JP3128268B2 - Liquid crystal display - Google Patents

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 having a switching element.

[0002]

2. Description of the Related Art Liquid crystal display devices widely used as various display devices include a simple matrix system and an active matrix system. The active matrix system, which is superior in image quality and response speed, is a personal computer.
Attention has been paid to display devices for computers and display terminals for industrial equipment. The active matrix method includes a three-terminal type using thin film transistors (TFTs) and a thin film diode (TF) by switching elements for each picture element.
There is a two-terminal type using D).

In general, the TFT type has high image quality but has problems in cost and yield, and the TFD type has high productivity and low cost but has problems in image quality.

[0004] Here, the yield may be affected by variations in element characteristics, but is often caused by image defects caused by the complexity of the manufacturing process. These image defects include white spots, black spots, spots and unevenness. The white spot defect, particularly the structure-induced defect, will be described by taking a TFD type as an example.

[0005] Normally, the same applies to the TFT type.
In the mold, a diode for each pixel is planarly arranged on a translucent substrate with a corresponding pixel electrode. For this reason, the components including the diode have an extremely close arrangement relationship, and if dust or the like is present when the pixel electrode is formed by etching, etching residue is generated and the components are easily short-circuited. This short becomes a white spot defect. The degree of occurrence of this white spot defect increases rapidly as the number of pixels increases.

[0006] This situation is described as one of the TFD types, MIM.
(Metal Insulator Metal) structure using a diode as an example will be described with reference to FIG.

FIG. 6 is a plan view showing an area for one pixel. Reference numeral 11 denotes a light-transmitting substrate selected from various types of glass. On the upper surface of the light-transmitting substrate 11, a bus line 12 formed by a sputtering method based on a metal tantalum (Ta) film and a light-transmitting substrate are formed. Is provided with a strip-shaped projection 13. Tantalum pentoxide (Ta ₂ O ₅ ), which is an insulator, is formed on the surface of the tantalum film forming the bus lines 12 and the projections 13 by anodic oxidation. In addition, since the pinhole-less film can be formed by the anodic oxidation method,
It is always used to form a TFD diode.

On the strip-shaped projection 13, a strip-shaped opposing metal film 14 is crossed and laminated in a cross shape to form a diode 15. As the counter metal film 14, a chromium (Cr) film is used in consideration of the stability of the diode characteristics.
Therefore, the diode 15 of the MIM in this example is Ta
/ Ta ₂ O ₅ / Cr. The diode 15 is electrically connected to the pixel electrode 16 at the opposing metal film 14. The pixel electrode 16 is made of an ITO (Indium Tin Oxide) film because it is easily etched, and is arranged in a plane so as to surround the diode 15 as shown in the figure.

In the above configuration, the components are arranged close to each other, but the smallest dimension is the area A where the bus line 12 and the pixel electrode 16 are adjacent to each other.
The interval is about 5 μm.

In such a dimensional relationship, the pixel electrode 16
If the dust is present when etching is performed, an etching residue 17 having the same shape as the dust is generated. This etching residue
If 17 occurs in the state as shown in the figure, the Ta ₂ O ₅ film formed on the surface of the bus line 12 is easily broken down, and the tantalum film of the bus line 12 and the pixel electrode 16 are short-circuited. That is, such a process is the cause of the white spot defect.

As a means for reducing such white spot defects, reduction of dust is the most important and direct means. Here, in the case of a semiconductor, a number of chips per wafer can be taken as non-defective products stochastically. However, in a liquid crystal display device, the area per one translucent substrate is extremely large, such as 10 inches, so that the number of charges is as small as 1 to 3 sheets.
Since the absolute number of dusts becomes a problem, and there is a possibility that no good product can be obtained, there is a difficulty different from that of a semiconductor.

In the above description, the problem of the image defect of the liquid crystal display device is a problem. Next, the decrease in the aperture ratio due to the higher definition will be described.

In recent years, there have been remarkable technological developments in color liquid crystal display devices, and the main one is an active matrix type in which an amorphous silicon film constitutes a TFT type switching element. The reason is that, as described above, the image quality of the active matrix type is good, and the amorphous silicon film is easy to control the valence electrons unlike other materials. This is because the technology has been evaluated as the most suitable material for forming the switching element, and the technology has been rapidly developing in the last ten years. In addition to the above, the two-terminal type described above as one of the active matrix types has been independently developed due to the easiness of the manufacturing method.

The current technological development of such a TFT type is roughly classified into two types. One is to increase the area, and the diagonal is 1
The main product is the 0-inch class. In this case, the number of pixels is a so-called medium-definition display of 640 (× 3 primary colors) × 480 pixels, which has begun to be used for a display of a personal computer. Another is high definition.

In any case, in these cases, the number of lines increases, and it is necessary to increase the storage capacity of the pixels. However, in the TFT type using an amorphous silicon film,
Since the mobility of the amorphous silicon film is small, each TF
It is becoming difficult to reduce the size of T and maintain the aperture ratio of the pixels.

Similarly, the two-terminal type liquid crystal display device described above also tends to have a large area, and a 12-inch class liquid crystal display device is being developed. Regarding high definition, in the case of the MIM type liquid crystal display device which is one of the two terminal types, a device having 9.8 inches and 640 pixels (× 3 primary colors) × 400 has been developed. The diode area of the two-terminal type liquid crystal display device is different from that of the TFT type, and usually has only an area of about 5 μm square.

However, regardless of the switching mode of the two terminals of the TFD type and the three terminals of the TFT type, a reduction in contrast due to a decrease in the aperture ratio can be avoided if the definition is further improved in the future. Absent.

These circumstances will be described with reference to FIGS. 7 and 8, taking a structure using an MIM type diode as an example.

The translucent substrate 11 shown in FIG. 7 is a plan view of a region for one pixel in binary display. The region for one pixel has a pitch of, for example, 210 μm in the vertical direction × 210 μm in the horizontal direction, as shown in FIG. Having. The reference numerals given to the respective constituent elements are the same as those in FIG. 8, and the same reference numerals indicate the corresponding constituent elements. These components have the following dimensional relationships as shown.

First, the bus line 12 has a line width of 20 μm, and the protrusion 13 has a width of 5 μm × length 20 μm.
And a counter metal film 14 laminated in a cross shape so as to intersect with this, a diode 15 of 5 μm
× 5 μm. The pixel electrode 16 has a size of 190 μm in the vertical direction × 170 μm in the horizontal direction, and has a cutout as shown to avoid the protrusion 13. In this case, the aperture ratio (the area of the pixel electrode 16 / the area of one pixel region) is about 72%.

Here, in the case of colorization, this one pixel region must be divided into three parts for three primary colors. In the case of the two-terminal type, the color filters are arranged in a stripe type. Therefore, as shown in FIG. 8 , one pixel area is divided into three equal parts for the three primary colors of RGB along the vertical direction. , Together with the projection 13, the diode 15
Are provided.

In this case, the size of each pixel area for each of the three equally divided RGB is 210 μm in the vertical direction × 70 μm in the horizontal direction.
m. Looking at the dimensions of each component, the bus line 12 cannot be made thinner due to the line resistance,
The width remains 20 μm. The size of the diode 15 cannot be reduced due to the limit of the current mask making technology, and is 5 μm ×
It remains at 5 μm.

Accordingly, only the pixel electrode 16 becomes smaller, and in the example shown in the figure, 190 μm in the vertical direction × 30 μm in the horizontal direction.
m. The aperture ratio at this time becomes about 35% when calculated in accordance with figure halved to around 72% aperture ratio in FIG. Further, the amount of transmission of light (luminance) even cause decreased than expected 16%, the percentage of decrease for the case of FIG. 7 is about 30%.

In order to solve such a problem, the area of one pixel region is increased by reducing the total number of pixels, or the size of the display device is enlarged so that one pixel is maintained while maintaining the number of pixels. It is to increase the area of the region.

However, such a change in the number of pixels and the size of the display device does not result in higher definition.

[0026]

As described above, since the constituent elements are arranged on the same plane, dimensional restrictions are imposed on these arrangements, and as a result, image defects such as white spot defects are caused. Or in the case of colorization, the aperture ratio is greatly reduced.

As a new attempt for such a situation, a three-dimensional arrangement has been considered. Generally, when the degree of integration due to planar arrangement is limited, in the field of semiconductors, dynamic ram (DRAM) or C
The technical flow is to arrange them three-dimensionally (three-dimensionally) like a video device such as a CD. There is an example in which such an attempt has been made also in a liquid crystal display device. For example, in the case of a liquid crystal projection display device for high-definition television, since the aperture ratio is greatly reduced in the transmission type, it is considered that the aperture ratio is not reduced as the reflection type.

Further, in the case of such a three-dimensional arrangement, if the upper and lower layers are to be electrically connected via the insulating layer, a through hole for contact must be formed in the insulating layer. On the other hand, when the insulating layer is thick, the through-hole becomes deep, the taper angle becomes steep, and there is a possibility that a step in contact with the contact hole is likely to occur.

The present invention has been made in view of the above problems, and has as its object to provide a liquid crystal display device that can reduce the occurrence of image defects such as white spot defects.

[0030]

According to the present invention, there is provided a bus line, a switching element connected to the bus line, and the bus line separately provided from the switching element.
A pad formed on the same layer as the switching element;
And over the pad.
Metal film, an interlayer insulating film formed to cover the metal film, and a through hole formed in the interlayer insulating film on the pad.
And Horu, wherein arranged in corresponds before kiss switching elements through an interlayer insulating film, shallow depth by the pad
It is obtained; and a pixel electrode which is conductively connected to the metal film by the through hole is.

The pixel electrodes are arranged so as to extend to the upper part of the bus line via the interlayer insulating film.

Further, the interlayer insulating film is made of an organic substance.

The interlayer insulating film is a polyimide film.

Further, the through holes are formed by dry etching.

Further, the through holes are etched by oxidizing plasma.

Further, a plurality of through holes are provided.

[0037]

DETAILED DESCRIPTION OF THE INVENTION The present invention, by which is disposed a pixel electrode and corresponds to the switching element through an interlayer insulating film, resulting dimensional allowance in the arrangement between the components, the size of each component In the same manner, even if the same amount of dust is loaded as before, the occurrence of image defects such as white spot defects is greatly reduced.

Further , a through hole is formed on the interlayer insulating film on the pad.
To reduce the depth of this through hole.
In the contact portion between the pixel electrode and the switching element,
While securing the area, the diameter at the top surface of the through hole is more
And the occurrence of disconnection of the pixel electrode is reduced.

[0039]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing one pixel region in one embodiment of a two-terminal type liquid crystal display device. The reference numerals assigned to the respective components correspond to the reference numerals given in FIG. They represent the same components.

Hereinafter, the structure of each part will be described in accordance with the manufacturing process of the liquid crystal display device. The light-transmitting substrate 11 is selected from various glass materials, and a coating film is applied to the surface thereof in advance as necessary. In this case, the coating film includes a tantalum pentoxide film (Ta ₂ Ox: x to 5) or a silicon oxide film (SiOx).

The light transmitting substrate 11 has a thickness of 2000 to 3000
An Angstrom tantalum (Ta) film is usually formed by a sputtering method. The tantalum film formed on the translucent substrate 11 is
Etching is performed so as to form 12, the projection 13 and the pad 27 as a pad. In this case, the bus line
The width of 12 is 10 μm, and the width of the protrusion 13 is 5 μm. In addition, in order to perform taper etching as etching, plasma etching is performed using a mixed gas of CF ₄ gas and O ₂ gas.

Next, an insulating film (Ta ₂ O ₅ film) is formed on the surface of these tantalum films by anodic oxidation. This anodic oxidation method is performed by applying a voltage of about 40 V in a solution in which 0.01 wt% of citric acid is mixed with pure water. The thickness is in the range of 500 to 1000 Å. That is, M using a tantalum pentoxide film
Since the IM-type diode uses the Pool-Frenkel conduction, if the film thickness is too thin, it tends to leak, and if it is too thick, the effect of the insulator becomes too large to allow current to flow, so the above-mentioned size range is selected.

Opposite Metal Film for Constituting Diode 15
First, a chromium film having a thickness of about 1500 angstroms is formed by sputtering using chromium (Cr). The reason why the chromium film was selected here is that the stability of the characteristics and the non-linearity are good. The chromium film formed in this manner is etched to form a cross shape crossing the protruding portion 13, and the opposed metal film 14 is formed in a laminated state at a position where the lower surface faces the pad portion 27. In this etching, a wet etching method is generally used in consideration of a selectivity with respect to a tantalum pentoxide film as a base. The width of the opposing metal film 14 is 5 μm. Therefore, a 5 μm × 5 μm MIM-type diode 15 is formed at the intersection of the cross. The process up to this point is the same as the conventional method of forming the MIM type diode 15.

Then, as described above, the bus line 12 and the MIM
A low-temperature fired polyimide film as an interlayer insulating film 18 is applied on the entire surface of the light-transmitting substrate 11 on which the diode 15 of the mold is formed. In this case, the curing temperature is 180 ° C. and the film thickness is 5000 Å.

Although the low-temperature fired polyimide film is exemplified as the interlayer insulating film 18, a silicon oxide film, a metal oxide, or another organic insulating film may be used. However, the following description is made on the assumption that the interlayer insulating film 18 is used.

As shown in FIG. 2, which is a cross-sectional view taken along the line II-II of FIG. 1, the surface of the MIM diode 15 is
It is completely covered by the interlayer insulating film 18. Thereafter, the interlayer insulating film 18 located just above the portion of the opposing metal film 14 that is outside the portion to be the MIM diode 15 is etched,
Two through holes 19 for contact are formed. This etching uses an oxidizing plasma. At this time, V in FIG.
As shown in FIG.
Is subjected to taper etching so as to form an upwardly open tapered shape. Further, since the pad portion 27 is provided in the through hole 19 formed in the interlayer insulating film 18, the thickness of the interlayer insulating film 18 up to the upper surface of the opposing metal film 14 is reduced, and the depth is reduced. Can be formed smoothly. In this way, the through hole 19 is tapered, the depth of the through hole 19 is made shallow, and the taper angle of the through hole 19 is formed smoothly.
This is to prevent a disconnection from occurring in the conductive portion formed in 19. Furthermore, the pad section is provided separately from the diode 15.
By providing 27, the depth of through hole 19 can be reduced
Wear. This secures the area of the contact area
The diameter at the top surface of the through hole 19 can be made smaller.
You. In particular, through holes 19 with taper etching
Therefore, the shallower the depth of the through hole 19, the better
Unnecessary enlargement of the diameter on the surface can be prevented. Since the low-temperature fired interlayer insulating film 18 has low adhesion to other laminated films, it is necessary to roughen the surface of the other layer by plasma. In addition,
As plasma, argon (Ar) plasma is used for the purpose of removing the surface oxide film of the opposing metal film 14.

Next, in order to form the pixel electrode 16 on the interlayer insulating film 18, the ITO film is sputtered to about 100
It is formed to a thickness of 0 Å and further etched with a dilute hydrochloric acid solution to form a pixel electrode 16 as shown. The shape of the pixel electrode 16 is different from the conventional one shown in FIG. 8, and can be made to cover the diode 15 located in the lower layer as shown in FIG. , A display with higher contrast can be obtained.

Here, when the ITO film is formed by the sputtering method as described above, the ITO film is connected to the lower opposing metal film 14 through the tapered through hole 19 as shown in FIG. Make an electrical connection. In this case, since the through-hole 19 has a smooth taper angle and is formed so as to decrease the depth at the pad portion 27, the pixel electrodes 16 face each other without causing disconnection due to so-called step disconnection as described above. Connected to metal film 14.

In the example of FIG. 1, two through holes 19 for contact are provided. However, any number of through holes 19 may be used as long as electrical connection is ensured.

The following structure and its manufacturing process are the same as those of a normal liquid crystal display. 2 and 3
As described above, after the pixel electrode 16 is formed, a low-temperature fired polyimide film is again applied as the insulating film 20 and an alignment process is performed. The thickness of the insulating film 20 is about 800 Å on the pixel electrode 16.

The opposing transparent electrode substrate 21 in the upper part of the figure is formed by forming a stripe-shaped ITO film 23 on a light-transmitting substrate 22 and coating a low-temperature baked polyimide film 24 thereon. Is also subjected to an orientation treatment.

Then, a liquid crystal 25 is injected between the two translucent substrates as shown in FIG. 2 to assemble a liquid crystal display.

According to the above configuration, the bus line 12 and the pixel electrode 16 are arranged in different layers via the through hole 19, and the depth of the through hole 19 is reduced by the pad portion 27 to reduce the taper angle. I tried not to be steep,
It is possible to prevent disconnection of the pixel electrode 16 and eliminate short circuit. Therefore, although the number of steps is slightly increased as compared with the conventional manufacturing process, white spot image defects can be reliably reduced.

Although the above embodiment has been described by taking an MIM type diode as an example, an MSI (Metal Semi-Insul
ator) and other general two-terminal liquid crystal display devices.

Next, another embodiment will be described with reference to FIGS. 4 shows one pixel region for one primary color among R, G, and B, and FIG. 5 is a sectional view taken along line VII-VII of FIG.

This embodiment is intended to prevent the aperture ratio of one divided pixel from being significantly reduced even when one pixel region is divided into three for R, G and B as described with reference to FIG. is there.

The biggest factor in lowering the aperture ratio is that the bus line 12 shown in FIG. 8 is opaque because it is made of metal such as tantalum. The bus line 12 in FIG.
As long as it can be separated from 13, it may be a permeable material. Of course, the condition is that the condition of the line resistance is satisfied. When the bus line 12 and the pixel electrode 16 are arranged in a plane as shown in FIG. 8, the area of the pixel electrode 16 is restricted. The rate is not affected. For this reason, there is a demand for a new three-dimensional arrangement capable of obtaining a large aperture ratio.

The size of one pixel region in FIG.
The same as in the case of 210 μm in the vertical direction × 70 μ in the horizontal direction
m. First, a bus line 31 of a transparent conductive film made of ITO is formed to a thickness of 1000 Å on the upper surface of a light-transmitting substrate 11 selected from various glass materials by an electron beam evaporation method. The sheet is formed at a temperature of 220 ° C. and completely poly-formed, so that the sheet resistance is set to an extremely low value of 15Ω / sheet. However, tantalum, a metal material,
Sheet resistance 5Ω / at 3000 Angstroms thickness
Since the sheet width is several times that of the sheet, the line width cannot be reduced, and wiring is performed almost completely in one pixel area as shown in the figure.
In the illustrated example, the line width is 50 μm.

Next, the light-transmitting substrate on which the bus line 31 is formed
An interlayer insulating film 32 is formed on the entire surface of the substrate 11 to a thickness of about 3000 angstroms. In this embodiment, a low temperature fired polyimide film is applied and solidified at about 180 ° C.

The reason why the low-temperature fired polyimide film is used as the interlayer insulating film 32 is that the grooves between the wirings can be sufficiently filled. However, if the shape of the bus line 31 is tapered or the like, any material can be used as the material of the interlayer insulating film 32 regardless of organic or inorganic, such as a silicon oxide film.

Next, a contact through hole 33 having a hole diameter of about 7 μm is formed in the interlayer insulating film 32, and a part of the pass line 31 is exposed to the outside through the through hole 33. The through holes 33 are formed by plasma etching of oxygen gas. At this time, a taper angle is given to the resist in advance, and a through hole 33 having a taper angle as shown in FIG. 5 is formed in the polyimide film which is the interlayer insulating film 32 after the etching. When the interlayer insulating film 32 is, for example, a silicon oxide film, reactive ion etching is performed by using a chlorofluorocarbon gas (CF ₄ gas) to form a through hole 33, and thereafter, the corner of the through hole 33 is round-etched. May be provided for the taper angle.

Next, the surface of the interlayer insulating film 32 and the surface of the bus line 31 exposed at the bottom of the through hole 33 are roughened by the reverse sputtering method to increase the film adhesion. Thereafter, a metal film such as a tantalum film is adhered to the upper surface of the interlayer insulating film 32 including the through hole 33, and thereafter, as shown in FIG. Electrodes around through hole 33
The shape of 34 is 15 μm square, and the shape of the projection 35 is
5 μm in width × 20 μm in length.

The reverse sputtering method and the attachment of the tantalum film are performed by a continuous sputtering apparatus.

Next, an oxide film is formed on the surface of the tantalum film composed of the electrode portion 34 and the projection 35. This oxide film is a tantalum oxide film and is formed by an anodic oxidation method in which 0.1% of citric acid is mixed in pure water. The thickness is set to 800 Å in consideration of the pool Frenkel conduction.

The opposite metal electrode 37 forming the MIM type diode 36 together with the projection 35 is formed of chromium and has a film thickness of 2000 Å by the same sputtering method. The line width of the counter metal electrode 37 is 5 μm in width and 20 μm in length. As a result, the area of the MIM type diode 36 is 5 μm × 5 μm.

Next, a transparent conductive film made of ITO is deposited as a pixel electrode 38 on the entire surface of the interlayer insulating film 32 on which the MIM diode 36 is formed at a thickness of 1000 Å. In order to avoid this, the etching is performed into the shape shown in FIG. In this case, the size of the pixel electrode 38 is approximately 170 μm in the vertical direction × 60 μm in the horizontal direction, and the aperture ratio is 64%. this is,
This is a great increase compared to the conventional aperture ratio of 35%. Further, the luminance reduction is 30%, which is a luminance reduction corresponding to R, G and B equally divided into three, and a reasonable value is obtained.

The other configuration and the manufacturing process are the same as those of a general liquid crystal display device, and the description thereof is omitted.

According to the above configuration, the bus line 31 is arranged in a different layer from the pixel electrode 38 also made of a transparent conductive film via the interlayer insulating film 32, so that the aperture ratio is greatly increased as compared with the conventional case. Thus, high-definition display can be performed without increasing the area of one pixel region or reducing the number of pixels as in the related art.

In the above embodiment, the bus line 31 is composed of only the transparent electrode film. However, for example, one part may be connected in parallel with a metal wiring in order to help reduce the line resistance. The width of the bus line 31 can be freely selected depending on its resistance value, and the number of contact through holes 33 may be determined as needed.

Further, the MIM type diode has been described as an example of the two-terminal type.
For example, it can be applied to the MSI type.

[0072]

According to the present invention, a switch is provided via an interlayer insulating film.
The pixel electrodes are arranged corresponding to the switching elements .
Ri, resulting dimensional allowance in the arrangement between the components, the magnitude of each component is the same, the amount of conventional level of dust loading
And even, the occurrence of image defects white point defects can be greatly reduced, also, a through hole formed in the interlayer insulating film on the pad
Because the depth of this through hole is shallow, the pixel
The diameter at the uppermost surface of the through hole can be reduced while securing the area of the contact portion between the electrode and the switching element, and the occurrence of disconnection of the pixel electrode can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of one pixel region showing one embodiment of a liquid crystal display device of the present invention.

FIG. 2 is a sectional view taken along line II - II of FIG.

It is a V cross-sectional view - [3] V of FIG.

FIG. 4 is a plan view of one pixel region showing a liquid crystal display device of another embodiment.

FIG. 5 is a sectional view taken along line VII-VII of FIG. 4;

FIG. 6 is a plan view of one pixel region showing a conventional liquid crystal display device.

FIG. 7 is a plan view of one pixel region showing another conventional liquid crystal display device.

FIG. 8 is a plan view of one pixel region showing still another conventional liquid crystal display device.

[Explanation of symbols]

12, 31 Bus line 16, 38 Pixel electrode 18, 32 Interlayer insulating film 19, 33 Through hole 27 Pad part as pad

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-33971 (JP, A) JP-A-2-157727 (JP, A) JP-A-1-293567 (JP, A) JP-A-2- 275417 (JP, A) JP-A-4-220625 (JP, A) JP-A-1-222226 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1362 G02F 1 / 1333 G09F 9/30 H01L 49/02

Claims (7)

(57) [Claims] 1. A bus line, a switching element formed to be connected to the bus line, and a switching element formed separately from the bus line in the same layer as the bus line.
And a part of the switching element is formed, and
A metal film formed to cover the pad, an interlayer insulating film formed to cover the metal film , and a through hole formed to the interlayer insulating film on the pad
Le and the interlayer insulating film is arranged to correspond to before kiss switching element via the scan depth is shallower by the pad
Pixel electrode conductively connected to the metal film by a through hole
A liquid crystal display device characterized by including and. 2. A pixel electrode, a liquid crystal display device according to claim 1, characterized in that disposed enlarged up to the top of the bus line <br/> down through the interlayer insulating film. 3. The liquid crystal display device according to claim 1, wherein the interlayer insulating film is made of an organic material. 4. The liquid crystal display device according to claim 1, wherein the interlayer insulating film is a polyimide film. 5. The liquid crystal display device according to claim 1, wherein the through holes are formed by dry etching. 6. The liquid crystal display device according to claim 1, wherein the through holes are etched by oxidizing plasma. 7. The liquid crystal display device according to claim 1, wherein a plurality of through holes are provided.