JPH1160282A - Polishing of glass substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for polishing and finishing a glass substrate to obtain the glass substrate small in surface roughness and used for a magnetic disk. SOLUTION: The method for polishing a glass substrate 1 comprises using a polishing liquid containing cerium oxide as a polishing agent. Therein, a low concentration polishing liquid having a cerium oxide content of 0.5-8 wt.% is used as the polishing liquid. Or, a polishing liquid having a cerium oxide content of 15-25 wt.% is used in the first process, and a polishing liquid having a cerium oxide content of 0. 5-8 wt.% is subsequently used in the second process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a glass substrate for a magnetic disk.

[0002]

2. Description of the Related Art As a typical external recording device of a personal computer, a magnetic disk device has remarkably increased in capacity, reduced in size, and reduced in price. Such advances in magnetic disk drives have led to higher performance magnetic disks and magnetic heads for recording and reproducing information,
This is also due to an increase in the performance of individual components or individual technologies constituting the apparatus, such as an increase in the speed of a recording / reproducing channel, an increase in the speed and accuracy of a servo circuit, and the like.

In particular, the characteristics of the magnetic disk and the magnetic head, which are the main components directly related to recording / reproduction, are largely due to the improvement of the characteristics of the magnetic disk. Greater flying height effect. With the latest magnetic disk drive, 25-40nm
Approximate flying height is about to be realized. To realize such a low flying height, the magnetic disk surface is required to be flat and smooth.

[0004] For this reason, advanced technology is required for finishing the magnetic disk substrate. In general, a double-sided lapping type polishing machine having high productivity and good flatness and smoothness is widely used for finishing a magnetic disk substrate, particularly a 2.5-inch or 3.5-inch substrate. On the other hand, in recent years, glass and crystallized glass have been put to practical use as magnetic disk substrates. These are promising because of their higher mechanical strength and better machinability than aluminum alloys. Glass or crystallized glass (hereinafter,
In the processing of both, which are referred to as glass), the polishing is performed by brittle fracture, so that the processed strain layer is shallow, and furthermore, burrs and abnormal projections are hardly generated, so that the material is easy to obtain surface smoothness.

The polishing of the glass magnetic disk substrate is performed by supplying a polishing tool having a polyurethane polishing pad attached to both sides of the substrate while supplying a polishing liquid in which cerium oxide is suspended to a double-side simultaneous polishing machine. It is common to apply a predetermined pressure to the pieces to bring them into close contact, rotate and slide. Cerium oxide is known as an abrasive capable of obtaining a good polished surface without damaging a glass magnetic disk substrate. Conventionally, finish polishing is usually performed with a cerium oxide content of 15 to 25% by weight.

[0006]

However, if the final polishing is performed with the cerium oxide content being 15 to 25% by weight, the surface roughness of the glass magnetic disk substrate often does not fall within a desired range. May occur, and the value of the surface roughness varies greatly.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polishing method for improving the flatness and smoothness of the surface in the finish polishing of a glass substrate for a magnetic disk.

[0008]

According to the present invention, when polishing a glass substrate for a magnetic disk using a polishing liquid containing cerium oxide as a polishing agent, the cerium oxide content in the polishing liquid is reduced to 0.5 to 0.5%. A polishing solution having a concentration as low as 8% by weight is used. In the first step, the cerium oxide content is 15 to 2
A polishing liquid of 5% by weight is used, and a polishing liquid having a cerium oxide content of 0.5 to 8% by weight is used in the second step.

That is, by reducing the cerium oxide content, the smoothness of the substrate surface is improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, when the final polishing is performed with the cerium oxide content being 15 to 25% by weight, the surface roughness of the magnetic disk glass substrate does not fall within a desired range. It is presumed to be due to the reason. In the conventional simultaneous double-side polishing, the content of cerium oxide in the polishing liquid is adjusted to 15 to 25 in order to increase the removal amount and increase the polishing rate.
The concentration was as high as% by weight. The average particle size of cerium oxide is as small as 1.2 μm and the maximum particle size is as small as 8.4 μm. As the polishing process proceeds, the cerium oxide is subdivided, and the substrate is polished with fine abrasive particles. However, since the content of cerium oxide is as high as 15 to 25% by weight, a phenomenon of agglomeration of the abrasive occurs. The aggregated abrasive is coarsened to an overall particle size of 10 μm or more, and is in the same state as when polishing is performed using an abrasive mixed with abrasive particles having a large particle size. Therefore, the surface roughness of the glass substrate for a magnetic disk becomes large.

[0011] Actually, the content of cerium oxide is 15 to 25.
When the final polishing was performed with the weight%, the surface roughness Ra of the glass substrate for a magnetic disk was as large as about 30 °. Here, Ra is one of the display methods of surface roughness Roughness, and indicates an average value of surface roughness measured on a substrate.
Therefore, it was considered that the average surface roughness Ra of the substrate could be reduced by setting the content of the polishing agent in the polishing liquid to 5% by weight or less so that the aggregation of the polishing agent was less likely to occur.

[Embodiment 1] To realize the polishing method of the present invention, a commercially available double-sided simultaneous polishing machine whose principle is shown in FIG. 1 was used.
FIG. 1 is a schematic diagram showing a main part of a double-sided simultaneous polishing machine.
A polishing pad 5 made of polyurethane is adhered to a contact surface between the upper platen 3 made of cast iron and the lower platen 4 made of cast iron and the glass substrate 1 for a magnetic disk. The glass substrate 1 for a magnetic disk is placed between these two polishing pads 5, and the polishing agent 2 is supplied between the polishing pad 5 and the glass substrate 1 for a magnetic disk to rotate and slide. Both sides are polished simultaneously.

FIG. 2 is a plan view of the double-sided simultaneous polishing machine as viewed from above, and shows a state in which an upper surface plate is removed. Usually, a plurality of magnetic disk glass substrates 1 are held by the respective carriers 6. The gear provided on the outer periphery of the carrier 6 is meshed with the sun gear 6 and the internal gear 8. The glass substrate 1 for a magnetic disk is sandwiched between an upper surface plate and a lower surface plate, and is polished by rotating the upper surface plate and the lower surface plate in opposite directions.

The polishing conditions in this embodiment are as follows. Average particle size 1.2μm, maximum particle size 8.4μm as abrasive
Is used as a polishing liquid by suspending it in a solution. The content of cerium oxide in the polishing liquid is about 5% by weight
Is set. The processing pressure during polishing is 30 to 120 g /
cm ² , lower platen rotation speed is 5 to 40 RPM, and upper platen rotation speed is 5 to 40 RPM, the polishing removal amount is 0.1 to 1 μm /
min. The surface roughness Ra of the glass substrate for a magnetic disk was 10 ° or less.

Example 2 Using the same double-sided polishing machine as in Example 1, polishing was performed under the following polishing conditions. First, the content of the abrasive is set to an arbitrary value of 15 to 25% by weight, the processing pressure is 30 to 120 g / cm ² , and the lower platen rotation speed is 5 to 40.
Assuming that the RPM and the upper platen rotation speed were 5 to 40 RPM, the polishing removal amount was 0.4 to 1 μm / min. This step is the first
Process. Next, as a second step, when the content of cerium oxide in the polishing liquid was set to about 5% by weight, and the polishing was performed without changing other conditions, the removal amount of polishing was 0.1 to 1 μm / min. The average surface roughness Ra of the magnetic disk glass substrate is 1
0 ° or less.

As described above, when the polishing is performed with the abrasive content in two stages, the polishing removal amount can be increased as a whole and the average surface roughness of the substrate can be reduced. In addition,
For measuring the surface roughness, a surface roughness / fine shape measuring device (Tencor P-12 manufactured by Tencor) dedicated to a contact type disk
Was used.

[0017]

According to the present invention, a flat and smooth magnetic disk substrate can be obtained by adjusting the content of cerium oxide, which is an abrasive, to 0.5 to 8% by weight in the finish polishing of the magnetic disk glass substrate. it can. As a result, the flying height of the magnetic head can be reduced, and the density of the magnetic disk can be increased, particularly, the linear recording density can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a main part of a double-sided simultaneous polishing machine.

FIG. 2 is a plan view of the double-sided simultaneous polishing machine as viewed from above.

[Explanation of symbols]

 1 ··· Glass substrate for magnetic disk 2 ··· Abrasive 3 ··· Upper platen 4 ··· Lower platen 5 ··· Polishing pad 6 ··· Carrier 7 ··· Taiyo Gear 8 Internal gear

Claims (2)

[Claims] 1. A method for polishing a glass substrate for a magnetic disk using a polishing liquid containing cerium oxide as a polishing agent, wherein the content of cerium oxide in the polishing liquid is 0.5 to 8% by weight.
A method for polishing a glass substrate for a magnetic disk. 2. A method for polishing a glass substrate for a magnetic disk using a polishing liquid containing cerium oxide as an abrasive, wherein the polishing liquid having a cerium oxide content of 15 to 25% by weight uses the polishing liquid for a magnetic disk. A first step of polishing a substrate; and a second step of polishing the glass substrate for a magnetic disk using a polishing liquid having a cerium oxide content of 0.5 to 8% by weight. Polishing method for glass substrates for disks.