Decomposition of hexamethyldisilane on a hot tungsten filament and gas-phase reactions in a hot-wire chemical vapor deposition reactor

摘要

To study the effect of an Si-Si bond on gas-phase reaction chemistry in the hot-wire chemical vapor deposition(HWCVD)process with a single source alkylsilane molecule,soft ionization with a vacuum ultraviolet wavelength of 118 nm was used with time-of-flight mass spectrometry to examine the products from the primary decomposition of hexamethyldisilane(HMDS)on a heated tungsten(W)filament and from secondary gas-phase reactions in a HWCVD reactor.It is found that both Si-Si and Si-C bonds break when HMDS decomposes on the W filament.The dominance of the breakage of Si-Si over Si-C bond has been demonstrated.In the reactor,the abstraction of methyl and H atom,respectively,from the abundant HMDS molecules by the dominant primary trimethylsilyl radicals produces tetramethylsilane(TMS)and trimethylsilane(TriMS).Along with TMS and TriMS,various other alkyl-substituted silanes(m/z=160,204,262)and silyl-substituted alkanes(m/z=218,276,290)are also formed from radical combination reactions.With HMDS,an increasing number of Si-Si bonds are found in the gas-phase reaction products aside from the Si-C bond which has been shown to be the major bond connection in the products when TMS is used in the same reactor.Three methyl-substituted 1,3-disilacyclobutane species(m/z-116,130,144)are present in the reactor with HMDS,suggesting a more active involvement from the reactive silene intermediates.