JPH1131337A - Optical recording medium and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress flawing on a transparent cover layer to be irradiated with light and the failure thereof, to assure reliability, to enable the dealing with higher NA and to make a capacity higher. SOLUTION: The one main surface side of a recording layer is provided with the transparent cover layer having a Young's modulus of >=70 (GPa) and the recording and/or reproducing of information is executed by using an objective lens having NA of >=0.7. The thickness of the transparent cover layer is specified to <=150 (μm). The transparent cover layer is formed of a two- layered structure and the Young's modulus of the layer which is a front surface side is specified to >=150 (Gpa). The thickness of the layer is specified to 2 to 230 (nm). The front surface side of the transparent cover layer is formed of a material contg. at least one kind among C100-x Hx (1(atomic.%)<X <45(atomic.%)), Si3 N4 , MgF2 , Al2 O3 and SiO2 . The thickness (t) of the transparent cover layer of the region of an information signal part 11 is specified to t=3 to 177 (μm) and the irregular thickness Δt of the transparent cover layer is so determined that the relation Δt<=±5.26(λ/NA<4> ) (μm) holds between NA and a wavelength λ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording layer having a transparent cover layer on one principal surface side, and irradiating information from the transparent cover layer side with an objective lens having a numerical aperture of 0.7 or more. The present invention relates to an optical recording medium on which recording and / or reproduction are performed. More specifically, the present invention relates to an optical recording medium that has a relatively high hardness on the surface side of a transparent cover layer, is hardly damaged, and has high reliability.

[0002]

2. Description of the Related Art In recent years, in the field of information recording, researches on optical information recording systems have been advanced in various places. This optical information recording system is capable of non-contact recording and reproduction, achieving a recording density that is at least an order of magnitude higher than the magnetic recording system, and can be used in read-only, write-once, and rewritable memory formats. It has a number of advantages such as compatibility, and is considered as a system that can realize an inexpensive large-capacity file for a wide range of uses from industrial use to consumer use.

In particular, digital audio discs and optical video discs, which are optical discs compatible with a read-only type memory, are widely used.

An optical disk such as the above digital audio disk has a reflective surface made of a metal thin film such as an aluminum film on one principal surface of a transparent substrate on which an uneven pattern such as pits or grooves indicating information signals is formed. A film is formed to form a recording layer, and a protective film for protecting the reflective film from atmospheric moisture and O ₂ is formed on the reflective film.

A magneto-optical disk corresponding to a rewritable memory mode has the following configuration.
That is, a transparent dielectric film such as silicon nitride is formed on one main surface of a transparent substrate, a magneto-optical recording film such as TbFeCo is formed thereon as a recording layer, and a transparent dielectric film such as silicon nitride is formed thereon. Then, a reflective film such as an aluminum film is formed, and a protective film made of an ultraviolet curable resin or the like is further formed. In this magneto-optical disk, information is recorded and reproduced by irradiating light from the transparent substrate side.

As a method for increasing the recording capacity of an optical recording medium such as an optical disk or a magneto-optical disk as described above, a numerical aperture of an objective lens of an optical pickup is increased to reduce a spot diameter of reproduction light. There has been proposed a method of increasing the recording density by performing recording in accordance with.

Therefore, recently, a DVD (Digital Video Recorder) for recording various data such as images, music, computer data, etc.
digital Versatile Disc,
It is called DVD. ) Is also on the market. In this DVD, the thickness of the substrate is set to about 0.6 (mm) so as to be compatible with an optical system having a short wavelength and to be compatible with an optical system having a high numerical aperture so as to have a high recording density. .

Under such circumstances, as a further next-generation optical recording medium, NTSC (National Televi) is provided on one side as shown in Japanese Patent Application No. 9-109660.
There has been proposed an optical recording medium capable of recording and reproducing data for 4 hours by using a system (Commission System).

This optical recording medium is capable of recording and reproducing for 4 hours as a home video disk recorder, thereby functioning as a new recording medium in place of a video tape recorder (Video Tape Recorder) which is currently mainstream. It is intended to have. In addition, this optical recording medium may have the same shape and size as a digital audio disc on which music data is recorded, so that the product is easy to use for users familiar with the simplicity and usability of the digital audio disc. ing. Further, in this optical recording medium, by making the shape of a disk, utilizing the speed of access which is the greatest feature of the disk shape, not only a compact and simple recording medium, but also an instant recording and reproduction Various functions such as trick play and editing are also considered.

Therefore, the above-mentioned optical recording medium is required to have a storage capacity of 8 (GB) or more in order to incorporate such various functions.

However, any of the conventional optical recording media, particularly those having a size equivalent to that of a digital audio disc and having an information recording layer on only one side, has achieved a storage capacity of 8 (GB). Absent. For example, even in a DVD having a high storage capacity, a radius of 24 to 58 (m
In the range of m), the wavelength λ is 0.65 (μm), the numerical aperture of the optical system (hereinafter, referred to as NA) is 0.6, and only a storage capacity of 4.7 (GB) is secured. Not.

For example, ECC (Error Colle)
In order to secure a storage capacity of 8 (GB) or more while maintaining the DVD format as the signal format such as the Ction Code) and the modulation method, the following equation 1 must be satisfied.

4.7 × (0.65 / 0.60 × NA / λ) ² ≧ 82 (Equation 1) From Equation 1, it is necessary that NA / λ ≧ 1.20. . That is, it is necessary to shorten the wavelength or increase the NA.

Here, for example, when the NA is increased, it is necessary to reduce the thickness of a portion through which the reproduction light is irradiated and transmitted. This is an angle at which the disk surface deviates from the optical axis of the optical pickup with respect to the optical axis of the optical pickup (so-called tilt angle, which is proportional to the square of the product of the reciprocal of the wavelength of the light source and the numerical aperture of the objective lens). This is because the permissible amount of the aberration generated due to the above becomes small, and the tilt angle is easily affected by the aberration due to the thickness of the substrate. Therefore, the thickness of the substrate is reduced to minimize the influence of aberration on the tilt angle.

[0015] For the same reason, it is necessary to keep the variation in the thickness of the portion through which the reproduction light is transmitted within a predetermined range.

However, it is considered that a higher recording density will be required in the future, and it will be necessary to further reduce the thickness of the substrate. Therefore, for example, irregularities are formed on one main surface of a substrate to form a recording layer, a reflective film is provided thereon, and a light transmitting layer, which is a thin film that transmits light, is further provided thereon. An optical recording medium that reproduces information on a recording layer by irradiating a reproducing light from the same, a reflective film is provided on one main surface of a substrate, and a magneto-optical recording film is formed thereon to form a recording layer. There has been proposed an optical recording medium in which a light transmitting layer, which is a thin film transmitting light, is provided thereon, and reproducing light is irradiated from the light transmitting layer side to reproduce information on a recording layer. In this case, it is possible to cope with a high NA of the objective lens by reducing the thickness of the light transmission layer.
Note that such a light transmitting layer is generally formed of an ultraviolet curable resin such as an acrylic polymer material.

[0017]

When the numerical aperture of the objective lens of the optical pickup is increased as described above, the working distance, which is the distance between the objective lens and the optical recording medium, is different from that of the conventional objective lens. If a similar lens is used, the size of the lens becomes extremely large, the weight becomes heavy, and the access time becomes slow, or a problem arises in that the band of the tracking and focus servo cannot be sufficiently secured.

To reduce the weight of the objective lens, in other words, to reduce the size of the objective lens, it is necessary to bring the objective lens closer to the optical recording medium, that is, to reduce the working distance. However, when the working distance is narrowed in this way, it is natural that the collision between the optical pickup and the optical recording medium easily occurs.

In the above-mentioned optical disk and magneto-optical disk, information is reproduced and / or recorded by irradiating light from the transparent substrate side. Since the shape can be easily formed by injection molding, it is generally formed of a plastic such as polycarbonate.

Therefore, when the optical pickup collides with the optical recording medium as described above, the optical recording medium is often damaged. That is, for example, when the objective lens of the optical pickup collides with the optical recording medium, the transparent substrate can be easily formed because the plastic such as polycarbonate forming the transparent substrate is much softer than the glass forming the objective lens. It is deformed, scratched and damaged. Further, a holder made of, for example, plastic for holding the objective lens is provided, and when the distance between the holder and the optical recording medium is smaller than the distance between the objective lens and the optical recording medium, the holder collides with the transparent substrate. Will be done. In this case, since the plastic forming the holder is softer than the glass forming the objective lens, the holder does not damage the transparent substrate,
If dust or fine dust in the air is trapped between the holder and the transparent substrate, they cause damage and damage. Such scratches due to dust and fine dust in the atmosphere can be dealt with by signal processing such as error correction when they occur discretely, but when they occur along the track direction, the error length is long, It is not preferable because error correction is difficult, and an error signal is continuously given to a tracking or focus servo signal, the servo is removed, and reliability is impaired.

Therefore, in a certain type of magneto-optical disk, displacement in the thickness direction due to a change in environmental temperature or humidity is ±±.
Although the collision with the optical pickup is suppressed as much as possible by suppressing it to 0.2 (mm) or less, if the working distance is narrowed, the collision is likely to occur.

By the way, in an optical recording medium in which a light transmitting layer is provided and light is irradiated from the light transmitting layer side as described above, since the light transmitting layer is a thin layer, if dust adheres to this surface, However, the error rate deteriorates, making it difficult to obtain sufficient reliability.

In a magnetic disk which is a magnetic recording medium, a fiber called a liner is brought into contact with the surface of the magnetic disk to remove dust, and such a method is very effective also in the above-mentioned optical recording medium. And implementation is desired. However, in this case,
It is necessary that the surface of the optical recording medium, here the light transmitting layer surface, has a strength that does not damage the fibers due to contact with the fibers or contact with the fibers in a state in which dust or dust in the air is sandwiched therebetween,
Such demands are increasing.

Further, in such an optical recording medium as provided with such a light transmitting layer and irradiating light from the light transmitting layer side.
It is strongly desired to achieve a storage capacity of (GB) or more.

Therefore, the present invention has been proposed in view of the actual situation in the related art, and a transparent cover layer formed on a recording layer such as a transparent substrate or a light transmitting layer to which light is irradiated is hardly damaged. An object of the present invention is to provide an optical recording medium in which damage is less likely to occur and reliability is ensured. It is another object of the present invention to provide an optical recording medium which can cope with an increase in NA and can record information of, for example, 8 (GB) or more, with an increase in capacity.

[0026]

Means for Solving the Problems As a result of diligent studies conducted by the present inventors to solve the above-mentioned problems, as a result, light is radiated on a recording layer such as a transparent substrate or a light transmitting layer of an optical recording medium. It has been found that by increasing the hardness of the surface side of the transparent cover layer, it is possible to suppress the occurrence of scratches on the transparent cover layer, suppress damage to the optical recording medium, and ensure reliability.

The present inventors have further studied and made it possible to cope with an increase in NA, and to increase the capacity, for example, to 8 (G
B) The present inventors have found appropriate conditions for an optical recording medium on which the above information can be recorded, and appropriate conditions for an optical disc device suitable for recording and / or reproduction of the optical recording medium.

That is, in order to achieve the above object, the optical recording medium of the present invention has a transparent cover layer made of a material having a Young's modulus of 70 (GPa) or more on one principal surface side of the recording layer. From the transparent cover layer side, the numerical aperture is 0.1.
The recording and / or reproduction of information is performed by irradiating light using seven or more objective lenses.

As the index of the hardness of the surface, Mohs hardness, Rockwell hardness, pencil hardness and the like can be cited, but there is no unified one and it is difficult to compare. Therefore, in the present invention, the Young's modulus (elastic modulus) in a bulk state, which is closely related to the hardness of the material, is used as an index.

In the optical recording medium of the present invention, the thickness of the transparent cover layer may be 150 (μm) or less.

In the above-mentioned optical recording medium of the present invention,
If the transparent cover layer is formed of the first layer disposed on the surface side and the second layer disposed on the recording layer side, the transparent cover layer is easily formed and is preferable.

In this case, the first layer has a Young's modulus of 15
0 (GPa) or more.
If the Young's modulus of the layer is smaller than 150 (GPa), it is difficult to secure sufficient hardness, which is not preferable. Also,
It is preferable that the thickness of the first layer is not less than 2 (nm) and not more than 230 (nm). If the thickness of the first layer is less than 2 (nm), it is difficult to secure the strength. If the thickness of the first layer is larger than 230 (nm), the surface reflection becomes too large, which is not preferable.

Further, in the optical recording medium of the present invention, the surface side of the transparent cover layer is C _100-X H _X (1 (at.%)).
<X <45 (atomic%)), Si ₃ N ₄ , MgF ₂ , Al ₂ O
₃ , it is preferable to be made of a material containing at least one of SiO ₂ .

Further, in the optical recording medium of the present invention, the recording layer
The thickness t of the transparent cover layer is t = 3 to 177 (μm), which is disposed on the support layer and at least in an information signal portion area of the recording layer where an information signal is recorded. When the thickness unevenness of the transparent cover layer is Δt, the numerical aperture N of the optical system for recording and / or reproducing the optical recording medium is described.
A and the wavelength λ, Δt ≦ ± 5.26 (λ / N
A ⁴ ) (μm).

In the optical recording medium of the present invention, the track pitch P satisfies P ≦ 0.64 (μm) and the skew Θ satisfies Θ ≦ ± 84.115 ° (λ / NA ³ / t). preferable.

Further, in the optical recording medium of the present invention, the wavelength λ is λ ≦ 0.68 (μm) and the numerical aperture NA is NA /
Recording or reproduction is preferably performed by a recording / reproducing optical system that satisfies λ ≧ 1.20. A laser light source having a wavelength of 680 (nm) or less and a numerical aperture NA for converging the laser light on a signal recording surface are set to 0.1. It is preferable to use an optical disk device having seven or more lenses.

In the optical recording medium of the present invention, since a transparent cover layer having a surface having a Young's modulus of 70 (GPa) or more is formed on one main surface side of the recording layer, an opening is formed from the transparent cover layer side. When the working distance is narrowed by using an objective lens of several 0.7 or more to irradiate light, even if a collision with an optical pickup occurs, generation of scratches on the transparent cover layer is suppressed, and optical recording is performed. Generation of scratches on the medium surface is suppressed. Further, in the optical recording medium of the present invention, even if the fibers used in the above-described magnetic disk are brought into contact with the transparent cover layer to remove dust on the surface, the generation of scratches on the transparent cover layer is suppressed. In addition, generation of scratches on the surface of the optical recording medium can be suppressed.

In the optical recording medium of the present invention,
When the thickness of the transparent cover layer is set to 150 (μm) or less, it can sufficiently cope with a high numerical aperture of the objective lens of the optical pickup.

Further, in the optical recording medium of the present invention,
If the transparent cover layer is formed by the first layer disposed on the surface side and the second layer disposed on the recording layer side, the hardness on the surface side can be easily increased, and the transparent cover layer can be easily formed. Formed.

Further, in the optical recording medium of the present invention,
Thus, the information in which at least the information signal in the recording layer is recorded
In the area of the signal section, the thickness t of the transparent cover layer is
t = 3 to 177 (μm), and the thickness unevenness of the transparent cover layer
Is Δt, the optical recording medium is recorded and / or
Δ between the numerical aperture NA of the optical system to be reproduced and the wavelength λ
t ≦ ± 5.26 (λ / NA^Four) (Μm)
And the track pitch P is P ≦ 0.64 (μ
m), the skew Θ is ± ≦ 84.115 ° (λ / NA ^Three
/ T), and the wavelength λ is λ ≦ 0.68 (μ
m), a description that the numerical aperture NA satisfies NA / λ ≧ 1.20.
If recording or reproducing is performed by the recording / reproducing optical system, high N
A, which is sufficiently compatible with A, and has a high capacity, for example, 8 (G
B) The above recording capacity is achieved.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described in detail.

The optical recording medium of this embodiment has a transparent cover layer on the one principal surface side of the recording layer whose surface is made of a material having a Young's modulus of 70 (GPa) or more. The recording and / or reproduction of information is performed by irradiating light using an objective lens of .7 or more.

As a first example of the optical recording medium of the present invention, an example in which the present invention is applied to a magneto-optical disk will be described.

That is, in the magneto-optical disk of this embodiment, a transparent dielectric film such as silicon nitride is formed on one main surface of a transparent substrate, and a magneto-optical recording film such as TbFeCo is formed thereon as a recording layer. Further, a transparent dielectric film such as silicon nitride is formed, a reflective film such as an aluminum film is formed, and a protective film made of an ultraviolet curable resin is formed.

In the magneto-optical disk of this embodiment, since light is irradiated from the transparent substrate side, the transparent substrate is formed as a transparent cover layer, and the surface side of the transparent substrate has a Young's modulus of 7.
It is formed of a material of 0 (GPa) or more.

In the magneto-optical disk of this embodiment,
The thickness of the transparent cover layer, that is, the transparent substrate is 150 (μ
m) is as follows.

Further, in the magneto-optical disk of the present invention, the transparent cover layer, that is, the surface side of the transparent substrate is C
_100-X H _X (1 (at.%) <X <45 (at.%)), Si
₃ N ₄ is formed _{by, MgF 2, Al 2 O 3} , the material contains at least one of SiO _2, the Young's modulus as described above have been made with 70 (GPa) or more.

In the magneto-optical disk of this embodiment, a transparent substrate made of a material having a Young's modulus of 70 (GPa) or more is used as a transparent cover layer, and an objective lens having a numerical aperture of 0.7 or more is formed from the transparent cover layer side. If the working distance is narrowed and light is applied, even if collision with the optical pickup occurs, the occurrence of scratches on the transparent cover layer is suppressed, and the occurrence of scratches on the surface of the magneto-optical disk is suppressed. Damage is less likely to occur and reliability is ensured.

In the magneto-optical disk of this embodiment,
Even when the transparent cover layer is brought into contact with a fiber called a liner used in a magnetic disk, the generation of scratches on the transparent cover layer is suppressed, the generation of scratches on the surface of the magneto-optical disk is suppressed, and the damage is prevented. Less likely to occur and reliability is ensured. Further, as the above-mentioned fiber, a non-woven fabric made of rayon, polyester, polypropylene, and nylon can be used. In this case, in order to prevent abrasion of the magneto-optical disk and the non-woven fabric, a transparent cover of the magneto-optical disk is used. The surface of the layer or the surface of the nonwoven fabric may be coated with a lubricating material.

In the magneto-optical disk of the present embodiment, the thickness of the transparent cover layer, that is, the transparent substrate is set to 150.
(Μm) or less, which sufficiently corresponds to a high numerical aperture of the objective lens of the optical pickup.

In the above-described example, the example in which the transparent substrate serving as the transparent cover layer is a single layer has been described. However, the transparent substrate is provided with the first layer disposed on the surface side and the transparent substrate disposed on the recording layer side. It may be formed by two layers, and in this case, the hardness on the surface side can be easily increased.

In this case, the first layer has a Young's modulus of 15
0 (GPa) or more.
If the Young's modulus of the layer is smaller than 150 (GPa), sufficient hardness cannot be secured, which is not preferable. Also,
It is preferable that the thickness of the first layer is not less than 2 (nm) and not more than 230 (nm). If the thickness of the first layer is less than 2 (nm), it is difficult to secure the strength. If the thickness of the first layer is larger than 230 (nm), the surface reflection becomes too large, which is not preferable.

Further, in this embodiment, an example in which the present invention is applied to a magneto-optical disk has been described. However, the present invention relates to an optical recording medium having an optical disk, a light-transmitting layer, and a transparent cover layer, which is irradiated with light. Needless to say, the present invention can be applied to any of the above.

When the transparent cover layer is made of an ultraviolet curable resin made of an acrylic polymer material or the like, the composition of the ultraviolet curable resin is changed or particles such as glass are mixed in the ultraviolet curable resin. By doing so, it is possible to increase the hardness on the surface side.

Next, as a second example of the optical recording medium of the present invention, an example will be described in which a light transmitting layer having a light transmitting layer is applied to an optical disk irradiated with light as a transparent cover layer.

The optical disk of this embodiment is also the same as the above-described magneto-optical disk, and has a transparent cover layer made of a material having a Young's modulus of 70 (GPa) or more on one main surface side of the recording layer. In addition, information is recorded and / or reproduced by irradiating light from the transparent cover layer side using an objective lens having a numerical aperture of 0.7 or more.

In the magneto-optical disk of this embodiment, since light is irradiated from the light transmitting layer side, the light transmitting layer is formed as a transparent cover layer, and the surface side of the light transmitting layer has a Young's modulus of 7.
It is formed of a material of 0 (GPa) or more.

Further, in the optical disk of this embodiment, 8
(GB) information can be recorded.

First, the thickness of the transparent cover layer will be described. In general, there is a correlation between the disc skew margin Θ and the wavelength λ of the recording / reproducing optical system, the numerical aperture NA, and the thickness t of the transparent cover layer. The relationship between these parameters and the skew に based on the example of a compact disk (hereinafter, referred to as a CD) is disclosed in Japanese Patent Application Laid-Open No. 3-225650.

According to this, Θ ≦ ± 84.115 ° (λ
/ NA ³ / t), which can be applied to the optical recording medium of the present invention, and is also applied to the optical disk of this example.

Here, considering a specific limit value of the skew 場合 when the disks are actually mass-produced, it is appropriate to set the skew to 0.4 °. This is because, when considering mass production, if the size is smaller than this, the yield decreases and the cost increases. Note that the existing optical recording medium is also set at 0.6 ° for a CD and 0.4 ° for a DVD. In the optical disk of the present embodiment, the skew 光 デ ィ ス ク is set to 0.4 ° or less.

Therefore, it is necessary to calculate how much the thickness of the light transmitting layer should be set in order to cope with the shortening of the wavelength of the laser beam used for recording and / or reproduction and the increase of the NA when Θ = 0.4 °. Then, assuming that λ = 0.65 (μm), N
A is required to satisfy NA / λ ≧ 1.20 to 0.78 or more. From this, t ≦ 288 (μm) is derived.

In the future, as the wavelength becomes shorter, λ = 0.4
(Μm), the NA is set to NA ≧ 0.78
If left as it is, t = 177 (μm). In this case, the thickness of the optical disk to which the present invention is applied is up to about 1.38 (mm) in consideration of diverting manufacturing equipment for CDs or the like having a substrate thickness of 1.2 (mm).

In consideration of the magnetic field modulation of the magneto-optical recording medium (hereinafter referred to as MO), the thickness of the transparent cover layer is preferably small. For example, when the thickness is set to 30 (μm) or less, recording and reproduction with the MO is easy. become.

On the other hand, the lower limit of the thickness of the transparent cover layer is determined by the protective function of the transparent cover layer for protecting the recording film or the reflective film. (Μm) or more is desirable.

As described above, it is essential to increase NA / λ in order to increase the recording density. In this case, for example, in order to achieve a storage capacity of 8 (GB), at least NA is set to 0.7 or more, and the wavelength λ of the laser is set to 0.1.
68 (μm) or less. At this time,
Although there is the relationship described above between the thickness of the transparent cover layer and the skew as described above, in consideration of supporting the current red laser to the blue laser expected to spread in the future, the transparent cover Layer thickness is 3-177
(Μm) is appropriate.

Therefore, in the optical disk of this embodiment, the thickness t of the transparent cover layer is set to 3 to 177 (μm).

Next, the track pitch will be described. In order to achieve a recording capacity of 8 (GB) as in the present invention, it is necessary to change the track pitch P and the linear density d. The condition may satisfy the following Expressions 2 and 3.

(0.74 / P) × (0.267 / d) × 4.7 ≧ 8 (Expression 2) d ≦ 0.1161 / P (μm / bit) (Expression 3) For example, when P = 0.56 (μm), d ≦ 0.206
(Μm / bit), which corresponds to the ROM (R
(Ead Only Memory),
Advances in signal processing technology for recording and reproduction (specifically, PRML
Application and reducing the redundancy of ECC)
Further, the linear density is expected to increase by about 15%, and the track pitch P can be increased accordingly. From this, it is derived that the track pitch P becomes 0.64 (μm) at the maximum.

Therefore, in the optical disk of this embodiment, the track pitch P is set to P ≦ 0.64 (μm).

Further, in the optical disk of the present embodiment, the tolerance for the track pitch unevenness ΔP becomes strict. C
If the recording / reproducing parameters of D and DVD are diverted as they are, the DVD pitch is 0.74 (μm) and the tolerance is ± 0.0.
From 3, ΔP ≦ ± 0.03P / 0.74 = ± 0.04P
Becomes Therefore, if P = 0.56, ΔP ≦ ±
0.023 (μm).

Therefore, in the optical disk of this embodiment, the track pitch unevenness ΔP is set to ΔP ≦ ± 0.04P.

Next, the thickness unevenness of the transparent cover layer will be described. In the optical disc of this example, even higher accuracy is required for the thickness unevenness Δt of the transparent cover layer.

When the thickness of the transparent cover layer deviates from the design center of the reproduction objective lens, the amount of aberration given to the spot by the thickness error is proportional to the fourth power of NA and proportional to the wavelength. Therefore, when increasing the density by increasing the NA or shortening the wavelength,
The amount (uneven thickness of the transparent cover layer) is more severely limited.

As a specific system example, a CD is practically used with NA = 0.45, and the thickness error standard of the transparent cover layer is ± 100 (μm). Also,
In DVD, it is specified that NA = 0.6 and ± 30 (μm). That is, the thickness irregularity Δt of the transparent cover layer is expressed as in the following Expression 4 on the basis of the permissible amount ± 100 (μm) in CD.

Δt = ± (0.45 / NA) ⁴ × (λ / 0.78) × 100 = ± 5.26 × (λ / NA ⁴ ) (μm) (Formula 4) Here, transparent For the center of the cover layer thickness 100 (μm),
FIG. 1 shows the results of an experiment conducted on the relationship between the transparent cover layer thickness error and the jitter value at a wavelength λ = 0.68 (μm) and NA = 0.875.

From FIG. 1, it can be seen that when ± 8 (%), which is the jitter reference when there is no perturbation such as skew in a DVD, is about ± 7 (μm).
The numerical value derived from the above equation is ± 6 (μm), and a good signal can be obtained from a disk medium satisfying this standard.

Therefore, as the density increases, the unevenness Δt allowed for the thickness of the transparent cover layer is ± 5.26 × (λ / N
A ⁴ ) (μm) or less.

Therefore, in the optical disk of this embodiment, when Δt is the thickness unevenness of the transparent cover layer, Δt ≦ Δt between the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing the optical disk. ± 5.26 (λ / NA ⁴ ) (μ
m) is established.

Next, the surface roughness Ra of the surface irradiated with light for recording and / or reproduction will be described. The thickness unevenness of the transparent cover layer described above is assumed to be uniform within the surface of the disk irradiated with the laser beam for recording and / or reproduction, and aberration can be corrected by shifting the focus point. However, if the thickness of the transparent cover layer is uneven in this area (in the spot), it cannot be corrected by adjusting the focus point. This amount needs to be suppressed to ± 3λ / 100 or less with respect to the thickness center value.

Therefore, in the optical disk of this embodiment, the surface to be irradiated with the light to be recorded and / or reproduced has a surface roughness Ra.
Is within ± 3λ / 10 within the spot size area on the surface
0 or less.

Next, eccentricity will be described. Regarding the eccentricity E as well, for the DVD of 50 (μm), E ≦ 50 × P /
0.74 = 67.57P (μm).

Therefore, in the optical disk of this embodiment, the eccentricity E is set to E ≦ 67.57P (μm).

That is, in the optical disk of this example,
At least the thickness t of the transparent cover layer in the area of the information recording section where the information signal is recorded is 3 to 177 (μm),
The difference Δt ≦ ± 5.26 (λ / NA ⁴ ) (μm) is established between the thickness variation Δt of the transparent cover layer and the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing the optical disk. And the track pitch P is set to P ≦ 0.64 (μ
m) and the track pitch unevenness ΔP is ΔP ≦ ± 0.04
P, and the linear density d is d ≦ 0.1161 / P (μm / bi
t) and the disk skew Θ is ± ≦ 84.115 °
(Λ / NA ³ / t) and the eccentricity E is E = 67.57P
(Μm) and the surface roughness Ra in the spot size area
Is Ra = ± 3λ / 100 or less, and the wavelength λ of the recording / reproducing optical system is λ ≦ 0.68 (μm), and NA /
By satisfying λ ≧ 1.20, a recording capacity of 8 (GB) is secured to achieve high density.

In order to manufacture the optical disk of the present example, a substrate is prepared by an injection molding method using a stamper which realizes the pitch and the pitch unevenness which meet the above-mentioned specifications required for the optical recording medium of the present invention. Such a high-precision stamper with little pitch unevenness is difficult to achieve with a conventional structure in which a feed is performed by a screw. Therefore, the stamper is manufactured using a master exposure apparatus having a linear motor feed structure. Furthermore, the optical system is covered with a cover for eliminating air fluctuations, and is formed by installing a vibration isolator between the laser and the exposure apparatus in order to eliminate the vibration of the cooling water of the exposure laser.

In the case of this example, a reflective film or a recording film is formed on the information signal surface of the substrate, and recording / reproducing is performed from above the recording film. Pits need to be formed on the substrate.

For example, in the case of a ROM having a capacity of 10 (GB), assuming that the asymmetry of a signal pit when viewed from the substrate side is 25 (%), the asymmetry when viewed from the side opposite to the substrate is 10 (%). ). That is, in this example, since an attempt is made to read a signal from the side opposite to the substrate side, for example, the asymmetry is 10 (%) when viewed from the light irradiation side.
In order to form a pit, the pit shape to be formed on the substrate must be asymmetry 25 (%).

Similarly, with respect to the guide groove (groove) formed on the recording disk, the groove duty is changed in the recording film. For example, in the case of groove recording (recording / reproducing to the concave portion as viewed from the recording / reproducing surface), the groove becomes narrower. Therefore, it is necessary to take measures such as making the shape of the stamper wider. For example, in the case of land / groove recording, in order to obtain a land and groove width duty of 50 (%) from the light irradiation side, it is preferable to set the width to 55 to 65 (%) from the substrate side.

When a single plate is used to form a disk, this substrate requires a certain degree of rigidity, so that the substrate has a thickness of 0.6 (m).
m) or more. Similarly, in the case of a structure in which two sheets are bonded to each other, it is preferable that the thickness is 0.3 (mm) or more, which is a half thereof.

Next, as shown in FIG. 2, an information recording film or a reflection film is formed on the information signal portion 11 of the substrate 10, and
It is a recording layer. At this time, the substrate 10 becomes a support layer. For example, when the disk is a ROM, a reflective film of Al or the like is formed to a thickness of 20 to 60 (nm).

As the information recording film, for example, when a phase change material is taken as an example, an Al film, ZnS—SiO ₂ , GeSbTe,
ZnS—SiO ₂ is formed in this order.

In the case of a magneto-optical disk, an Al film,
It is formed in the order of SiN, TbFeCo, and SiN.

In the case of the write-once type, after sputtering Au or Al, a cyanine-based or phthalocyanine-based organic dye film is applied by spin coating and dried.

In the example shown in FIG. 2, the recording / reproducing light is irradiated from the side opposite to the substrate 10 through the recording / reproducing objective lens L.

Next, as shown in FIG. 3, a transparent cover layer 12 is further formed thereon with an ultraviolet curable resin. For example, the transparent cover layer 12 is formed by dropping and rotating an ultraviolet curable resin on the film-forming surface of the substrate 10 formed with any of the structures formed as described above.

The viscosity of the ultraviolet curable resin is 3
Thicknesses between 00 (cps) and 6000 (cps) are suitable for forming the thickness described above.

For example, 5800 (cps) at 25 (° C.)
When an ultraviolet curable resin having a viscosity of is applied, the ultraviolet curable resin is dropped on the substrate, and then the substrate is 2,000 (r).
pm) for 11 seconds, finally
The transparent cover layer 12 having a thickness of about 0 (μm) can be formed.

Here, when the transparent cover layer 12 is formed, an ultraviolet curable resin is dropped on the inner peripheral portion of the substrate 10, for example, at a position of a radius of 25 (mm), and is rotated and stretched. Due to the relationship, there is a difference between the inner and outer circumference in the thickness. This amount is 3
0 (μm) or more, and cannot satisfy the described thickness range.

In order to avoid this, it is effective to drop the ultraviolet curable resin while the center hole 13 of the substrate 10 is filled by using any means. For example, 0.1
A (mm) -thick polycarbonate sheet is processed into a circular shape having a diameter Φ of 30 (mm) and adhered to the center of the substrate 10, and then an ultraviolet-curable resin is dropped from the center, subjected to rotational stretching, and subjected to rotation and stretching. Is applied to cure the ultraviolet curable resin, and then a center hole is punched out. According to this process, it is possible to obtain a light transmitting layer having a thickness within 10 μm pp (peak-to-peak) between the inner and outer circumferences.

In forming the transparent cover layer 12,
Since it is conceivable that the disk may protrude to the outer periphery of the disk, it is preferable that the maximum value of the disk diameter is 120 (mm) +5 (mm) based on the diameter of a CD or the like (120 (mm)).

Further, as shown in FIG.
0 (μm) polycarbonate sheet 14 is adhered with an ultraviolet curable resin 15 to form a transparent cover layer 12.
May be formed. In this case, the sum of the thickness unevenness of the sheet 14 and the thickness unevenness of the ultraviolet curable resin 15 for bonding is 10
(Μm) pp (peak-to-peak) or less.

For example, a sheet 14 processed to the same diameter as the substrate 10 is bonded to the substrate 10 via an ultraviolet curing resin 15 for bonding.
The sheet 14 becomes the weight of the ultraviolet-curable resin 15 by being placed on the upper side and is rotated and stretched to form an extremely thin layer of the ultraviolet-curable resin, and the total thickness unevenness is reduced to 10 (μ).
m) It can be less than pp (peak-to-peak).

Note that, in the present invention, as shown in FIG.
The present invention is also applicable to an optical recording medium having a multi-layer structure in which a second recording layer 18 is formed on a first recording layer 17 formed with an intermediate layer 16 on a first recording layer 17.

In the case of the optical disk having the above-described structure,
Skew is likely to occur. In the present invention, in particular, in order to reduce this skew, as shown in FIG. 6, an ultraviolet curable resin is used as a skew correction member 19 on the surface of the substrate 10 opposite to the surface on which the transparent cover layer 12 is formed. It is effective to apply.

In this case, the skew correction member 19 may be formed by coating with the same material as the transparent cover layer 12,
Alternatively, a material having a higher curing shrinkage than the ultraviolet curable resin as the material of the transparent cover layer 12 may be formed by applying a thin film.

In order to record / reproduce data on / from the above-described high-density optical disk, a pickup having a high NA objective lens, which will be described later, is required. In this case, as described above, it is desirable to make the distance between the objective lens and the disk surface and the working distance narrower than the conventional distance.

In this case, it is expected that the objective lens collides with the disk surface and damages the disk surface.

In order to prevent this, as shown in FIG. 7, a hard coat (pencil hardness) is formed on the transparent cover layer 12 so as to make the surface hardness of the transparent cover layer relatively high as in the above-described example. H or more) 20 may be applied.
When the thickness of the transparent cover layer 12 is reduced, the hard coat 20 may be provided with an antistatic function, because the transparent cover layer 12 is easily affected by dust. This prevention of charge makes it possible to prevent dust from adsorbing to the optical disk surface.

In the optical disk of this example, when the wavelength of the light for recording and / or reproduction is 780 (nm), the in-plane birefringence of the transparent cover layer averages 15 times in both directions.
(Nm) or less, it is preferable that the fluctuation in the circumference is 15 (nm) pp (peak-to-peak) or less.

In the optical disk of this example, for example,
A recording / reproducing experiment was performed when a transparent cover layer was formed using a 00 (μm) polycarbonate sheet and the recording layer was a phase change film. In this case, the linear density is 0.21 (μm
/ Bit), a jitter of 8 (%) was obtained. Further, the birefringence of such an optical disk was measured. FIG. 23 shows the measurement results. In FIG. 23, the horizontal axis indicates the radial position (mm), and the vertical axis indicates the birefringence (nm). In FIG. 23, the distribution is represented by vertical line segments, and the position of a horizontal line segment crossing each line segment is the average value. The birefringence amount is 15 (nm) or less on average in the round trip, and the fluctuation in the circumference is 15 (n).
m) It could be less than pp (peak-to-peak).

In the optical disc of the present example, a transparent cover layer is formed by applying a liquid photocurable resin on the information recording layer, stretching it by rotation, and then photocuring it to form a phase change film as the recording layer. A similar recording / reproducing experiment was performed.

In this case, the linear density is 0.21 (μm / bi
At t), a jitter of 7 (%) was obtained. Further, the birefringence of such an optical disk was measured. This measurement result is shown in FIG.
It is shown in FIG. In FIG. 24, the horizontal axis represents the position in the radial direction (m
m), and the vertical axis indicates the amount of birefringence (nm). In FIG. 24, the distribution is represented by vertical line segments, and the position of a horizontal line segment crossing each line segment is the average value. The birefringence amount can be further reduced as compared with the case where the transparent cover layer is formed of a polycarbonate sheet, and the birefringence amount is an average of 5 times in reciprocation.
(Nm) or less, the variation in the circumference is 5 (nm) pp (peak
To peak) or less.

As described above, the optical disk of the present example is a conventional C
It can be seen that D and DVD have stable and excellent characteristics as compared with the in-plane birefringence of 100 (nm).

In the optical recording medium of the present invention, the surface on which the recording layer is formed may be subjected to a silane treatment. By performing the silane treatment in this manner, it is possible to improve the adhesion between the ultraviolet curable resin forming the transparent cover layer and the recording layer surface.

Further, in the optical recording medium of this example, an antireflection film may be formed on the surface of the transparent cover layer by, for example, a method such as sputtering.

It is desirable that the refractive index N of the antireflection film is lower than the refractive index of the transparent cover layer, and the thickness of the antireflection film depends on the wavelength of light for recording and / or reproduction. Where λ is (λ / 3) / N (nm)
Hereinafter, it is more desirable to set it to about (λ / 4) / N (nm).

When the NA is high as in the optical recording medium of the present embodiment, the incident angle of recording / reproducing light for recording and / or reproducing is also increased, whereby the reflection of light on the surface of the transparent cover layer cannot be ignored.

For example, when NA = 0.45, the incident angle of the recording / reproducing light is 26.7 °, and when NA = 0.6, it is 36.9 °.

When NA = 0.8, the incident angle of the recording / reproducing light is as high as 53.1 °. It has been confirmed that the reflectance of light on the surface of the transparent cover layer depends on the incident angle of the recording / reproducing light. When the refractive index of the transparent cover layer is, for example, 1.52, the s-polarized light component The surface reflectance exceeds 15 (%). (See page 168 of "Laser and Optics Guide" published by Kinomeles Griot Co., Ltd.) In this case, the problem of light amount loss occurs and the effective NA decreases.

Therefore, in order to avoid such a problem, it is effective to form an antireflection film on the surface of the transparent cover layer.

When the refractive index of the transparent cover layer is 1.52, the material of the antireflection film has an optical refractive index of 1.
It is known that it is ideal to use about 23 (Kyoritsu Shuppan Optical Technology Series 11 Optical Thin Film
See page 28). However, industrially, for example, MgF ₂ is used. The refractive index N of MgF ₂ is 1.38.

Assuming that the wavelength of the recording / reproducing light is 650 (nm), the thickness of the antireflection film made of MgF ₂ is (λ / 4)
By substituting each numerical value into the equation of / N (nm), about 1
It can be seen that it is preferable to form the layer to a thickness of 20 (nm).

By the way, the amount of light reflected on the surface of the transparent cover layer is determined by changing the thickness of the antireflection film from zero to (λ / 4) / N.
(Λ) / N
(Nm), it has been confirmed that the minimum value is obtained. On the other hand, when the thickness of the antireflection film is (λ / 4) / N (nm)
, The amount of light reflection increases, and (λ / 2) / N (n
It has been confirmed that the maximum value is obtained when m). From this, it was confirmed that the thickness of the anti-reflection film should be not more than (λ / 3) / N (nm) for practical use in consideration of the film-forming technology.

When an antireflection film is formed on the surface of the transparent cover layer as described above, for example, a single layer of MgF ₂ (λ /
4) When formed to a thickness of / N (nm), when a recording / reproducing light having a thickness of 550 (nm) is used, the incident angle of the recording / reproducing light is not less than 50 (%) up to about 60 °. Can prevent the decrease in the amount of light (1 of Laser & Optics Guide published by Kinomeles Griot Co., Ltd.)
See page 74).

According to the present invention, not only a disk having a single plate structure but also a structure in which two substrates 51 and 52 each having a half thickness of the finally obtained substrate 10 are bonded together as shown in FIG. It is also applicable to optical recording media (optical disks). In this case, a maximum of 1 is applied to the substrates 51 and 52 having a thickness of 0.6 (mm).
Since a 70 (μm) transparent cover layer is formed and bonded, the thickness of the disc is (0.6 + 0.17) × 2 + (thickness of the adhesive layer), and the thickness of the adhesive layer is 0.06 (mm). )
Then, the thickness of the optical disk is 1.60 (mm). Further, as shown in FIG. 9, the present invention is also applicable to an optical recording medium (optical disk) having a structure in which an information signal portion and a transparent cover layer 12 are provided on both surfaces of one substrate 50.

An example of manufacturing the above optical disk will be described. As shown in FIG. 10, for example, a polycarbonate sheet 40 having a thickness of, for example, 100 (μm) made by extrusion molding or casting is prepared, and a roller 4 is placed on a stamper 41 heated to a temperature higher than the glass transition point.
2. Pressure is applied to 2 to apply pressure. The pressure in this case can be, for example, 280 (Kgf).

By this operation, information pits or guide grooves of the stamper 41 are transferred to the sheet 40 as shown in FIG. And after cooling this, stamper 4
The sheet is peeled from the substrate 1 to form a thin substrate 43 having a thickness of 100 (μm), for example.

Subsequently, a recording film or a reflection film is formed in the same manner as in the above-described manufacturing method, so that a thin optical recording medium can be finally obtained.

Using the thin substrate 43 shown in FIG. 11, an optical recording medium having a multilayer structure can be manufactured.

In this case, first, as shown in FIG. 12, the liquid ultraviolet curable resin 60 is dropped on the stamper 141, and the thin substrate 43 shown in FIG. And install it.

Then, as shown in FIG. 13, the stamper 141 on which the thin substrate 43 is superimposed is rotated while being placed on the rotating base 61 via the liquid ultraviolet curable resin 60, and the liquid ultraviolet curable resin 60 Is stretched to a required thickness, for example, 20 (μm). Thereafter, as shown in FIG. 14, ultraviolet rays are irradiated from the side of the thin plate substrate 43 by the lamp 62, and the liquid ultraviolet curable resin 60 is light-cured.

Subsequently, as shown in FIG.
3 and the UV-curable resin 60 having a thickness of, for example, 20 (μm), which has been photocured, are integrally separated from the stamper 141.

As described above, it is possible to form a recording layer by forming a metal thin film such as a Si compound or Al or Au on the fine irregularities transferred to the ultraviolet curable resin 60 by the stamper 141. it can.

Further, by repeating the steps described with reference to FIGS. 12 to 15, an optical disc in which an information recording film or a reflective film and a transparent cover layer are laminated in three or more layers can be produced.

Then, as shown in FIG. 16, the substrate 10 obtained by, for example, injection molding is placed on the finally obtained recording layer via an ultraviolet curable resin 60, for example, for 20 μm.
By bonding together at intervals of m), an optical disk having high rigidity can be obtained.

As shown in FIG. 17, a high-reflection film 70 of, for example, Al or Au is formed on the finally obtained recording layer, and a protective film 71 is further formed. A thin optical disk can be manufactured.

In this case, when the number of recording layers is N,
The thickness of the optical disk finally obtained is, for example, 100 (μm) of the thickness of the thin plate substrate 43, N times the thickness of the ultraviolet curable resin layer between the layers, and the thickness of the high reflection film 70 and the protection film 71. For example, 5 (μm). That is, for example, when the thickness of the ultraviolet curable resin layer between the respective layers is 20 (μm) and the thickness of the high reflection film 70 and the protective film 71 is 5 (μm), an optical disc having a four-layer structure is manufactured. Then, the entire optical disc has a thickness of 185 (μm).

However, the optical disk obtained in this way has a very low rigidity. Therefore, a rigid thick plate is bonded to the thin substrate 43 side and supported, or a flexible optical disk is rotated by high-speed rotation during recording and reproduction. A device such as recording / reproducing using the flatness is required.

The numerical value of 20 (μm) in the example of the thickness between the recording layers described above is determined by the number of layers of the optical disk finally obtained and the movable distance of the lens of the pickup for recording and reproducing the optical disk. Is done.

For example, when the movable distance of the lens, that is, the distance between the second group lenses is 50 (μm), as shown in FIG. 18, the substrate 10 and the thin substrate 43 are cured by ultraviolet rays at an interval of 50 (μm). It is sufficient to bond them together via a resin. When an optical disk having a three-layer structure is manufactured as shown in FIG.
(Μm) with the recording layer interposed therebetween.

Further, according to the present invention, in addition to the optical disk having the above-described structure, as shown in FIG. 20, a thin substrate 43 and a disk-like substrate 50 having a thickness of, for example, 1.1 (mm) formed by injection molding, for example. Can also be applied to an optical disc that is bonded by bonding by applying an ultraviolet curable resin and pressing it, and irradiating ultraviolet rays from the transparent substrate side.

Further, in the present invention, as shown in FIG. 21, a thin plate substrate 43 and a substrate 50 on which fine irregularities for forming a recording layer are transferred by injection molding and a thin plate substrate 43 are interposed via an ultraviolet curable resin. Laminated and crimped, thin substrate 4
The present invention can also be applied to an optical disc having a four-layer structure finally by irradiating ultraviolet rays from the three sides and bonding.

Next, the depth of pits or grooves formed on the substrate will be described. Hereinafter, the refractive index of the transparent cover layer is set to N.

The depth of the pit or groove at which the highest modulation is obtained is (λ / 4) / N, and the ROM or the like is set to this depth.

Further, in the case of trying to obtain a tracking error signal by push-pull in groove recording or land recording, the push-pull signal becomes maximum when the depth of the pit or land is (λ / 8) / N.

In land / groove recording,
The groove depth should consider the characteristics of the servo signal as well as the characteristics of crosstalk and cross-erase, and the crosstalk is experimentally determined to be (λ / 6) / N or (λ / 3)
/ N, and it is confirmed that deeper cross erase has less influence. In addition, if both characteristics are satisfied in consideration of the groove inclination and the like, (3λ /
8) Optimum around / N. In the present invention, it is preferable that the depth of the pit or groove is set within the above range.

Next, a description will be given of an embodiment of a lens which realizes a suitable high NA when applied to the optical disk apparatus of the present invention. FIG. 22 shows a configuration of a lens for realizing a high NA.

That is, the second lens 32 is disposed between the first lens 31 and the optical disk 21. As described above, the two-group lens configuration enables the NA to be 0.7 or more, and the first surface 32 of the second lens 32
a between the optical disk 21 and the surface of the optical disk 21 (WD) can be reduced.

It is preferable that the first surface 31a, the second surface 31b, the third surface 32a, and the fourth surface 32b of the first lens 31 and the second lens 32 have an aspheric shape, respectively.

In the optical disk device using the two-group lens, high-density recording and reproduction of the optical disk described above can be performed.

[0151]

EXAMPLES Next, in order to confirm the effects of the present invention, the following experiments were conducted.

EXPERIMENTAL EXAMPLE 1 In this experimental example, the relationship between the Young's modulus of the material forming the surface side of the transparent cover layer and the easiness of scratching was investigated.

That is, a radius of 60 (m) is used as an optical recording medium.
m) Various optical recording media are prepared and JIS
A small amount of dust JIS-15 specified by the standard was placed. Then, while a polyester fiber is put on the fiber and pressed with a pressure of 0.2 (g / cm ² ), the fiber is rotated for 1 minute at a rotation speed of 1800 (rpm) to obtain a radius of 40 (m).
The degree of scratch generation at the position m) was visually observed.

As the optical recording medium, one having a transparent cover layer made of polycarbonate and one having a transparent cover layer made of an ultraviolet-curable resin was prepared, and a 100 (μm) thick transparent cover layer was formed on the polycarbonate transparent cover layer. A film formed of a polycarbonate film, a film formed of a UV-curable resin having a thickness of 100 (μm) on a transparent cover layer formed of a UV-curable resin, and a transparent cover layer formed of a UV-curable resin CH of 50 (nm) thickness
That the (hydrogenated amorphous carbon) formed by a CVD method, was prepared _{Si 3 N 4, MgF 2,} Al 2 O 3, SiO 2 and those formed by respectively sputtering. That is, as a result, the transparent cover layer is constituted by the first layer disposed on the surface side and the second layer disposed on the recording layer side.

Table 1 shows the results.

[0156]

[Table 1]

In Table 1, the first layer forming material, the first layer thickness, the first layer forming material Young's modulus, the first layer forming material pencil hardness, the second layer forming material, Is also shown. However, the Young's modulus indicates the Young's modulus in a bulk state, and the pencil hardness is to indicate the hardness of the ultraviolet-curable resin from which accurate measurement of the Young's modulus is not possible. Pencil hardness indicates hardness in a state of being cured on a glass substrate.

From the results shown in Table 1, it can be seen that in the optical recording medium in which the first layer on the surface side is formed of a soft material such as polycarbonate or an ultraviolet curable resin, an extremely large number of scratches are observed. However, among these, the optical disk in which the first layer is formed of a relatively hard UV-curable resin is more resistant to scratching, and the hardness of the surface side of the transparent cover layer is less likely to cause scratching. It is understood that it is greatly involved in.

Further, from the results shown in Table 1, in the optical recording medium in which the first layer on the surface side is formed of SiO ₂ or MgF ₂ having a Young's modulus of 70 (GPa) or more, abrasion is considerably suppressed. And the first layer on the surface side has a Young's modulus of 15
It can be seen that no abrasion has occurred in the optical recording medium formed of Al ₂ O ₃ , Si ₃ N ₄ , CH (amorphous hydrogenated carbon) of 0 (GPa) or more. This is probably because the hardness of the surface is sufficiently hard.

That is, when the transparent cover layer is formed of a material having a Young's modulus of 70 (GPa) or more as in the present invention, the generation of scratches on the surface side of the transparent cover layer can be suppressed, and the optical recording medium can be prevented. It was confirmed that generation of scratches on the surface was suppressed, breakage hardly occurred, and reliability was ensured.

Further, as in the present invention, the transparent cover layer is formed by the first layer disposed on the surface side and the second layer disposed on the recording layer side, and the first layer has a Young's modulus of 150 ( GPa) or more, the generation of scratches on the surface side of the transparent cover layer is further suppressed, the generation of scratches on the surface of the optical recording medium is further suppressed, damage is less likely to occur, and reliability is further secured. It was confirmed that it would be.

Further, as in the present invention, the surface side of the transparent cover layer is formed of C _{100 -X} H _X (1 (at%) <X <45 (at%)), Si ₃ N ₄ , MgF ₂ , Al ₂ O ₃ , it was confirmed that the hardness of the surface side of the transparent cover layer can be easily improved by forming the material including at least one of SiO ₂ .

EXPERIMENTAL EXAMPLE 2 In this experimental example, the first side on the front side of the transparent cover layer was used.
The relationship between the thickness of the layer and the likelihood of scratching, and the relationship between the thickness of the first layer on the surface side of the transparent cover layer and the reflectance were investigated.

That is, an optical recording medium having a diameter of 60 (mm) and a transparent cover layer made of an ultraviolet curable resin was prepared in the same manner as in Experimental Example 1, and a transparent cover layer made of an ultraviolet curable resin was formed of SiO ₂ on the transparent cover layer. The film having a thickness of 1 (nm), 2 (nm), 10 (nm), 50 (n) is formed by sputtering.
m) and 200 (nm), and a film made of Si ₃ N ₄ having a thickness of 1 (nm), 2 (nm), 10 (nm) and 50 on a transparent cover layer made of an ultraviolet curable resin.
(Nm) were prepared.

Then, the likelihood of occurrence of scratches on these optical recording media was examined in the same manner as in Experimental Example 1. Table 2 shows the results.

[0166]

[Table 2]

In Table 2, the first layer forming material, the first layer thickness, the second layer forming material, and the degree of scratches are also shown.

From the results in Table 2, it can be seen that regardless of the type of the first layer forming material, the larger the first layer thickness, the more the occurrence of scratches can be suppressed. Further, the first layer forming material is Si ₃ N ₄
In the case where the first layer has a thickness of 2 (nm)
It can be seen that the effect can be obtained with.

Incidentally, the first layer thickness has an upper limit due to an optical problem in addition to the film forming time.

That is, the first layer having the different refractive index and the second layer
And the reflected light at the boundary between the atmosphere and the first layer and the reflected light at the boundary between the first layer and the second layer interfere with each other. And the amount of light reaching the recording layer decreases. This causes problems such as a decrease in the level of the reproduction signal and a shortage of recording power.

Therefore, the refractive index of the transparent cover layer with respect to the atmosphere was fixed at 1.52, and the change in the reflectance with respect to light having a wavelength of 640 (nm) when the thickness of the first layer was changed was calculated. The first layer is made of MgF ₂ , Si
O ₂ , Al ₂ O ₃ , CH, and Si ₃ N ₄ were formed. The results are shown in FIG. In FIG. 25, the horizontal axis indicates the first layer thickness, the vertical axis indicates the reflectance, and x in the figure indicates M
The results of gF ₂ are shown, ○ in the figure shows the result of SiO ₂ , △ in the figure shows the result of Al ₂ O ₃ , ◎ in the figure shows the result of CH, and □ in the figure shows the result of Si ₃ N ₄ . The results are shown.

[0172] The refractive index of each material, MgF ₂ is 1.
38, SiO ₂ is 1.46, Al ₂ O ₃ is 1.60, CH
Is 1.80 and Si ₃ N ₄ is 2.00.

Further, the refractive index of the transparent cover layer with respect to the atmosphere was fixed at 1.38, and the change in reflectance with respect to light having a wavelength of 640 (nm) when the thickness of the first layer was changed was obtained by calculation. The first layer is made of SiO ₂ , Al
_It was formed of each of ₂ O ₃ , CH, and Si ₃ N ₄ . The results are shown in FIG. In FIG. 26, the horizontal axis indicates the first layer thickness, the vertical axis indicates the reflectivity, 図 indicates the result of SiO ₂ , △ indicates the result of Al ₂ O ₃ , ◎ indicates the result Is C
The results for H are shown, and the squares in the figure show the results for Si ₃ N ₄ .

From the results of FIGS. 25 and 26, when CH, Si ₃ N ₄ having a high refractive index is used, the reflectivity may be 10% or more depending on the thickness of the first layer. I understand. The reflectance of a transparent substrate made of ordinary polycarbonate is about 5 (%), and the reproduction signal level is 0.95 × compared to the case where there is no surface reflection due to surface reflection.
0.95 = 0.90. Assuming that the allowable value is 10 (%) lower than the conventional value of 0.9, the surface reflectance is allowable up to 10 (%).

To satisfy this condition, when the refractive index of the first layer forming material is 1.65 or less, or when the refractive index of the first layer forming material is larger than 1.65, for example, the refractive index Is 2.0, the first layer thickness is 30 (n
m) or 130 (nm) or more and 190 (nm) or less.

However, when a material having a refractive index in the range of about the refractive index of the material used in the present experimental example is used, the above-mentioned change in the surface reflectivity,
Considering that the strength is improved, the upper limit of the thickness is 2
It is considered to be about 30 (nm). When the thickness is more than this, when a material having a high refractive index is used, there is a concern that the surface reflectance does not become an allowable value due to a variation in thickness or the like, and the film forming time is not practical, which is not preferable. .

That is, based on the results of this experimental example, in the optical recording medium of the present invention, the case where the transparent cover layer is formed by the first layer disposed on the surface side and the second layer disposed on the recording layer side , The thickness of the first layer is 2 (nm) or more,
It was confirmed that it is preferable to set the thickness to 30 (nm) or less.

[0178]

As is apparent from the above description, in the optical recording medium of the present invention, a transparent cover layer made of a material having a Young's modulus of 70 (GPa) or more is formed on one principal surface of the recording layer. Therefore, if the working distance is reduced by using an objective lens having a numerical aperture of 0.7 or more from the transparent cover layer side to irradiate light, even if collision with the optical pickup occurs, the transparent cover The generation of scratches on the surface of the layer is suppressed, the generation of scratches on the surface of the optical recording medium is suppressed, breakage hardly occurs, and reliability is secured.

Further, in the optical recording medium of the present invention, even when the fiber used in a magnetic disk is brought into contact with the transparent cover layer, the generation of scratches on the transparent cover layer is suppressed, and the surface of the optical recording medium is prevented. Scratch is suppressed, damage is less likely to occur, and reliability is ensured.

In the optical recording medium of the present invention,
When the thickness of the transparent cover layer is set to 150 (μm) or less, it can sufficiently cope with a high numerical aperture of the objective lens of the optical pickup.

In the optical recording medium of the present invention,
If the transparent cover layer is formed by the first layer disposed on the surface side and the second layer disposed on the recording layer side, the hardness on the surface side can be easily increased, and the transparent cover layer can be easily formed. Formed.

Further, in the optical recording medium of the present invention, the thickness t of the transparent cover layer is set at t = 3 to 177 (μm) in at least the area of the information signal portion where the information signal is recorded in the recording layer. When the thickness unevenness of the transparent cover layer is represented by Δt, the difference Δ between the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing the optical recording medium is represented by Δt.
The relationship of t ≦ ± 5.26 (λ / NA ⁴ ) (μm) is satisfied, and the track pitch P is P ≦ 0.64 (μm).
m), the skew Θ is ± ≦ 84.115 ° (λ / NA ³
/ T), and the wavelength λ is λ ≦ 0.68 (μ
m), if recording or reproduction is performed by a recording / reproduction optical system in which the numerical aperture NA satisfies NA / λ ≧ 1.20, a high N
A, which is sufficiently compatible with A, and has a high capacity, for example, 8 (G
B) The above recording capacity is achieved. In addition, the optical recording medium of the present invention can achieve a higher capacity than a conventional optical recording medium with a simple recording / reproducing apparatus.

[Brief description of the drawings]

FIG. 1 shows a relationship of a change in a jitter value due to a thickness error of a transparent cover layer.

FIG. 2 is a schematic cross-sectional view of a main part schematically showing a state in which a recording layer is formed on a substrate.

FIG. 3 is a schematic cross-sectional view of a main part schematically showing an example of an optical disk to which the present invention is applied.

FIG. 4 is a schematic sectional view of a main part schematically showing another example of the optical disk to which the present invention is applied.

FIG. 5 is a schematic sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 6 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 7 is a schematic cross-sectional view of a main part schematically showing still another example of an optical disc to which the present invention is applied.

FIG. 8 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 9 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 10 is a side view schematically showing a step of pressing a sheet onto a stamper.

FIG. 11 is a side view showing a step of preparing a thin plate substrate.

FIG. 12 is a cross-sectional view schematically showing a step of disposing a thin plate substrate on a stamper via an ultraviolet curable resin.

FIG. 13 is a cross-sectional view schematically showing a step of stretching the ultraviolet curable resin.

FIG. 14 is a cross-sectional view schematically showing a step of curing an ultraviolet curable resin.

FIG. 15 is a cross-sectional view schematically showing a step of separating from a stamper.

FIG. 16 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 17 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 18 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 19 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 20 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 21 is a schematic cross-sectional view of a main part schematically showing still another example of the optical disc to which the present invention is applied.

FIG. 22 is an enlarged view showing a second group lens used in an optical disk device for recording and reproducing an optical disk to which the present invention is applied.

FIG. 23 shows an example of a measurement result of a birefringence amount of a transparent cover layer of an optical disc to which the present invention has been applied.

FIG. 24 shows another example of the measurement result of the birefringence amount of the transparent cover layer of the optical disc to which the present invention is applied.

FIG. 25 is a characteristic diagram showing an example of the relationship between the first layer thickness and the reflectance.

FIG. 26 is a characteristic diagram showing another example of the relationship between the first layer thickness and the reflectance.

[Explanation of symbols]

10, 50, 51, 52 substrate, 11 information signal section, 1
2 transparent cover layer, 13 center hole, 14, 40 sheets, 15 ultraviolet curable resin, 16 intermediate layer, 17 first recording layer, 18 second recording layer, 19 skew correction member, 20 hard coat, 21 optical disk, 31
1st lens, 32 2nd lens, 41, 141 stamper, 42 roller, 43 thin substrate, 60 liquid ultraviolet curable resin, 61 rotating base, 62 lamp,
70 high reflection film, 71 protective film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 7/24 534 G11B 7/24 534K 534M 541 541F 561 561N 561P 7/00 7/00 Q 7/135 7/135 Z

Claims (35)

[Claims] 1. A recording medium having a transparent cover layer on one principal surface side of a recording layer, which is irradiated with light from the transparent cover layer side using an objective lens having a numerical aperture NA of 0.7 or more to record and / or record information. Alternatively, in the optical recording medium to be reproduced, the surface side of the transparent cover layer is made of a material having a Young's modulus of 70 (GPa) or more. 2. The method according to claim 1, wherein the thickness of the transparent cover layer is 150 (μ).
m) The optical recording medium according to claim 1, wherein: 3. The optical recording medium according to claim 1, wherein said transparent cover layer comprises a first layer disposed on a surface side and a second layer disposed on a recording layer side. 4. The method according to claim 1, wherein the first layer has a Young's modulus of 150 (GP).
4. The optical recording medium according to claim 3, wherein the optical recording medium is made of the above material. 5. The method according to claim 1, wherein the thickness of the first layer is 2 (nm) or more.
The optical recording medium according to claim 3, wherein the optical recording medium has a thickness of 230 (nm) or less. 6. The transparent cover layer having a surface side of C _100-X H _X
(1 (atomic%) <X <45 (atomic%)), Si ₃ N ₄ , M
_2. The optical recording medium according to claim 1, wherein the optical recording medium is made of a material containing at least one of gF ₂ , Al ₂ O ₃ , and SiO ₂ . 7. The recording layer is provided on a support layer, and the thickness t of the transparent cover layer is at least t = at least in an area of an information signal portion where an information signal is recorded in the recording layer.
3 to 177 (μm), and when the thickness unevenness of the transparent cover layer is Δt, Δt is set between the numerical aperture NA and the wavelength λ of the optical system for recording and / or reproducing the optical recording medium. ≤ ± 5.26 (λ / NA ⁴ )
2. The optical recording medium according to claim 1, wherein a relationship of (μm) is satisfied. 8. When the track pitch is P and the skew is Θ, P ≦ 0.64 (μm) and Θ ≦ ± 84.115 ° (λ /
The optical recording medium according to claim 7, wherein NA ³ / t) is satisfied. 9. A recording / reproducing optical system wherein the wavelength λ is λ ≦ 0.68 (μm) and the numerical aperture NA satisfies NA / λ ≧ 1.20.
The optical recording medium according to the above. 10. A plane circular shape having an outer diameter of 125 (m
The optical recording medium according to claim 7, wherein the thickness is not more than m) and the thickness is not more than 1.60 (mm). 11. The optical recording medium according to claim 7, wherein the recording capacity is a linear density of 8 (GB). 12. When the refractive index of the transparent cover layer is N, the depth of the groove or the information pit is (λ / 8) /
The optical recording medium according to claim 7, wherein the optical recording medium is in a range of N to (3λ / 8) N. 13. When the track pitch is P (μm), the track pitch unevenness ΔP is ΔP ≦ ± 0.04P (μ
The optical recording medium according to claim 7, wherein m), the eccentricity E is E ≦ 67.57P (μm), and the skew is 0.4 ° or less. 14. The method according to claim 7, wherein the surface to be irradiated with light for recording and / or reproduction has a surface roughness Ra of ± 3λ / 100 or less within a spot size area on the surface. Optical recording medium. 15. The substrate, wherein the support layer is made of a thermoplastic resin and has a thickness of 0.3 to 1.2 (mm), a guide groove is formed by transfer on the substrate, and a multilayer is sequentially formed on the guide groove. A film is formed or an organic dye is spin-coated to form a recording layer, on which at least one type of UV-curable resin is coated.
The optical recording medium according to claim 7, wherein the optical recording medium is coated with a thickness of 77 (μm) to form a transparent cover layer. 16. The substrate, wherein the support layer is made of a thermoplastic resin and has a thickness of 0.3 to 1.2 (mm), a guide groove is formed by transfer on the substrate, and a multilayer is sequentially formed on the guide groove. A film is formed or an organic dye is spin-coated to form a recording layer, on which a light-transmitting film is pasted as a transparent cover layer via an ultraviolet curable resin, and the sum of the thicknesses of the two is 3 to 1
8. The optical recording medium according to claim 7, wherein the thickness is set to 77 (μm). 17. The optical recording apparatus according to claim 7, wherein the transparent cover layer is formed by transferring a signal or a guide groove from a master stamper to a sheet made by injection molding or casting by heating at a high temperature. Medium. 18. The optical recording medium according to claim 17, wherein a support substrate having a thickness of 0.6 to 1.2 (mm) is attached to the sheet on which the signal or the guide groove is transferred. 19. The optical recording medium according to claim 18, wherein said support substrate is a transparent plate. 20. The optical recording medium according to claim 18, wherein the support substrate is bonded to a sheet to which a signal or a guide groove has been transferred via an ultraviolet curable resin. 21. The optical recording medium according to claim 20, wherein said ultraviolet curable resin is applied by spin coating. 22. The optical recording medium according to claim 7, which has a double-sided structure having an information signal portion and a transparent cover layer on both sides by simultaneous molding or laminating on both sides. 23. The optical recording medium according to claim 7, wherein the optical recording medium has a multilayer structure in which an information recording film or a reflection film and a plurality of transparent cover layers are laminated. 24. The optical recording medium according to claim 23, wherein the reflectivities of the plurality of reflection films decrease as going toward a light incident side. 25. The optical recording medium according to claim 7, wherein an ultraviolet curable resin is also applied to a surface opposite to the transparent cover layer. 26. The ultraviolet curable resin applied on the side opposite to the transparent cover layer has a higher curing shrinkage than a material forming the transparent cover layer. Optical recording medium. 27. The optical recording medium according to claim 7, wherein a hard coat is formed on a surface of said transparent cover layer. 28. The optical recording medium according to claim 15, wherein the surface of the recording layer to which the ultraviolet curable resin is applied has been subjected to a silane treatment. 29. The optical recording medium according to claim 16, wherein a silane treatment is applied to a surface of the recording layer to which the ultraviolet curable resin is applied. 30. The optical recording medium according to claim 7, wherein an antireflection film is formed on a surface of said transparent cover layer. 31. The refractive index N of the antireflection film is lower than the refractive index of the transparent cover layer, and the thickness of the antireflection film is such that the wavelength of light for recording and / or reproduction is λ. 31. The optical recording medium according to claim 30, wherein the ratio is (λ / 3) / N (nm) or less. 32. A transparent cover layer on one main surface side of the recording layer, and the thickness t of the transparent cover layer is at least t = at least in an area of an information signal portion where an information signal is recorded in the recording layer. An optical disk device for recording and / or reproducing an optical disk having a size of 3 to 177 (μm), comprising: a laser light source having a wavelength of 680 (nm) or less; An optical disk device comprising: a lens having a numerical aperture NA of 0.7 or more. 33. The optical disk according to claim 1, wherein when the thickness unevenness of the transparent cover layer of the optical disk is represented by Δt, a numerical aperture NA and a wavelength λ of an optical system for recording and / or reproducing the optical disk are provided. , Δt ≦ ± 5.26 (λ / N
A ⁴⁾ (μm) optical disk drive according to claim 32, wherein a relationship in which holds the. 34. The optical disk device according to claim 32, wherein said lens has a two-group configuration. 35. The optical disk device according to claim 32, wherein the lens has a numerical aperture NA of 0.78 or more.