Numerical simulation and design of superconducting cusp magnet for 400 mm Magnetic-field-applied Czochralski (MCZ) single crystal silicon growth

Abstract

Single crystal silicon is currently used for the production of chips and solar cells, commonly prepared using the Magnetic-field-applied Czochralski (MCZ) method. However, during the crystal growth process, the uneven heating distribution induces a strong thermal convection effect in the melt, which facilitates the doping of the crystal with oxygen impurities and affects the quality of the produced crystals. With the implementation of the cusp magnetic field method, the melt convection can be effectively suppressed. Two symmetrically placed superconducting coils generate a cusp magnetic field by passing currents in opposite directions. In this work, we selected a 42-inch crucible to prepare a single crystal silicon with a diameter of 400 mm. We systematically investigated the convective inhibition effect of the magnetic field by comparing the flow and temperature fields of the melt with and without the applied cusp magnetic field. To achieve a radial magnetic flux density (B_r) greater than 1000 G at the crucible wall, the parameters of the two superconducting coils were optimized. Based on the optimization results, we fabricated a YBCO high temperature superconducting (HTS) magnet with a coil inner radius of 900 mm and a coil spacing of 350 mm. The cooling structure and the tests were presented, which required 22 days to lower the coil’s temperature to 10.6 K. Finally, B_r at the crucible wall was measured, yielding a good consistency with the simulated values.