JPH06248458A - Plasma treatment device and production of magnetic disk by using this device - Google Patents

Abstract

PURPOSE:To provide the plasma treatment device capable of simultaneously and stably subjecting both surfaces of a substrate having a through hole to a plasma treatment. CONSTITUTION:Electrodes 2a, 2b are arranged respectively on both sides of the substrate 1 and are controlled to delay the phase of the one electrode voltage by detecting the phase of the potential of the generated plasma in such a manner that the phase difference attains the value smaller than a predetermined value. As a result, the magnetic disk having protective films provided with a uniform film thickness and film quality over the entire surface of both surfaces of the disk is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus for plasma processing a material to be processed, and more particularly to a plasma processing apparatus suitable for a method of manufacturing a magnetic disk having protective layers on both sides.

[0002]

2. Description of the Related Art In recent years, there has been an increasing need for miniaturization and high capacity of magnetic disk devices used as storage devices for computers and workstations, and in order to meet this, it is essential to dramatically improve the recording density. Has become. The first condition for this purpose is to reduce the distance between the magnetic head for recording and reproduction and the recording layer of the magnetic disk. Specifically, the flying height of the magnetic head is reduced and the recording layer is protected. It is necessary to reduce the thickness of the protective layer and smooth the surface of the magnetic disk. However, this may deteriorate the sliding resistance and cause a head crash, and at the same time, it is necessary to improve the strength of the magnetic disk.

The magnetic disk currently used is mainly formed by sputtering a ferromagnetic alloy thin film such as a Co alloy as a magnetic recording layer, and an amorphous layer formed by sputtering is used as a protective layer for protecting it. A high quality carbon thin film is often used. However, the strength of this amorphous carbon thin film is insufficient to realize the low flying height of the magnetic head and the thinning of the protective layer as described above, which hinders the improvement of the performance of the magnetic disk device.

Therefore, there is a need for a protective layer material which is thinner than the conventional one but has sufficient durability. For this purpose, it is known that even if the same carbon material is used, amorphous hydrogenated carbon formed by plasma decomposition of hydrocarbon gas instead of sputtering is preferably used. However, there are many types of amorphous hydrogenated carbons, which have different structures and compositions, and therefore have different protective effects. The present invention provides a method of manufacturing a magnetic disk having an amorphous hydrogenated carbon protective layer, which has a remarkably high protective effect as compared with the prior art.

Even if it is called carbon in a bit, its structure and properties are very different. Therefore, prior to explaining the material of the protective layer formed by the magnetic disk manufacturing method of the present invention, the carbon materials are first classified. Diamond and graphite, whose structures are well known crystallographically, consist of pure crystals composed only of sp3 and sp2 bonds of carbon, respectively. They have very different properties: graphite is electrically conductive and soft and absorbs light, whereas diamond is insulating and highly transparent. There are different substances such as single crystal graphite, polycrystalline graphite, glassy carbon, and fullerene in carbon composed of sp2 bonds, and their properties are also different. Amorphous carbon has been attracting attention in recent years, and it has intermediate physical properties between diamond and graphite. However, since the above-mentioned two have both extreme physical properties, even amorphous carbon is structurally different. It can be said that they are completely different materials. In addition, by devising the manufacturing method, materials with new properties that have never existed before are being found.

Among the amorphous carbons, the sputtered carbon described above sputters a graphite target and deposits particles smashed, so sp2
It has a large bond ratio, is electrically conductive, and has properties close to those of graphite. However, the hardness is higher than that of graphite, and the Vickers hardness is about 1000 to 1500. On the other hand, there is a material called amorphous hydrogenated carbon, which has a larger proportion of sp3 bonds than the above sputtered carbon because it contains hydrogen, and is generally insulating. However, some amorphous hydrogenated carbons have different properties and are not suitable as a classification of carbons. For example, when a hydrocarbon gas is reacted with plasma and a film is deposited by the action of radicals generated as in the so-called plasma polymerization method, the film has a high hydrogen content and becomes a soft film close to an organic substance. In addition, in the case of depositing a film by mixing hydrocarbon gas or hydrogen gas with an inert gas in the above-mentioned sputtering method and depositing a film, a graphite component remains and it becomes a film in which hydrogen is bound to its periphery, which is also a soft film. Become. In contrast, hydrocarbon ions are accelerated by a high voltage of 100 V or more and hit the substrate, and when the film is deposited while dehydrogenating with this energy, the place where hydrogen escapes is sp3 between carbon atoms.
Bonding results in the formation of many three-dimensional dense mesh structures, resulting in a film with high hardness and properties relatively close to those of diamond.

This high hardness amorphous hydrogenated carbon is formed by various methods. For example, in Japanese Patent Laid-Open No. 60-157726, a high frequency plasma C having a disk substrate as one electrode is used.
An example of forming by the VD method is disclosed. In addition, JP-A-61
-210518 discloses a method of extracting ions from an induction plasma generator by an electric field to form the ions. Also,
A method of forming by DC discharge is also known.

Of these, the high frequency plasma CVD method is most preferable in view of mass productivity. According to this method, even an insulating film can be stably formed, and even a relatively large area can be formed uniformly.

A method of forming this high hardness amorphous hydrogenated carbon film by a high frequency plasma CVD method will be further described. Generally, at the boundary between the plasma and the electrode material, a difference in potential occurs due to the difference in mobility of electrons and ions, and since the moving speed of ions is slower, the plasma has a self-bias effect in which it has a positive potential. The magnitude of this self-bias is
It depends on the plasma state and electrode configuration. In high frequency bipolar discharge, it is known that the size of the area (hereinafter referred to as the effective electrode area) in which plasma contacts each electrode (and a member electrically connected thereto) can be changed.
A large self-bias voltage is generated on the electrode side where the effective electrode area is small. In a normal high-frequency plasma CVD apparatus, since the high-frequency electrode is incorporated in a vacuum container having a ground potential, most of the plasma comes into contact with a member having a ground potential.
Therefore, a large self-bias voltage is generated on the high frequency electrode side. The formation of high hardness amorphous hydrogenated carbon by the high frequency plasma CVD method described in the above-mentioned JP-A-60-157726 utilizes exactly this effect. A substrate is attached to the high frequency electrode and a hydrocarbon gas is supplied. It is introduced to generate plasma, and positive ions such as methyl cations are accelerated by a self-bias voltage to collide with the substrate.

However, it is difficult to uniformly form a high hardness amorphous hydrogenated carbon film on both surfaces of the disk substrate by this method for the following reason.

1) In a magnetic disk, a metal alloy thin film such as Co is usually formed as a recording layer, and then a protective layer is continuously formed by the same device. Therefore, in order to apply a high voltage to the disk substrate, it is necessary to insulate the substrate transfer system once or float the entire substrate at a high voltage, which requires a very complicated device configuration.

2) In order to apply a voltage to the disk substrate itself, the disk substrate and the voltage introducing terminal must be brought into contact with each other with a sufficient contact area, and a film is not formed at the contacted portion, so that the film thickness distribution You can

In order to solve these problems, the present inventors have disclosed a method of manufacturing a magnetic disk in which the disk substrate is at the ground potential, as disclosed in Japanese Patent Laid-Open Nos. 59-247945, 63-206471 and 63-206471.
It is disclosed in Japanese Patent Laid-Open No. 3-120362. The reason why a high hardness amorphous hydrogenated carbon can be formed by this method is as follows.

In the methods described in JP-A-59-247945, JP-A-63-206471 and JP-A-3-120362, the substrate (and the substrate holder) is set to the ground potential, and the high frequency electrode is arranged so as to surround it. However, plasma is generated during this period. As a result, the contact area between the ground potential portion and the plasma becomes smaller than the contact area between the high frequency electrode and the plasma. Since the self-bias voltage generated between the plasma and the electrode is distributed by the relative symmetry of the electrode area, a large self-bias voltage is applied to the ground side in this method. Therefore, by utilizing this voltage, highly hard amorphous hydrogenated carbon can be formed on the disk substrate at the ground potential.

[0015]

However, this method described in the above-mentioned JP-A-59-247945, JP-A-63-206471 and JP-A-3-120362 is actually applied to simultaneous film formation on both sides of a magnetic disk. However, the following problems were found to occur.

1) Since plasma is connected through the hole in the center of the disk, the two plasmas interfere with each other and become unstable.

2) A strong plasma portion is formed in the hole at the center of the disk, and the film thickness increases at the edge of the hole.

For this reason, the distribution of the film thickness and film quality is remarkable, and when the head is levitated in the thick film portion, the distance between the head element portion and the recording film becomes large, which hinders recording and reproduction. Further, there is a problem that the protection performance is poor and the reliability is deteriorated in the thin portion. Further, in extreme cases, the plasma concentrates at one point and becomes an arc state, the plasma potential is extremely lowered, and the decomposition of hydrocarbon is not progressed, so that there is a problem that only an organic film can be formed.

In order to prevent this, there is a method in which a cap is attached to the hole to prevent plasma from connecting, but the attachment of the cap is complicated and not suitable for mass production, and the generation of dust is promoted to improve the reliability of the magnetic disk. It will damage the sex. Furthermore, since the protective film is not attached to the inner peripheral end surface with the cap attached, the substrate on the inner peripheral end surface is exposed, and there is a problem that corrosion or the like occurs from here and the disk surface is contaminated.

A first object of the present invention is to provide a plasma processing apparatus capable of stably processing both surfaces of a substrate having a through hole. A second object of the present invention is to provide a method for producing a magnetic disk capable of forming a protective layer of high hardness amorphous hydrogenated carbon on both sides of the magnetic disk at the same time with a substantially uniform film thickness distribution. Especially.

[0021]

According to the present invention, in order to achieve the first object, a vacuum container, a substrate holder for holding a substrate in the vacuum container, and two contacting surfaces of the substrate are provided. Two electrodes respectively disposed in the two spaces to generate plasma in the spaces;
A plasma processing apparatus having voltage supply means for applying a high-frequency voltage of the same frequency to one electrode, wherein detection means for detecting potentials of plasma generated in two spaces contacting both surfaces of the substrate, and the voltage supply means Is a phase difference adjusting means for adjusting the difference between the phase of the high frequency voltage applied to the one electrode and the phase of the high frequency voltage applied to the other electrode, and the potential of the plasma in the two spaces detected by the detecting means. If there is a difference, the plasma processing apparatus is provided with a control unit that controls the phase difference adjusting unit so that the potential difference becomes smaller than a predetermined value. The detecting means may be one that detects the potentials of the plasma generated in the two spaces by detecting the potentials of the two electrodes, respectively. Further, the detection means has a means for applying a voltage to the plasma and a means for detecting a current flowing in the plasma when the voltage is applied, and detects the potential of the plasma from the magnitude of the current. Any thing can be used.

The two electrodes are arranged so as to respectively surround spaces in contact with both surfaces of the substrate where plasma is generated, and the area of the electrodes may be larger than the area of the substrate. .

According to the present invention to achieve the second object, there is provided a method of manufacturing a magnetic disk having a substrate and a magnetic layer and a protective layer on both surfaces of the substrate, the method comprising: When magnetic layers are formed on both surfaces, plasma is generated in each of the two spaces where both surfaces of the substrate are in contact with each other, the electric potentials of the plasmas in the two spaces are respectively measured, and when there is a difference in the electric potentials of the plasmas in the two spaces, The phase of the plasma in the one space is relatively delayed from the phase of the plasma in the other space to make the potential difference smaller than a predetermined value, and a gas of hydrocarbons is introduced into the two spaces. There is provided a method for manufacturing a magnetic disk, which comprises depositing a hydrogenated carbon film as the protective layer on the magnetic film.

[0024]

The reason why the present invention makes it possible to form a uniform high hardness amorphous hydrogenated carbon on both sides of a magnetic disk substrate will be described below.

FIG. 8 shows a plasma processing apparatus with A,
B shows changes in the bias voltage on the A surface side and the B surface side of the electrode 3 when the phase difference between the outputs of the high frequency voltage applied to the two electrodes is changed. It was observed that plasma was concentrated in the inner hole of the disk substrate when there was a large difference in the bias voltage. When the phase difference was adjusted to point (a) in FIG. 4, the bias voltage difference was minimized, and plasma concentration in the inner hole was almost eliminated. If the film is formed under this condition, the effective use area of the disk, that is, 5.25
With an inch disc, a uniform film thickness distribution can be achieved over a radius of 30 mm to 62 mm.

Here, the fact that balancing the bias voltage between the two electrodes is effective in making the film thickness and film quality uniform is as follows.

The bias voltage represents the average potential of each high-frequency electrode, and the plasma potential is several V to several tens V higher than this, but the bias voltage difference is substantially the difference between the plasmas. Can be thought of as indicating. Therefore, if this value is different, a difference occurs in the potentials of plasmas contacting each other in the disc inner hole. If the potential difference exceeds a certain value, the electrons are accelerated by this potential difference and the energy increases, and Plasma density increases in the space and plasma concentration occurs. When this plasma concentration occurs, the decomposition of the raw material gas is promoted and the film forming rate is partially increased, so that the film thickness in the vicinity of the inner hole of the disk becomes thick and the film thickness distribution is significantly deteriorated. Therefore, by making this potential difference as small as possible, uniform film formation on both surfaces can be achieved.

Therefore, in the present invention, the detection means detects the plasma potential, and the control means controls the voltage output from the voltage supply means so that the potential difference between the plasmas in the two spaces is smaller than a predetermined value. The potential difference of plasma is reduced by controlling the means for adjusting the phase difference.

The detecting means is, as described above,
The plasma potential can be measured by measuring the bias voltage of the electrodes, but a means such as a Langmuir probe for applying a voltage to the plasma and measuring the flowing current can also be used.

The present invention is characterized in that the above-mentioned detecting means, phase difference adjusting means, and control means are provided. However, in simple terms, such means are not provided,
It is considered that the object of the present invention can be achieved by dividing the output from one power supply into two and supplying the two outputs to two electrodes. However, this does not provide a sufficient effect. This is because a slight difference in impedance occurs between the two electrodes due to an extremely slight difference in conditions, such as a difference in distance between the electrode and the ground shield and a difference in cooling efficiency of the matching circuit. Therefore, it is impossible in reality to completely match the impedances of the two electrodes. When there is such a difference in impedance, this causes a difference in the phase of the high frequency voltage at the electrodes,
The bias voltage is different. Therefore, in order to obtain a bias voltage equal to the extent that plasma concentration does not occur in the through hole of the substrate, a means for relatively adjusting the phase difference of one electrode is provided as in the present invention, and this means is provided as a detecting means. It is necessary to control using the detection result.

In the plasma processing apparatus of the present invention,
When the two electrodes are arranged so as to surround the spaces in contact with both surfaces of the substrate where plasma is generated, and the area of the electrodes is larger than the area of the substrate, the following effects are obtained. .

That is, since the area of the electrode on the high voltage side is sufficiently larger than the area of the substrate, the plasma potential has a positive value higher than the potential of the substrate in order to balance the ion current and the electron current. That is, since it is necessary to allow more ions to flow in per unit area on the side of the substrate having a small area, a large voltage effect is generated in the vicinity of this.
On the other hand, the high-voltage electrode side is dragged by the plasma potential and becomes a large positive potential.

An apparatus in which electrodes are arranged on both sides of the substrate is shown in FIGS. When the plasma potential is not controlled as in the conventional case, the potentials of the plasmas generated in the two spaces are not symmetrical as shown in FIG. Therefore, since there is a potential gradient in the plasma on both sides of the substrate, when the substrate has a through hole, the plasma concentrates near this through hole. However, in the present invention, when the detection means detects the phase of the plasma and the control means controls the high frequency power supply so as to reduce the predetermined value of the phase difference, as shown in FIG. Since the plasma potential is symmetrical, the entire surface of the substrate can be stably processed.

[0034]

An embodiment of the present invention will be described with reference to the drawings.

In this embodiment, high hardness amorphous hydrogenated carbon is formed on both surfaces of the magnetic disk by the improved high frequency plasma CVD method. That is, a positive bias high frequency electrode is used as the electrode, and by controlling the high frequency voltage applied to both surfaces and the phase thereof by a specific method, substantially uniform film formation on both sides is possible.

The structure of the high-frequency plasma CVD apparatus of this embodiment will be described with reference to FIGS. 1, 2, 5, and 7.

As shown in FIGS. 1, 2 and 5, a pair of high frequency electrodes 2a sandwiching the magnetic disk substrate 1 are provided.
2b is arranged, and the ground electrodes 3a and 3b surround the outside. Ground electrodes 3a, 3b and high frequency electrodes 2a, 2
It is insulated from b by the insulating materials 110a and 110b. The magnetic disk substrate 1 is mounted on the substrate holder 4, and is carried into the vacuum chamber 5 together with it, and is carried out after the process is completed. The substrate holder 4 is connected to the ground, so that the substrate 1 is at the ground potential.

The area of the substrate 1 and the ground electrodes 3a, 3
The total effective electrode area of b is sufficiently smaller than the effective electrode areas of the high frequency electrodes 2a and 2b. The high frequency electrodes 2a and 2b and the ground electrodes 3a and 3b are combined to form a positive bias electrode.

High frequency electrodes 2a, 2b and ground electrode 3
a and 3b are installed inside the vacuum chamber 5. The vacuum chamber 5 includes an exhaust device (not shown) and a gas introduction device 13
a, 13b and a pressure measuring device (not shown) are attached.

High frequency power supplies 7a and 7b are connected to the two high frequency electrodes 2a and 2b via matching controllers 6a and 6b, respectively. The matching controllers 6a and 6b are circuits for matching the output impedance of the high frequency power supplies 7a and 7b and the impedance of the electrodes 2a and 2b, and the blocking capacitors 8a and
8b is included. As a result, the potentials of the high frequency electrodes 2a and 2b are separated from the ground potential, and self bias can be generated.

The feature of this embodiment is that the bias voltage measuring circuits 9a and 9b are connected to the high frequency electrodes 2a and 2b, the bias voltages generated in the two high frequency electrodes 2a and 2b are measured, and the values are as close as possible to each other. There is a mechanism to adjust to a large positive value.

Specifically, as shown in FIG. 1 and FIG. 7, this mechanism includes a phase difference adjusting circuit 10 and a bias control mechanism 11.
Consists of. As shown in FIG. 7, the phase difference adjusting circuit 10 has a delay signal generating circuit 101, a delay circuit 102, and a high frequency oscillating circuit 103, and has two high frequency power supplies 2a and 2b.
The output voltage waveform phase difference is adjusted to an arbitrary value. The high frequency oscillator circuit 103 includes high frequency power supplies 7a and 7b.
It oscillates a signal of 13.56MHZ. High frequency power supplies 7a, 7b
Applies a high frequency voltage to the electrodes 2a and 2b in accordance with the timing of this signal. The delay circuit 102 uses the B-side power supply 7
It is arranged between b and the high frequency oscillation circuit 103. The delay signal generation circuit 101 is connected to the delay circuit 102. In the delay circuit 102, the high frequency oscillation circuit 103 is B
The phase of the 13.56MHZ signal output to the side power supply 7b is
The delay is generated according to the magnitude of the DC voltage signal X output from the delay signal generation circuit 101. The delay signal generation circuit 101 is
The bias control mechanism 11 outputs the direct-current voltage signal X having the instructed magnitude.

The bias control mechanism 11 receives the outputs from the two bias voltage measuring circuits 9a and 9b as inputs,
Both have a role of controlling the output X of the phase difference adjusting circuit 10 so that both values are large and the difference between them is small.
In this embodiment, the bias control mechanism 11 is composed of a programmable controller.

Next, a method of actually forming a protective film on a magnetic disk substrate using the plasma processing apparatus of the above-described embodiment will be described. First, the magnetic disk substrate 1 is mounted on the substrate holder 4, and the substrate 1 and the holder 4 are inserted through the gaps between the two electrodes 2a and 2b. The shortest distance between the substrate 1 or the holder 4 and the electrodes 2a and 2b is kept to 2 mm or less. Next, methane gas is introduced at a constant flow rate from the gas introduction ports 13a and 13b, the exhaust speed of the exhaust device is adjusted, and the gas pressure is maintained at a constant value in the range of 10 to 100 mTorr. Next, the high frequency oscillation circuit 103 starts the output of a signal,
A high frequency voltage of 13.56 MHz is applied from the high frequency power supplies 7a and 7b to generate plasma.

Next, the electric potentials of the plasmas on both surfaces of the magnetic disk substrate 1 generated in the above step are adjusted to achieve balance. Inside the bias control mechanism 11, a memory that stores a program and a calculation unit that reads the program in the memory and calculates according to the program are arranged. A program as shown in the flowchart of FIG. 13 is stored in the memory. First, in step 201 of FIG. 13, the bias control mechanism 11 sets the initial value X as the voltage value instructed to the delay signal generation circuit 101.
₀ is read, and in step 202, the delay signal generation circuit 1
01 indicates the voltage value X ₀ .

The bias voltage measuring circuits 9a and 9b measure the value of the bias voltage of each of the electrodes 2a and 2b. In step 203, the bias control mechanism 11 controls the bias voltage measuring circuit 9 attached to both electrodes 2a and 2b.
The values of the bias voltage measured by a and 9b are fetched. In step 204, the bias control mechanism 11 controls the A-side electrode 2
When the value of the bias voltage of a is p and the bias voltage of the B-side electrode 2b is q, (p−q) / (p + q) is calculated, and when (p−q) / (p + q) <a Proceeds to step 206, and if (p−q) / (p + q) ≧ a, proceeds to step 205. However, a is a predetermined constant value. In the present embodiment, a is a value obtained by calculation from a voltage value at which plasma will not be concentrated in the hole portion of the disk substrate 1 obtained by an experiment in advance.

The voltage values p and q represent the average potentials of the electrodes 2a and 2b, as described in the section of the action, and are values several V to several tens V lower than the plasma potential. Therefore, (p−q) / (p + q) ≧ a means that
Since it indicates that the potential difference of the plasma is large, in step 205, X = X + k (p−q) / (p + q) is instructed to the delay signal generation circuit 101 as a new voltage value X. Here, k is a constant determined in advance by an experiment. Then, the process returns to step 202 and steps 203 and 204
repeat. In step 204, (p−q) / (p +
If q) <a, it means that the plasma potential difference is within a predetermined range.
In step 6, X is held at the current value and the process returns to step 202.

By repeating steps 202 to 206 in this manner, the phase difference signal X is adjusted so that the potential difference between the plasma on the A side and the plasma on the B side is as small as possible and the sum thereof is as large as possible. can do. Therefore, the plasma is efficiently and well-balancedly generated, and the plasma is not concentrated in the hole portion of the disk substrate 1. According to the experiments conducted by the inventors, the difference pq between the bias voltages of the two electrodes is 30 V or less, preferably 15 V or less.
When it was set to V or less, plasma concentration disappeared.

Next, the film forming conditions that can be used in this embodiment are shown below.

(1) Gas type: Any gas can be used as long as it can form a hard protective film containing mainly carbon. For example, the following gas is preferable.

Saturated hydrocarbons such as methane, ethane, propane and butane Unsaturated hydrocarbons such as ethylene, acetylene, propylene and butene Aromatic hydrocarbons such as benzene, toluene and xylene Methanol, ethanol, acetone, ethyl ether Oxygen-containing hydrocarbons such as acetonitrile Nitrogen-containing hydrocarbons such as methylamine CF4, C2F6, C2F4, C6F6 and other fluorocarbons CH3F, C2H2F2 and other fluorocarbons Two or more selected from the above gases Mixed gas of the above gas and mixed gas of inert gas such as Ar, He, Ne, Xe or oxygen, nitrogen, hydrogen, etc. (2) Gas pressure: The upper limit is under the condition that the bias voltage in high frequency discharge is generated normally. It depends on the type of gas, but it is less than 500mTorr. If it is higher than this, the value of the bias voltage itself is lowered, and it becomes impossible to form an amorphous carbon film having good performance. The lower limit depends on the stability of the discharge, and is about 1 mTorr. Preferred is 10
It is in the range of ~ 100mTorr.

(3) Bias voltage: The bias voltage is determined by the applied power, gas pressure, gas species and electrode shape. If this value is small, the decomposition of the raw material gas does not proceed and a film similar to a polymer is formed. The range is preferably such that etching by energetic ions will occur. About 150 to 1500V is good for this range.

The method of manufacturing the protective film using the high frequency plasma CVD apparatus of this embodiment does not depend on the kind of the substrate 1 of the magnetic disk, but in order to obtain an excellent magnetic disk, the substrate Choice is also important. In this embodiment, NiP plated Al-M is preferable.
g substrate, tempered glass substrate, ceramics substrate, glassy carbon substrate and the like. In order to obtain a magnetic disk having excellent sliding resistance and flying stability of the head, it is preferable to improve the flatness of the substrate as much as possible and reduce the contact area with the head by roughening the surface. For example, NiP plated Al-Mg
In the case of a substrate, it is preferable to carry out a texture treatment for making fine irregularities with a polishing tape or abrasive grains, and in the case of a tempered glass substrate or a ceramic substrate, it is preferable to make irregularities by selective etching with a chemical agent. However, the height of these irregularities is 100 nm so as not to hinder the stable flying of the head.
The following is better.

It is desirable that the substrate 1 is continuously formed by a continuous film forming apparatus incorporating the high frequency plasma CVD apparatus of the present embodiment as shown in FIG. For example, as shown in the flow chart of FIG. 4, first, after thoroughly washing and removing foreign matter (step 301), the substrate is loaded into the preparation chamber 401 (step 302), and the substrate is heated in the heating chamber 402 (step 303). , Forming a base film in the sputtering chamber 403 (step 304a), forming a magnetic film in the sputtering chamber 404 (step 304b), and further isolating chamber 405.
Through the high frequency plasma CVD of this embodiment.
The substrate 1 is loaded into the device 406 (step 305). In the high-frequency plasma CVD apparatus 406, the source gas is introduced as described above (step 306), discharge is started (step 307), and step 201 to step 206 of FIG. 13 are performed to control the bias voltage (step 308). . After a certain period of time has passed in this state, the protective film has been formed, so the discharge is terminated (step 30
9), the source gas is stopped (step 310), and the substrate 1 is unloaded into the unloading chamber 407 (step 311).

As described above, by continuously forming a film from the magnetic recording layer, an oxide film is not formed at the interface of the protective film, and the adhesion can be improved.

The substrate heating in step 303 is performed to control the crystal growth of the underlayer and the magnetic layer, and should be set to a temperature suitable for the material used. The underlayer controls the crystal growth of the magnetic film, and Cr or its alloy is often used. Further, a ferromagnetic alloy thin film is used as the magnetic layer, and in the present embodiment, the following materials were selected and used.

CoCr, CoCrTa, CoCrPt,
CoCr alloys such as CoCrV and CoCrMo, CoN
i, CoNi-based alloys such as CoNiZr, or quaternary alloys in which a fourth element is further added.

The protective layer obtained in this example is an amorphous hydrogenated carbon film, the structure of which is an excitation wavelength of 514.5n.
When the Raman spectrum was measured using a laser beam of m, the main peak was a wave number of 1550 cm ^-1 or less. This peak position indicates the amount of graphite-like bonds in the amorphous carbon, and if it is 1550 cm- ¹ or more, a relatively soft film having strong graphitization is obtained. Also,
The amount of hydrogen in the film was about 10 to 45%, and other materials could be produced depending on the conditions, but the wear resistance was better in this range.

After the above film formation, the substrate is once taken out from the apparatus, and if necessary, a step of removing surface protrusions and the like is performed, and then a lubricating layer is formed. The lubricating layer is preferably a fluorinated polyether polymer, and a polymer having a molecular weight of 2000 to 10,000 is preferably used. Although the present invention does not depend on the type of the lubricating layer, it is better to use a specific lubricating layer in order to improve the sliding resistance of the magnetic disk. Particularly, an ester, a carboxyl group, an amide group or an amine group is added to the terminal. , Amine salts, those having a polar group such as an azide group, and those which react and stick to the surface of the protective layer can be used.

FIG. 9 shows the relationship between the bias voltage difference and the film thickness distribution at the time of manufacturing the protective film obtained in this example.
In this case, the film thickness distribution of ± 5% or less could be realized by setting the bias voltage difference p−q to 10% or less of the average bias voltage. However, since this threshold value differs depending on the film forming conditions, it is actually preferable to obtain it by experiment. Empirically, when the gas pressure (mTorr) is doubled, this value should be half, that is, 5% or less.

FIG. 10 is a schematic view of the cross-sectional structure of the magnetic disk having the protective film formed in this example formed thereon, and it can be seen that the protective film is formed uniformly over the entire surface of the disk. As a comparative example, FIG. 11 is a schematic diagram showing a cross-sectional structure of a magnetic disk having a protective film formed without performing the bias voltage control of steps 202 to 206 of FIG. The protective film around the disk hole is thickly formed.

Further, in FIG. 12, the magnetic disk provided with the protective film of FIGS. 10 and 11 was incorporated into a drive, a thin film head was mounted, and it was operated in an actual contact start / stop mode to record / reproduce signals. FIG. 6 is a diagram showing a change in reproduction output in the radial direction of the disc at the time. As is clear from this figure, in the case of the comparative example, the reproduction signal becomes extremely weak because the film thickness becomes thicker in the inner circumference, whereas in the case of the present example, a uniform reproduction signal is obtained. I understand.

The method of manufacturing the magnetic disk according to the present embodiment using the manufacturing apparatus shown in FIG. 3 will be described below in more detail by showing numerical values.

First, in step 302 of the flow of FIG. 4, 20 sets of five disc substrates 1 having a diameter of 5.25 inches mounted on the holder 4 are prepared in the preparation chamber 401.
And was evacuated. A Cr target for a base film is set in advance in the sputtering cathode of the sputtering chamber 403, and CoC for a magnetic film is set in the sputtering chamber 404.
The rTa alloy targets were set one by one, evacuated once, and then argon was introduced, the gas pressure was maintained at 10 mTorr to generate direct current plasma, and dummy sputtering was performed for 1 to 2 hours, and then the plasma was stopped.

Next, in step 302, the holder-4
Is conveyed toward the ejection chamber side, and once it reaches the heating chamber 402, it is temporarily stopped.
The substrate 1 was heated to about 200 ° C. Next, the holder 4 was transferred to the sputtering chamber 403, and at the same time, the next holder 4 was sent from the charging chamber 401 to the heating chamber 402. In this way, the holder 4 was sequentially sent out while performing the processing in each heating chamber 402. In steps 304a and 304b, about 1% of Cr is deposited on the disk substrate 1 in the sputtering chamber 403.
00 nm sputter, then CoC in sputter chamber 404
30 nm of rTa alloy was sputtered.

Next, in step 305, the holder 4
Through the isolation chamber 405 and the plasma CVD chamber 406
Transported to. At this time, the vacuum chamber 5 is evacuated in advance,
Moreover, the side surfaces of the electrodes 2a and 2b were moved in a direction away from the substrate 1 to secure an interval through which the holder 4 could easily pass. When the holder 4 reached the portion to be processed and stopped, the side surface moved toward the substrate 1 to narrow the gap between the electrodes 2a and 2b and the holder.

Then, proceeding to step 306, CH ₄ gas was introduced, and the flow rate and exhaust speed were adjusted so that the pressure was constant at 50 mTorr. Then, in step 307, a high voltage having a frequency of 13.56 MHz was applied to generate plasma. The effective power was 500W.

At this time, by operating the bias adjusting mechanism 11 in step 308, step 20 in FIG.
Repeat steps 2 to 206 to set the bias voltage on both sides of AB to 500V.
It was maintained at ± 10V. After holding the plasma for 30 seconds, the voltage application is stopped (step 309), the electrodes 2a and 2b are moved away from the substrate 1 again, the gas is stopped, the gas is exhausted, and then the holder 4 is taken out to the chamber 407 (step 311).
At the same time, the next substrate 1 was introduced. By repeating the above cycle, a protective film was formed on the disk substrates 1 mounted on the 20 holders 4.

The peak position of the Raman spectrum of the protective film of the magnetic disk substrate formed in the above process was measured over the entire surface. In all cases, it was 1520 cm to ^{1 to} 1540 cm to ^1.
Was in between.

A perfluoropolyether lubricant was applied to this disk substrate by a dipping process, and a CSS test with an actual head was conducted. Results are inner circumference (R30mm), middle circumference (R4
Both of 5) and the outer circumference (R62) were not damaged even by 50k CSS, and the friction coefficient was 0.2 or less. In addition, when recording and reproducing were performed, there was no change in reproduction output at any of the inner circumference (R30 mm), the middle circumference (R45), and the outer circumference (R62), and a good reproduction waveform was obtained. Further, when a humidification test was conducted on the disk under the conditions of 80 ° C. and 90% RH, no corrosion occurred even after 200 hours.

Further, as a comparative example, a magnetic disk was prepared in which an underlayer, a magnetic layer and a protective layer were provided on a magnetic disk substrate as in the above specific examples. However, the bias adjustment in steps 202 to 206 of FIG. 13 was not performed at the time of forming the protective layer. As a result, the bias value is 535 on the A side.
It was 470V on the V and B sides. When the film thickness distribution of the protective film was examined on the magnetic disk thus formed,
The film thickness clearly increased to about mm, and the maximum film thickness was 5 times the average film thickness. Moreover, when the Raman spectrum was examined, the peak of the thick film portion was 1560 to 1580.
It was found to be at a position of cm ~ ¹ and the film quality was different. When a CSS test was conducted by applying a lubricant to this disk, it crashed 5k times at the innermost circumference. When recording and reproduction were performed, the reproduction output became smaller toward the inner circumference side, and was 1/2 or less of the average.

In the above embodiment, the plasma potential is detected by detecting the voltage of the electrodes 2a and 2b.
It is also possible to detect the plasma potential by using a Langmuir probe. In this case, as in the above-described embodiment, the steps 304a, 3b are performed on the disc substrate 1.
After forming a Cr film and a CoCrTa film by sputtering in 04b, the substrate 1 is introduced into the plasma CVD apparatus 406. A Langmuir probe is provided in the plasma CVD apparatus 406 so as to be close to both surfaces of the disk substrate 1. Apply a constant voltage to this probe,
The inflowing current values s and t are monitored.

The bias control mechanism 11 sets the obtained current values s and t to the above-mentioned steps 202 to 206 of FIG.
The processing is performed in the same manner as p and q in FIG. However, in steps 204 and 205, a and k are changed in advance to values that are obtained by experiments and are suitable for the case of using the Langmuir probe. As a result, the potential difference of the plasma is maintained at a certain value or less, and the steps 309 to 3 are performed thereafter as in the above-described embodiment.
If step 11 is performed, a magnetic disk is obtained. As a result, the film thickness distribution on the disk surface was ± 3% or less, and good results were obtained. Further, the Raman spectrum as an index representing the film thickness was also in good agreement with the above-mentioned examples.

As described above, according to the present embodiment, when the hard amorphous carbon protective film is formed by plasma CVD, the plasma does not penetrate through the hole in the center of the disk, so that plasma does not interfere even near the hole. Becomes stable. As a result, the film thickness distribution at the inner and outer circumferences of the disc is greatly improved, so that a high-performance protective layer can be formed uniformly on both sides of the disc. In addition, by using a magnetic disk having a protective layer having a uniform film thickness in this way, it is possible to increase the effective recording area and reduce the output fluctuation during recording / reproducing, thereby achieving high recording density and high reliability. Has a great effect on.

Further, since the plasma becomes stable, the raw material gas is efficiently decomposed and a high quality hard amorphous carbon protective film can be obtained.

Further, since the protective film can be stably formed on both surfaces simultaneously, the manufacturing efficiency can be improved.

Further, in the plasma CVD apparatus of this embodiment, since it is not necessary to close the holes of the disk substrate to stabilize the plasma, there is no risk of contaminating the substrate, and the inner peripheral edge of the disk substrate is reached. A protective film can be formed.

Although this embodiment has been described focusing on the application to a magnetic disk, it goes without saying that it is also effective for an optical disk, a magneto-optical disk and the like. Further, it is needless to say that the same effect can be obtained when the double-sided plasma treatment such as plasma CVD, plasma etching, and surface modification is generally performed under the condition that a high bias is applied to the substrate.

[0079]

As described above, according to the present invention, it is possible to provide a plasma processing apparatus capable of stably processing both surfaces of a substrate having a through hole by controlling the plasma potential. Further, by using this apparatus, a method for producing a magnetic disk is provided, which can form a protective layer of high hardness amorphous hydrogenated carbon on both sides of the magnetic disk at the same time with a substantially uniform film thickness distribution. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a high frequency plasma CVD apparatus according to an embodiment of the present invention.

FIG. 2 is a cutaway perspective view showing a partial positional relationship between electrodes and a substrate of the high frequency plasma CVD apparatus of FIG.

3 is a block diagram showing a configuration of a magnetic disk manufacturing apparatus using the high frequency plasma CVD apparatus of FIG.

FIG. 4 is a flowchart showing a procedure of manufacturing a magnetic disk using the apparatus of FIG.

5 is an explanatory view showing a state of plasma of the high frequency plasma CVD apparatus of FIG. 1. FIG.

FIG. 6 is an explanatory view showing a plasma state of a conventional high frequency plasma CVD apparatus.

7 is a block diagram showing a circuit for controlling plasma potential of the high frequency plasma CVD apparatus of FIG.

FIG. 8 is a graph showing the relationship between the phase and the bias voltage when the phase of the voltage of the electrodes of the plasma processing apparatus of the present invention is adjusted.

FIG. 9 is a graph showing the relationship between the film thickness distribution of the protective film of the magnetic disk obtained in one example of the present invention and the bias voltage during manufacturing.

FIG. 10 is a sectional view showing a film thickness distribution of a protective film of a magnetic disk obtained in an example of the present invention.

FIG. 11 is a sectional view showing a film thickness distribution of a protective film of a magnetic disk of a comparative example.

FIG. 12 is a graph showing the reproduction output of the magnetic disk obtained in one example of the present invention.

FIG. 13 is a flowchart showing control of the bias control mechanism 11 of the plasma CVD apparatus according to the embodiment of the present invention.

[Explanation of symbols]

1 ... Substrate, 2a, 2b ... High frequency electrode, 3a, 3b ... Ground electrode, 4 ... Substrate holder, 5 ... Vacuum chamber, 6a, 6b ... Matching controller, 7a, 7b ... High frequency power supply, 8
a, 8b ... Blocking capacitor, 9a, 9b ... Bias measuring circuit, 10 ... Phase difference adjusting circuit, 11 ... Bias control mechanism, 13a, 13b ... Gas introduction system

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ryo Kito, Ryo Kito, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa, Ltd., Hitachi, Ltd., Institute of Industrial Science (72) Naruhiko Fujimaki, 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock company Hitachi Production Engineering Laboratory (72) Inventor Keigo Iechika 2880 Kozu, Odawara, Kanagawa Stock Company Hitachi Storage Systems Division (72) Inventor Katsuo Abe 2880 Kozu, Odawara, Kanagawa Stock Company Hitachi Storage Systems Division

Claims (9)

[Claims] 1. A vacuum container, a substrate holder for holding a substrate in the vacuum container, and electrodes respectively arranged in the two spaces for generating plasma in the two spaces in contact with both surfaces of the substrate. A plasma processing apparatus having voltage supply means for applying a high-frequency voltage of the same frequency to the two electrodes, a detection means for detecting a potential of plasma generated in each of two spaces contacting both surfaces of the substrate; Phase difference adjusting means for adjusting the difference between the phase of the high frequency voltage applied to the one electrode by the voltage supply means and the phase of the high frequency voltage applied to the other electrode, and the plasma in the two spaces detected by the detecting means. When there is a difference in the electric potentials of the plasma, the control means controls the phase difference adjusting means so that the electric potential difference of the plasma becomes smaller than a predetermined value. Plasma processing device. 2. The plasma processing apparatus according to claim 1, wherein the detecting means detects the electric potentials of the plasma generated in the two spaces by detecting the electric potentials of the two electrodes, respectively. . 3. The detection means according to claim 1, further comprising means for applying a voltage to the plasma and means for detecting a current flowing through the plasma when the voltage is applied, and the magnitude of the current. A plasma processing apparatus, wherein the plasma processing apparatus detects the electric potential of the plasma. 4. The electrode according to claim 1, wherein the two electrodes are arranged so as to respectively surround a space in contact with both surfaces of the substrate where plasma is generated, and the area of the electrode is larger than the area of the substrate. A plasma processing apparatus characterized by the above. 5. The substrate holder according to claim 4, wherein:
A plasma processing apparatus, to which a voltage applying means for holding the substrate at a potential relatively lower than the potential of the high frequency power source is connected. 6. The plasma processing apparatus according to claim 1, further comprising means for supplying a gaseous substance to the two spaces. 7. A method of simultaneously plasma-treating both surfaces of a substrate having a through hole, wherein plasma is generated in each of two spaces where both surfaces of the substrate are in contact, and the potentials of the plasma in the two spaces are measured. When there is a difference in the electric potentials of the plasmas of the two spaces, the phase of the electric potential of the plasma of the one space is relatively delayed from the phase of the electric potential of the plasma of the other space, and the electric potential difference is a predetermined value. The plasma treatment method is characterized in that both sides of the substrate are plasma-treated in this state. 8. The method according to claim 7, wherein the predetermined value is
The plasma processing method is characterized in that it has a value that does not cause discharge concentration in the through hole of the substrate. 9. A method of manufacturing a magnetic disk having a substrate and a magnetic layer and a protective layer on both sides of the substrate, wherein magnetic layers are formed on both sides of the substrate, and both sides of the substrate are in contact with each other. Plasma is generated in each of the two spaces, the electric potentials of the plasmas of the two spaces are measured, and when there is a difference in the electric potentials of the plasmas of the two spaces, the phase of the electric potential of the plasma of the one space is changed to that of the other space. The potential difference of the plasma is relatively delayed to make the potential difference smaller than a predetermined value, a gas of hydrocarbons is introduced into the two spaces, and a hydrogenated carbon film is formed on the magnetic film. A method of manufacturing a magnetic disk, comprising depositing the protective layer.