JP2877201B2 - Method for manufacturing element substrate for liquid crystal display device - Google Patents

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 element substrate such as an active matrix substrate used for a liquid crystal display device, and more particularly to a method for preventing a back surface from being flawed, which deteriorates the quality of a displayed image.

[0002]

2. Description of the Related Art A display device using a liquid crystal panel is employed in a wide range of fields such as a wall-mounted TV, a projection TV, and a display for OA equipment. Among active liquid crystal panels, an active matrix liquid crystal display in which thin film transistors and the like are incorporated in a liquid crystal display device is advantageous in that the contrast and response speed do not decrease even when the number of scanning lines increases. In the projection type liquid crystal display, a large-screen display can be easily obtained.

In the projection type liquid crystal display, since the projection light is transmitted through the substrate, it is required that the back surface of the substrate does not lower the transmittance and has high flatness. FIG.
FIG. 2 is a cross-sectional view showing an example of a conventional method for manufacturing an active matrix substrate in the order of steps. First, as shown in FIG. 5A, a protective oxide film 2 is formed to a thickness of, for example, about 0.2 μm on the front and back surfaces of a transparent insulating substrate 1 made of quartz or the like. Next, as shown in FIG. 5B, after forming a polysilicon film, an island-shaped polysilicon film is formed by using a photo-etching technique, and a gate oxide film 11 is formed on the island-shaped polysilicon film. A gate electrode 12 is formed through the gate electrode, and a source region 13, a channel region 14 and a drain region 15 are formed in the island-shaped polysilicon, whereby the thin film transistor 10 is manufactured. Thereafter, an interlayer film 16 made of an insulator is formed, and a contact hole 17 is opened in the interlayer film.

Subsequently, as shown in FIG. 5C, after forming a wiring electrode 21 and a pad electrode 22 using, for example, Al, and connecting to the pad electrode 22 using, for example, indium-tin oxide (ITO). Then, the formation of the active electrode substrate is completed.

[0005]

In the above-described conventional manufacturing method, the back surface of the transparent insulating substrate 1 comes into contact with the jig of the manufacturing apparatus. The jig of the apparatus includes a transfer belt or a fork as a transfer system, and a vacuum chuck or a stage for fixing the transparent insulating substrate 1. Friction or contact with these jigs is performed in a cleaning process, This process is repeated in each manufacturing process such as a film forming process, a photolithography process, and an etching process.
Therefore, a flaw 41 occurs on the back surface of the transparent insulating substrate as shown in FIG. When the flaw is generated as described above, when the active matrix is assembled on the liquid crystal display panel, light transmitted through the active matrix substrate is damaged.
Since the portion 1 is occluded or significantly attenuated and a shadow is formed on the projected image, the quality of the displayed image is significantly reduced. Also,
When the scratch 41 is made, the active matrix substrate is easily damaged, which causes a problem that the yield and the reliability are reduced.

When the depth of the flaw 41 was measured by a surface roughness meter, it was 0.2 μm for a shallow one and about 1 μm for a deep one.
Met. Therefore, the flaw 41 penetrates through the protective oxide film 2 also formed on the back surface of the transparent insulating substrate 1 and reaches the transparent insulating substrate 1 itself. The scratch 41 once attached to the back surface of the transparent insulating substrate cannot be removed by etching the substrate. This is because the flaw 41 is simultaneously etched by simple etching. Scratches can be removed by polishing the back surface of the substrate, but the number of unnecessary steps increases, resulting in an increase in cost. Therefore, the problem to be solved by the present invention is:
An object of the present invention is to provide a method for manufacturing an element substrate for a liquid crystal display device, in which a scratch is not generated on a rear surface of a transparent insulating substrate in a manufacturing process and the quality of a display image and a projected image is not deteriorated.

[0007]

An object of the present invention is to form at least two protective films on the back surface of a transparent insulating substrate, and to remove at least the uppermost protective film after the fabrication of the element substrate. And by setting the uppermost protective film to a depth greater than or equal to the flaw that can occur.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The method for manufacturing an element substrate for a liquid crystal display device according to the present invention comprises the steps of (1) forming at least two layers on the back surface of a transparent insulating substrate in such a manner that adjacent protective films have different etching properties. Or
In the following step (2), the thickness of the upper protective film is
A step of forming a multi-layer protective film having a thickness equal to or greater than a depth of a flaw that can occur on the back surface of the substrate ; and (2) a step of forming necessary elements and wiring on the surface of the transparent insulating substrate. And (3) after the step (2), a step of etching and removing at least the uppermost protective film among the protective films formed on the back surface of the transparent insulating substrate.

[0009] Preferably, the multilayer protective film comprises:
The lower protective film is formed of an oxide film, the intermediate layer is formed of a polysilicon film or a silicon nitride film, and the upper layer is formed of a three-layer protective film having a silicon oxide film. Then, when removing these protective films, a wet method is used. Preferably, the thickness of the uppermost protective film is 1 μm or more, and the thickness of the lowermost protective film is 0.05 μm or less.

[Operation] According to the manufacturing method of the present invention configured as described above, at least the thin bottom protective film on the back surface of the transparent insulating substrate and the search for scratches that may occur during the manufacturing process are performed. Even if the back surface of the transparent insulating substrate may come in contact with jigs such as the conveyor belts of various devices and vacuum chucks in the manufacturing process, the uppermost protective film having a thick film thickness is formed. It is possible to stop within the uppermost protective film, and by removing the third protective film, it is possible to remove the flaw at the same time.

In removing each film on the back surface, when the upper protective film is etched, the lower protective film functions as an etching stopper film, so that excessive etching can be prevented. Finally, the lowermost protective film is removed by etching, but since this protective film is formed thin, the time required for the back surface of the transparent insulating substrate to be exposed to etching can be shortened, and etching damage to the substrate can be reduced. Can be minimized. Therefore, it is possible to obtain a transparent insulating substrate having a flat surface and a back surface with less roughness. In order to prevent the substrate from being roughened by etching, the lower the protective film, the better.
The thickness is preferably 0.05 μm or less. On the other hand, if the thickness is too small, the film cannot function as an etching stopper. Therefore, the thickness is preferably 0.01 or more.

[0012]

Next, embodiments of the present invention will be described in detail with reference to the drawings. [First Embodiment] FIGS. 1A to 1C and FIGS.
(F) is sectional drawing which showed 1st Example of this invention in process order. First, as shown in FIG. 1A, a first back oxide film 3 is formed on a transparent insulating substrate 1 to a thickness of about 0.05 μm, and a back polysilicon film 4 is formed to a thickness of 0.05 μm. The film is formed by a method. At this time, the first back surface oxide film 3 and the back surface polysilicon film 4 are also formed on the front surface side of the transparent insulating substrate 1, but these are removed by performing, for example, dry etching to remove the back surface of the transparent insulating substrate 1. Only the first back oxide film 3 and the back polysilicon film 4 are formed.

Next, as shown in FIG. 1B, a second back oxide film 5 is formed to a thickness of about 1 μm by the CVD method.
At this time, a base oxide film 6 having the same thickness is also formed on the front surface side of the transparent insulating substrate 1. Subsequently, as shown in FIG. 1C, after a polysilicon film is formed by a low pressure CVD method,
The island-shaped polysilicon film is processed using a photo-etching technique, and a gate electrode 12 is formed on the island-shaped polysilicon film via a gate oxide film 11. Then, the source region 13 and the drain region 15 sandwiching the channel region 14 are formed in the island-shaped polysilicon by ion implantation, and the thin film transistor 10 is manufactured. Thereafter, an interlayer film 16 made of an insulator is formed, and a contact hole 17 is opened in the interlayer film 16.

Subsequently, as shown in FIG.
Form wiring electrode 21 and pad electrode 22 using Al
After that, for example, indium-tin oxide (ITO) is used.
To form a transparent electrode 23 connected to the pad electrode 22.
You. Subsequently, as shown in FIG.
The surface side on which the data 10 and the transparent electrode 23 are formed
After covering with the photoresist film 31, first the second back surface oxide film
5 is removed using a hydrofluoric acid-based etchant.
The silicon film 4 is etched with a high etching ratio to the oxide film.
Etching solution such as HF: HNO_Three : CH _Three COOH
= 1: 10: 60, using a mixed solution or the like. further,
The first backside oxide film 3 is etched at a relatively low etching rate.
Ching liquid such as HF: H_Two Use O = 1: 30 mixture
And remove it. Finally, as shown in FIG.
The photoresist film 31 is removed and the active matrix substrate is removed.
Is completed.

In the active matrix substrate thus manufactured, even if the jig of each manufacturing apparatus and the back surface of the active matrix substrate come into contact with each other in the manufacturing process, the back surface of the substrate is thicker than the depth of a flaw that may occur. Since the second back oxide film 5 is covered with the second back oxide film 5 having a thickness and the jig and the like come into contact with the second back oxide film, as shown in FIG. Does not reach the rear surface of the transparent insulating substrate 1 and the rear surface of the transparent insulating substrate 1 is not scratched.

In removing the second back surface oxide film 5 and the back surface polysilicon film 4, the back surface polysilicon film 4 serves as an etching stopper film when the second back surface oxide film 5 is etched, and the second back surface oxide film 5 when the back surface polysilicon film 4 is etched. Since one backside oxide film 3 functions as an etching stopper film, no excessive etching occurs. In addition, since the thin first rear surface oxide film is finally removed, etching can be completed in a short time, and etching damage to the rear surface of the transparent insulating substrate 1 can be minimized. Therefore, even if the thick second backside oxide film is removed by etching and the backside of the substrate is exposed to an etching atmosphere, the flatness of the backside of the transparent insulating substrate 1 is not impaired. In addition, since the removal of each film formed on the back surface can be performed by a wet etching method, the process is not complicated and the workability is high.

In the first embodiment, since the thick underlying oxide film 6 is formed on the front surface side of the transparent insulating substrate 1 at the same time as the formation of the second back surface oxide film 5, the transparent insulating substrate 1
In this case, even if a contaminant is present, the diffusion of the contaminant can be shielded by the base oxide film 6, and the contamination of the thin film transistor 10 can be prevented.

[Second Embodiment] FIGS. 4 (a) to 4 (c)
It is sectional drawing which showed the 2nd Example of this invention in process order.
First, as shown in FIG.
The back oxide film 3 is formed to a thickness of about 0.05 μm, and the back polysilicon film 4 is formed to a thickness of 0.05 μm. At this time, the oxide film and the polysilicon film also grow on the surface side of the transparent insulating substrate 1, and the surface oxide film 3a and the surface polysilicon film 4a are formed. Next, as shown in FIG. 4B, a second back surface oxide film 5 is formed to a thickness of about 1 μm. At this time, an oxide film having the same thickness is also formed on the front surface side of the transparent insulating substrate 1, and this oxide film is removed by, for example, an etch-back method. Next, as shown in FIG. 4C, heat treatment is performed in an oxygen atmosphere to convert the surface polysilicon 4a into a thermal oxide film 7. Subsequent to this step, FIG.
2A to 2F, the same process as in the first embodiment shown in FIG. 2F is performed to manufacture an active matrix substrate.

In this embodiment, the same effect as that of the first embodiment can be obtained. In addition, since the second back oxide film 5 is subjected to the heat treatment, the film quality becomes dense and the resistance to scratches is improved. Further, since the oxide film formed on the surface of the transparent insulating substrate is formed by thermal oxidation, there is an advantage that a higher quality oxide film can be used as the surface oxide film.

In the above embodiment, the oxide film is used for the first and third protective films, and the polysilicon film is used for the second protective film. However, the present invention is not limited thereto, and the protective film of the second layer functions as an etching stopper when the protective film of the third layer is etched, and the protective film of the first layer functions as an etching stopper when etching the protective film of the second layer. For example, the first and third protective films may be an oxide film, and the second protective film may be a nitride film. Further, in the above embodiment, the protective film of the first layer (the first layer
Although the back surface oxide film was removed last, it is not always necessary to remove it, and it may be finally left on the back surface of the substrate as a protective film.

[0021]

As described above, according to the method for manufacturing an element substrate for a liquid crystal display device of the present invention, the uppermost layer on the back surface of a transparent insulating substrate is formed with a film thickness greater than the maximum depth that can occur during the manufacturing process. According to the present invention, since a protective film is formed and the uppermost protective film is removed by etching after the element forming step on the substrate surface is completed, according to the present invention, a scratch is caused by contact with a jig or the like during the manufacturing process. Even if there is a crack, the scratch can be removed together with the protective film, so that the transparent insulating substrate can be prevented from being scratched. Therefore, according to the present invention, it is possible to prevent a decrease in the quality of a displayed image due to a scratch and a decrease in yield and reliability due to damage to the substrate.
According to the present invention, since the lower protective film functions as an etching stopper when the upper protective film is etched, excessive etching can be prevented even if a margin is provided for the etching time, and the flatness of the back surface of the substrate can be reduced. It can be prevented from worsening. Further, since the lowermost protective film is formed thin, damage to the substrate can be minimized even when the protective film is removed by etching.

[Brief description of the drawings]

FIG. 1 is a part of a process order sectional view for explaining a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a first embodiment of the present invention;
Sectional sectional view in a step following the step.

FIG. 3 is a cross-sectional view illustrating an effect of the present invention.

FIG. 4 is a process order sectional view for explaining a second embodiment of the present invention.

FIG. 5 is a process order sectional view for explaining a conventional example.

FIG. 6 is a sectional view for explaining a problem of the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent insulating substrate 2 Protective oxide film 3 1st back surface oxide film 3a Surface oxide film 4 Back surface polysilicon film 4a Surface polysilicon film 5 2nd back surface oxide film 6 Base oxide film 7 Thermal oxide film 10 Thin film transistor 11 Gate oxide film 12 Gate Electrode 13 Source region 14 Channel region 15 Drain region 16 Interlayer film 17 Contact hole 21 Wiring electrode 22 Pad electrode 23 Transparent electrode 31 Photoresist film 41 Scratch

Claims (5)

(57) [Claims] (1) On the back surface of a transparent insulating substrate, at least two layers are formed in such a manner that adjacent protective films have different etching properties , and the thickness of the upper protective film is as follows:
The depth of scratches that can occur on the backside of the substrate in the process of
A step of forming a multilayer protective film having a thickness ; (2) a step of forming necessary elements and wirings on the surface of the transparent insulating substrate; and (3) a step of forming the transparent film after the step (2). A step of etching and removing at least the uppermost protective film of the protective film formed on the back surface of the insulating substrate. 2. The multi-layer protective film according to claim 1, wherein the lower protective film is silicon.
Oxide film, intermediate protective film is polysilicon film, upper protective film is
It is characterized by being a multi-layer protective film composed of silicon oxide film
The method for manufacturing an element substrate for a liquid crystal display device according to claim 1 . 3. The method for manufacturing an element substrate for a liquid crystal display device according to claim 1, wherein the thickness of the uppermost protective film is 1 μm or more. 4. The film thickness of the lowermost protective film is 0.05 μm.
4. The method for manufacturing an element substrate for a liquid crystal display device according to claim 1, wherein: 5. The method according to claim 1, wherein the etching in the step (3) is performed by a wet method.
5. The method for producing an element substrate for a liquid crystal display device according to 2, 3, or 4.