The Rohsilizium can be obtained in a further step, the trichlorosilane is the process called by many impurities are exempt. This effect is at a temperature of about 300 ° C, the binding of the silicon into trichlorosilane SiHCl3 whose boiling point at 32 ° C. The reaction is the reaction the following equation described:

Si + 3 HCl -> SiHCl3 + H2

The largest number is now associated with chlorine impurities evaporate only at a higher temperature than the trichlorosilane, so that by distillation at approximately 30 ° C as gas from the previously obtained material can be separated. However, the boiling point of the chlorine ties Dotierstoffe phosphorus, boron and carbon are very close at this temperature, so that these also be high parts as a gas leak. Their concentration is therefore usually not required under the border be pressed.

The following must finally trichlorosilane connection again, which is now in the reversal of the above-described reaction happens:

SiHCl3 + H2 -> Si + 3 HCl (running at temperatures above 1100 ° C.)

On thin silicon rods, called silicon souls brought into the feedstock gas mixture of hydrogen and trichlorosilane introduced and the reaction necessary for the temperature of 1100 ° C, then proposes the re-isolated silicon settled. Thus, the diameter of the rods to over 150 mm.

Especially since the Dotierstoffe boron and phosphorous remain in relatively high concentrations left behind, the resulting material is still not as a basis for electronic components.