Semiconductor device
Provided is a transistor which has favorable transistor characteristics and includes an oxide semiconductor, and a highly reliable semiconductor device which includes the transistor including the oxide semiconductor. In the semiconductor device including the transistor in which an oxide semiconductor film, a gate insulating film, and a gate electrode are stacked in this order, a sidewall insulating film is formed along side surfaces and a top surface of the gate electrode, and the oxide semiconductor film is subjected to etching treatment so as to have a cross shape having different lengths in the channel length direction or to have a larger length than a source electrode and a drain electrode in the channel width direction. Further, the source electrode and the drain electrode are formed in contact with the oxide semiconductor film.
1. A semiconductor device comprising:
an oxide semiconductor film comprising:
a channel formation region;
a first region and a second region with the channel formation region interposed therebetween, which are in contact with the channel formation region; and
a third region and a fourth region with the channel formation region, the first region, and the second region interposed therebetween, which are in contact with the channel formation region;
a source electrode in contact with the first region;
a drain electrode in contact with the second region;
a gate electrode overlapping with the first region, the second region, the third region, and the fourth region; and
an insulating film between the oxide semiconductor film and the gate electrode,
wherein a sum of a channel length, a length of the first region in a channel length direction, and a length of the second region in the channel length direction is larger than a length of the gate electrode in the channel length direction, and
wherein a sum of a channel width, a length of the third region in a channel width direction, and a length of the fourth region in the channel width direction is larger than a length of any of the first region and the second region in the channel width direction.
2. The semiconductor device according to claim 1 , wherein the gate electrode is over the oxide semiconductor film.
3. The semiconductor device according to claim 1 , wherein the oxide semiconductor film comprises indium, zinc, and a metal element other than indium and zinc.
4. The semiconductor device according to claim 3 , wherein the metal element is gallium.
5. The semiconductor device according to claim 1 , wherein the oxide semiconductor film has a cross shape.
6. The semiconductor device according to claim 1 ,
wherein the insulating film comprises:
a first insulating film comprising oxygen; and
a second insulating film comprising nitrogen between the first insulating film and the gate electrode.
7. The semiconductor device according to claim 1 , wherein a concentration of copper in the oxide semiconductor film is lower than or equal to 1×10 18 atoms/cm 3 .
8. The semiconductor device according to claim 1 , wherein a concentration of aluminum in the oxide semiconductor film is lower than or equal to 1×10 18 atoms/cm 3 .
9. The semiconductor device according to claim 1 , wherein a concentration of chlorine in the oxide semiconductor film is lower than or equal to 2×10 18 atoms/cm 3 .
10. The semiconductor device according to claim 1 , wherein each of the length of the third region and the length of the fourth region in the channel width direction is larger than the channel length.