Reaction Of SiH Research Articles

Neutral radical deposition from silane discharges

The fractional contributions of the various SiHn radicals (n=0–3) to deposition are calculated for low-power, pure-silane rf and dc discharges. This is done using a radical diffusion plus reaction equation, combined with current knowledge of SiH4 dissociation fractionation, of SiHn+SiH4 reactions, and of the distributed source of radicals. The conclusion reached is that more than 98% of neutral radical deposition is by SiH3 for typical deposition pressures (>100 mT at 240 °C). The effect of SiH3+SiH3 reactions at higher power is also evaluated using an estimated reaction rate coefficient (k3). The resulting loss in deposition rate is given as a function of film growth rate and of k3.

The reaction of SiH2 with no in the IR laser photochemistry of SiH4 - no mixtures

The effect of nitric oxide on the IR laser photochemistry of silane at 944.19 cm−1 has been studied in the pressure range 20 – 44 Torr and at ambient temperature. At nitric oxide concentration of less than 11% of the silane, there is a clear inhibition of disilane and trisilane formation because of reaction of silylene with the nitric oxide. A kinetic analysis of the retardation indicates that the rate constant for reaction of silylene with nitric oxide is comparable with that for reaction with silane. At nitric oxide concentrations in excess of 15% of silane, the reaction becomes explosively rapid, yielding as products only hydrogen and a brown powder.

ChemInform Abstract: Reaction of Silicon Ion (2P) with Silane (SiH4, SiD4). Heats of Formation of SiHn, SiH+ n (n = 1, 2, 3), and Si2H+ n (n = 0, 1, 2, 3). Remarkable Isotope Exchange Reaction Involving Four Hydrogen Shifts.

AbstractThe Si+/SiH4 reaction has been investigated as a function of relative kinetic energy by using a guided ion beam tandem mass spectrometer.

The SiH+(A 1Π–X 1Σ+) emission produced from the thermal energy reaction of He+ with SiH4 under single collision conditions

A flowing afterglow reactor has been coupled to a low-pressure chamber for an optical spectroscopic study of the charge–transfer reaction of He+ with SiH4 at thermal energy. The SiH+(A 1Π–X 1Σ+) emission was observed in the 380–610 nm region. The nascent vibrational and rotational distributions of SiH+(A) have been determined. The vibrational distribution for 0≤v′≤3 was approximately exponential with an effective vibrational temperature of 820±60 K. The rotational temperature decreased from 600 K for v′=0 to 300 K for v′=3. These data indicated that only about 3% of the excess energy is released as internal energy of SiH+(A). From the emission rate constant, SiH+(A) represents about 25% of the total SiH+ ion in the He++SiH4 reaction.

Characterization of plasma-deposited and dip-coated films for critical optical applications

Two types of coatings were evaluated with respect to their suitability for optical applications in which low scattering is required. The plasma-deposition technique produces dense pinhole-free films of refractory materials from a glow discharge plasma at typical substrate temperatures of 200-300 degrees C. Plasma-deposited films of SiO(2) and Si(3)N(4), produced from reactions of SiH(4) with N(2)O and NH(3), respectively, were evaluated in this study. SiO(2) films were also produced from metal-organic precursor solutions using dipping and spinning application techniques followed by pyrolysis at 600 degrees C. Coatings were deposited on the highest quality substrates available, which were characterized prior to deposition so that the effects of the coatings could be separated from those of the substrates. Nomarski microscopy, surface profiling, total integrated scattering, ellipsometry, and photon backscattering techniques were used for characterization. The properties of these coatings and information on how the quality depends on coating conditions are reported in this paper.

Superhyperfine interaction of the SiH3 radical with Xe

The SiH3 radical formed by the reaction of SiH4 with H in a Xe matrix was investigated by ESR spectroscopy. In addition to the spectra of the radicals SiH3 and SiH5 reported by the present authors [J. Chem. Phys. 83, 4504 (1985)], well resolved new lines were observed superimposed on a broad background signal. These lines were attributed to the superhyperfine structure of a species interacting with xenon nucleus. The magnetic parameters for the species which give rise to the superhyperfine structure were determined.

Chemiionization and chemiluminescence in the reaction of SiH4 with active nitrogen

The reaction of SiH4 with active nitrogen in a discharge-flow system was found to produce strong chemiionization besides the well-known SiN★ and Si★ chemiluminescences. In the presence of a large initial excess of N atoms, both N and SiH4 disappeared completely in the course of the reaction. Addition of as little O2 as 1013 cm−3 was sufficient to quench the chemiluminescence and suppress chemiionization completely. A mechanism explaining the experimental findings has to include a slow initiation step followed by a branched chain.

Direct determination of branching probability per chain unit in the reaction of SiH4 with Cl2 by pulsed photolysis time-resolved laser magnetic

Abstract A method to study chain branching reactions has been developed based on increasing the free-radical lifetime when approaching the self-ignition limit in the region of reaction mixture stability. The chain branching reaction of silane chlorination has been investigated by the method of pulsed photolysis and time-resolved LMR. The branching probability per chain unit is δ = (4.6 ± 0.6) × 10 −3 (±2σ) ( T = 298 ± 5 K, P Cl 2 = 560 Pa, P Si,H 4 = 0–28 Pa).

The Synchronous 1,4‐Addition of SiH2(1A1) to s‐cis‐buta‐1,3‐diene. A CI and CASSCF Study

AbstractA minimum energy path for the synchronous 1,4‐addition reaction of SiH2(1A1) with s‐cis‐buta‐l,3‐diene to 1‐silacyclopent‐3‐ene was determined by ab initio SCF and CI calculations. To analyse the changes of electronic structure along the reaction path CASSCF calculations and a population analysis were performed. From these and the geometrical variations it is concluded that the reaction is initiated by an electrophilic step involving the HOMO of butadiene and the empty p orbital of SiH2. Closed shell repulsions play a decisive role for the orientation of the SiH2 relative to the butadiene molecule. An activation energy of 17 kJ/mol is estimated and the exothermicity for the formation of the silacyclopentene is evaluated to be 283.82 kJ/mol. It follows from the CASSCF calculations that the activation barrier of the reaction is due to an avoided crossing between the ground and first excited singlet state of the composite system.

Reactions of SiH2(X1A1) with H2, CH4, C2H4, SiH4 and Si2H6 at 298 K

Reactions of SiH2(X1A1) with H2, CH4, C2H4, SiH4 and Si2H6 at 298 K

Reactions of SiH 2(X̄ 1A 1) with H 2, CH 4, C 2H 4, SiH 4 and Si 2H 6 at 298 K

Reaction rate constants of SiH 2(X̄ 1A 1) have been directly measured for the first time using the laser photolysis—laser-induced fluorescence method. The preparation of SiH 2 radical in the laser photolysis (193 nm) of phenylsilane and the concentration of the radical is demonstrated by a dye laser at 580.1 nm (X̄ 1A 1-Ā 1B 1). The reaction rate constants of SiH 2(X̄ 1A 1) with H 2, CH 4, C 2H 4, SiH 4 and Si 2H 6, are 0.001, 0.01, 0.97, 1.1 and 5.7×10 −10 cm 3 molecule −1 s −1, respectively. For SiH 2(Ā 1B 1(0.2,0)), the collision-free lifetime is 0.6 μs and the quenching rate constant for He is 3.8×10 −10 cm 3 molecule −1 s −1.

Free radicals formed by reaction of silane with hydrogen atoms in rare gas matrices at very low temperatures

The radicals formed by the reaction of SiH4 with H produced by the photolysis of HI in the matrices of Xe and Kr were investigated by electron spin resonance (ESR) spectroscopy at the temperatures between 4.2 and 100 K. The radicals observed were identified as SiH3 and SiH5. The newly observed radical SiH5 is considered as the intermediate of the reaction SiH4+H→SiH3+H2. The radical had two conformers; both were observed in a Xe matrix, while only one was observed in a Kr matrix. The ESR parameters of these radicals were determined by numerical deconvolution of the observed spectra. The hyperfine coupling of 29Si in silyl radicals isolated in Kr was determined accurately by the present method of the radical formation. The value obtained was 189.5 G instead of 266 G previously reported.

Theoretical investigations of elementary processes in the chemical vapor deposition of silicon from silane. Unimolecular decomposition of SiH4

The rates and mechanism for the unimolecular decomposition of SiH4 have been investigated using quasiclassical trajectory methods to follow the dynamics and Metropolis sampling procedures to average over the initial SiH4 phase space. The semiempirical potential-energy surface has been fitted to scaled SCF calculations and to a variety of experimental data. It gives the correct SiH4 equilibrium structure, reaction endothermicities, and bond energies for SiH4, SiH3, and SiH2. All hydrogen atoms are treated in an equivalent fashion. Excellent first-order decay plots are obtained for the microcanonical rates for the total SiH4 decomposition as well as for the separate decomposition channels. The low-energy pathway is found to be a three-center elimination to form SiH2+H2. The decomposition channel forming SiH3+H becomes important only at internal SiH4 energies in excess of 5.0 eV. Comparison of computed falloff curves with RRKM calculations fitted to experimental results indicates that the critical threshold energy for the three-center reaction lies in the range 2.10<E0<2.20 eV. The calculated high-pressure limiting rate coefficient is k(T,∞)=(1.08±0.02)×1013 exp(−49 600±1200/RT) s−1. The calculated distributions of relative translational energies for SiH2 and H2 reflect the fact that there is no barrier to the back reaction. Both concerted three-center eliminations and processes that resemble ‘‘half-collisions’’ of SiH3+H are found to be important decomposition pathways.

Thermal Reaction of Silane with Acetylene and The Thermal Decomposition of Ethynylsilane

The volatile products from the thermal reaction (414°C) of silane in excess acetylene are hydrogen, ethylene, vinylsilane, ethynylsilane, vinylethynylsilane (possibly divinylsilane) and ethynyl-divinylsilane (1,2). We have reexamined this reaction using a 3 C2 H2/1 SiH4 reaction mixture and have obtained product yield curves for these products versus percent silane loss. We have also found that product curves are unaffected when propylene at pressures equal to that of acetylene is also present. Since only trace quantities of propylsilane are produced in the presence of propylene, we can rule out reactions involving silyl radicals. Thus the SiH4−C2H2 reaction involves silylene and silene intermediates. The products can be explained by a mechanism similar to one proposed by Barton and Burns (3).

Collisional moderation by foreign gases in the reaction of SiH 3+ with C 2H 4

Collisional enhancement of the SiC 2H 7 + intensity in the reaction of SiH 3 + ions of 2.6 eV laboratory kinetic energy with C 2H 4 is due to moderation of the reactant-ion energy rather than removal of excess energy from the (SiC 2H 7 +)* collision complex. The effectiveness of (CD 3) 4Si, CH 4, CO 2, N 2, D 2 and Ar as kinetic energy moderators was studied at a constant C 2H 4 pressure of 2.5 × 10 −4 torr and at moderator pressures up to 5 × 10 −3 torr. The most important property determining moderator efficiency is molecular complexity, i.e. number of vibrational degrees of freedom. The moderator (CD 3) 4Si is not efficient, despite its large number of vibrational degrees of freedom, because it undergoes a rapid reaction with SiH 3 + to produce (CD 3) 3Si + ions.

Hg1−xCdxTe native oxide reduction by CVD SiO2

An interfacial reaction is shown to occur between the native oxide on Hg1−xCdxTe and a CVD SiO2 overlayer. Native oxides were grown by anodizing and coated with SiO2 by the reaction of SiH4 and O2 at 100 °C. The structure was analyzed by sputter-XPS profiling. The chemically split components of the Te(3d5/2) line indicate a much greater ratio of reduced to oxidized Te compared to the anodic oxide without SiO2. The reduced material is equivalent to roughly 15 Å of anodic oxide. Calculations indicate that reactions in which oxide compounds of Hg, Cd, and Te are reduced by SiH4, Si, and SiO are thermodynamically favored.

UV Laser-Initiated Formation of Si3N4

ABSTRACTSi3N4 films have been deposited on Si by using 193 nm ArF excimer laser radiation to initiate the reaction of SiH4 and NH3 at substrate temperatures between 200–600°C. Stoichiometric films having physical and optical properties comparable to those produced using low-pressure chemical vapor deposition (LPCVD) have been produced. The dielectric properties of the films are at present inferior to those of LPCVD material.

Kinetics and mechanism of the silane decomposition

AbstractThe homogeneous gas‐phase decomposition kinetics of silane has been investigated using the single‐pulse shock tube comparative rate technique (T = 1035–1184˚K, Ptotal ≈︁ 4000 Torr). The initial reaction of the decomposition SiH4 \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SiH}_{\rm 4} \mathop \to \limits^1 {\rm SiH}_{\rm 2} + {\rm H}_{\rm 2} $\end{document} SiH2 + H2 is a unimolecular process in its pressure fall‐off regime with experimental Arrhenius parameters of logk1 (sec−1) = 13.33 ± 0.28–52,700 ± 1400/2.303RT. The decomposition has also been studied at lower temperatures by conventional methods. The results confirm the total pressure effect, indicate a small but not negligible extent of induced reaction, and show that the decomposition is first order in silane at constant total pressures. RRKM‐pressure fall‐off calculations for four different transition‐state models are reported, and good agreement with all the data is obtained with a model whose high‐pressure parameters are logA1 (sec−1) = 15.5, E1(∞) = 56.9 kcal, and ΔE0±0(1) = 55.9 kcal. The mechanism of the decomposition is discussed, and it is concluded that hydrogen atoms are not involved. It is further suggested that silylene in the pure silane pyrolysis ultimately reacts with itself to give hydrogen: 2SiH2 → (Si2H4)* → (SiH3SiH)* → Si2H2 + H2. The mechanism of H ⟷ D exchange absorbed in the pyrolysis of SiD4‐hydrocarbon systems is also discussed.

ChemInform Abstract: REACTIONS OF SILANE WITH ZEOLITIC WATER

AbstractDie Modifizierungen von Na‐Y‐Zeolith und Na‐Mordenit durch Reaktion des zeolithischen Wassers mit SiH4 zu Siloxan‐artigen Produkten, die sich in den Kanälen abscheiden, werden untersucht.

Absolute rate constants for the reactions of O(3P) atoms and OH radicals with SiH4 over the temperature range of 297–438°K

AbstractAbsolute rate constants for the reaction of SiH4 with O(3P) atoms and OH radicals have been determined over the temperature range 297°–438°K using flash photolysis–NO2 chemiluminescence and flash photolysis–resonance fluorescence techniques, respectively. The Arrhenius expressions obtained are where the error limits in the Arrhenius activation energies are the estimated overall error limits. Rate data for the reactions of SiH4, CH4, and H2S with O(3P), H, and F atoms and with OH, CH3, and CF3 radicals are compared, showing that H2S and SiH4, which have similar bond energies, have reasonably similar reactivities toward these atoms and radicals.