JP2010079943A - Method for manufacturing glass substrate for magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a glass substrate for a double-sided magnetic disk and a glass substrate for a single-sided magnetic disk with a high yield. <P>SOLUTION: In surface defect inspection of the glass substrate for the magnetic disk, a glass substrate which is determined to be unusable as a double-sided magnetic disk according to a result of inspection to determine whether it is usable as the glass substrate for the double-sided magnetic disk or not, is subjected to a determination on which side of the substrate surface the surface defect exists (or on both sides). The substrate which has a surface defect only on either side, is used as a substrate for a single-sided magnetic disk by making the surface with no surface defect as a magnetic recording face. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk 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). The magnetic disk is manufactured by laminating a magnetic layer and 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.

  In addition, with the recent increase in recording density in HDD devices, the spacing between the recording / writing head (hereinafter referred to as the head) and the magnetic disk (hereinafter referred to as the flying height) has become very narrow, from several tens of nm to several nm. It is coming. For this reason, if a minute irregularity defect exists on the magnetic disk, the magnetic disk and the head come into contact with each other, causing a failure of the HDD device. In this minute irregularity defect, there are damage system defects in which the material of the magnetic disk substrate itself is damaged in some form, and abrasive grain residue generated during polishing to improve the flatness of the magnetic disk substrate, There is a foreign matter defect such as a foreign matter adhered / residual during cleaning or drying.

  Here, the damage system defect refers only to damage that has an adverse effect on the function of the magnetic disk or is likely to occur. That is, even if the material of the magnetic disk substrate itself is damaged, if the damage does not have a negative effect on the function of the magnetic disk, the damage is not a damaged defect. Similarly, a foreign substance defect refers only to a foreign substance or the like that adversely affects the function as a magnetic disk. That is, even if there is a foreign substance or the like on the surface of the magnetic disk substrate, the foreign substance is not a foreign substance defect if the foreign substance or the like is not likely to have a negative effect on the function of the magnetic disk. The foreign-system defect is caused by particles / contaminants attached at the time of processing the end face of the substrate being detached from the surface and reattached to the glass substrate surface in a subsequent cleaning process.

For the purpose of preventing foreign material defects caused by contaminants on the end face, the end face is polished after the glass substrate is shaped with a cutter or a drill, so that foreign matters / contaminants remain on the end face of the glass substrate. It has been proposed to make it difficult (for example, Patent Document 1).
JP-A-11-221742

  However, the method described in Patent Document 1 can prevent foreign matters from adhering to the substrate surface to some extent, but damage system defects such as scratches cannot be removed from the glass substrate surface. Also, some foreign-system defects cannot be removed by cleaning once attached to the substrate surface. Defects that cannot be corrected even after cleaning (hereinafter referred to as surface defects), such as damaged defects and foreign matter defects that cannot be removed by cleaning, are in the state of the magnetic disk substrate before vapor deposition of the magnetic material. It is important to inspect the presence or absence to prevent defective products from flowing into the subsequent process.

  Usually, surface defect inspection of a mass-produced glass substrate for magnetic disk is optical using reflected light (including scattered light) from the substrate such as visual or optical automatic visual inspection (AOI). The system must be used. However, since the glass substrate is a transparent body, when an inspection based on the reflected light of one surface is performed, it will be affected by the other surface (back surface), and the surface defect will be any surface of both surfaces of the substrate. It is difficult to identify what is in In addition, it is difficult to inspect all mass-produced substrates using a system that can inspect only one side from the viewpoint of inspection accuracy and productivity. Therefore, when a surface defect exists on either one of both surfaces of the substrate, it is usually determined as a defective product.

  Here, as described above, damage or foreign matter on the surface of the substrate becomes a defect only when they adversely affect the function of the magnetic disk or there is a possibility of such a problem. Therefore, criteria for the damage or foreign matter on the substrate surface that are determined in advance (the threshold value for the signal intensity from the damage or foreign matter in the inspection, or the defect count number exceeding the threshold value, the inspection criteria below). If it is not satisfied, the damage and foreign matter are judged as surface defects. The inspection criteria threshold value, reference value, and the like are determined empirically in relation to damage in inspection, signal intensity from foreign matter, defect count, and adverse effects on the function of the magnetic disk.

  On the other hand, due to recent market demands and advances in microfabrication technology, magnetic disks are becoming smaller and higher in density, and now, for example, a 1.8-inch magnetic disk has reached a storage capacity of 40 GB on both sides. Yes. However, depending on the application, a single-sided storage capacity (for example, 20 GB) may be sufficient, and there is such a need. When responding to such needs, a magnetic disk substrate (hereinafter referred to as a double-sided magnetic disk substrate) that uses both sides as a magnetic recording surface and a magnetic disk substrate (hereinafter referred to as a single-sided surface) that uses only one side as a magnetic recording surface. If a magnetic disk substrate is manufactured in separate steps, the waste is inevitably increased. That is, when the surface defect inspection of the double-sided magnetic disk substrate is performed visually or with an optical automatic visual inspection apparatus as described above, even if there is a surface defect on only one side, it becomes a defective product, and single-sided magnetic There has been a problem that even products that can be used as disk substrates are treated as defective products.

  In view of the above problems, an object of the present invention is to provide a method for efficiently producing a double-sided magnetic disk substrate and a single-sided magnetic disk substrate by efficiently extending the yield.

  In order to achieve the above object, the present inventors have inspected whether or not the magnetic disk substrate is used as a double-sided magnetic disk substrate in the surface defect inspection, and as a result, cannot be used as a double-sided magnetic disk substrate. Inspect the surface defect on which side of the substrate (or on both sides) against the judgment, and if there is a surface defect on only one side of the substrate, It was considered to be used as a single-sided magnetic disk substrate having a magnetic recording surface.

  That is, the method for manufacturing a glass substrate for a magnetic disk according to the present invention includes a step of producing a glass substrate for a magnetic disk processed so that two main surfaces of an annular transparent glass substrate are magnetic recording surfaces, The two main surfaces of the glass substrate for magnetic disk are inspected using reflected light including back surface reflected light from the substrate, and the glass substrate for magnetic disk uses both surfaces of the two main surfaces as magnetic recording surfaces. A first inspection step for determining whether or not it can be used, and a glass substrate for a magnetic disk that has been determined to be unusable in the first inspection step, respectively, inspecting the two main surfaces, and of the two main surfaces A second inspection step for determining whether only one of the two can be used as a magnetic recording surface, and manufacturing a glass substrate for a double-sided magnetic disk or a glass substrate for a single-sided magnetic disk It is characterized in.

  In the method for manufacturing a glass substrate for a magnetic disk, the first inspection step inspects for the presence or absence of surface defects on the two main surfaces, and when no surface defects are found on both of the two main surfaces, the magnetic disk A glass substrate for a double-sided magnetic disk can be used as the glass substrate. In addition, it is preferable that the first inspection process is performed by visual inspection or optical automatic appearance inspection.

  The second inspection step inspects which surface of the two main surfaces has a surface defect, and if a surface defect is found in only one of the two main surfaces, the magnetic disk A glass substrate for a single-sided magnetic disk can be used as the glass substrate. Furthermore, it is preferable that the second inspection step is an inspection using a shadowing effect.

  A magnetic disk according to the present invention comprises a glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk, and a magnetic recording layer formed on the glass substrate for a magnetic disk. To do.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention, as a result of the surface defect inspection of the glass substrate for a double-sided magnetic disk, the surface on either side of the substrate surface is compared with a substrate that has been treated as a defective product in the past. By inspecting whether there is a defect, a substrate that can be used as a glass substrate for a single-sided magnetic disk can be extracted, and the yield can be improved in manufacturing the glass substrate for a magnetic disk.

  Embodiments of the present invention will be described below with reference to the drawings, examples and the like. In addition, these figures, Examples, etc. and description illustrate the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments may belong to the category of the present invention as long as they match the gist of the present invention.

  As the material for the magnetic disk substrate, aluminosilicate glass, soda lime glass, borosilicate glass, 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 magnetic disk manufacturing process includes a material processing process and a first lapping process; an end shape process (a coring process for forming a hole, and a chamfered surface at an end (outer peripheral end and / or inner peripheral end). Chamfering step (chamfered surface forming step)); end surface polishing step (outer peripheral edge and inner peripheral edge); second lapping step; main surface polishing step (first and second polishing step); chemical strengthening step; recording layer It includes processes such as isoformation process.

Below, each process of the manufacturing process of a magnetic disc is demonstrated.
(1) Material processing step and first lapping step First, in the material processing step, for example, a molten glass is used as a material, and a known manufacturing method such as a press method, a float method, a down draw method, a redraw method, or a fusion method is used. Can be manufactured. 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.

(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 both surfaces of the glass substrate, it is preferable to perform the immersion 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, both main surfaces are mirror-polished using a soft foam resin polisher by a double-side polishing apparatus having a planetary gear mechanism. As the slurry, cerium oxide abrasive grains or colloidal silica finer than the cerium oxide abrasive grains used in the first polishing step can be used.

(8) 1st inspection process After wash | cleaning by the normal method the glass substrate which said final polishing process was finished, a 1st inspection process is performed. In the first inspection step, the presence or absence of surface defects is inspected on both surfaces of the glass substrate whose surfaces are mirror-polished in the steps as described above, using visual inspection or an optical automatic visual inspection apparatus.

  The inspection examines the presence or absence of damage or foreign matter on the glass surface after cleaning, and if there is damage or foreign matter, they are pre-determined inspection criteria (threshold for signal strength from damage or foreign matter in inspection, or It is examined whether or not a reference value or standard value defined by a defect count exceeding the threshold value is satisfied. If the inspection criteria are satisfied, it is determined that there is no surface defect. If the inspection criteria are not satisfied, it is determined that there is a surface defect. As the inspection criteria threshold value, reference value, etc., values empirically determined from the relationship between the signal intensity or defect count from damage or foreign matter in inspection and the adverse effect on the function of the magnetic disk are used.

  In this inspection, those having no surface defects on both sides are selected. The selected glass substrate can be used as a glass substrate for a double-sided magnetic disk. On the contrary, those having surface defects on at least one surface of the substrate are not selected and the next second inspection step is performed.

  In the first inspection step, it does not matter which surface of the glass substrate has a surface defect, so it can be carried out using a visual or optical automatic visual inspection device or the like, and at least the substrate. Since the inspection can be completed when it is determined that any one of the surfaces has surface defects, the inspection time can be shortened.

(9) Second inspection step In the second inspection step, the surface defect on either side of the glass substrate that is not selected in the first inspection step, that is, a glass substrate having a surface defect on at least one surface of the substrate. Check for the presence. This inspection is performed using a shadowing effect using a visual inspection by a CCD camera or human eyes. Here, a method using a CCD camera will be described with reference to the drawings.

  FIGS. 1A and 1B are views of a state in which a surface defect inspection in the second inspection step is performed on the glass substrate 11 from the side. In FIG. 1, the upper surface of the glass substrate 11 is the A surface and the lower surface is the B surface. CCD cameras 12 and 13 are installed on the A-side and B-side of the glass substrate 11, respectively. The CCD camera 12 on the A side is adjusted so that the surface of the A side is in focus, and the CCD camera 13 on the B side is adjusted so that it is in focus on the surface of the B surface. Light is incident on the glass substrate 11 from the A surface side by the light source 14. The CCD camera 12 on the A surface side is arranged at a position where the light reflected from the A surface of the light from the light source 14 can be received. The CCD camera 13 on the B surface side is arranged at a position where light transmitted from the light source 14 through the glass substrate 11 can be received.

  In the surface defect inspection apparatus having such a configuration, as shown in FIG. 1A, when there is a surface defect 15 on the A surface side, the surface of the A surface is focused on the CCD 12 on the A surface side. Therefore, the outline of the surface defect 15 can be clearly seen. On the other hand, in the CCD 13 on the B surface side, since the surface of the B surface is focused, the contour of the surface defect 15 looks blurred. On the contrary, as shown in FIG. 1B, when there is a surface defect 16 on the B surface side, the outline of the surface defect 16 can be clearly seen in the CCD 13 on the B surface side, and the surface defect in the CCD 12 on the A surface side. 16 outlines appear blurred. By such inspection, it can be determined whether the surface defect is on the A side or the B side.

  The optical glass substrate 11 is moved in the horizontal direction and the light from the light source 14 is scanned over the entire A surface of the glass substrate 11 to inspect for surface defects on the A surface or B surface of the glass substrate 11. .

  As a result of the above inspection, a glass substrate having a surface defect only on the A surface can be used as a single-sided magnetic disk glass substrate using the B surface having no surface defect as a magnetic recording surface. Conversely, a glass substrate having a surface defect only on the B surface can be used as a single-sided magnetic disk glass substrate using the A surface without a surface defect as a magnetic recording surface. Glass substrates having surface defects on both sides are treated as defective products.

  As described above, in the method for manufacturing a glass substrate for magnetic disk according to the present invention, as a result of the first inspection process which is a surface defect inspection of the glass substrate for double-sided magnetic disk, it can be used as a glass substrate for double-sided magnetic disk. In the second inspection step, a substrate that can be used as a single-sided magnetic disk glass substrate is extracted by inspecting which surface of the substrate surface has a surface defect in the second inspection step. Therefore, the yield can be improved as compared with the case where all the surface defects on one of the surfaces in the first inspection process are handled as defective products. Furthermore, productivity can be improved compared with the case where all the substrates manufactured in large quantities are test | inspected using the system which can test | inspect only one side.

  A magnetic disk can be manufactured by forming at least a magnetic layer on the glass substrate for a magnetic disk manufactured by the process described above. That is, a magnetic disk is usually manufactured by sequentially laminating an underlayer, a magnetic layer, a protective layer, and a lubricating layer on a magnetic disk glass substrate. The underlayer in the magnetic disk is appropriately selected according to the magnetic layer. A magnetic layer or the like is laminated on both sides of the glass substrate for a double-sided magnetic disk, and on the side having no surface defect in the case of a glass substrate for a single-sided magnetic disk.

  In addition, this invention is not limited to the said embodiment, It can implement by changing suitably. For example, in the above embodiment, the light source 14 is installed on the A surface side (upper surface side in FIG. 1) and light is incident from the A surface side in FIG. 1, but the light source 14 is installed on the B surface side. Then, light may be irradiated from the B surface side. In that case, the CCD camera 12 on the A side is disposed at a position where light transmitted from the light source 14 through the glass substrate 11 can be received. The CCD camera 13 on the B side is arranged at a position where the light reflected from the B side of the light from the light source 14 can be received.

  Moreover, in the said embodiment, in FIG. 1, the glass substrate 11 is moved to a horizontal direction, and the light from the light source 14 is scanned over the whole A surface of the glass substrate 11, A surface of the glass substrate 11 or Although an example of inspecting the presence or absence of surface defects on the B surface has been shown, conversely, the light source 14 and the CCD cameras 12 and 13 may be moved in the horizontal direction.

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

The figure for demonstrating the surface defect inspection in embodiment of this invention.

Explanation of symbols

11 Glass substrate 12, 13 CCD camera 14 Light source 15, 16 Surface defect

Claims (6)

A step of producing a glass substrate for a magnetic disk processed so that two main surfaces of an annular transparent glass substrate are magnetic recording surfaces;
The two main surfaces of the glass substrate for magnetic disk are inspected using reflected light including back surface reflected light from the substrate, and the glass substrate for magnetic disk has a magnetic recording surface on both surfaces of the two main surfaces. A first inspection step for determining whether or not it can be used as,
Whether or not each of the two main surfaces is inspected for each of the glass substrates for a magnetic disk determined to be unusable in the first inspection step, and whether only one of the two main surfaces can be used as a magnetic recording surface is determined. A second inspection step to determine;
The manufacturing method of the glass substrate for magnetic discs which manufactures the glass substrate for double-sided magnetic discs, or the glass substrate for single-sided magnetic discs.   The first inspection step inspects the presence or absence of surface defects on the two main surfaces, and if no surface defects are found on both of the two main surfaces, the magnetic disk glass substrate is used for the double-sided magnetic disk. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate is a glass substrate.   The method for manufacturing a glass substrate for a magnetic disk according to claim 2, wherein the first inspection step is performed by visual inspection or optical automatic appearance inspection.   The second inspection step inspects which surface of the two main surfaces has a surface defect, and if there is a surface defect in only one of the two main surfaces, the magnetic disk 4. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate is a glass substrate for a single-sided magnetic disk.   The method of manufacturing a glass substrate for a magnetic disk according to claim 4, wherein the second inspection step is an inspection using a shadowing effect.   A magnetic disk comprising: a magnetic disk glass substrate produced by the method for producing a magnetic disk glass substrate according to claim 1; and a magnetic recording layer formed on the magnetic disk glass substrate.

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