JPH11256340A - Formation of dlc film and magnetic recording medium produced thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently removing a DLC film adhered to each place in a vacuum tank though, in the case a DLC film is formed on a supporting body in a vacuum tank, since a DLC film has been adhered to deposit to each place in the vacuum tank, which is peeled off and fallen to generate defects, there has been need of executing the cleaning of the attachments by frequently breaking a vacuum in the tank, and considerable labors and times have been required. SOLUTION: This method includes a stage in which, at the time of forming a DLC film 3 as a protective film on a supporting body 1 to be carried in a vacuum tank, only a DLC film in the vacuum tank is subjected to etching to remove by oxygen plasma per prescribed period in a forming stage of a DLC film, and the oxygen gas pressure at the time of generating the oxygen plasma is regulated to <=800 Torr. A magnetic recording medium has a DLC film formed by using this film forming method as a protective film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a DLC film and a magnetic recording medium having a DLC film formed by the method as a protective film.

[0002]

2. Description of the Related Art In recent years, the relative speed between a magnetic head and a magnetic recording medium tends to increase as the density of the magnetic recording medium increases. When the relative speed between the magnetic head and the magnetic recording medium increases, the sliding speed inevitably increases, so that the wear resistance of the magnetic recording medium becomes an important issue. As a solution to this, use of a protective film has been proposed and put into practical use. In particular, a carbon protective film and a protective film mainly composed of carbon are generally used.

[0003] In the case of a magnetic tape for a video deck, for example, a carbon protective film was not necessary for a vapor deposition tape for Hi-8, but hydrogen was mixed in a carbon film for a DV format vapor deposition tape to reduce diamond properties. The so-called diamond-like carbon (Diamom)
d Like Carbon (hereinafter, referred to as DLC)
A film is used as a protective film.

The DLC film is formed by sputtering, C
VD (Chemical Vapor Deposit)
ion) method or the like is used. In the sputtering method, a gas is introduced into a vacuum chamber, plasma is generated by discharging between electrodes, and the plasma is applied to a target.
This is a method of depositing target particles scattered by a sputtering phenomenon. When a DLC film is formed by this sputtering method, a carbon target is generally used as a target, and a gas obtained by mixing a hydrogen gas or a hydrocarbon gas with an Ar gas is used as a gas.

On the other hand, in the CVD method, a gas is introduced into a vacuum chamber, and plasma is generated in the vacuum chamber by various methods.
In this method, a gas introduced into the vacuum chamber is caused to undergo a chemical reaction by the energy of the generated plasma, and a product generated by the chemical reaction is deposited. When a DLC film is formed by this CVD method, a hydrocarbon gas is often used as an introduction gas, and in some cases, an Ar gas may be mixed as a carrier gas. There are various methods of generating plasma, for example, a method of generating plasma by applying a direct current or a high frequency between electrodes,
A method of generating plasma using a microwave is mainly used.

[0006]

As described above, when a DLC film is formed on a magnetic recording medium in a vacuum chamber, the DLC film is deposited and deposited on various parts of the vacuum chamber other than the magnetic recording medium, and the deposition is performed. There is a problem that the DLC film peels off and the inside of the vacuum chamber is contaminated. Specifically, the DLC film often separates into particles and peels off, and if the particles adhere to the magnetic recording medium, it becomes a defect that adversely affects the recording / reproducing characteristics of the magnetic recording medium.

In the case of the aforementioned sputtering method, particles scattered from a carbon target are deposited on a magnetic recording medium,
The DLC film is formed, and the carbon particles are also scattered in portions other than the magnetic recording medium. However, since the scattered particles have directionality, the above-described problem can be considerably prevented by installing a shielding plate in a portion other than the magnetic recording medium that is not to be adhered. The DLC film may be deposited on the shielding plate and peeled off. However, by devising the positional relationship between the shielding plate and the magnetic recording medium and the shape of the shielding plate, the magnetic recording medium is adversely affected. The resulting defects can be reduced. As described above, the sputtering method is effective for producing a magnetic recording medium with few defects, but on the other hand, the sputtering method has a very low film formation rate, so that when a large number of magnetic recording media are manufactured, However, it is hard to say that it is appropriate in terms of productivity.

On the other hand, the CVD method has a much higher film forming rate than the sputtering method and is advantageous in terms of productivity. However, when the DLC film is formed by the CVD method, in principle, the DLC film is deposited on all portions in contact with the plasma of the reaction gas. Since the plasma is gaseous and diffusive, even if a shielding plate is provided, its effect is small, and the DLC film will be deposited on various places in the vacuum chamber except for the magnetic recording medium. Therefore, when a magnetic recording medium is manufactured by forming a DLC film by the CVD method, the DLC film is deposited and peeled off and adheres to the magnetic recording medium to adversely affect the characteristics of the magnetic recording medium. It is necessary to clean the inside of the vacuum chamber before any defects occur. This cleaning needs to be performed many times during the process of forming a long magnetic recording medium, and it is necessary to break the vacuum in the vacuum chamber when performing the cleaning. Therefore, the vacuum evacuation is performed again in order to restart the film formation process that has been interrupted after the cleaning is completed, and the operation requires a long time. Further, since cleaning in the vacuum chamber itself takes time and effort, there is a problem that productivity is lowered.

[0009]

The present inventor has conducted various studies to solve the above-mentioned problems. As a result, in order to efficiently remove the DLC film adhered to various places in the vacuum chamber, the vacuum in the chamber was reduced. The idea was obtained that the film forming step and the cleaning step should be performed continuously and alternately without breaking. As a cleaning process, it was confirmed that plasma etching performed by generating plasma at a predetermined oxygen gas pressure was extremely effective.

In other words, according to the present invention, when a DLC film is formed on a support conveyed in a vacuum chamber, oxygen plasma is generated in the vacuum chamber by oxygen plasma every predetermined period of the DLC film forming process. The process includes a step of etching and removing only the DLC film, and the oxygen gas pressure for generating the oxygen plasma is 800
A method of forming a DLC film having a mTorr or less is provided. Further, according to the present invention, there is provided a magnetic recording medium having a DLC film formed using the above-described film forming method as a protective film.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for forming a DLC film according to the present invention will be described in detail. The present invention relates to a method of forming a DLC film, and more specifically, to a method of removing a DLC film adhered to an unnecessary portion in a vacuum chamber in a process of forming a DLC film. In the present invention, the step of forming the DLC film itself may be performed in a vacuum chamber, for example, any method such as a CVD method and a sputtering method. Therefore, since it is easy to prevent adhesion to unnecessary portions by using a shielding plate or the like, it is more advantageous to apply to a CVD method in which it is difficult to prevent adhesion to unnecessary portions.

For example, in a step of forming a DLC film by a CVD method on a support conveyed in a vacuum chamber,
The film formation is temporarily stopped for each predetermined period, specifically, for each predetermined processing length of the film formation, and oxygen plasma is generated in the vacuum chamber to etch away the DLC film in the vacuum chamber. At this time, the oxygen gas pressure when generating the oxygen plasma is set to 800 mTorr.
It is necessary to be less than or equal to r. Oxygen gas pressure 800m
If the pressure exceeds Torr, the etching rate of the DLC film is significantly reduced, and it becomes almost impossible to remove the DLC film even if the etching time is lengthened.

In the above process, the interval at which the cleaning in the vacuum chamber is carried out may be, for example, in the case of forming a DLC film as a protective film of the magnetic recording medium, a desired time for the manufactured magnetic recording medium. In order to obtain the characteristics described above, it is desirable to determine in advance the processing length for cleaning, that is, the DLC film formation length, and to perform the cleaning step for each film formation length. A magnetic recording medium having a DLC film formed as a protective film formed by the above film forming method has high quality without defects over the entire length.

<Example> (Example 1) [Manufacture of magnetic recording medium] A magnetic recording medium having a structure as shown in Fig. 1, that is, a vapor-deposited magnetic tape was manufactured. That is, a CoO magnetic layer 2 having a thickness of 150 nm is deposited on a base film 1 made of polyethylene terephthalate (PET) having a thickness of 6.4 μm, a width of 300 mm and a length of 9000 m, and a DLC protective film having a thickness of 10 nm is formed thereon. 3 for CVD
The film was formed by the method. Subsequently, after forming a backcoat layer 5 having a thickness of 0.5 μm on the back surface of the base film 1,
A liquid lubricating film 4 was applied on the LC protective film 3. Thereafter, this was slit into a predetermined width and length to obtain a target magnetic tape.

In the above process, to form the DLC protective film 3, ethylene gas is introduced into the vacuum chamber while the base film 1 is running between a pair of electrodes provided in the vacuum chamber. The film was formed by a plasma CVD method in which a high frequency was applied to the electrode. Then, every time the DLC film is formed 3000 m on the base film 1 having a total length of 9000 m, the running of the base film and the formation of the DLC film are temporarily stopped, and in this state, oxygen gas is introduced into the vacuum chamber, The oxygen gas pressure was set to 200 mTorr, oxygen plasma was generated, the DLC film deposited and deposited in the vacuum chamber was etched for 10 minutes, and the inside of the vacuum chamber was cleaned. This cleaning operation is performed twice, that is, 3000 m and 6000 m.
m at the time of film formation, and finally 9000 m
DLC film formation was performed to complete a deposited magnetic tape.

[Evaluation Test] The magnetic tape manufactured as described above was digitally recorded and reproduced, and the error rate was measured. The error rate increases if the magnetic tape is defective. Specifically, the deposition length of the PET base film 1 from the beginning is 100 m, 2900 m, 3100 m, 5 m,
The 900 m, 6100 m and 8900 m portions were sampled and the error rates were measured for those portions.

(Example 2) In a cleaning operation in a vacuum chamber, a vapor-deposited magnetic tape was manufactured in the same manner as in Example 1 except that the oxygen gas pressure between the electrodes was 800 mTorr and the etching time was 200 minutes. Then, the same evaluation test was performed.

(Example 3) (Comparative Example 1) A vapor-deposited magnetic tape was manufactured in the same manner as in Example 1 except that the DLC film of 9000 m was continuously formed without performing any cleaning by oxygen plasma. Was evaluated.

A vapor deposited magnetic tape was manufactured in the same manner as in Example 1 except that the oxygen gas pressure between the electrodes was changed to 100 mTorr in the cleaning operation in the vacuum chamber, and the same evaluation test was performed.

Comparative Example 2 Example 1 was repeated except that the oxygen gas pressure between the electrodes was set to 1 Torr and the etching time was set to 400 minutes in the cleaning operation in the vacuum chamber.
A vapor-deposited magnetic tape was manufactured in the same manner as described above, and the same evaluation test was performed. Table 1 shows the above evaluation results.

[0021]

[Table 1] Measurement part 100m 2900m 3100m 5900m 6100m 8900m Example 1 6.6E-10 2.8E-9 8.8E-10 5.3E-9 4.7E-10 1.3E-9 Example 2 4.1E-10 5.8E-9 7.7E-10 8.8E-9 9.8E-10 1.6E-8 Example 3 5.9E-10 4.8E-9 3.6E-10 4.0E-9 9.9E-11 3.5E-9 Comparative Example 1 2.2E-10 3.9E-9 1.8E-9 6.8E-7 9.3E-7 2.0E-4 Comparative Example 2 8.5E-11 9.3E-10 2.5E-9 8.2E-6 2.8E-7 4.4E-4

As is clear from the results shown in Table 1, the error rate of the magnetic tape obtained in Comparative Example 1 in which the vacuum chamber was not cleaned by oxygen plasma increased as the DLC film length increased. It was confirmed that the defects of the magnetic tape had increased. On the other hand, in Examples 1 to 3, since the inside of the vacuum chamber was cleaned with oxygen plasma every predetermined period of DLC film formation, the error rate hardly increased over the entire length, and a magnetic tape with few defects was used. It turns out that it was obtained. Further, when comparing Examples 1 to 3, Examples 1 and 3 having a lower oxygen gas pressure have higher effects obtained by a shorter cleaning process. This indicates that as the oxygen gas pressure increases, the etching rate of the DLC film by oxygen plasma decreases, and it is difficult to obtain a sufficient effect even if the etching time is lengthened.

On the other hand, the magnetic tape obtained in Example 3 in which the oxygen gas pressure is as low as 100 mTorr has a large cleaning effect due to a large etching rate of the DLC film by the oxygen plasma, and hardly increases the error rate. . However, when the inside of the vacuum chamber after the cleaning process was examined, it was found that stainless steel, aluminum, and chromium plating, which are materials constituting the vacuum chamber, were etched by oxygen plasma and were significantly damaged. Therefore, if the processing as in the third embodiment is continued, serious damage occurs to the vacuum chamber, and it is highly possible that the vacuum chamber becomes difficult to use. Therefore, in order to prevent damage to the constituent members of the vacuum chamber, it is necessary to consider the constituent materials of each member. Further, in the magnetic tape obtained in Comparative Example 2 in which the oxygen gas pressure is as high as 1 Torr, the etching rate of the DLC film by oxygen plasma is extremely low, so that even if the processing time is prolonged, it is almost difficult to perform etching, and It was confirmed that there was no effect.

Thus, according to the present invention, as in the prior art,
It is possible to easily clean the DLC film deposited and deposited in the vacuum chamber by introducing oxygen gas without breaking the vacuum in the vacuum chamber. It can be manufactured. In the above cleaning step, the transport of the base film is stopped in the vacuum chamber, so that the DLC film formed on the base film is also etched during cleaning. Is a few tens of meters at most, and is a length that poses almost no problem when viewed from the entire length of the base film.

[0025]

As described in detail above, the D of the present invention
According to the method of forming the LC film, the inside of the vacuum chamber is cleaned by oxygen plasma etching for each predetermined processing length, so that the film can be formed efficiently without breaking the vacuum. A magnetic recording medium having a DLC film formed by such a film forming method as a protective film has high quality with few defects.

[Brief description of the drawings]

FIG. 1 is a conceptual longitudinal sectional view showing a configuration of a magnetic tape manufactured in an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 support (PET base film) 2 magnetic layer (CoO) 3 protective film (DLC film) 4 liquid lubricating film 5 back coat layer

Claims (2)

[Claims] 1. DLC on a support conveyed in a vacuum chamber
In the method for forming a film, the DL in the vacuum chamber is controlled by oxygen plasma every predetermined period of the DLC film forming process.
Including a step of etching and removing only the C film, the oxygen gas pressure when generating the oxygen plasma is 800 mTorr.
r or less, the method for forming a DLC film. 2. A magnetic recording medium having a DLC film formed by using the film forming method according to claim 1 as a protective film.