Equilibrium Deposition Rate of Silicon in Si-I2 and Si-H2-Cl2 Systems

Abstract

The thermodynamic equilibrium deposition rates of silicon in Si-I2 and Si-H2-Cl2 systems were analyzed. These rates are discussed in terms of their applicability in industrial processes of Si purification. The behavior of silicon deposition for silicon tetraiodide (SiI4), silicon di-iodide and whole spectrum of Silicon-Hydrogen-Chlorine compounds were evaluated within a wide range of pressures and temperatures. A strong agreement between the theoretical model predictions and the experimental data was found for the SiI4 compound. Alternatives to the Herrick-Krieble's approximation for experimental SiI4 decomposition rates have been proposed for the actual operating pressures. The di-iodine technology has been analyzed in terms of its deficient SiI2 formation at 1200°C and the subsequent Si deposition and SiI4 formation at 800–900°C. An original approach was created to analyze the theoretical results for the Si-H2-Cl2 system using quasi-binary system coordinates: SiH4-SiCl4. The analysis of the results shows that the silicon deposition rate is independent of the temperature and the pressure. Such independence assumes that one, single mechanism governs the decomposition reaction for the (Si-H2-Cl2) system. It was concluded that a homogeneous nucleation is taking place for all Silicon-Hydrogen-Chlorine compounds within a temperature of 800–1400°C and a pressure of 1–100 atm.