Influence of grain boundaries intentionally induced between seed plates on the defect generation in quasi-mono-crystalline silicon ingots

This work reports about the growth behavior and defect formation during the directional solidification of mono-crystalline lab-scale silicon ingots in which split seed crystals were used. Thereby the split seeds have certain crystallographic orientations which chosen to induce the growth of selected grain boundaries between the seeded regions. It will be shown that the grain boundary type which is formed inside the seed gap correlates quite well with the intentionally selected orientation relationship of the adjacent seeds. During further growth of the ingot the grain boundaries show a different behavior with respect to their structure and the formation of other crystal defects, e.g. dislocations. It was found that some of the grain boundaries continue straightly in growth direction without any change of structure or formation of other defects. In contrast, other grain boundaries split into several new grain boundaries with a simultaneous formation of dislocations around them. This behavior correlates very well with the energy content of the respective grain boundary, i.e. with its symmetry or coincidence lattice site parameter sigma. In consequence the use of special grain boundaries between the seeds can significantly reduce the defect generation above the seed joints during growth of quasi-mono silicon ingots.