JPH04143945A - Magneto-optical recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a magneto-optical recording medium excellent in a bias characteristic and EWR durability without scarcely causing a variance by forming a recording layer by holding the residual quantity of moisture in an atmosphere in a state that it is small at the time of forming the recording layer by spattering. CONSTITUTION:The recording medium is constituted so that a magnetic material is spattered onto a transparent substrate from a magnetic material target, while holding the residual quantity of moisture in a low pressure inert gas atmosphere to <=10000ppm against this low pressure inert gas partial pressure. In this constitution, a first dielectric protective layer consisting of a thin film of a dielectric is provided between the transparent substrate of a magneto-optical recording layer of a magneto- optical recording medium and the recording layer. Also, the thin film of a metallic reflecting layer is formed on the uppermost layer of the recording layer in order to improve a recording/reproducing characteristic. In the case of a three-layer constitution, laminated films are formed on the transparent substrate in order of a first dielectric protective layer, the recording layer and the metallic reflecting layer, and in the case of a 4-layer constitution, a second dielectric protective layer is provided between the recording layer and the metallic reflecting layer.

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 which has excellent bias magnetic field characteristics and excellent durability against repeated use of erasing, recording and reproducing. The present invention relates to media and methods for producing the same.

[Prior art and its stable points]

In recent years, magneto-optical recording media have been widely used for large-capacity data files as magneto-optical disks that can be written and read using laser light.

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, 513N=, S i Ox or 5iA42 is used as an interference layer between this recording layer and the transparent substrate.
A first dielectric layer made of N or the like is provided, and a second dielectric layer is often provided on the recording layer to improve the characteristics of the protective layer as well. Furthermore, in order to increase the C/N, Ai! , AN-Ti, Aj2-Ta, and the like are widely used. Magneto-optical recording media have magneto-optical recording layers with a three-layer or four-layer structure formed by laminating thin films of metal reflective layers such as , AN-Ti, and Aj2-Ta.

In addition, the recording layer may be a single layer of an alloy made of transition metals and rare earth metals, or a thin film mainly made of transition metals and a thin film made 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 bonded together with the side with the magneto-optical recording layer facing inward.

Each layer constituting the magneto-optical recording layer is usually formed by sputtering in a low-pressure inert gas atmosphere such as argon, helium, or neon, using the constituent metal of each layer as a target. It is a thin film with a thickness of 100 to several thousand people.

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. Then, a bias magnetic field is applied from the outside to magnetize the recording layer in a certain direction, and then recording information is written using a laser beam while applying a bias magnetic field for writing.

The relationship between the C/N and the bias magnetic field (Hb) is that, although the C/N is generally large in proportion to the bias magnetic field, the saturation bias magnetic field (Hbs) where the change in C/N is saturated is the characteristic of the medium surface. exist. 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, it is better to use a medium with a smaller saturation bias magnetic field. is advantageous in improving C/N.

The bias magnetic field (Hb) required during erasing and writing
Reducing the size allows the bias magnetic field applying magnet to be made smaller, which is also advantageous for downsizing the dryer.

In addition, recently, the usage patterns of magneto-optical recording media have been diversifying, and there is a strong demand for override recording.
It is expected that this will become an essential requirement for shortening access time.

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.

As a method of controlling bias characteristics, when a transition metal and rare earth metal is used as a recording layer, methods of changing the composition ratio or adding other metals are known as MAG87-177, J, A.
ppl, Phys, 61(7) (1987), J.
Appl.

Phys, 26(2) (1987), J. Appl.
Phys, 61(8) (1987), etc., but the variation is large and varies considerably between Ioo and 7000e.

In addition to the above-mentioned bias characteristics, important practical characteristics required for magneto-optical recording media include erasing, recording, and
It has durability against repeated reproduction (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 C/N drop when reproduction is repeated, and it is desirable that the C/N drop is within 6 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 10,000 times, the C/N deterioration could reach 6 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 problems]

As a result of intensive study, the inventor focused on the film formation conditions when forming a magneto-optical recording layer on a transparent substrate by sputtering.
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 reduce the residual amount of moisture in the low-pressure inert gas atmosphere by 1 with respect to the partial pressure of the low-pressure inert gas.
A method for producing a magneto-optical recording medium in which a recording layer is formed by sputtering a magnetic material from a magnetic material target onto a transparent substrate while maintaining the magnetic material at 10,000 pp or less, and a first dielectric protective layer, a recording layer, and a second dielectric material on the transparent substrate. At least 3 layers of body protection
In a magneto-optical recording medium having a magneto-optical recording layer in which layers are laminated in this order, each layer is a thin film formed by a sputtering method in a low-pressure inert gas, and the recording layer is in a low-pressure inert gas. This is achieved by a magneto-optical recording medium characterized in that it is a thin film formed by sputtering from a magnetic target while maintaining the amount of residual moisture in the atmosphere at 110,000 pp or less with respect to the partial pressure of the low-pressure inert gas. Ru.

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, Ar
, He, Kr, 'Ne, etc. can be used, but among them A
r 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, film formation is carried out using Ar, He, N
This is done under inert gas conditions such as e.g., but 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 moisture remaining in the inert gas improves the bias characteristics and EWR durability of the magneto-optical recording medium. This is important in order to obtain it stably in good condition. 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 top layer.

Therefore, when forming the recording layer of the magneto-optical recording medium of the present invention, it is necessary to maintain the residual amount of moisture in the low-pressure inert gas atmosphere at 1% by weight or less with respect to the partial pressure of the low-pressure inert gas, and to Sputtering a magnetic material from a target onto a transparent substrate is necessary to achieve the present invention.

The sources of the moisture are various, such as those contained in the inert gas, those remaining in the vacuum chamber, those mixed in from various piping, and those contained in the substrate.

It is not clear how the residual amount in the atmosphere during the deposition of the recording layer by sputtering affects the improvement of the characteristics of the magneto-optical recording medium, but when the recording layer is grown by sputtering, the residual amount It is presumed that water impedes the progress of surface diffusion of the film and greatly affects the film quality of the deposited recording layer.

The residual amount of moisture in the low-pressure gas atmosphere at the time of forming the recording layer is 1000 ppm or less, preferably 1000 ppm or less, more preferably 110 ppm or less, relative to the inert gas.
It is 0 pp or less.

In the magneto-optical recording medium and its manufacturing method of the present invention, there are various methods for controlling the amount of residual moisture when forming the recording layer to 110,000 pp or less with respect to the low-pressure inert gas.

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 residual amount of water can be adjusted by operating the capacity of an evacuation device such as a diffusion pump, cryopump, or turbo pump that performs differential evacuation and an orifice control device.

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

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

In other words, in the conventional method that does not limit the residual amount of water components, there was a variation of 100 to 7,000 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 3,000 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, Nj, 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, GdFeTb, TbFeCo,
DyFeCo5TbFeNi, GdFeCo, NdDF
Examples include FeCo. Among them, TbFeCo is most preferable because it has a large manufacturing tolerance, and furthermore, Cr, Ti, Ta, Nb, pt, etc. are contained in the composition from 0.5 to 10A.
A composition containing t%, preferably 3 to 8 at%, is preferable in terms of practically sufficient corrosion resistance.

Furthermore, a ptCo-based alloy is also preferable as a composition of the recording layer.3 When the magneto-optical recording layer has a four-layer structure, the film thickness of the recording layer is desirably 200 to 300 mm, and the magneto-optical recording layer has a 3N structure. In this case, 500 to 2000 people is desirable.

If the thickness of the recording layer is too small, a desirable C/N cannot be obtained in terms of sensitivity and reflectance in the case of a four-layer structure, and it is not preferable in terms of sensitivity and C/H in the case of a three-layer structure.

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 a transparent substrate by sputtering in this order. . 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, SiOx
, 5jNx, Ta0x=A1. Nx, 5iA2 and Z
Dielectrics such as oxides such as nS, nitrides and sulfides are used. Among them, optical properties, preservation II! From the Noh aspect, S.
i nitride, Al nitride or mixture thereof, 5
iAffi etc. are preferred.

The second dielectric protective layer is usually a dielectric thin film, like the first dielectric protective layer. 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, Al2. Al2-
Cu,, A'i! -Ti%A1. -Ta.

Ni, Ni-Cu, Au, Cu5Cu-Zn, AQ-C
A thin film formed by sputtering a metal such as r, PL, etc. on the second dielectric protective layer can be used. Among them, single Al or an alloy of Al achieves the object of the present invention-1
It is suitable for

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.

The transparent substrate of the magneto-optical recording medium of the present invention preferably has mechanical properties, particularly low surface runout acceleration and low 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 since 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 bonding 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) 1. Diameter 130cm, thickness 1 with guide grooves at 6μm pitch
．． A two-piece polycarbonate substrate was set on a rotating substrate holder of a sputtering device, and argon gas was introduced into the sputtering chamber, and the gas pressure was adjusted to within a range of 1 to 5 sTorr.

Then, a thin film of SiNx having a thickness of 1,100 wafers was formed as a first dielectric protective layer using a mag-two-tron sputtering method.

Next, the amount of residual moisture in the sputtering chamber was changed using a residual gas measuring device attached to the sputtering chamber by adjusting the exhaust capacity of the cryopump by adjusting the pump capacity and the opening degree of the orifice.

And under each condition, FeCoCr alloy target and T
By applying electric power to the target of b, T b +++F e is formed on the first dielectric protective layer by dual simultaneous sputtering.
A recording layer having a composition of b*c OllCr h was formed to a thickness of 250 nm.

After that, a second dielectric protective layer is formed on the recording layer,
One film of Si nNx was deposited to a thickness of 450 people.

Next, a thin film of Al is formed as a metal reflective layer on the second dielectric protective layer to a thickness of 500 mm, and the first dielectric protective layer, the recording layer, and the second dielectric layer are formed on the substrate. One hundred samples of magneto-optical recording media having a four-layer magneto-optical recording layer consisting of a protective layer and a metal reflective layer were prepared under each condition.

The control width of the residual amount of moisture relative to argon during film formation of the recording layer was varied as shown in Table 1, with partial pressure concentration expressed in ppm.

The residual amount of gas was measured by attaching a differential pump to a four-electrode mass spectrometer. In this method, the inside of the analysis tube is evacuated to generate ions, the mass of the ions is separated through the quadrupole electrode, and the ions are amplified and detected using a secondary electron multiplier. The pressure reduction ratio of the working exhaust at this time is I x 10-'Tor
It was made to be r.

While monitoring the argon gas used in sputtering film formation with a Baratron vacuum gauge, the emission voltage was determined so that the value would be the value reduced by I X I O-'' Torr on the display. Calculation of the measured value. For the analysis, the analysis chamber was sufficiently evacuated until the partial pressure of each residual gas component was below 5X10-"τorr, By devising the structure of the device, I x 10-'
Considerations were taken to make it possible to detect trace amounts of gas down to Torr levels.

The bias magnetic field characteristics and EWR durability of the sample of the magneto-optical recording medium obtained as described above were evaluated by the following method.

Evaluation of EWR durability: Recording and reproduction were performed using a drive equipped with a pickup with NA=0.55 and a semiconductor laser with a wavelength of 830 nm at a rotation speed of 2400 rpm and tracking pink-up while applying servo. The board has 1.
A 6 μm pitch was formed in advance, and recording and reproduction were performed by following the pickup while applying a servo. The recording conditions include erasing with a laser power of 8 - and an applied magnetic field of 3000 e, and erasing with a laser power of 5.51 and an applied magnetic field of 300 e.
The edge frequency was 4.93 MHz under the condition of an applied magnetic field of 0e.

A focus of 0.75 μm was recorded. The C/N was then read using a spectrum analyzer with a laser power of 1.5-. This erasing-recording-reproducing cycle was repeated 100,000 times at the same track position, and the degree of deterioration was evaluated by determining the difference between the 100,000th C/N and the initial C/N.

The results obtained are shown in Table 1.

Table 1 (Comparative Example) In the above example, by adjusting the exhaust capacity of the cryopump, the pump capacity, and the orifice opening degree, the residual water gas concentration during recording layer deposition was varied from E to G as shown in Table 2. Samples of 100 magneto-optical recording media were prepared under each condition under the same conditions as in the example except that the conditions were changed to the three types described above.

Table 2 [Effects of the Invention] When forming a magneto-optical recording layer on a transparent substrate by sputtering, the amount of residual moisture in the low-pressure gas atmosphere when forming the recording layer is 110,000 pp or less relative to the low-pressure gas. By making the amount smaller than a specific amount, it is possible to improve the bias characteristics and EWR durability of the resulting magneto-optical recording medium.

Claims (4)

[Claims] (1) A recording layer is formed by sputtering a magnetic material from a magnetic target onto a transparent substrate while maintaining the residual amount of moisture in a low-pressure inert gas atmosphere at 10,000 ppm or less with respect to the partial pressure of the low-pressure inert gas. A method for manufacturing a magneto-optical recording medium. (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 sputtering in a low-pressure inert gas atmosphere, and the recording layer maintains the amount of residual moisture in the low-pressure inert gas atmosphere at 10,000 ppm or less with respect 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. (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.