JPH057001A - Thin film transistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a TFT covered with a back passivation film excellent in step coverage. CONSTITUTION:The following are provided; a process for forming a first metal pattern 22 on the main surface of an insulative substrate 21, a process for forming an insulative layer 23 and a semiconductor layer 24 on the first metal layer pattern 22, a process for forming a metal thin film 25 on the insulative layer 23 and the semiconductor layer 24, forming selectively a resin pattern on the film 25, and forming a first insulator 26 by oxidizing in the thickness direction the whole metal thin film of the part which is not covered with the resin pattern, and a process wherein a second insulator 27 is formed by oxidizing a part from the surface of the metal thin film 25 after the resin pattern is eliminated, and a second metal layer pattern 25 buried in the first and the second insulators 26, 27 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor having a source electrode, a drain electrode and a back passivation film for use in a liquid crystal display device, and a method for manufacturing the thin film transistor.

[0002]

2. Description of the Related Art The structure of a conventional general TFT and its manufacturing method will be described with reference to FIG.

A gate electrode 12 is selectively formed on an insulating substrate 11, and a gate insulating film 1 is formed on the gate electrode 12.
3, the semiconductor layer 14 is formed, and the source electrode 15 and the drain electrode 16 are formed on the semiconductor layer 14 at predetermined intervals,
Further, the back passivation film 1 is formed so as to cover the entire surface.
By forming 7, the TFT is formed.

An inexpensive glass substrate is generally used as the insulating substrate 11. As the gate electrode 12, a metal such as aluminum, chromium, or gold, polysilicon, or the like is used. As the gate insulating film 13, silicon nitride, silicon oxide or the like is used. Amorphous silicon or the like is used for the semiconductor layer 14. Source electrode 15,
As the drain electrode 16, aluminum, chromium,
Gold, nickel, etc. are used. As the back passivation film 17, silicon nitride or the like is used.

[0005]

However, in the above-mentioned conventional structure, the process of forming and patterning the conductive thin film for the source electrode 15 and the drain electrode 16 and subsequently forming the insulating thin film 17 for back passivation is performed. Required, usually source electrode 15, drain electrode 1
The thickness of the conductive thin film for 6 is at least 400 nm to 500
However, there is a problem in that the insulating thin film 17 for back passivation cannot be sufficiently covered because a film thickness of 700 nm or more is required in some cases.

In consideration of the problems of the conventional method of manufacturing a thin film transistor, the present invention is a method of manufacturing a thin film transistor which can be easily manufactured and can obtain a highly reliable back passivation film with good step coverage. It is intended to provide.

[0007]

The present invention provides a step of forming a first metal layer pattern on one main surface of an insulating substrate, and an insulating layer or an insulating layer and a semiconductor layer on the first metal layer pattern. And a step of forming a metal thin film, selectively forming a resin pattern, and oxidizing the metal thin film in a portion not covered with the resin pattern in the thickness direction to form a first insulator. Performing a step of forming a second insulator by partially oxidizing the surface of the metal thin film that has not been oxidized after removing the resin pattern and forming a second metal layer pattern embedded in the insulator. To form a TFT.

[0008]

In the present invention, since the source electrode and the drain electrode of the second metal layer pattern are covered by the first insulator and the second insulator, the step coverage is good, the environment resistance is excellent, and the chemically stable oxidation is performed. It is possible to provide a TFT covered with a back passivation film made of an object thin film.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of the basic structure of a TFT using a back passivation film according to an embodiment of the present invention. Further, FIG. 2 is a cross-sectional view for explaining a method of manufacturing a TFT using a back passivation film in one embodiment of the present invention. 1 or 2, 21 is an insulating substrate, 22 is a first metal layer pattern, 23 is an insulating layer, 24 is a semiconductor layer, 25 is a second metal layer pattern, 2
6 is a first insulator and 27 is a second insulator.

A more specific example will be described with reference to FIG.

A glass substrate is used as the insulating substrate 21, and a chromium thin film is formed thereon by DC sputtering to a thickness of 100 nm.
The film is formed with a thickness of 1 mm, and is processed into a stripe shape by photolithography technology to form the first metal layer pattern 22 (FIG. 2).
(A)). On top of that, the insulating layer 2 is formed by the plasma CVD method.
200 nm of silicon nitride film as 3 and semiconductor layer 24
The amorphous silicon film is continuously formed to a thickness of 100 nm (FIG. 2B). Subsequently, aluminum having a thickness of 500 nm is formed as a metal film for forming the second metal layer pattern 25 and the first and second insulators 26, 27. Then, a mask 28 is formed on the second metal pattern 25 (source electrode, drain electrode) with a resist or the like. Then, the unmasked portion is anodized to form a porous type Al ₂ O ₃ as the first insulator 26.
An anodic oxide film is formed (FIG. 2C). In this case, the anodic oxidation is carried out by using an acidic anodic oxidation solution having a pH of 2 (for example, a 3% citric acid aqueous solution) at a solution temperature of 5
The temperature was kept at 0 ° C. and anodization was performed under a constant current.

Next, the mask 28 is removed and pH = 6 to
7. A neutral anodic oxidation solution of 7 (for example, 3% ammonium borate aqueous solution: ethylene glycol = 1: 9) was used to carry out anodic oxidation once more to form a barrier type Al ₂ O ₃ anodic oxide film as the second insulator 27. The thickness of 200 nm is obtained on the surface of the second metal pattern 25 (source electrode, drain electrode) (FIG. 2D). As a result, a TFT protected by the back passivation film having the structure shown in FIG. 1 can be manufactured.

The oxide thin film formed by this method has excellent characteristics such as being dense and having no film thickness unevenness. Furthermore, the anodic oxide film has a good step coverage and can completely cover the TFT. Here, FIG.
A similar TFT can be obtained by using a barrier type anodic oxide film instead of the porous type anodic oxide film in (c). In addition, this effect is universal, and the thin film material used for the back passivation film is Ta ₂ O ₅ ,
By using a material that can be formed into a film by anodic oxidation, such as TiO ₂ , an excellent TFT that exhibits the same effect can be realized.

Further, a TFT using a back passivation film as shown in FIG. 1 was manufactured and its operation was confirmed.
A display device having stable characteristics which is not different from that of the TFT by the conventional method of passivation even after being driven for a long time was obtained.

[0016]

As described above, according to the present invention, a back passivation film having good step coverage and high reliability can be obtained.

Further, by using the anodizing method,
It has an advantage that the manufacturing process can be simplified.

[Brief description of drawings]

FIG. 1 is a basic configuration cross-sectional view of a TFT using a back passivation film in an example of the present invention.

FIG. 2 is a cross-sectional view illustrating a method of manufacturing a TFT according to an embodiment of the present invention.

FIG. 3 is a diagram showing a cross-sectional structure of a conventional TFT.

[Explanation of symbols]

21 Insulating substrate 22 First metal layer pattern 23 Insulation layer 24 Semiconductor layer 25 Second metal layer pattern 26 First Insulator 27 Second insulator 28 masks

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomizo Matsuoka             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd.

Claims (5)

[Claims] 1. A first metal layer pattern formed on one main surface of an insulating substrate, an insulating layer or an insulating layer and a semiconductor layer formed on the first metal layer pattern, and the insulating layer. Or a second metal layer pattern embedded in an insulator formed by oxidizing a metal thin film on a semiconductor layer. 2. The thin film transistor according to claim 1, wherein the materials of the second metal layer pattern and the metal thin film are the same. 3. The thin film transistor according to claim 1, wherein the main component of the metal thin film is any one of aluminum, tantalum, and titanium. 4. A step of forming a first metal layer pattern on one main surface of an insulating substrate, a step of forming an insulating layer or an insulating layer and a semiconductor layer on the first metal layer pattern, Form a metal thin film on the insulating layer or semiconductor layer,
A step of forming a first insulator by selectively forming a resin pattern on the metal thin film in a portion not covered with the resin pattern in the thickness direction, and after removing the resin pattern. And a step of forming a second insulator by partially oxidizing the surface of the unoxidized metal thin film and forming a second metal layer pattern embedded in the first and second insulators. A method of manufacturing a thin film transistor, comprising: 5. The method of manufacturing a thin film transistor according to claim 1, wherein the method of oxidizing the metal thin film is an anodic oxidation method.