Sequential purification and crystal growth

A method for removing insoluble slag from the surface of a silicon melt contained in a crucible which comprises the steps of:

• rotating said crucible and said melt;
• directing a flow of gas onto a wall of said crucible;
• adjusting said rotating and said flow to cause said insoluble slag to coalesce at a location on said surface;
• inserting a seed crystal through said coalesced insoluble slag to contact said melt;
• cooling said melt to cause a portion of said melt to freeze to said seed, trapping said insoluble slag;
• and withdrawing said seed, said frozen melt and said insoluble slag.

A process for sequential purification and silicon crystal growth from an impure silicon charge which comprises the steps of:

• heating said impure silicon charge in a crucible to form a melt;
• manipulating insoluble impurities floating on said melt to coalesce said impurities;
• freezing a portion of said melt to trap said impurities;
• removing said frozen portion and said trapped impurities;
• removing soluble impurities dissolved in said melt;
• pulling a first ingot from a portion of said melt;
• charging a second crucible with said first ingot;
• heating said first ingot to form a second melt in said second crucible;
• and pulling a crystal from said second melt.

A method for purifying metallurgical grade silicon which comprises:

• melting said metallurgical grade silicon to form a first melt, said first melt containing insoluble and soluble impurities present in said metallurgical grade silicon;
• manipulating insoluble impurities floating on said melt to coalesce said impurities;
• freezing a portion of said melt to trap said impurities;
• removing said frozen portion and said trapped impurities;
• adding oxide-slag forming compounds to said first melt to remove soluble impurities;
• pulling a first ingot from a portion of said first melt;
• heating said first ingot to form a second melt, said second melt having less impurities than said first melt;
• reacting gas with said second melt to remove soluble impurities therefrom;
• pulling a second ingot from a portion of said second melt;
• heating said second ingot to form a third melt;
• pulling a third ingot from said third melt, said third ingot being substantially free of said impurities present in said metallurgical grade silicon.