Trichlorosilane

Trichlorosilane is an inorganic compound with the formula HCl3Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the semiconductor industry. In water, it rapidly decomposes to produce a siloxane polymer while giving off hydrochloric acid. Because of its reactivity and wide availability, it is frequently used in the synthesis of silicon-containing organic compounds.

Production
Trichlorosilane is produced by treating powdered metallurgical grade silicon with blowing hydrogen chloride at 300 °C. Hydrogen is also produced, as described in the chemical equation:
 * Si + 3 HCl → HCl3Si + H2

Yields of 80-90% can be achieved. The main byproducts are silicon tetrachloride (chemical formula SiCl4), hexachlorodisilane (Si2Cl6) and dichlorosilane (H2SiCl2), from which trichlorosilane can be separated by distillation.



It is also produced from silicon tetrachloride:
 * Si + 3 SiCl4 + 2 H2 → 4 HCl3Si

Uses
Trichlorosilane is the basic ingredient used in the production of purified polysilicon.
 * HCl3Si → Si + HCl + Cl2

It can be used in the Siemens process, which is a type of chemical vapor deposition process.

Ingredient in hydrosilylation
Via hydrosilylation, trichlorosilane is a precursor to other useful organosilicon compounds:
 * RCH=CH2 + HSiCl3 → RCH2CH2SiCl3

Some useful products of this or similar reactions include octadecyltrichlorosilane (OTS), perfluoroctyltrichlorosilane (PFOTCS), and perfluorodecyltrichlorosilane (FDTS). These reagents used in surface science and nanotechnology to form self-assembled monolayers. Such layers containing fluorine decrease surface energy and reduce sticking. This effect is usually exploited as coating for MEMS and microfabricated stamps for a nanoimprint lithography (NIL) and in injection molding tools.

Organic synthesis
Trichlorosilane is a reagent in the conversion of benzoic acids to toluene derivatives. In the first step of a two-pot reaction, the carboxylic acid is first converted to the trichlosilylbenzyl compound. In the second step, the benzylic silyl derivative is converted to the toluene derivative with base.

Safety
Trichlorosilane is highly reactive, and may respond violently (and even explosively) to many compounds. This also includes water, potentially producing silicon dioxide, chlorine, hydrogen, hydrogen chloride (and its aqueous form hydrochloric acid), and heat. Trichlorosilane can cause hazardous chemical reactions with moisture and humidity alone, and should be handled and stored under inert gas. Spills of trichlorosilane may be neutralized using a 1-1 ratio of sodium hydroxide, or a 2-1 ratio of sodium bicarbonate to trichlorosilane. Fires can be extinguished using alcohol-resistant aqueous film-forming foam (AR-AFFF).