JPH076417A - Production of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To efficiently produce a satisfactory magneto-optical recording medium having high sensitivity to a magnetic field and a small angle of warp of the substrate by forming the recording layer side part of a protective layer under a lower pressure of gas than the pressure at the time of forming the substrate side part. CONSTITUTION:The substrate side part 2 of a 1st dielectric layer is formed by a conventional method such as RF reactive sputtering with an Si target, gaseous Ar and N2. The recording layer side part 3 of the 1st dielectric layer is then formed preferably under 0.05-0.5Pa pressure. In the case of <0.05 Pa pressure, sputtering is liable to become unstable in a conventional sputtering device. In the case of >70.5 Pa pressure, sensitivity to a magnetic field becomes unsatisfactory. When the 1st dielectric layer is dividedly formed in two or more separate vacuum vessels, film formation time in the vacuum vessels is made uniform and the throughput of the entire producing device can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magneto-optical recording medium for recording, reproducing and erasing information by using a laser beam.

[0002]

2. Description of the Related Art In recent years, as the amount of information has increased, the capacity of a rewritable recording medium as an external memory of a computer has been increasing. As one of the means, recording and erasing of information is performed by changing the magnetization direction of the magnetic layer by heating with a laser beam and application of an external magnetic field, and using the rotation of the plane of polarization of light by the magnetic Kerr effect for recorded information. A magneto-optical disk using a read-out method has been put to practical use.

This magneto-optical recording medium generally has a disk structure in which a dielectric protective layer and a reflective layer are combined in order to enhance the magneto-optical effect of a rare earth metal-3d transition metal alloy used as a recording layer by the interference effect of light. Has been. The dielectric protective layer used for the above purpose is required to have a large refractive index and a large light transmittance and to be excellent in the effect of protecting the recording layer. As such materials, SiN, SiNH, SiON , SiAlON, etc. are known.

[0004]

At present, in order to reduce the size and power consumption of the magnetic head of the magneto-optical disk device and to cope with the magnetic field modulation direct overwrite, the recording medium has a further magnetic field. Improved sensitivity is required.
As one of the solutions to this problem, it is effective to control the film forming conditions so that the underlying dielectric layer is dense and has a smooth surface.

The problem here is that when the dielectric layer is formed under such conditions, the internal stress of the film increases,
The point is that the substrate after film formation warps. If the warp of the substrate is large, tracking and focusing at the time of recording / reproducing information becomes difficult. Further, if the internal stress of the film is not proper, peeling or cracking of the film is likely to occur, which causes a problem in durability of the recording medium. That is, the film formation conditions for the underlying dielectric material are closely related to the durability, tracking, and focusing characteristics of the magnetic medium, and it is not possible to select the conditions etc. only from the viewpoint of magnetic field sensitivity. It has been difficult to efficiently manufacture a magneto-optical recording medium in which the warp angle of the substrate is reduced.

The problem to be solved by the present invention is to efficiently manufacture a magneto-optical recording medium having a high magnetic field sensitivity and a high C / N ratio and good mechanical characteristics with a small warp angle of the substrate. is there.

[0007]

Means for Solving the Problems When observing the film surface shape of a dielectric protective film sputter-deposited under various gas pressures with an SEM or AFM, the film formed under a low gas pressure has a smooth surface and a high gas The film formed by pressure has irregularities on the surface. In a recording medium having a recording layer formed on such an uneven underlayer, the smooth movement of the domain wall is hindered, so that the magnetic field sensitivity is deteriorated and the C / N ratio is greatly reduced when recording is performed in a low magnetic field. .

On the other hand, in the case where the dielectric layer is formed by sputtering at a low gas pressure, the surface is smooth and good magnetic field sensitivity can be obtained, but since the film stress is large, the warp angle of the substrate increases and focusing and tracking characteristics are improved. make worse.

As a result of various studies on the above-mentioned properties, the present inventors have formed a recording film having a multi-layer structure including a protective layer made of a dielectric material, a recording layer (magnetic layer) made of a magnetic material, and a reflective layer on a substrate. It has been found that a magneto-optical recording medium having both high magnetic field sensitivity and good focusing and tracking characteristics can be produced by adjusting the gas pressure when the magneto-optical recording medium having the same is manufactured by the sputtering method.

That is, the present invention relates to a method of manufacturing a magneto-optical recording medium in which at least a protective layer made of a dielectric material and a recording layer made of a magnetic material are laminated on a substrate by a sputtering method to form a film. The present invention relates to a method for manufacturing a magneto-optical recording medium, which is characterized in that the film formation on the (magnetic layer) side portion is performed under a gas pressure lower than that at the time of film formation on the substrate side portion.

Next, the present invention will be described in more detail. FIG. 1 is a diagram showing a cross section of a magneto-optical recording medium obtained by the present invention. This magneto-optical recording medium is premised on that recording / reproducing is performed from the substrate side, and the first dielectric layer 2, 3, the recording layer 4, the second dielectric layer 5 and the reflective layer 6 are formed on the transparent substrate 1. They are laminated in this order.

Next, the film forming method of the present invention will be described.
A first dielectric layer is deposited on the transparent substrate, which layer is usually composed of a SiN layer. The film formation is performed by a usual method such as an RF reactive sputtering method using a Si target and Ar + N ₂ gas. 2 in the first dielectric layer is a layer formed under a relatively high gas pressure, which will be described later, and 3 is a layer formed under a gas pressure lower than that.

The gas pressure in the vacuum chamber is set by fixing the Ar gas flow rate and adjusting the valve opening of the exhaust system, and the refractive index of the dielectric layer film to be formed is adjusted by adjusting the N ₂ gas flow rate. .

The second dielectric layer is formed, for example, by an RF reactive sputtering method using a Si target and Ar + NH ₃ gas.
It can be formed by forming an iNH film.
The reflective layer is usually formed by using an Al target and Ar gas.
It can be formed by C sputtering.

The material of the dielectric layer used in the present invention is not limited to the above-mentioned ones, but S as the first dielectric layer.
The same effect can be obtained by using iNH, SiON, SiCN, SiAlON or the like, or the other oxide, and the same can be said for the second dielectric layer.

According to the present invention, in the above-described film forming method, when forming the first dielectric layer, the substrate side portion (the portion 2 in FIG. 1) is formed.
Gas pressure during film formation and recording layer side part (3 part in FIG. 1)
It is essential to make a difference with the gas pressure during the film formation, that is, the film pressure under the latter film formation is lower than the gas pressure during the former film formation.

The film formation on the substrate side portion (the portion 2 in FIG. 1) of the first dielectric layer is first carried out by the usual RF reactive sputtering method using a Si target and Ar and N ₂ gas as described above. The gas pressure at this time is, for example, 0.4 to 2 Pa, preferably higher than 0.5 to 2 Pa, although it depends on the film forming apparatus and the film forming speed.

Next, film formation is performed on the recording layer side portion (the portion 3 in FIG. 1) of the first dielectric layer. In this case, the film formation is performed at a lower gas pressure than when forming the substrate side portion. The film forming pressure at this time is preferably 0.05 to 0.5 Pa. If it is lower than this range, sputtering may become unstable in a normal sputtering apparatus, and if it is higher than this range, the magnetic field sensitivity is insufficient. It becomes unfavorable.

The total thickness of the first dielectric layer is 500 to 15
00A, and the total thickness of the second dielectric layer is 150 to 50
It is 0A.

In the present invention, the effect of improving the magnetic field sensitivity can be seen if the thickness of the low gas pressure film-forming portion (3 portion in FIG. 1) of the first dielectric layer is about 100 angstroms or more. However, when the thickness of this portion is two-thirds or more of the thickness of the entire first dielectric layer, the effect of reducing the substrate warp angle due to lamination is reduced, so the thickness of portion 3 in FIG. 2/3 of the total thickness of the first dielectric layer
The following is one guide.

Further, in the present invention, it is possible to form the first dielectric layer by dividing it into three or more divisions instead of two divisions. However, even in that case, it is essential that the portion of the dielectric layer in contact with the recording layer is formed under a gas pressure lower than that of the other portions.

The recording layer is formed by the components constituting the recording layer,
For example, a TbFeCo alloy film can be formed by simultaneously performing DC sputtering on each target of Tb and FeCo using Ar gas and rotating the substrate so as to alternately pass over each target.

As the recording layer, the TbFeC exemplified above is used.
In addition to o, GdTbFe, GdDyFe, DyFeCo,
GdTbFeCo, GdDyFeCo, TbDyFeC
A rare earth metal-3d transition metal alloy having a composition such as o can be used, and it is similarly effective in a system to which a small amount of a passive element typified by Cr, Ti, Ta, etc. is added to improve corrosion resistance. . Other than that, the same effect can be obtained when an intermetallic compound such as MnBi or a perpendicular magnetization film such as a Co / Pt-based artificial lattice thin film is used.

The film thickness of the recording layer is 100 to 500A.

According to the present invention, in manufacturing the magneto-optical recording medium having the laminated structure of the first dielectric layer, an in-line type film forming apparatus (a plurality of vacuum tanks are arranged side by side, each vacuum layer is not broken) The first dielectric layer is divided into two or more separate vacuum chambers to form a film by dividing the first dielectric layer into two or more separate vacuum chambers. The film forming time in the bath is made uniform, and the throughput of the entire manufacturing apparatus can be improved.

In the present invention, the reflection film can be formed by DC sputtering using an ordinary Al target and Ar gas. The thickness of the reflective film is 300 to 1000A.

[0027]

[Examples] Each layer was formed by the following method. The schematic structure of the magneto-optical recording medium manufactured in this example is shown in FIG.

A polycarbonate substrate having a diameter of 3.5 inches was used. The SiN layer as the first dielectric layer is formed by S
It was performed by RF reactive sputtering using an i target and Ar + N ₂ gas. The gas pressure in the vacuum chamber is set by fixing the Ar gas flow rate and adjusting the valve opening of the exhaust system. First, the thickness of the first dielectric layer (2 in FIG. 1) on the substrate side is set to about 70
The film was formed until it reached 0 A. The refractive index of the formed SiN film is adjusted to about 2. by adjusting the N ₂ gas flow rate during sputtering.
It was set to 05. Next, a film was formed on the magnetic layer side of the first dielectric layer (3 portion in FIG. 1) to a thickness of about 300A. The respective gas pressures at this time are shown in Table 1. These Figure 1
The second and third portions were divided into different vacuum chambers for film formation.

Next, the recording layer (magnetic layer 4 in FIG. 1) was replaced with Tb.
Target and FeCo alloy target, DC sputtering was performed at the same time using Ar gas while rotating the substrate so as to alternately pass over each target, and the thickness was about 2
A 50A TbFeCo alloy film was formed. The second dielectric layer (5 in FIG. 1) uses a Si target and Ar + NH _{3 gas.}
A SiNH film having a refractive index of about 2.05 and a film thickness of about 300 A was formed by RF reactive sputtering using a glass. The reflection layer (6 in FIG. 1) was formed by DC sputtering using an Ar target and Ar gas to a film thickness of about 600A.

As a comparative example, a portion having a thickness of about 700 angstroms (2 in the figure) and a portion having a thickness of about 300 angstroms (3 in the figure) are formed under the same film forming gas pressure as in the embodiment.
Samples prepared by forming films separately in two vacuum chambers were prepared. The film forming conditions for the portions other than the first dielectric layer are the same as those in the example.

In the test on the warp angle of the substrate, the warp angle of the substrate before the sputtering film formation was set to 0, and the change amount (milliradian) before and after the film formation was evaluated. The average of the measured values was used. The surface shape of the SiN film formed under each film forming condition was measured using an atomic force microscope (AFM). When measuring with AFM,
The reference length L (measurement length) is set to 330 nm, and the displacement of the measured roughness curve f (x) from the elevation center line is | f (x).
The smoothness was compared by using the value of the center line average roughness Ra expressed by the following equation when |.

[0032]

[Chemical 1]

Table 1 shows the measurement results of the film forming pressure of the first dielectric layer of each of the examples and the comparative examples, the variation of the substrate warp angle and the surface roughness of the underlying SiN film obtained by the above-mentioned method. Shown in.

[0034]

[Table 1]

When the first dielectric layer is a single-layer SiN film, the disk having the dielectric layer formed at a low gas pressure has a large substrate warp angle (Comparative Examples A and B), and focusing and tracking characteristics. Is not preferable in terms of. Therefore, among these samples, Examples a to
The relationship between the external magnetic field strength and the C / N ratio was examined for the disks of d and Comparative Examples C and D. C / N ratio is wavelength 780n
The measurement results are shown in FIGS.

2 and 3, the vertical axis represents the C / N ratio and the horizontal axis represents the external magnetic field. Further, (1) to (6) in the figure respectively show the results of Examples a to d and Comparative Examples C and D, respectively.

As is apparent from FIGS. 2 and 3, Comparative Examples C and D
The disk has a poor magnetic field sensitivity and requires a large external magnetic field during recording and erasing. On the other hand, Examples a to d
It can be seen that the disk indicated by (1) has a significantly reduced external magnetic field required for recording and erasing, and the magnetic field sensitivity is significantly improved. Further, from the results of surface roughness measurement by AFM shown in Table 1, the magnetic field sensitivity of the disk is governed by the smoothness of the surface of the underlayer SiN.
It can be seen that this is due to smoothing of N.

[0038]

According to the present invention, it is possible to efficiently manufacture a good magneto-optical recording medium in which the C / N ratio has good magnetic field dependence, in other words, high magnetic field sensitivity and a small warp angle of the substrate. This magneto-optical recording medium is also compatible with magnetic field modulation direct overwrite, and the reduction of the warp angle facilitates tracking and focusing and enables stable recording and reproduction.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross section of an embodiment of a magneto-optical recording medium obtained by the present invention.

FIG. 2 is a diagram showing the external magnetic field dependence of C / N of the magneto-optical recording media obtained in Examples a and b of the present invention and Comparative Example C.

FIG. 3 is a diagram showing the external magnetic field dependence of C / N of the magneto-optical recording media obtained in Examples c and d of the present invention and Comparative Example D.

[Explanation of symbols]

 1: Transparent Substrate 2: First Dielectric Layer 3: First Dielectric Layer 4: Recording Layer 5: Second Dielectric Layer 6: Reflective Layer

Front Page Continuation (72) Inventor Akio Kondo 5-10, Higashino Embankment, Konan City, Aichi Prefecture

Claims (2)

[Claims] 1. A method of manufacturing a magneto-optical recording medium in which at least a protective layer made of a dielectric material and a recording layer made of a magnetic material are laminated on a substrate to form a film. A method for manufacturing a magneto-optical recording medium, characterized in that the film formation is performed under a gas pressure lower than that at the time of film formation on the substrate side portion. 2. The method according to claim 1, wherein the magnetic layer side portion of the protective layer is formed under a gas pressure of 0.5 Pa or less.