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-C ₃H₆-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, H ₂:SiCl₄=10:1, and P_Total=0.01 atm. Taking the deposition of SiC into consideration, the deposition of Si₃N ₄ 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.