【作者】 王家鑫；

【导师】 尹盛；

【作者基本信息】 华中科技大学 ， 半导体芯片系统设计与工艺， 2007， 硕士

【摘要】 目前,硅材料的高成本使太阳电池的广泛应用受到了极大的限制。大量研究表明,使用纯度为4N～6N的太阳级硅制备太阳电池,效率可以达到单晶电池的80%,但是成本只有其四分之一。因此,研究太阳级硅的制备技术具有重要意义。本学位论文首先介绍了国内外太阳级硅制备技术的新工艺及新方法,并简要论述了冷等离子体刻蚀纯化冶金硅的机理。由于等离子体鞘层内才有能量足够大的粒子,要达到纯化效果,必须使硅粉处于阴极鞘层之内。文中对冷等离子体鞘层进行了分析和计算,得到了鞘层与电流密度、阴极偏压、气压的关系式,为增厚鞘层提供了理论指导。建立了硅粉在鞘层的动力学模型,对硅粉在直立平板反应室内的受力和运动进行了详细分析,得到了硅粉在鞘层的沉降时间表达式。考察了硅粉粒径、真空泵抽气速率、反应室气压等参数对硅粉沉降过程的影响。分析表明,当硅粉在100μm左右时有较好的纯化效果和较高的回收率。对冷等离子体中硅粉的刻蚀动力学进行了研究。基于一维流体模型,对阴极鞘层内的重粒子速度分布、粒子通量、能量等进行了计算,得到了鞘层内高能粒子的刻蚀速率。这些结果为合理调整工艺参数提供了依据,对冷等离子体刻蚀纯化硅具有指导意义。最后,对硅粉进行了物理刻蚀去除表面杂质的实验。实验是在氩气氛中进行的。实验结果表明利用冷等离子体刻蚀可将硅粉纯度从97.66%提高到98.47%。更多还原

【Abstract】 Owing to high cost of silicon materials, the wide application of solar cell is restricted extremely in the world. A lot of researches show that the efficiency can reach 80% of single crystal silicon, by using solar grade silicon with purity of 4N to 6N for solar cell fabrication,but the cost only a quarter of that. So, research on preparation of solar grade silicon is of great importance.In this thesis, firstly, the domestic and foreign new processes and methods for preparation of solar grade silicon is introduced. And then, the mechanism for cold plasma etching silicon is discussed in brief.On account of that in plasma sheath particles have enough energy, the silicon powders have to be located in the sheath to get better purification effect. The cold plasma sheath is analyzed and caculated.And the relation of the sheath thickness to current density, voltage on the cathode, pressure in chamber will serve as theoretical guide for increasing sheath thickness. A motional model for silicon particulates is developed to investigate the drop time. After analyzing in detail, the drop time in sheath for silicon particulates was demonstrated obviously. And when the size of silicon powder is about 100μm ,the purification effect and yield will give a good performance. Employing 1D model, toward the heavy particles in cathode sheath ,the velocity and energy distribution functions are deduced, the expression for neutral and ionic fluxes are obtained, and the etching rate is formed based on hydrodynamics. These results will guide the experiment for technical parameters regulation.Lastly, the experiment of physical etching silicon powders to remove surface impurities is carried out, with Ar as dominant gas in the chamber. And the experiment results show that impurities percentage decreases obviously from 97.66% to 98.47%.更多还原