Effects of static magnetic fields on thermal fluctuations in the melt of industrial CZ-Si crystal growth

A series of 3D unsteady computations was performed to study the effects of different static magnetic fields on melt turbulence and thermal fluctuations in a 300 mm Czochralski (CZ)-Si crystal growth. We adopted the large-eddy-simulation (LES) technique with the dynamic sub-grid scale (SGS) model for body-fitted grids to investigate turbulent melt convection in an ellipsoidal crucible. Numerical comparisons were carried out for three configurations: without magnetic field, with a transverse magnetic field (TMF) and with a cusp-shaped magnetic field (CMF). Magnetohydrodynamic (MHD) effects were investigated to ascertain the instantaneous behavior and statistical features of melt turbulence. The presence of magnetic fields was found to effectively suppress thermal fluctuations in the crystallization zone. Due to different damping mechanisms for TMF and CMF, thermal fluctuations depicted different distributions in the melt. For the same characteristic magnetic field intensity, a CMF provides stronger suppression effect of thermal instabilities than for a TMF. Comparisons also revealed that each of these fields is distinct in the manner it affects the time-averaged temperature distributions and flow structures in the melt.

► Magnetic fields suppress the melt turbulence to a quite stable flow.
► Thermal fluctuations under a CMF are decreased by an order of magnitude.
► CMF offers stronger suppression of the thermal fluctuations than the TMF.
► TMF and CMF affect the time-averaged fields in distinct manners.