JPH08293117A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE: To extremely reduce friction at the time of CSS by forming protrusions on the surface of a substrate or an underlayer by irradiating the surface with energy beams, mechanically texturing the surface and forming a required protective layer. CONSTITUTION: Protrusions are formed on the surface of the substrate or underlayer of a magnetic recording medium by irradiating the surface with energy beams, the surface is textured and a required underlayer, magnetic recording layer or protective layer is formed. For example, an underlayer of Cr or Cu having 20-200nm thickness is formed on a nonmagnetic substrate and protrusions are formed on the surface of the substrate or underlayer by irradiating the surface with energy beams having precisely controlled output along the circumferential direction of the surface while rotating the substrate. Argon gas laser light is used as laser light at <=100ns pulse width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium such as a hard disk or a magnetic tape used in a magnetic disk device. In particular, the present invention relates to a method for manufacturing a thin-film magnetic recording medium that enables good CSS (contact start and stop) characteristics, sticking characteristics of the head to the medium surface, and low flying height of the head at the same time in a magnetic disk device.

[0002]

2. Description of the Related Art Normally, when using a hard disk, the hard disk is rotated at a high speed to float a magnetic head,
Writing / reading to / from a hard disk is performed via this magnetic head. In order to improve the magnetic characteristics of a hard disk, a hard disk is mechanically concentrically formed in the circumferential direction of the magnetic disk on the base surface of the disk or on a base layer made of a non-magnetic material such as NiP plating provided on the base surface. Processing (hereinafter, referred to as mechanical texture) is performed by polishing to leave processing marks. Further, when a glass substrate having excellent surface properties and hardness is used, a method of etching the surface of the glass with hydrofluoric acid to make the surface uneven and a method of applying fine particles to the surface of the substrate are used.

Due to the recent increase in the amount of information and the demand for smaller and lighter devices, the linear recording density and track density have increased,
As the area per bit becomes smaller, scratches due to mechanical texture as in the conventional case have a higher probability of becoming an error in reading information. There is also a method of mechanically texturing only the CSS zone on the inner periphery and leaving the data recording area as it is, but when the surface of the data recording area is higher than the height of the surface of the CSS zone and the head seeks. There was a problem of crashing.

Also, a method of making a texture pattern by a laser has been proposed in place of such a mechanical texture. An example of a laser texture method is disclosed in US Pat. Nos. 5,062,021 and 5,108,781, in which a NiP layer is locally melted by a strong pulsed laser beam of Nd-YAG, A large number of crater-like concavities and convexities formed by melting and forming a concave hole portion and the molten NiP around the periphery of the hole and solidifying by swelling due to surface tension, forming a crater-like convex portion. Attempts have been proposed to improve CSS characteristics with the head by the rim. However, in the methods described in these patents, since the irradiation range of the laser beam is wide and the output of the laser is also large, the melting range of NiP is wide, and the central part of the melted liquid surface does not rise and the crater does not rise. In this case, the contact area between the tip of the convex part and the bottom surface of the head does not decrease dramatically, and the problem of sticking between the head and the disk is improved compared to mechanical texture. It is hard to say that

In addition, the present inventors previously filed Japanese Patent Application No. 6-152.
In No. 131, a method of using a convex protrusion formed by a pulse laser as a texture pattern was proposed. This method is extremely effective in improving the CSS characteristics, but even in this case, if the curvature of the tops of the convex protrusions is small, the CSS characteristics may deteriorate in an environment such as high temperature and high humidity.

A method of forming protrusions using photolithography has also been proposed, and the tribology preliminary papers of the Japan Lubricating Society (1991-5, A-11), (1992).
-10, B-6) discloses the CSS test results of a magnetic disk in which concentric convex portions or projections having an area ratio of 0.1 to 5% to the entire surface of the disk are formed by photolithography. . But with this method,
Since the tops of the projections are smooth, there is a drawback that friction increases with the number of times the head slides, and there is a problem that industrialization is not easy.

[0007]

With the increase in density of magnetic recording media and the improvement of surface properties of media, it is desired to improve the sliding characteristics between the head and the media by an industrially advantageous method. .

[0008]

The present invention has been made to a method of manufacturing such a medium for high density magnetic recording, and its gist is to provide an energy-saving method on the surface of a substrate or an underlayer of the magnetic recording medium. After irradiating a line to form protrusions on the surface of the substrate or the underlayer, mechanically texture the surface of the substrate or the underlayer, and then form the required underlayer, magnetic recording layer or protective layer. And a method of manufacturing a magnetic recording medium characterized by the above.

The present invention will be described in detail below. In the present invention, first, the surface of the substrate or the underlayer of the magnetic recording medium is irradiated with energy rays to form protrusions on the surface of the substrate or the underlayer. Then, a mechanical texture is applied to the surface of the substrate or the underlayer on which the protrusion is formed. In order to manufacture a magnetic recording medium, an underlayer such as Cr or Cu having a film thickness of 20 to 200 nm is usually provided on a nonmagnetic substrate. In some cases, a base layer made of NiP and having a thickness of 100 to 20,000 nm may be further provided between the substrate and the above layer.

As a preferred method of irradiating the surface of the substrate or the underlayer of the magnetic recording medium with energy rays to form protrusions on the surface of the substrate or the underlayer, a substrate for the magnetic recording medium or an underlayer is provided on the substrate. While the substrate is rotated, the surface thereof is irradiated with an energy ray whose output is accurately controlled along the circumferential direction to form protrusions on the surface. As the laser light, a gas laser such as Ar or a solid-state laser such as YAG capable of continuous oscillation in a single mode with an appropriate pulse length by a modulator, a solid-state Q-switch laser such as YAG or YLF, or a semiconductor A laser or the like is used. The pulse width is preferably 100 ns or more. In addition, since the longer the wavelength is, the higher the light transmittance to the protective layer is, the laser on the long wavelength side is preferable.

In the present invention, in the molten liquid portion formed by the irradiation of energy rays, there is almost no temperature gradient in the direction perpendicular to the scanning direction of the energy rays, and a temperature gradient occurs only in the scanning direction. In such a state, the liquid surface has a higher surface tension when the temperature is lower, so that the molten liquid part becomes a round convex part at the low temperature part, and finally the high temperature part that solidifies, that is, the last part when the beam is scanned. The portion becomes a concave portion, and by being rapidly cooled and solidified, a protrusion having a preferable shape as described later can be formed.

In order to achieve such conditions, it is preferable to set the melting range of the surface of the substrate or the underlayer of the magnetic recording medium by the irradiation of energy rays to a range of 5 μm or less. Particularly, it is preferable that the melting range in the direction perpendicular to the energy beam scanning direction is 5 μm or less, preferably 2.5 μm or less, more preferably 2 μm or less. When the melting range exceeds 5 μm, the central portion of the melted portion does not have a convex shape but is recessed into a concave shape, and the peripheral portion of the liquid portion rises in a convex shape. This is probably because a wide melting range causes a temperature gradient in the molten liquid during cooling. Usually, since the surface tension is large in the low temperature part, the surface tension of the outer peripheral part cooled from the surrounding area is large, and it is considered that the surface tension rises.

Preferably, the energy beam to be irradiated is a continuous or pulsed laser beam, particularly a pulsed laser beam, and the scanning distance of the pulsed laser in the irradiation time per irradiation is on the surface to be irradiated. Usually 1/4 or more of the spot diameter of the pulsed laser, preferably 1 /
2 or more.

In the present invention, the scanning direction of the energy beam is not limited to the direction in which the energy beam scans on the stationary irradiation target medium, but the energy beam is kept stationary and the irradiation target medium is rotated. This is a relative one that also indicates the rotation direction of the irradiation target medium in the case of, or the case where the energy beam and the irradiation target medium are moved. Further, in the present invention, the spot diameter of the energy ray means a diameter of 1 / e ² where 84% of energy is concentrated.

The height of the protrusions can be freely controlled by adjusting the intensity of the laser, the average irradiation time thereof, and the linear velocity of the disk. The protrusion density is defined as the number of protrusions per revolution,
It can be freely controlled by adjusting the irradiation interval of the pulsed laser in the radial direction and the conditions for controlling the height of the protrusions. Further, it is efficient in terms of time if the spiral scanning is performed by continuously moving in the radial direction.
Usually, the laser intensity is 20 to 500 mW, the average irradiation time is 0.05 to 5 μsec, and the laser spot diameter is 0.2.
˜4 μm, and the linear velocity of the substrate is preferably 1 to 15 m / sec. Here, the average irradiation time of the laser refers to the time during which the surface of the underlayer is irradiated with the laser to form one protrusion.

To change the irradiation area of the laser beam, it is usually necessary to change the wavelength of the laser used and the aperture ratio of the objective lens. By using an objective lens having an aperture ratio of 0.1 to 0.95, The irradiation diameter can be controlled to about 0.3 to 6 μm. The irradiation diameter of the beam used in the present invention is 2 μm.
Hereafter, it is more desirable to be 1 μm or less. As a laser system, a gas laser such as Ar capable of continuous oscillation using a modulator, a solid-state laser YAG, a semiconductor laser, or the like can be used. In any case, a system capable of reducing the spot diameter is desirable.

As a preferred embodiment of the present invention, in a hard disk or the like, the protrusion is present in an area where the magnetic head performs CSS (contact start and stop),
A method of producing a magnetic recording medium that does not exist in the data recording area or exists at a low density can be mentioned. By doing so, the surface of the magnetic layer can be made smooth in the data recording area, so that errors due to scratches as in the conventional case can be reduced.

In a further preferred embodiment, the protrusions are formed in the area where the magnetic head performs CSS and not in the data recording area, or are formed at a low density, and the height of the protrusion is directed toward the data recording area. The magnetic recording medium can be manufactured so that the number of magnetic recording media decreases. By decreasing the protrusion height toward the data recording area, the head can be stably sought from the data recording area to the CSS zone or the opposite direction. Further, by reducing the density of the protrusions toward the data recording area, the same effect as when the height of the protrusions is reduced can be obtained.
It is also preferable to reduce both the height and density of the protrusions toward the data recording area. Further, with respect to a tape or the like, the sliding characteristics at both ends of the tape affect the running, so that it is more effective to form the protrusions according to the present invention at both end portions of the tape.

In order to reduce the height of the protrusion toward the data recording area, there is a method of reducing the output of energy rays toward the data recording area. Further, in order to decrease the protrusion density toward the data recording area, there is a method of increasing the irradiation interval of energy rays toward the data recording area.

In the present invention, the height of the protrusions formed on the surface of the medium to be irradiated with energy rays is defined by JIS surface roughness (B0
601-1982), the height of the protrusion with respect to the center line of the roughness curve. The height of the protrusion is preferably 1 to 60 nm, particularly preferably 10 to
The thickness is 60 nm, and if it exceeds 60 nm, the CSS characteristics are good in a hard disk or the like, but the stable flying height of the head cannot be lowered, and in a tape or the like, the spacing between the medium and the magnetic head is large and the output is reduced. On the other hand, if the thickness is less than 1 nm, the substrate is buried in the original fine roughness, and the desired effect cannot be obtained.

The protrusion having the above-mentioned protrusion height is 1
mm²Per 10-10⁸It is preferable that there is one. 1
If the number is less than 0, the head bottom surface may be
It ’s difficult to support it by yourself, and it ’s 10⁸Protrusion beyond the individual
When you try to make the
It becomes difficult to obtain, especially preferable existence density is 1 mm ²
Per 10³-10⁶It is an individual. Where the density of protrusions is
Is not the average density of the entire medium, but the unit at the protrusion
It is the density per area. Also, is the protrusion
Area of the figure surrounded by contour lines at a height of 1 nm below
Average value (hereinafter referred to as contour area) is 2 μm²Below
Preferably 1.0 μm²Below, further
Preferably 0.5 μm²The following, particularly preferably 0.2μ
m²It has values in the following ranges: 2 μm²When it exceeds
Sticking is more likely to occur with the card. In addition,
The area of this contour line is the surface shape measurement device by laser interference.
Position, for example, measured with Zygo manufactured by Zygo, Inc.
Is possible.

In the present invention, after the protrusions are formed on the surface of the substrate or the underlayer as described above, the surface is mechanically textured. The extent of mechanical texture is grinding amount is 0.1 mg / cm ² or less, more preferably 0.05 mg / cm ² or less, even more preferably 0.0
The texture is preferably ² mg / cm ² or less. The purpose of this mechanical texture is to erase the polish marks on the substrate and to mechanically grind the tops of the convex projections produced by the laser to make sharp small projections at the tips.

In the present invention, the projections are formed on the surface of the substrate or the underlayer as described above, and after mechanical texturing, the required underlayer, magnetic recording layer or protective layer is produced. To film. In the present invention, a non-magnetic substrate such as an aluminum alloy plate or a glass substrate is usually used as the substrate of the magnetic recording medium, but a metal substrate such as copper or titanium, a ceramic substrate, a resin substrate or a silicon substrate may also be used. it can. The thermal conductivity of the substrate is important in terms of heat cooling by irradiation with energy rays, and is preferably 100 Watt / mK or less.

The film thickness is usually 20 to 200 n on a non-magnetic substrate.
m of Cr or Cu is provided as an underlayer, and the film thickness is usually 100 to 2 between the substrate and the above layer depending on the case.
You may provide an underlayer which consists of non-magnetic materials, such as a NiP alloy, of 10,000 nm. The underlayer is usually formed by electroless plating or sputtering. Further, the thermal conductivity of the underlayer and the thickness of the layer are also important in terms of the cooling of heat by irradiation with energy rays, and the thermal conductivity is preferably 100 Watt.
t / mK or less, and the layer thickness is preferably 50 to 30,
000 nm, particularly preferably 100 to 15,000 nm
Is.

The magnetic recording layer is formed by a method such as electroless plating, electroplating, sputtering or vapor deposition.
P, Co-Ni-P, Co-Ni-Cr, Co-Ni-
Pt, Co-Cr-Ta, Co-Cr-Pt, Co-C
A ferromagnetic alloy thin film such as an r-Ta-Pt-based alloy is formed, and its thickness is usually about 30 to 70 nm.

A protective layer is usually further provided on the magnetic recording layer. As the protective layer, a carbon film, a hydrogenated carbon film, or a carbon film is formed by a method such as vapor deposition, sputtering, plasma CVD, ion plating, or a wet method. Carbide films such as TiC and SiC, nitride films such as SiN and TiN, SiO and Al
An oxide film of O, ZrO, or the like is formed. Of these, a carbon film and a hydrogenated carbon film are particularly preferable, and a hydrogen abundance ratio (H / C, number of atoms%) containing carbon as a main component is 0.1 to 40 at%, and particularly 1 to 30at
% Hydrogenated carbon film is preferred.

A lubricant layer is usually provided on the protective layer. However, when a magnetic head having a diamond-like carbon layer on the slider surface is used, the tribological property with the medium is improved, so that it is not always necessary to provide a protective layer.

[0028]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. Examples 1 to 3 and Comparative Example 1 After plating NiP (thermal conductivity, about 10 Watt / mK) with a film thickness of 10 μm on a disk-shaped Al substrate with a diameter of 95 mm, the surface was adjusted so that the surface roughness Ra was 2 nm or less. Polishing was performed to obtain a substrate having a NiP underlayer. Next, a laser intensity of 163 mW, an average irradiation time of 0.6 μsec, and an aperture ratio NA of the objective lens used for focusing the laser, 84% (1 / e ² ) of energy is focused on a spot diameter (1.22 ×). λ / NA) 1.0 μm, substrate linear velocity 1
Under the condition of 714 m / sec, an Ar pulse laser was applied to the CSS area having a radius of 18 to 21 mm on the inner peripheral portion of the disk to form spiral protrusions with a pitch of 10 μm on the NiP underlayer surface. The wavelength of the Ar laser is 488n
m was used.

After the projections are generated by the laser, the grain size is about 1 μm.
Using free diamond abrasive grains of m, the substrate surface was mechanically textured in the circumferential direction so that the polishing amount shown in Table 1 was obtained. 1 and 3 show Example 1 and Comparative Example 1, respectively.
It is a figure showing the result of having observed the surface shape of the NiP base layer obtained by above with the surface shape measuring apparatus by laser interference ("ZYGO" by a Zigo company, USA), and FIG. 2 and FIG. 4 are the sectional views.

The protrusion according to the present invention has a shape as shown in FIG. Since the shape of the top is cut by mechanical texture, a cross section parallel to the texture direction (see FIG. 2).
(A cross section) of the projection is smoother than the shape of the projection tip created by the laser, but in the cross section perpendicular to the mechanical texture direction (cross section b of FIG. 2), the projection tip is created by the laser. The projection has a shape as if it was further divided.

Then, a Cr intermediate layer (100 nm) and a Co--Cr layer were sequentially formed on the NiP substrate by a sputtering method.
A -Ta alloy magnetic film (50 nm) was formed. Further, a carbon protective film (20 nm) is formed, and then a fluorine-based liquid lubricant (“DO” manufactured by Monte Edison Co., Ltd. is prepared by an immersion method.
L-2000 ") was applied to a thickness of 2 nm to prepare a magnetic recording medium.

Table 1 shows the conditions for forming projections on the substrates of Examples and Comparative Examples by laser, linear velocity, laser intensity, average laser irradiation time, average projection density (corresponding to laser irradiation interval), average projection height. Now, the numerical aperture NA of the objective lens used for focusing the laser and the amount of grinding per unit area of the surface by the subsequent mechanical texture are shown.

[0033]

[Table 1] Table-1 ------------------------------------- Substrate Laser Average Average Average Objective grinding amount Linear velocity Strength Irradiation time Protrusion density Protrusion height Lens (mm / sec) (mW) (μsec) (pieces / mm ² ) (nm) Aperture ratio (mg / cm ² ) −−−−−−−−−−−− −−−−−−−−−−−−−−−−−−−−−−−− Example 1 1714 163 0.6 9260 30 0.6 0.03 Example 2 1714 163 0.6 9260 30 0.6 0.02 Example 3 1714 163 0.6 9260 25 0.6 0.18 Comparative Example 1 1714 163 0.6 9260 35 0.6 − −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

Table 2 shows the static friction coefficient (initial stiction) and CSS2 before CSS test of these disks.
The frictional force after 10,000 times was shown. For the CSS test, a thin film head (slider material: Al2O3TiC) having a head flying height of 1.6 μinch and a loadgram of 6 gf was used. The stable flying heights of the CSS zones were all 1.2 μ inches. The experimental conditions were normal temperature and normal humidity. Table-
No. 3, the experiment shown in Table-2 was performed at a temperature of 35 ° C and a humidity of 8
It was performed under the condition of 0%.

[0035]

[Table 2] Table 2 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Initial stiction CSS after 20,000 times (Friction coefficient) Frictional force --------------------------------------------- Example 1 0.18 7gf Example 2 0.24 10 gf Example 3 3.25 25 gf Comparative Example 1 0.198 8 gf ------------------------. -----

[0036]

Table 3 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Initial stiction CSS after 20,000 times (Friction coefficient) Frictional force --------------------------------------------- Example 1 0.20 6gf Example 2 0.27 8gf Example 3 5.15 34gf Comparative Example 1 0.25 21gf ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -----

[0037]

According to the present invention, a protrusion whose tip shape and height are controlled is formed on the surface of a substrate or an underlayer of a magnetic recording medium, and the tip of the protrusion is mechanically textured. It is possible to further reduce the area of the tip of the protrusion, and therefore the contact area between the lower surface of the magnetic head and the surface of the magnetic recording medium is reduced, so that the friction during CSS becomes extremely small, and the surface of the medium of the head is reduced. No sticking will occur at all. In particular, it is possible to obtain a magnetic recording medium exhibiting stable CSS characteristics even in environmental tests such as under high temperature and high humidity.

Further, even if such a protrusion is formed only in the CSS area of the head, the mechanical texture makes the data recording area and the CSS area uniform, so that the average heights of the respective surfaces hardly change. When the head is sought between the data recording area and the CSS area, the fluctuation of the stable flying height of the head is small, and the head crash and the destabilization in the space of the head do not occur.

Furthermore, since the height and density of the protrusions produced by the laser can be controlled as they approach the data zone, the seek between the data recording area and the CSS area of the head can be performed extremely smoothly, and the head The flying height can be reduced. Therefore, it becomes possible to manufacture a high-density magnetic recording medium, which is of great industrial significance.

[Brief description of drawings]

FIG. 1 is a first example of the present invention observed by a surface profiler.
3 is a perspective view showing the shape of a protrusion on the surface of the NiP underlayer of FIG.

2 is a view showing a cross section (cross section a) parallel to the mechanical texture direction of the projection of FIG. 1 and a cross section (cross section b) perpendicular to the mechanical texture direction.

FIG. 3 is a comparative example 1 of the present invention observed by a surface profiler.
3 is a perspective view showing the shape of a protrusion on the surface of the NiP underlayer of FIG.

4 is a view showing a cross section (cross section a) parallel to the circumferential direction of the disk of the protrusion of FIG. 3 and a cross section (cross section b) perpendicular to the circumferential direction of the disk.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Kozu 1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa Mitsubishi Chemical Corporation Yokohama Research Institute

Claims (7)

[Claims] 1. A surface of a substrate or an underlayer of a magnetic recording medium is irradiated with energy rays to form protrusions on the surface of the substrate or the underlayer, and then the surface of the substrate or the underlayer is mechanically textured. After that, a required underlayer, magnetic recording layer or protective layer is formed into a film, which is a method for producing a magnetic recording medium. 2. The energy beam is a pulsed laser,
2. The method for manufacturing a magnetic recording medium according to claim 1, wherein a scanning distance of the pulsed laser on the irradiated surface per irradiation time is ½ or more of a spot diameter of the pulsed laser. 3. An energy beam having a laser power of 500
mW or less, irradiation time per time is 5 μsec or less, and the spot diameter of the focused beam on the irradiated surface is 4 μm or less, which is a pulsed laser, and is relatively relative to the irradiated surface at a scanning speed of 1 m / sec or more. The method of manufacturing a magnetic recording medium according to claim 1, wherein scanning is performed. 4. The thermal conductivity of the substrate or the base layer is 100.
4. The method for producing a magnetic recording medium according to claim 1, wherein the value is Watt / mK or less. 5. The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic head is provided with protrusions only in a region where CSS (contact start and stop) is performed. 6. The method of manufacturing a magnetic recording medium according to claim 1, wherein the output of energy rays is decreased toward the data recording area in the CSS area. 7. The method of manufacturing a magnetic recording medium according to claim 1, wherein the medium is disk-shaped, and the energy rays are swept in a spiral shape.