Semiconductor device comprising oxide semiconductor with c-axis-aligned crystals
An embodiment is a semiconductor device which includes a first oxide semiconductor layer over a substrate having an insulating surface and including a crystalline region formed by growth from a surface of the first oxide semiconductor layer toward an inside; a second oxide semiconductor layer over the first oxide semiconductor layer; a source electrode layer and a drain electrode layer which are in contact with the second oxide semiconductor layer; a gate insulating layer covering the second oxide semiconductor layer, the source electrode layer, and the drain electrode layer; and a gate electrode layer over the gate insulating layer and in a region overlapping with the second oxide semiconductor layer. The second oxide semiconductor layer is a layer including a crystal formed by growth from the crystalline region.
1. A semiconductor device comprising:
an electrode over a substrate;
a first insulating layer;
an oxide semiconductor layer overlapping with the electrode with the first insulating layer provided therebetween;
a source electrode and a drain electrode electrically connected to the oxide semiconductor layer;
a second insulating layer over the source electrode and the drain electrode and in contact with the oxide semiconductor layer; and
a third insulating layer over the second insulating layer,
wherein:
the oxide semiconductor layer comprises a first region and a second region, the first region being closer to the substrate than the second region,
the second region comprises a crystalline region, and
the crystalline region includes crystals whose c-axes are aligned.
2. The semiconductor device according to claim 1 , wherein side surfaces of the oxide semiconductor layer are covered by the source electrode and the drain electrode.
3. The semiconductor device according to claim 1 , further comprising a conductive layer overlapping with the electrode,
wherein the conductive layer comprises an indium zinc oxide.
4. The semiconductor device according to claim 1 , wherein the oxide semiconductor layer comprises a channel formation region.
5. The semiconductor device according to claim 1 ,
wherein the oxide semiconductor layer comprises a material represented by InGa x Zn y O z where each of x, y, and z is an arbitrary number other than zero, and
wherein at least one of x, y, and z is a non-integer number.
6. The semiconductor device according to claim 1 , wherein the second region has a higher electric conductivity than the first region.
7. A semiconductor device comprising:
a gate electrode over a glass substrate;
a gate insulating layer over the gate electrode;
an oxide semiconductor layer over the gate insulating layer;
a source electrode and a drain electrode electrically connected to the oxide semiconductor layer;
a first insulating layer over the source electrode and the drain electrode and in contact with the oxide semiconductor layer; and
a second insulating layer over the first insulating layer,
wherein:
the gate electrode has a two-layer structure,
each of the source electrode and the drain electrode has a three-layer structure,
the oxide semiconductor layer comprises a first oxide semiconductor layer and a second oxide semiconductor layer,
the first oxide semiconductor layer comprises a first crystalline region,
the second oxide semiconductor layer comprises a second crystalline region, and
one of the first crystalline region and the second crystalline region includes crystals whose c-axes are aligned.
8. The semiconductor device according to claim 7 , wherein side surfaces of the oxide semiconductor layer are covered by the source electrode and the drain electrode.
9. The semiconductor device according to claim 7 , further comprising a conductive layer overlapping with the gate electrode,
wherein the conductive layer comprises an indium zinc oxide.
10. The semiconductor device according to claim 7 , wherein the oxide semiconductor layer comprises a channel formation region.
11. The semiconductor device according to claim 7 ,
wherein the oxide semiconductor layer comprises a material represented by InGa x Zn y O z where each of x, y, and z is an arbitrary number other than zero, and
wherein at least one of x, y, and z is a non-integer number.
12. A semiconductor device comprising:
a gate electrode over a glass substrate;
a gate insulating layer over the gate electrode;
an oxide semiconductor layer, comprising a material represented by InGa x Zn y O z where each of x, y, and z is an arbitrary number other than zero, over the gate insulating layer;
a source electrode and a drain electrode electrically connected to the oxide semiconductor layer;
a first insulating layer over the source electrode and the drain electrode and in contact with the oxide semiconductor layer; and
a second insulating layer over the first insulating layer,
wherein:
the gate electrode has a two-layer structure, one of two layers of the two-layer structure comprising aluminum and the other of the two layers of the two-layer structure comprising molybdenum,
each of the source electrode and the drain electrode has a three-layer structure, the three-layer structure comprising a first layer comprising titanium, a second layer comprising aluminum, and a third layer comprising titanium,
the oxide semiconductor layer comprises a first oxide semiconductor layer and a second oxide semiconductor layer,
the first oxide semiconductor layer comprises a first region and a second region, the first region being closer to the glass substrate than the second region,
the second region comprises a crystalline region, and
the crystalline region has c-axis aligned in a direction perpendicular to a surface of the oxide semiconductor layer.
13. The semiconductor device according to claim 12 , wherein side surfaces of the oxide semiconductor layer are covered by the source electrode and the drain electrode.
14. The semiconductor device according to claim 12 , further comprising a conductive layer overlapping with the gate electrode,
wherein the conductive layer comprises an indium zinc oxide.
15. The semiconductor device according to claim 12 , wherein the oxide semiconductor layer comprises a channel formation region.
16. The semiconductor device according to claim 12 , wherein at least one of x, y, and z is a non-integer number.