Process for separating off solid reaction products, such as carbon, from carbothermically produced silicon

• Main Authors: LERCHENBERGER,AUGUST, URBACH,HANS-PETER,ER.NAT, EISENRITH,KARL-HEINZ, AULICH,HUBERT,DR, SCHULZE,FRIEDRICH-W.,ER.NAT
• Format: Patent
• Language: English; German
• Published: 22.10.1987
• Edition: 4
• Subjects: AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUSPOLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR; CHEMISTRY; CRYSTAL GROWTH; METALLURGY; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITHDEFINED STRUCTURE; REFINING BY ZONE-MELTING OF MATERIAL; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITHDEFINED STRUCTURE; SINGLE-CRYSTAL-GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL ORUNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL

Carbon, silicon carbide and SiO2 are separated off from molten silicon, produced in an arc furnace, after a so-called holding phase at a temperature above the melting point by directed solidification of the silicon in the melting vessel, the impurity-containing surface layers, after completion of the crystallisation process, being mechanically removed from the solidified silicon block. The directed solidification causes the silicon carbide particles separated out in the holding phase which do not deposit on the bottom of the melting vessel to be displaced in front of the crystallisation front and to be concentrated in the surface region. In this manner, silicon is obtained having a carbon concentration of approximately 10 ppm by weight. The silicon purified in this way, if required after single crucible drawing, is used as base material for solar cells having an efficiency greater than 10%.