Homogeneous and Heterogeneous Chemistry Models of the Codeposition of Silica, Alumina, and Aluminosilicates

Abstract

The chemical vapor codeposition ͑CVD͒ of silica, alumina, and aluminosilicates from mixtures of silicon tetrachloride or methyltrichlorosilane ͑MTS͒, aluminum trichloride, carbon dioxide, and hydrogen is addressed, and detailed homogeneous and surface reaction mechanisms that describe the chemistry of the codeposition process are formulated. Information obtained from the thermodynamic analysis of the equilibrium of the gas phase and from past experimental and theoretical studies is employed to determine which elementary reaction steps play an important role in the deposition process. Homogeneous and heterogeneous chemistry models that were formulated in past studies by us for the deposition of silica and the deposition of alumina from mixtures of chlorosilane ͑silicon tetrachloride or MTS͒ and aluminum trichloride, respectively, in carbon dioxide and hydrogen are used as submodels in the codeposition mechanism. Experimental data obtained in a hot-wall, CVD reactor in our laboratory are used to validate the predictions of the codeposition model. A comprehensive study of the effect of the operating conditions ͑e.g., temperature͒ and residence time on the variation of the gas-phase composition, surface species coverages, and deposition rate is conducted in the range of conditions employed in the experiments. The model is found to be capable of predicting most of the behavior patterns observed in the experiments, including those of the enhancement of the deposition rate of silica in the presence of AlCl 3 in the feed, the suppression of the incorporation rate of alumina in the deposit in the presence of silane species in the feed, and the higher rate of codeposition and deposition rate of silica from MTS.A comprehensive investigation of the chemical vapor codeposition ͑CVD͒ of SiO 2 , Al 2 O 3 , and aluminosilicate films from mixtures of SiCl 4 or CH 3 SiCl 3 ͑MTS͒ and AlCl 3 in CO 2 and H 2 was carried out in two previous studies. 1,2 In order to obtain reference data for the deposition of the simple oxides ͑silica and alumina͒ under comparable conditions, the deposition of pure silicon oxide and pure aluminum oxide from mixtures of silicon tetrachloride or methyltrichlorosilane and aluminum trichloride, respectively, with carbon dioxide and hydrogen was also studied in Ref. 1 and 2. The experiments revealed that the codeposition process exhibited deposition rates that were not only higher than those of the single oxides (SiO 2 and Al 2 O 3 ) in independent experiments in which only one of the two chlorides was present in the feed at the same concentration as in the mixture, but also larger than their sum by a factor that could in some cases be as large as one order of magnitude.The enhancement of the codeposition rate was taken as an indication of the existence of additional heterogeneous reaction steps that involve both silicon-and aluminum-bearing species. These steps lead to formation of solid product at rates that are greater than those of the surface reactions that generate the simple oxides in the independent...

Protection of Lithium Metal Surfaces Using Chlorosilanes

“…Our efforts at protecting and controlling the lithium surface chemistry have focused on using chemistry different from that typically employed for lithium metal. Chlorosilanes have been used for years as a means to add functional groups to the surface of silica, − and it is well-known that the chlorosilanes react with OH surface groups to form a siloxane bond and evolve HCl. , This chemistry has also been used as a means for functionalizing alumina, ,, titania, , and indium phosphide surfaces, , but to the best of our knowledge it has never been used to functionalize lithium.…”

“…Chlorosilanes have been used for years as a means to add functional groups to the surface of silica, [32][33][34][35][36][37][38] and it is well-known that the chlorosilanes react with OH surface groups to form a siloxane bond and evolve HCl. 39,40 This chemistry has also been used as a means for functionalizing alumina, 34,41,42 titania, 43,44 and indium phosphide surfaces, 45,46 but to the best of our knowledge it has never been used to functionalize lithium.…”

Multi-scale modeling of chemical vapor deposition processes for thin film technology

“…Such models have been made for CVD of e.g. epitaxial silicon [22], B-doped silicon [103], silicon-dioxide [104], silicon-carbide [24,105], cadmium-telluride [106], gallium-arsenide [107,108], silicon-germanium [109], TiSi 2 [110], aluminosilicates [111], tungsten [32,112], carbon [113], and diamond [30,114]. To an increasing extent, theoretical and computational chemistry tools are being used to determine reaction pathways and kinetics, both in the gas and at the surface [103,[115][116][117][118][119].…”

Deposition of Compositionally Graded Mullite/Alumina Coatings from Mixtures of SiCl4, AlCl3, CO2 and H2

“…For the specific problem considered in this study, we recently developed a mathematical model that involves detailed kinetic models for the gas phase and surface reactions. [24] 5. Experimental CVD experiments were carried out in a vertical hot-wall reactor, made of quartz, with an internal diameter of 15 mm.…”