Silicon float zone process with a weak transverse magnetic field and crystal rotation

This paper presents numerical calculations of the melt motion for a model of the float zone process with buoyant and thermocapillary convection, with rotation of the crystal and feed rod about their common vertical centerline, and with a uniform, steady, transverse magnetic field. With only buoyant and thermocapillary convection, there are two meridional circulations in which the radial flow adjacent to the crystal-melt interface is outward near the center and inward near the periphery. Adding crystal rotation or a transverse magnetic field decreases the magnitude of the buoyant and thermocapillary convection, but neither alone changes its pattern. Combining crystal rotation and a transverse magnetic field produces an axial variation in the centrifugal force due to the azimuthal melt velocity which overwhelms the radially inward convection and produces radially outward flow over the entire crystal-melt interface, and this pattern is desirable for both heat transfer and dopant transport. The magnetic field must be weak enough to produce negligible deviations from axisymmetry in the heat and mass transfer.