Marangoni效应下多晶硅真空定向凝固杂质富集和铸锭质量的模拟与实验

Simulation and Experimental Study on Impurity Enrichment and Ingot Quality of Polycrystalline Silicon Vacuum Directional Solidification under Marangoni Effect

对于多晶硅垂直布里奇曼真空定向凝固过程,由熔体自由表面张力梯度引起的Marangoni对流对杂质富集和铸锭质量有着明显的影响。基于多晶硅真空定向凝固过程多物理场模型,采用数值模拟和实验结合研究了在Marangoni效应下硅料的温度场、流场、应力场对硅晶体质量的影响及硅锭中Al、Fe等杂质的分凝、富集规律。结果表明:Marangoni效应使硅锭内部的温度场分布更加均匀,硅料的轴向温度梯度降低,从而硅锭内部的热应力值要小于不存在此效应时硅锭内部的热应力值,热应力降低了8.7%~22.5%,且硅锭的应力范围在3.36~96.7 MPa。硅锭顶部金属杂质Al、Fe富集程度较高,界面Marangoni效应加强了金属杂质原子转移,其分布从最初的小面积块状转变成大面积网络状存在。

In the vertical Bridgman vacuum directional solidification process of polycrystalline silicon,Marangoni convection caused by the free surface tension gradient of the melt has a significant effect on impurity enrichment and ingot quality.Based on the multi-physical field model of polysilicon vacuum directional solidification process,the effects of temperature field,flow field and stress field on the quality of silicon crystal under Marangoni effect and the segregation and enrichment of Al,Fe and other impurities in silicon ingot were studied by numerical simulation and experiment.The results show that the Marangoni effect makes the temperature field distribution inside the silicon ingot more uniform,and the axial temperature gradient of the silicon material decreases.Therefore,the thermal stress inside the silicon ingot is smaller than the thermal stress inside the silicon ingot without this effect.The thermal stress is reduced by 8.7%—22.5%,and the stress range of the silicon ingot is about 3.36—96.7 MPa.At the top of the silicon ingot,the metal impurities Al and Fe are highly enriched.The interface Marangoni effect strengthens the transfer of metal impurity atoms,and its distribution changes from the initial small area block to a large area network.