Method for manufacturing semiconductor device with removable spacers

• US 5,719,065 A
• Filed: 09/28/1994
• Issued: 02/17/1998
• Est. Priority Date: 10/01/1993
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Teramoto, Satoshi, Takemura, Yasuhiko
• Primary Examiner(s): Bowers, Jr., Charles L.
• Assistant Examiner(s): Radomsky, Leon
• Application Number:
  US08/313,910
• Time in Patent Office: 1,238 Days
• Field of Search: 437/21, 437/24, 437/40 TFT, 437/41 TFT, 437/40 SW, 437/41 SW, 437/44, 257/61, 257/66, 257/70, 257/75, 257/408, 257/410, 257/405, 257/900
• US Class Current: 438/163
• 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 27/1248 with a particular composition or shape of the interlayer dielectric specially adapted to the circuit arrangement
• CPC Class Codes: H01L 27/1255 integrated with passive devices, e.g. auxiliary capacitors
• 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

A thin film transistor of the present invention has an active layer including at least source, drain and channel regions formed on an insulating surface. A high resistivity region is formed between the channel region and each of the source and drain regions. A film capable of trapping positive charges therein is provided on at least the high resistivity region so that N-type conductivity is induced in the high resistivity region. Accordingly, the reliability of N-channel type TFT against hot electrons can be improved.

Claims

1. A method for manufacturing a semiconductor device comprising the steps of:

forming an active semiconductor layer including at least source, drain and channel regions on an insulating surface;

forming an insulating film on said active semiconductor layer;

forming a gate electrode on said insulating film;

subjecting said gate electrode to anodization in an electrolyte in order to form an oxide of said gate electrode on at least a side surface thereof;

etching at least a part of said insulating film using said oxide as a mask, thereby forming a gate insulating film;

removing said oxide formed on the side surface of said gate electrode to expose a portion of said gate insulating film; and

then

forming a film capable of trapping positive ions therein on said gate electrode and the exposed portion of said gate insulating film.

2. The method of claim 1 further comprising forming a barrier type anodic oxide film on said gate electrode after said subjecting step but before said etching.

3. The method of claim 1 further comprising the step of introducing an impurity ion into a portion of said active layer with said gate electrode used as a mask after said etching.

4. The method of claim of claim 3 further comprising the step of activating said impurity ion introduced into said active layer.

5. The method of claim 1 further comprising introducing hydrogen by ion doping into a portion between said channel and said source and between said channel and said drain at a concentration 0.01 to 10 atoms/cm³.

6. The method of claim 5 further comprising the step of annealing said active layer at 200°

-400°

C. after introducing said hydrogen.

7. A method for manufacturing a semiconductor device comprising the steps of:

forming a crystalline semiconductor layer on an insulating surface;

forming an insulating fill comprising silicon oxide on said crystalline semiconductor layer;

forming a gate electrode on said insulating film;

subjecting said gate electrode to anodization in an electrolyte in order to form an oxide of said gate electrode on at least a side surface thereof;

etching at least a part of said insulating film using said oxide as a mask, thereby forming a gate insulating film;

after said etching, removing said oxide formed on the side surface of said gate electrode to expose a portion of said gate insulating film;

after said removing, selectively introducing impurity ions into said semiconductor layer for giving one conductivity type thereto with said gate electrode and said gate insulating film as a mask wherein portions of said semiconductor layer which extend beyond said oxide are doped with said impurity ions at a first concentration and portions of said semiconductor layer which are positioned below the exposed portion of the gate insulating film are doped with said impurity ions at a second concentration smaller than said first concentration; and

forming a film comprising silicon nitride at least on said gate electrode and the exposed portion of said gate insulating film.

8. The method of claim 7 further comprising forming a barrier type anodic oxide film on said gate electrode after said subjecting step but before said etching.

9. The method of claim 7 where said first concentration is from 1×

10²⁰ to 2×

10²¹ atoms/cm³ and said second concentration is from 1×

10¹⁷ to 2×

10¹⁸ atoms/cm³.

10. A method for manufacturing a semiconductor device comprising the steps of:

forming a crystalline semiconductor layer on an insulating surface;

forming an insulating film comprising silicon oxide on said crystalline semiconductor layer;

forming a gate electrode on said insulating film;

subjecting said gate electrode to anodization in an electrolyte in order to form an oxide of said gate electrode on at least a side surface thereof;

selectively etching said insulating film using said oxide as a mask to define a gate insulating film, thereby, exposing first portions of said semiconductor which extends beyond said oxide;

after said etching, removing said oxide formed on the side surface of said gate electrode to expose a portion of said gate insulating film;

after said removing, selectively introducing impurity ions into said semiconductor layer for giving one conductivity type thereto with said gate electrode and said gate insulating film as a mask wherein said first portions of said semiconductor layer are doped with said impurity ions at a first concentration and portions of said semiconductor layer which are positioned below the exposed portion of the gate insulating film are doped with said impurity ions at a second concentration smaller than said first concentration;

forming a metal film on said first portions of said semiconductor layer;

reacting said metal film with said first portions of said semiconductor layer to increase the conductivity of said first portions; and

forming a film capable of trapping positive ions therein at least on said gate electrode and the exposed portion of said gate insulating film.

11. The method of claim 10 further comprising forming a barrier type anodic oxide film on said gate electrode after said subjecting step but before said etching.

12. A method for manufacturing a semiconductor device comprising the steps of:

forming a crystalline semiconductor layer on an insulating surface;

forming an insulating film on said crystalline semiconductor layer;

forming a gate electrode on said insulating film;

subjecting said gate electrode to anodization in an electrolyte in order to form an oxide of said gate electrode on at least a side surface thereof;

etching at least a part of said insulating film using said oxide as a mask, thereby forming a gate insulating film;

after said etching, removing said oxide formed on the side surface of said gate electrode to expose a portion of said gate insulating film; and

forming a film comprising silicon nitride with a thickness from 200 to 2000 Å

at least on said gate electrode and the exposed portion of said gate insulating film.

13. The method of claim 12 further comprising a step of, after said removing, selectively introducing impurity ions into said semiconductor layer for giving one conductivity type thereto with said gate electrode and said gate insulating film as a mask wherein said first portions of said semiconductor layer are doped with said impurity ions at a first concentration and portions of said semiconductor layer which are positioned below the exposed portion of the gate insulating film are doped with said impurity ions at a second concentration smaller than said first concentration.

14. The method of claim 12 further comprising forming a barrier type anodic oxide film on said gate electrode after said subjecting step but before said etching step.

15. A method for manufacturing a semiconductor device comprising the steps of:

forming a crystalline semiconductor layer on an insulating surface;

forming an insulating film comprising silicon oxide on said crystalline semiconductor layer;

forming a gate electrode on said insulating film;

forming masks on side surfaces of said gate electrode where said insulating film has portions uncovered by said masks;

etching the uncovered portions of said insulating film to define a gate insulating film;

after said etching, removing said masks to expose a portion of said gate insulating film; and

forming a first pair of impurity regions in portions of said semiconductor layer which extend beyond said masks and a second pair of impurity regions in portions of said semiconductor layer which are positioned below the exposed portion of the gate insulating film where said first pair of impurity regions are doped with impurity ions for giving one conductivity at a first concentration and said second pair of impurity regions are doped with impurity ion at a second concentration smaller than said first concentration.

16. The method of claim 15 further comprising forming a film comprising silicon nitride with a thickness 200 to 2000 Å

at least on said gate electrode and the exposed portion of said gate insulating film.