A mold including insulation layers and sacrificial layers is formed on a substrate. A channel hole is formed through the mold. A first deposition process is performed using a first precursor including silane and a second precursor including silane and a halogen element to form a first preliminary blocking layer on a sidewall of the channel hole. A second deposition process is performed using the first precursor to form a second preliminary blocking layer on the sidewall of the channel hole. The first and second preliminary blocking layers form a third preliminary blocking layer. An oxidation process is performed on the third preliminary blocking layer to transform the third preliminary blocking into a first blocking layer. A charge storage layer, a tunnel insulation layer, and a channel layer are formed on the first blocking layer. The sacrificial layer is replaced with a gate electrode.