硅表面水热法原位构建含氧多孔层及其诱生缺陷对B、P的吸除作用

The key restrictive problem of industrializationin of solar grade silicon with metallurgical method is the difficulty of removing boron (B) and phosphorus (P). It is an effective way to solve the problem that the porous layer containing-oxygen is formed on Si surface, and B, P are removed by it’s induced defects. In the project, choosing the raw material of metallurgical grade silicon as the research object, porous layer containing-oxygen are constructed on the silicon surface in situ by hydrothermal method. Firstly, in order to control the pore structure and oxygen content, the effects of the type and concentration of acid and oxidant and auxiliary agent, the corrosion temperature and time on the formation of porous layer containing-oxygen on silicon surface are investigated. Secondly, the influence of pore structure and oxygen content on the distribution of induced defects in porous layer are investigated, in order to make clear the regulation methods of induced defects. Then, the intrinsic relationship between the defect adsorption and the distribution of B and P is studied to reveal the mechanism of gettering interaction between defects and B, P. Finally, the thermodynamic behavior of the adsorption of B and P with acid or alkali solution is studied, and the chemical reaction mechanism of B and P removal is clarified. Based on the above research, this paper will provides a new idea for the removal of B and P in the processing of silicon materials.

冶金法制备太阳能级硅产业化的关键问题是杂质硼（B）和磷（P）难以去除。在硅表面构建含氧多孔层，利用含氧多孔层中的诱生缺陷对B、P进行吸除是解决这一问题的有效途径。本项目拟以冶金级硅为研究对象，采用水热法在硅表面原位构建含氧多孔层。首先，研究酸、氧化剂和辅助剂种类、浓度、腐蚀温度、腐蚀时间等因素对硅表面含氧多孔层的影响规律，实现孔结构与氧含量的有效控制。其次，研究孔隙率、孔径大小和氧含量等对多孔层中诱生缺陷的类型、密度和尺寸等分布特征的影响规律，明确对诱生缺陷形成的调控手段。然后，研究含氧多孔层的缺陷吸附与B、P分布的内在关系，揭示缺陷对B、P的吸杂作用机理。最后，研究吸附B、P的缺陷与酸液或碱液作用的热力学行为，阐明B、P溶解去除的化学反应机理。通过以上研究，为硅材料加工过程中B、P的去除提供借鉴。

冶金法制备太阳能级硅B、P去除是需要解决的关键问题。项目主要以工业硅为研究对象，采用水热金属离子辅助法原位构建多孔层吸除 B、P。论文主要研究内容和结论如下：. （1）硅表面多孔层的原位构建。先以单晶硅为对象，比较了 HF-Mex(NO3)y-HNO3中金属离子种类等对多孔层形貌的影响规律，初步确定了水热金属离子辅助法的工艺参数；并用工业硅片和工业硅粉验证了HF-Mex(NO3)y-HNO3体系刻蚀制备多孔层的可行性。实验结果表明，工业硅粉在HF-Fe(NO3)3- HNO3刻蚀体系中，获得的多孔层结构孔道分布较为均匀且密集。 . （2）HF-Fe(NO3)3-HNO3刻蚀体系中各因素对工业硅中 B、P吸除影响规律。 实验是研究了HF浓度、刻蚀温度对B杂质的吸除具有显著影响；Fe(NO3)3浓度、刻蚀时间、HNO3浓度对P杂质的吸除效果显著；在最佳实验条件下，工业硅中B、P去除率分别达到75.862%、74.576%；再经950 ℃退火强化吸除后酸洗，B、P去除率提高到82.759%、76.271%。. （3）含氧多孔层诱生缺陷对B、P的吸杂作用及B、P溶解去除反应机理。分析了多孔层结构、多孔层中氧含量与B、P吸除的关系，结果表明多孔层中含有非晶SiO2，多孔层的比表面积、孔径体积和孔隙率与P杂质的去除率成正相关，非晶SiO2含量与B杂质的去除率成正相关；热力学计算表明，因O对B、P的结合能力比Si与B、P的结合能力更强，非晶SiO2多孔层又因有大量诱生缺陷所形成的空位，而对B、P产生吸附迁移作用，使B、P进入非晶SiO2多孔层并与HF反应生成易溶于水的离子而去除，在此基础上，提出了多孔层对B、P杂质吸除作用机理模型。