Semiconductor device and method of fabricating the same

• US 7,235,810 B1
• Filed: 12/03/1999
• Issued: 06/26/2007
• Est. Priority Date: 12/03/1998
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Ohtani, Hisashi, Takayama, Toru, Suzawa, Hideomi, Yamazaki, Shunpei
• Primary Examiner(s): Crane; Sara
• Application Number:
  US09/454,146
• Time in Patent Office: 2,762 Days
• Field of Search: 257/57, 257/59, 257/66, 257/69, 257/344, 257/346, 257/408, 257/412, 257/413
• US Class Current: 257/59
• CPC Class Codes: G02F 1/136245 having complementary transistors
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G02F 2202/105 single crystal Si
• 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 21/28061 the conductor comprising a metal or metal silicide formed by deposition, e.g. sputter deposition, i.e. without a silicidation reaction H01L21/28052 takes precedence
• 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 29/4908 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 29/78621 with LDD structure or an extension or an offset region or characterised by the doping profile
• 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

There is provided a crystalline TFT in which reliability comparable to or superior to a MOS transistor can be obtained and excellent characteristics can be obtained in both an on state and an off state. A gate electrode of the crystalline TFT is formed of a laminate structure of a first gate electrode made of a semiconductor material and a second gate electrode made of a metal material. An n-channel TFT includes an LDD region, and a region overlapping with the gate electrode and a region not overlapping with the gate electrode are provided, so that a high electric field in the vicinity of a drain is relieved, and at the same time, an increase of an off current is prevented.

Claims

1. A semiconductor device comprising:

a semiconductor layer on an insulating surface;

a gate insulating film formed to be in contact with the semiconductor layer; and

a gate electrode formed to be in contact with the gate insulating film;

wherein;

the gate electrode includes;

a first layer of the gate electrode made of a semiconductor film formed to be in contact with the gate insulating film; and

a second layer of the gate electrode formed to be in contact with the first layer of the gate electrode, wherein a part of the first layer of the gate electrode extends beyond at least one of side edges of the second layer of the gate electrode;

the semiconductor layer includes;

a channel formation region;

a first impurity region of one conductivity type in contact with the insulating surface; and

a second impurity region of the one conductivity type sandwiched between the channel formation region and the first impurity region of the one conductivity type and being in contact with the channel formation region, the second impurity region having a first portion and a second portion,

wherein the second portion of the second impurity region overlaps with at least a portion of the part of the first layer of the gate electrode, that extends beyond at least one side edge of the second layer of the gate electrode,

wherein the first portion of the second impurity region does not overlap with the first layer of the gate electrode,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first layer of the gate electrode is different from a second material included in the second layer of the gate electrode, and

wherein a concentration of the impurity element of the one conductivity type in the second impurity region is lower than a concentration of the impurity element of the one conductivity type in the first impurity region.

29. A semiconductor device according to claim 1, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

40. A semiconductor device according to claim 1, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

2. A semiconductor device comprising:

a semiconductor layer on an insulating surface;

a gate insulating film formed to be in contact with the semiconductor layer; and

a gate electrode formed to be in contact with the gate insulating film;

wherein;

the gate electrode includes;

a first layer of the gate electrode made of a semiconductor film formed to be in contact with the gate insulating film; and

a second layer of the gate electrode formed to be in contact with the first layer of the gate electrode and to be disposed inside the first layer of the gate electrode;

the semiconductor layer includes;

a channel formation region;

a first impurity region of one conductivity type in contact with the insulating surface; and

a second impurity region of the one conductivity type sandwiched between the channel formation region and the first impurity region of the one conductivity type and being in contact with the channel formation region, the second impurity region having a first portion and a second portion,

wherein the second portion of the second impurity region overlaps with at least a portion of the first layer of the gate electrode,

wherein the second portion extends beyond a side edge of the second layer of the gate electrode,

wherein the first portion of the second impurity region does not overlap with the first layer of the gate electrode,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first layer of the gate electrode is different from a second material included in the second layer of the gate electrode, and

wherein a concentration of the impurity element of the one conductivity type in the second impurity region is lower than a concentration of the impurity element of the one conductivity type in the first impurity region.

30. A semiconductor device according to claim 2, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

41. A semiconductor device according to claim 2, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

3. A semiconductor device comprising:

a semiconductor layer on an insulating surface;

a gate insulating film formed to be in contact with the semiconductor layer; and

a gate electrode formed to be in contact with the gate insulating film;

wherein;

the gate electrode includes;

a first layer of the gate electrode made of a semiconductor film formed to be in contact with the gate insulating film; and

a second layer of the gate electrode formed to be in contact with the first layer of the gate electrode and having a length in a channel length direction shorter than the first layer of the gate electrode;

the semiconductor layer includes;

a channel formation region;

a first impurity region of one conductivity type in contact with the insulating surface; and

a second impurity region of the one conductivity type sandwiched between the channel formation region and the first impurity region of the one conductivity type and being in contact with the channel formation region, the second impurity region having a first portion and a second portion,

wherein the second portion of the second impurity region overlaps with at least a portion of the first layer of the gate electrode,

wherein the second portion extends beyond the shorter length in a channel length direction of the second layer of the gate electrode,

wherein the first portion of the second impurity region does not overlap with the first layer of the gate electrode,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first layer of the gate electrode is different from a second material included in the second layer of the gate electrode, and

wherein a concentration of the impurity element of the one conductivity type in the second impurity region is lower than a concentration of the impurity element of the one conductivity type in the first impurity region.

31. A semiconductor device according to claim 3, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

42. A semiconductor device according to claim 3, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

4. A semiconductor device comprising:

a semiconductor layer on an insulating surface;

a gate insulating film formed to be in contact with the semiconductor layer; and

a gate electrode formed to be in contact with the gate insulating film;

wherein;

the gate electrode has a structure of two layers having different lengths in a channel length direction and includes;

a first layer of the gate electrode made of a semiconductor film formed to be in contact with the gate insulating film; and

a second layer of the gate electrode formed to be in contact with the first layer of the gate electrode and having a length in the channel length direction shorter than the first layer of the gate electrode;

the semiconductor layer includes;

a channel formation region;

a first impurity region of one conductivity type in contact with the insulating surface; and

a second impurity region of the one conductivity type sandwiched between the channel formation region and the first impurity region of the one conductivity type and being in contact with the channel formation region, the second impurity region having a first portion and a second portion,

wherein the second portion of the second impurity region overlaps with at least a portion of the first layer of the gate electrode,

wherein the second portion extends beyond the shorter length in a channel length direction of the second layer of the gate electrode,

wherein the first portion of the second impurity region does not overlap with the first layer of the gate electrode,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first layer of the gate electrode is different from a second material included in the second layer of the gate electrode, and

wherein a concentration of the impurity element of the one conductivity type in the second impurity region is lower than a concentration of the impurity element of the one conductivity type in the first impurity region.

32. A semiconductor device according to claim 4, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

43. A semiconductor device according to claim 4, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

5. A semiconductor device comprising:

a pixel portion including an n-channel thin film transistor, wherein;

a gate electrode of the n-channel thin film transistor includes;

a first layer of the gate electrode made of a semiconductor film formed to be in contact with a gate insulating film; and

a second layer of the gate electrode formed to be in contact with the first layer of the gate electrode, wherein a part of the first layer of the gate electrode extends beyond at least one of side edges of the second layer of the gate electrode;

a semiconductor layer of the n-channel thin film transistor, on an insulating surface, includes;

a channel formation region;

a first impurity region of one conductivity type in contact with the insulating surface; and

a second impurity region of the one conductivity type sandwiched between the channel formation region and the first impurity region of the one conductivity type and being in contact with the channel formation region, the second impurity region having a first portion and a second portion,

wherein the second portion of the second impurity region overlaps with at least a portion of the part of the first layer of the gate electrode,

wherein the second portion extends beyond at least one side edge of the second layer of the gate electrode,

wherein the first portion of the second impurity region does not overlap with the first layer of the gate electrode,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first layer of the gate electrode is different from a second material included in the second layer of the gate electrode, and

wherein a concentration of the impurity element of the one conductivity type in the second impurity region is lower than a concentration of the impurity element of the one conductivity type in the first impurity region.

8. A semiconductor device according to claim 5, wherein a length of the second layer of the gate electrode is made shorter than that of the first layer of the gate electrode in a channel length direction.

9. A semiconductor device according to claim 5, wherein the first layer of the gate electrode is made of one kind or plural kinds of elements selected from the group consisting of silicon (Si) and germanium (Ge), or a compound containing the element as its main ingredient.

10. A semiconductor device according to claim 5, wherein the second layer of the gate electrode is made of one kind or plural kinds of elements selected from the group consisting of titanium (Ti), tantalum (Ta), tungsten (W), and molybdenum (Mo), or a compound containing the element as its main ingredient.

33. A semiconductor device according to claim 5, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

44. A semiconductor device according to claim 5, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

6. A semiconductor device comprising:

a CMOS circuit including an n-channel thin film transistor and a p-channel thin film transistor, wherein;

a gate electrode of the n-channel thin film transistor includes;

a first layer of the gate electrode made of a semiconductor film formed to be in contact with a gate insulating film; and

a second layer of the gate electrode formed to be in contact with the first layer of the gate electrode, wherein a part of the first layer of the gate electrode extends beyond at least one of side edges of the second layer of the gate electrode;

a semiconductor layer of the n-channel thin film transistor, on an insulating surface, includes;

a channel formation region;

a first impurity region of one conductivity type in contact with the insulating surface; and

a second impurity region of the one conductivity type sandwiched between the channel formation region and the first impurity region of the one conductivity type and being in contact with the channel formation region, the second impurity region having a first portion and a second portion,

wherein the second portion of the second impurity region overlaps with at least a portion of the part of the first layer of the gate electrode,

wherein the second portion extends beyond at least one side edge of the second layer of the gate electrode,

wherein the first portion of the second impurity region does not overlap with the first layer of the gate electrode,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first layer of the gate electrode is different from a second material included in the second layer of the gate electrode, and

wherein a concentration of the impurity element of the one conductivity type in the second impurity region is lower than a concentration of the impurity element of the one conductivity type in the first impurity region.

11. A semiconductor device according to claim 6, wherein a length of the second layer of the gate electrode is made shorter than that of the first layer of the gate electrode in a channel length direction.

13. A semiconductor device according to claim 6, wherein the first layer of the gate electrode is made of one kind or plural kinds of elements selected from the group consisting of silicon (Si) and germanium (Ge), or a compound containing the element as its main ingredient.

15. A semiconductor device according to claim 6, wherein the second layer of the gate electrode is made of one kind or plural kinds of elements selected from the group consisting of titanium (Ti), tantalum (Ta), tungsten (W), and molybdenum (Mo), or a compound containing the element as its main ingredient.

34. A semiconductor device according to claim 6, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

35. A semiconductor device according to claim 6, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

45. A semiconductor device according to claim 6, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

7. A semiconductor device comprising:

a pixel portion including an n-channel thin film transistor; and

a CMOS circuit formed with an n-channel thin film transistor and a p-channel thin film transistor, wherein;

a gate electrode of at least one of the n-channel thin film transistors of the pixel portion and the CMOS circuit includes;

a first layer of the gate electrode made of a semiconductor film formed to be in contact with a gate insulating film; and

a second layer of the gate electrode formed to be in contact with the first layer of the gate electrode, wherein a part of the first layer of the gate electrode extends beyond at least one of side edges of the second layer of the gate electrode;

a semiconductor layer of at least one of the n-channel thin film transistors of the pixel portion and the CMOS circuit, on an insulating surface, includes;

a channel formation region;

a first impurity region of one conductivity type in contact with the insulating surface; and

a second impurity region of the one conductivity type sandwiched between the channel formation region and the first impurity region of the one conductivity type and being in contact with the channel formation region, the second impurity region having a first portion and a second portion,

wherein the second portion of the second impurity region overlaps with at least a portion of the part of the first layer of the gate electrode, that extends beyond at least one side edge of the second layer,

wherein the first portion of the second impurity region does not overlap with the first layer of the gate electrode,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first layer of the gate electrode is different from a second material included in the second layer of the gate electrode, and

wherein a concentration of the impurity element of the one conductivity type in the second impurity region is lower than a concentration of the impurity element of the one conductivity type in the first impurity region.

12. A semiconductor device according to claim 7, wherein a length of the second layer of the gate electrode is made shorter than that of the first layer of the gate electrode in a channel length direction.

14. A semiconductor device according to claim 7, wherein the first layer of the gate electrode is made of one kind or plural kinds of elements selected from the group consisting of silicon (Si) and germanium (Ge), or a compound containing the element as its main ingredient.

16. A semiconductor device according to claim 7, wherein the second layer of the gate electrode is made of one kind or plural kinds of elements selected from the group consisting of titanium (Ti), tantalum (Ta), tungsten (W), and molybdenum (Mo), or a compound containing the element as its main ingredient.

46. A semiconductor device according to claim 7, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

17. A semiconductor device comprising:

a semiconductor layer on an insulating surface;

an insulating film formed over the semiconductor layer;

a gate electrode formed over the semiconductor layer with the insulating film therebetween, comprising a first conductive layer formed on the insulating film and a second conductive layer formed on the first conductive layer;

wherein the semiconductor layer comprises a channel formation region, a first impurity region in contact with the insulating surface, and a second impurity region adjacent to the channel formation region with the first impurity region therebetween, the second impurity region having a first portion and a second portion,

wherein a part of the first conductive layer extends beyond at least one of side edges of the second conductive layer,

wherein the part of the first conductive layer which extends beyond at least one of the side edges of the second conductive layer overlaps with the second portion of the second impurity region, and does not overlap with the first portion of the second impurity region,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first conductive layer is different from a second material included in the second conductive layer, and

wherein each of the first impurity region and the second impurity region includes an impurity element to give one conductivity type and a concentration of the impurity element in the second impurity region is lower than a concentration of the impurity element in the first impurity region.

18. A semiconductor device according to claim 17, wherein the first layer comprises a semiconductor material.

19. A semiconductor device according to claim 17, wherein the second layer comprises a material selected from the group consisting of titanium (Ti), tantalum (Ta), tungsten (W), and molybdenum (Mo), or a compound containing the element as its main ingredient.

36. A semiconductor device according to claim 17, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

47. A semiconductor device according to claim 17, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

20. A semiconductor device comprising:

a semiconductor layer on an insulating surface;

an insulating film formed over the semiconductor layer;

a gate electrode formed over the semiconductor layer with the insulating film therebetween, comprising a first conductive layer formed on the insulating film and a second conductive layer formed on the first conductive layer;

wherein the semiconductor layer comprises a channel formation region, a first impurity region in contact with the insulating surface, and a second impurity region adjacent to the channel formation region with the first impurity region therebetween, the second impurity region having a first portion and a second portion,

wherein a length of the first conductive layer is longer in a channel length direction than a length of the second conductive layer in a channel length direction,

wherein a portion of the first conductive layer that extends longer in the channel length direction than the length of the second conductive layer in the channel length direction overlaps with the second portion of the second impurity region, and does not overlap with the first portion of the second impurity region,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first conductive layer is different from a second material included in the second conductive layer, and

wherein each of the first impurity region and the second impurity region includes an impurity element to give one conductivity type and a concentration of the impurity element in the second impurity region is lower than a concentration of the impurity element in the first impurity region.

21. A semiconductor device according to claim 20, wherein the first layer comprises a semiconductor material.

22. A semiconductor device according to claim 20, wherein the second layer comprises a material selected from the group consisting Of titanium (Ti), tantalum (Ta), tungsten (W), and molybdenum (Mo), or a compound containing the element as its main ingredient.

37. A semiconductor device according to claim 20, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

48. A semiconductor device according to claim 20, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

23. A semiconductor device comprising:

a semiconductor layer on an insulating surface;

an insulating film formed over the semiconductor layer;

a gate electrode formed over the semiconductor layer with the insulating film therebetween, comprising a first conductive layer formed on the insulating film and a second conductive layer formed on the first conductive layer;

wherein the semiconductor layer comprises a channel formation region, a first impurity region in contact with the insulating surface, and a second impurity region adjacent to the channel formation region with the first impurity region therebetween, the second impurity region having a first portion and a second portion,

wherein a part of the first conductive layer extends beyond at least one of side edges of the second conductive layer,

wherein at least the part of the first conductive layer which extends beyond at least one of the side edges of the second conductive layer overlaps with the second portion of the second impurity region, and does not overlap with the first portion of the second impurity region,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first conductive layer is different from a second material included in the second conductive layer, and

wherein each of the first impurity region and the second impurity region includes an impurity element to give one conductivity type and a concentration of the impurity element in the second impurity region is lower than a concentration of the impurity element in the first impurity region.

24. A semiconductor device according to claim 23, wherein the first layer comprises a semiconductor material.

25. A semiconductor device according to claim 23, wherein the second layer comprises a material selected from the group consisting of titanium (Ti), tantalum (Ta), tungsten (W), and molybdenum (Mo), or a compound containing the element as its main ingredient.

38. A semiconductor device according to claim 23, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

49. A semiconductor device according to claim 23, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.

26. A semiconductor device comprising:

a semiconductor layer on an insulating surface;

an insulating film formed over the semiconductor layer;

a gate electrode formed over the semiconductor layer with the insulating film therebetween, comprising a first conductive layer formed on the insulating film and a second conductive layer formed on the first conductive layer;

wherein the semiconductor layer comprises a channel formation region, a first impurity region in contact with the insulating surface, and a second impurity region adjacent to the channel formation region with the first impurity region therebetween, the second impurity region having a first portion and a second portion,

wherein a length of the first conductive layer is longer in a channel length direction than a length of the second conductive layer,

wherein at least a portion of the first conductive layer that extends longer in the channel length direction than the length of the second conductive layer in the channel length direction overlaps with the second portion of the second impurity region, and does not overlap with the first portion of the second impurity region,

wherein the first portion and the second portion of the second impurity region are in contact with the insulating surface,

wherein a first material included in the first conductive layer is different from a second material included in the second conductive layer, and

wherein each of the first impurity region and the second impurity region includes an impurity element to give one conductivity type and a concentration of the impurity element in the second impurity region is lower than a concentration of the impurity element in the first impurity region.

27. A semiconductor device according to claim 26, wherein the first layer comprises a semiconductor material.

28. A semiconductor device according to claim 26, wherein the second layer comprises a material selected from the group consisting of titanium (Ti), tantalum (Ta), tungsten (W), and molybdenum (Mo), or a compound containing the element as its main ingredient.

39. A semiconductor device according to claim 26, wherein an insulating film including silicon nitride is formed on and in direct contact with the second layer of the gate electrode.

50. A semiconductor device according to claim 26, wherein the semiconductor device is incorporated into an electronic equipment selected from the group consisting of a portable electronic book, a mobile computer, a cellular phone, a video camera, a personal computer, a TV, a head mount display, an electronic game equipment, a digital camera, and a projector.