A method and a device for forming a highly dielectric metal oxide layer. The method includes repeatedly causing a plasma-off period and a plasma-on period while an organic metal compound and an oxidizing agent are continuously injected into a chamber. One cycle includes one plasma-off period and one plasma-on period. During the plasma-off period, a physical and chemical adsorption layer including an organic metal compound and a plurality of atomic layers is formed on a substrate. During the plasma-on period, a metal oxide layer that is thicker than two atomic layers is formed by a chemical reaction of metal atoms in the physical and chemical adsorption layer and oxygen atoms in the oxidizing agent.