JPH05189823A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enhance the sensitivity of the title medium and to enhance the power margin of the title medium by providing the following: an intereference layer composed of tantalum oxide; and a heat-insulating layer which is formed on the interference layer and which is composed of silicon nitride, silicon oxide or their mixture. CONSTITUTION:A substrate is introduced into a sputtering chamber; the chamber is vacuum-evacuated to 8X10<-7> Torr or lower; 50 to 500ccm of argon and 10 to 60ccm of oxygen are introduced under an argon partial pressure of 0.5 to 3.5X10<-3> Torr and under an oxygen partial pressure of 0.2 to 0.5X10<-3> Torr; an interference layer which uses Ta as a target and which is composed of tantalum oxide is formed. A layer which is composed of silicon nitride, silicon oxide or their mixture is formed as a heat-insulating layer on the surface of a recording layer. The silicon nitride film is formed in the following manner: silicon is used as a target; an argon partial pressure is set at 0.8 to 6.0X10<-3> Torr; a nitrogen partial pressure is set at 0.1 to 1.3X10<-3> Torr; 40 to 350ccm of argon and 5 to 100ccm of nitrogen are introduced; and a sputtering operation is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium used for optically recording / reproducing information.

[0002]

2. Description of the Related Art Among optical memories, a magneto-optical recording system has been put into practical use as an erasable type memory capable of additional recording and erasing. As a recording layer of a magneto-optical recording medium, an alloy thin film of rare earth and a transition metal is most often used at present from the viewpoint of comprehensive characteristics. As this magneto-optical recording medium, there is a system in which a reflective layer is provided on the recording layer in order to improve the recording / reproducing characteristics when irradiated with a laser beam. Further, in order to increase the heating efficiency of the recording layer, a heat insulating layer may be provided between the recording layer and the reflective layer. Due to the thermal effect of the reflective layer and the heat insulating layer, it is possible to expand the power margin of the recording light and reduce the sensitivity change with respect to the recording pulse width.

[0003]

Various materials have been used for the heat insulating layer and the interference layer provided between the substrate and the recording layer. However, what has been sufficiently satisfied has not yet been obtained in terms of the adhesion to the resin substrate, the life in a high temperature and high humidity environment, and the like. It has been earnestly desired to provide a magneto-optical recording medium which is excellent in adhesion to a substrate, has a long life in a high temperature and high humidity environment, is excellent in environmental resistance, and has high sensitivity, CNR and power margin.

[0004]

In order to solve the above problems, the inventors of the present invention have earnestly studied, and as a result, in a magneto-optical recording medium comprising an interference layer, a recording layer, a heat insulating layer and a reflective layer on a substrate, When tantalum oxide and / or silicon nitride and / or silicon oxide is used as the interference layer, the obtained magneto-optical recording medium has excellent adhesion between the substrate and the interference layer, and has no deterioration in life under high temperature and high humidity environment. The inventors have found that they are excellent in environmental friendliness and exhibit high sensitivity, CNR and power margin, and have completed the present invention based on this finding.

That is, the gist of the present invention is 500 to 12 consisting of a substrate and tantalum oxide formed on the substrate.
00 Å interference layer, a recording layer formed on the interference layer, a 200 to 500 Å heat insulating layer formed on the recording layer and made of silicon nitride, silicon oxide or a mixture thereof, and the heat insulating layer. A magneto-optical recording medium comprising a 400 to 1200 Å reflective layer made of Al or an alloy mainly composed of Al and formed on the layer.

Examples of the substrate used in the present invention include glass, plastics such as polycarbonate resin and acrylic resin, or those in which resin is formed in a grooved shape on glass. The thickness of the substrate is generally about 1 to 2 mm.
As the recording layer, for example, TbFe, TbFeCo, TbC
Alloys of rare earths and transition metals such as o, DyFeCo, and GdTbFeCo are used. As the magneto-optical recording layer, a single layer of the above alloy may be used, or GdFeCo and TbF may be used.
e, two or more layers such as TbFeCo and GdTbFeCo, TbFeCo, GdFeCo and GdTbFeCo may be stacked. The thickness of the magneto-optical recording layer is 200 to 30
0Å is preferred. If the film thickness of the recording layer is too thick, the sensitivity tends to deteriorate and the CNR tends to decrease. If it is too thin, it tends to become weak against oxidation as the CNR decreases.

An interference layer made of tantalum oxide is provided between the substrate and the recording layer. The purpose of the interference layer is to reduce the reflectance due to the interference effect of light to reduce noise and improve sensitivity,
This is to prevent the recording layer from being oxidized from the substrate side. Tantalum oxide has better adhesion to a substrate than conventional nitrides (SiN, AlN, etc.) and does not peel or crack even if the substrate expands or contracts due to heat or moisture. The effect of using tantalum oxide is particularly remarkable when the substrate is plastic. In tantalum oxide, oxygen has an optical stoichiometric composition (Ta:
O = 2: 5) or slightly deficient (eg T
a: O is preferably 2: 4.8 to 5), and the refractive index is preferably 2.1 to 2.3. The thickness of the interference layer is 500 to 1200Å. If too thick,
When the reflectance is too high or too thin, the reflectance tends to be too high and the CNR tends to decrease at the same time.

The heat insulation layer reflects the heat of the recording layer with high thermal conductivity.
To prevent direct transmission to the layer and improve recording sensitivity
It is a thing. AlN, SiN, Al as the heat insulating layer₂O
₃, SiO, SiO₂, TiO₂, Ta₂O_FiveEtc.
Mixtures of these are listed, but their thermal conductivity is relatively small and
SiN, SiO, SiO that can reduce the folding rate₂To use
Preferably. Small thermal conductivity means sensitivity
It means that the improvement effect is great, and the refractive index is small.
That is, the CNR can be increased by suppressing the ellipticity of the reflected light.
It is preferable in terms. The thickness of the heat insulation layer is 200 ~ 500Å
It If it is too thick, the reflected light will be elliptical and the CNR will decrease.
If it occurs too thin, the sensitivity improvement effect is not sufficient.
It The refractive index of the heat insulating layer is preferably 1.4 to 2.3
Yes. Ta₂O _Five Has a refractive index of about 2.0 to 2.3, SiN
Has a refractive index of about 1.6 to 2.2, and SiO has a refractive index of 1.
It is about 4 to 2.0.

As the reflective layer, a substance having a high light reflectance and a high thermal conductivity is used. Al as such substances,
Examples include simple substances of Au, Ag, Cu, and Pt or alloys containing them as a main component. Among them, Al or an alloy containing Al as the main component is the most excellent alloy having both low cost and corrosion resistance. In particular, Al alloys show very excellent corrosion resistance depending on the additives. As additives, Ta, Ti, Zr,
Mo and the like can be mentioned. Particularly, excellent properties can be obtained by adding 1 to 3% of Ta. The film thickness of the reflective layer is determined by the thermal conductivity of the reflective layer itself, but is in the range of approximately 400 to 1200Å. The larger the thermal conductivity, the thinner the film thickness selected. If it is too thick, the recording sensitivity tends to deteriorate, and if it is too thin, the recording power margin tends to decrease.

A protective layer may be provided on the reflective layer by using a known organic material such as an ultraviolet curable resin or a known inorganic material such as a ceramic thin film. The organic matter protective layer contains 10 ppm of alkali and / or alkaline earth metal as impurities.
The content of halogen ions is preferably 20 ppm or less. Since it is desirable that the protective layer formed of the ultraviolet curable resin covers not only the upper surface of the recording layer but also the side surface thereof, for example, when the recording layer is provided on the substrate, the peripheral portion of the central hole of the substrate and the outer peripheral portion of the substrate are provided. It is preferable that the recording layer is covered with a cover so that the recording layer is not formed in this portion, and the protective layer is in direct contact with the substrate at the peripheral portion and the outer peripheral portion of the central hole of the substrate to protect the recording layer. The thickness of the protective layer is preferably 1 to 12 μm in the case of an organic material, and 500 to 2000 Å in the case of a ceramic thin film.

To form each layer on the substrate, thermal evaporation, electron beam evaporation, CVD method, sputtering method and the like are used. A sputtering method is particularly preferable. The method for producing the magnetic recording medium of the present invention by the sputtering method will be described below. The substrate is introduced into the sputtering chamber, vacuum exhausted to 8 × 10 ⁻⁷ Torr or less, argon partial pressure 0.5 to 3.5 × 10 ⁻³ Torr and oxygen partial pressure 0.2 to 0.5 × 10 ^−. Argon 50-50 at ³ Torr
By introducing 0 ccm and 10 to 60 ccm of oxygen, an interference layer made of tantalum oxide is formed by using Ta as a target.

After tantalum oxide (TaOx) film formation, 1.7
〜 100 × under argon pressure of 5.0 × 10 ^-3 Torr
Introducing 200 ccm of argon, 0.15-0.5k
The surface of the tantalum oxide film is etched by reverse sputtering with a reverse sputtering force of W for 30 to 60 seconds. Then, a recording layer is formed on the surface of the tantalum oxide film by introducing an alloy of rare earth and a transition metal at 0.5 to 5.0 × 10 ⁻³ Torr and introducing argon at 50 to 250 ccm.

On the surface of the recording layer, a layer made of silicon nitride or silicon oxide or a mixture thereof is provided as a heat insulating layer. The silicon nitride film is formed by using silicon as the target and the argon partial pressure is 0.8 to 6.0 × 10 ⁻³ Tor.
r, the partial pressure of nitrogen is 0.1 to 1.2 × 10 ⁻³ Torr,
Argon 40 to 350 ccm, nitrogen 5 to 100 cc
m may be introduced and sputtering may be performed.

The silicon oxide film is formed by using silicon as a target and the argon partial pressure is 0.8 to 6.0 × 10 ⁻³ To.
rr, oxygen partial pressure is 0.1 to 1.2 × 10 ⁻³ Torr, argon is 40 to 350 ccm, oxygen is 1 to 10 c
cm may be introduced and sputtering may be performed. A film made of a mixture of silicon nitride and silicon oxide is formed with a silicon target and an argon partial pressure of 0.8 to 6.0 ×.
10 ^-3 Torr, nitrogen partial pressure 0.1-1.2 × 10 ^-3 T
orr, oxygen partial pressure 0.1 to 1.2 × 10 ⁻³ Torr, argon 40 to 350 ccm, nitrogen 5 to 100
It suffices to introduce ccm and oxygen of 1 to 10 ccm and perform sputtering.

Then, a metal or alloy having a high light reflectance and a high thermal conductivity is used as a target, and 1.0 to 4.0 × 10 ^{−3 is set.}
Argon was introduced at 50 to 300 ccm at Torr,
Form a reflective layer. The protective layer of the ceramic thin film is similarly formed by the sputtering method. The organic protective layer is provided by applying it with a spin coater and then curing it by irradiating it with ultraviolet rays.

The magneto-optical recording medium of the present invention has the largest CNR.
The recording power (P _CNR-max ) that can obtain is 5 to 7 mW,
The maximum CNR (CNR _max ) is 48 dB or more, the reflectance of the mirror part is 18 to 22%, and the temperature is high (85 _{° C} ).
The error rate after holding at 500 ° C and humidity of 85% for 500 hours is 1 × 10 ^-4 or less, and the error rate after holding at high temperature and high humidity for 500 hours [Error (500)] and high temperature and high humidity Error rate before error [Error
(0)] ratio [Error (500)] / [Erro
When r (0)] is 1.5 or less, the recording power (power margin) with which a CNR of (CNR _max −3 dB) or more can be obtained is 3.0 mW or more. The magneto-optical recording medium according to the present invention has high sensitivity, CNR, and power margin, and is also extremely excellent in environmental resistance.

[0017]

The present invention will be described in more detail with reference to the following examples. The present invention is not limited to the following examples unless it exceeds the gist. The P _CNR-max power margin, CNR _max, and reflectance were measured with a magneto-optical disk inspection device OMSL2000 manufactured by Nakamichi.

Example 1 A 130 mmφ polycarbonate substrate was introduced into a sputtering chamber and first evacuated to 8 × 10 ⁻⁷ Torr or less. Next, 60 ccm of Ar and 15 ccm of O ₂
After introduction, reactive sputtering of a Ta target was performed to form an interference layer of tantalum oxide having a refractive index of 2.15 of 900Å. After exhausting the chamber once, Ar is 100 ccm
Co-sputtering was carried out using a target of Tb and Fe ₉₀ Co ₁₀ (atomic%, the same applies hereinafter) introduced and Tb ₂₀ (Fe
A recording layer of ₉₀ Co ₁₀ ) ₈₀ was formed on 250 Å. Then Ar
Was introduced at 50 ccm and N ₂ at 10 ccm to carry out reactive sputtering of a Si target to form 300 Å of a heat insulating layer of silicon nitride having a refractive index of 2.0. Finally, using a target of AlTa alloy, a reflective layer of Al _98.6 Ta _1.5 is used.
0Å formed. The recording / reproducing characteristics of the obtained recording medium are shown in the table.
Shown in 1.

Example 2 As a heat insulating layer, Ar of 50 ccm and O ₂ of 8 ccm were introduced to carry out reactive sputtering of a Si target to form silicon oxide having a refractive index of 1.6 and having a pressure of 300 Å.
The other layers were formed in the same manner as in Example 1. Recording / reproducing characteristics are shown in Table 1.

Example 3 Ar is 50 ccm, N ₂ is 7 ccm, and O _{2 is a} heat insulating layer.
Of 3 ccm and reactive sputtering of a Si target are carried out to obtain a mixed film of silicon oxide and silicon nitride (N: O = 4.5: 5.
5) was formed, and the other layers were formed in the same manner as in Example 1. Recording / reproducing characteristics are shown in Table 1.

Example 4 A polycarbonate substrate was introduced into a sputtering chamber and evacuated in the same manner as in Example 1, and then an Ar layer was used as an interference layer.
Of 150 ccm and O ₂ of 28 ccm were introduced, and reactive sputtering of a Ta target was performed to form tantalum oxide having a refractive index of 2.25 to a thickness of 1200 Å.
A Tb ₂₀ (Fe ₉₀ Co ₁₀ ) ₈₀ layer having a thickness of Å was formed. Next, as a heat insulating layer, Ar is 100 ccm and N ₂ is 30 cc
Then, reactive sputtering of a Si target was performed to form silicon nitride having a refractive index of 1.8 and a thickness of 300 Å. Finally, a reflective layer of 800 Å was formed using an AlTa alloy target in the same manner as in Example 1. The obtained recording / reproducing characteristics are shown in Table 1.

Example 5 After forming a TbFeCo layer in the same manner as in Example 4, 100 ccm of Ar and 45 ccm of N ₂ were introduced as a heat insulating layer, and reactive sputtering of a Si target was performed to obtain a refractive index of 1.6 and a thickness. A 300 Å silicon nitride heat insulating layer was formed. After that, a reflective layer was formed in the same manner as in Example 4. Recording / reproducing characteristics are shown in Table 1.

Comparative Example 1 Evacuation was carried out in the same manner as in Example 1, 60 ccm of Ar and 1 of O ₂ were added.
After introducing 5 ccm and performing reactive sputtering of a Ta target, an interference layer of tantalum oxide having a refractive index of 2.15 was formed in 450Å. Then, the same treatment as in Example 1 was performed to form a recording medium. The results are shown in Table-1.

Comparative Example 2 A recording medium was prepared under exactly the same conditions as in Comparative Example 1 except that the thickness of the tantalum oxide interference layer was set to 1300Å. Table-1
The results shown in are obtained.

Comparative Example 3 In the same manner as in Example 1, an interference layer of tantalum oxide having a thickness of 900 Å and a Tb ₂₀ (Fe ₉₀ Co ₁₀ ) ₈₀ recording layer having a thickness of 100 Å were formed. Subsequently, similarly to Example 1, SiN of the heat insulating layer and the AlTn alloy of the reflective layer were formed to prepare a recording medium. Recording / reproducing characteristics are shown in Table 1.

Comparative Example 4 Tantalum oxide was formed in the same manner as in Example 1. Then Tb
_{A 20} (Fe ₉₀ Co ₁₀ ) ₈₀ recording layer was formed to a thickness of 500Å. Then, as in Example 1, SiN of the heat insulating layer and Al of the reflective layer were used.
A Ta alloy was formed to form a recording medium. Recording / reproducing characteristics are shown in Table 1.

Comparative Example 5 As in Example 1, tantalum oxide, Tb ₂₀ (Fe ₉₀ C
o ₁₀ ) After forming ₈₀ , Ar is 50 ccm and N ₂ is 10
Introducing ccm, reactive sputtering of Si target is performed, and a heat insulating layer of silicon nitride having a refractive index of 2.0 is formed by 100
Å formed. Then, a reflective layer of Al _98.5 Ta _1.5 was formed with a thickness of 800 Å using an AlTa alloy target. The recording / reproducing characteristics of the obtained recording medium are shown in Table 1. C / N
Was decreased by 1 dB, and the reflectance became 25% or more.

Comparative Example 6 As in Example 1, tantalum oxide, Tb ₂₀ (Fe ₉₀ C
o ₁₀ ) ₂₀ is formed, then Ar is 50 ccm and N ₂ is 10
ccm is introduced and reactive sputtering of a Si target is performed to form a heat insulating layer of silicon nitride having a refractive index of 2.0
Å formed. Then, a reflective layer of Al _98.5 Ta _1.5 was formed with a thickness of 800 Å using an AlTa alloy target. The recording / reproducing characteristics of the obtained recording medium are shown in Table 1.

Comparative Example 7 As in Example 1, tantalum oxide, Tb ₂₀ (Fe ₉₀ C
o ₁₀ ) ₈₀ is formed, then Ar is 50 ccm and O ₂ is 8 c
cm and introduce reactive sputtering of Si target, and heat insulating layer of silicon oxide with refractive index of 1.60 is 50Å
Formed. Then, as in Example 1, a reflective layer was formed using an AlTa alloy target. The recording / reproducing characteristics of the obtained recording medium are shown in Table 1.

Comparative Example 8 As in Example 1, tantalum oxide, Tb ₂₀ (Fe ₉₀ C
o ₁₀ ) ₈₀ is formed, then Ar is 50 ccm and O ₂ is 8 c
cm and introducing reactive sputtering of a Si target to 600 nm of a heat insulating layer of silicon oxide having a refractive index of 1.60.
Å formed. Then, as in Example 1, a reflective layer was formed using an AlTa alloy target. The recording / reproducing characteristics of the obtained recording medium are shown in Table 1.

Comparative Example 9 As in Example 1, tantalum oxide, Tb ₂₀ (Fe ₉₀ C
After forming o ₁₀ ) ₈₀ , SiN, a 300 Å reflective layer of Al _98.5 Ta _1.5 was formed using an AlTa target. The recording / reproducing characteristics of the obtained recording medium are shown in Table-1.

Comparative Example 10 Tantalum oxide and Tb ₂₀ (Fe ₉₀ C) were used as in Example 1.
After forming o ₁₀ ) ₈₀ , SiN, a reflective layer of Al _98.5 Ta _1.5 was formed with an AlTa target of 1300Å. The recording / reproducing characteristics of the obtained recording medium are shown in Table-1.

Comparative Example 11 As an interference layer, 60 ccm of Ar and 10 ccm of N ₂ were introduced, and reactive sputtering of a Si target was performed to form silicon nitride having a refractive index of 2.2 with 1000 Å, and other layers were formed. It was formed in the same manner as in Example 1. Recording / reproducing characteristics are shown in Table 1.

From the above, any Example and Comparative Example 11
Shows good characteristics in sensitivity, CNR, and reflectance. On the other hand, in Comparative Examples 1 to 10, at least one of sensitivity, CNR and reflectance was defective. Furthermore, Examples 1 to 5 and Comparative Example 11 having good recording and reproducing characteristics
Therefore, the disc is placed in an environment of 85 ° C and 85% RH for 500 times.
Table 2 shows the results of measuring the rate of increase in the drop-in error rate before and after holding the time. In each of the examples, the increase in error rate was within 1.5 times or less, but in comparative example 11, the entire surface was cracked and the measurement was impossible.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

The magneto-optical recording medium according to the present invention has high sensitivity, CNR, and power margin, and is extremely excellent in environmental resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshifumi Kawano 1000, Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Sanryo Kasei Co., Ltd.

Claims (7)

[Claims] 1. A substrate, an interference layer of 500 to 1200 Å made of tantalum oxide, formed on the substrate, a recording layer formed on the interference layer, and formed on the recording layer. And a heat insulating layer of 200 to 500 Å made of silicon nitride, silicon oxide, or a mixture thereof, and Al or an Al-based alloy formed on the heat insulating layer.
A magneto-optical recording medium comprising a reflective layer of 0 to 1200Å. 2. The magneto-optical recording medium according to claim 1, wherein the refractive index of the interference layer is 2.0 to 2.3. 3. The magneto-optical recording medium according to claim 1, wherein the recording layer has a thickness of 150 to 400 Å. 4. The magneto-optical recording medium according to claim 1, wherein the heat insulating layer is made of silicon nitride and has a refractive index of 1.6 to 2.1. 5. The magneto-optical recording medium according to claim 1, wherein the heat insulating layer is made of silicon oxide and has a refractive index of 1.4 to 2.0. 6. The magneto-optical recording medium according to claim 1, wherein the reflective layer is made of an Al alloy containing 1 to 3 atm% of Ta in Al. 7. The protective layer is formed on the reflective layer.
The magneto-optical recording medium according to.