Thin film transistor

• US 5,619,045 A
• Filed: 07/09/1996
• Issued: 04/08/1997
• Est. Priority Date: 11/05/1993
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Sugawara, Akira, Konuma, Toshimitsu, Tsuji, Takahiro
• Primary Examiner(s): TRAN, MINH LOAN
• Application Number:
  US08/677,175
• Time in Patent Office: 273 Days
• Field of Search: 257/72, 257/57, 257/66, 257/347, 257/349, 257/352, 257/900, 359/59
• US Class Current: 257/72
• 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: Y10S 257/90 MOSFET type gate sidewall insulating spacer

Abstract

A thin film transistor comprising a gate electrode offset from source and drain, which comprises a substrate having thereon a gate electrode fabricated on an active region provided on the substrate, wherein, an anodic oxide of the material constituting the gate electrode is provided on the side and the upper face of said gate electrode, and the anodic oxide on the side of the gate electrode is formed thicker than the anodic oxide formed on the upper face. Also claimed is a process for fabricating the above thin film transistor improved in device characteristics and product yield, which comprises forming a gate electrode with an anodically oxidizable material having thereon a masking material, providing a relatively thick porous anodic oxide film on the side of the gate electrode by anodic oxidation effected under a relatively low voltage, then forming a dense anodic oxide film on at least the upper face of the gate electrode after removing the masking material, and introducing impurities into the semiconductor layer using the gate electrode portion having thereon the anodic oxide films as a mask.

Claims

1. A thin film transistor comprising:

an active region provided on a substrate and comprising a source and drain and a channel provided between said source and drain;

a gate electrode provided on said active region; and

an anodic oxide of the material constituting the gate electrode provided on the side and the upper face of said gate electrode,

wherein said anodic oxide comprises a non-porous anodic oxide provided on the side of the gate electrode and a porous anodic oxide provided on the outer side of said non-porous anodic oxide, and

wherein said channel extends to an end of said porous anodic oxide.

2. The transistor of claim 1 wherein thickness of the anodic oxide formed on the upper face is 0.2 μ

m or less.

3. The transistor of claim 1 wherein said gate electrode comprises aluminum.

4. A thin film transistor comprising:

an active region provided on a substrate and comprising a source and drain and a channel provided between said source and drain;

a gate electrode provided on said active region; and

an anodic oxide of the material constituting the gate electrode provided on the side and the upper face of said gate electrode,

wherein the anodic oxide on the side of the gate electrode comprises two layers, and the anodic oxide in one of said two layers has the same porosity as the anodic oxide on the upper face of said gate electrode, and the anodic oxide in the other of said two layers has a higher porosity than the anodic oxide on the upper face of said gate electrode, and

wherein said channel extends to an end of the anodic oxide in the other of said two layers.

5. A thin film transistor comprising:

a semiconductor island provided on a substrate;

a source region and a drain region provided in said semiconductor island;

a channel region provided in said semiconductor island between said source and drain regions

lightly doped regions provided in said semiconductor island between said channel region and said source region and between said channel region and said drain region;

a gate electrode provided adjacent to said channel region with a gate insulating film therebetween; and

an anodic oxide of a material of said gate electrode provided at least on a side of said gate electrode,

wherein said channel region extends to an end of said anodic oxide, and

wherein said lightly doped regions provided between said channel region and said source region and between said channel region and said drain region have the same width as each other.

6. The thin film transistor of claim 5 wherein concentration of an impurity contained in said lightly doped regions is lower than that in said source and drain regions.

7. A thin film transistor comprising:

a semiconductor island provided on a substrate;

a source region and a drain region provided in said semiconductor island;

a channel region provided in said semiconductor island between said source and drain regions;

an offset region provided in said semiconductor island between said channel region and one of said source and drain regions and comprising a same material as said channel region;

a gate electrode provided adjacent to said channel region with a gate insulating film therebetween; and

non-porous anodic oxide of a material of said gate electrode provided at least on a side of said gate electrode,

wherein a boundary between said offset region and said one of said source and drain regions is self-aligned with a side end of said gate insulating film, and

wherein a semiconductor region comprising said channel region extends to said side end of said gate insulating film and said gate insulating film extends beyond said non-porous anodic oxide.

8. A thin film transistor comprising:

a semiconductor island provided on a substrate;

a source region and a drain region provided in said semiconductor island;

a channel region provided in said semiconductor island between said source and drain regions;

lightly doped regions provided in said semiconductor island between said channel region and said source region and between said channel region and said drain region;

a gate electrode provided adjacent to said channel region with a gate insulating film therebetween; and

an anodic oxide of a material of said gate electrode provided at least on a side of said gate electrode,

wherein said lightly doped regions provided between said channel region and said source region and between said channel region and said drain region have the same width as each other, and

wherein said channel region extends to an end of said anodic oxide and said gate insulating film extends beyond said anodic oxide.

9. The thin film transistor of claim 8 wherein concentration of an impurity contained in said lightly doped regions is lower than that in said source and drain regions.

10. A thin film transistor comprising:

a semiconductor island provided on a substrate;

a source and drain regions provided in said semiconductor island;

a channel region provided in said semiconductor island between said source and drain regions;

an offset region provided in said semiconductor island between said channel region and one of said source and drain regions;

a gate electrode provided adjacent to said channel region with a gate insulating film therebetween; and

a non-porous anodic oxide of a material of said gate electrode provided at least on a side of said gate electrode,

wherein a boundary between said offset region and said one of said source and drain regions is self-aligned with a side end of said gate insulating film,

wherein said gate insulating film extends on said offset region to said side end, and

wherein a semiconductor region comprising said channel region extends to said side end of said gate insulating film and said gate insulating film extends beyond said non-porous anodic oxide.