 | |
 | |
| Names | |
|---|---|
| IUPAC name Nitrogen trifluoride | |
| Other names Nitrogen fluoride Trifluoramine Trifluorammonia | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
|
| ECHA InfoCard | 100.029.097 |
| EC Number |
|
| 1551 | |
| RTECS number |
|
| UNII | |
| UN number | 2451 |
| |
| |
| Properties | |
| NF3 | |
| Molar mass | 71.00 g/mol |
| Appearance | colorless gas |
| Odor | moldy |
| Density | 3.003 kg/m3 (1 atm, 15 °C) 1.885 g/cm3 (liquid at b.p.) |
| Melting point | −207.15 °C (−340.87 °F; 66.00 K) |
| Boiling point | −129.06 °C (−200.31 °F; 144.09 K) |
| 0.021 g/100 mL | |
| Vapor pressure | 44.0 atm[1](−38.5 °F or −39.2 °C or 234.0 K)[a] |
Refractive index (nD) | 1.0004 |
| Structure | |
| trigonal pyramidal | |
| 0.234 D | |
| Thermochemistry | |
| 53.26 J/(mol·K) | |
Std molar entropy(S⦵298) | 260.3 J/(mol·K) |
Std enthalpy of formation(ΔfH⦵298) | −31.4 kcal/mol[2] −109 kJ/mol[3] |
Gibbs free energy(ΔfG⦵) | −84.4 kJ/mol |
| Hazards | |
| GHS labelling: | |
| H270,H280,H332,H373 | |
| P220,P244,P260,P304+P340,P315,P370+P376,P403 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LC50 (median concentration) | 2000 ppm (mouse, 4 h) 9600 ppm (dog, 1 h) 7500 ppm (monkey, 1 h) 6700 ppm (rat, 1 h) 7500 ppm (mouse, 1 h)[5] |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | TWA 10 ppm (29 mg/m3)[4] |
REL (Recommended) | TWA 10 ppm (29 mg/m3)[4] |
IDLH (Immediate danger) | 1000 ppm[4] |
| Safety data sheet (SDS) | AirLiquide |
| Related compounds | |
Otheranions | nitrogen trichloride nitrogen tribromide nitrogen triiodide ammonia |
Othercations | phosphorus trifluoride arsenic trifluoride antimony trifluoride bismuth trifluoride |
Related binary fluoro-azanes | tetrafluorohydrazine |
Related compounds | dinitrogen difluoride |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Nitrogen trifluoride is theinorganic compound with the formula (NF
3). It is a colorless, non-flammable,toxic gas with a slightly musty odor. In contrast with ammonia, it is nonbasic. It finds increasing use within the manufacturing offlat-panel displays,photovoltaics,LEDs and othermicroelectronics.[6]NF
3 is agreenhouse gas, with aglobal warming potential (GWP) 17,200 times greater than that ofCO
2 when compared over a 100-year period.[7][8][9]
Nitrogen trifluoride can be prepared from the elements in the presence of an electric discharge.[10] In 1903,Otto Ruff prepared nitrogen trifluoride by the electrolysis of a molten mixture ofammonium fluoride andhydrogen fluoride.[11] It is far less reactive than the other nitrogen trihalidesnitrogen trichloride,nitrogen tribromide, andnitrogen triiodide, all of which are explosive. Alone among the nitrogen trihalides it has a negativeenthalpy of formation. It is prepared in modern times both by direct reaction of ammonia and fluorine and by a variation of Ruff's method.[6] It is supplied in pressurized cylinders.
NF
3 is slightly soluble in water without undergoing chemical reaction. It is nonbasic with a lowdipole moment of 0.2340 D. By contrast, ammonia is basic and highly polar (1.47 D).[12] This contrast reflects the differing electronegativities of H vs F.
Similar todioxygen, NF3 is a potent yet sluggish oxidizer.[6] It oxidizes hydrogen chloride to chlorine:[citation needed]
However, it only attacks (explosively)organic compounds at high temperatures. Consequently it is compatible under standard conditions with several plastics, as well as steel andMonel.[6]
Above 200-300 °C, NF3 reacts with metals, carbon, and other reagents to givetetrafluorohydrazine:[13]
NF3 reacts with fluorine andantimony pentafluoride to give thetetrafluoroammonium salt:[6]
NF3 andB2H6 react vigorously even at cryogenic temperatures to givenitrogen gas,boron trifluoride, andhydrofluoric acid.[14]
High-volume applications such asDRAM computer memory production, the manufacturing offlat panel displays and the large-scale production ofthin-film solar cells useNF
3.[15][16]
Nitrogen trifluoride is primarily used to removesilicon and silicon-compounds during the manufacturing of semiconductor devices such asLCD displays, somethin-film solar cells, and other microelectronics. In these applicationsNF
3 is initially broken down within aplasma. The resulting fluorineradicals are the active agents that attackpolysilicon,silicon nitride andsilicon oxide. They can be used as well to removetungsten silicide,tungsten, and certain other metals. In addition to serving as anetchant in device fabrication,NF
3 is also widely used to cleanPECVD chambers.
NF
3dissociates more readily within alow-pressure discharge in comparison toperfluorinated compounds (PFCs) andsulfur hexafluoride (SF
6). The greater abundance of negatively-charged free radicals thus generated can yield higher silicon removal rates, and provide other process benefits such as less residual contamination and a lower net charge stress on the device being fabricated. As a somewhat more thoroughly consumed etching and cleaning agent, NF3 has also been promoted as an environmentally preferable substitute forSF
6 or PFCs such ashexafluoroethane.[17]
The utilization efficiency of the chemicals applied inplasma processes varies widely between equipment and applications. A sizeable fraction of the reactants are wasted into the exhaust stream and can ultimately be emitted into Earth's atmosphere. Modernabatement systems can substantially decrease atmospheric emissions.[18]NF
3 has not been subject to significant use restrictions. The annual reporting ofNF
3 production, consumption, and waste emissions by large manufacturers has been required in many industrialized countries as a response to the observed atmospheric growth and the internationalKyoto Protocol.[19]
Highly toxic fluorine gas (F2, diatomicfluorine) is aclimate neutral replacement for nitrogen trifluoride in some manufacturing applications. It requires more stringent handling and safety precautions, especially to protect manufacturing personnel.[20]
Nitrogen trifluoride is also used inhydrogen fluoride and deuterium fluoride lasers, which are types ofchemical lasers. There it is also preferred to fluorine gas due to its more convenient handling properties
The GWP ofNF
3 is second only toSF
6 in the group ofKyoto-recognised greenhouse gases, andNF
3 was included in that grouping with effect from 2013 and the commencement of the second commitment period of the Kyoto Protocol. It has an estimatedatmospheric lifetime of 740 years,[7] although other work suggests a slightly shorter lifetime of 550 years (and a corresponding GWP of 16,800).[15]
Since 1992, when less than 100 tons were produced, production grew to an estimated 4000 tons in 2007 and is projected to increase significantly.[15] World production of NF3 is expected to reach 8000 tons a year by 2010. By far the world's largest producer ofNF
3 is the USindustrial gas and chemical companyAir Products & Chemicals. An estimated 2% of producedNF
3 is released into the atmosphere.[23][24] Robson projected that the maximum atmospheric concentration is less than 0.16 parts per trillion (ppt) by volume, which will provide less than 0.001 Wm−2 of IR forcing.[25]The mean global tropospheric concentration of NF3 has risen from about 0.02 ppt (parts per trillion, dry air mole fraction) in 1980, to 0.86 ppt in 2011, with a rate of increase of 0.095 ppt yr−1, or about 11% per year, and an interhemispheric gradient that is consistent with emissions occurring overwhelmingly in the Northern Hemisphere, as expected. This rise rate in 2011 corresponds to about 1200 metric tons/y NF3 emissions globally, or about 10% of the NF3 global production estimates. This is a significantly higher percentage than has been estimated by industry, and thus strengthens the case for inventorying NF3 production and for regulating its emissions.[26]One study co-authored by industry representatives suggests that the contribution of the NF3 emissions to the overallgreenhouse gas budget of thin-film Si-solar cell manufacturing is clear.[27]
TheUNFCCC, within the context of the Kyoto Protocol, decided to include nitrogen trifluoride in the secondKyoto Protocol compliance period, which begins in 2012 and ends in either 2017 or 2020. Following suit, the WBCSD/WRI GHG Protocol is amending all of its standards (corporate, product and Scope 3) to also cover NF3.[28]
Skin contact withNF
3 is not hazardous, and it is a relatively minor irritant tomucous membranes and eyes. It is a pulmonary irritant with atoxicity considerably lower thannitrogen oxides, and overexposure via inhalation causes the conversion ofhemoglobin in blood tomethemoglobin, which can lead to the conditionmethemoglobinemia.[29] TheNational Institute for Occupational Safety and Health (NIOSH) specifies that the concentration that is immediately dangerous to life or health (IDLH value) is 1,000 ppm.[30]
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