JPH11213470A - Magneto-optical disk and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To diminish noise from the groove by forming a magneto-optical film having a magneto-optical effect, on a disk substrate on which grooves are formed along recording tracks, giving the edge of the groove a curved surface, reducing the radius of curvature of the edge part to a specific value or less, and thereby making disturbance hard to emerge in the magnetizing direction of the magneto-optical film formed on the curved surface. SOLUTION: If an angle is sharply changes at a boundary between the land 6 and the slope 7 (edge 8 on the land side) or between the groove 5 and the slope 7 (edge 9 on the groove side) of a disk substrate 2, the magnetic anisotropy of a magneto-optical film formed on the boundaries is disturbed, inducing disturbance also in the magnetic anisotropy of the film formed on the slope 7, with the disturbed magnetization giving rise to Kerr effect to cause noise. Under the circumstances, the radius of curvature R1 , R2 is designed to be 20 nm or more at the edge 8, 9 on the land and the groove side respectively. As a result, noise is reduced, enabling a high C/N to be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magneto-optical disk having a groove for tracking control formed thereon and a method of manufacturing the same.

[0002]

2. Description of the Related Art In a magneto-optical recording system, a recording layer made of a magnetic material is partially heated to a temperature higher than a Curie point or a temperature compensation point to reduce a coercive force, and recording is performed by externally applying a recording magnetic field. In this method, information signals are recorded by changing the magnetization direction of the layer. This magneto-optical recording method is being put to practical use in an optical filing system, an external storage device of a computer, or a recording device for audio information and video information.

A magneto-optical disk on which recording is performed by the above-described magneto-optical recording method is, for example, a magneto-optical disk having a recording layer having a magneto-optical film formed on a disk substrate made of plastic such as polycarbonate or glass. is there.

Usually, grooves for tracking control are provided in a spiral shape along recording tracks on the surface of a disk substrate used for such a magneto-optical disk.

With the recent increase in recording density, there has been a strong demand for improvements in recording density of magneto-optical disks. In order to respond to this demand, researches on increasing the NA of the objective lens for a magneto-optical disk and shortening the wavelength of a laser beam have been advanced. Along with this, the track pitch of the magneto-optical disk has been narrowed, and the track width with respect to the light spot diameter has become considerably narrower than that of the initial magneto-optical disk.

[0006]

However, when the track pitch of the magneto-optical disk is reduced, noise caused by disturbance of the magnetization of the recording layer formed on the side wall of the tracking control groove becomes a serious problem. . That is, when the light spot diameter is fixed and the track pitch is reduced, noise increases due to the side wall of the groove approaching the center of the spot. Even when the NA of the objective lens is increased, even if the light spot diameter is reduced and the track pitch is reduced, the size of the side wall of the groove, which is a region in which magnetization is disordered, is constant, which also causes an increase in noise. Also, shortening the wavelength of the laser light similarly causes noise.

To reduce noise from the groove, it is effective to change the shape of the groove. Conventionally, at the time of polycarbonate molding, the optimum condition has been obtained by changing the shape of the groove by changing the transferability of the unevenness from the master. However, this method could not sufficiently reduce the noise from the groove.

The present invention has been proposed in view of the above-mentioned conventional situation, and a magneto-optical disk in which the shape of a groove is defined by irradiating a disk substrate with far ultraviolet rays to reduce noise from the groove. An object of the present invention is to provide a disk and a method of manufacturing the same.

[0009]

According to the magneto-optical disk of the present invention, a magneto-optical film having a magneto-optical effect is formed on a disk substrate having grooves formed along recording tracks, and the edge portions of the grooves are formed. It is characterized by being curved surfaces and having a radius of curvature of 20 nm or more.

In the above-described magneto-optical disk according to the present invention, the edge portions of the grooves are curved and their radii of curvature are set to 20 nm or more. Disturbance does not easily occur in the magnetization direction of the film, and noise is reduced.

A method of manufacturing a magneto-optical disk according to the present invention includes a disk substrate manufacturing step of manufacturing a disk substrate having a groove, and a method of manufacturing the disk substrate manufactured in the disk substrate manufacturing step by using far-ultraviolet light under an inert gas atmosphere. And a film forming step of forming a magneto-optical film having a magneto-optical effect on the disk substrate irradiated with the far ultraviolet light in the far ultraviolet light irradiating step.

In the above-described method for manufacturing a magneto-optical disk according to the present invention, since the disk substrate having the groove is irradiated with far ultraviolet rays in an inert gas atmosphere, the shape of the groove is optimized, and the groove portion is optimized. The magnetization direction of the magneto-optical film formed on the substrate is less likely to be disturbed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration example of a magneto-optical disk according to the present invention. The magneto-optical disk 1 includes a disk substrate 2 made of a synthetic resin material, a recording layer 3 formed on the disk substrate 2 for recording information signals, and a protective layer 4 for protecting the recording layer 3. It is laminated.

The disk substrate 2 is a disk-shaped substrate having a thickness of about several mm. As a material of the disk substrate 2, for example, a plastic material such as a polycarbonate resin, a glass material, or the like is used.

The recording layer 3 is formed on the disk substrate 2. The recording layer 3 is formed, for example, by stacking a magneto-optical film on which an information signal is recorded and a reflective film in this order. Here, the magneto-optical film has an easy axis of magnetization in a direction perpendicular to the film surface and has a large magneto-optical effect. Examples of such a magneto-optical film include a magneto-optical thin film made of a rare earth-transition metal alloy amorphous thin film or the like.

The protective layer 4 is formed on the recording layer 3 and is made of, for example, an ultraviolet curable resin.

In the magneto-optical disk 1, a groove 5 for tracking control is formed on the surface of the disk substrate 2.
Has a width of about 0.1 μm to about 1 μm and a width of about 0.5 μm
It is formed spirally over the entire surface of the disk at a pitch of about 1.6 μm.

FIG. 2 is an enlarged sectional view showing the disk substrate 2 on which such a groove 5 is formed. The boundary between the groove 5 and the land 6 which is a convex portion between the groove 5 and the groove 5 is a slope 7.

A major cause of the noise of the magneto-optical disk is a disturbance of the magnetization of the magneto-optical film formed on the slope 7.

The magneto-optical film is a thin perpendicular magnetization film.
The normal direction of the magneto-optical film formed on the slope 7 does not coincide with the light incident direction. Therefore, when the magneto-optical film shows almost no disturbance in magnetization, the Kerr effect is small at the slope 7, so that it does not cause noise.

However, a boundary portion between the land 6 and the slope 7 (hereinafter referred to as a land side edge 8) or the groove 5
If the angle changes steeply at the boundary between the groove and the slope 7 (hereinafter, referred to as the groove-side edge 9), the magnetic anisotropy of the magneto-optical film formed at the edge will be disturbed, and this will be accompanied. As a result, the magnetic anisotropy of the magneto-optical film formed on the slope 7 is disturbed. It is considered that the disordered magnetization causes the Kerr effect and causes noise.

Therefore, in the magneto-optical disk 1 according to the present invention, the land side edge 8 and the groove side edge 9 of the disk substrate 2 are curved as shown in FIG. Then, in the disc substrate 2, the radius of curvature R ₂ of the radius of curvature R ₁ and a groove-side edge 9 of the land side edge 8 20n
m or more.

[0024] In the magneto-optical disc 1, the radius of curvature R ₂ of the radius of curvature R ₁ and a groove-side edge 9 of the land side edge 8 of the disc substrate 2, since being made more sufficiently large 20 nm, on the disk substrate 2 The direction of the magnetic anisotropy axis of the formed magneto-optical film gradually changes on this curved surface.
Therefore, the magnetic anisotropy axis of the magneto-optical film formed on the slope 7 is less likely to be disturbed, and noise can be reduced.

In the magneto-optical disk 1, the recording layer 3 may have a dielectric film disposed above or below the magneto-optical film.

The magneto-optical disk 1 as described above is manufactured as follows.

First, a disk substrate having a groove for optical tracking is manufactured.

As the disk substrate, a known material that is generally used as a substrate for a magneto-optical disk is used. Specifically, for example, a plastic such as a polycarbonate resin, a glass material, or the like is used.

A disk substrate having grooves can be manufactured by a known method such as an injection molding method or an ultraviolet curing resin method.

For example, when glass is used as a substrate material, for example, an ultraviolet curable resin is applied on a glass substrate,
After the master is brought into close contact with the ultraviolet-curable resin to cure the ultraviolet-curable resin with ultraviolet rays, the master is peeled off to transfer and form grooves on the ultraviolet-curable resin on the substrate (hereinafter, such a substrate is referred to as a glass 2P substrate). In the case where polycarbonate is used as the substrate material, a groove can be formed by molding a disk substrate by injection molding using a master having predetermined irregularities.

Next, the surface of the disk substrate on which the grooves are formed is irradiated with far ultraviolet rays having a wavelength of about 100 nm to about 400 nm. By irradiating far ultraviolet rays, as shown in the general formula (1), organic substances on the surface of the disk substrate are decomposed into volatile substances such as CO, CO ₂ , and H ₂ O,
Volatilized and removed.

[0032] _{C m -H n -O k → C} m · H n · O k → CO, CO 2, H 2 O (1) was irradiated with far ultraviolet ray on the surface of the disc substrate, the portion of the disc substrate surface By decomposing and volatilizing and removing, the land side edge and the groove side edge can be curved surfaces having a large radius of curvature, and the disk substrate surface can be smoothed.

By forming the land side edge and the groove side edge as curved surfaces having a large radius of curvature, disturbance of the magnetic anisotropy axis of the magneto-optical film formed on the curved surface portion is prevented.

Considering the thickness of the magneto-optical film and the track pitch, the radius of curvature of this curved surface is about 20 nm to about 2 μm.
It should be about the degree.

As described above, by making the radius of curvature of the edge sufficiently large, the direction of the magnetic anisotropy axis of the magneto-optical film formed at the edge portion can be gradually changed, and formed at the slope portion. Disturbance of the magnetic anisotropy axis of the magneto-optical film can be prevented. Therefore, it is possible to suppress noise due to disturbance of the magnetization of the slope portion.

As a light source for supplying such far ultraviolet rays, for example, a low-pressure mercury lamp (the spectrum is concentrated at a wavelength of 184.0 nm and 253.7 nm), a high-pressure mercury lamp (a wavelength of about 200 nm to about 300 nm), an Fe-based lamp Metal halide lamp (wavelength about 300 nm to about 400 nm), mercury-xenon short arc lamp (wavelength about 3 nm)
(About 00 nm to 400 nm).

Irradiation with far ultraviolet rays is preferably performed in an atmosphere of an inert gas such as nitrogen gas. When the far ultraviolet irradiation is performed in an N ₂ gas atmosphere, the decomposition rate of the organic substance on the disk substrate surface can be suppressed. Further, when far-ultraviolet radiation is performed in a gas atmosphere containing oxygen, far-ultraviolet light having a wavelength of 185 nm is absorbed by oxygen, the amount of light reaching the disk substrate is small, and the efficiency of decomposing organic substances on the disk substrate surface is reduced. Decrease.

In the case of using a far-ultraviolet ray irradiation, for example, when a disk substrate made of polycarbonate is used, the irradiation energy of the far-ultraviolet ray is preferably set to 50 mJ / cm ² or more. When a glass 2P substrate is used, the irradiation energy of far ultraviolet rays is preferably set to 200 mJ / cm ² or more. By setting the irradiation energy of the far ultraviolet as described above, the organic substance on the surface of the disk substrate can be efficiently decomposed.

Next, a magneto-optical disk 1 having the structure shown in FIG. 1 is manufactured by forming a recording layer and a protective layer on the disk substrate that has been irradiated with the far ultraviolet rays.

The recording layer is formed, for example, by laminating a magneto-optical film on which an information signal is recorded and a reflective film. These magneto-optical films and reflective films are formed by a so-called vapor phase plating method such as a vapor deposition method or a sputtering method. Further, a dielectric film may be formed above or below the magneto-optical film.

The protective layer is formed, for example, by applying an ultraviolet curable resin onto the recording layer by, for example, spin coating, and irradiating far ultraviolet rays to cure the ultraviolet curable resin.

Hereinafter, an experimental example in which far ultraviolet irradiation is performed on a disk substrate will be described.

<Experimental Example 1> The surface of a disk substrate using polycarbonate as a substrate material was irradiated with far ultraviolet rays. FIG. 3 shows the shape of the disk substrate before irradiation with deep ultraviolet rays.
Shown in Before the irradiation with the far ultraviolet rays, the radius of curvature of the land side edge is about 10 nm, and the radius of curvature of the groove side edge is about 10 n.
m.

The irradiation with far ultraviolet rays was performed in an atmosphere substituted with N ₂ . A low-pressure mercury lamp was used as a light source. The far ultraviolet irradiation was performed at an irradiation energy of 180 mJ / cm ² for about 3 minutes. At this time, the light intensity on the disk substrate was about 1 mW / cm ² .

FIG. 4 shows the shape of the disk substrate after irradiation with far ultraviolet rays for about 3 minutes. As is clear from FIG.
Deformation of the shape of the disk substrate was confirmed. The deformation of the disk substrate started about 1 minute after the start of the irradiation with the far ultraviolet light, and the depth of the groove became about half of the depth of the groove before the irradiation about 3 minutes after the irradiation with the far ultraviolet light. The lands and grooves have rounded edges, and the smoothness of the disk substrate surface is improved. After irradiating far ultraviolet rays, the radius of curvature of the land side edge is about 80n.
m, the radius of curvature of the groove side edge was about 30 nm.

After the surface of the disk substrate was deformed by irradiating it with far ultraviolet rays, a magneto-optical film was formed, and the noise characteristics were evaluated.

FIG. 5 shows the relationship between the irradiation time of far ultraviolet rays and C / N. At this time, the wavelength of the laser beam is 690 nm, and the NA of the objective lens is 0.55. The track pitch is 0.85 μm. As is clear from FIG. 5, when the far ultraviolet irradiation time is up to 3 minutes, C / N
Gradually increased, and the effect of the irradiation with far ultraviolet rays was clearly recognized.

FIG. 6 shows the relationship between the irradiation time of far ultraviolet rays and the pull-in level (the amount of light returning from the light level). From FIG. 6, it can be seen that the pull-in level increases as the far ultraviolet irradiation time increases. The increase in the pull-in level is due to the fact that the depth of the groove becomes shallower due to the irradiation of the far ultraviolet light and the width of the land portion is widened.

FIG. 7 shows the relationship between the far ultraviolet irradiation time normalized by the pull-in level, the carrier level and the noise level. FIG. 7 shows that the carrier level is almost constant irrespective of the far ultraviolet irradiation time, but the noise level gradually decreases with the far ultraviolet irradiation time. Therefore, it can be confirmed that the deformation of the shape of the disk substrate due to the irradiation of far ultraviolet rays is effective in reducing the noise level.

FIG. 8 is a diagram showing the relationship between the radius of curvature of the land side edge and C / N. As is clear from FIG. 8, the larger the radius of curvature of the edge portion is, the less the disturbance of the magnetization of the magneto-optical film is, and the higher the radius of curvature is 20 nm or higher, the higher the C / N ratio is obtained.

<Experimental Example 2> The surface of the glass 2P substrate was irradiated with far ultraviolet rays. FIG. 9 shows the shape of the disk substrate before the irradiation with far ultraviolet rays. Before the irradiation with the far ultraviolet ray, the radius of curvature of the land side edge was about 95 nm, and the groove side edge was bent so steeply that the radius of curvature could not be measured.

The irradiation with far ultraviolet rays was performed in an atmosphere substituted with N ₂ . A low-pressure mercury lamp was used as a light source. The far ultraviolet irradiation was performed at an irradiation energy of 600 mJ / cm ² for about 10 minutes. At this time, the light intensity on the disk substrate was about 1 mW / cm ² .

FIG. 10 shows the shape of the disk substrate after irradiation with far ultraviolet rays. As is clear from FIG. 10, deformation of the shape of the substrate was confirmed. The depth of the groove was reduced to about half of that before irradiation. Further, by performing the irradiation with the far ultraviolet rays, the smoothness of the disk substrate surface is clearly improved. After the irradiation with the far ultraviolet rays, the radius of curvature of the land side edge was about 110 nm, and the radius of curvature of the groove side edge was about 40 nm.

When a similar experiment was performed using a far ultraviolet irradiation apparatus in which the replacement of nitrogen gas was not sufficient, the efficiency of groove deformation was low, and even at ² J / cm ² irradiation, a part of the groove edge remained, and The smoothness was also poor. Therefore,
In the present invention, the effect is more remarkable when far ultraviolet irradiation is performed in a nitrogen gas atmosphere.

As described above, after the surface of the disk substrate is deformed by irradiating it with ultraviolet rays, a magneto-optical film is formed.
The properties were evaluated.

FIG. 11 shows the relationship between the irradiation time of far ultraviolet rays and C / N. The wavelength of the laser beam at this time is 640 n
m, the NA of the lens is 0.85. Although the light spot diameter is small, the track pitch is 0.55 μm, and the track width is the same as the light spot diameter as in the experimental example using polycarbonate.

As is clear from FIG. 11, in the range where the irradiation time of the far ultraviolet rays is up to 10 minutes, the C / N gradually increases with the irradiation time of the far ultraviolet rays. After irradiating with far ultraviolet rays for 10 minutes, the C / N is about 5 times higher than before irradiating with far ultraviolet rays.
The dB is also improved, and it can be confirmed that, in the case of a narrow track pitch, the effect of the deformation of the groove shape by irradiation with far ultraviolet rays is higher.

FIG. 12 is a diagram showing the relationship between the radius of curvature of the groove side edge and C / N. As is clear from FIG. 12, the larger the radius of curvature of the groove-side edge is, the less the magnetization of the magneto-optical film is disturbed, and the larger the radius of curvature becomes.
It can be seen that a high C / N is obtained when the thickness is equal to or more than nm.

FIG. 13 shows the shape of an inverted substrate manufactured based on the disk substrate before the irradiation with the far ultraviolet rays in FIG. A magneto-optical film is formed on this disk substrate, and C
When the / N was evaluated, the result that the C / N was low was obtained. Therefore, the magnetization of the magneto-optical film is disturbed at the edge portion of the groove even if either one is steep, so both the land side and the groove side edges are curved surfaces, and the radius of curvature thereof is sufficiently large. Is preferred.

[0060]

According to the magneto-optical disk of the present invention, the boundary between the land and the slope and the boundary between the groove and the slope are curved, and the radius of curvature is 20 nm.
As described above, it is possible to realize an excellent magneto-optical disk in which the magnetization direction of the magneto-optical film formed on the curved surface portion hardly disturbs, the noise is small, and the C / N is high.

In the method for manufacturing a magneto-optical disk according to the present invention, the disk substrate on which the groove is formed is irradiated with far ultraviolet rays in an inert gas atmosphere, so that the shape of the groove is optimized, and Since the magnetization direction of the formed magneto-optical film is less likely to be disturbed, an excellent magneto-optical disk having low noise and high C / N can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing the shape of the disk substrate of FIG.

FIG. 3 is a sectional view showing a shape of a disk substrate before irradiation with far ultraviolet rays.

FIG. 4 is a cross-sectional view showing the shape of a disk substrate after irradiation with far ultraviolet rays.

FIG. 5 is a diagram showing a relationship between a far ultraviolet irradiation time and C / N.

FIG. 6 is a diagram showing a relationship between a far ultraviolet irradiation time and a pull-in level.

FIG. 7 is a diagram showing a relationship between a far ultraviolet irradiation time, a noise level, and a carrier level.

FIG. 8 is a diagram showing the relationship between the radius of curvature of the edge of the disk substrate and C / N.

FIG. 9 is a cross-sectional view showing a shape of a disk substrate before irradiation with far ultraviolet rays.

FIG. 10 is a cross-sectional view showing the shape of the disk substrate after irradiation with far ultraviolet rays.

FIG. 11 is a diagram showing a relationship between a far ultraviolet irradiation time and C / N.

FIG. 12 is a diagram showing the relationship between the radius of curvature of the edge of the disk substrate and C / N.

13 is a cross-sectional view illustrating a shape of a disk substrate obtained by inverting the disk substrate of FIG.

[Description of Signs] 1 magneto-optical disk, 2 disk substrate, 3 recording layer, 4 protective layer, 5 groove, 6 land, 7
Slope, 8 Land side edge, 9 Groove side edge

Claims (7)

[Claims] 1. A magneto-optical film having a magneto-optical effect is formed on a disk substrate on which a groove is formed along a recording track, and the edge of the groove has a curved surface and the radius of curvature thereof is 20 nm. A magneto-optical disk characterized by the above. 2. The groove has a side wall and a bottom surface,
The boundary between the side wall and the bottom surface is a curved surface,
2. The magneto-optical disk according to claim 1, wherein the radius of curvature thereof is 20 nm or more. 3. The magneto-optical disk according to claim 1, wherein said disk substrate is made of polycarbonate. 4. The magneto-optical disk according to claim 1, wherein said disk substrate has an ultraviolet curable resin layer. 5. A disk substrate manufacturing step for manufacturing a disk substrate having a groove, and a far ultraviolet irradiation step of irradiating the disk substrate manufactured in the disk substrate manufacturing step with far ultraviolet light in an inert gas atmosphere. And a film forming step of forming a magneto-optical film having a magneto-optical effect on the disk substrate irradiated with the far ultraviolet light in the far ultraviolet light irradiating step. 6. The method for manufacturing a magneto-optical disk according to claim 5, wherein said inert gas is nitrogen. 7. The wavelength of the far ultraviolet light is from 100 nm to 40 nm.
6. The method for manufacturing a magneto-optical disk according to claim 5, wherein the thickness is set to 0 nm.