多场耦合下定向凝固法制备多晶硅的数值模拟

发布时间：2018-11-28 10:10

【摘要】：太阳能是一种清洁的可再生能源,是解决未来能源危机的理想选择。目前,多晶硅太阳电池具有生产工艺简单,成本低廉等优点而被广泛使用。然而,多晶硅的定向凝固是多物理场耦合作用下一个复杂的晶体生长过程。在实际生产过程中,难以精确的掌握硅熔体中各个物理场的变化规律。随着计算机数值模拟技术的发展,模拟仿真方法成为了一种直观了解晶体生长的有效手段。本工作借助Comsol Multiphysics 4.3 a多物理场仿真软件对多晶硅晶体生长的过程进行了数值模拟,并获得了硅熔体的热场、流场、磁场、应力场的分布规律,为探索多晶硅定向生长提供了一种新的途径。本文采用热场和流场或应力场耦合研究了多晶硅定向凝固炉内的坩埚和冷却平台组合结构以及加热器分布对硅熔体热场和流场的影响,并分析了坩埚形状、坩埚倒角半径和晶体内温度梯度对硅晶体内热场和应力场的影响规律。采用倒锥形坩埚有利于减小多晶硅铸锭中的热应力。随着坩埚倒角半径的增加,晶体中的热应力值下降幅度逐渐减小。当硅晶体中温度梯度增加时,晶体中的热应力平均值增加幅度逐渐降低。运用热场、流场和磁场耦合研究了多晶硅晶体定向生长的过程,重点分析了不同磁场结构、不同磁场分布和不同磁场强度作用下多晶硅定向凝固工艺参数的变化情况。当磁场线圈与硅熔体中心面的距离由60mm减小到-60mm时,硅熔体的最大流速由70μm/s减小到了41μm/s,相比减小了41.43%。当磁场线圈保持在硅熔体中心面下方60mm处,磁场强度逐渐由0T逐渐增加到0.8T时,硅熔体的轴向温度梯度最大降幅为15K/cm。另外,通过建立二维轴对称瞬态模型,揭示了多物理场作用下多晶硅结晶阶段三个时期(初期、中期、后期)的流场变化规律。在多晶硅结晶阶段施加0T到1T的变化磁场时,硅熔体的流速峰值由结晶初期的51.644μm/s减小到了后期的21.074μm/s,而且其三个时期的平均流速在多场耦合作用下分别减小了42.11%、58.59%、45.16%。以上模拟结果表明,数值模拟技术对多晶硅实际生产具有重要的理论指导意义。
[Abstract]:Solar energy is a kind of clean renewable energy, which is the ideal choice to solve the future energy crisis. At present, polysilicon solar cells are widely used because of their simple production process and low cost. However, the directional solidification of polysilicon is a complex crystal growth process under the coupling of multiple physical fields. In the actual production process, it is difficult to accurately grasp the changes of each physical field in silicon melt. With the development of computer numerical simulation technology, simulation method has become an effective method to directly understand crystal growth. In this work, the growth process of polycrystalline silicon crystal is numerically simulated with the help of Comsol Multiphysics 4.3a multi-physical field simulation software, and the distribution of thermal field, flow field, magnetic field and stress field of silicon melt is obtained. It provides a new way to explore the directional growth of polysilicon. In this paper, the combined structure of crucible and cooling platform in polysilicon directional solidification furnace and the influence of heater distribution on the thermal field and flow field of silicon melt are studied by means of the coupling of heat field and flow field or stress field, and the shape of the crucible is analyzed. The influence of crucible chamfer radius and temperature gradient in crystal on thermal field and stress field in silicon crystal. The use of inverted conical crucible can reduce the thermal stress in polysilicon ingot. With the increase of the corner radius of the crucible, the decrease of thermal stress in the crystal decreases gradually. When the temperature gradient in silicon crystal increases, the average value of thermal stress in silicon crystal decreases gradually. The process of oriented growth of polysilicon crystal was studied by means of thermal field, flow field and magnetic field coupling. The variation of technological parameters of polysilicon directional solidification under different magnetic field structure, different magnetic field distribution and different magnetic field intensity was analyzed. When the distance between the magnetic coil and the central surface of the silicon melt decreases from 60mm to-60mm, the maximum flow velocity of the melt decreases from 70 渭 m / s to 41 渭 m / s, which is 41.43%. When the magnetic field coil is kept at 60mm below the central surface of the silicon melt and the magnetic field intensity gradually increases from 0 T to 0.8 T, the maximum decrease of the axial temperature gradient of the silicon melt is 15 K / cm ~ (-1). In addition, by establishing a two-dimensional axisymmetric transient model, the variation of flow field in three phases (initial, middle and late) of polycrystalline silicon crystallization phase under the action of multi-physical field is revealed. When the magnetic field from 0T to 1T is applied in the crystallization phase of polysilicon, the peak velocity of the melt velocity decreases from 51.644 渭 m / s in the early stage of crystallization to 21.074 渭 m / s in the later stage of crystallization. Moreover, the mean velocity in three periods decreased by 42.1158.59 and 45.1659 respectively under the action of multi-field coupling. The above simulation results show that the numerical simulation technology has important theoretical significance for the practical production of polysilicon.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN304.12

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