Semiconductor device and method for manufacturing the same
It is an object to manufacture and provide a highly reliable display device including a thin film transistor with a high aperture ratio which has stable electric characteristics. In a manufacturing method of a semiconductor device having a thin film transistor in which a semiconductor layer including a channel formation region is formed using an oxide semiconductor film, a heat treatment for reducing moisture and the like which are impurities and for improving the purity of the oxide semiconductor film (a heat treatment for dehydration or dehydrogenation) is performed. Further, an aperture ratio is improved by forming a gate electrode layer, a source electrode layer, and a drain electrode layer using conductive films having light transmitting properties.
1. A method for manufacturing a semiconductor device comprising the steps of:
forming a gate electrode;
forming a gate insulating layer over the gate electrode;
forming an oxide semiconductor layer over the gate insulating layer;
performing a first heat treatment at a temperature higher than or equal to 400° C. on the oxide semiconductor layer, whereby a carrier concentration of the oxide semiconductor layer is increased;
forming a source electrode and a drain electrode over the oxide semiconductor layer after the first heat treatment;
forming an oxide insulating layer over and in contact with a part of the oxide semiconductor layer, whereby the carrier concentration of the oxide semiconductor layer is decreased; and
performing a second heat treatment after forming the oxide insulating layer,
wherein the part of the oxide semiconductor layer has a carrier concentration of less than 1×10 18 /cm 3 after the second heat treatment, and
wherein the source electrode and the drain electrode each comprises a conductive film having a light-transmitting property.
2. The method for manufacturing a semiconductor device according to claim 1 , wherein the first heat treatment is performed under a nitrogen atmosphere, a rare gas atmosphere, or an oxygen atmosphere.
3. The method for manufacturing a semiconductor device according to claim 2 , further comprising a step of cooling the oxide semiconductor layer after the first heat treatment under the oxygen atmosphere.
4. The method for manufacturing a semiconductor device according to claim 1 , wherein the first heat treatment is performed under reduced pressure.
5. The method for manufacturing a semiconductor device according to claim 1 , wherein the carrier concentration of the oxide semiconductor layer increased by the first heat treatment is higher than or equal to 1×10 18 /cm 3 by the first heat treatment.
6. The method for manufacturing a semiconductor device according to claim 1 , wherein the gate electrode comprises a transparent conductive film.
7. The method for manufacturing a semiconductor device according to claim 1 , wherein the oxide semiconductor layer comprises indium, gallium and zinc.
8. The method for manufacturing a semiconductor device according to claim 1 , wherein a temperature of the second heat treatment is higher than or equal to 150° C. and lower than 350° C.
9. The method for manufacturing a semiconductor device according to claim 1 , further comprising a step of forming a pixel electrode over the oxide insulating layer,
wherein the pixel electrode is electrically connected to one of the source electrode and the drain electrode.
10. The method for manufacturing a semiconductor device according to claim 9 ,
wherein the part of the oxide semiconductor layer comprises a channel formation region, and
wherein the pixel electrode overlaps with the channel formation region.
11. A method for manufacturing a semiconductor device comprising the steps of:
forming a gate electrode;
forming a gate insulating layer over the gate electrode;
forming an oxide semiconductor layer over the gate insulating layer;
performing dehydration or dehydrogenation on the oxide semiconductor layer by a first heat treatment at a temperature of higher than or equal to 400° C., whereby a carrier concentration of the oxide semiconductor layer is increased;
forming a source electrode and a drain electrode over the oxide semiconductor layer after the first heat treatment;
forming an oxide insulating layer over and in contact with a part of the oxide semiconductor layer, whereby the carrier concentration of the oxide semiconductor layer is decreased; and
performing a second heat treatment after forming the oxide insulating layer,
wherein the part of the oxide semiconductor layer has a carrier concentration of less than 1×10 18 /cm 3 after the second heat treatment, and
wherein the source electrode and the drain electrode each comprises a conductive film having a light-transmitting property.
12. The method for manufacturing a semiconductor device according to claim 11 , wherein the first heat treatment is performed under a nitrogen atmosphere, a rare gas atmosphere, or an oxygen atmosphere.
13. The method for manufacturing a semiconductor device according to claim 12 , further comprising a step of cooling the oxide semiconductor layer after the first heat treatment under the oxygen atmosphere.
14. The method for manufacturing a semiconductor device according to claim 11 , wherein the first heat treatment is performed under reduced pressure.
15. The method for manufacturing a semiconductor device according to claim 11 , wherein the carrier concentration of the oxide semiconductor layer increased by the first heat treatment is higher than or equal to 1×10 18 /cm 3 by the first heat treatment.
16. The method for manufacturing a semiconductor device according to claim 11 , wherein the gate electrode comprises a transparent conductive film.
17. The method for manufacturing a semiconductor device according to claim 11 , wherein the oxide semiconductor layer comprises indium, gallium and zinc.
18. The method for manufacturing a semiconductor device according to claim 11 , wherein a temperature of the second heat treatment is higher than or equal to 150° C. and lower than 350° C.
19. The method for manufacturing a semiconductor device according to claim 11 , further comprising a step of forming a pixel electrode over the oxide insulating layer,
wherein the pixel electrode is electrically connected to one of the source electrode and the drain electrode.
20. The method for manufacturing a semiconductor device according to claim 19 ,
wherein the part of the oxide semiconductor layer comprises a channel formation region, and
wherein the pixel electrode overlaps with the channel formation region.