JP3106528B2 - Method and apparatus for forming hard carbon film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for forming a hard carbon film, and more particularly, to applying a bias voltage to a substrate,
The present invention relates to a method and an apparatus for forming a hard carbon film for forming a hard carbon film.

[0002]

2. Description of the Related Art Recently, a hard carbon film such as a diamond film has been used as a protective film for a magnetic disk or a magnetic head.

As a method for forming a hard carbon film, for example, an ion beam method, a sputtering method, an ion plating method, a plasma CVD method, and the like are employed. For example,
In a plasma CVD apparatus, a negative self-bias is applied to a substrate (for example, a magnetic disk) on which a hard carbon film is formed. When a plasma flow of a film forming gas (for example, a mixed gas of methane and hydrogen) is irradiated onto the substrate, a hard carbon film is formed on the substrate.

However, when a hard carbon film is formed on a substrate by the above-mentioned forming method, a so-called wedge phenomenon occurs because ions are accelerated and collide with the substrate, and the hard carbon film has a density of about 10 ¹⁰ dyne / cm ^2. Compressive stress remains. For this reason, the adhesion between the hard carbon film and the substrate is poor, and the hard carbon film may be peeled or cracked. In particular, when a hard carbon film having a large thickness is formed, peeling and cracking are likely to occur.

Therefore, in the above-described method for forming a hard carbon film, the substrate is annealed after the film formation. When the annealing treatment is performed, a hydrogen elimination reaction occurs in the hard carbon film, and the surface temperature of the hard carbon film increases. Thereby, hydrogen in the hard carbon film is removed, and the compressive residual stress of the hard carbon film is reduced.

[0006]

In the above-mentioned conventional method for forming a hard carbon film, since the compressive residual stress of the hard carbon film is reduced by annealing the substrate, the formed substrate is taken out of the film forming apparatus. After that, a step of annealing is required. When the substrate is made of a material having low heat resistance such as plastic, the annealing temperature cannot be set high, and the compressive stress cannot be sufficiently reduced.

An object of the present invention is to provide a hard carbon film forming method and a hard carbon film forming apparatus capable of easily forming a hard carbon film having a small compressive stress regardless of the type of a substrate.

A hard carbon film forming method according to a first aspect of the present invention is a method for forming a hard carbon film by applying a negative bias voltage to a substrate to form a hard carbon film. A first step of forming a hard carbon film while increasing the bias voltage from 1 to a second bias voltage approximately 100 V higher than that, and maintaining the bias voltage applied to the substrate at the second bias voltage to maintain the hard carbon film. A second step of forming a carbon film.

[0009] A hard carbon film forming apparatus according to a second aspect of the present invention includes a plasma generating means, a bias voltage applying means, and a bias voltage controlling means.

[0010] The plasma generating means is means for generating plasma in the chamber. The bias voltage applying unit is a unit that applies a negative bias voltage to the substrate disposed in the chamber. The bias voltage control means changes the applied bias voltage from the first bias voltage to about one lower than the first bias voltage so as to change the carbon concentration of the film formed on the substrate.
This is a means for raising the second bias voltage to 00V higher in a predetermined time.

[0011]

In the first aspect of the present invention, when forming a hard carbon film by applying a negative bias voltage to the substrate, first, a bias voltage lower than a normal bias voltage is applied. Thus, a mixed layer of the substrate material and carbon is formed on the substrate surface side. When the bias voltage is gradually increased, the carbon concentration of the film formed on the substrate surface is gradually increased. Thereafter, a hard carbon film is formed with a normal bias voltage.

As described above, by forming the intermediate layer having a gradually changing carbon concentration between the substrate and the hard carbon film, a carbon film having a small compressive stress as a whole and hard to peel off can be formed on the substrate.

In the hard carbon film forming apparatus according to the second aspect of the present invention, first, a predetermined film forming gas is introduced into the chamber. Then, plasma is generated in the chamber by the plasma generating means, and a negative bias voltage is applied to the substrate by the bias voltage applying means. At this time, the bias voltage applied to the substrate is increased from the first bias voltage to a second bias voltage higher than the first bias voltage by a bias voltage control means for a predetermined time, and the carbon concentration of the film formed on the substrate is gradually reduced. Change. As a result, an intermediate layer having a small compressive stress is formed on the substrate in a state where the substrate and ions of the film forming gas are mixed, and a hard carbon film having a desired carbon concentration is formed thereon. Therefore, the compressive stress of the hard carbon film is reduced as a whole.

[0014]

FIG. 1 is a longitudinal sectional view of a hard carbon film forming apparatus according to one embodiment of the present invention. The hard carbon film forming apparatus 1 is an apparatus employing an ECR plasma CVD method, and mainly includes a plasma chamber 2 and a film forming chamber 3.

[0015] The plasma chamber 2 is configured such that the cavity resonator with respect to the introduced microwave (frequency 2.45 GHz _Z). A microwave introduction waveguide 5 is connected to the upper part of the plasma chamber 2 via a microwave introduction window 4 made of quartz or the like. Around the plasma chamber 2, electromagnetic coils 6a and 6b are provided as a magnetic circuit for generating plasma. The electromagnetic coils 6a,
The strength of the magnetic field by 6b is determined so that the condition of electron cyclotron resonance by microwave is satisfied inside the plasma chamber 2. Also, the electromagnetic coils 6a, 6b
Thereby, a diverging magnetic field diverging downward may be formed.

Further, one end of a gas introducing pipe 7 is connected to the upper part of the plasma chamber 2. The gas introduction pipe 7 has a control valve 8, and the other end is connected to a gas cylinder 9 filled with a film forming gas. Note that a hydrocarbon gas such as methane gas is used as the film forming gas.

The film forming chamber 3 is arranged below the plasma chamber 2. A communication port 10 for communicating with the plasma chamber 2 is provided in an upper part of the film forming chamber 3. A holder 11 is arranged below the communication port 10. The substrate 12 can be held on the holder 11. Holder 1
1 is attached to the support shaft 13. Also, holder 1
The 1, a high frequency power source (e.g., frequency 13.56MH _Z) 14 via the support shaft 13 and the matching device 15 is connected, thereby so it can apply a predetermined high frequency voltage to the holder 11 I have. The holder 11 has
A jacket (not shown) through which cooling water circulates is mounted.

An openable and closable shutter 15 is provided between the communication port 10 and the holder 11 in the film forming chamber 3. The opening of the shutter 15 can be adjusted. Also,
An exhaust port 16 is provided at a lower portion of the film forming chamber 3, and the exhaust port 16 is connected to an exhaust system (not shown).

The matching device 15 is provided for matching the impedance and the phase between the high-frequency power supply 14 and the hard carbon film forming device 1 as a load.
As described above, the output of the matching device 15 is provided to the holder 11 via the support shaft 13 and to the voltage detector 20 having one end grounded via the coil 16 and the resistor 18. The resistor 19 is connected in parallel to the voltage detector 20. An intermediate node between the coil 16 and the resistor 18 is connected to the other electrode of the capacitor 17 having one electrode grounded. The capacitor 17 and the coil 16 constitute a low-pass filter that cuts a high frequency from a high-frequency voltage and passes a DC bias voltage component. The resistor 18 is for lowering the voltage to a voltage for measurement, and the resistor 19 is for detecting a voltage.

The detection output of the voltage detector 20 is given to a bias voltage control circuit 21. The support shaft 1 is attached to the holder 11.
Since a high-frequency voltage is applied via the matching device 3 and the matching device 15, positive and negative potentials are applied periodically. As a result, a negative bias voltage is generated on the substrate 12. The bias voltage control circuit 21 performs feed hack control of the bias voltage by detecting the output voltage of the matching device 15. Here, as shown in FIG. 2, a bias voltage that gradually increases from a first bias voltage (for example, -400 V) to a second bias voltage (for example, -300 V) in a predetermined time is applied from the bias voltage setting unit 22. Then, the set bias voltage is compared with the bias voltage detected by the voltage detector 20, and a control signal corresponding to a deviation of the comparison result is output to the high frequency power supply 14. The high frequency power supply 14 increases or decreases the high frequency voltage according to the control signal.

Next, a method for forming a hard carbon film using the hard carbon film forming apparatus 1 will be described. First, the inside of the plasma chamber 2 and the film forming chamber 3 is set to a vacuum state by an exhaust system (not shown). Next, the control valve 8 is opened, and a film forming gas is introduced into the plasma chamber 2 from the gas cylinder 9 via the introduction pipe 7. Here, the gas is introduced while adjusting the control valve 8 to control the flow rate of the film forming gas.

On the other hand, the electromagnetic coils 6a and 6b provided around the plasma chamber 2 are energized to set the magnetic flux density in the plasma chamber 2 to, for example, 875 gauss. Then, introducing microwaves of a frequency 2.45 GHz _Z in the plasma chamber 2 through the waveguide 5.

[0023] By such operation, in the plasma chamber 2, 875 and an electronic frequency rotated by Gauss magnetic field, match the frequency 2.45 GHz _Z microwave, electron cyclotron resonance occurs. As a result, in the plasma chamber 2, electrons efficiently absorb energy from microwaves, and high-density plasma is generated at a low gas pressure. This plasma is a plasma of a film forming gas. The plasma generated in the plasma chamber 2 is supplied to the electromagnetic coils 6a,
The plasma flow M flows along the lines of magnetic force of the diverging magnetic field formed by the magnetic field 6b, and is drawn into the film forming chamber 3 through the communication port 10.

When the shutter 15 in the film forming chamber 3 is opened, the plasma flow M from the plasma chamber 2 is irradiated onto the substrate 12 while the flow rate is adjusted by the shutter 15. Holder 11
As described above, since the high-frequency voltage is applied from the high-frequency power supply 14 via the support shaft 13 and the matching device 15 as described above, positive and negative potentials are applied periodically. As a result, the substrate 1
2, a negative bias voltage is generated. With this negative bias voltage, positive ions in the plasma of the film forming gas are drawn into the substrate 12 side, and a hard carbon film is formed on the substrate 12.

This bias voltage is obtained by feedback-controlling the bias voltage set by the bias voltage setting unit 22 by the bias voltage control circuit 21.

FIG. 2 is a graph showing an example of the setting contents of the bias voltage. The vertical axis represents the bias voltage, and the horizontal axis represents the time t.
Has taken. The bias voltage is set by the bias voltage setting unit 22 at the time when the shutter 15 is opened, to the first bias voltage of -400V, and after the time T, to -300V.
Gradually from time T to shutter 15
Until the closing time, the second bias voltage is set to -300V.

By setting the bias voltage in this way and performing feedback control by the bias voltage control circuit 21, the bias voltage can be set arbitrarily and the bias voltage can be varied. In addition, even when the pressure in the film forming chamber 3 fluctuates, the bias voltage to the substrate can be accurately controlled by the feedback control. Thereby, the bias voltage is changed from -400V to -30V.
In the region where the voltage rises to 0 V, a mixed film (intermediate layer) in which carbon is diffused into a substance on the substrate 12 is formed. Since the mixed film has a low residual compressive stress, a hard carbon film having a low residual compressive stress as a whole is formed. It is formed.

In the method for forming hard carbon as described above using the hard carbon film forming apparatus 1, a hard carbon film having a small compressive stress can be formed without heating the substrate 12 as in the conventional example. A hard carbon film having a small compressive stress can be formed even on a substrate having a low heat resistance such as the above.

EXPERIMENTAL EXAMPLE The first bias voltage was set at -400 V, the bias voltage was gradually increased, and after 7 minutes, the bias voltage was set at -30.
Set to 0V. Thereafter, the time until the film thickness reaches a predetermined value is -300.
V was used to form a film. As a result, the peel strength was several times higher than that of the fixed bias film.

[Other Embodiments] In the above embodiment, an ECR plasma CVD apparatus was used as the hard carbon film forming apparatus 1, but the present invention is not limited to this. For example, even in a plasma CVD apparatus that does not use ECR, a carbon film having a small compressive stress can be obtained by controlling the bias voltage on the substrate as in the above-described embodiment.

In the above embodiment, the first bias voltage is -400 V, and the second bias voltage is -400 V.
Although 300 V was set for each, the present invention is not limited to this. That is, the first bias voltage may be lower than the second bias voltage by about 100 V, and the second bias voltage may be a voltage capable of obtaining a desired carbon concentration.

[0032]

The first invention includes a step of raising the bias voltage from the first bias voltage to a second bias voltage higher than the first bias voltage when forming the hard carbon film. Further, the hard carbon film forming apparatus of the second invention includes a bias voltage control means for increasing a bias voltage applied to the substrate from the first bias voltage to a higher second bias voltage for a predetermined time. I have. Therefore, according to the present invention, a mixed film in which carbon is diffused in a material constituting a substrate having a low residual compressive stress is formed, and a hard carbon film having a desired carbon concentration is formed thereon, regardless of the type of the substrate. Therefore, hard carbon having a small residual compressive stress can be easily formed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a hard carbon film forming apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of setting contents of a bias voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hard carbon film forming apparatus 2 Plasma chamber 3 Film formation chamber 5 Waveguide 6a, 6b Electromagnetic coil 12 Substrate 14 High frequency power supply 20 Voltage detector 21 Bias voltage control circuit 22 Bias voltage setting device

Claims (2)

(57) [Claims] 1. A hard carbon film forming method for forming a hard carbon film on a substrate by applying a negative bias voltage to the substrate, wherein the bias voltage applied to the substrate is changed from a first bias voltage. A first step of forming the carbon film while increasing the voltage to a second bias voltage approximately 100 V higher than that, and maintaining the voltage applied to the substrate at a second bias voltage after the first step. Second to form carbon film
A method for forming a hard carbon film, comprising: 2. A hard carbon film forming apparatus for forming a hard carbon film on a substrate disposed in a chamber, comprising: a plasma generating means for generating plasma in the chamber; Bias voltage applying means for applying a bias voltage, and a bias voltage applied to the substrate by the bias voltage applying means so as to change the carbon concentration of a film formed on the substrate. Bias voltage control means for increasing the voltage from a voltage to a second bias voltage higher by about 100 V for a predetermined time, and a hard carbon film forming apparatus.