Silicon single crystal substrate and method of manufacturing the same

1. A method of manufacturing a silicon single crystal substrate, comprising the steps of:

preparing an initial silicon melt having a boron concentration and a phosphorous concentration, said boron concentration being not higher than 4×10 14 atoms/cm 3 and a ratio of phosphorus concentration to boron concentration being not lower than 0.42 and not higher than 0.50;

growing a silicon single crystal by the Czochralski method from said initial silicon melt; and

slicing said silicon single crystal to form a silicon single crystal substrate;

wherein in said step of growing said silicon single crystal, said silicon single crystal is grown under conditions such that a ratio of the rate of cooling of an edge portion of the silicon single crystal to a rate of cooling a central portion of the silicon single crystal from the melting point of silicon to 1350° C. is not lower than 1.4 and not higher than 2.0, and the rate of cooling the central portion from 1200° C. to 1100° C. is not less than 6° C./minute, said silicon single crystal having an oxygen concentration not lower than 5.0×10 17 atoms/cm 3 and not higher than 7.0×10 17 atoms/cm 3 and a nitrogen concentration not lower than 2.0×10 13 atoms/cm 3 and not higher than 4.0×10 14 atoms/cm 3 .

2. The method of claim 1 , further comprising a step of annealing the silicon single crystal substrate by

heat treatment at a temperature not lower than 1200° C. and not higher than 1250° C. for a period not less than 1 hour and not longer than 8 hours in a noble gas atmosphere in which the concentration of impurities is not higher than 0.5% by volume, or in a non-oxidizing atmosphere.

3. The method of claim 1 , wherein a pull rate of the crystal during the step of growing is from 0.9 mm/min to 1.9 mm/min.

4. The method of claim 1 , wherein the oxygen concentration is in the range of 5.0×10 17 atoms/cm 3 to 6.0×10 17 atoms/cm 3 .

5. The method of claim 1 , wherein the nitrogen concentration is in the range of 1.0×10 14 atoms/cm 3 to 4.0×10 14 atoms/cm 3 .

6. The method of claim 4 , wherein the nitrogen concentration is in the range of 1.0×10 14 atoms/cm 3 to 4.0×10 14 atoms/cm 3 .

7. The method of claim 1 , wherein the height difference between position of the melt interface at the axial center of the crystal and the position of the melt interface at the radial edge of the crystal during growing is between 5 mm and 15 mm.

8. The method of claim 1 , wherein a wafer substrate sliced from the silicon single crystal substrate has a first main surface, and a second main surface opposite said first main surface, has a resistivity in the center of the first main surface of not less than 50 Ω·cm, a rate of change in resistivity from the center of the first main surface to its edge of not more than 3%, an average density of oxygen precipitate BMDs in a device forming region bounded by the surface of the first main surface and a plane 50 μm below this surface lower than 1×10 8 /cm 3 , and an average density of oxygen precipitate BMDs in a region bounded by a first plane at a depth of 300 μm from the first main surface and a second plane at a depth of 400 μm from the first main surface in the range of 1×10 8 /cm 3 to 1×10 9 /cm 3 .

9. The method of claim 1 , wherein the resistivity in the center of a wafer sliced from the silicon single crystal is ≧50 Ω·cm.