JPH0690814B2 - Magneto-optical disk manufacturing method - Google Patents

Description

DETAILED DESCRIPTION [Outline] A first protective film is formed on a transparent disk substrate 1 having a guide groove.
In a magneto-optical disk in which a film 2, a recording layer 3, and a second protective film 4 are sequentially formed, a film of nitride and a rare earth element is simultaneously formed on a transparent disk substrate 1, and a mixture of both is formed. After the first protective film 6 is formed, a stabilizing treatment of heating the substrate 1 is performed, and then the recording layer 3 and the second protective film 4 are formed to form a magneto-optical disk manufacturing method. Constitute.

[Industrial application field]

The present invention relates to a method for manufacturing a magneto-optical disk that suppresses the change over time.

A magneto-optical disk is a memory that records information at high density using laser light, has a large recording capacity like an optical disk, can record and reproduce in a non-contact manner, and is excellent in that it is not affected by dust. It is a memory with unique characteristics.

That is, the laser beam can be focused by a lens into a small spot having a diameter of 1 μm or less.
The area required to record information on bits is about 1 μm ² .

For this reason, the magnetic disk or magnetic tape requires much less area than several tens to several hundreds of μm ² for recording 1-bit information, so that large capacity recording is possible.

As described above, the magneto-optical disc and the optical disc using the laser light as the light source have excellent characteristics. However, by comparing the two, the optical disc uses a non-metal having a low melting point or an alloy with a metal as a recording medium to record information. Mainly read-only memory (Read Only Memory) that plays with and without holes (pits) is already in practical use.

On the other hand, a magneto-optical disk is a rewritable memory (Erasab
It was developed as a le memory), and the recording and erasing of information is performed when the temperature of the magnetic film rises due to laser irradiation.
The coercive force of the magnetic film is lowered, and the magnetization reversal is caused by the application of a slight external magnetic field.Information is read out by changing the rotation direction of the polarization plane depending on the magnetization direction of the magnetic film. It is done by using.

[Conventional technology]

As shown in the sectional structure of FIG. 3, the magneto-optical disk has a disk-shaped substrate 1 on which a first protective film 2 is provided, on which a recording layer 3 and a second protective film 4 are sequentially formed. It is configured.

Here, the substrate 1 is a polymethylmethacrylate (abbreviated as PMM) provided with a guide groove (pre-groove) for track following.
A), a polycarbonate resin (abbreviated as PC), polystyrene (abbreviated as PS), epoxy resin substrate, or a transparent resin substrate in which the flat resin substrate is coated with UV curable resin on a glass substrate to form guide grooves. On this, aluminum nitride (Al N) as the first protective film,
It is formed by coating a nitride film such as titanium nitride (Ti N) or silicon nitride (Si ₃ N ₄ ) to a thickness of about 1000Å.

Here, the necessary condition of the first protective film 2 is that, in the processing such as recording and reproducing of information, the laser light is applied to the recording layer 3 through the substrate 1, so that it is transparent and has little light absorption, and it is possible to prevent moisture and oxygen from being absorbed. It is made of a material that prevents permeation.

Next, as a constituent material of the recording layer 3, an amorphous alloy film composed of a rare earth-transition metal element is used for reasons such as ease of film formation and low noise.

Here, the rare earth elements are lanthanum (La), cerium (Ce), P
r (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (eurobium), gadolinium (Gd), terbium (Tb), dysprosium (D
y), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu) 17
A transition metal is an element that has an incomplete d-shell in the electronic configuration of an atom, or an element that produces a cation with an incomplete d-shell and has an atomic number of 21 (Sc) to 29 (Cu).
From 39 (Y) to 49 (Ag), from 57 (La) to 79 (A
elements up to u).

Both of these amorphous alloy films are used as a recording medium for a magneto-optical disk. The typical Kerr rotation angles for the first and second compositions are 0.35 ° for Gd Fe and 0.30 ° for Tb Fe. ,
It is 0.41 ° of Gd Fe Bi.

Next, the second protective film 4 is provided on the recording layer 3 for the same purpose as that of the first protective film 2. However, since it is not the surface irradiated with laser light, it has moisture resistance and acid resistance such as Al and Ti. A metal thin film having excellent chemical properties is used.

However, even with such a structure, the effect of suppressing the change over time is not sufficient.

A broken line 5 in FIG. 2 uses PMMA as the substrate 1, a Si ₃ N ₄ film having a thickness of about 1000 Å as the first protective film 2, and a Tb Fe Co layer having a thickness of about 1000 Å as the recording layer 3, The figure shows the change over time in coercive force when a magneto-optical disk formed by sputtering a Ti film having a thickness of about 1000Å as the second protective film 4 is left in the atmosphere at 60 °. After 80 hours, the holding power has increased about 3 times.

Here the vertical axis represents the initial value of the coercive force (H _CO) for coercive force (H
_C ) shows the rate of increase.

As described above, in the conventional magneto-optical disk, the protective layers are provided on the upper and lower sides of the recording layer 3, so that the recording layer is inevitably changed over time and needs to be improved in order to improve reliability. .

[Problems to be solved by the invention]

As described above, in the conventional magneto-optical disk, the first protective film and the second protective film are formed above and below the recording layer in order to prevent the recording layer from changing with time.
Although the above protective film is provided, it still does not sufficiently contribute to suppressing the deterioration of the recording layer.

Therefore, it is a subject to improve this to prevent deterioration of characteristics and ensure long-term stability.

[Means for solving problems]

The above-mentioned problem is, in a magneto-optical disk in which a first protective film, a recording layer, and a second protective film are layered on a transparent disk substrate having a guide groove, a first protective film for protecting the recording layer. Can be solved by adopting a structure of a mixture of a nitride and a rare earth element.

[Action]

The cause of the remarkable characteristic deterioration in the conventional magneto-optical disk as shown by the broken line 5 in FIG. 2 is oxygen and moisture diffused from the substrate or the first protective film 2 as is conventionally known. This is due to deterioration of the recording layer 3.

Here, the reason why nitrides such as Al N, Si ₃ N ₄ and Ti N, which have a sufficient track record as weather-resistant protective films in semiconductor devices and thin film hybrid devices, do not show sufficient effects, is that rare earths that constitute the recording layer 3 are used. This is because the element is a metal that is very easily oxidized.

Therefore, the present invention takes advantage of the fact that the rare earth element is easily oxidized, and by forming the first protective film with a mixture of a nitride and a rare earth element, the first protective film is combined with oxygen gas or moisture from the substrate to completely remove the element. It serves as a stopper.

FIG. 1 shows the principle of the present invention. The difference from the conventional FIG. 3 is that the first protective film 6 provided in contact with the substrate 1 is not a conventional nitride but a nitride and a rare earth element. The only difference is that it consists of a mixture of.

Here, some rare earth elements include colored elements, and the first protective film 6 made of a mixture of a nitride and a rare earth element seems to absorb a large amount of laser light, but rare earth elements in a mixed state are considerably large. Since it is nitrided, the first protective film 6 having a thickness of about 1000Å is transparent and has a small optical loss.

Especially, when the nitride and the rare earth element are formed by sputtering in a nitrogen atmosphere, the light loss is particularly small.

According to the present invention, the first protective film 6 thus formed on the substrate 1 is heated in the atmosphere to trap oxygen (O) and water remaining in the substrate 1 and stabilize crystallographically. By forming the recording layer 3 in the converted state, a magneto-optical disk with little change with time is manufactured.

〔Example〕

Set a PMMA disk substrate with a diameter of 8 inches in the sputtering system and place it on a Si ₃ N ₄ target with a diameter of 6 inches and a thickness of 5 mm.
Eight Tb chips having a 10 mm square and a thickness of 1 mm were arranged to form a composite target.

In this case, the ratio of Tb target to Si ₃ N ₄ target is 5 to 5.2%.

The N ₂ pressure was 1 × 10 ^-1 Pa, the RF power was 600 W, and the film deposition rate was 10
The first protective film having a thickness of 1000 Å was formed under the condition of Å / min.

Next, the substrate was heat-treated in the air at 60 ° C. for 10 hours to be stabilized.

Next, a Tb Fe Co layer is formed on the substrate in the same manner as the conventional method.
A magneto-optical disk was prepared by depositing 00Å and Ti as a second protective film to a thickness of 1000Å.

The solid line 6 in FIG. 2 shows the change over time in coercive force when the magneto-optical disk thus formed was left in the air at 60 ° C. No increase in coercive force was observed even after 1000 hours. .

When a nitride such as AlN or TiN was used as the target and another element was used as the rare earth element, the same effect was exhibited, and the deterioration of the recording layer could be suppressed.

〔The invention's effect〕

As described above, by carrying out the present invention, it becomes possible to suppress the oxidation due to the permeation of oxygen atoms and moisture from the substrate, and thus it becomes possible to secure the long-term stability of the magneto-optical disk.

[Brief description of drawings]

 FIG. 1 is a principle diagram of the present invention, FIG. 2 is a view showing a change with time of a magneto-optical disk, and FIG. 3 is a sectional view of a conventional magneto-optical disk substrate. In the figure, 1 is a substrate, 2 and 6 are first protective films, 3 is a recording layer, and 4 is a second protective film.

Front page continuation (72) Inventor Seiji Okada 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (56) References JP-A-62-219348 (JP, A) JP-A-59-129956 (JP, A) JP 61-22458 (JP, A)

Claims (1)

[Claims] 1. A transparent disk substrate (1) having a guide groove.
A magneto-optical disk having a first protective film (2), a recording layer (3), and a second protective film (4) sequentially formed thereon by a sputtering method, the transparent disk substrate (1) A film of nitride and a rare earth element is simultaneously formed on the upper surface to form a first protective film (6) made of a mixture of both, and then a stabilizing treatment of heating the substrate (1) is performed. A method for manufacturing a magneto-optical disk, which comprises forming a layer (3) and a second protective film (4).