Enhancing B removal from Si with small amounts of Ti in electromagnetic solidification refining with Al-Si alloy

Small amounts of Ti (<2037 ppma) were employed as an additive to enhance B removal from Si in electromagnetic solidification refining with an Al-Si alloy. The B removal process was investigated by varying the initial concentration of Ti, the cooling rate, and the liquidus temperature of the Al-Si alloy. Experimental results show that the small amounts of Ti were primarily responsible for enhancing B removal. This B removal process was more efficient at lower cooling rates combined with the use of Al-Si alloy solvents having lower liquidus temperatures. With the addition of 2037 ppma Ti, the residual B in the refined Si could be controlled to 1.2 ppma, which meets the requirements for manufacturing solar cells. The added Ti could be simultaneously removed because of its extremely low segregation coefficient between solid Si and liquid Al-Si alloy. Although trace amounts of Ti and Al were present in the refined Si, they are expected to be removed in the next processing step, which is directional solidification in vacuum. Finally, the mechanism of this B removal process is discussed.