JPH1196535A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which facilitates the control of projection height in the technique of forming projections by irradiating the ground surface metallic layer formed on a glass substrate with a laser beam, has ground surface layers of good surface characteristics without the execution of a smoothing treatment and has an excellent glide height and CSS characteristics and a process for producing the same. SOLUTION: This magnetic recording medium consists of the first ground surface layer 3 consisting of a Cr30Nb alloy, the second ground surface layer 4 consisting of an Ni33P alloy, the Cr ground surface layer 5, a magnetic layer 6 consisting of a CoCrTa alloy, a carbon protective layer 7 and a lubricant layer 8 on a glass substrate 2. The first ground surface layer 3 is harder to be processed by the laser than the second ground surface layer 4 and the projections 41 by the irradiation with the laser are formed on the second ground surface layer 4. Texture is constituted in accordance therewith.

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 such as a magnetic disk drive, and more particularly, to improving the sliding durability between a magnetic disk (hereinafter referred to as HD) and a magnetic head. The present invention relates to a magnetic recording medium and a method for manufacturing the same.

[0002]

2. Description of the Related Art The progress of high-density magnetic recording has been steadily increasing, and the speed of improving the recording density of a hard disk drive (HDD), which was once said to be 10 times in 10 years, has recently been 100 times in 10 years. Voices have also been heard.
HDD is popularly called Winchester style.
The CSS (contact start / stop) method, which basically includes contact sliding between magnetic heads, head floating, and contact sliding, is mainly used.
Although this system is a revolutionary one that has rapidly accelerated the increase in the recording density of HDDs, it has also begun to introduce serious tribological issues. The recent increase in recording density has been accompanied by an increase in disk rotation speed and a proposal for the flying height of the magnetic head, and the demands for sliding durability / stability and smoothness of the HD surface in the CSS method are increasing. It is the present situation.

The key to improving the sliding durability between the magnetic head and the HD lies in the improvement of the material strength and the reduction of the friction coefficient including the lubricating property. Like carbon (DLC) protective film,
Efforts have been made to reduce the coefficient of friction by roughening the HD surface along with various types of applied lubricants. This is called texturing, and is intended to reduce the coefficient of friction by effectively reducing the contact area to increase CSS durability / stability. Roughening is basically forming irregularities having a predetermined range of height difference on the HD surface. This texture processing is an important elemental technology of the HD manufacturing technology.

[0004] The above-mentioned texture technique is, of course, inseparable from the material of the substrate.
In the case of a substrate, a method of forming irregularities by mechanical polishing using polishing powder or the like has been mainly used. For a glass substrate or the like, lithography or an etching technique combining the lithography and the printing technique has been proposed, and some of them have been put to practical use.

[0005] As can be said about texture technology in general,
Efficiency in the process is also a necessary condition along with precise unevenness control, but the two are often in opposition to each other, and in particular, as described above, the increase in the recording density of HDDs is progressing at an amazing speed. Under the circumstances, the conventional technology is not only unable to satisfy a predetermined specification, but also exposes various problems that can no longer be covered by accumulating ideas and improvements. For example, the mechanical polishing method is already near the limit of fine processing control, and fundamental difficulties are encountered not only in the level of unevenness but also in precision control of a texture area which is important in zone texturing and the like. More specifically, there are irregularities (over-polishing, burrs, etc.) that occur at a constant rate and indicate a height difference outside a predetermined range, and blurring of texture boundaries. In addition, although the lithographic method has no problem in terms of precision system, the complexity of the process is inevitable, which is the Achilles' heel in terms of efficiency.

On the other hand, a higher recording capacity and a higher quality of an HDD inevitably include achieving a high degree of cleanliness in an HD manufacturing environment, and removal / removal of various contaminants and dust at a high level.
At present, elimination is the ultimate goal for each process. From this point of view, it is desirable that each step is dry, and there is great expectation for this dry texturing.

[0007] It can be said that an attempt to apply laser light to material processing and measurement started from the beginning of the invention of the laser. However, recent development / development of laser light sources has brought about remarkable improvements in basic characteristics and handling properties, and has shifted from high energy processing to ultra-high energy processing. It forms a wide range of utilization technologies, from fine processing to precision measurement. Laser ablation (erosion) or laser etching, which forms a material by a laser beam or processes a material surface, has been actively studied since the 1980s. Recently attracted interest (eg USP
5062021, JP-A-62-209788, JP-A-3-272018, JP-A-7-182655
JP-A-8-129949). The laser texture technique has an advantage that a crater-like projection can be formed on a substrate at an arbitrary height, interval, and position with good control by laser beam irradiation, and is basically a dry process. JP-A-3-272018 discloses an Nd-YAG laser of Q-switch pulse oscillation (wavelength 1064).
nm, oscillation frequency 12 KHz) and a diameter of 2.5 to 1
Crater-like projections of 00 μm are spaced from 12.7 to 25.4 μ
m is formed on a NiP plated Al substrate.

Until now, NiP plating A using a laser
Effective methods such as the above patents have been proposed as a method of texturing a 1-substrate, and some of the techniques have been successfully commercialized in a mass production stage. However,
It is extremely difficult to simply apply a texture to a NiP-plated Al substrate to a nonmetallic substrate, specifically, a glass substrate. For laser texturing of a NiP plated Al substrate, a normal wave of YAG (wavelength 1.0
6 μm), second harmonic (SHG: SECOND HARMONIC GENE)
RATOR wavelength 0.53 μm) or Ar laser (wavelength 0.33 μm to 0.53 μm) is used, but these wavelengths are not absorbed by silicon oxide (SiO ₂ ) which is a main component of glass. Silicon oxide (Si
This is because the absorption wavelength of O ₂ ) is 0.3 μm or less and 5 μm or more. Therefore, as a method of applying a laser texture to a glass substrate, several methods using a laser having a wavelength within the absorption wavelength range of the silicon oxide (SiO ₂ ) have been proposed. For example,
In Japanese Patent Application Laid-Open No. 6-295433, an ultraviolet laser beam is irradiated on a glass substrate, and a convex portion made of a base paper and a molecular deposit generated by ablation is textured.

[0009]

On the other hand, a technique for applying a laser texture without directly irradiating the glass substrate with the laser beam, that is, projecting the laser beam onto the underlying metal layer formed on the glass substrate. Are being studied. This method has an advantage that the laser used for the NiP-plated Al substrate can be applied since the laser processing target is a metal layer. However, this method has the following problems.

Although fine projections can be formed with low laser beam energy, if the thickness of the underlying metal layer is small, the laser may penetrate the film and reach the glass surface. In this case, the height of the projection is at least five times the height of the non-penetrating portion, which is extremely disadvantageous in reducing the glide height (G / H). The protrusion height can be easily controlled by increasing the thickness of the base metal layer.
This leads to deterioration in S characteristics, low glide height, and electromagnetic conversion characteristics (such as signal output stability and noise). Further, in order to suppress an increase in surface roughness, a smoothing treatment such as polishing of the surface is required.

Therefore, the present invention relates to a technique for forming projections by irradiating a base metal layer formed on a glass substrate with a laser beam, in which the height of the projections is easily controlled and the surface is smoothened without performing a smoothing treatment. It has an underlayer with excellent qualities,
It is an object of the present invention to provide a magnetic recording medium having a low glide height and excellent CSS characteristics and a method for manufacturing the same.

[0012]

According to the present invention, there is provided a magnetic recording medium comprising a glass substrate, on which a metal underlayer, a magnetic layer and a protective layer are sequentially laminated, wherein the metal underlayer is provided with a laser texture and a metal underlayer. The object has been solved by a magnetic recording medium characterized in that the ground layer comprises a first underlayer from the glass substrate side and a second underlayer having a different composition from the first underlayer. Further, the magnetic recording medium of the present invention is a method of manufacturing a magnetic recording medium in which a metal underlayer, a magnetic layer, and a protective layer are sequentially laminated on a glass substrate. And forming a second underlayer having a composition different from that of the first underlayer, and then irradiating the surface thereof with a laser beam.

In the present invention, the first underlayer comprises the second underlayer.
It is desirable that the workability with respect to the laser beam is more difficult than that of the underlayer. This is because even if the laser beam penetrates the second underlayer which is easy to process, the first underlayer is hardly processed because it is difficult to process, and the laser beam does not penetrate to the glass substrate. In this case, although the first underlayer is difficult to process, it is much easier to process than a glass substrate, so even if a laser beam penetrates to the first underlayer, a projection of an abnormal height may be formed. It does not occur.

The workability with respect to the laser in the present invention is determined not by an absolute evaluation but by a relative evaluation. That is, it suffices that the second underlayer is easier to process than the first underlayer. Underlayers A, B, and C have processing characteristics of A>B>
Assuming that the workability is easy in the order of C, the combination according to the present invention includes a first underlayer C, a second underlayer A, a first underlayer C, a second underlayer B, a first underlayer B, a second underlayer, and a second underlayer. Underlayer C,
The following three combinations are conceivable. In this case, C can be classified as a first underlayer and A can be classified as a second underlayer, but B belongs to both the first and second underlayers. As can be seen from this, in the present invention, the metal of the first underlayer and the metal of the second underlayer are not specified, but can be understood only in a relative relationship.

As a specific evaluation of workability, a case where a metal film is formed on a glass substrate with the same film thickness and then a laser beam is irradiated under the same conditions (output, beam diameter, pulse width, processing speed). The height of the protrusion is measured, and the higher the protrusion height is, the easier the processability is compared with the two types of metals, and the lower the protrusion height is, the harder the processability is defined. The first underlayer may be any material that is difficult to process as compared with the second underlayer. However, when the laser beam is irradiated under the same conditions as the above except for the output, the output value at which the protrusion heights are equal becomes smaller. Desirably, the range is 1.1 to 10 times. If the output value is less than 1.1 times, the difference in processing characteristics between the first underlayer and the second underlayer is too small,
This is because there is a possibility of being treated as a single layer in a simulated manner, and if it is 10 times or more, the workability of the first underlayer approaches that of glass, and the same behavior as in the case of the glass surface is exhibited.

In the magnetic recording medium of the present invention, in order to sufficiently fulfill the function as a texture and to meet the demand for a low glide height, the height of a projection formed by laser beam irradiation is 100 to 300 °. Is desirable. When judging the height of the protrusion, the height of the protrusion becomes abnormally high when the laser beam reaches the glass substrate through the base layer. In this case, the height of the protrusion in the present invention is used. Excluded. Also, the first
It is desirable that the thickness of the second underlayer be 10 to 2000 °. If the thickness is less than 10 °, the thickness is too thin to form projections, and if it exceeds 2000 °, the surface roughness increases as the thickness increases, and the CSS characteristics, the low glide height, and the electromagnetic conversion characteristics ( This is because deterioration in signal output stability and noise) is caused.

The metals used for the first and second underlayers in the present invention include Ti, V, Cr, Mn, Fe, C
o, Ni, Cu, Zn, Zr, Nb, Mo, Te, R
u, Rh, Pd, Ag, Cd, Hf, Ta, W, Re,
Simple substances of Os, Ir, Pt, Au, Hg, Al, Si, and P or alloys thereof are listed, and preferable combinations include the following combinations. First underlayer: Cr-1 to 50 at.% Nb alloy Second underlayer:
Ni-1-50at.% P alloy First underlayer: Cr-1-50at.% Ti alloy Second underlayer:
Ni-1-50at.% P alloy First underlayer: Cr-1-50at.% Ti alloy Second underlayer:
Cr-1 to 50 at.% Nb alloy The first and second underlayers in the present invention include:
The first underlayer is not limited to a single layer (metal), and may have a structure in which two different alloy layers are laminated.

In the present invention, any laser having a wavelength capable of absorbing metal can be selected, but it is preferable to use a laser having high repetition and high stability.
That is, a semiconductor laser (LD: LASER DIODE) excitation Y
AG pulse laser, LD pumped YAG-SHG pulse laser, LD pumped YAG-continuous oscillation (CW: CONTNUOUS WAV
E) Laser, LD pumped YAG-SHG-CW laser, C
It is desirable to use a W-argon laser. Note that C
When a W laser is used, an electro-optic effect modulator (Ele
ctro-Optic-Modulator, E for short
OM) or an acousto-optic modulator (Acoustic-O)
It is desirable that the laser beam be pulsed by an external modulator such as a optic-modulator (AOM for short).

The EOM is capable of continuously changing the laser output by changing the optical path of an incident continuous wave laser by applying a voltage to an optical crystal and utilizing the electro-optic effect of changing the refractive index of the crystal. Modulator. In addition, the AOM continuously changes the laser output transmitted straight through by introducing an ultrasonic wave from the outside into the optical crystal and changing the analysis angle of the incident continuous wave laser beam using the optical elasticity effect of the crystal. Modulator that can be.
Any of the modulators described above uses the MH signal based on an externally input signal.
Laser output modulation in the z band is possible, and the output modulation can be arbitrarily changed.

The outline of the laser processing apparatus used in the present invention will be described with reference to FIG. In FIG. 2, when a CW laser is used as a laser beam, a laser beam is oscillated from a laser transmitting device 11 and this beam is transmitted to an external modulator 12.
Pulsed by The pulsed laser beam is processed by a lens 13 into a disc-shaped substrate 14 which is a workpiece.
It is collected on the surface of. The substrate 14 is rotated by a spindle 15, and moves in one axial direction (the left-right direction in the figure) to form minute projections in the circumferential direction of the substrate 14. The height of the microprojections depends on the energy of the irradiated laser beam, the beam diameter, the pulse width, and the substrate 1 relative to the laser beam.
4 can be adjusted by the relative rotation speed or the like.

When a pulse laser is used, the processing can be performed in the same manner as described above by replacing the laser transmission device 11 with a pulse laser oscillation device and removing the external modulator 12. In the above description, an example in which the spindle moves in one axis direction has been described. However, the same processing can be performed by moving the lens 13 in one axis direction instead of the spindle.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments. LD excitation YAG-S with wavelength 532nm and output 5W
The HG-CW laser was repeatedly irradiated with a pulse beam having a frequency of 200 kHz and a pulse width of 100 to 800 ns by an external modulator EOM to a base film formed on a glass substrate through a lens having a beam diameter of 7 mm and an NA of 0.13. In addition,
The glass substrate was rotated at a constant peripheral speed of 4 m / s during laser beam irradiation.

A glass substrate having a surface roughness of about 6 ° was used as a glass substrate, and a film having a composition shown in Table 1 was formed as a base film by a sputtering method.

Table 1 shows the thickness of the underlayer, the surface roughness after the underlayer was formed, the laser power on the processed surface of the laser beam to be irradiated, the height of the protrusion, the presence or absence of abnormal protrusions, and the height of abnormal protrusions. Also shown. The surface roughness was measured by AFM (Atomic Force).
Microscope, Atomic Force Microscope)
The height of the projections was measured using TENCOR P-12 (trade name of Tencor).

[0025]

[Table 1]

Each of the alloys used for the underlayer was formed on a glass substrate in a thickness of 1000.degree. With an output of 300 mW and a beam diameter of 7 m.
m, a pulse width of 400 ns, and a processing speed of 4 m / s, the heights of the projections formed are as shown in Table 2. The Cr-30 at.% Ti alloy shows the most difficult workability,
The i-33at.% P alloy shows the easiest workability.

[0027]

[Table 2]

In all of Examples 1 to 6 according to the present invention, the surface roughness after the formation of the underlayer was 10 ° or less, and the occurrence of abnormal projections was not observed. In contrast, the comparative example
When the surface roughness is small, abnormal protrusions have occurred (Comparative Examples 1 to 3 and Comparative Examples 5 to 8). In order to eliminate the occurrence of abnormal protrusions, the thickness of the underlying layer is increased, and In addition, the surface roughness exceeds 10 ° (Comparative Examples 4 and 8).

Following the substrate shown in Table 1, the substrate temperature 2
At 00 ° C., a nonmagnetic underlayer of Cr 100 nm, a magnetic layer of Co-12 at.% Cr-2 at.% Ta alloy 20 nm,
As a protective film, 20 nm of carbon is sequentially formed by a sputtering method, and further, PFPE (perfluoropolyether) is formed.
A magnetic recording medium was prepared by coating a system lubricant. FIG. 1 shows a schematic partial cross-sectional view of the magnetic recording medium of the first embodiment. As shown in FIG. 1, a magnetic recording medium 1 of Example 1 has a first underlayer 3 made of a Cr-30 at.% Nb alloy and a second lower layer made of a Ni-33 at. Underlayer 4, Cr underlayer 5, Co-12at.% Cr-2a
It has a cross-sectional structure in which a magnetic layer 6 made of t.% Ta alloy, a carbon protective layer 7, and a lubricant layer 8 made of PFPE are sequentially laminated, and has a texture based on the protrusions 41 formed on the second underlayer 4. Is configured.

As in this embodiment, the magnetic properties can be improved by laminating a Cr underlayer on the first and second underlayers. Glide height characteristics and CSS characteristics (friction value after 10,000 times of CSS) were evaluated using the obtained magnetic recording medium. The results are shown in Tables 3 and 4.

[0031]

[Table 3]

[0032]

[Table 4]

From Table 3, the glide height of the magnetic recording media according to Examples 1 to 6 is 1.0 to 1.2 μinch, while Comparative Examples 1 to 3 and Comparative Examples 5 to 8 in which abnormal protrusions are generated.
In Comparative Examples 4 and 8 having no protrusions, the thickness was 1.5 μinch or more due to high surface roughness. As for the CSS characteristics, Examples 1 to 6, Comparative Example 4,
In No. 8, the magnetic recording medium of Comparative Examples 1 to 3 and Comparative Examples 5 to 8 in which abnormal protrusions occurred was in the level of 0.4 to 0.5, but a head crash occurred.

Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and may be embodied in any form unless the description in the claims is changed. it can. For example, an underlayer, a magnetic film, a protective film, a lubricant, and the like formed on a glass substrate are not particularly limited to the material and composition, the film forming method, and the like.
Known materials and methods can be appropriately selected and used in combination.

[0035]

As described above, according to the present invention,
The protrusions can be formed by laser without increasing the surface roughness and without causing abnormal protrusions. This makes it possible to obtain a magnetic recording medium having a low glide height and good CSS characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic partial sectional view of one embodiment of the magnetic recording medium of the present invention.

FIG. 2 is a diagram illustrating an example of a laser processing apparatus applicable to the present invention.

[Explanation of symbols]

 Reference Signs List 1 magnetic recording medium 2 glass substrate 3 first underlayer 4 second underlayer 41 protrusion 5 Cr underlayer 6 magnetic layer 7 protective layer 8 lubricant layer

Claims (6)

[Claims] In a magnetic recording medium in which a metal underlayer, a magnetic layer, and a protective layer are sequentially laminated on a glass substrate, a laser texture is applied to the metal underlayer, and the metal underlayer is a first layer from the glass substrate side. And a second underlayer having a composition different from that of the first underlayer. 2. The magnetic recording medium according to claim 1, wherein the first underlayer is harder to process a laser beam than the second underlayer. 3. The thickness of the first and second underlayers is 10
The magnetic recording medium according to claim 1, wherein the angle is Å2000 °. 4. A method for manufacturing a magnetic recording medium, comprising sequentially laminating a metal base layer, a magnetic layer, and a protective layer on a glass substrate,
A first underlayer from the glass substrate side as a metal underlayer;
A method for manufacturing a magnetic recording medium, comprising: forming a second underlayer having a composition different from that of the first underlayer, and irradiating the surface with a laser beam. 5. The method for manufacturing a magnetic recording medium according to claim 4, wherein the first underlayer is harder to process the laser beam than the second underlayer. 6. The thickness of the first and second underlayers is 10
The method of manufacturing a magnetic recording medium according to claim 4, wherein the angle is Å2000 °.