Preparation of 6N grade silicon ingot by combined purification processes from waste silicon cutting sludge

This study is aimed at fabricating ultrahigh-purity silicon ingots from silicon cutting sludge-a byproduct of the ingot for solar cells cutting process. Firstly, silicon powder from the silicon cutting sludge was recovered by 1^st purification, such as ultrasonication, centrifugation, and acid treatment before preparation of the silicon ingots. After the 1^st purification, the silicon cutting sludge yielded silicon powder with a purity of 99.7612 %. The 1^st-purified silicon powder was subjected to 2^nd purification-3 cycles hydrogen plasma arc melting (HPAM), resulting in ultrahigh-purity silicon ingot with a purity of 99.9999 %. HPAM has been verified to be an effective process for removal of B and P-the major impurities of silicon for semiconductors and solar cells- to levels of total ≤ 0.3 ppm.