JP2001357571A - Method for manufacturing optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium which large recording capacity. SOLUTION: In the method for manufacturing an optical recording medium having an information signal part 11 and a light-transmitting layer 12 on the face where laser light enters, signals with <=0.65 μm track pitch P are recorded on the substrate 10 having >=0.6 mm film thickness, then at least, either a reflection film or a recording film is disposed thereon and then the light-transmitting layer 12 is formed from a UV-curing resin on the deposited film. The thickness t of the light-transmitting layer 12 is controlled to 10 to 177 μm, and variance Δt in the thickness of the light transmitting layer 12, the numerical aperture N.A. of the lens in the optical system for reproducing or recording and reproducing the optical recording medium, and the wavelength λ of laser light satisfy the relation of |Δt| <=5.26(λ/N.A.4) (μm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing an optical recording medium.

[0002]

2. Description of the Related Art As a next-generation optical disk medium, an optical disk medium capable of recording and reproducing NTSC for 4 hours on one side has been proposed. This is to provide a function as a new recording medium replacing the current VTR (VideoTape Recorder) by enabling recording and reproduction for about 4 hours as a home video disk recorder.

[0003] As such a recording medium, a CD is used.
By selecting the same shape and size as (Compact Disc), it is possible to make the product comfortable for users who are accustomed to the simplicity and convenience of the CD.

[0004] Furthermore, utilizing the speed of access as the biggest feature of the disk form, it is not only a compact and simple recorder, but also a product incorporating various functions such as instant recording, playback, trick play, and editing. Can be realized.

[0005] In order to realize the above products, it is required to have a recording capacity of, for example, 8 GB or more.

[0006]

However, conventionally,
No optical recording medium having a recording capacity of 8 GB or more existed in a disk having the same diameter as a CD and having a single information signal layer on only one main surface.

[0007] DVDs (Digital Vers
Atile Disc), the irradiation laser light wavelength λ = 0.65 μm in the region of the information signal portion, that is, in the region having a radius of 24 to 58 (mm) from the center of the disc.
m, the numerical aperture of the lens N. A. The recording capacity is 4.7 GB under the condition of = 0.6. When the capacity is to be further increased than that of the DVD without changing the signal format such as the ECC or the modulation method, for example, in order to realize 8 GB or more, it is necessary to satisfy the following [Equation 1].

## EQU1 ## 4.7 × (0.65 / 0.60 × NA / λ) ² ≧ 8

From the above equation, N.I. A. It is necessary to satisfy /λ≧1.20. Therefore, the wavelength λ of the irradiation laser light is reduced, or the numerical aperture N. A.
Either condition of increasing the value of is required.

To satisfy the above conditions, for example, A.
In order to increase the thickness, it is necessary to reduce the thickness of the light transmitting layer formed on the information signal of the optical disk and on the side of the reproduction laser beam irradiation surface. This is because the tolerance of the angle (tilt angle) at which the disk surface deviates from the perpendicular with respect to the optical axis of the optical pickup becomes small, and this tilt angle is easily affected by aberration due to the thickness of the light transmitting layer. It is.

Further, in order to manufacture a high-density optical recording medium as described above, it is necessary to reduce the thickness unevenness (Δt) of the light transmitting layer for the same reason.

In view of the above, in the present invention, in particular, the numerical aperture of the lens N.P. A. It is possible to provide a method for producing a large-capacity optical recording medium of, for example, 8 GB or more.

[0012]

According to the present invention, there is provided a method for manufacturing an optical recording medium having an information signal portion and a light transmitting layer on a surface on which a laser beam is incident. In the present invention, a signal having a track pitch P ≦ 0.65 μm is formed on a substrate having a thickness of 0.6 mm or more, and a reflection film and a recording film are formed on the surface on which the signal is formed. An optical recording medium is manufactured by forming a light-transmitting layer on the surface with an ultraviolet-curable resin. In particular, the thickness t of the light-transmitting layer is t = 10 to 177 μm,
When the thickness unevenness of the light transmitting layer is Δt, the numerical aperture N.sub.N of the optical system for reproducing or recording / reproducing the optical recording medium is set. A.
And between the wavelength lambda of the laser beam to be irradiated, | Δt | ≦ 5.26 (. Λ / N.A 4) shall be to satisfy the relation ([mu] m).

According to the manufacturing method of the present invention, the numerical aperture of the lens is particularly high. A. Can be increased, for example, 8
A large-capacity optical recording medium of GB or more can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, an example will be described in which the present invention is applied to an optical disc, which reproduces a signal by irradiating a laser beam by passing through a light transmitting layer on a substrate having an information signal portion. However, the present invention is not limited to the embodiments described below.

Generally, the disc skew margin Θ, the wavelength λ of the laser beam of the recording / reproducing optical system, the numerical aperture of the lens N.P. A. , And the thickness t of the light transmitting layer formed on the information signal on the laser irradiation surface side of the optical recording medium. The relationship between these parameters and Θ is described in Japanese Patent Application Laid-Open No. 3-0971 based on an example of a compact disk (CD) whose playability has been sufficiently demonstrated for practical use.
No. 34 publication. According to this, | Θ | ≦ 8
The angle may be 4.115 ° (λ / NA ³ / t), and this can be applied to the optical recording medium of the present invention.

Here, considering the specific limit value of the skew margin 場合 when the disks are actually mass-produced,
A value of 4 ° is reasonable. This is because, when considering mass production, if the size is smaller than this, the yield decreases and the cost increases. The existing recording medium is also 0.6 ° for a CD and 0.4 ° for a DVD.

Accordingly, by setting the skew margin Θ = 0.4 °, shortening the wavelength of the laser beam and increasing the N.V. A. Calculating how much the thickness of the light transmitting layer should be set by the conversion, first, assuming that the wavelength λ of the laser light is λ = 0.65 μm,
N. A. Is N.V. in the result equation of [Equation 1]. A. / Λ ≧ 1.
From 20, it is required that it be 0.78 or more. That is, it is derived that t ≦ 288 μm.

Further, the wavelength of the laser light is shortened, and λ = 0.
When it is about 4 μm, the numerical aperture of the lens is
N. A. Assuming that ≧ 0.78, the thickness t of the light transmitting layer is t = 177 μm. In this case, the thickness of the entire disc is about 1.38 mm at the maximum in consideration of diverting manufacturing equipment for a CD or the like having a substrate thickness of 1.2 mm.

In consideration of the magnetic field modulation of the MO, the thickness t of the light transmission layer is required to be further reduced. For example, by forming the thickness t to 30 μm or less, recording and reproduction with the MO becomes easy.

On the other hand, the lower limit of the thickness t of the light transmission layer is determined by the protection function of the light transmission layer for protecting the recording film or the reflection film, and is 10 μm in consideration of the reliability and the influence of the collision of the second group lens described later. It is desirable that this is the case.

In order to increase the recording density as described above, N. A. It is essential to increase the value of / λ. In this case, for example, in order to achieve a storage capacity of 8 GB,
At least N. A. Is set to 0.7 or more, and the wavelength λ of the laser is set to 0.68 μm or less. Further, as described above, the relationship between the thickness of the light transmitting layer and the skew is as described above. However, in consideration of the correspondence from the red laser to the blue laser, the thickness of the light transmitting layer is 10 to 17
It is appropriate to set it to 7 μm.

In order to achieve a recording capacity of 8 GB in the optical recording medium, it is necessary to adjust the track pitch P and the linear density d of the recording signal. The condition is
It is necessary to satisfy the following [Equation 2].

(0.74 / P) × (0.267 / d) × 4.7 ≧ 8 That is, d ≦ 0.1161 / P (μm / bit) may be satisfied.

When the track pitch P is 0.56 μm,
The linear density d ≦ 0.206 μm / bit is obtained.
Based on VD ROM (Read 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, the track pitch P can be set to about 0.64 μm at the maximum.

Further, in a high-density recording medium, the tolerance for the track pitch fluctuation ΔP becomes strict. If the recording and playback parameters of CD and DVD are diverted as they are, D
Track pitch in VD 0.74 μm, tolerance ± 0.03
Thus, the following [Equation 3] is obtained.

| ΔP | ≦ 0.03P / 0.74 = 0.04P Therefore, if the track pitch P = 0.56, then |
ΔP | ≦ 0.023 μm.

Further, a higher accuracy is required for the thickness irregularity Δt of the light transmitting layer.

When the thickness t of the light transmission layer deviates from the design center of the objective lens for reproduction, the amount of aberration given to the spot by the thickness error depends on the numerical aperture of the lens. A. To the fourth power and to the wavelength λ of the laser light. Therefore, high N.I. A. In the case where high-density recording is to be achieved by reducing the wavelength or shortening the wavelength, the amount (the thickness unevenness of the light transmitting layer Δ
t) is further severely restricted. Regarding CD as a specific system example, N.A. A. = 0.45 has been put to practical use, and the error standard for the thickness of the light transmitting layer is ± 100 μm. Regarding DVD, N.I. A. = 0.6 has been put to practical use, and the error standard for the thickness of the light transmitting layer is ± 30 μm. Here, on the basis of the permissible amount of the thickness of the light transmitting layer in the CD ± 100 μm, the following [Equation 4] is obtained.

[Number 4] Δt = ± (0.45 / N.A. ) 4 × (λ / 0.78) × 100 = ± 5.26 × (λ / N.A. 4) μm (N.A. is , Numerical aperture)

Here, with respect to the center of the light transmitting layer having a thickness of 100 μm, the wavelength is 0.68 μm and the N.D. A. FIG. 1 shows the result of an experiment conducted on the relationship between the thickness error of the light transmitting layer and the jitter value at 0.875. From FIG. 1, for example, 8% which is a jitter standard when there is no perturbation such as skew in DVD
It can be seen from FIG.
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 light transmitting layer is as shown in the following [Equation 5].

| Δt | ≦ 5.26 × (λ / NA ⁴ ) μm

In addition, the above-mentioned thickness variation of the light transmitting layer (Δt)
Is based on the premise that the recording / reproducing laser light is uniform on the surface of the disk, and aberration can be corrected by shifting the focus point. However, if there is unevenness in the thickness of the light transmitting layer 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.

Further, regarding the eccentricity E, 50 μm
E ≦ 50 × P / 0.74 = 67.57P (μ
m).

From the above, the conditions necessary for an optical recording medium to achieve a high storage capacity of 8 GB are summarized as follows. If the recording / reproducing optical system has λ ≦ 0.68 μm and A. /Λ≧1.20, and the thickness t = 1 of the light transmitting layer in at least the formation region of the information signal portion.
0 to 177 μm, light transmission layer thickness unevenness | Δt | ≦ 5.26 (λ / N.
A. ⁴ ) (μm) Track pitch P ≦ 0.64 μm Tolerance | ΔP | ≦ 0.04 Pμm Linear density d ≦ 0.1161 / P (μm / bit) Disk skew Θ ≦ 84.115 × (λ / NA.
³ / t) Eccentricity E ≦ 67.57P (μm) Surface roughness | Ra | ≦ 3λ / 100 (within spot irradiation area)

In order to manufacture an optical recording medium, first,
A substrate is manufactured by an injection molding method using a transfer stamper that realizes the pitch and the pitch unevenness that meet the specifications required for the optical recording medium as described above, and at the same time, the fine irregularities forming the information signal are formed. 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. Further, the optical system is covered with a cover for eliminating air fluctuation, and a vibration isolator is provided between the laser and the exposure apparatus in order to eliminate vibration of cooling water of the exposure laser.

A reflective film, a recording film, or both are formed on the information signal surface of the substrate. In the optical recording medium manufactured according to the present invention, since signal recording and reproduction are performed by irradiating a laser beam from the light transmitting layer formed on the reflective film or the recording film, the reflective film or the recording film is formed in advance. It is necessary to form pits on the substrate in consideration of the deformation of the signal shape due to the film.

For example, in the case of a 10 GB ROM, the asymmetry of the signal pit when viewed from the substrate side is 25.
%, The asymmetry when viewed from the opposite side of the substrate is 10%. That is, in the present invention, since the signal is reproduced by irradiating the laser beam 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, it is necessary to make the pit shape formed on the substrate 25% asymmetry.

Similarly, with respect to the guide groove (groove) formed on the recording disk, the groove duty changes 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 widening the shape of the stamper in advance.
For example, in the case of land / groove recording, in order to obtain a land and groove width duty of 50% when viewed from the light irradiation side, it is preferable to set the width to 55 to 65% when viewed from the substrate side.

When a disk is formed of a single plate, the substrate is required to have a certain degree of rigidity. Similarly, in the case of a structure in which two substrates are bonded, it is preferable that one substrate has a thickness of 0.3 mm or more, which is half of that.

After the substrate is manufactured by injection molding as described above, a recording film or a reflection film is formed on the information signal portion 11 of the substrate 10 as shown in FIG. For example, when the target optical disk is a ROM, a reflective film of Al or the like is formed to a thickness of 20 to 60 nm.

When an information recording film is formed on the information signal section 11, for example, when a phase change type optical recording medium is manufactured, for example, an Al film, a ZnS—SiO ₂ film, a Ge
An SbTe film and a ZnS-SiO ₂ film are sequentially laminated and formed.

When the target optical disk is a magneto-optical disk, for example, an Al film, a SiN film, a TbF
An eCo film and a SiN film are sequentially laminated to form a film.

When the target optical disk is a write-once disk, the Au film or the Al film is sputtered, and then a cyanine or phthalocyanine organic dye film is applied by spin coating and dried. Film.

In the example shown in FIG. 2, recording and reproduction laser light L is applied through the recording and reproduction objective lens L from the main surface side opposite to the substrate 10 side.

Next, as shown in FIG. 3, a light transmitting layer 12 is further formed thereon by using an ultraviolet curable resin. That is,
A liquid ultraviolet curable resin is dropped on the film formation surface on the information signal portion of the optical disc having any of the structures formed as described above, and is further rotationally stretched to form the light transmitting layer 1.
Form 2 The viscosity of the ultraviolet curable resin is 30
Those having a value of 0 cps or more and 3000 cps or less are preferable.
For example, when an ultraviolet curable resin having a viscosity of 5800 cps at 25 ° C. is applied, the ultraviolet curable resin is dropped on the substrate 10, and the substrate 10 is rotated at 2000 rpm for 11 seconds, and finally, about 100 μm. Of the light transmitting layer 12 can be formed.

Here, when the light transmitting layer 12 is formed, an ultraviolet curable resin is dropped on the inner peripheral portion of the substrate 10, for example, at a position having a radius of 25 mm, and is rotated and stretched. There is a difference between the inner and outer circumferences in the thickness of the light transmitting layer 12. This amount becomes 30 μm or more, and there is a possibility that the above-described thickness range of the light transmission layer 12 cannot be satisfied.

In order to avoid such a difference between the inner and outer peripheries of the light transmitting layer 12, it is effective to drop the ultraviolet curable resin while the center hole 13 of the substrate 10 is filled with some means. . For example, a sheet of polycarbonate having a thickness of 0.1 mm is processed into a circle having a diameter Φ of 30 mm,
After bonding to the central portion of the substrate 10, an ultraviolet curable resin is dropped from the center, rotationally stretched, irradiated with ultraviolet light to cure the ultraviolet curable resin, and then a center hole is punched out. According to this process, the difference between the inner and outer circumferences, that is, the undulation of the light transmitting layer 12 is 10 μmp-p (peak
A reduced light transmission layer could be obtained within two peaks (the same applies hereinafter).

When the light transmitting layer 12 is formed, it is conceivable that the light transmissive layer 12 protrudes to the outer periphery of the disk. Therefore, the diameter of the disk is determined based on the diameter (120 mm) of a CD or the like.
It is desirable to set mm + 5 mm as the maximum value.

Further, as shown in FIG.
The light transmitting layer 12 may be formed by bonding a sheet of polycarbonate having a thickness of 0 μm via an ultraviolet curable resin 15. 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.
mp-p or less is sufficient. For example, a sheet 14 processed into the same diameter as the substrate 10 is placed on the substrate 10 via an ultraviolet-curable resin 15 for adhesion, and is rotated and stretched so that the sheet 14 becomes a weight of the ultraviolet-curable resin 15. A very thin UV-curable resin layer is formed, and the total thickness unevenness can be 10 μm or less, that is, the difference between the maximum value and the minimum value of the UV-curable resin layer thickness can be 10 μm or less. .

In the method of manufacturing an optical recording medium according to the present invention, a second recording layer 18 is formed on a first recording layer 17 formed on a substrate 10 via an intermediate layer 16 as shown in FIG. The present invention can also be applied to the case where an optical recording medium having a multilayer structure is manufactured.

Also, skew is likely to occur in the optical discs of the above-described configurations, but in order to reduce the skew, as shown in FIG.
It is effective to apply an ultraviolet curable resin as the skew correction member 19 on the surface opposite to the surface on which the second member 2 is formed. In this case, the skew correction member 19 may be coated with the same material as the light transmitting layer 12, or may be thinly coated with a material having a higher curing shrinkage than the ultraviolet curable resin that is the material of the light transmitting layer 12. Is also good.

In order to record / reproduce data on / from the above-described optical disk of high-density recording, a high N.D. A. A pickup having an objective lens is required. In this case, the distance between the objective lens and the disk surface (hereinafter referred to as “W.
D. That. ) Is desirably shorter than the conventional distance. However, if the distance between the objective lens and the disk surface is reduced, the objective lens may collide with the disk surface and damage the disk surface.

To prevent this, a surface hard coat (pencil hardness H or more) is formed on the light transmitting layer 12 as shown in FIG.
Applying 20 is effective. When the thickness of the light transmitting layer 12 is reduced, signal reproduction failure is likely to occur when dust adheres. Therefore, a material having an antistatic function is preferable as the material of the hard coat 20. The prevention of the charge prevents dust from adsorbing to the surface of the optical disk, thereby effectively preventing signal defects.

In the optical disk manufactured by the method of the present invention, when the wavelength of the measurement light is 780 nm, the in-plane birefringence of the light transmitting layer is 15 nm or less on average in a reciprocating manner, and the fluctuation in the circumference is 15 nm pp. It is preferred that

In the optical disc manufactured by the method of the present invention, a recording / reproducing experiment was performed when the light transmitting layer was formed using a polycarbonate sheet having a thickness of, for example, 100 μm and the information recording layer was a phase change film. went. In this case, when the linear density is 0.21 μm / bit and the jitter is 8%
was gotten. 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 horizontal line segment position crossing each line segment is the average value. This birefringence amount is 15 nm or less on average in round trip,
The intra-period variation could be 15 nm pp or less.

Further, in the optical disk manufactured by the method of the present invention, the light transmitting layer 12 is formed by applying a liquid photo-curable resin on the information recording section 11, rotating and stretching, and then photo-curing. A similar recording / reproducing experiment was performed when the information recording layer was a phase change film. in this case,
In this case, when the linear density is 0.21 μm / bit and the jitter is 7
%was gotten. Further, the birefringence of such an optical disk was measured. FIG. 24 shows the measurement results. In FIG. 24, the horizontal axis indicates the radial position (mm), and the vertical axis indicates the 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. This birefringence amount can be further reduced as compared with the case where the light transmission layer is formed of a polycarbonate sheet.
pp or less could be achieved.

As described above, the optical disk manufactured by the method of the present invention has a conventional CD or DVD having an in-plane birefringence of 1 unit.
It can be seen that the composition has stable and excellent characteristics as compared with the case where the thickness is 00 nm.

In the optical recording medium manufactured by the method of the present invention, the surface on which various recording films are formed may be subjected to a silane treatment. By performing the silane treatment, it is possible to improve the adhesion between the ultraviolet curable resin used for forming the light transmitting layer 12 and various recording films.

In the optical recording medium manufactured by the method of the present invention, an antireflection film may be formed on the surface of the light transmitting layer 12 by 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 light transmitting layer 12, and the thickness of the antireflection film is determined when the wavelength of light for recording and reproduction is λ. In addition, (λ / 3) / n (nm) or less, preferably (λ
/ 4) / n (nm).

As in the case of the optical recording medium manufactured by the method of the present invention, the numerical aperture N.L. A. If the height corresponds to a high value, the incident angle of the recording / reproducing laser beam also becomes large, so that the reflection of light on the surface of the light transmitting layer 12 cannot be ignored. For example, N. A. = 0.4
In the case of 5, the incident angle of the recording / reproducing light is 26.7 °,
N. A. In the case of = 0.6, it is 36.9 °.

Here, N.I. A. In the case of = 0.8, the incident angle of the recording / reproducing light is as high as 53.1 °, and the influence of light reflection is large. That is, it has been confirmed that the reflectivity of light on the surface of the light transmitting layer 12 depends on the incident angle of the recording / reproducing laser light, and when the refractive index of the light transmitting layer 12 is 1.52, for example. Indicates that the surface reflectance of the s-polarized light component exceeds 15%. (See page 168 of "Laser and Optics Guide" published by Kinomeles Griot Co., Ltd.) A. Causes a decrease. In order to avoid such a problem, it is effective to form an antireflection film on the surface of the light transmitting layer 12.

When the refractive index of the light transmitting layer 12 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 laser beam is 650 nm, M
The thickness of the antireflection film made of gF ₂ is (λ / 4) / n
By substituting each numerical value into the equation (nm), about 120
It can be seen that it is preferable to form the layer with a thickness of nm.

Incidentally, the amount of light reflected on the surface of the light transmitting layer 12 is determined by setting the thickness of the antireflection film from 0 to (λ / 4) / n.
(Λ / 4) / 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)
Is exceeded, 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 antireflection film should be not more than (λ / 3) / n (nm) for practical use in consideration of the film forming technology in industry.

When an anti-reflection film is formed on the surface of the light transmission layer 12 as described above, for example, a single layer of MgF ₂ (λ /
4) When formed at a thickness of / n (nm), when a laser beam for recording / reproducing having a thickness of 550 nm is used, the incident angle of the laser beam for recording / reproducing is about 50% until the incident angle is about 60 °. It is possible to prevent the above reduction in light amount (see page 174 of “Laser and Optics Guide” published by Kinomeles Griot Co., Ltd.).

The method of manufacturing an optical recording medium according to the present invention is not limited to a disk having a single-plate structure, but also includes two substrates 51 and 52 each having a thickness half that of the finally obtained substrate 10 as shown in FIG.
Can be applied to the case where two sheets are bonded together to produce an optical recording medium having a so-called double-sided structure having information signal recording portions on both sides. In this case, the substrates 51 and 52 having a thickness of 0.6 mm are used.
In addition, since a light transmitting layer 12 having a maximum of 170 μm is formed and bonded, the thickness of the disc is (0.6 + 0.17) × 2.
+ (Thickness of adhesive layer), and the thickness of the adhesive layer is 0.06 m
If m, the thickness of the disk is 1.60 mm. In addition, as shown in FIG. 9, the method for manufacturing an optical recording medium of the present invention produces an optical recording medium having a so-called double-sided structure in which an information signal recording surface and a light transmitting layer 12 are provided on both surfaces of one substrate 50. It can be applied to the case.

Next, a specific application example of the method for manufacturing an optical recording medium of the present invention will be described. As shown in FIG. 10, for example, 100 μm made by extrusion molding or casting method.
An m-thick polycarbonate sheet 40 is prepared, placed on a stamper 41 heated to a temperature higher than the glass transition point of the sheet 40, and pressed against a roller 42 by applying pressure. The pressure in this case can be, for example, 280 kgf.

By this operation, information pits or guide grooves of the stamper 41 can be transferred onto the sheet 40 as shown in FIG. And after cooling it,
By peeling the sheet 40 from the stamper 41, a thin substrate 43 having a thickness of, for example, 100 μm is obtained.

Subsequently, by forming a recording film and a reflection film in the same manner as in the above-described manufacturing process, a target thin optical recording medium can be finally manufactured.

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

First, as shown in FIG.
A liquid ultraviolet curable resin 60 is dropped on 41, and the thin substrate 43 shown in FIG. 11 is placed with the recording layer side in contact with the liquid ultraviolet curable resin 60.

In this way, as shown in FIG. 13, the stamper 141 on which the thin substrate is superimposed is rotated while being placed on the rotating base 61 via the liquid photocurable resin, and the liquid ultraviolet curable resin is Stretch 60, the required thickness,
For example, the thickness is set to 20 μm. Thereafter, as shown in FIG. 14, ultraviolet rays are irradiated from the thin plate substrate 43 side by a lamp 62 to cure the liquid ultraviolet curable resin 60.

As shown in FIG. 15, a thin plate substrate 43 and a photo-cured ultraviolet curable resin 6 having a thickness of, for example, 20 μm are formed.
0 is integrally removed from the stamper 141.

As described above, various recording films are formed by forming a metal thin film of, for example, an Si compound, Al, Au, or the like on the fine irregularities transferred to the ultraviolet curable resin 60 by the stamper 141. be able to.

Further, by repeating the steps described with reference to FIGS. 12 to 15, an optical disk having three or more layers can be manufactured.

As shown in FIG. 16, a substrate 10 obtained by, for example, injection molding is adhered to the recording film obtained as described above at an interval of, for example, 20 μm via an ultraviolet curable resin, thereby obtaining rigidity. An optical disk with high performance can be manufactured.

As shown in FIG. 17, a high-reflection film 70 of, for example, Al, Au or the like is formed on the finally obtained recording film, and a protective film 71 is further formed. A thin optical disk can be manufactured. In this case, assuming that the number of recording layers is N, the thickness of the optical disc finally obtained is the thickness of the thin substrate 43, for example, 100
μm, N times the thickness of the ultraviolet curable resin layer between each layer,
The sum of 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, when an optical disk having a four-layer structure is manufactured, Is 185 μm thick. However, the optical disk obtained in this way has a very low rigidity, so that a rigid thick plate is bonded and supported on the thin plate 43 side, or a flexible optical disk becomes flat by high-speed rotation during recording and reproduction. It is necessary to devise recording and reproduction utilizing this fact.

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. 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.
May be bonded at an interval of 50 μm via an ultraviolet curable resin, and when an optical disc having a three-layer structure is manufactured as shown in FIG.
May be formed with the recording layer interposed at an interval of 25 μm.

In the method of manufacturing an optical recording medium according to the present invention, in addition to the optical disk having the above-described structure, as shown in FIG. And the disk-shaped substrate 50 of
It can be applied to an optical disk even if it is bonded by pressing and bonding through an ultraviolet curable resin and irradiating ultraviolet rays from the substrate side.

Further, in the present invention, as shown in FIG. 21, the thin plate substrate 43 and the substrate 50 on which the fine irregularities forming the recording layers are transferred by injection molding are transferred via the ultraviolet curable resin. It is bonded and crimped, and the thin substrate 43
By irradiating ultraviolet rays from the side and bonding, an optical disc having a four-layer structure can be finally manufactured.

Next, the depth of pits or grooves formed on the substrate will be described. Hereinafter, the refractive index n of the light transmitting layer is referred to. The depth of the pit or groove at which the highest degree of modulation can be obtained is (λ / 4) / n, and the ROM or the like is set to this depth.

Further, in the case of obtaining 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.

Further, in land / groove recording,
The groove depth should take into account the characteristics of the servo signal as well as the characteristics of crosstalk and cross-erase. Experimentally, the crosstalk is (λ / 6) / n to (λ / 3) / n, which is the minimum. It has been confirmed that the deeper the cross erase, the less the effect. Also, considering the groove inclination, etc.,
In order to satisfy both characteristics, (3λ / 8) / n is optimal. The optical recording medium for high-density recording manufactured by the manufacturing method of the present invention can be applied within the above-described depth range.

Next, at the high N.P. A. A description will be given of an embodiment of recording and reproduction for realizing the above. FIG. 22 shows a configuration of an optical disk and a recording / reproducing lens.

The second lens 32 is disposed between the first lens 31 and the optical disk 21. With this two-group lens configuration, the N.D. A. Can be set to 0.7 or more, and the first surface 32a of the second lens 32 and the optical disk 2
1 can be narrowed with respect to the surface (WD). Further, it is desirable 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.

By using this two-group lens, it is possible to perform high-density recording and reproduction on the optical disk described above.

[0083]

According to the method of manufacturing an optical recording medium of the present invention, the numerical aperture N.sub. A.
, And a large capacity optical recording medium of, for example, 8 GB or more was obtained.

Further, according to the method of manufacturing an optical recording medium of the present invention, the light-transmitting layer is formed by dropping the ultraviolet-curable resin on the substrate and rotating and stretching the resin. Could be uniformly and easily formed.

Further, according to the method of manufacturing an optical recording medium of the present invention, the central hole of the substrate is covered with a sheet, an ultraviolet curable resin is dropped on the substrate, the film is rotated and stretched, and cured by irradiating ultraviolet light. Then, by punching out the center portion of the substrate to form a center hole, it was possible to manufacture the light transmitting layer with extremely small thickness unevenness between the inner and outer peripheral portions of the optical disk.

According to the method of manufacturing an optical recording medium of the present invention, the light transmitting layer is formed by bonding the light transmitting layer to a polycarbonate sheet via an ultraviolet curable resin. It could be easily formed with a uniform thickness, and the manufacturing process of the optical recording medium could be simplified.

Further, according to the method of manufacturing an optical recording medium of the present invention, by applying a hard coat on the light transmitting layer, the rigidity of the optical disk can be increased to prevent the occurrence of scratches and to have an antistatic effect. As a result, dust was prevented from adhering and defective reproduction signals could be effectively avoided.

[Brief description of the drawings]

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

FIG. 2 shows a schematic cross-sectional view of an example of an optical disk manufactured by the method of the present invention.

FIG. 3 shows a schematic cross-sectional view of an example of an optical disk manufactured by the method of the present invention.

FIG. 4 is a schematic cross-sectional view of another example of the optical disk manufactured by the method of the present invention.

FIG. 5 is a schematic cross-sectional view of another example of the optical disk manufactured by the method of the present invention.

FIG. 6 is a schematic cross-sectional view of another example of the optical disk manufactured by the method of the present invention.

FIG. 7 is a schematic sectional view of another example of the optical disk manufactured by the method of the present invention.

FIG. 8 is a schematic sectional view of another example of the optical disk manufactured by the method of the present invention.

FIG. 9 is a schematic sectional view of another example of the optical disk manufactured by the method of the present invention.

FIG. 10 is a manufacturing process drawing of an example of an optical disk according to the method of the present invention.

FIG. 11 is a schematic sectional view of a thin substrate constituting a multilayer optical disk manufactured by the method of the present invention.

FIG. 12 is a process chart of an example of a multilayer optical disc according to the method of the present invention.

FIG. 13 shows a manufacturing process diagram of an example of a multilayer optical disk according to the method of the present invention.

FIG. 14 is a view showing a manufacturing process of an example of a multilayer optical disk according to the method of the present invention.

FIG. 15 shows a manufacturing process chart of an example optical disk according to the method of the present invention.

FIG. 16 is a schematic sectional view of an example of an optical disk manufactured by the method of the present invention.

FIG. 17 is a schematic cross-sectional view of an example of an optical disk manufactured by the method of the present invention.

FIG. 18 is a schematic sectional view of an example of an optical disc having a two-layer structure manufactured by the method of the present invention.

FIG. 19 is a schematic sectional view of an example of an optical disk having a three-layer structure manufactured by the method of the present invention.

FIG. 20 is a schematic sectional view of an example of an optical disk manufactured by the method of the present invention.

FIG. 21 is a schematic sectional view of an example of an optical disk in the method of the present invention.

FIG. 22 is a configuration diagram of a two-unit lens used in an optical system that records or reproduces data on or from an optical disc manufactured by the method of the present invention.

FIG. 23 shows a measurement result of a birefringence amount of a light transmitting layer of an optical disc manufactured by the method of the present invention.

FIG. 24 shows a measurement result of a birefringence amount of a light transmitting layer of an optical disc manufactured by the method of the present invention.

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

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Arikatsu Nakaoki 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Masahiko Kaneko 6-7-1, Kita-Shinagawa, Shinagawa-ku, Tokyo No. 35 Sony Corporation F term (reference) 5D029 LB07 LB20 WB11 5D119 AA22 BA01 BB04 JA43 JB02 5D121 AA04 EE22 FF03 GG02 GG24

Claims (6)

[Claims] 1. A method for manufacturing an optical recording medium comprising an information signal portion and a light transmitting layer on a surface on which laser light is incident, comprising: a substrate having a track pitch of 0.6 mm or more; P ≦
A step of forming a signal of 0.65 μm; a step of forming at least one of a reflection film and a recording film on the surface on which the signal is formed; and a light transmission by an ultraviolet curable resin on the film formation surface of the substrate. Forming a layer, wherein the light transmitting layer transmits a signal to the optical recording medium when the thickness t is t = 10 to 177 μm and the thickness unevenness of the light transmitting layer is Δt. The numerical aperture N. of the lens of the optical system for reproducing or recording / reproducing. A. And between the wavelength of the irradiated laser beam λ, | Δt | ≦ 5.26 ( . Λ / N.A 4) The method of manufacturing an optical recording medium, characterized in that to satisfy the relation ([mu] m) . 2. The method for manufacturing an optical recording medium according to claim 1, wherein the light transmitting layer is formed by dropping the ultraviolet curable resin onto the substrate and subjecting the resin to rotational stretching. 3. A step of closing a central hole formed in the substrate with a sheet, a step of dropping the ultraviolet-curable resin on the substrate and performing rotational stretching, and a step of irradiating ultraviolet rays to the ultraviolet-curable resin. 3. The method for manufacturing an optical recording medium according to claim 2, further comprising a step of punching a center portion of the substrate after hardening the substrate to form a center hole. 4. The light-transmitting layer having a thickness of t = 10 to 177 μm is formed by adhering the substrate and a 100 μm-thick polycarbonate sheet via the ultraviolet-curable resin. The method for producing an optical recording medium according to claim 1. 5. The method for manufacturing an optical recording medium according to claim 4, wherein the sheet is placed on the substrate via the ultraviolet-curable resin, and is then stretched by rotation. 6. The method according to claim 1, wherein a hard coat is applied on the light transmitting layer.