JP4639477B2 - Method for manufacturing magnetic recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium including a magnetic film used in a hard disk drive (HDD) mainly used as an external recording device of a computer at present, and a manufacturing method thereof. More specifically, the present invention relates to a magnetic recording medium having a carbon protective film having a function of protecting a magnetic film forming a recording layer from head impact and corrosion of an external corrosive substance and a manufacturing method thereof. More specifically, the present invention relates to a magnetic recording medium that realizes high reliability by reducing particles generated in the protective film when the carbon protective film is formed, and a manufacturing method thereof.
[0002]
[Prior art]
Currently, the surface recording density of magnetic recording media used in HDDs reaches ²⁰ Gbits / in ² at the development stage, and is improving at an annual rate of 100%. Due to the further increase in the density of magnetic recording, it has become necessary to bring the write / read head closer to the surface of the recording medium in order to read a smaller magnetization region with a high SN ratio. Currently, the head flying height, at 20 Gbits / in ^2, 19 nm or less, the 50Gbits / in ^2, it is estimated to 15nm or less. In the future, it is expected that it will be required to reduce the flying distance between the magnetic recording medium and the data R / W head in response to the higher density of magnetic recording. Therefore, it is naturally necessary to reduce the thickness of the protective film on the surface of the magnetic recording medium.
[0003]
Such a protective film is conventionally formed by sputtering. According to the sputtering method, as is well known, a protective film having durability and corrosion resistance can be formed, but it is difficult to reduce the film thickness to 80 mm or less. Therefore, as a process for forming a next-generation carbon protective film in place of the sputtering method, a plasma CVD method capable of obtaining a higher-density film has attracted attention and has been actively researched.
[0004]
However, when film formation is started by the CVD method, a carbon film is unavoidably formed on the inner wall of the film formation chamber in the initial stage of operation of the apparatus, and this carbon film peels off from the wall surface, falls, and adheres to the recording medium as particles. To do. At this time, the number of particles is very large, and a manufactured magnetic recording medium cannot be obtained. If the operation is continued as it is, the carbon film adhering to the wall surface will be consumed by peeling, and the number of particles adhering to the surface of the recording medium will gradually decrease, but it will be reduced to a target number that does not cause any practical problems for the magnetic recording medium. This takes time and leads to a decrease in yield.
[0005]
On the other hand, conventionally, a method has been proposed in which the inner wall surface of the film forming chamber is made of a substance containing silicon and oxygen or a substance containing carbon (Japanese Patent Laid-Open No. 11-189876). Specific examples of the carbon-containing substance include graphite, amorphous carbon, polyethylene, and the like. The characteristics of the film formed on the inner wall of the chamber by such a substance containing carbon, and the surface of the magnetic recording medium The relationship between the number of particles adhering to the particle and the particle size is not disclosed or suggested. This prior art document discloses that the number of adhered particles is about 200 per side when a magnetic recording medium is formed using a chamber containing a film containing carbon on the inner wall of the chamber. There is no disclosure of particle size. In order to improve the glide characteristics in a magnetic recording medium, it is necessary to control both the number of particles attached and the particle size. For that purpose, it is important to know the number of adhering particles and the allowable limit of the particle size. It is necessary to know the correlation between these allowable limits and the characteristics of the film formed on the inner wall of the chamber. For the first time, it is possible to ensure the reproducibility and reliability of the control system that suppresses particles that inevitably adhere to the surface of the magnetic recording medium to a practically unproblematic range by knowing these matters. However, this prior art document has no disclosure.
[0006]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a method for reducing the increase in particles generated from the inner wall of the film formation chamber in the initial stage of operation of the apparatus and reducing the time required for the reduction to the target number in the manufacture of the magnetic recording medium. An object of the present invention is to increase the yield of manufacturing the magnetic recording medium and improve the quality of the manufactured magnetic recording medium. More specifically, the allowable number of particle adhesion and particle size are determined, and a correlation between the allowable limit and the characteristics of the film formed on the inner wall of the chamber is obtained, thereby making it difficult to avoid the surface of the magnetic recording medium. It is an object of the present invention to provide a method for producing a magnetic recording medium capable of suppressing adhering particles to a practically no problem range, and a high-quality magnetic recording medium obtained by the method.
[0007]
[Means for Solving the Problems]
In order to solve such problems, the present inventors have intensively conducted experiments and examinations, and have obtained the following knowledge. Before the main film formation of the carbon protective film on the magnetic layer, a carbon film with low stress is formed on the inner wall of the film formation chamber, and if the carbon film is difficult to peel off, the number of particles at the initial stage of moving the device can be increased. I found that it can be reduced. More specifically, when a carbon film having a compressive stress of 1.0 to 2.5 GPa is formed on the inner wall of the film forming chamber before the main formation of the carbon protective film on the magnetic layer , the magnetic recording medium The amount of particles having a size of 0.3 μm or more among the particles adhering to the protective film can be reduced to 100 / 3.5 inch substrate or less. As a result, it has been found that a magnetic recording medium having a high quality magnetic recording density can be produced with a high yield.
[0009]
The method of manufacturing a magnetic recording medium according to the present invention includes a method of manufacturing a magnetic recording medium in which at least a magnetic layer, a carbon protective film, and a liquid lubricant are sequentially laminated on a nonmagnetic substrate. Before the main film formation, a carbon film having a compressive stress of 1.0 to 2.5 GPa is formed on the inner wall of the film formation chamber, and from the inner wall of the film formation chamber during the main film formation of the carbon protective film. The carbon film is prevented from peeling off, and particles adhering to the surface of the protective film are reduced.
[0010]
In the present invention having the above-described configuration, more preferably, the compressive stress of the carbon film is 1.5 to 2.0 GPa.
[0011]
The film thickness of the carbon film on the inner wall of the chamber is preferably 3.0 to 5.0 μm, and more preferably the film thickness of the carbon film is 3.5 to 4. 0 μm.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The magnetic recording medium of the present invention has at least a magnetic layer, a carbon protective film, and a liquid lubricating layer that are sequentially laminated on a nonmagnetic substrate.
[0013]
The nonmagnetic substrate used in the present invention may be any conventional nonmagnetic substrate such as an aluminum alloy, glass, or plastic substrate. Specific examples of the plastic substrate include substrates made of polycarbonate, polyolefin, polyethylene terephthalate, polyethylene naphthalate, polyimide, and the like.
[0014]
The board may be a disk board of any size of 2.5 inch, 3 inch, 3.3 inch, 3.5 inch, 5 inch, and the form is not limited to the disk shape, and the card Any shape such as a shape or a belt shape may be used. In addition, it should be understood that the size shown here is a nominal value and is widely used in the art.
[0015]
The magnetic film used in the present invention includes a ferromagnetic metal that can be used as a recording layer. Specifically, CoCrTaPt, CoCrTaPt—Cr ₂ O ₃ , CoCrTaPt—SiO ₂ , CoCrTaPt—ZrO ₂ , CoCrTaPt—TiO ₂ , A magnetic film containing CoCrTaPt—Al ₂ O ₃ or the like as a component.
[0016]
The thickness of the magnetic layer is 20 nm or less, preferably 10 to 20 nm. A plurality of magnetic films may be used to form a multilayered recording layer.
[0017]
An underlayer may be formed between the magnetic layer and the substrate. The underlayer may be formed from any conventional component that forms the underlayer, and is not particularly limited. Specifically, it consists of Cr, Cr—W, Cr—V, Cr—Mo, Cr—Si, Ni—Al, CoCr, Mo, W, Pt, and the like.
[0018]
The thickness of the underlayer is 20 nm or less, preferably 10 to 20 nm.
[0019]
As the lubricant, perfluoro-polyether is used as a liquid lubricant, and among them, Z-dol (trade name, manufactured by Augmont) is desirable.
[0020]
The protective film has a function of protecting the magnetic film forming the recording layer from the impact of the head and the corrosion of corrosive substances in the outside world. The thickness of the protective film is 8 nm or less, preferably 3 to 8 nm.
[0021]
The protective film can be obtained by forming DLC (Diamond-like Carbon) by plasma CVD. The plasma CVD method is a method of forming a thin film at a low temperature by decomposing a gas as a raw material with electrons instead of heat energy and applying electromagnetic energy. Specifically, a thin film can be formed using an apparatus that combines a CVD apparatus that performs film growth by vapor deposition and an apparatus that discharges. Examples of the plasma CVD method include filament type ion beam-CVD, hollow cathode type ion beam-CVD, electron cyclotron resonance-CVD, high-frequency-CVD, and electron beam excitation plasma-CVD. May be.
[0022]
As a source gas for forming a DLC film, a hydrocarbon gas such as methane (CH ₄ ), ethylene (C ₂ H ₄ ), acetylene (C ₂ H ₂ ), toluene (C ₇ H ₈ ), or the like is used. .
[0023]
As a result of examining the stress of the carbon film formed on the substrate having the same potential as the inner wall of the chamber, when the carbon film formed on the inner wall of the chamber has a certain stress, particles having a size of 0.3 μm or more are generated. It has been found that there are no more than 100 / 3.5 inch substrates.
[0024]
The stress was obtained by the substrate warpage deformation method. The average residual stress generated in the film was obtained from the amount of warpage deformation of the substrate itself caused by the residual stress existing in the film.
[0025]
As shown in FIG. 1, the carbon film formed on the inner wall of the chamber according to the present invention has a stress of 1.0 to 2.5 GPa, preferably 1.5 to 2.0 GPa. If the stress is greater than 2.5 GPa, it will be easy to peel off from the inner wall of the chamber, while if it is less than 1.0 GPa, the stress difference from the deposited carbon having a large stress will be large, resulting in poor adhesion. The film carbon easily peels off from the inner wall of the chamber and becomes a source of particles.
[0026]
The carbon film having a stress of 1.0 GPa can be formed at a voltage of 1/4 of the voltage between the anode and the ground, which is a parameter related to the acceleration of ions during the main film formation, and has a stress of 2.5 GPa. Can be formed at a voltage of 5/8.
[0027]
Moreover, the thickness of the carbon film formed on the inner wall of the chamber before the main film formation is 3.0 to 5.0 μm, preferably 3.5 to 4.0 μm. If the film thickness is less than 3.0 μm, the buffering effect between the inner wall of the chamber and the film-forming carbon cannot be obtained because it is too thin. On the other hand, if the film thickness is larger than 5.0 μm, the film formation time is too long and the operation rate of the apparatus is lowered.
[0028]
An optical appearance tester was used for measuring the number of particles on the surface of the protective film.
[0029]
【Example】
Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the following examples.
[0030]
Example 1
FIG. 2 is a schematic sectional view of the magnetic recording medium 1 of this embodiment. As shown in FIG. 2, a NiP plating (plating layer) 3 is applied on an aluminum alloy substrate (nonmagnetic substrate) 2, and a 20 nm Cr underlayer 4 and a 20 nm Co magnetic layer 5 are formed thereon by sputtering. Filmed. Furthermore, a DLC protective film 6 was formed using ethylene (C ₂ H ₄ ) as a raw material by hollow cathode type ion beam-CVD described in detail below.
[0031]
FIG. 3 is a principle diagram of hollow cathode-CVD. The apparatus includes a hollow cathode 110, an anode electrode 111, and a magnet 112. Thermoelectrons generated from the hollow cathode 110 are attracted to the anode side by the anode voltage, collide with Ar gas introduced from the anode side, and Ar ⁺ Ar ⁺ generated and pushed by the anode voltage collides with C ₂ H ₄ to generate plasma. The magnet 112 controls the plasma density. Ions in the plasma are pushed out to the substrate 113 side by an anode voltage.
[0032]
Before the main film formation, a carbon film having a stress of 2.0 GPa was formed on the inner wall of the chamber at a thickness of 3.5 μm, and then the main film formation was performed.
[0033]
Next, Z-dol (trade name, manufactured by Augmont) was applied to the surface of the protective film to form a 2 nm liquid lubricating layer.
[0034]
When a reliability test was performed using the obtained magnetic recording medium, the number of particles having a size of 0.3 μm or more on a 3.5-inch substrate was mostly about 60 particles / surface, and the yield rate was about 80%. there were.
[0035]
(Comparative Example 1)
In this comparative example, the main film was formed before the main film formation, without forming a carbon film having a low stress on the inner wall of the chamber.
[0036]
Next, Z-dol (trade name, manufactured by Augmont) was applied to the surface of the protective film to form a 2 nm liquid lubricating layer.
[0037]
When a reliability test was performed using the obtained magnetic recording medium, the number of particles having a size of 0.3 μm or more on a 3.5 inch substrate was as large as 1000 particles / surface, and the yield rate was 0%.
[0038]
【The invention's effect】
According to the present invention, a carbon film having a low stress is formed on the inner wall of the chamber before the main film formation of the carbon protective film, thereby making it difficult to peel off the carbon film from the inner wall of the chamber after the main film formation. By eliminating adhesion to the medium, particles on the surface of the protective film can be reduced, and a high yield rate can be achieved. Therefore, the present invention can provide a highly reliable magnetic recording medium that can sufficiently cope with higher density of magnetic recording.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the stress of a carbon film formed on the inner wall of a chamber and the number of particles immediately after operation of the apparatus.
FIG. 2 is a schematic cross-sectional view of a medium showing an embodiment of the magnetic recording medium of the present invention.
FIG. 3 is a schematic configuration diagram of a hollow cathode type ion beam-CVD apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Nonmagnetic board | substrate 3 Mating layer 4 Underlayer 5 Magnetic layer 6 DLC protective film 110 Hollow cathode 111 Anode electrode 112 Magnet 113 Substrate 114 Power supply

Claims (4)

In a method of manufacturing a magnetic recording medium, a magnetic recording medium is obtained by sequentially laminating at least a magnetic layer, a carbon protective layer, and a liquid lubricant on a nonmagnetic substrate.
Before the main film formation of the carbon protective layer on the magnetic layer, a carbon film having a compressive stress of 1.0 to 2.5 GPa is formed on the inner wall of the film formation chamber. A method of manufacturing a magnetic recording medium, wherein the carbon film is prevented from peeling from the inner wall of the film forming chamber and particles adhering to the surface of the protective film are reduced.   2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the compressive stress of the carbon film is 1.5 to 2.0 GPa.   3. The method of manufacturing a magnetic recording medium according to claim 1, wherein a film thickness of the carbon film on the inner wall of the chamber is set to 3.0 to 5.0 μm.   4. The method of manufacturing a magnetic recording medium according to claim 1, wherein a thickness of the carbon film formed on the inner wall of the chamber is set to 3.5 to 4.0 μm.

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