in (100) oriented tungsten crystallites whereas higher values favor the (111) orientation. Formation of HF is a drawback, as the HF vapor is very aggressive and etches away most materials. Also, the deposited tungsten shows poor adhesion to the silicon dioxide which is the main passivation material in semiconductor electronics. Therefore, SiO2 has to be covered with an extra buffer layer prior to the tungsten deposition. On the other hand, etching by HF may be beneficial to remove unwanted impurity layers. Silane and germane The characteristic features of tungsten deposition from the WF6/SiH4 are high speed, good adhesion and layer smoothness. The drawbacks are explosion hazard and high sensitivity of the deposition rate and morphology to the process parameters, such as mixing ratio, substrate temperature, etc. Therefore, silane is commonly used to create a thin tungsten nucleation layer. It is then switched to hydrogen, that slows down the deposition and cleans up the layer. Deposition from WF6/GeH4 mixture is similar to that of WF6/SiH4, but the tungsten layer becomes contaminated with relatively (compared to Si) heavy germanium up to concentrations of 10–15%. This increases tungsten resistance from about 5 to 200 μΩ·cm. Other applications WF6 can be used for the production of tungsten carbide. As a heavy gas, WF6 can be used as a buffer to control gas reactions. For example, it slows down the chemistry of the Ar/O2/H2 flame and reduces the flame temperature. Safety Tungsten hexafluoride is an extremely corrosive compound that attacks any tissue. Because of the formation of hydrofluoric acid upon reaction of WF6 with humidity, WF6 storage vessels have Teflon gaskets. References Tungsten halides Hexafluorides Lachrymatory agents Octahedral compounds Industrial gases