Example embodiments are directed to methods of forming a metallic oxide film using Atomic Layer Deposition while controlling the power reflected by a reactor. The method may include feeding metallic source gases, for example, first and second metallic source gases, and/or a reactant gas including oxygen into the reactor individually. One of the metallic source gases may include an amino-group or an alkoxy-group and another metallic source gas may include neither an amino-group nor an alkoxy-group. A plasma may be produced in the reactor from the reactant gas.