JP2013214341A - Method of manufacturing glass substrate for magnetic disk and method of manufacturing magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality glass substrate for a magnetic disk, which can reduce surface defects of a glass substrate caused by cerium oxide abrasive grains used in a polishing step, and also reduce missing errors of a magnetic disk manufactured using the glass substrate.SOLUTION: A method of manufacturing a glass substrate for a magnetic disk includes a polishing step of using free abrasive grains including cerium oxide as a polishing agent to polish an end face or principal face of a glass substrate 1, a contact step of bringing the glass substrate after the polishing step into contact with an aqueous solution including alkali metal ion and phosphate ion, and a washing step of washing the glass substrate after the contact step.

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 disk device such as a hard disk drive (HDD), and a method of 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, there has been an increasing demand for HDDs with higher recording capacity and lower prices. In order to achieve this, it is necessary to further improve the quality and cost of glass substrates for magnetic disks. It is coming.

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 a high smoothness on the surface of the magnetic disk, a substrate surface with a high smoothness is required in the end. Therefore, it is necessary to polish the glass substrate surface with high accuracy.
Conventionally, it is known that the main surface of a glass substrate for a magnetic disk is polished with free abrasive grains containing various abrasive grains such as cerium oxide (CeO ₂ ), zirconium oxide (ZrO ₂ ) and colloidal silica (SiO ₂ ). Yes.

In the following Patent Document 1, by transporting the substrate so as not to be dried when the substrate is transported between each step from the polishing step to the chemical strengthening step, the affinity between the glass substrate surface and the adhered material is reduced and the main surface is reduced. It describes that foreign substances are reduced.
Further, in Patent Document 2 below, after a polishing process using cerium oxide, the glass substrate is washed with a cleaning solution containing at least three components of ascorbic acid, inorganic acid, and aluminum chloride without etching the substrate surface. In addition, a technique for selectively dissolving cerium oxide is described.

JP 2003-141717 A Japanese Patent No. 4831096

  The current HDD has reached a recording density of about 500 gigabits per square inch. For example, it is possible to store about 320 gigabytes of information on a 2.5 inch magnetic disk (diameter 65 mm). However, higher recording density, for example, 375 to 500 gigabytes, and further 1 terabyte has been required. 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, the gap between the element portion of the magnetic head and the medium surface is expected to be extremely small, less than 2 nm. Under such circumstances, when the average roughness of the substrate surface is extremely small, if there are surface defects due to adhesion of very small foreign matter, which has not been a problem in the past, surface defects will also occur on the surface of the medium as they are. The risk of head collision increases.

  By the way, after the glass substrate main surface is polished with cerium oxide, the cleaning disclosed in Patent Document 2 is performed, and the main surface is further polished with silica abrasive grains to produce a glass substrate. As a result of manufacturing a medium (magnetic disk), it was found that there is a medium that detects many missing errors in the inspection after film formation or HDD assembly. This missing error is a recording / reproduction failure error caused by a phenomenon in which a reproduction signal falls below a predetermined threshold due to a defect on the medium.

  The present invention has been made to solve such conventional problems, and its object is to reduce the surface defects of the glass substrate and to reduce the occurrence of missing errors in a magnetic disk manufactured using the glass substrate. A method of manufacturing a glass substrate for a magnetic disk capable of manufacturing a high-quality glass substrate that can be used as a next-generation substrate that has been reduced, and demands on the substrate surface quality are more severe than the present, and It is an object of the present invention to provide a method of manufacturing a magnetic disk using a glass substrate obtained thereby.

As a result of detailed analysis of the missing error detection location on the main surface of the magnetic disk, the present inventor has found very fine cerium oxide abrasive grains along with very small film loss.
The inventor presumed that cerium oxide abrasive grains remained on the main surface of the glass substrate (product), and investigated the main surface of the glass substrate after the final cleaning in detail. Was not found.

  Therefore, it is assumed that the cerium oxide abrasive grains pierced deeply into the glass substrate main surface after polishing with cerium oxide, and could not be removed by subsequent polishing using silica abrasive grains, and at the time of polishing using silica abrasive grains It was confirmed whether the polishing error was improved by increasing the polishing allowance. Surprisingly, however, the missing error was not improved even when the polishing allowance was increased.

  Therefore, as a result of further detailed investigation assuming the transfer of abrasive grains from other than the main surface of the substrate, the inventor found cerium oxide particles attached to the end surface (side wall surface or chamfered surface) of the glass substrate. It was. That is, this means that the cerium oxide abrasive grains adhered to the substrate end face during the end face polishing using the cerium oxide abrasive grains or the first main surface polishing (first polishing) and could not be removed in the subsequent cleaning process. It was assumed that it was detached by the clamp on the side wall surface in the media film formation process and HDD assembly process and transferred to the main surface. In addition, when the side wall surface and the chamfered surface were compared among the end surfaces of the glass substrate, many cerium oxide particles were found on the side wall surface. This is presumably because the pressure of the cerium oxide abrasive grains is higher on the side wall surface in both the end face polishing and the main surface first polishing. That is, in the first main surface polishing step, the cerium oxide abrasive grains sandwiched between the side wall surface of the glass substrate and the side surface of the carrier are strongly pressed against the glass substrate and pierced or rubbed with the carrier. It is presumed that the cerium oxide abrasive grains were likely to remain in the end face polishing process and could not be removed in the subsequent cleaning process because the pressure by the polishing brush was high in the end face polishing process. . It should be noted that cerium oxide has a high chemical polishing effect on silica and is considered to be related to the property that it is particularly easy to stick (high affinity).

  As a result of diligent efforts to solve the above problems, the present inventors have found that the state of the storage liquid that temporarily stores the glass substrate after the end surface polishing step or the main surface first polishing step is a missing error in the magnetic recording medium. As a result of ascertaining that it is related to the generation amount, and further earnestly researching it, the present invention has been completed. That is, the dispersibility of cerium oxide abrasive grains from the glass substrate surface into the liquid by bringing the glass substrate after polishing with cerium oxide abrasive grains into contact with a storage liquid to which an appropriate dispersant is added (for example, immersion). And re-adhesion can be prevented, and as a result, the missing error when used as a medium has been successfully reduced.

That is, the present invention has the following configuration.
(Configuration 1)
A polishing step of polishing the end surface or main surface of the glass substrate using free abrasive grains containing cerium oxide as an abrasive, and contact for bringing the glass substrate after the polishing step into contact with an aqueous solution containing alkali metal ions and phosphate ions A method of manufacturing a glass substrate for a magnetic disk, comprising at least a step and a cleaning step of cleaning the glass substrate after the contact step.

(Configuration 2)
The said phosphate ion is at least 1 chosen from an orthophosphate ion, a pyrophosphate ion, a tripolyphosphate ion, a tetraphosphate ion, and a hexametaphosphate ion, The manufacture of the glass substrate for magnetic discs of the structure 1 characterized by the above-mentioned. Is the method.
(Configuration 3)
3. The method for producing a glass substrate for a magnetic disk according to Configuration 1 or 2, wherein the alkali metal ions are sodium ions or potassium ions.

(Configuration 4)
4. The method of manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 3, wherein the cleaning step uses a cleaning liquid containing at least a reducing agent, an inorganic acid, and fluorine ions.
(Configuration 5)
5. The method of manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 4, wherein the cleaning step includes a step of finally drying the glass substrate.

(Configuration 6)
6. The method for manufacturing a glass substrate for a magnetic disk according to any one of Structures 1 to 5, wherein the glass substrate is chemically strengthened after the cleaning step.
(Configuration 7)
7. The method for producing a glass substrate for a magnetic disk according to any one of configurations 1 to 6, further comprising a polishing step of polishing a main surface of the glass substrate using polishing abrasive grains containing colloidal silica.

(Configuration 8)
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 7.

  According to the present invention, the surface defect of the glass substrate due to the cerium oxide abrasive used in the polishing process is reduced, the occurrence of missing errors in the magnetic disk manufactured using this glass substrate is reduced, and the substrate surface quality is improved. Therefore, it is possible to provide a high-quality glass substrate for a magnetic disk that can be used as a substrate for the next generation in which the demands of the above are stricter than the present. In addition, the occurrence of the above-mentioned missing error is reduced and the operation is stable for a long time even when the glass substrate obtained by the present invention is used and combined with a magnetic head of an extremely low flying height design equipped with a DFH function. Therefore, a highly reliable magnetic disk capable of achieving the above can be obtained.

It is sectional drawing of the glass substrate for magnetic discs. It is a whole perspective view of the glass substrate for magnetic discs. It is a longitudinal cross-sectional view which shows schematic structure of a double-side polish apparatus.

Hereinafter, embodiments of the present invention will be described in detail.
The glass substrate for a magnetic disk is usually a rough grinding step (rough lapping step), a shape processing step, a fine grinding step (fine lapping step), an end surface polishing step, a main surface polishing step (first polishing step, second polishing step). It is manufactured through a chemical strengthening process.
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 (lapping) for improving dimensional accuracy and shape accuracy. This grinding process usually uses a double-sided lapping machine 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 the grinding process is finished, end face polishing and mirror polishing for obtaining a highly accurate main surface are performed. As a method for polishing the end face of the glass substrate, it is preferable to use a polishing brush while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide. Further, as a mirror polishing method for the main surface of the glass substrate, a polishing pad made of polyurethane or the like is used while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica. Is preferred.

  The present invention includes a polishing step of polishing an end face or a main surface of a glass substrate using free abrasive grains containing cerium oxide as an abrasive as in Configuration 1, and the glass substrate after the polishing step is treated with an alkali metal ion. And a washing step of washing the glass substrate after the contacting step, and a method for producing a glass substrate for a magnetic disk.

  That is, the characteristic configuration of the present invention uses a free abrasive grain after a polishing step of polishing an end surface of a glass substrate using a free abrasive grain containing cerium oxide as an abrasive or a cerium oxide as an abrasive. Then, after the polishing step (especially the first first polishing step) for polishing the main surface of the glass substrate, there is a contact step of bringing the glass substrate into contact with an aqueous solution containing a specific dispersant and the like. The aqueous solution used in this contact step is specifically an aqueous solution containing alkali metal ions and phosphate ions.

  According to the present invention, in the contacting step, the cerium oxide abrasive grains brought into the aqueous solution (hereinafter also referred to as storage solution) while adhering to the glass substrate surface (particularly the end face) are phosphoric acid in the aqueous solution. Dispersed by ions. Furthermore, when the alkali metal ions in the aqueous solution adhere to and cover the glass surface, the dispersed cerium oxide abrasive grains can be prevented from reattaching to the glass surface. As a result, the cerium oxide abrasive grains remaining on the glass substrate surface (particularly, the end face) can be reduced, so that the occurrence of missing errors when the glass substrate is used as a magnetic recording medium can be reduced.

  In the present invention, the phosphate ion is preferably at least one selected from orthophosphate ion, pyrophosphate ion, tripolyphosphate ion, tetraphosphate ion, and hexametaphosphate ion. Since these phosphate ions become trivalent or more anions in an aqueous solution, they are strongly attracted to the surface of cerium oxide, which has very strong electrical positivity. As a result, the adhesion between the cerium oxide abrasive grains and the glass substrate surface is weakened to disperse the cerium oxide abrasive grains in the aqueous solution from the glass substrate surface, and the glass surrounding the cerium oxide abrasive grains dispersed in the aqueous solution is surrounded. Reattachment to the surface can be suppressed.

In the present invention, the alkali metal ion is preferably a sodium ion or a potassium ion. These alkali metal ions are preferably supplied as cations constituting the phosphate. That is, it is not preferable to add and supply NaOH or KOH separately because the roughness may be deteriorated.
These alkali metal ions have strong adhesion to the glass surface, and can adhere to and cover the glass substrate surface, thereby suppressing reattachment of the cerium oxide abrasive grains to the glass surface.
In the present invention, the phosphate ion content is preferably 0.001 to 1 mol / L, and the alkali metal ion content is preferably 0.001 to 1 mol / L.
Further, the pH of the aqueous solution is preferably adjusted to a range of 6 to 12 because alkali metal ions are sufficiently adsorbed on the substrate surface and the substrate surface roughness is not deteriorated.

In the contact step, as a method of bringing the glass substrate after the polishing step into contact with the aqueous solution, it is preferable to immerse the glass substrate after the polishing step in the aqueous solution. At this time, it is also preferable to appropriately stir the aqueous solution or to swing the glass substrate appropriately.
Further, the method is not limited to the immersion method, and the aqueous solution may be brought into contact with the glass substrate after the polishing step by, for example, showering or jet cleaning. For example, it is also preferable to apply such a cleaning method to the glass substrate in the contact step performed after the end face polishing step.

Moreover, it is preferable to perform the washing | cleaning process implemented after the said contact process using the washing | cleaning liquid which contains a reducing agent, an inorganic acid, and a fluorine ion at least.
After the contact step, the glass substrate is subjected to a cleaning step using a cleaning solution containing at least a reducing agent, an inorganic acid, and fluorine ions, so that the aqueous solution (storage solution) is removed from the glass substrate in the contact step. It becomes easy to wash and remove the residual cerium oxide abrasive grains dispersed in the glass, and reattachment to the glass substrate can be prevented.

  As said reducing agent used for the said washing | cleaning liquid, ascorbic acid etc. are preferable, for example, As said inorganic acid, a sulfuric acid etc. are mentioned, for example. The fluorine ions are supplied by adding, for example, hydrofluoric acid. In the present invention, it is particularly preferable to use a cleaning solution (aqueous solution) containing at least three components of an acid (such as sulfuric acid), a reducing agent (such as ascorbic acid), and hydrofluoric acid. By using this cleaning solution, an effect of chemically dissolving cerium oxide abrasive grains and a strong etching effect by hydrofluoric acid can be obtained. In addition, content of the said reducing agent, an inorganic acid, and a fluorine ion can be set suitably.

  Moreover, this invention is suitable when the said washing | cleaning process includes the process of drying a glass substrate last. When the glass substrate surface is dried, the adhesion between the remaining foreign matter and the glass substrate surface is strengthened, but in the present invention, the residual cerium oxide abrasive grains after the polishing step can be reduced. Even if the glass substrate is dried, the remaining abrasive grains can be prevented from sticking to the glass substrate.

  Moreover, this invention is suitable when performing the chemical strengthening of the glass substrate after the said washing | cleaning process. When chemical strengthening is performed in a state in which foreign matter remains on the glass substrate surface, adhesion between the remaining foreign matter and the glass substrate surface becomes strong. In the present invention, since the residual cerium oxide abrasive grains after the polishing process can be reduced, even if the glass substrate is chemically strengthened after the cleaning process, the residual abrasive grains are prevented from sticking to the glass substrate. Can do.

  In the present invention, after the main surface first polishing step using the cerium oxide abrasive, the main surface of the glass substrate is formed using polishing abrasives containing colloidal silica in order to further improve the smoothness of the substrate main surface. It is preferable to carry out a polishing step (a main surface second polishing step described later) for polishing.

  The polishing liquid used for the polishing process is basically a combination of an abrasive and pure water (for example, RO water) as a solvent, and further a pH adjuster and other additives for adjusting the pH of the polishing liquid. Is contained as required. Here, RO water is pure water that has been subjected to RO (Reverse Osmotic Pressure Membrane) treatment. It is particularly preferable to use RO-DI water that has been subjected to RO treatment and DI treatment (deionization treatment). This is because RO water or RO-DI water has a very low content of impurities, such as alkali metals, and also has a low ion content. As described above, the present invention is applied to a method for manufacturing a glass substrate for a magnetic disk having a polishing step using a polishing agent containing cerium oxide abrasive grains.

  Moreover, it is preferable that the polishing liquid applied to the polishing process of the present invention (particularly the finish mirror polishing process (second polishing process described later)) is adjusted to an acidic range, for example. For example, sulfuric acid is added to the polishing liquid to adjust the pH to a range of 1-5. The reason why the polishing liquid adjusted to the acidic range is preferably used in the present invention is from the viewpoint of productivity and cleanliness.

For example, the cerium oxide abrasive contained in the polishing liquid used in the end face polishing step or the main surface first polishing step preferably has an average particle size of about 0.5 to 4 μm. In particular, the colloidal silica abrasive contained in the polishing liquid used in the finishing mirror polishing step (second polishing step described later) has an average particle size of about 10 to 40 nm from the viewpoint of further reducing the surface roughness. Is preferable, and a fine one of about 10 to 20 nm is particularly preferable.
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 device (Nikki Co., Ltd., Nanotrac UPA-EX150). .

The polishing method in the polishing step of the present invention is not particularly limited. For example, in the end surface polishing of a glass substrate, polishing may be performed using a polishing brush while supplying a polishing liquid containing polishing abrasive grains. In the main surface polishing of the glass substrate, 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 may be polished into a mirror surface.
For example, FIG. 3 is a longitudinal sectional view showing a schematic configuration of a planetary gear type double-side polishing apparatus that can be used in a mirror polishing process of a glass substrate. The double-side polishing apparatus shown in FIG. 3 meshes with the sun gear 2, the internal gear 3 arranged concentrically on the outer side, the sun gear 2 and the internal gear 3, and the sun gear 2 and the internal gear 3. An upper surface plate 5 and a lower surface plate 6 on which a carrier 4 that revolves and rotates according to rotation, and a polishing pad 7 that can hold the workpiece 1 held by the carrier 4 are attached, and an upper surface plate A polishing liquid supply unit (not shown) for supplying a polishing liquid is provided between 5 and the lower surface plate 6.

  By such a double-side polishing apparatus, during polishing, the workpiece 1 held by the carrier 4, that is, the glass substrate is sandwiched between the upper surface plate 5 and the lower surface plate 6, and the upper and lower surface plates 5, 6 are polished. While supplying the polishing liquid between the pad 7 and the workpiece 1, the carrier 4 revolves and rotates according to the rotation of the sun gear 2 and the internal gear 3, and the upper and lower surfaces of the workpiece 1 are moved. Polished.

  In particular, the polishing pad for finishing mirror 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 present invention, the glass constituting the glass substrate is preferably an amorphous aluminosilicate glass. 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 in an amount of 4 wt% or more and 13 wt% or less (however, an aluminosilicate glass containing no phosphorus oxide) 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. An example of such glass is N5 glass (trade name) manufactured by HOYA Corporation.

In addition, heat resistance may be required as a characteristic of next-generation substrates. The heat-resistant glass in this case, for example, in mol%, the _{SiO 2 50~75%, Al 2 O} 3 0-6%, 0-2% of BaO, and Li ₂ O 0 to 3% ZnO 0 to 5%, Na ₂ O and K ₂ O 3 to 15% in total, MgO, CaO, SrO and BaO 14 to 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)] is in the range of 0.85 to 1 And 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 main surface mirror polishing is a mirror surface having an arithmetic average surface roughness Ra of 0.20 nm or less, particularly 0.15 nm or less, more preferably 0.12 nm or less. It is preferable. 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.
Further, in the present invention, the surface roughness (for example, the maximum roughness Rmax, the arithmetic average roughness Ra) is measured with a resolution of 256 × 256 pixels in a range of 1 μm × 1 μm using an atomic force microscope (AFM). It is practically preferable to obtain the surface roughness of the obtained surface shape.

  In the present invention, it is preferable to perform chemical strengthening treatment before or after the main surface mirror polishing step. As a method of chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range that does not exceed the temperature of the glass transition point, for example, a temperature of 300 degrees Celsius or more and 400 degrees Celsius or less 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. As the chemical strengthening salt, alkali metal nitric acid 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 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, the easy magnetization direction of the magnetic layer can be oriented along the normal line 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. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. 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 for magnetic disk obtained by the present invention, a highly reliable magnetic disk with reduced occurrence of missing errors 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
The following (1) rough lapping step (rough grinding step), (2) shape processing step, (3) fine lapping step (fine grinding step), (4) end surface polishing step, (5) main surface first polishing step, A glass substrate for a magnetic disk of this example was manufactured through (6) chemical strengthening step and (7) main surface second polishing step.

(1) Coarse lapping process 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 mold, a lower mold, and a trunk mold. 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 lapping process was performed on the glass substrate in order to improve dimensional accuracy and shape accuracy. This lapping process was performed using a double-sided lapping machine and using abrasive grains having a particle size of # 400. Specifically, the glass substrate held by the carrier is closely attached between the upper and lower surface plates, the load is set to about 150 g / cm ² , and the sun gear and the internal gear of the wrapping device are rotated to enter the carrier. Both sides of the housed glass substrate were lapped to a surface accuracy of 0 to 1 μm and a surface roughness (Rmax) of about 6 μm.

(2) Shape processing step Next, a cylindrical grindstone is used to make a hole in the central portion of the glass substrate, and the outer peripheral end face is ground to a diameter of 65 mmφ. Chamfered. The surface roughness of the end face of the glass substrate at this time was about 4 μm in Rmax. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) Fine wrapping process This fine wrapping process uses a double-sided wrapping device, and adheres a glass substrate held by a carrier between upper and lower surface plates to which pellets of diamond abrasive grains of particle size # 1000 fixed with acrylic resin are attached. I did it.
Specifically, by setting the load to about 100 kg and rotating the sun gear and the internal gear of the wrapping device, both surfaces of the glass substrate housed in the carrier are approximately 2 μm in surface roughness Rmax and 0 in Ra. Wrapped to about 2 μm.
The glass substrate after the lapping process was immersed in each washing tank (applied with ultrasonic waves) in a neutral detergent and water in order to perform ultrasonic cleaning.

(4) End face polishing step Next, the surface roughness of the end face (inner circumference, outer circumference) of the glass substrate was polished by brush polishing to about 1 μm at Rmax and about 0.3 μm at Ra while rotating the glass substrate. And the surface of the glass substrate which finished the said end surface grinding | polishing was water-washed.

(5) Main Surface First Polishing Step Next, a first polishing step for removing scratches and distortions remaining in the lapping step described above was performed using the double-side polishing apparatus shown in FIG. In the double-side polishing apparatus, the glass substrate held by the carrier 4 is closely attached between the upper and lower polishing surface plates 5 and 6 to which the polishing pad 7 is attached, and the carrier 4 is engaged with the sun gear 2 and the internal gear 3. The glass substrate is sandwiched between upper and lower surface plates 5 and 6. Thereafter, the polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass substrate, so that the glass substrate revolves while rotating on the surface plates 5 and 6, 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. The polishing liquid used was adjusted to neutrality by adding an ethanol-based low molecular weight surfactant to RO water in which 10% by weight of cerium oxide (average particle size 1 μm) was dispersed as an abrasive. The load was 100 g / cm ² and the polishing time was 15 minutes.

  The glass substrate after the first polishing step is added to a storage solution adjusted to pH = 7 containing hexametaphosphate ions and sodium ions by adding sodium hexametaphosphate in RO water (addition amount 0.1 mol / L). It was immersed (said contact process). The immersion time was 3 minutes.

  After immersing in the storage solution in this manner, the glass substrate was immersed in a cleaning solution (aqueous solution) bath containing sulfuric acid (4.5% by weight), ascorbic acid (1% by weight) and hydrofluoric acid (10 ppm). (Isopropyl alcohol) and IPA (steam-dried) were sequentially immersed in each washing tank, subjected to ultrasonic cleaning and dried.

(6) Chemical strengthening process Next, the glass substrate which finished the said washing | cleaning was chemically strengthened. For chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, the chemical strengthening solution was heated to 380 ° C., and the cleaned and dried glass substrate was immersed for about 4 hours to perform chemical strengthening treatment. The glass substrate after the chemical strengthening was immersed in each of washing tanks of sulfuric acid, neutral detergent, pure water, and pure water, and ultrasonically cleaned.

(7) Main surface second polishing step Next, using the same double-side polishing apparatus as used in the first polishing step, 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, for example, mirror polishing for finishing the surface roughness of the glass substrate main surface to a smooth mirror surface with an Rmax of about 2 nm or less while maintaining the flat surface obtained in the first polishing step. It is processing. The polishing liquid used was adjusted to acidity (pH = 2) by adding sulfuric acid to RO water in which 15% by weight of colloidal silica (average particle diameter of 15 nm) was dispersed as an abrasive. The load was 100 g / cm ² and the polishing time was 10 minutes.
The glass substrate after the second polishing step was subjected to ultrasonic cleaning and dried.

When the surface roughness of the main surface of the five glass substrates obtained through each of the above steps was measured with an atomic force microscope (AFM), Ra = 0.120 nm, which was a super-smooth surface compared to the conventional product. A glass substrate was obtained. The value of the surface roughness is an average value of five manufactured glass substrates.
Moreover, the foreign material defect was evaluated with respect to the obtained 5 glass substrate. The end face and main surface of the obtained glass substrate are observed with a microscope and OSA (Optical Surface Analyzer), respectively, and 10 points are selected from the detected surface defects, respectively, with an atomic force microscope (AFM) and SEM / EDX. analyzed. In any of the five glass substrates obtained in this example, no cerium oxide particles were found from either the main surface or the end face.

In addition, 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.

The following missing error test was performed on the obtained magnetic disk.
[Missing error test]
The produced magnetic disk was built into the HDD together with the DFH head to manufacture the HDD. DFH control is performed so that the gap between the magnetic head element section and the magnetic disk surface is 2 nm, a signal of a predetermined frequency is written on the main surface, the signal is read, and a predetermined threshold is set for the signal intensity. The number of missing errors was detected.
As a result, the number was 10 or less in this example.

(Example 2)
Alkaline (pH = 10) containing tripolyphosphate ions and sodium ions by adding sodium tripolyphosphate in RO water (addition amount 0.1 mol / L) to the glass substrate that has finished the first polishing step in Example 1 Main surface polishing was carried out in the same manner as in Example 1 except that it was immersed in a storage solution adjusted to 1 and other steps were carried out in the same manner as in Example 1 to produce 5 glass substrates. .
In the same manner as in Example 1, evaluation of foreign matter defects was performed on the obtained five glass substrates. In all of the five glass substrates obtained in this example, CeO ₂ particles were not found from either the main surface or the end surface.
A magnetic disk for perpendicular magnetic recording was produced in the same manner as in Example 1 using the glass substrate produced in this example.
The resulting magnetic disk was subjected to the same missing error test as in Example 1. As a result, the number was 10 or less in this example.

(Comparative example)
The glass substrate that has finished the first polishing step is omitted from the contact step of immersing the glass substrate in a storage solution containing hexametaphosphate ions and sodium ions, and immediately immersed in a cleaning solution (aqueous solution) bath containing sulfuric acid, ascorbic acid and hydrofluoric acid, Furthermore, it was immersed in each washing tank of pure water, IPA (isopropyl alcohol), and IPA (steam drying) sequentially, ultrasonically cleaned, and dried.
A glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except for this.
As a result of evaluating the foreign substance defect on the obtained five glass substrates in the same manner as in Example 1, CeO ₂ was found from any of the five glass substrates obtained by this comparative example. From the end face, CeO ₂ was found on all the disks.
Furthermore, a magnetic disk for perpendicular magnetic recording was produced in the same manner as in Example 1 using the glass substrate produced in this comparative example.
The resulting magnetic disk was subjected to the same missing error test as in Example 1. As a result, in this comparative example, the number of missing errors was 10 or more on an average on one surface, which was unacceptable.

From the above results, according to this example, it was confirmed that foreign matter defects due to the residual cerium oxide abrasive grains used in the first main surface first polishing step can be greatly reduced. That is, according to the present embodiment, it can be used as a substrate for the next generation in which the demand for the substrate surface quality is more severe than the present. In addition, in the magnetic disk for perpendicular magnetic recording manufactured using the glass substrate of this example, the incidence of missing errors was very small, and good results were obtained.
On the other hand, in the comparative example, the occurrence of foreign matter defects due to the residual cerium oxide abrasive grains is particularly noticeable on the substrate end face, and in the magnetic disk for perpendicular magnetic recording manufactured using the glass substrate of this comparative example, a missing error occurs. The incidence is high and the reliability is low.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Sun gear 3 Internal gear 4 Carrier 5 Upper surface plate 6 Lower surface plate 7 Polishing pad 11 Main surface 12, 13 End surface of substrate

Claims (8)

  A polishing step of polishing the end surface or main surface of the glass substrate using free abrasive grains containing cerium oxide as an abrasive, and contact for bringing the glass substrate after the polishing step into contact with an aqueous solution containing alkali metal ions and phosphate ions The manufacturing method of the glass substrate for magnetic discs which has a process and the washing | cleaning process of wash | cleaning the said glass substrate after this contact process.   2. The glass substrate for a magnetic disk according to claim 1, wherein the phosphate ion is at least one selected from orthophosphate ion, pyrophosphate ion, tripolyphosphate ion, tetraphosphate ion, and hexametaphosphate ion. Production method.   The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the alkali metal ions are sodium ions or potassium ions.   The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the cleaning step uses a cleaning liquid containing at least a reducing agent, an inorganic acid, and fluorine ions.   5. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the cleaning step includes a step of drying the glass substrate at the end.   6. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate is chemically strengthened after the cleaning step.   The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 6, further comprising a polishing step of polishing the main surface of the glass substrate using abrasive grains containing colloidal silica. A method of 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.

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