WO2013099082A1 - Method for manufacturing glass substrate for hdd - Google Patents

Abstract

This method for manufacturing a glass substrate for an HDD is a method for manufacturing a glass substrate for a magnetic disc, said method having a glass substrate final cleaning step. The final cleaning step has an ultrasonic cleaning step wherein a glass substrate held by means of a holding jig is irradiated with ultrasonic waves at a high frequency of 430-2,000 kHz in a cleaning tank, and in the ultrasonic cleaning step, the ultrasonic waves are asymmetrically radiated to end surfaces of the glass substrate such that the glass substrate rotates. In the manufacturing method, the ultrasonic waves can be radiated to the whole surface, and not only the main surface but also the end surfaces of the glass substrate are cleaned at one time, thereby removing, at high efficiency, fine material adhered on the main surface and the end surfaces.

Description

Manufacturing method of glass substrate for HDD

The present invention relates to a method for manufacturing a glass substrate for HDD. More specifically, in the present invention, when a glass substrate is cleaned by high-frequency ultrasonic waves, the glass substrate is cleaned while rotating without adding a complicated mechanism. The present invention relates to a method for manufacturing a glass substrate for HDD, which includes a process capable of simultaneously cleaning both to remove fine deposits and can manufacture a glass substrate with few subsequent errors.

In recent years, with the improvement in performance of disk devices (for example, hard disk drives and HDDs) equipped with information recording media, the quality level required for the media used has increased.

Recently, there is a 2.5-inch medium having a recording capacity of 500 GB or more, that is, a large-capacity medium having a recording density of 630 Gb / square inch or more. Such a medium has a small distance (flying height) between the magnetic head and the magnetic disk. In general, as the flying height becomes smaller, head crashes due to surface defects of the glass substrate tend to occur. Therefore, regarding the surface defects of the glass substrate for HDD (hereinafter sometimes simply referred to as “glass substrate”), the requirements for the size and the number are becoming strict.

Surface defects can be reduced by devising a glass substrate polishing and cleaning method. As one of the methods, there is a method of performing cleaning (megasonic ultrasonic cleaning) using high-frequency ultrasonic waves in the final cleaning step in order to remove minute deposits of about 100 nm or less (see Patent Document 1). As shown in FIG. 9, the glass substrate 101 held by the holder 51 is cleaned by high-frequency ultrasonic waves irradiated from the high-frequency ultrasonic generator 21. An arrow A1 indicates the irradiation direction of the irradiated high-frequency ultrasonic waves.

JP 2010-92524 A

However, according to the manufacturing method described in Patent Document 1, high-frequency ultrasonic waves are irradiated from one direction while scrub cleaning is performed on the glass substrate placed on the holder. Since high frequency ultrasonic waves have high straightness, the fine deposits on the main surface of the glass substrate can be removed relatively well. However, the minute deposits on the portion of the end surface that has not been irradiated with the high frequency ultrasonic waves (FIG. 9). There is a problem that the minute deposits E) remain. If the remaining minute deposits are detached in a manufacturing process such as a magnetic film forming process and adhere to the main surface, for example, it causes a subsequent error.

The present invention has been made in view of such conventional problems. In the final cleaning process of the glass substrate, the glass substrate is rotated by irradiating and cleaning the high-frequency ultrasonic wave while rotating the glass substrate. The manufacturing method of the glass substrate for HDD which can irradiate the whole surface and can clean not only the main surface but also the end surface of the glass substrate at the same time and remove the fine deposits on the main surface and the end surface with high efficiency. With the goal.

A method for manufacturing a glass substrate according to an aspect of the present invention is a method for manufacturing a glass substrate for a magnetic disk having a final cleaning step for a glass substrate, and the final cleaning step is held by a holding jig in a cleaning tank. The glass substrate has an ultrasonic cleaning step of irradiating a high-frequency ultrasonic wave of 430 to 2000 kHz. In the ultrasonic cleaning step, the ultrasonic wave is asymmetric with respect to the end surface of the glass substrate so that the glass substrate rotates. Irradiated. In the present invention, the asymmetrical irradiation with respect to the end face of the glass substrate means that when high-frequency ultrasonic waves are irradiated, the outer peripheral end closest to the ultrasonic oscillation source is used as a symmetry axis. It means that the irradiation intensity of ultrasonic waves in the circumferential direction becomes asymmetric with respect to the symmetry axis. The ultrasonic wave may not be applied to one side and the ultrasonic wave may be applied only to the other side with the symmetry axis as a boundary, and the irradiation intensity on one side is stronger than the irradiation intensity on the other side. It may be.

The objects, features and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

FIG. 1 is an explanatory diagram of a state in which a glass substrate of one embodiment (Embodiment 1) of the present invention is being cleaned in an ultrasonic cleaning process. FIG. 2 is an explanatory diagram of a state in which the glass substrate of one embodiment (Embodiment 1) of the present invention is arranged in a holder. FIG. 3 is an explanatory diagram of a state in which the glass substrate of one embodiment (Embodiment 1) of the present invention is subjected to roll scrub cleaning. FIG. 4 is an explanatory diagram of a state in which the glass substrate of one embodiment (Embodiment 1) of the present invention is subjected to cup scrub cleaning. FIG. 5 is an explanatory diagram of a state in which the glass substrate of one embodiment (Embodiment 2) of the present invention is being cleaned in the ultrasonic cleaning process. FIG. 6 is an explanatory diagram of a state in which the glass substrate of one embodiment (Embodiment 3) of the present invention is cleaned in the ultrasonic cleaning process. FIG. 7 is an explanatory diagram of a state in which the glass substrate of one embodiment (Embodiment 4) of the present invention is being cleaned in the ultrasonic cleaning process. FIG. 8 is a schematic diagram showing the positional relationship between the magnetic head and the deposit in the flying test. FIG. 9 is an explanatory view of a state in which the glass substrate is cleaned by a conventional cleaning method.

(Embodiment 1)
Hereinafter, the manufacturing method of the glass substrate of this Embodiment is demonstrated in detail. In the manufacturing method of the glass substrate of this Embodiment, a glass substrate is a blanks manufacturing process, a 1st grinding process, a coring process, an inner periphery grinding | polishing process, an outer periphery grinding | polishing process, a 1st grinding | polishing process (rough grinding | polishing process), chemical, for example. It is manufactured through a strengthening process, a second polishing process (mirror polishing process), and a final cleaning process. Hereinafter, the final cleaning process, which is a characteristic part of the present embodiment, will be described in detail.

<Final cleaning process>
As shown in FIG. 1, the final cleaning process is performed while rotating the glass substrate 1 by rotating the glass substrate 1 asymmetrically by irradiating high-frequency ultrasonic waves to the end surface of the glass substrate 1 that has undergone a mirror polishing process, which will be described later. This is a step of cleaning the glass substrate 1 cleanly by simultaneously removing the fine deposits attached to both the main surface and the end surface of the glass substrate 1. Reference sign A1 indicates the irradiation direction of high-frequency ultrasonic waves.

In the final cleaning step, the glass substrate 1 is cleaned by immersing it in a cleaning tank with, for example, several tens to several hundreds of glass substrates 1 stored in one holder H (see FIG. 2). The number of washing tanks is not particularly limited. Even when the glass substrate 1 is cleaned using a plurality of cleaning tanks, the glass substrate 1 is cleaned by moving each tank in order while being accommodated in the holder. When a plurality of cleaning tanks are used, each of the tanks is, for example, a first cleaning tank (cleaning using an alkaline detergent), a second cleaning tank (pure water cleaning), and a third cleaning tank (cleaning using a neutral detergent). ), Fourth cleaning tank (pure water cleaning), fifth cleaning tank (cleaning using isopropyl alcohol (IPA)), sixth cleaning tank (IPA vapor drying), and the like. In this embodiment, when the glass substrate 1 is cleaned using a plurality of cleaning tanks, ultrasonic cleaning described later is performed in at least one cleaning tank. For example, ultrasonic cleaning is performed in the fourth cleaning tank.

In the present embodiment, high-frequency ultrasonic waves are applied to at least the end surface of the glass substrate (ultrasonic cleaning process). The high frequency ultrasonic wave in the present invention means that the frequency is 430 to 2000 kHz, and more preferably 950 to 1000 kHz. High frequency ultrasonic waves are generated from the ultrasonic generator 2. In FIG. 1, reference numeral 3 indicates an ultrasonic generator body, and reference numeral 4 indicates a diaphragm. The glass substrate 1 is held by a plurality of holders 5 (three holders 5 are illustrated in FIG. 1).

The number and size of the holders 5 are not particularly limited. According to the cleaning method of the present embodiment, since the glass substrate 1 is rotated by being irradiated with high-frequency ultrasonic waves, there is a low possibility that the portion held by the holder 5 will not be sufficiently cleaned. However, from the viewpoint of further improving the cleaning efficiency, the number of the holders 5 is as small as possible, the size of the holders 5 is as small as possible, the rotating glass substrate 1 can be held, and the holding area of the glass substrate 1 can be reduced. It is preferable that the number and size be as large as possible. Therefore, the number of holders 5 is preferably 1 to 5, for example. The size of the holder 5 is preferably about 0.5 to 1.0 cm in diameter.

As shown in FIG. 1, the high frequency is irradiated from the side surface direction of the glass substrate 1. High frequency ultrasonic waves are irradiated asymmetrically to the glass substrate 1 so that the glass substrate 1 rotates. In FIG. 1, ultrasonic waves are applied to the right side of the glass substrate 1 so that the glass substrate 1 rotates in the direction of arrow A2 (counterclockwise). In the present embodiment, as shown in FIG. 1, the horizontal width of the ultrasonic generator 2 is designed to be approximately the same width as the right half of the paper surface of the glass substrate 1. The width of the ultrasonic generator 2 is not particularly limited as long as the glass substrate 1 can be irradiated with ultrasonic waves nonuniformly. Further, for example, the ultrasonic generator body 3 is provided with a width larger than the diameter of the glass substrate 1, and only the diaphragm 4 is provided on the right side of the paper surface so that the ultrasonic wave is irradiated more frequently on the right side of the paper surface of the glass substrate 1. You may adjust. Furthermore, you may control the ultrasonic generator 2 so that many ultrasonic waves may be irradiated to the paper surface right side of the glass substrate 1. FIG. In addition to the end surface direction of the glass substrate 1, high-frequency ultrasonic waves may be irradiated from the main surface direction.

The rotation direction of the glass substrate 1 is not particularly limited, and the rotation direction of the glass substrate 1 is appropriately determined depending on whether high-frequency ultrasonic waves applied to the glass substrate 1 are strongly applied to any one of the end surfaces of the glass substrate 1. Is done.

The irradiation time of the high frequency ultrasonic wave is not particularly limited and is, for example, 1 to 7 minutes. When the irradiation time of the high frequency ultrasonic wave is less than 1 minute, there is a tendency that the fine deposits are not sufficiently removed. On the other hand, when the irradiation time of the high frequency ultrasonic wave exceeds 7 minutes, the fine deposits once removed may aggregate in the tank and reattach to the substrate.

The rotation speed of the glass substrate 1 is not particularly limited, and can be set to about 5 to 15 rpm, for example.

In ultrasonic cleaning, it is preferable to perform cleaning with a solvent at the same time. Examples of the solvent include hydrogen water, water, ozone water and dilute hydrofluoric acid aqueous solution, sulfuric acid and organic acid, alkaline aqueous solution, neutral aqueous solution, surfactant, chelating agent, distilled water (pure water), isopropyl alcohol (IPA), etc. Can be used.

When hydrogen water is used as the solvent, the dissolved hydrogen concentration in the hydrogen water is preferably 0.5 to 1 ppm (0.5 to 1 mg / L), more preferably 0.6 to 0.8 ppm. . When the dissolved hydrogen concentration in the hydrogen water is within the above range, the efficiency of ultrasonic cleaning is further improved since oxygen and nitrogen, which are straight-line inhibition factors in pure water, are excluded. When the dissolved hydrogen concentration of the hydrogen water is less than 0.5 ppm, there is a possibility that the ultrasonic irradiation time necessary for removing the fine deposits will be long. On the other hand, when the dissolved hydrogen concentration in the hydrogen water exceeds 1 ppm, bubbling (bubbles) due to hydrogen gas is likely to occur, and the generated bubbles may hinder the straightness of the ultrasonic wave. Time tends to be longer.

In ultrasonic cleaning, when cleaning is performed while circulating a solvent, it is preferable to use a filter having an opening diameter of 0.02 μm from the viewpoint of keeping the circulating solvent clean. Thereby, since the minute deposits removed from the glass substrate 1 are captured by the filter, the minute deposits can be prevented from circulating in the cleaning tank.

In the present embodiment, it is preferable to have a scrub cleaning step before the ultrasonic cleaning step. As scrub cleaning performed in the scrub cleaning process, roll scrub cleaning shown in FIG. 3 or cup scrub cleaning shown in FIG. 4 can be employed. By performing these scrub cleaning steps before the ultrasonic cleaning step, large-sized deposits among the fine deposits adhering to the glass substrate 1 are removed in advance. Moreover, the deposits on both main surfaces are efficiently removed. As a result, the glass substrate 1 is cleaned by high-frequency ultrasonic waves on both the main surface and the end face at the same time in a state where the fine deposits on both the main surfaces are removed in advance. As a result, the cleaning efficiency is further improved.

(Roll scrub cleaning)
Roll scrub cleaning is performed by a roll scrub cleaning device 6, as shown in FIG. A sponge brush 8 is wound around the surface of the rollers 7 (only one is shown in FIG. 3) arranged in parallel to each other. A glass substrate 1 is sandwiched between the rollers 7, and the lower end of the glass substrate 1 is rotatably supported by a rotation support roller 9.

The roller 7 and the rotation support roller 9 are controlled to be rotatable by a control device (not shown) and a drive device (not shown) that controls the control device. The arrow A3 indicates the rotation direction of the roller 7, the arrow A4 indicates the rotation direction of the rotation support roller 9, and the arrow A5 indicates the rotation direction of the glass substrate 1.

A cleaning agent discharge nozzle Na is provided above the roller 7, and the cleaning agent is supplied from the cleaning agent discharge nozzle Na toward the glass substrate 1.

In the cleaning of the glass substrate 1 using the roll scrub cleaning device 6, both main surfaces of the glass substrate 1 are cleaned by rotating the sponge brush 8 while the glass substrate 1 is rotated by the rotation support roller 9. And minute deposits are removed.

Rotational speed of the rotating shaft in roll scrub cleaning is not particularly limited, but if the rotational speed is too small, the amount of work becomes small, and if the rotational speed is excessively large, the friction coefficient becomes small, so about 500 to 1000 rpm is preferable.

(Cup scrub cleaning)
Cup scrub cleaning is performed by a cup scrub cleaning device 10 as shown in FIG. The cup scrub cleaning apparatus 10 has a plurality of columnar sponge brushes 11 arranged radially from a rotation axis. A plurality of sponge brushes 11 are arranged along the axial direction of the rotating shaft 12 with a predetermined gap therebetween. End disks 13 are provided at both ends of the rotating shaft 12.

The glass substrate 1 is sandwiched between sponge brushes 11 adjacent in the axial direction. The lower end of the glass substrate 1 is rotatably supported by a rotation support roller 14.

The rotary shaft 12 is controlled to be rotatable by a control device (not shown) and a drive device (not shown) that controls the control device. The arrow A6 indicates the rotation direction of the end disk 13, the arrow A7 indicates the rotation direction of the rotation support roller 14, and the arrow A8 indicates the rotation direction of the glass substrate 1.

A cleaning agent discharge nozzle Nb is provided above the sponge brush 11, and the cleaning agent is supplied toward the glass substrate 1 from the cleaning agent discharge nozzle Nb.

In the cleaning of the glass substrate 1 using the cup scrub cleaning device 10, both main surfaces of the glass substrate 1 are cleaned by rotating the sponge brush 11 while the glass substrate 1 is rotated by the rotation support roller 14. And minute deposits are removed.

The rotational speed of the rotating shaft 12 in the cup scrub cleaning is not particularly limited, but if the rotational speed is too small, the amount of work becomes small, and if the rotational speed is too large, the friction coefficient becomes small.

Next, other steps that can be adopted by the present embodiment will be described. In addition, the manufacturing method of the glass substrate of this Embodiment should just have the above-mentioned final washing process, and it does not specifically limit about other processes. For this reason, the other steps described below are examples, and the design can be changed as appropriate.

<Blanks manufacturing process>
The blanks manufacturing process is a process of melting a glass material and obtaining a glass substrate (blanks) from the molten glass material.

Examples of the glass material include aluminosilicate glass, soda lime glass, borosilicate glass, Li ₂ O—SiO ₂ glass, Li ₂ O—Al ₂ O ₃ —SiO ₂ glass, R′O—Al ₂ O _3. —SiO ₂ glass (R ′ = Mg, Ca, Sr, Ba) or the like can be used. The glass melting method is not particularly limited, and a method of melting the glass material at a high temperature at a known temperature and time can be usually employed.

The method for obtaining blanks is not particularly limited, and for example, a method of obtaining a disk-shaped glass substrate (blanks) by pouring a molten glass material into a lower mold and press molding with an upper mold can be employed. In addition, blanks are not restricted to press molding, For example, you may cut and produce the sheet glass formed by the down draw method, the float method, etc. with the grinding stone. In this molding process, foreign matter and bubbles are mixed in the vicinity of the surface of the blank, or scratches are generated, resulting in defects.

The size of the blanks is not particularly limited, and for example, blanks having various outer diameters of 2.5 inches, 1.8 inches, 1 inch, 0.8 inches, and the like can be produced. It does not specifically limit about the thickness of a glass substrate, For example, blanks of various thickness, such as 2 mm, 1 mm, 0.8 mm, 0.63 mm, can be produced.

The blanks produced by press molding or cutting are alternately laminated with heat-setter setters and passed through a high-temperature electric furnace, thereby reducing warpage and promoting glass crystallization.

<First grinding process>
The first grinding step is a step of preliminarily adjusting the parallelism, flatness and thickness of the glass substrate by grinding both surfaces of the blank.

In the first grinding process, a glass base material is obtained by lapping (grinding) the main surface of the blank. The lapping process is performed using alumina-based loose abrasive grains by a double-sided lapping apparatus using a planetary gear mechanism. Specifically, in the lapping process, both main surfaces of the blanks are pressed against the lapping platen from above and below, a grinding liquid containing free abrasive grains is supplied onto the main surface of the plate glass, and these are relatively moved. . By this lapping process, a glass substrate having a flat main surface is obtained.

<Coring process>
The coring step is a step of opening a circular hole (center hole) in the center of the glass substrate. Specifically, the coring step is a step of forming an annular glass substrate by forming an inner hole at the center of the glass substrate using a cylindrical diamond drill.

<Inner circumference polishing process>
The inner peripheral polishing step is a step of alternately laminating glass substrates and spacers one by one to create a laminate, and polishing the inner peripheral end surface with an inner peripheral end surface polishing machine. Although it does not specifically limit as a spacer, For example, the thing made from a polypropylene and having a thickness of 0.3 mm, an internal diameter of 21 mm, and an outer diameter of 64 mm is employable. For example, nylon fibers having a diameter of 0.2 mm can be used as the brush bristles of the polishing machine. The rotation speed of the rotating brush can be set to 10,000 rpm, for example. As the polishing liquid for inner circumference polishing, for example, a polishing liquid containing a hydrofluoric acid solvent can be used, and as the polishing agent, for example, cerium oxide having an average primary particle diameter of 3 μm can be used.

<Outer periphery polishing process>
The outer peripheral polishing step is a step of alternately laminating glass substrates and spacers one by one to create a laminate, and polishing the outer peripheral end surface by an outer peripheral end surface polishing machine. The polishing conditions of the spacer and the polishing machine used are the same as those employed in the inner peripheral polishing step.

<Rough polishing process>
In the rough polishing step (first polishing step), both main surfaces of the glass substrate are polished using an abrasive slurry so that the finally required surface roughness can be efficiently obtained in the subsequent mirror polishing step. It is a process to do. It does not specifically limit as a grinding | polishing method employ | adopted at this process, It is possible to grind | polish using a double-side polisher.

As the polishing pad used, it is preferable to use a hard pad, for example, urethane foam is preferable because the shape change of the polishing surface increases when the hardness of the polishing pad decreases due to heat generated by polishing. As the polishing liquid, cerium oxide having an average primary particle size of 0.6 to 2.5 μm is used, and cerium oxide is dispersed in a solvent to form a slurry. It does not specifically limit as a solvent, Water can be employ | adopted. In addition, a surfactant or a dispersant can be added to these solvents. The mixing ratio of the solvent and cerium oxide is about 1: 9 to 3: 7. When the average primary particle diameter is less than 0.6 μm, the polishing pad tends to fail to polish both main surfaces well. On the other hand, when the average primary particle diameter exceeds 2.5 μm, the polishing pad may deteriorate the flatness of the end face or generate scratches.

The addition amount of the abrasive slurry is not particularly limited, and is, for example, 1000 to 9000 mL / min.

The amount of polishing of the glass substrate in the rough polishing step is preferably about 25 to 40 μm. When the polishing amount of the glass substrate is less than 25 μm, scratches and defects tend not to be sufficiently removed. On the other hand, when the polishing amount of the glass substrate exceeds 40 μm, the glass substrate is polished more than necessary, and the production efficiency tends to decrease.

The glass substrate after the rough polishing step is preferably washed with a neutral detergent, pure water, IPA or the like.

<Chemical strengthening process>
The chemical strengthening step is a step of immersing the glass substrate in a strengthening treatment solution to improve the impact resistance, vibration resistance, heat resistance, and the like of the glass substrate.

The chemical strengthening step is a step of chemically strengthening the glass substrate. Examples of the strengthening treatment liquid used for chemical strengthening include a mixed solution of potassium nitrate (60%) and sodium nitrate (40%). The chemical strengthening can be performed, for example, by heating the strengthening treatment liquid to 300 to 400 ° C., preheating the glass substrate to 200 to 300 ° C., and immersing in the strengthening treatment liquid for 3 to 4 hours. In this immersion, it is preferable that the immersion is performed in a state of being housed in a holder that holds the end faces of the plurality of glass substrates so that both main surfaces of the glass substrate are chemically strengthened.

In addition, after the chemical strengthening process, a standby process for waiting the glass substrate in the air and a water immersion process are adopted to remove the strengthening treatment liquid adhering to the surface of the glass substrate and to homogenize the surface of the glass substrate. It is preferable. By adopting such a process, the chemically strengthened layer is formed uniformly, the compressive strain is uniform, deformation is difficult to occur, the flatness is good, and the mechanical strength is also good. The waiting time and the water temperature in the water immersing step are not particularly limited. For example, it may be kept in the air for 1 to 60 seconds and immersed in water at about 35 to 100 ° C., and may be determined appropriately in consideration of production efficiency.

<Mirror polishing process>
The mirror polishing step (second polishing step) is a step for further precisely polishing both main surfaces of the glass substrate. In the mirror polishing process, a double-side polishing machine similar to the double-side polishing machine used in the rough polishing process can be used.

The polishing pad is preferably a soft pad having a lower hardness than the polishing pad used in the rough polishing step, and for example, urethane foam or suede is preferably used.

As the abrasive slurry, the same slurry containing cerium oxide as in the rough polishing step can be used. However, in order to make the surface of the glass substrate smoother, it is preferable to use an abrasive slurry having a finer grain size and less variation. For example, it is preferable to use a slurry obtained by dispersing colloidal silica having an average particle diameter of 20 to 70 nm in a solvent to form a slurry. It does not specifically limit as a solvent, Water can be employ | adopted. In addition, a surfactant or a dispersant can be added to these solvents. The mixing ratio of the solvent and colloidal silica is preferably about 1: 9 to 3: 7.

The addition amount of the abrasive slurry is not particularly limited, and is, for example, 100 to 600 mL / min.

The polishing amount in the mirror polishing step is preferably about 2 to 5 μm. By setting the polishing amount in such a range, the obtained glass substrate can remove fine defects such as minute roughness and waviness generated on the surface of the glass substrate, or minute scratches generated in the previous process. Is done. As a result, the glass substrate manufacturing method of the present embodiment can improve the flatness of the obtained glass substrate, and can produce a glass substrate on which the magnetic head can float more stably in the end region. it can.

In this step, by appropriately adjusting the polishing conditions in the mirror polishing step, the flatness of both main surfaces of the glass substrate is reduced to 3 μm or less, and the surface roughness Ra of both main surfaces of the glass substrate is reduced to 0.1 nm. be able to.

<Final cleaning process>
The final cleaning step is as described above. In the present embodiment, in the final cleaning step, ultrasonic cleaning is simultaneously performed while rotating the glass substrate with respect to both the main surface and the end surface of the glass substrate. For this reason, there is little residue of fine deposits on both the main surface and the end surface of the glass substrate, and the resulting glass substrate is less likely to cause subsequent errors.

After the final cleaning process, the glass substrate is inspected for scratches, cracks, foreign matter, etc., and then stored in a dedicated storage cassette in a clean environment and vacuum packed to prevent foreign matter from adhering to the surface. Shipped.

<Magnetic film formation process>
A magnetic film formation process is a process of forming a magnetic film on a glass substrate using a vapor deposition apparatus. The method for forming the magnetic film is not particularly limited, and a conventionally known method can be employed. For example, a method of forming a thermosetting resin in which magnetic particles are dispersed by spin coating on a substrate, or a method of forming by sputtering or electroless plating can be employed. The film thickness by spin coating is about 0.3 to 1.2 μm, the film thickness by sputtering is about 0.04 to 0.08 μm, and the film thickness by electroless plating is 0.05 to 0.1 μm. Degree. When the magnetic film is formed by these forming methods, the glass substrate is held at about 100 to 500 ° C. depending on the type of the magnetic film.

The magnetic material used for the magnetic film is not particularly limited, and a conventionally known magnetic material can be used. In order to obtain a high coercive force, it is possible to use a Co-based alloy based on Co having a high crystal anisotropy and added with Ni or Cr for the purpose of adjusting the residual magnetic flux density.

Further, when a recording medium is manufactured, an alloy composed of a transition metal element and a noble metal element, such as a Co—Pt alloy, and an atom of the transition metal element (Co) and the noble metal element (Pt). Alloys with almost the same content, or Co—Ni in which the atomic content of the transition metal element (Co) and the noble metal element (Pt) is almost equal and the atomic content of Ni is 0.1% or more and 50% or less -Pt alloy, Co-Ni-Pt alloy, Co-Cr-Pt alloy, Fe-Pt alloy, Cu, and the like, in which the atomic contents of transition metal elements (Co and Ni) and noble metal element (Pt) are almost equal. It is preferable to form a thin film containing an oxide. In this case, a soft magnetic layer (a material having a small coercive force, a Co-based amorphous material, etc.) is preferably laminated below the thin film.

Also, in order to improve the sliding of the magnetic head, a lubricant may be coated on the surface of the magnetic film.

Further, if necessary, the magnetic film may be provided with an underlayer or a protective layer. The underlayer and the protective layer are selected according to the type of the magnetic film.

As described above, according to the method for manufacturing a glass substrate of the present embodiment, in the final cleaning step of the glass substrate, the entire surface can be irradiated with ultrasonic waves by cleaning the glass substrate while rotating, so that it is highly efficient and minute. The manufacturing method of the glass substrate for HDD which can remove surface defects, such as a deposit | attachment, can be provided.

The present embodiment is not limited to the HDD manufacturing method, and can be used as a manufacturing method of a magneto-optical disk, an optical disk, or the like.

Further, according to the present embodiment, if necessary, the grinding process is divided into two processes sequentially, or the chemical strengthening process is performed after any of the coring process, the grinding process, the rough polishing process, and the mirror polishing process. The design may be changed as appropriate.

Furthermore, in this embodiment, the glass substrate may be subjected to a hydrogen fluoride immersion treatment as an edge mitigation treatment for scratches generated on the glass substrate.

(Embodiment 2)
In the glass substrate manufacturing method of the present embodiment, in the final cleaning step, the shielding member B that shields the ultrasonic wave irradiated from the ultrasonic generator 2a is provided, and the ultrasonic generator 2a has a diameter of the glass substrate. The method is the same as the method for manufacturing the glass substrate 1 of the first embodiment except that it has a larger width. Therefore, description of the overlapping steps is omitted.

As shown in FIG. 5, the shielding member B is provided in a path where high-frequency ultrasonic waves reach the glass substrate 1 in order to partially shield high-frequency ultrasonic waves irradiated from the ultrasonic generator 2 a. Yes.

The shielding member B is not particularly limited. For example, a material that reflects ultrasonic waves such as a metal plate or a wire mesh, a material that absorbs less ultrasonic waves such as a fluororesin or polyester, or a single material such as an epoxy resin or a urethane resin that is super A material that is easy to absorb sound waves is mixed with materials that are hard to absorb ultrasonic waves, such as glass balloons and quartz, and as a result, materials that are hard to absorb ultrasonic waves are formed, and these materials are provided on the surface. Can be used.

The size (length, shape, width) of the shielding member B is not particularly limited as long as it has a length, shape, and width that can shield a part of the ultrasonic wave irradiated from the ultrasonic generator 2a. Good.

In the present embodiment, as shown in FIG. 5, the shielding member B is an ultrasonic wave irradiated from a position irradiated to the left side of the paper surface of the glass substrate 1 among the ultrasonic waves irradiated from the ultrasonic generator 2a. It is provided in the position which shields. An arrow A9 indicates the irradiation direction of the ultrasonic wave shielded by the shielding member. Thereby, since an ultrasonic wave is irradiated only to the paper surface right side of the glass substrate 1, the glass substrate 1 rotates in the arrow A2 direction. As a result, the entire end face is irradiated with ultrasonic waves, and minute deposits are removed.

(Embodiment 3)
In the glass substrate manufacturing method of the present embodiment, the thickness of the diaphragm 4a provided in the ultrasonic generator 2b is not uniform in the final cleaning step, and the ultrasonic generator 2b is larger than the diameter of the glass substrate. Except for having a width, it is the same as the manufacturing method of the glass substrate 1 of Embodiment 1. Therefore, description of the overlapping steps is omitted.

As shown in FIG. 6, the diaphragm 4a is formed so that the thickness increases from the right side of the drawing to the left side of the drawing. As a result, the intensity of the ultrasonic wave irradiated on the left side of the paper substrate 1 becomes smaller than that on the right side of the glass substrate 1. An arrow A10 indicates an irradiation direction of ultrasonic waves with low intensity.

In the present embodiment, the vibration plate 4a formed so as to increase in thickness from the right side to the left side of the paper is illustrated, but the shape of the vibration plate 4a is not particularly limited. The shape of the diaphragm 4a may be any shape that can irradiate the glass substrate 1 with ultrasonic waves asymmetrically.

In the present embodiment, as shown in FIG. 6, since the ultrasonic wave is often irradiated on the right side of the glass substrate 1, the glass substrate 1 rotates in the direction of arrow A2. As a result, the entire end face is irradiated with ultrasonic waves, and minute deposits are removed.

(Embodiment 4)
The glass substrate manufacturing method of the present embodiment is different in the final cleaning step, except that the position of the holder 5 that holds the glass substrate 1 is different and the ultrasonic generator 2c has a width larger than the diameter of the glass substrate. This is the same as the manufacturing method of the glass substrate 1 of the first embodiment. Therefore, description of the overlapping steps is omitted.

As shown in FIG. 7, the holder disposed on the right side of the drawing is provided on the downstream side in the ultrasonic irradiation direction with respect to the holder shown in the first embodiment. Reference numeral 5a indicates a holder provided on the downstream side. Therefore, the ultrasonic wave irradiated to the right side of the glass substrate 1 is irradiated to the glass substrate 1 without being shielded or attenuated by the holder 5. As a result, the glass substrate 1 is cleaned while rotating in the A2 direction.

It should be noted that the position of the holder is not particularly limited, and may be provided at a position where the end surface of the glass substrate 1 is asymmetrically irradiated with high-frequency ultrasonic waves and, as a result, the glass substrate 1 can rotate. Moreover, as above-mentioned, the number of holders and a magnitude | size are not specifically limited.

According to the cleaning method of the present embodiment, the glass substrate 1 is rotatably arranged by changing the position of the holder 5. Therefore, the ultrasonic wave irradiated from the ultrasonic generator 2c is not shielded by the shielding plate or attenuated by the diaphragms having different thicknesses. As a result, the glass substrate is irradiated with a lot of ultrasonic waves, and is cleaned more cleanly in a shorter time.

The technical features of the glass substrate manufacturing method are summarized below.

The method for producing a glass substrate of the present invention is a method for producing a glass substrate for a magnetic disk having a final cleaning step for a glass substrate, and the final cleaning step is performed on a glass substrate held by a holding jig in a cleaning tank. A high-frequency cleaning step of irradiating a high-frequency ultrasonic wave of 430 to 2000 kHz, and in the ultrasonic cleaning step, the ultrasonic wave is irradiated asymmetrically to the end face of the glass substrate so that the glass substrate rotates. It is characterized by.

High-frequency ultrasonic waves of 430 kHz or higher have a strong tendency to go straight in the irradiation direction compared to low frequencies. The glass substrate rotates by being asymmetrically irradiated with high-frequency ultrasonic waves that travel straight. Therefore, both main surfaces and end surfaces (inner end surface and outer end surface) of the glass substrate are simultaneously and uniformly cleaned. As a result, according to the present invention, it is possible to obtain a glass substrate in which surface defects such as minute deposits are removed with high efficiency, and a subsequent error is hardly generated.

It is preferable that the ultrasonic wave is applied to a part of the glass substrate.

The ultrasonic wave is easily rotated by being irradiated on a part of the glass substrate and holding the glass substrate on a holding jig. As a result, the surface defects of the glass substrate are easily removed.

In the present invention, the mode of irradiating a part of the glass substrate is not limited to the mode of irradiating only a part of the glass substrate with the high frequency ultrasonic wave by changing the irradiation position of the high frequency ultrasonic wave. The mode of irradiating a glass substrate with a part of the ultrasonic wave irradiation path and the intensity of the high frequency ultrasonic wave to be irradiated are partially changed, and the high frequency ultrasonic wave irradiated to the glass substrate is changed. The aspect which changes an intensity | strength, the aspect which adjusts the position of the holder holding a glass substrate, a magnitude | size, etc., and changes the ratio of the high frequency ultrasonic wave irradiated to a glass substrate are included.

It is preferable that 0.5 to 1 ppm of hydrogen water is used in the cleaning tank.

When 0.5 to 1 ppm of hydrogen water is used in the washing tank, the efficiency of ultrasonic cleaning is further improved because oxygen and nitrogen, which are the straight-line inhibition factors in pure water, are excluded.

In the cleaning tank, it is preferable to use a filter having an opening diameter of 0.02 μm.

By using a filter with an opening diameter of 0.02 μm in the cleaning tank, surface defects such as removed fine deposits are easily captured by the filter. As a result, the inside of the cleaning tank is kept clean.

The present invention preferably includes a scrub cleaning step before the ultrasonic cleaning step.

Since the present invention has a scrub cleaning step before the ultrasonic cleaning step, it is possible to perform ultrasonic cleaning on the end surfaces in a state where surface defects on both main surfaces are removed in advance by scrub cleaning, so that the cleaning efficiency is improved. Can be further improved.

Hereinafter, the method for producing a glass substrate of the present invention will be described in detail with reference to examples. In addition, the manufacturing method of the glass substrate of this invention is not limited to the Example shown below at all.

<Example 1>
A glass substrate was prepared by the following method.

[Blanks manufacturing process]
As the glass material, an aluminosilicate glass mainly composed of SiO ₂ , Al ₂ O ₃ , R ₂ O (R = K, Na, Li) is used, and the molten glass material is press-molded, and the outer diameter is 67 mm. Disk-shaped blanks were produced. The thickness of the blanks was 1.0 mm.

[First grinding process]
Both main surfaces of the glass substrate were roughly polished using a double-side polishing machine (manufactured by Hamai Sangyo Co., Ltd., 16B type). As the polishing pad, a polishing pad in which diamond abrasive grains having an average primary particle diameter of 9 μm were embedded in a resin pad was used, and water and coolant mixed at 9: 1 were used as polishing water. The weight was 200 g / cm ² . The amount of abrasive slurry added was 4.5 L / min.

[Coring]
Using a core drill equipped with a cylindrical diamond grindstone, a circular center hole having a diameter of about 19.6 mm was formed in the center of the blank. Using a drum-shaped diamond grindstone, the outer peripheral end surface and the inner peripheral end surface of the blanks were processed to have an inner diameter and an outer diameter of 65 mm in outer diameter and 20 mm in inner diameter.

[Inner grinding / outer grinding]
100 blanks were stacked, and in this state, the outer peripheral end surface and the inner peripheral end surface of the blanks were polished using an end surface polishing machine (TKV-1 manufactured by Hadano Machinery Co., Ltd.). Nylon fiber having a diameter of 0.2 mm was used as the brush hair of the polishing machine. As the polishing liquid, a slurry containing cerium oxide having an average primary particle diameter of 3 μm as abrasive grains (polishing liquid component) was used.

[Rough polishing process]
Both main surfaces of the glass substrate were roughly polished using a double-side polishing machine (manufactured by Hamai Sangyo Co., Ltd., 16B type). The polishing pad was a urethane foam pad, the abrasive grains were cerium oxide abrasive grains having an average primary particle size of 1 μm, and the mixing ratio of water and cerium oxide was 80:20. Furthermore, pH was adjusted with the adjustment liquid containing a sulfuric acid. The load was 100 g / cm ² . The amount of abrasive slurry added was 8000 mL / min.

[Chemical strengthening process]
A strengthening salt mixed with sodium nitrate: potassium nitrate 3: 7 was melted at 300 ° C., and the glass substrate was immersed for 30 minutes. Thereby, the lithium ion and sodium ion of the inner peripheral end surface and outer peripheral end surface of a glass substrate were each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and the glass substrate was strengthened.

[Mirror polishing process]
Both main surfaces of the glass substrate were polished more precisely using a double-side polishing machine (Hamai Sangyo Co., Ltd., 16B type). As the abrasive slurry, colloidal silica having an average primary particle diameter of 20 nm was dispersed in water as abrasive grains to form a slurry, and the mixing ratio of water and colloidal silica was 80:20. Furthermore, pH was adjusted with the adjustment liquid containing a sulfuric acid. The load was 120 g / cm ² . The amount of abrasive slurry added was 500 mL / min. In this step, 100 batches of glass substrates were processed into 5 batches. Ra of the obtained glass substrate was 2 or less.

[Final cleaning process]
As shown in FIG. 1, each glass substrate 1 was held by three holding jigs 5 and placed in a holder H. In the holder H, 100 glass substrates 1 were arranged. Cleaning is performed in the order of alkaline detergent tank (80 kHz), pure water tank (80 kHz), neutral detergent tank (120 kHz), pure water tank (120 kHz), ultrasonic cleaning tank (pure water, 430 kHz), IPA, and IPA vapor drying. It was performed by sequentially immersing in a washing tank. Each ultrasonic wave was irradiated for 5 minutes.

In the ultrasonic cleaning tank, as shown in FIG. 5, only the right half of the paper surface of the glass substrate was irradiated with ultrasonic waves. The glass substrate was rotated at 7 rpm by ultrasonic irradiation.

[Magnetic film forming process]
After cleaning the glass substrate, both main surfaces have an adhesion layer made of a Cr alloy, a soft magnetic layer made of a Co—Fe—Zr alloy, an orientation control underlayer made of Ru, a perpendicular magnetic recording layer made of a Co—Cr—Pt alloy, A C-type protective layer and an F-type lubricant layer were sequentially formed, and the perpendicular magnetic recording disk of Example 1 was manufactured.

<Example 2>
A perpendicular magnetic recording disk was produced in the same manner as in Example 1 except that the ultrasonic frequency in the ultrasonic cleaning tank was changed to 950 kHz.

<Example 3>
A perpendicular magnetic recording disk was manufactured in the same manner as in Example 2 except that hydrogen water in which 0.7 ppm of hydrogen was dissolved after degassing pure water was used instead of pure water in an ultrasonic cleaning tank.

<Example 4>
A perpendicular magnetic recording disk was manufactured by the same method as in Example 2 except that the pump was circulated through a filter having a diameter of 0.02 μm in an ultrasonic cleaning tank.

<Example 5>
A perpendicular magnetic recording disk was produced in the same manner as in Example 4 except that cup scrub cleaning was performed as a pre-process of the final cleaning process to remove or activate the deposits of about 500 nm or more in advance. Cup scrub cleaning was performed for 3 minutes by rotating the sponge brush at 100 rpm while supplying an alkaline detergent from a cleaning agent discharge nozzle provided on the top.

<Comparative Example 1>
A perpendicular magnetic recording disk was manufactured by the same method as in Example 1 except that the apparatus shown in FIG. 9 was used.

<Comparative example 2>
A perpendicular magnetic recording disk was manufactured in the same manner as in Comparative Example 1 except that the frequency of the ultrasonic wave in the ultrasonic cleaning tank was changed to 430 kHz.

Glide evaluation was performed on the perpendicular magnetic recording disks obtained in Examples 1 to 5 and Comparative Examples 1 and 2. The test method is shown below, and the results are shown in Table 1.

[Glide evaluation]
The levitation test shown in FIG. 8 was performed. As shown in FIG. 8, the magnetic head MH is held by the suspension S, and the flying height (flying height) of the magnetic head MH from the surface of the glass substrate 1 is h.

Normally, a magnetic thin film layer is formed on the glass substrate 1 and the test is performed in the state of an information recording medium (magnetic disk recording medium). This time, only a lubricating layer is formed on the glass substrate 1 to perform a glide test. Carried out. This is because, if a magnetic thin film layer (about 100 nm) is formed on the deposit P in the state where the deposit P exists on the glass substrate 1, the deposit P is gradually buried in the film formation process. This is because it is not a severe test. In the evaluation method of the present invention, since a glide test was performed by forming only a lubricating layer (about several nm) on the glass substrate 1, it can be said that the evaluation is based on a more severe test.

Table 1 shows the results of the error rate after the floating test and full scan. In each example and comparative example, a floating test was performed on 100 glass substrates, and the error occurrence rate was investigated.

As shown in Table 1, in the glass substrate manufacturing methods of Examples 1 to 5, since the ultrasonic cleaning was performed while rotating the glass substrate, the entire main surface and end face of the glass substrate could be cleaned simultaneously. For this reason, the obtained perpendicular magnetic recording disk had good surface properties because the number of perpendicular magnetic recording disks causing subsequent errors was 10 or less out of 100 in the glide evaluation. On the other hand, in the manufacturing method of Comparative Example 1 in which the ultrasonic wave was irradiated without rotating the glass substrate during the ultrasonic cleaning, it was considered that the minute deposits remained on the surface of the end surface that was not irradiated with the ultrasonic wave. It was. Therefore, in the obtained perpendicular magnetic recording disk, the number of perpendicular magnetic recording disks that cause subsequent errors was 20 out of 100 in the glide evaluation, and the surface properties were not good. Further, in Comparative Example 2 in which the glass substrate was not rotated at the time of ultrasonic cleaning and the frequency of the ultrasonic wave was 430 kHz, it was considered that more minute deposits remained than in Comparative Example 1. Therefore, in the obtained perpendicular magnetic recording disk, in the glide evaluation, the number of perpendicular magnetic recording disks causing a subsequent error was 25 out of 100, and the surface properties were not good.

DESCRIPTION OF SYMBOLS 1,101 Glass substrate 2, 21, 2a, 2b, 2c Ultrasonic generator 3 Ultrasonic generator main body 4, 4a Diaphragm 5, 51, 5a, Holder 6 Roll scrub cleaning device 7 Roller 8, 11 Sponge brush 9 , 14 Rotating support roller 10 Cup scrub cleaning device 12 Rotating shaft 13 End disk B Shielding member H Holder h Flying amount MH Magnetic head Na, Nb Cleaning agent discharge nozzle P Adherence S Suspension

Claims (5)

A method for producing a glass substrate for a magnetic disk having a final cleaning step of the glass substrate,
The final cleaning step includes an ultrasonic cleaning step of irradiating a glass substrate held by a holding jig with high frequency ultrasonic waves of 430 to 2000 kHz in a cleaning tank,
In the ultrasonic cleaning step, the ultrasonic wave is irradiated asymmetrically with respect to the end surface of the glass substrate so that the glass substrate rotates. The method for manufacturing a glass substrate for HDD according to claim 1, wherein the ultrasonic wave is applied to a part of the glass substrate. The method for producing a glass substrate for HDD according to claim 1 or 2, wherein 0.5 to 1 ppm of hydrogen water is used in the cleaning tank. The method for producing a glass substrate for HDD according to any one of claims 1 to 3, wherein a filter having an opening diameter of 0.02 µm is used in the cleaning tank. The method for producing a glass substrate for HDD according to any one of claims 1 to 4, further comprising a scrub cleaning step before the ultrasonic cleaning step.

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