Development of high performance multicrystalline silicon with controlled seeding
High Performance multicrystalline silicon ingots are mostly produced with seeded growth on small size silicon material, which determines the beneficial initial grain structure and orientations of the crystallites. A drawback of this approach is the increased area of low minority charge carrier lifetime in the lower part of the ingot and thus a worse yield. Also, the solidification process time is increased as the seed has to remain solid in a well controlled manner. Both drawbacks can be addressed by using a thin seeding layer on the crucible bottom, which has a higher melting point than silicon. The area of low minority carrier lifetime at the ingot bottom is comparable to standard multicrystalline silicon, whereas the crystal structure is significantly improved. Several seeding layer configurations were investigated and SiO2 with different grain sizes was chosen for G1-sized experiments. The resulting brick shows a grain and defect structure close to the High Performance multicrystalline silicon reference while reducing the width of the impurity indiffusion zone in the bottom. By optimizing the seeding layer in conjunction with the thermal process, a higher yield of high quality material is possible.