JP2004091244A - Alkali-free glass substrate and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an alkali-free glass substrate by which the generation of bubbles or heterogeneous layers can be suppressed, and the waviness of the surface can be made small even when SnO<SB>2</SB>is used as a clarifier in place of As<SB>2</SB>O<SB>3</SB>. <P>SOLUTION: In the method for manufacturing the alkali-free glass substrate, comprising preparing a glass raw material, melting, clarifying, and forming the resulting melt into a plate-like form, a raw material having an average particle diameter (D<SB>50</SB>) of ≤60 μm is used as a silica raw material, and SnO<SB>2</SB>is used as the clarifier. <P>COPYRIGHT: (C)2004,JPO

Description

【００４９】
【表２】

【００５０】
【表３】

【００５１】
表中の各ガラス試料は、次のようにして作製した。
【００５２】
まず表の組成となるようにガラス原料を調合したバッチを白金ルツボに入れ、１６００℃で２４時間溶融した後、カーボン板上に流し出し、板状に成形した。こうして得られたガラス試料を用いて、密度、熱膨張係数、歪点、１０^２．５ポイズ温度、液相温度、耐薬品性を測定した。またこれらのガラスを実際のガラス溶融炉を模して作製された小型のガラス溶融装置（ＺｒＯ_２質耐火物製）で溶融し、オーバーフローダウンドロー法で板状に成形した後、３７０×４７０×０．７ｍｍに切断加工し、こうして得られたガラス基板の泡個数を計測すると共に、うねり量を測定した。尚、Ｎｏ．１〜５の実施例ガラスのＳｉＯ_２原料は、平均粒径（Ｄ_５０）が４０μｍの珪砂を使用し、またＮｏ．６〜１０の実施例ガラスのＳｉＯ_２原料は、平均粒径（Ｄ_５０）が５６μｍの珪砂を使用し、さらにＮｏ．１１〜１３の比較例ガラスのＳｉＯ_２原料は、平均粒径（Ｄ_５０）が９５μｍの珪砂を使用した。
【００５３】
表から明らかなように、Ｎｏ．１〜１０の実施例ガラスは、低密度で、熱膨張係数が３２〜３８×１０^−７／℃であり、歪点が６６０℃以上であった。また１０^２．５ポイズに相当する温度が１５９７℃以下であり、液相温度は１１０５℃以下、耐ＨＣｌ性と耐ＢＨＦ性に優れていた。さらに泡個数が６．０個／ｋｇ以下、うねり量が０．０２μｍ以下であった。
【００５４】
一方、Ｎｏ．１１〜１３の比較例ガラスは、泡個数が２０個／ｋｇ以上と多く、またうねり量が０．０３μｍ以上と大きかった。
【００５５】
尚、表中の密度は、周知のアルキメデス法で求め、熱膨張係数は、ディラトメーターを用いて３０〜３８０℃における平均熱膨張係数を測定した。歪点は、ＡＳＴＭ　Ｃ３３６−７１に基づいて測定した。１０^２．５ポイズ温度は、高温粘性である１０^２．５ポイズの粘度に相当する温度を示すものであり、この温度が低いほど溶融性に優れていることになる。液相温度は、ガラス試料を３００〜５００μｍの粒径に破砕し、これを白金ボート中に投入し、温度勾配炉中で２４時間熱処理した後、これを取り出し、ガラス中に失透（結晶異物）の見られた温度を示したものである。耐ＨＣｌ性と耐ＢＨＦ性は、以下の方法で浸食量を求めて評価した。まず各ガラス試料の両面を光学研磨した後、その一部をマスキングしてから所定の濃度に調合した薬液中で下に示す条件で浸漬した。このように薬液で処理した後、マスクを外し、マスク部分と浸食部分の段差を表面粗さ計で測定し、その値を浸食量とした。この浸食量が多いほど耐ＨＣｌ性と耐ＢＨＦ性が悪いということになる。耐ＨＣｌ性は、１０質量％塩酸水溶液を用いて８０℃、２４時間の処理条件で測定した。また耐ＢＨＦ性は、１３０ＢＨＦ溶液（ＮＨ_４ＨＦ_２：４．６質量％、ＮＨ_４Ｆ：３６質量％）を用いて２０℃、３０分間の処理条件で測定した。
【００５６】
泡個数は、ガラス基板中を顕微鏡で観察し、長さ０．１ｍｍ以上の泡の個数を示した。うねり量は、触針式の表面形状測定装置を用いて、ＪＩＳ　Ｂ−０６１０に記載のＷＣＡ（ろ波中心線うねり）を測定した。この測定は、ＳＥＭＩ　ＳＴＤ　Ｄ１５−１２９６に準拠した方法で行い、測定時のカットオフは０．００８〜０．８ｍｍ、ガラス基板の引き出し方向に対して垂直な方向に３００ｍｍの長さで測定し、うねりの最大値を求め、それを表示した。
【００５７】
【発明の効果】
以上説明したように、本発明の無アルカリガラス基板の製造方法によると、シリカ原料として、平均粒径（Ｄ_５０）が６０μｍ以下の原料を使用するため、清澄剤としてＳｎＯ_２を使用しても、泡や異質層の発生を抑えることができ、その結果、表面のうねり量の小さなガラス基板が得ることが可能となる。
【００５８】
またこうして得られる無アルカリガラス基板は、液晶ディスプレイ、ＥＬディスプレイ等の高性能のフラットディスプレイ基板を始めとして、電荷結合素子（ＣＣＤ）、等倍近接型固体撮像素子（ＣＩＳ）、ＣＭＯＳイメージセンサー等の各種イメージセンサー、ハードディスク、フィルター等のガラス基板として好適である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flat panel display substrate such as a liquid crystal display and an EL display, various image sensors such as a charge-coupled device (CCD), a 1 × proximity solid-state imaging device (CIS), a CMOS image sensor, and a glass such as a hard disk and a filter. The present invention relates to an alkali-free glass substrate suitable as a substrate.
[0002]
[Prior art]
BACKGROUND ART Conventionally, glass substrates have been widely used as flat display substrates for liquid crystal displays, EL displays, and the like.
[0003]
In particular, electronic devices such as thin film transistor type active matrix liquid crystal displays (TFT-LCDs) are thin and consume little power, so they are used for various purposes such as car navigation, viewfinders for digital cameras, monitors for personal computers, and TVs. I have.
[0004]
In order to drive a liquid crystal display, it is necessary to form a driving element typified by a TFT element on a glass substrate, but in a manufacturing process of the TFT element, a transparent conductive film, an insulating film, a semiconductor film, In a photolithography-etching step, a glass substrate is subjected to various heat treatments and chemical treatments. For example, in a TFT active matrix liquid crystal display, 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 (thin film transistors) are formed on the glass substrate by a photolithography-etching process. You. In the TFT manufacturing process, the glass substrate is subjected to a heat treatment at 300 to 600 ° C. and is treated with various chemicals such as sulfuric acid, hydrochloric acid, an alkaline solution, hydrofluoric acid, and buffered hydrofluoric acid. Therefore, the glass substrate for a TFT liquid crystal display is required to have the following characteristics.
[0005]
(1) When an alkali metal oxide is contained in glass, alkali ions diffuse into a formed semiconductor material during heat treatment, causing deterioration of film properties. Do not contain.
[0006]
(2) It has excellent resistance to a solution such as an acid and an alkali used in a photolithography-etching step, that is, excellent chemical resistance.
[0007]
(3) In a process such as film formation and annealing, the glass substrate is heated to a high temperature of several hundred degrees Celsius. At that time, the strain point must be high so that the glass substrate does not shrink thermally. At present, the process temperature of a low-temperature polycrystalline silicon TFT-LCD that has attracted attention as a high-performance liquid crystal display has a relatively high process temperature of about 400 to 600 ° C. It is desired that the glass substrate used for this purpose has a strain point of 640 ° C. or higher.
[0008]
(4) It is excellent in devitrification resistance so that foreign matter is not generated in the glass during the glass melting step or the forming step. In particular, when glass is formed by a downdraw method such as an overflow downdraw method, the devitrification resistance of the glass is important, and when the glass forming temperature is considered, the liquidus temperature may be 1200 ° C or less. Required.
[0009]
(5) Low density to reduce the weight of the liquid crystal display. In particular, there is a strong demand for a glass substrate mounted on a notebook personal computer to be reduced in weight, and specifically, a glass substrate of not more than 2.50 g / cm ³ is required.
[0010]
Further, in addition to the above characteristics, a glass substrate used for a liquid crystal display is required to have high surface flatness. For example, in a liquid crystal display, a liquid crystal layer sandwiched between two thin glass substrates functions as an optical shutter, and display is performed by blocking or seeing through the light. This liquid crystal layer is held at a very small thickness of several μm to several tens μm. Therefore, the flatness of the surface of the glass substrate, particularly irregularities at the μm level called undulation, easily affects the thickness of the liquid crystal layer (called cell gap). If the undulation of the surface is large, display defects such as display unevenness may occur. Cause.
[0011]
In recent years, in liquid crystal displays, the cell gap has tended to be thinner for the purpose of high-speed response and high definition. Therefore, it has become increasingly important to reduce the undulation of the glass substrate used for this purpose. ing.
[0012]
The most effective method for reducing the waviness on the surface of the glass substrate is to precisely polish the surface of the glass substrate after molding. However, this method greatly increases the manufacturing cost of the glass substrate.
[0013]
For this reason, at present, glass substrates with as little surface undulation as possible are formed by molding methods such as the overflow down draw method and the float method, and they are shipped with no polishing or with extremely light polishing (touch polish). I have.
[0014]
In addition, glass substrates for liquid crystal displays have various required characteristics in addition to the flatness of the surface, but the required quality for internal defects such as bubbles and crystalline foreign matter in glass is extremely severe. However, since the liquid crystal display substrate is made of non-alkali glass and does not contain an alkali metal oxide component acting as a flux, the viscosity of the glass melt is high, and the composition of the glass melt tends to be non-uniform, Difficult to melt.
[0015]
Therefore, conventionally, when melting non-alkali glass, As ₂ O ₃ which is a fining agent (an antifoaming agent that cuts bubbles in the molten glass) that operates at a relatively high temperature is used, and the maximum temperature of the glass melting furnace is used. Is set to be a high temperature of more than 1600 ° C. to enhance the melting property of the glass.
[0016]
[Problems to be solved by the invention]
By the way, in recent years, attention has been increasingly paid to environmental issues. However, As ₂ O ₃ is a compound classified as a toxic substance and is an environmentally hazardous chemical substance. Therefore, it is strongly required to avoid its use. When melting the alkali-free glass, if As ₂ O ₃ is not contained, the clarity decreases and the number of bubbles in the glass increases, but by including SnO ₂ , it is possible to reduce bubbles. It is.
[0017]
SnO ₂ is a fining agent that acts at a high temperature, but is inferior to As ₂ O ₃ in fining action of glass, so that it is difficult to obtain glass with sufficiently reduced bubbles. In addition, an extraneous layer remaining without being completely melted in the glass is likely to be generated, and this causes the surface of the glass substrate to swell easily.
[0018]
The present invention has been made in view of the above circumstances, and even if SnO ₂ is used instead of As ₂ O ₃ as a fining agent, it is possible to suppress the generation of bubbles and foreign layers and reduce the surface undulation. An object of the present invention is to provide a method for producing an alkali-free glass substrate that can be used.
[0019]
[Means for Solving the Problems]
According to the knowledge of the present inventor, the first reason that a heterogeneous layer occurs in alkali-free glass is that a vitreous layer having a high SiO ₂ concentration, which is a main component of this type of glass, remains in the glass. . The second reason is that a melting furnace for melting this kind of glass is generally made of ZrO ₂ refractory, but ZrO ₂ is eluted into the glass by a reaction between the glass melt and the refractory. However, this is because a glassy layer having a high ZrO ₂ concentration remains in the glass. However, generation of such a foreign layer can be suppressed by appropriately selecting a silica raw material.
[0020]
That is, in the method for producing an alkali-free glass substrate of the present invention, in the method for producing an alkali-free glass substrate in which a glass raw material is prepared, melted, and clarified, and then formed into a plate, an average particle diameter (D ₅₀ ) Is characterized by using a raw material having a particle size of 60 μm or less and using SnO ₂ as a fining agent.
[0021]
In the alkali-free glass substrate of the present invention, the content of As ₂ O ₃ is less than 0.1% by mass, the content of SnO ₂ is 0.005 to 0.5% by mass, and the undulation amount of the surface of the glass substrate. Is not more than 0.02 μm.
BEST MODE FOR CARRYING OUT THE INVENTION
In the method for producing an alkali-free glass of the present invention, SnO ₂ used as a fining agent has a function of releasing oxygen in a temperature range of 1400 ° C. or more to generate a fining gas and reduce bubbles in the glass. This SnO ₂ is inferior to As ₂ O ₃ in refining action, but when a raw material having an average particle diameter (D ₅₀ ) of 60 μm or less is used as a silica raw material, that is, silica sand or silica powder, the melting property of the glass is reduced. This significantly improves the amount of undulation of the glass substrate, and significantly reduces bubbles in the glass.
[0023]
That is, when a silica raw material having an average particle diameter (D ₅₀ ) of 60 μm or less is used, a heterogeneous layer having a high SiO ₂ concentration is less likely to be generated in the glass, so that the undulation of the surface of the glass substrate due to this is reduced. Further, when the melting property of the glass is improved, the maximum temperature of the glass melting furnace can be lowered, so that the elution of ZrO ₂ from the refractory can be suppressed, and a heterogeneous layer having a high ZrO ₂ concentration is hardly generated in the glass. Therefore, the undulation on the surface of the glass substrate due to this is also reduced. Moreover, by obtaining a homogeneous molten glass, fining becomes easy, and bubbles can be sufficiently reduced by the fining action of SnO ₂ .
[0024]
The average particle size (D ₅₀ ) of the silica raw material is preferably 58 μm or less, more preferably 55 μm or less.
[0025]
In the present invention, the content of SnO ₂ in the glass, 0.005 wt% (preferably 0.01 to 0.3 wt%) is preferably regulated to be a. That is, if the SnO ₂ contained in the glass is less than 0.005% by mass, a sufficient fining effect cannot be obtained even when the above-mentioned silica raw material is used, and if it is more than 0.5% by mass, This is because SnO ₂ devitrified material tends to precipitate during molding. In particular, when molding by the overflow down draw method, care must be taken because devitrification tends to occur. SnO ₂ is preferable when tin oxide is added as a glass raw material, since the content is easy to regulate, but it may be mixed into glass in the production process. For example, when a tin electrode is used in a glass melting furnace, about several ppm to several hundred ppm of SnO ₂ is mixed into the glass and acts as a fining agent.
[0026]
As ₂ O ₃ is an environmentally hazardous chemical substance, so it is preferable that it is not essentially contained in glass, that is, that arsenic oxide is not added to glass raw materials. The fact that As ₂ O ₃ is not essentially contained in the glass means that As ₂ O ₃ in the glass is 0.1% by mass or less. The preferred content of As ₂ O ₃ is 0.05% by mass or less, and the more preferred content is 0.01% by mass or less.
[0027]
In the present invention, it is preferable to add a chloride to the glass raw material for the purpose of promoting the dissolution of the silica raw material. Chloride decomposes and volatilizes in a temperature range of 1200 ° C. or more to generate a fining gas, and suppresses formation of a foreign layer by its stirring action. Chloride has the effect of taking in and dissolving silica during its decomposition. However, if the chloride content is too large, the glass is liable to deteriorate due to excessive volatilization, which is not preferable. Therefore, the amount of chloride added is regulated such that Cl in the glass is 0.5% by mass or less, preferably 0.01 to 0.5% by mass, more preferably 0.01 to 0.3% by mass. It is important to. As the chloride, BaCl ₂ , CaCl ₂ , SrCl ₂ or the like may be used.
[0028]
In the present invention, it is preferable to add antimony oxide to the glass raw material and to make the glass contain Sb ₂ O ₃ because the fining effect is further promoted. That is, Sb ₂ O ₃ has a lower fining gas emission temperature than As ₂ O _3, but in the present invention, since a silica raw material having an average particle diameter (D ₅₀ ) of 60 μm or less is used, the raw material is relatively dissolved. Can be performed at low temperatures. Therefore, the temperature of the fining step, which is a subsequent step, can be reduced, and the fining effect of Sb ₂ O ₃ can be obtained. However, Sb ₂ O _{3 is} also an environmentally unfavorable chemical substance, although not as large as As ₂ O _3, so that it is not preferable to contain it in a large amount. Therefore, the content of Sb ₂ O ₃ in the glass is regulated to be 1.8% by weight or less, preferably 0.01 to 1.8% by weight, more preferably 0.05 to 1.5% by weight. This is very important.
[0029]
As described above, in the present invention, while using SnO ₂ as a fining agent, a silica raw material having an average particle diameter (D ₅₀ ) of 60 μm or less is used, so that bubbles and foreign layers can be reduced. As a result, it is possible to manufacture an alkali-free glass substrate having a surface undulation of 0.02 μm or less. When an alkali-free glass substrate having a surface undulation of 0.02 μm or less is used for a liquid crystal display, it is possible to suppress the occurrence of display defects even when the cell gap of the liquid crystal display is about 1 μm.
[0030]
The method for producing an alkali-free glass substrate of the present invention comprises mixing, melting, and refining glass raw materials, and forming the mixture into a plate shape. Examples of the forming method include an overflow down draw method, a slot down draw method, and a float method. Method and rollout method can be applied. In particular, molding by an overflow down draw method is preferable because a glass substrate having a very small surface undulation can be easily obtained without polishing the surface.
[0031]
When the alkali-free glass substrate of the present invention has a thickness of 0.1 to 1.1 mm, it is suitable as a liquid crystal display substrate.
[0032]
The alkali-free glass substrate of the present invention, in _{mass%, SiO 2 55~70%, Al} 2 O 3 12~20%, B 2 O 3 5~15%, MgO 0~7%, CaO 0~12% , BaO 0-10%, SrO 0-10%, and ZnO 0-5%.
[0033]
The reasons for defining the basic composition of the alkali-free glass substrate of the present invention as described above are as follows.
[0034]
If the content of SiO ₂ is less than 55%, the chemical resistance, particularly the acid resistance, is reduced, and it is difficult to reduce the density. If it is more than 70%, the high-temperature viscosity increases, the melting property decreases, and cristobalite devitrified foreign matter is easily generated in the glass. The preferred content of SiO ₂ is 56 to 68%.
[0035]
When the content of Al ₂ O ₃ is less than 12%, the devitrification temperature rises, and the devitrified foreign substances of cristobalite are easily generated in the glass, and the strain point is lowered. On the other hand, if it exceeds 20%, the buffered hydrofluoric acid resistance of the glass is reduced, the glass surface is likely to be clouded, and the devitrification resistance of the glass is reduced. The preferred content of Al ₂ O ₃ is 13 to 18%.
[0036]
B ₂ O ₃ is a component that acts as a flux, lowers the viscosity, and improves the meltability. If the amount is less than 5%, the function as a flux becomes insufficient, and the resistance to buffered hydrofluoric acid decreases. If it is more than 15%, the strain point of the glass decreases, and the acid resistance decreases.
[0037]
MgO is a component that lowers the high-temperature viscosity without lowering the strain point and improves the meltability of glass. MgO is most effective in reducing the density of alkaline earth metal oxides. However, when MgO is contained in a large amount, the devitrification temperature rises, and crystal foreign substances tend to precipitate in glass. Further, MgO reacts with buffered hydrofluoric acid to form a product, which may stick to an element formed on the surface of the glass substrate or may adhere to the glass substrate to make it cloudy. Has limitations. Therefore, MgO is desirably 7% or less, preferably 5% or less, and more preferably 1% or less.
[0038]
Like CaO, CaO also has the effect of lowering the high-temperature viscosity without lowering the strain point and significantly improving the melting property of glass. If the content of CaO is more than 12%, the buffered hydrofluoric acid resistance of the glass is reduced, the glass substrate is easily eroded, and the reaction product adheres to the surface of the glass substrate to cloud the glass. A more desirable content of CaO is 3 to 10%.
[0039]
BaO is a component for improving the chemical resistance and devitrification resistance of glass, but when contained in a large amount, the density of the glass increases. BaO is a component that deteriorates the melting property among the alkali metal oxides. For this type of glass, reducing SiO ₂ is the most effective in increasing the melting property, but reducing SiO ₂ is not preferable because acid resistance decreases. Therefore, in order to increase the melting property of the glass without reducing SiO ₂ , it is necessary to limit the amount of BaO, and it should be 10% or less. The preferred amount of BaO is 5% or less.
[0040]
SrO is a component that improves the chemical resistance of the glass and also improves the devitrification. However, when contained in a large amount, the density of the glass increases. SrO, like BaO, is a component that deteriorates the melting property in the alkali metal oxide. Therefore, SrO is at most 10%, more preferably at most 8%.
[0041]
ZnO is a component that improves the buffered hydrofluoric acid resistance and the melting property of the glass. However, when the content is 5% or more, the glass is easily devitrified and the strain point is lowered.
[0042]
By mixing and containing alkaline earth metal oxides, the devitrification temperature of glass can be significantly reduced, and crystal foreign substances can be less likely to occur in the glass. However, if it is contained in a large amount, the density of the glass increases and it becomes impossible to reduce the weight of the substrate. Therefore, the total amount of these components should be suppressed to 15% or less.
[0043]
In addition to the above components, fining agents such as F ₂ and SO ₃ , Y ₂ O ₃ , La ₂ O ₃ , Nb ₂ O ₃ , TiO _{2 and the} like are added as long as the glass characteristics which are the characteristics of the present invention are not impaired. You may. Further, the present invention is characterized by substantially not containing an alkali metal oxide. The phrase "contains substantially no alkali metal oxide" means that the content is suppressed to 0.1% by mass or less, preferably 0.05% by mass or less.
[0044]
Further, since the alkali-free glass substrate of the present invention needs to be melted at a high temperature of around 1600 ° C., it is desirable that the glass melting furnace is made of a ZrO ₂ refractory having excellent corrosion resistance even at a high temperature. However, as described above, even when a glass melting furnace made of a ZrO ₂ -based refractory is used, ZrO _{2 as} a component of the refractory gradually elutes into the glass during long-term operation. Since the diffusion of ZrO ₂ in the glass melt is very slow, if a large amount of ZrO ₂ is mixed in the glass, the glass melt becomes inhomogeneous, and the surface of the glass substrate is likely to undulate. However, in the present invention, a silica raw material having an average particle size (D ₅₀ ) of 60 μm or less can be used to improve the melting property of glass, so that the maximum temperature of the glass melting furnace can be reduced, and ZrO ₂ It is possible to suppress the elution of ZrO ₂ due to erosion of the refractory. Further, since the melting property of the glass is improved, a homogeneous glass melt can be obtained even if a small amount of ZrO ₂ elutes.
[0045]
However, in actual operation, there are times when the flow rate of the glass must be reduced, and as a result, the residence time of the glass in the glass melting furnace increases, the refractory elutes into the glass, and the ZrO _The amount may increase. In this case, the undulation of the surface of the glass substrate is likely to be large. Therefore, it is desirable to devise so as to minimize mixing not only from the raw materials but also from the manufacturing process. For this purpose, part or all of the material (refractory) for constructing the glass melting furnace is changed to ZrSiO ₄ refractory or Al ₂ O ₃ refractory, or the refractory is cooled by water cooling or air cooling. In this case, a method of suppressing elution into glass by performing the method is effective. As described above, from the viewpoint of reducing the undulation of the surface of the glass substrate, ZrO ₂ should avoid mixing from the raw materials and the manufacturing process as much as possible, and the content in the glass should be 0.2% by mass or less, Preferably, it should be 0.1% by mass or less.
[0046]
【Example】
Hereinafter, the alkali-free glass substrate of the present invention will be described in detail based on examples.
[0047]
Tables 1 to 3 show examples (samples Nos. 1 to 10) and comparative examples (samples Nos. 11 to 13) of the present invention.
[0048]
[Table 1]

[0049]
[Table 2]

[0050]
[Table 3]

[0051]
Each glass sample in the table was produced as follows.
[0052]
First, a batch prepared by mixing glass raw materials so as to have the composition shown in the table was put in a platinum crucible, melted at 1600 ° C. for 24 hours, poured out onto a carbon plate, and formed into a plate shape. Using a glass sample thus obtained, the density, thermal expansion coefficient, strain point, 10 ^2.5 poise temperature, liquidus temperature was measured chemical resistance. Further, these glasses are melted by a small glass melting apparatus (made of ZrO ₂ refractory) simulating an actual glass melting furnace, formed into a plate shape by an overflow down draw method, and then 370 × 470 × The glass substrate was cut into 0.7 mm, the number of bubbles on the glass substrate thus obtained was measured, and the amount of undulation was measured. In addition, No. As the SiO ₂ raw material of the example glasses of Examples 1 to 5, silica sand having an average particle diameter (D ₅₀ ) of 40 μm was used. As the SiO ₂ raw material of the example glasses of Nos. 6 to 10, silica sand having an average particle diameter (D ₅₀ ) of 56 μm was used. Silica sand having an average particle diameter (D ₅₀ ) of 95 μm was used as the SiO ₂ raw material of the comparative examples 11 to 13.
[0053]
As is clear from the table, No. Example glasses 1 to 10 had a low density, a coefficient of thermal expansion of 32 to 38 × 10 ⁻⁷ / ° C., and a strain point of 660 ° C. or higher. The temperature corresponding to ^{10 2.5} poise or less 1597 ° C., the liquidus temperature is 1105 ° C. or less, were excellent in HCl resistance and the BHF resistance. Further, the number of bubbles was 6.0 / kg or less, and the amount of undulation was 0.02 μm or less.
[0054]
On the other hand, No. The comparative examples 11 to 13 had a large number of bubbles of 20 / kg or more and a large undulation of 0.03 μm or more.
[0055]
In addition, the density in a table | surface was calculated | required by the well-known Archimedes method, and the coefficient of thermal expansion measured the average coefficient of thermal expansion in 30-380 degreeC using the dilatometer. The strain point was measured based on ASTM C336-71. 10 ^2.5 poise temperature is indicative of the temperature corresponding to a viscosity of 10 ^2.5 poise is hot viscous, so that this temperature is better to lower the melting property. The liquidus temperature is such that a glass sample is crushed to a particle size of 300 to 500 μm, put into a platinum boat, heat-treated in a temperature gradient furnace for 24 hours, taken out, and devitrified in the glass (crystal foreign matter). ) Is the temperature at which the temperature was observed. The HCl resistance and the BHF resistance were evaluated by determining the amount of erosion by the following method. First, both surfaces of each glass sample were optically polished, a part of which was masked, and then immersed in a chemical solution prepared to a predetermined concentration under the conditions shown below. After treatment with the chemical solution in this manner, the mask was removed, and the step between the mask portion and the eroded portion was measured with a surface roughness meter, and the value was used as the erosion amount. The greater the amount of erosion, the worse the HCl resistance and BHF resistance. HCl resistance was measured using a 10% by mass aqueous hydrochloric acid solution at 80 ° C. for 24 hours. The BHF resistance was measured using a 130 BHF solution (NH ₄ HF ₂ : 4.6% by mass, NH ₄ F: 36% by mass) at 20 ° C. for 30 minutes.
[0056]
The number of bubbles was obtained by observing the inside of a glass substrate with a microscope and indicating the number of bubbles having a length of 0.1 mm or more. The waviness was measured by using a stylus-type surface shape measuring device for WCA (filtering centerline waviness) described in JIS B-0610. This measurement is performed by a method in accordance with SEMI STD D15-1296, the cutoff at the time of measurement is 0.008 to 0.8 mm, and the length is measured 300 mm in a direction perpendicular to the drawing direction of the glass substrate. The maximum value of the swell was determined and displayed.
[0057]
【The invention's effect】
As described above, according to the method for producing an alkali-free glass substrate of the present invention, since a raw material having an average particle diameter (D ₅₀ ) of 60 μm or less is used as a silica raw material, even if SnO ₂ is used as a fining agent, In addition, the generation of bubbles and foreign layers can be suppressed, and as a result, a glass substrate having a small surface undulation can be obtained.
[0058]
The alkali-free glass substrates thus obtained include high-performance flat display substrates such as liquid crystal displays and EL displays, as well as charge-coupled devices (CCDs), 1 × proximity solid-state imaging devices (CIS), and CMOS image sensors. It is suitable as a glass substrate for various image sensors, hard disks, filters, and the like.

Claims (11)

In a method for producing an alkali-free glass substrate, which is prepared by mixing, melting and refining glass raw materials, the raw material having an average particle size (D ₅₀ ) of 60 μm or less is used as a silica raw material, and SnO is used as a fining agent. _{2. A} method for producing an alkali-free glass substrate, comprising using: Method for producing an alkali-free glass substrate of claim 1 wherein the SnO ₂ in the glass is characterized by restricted so that 0.005 to 0.5 mass%. 3. The method for producing an alkali-free glass substrate according to claim 1, wherein arsenic oxide is not added to the glass raw material. The alkali-free glass substrate according to any one of claims 1 to 3, wherein a chloride is added to the glass raw material so that Cl in the glass is 0.01 to 0.5% by mass. Method. As Sb ₂ O ₃ in the glass is 0.1 to 1.8 wt%, the alkali-free according to claim 1, characterized in that the addition of antimony oxide in the glass material A method for manufacturing a glass substrate. The method for producing an alkali-free glass substrate according to any one of claims 1 to 5, wherein the glass substrate is formed so that the amount of undulation on the surface of the glass substrate is 0.02 µm or less. The method for producing an alkali-free glass substrate according to any one of claims 1 to 6, wherein the molding is performed by an overflow down draw method. The method for producing an alkali-free glass substrate according to any one of claims 1 to 7, wherein the glass substrate is formed so that the thickness thereof is 0.1 to 1.1 mm. The content of As ₂ O ₃ is less than 0.1% by mass, the content of SnO ₂ is 0.005 to 0.5% by mass, and the undulation amount of the surface of the glass substrate is 0.02 μm or less. Alkali-free glass substrate. Alkali-free glass substrate according to claim 9, wherein the content of ZrO ₂ is equal to or less than 0.2 wt%. By _{mass%, SiO 2 55~70%, Al} 2 O 3 12~20%, B 2 O 3 5~15%, MgO 0~7%, CaO 0~12%, BaO 0~10%, SrO 0~ The alkali-free glass substrate according to claim 9 or 10, having a basic composition of 10% and ZnO of 0 to 5%.