JP2003242632A - Method for manufacturing glass substrate for magnetic recording medium and method for manufacturing magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass substrate for enabling a low floating amount and to improve recording density by miniaturizing the grain size of a layer film- formed on the substrate and realizing a reduction in dispersion. <P>SOLUTION: In a substrate for a magnetic recording medium with concentric circular grooves formed on a principal surface, the height between concentric circular recessed and projecting parts is defined to be a height that does not have magnetic anisotropy in a circumferential direction when at least a magnetic layer is formed on the substrate. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium substrate and a method for manufacturing the same. Furthermore, the present invention relates to a magnetic recording medium and a manufacturing method thereof.

[0002]

2. Description of the Related Art With the increase in capacity of magnetic disk storage devices, the technology of each component constituting the device has been improved, such as improvement in performance of magnetic recording media and magnetic heads and increase in speed of recording / reproducing channels. There is. In order to improve the performance of a magnetic disk storage device, it is important to improve the recording density, and it is essential to improve the magnetic recording medium and the magnetic head that are directly involved in recording and reproduction. Particularly in the field of magnetic recording media, the PW50 and medium S / N, which are greatly related to high recording density, are improved, and the spacing between the magnetic head and the magnetic layer of the magnetic recording medium is reduced.

In order to obtain a high PW50 characteristic and a high S / N ratio in a magnetic recording medium composed of an underlayer, a magnetic layer, a protective layer, and a lubricating layer, a high coercive force of the magnetic layer as a recording layer, a finer crystal grain, It is necessary to reduce dispersion. In order to increase the coercive force, refine the crystal grains, and reduce the dispersion, the lattice constants of the underlayer and the magnetic layer should be matched (higher coercive force), or the crystal grains of the magnetic layer should be formed between the substrate and the underlayer. There are methods such as interposing a seed layer to be miniaturized (crystal grains are miniaturized, dispersion is reduced), etc., and high PW50 characteristics and high recording density due to high S / N are being advanced every day.

Further, in order to reduce the spacing, which is another great solution to the higher recording density, it is necessary to reduce the flying height of the magnetic head. In order to reduce the flying height, the thickness of the magnetic layer is 100 n in the current magnetic recording medium.
Since it is m or less, the smoothness of the substrate directly affects the flying height of the magnetic head, and therefore it is important to improve the smoothness of the magnetic recording medium substrate. For example, at a recording density of 25 Gbit / inch ^2, it is necessary to realize a flying height of 6 nm or less. At this time, the smoothness of the magnetic recording medium substrate is required to have a maximum height Rmax = 3 nm or less. In such requirements, the glass substrate as the substrate material can be easily smoothed by polishing,
Increasingly, it is attracting attention as a substrate for magnetic recording media.

Usually, a glass substrate for a magnetic recording medium is manufactured by shaping the glass substrate for a magnetic recording medium into a predetermined shape and then lapping the flatness within a predetermined range to improve smoothness. It is produced through. In the case of a chemically strengthened glass substrate, ion exchange treatment is performed to strengthen the glass substrate. The ion exchange treatment is a method of strengthening the substrate by applying stress to the substrate surface by exchanging alkali ions on the outermost surface of the glass substrate with alkali ions having a larger atomic radius. In the magnetic recording medium using a glass substrate, at least an underlayer, a magnetic layer, and a protective layer are sputter-deposited on the glass substrate manufactured by the above process, and a lubricating layer for reducing friction with a magnetic head is applied. It is produced by

[0006]

As described above, in order to improve the recording density, the flying height of the magnetic head has been reduced. However, when the flying height is 6 nm or less, the magnetic head is flying in a region close to the contact with the substrate surface, and it is highly possible that minute or minute amounts of protrusions and contamination (contamination) on the substrate surface become a serious problem. For example, there is concern that the reduction of the flying height may be hindered and the reliability may be lost after the magnetic recording medium is manufactured due to contamination. Further, in general, there is a concern about a change over time in the surface of the glass substrate from the production of the glass substrate to the introduction of sputtering. For example, in the case of a chemically strengthened glass substrate, as shown in Japanese Patent Application Laid-Open No. 8-124153, a chemically strengthened glass substrate subjected to an ion exchange treatment has a high concentration of ion-exchanged alkali ions on the outermost surface and changes with time. It has been pointed out that there is a possibility of elution due to, which may impair the reliability of the magnetic recording medium.

Further, in order to improve the recording density of the magnetic recording medium, it is necessary to make the PW50 value thin (small) or increase the medium S / N. Especially MR
In a magnetic head (MR head) using a (magnetoresistive) element, the output is small due to the relation of sensitivity, so the medium noise Nm
It is necessary to reduce (noise due to the medium) in order to realize high S / N. Therefore, higher coercive force, finer crystal grains, and reduced dispersion are required. In order to reduce the size and dispersion of the magnetic crystal grains, it is necessary to reduce the size and dispersion of the crystal grain size of the underlayer that influences the growth of the crystal grains of the magnetic layer.

Further, as a method for reducing the crystal grain size of the underlayer, a method called a seed layer having the same crystal structure as the underlayer and fine crystal grains is used as the underlayer of the underlayer. Is also disclosed in Japanese Patent Laid-Open No. 9-259418. As described above, since the thin film is epitaxially grown (the thin film to be formed grows while reflecting the crystal state of the lower layer), the control of the crystal grains of the magnetic layer to improve the recording density is performed as the underlayer of each layer. This is largely due to the crystal grain growth of the layer to be filmed. In other words, it can be said that the layer formed directly on the substrate has a great influence on the growth of magnetic crystal grains, and controlling the crystal growth of the layer directly on the substrate by the substrate greatly improves the recording density. It is considered to contribute.

In view of such circumstances, the present invention provides a 6 nm
Realizes the roughness of the glass substrate that enables the following flying height,
Provided is a method of manufacturing a magnetic recording medium with high reliability, and further, by the surface shape of the glass substrate, the crystal grain size of the layer formed on the substrate can be reduced and the dispersion can be reduced. Therefore, it is an object of the present invention to provide a method for improving recording density.

[0010]

The present invention includes the following configurations. (Structure 1) In a substrate for a magnetic recording medium having a concentric groove formed on the main surface thereof, the height of the concentric concavo-convex pattern is in the circumferential direction when at least a magnetic layer is formed on the substrate. A substrate for a magnetic recording medium, which is characterized by having no anisotropy.

(Structure 2) When at least a magnetic layer is formed on the substrate, an external magnetic field is applied in a circumferential direction and a radial direction at an arbitrary position on the magnetic recording medium to obtain a coercive force in the circumferential direction. When the ratio (Hc1 / Hc2) of coercive forces Hc1 and Hc2, where Hc1 and the coercive force in the radial direction are Hc2, is defined as magnetic anisotropy, the magnetic anisotropy is 0.90 to
1. The substrate for a magnetic recording medium according to the constitution 1, characterized in that (Structure 3) The substrate for a magnetic recording medium according to Structure 1 or 2, wherein the height of the concentric concavo-convex is 3 nm or less. (Structure 4) The radial width of the concentric concavo-convex pattern is 20
The magnetic recording medium substrate according to any one of configurations 1 to 3, which has a thickness of not less than 60 nm and not more than 60 nm.

(Structure 5) The substrate for a magnetic recording medium according to any one of structures 1 to 4, wherein the substrate for a magnetic recording medium is made of glass. (Structure 6) A magnetic recording medium characterized in that at least a magnetic layer is formed on the main surface of the magnetic recording medium substrate according to any one of structures 1 to 5. (Structure 7) In a manufacturing method for manufacturing a substrate for a magnetic recording medium by polishing a main surface of a disk-shaped substrate, after polishing the main surface of the disk-shaped substrate, a polishing liquid containing an abrasive is supplied to both main surfaces. However, a method for manufacturing a substrate for a magnetic recording medium, characterized in that a polishing tape is brought into contact with the main surface of the disk-shaped substrate that rotates about the center of the disk-shaped substrate. The substrate is preferably a glass substrate.

(Structure 8) The abrasive has an average particle size of 1.0.
8. The method for manufacturing a substrate for a magnetic recording medium according to the structure 7, characterized in that it is not more than μm. (Structure 9) The method for manufacturing a substrate for a magnetic recording medium according to Structure 7 or 8, wherein the abrasive does not cause a bond due to a chemical reaction with the material of the substrate. (Structure 10) The abrasive is diamond abrasive, alumina abrasive, colloidal silica abrasive, zirconia oxide abrasive,
10. The method for manufacturing a substrate for a magnetic recording medium according to the structure 9, comprising at least one selected from silicon carbide abrasive grains.

(Structure 11) The method for manufacturing a substrate for a magnetic recording medium according to any one of Structures 7 to 10, wherein the polishing amount (removal margin) of the re-polishing is 5 to 30 nm. (Structure 12) The method for manufacturing a substrate for a magnetic recording medium according to any one of structures 7 to 11, wherein the substrate is made of glass. The glass may be chemically strengthened glass as described in paragraph [0029]. (Structure 13) In the method for producing a glass substrate for a magnetic recording medium, which polishes and smoothes the main surface of a glass substrate subjected to a chemical strengthening treatment, the glass thickness to be polished and reduced is 5 to 30 nm for each polished surface. A method of manufacturing a glass substrate for a magnetic recording medium, comprising: (Structure 14) At least a magnetic layer is formed on the main surface of the glass substrate for a magnetic recording medium manufactured by the method for manufacturing a glass substrate for a magnetic recording medium according to any one of structures 7 to 13. Method for manufacturing magnetic recording medium. (Structure 15) After the main surface of the disk-shaped glass substrate is polished, the center of the disk-shaped glass substrate is moved to the chemically strengthened glass substrate while supplying a polishing liquid containing an abrasive to the main surface. A method of manufacturing a glass substrate for a magnetic recording medium, which comprises bringing a polishing tape into contact with the main surface of the disk-shaped glass substrate that rotates as a central axis and re-polishing. The configuration 15 includes the description of the configuration 7 and paragraph [0029]. (Structure 16) In the method for manufacturing a glass substrate for a magnetic recording medium according to any one of structures 7 to 12 and 15, the radial width of the concentric concavo-convex pattern formed on the main surface of the glass substrate by the repolishing. Is 20 nm or more and 60 nm or less, and a method for manufacturing a glass substrate for a magnetic recording medium. The configuration 16 includes the configuration 4. (Structure 17) In the method of manufacturing a glass substrate for a magnetic recording medium according to any one of structures 7 to 12, 15, and 16, scrub cleaning is performed after the repolishing, and the glass substrate for a magnetic recording medium. Manufacturing method. The configuration 17 includes the description in paragraph [0032].

As described in Structure 1, by forming concentric concavo-convex patterns on the main surface of the magnetic recording medium substrate, the crystal grains of the film formed on the substrate are miniaturized and the crystal grain size is reduced. Since the dispersion is reduced, the S / N ratio becomes high. This is because the concentric concavo-convex formed on the substrate causes the concentric grooves (concave) to reduce the grain size of the crystal grain and reduce the dispersion during crystal growth of the film formed on the concentric concavo-convex. It is considered that the effect of suppressing the disorder of the crystal grains in the direction perpendicular to the direction of the irregularities is provided.

Further, the concentric concavo-convex shape is the height of the concavo-convex shape having no anisotropy in the circumferential direction when at least the magnetic layer is formed on the substrate. This is because it is a concentric concavo-convex pattern for promoting the miniaturization of the crystal grains during the initial growth of the thin film crystals formed on the magnetic recording medium substrate and the reduction of the dispersion of the crystal grain sizes. This is to distinguish from the effect obtained by the sexual medium. An anisotropic medium means a magnetic recording medium in which the coercive force in the circumferential direction is always larger than the coercive force in the radial direction. It should be noted that the term “having no magnetic anisotropy in the circumferential direction” means that an external magnetic field is applied in the circumferential direction and the radial direction at an arbitrary position on the magnetic recording medium so that the coercive force in the circumferential direction is Hc1. When the ratio (Hc1 / Hc2) of the coercive forces Hc1 and Hc2 when the coercive force in the radial direction is Hc2 is defined as magnetic anisotropy, it means a state of 1.10 or less.

Specifically, as in the configuration 2, when at least the magnetic layer is formed on the substrate, an external magnetic field is applied in the circumferential direction and the radial direction at an arbitrary position on the magnetic recording medium, When the coercive force in the circumferential direction is Hc1 and the coercive force in the radial direction is Hc2, the ratio of the coercive forces Hc1 and Hc2 (H
When c1 / Hc2) is defined as magnetic anisotropy, the value is 0.90 to 1.10. Preferably,
0.95 to 1.05, more preferably 0.98 to 1.
02.

Further, as in the constitution 3, the height of the concentric concavities and convexities is preferably 3 nm or less. If it exceeds 3 nm, it is difficult to achieve a flying height of 6 nm or less, and high-density recording / reproduction cannot be performed, which is not preferable. Preferably 2.5n
m or less, more preferably 2 nm or less is desirable. Further, as in the configuration 4, the width in the radial direction of the concentric concavo-convex shape is preferably 20 nm or more and 60 nm or less. If it exceeds 60 nm, the effect of controlling the crystal grain size due to concentric concavities and convexities is lost. If it is less than 20 nm, the crystal grains become too fine and the PW50 characteristics deteriorate. Therefore, preferably 2
5 nm or more and 50 nm or less, more preferably 25 nm
It is desirable to be 40 nm or less.

The material of the substrate used in the present invention is not particularly limited. For example, glass (including glass ceramics (crystallized glass)), ceramics, silicon, carbon, metallic substrates of titanium, aluminum, etc. may be used. Above all, as in the constitution 5, glass is preferable in terms of smoothness and hardness. The glass type of glass is not particularly limited. Examples include aluminosilicate glass, borosilicate glass, aluminoborosilicate glass, soda lime glass, chemically strengthened glass, and crystallized glass.
Further, as in the constitution 6, by forming at least a magnetic layer on the substrate described in the constitutions 1 to 5 to form a magnetic recording medium, the S / N is improved and the flying height is 6 nm or less. Is obtained.

Further, as in the structure 7, after polishing the main surface of the disk-shaped substrate, while supplying a polishing liquid containing an abrasive to both main surfaces of the disk-shaped substrate, the center of the disk-shaped substrate is set to the central axis. By bringing a polishing tape into contact with the main surface of the rotating disc-shaped substrate and re-polishing it, it is possible to stably produce a substrate having concentric concavities and convexities with little variation in quality among the substrates. The polishing tape always keeps the new surface in contact with the main surface of the substrate at a constant speed. The material and width of the polishing tape used are not particularly limited. Examples of the polishing tape include flock, woven fabric, non-woven fabric, polyurethane and the like. Of these, woven tape is preferable. The material is not limited in terms of easy formation of concentric concavities and convexities and smoothness. Examples of the material include polyester and nylon. Further, the width of the polishing tape is appropriately adjusted depending on the size of the substrate. Specifically, it is 5 to 40 mm. Further, the feed rate of the polishing tape, the load of the polishing tape on the substrate, and the pressure are also appropriately adjusted according to the smoothness and the concentric concavo-convex shape. For example, the feed rate of the polishing tape is 1 to 10 mm / sec.
Is. It is preferably 2 mm / sec. Further, the weight and pressure of the polishing tape are also adjusted appropriately according to the smoothness. For example, the weight is 0.5 to 5 kg. Preferably, about 1.5 kg is desirable. Pressure is
It is 4.5 to 45 g / mm ² . The surface roughness of the substrate before re-polishing is preferably Rmax of 8 nm or less. This is because the polishing amount (removal margin) is 10 nm or less. Polishing amount is 1
The reason why the thickness is 0 nm or less will be described later.

Further, as in the constitution 8, the average particle diameter of the abrasive is preferably 1.0 μm or less. When the average particle diameter of the abrasive exceeds 1.0 μm, the surface roughness of the substrate is Rmax and is 3n.
This is because smoothness of m or less cannot be realized. Preferably 0.5 μm or less, more preferably 0.25 μm
The following is desirable. However, if the average particle size is made too small, the polishing rate will decrease and the production efficiency will decrease, so it is preferable to limit the average particle size to about 0.125 μm.

Further, as in the constitution 9, it is desirable that the polishing agent does not cause a bond with the material of the substrate due to a chemical reaction. This is because it is difficult to remove the abrasive that chemically reacts with the substrate material by scrubbing with a neutral detergent. Here, the term "no chemical reaction" means a state in which the substrate material and the polishing agent are not adsorbed by a chemical bond. Specific abrasives include diamond abrasive grains, alumina abrasive grains, and
Examples thereof include colloidal silica abrasive grains, zirconia oxide abrasive grains, silicon carbide abrasive grains, and the like. The abrasive has a smoothness,
It is appropriately selected according to the concentric concavo-convex shape. Above all, when the substrate is glass, polycrystalline diamond abrasive grains having a small particle size distribution are desirable from the viewpoint of stable polishing and texture treatment. Note that these abrasives are not limited to one kind when used, and two or more kinds of abrasives may be mixed and used.

Further, as in the constitution 11, the polishing amount (removal margin) of the re-polishing is preferably 5 to 30 nm. If it is less than 5 nm, the protrusions and dirt on the substrate surface cannot be completely removed, and 3n
It is not preferable because smoothness of m or less cannot be obtained. Also,
If the thickness exceeds 30 nm, in the case of polishing with a tape, the processing time becomes long, and the surface roughness obtained due to the influence of heat due to the long processing time varies, which is not preferable. Further, as in the configuration 12, by using glass as the material of the substrate, there are advantages in manufacturing that the substrate has high smoothness and flatness, and waviness is small.

Further, as in the structure 13, for the glass substrate subjected to the chemical strengthening treatment, the thickness of the glass to be polished and removed is set to 5 to 30 nm for each polished surface. Here, examples of the polishing method include a batch type polishing method and a method using a tape type texture device. In the batch-type polishing method, since a large amount of polishing is performed at one time, the polishing conditions for each substrate are not stable, and delicate control is difficult. Therefore, if a hard polishing agent is used, Pit, Scrat
Ch is easy to enter and smoothness cannot be improved. By using a tape-type texture device, it is possible to always perform polishing with a new tape surface and an abrasive, which is preferable because stable polishing can be performed. Further, as in the constitution 14, by forming at least the magnetic layer on the substrate of the constitutions 7 to 13, a magnetic recording medium having a high recording density compatible with high-density recording / reproduction can be obtained, and a magnetic characteristic high S can be obtained. A magnetic recording medium with stable / N can be manufactured. In the magnetic recording medium, at least a magnetic layer is formed on the substrate.

The magnetic layer preferably contains Co and Pt having high coercive force as main components. The alloy containing Co and Pt as main components is Co + P from the viewpoint of obtaining a sufficient coercive force.
It is desirable that t is 70% or more. Also, Co and P
Considering coercive force, medium noise, and cost, the ratio of t is Pt (at%) / Co (at%), and is preferably 0.05 or more and 0.2 or less. Components other than Co and Pt are not particularly limited, but for example, Cr, Ta, Ni,
Si, B, O, N, Nb, Mn, Mo, Zn, W, P
One or two or more of b, Re, V, Sm and Zr can be appropriately used. The addition amount of these elements is
It is appropriately determined in consideration of electromagnetic conversion characteristics and the like, and is usually preferably 30% or less.

In addition to the magnetic layer 5, for example, as shown in FIG. 1, a seed layer 2, an underlayer 3, an intermediate layer 4,
The protective layer 6 and the lubricating layer 7 may be included. As these seed layer 1, underlayer 2, intermediate layer 3, protective layer 6, and lubricating layer 7, known materials can be used as they are. The seed layer 2 is generally made of a material having a small crystal grain size and uniform crystal grains, and the underlayer 3 and the intermediate layer 4 formed on the seed layer 2 have fine crystal grains of the magnetic layer 5. It is provided for the purpose of improving the crystal growth while keeping it. NiAl is a typical material for the seed layer 2.
B2 type crystal structure materials such as alloys and CrTi
Alloys, CrNi alloys, etc. may be mentioned. The seed layer 2 may be laminated in order to improve crystal growth.

The underlayer 3 is preferably made of a material that provides a high coercive force. The base layer 3 is one layer or two.
It can be composed of more than one layer. As the underlayer 3,
For example, CrMo alloy, CrV alloy, CrW alloy, etc. can be used. As described above, the use of the Cr alloy improves the matching of the lattice plane spacing between the magnetic layer 5 and the underlayer 3, so that the easy axis of magnetization of the magnetic layer 5 is easily oriented in the plane. As a result, the in-plane coercive force is increased, and if the coercive force when Cr is used, the thickness of the underlayer can be reduced, and the electromagnetic conversion characteristics are improved.

The intermediate layer 4 is formed between the underlayer 3 and the magnetic layer 5,
The magnetic layer 5 is preferably formed at a position in contact with the magnetic layer 5.
It is provided for the purpose of improving the orientation of the C axis. Middle layer 4
Is a non-magnetic material, and its crystal system is preferably matched with that of the magnetic layer 5. The protective layer 6 is provided for the purpose of protecting the magnetic layer 5 from damage due to contact sliding of the head.
Provided on top of. The protective layer 6 can be composed of one layer or two or more layers. As the protective layer 6, for example,
Examples thereof include a silicon oxide film, a carbon film, a zirconia film, a hydrogenated carbon film, a hydrogen-nitrogenated carbon film, a carbon nitride film, a silicon nitride film, and a SiC film. The protective layer 6
Can be provided by a known film forming method such as a sputtering method. The lubricating layer 7 is provided for the purpose of reducing the resistance due to contact sliding with the head, and for example, perfluoropolyether or the like is generally used.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in more detail below with reference to examples. [Examples 1 and 2] A glass substrate 1 for a magnetic recording medium of this example is, as shown in FIG. 1, a substrate obtained by polishing a chemically strengthened aluminosilicate glass and giving it a concentric circular texture. The magnetic recording medium of this embodiment using this glass substrate 1 is a magnetic disk in which a seed layer 2, an underlayer 3, an intermediate layer 4, a magnetic layer 5, a protective layer 6 and a lubricating layer 7 are sequentially laminated. The glass substrate 1 has Rmax = 7 nm, Ra
= 0.8 nm of mirror-polished chemically strengthened aluminosilicate glass is subjected to polishing and concentric texture processing using a tape type texture device.

FIG. 2 shows a schematic view of a tape type texture device used in this embodiment. In the tape-type texture device used in this example, a glass substrate fixed to a spindle was rotated, and an abrasive was supplied to the tape from a slurry dropping port, and both main surfaces of the glass substrate were wound around rollers. By sandwiching with a tape, a circumferential groove is formed on the main surface of the glass substrate. The roller around which the tape is wound is rotating at a constant rotation speed so that the new surface of the tape always contacts the glass substrate.

The glass substrate is centered on the fulcrum a in FIG.
The glass substrate is sandwiched by the movement of the plate-shaped members fixed to the shafts of the rollers. At this time, the force (weight) applied to the glass substrate is determined by the force of the spring stretched between the plate-shaped members. The weight is applied by measuring the tension of the spring during processing with a tensiometer attached to one side of the spring. Fabrication of this glass substrate 1 was performed using a woven type tape as a tape and a slurry in which polycrystalline diamond having an average particle diameter of 0.125 μm was dissolved in a dispersant as a hard abrasive.

Further, the processing conditions of the other texture apparatus are as follows: for example 1, processing load of 1.4 kg, processing pressure of 12 g / mm ² , substrate rotation speed of 1000 rpm, tape feeding speed of 2 mm / sec, and processing time of 30 sec. Regarding Example 2, the processing load was 1.4 kg, the processing pressure was 12 g / mm ² , the substrate rotation speed was 500 rpm, the tape feeding speed was 2 mm / sec, and the processing time was 30 sec. After that, in a cleaning tank containing a weak alkaline cleaner,
After performing rubbing and washing (scrub washing) with a velclin cloth, ultrasonic cleaning and drying were performed. The seed layer 2 is N
It is composed of an iAl thin film (film thickness: 500 angstrom). In addition, this NiAl thin film is Ni: 50 at%, A
The composition ratio is 1:50 at%.

The underlayer 3 is a CrMo thin film (film thickness: 300
Å) for improving the crystal structure of the magnetic layer. The CrMo thin film is C
The composition ratio is r: 90 at% and Mo: 10 at%. The intermediate layer 4 is made of a CoCr thin film (film thickness: 30 angstrom). This CoCr thin film is Co:
The composition ratio is 65 at%, Cr: 35 at%.

The magnetic layer 5 is made of a CoPtCrTa alloy and has a film thickness of 200 Å. The contents of Co, Pt, Cr and Ta in this magnetic layer are as follows. That is, Co: 73 at%, Pt: 7 at%,
Cr: 18 at% and Ta: 2 at%. Protective layer 6
Is for preventing the magnetic layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon having a film thickness of 50 angstrom, and wear resistance is obtained. The lubricating layer 7 is made of a liquid lubricant of perfluoropolyether, and this film alleviates the contact with the magnetic head. The film thickness is 9 Å.

The magnetic recording media of Comparative Examples 1 and 2 are magnetic disks prepared by using a glass substrate on which the magnetic recording medium of the present invention has not been subjected to polishing or concentric circular texture treatment. Comparative Example 1 and Comparative Example 2 are glass substrates having different substrate surface roughnesses Rmax and Ra. The magnetic recording medium of Comparative Example 1 has Rmax = 2.95 nm, Ra
= 0.26 nm, Comparative Example 2 has Rmax = 7.10 nm,
A magnetic disk manufactured by using a glass substrate having a roughness of Ra = 0.84 nm.
Same as.

Table 1 shows the surface roughness of the substrate with respect to the glass substrate of Example 1, and the flying height of the magnetic head measured on the magnetic disk manufactured using the glass substrate of Example 1,
The results of coercive force, remanent magnetization, medium noise, and glide inspection are shown. The definition of each parameter and the measurement method of each measurement are shown below.

Substrate surface roughness The obtained glass substrate is manufactured by Digital Instruments Co., Ltd., atomic force microscope (AFM), trade name: Nan
Surface roughness (Rmax, Ra) was measured using o Scope. Considering the correlation with the resolution, measurement time, and head flying height, the measurement range is 5 μm □, the number of samplings in the field of view of 5 μm is 256 dots (0.02 μ per dot).
m measurement interval).

Magnetic Head Flying Height Touchdown height (TDH) was measured as an index for measuring the magnetic head flying height capability of this magnetic recording medium. T
The DH is a method of measuring the flying height of the magnetic disk by sequentially lowering the flying height of the flying head and obtaining the flying height at which the head starts contact with the magnetic disk. In order to reduce the flying height of the head, the head is floated by the rotation of the magnetic disk.
The measurement radius used in this example is 22 mm.

8 mmφ sample for coercive force measurement was cut out from the coercive force magnetic disk, and the maximum applied magnetic field was applied in the circumferential direction and radial direction of the substrate in the film plane using a vibrating sample type magnetometer (VSM). 10
A coercive force (Oe) was obtained by applying a magnetic field as kOe.

The medium noise electromagnetic conversion characteristic measuring instrument (Guzik) is equipped with a magnetic resistance type (M
R) A head was attached and the medium noise (μVrms) was measured. The MR head is a thin film head having a flying height of 0.018 μm, and the relative speed to the magnetic disk is 9.77 m.
The recording / reproducing output at a linear recording density of 430 kfci (a linear recording density of 430,000 bits per inch) was measured. Also, the carrier frequency is 82.3 MHz
Then, the noise spectrum during signal recording / reproduction was measured by a spectrum analyzer with the measurement band set to 98.76 MHz. The thin film head used for this measurement is
Track width 0.85 / 0.6μ on the reading side
m, the magnetic head gap length is 0.15 / 0.14 μm.

Glide test The glide test is a test in which the head is levitated on the surface of the magnetic disk with a constant flying height, and the head radial position is changed while checking for the collision between the head and the magnetic disk.
The cause of the collision is the protrusion present on the magnetic disk surface,
A depression or the like is considered, and this inspection is on the glass substrate and the magnetic disk surface. It is performed to detect protrusions, dents, and the like. The collision at this time was detected by sensing the vibration at the time of collision using an AE sensor (sensor that converts vibration into voltage) attached to the base of the head arm.

With respect to the 100 magnetic disks of Examples 1 and 2 and Comparative Example 1, a head floated at a flying height of 6 nm was used in the radius area of the magnetic disk data zone (area on the magnetic disk for recording and reproduction). Move the head position,
The presence or absence of collision between the head and the magnetic disk was examined. Table 1 shows the number of magnetic disks that did not collide among the 100 tested sheets. The radius tested in this example is from 12.0 mm to 32.0 mm.

[0043]

[Table 1]

From the results of Examples 1 and 2 in Table 1, by introducing a re-polishing process using a tape using a slurry before producing a magnetic recording medium, it has a concentric circular texture, and Rmax = 3 nm and Ra = Since it could be reduced to 0.3 nm or less, TDH could be suppressed to 6 nm or less. In addition, the result of the glide inspection is shown in Example 1.
The magnetic disk of No. 2 has a larger number of magnetic disks with no collision than the magnetic disk of Comparative Example 1. The difference between the magnetic disk manufacturing process of Examples 1 and 2 and the comparative example 1 is the presence / absence of the re-polishing process before film formation. Therefore, the protrusions on the glass substrate due to foreign substances and the like were removed by polishing and removed. As a result, the proportion of magnetic disks that collide is considered to have decreased. Therefore, by the re-polishing treatment of the glass substrate before manufacturing the magnetic recording medium according to the present invention, it was possible to realize a low flying height of the magnetic head, and to obtain a magnetic disk with high production stability and reliability.

Furthermore, the magnetic recording media of Examples 1 and 2 are
The medium noise is smaller than those of the magnetic recording media of Comparative Examples 1 and 2. This is because the concentric circular texture formed on the glass substrate reduces the crystal grain size of the seed layer formed on the substrate, and the crystal grains with less dispersion are formed, and further, the underlayer epitaxially grown on the seed layer. This is probably because the crystal grain size of the magnetic layer was small and the dispersion could be suppressed.

Further, the magnetic recording media of Examples 1 and 2 had substantially the same coercive force when a magnetic field was applied in the circumferential direction and the radial direction. Generally, a magnetic recording medium manufactured by using a substrate in which a concentric circular texture is applied to an Al / NiP substrate is called an anisotropic medium, and a magnetic field is applied in a circumferential direction and a radial direction in a magnetic disk film surface. The coercive force at this time is different, and the coercive force in the circumferential direction becomes higher than the coercive force in the radial direction, resulting in high coercive force. However, the magnetic recording medium of Example 1 in which the glass substrate has a concentric circular texture has substantially the same coercive force when a magnetic field is applied in the circumferential direction and the radial direction (generally called an isotropic medium). Al / Ni
It can be said that the magnetic recording medium of this example achieves a high coercive force in a form different from the effect of the anisotropic medium using the P substrate.

[Example 3 and Comparative Example 4] Confirmation of Effect of Concentric Circular Texture Example 3 is a glass substrate 1 manufactured under the same conditions as in Example 1.
The disk has a seed layer film thickness of 500 Å. FIG. 3 is an electron microscope SEM surface photograph of the seed layer surface of Example 3. The seed layer used in this example is the same as the seed layer used in Example 1. Comparative Example 3 is the glass substrate used in Comparative Example 2,
The same seed layer as in Example 3 was formed to a film thickness of 500 angstrom.

FIG. 4 shows an SEM surface photograph of the surface of the seed layer. Table 2 shows the crystal grain size of the seed layer calculated from the SEM surface photograph. As shown in Table 2, when the concentric texture is formed on the glass substrate, the crystal grain size is smaller,
It also indicates that it promotes the crystal grain growth of the seed layer with less dispersion. Here, the dispersion is the half-value width of the normal distribution when the crystal grain size of the crystal grains within a predetermined area is measured and the distribution of the crystal grain size is plotted, and indicates the variation of the crystal grain size. Therefore, in this example, the concentric circular texture on the glass substrate surface promotes crystal growth with a small seed layer grain size and little dispersion, and further, the grain size of the underlayer and magnetic layer for epicapital growth. Can also be small, and the dispersion can be suppressed. Thereby, medium noise can be reduced and good electromagnetic conversion characteristics can be obtained. This is the value in Table 1 and corroborates the media noise results.

[0049]

[Table 2]

[Examples 4 to 7, Reference Example 1] In the production of the glass substrate 1 of this example, a woven type tape was used as the tape, and polycrystalline diamond was dissolved in the dispersant as the hard abrasive. This was done using a slurry. The average grain size of the polycrystalline diamond used in this example is 0.1 μm.
(Example 4), 0.125 μm (Example 5), 0.5 μ
m (Example 6), 1.0 μm (Example 7), 1.2 μm
(Comparative example 5). Other processing conditions of the texture apparatus were: processing load 1.0 kg, processing pressure 9 g / mm ² , substrate rotation speed 1000 rpm, tape feed speed 2 mm / sec, processing time 30 sec. The magnetic recording medium using this glass substrate 1 has the same seed layer 2, underlayer 3, magnetic layer 5,
This is a magnetic disk in which a protective layer 6 and a lubricating layer 7 are sequentially laminated.

For each of Examples 4 to 7 and Comparative Example 5, the surface of the glass substrate 1 was 0.5 μm square by AFM.
The width of the concentric textured groove was determined from the cross-sectional profile in the direction perpendicular to the texture direction (radial direction) with respect to the texture direction. Table 3 shows Examples 4 to 7
The widths of the texture grooves in the glass substrate of Reference Example 1 and Comparative Example 5 not having the concentric circular texture and the values of the medium noise of each magnetic recording medium are also shown.

[0052]

[Table 3]

From the results shown in Table 3, it can be seen that the medium noise becomes worse as the width of the concentric circular texture groove is increased. When the width of the texture groove exceeds 60 nm, it becomes almost the same as the medium noise of the magnetic recording medium not provided with the concentric circular texture, so that it is understood that the effect of the concentric circular texture on the medium noise disappears. Therefore, the width of the concentric textured groove is preferably 60 nm or less.

Weighting / polishing thickness of tape on substrate and
Relationship between Surface Roughness of Substrate Surface [Example 8] In the production of the glass substrate 1 of this example, a woven type tape was used as the tape, and the hard abrasive was polycrystal having an average particle size of 0.125 μm. This was done using a slurry of diamond dissolved in a dispersant. In this embodiment, the processing load is 0 kg, 0.50 kg, 0.75 kg,
1.00kg, 1.20kg, 1.4kg, 1.5kg
Other texture devices were set as follows: substrate rotation speed 1000 rpm tape feed rate 2 mm / sec processing time 30 sec. FIG. 3 shows the polishing thickness (the thickness of the glass surface polished in the present invention) and the surface roughness Rmax of the substrate surface with respect to the processing load.

As shown in FIG. 3, it is understood that the polishing thickness monotonously increases as the working load increases, and Rmax decreases accordingly. However, when the polishing thickness is about 6 nm, R
The decrease in max becomes gradual, and the polishing thickness is at most 10n
It can be seen that when m is exceeded, the surface roughness of the substrate remains almost unchanged. It is also understood that when the polishing thickness is less than 3 nm, sufficient smoothness cannot be obtained. Although not shown in FIG. 3, it was confirmed that when the processing time was increased and the polishing thickness exceeded 30 nm, the surface roughness varied due to the heat of the processing. Incidentally, the measurement of the polishing thickness, on the glass substrate,
A polished portion and a non-polished portion were formed, and the step difference in the boundary region was measured using an interference type surface profiler (WYKO).

[0056]

According to the present invention, in the step before sputtering, the surface of the glass substrate is re-polished with a polishing thickness of 5 to 30 nm, thereby providing a highly reliable glass substrate satisfying the levitation of 6 nm or less. Further, by providing a concentric texture having a groove width of 60 nm or less, the seed layer on the glass substrate has a small crystal grain size, promotes growth with small dispersion, and has a magnetic characteristic of low medium noise. A magnetic recording medium can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a film structure of a magnetic disk.

FIG. 2 is a schematic view of a tape-type texture device.

FIG. 3 is a diagram showing a relationship between a processing load and a polishing thickness and a surface roughness of a substrate surface.

FIG. 4 is an SEM surface photograph of the seed layer surface of Example 3.

5 is a SEM surface photograph of the seed layer surface of Comparative Example 3. FIG.

Continued front page    (72) Inventor Hiroshi Tomiyasu             2-7-5 Nakaochiai, Shinjuku-ku, Tokyo Ho             Within Ya Co., Ltd. F-term (reference) 5D112 AA02 AA24 BA03 BA09 GA08                       GA13 GA14 GA28

Claims (11)

[Claims] 1. A method for manufacturing a glass substrate for a magnetic recording medium by polishing a main surface of a disk-shaped glass substrate, the method comprising: polishing the main surface of the disk-shaped glass substrate; While supplying a polishing liquid, a glass tape for a magnetic recording medium is characterized in that a polishing tape is brought into contact with the main surface of the disk-shaped glass substrate that rotates about the center of the disk-shaped glass substrate as a central axis for re-polishing. Production method. 2. The method for producing a glass substrate for a magnetic recording medium according to claim 1, wherein the abrasive has an average particle size of 1.0 μm or less. 3. The method for manufacturing a glass substrate for a magnetic recording medium according to claim 1, wherein the abrasive does not cause a bond due to a chemical reaction with the material of the glass substrate. 4. The abrasive is composed of at least one selected from diamond abrasive grains, alumina abrasive grains, colloidal silica abrasive grains, zirconia oxide abrasive grains, and silicon carbide abrasive grains. 4. The method for manufacturing a glass substrate for a magnetic recording medium according to 3. 5. The polishing amount (removal margin) of the re-polishing is 5 to 5.
It is 30 nm, The manufacturing method of the glass substrate for magnetic recording media of any one of Claim 1 thru | or 4 characterized by the above-mentioned. 6. The glass substrate according to claim 1, wherein the glass substrate is made of chemically strengthened glass.
Item 8. A method for manufacturing a glass substrate for a magnetic recording medium according to item. 7. A method of manufacturing a glass substrate for a magnetic recording medium, which comprises polishing and smoothing a main surface of a chemically strengthened glass substrate, wherein the glass thickness to be polished and reduced is 5 to 30 n for each polished surface.
m is a method for manufacturing a glass substrate for a magnetic recording medium, wherein 8. Forming at least a magnetic layer on the main surface of a glass substrate for a magnetic recording medium manufactured by the method for manufacturing a glass substrate for a magnetic recording medium according to claim 1. And a method for manufacturing a magnetic recording medium. 9. After the main surface of the disk-shaped glass substrate is polished, the center of the disk-shaped glass substrate is supplied to the chemically strengthened glass substrate while supplying a polishing liquid containing an abrasive to the main surface. A method of manufacturing a glass substrate for a magnetic recording medium, which comprises bringing a polishing tape into contact with the main surface of the disk-shaped glass substrate which rotates around the center axis and re-polishing. 10. The method for manufacturing a glass substrate for a magnetic recording medium according to claim 1, wherein the re-polishing forms concentric concavo-convex patterns on the main surface of the glass substrate. Radial width of 20 nm to 60 nm
A method for manufacturing a glass substrate for a magnetic recording medium, comprising: 11. The method of manufacturing a glass substrate for a magnetic recording medium according to claim 1, wherein scrub cleaning is performed after the repolishing. Manufacturing method of glass substrate for medium.