This paper presents the scheme depicting the formation and transformation mechanism of the grown-in microdefects in FZ-Si and CZ-Si crystals as a function of a crystal growth rate. In is established and proved experimentally that concentrations of vacancies and self-interstitials at the crystallization front near the melting point are comparable, recombination of intrinsic point defects during the silicon cooling below the crystallization temperature follows two independent mechanisms: vacancy-type and interstitial-type. The driving force of the defect formation is initial oxygen-vacancy agglomerates and carbon-interstitial agglomerates formed on impurities centers. At a certain thermal growth conditions the aggregation of point defects under vacancy-interstitial-type or interstitial type growth mode in the course of crystal cooling may cause the secondary defects occurrence around primary oxygen-vacancy and carbon-interstitial aggregates, namely vacancy microvoids and interstitial-type dislocation loops, accordingly. On the basis of experimental results the physical classification of the grown-in microdefects are proposed. The classification suggested follows from the heterogeneous formation and transformation mechanism of the grown-in microdefects.