In situ diagnostics of the decomposition of silacyclobutane on a hot filament by vacuum ultraviolet laser ionization mass spectrometry

Abstract

The gas-phase reaction products of silacyclobutane (SCB) and 1, 1-dideuterio-silacyclobutane (SCB-d(2)) from a hot-wire chemical vapor deposition (HWCVD) chamber were diagnosed in situ using vacuum ultraviolet (VUV) laser single-photon ionization (SPI) coupled with time-of-flight (TOF) mass spectrometry. The SCB molecule was found to decompose at a filament temperature as low as 900 degrees C. Both Si- (silylene, methylsilylene, and silene) and C-containing (ethene and propene) species were produced from the SCB decomposition on the filament. Ethene and propene were detected by the mass spectrometer. It is demonstrated that the formation of ethene is favored over that of propene. The experimental study of hot-wire decomposition of SCB-d(2) shows that propene is most likely produced by a process that is initiated by a 1,2-H(D) migration to form n-propylsilylene, followed by an equilibration with silacyclopropane, which then decomposes to propene. The detection of ethene in our experiment indicates that a competitive route of fragmentation exists for SCB decomposition on the filament. It has been shown that this competitive route occurs without H/D scrambling. The highly reactive silylene, silene, and methylsilylene species produced from SCB decomposition underwent either insertion reactions into the Si-H bonds of the parent molecule or pi-type addition reaction across the double and triple CC bonds. The dimerization product of silene, 1,3-disilacyclobutane, at m/z = 88 was also observed.

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

“…Maier et al [33] found that silene was stable only under argon matrix isolation at 10 K and it dimerized to 1,3-disilacyclobutane upon thawing of the matrix at 35 K. In a study of thermal decomposition of 1,1-dimethyl-1-silacyclobutane [34], although kinetic evidence supports the existence of an unstable intermediate, 1,1-dimethyl-1-silene, the only products detected are ethene and 1,1,3,3-tetramethyl-1,3-disilacyclobutane. 1,1-Dimethylsilene, an analog of silene, was found to undergo similar dimerization reactions to yield 1,1,3,3-tetramethyl-1,3-disilacyclobutane: (16) Our study of the hot wire decomposition of silacyclobutane [35] also showed that silene (H 2 Si CH 2 ) was produced, supported by the observation of its dimer signal, 1,3-disilacyclobutane. For the pyrolysis of TMS, 1,1,3,3-tetramethyl-1,3-disilacyclobutane (m/z = 144) [24,29] were previously observed as a product from the analysis by gas chromatography (GC) or GC-MS.…”

Application of laser induced electron impact ionization to the deposition chemistry in the hot-wire chemical vapor deposition process with SiH4-NH3 gas mixtures

“…A detailed description of the experimental setup using VUV SPI, including the ionization laser source, HWCVD reactor, and the TOF MS, has been reported previously [18,19,26]. Briefly, a HWCVD chamber is connected through a 0.15 mm diameter pinhole to the high-vacuum ionization chamber housing the TOF MS. A tungsten filament (0.5 mm diameter, 10 cm length) is placed in the HWCVD reactor and is resistively heated by a DC power supply.…”

“…Therefore, single-photon ionization (SPI) using 118 nm vacuum ultraviolet (VUV) laser radiation has proven to be a powerful technique for examining silane chemistry [6]. Our recent studies have shown that VUV SPI also works well with alkylsilane molecular systems in the HWCVD process [18,19]. However, many of the products predicted for the NH 3 and SiH 4 /NH 3 systems, notably H 2 and N 2 , have IPs greater than 10.5 eV.…”

Formation of aminosilanes in the hot-wire chemical vapor deposition process using SiH4-NH3 gas mixtures

“…20,21 In brief, a HWCVD reactor, housing a heated tungsten filament, is incorporated by way of a 0.15 mm diameter pinhole into a high-vacuum ionization chamber for the TOF mass spectrometer (R. M. Jordan Inc.). The total pressures in the reactor are maintained at ~ 12 Torr using a mass flow controller (MFC), while those in the ionization chamber are ~ 4.0 x 10 -6 Torr under working conditions.…”