Analysis of the Effect of a Vertical Magnetic Field on Melt Convection and Oxygen Transport During Directional Solidification of Multi-Crystalline Silicon by Numerical Simulation

Botao Song,Yufeng Luo,Fayun Zhang,Senlin Rao,Yun Hu

doi:10.3390/cryst10010008

Abstract

Melt convection during the directional solidification process of multi-crystalline silicon plays a critical role in the transport of impurities. The utilization of a static magnetic field is an effective way to control the melt convection pattern. Studying the effect of the Lorentz force induced by the vertical magnetic field (VMF) on the melt convection of silicon in detail is beneficial to optimize the magnetic field parameters in the production process. Based on the numerical simulation method of multi-physics coupling, this paper explores the effects of different VMF intensities on the convection of silicon melt and the transport of oxygen in the melt during the directional solidification of polycrystalline silicon. The results show that in the first 125 minutes of the crystallization stage, the melt convection velocity is affected significantly by the magnetic field intensities. When different convection circulations are present in the silicon melt, the upper circulation easily transports oxygen to the furnace atmosphere, and the subjacent circulation easily lead to the retention and accumulation of oxygen. Enhancing the VMF intensity to a certain extent can reduce the size of the oxygen retention region in the silicon melt, and the time of the first disappearance of the subjacent circulation near the sidewall of the crucible is shortened. Then the average oxygen concentration in the silicon melt can be reduced. However, a larger vertical magnetic field intensity can result in greater average oxygen concentration in the oxygen retention region.

Highlights

Directional solidification technology is widely used in the production process of polycrystalline silicon ingots [1]
The results show that can affect themelt size convection of the melt circulations at different positions in the silicon melt during directional solidification, and can affect convection circulations at different positions in the silicon melt during directional solidification, and the oxygen in different circulations in the silicon melt
Of the crystallization was as the illustration analyze shows the Lorentz force and melt flow velocity in the silicon melt at the beginning, the 45th minute, of magnetic flux density of vertical magnetic field (VMF) on the melt convection and oxygen transportation in silicon melt

Summary

Introduction

Directional solidification technology is widely used in the production process of polycrystalline silicon ingots [1]. Impurities such as oxygen, carbon, and metals will be inevitably introduced during directional solidification in silicon. Controlling the content of impurities in the polysilicon can improve the properties of the silicon wafers [2,4]. Lots of studies have indicated that optimizing the solidification process can reduce the impurity in polysilicon [5,6,7,8,9,10,11,12]. Factors like growth rate [10], the power ratio of heaters [13,14] and the magnetic field [15,16,17,18] affect the content of impurities in the silicon significantly

Methods

Discussion

Conclusion