REACTIONAL MECHANISMS OF THE CHEMICAL-VAPOR-DEPOSITION OF SIC-BASED CERAMICS FROM CH3SICL3/H-2 GAS PRECURSOR

The kinetics of SiC-based ceramics deposition from CH(3)SiCL(3) (MTS)/H-2 gas precursor has been investigated over a range of reduced pressure and low temperature, where kinetics are controlled by chemical reactions. Overall kinetic laws have been determined from the measurement of the apparent activation energy and the influence of MTS, H-2, CH4 and HCl. The kinetics of SIC deposition highly depends on both the dilution ratio alpha = P-H2/P-MTS and the total pressure. For 3 less than or equal to alpha less than or equal to 10 and T = 825 degrees C, the reaction order with respect to MTS equals 2. At T = 925 degrees C, it becomes nil in the low pressure range and 1 for P greater than or equal to 10 kPa, whereas at 825 and 925 degrees C, P-H2 has no influence on the growth rate. The apparent reaction orders are explained on the basis of a Langmuir-Hinshelwood model. The limiting step is evidenced as being HCl elimination by both Si-CI and C-H bonds breaking.