JPH11213387A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the variance in height of a bump and to shorten the processing time in a texture processing where pulse laser light obtained from continuously oscillated laser light is used to form the bump on a glass substrate. SOLUTION: At the time of irradiating a glass substrate 8 with a converged light spot, the irradiation section of the converged light spot is preliminarily formed in an ellipse, and its minor diameter ds is set in the peripheral direction of the glass substrate 8. The converged light spot is scanned relatively in the direction of the minor diameter from the irradiation start point shown by a solid line to the irradiation end point shown by the double dotted chain line through the irradiation halfway point shown by the alternate short and long dash line. As the result, the irradiated area is approximately circular to form a false circle-shaped conic bump. The pulse width and the ellipticity are optimized without increasing the power density of laser, thereby realizing a prescribed bump height and forming a bump plane into a circle regardless of the increase of the relative rotation speed of the substrate 8.

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, and more particularly to a texture processing step using a laser beam for reflecting an uneven surface on the medium surface.

[0002]

2. Description of the Related Art In a fixed magnetic disk drive, when a disk is stopped, a magnetic head slider is in contact with a CSS (contact start / stop) area on the inner peripheral side of the disk. In this case, a CSS method is used, in which the data is slightly floated from the surface to read or write information in the data area on the outer peripheral side of the disk. In the CSS area, head contact sliding, head floating, and head contact sliding are repeatedly performed. Therefore, in order to increase the recording density, it is necessary to rotate the disk at a high speed and reduce the head flying height. Durability and stability of sliding are required. In order to satisfy these requirements, it is required to reduce the friction coefficient by roughening the disk surface, in addition to the properties of the protective film and the lubricating film on the disk surface.

[0003] The surface roughening treatment of the disk surface is called texturing (texturing), which imparts a predetermined uneven shape to the substrate surface. An aluminum substrate is generally used for a magnetic disk, but in recent years, a glass substrate having excellent flatness, rigidity, and the like has been used. In the case of an aluminum substrate, mechanical polishing is mainly used as a texture processing method, but in the case of a glass substrate, lithography, etching using a printing technique, or a sputtering technique called a film texture is known.

[0004] In recent years, dry textures that can be textured without the above-mentioned wet or complicated process have become the mainstream. That is, in the dry texturing, a laser beam is condensed, a minute spot is irradiated on a substrate surface by pulses, and the substrate is melted and solidified to generate an uneven portion (bump). A predetermined bump shape can be obtained by selecting a laser type, a wavelength, a laser output, and the like according to the surface material of the substrate.

[0005] This laser texturing is performed using Ni
The aluminum substrate provided with a P plating film is a technique generally used, and various bump shapes can be obtained. 7A to 7D are enlarged cross-sectional views showing cross sections of different bump shapes. These bump shapes can be determined by a combination of the energy density (or power density) of the laser, the pulse width and wavelength of the laser, the relative speed between the substrate and the laser beam, and the like.

For example, in the case of an aluminum substrate coated with NiP plating, as a processing condition for forming a bump, a laser type is a Q switch pulse oscillation type of a Nd: YVO ₄ laser, a wavelength is 1.06 μm, and a pulse width is 20 to 150. nsec
(~ 350nsec), laser beam focusing spot diameter is 10
~ 30μm, laser pulse energy 1 ~ 10μJ /
p, pulse repetition frequency in the range of 10 to 100 KHz, bump diameter φ (in the case of FIG.
(For (b) to (d), the distance between the outermost protrusion vertices)
Is 5 to 25 μm, and the bump height h (the distance between the substrate surface and the top of the protrusion in the case of FIG. 7A, the distance between the substrate surface and the highest protrusion apex in FIGS. 7B to 7D) is 70-1000 mm bumps are typically formed.

However, in recent years, as the demand for high recording density and high reliability has increased, when forming these bumps,
For example, accuracy requirements for variations in the bump height h are increasing. The variation in the bump height h is caused by variations in the laser output on the laser irradiation side and subtle differences in the surface properties (surface roughness, component concentration of the NiP plating film, degree of surface oxidation) on the substrate side.

Normally, the peak value of the pulse laser output from the above-mentioned Q-switch pulse oscillation type laser (solid laser such as Nd: YVO ₄ laser, Nd: YAG laser, Nd: YLF laser) is from several tens of watts to several Ten
0 W. For example, in the case of an aluminum substrate with a NiP plating film, when forming a bump having a bump diameter φ of 10 μm and a bump height of 280 °, the peak value of the pulse laser output with a laser output energy of 3 μJ / p and a pulse width of 150 nsec is 20 W. . In this case, the laser irradiation power density is as high as 2.7 × 10 ⁷ W / cm ² . Bump (height
The number of tens of thousands formed on the CSS region of the substrate
Although the number of bumps reaches 200,000, the variation in bump height h (σ /
h and σ are standard deviations) of 4 to 5%. In the case of a Q-switch pulse oscillation type laser, the average laser output varies even within a high performance type by ± 1 to 3% (when operated continuously for 24 hours or more). In addition, considering the regular laser maintenance for managing the bump height h and the frequency of sampling inspections for bump quality control, this is one of the factors that increase the production cost.

On the other hand, in the laser texturing method on a glass substrate, a thin film (for example, a NiP plating film) is provided on a glass substrate, and a laser is irradiated on the film to form a bump (hereinafter referred to as a laser thin film). There is a method of directly irradiating a glass substrate with a laser to form a bump (hereinafter, referred to as a laser direct processing method). The laser thin film addition method uses the conventional NiP
Since it is almost similar to the method of forming a bump on a plated aluminum substrate, it is advantageous in terms of technical reliability. Further, the laser direct processing method is advantageous in that the number of steps is reduced as compared with the laser thin film addition method. Hereinafter, the laser direct processing method will be described.

The laser used for the laser direct processing method includes a carbon dioxide (CO ₂ ) laser, Nd: YAG
There are second harmonic, third harmonic, fourth harmonic, argon laser, and excimer laser of laser / Nd: YVO ₄ laser / Nd: YLF laser. The material of the glass substrate is selected so as to easily absorb the laser light.

In particular, the above CO ₂ laser (wavelength 10.6 μm)
Lasers other than m) are all visible light lasers and ultraviolet lasers in the wavelength range of 0.532 μm to 0.248 μm, and various glass substrates that easily absorb laser light in this band are provided by various manufacturers.

However, the laser direct processing method on a glass substrate requires several times to more than ten times the laser output energy as compared with the case of forming a bump on an aluminum substrate with a NiP plating film. The above-mentioned second harmonic (wavelength 0.532 μm) and third harmonic (wavelength 0.355 μm)
), In the case of the fourth harmonic (wavelength 0.266 μm), it is difficult to secure laser output stability, and the laser output stability is (±
(2-3%)-(± 10 several%), the worse the higher the order of the laser, and the variation in bump height h is (± 5-7%)
~ (± 20 several percent).

In the laser direct processing method, for example, when an excimer laser is used, a discharge excitation laser which can be used for industrial purposes has a problem in terms of pulse oscillation life. That is, from the viewpoint of forming tens of thousands to two hundreds of thousands of bumps on only one surface of the substrate, it cannot be used for industrial purposes. However, taking advantage of the advantage that the beam cross-sectional shape of the excimer laser has a large rectangular area, it is possible to propose a method in which a large number of holes are formed in a mask in advance and a large number of bumps are formed at once by a mask projection method. However, at present, the uniformity of the laser power distribution of the rectangular cross section beam has not been technically overcome.

In the case of a CO ₂ laser, since it is a near-infrared laser having a long wavelength (wavelength 10.6 μm), the diameter of the condensed spot is reduced to a small size (a bump of φ10 μm) due to the demand for a higher density of bumps and a lower bump height. Diameter) is difficult.

By the way, in the case of forming a bump on a glass substrate by a laser direct processing method, the above-mentioned Q-switch pulse oscillation type laser is, for example, Nd: YA.
When bumps are formed at the second harmonic, the third harmonic, and the fourth harmonic of the G laser, a cone-shaped (projection-shaped) bump having a bump diameter of φ10 μm and a bump height of 100 to 300 ° can be formed. The bumps do not have a variety of bump shapes as in the case of an aluminum substrate with a NiP plating film, but are cone-shaped bumps or V-shaped hole-shaped bumps as shown in FIG. Usually, cone-shaped bumps are predominant in terms of the degree of freedom in processing conditions and quality. Therefore, unless stated otherwise:
The bump shape is a cone shape.

In the laser direct processing method, in the case of an Ar laser (wavelength: 0.515 μm), which is a visible light laser, a continuous wave laser beam is pulsed by an EOM (electro-optical modulation) pulse modulator, and then the pulse laser is emitted. Light is condensed and irradiated on the glass substrate.
In this EOM method, the pulse width can be arbitrarily varied from several tens nsec to 0.999 sec, and the pulse repetition frequency is also from 1 Hz to several tens M
Variable up to Hz. Also, the variation of the bump height h is
It is extremely small compared to a Q-switch pulse oscillation type laser. Continuous oscillation type laser output stability ± 0.2%
This is because the level can be made extremely small. Furthermore, this E
Since the OM method is comparable to high-speed pulse oscillation, the processing time can be reduced in texture processing for forming tens of thousands to 200,000 bumps in the CSS region.

[0017]

However, in practice,
High-speed processing is possible for aluminum substrates, but high-speed processing is difficult for glass substrates, as described above, because laser output energy is several times to ten and several times higher than aluminum substrates. . That is, since the peak value of the output of the pulse laser light obtained from the continuous wave laser light is only about 2 to 3 W at most, in order to actually secure the output energy of the laser necessary for forming the bump, A pulse width of several μsec to 30 μsec is required for the Q-switched pulse laser.
10 nsec to several 100 nsec). In the case of the current commercial Ar laser for industrial use, the maximum output at the oscillator level is about 5 W, and is attenuated on the optical path passing through the EOM modulator, power controller, mirror, and condenser lens. The effective laser power that can be substantially irradiated falls to 1 to 1.5 W. Therefore, for example, when forming a bump diameter φ3 μm and a bump height 280 °, the processing conditions are a peak output of 1 W, a pulse width of 20 μsec, and an output energy of 20 μJ / p.

As described above, when the pulse width becomes longer, CS becomes larger.
The texture processing time for the S region becomes slow. That is, C
In the method of forming a bump on the SS region, a pulse laser is focused and irradiated while rotating the glass substrate. When the rotation speed is high, the distance over which the substrate surface moves relatively within the laser pulse width is long. As a result, as a result, an asymmetric bump shape of an elliptical shape or an elliptical shape is formed, so that the rotation speed cannot be increased, and therefore, the texture processing time is reduced. For example, when the rotation speed of the substrate is 100 RPM, the relative movement distance at a position 20 mm in the radial direction from the center of the substrate (disk) is about 4.2 μm. Here, if the bump shape is oval, CSS
Increases the friction coefficient.

In view of the above problems, it is an object of the present invention to reduce variations in bump height in texture processing for forming bumps on a glass substrate using pulsed laser light obtained from continuous wave laser light. It is another object of the present invention to provide a method for manufacturing a magnetic recording medium capable of realizing a reduced texture processing time.

[0020]

Means for Solving the Problems In order to solve the above-mentioned problems, the means adopted by the present invention is to convert a continuous wave laser beam into a pulse by electro-optic modulation, and rotate the pulse laser beam relatively. In a method for manufacturing a magnetic recording medium including a texture processing step of forming a bump by irradiating a converging spot on a surface of a substrate, an irradiation section of the converging spot has an elliptical shape whose minor axis is aligned in a circumferential direction of the glass substrate. It is characterized by being.

Since the substrate relatively moves in the circumferential direction within the pulse width, the condensed spot is temporarily scanned in the relatively short diameter direction. Because the minor axis of the cross section is aligned in the circumferential direction of the glass substrate,
During that time, the focused spot is dragged in the minor axis direction,
As a result, the irradiation area has a substantially circular shape. For this reason, the melting and solidification of the glass material is promoted around the substantially circular irradiation region, and therefore, a pseudo circular cone-shaped bump is formed. By optimizing the pulse width and the ellipticity without increasing the power density of the laser, it is possible to achieve a predetermined bump height and a circular bump planar shape even when the relative rotation of the substrate is accelerated. The texture processing time can be shortened, and the productivity can be greatly improved.

When the difference between the major axis and the minor axis of the elliptical shape has a relation approximately equal to the product of the pulse width of the pulsed laser beam and the relative peripheral velocity at the irradiation point of the glass substrate, light is condensed. Since the irradiation area of the spot can be made closer to a pseudo circular shape, it is easy to make the bump planar shape circular.

In order to obtain a condensed spot having an oval irradiation cross section, it is preferable to use a parallel beam cross section deforming optical system after the electro-optic modulator. Although an astigmatism-type condensing lens system can obtain a condensed spot with an oblong irradiation cross section, adjustment of the distance from the substrate and the focal length becomes complicated. The use of the collimated beam cross section deforming optical system does not need to change the condenser lens system, which also facilitates maintenance.

As the parallel beam section deforming optical system, an obliquely incident prism system, a toric lens system or the like can be used, but it is preferable to use a cylindrical lens optical system. The optical configuration is simple, and the major axis and minor axis of the desired size of the irradiation cross section ellipse can be created relatively easily.

[0025]

FIG. 1 is a block diagram showing a laser processing apparatus used in a method for manufacturing a magnetic recording medium according to an embodiment of the present invention, and FIG. 2A shows a cylindrical lens optical system in the laser processing apparatus. Plan view, FIG. 2
(B) is a front view showing the cylindrical lens optical system.

As shown in FIG. 1, a laser processing apparatus includes a continuous oscillation type laser oscillator (for example, an Ar laser oscillator) 1 and a circular cross section (diameter D) emitted from the laser oscillator.
₀ ) a power stabilizer 3 for stabilizing the laser output by passing a continuous laser beam 2a, and a pulse for pulsating the continuous passing beam 2b with an arbitrary pulse width and a pulse repetition frequency by electro-optic modulation (EOM). The modulator 4, a cylindrical lens optical system 5 for changing the circular cross section of the pulse laser 2 c into an elliptical shape or an elliptical shape, and the horizontal emission beam 2 d of the cylindrical lens optical system 5 is vertically deflected. And a condensing lens 7 for condensing the reflected beam 2e and irradiating the condensed beam 2f with a spot on the surface of a disk-shaped glass substrate 8 rotated by a spindle motor 9. . The irradiation cross section of the condensed beam 2f has an elliptical shape (elliptical shape) whose minor axis is aligned in the circumferential direction of the glass substrate 8. Therefore, the major axis of the oval shape is aligned in the radial direction of the glass substrate 7.

The cylindrical lens optical system 5 of the present embodiment includes:
As shown in FIG. 2, the incident-side cylindrical lens (cylindrical lens) L _1, which the consist exit side cylindrical lens L ₂ Metropolitan parallel, the X-axis one-dimensional converting a narrow collimated beam into a thick collimated beam collimator (beam an expander), so as to form a Kyokokoro beam between the objective lens serving as lens L ₁ and the collimator lens serving as a lens L _2,
The focal point of the lens distance lens L ₁ distance f ₁ and the lens L ₂
Is set to the sum of the focal length f ₂ and the focal length f ₂ . Incident beam 2c
The expansion magnification for the beam diameter of the meridional ray (the ray included in the plane including the principal ray and the optical axis) is f ₂ / f ₁
(> 1), and the sagittal ray (the ray included in a plane orthogonal to the plane including the principal ray and the optical axis) is aligned with the generating line of the cylindrical lens. Therefore, the beam cross-section of the exit beam. 2d minor axis D _S
(= D ₀ ), and has an elliptical shape with a long diameter D _L (= D ₀ f ₂ / f ₁ ).

Here, generally, the focused spot diameter d ₀ of the laser beam after passing through the focusing lens is given by the following equation. d ₀ = (Kfλ) / D (1) where K is a multi-mode coefficient (a value determined by the inherent characteristics of the laser oscillator) D is the diameter of the laser beam before entering the condenser lens f is the diameter of the condenser lens The focal length λ is the wavelength of the laser light. From this equation, the focused spot diameter d ₀ of the laser light is inversely proportional to the luminous flux diameter D of the incident laser light. Therefore, in this example,
The major axis of the incident beam 2e of the condenser lens 2e is
Are set so as to be aligned in the circumferential tangent direction, and the minor axis is aligned in the radial direction of the glass substrate 8.

As a result, the minor axis d _S and major axis d _L of the condensed spot irradiated on the glass substrate 8 are given by the following equations. d _S = (Kfλf ₁ ) / (D ₀ f ₂ ) (2) d _L = (Kfλ) / D ₀ (3) The minor diameter d _S of the irradiation cross-section of the elliptical condensed spot is Since the substrate 8 is aligned in the circumferential direction, the substrate 8 relatively moves in the circumferential direction within the pulse width t, and as shown in FIG.
In the meantime, the condensed spot is temporarily scanned relatively in the minor axis direction from the irradiation start time indicated by the solid line to the irradiation end time indicated by the two-dot chain line after the irradiation halfway indicated by the dashed line. In the meantime, the condensed spot is dragged in the short diameter direction, and as a result, the irradiation area becomes substantially circular, so that the melting and solidification of the glass material is promoted centering on the substantially circular irradiation area, and therefore, pseudo A circular cone-shaped pump is formed.

In order to obtain a substantially circular irradiation area, it is desirable to satisfy the following equation, where V is the relative peripheral velocity at the spot irradiation position of the glass substrate 8. _{Vt = d L -d S ... (} 4) where, Vt is the relative movement distance, that is, dragging a length of the focusing spot, d _L -d _S is the difference of the major axis and the minor axis.
The peripheral velocity V can be considered to be substantially constant in the CSS area (the area on the inner peripheral side of the substrate).

If the trailing length of the focused spot exceeds the minor axis, the focused spot at the start of irradiation and the focused spot at the end of irradiation do not overlap, and the power density of the laser is densely concentrated on the glass material. It becomes difficult to do. In such cases,
It is necessary to suppress the drag length Vt to less than the minor axis, and in such a case, the following equation is established.

D _L −d _S <d _S (5) Accordingly, it can be said that it is also effective to keep the ellipticity (ellipticity) = f ₂ / f ₁ within ₁ or 2.

Further, since the power density at the center of the focused spot size of the laser beam is the largest and the power at the periphery is low, if the power density at the center of the substantially circular irradiation area is increased as much as possible, It is easy to obtain a perfect circular cone-shaped bump with a small diameter. In such a case, if the central part of the focused spot at the start of the irradiation is located around the focused spot at the end of the irradiation, the power density at the center of the substantially circular irradiation area can be increased.

In such a case, the following equation is established.

D _L −d _S <d _S / 2 (6) Accordingly, the ellipticity (ellipticity) = f ₂ / f ₁ is calculated as ₁ to 3/2.
It can be said that it is effective to keep it within.

FIG. 4A is a plan view showing another cylindrical lens optical system in the laser processing apparatus.
(A) is a front view showing the cylindrical lens optical system.

The cylindrical lens optical system includes a one-dimensional Y-axis collimator 5a and a one-dimensional X-axis collimator 5b.
Consisting of Y-axis one-dimensional collimator 5a consists exit side cylindrical lens L ₄ Metropolitan parallel thereto an incident-side cylindrical lens L _3, the lens L ₃ and the lens L ₄
Between so as to form a Kyokokoro rays, have set the lens distance between the sum of the focal length f ₄ of the focal length f ₃ and lens L ₄ of the lens L _3. The expansion magnification of the beam diameter of the meridional light beam of the incident beam 2c is f ₄ / f ₃ (<1), and the expansion magnification of the sagittal light beam is 1. For this reason,
Beam cross-section of the exit beam in the Y-axis one-dimensional collimator 5a is short diameter D _S of the Y-axis direction is D ₀ f ₄ / f _3, the long diameter D _L of the X-axis direction has an elliptical shape is D ₀ .

The one-dimensional X-axis collimator 5b
An incident-side cylindrical lens L ₅ which is perpendicular to the exit side cylindrical lens L ₄ of the shaft 1 dimensional collimator 5a,
It consists exit side cylindrical drain lens L ₆ Metropolitan parallel, so as to form a Kyokokoro beam between lens L ₅ and the lens L _6, the focal length f ₅ of the lens of the inter-lens distance lens L ₅ L ₆ Is set to the sum of the focal length f ₆ and Expansion magnification of beam diameter of Merijionru ray of the incident beam of lens L ₅ is _{f 6 / f 5 (> 1} ), extended magnification in the sagittal ray is 1.

As a result, the beam cross section of the exit beam 2d from the X-axis one-dimensional collimator 5b has a minor axis D in the Y-axis direction.
_S ′ is D ₀ f ₄ / f ₃ , and the major axis D _L ′ in the X-axis direction is an elliptical shape of D ₀ f ₆ / f ₅ . Thus, ovality of the elliptical shape is _{f 3 f 6 / f 4 f} 5. When such a cylindrical lens optical system is used, both the minor axis and the major axis can be deformed, and it is easy to select the optimal oblong diameter.

The outgoing beam 2d is reflected by the reflector 6 and passes through the condenser lens 7, and the condensed spot of the condensed light beam 2f is irradiated on the glass substrate 7. And the major axis is aligned in the radial direction.

According to the cylindrical lens optical system shown in FIG. 4, the short diameter d _S ′ of the condensed spot applied to the glass substrate 8
And the major diameter d _L ′ are given by the following equation. d _S ′ = (Kfλf ₅ ) / (D ₀ f ₆ ) (7) d _L ′ = (Kfλf ₃ ) / (D ₀ f ₄ ) (8) Short diameter d _S ′
Are aligned in the circumferential direction of the glass substrate 8, so that even if a condensing spot is dragged in the minor diameter direction, the resulting irradiation area becomes a substantially circular shape. , A pseudo circular cone-shaped pump is formed.

FIG. 5 is a graph showing the relationship between the pulse width (time per pulse) of the laser pulsed by the EOM modulator and the height h of the cone-shaped pump formed at this time.

As can be seen from this figure, the bump height h depends on the laser power density. When the laser irradiation time, that is, the pulse width t becomes 5 μsec or more in the plot, the bump height h gradually increases monotonically. Accordingly, since the bump height h is substantially uniquely determined by the pulse width t, variations in the bump height h can be suppressed. The required bump height h is about 280 ° in the plot, and the optimal pulse width t is 20 μsec.

FIG. 6 is a plan view showing a pump shape formed when the pulse width is changed. FIG. 6 (a) shows a transition of the pump shape by the conventional laser irradiation method without using the cylindrical lens optical system 5, (B) shows the transition of the pump shape by the laser irradiation method of the present embodiment using the cylindrical lens optical system 5.

In the conventional irradiation method, a bump having a substantially circular planar shape is formed when the pulse width t is between 5 μsec on the plot and 9 μsec on the plot, but the pump height h is about
When the pulse width t is 15 μsec or more in the plot, the bump height is increased, but the bump has an elliptical shape extending in the circumferential direction or a track-shaped elliptical shape. Therefore, in the conventional irradiation method,
In order to form a planar circular bump so that the bump height h is about 280 mm with a pulse width of 20 μsec, the rotation speed of the glass substrate must be reduced and set to a low speed, and the laser power density is not increased In principle, high-speed rotation of the glass substrate is impossible in principle.

On the other hand, in the irradiation method of this embodiment, the pulse width t
Is between 5 μsec on the plot and 15 μsec on the plot.
Within the pulse width, the trailing length of the converging spot is not enough, so that a bump having a substantially elliptical flat surface is formed, and since the laser power density is still low, it becomes about 150 mm or less, whereas the pulse width t However, in the vicinity of 20 μsec in the plot, the drag length becomes necessary and sufficient, a substantially circular bump is formed on a plane, and the laser power density is sufficient, so that the pump height h becomes about 280 °. Therefore, in this irradiation method,
High-speed rotation of the glass substrate becomes possible without increasing the laser power density.

Hereinafter, a description will be given using specific numerical values. C
When bumps are formed in the SS area, the rotation speed of the glass substrate
Assuming 100 RPM, a peripheral velocity of 125.6 mm / sec at a radius of 20 mm from the substrate (disk) center, and a pulse width t = 20 μsec, the relative movement distance (dragging length) Vt is about 4.2 μm.
m. For example, in the case of bump formation by the conventional irradiation method, the bump diameter per pulse at the time of stop (at the time of non-rotation) is
If it is 10 μm, a pump formed by rotating the substrate at a rotation speed of 100 RPM has an elliptical shape having a width (minor axis) of 10 μm and a length (major axis) of 14.2 μm. On the other hand, in the present irradiation method, when irradiating a condensed spot having an oval cross section whose minor axis is aligned in the circumferential direction by the cylindrical lens optical system 5, the bump diameter per pulse at the time of stop (at the time of non-rotation). If the major axis is 10 μm and its minor axis is 5.8 μm,
A pseudo circular bump having a width of 10 μm and a length of 10 μm is formed.

When bumps of, for example, φ10 μm are formed by the conventional irradiation method, the number of rotations of the substrate is greatly reduced, and
With the use of RPM, the drag length Vt is reduced to about 1.1 μm, so that a substantially pseudo-circular bump can be formed. However, when the number of tracks in the CSS area is set to 100, for example, the texture processing time is about 4 minutes, which is inferior in productivity. However, in the processing method including this irradiation method, it takes about 1 minute, and the productivity is greatly improved. it can. In particular, in this example, the rotational speed of the substrate can be increased in order to increase the productivity. At this time, the ellipticity may be increased in proportion to the rotation speed.

[0049]

As described above, the present invention is characterized in that the irradiation cross section of the condensed spot is formed in an elliptical shape in which the minor axis is aligned in the circumferential direction of the glass substrate in advance. It works.

Since the short diameter of the irradiation cross section of the oval condensed spot is aligned in the circumferential direction of the glass substrate,
Since the converging spot is dragged in the minor axis direction, the irradiation area becomes substantially circular as a result. For this reason, the melting and solidification of the glass material is promoted around the substantially circular irradiation region, and therefore, a pseudo circular cone-shaped bump is formed. By optimizing the pulse width and the ellipticity without increasing the power density of the laser, it is possible to achieve a predetermined bump height and a circular bump planar shape even when the relative rotation of the substrate is accelerated. The texture processing time can be shortened, and the productivity can be greatly improved.

The difference between the major axis and the minor axis of the oval
If the relationship between the pulse width of the laser beam and the product of the relative peripheral velocity at the irradiation point of the glass substrate is approximately equal, the irradiation area of the focused spot can be made closer to a pseudo-circle, so that the bump plane shape Circularization becomes easy.

Using a parallel beam cross-section deforming optical system to obtain a converging spot with an oblong irradiation cross section does not require changing the condensing lens system, which facilitates maintenance.

When a cylindrical lens optical system is used as the parallel beam section deforming optical system, the optical configuration is simple, and the major and minor axes of the desired size of the irradiation section ellipse can be relatively easily created.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a laser processing apparatus used in a method for manufacturing a magnetic recording medium according to an embodiment of the present invention.

2A is a plan view showing a cylindrical lens optical system in the laser processing apparatus shown in FIG. 1, and FIG. 2B is a front view showing the cylindrical lens optical system.

FIG. 3 is a conceptual diagram showing a process of irradiating a condensed spot on a substrate surface in the present embodiment.

FIG. 4A is a plan view showing another cylindrical lens optical system in the laser processing apparatus shown in FIG. 1, and FIG.
FIG. 3 is a front view showing the cylindrical lens optical system.

FIG. 5 is a graph showing a relationship between a pulse width of a pulse laser pulsed by an EOM and a height of a cone-shaped pump formed at this time in the embodiment.

FIG. 6 is a plan view showing a transition of a formed pump shape when a pulse width is changed, and FIG. 6A shows a transition of a pump shape by a conventional laser irradiation method without using a cylindrical lens optical system; (B) shows the transition of the pump shape by the laser irradiation method of the present embodiment using the cylindrical lens optical system.

FIGS. 7A to 7D are enlarged cross-sectional views showing various bump shapes obtained by laser texturing on an aluminum substrate having a NiP plating film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Continuous oscillation type laser oscillator 2a, 2b ... Continuous laser beam with circular beam cross section 2d, 2e ... Pulse laser beam with elliptical beam cross section 2f ... Condensed beam with elliptical beam cross section 3 ... Power stabilizer 4 ... EOM pulse modulator 5 ... cylindrical lens optical system 5a ... Y-axis one-dimensional collimator 5b ... X-axis one-dimensional collimator 6 ... reflector 7 ... condenser lens 8 ... glass substrate 9 ... spindle motor L ₁ ~L ₆ ... cylindrical lens the focal length of f ₁ ~f ₆ ... cylindrical lens.

Claims (4)

[Claims] 1. A texture processing step of forming a bump by pulsing a continuous wave laser beam by electro-optic modulation and irradiating the pulsed laser beam onto a surface of a relatively rotating glass substrate with a focused spot. In the method for manufacturing a magnetic recording medium, the irradiation cross section of the condensing spot is an elliptical shape whose minor axis is aligned in a circumferential direction of the glass substrate. 2. A relation according to claim 1, wherein a difference between a major axis and a minor axis of the elliptical shape is substantially equal to a product of a pulse width of the pulsed laser beam and a relative peripheral velocity at an irradiation point of the glass substrate. A method for manufacturing a magnetic recording medium, comprising: 3. The method of manufacturing a magnetic recording medium according to claim 1, wherein the condensed spot is formed using a parallel beam cross-sectional deformation optical system at a stage subsequent to the electro-optic modulator. . 4. The method for manufacturing a magnetic recording medium according to claim 3, wherein said parallel beam section deforming optical system is a cylindrical lens optical system.