JPH06131714A - Production of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the process for production of the magneto-optical recording medium capable of recording or erasing signals while maintaining signal quality of a high level even under a small external magnetic field by decreasing the noises in a low magnetic field and increasing CNR. CONSTITUTION:The film of a lower layer 4a in contact with a dielectric substance layer 3 of a lower layer is formed at >=100 angstrom/min deposition rate at the time of forming a recording film 4. An upper layer 4b in contact with the dielectric substance layer 5 of the upper layer is formed to 10 to 30 angstrom thickness at <=15 angstrom/min deposition rate. After the formation of the film of the upper layer, the surface thereof is subjected to an oxidation treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magneto-optical recording medium having a recording layer made of a rare earth-transition metal amorphous alloy, and more particularly to a technique for improving magnetic field recording characteristics.

[0002]

2. Description of the Related Art Conventionally, various optical recording elements have been proposed, and among them, a magneto-optical recording medium having the advantage of being capable of additional recording and erasing has already been put into practical use.
A magnetic field modulation method is one of recording methods using a magneto-optical recording medium. As a recording film of a magneto-optical recording medium by this magnetic field modulation method, a thin film made of a rare earth-transition metal alloy is most often used at present because of its suitable comprehensive characteristics. The rare earth-transition metal amorphous alloy film is a perpendicular magnetization film whose saturation magnetization is perpendicular to the film surface,
The signalized information is written by changing the direction of the magnetization at the recording location on the film.

A Curie point recording method is one of the methods for recording or erasing information using the above magnetic field modulation method. This is because an external magnetic field is applied to the recording film using an electromagnet or the like, and at the same time, the recording film is irradiated with laser light focused by a lens to raise the temperature of the recording film to the Curie temperature. Information is recorded or erased by magnetizing in the same direction. In the Curie point recording method, for example, when the recording medium is a magneto-optical disk provided with a general single-layer structure rare earth-transition metal amorphous alloy recording film, 200 to 200
A magnetic field of about 400 (Oe) is required. If recording / erasing can be performed with a smaller magnetic field, the magnet for generating the external magnetic field can be made smaller and lighter, and in the case of the magnetic field modulation method, high-speed modulation of the magnetic field becomes possible. A technique for further improving the magnetic field sensitivity characteristic of a recording medium is desired.

FIG. 6 is a magnetic field sensitivity characteristic diagram of a magneto-optical disk which is a typical magneto-optical recording medium. An external magnetic field is applied to a magneto-optical disk which is initialized by aligning the direction of magnetization in advance, and laser light is irradiated. The relationship between the external magnetic field and the CNR when the data is written by the following is shown. In order to reduce the recording / erasing magnetic field in the magnetic field modulation method, it is desirable that the external magnetic field Hs at which the CNR saturates and the external magnetic field H0 at which the CNR begins to appear are both small as characteristics of the recording medium. That is, in the magnetic field modulation method, the magnetic field is reversed between Hs and H0, so that Hs and H0 are small and
The smaller the difference between s and H0, the faster the modulation operation becomes possible. If Hs and H0 are small, the electromagnet coil for generating them can be made small and lightweight.

On the other hand, as shown in FIG. 7, in the perpendicularly magnetized film 71 at the time of writing, the high temperature portion 72 irradiated with the laser beam L has an external magnetic field Hex from an electromagnet or the like and a curie around the high temperature portion 72. Two magnetic fields, a demagnetizing field Hd generated from a portion below the temperature, are applied. It is this demagnetizing field Hd that has a great effect on H0 shown in FIG. 6, and if Hd is large, H0 is necessary to cancel it. This H
Since d depends on the magnitude of magnetization around the high temperature portion 72,
In the case of a disc with a single recording film, the composition of the recording film may be designed by selecting a compensating composition that reduces the magnetization, but since the characteristics change greatly due to subtle changes in the composition, recording with the desired quality It is difficult to stably supply the membrane. Therefore, without adjusting the compensating composition by adjusting the input power at the time of forming the dielectric layer or the recording film, the sputtering gas pressure, or by performing reverse sputtering of the dielectric layer,
A method of reducing H0 has been adopted.

[0006]

However, it has become a problem that the noise level becomes large under the action of a low magnetic field by reducing H0. When reversing the magnetic field in the magnetic field modulation method, the external magnetic field always goes to a state of zero. Therefore, reducing the noise at the zero magnetic field in the external magnetic field characteristics shown in FIG. 6 and increasing the CNR is of high quality. This is one of the extremely important problems in manufacturing a magneto-optical recording medium.

The present invention has been made to solve the above-mentioned problems, and is an apparatus provided with a small and lightweight electromagnet by reducing noise under a low magnetic field and increasing CNR. It is an object of the present invention to provide a method for manufacturing a magneto-optical recording medium capable of stable recording / erasing operations.

[0008]

In order to achieve the above object, the present invention provides a substrate on which a lower dielectric layer, a recording film made of a rare earth-transition metal amorphous alloy, and an upper dielectric layer are sequentially formed. In the method for manufacturing a laminated magneto-optical recording medium, the recording film is formed at a deposition rate of 100 Å / min or more on the side in contact with the lower dielectric layer, and on the side in contact with the upper dielectric layer, Deposition rate is 1
The film is formed at a thickness of 5 to 30 Å / min and a thickness of 10 to 30 Å, and the surface of the recording film is oxidized.

[0009]

With the above structure, when the recording film is formed, the deposition rate on the side in contact with the lower dielectric layer, the deposition rate on the side in contact with the upper dielectric layer, and the film thickness satisfy predetermined conditions. And by oxidizing the surface of the recording film after film formation,
It is possible to manufacture a magneto-optical recording medium capable of stable recording and erasing by reducing noise under the action of a low external magnetic field and improving CNR.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration example of a magneto-optical disk (hereinafter referred to as a disk) created in this embodiment.
The disk 1 is a substrate 2 having a thickness of 1.2 mm and a thickness of 1100.
A dielectric layer (interference layer) 3 below angstrom, a recording film 4 having a thickness of 200 angstrom which is a perpendicular magnetization film,
The dielectric layer (protective layer) 5 is an upper layer of 350 Å thick, and the reflective layer 6 is 500 Å thick. The recording film 4 has a two-layer structure and includes a lower dielectric layer 3
The lower layer 4a in contact with and the upper layer 4b in contact with the upper dielectric layer 5 were formed under different conditions.

The material of the substrate 2 may be selected from plastics such as polycarbonate and epoxy resin, glass, ceramics, metals and the like. The material of the dielectric layers 3 and 5 is SiN, AlSiN, AlSiO.
N, SiO, ZnS or the like is used. The recording film 4 is formed as a lower layer 4 by sputtering a rare earth-transition metal amorphous alloy.
a and the upper layer 4b are formed in this order, and after the upper layer 4b is formed, the surface of the recording film 4 is oxidized. The reflective layer 6 may be made of Al, Au, Ag, Pt, etc., Ti, Cr, I.
One or more of n and Cu added is used.
In this example, polycarbonate was used for the substrate 2, SiN was used for the dielectric layers 3 and 5, TbFeCoCr was used for the recording film 4, and AlTi was used for the reflective layer 6. The gases used when forming the recording film 4 by sputtering are Ar and N ₂ . The oxidation treatment on the surface of the recording film 4 was performed by introducing an argon / oxygen mixed gas. The gas used for the oxidation treatment may be any gas as long as it has the ability to oxidize the surface of the recording film 4, and may be a gas containing only oxygen or a gas containing a large number of substances other than oxygen, in addition to the above-described argon-oxygen mixed gas. .

In order to investigate the effect of making the recording film have a two-layer structure as described above, a disk having a general recording film having a single-layer structure (hereinafter referred to as a single-layer film disk) and a disk according to this embodiment are used. A disc having a recording film with a two-layer structure (hereinafter referred to as 2
The difference in the recording characteristics of the layer film disk) was compared. As the single-layer film disk, the one in which the recording film 4 shown in FIG. 1 was constituted only by the lower layer 4a was used. The recording film 4 has a film thickness of 200 angstroms for both the single-layer film disc and the double-layer film disc. For a dual-layer membrane disc, the lower layer is 100
A film thickness of 180 at a deposition rate of Angstrom / min
Sputter film formation to be Angstrom,
The upper layer was sputtered at a deposition rate of 10 Å / min to form a film having a thickness of 20 Å. Oxidation is performed by applying 0.2 Pa after forming the recording film on both disks.
Oxygen gas was introduced so as to maintain the degree of vacuum for 90 seconds.

FIG. 2 shows the results of measuring the magnetic field characteristics of the single-layer and double-layered discs produced by the above procedure. In the same figure, (a) and (c) show CNR with respect to an external magnetic field, (b) and (d) show the noise level under the action of a low external magnetic field (-200 to 200 [Oe]). As the measurement conditions, the linear velocity was 7.54 m / s, the recording frequency was 4.93 MHz, the duty was 25%, and the power of the laser beam used for recording was 7 mW. Regarding the magnitude of the external magnetic field at which CNR begins to appear, in the single-layer film disc, there is almost no difference between the case where no oxidation treatment is performed (H01) and the case where oxidation treatment is performed (H02), as shown in FIG. 2A. However, in the two-layer disc, the external magnetic field at which CNR begins to appear is closer to zero in the case of being oxidized (H02) as compared to the case of not being oxidized (H01) as shown in FIG. 2 (c). Has become. In addition, CN near zero external magnetic field
Regarding R, in the single-layer film disc, no change due to the oxidation treatment is observed, but in the double-layer film disc, the CNR becomes large due to the oxidation treatment. On the other hand, regarding the noise level under a low magnetic field, in the case of the single-layer film disk, the noise level in
Although a slight change is observed as shown in Fig. 2, the double-layer film disc is significantly reduced as shown in Fig. 2 (d), and the double-layer film disc is excellent in that noise in a low magnetic field is small. It can be seen that it has excellent recording characteristics.

Further, in the two-layer film disc, the structure and the procedure for producing more desirable recording characteristics were investigated. FIG. 3 is a characteristic diagram showing the relationship between the thickness of the upper layer of the recording film and the magnetic field characteristics. The magnitude of the external magnetic field at which CNR begins to appear when the thickness of the upper layer 4b shown in FIG. 1 is changed. It is a measurement of changes in H0 and noise level. The deposition rate when the recording film 4 was formed by sputtering was 100 angstrom / min for the lower layer 4a and 10 angstrom / min for the upper layer 4b. After forming the upper layer 4b, the surface of the recording film 4 was oxidized. . In the oxidation treatment, oxygen gas was introduced so that the vacuum degree of 0.2 Pa was maintained for 90 seconds after the recording film 4 was formed, as in the above. The measurement conditions for the magnetic field characteristics are the same as above. As shown in the figure, when the film thickness is set to 10 to 30 Å, the value of H0 becomes small and the noise level becomes low.

FIG. 4 is a characteristic diagram showing the relationship between the deposition rate of the lower layer of the recording film and the magnetic field characteristics. CNR begins to appear when the deposition rate of the lower layer 4a shown in FIG. 1 is changed. This is a measurement of changes in the magnetic field magnitude H0 and noise level. The thickness of the lower layer 4a is 180 Å /
The upper layer 4b has a deposition rate of 10 Å / min and a film thickness of 20 Å.
The oxidation treatment was performed by the same procedure as above. The measurement conditions for the magnetic field characteristics are the same as above. As shown in the figure, as the deposition rate of the lower layer 4a is increased, the value of H0 sharply decreases, and when the value is 100 angstrom / min or more, H0 becomes a desirable size. On the other hand, as for the noise level, contrary to the value of H0, the level gradually increases as the deposition rate increases, but the level is not high enough to adversely affect the recording characteristics of the disc. Also, since it is desirable to increase the deposition rate of the recording film to some extent in order to mass-produce the disc, the desirable value of the deposition rate of the lower layer is 100 angstroms /
It was set to min or more.

FIG. 5 illustrates the relationship between the deposition rate of the upper layer of the recording film and the magnetic field characteristics. Upper layer 4 shown in FIG.
It is a characteristic view which shows the magnitude | size H0 of the external magnetic field which CNR begins to appear, and the change of a noise level when the deposition rate of b is changed. The lower layer 4a is 120 angstrom / min
Was sputtered at a deposition rate of 180 .ANG. / Min. The film thickness of the upper layer 4b was 20 angstrom. The surface of the recording film 4 was oxidized by the same procedure as above. The measurement conditions of the magnetic field characteristics are the same as above. As shown in the figure, when the deposition rate of the upper layer 4b is 15 angstroms / min or less, the value of H0 is small, but when it exceeds 15 angstroms / min, the value of H0 rapidly increases. On the other hand, as for the noise level, below 15 Å / min,
It is a desirable low level, but as the deposition rate increases, the level increases, and it is 20 Å / min.
When it exceeds, it is getting higher rapidly. This gives a desirable value for the top layer deposition rate of 15 Å / mi.
It was set to n or less.

As shown in FIGS. 2 to 5, in order to enhance the effect of oxidizing the surface of the recording film and obtain desired recording characteristics, the following conditions are required in the structure and the production procedure. (1) The recording film has a two-layer structure, and the lower layer which is the first layer and the upper layer which is the second layer are formed under different conditions. (2) The film thickness of the upper layer is 10 to 30 Å. (3) The deposition rate of the lower layer is 100 Å / min or more. (4) The deposition rate of the upper layer is set to 15 Å / min or less.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned configuration, and various modifications can be made. For example, with respect to the structure of the recording film 4 shown in FIG. 1, in the above-described embodiment, the two-layer structure including the lower layer 4a and the upper layer 4b, which are different in film forming conditions, is used. If the side in contact with 3 and the side in contact with the upper dielectric layer 5 can each have a predetermined configuration, increase the number of layers according to the purpose and application of the magneto-optical recording medium to be manufactured, the manufacturing environment, etc. Good. In addition, the disc 1 shown in FIG. 1 includes a first dielectric layer 3, a recording film 4, and a second dielectric layer on a substrate 2.
The dielectric layer 5 and the reflective layer 6 are laminated in this order, but this is a structure based on a general example of a magneto-optical disk. 6, the second dielectric layer 5, the recording film 4, and the first dielectric layer 3 are laminated in this order. Further, although the magneto-optical disk having the reflective layer is taken as an example in the above-mentioned embodiment, the structure without the reflective layer may be adopted.

The present invention can be widely applied not only to the illustrated magneto-optical disk but also to other magneto-optical recording media, can be carried out extremely easily, and requires a large amount of manufacturing equipment conventionally used. You can utilize the part. Furthermore, it can be used in combination with other manufacturing methods for the purpose of improving the recording characteristics of the magneto-optical recording medium.

[0020]

As described above, according to the manufacturing method of the present invention, since the recording film has a predetermined laminated structure and the surface thereof is oxidized, the recording / erasing operation can be performed under the action of a small external magnetic field. It is possible to produce a recording medium having desirable characteristics for the system. Further, the present invention can be carried out very easily, and the procedure is simple, so that it is possible to respond to mass production, and it is possible to effectively utilize the manufacturing equipment and the like which has been conventionally used. On the other hand, when recording or erasing information using the magneto-optical recording medium manufactured by the manufacturing method of the present invention, it is not necessary to equip the device with a large magnetic head, and the size and weight of the device can be reduced. Moreover, since the required external magnetic field is small, the processing speed in magnetic field modulation can be increased.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a magneto-optical disk according to an embodiment of the present invention.

FIG. 2 is a diagram showing changes in magnetic field characteristics of a general single-layer film disk and a dual-layer film disk according to an example of the present invention when subjected to an oxidation treatment.

FIG. 3 is a characteristic diagram showing changes in CNR and noise level when the thickness of the upper layer is changed in the two-layer film disk according to the embodiment of the present invention.

FIG. 4 is a characteristic diagram showing changes in CNR and noise level when a deposition rate of a lower layer is changed in a two-layer film disk according to an example of the present invention.

FIG. 5 is a characteristic diagram showing changes in CNR and noise level when a deposition rate of an upper layer is changed in a two-layer film disk according to an example of the present invention.

FIG. 6 is a magnetic field sensitivity characteristic diagram of a general magneto-optical recording medium.

FIG. 7 is an explanatory diagram showing an external magnetic field and a demagnetizing field in the perpendicular magnetization film at the time of writing.

[Explanation of symbols]

 1 Magneto-Optical Disk 2 Substrate (Polycarbonate) 3 Lower Dielectric Layer (SiN) 4 Recording Film (TbFeCoCr) 4a Lower Recording Film Layer 4b Upper Recording Film Layer 5 Upper Dielectric Layer (SiN) 6 Reflective Layer (AlTi)

Claims (1)

[Claims] 1. A method of manufacturing a magneto-optical recording medium, comprising: a lower dielectric layer, a recording film made of a rare earth-transition metal amorphous alloy, and an upper dielectric layer, which are sequentially laminated on a substrate. 10 on the side in contact with the lower dielectric layer
The film is formed at a deposition rate of 0 angstrom / min or more,
Magneto-optical recording, characterized in that a film having a deposition rate of 15 Å / min or less and a thickness of 10 to 30 Å is formed on the side of the upper dielectric layer in contact with the surface of the recording film. Medium manufacturing method.