The diffuse X-ray scattering technique (DXS) has been employed for the study of point defects and their aggregates, and their interaction with oxygen impurities in heavily boron-doped Czochralski (Cz) Si wafers during various thermal treatments between 450 degree C - 1050 degree C. Our data have shown that: 1) the nature of predominant defects during thermal annealing at 450 degree C depends upon annealing times (for 2 and 8h anneals vacancy-type defects are predominant whereas for 32 and 128h anneals interstitial-type defects are predominant); 2) defects of interstitial nature predominate in samples annealed at 650 degree C and 800 degree C; and 3) the ramp rate influences predominant defect types for the case of 1050 degree C thermal treatments. Wafers annealed with ramping cycles exhibit defects of the interstitial type while those without ramping are of the vacancy type.