Physical Metallurgical Method To Produce Solar-grade Silicon

Because of the shortage of conventional source of energy, new source of energy made rapid expansion in recent years, especially PV industry. However the development of PV industry in our country was interrupted because of the shortage of raw materials and a lot of solar cell factories stopped production. On other hand our country has to import most of its raw materials, at the same time the factories aboard which produce multi-crystalline silicon run up the price of silicon and render the price reached $300 per kilogram. So the solar cell factories in our country just earn the meager profits. Until now we did not hold the major tech of the two technologies. Exploring new tech of producing solar grade silicon is the very way to solve the problem of multi-crystalline silicon industry. Physical metallurgical method to produce solar grade silicon has the merit of low cost and no pollution and so on. But the tech is not yet mature. So, it plays a great role to develop good melting parameters.In this research we use electron-beam furnace and vacuum melting fuanace which are designed by ourselves to study the purification of metallurgical silicon and we also study the effect of melting paramenters such as different vacuum states; melting power; melting time on the impurities extraction. From the study we get the follwing results:Vacuum melting has good effect on extraction Ca,Al,P in metallurgical silicon.The distribution of impurity elements in silicon button is uneven after vacuum melting, the ingredient in medicun position of silicon is better. The higher temperature and the longer heat preservation time, the better effect on extraction. Being protected by Ar is good to extraction and reduces the volatilization of silicon but is bad to heat preservation and increases energy consume. With the proper process, the content of P can be reduced to 3 ppm, and Ca below 1 ppm.The distribution of metal impurity elements in silicon button is uneven after EB melting and will gather onto the surface; the distribution of non-metallic impurity elements is very even, no segregation phononmenon exists. Electron-beam melting has not very clear effect on extraction of Fe, but good effect on Ca,Al,P,B. Increasing melting power, melting time is good to impurities extraction. With the proper process, the content of P,Ca,B can be reduced to below 1 ppm.In a word vacuum melting and electron-beam melting are effective method to purify silicon. With the proper melting parameters we can acquire very good results. If assistanted with directional solidification, the content of impurities can be reduced much more, and may satisfy the request of solar grade silicon.