Thin film transistor, having a nitride film on the gate insulation layer and an organic resin interlayer film on the transistor

• US 6,013,929 A
• Filed: 07/07/1998
• Issued: 01/11/2000
• Est. Priority Date: 07/08/1997
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Ohtani, Hisashi
• Primary Examiner(s): Abraham, Fetsum
• Application Number:
  US09/110,894
• Time in Patent Office: 553 Days
• Field of Search: 257/59, 257/72, 257/349, 257/66, 257/69, 257/347, 257/324, 257/382, 257/389
• US Class Current: 257/349
• CPC Class Codes: H01L 29/42384 for thin film field effect transistors, e.g. characterised by the thickness or the shape of the insulator or the dimensions, the shape or the lay-out of the conductor
• 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 29/78675 with normal-type structure, e.g. with top gate

Abstract

A gate insulating film 103 is oxidized by a thermal oxidation method using a gate electrode 104 as a mask. At this time, the thickness of the gate insulating film 103 becomes thicker so that the portions indicated by 106 and 107 are obtained. The thickness of an active layer becomes thin at an end 112 of a channel, so that the distance from the gate electrode becomes long by the thickness. Then the strength of an electric field between a source and drain is relaxed by this portion. In this way, a thin film transistor having improved withstand voltage characteristics and leak current characteristics is obtained.

Claims

1. A semiconductor device comprising:

a thin film transistor being formed over a substrate, said thin film transistor including;

an active layer including a source region, a drain region and a channel region formed between the source and drain regions;

a gate insulating film comprising silicon oxide and covering the active layer; and

a gate electrode formed on the gate insulating film;

a silicon nitride film formed in direct contact with the gate insulating film;

a leveling film comprising organic resin formed in direct contact with the silicon nitride film;

a source electrode formed in contact with the leveling film and the source region in the active layer through the gate insulating film, the silicon nitride film and the leveling film;

a drain electrode formed in contact with the leveling film and the drain region in the active layer through the gate insulating film the silicon nitride film and the leveling film;

wherein the active layer is oxidized using the gate electrode as a mask.

2. A device according to claim 1, wherein an upper end portion of the channel region formed in the active layer is selectively oxidized.

3. A device according to claim 1, wherein a thickness of the gate insulating film in a portion under a side of the gate electrode is gradually changed toward the source and drain regions.

4. A device according to claim 1, wherein a thickness of the thinnest portion of the gate insulating film in a portion under the gate electrode is thinner than a thickness of the thickest portion of the gate insulating film in a portion other than the portion under the gate electrode.

5. A device according to claim 1 further comprising offset regions formed between the channel region and each of the source and drain regions of the active layer,

wherein a thickness of the gate insulating film in the offset regions gradually become thicker in a direction from portions where the offset regions are formed to the source and drain regions.

6. A device according to claim 1, wherein a thickness of the gate insulating film gradually becomes thicker in a portion under the gate electrode toward the source and drain regions.

7. A device according to claim 1, wherein the gate electrode comprises a material which is able to be anodized and to withstand a thermal oxidation step.

8. A device according to claim 1,

wherein the gate electrode comprises tantalum, and

wherein an anodic oxidation film is formed on the surface of the gate electrode.

9. A device according to claim 1, wherein said semiconductor device is one selected from the group consisting of a portable information processing terminal, a head mount display device, a front projection type liquid crystal display device, a portable telephone, a portable video camera and a rear projection type liquid crystal display device.

10. A device according to claim 1, wherein said organic resin includes at least one selected from the group consisting of acryl, polyimide, polyamide, polyimide amide, and epoxy.

11. A semiconductor device comprising;

a thin film transistor being formed over a substrate said thin film transistor including;

an active layer including a source region, a drain region and a channel region formed between the source and drain regions;

a silicon oxide film covering the active layer; and

a gate electrode formed on the silicon oxide film

a silicon nitride film formed in direct contact with the silicon oxide film;

a leveling film comprising organic resin formed in direct contact with the silicon nitride film;

a source electrode formed in contact with the leveling film and the source region in the active layer through the silicon oxide film, the silicon nitride film and the leveling film;

a drain electrode formed in contact with the leveling film and the drain region in the active layer through the silicon oxide film, the silicon nitride film and the leveling film;

wherein said silicon oxide film is thermally oxidized using the gate electrode as a mask to thicken a thickness of the silicon oxide film,

wherein an end of the thermally oxidized region extends to a portion under the gate electrode.

12. A device according to claim 11, wherein an upper end portion of the channel region is selectively oxidized.

13. A device according to claim 11, wherein a thickness of the silicon oxide film at an upper end portion of the channel region gradually becomes thicker toward the source and drain regions.

14. A device according to claim 11, wherein said semiconductor device is one selected from the group consisting of a portable information processing terminal, a head mount display device, a front projection type liquid crystal display device, a portable telephone, a portable video camera and a rear projection type liquid crystal display device.

15. A device according to claim 11, wherein said organic resin includes at least one selected from the group consisting of acryl, polyimide, polyamide, polyimide amide, and epoxy.

16. A semiconductor device including:

at least one thin film transistor, said thin film transistor comprising;

a semiconductor layer formed on an insulating surface;

source, drain and channel regions formed in said semiconductor layer;

a gate insulating film covering said semiconductor layer; and

a gate electrode formed on said gate insulating film, said gate electrode comprising tantalum;

a silicon nitride film formed in direct contact with the gate insulating film;

a leveling film comprising organic resin formed in direct contact with the silicon nitride film;

a source electrode formed in contact with the leveling film and the source region in the active layer through the gate insulating film, the silicon nitride film and the leveling film;

a drain electrode formed in contact with the leveling film and the drain region in the active layer through the gate insulating film, the silicon nitride film and the leveling film;

wherein a thickness of said gate insulating film at each boundary between said channel region and said source and drain regions increases toward said source and drain regions.

17. A device according to claim 16, wherein said gate electrode is covered with a tantalum oxide film.

18. A device according to claim 16, wherein said semiconductor device is one selected from the group consisting of a portable information processing terminal, a head mount display device, a front projection type liquid crystal display device, a portable telephone, a portable video camera and a rear projection type liquid crystal display device.

19. A device according to claim 16, wherein said organic resin includes at least one selected from the group consisting of acryl, polyimide, polyamide, polyimide amide, and epoxy.