Silicon Chemistry in Fluorinated Chemical Vapor Deposition of Silicon Carbide

Abstract

The use of chlorinated chemical vapor deposition (CVD) chemistry for growth of homoepitaxial layers of silicon carbide (SiC) has diminished the problem of homogeneous gas-phase nucleation, mainly the formation of Si droplets, in CVD of SiC by replacing Si-Si bonds with stronger Si-Cl bonds. Employing the even stronger Si-F bond could potentially lead to an even more efficient CVD chemistry; however, fluorinated chemistry is very poorly understood for SiC CVD. Here, we present studies of the poorly understood fluorinated CVD chemistry for homoepitaxial SiC layers using SiF4 as Si precursor. We use a combination of experimental growth studies, thermal equilibrium calculations of gas-phase composition, and quantum chemical computations (i.e., hybrid density functional theory) of the surface chemistry to probe the silicon chemistry in the CVD process. We show that although growth rates on the order of 35 μm/h can be achieved with a fluorinated chemistry, the deposition chemistry is very sensitive to the mass flows of the precursors and not as robust as the chlorinated CVD chemistry, which routinely yields 100 μm/h over wide conditions. By using the position for the onset of epitaxial growth along the gas flow direction as a measurable, together with modeling, we conclude that SiF is the main Si growth species with SiHF as a minor Si species contributing to growth.