JPH11151665A - Back pad and water absorption prevention method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent local stress from being applied on a polishing face of a substrate and a crack thereof. SOLUTION: In a back pad 3 used in a method for polishing one face of a substrate 2 by attaching the substrate 2 on a lower face of an upper surface plate 1 through the back pad 3 of a foaming elastic body and rotating and pressurizing a grinding panel 5 provided in a lower part thereof, a water absorption rate from a surface thereof is 20 mg/cm<2> or less. Moreover, according to a water absorption prevention method of the back pad 3, a thin coat of resin paint is applied on a surface of the back pad 3 and then the surface thereof is dried and hardened, a part of an air hole on the surface of the back pad is blocked to control the water absorption rate from the surface thereof, and then the back pad 3 is mounted on a lower face of the upper surface plate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back pad used for polishing one side of a substrate such as glass for a liquid crystal substrate or a semiconductor wafer, and a method of preventing water absorption thereof.

[0002]

2. Description of the Related Art Ultra-high-precision surface smoothness is required for thin-plate substrates used for glass for liquid crystal substrates or semiconductor wafers. For example, in the case of glass for liquid crystal substrates, a normal glass plate is manufactured. Glass manufactured by the fire method such as the float method or the down draw method has irregularities on the glass surface, small invisible scratches, or undulations, and cannot be used as it is for substrates. .
Conventionally, a method of polishing one surface of a substrate has been used as a method of improving the surface of a substrate such as a thin glass or a semiconductor wafer. The single-side polishing method generally involves placing a substrate between an upper platen and a lower platen on which a polishing plate is integrally mounted, and using a polishing plate that supplies a polishing liquid while pressing the upper platen. Rotate, a method of polishing one side of the substrate smoothly, for example,
It is known in JP-A-7-285066, JP-A-8-1509, JP-A-9-57592 and the like. In the case of this polishing method, a plate-like body called an elastic back pad is usually interposed between the upper surface plate and the substrate to hold the substrate and to prevent concentrated stress from being applied to the substrate during pressure polishing. It is protected by an elastic back pad.

[0003]

In the above-described conventional single-side polishing method, the substrate often breaks for unknown reasons, which may hinder production.

[0004]

Means for Solving the Problems As a result of diligent research, the present inventor has found that the water absorption of the back pad used for polishing and the rate of occurrence of cracks with the substrate are correlated. That is, for example, a urethane resin or the like having open cells is usually used as the back pad.However, during polishing, a large amount of polishing liquid is absorbed from the surface of the urethane back pad to the inside of the resin having open cells. When water is inserted and hydrolysis of the urethane resin occurs during use, defects such as partial swelling occur, and if polishing is continued while using the back pad with the partially swelled defect, It has been found that local stress is generated in the substrate, which leads to cracking of the substrate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. By controlling the water absorption of a back pad of a foamed elastic body to a predetermined amount or less, the resin of the foamed elastic resin due to water absorption is controlled. A back pad that extremely slows degradation due to hydrolysis and contributes to reducing cracks by eliminating local stress on the substrate, reducing the work of monitoring the back pad, reducing the frequency of back pad replacement, reducing costs, improving the polishing operation rate, etc. And a method for preventing water absorption thereof.

That is, according to the present invention, a substrate is mounted on a lower surface of an upper surface plate through a back pad of a foamed elastic body having open cells, and the upper surface plate and a polishing plate provided below are rotated.
In a back pad used for a method of polishing one surface of a substrate while applying pressure, the water absorption from the surface is 20 mg / cm ^2.
The following relates to the back pad.

Further, it is preferable to control the amount of water absorption from the surface by coating the surface of the back pad before mounting on the upper surface plate with a thin resin paint and closing some of the pores on the surface with the paint. . Further, according to the present invention, a substrate is attached to the lower surface of an upper surface plate through a foamed elastic body back pad having open cells, and the upper surface plate is rotated while supplying a polishing liquid to a lower polishing surface while applying pressure. Then, in the method of polishing one surface of the substrate, after the surface of the back pad is thinly coated with a resin paint, dried and cured, and partially closed the pores of the back pad surface to control the water absorption from the surface, The present invention relates to a method for preventing water absorption of a back pad in which a back pad is attached to a lower surface of an upper surface plate.

Further, a metal ring is placed on the painted surface of the painted back pad before being mounted on the upper surface plate, a predetermined amount of water is filled in the ring, and the water absorption after a predetermined time has elapsed is measured. Then, it is preferable to determine the required coating amount by determining the water absorption from the surface.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a back pad and a method for preventing water absorption of the back pad according to the present invention. Note that the present invention is not limited to this embodiment.

In FIG. 1, a back pad 3 made of a foamed elastic resin larger than the size of a substrate 2 to be polished is adhered to the lower surface of an upper platen 1 with an adhesive. Paste on the surface. On the other hand, a polishing plate 5 is integrally mounted on the upper surface of the lower platen 4, so that a polishing liquid can be supplied to the polishing plate 5 from below when polishing, and the lower platen 4 integrated with the polishing plate 5 is provided. The polishing liquid is supplied while rotating the. Then, the upper platen 1 is
Then, the upper surface plate 1 is further pressed against the polishing plate 5 on the lower surface plate 4, and one surface of the substrate 2 is polished in the pressed state. After polishing for a certain time,
The upper pressure platen 1 is moved upward, and the substrate 2 polished on one side is moved.
Is removed from the back pad 3, and polishing of one substrate 2 is completed.

The back pad of the foamed elastic body having open cells is coated with a resin paint before being adhered to the upper surface plate, dried and cured to partially close the pores on the surface,
After controlling the water absorption from the surface to 20 mg / cm ² or less, it is adhered to the upper surface plate. By closing a part of the pores on the surface of the back pad, it does not absorb much water at the time of polishing, so that it does not hydrolyze even if used for a long time, can withstand long-term use, and has improved durability.

The water absorption of the back pad can be used as long as it is 20 mg / cm ² or less. However, if the water absorption exceeds 15 mg / cm ² , the durability of the back pad greatly varies, and 1.5 to 10 mg / cm ^2. / Cm ² is more preferable. 1.
If it is 5 mg / cm ² or less, the holding power of the substrate is reduced when the substrate is adhered with water, and the substrate is detached from the back pad during polishing, so that the substrate is easily damaged.

It is preferable that the area to be coated on the surface of the back pad be the entire surface except for the portion that is bonded to the upper surface plate. When the substrate is attached to the back pad only by the surface tension of water, it is preferable to apply the coating to such a thickness that the holding force of the substrate does not decrease.

The back pad is for holding the substrate firmly when polishing the substrate sandwiched between the upper and lower platens as described above, and therefore has a structure of a foamed elastic body having open cells. Is preferred, and can be used as long as it has a certain strength and durability,
In particular, foamable urethane resin, acrylic resin and the like are preferable.

To bond the back pad to the lower surface of the upper platen, a normal adhesive may be used, but it is preferable to use a double-sided adhesive sheet in terms of workability because it is efficient. The method of attaching the substrate to the back pad is, considering the desorption property of the substrate, it is preferable to wet the lower surface of the back pad with water and affix the substrate to the surface using the surface tension of water, but it is not limited thereto. It is not necessary to attach it and it may be attached with an adhesive.

When polishing, the lower platen is driven and rotated at a constant speed, and the polishing plate also rotates accordingly. However, the upper platen on which the substrate is mounted is free and rotates with the rotation of the lower platen. It is preferable to use a rotating mechanism. The upper surface plate may be rotated.

As the substrate, other than a glass substrate for liquid crystal, a substrate such as a semiconductor wafer can be used. However, the present invention is not limited to this, and any substrate can be used for polishing a thin plate on one side. In the case of a glass substrate, the thickness of the glass plate is mainly about 0.3 to 3.0 mm, and is a normal plate glass, a so-called float plate glass, and it goes without saying that various colored glasses including clear can be used. No. The glass composition is soda lime glass, aluminosilicate glass, borosilicate glass, or the like, but it is needless to say that the composition is not limited to these.

The coating method is preferably a spray method, a roll method or the like, but is not limited thereto. Furthermore, the back pad after application is dried at about 60 to 100 ° C. for about 10 minutes in order to dry and harden the coating film.

Examples 1 to 3 were performed in the following order. Glass as substrate (size: 450mm x 500mm x
0.7mm) and back pad (Material: Urethane resin with open cells, Size: 40mm each side length from glass
Are prepared). Note that a double-sided adhesive sheet is attached in advance to the surface of the back pad that is to be bonded to the upper surface plate.

A mixture of a urethane resin paint and a curing agent (mainly butyl acetate) mixed at a ratio of 100: 5 is applied thinly to all surfaces of the back pad except for the adhesive layer by using a sprayer. And dried and cured in a dryer at 90 ° C. for 10 minutes to block some of the pores on the surface of the urethane resin back pad. The test samples were three types shown in Table 1 in which the amount of coating on the surface was variously changed.

The back pad is adhered to the lower portion of the upper platen with the adhesive layer of the back pad facing upward. After the lower surface of the back pad is wetted with water, the above-mentioned glass plate is attached to the portion.

After the upper platen is moved downward to the vicinity of the polishing plate, the lower platen is rotated (the polishing plate also rotates) while supplying the polishing liquid to the polishing plate. The rotation speed is 15
Performed at 0 times / minute.

The upper platen is moved further downward, and the glass plate is pressed against the polishing plate and polished for 10 minutes. The pressurizing pressure was 90 g / cm ² . When the polishing is completed, the upper platen is released upward, the rotation of the polishing plate is stopped, and the glass sample is removed from the back pad.

The above-mentioned polishing was continuously performed without replacing the back pad until swelling occurred. As a result, as shown in Table 1, Examples 1 to 3 having a water absorption of 20 mg / cm ² or less
The durability was good at 70 hours or more.

The water absorption of the back pad was measured by the following method. Aluminum ring (diameter: 30mmφ, depth: 5m) on the painted surface of the back pad sample
m) was placed, and the ring was filled with 5 ml of water, and the amount of water absorption (mg) when left for 5 minutes was measured. The water absorption is (water absorption (mg) ÷ cross-sectional area of the ring (7.07 cm ² )).
I asked for it.

Comparative Examples 1-2 Coating and durability were evaluated in the same manner as in Examples 1-3. As a result, as shown in Table 1, the water absorption was 20 mg / cm
^The durability of Comparative Examples 1 and ^{2 of 2} or more was as short as 30 hours or less,
It was not preferred.

[0027]

[Table 1]

[0028]

According to the present invention, the surface of the foamed elastic back pad is coated with a resin paint or the like to partially close the pores on the surface,
By controlling the water absorption from the surface, it does not absorb water even if it is polished for a long time, and the degradation of the foamed elastic resin due to hydrolysis becomes extremely slow. This has a remarkable effect that can contribute to reducing the work of monitoring the back pad, reducing the frequency of replacing the back pad, reducing the cost, improving the polishing operation rate, and the like.

[Brief description of the drawings]

FIG. 1 is a side view of a single-side polishing machine that can be used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper surface plate 2 Substrate 3 Back pad 4 Lower surface plate 5 Polishing disk

Claims (4)

[Claims] 1. A substrate is mounted on the lower surface of an upper platen via a foamed elastic back pad having open cells, and the upper platen and a polishing plate provided below are rotated to press one surface of the substrate while pressing. A back pad used in a polishing method, wherein a water absorption from a surface is set to 20 mg / cm ² or less. 2. The method according to claim 1, wherein the surface of the back pad before being attached to the upper surface plate is thinly coated with a resin paint, and pores on the surface are partially covered with the paint to control the amount of water absorption from the surface. 1. The back pad according to 1. 3. A substrate is mounted on the lower surface of an upper surface plate via a back pad made of foamed elastic material having open cells, and the upper surface plate is rotated while supplying polishing liquid to a lower polishing surface while applying pressure. In the method of polishing one side of the substrate, the surface of the back pad is thinly coated with a resin paint, and then dried and
A method of preventing water absorption of a back pad, comprising: curing, controlling a water absorption rate from a surface by closing a part of pores on the surface of the back pad, and then attaching the back pad to a lower surface of an upper surface plate. 4. A metal ring is placed on the painted surface of the painted back pad before being mounted on the upper surface plate, and the ring is filled with a predetermined amount of water, and the water absorption after a predetermined time has elapsed is measured. 4. The method according to claim 3, wherein the required amount of coating is determined by determining the water absorption from the surface.