JPH02108253A - Magneto-optical recording medium and production thereof - Google Patents

Abstract

PURPOSE:To improve reproduction characteristics and durability by specifically adjusting the compsn. of an enhancement film of a silicon nitride to be formed on the signal surface of a substrate. CONSTITUTION:Gaseous argon mixed with 10 to 30(vol.%) gaseous nitrogen is supplied from a gaseous argon cylinder 14 and a gaseous nitrogen cylinder 15 into a vacuum vessel 11 evacuated to a high vacuum degree and the gaseous pressure in the vacuum vessel 11 is regulated to 0.1 to 0.5(Pa). A power source 16 is driven in the stable state of the gaseous pressure in the vacuum vessel 11 to supply 2.0 to 12.0(W/cm<2>) electric power to a target 17 for which silicon or silicon nitride is used. The power source 16 is stopped when the enhancement film expressed by formula is formed on the signal surface of the substrate 19. In formula, R<x<49, 37<y<57; R is the value satisfying 10x+y=487 and the unit is atomic%. The reproducing characteristics and the durability are thus improved.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a magneto-optical recording medium and a method for manufacturing the same, and more particularly relates to a silicon nitride-based enhancement film (optical interference transparent film) formed on the signal surface of a substrate. ) and the sputtering conditions for sputtering the film.

[Conventional technology]

In recent years, so-called magneto-optical recording media that read signals using the magnetic Kerr effect have attracted attention as rewritable optical recording media. In this magneto-optical recording medium, signals are written by locally irradiating the surface of the magneto-optical recording layer with optical energy such as a laser beam, heating the area above the Curie temperature, and applying an external magnetic field. In addition, the surface of a magnetic material is irradiated with a light beam having a specific polarization plane, such as a laser beam, and the polarization plane of the reflected light changes with respect to the polarization plane of the irradiated light (hereinafter referred to as
Detecting the Kerr rotation angle 9) and reading the signal, this type of magneto-optical recording medium is used. 1-1 Conventionally, as shown in FIG. It is proposed that an enhancement film 3 made of a dielectric material be provided on the substrate. lO
[1 issue, pp. 93-95).

In the magneto-optical recording medium of , =, the reproducing light 1'' enters from the substrate I side and recedes at the 71 plane between the enhancement film 3 and the magneto-optical recording layer and at the interface between the group Fi,1 and the enhancement film 3. Since it is reflected and the apparent Kerr rotation angle of 15F can be increased, the signal can be read out more easily compared to a device without an enhancement film.

The Kerr rotation angle, which is multiplied by 1, becomes larger as the enhancement film 3 with a larger refractive index is used. Silicon nitride (SiaN4) is particularly suitable because it has a high protective effect for the magnetic recording layer 2. From this point of view, silicon nitride is the main component, and certain elements are added to it. (adjusted to 2゜l or more) 1, l-
Equipped with an enhanced membrane!・-Magneto-optical recording media were conventionally l
, the frame design is -'5 (Japanese Unexamined Patent Publication No. 61-22458) 1. [Problem to be solved by the invention] By the way, the magneto-optical recording medium LT contributes to the playback output 4
It is not the magnitude of Kerr's rotation angle but the intensity of the reflected light that is affected, so in order to obtain good reproduction characteristics, 13-rotation angle, j is reflectance + J, and 46 is approximately equal to must not.

However, as shown in FIG. 9, an approximately large Kerr rotation angle oh t;, - can be obtained by using 71(t, /i11 refractive index n is dog Mn hannos I]%3, but on the other hand, 1 reflectance R is low F1''.The Kerr rotation angle θ should be at least 0.55 degrees or more, preferably 0.
o 60 degrees or more is required, and on the other hand, the reflectance R is o I-
In order to facilitate focus servo and 1-racking servo, at least 22 (%) or more is required. From FIG. 9, it can be seen that in order to obtain a suitable Kerr rotation angle Ok and reflection -4t, R, it is necessary to adjust the refractive index of the enhancement film 3 to 2.0 to 2°15.

As stated in the above-mentioned publication, the refractive index of silicon nitride (Si3N-) is 1.9 to 1.9 in the case of a bulk material.
・It is 2.1. However, as a result of experiments, the enhancement film 3 obtained by sputtering this film contains oxygen as shown in Figure 1O, and depending on the sputtering conditions, the refractive index is in the range of 2.0 to 2.8. It has been found that it is difficult to stably form the enhancement film 3 having a predetermined refractive index. Silicon nitride-based enhancement films generally have excellent moisture impermeability and are said to be highly effective in protecting the magneto-optical recording layer, but unless sputtered under appropriate conditions, pinhole density and internal stress may occur. It has been found that the adhesiveness with the substrate becomes worse.

Under these circumstances, it was necessary to establish sputtering conditions to obtain an enhanced film with a refractive index of 2.0 to 2.15, sufficiently low pinhole density and internal stress, and good adhesion to the substrate, and to establish acceptable oxygen It is hoped that the suspects will be identified as being mixed up and imprisoned.

The present invention has been made to meet such technical demands, and its first purpose is to have a good balance between Kerr rotation angle and reflectance R, excellent reproduction characteristics, and to improve the physical properties of the enhancement film. Another object of the present invention is to provide a magneto-optical recording medium with good properties and excellent durability, and a second object is to provide a method suitable for manufacturing such a magneto-optical recording medium.

[Failure to solve the problem]

In order to achieve the first object of the present invention, the composition of the enhancement film is adjusted as shown in the following formula.

S i x N y Ozoo-(x-+y) However, R
<x<49 37<y<57 R satisfies lOx+y=487, and the value unit is atomic %.

In addition, in order to achieve the second objective, when forming a silicon nitride-based enhancement film by sputtering, 10 (vol%) to 30 (vol%)
The gas pressure in the vacuum chamber was adjusted to 0.1 to 0.5 (Pa) by supplying argon gas mixed with nitrogen gas, and the pressure was 2.0 to 12.0 (W/cm") to the electrode. A third element was not added as a means of adjusting the refractive index of the enhancement film.

[Effect]

It goes without saying that the lower the pit error rate of the magneto-optical recording medium is, the more preferable it is, but it is practical if the pit 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 generated in the enhancement film must be 270 (pieces/cm').
It must be as follows.

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, it is not possible to obtain the above enhanced film.

Furthermore, if the internal stress of the enhancement film is high, the unevenness of the film surface becomes large and the amount of reflected light returning from the film surface to the objective lens decreases, and it becomes easy to peel off from the substrate.
Forming an enhancement film with low internal stress is also important in obtaining a magneto-optical recording medium with excellent reproduction characteristics and durability.

As a means of forming an enhanced film with low internal stress,
It is also possible to use pure argon as the sputtering gas and adjust the gas pressure in the vacuum chamber to a high pressure of 0.6 (Pa) or higher, but this increases the pinhole density as described above. This method cannot be used because the pit error rate of the magneto-optical recording medium becomes high.

In contrast, add nitrogen gas to argon gas at 10% (volume%).
When ~30 (volume %) is mixed, the gas pressure in the vacuum chamber is reduced to 0.
2 (Pa) or less, and the internal stress can be reduced to a value almost equivalent to that when pure argon gas is used.

Furthermore, the influence of the gas pressure during sputtering of the enhancement film on the adhesion between the substrate and the enhancement film is significant, and the enhancement film formed under gas pressure conditions of 0.6 (Pa) or higher is Easy to peel off under high humidity.

On the other hand, in order to obtain an enhanced film with a refractive index of 2.0 to 2.15, nitrogen gas must be added in an amount of 10 (vol%) to 30 (vol%).
When using mixed argon gas, reduce the gas pressure to 0.
．． 1 (Pa) ~1. It must be adjusted to O (Pa).

Similarly, in order to obtain an enhanced film with a refractive index of 2.0 to 2.15, the amount of nitrogen gas is 10 (vol.%) to 30 (vol.%).
) When using mixed argon gas, the power applied to the electrodes must be adjusted to 2.0 to 12.0 (W/cm'').

Therefore, by setting the sputtering conditions as described above, it is possible to provide a magneto-optical recording medium with excellent reproduction characteristics and excellent durability.

〔Example〕

Hereinafter, a method for manufacturing a magneto-optical recording medium according to the present invention will be explained. It should be noted that methods of manufacturing magneto-optical recording media other than the method of forming the enhancement film, that is, methods of manufacturing the substrate, methods of forming the recording layer, methods of forming the protective layer, methods of bonding recording single plates, etc., have been known for a long time. Since the method described above can be applied as is, the explanation will be omitted.

FIG. 7 is a diagram showing an example of a sputtering apparatus applied to the implementation of the present invention, which includes a vacuum chamber 11, a diffusion pump 12,
A mechanical pump 13, an argon gas cylinder 14,
It mainly consists of a nitrogen gas cylinder 15 and a tt source 16. In the vacuum chamber 11, targets 17 and 17a connected to a power source 16 and a grounded counter electrode 18 are arranged facing each other, and a substrate 19 on which a predetermined signal pattern is formed in advance on the counter electrode 18 is arranged. is installed. The substrate 19 connects the signal pattern to the target 1.
6 attached to the counter electrode 18 toward 7 and 17a; the diffusion pump 12 and the mechanical pump 13; and the vacuum chamber 1.
Valves 22 and 23 are respectively installed in the pipes 20 and 21 connecting the pipes 1 and 1 to prevent air from entering the vacuum chamber 11 from the pipes 20 and 21. In addition, argon gas cylinders 1 are installed in pipes 24 and 25 connecting the argon gas cylinders 14 and nitrogen gas cylinders 15 to the vacuum chamber 11, respectively.
4 and pressure valves 26 and 27 which are operated by the differential pressure between the nitrogen gas cylinder 15 and the vacuum chamber 11 are set, and when the degree of vacuum in the vacuum layer 11 reaches a predetermined value, the argon gas cylinder 14 and the Argon gas and nitrogen gas according to the differential pressure are automatically supplied from the nitrogen gas cylinder 15 into the vacuum chamber 11.

In forming the enhancement film, first, the diffusion pump 12 and the mechanical pump 13 are driven to exhaust the air in the vacuum chamber 11. In order to obtain a highly pure enhanced film, it is preferable to evacuate the inside of the vacuum chamber 11 to a degree of vacuum as high as possible, and the vacuum is preferably evacuated to a degree of vacuum higher than at least 1O-4 (Pa).

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

When the gas pressure in the vacuum chamber 11 is stabilized, the power supply 16 is activated and the switch 28 is activated to apply 2.0 to 100 liters to the target 17.
2. 0 (W/cm") of power is applied.

When the enhancement film of a predetermined thickness (usually about 900 to 1000 angstroms) is formed on the substrate 19, the power supply 1 is turned on.
6 is stopped, and the vacuum is again evacuated to a high vacuum of 10 −' (Pa) or less. Thereafter, a magneto-optical recording layer is laminated on the enhancement film using a target 17a to obtain a magneto-optical recording medium similar to that shown in FIG.

Note that in the present invention, silicon or silicon nitride is used for the target 17, and no special additive element for adjusting the refractive index of the enhancement film is added. Furthermore, 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 pit error rate of the magneto-optical recording medium. As is clear from this figure, as the gas pressure in the vacuum chamber 11 increases, the density of pinholes generated in the enhancement film and the pit error rate of the magneto-optical recording medium increase. In practice, the pit error rate of magneto-optical recording media is required to be 10-5 or less even after a life test, so from this figure, the gas pressure in the vacuum chamber 1 is set to 0.5 (Pa) or less. It turns out that it is necessary to adjust.

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 reduced to 0.6 (P
a) By adjusting the pressure to a higher level, the internal stress can be reduced by approximately 3
×log (dyn/cm2) or less.

FIG. 3 shows the relationship between the gas pressure, the nitrogen gas mixture ratio, and the internal stress of the enhancement film when a mixed gas of argon gas and nitrogen gas is introduced into the vacuum chamber 11. 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 enhancement film is reduced by about 3X under a low gas pressure of about 0.2 (Pa). 10'
(dyn/cm2) or less. The mixing ratio of nitrogen gas to argon gas is 10 (vol%) ~
Even if the internal stress is varied within a range of 30 (volume %), the internal stress hardly changes.

The table below shows the relationship between the gas pressure in the vacuum chamber 11 and the adhesion of the enhancement film to the substrate 19 when forming the enhancement film. Adhesion was determined by placing the substrate on which the enhancement film was formed in a high temperature and high humidity environment of 60°C x 90% RH.
Judgment was made based on whether or not peeling occurred after 0 hours.

In the table, the mark 0 indicates that no peeling occurred, the mark Δ indicates that peeling occurred in a part, and the mark X indicates that peeling occurred over the entire surface.

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

FIG. 4 shows changes in the refractive index of the enhancement film when the mixing ratio of nitrogen gas mixed into argon gas and the gas pressure are changed. As is clear from this figure, when the gas pressure is adjusted to a range of O,l (Pa) to 1.0 (Pa), an enhancement film with a refractive index of 2.0 to 2.15 can be formed. It can be membraned. However, when the gas pressure is reduced to 0
．． If the pressure is less than 1 (Pa), stable discharge cannot be continued and stable film formation cannot be performed. Therefore.

The gas pressure inside the vacuum chamber 11 when forming the enhancement film is 0.
．． It turns out that it is necessary to adjust it to 1 (Pa) or more.

Note that as the gas pressure in vacuum chamber 1 increases, the change in the refractive index of the enhancement film with respect to the nitrogen gas mixture ratio becomes more rapid, making it difficult to control the nitrogen gas mixture ratio. Setting the pressure as low as possible makes it easier to form the enhancement film.

FIG. 5 shows changes in the refractive index of the enhancement film when the mixing ratio of nitrogen gas mixed into argon gas and the electric power applied to the counter electrode 18 from the power source 16 are changed. As is clear from this figure, the power is 2.0 (W/cm”
) to 12.0 (W/cm2), an enhancement film having a refractive index of 2.0 to 2.15 can be formed. Note that as the applied power decreases, the change in the refractive index of the enhancement film with respect to the mixing ratio of nitrogen gas becomes more rapid, making it difficult to control the mixing ratio of nitrogen gas. Therefore, it is better to set the applied power as high as possible to improve the film formation becomes easier. On the other hand, the power is 12
．． If it exceeds 0 (W/cm"), the target surface temperature during sputtering may exceed the limit and the target may crack.

Therefore, the power applied to the target 17 when forming the enhancement film is 2.0 (W/cm2) to 12.0 (W/cm2). O(
It can be seen that the adjustment must be made within the range of W/cm").

From the above facts, by setting the sputtering conditions as described above, it is possible to provide a magneto-optical recording medium with excellent reproduction characteristics and excellent durability.

FIG. 6 shows the composition and refractive index of the enhancement film formed under the sputtering conditions listed in the above example. In this figure, the region surrounded by thick lines is the composition and refractive index of the enhancement film formed under the sputtering conditions listed in the above example. The composition of the enhancement film is expressed as follows.

S i x N y O1oo-<x + V) However,
R<x<49 37<y<57 The short unit of R satisfies 10x+Y=487 is atomic %.

In the above embodiment, a case was explained in which a two-layer thin film layer consisting of an enhancement film and a magneto-optical recording film was formed on the signal surface of the substrate, but it is not possible to add another thin film to this thin film layer. This can be done 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 successively laminated on the magneto-optical recording film to form a four-layer structure to improve the recording characteristics and durability of the medium.

〔Effect of the invention〕

As explained above, according to the present invention, the sputtering conditions and allowable oxygen mixing rate when forming a silicon nitride-based enhancement film by sputtering are specified, and the refractive index is 2.0 to 2.1.
In step 5, an enhanced film having sufficiently low pinhole density and internal stress and good adhesion to the substrate can be formed. Furthermore, since no element is added to adjust the physical properties of the enhancement film, a homogeneous enhancement film can be formed.

[Brief explanation of the drawing]

Figure 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 pit error rate of the magneto-optical recording medium. An explanatory diagram showing the relationship between the gas pressure when introduced and the internal stress of the enhancement film. Figure 3 shows the relationship between the gas pressure, nitrogen gas mixture ratio, and enhancement when a mixed gas of argon gas and nitrogen gas is introduced into the vacuum chamber. An explanatory diagram showing the relationship with the internal stress of the film. Figure 4 is an explanatory diagram showing the change in the refractive index of the enhancement film when the mixing ratio of nitrogen gas mixed in argon gas and the gas pressure are changed. , FIG. 5 is an explanatory diagram showing changes in the refractive index of the enhancement film when the mixing ratio of nitrogen gas mixed in argon gas and the electric power applied to the counter electrode are changed, and FIG. FIG. 7 is a cross-sectional view showing an example of a sputtering apparatus applied to the implementation of the present invention, and FIG. 8 is a conventionally known 9 is an explanatory diagram showing the relationship between the refractive index of the enhancement film and the Kerr rotation angle and reflectance of the magneto-optical recording medium. FIG. 1O is a cross-sectional view of the enhancement film formed by the conventional method. FIG. 2 is an explanatory diagram showing the composition and refractive index of . ■=Substrate, 2: Magneto-optical recording layer, 3: Enhancement film, 11
: Vacuum chamber, 12, 13: Pump, 14: Argon gas cylinder, I5: Nitrogen gas cylinder. 16: power supply, 17: target, 19: board. Gonfuho 2 Kei C (lΔ Aburi 5 Mi 6 N L&I
7 Fig. 8 Fig. 7.9 2.0 2.1 2.2 Continuation of the following 1) Ordinary placement (method) % type % Magneto-optical recording medium and its manufacturing method 1st case relationship

Claims (2)

[Claims] (1) A magneto-optical recording medium comprising a silicon nitride-based enhancement film formed by sputtering on a signal surface of a substrate, wherein the composition of the enhancement film is adjusted as shown in the following formula. Si_xN_yO_1_0_0_-_(_x_+_y_
) However, R<x<49 37<y<57 R satisfies 10x+y=487, and the value unit is atomic %. (2) In a method for manufacturing a magneto-optical recording medium that includes a step of sputtering a silicon nitride-based enhancement film on the signal surface of a substrate, when sputtering the enhancement film, a vacuum is drawn to a high degree of vacuum. 10 (volume%) to 3 in the tank
Argon gas mixed with 0 (vol.%) nitrogen gas was supplied, the gas pressure in the vacuum chamber was adjusted to 0.1-0.5 (Pa), and the electrode had a pressure of 2.0-12.0 (Pa). A method for manufacturing a magneto-optical recording medium, which comprises inputting a power of W/cm^2).