JP3048489B2 - 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. More specifically, the present invention relates to a liquid crystal display device in which a substrate protective film includes a plurality of layers.

[0002]

2. Description of the Related Art FIG. 1 is a plan view of a thin film transistor (hereinafter abbreviated as TFT) liquid crystal display substrate as an example of a conventional liquid crystal display substrate. This liquid crystal display substrate includes a thin film transistor and a pixel electrode 11 arranged on a matrix on a glass substrate via a protective insulating film, and a gate electrode line 4 and a source electrode line 9. Gate electrode line 4 and source electrode line 9
Means that each has a uniform line width and crosses each other to form a lattice-like pattern. A pixel electrode 11 is formed on the glass substrate protective film in a region surrounded by the gate electrode line 4 and the source electrode line 9. The picture element electrode 11 is connected to the drain electrode 10 of the thin film transistor functioning as an address element. Gate electrode line 4
, A scanning signal is input to the source electrode line 9, and an image signal is input to each pixel electrode 11 from the source electrode line 9 when the thin film transistor is turned on by the scanning signal. I have.

FIG. 2 is a sectional view taken along the line AA of FIG. 1 for explaining the structure of the thin film transistor formed on the TFT liquid crystal display substrate. A glass substrate protection film 2 is formed on a glass substrate 1, on which a gate electrode 4, a gate insulating film 5, a channel intrinsic semiconductor film 6 (amorphous silicon film or polycrystalline film), and a channel protection. Insulating film 7, n-type (or p-type) semiconductor film 8 (amorphous silicon film or polycrystalline film) of contact portion, source electrode 9 and drain electrode 10, picture element electrode 11, protective insulating film 1
2 are formed in this order from the insulating substrate 1 side. In the above TFT structure, a resist mask having a wiring pattern is formed by photolithography on a thin film formed by sputtering or CVD on a glass substrate, an unnecessary thin film is removed by etching, and these processes are cycled. It is manufactured in.

At this time, the glass substrate protective film 2 is formed by sputtering or CVD on the glass substrate in order to protect the insulating substrate from a strong acid or alkali treated during etching.

[0005]

The conventional single-layer glass substrate protective film using Ta ₂ O ₅ or SiNx has high corrosion resistance to strong acids and alkalis during wet etching.
Low corrosion resistance to halogen-based gas during dry etching. Therefore, the Ta ₂ O ₅ or SiNx film is not sufficient as a glass substrate protective film for dry etching, and causes a defect of a liquid crystal display substrate, leading to a decrease in yield.

Therefore, as a substrate protective insulating film for dry etching, an SiO ₂ film having a relatively high selectivity can be considered, but an SiO ₂ film formed by PCVD or sputtering has poor density and a large number of pinholes. Therefore, it damages the base and leads to a failure of the liquid crystal panel. SiO ₂ film by the thermal CVD method and the like as a SiO ₂ film with a denseness. However, in this method, the film formation temperature is high, and in a large-area glass substrate, the occurrence of heat warpage and cracking is a serious problem.

[0007]

According to the present invention, a substrate protective film, a plurality of linear signal electrodes, a plurality of scanning electrodes substantially orthogonal to the signal electrodes, a protective insulating film, An alignment film is provided in this order, an overlapping portion of the signal electrode and the scanning electrode is a pixel portion, a thin film transistor is connected to the pixel portion, and a counter electrode, a protective insulating film and an alignment film are formed on the other transparent substrate. Are provided in this order, and a liquid crystal is interposed between the two substrates. In the liquid crystal display device, the substrate protective film has at least a first layer and a second layer which are different in material or forming method.
The first layer is made of SiO _x and the second layer is made of Ta ₂ O ₅ , or the second layer is made of
There is provided a liquid crystal display device, wherein the layer is a film formed by a liquid phase growth method.

As the transparent substrate of the present invention, a light-transmitting insulating substrate is used, and usually a glass substrate is used. A substrate protective film is formed on one of the transparent substrates. The substrate protective film is
A first layer film is formed on a transparent substrate, and a second layer film is formed thereon. If necessary, a third or more layer film is formed in the same manner as the first film and the second film. . Further, the first layer film and the second film
The order of the layers may be reversed.

The composition of the film of the first layer is SiOx, Ta
_It consists of ₂ O ₅ , SiNx, TiO ₂ or Y ₂ O ₃ . SiO
x, Ta ₂ O ₅ and SiNx are preferred. In particular, SiOx
Is preferred. The preferred range of the film thickness is 50 ° or more and 500μ
m or less. If the thickness is less than 50 °, the effect of protection is not sufficiently exhibited. If the thickness is more than 500 μm, it is not economical. The film of the first layer is preferably formed by a sputtering method or a CVD method. The sputtering method is a usual method, for example, a chemical handbook,
The method described in Applied Chemistry II, pages 953 to 954 can be applied. Similarly, a general method, for example, a method described in Chemical Handbook, Applied Chemistry II, pages 954 to 955 can be applied to the CVD method.

The film of the second layer is made of SiOx, Ta ₂ O ₅ , Ti
It consists of O ₂ or Y ₂ O ₃ . SiOx and Ta ₂ O ₅ is preferred. Particularly, Ta ₂ O ₅ is preferable. A preferable range of the film thickness is 50 ° or more. If the thickness is less than 50 °, the protective effect is not sufficiently exhibited.
). The LPD is formed by a usual method, for example, a method described in CMC Corporation, Advanced Electronic Materials Encyclopedia, pages 155 to 157. The apparatus of the present invention can be applied to any of the tilt method and the slide board method generally used for LPD, but the slide board method is preferable. The apparatus of the slide board method includes, for example, a container 20 filled with an aqueous solution, a stirrer 19 and an aqueous solution dropping device 15, as shown in FIG. A solution, for example, an aqueous solution of boric acid is dropped from a solution dropping device 15 into a saturated aqueous solution 17, for example, a saturated aqueous solution of hydrosilicofluoric acid and silicon oxide, to cause a reaction, and a target deposit, for example, silicon oxide is turned into a supersaturated solution. . A target deposit, for example, a silicon oxide film is deposited on the surface of the substrate 18 from the supersaturated solution. In order to improve the uniformity of the film, it is preferable to appropriately stir the stirrer 19 and slide the substrate 18 during the deposition process.

The most preferred combination is SiOx formed on the first layer film by CVD or sputtering.
It is a combination of a Ta ₂ O ₅ film by LPD for the film and the second layer film.

Each of the substrate protective films is made of InO._3,Sn
O_2,It is made of conductive thin film such as ITO (Indium Tin Oxide).
Transparent electrode is formed. Transparent electrode has multiple linear signals
From multiple scanning electrodes that are almost orthogonal to the electrodes and signal electrodes
The overlap between the signal electrode and the scanning electrode is
Is done. The TFT is connected to the picture element. TF of the present invention
T is a CVD method in which an insulating film is
SiO 2 by a known method such as_Two, SiO_Two/ SiN film, etc.
About 500-3000 Å
You. Further, 100-1 polysilicon is formed on the insulating film.
About 2,000 angstroms, Si as gate oxide film
O_TwoFilm or SiO _Two/ SiN film is 50 ~ 200mm
Polysilicon, as gate electrode,
Or polycide with silicide such as Ti, Ta, W, etc.
About 200 to 1500 angstroms, stacked sequentially
Thus, a TFT is formed.

Further, the TFT formed on the insulating film
May be formed by sequentially stacking a gate electrode, a gate oxide film, and polysilicon on an insulating film. further,
The TFT may be a double gate electrode in which polysilicon is stacked on a gate electrode via a gate oxide film, and a gate oxide film and a gate electrode are further formed on the polysilicon.

Further, on the other transparent substrate, InO _3,
A counter electrode made of a conductive thin film such as SnO _{2 or} ITO is formed. A protective insulating film is formed on these electrodes. This protective insulating film is made of, for example, SiO _2, SiNx, Al
An inorganic thin film such as ₂ O ₃ , an organic thin film such as polyimide, a photoresist resin, or a polymer liquid crystal can be used. When the protective insulating film is an inorganic thin film, it can be formed by an evaporation method, a sputtering method, a CVD method, a solution coating method, or the like. When the protective insulating film is an organic thin film, a solution in which an organic substance is dissolved or a precursor solution thereof is used.
Spinner coating method, dip coating method, screen printing method,
A method of applying by a roll application method or the like, and curing and forming under predetermined curing conditions (heating, light irradiation, etc.), or an evaporation method,
It can be formed by sputtering, CVD, etc.
It can also be formed by a uir-Blodgett method or the like.

An alignment film is formed on the protective insulating film.
There are a case where an inorganic layer is used and a case where an organic layer is used for the alignment film. When an inorganic alignment film is used, oblique deposition of silicon oxide is a commonly used method. Alternatively, a method such as rotary evaporation can be used. When an organic alignment film is used, nylon, polyvinyl alcohol, polyimide, or the like can be used, and rubbing is usually performed thereon. In addition, alignment using a polymer liquid crystal or an LB film, alignment by a magnetic field, alignment by a spacer edge method, and the like are also possible. Further, a method of depositing SiO _2, SiNx or the like and rubbing the deposited material is also possible.

As the alignment treatment method of the present invention, there are a rubbing method, an oblique evaporation method and the like. In the case of mass production of a large-screen liquid crystal display device, the rubbing method is advantageous. In the case of the rubbing method, a rubbing treatment is performed after forming an alignment film. A parallel rubbing method (a method in which both substrates are rubbed and bonded so that the rubbing directions are the same), an anti-parallel method. There are a rubbing method (a method in which rubbing is performed on both of a pair of substrates and bonding is performed so that the rubbing directions are reversed), and a single rubbing method (a method in which rubbing is performed on only one of the pair of substrates). In the case of the liquid crystal display device of the present invention, any alignment method can be used.

The liquid crystal which can be used in the present invention is a mixture of organic substances which shows a liquid crystal state at around normal temperature, and is a nematic liquid crystal (2).
Liquid crystal for frequency driving, liquid crystal with Δε <0), cholesteric liquid crystal, smectic liquid crystal, ferroelectric liquid crystal, discotic liquid crystal, and the like. Specifically, for nematic liquid crystal, ZL
I-4801-000, ZLI-4801-001, ZLI-4792 (all manufactured by Merck), and ZLI-4237-000, ZLI-4003 (all manufactured by Merck) are preferable for ferroelectric liquid crystal. It is not limited to.

Further, these liquid crystal compounds may be appropriately mixed and used. Further, a compound other than the liquid crystal compound may be appropriately mixed. This compound does not necessarily have to exhibit a liquid crystal phase, but (a) a compound for adjusting the temperature range of the liquid crystal phase of the composition to be produced; (b) a large spontaneous polarization in the ferroelectric liquid crystal phase or an induction. An optically active compound,
(C) An optically active compound for adjusting the helical pitch of the liquid crystal phase of the composition to be produced, and the like.

After the liquid crystal is injected or applied by a vacuum injection method and interposed between the substrates, the injection port is sealed with a sealing portion of a UV-curable resin such as an acrylic resin or a thermosetting resin such as an epoxy resin. To form a liquid crystal cell. In addition, if necessary,
A polarizing plate whose polarization axes are substantially orthogonal to each other is arranged above and below the liquid crystal cell, and one of the polarization axes of the polarizing plate is substantially coincident with one of the optical axes of the liquid crystal of the cell, whereby a liquid crystal display device can be obtained. .

[0020]

According to the present invention, the number of pinholes can be reduced by forming the substrate protective film of the transparent substrate of the liquid crystal display device into a two-layer structure. In particular, when an SiO ₂ film is formed on the upper layer of the two-layer structure by the liquid layer growth method, the SiO ₂ film is very dense and has a smaller number of pinholes than the SiO ₂ film formed by the sputtering method or the CVD method. Less is.

Moreover, the SiO ₂ film formed by the liquid layer growth method is
It has better quality than a SiO ₂ film formed by thermal CVD (on par with quartz), and has high corrosion resistance to acids and alkalis during wet etching. Therefore, it is suitable as a substrate protective film for both wet and dry etching, and particularly, a film having a two-layer structure of SiO ₂ / Ta ₂ O ₅ by a liquid layer growth method is suitable.

[0022]

FIG. 3 is a sectional view of a TFT substrate having a glass substrate protective film having a two-layer structure including a glass substrate protective film (SiO ₂ ) formed by LPD as an embodiment of the present invention.
A glass substrate protective film 2 (Ta ₂ O ₅ ) on a glass substrate 1;
A glass substrate protective film 3 (SiO ₂ ) is formed in a two-layer structure, on which a gate electrode 4 (Ta), a gate insulating film 5 (SiNx), a channel intrinsic semiconductor film 6 (amorphous silicon film) A channel portion protective insulating film 7, an n-type (or p-type) semiconductor film 8 (amorphous silicon film) of a contact portion, a source electrode 9 (Ti) and a drain electrode 10 (Ti), a pixel electrode 11 (transparent electrode), The protective insulating film 12 (SiNx) is formed in this order from the glass substrate 1 side.

This TFT substrate has a gate electrode 4 (Ta)
Is formed by sputtering and dry-etched to form the gate insulating film 5 (SiNx), the channel portion intrinsic semiconductor portion 6 (amorphous silicon film), and the n-type (or p-type) of the contact portion.
(Type) semiconductor film 8 (amorphous silicon film), source electrode 9 (Ti) and drain electrode 10 (Ti), picture element electrode 1
1 (transparent electrode), protective insulating film 12 (SiNx) CVD
And a pattern was formed by wet etching.
Then, in order to prevent the glass substrate 1 from being damaged by wet etching, Ta ₂ O ₅ is formed as a glass substrate protective film, and the glass substrate protective film 2 (T
a ₂ O ₅ ) and S to prevent the glass substrate 1 from being damaged.
iO ₂ was formed as a glass substrate protective film. In this case, a glass substrate protective film 3 (SiO ₂ ) having a structure of a TFT having a two-layer glass substrate protective film was formed by using the LPD method.

Next, a method for producing a SiO ₂ film by LPD will be described below. As shown in FIG. 4, the basic structure of the LPD film forming apparatus includes a container 20 filled with an aqueous solution,
It comprises a stirrer 19 and a boric acid aqueous solution dropping device 15. A method of dissolving SiO ₂ in hydrofluorosilicic acid (H ₂ SiF ₆ ) to make a saturated aqueous solution, and then adding a boric acid (H ₃ BO ₃ ) aqueous solution to create a supersaturated state, depositing and depositing SiO ₂ It is. The chemical reaction formula that occurs at this time is shown below.

H ₂ SiF ₆ + 2H ₂ O = 6HF + SiO ₂ ... H ₃ BO ₃ + 4HF = BF ₄ + H ₃ O + 2H ₂ O... That is, by adding boric acid, the chemical reaction of the formula proceeds rightward, and Hydrofluoric acid (HF) is consumed. Therefore, the chemical reaction represented by the formula proceeds rightward, and the SiO ₂
Is deposited on the substrate.

As shown in FIG. 4, the LPD-SiO ₂ film manufacturing apparatus has a very simple structure, and is considerably advantageous in terms of cost reduction as compared with a CVD apparatus having a complicated apparatus such as a vacuum apparatus. It is. Furthermore, SiH as used in CVD
_{It is} safe because it does not handle dangerous gases such as _4th . From the viewpoint of the substrate processing process, LPD-SiO ₂ can be formed at a low temperature (40 ° C. or lower) and can be used for a relatively large substrate. And the SiO ₂ film formed by this method is
The physical / chemical properties and electrical properties are not inferior to those formed by the CVD method.

As in the above embodiment, by forming the glass substrate protective film into a two-layer structure, the number of pinholes could be reduced as compared with the case of one layer. Particularly, in the case of forming an SiO ₂ film by a liquid layer deposition in the upper part of the two-layer structure, the SiO ₂
The film is very dense and is made of SiO by sputtering or CVD.
Fewer pinholes compared to _two films. In addition, the SiO ₂ film formed by the liquid layer growth method has better quality (comparable to quartz) than the SiO ₂ film formed by the thermal CVD method, and has high corrosion resistance to acids and alkalis during wet etching. Therefore, it was found that a film having a two-layer structure of SiO ₂ / Ta ₂ O ₅ by a liquid layer growth method was particularly suitable as a substrate protective film during both wet and dry etching.

Table 1 shows that the liquid phase growth SiO_TwoInterlayer insulating film
The adaptability as the thermal characteristics of thermal CVD method -Si
O_TwoCompared to membrane. Liquid phase growth SiO_TwoSeen in the membrane
Insulation characteristics that occur immediately after film formation
Thermal CVD-SiO withstand pressure _TwoOvercome the film and anneal
It has been found that the ratio is further improved by reason. Such excellent
The electrical characteristics of the liquid phase grown SiO_TwoThe membrane is the pinhole
That the film was formed in a small amount
You.

One of the features of the liquid phase growth method is an effect of flattening a film. In the liquid phase growth method, a thin SiO ₂ film can be formed uniformly along the surface shape of the concave groove,
As the SiO ₂ film became thicker, the inside of the concave groove was filled and a flattening phenomenon occurred. The flattening of the surface of the glass substrate protective film has an advantage that the subsequent manufacturing process proceeds smoothly. Then, a film could be formed even on a large substrate.

Further, the SiO ₂ film formed by the liquid phase growth method can be formed at a low temperature (40 ° C. or lower), and there is no problem such as warpage or thermal cracking of the glass substrate.

[0031]

[Table 1]

According to the present invention, by forming the substrate protective film from a laminated film of at least a first layer and a second layer having different materials or forming methods, pinholes can be reduced as compared with a single layer. In both wet and dry etching, the corrosion resistance of the transparent substrate can be effectively secured and the transparent substrate can be protected. Therefore, it is possible to reduce defects of the liquid crystal panel caused by damaging the transparent substrate, thereby improving product yield, suppressing an increase in manufacturing cost, and extending a product life as a liquid crystal panel. It can be improved.

[Brief description of the drawings]

FIG. 1 shows a matrix type TFT which is an example of a liquid crystal display substrate.
FIG. 3 is a plan view of a liquid crystal display substrate.

FIG. 2 is a sectional view of a conventional TFT structure.

FIG. 3 is a sectional view of a TFT structure of the present invention.

FIG. 4 is a basic structure of an apparatus for forming a liquid phase growth SiO ₂ film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Glass substrate protective film 3 Glass substrate protective film 4 Gate electrode 5 Gate insulating film 6 Channel part i type semiconductor film (amorphous silicon film or polycrystalline film) 7 Channel part protective insulating film 8 Contact part n type ( Or p-type) semiconductor film (amorphous silicon film or polycrystalline film) 9 source electrode 10 drain electrode 11 picture element electrode 12 protective insulating film (SiNx) 13 protective insulating film (SiO ₂ ), (signal line) 14 insulating substrate 15 H ₃ BO ₃ suspended solution dropping device 16 agitator 17 H ₂ SiF ₆ + SiO ₂ saturated aqueous 18 substrate 19 cassette arm 20 the control box 21 substrate cassette

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-362616 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1333 505 G02F 1/136

Claims (5)

(57) [Claims] 1. A substrate protective film, a plurality of linear signal electrodes, a plurality of scanning electrodes substantially orthogonal to the signal electrodes, a protective insulating film, and an alignment film are provided in this order on one transparent substrate,
The overlapping part of the signal electrode and the scanning electrode is a picture element part, a thin film transistor is connected to the picture element part, and a counter electrode, a protective insulating film and an orientation film are provided in this order on the other transparent substrate. In a liquid crystal display device having a liquid crystal interposed therebetween, the substrate protective film is composed of a laminated film of at least a first layer and a second layer having different materials or forming methods, and the first layer is made of SiO _x , A liquid crystal display device characterized in that two layers are made of Ta ₂ O ₅ . 2. A substrate protective film, a plurality of linear signal electrodes, a plurality of scanning electrodes substantially orthogonal to the signal electrodes, a protective insulating film, and an alignment film are provided in this order on one transparent substrate;
The overlapping part of the signal electrode and the scanning electrode is a picture element part, a thin film transistor is connected to the picture element part, and a counter electrode, a protective insulating film and an orientation film are provided in this order on the other transparent substrate. In a liquid crystal display device having a liquid crystal interposed therebetween, the substrate protective film is formed of a laminated film of at least a first layer and a second layer having different materials or forming methods, and the second layer is formed by a liquid phase growth method. A liquid crystal display device, characterized in that it is a coated film. 3. The method of claim 1, wherein the first layer of the substrate protective film is made of SiO _x , Ta ₂ O ₅
3. The liquid crystal display device according to claim 2, comprising SiN _x . 4. The method according to claim 1, wherein the second layer of the substrate protective film is made of SiO _x or Ta _2.
4. The liquid crystal display device according to claim 2, comprising O ₅ . 5. The method according to claim 1, wherein the first layer of the substrate protective film is formed by sputtering or C
The liquid crystal display device according to any one of claims 2 to 4, wherein the liquid crystal display device is a film formed by a VD method (vapor phase chemical vapor deposition).