Method of forming a semiconductor device

• US 7,776,712 B2
• Filed: 05/02/2007
• Issued: 08/17/2010
• 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): COLEMAN, WILLIAM D
• Application Number:
  US11/799,713
• Publication Number:
  US 20070281401A1
• Time in Patent Office: 1,203 Days
• Field of Search: 438/197, 438/588, 438/533, 257/E21.179
• US Class Current: 438/433
• 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 method of forming a semiconductor device comprising:

forming a semiconductor layer over a substrate;

forming a gate insulating film over the semiconductor layer;

forming a first conductive film over the gate insulating film;

forming a second conductive film over the first conductive film;

forming a second layer of a gate electrode from the second conductive film;

adding an impurity element having one conductivity type to the semiconductor layer through the gate insulating film and the first conductive film after forming the second layer of the gate electrode;

forming a first layer of the gate electrode from the first conductive film so that a part of the first layer of the gate electrode extends beyond at least one of the side edges of the second layer of the gate electrode after adding the impurity element having one conductivity type to the semiconductor layer through the gate insulating film and the first conductive film; and

adding an impurity element having the one conductivity type to the semiconductor layer through the gate insulating film after forming the first layer of the gate electrode.

2. A method of forming a semiconductor device according to claim 1, 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.

3. A method of forming a semiconductor device according to claim 1, wherein the semiconductor device is one selected from the group consisting of a liquid crystal display device, an EL display device, and an image sensor.

4. A method of forming a semiconductor device according to claim 1, wherein the semiconductor device is one selected from the group consisting of a video camera, a digital camera, a projector, a projection TV, a goggle display, a car navigation system, a personal computer, and a portable information terminal.

5. A method of forming a semiconductor device according to claim 1, wherein the semiconductor layer is a crystalline semiconductor, a microcrystalline semiconductor, or a single crystal silicon layer.

6. A method of forming a semiconductor device according to claim 1, 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.

7. A method of forming a semiconductor device comprising:

forming a semiconductor layer over a substrate;

forming a gate insulating film over the semiconductor layer;

forming a first conductive film over the gate insulating film;

forming a second conductive film over the first conductive film;

forming a second layer of a gate electrode from the second conductive film;

adding an impurity element having one conductivity type to the semiconductor layer through the gate insulating film and the first conductive film after forming the second layer of the gate electrode;

forming a first layer of the gate electrode from the first conductive film so that a part of the first layer of the gate electrode extends beyond at least one of the side edges of the second layer of the gate electrode after adding the impurity element having one conductivity type to the semiconductor layer through the gate insulating film and the first conductive film; and

adding an impurity element having the one conductivity type to the semiconductor layer through the gate insulating film after forming the first layer of the gate electrode; and

removing a part of the first layer of the gate electrode.

8. A method of forming 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.

9. A method of forming 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.

10. A method of forming a semiconductor device according to claim 7, wherein the semiconductor device is one selected from the group consisting of a liquid crystal display device, an EL display device, and an image sensor.

11. A method of forming a semiconductor device according to claim 7, wherein the semiconductor device is one selected from the group consisting of a video camera, a digital camera, a projector, a projection TV, a goggle display, a car navigation system, a personal computer, and a portable information terminal.

12. A method of forming a semiconductor device according to claim 7, wherein the semiconductor layer is a crystalline semiconductor, a microcrystalline semiconductor, or a single crystal silicon layer.

13. A method of forming a semiconductor device comprising:

forming a first semiconductor layer and a second semiconductor layer over a substrate;

forming a gate insulating film over the first semiconductor layer and the second semiconductor layer;

forming a first conductive film over the gate insulating film;

forming a second conductive film over the first conductive film;

forming a second layer of a gate electrode from the second conductive film;

adding an impurity element having first conductivity type to at least the first semiconductor layer through the gate insulating film and the first conductive film after forming the second layer of the gate electrode;

adding an impurity element having second conductivity type opposite to the first conductivity type to the second semiconductor layer;

forming a first layer of the gate electrode from the first conductive film so that a part of the first layer of the gate electrode extends beyond at least one of the side edges of the second layer of the gate electrode after adding the impurity element having one conductivity type to the semiconductor layer through the gate insulating film and the first conductive film;

adding an impurity element having the first conductivity type to at least the first semiconductor layer through the gate insulating film after forming the first layer of the gate electrode.

14. A method of forming a semiconductor device according to claim 13, 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 method of forming a semiconductor device according to claim 13, 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.

16. A method of forming a semiconductor device according to claim 13, wherein the semiconductor device is one selected from the group consisting of a liquid crystal display device, an EL display device, and an image sensor.

17. A method of forming a semiconductor device according to claim 13, wherein the semiconductor device is one selected from the group consisting of a video camera, a digital camera, a projector, a projection TV, a goggle display, a car navigation system, a personal computer, and a portable information terminal.

18. A method of forming a semiconductor device according to claim 13, wherein each of the first and second the semiconductor layers is a crystalline semiconductor, a microcrystalline semiconductor, or a single crystal silicon layer.

19. A method of forming a semiconductor device comprising:

forming a first semiconductor layer and a second semiconductor layer over a substrate;

forming a gate insulating film over the first semiconductor layer and the second semiconductor layer;

forming a first conductive film over the gate insulating film;

forming a second conductive film over the first conductive film;

forming a second layer of a gate electrode from the second conductive film;

adding an impurity element having first conductivity type to at least the first semiconductor layer through the gate insulating film and the first conductive film after forming the second layer of the gate electrode;

adding an impurity element having second conductivity type opposite to the first conductivity type to the second semiconductor layer;

forming a first layer of the gate electrode from the first conductive film so that a part of the first layer of the gate electrode extends beyond at least one of the side edges of the second layer of the gate electrode;

adding an impurity element having the first conductivity type to at least the first semiconductor layer through the gate insulating film after forming the first layer of the gate electrode; and

removing a part of the first layer of the gate electrode.

20. A method of forming a semiconductor device according to claim 19, 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.

21. A method of forming a semiconductor device according to claim 19, 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.

22. A method of forming a semiconductor device according to claim 19, wherein the semiconductor device is one selected from the group consisting of a liquid crystal display device, an EL display device, and an image sensor.

23. A method of forming a semiconductor device according to claim 19, wherein the semiconductor device is one selected from the group consisting of a video camera, a digital camera, a projector, a projection TV, a goggle display, a car navigation system, a personal computer, and a portable information terminal.

24. A method of forming a semiconductor device according to claim 19, wherein each of the first and second the semiconductor layers is a crystalline semiconductor, a microcrystalline semiconductor, or a single crystal silicon layer.