Fluorides and chemical vapor deposition

Chemical vapor deposition (CVD) is a method of vacuum deposition of thin films from gaseous precursors. Many liquid or gaseous fluorides at room temperature are used as precursors of thin-film deposition, particularly in the field of semiconductors.

For example, tungsten, molybdenum, and rhenium fluorides are highly used products for the production of refractory coatings capable of withstanding high temperatures. Germanium or phosphorus fluorides are advantageously used in ion implantation instead of their hydrogenated equivalents (phosphine, PH3,is a very toxic gas).

Titanium fluorides, TiF4,and tantalum, TaF5,make it possible to obtain thin layers of fluorides of alkali metals and rare earths (CaF2,MgF2,LaF3,YF3…) of better quality and faster than with the commonly used hydrofluoric acid.

In General, high Valence fluorides are lighter than their chlorinated correspondents and can be implemented more easily than the latter. However, they may have a larger dissociation energy value.For example, the melting point of tantalum chloride, TaCl5,is 216°C, while that of tantalum fluoride, TaF5,is 96.8°C. But the dissociation energy of the latter is 1.2 times higher than that of the chlorinated derivative.