JP2000086300A - Thin-sheet glass substrate and its polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the surface smoothness of a thin-sheet glass substrate and to ameliorate its quality by measuring the star-shaped patch as a local recess with a specified quality evaluation method and imparting the surface smoothness with the inclination within a specified range to the substrate surface. SOLUTION: The polishing soln. used in polishing the surface of a glass substrate is composed mainly of an abrasive, a pH regulator and water. The pH regulator is added to keep the polishing soln. always neutral not to lower the polishing efficiency, and a mineral acid such as sulfuric acid is used. The polished glass substrate is vertically erected in parallel with a screen, the polished face is irradiated with a mercury lamp, and the state of the substrate face is observed. The substrate is gradually rotated around its vertical axis, the angle (inclination) between the substrate and beam vertically projected on the screen is measured when the star-shaped patch is observed on the screen, and the substrate is accepted when the angle is 17-25 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin glass substrate such as a liquid crystal glass substrate and a polishing method thereof.

[0002]

2. Description of the Related Art Ultra-high precision surface smoothness is required for a thin glass substrate used for liquid crystal and the like, and a fire method such as a float method for manufacturing a general-purpose glass sheet or a down-draw method. In the glass plate manufactured by the method described above, fine irregularities, invisible small scratches, undulations, and the like are present on the surface of the glass plate, and the glass plate cannot be used for a substrate as it is.

Conventionally, as a method of improving the surface of such a thin glass substrate or the like, a method of polishing one surface of the substrate has been used. For example, a glass substrate is disposed between an upper polishing plate and a lower polishing plate, and an upper polishing plate is provided. JP-A-7-285066 and JP-A-8-1509 disclose a method of rotating a polishing plate while applying pressure and supplying a polishing liquid from the lower platen to the lower surface of the glass substrate to smoothly polish one surface of the substrate. JP-A-9-57592
This is disclosed in Japanese Patent Application Publication No. As for the polishing agent, a cleaning method for dissolving and removing the polishing agent attached to the surface of a substrate such as glass with a mineral acid solution containing a reducing agent to prevent the generation of scratches and the like is disclosed in JP-A-58-198599. Are known.

[0004]

However, in the above-mentioned conventional single-side polishing method, a large number of local dents (star-like unevenness) of several millimeters to several tens of millimeters are generated on the polished glass substrate surface, and the product is polished. The surface is out of specification and hinders production. In the method disclosed in JP-A-58-198599, a polished glass substrate or the like is again dissolved and removed with a mineral acid solution to remove the abrasive adhered to the substrate surface. There is a problem that the property is reduced.

[0005]

Means for Solving the Problems The present inventor has conducted intensive studies on local dents and the like generated on a substrate surface of polished glass or the like, which has been a problem in the prior art, and as a result, it has been found that the dents are added to a conventional polishing liquid. Acetic acid as a pH adjuster reacts with cerium oxide as an abrasive and glass components removed by polishing to produce a tacky reactant, causing local polishing abnormalities, and polishing the glass substrate surface. It has been found that a local dent (star-like unevenness) of several millimeters to several tens of millimeters is generated on the surface. It has also been found that the above method can eliminate abrasives remaining on the surface of a substrate such as glass after polishing.

As described above, the present invention uses a mineral acid as a pH adjuster to be added to a polishing liquid to thereby provide a surface smoothness free of local depressions (star-like unevenness) on the surface of a glass substrate after polishing as in the prior art. An object of the present invention is to provide a glass substrate capable of obtaining a high-quality glass substrate having good properties by a simple method and a polishing method thereof.

That is, the present invention relates to a thin glass substrate having a thickness of 0.3 to 1.3 mm polished by a polishing liquid containing a cerium oxide abrasive, wherein the surface of the substrate has a star-like shape having local depressions. The present invention relates to a thin glass substrate having a surface smoothness having an inclination angle of 17 to 25 degrees as measured by a predetermined quality evaluation method for unevenness.

The present invention also provides a method for polishing a glass substrate surface with a polishing liquid containing a cerium oxide polishing agent.
The present invention relates to a method for polishing a thin glass substrate to obtain a high-quality polished surface with good surface smoothness by adding a mineral acid as a pH adjuster to the polishing liquid and polishing the polishing liquid. It is preferred that

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described. The polishing liquid used for polishing the surface of the glass substrate is mainly composed of a polishing agent, a pH adjuster, and water as a lapping liquid.

As the polishing agent, cerium oxide (CeO2), which is chemically stable, inexpensive and has a high polishing efficiency, is used in an amount of about 5 to 25% by weight based on the polishing liquid. However, it is preferably 10 to 20% by weight. Note that the polishing agent may usually contain other additives such as alkaline earth metals or dispersants. The abrasive may have a particle size of about 0.5 to 1.0 μm (average particle size), but is not limited thereto.

When a glass substrate is polished with a polishing liquid, alkali ions contained in the glass substrate to be polished usually elute, and the polishing liquid gradually becomes alkaline, resulting in a decrease in polishing efficiency. The pH adjuster is added to keep the polishing liquid neutral at all times so that the polishing efficiency does not decrease. Mineral acids such as sulfuric acid, hydrochloric acid, and nitric acid can be used. The pH adjuster adjusts the pH of the polishing liquid to about 7.
The neutralization is maintained at 5 to 8.5, and usually about 3 to 6% by weight of the polishing liquid is added.

When sulfuric acid is used as the mineral acid,
Since several kinds of dispersants added in the abrasive and sulfuric acid as a PH adjuster rarely react to produce a sticky substance, and there is no occurrence of local polishing abnormality,
Particularly preferred. As a polishing lap liquid, there is no oiliness,
Water that is low in viscosity, has a large cooling effect, is inexpensive, and has no fear of corroding the product is usually used. The addition of an additive such as a dispersant to the polishing liquid is not particularly limited.

The glass substrate is not particularly limited, such as soda-lime silicate glass, alkali-free glass or quartz glass, and the glass size and plate thickness are not limited. 0.3-1.
A thin plate of about 3 mm is preferable. In this case, a polishing pressure of about 80 to 130 g / cm 2 (glass) is usually applied, and these can be appropriately selected depending on the size and thickness of the glass substrate. Next, an embodiment of the present invention will be described.
It is not limited to these.

Example 1 After a glass substrate was attached to the lower surface of an upper surface plate in a polishing apparatus, the upper surface plate was pressed against a rotating lower polishing surface, and the upper surface plate was swung right and left in the horizontal direction. The lower surface of the glass substrate was polished while moving. The polishing liquid is continuously supplied to the glass polishing surface from a hole formed in the center of the lower polishing plate. Polishing 2 shown below
Polishing is continuously performed under the same conditions by one polishing machine one after another, and the polishing is completed. The polishing process, polishing conditions and quality evaluation were performed as follows.

Preparation of polishing liquid: 1500 g of cerium oxide as a polishing agent (cerium oxide content 92% by weight), PH
After weighing 70 g of sulfuric acid having a concentration of 10% as an adjusting agent, each was uniformly mixed with 8500 g of water to obtain a polishing liquid.

Polishing conditions: Polishing was performed under the following conditions.・ Glass size: 355 mm in length × 355 mm in width × 1.1 mm in thickness ・ Polishing pressure: 130 g / cm 2 −Glass ・ Swing width: 600 mm

Evaluation: The glass substrates polished by 20 polishers were evaluated for star-like unevenness, polishing unevenness, and polishing amount. At the same time, the polishing tact was also evaluated.

(A) Star-shaped unevenness: The quality of star-shaped unevenness of the polished glass substrate was evaluated by the following method. The polished glass substrate is vertically set in parallel with a screen described later, and the glass substrate is irradiated with a mercury lamp from the front of the glass substrate, and the transmitted light is projected onto a screen vertically arranged behind the glass substrate. Then, the surface condition of the glass substrate surface (polished surface) is observed with a transmission image. FIG. 1 shows that the glass substrate was gradually rotated around a vertical axis while standing upright, and a star-like unevenness was observed on the screen.
As shown in (1), the angle formed by the light beam from the light source and the light beam emitted from the light source perpendicularly to the screen (referred to as the tilt angle) is measured, and the glass substrate having the tilt angle of 25 ° or less is accepted. . As a result of the measurement, the star-shaped unevenness was in the range of 17 ° to 22 ° in any place, although the star-shaped unevenness was varied over the entire surface of the glass as shown in Table 1, which was within the standard.

(B) The method for measuring polishing unevenness was the same as that for the above star-shaped unevenness, and the inclination angle was 25 ° or less. As a result of the measurement, the polishing unevenness was a good value of 17 ° to 25 °.

(C) Amount of polishing: The measuring method was such that the weight of the glass before and after polishing was measured, and the difference in weight was converted into a thickness.
As a result of the measurement, the polishing amount was as good as 4.1 μm.

(D) Polishing tact: The measuring method is as follows. The pressing plate to which the glass substrate is attached descends from the center of the polishing platen to perform polishing. The time required to return to the position and rise. As a result of the measurement, the polishing tact was as good as 15 seconds / cycle.

[0022]

[Table 1]

Example 2 Polishing was performed under the same conditions as in Example 1 except that the size of the glass was 500 mm long × 400 mm wide × 0.7 mm thick. As a result, the star-shaped unevenness was 17 to 22 ° as shown in Table 1, and all the positions were within the standard.

Example 3 Polishing was performed under the same conditions as in Example 1 except that the size of the glass was 350 mm in length × 270 mm in width × 1.1 mm in thickness. As a result, the star-shaped unevenness was 19 to 21 ° as shown in Table 1 and all the positions were within the standard.

Example 4 Polishing was performed under the same conditions as in Example 1 except that the size of the glass was 350 mm long × 300 mm wide × 0.7 mm thick. As a result, the star-shaped unevenness was 18 to 21 ° as shown in Table 1, and all the positions were within the standard.

Comparative Example 1 A polishing liquid was prepared in the same manner as in Example 1 except that acetic acid having a concentration of 10% was used as a pH adjuster and the amount of acetic acid added was 80 g.

Evaluation: Star-shaped unevenness; values of 24 ° to 29 ° and 25 ° or more were present in some places and were out of the standard. Polishing unevenness: 18 ° to 25 °, which was equivalent to that of the example and was acceptable.・ Abrasion amount: 3.4 μm, about 20% compared to the embodiment
Polishing amount is inferior. Polishing tact: 18 seconds / cycle, about 20% lower than that of the example.

Comparative Example 2 Polishing was performed under the same conditions as in Comparative Example 1 except that the size of the glass was 300 mm long × 320 mm wide × 1.1 mm thick. As a result, as shown in Table 1, the star-shaped unevenness was 26 to 28 °, which was out of the standard.

Comparative Example 3 Polishing was performed under the same conditions as in Comparative Example 1 except that the size of the glass was 500 mm long × 400 mm wide × 0.7 mm thick. As a result, the star-shaped unevenness was 23 to 27 ° as shown in Table 1, and there were some places of 25 ° or more, which was out of the standard.

Next, the glass substrates were continuously polished under the conditions of Example 1 and Comparative Example 1, and the relationship between the number of polished substrates (horizontal axis), the star-shaped unevenness, and the polishing amount (vertical axis) was determined. The results are shown in FIG. Note that the values in Example 1 are shown in FIG.
Indicates the value of Comparative Example 1 described later. As a result, in the case of polishing continuously under the conditions of Example 1, the star-shaped unevenness tended to gradually decrease with the number of polished sheets, and after 110 sheets, the star-shaped unevenness showed a good value of about 21 °. At the same time, the polishing amount after polishing 110 wafers was as large as about 4.0 μm, and almost no decrease in the polishing amount due to the passage of the number of polished wafers was observed.

On the other hand, in the case of polishing continuously under the conditions of Comparative Example 1, the star-shaped unevenness tends to gradually increase with the passage of time. After 100 seconds, the star-shaped unevenness increases to about 30 °, which is not preferable. Also, unlike the tendency of Example 1, the polishing amount showed a tendency to gradually decrease with time, and was not a desirable value of about 3.4 μm after 100 seconds.

[0032]

According to the present invention, P added to the polishing liquid
By using a mineral acid as an H adjuster, the quality of local dents (star-like unevenness) of several millimeters to several tens of millimeters generated on the polished surface of the glass substrate is remarkably improved, and the polishing amount, polishing tact, etc. Has a remarkable effect such as improvement in quality and polishing efficiency by a simple method.

[Brief description of the drawings]

Fig. 1 Tilt angle measurement diagram

FIG. 2 shows the relationship between star-shaped unevenness and the polishing amount and the number of polished sheets.

Claims (3)

[Claims] 1. A thin glass substrate having a thickness of 0.3 to 1.3 mm polished with a polishing liquid containing a cerium oxide abrasive, wherein the surface of the substrate has a predetermined shape of star-shaped unevenness which is a local depression. A thin glass substrate having a surface smoothness having an inclination angle measured by the quality evaluation method of 17 to 25 degrees. 2. A method of polishing a glass substrate surface with a polishing liquid containing a cerium oxide polishing agent, wherein P is contained in the polishing liquid.
A method for polishing a thin glass substrate, characterized in that a high-quality polished surface having good surface smoothness is obtained by adding and polishing a mineral acid as an H adjuster. 3. The method for polishing a surface of a glass substrate according to claim 2, wherein the mineral acid is sulfuric acid.