基于迁移学习的大尺寸铸锭晶体硅热场设计

不同尺寸的铸锭晶体硅生长过程具有相似性,小尺寸晶体的生长规律可以迁移至大尺寸。本文采用迁移学习(TL)对G8型铸锭炉进行热场设计,设计对象为侧、顶加热器位置及体积、侧隔热笼分区块高度,主要设计目标为减少晶体内部的位错缺陷、抑制硅锭边缘多晶且使晶体生长界面微凸。首先使用神经网络对已有的G7铸锭炉建立热场几何参数与热场评价参数间的映射模型,然后将该模型迁移至G8铸锭炉,对比不同模型结构对迁移过程的影响,采用Dropout分析模型是否存在过拟合,并使用遗传算法(GA)结合聚类算法(CA)对热场几何参数进行优化,以上为G8热场设计过程。最后对优化结果采用数值模拟方法研究其在晶体生长过程中的温度分布、固液界面形状等,最终选定的优化方案能够实现较高质量的长晶。将该方案同时应用于G7和G8热场并进行对比,结果表明G8在硅熔体和硅晶体中的轴向温度梯度均小于G7,在晶体生长界面沿径向的温度梯度也小于G7,这有利于减小晶体内部的热应力。

Hot Zone Design of Large Size Ingot Crystalline Silicon Using Transfer Learning

There are similarities between the growth processes of ingot crystalline silicon with different sizes, so the growth law of small size crystals could be transferred to large size crystals. In this paper, transfer learning (TL) was used to design the hot zone of the G8 ingot furnace. The design targeted parameters are the positions and volumes of the side and top heaters, and the height of the partition block on the side insulation cage. The main design goals are to reduce the dislocation defects inside the crystal, suppress polycrystalline at the edge of the silicon ingot and make the solid-liquid interface slightly convex. First, a neural network was used to establish a mapping model between the hot zone geometric parameters and hot zone evaluation parameters for the existing G7 ingot furnace. Then the model was transferred to the G8 ingot furnace. The effects of different model structures on the transfer process were analyzed. Then Dropout was used to determine whether the model is overfitting. The genetic algorithm (GA) and the clustering algorithm (CA) were applied to optimize the hot zone geometric parameters. The above is the process of G8 hot zone design. Finally, the numerical simulation method was used to study the temperature distribution and solid-liquid interface shape of the optimized schemes. The final selected scheme could achieve high quality crystal growth. Then the scheme was applied to the hot zones of G7 and G8 furnaces. The results show that the axial temperature gradient of G8 in silicon melt and silicon crystal is smaller than that of G7, and the radial temperature gradient at the solid-liquid interface is also smaller than that of G7. It is beneficial to reduce the thermal stress inside the crystal.