JP5510030B2 - Manufacturing method of glass substrate for magnetic recording medium and glass substrate for magnetic recording medium - Google Patents

Description

  The present invention relates to a method for producing a glass substrate for a magnetic recording medium and a glass substrate for a magnetic recording medium, which have excellent thickness deviation in the glass substrate surface.

  With the recent increase in recording density of magnetic disks, the required characteristics for glass substrates for magnetic recording media are becoming stricter year by year. In order to increase the recording density of the magnetic disk, the magnetic head has been passed to the end of the glass substrate in order to effectively utilize the area of the main plane of the glass substrate. In addition, in order to quickly record and reproduce a large amount of information on a magnetic disk, studies have been made to increase the rotation speed of the magnetic disk.

  When passing the magnetic head to the edge of the glass substrate or increasing the rotational speed of the magnetic disk, the shape of the glass substrate for magnetic recording media (eg, thickness deviation, edge shape, flatness, etc.) is disturbed. If so, the flying posture of the magnetic head is disturbed, and the magnetic head may come into contact with the magnetic disk and cause a failure.

  A carrier (Patent Document 1) has been proposed that improves the shape of a glass substrate for a magnetic recording medium, particularly the smoothness of the outer peripheral edge of the substrate. Further, Non-Patent Document 1 examines the influence of the difference in diameter of the glass substrate holding hole with respect to the glass substrate on the behavior of the glass substrate during polishing.

  Non-Patent Document 1 shows that when a glass substrate is polished using a double-side polishing apparatus with a diameter difference of 1.0 mm between the glass substrate holding hole and the glass substrate, the glass substrate hardly rotates in the glass substrate holding hole. Has been observed. The carrier described in Patent Document 1 polishes the glass substrate by setting the diameter difference of the glass substrate holding hole to the glass substrate for magnetic recording medium to 0.5 mm to 1.0 mm. Since the substrate hardly rotates, the in-plane surface of the glass substrate for magnetic recording medium cannot be uniformly polished, and there is a possibility that a glass substrate for magnetic recording medium having excellent thickness deviation in the glass substrate surface cannot be obtained.

  If the polishing of the glass substrate is continued, the polishing surface of the upper surface plate and the polishing surface of the lower surface plate are scraped by the glass substrate, and there is a step at the boundary between the polishing surface that contacts the glass substrate and the polishing surface that does not contact during polishing. It is formed. As described above, the step formed on the polishing surface of the upper surface plate and the polishing surface of the lower surface plate is in contact with the outer diameter side region of the glass substrate during polishing of the glass substrate, and the outer diameter side region of the glass substrate is locally localized. There is a risk of overpolishing. Therefore, it becomes difficult to make the polishing amount in the same glass substrate surface uniform, and it may be difficult to obtain a glass substrate for a magnetic recording medium excellent in parallelism.

JP 2006-198751 A

2010 Precision Engineering Society Spring Conference Academic Lecture Proceedings Page 75-76, A74 Elucidation of polishing phenomenon in skeleton double-side polishing machine Saitama University Graduate School

  An object of this invention is to provide the glass substrate for magnetic recording media which is excellent in the plate | board thickness deviation in a glass substrate surface. Also, a method of polishing a glass substrate for polishing a glass substrate for magnetic recording medium having excellent plate thickness deviation in the surface of the glass substrate with high productivity, and a method for manufacturing a glass substrate for magnetic recording medium having a process using the polishing method. For the purpose of provision.

The present invention provides a polishing step for polishing both main planes of a glass substrate for a magnetic recording medium, wherein the roundness for promoting the rotation of the glass substrate is 100 μm or less and the diameter is 1 with respect to the diameter of the disk-shaped glass substrate. A glass substrate for a magnetic recording medium, wherein a carrier having a glass substrate holding hole having a size of .10 mm to 1.90 mm is used, and the total polishing amount of both main planes of the disk-shaped glass substrate to be polished is 4 to 75 μm. A manufacturing method is provided.

  The method for producing a glass substrate for a magnetic recording medium having a polishing step using the carrier of the present invention can produce a glass substrate for a magnetic recording medium excellent in plate thickness deviation in the glass substrate surface with high productivity. A magnetic disk manufactured by forming a thin film such as a magnetic layer on a glass substrate for magnetic recording medium manufactured by the method for manufacturing a glass substrate for magnetic recording medium of the present invention is a magnetic head in an HDD (Hard Disk Drive) test. The flying posture of the magnetic head is not disturbed, and the trouble caused by the magnetic head contacting the magnetic disk can be reduced.

The perspective view of the glass substrate for magnetic recording media. The cross-sectional perspective view of the glass substrate for magnetic recording media. Schematic of a double-side polishing apparatus. Schematic of carrier. The example which measured the parallelism of the glass substrate for magnetic recording media with the laser interferometer. Interference fringe images observed with a laser interferometer and parallelism values obtained by analyzing the interference fringes.

  Hereinafter, although the form for implementing this invention is demonstrated, this invention is not restricted to embodiment described below.

  FIG. 1 is a perspective view of a glass substrate 10 for a magnetic recording medium according to the present invention, and FIG. 2 is a cross-sectional perspective view of the glass substrate 10 for a magnetic recording medium cut. In FIG. 1 and FIG. 2, each symbol indicates a main plane 101, an inner peripheral side surface 102, an outer peripheral side surface 103, an inner peripheral chamfered portion 104, and an outer peripheral chamfered portion 105 of the magnetic recording medium glass substrate. In FIG. 2, A1 and A6 are the thickness of the outer diameter side region of the glass substrate for magnetic recording medium, A2 and A5 are the thickness of the intermediate region of the glass substrate for magnetic recording medium, and A3 and A4 are the glass substrate for magnetic recording medium. The plate | board thickness of the internal diameter side area | region is shown, respectively. In the present invention, the diameter of the disk-shaped glass substrate is the diameter of the outermost peripheral surface of the outer peripheral side surface 103.

  Generally, the manufacturing process of the glass substrate for magnetic recording media and the magnetic disk includes the following processes. (1) After processing the glass base substrate formed by the float method, the fusion method or the press molding method into a disk shape, chamfering is performed on the inner peripheral side surface and the outer peripheral side surface. (2) Lapping is performed on the upper and lower main planes of the glass substrate. (3) End face polishing is performed on the side surface portion and the chamfered portion of the glass substrate. (4) Polish the upper and lower main planes of the glass substrate. The polishing step may be only primary polishing, primary polishing and secondary polishing may be performed, or tertiary polishing may be performed after secondary polishing. (5) A glass substrate for a magnetic recording medium is manufactured by precision cleaning of the glass substrate. (6) A thin film such as a magnetic layer is formed on a glass substrate for a magnetic recording medium to manufacture a magnetic disk.

  In the manufacturing process of the glass substrate for magnetic recording medium and the magnetic disk, glass substrate cleaning (inter-process cleaning) or etching of the glass substrate surface (inter-process etching) may be performed between the processes. Furthermore, when high mechanical strength is required for the glass substrate for magnetic recording media, a strengthening step (for example, a chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate is performed before the polishing step, after the polishing step, or the polishing step. You may carry out between.

  In the present invention, the glass substrate for a magnetic recording medium may be amorphous glass, crystallized glass, or tempered glass (for example, chemically tempered glass) having a tempered layer on the surface layer of the glass substrate. Moreover, the glass base substrate of the glass substrate of the present invention may be made by a float method, may be made by a fusion method, or may be made by a press molding method.

  The present invention relates to (4) a step of polishing the upper and lower main planes of a glass substrate, and relates to polishing of a glass substrate for a magnetic recording medium.

  FIG. 3 is a schematic view of the double-side polishing apparatus 20. In FIG. 3, 10 is a glass substrate for a magnetic recording medium, 30 is a polishing surface of an upper surface plate, 40 is a polishing surface of a lower surface plate, 50 is a carrier, 201 is an upper surface plate, 202 is a lower surface plate, 203 is a sun gear, 204 Indicates internal gear.

  FIG. 4 shows a schematic diagram of the carrier 50 used in the manufacturing process of the glass substrate for a magnetic recording medium. In the figure, 50 is a carrier, 501 is a glass substrate holding hole, 501A is an inner diameter side holding hole, 501B is an intermediate part holding hole, and 501C is an outer diameter side holding hole. The glass substrate holding hole 501 of the carrier 50 is formed concentrically around the center of the carrier 50.

  If the polishing of the glass substrate is continued, the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate are scraped by the glass substrate, and a step is formed at the boundary between the polishing surface that contacts the glass substrate and the polishing surface that does not contact during polishing. It is formed. The steps formed on the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate locally overpolish the outer diameter side region of the glass substrate held in the outer diameter side holding hole 501C.

  As a result of intensive studies by the present inventors, the glass substrate 10 for magnetic recording medium has the shape (roundness) of the glass substrate holding hole 501 that is easy to rotate in the glass substrate holding hole 501, and more preferably glass. When the diameter of the substrate holding hole 501 is increased with respect to the diameter of the glass substrate 10 for magnetic recording medium so that the glass substrate 10 for magnetic recording medium rotates in the glass substrate holding hole 501, the outer diameter of the glass substrate. It has been found that the side region can be suppressed from being excessively polished locally.

  The roundness of the glass substrate holding hole 501 that reliably rotates the magnetic recording medium glass substrate 10 in the glass substrate holding hole 501 is 100 μm or less. When the roundness of the glass substrate holding hole 501 is 100 μm or less, the glass substrate 10 for magnetic recording medium can surely rotate in the glass substrate holding hole 501 during polishing of the glass substrate. A side substrate is not locally overpolished and a glass substrate for a magnetic recording medium excellent in parallelism is obtained. The roundness of the glass substrate holding hole 501 is 100 μm or less, preferably 80 μm or less, particularly preferably 50 μm or less. The shape of the glass substrate holding hole 501 is measured using a contour shape measuring machine.

  The diameter of the glass substrate holding hole 501 is preferably 1.10 mm to 1.90 mm larger than the diameter of the glass substrate for magnetic recording medium.

  If the diameter of the glass substrate holding hole 501 is less than 1.10 mm, the glass substrate 10 for magnetic recording medium cannot sufficiently rotate in the glass substrate holding hole 501, and the outer diameter side region of the glass substrate is locally localized. It may be difficult to obtain a glass substrate for a magnetic recording medium that is excessively polished and has excellent parallelism. In addition, if the gap between the glass substrate 10 for magnetic recording medium and the glass substrate holding hole 501 is small, the flow of the polishing liquid becomes poor, and it becomes difficult to uniformly supply the polishing liquid to the polishing surface. Variations may occur and the plate thickness within the same lot may vary.

  When the diameter of the glass substrate holding hole 501 exceeds 1.90 mm, bubbles are likely to be mixed into the glass substrate holding hole 501, vibration is generated by the mixed bubbles, and it becomes difficult to uniformly polish the glass substrate. Or, the glass substrate or the carrier may be damaged (crash) during polishing. Further, when the diameter of the glass substrate holding hole 501 exceeds 1.90 mm, the number of glass substrates that can be filled in one carrier decreases, the strength of the carrier decreases, and the glass substrate and the carrier are damaged during polishing ( Crash) may occur.

  The diameter of the glass substrate holding hole 501 is preferably 1.10 mm to 1.90 mm larger than the diameter of the glass substrate for magnetic recording medium, more preferably 1.30 mm to 1.90 mm, and more preferably 1.30 mm to 1.90 mm. A thing larger by 85 mm is particularly preferable.

  The glass substrate 10 for magnetic recording medium is held between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate while being held in the glass substrate holding hole of the carrier 50, In a state where the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate are pressed against each other in a plane, the polishing liquid is supplied to both main surfaces of the glass substrate, and the glass substrate and the polishing surface are relatively moved, Both main planes of the glass substrate are polished simultaneously.

  The double-side polishing apparatus 20 drives the sun gear 203 and the internal gear 204 to rotate around the sun gear 203 while rotating the carrier 50 by rotating the sun gear 203 and the internal gear 204 at predetermined rotation ratios (plane driving). The surface plate 201 and the lower surface plate 202 are rotationally driven at their respective rotational speeds, and both main planes of the glass substrate are polished simultaneously.

  A polishing pad is mounted on the surface of the upper surface plate 201 and the lower surface plate 202 facing the glass substrate. The polishing pads mounted on the upper surface plate 201 and the lower surface plate 202 are subjected to dressing using a dressing jig so that the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate each have a predetermined shape. Is done. In the dressing process, dressing water is supplied between the dressing jig and the polishing pad, and the dressing jig and the polishing pad are relatively moved so that the surface of the polishing pad (the surface that becomes the polishing surface 30 of the upper surface plate) The surface to be the polishing surface 40 of the lower surface plate is cut.

  In the polishing step of the present invention, the total polishing amount of both main planes of the glass substrate for a magnetic recording medium to be polished is preferably 2 μm to 80 μm. When the carrier according to the present invention is used in a polishing process in which the total polishing amount of both main planes is 2 μm to 80 μm, the glass substrate 10 for magnetic recording medium is sufficiently rotated in the glass substrate holding hole 501, so that the glass substrate An effect of suppressing local overpolishing of the outer diameter side region locally and improving the parallelism of the glass substrate for a magnetic recording medium is shown. The total polishing amount of both main planes is preferably 2 μm to 80 μm, more preferably 4 μm to 75 μm, and particularly preferably 6 μm to 70 μm.

  Regarding the parallelism of both main planes of the glass substrate for magnetic recording medium, the plate thickness (for example, A1 to A6) in each region of the glass substrate for magnetic recording medium is uniform (the plate thickness deviation in the glass substrate plane is small). It is inferior if the plate thickness in each region is non-uniform (the plate thickness deviation within the glass substrate surface is large).

  The plate thickness and parallelism of the magnetic recording medium glass substrate are measured using a measuring instrument such as a micrometer, a laser displacement meter, or a laser interferometer.

  The measurement of the plate thickness using a micrometer or a laser displacement meter is performed by measuring the plate thickness at a plurality of locations arbitrarily determined within the plane of the magnetic recording medium glass substrate, and obtaining the average value.

  The parallelism a using a micrometer or a laser displacement meter is measured by measuring the plate thickness at a plurality of points arbitrarily determined within the plane of the glass substrate for a magnetic recording medium, and calculating the maximum plate thickness value and the minimum plate thickness value. Find the difference.

  Since the laser interferometer uses the wavelength of light as a rule, it can measure the parallelism b with high accuracy. Moreover, since the parallelism b of both main planes of the glass substrate for magnetic recording media can be measured by one data acquisition, the measurement efficiency is excellent. The parallelism b of both main planes of the glass substrate for a magnetic recording medium using a laser interferometer is measured by observing interference fringes formed by the phase difference of reflected light reflected from both main planes, and the obtained interference fringes This is done by analyzing The bright and dark interference fringes observed with the laser interferometer are contour lines, and the interval is determined by the wavelength of the light source and the incident angle.

  As a result of measuring the parallelism b of both main planes of the glass substrate for magnetic recording medium with the laser interferometer (product name: Fizeau interferometer for plane measurement) used in the examples of the present invention, interference fringes The value of parallelism b obtained by analyzing the image and the interference fringes is shown in FIG.

  The smaller the number of interference fringes observed with the laser interferometer, the better the parallelism of both main planes of the glass substrate for magnetic recording media, that is, the smaller the thickness deviation in the region where the parallelism b is measured, the same. It means that the plate thickness distribution in the surface of the glass substrate is excellent.

  According to the method for manufacturing a glass substrate for a magnetic recording medium having a polishing process using the polishing method of the present invention, the outer diameter side region of the glass substrate is not locally excessively polished, and the parallel recording a has a parallelism a of 0.5 μm or less. The glass substrate for media can be manufactured with high productivity. The parallelism a of the glass substrate for a magnetic recording medium is preferably 0.5 μm or less, and particularly preferably 0.4 μm or less. Further, a glass substrate for magnetic recording medium having a deviation of the parallelism a of 0.2 μm or less between the glass substrates for magnetic recording medium polished in the same lot can be produced with high productivity.

  By the method for manufacturing a glass substrate for magnetic recording medium having a polishing step using the polishing method of the present invention, the outer diameter side region of the glass substrate is not locally excessively polished, and at least the recording / reproducing region of the glass substrate for magnetic recording medium The glass substrate for a magnetic recording medium having a parallelism b of both main planes measured by using a laser interferometer of 0.6 μm or less can be produced with high productivity. The parallelism b of the glass substrate for magnetic recording media is preferably 0.6 μm or less, and particularly preferably 0.4 μm or less. Furthermore, it is possible to manufacture a glass substrate for magnetic recording medium having a deviation of the parallelism b of 0.4 μm or less between the glass substrates for magnetic recording medium polished in the same lot.

  According to the method for manufacturing a glass substrate for a magnetic recording medium having the polishing step of the present invention, a glass substrate for a magnetic recording medium having a thickness deviation of 0.8 μm or less between glass substrates polished in the same lot is obtained with high productivity. Can be manufactured.

  In the present invention, the same lot means a glass substrate that is simultaneously polished using the same double-side polishing apparatus. For example, when polishing a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, the number of glass substrates in one lot of the 22B type double-side polishing apparatus is 150 to 222, and the number of glass substrates in one lot of the 16B type double-side polishing apparatus is 90. The number of glass substrates in one lot of 115 to 115 and 9B type double-side polishing apparatus is generally 20 to 30.

  The glass substrate for a magnetic recording medium produced by the method for producing a glass substrate for a magnetic recording medium having a polishing step using the polishing method of the present invention has a shape characteristic of the glass substrate for a magnetic recording medium (for example, plate thickness deviation, parallel Excellent). Therefore, the magnetic disk manufactured by forming a thin film such as a magnetic layer on the glass substrate for a magnetic recording medium of the present invention can be obtained without disturbing the flying posture of the magnetic head in the HDD (Hard Disk Drive) test. There is no failure to touch the magnetic disk.

  Hereinafter, the present invention will be further described with reference to examples and comparative examples, but the present invention is not limited thereto.

[Adjustment of glass substrate for magnetic recording medium]
For a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm, a glass substrate mainly composed of SiO ₂ formed by a float method is used as a donut-shaped circular glass substrate (a circular hole is formed at the center) A disk-shaped glass substrate).

  The doughnut-shaped circular glass substrate is chamfered so that a glass substrate for a magnetic recording medium having a chamfering width of 0.15 mm and a chamfering angle of 45 ° is obtained on the inner peripheral side surface and the outer peripheral side surface. The upper and lower main planes of the substrate were lapped and the abrasive grains were washed away.

  Next, the outer peripheral side surface and outer peripheral chamfered portion of the glass substrate were polished using a polishing brush and cerium oxide abrasive grains, scratches on the outer peripheral side surface and outer peripheral chamfered portion were removed, and the outer peripheral end surface was polished so as to be a mirror surface . The abrasive grains are washed and removed from the glass substrate after the outer peripheral end surface is polished. After the outer peripheral end surface is polished, the inner peripheral side surface and the inner peripheral chamfered portion of the glass substrate are polished with a polishing brush and cerium oxide abrasive grains, and scratches on the inner peripheral side surface and the inner peripheral chamfered portion are removed so that the inner surface becomes a mirror surface The peripheral end surface was polished. Abrasive grains are washed and removed from the glass substrate subjected to the inner peripheral end surface polishing.

[Primary to tertiary polishing of glass substrate for magnetic recording medium]
Next, the glass substrate is a polishing liquid containing a polishing pad made of hard urethane and cerium oxide abrasive grains as an abrasive (average particle diameter, hereinafter abbreviated as average particle diameter, polishing mainly composed of about 1.3 μm of cerium oxide. Liquid composition), 22B type double-side polishing machine (product name: DSM22B-6PV-4MH) or 16B type double-side polishing machine (product name: DSM16B-6PV-4MH) The upper and lower main planes were subjected to primary polishing.

  In the primary polishing step, the polishing pads mounted on the upper and lower surface plates of the double-side polishing apparatus are subjected to a dressing process using a dressing jig and formed on a predetermined polishing surface before polishing the glass substrate. The

The primary polishing was performed by setting the polishing time so that the main polishing pressure was 85 g / cm ² , the platen rotation speed was 30 rpm, and the total polishing amount was 40 μm in total in the thickness direction of the upper and lower main planes. In this example, one lot when polishing with the 22B type double-side polishing apparatus was 180 sheets, and one lot when polishing with the 16B type double-side polishing apparatus was 100 sheets. The glass substrate after polishing was subjected to cleaning and removal of cerium oxide, and then the plate thickness, parallelism a, and parallelism b were measured.

  The glass substrate after the primary polishing is a polishing liquid containing a polishing pad made of soft urethane as a polishing tool and cerium oxide abrasive grains having an average particle diameter smaller than that of the cerium oxide abrasive grains (average particle diameter of about 0.5 μm). 22B type double-side polishing machine (manufactured by Speedfam, product name: DSM22B-6PV-4MH), or 16B type double-side polishing machine (manufactured by Speedfam, Product name: DSM16B-6PV-4MH), the upper and lower main planes were secondarily polished.

  In the secondary polishing step, the polishing pads mounted on the upper and lower surface plates of the double-side polishing apparatus are subjected to a dressing process using a dressing jig and formed on a predetermined polishing surface before polishing the glass substrate. The

The main polishing processing pressure of the secondary polishing was 85 g / cm ² , the platen rotation speed was 30 rpm, the polishing time was set so that the total polishing amount was 6 μm in total in the thickness direction of the upper and lower main planes, and the glass substrate was polished . In this example, one lot when polishing with the 22B type double-side polishing apparatus was 180 sheets, and one lot when polishing with the 16B type double-side polishing apparatus was 100 sheets. The glass substrate after polishing was subjected to cleaning and removal of cerium oxide, and the thickness, parallelism a, and parallelism b were measured.

  The thickness and parallelism a of the polished glass substrate were measured using a CCD laser displacement meter (manufactured by Keyence Corporation, laser head LK-G15 / amplifier LK-G3000V).

  Plates at 8 locations in total of 0 °, 90 °, 180 °, and 270 ° in the 15 mm and 25 mm regions from the center of the glass substrate for magnetic recording media (the inner and outer diameter regions of the recording / reproducing region). The thickness was measured. The difference (plate thickness deviation in the same glass substrate surface) between the maximum thickness value and the minimum plate thickness value measured at eight positions in the same glass substrate surface was defined as parallelism a. The degree of parallelism a was measured using a total of two glass substrates, one glass substrate being extracted from the inner diameter side holding hole 501A and the outer diameter side holding hole 501C for each lot.

  As for the plate thickness, one glass substrate is pulled out from the inner diameter side holding hole 501A and the outer diameter side holding hole 501C of each carrier for one lot, a total of 12 sheets for the 22B type double-side polishing apparatus, and a total of 10 for the 16B type double side polishing apparatus. It measured using the glass substrate of 1 sheet. The thickness of the glass substrate for the magnetic recording medium is measured at two positions of 0 ° and 180 ° in an area 20 mm from the center of the glass substrate (intermediate area of the recording / reproducing area), and the average value is calculated as the thickness of the glass substrate. It was. The deviation of the plate thickness between the glass substrates for magnetic recording media polished in the same lot was determined from the difference between the maximum plate thickness and the minimum plate thickness in the same lot.

  The parallelism b of the glass substrate was measured using a laser interferometer (manufactured by Fujinon, product name: Fizeau interferometer G102 for plane measurement). As shown in FIG. 3, the parallelism b is calculated by observing interference fringes formed by the phase difference of reflected light from both main planes of the glass substrate and adding 0.32 to the number of observed interference fringes. did. The measurement region of the parallelism b is set so as to include the recording / reproducing region of the glass substrate for a magnetic recording medium having an outer diameter of 65 mm and an inner diameter of 20 mm. In this example, the measurement area was set to an area of 10.0 mm to 32.5 mm from the center of the disk and measured.

  The parallelism b was measured by extracting one glass substrate from the carrier inner diameter side holding hole 501A and the outer diameter side holding hole 501C for each lot in the same manner as the parallelism a.

  The roundness of the glass substrate holding hole 501 of the carrier was measured using a contour shape measuring machine (manufactured by Kosaka Laboratory, product name: Foam Coder EF-150E). For roundness, the roundness of each of the inner diameter side holding hole 501A, the intermediate part holding hole 501B, and the outer diameter side holding hole 501C was measured, and the average value of three points was taken as the roundness of the glass substrate holding hole.

  Using a 22B-type or 16B-type double-side polishing apparatus, the glass substrate is held in a carrier having glass substrate holding holes 501 of each diameter and roundness, and the thickness deviation in the lot of the glass substrate subjected to primary polishing, parallelism Table 1 shows the measurement results of a and parallelism b, and Table 2 shows the measurement results of the in-lot thickness deviation of the glass substrate subjected to secondary polishing, and the parallelism a and parallelism b. In Tables 1 and 2, Examples 1 to 4 and Examples 6 to 9 are Examples, and Examples 5 and 10 are Comparative Examples.

  In Example 5 and Example 10 in which the roundness of the glass substrate holding hole is 100 μm or more, the parallelism a, the parallelism b, and the deviation of the plate thickness between the glass substrates polished in the same lot (maximum plate thickness The difference between the value and the minimum plate thickness value) was poor, and a glass substrate excellent in plate thickness deviation could not be obtained.

  After secondary polishing, the glass substrate is a polishing solution containing a soft urethane polishing pad and colloidal silica as a polishing tool (a polishing liquid composition mainly composed of colloidal silica having an average primary particle size of 20 to 30 nm). Then, the upper and lower main planes were subjected to tertiary polishing by a double-side polishing apparatus. The tertiary polishing was performed by setting the polishing time so that the total polishing amount in the thickness direction of the upper and lower main planes was 1 μm. In the third polishing, since the total polishing amount is as small as 1 μm, the parallelism “a” and the parallelism “b” of the glass substrate after polishing are not so much affected as in the first polishing and the second polishing.

  The glass substrate that has been subjected to the third polishing is sequentially subjected to scrub cleaning with an alkaline detergent, ultrasonic cleaning in a state immersed in an alkaline detergent solution, and ultrasonic cleaning in a state immersed in pure water. Dried.

  After washing and drying, the parallelism a and the parallelism b of the glass substrate for magnetic recording medium were measured. The parallelism a and the parallelism b were measured by the same measurement method as that for the glass substrate after the primary polishing and the glass substrate after the secondary polishing.

  The glass substrate for magnetic recording medium obtained by subjecting the glass substrates of Examples 6 to 8 after the secondary polishing to the third polishing, washing and drying, has a parallelism a of 0.5 μm or less, and the parallelism b is The difference in thickness between glass substrates polished by the same lot (difference between the maximum thickness value and the minimum thickness value) was 0.8 μm or less.

  The present invention can be applied to a method for manufacturing a glass substrate, which includes a step of polishing the glass substrate. Specific examples of glass substrates to which the present invention can be applied include glass substrates for magnetic recording media, photomasks, displays for liquid crystals and organic EL, optical components such as optical pickup elements, optical filters, and optical lenses. It is mentioned as a thing.

10: glass substrate for magnetic recording medium, 101: main plane of glass substrate for magnetic recording medium, 102: inner peripheral side surface, 103: outer peripheral side surface, 104: inner peripheral chamfered portion, 105: outer peripheral chamfered portion,
A1 and A6: Thickness of the outer diameter side region of the glass substrate for magnetic recording medium, A2 and A5: Thickness of the intermediate region of the glass substrate for magnetic recording medium, A3 and A4: Inner diameter side region of the glass substrate for magnetic recording medium Board thickness,
20: Double-side polishing apparatus, 30: Polishing surface of upper surface plate, 40: Polishing surface of lower surface plate, 50: Carrier, 201: Upper surface plate, 202: Lower surface plate, 203: Sun gear, 204: Internal gear,
501: Glass substrate holding hole, 501A: inner diameter side holding hole, 501B: middle part holding hole, 501C: outer diameter side holding hole.

Claims (4)

A polishing pad is mounted on the opposing surface of the upper and lower surface plates of the double-side polishing machine, and the disk is between the polishing surface of the polishing pad mounted on the upper surface plate and the polishing surface of the polishing pad mounted on the lower surface plate. A carrier holding a glass substrate having a shape is arranged, and the main surface of the glass substrate is pressed with the polishing surface of the polishing pad of the upper surface plate and the polishing surface of the polishing pad of the lower surface plate against each other on both main surfaces of the glass substrate. In the method for producing a glass substrate for a magnetic recording medium, the method includes supplying a polishing liquid to a flat surface and relatively moving the glass substrate and the polishing surface to simultaneously polish both main flat surfaces of the glass substrate.
In the polishing step,
The carrier has a plurality of glass substrate holding holes for holding a disk-shaped glass substrate, the roundness of the glass substrate holding hole is 100 μm or less , and the diameter of the glass substrate holding hole is the diameter of the disk-shaped glass substrate. 1. A method for producing a glass substrate for a magnetic recording medium, characterized in that the total polishing amount of both main planes of the disk-shaped glass substrate to be polished is 4 to 75 μm, which is 1.10 mm to 1.90 mm larger than . A glass substrate for a magnetic recording medium manufactured by the manufacturing method according to claim 1 ,
Using a micrometer or a laser displacement meter at a total of eight positions of 0 °, 90 °, 180 °, and 270 ° in the inner diameter side region and the outer diameter side region of the recording / reproducing region of the glass substrate for magnetic recording medium. A glass substrate for a magnetic recording medium having a parallelism a of 0.5 μm or less determined from a difference (plate thickness deviation within the same glass substrate surface) between a maximum plate thickness value and a minimum plate thickness value of the measured plate thickness. A glass substrate for a magnetic recording medium manufactured by the manufacturing method according to claim 1 ,
A glass substrate for magnetic recording medium, wherein the parallelism b of both main planes measured with a laser interferometer is at least 0.6 μm or less in at least the recording / reproducing region of the glass substrate for magnetic recording medium. A glass substrate for a magnetic recording medium manufactured by the manufacturing method according to claim 1 ,
A glass substrate for a magnetic recording medium in which a deviation in thickness between glass substrates for magnetic recording media polished in the same lot is 0.8 μm or less.

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