An advanced model taking into account formation of silicon clusters in the gas phase is employed for modeling analysis of CVD of SiC in commercial vertical rotating disc reactor. It has been found that two main parameters have significant influence on the nucleation and transport of the clusters in the gas phase: input flow rate of silane and the temperature gradient near the growing surface determining the thermophoretic force. The results of modeling the deposition are in good agreement with experimental data. The silicon-to-carbon ratio in the gas phase over the SiC wafer is analyzed.