JP2010231845A - Method for manufacturing glass substrate for magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To grind a surface in a state in which fluctuation of flatness is reduced, when glass substrates for magnetic disks worked under differing conditions are assembled and surfaces ground together. <P>SOLUTION: The method for manufacturing the glass substrate for the magnetic disk includes a surface-grinding step of adjusting the flatness of a principal surface of the glass substrate for the magnetic disk, by using fixed abrasive grains; and in the surface grinding step, when the glass substrates for the magnetic disks worked under various conditions are assembled and worked as one batch, the glass substrates for the magnetic disks are assembled to form the one batch, in such a way that the fluctuations in the plate thickness are reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for 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”).

  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. Further, 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.

  By the way, in the grinding process of the lap 2, the fixed abrasive grains having a smaller particle diameter than the loose abrasive grains are used as a grinding pad, the cracks generated in the glass substrate are made shallow, and the lap 2 is finished at the end of the grinding process. The surface roughness is reduced (Patent Document 1). 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.

JP 2008-254166 A

  In the manufacturing process of the magnetic disk glass substrate, there are various processes up to wrap 2 such as wrap 1, coring, chamfering and the like. Inferior goods may occur in the process up to these laps 2. In addition, the number of batches that can be processed in each process may be different. For this reason, in the lap 2, it is considered that the predetermined number that can be mounted on the apparatus used in the lap 2 is not all processed under the same conditions (same batch). As described above, when surface grinding is performed by combining magnetic disk glass substrates processed under different conditions, there is a problem that flatness varies if surface grinding is performed as it is. In particular, when lapping 2 is performed using fixed abrasive grains, this tendency becomes remarkable.

  The present invention has been made in view of such points, and when surface grinding is performed by combining magnetic glass glass substrates processed under different conditions, the surface grinding can be performed in a state where flatness is reduced in variation. An object of the present invention is to provide a method for producing a glass substrate for a magnetic disk.

  A method for producing a glass substrate for a magnetic disk according to the present invention is a method for producing a glass substrate for a magnetic disk comprising a surface grinding step for adjusting the flatness of the main surface of the glass substrate for a magnetic disk using fixed abrasive grains. In the surface grinding step, when the magnetic disk glass substrates processed under different processing conditions are combined and processed in one batch, one batch of the magnetic disk glass substrates is combined so as to reduce the thickness variation. It is characterized by.

  According to this method, since the variation in plate thickness is reduced and the glass substrates for magnetic disks are combined into one batch, when the surface grinding is performed by combining the glass substrates for magnetic disks processed under different conditions. In addition, surface grinding can be performed in a state where the flatness is reduced in variation.

  In the method for manufacturing a glass substrate for a magnetic disk of the present invention, it is preferable that the plate thickness variation is within a range of 1/10 of a processing amount in the surface grinding step. In this case, the processing amount is preferably 5% to 20% of the entire plate thickness.

  In the method for manufacturing a glass substrate for a magnetic disk of the present invention, the plate thickness variation is preferably within ± 10 μm.

  The method for manufacturing a glass substrate for a magnetic disk of the present invention includes a surface grinding step for adjusting the flatness of the main surface of the glass substrate for a magnetic disk using fixed abrasive grains, and in the surface grinding step, different processing conditions are provided. When the magnetic disk glass substrates processed in step 1 are combined and processed in one batch, the thickness variation is reduced and the magnetic disk glass substrate is combined into one batch, so that the processing was performed under different conditions. When surface grinding is performed in combination with a magnetic disk glass substrate, surface grinding can be performed in a state in which the flatness is reduced in variation.

It is a schematic diagram of a diamond sheet.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
In the manufacturing process of a magnetic disk glass substrate, there are usually a shape processing process, a lapping process, and a cutting process (coring, forming, chamfering). After these steps, inspection is performed, and defective products are removed. When defective products are removed in this way, it is considered that not all the predetermined numbers that can be mounted on the apparatus used in the lap 2 are processed under the same conditions (same batch). For example, if the predetermined number that can be attached to the apparatus used in the lap 2 is 100 sheets, and 248 sheets before the lap 2 are processed in the same batch, 200 of the batches are under the same conditions. Wrapping 2 can be performed with the processed one (100 sheets × 2 batches), but the remaining 48 sheets are combined with substrates processed under different conditions to perform lapping 2 as one batch.

  Normally, the variation in the plate thickness of the substrates in one batch is not so large, but there is a possibility that the variation in the plate thickness occurs between the substrates processed under such different conditions. This is due to the fact that there is a plate thickness distribution for each batch, and the peak of the plate thickness is different for each batch. Therefore, if the substrates processed under different conditions (batch) are combined into one batch, the variation in the plate thickness will inevitably increase. As described above, when surface grinding is performed by combining magnetic disk glass substrates processed under different conditions, the flatness will vary if the surface grinding is performed as it is. This becomes prominent when fixed abrasive grains are used for the wrap 2.

  When surface grinding is performed using fixed abrasive grains, a fixed abrasive pad is mounted on the upper and lower surface plates. This fixed abrasive pad is formed by dispersing abrasive grains on a base material. For example, as the fixed abrasive pad, a diamond sheet 10 as shown in FIG. The diamond sheet 10 includes a base material sheet 11 and diamond abrasive grains 12 as abrasive grains. As the substrate, PET (polyethylene terephthalate) or the like can be used.

  When surface grinding is performed using such fixed abrasive grains, the flatness of the substrate is affected by the manner of contact of the fixed abrasive pad, unlike the case of using loose abrasive grains. In other words, when loose abrasive grains are used, the abrasive grains can move, so that the abrasive grains are spread to some extent on the substrate having a large thickness and the substrate having a small thickness. For this reason, it is thought that the extent to which the variation in plate thickness affects the flatness is small. On the other hand, when using fixed abrasive grains, the abrasive grains themselves do not move, so that the fixed abrasive pad is processed in contact with a substrate having a large plate thickness and a substrate having a small plate thickness. For this reason, if the variation in the thickness of the substrate is large, the fixed abrasive pad comes into contact so as to absorb the variation, so the contact of the fixed abrasive pad on each substrate does not become uniform in the surface. As a result, the flatness is lowered.

  The present inventors pay attention to the above points, and in the surface grinding process using fixed abrasive grains, when the glass substrates for magnetic disks processed under different processing conditions are processed in one batch, the plate thickness variation By making the glass disk substrates for magnetic disks into one batch so that the surface roughness is reduced, the flatness of the magnetic disk glass substrates processed under different conditions is reduced. The present inventors have found that surface grinding can be performed in a state, and have reached the present invention.

  If there is a polishing process after the surface grinding process using fixed abrasive grains, the flatness of the substrate is adjusted up to this surface grinding process, that is, the flatness of the substrate is adjusted in the process after the surface grinding process. In this surface grinding process, it is very effective to combine the glass substrates for magnetic disks into one batch so that the plate thickness variation is reduced.

  In the present invention, different conditions in the process prior to the surface grinding process using fixed abrasive grains include different batches, different apparatuses used, and different product quality of the glass substrate. .

  Further, in the present invention, in the surface grinding process using the fixed abrasive grains, when the magnetic disk glass substrate is combined into one batch so as to reduce the plate thickness variation, In consideration of flatness and the like, it is preferable that the processing amount in the surface grinding step (so-called margin) is within a range of 1/10. In this case, in consideration of variations in the plate thickness, the processing amount is preferably 5% to 20% of the total plate thickness. In addition, in the surface grinding process using fixed abrasive grains, the plate thickness variation is reduced, and when the magnetic disk glass substrates are combined into one batch, the parallelism (plate thickness deviation) of the substrate is taken into consideration. Then, it is preferable that the thickness variation is within ± 10 μm.

  As described above, the method for manufacturing a magnetic disk glass substrate according to the present invention includes a surface grinding step of adjusting the flatness of the main surface of the magnetic disk glass substrate using fixed abrasive grains. When the magnetic disk glass substrates processed under different processing conditions are combined and processed in one batch, the thickness variation is reduced so that the magnetic disk glass substrates are combined into one batch. When the surface grinding process is performed by combining the glass substrates for magnetic disks processed in step 1, the surface grinding process can be performed with the flatness being reduced in variation. Thereby, the glass substrate for magnetic disks can be used for the main surface polishing process which is a post process in the state of desired flatness.

  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 step and a first lapping step (lapping 1); an end shape step (a coring step for forming a hole, an end portion (an outer peripheral end portion and / or an inner peripheral end portion) Chamfering step (chamfered surface forming step)); second lapping step (lap 2); end surface polishing step (outer peripheral end and inner peripheral end); main surface polishing step (first and first) 2 polishing step); chemical strengthening step: including steps such as a cleaning step. 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) 2nd lapping process In a 2nd lapping process, the 2nd lapping process is performed about both the main surfaces of the obtained glass substrate. 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. In the present invention, a fixed abrasive pad as shown in FIG. 1 is used.

(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.

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.

  Next, a second lapping process was performed on the glass substrate using fixed abrasive grains. The number of processing of one batch at this time was 100 sheets, and for this one batch, glass substrates processed under different processing conditions (different batches) were combined. At this time, the variation in the thickness of the glass substrates to be combined as one batch was small, specifically, within ± 10 μm which is 1/10 of about 100 μm which is the processing amount (allowance). This was 12% to 14% of the total thickness. When the flatness of each glass substrate after the second lapping was measured by FT-17 made by NIDEK, the flatness variation was 10 μm.

  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.

  A NiAl seed layer, a CrV underlayer, a CoPtCrB magnetic layer, and a hydrogenated carbon protective layer are formed on the glass substrate for a magnetic disk obtained through the above-described processes using an in-line type sputtering apparatus, and a dip method is used to form a part. A magnetic disk was produced by forming a fluoropolyether lubricating layer. A long-term reliability test was performed on the obtained magnetic disk. As a long-term reliability test, durability when mounted on a load / unload type HDD device was examined. The durability test was performed by performing a load / unload test a specified number of times (1 million times) using a DFH head with a head flying height (slider flying height) of 9 nm. As a result, problems such as head crashes did not occur on the magnetic disk produced from the glass substrate.

(Comparative example)
In the second lapping process, when the glass substrates processed under different processing conditions (different batches) are combined, the variation in the thickness of the glass substrate is set to ± 10 μm to 20 μm in the same manner as in the example. A disk glass substrate was prepared. In addition, when the flatness of each glass substrate after the second lapping was measured in the same manner as in the example, the flatness variation exceeded 10 μm. Using the magnetic disk glass substrate thus obtained, a magnetic disk was produced in the same manner as in the example. When the obtained magnetic disk was subjected to a long-term reliability test in the same manner as in the example, a head crash occurred after 300,000 times.

  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.

10 Diamond sheet 11 Sheet 12 Diamond abrasive grains

Claims (4)

  A method for manufacturing a glass substrate for a magnetic disk comprising a surface grinding step for adjusting the flatness of the main surface of the glass substrate for a magnetic disk using fixed abrasive grains, wherein the surface grinding step is performed under different processing conditions. When the magnetic disk glass substrates are processed in one batch, the magnetic disk glass substrate is made into one batch by combining the magnetic disk glass substrates so as to reduce variation in plate thickness. Production method.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the thickness variation is within a range of 1/10 of a processing amount in the surface grinding step.   3. The method of manufacturing a glass substrate for a magnetic disk according to claim 2, wherein the amount of processing is 5% to 20% of the entire plate thickness.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the thickness variation is within ± 10 μm.

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