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

Abstract

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

Experimental study of the chemical vapor deposition from CH3SiHCl2/H2: Application to the synthesis of monolithic SiC tubes

“…for 1 < α < 4, a maximum of 930 µm/h can be achieved, which is high enough to synthesize both long and thick tubes in a relatively short period of time. After reaching this maximum, the deposition rate decreases at particularly low α values, as already observed for the CH 3 SiCl 3 /H 2 system [21]. Together with the increase of deposition rate, it is worthy of note that solid particles tend to grow from the gas phase beyond 1100°C and for low  values.…”

“…and HSiCl 2˙ radicals in the hot zone [21,[42][43][44]. This assumption was confirmed by the ab initio calculations of Allendorf et al [44].…”

“…A similar behavior was reported in several studies of the MTS/H 2 system in relatively similar T and P conditions. Papasouliotis et al and Huttinger et al indeed evidenced, for T = 1000 °C, a decrease of both the deposition rate and the silicon excess along the hot zone [21,[41][42]. The decreasing of the total flow rate also leads to a drop of the deposition rate (due to increase of the residence time) [41].…”

“…A decomposition route of the DCMS during the APCVD process can be tentatively proposed by the analysis of the above results and the previous conclusions from the literature. Zhang and Hüttinger [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] proposed a mechanism for the deposition of SiC at near atmospheric pressure from the MTS/H 2 mixture, as did Cagliostro et al for DCDMS [41]. As for MTS, the Si-C bond is probably readily dissociated into CH 3˙…”

“…Whatever the single source precursor [14,[16][17][18][19][20][21] used (CH 3 SiCl 3 , (CH 3 ) 2 SiCl 2 , CH 3 SiHCl 2 ), the key parameters in the deposition of SiC by CVD are the temperature, the total pressure, the global gas flow rate (or residence time) and the nature of the precursor dilution, characterized by the α ratio:…”