Semiconductor device comprising oxide semiconductor
A highly reliable semiconductor device having stable electric characteristics is provided by suppressing, in a transistor including an oxide semiconductor film, diffusion of indium into an insulating film in contact with the oxide semiconductor film and improving the characteristics of the interface between the oxide semiconductor film and the insulating film. In an oxide semiconductor film containing indium, the indium concentration at a surface is decreased, thereby preventing diffusion of indium into an insulating film on and in contact with the oxide semiconductor film. By decreasing the indium concentration at the surface of the oxide semiconductor film, a layer which does not substantially contain indium can be formed at the surface. By using this layer as part of the insulating film, the characteristics of the interface between the oxide semiconductor film and the insulating film in contact with the oxide semiconductor film are improved.
1. A semiconductor device comprising:
a first insulating layer over a substrate;
an oxide semiconductor layer over the first insulating layer, the oxide semiconductor layer containing indium, gallium and zinc; and
a second insulating layer over the oxide semiconductor layer,
wherein the oxide semiconductor layer includes:
a first oxide semiconductor layer over the first insulating layer; and
a second oxide semiconductor layer over the first oxide semiconductor layer,
wherein the first insulating layer is in contact with the first oxide semiconductor layer,
wherein the second insulating layer is in contact with the second oxide semiconductor layer,
wherein a concentration of indium in the second oxide semiconductor layer is lower than a concentration of indium in the first oxide semiconductor layer, and
wherein the second oxide semiconductor layer comprises a crystal, a c-axis of the crystal being parallel to a normal vector of a surface of the second oxide semiconductor layer.
2. The semiconductor device according to claim 1 ,
wherein a gate electrode layer is between the substrate and the first insulating layer, and
wherein the first insulating layer is a gate insulating layer.
3. The semiconductor device according to claim 1 ,
wherein a gate electrode layer is over the second insulating layer, and
wherein the second insulating layer is a gate insulating layer.
4. The semiconductor device according to claim 1 , wherein the oxide semiconductor layer further contains at least one element selected from the group consisting of Ga, Sn, and Zn.
5. The semiconductor device according to claim 1 , wherein the concentration of indium in the first oxide semiconductor layer is higher than or equal to 10 at. % and lower than or equal to 25 at. %.
6. The semiconductor device according to claim 1 , wherein the second oxide semiconductor layer does not substantially contain indium.
7. The semiconductor device according to claim 1 , wherein the concentration of indium in the second oxide semiconductor layer is higher than or equal to 0 at. % and lower than 13 at. %.
8. A semiconductor device comprising:
a first insulating layer over a substrate;
an oxide semiconductor layer over the first insulating layer, the oxide semiconductor layer containing indium, gallium and zinc; and
a second insulating layer over the oxide semiconductor layer,
wherein the oxide semiconductor layer includes:
a first oxide semiconductor layer over the first insulating layer; and
a second oxide semiconductor layer over the first oxide semiconductor layer,
wherein the first insulating layer is in contact with the first oxide semiconductor layer,
wherein the second insulating layer is in contact with the second oxide semiconductor layer,
wherein a concentration of indium in the second oxide semiconductor layer is lower than a concentration of indium in the first oxide semiconductor layer, and
wherein at least a region of the oxide semiconductor layer comprises crystals, wherein c-axis of each crystal is substantially parallel to a normal vector of a surface of the oxide semiconductor layer at a location of the crystal.
9. The semiconductor device according to claim 8 ,
wherein a gate electrode layer is between the substrate and the first insulating layer, and
wherein the first insulating layer is a gate insulating layer.
10. The semiconductor device according to claim 8 ,
wherein a gate electrode layer is over the second insulating layer, and
wherein the second insulating layer is a gate insulating layer.
11. The semiconductor device according to claim 8 , wherein the oxide semiconductor layer further contains at least one element selected from the group consisting of Ga, Sn, and Zn.
12. The semiconductor device according to claim 8 , wherein the concentration of indium in the first oxide semiconductor layer is higher than or equal to 10 at. % and lower than or equal to 25 at. %.
13. The semiconductor device according to claim 8 , wherein the second oxide semiconductor layer does not substantially contain indium.
14. The semiconductor device according to claim 8 , wherein the concentration of indium in the second oxide semiconductor layer is higher than or equal to 0 at. % and lower than 13 at. %.