Semiconductor device

• US 6,501,098 B2
• Filed: 11/23/1999
• Issued: 12/31/2002
• Est. Priority Date: 11/25/1998
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yamazaki, Shunpei
• Primary Examiner(s): Thomas, Tom
• Assistant Examiner(s): Nadav, Ori
• Application Number:
  US09/447,574
• Publication Number:
  US 20020139980A1
• Time in Patent Office: 1,134 Days
• Field of Search: 257/72, 257/59, 257/347-354
• US Class Current: 257/72
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: H01L 2029/7863 with an LDD consisting of more than one lightly doped zone or having a non-homogeneous dopant distribution, e.g. graded LDD
• CPC Class Codes: H01L 21/28114 characterised by the sectional shape, e.g. T, inverted-T
• CPC Class Codes: H01L 27/088 the components being field-effect transistors with insulated gate
• CPC Class Codes: H01L 27/124 with a particular composition, shape or layout of the wiring layers specially adapted to the circuit arrangement, e.g. scanning lines in LCD pixel circuits wiring structures per se H01L23/52
• CPC Class Codes: H01L 29/42384 for thin film field effect transistors, e.g. characterised by the thickness or the shape of the insulator or the dimensions, the shape or the lay-out of the conductor
• CPC Class Codes: H01L 29/4908 for thin film semiconductor, e.g. gate of TFT
• CPC Class Codes: H01L 29/66757 Lateral single gate single channel transistors with non-inverted structure, i.e. the channel layer is formed before the gate
• CPC Class Codes: H01L 29/786 Thin film transistors, i.e. transistors with a channel being at least partly a thin film transistors having only the source or the drain region on an insulator layer H01L29/0653; thin film FinFETs H01L29/785
• CPC Class Codes: H01L 29/78624 the source and the drain regions being asymmetrical
• CPC Class Codes: H01L 29/78627 with a significant overlap between the lightly doped drain and the gate electrode, e.g. GOLDD

Abstract

The gate electrode of a crystalline TFT is constructed as a clad structure which consists of a first gate electrode, a second gate electrode and a third gate electrode, thereby to enhance the thermal resistance of the gate electrode. Besides, an n-channel TFT is provided with a low-concentration impurity region which adjoins a channel forming region, and which includes a subregion overlapped by the gate electrode and a subregion not overlapped by the gate electrode, thereby to mitigate a high electric field near the drain of the TFT and to simultaneously prevent the OFF current of the TFT from increasing.

Claims

1. A semiconductor device including at least one TFT formed over a substrate, said TFT including a semiconductor layer, a gate insulating film formed in contact with the semiconductor layer and a gate electrode formed in contact with the gate insulating film,

wherein said gate electrode includes a first conductive layer which is formed in contact with said gate insulating film, a second conductive layer which is formed on and inside a periphery of an upper surface of said first conductive layer, and a third conductive layer which is formed in contact with said first conductive layer and with top and side surfaces of said second conductive layer, wherein said second conductive layer comprises a different material from that of said first and third conductive layers;

wherein said semiconductor layer includes a channel forming region, a first impurity region of one conductivity type, and a second impurity region of said one conductivity type which is formed between said channel forming region and said first impurity region; and

wherein a part of said second impurity region of said one conductivity type lies under said first conductive layer of said gate electrode.

2. A semiconductor device according to claim 1, wherein a concentration of an impurity element of said one conductivity type is lower in said second impurity region of said first conductivity type than in said first impurity region of said first conductivity type.

3. A semiconductor device according to either of claims 1 and 2, wherein a retention capacitance is formed of an impurity region of said one conductivity type which is provided at one end of said semiconductor layer, said gate insulating film, and a wiring line which is constituted by said first conductive layer of said gate electrode, said second conductive layer thereof and said third conductive layer thereof, and said retention capacitance is connected to either of a source and a drain of said TFT.

8. A semiconductor device according to any one of claims 1, 4, 5 and 6, wherein each of said first conductive layer and said third conductive layer comprises at least one material selected from the group consisting of silicon, titanium, tantalum, tungsten and molybdenum, and a compound thereof.

9. A semiconductor device according to any one of claims 1, 4, 5 and 6, wherein said second conductive layer of said gate electrode comprises at least one material selected from the group consisting of aluminum and copper, and a compound thereof.

4. A semiconductor device wherein a pixel portion has at least one pixel TFT,

wherein a gate electrode of said pixel TFT includes a first conductive layer which is formed in contact with a gate insulating film, a second conductive layer which is formed on said first conductive layer and inside a periphery of an upper surface of said first layer, and a third conductive layer which is formed in contact with said first conductive layer and with top and side surfaces of said second conductive layer wherein said second conductive layer comprises a different material from that of said first and third conductive layers;

wherein a semiconductor layer of said pixel TFT includes a channel forming region, a first impurity region of one conductivity type, and a second impurity region of said one conductivity type which is formed between said channel forming region and said first impurity region; and

wherein a part of said second impurity region of said one conductivity type lies under said first layer of said gate electrode.

7. A semiconductor device according to either of claims 4 and 6, wherein a retention capacitance is formed of an impurity region of said one conductivity type which is provided at one end of said semiconductor layer, said gate insulating film, and a wiring line which is constituted by said first conductive layer, said second conductive layer and said third conductive layer of said gate electrode, and said retention capacitance is connected to either of a source and a drain of said pixel TFT.

5. A semiconductor device including at least one CMOS circuit which is constituted by an n-channel TFT and a p-channel TFT, wherein

a gate electrode of said n-channel TFT includes a first conductive layer which is formed in contact with a gate insulating film, a second conductive layer which is formed on said first conductive layer and inside a periphery of an upper surface of said first conductive layer, and a third conductive layer which is formed in contact with said first conductive layer and said second conductive layer wherein said second conductive layer comprises a different material from that of said first and third conductive layers;

a semiconductor layer of said n-channel TFT includes a channel forming region, a first impurity region of one conductivity type, and a second impurity region of said one conductivity type which is formed between said channel forming region and said first impurity region;

a part of said second impurity region of said one conductivity type lies under said first conductive layer of said gate electrode;

a semiconductor layer of said p-channel TFT includes a channel forming region, and a third impurity region which lies in contact with said channel forming region; and

said third impurity region includes a subregion which lies in contact with said channel forming region and which contains an impurity element of a conductivity type opposite to said one conductivity type, and a subregion which contains an impurity element of said one conductivity type and an impurity element of the opposite conductivity type.

6. A semiconductor device including a pixel portion which is constituted by at least one pixel TFT, and a CMOS circuit which is constituted by an n-channel TFT and a p-channel TFT, wherein:

a gate electrode of each of said pixel TFT and said n-channel TFT includes a first conductive layer which is formed in contact with a gate insulating film, a second conductive layer which is formed on said first conductive layer and inside a periphery of an upper surface of said first conductive layer, and a third conductive layer which is formed in contact with said first conductive layer and said second conductive layer wherein said second conductive layer comprises a different material from that of said first and third conductive layers;

a semiconductor layer of each of said pixel TFT and said n-channel TFT includes a channel forming region, a first impurity region of one conductivity type, and a second impurity region of said one conductivity type which is formed between said channel forming region and said first impurity region;

a part of said second impurity region of said one conductivity type lies under said first conductive layer of said gate electrode;

a semiconductor layer of said p-channel TFT includes a channel forming region, and a third impurity region which lies in contact with said channel forming region; and

said third impurity region includes a subregion which lies in contact with said channel forming region and which contains an impurity element of a conductivity type opposite to said one conductivity type, and a subregion which contains an impurity element of said one conductivity type and an impurity element of the opposite conductivity type.

10. A semiconductor device comprising:

at least one thin film transistor formed over a substrate, said thin film transistor comprising;

a semiconductor layer comprising a channel forming region, a first impurity region of one conductivity type and a second impurity region between the channel forming region and the first impurity region;

an insulating film over the semiconductor layer;

a gate electrode formed over the semiconductor layer with the insulating film interposed therebetween, said gate electrode comprising a first conductive layer which contacts said insulating film, a second conductive layer formed on said first conductive layer, and a third conductive layer formed on said second conductive layer, wherein said first conductive layer extends beyond side edges of the second conductive layer, and said third conductive layer extends beyond the side edges of the second conductive layer and at least one side edge of the third conductive layer is coextensive with a side edge of the first conductive layer, wherein said second conductive layer comprises a different material from that of said first and third conductive layers;

wherein a part of said second impurity region is located below the first conductive layer of the gate electrode.

11. A semiconductor device according to claim 10, wherein said second impurity region has a same conductivity type as said first impurity region.

12. A semiconductor device according to claim 10, wherein said second impurity region contains an impurity at a lower concentration than said first impurity region.

13. A semiconductor device according to claim 10 further comprising a capacitance which comprises a portion of the semiconductor layer, a portion of the insulating film and a wiring, wherein said wiring is constituted by same layers as said first, second and third conductive layers of the gate electrode.

14. A semiconductor device according to claim 10, wherein at least one of said first and second conductive layers of the gate electrode comprises at least one material selected from the group consisting of silicon, titanium, tantalum, tungsten, molybdenum, and a compound thereof.

15. A semiconductor device according to claim 10, wherein said second conductive layer of the gate electrode comprises at least one material selected from the group consisting of aluminum, copper, and a compound thereof.

16. A semiconductor device according to claim 10, wherein said semiconductor device is a display device which employs an electroluminescent material.

17. A semiconductor device according to claim 10 wherein said thin film transistor is connected to a pixel electrode.

18. A semiconductor device according to claim 10, wherein said semiconductor device is selected from the group consisting of a personal computer, a video camera, a portable information terminal, a digital camera, a player used for a recording medium, a goggle type display device, an electronic book, a portable telephone set and a projector.

19. A semiconductor device comprising:

at least one thin film transistor formed over a substrate, said thin film transistor comprising;

a semiconductor layer comprising a channel forming region, a first impurity region of one conductivity type and a second impurity region between the channel forming region and the first impurity region;

an insulating film formed over the semiconductor layer;

a gate electrode adjacent to the channel forming region with the insulating film interposed therebetween, said gate electrode comprising a first conductive layer formed on said insulating film, a second conductive layer formed on said first conductive layer, and a third conductive layer formed on and in contact with said second conductive layer, wherein said first conductive layer extends beyond side edges of the second conductive layer, and said third conductive layer extends beyond the side edges of the second conductive layer so that said third conductive layer contacts upper surfaces of the first conductive layer which are not covered by the second conductive layer, wherein the second conductive layer comprises a different material from that of said first and third conductive layers;

wherein a part of said second impurity region is located below the first conductive layer of the gate electrode.

20. A semiconductor device according to claim 19, wherein said second impurity region has a same conductivity type as said first impurity region.

21. A semiconductor device according to claim 19, wherein said second impurity region contains an impurity at a lower concentration than said first impurity region.

22. A semiconductor device according to claim 19 further comprising a capacitance which comprises a portion of the semiconductor layer, a portion of the insulating film and a wiring, wherein said wiring is constituted by same layers as said first, second and third conductive layers of the gate electrode.

23. A semiconductor device according to claim 19, wherein at least one of said first and second conductive layers of the gate electrode comprises at least one material selected from the group consisting of silicon, titanium, tantalum, tungsten, molybdenum, and a compound thereof.

24. A semiconductor device according to claim 19, wherein said second conductive layer of the gate electrode comprises at least one material selected from the group consisting of aluminum, copper, and a compound thereof.

25. A semiconductor device according to claim 19, wherein said semiconductor device is a display device which employs an electroluminescent material.

26. A semiconductor device according to claim 19, wherein said thin film transistor is connected to a pixel electrode.

27. A semiconductor device according to claim 19, wherein said semiconductor device is selected from the group consisting of a personal computer, a video camera, a portable information terminal, a digital camera, a player used for a recording medium, a goggle type display device, an electronic book, a portable telephone set and a projector.