Mass spectrometric study of gas-phase chemistry in a hot-wire chemical vapor deposition reactor with tetramethylsilane

To understand the gas-phase chemistry in the processes of hot-wire chemical vapor deposition (HWCVD) with tetramethylsilane (TMS), the gas-phase products from the decomposition of TMS on a hot tungsten filament and the secondary gas-phase reactions in a HWCVD reactor have been studied using vacuum ultraviolet laser single photon ionization time-of-flight mass spectrometry. It is found that TMS decomposes on the filament to methyl and trimethylsilyl radicals. Subsequent reactions between these two primary radicals and with the parent molecule have resulted in the formation of alkyl-substituted silanes (m/z = 102, 116, 146) and silyl-substituted alkanes (m/z = 160, 174, 188, 232, 246). Small alkenes (CnH2n, n ≤ 4) are produced at high filament temperatures (T ≥ 1800 °C). The dominant pathways in the secondary gas-phase reactions are found to be the biradical combination reactions involving the alkylsilyl-substituted methyl radicals formed from the H abstraction reaction of either alkyl-substituted silane or silyl-substituted alkanes by methyl radicals. Silicon carbon (SiC) bond is found to be the major bond connection in the gas-phase reaction products in mass regions higher than the parent mass. 1,1,3,3-Tetramethyl-1,3-disilacyclobutane molecule (m/z = 144) is believed to be formed in the HWCVD reactor, implying the existence of the unsaturated silene intermediates.