JP3219696B2 - Magneto-optical recording medium - Google Patents

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 such as a magneto-optical disk.

[0002]

2. Description of the Related Art A magneto-optical disk is a recording medium on which information is recorded by a photo-thermomagnetic effect using a laser beam and reproduced by a magnetic Kerr effect or a Faraday effect, and it is possible to repeatedly erase and reproduce recorded information. It is a recording medium capable of high-density recording.

In such a magneto-optical recording medium, a recording layer made of an amorphous perpendicular magnetization film of a rare earth-transition metal alloy such as TbFe, TbFeCo, GdFe, etc. is provided on a substrate. In general, a protective layer is provided on the surface to improve heat resistance, humidity resistance, light resistance, wear resistance, and the like. In particular, on the surface on the recording layer side,
If a scratch is formed or dust or dust adheres to the recording layer, the reproduced signal becomes noise. Therefore, a protective layer having excellent wear resistance and the like is provided on the surface on the recording layer side. As such a protective layer, a protective layer generally made of an ultraviolet curable resin or the like is provided.

Further, it has been proposed to use a hard carbon coating such as a diamond-like carbon coating as such a protective layer (for example, JP-A-62-195744 and JP-A-63-239633). ).

[0005]

However, when a hard carbon film is used as such a protective layer, there has been a problem that the adhesion is poor and the film is easily peeled off. In addition, when peeling does not occur, there is a problem that the substrate is deformed such as warpage.

SUMMARY OF THE INVENTION An object of the present invention is to solve such a conventional problem, and to prevent the occurrence of deformation such as warpage of a substrate even when a hard carbon film is used as a protective layer. It is to provide a recording medium.

[0007]

The magneto-optical recording medium of the present invention is characterized in that a hard carbon film having a gradient structure in which the hydrogen concentration changes in the film thickness direction is provided as a protective layer.

In the present invention, the “graded structure” may be a structure in which the hydrogen concentration is high at one end in the film thickness direction of the hard carbon coating and the hydrogen concentration is low at the other end, and is not necessarily continuous in the film thickness direction. It is not necessary that the hydrogen concentration be changed. Therefore, the case where the hydrogen concentration changes stepwise in the film thickness direction is also included.

In the present invention, the term "hard carbon coating" includes an amorphous carbon coating and a crystalline carbon coating called a so-called diamond-like carbon coating. Good. The thickness of the hard carbon film is not particularly limited, but is
Approximately Å2000 ° is common.

In the present invention, it is preferable that the hydrogen concentration of the hard carbon film differs by 10% or more between both ends in the film thickness direction. More preferably, at one end in the film thickness direction, 60 to
40% and 30-10% at the other end. The percentage of hydrogen concentration indicates atomic%, and can be measured by, for example, secondary ion mass spectrometry (SIMS).

When the hydrogen concentration in the hard carbon coating becomes relatively high, the hardness becomes relatively low and the internal stress becomes relatively low. On the other hand, when the hydrogen concentration in the hard carbon film becomes relatively low, the hardness becomes relatively high, and the internal stress also becomes relatively high.

In the present invention, the hydrogen concentration is reduced at one end of the hard carbon film by forming an inclined structure in which the hydrogen concentration is changed in the film thickness direction, and a carbon film composition having high hardness and internal stress is obtained. At the other end, the hydrogen concentration is relatively increased to provide a carbon coating composition having low hardness and low internal stress. Therefore, at one end having a low hydrogen concentration, a carbon coating composition having high hardness and excellent wear resistance, humidity resistance, corrosion resistance, etc. can be obtained, and at the other end having a high hydrogen concentration, internal stress can be reduced. Low carbon coating composition. Therefore, a hard carbon film having excellent wear resistance, humidity resistance, corrosion resistance, etc., low internal stress as a whole, and excellent adhesion can be obtained.

In the present invention, a hard carbon coating may be further provided via an intermediate layer. By providing the hard carbon coating via the intermediate layer in this manner, the adhesion of the hard carbon coating is further enhanced, the occurrence of peeling can be prevented, and the deformation such as warpage of the substrate can be prevented. As such an intermediate layer, at least one selected from metals of Si, Zr, Ti, and Ge and oxides and nitrides of these metals can be used. The thickness of the intermediate layer is preferably about 10 to 500 °.

In the present invention, the protective layer comprising a hard carbon film may be provided as the outermost layer on the recording layer side.
Also, it may be provided as the outermost layer on the substrate side. Furthermore, it may be provided on both the outermost layer on the recording layer side and the outermost layer on the substrate side. In such a case, the hydrogen concentration of the hard carbon coating may be set so as to be relatively high at the end near the substrate in the thickness direction and relatively low at the end far from the substrate. Generally preferred. By using such a hydrogen concentration gradient, the internal stress is low on the substrate side, and a coating composition having excellent hardness and the like can be formed on the outermost surface side. A magneto-optical recording medium that does not easily occur can be provided.

Further, in the present invention, a protective layer made of a hard carbon coating may be provided inside the outermost surface layer.
For example, a protective layer made of a hard carbon film may be provided on both sides of the recording layer.

In the present invention, the method of forming the hard carbon film is not particularly limited, but can be formed by, for example, a CVD method. For example, plasma CVD
By applying a high-frequency voltage to the substrate holder using the method, a self-bias voltage is generated in the substrate holder, and the self-bias voltage is changed with the progress of the film formation, thereby reducing the hydrogen concentration in the hard carbon film. It can be varied in the thickness direction. As a plasma generating means in the plasma CVD method, for example, an electron cyclotron resonance (ECR) plasma CVD apparatus or the like can be used. By using such an apparatus, the density of the plasma can be further increased, and a high-quality hard carbon film can be formed at a low temperature.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a sectional view showing a magneto-optical disk according to an embodiment of the present invention. Referring to FIG. 1, a recording layer 3 sandwiched between a pair of dielectric layers 2 and 4 is provided on a transparent substrate 1 made of PC (polycarbonate) and PMMA (polymethyl methacrylate) or glass. Is provided. As the recording layer 3, a magneto-optical material that can be used for a recording layer of a magneto-optical disk is used.
rare earth-transition metal alloy films such as bFeCo, TbFe, GdFe, or magnetic garnet, Co ferrite,
It is formed from a magneto-optical material such as a polycrystalline film such as MnBi or MnPtSb. The dielectric layers 2 and 4 are formed of a transparent dielectric film made of a silicon nitride film (SiN) or the like.

A heat radiating layer 5 made of Al or the like is provided on the dielectric layer 4, and an ultraviolet curable resin is applied on the heat radiating layer 5, and the UV curable resin is cured by irradiating ultraviolet rays. A protective layer 6 is provided.

On the UV protection layer 6, a hard carbon coating 7 is provided. The hard carbon film 7 is formed such that the hydrogen concentration on the substrate 1 side is high and the hydrogen concentration on the surface side opposite to the substrate 1 side is low. Such a hard carbon film 7 is formed, for example, by ECR plasma CVD as shown in FIG.
It can be formed by a device.

FIG. 7 is a schematic sectional view showing an example of an ECR plasma CVD apparatus. Referring to FIG. 7, inside of vacuum chamber 108, plasma generation chamber 104 and substrate 1 are provided.
There is provided a reaction chamber in which 13 is installed. One end of the waveguide 102 is attached to the plasma generation chamber 104, and the other end of the waveguide 102 is connected to the microwave supply unit 1.
01 is provided. Microwaves generated by the microwave supply means 101 are guided to the plasma generation chamber 104 through the waveguide 102 and the microwave introduction window 103.
The plasma generation chamber 104 is provided with a discharge gas introduction pipe 105 for introducing a discharge gas such as an argon (Ar) gas into the plasma generation chamber 104. A plasma magnetic field generator 106 for guiding plasma to the reaction chamber is provided around the plasma generation chamber 104.

In the reaction chamber in the vacuum chamber 108, a drum-shaped substrate holder 112 is installed so as to be rotatable around a rotation axis perpendicular to the paper surface of FIG. , A motor not shown is connected. A plurality (six in this embodiment) of substrates 113 are mounted on the outer peripheral surface of the substrate holder 112 at equal intervals. The substrate holder 112 has a high-frequency power supply 11
0 is connected.

Around the substrate holder 112, a metal cylindrical shield cover 114 is provided at a distance of about 5 mm from the substrate holder 112. This shield cover 114 is connected to a ground electrode. When a film is formed, the shield cover 114 is connected to the substrate holder 112 and the vacuum chamber 10 other than where the film is formed by a high frequency (RF) voltage applied to the substrate holder 112.
8 is provided to prevent the occurrence of a discharge between them.

The shield cover 114 has an opening 115
Are formed. The plasma drawn from the plasma generation chamber 104 passes through the opening 115 and is emitted to the substrate 113 mounted on the substrate holder 112. In the vacuum chamber 108, a reaction gas introduction pipe 116 is provided. This reaction gas introduction pipe 116
Is located above the opening 115.

FIG. 8 is a plan view showing the vicinity of the tip of the reaction gas introduction pipe 116. Referring to FIG. 8, a reaction gas introduction pipe 116 has a gas introduction section 116a for introducing CH ₄ gas from the outside into the vacuum chamber, and a gas introduction section 1a.
Outgassing portion 116b connected vertically to 16a
It is composed of The gas discharge section 116b is arranged perpendicular to the rotation direction A of the substrate holder 112 and is provided above the opening 115 and upstream of the rotation direction in the rotation direction. In the gas discharge part 116b,
A plurality of holes 117 are formed in a direction of about 45 degrees downward. In this embodiment, eight holes 117 are formed. The interval between the holes 117 is formed so as to gradually decrease from the center toward both sides. By forming the holes 117 at such intervals, the gas introduction portions 116a
CH ₄ gas introduced from the holes 117 is almost uniformly released from the holes 117, respectively.

An embodiment in which a hard carbon film is formed on a substrate (UV protective layer 6 shown in FIG. 1) using the above film forming apparatus will be specifically described below. First, the inside of the vacuum chamber 108 is evacuated to 10 ^-5 to 10 ^-7 Torr, and the substrate holder 112 is rotated at a speed of about 10 rpm. Next, 5.7 × 10 10 Ar gas was supplied from the discharge gas introduction pipe 105.
^-4 Torr and microwave supply means 1
A microwave of 01 to 2.45 GHz and 100 W is supplied to radiate the Ar plasma formed in the plasma generation chamber 104 to the surface of the substrate 113. At the same time, CH ₄ gas is supplied from the reaction gas pipe 116 to 1.3 × 10 ⁻³ Torr.
13.56 MHz from the high frequency power supply 110
z RF power is applied to the substrate holder 112. As shown in FIG. 9, the application of the RF power to the substrate holder 112 is such that the self-bias voltage generated on the substrate is 0 V at the initial stage of the film formation, and −15 minutes after the completion of the film formation.
The RF power was adjusted to be 0 V and applied. Through the above steps, a hard carbon film having a thickness of 1000 ° was formed on the substrate.

FIG. 10 is a diagram showing the relationship between the self-bias voltage generated in the substrate holder and the hardness, internal stress, and hydrogen concentration of the hard carbon film formed at the self-bias voltage. These measured values are obtained by forming a hard carbon coating under the condition that the self-bias voltage generated in the substrate holder is kept constant using the apparatus shown in FIG. 7 and measuring each characteristic of the obtained hard carbon coating. Is the obtained number,
FIG. 10 shows the relationship between the self-bias voltage thus obtained and each characteristic value.

As is apparent from FIG. 10, when the self-bias voltage is 0 V, the hardness is about 850 Hv, the internal stress is about 5 GPa, and the hydrogen concentration is about 60%. When the self-bias voltage is -150 V, the hardness is about 3400 Hv, the internal stress is about 8 GPa, and the hydrogen concentration is about 10%.

Therefore, in the hard carbon coating of the above embodiment in which the self-bias voltage was changed from 0 to -150 V with the progress of the coating formation, each characteristic change as shown in FIG. 10 occurred in the thickness direction. The hydrogen concentration on the substrate side is about 60%, and the hydrogen concentration on the surface side is about 10%. As described above, a magneto-optical disk having the hard carbon coating 7 as the outermost protective layer on the side opposite to the substrate 1 as shown in FIG. 1 was produced.

Embodiment 2 FIG. 2 is a sectional view showing a magneto-optical disk of another embodiment according to the present invention. In this embodiment, a hard carbon coating 7 is provided on the UV protection layer 6 with an intermediate layer 8 interposed therebetween. In this embodiment, an intermediate layer 8 made of Si and having a thickness of 50 ° was formed by a sputtering method, and a hard carbon film 7 having a thickness of 1000 ° was formed on the intermediate layer 8 in the same manner as in the first embodiment.

Embodiment 3 In this embodiment, in the magneto-optical disk structure shown in FIG. 2, an intermediate layer made of SiO ₂ and having a thickness of 50 ° is formed as the intermediate layer 8 by a sputtering method. Then, a hard carbon film 7 having a thickness of 1000 ° was formed in the same manner as in Example 1 above.

COMPARATIVE EXAMPLE 1 As a comparison, the self-bias voltage was set to -150 V during film formation.
A hard carbon film was formed in the same manner as in Example 1 except for the above, and a comparative magneto-optical disk having a hard carbon film 7 on a UV protective layer 6 as shown in FIG. 1 was produced.

Comparative Example 2 As a comparison, a hard carbon film was formed in the same manner as in Example 1 except that the self-bias voltage was kept constant at 0 V during film formation, and the UV protective layer 6 as shown in FIG. A comparative magneto-optical disk having a hard carbon film 7 on the disk was prepared.

The hard carbon coatings of Examples 1 to 3 and Comparative Examples 1 and 2 obtained as described above were subjected to an adhesion evaluation test. The evaluation of the adhesion was performed by an indentation test with a constant load (load = 1 kg) using a Vickers indenter. The number of samples was set to 50, and the number of the hard carbon coatings where peeling occurred was counted and evaluated. Table 1 shows the evaluation results.

[0034]

[Table 1]

As is evident from Table 1, the hard carbon coatings of Examples 1 to 3 according to the present invention have a significantly reduced number of peelings than the hard carbon coating of Comparative Example 1.
Therefore, according to the present invention, a protective layer made of a hard carbon film having excellent adhesion can be obtained.

Next, the hardness of the hard carbon coatings of Examples 1 to 3 and Comparative Examples 1 and 2 were measured, and the results are shown in Table 2.

[0037]

[Table 2]

As is clear from Table 2, the hard carbon coatings of Examples 1 to 3 according to the present invention have the same high hardness as Comparative Example 1. As shown in Table 1 above, the hard carbon coating of Comparative Example 2 has a small number of occurrences of peeling and is excellent in adhesion, but has a very low film hardness.

Next, the abrasion resistance of the hard carbon coatings of Examples 1 to 3 and Comparative Examples 1 and 2 was evaluated by a general method, and the results are shown in Table 3. Wear resistance is 3m in diameter
m alumina ball as indenter, load 200g
The sliding speed was 660 mm / min, the sliding distance was 5 mm, and the number of times of sliding was 2,000.

[0040]

[Table 3]

As is apparent from Table 3, the hard carbon coatings of Examples 1 to 3 according to the present invention have the same abrasion resistance as Comparative Example 1. Further, it can be seen that the hard carbon coating of Comparative Example 2 was inferior in abrasion resistance as well as the film hardness.

As a result, a magneto-optical disk having a hard carbon film according to the present invention as a protective layer has excellent adhesion to the protective layer, a sufficiently high surface film hardness, and excellent wear resistance. It can be.

In the embodiment shown in FIGS. 1 and 2, the hard carbon coating 7 is applied directly on the UV protection layer 6 or on the intermediate layer 8.
Is provided via By providing the hard carbon film 7 having excellent wear resistance as a protective layer as described above, wear due to contact with a magnetic head or the like can be reduced.

FIG. 3 is a schematic diagram showing the positional relationship between the magneto-optical disk of the present invention and the magnetic head. As shown in FIG. 3, a protective layer 22 made of a hard carbon coating is provided on the uppermost surface of the magneto-optical disk 21. The magnetic head 23 is located above such a protective layer 22, and applies a magnetic field when recording information. Here, a protective layer 24 is also provided on the surface of the magnetic head 23. Such a protective layer 24 may be formed from a hard carbon film in which the hydrogen concentration changes in the thickness direction as in the present invention. in this case,
It is preferable that the hydrogen concentration be lower toward the surface. As shown in FIG.
Comes close to the magneto-optical disk 21, and the magnetic head 23 moves relatively on the magneto-optical disk 21, so that the surface of the magneto-optical disk 21 is worn by contact with the magnetic head 23. According to the present invention, the surface of the protective layer 22 has a relatively low hydrogen concentration, a high hardness, and a composition having excellent wear resistance, so that good wear resistance can be exhibited. Further, since the protective layer 22 has a composition in which the hydrogen concentration is relatively high and the internal stress is low on the substrate side, the adhesion is good, the peeling can be prevented, and the substrate is warped or deformed. Can be prevented.

In the embodiment shown in FIGS. 1 and 2, a hard carbon coating 7 is provided on the UV protection layer 6. The hard carbon coating 7 is excellent in abrasion resistance as described above, but is generally formed with a small thickness. Therefore, when a large scratch such as a scratch is generated, the hard carbon coating 7 is not shown in FIGS. The UV protection layer 6 is provided as described above, and this UV protection layer can prevent such a large scratch from reaching the inside.

FIG. 4 is a sectional view showing still another embodiment according to the present invention. In this embodiment, a protective layer made of the hard carbon coating 9 is also provided on the substrate 1 side. The hard carbon coating 9 also has a gradient structure of hydrogen concentration in the film thickness direction, and the hydrogen concentration on the substrate 1 side is high and the hydrogen concentration on the surface side is low. Accordingly, the surface has a composition having high hardness and excellent wear resistance, and the substrate side has a composition having low internal stress and good adhesion. By forming such a hard carbon coating 9, the hardness of the outermost surface on the substrate 1 side can be increased, the wear resistance can be improved, and corrosion resistance such as humidity resistance can be improved. In particular, if the substrate 1 is P
When formed from a plastic substrate such as C,
Such improvement in corrosion resistance is required.

FIG. 5 is a sectional view showing a magneto-optical disk according to still another embodiment of the present invention. In the present embodiment, the hard carbon coating 9 on the substrate 1 side is provided via the intermediate layer 10. The intermediate layer 10 can be formed with the same composition and thickness range as the intermediate layer 8. Such an intermediate layer 10
Is formed, the adhesion to the substrate 1 can be further improved, and deformation such as warpage of the substrate 1 can be prevented.

In the embodiment shown in FIG.
The hard carbon coating 9 may be formed directly on the substrate 1 by omitting the intermediate layer 10 on the side. Similarly, the hard carbon coating 7 may be formed directly on the UV protection layer 6 by omitting the intermediate layer 8 on the surface side.

FIG. 11 shows a carbon film 121 having a gradient structure in which the hydrogen concentration changes substantially continuously in the film thickness direction, like the hard carbon film of the above embodiment. The carbon coating 121 is formed on the underlayer 120. In such a hard carbon coating 121, an inclined structure is formed such that an end portion 121a close to the base layer 120 has a relatively high hydrogen concentration and a front-side end portion 121b has a relatively low hydrogen concentration. .

FIG. 12 is a sectional view showing another example of the structure of the hard carbon film according to the present invention. The hard carbon film 122 has a two-layer structure. The first layer 122a on the side close to the underlayer 120 has a relatively high hydrogen content, and the second layer 122b on the surface side has a relatively high hydrogen content. It is formed so that the concentration becomes low. Thus, the gradient structure of the hydrogen concentration in the present invention does not necessarily have to be continuous,
It may be a stepwise graded structure composed of a multi-layer structure having more than two layers.

When a hard carbon film having a gradient structure as shown in FIG. 12 is formed, as shown in FIG. 13, a structure of two or more layers is formed by changing the self-bias voltage stepwise. be able to.

[0052]

According to the present invention, it is possible to obtain a magneto-optical recording medium which is excellent in abrasion resistance, corrosion resistance and the like, hardly causes peeling of the protective film, and hardly deforms the substrate such as warpage.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a magneto-optical disk of one embodiment according to the present invention.

FIG. 2 is a sectional view showing a magneto-optical disk of another embodiment according to the present invention.

FIG. 3 is a side view showing the positional relationship between the magneto-optical disk and the magnetic head of the embodiment according to the present invention.

FIG. 4 is a sectional view showing a magneto-optical disk according to still another embodiment according to the present invention.

FIG. 5 is a sectional view showing a magneto-optical disk according to still another embodiment according to the present invention.

FIG. 6 is a side view showing the magneto-optical disk having the protective layers on both sides shown in FIGS. 4 and 5;

FIG. 7 is a schematic configuration diagram showing one example of an ECR plasma CVD apparatus for forming a hard carbon film in the present invention.

8 is a plan view showing the vicinity of an opening of the ECR plasma CVD apparatus shown in FIG.

FIG. 9 is a diagram showing a relationship between a film forming time and a self-bias voltage in an example according to the present invention.

FIG. 10 is a diagram showing a relationship between a self-bias voltage, hardness, internal stress, and hydrogen concentration.

FIG. 11 is a cross-sectional view illustrating an example of a hard carbon film according to the present invention.

FIG. 12 is a cross-sectional view showing another example of the hard carbon film in the present invention.

FIG. 13 is a view showing the relationship between the film forming time and the self-bias voltage when forming the hard carbon film shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Dielectric layer 3 ... Recording layer 4 ... Dielectric layer 5 ... Al heat dissipation layer 6 ... UV protection layer 7 ... Hard carbon coating 8 ... Intermediate layer 9 ... Hard carbon coating 10 ... Intermediate layer

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Satoshi Sumi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-5-258369 (JP, A) (58 ) Surveyed field (Int.Cl. ⁷ , DB name) G11B 11/105

Claims (9)

(57) [Claims] 1. A magneto-optical recording medium comprising a substrate and a recording layer, wherein a hard carbon film having a gradient structure in which the hydrogen concentration changes in the film thickness direction is provided as a protective layer. . 2. The magneto-optical recording medium according to claim 1, wherein the hydrogen concentration of the hard carbon film differs by 10% or more between both ends in the film thickness direction. 3. The hydrogen concentration of the hard carbon coating is 60 to 40% at one end in the film thickness direction and 30 to 1 at the other end in the thickness direction.
3. The magneto-optical recording medium according to claim 1, wherein the content is 0%. 4. The magneto-optical recording medium according to claim 1, wherein the hard carbon film is provided with an intermediate layer interposed therebetween. 5. The method according to claim 1, wherein the intermediate layer is made of Si, Zr, Ti and Ge.
5. The magneto-optical recording medium according to claim 4, wherein the magneto-optical recording medium is formed of at least one selected from the group consisting of metals and oxides and nitrides of these metals. 6. The hard carbon coating is provided as a protective layer located on at least one of the outermost surface layer on the recording layer side and the outermost surface layer on the substrate side. 7. The magneto-optical recording medium according to claim 1. 7. The light according to claim 6, wherein the hydrogen concentration of the hard carbon coating is relatively high at an end near the substrate in the thickness direction and relatively low at an end far from the substrate. Magnetic recording medium. 8. The method according to claim 1, wherein the hard carbon coating is provided as a protective layer inside the outermost surface layer.
Item 13. A magneto-optical recording medium according to item 1. 9. The magneto-optical recording medium according to claim 8, wherein said hard carbon coating is provided as a protective layer on both sides of said recording layer.