Tungsten hexafluoride

Chemical Name Synonyms Chemical Formula CAS number Molecular Weight Boiling point Melting point Relative density Solubility in water DOT classification DOT label UN Number CGA Connection NFPA hazard identification 

Severe eye, mucous membrane and skin irritant. Fluoride poisoning affects the digestive, circulatory, respiratory systems and the central nervous system. Upon contact with moistirre WFg readily hydrolyzes thus it is extremely irritating to throat, nose, and respiratory tract and may cause pirlmonary edema. High level closure can be fatd. Fluoride may bind with body Ca and Mg inhibiting enzyme systems. 

Releases HF upon contact with water. Decomposition may release toxic and corrosive fumes of fluorine. 

Self contained breathing apparatus operated in positive pressure mode with full face piece. Impervious clothing should be worn to prevent skin contact as well as gloves and splash proof goggles, and a full face shield. 

Stop leak if it can be accomplished without risk. If possible, remove leak to exhausted enclosure and direct exhaust to suitable scrubber media. If leak can not be contained, apply water spray from a distance to minimize dispersal of gas but note that reaction is highly exothermic and generates corrosive and toxic HF resultant solution is corrosive. 

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The reactivity of fluorine compounds varies from extremely stable, eg, compounds such as sulfur hexafluoride [2551-62 ] nitrogen trifluoride [7783-54-2] and the perfluorocarbons (see Fluorine compounds, organic) to extremely reactive, eg, the halogen fluorides. Another unique property of nonionic metal fluorides is great volatiUty. Volatile compounds such as tungsten hexafluoride [7783-82-6] molybdenum hexafluoride [7783-77-9] ... 

Fluorination of tungsten and rhenium produces tungsten hexafluoride, WF, and rhenium hexafluoride [10049-17-9J, ReF, respectively. These volatile metal fluorides are used in the chemical vapor deposition industry to produce metal coatings and intricately shaped components (see Thin films,... 

Specifications. The use of tungsten hexafluoride in CVD appHcations in the manufacture of high density siUcon chips requires a high purity product, essentially free of all metallic contaminants. Several grades of WF are available. Table 2 shows the specifications for three grades of WF. ... 

Tungsten hexafluoride is shipped as a Hquid under its own vapor pressure in nickel or steel cylinders in quantities of 45 kilograms per cylinder or less however, it has been shown that the purity of WF packaged in steel cylinders can degrade over time (21). It is classified as a corrosive Hquid by the... 

Handling and Toxicity. Tungsten hexafluoride is irritating and corrosive to the upper and lower airways, eyes, and skin. It is extremely corrosive to the skin, producing bums typical of hydrofluoric acid. The OSHA permissible exposure limits is set as a time-weighted average of 2.5 mg/kg or 0.2 ppm (22). 

CVD processing can be used to provide selective deposition on certain areas of a surface. Selective tungsten CVD is used to fill vias or holes selectively through siUcon oxide layers in siUcon-device technology. In this case, the siUcon from the substrate catalyzes the reduction of tungsten hexafluoride, whereas the siUcon oxide does not. Selective CVD deposition can also be accompHshed using lasers or focused electron beams for local heating. 

Direct fluoridation of pure tungsten in a flow system at atmospheric pressure at 350—400°C is the most convenient procedure (4). Tungsten hexafluoride is extremely unstable in the presence of moisture and hydroly2es completely to tungstic acid [7783-03-1] ... 

Tungsten hexafluoride dissolves in ben2ene or cyclohexane to give a bright red color, in dioxane a pale red, and in ether a violet-brown. 

Tungsten disilicide (WSi2) is refractory and stable with low resistivity. As with other silicides, a common deposition system uses silane as the silicon source with tungsten hexafluoride as follows ... 

Kara, T., Miyamato, T., Hagiwara, H., Bromley, E., and Harshbarger, W., Composition of Tungsten Silicide Films Deposited by Dichlorosilane Reduction of Tungsten Hexafluoride, /. Electrochem. Soc., 137(9) 2955-2959 (Sept. 1990)... 

Fawcett, J. et al., J. Chem. Soc., Dalton Trans., 1980, 2294-2296 Trimethylsilyl azide reacts with excess tungsten hexafluoride in solvent to give the title compound, which explodes at 63 °C or if dried in dynamic vacuum. A deficiency of the hexafluoride gave a mixture (presumably containing poly-azides) which exploded at ambient temperature. 

Safety procedures for use of tungsten hexafluoride in CVD processing operations are emphasized. 

De Wall, R. Neuert, H. The Formation of Negative Ions From Electron Impact Widi Tungsten Hexafluoride. Z Naturforsch., A 1977,32A, 968-971. 

Another class of octahedral structures whose stereochemistry was established by NMR is tungsten hexafluoride complexes with donor molecules, e.g., WF6-(C6H6)3P (87a). For these, the F19 spectra consist of a low-field doublet, a medium-field quintet and a high-field singlet of relative intensities 4 1 1. The doublet and quintet resonances establish the geometry... 

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