Method for forming a field-effect transistor including anodic oxidation of the gate

• US 5,521,107 A
• Filed: 03/29/1994
• Issued: 05/28/1996
• Est. Priority Date: 02/16/1991
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Hiroki, Masaaki, Mase, Akira, Takemura, Yasuhiko, Uochi, Hideki, Yamazaki, Shunpei, Zhang, Hongyong, Nemoto, Hideki
• Primary Examiner(s): Fourson, George
• Assistant Examiner(s): TSAI, H JEY
• Application Number:
  US08/219,819
• Time in Patent Office: 791 Days
• Field of Search: 437/170, 437/983, 148/DIG. 117, 148/DIG. 163
• US Class Current: 438/303
• CPC Class Codes: G02F 1/136227 Through-hole connection of the pixel electrode to the active element through an insulation layer
• CPC Class Codes: G09G 2300/0823 used to establish symmetry in driving, e.g. with polarity inversion
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 3/3651 using multistable liquid crystals, e.g. ferroelectric liquid crystals
• CPC Class Codes: G09G 3/3659 the addressing of the pixel involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependant on signal of two data electrodes
• 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 29/4908 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 29/78618 characterised by the drain or the source properties, e.g. the doping structure, the composition, the sectional shape or the contact structure silicide contacts, electrodes in general H01L29/458
• CPC Class Codes: H04N 3/127 using liquid crystals
• CPC Class Codes: Y10S 148/117 Oxidation, selective
• CPC Class Codes: Y10S 148/163 Thick-thin oxides

Abstract

An insulated-gate field-effect transistor adapted to be used in an active-matrix liquid-crystal display. The channel length, or the distance between the source region and the drain region, is made larger than the length of the gate electrode taken in the longitudinal direction of the channel. Offset regions are formed in the channel region on the sides of the source and drain regions. No or very weak electric field is applied to these offset regions from the gate electrode.

Claims

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

forming gate electrodes of at least two transistors with said gate electrodes electrically connected with each other by a wiring;

anodic oxidizing surface portions of said gate electrodes by passing current through said wiring;

electrically separating at least one of said gate electrodes from said wiring after said anodic oxidizing step; and

anodic oxidizing surface portions of the gate electrodes connected to said wiring after said separating step by passing current through said wiring.

2. The method of claim 1 wherein said gate electrodes comprise metal or semiconductor.

3. A method for forming a semiconductor device for an electro-optical device comprising the steps of:

forming a gate insulating layer on a semiconductor layer provided on an insulating surface;

forming on said gate insulating layer a gate electrode part connected with a power source by a wiring;

doping an impurity ion into said semiconductor layer for imparting p-type or n-type conductivity thereto with said gate electrode part as a mask to form a source or drain region in said semiconductor layer;

anodic oxidizing a surface portion of said gate electrode part by passing current through said wiring from said power source after said doping step;

electrically separating said gate electrode part from said wiring after said anodic oxidizing step; and

activating said impurity ion after said anodic oxidizing step.

4. The method of claim 3 wherein said activating step is carried out by subjecting said semiconductor layer to thermal treatment or a laser radiation.

5. The method of claim 3 wherein said gate electrode part comprises metal or semiconductor.

6. A method for forming a semiconductor device for an electro-optical device comprising the steps of:

forming a gate insulating layer on a semiconductor layer provided on an insulating surface;

forming on said gate insulating layer a gate electrode part connected with a power source by a wiring;

anodic oxidizing a surface portion of said gate electrode part by passing current through said wiring from said power source;

electrically separating said gate electrode part from said wiring after said anodic oxidizing step;

doping an impurity ion into said semiconductor layer for imparting p-type or n-type conductivity thereto with the gate electrode part including the anodic oxidized surface portion as a mask to form a source or drain region in said semiconductor layer after said anodic oxidizing step; and

activating said impurity ion after said doping step.

7. The method of claim 6 wherein said activating step is carried out by subjecting said semiconductor layer to thermal treatment.

8. The method of claim 6 wherein said electrode part comprises metal or semiconductor.

11. The method of claim 6 further comprising the step of introducing phosphorus into said gate insulating layer after said gate insulating layer forming step.

9. A method for forming a semiconductor device comprising the steps of:

covering a semiconductor island provided on an insulating surface with an insulating layer;

forming on said semiconductor island a gate electrode part connected with a power source by a wiring with said insulating layer between said gate electrode part and said semiconductor island;

anodic oxidizing a surface portion of said gate electrode part by passing current through said wiring from said power source; and

electrically separating said gate electrode part from said wiring.

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

forming gate electrodes of at least two transistors on one substrate;

first anodic oxidizing surface portions of all of said gate electrodes; and

further anodic oxidizing surface portions of at least one of said gate electrodes where the number of gate electrodes subjected to said further anodizing step is less than the number subjected to said first anodizing step,

wherein the thickness of anodic oxidation film formed on the at least one gate electrode subjected to the further anodic oxidizing step is greater than the thicknesses of the anodic oxidation films formed on the gate electrodes not subjected to the further anodic oxidizing step so that the speed of the transistor not subjected to the further anodic oxidizing step is faster than that of the transistor subjected to the further oxidizing step.