METHOD OF REFORMING SILICON POLYCRYSTAL SUBSTRATE

PURPOSE:To reform the title substrate which has a large crystal grain size and contains less impurities by melting and solidifying the front surface of a silicon substrate on which an oxide film or nitride film is formed, then turning the substrate upside down and melting and solidifying the surface. CONSTITUTION:The silicon substrate 4 is loaded into a preheating furnace 9 and is preheated for 1 to 5 minutes at 1000 to 1350 deg.C in an oxidizing or nitriding atmosphere to form the oxide film or nitride film of 0.1 to 10mum on the surface of the substrate 4. The substrate 4 is horizontally disposed and is irradiated with a halogen lamp 7 from above, by which the substrate is heated and a molten part 1 is formed down to the depth of >=1/2 the thickness of the substrate from the front surface of the substrate 4 except the solid phase part 2 made to remain on the upper part of the substrate 4; thereafter, the molten part 1 is solidified upward from the boundary of the molten part 1 and the solid phase part 2. The substrate 4 is then turned upside down and is subjected successively to the above-mentioned melting stage and solidifying stage and thereafter, the surface of the substrate 4 is melted.