JPH0193004A - Transparent conductive glass substrate and its manufacture - Google Patents

Abstract

PURPOSE:To reduce the deterioration in strength remarkably by applying the Na<+> Li<+> ion exchange reinforcement treatment to a glass substrate including Na at the temperature higher than the gradually cooling point of the glass substrate prior to the formation of a transparent conductive membrane. CONSTITUTION:As the glass substrate including Na, a transparent glass plate of insulating property, a high chemical and physical durabilty, and a good optical property, and sutable to an ion exchange reinforcement, such as a sodalimesilicate glass with the thickness 0.5 to 6mm level is used. The reinforced glass substrate is obtained by soaking in a fused salt bath including Li<+> at the temperature 500 to 650 deg.C. As the composition Li salt in the fused salt bath, Li sulfate is preferable. Since the melting point of the single body of the Li sulfate salt is 860 deg.C, and higher than the gradually cooling point of the glass substrate about 500 to 560 deg.C, it is effective to add the other salt to make a eutectic mixture to lower the melting point, and it is preferable to use a salt of Zn, K, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a transparent conductive glass substrate used for solar cells, transparent electrodes of display devices, etc., and a method for manufacturing the same.

[Prior Art] Transparent conductive glass substrates are often provided directly on the surface of products, and therefore require a certain level of physical strength. In particular, for transparent conductive glass substrates for large-area solar cells used outdoors, it is desired to strengthen the glass substrates in order to protect them from external impacts such as snow.

Physical strengthening methods such as air-cooling strengthening and chemical strengthening methods using ion exchange treatment are known methods for strengthening glass substrates, but relatively thin glass such as glass substrates for solar cells For substrates, the latter chemical strengthening method is superior since physical strengthening is difficult. As a chemical strengthening method, the typical Na"-=K" ion exchange method is a relatively low temperature range below the transition temperature of glass.
In this method, a+ ions are replaced with 3 ions having a larger ionic radius to generate compressive strain on the glass surface, but such compressive strain is relaxed at temperatures above the strain point of the glass.

On the other hand, as a manufacturing method for a transparent conductive glass substrate on which a transparent conductive film containing tin oxide as the main component is formed, chemical vapor deposition is a method for manufacturing transparent conductive glass substrates on which a transparent conductive film mainly composed of tin oxide is formed. (CVD method), especially at high temperatures, e.g.
CVD at a temperature of about 600°C, particularly preferably about 500 to 600°C, is optimal. In the case of soda lime silicate glass, which is commonly used as a transparent conductive glass substrate, this particularly preferred temperature is a temperature equal to or higher than its annealing point. Therefore, at the temperature of the glass during film formation by the CVD method, the compressive strain formed on the surface of the glass substrate by the Na"-K" ion exchange method is relaxed as described above. There is a problem in that the above-mentioned Na''-=+ ion exchange method is not suitable for a tin oxide CVD film forming process which is usually performed at a temperature above the annealing point, that is, about 500° C. or above.

[Problems to be Solved by the Invention] An object of the present invention is to use a glass substrate in which compressive stress strain is difficult to be relaxed even at a temperature at which a film of tin oxide is formed by a CVD method, which is usually a temperature higher than the annealing point of glass. An object of the present invention is to provide a transparent conductive glass substrate and a method for manufacturing the same.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and the first invention is to apply oxidation to the surface of a glass substrate containing sodium by chemical vapor deposition. In a transparent conductive glass substrate on which a transparent conductive film mainly composed of tin is formed,
The sodium-containing glass substrate is heated to a temperature higher than the annealing point of the glass substrate prior to the formation of the transparent conductive film.
A second invention provides a chemically strengthened transparent conductive glass substrate characterized by being subjected to ion exchange strengthening treatment of a3-Li3. A Na"-Li" ion exchange strengthening treatment is performed at a temperature above the annealing point of the substrate, and then a transparent conductive film containing tin oxide as a main component is formed on the surface of the glass substrate by chemical vapor deposition. The present invention provides a method for manufacturing a transparent conductive glass substrate.

The present invention will be explained in more detail below.

The sodium-containing glass substrate used in the present invention is a transparent glass plate that is insulating, has high chemical and physical durability, and has good optical properties and is suitable for ion exchange strengthening, such as soda lime silicate. Glass, silicate glass, alumino silicate glass, etc. can be used. In particular, the basic composition is 5i due to the price and ease of acquisition.
(h (65-75 wt%), Na2O (10-20
wt%), Ca0 (5-15 wt%), A1203 (
0.5-4 wt%), Mg0 (0.5-4 wt%)
, Fe203 (<2 wt%) soda lime silicate glass substrates are optimal. In addition, the thickness of the glass substrate is not particularly limited, but it may cause a decrease in light transmittance, a decrease in strength,
0.5mm to 6mm to avoid inconvenience in handling.
is appropriate.

The tempered glass substrate in the present invention is obtained by immersing it in a molten salt bath containing Li0 at a temperature of 500 to 650°C. The composition of the lithium salt in such a molten salt bath is preferably a nitrate or a sulfate, but lithium sulfate is particularly preferred in order to obtain a high-quality transparent glass substrate with little haze.

In addition, the melting point of lithium sulfate alone is 860°C, which is higher than the annealing point of the glass substrate (approximately 500 to 560°C), so it is possible to create a eutectic system by mixing it with other salts. Lowering the melting point is also effective. The salt used in this case is preferably a salt such as zinc or potassium, and particularly when a lithium sulfate salt is used as the lithium salt, zinc sulfate or potassium sulfate is preferable. The salt is preferably added in a molar concentration (%) of 5 to 40% relative to lithium sulfate.

Next, the strengthening mechanism by ion exchange of Na+→Li0 will be outlined. When a glass substrate is immersed in a molten salt bath containing lithium ions, the sodium ions in the glass are replaced by the lithium ions in the bath. Since lithium ions have a smaller ionic radius than sodium ions, tensile stress is temporarily generated in the exchange layer on the surface of the glass substrate during ion exchange. However, when the processing temperature is higher than the annealing point of the glass, this stress is alleviated by the viscous flow of the glass, so the sodium ions in the substrate surface layer are replaced with lithium ions without distortion, and the glass substrate is then replaced with lithium ions. When cooled, compressive stress is generated in the surface layer of the substrate because the cooling shrinkage of the surface layer containing many lithium ions is smaller than that of the inner layer containing many sodium ions. The compressive stress value generated at this time is about 10 to 50 g/mm.
Compressive stress values of 30-80 g/
mm", but the ion exchange layer on the surface is Na"-
Since it is thicker than in the case of K'' ion exchange, sufficient practical strength can be obtained.In addition, the compressive strain obtained by the ion exchange treatment above the annealing point in the present invention is reheated near the annealing point. Also, since the degree of stress relaxation of compressive strain is much smaller than that of compressive strain caused by Na''-+ ion exchange treated below the strain point, it is possible to provide a tempered glass substrate meeting the purpose of the present invention.

In the present invention, the method for forming the tin oxide transparent conductive film is a CVD method in which the glass substrate surface is brought into contact with the vapor of a tin compound and tin oxide is deposited by a thermal decomposition oxidation reaction or the like to form a tin oxide film. Applicable.

The tin compound that is the starting material when forming such a tin oxide transparent conductive film by the CVD method has excellent optical performance,
A tin compound is chosen that can provide chemical durability, physical durability and low resistance. For example, alkyltin compounds such as tetramethyltin and tetraethyltin, tin chloride compounds such as tin tetrachloride and tin dichloride, alkyltin chloride compounds such as 2methyltin dichloride and monobutyltin trichloride, and alkyltin compounds such as dibutyltin diacetate. Preferred examples include tin acetate compounds, but the present invention is not limited thereto. Such tin compounds may be used alone or as a mixture of two or more. Alternatively, the tin compound may be dissolved in a solvent and used as a solution. When used as a solution, organic solvents that are compatible with the tin compound and have the property of not lowering the decomposition temperature while maintaining a high vapor pressure as a solution, such as methanol, ethanol, isopropanol, etc. It is preferable to use alcohols or hydrocarbons such as cyclohexane and hexane, methyl ethyl ketone, methyl acetate, ethyl acetate, etc., or a mixture of two or more thereof.

When using the CVD method, fluorine or antimony is optimal as a component to be doped into tin oxide in order to impart conductivity to the tin oxide. In the case of fluorine, the doping raw materials include organic fluoride compounds such as bromotrifluoromethane (CFJr), chlorodifluoromethane (CHF2C1), iodopentafluoroethane (C, FsI), trifluoroacetic acid, hydrogen fluoride, Sulfur fluoride (SF6),
Fluorine-containing compounds such as tin difluoride (SnFz) are preferred, and in the case of antimony,
Examples include antimony compounds such as 5bC13, 5bC1s, tributoxyantimony, and antimony acetylacetonate, but are of course not limited to these.

The above-mentioned tin compound is heated as a liquid or solution in a vaporization chamber to form a vapor, and is applied to the surface of a glass substrate using an inert gas such as N2 gas or argon as an accompanying gas.

When the doping raw material is a solution, it is heated in a vaporization chamber, vaporized, and applied to the glass substrate surface using the accompanying gas as described above, if necessary.

The tin compound and the vapor of the doping raw material are applied to the glass substrate surface through an injector using entrained gas together with oxygen gas, and a tin oxide transparent conductive film doped with fluorine or antimony is formed by thermal decomposition. Like this C
When forming a film by the VD method, it is appropriate to heat the glass substrate to a temperature below the softening point of the glass so that the optical properties, chemical properties, and electrical properties of the glass substrate are improved by a thermal decomposition reaction. It is. When the heated glass substrate surface contacts the tin compound and the vapor of the doping raw material,
A tin oxide transparent conductive film is formed on the surface of the glass substrate by the thermal decomposition reaction.

The CVD method is extremely useful as a method for producing tin oxide films because the process is easy to control and a film with good conductivity can be obtained.

In addition, since the glass substrate in the present invention contains an alkali metal element, silicon oxide film and aluminum oxide film are used to prevent the alkali metal from eluting from the surface of the glass and having an adverse effect on the transparent conductive film formed on the top surface. An alkaline barrier coat such as a zirconium oxide film or a zirconium oxide film may be applied to the surface of the glass substrate. In this case, Na of the glass substrate
The +→Li+ ion exchange is performed prior to the alkali barrier coating.

[Example] The present invention will be explained in detail below.

Soda lime silicate glass substrate with a plate thickness of 3 mm (basic composition of the glass substrate Sing +72.5w, t%, A
1xO+: 1.5wt%, FezL: 0.2wt
%, Cab: 7.6wt%, MgO: 4.0wt%
, NaJ: 13.9 wt%) was prepared, and 20 to 28 meshes of fused mullite were dropped from a height of 30 cm to create a scratch with a depth of 20 μm on the substrate surface.
After ion exchange treatment by immersion in a 550°C molten salt bath consisting of i25O,80 and K2S0420 for 10 minutes,
It was taken out from the molten salt bath and left to stand until it reached room temperature, yielding Sample 1.

Similarly, molten salt composition, processing temperature, and processing time are shown in Tables 1 and 2.
Samples 2 to 21 were obtained with various changes as shown in FIG.

For Samples 1 to 18, the scratched bending strength (when the glass substrate is subjected to ion exchange strengthening treatment, the glass substrate is subjected to the above scratching treatment before the ion exchange treatment, and then the bending strength after the ion exchange treatment (Kg/ Table 1 shows the measured values of mm2). Note that the damage bending strength after the above-mentioned damage treatment is applied to the glass substrate which has not been subjected to the ion exchange strengthening treatment is 15 g/mm''.

Table 1 As is clear from Table 1, by applying ion exchange strengthening treatment, the strength of the glass is several times that of a glass plate of the same thickness without ion exchange strengthening treatment (damaged bending strength 15 g/mm2). Plate (sample 18 has a bending strength of 45K)
g/mm2) was obtained.

For Samples 7-12.19-21, the depth of the compressive stress layer (μ
Table 2 shows the measured values of m).

Table 2 Next, soda lime silicate glass substrates similar to Samples 1 to 21 were subjected to the scratching treatment described above, and then immersed in a potassium nitrate molten salt bath at 460°C for 120 minutes to remove Na.
After the "-+K" ion exchange treatment, the sample was taken out from the molten salt bath and left to stand until it reached room temperature to obtain Sample A. The bending strength of sample A at this point is 72 (K
g/mm”).

Sample B is a soda lime silicate glass plate similar to Samples 1 to 21, but not subjected to ion exchange treatment after being scratched.

Above sample 12 (-11-ratio L125On 60
．． Three types of glass substrates (KzS0420, ZnS0420 treated with Na"-Li" ion exchange treatment for 120 minutes in a 620°C molten salt bath), sample A, and sample B were placed in an atmospheric pressure CVD apparatus, and each
The glass substrate was heated to 80°C (glass substrate temperature), and nitrogen gas containing tetramethyltin vapor, oxygen, and bromotrifluoromethane vapor was sprayed onto the glass substrate surface from a CVD nozzle to form a tin oxide film of about 8,000 layers using the CVD method. . CVD
Table 3 shows the measured values of the damage bending strength of the glass substrate before the formation of the tin oxide film by the method and the transparent conductive glass substrate obtained as described above, and the strength ratio before and after the formation of the tin oxide film by the above CVD process. Shown below.

Table 3 As is clear from Table 3, the glass substrate obtained by the Na"-K" ion exchange strengthening treatment has a large bending strength, that is, a large compressive stress value, but the compressive strain is CV
While the heat treatment at 500 to 600 °C during the formation of a tin oxide film by method D significantly lowers the strength, the glass substrate obtained by the Na''→Li1 ion exchange strengthening treatment of the present invention does not undergo oxidation by the above-mentioned CVD method. It is recognized that the strength hardly decreases depending on the heat treatment at 500 to 600° C. during the formation of the tin film.

[Effects of the Invention] As described above, the present invention shows that the decrease in strength is extremely small when forming a transparent conductive film, especially a transparent conductive film containing tin oxide as a main component, by the CVD method, and that the strength is maintained sufficiently even after the transparent conductive film is formed. This has the excellent effect that a transparent conductive tempered glass substrate having high strength can be obtained. Further, according to the present invention, a glass substrate having sufficient strength to withstand external impact can be obtained even if the plate thickness is small, so it is very advantageous especially when used as a substrate for solar cells. Furthermore, in the present invention, since the glass substrate is treated at a high temperature above the annealing point and below the softening point, the glass substrate has an excellent property that the strength does not decrease even when an amorphous silicon film is formed and other heat treatments are further performed. The effect is also recognized.

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Claims (6)

[Claims] (1) In a transparent conductive glass substrate in which a transparent conductive film containing tin oxide as a main component is formed on the surface of the glass substrate containing sodium by chemical vapor deposition method, the glass substrate containing sodium is A chemically strengthened transparent conductive glass substrate characterized by being subjected to ion exchange strengthening treatment of Na^+→Li^+ at a temperature above the annealing point of the glass substrate prior to the formation of a transparent conductive film. . (2) Claim 1, characterized in that the glass substrate is brought into contact with a molten salt at a temperature higher than its annealing point to undergo ion exchange strengthening treatment of Na^+ → Li^+. The transparent conductive glass substrate described in Section 1. (3) The transparent conductive glass substrate according to claim 2, wherein the molten salt that undergoes the Na^+→Li^+ ion exchange strengthening treatment is a sulfate. (4) A glass substrate containing sodium is subjected to ion exchange strengthening treatment of Na^+ → Li^+ at a temperature above the annealing point of the glass substrate, and then a chemical vapor deposition method is applied to the surface of the glass substrate. A method for manufacturing a transparent conductive glass substrate, comprising forming a transparent conductive film containing tin oxide as a main component. (5) The transparent conductive material according to claim 4, characterized in that the glass substrate is brought into contact with a molten salt at a temperature equal to or higher than its annealing point to undergo ion exchange strengthening treatment of Na^+→Li^+. A method for manufacturing a synthetic glass substrate. (6) The method for manufacturing a transparent conductive glass substrate according to claim 5, characterized in that the molten salt brought into contact with the glass substrate in the Na^+→Li^+ ion exchange strengthening treatment is a sulfate. .