U.S. patent application number 10/778578 was filed with the patent office on 2004-09-30 for method and apparatus of optical information recording medium, and optical information recording medium.
Invention is credited to Hayashi, Kazuhiro, Hisada, Kazuya, Ohno, Eiji.
Application Number | 20040190433 10/778578 |
Document ID | / |
Family ID | 27344593 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040190433 |
Kind Code |
A1 |
Hisada, Kazuya ; et
al. |
September 30, 2004 |
Method and apparatus of optical information recording medium, and
optical information recording medium
Abstract
An optical disk is manufactured by bonding a resin stamper
having, on a principal plane, asperity pits on which a thin film is
formed and a second substrate having a thickness of 0.3 mm or less
with radiation cured resin such that the asperity pits face to the
second substrate. The resin stamper is peeled off after curing the
radiation cured resin to form asperity pits on the second
substrate. A metal film is formed on the asperity pits on the
second substrate to attain an information recording layer on the
second substrate. A first substrate having an information recording
layer and the second substrate having the formed information
recording layer are bonded such that the both information recording
layers face each other.
Inventors: |
Hisada, Kazuya; (Osaka-shi,
JP) ; Hayashi, Kazuhiro; (Kadoma-shi, JP) ;
Ohno, Eiji; (Hirakata-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27344593 |
Appl. No.: |
10/778578 |
Filed: |
February 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10778578 |
Feb 17, 2004 |
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09950079 |
Sep 12, 2001 |
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6743320 |
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Current U.S.
Class: |
369/275.1 ;
G9B/7.196 |
Current CPC
Class: |
G11B 7/24038 20130101;
G11B 7/263 20130101; B29D 17/005 20130101 |
Class at
Publication: |
369/275.1 |
International
Class: |
G11B 007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2000 |
JP |
2000-275986 |
Sep 22, 2000 |
JP |
2000-288345 |
Dec 28, 2000 |
JP |
2000-400442 |
Claims
What is claimed is:
1. An optical information recording medium comprising: a first
substrate having a thickness of 0.3 mm or less and having a groove
or asperity pits formed thereon by a radiation cured resin and a
thin film; a second substrate; and a metal film or a recording film
on the groove or the asperity pits on the first substrate so as to
create an information recording layer on the first substrate,
wherein the first substrate and the second substrate are bonded
such that the information recording layer is placed between the
first and second substrates.
2. An optical information recording medium having a substrate,
comprising: a information recording layer formed on the substrate;
at least one basic layer which is stacked on the information layer,
and includes an intermediate layer and a recording layer; and a
light transmission layer formed on the basic layer.
3. The optical information recording medium according to claim 2,
the basic layer further includes a protection layer.
4. The optical information recording medium according to claim 2,
wherein a thickness of the light transmission layer is 0.3 mm or
less.
5. The optical information recording medium according to claim 4,
wherein the thickness of the light transmission layer is
substantially 0.1 mm.
6. The optical information recording medium according to claim 5,
wherein the thickness of the basic layer is 15 .mu.m to 45
.mu.m.
7. The optical information recording medium according to claim 2,
wherein the light transmission layer comprises radiation cured
resin.
8. The optical information recording medium according to claim 2,
wherein the light transmission layer comprises radiation cured
resin and a resin substrate.
9. The optical information recording medium according to claim 2,
wherein the recording layer comprises radiation cured resin having
the groove or the asperity pits, and a reflective film or a
recording film formed on the groove or the asperity pits.
10. The optical information recording medium according to claim 2,
wherein the intermediate layer has a function as adhesive.
11. The optical information recording medium according to claim 2,
wherein the intermediate layer is made of radiation cured
resin.
12. The optical information recording medium according to claim 2,
wherein the protection layer has a pencil hardness of B or
more.
13. The optical information recording medium according to claim 2,
wherein the protection layer is made of radiation cured resin.
14. The optical information recording medium according to claim 2,
wherein the protection layer and the intermediate layer have
substantially equal refractive indexes.
15. The optical information recording medium according to claim 2,
wherein the protection layer and the intermediate layer are
substantially transparent to transmit a light for recording or
reproducing data.
16. The optical information recording medium according to claim 13,
wherein the protection layer is substantially transparent to
transmit light for recording or reproducing data.
17. An optical information recording medium comprising: a first
substrate; and a second substrate which is thinner than the first
substrate, wherein two information recording layers are provided
between the first and second substrates.
18. An optical information recording medium comprising: a first
substrate; and a light transmission layer which is provided on the
first substrate and is made of radiation cured resin, wherein two
information recording layers are provided between the first
substrate and the light transmission layer.
Description
[0001] This application is a divisional application of application
Ser. No. 09/950,079, filed Sep. 12, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a manufacturing method and
an optical information recording medium, and more specifically
relates to a multilayer manufacturing method and a multilayer
optical information recording medium.
[0004] 2. Description of the Prior Art
[0005] In recent years, various types of optical information
recording technology have been studied. According to the optical
information recording, high density recording and non-contact
recording/reproduction can be realized at a low cost. The method
therefore has begun to be applied to various technical fields. An
optical disk is used as a medium for the optical information
recording. Optical disks are roughly classified into three types:
read-only type; additional written type; and rewritable type. All
the types of optical disks are commercialized and widely
distributed. For example, the read-only type disk is distributed as
a disk called as a compact disk (CD) on which music data is
recorded or a laser disk (LD) on which image data is recorded. The
additional written type disk is used for a document file or a still
picture file. The rewritable type disk is used for a data file for
a personal computer, or the like. The optical disk is formed in a
structure in which an information recording layer is formed on a
transparent resin substrate having a thickness of 1.2 mm and
covered with an overcoat layer, or a structure in which an
information recording layer is formed on one side or both sides of
a transparent resin substrate having a thickness of 1.2 mm and the
two substrates are bonded to each other.
[0006] In addition thereto, a digital versatile disk (DVD) having a
larger capacity has been developed and commercialized to record not
only audio data, but also video data such as a movie, and has begun
to be popularized. In order to realize a high-density optical disk,
a laser light beam having a short wavelength and an objective lens
having a large numerical aperture (NA) are used. With use of the
laser light beam having a short wavelength and the objective lens
having a large NA, however, the tolerance of the inclination angle
(tilt) of the disk to the incident direction of the laser beam will
be decreased. In order to increase the tolerance of the tilt of the
disk, it is effective to decrease the substrate in thickness. For
example, in a DVD, the laser beam of the wavelength of 650 nm, and
NA of 0.60, and the disk of the thickness of 0.6 mm are used. The
resin substrate of 0.6 mm thick has poor mechanical strength and
generates a tilt, and thus the DVD is formed by bonding two
substrates to each other such that information recording face
thereof is inside.
[0007] On the other hand, "a one side face reproduction and double
layer DVD" has been also put into practical use, in which one
substrate having a transparent reflective layer formed of gold,
silicon, or the like on the information recording face and another
substrate having a reflective layer formed of aluminum or the like
on the information recording face are bonded each other such that
the information recording faces thereof are bonded each other. For
that DVD, the data on the information recording faces are
reproduced by emitting a laser beam from the substrate side
provided with the transparent reflective layer. Also, a rewritable
DVD having the double layer structure as mentioned above in which a
rewritable thin film recording layer is formed on the information
recording face instead of a metal reflective layer, is also
proposed.
[0008] Recently, the amount of the information grows larger as
exemplarily seen in high definition television broadcasting, and
therefore, the recording medium having high density is further
required. In order to increase the recording density of the optical
disk, various methods have been proposed: forming of the disk
having a multilayer structure of more than three layers; increasing
the NA of the objective lens; and using a blue-violet laser beam.
As the method of forming the multilayer structure, a signal
transferring (2P method) using a metal stamper has been widely
used.
[0009] When the optical disk is formed to the multilayer structure,
however, it is difficult to form an information recording face
other than that having a groove or asperity pits formed by
injection molding. It is proposed to decrease the
recording/reproducing substrate in thickness and set the NA at
0.85, and the wavelength of the laser beam at 400 nm because the
thinner the recording/reproducing substrate the larger the
tolerance of the tilt of the disk, as described before. In a case
where the recording/reproducing substrate is formed thinner than
0.3 mm that is the limit to form the groove or pits by the
injection molding, the double layer structure cannot be easily
formed. Also with use of the metal stamper, some problems will
occur because a radiation cured resin film for transferring a
signal recording face onto the disk cannot be easily formed
uniformly, a radiation cured resin film cannot be formed uniformly
and the radiation can not pass easily through the stamper. There
are also some problems such that the radiation cured resin cannot
be easily cured, a disk manufacturing apparatus is inevitably
formed large, and signal transferring requires a long time.
SUMMARY OF THE INVENTION
[0010] The present invention intends to provide a manufacturing
method of an optical information recording medium and an optical
information recording medium having a multilayer structure, and
more specifically, the optical information recording medium having
a multi optical information recording layer and a thinner
recording/reproducing substrate.
[0011] In a first aspect of the invention, provided is a method of
manufacturing an optical information recording medium. The method
comprises bonding a stamper having a principal plane formed with a
groove or asperity pits and a second substrate having a thickness
of 0.3 mm or less with radiation cured resin so as to cause the
groove or the asperity pits to face to the second substrate, the
stamper being transparent, the groove or asperity pits having a
thin film formed thereon, curing the radiation cured resin, peeling
off the stamper to form the groove or the asperity pits on the
second substrate, forming a metal film or a recording film on the
groove or the asperity pits on the second substrate to create a
second information recording layer on the second substrate, and
bonding a first substrate and the second substrate on which the
second information recording layer is formed, such that the
information recording layers are placed between the first and
second substrates.
[0012] According to the above-mentioned manufacturing method, the
optical disk having information recording layers can be formed on
the substrate having a thickness of 0.3 mm or less which cannot be
formed by the injection molding. Further, when the first substrate
is provided with an information recording layer, the optical disk
having a double layer structure can be attained.
[0013] According to the above-mentioned first manufacturing method,
the stamper may be formed by injection molding. With this method,
the disk can be formed at a low cost by the conventional optical
disk manufacturing apparatus.
[0014] Preferably the stamper may be made of resin material, and
more specifically, polycarbonate. With this method, a light and
low-cost stamper can be attained. With this stamper, the radiation
cured resin can be uniformly spread by spinning after overlapping
the stamper and the first substrate by the radiation cured
resin.
[0015] In the above-mentioned method, a metal film or a semimetal
film may be formed on the information recording layer of the
stamper. With this method, the stamper can be easily peeled off the
first substrate.
[0016] The metal film may be formed from Al or metal mainly
composed of Al. Thus, the stamper can be easily peeled off at a low
cost. Further, the semimetal film of the information recording
layer of the stamper may be formed from Si (silicon) or metal
mainly composed of Si, and the manufacturing at lower cost can be
attained.
[0017] In the above-mentioned first manufacturing method, the thin
film may be applied with release agent thereon. With this method,
the stamper can be more easily peeled off.
[0018] According to the above-mentioned first manufacturing method,
the thickness of the second substrate may be substantially 0.1 mm.
With this constitution, especially, when the objective lens of the
pick-up has a large N.A., the high density optical disk can have
the tilt margin equal to the conventional DVD.
[0019] In the above-mentioned first manufacturing method, the
thickness at a clamp portion after the first substrate and the
second substrate are bonded each other may be substantially 1.2 mm.
With this constitution, compatibility to the conventional DVD and
CD in a thickness of the clamp portion can be attained.
[0020] In the above-mentioned first manufacturing method, the
thickness of the stamper may be substantially equal to that of the
first substrate. With this constitution, both the stamper and the
first substrate can be manufactured by substantially the same
apparatus.
[0021] In the above-mentioned first manufacturing method, the
center holes of the stamper and the second substrate may have
different diameters. With this constitution, the stamper can be
easily peeled off the first substrate.
[0022] In the above-mentioned first manufacturing method, each of
the stamper and the second substrate may be different in outer
diameter. With this constitution, the stamper can be easily peeled
off the first substrate.
[0023] In the above-mentioned first manufacturing method, the
second substrate having the information recording layer may be
bonded with a supporting substrate on a face opposite to the face
on which the information recording layer is formed, and a
reflective film or a recording film is deposited on the information
recording layer. With this constitution, the strength of the
stamper having a thickness as thin as 0.3 mm or less can be
increased to help the handling and film-forming.
[0024] In the above-mentioned first manufacturing method, it is
preferable that a sum of thicknesses of the second substrate and
the supporting substrate is substantially equal to that of the
stamper or the first substrate. With this constitution, the
manufacturing can be performed by substantially the same apparatus
used for the film deposition of the stamper or the first
substrate.
[0025] In a second aspect of the invention, provided is a method of
manufacturing an optical information recording medium. The method
comprises bonding a stamper having a principal plane formed with a
groove or asperity pits and a first substrate having a first
information recording layer with radiation cured resin so as to
cause the groove or the asperity pits to face to the first
information recording layer, the stamper being transparent, curing
the radiation cured resin, peeling off the stamper to form the
groove or the asperity pits on the first information recording
layer of the first substrate, forming a metal film or a recording
film over the groove or the asperity pits on the first substrate to
create a second information recording layer on the first substrate,
and forming a light transmission layer over the second information
recording layer.
[0026] This method can produce an optical disk having plural
information recording layers. The stamper is formed of light and
flexible resin, and thus can be easily handled. Therefore, the
radiation cured resin for transmitting signal pits can be spread
substantially uniformly on the substrate by rotating the substrate
with the spin-coating. The stamper can be easily handled and formed
in mass production at a low manufacturing cost in comparison with
the metal stamper.
[0027] In the above-mentioned second manufacturing method, the
thickness of the light transmission layer may be 0.3 mm or less.
With this structure, the NA of the recording/reproducing optical
system can be easily increased, thereby the recording density of
the optical disk can be increased.
[0028] In the above-mentioned second manufacturing method, the
thickness of the light transmission layer may be substantially 0.1
mm. With this structure, the optical disk can maintain the tilt
margin equal to that of the DVD even if the NA of the
recording/reproducing optical system is increased to around
0.9.
[0029] In the above-mentioned second manufacturing method, the
light transmission layer may be formed of radiation cured resin. By
forming the layer in this manner, the layer can be manufactured at
a low cost.
[0030] In the above-mentioned second manufacturing method, the
light transmission layer may be formed by bonding the first and
second substrates. By forming the layer in this manner, the variety
of the light transmission layer can be suppressed.
[0031] In the above-mentioned second manufacturing method, the
stamper may be formed by injection molding. With this method, the
disk can be formed at a low cost by the conventional optical disk
manufacturing apparatus.
[0032] In the above-mentioned second manufacturing method, the
stamper may be formed from resin material, and more specifically,
polycarbonate.
[0033] By forming the stamper from polycarbonate, a light and
low-cost stamper can be attained. With this stamper, the radiation
cured resin can be uniformly spread by spinning after overlapping
the stamper and the first substrate by the radiation cured
resin.
[0034] Further, the first substrate and the stamper are bonded in a
vacuum, and no bubbles may be inserted.
[0035] In the above-mentioned second manufacturing method, the thin
film may be applied with release agent thereon. With this method,
the stamper can be more easily peeled off, and the transferring of
the groove and the pits can be improved.
[0036] In the above-mentioned second manufacturing method, a thin
film may be formed on the groove or asperity pits of the stamper.
By forming the thin film, the stamper can be more easily peeled
off.
[0037] In the above-mentioned second manufacturing method, the thin
film may be a metal film or a dielectric film. With this method, if
the Si is used as the metal, the manufacturing at lower cost can be
attained. Further, the thin film is applied with release agent, and
thus the stamper can be more easily peeled off.
[0038] In the above-mentioned second manufacturing method,
radiation may be emitted substantially parallel to the principal
plane of the stamper when the radiation cured resin is cured after
the stamper and the first substrate are integrated by the radiation
cured resin. With this method, the radiation cured resin can be
cured even if the stamper and the first substrate have principal
planes with poor radiation transmittance.
[0039] In the above-mentioned second manufacturing method, the
thickness at a clamp portion may be substantially 1.2 mm. With this
constitution, the interchangeability to the conventional DVD and CD
in the thickness of the claim portion can be attained.
[0040] In the above-mentioned second manufacturing method, the
thickness of the stamper may be substantially equal to that of the
first substrate. With this constitution, both the stamper and the
first substrate can be manufactured by substantially the same
apparatus.
[0041] In the above-mentioned second manufacturing method, the
center holes of the stamper and the first substrate may have
substantially the same diameter. With this constitution, the center
of the groove or asperity pits of the stamper can be aligned to the
center of the signal recording layer of the first substrate by
aligning the center holes.
[0042] In the above-mentioned second manufacturing method, it is
preferable that each of the stamper and the first substrate are
different in outer diameter. With this constitution, the stamper
can be easily peeled off the first substrate.
[0043] In the third aspect of the invention, provided is a method
of manufacturing an optical information recording medium. The
method comprises: applying first radiation cured resin onto a
groove or asperity pits formed on a principal plane of a stamper;
bonding the stamper and a first substrate having a principal plane
on which a first information recording layer is formed with second
radiation cured resin such that the first radiation cured resin and
the first information recording layer face each other, and curing
the second radiation cured resin; peeling off the stamper to form a
groove or asperity pits made of the first radiation cured resin on
the first substrate; and forming a reflective film or a recording
film on the groove or the asperity pits on the first substrate to
make a second information recording layer.
[0044] With this method, the multilayered optical disk can be
easily formed even if the disk has a thin recording/reproducing
side substrate. Since the stamper is formed of light and flexible
resin, it can be easily handled. Therefore, the radiation cured
resin for transmitting signal pits can be spread substantially
uniformly on the substrate by rotating the substrate with the use
of the spin-coating. The stamper can be easily handled and formed
in mass production at a low manufacturing cost in comparing with
the metal stamper.
[0045] In the fourth aspect of the invention, provided is a method
of manufacturing an optical information recording medium. The
method comprises: applying second radiation cured resin onto a
first information recording layer formed on a principal plane of a
first substrate, and curing the second resin; bonding a stamper
having a principal plane formed with a groove or asperity pits and
the first substrate with first radiation cured resin such that the
groove or asperity pits and the second resin face each other, and
curing the first radiation cured resin; peeling off the stamper to
form groove or asperity pits made of the first radiation cured
resin on the first substrate; and forming a reflective film or a
recording film on the groove or the asperity pits on the first
substrate to make a second information recording layer.
[0046] With this manufacturing method, equivalent advantages to
those described for the first method can be attained.
[0047] In the fifth aspect of the invention, provided is a method
of manufacturing an optical information recording medium. The
method comprises: applying first radiation cured resin onto a
groove or asperity pits formed on a principal plane of a stamper;
applying second radiation cured resin onto a first information
recording layer formed on a principal plane of a first substrate;
bonding the stamper and the first substrate such that the first
radiation cured resin and the second radiation cured resin face
each other, and curing the first and second radiation cured resin;
peeling off the stamper to form a groove or asperity pits made of
the first radiation cured resin on the first substrate; and forming
a reflective film or a recording film over the groove or the
asperity pits on the first substrate to form a second information
recording layer.
[0048] With this manufacturing method, equivalent advantages to
those described for the first method can be attained.
[0049] In the sixth aspect of the invention, provided is a method
of manufacturing an optical information recording medium. The
method comprises: forming a first thin film comprising at least one
layer on a groove or asperity pits formed on a principal plane of a
stamper; forming a second thin film comprising at least one layer
over the first thin film; bonding the stamper and a first substrate
having a principal plane on which a first information recording
layer is formed with radiation cured resin such that the second
thin film and the first information recording layer face each
other; peeling off the stamper and the first substrate at an
interface of the first and second thin films to form a groove or
asperity pits made of the second thin film on the first substrate;
and forming a reflective film or recording film on the groove or
the asperity pits on the first substrate to form a second
information recording layer.
[0050] In the above-mentioned the third to sixth manufacturing
methods, third radiation cured resin may be applied on the first
information recording layer SA of the first substrate in advance,
and the third radiation cured resin HC is cured. In this manner,
the first information recording layer SA can be prevented from
being damaged when the stamper is peeled off. Especially, this is
more effective for a case where the first information recording.
layer SA is a rewritable recording layer comprising a plurality of
thin films, since the thin films may have poor strength. The
advantage of protecting the first information recording layer SA
from deterioration such as corrosion can also be attained.
[0051] Further, the third radiation cured resin may have a pencil
hardness of B or more. The first information recording layer SA can
be thereby prevented from being damaged. The third radiation cured
resin HC also may be applied at least from an inner peripheral edge
to an outer peripheral edge of the first information recording
layer. By applying the resin HC in this manner, the resin HC can
function effectively.
[0052] In the above-mentioned third to sixth manufacturing methods,
a light transmission layer may be formed on the second information
recording layer SB. By forming this layer, the second information
recording layer SB can be protected. The thickness of the light
transmission layer may be 0.3 mm or less. By forming the layer so
thick, the wavelength of the light emitted from the
recording/reproducing optical system can be shortened, and the NA
can be easily increased. Further, the optical disk having
information recording layers can be formed on the substrate having
a thickness of 0.3 mm or less which cannot be formed by injection
molding, and the optical disk having high density can be
attained.
[0053] Further, the thickness of the light transmission layer may
be substantially 0.1 mm. With this structure, the optical disk can
maintain the tilt margin equal to that of the DVD even if the NA of
the recording/reproducing optical system is increased to around
0.9. Also, the light transmission layer may be formed of radiation
cured resin. With this method, the disk can be formed at a low
cost. Further, the light transmission layer may be formed of
radiation cured resin and a resin substrate. By forming the layer
in this manner, the variety of the light transmission layer in
thickness can be suppressed, and the layer can be easily
formed.
[0054] In the above-mentioned the third to fifth manufacturing
methods, it is preferable that the stamper transmits at least one
of radiations having wavelengths for curing the first or second
radiation cured resin LA or LB. In the above-mentioned the fourth
manufacturing method, the stamper and the first and second thin
films FA and FB may transmit at least one of radiations having
wavelengths for curing the first or second radiation cured resin.
With this method, the first radiation cured resin LA, the second
radiation cured resin LB, or the radiation cured resin can be cured
even if radiation cannot transmit through the first substrate or
the information recording layer SA.
[0055] In the above-mentioned the third to fifth manufacturing
methods, the stamper may be formed from resin material. The stamper
is formed of light and flexible resin in comparison with the metal
stamper. Therefore, the radiation cured resin for transmitting
signal pits can be spread substantially uniformly on the substrate
by rotating the substrate with use of the spin-coating employed for
DVD manufacturing, not by applying a high pressure as in the 2P
method employed for the metal stamper or taking a long period of
time, and can be easily handled. The stamper can be easily handled
and formed in mass production by the injection molding at a low
manufacturing cost in comparison with the metal stamper. It is
difficult to prepare a lot of spare metal stampers, and thus the
replacing of the stamper is troublesome.
[0056] The stamper may be formed by injection molding. With this
method, the disk can be formed at a low cost by the conventional
optical disk manufacturing apparatus. The stamper may be formed
mainly of polycarbonate. With this method, the disk can be formed
by the conventional optical disk manufacturing apparatus.
[0057] In the above-mentioned the third, fourth, and sixth
manufacturing methods, the radiation cured resin may be spread by
spinning after overlapping the stamper and the first substrate by
the radiation cured resin in order to uniformly spread the
radiation cured resin. By forming the stamper from resin material,
a light and low-cost stamper can be attained. With this method, the
disk can be formed by the conventional manufacturing apparatus
employed for adhesion of the DVD. Further, the first substrate and
the stamper may be bonded in a vacuum, and thus no bubbles may be
inserted. In addition, the radiation cured resin and the stamper
can be stuck more strongly, and the transferability can be
improved.
[0058] In the above-mentioned the third manufacturing method, an
inner diameter of the first radiation cured resin LA may be smaller
than an inner diameter of the second radiation cured resin LB. By
applying resin in this manner, the second radiation cured resin LB
will not adhere to the stamper in the inner peripheral portion, and
thus the stamper can be easily peeled off the first substrate.
[0059] In the above-mentioned third and fifth manufacturing
methods, the first radiation cured resin LA may be applied toward
an outer peripheral edge of the stamper. By applying resin in this
manner, the second radiation cured resin LB will be prevented from
contacting with the stamper in the inner peripheral portion, and
thus the stamper can be easily peeled off the first substrate.
[0060] In the above-mentioned fourth manufacturing method, an inner
diameter of the second radiation cured resin LB is smaller than an
inner diameter of the first radiation cured resin LA. By applying
resin in this manner, the first radiation cured resin LA will not
adhere to the first substrate in the inner peripheral portion, and
thus the stamper can be easily peeled off the first substrate.
[0061] In the above-mentioned fourth and fifth manufacturing
methods, the second radiation cured resin LB is applied toward an
outer peripheral edge of the first substrate. By applying resin in
this manner, the first radiation cured resin LA will not adhere to
the first substrate in the inner peripheral portion, and thus the
stamper can be easily peeled off the first substrate.
[0062] In the above-mentioned sixth manufacturing method, inner
diameters of the thin first and second thin films FA and FB may be
smaller than an inner diameter of the radiation cured resin. By
forming the thin films in this manner, the radiation cured resin
will be prevented from adhering to the first substrate in the inner
peripheral portion, and thus the stamper can be easily peeled off
the first substrate.
[0063] In the above-mentioned sixth manufacturing method, the thin
first and second thin films FA and FB may be formed to cover an
outer peripheral edge of the stamper. By forming the thin films in
this manner, the radiation cured resin will be prevented from
adhering to the first substrate in the outer peripheral portion,
and thus the stamper can be easily peeled off the first
substrate.
[0064] In the above-mentioned third to fifth manufacturing methods,
the groove or the asperity pits of the stamper may be subjected to
a process for facilitating the peeling of the stamper. With this
method, the stamper can be more easily peeled off, and the
transferring can be improved. The groove or the asperity pits of
the stamper may be applied with release agent. With this method,
the stamper can be more easily peeled off, and the transferring can
be improved. A film mainly formed from metal may be formed on the
groove or the asperity pits of the stamper. With this method, the
stamper can be more easily peeled off, and the transferring can be
improved.
[0065] In the above-mentioned the sixth manufacturing method, the
first thin film FA may be formed of Au and the second thin film FB
may be formed of SiO.sub.2. With this method, the stamper can be
more easily peeled off.
[0066] In the above-mentioned third to sixth manufacturing methods,
center holes of the stamper and the first substrate may be
substantially equal to each other in diameter. With these center
holes, centers of a plurality of information recording layers
formed on the first substrate can be aligned with ease.
[0067] With use of the optical information recording medium
manufactured according to the above-mentioned third to sixth
manufacturing methods, high-density recording using a plurality of
information recording layers can be attained.
[0068] In the seventh aspect of the invention, provided is an
optical information recording medium having a substrate. The medium
comprises: an information recording layer formed on the substrate;
at least one basic layer which is stacked on the information layer,
and includes an intermediate layer and a recording layer; and a
light transmission layer formed on the basic layer. With the
optical information recording medium of the present invention,
high-density recording using a plurality of information recording
layers can be attained. Further, the protection layer and the light
transmission layer protect the information recording layers, and
thus stable manufacturing can be secured. The medium is also
advantageous in being manufactured by the above-mentioned first,
second, third, and fourth manufacturing methods with ease.
[0069] In the medium, the thickness of the light transmission layer
may be 0.3 mm or less. By forming the layer so thick, the
wavelength of the light emitted from the recording/reproducing
optical system can be shortened, and NA can be easily increased,
thereby the recording density of the optical recoding medium can be
increased. Further, the thickness of the light transmission layer
may be substantially 0.1 mm. With this structure, the optical disk
can maintain the tilt margin equal to that of the DVD even if the
wavelength of the recording/reproducing light beam is shortened to
around 400 nm and the NA of the recording/reproducing optical
system is increased to around 0.9. The thickness of the basic layer
may be not less than 15 .mu.m and not more than 45 .mu.m when the
thickness of the light transmission layer is substantially 0.1 mm.
By setting the thickness in this manner, the influence of the
interference of reproduction signals of a plurality of optical
recording media and the influence of the recording light can be
suppressed. Further, the recording/reproducing with use of the lens
having the high NA can be easily prevented from being influenced by
spherical aberration or the like.
[0070] Further, the light transmission layer may be formed of
radiation cured resin. With this method, the disk can be securely
formed at a low cost, and the variety of the light transmission
layer in thickness can be suppressed, and the layer can be formed
uniformly. Further, the light transmission layer may be formed of
radiation cured resin and a resin substrate. By forming the layer
in this manner, the variety of the light transmission layer can be
suppressed, and the layer can be easily formed.
[0071] The recording layer may comprise radiation cured resin
having the groove or the asperity pits, and a reflective film or a
recording film formed on the groove or the asperity pits. With this
structure, the high-density recording medium comprising a plurality
of information recording layers can be attained. Using radiation
cured resin, the manufacturing can be performed with ease at a low
cost.
[0072] The intermediate layer may have a function as adhesive.
Thus, the optical information recording medium can be stabilized.
The intermediate layer may be formed of radiation cured resin.
Thus, the manufacturing can be performed with ease at a low
cost.
[0073] The protection layer may have a pencil hardness B or more.
By setting the hardness of the protection layer in this manner, the
information recording layer can be protected from corrosion or
shock, and damage applied to the information recording layer during
the manufacturing can be also suppressed. The protection layer may
be formed of radiation cured resin. Thus, the manufacturing can be
performed with ease at a low cost.
[0074] The protection layer and the intermediate layer may have
substantially equal refractive indexes. By setting the refractive
indexes in this manner, the recording/reproducing light can stably
perform the recording/reproducing without optical interference of
spherical aberration. The protection layer and the intermediate
layer may be substantially transparent to transmit
recording/reproducing light. By employing such layers, the
recording/reproducing light can stably perform the
recording/reproducing without optical interference of absorption or
dispersion.
[0075] The intermediate layer may be substantially transparent to
transmit recording/reproducing light. By employing such a layer,
the recording/reproducing light can stably perform the
recording/reproducing without optical interference of absorption or
dispersion.
[0076] In an eighth aspect of the invention, provided is an optical
information recording medium comprising a first substrate, and a
second substrate which is thinner than the first substrate. Two
information recording layers are provided between the first and
second substrates.
[0077] In a ninth aspect of the invention, provided is an optical
information recording medium comprising a first substrate, and a
light transmission layer which is provided on the first substrate
and is made of radiation cured resin. Two information recording
layers are provided between the first substrate and the light
transmission layer.
[0078] The manufacturing method of the optical information
recording medium according to the present invention can be more
fully understood from the following detailed description of
embodiments of the invention in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0079] FIG. 1 is a flowchart showing a flow of the manufacturing
method of the optical disk according to the first embodiment of the
present invention;
[0080] FIG. 2A is a sectional view showing the structure of the
optical disk manufactured according to the manufacturing method of
the present invention;
[0081] FIG. 2B is a view showing dimensions of the optical disk
manufactured according to the manufacturing method of the present
invention;
[0082] FIGS. 3A to 3C are drawings showing a process (1) of the
manufacturing method of the optical disk according to the first
embodiment of the present invention;
[0083] FIGS. 4A to 4C are drawings showing a process (2) of the
manufacturing method of the optical disk according to the first
embodiment of the present invention;
[0084] FIGS. 5A and 5B are drawings showing a process (3) of the
manufacturing method of the optical disk according to the first
embodiment of the present invention;
[0085] FIGS. 6A to 6C are drawings showing a process (4) of the
manufacturing method of the optical disk according to the first
embodiment of the present invention;
[0086] FIG. 7 is a drawing showing a process (5) of the
manufacturing method of the optical disk according to the first
embodiment of the present invention;
[0087] FIGS. 8A and 8B are drawings showing a process (6) of the
manufacturing method of the optical disk according to the first
embodiment of the present invention;
[0088] FIG. 9 is a flowchart showing a flow of the manufacturing
method of the optical disk according to the second embodiment of
the present invention;
[0089] FIGS. 10A to 10C are drawings showing a process (1) of the
manufacturing method of the optical disk according to the. second
embodiment of the present invention;
[0090] FIGS. 11A and 11B are drawings showing a process (2) of the
manufacturing method of the optical disk according to the second
embodiment of the present invention;
[0091] FIGS. 12A and 12B are drawings showing a process (3) of the
manufacturing method of the optical disk according to the second
embodiment of the present invention;
[0092] FIGS. 13A and 13B are drawings showing a process (4) of the
manufacturing method of the optical disk according to the second
embodiment of the present invention;
[0093] FIGS. 14A and 14B are drawings showing a process (5) of the
manufacturing method of the optical disk according to the second
embodiment of the present invention;
[0094] FIGS. 15A and 15B are drawings showing a process (6) of the
manufacturing method of the optical disk according to the second
embodiment of the present invention;
[0095] FIGS. 16A and 16B are drawings showing a process (7) of the
manufacturing method of the optical disk according to the second
embodiment of the present invention;
[0096] FIG. 17 is a flowchart showing a flow of the manufacturing
method of the optical disk according to the third embodiment of the
present invention;
[0097] FIGS. 18A and 18B are drawings showing a process (1) of the
manufacturing method of the optical disk according to the third
embodiment of the present invention;
[0098] FIGS. 19A and 19B are drawings showing a process (2) of the
manufacturing method of the optical disk according to the third
embodiment of the present invention;
[0099] FIG. 20 is a flowchart showing a flow of the manufacturing
method of the optical disk according to the fourth embodiment of
the present invention;
[0100] FIGS. 21A to 21C are drawings showing a process (1) of the
manufacturing method of the optical disk according to the fourth
embodiment of the present invention;
[0101] FIGS. 22A to 22C are drawings showing a process (2) of the
manufacturing method of the optical disk according to the fourth
embodiment of the present invention;
[0102] FIGS. 23A to 23C are drawings showing a process (3) of the
manufacturing method of the optical disk according to the fourth
embodiment of the present invention;
[0103] FIGS. 24A and 24B are drawings showing a process (4) of the
manufacturing method of the optical disk according to the fourth
embodiment of the present invention;
[0104] FIG. 25 is a drawing showing a process (5) of the
manufacturing method of the optical disk according to the fourth
embodiment of the present invention;
[0105] FIGS. 26A to 26C are drawings showing a process (6) of the
manufacturing method of the optical disk according to the fourth
embodiment of the present invention;
[0106] FIGS. 27A and 27B are drawings showing a process (7) of the
manufacturing method of the optical disk according to the fourth
embodiment of the present invention;
[0107] FIG. 28 is a flowchart showing a flow of the manufacturing
method of the optical disk according to the fifth embodiment of the
present invention;
[0108] FIGS. 29A and 29B are drawings showing a process of the
manufacturing method of the optical disk according to the fifth
embodiment of the present invention;
[0109] FIG. 30 is a flowchart showing a flow of the manufacturing
method of the optical disk according to the sixth embodiment of the
present invention;
[0110] FIGS. 31A to 31C are drawings showing a process of the
manufacturing method of the optical disk according to the sixth
embodiment of the present invention;
[0111] FIG. 32 is a flowchart showing a flow of the manufacturing
method of the optical disk according to the seventh embodiment of
the present invention;
[0112] FIGS. 33A to 33C are drawings showing a process (1) of the
manufacturing method of the optical disk according to the seventh
embodiment of the present invention;
[0113] FIGS. 34A to 34C are drawings showing a process (2) of the
manufacturing method of the optical disk according to the seventh
embodiment of the present invention;
[0114] FIGS. 35A and 35B are drawings showing a process (3) of the
manufacturing method of the optical disk according to the seventh
embodiment of the present invention; and
[0115] FIGS. 36A and 36B are drawings showing a process of the
manufacturing method of the optical disk having a multilayer
structure according to the eighth embodiment of the present
invention.
PREFERRED EMBODIMENTS OF THE INVENTION
[0116] The preferred embodiments of the present invention are
described below with reference to the accompanying drawings.
[0117] First Embodiment
[0118] FIG. 1 is a flowchart showing a flow of a manufacturing
method of the optical information recording medium according to the
first embodiment of the present invention.
[0119] FIG. 2 is a sectional view showing the structure of the
optical disk as the optical information recording medium
manufactured according to the present invention. As shown in FIG.
2, an optical disk 1 comprises a first substrate 111 and a second
substrate 121 thinner than the first substrate 111, and has a first
information recording layer 116 and a second information recording
layer 119 between these substrates. The distance A between the
recording/reproducing surface of the optical disk 1 and the second
information recording layer 119 is set at 10 to 300 .mu.m, more
preferably 60 to 100 .mu.m. The distance B between the first
information recording layer 116 and the second information
recording layer 119 is set at 5 to 60 .mu.m, more preferably 10 to
40 .mu.m. A track width C is set at 0.16 to 0.20 .mu.m. A track
pitch D is set at 0.1 to 1 .mu.m, more preferably 0.2 to 0.4 .mu.m.
A pitch height E is set at 10 to 100 nm, more preferably 50 to 80
nm. The second substrate 121 preferably has a thickness of 0.3 mm
or less, more preferably, approximate 0.1 mm or less. The
recording/reproducing of data to/from the optical disk is performed
with use of a laser beam emitted from the side of the thinner
substrate, i.e., the second substrate.
[0120] A resin stamper 101 shown in FIG. 3A is formed of a
polycarbonate substrate made by injection molding to have a
thickness of 1.1 mm, a diameter 120 mm, and a center hole 102 with
a 15 mm diameter. The resin stamper 101 has asperity pits 103 on a
principal plane. The resin stamper 101 may be formed of resin
material other than polycarbonate, such as acrylic resin,
polyolefin-based resin, or the like. The sputtering is performed on
the asperity pits 103 to deposit metal 115 mainly composed of Al
for 100 nm. In this time, metal mainly composed of Si may be
sputtered on the asperity pits to manufacture the optical disk at a
lower cost. By forming the metal film 115 in this manner, the resin
stamper 101 and the second substrate 121 can be easily peeled off
each other. The resin stamper 101 has the thickness of 1.1 mm in
this embodiment, but may have a smaller thickness, for example, of
0.6 mm. By forming the resin stamper 101 to have the smaller
thickness, the material cost can be further decreased.
[0121] The second substrate 121 shown in FIG. 3B is formed of a
polycarbonate or acrylic sheet substrate having a thickness of 80
.mu.m, an outer diameter 119.5 mm, and a center hole with a 22 mm
diameter. The second substrate 121 has no information recording
layer, and is formed smooth. The second substrate 121 is formed by
cutting the sheet made by the casting method. The second substrate
121 may be formed of acrylic resin, norbolnane-based resin, or the
like.
[0122] At first, in the manufacturing process, as shown in FIG. 3C,
radiation cured resin 202 is applied onto the second substrate 121
to make a circle having a radius of approximate 27 mm with a nozzle
201. In this time, a spin table 203 on which the second substrate
121 is placed or the nozzle 201 is rotated at a low speed (20 to
120 rpm)
[0123] Next, the resin stamper 101 is overlaid on the second
substrate 121 to make a concentric circle as shown in FIG. 4A.
[0124] In overlaying the stamper, radiation cured resin 202 may be
applied circularly onto the stamper 101, then overlaid on the
second substrate 121. The radiation cured resin is resin cured by
radiation, and the radiation includes all electromagnetic waves and
particle waves. The radiation cured resin includes resin which is
cured by ultraviolet ray, resin which is cured by electron beam, or
the like.
[0125] After overlaying the stamper and the second substrate, the
spin table 203 is rotated at a high speed (1000 to 10000 rpm, for
example) to rotate the substrate so that the radiation cured resin
202 may be scattered to the outer periphery of the substrate, as
shown in FIG. 4B. By rotating the substrate in this manner, the
formation of bubbles may be minimized on the bonded interface and
the surplus radiation cured resin may be shaken off. The stamper
according to the present invention is formed of resin material
lighter than metal, and thus the rotation handling can be easily
performed and the radiation cured resin 202 can be easily extended
uniformly by the rotation. In addition, when the stamper is rotated
at a high speed, the curve or distortion may easily occur in the
metal stamper, but will not easily occur in the resin stamper.
Further, the rotation step can be performed with use of the
conventional bonding step and the conventional apparatus used for
the manufacturing of the DVD.
[0126] Subsequently, rays (ultraviolet) 205 and 206 are emitted as
shown in FIG. 4C to cure the radiation cured resin 202. The light
may be emitted from one of resin stamper side (rays 205) and first
substrate side (rays 206), or from both the sides. It is preferable
to select the optimum emitting method in accordance with the
transmittance of the thin film formed on the resin stamper 101.
[0127] The resin stamper 101 is then peeled off the second
substrate 121 as shown in FIGS. 5A and 5B. In this embodiment, a
part of the outer or inner periphery of the resin stamper 101 is
raised with a hook 301 formed in a hook shape, and an air blower
blows air 209 into a space between the stamper and the second
substrate to separate them. The inner or outer periphery of the
resin stamper 101 may be approximately equal to that of the second
substrate 121. When the resin stamper 101 is formed to have the
inner or outer periphery smaller or larger than that of the second
substrate 121, the insertion of the hook 301 can be facilitated to
effectively separate them. The inner or outer periphery of the
resin stamper 101 may be either smaller or larger than that of the
second substrate 121. By forming an Al film or a Si film on the
resin stamper 101 in advance, the separation can be easily
performed. The film may be formed of film other than metal, such as
a dielectric thin film. The thin film of the resin stamper 101 may
be applied with release agent such as siloxane, a
fluoromonomoleclular film, or the like.
[0128] As shown in FIG. 6B, a semitransparent reflective film 118
(in this embodiment, a film made of approximately 20 nm deposited
metal mainly composed of Ag) is then formed on the second substrate
121 (shown in FIG. 6A) on which the asperity pits are transferred.
The semitransparent reflective film 118 may be formed from metals
mainly composed of Rh, Au, or Si, or formed of a dielectric
reflective film. The second substrate 121 is formed as thin as 80
.mu.m and thus has poor strength. In forming the semitransparent
reflective film, the second substrate may not be easily handled or
the film cannot be formed easily.
[0129] In order to facilitate the handling and film forming, a
supporting substrate 131 is bonded to the second substrate 121 on
the side face opposite to the principal plane on which the asperity
pits are formed, as shown in FIG. 6B. By bonding the supporting
substrate 131 in this manner, the second substrate 121 has
excellent strength to help the handling and film forming. The
supporting substrate 131 is formed of a polycarbonate substrate
having a thickness of 1.0 mm, a diameter 120 mm, and a center hole
with a 15 mm diameter. The resin stamper after transferring the
signal pits which cannot be used for the signal transfer any more
may be used as the supporting substrate 131. The second substrate
121 and the supporting substrate 131 are bonded with radiation
cured resin having weak adhesion in this embodiment, but may be
bonded with another adhesive or static electricity. The second
substrate 121 is preferably maintained substantially flat and
horizontal to form the film 118 uniformly after the adhesion of the
second substrate 121 and the supporting substrate 131. The second
substrate 121 and the supporting substrate 131 may be separated
after forming the film, or the first substrate 111 may be placed
such that the center hole 112 of the first substrate 111 is
eccentric to a center hole 134 of the supporting substrate 131 when
the first substrate 111 and the second substrate 121 are bonded
each other.
[0130] After separating the supporting substrate 131, it is
preferable that there is no residual adhesive or damage on the
principal plane of the second substrate 121 to which the supporting
substrate 131 was bonded. The second substrate 121 and the
supporting substrate 131 are separated by the same method as used
to separate the resin stamper 101 from the second substrate 121. By
forming the second substrate 121 and the supporting substrate 131
to have different inner or outer peripheries, the separation can be
performed easily. If the handling and the film forming can be
performed alone, the second substrate 121 needs not to be bonded
with the supporting substrate 131.
[0131] The first substrate 111 shown in FIG. 6C is formed of a
polycarbonate substrate made to have a thickness of 1.1 mm, a
diameter 120 mm, and a center hole with a 15 mm diameter. The first
substrate 111 has asperity pits 113 on a principal plane. The first
substrate 111 may be formed of resin material other than
polycarbonate, such as acrylic resin, polyolefin-based resin, or
the like. The sputtering is performed on the asperity pits 113 to
deposit a reflective film 115 mainly composed of Al of 100 nm. In
this time, the reflective film 115 may be formed from metal other
than Al, for example, Ag. The first substrate 111 is formed by the
injection molding. Since the first substrate 111 and the resin
stamper 101 have the same thickness, the injection molding and the
film forming of the first substrate 111 and the resin stamper 101
can be performed with the same facility. The first substrate 111 is
not the substrate on which the recording/reproduction is performed,
and thus it may be formed from non-transparent resin having low
transmittance.
[0132] The second substrate 121 and the first substrate 111 on
which the information recording layer is formed are bonded to each
other with use of radiation cured resin 210 such that the
information recording layers 119 and 116 face to each other, as
shown in FIG. 7. The method of the bonding is the same method as
used to bond the resin stamper 101 and the first substrate 111.
More specifically, the radiation cured resin 210 is applied on one
of the substrates, the substrates are wrapped over each other, and
then the substrates are rotated to spread the radiation cured resin
210 substantially uniformly. After spreading the resin, ultraviolet
radiation is emitted to cure the radiation cured resin 210. By
setting the thickness of a clamp portion at approximate 1.2 mm
after bonding the first substrate 111 and the second substrate 121,
it can maintain the compatibility to CD or DVD thickness.
[0133] The resin stamper 101 and the first substrate 111, or the
first substrate 111 and the second substrate 121 may be bonded in a
vacuum circumstance. In this case, radiation cured resin 211 is
spin-coated on one or both of the substrates or on the bonding
plane of the resin stamper as shown in FIG. 8A, and then the
substrates or the resin stamper are wrapped over each other in a
vacuum as shown in FIG. 8B, and the radiation cured resin 211 is
cured by radiation thereafter. By bonding in a vacuum, no bubbles
are inserted into the interface thereof. Similarly, the stamper is
formed from light resin material, and thus can be easily rotated
for spin-coating the radiation cured resin on the stamper. In
addition, the resin stamper will not easily curved or distorted in
contrast to the metal stamper.
[0134] As described above, according to the above-mentioned
manufacturing method, the optical disk having information recording
layers can be formed on the substrate having a thickness of 0.3 mm
or less which cannot be formed by the injection molding, resulting
in the optical disk having high density.
[0135] It will be obvious to those of ordinary skill in the art
that the present embodiment can be applied to other embodiments
such as a rectangular or polygonal card-like recording medium,
modifications of a disk-like recording medium, or the like within a
scope from where the spirit of the invention as defined can be
maintained free from any deviation.
[0136] Second Embodiment
[0137] Another embodiment of a manufacturing method of an optical
disk according to the present invention will be described in
conjunction with FIGS. 9 to 16B. FIG. 9 is a flowchart showing a
flow of manufacturing method of the optical disk according to the
second embodiment.
[0138] A resin stamper 101 shown in FIG. 10A is formed of a
polycarbonate substrate made by the injection molding to have a
thickness of 1.1 mm, a diameter 120 mm, and a center hole with a 15
mm diameter. The resin stamper 101 has asperity pits 103 on one of
principal planes. A resin stamper 101 may be formed of resin
material other than polycarbonate, such as acrylic resin,
polyolefin-based resin, or the like. The sputtering is provided on
the asperity pits to deposit metal 105 mainly composed of Si for 20
nm.
[0139] The first substrate 111 shown in FIG. 10B is formed of a
polycarbonate substrate made to have a thickness of 1.1 mm, a
diameter 120 mm, and a center hole with a 15 mm diameter. The first
substrate 111 has a principal plane on which an information
recording layer (SA) 116 comprising asperity pits 113 and an Al
reflective film 115 is formed. The first substrate 111 may be
formed of resin material other than polycarbonate, such as acrylic
resin, polyolefin-based resin, or the like. The first substrate 111
is not the substrate from which side the recording/reproduction is
performed, and thus it may be formed from non-transparent resin
having low transmittance.
[0140] After preparing the resin stamper 101 and the first
substrate 111 as shown in FIGS. 10A and 10B, radiation cured resin
202 is applied onto the first substrate 111 to make a circle having
a radius of approximate 27 mm with a nozzle 211, as shown in FIG.
10C. In this time, a spin table 203 on which the first substrate
111 is placed or the nozzle 211 is rotated at a low speed (20 to
120 rpm).
[0141] Next, the resin stamper 101 is placed on the first substrate
111 to be concentric with the first substrate 111, as shown in FIG.
11A. It is noted that, instead of this, the radiation cured resin
202 may be applied onto the stamper 101 circularly, and then the
stamper 101 may be placed over the first substrate 111.
[0142] After placing the stamper and the first substrate, the spin
table 203 is rotated at a high speed (1000 to 10000 rpm, for
example) to rotate the substrate so that the radiation cured resin
202 may be extended to the outer periphery of the substrate, as
shown in FIG. 11B. By rotating the substrate in this manner, the
formation by bubbles may be easily minimized on the bonded
interface and the surplus radiation cured resin may be shaken
off.
[0143] By making inner circumference diameters of the resin stamper
101 and the first substrate 111 to be substantially equal, the
center of the information recording layer 116 of the first
substrate 111 can be aligned to the center of the groove or
asperity pits of the resin stamper 101. The alignment can be easily
attained by providing the spin table 203 with a center pin having
substantially equal size to that of the center holes 102 and 112.
In order to decrease the eccentricity more, a mechanism for
aligning the centers before extending and curing the radiation
cured resin may be provided.
[0144] Subsequently, radiation 205 and 206 is emitted as shown in
FIG. 12A to cure the radiation cured resin 202. The radiation may
be emitted from resin stamper side (radiation 205) and/or first
substrate side (radiation 206). In this time, the transmittance of
the radiation may be decreased depending on the material of the
resin stamper 101 and the first substrate 111 or the film. Thus,
the radiation cured resin may not be easily cured by the radiation
incident in a direction vertical to the principal planes of the
resin stamper 101 and the first substrate 111. Therefore, to cure
the resin, it is effective to emit radiation 208 parallel to the
principal plane of the resin stamper 101 and the first substrate
111 so that the radiation is emitted into the edge of the principal
planes, as shown in FIG. 12B. It is more effective to focus the
radiation by a lens 209 such that the radiation is effectively
incident into the edge faces. In order to more securely attain the
curing, it is preferable to emit the radiation from a plurality of
positions.
[0145] The resin stamper 101 is then peeled off the first substrate
111 as shown in FIGS. 13A and 13B. In this embodiment, a part of
the outer or inner periphery of the resin stamper 101 is raised
with a hook 301 formed in a hook shape and blow air 302 into the
interface between the stamper 101 and the second substrate 111 with
use of an air blower to separate them. The outer circumference
diameter of the resin stamper 101 may be approximately equal to
that of the first substrate 111. The resin stamper 101 may be
formed to have the outer circumference diameter different from that
of the first substrate 111. Thus, the hook 301 can be easily
inserted into the interface of the stamper 101 and the first
substrate 111 to effectively separate them.
[0146] It is preferable to employ, as the radiation cured resin
202, radiation cured resin which is excellent. in transferability
and has poor adhesion to the stamper 101 and excellent adhesion to
the information recording layer 116 of the first substrate 111. In
this embodiment, the radiation cured resin having excellent
adhesion to Al and poor adhesion to Si is employed. Accordingly,
forming a Si film on the resin stamper 101 in advance allows the
separation to be easily performed. The stamper 101 may have the
film formed from another metal such as Ag, Au, or Al, or a
non-metal film such as a dielectric thin film, depending on a type
of the radiation cured resin 202. The thin film on the resin
stamper 101 such as the metal film needs not to be formed if the
adhesion of the stamper 101 to the resin material forming the resin
stamper 101 is week. The asperity pits on the resin stamper 101 or
the thin film formed on the resin stamper 101 may be applied with a
release agent.
[0147] As shown in FIG. 14B, a semitransparent reflective film 118
(in the present embodiment, a film made of approximately 20 nm of
deposited metal mainly composed of Ag) is then formed on the first
substrate 111 (shown in FIG. 14A) on which the asperity pits are
transferred, thereby forming the information recording layer 119.
The reflective film 118 may be formed of metal mainly composed of
Rh, or formed of a dielectric reflective film.
[0148] The second substrate 121 shown in FIG. 15A is formed of a
polycarbonate sheet-like substrate having a thickness of 80 .mu.m,
a diameter 119.5 mm, and a center hole with a 22 mm diameter. The
second substrate 121 has no information recording layer, and is
formed smooth. The second substrate 121 is formed by cutting a
sheet made by the casting method. The second substrate 121 may be
formed of acrylic resin, norbolnane-based resin, or the like.
[0149] The second substrate 121 and the first substrate 111 on
which the information recording layers 116 and 119 are formed are
bonded each other via the radiation cured resin 210 such that the
information recording layers 116 and 119 formed on the principal
planes face each other, as shown in FIG. 15B. The substrates are
bonded by the same method as used to bond the resin stamper 101 and
the first substrate 111. More specifically, the radiation cured
resin 210 is applied on one of the substrates circularly, the
substrates are overlapped each other, and then the first and second
substrates 111 and 121 integrated by the radiation cured resin 210
are rotated to extend the radiation cured resin 210 substantially
uniformly. After extending the resin, ultraviolet radiation is
emitted to cure the radiation cured resin 210. With use of the
sheet-like second substrate 121 as a light transmission layer, the
light transmission layer can be formed to have a substantially
uniform thickness. The light transmission layer preferably has a
thickness of 0.3 mm or less, more preferably, of approximate 0.1 mm
or less.
[0150] The resin stamper 101 and the first substrate 111, and the
first substrate 111 and the second substrate 121 may be bonded in a
vacuum circumstance. In this case, the radiation cured resin 211 is
spin-coated on one of the substrates or on the bonding plane of the
resin stamper as shown in FIG. 16A, and then the substrates or the
resin stamper are overlapped on each other in a vacuum as shown in
FIG. 16B. The radiation cured resin 211 is cured by radiation
thereafter. By bonding the substrates or the resin stamper in a
vacuum, no bubbles are inserted into the interface thereof.
[0151] As described above, according to the above-mentioned
manufacturing method, the optical disk having high density can be
attained.
[0152] Third Embodiment
[0153] Another embodiment of a manufacturing method of an optical
disk according to the present invention will be described in
conjunction with FIGS. 17 to 19B. The same or like description as
presented in the above embodiments will be omitted.
[0154] FIG. 17 is a flowchart showing a flow of manufacturing
method of the optical disk according to this embodiment.
[0155] The manufacturing steps to the step of forming a first
substrate 511 having a first information recording layer 517, and a
second information recording layer 518 are the same as those
described in the second embodiment (layers 119 and 116), as shown
in FIG. 18A.
[0156] In the present embodiment, a light transmission layer on the
information recording layer 518 of the first substrate 511 is
formed with the radiation cured resin.
[0157] As shown in FIG. 18B, the radiation cured resin 602 is
applied on the information recording layer 518 on the first
substrate 511 to make a circle with a radius of approximate 24 mm
by a nozzle 601. In this time, a spin table 603 on which the first
substrate 511 is placed or the nozzle 601 is rotated at a low speed
(20-120 rpm).
[0158] Next, the spin table 603 is rotated at a high speed (200 to
10000 rpm) to rotate the first substrate 511 so that the radiation
cured resin 602 may be spread substantially uniformly over the
information recording layer 518, as shown in FIG. 19A. Rotating
speed or the rotation time may be changed according to viscosity of
the radiation cured resin 602. Thus, the radiation cured resin 602
can be spread substantially uniformly on the first substrate
511.
[0159] Subsequently, as shown in FIG. 19B, radiation 605 is emitted
to cure the radiation cured resin 602. In this embodiment, the
light transmission layer made of the radiation cured resin 602 with
a thickness of approximate 0.1 mm is formed. Most of the radiation
cured resins cannot be easily cured in contact with oxygen.
Therefore, the radiation 605 is emitted in a nitrogen atmosphere
612 to cure the radiation cured resin 602. By forming the light
transmission layer from the radiation cured resin, the optical disk
can be attained with a lower manufacturing cost.
[0160] As described above, according to the above-mentioned
manufacturing methods of the second and third embodiments, it is
possible to produce an optical disk that has a thin substrate from
a side of which data is recorded/reproduced and which has multiple
information recording layers. More specifically, since the used
stamper is formed of light and flexible resin, it can be easily
handled. Further, the radiation cured resin for transmitting signal
pits can be spread or extended substantially uniformly on the
substrate by rotating the substrate by using substantially the same
facility as that used for the adhesion step in the manufacturing
step of the DVD. In addition, even if the stamper cannot be easily
peeled off the substrate and needs to be replaced, the stamper can
be easily replaced with a new one since the stamper is formed of
resin and can be formed with mass production at a low manufacturing
cost.
[0161] Fourth Embodiment
[0162] A further embodiment of a manufacturing method of an optical
disk according to the present invention will be described in
conjunction with FIGS. 20 to 27B. FIG. 20 is a flowchart showing a
flow of a manufacturing method of the optical disk according to the
fourth embodiment.
[0163] A resin stamper 101 shown in FIG. 21A is formed of a
polycarbonate substrate made by the injection molding to have a
thickness of 1.1 mm, a diameter 120 mm, and a center hole with a 15
mm diameter. The resin stamper 101 has asperity pits 103 at a
principal plane. The resin stamper 101 may be formed of resin
material other than polycarbonate, such as acrylic resin,
polyolefin-based resin, or the like. The resin stamper 101 having
the thickness of 1.1 mm is used in this embodiment, but the stamper
may have a smaller thickness, for example, of 0.6 mm. By forming
the resin stamper 101 to have the smaller thickness, the material
cost can be further decreased more. As shown in FIG. 21B, first
radiation cured resin (hereinafter referred to as "radiation cured
resin LA") 104 is dropped onto the asperity pits 103 of the resin
stamper 101 circularly by a nozzle 201. The resin stamper is then
rotated to shake off surplus resin and spread the resin
substantially uniformly.
[0164] Subsequently, radiation 202 is emitted as shown in FIG. 22A
to cure the radiation cured resin LA 104. In the present
embodiment, it is preferable to rotate the resin stamper 101 in a
vacuum. By rotating the resin stamper 101 in a vacuum, the resin
can be inserted into the groove deeply. In this time, it is
preferable to perform the resin curing subsequent to the rotation
in the atmosphere, i.e., under the atmosphere pressure, and thus
the resin can be strongly stuck to the stamper. That is, it is
preferable to perform a process of placing the radiation cured
resin 104 onto the resin stamper 101 by rotating the resin stamper
101 under a pressure lower than that of the following process of
curing the resin 104. Thus, filling and transferring the radiation
cured resin to the stamper 101 can be effectively performed.
[0165] The first substrate 111 shown in FIG. 22B is formed of a
polycarbonate substrate made to have a thickness of 1.1 mm, a
diameter 120 mm, and a center hole 112 with a 15 mm diameter. The
first substrate 111 has a principal plane on which an information
recording layer (SA) 116 comprising asperity pits 113 and an Al
reflective film 115 is formed. The first substrate 111 may be
formed of resin material other than polycarbonate, such as acrylic
resin, polyolefin-based resin, or the like. Since the first
substrate 111 is not a substrate from a side of which data is
recorded/reproduced, it may be formed from non-transparent resin
having low transmittance. The second radiation cured resin
(hereinafter referred to as "radiation cured resin LB") 114 is
applied onto the first substrate 111 to make a circle having a
radius of approximate 27 mm by a nozzle 211, as shown in FIG.
22C.
[0166] Next, the resin stamper 101 is placed concentrically on the
first substrate 111, as shown in FIG. 23A. It is noted that the
resin stamper 101 may be placed on the first substrate 111 after
the radiation cured resin LB 114 is applied circularly onto the
radiation cured resin LA 104 on the stamper 101. After placing the
stamper 101 on the first substrate 111, they are rotated at a high
speed (1000 to 10000 rpm, for example) so that the radiation cured
resin LB 114 may be extended to the outer periphery of the
substrate, as shown in FIG. 23B. By rotating the substrate in this
manner, the formation of bubbles may be easily minimized on the
bonded interface and the surplus radiation cured resin LB 114 may
be shaken off.
[0167] By making center hole diameters of the resin stamper 101 and
the first substrate 111 equal, the center of the information
recording layer SA of the first substrate 111 can be aligned to the
center of the asperity pits of the resin stamper 101. The alignment
can be easily attained by providing the spin table with a center
pin having approximately equal size to that of the center holes 102
and 112. In order to decrease the eccentricity more, a mechanism
for aligning the centers before extending and curing the radiation
cured resin LB 114 may be provided.
[0168] Subsequently, as shown in FIG. 23C, radiation 212 is emitted
to cure the radiation cured resin LB 114. The first substrate 111
has the information recording layer 116, and therefore, the
radiation cured resin LB 114 cannot be easily cured by the
radiation emitted from the side of the first substrate 111.
Accordingly, the radiation transmittance of the resin stamper 101
must be sufficient to cure the radiation cured resin. In the
present embodiment, the stamper is formed from transparent
polycarbonate to facilitate the resin curing. The stamper may be
formed from another material as long as the material has sufficient
radiation transmittance.
[0169] The resin stamper 101 is then peeled off at the interface
between the resin stamper 101 and the radiation cured resin LA 108
(the radiation cured resin LA 104 to which the asperity pits are
transferred) as shown in FIGS. 24A and 24B. This allows the
radiation cured resin LA 108 to which the asperity pits are
transferred to be formed on the information recording layer 116 of
the first substrate 111. In this embodiment, a part of the outer or
inner periphery of the resin stamper 101 raised up with a hook 301
formed in a hook shape and blow air 302 into the interface between
the stamper and the first substrate with using an air blower to
separate them. The outer circumference diameter of the resin
stamper 101 may be approximately equal to that of the first
substrate 111. In FIG. 24A, the outer diameters of the stamper 101
and the first substrate 111 may be set to be different, and thus
the hook 301 can be easily inserted into the interface of the
stamper and the first substrate, to effectively separate them. For
example, the resin stamper 101 may be formed to have a diameter
larger than that of the first substrate 111 by 0.5 to 1 mm, for
example. The outer periphery of the resin stamper 101 can formed to
have a thickness smaller than that of the inner portion by about
0.1 to 0.3 mm such that the hook 301 can be easily inserted into
the interface. It is preferable to employ as the radiation cured
resin LA 108 the radiation cured resin excellent in stickability
and transferability and having poor adhesion to the resin stamper
101.
[0170] Especially, it is preferable to employ, as the radiation
cured resin LB 114, the radiation cured resin having high adhesion
to the information recording layer 116 of the first substrate 111
and the radiation cured resin LA 108. In contrast, it is preferable
to employ, as the radiation cured resin LA 104, the radiation cured
resin having poor adhesion to the resin stamper 101. In this
manner, by employing the radiation cured resin LA that has poor
adhesion to the resin stamper 101, and the radiation cured resin LB
that has high adhesion to both the information recording layer 116
of the first substrate 111 and the radiation cured resin LA, the
resin stamper 101 can be separated from the radiation cured resin
LA more easily. In order to avoid the sticking the radiation cured
resin LA 108 (104) to the resin stamper 101, which makes the
separation difficult, the radiation cured resin LA 108 may be
applied such that the resin LA 108 is extended to the outer
periphery of the resin stamper 101 and that the inner circumference
diameter of the resin LA 108 is smaller than that of the resin LA
104. It is preferable that the hardness of the radiation cured
resin LA which adheres to the stamper to transfer the pits is
higher than that of the radiation cured resin LB for bonding the
radiation cured resin LA and the information recording layer, and
that the glass transition temperature of the radiation cured resin
LA is higher than that of the radiation cured resin LB. By
employing two types of radiation cured resins in this manner, the
transferability and the stickability can be separated to the
different types of the radiation cured resins, which makes the
development of the radiation cured resin easy.
[0171] The stamper 101 may be processed to facilitate the
separation in consideration of the separation of the radiation
cured resin LA. The stamper 101 may have the film mainly formed
from metal such as Si, Ag, or Au, or a non-metal film such as a
dielectric thin film. The asperity pits 103 on the resin stamper
101 or the thin film formed on the resin stamper 101 may be applied
with a release agent such as siloxane, a fluoromonomoleclular film,
or the like. The stamper 101 may be formed from material having a
predetermined level of transmittance of ultraviolet rays, such as
glass or metal silicon, instead of resin.
[0172] The information recording layer 116 has poor tensile
strength, the information recording layer 116 may be damaged in
peering the resin stamper 101. By applying third radiation cured
resin (hereinafter referred to as "radiation cured resin HC") onto
the information recording layer 116 to protect it as shown in FIG.
25 in advance, the damage to the information recording layer 116
may be prevented. In this time, the radiation cured resin HC is
preferably applied to cover at least the inner peripheral edge to
the outer peripheral edge of the information recording layer 116.
Further, it is preferable that the inner periphery of the radiation
cured resin HC covers a part or all of the clamp region of the
first substrate 111, and the outer periphery of the radiation cured
resin HC covers the outer peripheral edge of the first substrate
111. In this time, the radiation cured resin HC preferably has
hardness higher than the pencil hardness of B.
[0173] As shown in FIG. 26A, a semitransparent reflective film 118
(in the present embodiment, a metal film mainly composed of Ag) is
formed with a thin 20 nm thickness onto the first substrate 111 on
which the asperity pits are transferred, in order to make the
second information recording layer 119. The reflective film 118 may
be formed from metal mainly composed of Rh, or formed of a
dielectric reflective film. The second substrate 121 shown in FIG.
26B is formed of a polycarbonate sheet-like substrate having a
thickness of 80 .mu.m, an outer circumference diameter 119.5 mm,
and a center hole 122 with a 22 mm diameter. The second substrate
121 has no information recording layer, and is formed smooth. The
second substrate 121 is formed by cutting a sheet made by the
casting method. The second substrate 121 may be formed of acrylic
resin, norbolnane-based resin, or the like.
[0174] The second substrate 122 and the first substrate 111 on
which the information recording layer 116 and the information
recording layer 119 are formed are bonded to each other via fourth
radiation cured resin (hereinafter referred to as "radiation cured
resin LC") 124 such that the information recording layers 116 and
119 formed on the principal planes face to each other, as shown in
FIG. 26C. The substrates are bonded by the same method as used to
bond the resin stamper 101 and the first substrate 111. More
specifically, the radiation cured resin LC is applied on one of the
substrates substantially circularly, the substrates are overlapped
on each other, and then the first and second substrates 111 and 121
integrated by the radiation cured resin LC are rotated to spread
the radiation cured resin LC substantially uniformly. After
spreading the resin, ultraviolet radiation is emitted to cure the
radiation cured resin LC.
[0175] Using the sheet-like second substrate 121 as a light
transmission layer, the light transmission layer can be formed to
have a substantially uniform thickness. The radiation cured resin
LB and the radiation cured resin LC may be made of the same
material. The thickness of the optical information recording medium
formed with the light transmission layer is set at 1.2 mm to have a
compatibility to CD or DVD thickness.
[0176] The resin stamper 101 and the first substrate 111, and the
first substrate Ill and the second substrate 121 may be bonded in a
vacuum circumstance. The case wherein the first substrate 111 and
the second substrate 121 are bonded each other will be described
below as an example. Radiation cured resin is spin-coated on either
or both of the substrates 111 and 121, (or on the plane adhering to
the resin stamper 101) as shown in FIG. 27A. Then the substrates
are overlapped on each other in a vacuum chamber 303 as shown in
FIG. 27B, and the radiation cured resin is cured by radiation
thereafter. By bonding the substrates or the resin stamper in a
vacuum in this manner, no care needs to be taken for preventing the
insertion of bubbles into the interface thereof. Further, the
stickiness between the radiation cured resin and the substrate or
the stamper can be thereby improved. With the improvement of the
stickiness of the substrate, the transferability of the asperity
pits can be also improved.
[0177] When the light transmission layer is formed from the
radiation cured resin, the manufacturing cost can be reduced.
According to the present embodiment, the light transmission layer
is provided to the optical disk. If the optical information
recording medium is stable without the light transmission layer,
the light transmission layer does not need to be formed.
[0178] Fifth Embodiment
[0179] An additional embodiment of a manufacturing method of an
optical disk according to the present invention will be described
in conjunction with FIGS. 28 to 29B. FIG. 28 is a flowchart showing
a flow of manufacturing method of the optical disk according to the
fifth embodiment. The same or like description as presented in the
above embodiments will be omitted. A resin stamper 401 and a first
substrate 411 are the same as those of the above-mentioned
embodiments (101 and 111).
[0180] As shown in FIG. 29A, radiation cured resin LB 414 is
applied onto an information recording layer 416 of the first
substrate 411, and the radiation cured resin LB is cured by
emitting radiation. The radiation cured resin is applied
substantially uniformly by the spinning in the same method as the
case in conjunction with FIGS. 21B and 21C in the fourth
embodiment. Then, with the same method shown in FIGS. 23C and 24A
of the fourth embodiment, the resin stamper 401 is bonded with the
first substrate 411 by radiation cured resin LA 404 as shown in
FIG. 29B, and the radiation is emitted to cure the radiation cured
resin LA.
[0181] By making inner circumference diameters of the resin stamper
401 and the first substrate 411 equal, the center of the
information recording layer SA of the first substrate 411 can be
aligned to the center of the asperity pits 403 of the resin stamper
401. The alignment can be easily attained by providing the spin
table with a center pin having substantially equal size to that of
center holes 402 and 412. In order to decrease the eccentricity
more, a mechanism for aligning the centers before extending and
curing the radiation cured resin may be provided. The radiation is
emitted to cure the radiation cured resin LA. As described in the
first embodiment, since the first substrate has the information
recording layer SA, the radiation cured resin LA cannot be easily
cured by the radiation emitted from the side of the first
substrate. Accordingly, the radiation transmittance of the resin
stamper must be sufficient to cure the radiation cured resin. In
the present embodiment, the stamper is made of transparent
polycarbonate to facilitate the resin curing. The stamper may be
made of another material if the material has sufficient radiation
transmittance.
[0182] As described in the fourth embodiment, the resin stamper 401
and the first substrate 411 may be bonded in a vacuum circumstance.
By bonding in a vacuum circumstance, no care needs to be taken for
preventing bubbles from being inserted into the interface thereof.
Further, the stickiness of the radiation cured resin to the
substrate or the stamper can be thereby improved. Further, the
transferability of the asperity pits onto the radiation cured resin
can be also thereby improved.
[0183] The resin stamper 401 is then peeled off the radiation cured
resin LA 108 as described in conjunction with FIGS. 24A and 24B in
the fourth embodiment. It is preferable to employ as the radiation
cured resin LA the radiation cured resin which is excellent in
stickability and transferability and which has poor adhesion to the
resin stamper 401. In order to avoid the sticking the radiation
cured resin LA to the resin stamper 401, which makes the separation
difficult, the radiation cured resin LB is applied such that the
radiation cured resin LB is extended to the outer periphery of the
resin stamper 401, and that the inner circumference diameter of the
radiation cured resin LB is smaller than that of the radiation
cured resin LA. By employing two types of radiation cured resins,
effects of the transferability and the stickability can be
separated to the different types of the radiation cured resins,
respectively, resulting in more easiness in developing the
radiation cured resin.
[0184] The stamper 401 may be processed to facilitate the
separation in consideration of the separation of the radiation
cured resin LA. For example, the stamper 401 may have the film
mainly made of metal such as Si, Ag, or Au, or a non-metal film
such as a dielectric thin film. The asperity pits on the resin
stamper 401 or the thin film formed on the resin stamper 401 may be
applied with a release agent.
[0185] When the information recording layer 416 has poor tensile
strength, the information recording layer 416 may be damaged in
peering the resin stamper 401. By applying radiation cured resin HC
onto the information recording layer 416 to protect it in advance
as shown in FIG. 25 of the fourth embodiment, the damage to the
information recording layer 416 may be prevented. In this time, the
radiation cured resin HC is preferably applied to cover from the
inner peripheral edge to the outer peripheral edge of the
information recording layer 416. Further, it is preferable that the
inner periphery of the radiation cured resin HC covers a part or
all of the clamp region of the first substrate 411, and that the
outer periphery of the radiation cured resin HC covers the outer
peripheral edge of the first substrate 411. In this time, the
radiation cured resin HC preferably has a hardness higher than the
pencil hardness B.
[0186] The following steps of forming a semitransparent reflective
film to make a light transmission layer are performed by the same
way as in the fourth embodiment. Thus, the optical information
recording medium such as shown in FIG. 26C of the fourth embodiment
can be attained.
[0187] Sixth Embodiment
[0188] Another embodiment of a manufacturing method of an optical
disk according to the present invention will be described in
conjunction with FIGS. 30 to 31C. FIG. 30 is a flowchart showing a
flow of manufacturing method of the optical disk according to the
sixth embodiment. The same or like description as presented in the
above embodiments will be omitted. The resin stamper and the first
substrate are the same as those of the above-mentioned
embodiments.
[0189] As shown in FIG. 31A the radiation cured resin LA 504 is
applied onto the asperity pits 503 of the resin stamper 501, and as
shown in FIG. 31B the radiation cured resin LB 514 is applied onto
a signal recording layer SA 116 of the first substrate 511. As in
the steps in conjunction with FIGS. 21B and 21C of the fourth
embodiment, the radiation cured resin is applied substantially
uniformly by the spinning.
[0190] Then, with the same method shown in FIG. 21C, the resin
stamper 501 is placed over the first substrate 511 such that the
radiation cured resins LA and LB face each other (see FIG. 31C).
The placing is performed in a vacuum to prevent the insertion of
bubbles. After the placing, the radiation is emitted to cure the
radiation cured resins LA and LB. Since the first substrate 511 has
the information recording layer 516, the radiation cured resin LA
cannot be easily cured by the radiation emitted from the side of
the first substrate 511. Accordingly, the radiation transmittance
of the resin stamper 501 must be sufficient to cure the radiation
cured resin. In the present embodiment, the stamper is made of
transparent polycarbonate to facilitate the resin curing. The
stamper may be made of another material if the material has
sufficient radiation transmittance.
[0191] By making the inner circumference diameters of the resin
stamper 501 and the first substrate 511 equal, the center of the
information recording layer SA of the first substrate 511 can be
aligned to the center of the asperity pits 503 of the resin stamper
503. The alignment can be easily attained by providing the spin
table with a center pin having substantially equal size to that of
the center holes 502 and 512. In order to decrease the eccentricity
more, a mechanism for aligning the centers after extending the
radiation and before curing the radiation cured resin may be
provided.
[0192] The resin stamper is then peeled off in a way as shown in
FIGS. 24A and 24B in the fourth embodiment. It is preferable to
employ as the radiation cured resin LA the radiation cured resin
which is excellent in stickability and transferability and which
has poor adhesion to the resin stamper. It is preferable to employ
as the radiation cured resin LB the radiation cured resin which has
high adhesion to the information recording layer of the first
substrate and the radiation cured resin LA. Adherence of the
radiation cured resin LA to the first substrate, or the radiation
cured resin LB to the resin stamper makes the separation difficult.
To solve the problem, the radiation cured resin LB is extended to
the outer periphery of the first substrate, and the radiation cured
resin LA is extended to the outer periphery of the stamper. By
employing two types of radiation cured resins, effects of the
transferability and the adhesion can be separated to the different
types of the radiation cured resins, respectively, resulting in
easiness in developing the radiation cured resin.
[0193] The stamper 501 may be processed to facilitate the
separation in consideration of the separation of the radiation
cured resin LA, as in the fourth embodiment.
[0194] By placing radiation cured resin HC onto the information
recording layer SA to protect it in advance as shown in FIG. 25 of
the fourth embodiment, the damage to the information recording
layer SA may be reduced. In this time, the radiation cured resin is
preferably applied to cover at least from the inner peripheral edge
to the outer peripheral edge of the information recording layer SA.
Further, it is preferable that in the inner periphery, the
radiation cured resin HC covers a part or all of the clamp region
of the first substrate, and in the outer periphery, the radiation
cured resin HC covers the outer peripheral edge of the first
substrate. In this time, the radiation cured resin HC preferably
has the hardness higher than the pencil hardness B.
[0195] The following steps including forming a semitransparent
reflective film on the first substrate to which the pits are
transferred to make a light transmission layer are the same as
those in the first embodiment. With this method, the optical
information recording medium as shown in FIG. 26C of the fourth
embodiment can be obtained.
[0196] Seventh Embodiment
[0197] Another embodiment of a manufacturing method of an optical
disk according to the present invention will be described in
conjunction with FIGS. 32 to 35B. FIG. 32 is a flowchart showing a
flow of manufacturing method of the optical disk according to this
embodiment. The same or like description as presented in the above
embodiments will be omitted. The resin stamper and the first
substrate are the same as those of the above-mentioned
embodiments.
[0198] A resin stamper 801 shown in FIG. 33A is formed of a
polycarbonate substrate made by the injection molding to have a
thickness of 1.1 mm, a diameter 120 mm, and a center hole 802 with
a 15 mm diameter. The resin stamper 801 has asperity pits 803 on
one of principal planes. A resin stamper 801 may be made of resin
material other than polycarbonate, such as acrylic resin,
polyolefin-based resin, or the like. The resin stamper 801 has the
thickness of 1.1 mm in this embodiment, but may have a smaller
thickness, for example, of 0.6 mm. By reducing the thickness, the
material cost can be further decreased.
[0199] As shown in FIG. 33B, a first thin film (hereinafter
referred to as "thin film FA") 804 is formed over the asperity pits
803 of the resin stamper 801. The thin film FA is formed by
sputtering Au for an approximate 20 nm thickness. Subsequently, as
shown in FIG. 33C, a second thin film (hereinafter referred to as
"thin film FB") 814 is formed over the thin film FA. The thin film
FB is formed by sputtering SiO.sub.2 for a approximate 20 nm
thickness.
[0200] The first substrate 811 shown in FIG. 34A is formed from a
polycarbonate substrate made by injection molding to have a
thickness of 1.1 mm, a diameter 120 mm, and a center hole 812 with
a 15 mm diameter. The first substrate 811 has on one of its
principal planes an information recording layer SA 816 comprising
asperity pits 813 and an Al reflective film 815. The first
substrate 811 may be formed of resin material other than
polycarbonate, such as acrylic resin, polyolefin-based resin, or
the like. The first substrate 811 is not the substrate on which the
recording/reproduction is performed, and thus may be formed from
non-transparent resin having low transmittance.
[0201] In the same manner as shown in FIGS. 22C to 23C of the
fourth embodiment, the resin stamper 801 is bonded to the first
substrate 811 with radiation cured resin LD 824 as shown in FIG.
34B. By making inner circumference diameters of the resin stamper
801 and the first substrate 811 equal to each other, the center of
the information recording layer 816 of the first substrate 811 can
be aligned to the center of the asperity pits 803 of the resin
stamper 801. The alignment can be easily attained by providing the
spin table with a center pin having substantially equal size to
that of the center holes 802 and 812. In order to decrease the
eccentricity more, a mechanism for aligning the centers after
extending and before curing the radiation cured resin may be
provided.
[0202] The resin stamper 801 is then peeled off at the interface of
the thin film FA 804 and the thin film FB 814 in the same manner as
shown in FIGS. 24A and 24B in the fourth embodiment. By peeling the
stamper in this manner, the asperity pits 808 made of SiO.sub.2 are
formed on the first substrate 811 as shown in FIG. 34C. Since Au
and SiO.sub.2 have low adhesion, it is easy to separate them. The
combination of the materials of the thin films can be changed in
consideration of adhesion and transferability. The thin films FA
and FB can be formed from a plurality of materials, respectively.
The thin film FB is preferably transparent since the
recording/reproducing light passes therethrough. Since bond of the
thin film FB and the resin stamper makes the separation difficult,
it is preferably that the outer circumference diameter of the thin
film FA is set to be larger than that of the thin film FB, and that
the inner circumference diameter of the thin film FA is set to be
smaller than that of the thin film FB.
[0203] By placing radiation cured resin HC over the information
recording layer SA to protect it in advance as shown in FIG. 25,
the damage to the information recording layer SA may be prevented.
In this time, the radiation cured resin HC is preferably applied to
cover at least the inner peripheral edge to the outer peripheral
edge of the information recording layer SA. Further, it is
preferable that in the inner periphery the radiation cured resin HC
covers a part or all of the clamp region of the first substrate,
and that in the outer periphery the radiation cured resin HC covers
the outer peripheral edge of the first substrate. In this time, the
radiation cured resin HC preferably has the hardness higher than
the pencil hardness B.
[0204] The semitransparent reflective film (in this embodiment, a
film formed from metal mainly composed of Ag) 818 is formed to have
a thickness of 20 nm on the first substrate 811 on which the
asperity pits are transferred as shown in FIG. 35A, to form a
second information recording layer 819. The following steps
including forming a semitransparent reflective film to make a light
transmission layer are performed as in the fourth embodiment. This
can provide the optical information recording medium as shown in
FIG. 35B.
[0205] Eighth Embodiment
[0206] It is described above that the second information recording
layer can be easily formed over the first information recording
layer of the first substrate according to any one of the
manufacturing methods of the fourth to seventh embodiments. In the
first to seventh embodiments, the information recording medium
having a double layer structure as shown in FIGS. 26C and 35B is
described. Furthermore, the information recording medium having a
triple, a four layer, as shown in FIGS. 36A and 36B, or a five or
more layer (multilayer) structure can be formed over the first
information recording layer of the first substrate by repeatedly
performing the process as described in the fourth to seventh
embodiments.
[0207] In this embodiment, the radiation cured resin HC is used for
a protection layer, the radiation cured resin LB or the radiation
cured resin LD for an intermediate layer, the radiation cured resin
LA or the thin film FB, and the information recording layer for a
recording layer. As described in the fourth to seventh embodiments,
the protection layer does not have to be provided to the optical
disk if the information recording layer will not be deteriorated by
damage or corrosion. As described in the above-mentioned
embodiments, a light transmission layer is not essential for the
optical disk, but it is preferable to be provided to the optical
disk in order to protect the information recording layer. The
optical recording/reproducing system of the present embodiment can
set N.A. to around 0.9 and the wavelength to around 400 nm. In
order to maintain the tilt margin at the same level as that of the
DVD, the light transmission layer has a thickness of approximate
0.1 mm.
[0208] When the information recording medium is formed to have more
than one basic layer comprising the protection layer, the
intermediate layer, and the recording layer, or comprising the
intermediate layer and the recording layer, as described above, a
high-density information recording medium having a plurality of
information recording layers can be attained and manufactured with
ease by using the method described in any of the fourth to seventh
embodiments. In consideration of the influence of the crosstalk,
the crosserase, and the spherical aberration during recording or
reproducing operation, the thickness of the basic layer may be
preferably set within a scope from 15 .mu.m to 45 .mu.m, more
preferably, from 20 .mu.m to 40 .mu.m.
[0209] In consideration of the influence of the deterioration or
the like of the recording/reproducing light beam, the refractive
indexes of the protection layer and the intermediate layer are set
substantially equal. In consideration of the influence of the
deterioration or the like of the recording/reproducing light beam
due to the absorption, the protection layer and the intermediate
layer are made of substantially transparent material. The
information recording layer and the recording layer thereof may be
formed as a read-only type, or a rewritable type. Similarly, one
information recording medium may have both the recording types.
[0210] According to the third to eighth embodiments, the multilayer
optical information recording medium can be easily formed.
Especially, it is possible to make a multilayer optical disk having
a thin substrate from a side of which laser beam is emitted to
record/reproduce data. Since the stamper is made of hard material
operable to pass a part of the radiation having a specific
wavelength, more specifically of resin, the stamper is light and
flexible to be easily handled.
[0211] Further, the radiation cured resin for transmitting signal
pits can be spread substantially uniformly on the substrate by
rotating the substrate with the use of substantially the same
apparatus used for the adhesion step in the manufacturing step of
the DVD. In addition, even if the stamper cannot be easily peeled
off the substrate and needs to be replaced with a new one, the
stamper can be easily replaced with the new one, since the stamper
is made of resin and can be formed in mass production at a low
manufacturing cost. According to the present invention, the
above-mentioned advantages can be attained.
[0212] In the above-mentioned embodiments, the resin stamper
separated to transfer the asperity pits can be re-used, or may be
abandoned if the efficiency of transferring the signal is
deteriorated by repeated use. The stamper can be made of low-cost
material, and thus the disk manufacturing cost will be decreased in
comparison with the case using a plurality of metal stampers.
Further, the resin stamper can be formed in mass-production by
injection molding.
[0213] In the above-mentioned embodiments, a so-called read-only
type information recording medium is described which has an
information recording layer comprising the asperity pits
corresponding to the recorded data signal and the reflective layer.
The present invention is, however, not limited to such a read-only
type information recording medium, but also can be applied to the
recordable type recording medium comprising a thin film layer on
which a data signal can be recorded after the disk has been
manufactured.
[0214] In the above-mentioned embodiments, on the stamper, a groove
may be provided instead of or as well as the asperity pits.
[0215] According to the above-mentioned manufacturing method, the
optical disk having information recording layers can be formed on
the substrate having a thickness of 0.3 mm or less which cannot be
formed by the injection molding, and the optical disk having high
density can be attained.
[0216] Although the present invention has been described in
connection with specified embodiments thereof, many other
modifications, corrections and applications are apparent to those
skilled in the art. Therefore, the present invention is not limited
by the disclosure provided herein but limited only to the scope of
the appended claims.
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