| 摘要 |
A silicon wafer characterized in that the laser scattering tomography defect occurrence region accounts for at least 80% of the wafer surface area and that the laser scattering tomography defects have a mean size of not more than 0.1 mum, with the density of those defects which exceed 0.1 mum in size being not more than 1x105 cm-3, and wafers derived from this wafer as the raw material by heat treatment for oxide precipitate formation, by heat treatment for denuded layer formation or by epitaxial layer formation on the surface are useful as semiconductor materials. In producing this wafer, a single crystal is pulled up under pulling conditions such that while the temperature of the central portion of the single crystal being pulled up from the melt is within the range from the melting point to 1,370° C., the temperature gradient Gc in the central portion in the single crystal pulling axis direction is not less than 2.8° C./mm and the ratio Gc/Ge, where Ge is the temperature gradient in the peripheral portion in the pulling axis direction, is not less than 1. By doing so, silicon wafers very low in surface defect density and allowing the uniform and sufficient formation of BMDs can be obtained.
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