Thin film transistor, TFT substrate and liquid crystal display unit

• US 20040149989A1
• Filed: 12/01/2003
• Published: 08/05/2004
• Est. Priority Date: 01/31/2003
• Status: Active Grant

• Current Assignee: Vista Peak Ventures LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: NEC Corporation
• Inventors: Sera, Kenji, Matsunaga, Naoki
• Granted Patent: US 7,105,905 B2
• Time in Patent Office: Days
• US Class Current: 257/59
• CPC Class Codes: G02F 1/136209 Light shielding layers, e.g. black matrix, incorporated in the active matrix substrate, e.g. structurally associated with the switching element
• CPC Class Codes: H01L 27/12 the substrate being other than a semiconductor body, e.g. an insulating body
• 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 27/1218 with a particular composition or structure of the substrate
• 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 29/78633 with a light shield

Abstract

A thin film transistor is provided including an active layer, in which a source region and drain region are formed, a first light-shielding film shielding a light incident on the active layer, and a second light-shielding film between the active layer and the first shielding film. A carrier concentration of at least surface portion of the second light-shielding film which opposes the active layer is about 10¹⁷/cm³ or less.

Claims

1. A thin film transistor comprising:

an active layer, in which a source region and drain region are formed;

a first light-shielding film shielding a light incident on said active layer; and

a second light-shielding film disposed between said active layer and said first light-shielding film,

wherein a carrier concentration of at least a surface portion of said second light-shielding film which opposes said active layer is about 10¹⁷/cm³ or less.

2. The thin film transistor according to claim 1, wherein a distance between said second light-shielding film and said active layer is from about 100 nm to about 350 nm.

3. The thin film transistor according to claim 1,

wherein said active layer has a low-concentration carrier region between a source region and a channel region, and

wherein between a drain region and the channel region, said low-concentration carrier region has the same conductive type as the source region and the drain region and has lower impurity concentration than the source region and the drain region, and

wherein said second light-shielding film has a portion which overlaps said channel region and said low-concentration carrier region in terms of plane.

4. The thin film transistor according to claim 1,

wherein said second light-shielding film has a photo-absorption property.

5. The thin film transistor according to claim 1, further comprising a dielectric film disposed between said first light-shielding film and said second light-shielding film.

6. The thin film transistor according to claim 1, wherein said second light-shielding film is formed on said first light-shielding film.

7. A thin film transistor comprising:

an active layer, in which a source region and drain region are formed;

a first light-shielding film shielding a light incident on said active layer; and

a second light-shielding film disposed between said active layer and said first light-shielding film,

wherein an electric field intensity of a surface portion of said second light-shielding film which opposes said active layer includes about 80% or less of that of a surface portion of said second light-shielding film which opposes said first light-shielding film.

8. The thin film transistor according to claim 7,

wherein a distance between said second light-shielding film and said active layer is from about 100 nm to about 350 nm.

9. A thin film transistor comprising:

an active layer, in which a source region and drain region are formed;

a first light-shielding film shielding a light incident on said active layer; and

a second light-shielding film disposed between said active layer and said first light-shielding film,

wherein said second light-shielding film is made of a semi-insulating film.

10. The thin film transistor according to claim 9, wherein a carrier concentration of said second light-shielding film is about 10¹⁷/cm³ or less.

11. A thin film transistor comprising:

an active layer, in which a source region and drain region are formed;

a first light-shielding film shielding a light incident on said active layer;

a second light-shielding film disposed between said active layer and said first light-shielding film,

wherein said second light-shielding film is made of a material selected from a group consisting of amorphous silicon, crystallite silicon, amorphous Silicon Germanium, poly germanium, amorphous germanium, poly Silicon Germanium, and any combination thereof.

12. The thin film transistor according to claim 11, wherein a carrier concentration of said second light-shielding film is about 10¹⁷/cm³ or less.

13. A thin film transistor substrate comprising:

a light transmission substrate;

a transistor array including a plurality of thin film transistors disposed on said light transmission substrate;

a first light-shielding film disposed between said light transmission substrate and at least one of said thin film transistors;

a second light-shielding film disposed between said first light-shielding film and an active layer of said thin film transistor,

wherein a carrier concentration of a surface portion of said second light-shielding film which opposes said active layer is about 10¹⁷/cm³ or less.

14. The thin film transistor substrate according to claim 13,

further comprising pixel electrodes corresponding to each of said plurality of thin film transistors,

wherein each of said pixel electrode is driven by a thin film transistor which said pixel electrode corresponds to.

15. The thin film transistor substrate according to claim 14, wherein a dielectric film inbetween capacitance electrodes is connected to said pixel electrodes in parallel.

16. The thin film transistor substrate according to claim 15,

further comprising another thin film transistor which comprises neither said first light-shielding film nor said second light-shielding film.

17. The thin film transistor substrate according to claim 13,

wherein an electric field intensity of a surface portion of said second light-shielding film which opposes said active layer includes about 80% or less of that of a surface portion of said second light-shielding film which opposes said first light-shielding film.

18. The thin film transistor substrate according to claim 13,

wherein said second light-shielding film is made of a material selected from a group consisting of amorphous silicon, crystallite silicon, amorphous Silicon Germanium, poly germanium, amorphous germanium, poly Silicon Germanium, and any combination thereof.

19. A liquid crystal display unit comprising:

a thin film transistor substrate according to claims 13;

an opposite substrate disposed to oppose said thin film transistor substrate; and

a liquid crystal layer disposed between said thin film transistor substrate and said opposite substrate.

20. A thin film transistor manufacturing method comprising:

providing a substrate;

forming a ground dielectric film on said substrate;

forming a first light-shielding film;

forming a second light-shielding film above said first light-shielding film;

doping carrier into the second light-shielding film, in such a manner that a carrier concentration of at least a surface portion opposite to said first light-shielding film of the second light-shielding film is about 10¹⁷/cm³ or less;

forming a dielectric film above said second light film; and

forming an active layer for a thin film transistor on said dielectric film.

21. The thin film transistor manufacturing method according to claim 20,

wherein the dielectric film is formed after forming the first light-shielding film and before forming the second light-shielding film on said first light-shielding film.