JPH0594618A - Texture treatment of amorphous carbon substrate for magnetic disk - Google Patents

Abstract

PURPOSE:To form a good texture surface by polishing the surface of the amorphous carbon substrate to the roughness of a prescribed range and the ratio of the surface roughness in a circumferential direction and a radial direction in a prescribed range, then subjecting the substrate to a prescribed heating treatment. CONSTITUTION:The surface of the amorphous carbon substrate is polished, by which the surface roughness Ra thereof is made into 4 to 40Angstrom and the ratio Ra2/Ra1 of the surface roughness Ra1 in the circumferential direction and the surface roughness Ra2 in the radial direction is made within the 0.85 to 1.15 range. The carbon substrate subjected to the surface roughening is subjected to the heating treatment in the presence of an oxidative gas selected from a group consisting of steam, hydrogen, ozone, and carbon dioxide and the texture is thereby formed. The attraction of a magnetic head to a magnetic disk is prevented in this way and the floating height of the magnetic head is decreased. Since the formation of the texture is executed by oxidative gases exclusive of gaseous oxygen, the surface roughness is uniformized.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a magnetic disk is constructed by forming a magnetic film on an Al substrate coated with a Ni--P plated material or the like. Then, in the magnetic disk reproducing apparatus, a floating magnetic head is arranged on the magnetic disk, and the magnetic head is levitated by rotating the magnetic disk, and the magnetic head writes or reproduces on the magnetic disk. To do. However, when writing to or reproducing from a magnetic disk, adsorption may occur between the magnetic head levitation surface and the magnetic disk surface when the disk is stationary. This adsorption phenomenon is caused by the fact that when the magnetic head levitation surface and the magnetic disk surface are extremely smooth and both face each other with a minute gap, the gap is filled with molecules such as O ₂ , N ₂ or H ₂ O. This is due to the generation of a large adsorption force due to the interfacial tension. If such an adsorption phenomenon occurs, it causes a disadvantage that a large amount of electric power is consumed when the motor that drives the magnetic disk is started.

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 surface of the substrate is once mirror-finished and then textured 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 a roller so as to be in 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 manner, concentric circular scratches are formed on the surface of the Al substrate for a magnetic disk, and a rough surface in which the scratches are oriented in the circumferential direction can be obtained.

Incidentally, 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, and 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 for 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 viewpoint 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 head adsorption of a 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 treatment 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 an amorphous carbon substrate to have a surface roughness Ra of 5 to 40Å and a circumferential direction. Polishing step for making the ratio Ra ₂ / Ra ₁ of the surface roughness Ra ₁ and the surface roughness Ra ₂ in the radial direction within the range of 0.85 to 1.15 or 1.50 or more, and the surface-polished amorphous carbon substrate with water vapor, hydrogen, And a heating step of performing heat treatment in the presence of an oxidizing gas selected from the group consisting of ozone and carbon dioxide.

[0008]

The inventors of the present application focused on the properties of the amorphous carbon substrate and conducted various studies on the texture processing method. As a result, after polishing the amorphous carbon substrate 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. It was found that the invention was completed based on this principle, and we have already applied for it as Japanese Patent Application Nos. 2-410434 and 2-410436.

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 will not be roughened more than necessary. As a result, it is possible to prevent head adsorption of the magnetic disk, improve the characteristics of the magnetic film formed on the amorphous carbon substrate, and make the flying height of the magnetic head smaller than before.

As described above, according to the invention of the above-mentioned prior application, although the effect which cannot be obtained by the conventional texture processing is obtained and the intended purpose thereof is achieved, the following insufficient points are also found. Came to be.

That is, in a hard disk, uniform texture processing is required to promote stable head flying. However, since the invention according to the above-mentioned prior application is the chemical texture treatment of the carbon substrate using oxygen in the atmosphere, the change in roughness due to the change in the treatment temperature is relatively large. Moreover, as the temperature distribution in the heating furnace becomes higher, it becomes more difficult to control the temperature. In addition, in a temperature range where the oxidation reaction occurs violently, there is a problem that the amount of oxidation varies depending on the substrate position from the convection state of the atmosphere. Due to these factors, the roughness of the textured surface is likely to be uneven. As described above, it is difficult to adjust the surface roughness of the NiP substrate or the like when the mechanical texture is applied to the texture treatment of the carbon substrate.

Therefore, as a result of various investigations by the present inventors, the use of an oxidizing gas other than oxygen gas, that is, steam, hydrogen, ozone or carbon dioxide, slows down the oxidation reaction rate, It has been found that a uniform textured surface can be formed over the entire surface of the substrate. That is, the present invention utilizes oxidation of the substrate surface by the oxidizing gas by heating after the polishing step in the presence of an oxidizing gas selected from the group consisting of water vapor, hydrogen, ozone and carbon dioxide. It is characterized by performing texture processing.

The reaction constant at the oxidation temperature of the carbon substrate differs depending on the firing temperature of the carbon substrate and the type of oxidizing agent. The oxidation reaction of the dry carbon substrate occurs not only with oxygen but also with water vapor, hydrogen, ozone and carbon dioxide. The oxidation reaction of the carbon substrate with these oxidizing gases is shown below. C + H ₂ O = CO + H ₂ C + 2H ₂ ═CH ₄ C + CO ₂ = 2CO These oxidizing gases have small changes in reaction rate due to changes in the oxidation temperature. Therefore, by performing the texture treatment using these oxidizing gases, it is possible to form a uniform textured surface without strictly controlling the temperature. This makes it possible to easily manufacture an amorphous carbon substrate having a textured surface with uniform roughness.

Next, the surface roughness Ra and the surface roughness R in the circumferential direction of the amorphous carbon substrate in the surface polishing step.
Ratio of a ₁ to surface roughness Ra ₂ in the radial direction Ra ₂ / Ra ₁
The reason for the limitation will be described. Random orientation When the orientation of the texture with respect to the substrate surface is randomly oriented, that is, the surface roughness R of the amorphous carbon substrate
When a is not biased in the circumferential direction or the radial direction, it is possible to reduce the recording / reproducing error and the noise (S / N ratio) in practical use as a magnetic disk, and it is possible to increase the recording density.

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 during practical use as a magnetic disk. On the other hand, if 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, 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. It is suitable for use in. It should be noted that the amorphous carbon substrate in the present invention refers to glassy carbon and ultra-high temperature HI.
By performing P (hot isostatic pressing), 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 that is close to 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 diameter 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, minute recesses called so-called orange peels 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, if 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 peels and chippings occur on the surface of the amorphous carbon substrate. It happens frequently. On the other hand, when a 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.

It is necessary to dress the rough surface after using the above-mentioned soft surface plate for a predetermined period. Therefore, a soft surface plate or a hard surface plate on which a hard pad made of polyurethane or the like having a hardness of 60 or more is adhered can be used. In this case, similar to the soft surface plate, no defects occur on the surface of the amorphous carbon substrate, and it is only necessary to replace the hard pad instead of dressing the surface of the surface plate, which is advantageous in that the processing cost can be reduced. is there.

As described above, in the present invention, the average particle size is
Diamond less than 1μm, alumina, SiC, ZrO
₂ , using at least one type 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. Circumferential Orientation Unlike the random orientation, the circumferential orientation can improve the magnetic properties in the circumferential direction. In this case, 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 50 Å, it becomes difficult to reduce the flying height of the magnetic head as compared with the conventional one. Therefore, the surface roughness Ra of the amorphous carbon substrate after surface polishing is set to 5 to 50 Å.

The main purpose of texturing an amorphous carbon substrate for a magnetic disk is to prevent the magnetic head from adsorbing, but if the directionality of the texture with respect to the substrate surface is concentric circular orientation, that is, the surface roughness of the amorphous carbon substrate becomes rough. When Ra is made larger in the radial direction than in the circumferential direction, the coercive force and the squareness ratio in the circumferential direction can be improved by 20 to 30% as compared with those in the radial direction. Since the magnetic head moves in the circumferential direction relative to the magnetic disk during recording and reproduction, if the texture is oriented in the circumferential direction as described above, the magnetic characteristics of the magnetic film in the circumferential direction are remarkably increased. Can be improved. Therefore, it is not necessary to improve the magnetic characteristics of the magnetic film by adding an expensive element such as Pt or Ta to the magnetic film (media layer). The circumferential orientation of this texture is determined by surface polishing before heat treatment. However, the ratio Ra ₂ 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 / Ra ₁ is less than 1.50, the circumferential orientation of the texture is insufficient and the magnetic properties of the media layer in the circumferential direction are insufficiently improved. 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 1.50 or more.

As described above, the amorphous carbon substrate for a magnetic disk according to the present invention can make the flying height of the magnetic head small, and can form the media layer without adding an expensive element such as Pt or Ta. Since the magnetic characteristics can be improved, it is particularly suitable for use in a low-cost magnetic disk.

The amorphous carbon substrate in the present invention is obtained by subjecting glassy carbon to ultra-high temperature HIP (hot isostatic pressing) treatment to eliminate most of the pores and increase the density to 1.80 g / cm ³ or more. It is made of high-density amorphous carbon that is made higher and its characteristics are closer to those of graphite.

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

In the polishing step, an abrasive material such as a tape polisher used when mechanically texture-processing a conventional Al substrate for magnetic disk is effective. That is, while the abrasive material is brought into contact with the amorphous carbon substrate while the amorphous carbon substrate is rotated, the abrasive material is moved in the radial direction of the amorphous carbon substrate, for example, from the outer peripheral portion to the inner peripheral portion of the substrate. .. A polishing tape to which fine powdery abrasive particles are attached can be used as the polishing material. Abrasive grains having hardness equal to or higher than that of an amorphous carbon substrate and industrially inexpensive, for example, diamond, alumina, SiC, Zr
O ₂ , cerium oxide, SiO ₂ or the like is used. As a result, the surface of the amorphous carbon substrate is cut by the abrasive grains as it rotates. Therefore, by appropriately selecting the number of rotations of the substrate, the number of the polishing tape to be used, the moving speed of the polishing tape, etc., the surface roughness Ra of the amorphous carbon substrate after the surface polishing is set to 5 to 50Å and the the ratio Ra ₂ / Ra ₁ and the surface roughness Ra ₁ and radial surface roughness Ra ₂ can be 1.50 or more, it is possible to form the concentric striations on the surface of the amorphous carbon substrate.

[0029]

EXAMPLES A method of texturing an amorphous carbon substrate for a magnetic disk according to an example of the present invention and a comparative example outside the scope of the claims of the present application will be described below. Regarding the case of performing texture treatment using water vapor (this example) and the case of performing texture treatment under oxygen gas (atmosphere) as in the above-mentioned prior application (comparative example),
The changes in the surface roughness are shown in Table 1 below with the passage of time. However, in the case of the comparative example, in order to slow down the reaction rate, the carbon substrate was heated while the atmosphere was sealed in the furnace. Further, in the case of the example, steam was generated by the processing apparatus shown in FIG. 1 to perform the texture processing.

That is, pure water 2 is enclosed in a container 1 which is hermetically sealed, and N ₂ gas is introduced into the pure water 2 in the container 1 from the outside through a pipe 3 at a rate of 3 liters / minute. Introduced in.
Further, the container and the tubular furnace 4 were airtightly connected by a pipe 5, and the carbon substrate 6 was loaded in the tubular furnace 4. And container 1
Pure water 2 therein was heated to 70 to 80 ° C., controlled by an ordinary thermometer and kept in this temperature range. On the other hand, tubular furnace 4
Were held at various temperatures within the range of 500 to 900 ° C. as shown in Table 1. The heating time of the substrate 6 in the tubular furnace 4 is 30 minutes, and the pressure in the tubular furnace 4 is 1 atm.

[0031]

[Table 1]

As a result, as is clear from Table 1, the surface roughness of the carbon substrate becomes rougher as the temperature of the oxidizing gas becomes higher. However, when water vapor is used as in this example. , Because the oxidation reaction of the carbon substrate is slow,
Even when heated to 900 ° C., a uniform roughness that could be sufficiently used as a textured surface was obtained. In contrast,
When oxygen gas (atmosphere) was used, the surface roughness became 250Å at 700 ° C, and the roughness could not be measured at higher temperatures.

The variation in surface roughness is 800 ° C. ± 7Å in the case of water vapor of the present embodiment, and ±± 6Å in the case of oxygen of the comparative example at 600 ° C. It was 13Å.

As shown in Table 1, the surface roughness of the obtained textured surface can be controlled by adjusting the oxidation temperature. In addition to this, the conditions such as processing time and used gas can be selected. By doing so, it is possible to control to an arbitrary roughness. When steam is used, it is preferable to perform heat treatment at 900 ° C or lower in consideration of cost and productivity. Also, for example, when hydrogen gas is used, 1000 ° C or higher, when carbon dioxide gas is used, 600 ° C or lower, and when ozone is used, 300 ° C.
The following are preferred. In the case of ozone, unless the baking temperature of the substrate is set to 600 ° C. or lower, the progress of oxidation becomes extremely slow.

[0035]

As described above, according to the present invention, the surface roughness Ra of the amorphous carbon substrate for a magnetic disk is polished to 5 to 40 Å and the surface roughness Ra in the circumferential direction is increased. ₁ and surface roughness R in the radial direction
The ratio Ra ₂ / Ra ₁ with respect to a ₂ is set to 0.85 to 1.15 or more, or the surface roughness Ra is set to 5 to 50Å, and the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra ₂ in the radial direction are set. Since the ratio Ra ₂ / Ra ₁ of the substrate is set to 1.50 or more, the substrate is heat-treated in the presence of an oxidizing gas containing no oxygen gas. Can be appropriate. For this reason,
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. Further, since the texture is formed by using an oxidizing gas other than oxygen gas, the surface roughness can be made uniform.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a texture processing device using water vapor.

[Explanation of symbols]

 1; container 2; pure water 4; tubular furnace 6; substrate

Claims (5)

[Claims] 1. A circumferential surface roughness Ra ₁ and radial surface roughness R together with the table surface roughness Ra to 5 to 40Å by polishing the surface of the amorphous carbon substrate
a polishing step for adjusting the ratio Ra ₂ / Ra ₁ with a ₂ to 0.85 to 1.15, and heating the surface-polished amorphous carbon substrate in the presence of an oxidizing gas selected from the group consisting of water vapor, hydrogen, ozone and carbon dioxide. And a heating step of treating the amorphous carbon substrate for a magnetic disk. 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.
A method for texture-treating 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. 4. The surface roughness Ra of the amorphous carbon substrate is adjusted to 5 to 50 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.
a polishing step for making the ratio Ra ₂ / Ra ₁ with respect to a ₂ 1.50 or more;
And a heating step of performing heat treatment in the presence of an oxidizing gas selected from the group consisting of hydrogen, ozone and carbon dioxide, and a method for texture-treating an amorphous carbon substrate for a magnetic disk. 5. In the polishing step, while the amorphous carbon substrate is being rotated, a polishing material is brought into contact with the amorphous carbon substrate and is moved in the radial direction thereof to form concentric scratches on the surface of the amorphous carbon substrate. The method for texture treatment of an amorphous carbon substrate for a magnetic disk according to claim 4, wherein