High silicate glass substrate manufacturing method, high silicate glass substrate and porous glass

Abstract

The objective of the present invention is to provide: a method for manufacturing a high silicate glass substrate, which is suitable for a high-frequency substrate material, has a large area, and can be sintered without cracking; a high silicate glass substrate; and a porous glass. The present invention relates to a method for manufacturing a high silicate glass substrate, the method comprising (1) obtaining a glass precursor having a specific composition range, (2) obtaining a phase-separated glass by performing a first heat treatment on the glass precursor and phase-separating the glass precursor, (3) obtaining a porous glass by performing an acid-treatment on the phase-separated glass and making the same be a porous glass, (4) drying the porous glass and making the mass change rate (%)=[(mass before drying-mass after drying) / mass before drying]×100 (equation 1) fall within a specific range, and (5) obtaining a high silicate glass substrate by performing a second heat treatment on the porous glass and sintering the porous glass.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a high silicate glass substrate, a high silicate glass substrate, and porous glass. [Background technology]

[0002] In recent years, wireless transmission using microwave and millimeter wave bands has been attracting attention as a large-capacity transmission technology. This has led to the development of technologies such as computer peripherals, wireless communication devices, ubiquitous communication devices, and wireless power supply technology. High-frequency substrate materials with excellent basic high-frequency characteristics are required for use in these devices.

[0003] However, as the signal frequency increases with the expansion of the frequency range used, the dielectric loss in the dielectric layers of high-frequency devices increases. Therefore, materials with low dielectric loss are required as high-frequency substrate materials. Among them, glass with a high silica content, such as quartz glass, has particularly low dielectric loss and is excellent as a high-frequency substrate material.

[0004] However, the manufacturing and processing costs of silica glass are high, so costs can be reduced by producing phase-separated borosilicate glass, dissolving components other than silica with acid to form porous glass, and then sintering it to densify the resulting high-silica glass, which can then be used as a high-frequency substrate material.

[0005] Patent Document 1 discloses a method for producing high silicate glass containing silica as the main component, in which alkali borosilicate glass is subjected to heat treatment to separate into an SiO2-rich insoluble phase and a B2O3-rich soluble phase, and then the soluble phase is eluted with an acid to produce porous glass containing SiO2 as the main component, and the porous glass is then fired to produce high silicate glass. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 2,106,744 Summary of the Invention [Problem to be solved by the invention]

[0007] In order to actually manufacture high-frequency substrate materials, 2 It is necessary to sinter such large-area porous glass. However, porous glass is prone to cracking during manufacturing due to moisture remaining in the glass, making it difficult to achieve both a large area and sintering without cracking.

[0008] Therefore, an object of the present invention is to provide a method for producing a high silicate glass substrate suitable for use as a high frequency substrate material, which can be sintered without cracking and has a large area, a high silicate glass substrate, and porous glass. [Means for solving the problem]

[0009] The present inventors have discovered that by drying porous glass having a specific composition so that the moisture content falls within a specific range before sintering, a large-area high silicate glass substrate can be obtained by sintering the glass without cracking, and have completed the present invention based on this finding.

[0010] The present invention relates to a method for producing a high silicate glass substrate, which includes the following (1) to (5). (1) Obtain a glass precursor containing, expressed in mole percentage on an oxide basis, 60% to 75% SiO2, 0% to 15% Al2O3, 15% to 30% B2O3, 0% to 3% P2O5, and a total of 1% to 10% of one or more selected from R2O (R is at least one selected from Li, Na, and K) and R'O (R' is at least one selected from Mg, Ca, Sr, and Ba). (2) subjecting the glass precursor to a first heat treatment to cause phase separation to obtain a phase-separated glass; (3) The phase-separated glass is acid-treated to make it porous, thereby obtaining porous glass. (4) The porous glass is dried to have a mass change rate defined by the following formula 1 of 10 to 50%. Mass change rate (%) = [(mass before drying - mass after drying) / mass before drying] x 100 (Equation 1) (5) subjecting the porous glass to a second heat treatment and sintering to obtain a high silicate glass substrate.

[0011] The present invention is directed to a ceramic substrate containing, in mole percentages based on oxides, 90% to less than 100% SiO2, 0% to 1% Al2O3, and 0% to 10% B2O3, and having a base area of ​​300 cm 2 The present invention relates to a high silicate glass substrate having an OH group concentration of 1200 mass ppm or less.

[0012] The present invention is directed to a ceramic substrate containing, in mole percentages based on oxides, 90% to less than 100% SiO2, 0% to 1% Al2O3, and 0% to 10% B2O3, and having a base area of ​​300 cm 2 The present invention relates to porous glass having the above-mentioned properties, a thickness of 3 mm or less, and a median value of pore size distribution of 150 nm or less. [Effects of the Invention]

[0013] According to the method for producing a high silicate glass substrate of the present invention, porous glass having a specific composition is dried so that the moisture content falls within a specific range before sintering, thereby enabling the production of a large-area, crack-free high silicate substrate by sintering. The high silicate glass substrate of the present invention has a specific composition and a specific range of OH group concentration, allowing it to be produced in a large area and suitable as a high-frequency substrate material. The porous glass of the present invention has a composition, thickness, and a median pore size distribution within a specific range, allowing the production of a high-frequency substrate material without cracking even when sintered. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a graph showing the change in dielectric loss tangent depending on the OH group concentration of glass. [Figure 2] FIG. 2 shows the results of fluorescence measurement of glass. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes embodiments for implementing the present invention, but the present invention is not limited to the following embodiments, and various modifications and substitutions may be made to the following embodiments without departing from the scope of the present invention.

[0016] In this specification, glass compositions are expressed in mole percentages based on oxides, and mole % may be simply referred to as %. Furthermore, the symbol "to" indicating a range of values ​​is used to mean that the values ​​before and after it are included as the lower and upper limits.

[0017] 1. Manufacturing method for high silica glass substrate The method for producing a high silicate glass substrate of the present invention includes the following steps (1) to (5). (1) Obtain a glass precursor containing, expressed in mole percentage on an oxide basis, 60% to 75% SiO2, 0% to 15% Al2O3, 15% to 30% B2O3, 0% to 3% P2O5, and a total of 1% to 10% of one or more selected from R2O (R is at least one selected from Li, Na, and K) and R'O (R' is at least one selected from Mg, Ca, Sr, and Ba). (2) subjecting the glass precursor to a first heat treatment to cause phase separation to obtain a phase-separated glass; (3) The phase-separated glass is acid-treated to make it porous, thereby obtaining porous glass. (4) The porous glass is dried to have a mass change rate defined by the following formula 1 of 10 to 50%. Mass change rate (%) = [(mass before drying - mass after drying) / mass before drying] x 100 (Equation 1) (5) subjecting the porous glass to a second heat treatment and sintering to obtain a high silicate glass substrate. Each step will be described below.

[0018] <Step (1): Glass precursor preparation step> Step (1) is a step of preparing a glass precursor. In step (1), glass raw materials are mixed to obtain a glass composition containing, in mole percentages based on oxides, 60% to 75% SiO2, 0% to 15% Al2O3, 15% to 30% B2O3, 0% to 3% P2O5, and a total of 1% to 10% of one or more selected from R2O (R is one selected from Li, Na, and K) and R'O (R' is one selected from Mg, Ca, Sr, and Ba).

[0019] SiO2 is the main component that forms the skeleton of glass, and is also the main component of glass after it has been made porous by acid treatment, and is a component that improves dielectric properties. The SiO2 content is 60% or more, preferably 62% or more, more preferably 63% or more, and particularly preferably 65% ​​or more. When the SiO2 content is 60% or more, weather resistance can be improved. The SiO2 content is 75% or less, preferably 72% or less, more preferably 70% or less, and particularly preferably 69% or less. When the SiO2 content is 75% or less, the composition range is suitable for phase separation.

[0020] Al2O3 is a component that improves the mechanical strength of the glass precursor and suppresses the expansion of the phase-separated structure. When Al2O3 is contained, its content is preferably 0.5% or more, more preferably 1% or more, even more preferably 1.5% or more, and particularly preferably 2% or more. When the Al2O3 content is 0.5% or more, it suppresses the phase-separated structure from becoming too large, and exhibits the effect of suppressing shrinkage during sintering and making it less likely to crack. The Al2O3 content is 15% or less, preferably 10% or less, more preferably 8% or less, even more preferably 6% or less, and particularly preferably 4% or less. When the Al2O3 content is 15% or less, it is in a composition range suitable for phase separation.

[0021] B2O3 is a component that promotes the melting of glass raw materials and reduces the viscosity of molten glass. It also improves the mechanical properties and weather resistance of glass precursors and promotes phase separation. It also reduces the dielectric tangent of glass after porosity formation. The B2O3 content is 15% or more, preferably 20% or more, more preferably 22% or more, and particularly preferably 24% or more. When the B2O3 content is 15% or more, phase-separated glass can be obtained. The B2O3 content is 30% or less, preferably 28% or less, more preferably 26% or less, and particularly preferably 25% or less. When the B2O3 content is 30% or less, volatilization during glass melting can be suppressed.

[0022] Although R2O (R is at least one selected from Li, Na, and K) is not an essential component, it is useful for accelerating the melting of glass raw materials, adjusting thermal expansion, viscosity, etc., and promoting phase separation of the glass precursor. The total content of R2O is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 4% or more. On the other hand, the content of R2O is preferably 10% or less, more preferably 9% or less, even more preferably 8% or less, and particularly preferably 7% or less. When the content of R2O is 10% or less, the weather resistance of the glass precursor can be ensured.

[0023] R'O (R' is at least one selected from Mg, Ca, Sr, and Ba) is not an essential component, but it does not increase the devitrification temperature of the glass, improves the melting point, and promotes phase separation. The total content of R'O is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 4% or more. When the R'O content is 1% or more, phase separation can be promoted. If the R'O content is too high, phase separation becomes difficult. The total content of R'O is preferably 10% or less, more preferably 9% or less, even more preferably 8% or less, and particularly preferably 7% or less. When the R'O content is 10% or less, phase separation is facilitated.

[0024] The total content of R2O and R'O is 10% or less, preferably 8% or less, and more preferably 7% or less. When the total content of R2O and R'O is 10% or less, components that gel during acid treatment can be suppressed, thereby suppressing cracking during acid treatment. Furthermore, alkaline washing for removing gel can be omitted in the washing step after acid treatment. On the other hand, the total content of R2O and R'O is 1% or more, preferably 2% or more, more preferably 3% or more, and particularly preferably 4% or more.

[0025] P2O5 is a component that promotes phase separation. When P2O5 is contained, its content is preferably 0.1% or more, more preferably 0.2% or more, even more preferably 0.3% or more, and particularly preferably 0.4% or more. When the P2O5 content is 0.1% or more, the phase separation promotion effect is sufficient, and phase separation can be achieved online in continuous molding processes such as float molding, eliminating the need for additional heat treatment for phase separation. The P2O5 content is 3% or less, preferably 2% or less, more preferably 1% or less, and particularly preferably 0.9% or less. When the P2O5 content is 3% or less, brick erosion and volatilization during glass melting in mass production furnaces are suppressed, and an excessive increase in the thermal expansion coefficient is suppressed, thereby suppressing glass cracking during acid treatment.

[0026] Cl is a component that improves the clarification of molten glass. The Cl content is preferably 0.1% or more, more preferably 0.15% or more, even more preferably 0.2% or more, and particularly preferably 0.25% or more. When the Cl content is 0.1% or more, sufficient clarification is obtained, thereby reducing the number of bubbles in the glass precursor and phase-separated glass. Reducing the number of bubbles reduces the probability of breakage and cracks occurring during acid treatment or sintering from bubbles during mass production. The Cl content is preferably 1% or less, more preferably 0.7% or less, even more preferably 0.5% or less, and particularly preferably 0.3% or less.

[0027] In addition to the above components, various other components may be contained within the range that does not impair the effects of the present invention. For example, ZrO2, TiO2, La2O3, Ta2O5, TeO2, Nb2O5, Gd2O3, Y2O3, Eu2O3, Sb2O3, SnO2, and Bi2O3 may be contained in an amount of preferably 5% or less, more preferably 3% or less, and particularly preferably 1% or less, respectively.

[0028] Next, the prepared glass batch is melted at 1300 to 1600°C for 4 to 12 hours. The molten glass is then formed into a plate and slowly cooled at 400 to 600°C for 10 minutes to 10 hours to obtain a glass precursor. The method for obtaining the glass precursor is not particularly limited, but for small-scale production, a crucible and mold may be used, for example, and for mass production, continuous production using a refractory furnace may be used, for example.

[0029] In the case of continuous production using a refractory furnace, more preferably, molten glass at a temperature equal to or higher than the softening point is discharged from the refractory furnace in a band shape to form a glass ribbon, which is supplied onto the surface of molten metal, the glass ribbon supplied onto the surface of the molten metal is transported, and the transported glass ribbon is then cooled in a region upstream in the transport direction so that the temperature of the glass ribbon becomes lower than the softening point over the entire width direction. Through the above steps, the molten glass is formed into a sheet having a desired width and thickness.

[0030] The viscosity of the molten glass when supplied to the surface of the molten metal is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 1.5 or more, and particularly preferably 2.0 or more, in log η. It is also preferably 5.5 or less, more preferably 5.0 or less, even more preferably 4.5 or less, particularly preferably 4.0 or less, and even more preferably 3.5 or less. The temperature of the molten metal is preferably above the annealing point and below the softening point of the glass to be produced. This is particularly preferred because it allows the glass to be formed into a wide plate while being rapidly cooled, which not only reduces the load of subsequent plate processing but also suppresses the inhomogeneity of the glass that occurs during the forming of the molten glass, thereby producing a more homogeneous glass plate.

[0031] The glass precursor of the present invention has a glass viscosity of 10 2 The temperature T2 at which the melting point reaches dPa·s is preferably 1700°C or lower. Having T2 of 1700°C or lower allows for excellent glass melting properties and reduces the burden on manufacturing equipment. For example, the life of equipment such as a furnace for melting glass can be extended, improving productivity. Furnace-related defects (e.g., pitting defects, Zr defects, etc.) can also be reduced. T2 is more preferably 1680°C or lower, and even more preferably 1670°C or lower. T2 is preferably 1630°C or higher.

[0032] The glass precursor of the present invention has a glass viscosity of 10 4 It is preferable that the temperature T4 at which the glass viscosity reaches dPa·s is 1290°C or lower. This results in excellent formability of the glass. Furthermore, for example, by lowering the temperature during glass forming, it is possible to reduce volatile substances in the atmosphere around the glass, thereby reducing defects in the glass. Since glass can be formed at low temperatures, the burden on manufacturing equipment can be reduced. For example, the life of equipment such as float baths used to form glass can be extended, improving productivity. It is more preferable that T4 is 1280°C or lower.

[0033] T4 is measured using a rotational viscometer according to the method specified in ASTM C 965-96. 4 It is calculated as the temperature at which the viscosity becomes dPa·s. In the examples described later, NBS710 and NIST717a were used as reference samples for calibrating the instrument.

[0034] The obtained plate-shaped glass may be subjected to processing such as cutting, milling, polishing, etc. to obtain a desired size and shape. The shape of the main surface is not particularly limited, but is preferably rectangular or circular, for example.

[0035] The bottom area of ​​the glass precursor obtained as described above is 300 to 5000 cm 2 is preferably 700 to 3600 cm 2 , and more preferably 900 to 2000 cm 2The thickness of the glass precursor is preferably 0.5 to 3 mm, more preferably 0.7 to 2.5 mm, and even more preferably 1 to 2 mm. In this specification, the term "bottom area" refers to the area of ​​the main surface.

[0036] The aspect ratio of the glass precursor is preferably 500 to 36,000, more preferably 1,000 to 20,000, and even more preferably 5,000 to 10,000. If the aspect ratio is too small, there will be a large difference in the rate of removing the boron oxide-rich phase between the surface and the interior of the glass precursor in the porous glass forming step (3) described below, which will result in stress being easily generated and the porous glass being prone to cracking. On the other hand, if the aspect ratio is too large, the glass will be difficult to handle. In this specification, the term "aspect ratio" refers to the area (cm) of the main surface. 2 ) / Refers to thickness (cm).

[0037] The number of bubbles in the glass precursor is 0.1 / cm on the main surface. 2 It is preferable that the number of bubbles be less than 100 in order to reduce the probability of breakage or cracks occurring during acid treatment or sintering in mass production, which may be caused by bubbles. The number of bubbles in the glass precursor is measured visually or under an optical microscope using a high-intensity light source.

[0038] <Process (2): Phase separation process> In step (2), the glass precursor obtained in step (1) is subjected to a first heat treatment to separate it into an insoluble phase (silicic acid phase) mainly composed of SiO2 and a soluble phase (boric acid phase) mainly composed of B2O3, thereby obtaining phase-separated glass. Whether or not the glass is phase-separated can be determined using SEM. If the glass is phase-separated, observation with SEM will reveal that it is divided into two or more phases.

[0039] Phase-separated glasses include binodal-type phase-separated glasses in a binodal state and spinodal-type phase-separated glasses in a spinodal state. The binodal state is phase separation due to a nucleation-growth mechanism, and is generally spherical. The spinodal state is a state in which the separated phases are three-dimensionally and continuously intertwined with each other with a certain degree of regularity. As the phase-separated glass of the present invention, the spinodal-type phase-separated glass described below is particularly preferred.

[0040] The heat treatment temperature is preferably at least 50° C. higher than the glass transition point, more preferably at least 100° C. In order to prevent deformation of the glass, the heat treatment temperature is preferably not more than 400° C. higher than the glass transition point, more preferably not more than 300° C. higher.

[0041] Specifically, the heat treatment temperature is, for example, preferably 400°C or higher and 1000°C or lower, more preferably 500°C or higher and 900°C or lower, and even more preferably 550°C or higher and 800°C or lower. If the heat treatment temperature is too high, the glass precursor softens, making it difficult to obtain the desired shape. On the other hand, if the heat treatment temperature is too low, it becomes difficult to phase separate the glass precursor.

[0042] The heat treatment time is preferably 10 minutes or more, more preferably 1 hour or more, and even more preferably 3 hours or more. If the heat treatment time is too short, it becomes difficult to cause phase separation of the glass precursor. The upper limit of the heat treatment time is not particularly limited, but from the viewpoint of mass productivity, it is preferably 36 hours or less, more preferably 24 hours or less, and even more preferably 12 hours or less.

[0043] Examples of methods for phase separation of glass include a method of heat treating glass after molding and a method of holding glass at a temperature equal to or higher than the phase separation temperature before molding. Examples of methods for holding glass at a temperature equal to or higher than the phase separation temperature before molding include a method of holding glass at a temperature equal to or higher than the phase separation onset temperature and then holding it at a temperature equal to or lower than the phase separation onset temperature to cause phase separation. Specific examples of such methods include a method of holding glass online at a temperature equal to or higher than the phase separation onset temperature and then holding it at a temperature equal to or lower than the phase separation onset temperature to cause phase separation during continuous production using a refractory furnace such as the float process.

[0044] <Step (3): Acid Treatment Step> In step (3), the phase-separated glass obtained in step (2) is immersed in an acid for acid treatment to remove the soluble phase (boric acid phase) mainly composed of B2O3, thereby forming a porous glass. Examples of acids include hydrochloric acid and nitric acid. These acids may be used alone or in combination. The acid concentration is preferably 0.1 to 5 mol / L, more preferably 0.5 to 4 mol / L, and even more preferably 1 to 3 mol / L. The temperature for the acid treatment (immersion temperature) is preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, and particularly preferably 80°C or higher. If the immersion temperature is low, abnormal expansion or contraction occurs in the early stage, making the glass more susceptible to cracking. This is because a low immersion temperature increases the Na2O / B2O3 elution ratio, and Na + and H3O + This is because the swelling of the glass due to the substitution of B is greater than the shrinkage of the Si skeleton due to the dissolution of B. By setting the immersion temperature to 40°C or higher, such abnormal expansion and shrinkage at the initial stage can be suppressed, making the glass less likely to crack. There is no particular upper limit to the immersion temperature, but in reality, it is preferably 100°C or lower.

[0045] The acid immersion time is preferably 1 hour or more, more preferably 5 hours or more, even more preferably 10 hours or more, and particularly preferably 20 hours or more. If the immersion time is too short, it becomes difficult to obtain porous glass. There is no particular upper limit to the immersion time, but in reality it is 50 hours or less.

[0046] Porous glass obtained by acid-treating phase-separated glass to make it porous preferably has a median pore size distribution of 150 nm or less, more preferably 100 nm or less, and even more preferably 80 nm or less. A median pore size distribution of 150 nm or less can suppress fractures and cracks during sintering. The median pore size distribution is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or less. Phase separation such that the median pore size distribution falls within the above range allows acid to easily penetrate the pores during leaching, thereby reducing the acid treatment time required for making the glass porous. The pore size distribution can be determined by the BHJ method from the nitrogen adsorption isotherm obtained by gas adsorption.

[0047] <Process (4): Drying process> Step (4) is a step of drying the porous glass obtained in step (3). When the porous glass is dried in the drying step, the water adhering to the porous glass evaporates to form water vapor, which is then removed from the porous glass. Between steps (3) and (4), a cleaning step may be performed by immersing the porous glass in water (e.g., purified water). To prevent the porous glass from cracking due to a sudden change in temperature, it is preferable that the temperature of the water used in the cleaning step be within ±20°C, more preferably ±10°C, and even more preferably ±5°C of the temperature used in the acid treatment. Furthermore, ultrasonic waves may be applied during cleaning to remove residual components from the porous glass.

[0048] In step (4), the mass change rate defined by the following formula 1 is 10% or more, preferably 11% or more, more preferably 12% or more, and even more preferably 13% or more. Porous glass is prone to cracking during production due to moisture remaining in the glass, but by drying the glass in step (3) so that the mass change rate is 10% or more and then sintering it in step (4), it can be sintered into a plate without cracking. There is no particular upper limit to the mass change rate, but it is usually preferably 20% or less, more preferably 15% or less.

[0049] Mass change rate (%) = [(mass before drying - mass after drying) / mass before drying] x 100... (Equation 1) The mass change rate is measured by leaving the porous glass obtained in step (3) overnight under normal atmospheric pressure (this state is referred to as "before drying"), measuring the mass before drying, then subjecting it to a drying treatment, and measuring the mass after heating.

[0050] The drying method is not particularly limited, and examples include a method of drying under atmospheric pressure at a temperature of preferably 20°C or higher and 100°C or lower, more preferably 30°C or higher and 90°C or lower, and even more preferably 40°C or higher and 80°C or lower, for preferably 1 hour or higher and 36 hours or lower, more preferably 2 hours or higher and 24 hours or lower, and even more preferably 3 hours or higher and 12 hours or lower; and a method of drying under vacuum for preferably 1 hour or higher and 36 hours or lower, more preferably 2 hours or higher and 24 hours or lower, and even more preferably 3 hours or higher and 12 hours or lower.

[0051] <Step (5): Sintering step> Step (5) is a step of sintering the porous glass dried in step (4) by a second heat treatment to obtain a high silicate glass substrate.

[0052] In the second heat treatment, the temperature is preferably raised to the control temperature at a rate of 100°C / hour or less, more preferably 70°C / hour or less, and even more preferably 50°C / hour or less. By setting the temperature rise rate to 100°C / hour or less, cracking of the glass can be suppressed. There is no particular lower limit to the temperature rise rate, but it is usually 10°C / hour or more.

[0053] From the viewpoint of sintering the glass, the controlled temperature in the second heat treatment is preferably 900° C. or higher, more preferably 1000° C. or higher, and even more preferably 1100° C. or higher. From the viewpoint of suppressing fusion with the setter, the controlled temperature is preferably 1250° C. or lower, more preferably 1200° C. or lower, and even more preferably 1150° C. or lower. From the viewpoint of sintering the glass, it is preferable to hold the glass at the controlled temperature for preferably 3 hours or more and 25 hours or less, more preferably 4 hours or more and 15 hours or less, and even more preferably 5 hours or more and 10 hours or less.

[0054] The second heat treatment is preferably carried out in an environment where the dew point is preferably 60°C or lower, more preferably 56°C or lower, even more preferably 39°C or lower, even more preferably 22°C or lower, even more preferably 20°C or lower, particularly preferably 10°C or lower, and most preferably 0°C or lower. If the dew point during the second heat treatment is too high, moisture tends to be adsorbed by the porous glass. By setting the dew point to 60°C or lower, moisture adsorption by the porous glass can be suppressed, the OH group concentration in the resulting high silicate glass substrate can be suppressed, and the dielectric loss tangent can be improved. The lower limit of the dew point is not particularly limited, but in practice it is -40°C or higher.

[0055] The second heat treatment may be carried out under atmospheric pressure, but is preferably carried out under an atmosphere of nitrogen, dry air, or hydrogen, or a mixture thereof, in order to control the concentration of OH groups.

[0056] Specifically, in step (5), for example, the porous glass is sandwiched between setters and heated to sinter it, suppress warping, and flatten it. The material of the setter is not particularly limited, but examples include ceramic materials such as alumina, cordierite, and mullite. The surface roughness Ra of the setter is preferably 1 μm or less, more preferably 0.5 μm or less, and even more preferably 0.1 μm or less. By making Ra 1 μm or less, the roughness of the glass surface after sintering can be reduced, and the load in the subsequent processing steps can be reduced. On the other hand, Ra is typically 1 nm or more. Furthermore, the weight of the setter is preferably such that the load per unit area is 3 g / cm. 2If the flatness is equal to or greater than this, warpage can be effectively suppressed. Furthermore, the flatness of the setter, as defined by JIS0621-1984, is preferably 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.1 mm or less. By achieving a flatness of 1 mm or less, warpage of the glass substrate after sintering can be reduced, and the load on the subsequent processing steps can be reduced. On the other hand, the flatness is typically 0.001 mm or more.

[0057] The bottom area of ​​the setter is preferably 1 to 1.5 times, more preferably 1.05 to 1.3 times, and even more preferably 1.1 to 1.2 times the bottom area of ​​the porous glass.

[0058] The SiO2 content after sintering is 90% or more, preferably 92% or more, more preferably 94% or more, and particularly preferably 96% or more. If the SiO2 content after sintering is 90% or more, weather resistance can be improved. The SiO2 content after sintering is less than 100%, preferably 99% or less, more preferably 98% or less, and particularly preferably 97% or less. If the SiO2 content is less than 100%, a decrease in mechanical strength can be suppressed.

[0059] Al2O3 is a component that improves mechanical strength. It is also a component that controls the expansion and contraction of glass during acid treatment when making the glass precursor porous, and may be contained. When Al2O3 is contained after sintering, its content is preferably 0.05% or more, more preferably 0.1% or more. When the Al2O3 content after sintering is 0.05% or more, mechanical strength can be improved. When the Al2O3 content is 1% or less, preferably 0.5% or less, more preferably 0.3% or less. When the Al2O3 content is 1% or less, devitrification during sintering can be suppressed.

[0060] If B2O3 is contained after sintering, the B2O3 content after sintering is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, and particularly preferably 3% or more. If the B2O3 content after sintering is 0.5% or more, it is possible to reduce the viscosity and the sintering temperature. The B2O3 content after sintering is 10% or less, preferably 8% or less, even more preferably 6% or less, and particularly preferably 4% or less. If the B2O3 content is 10% or less, it is possible to suppress a decrease in weather resistance.

[0061] In addition to the above components, various other components may be contained within a range that does not impair the effects of the present invention. For example, R2O (R is at least one selected from Li, Na, and K), R'O (R' is at least one selected from Mg, Ca, Sr, and Ba), ZrO2, TiO2, La2O3, Ta2O5, TeO2, Nb2O5, Gd2O3, Y2O3, Eu2O3, Sb2O3, SnO2, P2O5, and Bi2O3 may each be contained in a range of preferably 3% or less, more preferably 2% or less, particularly preferably 1% or less, even more preferably 0.5% or less, and even more preferably 0.1% or less. When the R2O and R'O contents of the high silicate glass are within the above ranges, the dielectric loss tangent is not deteriorated, and when the glass precursor contains R2O and R'O during production, the high silicate glass can be manufactured without cracking even over a large area.

[0062] Through the above steps, a high silica glass substrate can be formed.

[0063] <Other processes> When the high silicate glass substrate of the present invention is used as a high-frequency substrate material, holes may be formed in the high silicate glass. The hole-forming method is not particularly limited, but for example, a method of irradiating the high silicate glass substrate with a laser is preferred to accurately form small holes with a diameter of 200 μm or less. The high silicate glass substrate of the present invention has excellent processability by laser irradiation. The laser wavelength is not particularly limited, but examples include lasers with wavelengths of 10.6 μm or less, 3000 nm or less, 2050 nm or less, 1090 nm or less, 540 nm, and 400 nm or less. In particular, when forming small holes with a diameter of 50 μm or less, the following two methods are preferred.

[0064] (Processing with UV laser) Holes are formed inside the high silicate glass substrate by irradiating it with a UV laser having a wavelength of 400 nm or less. The UV laser is preferably pulsed, and an absorption layer is preferably provided on the surface of the high silicate glass substrate during laser irradiation. After laser irradiation, the high silicate glass substrate may be etched with a solution containing hydrofluoric acid to enlarge the holes. This method allows for the formation of holes with high verticality and reduced constriction.

[0065] (Processing by forming modified parts) A modified region is formed inside the high silicate glass substrate by irradiating it with a laser having a wavelength of 400 to 540 nm, for example, a wavelength of approximately 532 nm. The high silicate glass substrate is then etched with a solution containing hydrofluoric acid to selectively remove the modified region and form holes. This method uses pulsed oscillation of a laser or the like, and can form the modified region with just one pulse irradiation, resulting in a fast hole formation rate and excellent productivity.

[0066] 2. High silica glass substrate The high silicate glass substrate of the present invention contains, expressed as mole percentages based on oxides, 90% to less than 100% SiO2, 0% to 1% Al2O3, and 0% to 10% B2O3. The reasons for specifying the content of each component within the above ranges are explained below.

[0067] SiO2 is the main component that forms the skeleton of glass, and is a component that improves weather resistance and lowers the dielectric tangent. The SiO2 content is 90% or more, preferably 92% or more, more preferably 94% or more, and particularly preferably 96% or more. When the SiO2 content is 90% or more, weather resistance can be improved. The SiO2 content is less than 100%, preferably 99% or less, more preferably 98% or less, and particularly preferably 97% or less. When the SiO2 content is less than 100%, a decrease in mechanical strength can be suppressed.

[0068] Al2O3 is a component that improves mechanical strength. It is also a component that controls the expansion and contraction of glass during acid treatment when making the glass precursor porous. When Al2O3 is contained, the Al2O3 content is preferably 0.05% or more, more preferably 0.1% or more. When the Al2O3 content is 0.05% or more, the mechanical strength can be improved. The Al2O3 content is 1% or less, preferably 0.5% or less, more preferably 0.3% or less. When the Al2O3 content is 1% or less, devitrification during sintering can be suppressed.

[0069] B2O3 is a component that lowers viscosity and sintering temperature. It also lowers dielectric loss tangent. When B2O3 is contained, the B2O3 content is preferably 0.5% or more, more preferably 1% or more, even more preferably 2% or more, and particularly preferably 3% or more. A B2O3 content of 0.5% or more has the effect of lowering viscosity. The B2O3 content is 10% or less, preferably 8% or less, more preferably 6% or less, and particularly preferably 4% or less. A B2O3 content of 10% or less can suppress a decrease in weather resistance.

[0070] In addition to the above components, various other components may be contained within a range that does not impair the effects of the present invention. For example, R2O (R is at least one selected from Li, Na, and K), R'O (R' is at least one selected from Mg, Ca, Sr, and Ba), ZrO2, TiO2, La2O3, Ta2O5, TeO2, Nb2O5, Gd2O3, Y2O3, Eu2O3, Sb2O3, SnO2, P2O5, and Bi2O3 may each be contained in a range of preferably 3% or less, more preferably 2% or less, particularly preferably 1% or less, even more preferably 0.5% or less, and even more preferably 0.1% or less. When the R2O and R'O contents of the high silicate glass are within the above ranges, the dielectric loss tangent is not deteriorated, and when the glass precursor contains R2O and R'O during production, the high silicate glass can be manufactured without cracking even over a large area.

[0071] The high silica glass substrate of the present invention has a base area of ​​300 cm 2 More than 600cm 2 More than 900cm, preferably 2 More preferably, 1200 cm 2 That's all. The base area is 300cm 2 This makes it suitable for use as a high-frequency substrate material. To ensure strength, the base area is 5000 cm 2 It is preferable that the following exists:

[0072] The high silicate glass substrate of the present invention has an OH group concentration of 1200 mass ppm or less, more preferably 1000 mass ppm or less, and particularly preferably 800 mass ppm or less. By having an OH group concentration of 1200 mass ppm or less, the dielectric loss tangent (dissipation factor, hereinafter also abbreviated as Df) can be reduced. The lower limit of the OH group concentration is not particularly limited, but is typically 10 mass ppm or more.

[0073] The OH group concentration is measured using an infrared spectrophotometer according to the literature [Cer. Bull., 55(5), 524, 1976]. The detection limit of this measurement is 1 mass ppm. The OH group concentration can be adjusted by adjusting the atmosphere, dew point, etc. in the sintering process described below. Specific examples of means for adjusting the OH group concentration include using nitrogen or dry air as the atmosphere in the sintering process and setting the dew point to 60°C or less.

[0074] The high silicate glass substrate of the present invention preferably has a dielectric loss tangent at 60 GHz of 0.001 or less, more preferably 0.0009 or less, even more preferably 0.0008 or less, and particularly preferably 0.0007 or less. There is no particular lower limit to the dielectric loss tangent at 60 GHz, but it is typically 0.0001 or more.

[0075] The dielectric loss tangent can be measured using the method described in the literature [Y. Kato and M. Horibe, “Permittivity measurements and associated uncertainties up to 110 GHz in circular-disk resonator method,” Proceedings of the 46th European Microwave Conference (2016) 4-6 Oct 2016.].

[0076] The high silicate glass substrate of the present invention preferably has a thickness of 0.05 to 2 mm, more preferably 0.1 to 1 mm, and even more preferably 0.3 to 0.8 mm. By keeping the thickness within this range, it can be suitably used as a high frequency substrate material.

[0077] The high silicate glass substrate of the present invention is suitable for use as a high-frequency substrate material, aerospace materials, and heat-resistant materials. In addition, because of its low fluorescence, it is also suitable as a substrate material for DNA chips and cell culture vessels.

[0078] When the high silicate glass substrate of the present invention is used as a high frequency substrate material, a substrate material for DNA chips, or a cell culture vessel, holes may be formed in the high silicate glass, and these holes are used, for example, as electrodes. The high silicate glass substrate of the present invention has excellent processability, and fine holes can be easily formed using a laser or the like. The holes may be through holes or blind holes. The opening diameter of the holes is, for example, 200 μm or less, 100 μm or less, or 50 μm or less.

[0079] 3.Porous glass The porous glass of the present invention contains, in terms of mole percentages based on oxides, 90% to less than 100% of SiO2, 0% to 1% of Al2O3, and 0% to 10% of B2O3, and has a bottom area of ​​300 cm 2 The thickness is 3 mm or less, and the median value of the pore size distribution is 150 nm or less. The reasons for setting the composition range, bottom area, thickness, and median value of the pore size distribution within the above ranges are the same as those described above in <1. Method for producing high silicate glass substrate> and <2. High silicate glass substrate>.

[0080] By sintering the porous glass of the present invention, high-frequency substrate materials can be produced without cracking, even when they have a large surface area. Applications of the porous glass of the present invention include, for example, window materials, which combine its characteristics of transparency and gas permeability, and base materials for impregnating and supporting various functional materials in the pores. A preferred method for producing the porous glass of the present invention is the method comprising steps (1) to (3) described above in <1. Method for producing high silicate glass substrate>, because this method produces porous bodies with a large base surface area. [Example]

[0081] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0082] [Method of measuring physical properties] The methods for measuring each physical property are shown below. (dielectric loss tangent) The dielectric loss tangent was measured according to the method described in Y. Kato and M. Horibe, “Permittivity measurements and associated uncertainties up to 110 GHz in circular-disk resonator method,” Proceedings of the 46th European Microwave Conference (2016) 4-6 Oct 2016.

[0083] (OH group concentration) The OH group concentration was measured by infrared spectrophotometer according to the literature [Cer. Bull., 55(5), 524, 1976]. The detection limit of this measurement is 1 ppm by mass.

[0084] [Experimental Example 1] <Preparation of porous high silica glass> <<Step (1): Glass precursor production process>> Raw materials such as silica sand were mixed to prepare 500g batches of glass having the composition shown in Tables 1A and 1B (in mole percent based on oxides). The raw materials were placed in a platinum crucible and heated in an electric furnace at 1600°C for 3 hours to melt the materials into molten glass. A platinum stirrer was inserted into the platinum crucible and the glass was stirred for 1 hour to homogenize the glass. The molten glass was poured onto a carbon plate and formed into a plate. The plate was then placed in an electric furnace at a temperature of approximately Tg + 50°C and held there for 1 hour. After that, the electric furnace was cooled to Tg - 100°C at a rate of 1°C / min, and the glass was then allowed to cool to room temperature.

[0085] <<Process (2): Phase separation process>> The glass obtained in step (1) was kept at 600°C for 27 hours, and then the electric furnace was cooled to Tg-100°C at a cooling rate of 1°C / min. The glass was then allowed to cool to room temperature to cause phase separation. The glass was then cut and polished to prepare a glass substrate with a thickness of 1.0 mm, a shape of 50 x 50 mm, and an arithmetic mean roughness Ra of 1.0 nm on the main surface.

[0086] <<Step (3): Acid Treatment Step>> The glass separated in step (2) and 10 L of 2 mol / L HCl solution were placed in a sealed container and subjected to acid treatment at 40, 60 or 90°C for 20 hours, and cracking during the acid treatment was examined. The results are shown in Tables 1A and 1B. In Tables 1A and 1B, Examples 1, 2, and 4 、1 0, 11 are examples, Example 5 is a reference example, Examples 3, 6 to 9, and 12 to 18 are comparative examples.

[0087] In Tables 1A and 1B, "cracking during acid treatment" was evaluated according to the following criteria. 〇: No visible cracks ×: Visually observed cracks

[0088] <<Process (4): Drying process>> The glass obtained in step (3) was immersed in purified water at 80°C and washed for 20 minutes while applying ultrasonic waves at 28 kHz. After that, it was taken out and left at room temperature for 12 hours, and then dried in a vacuum furnace under reduced pressure of 20 kPa for 3 hours so that the mass change rate was 10 to 50%.

[0089] <<Step (5): Sintering process>> The glass dried in step (4) was sandwiched between 60mm x 60mm x 1mm alumina setters and sintered under atmospheric pressure under the following conditions. The results of investigating cracks during sintering are shown in Tables 1A and 1B. Heating rate and time: 100°C / hr, 11-hour controlled temperature, time: 1100°C, 10-hour cooling rate and time: 100°C / hr

[0090] In Tables 1A and 1B, "cracks during sintering" was evaluated according to the following criteria (n=3). 〇: No visible cracks or breaks. ×: Visually observed cracks.

[0091] [Table 1A]

[0092] [Table 1B]

[0093] As shown in Table 1A and Table 1B, Examples 1, 2, and 4 、1 0, 11 and Reference Example 5 is a high silicate glass precursor having a composition within the range specified in the present invention, and fractures and cracks occurred during the acid treatment and sintering. On the other hand, fractures and cracks occurred in Examples 3, 6 to 9, and 12 to 18, which are comparative examples, during the acid treatment and sintering.

[0094] [Experimental Example 2] <Glass precursor clarity test> As shown in Table 2 (mol % oxide basis), raw materials such as silica sand were mixed to prepare a 500g batch to obtain glass having the same composition as Example 1. The raw materials were placed in a φ100mm platinum crucible and heated in an electric furnace at 1600°C for 3 hours to melt the glass. The molten glass, along with the platinum crucible, was placed in an electric furnace at a temperature of approximately Tg + 50°C and held there for 1 hour. After that, the electric furnace was cooled to Tg - 100°C at a rate of 1°C / min, and the glass was allowed to cool to room temperature. The resulting glass block was then cored out of the crucible using a φ50mm core drill. The glass was then ground and polished to a thickness of approximately 10mm to produce an optically mirrored surface parallel to the cross-sectional direction. The number of bubbles was evaluated using an optical microscope. The results are shown in Table 2. In Table 2, Examples 19 to 22 are working examples.

[0095] In Table 2, "clarity" is 1 cm 2 The number of bubbles per unit area was shown.

[0096] [Table 2]

[0097] As shown in Table 2, in Examples 20 to 22, in which the Cl content was 0.1% or more, the composition contained 0.1% or more Cl in the high silicate glass precursor production process, and as a result, the generation of bubbles was suppressed and excellent clarity was achieved compared to Example 19, in which the Cl content was less than 0.1%.

[0098] [Experimental Example 3] <Production of large high silicate glass> <<Step (1): Glass precursor production process>> Each reagent was weighed and mixed to obtain a 13 kg blended batch so as to obtain the glass composition shown in mole percentage based on oxides in Example 20. Next, using a platinum crucible, the raw materials were charged at 1550°C over a period of 4 hours, followed by stirring using a platinum stirrer for 1 hour and leaving to stand for 2 hours. After that, the temperature was lowered to 1250°C, and then the mixture was cast into a carbon mold to obtain a 400 mm × 400 mm × 30 mm glass (glass precursor) block.

[0099] <<Process (2): Phase separation process>> The glass obtained in step (1) was polished and then heat-treated under the conditions shown in Table 1 to cause phase separation. The block was then sliced ​​and ground to obtain a glass substrate measuring 375 mm × 375 mm × 1.2 mm.

[0100] <<Step (3): Acid Treatment Step>> The glass that had been phase-separated in step (2) and 10 L of 2 mol / L HCl were placed in a sealed container and subjected to an acid treatment at 90° C. for 20 hours to obtain porous glass.

[0101] <<Process (4): Drying process>> While the glass obtained in step (3) was immersed in acid, the temperature of the acid solution was lowered to 40°C, and then the glass was immersed in purified water at 40°C and washed for 20 minutes while applying ultrasonic waves at 28 kHz. After that, the glass was taken out and left at room temperature for 12 hours, and then dried according to the conditions in Table 3. The mass change rate during the drying process is shown in Table 3.

[0102] <<Step (5): Sintering process>> The glass dried in step (4) was sandwiched between a 400 mm x 400 mm x 10 mm alumina setter and sintered under the conditions (heating, controlled temperature, cooling) shown in Table 3. The results of examining cracks during sintering are shown in Table 3. In Table 3, Examples 23 and 24 are working examples, and Examples 25 and 26 are comparative examples. During sintering, the load per unit area on the glass was 4.5 g / cm. 2 was

[0103] In Table 3, "cracks during sintering" was evaluated according to the following criteria (n=3). 〇: No visible cracks or breaks. ×: Visually observed cracks. [Table 3]

[0104] As shown in Table 3, in both Examples 23 and 24, which are working examples, the porous glass was dried in the drying step before being sintered in the sintering step so that the moisture content fell within the range specified in the present invention, whereby a large-area, crack-free, high silicate glass substrate could be produced by sintering.

[0105] On the other hand, in Examples 25 and 26, which are comparative examples, the moisture content in the drying step was outside the range specified in the present invention, and cracks occurred during sintering.

[0106] [Experimental Example 4] For Example 24 in Experimental Example 3, <<Step (5): Sintering Step>> in Experimental Example 3 was carried out under the sintering conditions shown in Table 4. The OH group concentration of the obtained glass substrate was measured, and the results are shown in Table 4. Examples 27 to 32 are working examples.

[0107] [Table 4]

[0108] As shown in Table 4, it was found that the OH group concentration changes depending on the sintering conditions.

[0109] [Experimental Example 5] The change in Df depending on the OH group concentration was evaluated for the glass plate obtained in Experimental Example 4, and the results are shown in Figure 1. As shown in Figure 1, it was found that the lower the OH group concentration, the more improved the dielectric loss tangent.

[0110] [Experimental Example 6] The composition of the glass plate obtained in Example 24 of Experimental Example 3 was analyzed by ICP atomic emission spectrometry. The results are shown in Table 5 in terms of mole percentage based on oxides.

[0111] [Table 5]

[0112] [Experimental Example 7] The glass plate obtained in Example 24 of Experimental Example 3 was subjected to fluorescence measurement under the following conditions. The results are shown in FIG. Device: Horiba LabRAM HR Evolution Excitation wavelength: 532nm Power: 6mW@sample Objective lens: ×100, NA=0.8 Confocal pinhole: 200 μm Grating: 300gr / mm Measurement time: 1 sec x 10 times Measured at a depth of approximately 15 μm from the sample surface

[0113] As shown in FIG. 2, the glass plate of Example 24 had a relative fluorescence intensity of 100 or less in the fluorescence spectrum from 550 nm to 850 nm, which was lower than that of EN-A1 manufactured by AGC and D263-bio manufactured by Schott.

[0114] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-097128) filed on June 3, 2020, the entirety of which is incorporated by reference. All references cited herein are incorporated in their entirety.

Claims

1. A method for producing a high silicate glass substrate, comprising the following steps (1) to (5): (1) In terms of mole percentage based on oxides, SiO ２ 60% to 75% Al ２ O ３ 1.5% to 15%, B ２ O ３ 15% to 30%, P ２ O ５ 0% to 3%, R ２ To obtain a glass precursor containing 1% to 10% in total of one or more elements selected from O and R'O, where R is at least one element selected from Li, Na, and K, and R' is at least one element selected from Mg, Ca, Sr, and Ba. (2) subjecting the glass precursor to a first heat treatment to cause phase separation to obtain a phase-separated glass; (3) The phase-separated glass is acid-treated to make it porous, thereby obtaining porous glass. (4) The porous glass is dried to have a mass change rate defined by the following formula 1 of 10 to 50%: Mass change rate (%) = [(mass before drying - mass after drying) / mass before drying] x 100 (Equation 1) (5) subjecting the porous glass to a second heat treatment and sintering to obtain a high silicate glass substrate.

2. In the above (1), the bottom area of ​​the glass precursor is 300 cm ２ The method for producing a high silicate glass substrate according to claim 1 , wherein the above-mentioned step is carried out.

3. 3. The method for producing a high silicate glass substrate according to claim 1, wherein the glass precursor has a rectangular shape and an aspect ratio of 500 to 36,000.

4. In the above (1), the glass precursor is P ２ O ５ 4. The method for producing a high silicate glass substrate according to claim 1, wherein the content is 0.1% or more in mole percentage based on oxides.

5. The method for producing high silicate glass according to any one of claims 1 to 4, further comprising shaping the glass precursor after (1) or after (2).

6. 6. The method for producing high silicate glass according to claim 5, wherein steps (1) and (2) and shaping the glass precursor are carried out during continuous production in a refractory furnace.

7. 7. The method for producing a high silicate glass substrate according to claim 1, wherein in step (4), the porous glass is dried by being maintained at a temperature of 20° C. or higher and 100° C. or lower.

8. 8. The method for producing a high silicate glass substrate according to claim 1, wherein in step (4), the porous glass is dried for one hour or more.

9. 9. The method for producing a high silicate glass substrate according to claim 1, wherein in (3), the temperature of the acid treatment is 40° C. or higher and 100° C. or lower.

10. 10. The method for producing a high silicate glass substrate according to claim 1, wherein in the step (5), the second heat treatment is performed by sintering in an atmosphere having a dew point of 60° C. or less.

11. 11. The method for producing a high silicate glass substrate according to claim 1, wherein in the step (5), the second heat treatment is performed by increasing the temperature at a rate of 100° C. / hour or less.

12. 12. The method for producing a high silicate glass substrate according to claim 1, wherein in (1), the glass precursor contains Cl in an amount of 1% or less expressed in mole percentage.

13. 13. The method for manufacturing a high silicate glass substrate according to claim 1, further comprising, after step (5), irradiating the high silicate glass substrate with a laser to form holes in the high silicate glass substrate.

14. In terms of mole percentage based on oxide, SiO ２ 90% to 99%, Al ２ O ３ 0.3% to 1%, B ２ O ３ Contains 0% to 10% and has a base area of ​​300 cm ２ or more, and the OH group concentration is 1,200 ppm by mass or less.

15. 15. The high silicate glass substrate according to claim 14, having a dielectric loss tangent at 60 GHz of 0.001 or less.

16. R ２ 16. The high silicate glass substrate according to claim 14, wherein the glass substrate contains 0% to 3% in total of one or more elements selected from O and R'O, wherein R is at least one element selected from Li, Na, and K, and R' is at least one element selected from Mg, Ca, Sr, and Ba.

17. The high silicate glass substrate according to any one of claims 14 to 16, having holes with a diameter of 200 µm or less.

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