JPH06267126A - Production of magneto-optical recording medium and recording medium - Google Patents

Abstract

PURPOSE:To obtain a high performance magneto-optical recording medium ensuring a low noise level by forming an underlayer on a substrate with a dielectric film subjected to sputter etching and forming a thin MnBi film on the underlayer by an ion cluster beam method. CONSTITUTION:An underlayer 2 made of a silicon nitride film is formed on a glass substrate 1 by sputtering and subjected to sputter etching with gaseous Ar under the conditions of 24.5SCCM flow rate, 0.1Pa pressure of the gas, 350W supplied power and 0.1nm/min etching rate. An MnBi layer 3 is then formed on the underlayer 2 by an ion cluster beam method and an interference layer 4 made of a silicon nitride film is formed on the MnBi layer 3 by sputtering. A reflecting layer 5 of Al is further formed on the interference layer 4 by vapor deposition and heat treatment is carried out to produce the objective magneto-optical recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium, and more particularly, it is used for a rewritable magneto-optical disk or the like and can be read out by using a magneto-optical effect such as a magnetic Kerr effect or a magnetic Faraday effect. Recording medium

[0002]

2. Description of the Related Art Materials for magneto-optical recording media are mainly required to meet the following conditions. (A) A perpendicular magnetization film. (B) It has a large coercive force. (C) The car rotation angle is large.

It is known that when a heavy rare earth element such as Tb or Gd is added to Fe or Co, the magnetic anisotropy is increased to form a perpendicular magnetization film. For these reasons, GdTbFe, DyFe, GdCo, and Tb are used as materials for magneto-optical recording media.
Heavy rare earth such as Co, TbDyFe, TbFeCo-3d
The transition metal amorphous alloy thin film is promising because it satisfies the above conditions, is suitable for mass production, and has low read noise. In particular, TbFeCo is a promising and practical material.

As a means for increasing the density of magneto-optical recording, there is miniaturization of the recording area by narrowing the beam diameter of the laser. In order to reduce the beam diameter without changing the NA of the objective lens of the recording / reproducing head, it is necessary to shorten the wavelength of the laser light source. For this reason, development of a short wavelength light source using a non-linear optical element and the like is in progress. However, it is known that the heavy rare earth-3d transition metal amorphous alloy thin film currently put into practical use has a smaller Kerr rotation angle as the wavelength becomes shorter. Moreover, the quantum conversion efficiency of the photodetector also decreases due to the decrease in wavelength. Therefore, when reproducing with a short wavelength laser, the reproduction output is significantly reduced, and it is difficult to achieve a high recording density. Therefore, a new magneto-optical recording material having a large Kerr rotation angle in the short wavelength region is required.

Garnet, Pt / Co, and light rare earth-3d transition metal amorphous alloy thin films have been studied as magneto-optical recording materials for short wavelengths. However, these materials have the following drawbacks.

Since garnet has a large Farathe rotation angle, a large reproduction output can be obtained, but heating at 600 ° C. or higher is required to grow crystals during or after film formation, and ordinary glass is used. It is difficult to fabricate on a substrate. Therefore, it is necessary to use expensive heat-resistant glass as the substrate, and there is a drawback that the medium becomes expensive.

Pt / Co is a heavy rare earth-3d in the short wavelength region.
It has a larger Kerr rotation angle than the transition metal amorphous alloy,
The value is not large enough to compensate for the decrease in conversion efficiency of the photodetector. Further, since it is crystalline, medium noise is large and reproduction output in a short wavelength region is lowered. (Unexamined Japanese Patent Publication No. 3-162739) Light rare earths-3
In the case of the d-transition metal amorphous alloy thin film, as in the case of Pt / Co, there is a drawback that a sufficiently large Kerr rotation angle cannot be obtained in the composition range where recording and reproduction are possible.

Therefore, it is necessary to use new materials in place of these recording materials.

The MnBi compound is obtained by heating and reacting a Mn-Bi laminated film in which Bi and Mn are sequentially formed on a substrate.
The C-axis orientation of Bi is preserved, and a C-axis oriented MnBi compound is obtained. Since the MnBi compound has a strong magnetic anisotropy in the C axis, it becomes a perpendicular magnetization film. Furthermore, since the MnBi compound has a large Kerr rotation angle of 1 degree or more in the wavelength range of 400 nm to 900 nm, it is promising as a magneto-optical recording material for short wavelength.

Bi and Mn are sequentially formed on the substrate Mn-
In order to heat the Bi laminated film and generate the compound, 3
It is necessary to hold the laminated film in an atmosphere of a temperature of 00 ° C. or higher. Therefore, a glass substrate having high heat resistance is used as the substrate. When forming a thin film on a normal tempered glass substrate, an underlayer of a dielectric is used as a barrier layer because an alkali metal or the like from the glass substrate does not deteriorate MnBi.

Next, a method of manufacturing a conventional MnBi magneto-optical recording medium and the recording medium will be described with reference to the drawings.

FIG. 5 is a sectional view of the structure of a conventional MnBi magneto-optical recording medium before heat treatment.

An underlayer (silicon nitride film formed by sputtering) 52 having a thickness of 85 nm and a Bi layer 53 are formed on a glass substrate 51.
To a thickness of 20 nm by a vapor deposition method (ion cluster beam method), a Mn layer 54 to a thickness of 12 nm by a vapor deposition method, an interference layer (silicon nitride film by sputtering) 55 to a thickness of 200 nm, and a reflection layer (sputtering layer). Al film 56) was sequentially formed to a thickness of 20 nm. This disk is heat-treated at 380 ° C. for 3 hours to cause Mn and Bi to react with each other to produce a MnBi compound, thus producing a recording medium.

[0014]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
A problem in using the i compound as a magneto-optical recording material is medium noise generated because MnBi is crystalline. This is classified into reflectance fluctuation noise generated from grain boundaries and polarization noise caused by Kerr rotation angle fluctuation. Since MnBi has a very large Kerr rotation angle of 1 degree or more, it is particularly important to reduce the polarization noise.

[0015]

According to the method of manufacturing a magneto-optical recording medium of the present invention, an underlayer is formed of a dielectric film that has been subjected to sputter etching, and MnB having a perpendicular magnetic easy axis is formed.
It is characterized in that the i-compound thin film is laminated on the underlying layer.

The magneto-optical recording medium of the present invention is a magneto-optical recording medium manufactured by the above manufacturing method,
The center line average roughness (Ra) of the dielectric film is 1 nm or less.

[0017]

The easy axis of magnetization of the MnBi film is on the C-axis, and a decrease in C-axis orientation increases polarization noise. There is a proportional relationship between the C-axis orientation of the MnBi film generated by heat treatment from the laminated film and the C-axis orientation of the Bi film before heat treatment, and it is possible to improve the C-axis orientation of the Bi film by increasing the C-axis orientation of the MnBi film. It becomes important for enhancing the orientation. Since the Bi film tends to orient the C plane parallel to the surface of the underlayer, the crystal orientation decreases when the surface roughness of the underlayer is large. The surface roughness of the dielectric film depends on the type of the dielectric and the film forming method, but the surface smoothness can be improved by performing the sputter etching process.

Therefore, by sputtering the surface of the dielectric underlayer, the crystal orientation of the MnBi film can be enhanced and the polarization noise can be reduced. To obtain the effect of reducing the polarization noise, the centerline average roughness (Ra) is 1
It is necessary to be less than or equal to nm.

[0019]

Embodiments of the present invention will now be described with reference to the drawings.

First, a first embodiment of the present invention will be described.

FIG. 1 is a partial sectional view showing an embodiment of a magneto-optical recording medium according to the present invention.

In this magneto-optical recording medium, a base layer (silicon nitride film formed by sputtering) 2 of 85 nm is formed on a glass substrate 1.
, The MnBi layer 3 to a thickness of 32 nm by the ion cluster beam method, the interference layer (silicon nitride film by sputtering) to a thickness of 200 nm, and the reflective layer (Al by vapor deposition).
The film 5 is sequentially formed into a film having a thickness of 20 nm and heat-treated at 380 ° C. for 3 hours to produce the film. For comparison, two types of media, that is, the medium in which the sputter etching treatment of the surface of the underlayer of the first embodiment is performed and the medium in which the sputter etching treatment of the conventional example is not performed, are prepared.

The sputter etching treatment was carried out using Ar gas at a flow rate of 24.5 SCCM, a gas pressure of 0.1 Pa, an input power of 350 W and an etching rate of 0.1 nm / min. The etching time was 50 minutes, and the etching was 5 nm. Ra of the underlayer not subjected to the sputter etching treatment is 2n
m, and Ra of the underlayer etched by 5 nm is 1 nm
Met.

FIG. 2 is a graph showing the rocking curve of the (002) plane which is the C-axis oriented plane of the MnBi film of FIG.

This is a rocking curve of the medium 21 that has been subjected to the sputter etching treatment and the medium 22 that has not been subjected to the sputter etching treatment of the conventional example. By carrying out sputter etching, the full width at half maximum is greatly reduced from 13.2 ° to 2.3 °, and the C-axis orientation is improved.

FIG. 3 shows the magneto-optical recording medium of FIG.
7 is a graph showing a noise spectrum at the time of unrecording measured by a W device.

Medium 31 that has been sputter-etched
And the noise spectrum of the medium 32 that is not subjected to the sputter etching process of the conventional example. Measured at a linear velocity of 6 m / s. It can be seen that the noise level is lowered by performing the sputter etching process.

Next, a second embodiment in which the etching amount is changed will be described.

The structure of the magneto-optical disk medium is the same as that of the first embodiment shown in FIG.

The film thickness of the underlying layer of silicon nitride is 95 nm.
The sputter etching process uses Ar gas and the flow rate is 2
The conditions are the same as in the first embodiment, such as 4.5 SCCM, gas pressure 0.1 Pa, input power 350 W, and etching rate 0.1 nm / min. The etching time is 150 minutes, and the etching is 15 nm. By performing 15 nm etching, Ra of the underlayer became 0.5 nm.

FIG. 4 shows the magneto-optical recording medium of FIG.
7 is a graph showing a noise spectrum at the time of unrecording measured by a W device.

Medium 41 that has been sputter-etched
And the noise spectrum of the medium 42 that is not subjected to the sputter etching process of the conventional example. Measured at a linear velocity of 6 m / s. It can be seen that the noise level is lowered by performing the sputter etching process. Further, by decreasing Ra of the underlayer, the amount of decrease in noise level is increased.

For forming the MnBi layer, an evaporation method, a sputtering method and an ion plating method can be used in addition to the ion cluster beam method. In addition to silicon nitride, Z
Similar effects were obtained with dielectrics such as nS, SiO ₂ , SiO, and MnO.

[0034]

As described above, according to the manufacturing method of the present invention, the underlayer is formed on the substrate by the dielectric film subjected to the sputter etching process, and the MnBi thin film is formed on the underlayer by the heat treatment. By doing so, it is possible to manufacture a magneto-optical recording medium having a low noise level and provide a high-performance magneto-optical recording medium.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an embodiment of a magneto-optical recording medium according to the present invention.

2 is a C-axis oriented surface of the MnBi film of FIG. 1 (00
It is a graph which shows the rocking curve of 2) surface.

FIG. 3 is a graph showing a noise spectrum of the magneto-optical recording medium of FIG. 1 measured by a magneto-optical R / W device when unrecorded.

FIG. 4 is a graph showing a noise spectrum of the magneto-optical recording medium of FIG. 1 measured by a magneto-optical R / W device when unrecorded.

FIG. 5 is a sectional view of the structure of a conventional MnBi magneto-optical recording medium before heat treatment.

[Explanation of symbols]

 1 Glass Substrate 2 Underlayer 3 MnBi Layer 4 Interference Layer 5 Al Reflective Film 6 Underlayer 7 Interference Layer 21 Medium without Sputter Etching 22 Medium without Sputter Etching 31 Medium with Sputter Etching 32 Sputter Etching Medium not subjected to treatment 41 Medium subjected to sputter etching treatment 42 Medium not subjected to sputter etching treatment 51 Glass substrate 52 Underlayer 53 Bi layer 54 Mn layer 55 Interference layer 56 Reflective layer

Claims (3)

[Claims] 1. A MnB having a perpendicular magnetic easy axis formed by forming an underlayer of a dielectric film that has been subjected to a sputtering etching treatment.
A method for manufacturing a magneto-optical recording medium, which comprises laminating an i-compound thin film on an underlying layer thereof. 2. The manufacturing method according to claim 1, wherein the underlayer and the MnBi compound thin film are sequentially formed, and the temperature is set to 300 ° C.
A method for manufacturing a magneto-optical recording medium, which is characterized in that the manufacturing is carried out in the above temperature atmosphere. 3. A magneto-optical recording medium manufactured by the manufacturing method according to claim 1, wherein the center line average roughness (Ra) of the dielectric film is 1 nm or less. .