Influence of different seed materials on multi-crystalline silicon ingot properties

Abstract

Different silicon feedstock materials, Single Crystalline Crushed (SCS), Fluidized-Bed-Reactor (FBR) and Siemens (SIE) feedstock, were used as seeding layer for growing cylindrical shaped, high performance multi-crystalline ingots with a weight of 1.2kg. Within the investigations a systematic variation of the particle size of the seeding material in the range of <1mm up to 15mm was performed. Grain size, grain orientation, and grain boundary type were evaluated at different ingot heights. These results show clearly, that the microstructure size, respectively the particle size for the crushed single crystalline material, determines the resulting grain structure in the ingot near the seeding position. If the microstructure size is equal to the particle size, as it is the case for the SCS material, the particle size has a significant influence on grain size, grain orientation, and grain boundary distribution. With increasing average particle size of the SCS seed material the grain size increases, the grain orientation distribution becomes less uniform, and the random grain boundary length fraction decreases. If the microstructure size is smaller than the particle size, as it is the case for FBR and SIE feedstock materials, the particle size has no influence on the initial grain structure of the ingot. For FBR and SIE seeding material, small grains, with a homogeneous orientation distribution and a high random grain boundary length fraction are obtained. Therefore, all FBR and all SIE seeding materials, as well as the SCS with particle size <1mm, show lowest fractions of defected areas at about the same level which were determined by etch pit analysis.