JP3493061B2 - Magnetic recording medium substrate and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a substrate for a magnetic recording medium such as a magnetic disk.

[0002]

2. Description of the Related Art In recent years, with the increase in recording density of magnetic recording media, a magnetic layer made of a Co alloy having uniaxial crystal magnetic anisotropy such as CoNiCr and CoCrTa is formed on a non-magnetic substrate with a Cr underlayer interposed therebetween. A metal thin film type magnetic recording medium is used. Conventionally, amorphous Ni has been used as a substrate for media.
An Al alloy substrate with a plated P layer was used. Irregularities called texture are usually mechanically processed along the circumferential direction on the substrate surface. The mechanical texture mainly reduces friction between the head and the medium, and
(Contact start stop) It has the effect of improving the characteristics.

Recently, miniaturization and increase in capacity of hard disk devices have been spurred, and development of magnetic recording media in response to them has been required. As the recording density of the magnetic recording medium becomes higher, the recording bit size becomes smaller. Therefore, the flying height of the magnetic head must be made as small as possible to increase the read output. For that purpose, it is necessary to promote smoothing of the medium substrate on which the magnetic layer is formed and to lower the flying height of the head.

Therefore, as a medium substrate, the Ni--
Instead of a P / Al alloy substrate, a glass substrate having good flatness is used to form a texture by plasma etching as disclosed in JP-A-3-232117.

[0005]

However, since the plasma etching disclosed in the above publication irradiates the substrate with non-directional plasma, the height difference between the convex portion and the concave portion (peaks and valleys). (Interval distance) is small, and the convex part has a gentle mountain shape. For this reason, although it was effective for lowering the flying height of the head, there is a problem that the contact area between the head and the medium increases rapidly due to a slight abrasion of the convex portion, and the head may be attracted or damaged in a short time.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method of manufacturing a substrate for a magnetic recording medium having not only a low flying height but also excellent CSS characteristics.

[0007]

A substrate for a magnetic recording medium according to the present invention has an infinite number of long pillar-shaped or needle-shaped projections formed on the surface of a glass substrate, and an area of a reference plane provided in parallel with the substrate and The interval between the reference surface when the ratio of the total areas of the cross-sectional areas of the convex portions intersecting the reference surface is 0.2% and the reference surface when the area ratio is 1% is 4 nm or more, preferably 8 nm or more.

Further, according to the manufacturing method of the present invention, plasma is generated in a mixed gas atmosphere of oxygen gas and halocarbon gas, and the plasma is applied from a direction perpendicular to the surface of the glass substrate to which a negative bias voltage is applied. Irradiation is performed to form innumerable long pillar-shaped or needle-shaped convex portions on the surface of the glass substrate. In this case, the halocarbon gas is 10 to 75 vol%
(Preferably 25 to 75 vol%) O ₂ gas and 90 to ₂
In a mixed gas atmosphere of 5 vol% (preferably 75 to 25 vol%) CF ₄ gas, a high frequency discharge is generated between the flat plate-shaped electrodes arranged in parallel, and the plasma generated thereby is generated from -300 to-. 800 V (preferably -500 to-)
It is preferable to irradiate a glass substrate to which a bias voltage of 600 V) is applied and which is arranged between the flat plate-shaped electrodes in parallel with the electrodes.

As the material of the glass substrate, various materials such as soda lime glass, aluminosilicate glass, and crystallized glass can be used. The halocarbon gas may be C ₄ F ₆ , CHF, in addition to CF ₄ gas.
₃ , C ₃ F ₈ , CF ₄ + O, etc. can be used.

[0010]

According to the substrate of the present invention, since the fine protrusions forming the texture are columnar or needle-like, even if the tip of the protrusion is worn, it is projected like abrasion like a mountain-shaped protrusion. The low friction coefficient is maintained without the cross-sectional area of the part increasing rapidly. In addition, the ratio of the total area of the cross-sectional areas of the protrusions intersecting the reference plane and the area of the reference plane provided in parallel to the substrate (bear
Since the distance (referred to as "bearing depth") between the reference surface when the ing ratio) is 0.2% and the reference surface when the area ratio is 1% is 4 nm or more, preferably 8 nm or more. In comparison, the low coefficient of friction is maintained over a long period of time and the durability is excellent.

Further, according to the manufacturing method of the present invention, since a negative bias voltage is applied to the substrate and the generated plasma is vertically irradiated to the glass substrate, activated fluorine atoms in the plasma are changed by the bias voltage. Accelerated and injected vertically into the substrate, this fluorine atom
Volatile S that combines with i atoms and does not decompose in plasma
This produces iF ₄ gas. Therefore, innumerable long pillar-shaped or needle-shaped convex portions are formed on the surface of the glass substrate. Mixed gas concentration,
The desired bearing depth can be formed by appropriately setting the magnitude of the bias voltage, the plasma forming power, the processing time, and the like.

In this case, in a mixed gas atmosphere of 10 to 75 vol% (preferably 25 to 75 vol%) O ₂ gas and 90 to 25 vol% (preferably 75 to 25 vol%) CF ₄ gas. , A high-frequency discharge is generated between the flat plate-shaped electrodes arranged in parallel, and the plasma generated by this is -300
By applying a bias voltage of -800 V (preferably, -500 V to -600 V) and irradiating the glass substrate arranged between the flat electrodes in parallel with the electrodes, plasma generated between the flat electrodes is applied to the substrate surface. It is possible to irradiate in a vertical direction with high efficiency, and it is possible to easily form irregularities having a bearing depth of 4 nm or more by plasma irradiation for about several minutes.

[0013]

FIG. 1 shows an example of a plasma etching apparatus for carrying out the manufacturing method of the present invention, in which a pair of flat plate-shaped electrodes 2 arranged facing each other in a container 1 having a conductive inner wall, 2 ', and the glass substrate 3 is placed on the lower electrode 2'. The electrodes 2, 2 ′ are connected to a high frequency power source 5 via a matching device 4. On the other hand, to the lower electrode 2 ', a negative bias voltage is applied to the inner wall of the container by the DC bias power source 6. A gas source 7 for supplying a plasma generating gas (mixed gas of oxygen gas and halocarbon gas) is connected to the container 1,
An electromagnetic coil 8 for forming a magnetic field that prevents diffusion of discharge (plasma) generated between the electrodes is provided around it. Reference numeral 9 is an exhaust pipe connected to an exhaust pump. Further, as the gas source, oxygen gas and halocarbon gas may be provided separately.

To carry out the present invention, first, the inside of the container 1 is evacuated, then a mixed gas for etching is introduced from the gas source 7 into the container, the gas pressure is adjusted to about 1 to 1000 mTorr, and the electrode is A negative bias voltage is applied to 2 ', and high frequency power is supplied to the electrodes 2, 2'. This allows
A gas discharge (RF glow discharge) is generated between the electrodes 2 and 2 ', and plasma containing activated fluorine atoms is generated. This plasma is held between the electrodes 2 and 2'by the action of a magnetic field, and the fluorine atoms are held at a negative potential in the electrode 2 '.
And is irradiated onto the surface of the substrate 3. Note that a magnetic field for preventing plasma divergence is not always necessary.

Using the plasma etching apparatus described above, fine irregularities were formed on the surface of a glass substrate under the etching conditions shown in Table 1 to manufacture a magnetic recording medium substrate. The frequency of the high frequency power supply is 13.56 MHz. Sample No. 1 to 6,
11 to 16 are examples, and No. 21 is a conventional example. Incidentally, in the conventional example, no bias voltage was applied and no magnetic field was applied.

[0016]

[Table 1]

Using the substrates of Examples and Conventional Examples, the surface texture was observed by AFM (atomic force microscope) and the bearing depth was measured. The results are also shown in Table 1. From the table, it was confirmed that the example has a depth of at least twice as large as that of the conventional example. In addition, the example No.
From Nos. 1, 2, 6 and Nos. 11, 12, 16 it can be seen that if the mixed gas ratio is the same, the higher the bias voltage and the longer the treatment time, the greater the bearing depth can be obtained. An example of the surface roughness diagram of the substrate observed by AFM is shown in FIGS. 2 and 3. 2 is No. 1 of the embodiment, and FIG. 2 is No. 21 of the conventional example. The shape of the convex portion is a long columnar or needle-like discontinuous projection in the example, whereas it is observed that it is a mountain-shaped continuous projection in the conventional example.

Next, No. 1 (Example) and No. 21
Using a (conventional example) substrate, a Cr underlayer 60 is formed thereon.
0 Å, 400 Å magnetic layer of CoCrTa alloy, C
A protective layer of 150 l was formed by sputtering in the same order, and 15 l of a fluorine-based liquid lubricant was further coated on the C protective layer to manufacture a magnetic recording medium. Glide height and CSS characteristics were measured using this medium and a thin film head. The glide height was about 0.05 μm, which was almost the same as that of the example and the conventional example. On the other hand, as shown in FIG. 4, the CSS characteristics of the examples and the conventional example had a very low friction coefficient before the test, but as the number of times increases, the conventional example gradually increases, and the 30,000 times the initial friction coefficient. It became about 9 times. On the other hand, in the example, it is understood that the durability is 3 times or less, and the durability is excellent. Regarding No. 11 of the example,
When the CSS characteristics were examined in the same manner, the friction coefficient after 30,000 times stayed at about twice or less than the initial value and the bearing depth was 8
It was confirmed that good CSS characteristics can be obtained at a thickness of at least nm.

[0019]

As described above, according to the magnetic recording medium substrate of the invention according to claim 1, since the shape of the convex portion is formed in the shape of a long pillar or a needle and the bearing depth is 4 nm or more, It is possible to achieve a low flying height of the head and improve the CSS characteristics as compared with the conventional case. Further, according to the manufacturing method of the second aspect of the present invention, the shape of the convex portion formed on the surface of the glass substrate can be formed in the shape of a long column or a needle in which the variation of the friction coefficient hardly occurs. According to the third aspect of the present invention, plasma can be irradiated onto the surface of the substrate perpendicularly with high efficiency, and unevenness having a bearing depth of 4 nm or more can be easily formed by plasma irradiation for about several minutes. .

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of an electrode facing type plasma etching apparatus for carrying out the present invention.

FIG. 2 is a surface roughness diagram of a magnetic recording medium substrate according to an example.

FIG. 3 is a surface roughness diagram of a magnetic recording medium substrate according to a conventional example.

FIG. 4 is a graph showing the relationship between the number of CSSs and the coefficient of friction for magnetic recording media according to an example (present invention) and a conventional example.

[Explanation of symbols]

2 electrodes 3 glass substrates 6 Bias power supply

Front Page Continuation (72) Inventor Nobuo Kurataka 1-47 Shikitsu East, Naniwa-ku, Osaka City, Osaka Prefecture Kubota Co., Ltd. (72) Yuki Hara, 1-2 Shikitsu East, Naniwa-ku, Osaka City, Osaka Prefecture No. 47 Kubota Co., Ltd. (56) Reference JP-A-7-85463 (JP, A) JP-A-7-296538 (JP, A) JP-A-3-232117 (JP, A) JP-A-7- 244848 (JP, A) JP 5-189756 (JP, A) JP 60-229234 (JP, A) JP 62-219224 (JP, A) JP 4-61625 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 5/62-5/858

Claims (3)

(57) [Claims] 1. A method of manufacturing a substrate for a magnetic recording medium, comprising a plasma generation step of generating plasma in a mixed gas atmosphere of 10 to 75 vol% oxygen gas and 90 to 25 vol% halocarbon gas. And a plasma irradiation step of irradiating the surface of the glass substrate, to which a negative bias voltage of -300 to -800 V is applied, in a direction perpendicular to the surface of the glass substrate. A method for manufacturing a substrate for a magnetic recording medium, characterized in that innumerable parts are formed. 2. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein in the plasma generating step, plasma is generated by generating high frequency discharge between parallel flat plate electrodes in the mixed gas atmosphere. The plasma irradiation step is a step of arranging the glass substrate to which the negative bias voltage is applied between flat plate electrodes in parallel with the electrodes, and irradiating the glass substrate with plasma. A method for manufacturing a substrate for a magnetic recording medium, comprising: 3. The method for manufacturing a magnetic recording medium substrate according to claim 1, wherein the mixed gas is 25 to 75 vol% oxygen gas and 75 to 75 vol% oxygen gas.
A method of manufacturing a substrate for a magnetic recording medium, which is a mixed gas of 25 vol% halocarbon gas, and the negative bias voltage is -500 to -600V.