Characterization and Hazards of the Silicon-Based Polymers Produced in the Manufacture of Ultrapure Polysilicon

The process of making ultrapure polysilicon by the Siemens process results in an unwanted secondary reaction forming oligomers and polymers containing a silicon backbone. These byproducts accumulate in the exhaust piping and downstream equipment used in the polysilicon manufacturing process. They become extremely dangerous when exposed to moisture, including moisture contained in ambient air, becoming intensely flammable and shock-sensitive. This flammability is retained even in an inert atmosphere. Tragically, these byproducts were involved in the deadly explosion at the Yokkaichi Plant of Mitsubishi Materials Corporation in Japan. The work presented here characterizes these byproducts in their various states and provides insights into best practices for treating piping and equipment fouled by these materials. An example of the calculation of the energy released by ignition of these materials in an industrial piece of equipment is included.