Methods and apparatuses for manufacturing cast silicon from seed crystals

Abstract

Methods and apparatuses are provided for casting silicon for photovoltaic cells and other applications. With these methods, an ingot can be grown that is low in carbon and whose crystal growth is controlled to increase the cross-sectional area of seeded material during casting.

We claim: 
     
         1 . A method of manufacturing cast silicon, comprising:
 loading a seed layer of silicon comprising near-monocrystalline silicon into a crucible;   loading solid silicon feedstock into the crucible;   placing a lid over an opening of the crucible;   flowing an inert gas into the crucible through at least one hole in the lid;   expelling the inert gas from the crucible through at least one other hole in the lid;   melting the silicon feedstock while maintaining a part of the seed layer in a solid state;   forming a solid body of silicon comprising near-monocrystalline silicon; and   cooling the solid body.   
     
     
         2 . The method according to  claim 1 , wherein the loading of the seed layer paces the seed layer on a bottom surface of the crucible. 
     
     
         3 . The method according to  claim 1 , wherein the inert gas comprises argon or nitrogen. 
     
     
         4 . The method according to  claim 1 , wherein the expelling of the inert gas prevents backflow into the crucible. 
     
     
         5 . The method according to  claim 1 , wherein the flowing of the inert gas occurs during at least the melting the silicon feedstock and the forming of a solid body. 
     
     
         6 . The method according to  claim 1 , wherein the flowing of the inert gas pressurizes the crucible above a surrounding environment. 
     
     
         7 . The method according to  claim 1 , further comprising applying a vacuum to the crucible after loading the seed layer and the silicon feedstock, and before flowing of the inert gas begins. 
     
     
         8 . The method according to  claim 1 , wherein the forming a solid body comprises extracting heat through at least a bottom surface of the crucible. 
     
     
         9 . The method of according to  claim 1 , wherein the flowing and the expelling of the inert gas at least partially reduces or prevents carbon incorporation into the cast silicon. 
     
     
         10 . The method according to  claim 1 , wherein the flowing and the expelling of the inert gas at least partially reduces SiO in the crucible. 
     
     
         11 . The method according to  claim 1 , wherein the solid body comprises low carbon silicon.