JPH0778874B2 - Texture processing method for amorphous carbon substrate for magnetic disk - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a texture processing method for an amorphous carbon substrate for a magnetic disk, which is texture-processed to prevent an adsorption phenomenon between a magnetic head levitating surface and a magnetic disk surface. .

[0002]

[Prior art]  Conventionally, magnetic disks are Ni-P plated
A magnetic film is formed on an Al substrate coated with a material, etc.
Has been. And in the magnetic disk reproducing device,
Place the levitation type magnetic head on the magnetic disk and
The magnetic head is levitated by rotating the disk.
Writing to a magnetic disk with this magnetic head
Or play. However, writing on a magnetic disk
When recording or playing, the magnetic
If adsorption occurs between the floating surface and the magnetic disk surface.
There is a match. This adsorption phenomenon is caused by the magnetic head levitating surface and the magnetic head.
The surface of the disk is extremely smooth and both face each other with a minute gap.
The gap is O₂ , N₂ Or H₂ Such as O
Larger adsorption force due to interfacial tension filled with molecules
Due to the occurrence of. Such adsorption phenomenon occurs
Then, when the motor that drives the magnetic disk starts
This causes the inconvenience of consuming a large amount of power.

Therefore, in order to prevent the above-mentioned adsorption phenomenon,
In the Al substrate for a magnetic disk, before the magnetic film is deposited, the substrate surface is once mirror-finished and then subjected to a texture treatment to adjust the surface roughness. The following texture processing methods are available. That is, while the Al substrate (Ni-P plated material) is rotated, the polishing tape is moved in the radial direction of the Al substrate while the polishing tape is pressed against the Al substrate by the roller to make contact with the Al substrate. Silicon carbide as polishing tape,
Use those to which abrasive grains such as alumina or diamond are attached. By performing the mechanical texture treatment in this way, it is possible to form a concentric circular striation on the surface of the Al substrate for a magnetic disk and obtain a rough surface in which the striation is oriented in the circumferential direction.

As another conventional magnetic disk substrate, an amorphous carbon substrate (Kobe Steel Technical Report, vol. 3
9, No. 4, pages 35 to 38, issued in 1989) is proposed. This amorphous carbon substrate is lightweight and has high strength, is excellent in heat resistance and surface accuracy, and can improve the recording density of the magnetic disk as compared with the Al substrate.

[0005]

However, it is extremely difficult to adjust the surface roughness to an appropriate value in the conventional method of texture-treating an Al substrate for a magnetic disk, and it tends to be unnecessarily rough. In order to increase the recording density of the magnetic disk, it is preferable to further reduce the flying height (spacing) of the magnetic head. However, as described above, if the surface roughness of the Al substrate for the magnetic disk becomes larger than necessary, The flying height of the magnetic head increases,
The recording density of the magnetic disk cannot be improved.
Further, the conventional amorphous carbon substrate has a problem that the surface roughness itself has not been examined from the viewpoints of preventing adsorption of the magnetic head and improving magnetic recording characteristics.

The present invention has been made in view of the above problems. It is possible to prevent the magnetic head from sticking to the magnetic disk, improve the characteristics of the magnetic film, and make the flying height of the magnetic head smaller than before. It is an object of the present invention to provide a texture processing method for an amorphous carbon substrate for a magnetic disk, which can obtain a textured surface that can be obtained.

[0007]

A method of texturing an amorphous carbon substrate for a magnetic disk according to the present invention comprises polishing the surface of the amorphous carbon substrate to have a surface roughness Ra of 5 to 40Å and a circumferential direction. polishing step and a heating step of heating the amorphous carbon substrate having a surface polished in the presence of oxygen the ratio Ra ₂ / Ra ₁ and the surface roughness Ra ₁ and radial surface roughness Ra ₂ of the 0.85 to 1.15 And having.

[0008]

The present inventors paid attention to the properties of the amorphous carbon substrate and conducted various studies on the texture processing method. As a result, after the amorphous carbon substrate is polished to a predetermined surface roughness, the amorphous carbon substrate is heat-treated at a predetermined temperature in an oxidizing atmosphere to process the amorphous carbon substrate to a suitable surface roughness for a magnetic disk. I found that I can do it.

That is, an amorphous carbon substrate polished to a predetermined surface roughness is 300 to 1000 ° C., preferably 400
When heated to 700 to 700 ° C., an oxidation reaction of C + O ₂ → CO ₂ occurs, carbon is gasified, and fine irregularities are formed on the polished surface. Therefore, by controlling the heat treatment conditions such as the treatment temperature and time, the amorphous carbon substrate can be easily treated to have an appropriate surface roughness, and the surface is not roughened more than necessary. As a result, the magnetic disk head adsorption can be prevented, the characteristics of the magnetic film formed on the amorphous carbon substrate can be improved, and the flying height of the magnetic head can be made smaller than before.

Next, the surface roughness Ra and the surface roughness Ra in the circumferential direction of the amorphous carbon substrate after surface polishing.
_The reason for limiting the ratio Ra ₂ / Ra ₁ of ₁ to the surface roughness Ra ₂ in the radial direction will be described.

If the orientation of the texture with respect to the substrate surface is randomly oriented, that is, if the surface roughness Ra of the amorphous carbon substrate is not biased in the circumferential direction or the radial direction, a recording / reproducing error in practical use as a magnetic disk will occur. Also, noise (S / N ratio) can be reduced, and the recording density can be increased.

The random orientation of this texture is determined by surface polishing before heat treatment. However, the ratio R of the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra ₂ in the radial direction of the amorphous carbon substrate after surface polishing
When a ₂ / Ra ₁ is disengaged from 0.85 to 1.15, recording errors and noise of the magnetic disk (S / N ratio) is increased. Therefore, the ratio Ra ₂ / Ra ₁ of the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra ₂ in the radial direction of the amorphous carbon substrate after the surface polishing is set to 0.85 to 1.15.

If the surface roughness (average surface roughness) Ra of the amorphous carbon substrate after surface polishing is smaller than 5Å, adsorption of the magnetic head is likely to occur when it is practically used as a magnetic disk.
On the other hand, when the surface roughness Ra exceeds 40Å, it becomes difficult to reduce the flying height of the magnetic head to about 0.1 μm or less. Therefore, the surface roughness Ra of the amorphous carbon substrate after surface polishing is set to 5 to 40 Å.

As described above, since the amorphous carbon substrate for a magnetic disk according to the present invention can increase the recording density of the magnetic disk and can reduce the flying height of the magnetic head, the magnetic disk having a particularly high performance. It is suitable for use in.

[0015]

BACKGROUND OF THE INVENTION Incidentally, the amorphous carbon substrate in the present invention, ultra-high temperature HIP amorphous carbon
By performing (hot isostatic pressing) treatment, most of the pores are eliminated and the density is increased to 1.80 g / cm ³ or more, and the characteristics are made of high-density amorphous carbon whose properties are close to those of graphite.

Next, a polishing method for polishing the amorphous carbon substrate to the above-mentioned surface roughness will be described.

As the abrasive grains, those having hardness equal to or higher than that of the amorphous carbon substrate and industrially inexpensive are used. For example, diamond, alumina, SiC, ZrO
It is preferable to use at least one kind of abrasive grain selected from the group consisting of ₂ , cerium oxide and SiO ₂ . In this case, if the average particle size exceeds 1 μm, scratches are generated on the surface of the amorphous carbon substrate during polishing, so that it is difficult to achieve the desired surface roughness.
Further, when scratches occur, the scratch portion is locally oxidized by the heat treatment in the next step and expands in a groove shape to form a substrate defect, which lowers the practical durability as a magnetic disk. It is also possible to use abrasive grains other than those mentioned above, but if the cutting force as the abrasive grains is insufficient, so-called orange peel minute recesses occur on the surface of the amorphous carbon substrate.

It is preferable to use a soft surface plate made of Sn or Cu as the surface plate. Since an amorphous carbon substrate is more brittle than an Al substrate, when a hard surface plate made of cast iron or the like is used, abrasive grains roll on the hard surface plate and defects such as scratches, orange peel and chipping occur on the surface of the amorphous carbon substrate. It happens frequently. On the other hand, when the soft surface plate is used, the above-mentioned inconvenience does not occur because the abrasive grains are slightly buried in the soft surface plate and do not roll. In addition, it is necessary to dress the rough surface after using the above-mentioned soft surface plate for a predetermined period. Therefore, it is possible to use a soft surface plate or a hard surface plate on the surface of which a hard pad made of polyurethane or the like having a hardness of 60 or more is adhered.
In this case, similar to the soft surface plate, no defects occur on the surface of the amorphous carbon substrate, and it is sufficient to replace the hard pad instead of dressing the surface of the surface plate, which has the advantage of reducing the processing cost. is there.

As described above, in the present invention, the average particle size is
Diamond less than 1 μm, alumina, SiC, ZrO
₂ , using at least one kind of abrasive grains selected from the group consisting of cerium oxide and SiO ₂ , a soft surface plate or a surface plate having a hard pad with a hardness of 60 or more adhered to the surface of the amorphous carbon It is preferable to lapping the substrate.

The orientation of the texture can be randomly oriented as shown below. That is, while pressing the amorphous carbon substrate on the soft surface plate (or hard pad) on which the slurry of the above-mentioned abrasive grains is dropped,
This amorphous carbon substrate is rotated and revolved. As a result, since the surface of the amorphous carbon substrate is irregularly cut by the abrasive grains, the ratio Ra of the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra ₂ in the radial direction of the amorphous carbon substrate after surface polishing is Ra. ₂ / Ra ₁ is 0.85
To 1.15.

[0021]

EXAMPLES A method of texturing an amorphous carbon substrate for a magnetic disk according to examples of the present invention and comparative examples which depart from the scope of the claims of the present application will be described below.

First, a mixed resin of a thermosetting resin that becomes amorphous carbon after carbonization and firing and a phenol-formaldehyde resin is molded into a magnetic disk shape by hot pressing, and this molded body is subjected to about 1850 in an N ₂ gas atmosphere.
It was preheated by heating to a temperature of ° C. Then, the pre-fired body is heated to about 2150 using a hot isostatic pressing (HIP) device.
HIP by applying isotropic pressure of about 3000 atm while heating to ℃
Treated. As a result, an amorphous carbon substrate (untreated) was obtained.

Next, the untreated amorphous carbon substrate was textured under various conditions. When using a soft surface plate for the finishing polishing process First, use a 16B double-side polishing machine manufactured by Speed Fam Co.,
Rough polishing was performed on an untreated amorphous carbon substrate using a cast iron surface plate while dropping SiC abrasive grains as a slurry. In this rough polishing, the abrasive grain concentration was 35% by weight, the work load was 300 g / cm ² , and the lower platen rotation speed was 100 rpm.
The slurry dropping amount was 600 ml / min, and the polishing time was 45 min.

Next, the amorphous carbon substrate after the rough polishing was ultrasonically cleaned to sufficiently remove the abrasive grains for the rough polishing.
After that, a 12B single-side polishing machine was used to finish-polish the amorphous carbon substrate after rough polishing with a surface plate made of Sn. For comparison, when the amorphous carbon substrate after rough polishing was subjected to final polishing with a cast iron surface plate, rolling of abrasive grains occurred and chipping that could be visually determined occurred on the surface of the amorphous carbon substrate. In the finish polishing, ZrO ₂ was used as the abrasive grain. As the abrasive grains, in addition to ZrO ₂ , diamond, SiC, Al ₂
As long as it has hardness equal to or higher than that of carbon, such as O ₃ , SiO ₂ and cerium oxide, it can be used for finish polishing. In addition, there is a correlation between the grain size of the abrasive grains and the surface roughness of the amorphous carbon substrate. As a result of various studies on this correlation, the surface roughness was found when the average grain size was 1 μm or less. It was confirmed that a mirror surface of 40 Å or less was obtained. However, when the average grain size of the abrasive grains exceeds 1 μm, defects such as orange peel and scratches frequently occur on the surface of the amorphous carbon substrate, and the practical durability is lowered. By changing the grain size of the abrasive grains based on such a relationship, the surface roughness Ra and the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra in the radial direction of the amorphous carbon substrate after the final polishing are performed.
Was as in Example 1 to 5 and Comparative Examples 1 to 4 and the ratio Ra ₂ / Ra ₁ and ₂ in different ones. And Example 1
5 to 5 and the amorphous carbon substrates according to Comparative Examples 1 to 4, the surface roughness Ra after finish polishing was measured using a surface roughness meter, and the surface roughness Ra ₁ in the circumferential direction and the surface in the radial direction were measured. the ratio Ra ₂ / Ra ₁ and the roughness Ra ₂ was determined. The results are shown in Table 1 below.

Next, the amorphous carbon substrate after the final polishing was heat-treated in air (in the presence of oxygen) under predetermined conditions. Thus, the amorphous carbon substrates for magnetic disks according to Examples 1 to 5 and Comparative Examples 1 to 4 were manufactured.

The above Examples 1 to 5 and Comparative Examples 1 to 4
The surface roughness Ra after the texture treatment was measured for each of the amorphous carbon substrates for magnetic disks according to the above-mentioned method using a surface roughness meter to obtain a surface roughness Ra ₁ in the circumferential direction and a surface roughness Ra ₂ in the radial direction. The ratio Ra ₂ / Ra _{1 of} was determined.
The results are also shown in Table 1 below.

Next, after precisely cleaning the amorphous carbon substrate for each magnetic disk, C is formed on the amorphous carbon substrate by using a magnetron sputtering device.
A media layer (magnetic film) made of oNiCr and a carbon protective film were sequentially formed, and a lubricant was applied to the surface of the media layer to produce a magnetic disk having a diameter of 3.5 inch.

Then, using a disk certifier (trade name) manufactured by Proquip Co., Ltd., the magnetic disk according to the examples and the comparative examples were evaluated for head crash occurrence and noise characteristics. The results are also shown in Table 1 below. The head flying height between the magnetic disk and the thin film head was about 0.08 μm.

[0029]

[Table 1] As is clear from Table 1, the magnetic disks according to Examples 1 to 5 have excellent noise characteristics without causing a head crash even when the head flying height is as low as about 0.08 μm. there were.

On the other hand, the surface roughness Ra after finish polishing is 51Å
In the magnetic disk according to Comparative Example 1, the surface roughness Ra after the texture treatment is unnecessarily rough, so that a head crash occurs during recording and reproduction, and it is difficult to put the head into practical use at a low head flying height. Further, this magnetic disk could not control the random orientation after the texture treatment, and had poor noise characteristics. R after finish polishing
Comparative Example 2 in which a ₂ / Ra ₁ is out of the range of 0.85 to 1.15
The magnetic disks according to Nos. 4 to 4 had poor random orientation after the texture treatment, and had poor noise characteristics during recording and reproduction. Head crashes occurred in the magnetic disks of Comparative Examples 2 and 4. When using a hard pad in the finishing polishing process First, use a 16B double-side polishing machine manufactured by Speedfam,
Rough polishing was performed on an untreated amorphous carbon substrate using a cast iron surface plate while dropping SiC abrasive grains as a slurry. In this rough polishing, the abrasive grain concentration was 35% by weight, the work load was 300 g / cm ² , and the lower platen rotation speed was 100 rpm.
The slurry dropping amount was 600 ml / min, and the polishing time was 45 min.

Next, the amorphous carbon substrate after the rough polishing was ultrasonically cleaned to sufficiently remove the abrasive grains for the rough polishing.
Thereafter, a 9B double-side polishing machine was used, and the amorphous carbon substrate after rough polishing was subjected to finish polishing (polishing) on a surface plate having a high hardness pad made of polyurethane or the like attached to the surface thereof. The average grain size of the abrasive grain is 1 μm
The following ZrO ₂ , diamond, SiC, Al ₂ O ₃ ,
SiO ₂ and cerium oxide were used as a slurry. In addition, the polishing conditions, the average concentration of abrasive grains is 5% by weight,
The work load was 350 g / cm ² , the lower platen rotation speed was 80 rpm, the slurry dropping amount was 20 ml / min, and the polishing time was 18 minutes. Then, by changing the grain size of the abrasive grains, the surface roughness R of the amorphous carbon substrate after the final polishing is performed.
The ratio Ra ₂ / Ra ₁ of a and the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra ₂ in the radial direction are made different.

Hereinafter, a magnetic disk was prepared in the same manner as in the case where a soft surface plate was used in the finish polishing step, and its various characteristics were evaluated.

As a result, even when the finish polishing is performed by the surface plate with the hard pad attached, the head flying height of the magnetic disk using the amorphous carbon substrate included in the claims of the present invention is about 0.08 μm. Even if it was low, head crash did not occur and the noise characteristics were excellent.

[0034]

As described above, according to the present invention, the surface roughness Ra of the amorphous carbon substrate for a magnetic disk is adjusted to 5 to 40 Å and the surface roughness Ra in the circumferential direction is polished. ₁ and surface roughness R in the radial direction
Since the ratio Ra ₂ / Ra ₁ with respect to a ₂ is set to 0.85 to 1.15 and then heat treatment is performed in the presence of oxygen, the texture can be randomly oriented and the surface roughness can be made appropriate. Therefore, the magnetic head can be prevented from being attracted to the magnetic disk, and the flying height of the magnetic head can be made smaller than in the prior art to improve the recording / reproducing characteristics of the magnetic film formed on the amorphous carbon substrate. .

Therefore, the amorphous carbon substrate for a magnetic disk according to the present invention is particularly suitable as a substrate for a high performance magnetic disk.

Claims (3)

[Claims] 1. The surface roughness Ra of the amorphous carbon substrate is adjusted to 5 to 40 Å by polishing the surface thereof, and the surface roughness Ra ₁ in the circumferential direction and the surface roughness R in the radial direction are obtained.
Amorphous carbon for a magnetic disk, comprising: a polishing step for adjusting a ratio Ra ₂ / Ra ₁ with respect to a ₂ to 0.85 to 1.15; and a heating step for heat treating a surface-polished amorphous carbon substrate in the presence of oxygen. Substrate texture processing method. 2. The polishing step uses at least one kind of abrasive grains selected from the group consisting of diamond, alumina, SiC, ZrO ₂ , cerium oxide and SiO ₂ having an average grain size of 1 μm or less for softness determination. 2. An amorphous carbon substrate is lap-polished by a disk.
The method for texture treatment of an amorphous carbon substrate for a magnetic disk according to. 3. The polishing step is at least selected from the group consisting of diamond having an average particle size of 1 μm or less, alumina, SiC, ZrO ₂ , cerium oxide and SiO _2.
The amorphous carbon for a magnetic disk according to claim 1, wherein the amorphous carbon substrate is lap-polished by a surface plate having a hard pad having a hardness of 60 or more adhered to the surface thereof by using one kind of abrasive grains. Substrate texture processing method.