JPH08295530A - Alkali-free glass substrate - Google Patents

Abstract

PURPOSE: To produce an alkali-free glass substrate satisfying all of characteristics required by each substrate of a TFT type active matrix display. CONSTITUTION: This alkali-free glass substrate has a compsn. consisting of, by weight, 55-65% SiO2 , 11-20% Al2 O3 , 9-15% B2 O3 , 5-20%, in total, of 3-10% MgO, 0-4.5% CaO, 0-10% SrO, 0.5-9% BaO and 0-5% ZnO, 0-5% ZrO2 and 0-5% TiO2 , does not practically contain alkali metal oxides and has <=2.6g/cm<3> density.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a liquid crystal display, E
The present invention relates to a non-alkali glass substrate used as a substrate for displays such as L displays, filters, and sensors.

[0002]

2. Description of the Related Art Conventionally, glass substrates have been used as substrates for flat panel displays such as liquid crystal displays, filters and sensors.

A transparent conductive film, an insulating film, a semiconductor film, a metal film, etc. are formed on the surface of a glass substrate of this kind, and various circuits and patterns are formed by photolithography-etching (photoetching). . In these film formation and photo etching steps, the glass substrate is
Various heat treatments and chemical treatments are performed.

In the case of a thin film transistor (TFT) type active matrix liquid crystal display, for example, an insulating film or a transparent conductive film is formed on a glass substrate, and a large number of amorphous silicon or polycrystalline silicon TFTs are formed by photoetching. In such a step, the glass substrate is subjected to heat treatment at several hundreds of degrees and is also treated with various chemicals such as sulfuric acid, hydrochloric acid, an alkaline solution, hydrofluoric acid, and buffered hydrofluoric acid. Buffered hydrofluoric acid, in particular, is widely used for etching insulating films, but it tends to erode glass and cause its surface to become cloudy, and it also reacts with glass components to form reaction products that clog the filter during the process. In addition, it is very important to impart a buffered hydrofluoric acid resistance to this type of glass substrate, since it adheres to the substrate.

Therefore, the glass substrate used in the TFT type active matrix liquid crystal display is required to have the following characteristics.

(1) If the glass contains an alkali metal oxide, alkali ions are diffused during the heat treatment into the semiconductor material on which the film is formed, and the film characteristics are deteriorated. Do not contain oxides.

(2) It has chemical resistance so that it is not deteriorated by various chemicals such as acids and alkalis used in the photoetching process.

(3) The film should not shrink due to heat treatments such as film formation and annealing. Therefore, it must have a high strain point.

In consideration of meltability and moldability, the glass substrate of this type is also required to have the following characteristics.

(4) It has excellent meltability so that melting defects that are not desirable as a substrate glass will not occur in the glass.

(5) The glass is excellent in devitrification resistance so that foreign matter generated during melting and molding does not exist in the glass.

Further, in recent years, electronic devices such as TFT type active matrix liquid crystal displays have been increasingly used in personal fields, and it is required to reduce the weight of the devices. Along with this, the glass substrate is also required to be lightweight, and thinning is being promoted. However, this type of electronic device is also being made larger, and considering the strength of the glass substrate, there is naturally a limit to thinning.
Therefore, it is desired to reduce the density of the glass for the purpose of reducing the weight of the glass substrate.

[0013]

As the alkali-free glass conventionally used for the TFT type active matrix display substrate, there are quartz glass, barium borosilicate glass and aluminosilicate glass, but each has its advantages and disadvantages. .

That is, quartz glass is excellent in chemical resistance and heat resistance and has a low density, but has a drawback that the material cost is high.

As a barium borosilicate glass, there is a commercially available product # 7059 manufactured by Corning Co., Ltd. However, this glass is inferior in acid resistance, and alteration, white turbidity and roughness are likely to occur on the surface of the glass substrate in the photoetching step, Moreover, the chemical solution is easily contaminated by the components eluted from the substrate.
Furthermore, since this glass has a low strain point, it is likely to undergo heat shrinkage or thermal deformation, and is inferior in heat resistance. The density is also high at 2.76 g / cm ³ .

Aluminosilicate glass is excellent in heat resistance, but most of the glass substrates currently on the market have poor melting properties and are not suitable for mass production. In addition, many of these glass substrates have high density and are inferior in buffered hydrofluoric acid resistance, and the fact is that none of them satisfy all the required characteristics.

The object of the present invention is to satisfy all the above-mentioned required characteristic items (1) to (5) and to have a density of 2.6 g /
It is to provide a non-alkali glass substrate having a size of ³ cm ³ or less.

[0018]

The alkali-free glass substrate of the present invention has a weight percentage of SiO ₂ 55-65%, A _2.
l ₂ O _{3 11 to 20} %, B ₂ O ₃ 9 to 15%, Mg
O 3-10%, CaO 0-4.5%, SrO 0-
10%, BaO 0.5-9%, ZnO 0-5%, Z
rO ₂ 0-5%, TiO ₂ 0-5%, MgO + Ca
It is characterized by having a composition of O + SrO + BaO + ZnO 5 to 20%, containing substantially no alkali metal oxide, and having a density of 2.6 g / cm ³ or less.

The alkali-free glass substrate of the present invention preferably has a weight percentage of SiO ₂ 55 to 65% and Al _{2
O 3 11~20%, B 2 O} 3 9~15%, MgO
3-10%, CaO 0-2%, SrO 0.5-10
%, BaO 0.5-9%, ZnO 0-5%, ZrO
_{20 to} 1.8%, TiO _{20 to} 5%, MgO + Ca
It is characterized by having a composition of O + SrO + BaO + ZnO 5-20%.

[0020]

The reason why the components of the alkali-free glass substrate of the present invention are limited as described above will be described below.

SiO ₂ is a component which serves as a glass network former, and its content is 55 to 65%. If it is less than 55%, the chemical resistance, particularly the acid resistance is lowered and the strain point is lowered so that the heat resistance is deteriorated and it becomes difficult to make the density of the glass 2.6 g / cm ³ or less. On the other hand, if it is more than 65%, the viscosity at high temperature becomes large, the meltability becomes poor, and the devitrified substance of cristobalite tends to precipitate.

Al ₂ O ₃ is an essential component for enhancing the heat resistance and devitrification resistance of glass and reducing the density, and the content thereof is 11 to 20%. If it is less than 11%, the devitrification temperature rises remarkably, and devitrification foreign matter is likely to occur in the glass. When it is more than 20%, the acid resistance, particularly the buffered hydrofluoric acid resistance is lowered, and the surface of the glass substrate is liable to be clouded.

B ₂ O ₃ is a component that acts as a flux, lowers the viscosity, improves the meltability, and lowers the density, and its content is 9 to 15%. If it is less than 9%, the function as a flux becomes insufficient, the density of the glass increases, and the buffered hydrofluoric acid resistance decreases. On the other hand, if it is more than 15%, the strain point of the glass is lowered, the heat resistance is deteriorated, and the acid resistance of the glass is also deteriorated.

MgO has the effect of lowering the high temperature viscosity without lowering the strain point and improving the meltability of glass, and has the greatest effect of lowering the density of the divalent alkaline earth oxides. It is a component and its content is 3 to 10%.
If it is less than 3%, the above effect cannot be obtained, and if it is more than 10%, the devitrification temperature rises significantly and the enstatite (M
Crystalline foreign substances such as gO · SiO ₂ ) are likely to precipitate in the glass, and the buffered hydrofluoric acid resistance of the glass is significantly deteriorated.

CaO is also a component which, like MgO, has a function of lowering the high temperature viscosity without lowering the strain point and improving the meltability of glass, and the content thereof is 0 to 4.5%, preferably 0. ~ 2%. If it exceeds 4.5%, the buffered hydrofluoric acid resistance of the glass is significantly deteriorated.

Both SrO and BaO are components for improving the chemical resistance of the glass and improving the devitrification property. However, if contained in a large amount, the meltability is impaired and the density of the glass increases. Not preferable. Therefore, the content of SrO is 0 to 10%, preferably 0.5 to 10%, and the content of BaO is 0.5 to 9%.

ZnO is a component that improves the buffered hydrofluoric acid resistance and also improves the devitrification resistance, and the content thereof is 0 to 5%. On the other hand, if it is more than 5%, the glass tends to devitrify and the strain point decreases, so that heat resistance cannot be obtained.

However, if the total amount of MgO, CaO, SrO, BaO and ZnO is less than 5%, the viscosity of the glass at high temperature becomes high, the melting property deteriorates, and the glass tends to devitrify. When it is more, the density of the glass becomes higher, and it becomes difficult to reduce the density to 2.6 g / cm ³ or less.

ZrO ₂ is a component that improves the chemical resistance, particularly acid resistance, of the glass and lowers the high temperature viscosity to improve the meltability, and its content is 0 to 5%, preferably 0 to 1 0.8%. If it is more than 5%, the devitrification temperature rises, and devitrification foreign matter of zircon is likely to deposit.

TiO ₂ is a component that improves chemical resistance, particularly buffered hydrofluoric acid resistance, lowers high temperature viscosity and improves meltability, and the content thereof is 0 to 5%. When it is more than 5%, the glass is colored and the transmittance is lowered, which is not preferable as a glass substrate for a display.

In the present invention, in addition to the above-mentioned components, other components may be added within a range that does not impair the characteristics. For example, As ₂ O ₃ or Sb ₂ may be used as a fining agent.
It is possible to add components such as O ₃ , F ₂ , Cl ₂ , and SO ₃ .

However, PbO generally used as a fluxing agent
P ₂ O ₅ and, in order to significantly reduce the chemical resistance of the glass, should be avoided additives in the present invention. Especially P
bO is not preferable because it may volatilize from the surface of the melt during melting and may contaminate the environment.

[0033]

EXAMPLES The alkali-free glass substrate of the present invention will be described in detail below based on examples.

Tables 1 and 2 show the glasses of the examples (Sample No.
1 to 9) and comparative glass (Sample Nos. 10 to 13).

[0035]

[Table 1]

[0036]

[Table 2]

Each sample in the table was prepared as follows. First, glass raw materials were blended so as to have the composition shown in the table, put in a platinum crucible, melted at 1580 ° C. for 16 hours, poured out onto a carbon plate, and molded into a plate shape. Then, both surfaces of these plate-like glasses are optically polished to form glass substrates.

As is apparent from the table, N which is the embodiment
o. Each of the samples 1 to 9 has a density of 2.6 g / cm
^The strain point was ³ or lower, the strain point was 640 ° C. or higher, the devitrification temperature was 1100 ° C. or lower, and the temperature corresponding to 10 ^2.5 poise was 1580 ° C. or lower, and all had good characteristics. Moreover, these samples were also excellent in sulfuric acid resistance and buffered hydrofluoric acid resistance.

On the other hand, No. It is considered that the sample of No. 10 has a higher density than that of the sample of the example because of its high density. Moreover, since the strain point was low, the heat resistance was poor and the sulfuric acid resistance was also poor. In addition, No. Sample No. 11 also had a high density and a slightly low strain point. Furthermore, since the devitrification temperature is high, the meltability is poor, and
It was also inferior in buffered hydrofluoric acid resistance. Furthermore, No. Sample No. 12 was inferior in buffered hydrofluoric acid resistance,
No. The sample of No. 13 had high viscosity at high temperature, poor meltability, and high devitrification temperature.

The density in the table is measured by the well-known Archimedes method. The strain point is ASTM
The devitrification temperature is measured according to the method of C336-71.
A glass powder having a particle diameter of 300 to 500 μm was prepared from each sample, placed in a platinum boat, and held in a temperature gradient furnace for 24 hours, followed by devitrification observation.

The 10 ^2.5 poise temperature indicates a temperature corresponding to a high temperature viscosity of 10 ^2.5 poise, and the lower the temperature, the better the melting and moldability.

Further, the sulfuric acid resistance was evaluated by immersing each sample in a 10% by weight sulfuric acid aqueous solution kept at 80 ° C. for 24 hours and then observing the surface condition of the glass substrate.
When the surface of the glass substrate was cloudy or had cracks, x was shown, and when there was no change, it is shown as o.

The resistance to buffered hydrofluoric acid was determined by immersing each sample in buffered hydrofluoric acid consisting of 38.7% by weight ammonium fluoride and 1.6% by weight hydrofluoric acid kept at 20 ° C. for 30 minutes. It was evaluated by observing the surface condition of the glass substrate. The case where the surface of the glass substrate was clouded was shown by x, and the case where there was no change was shown by ◯.

[0044]

The alkali-free glass substrate of the present invention as described above contains substantially no alkali metal oxide, is excellent in heat resistance, chemical resistance, melt moldability and has a low density. Especially, it is suitable as a TFT type active matrix substrate which needs to be lightweight.

Claims (2)

[Claims] 1. A weight percentage of SiO ₂ 55-65.
%, Al ₂ O _{3 11 to 20} %, B ₂ O ₃ 9 to 15
%, MgO 3-10%, CaO 0-4.5%, Sr
O 0-10%, BaO 0.5-9%, ZnO 0-
5%, ZrO ₂ 0-5%, TiO ₂ 0-5%, MgO
+ CaO + SrO + BaO + ZnO 5 to 20% composition, containing substantially no alkali metal oxide, and having a density of 2.6 g / cm ³ or less, an alkali-free glass substrate. 2. SiO ₂ 55-65 by weight percentage.
%, Al ₂ O _{3 11 to 20} %, B ₂ O ₃ 9 to 15
%, MgO 3-10%, CaO 0-2%, SrO
0.5-10%, BaO 0.5-9%, ZnO 0-
5%, ZrO ₂ 0 to 1.8%, TiO ₂ 0 to 5%, M
The alkali-free glass substrate according to claim 1, which has a composition of gO + CaO + SrO + BaO + ZnO 5 to 20%.