JP2018177556A - Glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To create a glass substrate that has excellent productivity (particularly, devitrification resistance) and a high etching rate to HF chemical solutions.SOLUTION: This glass substrate is characterized by containing as the glass composition, in mass%, SiO55-65%, AlO15-25%, BO5.4-9%, MgO 0-5%, CaO 5-10%, SrO 0-5%, BaO 0-10%, PO0.01-10%, and having a mass ratio SiO/BOof 6-11.5 and a molar ratio (MgO+CaO+SrO+BaO)/AlOof 0.8-1.4.SELECTED DRAWING: None

Description

  The present invention relates to a glass substrate, and more particularly to a glass substrate suitable as a substrate of an organic EL (OLED) display and a liquid crystal display. Further, the present invention relates to a glass substrate suitable as a substrate of an oxide TFT, low temperature p-silicon TFT (LTPS) driven display.

  BACKGROUND ART Conventionally, glass substrates are widely used as substrates for flat panel displays such as liquid crystal displays, hard disks, filters, sensors and the like. In recent years, in addition to conventional liquid crystal displays, OLED displays have been actively developed for reasons of self-emission, high color reproducibility, high viewing angle, high-speed response, high definition, etc. It is done. In addition, since liquid crystal displays and OLED displays of mobile devices such as smartphones are required to display a large amount of information while having a small area, a screen with ultra high definition is required. Furthermore, in order to display a moving image, a high-speed response is also required.

  An OLED display emits light when a current flows in an OLED element constituting a pixel. Therefore, a material with low resistance and high electron mobility is used as the drive TFT element. As this material, in addition to the above-mentioned LTPS (Low Temperature Polycrystalline Silicon), an oxide TFT represented by IGZO (indium, gallium, zinc oxide) is attracting attention. Oxide TFTs have low resistance, high mobility, and can be formed at relatively low temperatures. Conventional p-silicon TFTs, in particular LTPS, form devices on large-area glass substrates due to the instability of the excimer laser used to polycrystallize films of amorphous silicon (a-silicon) At the time, the TFT characteristics tended to be uneven, and in the case of a TV application etc., the display unevenness of the screen was apt to occur. On the other hand, when forming an element on a glass substrate with a large area, oxide TFTs are attracting attention as potent TFT-forming materials because they are excellent in the uniformity of the TFT characteristics, and some of them have already been put to practical use.

  A glass substrate used for a high definition display is required to have many characteristics. In particular, the following characteristics (1) to (4) are required.

(1) When the alkali component is large in the glass substrate, alkali ions are diffused into the formed semiconductor substance at the time of heat treatment, resulting in deterioration of film characteristics. Therefore, the content of the alkali component (in particular, the Li component and the Na component) is low or substantially not contained.
(2) The glass substrate is heat-treated to several hundred degrees in the steps of film formation, annealing, etc. of the semiconductor element. During the heat treatment, when the glass substrate is thermally shrunk, pattern displacement or the like is likely to occur. Therefore, it is difficult to thermally shrink, and in particular, the strain point is high.
(3) The thermal expansion coefficient is close to a member (for example, a-silicon or p-silicon) to be deposited on a glass substrate. For example, thermal expansion coefficient of ^{30 × 10 -7 ~45 × 10 -7} / ℃. The thermal shock resistance is also improved when the thermal expansion coefficient is 40 × 10 ⁻⁷ / ° C. or less.
(4) A high Young's modulus (or a specific Young's modulus) in order to suppress a defect due to the bending of the glass substrate.

Furthermore, from the viewpoint of producing a glass substrate, the glass substrate is also required to have the following characteristics (5) and (6).
(5) Having excellent meltability to prevent melt defects such as bubbles, bumps and cords.
(6) Devitrification resistance should be excellent in order to avoid the mixture of devitrified foreign matter.

JP, 2016-11256, A

  By the way, chemical etching of a glass substrate is generally used for thickness reduction of a display. This method is a method of thinning a glass substrate by immersing a display panel in which two glass substrates are bonded together in an HF (hydrofluoric acid) -based chemical solution.

  However, the conventional glass substrate has a problem that the etching rate is very slow because it has high resistance to the HF chemical solution. When the HF concentration in the chemical solution is increased to accelerate the etching rate, the number of insoluble particles in the HF-based solution increases, and as a result, the particles easily adhere to the glass surface, and etching is performed in the surface of the glass substrate. The uniformity is lost.

In order to solve the above problems, Patent Document 1 discloses that the amount obtained by reducing the content twice as much as Al ₂ O ₃ from the content of SiO _{2 in} alkali-free glass is less than 65 mol%. There is. However, since the non-alkali glass described in Patent Document 1 has low devitrification resistance (a high liquidus temperature), devitrification tends to occur at the time of molding, and molding to a glass substrate is difficult. Therefore, it is difficult for the non-alkali glass described in Patent Document 1 to simultaneously achieve high etching rate and high devitrification resistance.

  Therefore, the present invention has been made in view of the above circumstances, and the technical object thereof is to create a glass substrate which is excellent in productivity (especially devitrification resistance) and has a high etching rate for HF-based chemicals. .

As a result of repeating various experiments, the present inventors strictly control the glass composition range in SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -RO (RO is an alkaline earth metal oxide) glass. It finds out that the said technical subject can be solved by this, and proposes as this invention. That is, the glass substrate of the present invention is, as a glass composition, SiO ₂ 55-65%, Al ₂ O ₃ 15-25%, B ₂ O ₃ 5.4-9%, MgO 0-5%, in mass%. CaO 5 to 10%, SrO 0 to 5%, BaO 0 to 10%, P ₂ O ₅ 0.01 to 10%, and a mass ratio SiO ₂ / B ₂ O _{3 of 6} to 11.5, a molar ratio (MgO + CaO + SrO + BaO) / Al ₂ O ₃ is in the range of 0.8 to 1.4. Here, “MgO + CaO + SrO + BaO” refers to the total amount of MgO, CaO, SrO and BaO. “Mole ratio (MgO + CaO + SrO + BaO) / Al ₂ O ₃ ” refers to a value obtained by dividing the molar percentage of MgO, CaO, SrO and BaO by the molar percentage of Al ₂ O ₃ .

According to the inventor's investigation, if the mass ratio SiO ₂ / B ₂ O ₃ is reduced to 11.5 or less, the etching rate can be increased, but on the other hand, it is difficult to stabilize the glass. become. Therefore, in the present invention, the content of _B 2 _{O 3} as an essential component in the glass composition 5.4 wt% or more, and has a _P 2 _{O 5} is introduced least 0.01 wt%. This makes it possible to stabilize the glass even if the mass ratio SiO ₂ / B ₂ O ₃ is small.

Further, the glass substrate of the present invention, it is preferable that the content of _{Li 2 O + Na 2 O +} K 2 O in the glass composition is less than 0.5 wt%. In this way, it is easy to prevent the situation in which the characteristics of the semiconductor film deteriorate due to the diffusion of alkali ions into the formed semiconductor film during heat treatment. Here, “Li ₂ O + Na ₂ O + K ₂ O” refers to the total amount of Li ₂ O, Na ₂ O and K ₂ O.

In the glass substrate of the present invention, the content of Fe ₂ O ₃ + Cr ₂ O _{3 in} the glass composition is preferably 0.012% by mass or less. Here, “Fe ₂ O ₃ + Cr ₂ O ₃ ” refers to the total amount of Fe ₂ O ₃ and Cr ₂ O ₃ .

  Further, the glass substrate of the present invention preferably has a strain point of 680 ° C. or more. Here, the "strain point" refers to a value measured based on the method of ASTM C336.

In the glass substrate of the present invention, the temperature at a viscosity of 10 ^4.5 dPa · s is preferably 1300 ° C. or less. Here, “the temperature at a viscosity of 10 ^4.5 dPa · s” refers to a value measured by a platinum ball pulling method.

Further, the glass substrate of the present invention preferably has a liquidus viscosity of 10 ^4.8 dPa · s or more. Here, "liquidus viscosity" refers to the viscosity at the liquidus temperature and refers to the value measured by a platinum ball pulling method. The “liquidus temperature” is passed through a standard sieve of 30 mesh (500 μm), and the glass powder remaining on 50 mesh (300 μm) is placed in a platinum boat and placed in a temperature gradient furnace set at 1050 ° C. to 1300 ° C. After holding for a long time, the platinum boat was taken out, and the temperature at which devitrification (crystal foreign matter) was observed in the glass was taken as the liquidus temperature.

  The glass substrate of the present invention preferably has an etching depth of 25 μm or more when immersed in a 10% by mass aqueous HF solution at room temperature for 30 minutes.

  Moreover, it is preferable that the glass substrate of this invention is 75 GPa or more in Young's modulus. Here, "Young's modulus" refers to a value measured by a dynamic elastic modulus measurement method (resonance method) based on JIS R1602.

Moreover, it is preferable that the glass substrate of this invention is 30 GPa / (g / cm < ³ >) or more in specific Young's modulus. Here, "specific Young's modulus" refers to a value obtained by dividing Young's modulus by density.

  Moreover, it is preferable to use the glass substrate of this invention for a liquid crystal display.

  Moreover, it is preferable to use the glass substrate of this invention for an OLED display.

  Moreover, it is preferable to use the glass substrate of this invention for the high definition display of polysilicon or oxide TFT drive.

The glass substrate of the present invention is, as a glass composition, by mass%, SiO ₂ 55-65%, Al ₂ O ₃ 15-25%, B ₂ O ₃ 5.4-9%, MgO 0-5%, CaO 5 10 to 10%, SrO 0 to 5%, BaO 0 to 10%, P ₂ O ₅ 0.01 to 10%, mass ratio SiO ₂ / B ₂ O _{3 6} to 11.5, molar ratio (MgO + CaO + SrO + BaO ) / Al ₂ O ₃ is 0.8 to 1.4. The reason for restricting the content of each component as described above will be described below. In addition, in description of each component, the following% indication points out the mass%, unless there is particular notice.

When the content of SiO ₂ is too small, the chemical resistance, particularly the acid resistance, is likely to be lowered, and the strain point is likely to be lowered. In addition, it is difficult to reduce the density. Furthermore, it becomes difficult to precipitate two or more types of crystals as an initial phase. On the other hand, when the content of SiO ₂ is too large, it becomes difficult to speed up the etching rate, and the high temperature viscosity becomes high, the meltability tends to decrease, and further, the SiO ₂ crystal, especially cristobalite precipitates. The line viscosity tends to decrease. Thus, the preferred upper limit content of SiO ₂ is 65%, 64.5%, 64%, 63.5%, especially 63%, the preferred lower limit content is 55%, 55.5%, 56%, 56.5%, especially 57%. The most preferable content range is 57 to 63%.

When the content of Al ₂ O ₃ is too small, the strain point is lowered, the thermal contraction value is increased, the Young's modulus is decreased, and the glass substrate is easily bent. On the other hand, when the content of Al ₂ O ₃ is too large, the resistance to BHF (buffered hydrofluoric acid) is lowered to easily cause white turbidity on the glass surface, and the crack resistance is easily lowered. Furthermore, SiO ₂ -Al ₂ O ₃ -based crystals, in particular mullite, precipitate in the glass, and the liquidus viscosity tends to decrease. Therefore, the preferable upper limit content of Al ₂ O ₃ is 25%, 24%, 23%, 22%, 21%, 20%, particularly 19.5%, and the preferable lower limit content is 15%, 15. 5%, 16%, 16.5%, 17%, in particular 17.5%. The most preferable content range is 17.5 to 19.5%.

B ₂ O ₃ is a component that acts as a flux and is a component that reduces the high temperature viscosity and enhances the meltability. When the content of B ₂ O ₃ is too small, it does not function as a flux sufficiently, and the BHF resistance and the crack resistance easily decrease. In addition, the liquidus temperature is likely to rise. On the other hand, when the content of B ₂ O ₃ is too large, the strain point and the acid resistance tend to be lowered. Furthermore, the Young's modulus is reduced, and the amount of deflection of the glass substrate tends to be large. The preferred upper limit content of B ₂ O _{3 is} thus 9%, 8%, 7.5%, 7%, in particular 6.5%, the preferred lower limit content is 5.4%, 5.6% , 5.8%, especially 6%. The most preferable content range is 6 to 6.5%.

As the mass ratio SiO ₂ / B ₂ O ₃ decreases, the etching rate tends to be faster. Thus, suitable upper limits for the mass ratio SiO ₂ / B ₂ O ₃ are 11.5, 11.1, 10.8, 10.5, 10.2, in particular 10. On the other hand, when the mass ratio SiO ₂ / B ₂ O ₃ becomes large, the strain point tends to be lowered. Thus, suitable lower limits for the mass ratio SiO ₂ / B ₂ O ₃ are 6, 6.5, 7, 7.5, 8, in particular 8.5. The optimum range of the mass ratio SiO ₂ / B ₂ O ₃ is 8.5 to 10.

MgO is a component that improves the meltability by lowering the high temperature viscosity without lowering the strain point. In addition, MgO has the effect of lowering the density most in RO, but when it is introduced in excess, SiO ₂ -based crystals, in particular cristobalite, precipitate and the liquidus viscosity tends to decrease. Furthermore, MgO is a component that easily reacts with BHF to form a product. The reaction product may stick to the element on the surface of the glass substrate or adhere to the glass substrate to cause the element or the glass substrate to become cloudy. Furthermore, impurities such as Fe ₂ O _{3 and the} like are mixed into the glass from the MgO introduction raw material such as dolomite, which may lower the transmittance of the glass substrate. Therefore, the content of MgO is preferably 0 to 5%, 0 to 4.5%, 0 to 4%, 0 to 3.5%, particularly 0.5 to 3.5%.

Similar to MgO, CaO is a component that significantly reduces the high temperature viscosity without lowering the strain point to significantly improve the meltability. However, when the content of CaO is too large, SiO ₂ -Al ₂ O ₃ -RO-based crystals, particularly anorthite are precipitated, and the liquidus viscosity is easily lowered, and the BHF resistance is lowered. There is a possibility that the reaction product adheres to the element on the surface of the glass substrate or adheres to the glass substrate to cause the element or the glass substrate to become cloudy. Thus, the preferred upper limit content of CaO is 10%, 9.5%, 9%, 8.5%, especially 8%, and the preferred lower limit content is 5%, 5.5%, 6%, 6 .5%, especially 7%. The most preferable content range is 7 to 8%.

  SrO is a component that improves devitrification resistance and chemical resistance, but if the ratio is too high in the entire RO, the meltability tends to decrease and the density and thermal expansion coefficient tend to increase. . Therefore, the content of SrO is preferably 0 to 5%, 0.5 to 4.5%, 1 to 4%, 1.5 to 3.5%, particularly 2 to 3%.

BaO is a component that improves the devitrification resistance and the chemical resistance, but if the content is too large, the density tends to increase. In addition, SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -RO-based glass is generally difficult to melt, so the meltability is enhanced from the viewpoint of supplying a high quality glass substrate inexpensively and in large quantities, It is very important to reduce the defect rate due to bubbles, foreign matter, etc. However, BaO is less effective in improving meltability in RO. Therefore, the content of BaO is preferably 0 to 10%, 0.1 to 8%, 1 to 6%, 1.5 to 4%, particularly 2 to 3%.

  When the content of CaO + SrO + BaO is too large, the density is increased, which makes it difficult to reduce the weight of the glass substrate. Thus, the content of CaO + SrO + BaO is preferably less than 16%, less than 15%, in particular less than 14%. "CaO + SrO + BaO" is the total amount of CaO, SrO and BaO.

When the molar ratio (MgO + CaO + SrO + BaO) / Al ₂ O ₃ is adjusted to a predetermined range, the liquidus temperature is significantly reduced, crystal foreign substances are less likely to be generated in the glass, and the meltability and the formability are improved. When the molar ratio (MgO + CaO + SrO + BaO) / Al ₂ O ₃ decreases, SiO ₂ -Al ₂ O ₃ based crystals are easily precipitated. On the other hand, when the molar ratio (MgO + CaO + SrO + BaO) / Al ₂ O ₃ increases, SiO ₂ -Al ₂ O ₃ -RO-based crystals and SiO ₂ -based crystals are easily precipitated. Preferred upper limits of the molar ratio (MgO + CaO + SrO + BaO) / Al ₂ O ₃ are 1.5, 1.4, 1.35, 1.3, 1.25, in particular 1.2, and the preferred lower limit is 0. 7, 0.8, 0.9, 0.95, 0.98, 1.0, 1.02, especially 1.05. The optimum range of the molar ratio (MgO + CaO + SrO + BaO) / Al ₂ O ₃ is 1.05 to 1.2.

When {2 × [SiO ₂ ]-[MgO + CaO + SrO + BaO]} is restricted to a predetermined value or less, the etching depth by the HF aqueous solution becomes large, and it becomes easy to accelerate the etching rate. _{{2 × [SiO 2] -} [MgO + CaO + SrO + BaO]} preferred upper limit of 130 mol%, 129 mol%, 128 mol%, 127 mol%, 126 mol%, 125.5 mol%, 125 mol%, 124. 5 mol%, 124 mol%, 123 mol%, in particular 123 mol%. The optimum range is {2 × [SiO ₂ ]-[MgO + CaO + SrO + BaO]} ≦ 123 mol%. Note that _{"2 × [SiO 2] - [} MgO + CaO + SrO + BaO] " refers to 2-fold molar% content of SiO _2, MgO, CaO, a value obtained by subtracting the molar% total content of SrO and BaO.

  It is desirable to mix and introduce 2 or more types (preferably 3 or more types) of RO. As a result, the liquidus temperature is significantly reduced, and crystal foreign substances are less likely to be generated in the glass, and the meltability and the formability are further improved.

P ₂ O ₅ is a component that lowers the liquidus temperature of SiO ₂ -Al ₂ O ₃ -CaO-based crystals (especially anorthite) and SiO ₂ -Al ₂ O ₃ -based crystals (especially mullite). Therefore, when P ₂ O ₅ is added, these crystals are difficult to precipitate, and two or more crystals are easily precipitated as the initial phase. As a result, the devitrification resistance can be significantly enhanced. However, when a large amount of P ₂ O ₅ is introduced, the glass is likely to be separated. Therefore, the content of P ₂ O ₅ is preferably 0.01 to 10%, 0.1 to 7%, 0.3 to 6%, 0.5 to 5%, 1 to 4%, particularly 1 to 3 %.

When {[Al ₂ O ₃ ] + 2 × [P ₂ O ₅ ]} is regulated to a predetermined value or more, the strain point can be easily increased even if the content of SiO ₂ is small. Preferred lower limits for {[Al ₂ O ₃ ] + 2 × [P ₂ O ₅ ]} are 10 mol%, 10.5 mol%, 11 mol%, 11.5 mol%, in particular 12 mol%. The optimum range is {[Al ₂ O ₃ ] + 2 × [P ₂ O ₅ ]} ≧ 12 mol%. Here, “[Al ₂ O ₃ ] + 2 × [P ₂ O ₅ ]” refers to the total amount of the molar percentage of Al ₂ O _{3 and} the molar percentage of twice the P ₂ O ₅ .

  Other than the above components, for example, the following components may be introduced.

  ZnO is a component that improves the meltability and BHF resistance, but if the content is too large, the glass is likely to be devitrified or the strain point is reduced, making it difficult to ensure heat resistance. . Therefore, the content of ZnO is preferably 0 to 5%, 0 to 4%, 0 to 3%, 0 to 2%, particularly 0 to 1%.

ZrO ₂ is a component that enhances chemical durability, but when the amount introduced is increased, devitrified foreign matter of ZrSiO ₄ tends to be generated. The preferable upper limit content of ZrO ₂ is 1%, 0.5%, 0.3%, 0.2%, particularly 0.1%, and from the viewpoint of chemical durability, 0.005% or more may be introduced. preferable. The most preferable content range is 0.005 to 0.1%. ZrO ₂ may be introduced from the raw material or may be introduced by elution from a refractory.

TiO ₂ has the effect of lowering the high temperature viscosity to enhance the meltability and enhancing the chemical durability, but when the introduced amount is excessive, the ultraviolet light transmittance tends to decrease. The content of TiO ₂ is preferably 3% or less, 1% or less, 0.5% or less, 0.3% or less, 0.2% or less, particularly 0.1% or less. When a very small amount of TiO ₂ is introduced (for example, 0.001% or more), the effect of suppressing the coloring due to ultraviolet light can be obtained.

As the fining agent, metal powders such as As ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , SO ₃ , Fe ₂ O ₃ , Ce ₂ , Ce ₂ , F ₂ , Cl ₂ , C, or Al, Si can be used. . The total content of these contents is preferably 1% or less.

As ₂ O ₃ and Sb ₂ O ₃ are environmentally harmful chemicals, it is desirable not to use them as much as possible. The content of As ₂ O ₃ and Sb ₂ O ₃ is less than 0.3%, less than 0.1%, less than 0.09%, less than 0.05%, less than 0.03%, less than 0.01%, respectively. Less than 0.005%, particularly less than 0.003% is preferred.

SnO ₂ works as a fining agent to reduce bubbles in glass, and also has the effect of maintaining a relatively high ultraviolet light transmittance when coexisting with Fe ₂ O ₃ or FeO. On the other hand, when the content of SnO ₂ is too large, devitrified foreign matter of SnO ₂ is easily generated in the glass. The preferable upper limit content of SnO ₂ is 0.5%, 0.45%, 0.4%, 0.35%, particularly 0.3%, and the preferable lower limit content is 0.01%, 0.02% , 0.03%, 0.04%, especially 0.05%. The most preferable content range is 0.05 to 0.3%.

Iron is a component mixed as a raw material impurity. If the iron content is too high, the ultraviolet light transmittance may be reduced. If the ultraviolet light transmittance decreases, problems may occur in a photolithography process for manufacturing a TFT or an alignment process of liquid crystal by ultraviolet light. Therefore, a suitable lower limit content of iron is 0.001% in terms of Fe ₂ O ₃ , and a suitable upper limit content is 0.012%, 0.011%, especially in terms of Fe ₂ O ₃ , in particular It is 0.01%. The most preferable content range is 0.001% to 0.01%.

Cr ₂ O ₃ is a component mixed as a raw material impurity. When the content of Cr ₂ O ₃ is too large, light is made incident from the end face of the glass substrate, and when foreign matter inspection inside the glass substrate is carried out by scattered light, light becomes difficult to pass through the inside of the glass and defects in foreign matter inspection There is a possibility that it will occur. In particular, when the substrate size is 730 mm × 920 mm or more, this problem is likely to occur. In addition, when the thickness of the glass substrate is small (for example, 0.5 mm or less, 0.4 mm or less, particularly 0.3 mm or less), the amount of light incident from the end surface of the glass substrate is reduced, so the content of Cr ₂ O ₃ is regulated. The significance of The preferable upper limit content of Cr ₂ O ₃ is 0.001%, 0.0009%, 0.0008%, 0.0007%, 0.0006%, particularly 0.0005%, and the preferable lower limit content is 0. It is 00001%. The most preferable content range is 0.00001 to 0.0005%.

The content of Fe ₂ O ₃ + Cr ₂ O ₃ is preferably 0.02% or less, 0.015% or less, 0.014% or less, 0.013% or less, particularly preferably 0. It is 012% or less.

In the case of containing 0.01 to 0.5% of SnO ₂ , when the content of Rh ₂ O ₃ is too large, the glass tends to be colored. Incidentally, Rh ₂ O ₃ is likely to be mixed from glass manufacturing vessel made of platinum. The content of Rh ₂ O ₃ is preferably 0 to 0.0005%, more preferably 0.00001 to 0.0001%.

SO ₃ is a component mixed from the raw material as an impurity, but if the content of SO ₃ is too large, it may generate bubbles called riboyl during melting or molding, which may cause defects in the glass. is there. The preferred upper limit content of SO ₃ is 0.005%, 0.003%, 0.002%, in particular 0.001%, the preferred lower limit content is 0.0001%. The most preferable content range is 0.0001% to 0.001%.

Alkali components, in particular Li ₂ O and Na ₂ O, deteriorate the characteristics of the semiconductor film. Therefore, the total content of Li ₂ O, Na ₂ O and K ₂ O is 0 to 0.5%, 0 to 0.4%, 0 to 0.3%, 0 to 0.2%, in particular 0 to 0.1% is preferable. In general, Li ₂ O, Na ₂ O and K ₂ O as raw material impurities are mixed into the glass substrate in a total amount of about 100 to 200 mass ppm.

  Other components may be introduced in addition to the above components. The amount introduced is preferably 2% or less, in particular 1% or less.

The glass substrate of the present invention can be formed of SiO ₂ -Al ₂ O ₃ -RO crystalline, SiO ₂ -based crystal, SiO ₂ -Al ₂ O _{3 in} the temperature range from liquidus temperature (liquidus temperature-50 ° C). Among the system crystals, it is preferable to have the property that a plurality of crystals precipitate. Also, when precipitating the plurality of _crystal, it is preferred to precipitate the SiO ₂ -Al ₂ O 3 -RO based crystal and SiO ₂ based crystal. In the vicinity of the region where the plurality of crystal phases are in equilibrium with the liquid, the glass is stabilized and the liquidus temperature is significantly lowered. As SiO ₂ -Al ₂ O ₃ -RO based _crystal, preferably SiO ₂ -Al ₂ O 3 -CaO based crystal, particularly anorthite is preferred. As the SiO ₂ -based crystal, cristobalite is preferable. Mullite is preferred as the SiO ₂ -Al ₂ O ₃ -based crystal.

  The glass substrate of the present invention preferably has the following characteristics.

In recent years, in displays for mobile applications, the demand for weight reduction is increasing, and weight reduction is also required for glass substrates. In order to satisfy this requirement, it is desirable to reduce the density of the glass substrate. Density is preferably 2.6 g / cm ³ or less, 2.57 g / cm ³ or less, 2.56 g / cm ³ or less, 2.55 g / cm ³ or less, 2.54 g / cm ³ or less, in particular 2.53 g / cm ³ or less. On the other hand, if the density is too low, the component balance of the glass composition may be impaired. As a result, an increase in the melting temperature and a decrease in the liquidus viscosity tend to occur, and the productivity of the glass substrate tends to decrease. In addition, the strain point also tends to decrease. Therefore, the density is preferably 2.4 g / cm ³ or more, 2.41 g / cm ³ or more, 2.42 g / cm ³ or more, 2.43 g / cm ³ or more, 2.44 g / cm ³ or more, especially 2. It is 45 g / cm ³ or more.

The thermal expansion coefficient is preferably 28 × 10 ^{-7 to} 45 × 10 ^-7 / ° C, 30 × 10 ^-7 to 43 × 10 ^-7 / ° C, 32 × 10 ^{-7 to} 42 × 10 ^-7 / ° C, 34 × 10 ^{−7 to} 41 × 10 ⁻⁷ / ° C., in particular 35 × 10 ⁻⁷ to 40 × 10 ⁻⁷ / ° C. This makes it easy to match the thermal expansion coefficient of a member (for example, a-silicon or p-silicon) to be deposited on a glass substrate. Here, the "thermal expansion coefficient" refers to an average thermal expansion coefficient measured in a temperature range of 30 to 380 ° C, and can be measured, for example, with a dilatometer.

In OLED displays, liquid crystal displays, etc., a large-area glass substrate (for example, 730 × 920 mm or more, 1100 × 1250 mm or more, particularly 1500 × 1500 mm or more) is used, and a thin glass substrate (for example, plate thickness 0.5 mm) Below, 0.4 mm or less, especially 0.3 mm or less) tends to be used. When the area of the glass substrate is increased and the thickness thereof is reduced, deflection due to its own weight becomes a serious problem. In order to reduce the deflection of the glass substrate, it is necessary to increase the specific Young's modulus of the glass substrate. The specific Young's modulus is preferably 28 GPa / g · cm ⁻³ or more, 28.5 GPa / g · cm ⁻³ or more, 29 GPa / g · cm ⁻³ or more, 29.5 GPa / g · cm ⁻³ or more, 30 GPa / g Cm ⁻³ or more, 30.5 GPa / g · cm ⁻³ or more, 31 GPa / g · cm ⁻³ or more, 31.5 GPa / g · cm ⁻³ or more, and particularly 32 to 40 GPa / g · cm ⁻³ . In addition, when the area of the glass substrate is increased and the thickness thereof is reduced, the warping of the glass substrate becomes a problem after the heat treatment process on the surface plate or the film formation process of various metal films, oxide films, semiconductor films, organic films, etc. Become. In order to reduce the warpage of the glass substrate, it is effective to increase the Young's modulus of the glass substrate. The Young's modulus is preferably 75 GPa or more, 76 GPa or more, 77 GPa or more, 78 GPa or more, particularly 79 to 100 GPa.

  The strain point is preferably 680 ° C. or more, 690 ° C. or more, 695 ° C. or more, 700 ° C. or more, 705 ° C. or more, and particularly preferably 710 to 800 ° C. Thus, the glass substrate is less likely to be thermally shrunk in the process of forming the semiconductor element.

  In the glass substrate of the present invention, the temperature is raised from room temperature (25 ° C.) to 500 ° C. at a rate of 5 ° C./min, held at 500 ° C. for 1 hour, and then lowered to room temperature at a rate of 5 ° C./min The shrinkage value is preferably 30 ppm or less, 25 ppm or less, 22 ppm or less, 20 ppm or less, 18 ppm or less, in particular 15 ppm or less. In this way, in the process of forming a semiconductor element, problems such as pixel pitch deviation are less likely to occur even when subjected to heat treatment. When the heat shrinkage value is too small, the productivity of glass tends to be reduced. Therefore, the heat shrinkage value is preferably 5 ppm or more, 8 ppm or more, particularly 10 ppm or more. The heat shrinkage value can also be reduced by reducing the cooling rate at the time of molding, in addition to increasing the strain point.

In the overflow down draw method, the molten glass flows down the surface of the refractory having a substantially wedge-shaped cross section, joins at the lower end of the crucible, and is formed into a plate shape. In the slot down draw method, for example, a ribbon-like molten glass is made to flow down from a platinum group metal container having a slit-like opening and cooled to form a plate. When the temperature of the molten glass in contact with the forming apparatus is too high, the forming apparatus is deteriorated, and the productivity of the glass substrate is likely to be reduced. Therefore, the temperature at a viscosity of 10 ^4.5 dPa · s is preferably 1350 ° C. or less, 1340 ° C. or less, 1330 ° C. or less, 1320 ° C. or less, 1310 ° C. or less, 1300 ° C. or less, particularly 1100 to 1290 ° C. The temperature at a viscosity of 10 ^4.5 dPa · s corresponds to the temperature of the molten glass at the time of molding.

Low-alkali glass and non-alkali glass generally have low meltability, so improvement in meltability is an issue. When the melting property is enhanced, the defective rate due to bubbles, foreign matters, and the like is reduced, so that high-quality glass substrates can be supplied in large quantities and inexpensively. On the other hand, if the viscosity of the glass in the high temperature range is too high, it is difficult to promote degassing in the melting step. Therefore, the temperature at a viscosity of 10 ^2.5 dPa · s is preferably 1700 ° C. or less, 1690 ° C. or less, 1680 ° C. or less, 1670 ° C. or less, 1660 ° C. or less, particularly 1650 ° C. or less. Here, “the temperature at a viscosity of 10 ^2.5 dPa · s” can be measured by a platinum ball pulling method. The temperature at a high temperature viscosity of 10 ^2.5 dPa · s corresponds to the melting temperature, and the lower the temperature, the better the melting property.

When forming by the down draw method etc., devitrification resistance becomes important. The liquidus temperature is preferably less than 1300 ° C., 1280 ° C. or less, 1270 ° C. or less, 1260 ° C. in consideration of the forming temperature of the glass containing SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ and RO in the glass composition. Hereinafter, the temperature is 1250 ° C. or less, 1240 ° C. or less, 1230 ° C. or less, 1220 ° C. or less, particularly 900 to 1210 ° C. The liquidus viscosity is preferably 10 ^4.3 dPa · s or more, 10 ^4.4 dPa · s or more, 10 ^4.5 dPa · s or more, 10 ^4.6 dPa · s or more, 10 ^4.7 It is dPa · s or more, 10 ^4.8 dPa · s or more, 10 ^4.9 dPa · s or more, particularly 10 ^5.0 to 10 ^7.0 dPa · s.

  The etching depth when immersed in a 10% by mass aqueous HF solution at room temperature (20 ° C.) for 30 minutes is preferably 25 μm or more, 27 μm or more, 28 μm or more, 29 to 50 μm, particularly 30 to 40 μm. The etching depth is an index of the etching rate. That is, if the etching depth is large, the etching rate is fast, and if the etching depth is small, the etching rate is slow.

  The β-OH value is preferably 0.35 / mm or less, 0.3 / mm or less, 0.25 / mm or less, 0.2 / mm or less, particularly 0.15 / mm or less. When the β-OH value is too large, the strain point tends to be lowered. On the other hand, when the β-OH value is too small, the meltability tends to be reduced. Therefore, the β-OH value is preferably 0.01 / mm or more, particularly 0.03 / mm or more.

  Here, "(beta) -OH value" points out the value calculated | required using the following numerical formula, measuring the transmittance | permeability of glass using FT-IR.

[Equation 1]
β-OH value = (1 / X) log (T ₁ / T ₂ )
X: Glass thickness (mm)
T ₁ : transmittance at a reference wavelength 3846 cm ⁻¹ (%)
T ₂ : Minimum transmittance in the vicinity of a hydroxyl group absorption wavelength of 3600 cm ⁻¹ (%)

The following methods (1) to (7) are available as methods for reducing the β-OH value, and among them, the methods (1) to (4) are effective. (1) Select raw materials with low water content. (2) Add a desiccant such as Cl, SO ₃ or the like into the glass batch. (3) Conduct electric heating by the heating electrode. (4) Adopt a small melting furnace. (5) Decrease the moisture content in the furnace atmosphere. (6) N ₂ bubbling is performed in the molten glass. (7) Increase the flow rate of molten glass.

  The glass substrate of the present invention preferably has a forming / merging surface at the center in the thickness direction, that is, it is formed by the overflow down draw method. The overflow down draw method is a method of forming a plate by stretching and forming downwards while causing the molten glass to overflow from both sides of the crucible-shaped refractory and joining the overflowed molten glass at the lower end of the crucible. In the overflow down draw method, the surface to be the surface of the glass substrate is not in contact with the refractory but is formed in the state of a free surface. Thereby, even if it is unpolished, a glass substrate with favorable surface grade can be manufactured cheaply. In addition, it is easy to increase the area and thickness of the glass substrate.

  Besides the overflow downdraw method, for example, it is also possible to form the glass substrate by the downdraw method (slot down method, redraw method, etc.), the float method or the like.

  Although the thickness of the glass substrate of the present invention is not particularly limited, it is preferably 0.5 mm or less, 0.4 mm or less, 0.35 mm or less, particularly 0.05 to 0.3 mm. The smaller the plate thickness, the easier it is to reduce the weight of the device. On the other hand, when the plate thickness is too small, the glass substrate is easily bent, but since the glass substrate of the present invention has a high Young's modulus and a specific Young's modulus, problems due to the bending hardly occur. The plate thickness can be adjusted by the flow rate at the time of glass production, the plate drawing speed, and the like.

  Hereinafter, the present invention will be described in detail based on examples. The following embodiments are merely illustrative. The present invention is not limited at all to the following examples.

  Table 1 shows examples of the present invention (samples No. 1 to 18).

Each sample was produced as follows. First, a glass batch prepared from glass materials was placed in a platinum crucible and melted at 1600 ° C. for 24 hours so that the glass composition in the table was obtained. At the time of melting of the glass batch, it was stirred using a platinum stirrer and homogenized. Next, the molten glass was poured onto a carbon plate and formed into a plate shape. For each sample obtained, the density, thermal expansion coefficient, Young's modulus, specific Young's modulus, strain point, annealing temperature, softening point, temperature at viscosity of 10 ^4.5 dPa · s, 10 ^4.0 dPa · s Temperature at viscosity, temperature at viscosity of 10 ^3.0 dPa · s, temperature at viscosity of 10 ^2.5 dPa · s, liquidus temperature, primary phase, liquidus viscosity log η, amount of H ₂ O, by HF aqueous solution The etching depth was evaluated.

  The density is a value measured by the well-known Archimedes method.

  The thermal expansion coefficient is an average thermal expansion coefficient measured by a dilatometer in a temperature range of 30 to 380 ° C.

  Young's modulus refers to a value measured by a dynamic elastic modulus measurement method (resonance method) based on JIS R1602, and the specific Young's modulus is a value obtained by dividing Young's modulus by density.

  The strain point, the annealing point, and the softening point are values measured based on the method of ASTM C336 and C338.

The temperature at a viscosity of 10 ^4.5 dPa · s, the temperature at a viscosity of 10 ^4.0 dPa · s, the temperature at a viscosity of 10 ^3.0 dPa · s, the temperature at a viscosity of 10 ^2.5 dPa · s, platinum It is the value measured by the ball lifting method.

  The liquidus temperature and the liquidus viscosity were measured as follows. Each sample is ground, passed through a standard sieve 30 mesh (500 μm), and the glass powder remaining on 50 mesh (300 μm) is placed in a platinum boat and held in a temperature gradient furnace set at 1050 ° C. to 1300 ° C. for 24 hours After that, the platinum boat was taken out, and the temperature at which devitrification (crystal foreign matter) was recognized in the glass was taken as the liquidus temperature. And the crystal | crystallization which has precipitated in the temperature range (liquidus temperature-50 degreeC) from liquidus temperature was evaluated as an initial phase. In the table, "Ano" indicates anorthite, "Cri" indicates cristobalite, and "Mul" indicates mullite. Furthermore, the viscosity of the glass at the liquidus temperature was measured by a platinum ball pulling method, and this was taken as the liquidus viscosity.

  After optically polishing both surfaces of each sample, a portion of the sample surface is masked and dipped in a 10% by mass aqueous HF solution at room temperature (20 ° C.) for 30 minutes, and then the masked portion of the obtained sample surface The etching depth was evaluated by measuring the step between the and the etched portions.

The amount of H ₂ O is a value obtained by measuring the β-OH value of glass by the above method.

Sample No. The thermal expansion coefficient of 1 to 18 is 35 × 10 ⁻⁷ to 40 × 10 ⁻⁷ / ° C., the strain point is 680 ° C. or higher, and the thermal contraction value can be reduced. In addition, the Young's modulus is 75 GPa or more, and the specific Young's modulus is 30 GPa / (g / cm ³ ) or more, and deflection and deformation hardly occur. The temperature at a viscosity of 10 ^4.5 dPa · s is 1290 ° C. or less, the temperature at a viscosity of 10 ^2.5 dPa · s is 1632 ° C. or less, the liquidus temperature is 1206 ° C. or less, and the liquidus viscosity is Since it is 10 ^4.9 dPa · s or more, it is excellent in meltability, formability and devitrification resistance, and is suitable for mass production. Furthermore, since the etching depth is 30 μm or more, the etching rate can be increased.

  The glass substrate of the present invention can simultaneously achieve high devitrification resistance, high strain point, and high etching rate. Therefore, the glass substrate of the present invention is suitable as a substrate of a display such as an OLED display or a liquid crystal display, and is suitable as a substrate of a display driven by LTPS and oxide TFT.

Claims (12)

As a glass composition, SiO ₂ 55 to 65%, Al ₂ O ₃ 15 to 25%, B ₂ O ₃ 5.4 to 9%, MgO 0 to 5%, CaO 5 to 10%, SrO 0 to 50% by mass. It contains 5%, BaO 0 to 10%, P ₂ O ₅ 0.01 to 10%, the mass ratio SiO ₂ / B ₂ O ₃ is 6 to 11.5, and the molar ratio (MgO + CaO + SrO + BaO) / Al ₂ O ₃ is The glass substrate characterized by being 0.8-1.4. Glass substrate according to claim 1, the content of _{Li 2 O + Na 2 O +} K 2 O in the glass composition is equal to or less than 0.5 wt%. Glass substrate according to any one of claims 1-2 in which the content of _{Fe 2 O 3 + Cr 2 O} 3 in the glass composition is equal to or less than 0.012 mass%.   The strain point is 680 degreeC or more, The glass substrate as described in any one of Claims 1-3 characterized by the above-mentioned. The glass substrate according to any one of claims 1 to 4, wherein the temperature at a viscosity of 10 ^4.5 dPa · s is 1300 ° C or less. The glass substrate according to any one of claims 1 to 5, which has a liquidus viscosity of 10 ^4.8 dPa · s or more.   The etching depth becomes 25 micrometers or more when immersed in 10 mass% HF aqueous solution at room temperature for 30 minutes, The glass substrate as described in any one of Claims 1-6 characterized by the above-mentioned.   The glass substrate according to any one of claims 1 to 7, wherein Young's modulus is 75 GPa or more. Glass substrate according to any one of claims 1 to 8, specific Young's modulus is equal to or is 30GPa / (g / cm ³⁾ or more.   The glass substrate according to any one of claims 1 to 9, which is used for a liquid crystal display.   The glass substrate according to any one of claims 1 to 10, which is used for an OLED display.   The glass substrate according to any one of claims 1 to 11, which is used for a high definition display driven by polysilicon or oxide TFT.