JPH04299866A - Manufacture of active matrix liquid crystal display - Google Patents

Abstract

PURPOSE:To reduce the drop of a liquid crystal driving voltage, in a TFT array surface protecting film. CONSTITUTION:By using a plasma CVD method, a surface protecting film is formed of a tantalum oxide film having high permittivity (20-30). Thereby the voltage drop in the surface protecting film is reduced to 1/4, as compared with the conventional silicon nitride film or silicon oxide film.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an active matrix liquid crystal display, and more particularly, to a method for manufacturing an active matrix liquid crystal display characterized by a method for manufacturing a thin film transistor array substrate.

0002

2. Description of the Related Art FIG. 2 is a sectional view of a thin film transistor (hereinafter referred to as "a-SiTFT") array substrate using amorphous silicon, and FIG. 3 is a flowchart of its manufacturing process. Hereinafter, a conventional method for manufacturing an active matrix liquid crystal display will be explained based on FIGS. 2 and 3.

The a-Si TFT substrate (lower substrate), which is the lower substrate of an active matrix liquid crystal display, is first prepared by depositing chromium (Cr) and nichrome (NiCr) on a glass substrate 1, as shown in FIG. 3(a). , a metal layer made of tantalum (Ta) is deposited by sputtering or vapor deposition to a thickness of 0.1 to 0.
A film of about 3 μm is formed, and then processed into a predetermined shape by photolithography to form the gate electrode 2.

[0004] Then, as shown in FIG. 3(b), NH3
and the plasma CVD method using SiH4 gas as the main components (
Silicon nitride film (hereinafter referred to as "PCVD method")
An a-Si film was formed to a thickness of 0.1 to 0.4 μm using a PCVD method using SiH4 gas as the main component.
05 to 0.2 μm is deposited on the entire surface of the substrate. Then, the gate insulating film 3 and the semiconductor layer 4 are formed by processing the a-Si film into a predetermined shape. The gate insulating film 3 is left on the entire surface of the substrate without being etched.

Next, as shown in FIG. 3(c), aluminum (Al), chromium (Cr), nichrome (NiCr)
A metal layer of 0.3
The source electrode 5 and the drain electrode 6 are formed by forming a film with a thickness of about 1.0 μm and processing it into a predetermined shape. Next, as shown in FIG. 3(d), an intermediate insulating film 7 made of a silicon nitride film (SiNx) or the like is formed by the PCVD method.

Thereafter, as shown in FIG. 3(e), the source and the next formed transparent electrode ITO film (In2 O3 +S
A contact hole 8 for conduction with nO2) is formed in a predetermined portion of the intermediate insulating film 7. Then, an ITO film is formed on the entire surface of the substrate to a thickness of about 0.1 μm by sputtering or vapor deposition. Then, a transparent electrode 9 that becomes a display electrode is formed by processing into a predetermined shape.

Finally, as shown in FIG. 3(f), a silicon nitride film (SiNx) or a silicon oxide film (SiOx) is formed.
is formed in a predetermined area by PCVD and processing to form the surface protective film 10. By two-dimensionally arranging the above-described transparent electrodes and a-SiTFTs, an a-SiTFT array substrate for liquid crystal is completed.

[0008] A film thickness of 0.1 μm is formed on this TFT array substrate.
An alignment film is formed by forming an organic film made of polyimide and subjecting it to rubbing treatment. Thereafter, spacers having a diameter of 3 to 10 μm are sprinkled on the alignment film to form and maintain uniform cell spacing, thereby completing the lower substrate. On the other hand, the upper substrate (counter electrode side) is formed as shown below. A counter transparent electrode made of an ITO film with a thickness of about 0.1 μm is formed on glass into a predetermined shape by sputtering or vapor deposition and processing. Next, a black matrix layer is formed to prevent light leakage and improve contrast. An organic film made of polyimide having a thickness of about 0.1 μm is formed on this counter electrode, and rubbed to form an alignment film. Furthermore, the upper substrate is completed by forming a sealing layer with a thickness of 5 to 20 μm in a predetermined pattern using a thick film screen printing method.

After the upper and lower substrates are completed, the upper and lower substrates are aligned and bonded together using the sealing layer with the sealing layer in between, and are fixed under pressure, and the sealing layer is heated and cured. moreover,
A liquid crystal display using an a-SiTFT is completed by vacuum deaerating the inside of the seal layer and pasting a polarizing film in a predetermined position.

0010

However, in the method for manufacturing an active matrix liquid crystal display having the above structure, the liquid crystal drive voltage applied to the transparent display electrode made of ITO connected to the source electrode is
A voltage drop (partial pressure between the liquid crystal and the surface protective film) occurs at a surface protective film such as a SiNx or SiOx film on the TO. This voltage drop causes a problem in that the effective voltage applied to the liquid crystal decreases, leading to deterioration in display quality (deterioration in contrast, decrease in viewing angle, decrease in response speed, etc.). This tendency is due to the decrease in the dielectric constant of the surface protective film (Si
This becomes noticeable as the dielectric constant of Ox≈4).

[0011] The present invention solves the above conventional problems, and
An object of the present invention is to provide a method for manufacturing an excellent active matrix liquid crystal display without deterioration in display quality.

0012

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a structure in which a gate electrode, a gate insulating film, an amorphous silicon semiconductor layer, a source-drain electrode, and an intermediate insulating layer are sequentially formed on a transparent insulating substrate. In a method for manufacturing an active matrix liquid crystal display in which an amorphous silicon thin film transistor array substrate is manufactured by forming a film, a transparent electrode for display, and a surface protection film, the surface protection film is formed from a tantalum oxide film (dielectric constant 25 to 30). This is what I did.

[0013]

According to the present invention, since the method for manufacturing an active matrix liquid crystal display is constructed as described above, the voltage drop in the surface protection film of the liquid crystal drive voltage is reduced.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a diagram according to an embodiment of the present invention.
- It is a flowchart of the manufacturing process of a SiTFT array substrate. Hereinafter, a method for manufacturing an active matrix liquid crystal display according to an embodiment of the present invention will be explained based on FIGS. 1 and 2. As is clear from FIG. 1, up to the formation of transparent electrodes in FIG. Since the process is the same as the conventional process up to the point where the film is formed, the explanation up to that point will be omitted.

The surface protective film 10 shown in FIG. 1(f) is formed using pentaethoxytantalum; Ta(
PCVD method (also called glow discharge method) using OC2 H5 )5 as the main component gas or inorganic gas such as tantalum chloride; TaCl5 etc. and N2 O as the main component gas (gas ratio N2 O/TaCl5 = 5 to 20) using T
A film with a thickness of 0.1 to 0.5 μm is formed over the entire surface of the FT substrate. The substrate temperature at this time is 200 to 300°C.

Here, the lower limit of the film thickness of the surface protective film 20 is I
It is determined based on film defects such as pinholes in the protective film such as TO, step coverage on the TFT surface, etc. Further, the upper limit of the film thickness is determined from the viewpoint of effective voltage drop. Note that the dielectric constant of tantalum (TaOx) is 25 to 30. After the surface protective film 10 is formed, tantalum oxide in unnecessary areas such as on the source-drain electrodes and upper and lower substrate connection pads for connection to external electrode terminals is removed by dry etching mainly containing CF2.

[0017] As a result, a TFT with transparent electrodes is completed. By two-dimensionally arranging the above a-SiTFTs with transparent electrodes, an a-SiTFT array substrate (lower substrate) is completed. The subsequent steps, that is, the counter electrode substrate (upper substrate)
, and the cell forming process are the same as those of the prior art. In this way, a liquid crystal display is completed.

It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0019]

[Effects of the Invention] As explained in detail above, according to the present invention, compared to silicon nitride films, silicon oxide films, etc.,
Since the surface protection film is formed from a tantalum oxide film with a high dielectric constant, voltage drop in the surface protection film can be reduced. Therefore, since the effective voltage applied to the liquid crystal can be increased, the liquid crystal can operate satisfactorily, and high contrast, wide viewing angle, and high-speed response can be realized, and display quality can be improved.

Furthermore, since the voltage drop can be reduced (the voltage drop at the protective film is reduced to about 1/4), the driving voltage can be reduced accordingly. As a result, the drive IC of the liquid crystal panel
In order to make it possible to lower the voltage of
As a result, a low-cost IC driver can be realized, and the cost of the entire liquid crystal display can be reduced.

[Brief explanation of drawings]

FIG. 1 is a flow diagram of a manufacturing process of an a-Si TFT array substrate according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an a-Si TFT array substrate.

FIG. 3 is a flow diagram of a conventional a-SiTFT array substrate manufacturing process.

[Explanation of symbols]

1 Glass substrate 2 Gate electrode 3 Gate insulating film 4 a-Si semiconductor layer 5 Source electrode 6 Drain electrode 7 Intermediate insulation film 8 Contact hole 9 Transparent electrode 10　　　　　Surface protective film

Claims (3)

[Claims] 1. An amorphous silicon thin film transistor is manufactured by sequentially forming a gate electrode, a gate insulating film, an amorphous silicon semiconductor layer, a source-drain electrode, an intermediate insulating film, a transparent electrode for display, and a surface protective film on a light-transmitting insulating substrate. 1. A method of manufacturing an active matrix liquid crystal display in which an array substrate is manufactured, wherein the surface protection film is formed of a tantalum oxide film. [Claim 2] The tantalum oxide surface protective film is coated with plasma C.
2. The method of manufacturing an active matrix liquid crystal display according to claim 1, wherein the active matrix liquid crystal display is manufactured by a VD method. 3. The thickness of the tantalum oxide surface protective film is 0.
3. The method of manufacturing an active matrix liquid crystal display according to claim 1, wherein the active matrix liquid crystal display is formed to have a thickness of 1 to 0.5 μm.