JPH11296846A - Surface modifying method for hard disk substrate, and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface free of projections and with scratches of <=5 Angstrom in the surface roughness Ra of a hard disk substrate and <=50 Angstrom in the max. surface roughness Rmax and to make the oxidation degree of Ni and P of an Ni-P plated surface constant. SOLUTION: The surface of the hard disk substrate 10 is irradiated with a laser beam of 1 to 100 shots per unit area impulsively at >=300 mJ per square cm of energy density and at a frequency of 1 to 500 Hz, by which the surface of the Ni-P layer is rapidly heated and rapidly cooled. The surface ruggedness of the Ni-P layer is thus reformed while the crystallization of the plating layer of the Ni-P is averted. More adequately the substrate is irradiated with the line beam of an excimer laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a processing method and a processing apparatus for modifying the surface of a substrate for a hard disk or the like using a laser.

[0002]

2. Description of the Related Art A hard disk, that is, a metal thin-film magnetic disk is a magnetic recording medium in which a magnetic layer is usually provided on a disk substrate made of aluminum, and further improvement in recording density is always desired. To achieve this, one of the major technical issues is to reduce the distance (head flying height) between the magnetic head and the magnetic disk. The disk substrate is usually divided into two areas, one is a CSS zone located on the inner diameter side and the magnetic head is contact-started / stopped, and the other is a so-called information recording portion which occupies most of the disk substrate. Consists of a data zone.

[0003] The CSS zone is formed on a polished substrate to stabilize the contact start / stop characteristics of the head by a laser texturing technique.
Irregularities (called bumps) of about nm are provided at a pitch interval of about 150 μm or less. On the other hand, in the data zone, the surface of the polished substrate is subjected to a texturing process in which a processing mark having a roughness of 1 nm or less is uniformly applied over the entire surface by using an abrasive grain of 1 μm or less in a circumferential method.

[0004] Uniform bump quality and shape during laser texturing in the CSS zone has a significant effect on the CSS characteristics of the disc. The quality and shape of the bumps are determined by the surface roughness of the substrate to be laser-textured, the size of the scratches, Ni-P (nickel
Phosphorus) It is affected by the degree of oxidation of the plating surface. The substrate surface is
Although it is desirable to have a certain degree of oxidation with a surface roughness Ra of 0.7 nm or less without scratches and protrusions, the conventional polishing technique has an ideal processing surface property, leaving time after processing, manufacturing environment, etc. It is difficult to stabilize the substrate surface including the degree of oxidation due to factors.

On the other hand, the data zone has a roughness R in the circumferential direction.
a1 nm or less is applied to the entire surface of the substrate by texturing, which is usually performed by pressing a slurry liquid containing abrasive cloth and abrasive grains onto the substrate surface while rotating the substrate, and the processing amount is extremely small. . Therefore, the polishing substrate (texture Ra 2.0 to 0.
If there is a slight scratch at 5 nm), a processing time of 10 to 20 seconds is required to remove the scratch and simultaneously form a surface with a predetermined roughness Ra of 0.7 nm. There is no guarantee that it has been completely removed within the processing time.

[0006] Japanese Patent Application Laid-Open No. 7-6362 discloses a method for modifying the surface of a magnetic recording medium. The surface of the magnetic recording medium is irradiated with an ultraviolet laser beam (excimer laser) to cause ablation, and the surface of the magnetic recording medium is irradiated near the beam irradiation part. A method for activating a gas to modify a surface is disclosed. However, since the nickel-phosphorus layer is magnetized when the temperature exceeds 260 ° C., there is a possibility that such a simple method may give an inappropriate magnetism as a magnetic recording medium. JP-A-8-323
No. 492, "Excimer Laser Beam Forming Apparatus" discloses an apparatus for making the intensity distribution of an excimer laser beam uniform, thereby ensuring surface accuracy of a processed surface and improving dimensional accuracy. Japanese Patent Application Laid-Open No. Hei 8-309573 discloses an apparatus for irradiating a laser beam onto a flat plate with a linear focusing shape of a laser beam.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a disk substrate having a surface roughness Ra (center line average roughness) Ra.
Is not more than 5 angstroms, and the maximum surface roughness (maximum surface projection height) Rmax is 50 angstroms or less, and a projection-free and scratch-free surface is obtained. Another object is to make the degree of oxidation of Ni and P on the Ni-P plated surface constant.

[0008]

In order to achieve the above-mentioned object, the present invention, in one aspect, provides a laser beam on a hard disk substrate, which is formed by plating a nickel-phosphorous layer on an aluminum substrate or a glass substrate. With an energy density of 300 millijoules or more per square cm and a unit area (1
Hard disk substrate that irradiates 1 to 100 shots per square cm, rapidly heats and cools the surface of the nickel-phosphorus layer, and modifies the surface irregularities of the nickel-phosphorus layer while avoiding crystallization of the nickel-phosphorus layer. The present invention provides a method for modifying the surface.

The laser beam has a wavelength of 11,000.
It can be widely used from a carbon dioxide gas laser of nm to an excimer laser of wavelength 248 nm. As a most preferable example, an excimer laser beam having a wavelength of 248 nm is irradiated with an excimer laser beam of 500 mJ / cm 2 or more for 1 H
The hard disk substrate was moved in the horizontal direction by irradiating two shots per unit area in a pulsed manner at a frequency of z. At this time, the feeding of the substrate was controlled so that the laser beam was sequentially and twice overshot per unit area.

[0010]

According to this method, for the data zone,
The amorphous nickel-phosphorus plating layer does not crystallize,
There was no magnetization, and the surface was thinly melted and the scratch was completely erased. Rmax 20 nm, Ra
The 1.5 nm substrate surface has a Rmax of 5 nm, Ra
A 0.2 nm plane was obtained. As a result, in the subsequent texturing process, a scratch-free surface with a Ra of 0.5 nm can be easily obtained in 5 seconds or less even under the same processing conditions as in the related art. In the CSS zone, the surface roughness can be similarly improved, and the oxidation degrees of Ni and P are constant regardless of the state before irradiation. Furthermore, the degree of oxidation of the surface can be changed by irradiating a laser while spraying a gas such as nitrogen, oxygen, or argon or a mixed gas thereof onto the laser irradiation part.

In a preferred aspect of the present invention, the laser beam is formed into a line beam having a narrow width and a length larger than the width of the hard disk substrate by an optical component such as a mirror or a slit and a homogenizer (homogenizer). You. In another preferred aspect of the present invention, the laser beam is scanned across the width of the hard disk substrate by a scanning mechanism.

According to another aspect of the present invention, a hard disk substrate formed by plating a nickel-phosphorous layer on an aluminum substrate or a glass substrate is irradiated with a pulse of a linear laser beam to perform surface modification. A device,
Provided is a substrate surface reforming device including a control device that controls the laser irradiation frequency and the number of pulses to be synchronized so that the number of pulses applied to all portions on a hard disk substrate is in a range of ± 50%. With this apparatus, the above-described surface modification method is effectively performed, and a hard disk substrate surface free of protrusions and scratches can be obtained.

When performing laser irradiation using this apparatus,
By providing a transfer mechanism that rotates the hard disk substrate under a linear laser beam in a perpendicular direction and a rotation mechanism that rotates the laser beam, the laser irradiation is overshot while the hard disk substrate is moving, and the number of laser shots per unit area is uniform. It is possible to control so that

Further, when performing laser irradiation, a mechanism for spraying a gas such as nitrogen, oxygen or argon or a mixed gas thereof is provided in the laser irradiation section, and the laser irradiation is performed while mixing these gases. It is possible to control the degree of oxidation of the surface of the nickel-phosphorus layer.

Also, by providing a mechanism for inserting a shielding plate between the laser beam and the hard disk substrate so that the laser is irradiated only to the CSS zone on the hard disk substrate when performing the laser irradiation, Can be partially irradiated. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view showing a principle for carrying out a method for modifying the surface of a hard disk substrate according to the present invention. A hard disk substrate 10 is formed by depositing a nickel-phosphorus layer on an aluminum substrate or a glass substrate. Is plated. Generally, the thickness of the nickel-phosphorus layer is 10 to 15 μm.
m, and has a surface roughness of about 100 to 200 angstroms.

In the surface modification method of the present invention, for example,
From the laser oscillator 12, a 248 nm wavelength excimer (KrF) having a rectangular cross section with a height of 10 mm and a width of 30 mm
The laser beam 14 is emitted in a pulsed manner. Laser intensity is more than about 500 millijoules per square cm,
The pulse period of the laser is about 10 Hz, and the number of shots is two.

The beam 14 is expanded through a cylindrical lens 16, a condenser lens 18, and a beam splitter 20 having a slit, and has a width of 0.3 mm and a length of 200 mm.
The beam is formed into a line beam 24 having a width of 200 mm and is applied to the entire surface of the hard disk substrate 10 having a width of 200 mm or less.

The hard disk substrate 10 is mounted on a conveyor (not shown) and moves in a horizontal direction at a constant speed.
This moving speed is synchronized with the frequency of laser irradiation, and the number of shots per unit area on the substrate is one or two. In addition, it is also possible to install a gas outlet as required and spray the gas onto the laser irradiation unit.

Thus, the surface of the nickel / phosphorous layer on the hard disk substrate 10 is melted by the irradiation of the laser beam, and the unevenness is reduced. The heating is rapid heating for 20 to 30 nsec, and the magnet is not magnetized due to the rapid cooling. The surface is thinly melted and the scratch is eliminated.

FIG. 2 is another schematic diagram showing the principle of the present invention. A beam oscillating beam 34 of an excimer (KrF) laser having a wavelength of 248 nm is emitted from a laser oscillator 32 in a pulsed manner. The beam light beam 34 is modulated by the modulator 36 and the beam expander 3.
8. Formed into a spot beam via a cylindrical lens 40, a polygon mirror 44 rotated by a motor 42, a cylindrical lens 46, and a condensing scanning lens 48, and act as a linear beam 50 by being scanned. I do. The scanning beam 50 is applied to the entire surface of the hard disk substrate 10 mounted on a conveyor (not shown) and moving at a constant speed in the horizontal direction.

The scanning mechanism of the laser beam is not limited to the polygon mirror, but may be a galvanometer, an ultrasonic deflector, or other various mechanisms.

[0023]

FIG. 3 shows a preferred embodiment of the present invention, in which a laser oscillator of the type L4308 manufactured by Lambda Physics Japan Co., Ltd. was used. A control device 62 for performing various controls is provided adjacent to the laser oscillator 60.

In FIG. 3, a beam oscillating beam 6 of an excimer (KrF) laser having a wavelength of 248 nm is emitted from a laser oscillator 60.
4 is emitted in a pulsed manner. The beam luminous flux 64 includes mirrors 65 and 66, a shutter 67, an attenuator 68, and a mirror 6
9, the light passes through the homogenizer 70 and the slit 71, is converted into a line beam 72, is reflected by the mirror 73, passes through the slits 74 and 75, and is irradiated onto the hard disk substrate 10.

The table 80 supporting the hard disk substrate 10 is fed in the front-rear direction by a table feed drive motor 82 or the table rotation motor 8
4 is rotated. The surface temperature of the hard disk substrate 10 can be detected by an infrared detection type temperature sensor 86. In order to adjust the surface temperature of the hard disk substrate 10, a fan 88 may be provided.

Further, a mechanism 90 for blowing a gas such as nitrogen, oxygen, argon, or a mixed gas thereof to the laser irradiating part when performing laser irradiation adjacent to the laser irradiating part.
Is provided. By performing laser irradiation while mixing these gases, it is possible to control the degree of oxidation of the surface of the nickel-phosphorus layer.

A cylinder mechanism 92 for inserting a shielding plate 93 between the laser beam and the hard disk substrate 10 is provided adjacent to the laser irradiation section. With this mechanism,
For example, laser irradiation can be performed only on the CSS zone on the hard disk substrate, or laser irradiation can be performed only on a predetermined portion.

The control device 62 performs the following control operation. (1) Control ON / OFF of laser beam irradiation, energy density of laser beam, frequency, number of pulses, etc. (2) The number of pulses applied to all portions on the hard disk substrate is within a range of ± 50%. (3) The transfer mechanism or the rotation mechanism is controlled so that the laser irradiation is repeated and the number of laser shots per unit area becomes uniform while the hard disk substrate is moving. (4) By controlling the degree of oxidation of the surface of the nickel-phosphorus layer by irradiating the laser while mixing the gas by a mechanism for spraying the mixed gas, (5) Laser irradiation is performed only at a specific location on the hard disk substrate. To control the operation of the mechanism to insert the shield between the laser beam and the substrate (6) Signal from the temperature sensor According to these control operations, the number of rotations of the fan is changed to control the temperature of the surface of the hard disk substrate to be kept constant, whereby the best laser irradiation effect can be obtained.

[0029]

As described above in detail, according to the method and apparatus for modifying the surface of a hard disk substrate according to the present invention, the nickel / phosphorous layer does not become magnetized, but the surface is thinly melted and scratches are erased. As a result, the texturing in the post-process can be completed in a short time. This allows
The technical effects of the hard disk are extremely remarkable, for example, local defects of the hard disk are prevented and the quality is remarkably improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the principle of a method for modifying the surface of a hard disk substrate according to the present invention.

FIG. 2 is a schematic view illustrating the principle of a method for modifying the surface of a hard disk substrate according to the present invention.

FIG. 3 is a perspective view illustrating a preferred embodiment of a surface modification apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Hard disk board 12, 32, 60 Laser oscillator 24, 50, 72 Line beam 82 Drive motor 84 Rotary motor 90 Gas blowing mechanism 92 Shield insertion mechanism

Claims (8)

[Claims] 1. A laser beam is applied to a hard disk substrate formed by plating a nickel / phosphorous layer on an aluminum substrate or a glass substrate, with an energy density of 1 cm 2.
Irradiate 1 to 100 shots per unit area in a pulsed manner at a frequency of 1 to 500 Hz or more at a frequency of 1 to 500 Hz to rapidly heat and cool the surface of the nickel-phosphorous layer to avoid crystallization of the nickel-phosphorous layer. A method for modifying the surface of a hard disk substrate, which comprises modifying the surface irregularities of a nickel / phosphorus layer while performing the method. 2. The laser beam, which is formed into a line beam having a narrow width and a length greater than the width of the hard disk substrate by an optical component such as a mirror or a slit and a homogenizer, and then irradiated onto the hard disk substrate. The surface modification method as described in the above. 3. The surface modification method according to claim 1, wherein the laser beam is scanned across the width of the hard disk substrate by a scanning mechanism. 4. An apparatus for performing a surface modification by irradiating a linear laser beam in a pulse form on a hard disk substrate formed by plating a nickel / phosphorous layer on an aluminum substrate or a glass substrate, comprising: A hard disk substrate surface improvement comprising a control device for controlling the laser irradiation frequency and the number of pulses so that the number of pulses applied to all portions on the substrate is within a range of ± 50%. Quality equipment. 5. A transfer mechanism for moving a hard disk substrate under a linear laser beam in a direction perpendicular to the laser beam when performing laser irradiation, wherein the control device controls the laser while the hard disk substrate is moving. 5. The apparatus according to claim 4, wherein the transfer mechanism is controlled so that the irradiation is repeated and the number of laser shots per unit area becomes uniform. 6. A rotation mechanism for rotating a hard disk substrate under a linear laser beam when performing laser irradiation, wherein the control device is configured to perform laser irradiation while the hard disk substrate is rotating and to perform unit irradiation. The apparatus according to claim 4, wherein the rotation mechanism is controlled so that the number of laser shots per area is uniform. 7. A mechanism for spraying a gas such as nitrogen, oxygen, or argon or a mixed gas thereof to a laser irradiation part when performing laser irradiation, wherein the control device performs laser irradiation while mixing the gas. 5. The apparatus according to claim 4, wherein the degree of oxidation of the surface of the nickel-phosphorus layer is controlled. 8. A mechanism for inserting a shielding plate between a laser beam and a hard disk substrate so as to irradiate only a CSS zone on a hard disk substrate when performing laser irradiation. 5. The apparatus according to claim 4, wherein partial irradiation of the substrate is possible.