Title of the Invention
Optical Recording Medium, Manufacturing Method for Optical
Recording Medium, and Reproducing Method for Optical Recording
Medium
Technical Field
The present invention relates to an optical recording
medium, particularly, an optical disk which is shaped like
a circular plate and is used to reproduce information.
Background Art
As a conventional optical recording medium, for example,
there is an optical disk, such as a CD-ROM and a DVD-ROM.
In such an optical disk, an uneven row of pits is formed
on a transparent substrate which is made of polycarbonate
or the like. On the substrate, a metal reflection film is
formed which is made of Al or the like. From the side of
the surface opposite to the surface on which this metal
reflection film is formed, a beam of light is applied to
the metal reflection film which is an information recording
surface. Thereby, information is reproduced.
Such an optical recording medium has been widely used
in which information is recorded and reproduced by applying
a beam of light. Thus, expectations have become greater of

heightening its recording density from now on. In recent
years, a variety of optical disks have been developed which
can reproduce large-capacity audio-visual data or digital
data. For example, research and development for a high-density
ROM optical disk is now going on, in which the density of
an optical disk which has a diameter of 12 centimeters is
expected to become higher to a storage capacity of 23.3 to
30 gigabits.
On the other hand, a DVD ROM recording medium is provided
with a security technique, specifically, the technique of
preventing someone from illicitly using and copying recorded
information or from doing such an act. As that security
technique, a BCA (or burst cutting area) area is provided
where medium identification information which is used to
identify each recording medium individually is overwritten
in a bar-code pattern. In this BCA area, when an optical
recording medium is manufactured, medium identification
information which differs for each optical recording medium
is recorded, and if necessary, a key of cryptograph or a
key of decoding is recorded.
For example, Japanese Patent Laid-Open No. 10-233019
specification discloses that a metal reflection film of an
optical disk on which a row of pits is formed as main data
is partially removed by a laser trimming, and modulated data
is recorded individually. Thus, medium identification
information is recorded which is used to protect against

illicitly using and copying, or such an act.
However, in order to heighten the above described
density, the pitch between tracks has to be narrowed, or
the shortest pit of a row of pits needs to be shortened.
Besides, with respect to a high-density optical disk, 23.3
GB or more data is recorded on a 12cm-diameter optical disk.
Therefore, it has been found out that if on a substrate used
for such an optical disk, a metal reflection film is formed
which is made of an Al alloy material having a film thickness
of 50 to 70nm so that it can be used in a DVD ROM optical
disk, that deteriorates the quality of a reproduced signal.
This is because a metal reflection film seems to be
difficult to form at the bottom of a minute pit about 0.2
µ m long. Thus, the shorter a pit becomes, the deeper and
the smaller it tends to be. Accordingly, as a metal reflection
film for the above described high-density ROM optical disk,
a metal reflection film which is used in a DVD ROM optical
disk could not be used as it is.
In addition, when a DVD ROM optical disk is manufactured,
medium identification information is recorded, using a
medium-identification-information recording apparatus which
is provided with a YAG (yttrium aluminum garnet) laser. However,
even if the medium identification information is recorded
in a bar-code pattern using this
medium-identification-information recording apparatus, on
an area where pits are not formed in a high-density ROM optical

disk or on a row of pits which is recorded at a track pitch
of 0.74 µ m which is the same as in the DVD ROM optical disk,
then the pattern could not be formed. Or, the reproduction
noise of the medium identification information became louder,
and thereby, an adequate defocus margin could not be secured.
This is because in a high-density ROM optical disk,
a metal reflection film is thinner than that of a DVD ROM
optical disk. Or, the material of a metal reflection film
in use is different, and thus, the heat capacity necessary
until the metal reflection film reaches its melting point
is largely different. Accordingly, a conventional
medium-identification-information recording apparatus
provided with a YAG could notbeusedas it is when a high-density
ROM optical disk is manufactured.
Disclosure of the Invention
It is an object of the present invention to provide
an optical recording medium in which data can be recorded
more densely than in a DVD ROM optical disk, and using a
conventional medium-identification-information recording
apparatus, medium identification information can be recorded
so that an adequate defocus margin can be secured.
An optical recording medium according to an aspect
of the present invention: which includes a main-information
area in which a metal reflection film is formed on a substrate
where a row of pits is formed as main data, and a sub-information

area in which medium identification information is recorded
which is used to identify the optical recording medium
individually by removing the metal reflection film partially
and forming a plurality of reflection-film removed areas;
and in which information is reproduced by irradiating the
metal reflection film with a beam of light, where in the
sub-information area, a row of pits or a groove is formed
on the substrate, and the track pitch of the row of pits
or the groove is 0.24 µ m or wider and 0.45 µ m or narrower.
In this optical recording medium, a row of pits or
a groove is formed in the sub-information area on the substrate ,
and the track pitch of the row of pits or the groove is set
at 0.24 µ m or wider and 0.45 µ m or narrower. Therefore, using
a beam of light for reproduction having a shorter wavelength
and an optical system having a higher numerical aperture,
data can be recorded at a higher density than in a DVD ROM
optical disk. In addition, even though the thermal conductivity
or melting point which is the intrinsic value of the metal
reflection film is different, using a conventional
medium-identification-information recording apparatus,
medium identification information can be recorded so that
an adequate defocus margin can be secured.
A manufacturing method for an optical recording medium
according to another aspect of the present invention,
including: a first step of preparing a substrate on which
a row of pits is formed as main data in a main-information

area, and a row of pits or a groove whose track pitch is
0.24 µ m or wider and 0.45 µ m or narrower is formed in a
sub-information area; a second step of forming a metal
reflection film on the substrate; a third step of forming
a resin layer on the metal reflection film; and a fourth
step of recording medium identification information which
is used to identify the optical recording medium individually
by partially removing the metal reflection film in the
sub-information area and forming a plurality of
reflection-film removed areas.
By this manufacturing method for an optical recording
medium, the row of pits or the groove is formed in the
sub-information area on the substrate, and the track pitch
of the row of pits or the groove is set at 0.24 µ m or wider
and 0.45 µ m or narrower. Therefore, using a beam of light
for reproduction having a shorter wavelength and an optical
system having a higher numerical aperture, data can be recorded
at a higher density than in a DVD ROM optical disk. In addition,
even though the thermal conductivity or melting point which
is the intrinsic value of the metal reflection film is different,
using a conventional medium-identification-information
recording apparatus, medium identification information can
be recorded so that an adequate defocus margin can be secured.
A reproducing method for an optical recording medium
according to still another aspect of the present invention,
in which: the optical recording medium includes a

main-information area in which a metal reflection film is
formed on a substrate where a row of pits is formed as main
data, and a sub-information area in which a row of pits or
a groove whose track pitch is 0.24 µ m or wider and 0.45µ m
or narrower is formed on the substrate, and medium
identification information is recorded which is used to
identify the optical recording medium individually by removing
the metal reflection film partially and forming a plurality
of reflection-film removed areas; and information is
reproduced by irradiating the metal reflection film of the
optical recording medium with a beam of light.
By this reproducing method for an optical recording
medium, information is reproduced by applying a beam of light
to the metal reflection film of the optical recording medium
which includes a sub-information area where the row of pits
or the groove is formed in the sub-information area on the
substrate and the track pitch of the row of pits or the groove
is set at 0.24 µ m or wider and 0 . 45 µ m or narrower . Therefore ,
using a beam of light for reproduction having a shorter
wavelength and an optical system having a higher numerical
aperture, a good-quality signal can be obtained by reproducing
the data which has been recorded at a higher density than
in a DVD ROM optical disk. In addition, even though the thermal
conductivity or melting point which is the intrinsic value
of the metal reflection film is different, using a conventional
medium-identification-information recording apparatus, the

medium identification information which has been recorded
at an adequate defocus margin can be steadily reproduced.
Brief Description of the Accompanying Drawings
Fig. 1 is a graphical representation, showing a
measurement result of the jitter value which corresponds
to the depth of a pit.
Fig. 2 is a graphical representation, showing a
measurement result of the jitter value which corresponds
to the film thickness of a metal reflection film which is
made of an AgPdCu alloy.
Fig. 3 is a graphical representation, showing a
measurement result of the jitter value which corresponds
to the film thickness of a metal reflection film which is
made of an Al alloy.
Fig. 4 is a sectional view of an optical disk in which
a metal reflection film which is made of an AgPdCu alloy
and has a film thickness of 100nm is formed on a substrate
where pits are formed.
Fig. 5 is a graphical representation, showing a
measurement result of the reflectance ratio which corresponds
to the film thickness of a metal reflection film which is
made of an AgPdCu alloy.
Fig. 6 is a graphical representation, showing a
measurement result of the reflectance ratio which corresponds
to the film thickness of a metal reflection film which is

made of an A1 alloy.
Fig. 7 is a top view of an optical disk, showing an
example of its main-information area and sub-information
area.
Fig. 8 is a block diagram, showing the configuration
of a medium-identification-information recording apparatus
which records medium identification information in a BCA
area.
Fig. 9 is a sectional view of an optical disk in which
a metal reflection film is formed on a substrate where pits
are formed, and in addition, a resin layer is formed on the
metal reflection film.
Fig. 10 is a graphical representation, showing a
measurement result of the defocus margin of a BCA recording
power which corresponds to the track pitch of a row of pits
which is formed in an optical disk that includes a 50nm metal
reflection film which is made of an AgPdCu alloy.
Fig. 11 is a graphical representation, showing a
measurement result of the defocus margin of a BCA recording
power which corresponds to the track pitch of a row of pits
which is formed in an optical disk that includes an Al reflection
film whose film thickness is 30nm.
Best Mode for Implementing the Invention
Hereinafter, a ROM optical disk will be described as
an example of the optical disk according to an embodiment

of the present invention. Herein, an optical recording medium
which is applied according to the present invention is not
limited especially to this example. The present invention
can also be applied to various optical recording mediums
whose information recording layer has, for example, a minute
unevenness , such as an optical magnetic disk and a phase-change
disk.
The ROM optical disk includes: a main-information area
in which a metal reflection film is formed on a substrate
where an uneven row of pits is formed as main data; and a
sub-information area in which medium identification
information is recorded which is used to identify the optical
disk individually by removing the metal reflection film
partially and forming a plurality of reflection-film removed
areas. In this optical disk, information is reproduced by
irradiating the metal reflection film with a beam of light.
Generally, in order to heighten the density of a ROM
optical disk, the pitch between tracks has to be narrowed,
and the shortest pit length (or the shortest mark length)
needs to be extremely shortened. However, if the track pitch
becomes too narrow, cross talk becomes greater in an RF-signal
characteristic. This hinders securing an adequate system
margin. If the shortest pit length becomes too short, then
the resolution of a reproduced signal lowers , thereby worsening
the jitter value of the reproduced signal.
Therefore, an examination is repeatedly made of the

most suitable track pitch, using an information reproducing
apparatus in which a wavelength λ of a light source of a beam
of light for reproduction is 405nm and a numerical aperture
NA of an objective lens is 0.85. As the result of such an
examination, the following measurement result is obtained.
This presents the fact that if a track pitch is 0.24 µ m or
wider, a cross-talk signal can be practically neglected,
compared with a main signal.

In addition, the most suitable shortest pit length
is examined, using the above described information reproducing
apparatus. As a result of the study of a resolution necessary
for obtaining a desirable reproduction signal, a measurement
result is obtained as follows. It has turned out that if
the length of the shortest pit is 0.12 µ m or longer, the
resolution of a reproduced signal can be adequately secured.


Herein, in consideration of various margins of an
optical disk or a drive, a jitter value which shows
characteristics of an optical disk needs to be 6.5% or below.
Herein, information on a 12cm-diameter optical disk
is reproduced, using the information reproducing apparatus.
In order to set the storage capacity of the optical disk
to 23.3GB or above, a relational expression (shortest pit
length) × (track pitch) ≤0.0512 µ m2 has to be satisfied. For
example, if the recording capacity is 23.3GB and the shortest
pit length is 0.12 µ m, the upper limit of the track pitch
is about 0.43 µ m. In the same way, if the recording capacity
is 23.3GB and the shortest pit length is 0.24 µ m, the upper
limit of the track pitch is about 0.21 µ m.
Next, a manufacturing method will be described of a
12cm-diameter optical disk which has a recording capacity
of 23.3GB or above. As described above, in order to create
a 12cm-diameter optical disk which has a recording capacity
of 23.3GB or above, a substrate has to be used whose track
pitch is 0.24 µ m or wider and 0.43 µ m or narrower, and its
shortest pit length is 0.12 µ m or longer and 0 . 21 Mm or shorter.
For example, in order to create a 12cm-diameter optical
disk which has a recording capacity of 25GB , first, a substrate
is prepared where a row of pits is formed which has a shortest
pit length of 0.149Mm and a track pitch of 0.32Mm. As this
substrate, for example, a substrate made of polycarbonate
can be used which is created by an injection molding machine.

pitch of 0.32 µ m. On top of it, the resin layer which had
a film thickness of 100 µ m is formed, and consequently, an
optical disk is manufactured.
Next, with respect to the optical disk which was
manufactured as described above, a study was made of the
depth of a pit which corresponds to the quality of a reproduced
signal, the material and film thickness of the metal reflection
film, and the like. Specifically, the manufactured optical
disk was set in the above described information reproducing
apparatus. Then, this information reproducing apparatus
allowed a beam of light to be incident upon the metal reflection
film through the 100 µ m-thick resin layer. Thereby, a
reproduced signal was obtained from the optical disk, and
then, it was assessed.
First, an examination was made how much the quality
of a reproduced signal depended upon the depth of a pit.
In the optical disk which was manufactured as described above,
jitter values were measured which showed the dispersion of
reproduced signals when the depth of a pit varied. Fig. 1
is a graphical representation, showing a measurement result
of the value of a jitter which corresponds to the depth of
a pit. Its horizontal axis is the depth (nm) of a pit and
the vertical axis is the value (%) of a jitter. In Fig. 1,
as the metal reflection film, the one was used which was
made of an Al alloy with a purity of 99wt% and had a film
thickness of 25nm. However, even when the one which was made

of an Ag98PdlCul(wt%) (hereinafter, referred to as the AgPdCu
alloy), the same result as the following was obtained.
Generally, in order to secure an adequate system margin,
the value of a jitter has to be 6.5% or below. In Fig. 1,
it could be seen that if the depth of a pit is set to 44nm
or above and 88nm or below, the value of a jitter would be
6.5% or lower. Herein, a refractive index n of the created
resin layer was 1.53, and a wavelength A of the beam of light
was 405nm. Therefore, taking the above described measurement
result into account, you could see that a depth D of a pit
at which a desirable reproduction signal would be obtained
is λ /(6×n) or above, and λ/(3×n) or below.
This seems to be for the following reason. Specifically,
the depth of a pit affects the amplitude of a reproduced
signal, and in an optical calculation, when the depth of
a pit is λ /(4×n), the amplitude becomes maximum. If the
refractive index n of the resin layer is 1.53 and the wavelength
A of the beam of light is 405nm, it becomes maximum when the
pit depth is about 66nm. But, even if the amplitude becomes
a little smaller, the jitter value of a reproduced signal
is almost unchanged. However, if the pit depth is below ×
/ ( 6×n) , orifthepit depth is above λ / ( 3×n) , then an adequate
signal-to-noise ratio (hereinafter, referred to as the S/N
ratio) cannot be obtained, thereby worsening the jitter value
of the reproduced signal.
Next, a study was made of a suitable film thickness

of a metal reflection film. First, a substrate was prepared
in which the depth of a pit is λ / ( 4 × n) . As the metal reflection
film, two kinds were used which were a metal reflection film
which was made of the AgPdCu alloy and a metal reflection
film which was made of an Al alloy with a purity of 99wt%.
Then, the value of a jitter was measured when their film
thickness was varied. Fig. 2 is a graphical representation,
showing a measurement result of the jitter value which
corresponds to the film thickness of the metal reflection
film which is made of the AgPdCu alloy. Fig. 3 is a graphical
representation, showing a measurement result of the jitter
value which corresponds to the film thickness of the metal
reflection film which is made of the Al alloy. In each figure,
the horizontal axis is the film thickness (nm) of the metal
reflection film, and the vertical axis is the value (%) of
a jitter.
As can be seen in Fig. 2, in the case of the metal
reflection film of the AgPdCu alloy, if its film thickness
was 25nm or above and 75nm or below, the value of a jitter
became 6.5% or lower. On the other hand, as shown in Fig.
3, in the case of the metal reflection film of the Al alloy,
if its film thickness was 15nm or above and 40nm or below,
the value of a jitter became 6 . 5% or lower . Herein, the material
of a metal reflection film is not limited especially to those
in the examples. Another material may also be used, as long
as it has a high reflectance ratio and can be uniformly formed

Next, ametal reflection film is formed on this substrate ,
using a film formation apparatus. As the film formation
apparatus, the one which can form a metal reflection film
uniformly, such as a magnetron sputtering apparatus and a
vapor depositing apparatus, can be used. For example, using
a magnetron sputtering apparatus, the time for film formation
can be varied, thereby controlling the film thickness of
themetal reflection film. Herein, thematerial, film thickness ,
or the like, of the metal reflection film will be described
later.
Next, the optical disk is placed on a spin coater,
with the metal reflection film kept up. Then, a resin to
be hardened by ultraviolet rays is dripped, and on top of
it, an 88 µ m-thick transparent sheet which is made of
polycarbonate is placed. In this state, the ultraviolet-ray
hardened resin is irradiated with ultraviolet rays while
the optical disk is being rotated by the spin coater. At
this time , the rotational speed of the spin coater is controlled,
so that the thickness of the ultraviolet-ray hardened resin
after it has hardened becomes 12 µ m. As a result, a transparent
resin layer which has a film thickness of 100 µ m is formed
on the metal reflection film. For example, an acrylic resin
can be used as this ultraviolet-ray hardened resin.
In such a way as described above, the metal reflection
film was formed on the substrate where the row of pits was
formed which had a shortest pit length of 0.149 µ m and a track

on a substrate by a film formation apparatus. In addition,
in order to enhance its corrosion resistance, a rare-earth
metallic element such as Nd, or a transition metallic element
such as Ti and Cr, may also be added a little to an Ag or
Al reflection-film material.
Next, the reflectance ratio of a metal reflection film
was examined. The thinner a metal reflection film becomes,
the smaller the quantity of reflected light will be. Then,
when the quantity of reflected light becomes smaller, in
proportion to that, a medium noise also lowers. This keeps
the S/N ratio unchanged. On the other hand, a system noise
or a laser noise does not depend upon the quantity of reflected
light. If the system noise or the laser noise is far lower
than the medium noise so that it can be neglected, then it
will not affect the quality of a reproduced signal, even
though the quantity of reflected light becomes smaller.
However, if the quantity of reflected light becomes
smaller, and the system noise or the laser noise reaches
the same level as the medium noise, then the quality of a
reproduced signal will deteriorate when the quantity of
reflected light decreases. Besides, if the metal reflection
film is made of a different material even though it has the
same film thickness, that will change its reflectance ratio,
and thereby, will change the film thickness at which the
signal quality worsens. In addition, if the metal reflection
film becomes thicker, the reproduced signal will become worse .

For example, in a magnetron sputtering apparatus , the metallic
atoms on a target which have been sputtered by Ar ions come
flying onto a substrate, so that a metal reflection film
is formed. The size of these metallic atoms also depends
upon the structure of a film formation apparatus, or the
conditions of film formation. But such a film tends to be
difficult to form at the bottom of the shortest pit.
Fig. 4 is a sectional view of an optical disk in which
a metal reflection film which is made of an AgPdCu alloy
and has a film thickness of 100nm is formed on a substrate
where pits are formed. As shown in Fig. 4, a shortest pit
11 and a long pit 12 which is longer than the shortest pit
11 are formed on a substrate 1. In this case, at the bottom
of the shortest pit 11, a metal reflection film 2 is more
difficult to form than at the bottom of the long pit 12.
Therefore, the shortest pit 11 after the metal reflection
film 2 has been formed becomes smaller, and at the same time,
deeper than it was on the substrate 1.
If you anticipate this phenomenon, and thus, make a
recording power greater so that the shortest pit 11 can be
greater, then the signal quality of the shortest pit 11 will
improve. However, when the recording power becomes greater,
the long pit 12 will be wider. This makes the cross talk
greater which comes from adjacent tracks, thus worsening
the value of a jitter. In consideration of the factors which
can worsen the signal quality of both kinds of films , substrates

were formed which were suitable for the metal reflection
films of an Al alloy and an AgPdCu alloy. As a result, the
maximum film thickness of the Al-alloy metal reflection film
at which the value of a jitter was prevented from worsening
was 40 nm, and the maximum film thickness of the AgPdCu-alloy
metal reflection film at which it was prevented from worsening
was 70 nm.
Based on this study, a reflectance ratio was measured
which corresponded to the film thickness of each of the
AgPdCu-alloy metal reflection film which is shown in Fig.
2 and the Al-alloy metal reflection film which is shown in
Fig. 3. Fig. 5 is a graphical representation, showing a
measurement result of the reflectance ratio which corresponds
to the film thickness of a metal reflection film which is
made of an AgPdCu alloy. Fig. 6 is a graphical representation,
showing a measurement result of the reflectance ratio which
corresponds to the film thickness of a metal reflection film
which is made of an Al alloy. In each figure, the horizontal
axis is the film thickness (nm) of the metal reflection film,
and the vertical axis is the reflectance ratio (%). Herein,
the refractive index n of the resin layer which was used
for measurement is 1.53, and the wavelength A of the beam of
light is 405nm.
As can be seen in Fig. 5, in the case of the AgPdCu-alloy
metal reflection film, the reflectance ratio which
corresponded to a film thickness of 25nm to 70nm at which

a desirable jitter value was obtained was 35% to 70%. In
the case of the Al-alloy metal reflection film in Fig. 6,
the reflectance ratio which corresponded to a film thickness
of 15nm to 40nm at which a desirable jitter value was obtained
was 35% to 70%. As a result, for each film, the reflectance
ratio of the metal reflection film at which the quality of
a reproduced signal could be guaranteed was 35% or higher
and 70% or lower.
Next, in order to obtain a reproduction signal which
has a desirable jitter value in such a way as described above,
an uneven row ofpits is formed as main data in a main-information
area of an optical disk. A detailed description will be given
of medium identification information which is formed in a
sub-information area of the optical disk. Fig. 7 is a top
view of an optical disk, showing an example of its
main-information area and sub-information area.
In the example shown in Fig. 7, a main-information
area 21 (which is a hatching part in the figure) is set in
the outer circular part on the optical disk. In the ring-shaped
part inside of the outer circular part, a BCA area 22 (which
is the area between two circles shown by broken lines in
the figure) is set which is a sub-information area. In the
BCA area 22, medium identification information 23 is recorded
in a bar-code pattern. A transparent resin layer of
polycarbonate or the like is formed on the metal reflection
film, and thereafter, the medium identification information

23 is recorded by irradiating, with a pulse laser (e.g.,
a YAG laser) , the metal reflection film which lies at a depth
of 0.1mm from the surface of the optical disk. At this time,
the metal reflection film seems to melt, and then, accumulate
at both boundary parts by surface tension. In this way, the
metal reflection film is partially removed, and thus, several
reflection-film removed areas are formed. This creates a
BCA area where medium identification information is recorded
which is used to identify the optical disk individually.
Next, the method of recording the medium identification
information in the BCA area of an optical disk will be described
in detail. Herein, in the following example, a method by
which a record is made in the BCA area is described, with
respect to a metal reflection film which is made of an
Ag98Pd1Cu1(wt%), or a metal reflection film which is made
of an A199Cr1(wt%), as the metal reflection film. However,
as long as the same effect can be obtained, the present invention
can also be applied to other kinds of metal reflection films,
a phase-change film, or an optical magnetic recording film.
Fig. 8 is a block diagram, showing the configuration
of a medium-identification-information recording apparatus
which records medium identification information in a BCA
area. The medium-identification-information recording
apparatus shown in Fig. 8 is a BCA-pattern recording apparatus
which is used to create a BCA area in a DVD-ROM. It includes:
a motor 101; a rotation control section 102 ; an optical pickup

103; a laser drive section 104; a waveform setting section
105; a BCA-signal generation section 106; a focus control
section 107; a pre-amplifier 108; and a system control section
109.
The rotation control section 102 controls the rotation
of the motor 101. The motor 101 rotates an optical disk 100
at a predetermined rotational speed. The BCA-signal generation
section 106 creates a BCA signal by modulating medium
identification information which is recorded in the optical
disk 100 . Based on the BCA signal, the waveform setting section
105 creates a laser modulation waveform. According to the
laser modulation waveform, the laser drive section 104 drives
a high-power laser inside of the optical pickup 103. The
optical pickup 103 converges a beam of light emitted from
the high-power laser, through its built-in optical system,
upon the optical disk 100. The pre-amplifier 108 amplifies
a reproduced signal which comes from the optical pickup 103,
and then, outputs it to the focus control section 107. Using
the amplified signal which comes from the pre-amplifier 108,
the focus control section 107 controls an objective lens
inside of the optical pickup 103, so that a beam of light
can be converged on the metal reflection film of the optical
disk 100. The system control section 109 systematically
controls the operation of the rotation control section 102,
the laser drive section 104, the waveform setting section
105, the BCA-signal generation section 106, and the focus

control section 107.
Next, a recording operation will be described of the
medium-identification-information recording apparatus which
is configured as described above . First, based on an instruction
from the system control section 109, the rotation control
section 102 drives the motor 101 to rotate the optical disk
100. The laser drive section 104 drives the high-power laser
as a light source, and then, a beam of light which is emitted
from the high-power laser is applied to the optical disk
100 from the optical pickup 103. At this time, the focus
control section 107 executes focus control so that the beam
of light which has been emitted from the high-power laser
is converged on the metal reflection film of the optical
disk 100.
Herein, the reflected light from the optical disk 100
is detected by a photo-detector inside of the optical pickup
103. Then, a reproduced signal is outputted as an electric
signal from the photo-detector. This reproduced signal is
amplified through the pre-amplifier 108 and is inputted in
the focus control section 107. In response to the amplified
signal, the focus control section 107 drives the objective
lens of the optical pickup 103 and moves it slightly in a
focus direction on the optical disk 100. Thus, it controls
the optical pickup 103 so that the beam of light can be converged
on the metal reflection film of the optical disk 100.
Next, the system control section 109 allows a position

detector (not shown) to detect the position of the optical
pickup 103 in a tracking direction. Based on the detected
positional information, it recognizes the optical pickup
103 to be located in a sub-information recording starting
position. Next, the system control section 109 instructs
the BCA-signal generation section 106 to generate a BCA signal.
Then, the BCA signal is outputted from the waveform setting
section 105, a BCA recording sequence starts, and the medium
identification information is recorded in the BCA area.
In an optical disk where a 50nm-thick metal reflection
film made of an AgPdCu alloy was formed, using the above
described medium-identification-information recording
apparatus, an attempt to record a BCA pattern (or a bar-code
pattern) was made in a part where neither a row of pits nor
a groove was formed. However, even if the output power of
a laser was heightened, a reflection-film removed area in
which the metal reflection film was removed could not be
created.
This is because the melting point of Al is 660°C while
the melting point of Ag is 960°C. It takes a larger quantity
of energy to melt the metal reflection film of an AgPdCu
alloy. In addition, the thermal conductivity of Al is 23 7W/(m.K)
while the thermal conductivity of Ag is 427°C . Therefore,
a larger quantity of heat is diffused by the conduction of
heat, even though the metal reflection film of an AgPdCu
alloy is irradiated with a beam of light. Herein, in general,

the melting point of metal is lowered by mixing a different
metal. However, in order to secure an adequate reflectance
ratio and avoid corrosion, the wt% of Ag in the metal reflection
film cannot be reduced to 97% or below.
Next, in the optical disk where the 50nm-thick metal
reflection film made of an AgPdCu alloy was formed, a row
of pits was formed at a track pitch of 0.24 µ m which was used
in the BCA area of a DVD-ROM, and a BCA pattern was recorded
in that part. At this time, the BCA pattern could not be
recorded at a predetermined width, and thus, information
could not be reproduced. However, a part of the AgPdCu-alloy
metal reflection film melts, and a small reflection-film
removed part could be formed. This is because a metal reflection
film tends to be difficult to form on an inclined surface
of an uneven substrate, and thus, the film thickness of the
metal reflection film in a pit inclined-surface part becomes
thin locally and heat conduction is hindered.
Fig. 9 is a sectional view of an optical disk in which
a metal reflection film is formed on a substrate where pits
are formed, and in addition, a resin layer is formed on the
metal reflection film. As shown in Fig. 9 , the metal reflection
film 2 is formed on the substrate 1 where the pit 12 is formed,
and in addition , a resin layer 3 is formed on the metal reflection
film 2 . In this case , the film thickness of the metal reflection
film 2 which is formed on an inclined-surface part 4 becomes
thinner than the film thickness of the metal reflection film

2 which is formed on each of a pit-bottom part 5 and a flat-plate
part 6. Thereby, the quantity of heat which is conducted
around becomes smaller. Hence, the narrower the track pitch
of a row of pits becomes and the larger the area of the
inclined-surface part 4 becomes, the more easily heat will
be conducted around. Besides, in the inclined-surface part
4, the volume per unit of the metal reflection film 2 is
smaller than any other part. Therefore, its heat capacity
necessary for reaching the melting point becomes smaller,
and thus , it reaches the melting point with a lower irradiation
power.
Based upon the above described knowledge, optical disks
were prepared in which a 50nm-thick metal reflection film
made of an AgPdCu alloy was formed on each substrate where
a row of pits was formed at various track pitches. Then,
a BCA pattern was recorded in each optical disk. Fig. 10
is a graphical representation, showing a measurement result
of the def ocus margin of a BCA recording power which corresponds
to the track pitch of a row of pits which is formed in an
optical disk that includes a 50nm metal reflection film which
is made of an AgPdCu alloy. Its horizontal axis is the track
pitch ( µ m) of a row of pits and the vertical axis is the
defocus margin (%).
As shown in Fig. 10, in the area where a row of pits
was formed at a track pitch of 0.54 µ m or below, a BCA pattern
could be recorded, and medium identification information

could be recorded. On the other hand, in the area where a
row of pits was formed at a track pitch of 0.54 µ m or above,
no defocus margin could be secured. Herein, the judgment
that a BCA pattern was recorded, was made by setting and
reproducing the created optical disks in an assessment machine .
It was made based upon whether or not the medium identification
information which was recorded in the BCA area could be
accurately reproduced. As the assessment machine, a
reproducing apparatus was used in which a beam of light for
reproduction had a wavelength λ of 405 nm and an objective
lens had a numerical aperture NA of 0.85.
Herein, if you take the mass production of optical
disks into account, you have to consider a number of factors,
such as the dispersion of the film thickness of a metal
reflection film, and a variation in a BCA recording power.
Therefore, a defocus margin of 20% or higher is required
as its adequate level. In Fig. 10, the track pitch at which
a defocus margin of 20% or higher is obtained is 0.24 µ m or
wider and 0.45 µ m or narrower. Hence, if the track pitch of
a row of pits which is recorded in the BCA area is 0.24 µ m
or wider and 0.45 µ m or narrower, an adequate defocus margin
can be secured, and medium identification information can
be recorded. The presumable reason for this is described
below.
Specifically, if the track pitch of a row of pits which
is recorded in the BCA area is beyond 0.45 µ m, the number

of pits per unit area becomes smaller, and thus, the area
of the inclined-surface parts of pits also becomes smaller.
This hinders heat conduction from being cut off adequately.
Therefore, if the heat capacity which is absorbed by a metal
reflection film varies according to the def ocus , a BCA pattern
whose noise is low cannot be recorded.
On the other hand, if the track pitch is narrower than
0.24 µ m, a pit is too close to its adjacent pits. Therefore,
the formation of a land part between pits becomes inadequate,
and the angle of the inclined-surface part of a pit becomes
narrower. Thereby, a metal reflection film becomes easier
to form on the inclined-surface parts of such pits, and thus,
the effect of cutting off heat conduction by the formation
of pits is reduced. Herein, in Fig. 10, a BCA pattern could
be recorded and reproduced up to the point where the track
pitch was 0.22 µ m, while a BCA pattern could not be recorded
when the track pitch was narrower than 0.22 µ m. Hence, in
Fig. 10, a dotted line is an estimated line which corresponds
to a track pitch of 0.22 µ m or below.
In addition. Fig. 10 shows that in an optical disk
where a 50nm-thick metal reflection film made of an AgPdCu
alloy was formed, the defocus margin is dependent upon the
track pitch. However, in an optical disk where a desirable
jitter value was obtained, a metal reflection film which
was made of Ag or an Ag alloy might also have a film thickness
of 25nm or above and 70nm or below. In that case, if the

track pitch of a row of pits which was recorded in a BCA
area was 0.24 µ m or wider and 0.45 µ m or narrower, a defocus
margin could be obtained at the same level as described above.
Similarly, instead of a row of pits , the same experiment
as described above was also conducted in an optical disk
where a groove was formed. Even in the case of a groove,
a metal reflection film tended to be difficult to form at
the inclined-surface part of the groove, as was the case
with a row of pits. Thus, if the track pitch of a groove
which was recorded in a BCA area was 0.24 µ m or wider and
0.45 µ m or narrower, a defocus margin could be obtained at
the same level as described above.
Therefore, in the case of an optical disk where a
desirable jitter value was obtained, a metal reflection film
which was made of Ag or an Ag alloy had a film thickness
of 25nm or above and 70nm or below, if the track pitch of
a row of pits or a groove which was recorded in a BCA part
was 0.24 µ m or wider and 0.45 µ m or narrower, then a defocus
margin could be adequately secured.
Next, an optical disk will be described whose metal
reflection film was created by using a metal reflection film
which was made of an A199Crl(wt%) (hereinafter, referred
to as the Al reflection film). First, an optical disk was
prepared where the Al reflection film having a film thickness
of 30nm was formed. Using the above described
medium-identification-information recording apparatus, an

attempt to record a BCA pattern was made in a part where
neither a row of pits nor a groove was formed. In this case,
a part could be formed in which the Al reflection film was
removed, and in addition, the medium identification
information which was recorded as the BCA pattern could also
be reproduced. However, the Al reflection film was thinner
than the one (i.e., 50 to 70nm) which was used in a DVD-ROM,
and thus, an adequate defocus margin could not be obtained.
In addition, in the optical disk where the Al reflection
film with a film thickness of 30nm was formed, if a BCA pattern
was recorded in the area where a row of pits was formed at
the 0.74 µ m track pitch which was used in the BCA area of
the DVD-ROM, then the same result as described above was
obtained.
Therefore, an optical disk was prepared where the Al
reflection film with a film-thickness of 30nm was formed
on a substrate where a row of pits was formed at various
track pitches. Then, a BCA pattern was recorded. Fig. 11
is a graphical representation, showing a measurement result
of the defocus margin of a BCA recording power which corresponds
to the track pitch of a row of pits which is formed in an
optical disk that includes an Al reflection film which has
a film thickness of 30nm. Its horizontal axis is the track
pitch (µ m) of a row of pits, and the vertical axis is the
defocus margin (%).
Even in the case of the Al reflection film, in the

same way as described above, a defocus margin of 20% or higher
is required at the time of BCA recording. In Fig. 11, the
track pitch at which a defocus margin of 20% or higher is
obtained is 0.24 µ m or wider and 0.45 µ m or narrower. Hence,
even in the optical disk where the Al reflection film with
a thinner film thickness than that of a DVD-ROM is formed,
if the track pitch of pits which is recorded in the BCA area
is 0 . 24 µ m or wider and 0.45 µ m or narrower, an adequate defocus
margin can be secured, and medium identification information
can be recorded. The presumable reason for this is described
below.
Specifically, if the track pitch of a row of pits which
is recorded in the BCA area is beyond 0 . 45 µ m, the heat capacity
necessary for reaching the melting point becomes extremely
small, because the Al reflection film is thin. Thereby, the
edge part of a BCA pattern is not formed desirably, thus
making louder the noise of a BCA reproduction signal.
On the other hand, if a row of pits is formed at a
track pitch of 0.45 µ m or narrower, the narrower the track
pitch becomes, the more likely a pit is formed at the edge
of a BCA pattern. Thus, the melted Al reflection film is
kept from flowing at the part where a pit is formed. Hence,
in the area where pits are formed at a narrower track pitch,
the noise of a BCA pattern becomes lower. As a result, if
a row of pits is formed at a track pitch of 0.45 µ m or narrower,
a BCA pattern which realizes an adequate defocus margin can

be recorded.
However, if the track pitch becomes narrower than 0.24
µ m, the angle of the inclined surface of a pit which is formed
becomes narrower. This weakens the force which prevents the
Al reflection film from flowing, and thus, an adequate defocus
margin cannot be obtained.
Therefore, if a row of pit is formed on a substrate
at a track pitch of 0.24 µ m or wider and 0.45 µ m or narrower,
the control of heat is easily conducted even in an Al reflection
film which has a thin film thickness. Consequently, the Al
reflection film could be removed almost completely, and thus,
a desirable BCA pattern could be recorded.
Herein, Fig. 11 shows that in an optical disk where
a 30nm-thick metal reflection film made of an A199Crl(wt%)
was formed, the defocus margin is dependent upon the track
pitch. However, in an optical disk where a desirable jitter
value was obtained, a metal reflection film which was made
of Al or an Al alloy might also have a film thickness of
15nm or above and 40nm or below. In that case, if the track
pitch of a row of pits which was recorded in a BCA area was
0.24 µ m or wider and 0.45 µ m or narrower, a defocus margin
could be obtained at the same level as described above.
Similarly, instead of a row of pits, the same experiment
as described above was also conducted in an optical disk
where a groove was formed. Even in the case of a groove,
the same effect could be produced. Thus, if the track pitch

of a groove which was recorded in a BCA area was 0.24 µ m or
wider and 0 . 4 5 µ m or narrower, a defocus margin could be obtained
at the same level.
Next, a multi-layer optical disk will be described
which is a multi-layer optical recording medium which is
formed by laminating a plurality of metal reflection films
as information recording layers. For example, on a first
polycarbonate substrate having a thickness of 1.1mm where
a row of pits is formed, a first metal reflection film which
is made of Al and has a film thickness of 45nm is formed,
using the above described magnetron sputtering apparatus.
Onto it, a second polycarbonate substrate having a thickness
of 15 µ m where pits are formed is glued, so that its side
where those pits are not formed comes into contact. As the
adhesive, for example, a resin to be hardened by light or
the like is used which is strong in adhesive bonding. Then,
on the second polycarbonate substrate which has been glued
in such a way as described above, a metal reflection film
is formed which is made of AgPdCu and has a film thickness
of 28nm. On top of it, a transparent resin layer is glued
which has a thickness of 70 µ m. As the adhesive, for example,
a pressure-sensitive adhesive sheet or the like is used.
Even in the double-layer optical disk which was created
in such a way as described above, if the track pitch of a
row of pits which was recorded in a BCA area is 0.24 µ m or
wider and 0.45 µ m or narrower, a focus was adjusted at the

time of a BCA recording, and thereby, a BCA pattern could
be recorded in both layers. Hence, a defocus margin could
be obtained at the same level as described above.
Herein, the method of creating a multi-layer optical
disk is not limited especially to the above described example.
Before a transparent resin layer is glued, a plurality of
substrates may also be formed, so that a multi-layer optical
disk can be obtained. In this case, even if an optical disk
is layered, a focus is adjusted at the time of a BCA recording,
and thereby, a BCA pattern can be recorded in a desired layer.
In addition, when a transparent resin layer and a polycarbonate
substrate are glued, a light-hardened resin and a
pressure-sensitive adhesive sheet are used. But instead of
them, an adhesive and transparent medium, such as a dry
photo-polymer, may also be used. Or, without gluing a
transparent resin layer, a transparent resin layer may also
be formed by using only a pressure-sensitive adhesive sheet,
or only a light-hardened resin.
As described above, in this multi-layer optical disk,
several layers were glued, thereby heightening its recording
density. In addition, the track pitch of a row of pits or
a groove which was formed in the BCA area was set to 0.24
µ m or wider and 0.45 µ m or narrower. Thereby, when a BCA
pattern was recorded, the focus of a laser beam of light
was adjusted to the metal reflection films in which the row
of pits or the groove was formed, so that a suitable laser

power could be applied. Consequently, a BCA pattern could
be recorded which had a low noise and a desired width.
Herein, in a ROM optical disk, the shorter its recording
time becomes, the lower its costs will be. Therefore, in
each of the above described examples, it is desirable that
a row of pits or a groove in the BCA area and a row of pits
in the main-information area be formed simultaneously. In
addition, if the track pitch of a row of pits or a groove
in the BCA area is largely different from the track pitch
of a row of pits in the main-information area, when a master
disk is manufactured, the rotational speed of the disk has
to be largely changed discontinuously. Or, the
main-information area is adjacent to the BCA area, and thus,
the rotational speed of the disk needs to be controlled so
that it becomes a desired rotational speed as fast as possible.
In order to make its linear velocity constant, preferably,
the track pitch of a row of pits in the main-information
area should be equal to the track pitch of a row of pits
or a groove in the BCA area.
Industrial Applicability
As described hereinbefore, according to the present
invention, using a beam of light for reproduction having
a shorter wavelength and an optical system having a higher
numerical aperture, data can be recorded at a higher density

than in a DVD ROM optical disk. In addition, even though
the thermal conductivity or melting point which is the intrinsic
value of a metal reflection film is different, using a
conventional medium-identification-information recording
apparatus, medium identification information can be recorded
so that an adequate defocus margin can be secured. Hence,
the present invention can be suitably applied to an optical
recording medium, for example, an optical disk which has
a circular-plate shape and is used to generate information,
or the like.

We Claim :
1. An optical recording medium comprising a substrate and a metal reflection film formed
on the substrate, and in which information is to be reproduced by irradiating the metal reflection film
with a beam of light having a wavelength of about 405 nm, the optical recording medium comprising :
a main-information area where a row of pits is formed as main data;
a sub-information area in which medium identification information is to be recorded by
trimming the metal reflection film partially and forming a plurality of reflection-film trimmed areas,
wherein the medium identification information is to be used to identify the optical recording medium
individually; and
a row of pits or a guide groove formed on the substrate in the sub-information area, with a track
pitch of the row of pits or the guide groove being at least 0.24µm wide and at most 0.45µm wide.
2. The optical recording medium as claimed in claim 1, wherein
in the event of a wavelength of a beam of light of a light source being λ and a refractive index
of a resin layer which is formed on the metal reflection film being n, a depth D of the row of pits or the
guide groove formed on the substrate in the sub-information area satisfies a relational expression of λ/
(6xn)≤D≤λ/(3xn).
3. The optical recording medium as claimed in claim 1, wherein
a depth of the row pits formed on the substrate in the main-information area is equal to a depth
of the row of pits or the guide groove formed on the substrate in the sub-information area.
4. An information reproducing method for reproducing the optical recording medium as
claimed in claim 1, wherein
the metal reflection film is irradiated with a beam of light whose wavelength is 405nm so as to
reproduce information in the main-information area where the row of pits is formed, and the sub-
information area in which is recorded the medium identification information.