Semiconductor device and display device including the semiconductor device
To improve field-effect mobility and reliability of a transistor including an oxide semiconductor film. A semiconductor device includes an oxide semiconductor film, a gate electrode, an insulating film over the gate electrode, the oxide semiconductor film over the insulating film, and a pair of electrodes over the oxide semiconductor film. The oxide semiconductor film includes a first oxide semiconductor film and a second oxide semiconductor film over the first oxide semiconductor film. The first oxide semiconductor film and the second oxide semiconductor film, include the same element. The first oxide semiconductor film includes a region having lower crystallinity than the second oxide semiconductor film.
1. A method for manufacturing a semiconductor device comprising:
forming a first gate electrode;
forming a gate insulating film over the first gate electrode;
forming an oxide semiconductor film over the gate insulating film;
forming a first insulating film over the oxide semiconductor film;
forming a first oxide film over the first insulating film by a sputtering method using an In—Ga—Zn metal oxide target in an atmosphere containing oxygen gas;
forming an island-shaped second oxide film by processing the first oxide film; and
performing a heat treatment at a temperature higher than or equal to 150° C. and lower than or equal to 350° C. after forming the island-shaped second oxide film,
wherein, in the process of forming the first oxide film, a proportion of the oxygen gas in a deposition gas is higher than or equal to 10% and lower than or equal to 100%,
wherein the island-shaped second oxide film overlaps with the first gate electrode with the oxide semiconductor film interposed therebetween, and
wherein a proportion of indium in the island-shaped second oxide film is higher than a proportion of indium in the oxide semiconductor film.
2. A method for manufacturing a semiconductor device comprising:
forming a first gate electrode;
forming a gate insulating film over the first gate electrode;
forming an oxide semiconductor film over the gate insulating film;
forming a first insulating film over the oxide semiconductor film;
forming a first oxide film over the first insulating film by a sputtering method using an In—Ga—Zn metal oxide target in an atmosphere containing oxygen gas;
forming an island-shaped second oxide film by processing the first oxide film; and
performing a heat treatment at a temperature higher than or equal to 150° C. and lower than or equal to 350° C. after forming the island-shaped second oxide film,
wherein, in the process of forming the first oxide film, a proportion of the oxygen gas in a deposition gas is higher than or equal to 10% and lower than or equal to 100%,
wherein, in the process of forming the first oxide film, oxygen is added to the first insulating film,
wherein the island-shaped second oxide film overlaps with the first gate electrode with the oxide semiconductor film interposed therebetween,
wherein an atomic ratio of In to Ga to Zn in the oxide semiconductor film is 1:1:1,
wherein an atomic ratio of In to Ga to Zn in the island-shaped second oxide film is 4:2:4.1, and
wherein the first insulating film is in contact with the gate insulating film.
3. The method for manufacturing the semiconductor device according to claim 1 ,
wherein the island-shaped second oxide film is configured to function as a second gate electrode.
4. The method for manufacturing the semiconductor device according to claim 2 ,
wherein the island-shaped second oxide film is configured to function as a second gate electrode.