Co-deposition of Silica, Alumina, and Aluminosilicates from Mixtures of CH3SiCl3, AlCl3, CO2, and H2. Thermodynamic Analysis and Experimental Kinetics Investigation

Abstract

The co-deposition of silica, alumina, and aluminosilicates from mixtures of methyltrichlorosilane, aluminum trichloride, carbon dioxide, and hydrogen was investigated in this study. In order to elucidate some aspects of the co-deposition process, the deposition of pure silica and pure alumina from mixtures of methyltrichlorosilane and aluminum trichloride, respectively, with CO 2 and H 2 was also investigated. Kinetic data were obtained by carrying out CVD experiments on SiC substrates in a hot-wall reactor of tubular geometry, which permitted continuous monitoring of the deposition rate through the use of a microbalance. Reaction rate data are presented for temperatures between 1073 and 1373 K (800±1100 C) at 13.3 kPa (100 torr) pressure for various feed compositions and various positions along the axis of the deposition reactor. Thermodynamic equilibrium computations were performed on the Al/Si/Cl/C/O/H, Al/Cl/C/O/H, and Si/Cl/C/O/H systems at the conditions used in the deposition experiments. The experimental observations are discussed in the context of the results of the equilibrium analysis and of past studies. Among the most interesting findings of this study is that the presence of AlCl 3 has a catalytic effect on the incorporation of silica in the deposit, leading to co-deposition rates that are a factor of 2±3 higher than the deposition rates that are obtained when only one of the two chlorides (CH 3 SiCl 3 or AlCl 3 ) is present in the feed.

Chemical Vapor Deposition of Aluminosilicates from Mixtures of SiCl[sub 4], AlCl[sub 3], CO[sub 2], and H[sub 2]

“…In a previous study, 22 we investigated the chemical vapor codeposition of SiO 2 , Al 2 O 3 , and aluminosilicates from mixtures of CH 3 SiCl 3 (methyltrichlorosilane, MTS), AlCl 3 , CO 2 , and H 2 . MTS was used as silicon source because preliminary experiments showed that the rates of deposition of silica and alumina from H 2 -CO 2 mixtures containing MTS and AlCl 3 , respectively, were of comparable magnitude for similar chloride concentrations, whereas mixtures of SiCl 4 , CO 2 , and H 2 gave much lower rates of deposition of silica.…”

Synthesis and characterization of rare earth‐doped silica nanoparticles for optimizing vapor phase doping technique

“…Here it is to be considered that in a typical MCVD system, residence time at hot zone is about 0.1 second which is sufficient enough for 100% conversion of SiCl 4 to SiO 2 at temperature above 1500°C. Moreover, co-deposition of silica and alumina lowers the conversion efficiency of AlCl 3 further as reported by Nitodas et al 28 31,32 Moreover, all the aluminosilicate phases convert to mullite and cristobalite in the temperature range of 1335-1625°C. 33 So, in this study possible crystal phases that can be present are a-Al 2 O 3 , cristobalite, and mullite.…”

“…Here it is to be considered that in a typical MCVD system, residence time at hot zone is about 0.1 second which is sufficient enough for 100% conversion of SiCl 4 to SiO 2 at temperature above 1500°C. Moreover, co‐deposition of silica and alumina lowers the conversion efficiency of AlCl 3 further as reported by Nitodas et al . Around 1100°C, conversion of AlCl 3 to Al 2 O 3 merely starts, whereas SiCl 4 almost completely converts to SiO 2 at this point.…”

Optimization of Chemical Vapor Deposition Parameters for Fabrication of Oxidation‐Resistant Mullite Coatings on Silicon Nitride

“…The increase resulted in the formation of a very Al 2 O 3rich mullite and has been described by other authors. 10,11 (…”

“…Nitodas and Sotirchos 10,11 report thermodynamic analysis and kinetics data for CVD of Al 2 O 3 , SiO 2 , and Al 2 O 3 -SiO 2 for CH 3 SiCl 3 (g), AlCl 3 (g), CO 2 (g), and H 2 (g) as the reactants. Their observation of suppressed Al 2 O 3 deposition during Al 2 O 3 -SiO 2 codeposition as the amount of CO 2 (g) increases is consistent with their thermodynamic calculations, which show a decrease in the concentration of aluminum-containing gaseous species as the amount of CO 2 (g) increases.…”