太阳能多晶硅锭中硬质夹杂及其形成

The Hard Inclusions in Multi-crystalline Silicon Ingot and their Formation

多晶硅锭中常出现的硬质夹杂是造成硅片线切割生产中断线的主要原因之一，同时影响到太阳能电池片的质量。我们采用扫描电镜-特征X射线能谱仪、3D数码显微镜、傅立叶红外光谱等手段对定向凝固多晶硅断面、抛光面、溶解沉淀以及硅片中的游离碳含量进行了分析。结果表明，硅锭顶表层出现大量SiC和Si3N4夹杂，其数量随深度迅速减小；硅锭内部SiC十分稀少，尺寸也一般很小，但有时会出现大颗粒（-100μm）。硅片中游离碳含量远低于形成SiC所需临界平衡C浓度。就以上结果对SiC形成原因进行了讨论，并提出了减少SiC夹杂的建议措施。

The hard inclusions are frequently found in multi - crystalline silicon ingot for solar cells. They may cause wire breaking in wire - cutting production of solar wafers, and affect adversely the quality of the solar cells. Scanning electron microscope associated with energy spectrometer for characteristic X - ray,3 D digital microscope and FTIR have been used to analyze the fractured and polished cross section surface of the multi - crystalline silicon samples, respectively, and precipitates after dissolving the silicon matrix, and the concentration of free carbon in the silicon wafer sample. The results indicate a high density of large SiC and Si3N4 particles in the top layer of the ingot. The density decreases rapidly with depth. In the middle of the ingot, very few and fine SiC inclusion can be found, though large SiC particles（ - 100 μm） do exist sometime. Concentration of free carbon in the wafer is found to be much lower than that in equilibrium with SiC. The reasons for formation of SiC are discussed with respect to the resuits. Possible solutions for reduction of SiC inclusions in multi - crystalline silicon ingot are suggested.