JP5704755B2 - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk mounted on a magnetic disk device such as a hard disk drive (HDD) and a method for manufacturing a magnetic disk.

  There is a magnetic disk as one of information recording media mounted on a magnetic disk device such as a hard disk drive (HDD). A magnetic disk is configured by forming a thin film such as a magnetic layer on a substrate, and an aluminum substrate has been conventionally used as the substrate. However, recently, in response to the pursuit of higher recording density, the ratio of the glass substrate capable of narrowing the distance between the magnetic head and the magnetic disk as compared with the aluminum substrate is gradually increasing. Further, the surface of the glass substrate is polished with high accuracy so as to increase the recording density so that the flying height of the magnetic head can be reduced as much as possible. In recent years, there has been an increasing demand for HDDs with higher recording capacity and lower prices. In order to achieve this, it is necessary to further improve the quality and cost of glass substrates for magnetic disks. It is coming.

As described above, high smoothness on the surface of the magnetic disk is indispensable for reducing the flying height (flying height) necessary for increasing the recording density. In order to obtain a high smoothness on the surface of the magnetic disk, a substrate surface with a high smoothness is required in the end. Therefore, it is necessary to polish the glass substrate surface with high accuracy.
A conventional glass substrate polishing method is performed using a polishing pad of a polisher such as polyurethane while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica. A glass substrate having high smoothness can be obtained by polishing using, for example, a cerium oxide-based abrasive and then finishing polishing (mirror polishing) using colloidal silica abrasive grains. Here, for example, it has been proposed to use a colloidal silica slurry whose pH is adjusted to be acidic for polishing a magnetic disk substrate (see Patent Document 1 below). In addition, it has also been proposed to use a colloidal silica slurry adjusted to have a pH of more than 10.2 and 12 or less by containing an alkali in the polishing liquid for polishing a glass substrate for magnetic disks (the following patents). Reference 2).

JP-A-7-240025 JP 2003-173518 A

  The current HDD has reached a recording density of about 500 gigabits per square inch. For example, it is possible to store about 320 gigabytes of information on a 2.5 inch magnetic disk (diameter 65 mm). However, higher recording density, for example, 375 to 500 gigabytes, and further 1 terabyte has been required. With the recent demand for larger capacity of HDDs, the demand for improvement of the substrate surface quality has become more severe than ever. In the next generation substrate for a magnetic disk of, for example, 375 to 500 gigabytes as described above, since the influence of the substrate on the media characteristics becomes large, not only the roughness of the substrate surface but also scratches, adhesion of foreign matters, etc. There is also a need for further improvements from the current product in the absence of surface defects.

In the next generation substrate, the influence of the substrate on the media characteristics becomes large for the following reasons.
For example, the flying height of the magnetic head (the gap between the magnetic head and the surface of the medium (magnetic disk)) is greatly reduced (lower flying height). By doing so, the distance between the magnetic head and the magnetic layer of the medium is reduced, so that signals of smaller magnetic particles can be picked up, and high recording density can be achieved. In recent years, a function called DFH (Dynamic Flying Height) has been mounted on a magnetic head in order to achieve a lower flying height than before. This is a function of providing a heating unit such as a very small heater in the vicinity of the recording / reproducing element part of the magnetic head and projecting only the periphery of the recording / reproducing element part toward the medium surface. In the future, with this DFH function, the gap between the element portion of the magnetic head and the medium surface is expected to be extremely small, less than 2 nm. Under such circumstances, when the average roughness of the substrate surface is extremely small, there are surface defects such as very small scratches that have not been a problem in the past, and convex surface defects due to adhesion of foreign substances. Both sides of the scratch on the substrate surface may swell, and the convex defect on the substrate surface becomes a convex defect on the medium surface as it is, which increases the risk of collision of the magnetic head. Further, at the bottom (valley) portion of the scratch, the distance between the magnetic layer of the medium and the element portion of the magnetic head is increased, so that an error is likely to occur when reading or writing a magnetic signal.

  By the way, the slurry in which a metal oxide abrasive such as cerium oxide or colloidal silica is turbid and the glass substrate quality after polishing have a strong correlation, for example, by controlling the particle size of the abrasive contained in the slurry. It is well known that it is effective in improving the quality of the main surface of the glass substrate. According to the study of the present inventors, the roughness of the main surface of the substrate can be reduced by controlling the particle size of the abrasive contained in the slurry, for example, by using a fine-grain abrasive. On the other hand, if the size is too small, problems such as an increase in roughness, a deterioration of the end face shape, and a decrease in the polishing rate occur. Further, the effect of improving surface defects due to scratches, foreign matter adhesion, and the like cannot be obtained by only miniaturizing the abrasive.

  The demand for improving the substrate surface quality accompanying the recent demand for higher capacity HDDs has become more severe than ever, and there is a limit to the further improvement of the substrate surface quality by the conventional improvement methods. There is.

  The present invention has been made to solve such a conventional problem, and its purpose is to further reduce surface defects due to scratches and adhesion of foreign substances, etc., compared to conventional products, and to improve the substrate surface quality. The manufacturing method of a glass substrate for a magnetic disk capable of manufacturing a high-quality glass substrate that can be used as a next-generation substrate at a lower cost, The present invention provides a method of manufacturing a magnetic disk using a glass substrate.

  In order to solve the above-mentioned problems, the present inventor has found friction between a glass substrate and a polishing pad at the time of polishing, which has not been sufficiently studied heretofore, and between polishing abrasive grains contained in a polishing liquid and a glass substrate. We focused on the interaction. Usually, when the friction between the glass substrate and the polishing pad during polishing is large, the occurrence of surface defects such as scratches becomes remarkable, and conversely, when the friction between the glass substrate and the polishing pad is small, scratches and the like are generated. The occurrence of surface defects is reduced, but the polishing rate is greatly reduced. In addition, when colloidal silica abrasive grains are used as the abrasive grains, the colloidal silica abrasive grains easily adhere to the surface of the glass substrate because it is the same component as the main component of the glass substrate that is the object to be polished. Even if it carries out, colloidal silica abrasive grains remain on the surface of the glass substrate and tend to be convex defects. In particular, when fine colloidal silica abrasive grains are used for improving (reducing) the surface roughness of the substrate, the occurrence of convex defects due to adhesion of foreign matters becomes significant. As a result of intensive studies, the inventor was surprised by immersing the glass substrate in an aqueous solution containing an acrylic polymer containing a sulfonic acid group before the polishing step, and then performing the polishing step. In addition, it has been found that not only surface defects such as scratches but also convex defects due to adhesion of foreign matters such as colloidal silica abrasive grains can be further reduced as compared with conventional products.

That is, the present invention has the following configuration.
(Configuration 1)
A method for producing a glass substrate for a magnetic disk having a polishing step of polishing a main surface of a glass substrate using a polishing liquid containing colloidal silica as polishing abrasive grains and a surface plate provided with a polishing pad, A method for producing a glass substrate for a magnetic disk, comprising immersing the glass substrate in an aqueous solution containing an acrylic polymer containing a sulfonic acid group before the polishing step, and then performing the polishing step. .

(Configuration 2)
2. The method for manufacturing a glass substrate for a magnetic disk according to Configuration 1, wherein the content of the acrylic polymer containing the sulfonic acid group in the aqueous solution is in the range of 0.01 to 1% by weight.

(Configuration 3)
The said colloidal silica abrasive grain is a manufacturing method of the glass substrate for magnetic discs of the structure 1 or 2 characterized by the particle size being 10-40 nm.

(Configuration 4)
4. The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 3, wherein a suede pad is used as the polishing pad.

(Configuration 5)
5. The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 4, wherein the glass substrate is made of amorphous aluminosilicate glass.

(Configuration 6)
A magnetic disk manufacturing method comprising forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the manufacturing method according to any one of Structures 1 to 5.

  According to the present invention, it is possible to manufacture a high-quality glass substrate for a magnetic disk that can further reduce surface defects due to scratches (scratches), adhesion of foreign matters, and the like as compared with conventional products at a low cost. The glass substrate for a magnetic disk obtained by the present invention can be suitably used as a substrate for the next generation in which the demand for the surface quality of the substrate is particularly stricter than the present. Further, by using the glass substrate obtained by the present invention, a highly reliable magnetic disk capable of long-term stable operation even when combined with a magnetic head with an extremely low flying height design equipped with a DFH function is obtained. Can do.

It is sectional drawing of the glass substrate for magnetic discs. It is a whole perspective view of the glass substrate for magnetic discs. It is a longitudinal cross-sectional view which shows schematic structure of a double-side polish apparatus.

Hereinafter, embodiments of the present invention will be described in detail.
The glass substrate for a magnetic disk is usually a rough grinding step (rough lapping step), a shape processing step, a fine grinding step (fine lapping step), an end surface polishing step, a main surface polishing step (first polishing step, second polishing step). It is manufactured through a chemical strengthening process.
In manufacturing the magnetic disk glass substrate, first, a disk-shaped glass substrate (glass disk) is molded from molten glass by direct pressing. In addition to such a direct press, a glass substrate (glass disk) may be obtained by cutting into a predetermined size from a plate glass manufactured by a downdraw method or a float method. Next, the molded glass substrate (glass disk) is ground (lapping) for improving dimensional accuracy and shape accuracy. This grinding process usually uses a double-sided lapping machine to grind the main surface of the glass substrate using hard abrasive grains such as diamond. By grinding the main surface of the glass substrate in this way, a predetermined plate thickness and flatness are processed, and a predetermined surface roughness is obtained.

  After this grinding process is finished, mirror polishing is performed to obtain a highly accurate plane. As a mirror polishing method for a glass substrate, it is usually preferable to use a polishing pad such as polyurethane while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica. It is.

  The present invention includes a polishing step of polishing a main surface of a glass substrate using a polishing liquid containing colloidal silica as polishing abrasive grains and a surface plate provided with a polishing pad, as in Configuration 1 above. A method for producing a glass substrate for a disk, wherein the glass substrate is immersed in an aqueous solution containing an acrylic polymer containing a sulfonic acid group before the polishing step, and then the polishing step is performed. A method for producing a glass substrate for a magnetic disk.

  In the present invention, before the polishing step, by immersing the glass substrate in an aqueous solution containing an acrylic polymer containing a sulfonic acid group, the acrylic polymer film containing the sulfonic acid group on the surface of the glass substrate. To form. As a result, the friction between the glass substrate and the polishing pad during polishing can be suitably reduced, and not only the effect of reducing the roughness of the substrate surface, but also the effect of reducing surface defects such as scratches on the substrate surface in particular. Is obtained. In addition, it is possible to moderately suppress the colloidal silica abrasive grains from being adhered to the glass substrate surface during polishing. As a result, surface defects such as scratches and convex surface defects due to adhesion of foreign matter such as colloidal silica abrasive grains can be further reduced compared to conventional products. It is possible to manufacture a high-quality magnetic disk glass substrate that can be suitably used as a next-generation substrate at low cost.

  In the present invention, before the polishing step, the glass substrate is immersed in an aqueous solution containing an acrylic polymer containing a sulfonic acid group. Examples of the acrylic polymer containing a sulfonic acid group used in the present invention include acrylic acid. Preferably, a copolymer of sulfonic acid group-containing monomer is used. Specific examples of the copolymer of acrylic acid and a sulfonic acid group-containing monomer include, for example, Aron A-6016A, Aron A-6012, Aron A-6017, Aron A-6020 (all trade names: Toa Synthetic Co., Ltd.). Among these, Aron A-6016A is particularly preferable because it has a lower molecular weight and lower viscosity than the others, and a decrease in the polishing rate during polishing performed later is small.

  The amount of the acrylic polymer containing a sulfonic acid group in the aqueous solution that immerses the glass substrate is such that surface defects such as scratches according to the present invention as described above, and convex surface defects due to adhesion of foreign matters such as colloidal silica abrasive grains. The amount may be such that the effect of further reducing the effect of the conventional product is obtained, and it is preferably in the range of 0.01 to 1% by weight, for example. If the addition amount is less than 0.01% by weight, the effects of the present invention may not be sufficiently exhibited. If the added amount exceeds 1% by weight, the viscosity of the aqueous solution increases and the thickness of the coating film formed on the surface of the glass substrate increases, so that the occurrence of surface defects such as scratches can be reduced. There is a possibility that the friction between the substrate and the polishing pad becomes too small, and the reduction of the polishing rate becomes large. In addition, the acrylic polymer containing the said sulfonic acid group may be used individually by 1 type, or may mix and use 2 or more types. The aqueous solution containing the acrylic polymer containing a sulfonic acid group is basically a solution obtained by dissolving the acrylic polymer in water as a solvent. An additive may be contained.

  In addition, regarding the time for immersing the glass substrate in the aqueous solution containing an acrylic polymer containing a sulfonic acid group, it is not possible to say unconditionally because it depends on the content of the acrylic polymer in the aqueous solution. About 10 minutes is preferable.

In the present invention, before the polishing step, after the glass substrate is immersed in an aqueous solution containing an acrylic polymer containing a sulfonic acid group, a polishing liquid containing colloidal silica as polishing abrasive grains and a polishing pad are provided. A polishing step for polishing the main surface of the glass substrate is performed using the surface plate.
Conventionally, the polishing liquid used for polishing processing is basically a combination of an abrasive and water as a solvent, and further requires a pH adjusting agent and other additives for adjusting the pH of the polishing liquid. Depending on the content.

  In the present invention, in order to compose a polishing liquid containing colloidal silica abrasive grains, pure water, for example, RO water may be used as the polishing liquid. Here, RO water is pure water that has been subjected to RO (Reverse Osmotic Pressure Membrane) treatment. It is particularly preferable to use RO-DI water that has been subjected to RO treatment and DI treatment (deionization treatment). This is because RO water or RO-DI water has a very low content of impurities, such as alkali metals, and also has a low ion content.

  Moreover, the said polishing liquid applied to the grinding | polishing process of this invention uses what was adjusted to the acidic region, for example. For example, sulfuric acid is added to the polishing liquid to adjust the pH to a range of 2 to 4. The reason why the polishing liquid adjusted to the acidic range is preferably used in the present invention is from the viewpoint of productivity and cleanliness.

  The colloidal silica abrasive grains contained in the polishing liquid are preferably those having an average particle diameter of about 10 to 100 nm from the viewpoint of polishing efficiency. In particular, in the present invention, the abrasive grains contained in the polishing liquid used in the finishing mirror polishing process (second polishing process, which will be described later) have an average particle diameter from the viewpoint of further reducing the surface roughness. It is preferable to use one having a thickness of about 10 to 40 nm.

The polishing method in the polishing step of the present invention is not particularly limited. For example, while the glass substrate and the polishing pad are brought into contact with each other and the polishing liquid containing the abrasive grains is supplied, the polishing pad and the glass substrate are relative to each other. And the surface of the glass substrate may be polished into a mirror surface.
For example, FIG. 3 is a longitudinal sectional view showing a schematic configuration of a planetary gear type double-side polishing apparatus that can be used in a mirror polishing process of a glass substrate. The double-side polishing apparatus shown in FIG. 3 meshes with the sun gear 2, the internal gear 3 arranged concentrically on the outer side, the sun gear 2 and the internal gear 3, and the sun gear 2 and the internal gear 3. An upper surface plate 5 and a lower surface plate 6 on which a carrier 4 that revolves and rotates according to rotation, and a polishing pad 7 that can hold the workpiece 1 held by the carrier 4 are attached, and an upper surface plate A polishing liquid supply unit (not shown) for supplying a polishing liquid is provided between 5 and the lower surface plate 6.

  By such a double-side polishing apparatus, during polishing, the workpiece 1 held by the carrier 4, that is, the glass substrate is sandwiched between the upper surface plate 5 and the lower surface plate 6, and the upper and lower surface plates 5, 6 are polished. While supplying the polishing liquid between the pad 7 and the workpiece 1, the carrier 4 revolves and rotates according to the rotation of the sun gear 2 and the internal gear 3, and the upper and lower surfaces of the workpiece 1 are moved. Polished.

  In particular, the polishing pad for finishing mirror polishing is preferably a polishing pad (suede pad) of a soft polisher. The polishing pad preferably has an Asker C hardness of 60 to 80. The contact surface of the polishing pad with the glass substrate is preferably made of a foamed resin with an open foam pore, particularly foamed polyurethane. When polishing is performed in this manner, the surface of the glass substrate can be polished into a smooth mirror surface.

  Normally, the mirror polishing process includes a first polishing process for removing scratches and distortions remaining in the lapping process as described above, and a flat surface obtained in the first polishing process while maintaining glass. In general, this is performed through two stages of the second polishing process that finishes the surface roughness of the substrate main surface into a smooth mirror surface (however, multistage polishing of three or more stages may be performed). It is desirable to perform a step of immersing the glass substrate in an aqueous solution containing the acrylic polymer containing a sulfonic acid group as described above, at least before the second polishing step in the subsequent stage.

In the present invention, the glass constituting the glass substrate is preferably an amorphous aluminosilicate glass. Such a glass substrate can be finished to a smooth mirror surface by mirror polishing the surface, and the strength after processing is good. As such an aluminosilicate glass, SiO ₂ is 58 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 23 wt%, Li ₂ O is 3 wt% to 10 wt%, Na ₂ An aluminosilicate glass containing O as a main component in an amount of 4 wt% or more and 13 wt% or less (however, an aluminosilicate glass containing no phosphorus oxide) can be used. Further, for example, SiO ₂ is 62 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 15 wt%, Li ₂ O is 4 wt% to 10 wt%, and Na ₂ O is 4 wt%. above 12 wt% or less, the ZrO ₂ 5.5 wt% to 15 wt% or less, while containing as the main component, the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.0, Al ₂ O ₃ An amorphous aluminosilicate glass containing no phosphorus oxide having a weight ratio of / ZrO ₂ of 0.4 or more and 2.5 or less can be obtained. In addition, it is desirable that the glass does not contain an alkaline earth metal oxide such as CaO or MgO. An example of such glass is N5 glass (trade name) manufactured by HOYA Corporation.

In addition, heat resistance may be required as a characteristic of next-generation substrates. The heat-resistant glass in this case, for example, in mol%, the _{SiO 2 50~75%, Al 2 O} 3 0-6%, 0-2% of BaO, and Li ₂ O 0 to 3% ZnO 0 to 5%, Na ₂ O and K ₂ O 3 to 15% in total, MgO, CaO, SrO and BaO 14 to 35% in total, ZrO ₂ , TiO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Yb ₂ O ₃ , Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂ in total ₂ to 9%, molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85 to 1 And a glass having a molar ratio [Al ₂ O ₃ / (MgO + CaO)] in the range of 0 to 0.30 can be preferably used.

In the present invention, the surface of the glass substrate after the mirror polishing is preferably a mirror surface having an arithmetic average surface roughness Ra of 0.20 nm or less, particularly 0.15 nm or less. Furthermore, it is preferable that the mirror surface has a maximum roughness Rmax of 2.0 nm or less. In the present invention, Ra and Rmax are roughnesses calculated in accordance with Japanese Industrial Standard (JIS) B0601.
In the present invention, the surface roughness (for example, the maximum roughness Rmax, the arithmetic average roughness Ra) is measured with a resolution of 512 × 256 pixels in an area of 1 μm × 1 μm using an atomic force microscope (AFM). It is practically preferable to obtain the surface roughness of the obtained surface shape.

  In the present invention, it is preferable to perform chemical strengthening treatment before or after the mirror polishing process. As a method of the chemical strengthening treatment, for example, a low temperature type ion exchange method in which ion exchange is performed in a temperature range that does not exceed the temperature of the glass transition point, for example, a temperature of 300 ° C. or more and 400 ° C. or less is preferable. The chemical strengthening treatment is a process in which a molten chemical strengthening salt is brought into contact with a glass substrate, whereby an alkali metal element having a relatively large atomic radius in the chemical strengthening salt and a relatively small atomic radius in the glass substrate. This is a treatment in which an alkali metal element is ion-exchanged, an alkali metal element having a large ion radius is permeated into the surface layer of the glass substrate, and compressive stress is generated on the surface of the glass substrate. Since the chemically strengthened glass substrate is excellent in impact resistance, it is particularly preferable for mounting on a HDD for mobile use, for example. As the chemical strengthening salt, alkali metal nitric acid such as potassium nitrate or sodium nitrate can be preferably used.

  As shown in FIGS. 1 and 2, the disk-shaped glass substrate having both main surfaces 11, 11 and an outer peripheral side end surface 12 and an inner peripheral side end surface 13 therebetween as shown in FIG. 1 and FIG. 1 is obtained. The outer peripheral side end surface 12 includes chamfered surfaces 12b and 12b between the side wall surface 12a and the main surfaces on both sides thereof. The inner peripheral side end face 13 has the same shape.

  The present invention also provides a method for manufacturing a magnetic disk using the above glass substrate for a magnetic disk. In the present invention, the magnetic disk is manufactured by forming at least a magnetic layer on the magnetic disk glass substrate according to the present invention. As a material for the magnetic layer, a hexagonal CoCrPt-based or CoPt-based ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method of forming the magnetic layer, it is preferable to use a method of forming a magnetic layer on a glass substrate by a sputtering method, for example, a DC magnetron sputtering method. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a hexagonal underlayer containing Ru or Ti, the easy magnetization direction of the magnetic layer can be oriented along the normal line of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by sputtering as with the magnetic layer.

In addition, a protective layer and a lubricating layer may be formed in this order on the magnetic layer. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. For example, the protective layer can be formed by a plasma CVD method. Further, as the lubricating layer, a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used. In particular, it is preferable that the main component is a perfluoropolyether compound having a terminal hydroxyl group as a polar functional group. The lubricating layer can be applied and formed by a dip method.
By using the glass substrate for magnetic disk obtained by the present invention, a highly reliable magnetic disk can be obtained.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. In addition, this invention is not limited to a following example.
(Example 1)
The following (1) rough lapping step (rough grinding step), (2) shape processing step, (3) fine lapping step (fine grinding step), (4) end surface polishing step, (5) main surface first polishing step, A glass substrate for a magnetic disk of this example was manufactured through (6) chemical strengthening step, (7) substrate dipping step, and (8) main surface second polishing step.

(1) Coarse lapping process First, a glass substrate made of disc-shaped aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.0 mm was obtained from molten glass by direct pressing using an upper mold, a lower mold, and a trunk mold. In addition to such a direct press, a glass substrate may be obtained by cutting into a predetermined size from a plate glass manufactured by a downdraw method or a float method. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: _{3~10 wt%,} Na 2 O: _4~13 chemical containing wt% Tempered glass was used.

  Next, a lapping process was performed on the glass substrate in order to improve dimensional accuracy and shape accuracy. This lapping process was performed using a double-sided lapping machine and using abrasive grains having a particle size of # 400. Specifically, a glass substrate held by a carrier is closely attached between the upper and lower surface plates, the load is set to about 100 kg, and the sun gear and the internal gear of the wrapping device are rotated, so that the glass stored in the carrier. Both surfaces of the substrate were lapped to a surface accuracy of 0 to 1 μm and a surface roughness (Rmax) of about 6 μm.

(2) Shape processing step Next, a cylindrical grindstone is used to make a hole in the central portion of the glass substrate, and the outer peripheral end face is ground to a diameter of 65 mmφ. Chamfered. The surface roughness of the end face of the glass substrate at this time was about 4 μm in Rmax. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) Fine wrapping process This fine wrapping process uses a double-sided wrapping device, and adheres a glass substrate held by a carrier between upper and lower surface plates to which pellets of diamond abrasive grains of particle size # 1000 fixed with acrylic resin are attached. I did it.
Specifically, by setting the load to about 100 kg and rotating the sun gear and the internal gear of the wrapping device, both surfaces of the glass substrate housed in the carrier are approximately 2 μm in surface roughness Rmax and 0 in Ra. Wrapped to about 2 μm.
The glass substrate after the lapping process was immersed in each washing tank (applied with ultrasonic waves) in a neutral detergent and water in order to perform ultrasonic cleaning.

(4) End face polishing step Next, the surface roughness of the end face (inner circumference, outer circumference) of the glass substrate was polished by brush polishing to about 1 μm at Rmax and about 0.3 μm at Ra while rotating the glass substrate. And the surface of the glass substrate which finished the said end surface grinding | polishing was water-washed.

(5) Main Surface First Polishing Step Next, a first polishing step for removing scratches and distortions remaining in the lapping step described above was performed using the double-side polishing apparatus shown in FIG. In the double-side polishing apparatus, the glass substrate held by the carrier 4 is closely attached between the upper and lower polishing surface plates 5 and 6 to which the polishing pad 7 is attached, and the carrier 4 is engaged with the sun gear 2 and the internal gear 3. The glass substrate is sandwiched between upper and lower surface plates 5 and 6. Thereafter, the polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass substrate, so that the glass substrate revolves while rotating on the surface plates 5 and 6, and both surfaces are polished simultaneously. . Specifically, a hard polisher (hard foamed urethane) was used as the polisher, and the first polishing step was performed. The polishing liquid used was adjusted to neutrality by adding an ethanol-based low molecular weight surfactant to RO water in which 10% by weight of cerium oxide (average particle size 1 μm) was dispersed as an abrasive. The load was 100 g / cm ² and the polishing time was 15 minutes.
The glass substrate after the first polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying), ultrasonically cleaned, and dried. .

(6) Chemical strengthening process Next, the glass substrate which finished the said washing | cleaning was chemically strengthened. For chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, the chemical strengthening solution was heated to 380 ° C., and the cleaned and dried glass substrate was immersed for about 4 hours to perform chemical strengthening treatment. The glass substrate after chemical strengthening was sequentially immersed in each of washing tanks of sulfuric acid, neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.

(7) Substrate immersion step Next, the glass substrate that has undergone the chemical strengthening step is 0.3 weight of Aron A-6016A (trade name: manufactured by Toa Gosei Co., Ltd.), which is an acrylic / sulfonic acid copolymer. It was immersed for 5 minutes in an aqueous solution containing 25% (liquid temperature 25 ° C.). In addition, it progressed to the following process, without drying a glass substrate after completion | finish of immersion.

(8) Main surface second polishing step Next, using the same double-side polishing apparatus as used in the first polishing step above, the polisher is replaced with a polishing pad of soft polisher (suede) (72 foam polyurethane with Asker C hardness). Then, the second polishing step was performed. This second polishing step is, for example, mirror polishing for finishing the surface roughness of the glass substrate main surface to a smooth mirror surface with an Rmax of about 2 nm or less while maintaining the flat surface obtained in the first polishing step. It is processing. The polishing liquid used was adjusted to acidity (pH = 2) by adding sulfuric acid to RO water in which 15% by weight of colloidal silica (average particle diameter of 15 nm) was dispersed as an abrasive. The load was 100 g / cm ² and the polishing time was 10 minutes.
The glass substrate after the second polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.

When the surface roughness of the main surface of 100 glass substrates obtained through each of the above steps was measured with an atomic force microscope (AFM), Ra = 0.137 nm, which was an ultra-smooth surface compared to the conventional product. A glass substrate was obtained. The value of the surface roughness is an average value of 100 manufactured glass substrates, and the same applies to the following examples.
For the evaluation of scratches and foreign object defects, the main surface of the obtained glass substrate is observed with OSA (Optical Surface Analyzer), and the detected surface defects (30 points) are analyzed with an atomic force microscope (AFM). did. As a result of AFM analysis, if the number of points on which surface defects are confirmed to be scratches is 10 points or less out of 30 points and more than 5 points, the number of scratches is “less”, and if it is 5 points or less, scratches are “particularly less” When there were more than 10 points, the number of scratches was “more”. As a result of AFM analysis, when the number of points at which the surface defect is confirmed to be a foreign matter defect (convex defect due to foreign matter adhesion) is 10 points or less out of 30 points and more than 5 points, the foreign matter defect is “less” In the case of 5 points or less, the number of foreign object defects is “particularly small”, and in the case of more than 10 points, the number of foreign object defects is “high”.
The obtained glass substrate had an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.8 mm.

  Thus, a glass substrate for magnetic disk of this example was obtained. Table 1 below shows the Ra value, polishing rate, scratch evaluation, and particle defect evaluation results. According to the present embodiment, a glass substrate for a magnetic disk capable of further reducing surface defects such as scratches and foreign object defects as compared with the conventional product is obtained, and the demand for the substrate surface quality becomes more severe than the present. It can be used as a next-generation substrate.

(Example 2)
In the substrate immersion process of Example 1, the substrate immersion process was performed in the same manner as in Example 1 except that the glass substrate was immersed for 5 minutes using an aqueous solution to which 0.1% by weight of Aron A-6016A was added. Carried out. And the glass substrate for magnetic disks was obtained like Example 1 except this board | substrate immersion process.
When the surface roughness of the main surface of the 100 glass substrates obtained was measured with an atomic force microscope (AFM), a glass substrate with an even smoother surface than that of the conventional product, Ra = 0.137 nm, was obtained. It was. Further, scratch evaluation and foreign object defect evaluation were performed in the same manner as in Example 1.
Table 1 below shows the Ra value, polishing rate, scratch evaluation, and foreign object defect evaluation results. According to the present embodiment, surface defects such as scratches and foreign object defects can be further reduced as compared with conventional products.

(Example 3)
In the substrate immersion step of Example 1, the substrate immersion step was performed in the same manner as in Example 1 except that the glass substrate was immersed for 5 minutes using an aqueous solution containing 0.01% by weight of Aron A-6016A. Carried out. And the glass substrate for magnetic disks was obtained like Example 1 except this board | substrate immersion process.
When the surface roughness of the main surface of the 100 glass substrates obtained was measured with an atomic force microscope (AFM), a glass substrate having an ultra-smooth surface of Ra = 0.140 nm as compared with the conventional product was obtained. It was. Further, scratch evaluation and foreign object defect evaluation were performed in the same manner as in Example 1.
Table 1 below shows the Ra value, polishing rate, scratch evaluation, and foreign object defect evaluation results. According to the present embodiment, surface defects such as scratches and foreign object defects can be further reduced as compared with conventional products.

Example 4
In the substrate immersion process of Example 1, the substrate immersion process was performed in the same manner as in Example 1 except that the glass substrate was immersed for 5 minutes using an aqueous solution containing 1.0% by weight of Aron A-6016A. Carried out. And the glass substrate for magnetic disks was obtained like Example 1 except this board | substrate immersion process.
When the surface roughness of the main surface of the 100 glass substrates obtained was measured with an atomic force microscope (AFM), a glass substrate with an even smoother surface than Ra and 0.135 nm was obtained. It was. Further, scratch evaluation and foreign object defect evaluation were performed in the same manner as in Example 1.
Table 1 below shows the Ra value, polishing rate, scratch evaluation, and foreign object defect evaluation results. According to the present embodiment, surface defects such as scratches and foreign object defects can be further reduced as compared with conventional products.

(Example 5)
In the substrate immersion step of Example 1, the substrate immersion step was performed in the same manner as in Example 1 except that the glass substrate was immersed for 5 minutes using an aqueous solution containing 0.005% by weight of Aron A-6016A. Carried out. And the glass substrate for magnetic disks was obtained like Example 1 except this board | substrate immersion process.
When the surface roughness of the main surface of the 100 glass substrates obtained was measured with an atomic force microscope (AFM), a glass substrate with an ultra-smooth surface of Ra = 0.142 nm than the conventional product was obtained. . Further, scratch evaluation and foreign object defect evaluation were performed in the same manner as in Example 1.
Table 1 below shows the Ra value, polishing rate, scratch evaluation, and foreign object defect evaluation results. According to the present embodiment, surface defects such as scratches and foreign object defects can be reduced as compared with conventional products.

(Example 6)
In the substrate immersion process of Example 1, the substrate immersion process was performed in the same manner as in Example 1 except that the glass substrate was immersed for 5 minutes using an aqueous solution to which Aron A-6016A was added at 1.5% by weight. Carried out. And the glass substrate for magnetic disks was obtained like Example 1 except this board | substrate immersion process.
When the surface roughness of the main surface of the 100 glass substrates obtained was measured with an atomic force microscope (AFM), a glass substrate with an even smoother surface than that of the conventional product, Ra = 0.134 nm, was obtained. It was. Further, scratch evaluation and foreign object defect evaluation were performed in the same manner as in Example 1.
Table 1 below shows the Ra value, polishing rate, scratch evaluation, and foreign object defect evaluation results. According to the present embodiment, surface defects such as scratches and foreign object defects can be further reduced as compared with conventional products. A slight decrease in the polishing rate was observed.

(Comparative Example 1)
A glass substrate for a magnetic disk was obtained in the same manner as in Example 1 except that the substrate immersion step in Example 1 was omitted.
The surface roughness of the main surface of the 100 glass substrates obtained was measured with an atomic force microscope (AFM), and scratch evaluation and foreign object defect evaluation were performed in the same manner as in Example 1.
Table 1 below shows the Ra value, polishing rate, scratch evaluation, and foreign object defect evaluation results. According to this comparative example, the occurrence of surface defects such as scratches and foreign object defects became significant. It is insufficient for use as a substrate for the next generation in which the demand for the substrate surface quality is more severe than the present.

  As is clear from the results in Table 1, the step of immersing the glass substrate in an aqueous solution containing an acrylic polymer containing a sulfonic acid group is performed before the polishing step as in the embodiment of the present invention. By doing so, an ultra-smooth substrate surface (Ra ≦ 0.150 nm) can be obtained, and surface defects such as scratches and foreign matter defects can be further reduced as compared with conventional products.

(Example 7)
The following film formation process was performed on the magnetic disk glass substrate obtained in Example 1 to obtain a magnetic disk for perpendicular magnetic recording.
That is, an adhesion layer made of a Ti-based alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, a carbon protective layer, and a lubricating layer are sequentially formed on the glass substrate. A film was formed. The protective layer is for preventing the magnetic recording layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon and provides wear resistance. The lubricating layer was formed by dipping a liquid lubricant of alcohol-modified perfluoropolyether.
The obtained magnetic disk was installed in an HDD equipped with a DFH head, and a load / unload durability test was conducted for one month while operating the DFH function in a high temperature and high humidity environment of 80 ° C. and 80% RH. There were no particular obstacles and good results were obtained.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Sun gear 3 Internal gear 4 Carrier 5 Upper surface plate 6 Lower surface plate 7 Polishing pad 11 Main surface 12, 13 End surface of substrate

Claims (6)

A method for producing a glass substrate for a magnetic disk having a polishing step of polishing a main surface of a glass substrate using a polishing liquid containing colloidal silica as abrasive grains and a surface plate provided with a polishing pad,
Prior to said polishing step, the Rukoto by immersing the glass substrate in an aqueous solution containing an acrylic polymer containing sulfonic acid groups, a coating of acrylic polymer containing a sulfonic acid group on the main surface of the glass substrate A method for producing a glass substrate for a magnetic disk, comprising forming and then performing the polishing step.   The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the content of the acrylic polymer containing the sulfonic acid group in the aqueous solution is in the range of 0.01 to 1% by weight.   The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the colloidal silica abrasive has a particle size of 10 to 40 nm.   4. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein a suede pad is used as the polishing pad.   5. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate is made of amorphous aluminosilicate glass. 6. A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the manufacturing method according to claim 1.

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