To manufacture an integrated circuit (IC) device, a lower structure having a step structure defining a trench is prepared. A material film is formed inside the trench. To form a material film, a first precursor including a first central element and a first ligand having a first size is supplied onto a lower structure to form a first chemisorbed layer of the first precursor on the lower structure. A second precursor including a second central element and a second ligand having a second size less than the first size is supplied onto a resultant structure including the first chemisorbed layer to form a second chemisorbed layer of the second precursor on the lower structure. A reactive gas is supplied to the first chemisorbed layer and the second chemisorbed layer.