We have developed a quantitative measurement method for the number density, size and morphology of grown-in defects in czochralski-grown silicon (CZ-Si) crystals with a bright-field infrared-laser interferometer (known as Oxygen Precipitate Profiler; OPP). Using this method we investigated the effect of crystal cooling condition during crystal growth on the formation of grown-in defects by growth holding experiments. The relation between gate oxide integrity (GOI) and grown-in defects was studied. It was revealed that the grown-in defects have octahedral shape and degrade the GOI performance. We estimate the density as well as cumulative volume of the grown-in defects and discuss the formation mechanism of them.