JP2631022B2 - Method for manufacturing magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium, and more particularly to a method of manufacturing a magneto-optical recording medium having excellent bias magnetic field characteristics and excellent recording / reproducing use durability. Things.

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

This magneto-optical recording medium is made of Si ₃ N ₄ , SiO ₂ or Si on a transparent substrate such as glass or plastic by sputtering.
A first dielectric protection layer (also referred to as an enhancement layer) such as AlN, a recording layer mainly composed of a transition metal such as TbFeCo and GdTbFeCo, and a rare earth metal, and a recording layer mainly composed of Al, Al-Ti, and Al-Ta; A high C / N is obtained in a configuration having a magneto-optical recording layer having a three-layer configuration in which thin films of a metal reflective layer are stacked or a four-layer configuration in which a second dielectric protective layer is provided between the recording layer and the metal reflective layer. So widely used.

In addition, a single layer of an alloy mainly composed of a transition metal and a rare earth metal, or a thin film mainly composed of a transition metal and a thin film mainly composed of a rare earth metal are alternately formed in a thickness of several to several tens of at least two layers each. There is a magneto-optical recording medium having a magneto-optical recording layer of a so-called alternately laminated film.

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

Each of the layers constituting the magneto-optical recording layer is usually formed by sputtering using a constituent metal of each layer as a target under a low-pressure inert gas atmosphere, and has a thickness of several hundreds to several thousand degrees. It is a thin film.

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

Generally, the relationship between C / N and the bias magnetic field (Hb) is such that C / N increases in proportion to the bias magnetic field, but the saturation bias magnetic field (Hbs) at which the change in C / N saturates is a characteristic inherent to the medium. Exists. Reducing the saturation bias magnetic field means that the bias magnetic field required for erasing and writing can be reduced, and a medium having a small saturation bias magnetic field is used even when the same bias magnetic field is applied at the same time. This is advantageous for improving C / N.

The bias magnetic field (Hb) required for erasing and writing
Is smaller, it is possible to reduce the size of the bias magnetic field applying magnet, which is advantageous for miniaturization of the drive.

Recently, the use of magneto-optical recording media has become more frequent, and there is a strong demand for overwrite recording. In this case, reducing the required bias magnetic field (Hb) can reduce the size of the device and shorten the access time. It is expected that this will be an essential requirement.

However, despite the above requirements for the bias magnetic field, in practice, it is difficult to obtain a magneto-optical recording medium in which the bias magnetic field required for erasing and recording is stable, and 100 to 700 Oe is required. There was variation in the range. The bias magnetic field is practically 100 to 700 Oe, preferably 200 to 300 Oe.
It is hoped that Oe can be obtained stably,
In fact, the conventional manufacturing method has a large variation,
It has been difficult to stably obtain a magneto-optical recording medium having excellent bias characteristics.

As a method of controlling bias characteristics, for example, when a transition metal rare earth metal is used as a recording layer, a method of changing the composition ratio or adding another metal is described in MAG-87-177, J. App.
l.Phys.61 (7) (1987), J.Appl.Phys.26 (2) (198)
7), J. Appl. Phys. 61 (8) (1987), etc., but the dispersion was large and varied considerably between 100 and 700 Oe.

In addition to the above-mentioned bias characteristics, another important characteristic required for the magneto-optical recording medium is the repetition durability of erasure-recording-reproduction (EWR durability). That is, it is desired that the characteristics are not deteriorated even when the magneto-optical recording medium is repeatedly used tens of thousands of times. In practice, it is evaluated by the degree of decrease in C / N when erasure-recording-reproduction is repeatedly performed on the same part of the magneto-optical recording layer of the medium. It is desired that the decrease in / N be within 4 dB. In order to improve the EWR characteristics, for example, in the case of the magneto-optical recording layer of the above-mentioned alternately laminated film,
Reducing the stacking cycle also had some effect.

However, that method was not enough, and the C / N deterioration sometimes reached 4 dB or more after 100,000 runs.

Even in the case of the EWR characteristics, as in the case of the above-mentioned bias magnetic field, there was considerable variation in characteristics even though actually made of the same composition.

[Problems to be Solved by the Invention] The present invention has been made in view of the problems of the related art, and has as its object to provide a method of manufacturing a magneto-optical recording medium with less variation in bias characteristics and EWR characteristics. And

[Means for Solving the Problems] The inventors of the present invention have made intensive studies when forming a magneto-optical recording layer having a metal reflective layer on a transparent substrate, paying particular attention to the conditions for forming the thin film of the metal reflective layer. As a result of the superposition, the present inventors have found that the amount of the residual gas present in the sputtering chamber of the sputtering apparatus when forming the recording layer and the metal reflection layer is important for achieving the object of the present invention, leading to the present invention. .

That is, the object of the present invention is, after forming a recording layer on a transparent substrate by a sputtering method in an atmosphere in which a low-pressure inert gas is present, the residual amount of hydrogen gas is 10,000 ppm or less with respect to the inert gas. This is achieved by a method for manufacturing a magneto-optical recording medium in which a metal reflective layer is formed above the recording layer by a sputtering method under an atmosphere.

The formation of the magneto-optical recording layer of the magneto-optical recording medium according to the present invention can be performed by a sputtering method. Usually, film formation is performed under a low-pressure inert gas condition of 1 × 10 ^{−3 to} 20 × 10 ⁻³ Torr, such as Ar, He, and Ne. Remains. For example, they remain in the form of atomic groups such as nitrogen, water, hydrogen, oxygen, and CH and OH. Of the various gases remaining in the inert gas atmosphere when the metal reflective layer is formed thereon after forming the recording layer, the remaining amount of hydrogen, in particular, is less than a specific amount with respect to the inert gas. It is important to stably obtain the bias characteristics and EWR characteristics of the magneto-optical recording medium according to the present invention in a good state, and the effect is further enhanced by reducing the residual amount of nitrogen gas to a specific amount or less. . The effect of the present invention is great when the metal reflective layer is mainly composed of Al alone or an Al-based alloy, and the recording layer is mainly composed of an alloy of a transition metal and a rare earth metal.

Therefore, in the method for manufacturing a magneto-optical recording medium of the present invention, the residual amount of hydrogen gas when forming the metal reflective layer is:
The inert gas content is 10,000 ppm or less, preferably 1,000 ppm or less, particularly preferably 100 ppm or less.

At the same time, the object of the present invention can be more effectively achieved by setting the residual amount of nitrogen gas to 1000 ppm or less, preferably 100 ppm or less, particularly preferably 10 ppm or less.

In a method of manufacturing a magneto-optical recording medium, during deposition of a metal reflective layer by sputtering, the residual amount of hydrogen or nitrogen in the sputtering chamber is reduced so that the metal is adsorbed on the surface of the formed metal reflective layer, It is thought that these gases in the metal reflective layer may be released by heat and corrode the recording layer and deteriorate the EWR characteristics while the magneto-optical recording medium is used by mixing.

Further, it is considered that the residual hydrogen or nitrogen gas affects the film quality of the metal reflective layer on which the film is formed, and also affects the adjacent recording layer, thereby increasing the variation in characteristics.

However, among the various gases remaining in the sputtering chamber, there are many unclear reasons why hydrogen gas and nitrogen gas have a large effect on the bias characteristics and EWR characteristics. It is also presumed that this is because the effect on the air pressure is large. Even when the magneto-optical recording layer of the magneto-optical recording medium according to the present invention has a four-layer structure in which the second dielectric protection layer is provided between the recording layer and the metal reflective layer, the above-described effect of the present invention is similarly obtained. Is expressed. In the case of a four-layered magneto-optical recording layer, the second dielectric protection layer has a very small thickness of 150 to 500 ° in order to reduce the Kerr ellipticity and eliminate the phase difference in recording sensitivity. It is considered that free gas molecules from the reflective layer are not sufficiently blocked and affect the recording layer.

There are various possible sources of hydrogen gas remaining in the sputtering chamber during sputtering. For example, hydrogen which originally existed as an impurity in the inert gas, hydrogen as a product in which molecules of water were decomposed as a catalyst by a metal such as a metal shield plate in the sputtering chamber during sputtering,
There is hydrogen formed by the decomposition of organic compounds.

Nitrogen gas also includes those present as impurities in the inert gas, those coming from the piping of the inert gas, and those derived from air remaining in the sputtering chamber without being completely exhausted.

In the method of manufacturing a magneto-optical recording medium according to the present invention, there are various methods for controlling the residual amounts of hydrogen gas and nitrogen gas in a sputtering chamber when forming a metal reflective layer. For example, a method of sufficiently exhausting the vacuum layer and the substrate may be employed. In the case of exhausting the substrate, heat treatment is performed at a temperature that does not cause thermal deformation of the substrate, and degassing is performed. The substrate may be subjected to heat treatment in a vacuum layer. In the case of the sputtering chamber, it is sufficient to sufficiently exhaust the gas. However, it is effective to perform the heat treatment from the outside or the inside similarly to the case of the substrate. After the sputtering chamber and the substrate are sufficiently degassed in this way, when forming the metal reflective layer, the capacity of the exhaust device such as a diffusion pump, a cryopump, and a turbo pump and the orifice control device are operated. Then, the concentration of hydrogen gas and the concentration of nitrogen gas are adjusted. Other methods for adjusting the residual gas concentration are conceivable, and it is needless to say that the above method is one example.

In the present invention, by setting the residual amount of the hydrogen gas and the residual amount of the nitrogen gas within the above range during the formation of the metal reflective film, the bias magnetic field required for erasing and recording can be reduced to 700 Oe or less, The variation can be considerably reduced. And the EWR characteristics are considerably improved. The formation of the magneto-optical recording layer of the magneto-optical recording medium according to the present invention can be performed by a sputtering method. During film formation, a low-pressure inert gas is introduced into the sputtering chamber. As the inert gas, Ar, He, Kr, Ne and the like can be used,
Among them, Ar is most desirable in terms of cost and film forming speed.

As the material of the metal reflection layer in the magneto-optical recording medium according to the present invention, various kinds of simple metals and alloys can be used. For example, Al, Al-Cu, Al-Ti, Al-Ta, Ni, Ni
-A thin film in which a metal such as Cu, Au, Cu, Cu-Zn, Al-Cr, and Pt is formed on the second dielectric protection layer by a sputtering method can be used. Among them, simple 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 according to the present invention is preferably from 300 to 1,000, more preferably from 400 to 800.

If the thickness of the metal reflective layer is less than 300 °, light is easily transmitted, and C / N is reduced. If it is more than 1000 °, the heat capacity is increased and the sensitivity is lowered, which is not preferable.

When the magneto-optical recording layer of the magneto-optical recording medium according to the present invention has a three-layer structure, an enhancement layer, a recording layer, and the metal reflection layer are sequentially laminated on a transparent substrate in this order by a sputtering method and a vacuum film forming method. A film is formed. When the magneto-optical recording layer has a four-layer configuration, a second dielectric protection layer is provided between the recording layer and the metal reflection layer.

The enhance layer is a layer made of a dielectric material and is formed on the transparent substrate to a thickness of 800 to 1300 °.

As the material of the enhance layer, for example, SiOx, SiN
Dielectrics such as oxides, nitrides and sulfides such as x, TaOx, AlNx, SiAl and ZnS are used. Among them, optical properties,
From the viewpoint of the protection function, Si nitride, Al nitride or a mixture thereof, SiAl, and the like are preferable.

On the enhance layer, a recording layer is formed with a thickness of 200 to 300 °.

The recording layer is preferably an amorphous alloy thin film mainly composed of a transition metal and a rare earth metal, and the method of the present invention works most effectively.

Examples of transition metals that can be the composition of the recording layer include Fe, Co, and Ni, and rare earth metals include Tb, Gd, Dy, Sm, and the like.
Nd or the like can be used. And, as a specific example of the composition of the recording layer, GdCo, GdFe, TbFe, DyFe, GdFeTb, TbF
eCo, DyFeCo, TbFeNi, GdFeCo, NdDyFeCo and the like.
Among them, TdFeCo is most preferable because of its large manufacturing tolerance, and further contains 0.5 to 10a of Cr, Ti, Ta, Nb, Pt, etc. in its composition.
It is preferable that the composition contains t%, preferably 3 to 8 at%, in order to have practically sufficient corrosion resistance. Further, a Pt—Co alloy is also preferable as the composition of the recording layer.

When the magneto-optical recording layer of the magneto-optical recording medium according to the present invention has a four-layer structure, an inorganic protective layer for protecting the recording layer is formed to a thickness of 200 to 600 ° on the recording layer. .

The inorganic protective layer is usually the same as the enhance layer,
It is a dielectric thin film.

It is desirable that the substrate of the magneto-optical recording medium according to the present invention has its mechanical characteristics and, in particular, its surface runout acceleration and surface runout reduced so that recording and erasing can be performed effectively even at high speed rotation.

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

The magneto-optical recording medium according to the present invention, by forming each layer on the substrate as described above to form a magneto-optical recording layer, and further covering the upper surface and side surfaces thereof with an organic resin protective layer such as an ultraviolet curable resin. The storage stability of the magneto-optical recording medium can be further improved by providing a layer of an ultraviolet curable resin or the like on the surface of the substrate opposite to the side on which the recording layer is provided.

In addition, a double-sided recording type magneto-optical recording having excellent mechanical properties is performed by bonding the inner surface of the magneto-optical recording layer of the substrate to the outside through an adhesive layer made of a hot-mel adhesive or an epoxy-based adhesive. It can also be a medium.

[Effects of the Invention] In a magneto-optical recording medium having at least a recording layer and a metal reflective layer on a transparent substrate, when the metal reflective layer is formed by a sputtering method, residual hydrogen gas in an atmosphere gas in a sputtering chamber is further reduced. By making the content of nitrogen gas smaller than the specified amount, the bias characteristics and EWR characteristics of the magneto-optical recording medium can be improved.

The novel features of the present invention will be specifically described with reference to the following Examples and Comparative Examples.

(Example) A polycarbonate substrate having a diameter of 130 mm and a thickness of 1.2 mm with a guide groove of 1.6 μm pitch was set on a rotating substrate holder of a sputtering apparatus, and argon gas was introduced into the sputtering chamber to reduce the gas pressure to 1 to 3. 5 mTorr.

Then, an SiNx thin film having a thickness of 1100 mm was formed as an enhance layer by magnetron sputtering.

Then, power was applied to the target of FeCoCr alloy and the target of Tb, and the recording layer having a composition of Tb ₁₈ Fe ₆₈ Co ₈ Cr ₆ was formed on the enhanced layer by a simultaneous dual sputtering method for 250 minutes.
The thickness was formed as follows.

Thereafter, a 250-nm-thick SiNx thin film was formed as a second dielectric protection layer on the recording layer.

Next, while controlling the hydrogen gas and the nitrogen gas in the sputtering chamber by changing the degassing time and the exhaust power of the cryopump with the residual gas measuring device attached to the sputtering chamber, five kinds of A to E shown in Table 1 were obtained. Under the conditions, a thin film having a thickness of 500 mm is formed on the second dielectric protection layer as a metal reflection layer, and an enhancement layer, a recording layer, a second dielectric protection layer and a metal reflection layer are formed on the substrate. Under each condition, 100 samples of a magneto-optical recording medium having a magneto-optical recording layer having a four-layer structure were prepared.

The control width of the residual amounts of the hydrogen gas and the nitrogen gas at the time of forming the metal reflective layer was changed as shown in Table 1 by expressing the partial pressure concentration with respect to the partial pressure of the argon gas in ppm.

And the measurement of the residual amount of gas was performed by attaching a working exhaust device to the quadrupole mass spectrometer. In this method, first, the inside of the analysis tube was operated and evacuated to generate ions, the mass was separated through the quadrupole electrode, amplified by a secondary electron multiplier, and detected. At this time, the pressure reduction ratio of the working exhaust was set to 1 × 10 ⁻³ Torr. On the other hand, while monitoring the argon gas used for sputtering film formation with a Baratron vacuum gauge, the emission voltage was determined such that the value was reduced by 1 × 10 ⁻³ Torr on the display. In calculating the measured values, correction was performed using the correction coefficient specific to each detection element, and the exhaust inside the analysis chamber was sufficiently performed to exhaust sufficiently until the partial pressure of each residual gas component became 5 × 10 ⁻¹¹ Torr or less. In addition, the structure of the analyzer was devised so that a trace gas of about 1 × 10 ⁻⁹ Torr could be detected.

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

Evaluation of bias magnetic field characteristics: Recording and reproduction were performed by following a pic-up while performing servo while setting the rotation speed to 2400 with a drive equipped with a pickup with NA = 0.55 and a semiconductor laser with a wavelength of 830 nm. 8mW for recording
Laser power and bias magnetic field 0 to 700 Oe, 5.5mW laser power, bias magnetic field 0 to 700
A pit of 0.75 μm was recorded under the conditions of Oe and a recording frequency of 4.93 MHz. Note that the values of the bias magnetic field at the time of erasing and writing were the same. Next, read C / N with a spectrum analyzer using a laser power of 1.5 mW and measure the C / N while changing the bias magnetic field.The bias magnetic field becomes -1 dB from the saturated C / N value for the first time after the C / N is saturated. The value of was used as the bias magnetic field value.

Evaluation of EWR characteristics: Erasing with the above drive using 8mW laser power and 300Oe applied magnetic field, recording under 5.5mW laser power and 300Oe applied magnetic field, 1.5mW
The C / N was read with a spectrum analyzer at a laser power of. This erase-record-reproduce cycle is repeated 100,000 times at the same track position, and the 100,000th C / N and initial C
/ N was determined and the degree of deterioration was evaluated.

 Table 1 shows the obtained results.

(Comparative Example) In the above embodiment, the residual gas concentration at the time of forming the metal reflective film was changed to six conditions from F to K as shown in Table 2 by changing the degassing time and the exhaust capacity of the cryopump. Except for changing, under each condition under the same conditions as in the example
Samples of 100 magneto-optical recording media were prepared.

Table 2 shows the evaluation results of the bias magnetic field characteristics and the EWR characteristics.

Claims (2)

(57) [Claims] After a recording layer is formed on a transparent substrate by a sputtering method in an atmosphere in which a low-pressure inert gas is present, the recording layer is formed in an atmosphere in which a residual amount of hydrogen gas is 10,000 ppm or less with respect to the inert gas. A method for manufacturing a magneto-optical recording medium, comprising forming a metal reflective layer above the recording layer by a sputtering method. 2. After a recording layer is formed on a transparent substrate by a sputtering method in an atmosphere in which a low-pressure inert gas is present, the residual amount of hydrogen gas is 10,000 ppm or less with respect to the inert gas and nitrogen gas is used. Residual amount of inert gas is 10
A method for producing a magneto-optical recording medium, wherein a metal reflective layer is formed by a sputtering method above the recording layer under an atmosphere of 00 ppm or less.