5 → NF+4SbF−6
[edit] Greenhouse gas
Although NF3 has a high global warming potential (GWP), its radiative forcing in the Earth's atmosphere is very small, as it is only released into the atmosphere in small quantities. Industrial applications involving NF3 routinely break it down as it is used, whereas the regulated compounds SF6 and PFCs are typically released.[6][7]
NF3 is a greenhouse gas, with a GWP 17,200 times greater than that of CO2 when compared over a 100 year period.[8][9][10] Its GWP would place it second only to SF6 in the group of Kyoto-recognised greenhouse gases, although NF3 is not currently included in that grouping. It has an estimated atmospheric lifetime of 740 years,[8] although recent work suggests a slightly shorter lifetime of 550 years (and a corresponding GWP of 16,800).[6]
In 2008, the estimated total atmospheric content of the gas was 5,400 metric tons, increasing at about 11 percent per year, more than the estimated 1,200 metric tons thought to be present in 2006.[11]
The projected maximum atmospheric concentration is less than 0.16 parts per trillion (ppt) by volume and will provide less than 0.001 Wm-2 of IR forcing.[12] A 2008 study utilizing an improved sampling technique has found a mean global tropospheric concentration of 0.454 ppt by dry air mole fraction.[13]
[edit] Production volume
Since 1992, when less than 100 tons were produced, production grew to an estimated 4000 tons in 2007 and is projected to increase significantly.[6]
World production of NF3 is expected to reach 8,000 tons a year by 2010. It is not currently known how much is ultimately released into the atmosphere; estimates are either less or more than 2%, but there are not good independent data about releases, nor measurements of atmospheric concentration.[14][15]
[edit] Safety
Skin contact with NF3 is not hazardous, and it is a relatively minor irritant to mucous membranes and eyes. It is a pulmonary irritant with a toxicity comparable with nitrogen oxides, and overexposure via inhalation causes the conversion of hemoglobin in blood to methemoglobin, which can lead to the condition methemoglobinemia.[16]
[edit] References
- ^ H. Reichardt , A. Frenzel and K. Schober (2001). "Environmentally friendly wafer production: NF3 remote microwave plasma for chamber cleaning". Microelectronic Engineering 56: 73–76. doi:.
- ^ J. Oshinowo, A. Riva, M Pittroff, T. Schwarze and R. Wieland (2009). "Etch performance of Ar/N2/F2 for CVD/ALD chamber clean". Solid State Technology 52: 20–24.
- ^ Otto Ruff, Joseph Fischer, Fritz Luft (1928). "Das Stickstoff-3-fluorid". Zeitschrift für anorganische und allgemeine Chemie 172 (1): 417–425. doi:.
- ^ Philip B. Henderson, Andrew J. Woytek "Fluorine Compounds, Inorganic, Nitrogen" in Kirk‑Othmer Encyclopedia of Chemical Technology, 1994, John Wiley & Sons, NY. doi:10.1002/0471238961.1409201808051404.a01 Article Online Posting Date: December 4, 2000
- ^ Thomas M. Klapötke “Nitrogen–fluorine compounds” Journal of Fluorine Chemistry Volume 127, 2006, pp. 679-687. doi:10.1016/j.jfluchem.2006.03.001
- ^ a b c Prather, M.J.; Hsu, J. (2008). "NF3, the greenhouse gas missing from Kyoto". Geophys. Res. Lett. 35: L12810. doi:. http://www.agu.org/journals/gl/gl0812/2008GL034542/.
- ^ Tsai, W.-T. (2008). "Environmental and health risk analysis of nitrogen trifluoride (NF3), a toxic and potent greenhouse gas". J. Hazard. Mat. 159: 257. doi:.
- ^ a b Climate Change 2007: The Physical Sciences Basis, IPCC, http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf, retrieved on 2008-07-03
- ^ Robson, J.I.; Gohar, L.K., Hurley, M.D., Shine, K.P. and Wallington, T. (2006). "Revised IR spectrum, radiative efficiency and global warming potential of nitrogen trifluoride". Geophys. Res. Lett. 33: L10817. doi:. http://cat.inist.fr/?aModele=afficheN&cpsidt=17893800.
- ^ Richard Morgan (2008-09-01). "Beyond Carbon: Scientists Worry About Nitrogen’s Effects". New York Times. http://www.nytimes.com/2008/09/02/science/02nitr.html?ref=science. Retrieved on 2008-09-07. mirror
- ^ Potent Greenhouse Gas More Prevalent in Atmosphere than Previously Assumed Newswise, Retrieved on October 23, 2008.
- ^ Robson, Jon, Nitrogen trifluoride (NF3), Royal Meteorological Society, http://www.rmets.org/activities/awards/scholarships/sch_2.php, retrieved on 10-27-2008
- ^ Weiss, Ray F.; J. Mühle, P.K. Salameh, C.M. Harth (2008-10-31). "Nitrogen trifluoride in the global atmosphere". Geophys. Res. Lett. (AGU) 35 (L20821): L20821. doi:. http://www.agu.org/pubs/crossref/2008/2008GL035913.shtml.
- ^ M. Roosevelt (2008-07-08). "A climate threat from flat TVs, microchips". http://www.latimes.com/news/nationworld/nation/la-na-climate8-2008jul08,0,7460950.story.
- ^ Hoag, Hannah (2008-07-10). "The Missing Greenhouse Gas". Nature Reports Climate Change (Nature News). doi:. http://www.nature.com/climate/2008/0808/full/climate.2008.72.html.
- ^ Malik, Yogender (2008-07-03). "Nitrogen trifluoride - Cleaning up in electronic applications". Gasworld. http://www.gasworld.com/news.php?a=2896. Retrieved on 2008-07-15.
