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 in a hydrochlorination process. Hydrogen is also produced, as described in the chemical equation:
Yields of 80-90% can be achieved. The main byproducts are silicon tetrachloride, hexachlorodisilane and dichlorosilane, from which trichlorosilane can be separated by distillation.
It is also produced from silicon tetrachloride in a direct chlorination process:
Both methods are widely used. The first method is cheaper but yield is hard to control. The second method doesn't require as much control, but needs twice as much capital investment and consumes 120 to 200 kWh/kg compared to 65-90 kWh/kg for the first method. The distillation of TCS purifies it substantially and with it, most of the impurities in the silicon are removed.

Uses

Trichlorosilane is the basic ingredient used in the production of purified polysilicon.
It can be used in a chemical vapor deposition process called the Siemens process.

Ingredient in hydrosilylation

Via hydrosilylation, trichlorosilane is a precursor to other useful organosilicon compounds:
Some useful products of this or similar reactions include octadecyltrichlorosilane, perfluoroctyltrichlorosilane, and perfluorodecyltrichlorosilane. 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 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 to many compounds. This also includes water, potentially producing silicon dioxide, chlorine, hydrogen, hydrogen chloride, 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.