TW201408433A - Glass substrate finish-polishing method, and alkali-free glass substrate finish-polished according to said method - Google Patents

Abstract

The present invention pertains to a glass substrate finish-polishing method, whereby a polishing slurry containing cerium oxide as abrasive grains is used to polish the main surface of a glass substrate, the composition of the glass substrate being the alkali-free glass described below. The glass substrate finish-polishing method includes a step in which polishing is conducted under conditions in which, when the amount of polishing of the glass substrate is denoted as X (μm) when the height of undulations converted to undulations having a 20 mm pitch on the main surface of the glass substrate changes from 0.14 μm to 0.10 μm, 0.04/X becomes 0.12 or higher. The alkali-free glass has: a strain point of 710 DEG C or higher; an average coefficient of thermal expansion at 50 to 350 DEG C of 30x10<SP>-7</SP> to 43x10<SP>-7</SP>/ DEG C; a temperature (T2) of 1710 DEG C or less at which the glass viscosity is 10<SP>2</SP> dPa.s; and a temperature (T4) of 1320 DEG C or less at which the glass viscosity is 10<SP>4</SP> dPa.s, Furthermore, the alkali-free glass contains, in terms of mol% on an oxide basis, 66 to 70% SiO2, 12 to 15% Al2O3, 0 to 1.5% B2O3, over 9.5 to 13% MgO, 4 to 9% CaO, 0.5 to 4.5% SrO, 0 to 1% BaO, and 0 to 2% of ZrO2; and MgO + CaO + SrO + BaO is 17 to 21, MgO / (MgO + CaO + SrO + BaO) is at least 0.40, MgO / (MgO + CaO) is at least 0.40, and MgO / (MgO + SrO) is at least 0.60.

Description

Final polishing method of glass substrate and alkali-free glass substrate finally polished by the method

The present invention relates to a method for finally grinding an alkali-free glass substrate substantially free of an alkali metal oxide for use as a glass substrate for various displays or a glass substrate for a photomask, and a non-alkali which is finally ground by the method glass substrate.

Conventionally, various glass substrates for displays, particularly those in which a metal or an oxide film is formed on the surface, are required to have the following characteristics.

(1) When an alkali metal oxide is contained, an alkali metal ion diffuses into a film and deteriorates film characteristics, and therefore substantially does not contain an alkali metal ion.

(2) The strain point is high so that the deformation of the glass and the shrinkage (heat shrinkage) accompanying the stabilization of the glass structure can be suppressed to a minimum when exposed to a high temperature in the film forming step.

(3) It has sufficient chemical durability for various chemicals used for semiconductor formation. In particular, a hydrofluoric acid buffer (BHF (Buffered Hydrofluoric Acid): a mixture of hydrofluoric acid and ammonium fluoride) for SiO _x or SiN _x etching, and ITO (Indium Tin Oxides, indium tin oxide) The etched hydrochloric acid-containing chemical solution, the various acids (nitric acid, sulfuric acid, etc.) for etching the metal electrode, and the base of the resist stripper have durability.

(4) There are no defects (bubbles, veins, inclusions, depressions, scars, etc.) inside and on the surface.

In addition to the above requirements, in recent years, the following conditions have been made.

(5) The display is required to be lightweight, and the glass itself is expected to have a lower density glass.

(6) The weight of the display is required to be reduced, and the thinning of the glass substrate is expected.

(7) In addition to the previous amorphous germanium (a-Si) type liquid crystal display, a polycrystalline germanium (p-Si) type liquid crystal display having a slightly higher heat treatment temperature (a-Si: about 350 ° C → p-Si: 350) was also started. ~550°C).

(8) In order to speed up the temperature rise and fall of the heat treatment of the liquid crystal display, improve productivity, or improve thermal shock resistance, glass having a small average thermal expansion coefficient of glass is required.

On the other hand, the progress of the drying of the etching progresses, and the requirement for the BHF resistance is weakened. In order to improve the BHF resistance, the conventional glass is often made of glass containing 6 to 10 mol% of B ₂ O ₃ . However, B ₂ O ₃ has a tendency to lower the strain point. As an example of the alkali-free glass containing no B ₂ O ₃ or a small amount, there are the following.

Patent Document 1 discloses a SiO ₂ -Al ₂ O ₃ -SrO glass containing no B ₂ O ₃ , but the temperature required for melting is high, which makes manufacturing difficult.

Patent Document 2 discloses a SiO ₂ -Al ₂ O ₃ -SrO crystallized glass containing no B ₂ O ₃ , but the temperature required for melting is high, which makes manufacturing difficult.

Patent Document 3 discloses a glass containing 0 to 3% by weight of B ₂ O ₃ , but the strain point of the example is 690 ° C or lower.

Patent Document 4 discloses a glass containing 0 to 5 mol% of B ₂ O ₃ , but the average thermal expansion coefficient at 50 to 350 ° C exceeds 50 × 10 ^-7 / ° C.

Patent Document 5 discloses a glass containing 0 to 5 mol% of B ₂ O ₃ , but has a large thermal expansion and a large density.

In order to solve the problem in the glass described in Patent Documents 1 to 5, the alkali-free glass described in Patent Document 6 is proposed. The alkali-free glass described in Patent Document 6 has a high strain point and can be formed by a floating method, and is preferably used for applications such as a substrate for a display and a substrate for a photomask.

In the final polishing performed for such a purpose, minute irregularities or undulations existing on the surface of the substrate can be removed with a smaller amount of polishing, which is preferable for the following reasons: The cost required for the grinding is reduced; the mixing of the glass powder or the glass cullet removed by the grinding into the polishing slurry is reduced, and the frequency of replacement of the polishing slurry can be reduced.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. 62-113735

Patent Document 2: Japanese Patent Laid-Open No. 62-100450

Patent Document 3: Japanese Patent Laid-Open No. 4-325435

Patent Document 4: Japanese Patent Laid-Open No. Hei 5-232458

Patent Document 5: US Patent No. 5,326,730

Patent Document 6: Japanese Patent Laid-Open No. Hei 10-45422

On the other hand, the glass substrate formed by the floating method has minute irregularities or undulations on the surface (a distance of 3 to 30 mm and a maximum height of about 0.3 μm). Such a slight unevenness or undulation is not problematic when the glass substrate formed by the floating method is used as a plate glass for automobiles, buildings, etc., but it is used when it is used as a glass substrate for various displays. The image of the display to be manufactured causes deformation or uneven color. Therefore, it is necessary to remove minute irregularities or undulations by final grinding.

For the final grinding performed for such a purpose, it is preferred to use a grinding using a polishing slurry containing cerium oxide as the abrasive particles.

However, although the solid phase crystallization method is used as a method for producing a high-quality p-Si TFT, in order to carry out the solid phase crystallization method, it is required to further increase the strain point.

Moreover, in terms of glass manufacturing processes, especially in melting and forming, it is required to reduce the viscosity of the glass, especially to lower the glass viscosity to 10 ⁴ dPa. s temperature T ₄ .

The object of the present invention is to provide a solution to the above defects, high strain point, low viscosity, especially glass viscosity of 10 ⁴ dPa. a final polishing method capable of removing minute irregularities or undulating glass substrates present on the surface of the substrate with a small amount of polishing, and final polishing by the method, when the alkali-free glass substrate having a lower temperature T ₄ is subjected to final polishing An alkali-free glass substrate.

The present invention provides a final polishing method (1) for a glass substrate, which is a final polishing method for polishing a glass substrate on which a main surface of a glass substrate is polished using cerium oxide as a polishing slurry; and the composition of the glass substrate is as follows The alkali-free glass; the final polishing method of the glass substrate includes the step of grinding the glass substrate when the height of the undulation of the main surface of the glass substrate is changed from 0.14 μm to 0.10 μm When the amount is X (μm), the polishing is carried out under conditions of 0.04/X of 0.12 or more; the alkali-free glass strain point is 710 ° C or higher, and the average thermal expansion coefficient at 50 to 350 ° C is 30 × 10 ^-7 to 43 ×10 ^-7 /°C, the glass viscosity becomes 10 ² dPa. The temperature T ₂ of s is below 1710 ° C, and the glass viscosity is 10 ⁴ dPa. s the temperature T ₄ at 1320 ℃, in mole% based on oxides of showing _{containing: SiO 2 66 ~ 70, Al} 2 O 3 12 ~ 15, B 2 O 3 0 ~ 1.5, MgO more than 9.5 and 13 or less , CaO 4~9, SrO 0.5~4.5, BaO 0~1, ZrO ₂ 0~2, MgO+CaO+SrO+BaO is 17~21, MgO/(MgO+CaO+SrO+BaO) is 0.40 or more, MgO / (MgO + CaO) is 0.40 or more, and MgO / (MgO + SrO) is 0.60 or more.

The present invention provides a final polishing method (2) for a glass substrate, which is a final polishing method for polishing a glass substrate on which a main surface of a glass substrate is polished using cerium oxide as a polishing slurry; and the composition of the glass substrate is as follows The alkali-free glass; the final polishing method of the glass substrate includes the step of grinding the glass substrate when the height of the undulation of the main surface of the glass substrate is changed from 0.14 μm to 0.10 μm When the amount is X (μm), the polishing is carried out under conditions of 0.04/X of 0.12 or more; the alkali-free glass strain point is 710 ° C or higher, and the average thermal expansion coefficient at 50 to 350 ° C is 30 × 10 ^-7 to 43 ×10 ^-7 /°C, the glass viscosity becomes 10 ² dPa. The temperature T ₂ of s is below 1710 ° C, and the glass viscosity is 10 ⁴ dPa. The temperature T ₄ of s is 1320 ° C or less, and the molar % of the oxide is represented by: SiO ₂ 66 to 70, Al ₂ O ₃ 12 to 15, B ₂ O ₃ 0 to 1.5, MgO 5 to 9.5, and CaO 4 . ~11, SrO 0.5~4.5, BaO 0~1, ZrO ₂ 0~2, MgO+CaO+SrO+BaO exceeds 18.2 and is 21 or less, and MgO/(MgO+CaO+SrO+BaO) is 0.25 or more, MgO/ (MgO + CaO) is 0.3 or more, MgO / (MgO + SrO) is 0.60 or more, and Al ₂ O ₃ × (MgO / (MgO + CaO + SrO + BaO)) is 5.5 or more.

In the final polishing method (1), (2) of the glass substrate of the present invention, it is preferred to finally study The height of the undulation of the main surface of the glass substrate before the grinding to a pitch of 20 mm is 0.2 μm or less.

The final polishing methods (1) and (2) of the glass substrate of the present invention preferably perform final polishing on the main surface of the glass substrate formed by the floating method.

Further, the present invention provides an alkali-free glass substrate which is subjected to final polishing using the final polishing method (1) or (2) of a glass substrate.

In the glass substrate of the present invention, it is preferable that the height of the undulation of the glass substrate after the final polishing is 20 mm pitch is 0.07 μm or less.

In the glass substrate of the present invention, it is preferable that the surface roughness of the main surface of the glass substrate after the final polishing is 5 μm square is 0.30 nm or less.

The glass substrate of the present invention preferably has a length of at least one side of 900 mm or more.

According to the method of the present invention, when the alkali-free glass substrate formed by the floating method is subjected to final polishing, minute irregularities or undulations existing on the surface of the substrate can be removed with a small amount of polishing, and it is suitable for use as a display. The higher flatness of the substrate used.

The alkali-free glass substrate finally polished by the method of the present invention is particularly suitable for a display substrate for a high strain point application, a substrate for a photomask, a glass substrate for a magnetic disk, and the like.

Hereinafter, the final polishing method of the glass substrate of the present invention will be described.

In the final polishing method (1) of the glass substrate of the present invention, an alkali-free glass substrate using a glass raw material obtained by blending the glass composition 1 described below is used.

The alkali-free glass is represented by SiO ₂ 66 to 70, Al ₂ O ₃ 12 to 15, B ₂ O ₃ 0 to 1.5, MgO exceeding 9.5 and 13 or less, and CaO 4 to 9, SrO 0.5~4.5, BaO 0~1, ZrO ₂ 0~2, MgO+CaO+SrO+BaO is 17~21, MgO/(MgO+CaO+SrO+BaO) is above 0.40, MgO/(MgO+CaO) It is 0.40 or more, and MgO / (MgO + SrO) is 0.60 or more.

Moreover, in the final polishing method (2) of the glass substrate of the present invention, an alkali-free glass substrate using a glass raw material obtained by blending the glass composition 2 described below is used.

The alkali-free glass is represented by an oxide-based molar %: SiO ₂ 66-70, Al ₂ O ₃ 12-15, B ₂ O ₃ 0-1.5, MgO 5-9.5, CaO 4-11, SrO 0.5~ 4.5, BaO 0~1, ZrO ₂ 0~2, MgO+CaO+SrO+BaO exceeds 18.2 and is 21 or less, MgO/(MgO+CaO+SrO+BaO) is 0.25 or more, and MgO/(MgO+CaO) is 0.3 or more, MgO/(MgO+SrO) is 0.60 or more, and Al ₂ O ₃ × (MgO/(MgO+CaO+SrO+BaO)) is 5.5 or more.

Next, the composition range of each component will be described. When SiO _{2 is} less than 66% (% by mole, the following is the same unless otherwise specified), the strain point is not sufficiently increased, the coefficient of thermal expansion is increased, and the density is increased. Further, the chemical durability of the glass, particularly the acid resistance, is lowered, and it is difficult to obtain the convex portion selectivity at the time of polishing, and it is difficult to obtain smoothness. It is preferably 66.5% or more, more preferably 67% or more. When it exceeds 70%, the meltability of glass will fall and the devitrification temperature will rise. It is preferably 69% or less.

Al ₂ O ₃ increases Young's modulus and suppresses deformation during polishing of glass, and suppresses phase separation of glass, lowers thermal expansion coefficient, increases strain point, increases hardness, and improves convexity selectivity during polishing, but if not At 12%, this effect is not exhibited, and other components which increase the expansion are increased, so as a result, the thermal expansion becomes large. It is preferably 12.2% or more. If it exceeds 15%, the meltability of the glass may deteriorate or the devitrification temperature may rise. It is preferably 14.5% or less, more preferably 14% or less, still more preferably 13.8% or less.

B ₂ O ₃ can be added up to 1.5% in order to improve the melt reactivity of the glass and lower the devitrification temperature. However, if it is too large, the photoelastic constant will become large, and when the stress is applied, color unevenness is likely to occur. Further, when the amount of B ₂ O _{3 is} too large, the Young's modulus is lowered, and it is difficult to obtain smoothness due to deformation during polishing, and the surface roughness after polishing is increased. Furthermore, the strain point is also reduced. Therefore, it is preferably 1.3% or less, more preferably 1% or less, and is preferably substantially not contained. The term "substantially free" means that it is not included except for unavoidable impurities (the same in this specification).

MgO increases the Young's modulus by not increasing the specific gravity, thus increasing the specific modulus of elasticity, This can reduce the deflection of the glass. Further, in the alkaline earth, there is a feature that the expansion is not increased and the strain point is not excessively lowered, and the meltability is also improved.

Here, in the glass composition 1, the MgO content exceeds 9.5% and is 13% or less. If it is 9.5% or less, the effect obtained by the above addition of MgO will not be sufficiently exhibited. However, if it exceeds 13%, the devitrification temperature rises. It is preferably 12.5% or less, more preferably 12% or less, still more preferably 11.5% or less.

On the other hand, in the glass composition 2, the MgO content is 5 to 9.5%. If it is less than 5%, the effect obtained by the addition of MgO described above does not sufficiently appear. It is preferably 6% or more, more preferably 7% or more. However, if it exceeds 9.5%, the devitrification temperature rises. It is preferably 9.3% or less, more preferably 9% or less.

CaO is second only to MgO in the alkaline earth type, and has a feature of increasing the Young's modulus and the specific elastic modulus without increasing the expansion and reducing the strain point excessively, and also improving the meltability.

Here, in the glass composition 1, the CaO content is 4 to 9%. If it is less than 4%, the effect obtained by the above addition of CaO will not be sufficiently exhibited. However, if it exceeds 9%, the devitrification temperature rises or a large amount of phosphorus, which is an impurity in limestone (CaCO ₃ ) as a CaO raw material, is mixed. It is preferably 7% or less, more preferably 6% or less, further preferably 5% or less.

On the other hand, in the glass composition 2, the CaO content is 4 to 11%. If it is less than 4%, the effect obtained by the above addition of CaO will not be sufficiently exhibited. It is preferably 5% or more. However, if it exceeds 11%, the devitrification temperature rises or the phosphorus which is an impurity in the limestone (CaCO ₃ ) which is a CaO raw material is mixed in a large amount. It is preferably 10% or less, more preferably 9% or less, further preferably 7% or less, and particularly preferably 6% or less.

SrO does not increase the devitrification temperature of the glass to improve the meltability, but if it is less than 0.5%, the effect does not sufficiently appear. It is preferably 1.0% or more, and more preferably 2.0% or more. However, if it exceeds 4.5%, the expansion coefficient increases. It is more preferably 4.0% or less, further preferably 3.5% or less.

Although BaO is not essential, it may be contained in order to improve meltability. But if too much, the glass It becomes brittle and becomes easily damaged, and the expansion and density of the glass are excessively increased, so that it is 1% or less. It is preferably less than 1%, more preferably 0.5% or less, and further preferably substantially not contained.

ZrO ₂ may be contained to 2% in order to increase the Young's modulus, to lower the glass melting temperature, or to promote crystallization during calcination. If it exceeds 2%, the glass becomes unstable, or the relative dielectric constant ε of the glass becomes large. It is preferably 1.5% or less, more preferably 1.0% or less, still more preferably 0.5% or less, and particularly preferably substantially not contained.

In the glass composition 1, when MgO, CaO, SrO, and BaO are less than 17% in total, the Young's modulus is low, and it is difficult to suppress deformation at the time of polishing, and it is difficult to obtain a convexity during polishing because of low hardness. Partial selectivity. Further, the photoelastic constant is increased, and the meltability is lowered. It is preferably 18% or more, and more preferably 18.5% or more. If it is more than 21%, there is a difficulty in that the coefficient of thermal expansion cannot be reduced. It is preferably 20% or less.

In the glass composition 2, when MgO, CaO, SrO, and BaO are 18.2% or less in total, the Young's modulus is low, and it is difficult to suppress deformation at the time of polishing, and since the hardness is low, the convexity at the time of polishing cannot be obtained. Partial selectivity. Further, the photoelastic constant is increased, and the meltability is lowered. If it is more than 21%, there is a difficulty in that the coefficient of thermal expansion cannot be reduced. It is preferably 20% or less.

In the glass composition 1, the combination of MgO, CaO, SrO, and BaO satisfies the above three conditions, and the Young's modulus is high, and the deformation at the time of polishing can be easily suppressed, and the specific modulus is higher than that of the elastic modulus. The strain point can be raised without increasing the devitrification temperature, thereby reducing the viscosity of the glass, especially the glass viscosity to 10 ⁴ dPa. s temperature T ₄ .

MgO/(MgO+CaO+SrO+BaO) is 0.4 or more, preferably 0.45 or more.

MgO/(MgO+CaO) is 0.4 or more, preferably 0.52 or more, and further preferably 0.55 or more.

MgO/(MgO+SrO) is 0.6 or more, preferably 0.7 or more.

In the glass composition 2, the combination of MgO, CaO, SrO, and BaO satisfies the above three conditions, and the Young's modulus is high, and the deformation at the time of polishing can be easily suppressed, and the specific modulus is higher than that of the elastic modulus. The strain point can be raised without increasing the devitrification temperature, thereby reducing the viscosity of the glass, especially the glass viscosity to 10 ⁴ dPa. s temperature T ₄ .

MgO/(MgO+CaO+SrO+BaO) is 0.25 or more, preferably 0.3 or more, more preferably 0.4 or more, still more preferably 0.45 or more.

MgO/(MgO+CaO) is 0.3 or more, preferably 0.4 or more, more preferably 0.52 or more, still more preferably 0.55 or more.

MgO/(MgO+SrO) is 0.6 or more, preferably 0.7 or more.

In the case of the glass composition 2, when Al ₂ O ₃ × (MgO / (MgO + CaO + SrO + BaO)) is 5.5 or more, the Young's modulus can be increased and the deformation at the time of polishing can be easily suppressed, which is preferable. It is preferably 5.75 or more, more preferably 6.0 or more, further preferably 6.25 or more, and particularly preferably 6.5 or more.

Further, in order to prevent deterioration of characteristics of a metal or an oxide film provided on the surface of the glass during the manufacture of the display using the alkali-free glass substrate of the present invention, the glass raw material preferably contains substantially no P ₂ O ₅ . Further, in order to facilitate the reuse of the glass, the glass raw material preferably contains substantially no PbO, As ₂ O ₃ or Sb ₂ O ₃ .

In order to improve the meltability, clarity, and formability of the glass, ZnO, Fe ₂ O ₃ , SO ₃ , F, Cl, and SnO ₂ may be added to the glass raw material in a total amount of 5% or less.

The production of the alkali-free glass substrate of the present invention is carried out, for example, by the following procedure.

The raw materials of the respective components are blended so as to be the target components (the glass compositions 1 and 2 described above), and they are continuously introduced into a melting furnace, and heated to 1500 to 1800 ° C to be melted. The molten glass is formed into a plate-shaped glass ribbon having a specific thickness by a molding device, and the glass ribbon is slowly cooled and then cut, whereby an alkali-free glass substrate can be obtained.

In the present invention, a glass ribbon formed into a plate shape by a float method is preferred.

Hereinafter, preferred embodiments of the final polishing method for a glass substrate of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 2 is a perspective view showing the overall configuration of a polishing apparatus 10 to which a final polishing method for a glass substrate according to an embodiment is applied. Figure 3 is a side elevational view of the polishing apparatus 10 of Figure 2.

The polishing apparatus 10 shown in the drawings is a polishing apparatus which uses a polishing tool to produce a glass sheet G by a floating method, that is, for example, a thickness of 0.7 mm or less and a length of one side of 900 mm or more and a Young's modulus. The main surface (polishing surface) of the glass plate G of 65 GPa or more is polished to the flatness necessary for the glass substrate for FPD (Flat Panel Display). In other words, the polishing apparatus 10 is a device that polishes the polished surface of the glass sheet G having an undulation height of 0.2 μm or less which is undulated by a pitch of 20 mm, and converts the undulating height of the undulation of 20 mm pitch. It is reduced to 0.07 μm or less, thereby producing a glass plate which is most suitable as a glass substrate for FPD without causing distortion or color unevenness of an image.

Further, in the present invention, by setting the Young's modulus of the glass sheet G to 82 GPa or more, for example, a thin plate having a thickness of 0.5 mm or less or a large plate having a length of 1000 mm or more on one side can be used. The flat surface of the glass plate G (grinding surface) is polished to the flatness necessary for the glass substrate for FPD.

Further, the measurement method of the above-mentioned undulation is a method described in JIS B0031: '82 and JIS B0601: '82. The pitch and undulation can be defined as shown in FIG. If the pitch is large, the undulation becomes large, but the height of the undulation of the undulation of 20 mm pitch can be obtained by linearly regressing the relationship between the pitch and the undulation.

The height of the undulation of the main surface of the glass substrate before the final polishing to a pitch of 20 mm is more preferably 0.17 μm or less. Further, the height of the undulation of the main surface of the glass substrate after the final polishing to a pitch of 20 mm is more preferably 0.05 μm or less.

The polishing apparatus 10 includes a polishing head 12 and a platen 14. The polishing head 12 includes a glass holding member 16 that holds a non-abrasive surface of the glass sheet G, a glass holding platen 20 that is mounted with a glass holding member 16 via a sealing material 18, and a canvas 22 that is mounted with a glass holder. Pressure plate 20. A rotating shaft 24 is fixed to the canvas 22 by making the rotating shaft 24 with its axis P1 The center rotates to rotate the polishing head 12, and the polishing head 12 revolves by rotating the rotating shaft 24 around the revolution axis P2.

Further, compressed air is supplied to the air chamber 23 of the canvas 22 via the hollow rotating shaft 24, and the pressure of the compressed air is transmitted to the glass sheet G via the glass holding platen 20, the sealing material 18, and the glass holding member 16.

The platen 14 includes a polishing tool 26 and a polishing tool holding platen 30 to which the polishing tool 26 is attached via a sealing material 28. The sealing material 28 is a sealing material made of a resin (for example, made of a polyurethane) which is soft and has improved adsorption retention.

Therefore, in the polishing apparatus 10 of the embodiment, the polishing surface of the glass sheet G is pressed against the polishing tool 26 by the pressure of the compressed air, and the polishing head 12 is rotated and revolved, thereby polishing the polishing surface of the glass sheet G. .

The polishing tool 26 preferably has an A hardness (according to ISO 7619) of 20 or more, a D hardness (according to ISO 7619) of 99 or less, a thickness of 1.0 to 2.5 mm, a thickness distribution of ±0.3 mm or less, and further preferably a thickness distribution of Within ±0.05mm.

If the A hardness of the polishing tool 26 is less than 20, the undulation of the glass sheet G cannot be lowered, and if the D hardness exceeds 99, the glass sheet G is easily broken. Further, if the thickness of the polishing tool 26 is less than 1 mm, the polishing tool 26 cannot be grooved. In particular, if the groove processing is not performed in the large-area polishing tool 26, the distribution of the abrasive grains becomes uneven, which causes a problem in the processing of the glass sheet G. On the other hand, when the thickness of the polishing tool 26 exceeds 2.5 mm, the deformation margin of the polishing tool 26 becomes large, and the processing quality of the glass plate G is lowered. Furthermore, the thickness distribution of the abrasive article 26 is the maximum thickness - the minimum thickness in the region other than the grooved portion. When the thickness distribution exceeds ±0.3 mm, the pressure distribution becomes large and the processing quality of the glass sheet is lowered. The thickness distribution is preferably within ±0.2 mm, more preferably within ±0.1 mm, and even more preferably within ±0.05 mm.

Thus, by specifying the hardness, thickness, and thickness distribution of the polishing tool 26 as described above, the glass sheet G produced by the floating method can be polished to be the most suitable glass for FPD. The glass plate of the substrate.

On the other hand, as a result of intensive research by the inventors of the present application, it is preferable to manage only the A hardness of the polishing tool 26 in order to make the height of the undulation of the 20 mm pitch to be 0.07 μm or less. The compressibility, compressive elasticity modulus, A hardness, thickness, and distribution of the retaining member 16 are maintained.

For example, if the A hardness of the glass holding member 16 is too low, the durability of the glass holding member 16 is lowered, and the glass holding member 16 cannot be used repeatedly. Further, when the A hardness of the glass holding member 16 is moderately low, since the glass holding member 16 absorbs the undulations existing on the non-polishing surface of the glass sheet G, it can be satisfactorily ground by the polishing tool 26 on the glass plate. The undulation of the polished surface of G. On the other hand, when the A hardness of the glass holding member 16 is too high, the grinding of the glass sheet G by the polishing tool 26 cannot be performed in a state where the glass holding member 16 cannot absorb the undulation of the non-polishing surface of the glass sheet G. Therefore, when the glass sheet G is detached from the glass holding member 16, the glass sheet G is caused to rebound, and as a result, the polished surface of the glass sheet G remains at a height of 0.07 μm in terms of the undulation of the undulation of 20 mm pitch. The ups and downs.

In addition, when the thickness distribution is larger than ±0.05 mm, there is a problem that unevenness occurs in the surface of the glass sheet G due to the cushioning property of the glass holding member 16, and the undulation does not become uniform.

The compression coefficient indicates the cushioning property following the initial glass sheet G, and the compressive elasticity coefficient indicates a parameter necessary for the degree of recovery in the case of repeated use. The glass holding member 16 is made of a foamed urethane.

In order to solve the above problem, the glass holding member 16 preferably has a compression coefficient (according to JIS L1021-6: '07 Attachment 1) of 10 to 70%, and a compression modulus (according to JIS L1021-6: '07 Attachment 1, but The initial load is set to 100 gf/cm ² , the final load is 1120 gf/cm ² ) is 70 to 98, the A hardness is 2 to 20, the thickness is 0.3 to 2.0 mm, and the thickness distribution is within ±0.05 mm.

Further, if the glass plate G is thinned in the management of the glass holding member 16, it is necessary to particularly narrow the management range. For example, in the case of the glass sheet G having a thickness of 0.5 mm or less, the glass holding member 16 preferably has a compression coefficient of 10 to 70%, a compressive elastic modulus of 70 to 98, an A hardness of 2 to 20, and a thickness of 0.5 to 1.5. Mm, the thickness distribution is within ±0.05 mm. Further, in the case of the glass sheet G having a thickness of 0.3 mm or less, the glass holding member 16 preferably has a compression coefficient of 10 to 70%, a compressive elastic modulus of 70 to 98, an A hardness of 2 to 20, and a thickness of 0.7 to 1.2. Mm, the thickness distribution is within ±0.05 mm.

By setting the compression coefficient, compression modulus, A hardness, thickness, and thickness distribution of the glass holding member 16 as described above, the glass sheet G produced by the floating method can be polished to be most suitable as a glass substrate for FPD. glass plate.

Moreover, it is preferable that the surface of the glass holding platen 20 to which the glass holding member 16 is attached via the sealing material 18 has a maximum cross-sectional height of the undulation curve of 20 μm or less when the evaluation length is 30 mm.

Even when the glass holding member 16 is managed, when the maximum cross-sectional height of the undulating curve of the glass holding platen 20 is too high, it is difficult to satisfactorily absorb the undulations existing on the non-polishing surface of the glass sheet G by the glass holding member 16. The undulation of the polished surface of the glass plate G was ground to a height of 0.07 μm or less in terms of the undulation of the undulations at a pitch of 20 mm.

By specifying the maximum cross-sectional height of the undulation curve of the glass holding platen 20 as described above, the glass holding member 16 can well absorb the undulations existing on the non-polishing surface of the glass sheet G, and thus can be floated by the floating method. The manufactured glass plate is ground into a glass plate which is most suitable as a glass substrate for FPD.

The surface of the polishing tool holding platen 30 to which the polishing tool 26 is attached via the sealing material 28 preferably has a maximum cross-sectional height of a cross-sectional curve of 100 μm or less when the evaluation length is 30 mm.

Even if the polishing tool 26 is managed, when the maximum profile height of the profile curve of the pressure plate 30 is kept too high, a large undulation is generated on the surface of the polishing tool 26, which is difficult. The undulation of the polished surface of the glass plate G was ground to a height of 0.07 μm or less in terms of the undulation of the undulations at a pitch of 20 mm.

Therefore, by arranging the maximum cross-sectional height of the cross-sectional curve of the platen 30 by the polishing tool as described above, the undulation of the surface of the polishing tool 26 can be suppressed, so that the glass plate manufactured by the floating method can be ground into the most suitable one. A glass plate for a glass substrate for FPD.

Furthermore, the maximum profile height of the undulation curve is described in JIS B0601: '01.

The maximum profile height of the undulation curve was measured by Surfcom "1400-D64" manufactured by Tokyo Precision Co., Ltd. under the measurement conditions of a measurement length of 30 mm and λC = 0.8 mm.

Further, the unevenness of the load of the polishing of the glass sheet G against the polishing tool 26 is preferably 10% or less of the average load.

By setting the load on the polishing tool 26 of the glass sheet G as described above, the glass sheet G produced by the floating method can be polished into a glass sheet which is most suitable as a glass substrate for FPD. Further, as the measuring means of the load distribution, "BIG-MAT" or "HUGE-MAT" of a large-area pressure distribution measuring system manufactured by NITTA Corporation can be used.

As described above, according to the polishing apparatus 10 of the embodiment, the glass sheet G produced by the floating method, that is, a glass sheet having a thickness of 0.7 mm or less and a length of one side of 900 mm or more and a Young's modulus of 65 GPa or more is used. G is the object to be polished, and the non-abrasive surface of the glass sheet G is held by the glass holding member 16, and the height of the undulation of the embossed surface of the glass sheet G which is converted to the pitch of 20 mm by the polishing tool 26 is 0.2 μm or less. The undulations were ground to reduce the thickness to 0.07 μm or less in terms of the undulations of the undulations at a pitch of 20 mm, thereby producing a glass substrate for a flat panel display. Thereby, it is possible to manufacture a glass sheet G which is most suitable as a glass substrate for FPD without causing distortion or color unevenness of an image.

In the final polishing method of the glass substrate of the present invention, when the polishing amount of the glass substrate converted from the fluctuation of the pitch of 20 mm is changed from 0.14 μm to 0.10 μm, the amount of polishing of the glass substrate is X (μm), which is 0.04/X. Grinding is carried out under conditions of 0.12 or more. In this way, the final research The cost required for the grinding is reduced, and the mixing of the glass powder or the glass cullet removed by the polishing into the polishing slurry is reduced, and the frequency of replacement of the polishing slurry can be reduced. More preferably, the polishing is carried out under the conditions of 0.04/X to 0.13 or more, and further preferably 0.14 or more, and particularly preferably the polishing is carried out under conditions of 0.15 or more.

In the final polishing method of the present invention, the polishing is performed in a state in which the height of the undulation of the 20 mm pitch is higher than 0.14 μm, and the polishing height is 0.14 μm. The polishing conditions are not limited to the above 0.04/X. Conditions above 0.12. However, it is preferably carried out under the conditions that the above 0.04/X is 0.12 or more.

Further, in the final polishing method of the present invention, the polishing conditions in the case where the height of the undulations of the undulations at a pitch of 20 mm is less than 0.10 μm are not limited to the condition that the above 0.04/X is 0.12 or more, and The above condition that 0.04/X becomes less than 0.12 is implemented.

In the final polishing method of the glass substrate of the present invention, it is preferable that the height of the undulation of the main surface of the glass substrate before the final polishing is 20 μm or less. Thereby, the grinding time required for the final processing can be reduced, and it becomes easy to obtain excellent flatness. The height of the undulation of the undulation of 20 mm pitch is more preferably 0.17 μm or less, further preferably 0.15 μm or less.

In the final polishing method of the glass substrate of the present invention, it is preferable that the height of the undulation of the main surface of the glass substrate after the final polishing is 20 mm pitch is 0.07 μm or less. Thereby, the image is less likely to be deformed or uneven in color in the display using the substrate. The height of the undulation of the undulation of 20 mm pitch is more preferably 0.05 μm or less, further preferably 0.03 μm or less.

The final polishing method of the glass substrate of the present invention is preferably a surface roughness Ra of 5 μm square measured by AFM (Atomic Force Microscopy) on the main surface of the finally polished glass substrate of 0.30 nm or less. Thereby, stable driving characteristics are easily obtained in the display using the substrate.

An example of the grinding specifications is shown below.

Grinding pressure: 2kPa~25kPa

Grinding slurry: supplying the cerium oxide aqueous solution from the slurry supply hole of the grinding tool holding the pressing plate

Grinding tool: a soft urethane-like suede-like surface, and a groove for flowing a slurry on the surface (groove pitch: 4.5 mm, groove width: 1.5 mm, groove depth: 1 to 1.5 mm)

Glass plate thickness: 0.2mm~0.7mm

Shape of glass plate: rectangular glass plate with 1 side of 900mm or more

Non-abrasive surface of glass plate: kept by glass holding member

The above is an example of the polishing specifications.

Further, in the polishing apparatus 10 of the embodiment, in order to maintain the polishing rate of the glass sheet G, the surface of the polishing tool 26 is periodically ground by a grinding stone containing diamond abrasive grains to perform grinding.

In the polishing apparatus 10 of the embodiment, as shown in FIG. 4, a rectangular frame 42 which does not contain diamond abrasive grains and has no grinding ability is attached to the glass holder so as to surround the shaping grindstone 40 as shown in the plan view of FIG. Member 16. Then, the orthodontic stone 40 and the frame 42 are pressed against the polishing tool 26 by the air pressure of the compressed air supplied to the air chamber 23 of the canvas 22, and the surface of the polishing tool 26 is ground by the shaping grindstone 40.

At this time, the above air pressure is concentrated on the frame 42 located on the outer circumference of the shaping stone 40. However, since the frame 42 does not have the grinding ability, the surface of one portion of the polishing tool 26 that is in contact with the frame 42 is not ground. That is, the surface of the polishing tool 26 is ground only by the orthodontic stone 40 to which the air pressure is uniformly supplied. Thereby, the entire surface of the polishing tool 26 is flatly ground, so that the grinding by the orthodontic stone 40 can be improved.

Further, the frame 42 is not used only for the shaping of the polishing tool 26, and it is preferable to use the frame 42 also for the polishing of the glass plate G. Thereby, it is possible to prevent the air pressure from being concentrated on the edge of the glass sheet G during the polishing of the glass sheet G, so that the edge of the glass sheet G can be prevented from being excessively ground. As the material of the frame 42, stainless steel, iron, aluminum, polyethylene, polyurethane, etc. may be exemplified. Material with grinding ability.

Further, in the polishing apparatus 10 of the embodiment, in order to maintain the polishing rate of the glass sheet G, the surface of the polishing tool 26 is periodically washed with water, and cerium oxide or the like which removes the polishing liquid adhering to the surface of the polishing tool 26 is removed. Finishing of the residue.

In the polishing apparatus 10 of the embodiment, as shown in the side view of Fig. 6, the dressing water nozzle 44 is inclined, and the injection angle θ of the washing water 48 sprayed from the injection hole 46 is set to an acute angle. Then, the residue adhering to the surface of the polishing tool 26 is removed by reciprocating the water nozzle 44 and the polishing tool 26 in the horizontal direction.

Thereby, the residue adhering to the surface of the polishing tool 26 is excavated by the pressure of the washing water 48 which is ejected by the inclination, and is efficiently removed. Further, the removed residue is washed by the inclined washing water 48 efficiently to the outside of the system of the polishing tool 26. Thereby, the trimming by the water nozzle 44 can be improved.

Further, the injection angle θ of the washing water 48 is preferably 10 to 45 degrees, more preferably 30 degrees, from the viewpoint of the efficiency of the residue excavation and the washing efficiency of the residue. Further, if the impact force when the washing water 48 collides with the polishing tool 26 is weak, the removal efficiency of the residue is lowered. If the polishing device 26 is high, the polishing tool 26 is damaged. Therefore, it is preferably 5 to 50 kPa. Further, if the relative speed of the polishing tool 26 and the water nozzle 44 is slow, the dressing efficiency of the polishing tool 26 is lowered, and if it is faster, the removal efficiency of the residue is lowered, so that it is preferably 3 to 20 m/min.

In the present invention, the alkali-free glass substrate of the glass compositions 1 and 2 has a strain point of 710 ° C or higher, and heat shrinkage at the time of manufacture of the display using the alkali-free glass substrate can be suppressed. Further, as a method of producing a p-Si TFT which is carried out in a display manufacturing step such as an LCD (Liquid Crystal Display), a solid phase crystallization method can be applied. More preferably, it is 715 ° C or more, and further preferably 720 ° C or more. Particularly good is 735 ° C or more. When the strain point is 735 ° C or higher, it is suitable for "high strain point use" (for example, for organic EL (Electroluminescence) having a thickness of 0.7 mm or less, preferably 0.5 mm or less, and more preferably 0.3 mm or less. Display substrate or illumination base A plate or a substrate for display or a substrate for illumination having a thickness of 0.3 mm or less, preferably 0.1 mm or less.

However, if the strain point of the glass is too high, it is necessary to increase the temperature of the molding apparatus according to this, and the life of the molding apparatus is lowered. Therefore, it is preferable that the alkali-free glass substrate of the glass compositions 1 and 2 has a strain point of 750 ° C or less.

Further, the glass transition point of the alkali-free glass substrate of the glass compositions 1 and 2 is preferably 760 ° C or higher, more preferably 770 ° C or higher, and still more preferably 780 ° C or higher, for the same reason as the strain point.

Moreover, the average thermal expansion coefficient of the alkali-free glass substrate of the glass compositions 1 and 2 at 50 to 350 ° C is 30 × 10 ^-7 to 43 × 10 ^-7 / ° C, and the thermal shock resistance is large, and the use of the alkali-free can be improved. Productivity in the manufacture of a glass substrate display. In the glass of the present invention, the average coefficient of thermal expansion at 50 to 350 ° C is preferably 35 × 10 ^-7 to 40 × 10 ^-7 / ° C.

Further, the specific gravity of the alkali-free glass substrate of the glass compositions 1 and 2 is preferably 2.65 or less, more preferably 2.64 or less, still more preferably 2.62 or less.

Further, the specific modulus of elasticity of the alkali-free glass substrate of the glass compositions 1 and 2 is preferably 32 MNm/kg or more. If it is less than 32 MNm/kg, it is difficult to obtain the convexity selectivity at the time of polishing due to self-weight deflection. More preferably, it is 33 MNm/kg or more.

Further, the Young's modulus of the alkali-free glass substrate of the glass compositions 1 and 2 is preferably 82 GPa or more. If it is less than 82 GPa, the glass substrate is deformed at the time of polishing, and it is difficult to obtain smoothness, and it is difficult to obtain the convexity selectivity at the time of polishing due to deformation. More preferably, it is 84 GPa or more, further preferably 86 GPa or more, and particularly preferably 87 GPa or more.

Further, the photoelastic constant of the alkali-free glass substrate of the glass compositions 1 and 2 is preferably 31 nm/MPa/cm or less.

Sometimes, the phenomenon that the glass substrate used in the display has birefringence by the LCD manufacturing step or the stress generated when the LCD device is used, whereby the black display becomes gray, and the contrast of the liquid crystal display is lowered. . By setting the photoelastic constant 31 nm/MPa/cm or less can suppress this phenomenon to a small extent. More preferably, it is 30 nm/MPa/cm or less, further preferably 29 nm/MPa/cm or less, particularly preferably 28 nm/MPa/cm or less, and most preferably 27.5 nm/MPa/cm or less.

When the ease of securing other physical properties is considered, the photoelastic constant is preferably 23 nm/MPa/cm or more, and more preferably 25 nm/MPa/cm or more.

Further, the photoelastic constant can be measured by a disk compression method at a measurement wavelength of 546 nm.

Further, the alkali-free glass substrate of the glass compositions 1 and 2 preferably has a relative dielectric constant of 5.6 or more.

Touch sensing is performed in the case of an in-cell type touch panel (incorporating a touch sensor in a liquid crystal display panel) as described in Japanese Laid-Open Patent Publication No. 2011-70092 From the viewpoint of improvement in sensing sensitivity, reduction in driving voltage, and power saving, it is preferable that the relative dielectric constant of the glass substrate is high. By setting the relative dielectric constant to 5.6 or more, the sensing sensitivity of the touch sensor is improved. It is preferably 5.8 or more, more preferably 6.0 or more, still more preferably 6.1 or more.

Further, the relative dielectric constant can be measured by the method described in JIS C-2141.

Further, the alkali-free glass substrate of the glass compositions 1 and ^{2 has a} temperature T ₂ of 10 ² poise (dPa.s) of 1710 ° C or less, preferably less than 1710 ° C, more preferably 1700 ° C or less. It is preferably 1690 ° C or less, and particularly preferably 1260 ° C or less, so that it is relatively easy to melt.

Further, in the alkali-free glass substrate of the glass compositions 1 and 2, the temperature T ₄ at which the viscosity η is 10 ⁴ poise is 1320 ° C or lower, preferably 1315 ° C or lower, more preferably 1310 ° C or lower, further preferably 1305 ° C or lower. It is particularly preferably 1295 ° C or less, so it is suitable for floating forming.

Further, in the case where the devitrification temperature of the alkali-free glass substrate of the glass compositions 1 and 2 is 1350 ° C or less, it is preferable to form by the floating method. Preferably it is 1330 ° C More preferably, it is 1310 ° C or less, and further preferably 1300 ° C or less.

The devitrification temperature in the present specification is a value obtained by adding pulverized glass particles to a disk made of platinum and heat-treating in an electric furnace controlled to a fixed temperature for 17 hours, according to optical microscopy after heat treatment. The average temperature of the highest temperature of precipitation of crystals on the surface and inside of the glass and the lowest temperature at which no crystals are precipitated.

10‧‧‧ grinding device

12‧‧‧ polishing head

14‧‧‧ Platen

16‧‧‧Glass holding member

18‧‧‧ Sealing material

20‧‧‧ glass holding platen

22‧‧‧ Canvas

23‧‧ Air Chamber

24‧‧‧Rotary axis

26‧‧‧Brazil

28‧‧‧ Sealing material

30‧‧‧Abrasive holding platen

40‧‧‧Shaping stone

42‧‧‧Frame

44‧‧‧ water nozzle

46‧‧‧ spray holes

48‧‧‧ Washing water

G‧‧‧glass plate

P ₁ ‧‧‧Axis

P ₂ ‧‧‧ public axis

Θ‧‧‧spray angle

Figure 1 is a schematic diagram showing the relationship between pitch and undulation.

Fig. 2 is a perspective view showing the entire structure of a polishing apparatus to which the final polishing method of the glass substrate of the embodiment is applied.

Figure 3 is a side elevational view of the polishing apparatus 10 of Figure 2.

Fig. 4 is a schematic view showing a method of sharpening a polishing tool by an orthodontic grinding wheel according to an embodiment.

Figure 5 is a plan view of a sharpened abrasive article by the grinding method shown in Figure 4.

Figure 6 is a side view showing the dressing method of the grinding tool by trimming the water nozzle Figure.

Example (Examples 1 to 2, Comparative Example 1)

The raw materials of the respective components were blended in such a manner as to have the target composition shown in Table 1, melted in a continuous melting kiln, and subjected to sheet forming by a float method to obtain an alkali-free glass substrate.

The yttrium oxide aqueous solution is supplied from the slurry supply hole of the grinding tool holding platen to the polishing pad having the groove pitch of 4.5 mm, the groove width of 1.5 mm, and the groove depth of 1 to 1.5 mm. The glass substrate (920 mm × 730 mm, thickness 0.5 mm) was polished. In the middle, the relationship between the amount of polishing and the height of the undulation of the main surface of the glass substrate was measured and the pulverization was performed, and the relationship between the amount of polishing and the height of the undulation of the undulation of the pitch of 20 mm was determined.

From the results, the polishing amount X (μm) of the glass substrate when the height of the undulation of the main surface of the glass substrate was changed from 0.14 μm to 0.10 μm, and the value of 0.04 /X was determined. Further, the measurement of the undulation height of the main surface of the glass substrate before and after the final polishing at a pitch of 20 mm and the surface roughness Ra of 5 μm square of the main surface of the glass substrate after the final polishing were also performed. The surface roughness Ra was set to 1 Hz by a NanoScope IIIa manufactured by Digital Instruments, and a surface roughness of 5 μm square was obtained by scanning at 256 points/1.

The results are shown in Table 2 below.

Further, the strain point, the Young's modulus, the specific elastic modulus, and the photoelastic constant were also measured for the alkali-free glass substrate obtained by the above procedure. The results are shown in Table 2. The brackets indicate the calculated value.

The present invention has been described in detail with reference to the specific embodiments thereof, and it is understood that various changes or modifications may be added without departing from the spirit and scope of the invention.

The present application is based on Japanese Patent Application No. 2012-128249, filed on Jun.

10‧‧‧ grinding device

12‧‧‧ polishing head

14‧‧‧ Platen

16‧‧‧Glass holding member

18‧‧‧ Sealing material

20‧‧‧ glass holding platen

22‧‧‧ Canvas

23‧‧ Air Chamber

26‧‧‧Brazil

28‧‧‧ Sealing material

30‧‧‧Abrasive holding platen

G‧‧‧glass plate

P ₁ ‧‧‧Axis

P ₂ ‧‧‧ public axis

Claims (8)

A final polishing method for a glass substrate, wherein a glass substrate comprising a cerium oxide as a polishing granule is used as a main surface of the glass substrate; and the composition of the glass substrate is an alkali-free glass; the final polishing method of the glass substrate comprises In the following stage, when the height of the undulation of the main surface of the glass substrate converted to a pitch of 20 mm is changed from 0.14 μm to 0.10 μm, the polishing amount of the glass substrate is X (μm), and 0.04 / X is polished to a condition of 0.12 or more; the alkali-free glass strain point is 710 ° C or higher, and the average thermal expansion coefficient at 50 to 350 ° C is 30 × 10 ^-7 to 43 × 10 ^-7 / ° C, and the glass viscosity becomes 10 ² dPa. The temperature T ₂ of s is below 1710 ° C, and the glass viscosity is 10 ⁴ dPa. The temperature T ₄ of s is 1320 ° C or less, and the molar % of the oxide is represented by: SiO ₂ 66 to 70, Al ₂ O ₃ 12 to 15, B ₂ O ₃ 0 to 1.5, and MgO exceeding 9.5 and 13 Hereinafter, CaO 4~9, SrO 0.5~4.5, BaO 0~1, ZrO ₂ 0~2, MgO+CaO+SrO+BaO is 17-21, and MgO/(MgO+CaO+SrO+BaO) is 0.40 or more. MgO/(MgO+CaO) is 0.40 or more, and MgO/(MgO+SrO) is 0.60 or more. A final polishing method for a glass substrate, wherein a glass substrate comprising a cerium oxide as a polishing granule is used as a main surface of the glass substrate; and the composition of the glass substrate is an alkali-free glass; the final polishing method of the glass substrate comprises In the following stage, when the height of the undulation of the main surface of the glass substrate converted to a pitch of 20 mm is changed from 0.14 μm to 0.10 μm, the polishing amount of the glass substrate is X (μm), and 0.04 / X is polished to a condition of 0.12 or more; the alkali-free glass strain point is 710 ° C or higher, and the average thermal expansion coefficient at 50 to 350 ° C is 30 × 10 ^-7 to 43 × 10 ^-7 / ° C, and the glass viscosity becomes 10 ² dPa. The temperature T ₂ of s is below 1710 ° C, and the glass viscosity is 10 ⁴ dPa. The temperature T ₄ of s is 1320 ° C or less, and the molar % of the oxide is represented by: SiO ₂ 66 to 70, Al ₂ O ₃ 12 to 15, B ₂ O ₃ 0 to 1.5, MgO 5 to 9.5, and CaO 4 . ~11, SrO 0.5~4.5, BaO 0~1, ZrO ₂ 0~2, MgO+CaO+SrO+BaO exceeds 18.2 and is 21 or less, and MgO/(MgO+CaO+SrO+BaO) is 0.25 or more, MgO/ (MgO + CaO) is 0.3 or more, MgO / (MgO + SrO) is 0.60 or more, and Al ₂ O ₃ × (MgO / (MgO + CaO + SrO + BaO)) is 5.5 or more. The final polishing method of the glass substrate according to claim 1 or 2, wherein the height of the undulation of the main surface of the glass substrate before the final polishing is 20 μm or less is 0.2 μm or less. The final grinding method of the glass substrate according to any one of claims 1 to 3, which is The main surface of the glass substrate formed by the floating method is subjected to final polishing. An alkali-free glass substrate which is subjected to final polishing using the final grinding method of the glass substrate according to any one of claims 1 to 4. The alkali-free glass substrate according to claim 5, wherein the height of the undulation of the main surface of the glass substrate after the final polishing is 20 mm pitch is 0.07 μm or less. The alkali-free glass substrate according to claim 5 or 6, wherein a surface roughness of 5 μm square of the main surface of the glass substrate after the final polishing is 0.30 nm or less. The alkali-free glass substrate according to any one of claims 5 to 7, wherein at least one side has a length of 900 mm or more.