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Polycrystalline silicon production

Polycrystalline silicon is a strategic raw material of semiconductor industry. Mainly polycrystalline silicon is used for production of siLPGe-crystalline silicon and multicrystalline-silicon. In terms of quality, polycrystalline silicon is divided into solar-grade silicon and electronic-grade silicon.

Electronic-grade polycrystalline silicon with the mass fraction of impurities of 10-7 — 10-8 % is used in modern microelectronics, industrial and power electronics.

Solar-grade polycrystalline silicon is used in energy engineering for manufacturing of solar cells.

Metallurgical-grade silicon with purity up to 98-99% is a raw material for production of polycrystalline silicon.

The companies of the USA, Japan, Germany and Italy control more than 90% of world market of polycrystalline silicon.

Currently there is shortage of polycrystalline silicon in the world, in this connection the programs on silicon production development are adopted in a number of countries.

Before the USSR produced up to 12% of world’s polycrystalline silicon, major production capacities were located in Ukraine and Kirgizia.

Russian producers of polycrystalline silicon are as follows:

  • Podolsk chemical and metallurgical plant
  • Krasnoyarsk mining and chemical industrial complex (Zheleznogorsk)
  • «Usolye-Sibirskiy Silicon» LLC of NITOL Group.

Currently at enterprises of Russia, siLPGe-crystalline silicon is produced from high-purity foreign raw material, therefore polycrystalline silicon production development remains relevant.

Production of pure and ultra-pure silicon requires the preliminary synthesis of the purest starter compounds of silicon (SiCl4, SiHCl3, SiH4), from which silicon is extracted by recovery or thermal decomposition.

Traditionally “Siemens C” technology is used for production of polycrystalline silicon that accounts for major part (>70%) of world production of polycrystalline silicon.

Trichlorosilane is synthesized by chlorination from technical silicon which is cleaned with multistage rectification from by-products of trichlorosilane synthesis - Н2, НСl, tetrachloride of silicon, and fed to the reactor of hydrogen recovery, where silicon deposition process on rods takes place. By-products, isolated during cleaning of synthesized trichlorosilane, return back to polycrystalline silicon production cycle. Hydrogen chloride returns to trichlorosilane synthesis, the synthesized trichlorosilane and part of hydrogen are transferred to conversion of tetrachloride of silicon (transformation of tetrachloride of silicon to trichlorosilane), other hydrogen is fed to hydrogen reduction of silicon.

In the process of reduction of silicon in reactors besides the product, that is, pure polycrystalline silicon, by-products, such as tetrachloride of silicon and chlorine hydride are produced, they in mixture with unreacted hydrogen and trichlorosilane, and also with conversion products of tetrachloride of silicon are sent to the units, where a separation of Н2, НСl, and also separation of circulating chlorosilanes at trichlorosilane and tetrachloride of silicon, which are returned to the process, takes place.

In 2007-2009, LENNIIHIMMASH Group implemented two projects on polycrystalline silicon production with capacity of 300 and 3000 t/year.

On the basis of an original process flowsheet, LENNIIHIMMASH developed chlorosilane condensation units and gas-vapor mixture separation units, including production of high-pure products - tetrachlorated silicon, trichlorosilane, hydrogen and chlorous hydrogen with the purpose of their further return to the production cycle of polycrystalline silicon and also to the treatment and neutralization plants of industrial effluents and off-gases, providing protection of environment from harmful emissions.

The calculation methods of off-gases treatment and industrial effluents disposal for industrial polycrystalline silicon production developed by LENNIIHIMMASH is applicable also for other products of semiconductor group.

LENINIIHIMMASH also developed, manufactured and delivered a larger part of major process equipment of the units, pipeline valves, and also instrumentation.

Construction of those units is currently carried out at LLC Usolye-Sibirskiy of NITOL company.