Display device and manufacturing method thereof
A gate insulating film is formed over a gate electrode; a microcrystalline semiconductor is formed over the gate insulating film; an impurity element for controlling the threshold value is added into the microcrystalline semiconductor film by an ion implantation method; the microcrystalline semiconductor film is irradiated with a laser beam so that the crystallinity of the microcrystalline semiconductor film is improved; and then, a buffer layer is formed over the microcrystalline semiconductor film, whereby a channel-etched thin film transistor is formed. Further, a display device including the thin film transistor is manufactured.
1. A method for manufacturing a display device, comprising the steps of:
forming a gate electrode over a substrate;
forming a first insulating film over the gate electrode;
forming a first semiconductor film over the first insulating film;
adding a first impurity into the first semiconductor film, the first impurity imparting a first conductivity type or a second conductivity type;
irradiating the first semiconductor film with laser light at a region in which the first semiconductor film and the gate electrode are overlapped, after adding the first impurity into the first semiconductor film;
forming a buffer layer over the first semiconductor film after irradiating the first semiconductor film with laser light;
forming a second semiconductor film over the buffer layer, the second semiconductor film including a second impurity which imparts the first conductivity type;
etching the first semiconductor film, the buffer layer, and the second semiconductor film;
forming a conductive film over the second semiconductor film so that the conductive film is in contact with the first insulating film and side surfaces of the first semiconductor film, the buffer layer, and the second semiconductor film; and
etching the conductive film to form a source electrode and a drain electrode over the second semiconductor film,
wherein the first semiconductor film is a microcrystalline semiconductor film, and
wherein the buffer layer is an amorphous semiconductor film.
2. The method for manufacturing a display device, according to claim 1 , after forming the first semiconductor film and before adding the first impurity, further comprising a step of irradiating the first semiconductor film with laser light.
3. The method for manufacturing a display device, according to claim 1 , wherein the first conductivity type is an n-type, and the second conductivity type is a p-type.
4. The method for manufacturing a display device according to claim 1 , further comprising the steps of:
etching the conductive film to form the source electrode over a first portion of the second semiconductor film and the drain electrode over a second portion of the second semiconductor film;
etching a first portion of the buffer layer between the first portion of the second semiconductor film and the second portion of the second semiconductor film; and
forming a second insulating film over the source electrode and the drain electrode so that the second insulating film is in contact with the first portion of the buffer layer.
5. The method for manufacturing a display device according to claim 1 , further comprising the steps of:
wet etching the conductive film to form the source electrode over a first portion of the second semiconductor film and the drain electrode over a second portion of the second semiconductor film;
etching a first portion of the buffer layer between the first portion of the second semiconductor film and the second portion of the second semiconductor film; and
forming a second insulating film over the source electrode and the drain electrode so that the second insulating film is in contact with the first portion of the buffer layer.
6. The method for manufacturing a display device, according to claim 1 , wherein the buffer layer includes nitrogen or hydrogen.
7. The method for manufacturing a display device, according to claim 1 , wherein the buffer layer includes fluorine, chlorine, bromine, or iodine.
8. A method for manufacturing a display device, comprising the steps of:
forming a gate electrode over a substrate;
forming a first insulating film over the gate electrode;
forming a first semiconductor film over the first insulating film;
adding a first impurity into the first semiconductor film;
irradiating the first semiconductor film with laser light after adding the first impurity into the first semiconductor film;
forming a buffer layer over the first semiconductor film after irradiating the first semiconductor film with laser light;
forming a second semiconductor film over the buffer layer;
etching the first semiconductor film, the buffer layer, and the second semiconductor film;
forming a conductive film over the second semiconductor film;
etching the conductive film to form a source electrode over a first portion of the second semiconductor film and a drain electrode over a second portion of the second semiconductor film;
etching a first portion of the buffer layer between the first portion of the second semiconductor film and the second portion of the second semiconductor film; and
forming a second insulating film over the source electrode and the drain electrode so that the second insulating film is in contact with the first portion of the buffer layer,
wherein the first semiconductor film is a microcrystalline semiconductor film, and
wherein the buffer layer is an amorphous semiconductor film.
9. The method for manufacturing a display device, according to claim 8 , wherein a conductivity type of the first impurity is an n-type or a p-type.
10. The method for manufacturing a display device, according to claim 8 , wherein the buffer layer includes nitrogen or hydrogen.
11. The method for manufacturing a display device, according to claim 8 , wherein the buffer layer includes fluorine, chlorine, bromine, or iodine.
12. A method for manufacturing a display device, comprising the steps of:
forming a gate electrode over a substrate;
forming a first insulating film over the gate electrode;
forming a first semiconductor film over the first insulating film;
adding a first impurity into the first semiconductor film;
cleaning a surface of the first semiconductor film;
irradiating the first semiconductor film with laser light after cleaning the surface of the first semiconductor film;
forming a buffer layer over the first semiconductor film after irradiating the first semiconductor film with laser light;
forming a second semiconductor film comprising a second impurity over the buffer layer;
forming a conductive film over the second semiconductor film;
wet etching the conductive film to form a source electrode over a first portion of the second semiconductor film and a drain electrode over a second portion of the second semiconductor film;
etching a first portion of the buffer layer between the first portion of the second semiconductor film and the second portion of the second semiconductor film; and
forming a second insulating film over the source electrode and the drain electrode so that the second insulating film is in contact with the first portion of the buffer layer,
wherein the first semiconductor film is a microcrystalline semiconductor film, and
wherein the buffer layer is an amorphous semiconductor film.
13. The method for manufacturing a display device according to claim 12 , further comprising the step of removing an oxide film formed on the first semiconductor film before forming the buffer layer over the first semiconductor film.
14. The method for manufacturing a display device according to claim 13 , further comprising the step of processing a surface of the buffer layer with at least one of hydrogen plasma, nitrogen plasma, and halogen plasma before forming the second semiconductor film.
15. The method for manufacturing a display device according to claim 12 , further comprising the step of irradiating the first semiconductor film with laser light before adding the first impurity into the first semiconductor film.
16. The method for manufacturing a display device according to claim 15 , further comprising the step of removing an oxide film formed on the first semiconductor film after adding the first impurity into the first semiconductor film.