In a method of forming a layer, a precursor including a metal and a ligand coordinating to the metal is stabilized by contacting the precursor with an electron donating compound to provide a stabilized precursor into a substrate. A reactant is introduced into the substrate to bind to the metal in the stabilized precursor. The precursor stabilized by the electron donating compound has an improved thermal stability and thus the precursor is not dissociated at a high temperature atmosphere, and the layer having a uniform thickness is formed on the substrate.