JPH07320325A - Film forming method for optical disc - Google Patents

Abstract

PURPOSE:To improve the signal defect characteristics by making uniform the thickness of film on the surface of an optical disc without lowering the film- forming speed through shuttering. CONSTITUTION:In order to reduce the peak value of cathode current being fed to a target plate 12 upon occurrence of arc discharge, a current control means 13 is provided on a feeder line 4 between a sputtering cathode section 5 and a high voltage DC power supply 3. Every time when an arc discharge takes place and the peak value of cathode current exceeds an upper limit, cathode current of the target plate is controlled and settled to a steady value.

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 predetermined target material on an optical disk surface by sputtering, and more particularly to a method for forming a dielectric protective film on the surface of a magneto-optical disk by sputtering.

[0002]

2. Description of the Related Art Usually, a magneto-optical disk has a four-layer structure of dielectric film / magnetic film / dielectric film / reflection film. In such a magneto-optical disk, it is essential to form the first dielectric film at a high speed and stably. A so-called reactive sputtering method is used as a method therefor.

Generally, in a reactive sputtering apparatus, an ionized Ar gas is sputtered on a target plate placed on the cathode by glow discharge, and a thin film is formed on a substrate placed on the anode by atoms or the like jumping out from the target plate. It is a device.

That is, in the above sputtering apparatus, first, a predetermined negative potential is applied to a cathode, that is, a target plate by a DC high voltage power source in an Ar gas atmosphere having a pressure of, for example, about 1 × 10 ^-4 Pa. Then, an electric field is generated between the cathode and the anode, which are a pair of electrodes, and glow discharge occurs and ionized Ar gas sputters the target plate. As a result, the target material is ejected from the target plate in the state of atoms and the like, and the target material is deposited on the substrate placed on the anode surface facing the target plate to form a thin film. It

Using the sputtering apparatus as described above,
The atmosphere gas to be supplied is Ar gas and N. ₂With a mixture of gases
The semiconductor material containing Si as the target plate
The surface of the magneto-optical disk
Si as a get material and N in the mixed gas₂Consists of
A first layer dielectric film of Si-N is formed.

[0006]

By the way, when a first-layer dielectric film is formed on a magneto-optical disk by using a sputtering apparatus, the cathode plate is formed by electrification on the surface of the target plate made of a semiconductor. A so-called arc discharge having a high current density and a low voltage drop may occur between the anodes. This state is shown in FIG. The peak current value of the cathode current supplied to the target plate, which is the cathode, during the discharge generation time of about 5 μs increases to about 100 A. This peak current value corresponds to about 15 times the cathode current value of about 7 A in the steady state.

When the arc discharge as described above occurs and the cathode current has a very large peak current value, Si particles emitted from the target plate are coarsened in proportion to the peak current, and the magneto-optical disk. So-called spats having a diameter of several μm are generated inside the first-layer dielectric film on the surface. It is known that the generation of the spats has a great influence on the signal defect characteristic (byte error characteristic) of the magneto-optical disk.

FIG. 7 shows the result of examination of the relationship between the number of occurrences of arc discharge and the signal defect amount (byte error rate) of the magneto-optical disk. As shown in this measured data,
It can be seen that the number of occurrences of arc discharge and the logarithmic value of the error rate are in a substantially linear proportional relationship.

At present, there is no suitable means for suppressing the arc discharge, and a stable film forming technique for the dielectric film of the magneto-optical disk has not been established.

The present invention has been made in view of the above problems, and an object of the present invention is to uniformly and uniformly form a thin film on the surface of an optical disk, which is a film-forming target, without lowering the film-forming rate by sputtering. Another object of the present invention is to provide a method for forming an optical disk, which can improve signal defect characteristics and can significantly improve the yield and reliability of products.

[0011]

The object of the present invention is a film forming method for forming a predetermined target material on the surface of an optical disk by a DC reactive sputtering method. The present invention is characterized in that when an abnormal current is generated, the cathode current supplied to the target plate is temporarily cut off and returned to a steady value.

In the present invention, a magneto-optical disk is particularly assumed as the optical disk. That is, in this case, for a magneto-optical disk mainly having a four-layer structure of dielectric film / magnetic film / dielectric film / reflection film, the first dielectric film is formed by high speed sputtering.

[0013]

In the optical disk film forming method according to the present invention, the cathode current supplied to the target plate is temporarily cut off when an abnormal current is generated, and is returned to a steady value. That is, during sputtering, when the target plate surface is charged and an arc discharge occurs and an abnormal current flows through the target plate, the cathode current of the target plate is temporarily cut off accordingly and then the cathode current reaches a steady value. Will be returned.
As a result, the peak current value is significantly reduced, and the amount of spats generated in the thin film formed on the surface of the optical disc, which causes signal defects of the optical disc, is drastically reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments in which the optical disk film forming method according to the present invention is applied to a magneto-optical disk will be described below with reference to the drawings.

Usually, a magneto-optical disk has a four-layer structure of dielectric film / magnetic film / dielectric film / reflection film. In such a magneto-optical disk, it is essential to form the first dielectric film at a high speed and stably. A so-called direct current reactive sputtering method is used as a method therefor.

Specifically, as shown in FIG. 1, the sputtering apparatus used in the DC reactive sputtering method includes a vacuum chamber 1 as a film forming chamber, and a vacuum controller for controlling the vacuum state in the vacuum chamber 1. 2, DC high-voltage power supply 3 for plasma discharge, this DC high-voltage power supply 3 and power supply line 4
A sputtering cathode portion 5 connected to each other, an anode 6 arranged to face the sputtering cathode portion 5 with a predetermined distance, and an Ar gas which is a sputtering gas.
And a sputtering gas supply unit 7 for supplying a mixed gas of N ₂ into the vacuum chamber 1.

A target plate 12, which will be described later, which functions as a cathode, which is a constituent element of the sputtering cathode portion 5, and a pair of electrodes are constituted by the anode 6, and a film is formed on the anode 6 so as to face the sputtering cathode portion 5. A magneto-optical disk 8 which is a body is installed.

The sputtering cathode portion 5 is composed of a target plate 12 made of a semiconductor material containing Si, which is arranged so as to face the magneto-optical disk 8, and a backing plate 11 on which the magneto-optical disk 8 is installed. ing. The backing plate 11 is connected to the DC high-voltage power supply 3 via the power supply line 4, and is further electrically connected to the target plate 12 for electrical continuity.

When using the above sputtering apparatus, first, the inside of the vacuum chamber 1 is set to a sufficiently good vacuum state, for example, about 1 × 10 ^-4 Pa by the vacuum controller 2. After that, a sputtering gas, for example, Ar is introduced into the vacuum chamber 1 from the sputtering gas supply unit 7 until the required pressure is reached. In this state, the DC high voltage power source 3 applies a predetermined negative potential to the backing plate 11, that is, the target plate 12. Then, an electric field is generated between the sputtering cathode portion 5 and the anode 6, which are a pair of electrodes, and glow discharge occurs and ionized Ar gas is discharged to the target plate 12.
Is sputtered. As a result, the target plate 1
The target material Si is knocked out from the surface 2, and the target material Si and N ₂ in the mixed gas are on the surface of the magneto-optical disk 8 placed on the surface of the anode 6 facing the target plate 12. To form a thin film of Si-N.

Here, when the first-layer dielectric film is formed on the magneto-optical disk 8 using the sputtering apparatus,
When the surface of the target plate 12 made of a semiconductor is charged, so-called arc discharge having a high current density and a low voltage drop may occur between the sputtering cathode portion 5 and the anode 6. In the present embodiment, the target plate 12 when this arc discharge occurs
In order to reduce the peak current value of the cathode current supplied to the sputtering cathode unit 5 and the DC high-voltage power supply 3
And the power supply line 4 is provided with the current control means 13.

As shown in FIG. 2, the current control means 13 comprises a voltage detection section 21, a voltage cutoff section 22, and a steady voltage restoration section 23. That is, the voltage detection unit 21 detects the voltage value when the cathode current supplied to the target plate 12 becomes an abnormal current, and the voltage cutoff unit 22 sets the voltage value detected by the voltage detection unit 21 to a predetermined value. If it is less than or equal to the value, it is left as it is,
When the voltage value exceeds a predetermined value (that is, the arc discharge occurs and the cathode current becomes an abnormal current value), the cathode current is cut off. Then, the steady voltage restoration unit 23
By the control described above, the cathode current is slightly disturbed and attenuated to become a steady voltage, and the cathode current value supplied to the target plate 12 returns to the steady value.

As described above, in the above-described embodiment, when the first plate dielectric film of the magneto-optical disk 8 is formed, an arc current is generated and an abnormal current is generated in the target plate 12. The supplied cathode current is temporarily cut off to return to a steady value. As a result, the peak current value is significantly reduced, and the amount of spats generated in the dielectric film formed on the surface of the magneto-optical disk 8 causing the signal defect of the magneto-optical disk 8 is drastically reduced. Become.

Actually, when a film was formed on the magneto-optical disk 8 by the film forming method of this embodiment using the above-mentioned sputtering apparatus, the cathode current value at the time of arc discharge and the value obtained by converting it into a voltage were obtained. As shown in FIG.
As shown in this waveform diagram, the peak current value of the cathode current supplied to the target plate 12, which is the cathode, during the discharge generation time of about 3 μs was reduced to about 20 A.
This value is ⅕ of the peak current value of the cathode current when the conventional arc discharge occurs, which is about 3 times the cathode current value of about 7 A in the steady state.

The signal defect amount (byte error rate) of the magneto-optical disk 8 manufactured at this time was compared with the bit error rate of the magneto-optical disk manufactured by the conventional film forming method. It became like. As shown in this frequency distribution chart, the magneto-optical disk 8 manufactured according to this example has a bite error rate reduced to about 1/5 as compared with the magneto-optical disk manufactured by the conventional method.
It was found that the signal defect characteristics of the magneto-optical disk were sufficiently satisfied.

[0025]

According to the optical disk film forming method of the present invention, when a predetermined target material is sputter-deposited on the surface of an optical disk (for example, a magneto-optical disk) by the DC reactive sputtering method, a target plate is produced when an abnormal current occurs. Since the cathode current supplied to the device is temporarily cut off and returned to a steady value, the thin film on the optical disk surface, which is the film-forming target, can be made uniform and homogeneous without lowering the film-forming speed by sputtering. It is possible to improve the signal defect characteristics and significantly improve the product yield and reliability.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a DC reactive sputtering apparatus according to this embodiment.

FIG. 2 is a schematic diagram showing a structure of a current control means.

FIG. 3 is a characteristic diagram showing a cathode current value when an arc discharge occurs and a value obtained by converting it into a voltage in the present embodiment.

FIG. 4 is a frequency distribution chart showing a bite error rate of a magneto-optical disk manufactured by a conventional film forming method.

FIG. 5 is a frequency distribution diagram showing a bite error rate of a magneto-optical disk manufactured by the film forming method of this example.

FIG. 6 is a characteristic diagram showing a cathode current value when an arc discharge is generated by a conventional film forming method and a value obtained by converting the cathode current value into a voltage.

FIG. 7 is a characteristic diagram showing a relationship between the number of occurrences of arc discharge and a bite error rate of a magneto-optical disk.

[Explanation of symbols]

 1 Vacuum Chamber 2 Vacuum Control Section 3 Electrode 4 Power Supply Line 5 Sputtering Cathode Section 6 Anode 7 Sputtering Gas Supply Section 8 Substrate 11 Backing Plate 12 Target Plate 13 Current Control Section 21 Voltage Detection Section 22 Voltage Breaking Section 23 Steady Voltage Recovery Section

Claims (4)

[Claims] 1. When a predetermined target material is sputter-deposited on the surface of an optical disk by a direct current reactive sputtering method, the cathode current supplied to the target plate when an abnormal current occurs is temporarily cut off to return to a steady value. A method for forming an optical disc, comprising: 2. The method for forming an optical disk according to claim 1, wherein the optical disk is a magneto-optical disk. 3. A magneto-optical disk comprising a dielectric film / magnetic film /
3. The method for forming an optical disk according to claim 2, wherein the dielectric film / reflection film has a four-layer structure. 4. The method of forming an optical disk according to claim 3, wherein the thin film formed by sputtering is the first-layer dielectric film.