JP2009289300A - Method for cleaning substrate for information recording medium, and method for manufacturing information recording medium - Google Patents

Abstract

The present invention provides a high-quality information recording medium substrate and a highly reliable information recording medium that can completely remove loose abrasive residues and achieve stable flying of a magnetic head.
An information recording medium substrate having a mirror-finished surface made of a non-magnetic material is immersed in a cleaning liquid made of pure water, and an electric field is applied in parallel to the surface to be cleaned in the cleaning liquid. A method for cleaning an information recording medium substrate, and a plate-like substrate made of a non-magnetic material having been mirror-finished on the surface thereof, then immersed in a cleaning solution made of pure water, and in the cleaning solution And a step of applying an electric field in parallel to the surface to be cleaned.
[Selection] Figure 1

Description

  The present invention relates to a method for cleaning an information recording medium substrate and a method for manufacturing an information recording medium. This information recording medium is suitable for mounting on a fixed magnetic recording device (hard disk device) which is an external storage device of a computer or a consumer device.

  With the recent increase in the amount of information handled by information processing equipment such as computers and the miniaturization of information processing equipment, the recording capacity required for magnetic recording devices continues to increase, and high recording density for magnetic recording media Is required.

  In order to achieve a high recording density, it is needless to say that high performance is required with respect to the characteristics of the magnetic recording medium and the magnetic recording head, but further reduction of magnetic spacing is required.

  Magnetic spacing is the distance between an element responsible for reading and writing with a magnetic recording head and a magnetic recording layer responsible for recording with a magnetic recording medium. Specifically, the thickness of the protective layer and the lubricating layer of the magnetic recording medium. And the flying height of the magnetic recording head.

  In recent years, the flying height of the magnetic recording head has been reduced to less than 10 nm, and even a very small protrusion causes contact with the magnetic recording head. The flying of the magnetic recording head is performed by using the dynamic pressure generated between the magnetic recording head and the magnetic recording medium by running the magnetic recording head at a high speed on the surface of the magnetic recording medium. Since the rotational speed at this time reaches several thousand revolutions / minute, when the magnetic recording head collides with the above-mentioned minute projections on the magnetic recording medium, a phenomenon called head crash occurs in which both are damaged. It becomes easier, and a sudden drop in durability, reliability, etc. due to head crashes becomes a problem.

  In order to avoid such a phenomenon, it is necessary to obtain an information recording medium substrate having a surface that is extremely smooth and free from minute protrusions. A nonmagnetic material such as an aluminum alloy or glass is used as the substrate for the information recording medium, but the surface is generally a polishing pad using free abrasive grains such as alumina-based slurry and colloidal silica-based slurry. The substrate is sandwiched between the two to perform mirror finishing. In particular, in order to realize a low flying height in recent years, it is common to use loose abrasive grains made of ultrafine particles having a size of about several tens of nanometers.

  If these loose abrasive grains remain on the surface as a residue, they become minute protrusions as described above, causing problems, and thus sufficient cleaning is necessary. To remove these loose abrasive grains, in order to obtain an appropriate ζ potential Scrub cleaning with a cleaning liquid with adjusted pH and ultrasonic cleaning are common.

  However, it is very difficult to remove the ultrafine particles as described above even if the ultrasonic frequency is increased. Furthermore, even if the ζ potential is adjusted appropriately, the repulsive force becomes weaker and the removal becomes difficult as the particle size becomes smaller.

Then, the proposal which raises a washing | cleaning effect more by applying an electric potential to a to-be-washed object actively is proposed (refer patent document 1, patent document 2, patent document 3, and patent document 4).
In Patent Document 5, a first potential is applied to a member to be cleaned, and a second potential that is the same polarity as the first potential and greater than the first potential is applied to an electrode disposed opposite to the member. Proposals for cleaning with a cleaning solution have been made.

JP-A-8-102456 JP 2001-17878 A JP 2005-44488 A JP 2006-159109 A JP-A-8-264501

  However, the proposals in Patent Documents 1 to 4 apply a voltage directly to an object to be cleaned, so that only a conductive object can be applied, and in addition, a foreign substance having a ζ potential opposite to the applied potential. Will be actively adsorbed. In particular, it is impossible to apply an insulating glass material to a substrate.

  On the other hand, Patent Document 4 proposes to generate and apply an electric field in a liquid and can be applied to an insulator, but in order to apply an electric field in a direction perpendicular to a surface to be cleaned, Similarly, a foreign substance having a ζ potential opposite to the applied potential is adsorbed.

  In Patent Document 5, a potential (electric field) is applied in the same direction as the direction in which particles are detached. That is, the detachment of particles is promoted only by the repulsive force of charges. However, the adsorbed particles cannot be easily removed by the repulsive force due to the charge, although it depends on the size (Van der Valls force is much larger). With ultrafine particles, the charge itself is small, making it even more difficult. Although the application of ultrasonic waves is also described in order to desorb particles from the object to be cleaned, ultrasonic waves have no effect on ultrafine particles. Therefore, in the same way as the potential application method in other cited documents, there is no effect on the ultrafine particles.

  The object of the present invention has been made in view of such a situation, and it is possible to completely remove free abrasive residues, achieve stable flying of the magnetic head, a high-quality information recording medium substrate, It is another object of the present invention to provide a highly reliable information recording medium.

  In order to achieve the above-mentioned object, the information recording medium substrate cleaning method of the present invention immerses a magnetic recording medium substrate in which a mirror-like surface is applied to a plate-like substrate surface made of a non-magnetic material in a cleaning solution made of pure water. And an electric field is applied in parallel to the surface to be cleaned in the cleaning liquid.

  Further, the method for producing the information recording medium of the present invention is such that a plate-like substrate made of a non-magnetic material is mirror-finished on the surface, then dipped in a cleaning liquid made of pure water, and the surface to be cleaned in the cleaning liquid. It has the process of applying an electric field in parallel with respect to.

  By applying an electric field parallel to the surface to be cleaned of the substrate immersed in pure water, it is possible to easily remove ultrafine particles that have been difficult to remove. Moreover, since the present invention can be applied to an object to be cleaned of any material, it is also effective for a glass substrate. Therefore, it is possible to completely remove the abrasive residue on the surface of the substrate of any material, and achieve stable flying of the magnetic head, thereby providing a high-quality information recording medium substrate and highly reliable information recording. Media can be provided.

FIG. 1 is a schematic view showing an example of an electric field application cleaning tank according to the present invention.
In the example of FIG. 1, a so-called overflow method is used in which pure water is constantly supplied from the pure water introduction pipe 16 into the cleaning layer 11, and the substrate 12 is immersed in the pure water. Electrodes 14 are installed at opposing positions so as to sandwich the substrate 12. Since the electric field is generated in the direction connecting the electrodes 14, the surface to be cleaned of the substrate 12 is installed in the same manner as the positional relationship in FIG. 1, that is, at a position parallel to the electric field. The electrode 14 is connected to the external power supply 13 through a conducting wire. The reason for using pure water as the cleaning liquid is that it is clean water and that an electric field can be applied effectively. Since water has low electrical conductivity from the beginning, it is difficult to conduct electricity, and a sufficient electric field can be applied.However, if excess electrolyte is mixed in the water, the electrical conductivity is extremely reduced, so a sufficient electric field can be applied. Disappear. In contrast, pure water has the advantage that the electric field can be applied effectively because the applied potential can be increased until the electrolysis of water occurs.

  Any electrode 14 may be used as long as it is made of a material having electrical conductivity and corrosion resistance so as to sandwich the substrate 12. When the electrode does not have corrosion resistance, the component eluted from the electrode may be deposited on the surface to be cleaned. Examples of the material having corrosion resistance include platinum (Pt) and stainless steel.

In the present invention, an electric field is applied in a direction parallel to the surface to be cleaned of the substrate. Thereby, the surface to be cleaned and the adsorbed state of particles can be released and desorbed.
The electric field applied between the electrodes may be a DC electric field, but is preferably an AC electric field. When the AC electric field is used, the effect of swinging particles adhering to the surface to be cleaned can be obtained.

  Since particles detached by application of an electric field may be reattached, it is preferable to remove the detached particles from the vicinity of the surface to be cleaned. If performed in an overflow type cleaning tank, every particle detached from the cleaning surface overflows from the cleaning tank and is discharged out of the system. Therefore, it is desirable to perform in an overflow type cleaning tank. Moreover, you may apply an ultrasonic wave simultaneously with the application of an electric field. In order to prevent reattachment, a surfactant or the like may be added to pure water. However, in order to apply an electric field, it is desirable that additives such as surfactants are nonionic.

Hereinafter, an embodiment of an information recording medium substrate according to the present invention will be described.
The material of the disk-shaped substrate having a donut shape to be cleaned by the cleaning method of the present invention is not particularly limited as long as it is a nonmagnetic material, but is not limited to amorphous glass, crystallized glass, quartz glass, sapphire, silicon Aluminum, carbon and the like are preferable materials.

In the method for producing an information recording medium of the present invention, first, the surface of the information recording medium substrate is mirror-finished by polishing with free abrasive grains such as colloidal silica. The substrate after mirror finishing is sequentially subjected to scrub cleaning and ultrasonic cleaning without drying. Subsequently, the substrate after ultrasonic cleaning is immersed in an electric field application cleaning tank as shown in FIG. 1 without drying, and an ultrafine particle is removed by applying an electric field.
The mirror-finished substrate from which the fine particles have been removed is subjected to IPA (isopropyl alcohol) cleaning to obtain a clean surface.

FIG. 2 is a diagram illustrating an example of an information recording medium.
A soft magnetic layer, an orientation control layer, a perpendicular recording layer, and a protective layer are sequentially formed on the surface of the substrate subjected to IPA cleaning by using a thin film forming method such as sputtering, CVD, vacuum deposition, or plating. Further, for example, a liquid lubricant is applied by a dip coating method to obtain an information recording medium (FIG. 2). Although the case where the information recording medium is a perpendicular magnetic recording medium will be described here, the present invention may be applied to an in-plane magnetic recording medium.

  Here, as the soft magnetic layer, for example, a CoZrNb amorphous soft magnetic layer or an FeTaC soft magnetic layer can be used. For the orientation control layer, a material for preferably controlling the crystal orientation, crystal grain size, and the like of the magnetic recording layer can be used without particular limitation. For example, if the magnetic recording layer is a perpendicular magnetization film made of a CoCr alloy, a CoCr alloy, Ti, Ti alloy, Ru or the like can be used as the orientation control layer, and the magnetic recording layer is a Co alloy. In the case of a so-called laminated perpendicular magnetization film in which Pt or Pd or the like is laminated, Pt, Pd or the like can be used as the orientation control layer.

  As the magnetic recording layer, any material that can perform recording and reproduction as a perpendicular magnetic recording medium can be used. That is, a so-called perpendicular magnetization film such as the above-described CoCr alloy, a film in which a Co alloy or the like is laminated with Pt or Pd, or the like can be used. As the protective layer, for example, a thin film mainly composed of carbon is used. Moreover, as a liquid lubricant applied after formation of a protective layer, the liquid lubricant which consists of perfluoro polyether etc. is mentioned, for example.

<Example 1>
In this example, a disk-shaped amorphous glass substrate having an outer diameter of 48 mm, an inner diameter of 15 mm, and a plate thickness of 1 mm was used as the substrate, and the substrate was polished by lapping to a plate thickness of 0.53 mm. For lapping, a lapping machine with a cast iron surface plate was used, the processing liquid was a 10 wt% aqueous dispersion of # 1500 silicon carbide (SiC) abrasive grains, and the processing pressure was 100 gf / cm ² . After processing, it was washed and dried.

Next, a first polishing process was performed. As a polishing apparatus used for the examination, a generally known double-side polishing apparatus as shown in FIG. 3 was used. The polishing cloth was a foamed urethane polishing pad, the slurry was 10 wt% ceria dispersed water having a particle size of 1.5 μm, and the processing pressure was 100 gf / cm ² .

Next, after washing, a second polishing process was performed. As a polishing apparatus used for the examination, a generally known double-side polishing apparatus as shown in FIG. 3 was used. The polishing cloth was a foamed urethane polishing pad, the slurry was 15 wt% colloidal silica dispersion with a particle size of 80 nm, and the processing pressure was 100 gf / cm ² .

Next, after washing, finish polishing was performed. In the final polishing process, the polishing cloth was a foamed urethane polishing pad, the slurry was 10 wt% colloidal silica having a particle size of 30 nm, and the processing pressure was 100 gf / cm ² .
Subsequently, scrub cleaning and ultrasonic cleaning were sequentially performed without drying the substrate after finish polishing.

  The cleaned substrate was immersed in the electric field application cleaning tank 11 without being dried, and an electric field was generated between the opposing electrodes 14 by applying an AC voltage of 1.5 V and a frequency of 50 Hz from the external power source 13. The pure water in the washing tank was always supplied / drained by overflow. In this state, the substrate was held for 5 minutes, and then the substrate 12 was pulled up and exposed to IPA vapor for about 1 minute to dry the substrate surface.

The obtained substrate was introduced into a sputtering apparatus, and a Co-4Zr-6Nb amorphous soft magnetic layer 100 nm, a Ru orientation control layer 10 nm, a Co-19Cr-10Pt-8SiO ₂ alloy magnetic recording layer 15 nm, and a carbon protective layer 5 nm. Were sequentially taken out from the vacuum apparatus. All of these sputtering films were formed by DC magnetron sputtering under an Ar gas pressure of 5 mTorr. Thereafter, a liquid lubricant layer 2 nm made of perfluoropolyether was formed by a dip method to obtain a perpendicular magnetic recording medium.

  A head flying test was performed on 1000 pieces of the perpendicular magnetic recording media thus obtained, and the yield was investigated. The head flying test is defective for a magnetic recording medium that detects a foreign matter projection with a height of 10 nm or more using a test head equipped with a PZT element that senses an impact that touches the foreign matter projection while the head is flying. Judgment was made. The results are shown in Table 1.

<Example 2>
A perpendicular magnetic recording medium was produced in the same manner as in Example 1 except that a DC voltage of 1.5 V was applied instead of an AC voltage of 1.5 V and a frequency of 50 Hz as the generation of an electric field in the electric field application cleaning tank 11. The 1,000 sheets were subjected to a head floating test, and the yield was investigated. The results are shown in Table 1 together with the results of Example 1.

<Example 3>
A perpendicular magnetic recording medium was prepared in the same manner as in Example 1 except that the pure water in the cleaning tank was not overflowed when an electric field was generated in the electric field applying cleaning tank 11 for 5 minutes. Conducted and investigated the yield. The results are shown in Table 1 together with the results of Examples 1 and 2.

<Comparative Example 1>
A perpendicular magnetic recording medium was produced in the same manner as in Example 1 except that no voltage was applied when the substrate was immersed in the electric field application cleaning tank 11 and the pure water was overflowed for 5 minutes. Then, a head floating test was conducted and the yield was investigated. The results are shown in Table 1 together with the results of each example.

  From Table 1, it can be seen that, by applying the present invention, the effect of removing the free abrasive residue, which is very fine particles, is recognized, and the flying performance of the magnetic head is improved. That is, it is apparent that the present invention can provide a high-quality information recording medium substrate and a highly reliable information recording medium.

It is a schematic diagram which shows an example of an electric field application cleaning tank. 1 is a schematic diagram showing a cross-sectional structure of a perpendicular magnetic recording medium according to an embodiment of an information recording medium of the present invention. It is a schematic diagram which shows the general double-side polish apparatus used by the Example and comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Cleaning tank 12 Substrate 13 External power supply 14 Electrode 15 Conductor 16 Pure water introduction pipe 21 Liquid lubricant 22 Protective layer 23 Vertical recording layer 24 Orientation control layer 25 Soft magnetic layer 26 Nonmagnetic substrate 31 Lower surface plate 32 Polishing cloth 33 Upper surface plate 34 Sun gear 35 Internal gear 36 Carrier for substrate polishing 37 Substrate 38 Slurry reservoir 39 Slurry containing abrasive 310 Pure water 311 Slurry supply valve 312 Pure water supply valve

Claims (6)

  An information recording medium substrate having a mirror-finished surface made of a nonmagnetic material is immersed in a cleaning liquid made of pure water, and an electric field is applied in parallel to the surface to be cleaned in the cleaning liquid. A method for cleaning an information recording medium substrate.   The method of cleaning an information recording medium substrate according to claim 1, wherein the electric field is an alternating electric field.   3. The immersion in the cleaning liquid comprising pure water is to immerse the substrate in a water tank in a state where pure water is supplied to the water tank and the pure water is overflowed. Cleaning method for substrate of information recording medium.   After a plate-like substrate made of a non-magnetic material is mirror-finished on its surface, it has a step of immersing it in a cleaning liquid made of pure water and applying an electric field in parallel to the surface to be cleaned in the cleaning liquid. A method for producing an information recording medium characterized by the above.   The method of manufacturing an information recording medium according to claim 4, wherein the electric field is an alternating electric field.   6. The immersion in the cleaning liquid comprising pure water is to immerse the substrate in a water tank in a state where pure water is supplied to the water tank and the pure water is overflowed. Manufacturing method of the information recording medium.

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