JPH03113754A - Production of magneto-optical disk - Google Patents

Abstract

PURPOSE:To improve a recording sensitivity by specifying the sputtering film forming speed of a recording film. CONSTITUTION:The magneto-optical disk 5 is formed by successively forming a 1st protective film 2, the recording film 3 and a 2nd protective film 4 on a disk substrate 1. The sputtering forming speed of the film 3 of the magneto- optical disk constituted in such a manner is set as low as 0.1 to 6nm/min. The recording film having a high transmittance and low reflectivity is obtd. in this way. Oxidation progresses and the signal quality degrades if the sputtering speed is lower than 0.1nm/min. In addition, too much time is required for the film formation and such film formation is not adequate for mass production. Oxidation is inadequate and the light transmittance is high so that the reforming to the film having the low reflectivity is not possible under the conditions faster than 6nm/min.

Description

[Detailed Description of the Invention] [Summary] Regarding a magneto-optical disk, the purpose of the present invention is to put into practical use a magneto-optical disk with excellent recording sensitivity. In the magneto-optical disk which is formed sequentially with the second protective film, the sputtering deposition rate of the recording film is set to 0.1 to 6n.
m/min.

(Industrial application field) The present invention relates to a magneto-optical disk with excellent recording sensitivity.

In a magneto-optical disk, the recording medium is made of a perpendicularly magnetized magnetic film, and when a laser beam is irradiated while applying an external perpendicular magnetic field in the direction opposite to the magnetization direction, the temperature of the irradiated magnetic film increases, causing it to become magnetic. This is a memory that records and erases information by utilizing magnetization reversal as the coercive force of the film decreases.

Information is reproduced by utilizing the fact that when the magnetic film is irradiated with laser light, the plane of polarization of the reflected light rotates, and the direction of this rotation differs depending on the magnetization direction of the magnetic film.

As described above, the magneto-optical disk is characterized in that it is a memory (t!rasable memory) in which information can be written.

[Conventional technology]

Figure 2 shows the structure of a magneto-optical disk.A mold is formed using an ultraviolet curing resin such as acrylic ester on a disk-shaped glass substrate approximately 1.2 mm thick, and guide grooves are formed. A disk substrate 1 with a mark is formed.

Furthermore, the disk substrate 1 with guide grooves is also formed by direct resin casting without using a glass substrate.

On top of the disk substrate 1 is a substrate made of silicon dioxide (Si02), silicon nitride (SiJ<), etc., with a thickness of approximately 1000 mm.
A first protective film 2 is formed by sputtering or the like, and terbium-iron-cobalt (Tb-Fe-Co) is deposited on top of this.
A recording film 3 made of an amorphous alloy of rare earth metals such as rare earth metals and transition metals and having a thickness of approximately 1000 mm is similarly formed by sputtering or the like. A magneto-optical disk 5 is formed by forming a thick second protective film 4.

Information is recorded on the magneto-optical disk 5 by focusing laser light into a small spot with a diameter of 1 μm using a lens and scanning the recording film 3 along a guide groove.

Therefore, the area required to record one bit of information is only about 1 μm2.

Therefore, it takes several tens to hundreds of micrometers to record one bit of information.
Compared to a magnetic disk, which requires an area of 2,000 yen, the area is much smaller than that of a magnetic disk, and therefore, large-capacity recording is possible, and it is expected to be used as a file memory for information processing devices.

However, magneto-optical disks have a problem in that their data transfer speed is slower than that of magnetic disks.

That is, while the data transfer rate of a magnetic disk is about 3 Mbytes/sec, it is slower at 0.8 Mbytes/sec, and there is a desire to improve this speed.

In order to increase the data transfer speed, it is possible to increase the number of revolutions of the disk, but increasing the number of revolutions requires insufficient laser power, which makes it impossible to record sufficient signals.

In other words, unsaturated recording results.

To solve this problem, it is necessary to increase the sensitivity of the recording film.

Therefore, the following method is being considered as a means to improve the sensitivity of the recording film.

■ Decrease the thickness of the recording film.

(2) Increase the light absorption of the recording film by increasing the refractive index and lowering the reflectance of the first protective film.

However, if the thickness of the recording film (2) is made thinner, the amount of transmitted light increases, so it becomes necessary to provide a reflective film between it and the second protective film, but in this case, in addition to complicating the structure, Unless a material with low thermal conductivity is used, there is a problem in that heat will escape through the reflective film and sensitivity will not increase.

Furthermore, materials with a high refractive index such as Si3N4 are currently used as the first protective film in (2), and the reflectance of the disk is approximately 30%. %, the required laser power is (1-0,3)/(1-0,1) = 0.78,
It can only be reduced by about 22% compared to the conventional method, and no significant improvement can be expected.

No such effective method has been found.

[Problem to be solved by the invention]

As described above, various methods have been studied to increase the sensitivity of the recording film, but all of them are insufficient.

The challenge, then, is to find a way to improve sensitivity without adversely affecting others.

[Means to solve the problem]

The above-mentioned problem is to reduce the sputtering deposition rate of the recording film to 0.1 to 6 nm in a magneto-optical disk in which a first protective film, a recording film, and a second protective film are sequentially formed on an optical disc substrate provided with a guide groove. This can be solved by configuring the method for manufacturing a magneto-optical disk with the characteristic that the speed is 1/min.

[Function] The present invention realizes high sensitivity by changing the film quality of the recording film.

That is, the recording film is made of an amorphous alloy of rare earth metals and transition metals, specifically terbium-iron-cobalt (TbF).
eCo), gadolinium/iron/bismuth (GaFeBi)
) + gadolinium, iron (GaFe), etc., but in many cases Tb is used due to the large Kerr rotation angle.
A FeCo-based amorphous alloy is used.

Since deterioration of magneto-optical disks is caused by oxidation due to moisture absorption in the recording film, as shown in FIG. The provision of the film 4 prevents oxidation, and the composition of the protective film itself is devised to prevent oxidation of the recording film.

That is, by forming the first and second protective films 2 and 4 from a solid solution of 5iOz and terbium (Tb) instead of silicon dioxide (SiOz), even if moisture penetrates, Tb will be oxidized. This prevents the recording film 3 from being oxidized.

In this way, conventional methods have been used to prevent oxidation of the recording film, and to prepare the recording film using an amorphous alloy of rare earth metals and transition metals, specifically Tb.
Magneto-optical disks have been constructed primarily from FeCo, but in the present invention, the recording film is oxidized to the extent that signal quality does not deteriorate, resulting in high light transmittance and high reflectance. This modifies the film to have a low

However, when this oxidation is carried out by increasing the oxygen partial pressure, clear oxidation of the recording film occurs and quality deteriorates.

Therefore, the present invention realizes a recording film with high light transmittance and low reflectance by forming the film at an extremely low sputtering speed compared to the conventional method.

In other words, the conventional sputtering speed is 15 to 20 nm/min, but the sputtering gas pressure remains the same as before, and only the sputtering speed is slowed to 0.1 to 60 m/min. By forming a film, oxidation progresses slightly and modification is performed.

The reason why the sputtering speed is limited to 0.1 to 6 nm/min is that if it is slower than 0.1 nm/min, oxidation will progress and the signal quality will deteriorate, and it will take too much time to form the film, making it difficult to mass produce. This is because it is not suitable, and also because if the oxidation rate is faster than 5 nmZ, the oxidation will be insufficient and the film will not be modified into a film with high light transmittance and low reflectance.

Example C] Example 1 A disk substrate with guide grooves was made by molding an ultraviolet curable resin on a glass substrate, and a Tb-3iO□ film was formed to a thickness of 90 nm on this by high-frequency sputtering. This was used as the first protective film.

The sputtering conditions were as follows: argon (Ar) gas pressure was 0.2 Pa, and sputtering power was 0.8 KW.

Next, a TbFeCo film was formed to a thickness of 90 nm by high frequency sputtering in the same manner to form a recording film.

This sputtering condition is such that the Ar gas pressure is 1. OPa, and sputtering power is 0. The sputtering speed was 2 nm/min under these conditions.

Next, a Tb 5iOz film was formed thereon to a thickness of 90 nm to form a second protective film.

The formation conditions were the same as those for the first protective film, and a magneto-optical disk was formed in this manner.

Comparative Example 1: A magneto-optical disk was formed in exactly the same manner as in Example 1 except that the conditions for forming the recording film were different.

The conditions for forming the recording film are: Ar gas pressure is 1. OPa, sputtering power was IKW, and sputtering speed was 20 nm/min.

Table 1 shows TbFeCo according to Example 1 to which the present invention is applied.
The film quality of the film and the film quality of the conventional comparative example 1 are compared.

As can be seen from Table 1, by implementing the present invention, the transmittance is high;
It can be seen that a recording film with low reflectance and low density is formed.

Next, FIG. 1 shows the relationship between the writing power and the linear velocity at which the second harmonic is minimized for the magneto-optical disk of the example and the magneto-optical disk of the comparative example.

In Comparative Example 7 shown in the figure, the second harmonic power is 5.6 mW at a linear velocity of 9.6 m/sec (rotation speed is 180 Orpm and radius is 51 mm); When power is applied to Example 6, the linear velocity is 18 m7 seconds (
At 3370 rpm, the radius is 5 Lmm), and it can be seen that a speed increase of about 1.9 times can be achieved with the same second harmonic power.

〔Effect of the invention〕

As described above, by carrying out the present invention in which a magneto-optical disk is formed by forming a recording film at a slower sputtering speed than in the past, recording sensitivity is improved and high-speed rotation becomes possible.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between linear velocity and second harmonic power of a magneto-optical disk, and FIG. 2 is a sectional view showing the structure of the magneto-optical disk. In the figure, 2 is a first protective film, 3 is a recording film, and 4 is a second protective film.

Claims (1)

[Claims] In a magneto-optical disk in which a first protective film, a recording film, and a second protective film are sequentially formed on an optical disc substrate provided with a guide groove, the sputtering deposition rate of the recording film is set to 0.1 to 6.
1. A method for manufacturing a magneto-optical disk, characterized in that the speed is nm/min.