CHLORINE AND OXYGEN INHIBITION EFFECTS IN THE DEPOSITION OF SIC-BASED CERAMICS FROM THE SI-C-H-CL SYSTEM

The inhibitory role of HCl and oxygen in the chemical vapour deposition of SiC-based ceramics from the Si-C-H-CI system, is pointed out in terms of nucleation and growth process on the basis of experimental and theoretical approaches. The addition of HCl to methyltrichlorosilane MTS-H-2 gaseous precursors (i) decreases the nucleation and growth rate, (ii) induces a transition from a diffusion to a reaction rate control of the deposition process, (iii) improves the smoothness of the films surface, (iv) results in a transition from anisotropic films with columnar microstructure and Si, C and O concentration gradients to nanocrystallized materials with quite constant Si, C and O contents. These behaviours are tentatively explained by assessments of the gas phase supersaturation and calculations of the chemisorbed layer composition. The occurrence of oxygen within the nanocrystallized films is then related to the growth inhibition effect and the presence of silicon excess shown by EELS analyses.