Method for forming a thin film semiconductor device utilizing a gate and gate side walls as masks

• US 5,786,241 A
• Filed: 12/28/1994
• Issued: 07/28/1998
• Est. Priority Date: 01/08/1994
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Shimada, Hiroyuki
• Primary Examiner(s): Trinh, Michael
• Application Number:
  US08/365,116
• Time in Patent Office: 1,308 Days
• Field of Search: 437/40 TFT, 437/41 TFT, 437/913, 437/21, 437/44, 437/40 SW, 437/41 SW, 148/DIG. 150, 438/163, 438/149, 438/596
• US Class Current: 438/163
• 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

Abstract

In a thin film transistor (TFT) having an active layer formed on an insulating film, a gate electrode is formed by using a metal material such as aluminum, an gate insulating film is formed by using a silicon insulator such as silicon oxide or silicon nitride. A film is formed on the gate electrode and the gate insulting film by using a silicon material such as amorphous silicon and then etched with anisotropic etching to form side walls made of a silicon material in sides of the gate electrode. In this etching, since an etching rate of the side walls is larger than that of the gate insulating film, the gate insulating film is not almost etched.

Claims

1. A method for forming a thin film semiconductor device comprising the steps of:

forming a semiconductor film on a substrate having an insulating surface;

forming a gate insulating film having a first etching rate on the semiconductor film;

forming a gate electrode including a metal on the gate insulating film;

introducing an impurity, using the gate electrode as a first mask to form impurity regions in the semiconductor film;

forming side walls on sides of the gate electrode having a second etching rate, which is larger than the first etching rate, said side walls comprising an amorphous semiconductive silicon; and

introducing an impurity providing the same conductivity type as the impurity regions into the impurity regions using the side walls as a second mask.

2. The method of claim 1 wherein said metal included in the gate electrode is selected from the group consisting of aluminum, tantalum, and titanium.

3. The method of claim 1 wherein the gate insulating film has one of a silicon oxide film, a silicon nitride film, and a compound film of silicon oxide and silicon nitride.

4. A method for forming a thin film transistor, comprising the steps of:

forming a semiconductor film on an insulating surface;

forming a gate insulating film having a first etching rate on the semiconductor film;

forming a gate electrode including a metal on the gate insulating film;

introducing an impurity having a first concentration into the semiconductor film using the gate electrode as a first mask;

forming a side wall forming film in contact with the gate electrode and having a second etching rate, which is larger than the first etching rate;

etching the side wall forming film to form side walls on sides of the gate electrode; and

introducing the impurity having a second concentration into the semiconductor film using the gate electrode and the side walls as a second mask to form impurity regions and LDD regions,

wherein the side wall forming film is a semiconductor film comprising amorphous silicon.

5. The method of claim 4 wherein said metal included in the gate electrode is selected from the group consisting of aluminum, tantalum, and titanium.

6. The method of claim 4 wherein the gate insulating film has one of a silicon oxide film, a silicon nitride film, and a compound film of silicon oxide and silicon nitride.

7. The method of claim 4 wherein the impurity regions has source and drain regions.

8. The method of claim 7 wherein the LDD regions are formed between the source and drain regions.

9. The method of claim 4 wherein the first concentration is lower than the second concentration.

10. A method for forming a thin film transistor, comprising the steps of:

forming a semiconductor film on an insulating surface;

forming a gate insulating film having a first etching rate on the semiconductor film;

forming a gate electrode including a metal on the gate insulating film;

introducing an impurity having a first concentration into the semiconductor film using the gate electrode as a first mask;

forming a side wall forming film in contact with the gate electrode and having a second etching rate, which is larger than the first etching rate;

etching the side wall forming film to form side walls on sides of the gate electrode;

introducing the impurity having a second concentration into the semiconductor film using the gate electrode and the side walls as masks to form impurity regions and LDD regions;

removing the side walls after the impurity regions and the LDD region are formed; and

performing a laser annealing with the impurity region and the LDD regions,

wherein the side wall forming film is a semiconductor film comprising amorphous silicon.

11. The method of claim 10 wherein said metal included in the gate electrode is selected from the group consisting of aluminum, tantalum, and titanium.

12. The method of claim 10 wherein the gate insulating film has one of a silicon oxide film, a silicon nitride film, and a compound film of silicon oxide and silicon nitride.

13. The method of claim 10 wherein the impurity regions have source and drain regions.

14. The method of claim 13 wherein the LDD regions are formed between the source and drain regions.

15. The method of claim 13 wherein the first concentration is lower than the second concentration.

16. A method for forming thin film transistor, comprising the steps of:

forming a semiconductor film on an insulating surface;

forming a gate insulating film having a first etching rate on the semiconductor film;

forming a gate electrode including a metal on the gate insulating film;

introducing an impurity into the semiconductor film using the gate electrode as a first mask;

forming side walls having a second etching rate, which is larger than the first etching rate, in contact with sides of the gate electrode; and

introducing the impurity into the semiconductor film using the gate electrode and the side walls as a second mask to form impurity regions and LDD regions,

wherein said side walls comprises an amorphous semiconductive silicon.

17. The method of claim 16 wherein said metal included in the gate electrode is selected from the group consisting of aluminum, tantalum, and titanium.

18. The method of claim 16 wherein the gate insulating film has one of a silicon oxide film, a silicon nitride film, and a compound film of silicon oxide and silicon nitride.

19. The method of claim 16 further comprising the steps of:

removing the side walls after the impurity regions and the LDD region are formed; and

performing a laser annealing with the impurity region and the LDD regions.

20. The method of claim 16 wherein the impurity regions has source and drain regions.

21. The method of claim 20 wherein the LDD regions are formed between the source and drain regions.

22. The method of claim 16 wherein a concentration of the impurity for the first introducing is lower than than for the second introducing.

23. A method for forming a thin film transistor, comprising the steps of:

forming a semiconductor film on an insulating surface;

forming a gate insulating film which having a first etching rate on the semiconductor film;

forming a gate electrode on the gate insulating film;

forming impurity regions by introducing an impurity into the semiconductor film using the gate electrode as a first mask;

forming side walls having a second etching rate, which is larger than the first etching rate, in contact with sides of the gate electrode;

forming LDD regions by introducing the impurity into the impurity regions using the side walls as a second mask;

removing the side walls after forming the LDD regions; and

performing a laser annealing with the impurity region and the LDD regions,

wherein said side walls comprise an amorphous semiconductive silicon.

24. The method of claim 23 wherein a material of the gate electrode is selected from the group consisting of tantalum, titanium, and aluminum.