JPH08133771A - Glass substrate for liquid crystal display element and its production - Google Patents

Abstract

PURPOSE: To reduce the heat shrinkage of an inexpensive soda lime glass capable of easily obtaining large surface area and to use for a low temp. liquid crystal display element forming process using this glass as a base material by annealing a specific float glass. CONSTITUTION: The glass substrate for liquid crystal display element having <=10ppm shrinkage is obtained by annealing and heating at 400 deg.C for 1hr the SiO2 -R2 O-CaO-MgO-Al2 O3 based float glass composed of a composition of 70-30wt.% SiO2 (hereafger %), 13-15% R2 O (R is alkali metal), 7-12% CaO, 1.0-4.5% MgO, 1.0-2.3% Al2 O3 , 0.05-0.5% Fe2 O3 and balance inevitable impurities under the time and temp. surrounded by (1) (1hr, 510 deg.C), (2) (1hr, 490 deg.C), (3) (6hr, 400 deg.C), (4) (12hr, 400 deg.C), (5) (12hr, 470 deg.C) and (6) (6hr, 510 deg.C) in a coordinate system with time (hr) as the axis of abscissa and temp. ( deg.C) as the axis of ordinate as shown by Figure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass substrate for a liquid crystal display device and a method for manufacturing the glass substrate. More specifically, the present invention relates to a glass substrate for a liquid crystal display element, which has a small amount of heat shrinkage in the process of forming the liquid crystal display element, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Glass substrates for liquid crystal display devices currently in use can be roughly classified into the following two types.

(A) A glass substrate which is made of a non-alkali glass (such as Corning Inc. # 7059) and has been heat-treated and polished.

(B) A glass containing an alkali component such as low alkali glass or soda lime glass is used as a material,
A glass substrate that has undergone treatments such as polishing and alkali elution prevention coating.

A TFT (thin film transistor circuit) method or MIM (diode circuit) of active matrix driving, which includes a semiconductor element forming step in the manufacturing process and has a high degree of integration.
For the liquid crystal display element of the type, the non-alkali glass substrate of (a) is currently used. Further, the simple matrix drive TN type and STN type, which are liquid crystal display elements having a relatively low degree of integration and being inexpensive, also use the soda lime glass substrate of (b).

When soda lime glass, which is inexpensive and easy to increase in area, is used for a liquid crystal display element substrate, alkali elution in the glass becomes a problem.

That is, for a film forming material or a liquid crystal material formed on a glass substrate, an alkali metal element (N
(a, K, etc.) causes deterioration of element characteristics. Therefore, when soda lime glass is used for a liquid crystal display element substrate, an elution preventing coating layer (passivation layer) such as SiO ₂ is provided on the glass surface. At present, coating is generally performed by a liquid phase film forming process such as a dip coating method.

Further, the glass substrate for liquid crystal display device is
Small heat shrinkage in the liquid crystal display element formation process is required especially when the process temperature is high and the degree of integration of the liquid crystal display element is high.

Since the process temperature and the degree of integration of the TN and STN type liquid crystal display elements are relatively low, no measures against heat shrinkage have been required so far.
As the FT type non-alkali glass substrate, one having a heat shrinkage amount of about 5 p.pm or less in the liquid crystal display element forming process is used.

On such a glass substrate, a transparent conductive film such as ITO is formed in a liquid crystal display device of simple matrix drive, and a transparent electrode is formed by patterning. In an active matrix drive liquid crystal display element, a transparent conductive film such as ITO is formed, and then a metal / semiconductor is formed and patterned to form a drive circuit portion.

In the case of a color type liquid crystal, a substrate provided with a transparent conductive film electrode such as ITO on a substrate provided with a color filter is used as a substrate opposite to the drive circuit side. In the monochrome type liquid crystal display element, the element that is not on the drive circuit side is composed only of the transparent conductive film electrode.

In the case of forming a color filter, it is generally used that a Cr metal thin film is sputter-deposited on the surface of the glass substrate as described above. The Cr metal thin film is patterned / etched and used for forming a black matrix.

As the transparent conductive film, an indium oxide (ITO) thin film or tin oxide thin film to which tin oxide is added is formed by a sputtering method or a CVD method.

[0014]

Soda lime glass is inexpensive and can easily be made to have a large area. However, since soda lime glass shows a large heat shrinkage when the process temperature in the liquid crystal display element manufacturing process is high, the soda lime glass has a high process temperature and liquid crystal. It was not suitable for use when the degree of display element integration was high.

The heat shrinkage of the glass substrate becomes a problem for the following reason.

The process for producing the patterned substrate of the liquid crystal display device includes a high temperature process of 200 ° C. to 500 ° C. That is, firing of the color filter and the flattening film (180 ° C-
200 ° C.), formation of transparent conductive film (350 ° C. to 450 ° C.)
(° C.) and baking of the liquid crystal alignment film (300 ° C.), the substrate glass contracts because it passes through a high temperature environment. Therefore, the following inconvenience occurs.

First, between the master mask that realizes the designed pattern and the glass that actually flows as a product, dimensional variation of the pattern itself may occur due to thermal contraction of the glass substrate.

Secondly, it is necessary to sequentially repeat patterning and firing (annealing) in the process of forming the R / G / B color filters and the semiconductor active element. At that time, the heat shrinkage of the glass substrate causes a change in the substrate dimension, which causes a pattern shift in these steps.

Thirdly, when two glass substrates are attached to each other to form a cell, a difference occurs in pattern dimensions between the two pattern substrates.

These are particularly highly integrated TFTs and MIMs.
Type becomes a noticeable issue.

Alkali-free glass currently used as a glass substrate for TFT type originally has a strain point temperature (600
In addition to the high temperature (° C to 640 ° C), the amount of thermal shrinkage is suppressed to about 5 p.pm by reannealing. On the other hand, a general soda lime glass substrate has a strain point temperature of 505 ° C to 5 ° C.
The heat shrinkage is large in the liquid crystal cell manufacturing method because it is as low as 10 ° C. (that is, the heat shrinkage tends to be large) and the appropriate annealing treatment has not been performed so far. Since the thermal properties such as the strain point temperature are different, it is impossible to apply the annealing conditions for a non-alkali glass substrate to soda lime glass as it is.

Incidentally, even in the glass substrates for TN and STN types, which have been required to be annealed up to now, in the fine line color filter firing (180 ° C. to 200 ° C.) of the pattern accompanying the high definition. There has been a demand for a glass substrate having a small shrinkage amount for all glass substrates for liquid crystal display devices, such as a problem of heat shrinkage of about 20 p.pm.

The present invention reduces the amount of heat shrinkage of soda lime glass which is inexpensive and easy to increase in area, and uses it as a material.
An object of the present invention is to provide a glass substrate for a liquid crystal display element that can be used in a liquid crystal display element forming process at a temperature of 00 ° C. or less, and a method for manufacturing the glass substrate.

[0024]

A glass substrate for a liquid crystal display device according to claim 1 comprises 70 to 73% by weight of SiO ₂ , and R ₂ O.
(R: alkali metal element) 13 to 15% by weight, CaO
7-12 wt%, MgO 1.0-4.5 wt%, Al ₂
O ₃ 1.0 to 2.3 wt%, Fe ₂ O ₃ 0.05~0.
SiO having a composition of 50% by weight and inevitable impurities
It is characterized in that the shrinkage amount by heat treatment at 400 ° C. for 1 Hr obtained by annealing _2- R ₂ O—CaO—MgO—Al ₂ O ₃ type float glass is 10 p.pm or less. .

According to a second aspect of the present invention, there is provided a glass substrate for a liquid crystal display device according to the first aspect, in which the horizontal axis represents time (Hr) and the vertical axis represents temperature (° C.), the following coordinates 1 Hr, 510 ° C.) (1 Hr, 490 ° C.) (6 Hr, 420 ° C.) (12 Hr, 400 ° C.) (12 Hr, 470 ° C.) (6 Hr, 510 ° C.) This is characterized in that the float glass is heat-treated and then cooled.

Incidentally, FIG. 1 is a coordinate system showing these coordinates.

According to a third aspect of the present invention, there is provided a method of manufacturing a glass substrate for a liquid crystal display element, wherein the cooling is performed in the second aspect.
The cooling rate in the temperature range higher than 350 ° C. is 35
It is characterized in that the cooling rate is lower than the cooling rate in the temperature region lower than 0 ° C.

A method for manufacturing a glass substrate for a liquid crystal display device according to a fourth aspect is the method for producing a glass substrate for a liquid crystal display element according to the second or third aspect, in which the heating temperature in the first half of the heat treatment time is changed to the heating temperature in the second half of the heat treatment time. It is characterized in that the temperature is higher than the temperature.

In the present invention, the soda lime type float glass having the above composition is heat-treated under appropriate conditions to obtain a glass having a small heat shrinkage, and further subjected to polishing treatment and formation of an alkali elution preventive film such as a SiO ₂ film, The glass substrate for a liquid crystal display element has a small amount of heat shrinkage during the liquid crystal display element forming step and the liquid crystal cell forming step.

Specifically, the following processes (1) to (3) are sequentially performed. After that, a metal thin film for the black matrix and a transparent conductive film for the liquid crystal driving electrode are formed.

(1) A soda lime type float glass is heat-treated. Here, the method of holding the soda-lime glass may be a method of shortening the temperature rising / falling time by opening a space between the respective glass substrates using a holder, or by adhering them to each other via an appropriate spacer such as frosted glass or a ceramic plate. However, a method of stacking and increasing the number of processed sheets per furnace volume may be used.

The heat treatment condition is a range surrounded by the above coordinates. The glass substrate is held under these processing conditions and then cooled to room temperature according to a continuous or stepwise temperature curve. By this treatment, the amount of heat shrinkage for heating at 400 ° C. × 1 hour can be reduced to 10 p.pm or less. The cooling process after the holding may include one or a plurality of constant temperature holding processes. Further, in the temperature range of 350 ° C. or less, even if it is rapidly cooled, the influence on the amount of heat shrinkage is very small, and there is no practical problem.

The grounds for this heat treatment condition will be described below.

First, regarding the heat treatment temperature, the maximum temperature for re-annealing must be 400 ° C. or higher because the environmental temperature in which the glass substrate is placed is 400 ° C. to 500 ° C. in the process of manufacturing the pattern substrate of the TFT type liquid crystal display element. Further, since the deformation of the glass substrate cannot be ignored at a high temperature exceeding the strain point temperature (about 510 ° C.) of general soda lime glass, it is necessary to be in the holding temperature range of 400 ° C. or higher and 510 ° C. or lower.

Regarding the time required for the heat treatment, the longer it is held, the more the effect of reducing the heat shrinkage is enhanced, but it is preferably 12 hours or less when considered as an industrial process,
It is more preferable that the treatment is completed in a shorter time. The higher the temperature, the shorter the required treatment time, and the above conditions are met.

The preferable heat treatment conditions are 450 to 4
It is 4 to 6 hours at 70 ° C.

That is, in actual production, the fusion temperature of the foreign matter on the surface of the soda-lime glass substrate, the remaining of the mold, and the warp become remarkable, so that the upper limit of the holding temperature is more preferably 470 ° C. However, when the method of performing re-annealing in a manner that the glass substrates are stacked and the surface does not come into contact with the atmosphere in the furnace, there is no obstacle due to foreign matter due to dust in the furnace, and in this case, even at a temperature exceeding 470 ° C. no problem.

(2) In many cases, the glass substrate for liquid crystal display device is polished to flatten the surface. The effect of reducing heat shrinkage by heat treatment does not change whether it is carried out before polishing or after polishing, but considering the actual production process, it is better to carry out before polishing to avoid scratches during the process. It is preferable from the viewpoint of suppressing.

For the above purpose, the polishing allowance is 10 μm at maximum.
Is sufficient, and practically no problem even with a polishing stock removal of 5 μm or less.

The surface roughness after polishing is preferably as small as possible, but the surface roughness of the substrate for liquid crystal display device is preferably 0.05 μm or less per 20 mm.

However, in the type utilizing the optical rotatory power of the liquid crystal such as the TN monochrome type, if the surface roughness is 0.10 μm or less per 20 mm, there is no practical problem.

(3) An alkali elution preventing coating is applied after polishing. A film thickness of a metal oxide thin film such as SiO ₂ or Ta ₂ O ₅ or a passivation film such as Si ₃ N ₄ or SiO ₂ —B ₂ O ₃ is 20 nm or more and 1000 nm or less, more preferably 30 nm or more and 1000 nm or less. It is necessary to provide it on the surface of soda-lime glass which has been heat-treated and polished.

The basis of the preferable coating film will be described below.

Regarding the structure of the coating film, it is necessary that the density of defects such as cracks and pinholes is sufficiently low in order to suppress the diffusion of alkali metal elements. Further, it is preferable to use a thin film having an amorphous structure because the liquid crystal display element substrate needs to have a flat surface, and in a polycrystalline thin film, a grain boundary is generally likely to serve as a diffusion path connecting the substrate surface and the thin film surface.

Further, in consideration of light transmittance, refractive index, chemical stability, thermal stability, and adhesion to glass or transparent conductive film, preferred film materials are SiO ₂ and Ta ₂ O.
_5, Si ₃ N _4, etc. SiO ₂ -B ₂ O ₃ and the like.

Regarding the coating method, any method may be used as long as it does not easily cause defects such as cracks and pinholes.
A vacuum film forming method (evaporation method, sputtering method, CVD method, etc.) or a wet film forming method (liquid phase deposition method, dipping method, sol-gel method, etc.) may be used.

From the viewpoint of productivity, it is considered that the wet method (liquid phase deposition method, dipping method), which facilitates film formation on both sides, is more preferable.

The film thickness is preferably 20 nm to 1000 nm, more preferably 30 nm to 1000 n.
m or less. If the film thickness is less than 20 nm, the defect density becomes large due to the discontinuity of the coating film.
If it is larger than 000 nm, defects such as cracks due to internal stress of the coating film and abnormal growth become remarkable. A film thickness of 30 nm or more and 1000 nm or less is more preferable because the probability of occurrence of defects is further reduced.

For a glass substrate having a small heat shrinkage manufactured by the above method, for a color liquid crystal application, a black matrix layer such as a metal Cr thin film and a color filter layer are formed, and then a transparent film such as tin oxide or indium oxide is formed. A conductive film is formed to be a glass substrate for liquid crystal display element. In monochrome liquid crystal, only a transparent conductive film is formed.

A known vacuum film forming method such as vapor deposition or sputtering can be used for forming the Cr thin film or the transparent conductive film, and a known material or method can be applied for forming the color filter.

The case of sputtering film formation will be described below. An apparatus such as magnetron sputtering is used for forming the Cr thin film. Generally, argon having a purity of 99.99% or more is introduced into a vacuum chamber evacuated to 1 × 10 ⁻⁶ Torr or less, and the argon pressure in the vacuum chamber is set to 1 × 10 ⁻³ Torr.
Glow discharge is generated at ˜1 × 10 ⁻² Torr, and sputtering film formation is performed.

A metal film used for a black matrix needs to have a low light transmittance, and generally has an optical density (optical density, defined as T as -log ₁₀ T where T is the transmittance) of 2 to 4 (transmittance). The film thickness is determined so that T is about 1% to 0.01%. This corresponds to a Cr film thickness of 75 nm to 150 nm under the above-described film forming conditions, a Cr film thickness of 100 nm and an optical density of about 2,
r becomes about 4 at a film thickness of 140 nm. The presence of oxygen impurities in the metal film causes a decrease in optical density.

When a transparent conductive film such as ITO is formed by sputtering, the oxygen partial pressure is 0.1% to 5 by introducing oxygen at the same time after making the vacuum chamber an argon atmosphere in the same manner as the Cr film formation.
Adjust the oxygen flow rate so that it becomes%. Although the specific resistance of the ITO film varies depending on the crystallinity of the thin film and the amount of impurities in the film,
For driving electrodes of liquid crystal display devices, the surface resistance at room temperature is 5
The film thickness is adjusted so as to be about Ω to 15Ω (preferably low).

It is necessary that both the black matrix film and the transparent conductive film have no defects such as pinholes, and it is generally necessary that there are no pinholes of 20 μm to 30 μm or more in the panel area, depending on the pixel size and the like. To be done.

[0055]

The reason why the glass substrate manufactured by the float glass manufacturing method undergoes heat shrinkage is as follows.

The glass produced by the melt-solidification process is
It has a non-equilibrium structure depending on its cooling rate. (If it has a non-uniform distribution in the glass it causes residual stress).

When the glass is reheated after cooling, the structure changes toward a more stable microscopic structure at that temperature, so that the glass size changes macroscopically.

In a general industrial flat glass manufacturing process, the cooling rate is high, and when the flat glass thus obtained is reheated, its size generally shrinks.

In the present invention, soda lime glass is brought to a stable microscopic structure at a subsequent process temperature by appropriate heat treatment. This reduces the amount of heat shrinkage of the glass substrate in the liquid crystal display element manufacturing process.

[0060]

EXAMPLES Examples and comparative examples will be described below.
The coordinates of the heat treatment time and the temperature in these examples and comparative examples are shown in FIG.

Example 1 Preparation of Sample Piece and Heat Treatment SiO ₂ = 72.4, Al ₂ O ₃ = 1.4, Fe ₂ O ₃
= 0.1, CaO = 8.0, MgO = 4.1, Na ₂ O
= 13.1, K ₂ O = 0.7, SO ₃ = 0.3 180 mm × 1.1 mm thick soda lime glass
It was cut into 60 mm and heat-treated under the temperature and time conditions shown in Table 1 and the temperature rising / falling pattern shown in FIG. Then, using a diamond pen,
After drawing parallel lines (lines for measuring dimensional change) at mm intervals,
180mm × 30mm by cutting in the direction perpendicular to this parallel line
2 test pieces were prepared.

Measurement of Heat Shrink One of the test pieces was heat-treated in an electric furnace at 400 ° C. for 1 hour and then cooled to room temperature. The shift length of the parallel line between the one test piece and the other test piece is measured, and the shift length is divided by the parallel line interval of the other sample, and the shift amount (unit: pp
m.). The results are shown in Table 1.

Comparative Example 1 A test was conducted in the same manner as in Example 1 except that the heat treatment conditions (heating temperature and holding time) were as shown in Table 1, and the amount of heat shrinkage was measured. The results are shown in Table 1.

[0064]

[Table 1]

Example 2 FIG. 3 (a) and FIG. 3 (b) show the temperature rising / falling pattern when the test piece is prepared.
And, the heat shrinkage amount was measured in the same manner as in Example 1 except that it was as shown in FIGS. 4 (a) and 4 (b). The heat treatment was performed under the conditions shown in Table 2.

The results are shown in Table 2. As shown in Table 2, according to the present Example 2, it was possible to obtain a substrate having a smaller thermal contraction in a shorter time than that of Example 1.

[0067]

[Table 2]

Example 3, Comparative Example 2 The same composition as in Example 1 with a thickness of 1.1 mm and dimensions of 300 mm.
A × 300 mm soda lime glass substrate was washed and dried with pure water ultrasonic cleaning and a warm pure water drying device. Then, the glass substrate was placed in a holder (cassette) having a shape to hold one by one and heat treatment was performed. Table 3 shows the heat treatment conditions.

Next, the surface of the substrate was polished. The surface roughness measured after polishing was 0.5 μm or less per 20 mm.

After polishing and cleaning, SiO 2 was formed by liquid phase film formation.
_Two films were formed on the surface of the substrate. The film is formed by JP-A-4-2544.
An amorphous SiO ₂ passivation film having a film thickness of 50 nm was formed by using a liquid phase film formation method described in JP-A No. 05-2005, in which a dense SiO ₂ film was formed by immersing in a SiO ₂ supersaturated H ₂ SiF ₆ aqueous solution.

Example 2 of JP-A-4-254405
The alkali elution amount was evaluated by a method of immersing the sample in pure water at 100 ° C. for 24 hours according to the Na elution test by immersion in hot water described as. The amount of eluted Na calculated from the Na concentration in pure water was 0.41 μg / cm ² . It should be noted that the amount of eluted Na was 9.5 μg / cm ² in the soda lime glass on which the passivation film was not formed, and it was confirmed that the elution of alkali was suppressed to the extent that it could be used for the liquid crystal display element substrate by forming the passivation film.

The heat shrinkage of the glass substrate for liquid crystal display device manufactured by the above procedure was measured by the method of Example 1. The results are also shown in Table 3. As shown in Table 3, polishing,
It can be seen that even if the passivation film is formed, a substrate having substantially the same amount of heat shrinkage can be obtained.

Comparative Example 3 A glass substrate for liquid crystal display was produced by omitting the heat treatment in the procedure of Example 3, and the thermal shrinkage was evaluated in the same manner as in Example 3. As shown in Table 3, this heat shrinkage amount is 59.4 p.p.
It was a very big one, m.

As is clear from the above Examples and Comparative Examples, the heat treatment of the method of the present invention produces a glass substrate having a significantly reduced amount of heat shrinkage.

[0075]

[Table 3]

[0076]

According to the present invention, it is possible to manufacture a glass substrate for a liquid crystal display element, which is made of soda lime glass which is inexpensive and whose area can be easily increased, and which has a very small amount of heat shrinkage.

As a result, it becomes possible to manufacture a liquid crystal display device having excellent pattern accuracy without using expensive alkali-free glass.

[Brief description of drawings]

FIG. 1 is a coordinate system showing heat treatment conditions.

FIG. 2 is a heating / cooling pattern diagram of the heat treatment.

FIG. 3 is a temperature raising / lowering pattern diagram of heat treatment.

FIG. 4 is a temperature raising / lowering pattern diagram of the heat treatment.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isamu Yamaguchi 1st under Konoike character highway in Itami City, Hyogo Prefecture Within Nippon Sheet Glass Techno Research Co., Ltd. (72) 1st person under Chino Sakai Koiike character road in Itami City, Hyogo Prefecture Nippon Sheet Glass Techno Research Co., Ltd. (72) Inventor Kenzo Sono 3-5-11 Doshomachi, Chuo-ku, Osaka City, Osaka Prefecture Japan Sheet Glass Co., Ltd. (72) Inventor Koichiro Kiyohara Nishichome, Sagamihara City, Kanagawa Prefecture 8-1 No. 1 Nippon Sheet Glass Fine Co., Ltd.

Claims (4)

[Claims] 1. 70 to 73% by weight of SiO ₂ , R ₂ O
(R: alkali metal element) 13 to 15% by weight, CaO
7-12 wt%, MgO 1.0-4.5 wt%, Al
₂ O ₃ 1.0 to 2.3 wt%, Fe ₂ O ₃ 0.05~
S consisting of 0.50% by weight and inevitable impurities
A glass substrate for a liquid crystal display device, which is obtained by annealing an iO ₂ —R ₂ O—CaO—MgO—Al ₂ O ₃ based float glass and has a shrinkage amount of 10 p.pm or less due to a heat treatment at 400 ° C. for 1 hr. 2. The method of manufacturing a glass substrate for a liquid crystal display device according to claim 1, wherein in the coordinate system in which the horizontal axis represents time (Hr) and the vertical axis represents temperature (° C.), the following coordinates ~ (1Hr , 510 ° C.) (1 Hr, 490 ° C.) (6 Hr, 400 ° C.) (12 Hr, 400 ° C.) (12 Hr, 470 ° C.) (6 Hr, 510 ° C.) The float of claim 1 within a time and temperature range. A method for manufacturing a glass substrate for a liquid crystal display element, which comprises heating glass and then cooling it. 3. The cooling rate in a temperature range higher than 350 ° C. when performing the cooling according to claim 2,
A method for manufacturing a glass substrate for a liquid crystal display element, which is characterized in that the cooling rate is made lower than a cooling rate in a temperature region lower than 350 ° C. 4. The liquid crystal display element according to claim 2, wherein when the heat treatment is performed, the heating temperature in the first half of the heat treatment time is higher than the heating temperature in the second half of the heat treatment time. Of manufacturing glass substrate for automobile.