JP2015069667A - Manufacturing method of glass substrate for magnetic disk, and manufacturing method of magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a glass substrate for magnetic disk, which provides highly smooth surface after cleaning treatment.SOLUTION: The manufacturing method includes cleaning treatment for performing acid cleaning and alkali cleaning in this order after a glass substrate is mirror-polished. In the acid cleaning, at least one of an alkali metal ion and an alkaline earth metal ion contained in the glass component is added to cleaning fluid for acid cleaning to perform cleaning. The manufacturing method thus reduces glass substrate surface roughness caused by the cleaning treatment, thereby providing a highly smooth surface after the cleaning treatment.

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk mounted on a magnetic disk device such as a hard disk drive (HDD) and a method for manufacturing a magnetic disk.

There is a magnetic disk as one of information recording media mounted on a magnetic disk device such as a hard disk drive (HDD). 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, the demand for further increase in recording capacity of HDDs has only increased, and in order to realize this, it has become necessary to further improve the quality of glass substrates for magnetic disks. A clean glass substrate surface is required.

As described above, high smoothness on the surface of the magnetic disk is indispensable for reducing the flying height (flying height) necessary for increasing the recording density. In order to obtain high smoothness of the magnetic disk surface, it is necessary to polish the surface of the glass substrate with high precision because the surface of the substrate is highly smooth. However, this is not sufficient, and cleaning after polishing is not sufficient. Therefore, it is necessary to remove the adhered foreign matter on the substrate surface to obtain a clean substrate surface.
As a conventional method, for example, as disclosed in Patent Document 1, after glass polishing, the glass substrate is subjected to alkali cleaning, or after polishing, the glass substrate is first subjected to acid cleaning, and then subjected to alkali cleaning. The method of performing is common.

JP 2010-86563 A JP 2007-60534 A

In the current HDD, a recording density of about 500 gigabits per square inch has been achieved, and for example, about 320 gigabytes of information can be stored in one 2.5 inch type (65 mm diameter) magnetic disk. Although it is possible, there is a demand for further higher recording density, for example, 375 to 500 gigabytes, and further 1 terabyte. With the recent demand for larger capacity of HDDs, the demand for improvement of the substrate surface quality has become more severe than ever. In the next generation substrate for a magnetic disk of, for example, 375 to 500 gigabytes as described above, since the influence of the substrate on the media characteristics becomes large, not only the surface roughness of the substrate but also surface defects due to adhesion of foreign matters do not exist. In this regard, further improvement from the current product is required.

In the next generation substrate, the influence of the substrate on the media characteristics becomes large for the following reasons.
For example, the flying height of the magnetic head (the gap between the magnetic head and the surface of the medium (magnetic disk)) is greatly reduced (lower flying height). By doing so, the distance between the magnetic head and the magnetic layer of the medium is reduced, so that signals of smaller magnetic particles can be picked up, and high recording density can be achieved. In recent years, a function called DFH (Dynamic Flying Height) has been mounted on a magnetic head in order to achieve a lower flying height than before. This is a function of providing a heating unit such as a very small heater in the vicinity of the recording / reproducing element part of the magnetic head and projecting only the periphery of the recording / reproducing element part toward the medium surface. In the future, with this DFH function, it is expected that the gap between the element portion of the magnetic head and the medium surface will be extremely small, less than 2 nm or less than 1 nm. Under such circumstances, when the average roughness of the substrate surface was made extremely small, there was a very small foreign matter (for example, a small one having a length in the in-plane direction of the main surface of about 10 to 40 nm) that did not cause a problem in the past. If there is a surface defect that is slightly convex due to adhesion or the like, it becomes a convex defect on the surface of the medium as it is, which increases the risk of collision of the magnetic head.

By the way, according to the study of the present inventor, even if various conventional precision polishing techniques and precision cleaning techniques including the method disclosed in the above-mentioned Patent Document 1 are used, or a combination thereof is used, after cleaning, It has been found that low roughness and high cleanliness cannot be achieved at the same time.
The demand for improving the surface quality of a substrate accompanying the recent demand for an increase in capacity of HDDs has become more severe than ever. Until several years ago, the required level for the smoothness of the substrate surface was, for example, about 0.3 to 0.4 nm for Ra, but currently it is required to be about 0.1 to 0.2 nm for Ra. It has become like this. That is, in the glass substrate for magnetic disks, the level of smoothness currently required is significantly different from that of several years ago, and it is expected that the required level will become higher in the future. Even with conventional acid cleaning and alkali cleaning, it has been possible to achieve some of the required levels up to several years ago, but at least the current required levels are difficult to achieve with the conventional methods. In short, under such circumstances, there is a limit to realizing further improvement of the substrate surface quality by the conventional improvement method.

The present invention has been made to solve such a conventional problem. The object of the present invention is to first perform a cleaning process without degrading the highly smooth surface state obtained by precision polishing as much as possible. It is possible to provide a method for manufacturing a glass substrate for a magnetic disk that can achieve ultra-low roughness (high smoothness) as a result, and secondly, maintain the high smoothness obtained by precision polishing It is another object of the present invention to provide a method for manufacturing a glass substrate for a magnetic disk capable of performing highly clean cleaning.

  In order to increase the cleanliness of the substrate, it is necessary to clean and remove the foreign matter having a small level that has not been a problem in the past and strongly adhered to the surface of the substrate. For this purpose, an alkaline chemical solution having a high pH (strong alkalinity) is required. It is preferable to wash with a high cleanliness because high cleanliness can be achieved. This is because the glass surface is strongly etched with an alkaline chemical solution having a high pH, and even a strongly adhered foreign substance can be removed. However, in alkali cleaning, the etching effect on glass increases as pH increases, but the surface roughness of the substrate increases due to cleaning, and it becomes impossible to maintain the ultra-smooth surface obtained by precision polishing. It was. In addition, it is well known that the glass substrate after polishing is first subjected to acid cleaning and then alkali cleaning. However, when acid cleaning is performed on the glass substrate, the surface of the glass substrate is caused by the leaching action by acid. When some elements are removed from the substrate and then alkali cleaning is performed, the etching action by the alkali is promoted, and the increase in the roughness of the glass substrate surface after the cleaning becomes large.

As explained before, even with these conventional cleaning methods, it was possible to achieve the required level of surface roughness up to several years ago. Achieving the current demanded level of surface roughness that has become severe is difficult with conventional methods.
Patent Document 2 discloses a technique for injecting alkali metal ions into a dealkalized glass substrate to prevent elution of alkali ions from the glass substrate, thereby increasing the strength and durability of the glass substrate. Although disclosed, it does not prevent alkali detachment and cannot solve the above conventional problems.

Therefore, the present inventor tried various approaches for a method of suppressing an increase in the surface roughness of the glass substrate after cleaning.
As a result, when performing alkali cleaning on a glass substrate polished to a mirror surface, before the alkali cleaning, the glass substrate is at least one ion of alkali metal ions and alkaline earth metal ions contained in the glass substrate. It has been found that an increase in the surface roughness of the glass substrate after the alkali cleaning can be suppressed by performing a treatment of immersing with a solution containing.
In addition, when acid cleaning and alkali cleaning are performed in this order on a glass substrate polished to a mirror surface, in the first acid cleaning, at least one ion of alkali metal ions and alkaline earth metal ions contained in the glass component is used. It has been found that by adding to the acid cleaning cleaning solution and performing cleaning, an increase in the surface roughness of the glass substrate after subsequent alkali cleaning can be suppressed.

The present inventor has completed the present invention based on the obtained knowledge.
That is, the present invention has the following configuration.
(Configuration 1)
A method of manufacturing a glass substrate for a magnetic disk including a cleaning process for performing alkali cleaning on a mirror-polished glass substrate, wherein before the alkali cleaning, the glass substrate is alkali metal ions contained in the glass substrate and A method for producing a glass substrate for a magnetic disk, comprising performing a treatment of immersing in a liquid containing at least one of alkaline earth metal ions.

(Configuration 2)
A method for producing a glass substrate for a magnetic disk, comprising a cleaning process in which acid cleaning and alkali cleaning are performed in this order on a mirror-polished glass substrate, wherein the alkali metal ions contained in the glass component A method for producing a glass substrate for a magnetic disk, wherein washing is performed by adding at least one ion of an alkaline earth metal ion to a washing solution for acid washing.

(Configuration 3)
The method for producing a glass substrate for a magnetic disk according to Configuration 1 or 2, wherein the glass substrate contains at least one of sodium, lithium and potassium in a glass component.
(Configuration 4)
4. The method for producing a glass substrate for a magnetic disk according to any one of Structures 1 to 3, wherein the glass substrate contains at least one of magnesium and calcium in a glass component.

(Configuration 5)
The content of the ions in the liquid containing at least one of the alkali metal ions and alkaline earth metal ions or the cleaning liquid to which the ions are added is in the range of 8 to 13 mol%. 5. A method for producing a glass substrate for a magnetic disk according to any one of 4 above.

(Configuration 6)
6. A magnetic disk manufacturing method comprising: forming at least a magnetic recording layer on a magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate according to any one of Structures 1 to 5.

According to the present invention, it is possible to perform a cleaning process without deteriorating the highly smooth surface state obtained by precision polishing as much as possible, and as a result, a magnetic disk capable of achieving ultra-low roughness (high smoothness). A method for producing a glass substrate can be provided. Moreover, according to this invention, the manufacturing method of the glass substrate for magnetic discs which can implement highly clean washing | cleaning can be provided, maintaining the high smoothness obtained by precision grinding | polishing. According to the present invention, a high-quality glass substrate for a magnetic disk that can remarkably reduce the roughness of the main surface of the substrate as compared with the prior art and can reduce surface defects due to adhesion of foreign substances or the like from the conventional product. It is possible to manufacture. The glass substrate for a magnetic disk obtained by the present invention can be suitably used as a current glass substrate for a magnetic disk in which the demand for the substrate surface quality is particularly severer than several years ago. . Further, by using the glass substrate obtained by the present invention, a highly reliable magnetic disk capable of long-term stable operation even when combined with a magnetic head with an extremely low flying height design equipped with a DFH function is obtained. Can do.

It is sectional drawing of the glass substrate for magnetic discs. It is a whole perspective view of the glass substrate for magnetic discs.

Hereinafter, embodiments of the present invention will be described in detail.
A glass substrate for a magnetic disk is usually manufactured through a rough grinding process, a shape processing process, a fine grinding process, an end surface polishing process, a main surface polishing process (first polishing process, second polishing process), a chemical strengthening process, and the like. The

In manufacturing the magnetic disk glass substrate, first, a disk-shaped glass substrate (glass disk) is molded from molten glass by direct pressing. In addition to such a direct press, a glass substrate (glass disk) may be obtained by cutting into a predetermined size from a plate glass manufactured by a downdraw method or a float method. Next, the molded glass substrate (glass disk) is ground to improve dimensional accuracy and shape accuracy. This grinding process usually uses a double-sided grinding apparatus to grind the main surface of the glass substrate using hard abrasive grains such as diamond. By grinding the main surface of the glass substrate in this way, a predetermined plate thickness and flatness are processed, and a predetermined surface roughness is obtained.

After this grinding process is finished, polishing is performed to obtain a highly accurate flat surface (mirror surface). As a method for polishing a glass substrate, it is preferable to use a polishing pad such as polyurethane while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica.

  The polishing liquid used in the polishing process is basically a combination of an abrasive and water as a solvent, and further contains a pH adjuster for adjusting the pH of the polishing liquid and other additives as necessary. Is done.

From the viewpoint of polishing efficiency, it is preferable to use abrasive grains such as colloidal silica contained in the polishing liquid having an average particle diameter of about 10 to 100 nm. In particular, in the present invention, the abrasive grains contained in the polishing liquid used in the final polishing step (second polishing step, which will be described later) have an average particle size of 10 from the viewpoint of further reducing the surface roughness. It is preferable to use a material having a thickness of about ˜40 nm, and particularly a fine material having a size of about 10 to 20 nm is preferable. However, the finer the abrasive grain, the harder it is to remove once adsorbed to the glass substrate. When the cleaning treatment of the present invention is applied after polishing of ultrafine colloidal silica abrasive grains having an average particle diameter of 20 nm or less, the abrasive grains are cleaned and removed while maintaining a very low surface roughness. It is effective because it can be cleaned.
In the present invention, the average particle size is a point where the cumulative curve is 50% when the cumulative curve is obtained with the total volume of the powder population in the particle size distribution measured by the light scattering method as 100%. (Hereinafter referred to as “cumulative average particle diameter (50% diameter)”). In the present invention, the cumulative average particle diameter (50% diameter) is specifically a value obtained by measurement using a particle diameter / particle size distribution measuring apparatus.

Moreover, the colloidal silica abrasive grain produced | generated by hydrolyzing an ion exchange method and an organosilicon compound can be used for the colloidal silica abrasive grain used for this invention. Since such abrasive grains are difficult to aggregate and difficult to form coarse particles, the surface of the glass substrate after the polishing treatment can be extremely low roughness and very little scratches, etc., It tends to adhere firmly to the glass substrate surface after the polishing process. Therefore, by applying the cleaning treatment according to the present invention, it is possible to clean the glass substrate surface by cleaning and removing the abrasive grains while maintaining an extremely low surface roughness.

In the present invention, the polishing method in the polishing step is not particularly limited. For example, the polishing pad and the glass substrate are brought into contact with the glass substrate and the polishing pad while supplying the polishing liquid containing the abrasive grains. The surface of the glass substrate may be polished in a mirror shape by relatively moving. For example, a planetary gear type double-side polishing apparatus can be preferably used.

In particular, the polishing pad for finish polishing is preferably a polishing pad (suede pad) of a soft polisher. The polishing pad preferably has an Asker C hardness of 60 to 80. The contact surface of the polishing pad with the glass substrate is preferably made of a foamed resin with an open foam pore, particularly foamed polyurethane. When polishing is performed in this manner, the surface of the glass substrate can be polished into a smooth mirror surface.

In the first embodiment of the present invention, as in the above configuration 1, the glass substrate is polished to a mirror surface in order to suppress an increase in the roughness of the glass substrate surface due to a cleaning process performed after the mirror polishing process of the main surface of the glass substrate. A method for producing a glass substrate for a magnetic disk including a cleaning process for performing alkali cleaning on a glass substrate, wherein the glass substrate is subjected to alkali metal ions and alkaline earth contained in the glass substrate before the alkali cleaning. It is characterized by performing a treatment of immersing in a liquid containing at least one metal ion.

The second embodiment of the present invention is a glass substrate for a magnetic disk including a cleaning process in which acid cleaning and alkali cleaning are performed in this order on a glass substrate polished to a mirror surface, as in Configuration 2 above. In the acid cleaning, the cleaning is performed by adding at least one ion of alkali metal ions and alkaline earth metal ions contained in the glass component to the cleaning solution for acid cleaning.

After mirror polishing of the glass substrate, if the conventional alkali cleaning or cleaning with a combination of acid cleaning and alkali cleaning is performed, foreign substances on the substrate surface are removed by alkali etching, acid leaching and alkali etching. However, the increase in the roughness of the glass substrate surface after cleaning becomes large.

Therefore, as a result of searching for a method for suppressing an increase in the surface roughness of the glass substrate after cleaning, the present inventor, when performing alkali cleaning on a glass substrate polished to a mirror surface, before the alkali cleaning, An increase in the surface roughness of the glass substrate after alkali cleaning can be suppressed by performing a treatment in which the substrate is immersed in a liquid containing at least one of alkali metal ions and alkaline earth metal ions contained in the glass substrate. I found. In addition, when acid cleaning and alkali cleaning are performed in this order on a glass substrate polished to a mirror surface, in the first acid cleaning, at least one ion of alkali metal ions and alkaline earth metal ions contained in the glass component is used. It has been found that by adding to the acid cleaning cleaning solution and performing cleaning, an increase in the surface roughness of the glass substrate after subsequent alkali cleaning can be suppressed.

According to the present invention, the inventor presumed the reason why the increase in the surface roughness of the glass substrate after cleaning can be suppressed as follows.
In the first embodiment of the present invention, before the alkali cleaning, the glass substrate is immersed in a liquid containing at least one ion of alkali metal ions and alkaline earth metal ions contained in the glass substrate. By suppressing the leaching from the glass substrate by the immersion solution, it becomes difficult to be etched even if the substrate is subsequently washed with an alkali, and an increase in the surface roughness of the glass substrate can be suppressed.

  In the second embodiment of the present invention, in the first acid cleaning, at least one ion of alkali metal ions and alkaline earth metal ions contained in the glass component is added to the cleaning solution for acid cleaning. By performing the above, the concentration gradient of alkali metal ions or alkaline earth metal ions between the acid cleaning solution and the glass substrate is small, and the movement of the ions from the glass substrate to the acid cleaning solution due to the difference in concentration gradient is suppressed. As a result, when acid cleaning is performed, a leaching layer in which alkali metal ions on the surface of the glass substrate are insufficient compared to the inside of the glass is less likely to be formed on the glass surface. Thus, the increase in the surface roughness of the glass substrate can be suppressed.

Examples of the alkali metal ion contained as a glass component of the glass substrate include sodium ion, potassium ion, and lithium ion. Moreover, the alkaline earth metal ion contained as a glass component in the glass substrate is, for example, magnesium ion or calcium ion.
Among these ions, alkali metal ions that are monovalent and have a small ion radius and high mobility in an aqueous solution and glass are more effective than divalent ions.

  In the first embodiment, the content of the ions in the liquid containing at least one of alkali metal ions and alkaline earth metal ions is preferably in the range of 8 to 13 mol%. When the content is less than 8 mol%, the effect of the present invention cannot be sufficiently obtained. On the other hand, if the content exceeds 13 mol%, no further effect can be obtained.

  About the treatment time of the treatment for immersing the glass substrate with a liquid containing at least one of alkali metal ions and alkaline earth metal ions contained in the glass substrate before the alkali cleaning, the pH, temperature, etc. of the treatment liquid Although not particularly limited, for example, the pH of the treatment liquid is preferably pH 2 or more and 4 or less.

In the second embodiment, the content of the ions in the acid cleaning solution to which at least one of alkali metal ions and alkaline earth metal ions is added is in the range of 8 to 13 mol%. preferable. When the content is less than 8 mol%, the effect of the present invention cannot be sufficiently obtained. On the other hand, when the content exceeds 13 mol%, no further effect can be obtained.
Moreover, oxalic acid, malic acid, citric acid, sulfuric acid and the like are suitable as the acid cleaning agent added to the acid cleaning solution. In addition, potassium pyrophosphate, an organophosphorus chelating agent, ammonium iron sulfate (II) and the like may be added.

  In the second embodiment, the cleaning time when performing acid cleaning by adding at least one of alkali metal ions and alkaline earth metal ions contained in the glass component to the acid cleaning solution, and the pH of the acid cleaning solution . The temperature and the like are not particularly limited. For example, the pH of the acid cleaning solution is preferably pH 2 or more and 4 or less.

Note that at least one of the alkali metal ions and alkaline earth metal ions may be added to the treatment liquid or the acid cleaning liquid as a salt containing the ions.

In addition, in order to prevent the foreign matter removed from the substrate surface by the alkali cleaning carried out in the present invention from reattaching to the substrate surface and increase the cleaning effect, in the cleaning liquid, in addition to the alkaline cleaning agent, You may make it contain additives, such as surfactant, a chelating agent, and a dispersing agent suitably.
Examples of the surfactant that can be preferably used in the present invention include anionic surfactants such as sodium alkyl sulfate ester, fatty acid sodium, and alkylaryl sulfonate, and nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene derivatives. Can be mentioned. Examples of the chelating agent include aminocarboxylic acids such as EDTA and organic acids such as citric acid. Furthermore, examples of the dispersant include phosphates, sulfates, and polymer dispersants.

  The treatment to be carried out before the alkali washing, or the washing treatment such as the acid washing or the alkali washing usually contains a treatment liquid containing the ions or salts thereof, a detergent, and necessary additives, and a washing liquid. For example, it is performed by immersing the glass substrate after the polishing step in the bath. At this time, it is also preferable to apply an ultrasonic wave in order to increase the treatment effect and the cleaning effect. In addition, the liquid temperature of the alkaline cleaning liquid, the cleaning time, and the like can be appropriately set in consideration of the cleaning effect and productivity.

In the present invention, the increase amount (ΔRa) of the surface roughness (Ra) due to the cleaning treatment can be set to 0.10 nm or less, more preferably 0.04 nm or less, and further preferably 0.03 nm or less. It is also possible.
Further, although depending on the surface roughness after polishing, the surface roughness (Ra) of the glass substrate main surface after the cleaning treatment can be 0.2 nm or less, more preferably 0.18 nm or less, Preferably, it can also be 0.15 nm or less.

Normally, the polishing process includes a first polishing process for removing scratches and distortions remaining in the grinding process as described above, and a glass substrate while maintaining a flat surface obtained in the first polishing process. Generally, it is performed through two stages of the second polishing step that finishes the surface roughness of the main surface into a smooth mirror surface (however, multistage polishing of three or more stages may be performed). It is preferable to apply the cleaning treatment of the present invention to at least the second polishing step in the subsequent stage, that is, the cleaning treatment performed after the final polishing step of the polishing step.

In the present invention, the glass (the glass type) constituting the glass substrate is preferably an aluminosilicate glass. Amorphous aluminosilicate glass is more preferable. Such a glass substrate can be finished to a smooth mirror surface by mirror polishing the surface, and the strength after processing is good. As such an aluminosilicate glass, SiO ₂ is 58 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 23 wt%, Li ₂ O is 3 wt% to 10 wt%, Na ₂ An aluminosilicate glass containing O as a main component of 4 wt% or more and 13 wt% or less can be used.
Further, for example, SiO ₂ is 62 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 15 wt%, Li ₂ O is 4 wt% to 10 wt%, and Na ₂ O is 4 wt%. above 12 wt% or less, the ZrO ₂ 5.5 wt% to 15 wt% or less, while containing as the main component, the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.0, Al ₂ O ₃ An amorphous aluminosilicate glass containing no phosphorus oxide having a weight ratio of / ZrO ₂ of 0.4 or more and 2.5 or less can be obtained.

In addition, heat resistance may be required as a characteristic of next-generation substrates. Examples of the heat-resistant glass in this case include 50 to 75% of SiO ₂ , 0 to 6% of Al ₂ O ₃ , 0 to 2% of BaO, and 0 to 3% of Li ₂ O in terms of mol%. ZnO 0-5%, Na ₂ O and K ₂ O 3-15% in total, MgO, CaO, SrO and BaO 14-35% in total, ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ in total ₂ to 9%, molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] in the range of 0.85 to 1 Further, a glass having a molar ratio [Al ₂ O ₃ / (MgO + CaO)] in the range of 0 to 0.30 can be preferably used.

In the present invention, the surface of the glass substrate after the above polishing process preferably has an arithmetic average surface roughness Ra of 0.20 nm or less, particularly 0.15 nm or less. Further, the maximum roughness Rmax is 2.0 nm or less, particularly 1.5 nm or less, more preferably 1.0 nm or less. In the present invention, Ra and Rmax are roughnesses calculated in accordance with Japanese Industrial Standard (JIS) B0601 (1982).
In the present invention, the surface roughness is practically the surface roughness obtained by measuring the range of 1 μm × 1 μm with a resolution of 512 × 512 pixels using an atomic force microscope (AFM). Above preferred.

In the present invention, it is preferable to perform a chemical strengthening treatment before or after the polishing process. As a chemical strengthening treatment method, for example, a low temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding the temperature of the glass transition point is preferable. The chemical strengthening treatment is performed by immersing a molten chemical strengthened salt and a glass substrate so that an alkali metal element having a relatively large atomic radius in the chemically strengthened 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. As the chemically strengthened salt, a molten salt of an alkali metal nitrate such as potassium nitrate or sodium nitrate can be preferably used.

As shown in FIGS. 1 and 2, the disk-shaped glass substrate having both main surfaces 11, 11 and an outer peripheral side end surface 12 and an inner peripheral side end surface 13 therebetween as shown in FIG. 1 and FIG. 1 is obtained. The outer peripheral side end surface 12 includes chamfered surfaces 12b and 12b between the side wall surface 12a and the main surfaces on both sides thereof. The inner peripheral side end face 13 has the same shape.

The present invention also provides a method for manufacturing a magnetic disk using the above glass substrate for a magnetic disk. In the present invention, the magnetic disk is produced by forming at least a magnetic recording layer (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, a protective layer, a lubricating layer, or the like may be formed on the magnetic recording layer. As the protective layer, an amorphous carbon-based protective layer is suitable. 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.
By using the magnetic disk glass substrate obtained by the present invention, a highly reliable magnetic disk can be obtained.

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.
Example 1
(1) Rough grinding step, (2) Shape processing step, (3) Fine grinding step, (4) End surface polishing step, (5) Main surface first polishing step, (6) Chemical strengthening step, (7) The glass substrate for magnetic disks was manufactured through the main surface 2nd grinding | polishing process and (8) washing | cleaning process.

(1) Coarse grinding step First, a glass substrate made of 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. In addition to such a direct press, a glass substrate may be obtained by cutting into a predetermined size from a plate glass manufactured by a downdraw method or a float method. As the aluminosilicate _glass, SiO 2: 58 to 75 wt%, Al ₂ O _3: 5~23 wt%, Li ₂ O: 3~10 wt%, Na ₂ O: 4~13 chemical containing wt% Tempered glass was used.

Next, a rough grinding process was performed on the glass substrate in order to improve dimensional accuracy and shape accuracy. This rough grinding process was performed using a double-sided grinder and loose abrasive grains. Specifically, the glass substrate held by the carrier is closely attached between the upper and lower surface plates, the load is appropriately set, and the sun gear and the internal gear of the grinding device are rotated, thereby the glass substrate stored in the carrier. Both sides were ground.

(2) Shape processing step Next, a cylindrical grindstone is used to make a hole in the center portion of the glass substrate, and the outer peripheral end face is ground to a diameter of 65 mmφ. Chamfered. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) Precision grinding process This precision grinding process uses the above-mentioned double-side grinding apparatus, and a glass substrate held by a carrier is brought into close contact between upper and lower surface plates to which pellets in which diamond abrasive grains are fixed with acrylic resin are attached. I did it.
Specifically, both surfaces of the glass substrate housed in the carrier were ground by rotating the sun gear and the internal gear of the grinding apparatus.

(4) End surface polishing step Next, the surface of the end surface (inner periphery, outer periphery) of the glass substrate was mirror-polished by brush polishing while rotating the glass substrate.

(5) Main surface first polishing step Next, a first polishing step for removing scratches and distortions remaining in the above-described grinding step was performed using a double-side polishing apparatus. In a double-side polishing apparatus, a glass substrate held by a carrier is brought into close contact between upper and lower polishing surface plates to which a polishing pad is attached, and the carrier is meshed with a sun gear and an internal gear, and the glass substrate is vertically fixed. It is clamped by the board. Thereafter, by supplying and rotating the polishing liquid between the polishing pad and the polishing surface of the glass substrate, the glass substrate revolves while rotating on the upper and lower surface plates, and both surfaces are polished simultaneously. Specifically, a hard polisher (hard foamed urethane) was used as the polisher, and the first polishing step was performed. As the polishing liquid, a polishing liquid in which 10% by weight of cerium oxide (average particle diameter (50% diameter) 1 μm) was dispersed in water as an abrasive was used. The load applied to the glass substrate surface was 100 g / cm ² and the polishing time was 15 minutes.

(6) Chemical strengthening step Next, chemical strengthening was performed on the glass substrate after the cleaning. The chemical strengthening treatment was performed by preparing a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed and melted, and immersing the glass substrate.

(7) Main surface second polishing step Next, using the same double-side polishing apparatus as used in the first polishing step above, the polisher is replaced with a soft polisher (suede) polishing pad (72 foam polyurethane with Asker C hardness) Then, the second polishing step was performed. This second polishing step is a mirror polishing process for finishing the surface roughness of the glass substrate main surface to a smooth mirror surface with an Rmax of 2 nm or less while maintaining the flat surface obtained in the first polishing step described above. It is. The polishing liquid used was adjusted to acidity (pH = 2) by adding sulfuric acid to water in which 10% by weight of colloidal silica (average particle diameter (50% diameter) 15 nm) was dispersed as an abrasive. The load was 100 g / cm ² and the polishing time was 10 minutes.
Here, in order to investigate the surface roughness Ra after polishing, one substrate was extracted from the same lot, washed with water only for 1200 seconds, dried, and measured under the above conditions by AFM. .20 nm. However, a large amount of colloidal silica particles adhered to the surface of the substrate, which was a rejected product level.

(8) Cleaning process Next, the glass substrate that had undergone the second polishing step was cleaned. In the cleaning treatment, acid cleaning was first performed, and then alkali cleaning was performed.
Specifically, the first acid cleaning was immersed for 10 minutes in a cleaning tank (liquid temperature: 40 ° C.) containing a cleaning liquid in which 8 mol% of sodium sulfate was added to a sulfuric acid aqueous solution of pH 2 to 4.
After the acid cleaning, the glass substrate was washed with water and dried, and immersed in a cleaning tank (liquid temperature: 50 ° C.) containing a pH 10 to 12 aqueous potassium hydroxide solution for 10 minutes for alkali cleaning. After alkali washing, the glass substrate was washed with water and IPA dried.
Each cleaning solution was circulated.

As a result of measuring the surface roughness (Ra) of the main surface of the glass substrate after the cleaning treatment with an atomic force microscope (AFM) for the glass substrate (100 sheets) of this example obtained through the above steps, It was 0.23 nm. Further, when Ra was increased after the second polishing process (before the cleaning process) (denoted as ΔRa), it was 0.03 nm. The results are shown in Table 1. The value of the surface roughness is an average value of 100 manufactured glass substrates.
Further, in order to confirm the etching amount by the cleaning process, a step difference measurement by AFM was performed. Note that the step measurement substrate was provided with a protective film for preventing etching in part, and the step was measured from the difference from the part. The results are shown in Table 1. In addition, the value of the said etching amount is an average value of 100 manufactured glass substrates.

(Comparative Example 1)
In the acid washing of the washing treatment in Example 1 above, the washing treatment was performed in the same manner as in Example 1 except that sodium sulfate was not added to the sulfuric acid aqueous solution of pH 2 to 4, and the glass substrate (100 of this comparative example) Sheet).
In the same manner as in Example 1, the surface roughness (Ra) of the main surface of the glass substrate after the cleaning treatment and the etching amount by the washing treatment were measured, and the results are shown in Table 1.

From the results of Table 1, as in Example 1, at least one ion (sodium ion in this example) of alkali metal ions and alkaline earth metal ions contained in the glass component is added to the acid cleaning cleaning solution. It can be seen that the surface roughness Ra of the main surface of the glass substrate after the cleaning treatment can be reduced to a predetermined value or less by performing.
On the other hand, when cleaning is performed without adding the sodium ions to the acid cleaning cleaning solution as in Comparative Example 1 (conventional cleaning method), the etching amount by the cleaning process is large, and the main surface of the glass substrate after the cleaning process The amount of increase in surface roughness Ra (0.10 nm) becomes large.

(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, on the glass substrate, an adhesion layer made of a CrTi alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, a seed layer made of NiW, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, carbon A protective layer and a lubricating layer were sequentially 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.
The obtained magnetic disk was installed in an HDD equipped with a DFH head, and a load / unload durability test was conducted for one month while operating the DFH function in a high temperature and high humidity environment of 80 ° C. and 80% RH. There were no particular obstacles and good results were obtained.

1 Glass substrate 11 Main surface 12, 13 End surface of substrate

Claims (6)

A method of manufacturing a glass substrate for a magnetic disk, including a cleaning process of performing alkali cleaning on a glass substrate polished to a mirror surface,
Before the alkali cleaning, the glass substrate for a magnetic disk is subjected to a treatment of immersing the glass substrate with a liquid containing at least one of alkali metal ions and alkaline earth metal ions contained in the glass substrate. Manufacturing method. A method for producing a glass substrate for a magnetic disk, including a cleaning process in which acid cleaning and alkali cleaning are performed in this order for a glass substrate polished to a mirror surface,
In the acid cleaning, a method of manufacturing a glass substrate for a magnetic disk, wherein cleaning is performed by adding at least one of alkali metal ions and alkaline earth metal ions contained in a glass component to an acid cleaning cleaning solution.   The method for producing a glass substrate for a magnetic disk according to claim 1 or 2, wherein the glass substrate contains at least one of sodium, lithium and potassium in a glass component.   4. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate contains at least one of magnesium and calcium in a glass component.   The content of the ions in a liquid containing at least one of the alkali metal ions and alkaline earth metal ions or in a cleaning liquid to which the ions are added is in the range of 8 to 13 mol%. The manufacturing method of the glass substrate for magnetic discs in any one of thru | or 4.   6. A method for manufacturing a magnetic disk, comprising forming at least a magnetic recording layer on the glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to claim 1.

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