Continuous solidification of photovoltaic multicrystalline silicon from an inductive cold crucible

An inductive cold crucible is used to melt photovoltaic granular silicon and to form massive multicrystalline billets by continuous pulling downwards. The cold crucible is noncontaminating. In the billet the impurity content is kept at the same low level as it is in the feed stock, even for copper, and somewhat lower for oxygen. Square billets are as easy to shape as circular ones. Continuous solidification gives the material uniform grain structure and properties, so that a considerable reduction in waste material is expected. Details are given on the experimental procedure and on measurements. For a given pulling rate, the optimal electrical conditions result from a fine compromise between the risk of a liquid leak, and the risk of nonmelting granules. Among the electrical and thermal measurements which were tested, the electrical frequency seems to give a possible gage for estimating the variation of the amount of liquid. (C) 1998 Elsevier Science B.V. All rights reserved.