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

• Published in: Physical chemistry chemical physics : PCCP Vol. 10; no. 18; pp. 2543 - 2551
• Main Authors: YUJUN SHI, XINMAO LI, LING TONG, TOUKABRI, Rim, EUSTERGERLING, Brett
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2008
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Filament; Hydrocarbon; Reaction product; Single molecules; Ions; Transition metal; Decomposition; Chemical vapor deposition; Hot wire; Wavelength; Chemistry; Alkyl; Ionization; Tungsten; Alkane; Gas phase; Reactor; Mass spectrometry; Silane
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/b718743b

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.