JP2013016217A - Glass substrate for hdd, manufacturing method of glass substrate for hdd, and magnetic recording media for hdd - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate for an HDD by which deformation of a magnetic recording medium can be suppressed when the magnetic recording medium is mounted on a hard disk drive.SOLUTION: A glass substrate 50 for an HDD has a circular hole 50a at a center part. When the radius of the circular hole is r, and the maximum value, minimum value, and average value of the thickness of the glass substrate 50 are tmax, tmin, and tave, respectively, measured along a circle C concentric with the circular hole 50a present between a first circle c1 having a radius of r+0.30 mm and concentric with the circular hole 50a and a second circle c2 having a radius of r+4 mm and concentric with the circular hole 50a, the following relationship is satisfied: tmax≤tave+0.05 μm and tmin≥tave-0.05 μm.

Description

  The present invention relates to a glass substrate for HDD, a method for producing a glass substrate for HDD, and a magnetic recording medium for HDD.

  2. Description of the Related Art Conventionally, an HDD magnetic recording medium mounted on a hard disk drive (HDD) is known as one of information recording media mounted on an information storage device. In recent years, magnetic recording media for HDDs are strongly demanded to increase the recording capacity. Therefore, there is an urgent need to expand the recording area and increase the recording density. In order to increase the recording density, it is necessary to reduce the flying height of the magnetic head and improve the positioning accuracy of the head slider.

  Generally, when a magnetic recording medium is mounted on a hard disk drive, as described in Patent Document 1, for example, the magnetic recording medium is assembled to a rotating shaft of a spindle motor using a hub and a clamp. First, a circular hole formed in the central portion of the magnetic recording medium is fitted into a hub provided integrally with the rotation shaft of the spindle motor. As a result, one surface side of the inner peripheral edge around the circular hole of the magnetic recording medium (hereinafter, the region in the vicinity of the substrate end face is referred to as an end) comes into contact with and is supported by the hub. Next, the clamp is integrally fastened to the rotation shaft of the hub and the spindle motor by a screw screwed into the shaft center of the hub. As a result, the other surface side of the inner peripheral edge around the circular hole of the magnetic recording medium is supported by being pressed to the hub side by the clamp. The inner peripheral edge of the magnetic recording medium is a clamped part when mounted on a hard disk drive, and this part is clamped between the hub and the clamp so that the magnetic recording medium is integrally coupled to the rotation shaft of the spindle motor. Is done.

  However, the magnetic recording medium may be deformed when mounted on the hard disk drive. This deformation hinders the reduction of the flying height of the magnetic head and the improvement of the positioning accuracy of the head slider, and hinders an increase in recording density and an increase in recording capacity.

  Therefore, as disclosed in Patent Document 1, for example, it has been proposed to improve the mechanical structure on the drive side for sandwiching the magnetic recording medium and to suppress deformation of the magnetic recording medium when mounted on a hard disk drive. Yes.

JP 2007-66476 A

  In recent years, high-density recording has been increasingly progressed, and in the future, for example, a magnetic recording medium for HDDs having a recording capacity of 500 GB and a surface recording density of 630 Gb / square inch or more with one 2.5-inch recording medium will appear. Expected. In addition, the track pitch width of recording media continues to decrease, and in fact, magnetic recording media for HDDs having a track pitch width of 250 kTPI or more have also appeared. With the progress of such high-density recording, the allowable amount of deformation of the magnetic recording medium when mounted on a hard disk drive has become increasingly severe. The current situation cannot be solved only by improving the mechanical structure on the drive side as described above.

  Therefore, an object of the present invention is to provide a hard disk drive with a surface recording density of a magnetic recording medium of 630 Gb / square inch or more or a track pitch width of 250 kTPI or more enough to cope with high density recording. An object of the present invention is to provide an HDD glass substrate, an HDD glass substrate manufacturing method, and an HDD magnetic recording medium, in which deformation of the magnetic recording medium can be suppressed.

  As described in Patent Document 1, the reason why the magnetic recording medium is deformed when mounted on a hard disk drive is that the inner peripheral edge around the circular hole that is the clamped portion is unevenly loaded from the hub and clamp side. Is known to be one of the reasons. Conventionally, in order to prevent the load from acting unevenly on the inner peripheral end portion, for example, the improvement on the drive side, such as increasing the mechanical accuracy of the hub and the clamp, has been mainly performed.

  The inventor of the present invention has focused on the fact that the improvement on the drive side that has been conventionally performed is based on the premise that the inner peripheral end, which is the clamped portion on the recording medium side, is sufficiently flat. However, the inner peripheral edge of the magnetic recording medium is not always sufficiently flat. If the thickness of the inner peripheral edge of the magnetic recording medium varies, even if the inner peripheral edge is sandwiched in parallel by the hub and the clamp, the load acts unevenly on the inner peripheral edge, and as a result, the recording medium May be deformed. The present inventor has found the above and completed the present invention.

  That is, one aspect of the present invention is a glass substrate for HDD having a circular hole in the center, wherein the circular hole has a radius r and a radius r + 0.30 mm, a first circle concentric with the circular hole, The maximum value of the thickness of the glass substrate measured along the concentric circle with the circular hole is tmax, the minimum value is tmin, and the average value is between the circular hole and the second concentric circle having a radius of r + 4 mm. The HDD glass substrate is characterized in that tmax ≦ tave + 0.05 μm and tmin ≧ tave−0.05 μm when tave is set.

  According to the glass substrate for HDD of such a configuration, the glass at the inner peripheral end portion around the circular hole (in the present invention, a range of 4 mm radially outward from the inner peripheral end surface of the glass substrate defining the outer periphery of the circular hole). Substrate thickness variation (= | (thickness t) − (average thickness value) |) is extremely small (up to 0.05 μm), and the difference in the thickness of the inner peripheral edge of the glass substrate is at most positive. Since the sum of 0.05 μm on the side and 0.05 μm on the negative side is only 100 nm, the inner peripheral edge of the glass substrate, which is the clamped part, is flat enough to cope with the recent high-density recording It is. Therefore, the glass substrate for HDD of the present invention has a uniform load applied to the inner peripheral end when the inner peripheral end is sandwiched between the hub and the clamp, and can sufficiently cope with the recent high-density recording. This is a high-quality glass substrate for HDD that can suppress deformation of the recording medium to such an extent.

  The glass substrate for HDD of the present invention is preferably used for a substrate of a magnetic recording medium for HDD having a surface recording density of 630 Gb / square inch or more or a magnetic recording medium for HDD having a track pitch width of 250 kTPI or more.

  According to the glass substrate for HDD of such a configuration, realization of a high-density magnetic recording medium for HDD that is expected to appear in the future, or high-density magnetic recording for HDD that is currently appearing. This can contribute to stable production of the medium.

  Another aspect of the present invention is a method for manufacturing the glass substrate for HDD, wherein the polishing step is performed by sandwiching the glass substrate between an upper surface plate and a lower surface plate, and the upper surface plate after the polishing step. And a parallelism correction step of correcting the parallelism between the lower surface plate and the lower surface plate.

  According to the method for manufacturing a glass substrate for HDD having such a configuration, the parallelism between the upper surface plate and the lower surface plate used in the polishing step is corrected every time the polishing step is completed. The parallelism between the two main surfaces is always maintained in a good state. For this reason, the variation in the thickness of the glass substrate to be manufactured is always extremely small, and the flatness of the inner peripheral end that is the clamped portion when mounted on the hard disk drive is always maintained in a good state. Therefore, when the inner peripheral edge is sandwiched between the hub and the clamp, the load is uniformly applied to the inner peripheral edge, and the deformation of the recording medium is suppressed to such an extent that it can sufficiently cope with the recent high-density recording. It is possible to always stably produce a high-quality glass substrate for HDD.

  Another aspect of the present invention is a method for manufacturing a glass substrate for HDD, wherein an inner peripheral edge polishing step for polishing an inner peripheral edge of a glass substrate between a first circle and a second circle. The manufacturing method of the glass substrate for HDD characterized by including.

  According to the method for manufacturing a glass substrate for HDD having such a configuration, a circular hole having a radius of r + 0.30 mm and a concentric circle (first circle), and a circular hole having a radius of r + 4 mm and a concentric circle (second circle). Since the inner peripheral end of the glass substrate between the two is polished, the flatness of the inner peripheral end, which is the clamped portion when mounted on the hard disk drive, is improved. Therefore, when the inner peripheral edge is sandwiched between the hub and the clamp, the load is uniformly applied to the inner peripheral edge, and the deformation of the recording medium is suppressed to such an extent that it can sufficiently cope with the recent high-density recording. It is possible to stably produce a high-quality glass substrate for HDD.

  Yet another aspect of the present invention is an HDD magnetic recording medium manufactured by providing a recording layer on a main surface of the HDD glass substrate.

  According to the magnetic recording medium for HDD of such a configuration, the inner peripheral end which is a clamped portion when mounted on a hard disk drive is flat enough to cope with the recent high-density recording, When the inner peripheral edge is sandwiched between the hub and the clamp, the load acts uniformly on the inner peripheral edge, and the deformation of the recording medium can be suppressed to the extent that it can sufficiently cope with the recent high density recording. Because a high-quality glass substrate for HDD is used as a substrate, deformation when mounted on a hard disk drive can be suppressed to a level that can sufficiently cope with the recent high-density recording. It is a magnetic recording medium. Therefore, the magnetic recording medium for HDD is capable of reducing the flying height of the magnetic head and improving the positioning accuracy of the head slider, thereby contributing to an increase in recording density and an increase in storage capacity.

  According to the present invention, an HDD glass substrate, an HDD glass substrate manufacturing method, and an HDD magnetic recording medium that can sufficiently cope with recent high-density recording are provided. This can contribute to an increase in recording capacity.

It is a perspective view of the glass substrate for HDD which concerns on embodiment of this invention. It is a manufacturing-process figure of the conventional glass substrate for HDD. It is a schematic side view which shows the structure of the principal part of the double-side polisher used by a secondary polishing process. It is a partial expanded longitudinal cross-sectional view of the glass substrate for demonstrating the thickness of the glass substrate which concerns on embodiment of this invention. It is a manufacturing-process figure of the glass substrate for HDD which concerns on embodiment of this invention. It is a manufacturing-process figure of another glass substrate for HDD which concerns on embodiment of this invention. It is a schematic longitudinal cross-sectional view which shows the structure of the principal part of the inner peripheral edge part grinder used at an inner peripheral edge part grinding | polishing process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to this embodiment.

<Method for producing glass substrate for HDD>
The manufacturing method of the glass substrate for HDD is demonstrated with reference to the glass substrate 50 shown in FIG. 1, and the manufacturing-process figure shown in FIG.

  In the present embodiment, the HDD glass substrate 50 includes a disk processing step, a lapping step, a primary polishing (rough polishing) step, a secondary polishing (precision polishing) step, a chemical strengthening step, a final cleaning step, an inspection step, and the like. It is manufactured after.

Glass material used for the glass substrate 50 is composed of a glass composition whose main component is silicon dioxide (SiO _2). The glass composition may or may not contain magnesium, calcium and / or cerium. Typical glass compositions include, for example, SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, BaO, SrO, ZnO and the like. is there.

[Disc machining process]
In the disk processing step, a disk-shaped glass substrate (blanks) is produced by pouring a molten glass material into a mold and press-molding it. As the size of the glass substrate at this time, for example, the outer diameter is 2.5 inches, 1.8 inches, 1.0 inches, 0.8 inches, etc., and the plate thickness is 2 mm, 1 mm, 0.8 mm, 0 .63 mm or the like. A circular hole 50a (see FIG. 1) is formed in the center portion of the obtained glass substrate using, for example, a diamond core drill or the like to obtain an annular glass substrate.

[Lapping process]
The lapping process includes a first lapping process and a second lapping process. In the first lapping step, both the front and back surfaces of the glass substrate are ground, and the overall shape of the glass substrate, that is, the parallelism, flatness, thickness and the like of the glass substrate are preliminarily adjusted. In the second lapping step, following the first lapping step, both the front and back surfaces of the glass substrate are ground again to further finely adjust the overall shape of the glass substrate, that is, the parallelism, flatness, thickness and the like of the glass substrate. In the lapping process, for example, a double-side grinding machine including an upper and lower surface plate on which diamond pellets are attached is used.

[Primary polishing process]
In the primary polishing step, the front and back surfaces of the glass substrate are roughly polished so that the surface roughness, parallelism, flatness, thickness, and the like of the glass substrate finally obtained in the next secondary polishing step can be efficiently obtained. . In this primary polishing step, for example, a double-side polishing machine including a pair of upper and lower surface plates to which a foamed urethane pad is attached as a polishing pad is used, and a polishing liquid (slurry) containing, for example, cerium oxide as polishing abrasives Is used. However, it is not limited to this.

[Secondary polishing process]
In the secondary polishing step, following the primary polishing step, the front and back surfaces of the glass substrate are precisely polished so that the finally obtained surface roughness, parallelism, flatness, thickness, etc. of the glass substrate are obtained. In the secondary polishing step, as shown in FIG. 3, a double-side polishing machine 10 capable of simultaneously polishing both the front and back surfaces of the glass substrate 50 is used.

  The double-side polishing machine 10 includes a disk-shaped upper surface plate 11 and a lower surface plate 12 which are arranged at intervals in the vertical direction so as to be parallel to each other and are rotatable in opposite directions. A polishing pad (a polyurethane suede pad in this embodiment) P for polishing the front and back surfaces of the glass substrate 50 is attached to the opposing surfaces of the pair of upper and lower surface plates 11 and 12. A plurality of rotatable carriers 13 are arranged between the surface plates 11 and 12, and a plurality of glass substrates 50 are fitted and set in each carrier 13. The carrier 13 revolves around the rotation center of the surface plates 11 and 12 while rotating while holding the glass substrate 50. A polishing liquid (slurry) containing abrasive grains (colloidal silica in this embodiment) is applied to the upper and lower surface plates 11 and 12 and the carrier 13 that are operating in this manner. 50 and between the polishing pad P of the lower surface plate 12 and the glass substrate 50, whereby the glass substrate 50 is sandwiched between the upper surface plate 11 and the lower surface plate 12, both front and back surfaces. Precision polishing is performed.

  In FIG. 3, reference numeral 14 denotes a polishing liquid recovery device, reference numeral 15 denotes a polishing liquid storage tank, reference numeral 16 denotes a polishing liquid supply pipe, reference numeral 17 denotes a lubricating liquid storage tank, and reference numeral 18 denotes a lubricating liquid supply pipe.

[Chemical strengthening process]
In the chemical strengthening step, a chemical strengthening layer is formed on the surface of the glass substrate. For example, by immersing a glass substrate in a chemical strengthening treatment solution containing sodium ions and potassium ions, lithium ions and sodium ions present on the surface layer of the glass substrate are replaced with sodium ions and potassium ions in the chemical strengthening treatment solution. The surface layer of the glass substrate becomes a chemically strengthened layer. A compressive stress is applied to the chemically strengthened layer. By forming such a chemically strengthened layer, the impact resistance, vibration resistance, heat resistance, and the like of the finally obtained glass substrate 50 are improved.

[Final cleaning process]
In the final cleaning step, foreign substances adhering to the glass substrate include, for example, filtered pure water, ion-exchanged water, ultrapure water, acidic detergent, neutral detergent, alkaline detergent, organic solvent, surfactant and the like. Wash and remove using various cleaning solutions. Thereafter, the glass substrate is dried.

[Inspection process]
In the inspection process, the flatness and thickness of the glass substrate, the surface roughness, the presence or absence of defects, etc. are inspected. Only the glass substrate that has passed the inspection is stored in a dedicated storage cassette and vacuum packed in a clean environment so that foreign matter or the like does not adhere to the surface, and then shipped as a glass substrate for HDD.

<Conventional problems>
When an HDD magnetic recording medium using the HDD glass substrate 50 manufactured as described above as a substrate is mounted on a hard disk drive, the magnetic recording medium may be deformed. The cause is that the flatness of the inner peripheral end, which is the clamped portion of the magnetic recording medium, is insufficient, the thickness of the recording medium at the inner peripheral end varies, and the inner peripheral end is sandwiched between the hub and the clamp. Sometimes, it has been found that the load acts unevenly on the inner peripheral edge, resulting in deformation of the recording medium.

<Improvements of this embodiment>
Therefore, in the present embodiment, as shown in FIG. 1, the HDD glass substrate 50 has a circular hole 50a in the center, and the circular hole 50a has a radius r and a radius of r + 0.30 mm. A glass substrate 50 measured along a circle C concentric with the circular hole 50a between the first circular c1 concentric with 50a and the circular hole 50a having a radius of r + 4 mm and the second concentric circle c2. An HDD glass substrate 50 in which tmax ≦ tave + 0.05 μm and tmin ≧ tave−0.05 μm and tmin ≦ tave + 0.05 μm, where tmax is the maximum value of thickness, tmin is the minimum value, and tave is the average value. Improved.

  In FIG. 1, symbol C is a concentric circle with a circular hole in the inner peripheral end, symbol c1 is a concentric circle (first circle) having a radius of r + 0.30 mm, and symbol c2 is a radius of r + 4 mm. The concentric circle (second circle) and the symbol c3 are concentric with the circular hole in the recording area. The symbol O is the center of the glass substrate 50, the symbol R is the radius of the circle C (that is, r + 0.30 mm or more and r + 4 mm or less), and the symbol r1 is the radius of the first circle c1 (that is, r + 0.30 mm). , R2 is a radius (that is, r + 4 mm) of the second circle c2.

  With reference to FIG. 4, the thickness t of the glass substrate 50 which concerns on this embodiment is demonstrated. In FIG. 4, reference numerals 50 b and 50 c are main surfaces of the glass substrate 50. In the present embodiment, a reference plane S is defined on one main surface (50b in the illustrated example) of the glass substrate 50. Examples of the reference surface S include a surface perpendicular to the rotation axis of the spindle motor when mounted on a hard disk drive. More specifically, it is a surface that is most fitted to the main surface, calculated using the least square method. And thickness t when measured perpendicularly to the reference plane S is adopted.

  Such thickness t is, for example, “SI-F80R manufactured by Keyence Corporation, which measures the thickness of the measurement object by irradiating the measurement object with laser light from one side of the measurement object and analyzing the reflected light. Can be measured. In addition, a method of measuring the thickness of the measurement object by simultaneously irradiating the measurement object with laser light from both sides of the measurement object and detecting reflected light or scattered light may be used.

<Improved glass substrate for HDD>
According to the improved glass substrate 50 for HDD as described above, as shown in FIG. 1, the inner peripheral end portion around the circular hole 50a (in this embodiment, the glass substrate 50 defining the outer periphery of the circular hole 50a). The variation in thickness (= | (thickness t) − (average thickness value) |) of the thickness of the glass substrate 50 in the range of 4 mm radially outward from the inner peripheral end face is extremely small (up to 0.05 μm). The difference in the thickness of the inner peripheral end portion of the glass substrate 50 is at most 100 nm as the sum of 0.05 μm on the positive side and 0.05 μm on the negative side. Is flat enough to cope with the recent high density recording. Therefore, the improved HDD glass substrate 50 according to the present embodiment has a uniform load applied to the inner peripheral end portion when the inner peripheral end portion is sandwiched between the hub and the clamp. This is a high-quality HDD glass substrate 50 in which the deformation of the recording medium can be suppressed to such a degree that it can sufficiently cope with the manufacturing process.

  The improved HDD glass substrate 50 according to the present embodiment is used as a substrate for an HDD magnetic recording medium having a surface recording density of 630 Gb / in 2 or more or an HDD magnetic recording medium having a track pitch width of 250 kTPI or more. Is preferred. The glass substrate for HDD 50 contributes to the realization of a high-density magnetic recording medium for HDD that is expected to appear in the future, or to the stable production of the magnetic recording medium for high-density recording that is currently appearing. Because it can be done.

  If the variation in thickness of the glass substrate 50 (= | (thickness t) − (average value of thicknesses) |) exceeds 0.05 μm, the flatness of the inner peripheral end becomes insufficient. Preferably, tmax ≦ tave + 0.03 μm and tmin ≧ tave−0.03 μm (thickness variation is 0.03 μm or less). More preferably, tmax ≦ tave + 0.02 μm and tmin ≧ tave−0.02 μm (thickness variation is 0.02 μm or less).

  The reason why the maximum value of the radius of the circle C is r + 4 mm is that it is rare that the magnetic recording medium is sandwiched between the hub and the clamp beyond this value.

<Specific manufacturing method 1>
With reference to FIG. 5, as described above, an example of a specific method for manufacturing the glass substrate 50 in which the variation in the thickness t at the inner peripheral end portion is extremely small and the flatness of the inner peripheral end portion is extremely good will be described. To do. However, the description of the same or similar processes as those in the manufacturing process diagram of FIG. 2 is omitted, and only characteristic processes are described.

  As shown in FIG. 5, in this specific manufacturing method 1, a parallelism correction step is performed after the secondary polishing step. In the parallelism correction step, the parallelism between the upper surface plate 11 and the lower surface plate 12 that simultaneously polish both the front and back surfaces of the glass substrate 50 with the glass substrate 50 interposed therebetween in the secondary polishing step is corrected.

  More specifically, while the load distribution is confirmed using pressure-sensitive paper, the cutting process of the surface of the polishing pad P by the dresser is repeated until sufficient parallelism is achieved. Further, periodically, the polishing pad P is peeled off from the upper surface plate 11 and the lower surface plate 12, the surfaces of the upper surface plate 11 and the lower surface plate 12 are cut with a dresser, and the load distribution is confirmed using pressure-sensitive paper. After the cutting process is repeated until a high degree of parallelism is achieved, a new polishing pad P is attached to the upper surface plate 11 and the lower surface plate 12. By doing this, the parallelism between the upper surface plate 11 and the lower surface plate 12 is corrected and maintained.

  According to this specific manufacturing method 1, since the parallelism between the upper surface plate 11 and the lower surface plate 12 used in the secondary polishing step is corrected every time the secondary polishing step is completed, the glass to be manufactured The parallelism between both main surfaces of the substrate 50 is always maintained in a good state. Therefore, the variation in the thickness t of the glass substrate 50 to be manufactured is always extremely small, and the flatness of the inner peripheral end that is the clamped portion when mounted on the hard disk drive is always maintained in a good state. Therefore, when the inner peripheral edge is sandwiched between the hub and the clamp, the load is uniformly applied to the inner peripheral edge, and the deformation of the recording medium is suppressed to such an extent that it can sufficiently cope with the recent high-density recording. The high-quality glass substrate 50 for HDD which can be always produced can be stably produced.

<Specific manufacturing method 2>
Referring to FIG. 6, as described above, another example of a specific method for manufacturing glass substrate 50 in which variation in thickness t at the inner peripheral end is extremely small and flatness at the inner peripheral end is extremely good. explain. However, the description of the same or similar processes as those in the manufacturing process diagram of FIG. 2 is omitted, and only characteristic processes are described.

  As shown in FIG. 6, in this specific manufacturing method 2, an inner peripheral end portion polishing step is performed after the secondary polishing step. In the inner peripheral edge polishing step, a first circle c1 (see FIG. 1) concentric with the circular hole having a radius of r + 0.30 mm and a second circle c2 concentric with the circular hole having a radius of r + 4 mm (see FIG. 1). The inner peripheral end portion of the glass substrate 50 between the glass substrate 50 and the glass substrate 50 is polished.

  Specifically, an inner peripheral edge grinder 20 as shown in FIG. 7 is used. The inner peripheral edge polishing machine 20 includes a pair of rotating bodies 21 and 22 that face each other. The rotating bodies 21 and 22 are adjusted so that the rotational axes coincide with each other precisely. Annular polishing pads (in this embodiment, polyurethane suede pads as in the secondary polishing step) 23 and 24 are attached to the rotating bodies 21 and 22, respectively. The polishing pads 23 and 24 are formed to have a size capable of polishing at least the inner peripheral edge of the glass substrate 50 between the first circle c1 and the second circle c2. The glass substrate 50 is supported at the outer peripheral end by the outer peripheral end supporting device 25.

  Between the polishing pads 23 and 24 rotated by the rotators 21 and 22 and both surfaces of the inner peripheral edge around the circular hole 50a of the glass substrate 50 (in this embodiment, a secondary polishing step). Similarly, a polishing liquid (slurry) containing colloidal silica is supplied, whereby the inner peripheral edge of the glass substrate 50 is sandwiched between a pair of polishing pads 23 and 24 facing each other, and both front and back surfaces are polished. The

  According to the second specific manufacturing method, the circular hole 50a having a radius of r + 0.30 mm and a concentric circle (first circle) c1, and the circular hole 50a having a radius of r + 4 mm and a concentric circle (second circle) c2 Since the inner peripheral end portion of the glass substrate 50 is polished, the flatness of the inner peripheral end portion, which is a clamped portion when mounted on the hard disk drive, is improved. Therefore, when the inner peripheral edge is sandwiched between the hub and the clamp, the load is uniformly applied to the inner peripheral edge, and the deformation of the recording medium is suppressed to such an extent that it can sufficiently cope with the recent high-density recording. The high-quality glass substrate 50 for HDD that can be manufactured can be stably produced.

<Magnetic recording medium for HDD>
Next, an HDD magnetic recording medium manufactured using the HDD glass substrate 50 will be described. The HDD magnetic recording medium according to this embodiment is manufactured by providing a magnetic film as a recording layer on the main surface of the HDD glass substrate 50. The magnetic film may be formed directly or indirectly on the main surface. The magnetic film may be formed on one side or both sides of the glass substrate 50.

  As a method for forming the magnetic film, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on the glass substrate 50, or a method in which sputtering or electroless plating is used. And the like. The film thickness by spin coating is about 0.3 μm to 1.2 μm, the film thickness by sputtering is about 0.04 μm to 0.08 μm, and the film thickness by electroless plating is 0.05 μm to 0.1 μm. From the viewpoint of thinning and high density, film formation by sputtering or electroless plating is preferable.

  The magnetic material used for the magnetic film is not particularly limited, and conventionally known materials can be used. Among them, a Co-based alloy or the like containing Ni and Cr as the basic material for adjusting the residual magnetic flux density is preferable in order to obtain high coercive force. Specifically, CoPt, CoCr, CoNi, CoNiCr, CoCrTa, CoPtCr, CoNiPt, CoNiCrPt, CoNiCrTa, CoCrPtTa, CoCrPtB, CoCrPtSiO, and the like whose main component is Co are preferable.

  The magnetic film may be divided into a non-magnetic film (for example, Cr, CrMo, CrV, etc.) to have a multilayer structure (for example, CoPtCr / CrMo / CoPtCr, CoCrPtTa / CrMo / CoCrPtTa, etc.) in which noise is reduced.

The other magnetic material, ferrite or iron - and that of the rare earth, in a non-magnetic film made of _SiO 2, BN, etc., Fe, Co, FeCo, in granular or the like of the structure obtained by dispersing magnetic particles such CoNiPt Good.

  The magnetic film may be either an inner surface type or a vertical type recording format.

  In order to improve the sliding of the magnetic head, a lubricant may be thinly coated on the surface of the magnetic film. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  In the present embodiment, if necessary, an underlayer or a protective layer may be provided in addition to the magnetic film as the recording layer. The underlayer in the HDD magnetic recording medium is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from the group consisting of nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni. In the case of a magnetic film containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving magnetic characteristics. 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. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV can be used.

  The protective layer is provided to prevent wear and corrosion of the magnetic film. Examples of the protective layer include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be continuously formed by an in-line sputtering apparatus together with the underlayer and the magnetic film. Further, these protective layers may be a single layer, or may have a multilayer structure composed of the same or different layers.

Another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, colloidal silica fine particles are dispersed and applied in a tetraalkoxysilane diluted with an alcohol solvent on the Cr layer, and further baked to obtain silicon dioxide (SiO ₂ ). A layer may be formed.

  As described above, by using the HDD magnetic recording medium manufactured using the HDD glass substrate 50 according to the present embodiment as the substrate, the operation of the magnetic head at the time of high-speed rotation of the HDD can be stabilized. Can do.

  In addition, the HDD magnetic recording medium according to the present embodiment has an inner peripheral end that is a clamped portion when mounted on a hard disk drive, which is flat enough to cope with recent high-density recording, When the inner peripheral edge is sandwiched between the hub and the clamp, the load acts uniformly on the inner peripheral edge, and the deformation of the recording medium can be suppressed to the extent that it can sufficiently cope with the recent high density recording. Since the high-quality glass substrate 50 for HDD is used as the substrate, the high-quality HDD capable of suppressing deformation when mounted on the hard disk drive to a level that can sufficiently cope with the recent high-density recording. Magnetic recording medium. Therefore, the magnetic recording medium for HDD is capable of reducing the flying height of the magnetic head and improving the positioning accuracy of the head slider, thereby contributing to an increase in recording density and an increase in storage capacity.

  In the present embodiment, the polishing step is performed twice. However, the polishing step is not limited to this and may be performed only once. Moreover, although the chemical strengthening process was performed after the polishing process, it may be performed before the polishing process depending on the situation. Further, the chemical strengthening step can be omitted depending on the situation.

  Furthermore, as measures against drop strength, the outer peripheral end face and the inner peripheral end face other than the main surface of the glass substrate may be strengthened, or the glass substrate is subjected to HF immersion treatment as an edge mitigation treatment for scratches generated on the glass substrate. Also good.

  The glass substrate for HDD according to the present embodiment is not limited to the use for manufacturing a magnetic recording medium for HDD, and can be used for the manufacture of, for example, a magneto-optical disk or an optical disk.

  Hereinafter, the present invention will be described in more detail through examples and comparative examples. However, the present invention is not limited to this embodiment.

<Manufacture of glass substrates for HDD>
Example 1 is according to the manufacturing process shown in FIG. 6 (using the inner peripheral edge polishing machine 20 shown in FIG. 7), and Example 2 is according to the manufacturing process shown in FIG. Is a glass material having the following composition (mass%) according to the manufacturing process shown in FIG. 2, each having an outer diameter of about 65 mm (2.5 inches), an inner diameter (diameter of the circular hole) of 20 mm, a plate An annular aluminosilicate glass substrate having a thickness of about 0.63 mm was produced.

(Composition of glass material)
・ SiO ₂ : 50 to 70%
· _Al 2 _O 3: 0.1~20%
・ B ₂ O ₃ : 0 to 5%
However, SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ = 50 to 85%, Li ₂ O + Na ₂ O + K ₂ O = 0.1 to 20%, and MgO + CaO + BaO + SrO + ZnO = 2 to 20%.

<Evaluation of glass substrate for HDD>
[Measurement of the thickness of the inner peripheral edge]
The thickness of the inner peripheral end of the obtained glass substrate was measured using “SI-F80R” manufactured by Keyence Corporation. The circle whose thickness is measured is a first circle c1 (radius 10.30 mm) concentric with the circular hole having a radius r (10 mm) +0.30 mm of the circular hole, and a radius r (10 mm) of the circular hole. ) +4 mm, a second circle c2 (radius 14 mm) concentric with the circular hole, and a circle C (radius) in the inner peripheral end concentric with the circular hole, the radius being the radius r (10 mm) +2 mm of the circular hole 12 mm) and three circles. And in each circle, thickness variation (= | (thickness t)-(average value of thicknesses) |) was calculated, the maximum value was recorded, and the average value was obtained. The number of samples was 100 in each of Examples 1 and 2 and Comparative Examples 1 and 2. The results are shown in Table 1. The value is an average value of 100 sheets.

<Manufacture of HDD magnetic recording media>
A magnetic film (recording layer) was provided on the main surface of the obtained glass substrate to obtain a magnetic recording medium. That is, from the glass substrate side, a base layer made of Ni—Al (thickness of about 100 nm), a recording layer made of Co—Cr—Pt (thickness 20 nm), and a protective film made of DLC (Diamond Like Carbon) (thickness 5 nm) are sequentially formed. Laminated.

<Evaluation of HDD magnetic recording media>
[Measure deformation when the drive is mounted]
The inner peripheral edge of the obtained magnetic recording medium was sandwiched between a hub and a clamp and mounted on a hard disk drive. In order to investigate the degree of deformation of the mounted magnetic recording medium, the TIR (Total Indicated Runout) in the circumferential direction of the magnetic recording medium was measured. The TIR is an index of the flatness of the surface. The TIR in the circumferential direction of the magnetic recording medium is a surface that is optimally fitted to the main surface of the magnetic recording medium by a least square method to determine the height of the magnetic recording medium. The absolute value (P-V value) of the difference between the highest point (P) whose height is above the plane and the lowest point (V) below the plane, measured in the direction.

  Such TIR in the circumferential direction is, for example, a method of measuring the surface shape using interference of white light (for example, “Optiflat” manufactured by Phase Shift Technology) or laser light obliquely with respect to the surface to be measured. Can be obtained by a method (for example, “Flat Master FM100XRA” manufactured by TROPEL) or the like that can measure even with a rough surface shape. .

  The circle whose TIR in the circumferential direction was measured was a circle c3 (see FIG. 1) having a radius of 28 mm and in a recording area concentric with the circular hole. The number of samples was 100 in each of Examples 1 and 2 and Comparative Examples 1 and 2. The results are shown in Table 1. The value is an average value of 100 sheets.

[Read / write test]
The obtained magnetic recording medium was subjected to a read / write test with a magnetic head equipped with a DFH mechanism, and the number of error occurrences was recorded and evaluated according to the following criteria. The number of samples was 10,000 in each of Examples 1 and 2 and Comparative Examples 1 and 2. The results are shown in Table 1.

(Evaluation criteria)
A: 0 to 5 error occurrences (excellent quality)
○: The number of error occurrences is 6 to 10 (good product)
Δ: The number of error occurrences is 11 to 20 (although it cannot be used, the quality defect rate is high)
×: 21 or more errors occurred (defective product)

<Consideration of results>
Examples 1 and 2 in which the thickness variation of the inner peripheral edge of the glass substrate was 0.05 μm or less were compared with Comparative Examples 1 and 2 in which it exceeded 0.05 μm, when mounted on a hard disk drive. The amount of deformation of the magnetic recording medium was small, and the number of read / write errors was also small.

DESCRIPTION OF SYMBOLS 10 Polishing machine 11 Upper surface plate 12 Lower surface plate 20 Inner peripheral edge part polishing machine 21, 22 Rotating body 23, 24 Polishing pad 25 Outer peripheral edge support apparatus 50 Glass substrate 50a Circular hole 50b, 50c Main surface C In inner peripheral edge part Circle c1 First circle c2 with radius r + 0.30 mm Second circle c3 with radius r + 4 mm Circle O in the recording area Glass substrate center P Radius r of polishing pad RC R of radius r1 of circle hole r1 c1 Radius S Reference surface t Glass substrate thickness

Claims (5)

A glass substrate for HDD having a circular hole in the center,
A circular hole having a radius of r and a radius of r + 0.30 mm, a first circle concentric with the circular hole and a radius of r + 4 mm between the circular hole and the second concentric circle; When the maximum value of the thickness of the glass substrate measured along the concentric circle is tmax, the minimum value is tmin, and the average value is tave, tmax ≦ tave + 0.05 μm and tmin ≧ tave−0.05 μm. There is a glass substrate for HDD.   2. The glass substrate for HDD according to claim 1, which is used for a substrate of a magnetic recording medium for HDD having a surface recording density of 630 Gb / square inch or more or a magnetic recording medium for HDD having a track pitch width of 250 kTPI or more. It is a manufacturing method of the glass substrate for HDD according to claim 1,
A polishing step of polishing by sandwiching a glass substrate between an upper surface plate and a lower surface plate,
The manufacturing method of the glass substrate for HDD characterized by including the parallelism correction process of correcting the parallelism of an upper surface plate and a lower surface plate after a grinding | polishing process. It is a manufacturing method of the glass substrate for HDD according to claim 1,
The manufacturing method of the glass substrate for HDD characterized by including the inner peripheral edge part grinding | polishing process of grind | polishing the inner peripheral edge part of the glass substrate between a 1st circle | round | yen and a 2nd circle | round | yen.   An HDD magnetic recording medium manufactured by providing a recording layer on a main surface of the HDD glass substrate according to claim 1.

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