Decomposition of SiCl4 and deposition of Si in inductively coupled plasmas of H2+SiCl4

The mechanism of homogeneous reactions in plasmas of H₂+5%SiCl₄ was studied by mass spectrometry and was compared to the mechanism observed in plasmas of Ar+H₂+SiCl₄. Contrary to the behavior with Ar, the results indicate that without argon the SiCl₄ molecule undergoes only fragmentation and the deposition proceeds through SiCl₂. No polymerization was observed. The deposition rates of c-Si were lower and the amounts of chlorine incorporated in the films were higher in the plasma of SiCl₄+H₂ than in the argon-containing plasma.     

Nouvelles syntheses de Me2SiCl2 et Me3SiCl

Partial reduction of MeSiCl₃ and Me₂SiCl₂ using CaH₂ or (TiH₂)_n at high temperature (300°C) leads to MeSiHCl₂ and Me₂SiHCl, respectively, in good yields but in low proportion. In the presence of AlCl₃ as catalyst the reaction affords Me₂SiCl₂ and Me₃SiCl, in yields higher than those previously observed in the absence of a reducing agent. These redistribution reactions involve MeSiHCl₂ and Me₂SiHCl as intermediates. Consequently Me₂SiHCl with or without Me₂SiCl₂ and Alcl₃ deposited on carbon black as catalyst can undergo disproportionation to give Me₃SiCl.     

Electron ionization of SiCl4

Relative partial ionization cross sections (PICS) for the formation of fragment ions following electron ionization of SiCl(4), in the electron energy range 30-200 eV, have been determined using time-of-flight mass spectrometry coupled with an ion coincidence technique. By this method, the contributions to the yield of each fragment ion from dissociative single, double, and triple ionization, are distinguished. These yields are quantified in the form of relative precursor-specific PICS, which are reported here for the first time for SiCl(4). For the formation of singly charged ionic fragments, the low-energy maxima appearing in the PICS curves are due to contributions from single ionization involving predominantly indirect ionization processes, while contributions to the yields of these ions at higher electron energies are often dominated by dissociative double ionization. Our data, in the reduced form of relative PICS, are shown to be in good agreement with a previous determination of the PICS of SiCl(4). Only for the formation of doubly charged fragment ions are the current relative PICS values lower than those measured in a previous study, although both datasets agree within combined error limits. The relative PICS data presented here include the first quantitative measurements of the formation of Cl(2) (+) fragment ions and of the formation of ion pairs via dissociative double ionization. The peaks appearing in the 2D ion coincidence data are analyzed to provide further information concerning the mechanism and energetics of the charge-separating dissociations of SiCl(4) (2+). The lowest energy dicationic precursor state, leading to SiCl(3) (+) + Cl(+) formation, lies 27.4 ± 0.3 eV above the ground state of SiCl(4) and is in close agreement with a calculated value of the adiabatic double ionization energy (27.3 eV).     

Synthese der Silatetraphospholane (tBuP)4SiMe2, (tBuP)4SiCl2 und (tBuP)4Si(Cl)SiCl3 Molekül- und Kristallstruktur von (tBuP)4SiCl2

Synthesis of the Silatetraphospholanes (tBuP)₄SiMe₂, (tBuP)₄SiCl₂, and (tBuP)₄Si(Cl)SiCl₃ Molecular and Crystal Structure of (tBuP)₄SiCl₂ The reaction of the diphosphide K₂[(tBuP)₄] 7 with the halogenosilanes Me₂SiCl₂, SiCl₄ or Si₂Cl₆ in a molar ratio of 1:1 leads via a [4 + 1]-cyclocondensation reaction to the silatetraphospholanes (tBuP)₄SiMe₂ 1,1-dimethyl-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 1 , (tBuP)₄SiCl₂, 1,1-dichloro-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 2 , and (tBuP)₄Si(Cl)SiCl₃, 1-chloro-1-trichlorsilyl-1-sila-2,3,4,5-tetra-t-butyl-2,3,4,5-tetraphospholane, 3 , respectively, with the 5-membered P₄Si ring system. The reaction leading to 1 is accompanied with the formation of the by-product Me₂(Cl)-Si–(tBuP)₄–Si(Cl)Me₂ 1a (5:1), which has a chain structure. On warming to 100°C 1a decomposes to 1 and Me₂SiCl₂. The compounds 2 and 3 do not react further with an excess of 7 due to strong steric shielding of the ring Si atoms by the t-butyl groups. 1, 2 and 3 could be obtained in a pure form and characterized NMR spectroscopically; 2 was also characterized by a single crystal structure analysis. 1a was identified by NMR spectroscopy only.     

The Combustion of SiCl4 in Hot O2/H2 Flames

A simple kinetic model describing the molecular gas phase reactions during the formation of fumed silica (AEROSIL®) was developed. The focus was on the formation of molecular SiO₂, starting from SiCl₄, hydrogen and oxygen. Wherever available, kinetic and thermodynamic parameters were taken from the literature. All other parameters are based on quantum chemical calculations. From these data, an adiabatic model for the combustion reaction has been developed. It was found that a significant amount of molecular SiO₂ forms after about 0.1 and 0.6 ms at starting temperatures between 1000 and 2000 K. The initial reaction of the SiCl₄ combustion in a hydrogen/oxygen flame was found to be different from the combustion in air: The high reactivity of SiCl₄ towards water is favored over the SiCl₄ dissociation, which is the initial and rate‐determining step during the combustion of SiCl₄ in air.     

(CH3)3SiCl/SiCl4 azeotrope grows superhydrophobic nanofilaments

We describe the vapor-phase reaction (at room temperature and 40-45% relative humidity) of silicon wafers with the azeotropic mixture of trimethylchlorosilane and tetrachlorosilane. Water contact angle analysis indicates that surfaces become nearly perfectly hydrophobic (thetaA/thetaR > or =176 degrees/> or =176 degrees) after 2 min of reaction. SEM analysis at various reaction times shows the growth of nanofilaments with diameters of approximately 30 nm. X-ray photoelectron spectroscopy of oxidized titanium surfaces that were exposed to the azeotrope vapor indicates that the product is derived from a approximately 10:1 ratio of SiCl4 and (CH3)3SiCl. A mechanism for filament growth is proposed.     

H2SiCl2分子Si-H振动"基座"SiCl2的有效质量

用傅立叶变换光谱仪和激光腔内吸收光谱仪记录了H2SiCl2分子2000～9000和12000～12900 cm-1的红外吸收光谱.依据局域模理论的非谐性耦合非谐振子(ACAO)模型,分析并拟合了Si-H的对称伸缩振动和反对称伸缩振动,得到描述Si-H伸缩振动的Morse离解能De 、 Morse振子参数α和键振子势能耦合系数frr′.分析中忽略了SiCl2"基座"对Si-H伸缩振动的影响,拟合结果与实验值符合的很好,拟合方差小于 1 cm-1,表明这一近似是可取的.分析拟合结果表明, Si-H振动时"基座"SiCl2的有效质量为75.     

Interaction of SiCl2 with CO2 in Ar matrices

1. Download : Download high-res image (70KB)
2. Download : Download full-size image

     

Electron-impact ionization of silicon tetrachloride (SiCl4)

We measured absolute partial cross sections for the formation of various singly charged and doubly charged positive ions produced by electron impact on silicon tetrachloride (SiCl4) using two different experimental techniques, a time-of-flight mass spectrometer (TOF-MS) and a fast-neutral-beam apparatus. The energy range covered was from the threshold to 900 eV in the TOF-MS and to 200 eV in the fast-neutral-beam apparatus. The results obtained by the two different experimental techniques were found to agree very well (better than their combined margins of error). The SiCl3(+) fragment ion has the largest partial ionization cross section with a maximum value of slightly above 6x10(-20) m2 at about 100 eV. The cross sections for the formation of SiCl4(+), SiCl+, and Cl+ have maximum values around 4x10(-20) m2. Some of the cross-section curves exhibit an unusual energy dependence with a pronounced low-energy maximum at an energy around 30 eV followed by a broad second maximum at around 100 eV. This is similar to what has been observed by us earlier for another Cl-containing molecule, TiCl4 [R. Basner, M. Schmidt, V. Tamovsky, H. Deutsch, and K. Becker, Thin Solid Films 374 291 (2000)]. The maximum cross-section values for the formation of the doubly charged ions, with the exception of SiCl3(++), are 0.05x10(-20) m2 or less. The experimentally determined total single ionization cross section of SiCl4 is compared with the results of semiempirical calculations.     

Recovery of Trimethylchlorosilane from Its Azeotropic Mixture with SiCl4

Reaction of tetraethoxysilane with the azeotropic mixture Me₃SiCl-SiCl₄ in the presence of certain cyclic (tetrahydrofuran, dioxane) and acyclic (diethyl ether) ethers, ethanol, or dimethylformamide was studied with the aim of SiMe₃Cl recovery.     

Luminescent Nitridophosphates CaP2N4:Eu2+, SrP2N4:Eu2+, BaP2N4:Eu2+, and BaSr2P6N12:Eu2+

Nitridophosphates MP₂N₄:Eu²⁺ (M=Ca, Sr, Ba) and BaSr₂P₆N₁₂:Eu²⁺ have been synthesized at elevated pressures and 1100–1300 °C starting from the corresponding azides and P₃N₅ with EuCl₂ as dopant. Addition of NH₄Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single‐crystal X‐ray diffraction data (CaP₂N₄:Eu²⁺ (P6₃, no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) ų, Z=24, 2033 observed reflections, 176 refined parameters, wR₂=0.096). Upon excitation by UV light, luminescence due to parity‐allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition was observed in the orange (CaP₂N₄:Eu²⁺, λ_max=575 nm), green (SrP₂N₄:Eu²⁺, λ_max=529 nm), and blue regions of the visible spectrum (BaSr₂P₆N₁₂:Eu²⁺ and BaP₂N₄:Eu²⁺, λ_max=450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline‐earth ions. The corresponding full width at half maximum values (2240–2460 cm^?1) are comparable to those of other known Eu²⁺‐doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba₃P₅N₁₀Br:Eu²⁺, this investigation represents the first report on the luminescence of Eu²⁺‐doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu²⁺‐doped nitridophosphates may have the potential to be further developed into efficient light‐emitting diode phosphors.     

激光等离子体诱发SiCl4解离沉积硅膜的研究

硅是重要半导体材料之一,其薄膜广泛应用于集成电路和太阳能电池。但用普通方法制备纯硅需要很高温度,而利用激光便可在低温下进行。因此激光诱导化学气相沉积技术是改革集成电路工艺和制备太阳能电池的一种很有希望的方法。本文用SiCl_4代替通常使用的SiH_4,用TEA CO_2激光诱导SiCl_4解离气相沉积硅膜。