Semiconductor device comprising thin film transistor comprising conductive film having tapered edge
View Patent ↗There is provided a thin film transistor having improved reliability. A gate electrode includes a first gate electrode having a taper portion and a second gate electrode with a width narrower than the first gate electrode. A semiconductor layer is doped with phosphorus of a low concentration through the first gate electrode. In the semiconductor layer, two kinds of n − -type impurity regions are formed between a channel formation region and n + -type impurity regions. Some of the n − -type impurity regions overlap with a gate electrode, and the other n − -type impurity regions do not overlap with the gate electrode. Since the two kinds of n − -type impurity regions are formed, an off current can be reduced, and deterioration of characteristics can be suppressed.
1. An electronic equipment having a display device comprising:
a substrate;
a pixel TFT only in a pixel portion which can display a picture over the substrate;
a driving circuit over the substrate;
an interlayer insulating film; and
a pixel electrode,
wherein the driving circuit is located outside the pixel portion,
wherein the pixel TFT comprises:
a first semiconductor island including at least a first channel formation region, a second channel formation region, lightly doped regions and source and drain regions;
a first gate insulating film formed over the first semiconductor island;
a first gate electrode formed over the first channel formation region with the first gate insulating film interposed therebetween; and
a second gate electrode formed over the second channel formation region with the first gate insulating film interposed therebetween,
wherein the driving circuit comprises a thin film transistor, said thin film transistor comprising:
a second semiconductor island including at least a third channel formation region;
a second gate insulating film formed over the second semiconductor island; and
a third gate electrode formed over the third channel formation region with the second gate insulating film interposed therebetween,
wherein the interlayer insulating film covers the first, second and third gate electrodes and said first and second semiconductor islands,
wherein the pixel electrode is formed over the interlayer insulating film and electrically connected to one of the source and drain regions of the first semiconductor island, and
wherein each of the first, second and third gate electrodes has tapered edges with a taper angle in a range of 3° to 60°.
2. The electronic equipment according to claim 1 , wherein each of said pixel TFT and thin film transistor in the driving circuit is an N-channel thin film transistor.
3. The electronic equipment according to claim 1 , wherein each of said first, second and third gate electrodes comprises a metal selected from the group consisting of chromium, tantalum, titanium, tungsten, and molybdenum.
4. The electronic equipment according to claim 1 , wherein said pixel electrode comprises zinc oxide.
5. The electronic equipment according to claim 1 , wherein said taper angle is in a range of 5° to 45°.
6. The electronic equipment according to claim 1 , wherein said taper angle is in a range of 7° to 20°.
7. The electronic equipment according to claim 1 , wherein said electronic equipment includes one of a video camera, a digital camera, a projector, a head mount display, a navigation system for a vehicle, a personal computer, and a portable information terminal.
8. An electronic equipment according to claim 1 , having a display device wherein each of said lightly doped regions is partly overlapped by tapered portions of the first or second gate electrode and extends beyond a side edge of the first or second gate electrode.
9. The electronic equipment according to claim 1 , wherein the first gate insulating film and the second gate insulating film are a same insulating film.
10. An electronic equipment having a display device comprising:
a substrate;
a pixel portion only in a region which can display a picture over the substrate;
a driving circuit over the substrate;
a capacitor electrode;
an interlayer insulating film; and
a pixel electrode,
wherein the driving circuit is located outside the pixel portion,
wherein the pixel portion comprises:
a first semiconductor island including at least a first channel formation region, a second channel formation region, lightly doped regions, and a capacitor forming region;
a first gate insulating film formed over the first semiconductor island;
a first gate electrode formed over the first channel formation region with the first gate insulating film interposed therebetween; and
a second gate electrode formed over the second channel formation region with the first gate insulating film interposed therebetween,
wherein the driving circuit comprises:
a second semiconductor island including at least a third channel formation region; and
a third gate electrode formed over the third channel formation region with a second gate insulating film interposed therebetween,
wherein the capacitor electrode is formed over the capacitor forming region of the first semiconductor island with the first gate insulating film interposed therebetween,
wherein the interlayer insulating film covers the first, second and third gate electrodes and said first and second semiconductor islands,
wherein the pixel electrode is formed over the interlayer insulating film and electrically connected to an impurity region of the first semiconductor island,
wherein each of the first, second and third gate electrodes and said capacitor electrode has tapered edges with a taper angle in a range of 3° to 60°,
wherein the first channel formation region, the second channel formation region, the lightly doped regions, the impurity region, at least a part of the first gate insulating film, the first gate electrode and the second gate electrode constitute at least a part of a pixel TFT, and
wherein the second semiconductor island, the third gate electrode and at least a part of the second gate insulating film constitute at least a part of a thin film transistor in the driving circuit.
11. The electronic equipment according to claim 10 , wherein each of said pixel TFT and thin film transistor in the driving circuit is an N-channel thin film transistor.
12. The electronic equipment according to claim 10 , wherein each of said first, second and third gate electrodes comprises a metal selected from the group consisting of chromium, tantalum, titanium, tungsten, and molybdenum.
13. The electronic equipment according to claim 10 , wherein said pixel electrode comprises zinc oxide.
14. The electronic equipment according to claim 10 , wherein said taper angle is in a range of 5° to 45°.
15. The electronic equipment according to claim 10 , wherein said taper angle is in a range of 7° to 20°.
16. The electronic equipment according to claim 10 , wherein said electronic equipment includes one of a video camera, a digital camera, a projector, a head mount display, a navigation system for a vehicle, a personal computer, and a portable information terminal.
17. The electronic equipment according to claim 10 , wherein the first gate insulating film and the second gate insulating film are a same insulating film.
18. An electronic equipment having a display device comprising:
a substrate;
a pixel TFT only in a pixel portion which can display a picture over the substrate; and
a driving circuit over the substrate,
wherein the driving circuit is located outside the pixel portion,
wherein the pixel TFT comprises:
a first semiconductor island including at least a first channel formation region, a second channel formation region, lightly doped regions and source and drain regions;
a first gate insulating film formed over the first semiconductor island;
a first gate electrode formed over the first channel formation region with the first gate insulating film interposed therebetween; and
a second gate electrode formed over the second channel formation region with the first gate insulating film interposed therebetween,
wherein the driving circuit comprises a thin film transistor, said thin film transistor comprising:
a second semiconductor island including at least a third channel formation region;
a second gate insulating film formed over the second semiconductor island; and
a third gate electrode formed over the third channel formation region with the second gate insulating film interposed therebetween,
wherein the interlayer insulating film covers the first, second and third gate electrodes and said first and second semiconductor islands;
wherein the pixel electrode is formed over the interlayer insulating film and electrically connected to one of the source and drain regions of the first semiconductor island,
wherein each of the first, second and third gate electrodes includes a lower conductive layer and an upper conductive layer formed on the lower conductive layer, and
wherein said lower conductive layer extends beyond side edges of the upper conductive layer and extending portions of the lower conductive layer are tapered with a taper angle of 3° to 60°.
19. The electronic equipment according to claim 18 , wherein each of said pixel TFT and thin film transistor in the driving circuit is an N-channel thin film transistor.
20. The electronic equipment according to claim 18 , wherein said lower conductive layer comprises a metal selected from the group consisting of chromium, tantalum, titanium, tungsten, and molybdenum.
21. The electronic equipment according to claim 18 , wherein said upper conductive layer comprises a metal selected from the group consisting of aluminum, tantalum, titanium, tungsten and molybdenum.
22. The electronic equipment according to claim 18 , wherein said pixel electrode comprises zinc oxide.
23. The electronic equipment according to claim 18 , wherein said taper angle is in a range of 5° to 45°.
24. The electronic equipment according to claim 18 , wherein said taper angle is in a range of 7° to 20°.
25. The electronic equipment according to claim 18 , wherein said electronic equipment includes one of a video camera, a digital camera, a projector, a head mount display, a navigation system for a vehicle, a personal computer, and a portable information terminal.
26. An electronic equipment according to claim 18 ,
wherein each of said lightly doped regions is partly overlapped by the extending portion of the lower conductive layer of the first or second gate electrode and extends beyond a side edge of the lower conductive layer of the first or second gate electrode.
27. The electronic equipment according to claim 18 , wherein the first gate insulating film and the second gate insulating film are a same insulating film.
28. An electronic equipment having a display device comprising:
a substrate;
a pixel portion only in a region which can display a picture over the substrate;
a driving circuit over the substrate;
a capacitor electrode;
an interlayer insulating film; and
a pixel electrode,
wherein the driving circuit is located outside the pixel portion,
wherein the pixel portion comprises:
a first semiconductor island including at least a first channel formation region, a second channel formation region, lightly doped regions, and a capacitor forming region;
a first gate insulating film formed over the first semiconductor island;
a first gate electrode formed over the first channel formation region with the first gate insulating film interposed therebetween; and
a second gate electrode formed over the second channel formation region with the first gate insulating film interposed therebetween,
wherein the driving circuit comprises:
a second semiconductor island including at least a third channel formation region; and
a third gate electrode formed over the third channel formation region with a second gate insulating film interposed therebetween,
wherein the capacitor electrode is formed over the capacitor forming region of the first semiconductor island with the first gate insulating film interposed therebetween,
wherein the interlayer insulating film covers the first, second and third gate electrodes and said first and second semiconductor islands;
wherein the pixel electrode is formed over the interlayer insulating film and electrically connected to an impurity region of the first semiconductor island,
wherein each of the first, second and third gate electrodes includes a lower conductive layer and an upper conductive layer formed on the lower conductive layer,
wherein said lower conductive layer extends beyond side edges of the upper conductive layer and extending portions of the lower conductive layer are tapered with a taper angle of 3° to 60°,
wherein the first channel formation region, the second channel formation region, the lightly doped regions, the impurity region, at least a part of the first gate insulating film, the first gate electrode and the second gate electrode constitute at least a part of a pixel TFT, and
wherein the second semiconductor island, the third gate electrode and at least a part of the second gate insulating film constitute at least a part of a thin film transistor in the driving circuit.
29. The electronic equipment according to claim 28 , wherein said lower conductive layer comprises a metal selected from the group consisting of chromium, tantalum, titanium, tungsten, and molybdenum.
30. The electronic equipment according to claim 28 , wherein said upper conductive layer comprises a metal selected from the group consisting of aluminum, tantalum, titanium, tungsten and molybdenum.
31. The electronic equipment according to claim 28 , wherein said pixel electrode comprises zinc oxide.
32. The electronic equipment according to claim 28 , wherein said taper angle is in a range of 5° to 45°.
33. The electronic equipment according to claim 28 , wherein said taper angle is in a range of 7° to 20°.
34. The electronic equipment according to claim 28 , wherein said electronic equipment includes one of a video camera, a digital camera, a projector, a head mount display, a navigation system for a vehicle, a personal computer, and a portable information terminal.
35. The electronic equipment according to claim 28 , wherein each of said pixel TFT and thin film transistor in the driving circuit is an N-channel thin film transistor.
36. The electronic equipment according to claim 28 , wherein the first gate insulating film and the second gate insulating film are a same insulating film.