Active Oxidation of Liquid Silicon in the Presence of Hydrogen: Extension of the Ratto Model

The rate of oxidation of silicon has been studied in the presence of hydrogen, in order to predict the rate of boron removal from liquid silicon in liquid/gas processes where a chemical equilibrium exists at the surface. A new 1D model for the reactive boundary layer above liquid silicon has been developed from existing literature, adding two gaseous species H2 and H2O. The classical model (O2 only) gives a layer of silica aerosol just above the surface, for oxygen pressures above some pascals. Adding some hydrogen, this layer is displaced away from the silicon and vanishes if the hydrogen ratio is sufficient. We applied this model on liquid silicon oxidation experiments with theoretically predicted mass boundary layer thicknesses for impinging jets. The needed thickness to reproduce the experimental purification rate on our plasma process is compatible with our model.