JP5333563B2 - Glass substrate for magnetic recording medium and magnetic recording medium - Google Patents

Description

The present invention relates to a glass substrate for a magnetic recording medium having excellent parallelism and having a small thickness deviation between glass substrates polished in the same lot , and a magnetic recording medium .

  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 the magnetic head is passed to the end of the glass substrate and the magnetic disk is rotated at a higher speed, the shape of the glass substrate for the magnetic recording medium (eg, thickness deviation, end shape, flatness, etc.) is disturbed. As a result, the flying posture of the magnetic head is disturbed, and there is a possibility that a failure of the magnetic head contacting the magnetic disk may occur.

  As a technique for controlling the shape of the glass substrate for magnetic recording medium, particularly the plate thickness, the same glass substrate (Patent Document 1) in which the plate thickness distribution in the same glass substrate surface of the glass substrate for magnetic recording medium is controlled to the same shape. There has been proposed a carrier (Patent Document 2) that reduces variations in plate thickness between glass substrates for magnetic recording media polished in a lot.

  However, the glass substrate for magnetic recording media described in Patent Document 1 is intended to prevent the glass substrate from cracking due to an external impact, and the plate thickness distribution (hereinafter referred to as parallelism) within the same glass substrate surface is glass. Although it is described that the main plane is inclined so that the plate thickness becomes thinner from the center of the substrate toward the outer surface, the flying posture of the magnetic head is stabilized and the magnetic head is made into a magnetic disk. There is no description or suggestion of performing recording / reproduction with high reliability. Moreover, there is no description about the relationship between the parallelism of a glass substrate for magnetic recording media and polishing.

  The carrier described in Patent Document 2 is effective only for polishing processing using a soft polishing pad. By designing the glass substrate holding portion and the gear portion of the carrier to have different materials and thicknesses, the glass substrate becomes a soft pad. Controlling the amount of polishing of the glass substrate by controlling the amount of polishing of the glass substrate by suppressing the sinking and preventing the load on the glass substrate from becoming uneven, and reducing the thickness variation. It does not improve the parallelism of the medium glass substrate.

  Also, a polishing method for reducing the glass substrate defects such as residual abrasive grains and cleaning damage by setting the temperature of the polishing liquid when polishing the glass substrate for magnetic recording media to be equal to or lower than the atmospheric temperature or 20 ° C. (patent) Document 3) has been proposed. However, the polishing method of Patent Document 3 does not describe the relationship between the parallelism and thickness variation of the glass substrate for magnetic recording medium and the polishing process, and improves the parallelism and thickness variation of the glass substrate for magnetic recording medium. It is not a thing.

  Furthermore, as a technique for polishing a semiconductor wafer, there has been proposed a surface plate (Patent Document 4) capable of obtaining a semiconductor wafer having excellent flatness by polishing while suppressing deformation of the surface plate shape due to heat generated by the polishing process. . However, the surface plate described in Patent Document 4 requires a very special design such as providing a water channel inside the surface plate in order to adjust the surface plate temperature by flowing cooling water inside the surface plate. It may be difficult to apply to a surface plate of a large polishing apparatus.

JP 2006-318583 A JP 2009-214219 A JP 2007-245265 A JP-A-2-274464

An object of the present invention is to provide a glass substrate for a magnetic recording medium having excellent parallelism and having a small thickness deviation between glass substrates polished in the same lot , and a magnetic recording medium .

The present invention is a disk-shaped glass substrate for a magnetic recording medium having an inner peripheral side surface, an outer peripheral side surface, and both main planes, and having a circular hole in the center, the glass substrate for a magnetic recording medium being polished By a manufacturing method including a polishing process for a main plane in which a polishing liquid temperature difference ΔTs (= Ts1−Ts2) obtained by subtracting a polishing liquid temperature Ts2 after polishing from a previous polishing liquid temperature Ts1 is −3 ° C. to 0 ° C. It is obtained
In the middle portion of the record and reproduction area, 0 °, 90 °, 180 °, 270 difference between the maximum thickness and minimum thickness value of the sheet thickness measured at the position of the four places ° (the same glass substrate surface A glass substrate for a magnetic recording medium is provided, wherein the parallelism a, which is a thickness deviation, is 0.2 μm or less . The present invention also provides a magnetic recording medium using the glass substrate for a magnetic recording medium.

  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 obstacles caused by the magnetic head contacting the magnetic disk can be eliminated or 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. The example which measured the parallelism of the glass substrate for magnetic recording media with the laser interferometer. (A) Relationship between the number of interference fringes observed with a laser interferometer and the parallelism of the glass substrate for a magnetic recording medium. (B) Relationship between the interference fringe image observed by the laser interferometer and the parallelism of the magnetic recording medium glass substrate. Schematic of a double-side polishing apparatus. Sectional drawing which represents typically the shape when the shape of the polishing surface of the upper surface plate of a double-side polish apparatus and the polishing surface of a lower surface plate is D1 <= D2 when both main surfaces of a glass substrate are grind | polished simultaneously. Schematic of the carrier which shows the position of the holding hole holding the glass substrate for magnetic recording media. The graph showing the relationship of the board | plate thickness deviation between the glass substrates grind | polished by polishing liquid temperature difference (DELTA) Ts (= Ts1-Ts2) and the same lot.

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

  First, FIG. 1 shows a perspective view of a glass substrate 10 for a magnetic recording medium according to the present invention, and FIG. 2 shows 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.

  The parallelism of both main planes of the glass substrate for magnetic recording medium is more excellent as the plate thickness (for example, A1 to A6) in each region of the glass substrate for magnetic recording medium is uniform, and the plate thickness in each region is not good. The more uniform (large thickness deviation), the worse.

  The parallelism of both main planes of the glass substrate for a magnetic recording medium is measured using a measuring machine such as a micrometer, a laser displacement meter, or a laser interferometer.

  The parallelism a using a micrometer or a laser displacement meter is measured by measuring the plate thickness at a plurality of locations arbitrarily determined within the plane of the magnetic recording medium glass substrate, and the difference between the maximum plate thickness value and the minimum plate thickness value. To do that.

  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.

  In FIG. 3, the parallelism b of both main planes of the glass substrate for a magnetic recording medium is measured with the laser interferometer (product name: Fizeau interferometer for plane measurement, G102S manufactured by Fujinon) used in the examples of the present invention. An example is shown. 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.

  FIG. 3 shows an image of interference fringes observed with a laser interferometer and the value of parallelism b obtained by analyzing the interference fringes. The smaller the number of interference fringes observed, the better the parallelism of both main planes of the glass substrate for magnetic recording media, that is, the smaller the thickness deviation of the region where the parallelism b of the glass substrate for magnetic recording media was measured. It means that the plate thickness distribution in the same glass substrate surface is excellent.

  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) Grinding 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 primary polishing only, 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. Further, 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. 4 is a schematic view of the double-side polishing apparatus 20. In FIG. 4, 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 an internal gear, tp1 indicates a surface temperature measurement region on the inner peripheral end side of the upper surface plate, and tp2 indicates a surface temperature measurement region on the outer peripheral end side of the upper surface plate.

  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 by the glass substrate holding portion 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. The 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 polishing surface 30 of the upper surface plate and the lower surface plate) This is done by cutting the surface to be the polishing surface 40.

  When both main planes of the glass substrate are simultaneously polished using the double-side polishing apparatus 20, the polishing liquid is supplied to both main planes of the glass substrate from the polishing liquid supply holes formed in the upper surface plate 201. The polishing liquid used for polishing the glass substrate is discharged to the sun gear side or the internal gear side from between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate, and is provided below the lower surface plate 202. It is collected in a certain drain.

  The temperature Ts1 of the polishing liquid before polishing the glass substrate is adjusted in the polishing liquid storage tank before being supplied from the polishing liquid supply holes formed in the upper surface plate 201 to both main surfaces of the glass substrate. The temperature Ts1 of the polishing liquid before polishing the glass substrate is measured using a thermometer in the polishing liquid storage tank. The temperature Ts2 of the polishing liquid after polishing the glass substrate is measured using a thermometer with the polishing liquid collected in the drain provided on the lower side of the lower surface plate 202.

  When a glass substrate is polished using the double-side polishing apparatus 20, the platen temperature changes due to heat generated during polishing. When the platen temperature changes, the platen volume changes due to temperature expansion, and the platen shape changes. The deformation of the surface plate shape changes the distance D between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate, and thus greatly affects the accuracy of the polishing process.

  When both main planes of the glass substrate are polished simultaneously, a polishing liquid temperature difference ΔTs (= Ts1) obtained by subtracting the polishing liquid temperature Ts2 after polishing the glass substrate from the polishing liquid temperature Ts1 before polishing the glass substrate. -Ts2) is from -3 ° C to 0 ° C. When the polishing liquid temperature difference ΔTs is −3 ° C. to 0 ° C., the polished surface that has risen due to heat generated during polishing can be cooled. Therefore, it becomes easy to make the temperature of the polishing surface 30 of the upper surface plate and the temperature of the polishing surface 40 of the lower surface plate uniform within the polishing surface, and the glass substrate can be accurately formed without thermally deforming the surface plate during polishing. Can be polished. The polishing liquid temperature difference ΔTs is preferably −3 ° C. to 0 ° C., more preferably −2.5 ° C. to 0 ° C., and particularly preferably −2.5 ° C. to −0.5 ° C.

  In the present invention, the difference Δtp (tp1-tp2) between the surface temperature tp1 measured on the inner peripheral end side of the upper surface plate and the surface temperature tp2 measured on the outer peripheral end side when both main planes of the glass substrate are polished simultaneously. The absolute value is preferably 3 ° C. or less. When the absolute value of Δtp exceeds 3 ° C., the surface plate shape is largely thermally deformed, and it becomes difficult to uniformly apply the polishing load to the glass substrate being polished. The amount and the polishing amount between glass substrates polished in the same lot become non-uniform, and it may be difficult to obtain a glass substrate for a magnetic recording medium excellent in parallelism. The absolute value of Δtp is more preferably 2.5 ° C. or less, and particularly preferably 2 ° C. or less.

  The means for setting the absolute value of Δtp to 3 ° C. or less is not particularly limited, and controls the balance of the amount of polishing liquid supplied in the surface plate radial direction, which controls the temperature of the polishing liquid supplied during polishing. For example, when the glass substrate is polished, the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate are strongly rubbed on the outer peripheral end side or the inner peripheral end side to suppress frictional heat generated.

  The upper surface plate surface temperature difference Δtp, which is the difference between the surface temperature tp1 measured on the inner peripheral end side of the upper surface plate and the surface temperature tp2 measured on the outer peripheral end side when both main planes of the glass substrate are polished simultaneously, is 0. It is preferable to set it to ~ + 3 degreeC. The upper surface plate surface temperature difference Δtp is preferably 0 to + 3 ° C, more preferably 0 to + 2.5 ° C, and particularly preferably 0 to + 2 ° C.

  When the upper surface plate surface temperature difference Δtp is less than 0 ° C. (for example, −3 ° C.), the main cause is the outer contact where the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate strongly hit the outer peripheral end side. Since the glass substrate is polished in the shape of the polished surface, the polished surface is rubbed on the outer peripheral end side, and the heat generated by the polishing process on the outer peripheral end side is increased. When the glass substrate is polished with the outer peripheral polishing surface shape and the upper surface plate surface temperature difference Δtp is less than 0 ° C., the polished glass substrate is polished in the same glass substrate surface or in the same lot. The amount of polishing between the glass substrates polished inside becomes uneven, and it may be difficult to obtain a glass substrate for a magnetic recording medium having excellent parallelism.

  In addition, the surface temperature tp of the upper surface plate 201 when both main planes of the glass substrate are polished simultaneously is measured using a thermocouple thermometer and a radiation thermometer. Since the upper surface plate surface temperature tp during polishing can be continuously measured, a thermocouple thermometer is preferably used as the thermometer.

  FIG. 5 shows an example of a cross-sectional view schematically showing the shapes of the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate when the glass substrate is being polished. In FIG. 5, D denotes a distance between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate at an arbitrary position within the surface plate surface, and D <b> 1 denotes the polishing surface 30 of the upper surface plate on the inner peripheral end side. The distance from the polishing surface 40 of the lower surface plate, D2 represents the distance between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate on the outer peripheral end side.

  The distance D between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate is measured using an eddy current displacement meter. The distance D between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate is a place where the measurement position of the polishing surface 30 of the upper surface plate and the measurement position of the polishing surface 40 of the lower surface plate are closest (on the upper surface plate). (Measurement position of the polishing surface 40 of the lower surface plate is defined as a position lowered from the measurement position of the polishing surface 30 perpendicularly to the polishing surface 40 of the lower surface plate).

  FIG. 5 is a cross-sectional view schematically showing the shape of the polishing surface where D1 <D2, where the upper surface polishing surface 30 and the lower surface polishing surface 40 strongly hit each other on the inner peripheral end side. Polished surface shape. In order to obtain a glass substrate for a magnetic recording medium having excellent parallelism by polishing the glass substrate using the double-side polishing apparatus 20, it is preferable to reduce the deviation of the polishing surface distance D in the surface plate surface.

  In order to improve the productivity of glass substrates for magnetic recording media, studies are being made to increase the number of glass substrates that are simultaneously polished (same lot) using the same double-side polishing apparatus. Examples of means for increasing the number of glass substrates in the same lot include increasing the size of the double-side polishing apparatus 20 and increasing the number of glass substrates held by the carrier 50.

  In the present invention, the same lot refers to 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 type of the double-side polishing apparatus is classified according to the size of the carrier used. The 22B type double-side polishing apparatus has a 22-inch carrier, the 16B type double-side polishing apparatus has a 16-inch carrier, and the 9B type double-side polishing apparatus has a 9-inch carrier. Are used respectively.

  FIG. 6 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 for a magnetic recording medium is polished on both main planes of the glass substrate at the same time while being held in the glass substrate holding hole 501 of the carrier 50.

  The glass substrate holding hole 501 of the carrier 50 is formed concentrically around the center of the carrier 50. When the glass substrate is polished using the double-side polishing apparatus 20, the carrier 50 holding the glass substrate revolves around the sun gear 203 while rotating (planetary drive). Therefore, the peripheral speed of the glass substrate to be polished differs depending on the position where the carrier 50 is held, and the peripheral speed of the glass substrate held at a position close to the center of the carrier 50 (inner diameter side holding hole 501A) is slow. The peripheral speed of the glass substrate held at a position away from the center of 50 (outer diameter side holding hole 501C) is increased. The difference in the peripheral speed of the glass substrate in the carrier becomes larger as the double-side polishing apparatus 20 becomes larger and the carrier size becomes larger.

  Further, when the glass substrate is polished by the large-sized double-side polishing apparatus 20, the peripheral speed of the glass substrate is faster when passing the outer peripheral end side than the inner peripheral end side of the polishing surface.

  The polishing rate of the glass substrate increases when the peripheral speed of the glass substrate is high (a large amount of polishing), and decreases when the peripheral speed of the glass substrate is low (the polishing amount is small). When polishing a glass substrate using the large-sized double-side polishing apparatus 20, variation in the polishing amount in the carrier 50 is suppressed, and a plate between the glass substrates held in the inner diameter side holding hole 501A and the outer diameter side holding hole 501C. Thickness and parallelism must be uniform.

  When the glass substrate is polished in the shape of the outer polished surface in which the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate strongly contact each other on the outer peripheral end side, the load of polishing processing on the glass substrate is the outer peripheral edge of the polishing surface. Get higher on the side.

  When the glass substrate is polished with the outer peripheral polishing surface shape, the peripheral speed of the glass substrate is high when the glass substrate passes the outer peripheral end side of the polishing surface, and the polishing pressure becomes high. The polishing amount of the glass substrate held in the hole 501C is larger than the polishing amount of the glass substrate held in the inner diameter side holding hole 501A. For this reason, when a glass substrate is polished with the outer polished surface shape, the amount of polishing in the same glass substrate surface and the amount of polishing between glass substrates polished in the same lot become non-uniform, and the magnetic recording medium has excellent parallelism. It may be difficult to obtain a glass substrate for use.

  When the glass substrate is polished by the large-sized double-side polishing apparatus 20, the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate may be parallel or inner polishing surface shapes (the shape shown in FIG. 5). Preferably, the deviation of the polishing surface distance D within the surface plate surface is preferably small.

  A glass substrate for a magnetic recording medium having a thickness deviation of 1.0 μm or less between glass substrates polished in the same lot by a method for producing a glass substrate for a magnetic recording medium having a polishing step using the polishing method of the present invention. Can be manufactured with high productivity. The plate thickness of the glass substrate for a magnetic recording medium is measured using a measuring machine such as a micrometer or a laser displacement meter.

  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, 0 °, 90 °, 180 °, 270 ° at the intermediate portion of the recording / reproducing area of the glass substrate for magnetic recording medium. The parallelism a calculated from the difference (plate thickness deviation in the same glass substrate surface) between the maximum plate thickness value and the minimum plate thickness value measured using a micrometer or a laser displacement meter at four positions in total. A glass substrate for magnetic recording media of 0.4 μm or less can be produced with high productivity.

  Further, the deviation of the parallelism a between the glass substrates for magnetic recording media polished in the same lot by the method for producing a glass substrate for magnetic recording media having a polishing step using the polishing method of the present invention is 0.4 μm. The following glass substrates for magnetic recording media can be produced with high productivity.

  The parallelism b of both main planes at least in the recording / reproducing area of the glass substrate for magnetic recording medium measured by a laser interferometer by the method for manufacturing a glass substrate for magnetic recording medium having the polishing step of the present invention is 0. A glass substrate for magnetic recording media of 3 μm or less can be produced with high productivity. The parallelism b of the glass substrate for magnetic recording media is preferably 0.3 μm or less, and particularly preferably 0.25 μm or less.

  Further, according to the method for manufacturing a glass substrate for magnetic recording medium having the polishing step of the present invention, the deviation of the parallelism b between the glass substrates for magnetic recording medium polished in the same lot is 0.2 μm or less. Glass substrates can be manufactured with high productivity.

  The glass substrate for a magnetic recording medium manufactured by the method for manufacturing a glass substrate for a magnetic recording medium having the polishing step of the present invention has a shape characteristic (parallelism, thickness deviation within the same lot) of the glass substrate for a magnetic recording medium. Excellent. Therefore, in the HDD (Hard Disk Drive) test of a 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, the magnetic head can be used without disturbing the flying posture of the magnetic head. There is no risk of touching 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 principal planes of the substrate were ground, and the abrasive grains were removed by washing.

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 glass substrate after the outer peripheral end surface polishing is cleaned and removed by scrub cleaning using an alkaline detergent and ultrasonic cleaning in a state immersed in an alkaline detergent solution.
The inner peripheral side surface and inner peripheral chamfered portion of the glass substrate after polishing the outer peripheral end surface are polished with a polishing brush and cerium oxide abrasive grains, and scratches on the inner peripheral side surface and inner peripheral chamfered portion are removed so that the inner surface becomes a mirror surface. The peripheral end surface was polished. The glass substrate on which the inner peripheral end face had been polished was cleaned and removed by scrub cleaning using an alkaline detergent and ultrasonic cleaning in a state immersed in an alkaline detergent solution.

[Primary to tertiary polishing of glass substrate for magnetic recording medium]
The glass substrate after end face processing is a polishing liquid containing a polishing pad made of hard urethane and cerium oxide abrasive grains as an abrasive (average particle diameter, hereinafter referred to as average particle diameter, approximately 1.3 μm of cerium oxide as a main component. The upper and lower main planes were subjected to primary polishing using a double-side polishing apparatus.

  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). The upper and lower main planes were subjected to secondary polishing using a 22B double-side polishing apparatus (product name: DSM22B-6PV-4MH, manufactured by Speedfam Co., Ltd.).

  In the secondary polishing step, the polishing pads mounted on the upper and lower surface plates of the double-side polishing apparatus are dressed using a dressing jig having diamond abrasive grains on the surface before polishing the glass substrate, Formed on the polished surface.

  The main polishing pressure of the secondary polishing was set to 9.5 kPa, the platen rotation speed was set to 9 rpm, and the polishing time was set to 20 minutes, and the glass substrate was polished. Six carriers were used, and 216 glass substrates were polished simultaneously. The polished glass substrate was washed and removed from cerium oxide, and then the thickness, parallelism a, and parallelism b were measured.

  The thickness and parallelism a of the polished glass substrate were measured using a laser displacement meter (manufactured by Keyence Corporation, laser head is LK-G15 / amplifier LK-G3000V). In the present embodiment, the plate thickness is 20 mm from the center of the glass substrate for magnetic recording medium (intermediate portion of the recording / reproducing area), and is at four positions of 0 °, 90 °, 180 °, and 270 °. It was measured. The average value of the plate thickness measured at four positions on the same glass substrate surface is defined as the glass substrate thickness, and the maximum and minimum plate thickness values measured at four positions on the same glass substrate surface. The difference in value (thickness deviation within the same glass substrate surface) was defined as parallelism a.

  The plate thickness and the degree of parallelism a were measured using a total of 18 glass substrates obtained by extracting 3 glass substrates from each carrier (6 sheets) per lot. The measurement glass substrates are extracted one by one from the inner diameter side holding hole 501A, the intermediate part holding hole 501B, and the outer diameter side holding hole 501C of each carrier, and the thickness and parallelism a in the same carrier and in the same lot are determined. The deviation was examined.

  The parallelism b of the polished glass substrate was measured using a laser interferometer (manufactured by Fujinon, product name: G102S). As shown in FIG. 3, the parallelism b is calculated by a fringe analyzer (product name: A1) by observing interference fringes formed by the phase difference of reflected light from both principal planes of the glass substrate. (Automatic calculation). The measurement region of the parallelism b was 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 the present example, the measurement area was set to a 10.0 mm to 32.5 mm area from the center of the disk.

  The parallelism b was measured by extracting nine glass substrates per lot. The glass substrates for measuring the parallelism b are extracted one by one from the inner diameter side holding holes 501A, the intermediate part holding holes 501B and the outer diameter side holding holes 501C of the carriers 1 to 3, and the parallelism within the same carrier and the same lot. The deviation of b was examined.

  In this example, the temperature Ts1 of the polishing liquid before polishing the glass substrate was measured with a thermocouple thermometer (type K) in the polishing liquid storage tank for circulating the polishing liquid. The polishing liquid temperature Ts2 after polishing the glass substrate was measured with a thermocouple thermometer (type K) for the polishing liquid recovered in the drain provided on the lower side of the lower surface plate 202.

  In this example, the surface temperature tp1 on the inner peripheral end side of the upper surface plate and the surface temperature tp2 on the outer peripheral end side when both main planes of the glass substrate are polished simultaneously are the points when the polishing process of the glass substrate is finished. In FIG. 1, the temperature was measured using a thermocouple thermometer (type K).

  The temperature Ts1 of the polishing liquid before polishing the glass substrate, the temperature Ts2 of the polishing liquid after polishing the glass substrate, and the inner peripheral end side of the upper surface plate when both main planes of the glass substrate are polished simultaneously. Table 1 shows the surface temperature tp1 and the surface temperature tp2 on the outer peripheral edge side, and Table 2 shows the plate thickness, parallelism a, and parallelism b of the glass substrate polished at each polishing liquid temperature Ts and upper surface plate surface temperature tp. Respectively. In Tables 1 and 2, Examples 1 to 6 are Examples, and Examples 7 to 10 are Comparative Examples.

  In Examples 1 to 6, the polishing liquid temperature difference ΔTs, which is obtained by subtracting the polishing liquid temperature Ts2 after polishing the glass substrate from the polishing liquid temperature Ts1 before polishing the glass substrate, is −3 ° C. to 0 ° C. The thickness deviation between the glass substrates polished in the same lot was 1.0 μm or less. FIG. 7 is a graph showing the relationship between the polishing liquid temperature difference ΔTs and the plate thickness deviation between glass substrates polished in the same lot.

In Examples 1 to 6, the parallelism a is 0.4 μm or less, and the deviation of the parallelism a between the glass substrates polished in the same lot (difference between the maximum parallelism value and the minimum parallelism value) is It was 0.4 μm or less. Further, the parallelism b is 0.3 μm or less, and the deviation of the parallelism b between glass substrates polished in the same lot (difference between the maximum parallelism value and the minimum parallelism value) is 0.2 μm or less. It was.
It was confirmed that a glass substrate for a magnetic recording medium having excellent shape characteristics (parallelism, plate thickness deviation in the same lot) can be obtained by a polishing process to which the polishing method of the present invention is applied.

  The glass substrate after the secondary polishing is subjected to tertiary polishing. Using a polishing pad made of soft urethane as a polishing tool for tertiary polishing and a polishing liquid containing colloidal silica (polishing liquid composition mainly composed of colloidal silica having an average primary particle diameter of 20 to 30 nm), The upper and lower main planes were polished by a double-side polishing apparatus.

  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 and thickness of the glass substrate for magnetic recording medium were measured. The parallelism and the plate thickness were measured by the same method as that for the glass substrate after the secondary polishing.

  The glass substrate for magnetic recording medium obtained by subjecting the glass substrate after secondary polishing of Examples 1 to 6 to tertiary polishing, washing and drying has a plate thickness deviation of 1 between the glass substrates polished in the same lot. 0.0 μm or less. Further, the parallelism a is 0.4 μm or less, and the deviation of the parallelism a between glass substrates polished in the same lot (difference between the maximum parallelism value and the minimum parallelism value) is 0.4 μm or less. It was. Further, the parallelism b is 0.3 μm or less, and the deviation of the parallelism b between glass substrates polished in the same lot (difference between the maximum parallelism value and the minimum parallelism value) is 0.2 μm or less. It was.

  According to the method for producing a glass substrate for a magnetic recording medium having a polishing step using the polishing method of the present invention, a glass substrate for a magnetic recording medium having excellent shape characteristics (parallelism, thickness deviation within the same lot) can be obtained. confirmed.

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,
tp1: surface temperature measurement region on the inner peripheral edge side of the upper surface plate, tp2: surface temperature measurement region on the outer peripheral edge side of the upper surface plate,
D: Distance between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate at an arbitrary position within the surface plate surface, D1: The polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate on the inner peripheral edge side D2: distance between the polishing surface 30 of the upper surface plate and the polishing surface 40 of the lower surface plate on the outer peripheral end side,
501: Glass substrate holding hole, 501A: inner diameter side holding hole, 501B: middle part holding hole, 501C: outer diameter side holding hole.

Claims (2)

A disk-shaped glass substrate for a magnetic recording medium having an inner peripheral side surface, an outer peripheral side surface, and both main planes, and having a circular hole in the center, the glass substrate for a magnetic recording medium being a polishing liquid before polishing Obtained by a manufacturing method including a polishing process of a main plane in which a polishing liquid temperature difference ΔTs (= Ts1−Ts2) obtained by subtracting a polishing liquid temperature Ts2 after polishing from a temperature Ts1 is set to −3 ° C. to 0 ° C. And
In the middle portion of the record and reproduction area, 0 °, 90 °, 180 °, 270 difference between the maximum thickness and minimum thickness value of the sheet thickness measured at the position of the four places ° (the same glass substrate surface A glass substrate for a magnetic recording medium, wherein the parallelism a, which is a thickness deviation, is 0.2 μm or less .   A magnetic recording medium comprising the glass substrate for a magnetic recording medium according to claim 1.

Images