Silane decomposition

Mass-spectrometric research on silane decomposition kinetics has been performed for flowing [298, 302-306] and static discharges [197, 307]. In a dc discharge of silane it is found that the reaction rate for the depletion of silane is a linear function of the dc current in the discharge, which allows one to determine a first-order reaction mechanism in electron density and temperature [302, 304]. For an RF discharge, similar results are found [303, 305]. Also, the depletion and production rates were found to be temperature-dependent [306]. Further, the depletion of silane and the production of disilane and trisilane are found to depend on the dwell time in the reactor [298]. The increase of di- and trisilane concentration at short dwell times (<0.5 s) corresponds to the decrease of silane concentration. At long dwell times, the decomposition of di- and trisilane produces... 

Following the determination of the geometry and the thermochemistry of transition states, the rate parameters for the two silane decomposition pathways can be obtained directly by the TST formulation presented earlier. These calculations have led to unimolecular rate constant expressions 10 exp(-91000/RT)s-S and 10 exp(-62000/l r)s" for Si-H bond scission and H2 elimination reactions, respectively. These results clearly... 

The flux summary within the boxes in Fig. 17.2 shows the mass flux (g/cm2-s) of both the silane and silylene to the surface, resulting in deposition of silicon and release of volatile hydrogen. At low temperature, the film growth is primarily from silane, although it is quite low. By Ts = 925 K, there is sufficient silane decomposition that the surface fluxes of the two species are becoming comparable. At Ts = 1300 K, the silylene flux is dominant, carrying most of the silicon to the surface. 

Radio frequency diode reactor Silane decomposition Well mixed Mean electron density and energy 70... 

Cylindrical tube with ring electrodes Silane decomposition and dispersion Plug flow with axial dispersion Mean electron density measured with interferometry 71... 

FIGURE 7S Silane decomposition versus time at various temperatures based on Col-trin s mechanism [26]. From Sawano [18]. 

Thermal Properties, Silanes have less thermal stabflity than hydrocarbon analogues. The C—H bond eneigy in methane is 414 kj / mol (98.9 kcal/mol) the Si—H bond energy in silane is 3781 /mol (90.3 kcal/mol) (10). Silane, however, is one of the most thermally stable inoiganic silanes. Decomposition occurs at 500 0 in the absence of catalytic surfaces, at 300°C in glass vessels, and at 180°C in the presence of charcoal (11). Disilanes and other members of the binary series are less stable. Halogen-substituted silanes are subject to disproportionation reactions at higher temperatures (12). 

An important point is that the micro- and nanopowders consisting of pyramidal crystallites (prepared by grinding silicon waste from semiconductor manufacturing) and single-crystal Si are identical in the temperature variation of the silicon oxide growth rate. At the same time, the nanopowders prepared via silane decomposition in an rf plasma and the micropowders consisting of spherical crystallites differ markedly in the temperature variation of the oxidation rate. The nanopowders are less sensitive to the oxidation temperature. 

The crystalline properties of silicon, silicon nitride, and silicon carbide nanoparticles produced in a laboratory aerosol reactor were measured by Cannon et al. (1982). Particles were produced using a COi laser to irradiate aerosol precursor gases. For example, silane (SiHj) u.sed to produce silicon particles could be healed adiabatically to the reaction temperature as long as the gas pressure wa.s maintained above 0,05 atm. At lower pressures, beat conduction to the cell walls balanced the heat absorbed by the gases, Silicon particles were generated at about 100() C by silane decomposition ... 

Laser-induced silane decomposition Deposition Mesoporous Voigt et al. (2005) 2005... 

More detailed discussion regarding the model performance is given by Wen and Fan (1975) and Mori and Wen (1975). The literature-reported applications of this model include a combustion study of coal with limestone injection by Horio and Wen (1975), a coal gasification study by Mori et al. (1983), a study on catalytic oxidation of benzene by Jafffes et al. (1983), a catalytic ammoxidation of propylent by Stergiou and Laguerie (1983), a silane decomposition study by Li et al. (1989), a catalytic oxidation of methane by Mleczko et al. (1992), and a study on chlorination of rutile by Zhou and Sohn (1996). 

Li KY, Peng SH, Ho TC. Prediction of silicon powder elu-triation in a fluidized bed reactor for the silane decomposition reaction. AIChE Symp Ser 85(270) 77-82, 1989. 

---