US Patent 7208043 Silicon semiconductor substrate and preparation thereof

A silicon semiconductor substrate has a structure possessing oxygen precipitate defects fated to form gettering sites in a high density directly below the defect-free region of void type crystals. The silicon semiconductor substrate is formed by heat-treating a silicon semiconductor substrate derived from a silicon single crystal grown by the Czochralski method or the magnetic field-applied Czochralski method and characterized by satisfying the relational expression (Oi DZ)−(COP DZ)≦10 μm wherein Oi DZ denotes a defect-free zone of oxygen precipitate crystal defects and COP DZ denotes a region devoid of a void type defect measuring not less than 0.11 μm in size, and having not less than 5×108 oxygen precipitate crystal defects per cm3. The method for making the substrate comprises the steps of deriving a silicon semiconductor substrate from a silicon single crystal grown by the Czochralski method or the magnetic field-applied Czochralski method using molten silicon containing not less than 5×1017 atoms and not more than 1.5×1019 atoms of nitrogen per cm3 and heat-treating the silicon semiconductor substrate in a non-oxidizing atmosphere at a highest final temperature of not lower than 1150° C. for not less than one hour.