U.S. patent application number 12/265241 was filed with the patent office on 2009-03-19 for optical recording medium.
This patent application is currently assigned to Sony Corporation. Invention is credited to Norio Mitsui, Jun Nakano, Mitsuaki Oyamada, Sakuya Tamada, Kouichi Yasuda.
Application Number | 20090073845 12/265241 |
Document ID | / |
Family ID | 32984598 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090073845 |
Kind Code |
A1 |
Yasuda; Kouichi ; et
al. |
March 19, 2009 |
OPTICAL RECORDING MEDIUM
Abstract
An optical recording medium using Sn as the recording material
to improve the jitter is provided, in which on the surface of a
disc substrate 11 where a concave and convex shape dividing a track
area is formed, are formed on the surface of the concave and convex
shape a first protective layer 31 for protecting at least an
optical recording layer 31, an optical recording layer 12 using a
chemical compound at least composed of tin (Sn), nitrogen (N) and
oxygen (O), formed on the first protective layer, a second
protective layer 32 for protecting this optical recording layer,
formed on this optical recording layer, and a light-transmittable
layer 13 formed on the second protective layer; with this
structure, the optical recording layer 12 under high temperature
and high humidity can be stabilized by means of the first and
second protective layers 31 and 32.
Inventors: |
Yasuda; Kouichi; (Tokyo,
JP) ; Oyamada; Mitsuaki; (Kanagawa, JP) ;
Nakano; Jun; (Tokyo, JP) ; Mitsui; Norio;
(Kanagawa, JP) ; Tamada; Sakuya; (Tokyo,
JP) |
Correspondence
Address: |
ROBERT J. DEPKE;LEWIS T. STEADMAN
ROCKEY, DEPKE & LYONS, LLC, SUITE 5450 SEARS TOWER
CHICAGO
IL
60606-6306
US
|
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
32984598 |
Appl. No.: |
12/265241 |
Filed: |
November 5, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10547199 |
Jan 30, 2007 |
7464391 |
|
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PCT/JP2004/003116 |
Mar 10, 2004 |
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12265241 |
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Current U.S.
Class: |
369/94 ;
G9B/7 |
Current CPC
Class: |
G11B 2007/2571 20130101;
G11B 2007/24322 20130101; G11B 7/243 20130101; G11B 2007/2432
20130101; G11B 7/257 20130101; G11B 2007/24312 20130101 |
Class at
Publication: |
369/94 ;
G9B/7 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2003 |
JP |
2003-68772 |
Claims
1. An optical recording medium including a substrate at the surface
of which a concave and convex shape determining a track area is
formed, the optical recording medium comprising: a first
intermediate layer formed over the surface of said substrate; an
optical recording layer formed over the first intermediate layer,
the optical recording layer using a chemical comprised of tin (Sn),
nitrogen (N) and oxygen (O); a second intermediate layer formed
over the optical recording layer; and a light-transmittable layer
formed over the second intermediate layer.
2. The optical recording medium according to claim 1, wherein the
first intermediate layer is comprised of a tin oxide.
3. The optical recording medium according to claim 2, wherein the
second intermediate layer is comprised of a silicon oxide.
4. The optical recording medium according to claim 3, wherein the
optical recording layer is made of a chemical compound comprised of
tin (Sn), nitrogen (N) and Oxygen (O), and whose composition
satisfies Sn.sub.xN.sub.yO.sub.z (x, y, z: atomic %) where x, y, z
are selected to be 30<x<70 (atomic %), 1<y<20 (atomic
%), and 20<z<60 (atomic %).
5. The optical recording medium according to claim 3, wherein the
optical recording layer is made of a chemical compound comprised of
tin (Sn), nitrogen (N) and oxygen (O) with palladium (Pd)
contained, and whose composition satisfies
(Sn.sub.xN.sub.yO.sub.z)(.sub.1-a)Pd.sub.a (x, y, z, a: atomic %)
where x, y, z, a are selected to be 30<x<70 (atomic %),
1<y<20 (atomic %), 20<z<60 (atomic %), and 1<a<20
(atomic %).
6. The optical recording medium according to claim 4, wherein at
least one of recording and reproduction is performed on the optical
recording layer through an objective lens having a numerical
aperture of 0.85.+-.0.05 with a laser beam having a wavelength of
380 nm to 420 nm.
7. The optical recording medium according to claim 5, wherein at
least one of recording and reproduction is performed on the optical
recording layer through an objective lens having a numerical
aperture of 0.85.+-.0.05 with a laser beam having a wavelength of
380 nm to 420 nm.
8. The optical recording medium according to claim 1, wherein the
second intermediate layer is comprised of a silicon oxide.
9. The optical recording medium according to claim 1, wherein the
first and second protective layers have a thickness in the range of
10 nm to 200 nm.
10. The optical recording medium according to claim 9, wherein the
first and second protective layers have a thickness in the range of
50 nm to 60 nm.
11. The optical recording medium according to claim 1, wherein the
recording layer has a thickness in the range of 10 nm to 200
nm.
12. The optical recording medium according to claim 1, wherein the
recording layer has a thickness in the range of 30 nm to 60 nm.
13. The optical recording medium according to claim 1, wherein the
depth of grooves formed via the convex and concave shape are in the
range of 20 nm to 100 nm.
14. The optical recording medium according to claim 4, wherein the
first intermediate layer is comprised of a tin oxide.
15. The optical recording medium according to claim 14, wherein the
second intermediate layer is comprised of a silicon oxide.
16. The optical recording medium according to claim 5, wherein the
first intermediate layer is comprised of a tin oxide.
17. The optical recording medium according to claim 16, wherein the
second intermediate layer is comprised of a silicon oxide.
18. The optical recording medium according to claim 1, wherein the
optical recording layer uses a chemical comprised of tin (Sn),
nitrogen (N) and oxygen (O) and palladium (Pd).
19. A method for manufacturing an optical recording medium
including a substrate at the surface of which a concave and convex
shape determining a track area is formed, the method for
manufacturing the optical recording medium comprising: forming a
first intermediate layer formed over the surface of said substrate;
forming an optical recording layer formed over the first
intermediate layer, the optical recording layer using a chemical
comprised of tin (Sn), nitrogen (N) and oxygen (O); forming a
second intermediate layer formed over the optical recording layer;
and forming a light-transmittable layer formed over the second
intermediate layer.
20. The method of manufacturing an optical recording medium
according to claim 19, wherein the first intermediate layer is
comprised of a tin oxide.
21. The method of manufacturing an optical recording medium
according to claim 20, wherein the second intermediate layer is
comprised of a silicon oxide.
22. The method of manufacturing an optical recording medium
according to claim 21, wherein the optical recording layer is made
of a chemical compound comprised of tin (Sn), nitrogen (N) and
Oxygen (O), and whose composition satisfies Sn.sub.xN.sub.yO.sub.z
(x, y, z: atomic %) where x, y, z are selected to be 30<x<70
(atomic %), 1<y<20 (atomic %), and 20<z<60 (atomic
%).
23. The method of manufacturing an optical recording medium
according to claim 21, wherein the optical recording layer is made
of a chemical compound comprised of tin (Sn), nitrogen (N) and
oxygen (O) with palladium (Pd) contained, and whose composition
satisfies (Sn.sub.xN.sub.yO.sub.z)(.sub.1-a)Pd.sub.a (x, y, z, a:
atomic %) where x, y, z, a are selected to be 30<x<70 (atomic
%), 1<y<20 (atomic %), 20<z<60 (atomic %), and
1<a<20 (atomic %).
24. The method of manufacturing an optical recording medium
according to claim 22, wherein at least one of recording and
reproduction is performed on the optical recording layer through an
objective lens having a numerical aperture of 0.85.+-.0.05 with a
laser beam having a wavelength of 380 nm to 420 nm.
25. The method of manufacturing an optical recording medium
according to claim 23, wherein at least one of recording and
reproduction is performed on the optical recording layer through an
objective lens having a numerical aperture of 0.85.+-.0.05 with a
laser beam having a wavelength of 380 nm to 420 nm.
26. The method of manufacturing an optical recording medium
according to claim 19, wherein the second intermediate layer is
comprised of a silicon oxide.
27. The method of manufacturing an optical recording medium
according to claim 19, wherein the first and second protective
layers have a thickness in the range of 10 nm to 200 nm.
28. The method of manufacturing an optical recording medium
according to claim 27, wherein the first and second protective
layers have a thickness in the range of 50 nm to 60 nm.
29. The method of manufacturing an optical recording medium
according to claim 19, wherein the recording layer has a thickness
in the range of 10 nm to 200 nm.
30. The method of manufacturing an optical recording medium
according to claim 19, wherein the recording layer has a thickness
in the range of 30 nm to 60 nm.
31. The method of manufacturing an optical recording medium
according to claim 19, wherein the depth of grooves formed via the
convex and concave shape are in the range of 20 nm to 100 nm.
32. The method of manufacturing an optical recording medium
according to claim 22, wherein the first intermediate layer is
comprised of a tin oxide.
33. The method of manufacturing an optical recording medium
according to claim 32, wherein the second intermediate layer is
comprised of a silicon oxide.
34. The method of manufacturing an optical recording medium
according to claim 23, wherein the first intermediate layer is
comprised of a tin oxide.
35. The method of manufacturing an optical recording medium
according to claim 34, wherein the second intermediate layer is
comprised of a silicon oxide.
36. The method of manufacturing an optical recording medium
according to claim 19, wherein the optical recording layer uses a
chemical comprised of tin (Sn), nitrogen (N) and oxygen (O) and
palladium (Pd).
Description
TECHNICAL FIELD
[0001] The present invention relates to an optical recording
medium, particularly to an optical recording medium capable of high
density recording, in which jitter and deterioration of the
recording characteristic under high temperature and high humidity
are improved.
BACKGROUND ART
[0002] In recent years, an optical information recording system has
widely been studied and developed in the field of information
recording.
[0003] The optical information recording system has a number of
advantages such as can deal with various memory types of
non-contact type recording and reproduction, reproduction-only
type, write-once type, and rewritable type; and therefore, from
industrial use to consumer use, it is contemplated as a system
capable of obtaining an inexpensive large-capacity file.
[0004] A large capacity of these various optical recording media
for the optical information recording system, for example, an
optical disc, has been accomplished mainly by making a wavelength
of a laser beam, which is a light source used for the optical
information recording system, short, as well as by using an
objective lens having a high numerical aperture (N.A.) to make a
spot size on a focal plane small.
[0005] For example, CD (Compact Disc) has a capacity of 650 MB when
a wavelength of a laser beam is 780 nm and a numerical aperture
(N.A.) of an objective lens is 0.45, whereas DVD-ROM (Digital
Versatile Disc--Read Only Memory) has a capacity of 4.7 GB when a
wavelength of a laser beam is 650 nm and a N.A. of an objective
lens is 0.6.
[0006] Further, in an optical disc system of the next generation,
by using an optical disc having a thin light-transmittable layer
with a film thickness of, for example, approximately 0.1 mm formed
on the optical recording layer, applying a laser beam from the side
of the light-transmittable layer, and making a wavelength of a
laser beam 450 nm or less and making N.A. 0.78 or more, a large
capacity of 22 GB or more is made to be possible.
[0007] FIG. 4A is a schematic perspective view showing a state of
optical recording or optical reproduction with respect to the
optical disc.
[0008] An optical disc DC is a disc having a center hole CH bored
in the center and is driven to rotate in the direction, for
example, shown by an arrow mark DR in FIG. 4A.
[0009] FIG. 4B is a schematic section of the optical disc DC. FIG.
4C is an enlarged section of a relevant part of the optical disc
DC.
[0010] This optical disc has the structure in which a concave
portion 101r is formed on the main surface of a disc substrate 101
made of, for example, polycarbonate resin having a thickness of
about 1.1 mm, and an optical recording layer 102 is formed along a
concave and convex surface including the concave portion 101r.
[0011] For example, in an optical disc DC of phase-change type, the
optical recording layer 102 is made of a laminate of, for example,
a dielectric film, a phase-change film, a dielectric film, a
reflective film, and so on. Further, on the optical recording layer
102 is formed a light-transmittable layer 103 having a film
thickness of, for example, 0.1 mm.
[0012] When information is recorded in or reproduced from the
optical disc DC, light LT by a laser beam having a wavelength of
450 nm or less, for example, 380 nm to 420 nm is focused and
applied to the optical recording layer 102 from the side of the
light-transmittable layer 103 of the optical disc DC through an
objective lens OL having a numerical aperture of 0.78 or more, for
example, 0.85.
[0013] When the recorded information is reproduced, returned light
reflected at the optical recording layer 102 is received by a
light-receiving element and a signal-processing circuit generates a
predetermined signal to provide a reproduced signal.
[0014] The optical recording layer 102 of this optical disc has a
concave and convex shape resulted from the above-described concave
portion 101r formed on the surface of the disc substrate 101.
[0015] The concave portion 101r forms, for example, a spiral
continuous groove or grooves of concentric circles with a
predetermined pitch, and with this concave and convex shape, a
track area is divided.
[0016] The concave portion and convex portion of the concave and
convex shape dividing the track area are called groove and land,
respectively. When a land-groove recording method for recording
information in both of the land and groove is employed, the large
capacity can be obtained. However, only one of the land and groove
can be made into a recording area.
[0017] In addition, for example, by making the concave and convex
shape caused by the concave portion 101r formed on the disc
substrate 101 into pits each having a length corresponding to
recording data, a read-only-memory (ROM) type optical disc can be
obtained.
[0018] It has been verified that tin oxide (SnOz, z<2) which is
a metal oxide with non-stoichiometric composition can be employed
as a recording material forming the optical recording layer (See
Journal of Materials Science Letters 19, 2000. 1833-1835).
[0019] However, in this case, when information is recorded using an
objective lens having a numerical aperture of about 0.8 and a laser
beam having a short wavelength of about 380 nm-420 nm, such a
problem is posed that no recording mark in a satisfactory shape is
formed and the jitter increases.
DISCLOSURE OF INVENTION
[0020] In order to solve this problem, the applicant of the present
invention previously proposed in Patent Application No. 2003-17877
an optical recording medium capable of improving the
above-described jitter and stabilizing the recording characteristic
even under high temperature and high humidity, in the case where Sn
is used for the optical recording layer.
[0021] In this application, a chemical compound made of tin (Sn),
nitrogen (N) and oxygen (O) with non-stoichiometric composition is
used for the optical recording layer, and it is considered to
utilize the fact that optical constants are changed by oxidative
reaction caused when irradiated with light such as a laser
beam.
[0022] However, when the chemical compound made of tin (Sn),
nitrogen (N) and oxygen (O) with non-stoichiometric composition is
used for the recording material as described above, the recording
characteristic under high temperature and high humidity is not
necessarily stabilized sufficiently.
[0023] The present invention provides an optical recording medium
capable of suppressing the jitter to enable a satisfactory
recording to be performed even when light such as a laser beam of a
short wavelength is applied through an objective lens of a high
numerical aperture to record information, and further of
maintaining a stable and excellent recording characteristic under
high temperature and high humidity.
[0024] Specifically, the optical recording medium according to the
present invention has the structure in which, on the surface of a
substrate where a concave and convex shape dividing the track area
is formed thereon, a first protective layer for protecting at least
an optical recording layer, an optical recording layer using a
chemical compound made of at least tin (Sn), nitrogen (N) and
oxygen (O), formed on the first protective layer, a second
protective layer for protecting the optical recording layer, formed
on the optical recording layer, and a light-transmittable layer
formed on the second protective layer are provided.
[0025] As described above, the optical recording layer is made of a
chemical compound SnxNyOz (x, y, z: atomic %) made of at least tin
(Sn), nitrogen (N) and oxygen (O), where x, y, z are selected to
be
[0026] 30<x<70 (atomic %), 1<y<20 (atomic %),
20<z<60 (atomic %).
[0027] The first protective layer can be made of tin oxide and the
second protective layer can be made of silicon oxide.
[0028] According to the above-described structure of the present
invention, the deterioration of the recording characteristic can be
improved well even under high temperature and high humidity. It is
assumed that because the optical recording layer made of tin (Sn),
nitrogen (N) and oxygen (O) is held between the first and second
protective layers, a change in oxygen concentration of the optical
recording layer under high temperature and high humidity can be
suppressed.
BRIEF DESCRIPTION OF DRAWINGS
[0029] FIG. 1A is a schematic perspective view showing a state in
which light is applied to an optical disc according to an
embodiment of the present invention;
[0030] FIG. 1B is a schematic section taken along a line A-A' in
FIG. 1A;
[0031] FIG. 1C is an enlarged section of the relevant part;
[0032] FIGS. 2A and 2B are sections each showing a step in a
process of manufacturing the optical disc according to the
embodiment;
[0033] FIGS. 3A and 3B are process diagrams each showing a step in
the embodiment of the present invention;
[0034] FIG. 4A is a schematic perspective view showing a state in
which light is applied to a conventional optical disc;
[0035] FIG. 4B is a schematic section taken along a line A-A' in
FIG. 4A; and
[0036] FIG. 4C is an enlarged section of the relevant part.
BEST MODE FOR CARRYING OUT THE INVENTION
[0037] An embodiment of an optical recording medium (optical disc)
according to the present invention will be described below.
However, the present invention is not limited to that
embodiment.
[0038] FIG. 1A is a schematic perspective view showing a state of
optical recording or optical reproduction with respect to an
optical disc DC according to this embodiment.
[0039] The optical disc DC is a disc having a center hole CH bored
therein and is driven to rotate in a direction, for example, shown
by an arrow mark DR.
[0040] FIG. 1B is a schematic section of the optical disc DC and
FIG. 1C is an enlarged section of the relevant part in FIG. 1B.
[0041] As described above, the optical disc DC is a disc having the
center hole CH and a concave portion 11r provided on one main
surface of a disc substrate 11 made of, for example, polycarbonate
resin having a thickness of about 1.1 mm. Along the concave and
convex shape including the concave portion 11r is formed a first
protective layer 31, on which an optical recording layer 12 is
formed. On the optical recording layer 12 is formed a second
protective layer 32, on which a light-transmittable layer 13 is
formed.
[0042] The first and second protective layers 31 and 32 are
provided to protect the optical recording layer 12 disposed
therebetween; and these first and second protective layers 31, 32
and optical recording layer 12 are each selected to have a
thickness between the range of 10 nm and 200 nm, for example, 50 nm
to 60 nm or so.
[0043] The optical recording layer 12 is made of a chemical
compound composed of at least tin (Sn), nitrogen (N) and oxygen (O)
with composition SnxNyOz (x, y, z: atomic %), where x, y, z are
selected to be
[0044] 30<x<70 (atomic %), 1<y<20 (atomic %),
20<x<60 (atomic %).
[0045] Alternatively, the optical recording layer 12 is made of a
chemical composition (SnxNyOz)1-aPda (x, y, z, a: atomic %) in
which palladium (Pd) is contained in the chemical compound composed
of tin (Sn), nitrogen (N) and oxygen (O), where x, y, z, a are
selected to be
[0046] 30<x<70 (atomic %), 1<y<20 (atomic %),
20<z<60 (atomic %) and 1<a<20 (atomic %).
[0047] With the above composition, jitter will be improved.
Particularly, by adding Pd, characteristics were stabilized. It is
conceivable that adding Pd increases viscosity of the recording
film melted at the time of recording.
[0048] The optical recording layer 12 can be made to have a film
thickness between 10 nm and 200 nm, for example, 30 nm to 60 nm or
so.
[0049] It is preferable that the first protective layer 31 is made
of tin oxide (SnO.sub.2). It was recognized that if the first
protective layer 31 is made of SiO.sub.2, then the air-tightness
becomes too high to make a satisfactory recording, because
oxidative reaction at the time of recording is obstructed. In
contrast, when the first protective layer 31 is made of tin oxide
(SnO.sub.2), a change in oxygen concentration of the optical
recording layer 12 under high temperature and high humidity was
suppressed without causing degradation of the recording
characteristic, thus allowing the deterioration of the recording
characteristic to be suppressed.
[0050] Further, it is preferable that the second protective layer
32 is made of SiO.sub.2. If the second protective layer 32 is made
of SnO.sub.2 or Si.sub.3N.sub.4, when the film thickness increases,
the reflectance decreases under the influence of combination of
optical constants. In contrast, when the second protective layer 32
is made of SiO.sub.2, because it has the optical constants close to
that of the light-transmittable layer 13 thereon, even if the film
thickness increases, the reflectance remains unchanged.
[0051] The light-transmittable layer 13 on the second protective
layer 32 has a film thickness of, for example, 0.1 mm and is
formed, for example, by hardening a coated film of
ultraviolet-curing resin. Alternatively, the layer may be formed,
for example, by sticking a film of light-transmittable resin such
as a polycarbonate resin having an adhesive layer laminated thereon
to the protective layer 32 by means of the adhesive layer.
[0052] Recording or reproduction of information with respect to the
optical disc DC in this embodiment is performed by driving the
optical disc DC to rotate in a direction, for example, indicated by
an arrow mark in FIG. 1A, and focusing and applying a laser beam LT
having a wavelength of, for example, 380 nm to 420 nm to the
optical recording layer 12 of the optical disc DC from the side of
the light-transmittable layer 13 through an objective lens OL
having a numerical aperture of, for example, 0.85.+-.0.05.
[0053] At the time of recording on the optical disc, the optical
recording layer 12 is irradiated with, for example, the
above-described laser beam LT to form a recording mark at the
light-irradiated portion. It is assumed that this recording mark is
formed because oxidative reaction is caused by the irradiation with
the laser beam LT to change optical constants of the
light-irradiated portion of the optical recording layer 12.
[0054] At the time of reproduction from the optical disc, for
example, returned light modulated by the change in optical
constants at the recording mark formed by irradiating the optical
recording layer 12 is received by a light-receiving element, and a
predetermined signal is generated by a signal-processing circuit to
be taken out as a reproduced signal.
[0055] In this optical disc, the optical recording layer 12 has a
concave and convex shape caused by the concave portion 11r formed
on the surface of the disc substrate 11.
[0056] For example, the concave portion 11r formed on the disc
substrate 11 constitutes a spiral continuous groove or grooves of
concentric circles with a predetermined pitch, and the track area
is divided by this concave and convex shape.
[0057] The pitch (distance from the center of the concave portion
to the center of the adjacent concave portion) of the continuous
groove or concentric-circle grooves is made to be, for example,
0.32 .mu.m or so.
[0058] The concave portion and convex portion forming the concave
and convex shape dividing the track area are called a groove and
land, respectively. By applying a land-groove recording method in
which information is recorded in both of the land and groove, a
large capacity can be obtained. However, only one of the land and
groove can also be made to be a recording area.
[0059] The depth of the concave and convex shape is approximately
several nm to 100 nm. For example, it can be set to 20 nm for a
groove recording system and to 40 nm for the land-groove recording
system.
[0060] Hereupon, in the case where the conventional optical
recording layer without containing N is employed, it has been known
from an X-ray diffraction experiment that a certain size of
particles exist in the film. Because the particles contribute to a
noise component when used as an optical disc, it is assumed that,
when the numerical aperture of an objective lens increases and the
wavelength of a laser beam is made short to obtain a large capacity
as described above, the grain boundary affects the characteristic
to make the jitter increase.
[0061] In contrast, it was verified that, because the optical disc
according to the above embodiment of the present invention has
employed the chemical compound at least composed of tin, nitrogen
and oxygen, namely, nitrogen (N) is added thereto for the recording
material, a peak in the x-ray diffraction vanished. This shows that
the particles in the optical recording film become smaller in
size.
[0062] In this way, when the particles become smaller in size, the
particles affecting the noise component becomes smaller, and
therefore, according to this optical disc, jitter can be suppressed
even if the numerical aperture of an objective lens is made to
increase and the wavelength of a laser beam is made short.
[0063] As to the composition of the chemical compound composed of
tin (Sn), nitrogen (N) and oxygen (O) used in the optical recording
layer of this optical disc, when a composition ratio x of tin (Sn)
is 30<x<70 (atomic %), a composition ratio y of nitrogen (N)
is made to be 1<y<20 (atomic %).
[0064] This is because, with 1 atomic % or less, an effectiveness
of making particles small in size becomes smaller, and with 20
atomic % or more, a light-absorption coefficient of the optical
recording layer falls to make large optical power required when
bringing the temperature rise enough to change the optical
constants at the time of light irradiation, that is, to make the
sensitivity fall.
[0065] A composition ratio z of oxygen (O) in the above-described
chemical compound is made to be 20<z<60 (atomic %).
[0066] This is because, with 20 atomic % or less, oxidation is
insufficient at the time of light-irradiation and with 60 atomic %
or more, a light-absorption coefficient of the optical recording
layer falls to make large optical power required when bringing the
temperature rise enough to change the optical constants at the time
of light irradiation, that is, to make the sensitivity fall.
[0067] As described above, in the composition of SnxNyOz of the
chemical compound composed of tin (Sn), nitrogen (N) and oxygen (O)
used for the optical recording layer according to the present
invention, in the case where the compound containing nitrogen (N)
is employed, the composition ratio x, y, z is made to be
30<x<70 (atomic %), 1<y<20 (atomic %), 20<z<60
(atomic %).
[0068] With this composition, an effectiveness of suppressing the
jitter can further be obtained, even if the numerical aperture of
an objective lens increases and the wavelength of a laser beam is
made short.
[0069] Next, a method of manufacturing the optical disc according
to this embodiment will be described.
[0070] First, as is shown in FIG. 2A, a stamper 10 to form the
concave and convex shape on a disc substrate by transferring is
formed. In other words, on the surface of the stamper 10 is formed
a convex portion 10p which is an inverse pattern to the concave
portion 11r on the disc substrate 11 shown in FIG. 1.
[0071] The stamper 10 can be manufactured by the following
method.
[0072] First, for example, a positive type photoresist which
becomes alkali-soluble when exposed to light is applied on a
grinded smooth surface of a glass substrate by spin coating or the
like. This photoresist layer is exposed with a pattern of a shape
corresponding to the concave and convex shape to be formed on the
disc substrate, such as the spiral shape or concentric-circle
shape, and then the exposed photoresist layer is treated for
development, for example, by an alkaline developing solution. From
the thus patterned photoresist layer is obtained a master on which
a resist film having the same pattern as that of the concave and
convex shape on disc substrate is formed.
[0073] Next, on this master is deposited a metal layer of nickel or
the like having a predetermined thickness by means of
non-electrolytic plating and plating. After that, this metal layer
is exfoliated from the master. In this way, the stamper 10 of a
plated layer having an inverse concave and convex shape to the
above-described concave and convex shape on the master is formed.
Or the stamper 10 is manufactured by transferring from a master
stamper or a mother stamper.
[0074] Next, the stamper 10 is disposed, for example, in a cavity
of a stamping die for forming the disc substrate 11 by injection
molding, and the injection molding is performed using, for example,
polycarbonate (PC) resin. In this way, as is shown in FIG. 2B, the
disc substrate 11 is formed on the concave and convex surface of
the stamper 10.
[0075] Thus, there is molded the disc substrate 11 on the surface
of which the pattern of the convex portion 10p on the stamper 10 is
transferred to form the concave portion 11r, that is, to form the
inverse pattern of the convex portion.
[0076] The disc substrate 11 thus molded is exfoliated from the
stamper 10 and gas such as air or nitrogen gas is blown to the
concave and convex surface to remove dust, and after that, as is
shown in FIG. 3A, a first protective layer 31, an optical recording
layer 12 where layers of chemical compound having a predetermined
composition ratio of tin (Sn), nitrogen (N) and oxygen (O) are
deposited, and a second protective layer 32 are formed into film,
for example, by a spattering method.
[0077] Next, as is shown in FIG. 3B, a light-transmittable layer 13
is formed on the optical recording layer 12 by coating
light-transmittable resin material such as ultraviolet-setting
resin thereon to be cured, or by sticking a film of
light-transmittable resin such as polycarbonate resin thereon by
means of an adhesive layer.
[0078] In this way, the optical disc 11 having the structure shown
in FIG. 1C can be manufactured.
[0079] According to the optical disc 11 of the present invention,
when Sn is employed as the recording material, a change in the
recording characteristic under high temperature and high humidity
is avoided, and even when an objective lens of a high numerical
aperture is employed to record information by a laser beam of a
short wavelength, the jitter is suppressed to allow a satisfactory
recording to be performed.
[0080] The above-described optical disc, that is, an optical
recording medium according to the present invention will be
described by citing the specific examples.
PRACTICE EXAMPLE 1
[0081] A disc substrate was prepared, on the surface of which the
concave and convex shape dividing the track area was formed. The
concave and convex shape was made as a spiral continuous groove
with a 0.32 .mu.m pitch, and the depth of the concave and convex
shape was made to be 20 nm.
[0082] On the surface of the concave and convex shape thus formed
on the disc substrate, the first protective layer 31 was formed by
spattering SnO.sub.2 with a thickness of 10 nm.
[0083] On the first protective layer 31 was deposited a composition
SnxNyOx (x=31 atomic %, y=10 atomic %, z=59 atomic %) using a
chemical compound composed of tin (Sn), nitrogen (N) and oxygen (O)
to have the above composition ratio, with a film thickness of 50 nm
to form an optical recording layer.
[0084] Further on that layer was deposited SiO.sub.2 with a film
thickness of 30 nm to form the second protective layer, and on that
layer was formed a light-transmittable layer of 0.1 mm thickness by
sticking a film of light-transmittable resin such as polycarbonate
resin with an adhesive layer. In this way, a sample A of the
optical disc was manufactured.
[0085] With respect to this sample A, a laser beam for recording
and reproduction having an oscillation wavelength of 405 nm was
applied through an objective lens with a numerical aperture of 0.85
to record a random signal with a bit length of 0.13 .mu.m, using an
estimation device having an optical system to focus light on the
optical recording layer of the optical disc.
[0086] The jitter of a signal recorded on the optical disc at that
time was 8%.
[0087] Further, after this optical disc was preserved at 80.degree.
C. and at 85% RH in a constant-temperature and constant-humidity
bath for 500 hours, then the jitter was measured similarly to the
above, the jitter was 8%, namely, no change was recognized.
COMPARISON EXAMPLE 1
[0088] A sample B of an optical disc was manufactured by excluding
the step of forming the first protective layer 31 in the process of
making the practice example 1.
[0089] A random signal having a bit length of 0.13 .mu.m was
recorded on this sample B using the same estimation device as in
the practice example 1. The jitter at that time was 8%.
[0090] However, after the sample B was preserved at 80.degree. C.
and at 85% RH in the constant-temperature and constant-humidity
bath for 500 hours, then the jitter was measured similarly to the
above, the jitter was deteriorated to 14%.
[0091] Note that, typically, unless the jitter is 13% or less, a
correct reproduction is difficult to be done; thus, the jitter is
required to be 13% or less in an optical recording medium, for
example, an optical disc.
PRACTICE EXAMPLE 2
[0092] In the composition SnxNyOz of the optical recording layer 12
in the practice example 1, the composition ratio x, y, z was made
to be x=69 atomic %, y=10 atomic %, z=21 atomic %.
[0093] In this optical disc also, no change in jitter was
recognized under high temperature and high humidity.
PRACTICE EXAMPLE 3
[0094] Although the structure is the same as that of the practice
example 1, the composition of the optical recording layer was
changed into SnxNyOz (x=45 atomic %, y=19 atomic %, z=36 atomic %)
to manufacture a sample I of an optical disc.
[0095] In this optical disc also, no change in jitter was
recognized under high temperature and high humidity.
[0096] While the above-described practice example has the optical
recording layer 12 composed of SnxNyOz, if the optical recording
layer 12 is composed of SnxNyOz (30<x<70 (atomic %),
1<y<20 (atomic %), 20<z<60 (atomic %)) mixed with a
refractory metal Pd of 1 atomic % to 20 atomic %, then it is
possible to increase the viscosity when the optical recording layer
is melted at the time of recording by irradiation with a laser
beam, to improve a decrease in sharpness of a recording mark and a
change in position due to arising fluidity, and to enhance further
improvement in jitter and the preservation property.
[0097] In this case, the concentration of Pd added to the chemical
compound made of tin (Sn), nitrogen (N) and oxygen (O) forming the
optical recording layer is selected to be 1 atomic % to 20 atomic
%. This is because, if it is less than 1 atomic %, the
effectiveness in suppressing fluidity becomes small to make the
improvement in the above-described preservation stability
insufficient, and if it exceeds 20 atomic %, the melting point and
thermal conductivity become large, so that the recording
sensitivity decreases disadvantageously; for this reason, the
concentration of Pd is selected to be 1 atomic % to 20 atomic
%.
[0098] A practice example of an optical recording medium having the
above-described optical recording layer mixed with Pd will be cited
for description.
PRACTICE EXAMPLE 4
[0099] This practice example has the same structure as the practice
example 1 except that the optical recording layer 12 is composed of
(SnxNyOz)1-aPda (x=31 atomic %, y=10 atomic %, z=59 atomic %, a=1
atomic %) by spattering.
PRACTICE EXAMPLE 5
[0100] This practice example has the same structure as the practice
example 1 except that the optical recording layer 12 is composed of
(SnxNyOz)1-aPda (x=31 atomic %, y=10 atomic %, z=59 atomic %, a=20
atomic %).
[0101] These optical recording media in which Pd is mixed with the
chemical compound composed of tin (Sn), nitrogen (N) and oxygen (O)
made it possible to improve the jitter and enhance the tolerance to
high temperature and high humidity.
[0102] In addition, the optical recording medium according to the
present invention is not limited to the above-described embodiments
and practice examples, and as a matter of course the present
invention can take various modification and alteration in
structure, such as taking the shape of an optical card, a sheet and
a layered structure accompanied by the change or the like.
[0103] As described above, according to the optical recording
medium of the present invention, in the case where tin is used as a
recording material, when the first and second protective layers 31
and 32 are provided to improve the jitter, it is possible to
suppress a change in concentration of oxygen under high temperature
and high humidity, and so an effectiveness of avoiding the
deterioration of recording characteristic can be obtained.
[0104] Therefore, according to the structure of the present
invention, a great advantageous result of providing an optical
recording medium having an excellent recording characteristic as
well as a large capacity can be obtained.
DESCRIPTION OF REFERENCE SYMBOLS
[0105] 10 . . . STAMPER [0106] 10p . . . CONVEX PORTION [0107] 11 .
. . DISC SUBSTRATE [0108] 11r . . . CONCAVE PORTION [0109] 12 . . .
OPTICAL RECORDING LAYER [0110] 13 . . . LIGHT-TRANSMITTABLE LAYER
[0111] 31 . . . FIRST PROTECTIVE LAYER [0112] 32 . . . SECOND
PROTECTIVE LAYER [0113] CH . . . CENTER HOLE [0114] DC . . .
OPTICAL DISC [0115] LT . . . LIGHT [0116] OL . . . OBJECTIVE
LENS
* * * * *