ARAS Measurements on the Thermal Decomposition of Silane

Abstract

In the present investigation the thermal dissociation of silane was measured behind reflected shock waves using the Atomic Resonance Absorption Spectroscopy (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 SiH4 diluted in Ar and 5 ppm SiH4 with 500 ppm O2 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 SiH4 + M ⇋ italick 1 SiH2 + H2 + M (1) SiH2 + M ⇋ italick 2 Si2 + H2 + M (2) were derived, which can be summarized by the following Arrhenis expressions: k1 = 9.9×1015exp(−24000 K/T) cm3mol−1 s−1 k2 = 9.1×1013exp(−15100 K/T) cm3mol−1 s−1. In the case of the SiH4/O2/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 O2 under comparable reaction conditions. This means that Si originating from the thermal decomposition of silane is directly converted into O by reaction with O2, i.e. O is in this system a measure of Si.

Thermochemistry and Kinetics of Silicon Hydride Cluster Formation during Thermal Decomposition of Silane

“…[1][2][3][4][5][6][7] There is also a substantial body of work on the kinetics of gas-phase reactions of small silicon hydrides. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] On the basis of this body of research, models of thermal CVD of silicon from silane can now predict film growth rates and precursor utilization with reasonable accuracy and reliability, at least under conditions where particle formation is negligible. However, understanding of the processes that lead to gas-phase particle nucleation is still quite limited, and models for nucleation and growth of particles in this system do not have the level of predictive capability that has been achieved in modeling film growth rates and gas-phase chemical composition.…”

High‐temperature kinetics of some Si‐ and Cl‐containing ceramic precursors

“…At temperatures T > 1500 K, Si 2 H 6 decomposes within a few microseconds, forming SiH 4 and SiH 2 , which subsequently dissociates into Si and H 2 [21]. SiH 4 highly diluted in Ar is known to produce instantaneously Si atoms at temperatures T ≥ 2000 K [22,23]. The upper temperature limit of T ≤ 2850 K was chosen such that only a maximum of 5% HCl was decomposed within the measurement time.…”

“…This was experimentally confirmed by Cl-absorption measurements which were analyzed using the simplified reaction mechanism of Table III. This reaction scheme contains decomposition reactions for HCl [27], Si 2 H 6 [21], and SiH 4 [22]. Again the SENKIN code [38] was used for modeling the concentration profiles.…”

Review of the potential of silanes as rocket/scramjet fuels

“…Nevertheless, intense research on the benefit of monosilane for scramjet combustion and examination of monosilane kinetics continued [29][30][31][32][33][34][35][36][37][38]. To some extent this is true also for disilane, again because of its interest to the semiconductor industry [39][40][41].…”