Theoretical study of the gas-phase reaction of hexachlorodisilane by thermodynamic analysis and kinetics calculation

We conducted thermodynamic analysis and kinetics calculations for hexachlorodisilane (Si₂Cl₆), which is used as source gas for the CVD of silicon nitride films. Thermodynamic analysis clarified Si₂Cl₆ decomposes almost completely to SiCl₄ and SiCl₂ in the range of 600 °C–1100 °C under equilibrium condition. Therefore, it is estimated that the main gas-phase reaction of Si₂Cl₆ is represented by the reaction Si₂Cl₆ → SiCl₄ + SiCl₂. Thermodynamic analysis also shows that the Si₂Cl₆ system has a larger equilibrium partial pressure of SiCl₂ than SiH_xCl_4-x (x = 1 ~ 3) systems. Kinetics calculations revealed Si₂Cl₆ decomposes by 90% in 0.11 s at 600 °C, and 0.55 × 10⁻³ s at 800 °C, respectively. The time-dependent pyrolysis ratio of Si₂Cl₆ becomes larger as the total pressure decreases at 600 °C. On the other hand, the ratio is almost the same regardless of total pressure at 800 °C. These results will help optimize CVD process conditions using Si₂Cl₆.