Vapor Pressure of Dichlorosilane, Trichlorosilane, and Tetrachlorosilane from 300 K to 420 K

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The method for the preparation of elemental silicon of sufficient purity for the fabrication of electronic devices is by first converting silicon oxide to silicon–hydrogen-chloride compounds, purifying the material as a fluid mixture, and then converting the product to solid silicon. During the purification process a mixture of dichlorosilane (SiH₂Cl₂), trichlorosilane (SiHCl₃), and tetrachlorosilane or silicon tetrachloride (SiCl₄) are formed with each of the components in significant quantities. Models that describe the vapor–liquid equilibrium behavior for the mixtures are required to design appropriate separation and purification processes. Pure fluid properties form the starting point for most mixture models, hence the importance of vapor pressures for the pure materials. In this work we report measurements of the vapor pressures for three of the most important fluids in the silicon production process, dichlorosilane, trichlorosilane, and tetrachlorosilane. Our results are compared with measurements reported previously. The instability of chlorosilanes complicates the experimental procedures because of the corrosive nature of the products formed, and in particular the potential for self-ignition upon exposure to moist air. The experimental procedures used to minimize the hazards and to avoid contamination of the fluids are described.