Effects of magnetic intensity and crystal-crucible rotation direction on heat and oxygen transport during continuous Czochralski growth of an 8-inch diameter silicon crystal

Abstract

The effect of variations of temperature, flow, and oxygen distribution on the CCz growth of 8-inch diameter silicon crystals was numerically studied under a cusp magnetic field. As in the Cz growth process, the oxygen concentration at the crystal-melt interface is lower and more homogeneous when using the same rotation direction (iso-rotation) between the crystal and the crucible. In iso-rotation mode, the oxygen atoms released from the quartz wall are mainly transported to the inner free-melt surface by diffusion due to the weak melt speed in the inner melt. The strong outward flow of the melt beneath the growth interface caused by the fast crystal rotation may prevent oxygen diffusion into the ingot and is favorable for enhancing the evaporation of oxygen at the inner free-melt surface. The flow motion in the inner melt is much stronger in counter-rotation mode than in iso-rotation mode. This can alter the oxygen diffusion flux from the quartz wall to directly reach the growth interface. Therefore, the oxygen level along the crystal-melt interface will be higher than in the iso-rotation mode. When the magnetic intensity is high enough, the flow motion in the inner melt in the counter-rotation mode is significantly weakened, resulting in lower oxygen concentration at the growth interface. In iso-rotation mode, there is a significant increase in the effect of the outward melt flow beneath the growth interface as the magnetic field becomes stronger, which causes a notable decrease in the oxygen level.