A method of forming a thin film and an integrated circuit device, including forming a first reaction inhibiting layer chemisorbed on a first portion of a lower film by supplying a reaction inhibiting compound having a carbonyl group to an exposed surface of the lower film at a temperature of about 300° C. to about 600° C.; forming a first precursor layer of a first material chemisorbed on a second portion of the lower film at a temperature of about 300° C. to about 600° C., the second portion being exposed through the first reaction inhibiting layer; and forming a first monolayer containing the first material on the lower film by supplying a reactive gas to the first reaction inhibiting layer and the first precursor layer and removing the first reaction inhibiting layer from the surface of the lower film, and thus exposing the first portion.