MULTILAYER INFORMATION RECORDING MEDIUM MANUFACTURING
METHOD, MULTILAYER INFORMATION RECORDING MEDIUM
MANUFACTURING APPARATUS, AND MULTILAYER INFORMATION
RECORDING MEDIUM
TECHNICAL FIELD
[0001] The invention relates to a multilayer information recording medium including at least
three information recording layers, plural intermediate layers formed between the information
recording layers, and a cover layer including a light incident surface; a multilayer information
recording medium manufacturing method for manufacturing the multilayer information
recording medium; and a multilayer information recording medium manufacturing apparatus for
manufacturing the multilayer information recording medium.
BACKGROUND ART
[0002] In recent years, as the information amount required for devices such as information
devices and video-audio devices has been increased, there has been increased a demand for
information recording media such as an optical disc easily accessible to data, capable of storing a
large amount of data, and advantageously used in miniaturizing the device. High density of
recording information is realized in such an optical disc. For instance, as means for realizing a
high-density optical disc, there have been proposed a single-layer optical recording medium
having a recording capacity of about 25 GB, and a two-layer optical recording medium having a
recording capacity of about 50 GB. In these optical recording media, information is recorded or
reproduced by a reproduction head using laser light having a wavelength of about 400 nm, and a
collecting lens for converging the laser light and having a numerical aperture (hereinafter, also
called as "NA") of 0.85. Further, there has also been proposed a multilayer information
recording medium having three or more information recording layers.
[0003] FIG. 19 is a cross-sectional view of a conventional multilayer information recording
medium. The multilayer information recording medium shown in FIG. 19 is constituted of a
signal substrate 201 having a transferred concave-convex information surface with pits or guide
grooves on one surface thereof, a first film layer 202 disposed on the concave-convex
information surface of the signal substrate 201, an intermediate layer 203 having a transferred
concave-convex information surface with pits or guide grooves on a surface thereof opposite to
the surface adhered to the first film layer 202, a second film layer 204 disposed on the concave-
convex information surface of the intermediate layer 203, a transparent substrate 206 disposed

opposite to the intermediate layer 203, and a transparent layer 205 adapted to adhere the second
film layer 204 and the transparent substrate 206 to each other.
[0004] Pits or guide grooves are transferred and formed on one surface of the signal substrate
201 by e.g. injection compression molding using a stamper. An information recording layer is
formed by forming a film layer on an information surface, as described above. The thickness of
the signal substrate 201 is about 1.1 mm. The first film layer 202 and the second film layer 204
include a recording film and a reflection film. The recording film and the reflection film are
formed on the surfaces of the signal substrate 201 and the intermediate layer 203 having the pits
or the guide grooves by e.g. sputtering or vapor deposition.
[0005] The intermediate layer 203 is formed by a spin coating method using a photo-curable
resin. Specifically, a transfer substrate having pits or guide grooves on one surface thereof like
the signal substrate 201 is adhered, with an information surface thereof opposed to the signal
substrate 201, by way of a photo-curable resin. After the photo-curable resin is photo-cured,
the transfer substrate is peeled off from a boundary with the photo-cured resin layer, whereby the
intermediate layer 203 is formed.
[0006] The transparent substrate 206 is made of a transparent material having transparency
with respect to recording light or reproducing light, and has a thickness of about 0.1 mm. The
transparent layer 205 is provided to adhere the two substrates 206 and 207 to each other, and is
made of an adhesive agent such as a photo-curable resin or a pressure sensitive adhesive agent.
The transparent substrate 206 and the transparent layer 205 as a whole may also be called as a
cover layer. The cover layer may be formed' by curing the transparent layer 205, without
adhering the transparent substrate 206. Recording or reproducing information with respect to
the multilayer information recording medium having the above construction is performed by
irradiating the multilayer information recording medium with recording layer light or
reproducing laser light from the side of the transparent substrate 206.
[0007] In the multilayer information recording medium having the above construction, it is
often the case that the intermediate layers and the cover layer are formed by a spin coating
method using e.g. a UV curable resin (see e.g. patent literature 1).
[0008] However, in the case where transparent intermediate layers for use in separating
adjacent information surfaces from each other, and a cover layer are formed by a spin coating
method, small film thickness variations in circumferential direction, and large film thickness
variations in radial direction may occur. In particular, there is a problem that film thickness
variations are likely to increase resulting from accumulation of film thickness variations in
laminating plural information recording layers and plural intermediate layers. Further, in the
case where a UV curable resin is coated by a spin coating method, the resin spreads to an outer

perimeter of a substrate to be coated. As a result, when the spin rotation is stopped, and the
resin is cured by light irradiation, the resin may be swollen on the outer perimeter of the
substrate to be coated by surface tension, with the result that the film thickness may be increased.
[0009] Because of the film thickness variations, when a signal is recorded or reproduced with
respect to the multilayer information recording medium by using a laser, spherical aberration
may be generated, which may affect variations of convergence of a beam spot, focus control of
collecting a beam spot on an information surface, and tracking control of controlling a beam spot
to follow a signal train. Further, in the spin coating method, since control on the conditions for
realizing coat thickness uniformity is complicated, and spin coating is performed layer by layer,
it is difficult to shorten a tact time.
[0010] On the other hand, in the case where the number of information recording layers to be
laminated is increased to increase the recording capacity, and plural resin layers are laminated,
high thickness precision is required. This is because of the following reason. Specifically, it
is necessary to know the positions of the respective layers in the multilayer information
recording medium by the main body of a reproducing device in advance in order to reproduce
signals from the multilayer information recording medium by the reproducing device. The
positional displacement between the respective layers results from a thickness distribution of a
resin layer. Further, as the number of resin layers to be laminated is increased, high-precision
position information is required. In view of the above, it is necessary to increase the thickness
precision of the respective resin layers in the multilayer information recording medium.
[0011] Further, if there is a thickness variation inherent to a process of forming a resin layer,
the thickness variation is accumulated, each time a resin layer is formed. As a result, the
thickness variation from a surface of the multilayer information recording medium to a farthest
information recording layer thereof is increased, which may make it difficult to perform focus
control, and may deteriorate the signal quality.
[0012] FIG. 20 is a diagram showing a signal substrate for a conventional optical disc. FIG.
21 is a cross-sectional view of the signal substrate for the optical disc shown taken along the line
21-21 in FIG. 20. FIG. 22 is a diagram for describing a thickness distribution of a resin layer.
[0013] In the case where a resin layer is formed on a signal substrate for an optical disc by
screen printing, a thickness distribution may vary depending on the shape of the substrate. For
instance, as shown in FIG. 20, a signal substrate 300 for an optical disc is formed with a convex
rib 301 on a central part thereof. The rib 301 is provided to prevent the user's difficulty in
picking up an optical disc which may be contacted with the optical disc surface with a table or a
floor, in the case where the optical disc is placed on a flat surface such as a table or a floor.
Forming a protrusion on an inner periphery of an optical disc makes it easy for the user to pick

up the optical disc, because there is formed a clearance between the table surface and the optical
disc surface.
[0014] The rib 301 exhibits the above advantage by protrusion from the optical disc surface.
In view of this, the rib 301 protrudes with a larger amount than the thickness of a resin layer to
be formed in a substrate. The rib 301, however, may seriously affect in forming a resin layer by
screen printing.
[0015] The rib 301 shown in FIG. 21 has a height of 0.2 mm from an information surface 302
at a position radially away from the center of the signal substrate 300 for an optical disc by 18
mm to 20 mm. A resin layer of 0.1 mm in thickness is formed on the information surface 302
of the substrate 300. Accordingly, the manufactured optical disc has a protrusion of 0.1 mm in
height.
[0016] As shown in FIG. 22, in the case where the signal substrate 300 for an optical disc
having the rib 301 at the inner periphery thereof is subjected to screen printing, the thickness of a
resin layer is increased by a region where a squeegee 401 is contacted with the rib 301. This
phenomenon is likely to occur particularly on an inner periphery of the disc near the rib 301.
[0017] Accordingly, as shown in FIG. 22, the thickness of a resin layer is increased on an
elliptical area 403 in the inner periphery of the signal substrate 300 for an optical disc, as
compared with the other area. In FIG. 22, the squeegee 401 slides in the direction shown by the
arrow 402.
[0018] The thickness distribution of a resin layer varies because the squeegee 401 is made of a
soft material such as rubber. FIG. 23 is a diagram showing a squeegee and a signal substrate
for an optical disc when the squeegee passes a central part of the signal substrate for an optical
disc. FIG. 24 is a cross-sectional view of the squeegee and the signal substrate for an optical
disc taken along the line 24-24 in FIG. 23. In FIG. 23, the squeegee 401 slides in the direction
shown by the arrow 402.
[0019] As shown in FIG. 24, when the squeegee 401 is contacted with the rib 301, the
squeegee 401 is pushed upward by the rib 301. As a result, there is formed a clearance 404
between the squeegee 401 and the signal substrate 300 for an optical disc, at a periphery of the
rib 301. Since the clearance between the squeegee 401 and the signal substrate 300 for an
optical disc at the periphery of the rib 301 is increased, as compared with the other part, the
thickness of a resin layer to be formed is increased at the periphery of the rib 301. This
phenomenon is serious on the area 403 near the rib 301, whereas the thickness of the resin layer
becomes substantially uniform on an area away from the rib 301. Further, the area 403 having
a larger resin layer thickness is formed only in a region where the squeegee 401 is contacted with
the rib 301.

[0020] As described above, a resin layer formed by screen printing has thickness variation
along the moving direction of the squeegee that the thickness is small on a disc end, and the
thickness is large on a disc inner periphery. As a result, particularly, in the case where plural
resin layers of a multilayer information recording medium having plural information recording
layers are formed by screen printing, the problem that the thickness variation is increased
becomes serious. Specifically, in the case where the areas each having a largest resin layer
thickness are overlapped on the disc inner periphery, the thickness variations are accumulated as
a whole. If a cover layer is formed on the resin layers in this condition, thickness variation
from the disc surface to the farthest information recording layer is increased, which may
seriously affect the signal quality in recording or reproducing information with respect to the
multilayer information recording medium.
CITATION LIST
PATENT LITERATURE
[0021] Patent Literature 1: JP 2005-259331A
SUMMARY OF INVENTION
[0022] In view of the above, an object of the invention is to provide a multilayer information
recording medium manufacturing method, a multilayer information recording medium
manufacturing apparatus, and a multilayer information recording medium that enable to make
the distance from a light incident surface of the multilayer information recording medium to a
farthest information recording layer thereof uniform within a plane of the medium.
[0023] A multilayer information recording medium manufacturing method according to an
aspect of the invention is a multilayer information recording medium manufacturing method for
manufacturing a multilayer information recording medium having at least three information
recording layers. The method includes a first information recording layer forming step of
forming a first information recording layer on a substrate; a first intermediate layer forming step
of forming a first intermediate layer on the first information recording layer by screen printing; a
second information recording layer forming step of forming a second information recording
layer on the first intermediate layer; a second intermediate layer forming step of forming a
second intermediate layer on the second information recording layer by screen printing in such a
manner that thickness variation of the multilayer information recording medium after the first
intermediate layer has been formed is suppressed; a third information recording layer forming
step of forming a third information recording layer on the second intermediate layer; and a cover
layer forming step of forming a cover layer by a spin coating method in such a manner that a

thickness of an inner periphery of the multilayer information recording medium after the third
information recording layer has been formed becomes smaller than a thickness of an outer
periphery of the multilayer information recording medium.
[0024] With the arrangement described above, the first information recording layer is formed
on the substrate, and the first intermediate layer is formed on the first information recording
layer by screen printing. Then, the second information recording layer is formed on the first
intermediate layer, and the second intermediate layer is formed on the second information
recording layer by screen printing in such a manner that thickness variation of the multilayer
information recording medium after the first intermediate layer has been formed is suppressed.
Then, after the third information recording layer has been formed on the second intermediate
layer, the cover layer is formed by a spin coating method in such a manner that the thickness of
the inner periphery of the multilayer information recording medium becomes smaller than the
thickness of the outer periphery of the multilayer information recording medium.
[0025] According to the invention, thickness variation in circumferential direction is reduced
in forming the respective intermediate layers by screen printing, and thickness variation in radial
direction is reduced in forming the cover layer by a spin coating method to thereby make the
distance from a light incident surface of the multilayer information recording medium to a
farthest information recording layer thereof uniform within a plane of the medium.
[0026] These and other objects, features and advantages of the present invention will become
more apparent upon reading the following detailed description along with the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0027] FIG. 1 is a diagram for describing a resin layer forming process in an embodiment of
the invention.
FIG. 2 is a diagram for describing a signal transferring process in the embodiment.
FIG. 3 is a diagram for describing a spin coating process in the embodiment.
FIG. 4 is a cross-sectional view of a multilayer information recording medium having
four information recording layers in the embodiment.
FIG. 5 is a diagram showing an arrangement of a recording film of the multilayer
information recording medium in the embodiment.
FIG. 6 is a diagram showing a schematic arrangement of an optical disc device in the
embodiment.
FIG. 7A is a diagram showing an arrangement of a multilayer information recording
medium where thickness correction has not been performed in a resin layer forming process, and

FIG. 7B is a diagram showing an arrangement of a multilayer information recording medium
where thickness correction has been performed in a resin layer forming process.
FIG. 8 is a block diagram showing an arrangement of a multilayer information
recording medium manufacturing apparatus in Example 1.
FIG. 9 is a diagram showing an example of an operation flow to be performed by a
multilayer information recording medium manufacturing processing in Example 1.
FIG. 10 is a diagram showing an example of a resin layer forming process in Example
1.
FIG. 11A is a cross-sectional view of a screen printing machine before a resin layer is
formed, and FIG. 11B is a cross-sectional view of the screen printing machine after a resin layer
has been formed.
FIG. 12A is a top plan view of the screen printing machine before a resin layer is
formed, and FIG. 12B is a top plan view of the screen printing machine after a resin layer has
been formed.
FIG. 13A is a cross-sectional view of the screen printing machine before a resin layer is
formed, and FIG. 13B is a cross-sectional view of the screen printing machine after a resin layer
has been formed.
FIG. 14A is a top plan view of the screen printing machine before a resin layer is
formed, FIG. 14B is a top plan view of the screen printing machine having a resin layer formed .
thereon, and FIG. 14C is a diagram showing a signal substrate after a resin layer has been formed.
FIG. 15 is a diagram for describing a resin layer thickness variation measuring method
and a thickness variation correcting method in Example 2.
FIG. 16 is a diagram for describing a resin layer thickness variation measuring method
and a thickness variation correcting method in a modification of Example 2.
FIG. 17 is a block diagram showing an arrangement of a multilayer information
recording medium manufacturing apparatus in Example 3.
FIG. 18 is a diagram showing a pattern of a screen, and a signal substrate having a resin
layer formed thereon by using the screen.
FIG. 19 is a cross-sectional view of a conventional multilayer information recording
medium.
FIG. 20 is a diagram showing a signal substrate for a conventional optical disc.
FIG. 21 is a cross-sectional view of the optical disc signal substrate taken along the line
21-21 in FIG. 20.
FIG. 22 is a diagram for describing a thickness distribution of a resin layer.
FIG. 23 is a diagram of a squeegee and an optical disc signal substrate, when the

squeegee passes a central part of the optical disc signal substrate.
FIG. 24 is a cross-sectional view of the squeegee and the optical disc signal substrate
taken along the line 24-24 in FIG. 23.
DESCRIPTION OF EMBODIMENTS
[0028] In the following, an embodiment of the invention is described referring to the
accompanying drawings. The following embodiment is merely an example embodying the
invention, and do not limit the technical scope of the invention.
[0029] In this embodiment, there is described a construction example of a disc-shaped
multilayer information recording medium. The multilayer information recording medium to be
manufactured is not limited to a disc-shaped medium. The invention is also directed to a
multilayer information recording medium manufacturing method and a multilayer information
recording medium manufacturing apparatus capable of forming intermediate layers (hereinafter,
also called as "resin layers") at a high speed, and making the resin layer thickness uniform.
[0030] Since the processing of manufacturing a multilayer information recording medium, and
the processing of recording information in the multilayer information recording medium are
constituted of plural processes, these processes are described one by one using the drawings.
[0031] Firstly, a process of coating a resin is described referring to FIG. 1. FIG. 1 is a
diagram for describing a resin layer forming process in this embodiment.
[0032] Examples of the resin layer forming method include a method of attaching an adhesive
sheet, a spin coating method of spreading a resin by a centrifugal force, a method of extruding a
resin through a nozzle, and an inkjet method. In this embodiment, a resin layer is formed by a
screen printing method having a feature that the resin forming speed is fast. The screen printing
method is an example of the resin layer forming method, and the invention is not limited to the
above.
[0033] Firstly, a signal substrate 101 having a first film layer 102 on a surface thereof is fixed
on a turntable 103 by means such as vacuum suction means (see the first step in FIG. 1.)
[0034] Then, a screen frame 106 is fixedly supported above the signal substrate 101, and a UV
curable resin 105 is supplied to a portion of a screen 104 devoid of holes. Then, the UV curable
resin 105 is filled in the holes formed in the screen 104 by sliding a scraper 107 in the direction
shown by the arrow Yl (see the second step in FIG. 1).
[0035] Then, the UV curable resin 105 is extruded onto the signal substrate 101 through the
openings of the hole-plate (screen) 104 by sliding a squeegee 109 fixed to a squeegee fixing jig
108 in the direction shown by the arrow Y2, while applying a pressure to an upper portion of the
screen 104 (see the third step in FIG. 1)

[0036] Thus, by screen printing, the signal substrate 101 coated with the UV curable resin 105
is obtained (see the fourth step in FIG. 1). Further, by repeating the first step through the fourth
step in FIG. 1 while replacing the signal substrate 101 with a new one, a plurality of signal
substrates 101 each having a resin layer formed on a surface thereof are manufactured. The
sum of a time required for setting the signal substrate 101, a time required for the scraper 107 to
slide over the screen 104, and a time required for the squeegee fixing jig 108 to slide over the
screen 104 corresponds to a tact time required for a resin layer forming process by screen
printing. Thus, it is relatively easy to shorten the tact time.
[0037] A material having a large elasticity such as rubber is selected as a material for the
squeegee 109. Enhancing the elasticity of the squeegee 109 enables to coat the UV curable
resin 105 on the first film layer 102 irrespective of whether there is a thickness variation, even if
the signal substrate 101 has thickness variation. Further, enhancing the elasticity of the
squeegee 109 allows the screen 104 to absorb a physical load to be applied to the first film layer
102 at the time of printing.
[0038] Next, a process to follow the screen printing is described referring to FIG. 2. FIG. 2 is
a diagram for describing a signal transferring process in this embodiment.
[0039] Firstly, the signal substrate 101 coated with the UV curable resin 105 is placed on a
table 151 (see the first step in FIG. 2).
[0040] Then, a transfer substrate 152 is pressed against the signal substrate 101 from above,
and the UV curable resin 105 is filled in guide grooves (see the second step in FIG. 2). The
transfer substrate 152 has a concave-convex portion corresponding to information to be recorded.
After the second step, the transfer substrate 152 is irradiated with UV light from above, and the
UV curable resin 105 is cured into a UV cured resin layer (see the third step in FIG. 2).
Thereafter, the transfer substrate 152 is peeled off from the layer of the UV cured resin 105 (see
the fourth step in FIG. 2).
[0041] By performing the first step through the fourth step in FIG. 2, the layer of the UV cured
resin 105 having a concave-convex portion, which is an inverse pattern of the concave-convex
portion of the transfer substrate 152, is formed on the signal substrate 101. Further, a desirable
peelability can be maintained by selecting a material having a high peelability with respect to the
transfer substrate 152 in advance, as a property of the UV curable resin 105.
[0042] After the signal transferring process shown in FIG. 2 is performed, a signal recording
layer (information recording layer) is formed by a film forming device such as a sputtering
device.
[0043] By repeating the resin coating process shown in FIG. 1, the signal transferring process
shown in FIG. 2, and the film forming process, information recording layers of a multilayer

information recording medium are formed. Further, by forming a transparent layer (cover
layer) after the information recording layers have been formed, manufacturing of the multilayer
information recording medium is completed.
[0044] In this section, a process of forming a transparent layer by a spin coating method is
described referring to FIG. 3. FIG. 3 is a diagram for describing a spin coating process in this
embodiment.
[0045] There is no need of forming a signal guide groove on a surface of a resin layer
(transparent layer) on a light incident surface side of a multilayer information recording medium.
However, since the transparent layer is exposed to the surface of the medium, the user may touch
the transparent layer with his or her hand, or the transparent layer may be contacted with foreign
matters. In view of this, the transparent layer is required to have oil repellency that fat/oil
contained in e.g. a fingerprint is less likely to adhere, and to have wear resistance against
scratches resulting from rubbing. Further, the surface of the transparent layer is required to be
smooth to stably reproduce signals. In order to satisfy these requirements, the transparent layer
on the light incident surface side is formed by a spin coating method.
[0046] Firstly, the signal substrate 101 is placed on a turntable 21 (see the first step in FIG. 3).
A resin layer and a film layer are formed on the signal substrate 101. A center hole 22 is
blocked by a conical cap 23, and a UV curable resin 24 is dropped onto the cap 23 through a
nozzle 25 by the amount of e.g. 1.5 g.
[0047] Then, the signal substrate 101 is accelerated to a rotation speed of about 3,500 turns in
about two seconds, and the rotation number is kept for about seven seconds. Thus, the UV
curable resin 24 is spread (see the second step in FIG. 3).
[0048] A rod 23a is formed on the cap 23 to facilitate attachment/detachment of the cap 23.
The cap 23 is easily detached by dropping the UV curable resin 24 in such a manner that the UV
curable resin 24 is not adhered to the rod 23a. The nozzle 25 for ejecting the UV curable resin
24 is disposed with an inclination of 90 degrees or less with respect to the disc surface. It is
thus possible to eject the UV curable resin 24 near the cap 23, thereby preventing air bubbles
from intruding into the UV curable resin 24.
[0049] Then, after the cap 23 is detached, UV light is irradiated by a UV irradiator (not shown)
(see the third step in FIG. 3). Thus, the UV curable resin 24 is cured, and formation of the
transparent layer is completed.
[0050] The spin coating method is advantageous in forming a resin layer having a uniform
thickness in radial direction and circumferential direction. Further, it is possible to change only
the thickness distribution in radial direction, while keeping the thickness distribution in
circumferential direction uniform by changing a spin coating condition.

[0051] In the case where an intermediate layer (resin layer) is formed by screen printing, an
inner peripheral thickness tends to increase due to e.g. existence of a rib (see FIG. 21). In view
of this, it is preferable to form a transparent layer with a small inner peripheral thickness and a
large outer peripheral thickness in forming the transparent layer (cover layer) by a spin coating
method. An example of the spin coating condition for forming a thickness distribution with a
small inner peripheral thickness and a large outer peripheral thickness is disposing an eject port
of the nozzle 25 shown in FIG. 3 away from the rod 23a, and dropping the UV curable resin 24
at a position away from the rod 23a. This enables to form an intermediate layer having a
thickness distribution that the outer peripheral thickness is large.
[0052] Further, it is also possible to adjust the thickness distribution in radial direction by
changing the sequence in rotating the turntable 21. In the foregoing, the turntable 21 is
accelerated to a rotation speed of 3,500 turns within two seconds. Alternatively, it is possible to
set the outer peripheral thickness larger than the inner peripheral thickness by reducing the
acceleration time from two seconds to one second.
[0053] It is preferable to select a condition for offsetting thickness distributions of intermediate
layers that have already been formed by optimally combining the aforementioned conditions
concerning the thickness distribution in radial direction.
[0054] For instance, in the case where a multilayer information recording medium having four
information recording layers is manufactured, the resin coating process, the signal transferring
process, and the film forming process are repeated three times, and then, a transparent layer is
formed by the spin coating process. FIG. 4 is a cross-sectional view of a multilayer information
recording medium having four information recording layers in this embodiment.
[0055] A multilayer information recording medium 10 having four information recording
layers includes a signal substrate 11 having a concave-convex information surface with pits or
guide grooves formed on a surface thereof, a first film layer 12 formed on the information
surface of the signal substrate 11, a first intermediate layer 13 having a concave-convex
information surface with pits or guide grooves formed on a surface thereof opposite to the signal
substrate 11, a second film layer 14 formed on the information surface of the first intermediate
layer 13, a second intermediate layer 15 having a concave-convex information surface with pits
or guide grooves formed on a surface thereof opposite to the first intermediate layer 13, a third
film layer 16 formed on the information surface of the second intermediate layer 15, a third
intermediate layer 17 having a concave-convex information surface with pits or guide grooves
formed on a surface thereof opposite to the second intermediate layer 15, a fourth film layer 18
formed on the information surface of the third intermediate layer 17, and a transparent layer 19
disposed on the fourth film layer 18. In this embodiment, the film layers correspond to an

example of information recording layers, and the transparent layer corresponds to an example of
a cover layer.
[0056] The signal substrate 11 is constituted of a polycarbonate or acrylic resin disc with a
diameter of 120 mm and a thickness of about 1.0 to 1.1 mm to prevent flexure of the multilayer
information recording medium, secure rigidity, and have thickness compatibility between optical
discs of different kinds such as CD, DVD, and Blu-ray Disc. The signal substrate 11 has a
concave-convex information surface with pits or guide grooves formed on a surface thereof by
resin molding such as injection compression molding, using a conventional stamper. A hole
(not shown) of 15 mm in diameter is formed in the central part of the signal substrate 11 to rotate
the optical disc while supporting the optical disc in recording or reproducing signals by an
optical disc device. In this embodiment, described is an exemplified arrangement, wherein
polycarbonate is used as a material for the signal substrate 11.
[0057] Further, the signal substrate 11 has a rib at a predetermined position on the inner
periphery thereof (see FIGS. 20 and 21).
[0058] The intermediate layers 13, 15, and 17 made of a photo-curable resin, and the
transparent layer 19 are laminated on the signal substrate 11. Accordingly, for instance, in the
case where an information surface is disposed at a position facing above, the laminated
multilayer information recording medium has a concave shape resulting from shrinkage by light
curing, which is a property of a photo-curable resin. In view of the above, the signal substrate
11 is formed to have a convex shape in advance when the information surface is disposed at a
position facing above. Thus, the multilayer information recording medium laminated with the
intermediate layers 13,15, and 17, and the transparent layer 19 has a flat shape.
[0059] The first film layer 12 has a reflectance characteristic with respect to reproducing laser
light, in the case where the multilayer information recording medium is an ROM optical disc.
For instance, the first film layer 12 is formed by depositing a metal such as Al, Ag, Au, Si, or
Si02, a semiconductor material, or a dielectric material by e.g. sputtering or vapor deposition.
[0060] An arrangement of a recording film in the case where a multilayer information
recording medium is a write-once optical disc is described referring to FIG. 5. FIG. 5 is a
diagram showing an arrangement of a recording film of a multilayer information recording
medium in this embodiment. For instance, a reflection film 32 made of AlCr, a ZnS film 33, a
TeOPd recording film 34, and a ZnS film 35 are successively formed on an information surface
31 with pits or guide grooves on the signal substrate 11 by e.g. sputtering or vapor deposition.
In other words, the first film layer 12 is constituted of the reflection film 32, the ZnS film 33, the
TeOPd recording film 34, and the ZnS film 35.
[0061] In this embodiment, described is an arrangement, wherein Al is used as a material for

the reflection film 32. Similarly to an ROM optical disc, a material containing a metal such as
Ag or Au as a primary component may be used. Further alternatively, a film layer may include
e.g. a pigmented coat. The second film layer 14, the third film layer 16, and the fourth film
layer 18 are formed substantially in the same manner as the first film layer 12. The thickness of
the reflection film 32 may be adjusted depending on the optical characteristic required in
recording/reproducing, or the reflection film 32 itself may be omitted. Further alternatively, the
thickness of the ZnS film 33 or the TeOPd recording film 34 may be adjusted depending on the
optical characteristic.
[0062] The first intermediate layer 13 is made of an approximately transparent material having
transparency with respect to recording/reproducing light, and is made of a UV curable resin
containing acryl as a primary component. The UV curable resin has a property that the resin is
not curable with respect to light of a wavelength other than the UV light wavelength, but is
curable in any condition by UV irradiation, by setting the wavelength of curing light in a UV
wavelength band. The UV curable resin having the above property is advantageous in
controlling the shape of a resin layer. The UV curable resin is coated in an area smaller than
the outer diameter of the signal substrate 11, but larger than the diameter of the central hole of
the signal substrate 11 (see FIG. 4). The second intermediate layer 15 and the third
intermediate layer 17 are formed substantially in the same manner and with substantially the
same shape as the first intermediate layer 13.
[0063] The transparent layer 19 is made of an approximately transparent material having
transparency with respect to recording light and reproducing light, and is made of a UV curable
resin containing acryl as a primary component. A UV curable resin in a liquid form is used for
the transparent layer 19. The transparent layer 19 is formed by coating the UV curable resin on
the fourth film layer 18. The UV cured resin layer is formed in such a manner as to cover the
signal substrates and the film layers, and is formed to adhere to the signal substrate 11 at an inner
periphery and an outer periphery of the signal substrate 11 (see FIG. 4).
[0064] The foregoing is a schematic explanation on the manufacturing process of the
multilayer information recording medium.
[0065] In this section, an example of an optical disc device for recording and/or reproducing
information with respect to the multilayer information recording medium is described. FIG. 6
is a diagram showing a schematic arrangement of the optical disc device in this embodiment.
[0066] FIG. 6 shows a state that the multilayer information recording medium 10 is loaded.
The optical disc device shown in FIG. 6 is provided with a spindle motor 42, a controller 43, a
modulator 44, an optical head 45, a laser driving circuit 46, a preamplifier 47, a binary circuit 48,
a data demodulating circuit 49, a signal quality determinator 50, a recording condition storing

section 51, a pulse condition setter 52, a recording track information storing section 53, a focus
control circuit 54, a tracking control circuit 55, and a mover 56.
[0067] The spindle motor 42 rotates the loaded multilayer information recording medium 10.
The controller 43 controls the overall operations of the optical disc device. The modulator 44
converts data to be recorded into a recording signal. The optical head 45 has a semiconductor
laser, an objective lens, and a detector. The optical head 45 records information by collecting
laser light on the multilayer information recording medium 10, and obtains a reproduction signal
based on reflected light from the multilayer information recording medium 10. The laser
driving circuit 46 drives the semiconductor laser in the optical head 45 in accordance with a
recording signal.
[0068] The preamplifier 47 amplifies a reproduction signal acquired by the optical head 45,
and generates an information reproduction signal 47S, a focus error signal 47F, and a tracking
error signal 47T. The binary circuit 48 converts the information reproduction signal 47S into a
binary signal. The data demodulating circuit 49 demodulates a binary signal. The signal
quality determinator 50 determines the quality of a test signal indicating test-recording of
specific data in a test recording area of the multilayer information recording medium 10. The
recording condition storing section 51 stores an optimum recording condition acquired by a
learning operation.
[0069] The pulse condition setter 52 controls laser pulses in accordance with a recording
condition stored in the recording condition storing section 51. The recording track information
storing section 53 stores recording track information read out from the multilayer information
recording medium 10. The focus control circuit 54 controls the optical head 45 to focus laser
light on an intended information recording layer of the multilayer information recording medium,
based on the focus error signal 47F. The tracking control circuit 55 controls the optical head 45
to allow the laser light to properly scan an intended track of the multilayer information recording
medium 10, based on the tracking error signal 47T. The mover 56 moves the optical head 45 in
radial direction of the multilayer information recording medium 10.
[0070] The focus error signal 47F is generated by a general astigmatism method. The
tracking error signal 47T is generated by a general push-pull method.
[0071] Firstly, in an activation process, the spindle motor 42 rotates the loaded multilayer
information recording medium 10, and thereafter, the optical head 45 irradiates the multilayer
information recording medium 10 with laser light for information reproduction, and focuses the
laser light on a target information recording layer.
[0072] In reproducing e.g. the recording track information, the optical head 45 acquires a
reproduction signal based on reflected light from the multilayer information recording medium

10, and the preamplifier 47 generates the information reproduction signal 47S based on the
reproduction signal acquired by the optical head 45. The binary circuit 48 has been set to a
predetermined binarization slice level. The binary circuit 48 binarizes the information
reproduction signal 47S generated by the preamplifier 47. Thereafter, the data demodulating
circuit 49 demodulates the signal binarized by the binary circuit 48, and outputs the demodulated
signal to the controller 43. Thus, the recording track information recorded in the multilayer
information recording medium 10 is reproduced.
[0073] Further, in recording information, the modulator 44 converts specified data outputted
from the controller 43 into a laser driving signal, and the laser driving circuit 46 drives the
semiconductor laser in the optical head 45 in accordance with the laser driving signal. The
optical head 45 collects the laser light emitted from the semiconductor laser on the multilayer
information recording medium 10, and records information in a recording area of the multilayer
information recording medium 10 by tracking the laser light on a groove portion or a land
portion of a track, based on the recording track information.
[0074] The controller 43 determines whether it is possible to properly record and reproduce a
signal with respect to the multilayer information recording medium 10 by comparing a signal
obtained by binarizing a reproduction signal of data recorded in the test recording area by the
binary circuit 48, with data outputted from the controller 43 in recording in the test recording
area.
[0075] A reproduction-only multilayer information recording medium has concave-convex pits
formed thereon. In using the reproduction-only multilayer information recording medium, the
tracking error signal 47T is generated by a general differential push-pull method to thereby cause
the laser light to track a pit train, and perform only information reproduction.
[0076] Next, described is an influence on a reproduction signal characteristic referring to FIGS.
7A and 7B, in the case where each of the intermediate layers of the multilayer information
recording medium has a thickness variation, and the intermediate layers having the thickness
variations are laminated one over the other.
[0077] FIG. 7A is a diagram showing an arrangement of a multilayer information recording
medium where thickness correction has not been performed in a resin layer forming process, and
FIG. 7B is a diagram showing an arrangement of a multilayer information recording medium
where thickness correction has been performed in a resin layer forming process. In this section,
a multilayer information recording medium having three information recording layers is
described referring to FIGS. 7A and 7B. However, the following phenomenon may occur, as
far as a multilayer information recording medium has three or more information recording layers
[0078] Referring to FIGS. 7A and 7B, a multilayer information recording medium 60 includes

a signal substrate 61 having a concave-convex information surface with pits or guide grooves
formed on one surface thereof, a first film layer 62 formed on the information surface of the
signal substrate 61, a first intermediate layer 63 having a concave-convex information surface
with pits or guide grooves formed on a surface thereof opposite to the signal substrate 61, a
second film layer 64 formed on the information surface of the first intermediate layer 63, a
second intermediate layer 65 having a concave-convex information surface with pits or guide
grooves formed on a surface thereof opposite to the first intermediate layer 63, a third film layer
66 formed on the information surface of the second intermediate layer 65, and a transparent layer
67 formed on the third film layer 66. An objective lens 68 is disposed within the optical head
45 (see FIG. 6) to collect laser light 69 for recording or reproducing information onto each of the
film layers. Further, optical path lengths 70, 71, and 72 each represents a distance from a light
incident surface 73 of the transparent layer 67 to the first film layer 62.
[0079] In the following, an influence on thickness variation in reproducing information from
the multilayer information recording medium is described. Substantially the same influence
may occur in recording information into the multilayer information recording medium.
[0080] In reproducing information from the multilayer information recording medium, the
laser light 69 is focused on an intended information recording layer (film layer). FIGS. 7A and
7B show a state that the laser light 69 is collected on the first film layer 62.
[0081] In this example, tracing a route of the laser light 69, firstly, the laser light 69 collected
by the objective lens 68 is transmitted through the transparent layer 67 by the light amount
obtained by multiplying an incident light amount with the transmittance of the transparent layer
67.
[0082] The wavelength of laser light to be used for a Blu-ray disc is near 405 nm, the
refractive index of the laser light having the aforementioned wavelength in the air is 1.00, and
the refractive index of the laser light having the aforementioned wavelength in the transparent
layer 67 is generally not smaller than 1.45 but not larger than 1.70.
[0083] The laser light 69 transmitted through the transparent layer 67 is then transmitted
through the third film layer 66 by the light amount obtained by multiplying an incident light
amount with the transmittance of the third film layer 66, and the refraction angle of the laser
light 69 is changed depending on a refractive index ratio between the transparent layer 67 and
the third film layer 66.
[0084] Before the laser light 69 reaches the first film layer 62, the light amount of the laser
light 69 is decreased depending on the transmittances of the second intermediate layer 65, the
second film layer 64, and the first intermediate layer 63; and refraction depending on the
refractive index ratio between the adjacent layers is repeated. Further, the laser light 69

collected on the first film layer 62 is reflected by the light amount obtained by multiplying an
irradiated light amount with the reflectance of the first film layer 62, and is emitted in the
direction opposite to the incident light direction, while repeating reduction of the light amount
depending on the transmittances of the respective intermediate layers and the respective film
layers. The laser light 69 emitted from the transparent layer 67 is entered into the detector (not
shown) for converting light of a certain intensity into an electrical signal, and data is read out
based on the converted electrical signal.
[0085] A lens is designed to reduce various aberrations so as to more accurately record and
reproduce information in recording and reproducing information with respect to the multilayer
information recording medium. Further, the focus control circuit 54 (see FIG. 6) is operable to
reduce the beam spot diameter on the first film layer 62 so that size variation of even smaller
recording marks is reduced in order to enhance the recording density.
[0086] Information is reproduced from an intended information recording layer by causing the
laser light 69 to pass along the aforementioned optical path. However, as shown in FIG. 7 A, in
the case where thickness correction is not performed in a resin layer forming process, the optical
path length may vary depending on which position within the multilayer information recording
medium the laser light passes. For instance, in the case where the first intermediate layer 63
and the second intermediate layer 65 locally have a small thickness within a plane of the
multilayer information recording medium, the optical path length 70 from the light incident
surface 73 of the transparent layer 67 to the first film layer 62 is shortened (see FIG. 7A).
Conversely, in the case where the first intermediate layer 63 and the second intermediate layer
65 locally have a large thickness within a plane of the multilayer information recording medium,
the optical path length 71 from the light incident surface 73 of the transparent layer 67 to the first
film layer 62 is extended (see FIG. 7A).
[0087] A change in the optical path length defouses the laser light 69, and deteriorates the
signal quality. It is needles to say that defocus of the laser light 69 can be prevented by using a
circuit for correcting an aberration depending on a change in the optical path length. However,
it is extremely difficult to provide an aberration correcting circuit, in the case where a position
where the optical path length is changed differs in each of the multilayer information recording
media.
[0088] On the other hand, in the case of FIG. 7B, although the first intermediate layer 63 has a
thickness variation and a thickness distribution substantially in the same manner as FIG. 7A, the
second intermediate layer 65 is formed in such a manner as to correct the thickness distribution
of the first intermediate layer 63. Accordingly, as is clear from FIG. 7B, the optical path length
72 from the light incident surface 73 of the transparent layer 67 to the first film layer 62 is

constant at any position.
[0089] As described above, in the manufacturing process of the multilayer information
recording medium, film layers and intermediate layers are laminated in a predetermined order on
the signal substrate 61. In view of this, preferably, the multilayer information recording
medium manufacturing apparatus is operable to grasp the thickness distribution of the first
intermediate layer 63 before the second intermediate layer 65 is formed, and to form the second
intermediate layer 65 in such a manner as to correct the thickness distribution of the first
intermediate layer 63.
[0090] In the foregoing, an example of the multilayer information recording medium
manufacturing method, and an example of the information recording/reproducing method for
recording or reproducing information with respect to the multilayer information recording
medium have been described. In the following, concrete examples of this embodiment are
described in detail along with the advantages of the invention.
[0091] (Example 1)
In the following, a multilayer information recording medium manufacturing method as
an example of the embodiment is described referring to FIG. 8, FIG. 9, FIG. 10, FIG. 11A, FIG.
11B, FIG. 12A and FIG. 12B.
[0092] FIG. 8 is a block diagram showing an arrangement of a multilayer information
recording medium manufacturing apparatus in Example 1. A multilayer information recording
medium manufacturing apparatus 1 shown in FIG. 8 is provided with an injection molding
machine 2, a sputtering device 3, a screen printing machine 4, and a spin coating device 5.
[0093] The injection molding machine 2 manufactures a substrate (signal substrate 11) using
e.g. polycarbonate as a resin material by injection molding. A concave-convex information
surface having pits or guide grooves is formed on a surface of the signal substrate 11.
[0094] The sputtering device 3 forms information recording layers (first film layer 12, second
film layer 14, third film layer 16, and fourth film layer 18) for recording information by e.g. a
magnetron sputtering process. The sputtering device 3 forms the first film layer 12 on the
information surface of the signal substrate 11, and forms the second film layer 14, the third film
layer 16, and the fourth film layer 18 on the first intermediate layer 13, the second intermediate
layer 15, and the third intermediate layer 17, respectively.
[0095] In this example, film layers are formed by a magnetron sputtering process. The
invention is not specifically limited to the above, and film layers may be formed by other
sputtering process.
[0096] The screen printing machine 4 forms resin layers (first intermediate layer 13, second
intermediate layer 15, and third intermediate layer 17) on the film layers by a screen printing

process. The screen printing machine 4 coats a UV curable resin on each of the film layers,
forms pits or guide grooves on the layers of the UV curable resin, and irradiates UV light to
thereby form the first intermediate layer 13, the second intermediate layer 15, and the third
intermediate layer 17, respectively. The screen printing machine 4 forms the first film layer 12,
the second intermediate layer 15, and the third intermediate layer 17 on the first film layer 12,
the second film layer 14, and the third film layer 16, respectively.
[0097] The screen printing machine 4 forms the first intermediate layer by screen printing, and
forms the second intermediate layer by screen printing in such a manner that thickness variation
of the multilayer information recording medium after the first intermediate layer has been
formed is suppressed. In the present specification, the second intermediate layer is an
intermediate layer to be formed following the first intermediate layer. Specifically, in the case
where the second intermediate layer is the second intermediate layer 15, the first intermediate
layer is the first film layer 12; and in the case where the second intermediate layer is the third
intermediate layer 17, the first intermediate layer is the second intermediate layer 15.
[0098] The screen printing machine 4 is provided with a thickness distribution measurer 81, a
thickness corrector 82, and a printer 83. The thickness distribution measurer 81 measures a
thickness variation of the multilayer information recording medium before the second
intermediate layer is formed and after the first intermediate layer has been formed. The
thickness distribution measurer 81 is constituted of e.g. a laser interferometer, and measures a
thickness distribution of the overall surface of the multilayer information recording medium by
irradiating the surface of the multilayer information recording medium (signal substrate) with
laser light.
[0099] The thickness corrector 82 sets a coating direction of coating a resin in forming the
second intermediate layer by screen printing different from a coating direction in forming the
first intermediate layer. Further, the thickness corrector 82 rotates a turntable for placing a
substrate of the multilayer information recording medium thereon relative to the moving
direction of a squeegee for coating a resin. Further, the thickness corrector 82 fixes the moving
direction of the squeegee for coating a resin, and rotates the turntable for placing a substrate of
the multilayer information recording medium thereon. Furthermore, the thickness corrector 82
rotates the turntable in such a manner that the position of the second intermediate layer having a
largest thickness in forming the second intermediate layer is not overlapped with the position of
the first intermediate layer having a largest thickness. In addition, the thickness corrector 82
rotates the turntable in such a manner that the position of the second intermediate layer having a
largest thickness in forming the second intermediate layer is overlapped with the position of the
first intermediate layer having a smallest thickness.

[0100] The printer 83 forms the second intermediate layer in such a manner that the thickness
variation measured by the thickness distribution measurer 81 is suppressed.
[0101] The spin coating device 5 forms a cover layer (transparent layer 19) by a spin coating
method. The spin coating device 5 forms the transparent layer 19 on the fourth film layer 18.
The spin coating device 5 forms the cover layer by a spin coating method in such a manner that
the inner peripheral thickness of the multilayer information recording medium becomes smaller
than the outer peripheral thickness thereof after the second intermediate layer has been formed.
[0102] In Example 1, the sputtering device 3 conesponds to an example of an information
recording layer forming section, the screen printing machine 4 corresponds to an example of an
intermediate layer forming section, and the spin coating device 5 corresponds to an example of a
cover layer forming section.
[0103] Next, a process of manufacturing a multilayer information recording medium by the
multilayer information recording medium manufacturing apparatus shown in FIG. 8 is described.
FIG. 9 is a diagram showing an example of an operation flow to be performed by a multilayer
information recording medium manufacturing processing in Example 1. The multilayer
information recording medium manufacturing processing of manufacturing a multilayer
information recording medium having four information recording layers is described referring to
FIG. 9.
[0104] Firstly, in Step SI, the injection molding machine 2 manufactures the signal substrate
11 by injection molding. The signal substrate 11 manufactured by the injection molding
machine 2 is carried to the sputtering device 3.
[0105] Then, in Step S2, the sputtering device 3 forms the first film layer 12 on the signal
substrate 11 by a magnetron sputtering process. The signal substrate 11 having the first film
layer 12 formed thereon by the sputtering device 3 is carried to the screen printing machine 4.
[0106] Then, in Step S3, the screen printing machine 4 forms the first intermediate layer 13 on
the first film layer 12 by a screen printing process. The signal substrate 11 having the first
intermediate layer 13 formed thereon by the screen printing machine 4 is carried to the sputtering
device 3.
[0107] Then, in Step S4, the sputtering device 3 forms the second film layer 14 on the first
intermediate layer 13 by a magnetron sputtering process. The signal substrate 11 having the
second film layer 14 formed thereon by the sputtering device 3 is carried to the screen printing
machine 4.
[0108] Then, in Step S5, the screen printing machine 4 forms the second intermediate layer 15
on the second film layer 14 by a screen printing process. The signal substrate 11 having the
second intermediate layer 15 formed thereon by the screen printing machine 4 is canied to the

sputtering device 3.
[0109] Then, in Step S6, the sputtering device 3 forms the third film layer 16 on the second
intermediate layer 15 by a magnetron sputtering process. The signal substrate 11 having the
third film layer 16 formed thereon by the sputtering device 3 is carried to the screen printing
machine 4.
[0110] Then, in Step S7, the screen printing machine 4 forms the third intermediate layer 17
on the third film layer 16 by a screen printing process. The signal substrate 11 having the third
intermediate layer 17 formed thereon by the screen printing machine 4 is carried to the sputtering
device 3.
[0111] Then, in Step S8, the sputtering device 3 forms the fourth film layer 18 on the third
intermediate layer 17 by a magnetron sputtering process. The signal substrate 11 having the
fourth film layer 18 formed thereon by the sputtering device 3 is carried to the spin coating
device 5.
[0112] Then, in Step S9, the spin coating device 5 forms the transparent layer 19 on the fourth
film layer 18 by a spin coating method.
[0113] By performing the aforementioned Steps SI through S9, a multilayer information
recording medium having four information recording layers can be manufactured.
[0114] A multilayer information recording medium manufacturing processing of
manufacturing a multilayer information recording medium having four information recording
layers has been described referring to FIG. 9. It is possible to manufacture a multilayer
information recording medium having information recording layers other than four information
recording layers by repeating a film layer forming process and an intermediate layer forming
process. Specifically, in the case where a multilayer information recording medium having N
layers is manufactured, a process of forming a film layer (information recording layer) is
performed N times, and a process of forming an intermediate layer (resin layer) is performed (N-
1) times. For instance, in the case where a multilayer information recording medium having
three information recording layers is manufactured, the operations in Steps S7 and S8 in FIG. 9
are omitted.
[0115] FIG. 10 is a diagram showing an example of the resin layer forming process in
Example 1. FIG. 11A is a cross-sectional view of a screen printing machine before a resin layer
is formed, FIG. 1 IB is a cross-sectional view of the screen printing machine after a resin layer
has been formed, FIG. 12A is a top plan view of the screen printing machine before a resin layer
is formed, and FIG. 12B is a top plan view of the screen printing machine after a resin layer has
been formed,
[0016] FIG. 10 shows the screen printing machine before printing, during printing, and after

printing. The screen printing machine shown in FIG. 10 is provided with a turntable 103 for
fixedly supporting a signal substrate 101, a screen 104, a screen frame 106, a squeegee fixing jig
108, and a squeegee 109.
[0117] A method for manufacturing the screen 104 is described. Firstly, a gauze as a screen
material is stretched over the screen frame 106, and a photosensitive emulsion is coated on the
screen material. Then, an area other than a predetermined position (position where plural holes
are to be formed) coated with the screen material is masked by a light shielding mask, and the
screen material is irradiated with UV light by an exposure device for a predetermined time.
The photosensitive emulsion exposed to the UV irradiation is washed by e.g. water jet for
development. In this way, the screen 104 is manufactured.
[0118] In FIGS. 12A and 12B showing Example 1, areas 111 and 112 correspond to portions
where the photosensitive emulsion remains on the gauge by the light shielding mask, and an area
113 corresponds to a portion where the gauze is exposed by light exposure.
[0119] Various materials such as wood, aluminium, stainless steel, or plastic may be used for
the screen frame 106. Among these, it is preferable to use lightweight aluminium having a high
rigidity. Various examples such as silk, nylon (registered trademark), tetron (registered
trademark), a V-screen (registered trademark), or stainless steel may be used as the gauze
serving as the screen material. Among these, it is preferable to use a V-screen in the aspect of
restorability against an external pressure. An example of the photosensitive emulsion is an
emulsion obtained by mixing and dissolving a diazonium salt or bichromate in PVA or a vinyl
acetate emulsion. The number of meshes (number of wires per inch) at a certain position of the
screen material is preferably from 100 to 600. As far as the number of meshes falls within a
range of from 100 to 600, it is possible to apply a coat containing a resin without extrusion
failure and thickness variation. The holes of the screen material are not limited to a mesh shape.
[0120] In Example 1, lightweight aluminium having a high rigidity is used as the screen frame
106, and a V-screen that enables to reduce a load to the signal substrate 101 is used as the screen
104. Alternatively, the example can be realized by using other material.
[0121] In the case where the viscosity of the UV curable resin 105 is low, the UV curable resin
105 after a coating step may flow out, with the result that the UV curable resin 105 may spread
out of an end of the signal substrate 101 or may form a partly thickened layer. On the other
hand, in the case where the viscosity of the UV curable resin 105 is high, the UV curable resin
105 is less likely to pass the screen 104, with the result that it is difficult to transfer the UV
curable resin 105 onto the signal substrate 101. Considering a change in e.g. viscosity of the
UV curable resin 105 resulting from a temperature change and a humidity change during a resin
layer forming process, it is preferable to set the viscosity of the UV curable resin 105 in a range

of from 30 cps to 10,000 cps.
[0122] It is possible to restrict a coating area of the UV curable resin 105 onto the signal
substrate 101 by setting the area 113 where an opening is formed on the screen 104. In
Example 1, it is thus possible to change an end position of a resin layer to be formed by changing
the boundary position between the area 113 and the area 111.
[0123] The area 121 in FIG. 12B is an area where the UV curable resin 105 is coated on the
signal substrate 101 by a screen printing process using the screen 104.
[0124] The thickness distribution of the UV curable resin 105 to be formed in the screen
printing process is preferably uniform. Actually, however, the thickness may locally vary
depending on mechanical precision of a jig to be used in the resin layer forming process.
[0125] Various factors are considered as factors of causing thickness variation. For instance,
thickness variation occurs, in the case where the squeegee 109 is tilted with respect to the
turntable 103, in the case where the squeegee 109 is partially damaged, or in the case where a
pressure to be applied to the signal substrate 101 by the squeegee 109 is not constant.
[0126] Thickness variation may also occur, in the case where the thickness of gauze of the
screen 104 differs depending on a position. Thickness variation may also occur, in the case
where the thickness distribution of the signal substrate 101 is not uniform.
[0127] As described above, there are many factors of causing thickness variation, and the
thickness variation depends on mechanical precision and dimensional precision of various parts
and members. Further, considering deterioration of various members of the screen printing
machine with time, it may be practically impossible to eliminate all the possible factors, and
form a resin layer substantially free of thickness variation.
[0128] However, since these factors are unique to a device, unique to a substrate, or unique to
a jig, reproducibility is very high, and it is possible to control the direction of thickness
distribution by determining the printing direction or the setting direction of the signal substrate
101.
[0129] In the following, these is described an arrangement, wherein thickness variation occurs
resulting from tilting of the turntable 103 with respect to the moving direction of the squeegee
109, referring to FIGS. 13A, 13B, 14A, 14B, and 14C.
[0130] FIG. 13A is a cross-sectional view of a screen printing machine before a resin layer is
formed, FIG. 13B is a cross-sectional view of the screen printing machine after a resin layer has
been formed, FIG. 14A is a top plan view of the screen printing machine before a resin layer is
formed, FIG. 14B is a top plan view of the screen printing machine after a resin layer has been
formed, and FIG. 14C is a diagram showing a signal substrate having a resin layer formed
thereon.

[0131] Referring to FIG. 13A, since the turntable 103 is tilted with respect to the moving
direction of the squeegee 109 by the angle 8, the signal substrate 101 is fixedly supported with
an inclination of the angle 6 with respect to the moving direction of the squeegee 109. As is
clear from FIG. 13A, although the distance between the squeegee 109 and the signal substrate
109 is short at the left-side coating start point on the screen 104, the distance between the
squeegee 109 and the signal substrate 101 is increased at the right-side coating end point on the
screen 104, as compared with the distance at the coating start point. As a result, the thickness
of the layer of the UV curable resin 105 to be coated varies.
[0132] In the above case, as shown in FIG. 14C, the thickness of the UV curable resin 105 to
be coated on an end of the signal substrate 101 in the direction of 90° is large, and the thickness
of the UV curable resin 105 to be coated on an end of the signal substrate 101 in the direction of
270° is small. In this way, in the case where the thickness variation results only from linear
inclination of the turntable 103 as shown in FIG. 13A, it is preferable to set the signal substrate
101 by turning the signal substrate 101 by 180°, so that the position of a succeeding resin layer
having a largest thickness in forming the succeeding resin layer is aligned with the position of a
preceding resin layer having a smallest thickness.
[0133] As described above, in the case where the thickness variation of the UV curable resin
105 results from a distance variation between the turntable 103 and the squeegee 109, the
thickness variation distribution is not changed even if the moving direction of the squeegee 109*
is reversed (changed from the rightward direction to the leftward direction in FIG. 13A).
[0134] Thus, the first intermediate layer is formed by screen printing, and the second
intermediate layer is formed by screen printing in such a manner that thickness variation of the
multilayer information recording medium after the first intermediate layer has been formed is
suppressed. Then, after the second intermediate layer has been formed, the cover layer is
formed by a spin coating method in such a manner that the inner peripheral thickness of the
multilayer information recording medium becomes smaller than the outer peripheral thickness
thereof.
[0135] The thickness distribution in radial direction of a multilayer information recording
medium can be controlled by a spin coating method. Accordingly, it is possible to suppress
thickness variation in radial direction of the multilayer information recording medium by the
spin coating method. However, in the spin coating method, it is difficult to suppress thickness
variation in circumferential direction of the multilayer information recording medium. Further,
as described above, in screen printing, the inner peripheral thickness of the multilayer
information recording medium tends to increase, as compared with the outer peripheral thickness,
and laminating plural intermediate layers may increase the inner peripheral thickness of the

multilayer information recording medium.
[0136] In view of the above, thickness variation in circumferential direction is reduced in
forming the respective intermediate layers by screen printing, and thickness variation in radial
direction is reduced in forming the cover layer by a spin coating method to thereby make the
distance from a light incident surface of the multilayer information recording medium to a
farthest information recording layer thereof uniform within a plane of the medium.
[0137] The thickness corrector 82 may rotate the turntable 103 in such a manner that the
coating direction in forming the second intermediate layer perpendicularly intersects with the
coating direction in forming the first intermediate layer.
[0138] In Example 1, the coating direction of coating a resin is changed by rotating the
turntable 103 on which the multilayer information recording medium is placed. The invention
is not limited to the above. It is possible to change the coating direction of coating a resin by
placing the multilayer information recording medium on a fixed table, and rotating the moving
direction of the squeegee 109.
[0139] Further alternatively, the coating direction of coating a resin may be changed by setting
a table on which the multilayer information recording medium is placed in a fixed state, and
placing and rotating the multilayer information recording medium on the table. In this case,
although the turntable 103 may be provided with a rotation mechanism, preferably, the turntable
103 may be fixed, without providing a rotation mechanism.
[0140] Specifically, the direction of placing a substrate on a substrate holding table for placing
a substrate of the multilayer information recording medium is made different between the
process of forming the first intermediate layer, and the process of forming the second
intermediate layer. Alternatively, the substrate may be held on the substrate holding table in
such a manner that the position of the second intermediate layer having a largest thickness in
forming the second intermediate layer, and the position of the first intermediate layer having a
largest thickness are not overlapped. Further alternatively, the substrate may be held on the
substrate holding table in such a manner that the position of the second intermediate layer having
a largest thickness in forming the second intermediate layer, and the position of the first
intermediate layer having a smallest thickness are overlapped. Further alternatively, the
substrate may be held on the substrate holding table in such a manner that the coating direction
in forming the second intermediate layer perpendicularly intersects with the coating direction in
forming the first intermediate layer.
[0141] In performing the above operation, the thickness corrector 82 is preferably provided
with a mechanism for placing a substrate on the substrate holding table. Further preferably, the
thickness corrector 82 may have a mechanism for placing and rotating a substrate on the

substrate holding table.
[0142] Screen printing is advantageous in forming a uniform resin layer by enhancing
alignment precision between the moving direction of a squeegee and a table. Accordingly, in
the case where the multilayer information recording medium is placed and rotated on a fixed
table, it is possible to reduce a film thickness error of a resin layer, as compared with an
arrangement of providing a rotation mechanism on a table.
[0143] Further, in the case where a multilayer information recording medium has N (N is an
integer of 4 or larger) information recording layers and (N-l) intermediate layers, the thickness
corrector 82 is operable to make the coating direction of coating a resin in forming the (N-l)
intermediate layers, and the coating direction of coating a resin in forming the first intermediate
layer to the (N-2) intermediate layers different from each other.
[0144] (Example 2)
In Example 1, there has been described an arrangement, wherein thickness variation
results from inclination of the turntable 103. Since mesh hole variation of the screen 104, and
thickness variation of the signal substrate 101 become thickness variation factors, in addition to
the distance variation between the turntable 103 and the squeegee 109, actual thickness
distribution of the UV curable resin 105 to be coated becomes very complicated.
[0145] A UV cured resin layer thickness measuring method, and a thickness correcting method
are described referring to FIG. 15. FIG. 15 is a diagram for describing a resin layer thickness
variation measuring method, and a thickness variation correcting method in Example 2. Since
the arrangement of a multilayer information recording medium manufacturing apparatus shown
in Example 2 is substantially the same as the arrangement of the multilayer information
recording medium manufacturing apparatus 1 shown in Example 1, description thereof is omitted
herein.
[0146] A predetermined radial direction of the signal substrate 101 is defined as the 0-degree
direction, and a surface area of the signal substrate 101 is divided into m areas Al, A2, A3, ... ,
and Am circumferentially from the 0-degree direction to measure thickness variation of a resin
layer formed on the signal substrate by a screen printing process. In this arrangement, it is
preferable to correlate the 0-degree direction with a direction of installing a screen printing
machine. Further, the surface area of the signal substrate 101 is divided into n areas Bl, B2, B3,
..., and Bn concentrically and radially outwardly from the inner periphery thereof. With this
arrangement, the surface area of the signal substrate 101 can be divided into (mxn) areas, and the
respective areas obtained by circumferentially and radially dividing the surface area of the signal
substrate 101 are called as areas AxBy (where x=l through m, and y= 1 through n). The
thickness distribution measurer 81 measures the thicknesses of the UV cured resin layer

(intermediate layer) of the divided areas AxBy. Further, an area of the UV cured resin layer
having a largest thickness is defined as an area AmaxBmax, and an area of the UV cured resin
layer having a smallest thickness is defined as an area AminBmin, based on a measurement
result on the thicknesses of the intermediate layers.
[0147] The thickness of the area AxBy may be an average value of the thicknesses within the
area AxBy, or a thickness at a central part of the area AxBy.
[0148] After an information recording layer (film layer) has been formed on the signal
substrate 101 by the sputtering device 3, a succeeding intermediate layer is formed by the screen
printing machine 4.
[0149] If the setting direction of the signal substrate 101 with respect to the screen printing
machine in forming a succeeding resin layer is the same as the setting direction in forming the
preceding resin layer, the thickness distribution becomes the same as in forming the preceding
resin layer. As a result, the multilayer information recording medium has the thickness
distribution shown in FIG. 7A, and a thickness difference between the position having a smallest
thickness and the position having a largest thickness tends to increase from the light incident
surface 73 to the first film layer 82.
[0150] In view of the above, it is desirable to rotate the angular position i.e. set the rotation
angle of the signal substrate 101 with respect to the screen printing machine in such a manner
that a circumferential position Amax where the area AmaxBmax resides is overlapped with a
circumferential position Amin where the area AminBmin resides in order to realize the thickness
distribution shown in FIG. 7B. Specifically, as shown in FIG. 15, it is preferable to rotate the
signal substrate 101 in clockwise direction by the angle defined by the circumferential position
Amin and the circumferential position Amax, and set the signal substrate 101 thereat on the
turntable 103. The thickness corrector 82 rotates the turntable 103 by the angle defined by the
circumferential position Amin and the circumferential position Amax.
[0151] In the above example, described is an arrangement, wherein the radial position
(distance from the center of the signal substrate to the area AminBmin) of the area AminBmin,
and the radial position (distance from the center of the signal substrate to the area AmaxBmax)
of the area AmaxBmax are relatively close to each other. However, it is not always the case
that the radial position of the area AminBmin and the radial position of the AmaxBmax are close
to each other.
[0152] In the following, described is an arrangement, wherein the radial position of the area
AminBmin and the radial position of the AmaxBmax are away from each other, referring to FIG.
16. FIG. 16 is a diagram for describing a resin layer thickness variation measuring method and
a thickness variation correcting method in a modification of Example 2.

[0153] Similarly to FIG. 15, a predetermined radial direction of the signal substrate 101 is
defined as the 0-degree direction, and a surface area of the signal substrate 101 is divided into m
areas Al, A2, A3, ... , and Am circumferentially from the 0-degree direction. Further, the
surface area of the signal substrate 101 is divided into n areas Bl, B2, B3, ..., and Bn
concentrically and radially outwardly from the inner periphery thereof. The respective areas
obtained by circumferentially and radially dividing the surface area of the signal substrate 101
are called as areas AxBy (where x=l through m, and y= 1 through n). Further, an area of the
UV cured resin layer having a smallest thickness is defined as an AminBmin, and an area of the
UV cured resin layer having a largest thickness is defined as an area AmaxBmax out of all the
divided areas of the signal substrate 101.
[0154] As shown in FIG. 16, the radial position of the area AminBmin and the radial position
of the area AmaxBmax are greatly away from each other. Accordingly, as described above,
even if the signal substrate 101 is rotated by the angle defined by the circumferential position
Amin and the circumferential position Amax, the effect of offsetting the mutual thickness
distribution variations is weak.
[0155] In view of the above, the thickness corrector 82 searches an area having a largest
thickness in radial position of the area AminBmin circumferentially, and defines an area having a
largest thickness in radial position of the area AminBmin, as an area AlargeBmin. Further, the
thickness corrector 82 searches an area having a smallest thickness in radial position of the area
AmaxBmax circumferentially, and defines an area having a smallest thickness in radial position
of the area AmaxBmax, as an area AsmallBmax.
[0156] Thus, it is preferable to rotate the angular position i.e. set the rotation angle of the
signal substrate 101 in such a manner that the circumferential position Amax where the area
AmaxBmax resides is overlapped with a circumferential position Asmall where the area
AsmallBmax resides to offset the thickness variations of the area AmaxBmax. Specifically, the
thickness corrector 82 rotates the turntable 103 by the angle defined by the circumferential
position Asmall and the circumferential position Amax, and the printer 83 forms a succeeding
resin layer.
[0157] Further, it is preferable to rotate the angular position of the signal substrate 101 i.e. set
the rotation angle of the signal substrate 101 in such a manner that the circumferential position
Amin where the area AminBmin resides is overlapped with a circumferential position Alarge
where the area AlargeBmin resides to offset the thickness variations of the area AminBmin.
Specifically, the thickness corrector 82 rotates the turntable 103 by the angle defined by the
circumferential position Amin and the circumferential position Alarge, and the printer 83 forms a
succeeding resin layer.

[0158] However, it is not always the case that the angle defined by the circumferential position
Asmall and the circumferential position Amax is equal to the angle defined by the
circumferential position Amin and the circumferential position Alarge. In view of the above, it
is preferable to estimate the effects obtained by the respective rotations, select one of the angles
which provides a greater effect, and determine the rotation angle of the signal substrate 101
(turntable 103).
[0159] For instance, the thickness corrector 82 calculates thicknesses of the respective areas
AxBy obtained by laminating resin layers, while rotating the signal substrate by the angle
defined by the circumferential position Asmall and the circumferential position Amax, and
thicknesses of the respective areas AxBy obtained by laminating resin layers, while rotating the
signal substrate by the angle defined by the circumferential position Amin and the
circumferential position Alarge, based on the measured thicknesses of the respective areas AxBy.
Then, the thickness corrector 82 calculates average values of thicknesses of the respective areas
AxBy after the lamination in both of the cases, and compares the respective calculated average
values with a predetermined value. Then, the thickness corrector 82 rotates the turntable 103
by the angle corresponding to a smaller difference between the respective calculated average
values and the predetermined value. The predetermined value is a predefined optimum
thickness value.
[0160] Thus, in the case where plural resin layers are formed by a screen printing method, it is
desirable to grasp in advance the direction of thickness variation or the position of thickness
variation of a resin layer that has already been formed, and to form a succeeding resin layer in
such a manner that a thickness distribution is generated in a direction of offsetting the thickness
variations. Specifically, in forming a succeeding resin layer, preferably, the screen printing
machine is operable to grasp the thickness distribution of a resin layer that has already been
formed, and to set the signal substrate 101 in a proper direction.
[0161] The thickness corrector 82 may be operable to correct a thickness distribution resulting
from the moving direction of the squeegee by changing the moving direction of the squeegee
depending on the direction of the signal substrate 101.
[0162] Further alternatively, in the case where a multilayer information recording medium has
N (where N is an integer of 4 or larger) information recording layers, and (N-l) intermediate
layers, the thickness distribution measurer 81 may measure the thickness of an intermediate layer
that has been formed immediately before the measurement, and the thickness corrector 82 may
correct the thickness of a succeeding intermediate layer to be formed, based on the measured
thickness. Further alternatively, the thickness distribution measurer 81 may measure the sum of
thicknesses of all the intermediate layers that have already been formed, and the thickness

corrector 82 may correct the thickness of a succeeding intermediate layer to be formed, based on
the measured thickness sum.
[0163] Further alternatively, in the case where the radial position (distance from the center of
the signal substrate) of the area AminBmin having a smallest thickness of the UV cured resin
layer, and the radial position of the area AmaxBmax having a largest thickness of the UV cured
resin layer are different from each other, the thickness corrector 82 may determine the angle by
which the turntable 103 is rotated, based on one of the areas AminBmin and the area AmaxBmax
which is located closer to the outer peripheral side.
[0164] Similarly to Example 1, in Example 2, the table on which the multilayer information
recording medium is placed may be fixed, and the coating direction of coating a resin may be
changed by placing and rotating the multilayer information recording medium on the table.
[0165] (Example 3)
In Example 3, there is described a thickness correcting method capable of suppressing
thickness variation of a resin layer with a less number of processes. As described above, the
thickness of a resin layer is likely to depend on the moving direction of the squeegee, in other
words, the setting direction of the signal substrate with respect to the screen printing machine.
Accordingly, if the information representing the setting direction of the signal substrate with
respect to the screen printing machine in performing screen printing, and thickness variation
inherent to the screen printing machine can be grasped in advance, the thickness variation of a
resin layer that has already been formed can be predicted. However, in this case, after a first
intermediate layer (resin layer) has been formed, the routine proceeds to a process of forming an
information recording layer (film layer). In a film forming process of forming an information
recording layer, a metal and dielectric film is formed by e.g. sputtering or vapor deposition. In
this case, generally, the signal substrate is rotated to make the thickness distribution of a
reflection film constant in circumferential direction.
[0166] As described above, the film forming process intervenes between the resin layer
forming processes. Accordingly, in the case where plural resin layers are formed, the signal
substrate may be rotated during the film forming process, which may make it difficult or
impossible to determine the printing direction of a resin layer that has already been formed.
[0167] In view of the above, in Example 3, a reference area is formed in an inner periphery of
the signal substrate to identify the printing direction in forming a resin layer. The reference
area can be formed by screen printing.
[0168] FIG. 17 is a block diagram showing an arrangement of a multilayer information
recording medium manufacturing apparatus in Example 3. A multilayer information recording
medium manufacturing apparatus 1 shown in FIG. 17 is provided with an injection molding

machine 2, a sputtering device 3, a screen printing machine 4, and a spin coating device 5. The
elements of the multilayer information recording medium manufacturing apparatus 1 shown in
FIG. 17, which are substantially equivalent or identical to those of the multilayer information
recording medium manufacturing apparatus shown in FIG. 8, are indicated with the same
reference numerals, and description thereof is omitted herein.
[0169] The screen printing machine 4 in Example 3 is provided with a reference area detector
84, a thickness corrector 82, and a printer 83. The printer 83 forms a reference area for use in
recognizing a disposition position of the multilayer information recording medium with respect
to the coating direction of coating a resin in forming the first intermediate layer. The printer 83
forms a reference area on the inner peripheral side than the area where the first intermediate
layer is formed.
[0170] The reference area detector 84 recognizes a current disposition position of the
multilayer information recording medium, based on the reference area. The thickness corrector
82 rotates the multilayer information recording medium to such a position that the current
disposition position of the multilayer information recording medium that has been recognized by
the reference area detector 84 coincides with the disposition position of the multilayer
information recording medium in forming the first intermediate layer. The printer 83 forms-the
second intermediate layer in such a manner that the thickness variation of the multilayer
information recording medium that has been rotated by the thickness corrector 82 is suppressed.
[0171] FIG. 18 is a diagram showing a pattern of a screen, and a signal substrate having a resin
layer formed thereon, using the screen. As shown in FIG. 18, in a normal state, an area 112 at
the inner periphery of the signal substrate is coated with a photosensitive emulsion, and is not
coated with a resin. However, in Example 3, a screen 104 is manufactured by removing a
photosensitive emulsion from an area 131, which is a part of the inner periphery of the area 112.
Screen printing is performed by using the screen 104. Since the area 131 is not coated with a
photosensitive emulsion, a resin passes the area 131. Thus, a resin is coated at a position,
corresponding to the area 131, of the inner periphery of the signal substrate 101, thereby forming
a reference area 132.
[0172] As described above, the reference area 132 is formed at the inner periphery of the
signal substrate 101, and the position of the reference area 132 is detected, which makes it
possible to grasp in which direction the signal substrate 101 is set with respect to the screen 104,
and in which direction the signal substrate 101 is set with respect to the screen printing machine.
[0173] Accordingly, the reference area detector 84 detects the reference area 132 formed on
the signal substrate 101, and the thickness corrector 82 rotates the turntable 103 to such a
position that the detected reference area 132 coincides with a predetermined reference position,

whereby the signal substrate 101 is disposed at a predetermined position. Thereafter, the
thickness corrector 82 rotates the turntable 103 by a rotation angle stored in advance in an
internal memory, and the printer 83 forms a resin layer.
[0174] For instance, thickness variation inherent to the screen printing machine 4 is measured
in advance, the rotation angle of the turntable 103 that enables to correct the measured thickness
variation is calculated, and the calculated rotation angle is stored in the internal memory. The
rotation angle is determined substantially in the same manner as Example 1 and Example 2.
Then, the position of the reference area 132 is detected in forming a first resin layer, and the
signal substrate 101 is disposed at the reference position, based on the detected position of the
reference area 132. Then, in forming a succeeding resin layer, the position of the reference area
132 is detected, and the signal substrate 101 is disposed at the reference position, based on the
detected position of the reference area 132. Then, the signal substrate 101 is rotated in
accordance with the rotation angle stored in the memory in advance, and a UV curable resin is
coated.
[0175] Thus, thickness variation inherent to the screen printing machine can be detected,
without measuring a thickness distribution of a resin layer.
[0176] Further, grasping the above directions of the signal substrate enables to optimize the
setting position of the signal substrate 101 in forming a succeeding resin layer.
[0177] In Example 3, the reference area 132 is formed in such a manner as to increase the
coating amount of a resin onto the inner periphery of the signal substrate 101. The invention is
not specifically limited to the above. As far as the reference area 132 has the dimensions
capable of detecting the position of the signal substrate 101 by a sensor, the shape and the
forming position of the reference area 132 are not limited. Further, in Example 3, the reference
area 132 is formed by additionally coating a resin on an inner periphery where the resin is not
supposed to be coated. Conversely, a resin may be coated on the entirety of an inner periphery,
and a reference area may be formed by removing the resin from a part of the inner periphery.
This enables to use the reference area as a mark indicating the disposing direction of the signal
substrate.
[0178] Further, the multilayer information recording medium manufacturing apparatus 1 in
Example 3 may be provided with the thickness distribution measurer 81 in Example 1 and
Example 2.
[0179] The screen is sandwiched between the squeegee and the signal substrate, when the
squeegee passes over the signal substrate. If the distance between the squeegee and the signal
substrate is small, the amount of resin which may flow over the screen is increased, and the
amount of resin to be coated on the signal substrate is reduced. In view of this, it is preferable

to set the distance between the signal substrate and the squeegee constant. Specifically, in the
case where the thickness of the signal substrate is small, or in the case where the turntable itself
is lowered, the distance between the squeegee and the signal substrate is increased, with the
result that the thickness of a resin layer may be increased. In other words, the thickness of a
resin layer is increased, in the case where the thickness of the signal substrate is small; and the
thickness of a resin layer is increased, in the case where the distance between the squeegee and
the signal substrate is large.
[0180] Further, the thickness corrector 82 may be operable to change the moving speed of the
squeegee for coating a resin in performing screen printing, depending on a position on the signal
substrate where a resin is coated. In the case where the moving speed of the squeegee which
moves over the screen is fast, a resin is less likely to follow the moving squeegee. As a result,
the resin is less likely to stay over the screen, and fall off through the meshes of the screen,
which may increase the amount of resin to be coated on the signal substrate. In other words, as
the moving speed of the squeegee is increased, the thickness of an mtermediate layer to be
formed is increased. In view of this, for instance, the thickness corrector 82 is operable to
change the moving speed of the squeegee between a case of forming an intermediate layer on an
inner periphery of the multilayer information recording medium, and a case of forming an
intermediate layer on an outer periphery of the multifayer information recording medium. In
particular, the thickness corrector 82 is operable to set the moving speed of the squeegee in
forming an intermediate layer on the inner periphery of the multilayer information recording
medium faster than the moving speed of the squeegee in forming an intermediate layer on the
outer periphery of the multilayer information recording medium. This enables to suppress
thickness variation of the multilayer information recording medium in circumferential direction
resulting from screen printing.
[0181] Further, the thickness corrector 82 may change the inclination of the squeegee for
coating a resin in performing screen printing, depending on a position where the resin is coated.
As the inclination of the squeegee with respect to the screen is increased, the thickness of an
intermediate layer to be formed is reduced. In view of this, for instance, the thickness corrector
82 is operable to change the inclination of the squeegee between a case of forming an
intermediate layer on an inner periphery of the multilayer information recording medium, and a
case of forming an intermediate layer on an outer periphery of the multilayer information
recording medium. In particular, the thickness corrector 82 is operable to set the inclination of
the squeegee in forming an intermediate layer on the inner periphery of the multilayer
information recording medium smaller than the inclination of the squeegee in forming an
intermediate layer on the outer periphery of the multilayer information recording medium. This

enables to suppress thickness variation of the multilayer information recording medium in
circumferential direction resulting from screen printing.
[0182] As described above, it is possible to form a multilayer information recording medium
having a more desirable signal characteristic by changing the moving speed of the squeegee
and/or the inclination of the squeegee depending on a position where a resin is coated.
[0183] Similarly to Example 1, in Example 3, the table on which the multilayer information
recording medium is placed may be fixed, and the coating direction of coating a resin may be
changed by placing and rotating the multilayer information recording medium on the table.
[0184] Although Examples 1 through 3 may be individually carried out, it is possible to form a
multilayer information recording medium having a more desirable signal characteristic by
carrying out the invention by combining Examples 1 through 3.
[0185] The aforementioned embodiment and examples mainly include the features having the
following arrangements.
[0186] A multilayer information recording medium manufacturing method according to an
aspect of the invention is a multilayer information recording medium manufacturing method for
manufacturing a multilayer information recording medium having at least three information
recording layers. The method includes a first information recording layer forming step of
forming a first information recording layer on a substrate; a first intermediate layer forming step
of forming a first intermediate layer on the first information recording layer by screen printing; a
second information recording layer forming step of forming a second information recording
layer on the first intermediate layer; a second intermediate layer forming step of forming a
second intermediate layer on the second information recording layer by screen printing in such a
manner that thickness variation of the multilayer information recording medium after the first
intermediate layer has been formed is suppressed; a third information recording layer forming
step of forming a third information recording layer on the second intermediate layer; and a cover
layer forming step of forming a cover layer by a spin coating method in such a manner that a
thickness of an inner periphery of the multilayer information recording medium after the third
information recording layer has been formed becomes smaller than a thickness of an outer
periphery of the multilayer information recording medium.
[0187] With the arrangement described above, the first information recording layer is formed
on the substrate, and the first intermediate layer is formed on the first information recording
layer by screen printing. Then, the second information recording layer is formed on the first
intermediate layer, and the second intermediate layer is formed on the second information
recording layer by screen printing in such a manner that thickness variation of the multilayer
information recording medium after the first intermediate layer has been formed is suppressed.

Then, after the third information recording layer has been formed on the second intermediate
layer, the cover layer is formed by a spin coating method in such a manner that the thickness of
the inner periphery of the multilayer information recording medium becomes smaller than the
thickness of the outer periphery of the multilayer information recording medium.
[0188] The thickness distribution in radial direction of a multilayer information recording
medium can be controlled by a spin coating method. Accordingly, it is possible to suppress
thickness variation in radial direction of the multilayer information recording medium by the
spin coating method. However, in the spin coating method, it is difficult to suppress thickness
variation in circumferential direction of the multilayer information recording medium. Further,
as described above, in screen printing, the inner peripheral thickness of the multilayer
information recording medium tends to increase, as compared with the outer peripheral thickness,
and laminating plural intermediate layers may increase the inner peripheral thickness of the
multilayer information recording medium.
[0189] In view of the above, thickness variation in circumferential direction is reduced in
forming the respective intermediate layers by screen printing, and thickness variation in radial
direction is reduced in forming the cover layer by a spin coating method to thereby make the
distance from a light incident surface of the multilayer information recording medium to a
farthest information recording layer thereof uniform within a plane of the medium.
[0190] In the multilayer infonnation recording medium manufacturing method, preferably, the
second intermediate layer forming step may include a measuring step of measuring thickness
variation of the multilayer information recording medium before the second intermediate layer is
formed and after the first intermediate layer has been formed; and a forming step of forming the
second intermediate layer in such a manner that the thickness variation measured in the
measuring step is suppressed.
[0191] With the arrangement described above, since the thickness variation of the multilayer
information recording medium before the second intermediate layer is formed and after the first
intermediate layer has been formed is measured, and the second intermediate layer is formed in
such a manner that the measured thickness variation is suppressed, it is possible to form the
second intermediate layer after the thickness variation of the first intermediate layer has been
grasped.
[0192] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, a coating direction of coating a resin in performing
the screen printing may be made different from a coating direction in forming the first
intermediate layer.
[0193] With the arrangement as described above, since the second intermediate layer is formed

in such a manner that the coating direction of coating the resin in performing the screen printing
is made different from the coating direction in forming the first intermediate layer, it is possible
to suppress thickness variation in circumferential direction resulting from screen printing.
[0194] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, a substrate holding table that places a substrate of the
multilayer information recording medium thereon may be rotated relative to a moving direction
of a squeegee that coats the resin.
[0195] With the arrangement described above, the coating direction of the resin in forming the
second intermediate layer is changed by rotating the substrate holding table that places a
substrate of the multilayer information recording medium thereon relative to the moving
direction of the squeegee that coats a resin. This enables to easily change the coating direction
of the resin in forming the second intermediate layer, as compared with an arrangement of
changing the moving direction of the squeegee.
[0196] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, the substrate holding table may be rotated in such a
manner that a position of the second intermediate layer having a largest thickness in forming the
second intermediate layer is not overlapped with a position of the first intermediate layer having
a largest thickness.
[0197] With the arrangement described above, since the substrate holding table is rotated in
such a manner that the position of the second intermediate layer having the largest thickness in
forming the second intermediate layer is not overlapped with the position of the first
intermediate layer having the largest thickness, it is possible to suppress thickness variation in
circumferential direction resulting from screen printing.
[0198] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, the substrate holding table may be rotated in such a
manner that a position of the second intermediate layer having a largest thickness in forming the
second intermediate layer is overlapped with a position of the first intermediate layer having a
smallest thickness.
[0199] With the arrangement described above, since the substrate holding table is rotated in
such a manner that the position of the second intermediate layer having the largest thickness in
forming the second intermediate layer is overlapped with the position of the first intermediate
layer having the smallest thickness, it is possible to suppress thickness variation in
circumferential direction resulting from screen printing.
[0200] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, the substrate holding table may be rotated in such a

manner that a coating direction in forming the second intermediate layer perpendicularly
intersects with a coating direction in forming the first intermediate layer.
[0201] With the arrangement described above, since the substrate holding table is rotated in
such a manner that the coating direction in forming the second intermediate layer
perpendicularly intersects with the coating direction in forming the first intermediate layer, it is
possible to suppress thickness variation resulting from the moving direction of the squeegee.
[0202] In the multilayer information recording medium manufacturing method, preferably, a
direction of placing the substrate on a substrate holding table that places a substrate of the
multilayer information recording medium thereon may be made different between the first
intermediate layer forming step and the second intermediate layer forming step.
[0203] With the arrangement described above, since the direction of placing the substrate on
the substrate holding table that places a substrate of the multilayer information recording
medium thereon is made different between the first intermediate layer forming step and the
second intermediate layer forming step, it is possible to suppress thickness variation in
circumferential direction resulting from screen printing.
[0204] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, the substrate may be placed on the substrate holding
table in such a manner that a position of the second intermediate layer having a largest thickness
in forming the second intermediate layer is not overlapped with a position of the first
intermediate layer having a largest thickness.
[0205] With the arrangement described above, since the substrate is placed on the substrate
holding table in such a manner that the position of the second intermediate layer having the
largest thickness in forming the second intermediate layer is not overlapped with the position of
the first intermediate layer having the largest thickness, it is possible to suppress thickness
variation in circumferential direction resulting from screen printing.
[0206] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, the substrate may be placed on the substrate holding
table in such a manner that a position of the second intermediate layer having a largest thickness
in forming the second intermediate layer is overlapped with a position of the first intermediate
layer having a smallest thickness.
[0207] With the arrangement described above, since the substrate is placed on the substrate
holding table in such a manner that the position of the second intermediate layer having the
largest thickness in forming the second intermediate layer is overlapped with the position of the
first intermediate layer having the smallest thickness, it is possible to suppress thickness
variation in circumferential direction resulting from screen printing.

[0208] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, the substrate may be placed on the substrate holding
table in such a manner that a coating direction in forming the second intermediate layer
perpendicularly intersects with a coating direction in forming the first intermediate layer.
[0209] With the arrangement described above, since the substrate is placed on the substrate
holding table in such a manner that the coating direction in forming the second intermediate
layer perpendicularly intersects with the coating direction in forming the first intermediate layer,
it is possible to suppress thickness variation resulting from the moving direction of the squeegee.
[0210] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, an inclination of a squeegee that coats a resin in
performing the screen printing may be changed depending on a position where the resin is coated.
[0211] With the arrangement described above, the inclination of the squeegee that coats a resin
in performing the screen printing is changed depending on the position where the resin is coated.
As the inclination of the squeegee with respect to the screen is increased, the thickness of an
intermediate layer to be formed is decreased. Accordingly, for instance, it is possible to
suppress thickness variation in circumferential direction resulting from screen printing by
changing the inclination of the squeegee between the case of forming an intermediate layer on
the inner periphery of the multilayer information recording medium, and the case of forming an
intermediate layer on the outer periphery of the multilayer information recording medium.
[0212] In the multilayer information recording medium manufacturing method, preferably, in
the second intermediate layer forming step, a moving speed of a squeegee that coats a resin in
performing the screen printing may be changed depending on a position where the resin is coated.
[0213] With the arrangement described above, the moving speed of the squeegee that coats a
resin in performing the screen printing is changed depending on the position where the resin is
coated. As the moving speed of the squeegee is increased, the thickness of an intermediate
layer to be formed is increased. Accordingly, for instance, it is possible to suppress thickness
variation in circumferential direction resulting from screen printing by changing the moving
speed of the squeegee between the case of forming an intermediate layer on the inner periphery
of the multilayer information recording medium, and the case of forming an intermediate layer
on the outer periphery of the multilayer information recording medium.
[0214] In the multilayer information recording medium manufacturing method, preferably, in
the first intermediate layer forming step, a reference area for use in recognizing a disposition
position of the multilayer information recording medium with respect to a coating direction of
coating a resin in forming the first intermediate layer may be formed, and the second
intermediate layer forming step may include a recognizing step of recognizing a current

disposition position of the multilayer information recording medium, based on the reference area,
a disposition position changing step of rotating the multilayer information recording medium in
such a manner that the current disposition position of the multilayer information recording
medium recognized in the recognizing step coincides with a disposition position of the
multilayer information recording medium in forming the first intermediate layer, and a forming
step of forming the second intermediate layer in such a manner that thickness variation of the
multilayer information recording medium rotated in the disposition position changing step is
suppressed.
[0215] With the arrangement described above, the reference area for use in recognizing the
disposition position of the multilayer information recording medium with respect to the coating
direction of coating a resin in forming the first intermediate layer is formed. Then, the current
disposition position of the multilayer information recording medium is recognized, based on the
reference area, and the multilayer information recording medium is rotated in such a manner that
the recognized current disposition position of the multilayer information recording medium
coincides with the disposition position of the multilayer information recording medium in
forming the first intermediate layer. Thereafter, the second intermediate layer is formed in such
a manner that thickness variation of the rotated multilayer information recording medium is
suppressed.
[0216] Generally, a process of forming an information recording layer, and a process of
forming an intermediate layer are performed by different devices. Accordingly, there is a
likelihood that the disposition position of the multilayer information recording medium after the
first intermediate layer has been formed, and the disposition of the multilayer information
recording medium in forming the second intermediate layer may differ from each other. In
view of this, the reference area for use in recognizing the disposition position of the multilayer
information recording medium after the first intermediate layer has been formed is formed; and
the multilayer information recording medium is rotated in such a manner that the current
disposition position of the multilayer information recording medium that has been recognized
based on the reference area coincides with the disposition position of the multilayer information
recording medium after the first intermediate layer has been formed.
[0217] Thus, since the disposition position of the multilayer information recording medium
after the first intermediate layer has been formed, and the disposition position of the multilayer
information recording medium in forming the second intermediate layer coincide with each other,
it is possible to suppress thickness variation inherent to a screen printing machine can be
suppressed without the need of measuring thickness variation of the multilayer information
recording medium after the first intermediate layer has been formed.

[0218] In the multilayer information recording medium manufacturing method, preferably, in
the first intermediate layer forming step, the reference area may be formed at an inner peripheral
side than an area where the first intermediate layer is formed.
[0219] With the arrangement described above, since the reference area is formed at the inner
peripheral side than the area where the first intermediate layer is formed, it is possible to form
the reference area simultaneously in forming the first intermediate layer, thereby easily forming
the reference area.
[0220] A multilayer information recording medium manufacturing apparatus according to
another aspect of the invention is a multilayer information recording medium manufacturing
apparatus for manufacturing a multilayer information recording medium having at least three
information recording layers. The apparatus includes an information recording layer forming
section that forms at least three information recording layers; an intermediate layer forming
section that forms a first intermediate layer by screen printing, and forms a second intermediate
layer by screen printing in such a manner that thickness variation of the multilayer information
recording medium having the first intermediate layer is suppressed; and a cover layer forming
section that forms a cover layer by a spin coating method in such a manner that a thickness of an
inner periphery of the multilayer information recording medium having the second intermediate
layer becomes smaller than a thickness of an outer periphery of the multilayer information
recording medium.
[0221] With the arrangement described above, at least the three information recording layers
are formed, the first information recording layer is formed by screen printing, and the second
information recording layer is formed by screen printing in such a manner that thickness
variation of the multilayer information recording medium after the first intermediate layer has
been formed is suppressed. Then, after the second information recording layer has been formed,
the cover layer is formed by a spin coating method in such a manner that the thickness of the
inner periphery of the multilayer information recording medium becomes smaller than the
thickness of the outer periphery of the multilayer information recording medium.
[0222] The thickness distribution in radial direction of a multilayer information recording
medium can be controlled by a spin coating method. Accordingly, it is possible to suppress
thickness variation in radial direction of the multilayer information recording medium by the
spin coating method. However, in the spin coating method, it is difficult to suppress thickness
variation in circumferential direction of the multilayer information recording medium. Further,
as described above, in screen printing, the inner peripheral thickness of the multilayer
information recording medium tends to increase, as compared with the outer peripheral thickness,
and laminating plural intermediate layers may increase the inner peripheral thickness of the

multilayer information recording medium.
[0223] In view of the above, thickness variation in circumferential direction is reduced in
forming the respective intermediate layers by screen printing, and thickness variation in radial
direction is reduced in forming the cover layer by a spin coating method to thereby make the
distance from a light incident surface of the multilayer information recording medium to a
farthest information recording layer thereof uniform within a plane of the medium.
[0224] A multilayer information recording medium according to yet another aspect of the
invention includes at least three information recording layers; a plurality of intermediate layers to
be formed between the information recording layers; and a cover layer including a light incident
surface, wherein the plurality of the intermediate layers include a first intermediate layer formed
by screen printing, and a second intermediate layer formed by screen printing in such a manner
that thickness variation of the multilayer information recording medium having the first
intermediate layer is suppressed, and the cover layer is formed by a spin coating method in such
a manner that a thickness of an inner periphery of the multilayer information recording medium
having the second intermediate layer becomes smaller than a thickness of an outer periphery of
the multilayer information recording medium.
[0225] With the arrangement described above, at least the three information recording layers
are formed, the first information recording layer is formed by screen printing, and the second
information recording layer is formed by screen printing in such a manner that thickness
variation of the multilayer information recording medium after the first intermediate layer has
been formed is suppressed. Then, after the second information recording layer has been formed,
the cover layer is formed by a spin coating method in such a manner that the thickness of the
inner periphery of the multilayer information recording medium becomes smaller than the
thickness of the outer periphery of the multilayer information recording medium.
[0226] The thickness distribution in radial direction of a multilayer information recording
medium can be controlled by a spin coating method. Accordingly, it is possible to suppress
thickness variation in radial direction of the multilayer information recording medium by the
spin coating method. However, in the spin coating method, it is difficult to suppress thickness
variation in circumferential direction of the multilayer information recording medium. Further,
as described above, in screen printing, the inner peripheral thickness of the multilayer
information recording medium tends to increase, as compared with the outer peripheral thickness,
and laminating plural intermediate layers may increase the inner peripheral thickness of the
multilayer information recording medium.
[0227] In view of the above, thickness variation in circumferential direction is reduced in
forming the respective intermediate layers by screen printing, and thickness variation in radial

direction is reduced in forming the cover layer by a spin coating method to thereby make the
distance from a light incident surface of the multilayer information recording medium to a
farthest information recording layer thereof uniform within a plane of the medium.
[0228] The embodiments or the examples described in the detailed description of the invention
are provided to clarify the technical contents of the invention. The invention should not be
construed to be limited to the embodiments or the examples. The invention may be modified in
various ways as far as such modifications do not depart from the spirit and the scope of the
invention hereinafter defined.
INDUSTRIAL APPLICABILITY
[0229] The inventive multilayer recording medium manufacturing method, the inventive
multilayer information recording medium manufacturing apparatus, and the inventive multilayer
information recording medium enable to make a distance from a light incident surface of the
multilayer information recording medium to a farthest information recording layer thereof
uniform within a plane of the medium; and accordingly are useful as a multilayer information
recording medium including at least three information recording layers, plural intermediate
layers formed between the information recording layers, and a cover layer having a light incident
surface, a multilayer information recording method for manufacturing the multilayer information
recording medium, and a multilayer information recording medium manufacturing apparatus for
manufacturing the multilayer information recording medium. Further, the invention is
applicable to e.g. manufacturing a large-capacity memory.

WHAT IS CLAIMED IS:
1. A multilayer information recording medium manufacturing method for
manufacturing a multilayer information recording medium having at least three information
recording layers, the method comprising:
a first information recording layer forming step of forming a first information recording
layer on a substrate;
a first intermediate layer forming step of forming a first intermediate layer on the first
information recording layer by screen printing;
a second information recording layer forming step of forming a second information
recording layer on the first intermediate layer;
a second intermediate layer forming step of forming a second intermediate layer on the
second information recording layer by screen printing in such a manner that thickness variation
of the multilayer information recording medium after the first intermediate layer has been
formed is suppressed;
a third information recording layer forming step of forming a third information
recording layer on the second intermediate layer; and
a cover layer forming step of forming a cover layer by a spin coating method in such a
manner that a thickness of an inner periphery of the multilayer information recording medium
after the third information recording layer has been formed becomes smaller than a thickness of
an outer periphery of the multilayer information recording medium.
2. The multilayer information recording medium manufacturing method
according to claim 1, wherein
the second intermediate layer forming step includes
a measuring step of measuring thickness variation of the multilayer
information recording medium before the second intermediate layer is formed and after the first
intermediate layer has been formed; and
a forming step of forming the second intermediate layer in such a manner that
the thickness variation measured in the measuring step is suppressed.
3. The multilayer information recording medium manufacturing method
according to claim 1 or claim 2, wherein
in the second intermediate layer forming step, a coating direction of coating a resin in
performing the screen printing is made different from a coating direction in forming the first
intermediate layer.

4. The multilayer information recording medium manufacturing method
according to claim 3, wherein
in the second intermediate layer forming step, a substrate holding table that places a
substrate of the multilayer information recording medium thereon is rotated relative to a moving
direction of a squeegee that coats the resin.
5. The multilayer information recording medium manufacturing method
according to claim 4, wherein
in the second intermediate layer forming step, the substrate holding table is rotated in
such a manner that a position of the second intermediate layer having a largest thickness in
forming the second intermediate layer is not overlapped with a position of the first intermediate
layer having a largest thickness.
6. The multilayer information recording medium manufacturing method
according to claim 5, wherein
in the second intermediate layer forming step, the substrate holding table is rotated in
such a manner that a position of the second intermediate layer having a largest thickness in
forming the second intermediate layer is overlapped with a position of the first intermediate layer
having a smallest thickness.
7. The multilayer information recording medium manufacturing method
according to claim 5, wherein
in the second intermediate layer forming step, the substrate holding table is rotated in
such a manner that a coating direction in fonning the second intermediate layer perpendicularly
intersects with a coating direction in forming the first intermediate layer.
8. The multilayer information recording medium manufacturing method
according to claim 3, wherein
a direction of placing the substrate on a substrate holding table that places a substrate of
the multilayer information recording medium thereon is made different between the first
intermediate layer forming step and the second intermediate layer forming step.
9. The multilayer information recording medium manufacturing method
according to claim 8, wherein

in the second intermediate layer forming step, the substrate is placed on the substrate
holding table in such a manner that a position of the second intermediate layer having a largest
thickness in forming the second intermediate layer is not overlapped with a position of the first
intermediate layer having a largest thickness.
10. The multilayer information recording medium manufacturing method
according to claim 8, wherein
in the second intermediate layer forming step, the substrate is placed on the substrate
holding table in such a manner that a position of the second intermediate layer having a largest
thickness in forming the second intermediate layer is overlapped with a position of the first
intermediate layer having a smallest thickness.
11. The multilayer information recording medium manufacturing method
according to claim 5, wherein
in the second intermediate layer forming step, the substrate is placed on the substrate
holding table in such a manner that a coating direction in forming the second intermediate layer
perpendicularly intersects with a coating direction in forming the first intermediate layer.
12. The multilayer information recording medium manufacturing method
according to any one of claims 1 through 11, wherein
in the second intermediate layer forming step, an inclination of a squeegee that coats a
resin in performing the screen printing is changed depending on a position where the resin is
coated.
13. The multilayer information recording medium manufacturing method
according to any one of claims 1 through 12, wherein
in the second intermediate layer forming step, a moving speed of a squeegee that coats
a resin in performing the screen printing is changed depending on a position where the resin is
coated.
14. The multilayer information recording medium manufacturing method
according to claim 1, wherein
in the first intermediate layer forming step, a reference area for use in recognizing a
disposition position of the multilayer information recording medium with respect to a coating
direction of coating a resin in forming the first intermediate layer is formed, and

the second intermediate layer forming step includes
a recognizing step of recognizing a current disposition position of the
multilayer information recording medium, based on the reference area,
a disposition position changing step of rotating the multilayer information
recording medium in such a manner that the current disposition position of the multilayer
information recording medium recognized in the recognizing step coincides with a disposition
position of the multilayer information recording medium in forming the first intermediate layer,
and
a forming step of forming the second intermediate layer in such a manner that
thickness variation of the multilayer information recording medium rotated in the disposition
position changing step is suppressed.
15. The multilayer information recording medium manufacturing method
according to claim 14, wherein
in the first intermediate layer forming step, the reference area is formed at an inner
peripheral side than an area where the first intermediate layer is formed.
16. A multilayer information recording medium manufacturing apparatus for
manufacturing a multilayer information recording medium having at least three information
recording layers, the apparatus comprising:
an information recording layer forming section that forms at least three information
recording layers;
an intermediate layer forming section that forms a first intermediate layer by screen
printing, and forms a second intermediate layer by screen printing in such a manner that
thickness variation of the multilayer information recording medium having the first intermediate
layer is suppressed; and
a cover layer forming section that forms a cover layer by a spin coating method in such
a manner that a thickness of an inner periphery of the multilayer information recording medium
having the second intermediate layer becomes smaller than a thickness of an outer periphery of
the multilayer information recording medium.
17. A multilayer information recording medium comprising:
at least three information recording layers;
a plurality of intermediate layers to be formed between the information recording
layers; and

a cover layer including a light incident surface, wherein
the plurality of the intermediate layers include a first intermediate layer formed by
screen printing, and a second intermediate layer formed by screen printing in such a manner that
thickness variation of the multilayer information recording medium having the first intermediate
layer is suppressed, and
the cover layer is formed by a spin coating method in such a manner that a thickness of
an inner periphery of the multilayer information recording medium having the second
intermediate layer becomes smaller than a thickness of an outer periphery of the multilayer
information recording medium.

The invention provides a multilayer information recording medium manufacturing
method, a multilayer information recording medium manufacturing apparatus, and a multilayer
information recording medium that enable to make a distance from a light incident surface of the
multilayer information recording medium to a farthest information recording layer thereof
uniform within a plane of the medium. A multilayer information recording medium
manufacturing apparatus (1) is provided with a sputtering device (3) that forms at least three
information recording layers, a screen printing machine (4) that forms a first intermediate layer
by screen printing, and forms a second intermediate layer by screen printing in such a manner
that thickness variation of the multilayer information recording medium having the first
intermediate layer is suppressed, and a spin coating device (5) that forms a cover layer by a spin
coating method in such a manner that a thickness of an inner periphery of the multilayer
information recording medium having the second intermediate layer becomes smaller than a
thickness of an outer periphery of the multilayer information recording medium.