JP2766520B2 - Method for manufacturing magneto-optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel method for manufacturing a magneto-optical recording medium in which a dielectric layer, a magneto-optical recording layer, and a dielectric layer are sequentially provided on a substrate. More specifically, the present invention controls the coercive force of the magneto-optical recording layer to a value within a predetermined range, and has a desired recording / reproducing characteristic.
The present invention relates to a method for efficiently manufacturing a magneto-optical recording medium capable of reproducing and erasing.

2. Description of the Related Art In recent years, a magneto-optical recording medium such as a magneto-optical disk has been developed as an optical recording medium capable of recording, reproducing, and erasing information with a light beam. Conventionally, alloys such as Mn-Bi have been used as a recording material for the magneto-optical recording layer for recording information in this magneto-optical recording medium, but today, transition metals such as Fe and Co and Nd and Dy are used. , Gd, Tb and other rare earth alloys are commonly used.

By the way, as an optical recording medium capable of recording and erasing information, another one utilizing a reversible phase change is known, but an optical recording medium utilizing the magneto-optical effect utilizes a phase change. Different from the above, it is characterized in that recording and erasing are performed only by reversing the direction of magnetization. That is, in an optical recording medium utilizing the magneto-optical effect, when recording, first, an external magnetic field is continuously applied while irradiating a magnetic material used as a recording layer with a light beam such as a laser as an initialization process to magnetize the magnetic material. After the orientations are aligned, a bit is formed by irradiating a light pulse while applying an external magnetic field in the opposite direction, and when erasing, the same operation as in the initialization process is performed. Since such a process does not involve the movement of atoms, there is an advantage that there is little possibility that the recording layer is deformed or the recorded state or the erased state is changed.

In addition, various methods for forming this kind of thin film have been studied. However, in the recording layer of the magneto-optical recording medium, a sputtering method is generally used from the viewpoints of vapor pressure of constituent elements and productivity. I have.

Among the sputtering methods, TbFeCo is used as the magneto-optical recording layer.
When forming alloys such as NdDyFeCo by sputtering, T
b, a rare earth such as NdDy and a transition metal of FeCo are separately sputtered together from a target, and TbFeCo, NdDyFeCo
May be sputtered from the composite alloy target of
The latter is more advantageous in terms of simplicity.

However, in an optical recording medium manufactured by sputtering from such a composite alloy target, the magnetic properties such as the coercive force and the Kerr rotation angle of the magneto-optical recording film are ferrimagnetic, so that the rare earth-transition metal ratio is large. Depends on
For example, in the case of TbFeCo, the atomic ratio of Tb in the film composition is 1 atomic%.
As a result, the coercive force changes greatly, and the Kerr rotation angle also changes. As a result, the magnetic field sensitivity during recording and the amplitude of the reproduced signal are greatly affected.
It is necessary to suppress the following. However, although the composition of this film is almost determined by the composition of the target, it is quite difficult to produce the target with a reproducibility of a rare earth composition of 1 atomic% or less. Therefore, the composition of the target is 1 to
It is necessary to keep the magnetic characteristics of the magneto-optical recording layer within a desired range even if the fluctuation is about 2 atomic%.

The composition of the magnetic recording layer, even when the same target is used, varies depending on the gas pressure and the power applied by sputtering.
The range is about 0.5%. Therefore, it is necessary to prepare the composition of the magneto-optical recording layer by another method.

Under these circumstances, the present invention apparently adjusts the rare earth-transition metal ratio of the magneto-optical recording layer in the magneto-optical recording medium to optimize the magnetic properties, It is an object of the present invention to provide a method for easily manufacturing a magneto-optical recording medium having recording / reproducing characteristics.

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, after forming a magneto-optical recording layer, a specific concentration range of oxygen was acted on to form a rare earth element in the recording layer component. By oxidizing a part of the magnetic recording medium, the necessary minimum recording magnetic field required for recording in the magneto-optical recording medium is reduced to a predetermined value or less, so that the rare earth-transition metal ratio is apparently adjusted to optimize the magnetic characteristics. Were found possible, and this finding led to the completion of the present invention.

That is, according to the present invention, a dielectric layer, a magneto-optical recording layer, and a dielectric layer are sequentially formed on a substrate by a sputtering method to manufacture a magneto-optical recording medium including at least three layers.
After the formation of the magneto-optical recording layer, oxygen is applied under conditions of an oxygen partial pressure of 0.1 to 10 mTorr, and a part of the magneto-optical recording layer is oxidized until the required minimum recording magnetic field of the magneto-optical recording medium becomes 300 or less. And a method for manufacturing a magneto-optical recording medium characterized by the following.

 Hereinafter, the present invention will be described in detail.

The magneto-optical recording medium obtained by the method of the present invention has a structure comprising at least three layers in which a dielectric layer, a partially oxidized magneto-optical recording layer and a dielectric layer are sequentially laminated on a substrate. According to the above, in order to increase the Kerr rotation angle, on the dielectric layer provided on the magneto-optical recording layer, further Al, Ni,
A reflective layer made of a metal such as Cr or Au may be provided.

As the substrate in the magneto-optical recording medium, those made of materials commonly used for substrates of ordinary optical recording materials, such as glass, glass or plastic provided with a polymer layer curable by ultraviolet light or the like, acrylic resin, A transparent substrate such as a styrene resin, a polycarbonate resin, a vinyl acetate resin, vinyl chloride, or a polyolefin resin, or a substrate made of an opaque material such as aluminum is used. Irregularities including address information and the like may be formed on these substrates.

As the magneto-optical recording layer provided on the substrate, an amorphous perpendicular magnetization film made of a material having a high coercive force Hc and a small magnetization Ms is used. As such,
For example, a ferrimagnetic film such as TbFe, GdTbFe, TbFeCo, NdDyFeCo, and TbFeNi is preferably exemplified. Further, in order to adjust the coercive force Hc, these materials may be laminated to form an exchange coupling film. Among these materials, especially TbFeCo, NdDy
FeCo is preferably used.

These materials have a feature that the coercive force Hc sharply decreases centering on the composition of the compensation point. The drawing is Tb _x (Fe _0.9
Co _0.1) is a graph showing the relationship between the coercive force Hc x (atomic%) in _1-x. As can be seen from this drawing, near the compensation point, the coercive force Hc greatly changes with a change in the composition of the rare earth element. For example, from Tb ₂₁ (Fe _0.9 Co _0.1 ) ₇₉ to Tb
By changing to ₂₀ (Fe _0.9 Co _0.1 ) ₈₀ , the coercive force Hc becomes
It changes greatly from 13K to 8K, and accompanying this, the minimum recording magnetic field required for recording on the magneto-optical recording medium (the minimum recording magnetic field is the minimum magnetic field where the maximum C / N is obtained when recording with the optimum recording laser power) Means the size of
Changes significantly from 400 (Oersted) to 250.

When an oxidizing atmosphere is applied to the material in a vacuum system, the rare-earth element selectively reacts to form a rare-earth oxide, and the apparent rare-earth-transition metal ratio changes. That Tb ₂₁ (Fe _0.9 Co _0.1) as were _79, the composition of the apparent Tb _{from 20 to 19} by Tb is partially oxidized (Fe _0.9 Co
_0.1 ) _{Equivalent to 80-81} . Thereby, the coercive force changes from 13K to 7 to 8K, and the required minimum recording magnetic field can be reduced from 400 to 300 to 200.

As an example of a method of applying an oxidizing atmosphere in a vacuum system, oxygen is introduced into the system after forming the magneto-optical recording layer, and the partial pressure is 0.1 to 10 mTorr, preferably 0.5 to 1 mTorr.
There is a method of exposing to an atmosphere in the range of This partial pressure is appropriately adjusted to a desired value. However, if it exceeds 10 mTorr, the magneto-optical recording layer is excessively oxidized, and the magnetic properties are adversely deteriorated, and if it is less than 0.1 mTorr, the effect of the present invention is not sufficiently exhibited. .

In the present invention, a part of the magneto-optical recording layer is oxidized under such oxidizing conditions until the required minimum recording magnetic field of the magneto-optical recording medium becomes substantially 300 or less.

The dielectric layers provided above and below the magneto-optical recording layer include, for example, SiN _x , SiN _x O _y , SiO _x , SiAlN _x , SiAlO _x N _y , AlN _x ,
Materials such as AlO _x N _y and ZnS are used. This dielectric layer may be provided by sputtering using the compound as a target, or may be provided by a reactive sputtering method using a metal or semimetal such as Si or Al as a target.

All of these methods are performed at the time of sputtering film formation.
As the sputtering apparatus, for example, a substrate passing type film forming method or a substrate revolving type film forming method is used. Among these, a substrate passing type film forming method is preferable from the viewpoint of mass productivity. .

According to the method of the present invention, even when the composition of a sputter target for forming a magneto-optical recording layer is different from the composition capable of obtaining desired magnetic characteristics, it is possible to adjust the apparent composition at the time of film formation. The coercive force can be controlled to a predetermined value, and a magneto-optical recording medium having desired recording / reproducing characteristics can be easily manufactured.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Comparative Example 1 A magneto-optical recording medium was produced by the following procedure using a polycarbonate substrate having a diameter of 130 mm and a thickness of 1.2 mm formed by injection molding by a pass-through sputtering method.

First, using Si ₃ N ₄ as a target, SiN _x at a gas pressure of 5 mTorr
After forming the layer to a thickness of 1000 mm, a TbFeCo magneto-optical recording layer was formed thereon with a thickness of 250 mm at a gas pressure of 3 mTorr using a TbFeCo composite alloy target A. The composition of this recording layer is Tb
₂₂ (Fe _0.9 Co _0.1 ) ₇₈ . Next, a SiN _x layer was formed to a thickness of 300 mm at a gas pressure of 5 mTorr using Si ₃ N ₄ as a target, and an Al layer was formed thereon as a reflective layer to a thickness of 400 mm.

When the recording and reproduction characteristics of the magneto-optical recording medium thus manufactured were evaluated, the coercive force Hc was larger than 15 K, the C / N ratio at the position of the substrate rotation speed of 1800 rpm, the recording frequency of 1 MHz, and the recording radius of 30 mm was 56 dB. Was. Also, the minimum recording magnetic field at which the C / N ratio was saturated at the optimum recording power required 400.

Example 1 130 mm molded by injection molding in the same manner as Comparative Example 1.
Using a polycarbonate substrate having a diameter and a thickness of 1.2 mm, a magneto-optical recording medium was manufactured by the following procedure by a pass-through sputtering method.

First, a SiN _x layer was formed to a thickness of 1000 mm at a gas pressure of 5 mTorr, and a TbFeCo magneto-optical recording layer was formed thereon at a gas pressure of 3 mTorr to a thickness of 250 mm using a target A of TbFeCo. The composition of this recording layer was Tb ₂₂ (Fe _0.9 Co
_0.1 ) ₇₈ . Next, O ₂ was introduced into the vacuum chamber to 5 mTorr, and after a treatment for 20 seconds, using Si ₃ N ₄ as a target,
An SiN _x layer was formed to a thickness of 300 mm at a gas pressure of 5 mTorr, and an Al layer was formed thereon as a reflective layer to a thickness of 400 mm.

When the recording / reproducing characteristics of the magneto-optical recording medium thus manufactured were evaluated, the coercive force Hc was 8K and the substrate rotation speed was 18
The C / N ratio at a position of 00 rpm, a recording frequency of 1 MHz, and a recording radius of 30 mm was 58 dB. The minimum recording magnetic field at which the C / N ratio was saturated at the optimum recording power was 250, indicating that the C / N ratio was improved and the magnetic field sensitivity was improved.

As a result, by performing oxygen treatment after forming the TbFeCo recording layer, the apparent composition was Tb ₂₀ (Fe _0.9 Co _0.1 ).
_{About 80} were obtained, and it was confirmed that the recording / reproducing characteristics could be improved.

[Brief description of the drawings]

The figure is a graph showing the coercive force Hc near the compensation composition of Tb _x (Fe _0.9 Co _0.1 ) _{1-x in} the magneto-optical recording layer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 11/10 541 G11B 11/10 501

Claims (1)

(57) [Claims] 1. A method of manufacturing a magneto-optical recording medium comprising at least three layers by sequentially forming a dielectric layer, a magneto-optical recording layer and a dielectric layer on a substrate by a sputtering method. After formation, oxygen is acted on under a condition of an oxygen partial pressure of 0.1 to 10 mTorr, and a part of the magneto-optical recording layer is oxidized until the required minimum recording magnetic field of the magneto-optical recording medium becomes 300 or less. A method for manufacturing a magnetic recording medium.