JPWO2019172442A1 - Non-alkali glass substrate - Google Patents

Abstract

The present invention is a non-alkali glass substrate having a strain point of 650 ° C. or higher and an average thermal expansion coefficient of 30 × 10-7 to 45 × 10-7 / ° C. at 50 to 350 ° C., based on oxides. In terms of mass%, SiO2 is 54 to 66%, Al2O3 is 10 to 25%, B2O3 is 0.1 to 12%, and one or more components selected from the group consisting of MgO, CaO, SrO and BaO are 7 in total. The present invention relates to a non-alkali glass substrate containing ~ 25% and containing 150 to 2000 mass ppm of Na2O, and the amount of Na2O on the surface of the glass substrate on at least one main surface is 20 mass ppm or more less than the amount of Na2O inside the glass substrate.

Description

The present invention relates to a glass substrate suitable for forming a thin film transistor (TFT) or the like.

As various display glass substrates, especially when a thin film such as a TFT is formed on the glass substrate, a borosilicate glass substrate (so-called alkali-free glass substrate) containing almost no alkali metal component is used. This is because when a glass substrate containing a large amount of an alkali metal component is used, the alkali metal component in the glass deteriorates the film characteristics and causes a decrease in the reliability of the TFT. Further, the glass substrate for a display is also required to have a high strain point and a high acid resistance.

Alkali-free glass, which has a high strain point and is excellent in acid resistance, requires that the glass raw material be melted at a high temperature of 1400 to 1800 ° C., and it is not easy to efficiently produce a high-quality glass substrate. Patent Document 1 describes a method in which 200 to 2000 ppm of an alkali metal oxide is contained in non-alkali glass, and heating by a burning flame of a burner and heating by energizing the molten glass are used in combination to melt the glass. ing.

The float method is known as a method for forming glass into a plate shape. In the float method, molten glass continuously supplied onto molten metal (for example, molten tin) in a float bath (hereinafter, may be simply referred to as “bus”) is flown on the molten metal to form a plate. To do.
The glass ribbon formed on the molten metal is then conveyed using a roller. At that time, it is known that the portion in contact with the roller is easily scratched.

As a method of preventing such scratches, sulfur dioxide gas (SO ₂ gas) is sprayed on the back surface of the glass substrate and reacted with an alkali metal (for example, sodium or the like) existing in the glass to form sodium sulfate on the back surface of the glass substrate. However, a method of using it as a protective film is known (for example, Patent Document 2). Further, Patent Document 3 describes a method of spraying sodium tetraborate or the like on the surface of glass for a display substrate and then spraying sulfur dioxide gas.

International Publication No. 2013/088432 International Publication No. 2002/051767 International Publication No. 2008/004480

However, the method described in Patent Document 2 cannot be applied to the production of a non-alkali glass substrate in which the amount of alkali metal present in the glass is extremely small. Further, the method described in Patent Document 3 can be applied to a non-alkali glass substrate, but since two kinds of gases are sprayed on the surface of the glass ribbon, the process is complicated and the apparatus is complicated.

Recently, the demand for TFT characteristics and glass substrate characteristics has become higher, and it has become more difficult to maintain the characteristics of the TFT on the glass substrate and improve the meltability of the glass.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-quality non-alkali glass substrate having less deterioration in the reliability of the TFT due to an alkali metal component, less scratches, and excellent productivity. To do.

As a result of diligent studies, the present inventors have found that the strain point and the average coefficient of thermal expansion at 50 to 350 ° C. are within a predetermined range, have a specific composition, and Na ₂ O on the surface of at least one glass substrate. amount can solve the above problems by 20 mass ppm or less glass substrate than Na 2 _O content of the glass substrate, thereby completing the present invention.

That is, the present invention is a non-alkali glass having a strain point of 650 ° C. or higher and an average coefficient of thermal expansion at 50 to 350 ° C. of 30 × ^{10-7 to} 45 × ^10-7 / ° C. the SiO ₂ from 54 to 66% by mass percentage, the _Al 2 _{O 3} 10 to _25%, is selected to _{B 2 O 3 0.1~12%, MgO} , CaO, from the group consisting of SrO and BaO 1 It contains 7-25% in total of the above components, Na ₂ O and containing 150 to 2000 mass ppm, 20 from Na ₂ O weight Na ₂ O amount is the glass substrate of the glass substrate surface in at least one major surface It is a non-alkali glass substrate with a mass less than ppm.

The non-alkali glass substrate of the present invention has a specific composition, and the amount of Na ₂ O on the surface of at least one glass substrate is 20 mass ppm or more less than the amount of Na ₂ O inside the glass substrate. There are few scratches, and the decrease in the reliability of the TFT due to the alkali metal component can be suppressed.

FIG. 1 is a diagram showing an example of a signal intensity ratio profile of ²³ Na ⁺ and ³⁰ Si ^{+ in} the thickness direction of the glass substrate. FIG. 2 is a diagram showing an example of the Na ₂ O content profile near the surface of the glass substrate. FIG. 3 is a conceptual diagram showing a glass manufacturing apparatus by the float method. Figure 4 is an example of the relationship between the Na 2 _O content of the variation amount and the glass substrate surface of the threshold voltage in a reliability test of the TFT formed on the glass substrate surface. FIG. 5 shows a schematic view of the TFT element.

Hereinafter, embodiments for carrying out the present invention will be described in detail. The present invention is not limited to the embodiments described below.

In the present specification, the glass composition is expressed in mass% based on the oxide as a general rule, and "%" and "ppm" used for the glass composition in the present specification are "mass%" and "mass%" unless otherwise specified. It means "mass ppm".

In the present specification, "alkali-free glass" refers to glass in which the content of alkali metal components such as lithium, sodium and potassium is 5000 ppm or less in terms of oxide.

In the present specification, the "glass ribbon" refers to a molten glass molded into a plate shape. The glass ribbon is cooled, cut, etc. to become a glass substrate.

The "bottom surface" is the surface of a glass ribbon or glass substrate manufactured by the float method that is in contact with the molten metal in the float bath. The "top surface" is the surface facing the bottom surface.

In the present specification, the Na ₂ O content of the glass substrate is determined by pulverizing the glass substrate, heat-decomposing the obtained glass powder with sulfuric acid, nitric acid and hydrofluoric acid, and then concentrating the glass powder until white smoke is produced. A constant volume solution dissolved in dilute nitric acid is obtained, and the Na concentration in the constant volume solution is quantified by the ICP mass analysis method [unit: mass ppm].
The “Na ₂ O content inside the glass substrate” is equal to the Na ₂ O content of the glass substrate obtained by the above method.

The standard "Na ₂ O content on the surface of the glass substrate" is a part of the glass substrate to be evaluated cut out and etched with a 5% hydrogen fluoride aqueous solution by about 10 μm (specifically, 8 to 12 μm) from the surface. as a sample, obtained from the Na content profile obtained in time-of-flight secondary ion mass spectrometry (TOF-SIMS) method using _{C 60} sputtering below.
Specifically, the average Na ₂ O content in the region where the depth from the surface is 0.25 μm to 0.30 μm, which is obtained from the Na content profile of the glass, is defined as the Na ₂ O content on the surface of the glass substrate.

FIG. 1 is a signal intensity ratio profile of ²³ Na ⁺ and ³⁰ Si ^{+ in} the thickness direction of the glass substrate obtained by the following procedure.
That is, five small pieces were cut out from the present glass substrate, and the surface of each of the four pieces was etched with a 5% hydrogen fluoride aqueous solution. By changing the etching time for the five small pieces, 1 μm, 3 μm, 5 μm, and 10 μm were etched from the surface of the glass substrate, respectively. The etching thickness was measured using a micrometer.
For each _piece, is shown in Figure 1 are plotted the results of the measurement of the signal intensity ratio of the time-of-flight secondary ion mass spectrometry (TOF-SIMS) method at ²³ Na ⁺ and the ³⁰ Si ⁺ using _{C 60} sputtering .. Since Si is the main component of this glass substrate and its content is almost uniform in the thickness direction of the glass substrate, the signal intensity ratio of ²³ Na ⁺ and ³⁰ Si ⁺ indicates a profile of Na content. Can be regarded.
From FIG. 1, in the region from the surface of the glass substrate to a depth of about 5 μm, the Na content is lower than that in the deeper portion, but at a depth of about 10 μm or more, the Na content is high. It can be seen that it does not change.

As a method for determining the Na ₂ O content on the surface of a glass substrate, a part of the glass substrate to be evaluated is cut out and etched with a 5% hydrogen fluoride aqueous solution by about 10 μm (specifically, 8 to 12 μm) from the surface. As a standard sample for Na ₂ O quantification, the Na content profile near the surface of the glass substrate is measured by measuring the signal intensity ratio of ²³ Na ⁺ and ³⁰ Si ⁺ to the sputter time for the unetched glass substrate. The method can be mentioned.

Since the Na content does not fluctuate at a depth of about 10 μm or more, the signal intensity ratio of ²³ Na ⁺ and ³⁰ Si ⁺ obtained for the standard sample is the Na ₂ O content obtained by IPC mass spectrometry. Equivalent to. Therefore, the value can be used to convert the signal intensity ratio into Na ₂ O content. Further, after the TOF-SIMS measurement, a surface shape measuring device (e.g. manufactured by Veeco; Dektak150) Measurement of the shaved depth _{C 60} sputtering using, can convert the sputtering time to depth from the glass surface.

This gives the Na ₂ O content profile as shown in FIG. In this way the content of Na ₂ O profile obtained, the average Na ₂ O content of the region of 0.30μm depth from the surface is from 0.25μm to Na ₂ O of the glass surface.

In the present specification, the "β-OH value" of the glass substrate is obtained by the following method.

That is, the infrared transmittance of the glass substrate is measured using an infrared spectrophotometer, and the minimum value of the transmittance at a wave number of 3000 to 3700 cm ^-1 is I _a [unit:%], and the transmittance at a wave number of 4000 cm ^-1 is I. _{Assuming that b} [unit:%] and the thickness of the glass substrate are d [unit: mm], the β-OH value is-(log (I _a / I _b )) / d [unit: mm ^-1 ]. ..

[Manufacturing method of glass substrate]
First, in order to help the understanding of the present invention, a method for manufacturing a glass substrate by the float method will be described as one aspect of the method for manufacturing the non-alkali glass substrate of the present invention (hereinafter, also referred to as “glass substrate of the present invention”). The method for manufacturing a glass substrate of the present invention is not limited to this.

Glass substrate manufacturing by the float method
(I) A "melting process" in which raw materials are melted to produce molten glass,
(II) A "molding process" in which molten glass is introduced into a float bath to form a glass ribbon.
(III) It has a "slow cooling step" in which the glass ribbon is slowly cooled in a slow cooling furnace.

Hereinafter, each step will be described with reference to FIG. 3, which is a conceptual diagram showing an example of a glass manufacturing apparatus by the float method.

<Dissolution process>
In the melting step, the molten glass 4 is obtained by putting the glass raw materials prepared and mixed according to the desired glass composition into the melting kiln 3. The temperature of the melting kiln 3 may be appropriately adjusted depending on the glass raw material used, and is, for example, about 1400 ° C to 1600 ° C.

<Molding process>
In the molding step, the molten glass 4 is continuously flowed from the melting kiln 3 onto the molten tin surface of the float bath 2 filled with the molten tin 1 to form a glass ribbon.

The glass ribbon formed on the molten metal is carried to the slow cooling furnace 6 by the transport roller 5 and slowly cooled. However, between the time when the glass ribbon exits the float bath 2 and the time when it comes into contact with the transport roller 5, the glass ribbon It is preferable to spray SO ₂ gas on the bottom surface of the ribbon.

By spraying the SO ₂ gas, Na ₂ O existing on the glass surface reacts with the SO ₂ gas to form sodium sulfate on the glass surface. The sodium sulfate has an effect of preventing the glass ribbon from being damaged by contact with the transport roller 5, and can be easily removed by washing with water, so that the quality of the glass substrate is not affected. ..

Here, in the process of manufacturing the glass substrate of the present invention, which is a non-alkali glass substrate having a low Na ₂ O content, for example, in order to form a sufficient amount of sodium sulfate on the glass surface to prevent scratches on the glass substrate, for example. By appropriately adjusting the water vapor concentration in the float bath, the temperatures on the upstream and downstream sides of the float bath 2, the residence time of the molten glass 4, the dissolved oxygen concentration in the molten tin 1, and the like, Na ₂ O inside the glass can be increased. It moves to the vicinity of the bottom surface and is unevenly distributed, and it becomes possible to sufficiently generate sodium sulfate on the glass surface by spraying SO ₂ gas, so that a glass substrate with few scratches can be obtained.

Further, by moving Na ₂ O inside the glass to the vicinity of the bottom surface and unevenly distributing it, the amount of Na ₂ O diffused from the glass surface to the molten tin can be increased, and Na ₂ contained in the entire glass substrate can be increased. The amount of O can be reduced.

Specific examples of the conditions of the temperature on the upstream side and the downstream side of the float bath 2, the residence time of the molten glass 4, and the dissolved oxygen concentration in the molten tin 1 include the following (1) to (4).
(1) The temperature on the upstream side of the float bath 2 is preferably 1400 ° C to 900 ° C, more preferably 1300 ° C to 1000 ° C, and even more preferably 1250 ° C to 1100 ° C. The temperature on the upstream side of the float bath 2 indicates the temperature of the glass ribbon on the upstream side, and can be measured by a radiation thermometer.
(2) The temperature on the downstream side of the float bath 2 is preferably 600 ° C. to 850 ° C., more preferably 650 ° C. to 850 ° C., and even more preferably 700 ° C. to 800 ° C. The temperature on the downstream side of the float bath 2 indicates the temperature of the glass ribbon on the downstream side, and can be measured by a radiation thermometer.
(3) The residence time of the molten glass 4 is preferably 5 minutes to 60 minutes, more preferably 10 minutes to 40 minutes, and further preferably 15 minutes to 30 minutes.
(4) The dissolved oxygen concentration in the molten tin 1 is preferably 10 ppm or less, more preferably 5 ppm or less, further preferably 3 ppm or less, and most preferably 0 ppm. The dissolved oxygen concentration in the molten tin 1 can be measured by a tin oxygen concentration meter (Redox).

Na ₂ O collected near the bottom surface of the glass substrate by spraying SO ₂ gas becomes sodium sulfate and goes out to the outside of the glass substrate. Therefore, in the glass substrate obtained by the above method, the amount of Na ₂ O on the glass surface on the bottom surface side is less than the amount of Na ₂ O inside the glass, specifically, 20 mass ppm or more, 40 mass ppm. It is preferably less than 90 mass ppm, and more preferably less than 90 mass ppm.

Normally, the temperature of the heat treatment during the manufacture of the TFT is 400 ° C to 500 ° C, but the temperature of the glass ribbon when the SO ₂ gas is sprayed is about 600 ° C to 750 ° C, which is higher than the temperature of the heat treatment during the manufacture of the TFT. .. Therefore, by spraying SO ₂ gas, Na ions existing at a position deeper than the depth at which Na ions in the glass substrate are diffused during the heat treatment during TFT manufacturing can be reacted with SO ₂ and removed. ..

Therefore, when a TFT is manufactured using the glass substrate obtained by the above method, the diffusion of Na ions in the glass into the TFT during heat treatment is small and the fluctuation of the threshold voltage can be suppressed, so that a TFT having excellent reliability can be manufactured. can do.

<Slow cooling process>
In the slow cooling step, the glass ribbon carried by the transfer roller 5 is slowly cooled in the slow cooling furnace 6 to obtain the glass substrate of the present invention. The temperature of the slow cooling furnace 6 is not particularly limited, but can be 550 to 750 ° C. on the upstream side of the slow cooling furnace 6 and 200 to 300 ° C. on the downstream side, as in the case of a general float method, for example.

[Glass composition]
Next, the glass composition of the glass substrate of the present invention will be described.

Glass substrate of the present invention, the SiO ₂ from 54 to 66% by mass% based on oxides, _{Al 2 O 3 10~25%, B} 2 O 3 and 0.1 to 12%, MgO, CaO, SrO and one or more components selected from the group consisting of BaO contain 7-25% in total, Na ₂ O and containing 150 to 2000 mass ppm, of at least one Na ₂ O of the glass surface of the inner glass Na _It is 20 mass ppm or more less than the amount of ₂ O.

Each component will be described in detail below.

<SiO ₂ >
SiO ₂ is an essential component of non-alkali glass.
When the content of SiO ₂ in the glass substrate of the present invention is low, the strain point is low, the coefficient of thermal expansion is high, and the density is high. Therefore, the content of SiO _{2 in} the glass substrate of the present invention is 54% or more, preferably 57% or more, and more preferably 58% or more.

On the other hand, the viscosity of the glass becomes high when the content of SiO ₂ becomes large, the temperature _{T 4} which is a temperature _{T 2} and ¹⁰ 4 dPa · s glass viscosity becomes ¹⁰ 2 dPa · s is increased, the devitrification temperature rises To do. Therefore, the content of SiO _{2 in} the glass substrate of the present invention is 66% or less, preferably 63% or less, and more preferably 62% or less.

<Al ₂ O ₃ >
When the content of Al ₂ O ₃ in the glass substrate of the present invention is low, the phase of the glass is separated and the strain point is also lowered. Therefore, the content of Al ₂ O _{3 in} the glass substrate of the present invention is 10% or more, preferably 14% or more, and more preferably 15% or more.

On the other hand, _Al 2 when the content of _{O 3} is increased, the possibility that the glass viscosity of ¹⁰ 2 temperature _{T 2} and the temperature _{T 4} which is a ¹⁰ 4 dPa · s as a dPa · s is increased, or the liquidus temperature rises is there. Therefore, the content of Al ₂ O _{3 in} the glass substrate of the present invention is 25% or less, preferably 21% or less, and more preferably 18% or less.

<B ₂ O ₃ >
When the content of B ₂ O ₃ in the glass substrate of the present invention decreases, the viscosity of the glass increases and the devitrification temperature increases. Therefore, the content of B ₂ O _{3 in} the glass substrate of the present invention is 0.1% or more, preferably 0.5% or more, more preferably 1% or more, still more preferably 2% or more. Further, from the viewpoint of preventing haze from being generated by etching with buffered hydrofluoric acid, 3% or more is preferable, and 5% or more is more preferable.

On the other hand, as the content of B ₂ O ₃ increases, the strain point decreases. Therefore, the content of B ₂ O _{3 in} the glass substrate of the present invention is 12% or less, preferably 11% or less, and more preferably 9% or less. Further, when it is desired to make the strain point particularly high, 7% or less is preferable, 5% or less is more preferable, and 3% or less is further preferable.

<MgO, CaO, SrO and BaO>
In the glass substrate of the present invention, none of MgO, CaO, SrO and BaO is essential, but these components have the effect of lowering the viscosity of the glass and maintaining the chemical durability. Therefore, in the glass substrate of the present invention, the total content of these components is 7% or more, preferably 9% or more, and more preferably 12% or more.

On the other hand, if these components are excessively contained, the coefficient of thermal expansion of the glass becomes excessive. Therefore, in the glass substrate of the present invention, the total content of these components is 25% or less, preferably 21% or less, and more preferably 18% or less.

MgO is a component of alkaline earth oxides that has a relatively small effect of increasing the coefficient of thermal expansion of glass. It is also a component that can increase Young's modulus while maintaining a low density of glass. The content of MgO is preferably 1% or more, more preferably 2% or more, still more preferably 3% or more. On the other hand, since the devitrification temperature can be lowered by reducing the MgO content, the MgO content is preferably 10% or less, more preferably 8% or less, still more preferably 6% or less.

CaO is a component capable of increasing Young's modulus without increasing the coefficient of thermal expansion and density so much. The CaO content is preferably 2% or more, more preferably 3% or more. On the other hand, when the CaO content is reduced, the glass is less likely to be devitrified. Therefore, the CaO content is preferably 15% or less, more preferably 10% or less, still more preferably 6% or less.

SrO has the effect of lowering the viscosity without raising the devitrification temperature of the glass, and is preferably contained in an amount of 6% or more. On the other hand, since the coefficient of thermal expansion can be reduced by lowering the content of SrO, the content of SrO is preferably 15% or less, more preferably 10% or less, still more preferably 9% or less.

BaO is a component that lowers the viscosity, but since the coefficient of thermal expansion can be reduced by lowering the content of BaO, the content of BaO is preferably 5% or less, more preferably 1% or less. Further, particularly when it is desired to reduce the density for the purpose of reducing the weight of the glass substrate, 0.5% or less is preferable, and it is more preferable that the density is substantially not contained.

<Na ₂ O>
Normally, when a TFT is formed on a glass substrate, heat treatment is performed after that, but if the glass contains a large amount of Na ₂ O, Na ions in the glass diffuse into the TFT during the heat treatment, and the threshold of the TFT is increased. Since the voltage fluctuates, the reliability of the TFT decreases. Therefore, the Na ₂ O content in the glass substrate of the present invention is 2000 mass ppm or less, preferably 1000 mass ppm or less, and more preferably 800 mass ppm or less.

On the other hand, if the Na ₂ O content of the glass is too small, the melting characteristics of the glass deteriorate. Therefore, the Na ₂ O content in the glass substrate of the present invention is 150 mass ppm or more, preferably 300 mass ppm or more, and more preferably 500 mass ppm or more.

As described above, the glass substrate of the present invention, by decreasing least 20 mass ppm from Na 2 _O content of the glass substrate to Na 2 _O of the glass substrate surface in at least one major surface, a wound surface of the glass substrate Can be reduced.

Therefore, in the glass substrate of the present invention, the amount of Na ₂ O on the surface of the glass substrate on at least one main surface is 20 mass ppm or more less than the amount of Na ₂ O inside the glass substrate, preferably 40 mass ppm or more, more preferably 90 mass. It shall be less than ppm.

In the glass substrate of the present invention, by setting the Na ₂ O content in the above range, it is possible to prevent a decrease in the reliability of the TFT when the TFT is formed on the glass substrate, but it particularly affects the reliability of the TFT. It is Na ₂ O present on the surface of the glass substrate. Therefore, in the glass substrate of the present invention, by making the amount of Na ₂ O on the surface of the glass substrate smaller than the amount of Na ₂ O inside the glass substrate on at least one main surface, the decrease in the reliability of the TFT is further suppressed. be able to.

The reliability of the TFT can be evaluated by, for example, a BT test (bias temperature stress test). FIG. 4 shows the fluctuation amount of the threshold voltage and Na on the glass substrate surface when a low-temperature polysilicon thin film transistor (LTPS-TFT) is formed on the bottom surface side surface of the glass substrate and a positive bias is applied to perform a BT test. It is a figure which showed the relationship of ₂ O content.

Here, the structure of this LTPS-TFT is a standard top gate coplanar structure, and the source drain region is formed by ion implantation of boron to form a p-channel TFT. The polysilicon film is obtained by irradiating an amorphous silicon film having a thickness of 50 nm obtained by a plasma CVD method with an XeCl excimer laser (wavelength 308 nm) to crystallize it.

Further, a silicon oxide film having a thickness of 100 nm is formed as a barrier film between the glass substrate and the silicon film. The LTPS-TFT is treated at a higher temperature than the currently mainstream amorphous silicon TFT, and is therefore characterized by being more strongly affected by the Na ₂ O content on the surface of the glass substrate.

From FIG. 4, the smaller the Na ₂ O content on the surface of the glass substrate, the smaller the fluctuation amount of the threshold voltage, that is, the higher the reliability of the TFT. Further, it can be seen that this feature becomes more remarkable as the Na ₂ O content on the surface of the glass substrate is smaller.

Therefore, the glass substrate of the present invention, Na ₂ O of the glass substrate surface is preferably at most 500 ppm by weight in at least one main surface, more preferably less 300 ppm by mass, further preferably 250 mass ppm or less.

<Other ingredients>
Although the glass substrate of the present invention is non-alkali glass, it is known that alkali metal oxides are inevitably mixed as impurities in the glass raw material. Normally, Na ₂ O accounts for most of the alkali metal oxides mixed as impurities in the raw material, but Li ₂ O and K ₂ O may also be contained. When these are contained, the total amount of the alkali metal oxide including Na ₂ O is 5000 mass ppm or less, preferably 2000 mass ppm or less, more preferably 1000 mass ppm or less, further preferably 800 mass ppm or less. ..

Further, the glass substrate of the present invention may contain F, Cl, SO ₃ , SnO ₂ , ZrO _{2, and the} like as long as the effects of the present invention are exhibited.

[Physical characteristics of glass substrate]
Subsequently, the physical characteristics of the glass substrate of the present invention will be described.
The glass substrate of the present invention has a strain point of 650 ° C. or higher and an average coefficient of thermal expansion of 30 × 10 ^{-7 to} 45 × 10 ^-7 / ° C. at 50 to 350 ° C.

<Distortion point>
When the strain point of the glass substrate of the present invention is low, when the glass substrate is exposed to a high temperature in a thin film forming process such as a display, the glass substrate is likely to be deformed and shrink (heat shrinkage) due to structural stabilization of the glass. Become. Therefore, the strain point of the glass substrate of the present invention is 650 ° C. or higher, preferably 660 ° C. or higher, and more preferably 670 ° C. or higher.

On the other hand, when the strain point is low, the temperature of the molding apparatus can be lowered, so that there is an advantage that the life of the molding apparatus can be improved, and it is preferable that the strain point is not too high. Therefore, the strain point of the glass substrate of the present invention is preferably 800 ° C. or lower, more preferably 750 ° C. or lower, and even more preferably 730 ° C. or lower.

The strain point can be measured by using the fiber stretching method according to the method specified in JIS R3103-2 (2001).

<Average coefficient of thermal expansion at 50-350 ° C>
In order to obtain a glass substrate having excellent thermal shock resistance and excellent productivity during TFT panel manufacturing, the average coefficient of thermal expansion of the glass substrate of the present invention at 50 to 350 ° C. is 30 × ^{10-7 to} 45 × ^10-7 /. Let it be ° C. The average coefficient of thermal expansion of the glass substrate of the present invention at 50 to 350 ° C. is preferably 33 × 10 ^-7 / ° C. or higher, and more preferably 35 × 10 ^-7 / ° C. or higher. Further, it is preferably 42 × 10 ^-7 / ° C. or lower, and more preferably 40 × 10 ^-7 / ° C. or lower.

The coefficient of thermal expansion can be measured using a thermal expansion meter according to the method specified in ASTM E831.

<Density>
The density of the glass substrate of the present invention is not particularly limited, but is preferably 3.0 g / cm ³ or less from the viewpoint of realizing weight reduction of the product and increasing the specific elastic modulus. It is more preferably 2.8 g / cm ³ or less, and further preferably 2.6 g / cm ³ or less.

<Temperature _T 2 at which the viscosity becomes 10 ² poise (dPa · s)>
The glass substrate of the present invention, it is easily dissolved since the viscosity η is 10 ² poise (dPa · s) and temperature T ₂ is relatively low made. From the viewpoint of solubility, the temperature T ₂ is preferably 1800 ° C. or lower, more preferably 1750 ° C. or lower, still more preferably 1700 ° C. or lower, and particularly preferably 1680 ° C. or lower.

<Temperature _T 4 at which the viscosity η is 10 ⁴ poise (dPa · s)>
Since the glass substrate of the present invention has a relatively low temperature T ₄ at which the viscosity η is 10 ⁴ poise (dPa · s) are suitable for float forming. From the viewpoint of float moldability, the temperature T ₄ is preferably 1350 ° C. or lower, more preferably 1325 ° C. or lower, further preferably 1300 ° C. or lower, and particularly preferably 1290 ° C. or lower.

The temperature T ₂ and the temperature T ₄ can be measured using a rotational viscometer according to the method specified in ASTM C965-96.

<Young's modulus>
The Young's modulus of the glass substrate of the present invention is preferably 70 GPa or more, more preferably 75 GPa or more. Young's modulus can be measured by the ultrasonic pulse method according to the method specified in JIS Z2280 (1993).

<Photoelastic constant>
The photoelastic constant of the glass substrate of the present invention is preferably 33 nm / MPa / cm or less.
Due to the stress generated during the liquid crystal display panel manufacturing process or the use of the liquid crystal display device, the glass substrate has birefringence, so that the black display becomes gray and the contrast of the liquid crystal display is lowered.

By setting the photoelastic constant to 33 nm / MPa / cm or less, this phenomenon can be suppressed to a small value, which is preferable. The photoelastic constant is more preferably 32 nm / MPa / cm or less, still more preferably 30 nm / MPa / cm or less.

The photoelastic constant of the glass substrate of the present invention is preferably 21 nm / MPa / cm or more, and more preferably 23 nm / MPa / cm or more, considering the ease of securing other physical properties. The photoelastic constant is measured at a measurement wavelength of 546 nm by a disk compression method.

<Relative permittivity>
When the glass substrate of the present invention is applied to an in-cell touch panel (a touch sensor is built in a liquid crystal display panel), the glass substrate is used from the viewpoint of improving the sensing sensitivity of the touch sensor, lowering the drive voltage, and saving power. The higher the relative permittivity of, the better.

Therefore, the relative permittivity of the glass substrate of the present invention is preferably 5.0 or more, more preferably 5.5 or more, and even more preferably 5.7 or more. The relative permittivity can be measured by the method described in JIS C-2141 (1992).

<β-OH value>
The β-OH value of the glass substrate of the present invention can be appropriately selected according to the required characteristics of the glass substrate. From the viewpoint of increasing the strain point of the glass substrate, it is preferable that the β-OH value is low. Specifically, beta-OH value is preferably 0.50 mm ^-1 or less, more preferably 0.45 mm ^-1 or less, more preferably 0.40 mm ^-1 or less.
The β-OH value can be adjusted by various conditions at the time of melting the raw material, for example, the amount of water in the glass raw material, the water vapor concentration in the melting kiln, the residence time of the molten glass in the melting kiln, and the like.

[TFT manufacturing method]
Next, in order to help understanding of the present invention, a method for manufacturing the TFT element 10 using a glass substrate will be described by taking as an example a method for manufacturing the top gate coplanar type LTPS-TFT shown in FIG. The use of the glass substrate is not limited to this.

If necessary, first, a barrier film 12 is formed on one main surface of the glass substrate 11. The barrier film 12 is composed of, for example, silicon oxide, silicon nitride, silicon nitride, alumina, or the like, but may be omitted. Next, an amorphous silicon layer is formed as a semiconductor on the barrier film 12 (or the glass substrate 11).

Next, if the hydrogen concentration in the amorphous silicon layer is reduced by performing heat treatment, it is possible to prevent film peeling and the like in the subsequent process. This heat treatment is performed, for example, in the range of 450 to 600 ° C. Next, amorphous silicon is crystallized by laser annealing to obtain a polysilicon layer 13. Laser annealing is performed, for example, by irradiating an excimer laser having a wavelength of 308 nm. After that, the polysilicon layer 13 is patterned into a predetermined shape. Patterning is performed by, for example, photolithography and etching methods. Subsequently, an insulating film and a conductive film are formed. This insulating film is composed of, for example, silicon oxide, silicon oxynitride, silicon nitride, and alumina, and later becomes the gate insulating film 14a. The thickness of the insulating film is, for example, 30 to 600 nm. The conductive film is made of, for example, a metal such as chromium, molybdenum, aluminum, copper, or silver, or an alloy containing them, and is later patterned to form a gate electrode 15. The thickness of the conductive film is, for example, 30 to 600 nm.

After the formation of the gate electrode 15, the portion of the polysilicon layer 13 protruding from the gate electrode 15 is subjected to a process of lowering the electrical resistance value (lowering resistance process). The resistance reduction treatment is performed by, for example, ion-implanting B (boron) ions into the polysilicon layer 13. Furthermore, the injected ions are activated by the heat treatment. This heat treatment may be performed, for example, at 450 to 600 ° C. for 10 to 60 minutes.
Next, the interlayer insulating film 14b is formed. The interlayer insulating film 14b is made of, for example, silicon oxide, silicon nitride, silicon nitride, alumina, or the like. The interlayer insulating film 14b is patterned so that a part of the protruding portion of the polysilicon layer 13 is exposed on both sides of the gate electrode 15.

Next, the source electrode 16 and the drain electrode 17 are formed. These electrodes are formed by patterning after forming a film of a conductive film made of a metal such as chromium, molybdenum, aluminum, copper, silver, or an alloy containing them.

Next, the passivation film 18 is formed so as to cover them. The passivation film 18 is composed of, for example, silicon oxide, silicon oxynitride, silicon nitride, and alumina. Its thickness is, for example, 30-600 nm.
The TFT element 10 can be manufactured as described above.

[Use of glass substrate]
The application of the glass substrate of the present invention is not particularly limited, but it is useful as a glass substrate or the like for a display such as a liquid crystal display device.

Hereinafter, the effects of the present invention will be described in more detail with reference to examples of the present invention, but the present invention is not limited thereto.

The glass raw material was melted and molded by the float method to obtain the glass substrates of Examples 1 to 5. In each of the examples, SO ₂ gas was sprayed on the bottom surface of the glass ribbon between the time when the glass ribbon left the float bath and the time when it came into contact with the transport roller in the float method.
The composition of the obtained glass substrate is shown in Table 1 in terms of mass% based on oxides. In addition, Example 1 was manufactured under the conventional manufacturing conditions, Examples 2 and 3 were manufactured so that the water vapor concentration in the float bath was slightly high, and Examples 4 and 5 were manufactured in the float bath. It was manufactured with a higher water vapor concentration.

In the glass substrate obtained by the float method, the compositions of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO and BaO do not change during the glass melting process, so the content of these components is high. , Obtained from the blending amount of the glass raw material.

Regarding the amount of Na ₂ O inside the glass substrate, the obtained glass substrate is pulverized, the obtained glass powder is thermally decomposed with sulfuric acid, nitric acid and hydrofluoric acid, and then concentrated until white sulfuric acid smoke is generated. A constant volume solution dissolved in nitric acid was obtained, and the Na concentration in the constant volume solution was quantified and determined by ICP mass analysis [unit: mass ppm].

The Na ₂ O of the glass substrate surface, the Na ₂ O content of the surface of the bottom side of the glass substrate by using a _{C 60} sputtering TOF-SIMS method, was measured by the method described above. The measurement conditions were as follows.
Measuring device: TOF manufactured by ION-TOF. SIMS5
Primary ion species: Bi ⁺
Primary ion acceleration voltage: 25kV
Current value of primary ion: 1pA (at 10kHz)
Raster size of primary ion: 20 × 20 μm ²
Primary ion bunching: Yes Spatter ion species: C ₆₀ ⁺⁺
Spatter ion acceleration voltage: 10kV
Spatter ion current value: 1.1 nA (at 10 kHz)
Raster size of spatter ion: 100 × 100 μm ²
Sputter mode: non-interlaced mode
Vacuum degree: 5.0 × ^10-6 mbar

For the glass substrates of Examples 1 to 5, β-OH value, density, Young's modulus, average coefficient of thermal expansion at 50 to 350 ° C., T ₂ , T ₄ , glass transition point, strain point, photoelastic constant, relative permittivity. The measurement results are shown in Table 1.

(Evaluation of fragility)
It is considered that sulfate is generated by the reaction between Na ₂ O on the surface of the glass substrate and SO _x in the atmosphere, and the sulfate acts as a buffer lubricant to prevent scratches. The amount of sulfate on the surface of the glass substrate is measured to evaluate the susceptibility to damage. It is considered that the larger the amount of sulfate, the higher the effect of suppressing scratches. The amount of sulfate on the surface of the glass substrate can be measured by measuring the amount of S using fluorescent X-rays.
A fluorescent X-ray analyzer (manufacturer: Rigaku, model: ZSX-PrimusII) was used to measure the amount of S, and the measurement conditions were a Target Rh tube voltage of 50 KV and a tube current of 60 mV. The optical conditions were attenuator 1/1 and slit S4, spectroscopic crystal Ge, and detector was PC.
A calibration curve was prepared using several standard samples, and the amount of sulfate in each sample was measured using the calibration curve. The results of the S amount measurement of each sample are shown in Table 2 below.

Next, each sample was evaluated for its susceptibility to scratches using a friction and wear tester (manufacturer: Shinto Kagaku Co., Ltd., model: TYPE40 (high temperature specification)).
Measurement temperature: 600 ° C
Scratch indenter: Silicon nitride pin (tip radius 25 microns)
Load condition: 10g
Indenter moving speed: 30 mm / min

As a result of the evaluation of the susceptibility to scratches of each sample, strong scratches were generated in Example 1, and no scratches were generated in Examples 2 to 5. In Example 1, since the amount of sulfate produced was small, the result was that it was easily damaged.
That is, the glass substrate of Example 1 the difference between the Na 2 _O content and the glass substrate inside the Na 2 _O content of the glass substrate surface is less than 20, scratched for production of sodium sulphate in the bottom surface the surface is insufficient It was easy and there was a quality control problem.
The glass substrates of Examples 2 and 3 were hard to be scratched because sodium sulfate was generated on the bottom surface surface. The glass substrates of Examples 4 and 5 were more resistant to scratches because a large amount of sodium sulfate was generated on the bottom surface.

Moreover, is likely that reduction in TFT characteristics in the case of forming a TFT on the bottom surface on the glass substrate even surface Na 2 _O content of any of Examples 2-5 is sufficiently small is small, the glass of Example 3 and 5 Since the surface Na ₂ O amount of the substrate is particularly small, it is considered that the deterioration of the TFT characteristics is particularly small.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on March 9, 2018 (Japanese Patent Application No. 2018-043493), the contents of which are incorporated herein by reference.

100 ... Float glass manufacturing equipment 1 ... Molten tin 2 ... Float bath 3 ... Melting kiln 4 ... Fused glass 5 ... Conveying roller 6 ... Slow cooling furnace 10 ... TFT element 11 ... Glass substrate 12 ... Barrier film 13 ... Polysilicon layer 14 ... Insulation layer 14a ... Gate insulating film 14b ... Interlayer insulating film 15 ... Gate electrode 16 ... Source electrode 17 ... Drain electrode 18 ... Passion film

Claims (8)

A non-alkali glass substrate having a strain point of 650 ° C. or higher and an average coefficient of thermal expansion of 30 × ^{10-7 to} 45 × ^10-7 / ° C. at 50 to 350 ° C.
SiO ₂ is 54 to 66% in mass% display based on oxides,
Al ₂ O ₃ 10-25%,
B ₂ O ₃ 0.1-12%,
A total of 7 to 25% of one or more components selected from the group consisting of MgO, CaO, SrO and BaO.
Containing 150-2000 mass ppm of Na ₂ O,
An alkali-free glass substrate in which the amount of Na ₂ O on the surface of the glass substrate on at least one main surface is 20 mass ppm or more less than the amount of Na ₂ O inside the glass substrate. Alkali-free glass substrate of claim 1 Na 2 _O of the glass surface in at least one main surface is not more than 500 mass ppm. The non-alkali glass substrate according to claim 1 or 2, wherein the amount of Na ₂ O inside the glass substrate is 300 mass ppm or more. Temperature _{T 4} which glass viscosity of ¹⁰ 4 dPa · s is 1350 ° C. or less, alkali-free glass substrate according to any one of claims 1 to 3. The non-alkali glass substrate according to any one of claims 1 to 4, wherein the temperature T _{2 at} which the glass viscosity is 10 ² dPa · s is 1800 ° C. or lower. The non-alkali glass substrate according to any one of claims 1 to 5, wherein the β-OH value is 0.50 mm ^-1 or less. The non-alkali glass substrate according to any one of claims 1 to 6 obtained by the float method. The non-alkali glass substrate according to claim 7, wherein one of the main surfaces is a bottom surface.

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