JP4716245B2 - Glass substrate and manufacturing method thereof - Google Patents

Description

  The present invention is a liquid crystal display, an organic EL display, a flat panel display such as a plasma display, a charge coupled device (CCD), an equal magnification proximity solid-state imaging device (CIS), various image sensors such as a CMOS image sensor, a hard disk, a filter, etc. In particular, the present invention relates to a glass substrate suitable for a liquid crystal display for TV.

  Conventionally, liquid crystal displays for TV use active matrix liquid crystal displays, especially TFT-LCDs driven by thin film transistors (TFTs), in order to obtain the image quality required for TVs such as response speed, viewing angle, and color reproducibility. Yes. A metal film, an insulating film, a transparent conductive film, and a semiconductor film are formed on the surface of the glass substrate for TFT-LCD, and various circuits including amorphous silicon and polycrystalline silicon TFTs are used in the photolithography-etching process. Many patterns are formed. In the TFT formation process, the glass substrate is heat-treated at a maximum of about 350 to 400 ° C. and treated with various chemicals such as sulfuric acid, hydrochloric acid, alkaline solution, hydrofluoric acid, and buffered hydrofluoric acid. If the glass contains an alkali metal oxide, the alkali ions in the glass may diffuse into the semiconductor film during the heat treatment and cause deterioration of the film characteristics. Is required.

Under such circumstances, this type of glass substrate uses a non-alkali glass substrate that is excellent in heat resistance and chemical durability and does not contain an alkali metal oxide, as disclosed in Patent Documents 1 to 3. Has been.
Japanese Patent No. 2644622 Japanese Patent No. 2990379 Japanese Patent No. 3465238

  In general, an alkali-free glass substrate used for a TFT-LCD has a very high viscosity and does not contain an alkali metal oxide that acts as a flux, so that it is difficult to melt. Bubbles in glass are typical internal defects in glass products, but in a glass substrate for TFT-LCD, a bubble of 100 μm in length is formed on a large glass substrate of 1 m square or more (about 2 kg or more in terms of glass mass). If there is even one, there is a strict product specification that does not become a non-defective product. For this reason, attempts have been made to melt glass at as high a temperature as possible to reduce bubbles in the glass, but it is very difficult to produce an alkali-free glass that is difficult to melt at a high yield. In addition, when the melting temperature rises, the temperature at which the glass is formed also rises, causing a problem of shortening the life of the forming equipment.

  By the way, in recent years, development for lowering the TFT formation temperature has been carried out. Conventionally, the maximum temperature is about 350 to 450 ° C., but this is being reduced to about 250 to 300 ° C. This technological innovation has made it possible to use glass substrates with low heat resistance. Specifically, conventionally, it has been required that the glass has a strain point of 650 ° C. or higher. However, it is becoming possible to use glass that is 100 ° C. or lower.

  In particular, a liquid crystal display used in a large liquid crystal TV is required to have high definition and high image quality. To achieve this, the flatness of the surface of the glass substrate is extremely important. In other words, the liquid crystal display is displayed by a liquid crystal layer sandwiched between two thin glass substrates serving as an optical shutter that blocks or transmits light. This liquid crystal layer is maintained at a very thin thickness of several μm to several tens of μm. If the flatness of the glass substrate, particularly micron-level irregularities called surface waviness is large, the thickness of this liquid crystal layer (cell gap) This may cause display defects such as display unevenness. In recent liquid crystal displays, in particular, liquid crystal TV applications, the cell gap tends to become thinner for the purpose of further high-speed response and high definition, and the reduction of the surface waviness of the glass substrate is becoming increasingly important. In order to reduce the surface waviness of the glass substrate, the surface of the glass substrate may be precisely polished and flattened, such as a silicon wafer, but the manufacturing cost of the glass becomes very high. Moreover, when the glass substrate is polished, countless minute scratches and cracks are likely to occur on the glass surface. In high-performance liquid crystal displays such as liquid crystal TV applications, the width of signal lines and electrode lines that drive TFTs tends to be narrow, and if there are minute scratches or cracks on the surface of the glass substrate, the signal lines and electrode lines Disconnection may cause display failure. Therefore, it is desirable for this type of glass substrate to form a plate glass with as little surface waviness as possible from molten glass, and to eliminate the need for surface polishing. In order to obtain such a glass substrate, the downdraw method, particularly overflow A molding method called a down draw method is suitable.

  The object of the present invention is that it has excellent melt moldability, has few internal defects such as bubbles, and can prolong the life of manufacturing equipment, so it is possible to achieve a significant cost reduction. Since it can be formed into a plate shape, it is to provide a glass substrate which has a small undulation and can be shipped without polishing, and a method for producing the same.

Glass substrate of the present invention, in _{mass%, SiO 2 50~70%, Al} 2 O 3 1~20%, B 2 O 3 0~15%, alkali metal oxides 1% to 25%, an alkaline earth metal oxide It contains 0-30% of a substance, is composed of glass having a strain point of 530-630 ° C., a temperature corresponding to 10 ^2.5 dPa · s of 1370-1520 ° C., and a viscosity at a liquidus temperature of 100,000 poise or more. face without polishing surface, the surface waviness 0.05μm or less, the surface roughness is characterized der Rukoto below 5 Å.

Process for producing a glass substrate of the present invention, in _{mass%, SiO 2 50~70%, Al} 2 O 3 1~20%, B 2 O 3 0~15%, alkali metal oxides 1% to 25%, alkaline earth A raw material is prepared so as to become a glass containing 0 to 30% of a metal oxide, melted, and then formed into a plate shape by a downdraw method, whereby a strain point of 530 to 630 ° C., 10 ^2.5 dPa A glass substrate having a temperature corresponding to s of 1370 to 1520 ° C., a viscosity at a liquidus temperature of 100,000 poise or more , a light-transmitting surface being an unpolished surface, a surface waviness of 0.05 μm or less, and a surface roughness of 5 mm or less. It is characterized by manufacturing.

  The glass substrate of the present invention has sufficient heat resistance with respect to a TFT forming temperature of 250 to 350 ° C., and has a glass melting temperature and a molding temperature lower than those of a conventional alkali-free glass substrate, and an overflow down draw. It can be formed into a plate shape by the method.

The glass substrate of the present invention has a strain point of 530 to 630 ° C., a temperature corresponding to 10 ^2.5 dPa · s, 1370 to 1520 ° C., and a viscosity at a liquidus temperature of 100,000 poise or more.

According to the knowledge of the present inventors, when the TFT formation temperature is lowered to 250 to 300 ° C., the heat resistance requirement for the glass substrate is relaxed, and a glass substrate having a strain point of 530 to 630 ° C. can be used. Even if an alkali metal oxide is contained in the glass substrate, such a low temperature process suppresses the diffusion of alkali ions into the semiconductor film, so that the alkali-containing glass substrate can also be used. However, when using an alkali-containing glass substrate, the composition should be regulated so that the amount of alkali elution from the glass is reduced. If necessary, an alkali barrier film may be formed on the surface of the glass substrate. Any alkali barrier film can be used as long as it can prevent alkali ions eluted from the glass substrate from diffusing into the semiconductor film. In particular, considering the film formability and cost, a SiO ₂ or SiNx film is suitable, and a film thickness of 500 mm or more is suitable.

Further, the glass substrate of the present invention has excellent meltability because the temperature corresponding to 10 ^2.5 dPa · s is 1370 to 1520 ° C. That is, since the temperature corresponding to 10 ^2.5 dPa · s is 1520 ° C. or lower, it is possible to melt at a temperature lower than the melting temperature of the conventional alkali-free glass substrate. Therefore, it is suitable as a large glass substrate that requires severe foam quality, such as a glass substrate having a substrate size of 1 m square (1000 × 1000 mm) or more. However, the temperature corresponding to 10 ^2.5 dPa · s is in a trade-off relationship with the strain point, and when the temperature is 1370 ° C. or lower, the strain point is excessively lowered, which is not preferable. Specifically, the strain point can be regulated to 530 to 630 ° C. by regulating the temperature corresponding to 10 ^2.5 dPa · s to 1370 to 1520 ° C.

  Further, since the glass substrate of the present invention has a viscosity at the liquidus temperature of 100,000 poise or more, it can be easily formed into a plate shape by the down draw method, and further can be formed into a plate shape by the overflow down draw method. . That is, when manufacturing a glass substrate by the overflow down draw method, it is requested | required that the devitrification resistance of glass should be high. This is because if the devitrification resistance of the glass is low, devitrification occurs in the glass at the time of molding, and the translucency is impaired. The higher the viscosity at the liquidus temperature, the better the devitrification resistance of the glass. When the value is 100,000 poise or more, actual production by the overflow downdraw method is possible. The overflow down draw method is a molding method in which both surfaces of the glass plate do not come into contact with the molded member at the time of molding, and both surfaces (translucent surface) of the obtained glass substrate have a surface waviness of 0. A high surface quality of 05 μm or less and a surface roughness of 5 mm or less can be easily obtained. It is desirable that the viscosity at the liquidus temperature is 200,000 poise or more, further 400,000 d poise or more, further 800,000 poise or more, and most desirably 1,000,000 poise or more.

  In particular, liquid crystal displays for large TV applications exceeding 20 inches tend to cause display unevenness due to minute deformation of the glass substrate. In order to suppress such deformation, it is necessary to increase the Young's modulus of the glass substrate. There is. The glass substrate of the present invention preferably has a Young's modulus of 65 GPa or more, more preferably 70 GPa or more.

The glass substrate of the present invention is, by mass%, SiO ₂ 50 to 70%, Al ₂ O ₃ 1 to 20%, B ₂ O _{3 0 to} 15%, alkali metal oxide 1 to 25%, alkaline earth metal oxidation. containing 0-30% objects, _{preferably, SiO 2 50~65%, Al 2} O 3 2~15%, B 2 O 3 0~10%, alkali metal oxides 2-20%, alkaline earth metal Contains 2-25% oxide.

  Hereinafter, the reason for limiting the composition of the glass substrate of the present invention as described above will be described.

SiO ₂ is a component that becomes a network former of glass. When the content of SiO ₂ decreases, the glass strain point tends to decrease, the heat resistance decreases, and the chemical durability tends to decrease. On the other hand, when it increases, the high temperature viscosity of the glass tends to increase, and the meltability and formability tend to decrease. Therefore SiO ₂ is 50 to 70%, preferably 50 to 65%.

Al ₂ O ₃ is a component that increases the strain point and Young's modulus of glass and improves devitrification. When the content of Al ₂ O ₃ is reduced, the above effect is reduced. On the other hand, when the content is increased, the high-temperature viscosity of the glass tends to increase, and the meltability and formability tend to decrease. Thus Al ₂ O ₃ is 1-20%, preferably 2-15%, more preferably 2-10%.

B ₂ O ₃ is a component that lowers the high-temperature viscosity of the glass, promotes meltability, and improves chemical resistance, particularly durability against hydrofluoric acid chemicals. However, when the content of B ₂ O ₃ increases, the glass strain point and Young's modulus tend to decrease. Thus B ₂ O ₃ is 0 to 15%, preferably 0-10%, more preferably 0-4%.

Alkali metal oxides (Na ₂ O, K ₂ O, Li ₂ O) are components that dramatically increase the meltability of glass. However, an increase in alkali metal oxide is not preferable because the amount of alkali elution from the glass tends to increase. Therefore, the content of the alkali metal oxide is 1 to 25%, preferably 2 to 20%. In particular, Na ⁺ is an alkali metal ion that is relatively mobile and has a property of easily diffusing into a thin film such as a TFT element. Therefore, the content of Na ₂ O is 0 to 10%, preferably 0 to 8%. More preferably, it should be regulated to 0 to 6%. K ⁺ is an alkali metal ion that is relatively difficult to move, so it can be contained more than Na ₂ O. Specifically, it is 0 to 15%, preferably 0 to 13%. Li ⁺ is a highly mobile alkali metal ion, so Li ₂ O should be kept to a minimum amount. Specifically, it is 0 to 3%, preferably 0 to 1%.

  Alkaline earth metal oxides (MgO, CaO, SrO, BaO) are components that improve the meltability of glass. However, an increase in alkaline earth metal oxide is not preferable because the tendency of glass to devitrify increases. Therefore, the alkaline earth metal oxide is 0 to 30%, preferably 2 to 25%. MgO is a component that lowers the high-temperature viscosity without lowering the strain point of the glass, improves the meltability, and increases the Young's modulus of the glass, but if it is contained in a large amount, the glass tends to be devitrified and the moldability becomes worse. The durability against hydrofluoric acid chemicals is reduced. Therefore, the content of MgO should be regulated to 0 to 10%, preferably 0 to 8%. CaO is a component having the same action as MgO. However, if it is contained in a large amount, it tends to devitrify the glass, making it difficult to mold and reducing the durability against hydrofluoric acid chemicals. Therefore, the content of CaO should be regulated to 0 to 15%, preferably 0 to 10%, more preferably 0 to 7%. SrO and BaO are components that improve the high temperature viscosity of the glass and improve the devitrification resistance and chemical resistance of the glass, although not as much as MgO and CaO. However, if a large amount of SrO or BaO is contained, devitrification due to Sr or Ba is likely to occur, and since these components have high raw material costs, production costs increase. Therefore, SrO should be regulated to 0 to 20%, preferably 0 to 15%, and BaO should be regulated to 0 to 20%, preferably 0 to 15%.

  In the present invention, components other than those described above can be contained within a range that does not impair the properties of the glass. However, if many components other than the above (other components) are contained, the ease of production of the glass is particularly impaired, and specifically, there is a high possibility that the devitrification resistance is lowered. is there. Therefore, the content of other components should be suppressed to 10% or less in total.

For example, ZrO ₂ is a component that is contained for the purpose of improving the chemical durability of glass. However, if it is contained in a large amount, the meltability of the glass is lowered and devitrification is likely to occur during molding. It should be regulated to 0-9%, preferably 0-7%, more preferably 0-5%.

TiO ₂ is a component that prevents the glass from being colored by ultraviolet rays. That is, in the manufacturing process of the liquid crystal display, the glass substrate is exposed to strong ultraviolet rays in a UV cleaning process or the like. In addition, the liquid crystal TV is exposed to ultraviolet rays even during operation because a large number of backlights are arranged on the back surface of the glass substrate in order to ensure the brightness of the screen. Therefore, the glass substrate is required not to be colored by ultraviolet rays. However, since TiO ₂ is a colorant, if this is added too much, the glass may be colored and the transmittance may be reduced. Therefore, TiO ₂ should be regulated to 0 to 5%, preferably 0 to 3%, more preferably 0 to 2%.

Further, it is desirable to contain up to 2% clarifier for the purpose of removing bubbles from the glass. As the fining agent, oxides such as Sb ₂ O ₃ , SnO ₂ , Cl, F, SO ₃ , C, CeO ₂ , Fe ₂ O ₃ , and metal powders such as Al and Si can be used. Note that As ₂ O ₃ is a component that is very effective as a fining agent, and is used in most commercially available non-alkali glass substrates. However, As ₂ O ₃ is a chemical substance with a large environmental load, and it is desirable that it is not substantially contained. Since the glass substrate of the present invention is excellent in meltability, even if a component other than As ₂ O ₃ is used as a clarifier, a high clarification action can be obtained and an excellent foam quality can be obtained.

Among other components, chemical substances with a large environmental load, such as PbO, ZnO, Cr ₂ O ₃ , V ₂ O ₅ , CdO, and TlO ₂ , should be contained as little as possible. Specifically, it is desirable that each content is less than 3%, preferably less than 1%, and further not substantially contained.

  Hereinafter, the glass substrate of this invention is demonstrated based on an Example.

  Tables 1 and 2 show examples.

  The glass substrates of Tables 1 and 2 were produced as follows. First, the raw materials were prepared so as to have the glass composition in the table, put into a platinum crucible, melted in an electric furnace at a temperature of 1500 to 1550 ° C. for 4 hours, and the molten glass was poured out onto the carbon plate. Formed into a shape. Subsequently, the glass substrate was produced by grind | polishing both surfaces of this glass plate.

Each glass substrate thus obtained was evaluated for density, thermal expansion coefficient, strain point, viscosity of 10 ^2.5 dPa · s, liquid phase temperature, viscosity at liquid phase temperature, thermal expansion coefficient, Young's modulus, chemical resistance, The results are shown in the table. As is apparent from the table, each glass substrate has a strain point of 520 ° C. or higher and a viscosity at the liquidus temperature of 120,000 poise or higher, so it has excellent devitrification resistance and is suitable for the overflow down draw method. there were. Further, since the temperature corresponding to 10 ^2.5 dPa · s was 1515 ° C. or less, the meltability was excellent. In addition, the Young's modulus and chemical resistance were sufficient for use as a glass substrate for TFT liquid crystal displays used in large TVs.

In addition, the density in a table | surface was calculated | required by the well-known Archimedes method. The thermal expansion coefficient is obtained by measuring an average thermal expansion coefficient in a temperature range of 30 to 380 ° C. using a dilatometer. The strain point was measured based on the method of ASTM C336-71. The 10 ^2.5 poise temperature was measured at a temperature of 10 ^2.5 poise, which is a high temperature viscosity, by a known platinum ball pulling method. The liquid phase temperature was obtained by putting glass powder having a particle size of 297 to 500 μm in a platinum boat, holding it in a temperature gradient furnace for 48 hours, and observing the temperature when devitrification was deposited. The viscosity at the liquidus temperature was obtained by determining the viscosity of the glass when devitrification was precipitated. The acid resistance was evaluated as ◯ when the glass surface was visually observed after the glass substrate was immersed in the chemical solution and there was no change at all. The treatment with the chemical solution was performed using 10% hydrochloric acid at 80 ° C. for 3 hours. The alkali elution amount was measured based on the method described in JIS R3502.

  Next, sample Nos. After melting 1 to 3 glasses, the glass was formed into a plate shape by the overflow downdraw method to produce a glass substrate having a size of 1000 × 1000 × 0.7 mm, and then the surface waviness and surface roughness were measured. The results are shown in Table 3.

  As apparent from Table 3, the surface waviness of each glass substrate was 0.04 μm or less, the surface roughness was 1 to 2 mm, and all had high surface quality. The surface waviness is measured by a method according to SEMI STD D15-1296 “Measurement method of surface waviness of FPD glass substrate”, and the cut-off at the time of measurement is 0.8 to 8 mm with respect to the drawing direction of the glass substrate. Measurements were taken in the vertical direction to determine the maximum value of the swell. Further, the surface roughness was measured by a method based on SEMI D7-94 “Measurement Method of Surface Roughness of FPD Glass Substrate”, the cut-off at the time of measurement was 0.08 mm, and the measurement length was 0.4 mm.

Further, when SiO ₂ films were formed on both light-transmitting surfaces of the glass substrate by sputtering, a homogeneous film having an average thickness of 1000 mm was obtained.

  The glass substrate of the present invention is a flat panel display such as a liquid crystal display, an organic EL display or a plasma display, a charge coupled device (CCD), an equal magnification proximity solid-state imaging device (CIS), various image sensors such as a CMOS image sensor, a hard disk. It can be applied to filters and the like, and is particularly suitable for TV liquid crystal displays.

Claims (9)

In mass%, SiO ₂ 50-70%, Al ₂ O ₃ 1-20%, B ₂ O ₃ 0-15%, alkali metal oxide 1-25%, alkaline earth metal oxide 0-30% The strain point is 530 to 630 ° C., the temperature corresponding to 10 ^2.5 dPa · s is 1370 to 1520 ° C., the viscosity at the liquidus temperature is 100,000 poise or more, and the light transmitting surface is an unpolished surface , A glass substrate having a surface waviness of 0.05 μm or less and a surface roughness of 5 mm or less . Glass, in _{mass%, SiO 2 50~65%, Al} 2 O 3 2~15%, B 2 O 3 0~10%, alkali metal oxides 2-20% alkaline earth metal oxide 2-25 The glass substrate according to claim 1 , comprising:%. Glass substrate according to claim 1 or 2 Young's modulus is equal to or not less than 65 GPa. The glass substrate according to any one of claims 1 to 3 , wherein an alkali barrier film is formed on one or both light-transmitting surfaces. It uses as a glass substrate for liquid crystal displays, The glass substrate in any one of Claims 1-4 characterized by the above-mentioned. In mass%, SiO ₂ 50-70%, Al ₂ O ₃ 1-20%, B ₂ O ₃ 0-15%, alkali metal oxide 1-25%, alkaline earth metal oxide 0-30% The raw material is prepared so as to be glass to be melted, melted, and then formed into a plate shape by a downdraw method, whereby a temperature corresponding to a strain point of 530 to 630 ° C. and 10 ^2.5 dPa · s is 1370 to 1520. A glass substrate characterized by producing a glass substrate having a viscosity at 100 ° C. and a liquidus temperature of 100,000 poise or more , a translucent surface being an unpolished surface, a surface waviness of 0.05 μm or less, and a surface roughness of 5 mm or less. Manufacturing method. Glass, in _{mass%, SiO 2 50~65%, Al} 2 O 3 2~15%, B 2 O 3 0~10%, alkali metal oxides 2-20% alkaline earth metal oxide 2-25 %. The manufacturing method of the glass substrate of Claim 6 characterized by the above-mentioned. The method for producing a glass substrate according to claim 6 or 7, wherein the downdraw method is an overflow downdraw method. A glass substrate is used as a glass substrate for liquid crystal displays, The manufacturing method of the glass substrate in any one of Claims 6-8 characterized by the above-mentioned.