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

Abstract

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.

Decomposition of 1,1‐dimethyl‐1‐silacyclobutane on a tungsten filament—evidence of both ring CC and ring SiC bond cleavages

“…The temperature‐dependent evolution of the CH 3 radical on the W filament shows an Arrhenius behavior between 1500 and 2100 °C. The apparent activation energy for producing methyl radicals on the W filament can be derived from the linear fit of the natural logarithm of the methyl radical intensities against the inverse of filament temperature 17. The value is determined to be 61.0 ± 2.2 kJ/mol.…”

“…Recently, there has been an increasing interest in the investigation of alternative single‐source precursor gases to replace the conventionally used mixtures of separate Si‐ (silane or chlorosilanes) and C‐containing (various hydrocarbons) gases for silicon carbide thin film formation using chemical vapor deposition (CVD) 14–17. The significant ring strain energy in the four‐membered ring structure in SCB molecules18, 19 reduces the decomposition temperatures compared with those using open‐chain alkylsilanes 14, 15.…”

Effect of trimethylsilane pressure on hot-wire chemical vapor deposition chemistry using vacuum ultraviolet laser ionization mass spectrometry

“…This is clearly visible in Fig. To our knowledge, this is the first time methane formation has been confirmed when using either open-chain alkylsilanes 14,20,21 or four-membered-ring (di)silacyclobutanes 19,[23][24][25][26] as an independent precursor gas in the hot-wire CVD process. With 4.0 Torr of TriMS, new peaks at m/z 16, 28, 40, and 42 were observed.…”

“…[19][20][21] Briefly, a cylindrical hot-wire CVD reactor housing the heated W filament (99.9þ%, Aldrich, length ¼ 10 cm and diameter ¼ 0.5 mm) is incorporated via a pinhole (diameter ¼ 0.15 mm) to the main chamber with the TOF mass detector. This is the same technique used in our previous study.…”

Gas-phase diagnoses in catalytic chemical vapor deposition (hot-wire CVD) processes

“…In the decomposition of H 2 O, the production of OH and H is major at low catalyst temperatures, but H and O production becomes more dominant at high temperatures [37]. As for organosilicon compounds, selective and efficient decomposition is possible [51][52][53][54][55][56][57]. The decomposition paths are different from those in thermal decomposition.…”