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ARAS Measurements on the Thermal Decomposition of Silane

1993; Volume: 97; Issue: 6 Linguagem: Inglês

10.1002/bbpc.19930970608

0005-9021

H.J. Mick, V. N. Smirnov, P. Roth,

Diamond and Carbon-based Materials Research

Abstract In the present investigation the thermal dissociation of silane was measured behind reflected shock waves using the A tomic R esonance A bsorption S pectroscopy (ARAS) for detecting Si, H, and O atoms. The experiments were performed at temperatures 1250 K ≤ T ≤ 2115 K and pressures between 0.7 and 1.5 bar. Initial mixtures of 0.15 to 5 ppm SiH 4 diluted in Ar and 5 ppm SiH 4 with 500 ppm O 2 diluted in Ar were studied. The H atom measurements show formation rates, which are much less than the respective rates for Si atom formation. This indicates that the H atoms were formed by secondary reactions and are not primary dissociation products of silane or silylene. A reaction mechanism suitable to describe all measured H atom concentration profiles is given in this paper. Si atoms also measured during the silane thermal decomposition were found to be useful to understand the kinetics of this process. From the Si concentration profiles together with computer simulations rate coefficients for the reactions SiH 4 + M ⇋ SiH 2 + H 2 + M (1) SiH 2 + M ⇋ Si 2 + H 2 + M (2) were derived, which can be summarized by the following Arrhenis expressions: k 1 = 9.9×10 15 exp(−24000 K/ T ) cm 3 mol −1 s −1 k 2 = 9.1×10 13 exp(−15100 K/ T ) cm 3 mol −1 s −1 . In the case of the SiH 4 /O 2 /Ar mixtures no detectable Si atom concentrations were found, while the observed O atom formation rates were identical to that of Si atoms in mixtures without O 2 under comparable reaction conditions. This means that Si originating from the thermal decomposition of silane is directly converted into O by reaction with O 2 , i.e. O is in this system a measure of Si.