Correlations between gas phase supersaturation, nucleation process and physico-chemical characteristics of silicon carbide deposited from Si-C-H-Cl system on silica substrates

International audienceIn the CH3SiCl3-H2 CVD system, from which SiC-based films are prepared, the supersaturation of the gas phase increases when temperature and total pressure decreases and when a diffusion-controlled kinetic process is changed in a reaction-controlled one. These conditions variations seem to induce a transition from a growth regime to a nucleation regime, as evidenced by a study of the initial stages of the deposition. A transition from a crystallized film with columnar crystals to a nanocrystalline deposit is also reported on the basis of accurate experiments using TEM and related techniques

Chlorine and oxygen inhibition effects in the deposition of SiC-based ceramics from the Si-C-H-Cl system

International audienceThe inhibitory role of HCl and oxygen in the chemical vapour deposition of SiC-based ceramics from the SiCHCl 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-H2 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 super saturation 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

Kinetic Processes in the CVD of SiC from CH3SiCl3-H2 in a Vertical Hot-Wall Reactor

The chemical vapour deposition of SiC-based ceramics from the CH3SiCl3-H2 precursor is investigated on the basis of large scale experimental and theoretical approaches. The use of a vetirtical cylindrical hot-wall LPCVD reactor permits to get a wide isothemal reaction zone with a creeping laminar flow around the substrate and a largely chemical control of the kinetics, which favours a high supersaturation and a nucleation regime. A calculation of the coverage of C (111) or Si(111) planes of SiC points out the importance of the chemisorption of SiCl3 and H radicals on C atoms and of CH3 and Cl radicals on Si atoms. On the basis of kinetic experiments and of chemical and structural investigations of the deposits, several domains of conditions are defined with different rnechanisms for the formation of SiC-based ceramics. For low temperatures and low pressures, a regime of growth of stoichiometric SiC microcrystals occurs from reaction of CH3 and SiCl3 intermediates. Higher pressures in the chemical control knetic domain, favour a regime of nucleation of nanocrystals with an excess of silicon resulting from SiCl3/SiCl2 silicon precursor