JP2009099249A - Method for manufacturing glass substrate for magnetic disc and method for manufacturing magnetic disc - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high processing rate from the start of polishing and to reduce processing time when a main surface of a mirror glass plate is polished with fine fixed abrasive grains. <P>SOLUTION: A method for manufacturing a glass substrate processes the mirror glass plate 3 having a mirror on its main surface to obtain required flatness and surface roughness by using a diamond sheet 10, i.e., fixed abrasive grains. As preprocessing, the surface of the mirror glass plate 3 is roughened by a mechanical or chemical method to the extent that the diamond sheet 10 effects polishing. Then, the diamond sheet 10 is used to machine the surface of the mirror glass plate 3 to obtain desired board thickness and flatness. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a glass substrate for a magnetic disk used in a magnetic disk device such as a hard disk drive (hereinafter referred to as “HDD”) and a method of manufacturing a magnetic disk using the glass substrate.

  In recent years, a glass substrate has been used as one of magnetic disk substrates suitable for increasing the recording density. Since the glass substrate has higher rigidity than the metal substrate, it is suitable for high-speed rotation of the magnetic disk device. Moreover, since a smooth and flat surface is obtained, the glass substrate is suitable for improving the S / N ratio and increasing the recording density by reducing the flying height of the magnetic head.

  In general, glass substrates for magnetic disks are prepared by heating and melting glass raw materials to prepare molten glass, forming the molten glass into a plate-shaped glass disk, and processing and polishing the glass disk formed into a plate shape. Then, the glass substrate is manufactured by sequentially executing the process of manufacturing the glass substrate.

  In forming molten glass into a plate-like glass disk, a forming method such as a press method or a float method is employed. In the pressing method, a cylindrical glass base material is cut into a glass disk having a thickness slightly thicker than the magnetic disk substrate, and the shape of the glass disk is adjusted and processed to a desired flatness and thickness. In a grinding process for processing a glass disk to a desired flatness and plate thickness, a lapping device is used to grind the glass disk to a target plate thickness and to process to a target flatness. A glass disk is sandwiched between an upper surface plate and a lower surface plate of a wrapping apparatus, and processed using loose abrasive grains (slurry) while rotating the glass disk in the opposite direction. As the loose abrasive grains, abrasive grains having a particle size according to the predetermined dimensional accuracy and shape accuracy of the glass disk are used. In the first grinding process (lap 1), loose abrasive grains having a large particle size (for example, an average particle size of about 30 μm) are used. The plate is ground using a grain until the plate thickness becomes 0.92 mm, and the second grinding process (lap 2: fine lapping process) uses a free abrasive grain having a small grain size (for example, an average grain size of about 10 μm). Grinding until the thickness is 0.67 mm.

In the float process, a glass disk is cut out from a sheet glass produced by the float process, the shape of the glass disk is adjusted, and the main surface is ground. Since the main surface of the plate glass produced by the float process is mirror-finished from the beginning, the flatness and the plate thickness are superior to the press glass. Therefore, the lapping 1 using the loose abrasive grains having a large particle diameter is omitted, and grinding (lap 2) using the loose abrasive grains having a small particle diameter is performed from the beginning.
JP 2002-55061 A

  By the way, in the grinding process of the lap 2, if fixed abrasive grains having a particle size smaller than that of loose abrasive grains are used as a grinding pad, cracks generated in the glass substrate can be reduced, and the grinding process of the lap 2 is completed. The surface roughness at the time can be reduced. For example, a diamond sheet having diamond particles attached to the sheet is used as a grinding pad. Since the diamond particles to be used are smaller than the particle size of the alumina-based particles used as the free abrasive grains, the cracks can be shallowed and the surface roughness can be reduced.

  However, mirror-like glass whose surface roughness is Ra = 0.001 μm or less like a plate glass manufactured by the float process is polished until the desired flatness is obtained without deteriorating the surface roughness as much as possible. For this purpose, fine abrasive grains are required. If mirror glass is to be processed using such a fine abrasive pad, the processing rate at the beginning of processing must be kept at a very low speed (1/5 to 1/10 or less of the normal processing rate). However, there is a problem that the processing time becomes long. In addition, deep scratches called scratches are likely to occur at the beginning of processing. If the machining allowance is less than the scratch depth, this scratch cannot be removed, resulting in poor quality.

  The problem that the processing rate at the start of the polishing is low is not limited to the mirror plate glass manufactured by the float process, and occurs in common when the mirror plate glass is processed using a grinding pad of fine abrasive grains. It is a problem.

  The present invention has been made in view of such points, and when processing the main surface of the mirror-finished plate glass with fine fixed abrasive grains, it is possible to realize a high processing rate from the start of processing, and to shorten the processing time. Another object of the present invention is to provide a method for manufacturing a glass substrate and a method for manufacturing a magnetic disk, which can prevent generation of scratches.

  The method for producing a glass substrate for a magnetic disk according to the present invention comprises a surface grinding step of processing a mirror plate glass whose main surface is a mirror surface into necessary flatness and surface roughness using fixed abrasive grains, Before the surface grinding step using the fixed abrasive, the method comprises a roughening step of roughening the mirror plate glass surface by a mechanical method or a chemical method to such an extent that the fixed abrasive grinds. And

  According to this manufacturing method, before processing the mirror-finished plate glass surface using fixed abrasive grains, the mirror-plate glass surface is roughened by a mechanical method or a chemical method to the extent that the fixed abrasive grains are polished. A convex portion that is caught by the fixed abrasive grains is formed on the mirror surface plate glass surface, and the fixed abrasive grains are prevented from sliding on the mirror surface plate glass surface, and a high processing rate can be realized from the start of processing by the fixed abrasive grains.

  As a mechanical method in the roughening step, polishing using free abrasive grains can be used. As a chemical method, an etching action by a chemical solution can be used. According to the mechanical method using the loose abrasive grains, it becomes easy to control and manage the quality of the processed surface, and according to the chemical method using the etching action by the chemical solution, the generation of cracks can be prevented. In particular, it is preferable that the chemical method using the etching action by the chemical solution is frost processing. By this frost processing, it is possible to efficiently roughen the surface of the specular plate glass to such an extent that the fixed abrasive grains polish.

  In the method for manufacturing a glass substrate for a magnetic disk of the present invention, in the roughening step, a mirror surface plate glass having a mirror surface roughness of Ra = 0.001 μm or less is applied to the surface roughness Ra = 0.01-0. The surface is preferably roughened to 4 μm.

  The method for producing a glass substrate of the present invention is characterized in that the surface roughness of the mirror-finished plate glass in the roughening step is A, the average grain size of the fixed abrasive grains is B, and B / A <50. . According to this manufacturing method, by satisfying the condition of B / A <50, the surface of the specular plate glass can be roughened to such an extent that the fixed abrasive grains polish.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention, in the step of processing the mirror-plate glass surface using the fixed abrasive, the surface roughness Ra is 0.1 μm or less and the flatness is 7 μm or less. Is preferred.

  The method for producing a magnetic disk of the present invention is characterized in that at least a magnetic layer is formed on the main surface of the glass substrate produced by the method for producing a glass substrate.

  According to the present invention, when the main surface of the mirror-finished plate glass is polished with fine fixed abrasive grains, a high processing rate can be realized from the start of polishing, the processing time can be shortened, and the occurrence of scratches can be prevented. Can do.

  Hereinafter, a method for manufacturing a glass substrate for a magnetic disk and a method for manufacturing a magnetic disk will be described as an embodiment of the present invention. In the following description, an example of using a sheet glass material manufactured by a float method as a material of a glass substrate for a magnetic disk will be described, but the present invention is not limited to a sheet glass material manufactured by a float method. The method can also be applied to a mirror plate glass manufactured by the method. In addition, the present invention can be similarly applied to applications other than the magnetic disk glass substrate as long as the surface of the specular glass plate is processed with fine fixed abrasive grains to obtain the desired flatness and surface roughness. is there. In addition, a mirror surface means here the surface whose surface roughness (arithmetic mean roughness (Ra)) is 0.01 micrometer or less.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present embodiment, the fixed abrasive grains effectively polish the plate glass material whose main surface is a mirror surface on the surface (mirror surface) of the plate glass material. The mirror surface of the plate glass surface is roughened by a mechanical method or a chemical method.

  As a mechanical method for roughening the mirror surface of the plate glass material, free abrasive polishing using a flat polishing machine can be used. Polishing is performed using loose abrasive polishing so that the entire surface of the mirror-finished plate glass has a substantially uniform surface roughness Ra = 0.01 to 0.4 μm. According to the roughening using the mechanical method, there is an advantage that the quality and control of the machined surface becomes easy.

As a chemical method for roughening the mirror surface of the plate glass material, an etching action by a chemical solution can be used. Examples of the chemical solution used in the chemical method include acidic ammonium fluoride and hydrofluoric acid. The mirror surface of the plate glass material can be roughened by an etching action with acidic ammonium fluoride or hydrofluoric acid. According to the roughening using a chemical method, there is an advantage that no cracks are generated. In addition, there is an advantage that the initial cost of introducing the equipment is low and automation becomes easy. As a chemical method for roughening the mirror surface of the plate glass material, frost processing is particularly preferable. Here, frost processing refers to processing in which the glass surface is treated with a chemical solution for etching added with a roughening agent. In this frost processing, etching proceeds in a state where the glass surface is locally masked by the surface roughening agent, so that the glass surface is effectively roughened (for example, surface roughness Ra after frost processing). However, the surface roughness Ra before frosting is about 5 times). As this roughening agent, those supplying HF ₂ ⁻ in the liquid are suitable, and examples thereof include HF, NH ₄ F, NaF, KF, and CaF ₂ . Moreover, the roughening state can be adjusted by adjusting the concentration and temperature of the chemical solution.

  The plate glass material having the mirror surface roughened as described above is ground using fixed abrasive grains so as to have a target flatness and plate thickness. The fixed abrasive is desirably finer than the loose abrasive. When the surface roughness of the plate glass material is “A” and the average grain size of the fixed abrasive grains is “B”, it is desirable that (B / A) <50 is satisfied.

  As a preferred embodiment, in order to remove scratches and distortions remaining in the grinding process using fixed abrasive grains, a hard polisher is used as a polisher and the glass substrate surface is polished, and the first polishing step A second polishing step of polishing the surface of the glass disk with a soft polisher instead of the hard polisher is performed to maintain a smooth surface while maintaining the flat surface obtained in the step.

  Moreover, the glass substrate which finished the grinding | polishing process may give chemical strengthening. When the type of glass is particularly aluminosilicate glass, the bending strength is increased and the depth of the compressive stress layer is also deepened by chemical strengthening. The chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method, but chemical strengthening by a low-temperature ion exchange method is preferable in practice.

  In the method for manufacturing a glass substrate for a magnetic disk, before processing the mirror-plate glass surface using the fixed abrasive (before the main surface grinding step), the mirror-plate glass surface is mechanically moved to the extent that the fixed abrasive is polished. Roughened by mechanical or chemical methods. Thereby, the convex part from which the fixed abrasive is caught is formed on the mirror surface plate glass surface, and the slip of the fixed abrasive on the mirror surface plate glass surface is prevented. Thereby, in a surface grinding process, a high processing rate can be realized from the start of processing by fixed abrasive.

  In the main surface grinding step, the mirror plate glass surface is processed using fixed abrasive grains. In this case, it is preferable that the surface roughness Ra = 0.1 μm or less and the flatness is 7 μm or less.

  By forming at least the magnetic layer on the magnetic disk glass substrate obtained by the present invention, a magnetic disk suitable for increasing the recording density can be obtained.

  As the magnetic layer material, a hexagonal CoPt ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method for forming the magnetic layer, a method of forming a magnetic layer on a glass substrate by sputtering, for example, DC magnetron sputtering can be used. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled.

  In addition, it is preferable to provide a protective layer on the magnetic layer. By providing the protective layer, the surface of the magnetic disk can be protected from the magnetic recording head flying over the magnetic disk. As a material for the protective layer, for example, a carbon-based protective layer is suitable. Further, it is preferable to further provide a lubricating layer on the protective layer. By providing the lubricating layer, wear between the magnetic recording head and the magnetic disk can be suppressed, and the durability of the magnetic disk can be improved. As a material for the lubricating layer, for example, PFPE (perfluoropolyether) is preferable.

  According to the present invention, a glass substrate used for a magnetic disk mounted on a load / unload type magnetic disk apparatus advantageous for increasing the recording density is stably manufactured from a plate-like glass obtained by a float process. be able to. In addition, by manufacturing a magnetic disk using the magnetic disk glass substrate obtained by the manufacturing method of the present invention, the manufacturing yield of the magnetic disk glass substrate is high, so that the manufacturing cost of the magnetic disk can be reduced. It becomes possible.

(Example)
Hereinafter, embodiments of the present invention will be specifically described with reference to examples. In addition, this invention is not limited to a following example.

  (1) Cutting step, (2) Shape processing step, (3) Roughening step, (4) Fine lapping step, (5) End surface polishing step, (6) Main surface polishing step, (7) Chemical strengthening Through the process, the magnetic disk glass substrate of this example was manufactured. The conceptual diagram of the process from (1) to (4) is shown in FIG.

  In addition, the plate-shaped glass raw material for manufacturing the glass substrate for magnetic discs was manufactured by the float process. In the float process, the melt is poured over molten tin and solidified as it is. Since both surfaces of the plate glass were the glass free surface and the glass / tin interface, a plate-like glass material having a mirror surface of Ra 0.001 μm or less was obtained without polishing.

(1) Cutting process Using a glass plate material 1 made of aluminosilicate glass having a thickness of 0.95 mm manufactured by the float method and cut into a square of a predetermined size, the top surface is magnetically A circular scoring line 2 was formed to describe substantially the outer peripheral side and the inner peripheral side of the region to be the disk glass substrate. As the aluminosilicate _{glass, SiO} 2: 58 wt% to 75 _wt%, Al _{2 O} 3: 5 wt% to 23 wt%, _Li 2 O: 3% to 10% by weight, _Na 2 O: 4 A glass for chemical strengthening containing from 13% by mass to 13% by mass was used. Next, the top surface side of the sheet glass 1 on which the cut lines 2 are formed is heated by a heater as a whole, and the cut lines 2 are advanced to the bottom surface side of the sheet glass 1 to have a predetermined diameter. (Specular surface glass) 3 was cut out.

(2) Shape processing step Next, after grinding the outer peripheral end surface and the inner peripheral end surface to an outer diameter of 65 mmφ and an inner diameter (diameter of a circular hole in the central portion) of 20 mmφ, a predetermined amount is applied to the outer peripheral end surface and inner peripheral end surface. Chamfered. The surface roughness of the end surface of the glass disk at this time was about 2 μm in Rmax. In general, a 2.5 (inch) type HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) Roughening step A mechanical method using loose abrasive polishing with a flat polishing machine was applied. Polishing was performed using loose abrasive polishing so that the entire surface of the specular glass disk 3 had a substantially uniform surface roughness Ra = 0.01 μm to 0.4 μm. It is desirable that the target surface roughness in the roughening step is determined in relation to the particle size of the fixed abrasive used in the subsequent fine lapping step. As described above, the average particle diameter B of the fixed abrasive grains is gradually calculated by the surface roughness (A) of the roughened glass disk 3 so that (B / A) <50 is satisfied. Here, the surface roughness of the glass disk 3 was Ra 0.27 μm.

(4) Precision lapping process (surface grinding process)
The main surface of the roughened glass disk 3 was ground using a fixed abrasive polishing pad. A diamond sheet 10 shown in FIG. 2 was used as a fixed abrasive polishing pad. The diamond sheet 10 is provided with diamond particles as abrasive grains. The diamond sheet 10 includes a sheet 11 made of PET as a base material. The average particle diameter of the diamond particles 12 was B = 4 μm. Therefore, B / A = 15, which satisfies the above (B / A) <50.

  In the fine lapping process, the roughened glass disk 3 is set in a lapping apparatus, and the surface of the disk is lapped using a diamond sheet 10 as shown in FIG. Was 0.1 μm or less, and the flatness was 7 μm or less.

  As described above, since the main surface of the glass disk 3 is roughened in advance in the roughening step, a convex portion that is caught by fine fixed abrasive grains is formed on the main surface of the glass disk 3, and the fixed abrasive. It is possible to prevent the problem that the grains slip on the surface of the material, and the processing rate in the fine lapping process can realize a high processing rate from the start of surface polishing.

(5) End face polishing step Next, the surface roughness of the end face (inner circumference, outer circumference) of the glass disk 3 is about 0.4 μm at Rmax and about 0.1 μm at Ra while rotating the glass disk 3 by brush polishing. Polished. Then, the surface of the glass disk 3 after the end face polishing was washed with water.

(6) Main surface polishing step Next, a first polishing step for removing scratches and distortions remaining in the lapping step described above was performed using a double-side polishing apparatus. In the double-side polishing apparatus, a glass disk 3 held by a carrier is brought into close contact between upper and lower polishing surface plates to which a polishing pad is attached, the carrier is meshed with a sun gear and an internal gear, and the glass disk is moved up and down. Clamping with a polishing platen. Thereafter, a polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass disk, whereby the glass disk revolves while rotating on the polishing surface plate to simultaneously polish both surfaces. Specifically, a hard polisher (hard foamed urethane) was used as the polisher, and the first polishing step was performed.

  Next, using the same double-side polishing apparatus as that used in the first polishing step, the second polishing step was performed by replacing the polisher with a polishing pad of soft polisher (suede). This second polishing step is, for example, mirror polishing for finishing the surface roughness of the main surface of the glass disk to a smooth mirror surface having an Rmax of about 3 nm or less while maintaining the flat surface obtained in the first polishing step. It is processing.

(7) Chemical strengthening process Next, the glass disk which finished the said washing | cleaning was chemically strengthened. Ion exchange is performed to ions (Na ⁺ and K ⁺ ) having a larger ion radius than ions existing on the surface of the glass substrate (for example, Li ⁺ and Na ⁺ when using an aluminosilicate glass). On the surface of the glass substrate (for example, from the surface of the glass substrate to about 5 μm), ions are exchanged with atoms having a large ion radius, thereby applying a compressive stress to the glass surface to increase the rigidity of the glass substrate. In this way, a glass substrate for a magnetic disk of this example was obtained.

  Next, the following film formation process was performed on the magnetic disk glass substrate obtained in this example to obtain a magnetic disk. Using a sputtering apparatus, an adhesion layer, a soft magnetic layer, a first underlayer, a second underlayer, and a magnetic layer are sequentially formed on the glass substrate, and then a carbon-based protective layer is formed by a plasma CVD method. A lubricating layer was formed thereon by a dip method.

  The adhesion layer is made of a Ti-based alloy thin film to a thickness of 10 nm, the soft magnetic layer is made of a Co-based alloy thin film to a thickness of 60 nm, and the first underlayer is made of a Pt-based alloy thin film. Was 7 nm, a Ru-based alloy thin film was used for the second underlayer, and the film thickness was 40 nm. A CoPtCr alloy thin film was used for the magnetic layer, and the film thickness was 20 nm. The protective layer was a diamond-like carbon protective layer and was formed by plasma CVD. The lubricating layer was formed by immersing the magnetic disk in a perfluoropolyether (PFPE) liquid lubricant and baking it at a temperature of 110 ° C. for 60 minutes. In this way, a magnetic disk for the perpendicular magnetic recording system was formed.

(Comparative example)
In the same manner as in the example, a cutting process and a shape processing process are performed on a sheet glass material 1 made of aluminosilicate glass having a thickness of 0.95 mm manufactured by a float process, and fixed abrasive grains are not passed through a roughening process. A precision wrapping process using was performed. When the processing rate in the fine lapping process was examined, it was very low as shown in FIG.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, the material, the number, the size, the 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.

FIG. 1 is a schematic view of some steps of a method for manufacturing a glass substrate for a magnetic disk according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a diamond sheet. FIG. 3 is a diagram showing a processing rate by fine lapping using fixed abrasive grains with and without a roughening step.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sheet-like glass material 2 Cutting line 3 Glass disk (mirror surface plate glass)
10 Diamond sheet 11 Sheet 12 Diamond particles

Claims (8)

A method for producing a glass substrate for a magnetic disk comprising a surface grinding step of machining a mirror-finished plate glass having a main surface as a mirror surface into a required flatness and surface roughness using fixed abrasive grains,
Before the surface grinding step using the fixed abrasive, the method comprises a roughening step of roughening the mirror plate glass surface by a mechanical method or a chemical method to such an extent that the fixed abrasive grinds. A method for manufacturing a glass substrate for a magnetic disk.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein in the roughening step, a polishing process using loose abrasive grains is performed as the mechanical method.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the roughening step uses an etching action by a chemical solution as the chemical method.   4. The method for producing a glass substrate for a magnetic disk according to claim 3, wherein the chemical method using the etching action by the chemical solution is frost processing.   2. The roughening step comprises roughening a mirror-finished plate glass having a mirror surface roughness Ra = 0.001 [mu] m or less to a surface roughness Ra = 0.01-0.4 [mu] m. The manufacturing method of the glass substrate for magnetic discs in any one of Claims 1-4.   The surface roughness of the mirror-finished plate glass in the roughening step is A, the average grain size of the fixed abrasive grains is B, and B / A <50. The manufacturing method of the glass substrate for magnetic discs as described in any one of.   7. The step of processing a mirror-finished plate glass surface using the fixed abrasive grains is processed to have a surface roughness Ra = 0.1 μm or less and a flatness of 7 μm or less. The manufacturing method of the glass substrate for magnetic discs as described in any one of.   A magnetic disk manufacturing method comprising: forming at least a magnetic layer on a main surface of a glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 7. Method.

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