JPH07114043A - Liquid crystal display device and its production - Google Patents

Abstract

PURPOSE:To obviate the generation of hillocks on a surface by adopting a laminated structure composed of a first layer consisting of a low-resistance metal forming scanning lines and recognition signals and a second layer consisting of the oxidized film of the low-resistance metal. CONSTITUTION:The first layer 2 and second layer 3 laminated on a transparent glass substrate 1 are etched by a liquid mixture composed of a nitric acid and hydrofluoric acid. The scanning line in common use as a gate electrode of such a shape as to extend in one way and the recognition mark exclusive of the effective region of the substrate 1 are simultaneously obtd. in this state. The oxidized films are grown in the tapered parts on both flanks of the layer 2. The layer 2 including the tapered parts on both flanks is coated with the oxidized film of the layer 3. The films of an SiNx layer 5 and a semiconductor layer 6 are formed by a plasma CVD method. Further, the film of the SiNx layer is formed as a protective film 7. Pixel display electrodes 9 are then formed and source electrodes 10 and drain electrodes 11 are patterned. The array substrate having thin-film transistors is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a thin film transistor and a manufacturing method thereof, and more particularly to an array substrate thereof.

[0002]

2. Description of the Related Art An image display device using a liquid crystal display device is
A minimum area defined by electrodes such as scanning lines and signal lines which are extended in one direction on a substrate and arranged at a predetermined pitch is used as a pixel, and a nematic liquid crystal composition is sandwiched between both substrates to form a matrix type. Liquid crystal display devices are commonly used. Among them, as a large-capacity, high-definition liquid crystal display device for TV images and graphic displays, it is possible to perform high-contrast display without crosstalk.
An active matrix type liquid crystal display device in which a switching element is arranged for each pixel as a driving and controlling means for each pixel has been put into practical use. As such a switching element, a three-terminal thin film transistor is often used in terms of high contrast ratio and response speed. As the thin film transistor, an amorphous silicon (a-Si) based semiconductor layer is used, and a gate electrode is formed in a lower layer and a source electrode and a drain electrode are formed in an upper layer with an amorphous silicon layer as an active layer interposed therebetween. In many cases, an inverted staggered structure is used.

In recent years, in such an active matrix type liquid crystal display device, a larger screen and a higher definition have been required, and with this, the length of the scanning line becomes longer and the aperture ratio of the pixel is increased. Since it is necessary to keep the scanning line almost constant, the width of the scanning line must be narrowed. However, the resistance value of the scanning line increases in proportion to the length and in inverse proportion to the cross-sectional area (width). The increase in the resistance of the scanning line distorts the waveform of the scanning signal, causes a signal propagation delay, and causes non-uniformity of the image and deterioration of the image quality.

To solve such a problem, it is possible to use low-resistance aluminum, for example, as the material of the scanning line in order to reduce the resistance of the scanning line. However, in the manufacturing process of the thin film transistor, a heat treatment process such as forming the gate insulating film at a substrate temperature of 300 ° C. or higher is indispensable. When Al is used alone as the scanning line, heat generated during the manufacturing process causes aluminum hillocks due to thermal stress that is considered to be due to the difference in thermal expansion from the substrate, and the interlayer insulating property is significantly impaired.

In order to prevent such aluminum hillocks, Al may be coated with a layer made of a material which hardly causes hillocks. As one of the means, a method of forming an oxide film on the surface of Al by the anodizing method of Al can be considered. The anodic oxidation method is a method in which a metal immersed in a chemical conversion solution is used as an anode electrode to apply a voltage and cause an electrochemical reaction on the metal surface to grow an oxide film.

However, the surface of the Al is covered with the anodic oxide film only at the portion electrically connected to the power supply terminal. Therefore, Al is exposed in a portion that is not electrically connected to the power supply terminal, which causes corrosion due to Al hillocks and chemicals. In order to avoid this, the portion not electrically connected to the power supply terminal may be formed of a metal that does not cause corrosion by Al hillock or chemicals, for example, a high melting point metal film.

2 and 3 show such an example. Figure 2
3A to 3F are process diagrams for explaining a manufacturing process of the array substrate, respectively. 3 shows the thin film transistor portion on the left side and the recognition symbol portion outside the effective area of the substrate on the right side.

First, as shown in FIG. 3A, a refractory metal such as a Cr film 15 is formed on the array substrate 1 by a sputtering method. Then, as shown in FIG. 3B, the array substrate 1
The recognition symbol 14 is patterned by a lithographic method outside the effective area of. At this time, the Cr film formed on the thin film transistor portion is entirely removed. The recognition symbol 14 has a shape as shown in FIG. 2 and serves as an alignment mark and a displacement measurement mark at the time of exposure in the lithography method in the subsequent steps.

Next, as shown in FIG. 3C, a low resistance metal such as an Al film 15 to be the scanning line 2 which also serves as the gate electrode 2 is formed on the array substrate 1 by the sputtering method. Then, as shown in FIG. 3D, patterning is performed by a lithography method into a predetermined shape. At this time, the Cr film 14 formed on the part of the recognition symbol 14 is completely removed, and the Cr film 14 is exposed.

Next, as shown in FIG. 3E, an Al film 2 is formed by using a chemical conversion liquid such as tartaric acid via the power supply terminal 12 for anodic oxidation.
An anodic oxide film 3 is formed on the surface of the Al film 2 and the surface of the Al film 2 is covered with the anodic oxide film 3. At this time, since the anodic oxidation power supply terminal 12 is not connected to the identification mark 14 portion, the Cr film 14 is left exposed.

After that, as shown in FIG. 3F, a SiOx layer 4 and a SiNx layer 5 are formed as a gate insulating layer by a plasma CVD method, and the SiNx layer 5 is formed into a predetermined shape. An a-Si film 6 and a protective film 7 are stacked as a semiconductor layer and patterned into a predetermined shape. Next, low resistance non-binding silicon (n + a-Si) 8 is deposited to form a semiconductor pattern. Further, an indium tin oxide film (ITO) is formed as a pixel display electrode 9 by a sputtering method to form a pattern.

The source electrode 10 or the drain electrode
One array substrate is completed by forming a signal line also serving as 11 and forming a pattern. At this time, the recognition symbol
The laminated film after the formation of the SiOx layer 4 is completely removed in the 14th part, and the surface of the identification symbol 14 part is finally in the state where the SiOx layer 4 remains as it is.

[0013]

As described above, when Al is used as the low resistance metal for the scanning electrode which also serves as the gate electrode to reduce the resistance, it is necessary to prevent corrosion due to Al hillocks and chemicals due to the subsequent thermal process. The structure is such that the surface of the Al film is covered by the anodic oxidation method. However, the recognition symbol outside the effective area of the array substrate is exposed to corrosion by Al hillocks and chemicals, and if the recognition symbol is partially missing in the subsequent steps, it becomes an important obstacle in the manufacturing process.

In order to avoid this, when the recognition symbol is formed of a refractory metal that is resistant to corrosion by hillocks or chemicals, first, the recognition symbol is formed of a refractory metal and then scanning also serves as a gate electrode made of a low resistance metal. The electrodes must be formed. That is, patterning by the lithographic method is required twice, resulting in an increase in the number of manufacturing steps and an increase in cost.

The present invention has been made in view of the above problems, and has a structure in which a hillock does not occur on the surface even if a scanning electrode also serving as a gate electrode made of a low resistance metal and an identification symbol are formed, and an array. It is an object of the present invention to provide a simple manufacturing method having high substrate process consistency.

[0016]

According to the present invention, a scanning line extending in one direction on a substrate and also serving as a gate electrode, a gate insulating layer covering the scanning line, and a gate electrode on the gate insulating layer are provided. An array substrate having at least a thin film transistor formed correspondingly, a pixel display electrode connected to the source or drain electrode of the thin film transistor, and an identification symbol formed outside the effective region of the substrate, and a predetermined array substrate. In a liquid crystal display device comprising at least a counter substrate arranged to face each other at an interval of, and a liquid crystal composition sandwiched between the array substrate and the counter substrate, the scanning line and the recognition symbol are made of a low resistance metal. A liquid crystal display device having a laminated structure of a first layer and a second layer made of the low resistance metal oxide film, wherein the scanning line and the identification mark are formed. A step of forming a first layer made of a low resistance metal on the substrate, and a step of forming a second layer made of an oxide film of the low resistance metal on the surface of the first layer; Patterning the first layer and the second layer into a predetermined shape, and forming the first layer and the second layer so that the angle formed between the side surfaces in the thickness direction of the substrate is an acute angle; An oxide film that is the same as the second layer is formed on a side surface of the scanning line in the thickness direction, and the first layer of the scanning line is formed into the second layer.
The method for producing a liquid crystal display device, which comprises the step of coating with a layer of.

[0017]

The scanning line electrode also serving as the gate electrode of the present invention is formed in a tapered shape so that the angle formed between the both side surfaces of the first layer having a low resistance and the substrate is an acute angle. This taper is easily obtained when an oxide film as the second layer is first formed on the surface of the first layer having a low resistance, and a portion corresponding to the width of the scanning line electrode is formed by the lithography method. .

The first scanning line electrode of low resistance is formed.
Simultaneously with the formation of the above layer, the recognition symbol outside the effective area of the array substrate is also formed of the same material, and an oxide film as the second layer is formed on the surface thereof similarly to the scanning line electrode. After that, the exposed surface of the first layer corresponding to the tapered portion of the scanning line electrode is completely covered by forming an oxide film again. With such a configuration and manufacturing method, the tapered portion has a larger surface area than before, and the step of the thickness portion due to the scanning line electrode becomes gentle, so that the first layer during the heat treatment step is formed. No hillocks are generated, and there is no disconnection or cross-shorting of the wiring electrodes laminated on top. In addition, since the oxidation process is added only once to form the scanning line electrodes and the recognition symbols, a simple manufacturing method having high compatibility with the array process can be obtained.

[0019]

EXAMPLES Examples of the present invention will be described in detail below. 1A to 1D show an embodiment of the present invention.
It is a schematic structure figure for explaining a manufacturing process of an array substrate which has a reverse stagger type thin film transistor. Incidentally, FIG.
The left side shows the thin film transistor portion, and the right side shows the recognition symbol portion outside the effective area of the substrate.

First, the transparent glass substrate 1 to be the array substrate.
An Al film having a thickness of 300 nm is formed on the first layer 2 as the first layer 2 of the scanning line which also serves as the gate electrode by the sputtering method. At this time, Al is simultaneously formed on a portion of the substrate 1 outside the effective region. The Al material may be, for example, an aluminum alloy containing 1 atomic% of copper and 0.5 atomic% of silicon. Then, FIG.
As shown in (A), the surface of Al of the first layer 2 is anodized by applying a formation voltage of 71 V in a 3% tartaric acid solution, and the first layer 2 including the portion outside the effective region of the substrate 1 is subjected to anodization. As the second layer 3, a 100 nm Al oxide film was grown.

After that, the lamination of the first layer 2 and the second layer 3 is etched by a photolithography method using, for example, a 5: 1 mixture of nitric acid and hydrofluoric acid. By this process,
As shown in FIG. 1B, a scanning line also serving as a gate electrode having a predetermined shape that extends in one direction and a recognition symbol outside the effective region of the substrate 1 can be obtained at the same time. Due to this etching process, the angle between the both sides of the first layer 2 and the substrate 1 is about 30.
A degree taper is formed. Then, anodic oxidation is performed again in the same chemical solution at a chemical conversion voltage of 110 V, and as shown in FIG. 1C, a 150 nm oxide film is formed on the tapered portions on both side surfaces of the first layer 2 of the scanning line electrode. Grow. By this step, the first layer 2 of the scanning line electrode is completely covered with the oxide film of the second layer 3 including the tapered portions on both side surfaces.

Then, a SiOx layer is formed as the gate insulating layer 4 by the plasma CVD method. Then, similarly, an a-Si layer made of amorphous silicon is formed as the SiNx layer 5 and the semiconductor layer 6 by the plasma CVD method. Further, a SiNx layer is similarly formed as the protective film 7 and is formed into a predetermined shape by photolithography corresponding to the gate electrode. After the pretreatment of the protective film 7, an n + a-Si layer 8 made of low-resistance amorphous silicon is formed as a contact between the source electrode and the drain electrode by a plasma CVD method, and is formed together with the semiconductor layer 6 by a photolithography method. Formed in the shape of.

Next, as the pixel display electrode 9, indium
A tin oxide film (ITO) is formed by a sputtering method, and the opening of the scanning line pad portion is patterned with an HF-based etching solution. Then, an Al film is formed by the sputtering method, and the source electrode
10 and the drain electrode 11 are patterned. Thereafter, reactive ion etching (RIE) is performed to remove the n + a-Si layer 8 on the back channel, thereby completing the array substrate having thin film transistors as shown in FIG. 1 (D). Note that a SiOx layer is simultaneously formed as the gate insulating layer 4 on the surface of the recognition symbol portion, but any film formed thereafter is removed.

Next, ITO electrodes corresponding to the pixels of the array substrate are formed on the other counter substrate (not shown),
An alignment film made of polyimide is formed on the surfaces of the array substrate and the counter substrate, and a rubbing treatment along one direction is performed. Then, the rubbing directions of the two substrates are opposed to each other at a predetermined interval so that the rubbing directions are orthogonal to each other, the peripheral portions are bonded and fixed, and, for example, a nematic liquid crystal composition is injected between the two substrates to complete a liquid crystal display device. (Not shown).

In the array substrate of the liquid crystal display device formed as described above, the scanning line has a length of 20 cm and a width of 30 μm.
Then, the resistance of the scanning line was about 1 kΩ, and a sufficiently low resistance value capable of driving high-definition display was obtained. Further, since the scanning lines and the recognition symbols are covered with an oxide film, they were not affected by any of the aqua regia-based, phosphoric acid / nitric acid-based, and dry etching solutions, and no disconnection or chipping occurred. Further, since both side surfaces of the scanning line are formed in a tapered shape, the step portion of the scanning line becomes gentle, and no interlayer short circuit or disconnection due to hillock or the like occurs.

[0026]

As described above, according to the present invention, in the array substrate of the liquid crystal display device, the scanning line also serving as the gate electrode and the recognition symbol are formed of the first layer of low resistance.
An oxide film as a second layer is formed on the surface of the layer by the anodizing method, both side surfaces are tapered by an etching solution, and then both side surfaces are completely covered with the oxide film by anodic oxidation again. . At this time, the recognition symbol outside the effective area of the array substrate is also patterned at the same time, so that the recognition symbol does not cause corrosion by Al hillocks or chemicals in the subsequent steps without increasing the patterning process. Can be prevented.

Further, the oxide film having excellent chemical resistance as the scanning line and the recognition symbol can prevent interlayer short circuit and disconnection. Even if a low resistance metal such as Al is used as the material of the scanning line, it is completely covered with an oxide film and both side surfaces are formed in a tapered shape. It can be prevented.

[Brief description of drawings]

1A to 1D are views showing an embodiment of the present invention.
FIG. 6 is a schematic configuration diagram for explaining a manufacturing process of an array substrate having an inverted stagger type thin film transistor.

FIG. 2 is a schematic plan view showing the overall configuration of an array substrate.

3A to 3F are schematic configuration diagrams for explaining a manufacturing process of a conventional array substrate having an inverted stagger type thin film transistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Glass substrate 2 ... 1st layer 3 ... 2nd layer 4 ... Gate insulating layer 5 ... SiNx layer 6 ... Semiconductor layer 7 ... Protective film 8 ... N + a-Si film 9 ... Pixel display electrode 10 ... Source electrode 11 ... Drain electrode 12 ... Anodizing power supply terminal 13 ... Thin film transistor 14 ... Recognition symbol 15 ... Cr film

Claims (2)

[Claims] 1. A scanning line extending in one direction on a substrate and also serving as a gate electrode, a gate insulating layer covering the scanning line, and a thin film transistor formed on the gate insulating layer corresponding to the gate electrode. An array substrate having at least a pixel display electrode connected to a source or drain electrode of the thin film transistor, and an identification symbol formed outside the effective area of the substrate, and an array substrate opposed to the array substrate at a predetermined interval. In a liquid crystal display device including at least a substrate and a liquid crystal composition sandwiched between the array substrate and a counter substrate, the scan line and the identification symbol are a first layer made of a low resistance metal, A liquid crystal display device comprising a laminated structure with a second layer made of a resistance metal oxide film. 2. A scanning line extending in one direction on a substrate and also serving as a gate electrode, a gate insulating layer covering the scanning line, and a thin film transistor formed on the gate insulating layer corresponding to the gate electrode. An array substrate having at least a pixel display electrode connected to a source or drain electrode of the thin film transistor, and an identification symbol formed outside the effective area of the substrate, and an array substrate opposed to the array substrate at a predetermined interval. In a method of manufacturing a liquid crystal display device comprising at least a substrate and a liquid crystal composition sandwiched between the array substrate and a counter substrate, the step of forming the scanning line and the identification symbol is performed on the substrate. Forming a first layer made of a low resistance metal, forming a second layer made of an oxide film of the low resistance metal on the surface of the first layer, and forming the first layer Patterning the second layer into a predetermined shape and forming an angle between the first layer and the substrate on the side surface in the thickness direction of the second layer to form an acute angle; and the thickness of the scanning line. Forming the same oxide film as the second layer on the side surface in the vertical direction and covering the first layer of the scanning line with the second layer. .