JP2009167098A - Glass substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate hardly causing electrification during the manufacture process of a liquid crystal display. <P>SOLUTION: In the glass substrate having a first surface on which an electrode wire or various devices are formed and a second surface on which these are not formed, the second surface is physically polished and the surface roughness Ra of the second surface is ≥0.3 and ≤10 nm and it is preferable that the surface roughness Ra of the first surface is ≤0.2 nm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a glass substrate, and more particularly to a glass substrate for a display, which is less likely to cause electrostatic charging even when contact peeling is performed.

  Glass substrates are widely used as substrates for flat panel displays such as liquid crystal displays. In particular, non-alkali glass substrates containing no alkali oxide are used in flat panel displays, particularly liquid crystal displays.

  In the applications as described above, the following characteristics are required for the glass substrate. (1) Excellent chemical resistance to chemicals such as various acids and alkalis used in the photolithographic etching process. (2) The glass substrate is heated to several hundred degrees Celsius in processes such as film formation and annealing. In that case, the strain point is high because the glass does not heat shrink. In the present polycrystalline silicon TFT-LCD, the process temperature is about 400-600 degreeC, and the strain point of the glass for substrates used for these uses has a desirable value of 600 degreeC or more.

  Moreover, the following characteristics are required in order to melt these and shape | mold into a thin plate shape and to manufacture a glass substrate. (3) The glass has excellent meltability so that it does not easily cause melting defects that are not desirable as transparent substrate glass such as bubbles, bumps and striae in the glass. (4) Excellent devitrification resistance in order to avoid foreign matters generated during melting or molding in the glass substrate.

JP 2001-343632 A Japanese Patent Laid-Open No. 2002-72922

  By the way, in an alkali-free glass substrate, electrostatic charging of the glass substrate often becomes a problem. Glass that is originally an insulator is very easily charged, but alkali-free glass containing almost no alkali oxide component is particularly easy to be charged, and there is a tendency that static electricity once charged is not lost. In the manufacturing process of flat panel displays such as liquid crystal displays, charging of the glass substrate is caused by various processes, but so-called peeling charging that occurs due to contact peeling with a metal or insulator plate in a film forming process or the like becomes a big problem. Yes. Charging due to contact and peeling between the plate and the glass substrate occurs in a vacuum process such as a process for etching a thin film on the substrate surface or a film forming process, as well as a process in an atmospheric pressure. When a conductive substance approaches the charged glass substrate in such a process, discharge occurs. Since the charged electrostatic voltage reaches several tens of kV, the discharge causes the destruction of the elements and electrode wires on the surface of the glass substrate, or in some cases the glass itself (insulation breakdown or electrostatic breakdown), which causes display defects. . Among liquid crystal displays, active matrix type liquid crystal displays represented by TFT-LCDs have fine semiconductor elements such as thin film transistors and electronic circuits formed on the surface of glass substrates. These elements and circuits are extremely susceptible to electrostatic breakdown. It is particularly problematic because it is weak. In addition, the charged substrate attracts dust present in the environment and causes contamination of the substrate surface.

  As an antistatic measure for the glass substrate, a method of neutralizing the charge using an ionizer or increasing the humidity in the environment to discharge the accumulated charge into the air is often used. However, these countermeasures increase the cost, and there are various places where charging is caused during the process, so that it is difficult to take effective countermeasures. Furthermore, these means cannot be used in a vacuum process such as a plasma process. Therefore, for flat panel display applications such as liquid crystal displays, there is a strong demand for glass substrates that are not easily charged (see Patent Documents 1 and 2).

  An object of the present invention is to provide a glass substrate that is less likely to cause charging during the process.

  The glass substrate of the present invention is a glass substrate having a first surface on which electrode wires and various devices are formed and a second surface on which these are not formed, and the second surface is physically polished, and The surface roughness Ra of the second surface is 0.3 nm or more and 10 nm or less.

  Further, the surface roughness Ra of the first surface is preferably 0.2 nm or less.

  The first surface is preferably a fire-making surface.

  The glass substrate of the present invention is preferably formed by an overflow down draw method.

  The glass substrate of the present invention preferably has a total content of alkali oxides of 0.1% by mass or less.

  Moreover, it is preferable that the glass substrate of this invention is used as a glass substrate for flat displays, especially a glass substrate for liquid crystal displays.

  The glass substrate of the present invention has a low peel charge amount and can suppress static electricity generated in the manufacturing process of a liquid crystal display or the like. For this reason, destruction of elements and wirings on the substrate can be prevented, so that these electronic devices can be manufactured with high yield. Therefore, the glass substrate of the present invention is suitable as a substrate for flat panel displays such as liquid crystal displays and EL displays.

It is explanatory drawing which shows the apparatus used for measurement of peeling electric strength, (a) is explanatory drawing which shows the state which mounted the glass substrate, (b) is explanatory drawing which shows the state which stuck the glass substrate and the table. .

  As a method of reducing the charging of the glass substrate, particularly the peeling charging, it is most effective to reduce the contact area between the glass substrate and the other stage as viewed microscopically. When the glass substrate and the stage come into contact with each other with a strong force, electrons are exchanged at the interface between the two. This appears as a charge when peeled off. Therefore, by adjusting the surface roughness of the surface of the glass substrate that contacts the stage (corresponding to the second surface in the present invention) to an appropriate range, the contact area can be reduced, and as a result, the charge amount can be reduced. .

  The roughness of the glass surface effective for preventing peeling-off of the glass substrate is Ra of 0.3 nm or more. The larger the roughness of the glass surface, the smaller the charge amount, but if it is too large, another problem occurs. A large roughness on the surface of the glass substrate means that there is a large defect on the glass surface, which may cause a decrease in strength of the glass substrate, which is not desirable.

  On the other hand, a very high precision surface is desired for the surface that does not come into contact with various stages (corresponding to the first surface in the present invention). This surface is generally referred to as the priority guarantee surface or “front surface” of the substrate. For example, in a thin film transistor type liquid crystal display (TFT-LCD), various wiring films and devices for driving pixels are formed as thin films on the priority guarantee surface of the substrate. If the priority guarantee surface is scratched or dirty, or if the surface roughness is large, it may cause disconnection of the wiring film, defective TFT formation, etc., leading to display defects. In particular, in recent years, an IPS liquid crystal display or an ultra-high-definition liquid crystal display, which has been attracting attention as a wide viewing angle technology for TV, is extremely severe with respect to scratches and dirt on the glass surface. Accordingly, the surface roughness Ra is required to be 0.2 nm or less for the priority guarantee surface. Further, it is most desirable if this priority guarantee surface is a fired (as-foam) surface formed by, for example, a known downdraw molding. The most appropriate method of known downdraw molding is now the overflow downdraw method. It is possible to create an as-foam surface by other plate glass forming methods such as the float method, but at present, unevenness called tin contamination on the surface of the plate glass or microscopic surface undulations deteriorates the display performance of the TFT-LCD. If the priority guarantee surface is not polished, it will not become a product.

  In the glass substrate of the present invention, the second surface is physically polished in order to achieve the object of the present invention. In this case, as described above, it is easy to roughen only the non-priority guaranteed surface of the glass by polishing. Generally, polishing of glass is performed using an abrasive such as cerium oxide. As a solvent for the abrasive, acid, alkali, etc. may be added in addition to water. As the carrier for holding the abrasive, various resins such as polyurethane and artificial leather and chemical fibers are used. This method can effectively roughen the surface at low cost.

  In addition to the above-described physical polishing, for example, a method in which only the second surface is subjected to chemical treatment or plasma treatment to obtain a predetermined surface roughness can be considered.

[Sample preparation]
The following table shows examples of the glass substrate of the present invention. No. in the table. 2 is an example of the present invention. 1 is a comparative example.

  Sample No. 1 used was a non-alkali glass substrate OA-10 for liquid crystal displays (manufactured by Nippon Electric Glass Co., Ltd., an alkali oxide content of 0.1% by mass or less) that is distributed in the market. The substrate size is 370 to 470 mm, and the thickness of the substrate is 0.7 mm. This glass substrate was formed by the overflow downdraw method, and both surfaces of the substrate were fired surfaces, and the surface roughness Ra was 0.1 nm.

  No. 2 treated the surface by polishing. An Oscar-type polishing apparatus was used, cerium oxide and pure water were used as the polishing agent, and polyurethane was used as the polishing cloth. After polishing the surface for 30 minutes, it was washed and dried and used for evaluation.

[Measurement of surface roughness]
The surface roughness of the glass substrate was measured at a cutoff of 9 μm using a stylus type surface roughness meter (Talystep manufactured by Taylor-Hobson). In addition, the measured value measured the surface roughness of several places in a board | substrate, and showed it with the average value.

[Peeling charge evaluation]
An apparatus as shown in FIG. 1 was used for peeling charge evaluation in this example. This apparatus has the following configuration.

  The support 1 for the glass substrate G includes a pad 2 made of Teflon (registered trademark) that supports the corners of the glass substrate 4. Further, the support table 1 is provided with a table 3 made of metal aluminum that can be raised and lowered. By moving the table 3 up and down, the glass substrate G and the table 3 can be brought into contact with each other and peeled to charge the glass substrate G. it can. The table 3 is grounded. A hole (not shown) is formed in the table 3, and this hole is connected to a diaphragm type vacuum pump (not shown). When the vacuum pump is driven, air is sucked from the hole of the table 3, and thereby the glass substrate G can be vacuum-adsorbed to the table 3. Further, a surface potential meter 4 is installed at a position 10 mm above the glass substrate G, thereby continuously measuring the amount of charge generated at the center of the glass substrate G. Further, an air gun 5 with an ionizer is installed above the glass substrate G, whereby charging of the glass substrate G can be gradually reduced.

  A method of measuring the peeling withstand voltage using this apparatus will be described. The experiment is performed in an environment of 25 ° C. and a humidity of 40%. Since this amount of charge changes greatly depending on the atmosphere, particularly the humidity in the atmosphere, it is necessary to pay particular attention to the humidity.

(1) Place the glass substrate G on the support base 1 with the physical polishing surface facing down.
(2) Next, the glass substrate G is gradually charged by the air gun 5 with an ionizer.
(3) The table 3 is raised and brought into contact with the glass substrate G and vacuum-adsorbed to bring the table 3 and the glass substrate G into close contact for 20 seconds.
(4) The glass substrate G is peeled by lowering the table 3, and the charge amount generated at the center of the glass substrate G is continuously measured by the surface potentiometer 4.
(5) By repeating (3) and (4), a total of five peeling evaluations are continuously performed.
The maximum charge amount in each measurement is obtained, and these are integrated to obtain the peel charge amount.

[Evaluation results]
In the examples of the present invention, the peel charge amount was relatively low. In comparison, no. Sample No. 1 showed a high charge amount of the substrate.

G Glass substrate 1 Support base 2 Pad 3 Table 4 Surface potential meter 5 Air gun with ionizer

Claims (7)

In a glass substrate having a first surface on which electrode wires and various devices are formed, and a second surface on which these are not formed,
A glass substrate, wherein the second surface is physically polished, and the surface roughness Ra of the second surface is from 0.3 nm to 10 nm.   The glass substrate according to claim 1, wherein the surface roughness Ra of the first surface is 0.2 nm or less.   The glass substrate according to claim 1, wherein the first surface is a fire-making surface.   The glass substrate according to any one of claims 1 to 3, which is formed by an overflow downdraw method.   The glass substrate according to any one of claims 1 to 4, wherein the total content of alkali oxides is 0.1% by mass or less.   It uses for the glass substrate for flat displays, The glass substrate in any one of Claims 1-5 characterized by the above-mentioned.   It is used as a glass substrate for liquid crystal displays, The glass substrate in any one of Claims 1-5 characterized by the above-mentioned.