Abstract: A manufacturing method of a semiconductor device includes the forming a first oxide over a substrate; depositing a first insulator over the first oxide; forming an opening reaching the first oxide in the first insulator; depositing a first oxide film in contact with the first oxide and the first insulator in the opening; depositing a first insulating film over the first oxide film by a PEALD method; depositing a first conductive film over the first insulating film; and removing part of the first oxide film, part of the first insulating film, and part of the first conductive film until a top surface of the first insulator is exposed to form a second oxide, a second insulator, and a first conductor. The deposition of the first insulating film is performed while the substrate is heated to higher than or equal to 300°.

Abstract: A semiconductor device with high reliability is provided. The present invention relates to a method for manufacturing a transistor including an oxide semiconductor. A stacked-layer structure of an oxide semiconductor and an insulator functioning as a gate insulator is subjected to microwave-excited plasma treatment, whereby the carrier concentration of the oxide semiconductor is reduced and the barrier property of the gate insulator is improved. In addition, a conductor functioning as an electrode and the insulator functioning as a gate insulator are formed in contact with the oxide semiconductor and then the microwave-excited plasma treatment is performed, whereby a high-resistance region and a low-resistance region can be formed in the oxide semiconductor in a self-aligned manner. Moreover, the microwave-excited plasma treatment is performed under an atmosphere containing oxygen with a high pressure, whereby a transistor having favorable electrical characteristics can be provided.