BY REACTION WITH RARE EARTH METALS-

SILICON IS THE SEMICONDUCTOR THAT IS PRESENTLY MOST GENERALLY USED IN THE UNITED STATES AND WORLDWIDE FOR PHOTOVOLTAIC (PV) DEVICES, POWER DEVICES, AND INTEGRATED CIRCUIT (IC) TECHNOLOGY APPLICATIONS. A PROBLEM WHICH IS COMMONLY NOTED IS THE PRESENCE OF UNWANTED IMPURITIES IN THE SINGLE-CRYSTAL SILICON MATERIAL IN WHICH THE DEVICES ARE FABRICATED. ASIDE FROM HEAVY METALS, WHICH ARE GENERALLY REDUCED TO UNDETECTABLE LEVELS IN CARE- FULLY PREPARED SINGLE-CRYSTAL SILICON, UNWANTED IMPURITIES INCLUDE OXYGEN, CARBON, BORON, AND PHOSPHORUS. SUCH IMPURITIES ARE INTRODUCED, FOR EXAMPLE, BY THE UBIQUITOUS PRESENCE OF OXYGEN AND CARBON, INCLUDING THE FURNACE COMPONENTS (I.E., SILICON DIOXIDE AND GRAPHITE) USED IN CONVENTIONAL SILICON CRYSTAL GROWTH. ADDITIONALLY, BECAUSE THE SEGREGATION COEFFICIENT OF PHOSPHORUS IS 0.3 AND THAT OF BORON IS 0.8, THESE IMPURITIES ARE RELATIVELY DIFFICULT TO REMOVE FROM SILICON BY PHYSICAL METHODS DURING CRYSTAL GROWTH. IN THIS PROGRAM, A METHOD IS OUTLINED FOR THE REMOVAL OF ALL FOUR OF THESE IMPURITIES BY REACTION WITH RARE EARTH METALS TO FORM THE RARE EARTH OXIDES, CARBIDES, BORIDES, AND PHOSPHIDES, ALL OF WHICH ARE HIGH-MELTING SOLIDS WITH LARGE FREE ENERGIES OF FORMATION. A PRO- CEDURE FOR THE GROWTH OF HIGH-QUALITY, SINGLE-CRYSTAL SILICON WITHOUT REINTRODUCTION OF THE IMPURITIES ALSO IS PLANNED.