轴向磁场对多晶硅定向凝固过程中热流场的影响

Effect of Axial Magnetic Field on Thermal Flow Field of Polysilicon During Directional Solidification

采用Comsol 4.3a软件建立了轴向磁场作用下多晶硅定向凝固的二维轴对称模型,通过有限元方法将硅熔体中的电磁场、温度场和流速场进行了耦合数值计算。结果表明:当磁场线圈中心面位于熔体中心面下方60 mm处时,其磁场线高密度集中在熔体中心面下方强浮力对流区域,且均匀分布。此时硅熔体的最大流速为41μm/s,相比磁场线圈位于熔体中心面上方60 mm处的流速场减小了41.43%。随着磁场强度的增加,硅熔体中等温线越来越稀疏。与未施加磁场相比,轴向温度梯度减小了15 K/cm,硅熔体中的晶体生长速率增加。硅熔体温度梯度与晶体生长速率之比GL/Vs值变小会使得其结晶前沿界面产生组分过冷,导致细晶的生成,这方面有待于进一步的研究。

A two dimensional axisymmetric model of polysilieon during directional solidification under the axial magnetic field was established by Comsol 4.3a software. The electromagnetic field, temperature field and flow velocity field in silicon melt were coupled and numerically calculated by using finite element method. The results show that when the center plane of magnetic field coil is located in the center of melt surface below 60mm, magnetic field lines high-density are concentrated in strong buoyancy convection zone below the melt center plane, and distribution is uniform. The maximum velocity of the silicon melt is 41μm/s in this position. It is reduced by 41.43% compared with the velocity field of the field coil of 60mm above the melt central plane. With the increase of magnetic field intensity, the isotherm line in the silicon melt becomes sparser and sparser. The axia!temperature gradient is reduced by 15 K/cm and the crystal growth rate increases compared with no applied magnetic field. The value of GL/Vs changing smaller can make crystalline front interface produce constituent supercooling resulting in the fine-grain generation. This aspects need to be further studied.