高效液相外延生长提纯冶金硅的机理及强化机制研究

Metallurgy method is a novel process, which combines several steps for selective removal of impurities from metallurgical grade silicon due to the different behaviors of impurities. Directional solidification is wildly used to remove metallic impurities. But limited by distribution rule and the transfer kinetics, directional solidification can be applied repeatedly to meet the purity requirements. Moreover, this method cannot remove impurities with larger segregation coefficient, like B and P. According to our previous results, it is found that the segregation effects at the Si solid-alloy melts interface were intensified, resulting in a decreased segregation coefficient. Therefore, in this project, we propose a new technique to produce bulk Si with high purity from alloy melts, which combined liquid-phase epitaxy with alloy solidification process. The thermodynamic properties of solid-liquid interfaces were studied. Moreover, the bulk Si growth was obtained by this method in order to separate Si from the alloy. In addition, an electric field was applied to influence the Si crystallization and impurity segregation behavior. Our project focuses on providing a theoretical basis for targeted removal of impurities.

冶金法是一种新型的多晶硅制备技术，主要利用硅和杂质物理化学性质的差异，采用多步骤集成的方式去除杂质。其中定向凝固技术是去除金属杂质的重要手段，主要利用杂质在固液两相间的分凝效应达到提纯目的。但是受到固液界面杂质分配规律及杂质传质动力学的限制，一次定向凝固提纯效果不够，只能通过多次重复的方式提高多晶硅纯度，并且对分凝系数接近1的B、P等杂质无法去除。我们前期研究表明，在固态硅与含有第二组元的硅基合金熔体形成的固液界面处，杂质的分凝系数会明显降低，有利于提纯。因此本文提出液相外延生长提纯冶金硅的方法。使用硅基合金熔体作为冶金硅净化体系，通过合金介质增加杂质在固液两相中的热力学差异，降低杂质分凝系数，优化杂质的分离提纯过程；同时引入硅源，通过定向凝固调控晶体硅熔析生长，实现固液两相分离；在此基础上，引入电场强化手段，改善晶体生长可控性，强化杂质分凝去除。为针对性去除冶金硅中的杂质提供理论基础。

冶金法是一种新型的多晶硅制备技术，主要利用硅和杂质物理化学性质的差异，采用多步骤集成的方式去除杂质。其中定向凝固技术是去除金属杂质的重要手段，主要利用杂质在固液两相间的分凝效应达到提纯目的。但是受到固液界面杂质分配规律及杂质传质动力学的限制，一次定向凝固提纯效果不够，只能通过多次重复的方式提高多晶硅纯度，并且对分凝系数接近1的B、P等杂质无法去除。我们前期研究表明，在固态硅与含有第二组元的硅基合金熔体形成的固液界面处，杂质的分凝系数会明显降低，有利于提纯。本项目提出采用温度梯度区域熔炼法（TGZM）在Si-Al合金中生长初晶硅，在完成除杂的同时，整块分离初晶硅，解决合金凝固精炼中出现的初晶硅回收问题。探索了块体硅的结晶形核生长机制，明确了影响块体硅生长形貌及生长速率的各类因素，最后分析了杂质的分布情况及去除效率。同时研究了在Al-Si合金精炼工艺的基础上引入稳恒电流，利用电流带来的电迁移、焦耳热等多种效应对硅原子的作用，改变初晶的析出行为，加强杂质的分凝过程。为针对性去除冶金硅中的杂质提供理论基础。