Nitrogen Trifluoride Research Articles

Properties of fluorinated amorphous silicon-nitrogen-oxygen alloy (a-SiN xO y:H) deposited by plasma-enhanced chemical vapor deposition

The properties of fluorinated amorphous silicon-nitrogen-oxygen (a-SiN x O y :H:F) alloys deposited in a plasma-enhanced chemical vapor deposition reactor using a mixture of monosilane (SiH 4) and nitrogen trifluoride (NF 3) were investigated. The deposition rate of the a-SiN x O y :H:F alloys was found to increase with increasing NF 3 flow rate. Auger electron spectroscopy revealed a uniform chemical composition in these alloys. An abrupt increase in the bulk conductivity of the a-SiN x O y :H:F alloys was observed when the NF 3 flow rate was increased from 4 sccm to 7 sccm, whereas the bulk conductivity decreased as the NF 3 flow rate was increased from 7 sccm to 24 sccm. This phenomenon is attributable to a structural transformation in the alloys deposited with 7 sccm of NF 3. Carrier conduction in bulk alloys exhibited three activation energies with transition temperatures at 373 and 240 K. Carrier conduction above 373 K is by thermionic emission of carriers from silicon grains. Between 240 and 373 K, conduction is by thermionic field emission of carriers. Below 240 K, carrier tunneling is the predominant conduction mechanism. Undoped a-SiN x O y :H:F alloys formed rectifying heterojunctions on crystalline p-type silicon. The electrical characteristics of these heterostructures are dominated by the silicon/alloy interface.

Atmospheric reactions and ultraviolet and infrared absorptivities of nitrogen trifluoride

Nitrogen trifluoride is found to be stable towards photo‐oxidation reactions that limit the atmospheric lifetimes of many gaseous species. Reactions with species such as OH and HO2 are thermodynamically unfavorable. The reaction with O3, while thermodynamically favorable, is found to be too slow to be of atmospheric importance. Measurements of the NF3 absorption cross‐sections from 180 to 250 nm yield values that are smaller than those previously reported, and indicate an atmospheric lifetime against photodissociation in the stratosphere of about seven hundred years. In addition, the infrared band strengths were determined in order to enable estimates of greenhouse warming potentials. A slow reaction with aqueous Fe2+ was observed at room temperature; it could provide an additional destruction mechanism in the environment.

Nitrogen Trifluoride: A New Reactant Gas in Chemical Reaction Interface Mass Spectrometry for Detection of Phosphorus, Deuterium, Chlorine, and Sulfur

A new set of reactions that involve fluorine have been investigated in chemical reaction interface mass spectrometry (CRIMS). The primary goal of this study was to provide a means to selectively detect phosphorus-containing compounds, which fluorine does by generating PF 5 . P F 4 + , the main fragment ion of PF 5 , provides a sensitive (10 pg/s), selective, and linear (> 10 5 dynamic range) channel for phosphorus-containing analytes. This fluorine-rich environment also provides new ways to selectively and simultaneously detect hydrogen isotopes, chlorine, and sulfur. NF 3 as a reactant gas provides the most comprehensive array of elemental and isotopic detection yet available for CRIMS. An application of phosphorus-selective detection was attempted by examination of a plasma sample from a patient who had been treated with cyclophosphamide. The phosphorus-selective channel showed six peaks: one is derivatized phosphate, two are t -butyldimethylsilyl (TBDMS) derivatives of cyclophosphamide, another two are TBDMS derivatives of 4-hydroxy-yclophosphamide, and one is from underivatized cyclophosphamide. The simultaneous detection of chlorinecontaining compounds confirmed our results for those peaks related to cyclophosphamide and its metabolite.

Effects of nitrogen trifluoride on the properties of plasma-enhanced chemical-vapor-deposited semi-insulating polysilicon films

The effects of nitrogen trifluoride (NF3) in the reactant gas stream on the properties of plasma-enhanced chemical-vapor-deposited (PECVD) semi-insulating polysilicon (SIPOS) films were investigated. The addition of NF3 to the reactant gas stream resulted in a significant increase in the deposition rate. The presence of Si−F species in the SIPOS was revealed by Fourier transform infrared and X-ray photoelectron spectroscopy. A gradual transformation of the Si−F species into Si−Ox is observed in fluorinated SIPOS films deposited with a higher nitrous oxide flow rate, or alternatively, in films containing a higher oxygen content. The fluorinated SIPOS films exhibit both a larger magnitude and temperature dependence in their current densities than unfluorinated films and also exhibit two activation energies, one below and one above 230 K. However, a lower forward current density is obtained for a fluorinated SIPOS heterojunction compared with an unfluorinated SIPOS heterojunction. Furthermore, thermionic emission was found to be the predominant conduction mechanism in heterojunctions of fluorinated SIPOS on p-type crystalline silicon.

Plasma fluorination of graphite

Fluorinated graphites are low surface energy, thermally stable solids that have applications as moisture resistant lubricants, water repellents, release agents, and lithium battery cathodes. Conventional methods of synthesizing fluorinated graphite, however, make inefficient use of fluorine feed stocks, are time consuming and limited by safety considerations. In this article, we demonstrate that plasma processing techniques can be used to fluorinate graphite surfaces and thereby reduce the surface free energy from an untreated value of 50 mJ/m2 to as low as 7 mJ/m2. Pressed graphite pellets and graphite foils are exposed to nitrogen trifluoride and sulfur hexafluoride plasmas. Fluorination is monitored with x‐ray photoelectron spectroscopy (XPS), while liquid contact angle measurements are used to assess the free energy of the treated surfaces. Results indicate that significant surface fluorination can be achieved in exposure times of 10–15 min and with only modest plasma energies of 0.2 W/cm2. X‐ray photoelectron spectroscopy (XPS) confirms the formation of CF2 and CF covalent bonds. Fluorine depth profiles show that CF2 species predominate on the fluorinated graphite surface, while CF species are found in the subsurface at depths less than 100 A.Fluorinated graphites are low surface energy, thermally stable solids that have applications as moisture resistant lubricants, water repellents, release agents, and lithium battery cathodes. Conventional methods of synthesizing fluorinated graphite, however, make inefficient use of fluorine feed stocks, are time consuming and limited by safety considerations. In this article, we demonstrate that plasma processing techniques can be used to fluorinate graphite surfaces and thereby reduce the surface free energy from an untreated value of 50 mJ/m2 to as low as 7 mJ/m2. Pressed graphite pellets and graphite foils are exposed to nitrogen trifluoride and sulfur hexafluoride plasmas. Fluorination is monitored with x‐ray photoelectron spectroscopy (XPS), while liquid contact angle measurements are used to assess the free energy of the treated surfaces. Results indicate that significant surface fluorination can be achieved in exposure times of 10–15 min and with only modest plasma energies of 0.2 W/cm2. X‐ray phot...

Studies of the effects of NF3on the growth of polysilicon films by low-pressure CVD. Part 1.—Effect on growth rate

The control of crystalline quality of polysilicon prepared by low-pressure chemical vapour deposition (LPCVD) is important for device applications. A number of reaction parameters affect this quality and, in general, it has been found previously that layers grown in the amorphous state show good structural perfection and low strain on annealing. We have investigated a new strategy for producing good crystalline polysilicon by attempting to etch layers during the deposition process in order to reduce the size of crystallites in the layers. In this paper we report on the effect of nitrogen trifluoride on the growth rate of polysilicon. We interpret the decreased growth rate in the presence of NF3 in terms of an etching effect by molecular fluorine and as a result of growth inhibition by strong surface adsorption of the NF3. The mechanism of this inhibition is discussed.

Experimental observation of stable cyanodiazonium ions, NC–N2+

The elusive cyanodiazonium ion, NC–N2+, proposed as a transient intermediate in solution, but never directly observed, can be obtained in the gas phase by ionization of a mixture of nitrogen trifluoride and cyanamide, and characterized by collisionally activated dissociation (CAD) mass spectrometry.

Effects of nitrogen trifluoride on the growth and properties of plasma-enhanced chemical-vapor-deposited diamond-like carbon films

Nitrogen-doped diamond-like carbon (DLC) or amorphous hydrogenated carbon (a-C:H) films were grown by plasma enhanced chemical vapor deposition using methane and nitrogen gases as precursors. The effects of nitrogen trifluoride (NF3) on these nitrogen-doped DLC films were also investigated. The deposition rate decreases sharply with the addition of nitrogen in the absence of NFF3 due to dilution, while it increases in the presence of NFF3 due, presumably, to the reduction of activated hydrogen species by the fluorine radical (F϶. X-ray photoelectron spectra reveal a nitrogen concentration in the range of 9.3 to 13.8% in these DLC films with a C Is electron binding energy of 287-288 eV, indicating the diamond-like structure. Infrared spectra of DLC films indicate the presence of amino groups (N-H) and nitrile and/or isonitrile (C= N) groups giving strong evidence of sp carbon. Diamond like carbon films deposited in CHF4 +NF4 (with and without NFF3) have a lower refractive index, a lower bulk resistivity, and a lower optical bandgap than films deposited using CHF4 due to a lower hydrogen content in the films. Moreover, the bulk resistivity of these films decreases by over four orders of magnitude and the optical bandgap decreases from 2.65 eV to about 0.75 eV following annealing at a temperature of 500°C.

Absorption coefficient determination of nitrogen trifluoride at 147 nm

The absorption coefficient of nitrogen trifluoride at 147 nm was determined using two Pyrex cells in series. Measurement of the saturation ion current in trimethylamine, induced by the absorption of photons transmitted through the LiF window separating the photoionization and photolysis cells, provides an easy and accurate measurement of the fraction of light absorbed by nitrogen trifluoride in the photolysis cell (R. L. Lilly, R. E. Rebbert and P. J. Ausloos, J. Photochem. , 2 (1973/1974) 49). The absorption coefficient of nitrogen trifluoride was found to be k =136±3 (atm at 298 K) −1 cm −1 (base e ).

Electrochemical fluorination of binary electrolytes

Electrochemical fluorination (ECF) has proved to be a versatile method for the production of pertluorinated organic and inorganic compounds [E. Hollitzer and P. Sartori, Chem.-Ing.-Tech., 58 (1986) 31; G.G. Furin, Sov. Sci. Rev. Sect. B Chem. Rev. 16 (1991) 5]. Derivatives of perfluorinated alkanesulfonic acids are of special interest due to their versatility in various industrial applications, for example as surfactants, ion exchangers, etc. [G.A. Olah, P.S. Iyer and G.K. Prakash, Synthesis (1986) 513; R.J. Terjeson, J. Mohtasham, R.M. Sheets and G.L. Gard, J. Fluorine Chem., 38 (1988) 3]. Increasing the economy of the ECF process is possible, as the generation of two perfluorinated molecules of industrial interest from one starting compounds may be achieved. The use of alkanesulfonamides in the ECF process produces, among other materials, perfluorinated alkanesulfonyl fluorides and nitrogen trifluoride in a one step operation. The ECF in anhydrous hydrogen fluoride was carried out with mono- and bifunctional alkanesulfonamides of short chain length.

ChemInform Abstract: Microwave and Far IR Spectrum of Nitrogen Trifluoride.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

NF3 plasma treatment of polymeric dielectrics

Polyimide and polyphenylquinoxaline are important dielectric materials used in microelectronics fabrication. These polymers could be used even more extensively if they had greater moisture resistance. We demonstrate that plasma processing techniques can be used to improve the moisture resistance of polyimide and polyphenylquinoxaline films. Films are exposed to nitrogen trifluoride plasmas to introduce fluorine into the surface of the polymers. Fluorination is monitored with x-ray photoelectron spectroscopy and Fourier-transform infrared absorption spectroscopy. Water-contact angle measurements are used to assess the hydrophobicity of the treated surfaces. The polyimide and polyphenylquinoxaline film surfaces are quickly fluorinated during plasma exposure, and the moisture resistance improves consequently. The water-contact angle of our best film, 102°, compares favorably with polytetrafluoroethylene (109°). Plasma conditions can be controlled to minimize polymer degradation. The polyphenylquinoxaline films are etched by less than 0.01 μm/min in these experiments. Spectroscopic studies show that the aromatic carbons in the polymers are more readily fluorinated than carbonyl group carbons, and that the fluorination is restricted to the surface.

Electrolytic production of nitrogen trifluoride from a molten CsFHFNH 4F system

In order to decrease the vapor pressure of hydrogen fluoride ( HF) and corrosion of the nickel anode in an electrolytic cell for the production of nitrogen trifiuoride, the electrochemical behavior of nickel was investigated in the temperature range of 50–100 °C using a molten CsFHFNH 4F system. Anodic reaction on nickel seemed to vary with increasing potential, permitting division into four regions as follows: anodic dissolution of nickel in Region I (0–1 V vs. H 2), deposition of a Ni(II) compound on nickel in Region II (1–3 V), oxidation of Ni(II) film to Ni(III) and/or Ni(IV) compounds in Region III (3–5 V), and electrochemical fluorination of NH 3 in Region IV (more positive than 5 V). The addition of CsF to the molten electrolyte reduces the corrosion of the nickel anode and reduces the vapor pressure of HF in the melt. A maximum current efficiency for NF 3 formation was recorded at 100 °C.

Microwave and far infrared spectrum of nitrogen trifluoride

The microwave and far infrared rotational spectrum in the ground vibrational state of 14NF 3 has been observed and analyzed up to J = 60. A tunable sideband spectrometer has been used in the FIR region. The resulting molecular constants are (in MHz) B 0 = 10 681.092679(39), D J = 14.61109(11) 10 −3 D JK = −22.77154(71) × 10 −3, H J = 0.019529(95) × 10 −6, H JJK = −0.09847(96) × 10 −6, H KKJ = 0.1490(10) × 10 −6, L JJK = −0.00072(12) × 10 −9, and ( eQq) N = −7.0854(18). The millimeter-wave spectrum of 15NF 3 has also been observed and analyzed, providing the following values of the rotational constants: B 0 = 10 629.47940(23), D J = 14.3234(12) 10 −3, D JK = −22.2093(33) 10 −3.

Comparative study of the preparation of negative electron affinity GaAs photocathodes with O2 and with NF3

We discuss the possibility of replacing oxygen with nitrogen trifluoride in the preparation of stable GaAs negative electron affinity (NEA) photocathodes. The different role of O2 versus NF3 exposure during the activation is examined by means of quantum yield and photocurrent lifetime measurements. Quantum yield results clearly demonstrate that NEA conditions can be attained also with NF3. Measurements performed on the same samples and in the same experimental conditions, show a remarkably different time evolution of the activation process in the two cases. However, as a result of a huge number of activations, no evidence of significantly larger lifetimes for NF3 prepared photocathodes can be deduced.

K = 3 splitting and quadrupole hyperfine structure in the ν1 fundamental of nitrogen trifluoride

We have investigated the ν 1 fundamental band of 14NF 3 at 1032 cm −1 using the infrared laser sideband technique, resolving the quadrupole hyperfine structure as well as splittings on some high- J K = 3 transitions.

Handling and security in the sythesis and purification of nitrogen trifluoride

Meanwhile nitrogen trifluoride is a commercially available product. It is used e.g. as a dry etching agent for semiconductors, as a fluorine source in high energy lasers or as in situ cleaning of chemical vapor deposition equipment. For all applications a more or less high purity of the nitrogen trifluoride is required. Apart from the problems with the synthesis there are many complications regarding the purification and handling of nitrogen trifluoride. A review of problems concerning the synthesis and purification of nitrogen trifluoride will be given.

A study of electrochemical synthesis of nitrogen trifluoride on new cabon anode impregnated with molten lithium fluoride

For the industrial electrolysis of molten salt containing hydofluoride such as KF·2HF, carbon has been mainly used for anode material due to no anodic dissolution. However, in this case, there are some disadvantages as follows; 1. anode effect, 2. evolution of carbon tetrafluoride(CF) 4 3. brakdown of anode. Recently, for reducing these disadvantages, an improved carbon anode has been devloped weth impregnation of molten lithium fluoride. In this study, the improved anode was applied to electrochemical synthesis of highly pure (little CF 4 contamination)nitrogen trifluoride(NF 3), for which only niclel anode is now available. In several mol ratio of KFNH 4FHF systems, anode behavior was investigated on cyclic voltammetry and on steady state method with 1 and 100 ampere scale cells. Evoluved products and current efficiency of NF 3 were confirmed with 100 ampere scale cell. Consequently, following results were observed. 1. Electrolysis in a molten salt containing no KF was possible without breakdown of anode. It was generally difficult with conventional carbon. 2. Anode effect had never occured at current density in the region of regular condition by nickel. 3. Highly pure NF 3 was obtained with little CF 4 contamination. The improved carbon is a promissing anode to reject nickel for the electrochemical synthesis of NF 3.

A new electrolytic production of nitrogen trifluoride in a molten CsFHFNH 4F system

In order to decrease the vapor pressure of hydrogen fluoride and the anodic dissolution of the nickel anode for the electrolytic production of nitrogen trifluoride, the electrochemical behavior of nickel and some nickel-based alloys were investigated at 50 °C or 100 °C in a molten CsFHFNH 4F system. A platinum wire was used as the reference electrode, and a part of potential was reduced to a standard of the hydrogen electrode. Anode gas was analyzed by both infrared spectroscopy and gas chromatography. In the potentiostatic electrolysis at 6 V vs. Pt and 50 °C, the ratio of the anodic dissolution of nickel to total amount of passing electricity ( Q a Q t ) was only 1.32 % in calculation from the electron number in the discharge of 2. In the case of nickel-based alloys, only monel consisted of nickel and copper was available for the anode material and its ratio of Q a Q t was almost similar to that of nickel. The anodic polarization curve on monel was also similar to that on nickel, but the current density was smaller than that of nickel. In the galvanostatic electrolysis at the current density of 25 mA·cm −2 and 100 °C, the anode gas was composed of N 2, O 2, N 2O, NF 3, N 2F 2 and so on. The current efficiency of NF 3 increased with decreasing the concentration of NH 4F and reached the value of about 60 % in the molten 0.3NH 4F·CsF·2.6HF. In contrast, the ratio of Q a Q t of nickel decreased with decreasing the concentration of NH 4F and its value in the same electrolyte was 2.78 %.

Wide Bandgap Fluorinated Silicon-Carbide-Nitride Films Using NF3

ABSTRACTAmorphous hydrogenated silicon carbide has been studied extensively because of its properties as a wide bandgap material. However, a large amount of methane is needed to deposit the material. Also, the high carbon content of these films poses some problems. The addition of NF3 to the gas stream results in wide bandgap films with a substantial reduction in the required CH4 flow for deposition. Amorphous SiCx Ny :H:F films were prepared using rf glow discharge decomposition of silane, methane, and nitrogen trifluoride in a parallel-plate stainless steel reactor. Gas flow rate and power density were varied. For a gas mixture containing 6% NF3 and 78% CH4, FTIR measurements reveal a reduction in C-H peak heights at 2960 cm-1 and 2880 cm-1 with respect to the Si-H peak at 2080 cm-1 indicating a smaller carbon content in the film. The C-H peaks shift to higher wavenumbers with increasing NF3. The use of NF3 increases the bandgap from 2.6 to 3.14 eV while reducing the refractive index from 2.12. to 1.87. A maximum deposition rate of 625 A/min was achieved. This should be compared to the very low deposition rate of 18 A/min for comparable bandgap Si-C films deposited using 97% methane in silane. Increasing the deposition power density resulted in a larger bandgap and a smaller refractive index.