直拉单晶硅磁场生长工艺及氧的掺入机理研究

发布时间：2018-09-08 08:55

【摘要】：单晶硅广泛用于光伏发电系统和微电子领域,随着行业的快速发展,单晶硅朝着大直径、高品质、低成本的方向发展。对于生产大直径单晶硅,坩埚的直径和投料量势必加大,熔体内对流变得更加剧烈复杂而难以控制,而磁场拉晶技术对控制剧烈复杂的对流更具有优势。为此本文首先研究了勾型磁场的结构,确定最佳磁场结构。在最佳磁场的基础上,继续研究晶转、埚转、拉速等工艺参数对晶体品质的影响。另外对于提高晶体的品质,晶体内氧含量是重要参量之一,而氧杂质主要来源于坩埚壁的受热分解,随后被输运至固液界面处再分凝至晶体内,而边界层是氧分凝的重要场所。为此本文进一步求解出边界层厚度的解析解,以边界层厚度在固液界面的分布形势研究氧的掺入机理,同时这也是本论文的创新点。本文模拟实验所得结果如下:(1)随着上下线圈间距(H)增大,晶体下方强迫对流强度增加,固液界面的中心挠度逐渐变大。当H较大时氧边界层厚度在固液界面分布较为均匀,利于氧在固液界面的均匀分布。随着磁场比(MR)的减小,洛伦兹力对熔体抑制作用变强,熔体内对流强度逐渐减小;当磁场比在1附近时,氧边界层厚度在固液界面分布较为均匀。(2)随着晶转数的增大,熔体内对流强度逐渐增大,固液界面中心挠度逐渐增大;当晶转数为6rpm、8rpm、12rpm时,氧边界层厚度在固液界面分布较为均匀。随着埚转值增大,坩埚壁温度逐渐升高;固液界面中心处挠度值逐渐降低,氧边界层厚度与埚转数成正比例关系。(3)随着拉速值增大,坩埚壁的温度逐渐降低,固液界面形状由凸型转变成凹型。氧边界层厚度与拉速值成反比例关系,当拉速为65mm/h时氧边界层在固液界面较为平缓。
[Abstract]:Monocrystalline silicon is widely used in photovoltaic power generation systems and microelectronics. With the rapid development of the industry, monocrystalline silicon is developing towards the direction of large diameter, high quality and low cost. For the production of large diameter monocrystalline silicon, the diameter and feeding amount of crucible will increase, and the convection in melt becomes more complex and difficult to control. In this paper, the structure of the hook magnetic field is studied, and the optimum magnetic field structure is determined. On the basis of the optimum magnetic field, the effects of the process parameters such as crystal transformation, pot rotation and drawing speed on the crystal quality are studied. In addition, the oxygen content in the crystal is one of the important parameters to improve the quality of the crystal. The oxygen impurity is mainly derived from the decomposition of the crucible wall, and then transported to the solid-liquid interface and then condensed into the crystal, and the boundary layer is the important place for the oxygen segregation. In this paper, the analytical solution of the boundary layer thickness is obtained, and the mechanism of oxygen doping is studied by the distribution of the boundary layer thickness at the solid-liquid interface, which is also the innovation of this paper. The results of the simulation experiments are as follows: (1) with the increase of the (H) distance between the upper and lower coils, the forced convection intensity under the crystal increases, and the central deflection of the solid-liquid interface gradually increases. When H is larger, the thickness of the oxygen boundary layer is more uniform at the solid-liquid interface, which is favorable to the uniform distribution of oxygen at the solid-liquid interface. With the decrease of magnetic field ratio (MR), the effect of Lorentz force on the melt becomes stronger and the convection intensity decreases gradually, and when the magnetic field ratio is near 1, the thickness of the oxygen boundary layer distributes more evenly at the solid-liquid interface. (2) with the increase of crystal number, The convection intensity in the melt increases gradually, and the central deflection of the solid-liquid interface increases gradually, and the thickness of the oxygen boundary layer distributes uniformly at the solid-liquid interface when the crystal number is 6rpmM ~ 8rpm ~ (-1) at 12rpm. With the increase of the value of crucible rotation, the temperature of crucible wall increases gradually, the deflection value at the center of solid-liquid interface decreases gradually, and the thickness of oxygen boundary layer is proportional to the number of crucible rotation. (3) with the increase of drawing speed, the temperature of crucible wall decreases gradually. The shape of solid-liquid interface changed from convex to concave. The thickness of oxygen boundary layer is inversely proportional to the drawing velocity. When the drawing speed is 65mm/h, the oxygen boundary layer is relatively flat at the solid-liquid interface.
【学位授予单位】：宁夏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN304.12

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