JPH05234135A - Substrate for optical recording medium - Google Patents

Abstract

PURPOSE:To provide the substrate for an optical recording medium which produces less noises, has high productivity and does not increase crosstalks in spite of forming tracks to a narrower pitch. CONSTITUTION:This substrate is constituted of a transparent dielectric base material 12 consisting of glass, etc., guide layers 14 consisting of a metallic thin film of Ta, etc., and a dielectric layer 16 consisting of a glass thin film, etc. Since injection molding is not used, the productivity is not degraded even if the track pitch is narrowed. Further, the guide layers are formable to a uniform thickness and therefore the noises generated in the substrate are decreased. Since both sides of the laser beam to be cast are shielded by the guide layers, the crostalks do not increase even if the track pitch is diminished.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the recording of information by light,
The present invention relates to an optical recording medium substrate used as an optical recording medium substrate for reproducing or erasing.

[0002]

2. Description of the Related Art Conventionally, a substrate 100 used for an optical recording medium is made of transparent resin such as polycarbonate and acrylic resin, and a guide groove 102 for tracking is provided on its surface as shown in FIG. Tracking is performed by the well-known push-pull method using the guide groove 102. The depth of the guide groove 102 is selected to be about 70 nm so that the push-pull signal necessary for tracking can be obtained with sufficient intensity. Such a substrate 100 is manufactured by injection molding.

On this substrate 100, for example, an interference layer 104 such as SiN, a recording layer 106 made of a magneto-optical recording material such as TbFeCo, and a protective layer 108 such as SiN are sequentially laminated to manufacture an optical recording medium. It

[0004]

However, in such a substrate, if the track pitch is narrowed, there is a problem that molding defects are likely to occur during injection molding and productivity is lowered. Further, since noise is generated due to the surface roughness of the side wall of the guide groove and the groove bottom and the distribution of the groove depth, the optical recording medium manufactured using such a substrate has a problem that the C / N is lowered. Furthermore, when the track pitch is narrowed, there is a problem that crosstalk increases.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to partially laminate a substrate for an optical recording medium on a dielectric base material and to provide a predetermined portion. A substrate for an optical recording medium, which is less prone to noise and has high productivity, and which does not increase crosstalk even when the track pitch is narrowed, by comprising a guide layer that is removed by a pattern and a dielectric layer. To provide.

[0006]

In order to achieve this object, an optical recording medium substrate of the present invention comprises a guide layer laminated on a dielectric substrate and partially removed in a predetermined pattern. , A dielectric layer. At this time, the dielectric material and the dielectric layer may have the same or substantially the same refractive index. Further, the surface of the dielectric layer on the side opposite to the dielectric substrate may be flat or the irregularity thereof may be 70 nm or less.

[0007]

In the optical recording medium substrate of the present invention having the above structure, the guide layer and the dielectric layer can be formed by thin film forming means such as a sputtering method and photolithography, and since injection molding is not used, the track pitch is narrowed. However, productivity does not decrease. Further, since the film thickness of the guide layer can be made uniform, the noise generated by the substrate is reduced. Also,
Dielectric base material and dielectric layer have the same refractive index, or
By making them substantially equal, unnecessary reflection does not occur between the dielectric base material and the dielectric layer. Further, by making the surface of the dielectric layer opposite to the dielectric substrate flat or making the unevenness 70 nm or less, the unevenness of the recording layer provided on the optical recording medium substrate becomes small, and the unevenness is generated. Reliability is improved because deterioration is also reduced. Further, since both sides of the irradiated laser light are shielded by the guide layers, crosstalk does not increase even if the track pitch is reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

An optical recording medium substrate 10 to which the present invention is preferably applied comprises a transparent dielectric substrate 12 such as glass and a metal thin film such as Ta laminated thereon, as shown in FIG. It is composed of a guide layer 14 and a dielectric layer 16 made of a glass thin film or the like. A part of the guide layer 14 is removed as shown in FIG. That is, a portion where the recording area 20 is formed by continuously removing a predetermined length with a predetermined width w _R becomes the data portion 22. Further, the portion where the guide layer 14 is removed and the pits 24 are formed in a predetermined pattern so as to generate a pre-formatted signal or the like becomes the index portion 26. The thickness of the guide layer 14 is selected to be smaller than 70 nm which is the depth of the guide groove of the conventional substrate, that is, about 20 nm.

Such an optical recording medium substrate 10 is manufactured by the method shown in FIG. That is, as shown in FIG. 3A, Ta, for example, is formed on the dielectric substrate 12 by a well-known thin film forming means such as a sputtering method or a vacuum deposition method.
The thin film 32 is formed. A photoresist 34 is applied thereon by spin coating. Then, while the dielectric substrate 12 is rotated, the Ar laser 35 or the like is irradiated to perform exposure. At this time, the index portion 26 is exposed by modulating the Ar laser 35 according to the preformat signal, and the data portion 22 is exposed by continuously irradiating. The width of the recording area 20 and the size of the pit 24 can be controlled by the power of the Ar laser 35 at the time of exposure.

After exposure and development, the portion of the photoresist 34 irradiated with the Ar laser 35 is removed as shown in FIG. Therefore, the photoresist 3 is removed by etching with a solution of acid, alkali or the like, dry etching such as plasma etching, ion etching or the like.
The metal thin film 32 in the portion where 4 is removed is etched, and after the etching is completed, the remaining photoresist 34 is removed by a solvent or the like, whereby the guide layer 14 is formed as shown in FIG. Finally, as shown in FIG. 3D, the dielectric layer 16 made of glass or the like is formed by a well-known thin film forming means such as a sputtering method, thereby completing the optical recording medium substrate. At this time, for example, the dielectric layer 16 is formed by a sputtering method.
In the case of forming, the sputtering may be performed by using a glass of the same material as the dielectric base material 12 as a target.

Thus, the guide layer 14 and the dielectric layer 1
Since injection molding is not used for forming No. 6, even if the track pitch is narrowed, productivity does not decrease due to defective molding.
Further, since the guide layer 14 and the dielectric layer 16 can be manufactured with a uniform film thickness, and the surface of the dielectric substrate 12 is sufficiently smooth, the guide layer 14 and the dielectric layer 16 formed on the guide layer 14 and the dielectric layer 16 have a sufficiently smooth surface. The surface is also smooth enough that there is little noise. Further, since the film thickness of the guide layer 14 is smaller than the depth of the guide groove of the conventional substrate, the removed portion 20 of the guide layer 14 is removed.
The generation of noise from the sidewalls of is also reduced. As a result, the noise generated by the optical recording medium substrate 10 of this embodiment is smaller than that of the conventional substrate with guide grooves.

As shown in FIG. 4, for example, an interference layer 40 made of SiN or the like and a TbFeCo layer are formed on the optical recording medium substrate 10 of this embodiment.
A recording layer 42 made of, for example, a protective layer 44 made of SiN,
The magneto-optical disk 46 can be manufactured by forming and stacking by a thin film forming means such as a sputtering method.

The laser light emitted from the side of the dielectric substrate 12 is applied to the recording layer 42 through the recording area 20 formed by removing the guide layer 14 to perform recording / reproduction. Here, as shown in FIG.
If w _P and the beam diameter of the laser spot 28 on the recording surface are w _L , then if the relation w _P + (w _P -w _R ) = 2w _P -w _R > w _L (1) is satisfied, Even if the track pitch is made smaller than the laser spot diameter, the adjacent recording area is not irradiated with the laser beam 28, so that the crosstalk does not increase.

The laser light emitted from the dielectric substrate 12 side is reflected by the guide layer 14 and the recording layer 42,
Diffraction occurs. Here, the dielectric layer 16 and the interference layer 40
When the film thicknesses are d ₁ and d ₂ , respectively, and the refractive indices are n ₁ and n ₂ , respectively, the light reflected by the recording layer 42 and the light traveling back and forth through the dielectric layer 16 and the interference layer 40 is reflected by the guide layer 14. The phase is delayed by φ = (4π / λ) [n ₁ d ₁ + n ₂ d ₂ ] (2) from the light. The push-pull signal strength required for tracking by the push-pull method becomes maximum when the phase difference is φ = π / 2 + mπ (3). However, m is an integer. Further, the Kerr effect enhancement becomes maximum due to the interference in the interference layer 40 when the interference layer film thickness d ₂ is d ₂ = λ / (4n ₂ ) (4). However, the dielectric layer 16 and the dielectric substrate 12
Have the same refractive index, the dielectric layer 16 and the dielectric substrate 12 are
No light is reflected at the boundary with. In addition, the interference layer 40
The multiple interference occurs in the interference layer 40 because the refractive index of is selected to be higher than that of the dielectric substrate 12.

Therefore, from equations (2), (3) and (4),
When the thickness of the dielectric layer 16 that maximizes the push-pull signal and the car enhancement is m = 1, d ₁ = λ / (8n ₁ ) (5). That is, by selecting the film thicknesses of the interference layer 40 and the dielectric layer 16 according to the equations (4) and (5), the push-pull signal strength is maximized, stable tracking can be realized, and at the same time, the Kerr effect enhancement is also achieved. Since it is the maximum, high C / N can be obtained.

Although one embodiment of the present invention has been described in detail above with reference to FIGS. 1 to 4, the present invention can be implemented in other modes.

That is, the material of each layer is not particularly limited, and acrylic resin, polycarbonate resin, amorphous polyolefin resin or the like may be used as the material of the dielectric base material 12 instead of glass. At this time, the material of the dielectric layer 16 does not have to be the same as that of the dielectric base material 12, and the refractive index thereof does not have to be exactly the same as that of the dielectric base material 12. The reflection at the boundary between the body layer 16 and the dielectric substrate 12 can be made sufficiently small. For example, as the dielectric layer 16, SiO ₂ having a refractive index of 1.46 is used.
It is possible to control the refractive index of the dielectric layer 16 over a wide range from 1.46 to about 2.2 by using a material in which TiO ₂ of 2.2 or more and 2.2 or more are mixed, and changing the mixing ratio. It can be made substantially equal to the refractive index of the material 12.

The refractive index of the dielectric layer 16 does not have to be the same as that of the substrate 12, and its refractive index and material are not particularly limited. For example, as the dielectric layer 16, a material such as SiN, AlN, or SiAlON having a refractive index larger than that of the dielectric base material 12 may be used. At this time, the effect of the interference layer 40 shown in FIG. 4 can also be produced in the dielectric layer 16.

Further, as shown in FIG. 5, SiO ₂ or the like produced by spin coating may be used as the dielectric layer 50.
In this case, since the surface of the dielectric layer 50 is flat, the recording layer 42 formed thereon is also flat. This allows
The deterioration of the film that has conventionally occurred at the stepped portion of the recording layer 42 does not occur, and the reliability is improved.

The material of the guide layer 14 need not be metal and is not particularly limited. In addition, the guide layer 14
Alternatively, a material having a large absorption may be used. As a result, the reflection on the guide layer 14 is reduced, and the noise is reduced accordingly, so that the C / N is improved. Further, the film thickness of the guide layer 14 is not particularly limited. For example, the guide layer 14,
When the thickness is small, the unevenness generated in the recording layer 42 is also small, so that the effect of suppressing the deterioration in the step portion of the recording layer 42 is increased. That is, if the film thickness of the guide layer 14 is smaller than 70 nm which is the depth of the guide groove in the conventional grooved disk, the effect of suppressing the deterioration becomes large.

The film thickness of the dielectric layer 16 is also λ / (8n ₁ ) in the above embodiment, but is not particularly limited. For example, by setting the film thickness of the dielectric layer 16 to λ / (6n ₁ ), the push-pull signal and the preformat signal can be obtained with sufficient strength, which is desirable.

In the above embodiment, the recording medium is
Although the case of manufacturing a magneto-optical disk has been described, the structure and type of the recording medium using the optical recording medium substrate 10 of the present invention are not particularly limited. That is, as the recording layer 42, not only a rare earth transition metal alloy other than TbFeCo, a multilayer film of PtCo or PdCo, an oxide magnetic material such as rare earth iron garnet and a magneto-optical material combining them, but also a perforated type such as Te or Bi is used. Alternatively, a phase change material such as GeSbTe or TeO _x , an organic material such as a pigment, or the like can be used. For example, as shown in FIG. 6, a recording layer 62 such as an oxide magnetic material or an organic dye is provided on the optical recording medium substrate 10, and the reflective layer 6 is provided thereon.
4 may be provided.

Also, the removal pattern of the guide layer 14 is not particularly limited, and for example, as shown in FIG. 7, the recording area 2 is defined by the width of the pits 24 for generating the preformat signal.
The width of 0 may be widened. As a result, the signal recorded in the recording area 20 of the data section 22 can be reproduced at a high C / N, and at the same time, the change in the amount of light due to diffraction in the pits 24 of the index section 26 increases, which is desirable.

Alternatively, the mirror portion 70 may be formed by removing all of the guide layer 14 in a certain area as shown in FIG.
The tracking offset can be reduced by adjusting the tracking servo circuit so that the push-pull signal becomes 0 in the mirror unit 70. On the contrary, a portion where the guide layer 14 is not removed may be formed and used as the mirror portion.

Further, the width of removing the guide layer 14 and the track pitch are not particularly limited. For example, the track pitch and the removal width may be narrowed toward the outer circumference. Thereby, the density of the optical recording medium can be further improved.

Further, in addition to the user recording area 74 where the recording area 20 is provided as shown in FIG. 9 on a part of the optical recording medium substrate, the recording area 20 is not provided and predetermined information is recorded. Based on this, the ROM area 78 in which the guide layer 14 is removed and the pits 76 are formed may be provided. As a result, information that does not need to be changed, such as programs and basic data, can be recorded in the ROM area 78 in advance. At this time, the user recording area 74 and the ROM area 78
There is no particular limitation on the arrangement. For example, in FIG.
You may arrange | position in a concentric form like (a). At this time, the optical recording medium substrate may be formed on the inner peripheral side, the outer peripheral side, or divided into a plurality of regions. Further, as shown in FIG. 7B, they may be arranged radially. ROM
On the dielectric layer 16 in the area 78, as shown in FIG.
The reflective layer 80 made of, for example, may be formed. Also,
On the dielectric layer 16 in the user recording area 74, for example,
The interference layer 40, the recording layer 42, and the protective layer 44 are formed. At this time, the interference layer 40, the recording layer 42, the protective layer 44
May be provided only in the user recording area 74, or may be provided on the reflective layer 80 in the ROM area 78.

Alternatively, the guide layer 14 may be continuously removed to form the recording area 20 continuously. At this time, the format information may be recorded in the recording layer.

Further, as shown in FIG. 12, the guide layer 14 is arranged between the spiral or concentric guide band 82 and the guide band 82, and the reflector 8 for generating the pre-format signal.
4 may be removed so as to form. At this time, the portion provided with the reflective material 84 becomes the index portion 26, and the portion not provided becomes the data portion 22. Furthermore, the guide band 82 does not have to be formed continuously, and there may be a part 86 that is not formed. That is, the portion 88 where the guide band 82 and the reflecting material 84 are not formed becomes the mirror portion described above.

In the embodiment of FIG. 3 (a), the photoresist 34 was exposed by Ar laser, but it may be exposed by ultraviolet rays or the like through a mask having a predetermined pattern, that is, by so-called mask exposure. Good. By using this mask exposure, the productivity is significantly improved as compared with the case of exposing with a laser.

The shape of the optical recording medium substrate of the present invention does not have to be disk-shaped, and may be card-shaped or the like, and is not particularly limited. In this case, the removal pattern of the guide layer may be linear.

[0032]

As is apparent from the above description, in the optical recording medium substrate of the present invention, the guide layer and the dielectric layer can be formed by a thin film forming means such as a sputtering method and photolithography, and injection molding is used. Therefore, the productivity does not decrease even if the track pitch is narrowed. Further, since the film thickness of the guide layer is smaller than the depth of the guide groove of the conventional substrate, and the film thickness of the guide layer can be made uniform, the noise generated by the substrate is reduced. Further, by making the refractive indexes of the dielectric base material and the dielectric layer equal or substantially equal to each other, unnecessary reflection does not occur between the dielectric base material and the dielectric layer. Further, the surface of the dielectric layer opposite to the dielectric substrate is flat or the unevenness thereof is 70 nm or less, whereby the unevenness of the recording layer provided on the optical recording medium substrate is reduced,
Since the deterioration caused by the uneven portion is also reduced, the reliability is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing an embodiment of a substrate for an optical recording medium of the present invention.

FIG. 2 is a plan view of the optical recording medium substrate of the present invention as viewed from the dielectric substrate side.

3 (a) to 3 (d) are explanatory views showing a method for manufacturing an optical recording medium substrate of the present invention.

FIG. 4 is a sectional view of an essential part showing an embodiment of an optical recording medium using the substrate for optical recording medium of the present invention.

FIG. 5 is a cross-sectional view of essential parts showing another embodiment of an optical recording medium using the substrate for optical recording medium of the present invention.

FIG. 6 is a cross-sectional view of essential parts showing another embodiment of an optical recording medium using the optical recording medium substrate of the present invention.

FIG. 7 is a plan view showing another embodiment of the guide layer removal pattern in the optical recording medium substrate of the present invention.

FIG. 8 is a plan view showing another embodiment of the guide layer removal pattern in the optical recording medium substrate of the present invention.

FIG. 9 is a plan view showing another embodiment of the guide layer removal pattern in the optical recording medium substrate of the present invention.

10A and 10B are plan views showing another embodiment of the substrate for an optical recording medium of the present invention.

FIG. 11 is a cross-sectional view of essential parts showing another embodiment of the substrate for an optical recording medium of the present invention.

FIG. 12 is a plan view showing another embodiment of the optical recording medium substrate of the present invention.

FIG. 13 is a cross-sectional view of an essential part showing a conventional substrate.

FIG. 14 is a cross-sectional view of an essential part showing an optical recording medium using a conventional substrate.

[Explanation of symbols]

 10 Optical Recording Medium Substrate 12 Dielectric Base Material 14 Guide Layer 16 Dielectric Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yumiko Ohashi 15-1 Naesehiro-cho, Mizuho-ku, Nagoya-shi Brother Industrial Co., Ltd. Within the corporation

Claims (3)

[Claims] 1. A substrate for an optical recording medium, which comprises a dielectric layer and a guide layer laminated on a dielectric base material, a part of which is removed in a predetermined pattern. 2. The substrate for an optical recording medium according to claim 1, wherein the dielectric base material and the dielectric layer have the same or substantially the same refractive index. 3. The optical recording medium substrate according to claim 1, wherein the surface of the dielectric layer opposite to the dielectric substrate is flat or has irregularities of 70 nm or less. Substrate for medium.