SEMICONDUCTOR DEVICE, DISPLAY DEVICE INCLUDING SEMICONDUCTOR DEVICE, ELECTRONIC DEVICE INCLUDING SEMICONDUCTOR DEVICE, AND METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE

1 . A method for manufacturing a semiconductor device, comprising the steps of:

forming a gate electrode;

forming a gate insulating film over the gate electrode;

forming an oxide semiconductor film over the gate electrode with the gate insulating film interposed between the gate electrode and the oxide semiconductor film; and

forming a source electrode and a drain electrode over the oxide semiconductor film,

wherein the steps of forming the source electrode and the drain electrode comprises the steps of:

forming a first metal film;

forming a second metal film over the first metal film;

performing a first photolithography process on the second metal film and partly removing the second metal film by first etching;

forming a third metal film over the first metal film and the second metal film to cover the second metal film; and

performing a second photolithography process on the third metal film and partly removing the first metal film and the third metal film by second etching, and

wherein the second etching partly remove the first metal film and the third metal film at an outer side of end portions of the second metal film which is removed by the first etching.

2 . The method for manufacturing a semiconductor device, according to claim 1 , further comprising the steps of:

forming a first insulating film over the source electrode and the drain electrode;

introducing oxygen into the first insulating film;

forming a second insulating film over the first insulating film;

forming an aluminum film over the second insulating film;

introducing oxygen into the aluminum film to form an aluminum oxide film; and

forming a planarization insulating film over the aluminum oxide film.

3 . The method for manufacturing a semiconductor device, according to claim 1 ,

wherein each of the first metal film and the third metal film is a metal film or a metal nitride film containing one or more elements selected from tungsten, tantalum, titanium, and molybdenum.

4 . The method for manufacturing a semiconductor device, according to claim 1 ,

wherein the second metal film contains a copper element.

5 . The method for manufacturing a semiconductor device, according to claim 1 ,

wherein the first etching is a wet etching method.

6 . The method for manufacturing a semiconductor device, according to claim 1 ,

wherein the second etching is a dry etching method.

7 . A semiconductor device comprising:

a gate electrode;

a gate insulating film over the gate electrode;

an oxide semiconductor film over the gate electrode with the gate insulating film interposed between the gate electrode and the oxide semiconductor film; and

a source electrode and a drain electrode over the oxide semiconductor film,

wherein the source electrode and the drain electrode each comprise a first metal film, a second metal film, and a third metal film, and

wherein the second metal film is provided in an inner region of end portions of the first metal film and the third metal film.

8 . A semiconductor device comprising:

a gate electrode;

a gate insulating film over the gate electrode;

an oxide semiconductor film over the gate electrode with the gate insulating film interposed between the gate electrode and the oxide semiconductor film;

a source electrode and a drain electrode over the oxide semiconductor film; and

a signal line electrically connected to the source electrode,

wherein the signal line comprises a first metal film, a second metal film, and a third metal film,

wherein the second metal film is provided in an inner region of end portions of the first metal film and the third metal film, and

wherein the source electrode and the drain electrode each comprise the first metal film and the third metal film.

9 . The semiconductor device according to claim 7 , further comprising, over the source electrode and the drain electrode:

a first insulating film;

a second insulating film over the first insulating film;

an aluminum oxide film over the second insulating film; and

a planarization insulating film over the aluminum oxide film.

10 . The semiconductor device according to claim 8 , further comprising, over the source electrode and the drain electrode:

a first insulating film;

a second insulating film over the first insulating film;

an aluminum oxide film over the second insulating film; and

a planarization insulating film over the aluminum oxide film.

11 . The semiconductor device according to claim 7 ,

wherein each of the first metal film and the third metal film is a metal film or a metal nitride film containing one or more elements selected from tungsten, tantalum, titanium, and molybdenum.

12 . The semiconductor device according to claim 8 ,

wherein each of the first metal film and the third metal film is a metal film or a metal nitride film containing one or more elements selected from tungsten, tantalum, titanium, and molybdenum.

13 . The semiconductor device according to claim 7 ,

wherein the second metal film contains a copper element.

14 . The semiconductor device according to claim 8 ,

wherein the second metal film contains a copper element.

15 . The semiconductor device according to claim 7 ,

wherein the gate electrode contains one or more elements selected from tungsten, tantalum, titanium, molybdenum, and copper.

16 . The semiconductor device according to claim 8 ,

wherein the gate electrode contains one or more elements selected from tungsten, tantalum, titanium, molybdenum, and copper.

17 . A display device comprising the semiconductor device according to claim 7 .

18 . A display device comprising the semiconductor device according to claim 8 .

19 . An electronic device comprising the semiconductor device according to claim 7 .

20 . An electronic device comprising the semiconductor device according to claim 8 .