A method for fabricating a semiconductor device includes forming a structure with a height difference on a substrate and forming a dielectric layer structure on the structure using an atomic layer deposition (ALD) method. Forming the dielectric layer structure includes forming a first dielectric layer including silicon nitride on the structure with the height difference. Forming the first dielectric layer includes feeding a first gas including pentachlorodisilane (PCDS) or diisopropylamine pentachlorodisilane (DPDC) as a silicon precursor, and a second gas including nitrogen components into a chamber including the substrate such that the first dielectric layer is formed in situ on the structure having the height difference.