Semiconductor device having LDD regions

• US 6,909,114 B1
• Filed: 11/04/1999
• Issued: 06/21/2005
• Est. Priority Date: 11/17/1998
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yamazaki, Shunpei
• Primary Examiner(s): LOKE, STEVEN HO YIN
• Application Number:
  US09/433,705
• Time in Patent Office: 2,056 Days
• Field of Search: 257/347, 257/66, 257/72, 257/344, 257/408, 257/412, 257/413, 257/59, 257/57
• US Class Current: 257/66
• 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 27/12 the substrate being other than a semiconductor body, e.g. an insulating body
• CPC Class Codes: H01L 27/1214 comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
• CPC Class Codes: H01L 27/1222 with a particular composition, shape or crystalline structure of the active layer
• 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 29/66492 with a pocket or a lightly doped drain selectively formed at the side of the gate
• CPC Class Codes: H01L 29/66598 forming drain [D] and lightly doped drain [LDD] simultaneously, e.g. using implantation through the wings a T-shaped layer, or through a specially shaped layer
• 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 29/78627 with a significant overlap between the lightly doped drain and the gate electrode, e.g. GOLDD
• CPC Class Codes: H01L 29/78675 with normal-type structure, e.g. with top gate
• CPC Class Codes: H01L 29/78696 characterised by the structure of the channel, e.g. multichannel, transverse or longitudinal shape, length or width, doping structure, or the overlap or alignment between the channel and the gate, the source or the drain, or the contacting structure of the channel H01L29/78612 takes precedence; transistors having a drain offset region or a lightly doped drain [LDD] H01L29/78621
• CPC Class Codes: H10K 50/8445 multilayered coatings having a repetitive structure, e.g. having multiple organic-inorganic bilayers
• CPC Class Codes: H10K 59/10 OLED displays
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/1213 the pixel elements being TFTs
• CPC Class Codes: H10K 59/123 Connection of the pixel electrodes to the thin film transistors [TFT]

Abstract

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.

Claims

1. A semiconductor device having an active matrix display device, said display device comprising:

a first thin film transistor formed over an insulating surface;

a pixel electrode electrically connected to said first thin film transistor;

a driver circuit including a second thin film transistor formed over said insulating surface for driving said first thin film transistor,

wherein said first thin film transistor comprises;

a first semiconductor island over the insulating surface;

source and drain regions formed in the semiconductor island;

a first channel forming region in the first semiconductor island between the source and drain regions;

a pair of lightly doped regions formed between the first channel forming region and the source and drain regions, wherein an impurity concentration in the lightly doped regions is smaller than that in the source and drain regions;

a gate electrode formed over the semiconductor island with a gate insulating film Interposed therebetween;

an insulating film formed over the gate electrode and the gate insulating film;

wherein said gate electrode comprises at least a first conductive layer and a second conductive layer formed on the first conductive layer, said first conductive layer having a pair of tapered portions which extend beyond side edges of the second conductive layer,

wherein the pair of lightly doped regions has a pair of first portions which are overlapped by the pair of tapered portions of the first conductive layer, and a pair of second portions which extend beyond side edges of the first conductive layer, and

wherein said insulating film is in direct contact with at least side surfaces and a top surface of the second conductive layer.

2. A device according to claim 1, wherein an angle between top surfaces of the tapered portions of the first conductive layer and a top surface of the gate insulating film is in a range of 3 to 60 degrees.

3. A device according to claim 1, wherein the first semiconductor island comprises crystalline silicon.

4. A device according to claim 1, wherein the first conductive layer includes at least one selected from the group consisting of chromium (Cr), tantalum (Ta), an n-type silicon containing phosphorus, titanium (Ti), tungsten (W), and molybdenum (Mo) while the second conductive layer includes at least one selected from the group consisting of aluminum (Al), copper (Cu), chromium (Cr), tantalum (Ta), titanium (Ti), tungsten (W), molybdenum (Mo), an n-type silicon containing phosphorus, and silicide.

5. A device according to claim 1, wherein the semiconductor device is one selected from the group consisting of a video camera, a digital camera, a rear-type projector, a front-type projector, a head mount display, a goggle-type display, a navigation system for vehicles, a personal computer, a mobile computer, a cellular phone, and an electronic book.

6. A device according to claim 1 wherein said active matrix display device Is a liquid crystal device.

7. A device according to claim 1 wherein said active matrix display device is an electroluminescent display device.

8. A semiconductor device according to claim 1, wherein the insulating film comprises silicon oxide.

9. A semiconductor device according to claim 1, wherein the insulating film is a protective film.

10. A semiconductor device according to claim 1, wherein the insulating film comprises a laminate of a first film comprising silicon oxide and a second film comprising silicon nitride.

11. A semiconductor device having an active matrix display device, said display device comprising;

a first thin film transistor formed over an insulating surface;

a pixel electrode electrically connected to said first thin film transistor;

a driver circuit including a second thin film transistor and a third thin film transistor formed over said insulating surface for driving said first thin film transistor, wherein the second thin film transistor is an n-channel thin film transistor and the third thin film transistor is a p-channel thin film transistor,

wherein said n-channel thin film transistor comprises;

a first semiconductor island over the insulating surface;

first source and drain regions formed in the first semiconductor island;

a first channel forming region in the first semiconductor island between the first source and drain regions;

pair of lightly doped regions formed between the first channel forming region and the first source and drain regions, wherein an impurity concentration in the lightly doped regions is smaller than that in the first source and drain regions;

a first gate electrode formed over the semiconductor island with a gate insulating film interposed therebetween,

wherein said first gate electrode comprises at least a first conductive layer and a second conductive layer formed on the first conductive layer, said first conductive layer having a pair of tapered portions which extend beyond side edges of the second conductive layer,

wherein the pair of lightly doped regions has a pair of first portions which are overlapped by the pair of tapered portions of the first conductive layer, and a pair of second portions which extend beyond side edges of the first conductive layer,

wherein said third thin film transistor comprises;

a second semiconductor Island over the insulating surface;

second source and drain regions formed in the second semiconductor island;

a second channel forming region in the second semiconductor island between the second source and drain regions;

second gate electrode formed over the second semiconductor island with the gate insulating film interposed therebetween,

wherein said second gate electrode comprises at least a third conductive layer and a fourth conductive layer formed on the third conductive layer,

wherein side edges of said third conductive layer are coextensive with side edges of said fourth conductive layer.

12. A device according to claim 11, wherein an angle between top surfaces of the tapered portions of the first conductive layer and a top surface of the gate insulating film is in a range of 3 to 60 degrees.

13. A device according to claim 11, wherein the first and second semiconductor islands comprise crystalline silicon.

14. A device according to claim 11, wherein the first conductive layer includes at least one selected from the group consisting of chromium (Cr), tantalum (Ta), an n-type silicon containing phosphorus, titanium (Ti), tungsten (W), and molybdenum (Mo) while the second conductive layer Includes at least one selected from the group consisting of aluminum (Al), copper (Cu), chromium (Cr), tantalum (Ta), titanium (Ti), tungsten (W), molybdenum (Mo), an n-type silicon containing phosphorus, and silicide.

15. A device according to claim 11, wherein the semiconductor device is one selected from the group consisting of a video camera, a digital camera, a rear-type projector, a front-type projector, a head mount display, a goggle-type display, a navigation system for vehicles, a personal computer, a mobile computer, a cellular phone, and an electronic book.

16. A device according to claim 11 wherein said active matrix display device is a liquid crystal device.

17. A device according to claim 11 wherein said active matrix display device is an electroluminescent display device.

18. A semiconductor device having an active matrix display device, said display device comprising:

a first thin film transistor formed over an insulating surface;

a pixel electrode electrically connected to said first thin film transistor;

a driver circuit including a second thin film transistor formed over said insulating surface for driving said first thin film transistor,

wherein said second thin film transistor comprises;

semiconductor Island over the insulating surface;

source and drain regions formed In the semiconductor island;

a channel forming region in the semiconductor island between the source and drain regions;

a pair of tightly doped regions formed between the channel forming region and the source and drain regions wherein an Impurity concentration In the lightly doped regions is smaller than that In the source and drain regions;

a gate electrode formed over the semiconductor island with a gate insulating film interposed therebetween;

an insulating film formed over the gate electrode and the gate insulating film;

wherein said gate electrode comprises at least a first conductive layer and a second conductive layer formed on the first conductive layer, said first conductive layer having a pair of tapered portions which extend beyond side edges of the second conductive layer,

wherein the pair of lightly doped regions has a pair of first portions which are overlapped by the pair of tapered portions of the first conductive layer, and a pair of second portions which extend beyond side edges of the first conductive layer, and

wherein said insulating film is In direct contact with at least side surfaces and a top surface of the second conductive layer.

19. A device according to claim 18, wherein an angle between top surfaces of the tapered portions of the first conductive layer and a top surface of the gate insulating film is in a range of 3 to 60 degrees.

20. A device according to claim 18, wherein the first conductive layer includes at least one selected from the group consisting of chromium (Cr), tantalum (Ta), an n-type silicon containing phosphorus, titanium (Ti), tungsten (W), and molybdenum (Mo) while the second conductive layer includes at least one selected from the group consisting of aluminum (Al), copper (Cu), chromium (Cr), tantalum (Ta), titanium (Ti), tungsten (W), molybdenum (Mo), an n-type silicon containing phosphorus, and silicide.

21. A device according to claim 18, wherein the semiconductor device is one selected from the group consisting of a video camera, a digital camera, a rear-type projector, a front-type projector, a head mount display, a goggle-type display, a navigation system for vehicles, a personal computer, a mobile computer, a cellular phone, and an electronic book.

22. A device according to claim 18 wherein said active matrix display device is a liquid crystal device.

23. A device according to claim 18 wherein said active matrix display device is an electroluminescent display device.

24. A device according to claim 18, wherein the semiconductor island comprises crystalline silicon.

25. A semiconductor device according to claim 18, wherein the insulating film comprises silicon oxide.

26. A semiconductor device according to claim 18, wherein the insulating film is a protective film.

27. A semiconductor device according to claim 18, wherein the insulating film comprises a laminate of a first film comprising silicon oxide and a second film comprising silicon nitride.

28. A semiconductor device having an active matrix display device, said display device comprising:

a first thin film transistor formed over an Insulating surface;

a pixel electrode electrically connected to said first thin film transistor;

a driver circuit including a second thin film transistor formed over said insulating surface for driving said first thin film transistor, each of the first and second thin film transistors comprising;

a semiconductor island over the insulating surface;

source and drain regions formed in the semiconductor island;

a channel forming region in the semiconductor island between the source and drain regions;

a pair of lightly doped regions formed between the channel forming region and the source and drain regions, wherein an impurity concentration in the lightly doped regions is smaller than that in the source and drain regions;

a gale electrode formed over the semiconductor island with a gate insulating film interposed therebetween;

an insulating film formed over the gate electrode and the gate insulating film;

wherein said gate electrode comprises at least a first conductive layer and a second conductive layer formed on the first conductive layer, said first conductive layer having a pair of tapered portions which extend beyond side edges of the second conductive layer,

wherein the pair of lightly doped regions has a pair of first portions which are overlapped by the pair of tapered portions of the first conductive layer, and a pair of second portions which extend beyond side edges of the first conductive layer, and

wherein said insulating film is in direct contact with at least side surfaces and a top surface of the second conductive layer.

29. A device according to claim 28, wherein an angle between top surfaces of the tapered portions of the first conductive layer and a top surface of the gate insulating film is In a range of 3 to 60 degrees.

30. A device according to claim 28, wherein the semiconductor island comprises crystalline silicon.

31. A device according to claim 28, wherein the first conductive layer Includes at least one selected from the group consisting of chromium (Cr), tantalum (Ta), an n-type silicon containing phosphorus, titanium (Ti), tungsten (W), and molybdenum (Mo) while the second conductive layer includes at least one selected from the group consisting of aluminum (Al), copper (Cu), chromium (Cr), tantalum (Ta), titanium (Ti), tungsten (W), molybdenum (Mo), an n-type silicon containing phosphorus, and silicide.

32. A device according to claim 28, wherein the semiconductor device is one selected from the group consisting of a video camera, a digital camera, a rear-type projector, a front-type projector, a head mount display, a goggle-type display, a navigation system for vehicles, a personal computer, a mobile computer, a cellular phone, and an electronic book.

33. A device according to claim 28 wherein said active matrix display device is a liquid crystal device.

34. A device according to claim 28 wherein said active matrix display device Is an electroluminescent display device.

35. A semiconductor device according to claim 28, wherein the insulating film comprises silicon oxide.

36. A semiconductor device according to claim 28, wherein the insulating film is a protective film.

37. A semiconductor device according to claim 28, wherein the Insulating film comprises a laminate of a first film comprising silicon oxide and a second film comprising silicon nitride.