INFLUENCE OF THE INCORPORATION OF UMG-SILICON ON THE YIELD AND QUALITY OF P-TYPE MULTICRYSTALLINE SILICON INGOTS AND WAFERS

摘要

The high demand of polysilicon has led to the well known silicon feedstock shortage in recent years and it can occur again in the future. Therefore, other sources must be investigated and UMG silicon is one of the most promising materials. The aim of this work is to evaluate the influence of the introduction of UMG silicon from three different suppliers and blended in different ratios with polysilicon in p-type multicrystalline silicon ingots for wafer production. To this purpose, five 430kg ingots were grown by directional solidification with UMG silicon percentages in composition varying from 10 to 100%. Additionally, an extra ingot per each UMG ingot was grown as Reference, in the same conditions but UMG-Si was substituted by polysilicon. Each ingot was sectioned in 25 bricks, and each brick sliced into 156*156mm wafers. In order to evaluate the resulting quality, several parameters were analyzed (such as lifetime, resistivity, inclusions…). The introduction of UMG decreased the yield in the five ingots due to the higher P concentration; lifetime also decreased due to the higher impurities concentration in these materials. However, the effects depend highly on the UMG supplier and the concentration. Adjusting correctly the resistivity in the UMG ingot is basic, because by adding B it is possible to increase the yield, although at the expense of reducing the base resistivity.