Silicon in different grades of purity is used for growing silicon ingots, which are sliced to wafers in a process called wafering. Compositionally pure polycrystalline or monocrystalline silicon wafers are useful for photovoltaics. Dislocation-free and extremely flat single-crystal silicon wafers are required in the manufacture of computer chips.


Manufacturing of silicon metal

Metallurgical grade silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal in an electric arc furnace using carbon electrodes. At temperatures above 1900 °C (3,450 °F) carbon reduces silicon to silicon metal.

Less than 1 to 2% of the metallurgical grade silicon is transformed into high-purity silicon for electronics applications.


Manufacturing of high-purity silicon

Trichlorosilane is obtained by reacting anhydrous hydrochloric acid (HCl) with silicon metal powder (Si). The reaction either takes place in a fluidized bed reactor (conventional technology) or in a graphite block converter (more recent technology).

Hydrochloric acid is recovered from the chemical vapor deposition process (CVD). Anhydrous hydrochloric acid is usually obtained by passing hydrochloric gas through a 98+% sulfuric acid containing drying column. Powdered metallurgical grade silicon is reacted with anhydrous hydrochloric acid (HCl) at 300°C (572°F) in a fluidized bed reactor or graphite block converters to form trichlorosilane (SiHCl3).

During this reaction impurities react to form their halides (e.g. FeCl3). SiHCl3 has a low boiling point and distillation is used to separate it from the impurities.

Finally, the pure SiHCl3 is reacted with hydrogen at 1100°C for 200 to 300 hours to produce a very pure form of silicon. The reaction takes place inside large vacuum chambers. High-purity (10N to 11+N) polysilicon U-shaped rods of diameter 150 to 200 mm are produced with the Siemens process. Solar cells can tolerate higher levels of impurity than integrated circuit fabrication


GAB Neumann’s process equipment

Some processes used graphite blocks that look similar to large impervious graphite heat exchangers’ blocks. However, these graphite locks are not impregnated with phenolic resin. They are made of raw graphite. These blocks are stacked together to form a pile in the reactor. The size, shape and quantity of blocks may vary. GAB Neumann produces non-impregnated graphite blocks for high-purity silicon producers.

The production of high-purity silicon involves the use and processing (absorption, desorption, concentration) of large amounts of hydrochloric acid. GAB Neumann offers annular groove graphite heat exchangers, graphite block heat exchangers, graphite coolers, graphite heaters, graphite absorbers, graphite evaporators, and well as fractioning graphite columns to the high-purity silicon producers. GAB Neumann also offers hydrochloric acid recovery units and dry hydrochloric acid generation units to the high-purity silicon producers.


Associated products:

Impervious graphite annular groove interchangers

Impervious graphite annular groove heavy-duty condensers

Impervious graphite annular groove partial condensers

Impervious graphite block heat exchangers

Impervious graphite annular groove isothermal absorbers

Impervious graphite columns

Hydrochloric acid recovery units

GAB Neumann GmbH

Alemannenstrasse 29

79689 Maulburg


Tel: +49 (7622) 6751 0

Fax: +49 (7622) 6751 20

GAB Neumann GmbH | Alemannenstrasse 29 | D-79689 Maulburg | Phone +49 (7622) 6751 0 | Fax +49 (7622) 6751 20 | E-Mail |