多晶硅晶锭质量的研究和改善

Quality study & improvement of a multi-crystal silicon casting

现在多晶硅晶锭生长工艺的主要特点是:长晶方向为由下往上,这就使得分凝系数大于1的极少部分金属原子及氧原子集中分布在晶锭底部,大部分分凝系数小于1的金属原子及大部分非金属原子分布在铸锭的顶部,这使得少子寿命呈现低部和顶部低、中间高的分布趋势;同时,由于坩埚及SiN粉末中金属杂质的扩散,多晶硅晶锭四周晶棒靠坩埚面少子寿命偏低。目前国内外关于电池片的少子寿命与电池质量关系的研究报道很多,但是尚没有把多晶硅晶锭生长、晶锭不同位置对应硅片少子寿命,以及晶锭不同位置对应电池片质量相关联起来的研究报告。本文通过精细的试验安排、测试、分析及总结,把多晶硅晶锭生长、晶锭不同位置对应硅片少子寿命及其对应电池片质量相互关联起来,同时找到了电池端电池片质量差异较大的最根本原因,并且通过试验从根本上给出了提高电池端电池片质量稳定性的方向,提高多晶收率的同时提高了电池片平均效益0.2%。

The main characteristic of Multi-Crystal Silicon casting growth process is： growth direction is from the bottom side to the top side, which makes the minority metal elements with higher segregation coefficients than 1 and oxygen content mainly concentrates at the bottom side, while the majority metal elements with lower segregation coefficients than 1 and nonmetallic impurity locates at the top side, all of these makes the minority carrier life time （MCLT） is higher for the center part of a casting than the top and bottom part; meanwhile the MCLT is relatively lower for those sides near the crucible of the surrounding bricks of a casting due to the impurity diffusion from the crucible and SiN power. Now there are many report on the relation between cell MCLT and cell efficiency, however, seldom are there any research report on the correlation between characteristic of Multi^Crystal Silicon casting growth process, MCLT for wafers located at different parts of a casting and efficiency for cells corresponding to the wafers at different parts of a casting. In this paper, we correlated the above factors through elaborate experiment arrangement, careful test, detail analysis and summarize, meanwhile the root cause of big range of efficiency difference for a same casting at cell workshop is discovered, we also provided the ways to improve the cell stability for a same casting by confirmation experiment, all of these actions not only helped to improve casting yield but also improved the average cell Efficiency by 0.2%.