Letter: Thermal Decomposition of Methyltrichlorosilane, Dimethyldichlorosilane and Methyldichlorosilane by Flash Pyrolysis Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry

Abstract

The thermal decompositions of methyltrichlorosilane (MTS) (CH3SiCl3), dimethyldichlorosilane (Si(CH3)2Cl2), and methyldichlorosilane (SiHCH3Cl2) were studied at temperatures from -1000 K to 1500 K on a short timescale of 20 μs to 100 μs using flash pyrolysis vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry. The pyrolysis of MTS proceeds primarily via Si-C bond homolysis to form the SiCl3 and methyl radicals. At elevated temperatures, SiCl2 production from secondary decomposition of SiCl3 becomes more important, and other pyrolysis pathways of MTS, including C-H bond fission and HCl elimination make minor contributions. The pyrolysis of Si(CH3)2Cl2 occurs mainly by the sequential loss of methyl radicals, ultimately forming a significant amount of SiCl2. Si(CH3)2Cl2 also has two minor decomposition channels at higher temperatures, molecular elimination of CH4 to form SiCH2Cl2 and of CH3Cl to form SiCH3Cl. The pyrolysis of SiHCH3Cl2 mainly undergoes sequential CH3 and H loss and/or molecular elimination of CH4 to form SiCl2, while molecular elimination of HCl to form SiCH3Cl also contributes. SiCl2 is produced in significant concentrations in the pyrolysis of all three molecules, suggesting that it is an important intermediate in SiC chemical vapor deposition from chloroorganosilanes.

Microstructure and mechanical property of high growth rate SiC via continuous hot‐wire CVD

“…In this model, Ge et al's comprehensive kinetic mechanism is applied to analysis the rapid decomposition process of MTS in gas phase . Considering the short resident time of the reactants during this process, the most reactive intermediates, C 2 H 2 and SiCl 2 , are selected as primary reactants for surface reactions . In this case, the deposit composition is determined from the revised Hertz‐Knudsen equation:where γ i is the surface sticking coefficient of specie i , [ X i ] is the molar fraction of specie i with a molar mass M produced by MTS decomposition in gas phase, R is the molar gas constant and T is the reference deposition temperature.…”

“…49 Considering the short resident time of the reactants during this process, the most reactive intermediates, C 2 H 2 and SiCl 2 , are selected as primary reactants for surface reactions. [50][51][52] In this case, the deposit composition is determined from the revised Hertz-Knudsen equation:…”

Modeling of the elementary gas‐phase reaction during chemical vapor deposition of silicon carbide from CH3SiCl3/H2

“…Many techniques have been used to measure gas partial pressures in situ or ex situ and have been applied to study SiC-CVD from MTS/H 2 . 10,11,16,[23][24][25][26][27][28] Ganz et al employed coherent anti-Stokes Raman spectroscopy (CARS) to measure the partial pressures of 13 gases upstream and downstream of a reactor hot zone. 10 Chollon et al 11 and Jonas et al 23,24 employed Fourier transform infrared spectroscopy (FT-IR) to explore flow within a hot-walled tubular reactor, measuring the average concentrations of MTS and gaseous species generated from it over time.…”

“…16,26,27 Mousavipour et al calculated rate constants not by measuring the partial pressure of residual MTS, but rather via steady-state approximation (measures of the partial pressures of other products), 27 Lemieux and Zhang used flash pyrolysis vacuum-ultraviolet photoionization time-of-flight mass spectrometry to study gaseous radicals in a reactor in which MTS pyrolyzed into CH 3 and SiCl 3 radicals at temperatures above 907 • C and also into the CH 2 SiCl 3 radical at temperatures above 1077 • C. At > 1177 • C, the CH 2 Cl radical was also generated via secondary decomposition of MTS. 28 However, the principal deposition species forming SiC remains unclear. Thus, an accurate elementary reaction model is required to assess gas composition via chemical kinetic simulation.…”

“…Methyltrichlorosilane (CH 3 SiCl 3 , MTS) is used as the SiC‐CVD precursor because: (i) the MTS molecule contains the same number of Si and C atoms, (ii) MTS has a high vapor pressure (eg, 17 kPa at 25°C), 5 and (iii) MTS is a stable liquid at room temperature, facilitating injection via bubbling or effusion 5 . SiC‐CVD from MTS/H 2 has been extensively studied for more than 40 years 6–36 in terms of both the gas‐phase precursor and surface reactions 7–35 . The kinetics of SiC‐CVD using MTS/H 2 are key in terms of deposition control, obviating the need for a trial‐and‐error approach.…”