Thermodynamic calculations on the chemical vapor deposition of Si–C–N from the SiCl4–NH3–C3H6–H2–Ar system

Based on the Gibbs free energy minimum principle and Factsage software, the thermodynamic phase diagram for the SiCl4–NH3–C3H6–H2–Ar system was calculated. The effects of temperature, dilution ratio of H2, total pressure on product types and distribution regions of reacted solid products were discussed. The results show that: (1) The area of SiC–Si3N4 increases at first, then decreases with the rising of temperature and reaches the maximum value at 1273.15 K. (2) The ratio of C/Si is the main factor for the deposition of SiC in the double phase of SiC–Si3N4. (3) The preferred deposition conditions of Si3N4 are: T=1173.15 K, H2:SiCl4=10:1, and PTotal=0.01 atm. Taking the deposition of SiC into consideration, the deposition of Si3N4 influences the formation of Si–C–N directly. (4) According to the influencing factors of depositing SiC and Si3N4, the suitable parameter for Si–C–N deposition can be determined. (5) Through the experimental verification, it can be demonstrated that Si–C–N can be obtained by low-pressure chemical vapor deposition (CVD), its product being amorphous and mainly constituted by Si–N and Si–C bonds. The obtained Si–C–N ceramics can transform to α-Si3N4 and SiC nano-crystal when heat-treated at 1773.15 K in N2 for 2 h.