JP2010238303A - 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 magnetic disks, which has a considerably small number of defects existing on a surface with an arithmetic mean roughness (Ra) being at a level close to 0.1 nm, and is suitable as a substrate for a high-recording density magnetic disk. <P>SOLUTION: The magnetic disk glass substrate manufacturing method includes a washing step of washing the magnetic disk glass substrate. In the washing step, the magnetic disk glass substrate is washed by scrubbing with a liquid in which carbon dioxide is dissolved. <P>COPYRIGHT: (C)2011,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 depositing a NiP film on a metal substrate made of an aluminum-magnesium alloy or the like, or laminating a magnetic layer or a protective layer on a glass substrate or a ceramic substrate. 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.

  With respect to magnetic disks in which at least a magnetic layer is formed on a glass substrate for magnetic disks, the recording density has been increasing year by year, and magnetic disks having a magnetic layer containing granular particles have become mainstream. In such a magnetic layer, in order to achieve a higher recording density (for example, 160 GB or more / sheet), it is necessary to reduce the particle size of the granular particles or to increase the crystal orientation of the granular particles. . Thus, in order to reduce the particle size of the granular particles or increase the crystal orientation of the granular particles, it is required to reduce the characteristics, particularly the surface roughness, of the glass substrate for magnetic disks. An example of a magnetic disk glass substrate having a reduced surface roughness is disclosed in Patent Document 1.

JP 2006-95676 A

  On the other hand, in the manufacture of a magnetic disk glass substrate, a polishing process using a slurry is included. After the polishing step, foreign matters (for example, Fe contamination) derived from the slurry adhere to the magnetic disk glass substrate. The Fe contamination adhered to the magnetic disk glass substrate in this manner can be removed by acid cleaning. However, in acid cleaning under conditions where Fe contamination can be removed, magnetic disk glass is used. The main surface of the substrate becomes rough. As described above, in the current situation where it is required to reduce the surface roughness in order to increase the recording density, Fe contamination cannot be removed by such acid cleaning.

  The present invention has been made in view of the above points, and as a substrate for a high recording density magnetic disk, the arithmetic average roughness (Ra) has a very small amount of Fe contamination adhering to the surface at a level near 0.15 nm. It is an object of the present invention to provide a suitable method for producing a glass substrate for a magnetic disk.

  The method for producing a magnetic disk glass substrate of the present invention is a method for producing a magnetic disk glass substrate including a washing step of washing the magnetic disk glass substrate, and in the washing step, the magnetic disk glass substrate comprises: It is characterized by scrub cleaning with a liquid in which carbon dioxide gas is dissolved.

  According to this method, since the glass substrate for magnetic disks is scrubbed using a carbon dioxide gas solution, Fe contamination can be efficiently removed. Further, according to this scrub cleaning, since the glass substrate for magnetic disk is not roughened, it is possible to maintain a very low arithmetic surface roughness.

  In the method for producing a glass substrate for magnetic disk of the present invention, it is preferable that the cleaning step is performed on the glass substrate for magnetic disk whose main surface has been processed.

  In the method for manufacturing a magnetic disk glass substrate of the present invention, the scrub cleaning is preferably performed after acid cleaning and alkali cleaning are performed on the magnetic disk glass substrate.

  The method for manufacturing a magnetic disk glass substrate according to the present invention includes a cleaning step of cleaning the magnetic disk glass substrate. In the cleaning step, the magnetic disk glass substrate is scrubbed with a liquid in which carbon dioxide gas is dissolved. When the arithmetic average roughness (Ra) is in the vicinity of 0.15 nm, it is possible to obtain a glass substrate for a magnetic disk suitable for a high recording density magnetic disk with very little Fe contamination adhering to the surface.

It is a figure which shows the structure of a scrub cleaning apparatus.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a configuration of a scrub cleaning apparatus. The scrub cleaning apparatus shown in FIG. 1 is an apparatus that cleans the main surface 4 of the glass substrate 3 with a scrub brush 5 while ejecting a carbon dioxide gas solution 2 as a cleaning liquid from a shower nozzle 1. The scrub brush 5 is formed in a roller shape and sandwiches the glass substrate 3 from both sides. In this state, the scrub brush 5 is rotated and the glass substrate 3 is also rotated.

  In the present embodiment, the carbon dioxide gas solution 2 is generated by mixing carbon dioxide into ultrapure water (DL water). The carbon dioxide gas flow path 6 extends from a gas tank 7 filled with carbon dioxide gas, and is connected to a pure water flow path 8 for cleaning. Carbon dioxide gas is mixed and dissolved in pure water flowing through the flow path 8 at a connection point at a predetermined pressure (for example, 0.05 to 0.15 MPa). The carbon dioxide gas solution 2 generated in this way reaches the shower nozzle 1 through the flow path 8 and is subjected to scrub cleaning. In addition, the flow path 6 and 8 is provided with a valve 9 and valves 10, 11 and 12 in the middle thereof, and the flow paths 6 and 8 can be freely opened and closed. This makes it possible to control the amount of carbon dioxide mixed in, the pressure, and the route of pure water.

  Here, since carbon dioxide gas is easy to escape, it is preferable to mix in pure water as soon as possible before spraying on the glass substrate for magnetic disks. In particular, rather than preparing carbonated water in advance, by mixing carbon dioxide into the cleaning liquid at the time of use, a carbon dioxide solution having a desired concentration can always be obtained, and process management can be simplified. it can.

  Note that the amount of carbon dioxide mixed may be about 6.3 cc per 1 L (liter) of pure water, for example, in order to obtain a good cleaning effect. The specific resistance value of the carbon dioxide gas solution is preferably 0.05 to 0.11 MΩ · cm, for example, in order to obtain a good cleaning effect.

  As described above, scrub cleaning of the glass substrate for magnetic disk using the carbon dioxide gas solution 2 reduces the charge on the surface of the substrate, so that Fe contamination can be efficiently removed. Further, according to this scrub cleaning, since the glass substrate for magnetic disk is not roughened, it is possible to maintain a very low arithmetic surface roughness.

  The scrub cleaning of the magnetic disk glass substrate using the carbon dioxide gas solution 2 is preferably performed on the magnetic disk glass substrate whose main surface has been processed. Here, “processing of the main surface is completed” means that final polishing on the main surface is completed. This scrub cleaning is effective when chemical strengthening is performed on the magnetic disk glass substrate. Since chemical strengthening is performed by heating to 300 ° C. or higher, Fe contamination adheres to the surface of the magnetic disk glass substrate due to the high temperature. Although it is difficult to remove the Fe contamination thus fixed, this scrub cleaning can effectively remove the Fe contamination.

  The scrub cleaning is preferably performed after acid cleaning and / or alkali cleaning is performed to such an extent that the main surface of the magnetic disk glass substrate is not roughened. Here, acid cleaning refers to cleaning using acid chemicals, and alkali cleaning refers to cleaning using an alkaline detergent.

  As a preferred glass material for the magnetic disk glass substrate, aluminosilicate glass can be mentioned. The aluminosilicate glass can realize an excellent smooth mirror surface and can increase the breaking strength by, for example, chemical strengthening.

As the aluminosilicate glass, SiO ₂ : 62 wt% to 75 wt%, Al ₂ O ₃ : 5 wt% to 15 wt%, Li ₂ O: 4 wt% to 10 wt%, Na ₂ O: 4 wt% to 12% by weight, ZrO ₂ : 5.5% by weight to 15% by weight as a main component, and a weight ratio of Na ₂ O to ZrO ₂ is 0.5 to 2.0, Al ₂ O ₃ and ZrO ₂ The glass for chemical strengthening whose weight ratio is 0.4 to 2.5 is preferable.

  Further, the material forming the glass substrate for a magnetic disk manufactured in the present invention is not limited to the above-described materials. That is, as the material of the glass substrate, in addition to the aluminosilicate glass described above, for example, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or crystallized glass Examples thereof include glass ceramics.

  The manufacturing process of the glass substrate for a magnetic disk includes a material processing process and a first lapping process; an edge shape process (a coring process for forming a hole, a chamfered surface at an outer edge and / or an inner edge) Chamfering step (chamfered surface forming step)); second lapping step; end surface polishing step (outer peripheral end and inner peripheral end); main surface polishing step (first and second polishing step); chemical strengthening step : Includes processes such as a cleaning process. The main surface polishing step (second polishing step) and the chemical strengthening step may be in reverse order.

Below, each process of the manufacturing process of the glass substrate for magnetic discs is demonstrated.
(1) Material processing step and first lapping step First, in the material 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 pressing 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) Main surface polishing step (final polishing step)
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, colloidal silica abrasive grains (average particle diameter of 0.5 μm or less) finer than the cerium oxide abrasive grains used in the first polishing step can be used.

(7) Chemical strengthening step In the chemical strengthening step, the glass substrate that has been subjected to the lapping step and 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.

(8) Cleaning step The glass substrate for magnetic disk after chemical strengthening is immersed in a 20 ° C. water bath, maintained for about 10 minutes and rapidly cooled, and the alkali using ultrasonic waves is applied to the glass substrate for magnetic disk that has been quenched. After washing, rinse with water. Thereafter, scrub cleaning with a carbon dioxide gas solution is performed using the apparatus shown in FIG. 1, and then cleaning with acid, dip cleaning with pure water, IPA (isopropyl alcohol) cleaning, and vapor drying with IPA are performed. In addition, an ultrasonic wave is applied to each washing tank.

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 end of the glass substrate was mirror polished by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. And the glass substrate which finished the mirror polishing process was washed with water.

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. A urethane pad was used as a polishing pad in this polishing apparatus. 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, 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, density: 0.53 g / cm ³ ) was used. Moreover, as an abrasive | polishing agent, the colloidal silica abrasive | polishing agent with an average particle diameter of 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.

  Next, chemical strengthening was applied to the glass substrate after the final 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. And the alkali cleaning was performed with respect to the glass substrate which finished this chemical strengthening. Next, scrub cleaning was performed with a carbon dioxide solution using the apparatus shown in FIG. Thereafter, cleaning with acid, dip cleaning with pure water, IPA (isopropyl alcohol) cleaning, and steam drying with IPA were performed.

  When the surface defect of the obtained magnetic disk substrate was examined by an optical defect inspection apparatus (OSA), there were 8 particles of 0.3 μm or less. Further, when elemental analysis was performed on this defect using SEM / EDX, there was no Fe contamination. Further, when the arithmetic surface roughness of the obtained magnetic disk substrate was measured using an atomic force microscope having a resolution of 256 divisions of 5 μm × 5 μm, Ra = 0.14 nm. This is considered to be because Fe contamination was effectively removed without roughening the surface of the magnetic disk glass substrate by scrub cleaning with a carbon dioxide gas solution.

(Comparative Example 1)
A magnetic disk substrate was obtained in the same manner as in the example except that scrub cleaning was performed on the glass substrate after the chemical strengthening instead of scrubbing with a carbon dioxide gas solution (without using a carbon dioxide gas solution). It was. When defects on the surface of the obtained magnetic disk substrate were examined by an optical defect inspection apparatus, 30 particles of 0.3 μm or less were found. Further, when elemental analysis was performed on this defect using SEM / EDX, there were 6 Fe contaminations. Further, when the arithmetic surface roughness of the obtained magnetic disk substrate was measured using an atomic force microscope having a resolution of 256 divisions of 5 μm × 5 μm, Ra = 0.15 nm.

(Comparative Example 2)
Substrate for magnetic disk in the same manner as in the examples except that the glass substrate after this chemical strengthening was cleaned with carbon dioxide gas (without using scrub) instead of scrub cleaning with a carbon dioxide solution. Got. When defects on the surface of the obtained magnetic disk substrate were examined by an optical defect inspection apparatus, 103 particles of 0.3 μm or less were found. Further, when elemental analysis was performed on this defect using SEM / EDX, there were 10 Fe contaminants. Further, when the arithmetic surface roughness of the obtained magnetic disk substrate was measured using an atomic force microscope having a resolution of 256 divisions of 5 μm × 5 μm, Ra = 0.15 nm.

(Comparative Example 3)
A substrate for a magnetic disk was obtained in the same manner as in the example except that the glass substrate after the chemical strengthening was cleaned with water instead of scrub cleaning with a carbon dioxide gas solution. When defects on the surface of the obtained magnetic disk substrate were examined by an optical defect inspection apparatus, 150 particles of 0.3 μm or less were found. Further, when elemental analysis was performed on this defect using SEM / EDX, 13 Fe contaminations were found. Further, when the arithmetic surface roughness of the obtained magnetic disk substrate was measured using an atomic force microscope having a resolution of 256 divisions of 5 μm × 5 μm, Ra = 0.12 nm.

(Comparative Example 4)
A magnetic disk substrate was obtained in the same manner as in the example except that acid cleaning (pH 2) was performed on the glass substrate after chemical strengthening instead of scrub cleaning with a carbon dioxide gas solution. When defects on the surface of the obtained magnetic disk substrate were examined by an optical defect inspection apparatus, there were five particles of 0.3 μm or less. Further, when elemental analysis was performed on this defect using SEM / EDX, there was one Fe contamination. Further, when the arithmetic surface roughness of the obtained magnetic disk substrate was measured using an atomic force microscope of 5 μm × 5 μm and a resolution of 256 divisions, Ra = 0.17 nm. This is considered to be because the surface of the magnetic disk glass substrate was roughened by performing acid cleaning using an acid having a low pH.

  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.

DESCRIPTION OF SYMBOLS 1 Shower nozzle 2 Carbon dioxide gas solution 3 Glass substrate 4 Main surface 5 Scrub brush 6 Channel (for carbon dioxide) 7 Gas tank 8 Channel (for pure water and carbon dioxide solution) 9, 10, 11, 12 Valve

Claims (3)

  A method of manufacturing a glass substrate for a magnetic disk including a cleaning step for cleaning the glass substrate for a magnetic disk, wherein in the cleaning step, the glass substrate for a magnetic disk is scrubbed with a liquid in which carbon dioxide gas is dissolved. 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 the cleaning step is performed on the glass substrate for a magnetic disk whose main surface has been processed.   3. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the scrub cleaning is performed after acid cleaning and alkali cleaning are performed on the magnetic disk glass substrate.

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