Effect of HCl addition on gas-phase and surface reactions during homoepitaxial growth of SiC at low temperatures

摘要

A complex influence of HCl addition on gas-phase and surface reactions during the low-temperature halo-carbon homoepitaxial growth of 4H-SiC was investigated. The addition of HCl was employed to reduce the undesirable effects of homogeneous gas-phase nucleation leading to formation of silicon clusters in the gas phase. It was established that dissociation of silicon clusters by HCl is efficient even at untraditionally low homoepitaxial growth temperature below 1300℃. The information about the spatial distribution of this dissociation process along the gas flow direction was obtained. It was established that the influence of HCl is more complicated than the simple model suggesting that the enhanced dissociation of silicon clusters in the gas phase leads to an additional supply of silicon species for the epitaxial growth. While the growth rate does significantly increase at least for some HCl flow rates, complex changes in the effective silicon-to-carbon ratio in the growth zone of the reactor indicate that the supply of carbon species may also be enhanced at least at low HCl flow rates. This fact supports the hypothesis that the gas-phase clusters may contain a significant amount of carbon in addition to silicon. Also, the magnitude of the growth rate enhancement was found to be less significant than what was expected from the apparent degree of the cluster dissociation. Evidence of a new mechanism for precursors' depletion are provided. Pronounced changes in the pattern of the polycrystalline deposits at the upstream portion of the hot zone of the reactor were caused by the HCl addition. Premature dissociation of the gas-phase clusters and release of silicon may cause depletion of silicon by vigorous polycrystalline deposition. Depending on the kinetics of the process, the carbon species may also get depleted by the polycrystalline deposition mechanism. This mechanism partially reduces the benefits of the HCl addition unless its influence is minimized.