Trichlorosilane (TCS) is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the formula HCl₃Si. It is a colourless, volatile liquid. Purified trichlorosilane is the principal precursor to ultrapure silicon in the

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

industry. In water, it rapidly decomposes to produce a

siloxane In organosilicon chemistry, a siloxane is an organic compound containing a functional group of two silicon atoms bound to an oxygen atom: . The parent siloxanes include the oligomeric and polymeric hydrides with the formulae and . Siloxanes ...

polymer while giving off

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

. 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 The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...

at 300 °C in a hydrochlorination process. Hydrogen is also produced, as described in the

chemical equation A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and chemical formulas. The reactant entities are given on the left-hand side and the Product (chemistry), product entities are on the right-hand side ...

: :Si + 3 HCl → HCl₃Si + H₂ Yields of 80-90% can be achieved. The main byproducts are

silicon tetrachloride Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colorless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications. It is a part of the ...

(

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

SiCl₄), hexachlorodisilane (Si₂Cl₆) and dichlorosilane (H₂SiCl₂), from which trichlorosilane can be separated by

distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

It is also produced from silicon tetrachloride in a direct chlorination process: :Si + 3 SiCl₄ + 2 H₂ → 4 HCl₃Si 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 Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry. Polysilicon is produ ...

. :HCl₃Si → Si + HCl + Cl₂ It can be used in a

chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (electro ...

process called the Siemens 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 monolayer Self-assembled monolayers (SAM) are assemblies of organic molecules that form spontaneously on surfaces by adsorption and organize themselves into more or less distinct domains (head group, chain/backbone, and tail/end group). In some cases, mole ...

s. Such layers containing fluorine decrease surface energy and reduce sticking. This effect is usually exploited as coating for

MEMS MEMS (micro-electromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices ...

and microfabricated stamps for a nanoimprint lithography (NIL) and in

injection molding Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...

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.George S. Li, David F. Ehler, R. A. Benkeser "Methyl Groups By Reduction Of Aromatic Carboxylic Acids With Trichlorosilane - Tri-n-propylamine: 2-methylbiphenyl" Org. Synth. 1977, volume 56, pp. 83.

Safety

Trichlorosilane is highly reactive, and may respond violently (and even explosively) to many compounds. This also includes

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

, potentially producing

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

(and its

aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in wat ...

form

), and heat. Trichlorosilane can cause hazardous chemical reactions with

moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Moisture is defined as water in the adsorbed or absorbed phase. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some comme ...

and

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

alone, and should be handled and stored under

inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. Though inert gases have a variety of applications, they are generally used to prevent u ...

. Spills of trichlorosilane may be neutralized using a 1-1 ratio of

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

, or a 2-1 ratio of

sodium bicarbonate Sodium bicarbonate ( IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda (or simply “bicarb” especially in the UK) is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cat ...

to trichlorosilane.{{Cite report , url=https://www.nj.gov/health/eoh/rtkweb/documents/fs/1903.pdf , title=Hazardous Substance Fact Sheet: Trichlorosilane , date=October 2010 , publisher=New jersey department of health Fires can be extinguished using alcohol-resistant aqueous film-forming foam (AR-AFFF).

References

External links

Semiconductors: Silicon: Substrate Manufacture: Polycrystalline silicon Production
Chlorosilanes