Transient stages during the chemical vapour deposition of silicon carbide from CH3SiCl3/H2: impact on the physicochemical and interfacial properties of the coatings

International audienceTransient CVD experiments were produced from CH 3 SiCl 3 (MTS)/H 2 mixtures, by varying linearly as a function of time the deposition temperature or the initial gas flow rates (Q MTS or Q H2). The consequences on the composition of the gas phase, the deposition rates, and the physicochemical properties of the transient coating layers ( Tr) have been respectively examined by in situ FTIR, thermogravimetric analyses, Raman spectroscopy and TEM. Finally, the adhesion of SiC/ Tr /SiC bilayers, obtained using various transient stages, was investigated by scratch testing. For transient stages resulting from a decrease of Q MTS or T, crystallized or amorphous silicon can be co-deposited, due the higher reactivity of SiCl x radicals as compared to hydrocarbons. In this case, the continuous covalent bonding through the Si-rich interfacial layers preserves the strong adhesion between the two stoichiometric layers. Transient stages resulting from a decrease of Q H2 close to zero eventually lead to the co-deposition of anisotropic carbon, due to the formation of unsaturated hydrocarbons in the gas phase. The interfacial layers with the largest thicknesses and including a continuous anisotropic carbon interlayer lead to poor adhesion properties. Conversely, thin and discontinuous carbon-rich interfacial layers do not affect the interfacial properties significantly. Highlights Systematic investigations of various CVD transient stages: f(T or H 2 /CH 3 SiCl 3) Correlation between changes of CVD parameters and in situ gas phase composition Correlation between CVD parameters and deposition rate Correlation between CVD parameters and nature of the gradient Si-C coating