JP2010080026A - Method for manufacturing substrate for magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce quality variation of an outer peripheral end part and an inner peripheral end part of a substrate for a magnetic disk between processing batches. <P>SOLUTION: The method for manufacturing the substrate for the magnetic disk includes an end surface polishing process for performing mirror surface polishing by a brush polishing method to an outer peripheral end surface and/or an inner peripheral end surface of an annular glass substrate. In the end surface polishing process, the weight of a polishing agent included in a slurry is controlled so that the specific gravity of the slurry is made constant between a plurality of batches. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a magnetic disk substrate mounted on a hard disk drive device.

  There is a magnetic disk as a magnetic recording medium mounted on a hard disk drive device (HDD device). A magnetic disk is manufactured by laminating a magnetic layer or a protective layer on a substrate, a glass substrate, or a ceramic substrate on which a NiP film is deposited on a metal plate made of an aluminum-magnesium alloy or the like. Conventionally, an aluminum alloy substrate has been widely used as a substrate for a magnetic disk. However, with recent downsizing, thinning, and high-density recording of magnetic disks, surface flatness and A glass substrate having excellent strength with a thin plate has been used.

  Such a magnetic disk substrate includes a shape processing step and a first lapping step (first grinding step); an end shape step (a coring step for forming a hole, an end (outer peripheral end and inner peripheral end) Chamfering step for forming a chamfered surface (chamfered surface forming step)); end surface polishing step (outer peripheral edge and inner peripheral edge); second lapping step (second grinding step); main surface polishing step (first and second) Second polishing step); manufactured through steps such as a chemical strengthening step.

As a method for polishing the outer peripheral end surface of the glass substrate, as disclosed in Patent Document 1, a polishing method using a rotating brush is known. In this polishing method, a plurality of glass substrates are stacked to form a columnar shape, a pair of columnar rotating brushes and a glass substrate are respectively rotated, and a polishing slurry is supplied to the outer peripheral end surface of the glass substrate. Contact.
JP-A-11-28649

  If the end surface of the outer peripheral end portion and / or inner peripheral end portion of the glass substrate is scratched, so-called white fogging may occur. Therefore, in the end face polishing step, it is necessary to reduce the scratches on the end face as much as possible to prevent the occurrence of white fogging. However, the polishing slurry used in the end surface polishing step is not discarded after being provided to the polishing apparatus, but is recycled by returning it to the polishing slurry tank (circulation method). When the polishing slurry is repeatedly used in this way, the polishing abrasive grains are worn down and the polishing efficiency is deteriorated. For this reason, when the number of processing batches increases, the end face quality differs between the initial stage and the late stage of the processing batch, and there is a possibility that the quality variation among the processing batches becomes large.

  The present invention has been made in view of the above points, and provides a method for manufacturing a magnetic disk substrate capable of reducing the quality variation of the outer peripheral end and / or inner peripheral end of the magnetic disk substrate between processing batches. The purpose is to provide.

  The method for manufacturing a magnetic disk substrate of the present invention is a method for manufacturing a magnetic disk substrate having an end surface polishing step of performing mirror polishing on the outer peripheral end surface and / or inner peripheral end surface of an annular glass substrate by a brush polishing method. In the end face polishing step, the weight of the abrasive contained in the slurry is controlled so that the specific gravity of the slurry is constant among a plurality of batches.

  According to this method, in the end face polishing step, since the polishing slurry whose concentration variation is adjusted within a predetermined range is used, variation in the polishing ability of the polishing slurry can be suppressed. And / or the quality dispersion | variation in each edge part of an inner peripheral edge part can be made small between process batches.

  In the method for manufacturing a magnetic disk substrate of the present invention, it is preferable that the range of variation in the specific gravity of the slurry is ± 4%.

  The method for manufacturing a magnetic disk substrate of the present invention is a method for manufacturing a magnetic disk substrate having an end surface polishing step of performing mirror polishing on the outer peripheral end surface and / or inner peripheral end surface of an annular glass substrate by a brush polishing method. In the end surface polishing step, the weight of the abrasive contained in the slurry is controlled so that the specific gravity of the slurry is constant among a plurality of batches, so that the outer peripheral end and / or the inner peripheral end Variation in quality at each end can be reduced between processing batches.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, the case where the magnetic disk substrate is a glass substrate will be described.

  Here, as the material for the magnetic disk substrate, aluminosilicate glass, soda lime glass, borosilicate glass, aluminum-magnesium alloy, or the like can be used. In particular, aluminosilicate glass can be preferably used in that it can be chemically strengthened and can provide a magnetic disk substrate excellent in flatness of the main surface and substrate strength.

  The manufacturing process of the magnetic disk substrate includes a shape processing step and a first lapping step; an end shape step (a coring step for forming a hole, a chamfered surface at an end (outer peripheral end and / or inner peripheral end)) Chamfering step to be formed (chamfered surface forming step)); end surface polishing step (outer peripheral end and inner peripheral end); second lapping step; main surface polishing step (first and second polishing step); chemical strengthening step, etc. These steps are included. In the method of the present invention, since the polishing slurry whose concentration variation is adjusted within a predetermined range is used in the end surface polishing step, variation in the polishing ability of the polishing slurry can be suppressed. And / or quality variation at each end of the inner peripheral end can be reduced between processing batches.

Below, each process of the manufacturing process of the board | substrate for magnetic discs is demonstrated.
(1) Shape processing step and first lapping step First, in the shape processing step, the surface of the sheet glass is lapped (ground) to form a glass base material, and the glass base material is cut to cut out a glass disk. Various plate glasses can be used as the plate glass. This plate-like glass can be manufactured by using a known manufacturing method such as a press method, a float method, a downdraw method, a redraw method, or a fusion method using a molten glass as a material. Of these methods, if a press method is used, a sheet glass can be produced at a low cost.

  In the first lapping step, both main surfaces of the sheet glass are lapped to form a disk-shaped glass substrate. This lapping process can be performed using alumina free abrasive grains with a double-sided lapping apparatus using a planetary gear mechanism. Specifically, the lapping platen is pressed on both sides of the plate glass from above and below, the grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are moved relative to each other for lapping. Do. By this lapping process, a glass substrate having a flat main surface can be obtained.

(2) End shape process (coring process for forming a hole, chamfering process for forming a chamfer on the end (outer peripheral end and inner peripheral end) (chamfered surface forming process))
In the coring step, for example, an inner hole is formed at the center of the glass substrate using a cylindrical diamond drill to obtain an annular glass substrate. In the chamfering step, the inner peripheral end surface and the outer peripheral end surface are ground with a diamond grindstone, and a predetermined chamfering process is performed.

(3) Second Lapping Step In the second lapping step, the second lapping process is performed on both main surfaces of the obtained glass substrate in the same manner as in the first lapping step. By performing this second lapping process, it is possible to remove in advance the fine irregularities formed on the main surface in the previous cutting process and end face polishing process, and shorten the subsequent polishing process on the main surface. Will be able to be completed in time.

(4) End surface polishing step In the end surface polishing step, the outer peripheral end surface and the inner peripheral end surface of the glass substrate are mirror-polished by a brush polishing method. At this time, as the abrasive grains, for example, a slurry containing cerium oxide abrasive grains (free abrasive grains) can be used. By this end face polishing step, the end face of the glass substrate is in a mirror state that can prevent the precipitation of sodium and potassium.

  Here, an end surface polishing apparatus used in the end surface polishing step will be described. FIG. 1 is a diagram showing an end surface polishing apparatus for a magnetic disk substrate. In the end surface polishing apparatus shown in FIG. 1, a plurality of glass substrates 1 are stacked and held in a columnar shape. In the present embodiment, the case where the cylindrical glass substrate 1 is polished with a pair of rotating brushes will be described. A pair of rotating brushes 2 are in contact with the laminated glass substrate 1. The outer peripheral surface of the glass substrate 1 is polished by rotating the glass substrate 1 and the pair of rotating brushes 2 in the same direction with parallel axes. A nozzle 3 is in close proximity to the contact point between the glass substrate 1 and the pair of rotating brushes 2, and polishing slurry is supplied from this nozzle.

  In the present embodiment, the polishing slurry 6 is circulated for use. The polishing slurry 6 discharged from the nozzle 3 is subjected to polishing between the glass substrate 1 and the rotating brush 2, then flows down and is collected by the collection tank 4. The polishing slurry 6 is stored in the second tank 9.

  In the second tank 9, the concentration of the polishing slurry 6 is controlled. That is, the concentration of the polishing slurry 6 stored in the second tank 9 is monitored and adjusted so that the concentration falls within a certain range. Specifically, a specific gravity meter 11 is attached to the second tank 9, and the specific gravity of the polishing slurry 6 is sequentially or periodically measured by the specific gravity meter 11. The specific gravity and concentration of the polishing slurry are associated in advance, and the concentration can be obtained from the obtained specific gravity value. Therefore, the specific gravity of the polishing slurry 6 in the second tank 9 is monitored, and when it falls below a predetermined threshold value, it is determined that the concentration of the polishing slurry 6 has decreased, and the polishing slurry 6 has a high concentration. Refill the slurry. In this way, the concentration of the polishing slurry 6 is adjusted, for example, the concentration is adjusted within a predetermined range with respect to a reference concentration (for example, 14% to 16%). This concentration range is preferably within ± 4% of the reference concentration. When the reference concentration is, for example, 14% to 16%, the concentration of the high concentration polishing slurry is about 20%. Therefore, when the specific gravity of the polishing slurry 6 is measured and the measured value falls below a predetermined threshold value, it is used for polishing at a high concentration (for example, 20%) so that it falls within a predetermined variation range (for example, within ± 4%). Replenish the slurry. Thus, by replenishing the polishing slurry having a high concentration based on the specific gravity (concentration) of the polishing slurry, the concentration of the polishing slurry can always be maintained within a certain range. As a result, the quality variation at each end of the outer peripheral end and / or inner peripheral end can be reduced between processing batches.

  The polishing slurry 6 whose concentration has been adjusted in the second tank 9 in this manner is sent out by the pump 10, and is discharged from the nozzle 3 again and supplied to the polishing position. In such an end surface polishing apparatus, the rotating brush 2 and the glass substrate 1 rotate while being in contact with each other, whereby the rotating brush 2 mirror-polishes the outer peripheral end surface of the glass substrate 1 through the polishing slurry 6.

(5) Main surface polishing step (first polishing step)
As the main surface polishing step, first, a first polishing step is performed. The first polishing process is a process whose main purpose is to remove scratches and distortions remaining on the main surface in the lapping process described above. In the first polishing step, the main surface is polished using a hard resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the abrasive, cerium oxide abrasive grains can be used.

(6) Chemical strengthening step In the chemical strengthening step, the glass substrate that has been subjected to the lapping step and the polishing step described above is chemically strengthened. As a chemical strengthening solution used for chemical strengthening, for example, a mixed solution of potassium nitrate (60%) and sodium nitrate (40%) can be used. In the chemical strengthening, the chemical strengthening solution is heated to 300 ° C. to 400 ° C., the cleaned glass substrate is preheated to 200 ° C. to 300 ° C., and immersed in the chemical strengthening solution for 3 hours to 4 hours. In soaking, in order to chemically strengthen the entire surface of the glass substrate, the immersion is preferably performed in a state of being accommodated in a holder so that the plurality of glass substrates are held at the end surfaces.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions in the surface layer of the glass substrate are respectively replaced with sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution. Will be strengthened.

(7) Main surface polishing process (final polishing process)
Next, a second polishing process is performed as a final polishing process. The second polishing step is a step aimed at finishing the main surface into a mirror surface. In the second polishing step, mirror polishing of the main surface is performed using a soft foam resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the slurry, cerium oxide abrasive grains (average particle diameter 0.8 μm) finer than the cerium oxide abrasive grains used in the first polishing step can be used.

Next, examples performed for clarifying the effects of the present invention will be described.
(Example)
First, the melted aluminosilicate glass was molded into a disk shape by direct pressing using an upper mold, a lower mold, and a barrel mold to obtain an amorphous plate glass material (blanks). At this point, the diameter of the blanks was 66 mm. Next, both main surfaces of the blanks were subjected to a first lapping process, and then a cylindrical core drill was used to form a hole in the center of the glass substrate to process it into an annular glass substrate (coring). . And the chamfering process (chamfering surface formation process) which forms a chamfering surface in the edge part (an outer peripheral edge part and an inner peripheral edge part) was given, and it was set as the glass substrate of diameter 2.5 inches. Thereafter, a second lapping process was performed on the glass substrate.

  Next, the outer peripheral edge of the glass substrate was mirror polished by the brush polishing method using the apparatus shown in FIG. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. In the mirror polishing by the brush polishing method, polishing was performed while adjusting the concentration of the polishing slurry in the range of 14% to 16%. Further, the inner peripheral end portion was mirror polished by a magnetic polishing method.

  And the glass substrate which finished the mirror polishing process was washed with water. As a result, the diameter of the glass substrate was 27.4 mm, and the substrate used for a 1-inch magnetic disk could be obtained. Next, lapping processing was performed on both main surfaces of the obtained glass substrate in the same manner as the above lapping.

Next, as a main surface polishing step, a first polishing step was performed on both main surfaces of the glass substrate. In the first polishing step, a double-side polishing machine was used as the polishing apparatus. As a polishing pad in this polishing apparatus, a soft suede pad was used. A cerium abrasive was used as the abrasive. The polishing conditions were a processing surface pressure of 130 g / cm ² and a processing rotation speed of 22 rpm. As a result, the surface roughness Ra of the main surface of the glass substrate was about 1.0 nm.

  Next, chemical strengthening was performed on the glass substrate after the first polishing step described above. For chemical strengthening, a chemical strengthening solution in which potassium nitrate (60%) and sodium nitrate (40%) are mixed is prepared, this chemical strengthening solution is heated to 380 ° C., and the cleaned glass substrate is placed therein for about 4 hours. This was done by dipping. Then, acid cleaning, alkali cleaning, and pure water cleaning were sequentially performed on the glass substrate after the chemical strengthening. The thickness of the strengthened stress layer thus formed was 100 μm.

Next, a second polishing step for finishing the main surface into a mirror surface was performed on both main surfaces of the glass substrate. In the second polishing step, a double-side polishing machine was used as the polishing apparatus. As a polishing pad in this polishing apparatus, a soft suede pad (Asker C hardness: 54, compression deformation amount: 476 μm or more, density: 0.53 g / cm ³ or less) was used. As the abrasive, a colloidal silica abrasive having an average particle size of about 20 nm was used. The polishing conditions were a processing surface pressure of 60 g / cm ² and a processing rotation speed of 20 rpm.

  The glass substrate after the second polishing step is immersed in an alkali solution, cleaned by applying ultrasonic waves, scrubbed using an alkali cleaning solution, diluted with a very small amount of diluted sulfuric acid and the alkali cleaning solution. After washing, IPA (isopropyl alcohol) was vapor-dried.

  About the glass substrate for magnetic discs obtained through such a process, the arithmetic mean roughness (Ra) of the outer peripheral end face was measured using a surface roughness shape measuring machine. Further, the arithmetic average roughness (Ra) was compared between the first batch and the tenth batch. As a result, the arithmetic average roughness of the first batch was 0.04 μm, the arithmetic average roughness of the tenth batch was 0.011 μm, and the quality variation between the processing batches was very small. As described above, the reason why the quality variation between the processing batches was very small is considered to be that the concentration of the polishing slurry used in the end face polishing step was adjusted within a predetermined range.

(Comparative example)
A glass substrate for a magnetic disk was produced in the same manner as in the example except that in the end surface polishing step, a polishing slurry without adjusting the concentration was used. About this glass substrate for magnetic disks, the arithmetic mean roughness of the outer peripheral end face of the 1st batch and the 10th batch was calculated | required similarly to the Example. As a result, the arithmetic average roughness of the first batch was 0.09 μm, the arithmetic average roughness of the 10th batch was 0.01 μm, and the quality variation among the processing batches was very large. This is presumably because the concentration of the polishing slurry used in the end face polishing step is not adjusted.

  As described above, according to the present invention, the concentration of the polishing slurry used in the end face polishing step is adjusted within a predetermined range, so that the quality variation at each of the outer peripheral end and / or the inner peripheral end can be reduced. Can be reduced between processing batches.

  The present invention is not limited to the above embodiment, and can be implemented with appropriate modifications. For example, in the above embodiment, the case where end surface polishing is performed on the outer peripheral end portion is described. However, the present invention is not limited to this, and the case where end surface polishing is performed on the inner peripheral end portion is also described. The same can be applied. Further, the material, number, size, processing procedure, and the like in the above embodiment are merely examples, and various modifications can be made within the range where the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

It is a figure which shows the end surface grinding | polishing apparatus of the board | substrate for magnetic discs concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Rotating brush 3 Nozzle 4 Collection tank 5 1st tank 6 Polishing slurry 7,10 Pump 9 2nd tank 11 Hydrometer

Claims (2)

  A method of manufacturing a magnetic disk substrate having an end surface polishing step in which an outer peripheral end surface and / or an inner peripheral end surface of an annular glass substrate is mirror-polished by a brush polishing method, wherein a plurality of batches are formed in the end surface polishing step. A method for manufacturing a substrate for a magnetic disk, wherein the weight of the abrasive contained in the slurry is controlled so that the specific gravity of the slurry is constant.   2. The method for manufacturing a substrate for a magnetic disk according to claim 1, wherein a range of variation in specific gravity of the slurry is ± 4%.

Images