JP2014116046A - Manufacturing method of glass substrate for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a glass substrate for a magnetic disk, which achieves the prevention of zirconia particles from remaining on a main surface of the glass substrate after the main surface of the glass substrate is polished by using a polishing solution containing particulate zirconia as an abrasive.SOLUTION: A manufacturing method of a glass substrate for a magnetic disk comprises: a polishing process of polishing a main surface of a glass substrate G by using a polishing solution containing zirconia abrasive grains; and a cleaning process of cleaning the glass substrate G after the polishing process by using a cleaning solution. The cleaning solution contains at least fluorine ions. The glass substrate G is brought into contact with a solution containing a phosphonic acid between the polishing and cleaning processes.

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk.

  2. Description of the Related Art Today, a personal computer, a DVD (Digital Versatile Disc) recording device, or the like has a built-in hard disk device (HDD: Hard Disk Drive) for data recording. In particular, in a hard disk device used in a portable computer such as a notebook personal computer, a magnetic disk in which a magnetic layer is provided on a glass substrate is used, and the magnetic head slightly floats above the surface of the magnetic disk. Thus, magnetic recording information is recorded on or read from the magnetic layer. As a substrate for this magnetic disk, a glass substrate is preferably used because it has a property that it is less likely to be plastically deformed than a metal substrate (aluminum substrate) or the like.

Further, in response to a request for an increase in storage capacity in a hard disk device, the density of magnetic recording has been increased. For example, the magnetic recording information area is miniaturized by using a perpendicular magnetic recording method in which the magnetization direction in the magnetic layer is perpendicular to the surface of the substrate. Thereby, the storage capacity of one disk substrate can be increased. In such a disk substrate, it is preferable to make the surface of the substrate as flat as possible and align the growth direction of the magnetic grains in the vertical direction so that the magnetization direction of the magnetic layer is substantially perpendicular to the substrate surface.
Furthermore, in order to further increase the storage capacity, a magnetic head equipped with a DFH (Dynamic Flying Height) mechanism is used to significantly shorten the flying distance from the magnetic recording surface, so that the recording / reproducing element of the magnetic head and the magnetic It is also practiced to increase the accuracy of recording / reproducing information (to improve the S / N ratio) by reducing the magnetic spacing between the magnetic recording layers of the disk. Even in this case, the surface irregularities of the substrate of the magnetic disk are required to be as small as possible in order to read and write magnetic recording information by the magnetic head stably over a long period of time.

In the process of producing the glass substrate for magnetic disk, for example, a grinding process of grinding with fixed abrasive grains to improve the flatness of the main surface of the glass substrate that has become flat after press molding, and this grinding process A polishing process of the main surface for the purpose of removing scratches and distortions remaining on the main surface is included.
Conventionally, a method using cerium oxide (cerium dioxide) abrasive grains as an abrasive is known in the polishing step of the main surface (Patent Document 1). According to the method using cerium oxide abrasive as the abrasive, scratches and distortions remaining on the main surface of the magnetic disk glass substrate can be removed at a high polishing rate, and the surface of the main surface required for the magnetic disk glass substrate Unevenness can be achieved efficiently.

JP 2008-254166 A

By the way, in recent years, it has become difficult to procure cerium, which is a rare earth, and the price of cerium has risen accordingly. Development of alternative abrasives is required.
As an alternative to cerium oxide, zirconium oxide (zirconia) is one of the promising candidates. However, when an abrasive containing zirconia is used as the abrasive, the chemical interaction of zirconia with the glass substrate for magnetic disks. It has been found that due to surface tension and the like, zirconia particles adhere to the surface of the magnetic disk glass substrate after polishing, or remain at a high rate by being buried in the surface.
If zirconia particles remain on the surface of the magnetic disk glass substrate after polishing, even if the overall surface irregularity of the substrate is reduced as much as possible, the surface irregularity of the magnetic disk produced from the glass substrate is localized. Thus, stable reading and writing of magnetic recording information for a long time by the magnetic head is hindered. In addition, after polishing with zirconia particles, when performing a final polishing step using colloidal silica or the like having a particle diameter smaller than that of zirconia particles as an abrasive, scratches and scratches are caused on the substrate surface due to residual zirconia particles. It occurs and degrades the quality of the substrate surface.
It has also been found that zirconia particles are likely to remain on the edge of the substrate other than the main surface. This is presumably because when the polishing of the main surface of the substrate is carried out while holding the substrate on the carrier, the edge of the substrate and the carrier rub during polishing. Since the carrier is harder than the polishing pad, it is considered that the force of pressing or embedding zirconia particles against the substrate acts stronger than the main surface. The zirconia particles remaining at the edge of the substrate may be contaminated by peeling off and transferring to the main surface little by little in a subsequent film formation process or the like, which may reduce the yield in the film formation process.

It is only necessary that the zirconia particles remaining on the surface of the glass substrate after being polished can be removed by washing, but zirconia is a chemically very stable and hardly soluble substance, and zirconia particles are effectively removed from the surface of the glass substrate. There is no known cleaning method to remove.
For example, the alkaline aqueous solution has a weak chemical action force on zirconia, which is an inorganic substance, and cannot sufficiently remove zirconia particles remaining on the surface of the glass substrate. Further, in a cleaning method using a strongly acidic aqueous solution at a high temperature as a cleaning solution or a cleaning method using a cleaning solution containing chloride ions, the surface of the magnetic disk glass substrate is etched to remove zirconia remaining on the surface. However, the surface of the glass substrate may be damaged, and the quality of the glass substrate as a product may be deteriorated.
In addition, a cleaning method using a cleaning solution containing fluorine ions is known, and this cleaning method is an effective method for dissolving and removing a polishing agent containing cerium oxide, but chemically very stable zirconia is used. The effect is not sufficient for the contained abrasive. That is, it has been found that even if this cleaning method is used, a large amount of zirconia particles remain on the glass substrate.

  Therefore, the present invention is for a magnetic disk in which the main surface of a glass substrate is polished using a polishing liquid containing granular zirconia as an abrasive and the zirconia particles are prevented from remaining on the main surface of the glass substrate. It aims at providing the manufacturing method of a glass substrate.

As a result of intensive studies by the inventors on the above problems, the following points have been found. That is, before the glass substrate is cleaned with the cleaning liquid containing fluorine ions, the glass substrate is brought into contact with the liquid containing phosphonic acid. As a result, the amount of zirconia particles remaining on the glass substrate is improved. There was no level. Although the detailed mechanism is unknown, the phosphonic acid enters the gap between the zirconia abrasive grains and the glass substrate due to the chelating effect of phosphonic acid, weakens the adhesion, and the zirconia particles are effectively etched by the cleaning effect of fluorine ions. Can be removed from the glass surface. In addition, since phosphonic acid also has a dispersion effect, it is considered that the phosphonic acid also adhered to the periphery of the zirconia particles separated from the surface of the glass substrate, thereby suppressing the reattachment of the zirconia particles to the glass substrate.
From the above viewpoints, the present invention provides a polishing process for polishing a main surface of a glass substrate using a polishing liquid containing zirconia abrasive grains, and a cleaning process for cleaning the glass substrate after the polishing process using a cleaning liquid. The cleaning liquid contains at least fluorine ions, and is contacted with a liquid containing phosphonic acid between the polishing process and the cleaning process.

  In the method for producing a glass substrate for a magnetic disk of the present invention, the phosphonic acid is preferably hydroxyethylidene diphosphonic acid (HEDP) or nitrilotrismethylenephosphonic acid (NTMP) having a molecular weight of 300 or less.

  In the method for manufacturing a glass substrate for a magnetic disk of the present invention, it is preferable that the cleaning liquid further contains at least one of an acid and a reducing agent.

  According to the method for manufacturing a glass substrate for a magnetic disk according to the present invention, zirconia particles remain on the main surface of the glass substrate after polishing the main surface of the glass substrate using a polishing liquid containing granular zirconia as an abrasive. This can be suppressed.

The schematic sectional drawing of the polish device (double-side polish device) used at the 1st polish process.

  Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated in detail.

[Magnetic disk glass substrate]
Aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used as the material for the magnetic disk glass substrate in the present embodiment. 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. More preferably, it is an amorphous aluminosilicate glass.

Although the composition of the glass substrate for a magnetic disk of this embodiment is not limited, the glass substrate of this embodiment is preferably converted to an oxide standard and expressed in mol%, SiO ₂ is 50 to 75%, Al _{2 to} O ₃ is selected from 1 to 15%, at least one component selected from Li ₂ O, Na ₂ O and K ₂ O in total 5 to 35%, selected from MgO, CaO, SrO, BaO and ZnO 0-20% in total of at least one component, as well as _{ZrO 2, TiO 2, La 2} O 3, Y 2 O 3, Ta 2 O 5, Nb 2 O 5 and at least one selected from HfO ₂ An amorphous aluminosilicate glass having a composition having 0 to 10% in total.

The glass substrate of this embodiment is preferably 57% to 75% SiO ₂ , 5% to 20% Al ₂ O ₃ in mass% as disclosed in, for example, JP 2009-99239 A, ( However, the total amount of SiO ₂ and Al ₂ O ₃ is 74% or more), ZrO ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , La ₂ O ₃ , Y ₂ O ₃ and TiO ₂ in total 0 %, 6% or less, Li ₂ O exceeds 1%, 9% or less, Na ₂ O 5 to 18% (however, the mass ratio Li ₂ O / Na ₂ O is 0.5 or less), K ₂ O is 0 to 6%, MgO is 0 to 4%, CaO is more than 0% and 5% or less (however, the total amount of MgO and CaO is 5% or less, and the content of CaO is the content of MgO) More than 0), SrO + BaO is 0 to 3% of amorphous composition composed of It may be a luminometer silicate glass.

Glass substrate of the present embodiment, for example, as disclosed in Japanese Patent 4815002, in mass percent on the oxide _basis, SiO 2: from 45.60 to 60%, and _Al 2 _O 3: _7~20%, and B ₂ O ₃ : less than 1.00 to 8%, and P ₂ O ₅ : 0.50 to 7%, and TiO ₂ : 1 to 15%, and the total amount of RO: 5 to 35% (where R is Zn and Mg), the CaO content is 3.00% or less, the BaO content is 4% or less, the PbO component, the As ₂ O ₃ component, the Sb ₂ O ₃ component, Cl ⁻ , NO ^{-, SO} 2-, F ^- does not contain _{ingredients, RAl 2 O 4, R 2} TiO 4 as a main crystal phase, (wherein R is one or more selected Zn, from Mg) containing one or more kinds selected from The crystal grain size of the main crystal phase is 0.5 nm to 20 It may be a crystallized glass having a range of nm, a crystallinity of 15% or less, and a specific gravity of 2.95 or less.

The composition of the glass substrate for a magnetic disk according to the present embodiment includes, as an essential component, at least one alkaline earth metal selected from the group consisting of SiO ₂ , Li ₂ O, Na ₂ O, and MgO, CaO, SrO, and BaO. The molar ratio of the CaO content to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO)) is 0.20 or less and the glass transition temperature is 650 ° C. or more. Also good. A glass substrate for a magnetic disk having such a composition is suitable for a glass substrate for a magnetic disk used for a magnetic disk for energy-assisted magnetic recording.

  The glass substrate for a magnetic disk in the present embodiment is an annular thin glass substrate. Although the size of the glass substrate for magnetic disks is not ask | required, for example, it is suitable as a glass substrate for magnetic disks with a nominal diameter of 2.5 inches.

[Method of manufacturing glass substrate for magnetic disk]
Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this embodiment is demonstrated for every process. However, the order of each step may be changed as appropriate.

(1) Molding and lapping process of glass substrate For example, after a plate glass is formed by a float process, a glass substrate having a predetermined shape as a base of the glass substrate for a magnetic disk is cut out from the plate glass. Instead of the float process, the glass substrate may be molded by press molding using an upper mold and a lower mold, for example. In addition, a glass substrate can also be manufactured using well-known manufacturing methods, such as not only these methods but a downdraw method, a redraw method, and a fusion method.
In addition, you may perform the lapping process using an alumina type loose abrasive grain with respect to both the main surfaces of a glass substrate as needed.

(2) Coring process Using a cylindrical diamond drill, an inner hole is formed in the center of the disc-shaped glass substrate to form an annular glass substrate. Scribing with a diamond cutter or the like can also be used.

(3) Chamfering step After the coring step, a chamfering step of forming a chamfered surface at the end (outer peripheral end surface and inner peripheral end surface) is performed. In the chamfering step, chamfering is performed on the outer peripheral surface and the inner peripheral surface of the laminated body processed into a cylindrical shape by the coring step by, for example, a metal bond grindstone using diamond abrasive grains.

(4) End face polishing process (machining process)
Next, end face polishing (edge polishing) of the annular glass substrate is performed.
In the end surface polishing, the inner peripheral end surface and the outer peripheral end surface of the annular glass substrate are mirror-finished by brush polishing. At this time, a slurry containing fine particles such as cerium oxide as free abrasive grains is used. By polishing the end face, removal of contamination such as dust on the end face of the annular glass substrate, damage or scratches can be prevented to prevent the occurrence of thermal asperity and corrosion of sodium and potassium. It is possible to prevent the occurrence of ion precipitation that is a cause.

(5) Grinding process with fixed abrasive In the grinding process with fixed abrasive, grinding is performed on the main surface of the glass substrate using a double-sided grinding device. The machining allowance by grinding is, for example, about several μm to 100 μm. The double-sided 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 the upper surface plate and the lower surface plate. And, by moving either the upper surface plate or the lower surface plate, or both, the glass substrate and each surface plate are moved relatively to grind both main surfaces of the glass substrate. Can do.

(6) 1st grinding | polishing (main surface grinding | polishing) process Next, 1st grinding | polishing is given to the main surface of the ground glass substrate. The machining allowance by the first polishing is, for example, about several μm to 50 μm. The purpose of the first polishing is to remove scratches and distortions remaining on the main surface by grinding with fixed abrasive grains, and to adjust surface irregularities (microwaveness, roughness).
[Polishing equipment]
A polishing apparatus used in the first polishing step will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of a polishing apparatus (double-side polishing apparatus) used in the first polishing step. Note that the same configuration as this polishing apparatus can be applied to a grinding apparatus used in the above-described grinding process.

  As shown in FIG. 1, the polishing apparatus has a pair of upper and lower surface plates, that is, an upper surface plate 40 and a lower surface plate 50. The glass substrate G is sandwiched between the upper surface plate 40 and the lower surface plate 50, and either one or both of the upper surface plate 40 and the lower surface plate 50 are moved to operate the glass substrate G and each surface plate. Both main surfaces of the glass substrate G can be polished by relatively moving.

The configuration of the polishing apparatus will be described more specifically with reference to FIG.
In the polishing apparatus, an annular flat polishing pad 10 (resin polisher) is attached to the upper surface of the lower surface plate 50 and the bottom surface of the upper surface plate 40 as a whole. The sun gear 61, the internal gear 62 provided on the outer edge, and the disk-shaped carrier 30 constitute a planetary gear mechanism centered on the central axis CTR as a whole. The disc-shaped carrier 30 meshes with the sun gear 61 on the inner peripheral side and meshes with the internal gear 62 on the outer peripheral side, and accommodates and holds one or more glass substrates G (workpieces). On the lower surface plate 50, the carrier 30 revolves while rotating as a planetary gear, and the glass substrate G and the lower surface plate 50 are relatively moved. For example, if the sun gear 61 rotates in the CCW (counterclockwise) direction, the carrier 30 rotates in the CW (clockwise) direction, and the internal gear 62 rotates in the CCW direction. As a result, relative movement occurs between the polishing pad 10 and the glass substrate G. Similarly, the glass substrate G and the upper surface plate 40 may be relatively moved.

During the relative motion, the upper surface plate 40 is pressed against the glass substrate G (that is, in the vertical direction) with a predetermined load, and the polishing pad 10 is pressed against the glass substrate G. A polishing liquid (slurry) is supplied between the glass substrate G and the polishing pad 10 from the polishing liquid supply tank 71 via one or a plurality of pipes 72 by a pump (not shown). The main surface of the glass substrate G is polished by the abrasive contained in the polishing liquid. Here, it is preferable that the polishing liquid used for polishing the glass substrate G is discharged from the upper and lower surface plates, returned to the polishing liquid supply tank 71 through a return pipe (not shown), and reused.
In this polishing apparatus, it is preferable that the load of the upper surface plate 40 applied to the glass substrate G is adjusted for the purpose of setting a desired polishing load on the glass substrate G.

The polishing liquid used in the polishing apparatus of this embodiment may be any component as long as it contains zirconia as an abrasive, but examples of preferable components of the polishing liquid are disclosed below.
(A) Abrasive containing granular zirconia (zirconium dioxide; fine particles of ZrO ₂ ) (B) including at least one selected from the group consisting of phosphate, sulfonate, polycarboxylic acid and polycarboxylate 1st additive (C) 2nd additive containing a re-aggregation inhibitor Moreover, in order to improve the dispersibility of an abrasive | polishing agent, the said polishing liquid is further (D) granular form whose particle size is smaller than the said zirconia. It is further preferable to include a third additive containing silicon dioxide and / or titanium dioxide.

The abrasive and the first to third additives are turbid in a liquid such as water or an alkaline solution to produce a polishing liquid (slurry).
In addition, it is preferable to add the said additive to polishing liquid for the following reasons. That is, if only zirconia is made turbid in the polishing liquid, the zirconia particles are hard-caked during polishing or in the polishing liquid supply tank (the abrasive grains in the abrasive once dispersed are firmly bonded and dispersed again. Easy to do) By making the zirconia particles into a hard cake, the polishing rate and the accuracy of surface irregularities on the main surface are degraded, and scratches on the main surface are likely to occur. Therefore, it is preferable to mix the first to third additives in the polishing liquid for the purpose of sufficiently dispersing the zirconia particles that are likely to form a hard cake and preventing recondensation.

  Further, from the viewpoint of the polishing ability of the polishing agent on the glass substrate, it is preferable to add a polishing liquid having a pH of about 6 to 12 by adding, for example, potassium hydroxide or sodium hydroxide to the polishing liquid.

In the example of the preferable polishing liquid described above, it is preferable that 5 to 20% by weight of an abrasive made of granular zirconia is included. The average particle size (D50) of zirconia as an abrasive (polishing abrasive) has a sufficient polishing rate (for example, 0.5 μm / min), and the surface irregularities of the glass substrate G are inspected by a condenser lamp. From the viewpoint of ensuring a polishing ability in which scratches are not confirmed, waviness is 1 nm or less, and micro waviness is 2 nm or less, preferably 0.2 to 10 μm, more preferably 0.2 to 2 μm. More preferably, it is 0.2 to 0.6 μm. The average particle size (D50) means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle size.
The swell (Waviness) can be measured by, for example, Optiflat manufactured by KLA-TENCOR, and the micro swell (Micro Waviness) can be measured by, for example, Hot manufactured by Polytech.

  In the example of the preferable polishing liquid described above, the first additive containing at least one selected from the group consisting of phosphate, sulfonate, polycarboxylic acid and polycarboxylate is contained in an amount of 0.01 to 5% by weight. It is preferable that Examples of the phosphate include sodium hexametaphosphate, sodium pyrophosphate, and potassium pyrophosphate.

  In the example of the preferable polishing liquid described above, it is preferable that the second additive containing the reaggregation inhibitor is contained in an amount of 0.01 to 5% by weight. The type of the reaggregation inhibitor is not particularly limited, and may be appropriately selected from saccharides and fibers such as cellulose (microcrystal), carboxymethylcellulose, maltose, and fructose.

In the example of the preferable polishing liquid described above, 0.05 to 5% by weight of the third additive containing granular silicon dioxide (SiO ₂ ) and / or titanium dioxide (TiO ₂ ) having a particle size smaller than that of the zirconia is further included. It is preferable that Further, powdery quartz (quartz) may be added as the third additive. For example, when the average particle diameter (D50) of zirconia is 0.2 to 10 μm, the particle diameter (average particle diameter) of silicon dioxide and / or titanium dioxide contained in the third additive is 10 to 100 nm. Silicon dioxide may be appropriately selected from colloidal silica, fumed silica, fused silica, and the like.

After polishing the glass substrate using the polishing liquid, the glass substrate is washed. In cleaning the glass substrate, a cleaning liquid containing fluorine ions is used. Fluorine ions can be supplied, for example, by including silicic acid in the cleaning solution. The cleaning liquid preferably further contains at least one of ascorbic acid as a reducing agent and a strong acid such as sulfuric acid. Thereby, zirconia particles can be slightly removed by dissolution. For example, the cleaning liquid has a fluorine ion of 0.001 to 0.02 [mol / L], a sulfuric acid of 0.05 to 1 [mol / L], an ascorbic acid of 0.001 to 0.2 [mol / L], Including.
For the cleaning liquid containing fluorine ions, see, for example, Japanese Patent No. 4041110.

  In this embodiment, the glass substrate after polishing is not immediately subjected to cleaning with a cleaning solution containing fluorine ions, but in the meantime, the glass substrate is brought into contact with a solution containing phosphonic acid (phosphonic acid solution). This is intended to effectively remove zirconia particles remaining on the surface of the glass substrate after polishing. The reason why the zirconia particles can be effectively removed is estimated as follows. That is, by bringing the surface of the glass substrate into contact with the phosphonic acid solution, the chelating effect of phosphonic acid enters between the glass substrate and the zirconia particles remaining on the surface to weaken the adhesive force, and then the subsequent fluorine It is considered that the zirconia particles are effectively removed from the surface of the glass substrate by the etching effect of the ion cleaning. Moreover, since phosphonic acid also has a dispersion effect, it is considered that the phosphonic acid also adheres around the zirconia particles separated from the surface of the glass substrate and suppresses the reattachment of the zirconia particles to the glass substrate.

Examples of the phosphonic acid contained in the phosphonic acid solution include PBTC (Phosphonobutane Tricarboxylic Acid), Hydroxyethylidene Diphosphonic Acid (HEDP), Nitrilotris Methylenephosphonic Acid (NTMP), And EDTMP (Ethylene Diamine Tetra (Methylene Phosphonic Acid)). Each of these phosphonic acids has 1 to 4 phosphate groups.
The phosphonic acid contained in the phosphonic acid solution is preferably hydroxyethylidene diphosphonic acid (HEDP) or nitrilotrismethylenephosphonic acid (NTMP). This is because these phosphonic acids have particularly high chelating effects and dispersion effects on zirconia particles.
The phosphonic acid preferably has a molecular weight of 300 or less. This is because the solubility of the phosphonic acid in the phosphonic acid solution can be increased, so that there is no fear of being deposited on the surface of the glass substrate and becoming a contamination source, and the chelating effect and the dispersing effect on the zirconia particles are increased.
The method for contacting the glass substrate with the phosphonic acid solution is not particularly limited. For example, it is preferable to immerse the glass substrate in the phosphonic acid solution for a predetermined time. Moreover, it is more preferable to irradiate ultrasonic waves. The phosphonic acid solution can be prepared by adding 0.1 to 10 vol% of phosphonic acid to pure water. Moreover, it is preferable to adjust to pH 1-3. By setting the pH to 1 to 3, the water solubility of the phosphonic acid can be increased to easily exhibit the chelating effect and the dispersing effect, and the zirconia particles can be easily separated from the glass substrate surface by the etching action on the glass substrate surface. Because.

  Although it is known that the zirconia particles remain more easily on the end face of the glass substrate than the main surface, the glass substrate is cleaned with a cleaning solution containing fluorine ions after being brought into contact with the phosphonic acid solution as in this embodiment. By doing so, the zirconia particles remaining on the end face can be removed. This point is particularly effective when the surface roughness Ra of the end face of the glass substrate is 0.015 μm or less. The surface roughness Ra of the end surface of the glass substrate can be a value measured for a region of a predetermined size (for example, an evaluation region of 50 μm square) on the side wall surface and / or the chamfered surface. As a laser microscope, Keyence VK-X200 (for example, resolution: 0.7 nm, observation magnification: 1000 times, Z-axis measurement pitch: 0.1 μm, cut-off value λs: 0.08 μm, cut-off value λc: 0. 25 nm) can be used.

The zirconia abrasive grains to be contained in the polishing liquid are preferably zirconia particles produced by a wet method and formed by aggregating primary particles having a particle size in the range of 70 to 200 nm. Further, the BET specific surface area is known as an index having a certain correlation with the primary particle diameter of the abrasive grains. From this viewpoint, the zirconia abrasive grains are produced by a wet method, and the BET specific surface area is obtained. Is preferably in the range of 4 to 15 m ² / g. By using such zirconia abrasive grains composed of an aggregate of primary particles as an abrasive, zirconia particles remaining on the glass substrate can be more effectively removed. This is because the surface area of the zirconia particles to which phosphonic acid comes into contact (adsorption) increases because the zirconia particles are very small, and the adhesion force between the glass substrate and the zirconia particles remaining on the surface is more effectively reduced. This is thought to be possible.

Examples of the cleaning method include an immersion cleaning method, a shower cleaning method, a brush cleaning method, an ultrasonic cleaning method, a scrub cleaning method, and the like. Of these, at least one type or a combination of two or more types may be used. It is preferable to adopt a sonic cleaning method. The ultrasonic cleaning method is a method of irradiating a glass substrate immersed in a cleaning liquid in a cleaning tank with ultrasonic waves and cleaning using a physical force such as a cavitation effect. The ultrasonic cleaning method is preferable as a cleaning method because it hardly damages the surface of the glass substrate and physically removes foreign matters, so that it is easy to increase cleanliness while maintaining smoothness.
The frequency of ultrasonic waves in ultrasonic cleaning is, for example, about 28 to 1,000 kHz, but is relatively low in the range of 28 to 80 kHz because the glass substrate surface is hardly damaged while obtaining a sufficient cavitation effect on the glass substrate surface. A frequency is preferred.

In the ultrasonic cleaning, it is more preferable to swing the glass substrate in the vertical or horizontal direction while irradiating the glass substrate immersed in the cleaning liquid in the cleaning tank with ultrasonic waves.
This is due to the following reason. That is, since ultrasonic cleaning is performed by vibrating a vibration plate provided at the bottom of the cleaning tank in the vertical direction with ultrasonic waves, the generated ultrasonic waves propagate in the cleaning liquid as vertical waves. That is, since the vibration direction of the wave by the ultrasonic wave is only one direction, depending on the arrangement of the glass substrate which is the work in the cleaning tank, a strong part and a weak part of the ultrasonic cavitation effect are generated. About the part with a weak cavitation effect by an ultrasonic wave, the washing | cleaning effect of the zirconia particle of an abrasive grain becomes weak, and possibility that it will remain on a glass substrate becomes high. Therefore, in addition to the ultrasonic vibration in the vertical direction, the cavitation effect due to the ultrasonic wave is made more uniform on the glass substrate regardless of the position on the glass substrate by using the horizontal oscillation of the cleaning tank. Will be able to.

(7) Chemical Strengthening Step Next, the glass substrate after the first polishing step is chemically strengthened.
As the chemical strengthening solution, for example, a mixed solution of potassium nitrate (60% by weight) and sodium sulfate (40% by weight) can be used. In the chemical strengthening, the chemical strengthening liquid is heated to, for example, 300 ° C. to 400 ° C., and the cleaned glass substrate is preheated to, for example, 200 ° C. to 300 ° C. Soak for 5 hours.
Thus, by immersing the glass substrate in the chemical strengthening solution, lithium ions and sodium ions on 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, The glass substrate is strengthened. Note that the chemically strengthened glass substrate is cleaned. For example, after washing with sulfuric acid, it is washed with pure water or the like.

(8) Second Polishing (Final Polishing) Step Next, the second polishing is performed on the glass substrate that has been chemically strengthened and sufficiently cleaned. The second polishing is intended for mirror polishing of the main surface. The machining allowance by the second polishing is, for example, about 5 μm. In order to stably mass-produce a substrate from which all the nanopits and / or nanoscratches have been removed by the second polishing process, the machining allowance more than 10 times the depth of the nanopits and / or nanoscratches generated in the first polishing process is required. It is preferable to do. In the second polishing, for example, the polishing apparatus used in the first polishing is used. At this time, the difference from the first polishing is that the type and particle size of the free abrasive grains are different and the hardness of the resin polisher is different.
As the free abrasive grains used in the second polishing, for example, fine particles (particle size: diameter of about 10 to 50 nm) such as colloidal silica made turbid in the slurry are used. Thereby, the surface roughness of the main surface of a glass substrate can further be reduced, and an edge part shape can be adjusted to a preferable range.
The polished glass substrate is washed with a neutral detergent, pure water, IPA or the like to obtain a glass substrate for a magnetic disk.

[Magnetic disk]
A magnetic disk is obtained as follows using a magnetic disk glass substrate.
The magnetic disk is, for example, on the main surface of a glass substrate for magnetic disk (hereinafter simply referred to as “substrate”), in order from the closest to the main surface, at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), and a protective layer. A layer and a lubricating layer are laminated.
For example, the substrate is introduced into a film forming apparatus that has been evacuated, and a film is sequentially formed from an adhesion layer to a magnetic layer on the main surface of the substrate in an Ar atmosphere by a DC magnetron sputtering method. For example, CrTi can be used as the adhesion layer, and CrRu can be used as the underlayer. As the magnetic layer, for example, a CoPt alloy can be used. It is also possible to form a CoPt-based alloy and FePt based alloy L ₁₀ regular structure and magnetic layer for heat-assisted magnetic recording. After the above film formation, a magnetic recording medium can be formed by forming a protective layer using, for example, C ₂ H ₄ by a CVD method and subsequently performing nitriding treatment for introducing nitrogen into the surface. Thereafter, for example, PFPE (perfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.
The manufactured magnetic disk is preferably a magnetic disk drive device (HDD) as a magnetic recording / reproducing device, which includes a magnetic head equipped with a DFH (Dynamic Flying Height) control mechanism and a spindle for fixing the magnetic disk. (Hard Disk Drive)).

  In the following, the present invention is further illustrated by examples. However, this invention is not limited to the aspect shown in the Example.

(1) Production of Molten Glass In order to confirm the effect of the magnetic disk glass substrate of the present embodiment, a 2.5-inch magnetic disk (outer diameter 65 mm, inner diameter 20 mm, plate thickness 0) from the manufactured magnetic disk glass substrate. .635 mm). The composition of the glass of the produced magnetic disk glass substrate is as follows.
(Glass composition)
In terms of mass%, SiO ₂ is 65.08%, Al ₂ O ₃ is 15.14%, Li ₂ O is 3.61%, Na ₂ O is 10.68%, K ₂ O is 0.35%, An amorphous aluminosilicate glass having a composition having 0.99% MgO, 2.07% CaO, 1.98% ZrO ₂ and 0.10% Fe ₂ O ₃ , and has a glass transition temperature of 510 ° C. It is.

(2) Production of glass substrate Melted glass that flows out from the pipe at a constant flow rate and is received by a lower mold for press molding so that a predetermined amount of molten glass lump is obtained on the lower mold. The glass was cut with a cutting blade. Then, the lower mold on which the molten glass block was placed was immediately carried out from below the pipe, and was press-formed into a thin disk shape using the upper mold and the barrel mold opposed to the lower mold. After the press-formed product is cooled to a temperature at which it does not deform, it is removed from the mold and annealed. Then, the lapping process was performed with respect to the glass substrate obtained by press molding. In the lapping process, alumina abrasive grains (# 1000 grain size) were used as free abrasive grains.

(3) Coring processing and chamfering processing Using a cylindrical diamond drill, an inner hole was formed at the center of a disk-shaped glass substrate to obtain an annular glass substrate (coring). Then, the inner peripheral end face and the outer peripheral end face were ground with a diamond grindstone and subjected to predetermined chamfering (chambering).

(4) End face polishing step Next, the end face of the annular glass substrate was subjected to mirror polishing by a brush polishing method. At this time, as the abrasive grains, a slurry (free abrasive grains) containing cerium oxide abrasive grains was used. By this end surface polishing step, the end surface of the glass substrate was processed into a mirror surface state capable of preventing generation of particles and the like.

(5) First polishing step for main surface A glass substrate was set in the polishing apparatus shown in FIG. The polishing liquid used in the polishing step is 5 to 20% by weight of zirconia (ZrO ₂ ) as an abrasive, 0.01 to 5% by weight of sodium hexametaphosphate as a first additive, and as a second additive. It was produced by mixing 0.01 to 5% by weight of cellulose in pure water filtered water (RO water) or pure water and stirring sufficiently. At this time, the average particle diameter (D50) of zirconia was 0.5 μm, and it was manufactured by a wet method. The primary particle diameter of the zirconia particles is 120 nm.
About the glass substrate of an Example, it was immersed in the phosphonic acid liquid after grinding | polishing. Specifically, phosphonic acid solution prepared by adding 1 vol% of phosphonic acid to pure water and adjusting the pH to 1 to 3 and the temperature of 40 ° C. was prepared, and the glass substrate was irradiated with ultrasonic waves of 40 to 80 kHz. It was immersed for 10 minutes. As shown in Table 1, in Examples 1 to 4, the phosphonic acid contained in the phosphonic acid solution is different. The glass substrate of the comparative example was not immersed in the phosphonic acid solution after polishing.
Then, about the glass substrate of the Example and the comparative example, it wash | cleaned by the ultrasonic cleaning method using the washing | cleaning liquid containing a fluorine ion, Furthermore, the rinse washing | cleaning using the pure water was performed, and IPA vapor drying was performed finally. A cleaning solution containing 0.01 [mol / L] silicic acid, 1 [mol / L] sulfuric acid, and 0.1 [mol / L] ascorbic acid was used. In the ultrasonic cleaning method, the frequency of ultrasonic waves was 40 kHz, and cleaning was performed at 50 ° C. for 4 minutes.

[Evaluation method]
After cleaning the glass substrate, the cleanliness (degree of soiling) of the surface of the glass substrate of Examples and Comparative Examples was evaluated by visual inspection and a microscope. The cleanliness was evaluated by evaluating 100 samples of each of the glass substrates of Examples and Comparative Examples using a condensing lamp in the dark curtain area of a clean room, and no contamination was observed on the edge of the glass substrate. The ratio (%) of the number of substrates was calculated. In addition, as for the main surface, all were substantially favorable. Further, when the soiled samples were examined in detail by SEM / EDX, the zirconia abrasive grains were found. Therefore, it is judged that the higher the cleanliness, the better the zirconia abrasive grains can be washed away.

According to the evaluation results in Table 1, after polishing the main surface of the glass substrate using a polishing liquid containing zirconia abrasives as an abrasive, the glass substrate is added to the phosphonic acid liquid before cleaning with a cleaning liquid containing fluorine ions. It is understood that the cleanliness of the surface of the end portion of the glass substrate is improved by immersing (contacting). In particular, it is understood that the cleanliness of the surface of the glass substrate becomes extremely good by immersing the glass substrate in a solution containing HEDP or NTMP as phosphonic acid. This is because HEDP and NTMP have particularly high chelating effects and dispersion effects on zirconia particles.
Moreover, it turns out from the evaluation result of Table 1 that the degree of cleanliness becomes better as the molecular weight of phosphonic acid decreases. This is because the solubility of the phosphonic acid in the phosphonic acid solution can be increased, so that there is no fear of being deposited on the surface of the glass substrate and becoming a contamination source, and the chelating effect and the dispersing effect on the zirconia particles are increased. In particular, when the molecular weight is 300 or less (HEDP, NTMP, or PBTC), the cleanliness is relatively good.

  As mentioned above, although the manufacturing method of the glass substrate for magnetic discs of this invention was demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, even if various improvement and a change are carried out. Of course it is good.

DESCRIPTION OF SYMBOLS 10 Polishing pad 30 Carrier 40 Upper surface plate 50 Lower surface plate 61 Sun gear 62 Internal gear 71 Polishing liquid supply tank 72 Piping

Claims (3)

Manufacture of a glass substrate for a magnetic disk, comprising: a polishing process for polishing a main surface of a glass substrate using a polishing liquid containing zirconia abrasive grains; and a cleaning process for cleaning the glass substrate after the polishing process using a cleaning liquid. A method,
The cleaning liquid contains at least fluorine ions,
Between the polishing treatment and the cleaning treatment, a liquid containing phosphonic acid is contacted,
Manufacturing method of glass substrate for magnetic disk. The phosphonic acid is hydroxyethylidene diphosphonic acid (HEDP) or nitrilotrismethylene phosphonic acid (NTMP) having a molecular weight of 300 or less,
The manufacturing method of the glass substrate for magnetic discs described in Claim 1. The cleaning liquid further includes at least one of an acid and a reducing agent.
A method for producing a glass substrate for a magnetic disk according to claim 1 or 2.

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