| abstract |
A change in electrical characteristics of a semiconductor device including an oxide semiconductor is prevented, and the reliability of the semiconductor device is improved. An oxide semiconductor is formed over a substrate; an insulator is formed over the oxide semiconductor; a metal oxide is formed over the insulator; a conductor is formed over the metal oxide; a portion of the oxide semiconductor is exposed by removing the conductor, the metal oxide, and the insulator over the oxide semiconductor; plasma treatment is performed on a surface of the exposed portion of the oxide semiconductor; and a nitride insulator is formed over the exposed portion of the oxide semiconductor and over the conductor. The plasma treatment is performed in a mixed atmosphere of an argon gas and a nitrogen gas. |