Kinetics of the Conversion of Silicon Tetrachloride into Trichlorosilane Obtained through the Temperature Control along a Plug-Flow Reactor

Abstract

A process for obtaining trichlorosilane (TCS or SiHCl3) from hydrogenation of silicon tetrachloride (STC or SiCl4) through control of the temperature along a one‐dimensional plug‐flow reactor at atmospheric pressure was simulated using a reaction model that was built based on a literature review: Rate coefficients for reactions that occur in silicon CVD processes were adopted from published data. A compact model made available recently in the literature for simulating reactions occurring in silicon chemical vapor deposition (CVD) reactors was used as a basis, and more reactions from other sources were added for better description of the thermal decomposition of STC. The kinetic model built in this work comprised 63 elementary reactions occurring among 26 species. This model was applied to the calculation of the species concentration profiles along the reactor, which was divided into two parts: a STC hydrogenation step, proceeding at a high and constant temperature in the first, and a cooling step, where the gases are brought to room temperature, in the second part. When the hydrogenation temperature was set to 1273 K or higher, the first step was just a stage where the gases reached chemical equilibrium. More interesting reactions occur in the second step, where cooling prevents reactions from reaching equilibrium. This leads to the production of TCS from SiCl2 and HCl, with efficiencies that depend on the conditions. Among the conditions investigated in this work, hydrogenation of a mixture of molar composition STC:H2 = 1:4 at 1473 K followed by cooling at a rate of −50.92 K cm–1 gave the highest conversion efficiency from STC into TCS.

Pressure dependence of rate coefficients of unimolecular and chemical activation reactions connected to the potential energy wells of chlorinated monosilanes by RRKM calculations

“…Based on an extensive literature survey, our group has already built a kinetic model that was able to reproduce experimental results related to the so-called "clean conversion" process, or the reaction of SiCl 4 with H 2 to produce SiHCl 3 (trichlorosilane or TCS) and HCl at atmospheric pressure. 3 Most of the elementary reactions in the model were obtained from models of gas-phase decomposition of TCS in CVD reactors available in the literature. 4,5 Many of the elementary reactions in this model are unimolecular decomposition or recombination reactions, so that their rate coefficients are expected to depend on pressure, but most of the rate coefficients that can be found in the literature are available only for the high-pressure limit.…”

“…Typical reactions that proceed from DCS decomposition include The above reactions may also occur when chlorosilanes other than DCS are employed as the source gas, because the intermediate species participating in the reactions above also form in processes starting from TCS, or even silicon tetrachloride (STC) if hydrogen molecules are present. 3 In this work, we analyze the pressure dependence of rate coefficients of unimolecular decomposition, recombination, and chemical activation reactions related to the potential wells of some Si 1 chlorinated silanes (SiHCl 3 , SiH 2 Cl 2 , SiH 3 Cl, and SiHCl 2 ) that are reactants or intermediates of interest in CVD processes. Detailed knowledge of the pressure dependence of the rate coefficients of these reactions is expected to be important for modeling accurately the gas-phase chemistry of CVD processes where a chlorinated silane is used as the source gas under low to atmospheric pressure conditions.…”

Pressure Dependence of Rate Coefficients for Formation and Dissociation of Pentachlorodisilane and Related Chemical Activation Reactions

“…For realizing faster and cheaper production of highquality solar-grade silicon, the chemical reactions taking place both at the gas phase and at the surface need first to be understood in detail. Much effort has been devoted for elucidating the reaction mechanisms involved in the gas phase of silicon CVD processes, and the rate coefficients of many elementary reactions have been made available [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]; recently, we compiled a reaction model comprising 63 elementary steps based on a survey of the literature, and the model was able to predict the variation of species concentrations along a plug-flow reactor designed to convert silicon tetrachloride into trichlorosilane, and predicted conversion efficiencies that agreed well with experimental results [20]. However, all rate coefficients for the numerous unimolecular reactions included in the model were for the high-pressure limit case, because too few sources of pressure-dependent rate coefficients were available.…”

“…The decomposition path of chlorosilanes through species containing two silicon atoms, proposed by Swihart and Carr and included in the reaction model mentioned above , may especially show strong pressure dependence, as reactions in this path necessarily involve recombination of smaller molecules in systems where monosilane or chloromonosilanes are used as precursors. Ran et al pointed out that this Si 2 path can be neglected at the high‐temperature conditions that are typical of CVD processes , but Ravasio et al did include it in their mechanism .…”

“…The simulation of a plug‐flow reactor at atmospheric pressure indicated that the formation of Si 2 HCl 5 through reaction (R1) and its subsequent decomposition through (R2) proceeded with significant reaction rates , and therefore the reactions above deserve a detailed analysis, to either confirm or refute their importance at atmospheric and lower pressure.…”