JPH08147782A - Magneto-optical recording medium and tis production - Google Patents

Abstract

PURPOSE: To obtain a magneto-optical recording medium capable of diminishing a bias magnetic field required in the conventional light modulated recording, capable of reducing the size of a bias magnet and the consumption of electric power and well adaptable even to a levitated head used in a magnetic field modulated overwriting system. CONSTITUTION: When a transparent dielectric layer is interposed between a magneto-optical recording layer and a transparent substrate to obtain a magneto-optical recording medium, its dielectric layer is composed of Si, Al and N and the number of Si atoms x, with the sum of Si and Al atoms (ratio) taken to be 1, is regulated to be in the range 0.4<x<0.7. The dielectric layer is formed by sputtering under >4.0 to <16.0mTorr pressure of sputtering gas. The center line average surface roughness Ra of the recording layer side of the dielectric layer is <=0.3nm.

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 for recording, reproducing and erasing information on a perpendicular magnetization film by using a focused laser beam.

[0002]

2. Description of the Related Art The so-called magneto-optical recording method for recording on a perpendicularly magnetized film provided on a substrate by using a laser beam has been widely used as a method for recording rewritable high density and large capacity. ing. In the magneto-optical recording method, a minute portion is heated by a converged laser beam while applying a predetermined magnetic field to the recording film to change the magnetization direction of the recording film to record information. Further, when linearly polarized light is incident on the recorded portion, the polarization direction rotates depending on the magnetization direction, so-called Kerr effect or Faraday effect is used to read information.

A recording film used in the above-described magneto-optical recording medium has an easy axis of magnetization in a direction perpendicular to the film surface, has no noise due to crystal grain boundaries, and has a relatively large Kerr rotation angle. However, an amorphous alloy of a rare earth-transition metal is generally used because it has a large coercive force and is easy to form a film on a substrate having a large area.

In the conventional magneto-optical recording medium, when old data exists at a place where new data is written, it is necessary to erase the old data and then write the new data. In order to shorten the time, it is desired to realize an overwrite method in which a new signal is directly overwritten on an old signal without undergoing an erasing process. As one of the overwrite methods, a magnetic field modulation recording method has been proposed in which a magnetic field is modulated by a recording signal and recorded while continuously irradiating a laser beam with a constant power.

[0005]

As the magnetic field generating magnet used in the above magnetic field modulation recording method, a floating magnetic head generally used in magnetic disks is used. However, since the magnetic field is inverted at a high speed, the inductance of the head is limited, and the resulting magnetic field is smaller than the recording magnetic field used in the conventional magneto-optical disk. On the other hand, in the conventional recording medium, since the magnetic field required for recording is too high, it is necessary to improve the sensitivity to the magnetic field in order to perform this magnetic field modulation recording.

Conventionally, as a method of improving the recording magnetic field sensitivity of a magneto-optical recording medium, a dielectric layer (mostly a silicon nitride film is used between a rare earth-transition metal layer (magneto-optical recording layer) and a substrate is used. Known method) and a method of lowering the sputtering gas pressure at the time of forming the dielectric layer are known, but these methods make the process complicated. There is also a problem that the CN ratio, which is a recording characteristic, becomes low.

[0007]

The present inventor has completed the present invention as a result of extensive studies to solve the above problems. That is, the present invention relates to a magneto-optical recording medium having a transparent dielectric layer provided between a magneto-optical recording layer and a transparent substrate, and a method for manufacturing the same, wherein the transparent dielectric layer comprises Si, Al and N. And the sum of the number of atoms (ratio) of Si and Al is 1
, The number x of Si atoms is in the range of 0.4 <x <0.7, and the center line surface roughness (Ra) of the transparent dielectric layer on the magneto-optical recording layer side is 0.3 nm or less. And a sputtering gas pressure p (mtor) when the transparent dielectric layer is formed.
r) provides a method for manufacturing the above-mentioned magneto-optical recording medium, characterized in that the film formation is performed by sputtering in the range of 4.0 <p <16.0.

The most general magneto-optical recording film using the dielectric layer of the present invention is one having a structure of dielectric layer / magneto-optical recording layer / dielectric layer / reflection layer from the substrate side. . The magneto-optical recording layer used here is TbFe
Co, DyFeCo, GdDyFeCo, NdDyFe
Examples thereof include rare earth-transition metal amorphous alloys such as Co, TbFe, TbCo, and NdDyTbFeCo, and alloys in which metals such as Ti and Cr are added to these for the purpose of improving oxidation resistance. Further, the present invention can be applied to a recording film composed of a repeated laminated film such as Pt / Co and Au / Co.

The dielectric layer made of Si, Al and N is disclosed in Japanese Patent Publication No.
As described in Japanese Patent Publication No. 70297, the present inventor has found that a magneto-optical recording medium having high sensitivity to a magnetic field and high CN ratio can be obtained by forming this dielectric layer under specific conditions. It was

The simplest and preferred method is to form this SiAlN dielectric layer by a reactive sputtering method using an alloy target of Si and Al in an N ₂ gas atmosphere. The total pressure of the sputtering gas at this time is 16.0 mtorr.
When it is less than the above range, a smooth thin film with less surface irregularities is formed. If the surface of the dielectric layer underlying the magneto-optical recording layer is smooth, the domain wall movement in the magneto-optical recording layer laminated thereon becomes easy, and as a result, the sensitivity of the magneto-optical recording medium to the magnetic field is improved. It is considered to be a thing. When the surface of the dielectric layer was measured using an atomic force microscope (AFM), the center line surface roughness (Ra) was measured by the above method.
It was found that a magneto-optical recording film having a high magnetic field sensitivity can be obtained when is less than 0.3 nm.

On the other hand, SiN, which has been often used as a dielectric layer, has a low CN ratio due to an increase in noise caused by the dielectric layer when the film is formed at a low sputtering gas pressure as described above. If the composition of the SiAlN dielectric layer is the sum of the atomic numbers (ratio) of Si and Al being 1, and the number of Si atoms is in the range of 0.4 <x <0.7, Even if film formation is performed with a relatively low sputter gas pressure, noise originating from the dielectric layer is small, and as a result, a magneto-optical recording medium having a high CN ratio can be obtained. However, even in this case, if the sputter gas pressure is 4.0 mtorr or less, noise derived from the dielectric layer increases even with SiAlN. Therefore, in the present invention, the sputter gas pressure p (mtor
r) is preferably in the range of 4.0 <p <16.0.

In the above, the case where the magneto-optical recording film is composed of four layers of dielectric layer / magneto-optical recording layer / dielectric layer / reflection layer from the substrate side has been described. Any structure is effective as long as it has a dielectric layer between it and the magnetic recording layer. For example, after increasing the thickness of the magneto-optical recording layer, the dielectric layer / magneto-optical recording layer / dielectric It is needless to say that the present invention can be applied to a structure having three body layers and a case where the magneto-optical recording layer is composed of a plurality of layers having different compositions.

[0013]

EXAMPLES The details of the present invention will be described below with reference to examples. (Example 1) This recording film was produced by the following procedure. A 86 mm diameter plastic substrate provided with a guide groove was attached to a rotary substrate holder in a magnetron sputtering apparatus, and recording layers were sequentially laminated. First, as a first dielectric layer, SiAlN having a thickness of 100 nm was formed by RF sputtering. This SiAlN was formed into a film by the reactive sputtering method using Si _0.5 Al _0.5 as a target and Ar gas in which N ₂ was mixed in the sputtering gas. Next, the magnetic layer was formed by a DC method using a TbFeCo target and Ar as a sputtering gas.

Next, a SiAlN film having a thickness of 30 nm was laminated as a second dielectric layer by the same method as the first method, and finally an AlTi film having a thickness of 70 nm was laminated by the DC sputtering method. When the film is formed in this manner, the total pressure of the sputtering gas at the time of forming the first SiAlN dielectric layer is set from 2 mtorr to 20
It was changed to mtorr. For the purpose of protecting the recording film sputter-deposited on the substrate as described above, spin-coating of a UV curable resin was performed on the recording film. The magnetic field sensitivity and the CN ratio were measured by the following method after the entire disk was once erased. Recording was performed using a semiconductor laser of 830 nm under the conditions of a rotation speed of 2400 rpm, a laser light modulation frequency of 3.9 MHz, a recording pulse width of 60 nsec, and a recording power of 7.0 mW while changing the bias magnetic field. As an example, FIG. 1 shows the change in the CN ratio with respect to the recording bias magnetic field when the gas pressure during sputtering of the first dielectric layer is 5.0 mtorr.

The negative direction on the horizontal axis of the drawing indicates that the bias magnetic field is applied to the erasing side, and the positive direction to the recording side. In such optical modulation recording, it can be said that the magnetic field sensitivity is high when the recording start magnetic field (the magnetic field of A in FIG. 1) and the saturation magnetic field (the magnetic field of B in FIG. 1) are both close to 0, and also in the magnetic field modulation recording. Shows high magnetic field sensitivity.

FIG. 2 shows the relationship between the sputtering gas pressure at the time of forming the first dielectric layer, the recording start magnetic field and the CN ratio. From the figure, it can be seen that when the sputtering gas pressure is less than 16.0 mtorr, a high magnetic field sensitivity of the recording start magnetic field of -200 Oe or more can be obtained, but when it is less than 4.0 mtorr, the CN ratio decreases. From the above results, the sputtering gas pressure p is
It can be seen that a magneto-optical recording medium having a high CN ratio and high magnetic field sensitivity can be obtained in the range of 4.0 <p <16.0.

The same dielectric film as the first dielectric layer produced at this time was formed on a silicon wafer, and the surface roughness was measured using an atomic force microscope (AFM). FIG. 3 shows the relationship between the sputtering gas pressure during film formation and the surface roughness obtained as a result of this. From FIG. 3, it can be seen that the center line surface roughness (Ra) in the range of the sputtering gas pressure at which high magnetic field sensitivity is obtained is 0.3 nm or less.

(Comparative Example) A recording film was formed on the same plastic substrate as in Example 1 by using the same sputtering apparatus. In this comparative example, Si _0.5 Al _{0.5 of} Example 1 is used.
The first and second dielectric layers were formed using a Si target instead of the target. Further, as in Example 1, the sputtering gas pressure when forming the first dielectric layer was set to 1.0.
It was changed from mtorr to 10 mtorr. The recording characteristics of the thus-produced magneto-optical recording medium were measured under the same conditions as in Example 1. FIG. 4 shows the relationship between the sputtering gas pressure at the time of forming the first dielectric layer of these magneto-optical recording media, the recording start magnetic field, and the CN ratio.

As shown in the figure, when the sputter gas pressure is 3 mtorr or less, the recording start magnetic field is -200 Oe or more, and high magnetic field sensitivity can be obtained, but the CN ratio is considerably lower than that of the magneto-optical recording medium formed at a high sputter gas pressure. You can see that

(Example 2) A magneto-optical recording medium was manufactured in the same procedure as in Example 1, but Al-Si targets at the time of film formation of the first and second dielectric layers were changed to several types. Film formation was performed in place of the target. The sputtering gas pressure at this time was fixed at 5 mtorr. The recording characteristics of the thus-produced magneto-optical recording medium were measured under the same conditions as in Example 1. FIG. 5 shows the relationship between the recording start magnetic field and the composition ratio of Al and Si in the dielectric layers of these magneto-optical recording media.

From FIG. 5, when the sum of the atomic numbers (ratio) of Si and Al in the dielectric layer is 1, the atomic number x of Si is
It can be seen that a magneto-optical recording medium with high magnetic field sensitivity can be obtained in the range of 0.4 <x <0.7.

[0022]

By using the dielectric layer according to the present invention, the magnetic field sensitivity to the applied magnetic field during recording and erasing can be improved. Therefore, not only the bias magnetic field required in the conventional optical modulation recording can be reduced, the bias magnet can be downsized and the power consumption can be reduced, but also the flying magnetic head used in the magnetic field modulation overwrite method can be sufficiently supported. A recording medium is obtained.

[Brief description of drawings]

FIG. 1 shows an example of the first embodiment of the present invention in which the sputtering gas pressure during film formation of the first dielectric layer is 5.0 m.
7 is a graph showing changes in the CN ratio with respect to the recording magnetic field when the value is torr.

FIG. 2 is a graph showing changes in a recording start magnetic field and a CN ratio as an index of magnetic field sensitivity with respect to a sputtering gas pressure during film formation of a first dielectric layer in Example 1 of the present invention.

FIG. 3 is a graph showing the relationship between the surface roughness measured by AMF and the sputtering gas pressure when depositing a SiAlN dielectric layer in Example 1 of the present invention.

FIG. 4 is a graph showing the relationship of magnetic field sensitivity to changes in sputtering gas pressure during SiN dielectric layer formation in a comparative example of the present invention.

FIG. 5 is a graph showing the relationship between the atomic ratio of Si and Al in the SiAlN dielectric layer and the magnetic field sensitivity in Example 2 of the present invention.

Claims (2)

[Claims] 1. A transparent dielectric layer provided between a magneto-optical recording layer and a transparent substrate is made of Si, Al and N, and the sum of the atomic numbers (ratio) of Si and Al is 1. , S
The number x of atoms of i is in the range of 0.4 <x <0.7, and the center line surface roughness (Ra) of the transparent dielectric layer on the magneto-optical recording layer side is 0.3 nm or less. A magneto-optical recording medium characterized by: 2. A method of manufacturing a magneto-optical recording medium, which is provided between a magneto-optical recording layer and a transparent substrate and has a composition of S.
i, Al and N, and when the sum of the atomic numbers (ratio) of Si and Al is 1, the atomic number x of Si is 0.
The sputtering gas pressure p (mtorr) when forming the transparent dielectric layer in the range of 4 <x <0.7 by sputtering is 4.0.
A method for manufacturing a magneto-optical recording medium, characterized in that <p <16.0.