JP6429354B2 - Glass substrate polishing method, polishing liquid, glass substrate manufacturing method, magnetic disk glass substrate manufacturing method, and magnetic disk manufacturing method - Google Patents

Description

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

  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 alloy substrate or a glass substrate has been used as the substrate. 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 alloy substrate is gradually increasing. Further, the surface of the magnetic disk substrate is polished with high accuracy so that the flying height of the magnetic head can be lowered as much as possible to achieve high recording density. In recent years, the demand for further increase in recording capacity of HDDs has only increased, and in order to realize this, it has become necessary to further improve the quality of the magnetic disk substrate, which is smoother and cleaner. It is required that the substrate surface be a proper surface.

  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.

As a conventional method, for polishing, for example, Patent Document 1 discloses an abrasive slurry containing an abrasive such as aluminum oxide, a water-soluble inorganic aluminum salt, an inorganic salt selected from nickel salts, and a water-soluble chelating agent. An invention has been disclosed in which scratches are reduced by removing a sparingly soluble chelate salt generated by reacting with the chelating agent in advance when polishing a magnetic disk substrate such as aluminum.
Patent Document 2 discloses that a magnetic disk substrate is polished with a polishing liquid containing an organic reducing agent such as phenols or reductones, so that the polishing speed (especially the persistence of the polishing speed) and the surface quality after polishing (cleanness). The invention which improves the property) is disclosed.

JP 2000-63806 A JP 2013-32502 A

  Conventionally, the polishing process of the main surface of the magnetic disk substrate has been performed in a plurality of stages, and usually the first first polishing process has been performed using cerium oxide as the abrasive grains. In the polishing process using this cerium oxide abrasive, it has been found that the polishing rate is low and the reduction in the polishing rate during the continuous polishing process is large, and this is a large amount of substrates with improved surface quality. It was an obstacle to realizing production. In addition, the present inventor has tried to apply various conventional polishing techniques including the method disclosed in the above patent document to the polishing process using the cerium oxide abrasive described above. It was difficult to improve. In addition, it is difficult to sufficiently reduce the reduction in the polishing rate during the continuous polishing process. Since the first first polishing process usually has the largest machining allowance among a plurality of polishing processes, the polishing rate is particularly important.

The present invention has been made to solve such conventional problems, and its purpose is to polish a glass substrate capable of improving the polishing rate in the polishing treatment of the main surface of the glass substrate using cerium oxide as abrasive grains. Is to provide a method. It is another object of the present invention to provide a glass substrate polishing method capable of maintaining such an effect of improving the polishing rate over a long period of time. Another object of the present invention is to provide a polishing method particularly suitable for a glass substrate for a magnetic disk.
It is another object of the present invention to provide a polishing liquid suitably used in the method for polishing a glass substrate of the present invention.

Therefore, as a result of searching for means for solving the above-described conventional problems, the present inventor includes an inorganic reducing agent in the polishing liquid used for the polishing process using cerium oxide as abrasive grains, and the polishing liquid is alkaline. It has been found that the polishing rate is improved. It has also been found that the effect of improving the polishing rate can be maintained over a long period of time.
The present inventor has completed the present invention as a result of intensive studies based on the obtained knowledge. That is, the present invention has the following configuration.

(Configuration 1)
A glass substrate polishing method for polishing a surface of a glass substrate with a polishing liquid containing cerium oxide as abrasive grains, wherein the polishing liquid contains an inorganic reducing agent and is alkaline. Polishing method.

(Configuration 2)
The glass according to Configuration 1, wherein the inorganic reducing agent is at least one selected from thiosulfates, phosphinates, dithionites, or sulfites with alkali metals or alkaline earth metals. A method for polishing a substrate.

(Configuration 3)
The polishing method for a glass substrate according to Configuration 1 or 2, wherein the pH of the polishing liquid is in the range of 8 to 12.
(Configuration 4)
4. The method for polishing a glass substrate according to any one of configurations 1 to 3, wherein the cerium oxide abrasive grains contain lanthanum (La).

(Configuration 5)
A method for producing a glass substrate, comprising a polishing treatment to which the glass substrate polishing method according to any one of Configurations 1 to 4 is applied.

(Configuration 6)
A method for producing a glass substrate for a magnetic disk, wherein the method for producing a glass substrate according to Configuration 5 is applied, and the glass substrate is a glass substrate for a magnetic disk.

(Configuration 7)
A magnetic disk manufacturing method comprising forming at least a magnetic film on a magnetic disk glass substrate manufactured by the magnetic disk glass substrate manufacturing method according to Configuration 6.

(Configuration 8)
A polishing liquid used for polishing a surface of a glass substrate, wherein the polishing liquid contains cerium oxide as abrasive grains, further contains an inorganic reducing agent, and is alkaline.

ADVANTAGE OF THE INVENTION According to this invention, the grinding | polishing method of the glass substrate which can improve a grinding | polishing speed in the grinding | polishing process of the glass substrate main surface which uses cerium oxide as an abrasive grain can be provided. In addition, it is possible to provide a glass substrate polishing method capable of maintaining the effect of improving the polishing rate over a long period of time. The glass substrate polishing method of the present invention is particularly suitable for polishing a glass substrate for a magnetic disk.
Moreover, according to this invention, the polishing liquid used suitably for the grinding | polishing method of such a glass substrate of this invention can be provided.

  And, for example, the glass substrate for magnetic disk obtained by the present invention has high productivity, and can be suitably used as a next-generation substrate in which the demand for the substrate surface quality is particularly severer than the current one. Is possible. Further, a highly reliable magnetic disk capable of long-term stable operation even when combined with a magnetic head of a low flying height design equipped with a DFH function, for example, using a glass substrate for a magnetic disk obtained by the present invention. Can be obtained.

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. In the present embodiment, a magnetic disk glass substrate suitable as a magnetic disk substrate will be mainly described.

  A glass substrate for a magnetic disk is usually manufactured through glass substrate molding, drilling processing, chamfering processing, grinding processing, end surface polishing processing, main surface polishing processing, and the like. Note that the order of processing is not limited to the above.

  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. Thereafter, a drilling process and a chamfering process are performed as appropriate to obtain a disk-shaped glass substrate (glass disk) having a circular hole in the center.

  Next, a grinding process for improving dimensional accuracy and shape accuracy is performed on the disk-shaped glass substrate (glass disk). This grinding process usually uses a double-side grinding machine to grind the main surface of the glass substrate. 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 the end of this grinding process, a main surface polishing process for obtaining a highly accurate main surface (mirror surface) is performed through an end surface polishing process such as brush polishing.
In the present invention, as a method for polishing the surface (end surface and main surface) of the glass substrate, it is preferable to use a polishing pad such as polyurethane while supplying a polishing liquid containing cerium oxide as polishing abrasive grains. is there.

  As described above, the present invention provides a glass substrate polishing method in which the surface of a glass substrate is polished with a polishing liquid containing cerium oxide as abrasive grains. The polishing liquid contains an inorganic reducing agent and is alkaline. It is characterized by.

The polishing liquid used for such a polishing treatment is a combination of abrasive grains and water as a solvent. In the present invention, an inorganic reducing agent is included, and other additives are included as necessary.
In order to compose a polishing liquid containing cerium oxide abrasive grains, for example, pure water is used, and an inorganic reducing agent and other additives may be added as necessary to obtain a polishing liquid.

In the present invention, the cerium oxide abrasive particles contained in the polishing liquid are preferably those having an average particle diameter of about 0.1 to 2.0 μm from the viewpoint of polishing efficiency. In particular, it is preferable to use those having an average particle size of about 0.8 to 1.3 μm.
In the present invention, the average particle size is a point where the cumulative curve is 50% when the cumulative curve is obtained with the total volume of the powder population in the particle size distribution measured by the light scattering method as 100%. (Hereinafter referred to as “cumulative average particle diameter (50% diameter)”). In the present invention, the cumulative average particle diameter (50% diameter) can be specifically measured using a particle diameter / particle size distribution measuring apparatus.

Further, as the cerium oxide abrasive grains, high-purity cerium oxide that does not contain impurities can be basically used, but in the present invention, it is also preferable to contain lanthanum (La). Cerium oxide abrasive grains containing lanthanum (La) have a greater effect of improving the polishing rate. The content of lanthanum is expressed as the content of lanthanum oxide (La ₂ O ₃ ) relative to TREO (total rare-earth oxides).

Thus, when the cerium oxide abrasive grains contain lanthanum (La), the content of lanthanum oxide with respect to TREO (La ₂ O ₃ ) is preferably in the range of, for example, 1 to 50%. . When the content of lanthanum oxide (La ₂ O ₃ ) is less than 1%, the effect of including lanthanum (La) is not obtained so much. When the content of lanthanum oxide (La 2 _{O 3)} is greater than 50%, a cerium oxide component is relatively small, the polishing rate may be decreased.

  The content of the cerium oxide abrasive grains in the polishing liquid is not particularly limited and can be appropriately adjusted and used. From the viewpoint of polishing rate and cost, for example, 1 to 20% by weight. It is preferable.

In the present invention, an inorganic reducing agent is contained in the polishing liquid applied to the polishing treatment.
In the present invention, examples of the inorganic reducing agent include thiosulfuric acid with an alkali metal (Li, Na, K, Rb, Cs, Fr) or an alkaline earth metal (Be, Mg, Ca, Sr, Ba, Ra). It is preferably at least one selected from a salt, a phosphinate, a dithionite, or a sulfite.

The reason why the polishing rate can be improved by including an inorganic reducing agent in the polishing liquid containing cerium oxide as abrasive grains is presumed as follows.
An inorganic reducing agent, for example, the above thiosulfate has reducibility and reduces cerium (tetravalent) to trivalent. Since trivalent cerium weakens the bond by giving electrons to Si-O of glass, the polishing rate is improved.

Among the inorganic reducing agents, the above-mentioned inorganic reducing agents are considered to be stable and resistant to oxidation under alkaline conditions and have a long reducing effect. In particular, thiosulfate has a very low reactivity with oxygen (a powerful oxidant), and thus hardly causes an oxidation-reduction reaction with dissolved oxygen in the polishing liquid and oxygen in the air. Therefore, even when the polishing treatment is performed for a long time, the reducing property of the inorganic reducing agent in the polishing liquid is not easily impaired. Therefore, by including the inorganic reducing agent of the present invention in the polishing liquid, it is possible to suppress a decrease in the polishing rate during continuous polishing.
In addition, in the organic reducing agent as described in the above-mentioned conventional Patent Document 2, the reduction effect disappears immediately by reacting with dissolved oxygen in the polishing liquid or oxygen in the air, so that the polishing rate is reduced. The improvement effect and the effect that the effect lasts long cannot be obtained. Moreover, it may decompose in an alkaline environment.

  In the present invention, among the inorganic reducing agents, thiosulfate is particularly preferable in that it hardly reacts with oxygen and has a large effect. More preferred is thiosulfate with Na, K, Mg, or Ca.

  The content (addition amount) of the inorganic reducing agent in the polishing liquid is preferably in the range of 0.5 wt% to 10 wt%. If the content is less than 0.5% by weight, the effects of the present invention may not be sufficiently obtained. On the other hand, when the content is more than 10% by weight, the polishing liquid is easily separated, and the polishing rate may be lowered instead. The content of the inorganic reducing agent in the polishing liquid is more preferably in the range of 1% by weight to 5% by weight.

  In addition, it is important that the polishing liquid containing the cerium oxide abrasive grains and the inorganic reducing agent of the present invention is alkaline. By using the polishing liquid of the present invention in an alkaline state, it is possible to prevent the cerium oxide fine particles, which are polishing abrasive grains, from agglomerating and settling, thereby increasing the polishing rate and reducing polishing scratches. In addition, the decomposition reaction of the inorganic reducing agent can be suppressed, and it is difficult to be oxidized and stable, and the effect of adding the inorganic reducing agent is further sustained.

  In the present invention, the pH of the polishing liquid is preferably in the range of 8 to 12 from the viewpoint of preventing aggregation and settling of abrasive grains and suppressing the decomposition reaction of the inorganic reducing agent. More preferably, it exists in the range of 9-11. The polishing liquid containing the inorganic reducing agent often has a pH within the above range, but in some cases, it may be adjusted by appropriately adding an appropriate alkali agent or acid.

In the present invention, the polishing method in the polishing treatment is not particularly limited. For example, in the polishing treatment of the main surface of the substrate, the glass substrate and the polishing pad are brought into contact with each other, and the cerium oxide abrasive grains and the inorganic reducing agent are contacted. The main surface of the glass substrate may be polished by relatively moving the polishing pad and the glass substrate while supplying the polishing liquid containing.
For example, FIG. 3 is a longitudinal sectional view showing a schematic configuration of a double-side polishing apparatus of a planetary gear system that can be used for a glass substrate polishing process. 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.

  With such a double-side polishing apparatus, the workpiece 1 held on 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 and 6 are polished during the polishing process. While supplying the polishing liquid between the pad 7 and the workpiece 1, while the carrier 4 revolves and rotates according to the rotation of the sun gear 2 and the internal gear 3, the upper and lower surfaces of the workpiece 1 ( The main surface) is polished. As the polishing pad, it is preferable to use a resin polisher (made of urethane foam or polyurethane foam). From the viewpoint of increasing the polishing rate, it is preferable to use a polishing pad having an Asker C hardness of 75 to 90. In addition, it is preferable to use a suede type polishing pad from the viewpoint of suppressing minute scratches due to polishing.

Moreover, it is preferable that the load applied to a board | substrate at the time of grinding | polishing is 50-200 g / cm < ² > from a viewpoint of grinding | polishing speed | rate and grinding | polishing quality.
Moreover, in this invention, it is preferable to hold | maintain several board | substrates simultaneously on a carrier and to make planetary gear motion and grind | polish both surfaces of several board | substrates simultaneously. In particular, it is preferable to polish 50 or more substrates simultaneously in one polishing process (1 batch).

  Normally, the polishing process of the main surface of the substrate includes a first polishing process for removing scratches and distortions remaining in the grinding process to obtain a predetermined smooth surface, and a mirror surface with a smoother surface roughness of the main surface of the glass substrate. In general, it is performed through two stages of the second polishing process that finishes (however, multistage polishing of three or more stages may be performed). In this case, at least the first polishing process in the previous stage is used in the present invention. Is preferably applied. Since the first polishing process usually has the largest machining allowance among a plurality of polishing processes, the polishing rate is particularly important. In addition, from the viewpoint of improving productivity by reducing the machining allowance as much as possible, the surface roughness of the main surface of the glass substrate on which the first polishing treatment is performed is preferably 100 nm or less in terms of Ra. Similarly, from the viewpoint of reducing the allowance for the second polishing treatment, the first polishing treatment is preferably performed so that the surface roughness of the main surface is 1.5 nm or less.

  In this case, it is preferable that the subsequent finishing (precision) polishing process (second polishing process) is performed using a polishing liquid containing colloidal silica abrasive grains having an average particle diameter of about 10 to 100 nm, for example. In this case, it is preferable to use a polishing liquid adjusted to an acidic range from the viewpoint of improving the polishing rate. For example, the pH is preferably 5 or less, more preferably 4 or less. Further, from the viewpoint of reducing the increase in surface roughness at the final cleaning, the pH is preferably 1 or more, more preferably 2 or more. Further, the polishing pad for final polishing is preferably a polishing pad (suede pad) of a soft polisher. The polishing method is the same as described above.

The polishing method of the present invention can be preferably applied not only to the polishing treatment of the main surface of the glass substrate but also to the polishing treatment of the end face of the glass substrate.
Next, the end surface polishing treatment of the glass substrate will be described.

  In the end surface polishing treatment, for example, the outer peripheral end surface 12 (see FIGS. 1 and 2) of the glass substrate 1 is polished with a rotating brush (also referred to as a polishing brush). In addition, since the method of grind | polishing the chamfering surface and side wall surface which are formed in the inner peripheral end surface 13 of the glass substrate 1 is the same, description is abbreviate | omitted.

  The rotating brush has a rotating shaft perpendicular to the main surfaces 11 and 11 of the front and back surfaces of the glass substrate 1 and brush hairs attached to the outer periphery of the rotating shaft. The rotating brush polishes the two chamfered surfaces 12b and 12b and the side wall surface 12a of the outer peripheral end surface 12 of the glass substrate 1 with the brush bristles while rotating around the rotation axis.

  A polishing liquid is supplied from a nozzle to the polishing portion of the glass substrate 1 by the rotating brush. The polishing liquid contains an abrasive, and when the present invention is applied, cerium oxide abrasive grains are used as the abrasive. The polishing liquid contains the inorganic reducing agent and is alkaline.

  In the end surface polishing treatment, a plurality of glass substrates 1 may be laminated and polished together. In this case, a spacer may be disposed between the glass substrates 1. The rotating brush may be swung in the stacking direction of the glass substrate 1 (a direction parallel to the center line of the rotating shaft) while rotating around the rotating shaft.

  The amount of polishing liquid supplied to the part to be polished is, for example, 5 to 20 liters / minute, the rotation speed of the rotating brush is, for example, 100 to 500 rpm, and the rocking speed of the rotating brush in the rotation axis direction is, for example, 3 to 10 rpm (1 minute) The rotation speed of the glass substrate (laminated body) can be appropriately set within a range of 50 to 100 rpm, for example.

  By applying the present invention also to the polishing treatment of the end face of the glass substrate, the polishing rate can be improved and the effect of improving the polishing rate can be maintained for a long period of time. In other words, the effect lasts longer.

In the present invention, the glass type constituting the glass substrate is preferably aluminosilicate glass. Amorphous aluminosilicate glass is more preferable. 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 of 4 wt% or more and 13 wt% or less 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 having a weight ratio of / ZrO ₂ of 0.4 to 2.5 can be obtained.

In addition, heat resistance may be required as a characteristic of next-generation substrates. Such a glass substrate has a high glass transition point (Tg) of, for example, 600 ° C. or higher. For example, the glass composition has a glass composition having an alumina (Al ₂ O ₃ ) amount of 8 mol% or less. For example, in terms of mol%, SiO ₂ is 50 to 75%, Al ₂ O ₃ is 0 to 6%, BaO is 0 to 2%, Li ₂ O is 0 to 3%, ZnO is 0 to 5%, Na ₂ O and K ₂ O in total 3 to 15%, MgO, CaO, SrO and BaO in total 14 to 35%, 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 are included in a total amount of ₂ to 9%, the molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85 to 1, and the molar ratio [Al ₂ A glass in which O ₃ / (MgO + CaO)] is in the range of 0 to 0.30 can be preferably used.

  The present invention is particularly suitable for polishing treatment of such a heat-resistant glass substrate having a high glass transition temperature (Tg). The heat-resistant glass substrate having such a composition has a relatively large number of Si—O bonds, and in particular, by performing a polishing process using a polishing liquid containing a cerium oxide abrasive grain and an inorganic reducing agent of the present invention, a continuous polishing process is performed. The effect of suppressing a decrease in the polishing rate is greater than, for example, the case of the aluminosilicate glass.

  The present invention is particularly suitable for polishing a glass substrate for a magnetic disk, but can also be applied to, for example, optical lenses, mask blank substrates, and liquid crystal panels other than those for magnetic disks.

In the present invention, the surface of the glass substrate after the final polishing treatment preferably has an arithmetic average surface roughness Ra of 0.20 nm or less, particularly 0.15 nm or less, more preferably 0.10 nm or less. Further, the maximum roughness Rmax is 2.0 nm or less, particularly 1.5 nm or less, more preferably 1.0 nm or less. In the present invention, Ra and Rmax are roughnesses calculated in accordance with Japanese Industrial Standard (JIS) B0601: 1982. Ra is the arithmetic average roughness, and Rmax is the maximum height. These surfaces are preferably mirror surfaces.
In the present invention, the surface roughness is practically the surface roughness of the surface shape obtained when measuring the range of 1 μm × 1 μm with a resolution of 256 × 256 pixels using an atomic force microscope (AFM). Preferred above. However, when Ra exceeds 50 nm, it is preferable to measure the surface roughness using a stylus roughness meter.

  In the present invention, chemical strengthening treatment can be performed before or after the substrate main surface polishing treatment. 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 nitrates such as potassium nitrate and sodium nitrate can be preferably used.

  By manufacturing a glass substrate for a magnetic disk including a polishing process to which the glass substrate polishing method of the present invention is applied, as shown in FIGS. 1 and 2, both main surfaces 11 and 11 and an outer peripheral side end surface 12 between them are provided. A disk-shaped glass substrate 1 having a peripheral end face 13 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.

As described above, according to the present invention, the polishing rate can be improved in the polishing treatment of the surface of the glass substrate using cerium oxide as abrasive grains. In addition to this, the effect of improving the polishing rate lasts for a long time, and the reduction of the polishing rate during the continuous polishing process can be effectively suppressed. The glass substrate polishing method of the present invention is particularly suitable for polishing a glass substrate for a magnetic disk.
And, for example, the glass substrate for magnetic disk obtained by the present invention has high productivity, and can be suitably used as a next-generation substrate in which the demand for the substrate surface quality is particularly severer than the current one. Is possible.

The present invention also provides a method for manufacturing a magnetic disk using the above glass substrate for a magnetic disk.
The magnetic disk is manufactured by forming at least a magnetic film on the magnetic disk glass substrate obtained by the present invention. As the material for the magnetic film, a CoCrPt-based or CoPt-based ferromagnetic alloy that is a hexagonal crystal system having a large anisotropic magnetic field can be used. As a method for forming the magnetic film, it is preferable to use a sputtering method, for example, a DC magnetron sputtering method.

Moreover, it is preferable to form a protective layer and a lubricating layer in this order on the magnetic film. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. In addition, a lubricant of a perfluoropolyether compound can be used for the lubricating layer.
By using the glass substrate for a magnetic disk obtained by the present invention, a highly reliable magnetic disk capable of long-term stable operation even when combined with a magnetic head of a low flying height design equipped with a DFH function is obtained. be able to.

  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 grinding process, (2) shape processing process, (3) fine grinding process, (4) end face polishing process, (5) main surface first polishing process, (6) chemical strengthening process, (7) The glass substrate for a magnetic disk of this example was manufactured through the main surface second polishing treatment.

(1) Coarse grinding treatment First, a glass substrate made of a 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 body 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% Temperable glass was used. Note that the content of Al ₂ O ₃ was 8.5 mol% in terms of mol%. Hereinafter, this glass material is referred to as glass material 1.

  Next, in order to improve the dimensional accuracy and shape accuracy of this glass substrate, rough grinding treatment was performed using alumina-based loose abrasive grains. This rough grinding process was performed using a double-side grinding machine.

(2) Shape processing treatment 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. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) Precision grinding process This precision grinding process uses a double-sided grinding machine to supply the coolant by bringing the glass substrate held by the carrier into close contact between the upper and lower surface plates to which the pellets with diamond abrasive grains fixed are attached. While doing so. The roughness of the main surface of the substrate after the fine grinding treatment was 100 nm or less in terms of Ra. However, the surface roughness after the precision grinding treatment was measured using a stylus type roughness meter.
The glass substrate after the fine grinding process was washed.

(4) End surface polishing treatment Next, the end surface (inner periphery, outer periphery) of the glass substrate was polished by brush polishing while rotating the glass substrate. The roughness of the end face of the substrate after the end face polishing treatment was 100 nm or less in terms of Ra. And the glass substrate which finished the said end surface grinding | polishing was wash | cleaned.

(5) Main surface first polishing process Next, the first polishing process for removing scratches and distortions remaining in the above-described grinding process to obtain a predetermined smooth surface is performed using the above-described double-side polishing apparatus shown in FIG. I did it. 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. After that, by supplying a polishing liquid between the polishing pad and the polishing surface of the glass substrate and rotating the gears and the upper and lower surface plates, the glass substrate revolves while rotating on the surface plates 5 and 6, and the planets. Both sides are simultaneously polished by a gear mechanism. Specifically, a first polishing process was performed using a suede type polisher (made of polyurethane foam) having an Asker C hardness of 80 as a polisher (polishing pad).

As the polishing liquid, 10% by weight of cerium oxide (average particle size 1 μm) was used as abrasive grains, 5% by weight of sodium thiosulfate was used as an inorganic reducing agent, and an alkaline solution having a pH of 10 was used. The polishing load was 120 g / cm ² and the machining allowance was 30 μm in terms of plate thickness. The roughness of the substrate surface after polishing was 1.5 nm or less in terms of Ra.
In the first polishing process, 20 batches (100 batches) were processed without changing the polishing liquid. The glass substrate after the first polishing treatment was washed.

(6) Chemical reinforcement | strengthening process Next, the chemical strengthening was performed to the glass substrate which finished the said washing | cleaning. The cleaned and dried glass substrate was immersed in a chemical strengthening liquid, which is a molten salt mixed with potassium nitrate and sodium nitrate, to perform chemical strengthening treatment. The glass substrate after chemical strengthening was cleaned.

(7) Main surface second polishing process Next, using a double-side polishing apparatus similar to that used in the first polishing process, the polisher is a soft polisher (suede type) polishing pad (made of polyurethane foam) with an Asker C hardness of 70 ) And the second polishing process was performed. This second polishing process finishes the surface roughness of the glass substrate main surface to a smoother mirror surface, for example, the surface roughness of the glass substrate main surface is finished to a smooth mirror surface with Ra of 0.2 nm or less and Rmax of 2 nm or less. For the mirror polishing. As the polishing liquid, a polishing liquid containing 10% by weight of colloidal silica (average particle diameter of 15 nm) as polishing abrasive grains was used. The pH of the polishing liquid was adjusted to be acidic (pH = 2) by adding sulfuric acid in advance. The polishing load was 100 g / cm ² and the machining allowance was 3 μm in terms of plate thickness.

  Next, the glass substrate after the second polishing process was cleaned (final cleaning process). Specifically, it was immersed in a cleaning tank in which an alkaline detergent was added to pure water, and ultrasonic cleaning was performed. Thereafter, the glass substrate was sufficiently rinsed with pure water and then dried.

  About the glass substrate obtained through each said process, when the surface roughness (Ra) of the glass substrate main surface after the said last washing process was measured with the atomic force microscope (AFM), Ra is 0.2 nm or less, It was finished to a smooth mirror surface with an Rmax of 2 nm or less.

(Examples 2 to 4)
Except that the inorganic reducing agent contained in the polishing liquid used for the first main surface polishing process in Example 1 was replaced with sodium phosphinate, sodium dithionite, and sodium sulfite, respectively. In the same manner as in Example 1, glass substrates of Examples 2 to 4 were produced.

(Comparative Example 1)
A glass substrate of Comparative Example 1 was produced in the same manner as in Example 1 except that a polishing liquid containing no inorganic reducing agent was used as the polishing liquid used in the first main surface polishing process in Example 1 above. .

The polishing rate in the first main surface polishing process of Examples 1 to 4 and Comparative Example 1 was measured in the first batch and the 10th batch, respectively, and the improvement rate of the polishing rate in each Example with respect to the polishing rate in Comparative Example 1 Were determined according to the following criteria, and the results are summarized in Table 1 below. Here, in Comparative Example 1, the ratio of the polishing rate of the 10th batch to the 1st batch (the polishing rate of the 10th batch / the polishing rate of the 1st batch) was calculated to be 0.9.
In addition, when the glass substrate was produced like Example 1 except having changed the inorganic reducing agent in Example 1 to ascorbic acid which is an organic reducing agent, the polishing rate of the 1st batch and the 10th batch was a comparative example. It was equivalent to 1.
[Judgment criteria]
For the polishing rate of the comparative example of the same batch,
● (Level 5) Greater than 115% ◎ (Level 4) Greater than 110% and 115% or less ○ (Level 3) Greater than 105% and 110% or less △ (Level 2) Greater than 100% and 105% or less × (Level 1) 100% or less

The following can be seen from the results in Table 1 above.
1. According to the examples of the present invention, the polishing liquid containing cerium oxide abrasive grains contains the inorganic reducing agent of the present invention under alkalinity, thereby improving the polishing rate relative to the comparative example not containing the inorganic reducing agent. Can do.
Of the inorganic reducing agents, thiosulfate is particularly preferable because of its great effect of improving the polishing rate.
2. In addition, according to the embodiment of the present invention, such a tendency is maintained not only in the first batch but also in the tenth batch, and even when a large amount of substrates are polished by a continuous polishing process, the tendency is reduced. It can be seen that the effect of improving the polishing rate by adding the agent lasts long. Therefore, it is possible to effectively suppress a decrease in the polishing rate during the continuous polishing process.

(Examples 5 to 8)
Polishing abrasive grains contained in each of the polishing liquids used for the first main surface polishing treatment in Examples 1 to 4 were replaced with cerium oxide abrasive grains containing 20% La as a ratio of La ₂ O ₃ to TREO. Except having used the liquid, it carried out similarly to Examples 1-4, and produced the glass substrate of Examples 5-8.

(Comparative Example 2)
The polishing liquid contained in the polishing liquid used for the main surface first polishing treatment in Comparative Example 1 was replaced with cerium oxide abrasive containing 20% La as a ratio of La ₂ O ₃ to TREO. Except for this, a glass substrate of Comparative Example 2 was produced in the same manner as Comparative Example 1.

The polishing rate in the main surface first polishing treatment of Examples 5 to 8 and Comparative Example 2 was measured in the first batch and the 10th batch, respectively, and the improvement rate of the polishing rate in each Example with respect to the polishing rate in Comparative Example 2 Were determined according to the same criteria as described above, and the results are summarized in Table 2 below. Here, in Comparative Example 2, the ratio of the polishing rate of the 10th batch to the first batch (the polishing rate of the 10th batch / the polishing rate of the 1st batch) was calculated to be 0.9.
In addition, when the glass substrate was produced like Example 5 except having changed the inorganic reducing agent in Example 5 to ascorbic acid which is an organic reducing agent, the polishing rate of the 1st batch and the 10th batch was a comparative example. It was equivalent to 2.

The following can be seen from the results in Table 2 above.
1. Even in the case of using La-added cerium oxide abrasive, the polishing rate can be improved as compared with the comparative example not containing the inorganic reducing agent by containing the inorganic reducing agent of the present invention in the polishing liquid.
Of the inorganic reducing agents, thiosulfate is particularly preferable because of its great effect of improving the polishing rate. Moreover, it turns out that the improvement rate of polishing rate becomes large by using the cerium oxide abrasive grain which added La from the comparison with the result of above-mentioned Table 1.
2. Moreover, according to the Example of this invention, such a tendency is maintained not only in the 1st batch but also in the 10th batch, and effectively suppresses a decrease in the polishing rate during the continuous polishing process. Can do. In particular, thiosulfate has a polishing rate equal to or higher than that of the first batch of Comparative Example 2 even in the 10th batch, and shows a particularly high effect.

(Example A)
In the same manner as in Example 1, (1) rough grinding treatment, (2) shape processing treatment, (3) fine grinding treatment, (4) end surface polishing treatment, and (5) main surface first polishing treatment were sequentially performed. .
However, the glass substrate was used the content of Al ₂ O ₃ in the glass material 1 of the above 10 mol%. This glass material is called glass material A.

Further, as the polishing liquid for the first main surface polishing treatment, cerium oxide (average particle diameter: 1 μm) containing 20% La as a ratio of La ₂ O ₃ to TREO is contained as abrasive grains (content: 10% by weight). As the inorganic reducing agent, an alkaline reducing agent containing 5% by weight of sodium thiosulfate and having pH = 10 was used. The other polishing conditions were the same as in Example 1.

(Example B)
The same processing as in Example A was performed except that the following glass material B was used instead of the glass material A used in Example A.
Glass material B In terms of mol%, SiO ₂ is 50 to 75%, Al ₂ O ₃ is 0 to 6%, BaO is 0 to 2%, Li ₂ O is 0 to 3%, ZnO is 0 to 5%, Na ₂ O and K ₂ O in total 3 to 15%, MgO, CaO, SrO and BaO in total 14 to 35%, 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 are included in a total amount of ₂ to 9%, the molar ratio [(MgO + CaO) / (MgO + CaO + SrO + BaO)] is in the range of 0.85 to 1, and the molar ratio [Al ₂ O ₃ / (MgO + CaO)] is a heat resistant glass in the range of 0 to 0.30.

  The ratio of the polishing rate of the 20th batch when the polishing rate in the first polishing treatment of the main surface of Examples A and B is measured in the first batch and the 20th batch, respectively, and the polishing rate in the first batch is 1. The results are summarized in Table 3 below.

  As can be seen from the results in Table 3, the present invention is particularly suitable for polishing treatment of a heat-resistant glass substrate (glass material B) having a high glass transition temperature (Tg). By carrying out the polishing treatment using the polishing liquid containing the cerium oxide abrasive grains and the inorganic reducing agent of the present invention, the effect of suppressing the decrease in the polishing rate particularly during the continuous polishing treatment is, for example, the above-mentioned aluminosilicate glass (glass material A ) Is greater than

(Examples 9 to 12, Comparative Example 3)
In the same manner as in Example 1, (1) rough grinding treatment, (2) shape processing treatment, and (3) fine grinding treatment were sequentially performed, and then the following end face polishing treatment was performed. In addition, the said glass material 1 was used for the glass substrate.
The glass substrate after the grinding treatment was laminated using a supporting jig to form a glass substrate laminate. At this time, resin spacers were inserted between the glass substrates and a total of 200 glass plates were stacked to form a glass substrate laminate.

The glass substrate laminate formed as described above was inserted into an outer peripheral end surface polishing jig, and was clamped and fixed from above and below the glass substrate laminate. This glass substrate laminate was placed at a predetermined position of the outer peripheral end surface polishing apparatus. A rotating brush for end face polishing was brought into contact with the end face on the outer peripheral side of the glass substrate laminate, and further pressed by a predetermined amount.
Polishing liquid was supplied to the outer peripheral end surface portion of the glass substrate laminate, the rotating brush and the glass substrate laminate were rotated in opposite directions, and further, the polishing was performed while the rotating brush was swung in the laminating direction of the glass substrate laminate.

As the polishing liquid, the same polishing liquid as that used in each of Examples 5 to 8 and Comparative Example 2 (that is, cerium oxide (average particle diameter: 1 μm) containing 20% La as a ratio of La ₂ O ₃ to TREO). Including abrasive grains (content 10% by weight), containing 5% by weight of inorganic reducing agent in Table 4 and having an alkaline pH = 10).

In this example and comparative example, the polishing liquid supply rate was 10 to 15 liters / minute, the rotation speed of the rotating brush was 300 rpm, and the swinging speed of the rotating brush in the support shaft direction was 3 to 5 rpm (3 to 3 minutes per minute). 5 times), the rotation speed of the glass substrate laminate was set to 80 to 90 rpm. The machining allowance was 40 μm in terms of plate thickness.
In each of the examples and comparative examples, the polishing liquid was not replaced, and 20 batches were continuously processed while the polishing liquid was collected and circulated.

  The polishing rates in the end face polishing treatment of Examples 9 to 12 and Comparative Example 3 were measured in the first batch and the 10th batch, respectively, and the polishing rates in Comparative Example 3 using a polishing liquid containing no inorganic reducing agent were measured. The rate of improvement of the polishing rate in the examples was determined based on the same criteria as described above, and the results are summarized in Table 4 below. Here, in Comparative Example 3, the ratio of the 10th batch polishing rate to the 1st batch (10th polishing rate / 1st polishing rate) was calculated to be 0.80.

The following can be seen from the results in Table 4 above.
Also in the end surface polishing treatment of the glass substrate, the polishing rate can be improved with respect to the comparative example not containing the inorganic reducing agent by containing the inorganic reducing agent of the present invention in the polishing liquid.
Of the inorganic reducing agents, thiosulfate is particularly preferable because of its great effect of improving the polishing rate. Moreover, according to the Example of this invention, such a tendency is maintained not only in the 1st batch but also in the 10th batch, and effectively suppresses a decrease in the polishing rate during the continuous polishing process. Can do. In addition, in the 10th batch, since the drop of the comparative example was large, the effect of the inorganic reducing agent was relatively increased, and the improvement rate of the polishing rate was larger than that in the 1st batch. The end surface polishing process is particularly effective because the polishing rate tends to be lower than that of the main surface polishing process.

(Examples 13 to 16)
Polishing liquid used in Example 5 (containing 20% cerium oxide (average particle diameter: 1 μm) as La ₂ O ₃ ratio relative to TREO) 5% by weight sodium thiosulfate as an inorganic reducing agent The glass substrates of Examples 13 to 16 were produced in the same manner as in Example 5 except that the polishing liquid was used in which the pH was changed to 8, 9, 11, and 12, respectively. .

  The polishing rate in the main surface first polishing treatment of Examples 13 to 16 and Example 5 is measured at the 20th batch, and the polishing rate at pH 10 (Example 5) is 1 in each Example. The ratios of the polishing rates were determined and the results are summarized in Table 5 below.

  From the results in Table 5 above, in the present invention, the pH of the polishing liquid is particularly preferably in the range of 9-11. It is presumed that at a pH in this range, the decomposition of the inorganic reducing agent is favorably suppressed.

(Manufacture of magnetic disk)
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, on the glass substrate, an adhesion layer made of a CrTi alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, a seed layer made of NiW, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, carbon A protective layer and a lubricating layer were sequentially 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. Similar results were obtained when the magnetic disk glass substrates obtained in other examples were used.

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 (15)

A glass substrate polishing method for polishing a surface of a glass substrate with a polishing liquid containing cerium oxide as abrasive grains,
A polishing method for a glass substrate, wherein the polishing liquid contains an inorganic reducing agent that reduces cerium (tetravalent) to trivalent , excluding sulfite, and is alkaline. A glass substrate polishing method for polishing a surface of a glass substrate with a polishing liquid containing cerium oxide as abrasive grains,
The polishing liquid contains at least one selected from a thiosulfate, a phosphinate, or a dithionite with an alkali metal or an alkaline earth metal and is alkaline, and is a method for polishing a glass substrate .   2. The glass substrate according to claim 1, wherein the inorganic reducing agent is at least one selected from a thiosulfate, a phosphinate, or a dithionite with an alkali metal or an alkaline earth metal. Polishing method.   The glass substrate polishing method according to claim 1 or 3, wherein the content of the inorganic reducing agent is in the range of 0.5 wt% to 10 wt%. The content of at least one selected from thiosulfate, phosphinate, or dithionite with the alkali metal or alkaline earth metal is in the range of 0.5 wt% to 10 wt%. The method for polishing a glass substrate according to claim 2.   The glass substrate polishing method according to any one of claims 1 to 5, wherein the pH of the polishing liquid is in a range of 8 to 12.   The method for polishing a glass substrate according to claim 1, wherein the cerium oxide abrasive grains contain lanthanum (La).   A method for producing a glass substrate, comprising a polishing treatment to which the glass substrate polishing method according to claim 1 is applied.   A method for producing a glass substrate for a magnetic disk, wherein the method for producing a glass substrate according to claim 8 is applied, and the glass substrate is a glass substrate for a magnetic disk.   A method for producing a magnetic disk, comprising forming at least a magnetic film on the glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk according to claim 9. A polishing liquid used for polishing the surface of a glass substrate,
The polishing liquid is characterized in that it contains cerium oxide as abrasive grains, further contains an inorganic reducing agent that reduces cerium (tetravalent) to trivalent , excluding sulfite, and is alkaline. A polishing liquid used for polishing the surface of a glass substrate,
The polishing liquid contains cerium oxide as abrasive grains, and further contains at least one selected from thiosulfates, phosphinates, or dithionites with alkali metals or alkaline earth metals, and is alkaline. A polishing liquid characterized by that.   The polishing liquid according to claim 11, wherein the inorganic reducing agent is at least one selected from thiosulfates, phosphinates, and dithionites with alkali metals or alkaline earth metals.   The polishing liquid according to claim 11 or 13, wherein the content of the inorganic reducing agent is in the range of 0.5 wt% to 10 wt%. The content of at least one selected from thiosulfate, phosphinate, or dithionite with the alkali metal or alkaline earth metal is in the range of 0.5 wt% to 10 wt%. The polishing liquid according to claim 12.

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