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Nitrogen trifluoride

NF3

CAS:7783-54-2

Chemicals:

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.

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 considered as an environmentally preferable substitute for sulfur hexafluoride or perfluorocarbons such as hexafluoroethane.The process utilization of the chemicals applied in plasma processes is typically below 20 %.Therefore some of the PFCs and also of the NF3 always escape into the atmosphere.Modern gas abatement systems can decrease such emissions.Elemental fluorine has been introduced as an environmentally friendly replacement for nitrogen trifluoride in the manufacture of flat panel displays and solar cells.

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.

Synthesis and reactivity:
Nitrogen trifluoride is a rare example of a binary fluoride that can prepared directly from the elements only at very uncommon conditions,such as electric discharge.After first attempting the synthesis in 1903,Otto Ruff prepared nitrogen trifluoride by the electrolysis of a molten mixture of ammonium fluoride and hydrogen fluoride.It proved to be far less reactive than the other nitrogen trihalides nitrogen trichloride,nitrogen tribromide and nitrogen triiodide,all of which are explosive.Alone among the nitrogen trihalides it has a negative enthalpy of formation.Today,it is prepared both by direct reaction of ammonia and fluorine and by a variation of Ruff's method.It is supplied in pressurized cylinders.

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).This difference arises from the fluorine atoms acting as electron withdrawing groups,attracting essentially all of the lone pair electrons on the nitrogen atom.NF3 is a potent yet sluggish oxidizer.

It oxidizes hydrogen chloride to chlorine:

2 NF3 + 6 HCl → 6 HF + N2 + 3 Cl2

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 → NF4+SbF6

Greenhouse gas:
NF3 is a greenhouse gas,with a global warming potential (GWP) 17,200 times greater than that of CO2 when compared over a 100 year period.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,although other work suggests a slightly shorter lifetime of 550 years (and a corresponding GWP of 16,800).

Although NF3 has a high GWP,for a long time its radiative forcing in the Earth's atmosphere has been assumed to be small,spuriously presuming that only small quantities are released into the atmosphere.Industrial applications of NF3 routinely break it down,while in the past previously used regulated compounds such as SF6 and PFCs were often released.Research has questioned the previous assumptions.High-volume applications such as DRAM computer memory production,the manufacturing of flat panel displays and the large-scale production of thin-film solar cells in regions with insufficient ecological awareness continues to increase the emissions of NF3.

Since 1992,when less than 100 tons was produced,production has grown to an estimated 4000 tons in 2007 and is projected to increase significantly.World production of NF3 is expected to reach 8000 tons a year by 2010.By far the world's largest producer of NF3 is the US chemical company Air Products & Chemicals.An estimated 2% of produced NF3 is released into the atmosphere.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.The mean global tropospheric concentration of NF3 has risen quasi-exponentially from about 0.02 ppt (parts per trillion,dry air mole fraction) at the beginning of the measured record in 1978,to a July 1,2008 value of 0.454 ppt,with a rate of increase of 0.053 ppt yr−1,or about 11% per year,and an interhemispheric gradient that is consistent with these emissions occurring overwhelmingly in the Northern Hemisphere,as expected.This rise rate corresponds to about 620 metric tons/y of 2009 NF3 emissions globally,or about 16% of the NF3 production estimate of 4000 metric tons yr−1.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.One study suggests that the contribution of the NF3-Emissions to the overall greenhouse gas budget of thin-film Si-solar cell manufacturing is overestimated.Instead,the contribution of the nitrogen trifluoride to the CO2-budget of thin film solar cell production is compensated already within a few months by the CO2 saving potential of the PV technology.

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.



NITROGEN TRIFLUORIDE ICSC: 1234

Nitrogen fluoride
Trifluoroamine
Trifluoroammonia
Perfluoroammonia
(cylinder)
CAS # 7783-54-2 NF3
RTECS # QX1925000 Molecular mass: 71.0
UN # 2451
EC Index #
TYPES OF HAZARD / EXPOSURE ACUTE HAZARDS / SYMPTOMS PREVENTION FIRST AID / FIRE FIGHTING
FIRE Not combustible but enhances combustion of other substances.Gives off irritating or toxic fumes (or gases) in a fire.Heating will cause rise in pressure with risk of bursting.
NO contact with flammable substances.NO contact with reducing agents.
In case of fire in the surroundings: use appropriate extinguishing media.
EXPLOSION

In case of fire: keep cylinder cool by spraying with water.
EXPOSURE


Inhalation
Ventilation,local exhaust,or breathing protection.
Fresh air,rest.
Skin

Remove contaminated clothes.
Eyes
Safety goggles.
First rinse with plenty of water for several minutes (remove contact lenses if easily possible),then take to a doctor.
Ingestion


SPILLAGE DISPOSAL PACKAGING & LABELLING
Ventilation.NEVER direct water jet on liquid.Personal protection: self-contained breathing apparatus.
EU Classification
UN Classification
UN Hazard Class: 2.2
UN Subsidiary Risks: 5.1

EMERGENCY RESPONSE STORAGE
Transport Emergency Card: TEC (R)-20G1O
Fireproof if in building.Separated from combustible and reducing substances.Cool.
IPCS
International
Programme on
Chemical Safety
Prepared in the context of cooperation between the International Programme on Chemical Safety and the Commission of the European Communities � IPCS,CEC 2005

SEE IMPORTANT INFORMATION ON BACK
NITROGEN TRIFLUORIDE ICSC: 1234
IMPORTANT DATA
PHYSICAL STATE;APPEARANCE:
COLOURLESS GAS,WITH CHARACTERISTIC ODOUR.

PHYSICAL DANGERS:
The gas is heavier than air and may accumulate in lowered spaces causing a deficiency of oxygen.

CHEMICAL DANGERS:
The substance decomposes on heating producing toxic fumes including fluoride.The substance is a strong oxidant and reacts with combustible and reducing materials.Reacts violently with ammonia,carbon monoxide,diborane,hydrogen,hydrogen sulfide,methane or tetrafluorohydrazine causing explosion hazard.Attacks metal.The substance is decomposed by electric sparks.

OCCUPATIONAL EXPOSURE LIMITS:
TLV: 10 ppm as TWA;BEI issued;(ACGIH 2004).
MAK not established.
ROUTES OF EXPOSURE:
The substance can be absorbed into the body by inhalation.

INHALATION RISK:
On loss of containment,a harmful concentration of this gas in the air will be reached very quickly.

EFFECTS OF LONG-TERM OR REPEATED EXPOSURE:
The substance may have effects on the liver and kidneys.Repeated or prolonged inhalation exposure may cause fluorosis.
PHYSICAL PROPERTIES
Boiling point: -129℃
Melting point: -208.5℃
Relative density (water = 1): see Notes
Solubility in water: none
Relative density of the vapour/air-mixture at 20℃ (air = 1): 2.45
ENVIRONMENTAL DATA

NOTES
Density of the liquid at boiling point: 1.885 kg/l.The odour warning when the exposure limit value is exceeded is insufficient.Methemoglobinemia has been observed in animals,but relevance to humans is unclear.Turn leaking cylinder with the leak up to prevent escape of gas in liquid state.Wear protective equipment during this operation.Check oxygen content before entering area.High concentrations in the air cause a deficiency of oxygen with the risk of unconsciousness or death.
ADDITIONAL INFORMATION


LEGAL NOTICE Neither the CEC nor the IPCS nor any person acting on behalf of the CEC or the IPCS is responsible for the use which might be made of this information
� IPCS,CEC 2005
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