Semiconductor device with oxide semiconductor channel
View Patent ↗To give stable electrical characteristics to and improve reliability of a semiconductor device including a transistor in which an oxide semiconductor film is used for a channel formation region. As a base film, an insulating film or an oxide semiconductor film is used. A single-layer metal film is formed over the base film. After that, a resist mask is formed, and etching is performed plural times. Accordingly, electrodes each including projecting portions when seen in cross-section are formed. Even when a gate insulating film over the source electrode layer and the drain electrode layer or an oxide semiconductor film has a small thickness, disconnection of the gate insulating film is unlikely to occur.
1. A semiconductor device comprising:
a first conductive layer;
a first insulating film over the first conductive layer;
an oxide semiconductor film which is over the first insulating film and comprises a channel formation region;
a source electrode layer which is over the oxide semiconductor film and is electrically connected to the oxide semiconductor film;
a drain electrode layer which is over the oxide semiconductor film and is electrically connected to the oxide semiconductor film;
a second insulating film over the oxide semiconductor film, the source electrode layer, and the drain electrode layer; and
a second conductive layer which is over the second insulating film and overlaps with the channel formation region,
wherein each of the source electrode layer and the drain electrode layer comprises a single-layer metal film,
wherein the single-layer metal film comprises a first region and a second region,
wherein the first region overlaps with the oxide semiconductor film and the first conductive layer, and the second region does not overlap with the oxide semiconductor film and the first conductive layer, the first region comprising a first portion and a second portion,
wherein the second portion projects from the first portion along a channel length direction and is closer to a center of the first conductive layer than the first portion, and
wherein each of the first portion and the second portion has a top flat surface substantially parallel to a bottom flat surface, both surfaces extending in the channel length direction, wherein a distance between the top flat surface and the bottom flat surface measures a thickness and the thickness of the second portion is smaller than that of the first portion.
2. The semiconductor device according to claim 1 ,
wherein the first insulating film comprises an oxygen-excess region, and
wherein the first insulating film has a smaller thickness in a region overlapping with the first conductive layer than in another region.
3. The semiconductor device according to claim 1 , wherein the oxide semiconductor film is stacked oxide semiconductor films having different compositions.
4. The semiconductor device according to claim 1 ,
wherein the oxide semiconductor film comprises a depressed portion and overlaps with the first conductive layer, and
wherein a region having a small thickness of the oxide semiconductor film is the channel formation region.
5. The semiconductor device according to claim 1 , wherein a channel length is a distance between the second portion of the source electrode layer extending in the channel length direction and the second portion of the drain electrode layer extending in the channel length direction.
6. The semiconductor device according to claim 1 , further comprising:
a third insulating film overlapping with the source electrode layer and the drain electrode layer,
wherein the second insulating film is over and in contact with the first insulating film.
7. A semiconductor device comprising:
a first conductive layer;
a first insulating film over the first conductive layer;
a second insulating film containing gallium oxide over the first insulating film;
an oxide semiconductor film which is over and in contact with the second insulating film and comprises a channel formation region;
a source electrode layer which is over the oxide semiconductor film and is electrically connected to the oxide semiconductor film;
a drain electrode layer which is over the oxide semiconductor film and is electrically connected to the oxide semiconductor film;
a third insulating film containing gallium oxide over the oxide semiconductor film, the source electrode layer, and the drain electrode layer;
a second conductive layer which is over the third insulating film and overlaps with the channel formation region,
wherein each of the source electrode layer and the drain electrode layer comprises a single-layer metal film,
wherein the single-layer metal film comprises a first region and a second region,
wherein the first region overlaps with the oxide semiconductor film overlap with the first conductive layer, and the second region does not overlap with the oxide semiconductor film and the first conductive layer, the first region comprising a first portion and a second portion,
wherein the second portion projects from the first portion along a channel length direction and is closer to a center of the first conductive layer than the first portion, and
wherein each of the first portion and the second portion has a top flat surface substantially parallel to a bottom flat surface, both surfaces extending in the channel length direction, wherein a distance between the top flat surface and the bottom flat surface measures a thickness and the thickness of the second portion is smaller than that of the first portion.
8. The semiconductor device according to claim 7 ,
wherein the oxide semiconductor film has a crystal structure, and
wherein the second insulating film and the third insulating film have a lower crystallinity than the oxide semiconductor film.
9. The semiconductor device according to claim 7 , wherein an end portion of the second insulating film is continuously changed to an end of the oxide semiconductor film.
10. The semiconductor device according to claim 7 , wherein the oxide semiconductor film is stacked oxide semiconductor films having different compositions.
11. The semiconductor device according to claim 7 ,
wherein the oxide semiconductor film comprises a depressed portion and overlaps with the first conductive layer, and
wherein a region having a small thickness of the oxide semiconductor film is the channel formation region.
12. The semiconductor device according to claim 7 , wherein a channel length is a distance between the second portion of the source electrode layer extending in the channel length direction and the second portion of the drain electrode layer extending in the channel length direction.
13. The semiconductor device according to claim 7 , further comprising:
a fourth insulating film overlapping with the source electrode layer and the drain electrode layer,
wherein the third insulating film is over and in contact with the first insulating film.
14. The semiconductor device according to claim 7 , further comprising:
a fourth insulating film is over and in contact with the top surface of the second portion.
15. The semiconductor device according to claim 1 , further comprising:
a third insulating film is over and in contact with the top surface of the second portion.