WO2016039482A1

WO2016039482A1 - Method for manufacture of substrate for magnetic disk and substrate for magnetic disk

Info

Publication number: WO2016039482A1
Application number: PCT/JP2015/076048
Authority: WO
Inventors: 俵　義浩
Original assignee: Hoya株式会社
Priority date: 2014-09-12
Filing date: 2015-09-14
Publication date: 2016-03-17
Also published as: WO2016038747A1; MY178489A; SG11201701758RA; CN106605264A; JPWO2016039482A1

Abstract

Provided is a method for manufacture of a substrate for a magnetic disk, comprising a polishing process of sandwiching a substrate with a pair of polishing pads, supplying a slurry which includes a dielectric and abrasive polishing particles between the polishing pads and the substrate, and sliding the polishing pads and the substrate relative to each other, thereby polishing both main surfaces of the substrate. Prior to the polishing process, a removal process is carried out on the abrasive polishing particles of passing the slurry through an alternating electric field with a uniform field strength which arises from electrode shapes, and, with dielectrophoresis, separating foreign matter in the slurry from the abrasive polishing particles, and removing same.

Description

Manufacturing method of magnetic disk substrate and magnetic disk substrate

The present invention relates to a method for manufacturing a magnetic disk substrate having a polishing process and a magnetic disk substrate.

Today, a personal computer, a notebook personal computer, or a DVD (Digital Versatile Disc) recording device has a built-in hard disk device for data recording. In particular, in a hard disk device used in a portable computer such as a notebook personal computer, a magnetic disk having a magnetic layer provided on a substrate is used, and a magnetic head slightly lifted above the surface of the magnetic disk ( Magnetic recording information is recorded on or read from the magnetic layer by a DFH (Dynamic Flying Height) head. As the substrate of this magnetic disk, a glass substrate is preferably used because it has a property that it is less likely to undergo plastic deformation than a metal substrate or the like. Moreover, in order to stably read and write magnetic recording information by the magnetic head, it is required to make the surface irregularities of the glass substrate of the magnetic disk as small as possible.

In order to reduce the surface unevenness of the magnetic disk glass substrate, the glass substrate is subjected to a polishing process. An abrasive containing fine abrasive grains of silica (SiO ₂ ) abrasive grains is used for precise polishing for making a glass substrate into a final product. In order to improve the surface quality of the glass substrate after the polishing treatment, such an abrasive is used as an abrasive in a predetermined size by filtering or centrifuging. Moreover, when using for grinding | polishing, circulating the slurry containing a silica abrasive grain at the time of a grinding | polishing process, after filtering the slurry used for grinding | polishing, it reuses for grinding | polishing.
For example, in a final polishing step of a polishing step using silica abrasive grains on the main surface of a glass substrate, a polishing slurry (silica abrasive grains) containing a buffering agent after filtering using a filter having a minimum trapping particle diameter of 1 μm or less A method for manufacturing a glass substrate for a magnetic disk using (including Patent Document 1) is known (Patent Document 1).

JP 2010-079948 A

However, foreign substances such as plate-like foreign substances derived from silica abrasive grains in the slurry used for the polishing process may adhere to the main surface of the glass substrate after the above-described polishing process. The adhesion of the plate-like foreign matter to the glass substrate has been recognized in recent years due to the progress of measurement technology. The plate-like foreign matter attached to the glass substrate creates surface irregularities on the main surface of the magnetic disk, which makes it difficult to read and write stable magnetic recording information in a magnetic head with a very short flying distance. Moreover, this plate-like foreign material cannot be easily removed even in the final cleaning process. If a cleaning liquid having a high cleaning power is used, irregularities are formed on the smooth surface of the main surface of the glass substrate, which is not preferable as a glass substrate for a magnetic disk.
This plate-like foreign material is a foreign material having an irregular shape having a size larger than the average particle size (d50) of the roughly spherical silica abrasive grains. Therefore, in order to make the particle size of the silica abrasive grains within a predetermined range, before the polishing process is performed. In addition, silica abrasive grains may be filtered using a filter. Here, the average particle diameter indicates a median diameter measured based on a volume distribution using a laser diffraction / scattering method. However, with such filtering, the filter easily clogs, and silica abrasive grains cannot be produced efficiently. Moreover, since the plate-like foreign material is deformed and passes through the filter after filtering, the plate-like foreign material cannot be sufficiently removed, and the plate-like foreign material remains, and polishing is performed using a slurry containing silica abrasive particles. In some cases, plate-like foreign matters still adhered to the main surface of the glass substrate. In addition, even when trying to remove large silica abrasive grains such as plate-like foreign matter by centrifugation, the plate-like foreign matter cannot be removed sufficiently, and the plate-like foreign matter still adheres to the main surface of the polished glass substrate There was also. For this reason, there exists a problem that the yield after the grinding | polishing process of a glass substrate falls. Such a problem occurs not only in the glass substrate but also in a metal substrate (aluminum substrate). These problems are particularly noticeable in the case of abrasive grains having an extremely small particle diameter such as an average particle diameter of 10 to 60 nm, more preferably 10 to 30 nm.

Accordingly, an object of the present invention is to provide a magnetic disk substrate manufacturing method and a magnetic disk substrate capable of improving the yield after the substrate polishing process.

The present inventor replaces a filter that is easily clogged and cannot sufficiently remove the above-mentioned plate-like foreign matters or a centrifugal separator that cannot sufficiently remove the above-mentioned plate-like foreign matters before the polishing treatment. A new method that can remove plate-like foreign matters was examined. Therefore, the present inventor noticed that the dielectrophoretic force of the silica abrasive grains being dielectrically polarized in an electric field and causing dielectrophoresis caused by the dielectric polarization is proportional to the cube of the diameter of the particles, and the following method is used. Invented. The present invention includes the following forms.

(Form 1)
A method for manufacturing a magnetic disk substrate, comprising:
By sandwiching the substrate between a pair of polishing pads, supplying a slurry containing abrasive grains of dielectric material between the polishing pad and the substrate, and sliding the polishing pad and the substrate relatively, Including a polishing process for polishing both main surfaces of the substrate;
Prior to the polishing treatment, the slurry is passed through an AC electric field having a non-uniform electric field intensity distribution caused by the electrode shape, and the foreign substances present in the slurry and the abrasive grains are separated by dielectrophoresis to form the foreign substances. A method of manufacturing a magnetic disk substrate, wherein a removal process for removing the magnetic disk is performed. That is, the removal treatment utilizes a difference in dielectrophoretic force that is received by particles having an average particle diameter of the abrasive grains and foreign matters (large-diameter particles) having a larger particle diameter than the average particle diameter. .

(Form 2)
The abrasive grains are silica abrasive grains,
The said silica abrasive grain is a manufacturing method of the board | substrate for magnetic discs of the form 1 which is obtained using water glass and ion-exchange resin.

(Form 3)
The magnetic disk according to mode 3, wherein an additive that decreases the absolute value of the surface potential of the silica abrasive grains is added to the slurry before the polishing treatment, and the addition of the additive is performed after the removal treatment. Manufacturing method for industrial use.

(Form 4)
The method for manufacturing a magnetic disk substrate according to any one of Embodiments 1 to 3, wherein the abrasive grains after the removal treatment are crushed.

(Form 5)
The magnetic content according to any one of aspects 1 to 4, wherein the content of the abrasive grains in the slurry before the removal treatment is higher than the content of the abrasive grains in the slurry after the polishing treatment. A method for manufacturing a disk substrate.

(Form 6)
After the polishing process, a cleaning process for cleaning the main surface of the substrate is performed, and in the cleaning process, an alkaline cleaning solution containing an inorganic alkali having a pH of less than 10 is used. A method of manufacturing a magnetic disk substrate.

(Form 7)
After the polishing process, a cleaning process for cleaning the main surface of the substrate is performed,
The method for manufacturing a magnetic disk substrate according to any one of Embodiments 1 to 6, wherein the cleaning treatment is non-scrub cleaning in which the substrate is immersed in or brought into contact with a cleaning liquid.

(Form 8)
In the removing treatment, the abrasive grains made of colloidal silica and the plate-like foreign matters made of layered silicate are separated by dielectrophoresis, and the plate-like foreign matters in the slurry are removed. A method for manufacturing the magnetic disk substrate according to claim.

(Form 9)
A method for manufacturing a magnetic disk substrate, comprising:
By sandwiching a substrate between a pair of polishing pads, supplying a slurry containing abrasive grains made of colloidal silica between the polishing pad and the substrate, and sliding the polishing pad and the substrate relatively, Including a polishing process for polishing both main surfaces of the substrate;
The slurry used in the polishing treatment is passed into the slurry stock solution by passing the slurry stock solution between electrodes having a shape capable of generating an electric field with an uneven electric field intensity distribution by applying an alternating current. A positive dielectrophoresis or a negative dielectrophoresis is caused to a plate-like foreign substance composed of a layered silicate contained therein, and the plate-like foreign substance is inhibited from passing between the electrodes, thereby causing the plate-like foreign substance to flow into the slurry. A method for producing a magnetic disk substrate, wherein the substrate is removed from a stock solution.

(Form 10)
A magnetic disk substrate having a pair of main surfaces having circular holes, an inner peripheral end surface forming a circular hole, and an outer peripheral end surface, wherein the main surface is made of a layered silicate having a maximum diameter of 100 nm or more. A magnetic disk substrate, wherein the number of adhered plate-like foreign matters is less than 2 / sheet.

According to the above-described method for manufacturing a magnetic disk substrate, plate-like foreign matters and the like can be removed from the abrasive grains used in the polishing process by utilizing the difference in dielectric constant, so that the plate-like foreign matters and the like are formed on the main surface of the substrate. Will not adhere. For this reason, the yield after the polishing process of the substrate can be improved. Further, according to the above-described magnetic disk substrate, it is possible to provide a magnetic disk substrate with a small number of plate-like foreign substances attached.

It is a figure which shows the example of the glass substrate for magnetic discs manufactured with the manufacturing method of this embodiment. (A), (b) is a figure explaining the grinding | polishing apparatus used by the grinding | polishing process of the manufacturing method of the glass substrate of this embodiment. It is a schematic diagram of the removal processing apparatus which performs the removal process of this embodiment.

Hereinafter, a method for manufacturing a magnetic disk substrate and a magnetic disk substrate according to an embodiment of the present invention will be described. In the following description, a glass substrate is used as an example, but the method for manufacturing a magnetic disk substrate according to the present embodiment can be similarly applied to a metal substrate (aluminum substrate). In this embodiment, silica abrasive grains are used as examples for the polishing abrasive grains. However, in addition to silica abrasive grains, polishing abrasive grains that serve as dielectric materials, such as titanium oxide, cerium oxide, and aluminum oxide, are used. Etc. can also be applied. Among the abrasive grains of silica, titanium oxide, cerium oxide, and aluminum oxide, silica abrasive grains are more preferable from the viewpoint of realizing further low roughness as a magnetic disk substrate.

(Magnetic disk glass substrate)
First, the glass substrate for magnetic disks manufactured by this embodiment is demonstrated. FIG. 1 is a view showing an example of a glass substrate 1 for a magnetic disk manufactured by the manufacturing method of the present embodiment. As shown in FIG. 1, a magnetic disk glass substrate 1 (hereinafter simply referred to as a glass substrate 1) has a disc shape and a ring shape in which a circular center hole concentric with the outer periphery is cut out. Yes. A magnetic disk is formed by forming magnetic layers (recording areas) in the annular areas on both sides of the glass substrate for a magnetic disk.
That is, the magnetic disk glass substrate 1 has a pair of main surfaces having circular holes, an inner peripheral end surface that forms the circular holes, and an outer peripheral end surface.

A glass blank, which is a base plate of a magnetic disk glass substrate, is produced by a float method or press molding. The glass blank is a circular glass plate and is in a form before the center hole is cut out. As a material for the glass blank, aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used. In particular, aluminosilicate glass can be suitably used in that it can be chemically strengthened and a glass substrate for a magnetic disk excellent in the flatness of the main surface and the strength of the substrate can be produced.

As will be described later, the glass substrate 1 obtained by subjecting the glass blank to shape processing, end surface polishing, grinding, and the like is subjected to final polishing and the glass substrate 1 becomes the final glass substrate. At this time, in the final polishing process, a polishing process using a slurry containing silica abrasive grains is performed using a polishing apparatus 10 as shown in FIGS. FIGS. 2A and 2B are diagrams illustrating a polishing apparatus used in the polishing process of the glass substrate manufacturing method of the present embodiment.

As shown in FIGS. 2A and 2B, the polishing apparatus 10 includes a lower surface plate 12, an upper surface plate 14, an internal gear 16, a carrier 18, a polishing pad 20, a sun gear 22, And an internal gear 24.
The polishing apparatus 10 sandwiches the internal gear 16 between the lower surface plate 12 and the upper surface plate 14 from the vertical direction. A plurality of carriers 18 are held in the internal gear 16 during polishing. In FIG. 2B, five carriers 18 are shown. A polishing pad 20 is planarly bonded to the lower surface plate 12 and the upper surface plate 14.

The carrier 18 is arranged so that the lower main surface of the glass substrate 1 contacts the polishing pad 20 on the lower surface plate 12 and the upper main surface of the glass substrate 1 contacts the polishing pad 20 on the upper surface plate 14. Is done. By polishing in such a state, the main surfaces on both sides of the glass substrate 1 processed into a ring shape can be polished.

As shown in FIG. 2B, the annular glass substrate 1 is held in a circular hole provided in each carrier 18. On the other hand, the glass substrate 1 is held on the lower surface plate 12 by a carrier 18 having a gear 19 on the outer periphery. The carrier 18 meshes with a sun gear 22 and an internal gear 24 provided on the lower surface plate 12.
With this configuration, the glass substrate 1 is polished by moving relative to the polishing pad 20 in a planetary gear system. The slurry used for polishing contains silica abrasive grains, is supplied to the upper surface plate 14 as shown in FIG. 2A, flows to the lower surface plate 12, and is collected in an external container.
That is, in the final polishing process, the glass substrate 1 is sandwiched between the pair of polishing pads 20, and slurry containing silica abrasive grains is supplied between the polishing pad 20 and the glass substrate 1, so that the polishing pad 20 and the glass substrate 1 are relative to each other. The main surfaces of the glass substrate 1 are polished by sliding them.
In addition, the silica abrasive grain contained in the slurry used for such a final polishing process is an abrasive grain subjected to the removal process described below.

(Removal process)
FIG. 3 is a schematic diagram of a removal processing apparatus that performs the removal processing of the present embodiment. The removal processing apparatus 50 includes a pair of

electrodes

52 and 54. An AC voltage is applied to the

electrodes

52 and 54. The electrode 52 is a flat plate electrode. The electrode 54 is an electrode having a smaller area than the area of the electrode 52, that is, a dot-like electrode. For this reason, when an AC voltage is applied between the electrode 52 and the electrode 54, the area of the electrode surface is different, so that an electric field having a nonuniform electric field strength is formed between the

electrodes

52 and 54. In other words, an electric field with non-uniform electric field strength means that the electric field strength (electric field strength) is high or low in space, or the electric flux density is dense in space. It means that the electric flux density becomes sparse as it approaches 52, and the electric flux density becomes denser as it approaches the electrode 54.
In the gap between the

electrodes

52 and 54, a flow path 55 through which slurry containing silica abrasive grains (colloidal silica) flows is provided.
A recovery pipe 56 is connected to the downstream end of the flow path 55. The recovery pipe 56 is provided on the electrode 52 side in the flow path 55.
In addition, as an electrode of the shape which can generate | occur | produce an electric field whose electric field intensity | strength is non-uniform | heterogenous by applying an alternating voltage, a well-known electrode shape can be used not only in the above-mentioned flat plate electrode and a dotted electrode. For example, a quadrupole electrode and an interdigital (comb-shaped) electrode are known. Interdigital shape is a shape in which electrodes such as triangles, squares, trapezoids, and sinusoidal waveforms are arranged repeatedly and continuously. Unlike inter-electrode flow paths, the distance between electrodes increases regularly and decreases. This is a channel between electrodes.

Plate-like foreign substances such as silica abrasive grains in the slurry flowing through the channel 55, layered silicate crystals containing aluminum, and metal oxide particles such as iron oxide or titanium oxide (hereinafter also referred to as foreign substances such as plate-like foreign substances) When passing through an electric field having the above-mentioned non-uniform electric field strength, dielectric polarization occurs according to the difference in dielectric constant with the dispersion medium (liquid in which particles in the slurry are dispersed). Due to the dielectrophoretic force generated in the electric field due to this dielectric polarization, foreign matters such as silica abrasive grains and plate-like foreign matter move in the electric field. At this time, a foreign substance such as a silica abrasive grain or a plate-like foreign substance having a larger particle diameter is more easily moved by a large dielectrophoretic force. In the case of positive dielectrophoresis in which foreign substances such as silica abrasive grains and plate-like foreign substances have a high dielectric constant with respect to the dispersion medium, the electrode 54 has a higher electric flux density as foreign substances such as silica abrasive grains and plate-like foreign substances having larger particle diameters. The electrode 54 is easily held and strongly held on the electrode 54 side. On the other hand, when the foreign particles such as silica abrasive grains and plate-like foreign substances are negative dielectrophoresis having a low dielectric constant with respect to the dispersion medium, the electric flux density is smaller as the foreign substances such as silica abrasive grains or plate-like foreign substances having larger particle diameters. Therefore, it is easy to move to the electrode 52 side, and a force is applied in the direction of repulsion from the electrode 54 side where the electric flux density is dense. In other words, the removal treatment of the present embodiment uses the difference in dielectrophoretic force received by the silica abrasive grains and the foreign substances such as plate-like foreign substances having a particle diameter larger than the average particle diameter. It is. The difference in the dielectrophoretic force due to the difference in particle diameter is more prominent when the difference in particle diameter is twice or more, and becomes more prominent when it is five or more times.

Positive dielectrophoresis refers to a behavior in which the dielectric constant of the dispersion medium in the slurry is smaller than that of the particles and the particles move toward a place where the electric flux density is dense due to the dielectric polarization of the particles. Negative dielectrophoresis refers to a behavior in which the dielectric constant of the dispersion medium in the slurry is larger than that of the particles, and the particles move toward a place where the electric flux density is sparse due to the dielectric polarization of the particles.
Therefore, in this embodiment, in order to cause dielectrophoresis in the silica abrasive grains, the dielectric constant is at least different between the liquid (dispersion medium) in the slurry and the silica abrasive grains.

When the silica abrasive grains perform positive dielectrophoresis, as shown in FIG. 3, the collection tube 56 is provided on the electrode 52 side (upper side of the drawing in FIG. 3) of the flow path 55. As a result, foreign matters such as plate-like foreign matters that are easily moved by a large dielectrophoretic force move in the direction of the electrode 54 where the electric flux density is higher than that of the silica abrasive grains, and stay in a region near the electrode 54. On the other hand, since the slurry flows as a uniform laminar flow in the flow path 54 from the left side of the paper in FIG. 3, the slurry containing silica abrasive grains with small movement due to dielectrophoresis is collected on the electrode 52 side. It flows into the tube 56 and is recovered as a slurry for polishing treatment. Further, when the silica abrasive grains undergo negative dielectrophoresis, the liquid as the dispersion medium moves toward the electrode 54 where the electric flux density is dense. It moves in the direction in which the density is sparse, that is, in the direction away from the electrode 54 side where the electric field strength (electric field strength) is sparse. For this reason, the plate-like foreign material and the metal oxide particles are pressed against the electrode 54 which is a flat plate electrode having a low electric flux density when a combination of a flat plate electrode and a dotted electrode is used.
In addition, when a quadrupole electrode or an interdigital electrode is used, foreign substances such as abrasive grains and plate-like foreign substances gather and gather at the center of the flow channel at the position farthest away from the surrounding electrodes. It will be held in the road. In this way, foreign substances such as abrasive grains and plate-like foreign substances in the slurry are held at the center of the flow path. At this time, a foreign substance such as a plate-like foreign substance having a larger particle diameter has a higher electrophoretic force than a polishing abrasive grain having a smaller particle diameter, and a stronger force is retained in the flow path. Abrasive grains having a smaller particle size have a small electrophoretic force and a relatively low force held in the flow path, and are recovered by the flow of the slurry. On the other hand, foreign matters such as plate-like foreign matter remain in the flow path by the dielectrophoretic force and are removed from the slurry used for the polishing process.
That is, in the present embodiment, the slurry is passed through an AC electric field having a non-uniform spatial distribution of electric field strength, and dielectrophoresis according to the size of the foreign particles such as silica abrasive grains and plate-like foreign particles in the slurry is performed. By causing them to occur in foreign matters such as grains and plate-like foreign matters, a removal process for removing foreign matters such as plate-like foreign matters having a particle size larger than the average particle size of silica abrasive grains from the slurry is performed.
As described above, in this embodiment, the abrasive grains made of colloidal silica and the plate-like foreign substances made of layered silicate can be separated by dielectrophoresis, and the plate-like foreign substances in the slurry can be removed.

The treatment conditions such as the alternating voltage used in the present embodiment, the flow rate of the slurry flowing in the flow path 55, the viscosity of the slurry, and the concentration of the silica abrasive grains in the slurry are not particularly limited, and abrasive grains, foreign matter, Dielectric migration is efficiently generated according to the difference in the dielectric constant of the dispersion medium and the size of the foreign particles such as abrasive grains and plate-like foreign particles. As long as foreign matter such as a plate-like foreign matter having a diameter can be removed from the slurry, it may be set appropriately. At least the flow of the slurry flowing through the flow path 55 needs to be a laminar flow so that the silica abrasive particles can move by dielectrophoresis according to the size of the foreign particles such as silica abrasive particles and plate-like foreign matters. The width of the flow path, which is the distance between the electrodes through which the slurry flows, is preferably as close as possible to the particle size of the foreign matter such as the plate-like foreign matter to be removed, and is preferably 100 μm or less, preferably 30 μm or less.

The average particle diameter (d50) of the silica abrasive subjected to such removal treatment is, for example, 10 to 60 nm, more preferably 10 to 30 nm. The size of coarse silica particles having a particle size larger than the particle size is 130 to 240 nm. That is, it is possible to suitably remove foreign matters having a particle size that is twice or more the average particle size (d50) of silica abrasive grains.
For example, when the silica abrasive grains are captured as a two-dimensional image, the rectangular frame is tilted in any direction around the silica abrasive grains and the rectangular frame is The maximum length of the long side of the rectangular frame when the rectangular frame surrounds the image of the silica abrasive grains so as to circumscribe the image of the grain. In addition, when the silica abrasive grains are imaged as a three-dimensional image, the rectangular parallelepiped frame is an image of the silica abrasive grains so that the rectangular parallelepiped frame is circumscribed by the silica abrasive grains image in all directions around the silica abrasive grains. The maximum length of the long side of the cuboid frame when enclosing.

The silica abrasive grains used in the present embodiment may be produced by any manufacturing method, for example, may be obtained by sol-gel method from tetramethyl orthosilicate or tetraethyl orthosilicate, but water glass and ion exchange resin are used. It is preferable that it is obtained by using. Such a silica abrasive can easily produce a large amount of silica abrasive without cost. Water glass is obtained using silica sand as a material. Specifically, sodium silicate is produced by mixing and melting silica sand and sodium carbonate, and after cooling the melt, water glass can be obtained by dissolving in water. Thus, since water glass has many impurities, such as aluminum, and uses silica sand as a raw material, water glass contains many impurities, such as aluminum. If a large amount of aluminum, which is one of these impurities, is contained, a plate-like foreign material made of the above-described layered silicate can be easily formed. However, even the silica abrasive grains obtained by using the water glass and the ion exchange resin that are easy to form the silica abrasive grains of the plate-like foreign matter, the silica abrasive grains of the plate-like foreign substance are sufficiently obtained by the above-described removal treatment. Can be removed.

Further, in order to improve the polishing rate and reduce the surface unevenness of the glass substrate after the polishing treatment, an additive such as K ₂ SO ₄ or Na ₂ SO ₄ is added to the slurry after the removal treatment before the polishing treatment. A sulfuric acid compound, a phosphoric acid compound such as K ₃ PO ₄ or Na ₃ PO _4, or a nitric acid compound such as NaNO ₃ is added. This additive also reduces the absolute value of the surface potential of the silica abrasive grains in the slurry. If the absolute value of the surface potential of the silica abrasive grains is reduced, the dielectric polarization of the silica abrasive grains may be affected, and the removal treatment effect may not be sufficiently obtained. For this reason, an additive is added to the slurry after the removal treatment before the polishing treatment.

Further, in this embodiment, the content of silica abrasive grains in the slurry before the above-described removal treatment is higher than the content of silica abrasive grains in the slurry after the polishing treatment. It is preferable for obtaining the effect of the removal treatment by the above.

In the removal treatment, it is preferable that the plate-like foreign material having a shape in which the ratio of the maximum width to the minimum width is 5 or more is removed from the silica abrasive grains. When the silica abrasive grains, which are such plate-like foreign substances, adhere to the main surface of the glass substrate, it is extremely difficult to remove them by a cleaning process or the like. For this reason, it is preferable to perform the above-mentioned removal process with respect to the silica abrasive grain before performing a polishing process. The above-mentioned minimum width and maximum width of the silica abrasive grains are, for example, when the silica abrasive grains are imaged as a two-dimensional image, while the rectangular frames are tilted in all directions around the silica abrasive grains and the rectangular frames are harmful to the image of the silica abrasive grains. Thus, when the rectangular frame surrounds the image of the silica abrasive grains, the minimum length of the short side and the maximum length of the long side of the rectangular frame are referred to. Further, when the silica abrasive grains are imaged as a three-dimensional image, the three-dimensional silica abrasive grains in the rectangular parallelepiped frame so that the rectangular parallelepiped frame circumscribes the image of the silica abrasive grains while tilting the rectangular parallelepiped frame in all directions around the silica abrasive grains. When the image is enclosed, the minimum length of the short side and the maximum length of the long side of the cuboid frame are referred to. In the case of a plate-like foreign material, the minimum width substantially corresponds to the thickness of the plate-like foreign material.

Moreover, it is preferable to crush the silica abrasive after the removal treatment. The crushing treatment includes, for example, a treatment for applying ultrasonic vibration to the silica abrasive grains. In some cases, the silica abrasive grains agglomerate in order to collect the silica abrasive grains having a desired particle diameter by causing dielectrophoresis in the silica abrasive grains by the removal treatment. For this reason, it is preferable to crush the aggregate of silica abrasive grains by applying ultrasonic vibration to the recovered silica abrasive grains after the removal treatment, for example. When aggregates of silica abrasive grains are generated, the aggregates easily cause scratches on the main surface of the glass substrate during the polishing process.

As described above, in the present embodiment, before the polishing treatment, the slurry is passed through an AC electric field having nonuniform electric field strength, and dielectrophoresis according to the particle size of the particles in the slurry is performed on the silica abrasive grains. It is generated in foreign matter such as plate-like foreign matter. This removes foreign matters such as plate-like foreign matters having a particle size larger than the average particle size of the silica abrasive grains from the slurry. For this reason, foreign matters such as plate-like foreign matters larger than the average particle size of the silica abrasive grains can be removed from the slurry. Therefore, even if the glass substrate is polished using the slurry, foreign matters such as plate-like foreign matters do not adhere to the main surface of the glass substrate after the polishing treatment. Therefore, in this embodiment, the yield after the polishing treatment of the glass substrate can be improved.
In addition, the slurry used for the polishing process is an electrode having a shape that can generate an uneven electric field with non-uniform electric field strength or a dense distribution of electric flux density by applying an alternating voltage. By passing the slurry stock solution in between, positive dielectrophoresis or negative dielectrophoresis is caused to the plate-like foreign substance made of layered silicate contained in this slurry raw solution, and the plate-like foreign substance passes between the electrodes. It is possible to prevent the plate-like foreign matter from being removed from the slurry stock solution. Even in this case, even if the glass substrate is polished by using the slurry, foreign matters such as plate-like foreign matters do not adhere to the main surface of the glass substrate after the polishing treatment. Therefore, in this embodiment, the yield after the polishing treatment of the glass substrate can be improved. The slurry stock solution here refers to a polishing solution containing new silica abrasive grains that have never been used for polishing treatment.
In the above description, it has been described that the silica abrasive grains of the plate-like foreign material can be removed by the removal process, but the larger the silica abrasive grains, the greater the dielectrophoretic force. For this reason, the particle | grains removed by this embodiment are not limited to foreign materials, such as a plate-shaped foreign material, The rough spherical silica abrasive grain larger than an average particle diameter is also contained.

(Method for producing glass substrate for magnetic disk)
Next, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated. First, a glass blank as a material for a plate-shaped magnetic disk glass substrate having a pair of main surfaces is produced by press molding (press molding process). In addition to producing the glass blank by press molding, a glass plate having the same shape as the glass blank may be cut out from the glass plate by forming a glass plate by a well-known float method, redraw method, or fusion method. Next, a circular hole is formed in the center part of the produced glass blank, and shape processing is performed on the glass substrate on which the circular hole is formed (shape processing treatment). Thereby, a glass substrate is produced | generated. Next, end-face polishing is performed on the shape-processed glass substrate (end-face polishing process). Grinding is performed on the main surface of the glass substrate that has been subjected to end face polishing (grinding treatment). Next, 1st grinding | polishing is performed to the main surface of a glass substrate (1st grinding | polishing process). Next, chemical strengthening is performed on the glass substrate as necessary (chemical strengthening treatment). Next, second polishing is performed on the chemically strengthened glass substrate (second polishing treatment). Thereafter, the glass substrate after the second polishing process is cleaned. The glass substrate for magnetic disks is obtained through the above processing.

(A) Press molding process The front-end | tip part of a molten glass flow is cut | disconnected with a cutter, the cut molten glass lump is pinched | interposed between the press molding surfaces of a pair of metal molds, and a glass blank is formed by pressing. After pressing for a predetermined time, the mold is opened and the glass blank is taken out.

(B) Shape processing The disk-shaped glass substrate with a circular hole is obtained by forming a circular hole using a drill etc. with respect to a glass blank. Further, chamfering is performed on the end of the glass substrate after the circular hole forming process. The chamfering process is performed using a grinding wheel or the like. By chamfering, a side wall surface of the substrate that extends perpendicularly to the main surface of the glass substrate on the end surface of the glass substrate, and a chamfer surface that is provided between the side wall surface and the main surface and extends at an angle to the side wall surface. Are formed.

(C) End face polishing process In the end face polishing process, the inner end face and the outer peripheral side end face of the glass substrate are polished using polishing abrasive grains to perform mirror finish.

(D) Grinding process In the grinding process, a grinding process is performed on the main surface of the glass substrate using a grinding apparatus (not shown) provided with a planetary gear mechanism. Specifically, the main surface on both sides of the glass substrate is ground while holding the outer peripheral side end face of the glass substrate made from the glass blank in the holding hole provided in the holding member of the grinding apparatus. The grinding apparatus has a pair of upper and lower surface plates (upper surface plate and lower surface plate), and a glass substrate is sandwiched between a fixed surface sheet such as a diamond grindstone between the upper surface plate and the lower surface plate. . Then, by moving one or both of the upper surface plate and the lower surface plate and relatively moving the glass substrate and each surface plate, both main surfaces of the glass substrate can be ground.

(E) 1st grinding | polishing process Next, 1st grinding | polishing is given to the main surface of the glass substrate of grinding. Specifically, the main surface on both sides of the glass substrate is polished while holding the outer peripheral side end face of the glass substrate in a hole provided in a polishing carrier of a polishing apparatus (not shown). The purpose of the first polishing is to remove scratches and distortions remaining on the main surface after the grinding treatment, or to adjust minute surface irregularities (microwaveness, roughness).

In the first polishing process, the glass substrate is polished while applying a slurry containing abrasive grains. As the abrasive grains used for the first polishing, for example, free abrasive grains such as cerium oxide abrasive grains or zirconia abrasive grains are used. In the polishing apparatus used for the first polishing process, similarly to the grinding apparatus, the glass substrate is sandwiched between a pair of upper and lower surface plates. An annular flat polishing pad is attached to the upper surface of the lower surface plate and the bottom surface of the upper surface plate as a whole. Then, by moving either the upper surface plate or the lower surface plate, or both, the glass substrate and each surface plate are relatively moved, thereby polishing both main surfaces of the glass substrate.

(F) Chemical strengthening treatment When chemically strengthening a glass substrate, for example, a mixed melt of potassium nitrate and sodium sulfate is used as the chemical strengthening solution, and the glass substrate is immersed in the chemical strengthening solution.

(G) Second polishing (final polishing) treatment Next, the glass substrate is subjected to second polishing. The second polishing treatment aims at mirror polishing of the main surface. In the second polishing process, a polishing apparatus 10 as shown in FIGS. 2A and 2B is used. Specifically, the main surface on both sides of the glass substrate 1 is polished while the outer peripheral side end surface of the glass substrate 1 is held in the hole provided in the carrier 18 of the polishing apparatus 10. In the second polishing process, the type and particle size of loose abrasive grains are different from those in the first polishing process, and the polishing pad 20 is also different in hardness from the polishing pad in the first polishing process. The slurry used for the second polishing treatment is a slurry containing the silica abrasive grains subjected to the above-described removal treatment. By performing the second polishing treatment, the arithmetic average roughness Ra of the roughness of the main surface can be set to 0.15 nm or less. Furthermore, the root mean square roughness Rq of the micro-waviness, which is a wave having a wavelength of 50 to 200 μm, on the main surface of the glass substrate can be set to 0.1 nm or less.
Thereafter, the glass substrate is cleaned with the surface of the glass substrate using an alkali cleaning solution containing an inorganic alkali to become a final glass substrate.
In the present embodiment, the chemical strengthening process is performed, but the chemical strengthening process may not be performed if necessary. In addition to the first polishing process and the second polishing process, another polishing process may be added, and the polishing process of the two main surfaces may be performed by one polishing process. Moreover, you may change suitably the order of said each process. The slurry containing the silica abrasive grains subjected to the removal treatment of this embodiment is used for final polishing so as to have surface irregularities as a final product.
In the second polishing treatment, the glass substrate is polished using the slurry that has been subjected to the above-described removal treatment, so that the number of plate-like foreign substances made of layered silicate having a maximum diameter of 100 nm or more is 2 on the main surface. Glass substrates that are less than pieces / sheet can be manufactured.

After the second polishing process, a cleaning process for cleaning the main surface of the glass substrate is performed as described above. At this time, in the cleaning process, it is preferable to use an alkaline cleaning liquid containing an inorganic alkali that has a weak cleaning power so that the difference in surface roughness Ra between the glass substrate before and after the cleaning process is within a range of 0.05 nm or less. Conventionally, since the plate-like foreign material adhering to the glass substrate is difficult to remove, an alkaline cleaning liquid having a strong cleaning power has been used. However, the alkaline cleaning liquid having a strong cleaning power not only removes the plate-like foreign matter but also acts on the main surface of the glass substrate to roughen the main surface. Therefore, in this embodiment, since the polishing process is performed using the silica abrasive grains subjected to the above-described removal process, the plate-like foreign matter does not adhere to the glass substrate, and an alkaline cleaning liquid having a weaker cleaning power than the conventional one, specifically In particular, an alkaline cleaning solution having a pH difference of 0.05 nm or less in the surface roughness Ra (arithmetic average roughness) of the glass substrate before and after the cleaning treatment, such as an alkaline cleaning solution containing an inorganic alkali having a pH of less than 10, is used. be able to. The inorganic alkali includes, for example, NaOH or KOH. Ra is the surface roughness specified in JIS B0601. This surface roughness is obtained based on data obtained by measuring a range of 1 μm × 1 μm with a resolution of 512 × 256 pixels using an atomic force microscope (AFM). Further, the fine waviness with a wavelength of 50 to 200 μm can be measured by, for example, an optical surface shape measuring device.

Further, the cleaning treatment is preferably non-scrub cleaning in which the glass substrate is immersed or brought into contact with the cleaning liquid, from the viewpoint of not scratching the glass substrate. In the conventional cleaning process, scrub cleaning is performed to remove the plate-like foreign matter by rubbing the glass substrate with a brush or a cleaning pad in order to remove the plate-like foreign matter firmly attached to the glass substrate. However, this scrub cleaning tends to damage the main surface of the glass substrate. In this embodiment, since it polishes using the slurry containing the silica abrasive grain which performed the removal process mentioned above, a plate-shaped foreign material does not adhere to a glass substrate. For this reason, it is not necessary to perform scrub cleaning as in the prior art. For this reason, in this embodiment, unnecessary scratches are not applied to the main surface of the glass substrate by performing non-scrub cleaning in which the glass substrate is immersed in or brought into contact with the cleaning liquid.
The present invention also provides a magnetic disk substrate having an arithmetic average roughness Ra of 0.15 nm or less, more preferably 0.12 nm or less, and even more preferably 0.10 nm or less, of the surface roughness of the main surface of the substrate. It is suitable for.
In particular, when the surface roughness Ra is set to 0.15 nm or less in the final polishing process, not only the plate-like foreign matter existing in the slurry is likely to stick to the substrate surface, but also a cleaning solution having a strong etching power as described above after the final polishing process. However, the plate-like foreign matter tends to remain on the glass substrate surface, but this problem can be solved by the manufacturing method of the present embodiment.

After the second polishing process described above, the main surface of the cleaned and dried glass substrate was subjected to detection of foreign matters or defects using a laser type surface inspection apparatus. The laser threshold is set to a range in which the number of detected foreign matters or defects is 10 to 20, and the detected foreign matter or defects are measured using the SEM (scanning electron microscope) or AFM (atomic force microscope). The number of foreign matters having a thickness of 100 nm or more was counted. Next, using a cross-sectional TEM (transmission electron microscope), it was confirmed whether or not a foreign material having a major axis of 100 nm or more is a layered flat foreign material (a plate-like foreign material made of layered silicate). In a glass substrate polished with a slurry containing silica by an ion exchange method that has not been subjected to removal treatment by dielectrophoresis, it was confirmed that a plurality of layered flat foreign matters were attached to the main surfaces of the front and back surfaces of the glass substrate (2 Pieces / sheet or more of layered flat foreign matter are attached). On the other hand, when the substrate was polished after removing the foreign matter by dielectrophoresis for the slurry containing silica by the ion exchange method, the layered flat foreign matter adhering to the main surfaces of the front and back surfaces of the glass substrate was not detected ( There is no adhesion of layered flat foreign material on the main surface of the substrate).

The magnetic disk substrate manufacturing method and the magnetic disk substrate of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the spirit of the present invention. Of course, you may do it.

DESCRIPTION OF SYMBOLS 1 Glass substrate 10 Polishing device 12 Lower surface plate 14 Upper surface plate 16 Internal gear 18 Carrier 20 Polishing pad 19 Gear 22 Sun gear 24 Internal gear 50

Removal processing device

52, 54 Electrode 55 Channel 56 Collection pipe

Claims

A method for manufacturing a magnetic disk substrate, comprising:
By sandwiching the substrate between a pair of polishing pads, supplying a slurry containing abrasive grains of dielectric material between the polishing pad and the substrate, and sliding the polishing pad and the substrate relatively, Including a polishing process for polishing both main surfaces of the substrate;
Prior to the polishing treatment, the slurry is passed through an AC electric field having a non-uniform electric field intensity distribution caused by the electrode shape, and the foreign substances present in the slurry and the abrasive grains are separated by dielectrophoresis to remove the foreign substances. A method of manufacturing a magnetic disk substrate, characterized in that a removal process is performed.
The abrasive grains are silica abrasive grains,
The method for manufacturing a magnetic disk substrate according to claim 1, wherein the silica abrasive grains are obtained using water glass and an ion exchange resin.
The magnetic material according to claim 2, wherein an additive that decreases an absolute value of a surface potential of the silica abrasive grains is added to the slurry before the polishing treatment, and the addition of the additive is performed after the removal treatment. A method for manufacturing a disk substrate.
The method for manufacturing a magnetic disk substrate according to any one of claims 1 to 3, wherein the abrasive grains after the removal treatment are subjected to a crushing treatment.
The content rate of the polishing abrasive grains in the slurry before the removal treatment is higher than the content rate of the polishing abrasive grains in the slurry after the polishing treatment. A method of manufacturing a magnetic disk substrate.
6. The polishing process according to claim 1, wherein a cleaning process for cleaning the main surface of the substrate is performed after the polishing process, and in the cleaning process, an alkaline cleaning solution containing an inorganic alkali having a pH of less than 10 is used. Of manufacturing a magnetic disk substrate.
After the polishing process, a cleaning process for cleaning the main surface of the substrate is performed,
7. The method for manufacturing a magnetic disk substrate according to claim 1, wherein the cleaning process is non-scrub cleaning in which the substrate is immersed in or brought into contact with a cleaning liquid.
The plate-like foreign material in the slurry is removed in the removal treatment by separating the abrasive particles made of colloidal silica and the plate-like foreign material made of layered silicate by dielectrophoresis. A method for producing a magnetic disk substrate as described in 1. above.
A method for manufacturing a magnetic disk substrate, comprising:
By sandwiching a substrate between a pair of polishing pads, supplying a slurry containing abrasive grains made of colloidal silica between the polishing pad and the substrate, and sliding the polishing pad and the substrate relatively, Including a polishing process for polishing both main surfaces of the substrate;
The slurry used in the polishing treatment is passed into the slurry stock solution by passing the slurry stock solution between electrodes having a shape capable of generating an electric field with non-uniform electric field intensity distribution by applying an alternating voltage. A positive dielectrophoresis or a negative dielectrophoresis is caused to a plate-like foreign substance composed of a layered silicate contained therein, and the plate-like foreign substance is inhibited from passing between the electrodes, thereby causing the plate-like foreign substance to flow into the slurry. A method for producing a magnetic disk substrate, wherein the substrate is removed from a stock solution.
A magnetic disk substrate having a pair of main surfaces having circular holes, an inner peripheral end surface forming a circular hole, and an outer peripheral end surface,
The main surface is a magnetic disk substrate characterized in that the number of plate-like foreign substances made of layered silicate having a maximum diameter of 100 nm or more is less than 2 / sheet.