JP2000144429A - Manufacture of carbonaceous protective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form, in a short time, a carbonaceous film of stable film quality as a protective film for a magnetic recording layer formed on a substrate by performing a plasma CVD process using hydrocarbon gas as main raw material under respectively specifiied conditions of flow rate of raw material gas, volume of a reaction chamber, and pressure in the reaction chamber. SOLUTION: Methane gas is supplied as raw material gas via a flow rate controller 6 into a reaction chamber 1 connected via a control valve 9 to a turbo-molecular pump 8, formed into plasmic state by means of the microwave introduced from a microwave power source 3 via a waveguide 4 and an insulation window 7 and the magnetic field applied by an electromagnet 10, and introduced to a substrate 11 on a substrate holder 12 whose potential is made negative by a DC electric power source 13 to form a carbonaceous protective film on a magnetic recording layer formed on the surface of the substrate 11. In this ECR plasma CVD process, the value of Vc×Pc/Qc1/2 is regulated to <=7000 when the flow rate of the raw material gas, the volume of the reaction chamber, and the pressure in the reaction chamber are represented by Qc [ml/min], Vc [ml], and Pc [Pa], respectively. By this method, plasma stabilizing time can be reduced to about <=1 sec, and the length of time required for film formation can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon-based protective film used as a protective film for a magnetic recording medium constituting a hard disk drive.

[0002]

2. Description of the Related Art A hard disk drive is a main external recording device of a computer, and a high recording density and a miniaturization are rapidly progressing with the development of multimedia. Accordingly, the magnetic recording medium, which is a main component of the hard disk device, is required to maintain the tribological mechanical strength while improving the recording density.

A magnetic recording medium is a component for magnetically recording information, and has a substrate on which nickel phosphide (hereinafter referred to as NiP) is formed.
A plating layer, a base film, a magnetic film, and a protective film are laminated, and a lubricant is applied. Usually, the substrate is made of an aluminum alloy, and the surface of the substrate is protected by applying a NiP plating layer. The magnetic film for recording information is made of a cobalt (hereinafter, referred to as Co) ferromagnetic material, and a chromium (hereinafter, referred to as Cr) base film is inserted in order to improve its magnetic properties. Further, in order to protect the magnetic film, a carbon-based protective film which is excellent in lubricity and hard to wear is coated.

The Cr underlayer, Co-based magnetic film, and carbon-based protective film are all successively formed in this order by a vacuum evaporation system. In each film formation, the film formation chamber is separated in order to eliminate mutual interference, and the substrate sequentially passes through each film formation chamber to form each layer. Substrate transfer methods include a pallet transfer method in which a pallet on which a plurality of substrates are placed is moved and a single-sheet transfer method in which substrates are moved one by one. The single-sheet transfer method is becoming mainstream. In order to increase the productivity by the single-sheet feed method, it is necessary to shorten the film-forming time per sheet, and the tact time has recently been reduced to about 10 seconds.

[0005] As the recording density of a magnetic recording medium has been improved, the magnetic flux leakage from the medium has been reduced. For this reason,
It is necessary to bring the magnetic head closer to the magnetic recording medium and reduce the spacing loss, and the distance between the magnetic head and the magnetic recording medium is decreasing year by year, and has become less than 100 nm. To reduce the spacing loss, it is necessary to further reduce the flying height of the magnetic head and to reduce the thickness of the protective film and the thickness of the lubricating layer of the magnetic recording medium. Although the current protective film has a thickness of 15 nm, further thinning is required.

As a method of manufacturing a carbon-based protective film, there are a sputtering method, a plasma CVD method (CVD is a common name for chemical vapor deposition), and the formed carbon film is an amorphous carbon film (hereinafter a-C film). And hydrogen, nitrogen and the like are added as necessary. Normally, the carbon-based protective film is formed by being vapor-deposited continuously with the Cr base film and the magnetic film by a sputtering method in the same manner as those films. In normal media production, several seconds to one
The carbon protective film is formed in about 0 seconds. The aC film thus formed contains many sp ² bonds since graphite is used as a target material for sputtering.

However, as the thickness of the protective film is reduced, a plasma CVD method having more excellent coverage characteristics is receiving attention. The most common plasma CVD method applied to the production of an aC film is a high frequency (R) of 13.56 MHz.
This is an RF-plasma CVD method using F). This method is simple and inexpensive. In addition, an electron cyclotron resonance (hereinafter abbreviated as ECR) -plasma CVD method capable of forming a film at a low pressure is also applied. In this method, since the absorption efficiency of microwaves (μ waves) is increased by electron cyclotron resonance (ECR), a film can be formed even at a pressure of 1 Pa or less, which is difficult with RF-plasma CVD. EC
An R plasma CVD apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-28827.
No. 4 discloses this.

In the plasma CVD method, since a hydrocarbon gas such as methane or ethylene is used as a source gas, the aC film formed by the method contains a large amount of hydrogen.
Further, since it contains many sp ³ bonds, which are three-dimensional structures, the film is denser than an aC film formed by a sputtering method. In fact, the density of a film containing 50% of hydrogen is as large as about 2.1 g / cm ³ . In addition, plasma CV
The aC film obtained by the D method is hard, and particularly, 300 m
It is known that hardness is increased by applying a negative bias of about V.

[0009]

As described above, it is known that a carbon-based film formed by a plasma CVD method has excellent characteristics as a protective film for a magnetic recording medium. In consideration of productivity, it is required to form a film in a short time.

[0010] In the plasma CVD method, active species are produced by the decomposition of a reaction gas by the plasma, so that there is a transient time from generation of the plasma to stabilization. In particular, RF plasma CV that forms a film at a relatively high reaction pressure
The D method requires a time of 10 seconds or more, and is capable of forming a film under a pressure lower by one digit or more than that of the RF plasma CVD method.
It takes about several seconds even in the R plasma CVD method.

FIG. 3 is an example of a graph showing the time change of the pressure in the reaction tank in the ECR plasma CVD method. The horizontal axis is time, and the vertical axis is pressure. In the plasma CVD method, a source gas is decomposed in plasma to generate various radicals, ions, molecules, and the like. A part of the decomposition product serves as a precursor to form a film. Usually, the pressure of the reaction tank tends to increase at first because the source gas produces a plurality of products by decomposition. The decomposition products spread in the reaction vessel.
On the other hand, the decomposition products in the reaction tank are exhausted by an exhaust system. At that time, the decomposition products have different pumping speeds depending on the types, and reach an equilibrium where the decomposition of plasma and the exhaust are balanced. Thus, it takes some time for the plasma to stabilize. Then, a stable film formation is performed after the plasma is stabilized.

For example, in a magnetic recording medium, a thickness of about 5
There is a demand to form a protective film of nm in a few seconds.
However, as described above, when a carbon-based protective film is deposited by the plasma CVD method, it takes several seconds for the ECR plasma CVD method to stabilize the reaction pressure. In order to shorten the film formation time, the plasma stabilization time needs to be short. Since the tact time is reduced to about 10 seconds in the single-sheet feed system, the plasma stabilization time is desirably within 1 second.

In view of such circumstances, an object of the present invention is to provide a manufacturing method for forming a carbon-based protective film of stable film quality in a short time as a protective film of a magnetic recording medium by a plasma CVD method.

[0014]

In order to shorten the time for stabilizing the plasma, the following three points can be considered. 1) Increase the flow rate of the source gas and increase the amount of generated decomposition products. This allows the decomposition products to spread quickly into the reactor. 2) Reduce the volume of the reaction tank. This speeds up the time for the decomposition products to spread into the reactor. 3) Reduce the reaction pressure and reduce the gas density in the reaction tank.
As in 2), the time during which the decomposition product spreads in the reaction tank is increased.

Based on the above considerations, when the flow rate of the source gas (standard state) is Q _c [ml / min], the volume of the reaction vessel is V _c [ml], and the pressure of the reaction vessel is P _c [Pa] , V _c × P _c / Q _c ^1/2 is set to 7000 or less.

By doing so, the time required to reach equilibrium is reduced, as shown in the experimental results described later, so that the film formation time can also be reduced. In particular, it is assumed that the source gas is methane gas. Methane is the lightest of the molecules containing carbon atoms and has a fast diffusion rate, so it reaches equilibrium quickly.

It is assumed that the plasma CVD method is an ECR plasma CVD method. Since the ECR plasma CVD method utilizes the generation of plasma by cyclotron motion of electrons, the plasma is stable even at a pressure lower by one digit or more than other high-frequency (RF) plasma CVD methods.
Therefore, this is a plasma CVD method suitable for the above condition 3).

[0018]

Embodiments of the present invention will be described below with reference to examples. Example 1 FIG. 2 shows the ECR plasma CV used in this experiment.
It is a cross section of D apparatus. The reaction chamber 1 is provided with a cavity 2 for forming an ECR plasma. Microwave power supply 3 (frequency 2.45 GHz) at the bottom of cavity 2
There is provided a waveguide 4 for transmitting microwaves emitted from a gas source and a gas introduction pipe 5 for supplying a raw material gas. The flow rate of the source gas is controlled by a gas flow controller 6. At the boundary between the waveguide 4 and the cavity 2, an insulating window 7 that allows microwaves to pass and does not allow gas to pass is fitted. A coil 10 for generating a magnetic field for generating electron cyclotron resonance (ECR) is provided outside the cavity 2.
Is provided. A turbo molecular pump 8 (displacement: 0.5 m ³ / sec) is connected to the reaction chamber 1, and the internal pressure is controlled by a control valve 9. In the reaction chamber 1, a substrate holder 12 for directly supporting a magnetic medium substrate 11 is mounted. The DC power supply 13 is connected to the substrate holder 12, and a negative bias potential is applied to the substrate 11.

As the magnetic medium substrate 11, a Cr underlayer,
An aluminum alloy magnetic disk substrate (outer diameter 65 mm, inner diameter 20 mm) having a Co-based magnetic layer formed by a sputtering method and a Si single crystal substrate were used. The substrate 11 was set at a position 100 mm from the exit of the cavity 2.

Typical film forming conditions are as follows. Reaction chamber volume (V _C ): 60000 ml, reaction gas: methane (CH ₄ ), gas flow rate (Q _C ): 10 ml / min, initial pressure (P _i ) in the reaction chamber: 1.3 Pa, microwave output: 200 W
Substrate bias voltage: -200 V, magnetic field: 2 kG, substrate temperature: 200 ° C. The film formation time was 2.5 seconds, and an aC film having a thickness of about 5 nm was formed. The flow rate of the raw material gas is a flow rate in a standard state, and is a sccm in a conventional cgs unit.
Is the same as The same applies to the following.

FIG. 3 shows the time change of the pressure in the reaction chamber. Hydrogen and hydrocarbons are formed by the decomposition of methane. For this reason, the pressure increases. A significant portion of the hydrocarbon becomes a film. Hydrogen having a small molecular weight has a large conductance. This causes the pressure to drop and reach equilibrium. Maximum pressure P _m and the equilibrium pressure P _e pressure P in the vacuum chamber with respect to the _{P = {(P m -P e} ) / e} + a P _e become time as tau, approximate time to reach equilibrium And Where e is the base of the natural logarithm. That is, after time τ, it can be considered that the equilibrium state has been considerably approached. FIG.
Was about 3.6 sec. The deposition rate is about 1
nm / sec. [Experiment 1] FIG. 4 shows the change in τ when the methane gas flow rate Q was changed to 2 to 20 ml / min. V _C = 60000m
l, P _i = 1.3 Pa. τ decreases in inverse proportion to Q ^1/2 . The volume V _c of Experiment 2 reaction chamber from 50000 to 60000
FIG. 5 shows the change in τ when the amount was changed to ml. P _i =
1.3Pa, and the Q _C = 10ml / min. τ increases in proportion to V _c . [Experiment 3] The initial pressure P _i in the reaction chamber was set to 0.067-2.
FIG. 6 shows the change in τ when the pressure was changed to 7 Pa. V _C =
60000ml, it was a Q _C = 10ml / min. τ increases in proportion to P _i . Since the initial pressure _Pi is adjusted by the control valve 9, it may be considered that the performance of the turbo molecular pump 8 does not matter.

Under any of the conditions within the range of the experiments described above,
A good quality carbon-based protective film could be formed. To summarize this result, τ can be expressed by the following equation. τ = k × P _i × V _c / Q ^1/2 where k is a proportional constant. When the units of P _i , V _c , and Q are [Pa], [ml], and [ml / min], k is 1.4.
It becomes 3 × 10 ^-4 .

FIG. 1 shows the parameters of τ (P _i × V _c / Q
^1/2 ) is a characteristic diagram showing dependence. The horizontal axis is a parameter (P _i × V _c / Q ^1/2 ), and the vertical axis is τ. τ is 1 sec
It can be seen that P _i × V _c / Q ^1/2 needs to be 7000 or less in order to achieve the following. This result becomes even more important as the deposited protective films tend to become thinner and shorter.

[0024]

As described above, according to the present invention, when an amorphous carbon protective film is formed by a plasma CVD method using a hydrocarbon gas as a source gas, the flow rate of the source gas Q, the volume V _{c of the} reaction chamber, When the initial pressure of the reaction was _Pi , by setting P _i × V _c / Q ^1/2 to 7000 or less, the initial plasma stabilization time could be made within 1 second. This makes it possible to form the carbon protective film in a sufficiently short time even in the plasma CVD method.

As a matter of course, there was no change in the time until the pressure reached equilibrium depending on the type of the substrate.

[Brief description of the drawings]

FIG. 1 shows a parameter (P _i × V _c / Q) of an equilibrium arrival time τ.
^1/2 ) Characteristic diagram showing dependence

FIG. 2 is a schematic cross-sectional view of an ECR plasma CVD apparatus.

FIG. 3 is a graph showing the time change of the pressure in the reaction chamber.

FIG. 4 is a characteristic diagram showing the dependence of τ on the gas flow rate (Q _C ).

FIG. 5 is a characteristic diagram showing the dependence of τ on the reaction chamber volume (V _C ).

FIG. 6 is a characteristic diagram showing dependence of τ on initial pressure (P _i ).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction chamber 2 Cavity 3 Microwave power supply 4 Microwave waveguide 5 Gas introduction pipe 6 Gas flow controller 7 Insulating window 8 Electromagnet 9 Turbo molecular pump 10 Control valve 11 Substrate 12 Substrate holder 13 DC power supply

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K030 AA09 AA10 BA27 BB05 CA02 CA04 DA02 FA01 FA02 HA04 JA05 JA09 JA20 KA08 KA30 LA20 5D112 AA07 AA24 BC05 FA10 FB09 FB19

Claims (3)

[Claims] A magnetic recording layer formed on a substrate;
In a manufacturing method for forming a carbon-based protective film by plasma CVD using a hydrocarbon gas as a main source gas, the flow rate (standard state) of the source gas is Q _c [ml / min], and the volume of the reaction chamber is V _c [ml]. , when the pressure in the reaction chamber and P _c [Pa], the method of manufacturing the carbon-based protective layer, characterized in that the value represented by _{V c × P c / Q c} 1/2 is 7000 or less. 2. The method according to claim 1, wherein the source gas is methane gas. 3. The plasma CVD method is ECR plasma CVD.
The method for producing a carbon-based protective film according to claim 1, wherein the method is a method.