Growth and Characterization of Multicrystalline Silicon Ingots Grown by Directional Solidification Technique

In order to produce high-quality multicrystalline(mc-) silicon ingots, mc-Si ingots were grown by the directional solidification technique with various heater transfer rate, V_H=15, 30, 60mm/hr . The grown ingots were sliced to a thickness of 0.5mm. The effective lifetime, substitutional carbon concentration, and etch-pit density (EPD) in the substrates were measured to characterize the grown ingots. The EPD was decreased with decreasing V_H. However, the lifetime of the ingot with V_H=15mm/hr was almost the same as that with V_H=30mm/hr. The reason is that the degree of iron contamination from a crucible and coating materials is increased with increasing the growth time. The dopant striation was observed by the thermal pulse technique, and it was confirmed that the crystal/melt interface is almost flat. In addition, the striation showed discontinuity at the grain boundaries. From these results, we focused on the constitutional supercooling, and developed new growth method, named as the successive relaxation of supercooling (SRS) method. The effectiveness of the SRS method was demonstrated