Solid particle sepn. from silicon melt - by time-variable crucible rotation during directional solidification

摘要

A process is claimed for sepg. solid particles (esp. of C and SiC) from silicon melts (esp. obtained by carbothermic redn. of quartz, in which the melt (3) is subjected, immediately after redn. and holding at above the melting pt., to directional upward solidification to form an ingot, the melt being moved during solidification. The process involves rotating the crucible (1) with time-variable speed about its axis to produce flow currents (8,10) within the melt (3) and between the melt and the crystallised silicon (11). Pref., the time-variable rotation may be achieved by accelerating and braking the rotating crucible (1) and/or by periodic interruption of crucible rotation. Pref. the interruptions comprise stop phases between rotation phases of durations which are a multiple of (pref. at least double) the stop phase durations. Pref. the rotational speed is 5 rpm., the rotation durations are 2.5 mins. and the stop phase durations are 0.5 min.. The rotational speed and the rotation durations are pref. reduced with decrease in melt height during crystallisation. The finished ingot is pref. ground to remove the outer skin and bottom contg. the solid particles. USE/ADVANTAGE - The process allows inexpensive sepn. of solid particles even from large melt volumes, this facilitating mfr. of cheap silicon for mass prodn. of solar cells.