Purification Of Metallurgical Grade Silicon By The Physical Method And Their Mechanism

Silicon is widely used for manufacturing solar cells due to their relative low price and high performance. Currently, solar grade silicon (SoG-Si) is primarily manufactured using the Siements Process, which however is high energy consumption and environmental-unfriendly. Consequently, with the development of the solar cells industries, various purification techniques based on low cost have been proposed to refine metallurgical grade silicon (MG-Si) to SoG-Si, including plasma treatment, directional solidification, gettering technique, etc. At present, the most commonly used approach involves plasma technology, which appears to be especially effective in extracting boron and phosphorus. However, while the literature on the purification of MG-Si using plasma processing is extensive, most of the work has been carried out with molten silicon. Unfortunately, any process that involves themelting of silicon is necessarily energy intensive and environmentally unfriendly. Therefore, urgency remains to develop new purification techniques that are marked by low energy consumption, high efficiency, and that are environmentally friendly. In this work, firstly, we purified MG-Si by annealing PS at different high temperatures for different time in air. A relatively new and complete theory for PS gettering technique is proposed. Under the direction of this theory, we demonstrated that the metallic impurities concentration (Fe, Ca, Al, Mg) in MG-Si could be effectively reduced. This theory might provide a new insight into the purification MG-Si via gettering technique. Secondly, we describe an alternative purification technique using microwave driven plasma to refine MG-Si. Compared with other plasma techniques, this method facilitates the removal of most impurities while maintaining temperatures that lie below the silicon melting point, which implies a significantly reduced enery consumption. Remarkably, while various impurities can be extracted in the presence of microwaves, phosphorus (P) was removed nearly completely, as verified by inductively coupled plasma-atomic emission spectrometry analysis (ICP-AES).