Film forming method

A film forming method comprising:

• preparing a substrate having a metal layer formed on a surface of a first region and an insulating layer formed on a surface of a second region, wherein the metal layer is formed of a first metal;
• forming a self-assembled film on a surface of the metal layer by supplying a source gas of the self-assembled film;
• after forming the self-assembled film, forming an oxide film of a second metal on the insulating layer through an atomic layer deposition method by repeating a supply of a precursor gas containing the second metal and a supply of an oxidizing gas;
• and
• reducing an oxide film of the first metal formed on the surface of the metal layer by supplying a reducing gas through an intermolecular gap in the self-assembled film formed on the surface of the metal layer such that the oxide film of the first metal is chemically reduced to a metal film of the first metal,
• wherein the supply of the reducing gas is performed after the supply of the oxidizing gas and before the subsequent supply of the precursor gas when repeating the supply of the precursor gas and the supply of the oxidizing gas.