In semiconductor devices and methods of manufacturing semiconductor devices, a zirconium source having zirconium, carbon and nitrogen is provided onto a substrate to form an adsorption layer of the zirconium source on the substrate. A first purging process is performed to remove a non-adsorbed portion of the zirconium source. An oxidizing gas is provided onto the adsorption layer to form an oxidized adsorption layer of the zirconium source on the substrate. A second purging process is performed to remove a non-reacted portion of the oxidizing gas. A nitriding gas is provided on the oxidized adsorption layer to form a zirconium carbo-oxynitride layer on the substrate, and a third purging process is provided to remove a non-reacted portion of the nitriding gas.