JP5071878B2 - Alkali-free glass and alkali-free glass substrate using the same - Google Patents

Description

  The present invention relates to an alkali-free glass suitable for a flat display substrate such as a liquid crystal display (hereinafter referred to as LCD) or an EL display, and an alkali-free glass substrate using the same. Further, the present invention provides an alkali-free glass suitable for a substrate for an electronic device such as a cover glass for an image sensor such as a charge-coupled device (CCD) or a solid magnification proximity solid-state imaging device (CIS), a substrate for a solar cell, and the like. The present invention relates to the alkali-free glass substrate used.

  Electronic devices such as thin film transistor type active matrix liquid crystal displays (hereinafter referred to as TFT-LCDs) are thin and have low power consumption. Therefore, they are used in various applications such as car navigation, digital camera finder, and recently, personal computer monitors and televisions. Is used.

  Conventionally, glass has been widely used as flat display substrates such as LCDs and EL displays (see, for example, Patent Document 1). In addition, TFT-LCD panel manufacturers manufacture multiple devices on a large glass substrate (mother glass substrate), and then divide and cut each device into products to improve productivity and reduce costs. ing.

  In recent years, displays such as personal computer monitors and televisions have been increased in screen size, and in order to take a large number of these devices, a glass substrate having a larger area than conventional ones, for example, a glass substrate of 2200 × 2400 mm is required. ing.

In particular, in television applications, there is a great demand for an increase in screen size. Therefore, a technology for efficiently producing a large glass substrate is important. In general, amorphous silicon TFT-LCDs (hereinafter referred to as a-Si • TFT-LCDs) are used in television applications.
JP-A-7-277762

The glass substrate used for the a-Si • TFT-LCD is required to have the following characteristics.
(1) If an alkali metal oxide is contained in the glass, alkali ions diffuse into the semiconductor material on which the film is formed during the heat treatment, resulting in deterioration of the film characteristics. Do not contain.
(2) To have chemical resistance that does not deteriorate due to various acids and alkalis used in the photoetching process.
(3) No thermal contraction due to heat treatment in processes such as film formation and annealing. Therefore, it must have a high strain point.

In consideration of meltability and moldability, this type of glass substrate is also required to have the following characteristics.
(4) The meltability is excellent so that undesirable melting defects as glass substrates do not occur in the glass. There should be no bubble defects.
(5) Devitrification resistance is excellent so that there is no foreign matter generated during melting and molding in the glass.

In addition, the manufacturing process of the a-Si • TFT-LCD has many heat treatment processes, and rapid heating and rapid cooling are repeated, so that the thermal shock applied to the glass substrate increases. Furthermore, when the glass substrate is enlarged, not only the temperature distribution is likely to occur in the glass substrate, but also the probability that minute scratches and cracks are generated on the end face increases, and the probability that the glass substrate is destroyed in the heat treatment process also increases. In order to solve this problem, it is most effective to reduce the thermal stress caused by the difference in thermal expansion coefficient. The smaller the thermal expansion coefficient of the glass substrate, the smaller the thermal stress generated in the heat treatment step. However, in order to reduce the thermal expansion coefficient of the glass substrate, it is necessary to sacrifice important characteristics in manufacturing the glass substrate such as the meltability and moldability of the glass material. Are naturally limited. On the other hand, the glass substrate used in the a-Si TFT-LCD needs to consider the thermal expansion coefficient consistency with various film materials and the like formed on the glass substrate. Specifically, various film materials are formed on a glass substrate from a low expansion oxide film such as SiNx to a high expansion metal film such as Al and Mo. If the thermal expansion coefficients of the glass substrate and these film materials do not match, the glass substrate is likely to warp, which may cause damage to the glass substrate. Therefore, it is desirable that the thermal expansion coefficient of the glass is set to a value that takes into consideration the productivity of the glass and consistency with various film materials, for example, 40 to 60 × 10 ⁻⁷ / ° C.

  Therefore, the present invention can satisfy the above required characteristics (1) to (5), and (6) thermal expansion considering glass productivity and consistency with various film materials while reducing thermal stress. (7) TFT-LCD having viscosity characteristics suitable for the production of thin and large glass substrates, especially alkali-free glass suitable for a-Si TFT-LCD and alkali-free using the same Obtaining a glass substrate is a technical issue.

The present inventors have found the extensive studies, _SiO 2 45 to _68% by _{mass%, Al 2 O 3 1 3} ~18%, B 2 O 3 5~15%, 0~3% MgO, CaO 7 ~20 %, SrO 5-20%, BaO 0-5%, ZnO 0-20%, ZrO ₂ 0-5%, TiO ₂ 0-5%, P ₂ O ₅ 0-5% , MgO + CaO + SrO + BaO 17-25% The present inventors have found that the above-mentioned problems can be solved by forming the glass composition within a range and substantially not containing an alkali metal oxide, and forming by the downdraw method, and propose as the present invention. Here, “substantially does not contain an alkali metal oxide” refers to a case where the content of the alkali metal oxide is 0.1% by mass or less.

By restricting the glass composition to the above range, a glass satisfying the above required characteristics (1) to (7) can be obtained, and this can be applied to a glass substrate used in an a-Si TFT-LCD. Can do. That is, the alkali-free glass of the present invention contains substantially no alkali metal oxide (Na ₂ O, K ₂ O, Li ₂ O) in the glass composition. Therefore, the alkali-free glass of the present invention causes the alkali ions to diffuse into the semiconductor material on which the film is formed during the heat treatment in the TFT manufacturing process, and the film characteristics are not deteriorated, and the reliability of the TFT-LCD is impaired. There is no. Moreover, since the alkali-free glass of the present invention has good chemical resistance, it is difficult to be deteriorated by various chemicals such as acid and alkali used in the photoetching process. Furthermore, since the alkali-free glass of the present invention has a high strain point, heat shrinkage hardly occurs due to heat treatment in processes such as film formation and annealing.

In addition, the alkali-free glass of the present invention is less susceptible to melting defects, particularly foam defects, as glass substrates in the glass, and has excellent meltability. Further, the alkali-free glass of the present invention is excellent in devitrification resistance because it does not easily generate foreign matters that are generated during melting and molding in the glass. Furthermore, the alkali-free glass of the present invention has a thermal expansion coefficient suitable for TFT-LCD, particularly a-Si • TFT-LCD. That is, the alkali-free glass of the present invention is easy to adjust the thermal expansion coefficient to an appropriate value, for example, 40 to 60 × 10 ⁻⁷ / ° C. Therefore, after reducing the thermal stress due to the difference in thermal expansion coefficient, Consistency with various film materials can be achieved without impairing productivity.

  Since the alkali-free glass of the present invention has suitable viscosity characteristics, a thin plate and a large glass substrate can be stably produced. In particular, since the alkali-free glass of the present invention restricts the glass composition to the above range, the glass has good devitrification resistance and has viscosity characteristics suitable for downdraw molding. Therefore, the alkali-free glass of the present invention is a glass suitable for downdraw molding, and can stably produce a glass substrate with excellent surface accuracy.

The alkali-free glass of the present invention does not substantially contain As ₂ O ₃ and preferably contains 0 to 2 % by mass of SnO ₂ . Here, "not substantially contain _As 2 _{O 3"} refers to the case where the content of _As 2 _{O 3} is 1000ppm or less. In addition , “containing 0 to 3% of Sb ₂ O ₃ + SnO ₂ + Cl + F” means containing one or more of Sb ₂ O ₃ , SnO ₂ , Cl, and F in a total amount of 0 to 3%. Is meant to do.

In order to obtain a glass free from bubbles, it is important to select a refining agent that generates a refining gas in the temperature range from the vitrification reaction to the homogenization melting. In other words, glass clarification removes the gas generated during the vitrification reaction from the glass melt by the clarification gas, and further lifts and removes the fine bubbles remaining by the clarification gas generated again during homogenization melting. . By the way, since the alkali-free glass used for TFT-LCD does not contain an alkali component in the glass composition, the viscosity of the glass melt is high and melting is performed at a high temperature. Conventionally, As ₂ O ₃ that generates clarification gas in a wide temperature range (about 1200 to 1600 ° C.) has been widely used as a clarifier. However, As ₂ O ₃ is very toxic and may contaminate the environment during the glass production process or waste glass processing, and its use is being restricted. In that regard, the alkali-free glass of the present invention can be a glass that does not substantially contain As ₂ O ₃ as a fining agent, and can avoid situations that contaminate the environment.

The alkali-free glass of the present invention preferably contains substantially no BaO. Here, “substantially free of BaO” refers to a case where the content of BaO is less than 0.2%. BaO is a component that has the least effect of improving the meltability of glass among the alkaline earth metal oxides and hardly reduces the density. Moreover, since BaO is an environmentally hazardous chemical substance, its content is preferably limited. In that respect, since the alkali-free glass of the present invention can be a glass that does not substantially contain BaO, the meltability of the glass can be improved, the density can be lowered, and environmental addition can be reduced. be able to.

The alkali-free glass of the present invention preferably contains substantially no MgO. Here, “substantially does not contain MgO” refers to a case where the content of MgO is 0.1% or less.

Alkali-free glass of the present invention, it is preferable that the content of MgO + CaO + SrO + BaO + ZnO is 1 7-25% in mass%.

Alkali-free glass of the present invention preferably has a thermal expansion coefficient in a temperature range of 30 to 380 ° C. is 40~60 × ^{10 -7} / ℃. Here , “thermal expansion coefficient in a temperature range of 30 to 380 ° C.” refers to a value measured using a dilatometer.

The alkali-free glass of the present invention preferably has a strain point of 600 ° C. or higher . Here , “strain point” refers to a value measured by a method based on ASTM C336.

The alkali-free glass of the present invention preferably has a liquidus temperature of 1150 ° C. or lower . Here, the “liquid phase temperature” refers to a temperature gradient furnace in which glass is crushed, passed through a standard sieve 30 mesh (a sieve opening of 500 μm), and glass powder remaining in a 50 mesh (a sieve opening of 300 μm) is placed in a platinum boat. The temperature at which crystals are precipitated in the glass after being held for 24 hours.

The alkali-free glass of the present invention preferably has a temperature corresponding to 10 ^2.5 dPa · s of 1530 ° C. or lower . Here, “temperature corresponding to 10 ^2.5 dPa · s” is a temperature corresponding to the melting temperature of glass, and indicates a value measured by a well-known platinum ball pulling method. The lower the liquidus temperature, the better the devitrification resistance of the glass.

The alkali-free glass of the present invention preferably has a density of 2.70 g / cm ³ or less. Here, “density” refers to a value measured by the well-known Archimedes method.

The alkali-free glass of the present invention preferably has a Young's modulus of 75 GPa or more. Here, “Young's modulus” refers to a value measured by a resonance method.

Alkali-free glass of the present invention preferably has a specific Young's modulus is 27GPa / (g · ^{cm -3)} or greater. Here, “specific Young's modulus” refers to a value calculated by dividing Young's modulus by density.

When the alkali-free glass of the present invention is immersed in a 10% aqueous HCl solution at 80 ° C. for 24 hours, the erosion amount is preferably 5 μm or less. Here, “the amount of erosion when immersed in a 10% HCl aqueous solution at 80 ° C. for 24 hours” means that the glass sample is first optically polished on both sides and then partially masked and then the concentration of the 10% HCl aqueous solution is reached. After dipping in the prepared 80 ° C. chemical solution for 24 hours, the mask is removed, and the level difference between the mask portion and the eroded portion is measured with a surface roughness meter.

When the alkali-free glass of the present invention is immersed in a 130 buffered hydrofluoric acid (hereinafter referred to as BHF) solution at 20 ° C. for 30 minutes, the erosion amount is preferably 2 μm or less. Here, “the amount of erosion when immersed in a 130 BHF solution for 30 minutes at 20 ° C.” is a 130 BHF solution (NH ₄ HF ₂ : 4.6 mass%, NH ₄ F: 36 mass%) at 20 ° C. , Refers to the value measured under the treatment conditions of 30 minutes, the sample preparation conditions, first optically polished on both sides of each glass sample, then masked a part, then in the chemical solution of 20 ℃ prepared to the above concentration for 30 minutes After immersion, the mask is removed, and the value obtained by measuring the level difference between the mask portion and the erosion portion with a surface roughness meter is indicated.

The alkali-free glass substrate of the present invention is preferably composed of any alkali-free glass described above.

Alkali-free glass substrate of the present invention, Rukoto preferably such are molded by an overflow down draw method.

In the alkali-free glass substrate of the present invention, the area of the glass substrate is preferably 0.1 m ² or more.

The alkali-free glass substrate of the present invention is preferably used for a display.

The alkali-free glass substrate of the present invention is preferably used for an LCD.

The alkali-free glass substrate of the present invention is preferably used for an a-Si • TFT-LCD.

  The reason why the glass composition range is limited as described above will be described in detail below. In addition, the following% display points out the mass% display except the case where there is especially limitation.

SiO ₂ is a component that forms a glass network, and its content is 45 to 68%, preferably 48 to 62%, more preferably 50 to 60%, and still more preferably 52 to 58%. If the content of SiO ₂ is less than 45%, the strain point tends to be lowered, the chemical resistance, particularly acid resistance tends to deteriorate, and the density tends to increase. On the other hand, when the content of SiO ₂ is more than 68%, the high-temperature viscosity becomes high, the meltability tends to deteriorate, and the defect of devitrified foreign matter (cristobalite) tends to occur in the glass.

Al ₂ O _3, together with the effect of enhancing the strain point is a component improving the Young's modulus of the glass, the content thereof is 1 3-18%, preferably from 13 to 16.5%, more preferably 14 to 16%. When the content of Al ₂ O ₃ is less than 1 to 3%, it becomes poor effect of enhancing the strain point and the Young's modulus tends to decrease. On the other hand, when the content of Al ₂ O ₃ is more than 18%, the liquidus temperature becomes high and devitrification is likely to occur.

B ₂ O ₃ is a component that acts as a flux, lowers the viscosity and improves the meltability, and lowers the liquidus temperature, and its content is 5 to 15%, preferably 6 to 13 %, More preferably 7 to 12%. When the content of B ₂ O ₃ is less than 5%, the function as a flux becomes insufficient, and the BHF resistance tends to deteriorate. Furthermore, when the content of B ₂ O ₃ is less than 5%, the liquidus temperature tends to increase because devitrification easily occurs. Further, when the content of B ₂ O ₃ is more than 15%, the strain point of the glass is lowered, together with the heat resistance is lowered, there is a possibility that acid resistance is deteriorated. Furthermore, when the content of B ₂ O ₃ is more than 15%, the Young's modulus decreases and the specific Young's modulus tends to decrease.

  MgO is a component that increases the Young's modulus, increases the strain point, lowers the high-temperature viscosity, and improves the meltability of the glass, and is the component that has the effect of reducing the density most among the alkaline earth metal oxides. is there. However, when MgO is contained in a large amount, devitrification is likely to occur, and MgO reacts with BHF to form a product, which adheres or adheres to the device on the surface of the glass substrate. There is a limit to the content thereof. Therefore, the content of MgO is 0 to 3%, preferably 0 to 2%, more preferably 0 to 1%, and still more preferably 0 to 0.5%. In particular, if the glass does not substantially contain MgO, the devitrification resistance of the glass can be remarkably improved, and a glass substrate can be stably formed by the downdraw method.

CaO is a component that lowers the high temperature viscosity without increasing the Young's modulus and lowering the strain point, and its content is 7 to 20%, preferably 7 to 16.5%, more preferably 8 to 16%, more preferably 9-15%. Since the glass composition system according to the present invention is not easily melted and bubbles are likely to remain in the glass, many bubble defects are generated in the glass substrate as a result. In order to reduce foam defects, it is important to increase the meltability. In the glass composition system according to the present invention, when SiO ₂ is decreased, the meltability can be increased, but on the other hand, in addition to the extreme decrease in acid resistance, the density and thermal expansion coefficient of the glass are increased. Therefore, it is not preferable. From such a viewpoint, the alkali-free glass of the present invention contains 7 % or more of CaO for the purpose of improving the meltability of the glass. On the other hand, if the content of CaO exceeds 20%, the BHF resistance of the glass deteriorates and the surface of the glass substrate is likely to be eroded, and the reaction product adheres to the surface of the glass substrate and causes the glass to become cloudy. Further, the density and the coefficient of thermal expansion become too high.

  SrO is a component that improves the chemical resistance of the glass, lowers the high temperature viscosity without reducing the strain point, and improves the meltability of the glass, and its content is 5 to 20%, preferably It is 6 to 18%, More preferably, it is 7 to 17%, More preferably, it is 8 to 15%. When the content of SrO is more than 20%, the density and thermal expansion coefficient of the glass increase or the glass tends to devitrify.

  BaO is a component that improves the chemical resistance and devitrification resistance of glass and improves the meltability of glass, but BaO most improves the meltability of glass among alkaline earth metal oxides. It is a component that is less effective and difficult to reduce density. Therefore, in order to improve the meltability of the glass and reduce the density, it is desirable to reduce the content of BaO in the total amount of the alkaline earth metal oxide. Moreover, since BaO is an environmentally hazardous chemical substance, its content is preferably limited. Specifically, the content of BaO is 0 to less than 5%, preferably 0 to less than 2%, more preferably 0 to less than 1%, and still more preferably 0.5% or less, and is substantially free. preferable. When the content of BaO is 5% or more, the devitrification resistance is deteriorated, the glass density and the thermal expansion coefficient are easily increased, and the load on the environment is increased.

  ZnO is a component that improves the BHF resistance of the glass and improves the meltability. However, if contained in a large amount, the glass tends to be devitrified or the strain point is lowered, which is not preferable. Therefore, the content of ZnO is 0 to 20%, preferably 0 to 10%, more preferably 0.1 to 5% or less, and most preferably 1 to 2%.

Alkaline earth metal oxides can be mixed and contained to effectively reduce the devitrification temperature of the glass, that is, it can be made difficult to produce crystal foreign matter in the glass, and the melting property and moldability of the glass can be reduced. An improvement effect is obtained. However, when these components are contained in a large amount, the density of the glass increases and it becomes difficult to reduce the weight of the glass substrate. Therefore, the total amount of these, that is, MgO + CaO + SrO + BaO + ZnO is preferably 17 to 25%. However, for the reasons already described, it is desirable that BaO and MgO are not substantially contained.

ZrO ₂ is a component that improves the chemical resistance of glass, particularly acid resistance, and improves the Young's modulus, and its content is 0 to 5%, preferably 0 to less than 2%, more preferably 0 to 0%. 1%, more preferably 0 to less than 0.5%, most preferably 0 to 0.3%. When the content of ZrO ₂ exceeds 5%, the liquidus temperature rises and zircon devitrified foreign matter is likely to be generated.

TiO ₂ is a component that improves the chemical resistance of glass, particularly acid resistance, and lowers the high temperature viscosity to improve the meltability, and its content is 0 to 5%, preferably less than 0 to 2%. More preferably, it is 0 to 1%, more preferably 0 to less than 0.5%, and most preferably 0 to 0.3%. When the content of TiO ₂ exceeds 5%, the glass is colored and its transmittance is lowered, so that it is difficult to use it for display applications.

P ₂ O ₅ is a component that improves the devitrification resistance of the glass, and its content is 0 to 5%, preferably 0 to 3%, more preferably 0 to 1%, and still more preferably 0 to 0%. Less than 0.5%, most preferably 0-0.3%. When the content of P ₂ O ₅ is more than 5%, in addition to the occurrence of phase separation and milk white in the glass, the acid resistance is remarkably deteriorated.

The alkali-free glass of the present invention can contain various components in addition to the above components. For example, Y ₂ O ₃ , Nb ₂ O ₅ , and La ₂ O ₃ can be contained up to 5%. . These components have a function of increasing the strain point, Young's modulus, etc., but if the content is more than 5%, the density tends to increase. In particular, from the viewpoint of improving the Young's modulus, it is preferable to contain 0.1% or more of Y ₂ O ₃ .

As described above, As ₂ O ₃ has been widely used as a glass fining agent, but the alkali-free glass of the present invention can be substantially free of As ₂ O ₃ from an environmental point of view. .

In the alkali-free glass of the present invention, it is preferable to use SnO ₂ as a fining agent, and its content is preferably 0 to 2%, more preferably 0 to 0.5%, further 0 to 0.3%. preferable. SnO ₂ can generate a large number of clarified gases by changing the valence of Sn ions generated in a high temperature range. In general, alkali-free glass has a higher melting point than glass containing an alkali metal oxide. Therefore, SnO ₂ can be suitably used as a clarifier for alkali-free glass. On the other hand, if the SnO ₂ content is more than 2%, the devitrification resistance of the glass may be lowered.

  F and Cl halogens are added as glass fluxes, but also have a function as fining agents. However, since the volatile matter generated at the time of melting the glass is toxic, it is preferable to reduce the amount used, and it is preferable not to contain it substantially. Here, “substantially free of halogens of F and Cl” means that they are not contained other than the amount mixed from the raw material as an impurity component. Specifically, in the glass composition, F, This refers to the case where the halogen of Cl is 500 ppm or less.

Furthermore, the alkali-free glass of the present invention can also use Sb ₂ O ₃ as a fining agent. Sb ₂ O ₃ is a clarifier that generates a large amount of clarification gas in a low temperature range, and the clarification effect can be enhanced by using it together with the above-described clarifiers such as SnO ₂ and halogen. Moreover, since the alkali-free glass of the present invention is excellent in meltability and can be melted at a low temperature, Sb ₂ O ₃ can be used alone as a fining agent. On the other hand, from an environmental point of view, it is preferred not to substantially contain Sb ₂ O ₃ as a fining agent. Although Sb ₂ O ₃ is less toxic than As ₂ O ₃ , it is an environmentally hazardous substance, so it is preferable to limit its use from an environmental point of view. By "substantially free of Sb ₂ O _3" refers to the case where the content of Sb ₂ O ₃ is 1000ppm or less.

In the alkali-free glass of the present invention, it is preferable that the clarifier does not substantially contain As ₂ O ₃ and Sb ₂ O ₃ + SnO ₂ + Cl + F is in the range of 0 to 3%. Sb ₂ O ₃ + SnO ₂ + Cl + F is more preferably 0 to 2%, still more preferably 0 to 1%. When _{Sb 2 O 3 + SnO 2 +} Cl + F is greater than 3%, devitrification resistance of the glass tends to decrease.

Incidentally, it is possible to use as long as the glass properties which is a feature of the present invention are not impaired, C, Al, a metal powder or SO _3, such as Si, as a fining agent. It is also possible to use also CeO _2, Fe ₂ O ₃ or the like as a fining agent.

In the above composition range, it is naturally possible to select a preferred composition range by arbitrarily combining preferred ranges of the respective components, but among them, a more preferred composition range as non-alkali glass is mass%. _{SiO 2 48~62%, Al 2 O} 3 13~16.5%, B 2 O 3 6~13%, 0~3% MgO, CaO 7~16.5%, SrO 6~18%, BaO 0~ Contains less than 1%, ZnO 0-10%, MgO + CaO + SrO + BaO + ZnO 17-22%, ZrO ₂ 0-2%, TiO ₂ 0-2%, P ₂ O ₅ 0-3%, substantially alkali metal oxidation The glass which does not contain a thing is mentioned. If the glass composition range is regulated as described above, a thin plate and a large glass substrate can be stably produced, and the thermal expansion coefficient is regulated to a more appropriate value, for example, 45 to 56 × 10 ⁻⁷ / ° C. be able to.

As a more preferable embodiment of the alkali-free glass, SiO ₂ 50-60%, Al ₂ O ₃ 14-16%, B ₂ O ₃ 7-12%, MgO 0-1%, CaO 8-16%, SrO by mass%. 7-17%, ZnO 0.1-5%, MgO + CaO + SrO + BaO + ZnO 18-21%, ZrO ₂ 0-1%, TiO ₂ 0-1%, P ₂ O ₅ 0-1%, substantially alkali metal Glasses containing no oxide, BaO, As ₂ O ₃ , halogen and Sb ₂ O ₃ are mentioned. If the composition range of the glass is regulated as described above, the melting property of the glass can be greatly improved, and an environment-friendly glass can be obtained.

The alkali-free glass of the present invention has a thermal expansion coefficient in the temperature range of 30 to 380 ° C. of 40 to 60 × 10 ⁻⁷ / ° C., preferably 42 to 58 × 10 ⁻⁷ / ° C., more preferably 45 to 56. × 10 ⁻⁷ / ° C., more preferably 47 to 55 × 10 ⁻⁷ / ° C. When the thermal expansion coefficient is less than 40 × 10 ⁻⁷ / ° C., peripheral materials (organic materials and metals, specifically, low expansion oxide films such as SiNx to high expansion metal films such as Al and Mo) and heat It becomes difficult to match the expansion coefficients, and as a result, the glass substrate warps and causes damage to the glass substrate. When the thermal expansion coefficient is larger than 60 × 10 ⁻⁷ / ° C., the glass substrate has a high probability of breakage in the TFT-LCD manufacturing process. In addition, since the TFT-LCD manufacturing process has many heat treatment processes, and the glass substrate is repeatedly heated and cooled repeatedly, the thermal shock to the glass substrate is further increased. Thermal shock resistance is also an important requirement. Even if chamfering is performed on the end face of the glass substrate, there are fine scratches and cracks. When tensile stress due to heat concentrates on the scratches and cracks, the glass substrate sometimes breaks. If the glass substrate is damaged, not only the operating rate of the production line is lowered, but also fine glass powder generated at the time of the damage may adhere to the glass substrate, causing disconnection failure or patterning failure. Furthermore, the glass substrate tends to be larger, and if the glass substrate is larger, not only the temperature difference is likely to occur on the glass substrate, but also the probability that minute scratches and cracks will occur on the end face increases, and the thermal process The probability that the glass substrate breaks inside increases. The most fundamental and effective method for solving this problem is to reduce the thermal stress resulting from the difference in thermal expansion, that is, to reduce the thermal expansion coefficient of the glass. Specifically, if the coefficient of thermal expansion of glass is set to 40 to 60 × 10 ⁻⁷ / ° C., the above problem can be effectively solved without impairing the meltability of the glass and the consistency of the coefficient of thermal expansion with other members. Can be resolved.

  In the alkali-free glass of the present invention, the liquidus temperature is preferably 1150 ° C. or less, more preferably 1100 ° C. or less, further preferably 1050 ° C. or less, and most preferably 1030 ° C. or less. In general, the downdraw method has a higher viscosity at the time of glass molding than other molding methods, so if the devitrification resistance of the glass is poor, devitrification will occur during molding, and the glass substrate will be molded. There is a risk that it will not be possible. Specifically, if at least the liquidus temperature is higher than 1150 ° C., molding by the downdraw method becomes difficult. In addition, when the liquidus temperature is 1150 ° C. or less, a large glass substrate can be efficiently produced even in a molding method such as a float method without causing devitrification.

The alkali-free glass of the present invention contains SnO ₂ as a fining agent, and when SnO ₂ is added so that SnO ₂ is 0.2% by mass as a glass composition, the liquidus temperature of the glass obtained is It is preferably 1160 ° C. or lower, and more preferably 1110 ° C. or lower. If there are internal defects such as bubbles in the glass, light transmission is hindered, which is a fatal defect for a glass substrate for display. In general, as the glass substrate becomes larger, the probability that bubbles remain is increased, the probability that defects are caused by bubbles increases, and the productivity of the glass substrate decreases. As a method for reducing bubbles contained in glass, there are a method of using a fining agent and a method of lowering the high temperature viscosity. In the former method, As ₂ O ₃ is the most effective as a clarifier for this kind of alkali-free glass, but As ₂ O ₃ is an environmentally hazardous chemical, its use needs to be reduced. . Therefore, from the environmental point of view, the introduction of SnO ₂ as an alternative fining agent for As ₂ O ₃ has been studied. However, SnO ₂ is likely to cause crystalline foreign matter (devitrification), which is considered to be an internal defect of the glass substrate. There is a risk of becoming. Therefore, if the glass is not easily devitrified with respect to SnO ₂ , even if SnO ₂ is introduced as a fining agent, it is difficult for devitrification to occur. It is possible to achieve both and is considered very effective. In addition, in the glass manufacturing process, a situation where the Sn electrode elutes into the glass is assumed to some extent, and therefore glass that is less susceptible to devitrification with respect to SnO ₂ is further advantageous. Therefore, in the alkali-free glass of the present invention, when the SnO ₂ content in the glass composition is 0.2%, if the liquidus temperature of the obtained glass is 1150 ° C. or less, the above-mentioned effect is fully enjoyed. be able to. On the other hand, when the SnO ₂ content in the glass composition is 0.2%, if the liquid phase temperature of the obtained glass is higher than 1150 ° C., it is difficult to receive the above effect.

In the alkali-free glass of the present invention, the temperature of the glass melt corresponding to 10 ^2.5 dPa · s is preferably 1530 ° C. or less, more preferably 1500 ° C. or less, still more preferably 1450 ° C. or less, and most preferably 1400 ° C. or less. Melting glass at a high temperature for a long time can reduce internal defects such as bubbles and foreign matters in the glass, but melting at a high temperature increases the burden on the glass melting furnace. For example, refractories such as alumina and zirconia used in a kiln are eroded more vigorously by the glass melt as the temperature rises, and the life cycle of the kiln is shortened accordingly. In addition, since members that can be used at high temperatures are limited, all the members that are used are expensive. Furthermore, since the running cost to keep the interior of the kiln always high is higher than that of glass that melts at low temperatures, melting at high temperatures is disadvantageous in producing glass. There is a need for alkali-free glass that can be used. Therefore, in the alkali-free glass of the present invention, the above-described effect can be enjoyed accurately if the temperature of the glass melt corresponding to the high temperature viscosity of 10 ^2.5 dPa · s is 1530 ° C. or lower. On the other hand, when the temperature of the glass melt corresponding to the high temperature viscosity of 10 ^2.5 dPa · s is higher than 1530 ° C., it is difficult to enjoy the above effect.

  The alkali-free glass of the present invention preferably has a strain point of 600 ° C. or higher, more preferably 610 ° C. or higher, still more preferably 620 ° C. or higher, particularly preferably 640 ° C. or higher, and most preferably 650 ° C. or higher. . If the heat resistance of the glass substrate is even lower, the glass substrate may be deformed or warped. Further, in order to prevent the glass substrate from being thermally contracted in the TFT-LCD manufacturing process such as a film forming process to cause a pattern shift, a glass having excellent heat resistance is required. Further, in a TFT-LCD manufacturing process, particularly a polycrystalline silicon TFT-LCD (hereinafter referred to as p-Si TFT-LCD) manufacturing process, the glass substrate is heat-treated at a high temperature. If the heat resistance of the glass substrate is low, when the glass substrate is exposed to a high temperature of 400 to 600 ° C. during the manufacturing process of the p-Si • TFT-LCD, a minute dimensional shrinkage called thermal shrinkage occurs, which is the TFT. There is a risk of causing a display defect by causing a shift in the pixel pitch. Therefore, in the alkali-free glass of the present invention, the above problem hardly occurs when the strain point is 600 ° C. or higher. On the other hand, if the strain point is less than 600 ° C., the above problem becomes serious.

Alkali-free glass of the present invention has a density of preferably at 2.70 g / cm ³ or less, more preferably 2.68 g / cm ³ or less, further preferably 2.66 g / cm ³ or less. The lower the density of the glass, the lighter the glass substrate can be, which can contribute to the weight reduction of the TFT-LCD. However, in a non-alkali glass, if the density of the glass is lowered, the viscosity of the glass increases, the meltability deteriorates, the tendency to devitrification increases, and the moldability also tends to deteriorate. For example, although quartz glass has a low density of 2.2 g / cm ³ , it must be melted at a very high temperature and is inferior in devitrification. It is unsuitable for melting large-area glass substrates. From such a viewpoint, it is preferable that the density of the alkali-free glass of the present invention is in an appropriate range in which both the weight reduction of the glass and the productivity are achieved, specifically 2.55 to 2.70 g / cm ³ .

In the alkali free glass of the present invention, the Young's modulus is preferably at least 75 GPa, more preferably 78GPa / g · cm ^-3 or more, 80GPa / g · cm ^-3 or more is more preferable. If the Young's modulus is 75 GPa / g · cm ⁻³ or more, even a large and thin glass substrate can be suppressed to a deflection amount that does not cause a problem.

In the alkali free glass of the present invention, the ratio (a value obtained by dividing the Young's modulus by the density) Young's modulus is preferably 27GPa / g · cm ^-3 or more, 28GPa / g · cm ^-3 or more preferably, 29 GPa / g · More preferably, it is cm ⁻³ or more. When the specific Young's modulus is set to 27 GPa / g · cm ⁻³ or more, even a large and thin glass substrate can be suppressed to a deflection amount that does not cause a problem.

When the alkali-free glass of the present invention is immersed in a 10% HCl aqueous solution at 80 ° C. for 24 hours, the amount of erosion is 5 μm or less and / or is immersed in a 10% HCl aqueous solution at 80 ° C. for 3 hours. It is preferable that no cloudiness or roughness is observed. Further, when the alkali-free glass of the present invention is immersed in a 130 BHF solution at 20 ° C. for 30 minutes, the erosion amount is 2 μm or less and / or 63 BHF at 20 ° C. (HF: 6 mass%, NH ₄ F: 30 mass%) When immersed in the solution for 30 minutes, it is preferred that no white turbidity or roughness is observed by visual surface observation. A transparent conductive film, an insulating film, a semiconductor film, a metal film, and the like are formed on the surface of the glass substrate for TFT-LCD, and various circuits and patterns are formed by photolithography etching (photoetching). In these film formation and photoetching steps, the glass substrate is subjected to various heat treatments and chemical treatments. In general, in the TFT array process, a series of processes including a film formation process, a resist pattern formation, an etching process, and a resist stripping process is repeated. At that time, as an etchant, a phosphoric acid solution is used for etching Al and Mo films, an aqua regia (HCl + HNO ₃ ) solution is used for etching ITO films, a BHF solution is used for etching SiNx, SiO ₂ films, and the like. A wide variety of chemical solutions are used, and in consideration of cost reduction, they are not disposable but are a circulating liquid system flow. If the chemical resistance of the glass is low, the reaction product between the chemical and the glass substrate will clog the filter of the circulating liquid system during etching, or the glass surface may become cloudy due to inhomogeneous etching, or the etching solution The change in the components may cause various problems such as an unstable etching rate. In particular, a hydrofluoric acid-based chemical solution typified by BHF erodes the glass substrate strongly, so that the above-described problems are likely to occur, and the glass substrate is required to have excellent BHF resistance. In other words, a small amount of erosion of the glass against the chemical solution is very important from the viewpoint of preventing contamination of the chemical solution and clogging of the filter during the process due to reaction products. In addition, the chemical resistance of the glass substrate is not only small in the amount of erosion with respect to the chemical solution, but also important in not causing an appearance change. It is a very important characteristic as a glass substrate for a display such as a TFT-LCD in which light transmittance is important because the appearance of the glass does not change due to chemical treatment, such as white turbidity or roughness. The evaluation results of the amount of erosion and the change in appearance do not necessarily coincide with each other particularly with respect to BHF resistance. For example, even if the glass shows the same amount of erosion, the appearance may or may not change after chemical treatment depending on the composition. There is. In that respect, according to the alkali-free glass of the present invention, when immersed in a 10% HCl aqueous solution at 80 ° C. for 24 hours, the erosion amount is 5 μm or less, and when immersed in a 10% HCl aqueous solution at 80 ° C. for 3 hours. In addition, since it is possible to prevent white turbidity and roughness from being observed by visual observation of the surface, the above-mentioned problems can be reliably solved. In particular, in the alkali-free glass of the present invention, when immersed in a 130 BHF solution at 20 ° C. for 30 minutes, the erosion amount is 2 μm or less, and when immersed in a 63 BHF solution at 20 ° C. for 30 minutes, white turbidity and roughness are visually observed. If this is not recognized, the above problem can be solved reliably.

  The alkali-free glass of the present invention is preferably used as a glass substrate. The alkali-free glass of the present invention can employ various molding methods. However, since the alkali-free glass of the present invention has excellent devitrification resistance and has an appropriate viscosity characteristic, it can be molded into a glass substrate satisfactorily. This can be applied to a display such as an LCD.

The alkali-free glass substrate of the present invention is formed by a down draw method. If the glass is formed by the downdraw method, the glass substrate can be produced efficiently and the surface quality of the glass substrate can be improved. In the alkali-free glass substrate of the present invention, a glass raw material prepared so as to have a desired glass composition is put into a continuous melting furnace, the glass raw material is heated and melted, clarified, and then supplied to a molding apparatus. It can be produced by forming into a plate shape by the downdraw method and slowly cooling it.

  The downdraw method includes various forming methods such as a slot downdraw method and an overflow downdraw method. In particular, if a glass substrate is formed by the overflow downdraw method, a glass substrate that is unpolished and has good surface quality can be produced. The reason for this is that, in the case of the overflow down draw method, the surface to be the surface of the glass substrate does not come into contact with the bowl-like refractory, and is molded in a free surface state. This is because it can be molded. Here, the overflow down draw method is to melt the molten glass from both sides of the heat-resistant bowl-like structure and draw the overflowed molten glass downward while joining at the lower end of the bowl-like structure. This is a method for producing a glass substrate. The structure and material of the bowl-shaped structure are not particularly limited as long as the dimensions and surface accuracy of the glass substrate can be set to a desired state and the quality usable for the glass substrate for TFT-LCD can be realized. Moreover, in order to perform the downward extending | stretching shaping | molding, you may apply force with what kind of method with respect to a glass substrate. For example, a method may be employed in which a heat-resistant roll having a sufficiently large width is rotated and stretched in contact with the glass substrate, or a plurality of pairs of heat-resistant rolls are only near the end face of the glass substrate. You may employ | adopt the method of making it contact and extending | stretching. The alkali-free glass of the present invention is excellent in devitrification resistance and has a viscosity characteristic suitable for molding, so that molding by the overflow down draw method can be performed with high accuracy.

  Various methods other than the downdraw method can be adopted as the method for producing an alkali-free glass substrate of the present invention. For example, various forming methods such as a float method, a redraw method, and a roll-out method can be employed. In particular, if glass is formed by the float process, a large glass substrate can be manufactured at low cost.

Although the glass substrate tends to increase in size, when the area of the glass substrate is increased, the probability of devitrification appearing in the glass substrate is increased, and the yield rate of the glass substrate is rapidly decreased. In that respect, since the alkali-free glass substrate of the present invention has good devitrification resistance, it is advantageous in producing a large glass substrate. For example, the area of the glass substrate is 0.1 m ² or more (specifically, a size of 320 mm × 420 mm or more), 0.5 m ² or more (specifically, a size of 630 mm × 830 mm or more), 1.0 m ² or more. (Specifically, a size of 950 mm × 1150 mm or more), 2.3 m ² or more (specifically, a size of 1400 mm × 1700 mm or more), 3.5 m ² or more (specifically, a size of 1750 mm × 2050 mm or more) ) And 4.8 m ² or more (specifically, a size of 2100 mm × 2300 mm or more), the greater the size. Speaking of the screen size of the display, the size of the glass substrate is preferably 32 inches or more, more preferably 36 inches or more, and still more preferably 40 inches or more.

  The alkali-free glass of the present invention has a viscosity characteristic suitable for the downdraw method and is excellent in devitrification resistance. Therefore, the thickness of the glass substrate is 0.8 mm or less (preferably 0.7 mm or less, more Even if it is preferably 0.5 mm or less, more preferably 0.4 mm or less, the glass substrate can be molded without reducing the production efficiency. In addition, the alkali-free glass substrate of the present invention can reduce the amount of deflection of the glass substrate as compared with the conventional glass substrate even if the plate thickness is reduced. It becomes easy to prevent breakage and the like. Note that if the thickness of the glass substrate is reduced, the weight of the display can be reduced.

  The alkali-free glass substrate of the present invention is preferably used for a display such as an LCD, particularly an a-Si • TFT-LCD. The alkali-free glass substrate of the present invention can satisfy the above-described properties (1) to (7) required for a glass substrate for LCD, and therefore can be suitably used for the above applications. The alkali-free glass of the present invention is excellent in devitrification resistance and has a viscosity characteristic suitable for downdraw molding, so that a large and / or thin glass substrate can be produced efficiently, and a recent glass substrate. Can be used suitably for a glass substrate for television use.

  The alkali-free glass substrate of the present invention can also be used for p-Si TFT-LCDs. Recent developments in the TFT-LCD field include high-definition, high-speed response, high aperture ratio, etc., in addition to large screens. Specifically, p-Si TFT-LCD Development is actively underway. In the conventional p-Si • TFT-LCD, the manufacturing process temperature was as high as 800 ° C. or higher, and it was not possible to use a glass substrate other than a quartz glass substrate having high heat resistance. However, as the development progresses, the manufacturing process temperature is currently reduced to 400 to 600 ° C., and the glass substrate for the p-Si TFT-LCD as well as the a-Si TFT-LCD is accompanied by the following. Alkali-free glass substrates have been used. Since the alkali-free glass substrate of the present invention can satisfy the characteristics required for such a glass substrate for p-Si • TFT-LCD, it can be suitably used in this application.

  Hereinafter, the present invention will be described in detail based on examples.

Tables 1 to 6 show examples of the alkali-free glass of the present invention (sample Nos. 1 to 11, 13 to 15, 17 to 24, 26, 31, and ) and comparative examples (sample No. A). Sample No. Reference numerals 12, 16, 25, and 27 to 30 are reference examples.

  First, a batch in which glass raw materials were prepared so as to have the composition shown in the table was put into a platinum crucible, melted at 1550 ° C. for 24 hours, and then poured out onto a carbon plate to be formed into a plate shape. For the glass sample thus obtained, density, thermal expansion coefficient, strain point, annealing point, softening point, high temperature viscosity, Young's modulus, specific Young's modulus, devitrification resistance (liquidus temperature, liquidus viscosity) Various characteristics of chemical resistance (BHF resistance, HCl resistance) were measured. The results are shown in Tables 1-6.

  The density was measured by the well-known Archimedes method.

  The thermal expansion coefficient was measured using a dilatometer in the temperature range of 30 to 380 ° C.

  The strain point and annealing point were measured by a method based on ASTM C336. In addition, the higher the strain point, the higher the heat resistance of the glass.

  The softening point was measured by a method based on ASTM C338.

Each temperature corresponding to a high temperature viscosity of 10 ^4.0 dPa · s, 10 ^3.0 dPa · s, 10 ^2.5 dPa · s was measured by a well-known platinum ball pulling method.

  Young's modulus was measured by a resonance method. Specific Young's modulus was calculated by dividing Young's modulus by density.

  The liquid phase temperature is obtained by crushing each glass sample, passing through a standard sieve 30 mesh (a sieve opening of 500 μm), putting the glass powder remaining in 50 mesh (a sieve opening of 300 μm) in a platinum boat, and putting it in a temperature gradient furnace. The temperature at which the crystals are precipitated in the glass is measured by holding for a time.

  BHF resistance and HCl resistance were evaluated by the following methods. The sample preparation conditions were as follows. First, both surfaces of each glass sample were optically polished, and then partly masked and then immersed in a chemical solution prepared to a predetermined concentration at a predetermined temperature for a predetermined time. After the chemical treatment, the mask was removed, the step between the mask portion and the erosion portion was measured with a surface roughness meter, and the value was taken as the erosion amount. The chemical solution and processing conditions are as follows: BHF-resistant erosion amount is measured using a 130 BHF solution at 20 ° C. for 30 minutes, and the erosion amount is less than 1 μm. It was set as “x”. The HCl resistance is measured using a 10% by mass hydrochloric acid aqueous solution at 80 ° C. for 24 hours. The erosion amount is less than 2.5 μm, “◯”, and the case where the erosion amount is 2.5 μm or more is “×”. "

  The chemical solution and processing conditions in the appearance evaluation are as follows: BHF resistance is 63BHF solution, 20 ° C for 30 minutes, and HCl resistance is 10 mass% hydrochloric acid aqueous solution at 80 ° C for 3 hours. I went there. The glass surface was visually observed, and “O” indicates that the glass surface is not clouded, rough, or cracked, and “X” indicates that the glass surface is clouded, rough, or cracked.

No. as an example. Each glass sample of 1 to 31 does not contain an alkali metal oxide, has a density of 2.68 g / cm ³ or less, a thermal expansion coefficient of 40 to 56 × 10 ⁻⁷ / ° C., and a strain point of 626 ° C. or more. Met. The specific Young's modulus was 29 GPa / g · cm ⁻³ or more. Furthermore, since each of these samples has a temperature corresponding to a high temperature viscosity of 10 ^2.5 dPa · s of 1434 ° C. or lower, it can be determined that the sample can be melted at a low temperature and the productivity of the glass substrate is excellent. Therefore, each sample of the examples is considered suitable as a glass substrate for TFT-LCD. On the other hand, since the glass sample of Comparative Example A contains a large amount of BaO at 5.0% by mass, it can be seen that the density is as high as 2.75 g / cm ³ .

Furthermore, No. which is an example. Glass samples 1 and 13 were melted in a test melting furnace and molded by an overflow downdraw method to produce a glass substrate for display having a substrate size of 900 mm × 1100 mm and a thickness of 0.5 mm. As a result, the warpage of this glass substrate is 0.05% or less, the waviness (WCA) is 0.1 μm or less, the surface roughness (Ry) is 50 mm or less (cutoff λc: 9 μm), and the surface accuracy is excellent. It was suitable as a glass substrate for LCD. In molding by the overflow downdraw method, the speed of the pulling roller, the speed of the cooling roller, the temperature distribution of the heating device, the temperature of the glass melt, the flow rate of the glass, the drawing speed, the rotation speed of the stirring stirrer, etc. are appropriately adjusted. Thus, the surface quality of the glass substrate was adjusted. Here, “warp” is measured by placing a glass substrate on an optical surface plate and using a clearance gauge described in JIS B-7524. “Waviness” is a value obtained by measuring WCA (filtered center line waviness) described in JIS B-0610 using a stylus type surface shape measuring device. This measurement is performed by SEMI STD D15-1296 “FPD”. Measured by a method in accordance with “Measurement method of surface waviness of glass substrate”, cut-off at the time of measurement is 0.8 to 8 mm, measured at a length of 300 mm in a direction perpendicular to the drawing direction of the glass substrate. is there. “Average surface roughness (Ry)” is a value measured by a method based on SEMI D7-94 “Measurement method of surface roughness of FPD glass substrate”. In addition, Sample No. The liquid phase viscosities of the glasses 1 and 13 were both 10 ^5.0 dPa · s. “Liquid phase viscosity” refers to the viscosity of the glass at the liquidus temperature, and the viscosity of the glass refers to a value measured by a known fiber elongation method or platinum ball pulling method. It can be said that the higher the liquidus viscosity of the glass, the better the devitrification resistance and the better the moldability.

  Therefore, the alkali-free glass of the present invention is suitable for flat display substrates such as LCDs and EL displays. Further, the alkali-free glass of the present invention is suitable for a substrate for an electronic device such as a cover glass for an image sensor such as a charge-coupled device (CCD) or an equal magnification proximity solid-state imaging device (CIS), or a substrate for a solar cell.

Claims (20)

A glass composition, _SiO 2 45 to _68% by _{mass%, Al 2 O 3 1 3} ~18%, B 2 O 3 5~15%, 0~3% MgO, CaO 7 ~20%, SrO 5~20% BaO 0 to less than 5%, ZnO 0 to 20%, ZrO ₂ 0 to 5%, TiO ₂ 0 to 5%, P ₂ O ₅ 0 to 5% , MgO + CaO + SrO + BaO 17 to 25% , substantially alkaline An alkali-free glass which does not contain a metal oxide and is formed by a downdraw method . The alkali-free glass according to claim 1, which is substantially free of As ₂ O ₃ and contains 0 to 2 mass % of SnO ₂ .   The alkali-free glass according to claim 1 or 2, wherein the glass contains substantially no BaO.   The alkali-free glass according to any one of claims 1 to 3, which contains substantially no MgO. The alkali-free glass according to any one of claims 1 to 4, wherein the content of MgO + CaO + SrO + BaO + ZnO is 17 % to 25% by mass%. 6. The alkali-free glass according to claim 1, wherein a coefficient of thermal expansion in a temperature range of 30 to 380 ° C. is 40 to 60 × 10 ⁻⁷ / ° C. 6.   The alkali-free glass according to any one of claims 1 to 6, wherein the strain point is 600 ° C or higher.   Liquid phase temperature is 1150 degrees C or less, The alkali free glass in any one of Claims 1-7 characterized by the above-mentioned. The alkali-free glass according to any one of claims 1 to 8, wherein a temperature corresponding to 10 ^2.5 dPa · s is 1530 ° C or lower. The alkali-free glass according to any one of claims 1 to 9, wherein the density is 2.70 g / cm ³ or less.   The alkali-free glass according to any one of claims 1 to 10, wherein Young's modulus is 75 GPa or more. The non-alkali glass according to claim 1, wherein the specific Young's modulus is 27 GPa / (g · cm ⁻³ ) or more.   The alkali-free glass according to any one of claims 1 to 12, wherein when immersed in a 10% HCl aqueous solution at 80 ° C for 24 hours, the erosion amount is 5 µm or less.   The alkali-free glass according to any one of claims 1 to 13, wherein the amount of erosion when immersed in a 130 buffered hydrofluoric acid solution at 20 ° C for 30 minutes is 2 µm or less.   An alkali-free glass substrate comprising the alkali-free glass according to claim 1. Alkali-free glass substrate according to claim 15, characterized in Rukoto such is molded by an overflow down draw method. The alkali-free glass substrate according to claim 15 or 16, wherein the area of the glass substrate is 0.1 m ² or more.   The alkali-free glass substrate according to claim 15, which is used for a display.   The alkali-free glass substrate according to claim 18, wherein the display is a liquid crystal display.   19. The alkali-free glass substrate according to claim 18, wherein the display is an amorphous silicon TFT liquid crystal display.