JP2009093744A - Method of manufacturing glass substrate for magnetic recording medium, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of flaws in the end face of a ring-shaped glass substrate for magnetic recording medium. <P>SOLUTION: In a manufacturing method of the ring-shaped glass substrate for magnetic recording medium, an end face is formed by etching when machining a glass material plate into the glass substrate 11 on a disk, thus obtaining the glass substrate for magnetic recording medium without any flaws on an outer-periphery end face 13 and an inner-periphery end face 14. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a glass substrate for a magnetic recording medium used as a recording medium for a computer or the like, and a magnetic recording medium.

  Conventionally, an aluminum substrate has been widely used as a magnetic disk substrate which is one of magnetic recording media used in hard disk drives (HDD) and the like. However, as the magnetic disk becomes smaller and thinner and has a higher recording density, it is gradually being replaced by a glass substrate that has superior substrate surface flatness and substrate strength compared to an aluminum substrate.

  One of the major problems in a magnetic disk using a glass substrate is to clean the surface of the glass substrate. If foreign matter adheres to the surface of the glass substrate, it causes film defects in the thin film formed on the surface of the glass substrate. Also, when reproducing a magnetic disk using a glass substrate with foreign matter attached to the surface in a state where the flying height (flying height) of the magnetoresistive head is lowered in order to improve the recording density of the magnetic disk, A malfunction of reproduction or reproduction may become impossible, which is a problem.

  This is because a convex portion is formed on the surface of the magnetic disk by a foreign substance (glass particle or the like) on the glass substrate, and the convex portion causes a thermal asperity failure.

  A thermal asperity failure is when a magnetoresistive element is heated by adiabatic compression or contact of air when a magnetic head passes over a small convex or concave part on the surface of a magnetic disk. It is a failure that causes an error. Therefore, for the magnetoresistive head, the magnetic disk surface is required to have extremely high smoothness and flatness. Further, if the magnetic layer is formed with dust or foreign matter attached, a convex portion is formed. Therefore, the glass substrate is required to prevent dust generation by removing irregularities and to perform advanced cleaning to remove foreign matter.

  It has been found that the cause of the foreign matter adhering to the surface of the magnetic disk glass substrate as described above is mainly due to scratches (cracks, scratches) on the glass end face. The scratches (cracks, chips) on the end surface are generated when the glass substrate is processed with a cutter or a drill. If this scratch (crack, chipping) remains on the end surface of the glass substrate, particles are captured by the scratch, and the captured particles may adhere to the surface of the glass substrate in a subsequent process.

  In order to prevent thermal asperity caused by scratches on the end face in this way, it has been proposed to remove scratches from the end face of the glass substrate by polishing the end face after shaping the glass substrate with a cutter or drill. (For example, Patent Document 1).

  The manufacturing process of the glass substrate for a magnetic disk described in Patent Document 1 can be summarized as follows: (1) Shape processing step and first lapping step (processing the glass base plate into a disk shape and aligning the thicknesses) Step), (2) end face shape processing step (step of making a circular hole in the center of the disk-shaped glass substrate and chamfering the end face), (3) end face polishing step, (4) second lapping step, (5) A surface polishing step (first and second polishing step) and (6) a chemical strengthening step.

In this conventional process, when processing the glass base plate into a disk shape, the glass is cut into a disk shape with a cutter, and a core drill is used to open a circular hole in the center of the disk-shaped glass substrate. In this case, a fine crack is generated on the end face. The crack is removed by grinding and polishing the end face.
JP-A-11-221742

  However, in recent years, with the advancement of recording density and diversification of uses of magnetic recording disks, smaller magnetic disks have been used. For example, in a small-diameter glass substrate used for a 1.8-inch type or smaller magnetic disk, the diameter of the circular hole at the center is also small, and it is difficult to appropriately mirror-polish the inner peripheral end face.

  In recent years, with the diversification of uses of magnetic recording disks, high quality at a level different from conventional ones has been demanded for glass substrates for magnetic disks. For this reason, for example, with respect to scratches (cracks, cracks) on the end face, those that have not been recognized as defective in the past have been recognized as defective.

  For example, in a high-speed rotation type magnetic disk having a rotation speed of 5400 rpm or more, or a magnetic disk used for an application that is susceptible to an impact at the time of use of a portable terminal or the like, the damage may be enlarged at the time of use. become. Further, in a small-diameter magnetic disk, the glass substrate is thinned. When the glass substrate is thinned, cracks may occur due to smaller scratches. Furthermore, when the process is simplified in order to reduce the cost of the magnetic disk, the process of strengthening the glass substrate such as chemical strengthening may be omitted. When the chemical strengthening step is omitted, since the glass substrate is not strengthened, a smaller scratch or the like becomes a problem.

  Therefore, the method of polishing the end surface after processing the glass substrate with a cutter or a drill as described in Patent Document 1 cannot sufficiently remove scratches (cracks, chips) on the end surface. It is. Moreover, when cutting a glass substrate from a sheet-like glass base plate, it is conventionally processed with a cutter or a drill, but this method has a problem that scratches (cracks, chips) are generated on the end surface. .

  The present invention eliminates scratches (cracks, chips) on the end surface of a glass substrate, reduces foreign matter on the main surface, and produces a high strength glass substrate for a magnetic recording medium, and uses the glass substrate. Another object of the present invention is to provide a magnetic recording medium in which the occurrence of thermal asperity is reduced.

  In order to achieve the above object, the present inventors have not used a method of removing the scratches on the end surface caused by the shape processing as in the conventional example by polishing the end surface, but a method in which the scratch is not generated on the end surface. We thought to shape the glass base plate. As a result, by etching the glass base plate, the outer shape of the glass substrate for a magnetic recording medium was formed and the end face of the glass substrate was formed. The present inventors employ a glass base plate etching process in the end face forming step, so that no minute cracks are generated on the end face during shape processing, and the end face is free from scratches (cracks, chips). The present inventors have found that a substrate can be obtained and have completed the present invention.

  That is, the method for producing a glass substrate for a magnetic recording medium according to the present invention includes a step of forming a protective film on a main surface of a sheet-like glass base plate in a region to be a main surface of the glass substrate, and an etching mask for the protective film. And an end face forming step of forming an end face of the glass substrate while forming an outer shape of the glass substrate by etching a glass material.

  According to this method, since the processing by etching is employed in the end surface forming step of the glass substrate for magnetic recording media, the end surface is not damaged, and the foreign matter on the main surface is caused by particles captured by the end surface scratch. The manufacturing method of the glass substrate for magnetic recording media with high glass strength can be provided. Furthermore, since the end face forming step in the present invention forms the outer shape by etching that does not cause scratches on the end face, the end face formed by etching is not required for grinding and polishing steps of the end face. The final end face can be obtained, and the number of man-hours can be reduced.

  The method for manufacturing a glass substrate for a magnetic recording medium may include a main surface polishing step for polishing the main surface of the glass substrate after the end surface forming step. According to this method, even if the main surface is roughened when the protective film is removed, a main surface that is mirror-finished by subsequent main surface polishing can be obtained.

  Furthermore, in the method for manufacturing a glass substrate for a magnetic recording medium, the protective film may be removed by polishing in the main surface polishing step. According to this method, the step of removing the protective film can be omitted, and the number of man-hours can be reduced.

  Furthermore, in the method for manufacturing the glass substrate for a magnetic recording medium, a step of mirror polishing the main surface of the glass base plate may be provided before the step of forming the protective film. According to this method, the main surface after polishing is protected by the protective film, so that the main surface is not damaged during the end face forming step.

  The method for manufacturing a glass substrate for a magnetic recording medium may include an end surface polishing step for polishing the end surface after the end surface forming step. According to this method, since the end face is not formed by machining, there are almost no cracks. By polishing the end face in this state (mirror surface), it is possible to further prevent particles from adhering to the end face.

  The magnetic recording medium of the present invention comprises a glass substrate produced by the above-described method for producing a glass substrate for a magnetic recording medium, and a magnetic layer formed on the glass substrate directly or via another layer. It is characterized by.

  According to this magnetic recording medium, since a glass substrate for a magnetic recording medium having no scratch on the end face can be used, thermal asperity caused by particles trapped by the scratch on the end face is reduced, and high-strength magnetic recording A medium can be provided.

  In the method for producing a glass substrate for a magnetic recording medium according to the present invention, in the step of forming the end surface of the glass substrate for a magnetic recording medium, shape processing with a conventionally used cutter or drill and subsequent grinding and polishing of the end surface are performed. Instead, by etching the glass base plate, the outer shape of the glass substrate was formed and the end face of the glass substrate was formed.

  As a result, the processing by etching does not cause scratches on the end surface, so that foreign substances on the main surface caused by particles trapped by the end surface scratches are reduced, and a glass substrate for a magnetic recording medium having high glass strength is obtained. Obtainable.

  Furthermore, the conventional end face forming step of the glass substrate for magnetic recording media required a shape processing step with a cutter or a drill and a grinding and polishing step of the end face, but the end face forming step in the present invention is performed on the end face. Since the outer shape is formed by etching without generating scratches, the end surface grinding and polishing steps are not required, and the end surface formed by etching can be used as the final end surface of the glass substrate for magnetic recording medium, thereby reducing the number of steps. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following, a magnetic substrate manufactured in the method for manufacturing a glass substrate for magnetic recording media (hereinafter simply referred to as “glass substrate”) according to the present embodiment is used for a magnetic recording used in a hard disk drive (HDD) or the like. Although it shows about the case where it applies to the glass substrate for media, it is not limited to this.

  FIG. 1 is a view for explaining the structure of a glass substrate manufactured in the method for manufacturing a glass substrate according to the present embodiment. FIG. 1 shows a glass substrate serving as a base of a magnetic disk that is one of magnetic recording media used in a hard disk drive (HDD) or the like. As shown in FIG. 1, the glass substrate 11 is an annular glass in which a circular hole (hereinafter referred to as “circular hole”) 12 is formed at the center of a disk-shaped glass substrate. The glass substrate 11 includes an outer peripheral end surface 13 which is an outer peripheral end surface and an inner peripheral end surface 14 which is an inner peripheral end surface.

  The details of the method of manufacturing the glass substrate for magnetic recording medium according to the present embodiment will be described later, but the outline thereof will be described as follows: (1) lapping step (step of aligning the thickness of the glass base plate), (2) end face Forming step (step of forming a glass base plate into an annular glass substrate and forming a final end face of the glass substrate for magnetic recording medium), (3) surface polishing step (first and second polishing steps), ( 4) A chemical strengthening step is provided.

  The manufacturing method of the glass substrate according to the present embodiment is an end surface forming step, that is, a step of shaping the glass base plate into an annular glass substrate and forming the final end surface of the glass substrate for magnetic recording medium. It is characterized by adopting shape processing by chemical etching. Hereinafter, the end face forming step will be described.

  FIG. 2 is a diagram showing a photomask used for shape processing of a glass base plate in the method for manufacturing a glass substrate according to the present embodiment. FIG. 2A is a plan view, and FIG. 2B is a cross-sectional view taken along line IIb-IIb in FIG. As the photomask, one in which a light shielding film patterned into a shape for processing a glass base plate into an annular shape is formed on the transparent substrate 21 is used. For example, the light shielding film is composed of two annular patterns having the same center, and includes an outer annular portion 22 for processing the outer shape of the disk and an inner annular portion 23 for processing a circular hole in the central portion. Become. Each of them has an annular shape with a width of about several mm.

  The shape and size of the photomask may be appropriately designed according to the shape and size of the magnetic disk to be manufactured. For example, when manufacturing a 2.5 inch (outer diameter 65 mm) magnetic disk, the diameter of the inner end of the outer ring portion 22 is considered to be isotropically etched. The glass substrate is designed to have a diameter of 65 mm when divided. Similarly, the diameter of the outer end portion of the inner annular portion 23 is designed so that the diameter of the circular hole is 20 cm when divided.

  FIG. 3 is a diagram for explaining a process of processing the shape of the glass base plate using the photomask shown in FIG. The shape processing of the glass base plate is performed by forming a resist pattern having a predetermined shape on both surfaces of the glass base plate and etching the glass using the resist as an etching mask (protective film).

  First, as shown in FIG. 3A, a negative resist 32 is applied to both surfaces of the glass base plate 31 after lapping the main surface. For resist application, a normal coating method such as a spin coating method or a roller coating method can be used. As the glass base plate 31, for example, a plate-like (sheet-like) one can be used.

  Next, as shown in FIG. 2B, by using the two photomasks 33 described in FIG. 2 and irradiating light on the negative resists 32 on both sides, other than the light shielding film formed on the photomask 33. Expose part. Specifically, the surfaces of the two photomasks 33 on which the outer ring portion 22 and the inner ring portion 23 are formed are made to face the negative resists 32 on both sides, respectively. Alignment is performed so that the patterns of the outer ring portion 22 and the inner ring portion 23 that are the light shielding films overlap, and the surface on which the outer ring portion 22 and the inner ring portion 23 are formed is the negative resist 32. Each photomask 33 is arranged so as to be in contact with or located in the very vicinity. Light irradiation is performed from both sides, and both sides can be performed simultaneously or separately.

  Next, as shown in FIG. 3C, by developing the negative resist 32, the unexposed portion of the negative resist 32 is dissolved and removed by the light shielding film of the photomask 33. After development, the negative resist 32 is dried.

  Next, as shown in FIG. 4D, the glass base plate 31 is etched using the developed and dried negative resist 32 as an etching mask (protective film). Etching can be performed by using a hydrofluoric acid aqueous solution as an etchant and spraying the etchant on both surfaces of the glass base plate 31 or immersing the glass base plate 31 in the etchant. When etching is performed until the glass base plate 31 is divided from both sides, an annular glass substrate 34 is obtained as shown in FIG.

  Finally, the negative resist 32 is removed as shown in FIG. In general, the resist may be peeled off by leaving it for a certain period of time. When the resist is dried and peeled off, the drying time is preferably left for 12 hours to 36 hours, for example. Or it can also peel by a chemical | medical solution process. In that case, the chemical solution is appropriately determined depending on the type of resist. For example, peeling can be easily performed by using an inorganic acid, an inorganic alkali, or an organic solvent.

  In the method according to the present invention, it is preferable to perform main surface polishing after end face formation. As a result, even if the main surface is roughened when the negative resist 32 as the protective film is removed, a main surface mirrored by the subsequent main surface polishing can be obtained. In this case, it is preferable to remove the negative resist 32 by polishing.

  Further, in the method according to the present invention, after polishing the main surface, a negative resist 32 as a protective film may be formed on the main surface to form an end face. In that case, since the main surface after polishing is protected by the protective film, it is not damaged during the end face forming step.

  As described above, in the present embodiment, since the processing by chemical etching is employed for the shape processing of the sheet-like glass base plate without using the cutter or the drill used in the conventional manufacturing process, the end surface is subjected to the shape processing. It is possible to obtain a glass substrate for a magnetic recording medium that does not generate scratches (cracks, chips), eliminates foreign matters on the main surface caused by particles trapped by scratches on the end face, and has high glass strength. Furthermore, when a magnetic recording medium is produced using the glass substrate, foreign matter on the main surface of the glass substrate can be reduced, so that thermal asperity can be reduced.

  In addition, scratching (cracking or chipping) does not occur on the end face during shape processing by chemical etching, so that grinding and polishing of the end face becomes unnecessary. Therefore, the end face formed by etching can be used as the final end face of the glass substrate for magnetic recording medium, and the number of steps can be reduced.

  Although a case where a negative resist is used is shown, the present invention can also be carried out using a positive resist. In that case, the light shielding portion and the exposure portion of the photomask 33 may be reversed. That is, a mask in which a light shielding film is formed only on a portion where the outer annular portion 22 and the inner annular portion 23 which are light shielding films of the photomask 33 are not formed may be used. Further, although an example in which a resist is used as an etching mask has been described, a similar mask can be used by forming a film of metal or the like that can withstand an etching solution. In that case, a film of metal or the like having the same shape as the resist pattern is formed on the glass base plate 31 to serve as an etching mask. By using a film having good adhesion to the glass base plate 31 as an etching mask, it is possible to prevent the etching liquid from entering the surface of the glass base plate 31, the etching mask, and the interface.

  Next, the magnetic recording medium according to the present invention will be described. The magnetic recording medium of the present invention is obtained by forming at least a magnetic layer on a glass substrate manufactured by the above-described glass substrate manufacturing method.

  In the magnetic recording medium of the present invention, since there is no scratch (crack or chipping) on the end face of the glass substrate, it becomes possible to produce a magnetic recording medium having high glass strength while reducing thermal asperity. .

  A magnetic recording medium is usually manufactured by sequentially laminating an underlayer, a magnetic layer, a protective layer, and a lubricating layer on a glass substrate. A magnetic recording medium usually has a predetermined flatness and surface roughness, and a base layer, a magnetic layer, a protective layer, and a lubricating layer are sequentially formed on a glass substrate subjected to a chemical strengthening treatment on the surface as necessary. Manufactured by stacking. The underlayer in the magnetic recording medium of the present invention is appropriately selected according to the magnetic layer.

  Examples of the underlayer include an underlayer made of at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, and Al. In the case of a magnetic layer containing Co as a main component, Cr alone or a Cr alloy is preferable from the viewpoint of improving magnetic characteristics. Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. Examples thereof include multilayer underlayers such as Cr / Cr, Cr / CrMo, Cr / CrV, CrV / CrV, Al / Cr / CrMo, Al / Cr / Cr, Al / Cr / CrV, and Al / CrV / CrV. .

  The material of the magnetic layer in the magnetic recording medium of the present invention is not particularly limited. Examples of the magnetic layer include magnetic thin films such as CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt containing Co as a main component, CoNiCrPt, CoNiCrTa, CoCrTaPt, and CoCrPtSiO. The magnetic layer may be a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrTaPt / CrMo / CoCrTaPt, etc.) in which the magnetic film is divided by a non-magnetic film (for example, Cr, CrMo, CrV) to reduce noise. Good.

As a magnetic layer corresponding to a magnetoresistive head (MR head) or a giant magnetoresistive head (GMR head), a Co-based alloy, an impurity element selected from Y, Si, rare earth elements, Hf, Ge, Sn, and Zn Or those containing oxides of these impurity elements. As the magnetic layer, in addition to the above, ferritic, iron - rare-earth and, Fe in a non-magnetic film made of SiO _2, BN, Co, FeCo, the structure in which the magnetic particles are dispersed, such CoNiPt granular It may be a film or the like. The magnetic layer may be used for an in-plane recording format or may be used for a vertical recording format.

  The protective layer in the magnetic recording medium of the present invention is not particularly limited. Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective films can be continuously formed by an in-line sputtering apparatus together with an underlayer, a magnetic layer, and the like. These protective films may be a single layer, or may have a multilayer structure composed of the same or different films.

  The lubricating layer in the magnetic recording medium of the present invention is not particularly limited. For example, the lubricating layer may be obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and applying it to the surface of the medium by dipping, spin coating, or spraying. Go and form.

  As described above, in the magnetic recording medium according to the present invention, since the glass substrate manufactured by the above-described method for manufacturing a glass substrate for magnetic recording medium according to the present invention is used, the occurrence of thermal asperity is reduced. At the same time, a magnetic recording medium having high glass strength can be manufactured.

[Example]
Examples carried out to clarify the effects of the present invention will be described below. In this example, a glass substrate for a magnetic recording medium and a magnetic disk were manufactured through the following steps. In the following description, an example of manufacturing a 2.5-inch magnetic disk glass substrate and a magnetic disk will be described. However, the size of the magnetic disk glass substrate and the magnetic disk is not particularly limited. 1.8 inch, 1 inch, and 3.5 inch sizes may be used.

(1) Lapping process First, a multicomponent glass base plate made of amorphous glass was prepared. The glass type of the glass is aluminosilicate glass, and this glass base plate was formed by a float process to form a glass base plate having a sheet shape and a size of 150 × 150 × 0.8 mm.

  Next, both main surfaces of the sheet glass were lapped to form a disk-shaped glass base material. This lapping process was performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism.

(2) End surface formation process This process is a process of forming the final end surface of the glass substrate for magnetic recording media by processing the glass base plate into an annular glass substrate. This process can be further divided into (2-1) resist coating process, (2-2) resist exposure, development process, (2-3) splitting process, and (2-4) resist stripping process. Hereinafter, each step will be described.

(2-1) Resist application process A resist application process is a process of apply | coating the resist film which plays the role of the etching mask (protective film) at the time of etching parting of glass. For the resist film, a hydrofluoric acid-resistant negative resist was used. Then, after applying the resist agent, the substrate was put into an oven to dry the resist film.

(2-2) Resist exposure and development process The resist exposure and development process is a process for dissolving the resist film on the etching portion in order to divide the glass etching into a predetermined shape. For exposure, exposure was performed through a photomask. As the photomask, the photomask having the shape described with reference to FIG. 2 was used. Then, both sides were exposed simultaneously. A developing solution (Na ₂ CO ₃ solution) was used in the developing step.

(2-3) Dividing Step The dividing step is a step in which glass is dissolved by etching using a hydrofluoric acid aqueous solution and divided into a predetermined shape. Etching was performed using a mixed acid aqueous solution of hydrofluoric acid and hydrochloric acid.

(2-4) Resist stripping step The resist stripping step is a step of stripping the resist film from the divided glass. By leaving the divided glass substrate for 1 day, the resist film was dried and peeled off. By drying and peeling the resist film, an increase in the surface roughness of the substrate used as the glass substrate for the magnetic disk can be reduced as compared with the case of peeling using the solution.

  As described above, the glass base plate was processed into an annular glass substrate by the (2) end face forming step. Furthermore, since it was processed by etching, there is no scratch on the end face, and it is not necessary to grind or polish the end face. Therefore, the end face formed by this process can be the final end face of the magnetic disk.

(3) Main surface polishing step As the main surface polishing step, first, a first polishing step was performed. This first polishing step is performed on the glass substrate after the end face is formed, and the main purpose is to remove scratches and distortions remaining on the main surface in the lapping step. A preliminary polishing step was performed using a polishing apparatus capable of polishing both surfaces. As the polishing pad, a hard urethane pad preliminarily containing zirconium oxide and cerium oxide was used. The polishing liquid was prepared by mixing cerium oxide abrasive grains having an average particle diameter of 1.2 μm with water.

  The glass substrate that has finished the first polishing step is sequentially immersed in cleaning baths of neutral detergent, pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying) for cleaning. did.

  Next, a second polishing step (mirror polishing step) was performed as the main surface polishing step. The second polishing step is a step of further polishing the first polished glass base plate until the surface of the glass base plate is mirror-finished. In the second polishing step, mirror polishing of the surface was performed using a polishing pad of a polyurethane-based soft polisher with a double-side polishing apparatus having a planetary gear mechanism. The polishing liquid was prepared by adding colloidal silica particles having a grain diameter of 40 nm to ultrapure water.

  And the glass base plate which finished this 2nd grinding | polishing process is made into neutral detergent (1), neutral detergent (2), pure water (1), pure water (2), IPA (isopropyl alcohol), IPA (steam). (Dry) was sequentially immersed in each washing tank and washed. Note that ultrasonic waves were applied to each cleaning tank.

(4) Chemical strengthening process Next, the glass substrate which finished the lapping process and the grinding | polishing process mentioned above was chemically strengthened. For chemical strengthening, a chemical strengthening solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed is prepared, this chemical strengthening solution is heated to 380 ° C., and the cleaned glass substrate is placed therein for about 4 hours. This was done by dipping. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, it was carried out in a state of being accommodated in a holder so that a plurality of glass substrates were held at the end surfaces.

  Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of the surface layer of a glass substrate are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass substrate is strengthened. The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 μm.

  The glass substrate that had been subjected to the chemical strengthening treatment was immersed in a water bath at 20 ° C. for rapid cooling and maintained for about 10 minutes. And the glass substrate which finished quenching was immersed in the concentrated sulfuric acid heated at about 40 degreeC, and was wash | cleaned. Further, the glass substrate after the sulfuric acid cleaning was cleaned by immersing in a cleaning tank of pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam drying). In addition, ultrasonic waves were applied to each cleaning tank.

  As described above, the lapping process, the edge forming process, the main surface polishing process (first and second polishing processes), and the chemical strengthening process are performed, so that the end face is not damaged and the glass substrate for a high-rigidity magnetic recording medium is used. Got.

(5) Precision cleaning process Next, the glass disk was precisely cleaned. This is to remove abrasive residues and the like that cause head crashes and thermal asperities, and to obtain a glass substrate having a smooth surface and a clean surface. This precision cleaning process includes the following series of cleaning processes.

  First, a cleaning process using a cleaning solution was performed. An alkaline chemical solution was used as the cleaning solution. The glass disk was immersed in this cleaning solution and then washed for 2 minutes while rocking. At this time, the temperature of the cleaning liquid was set to 50 ° C., and ultrasonic waves were applied to enhance the cleaning effect.

  Next, the water rinse washing | cleaning process was performed for 2 minutes. This is for removing the residue of the cleaning liquid used in the above-described cleaning. Then, the IPA cleaning process was performed for 2 minutes. This is for cleaning the glass disk and removing water on the glass substrate. Finally, the IPA vapor drying process was performed for 2 minutes. This is for drying while removing the liquid IPA adhering to the glass substrate with the IPA vapor.

(6) Magnetic disk manufacturing process A seed layer, Cr underlayer, CrMo underlayer, CoPtCrTa magnetic layer, hydrogenated carbon protection on both surfaces of the glass substrate obtained through the above-described steps using a single-wafer sputtering apparatus. A layer was formed, and a perfluoropolyether lubricating layer was formed by a dip method to produce a magnetic disk.

[Comparative Example 1]
In order to compare with the Example mentioned above here, as the comparative example 1, the end surface formation process by the conventional method was implemented, and the glass substrate was produced. That is, the outer periphery of the glass substrate was processed with a diamond cutter, and the center hole was processed with a core drill using diamond abrasive grains. Thereafter, the inner peripheral end face and the outer peripheral end face of the annular glass substrate obtained by the above processing were polished and mirror-finished. The polishing in this step was performed with a brush or the like using cerium oxide as an abrasive. Processes other than the end face forming process were the same as in this example. However, for Comparative Example 1, no chemical strengthening treatment was performed.

[Comparative Example 2]
Next, as Comparative Example 2, a glass substrate prepared in Comparative Example 1 was subjected to chemical strengthening treatment. The chemical strengthening treatment was performed under the same conditions as in the examples.

[Surface observation]
Surface observation of the end face and the main surface was performed on the glass substrate for magnetic recording medium manufactured by the method for manufacturing the glass substrate for magnetic recording medium in this example and the glass substrate manufactured by the above Comparative Examples 1 and 2. About the Example, the surface observation was carried out about what was not chemically strengthened (Example 1) and what was chemically strengthened (Example 2). Surface observation was performed using an electron microscope (4000 times).

  As a result, in Example 1 and Example 2, no foreign matter or scratches (cracks, chipping) were observed on the outer peripheral end surface and the inner peripheral end surface of the magnetic recording medium glass substrate, and the end surface was in a mirror state. No foreign matter was observed on the main surface of the glass substrate. This is because, in the case of the method for producing a glass substrate for a magnetic recording medium according to the present embodiment, the end surface is formed by etching, so that the end surface is not damaged, and the particle is not attached to the main surface due to the end surface. It shows that.

  When surface observation was similarly performed for Comparative Example 1 and Comparative Example 2, fine scratches (cracks, cracks) were observed on the outer peripheral end surface and the inner peripheral end surface. In addition, on the main surface of the glass substrate, particles that could cause thermal asperity were observed when a magnetic disk was produced using this glass substrate.

  This is because in Comparative Example 1 and Comparative Example 2, the outer peripheral end surface and the inner peripheral end surface were not sufficiently polished, so that fine scratches remained on the end surfaces, and the particles were captured by the scratches. It is thought that it adhered to the surface during this period.

[Bending strength test]
Furthermore, with respect to the above-described Example 1, Example 2, Comparative Example 1 and Comparative Example 2, the bending strength was measured using the bending strength tester (Shimadzu Autograph DDS-2000) shown in FIG. In this bending strength tester, a glass substrate 42 as a test object is placed on a substrate holder 41, a rigid sphere 43 is placed on a circular hole of the glass substrate 42, and the rigid sphere 43 is placed on the rigid sphere 43 via a load cell 44. And the bending strength of the glass substrate 42 is measured. Since only the outer peripheral portion of the glass substrate 42 is supported by the substrate holder 41, the glass substrate 42 bends and increases the pressure of pressure when the circular hole portion in the center is pressed from above. As a result, the glass substrate 42 is broken at the limit of the strength of the glass substrate. The pressure at that time is used as the bending strength of the glass substrate 42.

  As a result of performing the bending strength measurement for each of the above-described Example 1, Example 2, Comparative Example 1 and Comparative Example 2, the glass substrate for a magnetic recording medium according to this example was subjected to chemical strengthening treatment. Even in Example 1 that was not present, a higher bending strength was obtained compared to Comparative Example 1 (without chemical strengthening treatment) and Comparative Example 2 (with chemical strengthening treatment). About Example 2 which carried out the chemical strengthening process, the bending strength became higher than Example 1. FIG.

  These results show that in Comparative Example 1 and Comparative Example 2 in which the end surfaces are formed by the conventional method, as shown in the results of the surface observation, fine scratches remain on the end surfaces. This indicates that a glass substrate having high strength could not be obtained.

  On the other hand, in this example, by adopting etching for forming the end face of the glass substrate, scratches are not generated on the end face, and a high-strength glass substrate can be obtained even before chemical strengthening. It was.

[Recording and playback test]
Next, a magnetic disk was prepared using the glass substrates of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively, and a recording / reproducing test was performed. The recording / reproducing test was performed by a perpendicular recording method using a magnetic head in which the reproducing element portion was a magnetoresistive element, the recording element portion was a single magnetic pole element, and the flying height was 8 nm.

  As a result, in Example 1 and Example 2, it was confirmed that information was normally recorded and reproduced. At that time, recording / reproduction could be performed at 100 gigabits per square inch without detecting a thermal asperity signal as a reproduction signal. This indicates that in Example 1 and Example 2, since the end face was formed by the etching process, no scratch was generated on the end face, and there was no adhesion of particles to the main surface due to the scratch on the end face.

  On the other hand, in Comparative Example 1 and Comparative Example 2, a thermal asperity signal was detected in the reproduction signal. From this result, in Comparative Example 1 and Comparative Example 2, since the polishing of the outer peripheral end surface and the inner peripheral end surface was insufficient, fine scratches remained on the end surfaces, and the particles were captured by the scratches. It is thought that it adhered to the surface during the process.

  From the above inspection results, in the method for manufacturing a glass substrate for a magnetic recording medium according to the present invention, since the etching is used for forming the end surface of the glass substrate, the end surface is not damaged. It was confirmed that a glass substrate for a magnetic recording medium having a high glass strength can be obtained while reducing foreign matters on the main surface caused by particles.

  Moreover, in the magnetic recording medium using the glass substrate in the present invention, it was confirmed that the thermal asperity can be reduced because foreign matters on the main surface of the glass substrate can be reduced.

  Furthermore, since the end face forming step in the present invention forms the outer shape by etching that does not cause scratches on the end face, the end face formed by etching is not required for grinding and polishing steps of the end face. The final end face can be obtained, and man-hours can be reduced.

  Furthermore, in this embodiment, the main surface is polished after the end face is formed. Therefore, even when the main surface is roughened by a chemical solution or the like when the resist as the protective film is peeled off, it is mirrored by the subsequent main surface polishing. The main surface could be obtained.

  In addition, this invention is not limited to the said embodiment, It can implement by changing suitably. For example, in the present embodiment, the method of polishing the main surface after removing the resist that is the protective film is shown, but the present invention is not limited to this, and for example, the resist is removed by polishing in the main surface polishing step. You can also. In that case, the step of stripping the resist can be omitted, and the number of steps can be reduced.

  In this embodiment, the method of polishing the main surface after forming the end surface is shown, but the present invention is not limited to this. For example, after polishing the main surface, a protective film is formed on the main surface to form the end surface. You can also. In that case, since the main surface after polishing is protected by the protective film, it is not damaged during the end face forming step.

  In the present embodiment, an example in which the end face is not polished after the end face forming process is shown; however, the present invention is not limited to this, and the end face may be polished after the end face forming process. According to this method, since the end surface is not formed by machining, it is possible to further prevent particles from adhering to the end surface by polishing the end surface (mirror surface) with almost no cracks on the end surface.

  In addition, the material, size, processing procedure, and the like in the above-described embodiment are merely examples, and various modifications can be made within the range where the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

The figure which shows the external appearance of the magnetic disc in embodiment of this invention. The figure which shows the external appearance of the photomask used for the manufacturing process of the glass substrate for magnetic discs in embodiment of this invention. The figure for demonstrating the manufacturing process of the glass substrate for magnetic discs in embodiment of this invention. The figure which shows the external appearance of the bending strength tester in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Glass substrate 12 Circular hole 13 Outer peripheral end surface 14 Inner peripheral end surface 21 Transparent substrate 22 Outer ring part 23 Inner ring part 31 Glass base plate 32 Negative resist 33 Photomask 34 Annular glass substrate 41 Substrate holder 42 Glass substrate 43 Hard sphere 44 load cell

Claims (6)

A step of forming a protective film in a region of the main surface of the glass substrate in the main surface of the sheet-like glass base plate;
Etching the glass base plate using the protective film as an etching mask to form an outer surface of the glass substrate and form an end surface of the glass substrate,
The manufacturing method of the glass substrate for magnetic recording media containing this.   The method for producing a glass substrate for a magnetic recording medium according to claim 1, further comprising a main surface polishing step of polishing the main surface of the glass substrate after the end face forming step.   The method for manufacturing a glass substrate for a magnetic recording medium according to claim 2, wherein the protective film is removed by polishing in the main surface polishing step.   The method for producing a glass substrate for a magnetic recording medium according to claim 1, further comprising a step of mirror-polishing the main surface of the glass base plate before the step of forming the protective film.   The method for producing a glass substrate for a magnetic recording medium according to claim 1, further comprising an end surface polishing step for polishing the end surface after the end surface forming step.   A glass substrate produced by the method for producing a glass substrate for a magnetic recording medium according to any one of claims 1 to 5, and a magnetic layer formed on the glass substrate directly or via another layer. Magnetic recording medium.

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