JP2014216044A - Manufacturing method of magnetic disk glass substrate, and manufacturing method of magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a magnetic disk glass substrate composed of a crystallized glass having small strength variations.SOLUTION: The manufacturing method of a magnetic disk glass substrate includes: end face shape processing of performing a step of fabricating a disk-shaped amorphous glass substrate having a hole in the centre, and shape processing including chamfering an end face of the fabricated amorphous glass substrate; and etching processing that is performed after the end face shape processing and performs processing of bringing the end face into contact with etching liquid. Crystallization processing of crystallizing the amorphous glass substrate is performed at least after the etching processing.

Description

  The present invention relates to a method of manufacturing a glass substrate for a magnetic disk used for a magnetic disk mounted on a magnetic recording apparatus such as a hard disk drive (hereinafter abbreviated as “HDD”).

One of information recording media mounted on a magnetic recording device such as an HDD is a magnetic disk. A magnetic disk is configured by forming a thin film such as a magnetic layer on a substrate, and an aluminum substrate has been conventionally used as the substrate. However, recently, in response to the pursuit of higher recording density, the ratio of the glass substrate capable of narrowing the distance between the magnetic head and the magnetic disk as compared with the aluminum substrate is gradually increasing. Further, the surface of the glass substrate is polished with high accuracy so as to increase the recording density so that the flying height of the magnetic head can be reduced as much as possible. In recent years, demands for further increase in recording capacity of HDDs are increasing, and in order to realize this, it is necessary to further improve the quality of glass substrates for magnetic disks.

Examples of the material of such a glass substrate include aluminosilicate glass, soda lime glass, aluminoporosilicate glass, or glass ceramic such as crystallized glass.
Patent Document 1 discloses a method for producing a glass substrate for an information recording medium including forming a disk-shaped glass material from molten glass, and the glass material is further heat-treated to obtain crystallized glass. It is described that it can be.

JP 2008-169061 A

  For example, a disk-shaped glass material is obtained by press-molding molten glass, a hole is made in the center of the disk-shaped glass material, and then inner and outer peripheral end faces, main surface polishing, etc. are performed to obtain a magnetic disk Although the glass substrate for manufacture is manufactured, the said patent document 1 describes that crystallization of a glass raw material can be performed either before or after perforating for obtaining a disk.

  However, according to the study of the present inventor, as described in Patent Document 1, the glass material is crystallized either before or after drilling, and then the inner and outer peripheral end faces such as chamfering are processed. When the glass substrate for a magnetic disk was manufactured by polishing the main surface or the like, there was a problem that the variation in strength between the substrates of the obtained glass substrate for a magnetic disk was large.

Accordingly, the present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a method of manufacturing a glass substrate for a magnetic disk made of crystallized glass, which can reduce variations in substrate strength. That is.

Then, this inventor analyzed the reason for the dispersion | variation in the intensity | strength of the glass substrate manufactured according to the manufacturing method disclosed by the said patent document 1 being large. As a result, if the glass material is crystallized and then machined such as chamfering of the end face, latent (internal) cracks formed during the chamfering process remain, and finally the cracks cannot be removed sufficiently. I found that there is a possibility.

In addition, the present inventor has conducted further investigation focusing on the timing of crystallization in order to obtain a glass substrate made of crystallized glass with small strength variation. It has been found that there is a difference in the intensity variation of the finally obtained glass substrate depending on which stage of crystallization is performed.
Therefore, the present inventor has found that the above problems can be solved according to the invention having the following configuration based on the obtained knowledge, and has completed the present invention.

That is, this invention has the following structures in order to achieve the said subject.
(Configuration 1)
Machining the end face of a disk-shaped amorphous glass substrate having a circular hole in the center to form a side face and a chamfered surface interposed between the main surface and the side face; and an end face And an etching process in which an etching solution is brought into contact with the sidewall surface and the chamfered surface after the shape processing, and after the etching process, a crystallization process for crystallizing the amorphous glass constituting the glass substrate is performed. A method for producing a glass substrate for a magnetic disk.

(Configuration 2)
2. The method of manufacturing a glass substrate for a magnetic disk according to Configuration 1, wherein an end surface polishing process is performed to mirror-polish at least one of a side wall surface and a chamfered surface after the etching process and before the crystallization process.

(Configuration 3)
3. The magnetic disk glass according to claim 1, wherein a maximum valley depth Rv of at least one of a side wall surface and a chamfered surface of the glass substrate to be crystallized is 0.3 μm or less. A method for manufacturing a substrate.

(Configuration 4)
Correspondence between angle (A) formed by main surface and chamfered surface before crystallization treatment and angle (B) formed by main surface and chamfered surface after crystallization treatment 4. The magnetic disk according to claim 1, wherein a relationship is obtained in advance, and end face shape processing is performed so that the angle (B) has a desired value based on the correspondence relationship. Method for manufacturing glass substrate.
(Configuration 5)
The correspondence between the diameter of the circular hole before the crystallization treatment and the diameter of the circular hole after the crystallization treatment is obtained in advance, and the diameter of the circular hole after crystallization is determined based on the correspondence. 5. The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 4, wherein the end surface shape processing is performed so as to obtain a desired value.
(Configuration 6)
A magnetic disk manufacturing method comprising forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the manufacturing method according to any one of Structures 1 to 5.

With the above-described configuration of the present invention, it is possible to manufacture a glass substrate for a magnetic disk made of crystallized glass with less variation in substrate strength (for example, bending strength) between substrates.

Hereinafter, embodiments of the present invention will be described in detail.
The present invention is a method for producing a crystallized glass for a magnetic disk, and is produced through, for example, a grinding process, an end face shape process, an etching process, an end face polishing process, a main surface polishing process, a chemical strengthening process, etc. After the treatment, a crystallization treatment for crystallizing the glass is performed. The processes other than the end face shape processing, the etching process, and the crystallization process are merely examples, and are not limited to the processes described here and the order thereof, and the processes themselves may not be performed.
Among these processes, the end face shape processing, etching process and end face polishing process are processes performed on the end face (side wall face and chamfering face) of the substrate. The grinding process and the main surface polishing process are performed on the substrate. It is a process applied to the main surface.

Here, crystallized glass is also called glass ceramics, and is a material formed by precipitating crystals in the glass by heating the glass. That is, the glass has both a crystallized part and an amorphous part.
In the present invention, the magnetic disk glass substrate means one that has been subjected to a crystallization treatment described later. Specifically, for example, the glass substrate for a magnetic disk according to the present invention may be one immediately after the crystallization treatment is performed, or a main surface polishing process performed after the crystallization treatment, It may be in a state before post-processing such as chemical strengthening processing and before the magnetic film or the like is formed.

Here, the outline of the manufacturing method of the glass substrate for magnetic disks is demonstrated.
As a method for producing a disk-shaped amorphous glass substrate having a circular hole in the center, there is, for example, a method of forming a circular hole after molding a disk-shaped glass blank from molten glass by direct pressing. Specifically, a disk-shaped amorphous glass substrate having a circular hole in the center is created by opening a circular hole of a predetermined size in the center of a molded disk-shaped glass blank by, for example, machining with a core drill or the like. To do. In addition to such a direct press, a disc-shaped amorphous glass substrate having a circular hole in the center can be produced by cutting out to a predetermined size from a plate glass produced by a downdraw method or a float method. .

Next, a grinding process for improving dimensional accuracy and shape accuracy is performed on the main surface of the glass substrate manufactured as described above. In this grinding process, a main surface of the glass substrate is usually ground using a double-sided lapping machine and using abrasive grains such as diamond and alumina. By grinding the main surface of the glass substrate in this way, it can be processed to a predetermined plate thickness and flatness. The grinding step may be omitted depending on the thickness and flatness of the glass substrate used.

After the grinding step, end face shape processing is performed. In this end face shape processing, a chamfered surface interposed between the side wall surface, the main surface of the glass substrate and the side wall surface is formed by machining the end surface of the glass substrate. This end face shape processing can be performed by machining using a rotating grindstone having a groove shape. This rotating grindstone has a side wall surface (a surface substantially orthogonal to the substrate main surface) and a chamfered surface (a chamfered surface formed between the side wall surface and the main surface on the front and back surfaces) on the inner and outer peripheral end surfaces of the glass substrate It has a groove shape capable of transferring the shape of both surfaces. In other words, in the end face shape processing, the groove shape of the rotating grindstone is transferred so that the angle formed by the main surface and the chamfered surface and the angle formed by the chamfered surface and the side wall surface become a desired shape. Can be processed.

Since the end face shape processing described above is performed by machining, a crack accompanying the processing occurs on the end face of the glass substrate. Then, the residual crack which arose by this machining can be removed by making etching liquid contact the end surface (a chamfering surface and a side wall surface) after a machining. By performing this etching process, the residual crack layer on the surface of the end face by machining is removed by etching, so that a decrease in strength due to the residual crack can be suppressed. As an etchant used in the etching process, no problem if the chemical solution can dissolve the glass material, for example, hydrofluoric acid solution, HF-H ₂ SO ₄ solution, NH ₄ F solution, H ₂ It is preferable to apply an SiF ₆ aqueous solution or other various glass etching solutions.
The machining allowance in this etching process is specifically 10 μm or less, more preferably from the viewpoint of not changing the end shape of the glass substrate formed by machining (for example, the angle formed by the main surface and the side wall surface). It is preferably 5 μm or less, more preferably 1 μm or less. On the other hand, from the viewpoint of sufficiently removing cracks formed in the end face shape processing, the allowance in the etching process is preferably 0.5 μm or more.

After the above etching process, it is preferable to perform an end surface polishing process to obtain a desired mirror surface. This end surface polishing treatment is performed, for example, by brush polishing. In addition to brush polishing, the end surface polishing can also be performed using a grindstone having a small abrasive grain size or a polishing pad. By this end surface polishing treatment, the substrate end surface is finished to a desired mirror surface state. At this time, it is formed by end face polishing treatment.

After the etching process or after the end face polishing process, in other words, the maximum valley depth (Rv) of at least one of the chamfered surface and the side wall surface of the glass substrate for performing the crystallization process described later is 0.3 μm or less, The thickness is preferably 0.2 μm or less. The arithmetic average roughness (Ra) of at least one of the chamfered surface and the side wall surface is preferably 0.02 μm or less, more preferably 0.015 μm or less. Moreover, it is more preferable that both the chamfered surface and the side wall surface are within the range of the maximum valley depth and the arithmetic average roughness (Ra).

By the way, in the present invention, since a crystallized glass obtained by crystallizing amorphous glass is used as a glass substrate for a magnetic disk, a crystallization process for crystallizing amorphous glass is performed.

The method for manufacturing a glass substrate for a magnetic disk according to the present invention is configured to perform a crystallization process for crystallizing the glass constituting the amorphous glass substrate after the etching process.

According to the study of the present inventor, as described in the prior art (Patent Document 1), a circular hole having a predetermined size is formed in the center of a disk-shaped glass blank formed by direct press from molten glass. In the glass substrate obtained by crystallization of the glass material either before or after the process, and then through inner and outer end face shape processing such as chamfering, main surface polishing, etc. It was found that the variation in strength (for example, bending strength) was large depending on the processing conditions.

Therefore, as a result of analyzing the point where the strength variation is large, the present inventor has found that the latent material formed during the chamfering process depends on the processing conditions when the glass material is crystallized and then machined such as chamfering of the end face. It was found that (internal) cracks remained, and finally the cracks could not be sufficiently removed, and that the strength variation might increase due to the cracks.

And based on this knowledge, this inventor discovered that the dispersion | variation in intensity | strength could be reduced by removing the crack which arises in an end surface before performing a crystallization process.

And, when the crystallization process is performed after the etching process as in the present invention, the glass is crystallized after performing the end face shape process which is a mechanical process on the amorphous glass substrate. Therefore, it is not affected by crystallization during the end face shape processing. And the crack formed in the end face at the time of end face shape processing can be sufficiently removed by the subsequent etching process or end face polishing process, and finally the depth of the crack remaining inside is compared with the prior art. Can be reduced. For this reason, it is possible to suppress variations in strength.

In addition, by performing the above-mentioned etching treatment, the residual crack layer on the surface of the end surface by machining is removed by etching, but when the chemical treatment is performed on the crystallized glass material, the surface is damaged, the surface There is a problem that the roughness becomes large and the surface of the end face is not finished in a desired mirror state.
In addition, when the inventor performs end surface polishing or end surface etching after crystallization, the processing speed (polishing rate, etching rate) differs between the crystallized portion and the non-crystalline portion, resulting in rough surface roughness. I found out. Therefore, before performing the crystallization process, the end surface roughness is set to a desired value by the end surface polishing process, in other words, the required roughness as a glass substrate for a magnetic disk, and then the crystallization process is performed. It was found that the roughness of the end face can be suitably achieved because the end face polishing and etching steps are not performed later. The present invention has been found to be particularly effective when producing a crystallized glass substrate for a magnetic disk having a maximum valley depth (Rv) of at least one of the side wall surface and the chamfered surface of 0.3 μm or less. .

When the crystallization process is performed before the end face shape processing as in the above-described conventional technique, it is difficult to remove cracks generated in the end face shape processing. For example, when etching is performed to remove cracks, the surface roughness is large and the surface roughness is greatly deteriorated. If an attempt is made to improve the deterioration of the surface roughness by the subsequent end face polishing, a new problem arises that the polishing allowance increases and the load of the end face polishing increases. Further, if the etching process conditions are weakened to make the surface roughness as small as possible, the residual crack layer cannot be sufficiently removed.

On the other hand, according to the present invention, the etching treatment is performed on the amorphous glass substrate, and then the crystallization treatment is performed, so that the cracks generated by the end face shape processing can be easily removed, and the crystal Therefore, cracks can be removed and the surface roughness can be reduced.

Since the volume of the glass substrate is reduced by performing the crystallization treatment, the shape of the glass substrate is different before and after the crystallization treatment. In particular, the glass substrate for a magnetic disk according to the present invention has a very large diameter (high aspect ratio) compared to the plate thickness, so that the shape change due to the crystallization treatment is different between the plate thickness direction and the main surface direction. Will be different. Therefore, for the end face shape processing, etching process, and end face polishing process before the crystallization process, it is preferable to set the processing conditions in consideration of the influence of the shape change due to crystallization.
Specifically, regarding the shape of the end face, the angle (A) formed by the main surface and the chamfered surface before the crystallization treatment, and the main surface and the chamfered surface after the crystallization treatment are performed. The correspondence relationship with the angle (B) formed is determined in advance, and based on the correspondence relationship, the end face shape processing, etching process, and the like are performed so that the angle (B) has a desired value. It is more preferable to perform end face polishing treatment. Thereby, the end surface shape of the glass substrate after passing through a crystallization process can be made into the end surface shape requested | required as a glass substrate for magnetic discs.

This will be described in detail. As a manufacturing process in which the shape of the chamfered surface and the side wall surface is determined, end face shape processing, etching treatment, and end face polishing treatment are particularly affected. And by changing these processing conditions, creating a plurality of glass substrates in which the angle of the angle between the main surface and the chamfered surface is different in advance, and after crystallizing these glass substrates, The angle formed by the main surface and the chamfered surface is obtained in the same manner as before crystallization, and the correspondence between the angles before and after the crystallization treatment is obtained. Then, based on the obtained correspondence relationship, the end surface is selected by selecting a processing condition in which an angle formed between the main surface and the chamfered surface obtained after the crystallization process is an angle required for a glass substrate for a magnetic disk. Shape processing, etching processing, and end surface polishing processing may be performed. Further, in the above description, the description has been given of obtaining the correspondence relationship between the angle formed by the main surface and the chamfered surface, but the present invention is not limited to the above. For example, the length of the chamfered surface, the side wall surface The correspondence between the length and / or the angle between the chamfered surface and the side wall surface is obtained before and after the crystallization process, and the end face shape after the crystallization process (the shape of the chamfered surface and the side wall surface) is End surface shape processing, etching processing, and end surface polishing processing performed before crystallization processing may be performed so as to obtain a shape required as a glass substrate for a magnetic disk.

Further, the size of the circular hole is the same as described above. For example, the correspondence between the diameter of the circular hole before the crystallization treatment and the diameter of the circular hole after the crystallization treatment is obtained in advance. In addition, it is more preferable to perform the end face shape processing, the etching process, and the end face polishing process so that the diameter of the crystallized hole becomes a desired value based on the above correspondence. Thereby, the diameter of the circular hole after a crystallization process can be made into the diameter requested | required as a glass substrate for magnetic discs.

In the present invention, the bending strength of the glass substrate after the crystallization treatment is preferably 7 kgf or more, and particularly preferably 8 kgf or more from the viewpoint of improving impact resistance.

Next, the crystallization process will be described. In the crystallization treatment, for example, crystal nuclei are generated inside the glass by heat-treating the glass. Note that large crystal grains may be obtained by growing crystal nuclei. What is necessary is just to set suitably the conditions of the heat processing in a crystallization process according to the crystallinity of the crystallized glass obtained.
The size of the crystal grains generated by the crystallization treatment is preferably 10 nm or less, and more preferably 5 nm or less. By making the crystal grains in the above range, it is preferable because the surface roughness required for a glass substrate for a magnetic disk, which is the final product described later, is easily formed.
The Young's modulus of the magnetic disk glass substrate according to the present invention is preferably 100 GPa or more, more preferably 120 GPa or more. In order to increase the Young's modulus to 100 GPa or more, it is conceivable to increase the degree of crystallinity. In such a case, however, the degree of surface roughness due to etching becomes larger than that of crystallized glass having a low degree of crystallinity. Therefore, the present invention is applied to manufacture a glass substrate for a magnetic disk having a Young's modulus of 100 GPa or more and a maximum valley depth (Rv) of a side wall surface and a chamfered surface of 0.3 μm or less. Is more preferable.

The crystallized glass has a lower Young's modulus than the glass before crystallization, so the processing rate is low, but as in the present invention, the glass is crystallized after end-face polishing, thereby processing the glass. Since processing can be performed on amorphous glass having a high rate, the time required for processing can be shortened.

After passing through the crystallization treatment, a main surface mirror polishing process for obtaining a highly accurate main surface is performed. As a mirror polishing method for the main surface of the glass substrate, it is preferable to use a polishing pad while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica. Although the polishing method is not particularly limited, for example, the glass substrate and the polishing pad are brought into contact with each other, and the polishing pad and the glass substrate are relatively moved while supplying the polishing liquid containing the abrasive grains. The surface of the glass substrate may be polished in a mirror shape.

In the present invention, it is preferable to use an aluminosilicate glass containing SiO ₂ as a main component and further containing alumina as the glass (glass type) constituting the glass substrate. A glass substrate using such glass can be finished to a smooth mirror surface by mirror polishing the surface, and the strength after processing is good. Further, the strength can be further increased by chemical strengthening.

In the present invention, the main surface of the glass substrate after the mirror polishing is preferably a mirror surface having an arithmetic average surface roughness Ra of 0.20 nm or less, particularly 0.15 nm or less. Furthermore, it is preferable that the mirror surface has a maximum roughness Rmax of 2.0 nm or less. In the present invention, Ra and Rmax are roughnesses calculated in accordance with Japanese Industrial Standard (JIS) B0601.

In the present invention, the surface roughness (for example, Rz, Rmax, Ra) is a value obtained when an area of 1 μm × 1 μm is measured with a resolution of 256 × 256 pixels using an atomic force microscope (AFM). is there.
In the present invention, the maximum valley depth (Rz) of the end surface (at least one of the chamfered surface and the side wall surface) of the finally obtained magnetic disk glass substrate is 0.3 μm or less, more preferably 0.2 μm. The following is preferable. The arithmetic average roughness (Ra) is preferably 0.02 μm or less, more preferably 0.015 μm or less. In addition, what is necessary is just to measure the surface roughness of an end surface, for example using a laser microscope.

In the present invention, the chemical strengthening treatment may be performed after the crystallization treatment and before or after the mirror polishing process of the main surface. As a method of the chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding the glass transition temperature is preferable. The chemical strengthening treatment is a process in which a molten chemical strengthening salt is brought into contact with a glass substrate, whereby an alkali metal element having a relatively large atomic radius in the chemical strengthening salt and a relatively small atomic radius in the glass substrate. This is a treatment in which an alkali metal element is ion-exchanged, an alkali metal element having a large ion radius is permeated into the surface layer of the glass substrate, and compressive stress is generated on the surface of the glass substrate. Since the chemically strengthened glass substrate is excellent in impact resistance, it is particularly preferable for mounting on a HDD for mobile use, for example.

The present invention also provides a method for producing a magnetic disk using the above glass substrate for a magnetic disk. The magnetic disk is manufactured by forming at least a magnetic layer on the magnetic disk glass substrate according to the present invention. As a material for the magnetic layer, a hexagonal CoCrPt-based or CoPt-based ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method of forming the magnetic layer, it is preferable to use a method of forming a magnetic layer on a glass substrate by a sputtering method, for example, a DC magnetron sputtering method. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a hexagonal underlayer containing Ru or Ti, for example, the easy magnetization direction of the magnetic layer can be oriented along the normal of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by sputtering as with the magnetic layer.

In addition, a protective layer and a lubricating layer may be formed in this order on the magnetic layer. A hydrogenated carbon-based protective layer is suitable as the protective layer. For example, the protective layer can be formed by a plasma CVD method. Further, as the lubricating layer, a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used. In particular, it is preferable that the main component is a perfluoropolyether compound having a terminal hydroxyl group as a polar functional group. The lubricating layer can be applied and formed by a dip method.
By using the glass substrate obtained by the present invention, a highly reliable magnetic disk can be obtained.
Furthermore, the glass substrate for magnetic disk made of crystallized glass obtained by the present invention is preferably used for an energy-assisted magnetic recording type magnetic disk. By having crystal grains in glass, it is preferable because it is difficult to be deformed even in a high-temperature environment necessary for manufacturing an energy-assisted magnetic recording type magnetic disk.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. In addition, this invention is not limited to a following example.
(Examples 1 and 2 and Comparative Example 1)
The following (1) glass blank preparation process, (2) grinding process, (3) pilot hole process, (4) end face shape processing, (5) etching process, (6) end face polishing process, (7) main surface polishing process A glass substrate for a magnetic disk was manufactured through (first polishing treatment), (8) chemical strengthening step, and (9) main surface polishing treatment (second polishing treatment). In addition to these steps, a crystallization treatment described later was performed.

(1) Glass Blank Production Step First, a glass blank made of a disc-shaped aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.0 mm was obtained from molten glass by direct pressing using an upper die, a lower die, and a barrel die.

(2) Grinding step Next, a grinding step was performed on the glass substrate in order to improve dimensional accuracy and shape accuracy. This grinding process was performed using a double-side grinding apparatus.
(3) Pilot hole step Next, a cylindrical core drill was used to make a hole in the central portion of the glass blank (perforating process) to produce a disk-shaped amorphous glass substrate having a circular hole in the center.
(4) End face shape processing Next, using a cylindrical grindstone, the outer peripheral end face and the inner peripheral end face were subjected to predetermined chamfering to form a side wall face and a chamfered face.

(5) Etching treatment The etching treatment was performed by masking the main surface of the glass substrate after the end face shape processing and immersing the end face of the glass substrate in a silicic acid solution. The machining allowance here was 10 μm.
(6) End surface polishing treatment Next, the end surface (inner periphery, outer periphery) of the glass substrate was polished by brush polishing while rotating the glass substrate. And the surface of the glass substrate which finished the said end surface grinding | polishing was wash | cleaned.

(7) Main surface polishing step (first polishing step)
Next, the first polishing step was performed using a priority gear type double-side polishing apparatus. In a double-side polishing machine, a glass substrate held by a carrier is closely attached between an upper and lower polishing surface plate to which a polishing pad is attached, and this carrier is engaged with a sun gear (sun gear) and an internal gear (internal gear). The glass substrate is sandwiched between upper and lower surface plates. Thereafter, a polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass substrate, whereby the glass substrate revolves while rotating on the surface plate to simultaneously polish both surfaces. Specifically, a hard polisher was used as the polisher, and the first polishing process was performed. As the polishing liquid, cerium oxide was dispersed as an abrasive. The glass substrate after the first polishing step was washed and dried.

(8) Chemical strengthening step Next, chemical strengthening was performed on the glass substrate after the cleaning. The chemical strengthening was performed using a known method.

(9) Main surface polishing step (second polishing step)
Next, using the same double-side polishing apparatus as that used in the first polishing step, a second polishing step was performed using a polishing pad of a soft polisher. Colloidal silica was used as the abrasive grains. The glass substrate for the magnetic disk was obtained by washing and drying the glass substrate after the second polishing step. The main surface roughness (Ra) of the magnetic disk glass substrate according to Example 2 described later was 0.15 nm.

Then, (5) after the etching process (Example 1) and (6) after the end face polishing process (Example 2), crystallization treatments were performed, respectively.
The crystallization treatment was performed by setting the heat treatment conditions for the glass substrate so that the average crystal grain size of the crystal grains was 10 nm or less. Here, the “average crystal grain size” is the average value of the longest distance when crystals appearing in an image obtained using a TEM (transmission electron microscope) are sandwiched between two parallel straight lines.
In Comparative Example 1, a crystallization treatment was performed immediately after obtaining a glass blank molded by direct pressing, and thereafter, drilling, end face shape processing, etching treatment, and the like were performed.

In each of Example 1, Example 2, and Comparative Example 1, 100 magnetic disk glass substrates were prepared, and the bending strength was determined using a bending strength tester. When the difference between the maximum value and the minimum value of the bending strength measured from the glass substrate for magnetic disk of Comparative Example 1 is 100%, the maximum value and the minimum value of the bending strength in Examples 1 and 2 are obtained. When the percentage of each difference was evaluated, Example 1 was 53% and Example 2 was 46%. That is, it can be seen that the variation in the bending strength is smaller in both Examples 1 and 2 than in Comparative Example 1. That is, it can be seen that the variation in the bending strength can be reduced by performing the crystallization process after removing the cracks formed by the end face shape processing. In addition, about the said Examples 1 and 2 and the comparative example 1, (7) The glass substrate for magnetic discs created without performing a chemical strengthening process was created, and the variation in bending strength was investigated, but it was the same as the above Showed a trend.

Next, the maximum valley depth (Rv) of the chamfered surface was compared between Example 1 and Example 2. In Example 1 and Example 2, the processing conditions and machining allowance in (4) end surface shape processing, (5) etching processing, and (6) end surface polishing processing are the same. As a result, Rv of Example 1 was 0.29 μm, while Rv of Example 2 was 0.23 μm. Moreover, Rv of the comparative example 1 was 0.52 micrometer. That is, by comparing Examples 1 and 2 with Comparative Example 1, it can be seen that the end surface roughness can be reduced by crystallization after the end surface shape processing. Furthermore, comparing Examples 1 and 2, it can be seen that the end surface roughness can be further reduced by performing the end surface polishing treatment before the crystallization processing.

(Manufacture of magnetic disk)
The following film formation process was performed on the magnetic disk glass substrate obtained in Example 1 to obtain a magnetic disk for perpendicular magnetic recording.
That is, an adhesion layer made of a Ti-based alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, a carbon protective layer, and a lubricating layer are sequentially formed on the glass substrate. A film was formed. The protective layer is for preventing the magnetic recording layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon, and provides wear resistance. The lubricating layer was formed by dipping a liquid lubricant of alcohol-modified perfluoropolyether.

Claims (6)

By machining the end face of a disc-shaped amorphous glass substrate having a circular hole in the center, end face shape processing that forms a side wall surface and a chamfered surface interposed between the main surface and the side wall surface;
An etching process that is performed after the end surface shape processing, and an etching solution is brought into contact with the side wall surface and the chamfered surface,
A method for producing a glass substrate for a magnetic disk, comprising performing a crystallization process for crystallizing the glass constituting the glass substrate after the etching process.   2. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein after the etching process and before the crystallization process, an end surface polishing process for mirror polishing at least one of a side wall surface and a chamfered surface is performed. .   3. The glass substrate for a magnetic disk according to claim 1, wherein a maximum valley depth Rv of at least one of a side wall surface and a chamfered surface of the glass substrate to be crystallized is 0.3 μm or less. Production method. Correspondence between angle (A) formed by main surface and chamfered surface before crystallization treatment and angle (B) formed by main surface and chamfered surface after crystallization treatment Find the relationship in advance,
4. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the end surface shape processing is performed so that the angle of the angle (B) becomes a desired value based on the correspondence relationship. .   The correspondence between the diameter of the circular hole before the crystallization treatment and the diameter of the circular hole after the crystallization treatment is obtained in advance, and the diameter of the circular hole after crystallization is determined based on the correspondence. 5. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the end face shape processing is performed so as to obtain a desired value. 6. A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the manufacturing method according to claim 1.