JP2001305583A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the interference of light at a pixel opening part of a liquid crystal panel. SOLUTION: A first insulating film formed on each polycrystalline silicon thin film transistor, a second insulating film laminated on the first insulating film and a third insulating film laminated on the second insulating film are formed by using a silicon oxide film, a silicon nitride film 9 and an organic insulating film 10, respectively, and the second insulating film of the silicon nitride film 9 is provided on not entire surface of each opening part 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device used for a display of a personal computer or the like.

[0002]

2. Description of the Related Art An active matrix type display device having a liquid crystal display element tends to have a higher image quality and a larger size due to market trends.
Active matrix display devices using FT (Thin Film Transistor) have become the mainstream of high image quality and large size. Further, this active matrix display device is developed to make the driver IC for column and row electrodes monolithic with polycrystalline silicon TFTs in order to cope with lower power consumption and higher definition. Development for improving the transmissivity by increasing the aperture ratio is currently underway.

A polycrystalline silicon TFT differs from an amorphous silicon TFT in that a silicon oxide film is generally used for a gate insulating film. Further, since the polycrystalline silicon TFT has a higher crystallization temperature and a higher heat treatment temperature in the heat treatment step than the amorphous silicon TFT, the top gate type (positive stagger type) in which the gate electrode is located above the source electrode and the drain electrode is used. (Type) In many cases, it is a TFT.

As disclosed in Japanese Patent Application Laid-Open No. 7-7156, since polycrystalline silicon has dangling bonds in the crystal, the dangling bonds are terminated with hydrogen and the transistor It is necessary to improve the characteristics. The hydrogen termination (hereinafter referred to as hydrogenation) includes a method of introducing active hydrogen by plasma and a method of forcibly introducing hydrogen atoms by doping or the like. However, a plasma silicon nitride film having a large hydrogen content is used. Therefore, a method of introducing hydrogen by thermal diffusion is sometimes applied (Japanese Patent Application Laid-Open No.
196704). In this case, the thickness of the plasma silicon nitride film having a large hydrogen content is usually set to several hundred nm. This is because when a polycrystalline silicon layer is hydrogenated with a silicon nitride film, hydrogen is insufficient in a thin film, and cracks easily occur in the polycrystalline silicon layer due to stress when it is too thick. Further, the silicon nitride film has a capability of preventing diffusion of moisture, alkali, and hydrogen, and thus serves as a protective film for a transistor.

On the other hand, from the viewpoint of improving light use efficiency,
There is a demand for increasing the aperture ratio and transmittance of liquid crystal display elements. In order to secure a high aperture ratio, liquid crystal display elements are often arranged so that data lines and pixel electrodes overlap, in which case the parasitic capacitance between the data lines and pixel electrodes increases, There is a risk of causing crosstalk and the like. For this reason, the liquid crystal display element is provided with a thick low-dielectric-constant insulating film to reduce the coupling capacitance or to increase the additional capacitance to relatively reduce the influence of the coupling capacitance. I have. It is difficult to increase the additional capacitance of the liquid crystal display element from the viewpoint of improving the aperture ratio. Therefore, a thick low-dielectric-constant insulating film is required. Further, in the liquid crystal display element, when the thickness of the wiring is increased in order to reduce the resistance of the wiring, the step on the surface of the TFT substrate becomes large, and there is a possibility that the alignment of the liquid crystal is disturbed due to the step.

[0006] The high transmittance of the liquid crystal display element is realized by improving the transmittance of each layer. In order to improve the transmittance of each layer, film forming conditions with low light absorption are selected, and the refractive index of each layer is also set so as to reduce the influence of interface reflection, interface scattering and light interference of light. ing. JP-A-10-39334 discloses that
It is disclosed that light interference can be prevented by reducing the refractive index of each layer and setting the film thickness so that light interference hardly occurs.

[0007]

As described above, in the conventional high-definition liquid crystal panel, it was necessary to form a silicon nitride film for protecting the surface of the polycrystalline silicon TFT. There is a problem that light interference occurs depending on the film thickness, which causes a color shift and a decrease in light transmittance. In particular, when the thickness of the silicon nitride film changes, the color characteristics of the liquid crystal panel change greatly. Therefore, it is very important to control the thickness of the silicon nitride film.
If the thickness of the silicon nitride film is increased to reduce the influence of light interference, cracks may occur in the silicon nitride film.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a liquid crystal display device which prevents the influence of light interference at a pixel opening of a liquid crystal panel having a polycrystalline silicon TFT. That is.

[0009]

According to a liquid crystal display device of the present invention, a plurality of polycrystalline silicon thin film transistors are provided in a matrix on an insulating substrate, and the plurality of polycrystalline silicon thin film transistors are electrically connected to the respective polycrystalline silicon thin film transistors. Pixel electrode for each polycrystalline silicon thin film transistor,
A liquid crystal display device stacked via first to third insulating films in a stacked state, wherein the first insulating film stacked on each polycrystalline silicon thin film transistor is a silicon oxide film,
A second insulating film laminated on the first insulating film is formed of a silicon nitride film, and a third insulating film laminated on the second insulating film is formed of an organic insulating film. The second insulating film is not provided on the entire surface of each opening.

Further, in the liquid crystal display device according to the present invention, the first insulating film in the liquid crystal display device is formed of a silicon nitride film instead of a silicon oxide film, and the first insulating film and the first The second insulating film is not provided on the entire surface of each opening.

The organic insulating film is an acrylic resin having a refractive index in a visible light region of about 1.5 to 2.0.

The acrylic resin is a photosensitive acrylic resin having a refractive index of about 1.5 to 2.0 in a visible light region.

The silicon nitride film has a substrate temperature of 350
At a temperature of less than or equal to the temperature.

The thickness of the organic insulating film is about 3 μm.

[0015]

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

FIG. 1 is a schematic plan view of a main part of an active matrix type display substrate used in a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of the active matrix type display substrate. . The liquid crystal display device of the present invention has an active matrix type display substrate. In the active matrix type display substrate, a plurality of gate lines 7 are mutually formed on the main surface of the first transparent insulating substrate 1. A plurality of source lines 6 are arranged in parallel with each other and orthogonal to each gate line 7. Then, each gate line 7 and each source line 6
Are provided near the intersections of. The pixel electrodes 11 are arranged in regions surrounded by a pair of gate lines 7 and source lines 6 adjacent to each other. Thin film transistor (TFT)
Is a planar thin film transistor using polycrystalline silicon. First transparent insulating substrate 1 which is a TFT substrate
Is a high strain point aluminoborosilicate glass (refractive index: n =
1.55). On the main surface of the first transparent insulating substrate 1, an oxide film having a thickness of about 300 nm is formed as a base coat layer 2, and a polycrystalline silicon semiconductor thin film 3 is patterned in an island shape thereon. I have. Further, on the semiconductor thin film 3 of polycrystalline silicon, TEOS (Tet
An SiO ₂ film is formed as the gate insulating film 4 by using RaEthoxy Silane. The thickness of the gate insulating film 4 is about 100 nm.

The polycrystalline silicon semiconductor thin film 3 is crystallized by excimer laser annealing the amorphous silicon thin film. In the embodiment of the present invention, the gate insulating film 4 is formed as an oxide film of SiO ₂ by TEOS.
An O ₂ oxide film may be formed by plasma CVD, normal pressure CVD, sputtering, or the like.

On the gate insulating film 4, a gate electrode 7a is formed of an Al alloy.
Are formed integrally with and protruding from the gate line 7 as shown in FIG. Gate electrode 7
The material of a is not limited to the Al alloy, but may be any metal having a small resistance.

On the gate electrode 7a and on the gate insulating film 4 other than the gate electrode 7, a silicon oxide film formed by TEOS as a first interlayer insulating film 8 is formed by about 70%.
0 nm is formed. Although the first interlayer insulating film 8 is also formed of TEOS in the embodiment of the present invention, it is not particularly limited as long as the insulating film has good step coverage and good insulating properties and hydrogen permeability. Absent.

On the first interlayer insulating film 8, a drain electrode 5 and a source electrode 6 are formed of an Al alloy.
The drain electrode 5 and the source electrode 6 are electrically connected to the polycrystalline silicon semiconductor thin film 3 by through holes, respectively. The source electrode 6 is formed as a part of the source line 6 shown in FIG. Thus, a top-gate thin film transistor as a switching element is formed. Patterned drain electrode 5
The thickness of the electrode between the source electrode 6 and the source electrode 6 is set to be 500 to 800 nm for the Al electrode because it is necessary to reduce the resistance value in order to reduce the signal delay time. In the case of a stacked structure for forming a contact portion, the thickness of the electrode is further increased.

After the formation of the thin film transistor,
A silicon nitride film 9 is formed. The silicon nitride film 9
The film is formed by the plasma CVD method, and the film thickness is about 300 n
m. After the film formation, the silicon nitride film 9 is heat-treated at about 350 ° C. for about 1 hour. The heat treatment of the silicon nitride film 9 is performed for terminating dangling bonds of the polycrystalline silicon layer with hydrogen by hydrogenation to improve the characteristics of the thin film transistor. After the formation of the silicon nitride film 9, dry etching is performed on the silicon nitride film 9 only on the entire surface of the opening 17 of the pixel and the portion of the connection port (through hole) to the pixel electrode 11, and the silicon nitride film 9 is removed.

The entire surface of the pixel opening 17 and the pixel electrode 1
After removing the silicon nitride film 9 only in the portion of the connection port (through hole) to No. 1, a photosensitive acrylic resin (refractive index n = 1.6), which is the second interlayer insulating film 10, is about 3 μm by a coating method.
And a connection port (through hole) to the pixel electrode 11 is formed at the same time.

The thickness of the photosensitive acrylic resin used as the second interlayer insulating film 10 needs to be at least 2 μm in order to flatten the silicon nitride film 9 and the lower wiring. This is a thickness necessary for sufficiently covering the wiring pattern due to the resistance of the wiring and the like. The thicker the better, the better. However, the thickness of the through hole for making contact between the pixel electrode 11 and the drain electrode 5 is good. In some parts, the thickness is limited for its formation. When a through hole is formed by the exposure phenomenon of the photosensitive resin, the thickness of the photosensitive resin is limited to about 3 μm. Therefore, the thickness of the photosensitive acrylic resin is about 3 μm.

The method for applying the photosensitive acrylic resin is spin coating, but is not limited to spin coating.

Refraction of photosensitive acrylic resin as an organic resin
The rate depends on the underlying substrate and SiO _Two(Silicon oxide film)
Most preferably equal to the refractive index, its refractive index
Is about 1.5. With such a refractive index,
Of the thickness of the substrate and photosensitive acrylic resin
The sum can be of a thickness that does not cause interference. Photosensitivity
If the refractive index of the acrylic resin differs by more than n = 1.5
Since interference occurs, it is desirable that the difference in refractive index be small. Feeling
The refractive index of the optical acrylic resin is at least about
Intermediate value of the refractive index of the upper ITO and lower substrate of 2.0
To reduce the effect of interference
Is necessary.

Although a photosensitive acrylic resin is used as the resin, the resin is not limited to this resin. When a non-photosensitive resin is used, a connection port (through hole) to the pixel electrode 11 is formed by dry etching.

Further, a transparent conductive metal such as ITO (Indium Tin O 2) is formed on the second interlayer insulating film 10.
xide) is formed, and the pixel electrode 11 is electrically connected to the drain electrode 5 through a surface portion of a connection hole (through hole) formed in the silicon nitride film 9 and the second interlayer insulating film 10. Connected. Thus, an active matrix display substrate of the liquid crystal display device of the present invention is formed. ITO pixel electrode 1
No. 1 has a film thickness of 100 nm and a refractive index of n = 2.
0. In addition, by forming the second interlayer insulating film 10 by a spin coating method, which is a coating method, a film having a thickness of several microns can be formed flat, and the ITO pixel electrode 11 can be flattened. .

On the other hand, an opposing electrode 15 of ITO is formed on a main surface of an opposing substrate 16 which is a second transparent insulating substrate, and a surface opposing the pixel electrode 11 and the opposing electrode 15 is
Alignment films 12 and 14 are formed respectively. And
A liquid crystal 13 is sealed between the alignment films 12 and 14 to form an active matrix liquid crystal display.

FIG. 3 is a graph comparing the light transmittance of a liquid crystal display device manufactured using the active matrix type display substrate manufactured according to the procedure of the above-described embodiment and a substrate having a silicon nitride film left. is there. FIG. 3 shows that the liquid crystal display device using the active matrix type display substrate from which the silicon nitride film is removed according to the embodiment of the present invention has reduced light interference in the visible light region.

Since the thin film transistor, the wiring pattern of the gate line 7 and the source line 6 and the intersection of the wiring pattern of the gate line 7 and the source line 6 are covered with the silicon nitride film, the wiring pattern is reliable. Between the intersections of the wiring patterns and the upper pixel electrode, the layered structure of silicon nitride and the second interlayer insulating film prevents leakage due to pinholes and the like.

FIG. 4 is an enlarged sectional view of an active matrix type liquid crystal display device using another active matrix type display substrate. The embodiment shown in FIG. 4 uses a silicon nitride film instead of a silicon oxide film for the first interlayer insulating film 8.

The first transparent insulating substrate 1 serving as a TFT substrate is made of a high strain point aluminoborosilicate glass (refractive index: n =
1.55). On the main surface of the first transparent insulating substrate 1, an oxide film having a thickness of about 300 nm is formed as a base coat layer, and a polycrystalline silicon semiconductor thin film 3 is patterned in an island shape thereon. . Further, TEOS (Tetr) is formed on the semiconductor thin film 3 of polycrystalline silicon.
a film formed by Ethylene Silane)
iO ₂ is formed as the gate insulating film 4. The thickness of the gate insulating film 4 is about 100 nm.

The polycrystalline silicon semiconductor thin film 3 is crystallized by excimer laser annealing of the amorphous silicon thin film. In the embodiment of the present invention, the gate insulating film 4 is formed as an oxide film of SiO ₂ by TEOS.
An O ₂ oxide film may be formed by plasma CVD, normal pressure CVD, sputtering, or the like.

On the gate insulating film 4, a gate electrode 7a is formed of an Al alloy.
Are formed integrally with the gate line 7 so as to protrude from the gate line 7, as shown in FIG. The material of the gate electrode 7a is not limited to the Al alloy, but may be any metal having a small resistance.

A first interlayer insulating film 8 is formed on the gate electrode 7a and on the gate insulating film 4 other than the gate electrode 7a.
A silicon nitride film formed by plasma CVD is formed to a thickness of about 500 nm. The silicon nitride film of the first interlayer insulating film 8 has two functions, i.e., hydrogenation of dangling bonds and retention of insulation between layers, and a silicon nitride film formed by plasma CVD at a relatively low temperature is hydrogenated. And the insulating property is also good.

On the first interlayer insulating film 8, a drain electrode 5 and a source electrode 6 are formed of an Al alloy.
The drain electrode 5 and the source electrode 6 are electrically connected to the polycrystalline silicon semiconductor thin film 3 by through holes, respectively. The source electrode 6 is formed as a part of the source line 6, as shown in FIG. Thus, a top-gate thin film transistor as a switching element is formed. The electrode thickness of the patterned drain electrode 5 and source electrode 6 needs to have a small resistance value in order to reduce the signal delay time. For an Al electrode, the thickness is 500 to 800 nm. When a laminated structure is used for forming a contact portion or the like, the thickness of the Al electrode is further increased.

After the formation of the thin film transistor,
A silicon nitride film 9 is formed. The silicon nitride film 9
The film is formed by the plasma CVD method, and the film thickness is about 300 n
m. After the film formation, the silicon nitride film 9 is heat-treated at about 350 ° C. for about 1 hour. The heat treatment of the silicon nitride film 9 is performed for terminating dangling bonds of the polycrystalline silicon layer with hydrogen by hydrogenation and improving characteristics of the thin film transistor. After the formation of the silicon nitride film 9,
Dry etching is performed on the silicon nitride film and the silicon nitride film 9 of the first interlayer insulating film 8 only on the entire surface of the opening 17 of the pixel and the portion of the connection hole (through hole) to the pixel electrode 11, and both silicon nitride films are formed. Is removed. The step between the layers after the dry etching is larger than that in the case of FIG.

The entire surface of the pixel opening 17 and the pixel electrode 1
1 only after removing the silicon nitride film of the silicon nitride film 9 and the silicon nitride film 9 of the first interlayer insulating film 8, the photosensitive acrylic resin (refraction) as the second interlayer insulating film 10. Ratio n = 1.6) is about 3 μm depending on the coating method.
m, and a connection port (through hole) to the pixel electrode 11 is also formed at the same time.

The thickness of the photosensitive acrylic resin used as the second interlayer insulating film 10 needs to be at least 2 μm in order to flatten the silicon nitride film 9 and the lower wiring. This is a thickness necessary for sufficiently covering the wiring pattern due to the resistance of the wiring and the like. The thicker the better, the better. However, the thickness of the through hole for making contact between the pixel electrode 11 and the drain electrode 5 is good. In some parts, the thickness is limited for its formation. When a through hole is formed by the exposure phenomenon of the photosensitive resin, the thickness of the photosensitive resin is limited to about 3 μm. Therefore, the thickness of the photosensitive acrylic resin is about 3 μm.

The photosensitive acrylic resin is applied by a spin coating method, but is not limited to the spin coating method.

Refraction of photosensitive acrylic resin as organic resin
The rate depends on the underlying substrate and SiO _Two(Silicon oxide film)
Most preferably equal to the refractive index, its refractive index
Is about 1.5. With such a refractive index,
Of the thickness of the substrate and photosensitive acrylic resin
The sum can be of a thickness that does not cause interference. Photosensitivity
If the refractive index of the acrylic resin differs by more than n = 1.5
Since interference occurs, it is desirable that the difference in refractive index be small. Feeling
The refractive index of the optical acrylic resin is at least about
Intermediate value of the refractive index of the upper ITO and lower substrate of 2.0
To reduce the effect of interference
Is necessary.

Although a photosensitive acrylic resin is used as the resin, the resin is not limited to this resin. When a non-photosensitive resin is used, a connection port (through hole) to the pixel electrode 11 is formed by dry etching.

Further, on the second interlayer insulating film 10, a transparent conductive metal such as ITO (Indium Tin O 2) is formed.
xide) is formed, and the pixel electrode 11 is electrically connected to the drain electrode 5 through a surface portion of a connection hole (through hole) formed in the silicon nitride film 9 and the second interlayer insulating film 10. Connected. Thereby, the liquid crystal display device of the present invention is formed.
The ITO pixel electrode 11 has a thickness of 100 nm and a refractive index of n = 2.0. Also, the second interlayer insulating film 1
By forming 0 by a spin coating method as a coating method, a film having a thickness of several microns can be formed flat, and the pixel electrode 11 of ITO can be flattened.

On the other hand, a counter electrode 15 of ITO is formed on a main surface of a counter substrate 16 which is a second transparent insulating substrate, and a face of the pixel electrode 11 and the counter electrode 15 is
Alignment films 12 and 14 are formed respectively. And
A liquid crystal 13 is sealed between the alignment films 12 and 14 to form an active matrix liquid crystal display.

[0045]

According to the liquid crystal display device of the present invention, since the entire surface of the pixel opening is not covered with the silicon nitride film, the interference of light due to the difference in the refractive index of each layer in the pixel opening is suppressed and the liquid crystal display device is high. The transmittance can be realized, and the characteristics of the thin film transistor and the reliability of the wiring pattern can be secured.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a main part of an active matrix display substrate used in a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of the active matrix type display substrate.

FIG. 3 is a graph showing light transmittance of a liquid crystal display device using the active matrix display substrate.

FIG. 4 is an enlarged sectional view of an active matrix display substrate used in a liquid crystal display device according to another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first transparent insulating substrate (TFT substrate) 2 base coat layer 3 polycrystalline silicon semiconductor thin film 4 gate insulating film 5 drain electrode 6 source electrode (source line) 7 gate line 7 a gate electrode 8 first interlayer insulating film 9 nitride Silicon film 10 Second interlayer insulating film 11 Pixel electrode 12 Alignment film 13 Liquid crystal 14 Alignment film 15 Counter electrode 16 Second transparent insulating substrate (counter substrate) 17 Pixel opening

 ──────────────────────────────────────────────────続 き Continued from the front page F term (reference) 2H090 HA04 HA05 HB03X HB04X HB07X HD06 2H092 GA29 JA34 JA46 JB56 JB57 KA04 KA05 KA11 KA12 KB25 MA08 MA19 MA26 MA30 5C094 AA21 AA31 BA03 BA43 CA19 CA24 DA14 DA15 EB04 FB04 EA04 FB04

Claims (6)

[Claims] A plurality of polycrystalline silicon thin film transistors are provided in a matrix on an insulating substrate, and a plurality of pixel electrodes electrically connected to each polycrystalline silicon thin film transistor are provided for each polycrystalline silicon thin film transistor. A liquid crystal display device laminated via first to third insulating films in a laminated state, wherein the first laminated film is formed on each polycrystalline silicon thin film transistor.
Is formed by a silicon oxide film, a second insulating film laminated on the first insulating film is formed by a silicon nitride film, and a third insulating film laminated on the second insulating film is formed by an organic insulating film. And a second insulating film of a silicon nitride film is not provided on the entire surface of each opening. 2. The liquid crystal display device according to claim 1, wherein the first insulating film is formed of a silicon nitride film instead of a silicon oxide film, and wherein the first insulating film and the second insulating film are formed. A liquid crystal display device, wherein a film is not provided on the entire surface of each opening. 3. The liquid crystal display device according to claim 1, wherein the organic insulating film is an acrylic resin having a refractive index in a visible light region of about 1.5 to 2.0. 4. The liquid crystal display device according to claim 2, wherein the acrylic resin is a photosensitive acrylic resin having a refractive index in a visible light region of about 1.5 to 2.0. 5. The silicon nitride film has a substrate temperature of 35.
2. The method according to claim 1, wherein the film is formed by plasma CVD at a temperature of 0 degrees or less.
Or the liquid crystal display device according to claim 2. 6. The organic insulating film has a thickness of about 3 μm.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a thickness of: