Description
Nitrogen trifluoride is a colorless gas with little odor. Nitrogen trifluoride is an oxidizer that is thennodynamically stable except at elevated temperatures. At temperatures up to about 482°F (250°C), its reactivity is comparable to oxygen. At higher temperatures, its reactivity is similar to fluorine owing to appreciable dissociation into NF2 and F-. The thennal dissociation of nitrogen trifluoride has been studied by a number of investigators and has been found to peak in the temperature range of 1100K to 1500K. In handling nitrogen trifluoride, conditions should be avoided that can result in high temperatures such as adiabatic compression from the rapid pressurization of a system.
Nitrogen trifluoride acts primarily upon the elements as a fluorinating agent, but not a very active one at lower temperatures. At elevated temperatures, nitrogen trifluoride pyrolyzes with many of the elements to produce nitrogen tetrafluoride and the corresponding fluoride. The pyrolysis of nitrogen trifluoride over copper turnings produces nitrogen tetrafluoride in a 62 percent to 71 percent yield at 707°F (375°C). Pyrolysis over carbon is more complete.
Chemical Properties
Nitrogen trifluoride is a colorless gas. Moldy
odor. Shipped as a nonliquefied compressed gas.
Physical properties
Colorless gas; moldy odor; liquefies at -128.75°C; density of liquid 3.116 g/mL; vapor pressure at -158°C 96 torr; solidifies at -206.8°C; critical temperature -39.15°C; critical pressure 44.02 atm; critical volume 126 cm
3/mol; very slightly soluble in water.
Uses
Nitrogen trifluoride has been used successfully
in large quantities as a fluorine source for
high-energy chemical lasers. It is preferred over
fluorine because of its comparative ease of handling at ambient conditions.
Recently, an increasing amount of nitrogen
trifluoride is being used in the semiconductor
industry as a dry etchant, showing significantly
higher etch rates and selectivities when compared to carbon tetrafluoride and mixtures of
carbon tetrafluoride and oxygen.
Nitrogen trifluoride was also used as an oxidizer in rocketry in the early 1960s, but this
application was not commercialized.
Uses
Nitrogen trifluoride is a gas that is made of nitrogen and fluorine atoms. The global electronics industry uses nitrogen trifluoride in its cleaning processes, because the gas outperforms other alternatives, is easier and safer to handle, and helps reduce greenhouse gas emissions.
Manufacturers of semiconductors, thin film solar cells and flat-panel displays use nitrogen trifluoride to clean process chambers. Inside the chambers, thin layers of semiconductive and insulating films are applied to wafers and panels. Nitrogen trifluoride removes the residue that these films leave on the chamber walls so the chambers can operate efficiently and produce a quality device.
Nitrogen trifluoride offers many benefits over alternative cleaning agents. It is stable at room temperature, so it is relatively easy and safe to handle. It is also easy to use nitrogen trifluoride to form an energetic, or reactive, gas or a plasma—a gas with free electrons. The relatively long life of fluorine radicals made in the plasma makes nitrogen trifluoride an efficient cleaner.
Uses
Nitrogen trifluoride is an etchant and chamber cleaning agent.
Oxidizer for high-energy fuels, chemical synthesis.
Definition
ChEBI: Nitrogen trifluoride is a nitrogen halide.
Application
Nitrogen trifluoride (NF₃) is primarily used as a cleaning agent in the semiconductor and flat-panel display industries, where it serves to remove silicon and silicon nitride residues from chemical vapor deposition (CVD) chambers through plasma etching; it is also employed in the manufacturing of solar photovoltaic cells, as a fluorine source in high-energy chemical lasers, and in the production of hydrogen fluoride for industrial applications.
Preparation
Nitrogen trifluoride is prepared by electrolysis of either molten ammonium fluoride, NH
4F, or melted ammonium acid fluoride, NH
4HF
2 (or ammonium fluoride in anhydrous HF). While the NH
4F method is preferred because it forms nitrogen trifluoride as the only product, electrolysis of ammonium acid fluoride yields a small amount of dinitrogen difluoride, N
2F
2,and NF
3.
Also, nitrogen trifluoride can be prepared by reaction of ammonia with fluorine diluted with nitrogen in a reactor packed with copper. Other nitrogen fluorides, such as N
2F
2, N
2F
4, and NHF
2 also are produced. The yield of major product depends on fluorine/ammonia ratio and other conditions.
Production Methods
Nitrogen trifluoride can be formed from a wide variety of chemical reactions. The commercial process for production involves direct fluorination of ammonia with fluorine gas in the presence ofammonium fluoride.
Reactions
Hydrogen reacts with nitrogen trifluoride with the rapid liberation of large amounts of heat and is the basis for the use of nitrogen trifluoride in high-energy chemical lasers. The flammability range for nitrogen trifluoride-hydrogen mixtures is 9.4 mole percent to 95 mole percent nitrogen trifluoride. Nitrogen trifluoride reacts with organic compounds, but generally an elevated temperature is required to initiate the reaction. Under these conditions, the reaction will often proceed explosively, and great care must be exercised when exposing nitrogen trifluoride to organic compounds. Therefore, nitrogen trifluoride has found little use as a fluorinating agent for organic compounds.
General Description
A colorless gas with a moldy odor. Very toxic by inhalation. Slightly soluble in water. Corrosive to tissue. Under prolonged exposure to fire or heat the containers may rupture violently and rocket. Used to make other chemicals and as a component of rocket fuels.
Air & Water Reactions
Slightly soluble in water.
Reactivity Profile
Nitrogen trifluoride is a very powerful oxidizing agent. Presents dangerous fire hazard in the presence of reducing agents. Etches glass in the presence of moisture. Emits toxic and corrosive fumes of fluoride when heated to decomposition [Lewis, 3rd ed., 1993, p. 937]. Can react violently with hydrogen, ammonia, carbon monoxide, diborane, hydrogen sulfide, methane, tetrafluorohydrazine, charcoal. Explosive reaction with chlorine dioxide. A severe explosion may occur when exposed to reducing agents under pressure [Bretherick, 5th ed., 1995, p. 1427].
Hazard
Severe explosion hazard. Corrosive to tissue. Methemoglobinemia, liver and kidney damage.
Health Hazard
Inhaling nitrogen trifluoride can reduce the capacity of red blood cells to carry oxygen. This causes cyanosis, or a bluish discoloration of the skin. Breathing nitrogen trifluoride can also lead to headache, dizziness, weakness and confusion. After prolonged exposure to high concentrations, breakdown of red blood cells and changes in the liver, kidneys, spleen and heart muscle may occur as secondary effects. In fresh air, the initial red blood cell changes will clear over several hours, but the person should still be monitored for secondary effects.
Fire Hazard
Substance does not burn but will support combustion. Some may react explosively with fuels. May ignite combustibles (wood, paper, oil, clothing, etc.). Vapors from liquefied gas are initially heavier than air and spread along ground. Runoff may create fire or explosion hazard. Containers may explode when heated. Ruptured cylinders may rocket.
Industrial uses
Nitrogen trifluoride has been used successfully in large quantities as a fluorine source for high-energy chemical lasers. It is preferred over fluorine because of its comparative ease of handling at ambient conditions.
Recently, an increasing amount of nitrogen trifluoride is being used in the semiconductor industry as a dry etchant, showing significantly higher etch rates and selectivities when compared to carbon tetrafluoride and mixtures of carbon tetrafluoride and oxygen.
Nitrogen trifluoride was also used as an oxidizer in rocketry in the early 1960s, but this application was not commercialized.
Materials Uses
At temperatures less than 482°F (250°C), nitrogen trifluoride has a reactivity similar to that of
oxygen and is relatively inert to most materials
of construction. At ambient temperatures, brass,
aluminum, copper, steel, and stainless steels can
be used because corrosion rates of less than 0.1
mil/yr. at 160°F (71.1°C) have been determined
for these materials. Nitrogen trifluoride is also
compatible with fluorinated materials such as
Teflon at ambient temperatures.
At increased temperatures and pressures, nitrogen trifluoride's reactivity increases becoming more like that of fluorine, with nickel and
Monel being the preferred materials of construction.
Safety Profile
A poison. Mildly toxic
by inhalation. Prolonged absorption may
cause mottling of teeth, skeletal changes.
Severe explosion hazard by chemical
reaction with reducing agents, particularly
when under pressure. A very dangerous fire
hazard; a very powerful oxidner; otherwise
inert at normal temperatures and pressures.
Potential Exposure
This material has been used in chemical
synthesis and as an oxidizer for high-energy fuels (as
an oxidizer in rocket propellant combinations).
Physiological effects
ACGIH recommends a Threshold Limit ValueTime-Weighted Average (TLV-TWA) of 10
ppm (29 mgim3) for nitrogen trifluoride. The
TLV- TWA is the time-weighted average concentration for a nonnal 8-hour workday and a
40-hour workweek, to which nearly all workers
may be repeatedly exposed, day after day, without adverse effect.
OSHA lists an 8-hour Time-Weighted Average-Pennissible Exposure Limit (TWA-PEL)
of 10 ppm (29 mg/m3) for nitrogen trifluoride.
TWA-PEL is the exposure limit that shall not
be exceeded by the 8-hour TWAin any 8-hour
work shift of a 40-hour workweek.
The toxicity of nitrogen trifluoride is related
to its capacity to fonn methemoglobin, a modified fonn of hemoglobin incapable of oxygen
transport, and to destroy red blood cells
(hemolysis). Upon cessation of exposure, methemoglobin spontaneously reverts to hemoglobin. However, at high levels of exposure, therapeutic intervention may be necessary (oxygen,
methylene blue, exchange transfusion). The
occurrence of hemolysis requires careful monitoring for degree of anemia and the potential for
impaired kidney function.
Nitrogen trifluoride's TLV-TWA value of 10
ppm resulted from a study that exposed rats to
100 ppm for 7 hours per day, 5 days per week for 18 months. No changes were detected in the
animals' behaviors, heart or lung rates, blood
levels, or appearance of fluorosis. ACGIH set
the TLV-TWA at III 0 ofthe test level.
Gaseous nitrogen trifluoride is considered innocuous to the skin and a minor irritant to the
eyes and mucous membranes.
storage
Nitrogen trifluoride cylinders must be securely supported while in use to prevent movement and straining of connections. Full cylinders must be stored in a well-ventilated area, protected from excessive heat (125°F or 51.7°C), located away from organic or flammable materials, and secured. Valve protection caps and valve outlet caps must be securely in place at all times when the cylinder is not in use.
Shipping
UN2451 Nitrogen trifluoride, Hazard Class: 2.2;
Labels: 2.2-Nonflammable compressed gas; 5.1-Oxidizer.
Cylinders must be transported in a secure upright position,
in a well-ventilated truck. Protect cylinder and labels from
physical damage. The owner of the compressed gas cylinder
is the only entity allowed by federal law (49CFR) to
transport and refill them. It is a violation of transportation
regulations to refill compressed gas cylinders without the
express written permission of the owner.
Toxicity evaluation
The toxicity of nitrogen trifluoride is related to its capacity to fonn methemoglobin, a modified fonn of hemoglobin incapable of oxygen transport, and to destroy red blood cells (hemolysis). Upon cessation of exposure, methemoglobin spontaneously reverts to hemoglobin. However, at high levels of exposure, therapeutic intervention may be necessary (oxygen, methylene blue, exchange transfusion). The occurrence of hemolysis requires careful monitoring for degree of anemia and the potential for impaired kidney function.
Incompatibilities
The gas is a powerful oxidizer. Presents
dangerous fire hazard in the presence of reducing agents. Etches glass in the presence of moisture. Reacts with
oil, grease, reducing agents and other oxidizable materials;
combustibles, organics, ammonia, carbon monoxide; methane,
hydrogen, hydrogen sulfide; activated charcoal; diborane,
water. Can react violently with hydrogen, ammonia,
carbon monoxide, diborane, hydrogen sulfide, methane, tetrafluorohydrazine,
charcoal. Nitrogen trifluoride will
increase intensity of an existing fire.
Toxics Screening Level
The initial threshold screening level (ITSL) for nitrogen trifluoride is 290 μg/m3 based on an 8 hr.
averaging time.
Waste Disposal
Return refillable compressed
gas cylinders to supplier. Vent into large volume of concentrated
reducing agent (bisulfites, ferrous salts or hypo)
solution, then neutralize and flush to sewer with large
volumes of water.
GRADES AVAILABLE
Nitrogen trifluoride is available in grades ranging from 98 percent to 99.995 percent v/v
minimum purity.
