JP2559432B2 - Magneto-optical disk - Google Patents

Description

The present invention relates to a magneto-optical recording for recording / reproducing / erasing by using a laser beam, and in particular, it has high corrosion resistance of a magneto-optical recording material and thus high reliability. It relates to a magneto-optical disc suitable for obtaining.

[Conventional technology]

With the progress of the advanced information society in recent years, there is a growing need for high density and large capacity file memory. Among them, optical recording is attracting attention as a file memory that meets this need, and research and development have been activated in various places. Among various types of optical recording, magneto-optical recording is at the stage of practical use. The recording material used in this memory is an amorphous alloy composed of a rare earth-iron group element. This alloy is active towards water and oxygen in the atmosphere and reacts easily to form oxides and hydroxides. This reaction proceeds from the film interface to the inside of the film with the passage of time. Therefore, the performance of the magneto-optical disk is deteriorated, and the reliability is deteriorated. As measures for preventing this, for example, JP-A-61-188760 and JP-A-58-60444 show examples of providing a protective layer.

[Problems to be solved by the invention]

In the above prior art, since the light transmittance is small when the protective layer is provided on the information reading side, the laser light is absorbed by the protective layer, and the Kerr rotation angle is apparently reduced to lower the carrier level, and thus the carrier-to-noise ratio (C / N) was lowered. As a result, the thickness of the protective film used is limited.

An object of the present invention is to provide a magneto-optical disk having a thin film of a metal compound which has sufficient protective properties and is optically transparent.

[Means for solving problems]

The above object is achieved by providing a mixed layer of nitrogen and oxygen in both or either of the information recording layers.

[Action]

In the mixed layer, most of oxygen reacts with rare earth elements,
Nitrogen exists partly as a nitride. Since the diffusion coefficient of water and oxygen in this film is extremely small, it is effective as a film for protecting the recording film. In addition, the film made with a gas containing both oxygen and nitrogen is optically transparent,
Kerr The rotation angle does not decrease. Furthermore, the refractive index can be controlled by selecting the manufacturing conditions.
It can also be used as a Kerr enhance film.

〔Example〕

 Hereinafter, details of the present invention will be described using Examples 1 and 2.

Example 1 FIG. 1 shows a schematic diagram of a cross-sectional structure of a magneto-optical disk manufactured by using the present invention. The magneto-optical disk was manufactured by the following procedure. First, an information recording film (2-4) was formed on a plastic or glass substrate (1) having concave and convex grooves on the surface by a sputtering method. This film is composed of three parts of an information read side protective layer (2), an information recording layer (3), and a protective layer (4), of which (2)
The protective layers of (4) and (4) correspond to the mixed layer. The same target is used for the three parts, and the discharge gas is controlled and formed as described later. The target has (Tb _0.7 Nd _0.3 )
An alloy having a composition of _0.24 (Fe _0.8 Co _0.2 ) _0.71 Nb _0.05 was used. The discharge gas was controlled by the profile shown in FIG. In the initial stage of sputtering, the protective layer (2) on the information read side is formed by the mixed gas of Ar / O ₂ / N ₂ = 50/10/40 (Vol% / Vol% / Vol%) by the schedule shown in 5-7. ,
After 2 minutes, the O ₂ and N ₂ valves were closed, and pure Ar was used for 3′30 ″ sputtering to form the information recording layer (3).
A protective layer (4) was prepared by 4'30 ″ spattering with Ar / N ₂ = 60/40. Here, the gas was controlled by a pure O ₂ cylinder, a pure N ₂ cylinder and a pure Ar cylinder with a mass flow controller. After passing, it is introduced into the spatula chamber through a mixer, where
The protective layer (2) on the information read side has a thickness of 200Å, the information recording layer (3) has a thickness of 800Å, and the protective layer (4) has a thickness of 500Å, but the boundaries of each layer are clear from the analysis by the AES method. Nakatsuta. The protective layer (2) on the information reading side has a refractive index of 2.
6, the transmittance is 70% for light having a wavelength between 400 nm and 900 nm spectroscopically, which is remarkably large. When recording or erasing on the information recording layer (3) formed on this, reproduction is of course required. Even if it does, the force-rotation angle is not lowered.
Rather, force with only information recording film-rotation angle: θ _k = 0.32
° greater than theta _{k =} 0.50 ° and the information reading-side protective layer (2) had the function of increasing the Kerr effect. However, since the thermal conductivity of this layer is high, the recording sensitivity may be lowered and the film thickness is naturally limited, but at a film thickness of about 200Å, there was no significant effect. Moreover, after immersing the sample in which only the information reading side protective layer (2) and the protective layer (4) were formed on the glass substrate in 1N-Naclaq for 3 hours, the change in the light transmittance and the result of the microscopic observation showed that pitting corrosion Occurrence of discoloration and discoloration of the film surface were not observed.

The C / N ratio of the magneto-optical disk formed on the glass substrate thus manufactured is 50 dB (f = 2 MHz, laser power 8 m when the information read side protective layer (2) is present.
W), but not present, is rather small at 46 dB, and the protective layer (2) is present and the C / N is increased by the amount by which the Kerr rotation angle is amplified. In addition, the C / N when oxygen is not contained in the formation of the protective layer (2) is 43d.
This is because it is as small as B and is optically opaque. The change with time of C / N and error rate was investigated when this disk was left in an accelerated environment (acceleration coefficient 300) of 60 ° C-96% RH. FIG. 3 shows the results. For comparison, that of a disk without protective layers (2) and (4) is shown. From this figure, when the present invention is used, there is no change in the C / N (8) and the error rate (8 ') after standing for 2500 hours. On the other hand, in the comparative example not using the present invention, the C / N begins to decrease gradually after 1500 hours as shown by the curve 9, and 25
It decreased by 4 dB after 00 hours. On the other hand, the error rate is
As shown by the curve 9 ', it started to increase after 1000 hours, and after 2500 hours, it increased by one digit to 10 ^-5 units. As described above, the present invention is effective in improving reliability because only corrosion resistance can be improved without frustratingly lowering various characteristics of the disk. The effect of improving the corrosion resistance is due to the use of a gas containing nitrogen as the discharge gas, and the diffusion coefficient of oxygen in the metal film containing N is extremely small.
Figure 4 clearly shows that the Depth-profile of 0 by AES analysis. That is, as shown in the upper part of FIG. 4, oxygen is present up to the deep portion of the film when N is not contained (TbNdFeCoNb), whereas oxygen is present only near the surface in the film containing N (TbNdFeCoNbN). You can see it more clearly. On the other hand, the presence of oxygen in the discharge gas during the production of the information reading side protective layer (2) is to make the film transparent and prevent the force-rotation angle from decreasing.

On the other hand, the inclusion of this nitrogen and oxygen in the discharge gas and forming them as a spatter not only improves the corrosion resistance without lowering the magnetic properties, but also improves the adhesion between the substrate and the film. Also greatly contributes. For example, when a disk on which a magneto-optical recording film is directly formed on a polycarbonate (PC) substrate is left in 60 ° C.-95% RH, film peeling occurs on the entire surface of the disk after 50 hours. The magneto-optical disk produced by the sputtering with the contained Ar gas did not cause film peeling even if left in this environment for more than 2500 hours. However, the C / N was not different from the case of using a glass substrate. As described above, the present invention is also effective in improving the adhesion between the film and the substrate.

In this embodiment, TbNdFeCoNb system is used as the magneto-optical material, but when Gd, Dy, Ho, Pr, etc. are used as the rare earth element, Ti, Ta, Pt, etc. are used in addition to Nb. The same effect was obtained even when there was a problem.

Example 2 In this example, an ion implantation method is used as a method of introducing N ₂ or O ₂ . The disk produced in this example is similar to that in Example 1 and is as shown in FIG. The disk was manufactured using an apparatus capable of simultaneously performing ion implantation and vapor deposition or sputtering as shown in FIG. It is possible to attach 10 disk substrates to the revolution type substrate holder shown in (10) at a time. Nitrogen and oxygen are supplied as a neutral ion beam from the bucket type ion source (11). In addition, the magnetic material is (Dy _0.8 Pr _0.2 ) _0.25
It is supplied by the magnetron sputtering method from an alloy target (12) having a composition of (Fe _0.8 Co _0.2 ) _0.70 Nb _0.05 .
The magneto-optical disk was manufactured by the following procedure. First, a plastic or glass substrate having concave and convex grooves on the surface is set in the holder (10) and rotated at 120 rpm.
And first, nitrogen and oxygen ion beams are used as the ion source (11).
At the same time as generating more, spatter also starts. After the beam and discharge have stabilized, open the shutter (13). In the simultaneous vapor deposition of the ion beam 13 and the sputter, the accelerating voltage of the beam and the RF power of the sputter are controlled so that ion mixing occurs on the substrate surface. Then, when the film thickness reaches about 150Å, the formation of the information reading side protective layer (2) is completed and the shutter (13) is closed. Then, the information recording layer (3) is formed with a film thickness of 800 Å only by RF sputtering. After that, the shutter (13) is opened again, and ion beam irradiation and spatula are continued until the thickness becomes about 500Å. The characteristics of the magneto-optical disk manufactured in this way are C / N = 52dB
(= 2.2MHz, laser PW = 8mW). It should be noted that intense ion mixing increases the noise level of the disk.

The magneto-optical disk formed on the glass substrate thus manufactured was allowed to stand in 60 ° C.-95% RH, and the changes with time in C / N and error rate were measured. The results are shown in Fig. 6. Here, as a comparative example, a magneto-optical disk produced without ion beam irradiation was used. as a result,
Regarding the change with time of C / N, when the present invention is used, as shown in (14), there is no change, whereas the disk produced without using the present invention has 15
From around 00 hours, it begins to gradually decrease, and 30
It decreased by 5 dB after 00 hours. The error rate is
In the case of using the present invention, as shown in (14 '), there was no change even after 3000 hours, whereas in the case of not using the present invention, it gradually increased after 1000 hours, and increased by one digit. As described above, by using the present invention, a magneto-optical disk having high corrosion resistance could be obtained by a simpler method than the conventional method.

The effect described above is that even if any rare earth element of Gd, Dy, Ho, and Rr is used in addition to Tb and Pr, Cr, Ta, Ti, and Al are used in addition to Nb.
Similar effects can be obtained by using such elements as.

〔The invention's effect〕

According to the present invention, the protective layer on the information reading side can be made optically transparent, so that the Kerr rotation angle is not lowered, and thus C /
It does not decrease N. Further, the metal film containing N and O has a high corrosion resistance against the corrosion of wet corrosion and pitting corrosion, and it is possible to obtain a magneto-optical disk having extremely high reliability as compared with the conventional method. This is because the diffusion coefficient of water and oxygen in the film is small. Further, since the disk having this structure can be manufactured by a simple device and method, it is economically advantageous. Further, the film containing N and O is not only transparent, but also has the effect of amplifying the Kerr effect by multiple interference.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the cross-sectional structure of the magneto-optical disk of the present invention, FIG. 2 is a block diagram showing the change in the composition of the discharge gas with the sputtering time, and FIGS. 3 and 6 show the magneto-optical disk. C / N when left in ℃ -95% RH,
And Fig. 4 is a graph showing the change in error rate with time.
FIG. 5 is a diagram showing a Depth-profile measured by AES of a magneto-optical disk after being left in 95% RH for 2500 hours, and FIG. 5 is a schematic view of a magneto-optical disk manufacturing apparatus. 1 ... Substrate, 2 ... Information reading side protective layer, 3 ... Information recording layer, 4 ... Protective layer, 10 ... Substrate holder, 11 ... Ion source, 12 ... Source source, 13 ... Shutter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Noriyuki Ogihara Inventor No. 1-88, Tora, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd. (56) Reference JP-A-60-145525 (JP, A)

Claims (2)

(57) [Claims] 1. A magneto-optical disk capable of recording / reproducing / erasing with a laser beam and having an information recording film formed of a magnetic material, wherein the magnetic material contains nitrogen on at least one surface of the information recording film. And a magneto-optical disk having a mixed layer containing oxygen. 2. The magnetic material contains at least one element selected from Tb, Gd, Dy, Ho, Pr and Nd, and Fe and Co
The optical disk according to claim 1, wherein the optical disk is an alloy mainly composed of.