Czochralski-grown dislocation-free silicon crystals of 50 and 80 mm in diameter have been extensively studied by techniques of transmission electron microscopy and preferential etching. Crystals were grown at various growth rates, followed by subsequent processing (thermal treatment, ion implantation). The physical nature (positive/negative sign of silicon lattice imperfection) of grown-in microdefects inside and within the OSF ring was determined. It was found that background oxygen and carbon impurities mostly affect the formation mechanism of grown-in microdefects. It was shown that crystals might grow in interstitial and interstitial–vacancy regimes. The transformation scheme of the grown-in microdefects in the course of subsequent processing is clarified.