Cold Conversion

Poly Plant Project (PPP) provides customized process technology in the form of modular packages and complete plant solutions using our advanced and proven process designs. Our solutions are based on decades of polysilicon production plant engineering and operational experience at highly efficient, world-class plants.

PPP’s experience at multiple polysilicon production plants has enabled our team to develop advanced process technology packages based on proven processes and equipment. This experience ensures the safe, efficient, and reliable production of polysilicon materials as well as the production, recycling and storage of gases and liquids in the plant.

PPP offers two process technologies for production of TCS; an advanced Cold Conversion process, and an advanced hydrochlorination process. PPP’s Cold Conversion process is detailed on this page while the information on PPP’s advanced hydrochlorination process is here.

Trichlorosilane Production Using Cold Conversion

The process for TCS Production involves the chemical reaction of metallurgical grade silicon (MGSi) with STC and Hydrogen. This reaction was studied by the Massachusetts Institute of Technology (MIT) in 1980. Patents have been issued for variations of this process to Mitsubishi Metals, Osaka Titanium, Shin-Etsu Chemical, and Union Carbide Corporation. Union Carbide was the first to develop this in production volumes, using hydrogenation to form TCS, which then produced silane. The chemical reaction is MGSi with STC in an excess hydrogen atmosphere. Throughout the years this process has been referred to as hydrogenation. Note that some in the market are erroneously referring to this process as hydrochlorination.

PPP calls this hydrogenation process the Cold Conversion Process, because STC is converted to TCS at a lower temperature than in the thermal conversion process. In the Cold Conversion Process, STC and hydrogen react with MGSi according to the following endothermic chemical reaction:

MGSi + 2 H₂ + 3 SiCl₄   →   4 HSiCl₃

The largest advantage of the Cold Conversion Process, is the use of STC as the chlorine source for the production of TCS. STC is produced in large quantities as a co-product in TCS production, and as a co-product in polysilicon deposition. In addition, the STC and other chlorosilanes produced in this reaction are collected and recycled back to the Cold Conversion Reactor. Unreacted hydrogen from the process is collected and recycled back to the Cold Conversion Reactor.

Advantages of the Cold Conversion Process include:

• A completely closed loop process, since chlorosilanes and hydrogen are recycled
• Use of easily available STC as the chlorine source
• More reliable control of the endothermic reaction
• In production since 1984 demonstrating reliability
• Used by four current polysilicon suppliers
• Low capital cost
• Low electrical consumption