Dichlorosilane or DCS as it is commonly known, is usually mixed with ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 (NH₃) in LPCVD chambers to grow silicon nitride in semiconductor processing.

A higher concentration of DCS:NH₃ (i.e. 16:1), usually results in lower stress

Stress (physics)

In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...

 nitride films.

It is an intermediate between silane

Silane

Silane is a toxic, extremely flammable chemical compound with chemical formula SiH4. In 1857, the German chemists and Friedrich Woehler discovered silane among the products formed by the action of hydrochloric acid on aluminum silicide, which they had previously prepared...

 and silicon tetrachloride

Silicon tetrachloride

Silicon tetrachloride is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications.-Preparation:...

.

Physical Properties

Graphs obtained show different properties of Dichlorosilane. The vapor pressure vs. temperature graphs shows that as temperature increases, vapor pressure also increases. The gas vs. heat capacity graph shows that as temperature increases, gas heat capacity increases until it hits .24 Cal/GRx°C. The enthalpy of vaporization decreases as temperature decreases, until it reaches 0 at its critical point at 180°C. Liquid heat capacity increases as temperature increases, until the critical point is reached. Liquid density decreases as temperature increases, until the critical point is reached. Surface tension decreases steadily as temperature increases, until the surface tension is at 0 when the critical point is reached. Liquid viscosity decreases as temperature increases, until the critical point is reached. Gas thermal conductivity increases as temperature increases. Liquid thermal conductivity decreases as temperature increases, until the critical point is reached. Enthalpy of formation decreases at first as temperature increases, but then it begins to increase around 750°C. Gibbs energy of formation increases linearly as temperature increases.

History of Dichlorosilane

Dichlorosilane was originally prepared in 1919 by the gas-phase reaction of monosilane, SiH₄, with hydrogen chloride, HCl, and then reported by Stock and Somieski. It was found that in the gas phase, Dichlorosilane will react with water vapor to give a gaseous monomeric prosiloxane, H₂SO. Prosiloxane polymerizes rapidly in the liquid phase and slowly in the gas phase, which results in liquid and solid polysiloxanes [H2SiO]_n. The liquid portion of the product, which is collected via vacuum distillation, becomes viscous and gelled at room temperature. Hydrolysis was done on a solution of H₂SiCl₂ in benzene by brief contact with water, and the molecular weight was determined to be consistent with an average composition of [H₂SiO]₆. Through analytical and molecular weight determinations, n was decided to be between 6 and 7. Then, through more experimentation with the product, it was determined that n increases as time increases. After being in contact with the aqueous hydrolysis medium for a longer period of time, a polymer, [HSi(OH)O]_n, was produced. There was limited availability of Dichlorosilane until the silicone industry grew.

Reactions and Formation

• Trichlorosilane disproportionation- (preferable)
2SiHCl₃⇔SiCl₄ + SiH₂Cl₂

• The waste gas that is formed from silicon production by the use of silicon tetrachloride or Trichlorosilane, HSiCl₃, is reduced with oxygen to form dichlorosilane.

Dichlorosilane Hydrolysis,

Stock and Somieski completed the hydrolysis of dichlorosilane by putting the solution of H₂SiCl₂ in benzene in brief contact with a large excess of water. A large-scale hydrolysis was done in a mixed ether/alkane solvent system at 0 °C, which gave a mixture of volatile and nonvolatile [H₂SiO]_n. Fischer and Kiegsmann attempted the hydrolysis of dichlorosilane in hexane, using NiCl₂⋅6H₂O as the water source, but the system failed. They did, however, complete the hydrolysis using dilute Et₂O/CCl₄ at -10°C. The purpose of completing the hydrolysis of dichlorosilane is to collect the concentrated hydrolysis products, distill the solution, and retrieve a solution of [H₂SiO]_n oligomers in dichloromethane. These methods were used to obtain cyclic polysiloxanes.

Another purpose for hydrolyzing dichlorosilane is to obtain linear polysiloxanes, and can be done by many different complex methods. The hydrolysis of dichlorosilane in diethyl ether, dichloromethane, or pentane gives cyclic and linear polysiloxanes.

Decomposition of Dichlorosilane

Su and Schlegal studied the decomposition of dichlorosilane using transition state theory (TST) using calculations at the G2 level. Wittbrodt and Schlegel worked with these calculations and improved them using the QCISD(T) method. The primary decomposition products were determined by this method to be SiCl2 and SiClH.

Ultrapurification of Dichlorosilane

Dichlorosilane must be ultrapurified and concentrated in order to be used for the manufacturing of semiconducting epitaxial silicon layers, which are used for microelectronics. The build up of the silicon layers produces thick epitaxial layers, which creates a strong structure

Advantage of Use

Dichlorosilane is used as a starting material for semiconducting silicon layers found in microelectronics. It is used because it decomposes at a lower temperature and has a higher growth rate of silicon crystals.

Safety Hazards

It is a chemically active gas, which will readily hydrolyze and self ignite in air. Dichlorosilane is also very toxic, and preventative measures must be used for any experiment involving the use of the chemical. Safety hazards also includes skin and eye irritation, and inhalation.

External links

• Safety data for dichlorosilane from the Chemistry Department at Oxford University.