Influence of temperature and residence time on thermal decomposition of monosilane

Thermal decomposition experiments with monosilane diluted in hydrogen have been conducted in a free-space reactor with an extendable reaction zone, allowing for easy variation of residence time. Reactor effluent was analyzed by gas-chromatography combined with mass-spectrometry (GC-MS). The applied analysis technique enables detection of silanes with up nine silicon atoms, as well as absolute quantification of the concentrations of mono-, di-, and trisilane. For all the detected silanes, our gas analyses show a peak in reactor outlet concentration as function of temperature whose position and shape depend on the number of silicon atoms (nSi) contained in the silane species. The peak width decreases and the peak position shifts to higher temperatures with increasing nSi. At increased residence time, the concentration peak shifts to lower temperatures and the SiH4 consumption rate increases. This is consistent with the expected behavior for a system described by Arrhenius kinetics. The maximum outlet concentrations of all the measured silanes decrease with increasing residence time. However, the dependence of silane concentrations on temperature and residence time is not trivial: At a fixed temperature the measured outlet concentrations will increase with increasing residence time in some temperature regions and decrease with residence time in other temperature regions. By mapping outlet concentrations as function of temperature and residence time we attempt to decouple the effect of these two parameters and to untangle their effect from that of reactor geometry and operation.