多晶硅铸锭红外探伤阴影问题浅析

Analysis of Shade of Polycrystalline Ingots in Infrared Detector Images

太阳能光伏产业多晶硅片大多来源于定向凝固多晶铸锭方法。定向凝固多晶硅锭中心区硅棒底部常出现阴影区域,对多晶硅锭的品质及铸锭得料率有一定的影响。经实验研究分析,中心硅锭底部出现阴影的原因是在晶体生长初期,打开隔热笼,边角长晶速度相对比中心长晶速度快,固液界面呈"凹"状,熔体中杂质在硅锭中心底部沉积,造成硅锭红外探伤图上出现阴影。通过多晶铸锭炉热场结构的改进及工艺的优化,使得晶体生长初期边角长晶速度变慢,固液界面的"凹"度变小,甚至使固液界面变平或微"凸",底部杂质向硅锭四周扩散,可消除多晶硅锭中心区硅棒阴影。

In solar industry, polycrystalline silicon ingots are commonly casted by directional solidification method. In this paper, the polycrystalline silicon ingots were scanned by infrared detector. The IR images show shade at the bottom of the ingots from central region, which affects the quality and yield of the ingots. The experiment results show that, at the initial stage of crystalline growth, when the heat insulation cage is lifted, the crystalline growth rate at the edge is faster than the growth rate at the center, thus forming a concave liquid-solid interface. This results in deposition of impurities from the melt and appearing of the shade in the IR scan. In this paper, graphite heater structure was modified and process of polycrystalline ingot casting was optimized accordingly. This leads to lower initial crystalline growth rates at the edge, flattened solid-liquid interfaces or even convex solid-liquid interfaces, impurities diffusing toward the silicon melt and ultimately eliminationof the shade of the polysilicon ingots.