The method of producing ultrapure silicon from metallurgic silicon is based on the thermal decomposition of highly pure, rectified chlorosilanes or silanes to form silicon with the separation and recycling of gaseous byproducts. The conventional commercial technology passes through the stage of producing trichlorosilane in a fluidized-bed reactor from metallurgic grade silicon and hydrogen chloride. The trichlorosilane is then subjected to multi-stage rectification until the purity required for the desired application is reached (solar grade or electronic grade).

The thermal decomposition of trichlorosilane in a chemical vapor deposition (CVD) reactor to form silicon at 900 °C creates a mixture of gaseous by-products, which have to be prepared for recycling (vent gas recovery) back into the process. We have optimized the process for producing ultrapure silicon from monosilane. It now offers a significantly higher efficiency as temperatures are only around 600 °C, and the collection efficiency has been increased to almost 100% in comparison to the mere 25% achieved by conventional processes. Monosilane is obtained by the disproportionation of trichlorosilane and recirculation of the disproportionation products. Trichlorosilane is thus required in both methods.

The monosilane synthesis gas is stored temporarily in vacuum-insulated containers prior to further processing or filling. The containers are equipped with a pressure build-up vaporizer and an internal cooling coil to facilitate cooling. The containers are a special product of our subsidiary company, CRYOTEC, which specializes in special cryogenic applications.