Thermal decomposition of tetrabromosilane and deposition of crystalline silicon

Pyrolysis of tetrabromosilane (SiBr4) was carried out by passing vaporized SiBr4 with hydrogen over a substrate heated to less than 1000 °C. The substrate was then placed in a reaction furnace equipped with a flow system and the exhaust gas containing the reactants and products was analyzed versus temperature. SiBr4 began to decompose at 800 °C simultaneously with the evolution of tribromosilane (SiHBr3), which was followed by the deposition of silicon in a crystalline form. The conversion of SiBr4 increased with increasing reaction temperature. No reaction occurred in the absence of H2. An experiment with tetrachlorosilane (SiCl4) under the similar conditions led to a decrease in SiCl4 concentration at temperatures greater than 900 °C. This demonstrates that decomposition of SiBr4 is energetically favorable compared to that of SiCl4, as predicted from the Ellingham diagrams for the reactions of Br- and Cl-containing species. Thus, Si production from bromosilanes is an alternative to the process using SiHCl3, the so-called Siemens method, which is the main technology for Si production currently.