ø300 mm直拉硅单晶生长过程中的变晶现象及其影响因素

直拉法生长直径300 mm硅单晶过程中,直径均匀是获得高品质硅单晶的关键。在生产实践中发现,当硅晶体进入等径生长阶段,过高的提拉速度会引起晶体发生扭晶现象,导致晶线断裂随即变晶,对等径生长不利。本文采用数值模拟和理论相结合的方法分析了ø300 mm硅单晶生长过程中扭晶现象的成因,建立了不同提拉速度下晶体直径与熔体温度分布的关系,分析了晶体发生扭晶的影响因素。结果表明,随着提拉速度的增加,熔体自由表面产生过冷区且该过冷区随提拉速度的增加不断扩大,过冷区的产生是导致晶体发生扭晶的主要原因。提出了一种基于有限元热场数值模拟的最大稳定提拉速度的判别方法,并给出了通过改变晶体旋转速度来改善熔体自由表面温度分布的工艺措施建议,从而避免晶体扭晶现象的发生。研究结果对设计大尺寸硅单晶生长热场具有一定的指导作用。

Crystalloblast and Its Affecting Factors in ø300 mm Czochralski Silicon Single Crystal Growth

In the process of growing 300 mm diameter silicon single crystal by Czochralski method, uniform diameter is the key to obtain high quality silicon single crystal. It is found in production practice that too high pulling speed causes the phenomenon of twisting crystal at uniform diameter growth stage, which leads to the crystal line fracture and then crystalloblast, and it is unfavorable to uniform diameter growth. In this paper, the origin of the twisting crystal in the growth of ø300 mm silicon single crystal was analyzed by the combination of numerical simulation and theory analysis. For varying pulling speed, the correlation between crystal diameter and melt temperature distribution was established, the affecting factors on twisting crystal were obtained. The results show that with the increase of pulling speed, the supercooling zone is generated on the free surface of the melt, and continue to expand. The generation of supercooling zone is the main reason leading to twisting crystal. A method for identifying the maximum stable pulling speed is presented based on the numerical simulation of the finite element thermal field, and the method of varying the rotation speed of the crystal is proposed to improve the free surface temperature distribution of the melt, so as to avoid the crystal twisting. The results provide a guidance to the thermal field design of large diameter silicon monocrystalline growth.