Alkali-free glass

Abstract

To provide a low-thermal-shrinkage non-alkali glass, the glass being less prone to problems due to BHF, having high productivity, and a low thermal shrinkage.SOLUTION: Provided is a non-alkali glass having a strain point of 690°C or higher and 738°C or lower, an average thermal expansion coefficient of 30×10-7 to 45×10-7 / °C at 50 to 350°C, a Young's modulus of 77-86 GPa, containing SiO2, Al2O3, B2O3, MgO, CaO and SrO, with SiO2, Al2O3, B2O3, MgO and CaO being specific contents, the total amount of the MgO+CaO+SrO+BaO being 18.0% or less, CaO / (MgO+CaO+SrO+BaO) being 0.22 or more and 0.59 or less, SrO / (MgO+CaO+SrO+BaO) being 0.06 or more and 0.52 or less, Na2O / B2O3 being 0.001 or more and 0.3 or less, and the content of alkali metal oxide being 1000 mass ppm or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an alkali-free glass that is suitable for use as a substrate glass for various displays or a substrate glass for photomasks, does not substantially contain alkali metal oxides, and can be float-formed. Hereinafter, in this specification, the term "alkali-free" means that the content of alkali metal oxides (Li2O, Na2O, K2O) is 1000 mass ppm or less. [Background technology]

[0002] Conventionally, various types of display substrate glass, particularly those on whose surfaces a thin metal or oxide film is formed, have been required to have the following characteristics: (1) If alkali metal oxides are contained, alkali metal ions will diffuse into the thin film and deteriorate the film characteristics, so the content of alkali metal oxides must be extremely low; specifically, the content of alkali metal oxides must be 1,000 ppm by mass or less. (2) The deformation of the glass substrate due to heating during the thin film formation process, particularly thermal shrinkage, is minimal. In other words, the thermal shrinkage rate is small.

[0003] (3) It has sufficient chemical durability against various chemicals used in semiconductor formation. In particular, SiO x and SiN x It must be resistant to buffered hydrofluoric acid (BHF: a mixture of hydrofluoric acid and ammonium fluoride) used in etching of ITO, chemical solutions containing hydrochloric acid used in etching ITO, various acids (nitric acid, sulfuric acid, etc.) used in etching metal electrodes, and alkalis used in resist stripping solutions. (4) There are no internal or surface defects (bubbles, veins, inclusions, pits, scratches, etc.).

[0004] In addition to the above demands, the following situation has arisen in recent years: (5) There is a demand for lighter displays, and the glass itself needs to have a low density. (6) There is a demand for lighter displays, and therefore thinner substrate glass is desirable.

[0005] (7) In addition to the amorphous silicon (a-Si) type liquid crystal displays that have been used up until now, polycrystalline silicon (p-Si) type liquid crystal displays, which have a slightly higher heat treatment temperature, are now being produced (a-Si: approximately 350°C → p-Si: 350-550°C). (8) In order to increase the rate of temperature rise and fall in the heat treatment for the production of liquid crystal displays, thereby improving productivity and improving thermal shock resistance, glass with a small average coefficient of thermal expansion is required.

[0006] On the other hand, as dry etching progresses, the demand for BHF resistance is becoming weaker. Until now, glass containing 6 to 10 mol% B2O3 has been widely used to improve BHF resistance. However, B2O3 tends to lower the strain point. Examples of non-alkali glass that does not contain B2O3 or contains only a small amount of it are as follows:

[0007] Patent Document 1 discloses glass containing 0 to 3% by weight of B2O3, but the strain point in the examples is 690°C or lower.

[0008] Patent Document 2 discloses glass containing 0 to 5 mol % of B2O3, but the average thermal expansion coefficient at 50 to 350°C is 50 × 10 -7 / ℃.

[0009] In order to solve the problems with the glasses described in Patent Documents 1 and 2, an alkali-free glass described in Patent Document 3 has been proposed. The alkali-free glass described in Patent Document 3 has a high strain point, can be formed by a float method, and is said to be suitable for applications such as display substrates and photomask substrates. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 4-325435 [Patent Document 2] Japanese Patent Application Publication No. 5-232458 [Patent Document 3] Japanese Patent Publication No. 9-263421 Summary of the Invention [Problem to be solved by the invention]

[0011] In recent years, for high-definition small displays of mobile terminals such as smartphones, a method using laser annealing has been adopted as a manufacturing method for high-quality p-Si TFTs. However, in order to improve the commercial value, even higher definition is desired, and therefore glass with even smaller thermal shrinkage is required. On the other hand, due to requirements in the glass manufacturing process, especially float molding, the viscosity of glass, especially the glass viscosity, is required to be 10 4 It is necessary to lower the temperature T4 at which the glass becomes dPa·s and the devitrification temperature, and also to prevent the strain point from being excessively high.

[0012] As mentioned above, alkali-free glass used as substrate glass for various displays and substrate glass for photomasks is required to have a smaller thermal shrinkage. To achieve this, it is effective to change the main component composition of the glass to increase the strain point or to reduce the cooling rate of the glass. However, if the thermal shrinkage rate after heat treatment at 600°C for 80 minutes falls below 50 ppm, the influence of various impurities in the glass cannot be ignored.

[0013] In particular, alkali components (R2O: R is an alkali metal element such as Li, Na, or K) that are inevitably mixed in from the raw materials move quickly in the glass structure and therefore have a large effect on the thermal shrinkage rate, and in particular in glasses containing B2O3 components, the alkali components affect the coordination number of boron and cause changes in the glass structure, so the content ratio of alkali components to B2O3 components (R2O / B2O3 ratio) is an important parameter. However, in conventional alkali-free glasses, the R2O / B2O3 ratio has not been considered important, and because the B2O3 content is high, even when the content is, for example, 0.1 wt% (1000 ppm), which is considered to be the upper limit for alkali-free glasses, the R2O / B2O3 ratio is only about 0.02 or less, which is very small.

[0014] When the amount of B2O3 is reduced in order to obtain a low thermal shrinkage glass, the amount of alkali components must be further reduced in order to reduce this ratio. In order to reduce the amount of alkali components extremely, it is sufficient to use extremely high purity raw materials, but using such high purity raw materials is not preferable because it increases the cost. On the other hand, since the alkali components act as fluxes and improve the initial solubility, reducing the amount too much may lead to defects and a deterioration in quality.

[0015] In addition, since the alkaline components are impurities, they are difficult to control. Therefore, if there is any variation, there is a high possibility that the thermal shrinkage rate will vary between lots. On the other hand, due to the recent trend toward higher resolution displays, the variation between lots is of great concern because it may increase the defective rate in the panel manufacturing process.

[0016] An object of the present invention is to solve the above problems and to provide an alkali-free glass having a low thermal shrinkage rate, which is less susceptible to problems due to BHF, has good productivity, and has a low thermal shrinkage rate. [Means for solving the problem]

[0017] The present invention relates to a sintered body having a strain point of 680°C or more and less than 738°C, and an average thermal expansion coefficient of 30×10 at 50 to 350°C. -7 ~45×10-7 / ℃, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis. SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0-10% BaO: 1.3-5% MgO+CaO+SrO+BaO: 13~23% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) of 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) of 0.15 or more, CaO / (MgO+CaO+SrO+BaO) of 0.60 or less, SrO / (MgO+CaO+SrO+BaO) of 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) of 0.50 or less. The present invention also provides a sintered body having a strain point of 680° C. or higher and an average thermal expansion coefficient of 35×10 at 50 to 350° C. -7 / ℃ over 45×10 -7 / ℃ or less, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis, SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0-10% BaO: 1.3-5% MgO+CaO+SrO+BaO: 13~23% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) of 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) of 0.15 or more, CaO / (MgO+CaO+SrO+BaO) of 0.60 or less, SrO / (MgO+CaO+SrO+BaO) of 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) of 0.50 or less. The present invention also provides a sintered body having a strain point of 680° C. or higher and an average thermal expansion coefficient of 30×10 at 50 to 350° C. -7 ~45×10 -7 / ℃, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis. SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0 to 6.5% BaO: 1.3-5% MgO+CaO+SrO+BaO: 13~23% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) of 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) of 0.15 or more, CaO / (MgO+CaO+SrO+BaO) of 0.60 or less, SrO / (MgO+CaO+SrO+BaO) of 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) of 0.50 or less. The present invention also relates to a sintered body having a strain point of 680° C. or more and less than 738° C. and an average thermal expansion coefficient of 30×10 at 50 to 350° C. -7 ~45×10 -7 / ℃, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis. SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0-10% BaO: 0-5% MgO+CaO+SrO+BaO: 13% or more, less than 17% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) of 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) of 0.15 or more, CaO / (MgO+CaO+SrO+BaO) of 0.60 or less, SrO / (MgO+CaO+SrO+BaO) of 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) of 0.50 or less. The present invention also provides a sintered body having a strain point of 680° C. or higher and an average thermal expansion coefficient of 35×10 at 50 to 350° C. -7 / ℃ over 45×10 -7 / ℃ or less, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis, SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0-10% BaO: 0-5% MgO+CaO+SrO+BaO: 13% or more, less than 17% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) of 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) of 0.15 or more, CaO / (MgO+CaO+SrO+BaO) of 0.60 or less, SrO / (MgO+CaO+SrO+BaO) of 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) of 0.50 or less. The present invention also provides a sintered body having a strain point of 680° C. or higher and an average thermal expansion coefficient of 30×10 at 50 to 350° C. -7 ~45×10 -7 / ℃, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis. SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0 to 6.5% BaO: 0-5% MgO+CaO+SrO+BaO: 13% or more, less than 17% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) of 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) of 0.15 or more, CaO / (MgO+CaO+SrO+BaO) of 0.60 or less, SrO / (MgO+CaO+SrO+BaO) of 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) of 0.50 or less. The present invention also provides a sintered body having a strain point of 680° C. or higher and 718° C. or lower, and an average thermal expansion coefficient of 30×10 at 50 to 350° C. -7 ~45×10 -7 / ℃, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis. SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0-6% BaO: 0-5% MgO+CaO+SrO+BaO: 13~23% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) is 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) is 0.15 or more, CaO / (MgO+CaO+SrO+BaO) is 0.28 or more and 0.60 or less, SrO / (MgO+CaO+SrO+BaO) is 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) is 0.50 or less. The present invention also provides a sintered body having a strain point of 680° C. or higher and 718° C. or lower, and an average thermal expansion coefficient of 35×10 at 50 to 350° C. -7 / ℃ over 45×10 -7 / ℃ or less, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis, SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0-6% BaO: 0-5% MgO+CaO+SrO+BaO: 13~23% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) is 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) is 0.15 or more, CaO / (MgO+CaO+SrO+BaO) is 0.28 or more and 0.60 or less, SrO / (MgO+CaO+SrO+BaO) is 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) is 0.50 or less. The present invention also provides a sintered body having a strain point of 680° C. or higher and 718° C. or lower, and an average thermal expansion coefficient of 30×10 at 50 to 350° C. -7 ~45×10 -7 / ℃, devitrification viscosity η is log η = 3.5 [dPa s] or more, and expressed as mass% on an oxide basis. SiO2: 57-63% Al2O3: 18-23% B2O3: 0.2-5.5% MgO: 1-8.5% CaO: 3-12% SrO: 0-6% BaO: 0-5% MgO+CaO+SrO+BaO: 13~23% and 600 ppm by mass or less of Na2O, a mass ratio of Na2O to B2O3 (Na2O / B2O3) is 0.001 or more and 0.3 or less, MgO / (MgO+CaO+SrO+BaO) is 0.15 or more, CaO / (MgO+CaO+SrO+BaO) is 0.28 or more and 0.60 or less, SrO / (MgO+CaO+SrO+BaO) is 0.70 or less, and BaO / (MgO+CaO+SrO+BaO) is 0.50 or less. Effect of the Invention

[0018] The alkali-free glass of the present invention is particularly suitable for applications requiring a small thermal shrinkage rate, such as display substrates and photomask substrates, and is also easy to form by float forming. The alkali-free glass of the present invention can also be used as a glass substrate for magnetic disks. Moreover, because there is little variation in the thermal shrinkage rate due to the content of Na2O, which accounts for the majority of the alkali metal oxides inevitably mixed in from the raw materials, the possibility of variation in the thermal shrinkage rate between lots is suppressed, which is said to reduce the defective rate in the panel manufacturing process. [Brief description of the drawings]

[0019] [Figure 1] Figure 1 is a graph comparing the relationship between Na2O / B2O3 and C / C0. [Diagram 2] FIG. 2 shows a schematic diagram of a bottom gate structure. [Diagram 3] FIG. 3 shows the results of a TFT characteristic test carried out on Example 1. [Figure 4] FIG. 4 shows the results of a TFT characteristic test carried out on Example 9. [Diagram 5]FIG. 5 shows the results of a TFT characteristic test carried out on Example 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Next, the composition range of each component will be described. If the SiO2 content is less than 54% (mass%, the same applies hereinafter unless otherwise specified), the strain point does not rise sufficiently, and the thermal expansion coefficient increases, resulting in an increase in density, so the SiO2 content is 54% or more. When float molding is adopted as the molding method for using the alkali-free glass of the present invention as a display substrate or a photomask substrate, the SiO2 content is preferably 57% or more. On the other hand, when fusion molding is adopted as the molding method, the SiO2 content is preferably 58% or more.

[0021] If the SiO2 content exceeds 66%, the solubility decreases and the glass viscosity becomes 10 2 The temperature T2 and 10 4 The temperature T4 at which the viscosity becomes dPa s rises, and the devitrification temperature also rises, so the viscosity must be 66% or less. If float molding is used as the forming method, 63% or less is preferable. On the other hand, if fusion molding is used as the forming method, 65% or less is preferable.

[0022] Al2O3 suppresses the phase separation of glass, lowers the thermal expansion coefficient, and raises the strain point, but if it is less than 10%, this effect is not seen, and it also increases other components that increase expansion, resulting in large thermal expansion, so it is 10% or more. If float molding is used as the molding method, 18% or more is preferable. On the other hand, if fusion molding is used as the molding method, 14% or more is preferable.

[0023] If Al2O3 exceeds 27%, the melting property of the glass may deteriorate or the devitrification temperature may increase, so the content is set to 27% or less. When float molding is used as the forming method, the content is preferably 23% or less. On the other hand, when fusion molding is used as the forming method, the content is preferably 22% or less.

[0024] B2O3 improves the melting reactivity of glass, lowers the devitrification temperature, and improves BHF resistance, but if it is less than 0.2%, this effect is not fully exhibited, and the strain point becomes excessively high, making it difficult to form into a plate, and is prone to haze problems after treatment with BHF, so it is 0.2% or more. 0.3% or more is preferable, 0.5% or more is more preferable, 1% or more is even more preferable, and 1.5% or more is particularly preferable. However, if it exceeds 5.5%, the strain point becomes low and the Young's modulus becomes small, so it is 5.5% or less. 4.5% or less is preferable, 4% or less is more preferable, 3.5% or less is even more preferable, and 3% or less is even more preferable.

[0025] MgO is not essential, but it can be included to improve solubility because it does not increase expansion among alkaline earth metals and has the characteristic of increasing Young's modulus while maintaining low density. However, if it is too much, the devitrification temperature increases, so it is set to 10% or less. When float molding is used as the molding method, 1% or more is preferable. When float molding is used as the molding method, 8.5% or less is preferable. On the other hand, when fusion molding is used as the molding method, 6% or less is preferable.

[0026] CaO is not essential, but it can be included because it has the characteristic of not increasing expansion in alkaline earth metals, second only to MgO, and increasing Young's modulus while maintaining low density, and also improving solubility. However, if it is too much, the devitrification temperature may rise and there is a risk of a large amount of phosphorus, an impurity in limestone (CaCO3), the raw material for CaO, being mixed in, so it is set to 15% or less. 12% or less is preferable. In order to exert the above characteristics, 3% or more is preferable.

[0027] SrO is not essential, but can be contained to improve the melting property without increasing the devitrification temperature of the glass. However, if it is too much, the expansion coefficient may increase, so the content is set to 15% or less. It is preferably 10% or less, more preferably 6.5% or less, even more preferably 6% or less, and even more preferably 5.5% or less.

[0028] BaO is not essential, but can be contained to improve solubility. However, if it is too much, it will excessively increase the expansion and density of the glass, so it is set to 15% or less. When float molding is used as the molding method, it is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. On the other hand, when fusion molding is used as the molding method, it is preferably 10% or less, more preferably 8% or less, even more preferably 6% or less, and even more preferably 4% or less. In either case, it is more preferable that it is not substantially contained. "Substantially not contained" means that it is not contained except for unavoidable impurities. In the present invention, "substantially not contained" means, for example, 0.15% or less of BaO.

[0029] If the total amount of MgO, CaO, SrO, and BaO is less than 8%, the photoelastic constant tends to increase and the solubility tends to decrease, so it is 8% or more. Since it is preferable to contain a large amount of MgO, CaO, SrO, and BaO in order to reduce the photoelastic constant, the total amount of MgO, CaO, SrO, and BaO is more preferably 10% or more, even more preferably 13% or more, and particularly preferably 16% or more. If it is more than 25%, the average thermal expansion coefficient cannot be reduced and the strain point may be lowered, so it is 25% or less. It is preferably 22% or less, and even more preferably 20% or less.

[0030] When float forming is used as the forming method, the total amount of MgO, CaO, SrO and BaO satisfies the above, more preferably 13 to 23%, and also satisfies the following condition, so that the Young's modulus and specific elastic modulus can be increased and the viscosity of the glass, in particular T4, can be reduced without increasing the devitrification temperature. MgO / (MgO+CaO+SrO+BaO) is 0.15 or more, preferably 0.20 or more, and more preferably 0.25 or more. CaO / (MgO+CaO+SrO+BaO) is 0.60 or less, preferably 0.55 or less, and more preferably 0.50 or less. SrO / (MgO+CaO+SrO+BaO) is 0.70 or less, preferably 0.60 or less, and more preferably 0.50 or less. BaO / (MgO+CaO+SrO+BaO) is 0.50 or less, preferably 0.45 or less, and more preferably 0.40 or less.

[0031] When fusion molding is used as the molding method, it is preferable that the total content of MgO, CaO, SrO and BaO satisfies the above, more preferably satisfies the range of 8 to 22%, and also satisfies the following condition. MgO / (MgO+CaO+SrO+BaO) is 0.25 or less, preferably 0.20 or less, and more preferably 0.15 or less. CaO / (MgO+CaO+SrO+BaO) is 0.20 or more, preferably 0.30 or more, and more preferably 0.40 or more. SrO / (MgO+CaO+SrO+BaO) is 0.50 or less, preferably 0.45 or less, and more preferably 0.40 or less. BaO / (MgO+CaO+SrO+BaO) is 0.70 or less, preferably 0.50 or less, and more preferably 0.40 or less.

[0032] In order to facilitate recycling of the glass, it is preferable that the glass of the present invention contains substantially no PbO, As2O3, or Sb2O3.

[0033] For the same reason, it is preferable that the P2O5 content is substantially zero. The amount of P2O5 mixed in as an impurity is preferably 80 ppm by mass or less, more preferably 70 ppm by mass or less, further preferably 60 ppm by mass or less, and particularly preferably 50 ppm by mass or less.

[0034] In the glass of the present invention, alkali metal oxides are inevitably contained due to raw material impurities, and a very small amount of alkali metal oxide is allowed to be contained in order to improve solubility. However, if the content of alkali metal oxides is too high, the migration of alkali ions into the TFT element becomes significant, causing the transistor characteristics to become unstable and the reliability to be lost, so the content must be kept within an appropriate range.

[0035] Since Na2O accounts for the majority of alkali metal oxides inevitably mixed in from the raw materials, the present invention focuses on the content of Na2O. The glass of the present invention has a Na2O content of 600 mass ppm or less, preferably less than 600 mass ppm, more preferably 500 mass ppm or less, even more preferably 400 mass ppm or less, and even more preferably 300 mass ppm or less. It is particularly preferably 200 ppm or less, and most preferably 150 ppm or less.

[0036] However, when the alkali metal oxides inevitably mixed in from the raw material contain a significant amount of components other than Na2O (for example, K2O) (for example, when these components are contained in an amount of 100 mass ppm or more), the total content of alkali metal oxides including components other than Na2O is preferably 700 mass ppm or less, more preferably less than 700 mass ppm, even more preferably 600 mass ppm or less, even more preferably 500 mass ppm or less, even more preferably 400 mass ppm or less, particularly preferably 300 mass ppm or less, and most preferably 200 mass ppm or less.

[0037] On the other hand, since the alkali metal oxide in the glass acts as a flux to improve the initial solubility, if the content of the alkali metal oxide is too low, the glass produced may have defects and the quality may be deteriorated. The glass of the present invention preferably has a Na2O content of 50 ppm by mass or more, more preferably 100 ppm by mass or more.

[0038] The glass of the present invention contains a specified amount of B2O3 to enhance BHF resistance, and the inventors have found that by optimizing the ratio of Na2O, which accounts for the majority of the alkali metal oxides inevitably mixed in from the raw materials, to B2O3 in such glass, it is possible to achieve both good melting properties and low thermal shrinkage of the glass. This is believed to be due to the following.

[0039] The thermal shrinkage phenomenon occurs at the glass transition temperature (T g) is due to structural relaxation occurring near T g Since the bonds are easily changed by the above, the structural change due to the fictive temperature is large, and it is thought that thermal shrinkage is likely to occur. When a small amount of alkali ions are added to such glass, the alkali ions easily change boron to four-coordination. In addition, since the diffusion coefficient of alkali ions is large, they move more easily than alkaline earth ions. Therefore, when the alkali ions are in excess of the amount of boron, the rate of structural change increases, resulting in large thermal shrinkage. When the mass ratio (Na2O / B2O3) of Na2O, which accounts for the majority of the alkali metal oxides, exceeds 0.3, this effect becomes large, and the thermal shrinkage rate becomes unnecessarily large.

[0040] For the above reasons, Na2O / B2O3 is 0.3 or less, preferably 0.2 or less, more preferably 0.12 or less, even more preferably 0.08 or less, even more preferably 0.06 or less, and even more preferably 0.04 or less. If Na2O / B2O3 is too small, the initial solubility may decrease and the quality may deteriorate, so it is 0.001 or more. It is preferably 0.002 or more, more preferably 0.003 or more, and particularly preferably 0.005 or more.

[0041] The alkali-free glass of the present invention has a predetermined B2O3 content, and when the B2O3 content is within a predetermined range, there is little variation in the thermal shrinkage caused by Na2O / B2O3. Since Na2O is inevitably mixed in from the raw materials, it is difficult to strictly control the Na2O content. Since the alkali-free glass of the present invention has little variation in the thermal shrinkage caused by Na2O / B2O3, there is little variation in the thermal shrinkage caused by the content of Na2O that is inevitably mixed in from the raw materials. Therefore, the possibility of variation in the thermal shrinkage between lots is suppressed.

[0042] Furthermore, in the present invention, the inventors have found that the smaller the B2O3 content, the easier it is for alkali ions to diffuse from the glass surface to the mating member such as a TFT. In other words, the inventors have found that by reducing the content of alkali ions relative to the content of B2O3, it is possible to suppress the diffusion of alkali ions into the TFT element and improve the characteristics of the TFT element. To fully obtain this effect, Na2O / B2O3 is preferably less than 0.06, more preferably 0.05 or less, even more preferably 0.04 or less, even more preferably 0.02 or less, particularly preferably 0.01 or less, and most preferably 0.008 or less.

[0043] In addition to the above components, the alkali-free glass of the present invention may contain ZnO, Fe2O3, SO3, F, Cl, and SnO2 in a total amount of preferably 2% or less, more preferably 1% or less, even more preferably 0.5% or less, and most preferably 0.1% or less in order to improve the solubility, clarity, and formability (float formability) of the glass. It is more preferable that the glass is substantially free of ZrO2 and ZnO.

[0044] The alkali-free glass of the present invention has a strain point of 680°C or higher. Since the alkali-free glass of the present invention has a strain point of 680°C or higher, thermal shrinkage during panel manufacturing can be suppressed. In addition, a laser annealing method can be applied as a manufacturing method for p-Si TFT. A strain point of 685°C or higher is more preferable, and a strain point of 690°C or higher is even more preferable.

[0045] The alkali-free glass of the present invention has a strain point of 680° C. or higher, and is therefore suitable for high strain point applications (e.g., thin display substrates or lighting substrates having a plate thickness of 0.7 mm or less, preferably 0.5 mm or less, more preferably 0.3 mm or less, and even more preferably 0.1 mm or less). In forming such thin glass, the drawing speed during forming tends to be fast, which increases the fictive temperature of the glass and tends to increase the thermal shrinkage of the glass. In this case, the high strain point glass of the present invention can suppress the thermal shrinkage.

[0046] On the other hand, the alkali-free glass of the present invention preferably has a strain point of 780° C. or less. If the strain point of the alkali-free glass is too high, the temperature of the forming apparatus must be increased accordingly, which tends to shorten the life of the forming apparatus. For this reason, the strain point of the alkali-free glass of the present invention is more preferably 750° C. or less, even more preferably 740° C. or less, and particularly preferably 730° C. or less.

[0047] For the same reasons as for the strain point, the alkali-free glass of the present invention has a glass transition point of preferably 730° C. or higher, more preferably 740° C. or higher, and even more preferably 750° C. or higher. The glass transition point is preferably 840° C. or lower, more preferably 820° C. or lower, and particularly preferably 800° C. or lower.

[0048] In addition, the alkali-free glass of the present invention has an average thermal expansion coefficient of 30×10 -7 ~45×10 -7 / °C, the thermal shock resistance is high, and the productivity during panel production can be increased. In the alkali-free glass of the present invention, the average thermal expansion coefficient at 50 to 350°C is preferably 35×10 -7 / °C or more. The average thermal expansion coefficient at 50 to 350°C is preferably 43×10 -7 / ℃ or less, more preferably 41×10 -7 / ℃ or less, more preferably 40×10 -7 / ℃ or less.

[0049] Furthermore, the alkali-free glass of the present invention has a specific gravity of preferably 2.70 or less, more preferably 2.65 or less, and even more preferably 2.60 or less.

[0050] In addition, the alkali-free glass of the present invention has a viscosity of 10 2 The temperature T2 at which the melting point becomes dPa·s is 1800°C or lower, preferably 1750°C or lower, more preferably 1700°C or lower, further preferably 1680°C or lower, and particularly preferably 1670°C or lower, so that melting is relatively easy.

[0051] Furthermore, the alkali-free glass of the present invention has a viscosity of 10 4The temperature T4 at which the melt viscosity becomes dPa·s is 1350° C. or less, preferably 1325° C. or less, more preferably 1300° C. or less, and even more preferably less than 1300° C., 1295° C. or less, or 1290° C. or less, which is preferable for float molding.

[0052] The alkali-free glass of the present invention preferably has a devitrification temperature of 1300°C or less, since this facilitates forming by the float method. More preferably, it is less than 1300°C, even more preferably 1290°C or less, and most preferably 1280°C or less. The temperature T4 (when the glass viscosity is 10°C) is an index of float formability and fusion formability. 4 The difference between the temperature at which the viscosity becomes dPa s (unit: °C) and the devitrification temperature (T4 - devitrification temperature) is preferably -20°C or higher, more preferably -10°C or higher, even more preferably 0°C or higher, still more preferably 10°C or higher, particularly preferably 20°C or higher, and most preferably 30°C or higher.

[0053] In this specification, the devitrification temperature is the average value of the maximum temperature at which crystals precipitate on the surface and inside of the glass and the minimum temperature at which crystals do not precipitate, when crushed glass particles are placed in a platinum dish and heat-treated for 17 hours in an electric furnace controlled at a constant temperature, and observed with an optical microscope after the heat treatment.

[0054] When float forming is employed as the forming method for the alkali-free glass of the present invention, the devitrification viscosity η [dPa·s] preferably is log η = 3.5 or more. In this specification, the devitrification viscosity η is the viscosity value at the devitrification temperature. On the other hand, when fusion molding is used as the molding method, it is preferable that the devitrification viscosity η is log η = 4.5 [dPa·s] or more.

[0055] The alkali-free glass of the present invention has a Young's modulus of preferably 78 GPa or more, more preferably 79 GPa or more, more preferably 80 GPa or more, even more preferably 81 GPa or more, and even more preferably 82 GPa or more.

[0056] In addition, the alkali-free glass of the present invention preferably has a photoelastic constant of 31 nm / MPa / cm or less. When the glass substrate has birefringence due to stress generated during the liquid crystal display panel manufacturing process or during use of the liquid crystal display device, a phenomenon in which black display becomes gray and the contrast of the liquid crystal display decreases may be observed. By setting the photoelastic constant to 31 nm / MPa / cm or less, this phenomenon can be suppressed to a minimum. It is preferably 30 nm / MPa / cm or less, more preferably 29 nm / MPa / cm or less, even more preferably 28.5 nm / MPa / cm or less, and particularly preferably 28 nm / MPa / cm or less.

[0057] In addition, in consideration of the ease of ensuring other physical properties, the alkali-free glass of the present invention preferably has a photoelastic constant of 21 nm / MPa / cm or more, more preferably 23 nm / MPa / cm or more, and even more preferably 25 nm / MPa / cm or more. The photoelastic constant can be measured by a disk compression method at a measurement wavelength of 546 nm.

[0058] The alkali-free glass of the present invention can be produced, for example, by the following method: Raw materials for each component that are usually used are mixed to obtain the target composition, and this is continuously charged into a melting furnace and melted by heating to 1500 to 1800° C. The molten glass is formed into a plate of a predetermined thickness by a float method or a fusion method, slowly cooled, and then cut to obtain a plate glass. Since the glass of the present invention has a relatively low solubility, it is preferable to use the following as the raw materials for each component.

[0059] In addition, the alkali-free glass of the present invention preferably has a small amount of shrinkage during heat treatment. In liquid crystal panel manufacturing, the array side and the color filter side are subjected to different heat treatment steps. Therefore, in particular in high-definition panels, if the thermal shrinkage rate of the glass is large, there is a problem that dots are misaligned during fitting.

[0060] The thermal shrinkage can be evaluated and measured using the following procedure. After holding the sample at a temperature of glass transition point + 100°C for 10 minutes, it is cooled to room temperature at 40°C per minute. At this point, the total length L1 of the sample is measured. After that, it is heated to 600°C at 100°C / hour, held at 600°C for 80 minutes, cooled to room temperature at 100°C / hour, and the total length L2 of the sample is measured again.

[0061] Here, the thermal shrinkage rate C (ppm) can be calculated by the following formula. C = (L1-L2) / L1 x 10 6

[0062] In the above evaluation method, the heat shrinkage rate is preferably 90 ppm or less, more preferably 80 ppm or less, further preferably 70 ppm or less, further preferably 60 ppm or less, and particularly preferably 50 ppm or less.

[0063] The alkali-free glass of the present invention can incorporate a manufacturing method for improving low thermal shrinkage. Specifically, for example, the equivalent cooling rate is set to 400° C. / min or less. Here, the definition and evaluation method of the equivalent cooling rate are as follows.

[0064] Glass processed into a 10mm x 10mm x 1mm rectangular parallelepiped is held at Tg+120°C for 5 minutes in an infrared heating electric furnace, and then the glass is cooled to room temperature (25°C). At this time, multiple glass samples are produced at cooling rates ranging from 1°C / min to 1000°C / min. Using Shimadzu Devices KPR2000, the refractive index n d is measured by the V-block method. d is plotted against the logarithm of the cooling rate to obtain n d Obtain a calibration curve. Next, we will examine the actual glass produced through processes such as melting, forming, and cooling on the production line. d is measured by the above-mentioned measurement method. d The corresponding cooling rate (referred to as an equivalent cooling rate in the present invention) is determined from the calibration curve.

[0065] The alkali-free glass of the present invention can improve the transistor characteristics and reliability of the TFT fabricated on the glass substrate. In the present invention, the characteristics of the TFT fabricated on the glass substrate can be evaluated by the following procedure.

[0066] (TFT manufacturing method) A method for manufacturing a top-contact type TFT 10 with a bottom-gate structure shown in Fig. 2 will be described as an example. First, a gate electrode 12 is formed on one of the main surfaces of a glass substrate 11. After the film is formed, it is patterned into a predetermined shape by photolithography and etching or a lift-off method, if necessary. This forms the gate electrode 12. The gate electrode 12 preferably has high conductivity, and can be made of a metal such as Al or Mo.

[0067] After the gate electrode 12 is formed, a gate insulating layer 13 is formed on the gate electrode 12 and the exposed surface of the glass substrate 11. After the film formation, the film is patterned into a predetermined shape by photolithography and etching or lift-off, as necessary. This forms the gate insulating layer 13. The gate insulating layer 13 is preferably one having high insulating properties, and for example, SiO2, SiNx, etc. can be used.

[0068] After the gate insulating layer 13 is formed, an active layer 14 made of a semiconductor film is formed on the gate insulating layer 13 at a position facing the gate electrode 12. The active layer 14 can be made of amorphous silicon, polysilicon, or an oxide semiconductor such as In-Ga-Zn-O.

[0069] After the film formation, the film is patterned into a predetermined shape by photolithography and etching or lift-off, if necessary. Then, a heat treatment may be performed to adjust the electrical resistivity, etc., as appropriate. After the active layer 14 is formed, a source electrode 15 and a drain electrode 16 are formed on the active layer 14 and on the exposed surface of the gate insulating layer 13. The source electrode 15 and the drain electrode 16 preferably have high electrical conductivity, and may be made of a metal such as Al or Mo.

[0070] After the film formation, the film is patterned into a predetermined shape by photolithography and etching or lift-off, as necessary. This forms the source electrode 15 and the drain electrode 16. The gate electrode 12, the gate insulating layer 13, the active layer 14, the source electrode 15, and the drain electrode 16 are formed by a wet method or a dry method. An example of the wet method is a coating method, and an example of the dry method is a sputtering method.

[0071] (Method of evaluating TFT characteristics) In the present invention, the characteristics of the TFT on the glass substrate fabricated by the above method can be evaluated by performing current-voltage measurements using a semiconductor parameter analyzer. When the current-voltage measurements are performed using a semiconductor parameter analyzer, the threshold voltage V th On the other hand, if a bias voltage Vgs is applied between the gate electrode and the source and drain electrodes for a certain period of time and then the current-voltage measurement is performed again, the threshold voltage V th A shift in the threshold voltage is observed. th By evaluating the magnitude of ΔV, the characteristics of the TFT can be evaluated. th It can be said that the smaller the value, the better the characteristics of the TFT. In the present invention, high TFT characteristics includes high reliability of the TFT.

[0072] When a characteristic test was performed, a certain amount of V thA shift is observed. This is believed to be due to the injection and trapping of electrons from the semiconductor layer to the gate insulating film, and an increase in the local potential in the semiconductor film. This is due to the positive bias, i.e., when a positive bias voltage is applied to the gate electrode relative to the source and drain electrodes, the positive V th Shift, negative V when negative bias is applied th This is observed as a shift.

[0073] On the other hand, the glass substrate is the cause of V th The mechanism by which this shift occurs is thought to be that when a voltage is applied between the gate electrode and the source and drain electrodes, alkali metals such as Na diffuse from the glass substrate into the TFT layer and become localized between the source and drain, causing a change in the width of the depletion layer in the TFT.

[0074] It is also possible to perform characteristic tests by heating the TFT to a specified temperature. In this case, the diffusion speed of the alkali metal increases, so characteristic tests can be performed under higher load conditions.

[0075] The threshold voltage V th is the onset voltage V in the TFT, which is defined as follows: on In other words, the source-drain current I ds is a specific value I ds0 Gate voltage exceeding V gs V on Let us assume that ds0 is the W / L ratio (ratio of channel width to channel length) and V on In the present invention, the I ds0 =1×10 -9 When the voltage V on is the threshold voltage V th In addition, V th This is not limited to this method. For example, √I ds -V gs It may be calculated using the method or the like. EXAMPLES

[0076] In the following, Examples 1 to 3, 9, 11, 13, 15, 17, 19, 21, and 23 to 32 are working examples, and Examples 4 to 8, 10, 12, 14, 16, 18, 20, and 22 are comparative examples. The raw materials of each component were mixed to obtain the target composition and melted in a platinum crucible at a temperature of 1550 to 1650°C. During melting, the glass was homogenized by stirring using a platinum stirrer. The molten glass was then poured into a mold heated to 800°C, and cooled from a temperature 100°C higher than Tg to room temperature at a rate of 40°C / min to obtain a plate-shaped glass.

[0077] Tables 1 to 4 show the glass compositions (unit: mass %), the physical properties described above, and the thermal shrinkage measured by the procedures described above.

[0078] [Table 1]

[0079] [Table 2]

[0080] [Table 3]

[0081] [Table 4]

[0082] As is clear from Tables 1 to 4, in Examples 5 to 8 in which the B2O3 content was more than 5.5% and Examples 4, 10, 12, 14, 16, 18, 20, 22, and 23 to 32 in which the Na2O content was more than 600 ppm, the heat shrinkage was greater than 90 ppm. The heat shrinkage also increased according to the Na2O / B2O3 ratio. On the other hand, in Examples 1 to 3, 9, 11, 13, 15, 17, 19, and 21 in which the B2O3 content was 0.2 to 5.5%, the Na2O content was 600 ppm or less, and the Na2O / B2O3 ratio was 0.001 or more and 0.3 or less, the heat shrinkage increased according to the Na2O / B2O3 ratio, but all were 90 ppm or less.

[0083] FIG. 1 is a graph showing the relationship between Na2O / B2O3 and thermal shrinkage. The thermal shrinkage C is calculated by dividing the thermal shrinkage of each glass by C0, where C0 is the value obtained by extrapolating the regression line obtained by the least squares method to 0. This plot shows the variation in thermal shrinkage due to Na2O / B2O3. As shown in FIG. 1, the slope of the straight line showing the variation in thermal shrinkage in Examples 1 to 4, which have a B2O3 content of 0.2 to 5.5%, is about half that of Examples 5 to 8, which have a B2O3 content of more than 5.5% (however, Example 4 is a comparative example in that Na2O exceeds 600 ppm). Therefore, the alkali-free glass of the present invention reduces the variation in thermal shrinkage due to the content of Na2O, which accounts for the majority of the alkali metal oxides inevitably mixed in the raw materials, and also reduces the thermal shrinkage.

[0084] Figures 3, 4, and 5 show the results of TFT characteristic tests for Examples 1, 9, and 6. The glass substrate used was a plate-shaped glass prepared using the procedure described above, processed to a size of 40 mm square and a thickness of 0.5 mm. The TFT was fabricated using the method described above. The gate electrode was made of Mo with a thickness of 100 nm, the gate insulating film was made of SiO2 with a thickness of 200 nm, the semiconductor layer was made of In-Ga-Zn-O with a thickness of 35 nm, and the source and drain electrodes were made of Mo with a thickness of 100 nm.

[0085] The source and drain electrode width, i.e., the channel width, was 300 μm, and the source and drain electrode spacing, i.e., the channel length, was 50 μm. The TFT characteristics were evaluated using the method described above. The semiconductor parameter analyzer used was the B1500A manufactured by Keysight Technologies. The current-voltage measurements were performed at atmospheric pressure, in an air atmosphere, at 70°C, and in a light-shielded environment, with the source-drain voltage V ds Gate voltage V at 10V gs When the drain current I ds In addition, a positive bias voltage V of 10 V was applied to the gate electrode relative to the source and drain electrodes. gs After applying for 0 seconds, 3000 seconds, and 7000 seconds, current-voltage measurements were performed to measure the threshold voltage V th The presence or absence of a shift was observed.

[0086] As is clear from FIG. 3, in Example 1 where Na2O / B2O3 is 0.001 or more and less than 0.06, V th The shift in V is small, and V th It is clear that the TFT has high characteristics.

[0087] On the other hand, from Figure 4, for Example 9 where Na2O / B2O3 is 0.06 or more, V th has shifted in the negative direction, and it is believed that the characteristic tests have caused alkali ions to diffuse into the TFT, which is more likely to affect the TFT side than in Figure 3.

[0088] 5, Example 6 has the same Na2O as Example 9, but since Na2O / B2O3 is 0.001 or more and less than 0.06, the TFT has high characteristics. Therefore, in order to improve the characteristics of the TFT fabricated on the glass substrate, it is effective not to simply reduce Na2O, but to reduce Na2O / B2O3, especially when B2O3 is 5.5% or less.

[0089] Although the present invention has been described in detail using specific embodiments, it is clear to those skilled in the art that various modifications and variations are possible without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2014-216174) filed on October 23, 2014, and is incorporated by reference in its entirety.

Claims

1. The strain point is 690°C or more and 738°C or less, and the average thermal expansion coefficient at 50 to 350°C is 30 x 10 －７ ~45 x 10 －７ / °C, The content is expressed as mass% based on oxides. Yes ２ :57~63% <h2 style=";text-align:left;direction:ltr">Al<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> ３ <h2 style=";text-align:left;direction:ltr"> :18~233% B ２ O ３ :1.6~5.5% MgO: 1-8.5% CaO: 3.5-10% SrO: 0-6.5% BaO: 0 to 5% and The total amount of MgO+CaO+SrO+BaO is 13 to 23%; CaO / (MgO+CaO+SrO+BaO) is 0.22 or more and 0.59 or less, SrO / (MgO+CaO+SrO+BaO) is 0.06 or more and 0.52 or less, Na ２ O and B ２ O ３ Mass ratio to (Na ２ O / B ２ O ３ ) is 0.001 or more and 0.3 or less, The content of alkali metal oxides is 1000 ppm by mass or less, An alkali-free glass having a thermal shrinkage rate of 90 ppm or less.

2. 2. The alkali-free glass according to claim 1, wherein MgO / (MgO+CaO+SrO+BaO) is 0.10 or more.

3. 3. The alkali-free glass according to claim 1, wherein CaO / (MgO+CaO+SrO+BaO) is 0.30 or more.

4. The alkali-free glass according to any one of claims 1 to 3, which contains SrO and has a SrO / (MgO+CaO+SrO+BaO) ratio of 0.26 or less.

5. The alkali-free glass according to any one of claims 1 to 4, which contains BaO, and in which BaO / (MgO+CaO+SrO+BaO) is 0.08 or more and 0.55 or less.

6. Glass viscosity is 10 ２ Temperature T at which viscosity becomes dPa·s ２ The alkali-free glass according to any one of claims 1 to 5, wherein the melting point is 1,589°C or higher and 1,786°C or lower.

7. Glass viscosity is 10 ４ Temperature T at which viscosity becomes dPa·s ４ The alkali-free glass according to any one of claims 1 to 6, wherein the melting point is 1,253°C or higher and 1,381°C or lower.

8. The alkali-free glass according to any one of claims 1 to 7, having an equivalent cooling rate of 400°C / min or less.

Images