JPH04134651A - Magneto-optical recording medium and production thereof - Google Patents

Abstract

PURPOSE:To improve a bias characteristic and EWR durability and to lessen the fluctuation by sputtering a magnetic material from a magnetic material target and forming a recording layer on a transparent substrate while maintaining the residual amt. of residual oil at the prescribed value with respect to the partial pressure of a low-pressure inert gas. CONSTITUTION:At least three layers; a 1st dielectric protective layer, recording and 2nd dielectric protective layer are laminated in this order on the transparent substrate. The respective layers are made of the thin films formed by a sputtering method in the low-pressure inert gas. The recording layer is the thin film formed by sputtering from the magnetic material target while the residual amt. of the residual oil having >= 40 mass number in the low-pressure inert gaseous atmosphere is maintained at <= 100ppm with respect to the partial pressure of the above-mentioned low-pressure inert gas. The film formation in this case is executed under inert gaseous conditions of Ar, He, Ne, etc. of a low pressure ranging from 1x10<-3> to 20x10<-3> Torr. The repetitive (EWR) durability of erasing-recording-reproducing is improved in this way and the fluctuation in the characteristics including bias characteristics is prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magneto-optical recording medium, and in particular, a magneto-optical recording medium that has excellent bias magnetic field characteristics and excellent durability against repeated use of erasing and recording/reproduction. and its manufacturing method.

[Prior Art and its Problems] In recent years, magneto-optical recording media have been widely used for large-capacity data files, etc. as magneto-optical disks that can be written and read using laser beams.

This magneto-optical recording medium is made by depositing at least TbFe onto a transparent substrate such as glass or plastic by sputtering.
A magneto-optical recording layer is formed which has a recording layer mainly composed of transition metals such as Co, GdTbFeCo, and rare earth metals. Usually, an interference layer of 5iJnSin2 or SiA/! is formed between this recording layer and the transparent substrate. 1st of N etc.
A dielectric layer is provided, and a second dielectric layer is often provided on the recording layer to improve the characteristics of the protective layer as well. Moreover, on top of that, A
l, A/! Magneto-optical recording media having a magneto-optical recording layer with a three-layer or four-layer structure formed by laminating thin films of metal reflective layers such as -Ti and AP-Ta are widely used.

In addition, the recording layer may be a single layer of an alloy mainly composed of transition metals and rare earth metals, or a thin film mainly composed of transition metals and a thin film mainly composed of rare earth metals.
There is a magneto-optical recording medium having a magneto-optical recording layer of so-called alternately laminated films in which at least two or more layers are alternately laminated to a thickness of about 100 yen.

There is also a double-sided recording type bonded magneto-optical recording medium in which two media having a magneto-optical recording layer on one side of a transparent substrate are laminated together with the side with the magneto-optical recording layer facing inward.

Each layer constituting the magneto-optical recording layer is usually formed by a sputtering method in a low-pressure inert gas atmosphere such as argon, helium, or ion, using the constituent metal of each layer as a target. It is a thin film with a thickness of several hundred to several thousand.

When recording information on a magneto-optical recording medium, first, a bias magnetic field for erasing is applied to the medium and a laser beam is uniformly irradiated to heat the recording layer to its Curie temperature, erasing the recorded information that has already been written. After erasing, the recording layer is magnetized in a certain direction by applying a bias magnetic field from the outside, and then recording information is written using a laser beam while applying a bias magnetic field for writing.

The relationship between C/N and the bias magnetic field (Hb) is that C/N generally increases in proportion to the bias magnetic field, but C/N
A saturation bias magnetic field (Hbs) in which the change in Hbs is saturated exists as a characteristic unique to the medium. Reducing this saturation bias magnetic field means that the bias magnetic field necessary for erasing and writing can be reduced, and at the same time, even if the same bias magnetic field is applied, the medium has a small saturation bias magnetic field. Using it is more advantageous in improving C/N.

The bias magnetic field (Hb) required during erasing and writing
Reducing the bias magnetic field application magnet can be made smaller, which is also advantageous for downsizing the drive.

In addition, recently, the usage patterns of magneto-optical recording media have been diversifying, and there is a strong demand for override recording, but reducing the required bias magnetic field (Hb) is important in reducing the size of the device and shortening the access time. It is predicted that this will become an essential requirement.

However, despite the above-mentioned requirements for the bias magnetic field, it is difficult to obtain a magneto-optical recording medium in which the bias magnetic field necessary for erasing and recording is stable, There was variation within the range.

In practice, it is desirable to stably obtain a bias magnetic field of about 100 to 7000 e, preferably about 200 to 3000 e, but in reality, conventional manufacturing methods have large variations in the bias magnetic field, and it is difficult to obtain a bias magnetic field with excellent bias characteristics. It was difficult to obtain magnetic recording media stably.

For example, when using a transition metal rare earth metal as a recording layer, as a method to control bias characteristics, changing the composition ratio or adding other metals is known as MAG-87-177.
, J. Appl, Phys., 61 (7) (1987
), J, Appl, Phys, 26 (2) (1
987), J. Appl, Phys., 61 (8
) (1987), etc., but the variation was wide and varied considerably between 100 and 7000e.

In addition to the above-mentioned bias characteristics, an important practical characteristic required of a magneto-optical recording medium is repeated erasing-recording-return durability (hereinafter referred to as EWR durability).

In other words, it is desired that the characteristics of the magneto-optical recording medium do not deteriorate even after repeated use tens of thousands of times. In reality, erasing and recording are performed on the same part of the magneto-optical recording layer of the medium.
It is evaluated by the degree of decrease in C/N when reproduction is repeated, and for boat fishing, it is desired that the decrease in C/N is within 4 dB after 100,000 repetitions.

In order to improve this EWR durability, for example, in the case of the above-mentioned magneto-optical recording layer of alternately laminated films, reducing the lamination period has been effective to some extent.

However, even that method was not sufficient, and often after running 100,000 times, the C/N deteriorated by 4 dB or more.

Furthermore, in order to improve the EWR durability, it is possible to increase the thickness of the uppermost metal reflective layer in the magneto-optical recording layer of the four-layer structure, but this is not preferred because it causes a decrease in sensitivity.

Furthermore, when a rare earth metal-transition metal alloy is used as the recording layer, a method has been proposed in which the content of Tb in the rare earth metal is increased, but this is problematic because it involves deterioration of the C/N ratio.

Furthermore, in terms of EWR durability, as in the case of the bias magnetic field described above, there were considerable variations in characteristics even though they were actually made with the same composition.

[Problems to be Solved by the Invention] The present invention has been made in view of the problems of the prior art, and aims to provide a magneto-optical recording medium with excellent bias characteristics and EWR durability. Another object of the present invention is to provide a method for manufacturing a magneto-optical recording medium with less variation in bias characteristics and EWR durability.

[Means for Solving the Problems] As a result of intensive studies, the inventors focused on the film forming conditions when forming a magneto-optical recording layer on a transparent substrate by the spunter method.
The inventors have found that the amount of residual gas in the sputtering chamber when sputtering a magnetic material by applying electric power to a magnetic target is important in achieving the object of the present invention, and has thus arrived at the present invention.

That is, the object of the present invention is to remove the magnetic material from the magnetic target while maintaining the residual amount of residual oil having a mass number of 40 or more in the low-pressure inert gas atmosphere to 100 ppm or less with respect to the partial pressure of the low-pressure inert gas. A method for manufacturing a magneto-optical recording medium in which a recording layer is formed by sputtering on a transparent substrate, and at least three layers, a first dielectric protective layer, a recording layer, and a second dielectric protective layer are laminated in this order on the transparent substrate. In a magneto-optical recording medium having a magneto-optical recording layer, each layer is a thin film formed by sputtering in a low-pressure inert gas atmosphere, and the recording layer has a mass number of 40 in a low-pressure inert gas atmosphere. This is achieved by a magneto-optical recording medium characterized in that it is a thin film formed by sputtering from a magnetic target material while maintaining the residual amount of residual oil at 1100 pp or less with respect to the partial pressure of the low-pressure inert gas. be done.

The magneto-optical recording layer of the magneto-optical recording medium of the present invention is formed by a sputtering method. During film formation, low-pressure inert gas is introduced into the sputtering chamber. As the inert gas, A
, He, Kr, Ne, etc. can be used, but among them Ar
is the most desirable in terms of cost and film formation speed.

The magneto-optical recording layer of the magneto-optical recording medium of the present invention is formed by a sputtering method. Usually, the film is formed using Ar, He, Ne at low pressure of 1X10-' to 20X10-ffTorr.
However, various gases other than the inert gas remain in the vacuum layer. For example, nitrogen, water, hydrogen, oxygen, and others remain in the form of atomic groups such as CHlOH.

When forming a recording layer by sputtering by applying a predetermined power to a magnetic target, reducing the amount of oil remaining in the inert gas improves the bias characteristics and EWR durability of the magneto-optical recording medium. It is important to obtain it stably in good condition, and in particular, the effect will be further enhanced by reducing the residual amount of relatively large molecules or atomic groups with a mass number of 40 or more in the residual oil to a specific amount or less. .

Further, the effect of the present invention is particularly great in the case of a magneto-optical recording medium having a four-layer magneto-optical recording layer with a metal reflective layer as the uppermost layer.

Therefore, when forming the recording layer of the magneto-optical recording medium of the present invention, the amount of residual oil with a mass number of 40 or more in the low-pressure inert gas atmosphere must be set to 11% relative to the partial pressure of the low-pressure inert gas.
In order to achieve the present invention, it is necessary to sputter a magnetic material from a magnetic material target onto a transparent substrate while maintaining the temperature below 00I)P.

The oil is a molecule or atomic group that is mainly composed of carbon atoms and hydrogen atoms and may also contain oxygen, sulfur, nitrogen, etc., and is usually used in vacuum evacuation equipment such as rotary pumps and diffusion pumps. There are various sources of occurrence, such as components or their decomposition products flowing back, and oil mixed in due to contamination in the vacuum chamber or in each piping.

Among the remaining oils, reducing the remaining amount of oil whose size is above a certain value and whose mass number is 40 or above to a certain amount or less affects the film quality of the recording layer to be formed, and affects EWR durability and bias characteristics. Improve the dispersion of its characteristics, including

It is not clear whether the size and amount of residual oil in the atmosphere when the recording layer is formed by sputtering is effective in improving the characteristics of the magneto-optical recording medium, but when the recording layer is grown by sputtering, It is presumed that the residual oil component hinders the progress of surface diffusion of the film and greatly influences the film quality of the formed recording layer.

The residual amount of the oil component having a mass number of 40 or more in the low-pressure gas atmosphere during recording layer film formation is 1% relative to the inert gas.
It is 100 ppm or less, preferably 50 ppm or less, and more preferably 20 ppm or less. Oil component mass number 40
The above thing actually has a mass number of 43.57.73.7B
, 91.105.135 in many cases 6 In the magneto-optical recording medium of the present invention and its manufacturing method, the amount of residual oil having a mass number of 40 or more when forming the recording layer is replaced with a low-pressure inert gas. On the other hand, there are various methods for controlling the amount to 1100 pp or less. For example, there is a method for sufficiently exhausting the vacuum chamber and the substrate, a method for degassing the substrate by heat treatment at a temperature that does not cause thermal deformation in the case of exhaust treatment for the substrate, and a method for heating the substrate in the vacuum chamber. There is a way to do it. In the case of a sputtering chamber, it is sufficient to sufficiently exhaust the air, but as in the case of the substrate, it is effective to perform heat treatment from the outside or from the inside. In this way, the sputtering chamber and the substrate are sufficiently degassed, and while the recording layer is being formed by sputtering, the capacity of the exhaust equipment such as the diffusion pump, cryopump, or turbo pump that performs operational exhaustion is limited. The remaining oil amount can be reduced to U8 by operating the orifice control device. In the case of a diffusion pump, even if a liquid nitrogen trap is used, it is difficult to reduce the remaining amount of oil to the above specified amount or less, so it is desirable to use another method to deal with this problem.

It goes without saying that there are other methods of adjusting the residual oil concentration, and the above method is one example thereof.

In the present invention, by keeping the remaining amount of oil within the above range during the formation of the recording layer, the bias magnetic field required during erasing and recording can be reduced to 7000 e or less, and the variation thereof can be significantly reduced. .

That is, in the conventional method that does not limit the residual amount of the oil component, there was a variation of 100 to 7000 e, but with the method of the present invention, by keeping the residual amount small, it was possible to reduce the amount to about 100 to 3000 e.

Furthermore, EWR durability is considerably improved.

In the magneto-optical recording medium and its manufacturing method of the present invention, the composition of the recording layer includes an alloy of a transition metal and a rare earth metal. Examples of the transition metal include Fe,
Co, Ni, etc., as the rare earth metals, Tb, Gd, etc.
, Dy, Sm, Nd, etc. can be used. Specific examples of the composition of the recording layer include GdCo, Gd
Fe.

TbFe, DyFe, CdFeTb, TbFeC.

DyFeCo, TbFeNi, GdFeC.

Examples include NdDyFeCo. Among them, TbFeC
o is the most preferable because it has a large manufacturing tolerance, and furthermore, a composition containing 0.5 to 10 at%, preferably 3 to 8 at% of Cr, Ti, TaNd, Pt, etc. is preferred for practical use. It is preferable because it has sufficient corrosion resistance. Further, a PL-Co alloy is also preferable as a composition of the recording layer.

The thickness of the recording layer is preferably 200 to 300 layers when the magneto-optical recording layer has a four-layer structure, and 500 to 2,000 layers when the magneto-optical recording layer has a three-layer structure.

If the film thickness of the recording layer is too small, the sensitivity will decrease in the case of a four-layer structure.
A desired C/N ratio cannot be obtained from the viewpoint of reflectance, and the three-layer structure is unfavorable from the viewpoint of sensitivity and C/N ratio.

A first dielectric protective layer usually made of a dielectric thin film is provided between the transparent substrate and the recording layer of the magneto-optical recording layer of the magneto-optical recording medium of the present invention.

Furthermore, a thin film of a metal reflective layer is formed on the top layer of the magneto-optical recording layer in order to improve the recording and reproducing characteristics.

When the magneto-optical recording layer has a three-layer structure, a laminated film is formed by sequentially depositing a first dielectric protective layer, a recording layer, and the metal reflective layer on the transparent substrate by a sputtering method using this source. . When the magneto-optical recording layer has a four-layer structure, a second dielectric protective layer is provided between the recording layer and the metal reflective layer.

The first dielectric protection layer is a dielectric layer formed on the transparent substrate to a thickness of 800 to 1300 nm.

As the material of the first dielectric protective layer, for example, SiO
x, SiNx, TaOx, AlNx.

SiA/l! and dielectrics such as oxides such as ZnS, nitrides, and sulfides. Among these, Si nitride, Af nitride, a mixture thereof, 5iAf, etc. are preferable from the viewpoint of optical properties and protective function.

Like the first dielectric protection layer, the second dielectric protection layer is usually a dielectric thin film. The film thickness is preferably 200 to 500 people.

As the material of the metal reflective layer, various metals and alloys can be used. For example, Af Al-C
u, Al-Ti, Al-TaNi Ni-Cu A
u Cu Cu-Zn.

Metals such as Al-Cr and PL are sputtered,
A thin film deposited on the second dielectric protective layer can be used. Among these, single Al or an alloy of Al is suitable for achieving the object of the present invention.

The thickness of the metal reflective layer of the magneto-optical recording medium of the present invention is 30
0 to 1000 people, more preferably 400 to 800 people.

If the thickness of the metal reflective layer is less than 300 mm, light will easily pass through and the C/N will decrease.

If it is 1000 Å or more, the heat capacity increases, resulting in a decrease in sensitivity, which is not preferable.

Note that the effects of the present invention can be further enhanced by reducing residual hydrogen gas and nitrogen gas in the sputtering chamber when forming the metal reflective layer.

It is desirable that the transparent substrate of the magneto-optical recording medium of the present invention have low mechanical properties, particularly surface runout acceleration and surface runout, so that recording and erasing can be performed effectively even during high speed rotation.

As the material of the transparent substrate, polycarbonate, polymethyl methacrylate, epoxy resin, glass, etc. are used. Among these, resin substrates such as polycarbonate, polymethyl methacrylate, and epoxy resin are preferred in terms of cost, and polycarbonate is particularly preferred because it has advantages such as relatively low water absorption (and high glass transition temperature).

In the magneto-optical recording medium of the present invention, a magneto-optical recording layer is formed by forming each layer on a substrate as described above, and the top and side surfaces of the layer are further coated with an organic resin protective layer such as an ultraviolet curing resin. Furthermore, the storage stability of the magneto-optical recording medium can be further improved by providing a layer of ultraviolet curing resin or the like on the opposite side of the substrate to the side on which the recording layer is provided.

In addition, by laminating the magneto-optical recording layer of the substrate with the inner surface facing outward through an adhesive layer made of hot melt adhesive or epoxy adhesive, we have developed a double-sided recording type magneto-optical recording layer with excellent mechanical properties. It can also be used as a recording medium.

The novel features of the present invention will be specifically explained by the following Examples and Comparative Examples.

(Example) A diameter of 130 mm and a thickness of 1.6 μm with guide grooves at a pitch of 1.6 μm.
A 211n polycarbonate substrate was set on a rotating substrate holder of a sputtering apparatus, argon gas was introduced into the sputtering chamber, and the gas pressure was adjusted to within a range of 1 to 5 mTorr.

Then, a thin film of SiNx having a thickness of 1,100 mm was first formed as a first dielectric protective layer using the Mag7 Trons-Basota method.

Claims (4)

[Claims] (1) The residual amount of residual oil with a mass number of 40 or more in a low-pressure inert gas atmosphere is 10% relative to the partial pressure of the low-pressure inert gas.
A method for manufacturing a magneto-optical recording medium, which forms a recording layer by sputtering a magnetic material from a magnetic material target onto a transparent substrate while maintaining the magnetic material at 0 ppm or less. (2) In a magneto-optical recording medium having a magneto-optical recording layer in which at least three layers, a first dielectric protective layer, a recording layer, and a second dielectric protective layer are laminated in this order on a transparent substrate, each of the layers is The recording layer is a thin film formed by a sputtering method in a low-pressure inert gas atmosphere, and the recording layer has a residual amount of residual oil with a mass number of 40 or more in the low-pressure inert gas atmosphere relative to the partial pressure of the low-pressure inert gas. 1. A magneto-optical recording medium characterized in that it is a thin film formed by sputtering from a magnetic target while maintaining a concentration of 100 ppm or less. (3) The magneto-optical recording medium according to claim 2, wherein the recording layer is a thin film mainly composed of an amorphous alloy mainly composed of a transition metal and a rare earth metal. (4) The magneto-optical recording medium according to claim 2 or 3, wherein the uppermost layer of the magneto-optical recording layer has a metal reflective layer.