Research Of Refining Polysilicon By Alloying

Based on the energy crisis and environmental factors, Forcing the search for renewable energy to meet the needs of people are pouring, the photovoltaic power generation has entered the line of sight of people, and the advantages of photovoltaic power generation to meet environmental and geographical constraints, therefore the photovoltaic industry is growing rapidly, more than98%of the global solar cell are used silicon material preparation, but solar energy silicon materials which is rely on the microelectronics industry to provide has gone far from meeting the requirements, so many ways have to be develop to purified polysilicon. Metallurgical method as a way of purifying polysilicon become the focus of attention., because of the low production cost, short production cycle, relatively simple process, small pollution, size control, etc. There are many ways of metallurgical method, such as directional solidification, plasma refining, electron beam melting, etc. Due to the segregation coefficient of metal impurity in silicon segregation coefficient is small, using directional solidification can effectively get rid of metal impurities; saturation vapour pressure of non-metallic impurities P is higher, it can been removed used electron beam melting way; Plasma can refine silicon and remove impurities B to satisfing the requirements of solar energy silicon materials, however, Plasma have complex equipment and high energy consumption, so we need to seek alternative method of removing impurities B.Alloy method is also a kind of purification of polysilicon, mainly using the features of inverse solution of impurity elements in low temperature and interaction relationship between alloying elements and impurities, this paper adopted the method of Si-Al-Sn ternary alloy purified polysilicon. In order to determine the interaction force of impurities B and alloying element Sn, firstly the impurities B and the interaction coefficient of Sn is determined in this paper, the value is obtained as about2506(±143)(1173K) by thermodynamic calculation, the interaction coefficient of B and Sn is far greater than the interaction coefficient of Al and B, so the repulsive force between Sn and B is greater than that of Al and B. Then purification efficiency is discussed with the ratio of Si-Sn-Al alloy by the method of metallography and electron probe, namely with the increase of Sn content, the decrease of Al content, polysilicon purification efficiency enhanced. Removal efficiency of impurities B is discussed by thermodynamic means with Si-Sn-Al alloy, namely with the increase of Sn content, the decrease of Al content, Removal efficiency of impurities B is weakened to a certain extent.Based on the repulsive force between impurities B and alloy element Sn is stronger, then the way of Si-Sn alloy slag is adopted to purify polysilicon, because of relationship between the impurity B and alloy element Sn in the alloy phase the activity of B increases, it is easy to react with SiO2into slag phase as borides, it improved the slag reaction process to some extent. This experiment adopts two smelting ways such as the induction melting resistance and melting, two kinds of heat treatment such as quenching and furnace cooling way, two slag basicity such as0.55and1.2and different ratio of Si-Sn alloys. The relationship between the segregate coefficient of impurity B and activity coefficient of B is calculated by thermodynamic means, The relationship between removal efficiency of impurities B and the melting way is discussed by the dynamic way.