JP2688505B2 - Magneto-optical recording medium and method of manufacturing the same - Google Patents

Description

The present invention relates to a magneto-optical recording medium and a method for manufacturing the same,
More specifically, it relates to the composition of a silicon nitride-based enhancement film (optical interference transparent film) formed on the signal surface of the substrate, and the sputtering conditions for forming the film by sputtering.

[Conventional technology]

2. Description of the Related Art In recent years, a so-called magneto-optical recording medium for reading out a signal by utilizing a magnetic Kerr effect has been attracting attention as a rewritable optical recording medium. In this magneto-optical recording medium, a signal is written by locally irradiating the surface of the magneto-optical recording layer with optical energy such as laser light and heating the portion above the Curie temperature and applying an external magnetic field. Moreover, a magnetic flux such as a laser beam having a specific polarization plane is irradiated on the surface of the magnetic material, and a change in the polarization plane of the reflected light with respect to the polarization plane of the irradiation light (hereinafter, referred to as Kerr rotation angle) is detected to give a signal. Read out.

As a magneto-optical recording medium of this type, conventionally, as shown in FIG. 8, a magneto-optical recording medium in which an enhance film 3 made of a dielectric is provided between a substrate 1 and a magneto-optical recording layer 2 has been proposed (" Easy-to-understand optical disk ", Optronics Co., Ltd., December 10, 1985, pages 93-95).

In this magneto-optical recording medium, the reproducing light incident from the substrate 1 side is repeatedly reflected at the interface between the enhancement film 3 and the magneto-optical recording layer 2 and the interface between the substrate 1 and the enhancement film 3, and the apparent Kerr rotation angle is increased. Since it can be increased, it is larger than that without an enhance film, and the signal can be read easily.

The apparent Kerr rotation angle becomes larger as the enhance film 3 having a larger refractive index is used. In addition, the dielectric material forming the enhance film 3 has excellent moisture impermeability,
Silicon nitride (Si ₃ N ₄ ) is particularly preferable because it has a high protective effect on the magneto-optical recording layer 2. From this point of view, a magneto-optical recording medium including silicon nitride as a main component and an enhancement film whose refractive index is adjusted to 2.1 or more by adding a certain element to the main component has been conventionally proposed. (JP-A-61-2
2458 publication).

[Problems to be solved by the invention]

By the way, in the magneto-optical recording medium, it is not the magnitude of the Kerr rotation angle that contributes to the reproduction output but the intensity of the reflected light. Therefore, in order to obtain good reproduction characteristics, the reflectance should be increased to some extent along with the Kerr rotation angle. Must-have.

However, as shown in FIG. 9, a larger Kerr rotation angle θk can be obtained by using the enhancement film 3 having a larger refractive index n, but on the other hand, the reflectance R decreases. The car rotation angle θk is at least 0 to facilitate signal readout.
It is required to be 55 degrees or more, preferably 0.60 degrees or more, while the reflectance R is required to be at least 22 (%) or more in order to facilitate auto-focus servo and tracking servo.
From FIG. 9, it can be seen that the refractive index of the enhance film 3 needs to be adjusted to 2.0 to 2.15 in order to obtain the suitable Kerr rotation angle θk and the reflectance R.

As described in the above-mentioned publication, the refractive index of silicon nitride (Si ₃ N ₄ ) is 1.9 to 2.1 for the bulk material. However, as a result of the experiment, oxygen is mixed in the enhanced film 3 obtained by depositing this as shown in FIG. 10, and the refractive index varies in the range of 2.0 to 2.8 depending on the condition of the sputtering. Then, it was found that it is difficult to stably form the enhance film 3 having a predetermined refractive index. In addition, the silicon nitride-based enhancement film is
It is generally said that it has excellent moisture impermeability and a high protective effect on the magneto-optical recording layer, but unless it is sputtered under appropriate conditions, the pinhole density and internal stress will increase, resulting in poor adhesion to the substrate. It turns out that

From such circumstances, the refractive index is 2.0 to 2.15, the pinhole density and internal stress are sufficiently low, and the establishment of the sputtering condition for obtaining an enhanced film having good adhesion to the substrate,
And there is a strong demand for the specification of the allowable oxygen content.

The present invention has been made in order to meet such technical requirements, and its first object is to make a Kerr rotation angle and a reflectance R
The present invention provides a magneto-optical recording medium having a good balance with the above, excellent reproducing characteristics, excellent physical properties of the enhance film, and excellent durability. A second object is to provide such a magneto-optical recording medium. To provide a suitable method for manufacturing.

[Means for solving the problem]

In order to achieve the first object, the present invention is a magneto-optical recording medium formed by sputtering a silicon nitride-based enhance film on a signal surface of a substrate, and the enhance film is represented by the following composition formula. It has a composition and a refractive index of 2.
With one adjusted to 0-2.15.

SixNyOz where A <x <49 A is the value of x satisfying 10x + y = 487 37 <y <570 <z <18 Units are atomic%.

In order to achieve the second object, in a method of manufacturing a magneto-optical recording medium including a step of forming a silicon nitride-based enhancement film on a signal surface of a substrate by sputtering, when the enhancement film is formed by sputtering, Argon gas mixed with 10 (% by volume) to 30 (% by volume) of nitrogen gas is supplied into the vacuum chamber evacuated to a high degree of vacuum, and the gas pressure in the vacuum chamber is set to 0.1 to 0.5 (Pa). Adjust the electrode to 4.0-12.0 (W / cm ² )
Was applied to form an enhanced film having a refractive index of 2.0 to 2.15 and a pinhole density of 0 to 270 (pieces / cm ² ). The third element is not added as a means of adjusting the refractive index of the enhancement film.

[Action]

As a matter of course, the lower the bit error rate of the magneto-optical recording medium, the more preferable it is, but it is practical if the bit error rate after the life test is 10 ⁻⁵ or less. In order to obtain such a magneto-optical recording medium, the density of pinholes formed in the enhancement film must be 270 (pieces / cm ² ) or less. This pinhole density is closely related to the gas pressure in the vacuum chamber, and unless the gas pressure is adjusted to 0.5 (Pa) or less, the above-mentioned enhanced film cannot be obtained.

Further, when the internal stress of the enhance film is high, the unevenness of the film surface becomes large, the amount of reflected light returning from the film surface to the objective lens decreases, and peeling from the substrate easily occurs. Forming is also important in obtaining a magneto-optical recording medium excellent in reproduction characteristics and durability.

As a means for forming an enhanced film with a low internal stress, pure argon is used as a spatula gas, and the gas pressure in the vacuum chamber can be adjusted to a high pressure of 0.6 (Pa) or higher. Then, as described above, the pinhole density becomes high and the bit error rate of the magneto-optical recording medium becomes high, so that it cannot be adopted. On the other hand, nitrogen gas is added to argon gas at 10 (volume%) to 30%.
When mixed (volume%), the gas pressure in the vacuum chamber is 0.2 (Pa)
The internal stress can be reduced to the value below, and the internal stress can be reduced to almost the same value as when pure argon gas is used.

Furthermore, the effect of the gas pressure when depositing the enhancer film on the adhesion between the substrate and the enhancer film is significant, and the enhancer film formed under the gas pressure condition of 0.6 (Pa) or higher has high temperature and high humidity. Easy to peel off underneath.

On the other hand, in order to obtain an enhanced film having a refractive index of 2.0 to 2.15, when using argon gas mixed with nitrogen gas at 10 (volume%) to 30 (volume%), the gas pressure is 0.1 (Pa).
It must be adjusted to ~ 1.0 (Pa).

Similarly, in order to obtain an enhanced film having a refractive index of 2.0 to 2.15, when argon gas mixed with nitrogen gas of 10 (volume%) to 30 (volume%) is used, the power applied to the electrode is 2.0 to It must be adjusted to 12.0 (W / cm ² ).

Therefore, by performing the above operation under the spatter condition, it is possible to provide a magneto-optical recording medium having excellent reproduction characteristics and excellent durability.

〔Example〕

The method of manufacturing the magneto-optical recording medium according to the present invention will be described below. It should be noted that a method of manufacturing a magneto-optical recording medium other than a method of forming an enhance film, that is, a method for manufacturing a substrate, a method for forming a recording layer, a method for forming a protective layer, a method for laminating recording single plates, etc. are conventionally known. Since the method described above can be applied as it is, the description thereof will be omitted.

FIG. 7 is a diagram showing an example of a sputtering device applied to the implementation of the present invention, which is a vacuum chamber 11, a diffusion pump 12, a mechanical pump 13, an argon gas cylinder 14, a nitrogen gas cylinder 15, and a power supply 16. It is mainly composed of and. In the vacuum chamber 11, the targets 17 and 17a connected to the power source 16 are connected.
And a counter electrode 18 that is grounded are arranged to face each other, and a substrate 19 on which a predetermined signal pattern is formed in advance is attached to the counter electrode 18. The substrate 19 is attached to the counter electrode 18 with a signal pattern directed to the targets 17 and 17a.

Valves 22 and 23 are set in the pipes 20 and 21 connecting the diffusion pump 12 and the mechanical pump 13 to the vacuum chamber 11, respectively, to prevent air from entering the vacuum chamber 11 from the pipes 20 and 21. ing. Further, pressure valves 26 and 27 that operate by the differential pressure between the argon gas cylinder 14 and the nitrogen gas cylinder 15 and the vacuum tank 11 are set in the pipelines 24 and 25 that connect the argon gas cylinder 14 and the nitrogen gas cylinder 15 to the vacuum tank 11, respectively. When the degree of vacuum in the vacuum layer 11 reaches a predetermined value, the argon gas cylinder 14 and the nitrogen gas cylinder are
Argon gas and nitrogen gas corresponding to the above-mentioned differential pressure are automatically supplied from the 15 into the vacuum chamber 11.

In forming the enhance film, first, the diffusion pump 12 and the mechanical pump 13 are driven to discharge the air in the vacuum chamber 11. Vacuum chamber to obtain high-purity enhanced film
Unless preferably Write evacuated to a high vacuum degree as possible in 11, it is evacuated to a high vacuum degree than at least 10 ^-4 (Pa).

Next, the pressure valves 26 and 27 are opened and the argon gas cylinder 14 is opened.
Argon gas and nitrogen gas are introduced into the vacuum chamber 11 from the nitrogen gas cylinder 15 and the gas pressure in the vacuum chamber 11 is 0.1 to
Adjust to 0.5 (Pa). At this time, the introduction amount of nitrogen gas with respect to the introduction amount of argon gas is adjusted to 10 (volume%) to 30 (volume%).

When the gas pressure in the vacuum chamber 11 becomes stable, the power supply 16 is driven, and the switch 28 causes the target 17 to reach 2.0 to 12.0 (W / c).
Turn on the power of m ² ).

When an enhancement film having a predetermined thickness (usually about 900 to 1000 angstroms) is formed on the substrate 19, the power supply 16 is stopped and the vacuum is again evacuated to a high vacuum of 10 ⁻⁴ (Pa) or less. After that, a magneto-optical recording layer is laminated on the enhance film using the target 17a to obtain a magneto-optical recording medium similar to that shown in FIG.

In the present invention, the target 17 is made of silicon or silicon nitride, and no special additive element for adjusting the refractive index of the enhance film is added. A magneto-optical recording material such as TbFeCo is used for the target 17a.

FIG. 1 shows the relationship between the gas pressure in the vacuum chamber 11 and the density of pinholes generated in the enhancement film, and the relationship between the gas pressure in the vacuum chamber 11 and the bit error rate of the magneto-optical recording medium. As is clear from this figure, as the gas pressure in the vacuum chamber 11 is increased, the density of pinholes formed in the enhancement film and the bit error rate of the magneto-optical recording medium increase. In practice, the bit error rate of the magneto-optical recording medium is required to be 10 ^-5 or less even after the life test.
It turns out that it is necessary to adjust it to 0.5 (Pa) or less.

FIG. 2 shows the relationship between the gas pressure and the internal stress of the enhancement film when pure argon gas is introduced into the vacuum chamber 11.
As is clear from this figure, when pure argon gas is introduced into the vacuum chamber 11, the internal stress can be reduced as the gas pressure is increased, and the gas pressure is 0.6 (Pa) or higher. The internal stress is adjusted to about 3 × 10 ⁹ (d
yn / cm ² ) or less.

FIG. 3 shows the relationship between the gas pressure when the mixed gas of argon gas and nitrogen gas is introduced into the vacuum chamber 11, the nitrogen gas mixing ratio, and the internal stress of the enhancement film. As is clear from this figure, when a mixed gas of argon gas and nitrogen gas is introduced into the vacuum chamber 11, the internal stress of the enhance film is reduced to about 3 × 10 ⁹ under a low gas pressure of about 0.2 (Pa). (Dyn / cm ² ) or less. Even if the mixing ratio of nitrogen gas to argon gas is changed in the range of 10 (volume%) to 30 (volume%), the internal stress hardly changes.

The following table shows the relationship between the gas pressure in the vacuum chamber 11 and the adhesion of the enhance film to the substrate 19 when forming the enhance film. The quality of the adhesion is determined by checking the substrate on which the enhanced film is formed.
It was placed in a high temperature and high humidity environment of 60 ° C. × 90% RH, and it was judged whether or not peeling occurred after 1000 hours. In the table, ◯ indicates that peeling did not occur, Δ indicates that peeling occurred in part, and x indicates that peeling occurred over the entire surface.

As is clear from this data, also from the viewpoint of the adhesion between the substrate and the enhancement film, it is understood that the gas pressure when depositing the enhancement film into the sputtering film must be 0.5 (Pa) or less.

FIG. 4 shows changes in the refractive index of the enhancement film when the mixing ratio of the nitrogen gas mixed in the argon gas and the gas pressure thereof are changed. As is clear from this figure, when the gas pressure is adjusted within the range of 0.1 (Pa) to 1.0 (Pa), 2.
An enhancement film having a refractive index of 0 to 2.15 can be formed. However, if the gas pressure is less than 0.1 (Pa),
Discharge cannot be continued stably, and stable film formation cannot be performed. Therefore, it is understood that the gas pressure in the vacuum chamber 11 when forming the enhancement film must be adjusted to 0.1 (Pa) or more.

As the gas pressure in the vacuum chamber 11 becomes higher, the change in the refractive index of the enhance film with respect to the mixing ratio of the nitrogen gas becomes abrupt, and it becomes difficult to control the mixing ratio of the nitrogen gas. If the gas pressure is set as low as possible, the enhancement film can be formed easily.

FIG. 5 shows changes in the refractive index of the enhancement film when the mixing ratio of the nitrogen gas mixed in the argon gas and the power applied from the power source 16 to the counter electrode 18 are changed. As is clear from this figure, the power is 2.0 (W / cm ² ) to 12.0 (W / cm 2
^When adjusted within the range of ² ), an enhancement film having a refractive index of 2.0 to 2.15 can be formed. As the applied power decreases, the change in the refractive index of the enhance film with respect to the mixing ratio of nitrogen gas becomes sharp, and it becomes difficult to control the mixing ratio of nitrogen gas.Therefore, it is better to set the applied power as large as possible. The enhancement film is easily formed. On the other hand, when the power exceeds 12.0 (W / cm ² ), the target surface temperature in the spatula may exceed the limit and the target may crack.

Therefore, it is understood that the power applied to the target 17 when forming the enhanced film must be adjusted within the range of 2.0 (W / cm ² ) to 12.0 (W / cm ² ).

From the above facts, it is possible to provide a magneto-optical recording medium having excellent reproducing characteristics and excellent durability by setting the spatter condition above.

FIG. 6 shows the composition and the refractive index of the enhance film formed under the sputtering condition given in the above-mentioned embodiment. In this figure, the region surrounded by a thick line is the composition and the refractive index of the enhance film formed under the sputtering condition given in the above-mentioned embodiment. The composition of the enhance film is expressed by the following formula.

SixNyOz where A <x <49 A is the value of x satisfying 10x + y = 487 37 <y <570 <z <18 Units are atomic%.

In the above-mentioned embodiment, the case where a thin film layer having a two-layer structure composed of the enhancement film and the magneto-optical recording film is formed on the signal surface of the substrate has been described, but it is not necessary to add another thin film to this thin film layer. It can be appropriately performed as needed.

For example, a dielectric layer such as silicon nitride or a metal layer may be provided on the magneto-optical recording film to form a three-layer structure to improve the durability of the medium. Further, a dielectric layer such as silicon nitride and a metal layer may be sequentially laminated on the magneto-optical recording film to form a four-layer structure to improve the recording characteristics and durability of the medium.

〔The invention's effect〕

As described above, according to the present invention, the sputtering condition and the allowable oxygen mixing ratio when the sputtering film of the silicon nitride-based enhancement film is formed are specified, and the refractive index is 2.0 to 2.15.
Thus, it is possible to form an enhanced film having sufficiently low pinhole density and internal stress and good adhesion to the substrate. Moreover, since no element for adjusting the physical properties of the enhancement film is added, a uniform enhancement film can be formed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the relationship between the gas pressure in the vacuum chamber, the density of pinholes generated in the enhancement film, and the bit error rate of the magneto-optical recording medium. FIG. 2 shows the introduction of pure Arun gas into the vacuum chamber. FIG. 3 is an explanatory view showing the relationship between the gas pressure and the internal stress of the enhancement film, and FIG. 3 is the gas pressure when the mixed gas of the argon gas and the nitrogen gas in the vacuum chamber is introduced, the nitrogen gas mixing ratio, and the enhancement film. 4 is an explanatory view showing the relationship with the internal stress of FIG. 4, and FIG. 4 is an explanatory view showing the change in the refractive index of the enhance film when the mixing ratio of the nitrogen gas mixed in the argon gas and its gas pressure are changed. FIG. 5 is an explanatory diagram showing changes in the refractive index of the enhance film when the mixing ratio of the nitrogen gas mixed in the argon gas and the electric power applied to the counter electrode are changed, and FIG. Enha formed by the manufacturing method And FIG. 7 is a sectional view showing an example of a sputtering device applied to the practice of the present invention, and FIG. 8 is a sectional view of a conventionally known magneto-optical recording medium. 9 and 10 are explanatory views showing the relationship between the refractive index of the enhancement film and the Kerr rotation angle and reflectance of the magneto-optical recording medium, and FIG. 10 is the composition and refractive index of the enhancement film formed by the conventional method. It is explanatory drawing which shows and. 1: substrate, 2: magneto-optical recording layer, 3: enhance film, 11: vacuum chamber, 12, 13: pump, 14: argon gas cylinder, 15: nitrogen gas cylinder, 16: power supply, 17: target, 19: substrate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-275340 (JP, A) JP 63-76860 (JP, A) JP 1-91337 (JP, A)

Claims (2)

(57) [Claims] 1. A magneto-optical recording medium comprising a silicon nitride enhance film formed by sputtering on a signal surface of a substrate,
A magneto-optical recording medium comprising the enhance film having a composition represented by the following composition formula and having a refractive index adjusted to 2.0 to 2.15. SixNyOz where A <x <49 A is the value of x satisfying 10x + y = 487 37 <y <570 <z <18 Units are atomic%. 2. A method of manufacturing a magneto-optical recording medium, which comprises a step of forming a silicon nitride-based enhancement film on a signal surface of a substrate by sputtering. When the enhancement film is formed by sputtering, a vacuum is pulled to a high degree of vacuum. 10 (vol%) in the vacuum chamber
Argon gas mixed with ~ 30 (vol%) nitrogen gas is supplied to adjust the gas pressure in the vacuum chamber to 0.1 ~ 0.5 (Pa),
Applying power of 4.0 to 12.0 (W / cm ² ) to the electrode, the refractive index
A method for manufacturing a magneto-optical recording medium, which comprises forming an enhancement film having a pinhole density of 2.0 to 2.15 and a pinhole density of 0 to 270 (pieces / cm ² ).