Silane is a general term for a series of silicon and hydrogen compounds whose chemical formula is SinH2n+2. In this series of hydrosilanes, methane is customarily called silane. Silane (silicon tetrahydride) is a colorless, toxic and very active compressed gas at room temperature and pressure. Fire at room temperature and explosive combustion occurs in air or halogen gas. Silane is a strong reductant, which reacts intensely with heavy metal halides, explosively with chlorine and bromine, and intensely with carbon tetrachloride. Silane is mainly used in semiconductor industry to produce high purity polycrystalline silicon, low temperature silicon dioxide CVD, silicon nitride CVD, polycrystalline silicon isolation layer, polycrystalline silicon ohmic contact layer and heterogenous or homogeneous silicon epitaxy growth raw materials, as well as ion implantation source and laser medium. It can also be used to produce solar cells, photoconductive fibers and photoelectric sensors. With the development of electronic industry, silane has been more and more widely used. In the microelectronics and Optoelectronics industry, silane can be used to produce high purity polycrystalline silicon, monocrystalline silicon, microcrystalline silicon, amorphous silicon, silicon nitride, silicon oxide, silicon carbide, heterostructure silicon, various metal silicides, etc. Because of its high purity and fine control, it has become an important special gas which can not be replaced by many other silicon sources.


There are many methods to prepare silane. At present, there are three main production processes: metal hydride process, silicon-magnesium alloy process and chlorosilane disproportionation process.
(1) Metal hydride process uses metal hydride to react with silicon tetrachloride or silicon tetrafluoride to produce silane and metal halides, such as:
SiCl4+4LiH-> SiH4+4LiCl (lithium hydride method)
(2) The chemical reaction formula for preparing silane gas from silicon-magnesium alloy is as follows:
Si+Mg-> Mg2Si
Mg2Si+4NH4Cl->SiH4+2MgCl2+4NH3
The process flow is very concise. The disadvantage of this process is that impurities are entrained in salt. Under the current situation of increasing purity requirements, the disadvantage of this process is becoming more and more obvious.
(3) The chlorosilane disproportionation process uses the synthesis and disproportionation of chlorosilane to obtain silane. The whole process is closed-circuit. One side invests silicon and hydrogen, the other side obtains silane, so the discharge is less, which is beneficial to environmental protection and the utilization rate of materials. The chemical reaction formula is:
Si+2H2+3SiC14->4SiHCl3
6SiHCl3 - > 3SiH2Cl2 + 3SiCl4
4SiH2Cl2 - > 2SiH3Cl + 2SiHCl3
3SiH3Cl - > SiH2Cl2 + SiH4
With the development of electronic industry, the requirement for purity of silane is higher and higher. At present, "GB/T 15909-2017 Gas Silane for Electronic Industry" has required that the purity of silane should be more than 99.9999%, and some microelectronics enterprises even put forward higher requirements.


The purity of silane is inverted, that is, the total impurity content in silane is deducted as the purity content of silane. Its impurities mainly include hydrogen, nitrogen, oxygen + argon, methane, hydrocarbons (C2-C4), carbon monoxide, carbon dioxide, chlorosilane, ethylsilane and water. Gas chromatography combined with helium ionization detector can complete the analysis and quantification of most impurity components. Hydrogen content is not deducted as impurity because silane reacts with trace water in the container to produce hydrogen, so the control of water content in the container is also one of the research directions in the future. In addition, electronic grade silane also has high requirements for its metal impurities.
The following points should be noted when using silane:
Silane belongs to flammable and explosive gas, so it should be strictly leak-proof in use.
When in use, the pipeline should be fully replaced with inert gases such as nitrogen to prevent air residue in the pipeline.
There should be a special tail gas treatment device, and a combustion tower or furnace should be set at the tail gas end.
In case of leakage, relevant operations shall be carried out according to the safety warning of "GB/T15909-2017 Gas Silane for Electronic Industry".