Patent ID: 7273647

Claim:
A silicon annealed wafer, on the surface of which a COP defect free layer having a thickness of 5 μm or more is formed by annealing a base material wafer, wherein said base material wafer includes: a COP defect region of a single crystal containing nitrogen at a concentration of less than 1×10 14 atoms/cm 3 , wherein said COP defect has a size of 0.1 μm or less in the highest frequency of occurrence and there exist no COP defects having a size of more than 0.2 μm; oxygen precipitates formed at a density of 1×10 4 counts /cm 2 or more when said base material wafer is subjected to a oxygen precipitate evaluation heat treatment; wherein the ratio of the maximum to the minimum of BMD (oxygen precipitate) density is 3 or less in the radial direction of said base material wafer.