Tungsten Hexafluoride - Applications in Semiconductor Industry

Applications in Semiconductor Industry

The dominant application of tungsten fluoride is in semiconductor industry, where it is widely used for depositing tungsten metal in a chemical vapor deposition process. The expansion of the industry in the 1980s and 1990s resulted in the increase of WF₆ consumption, which remains at around 200 tonnes per year worldwide. Tungsten metal is attractive because of its relatively high thermal and chemical stability, as well as low resistivity (5.6 µΩ·cm) and electromigration. Whereas WF₆ is favored over related compounds, such as WCl₆ or WBr₆, because of its higher vapor pressure resulting in higher deposition rates. Since 1967, two WF₆ deposition routes have been developed employed, thermal decomposition and hydrogen reduction. The required WF₆ gas purity is rather high and varies between 99.98% and 99.9995% depending on the application.

WF₆ molecules have to be split up in the CVD process. The decomposition is usually facilitated by mixing WF₆ with hydrogen, silane, germane, diborane, phosphine, and related hydrogen-containing gases.