JP2002074766A - Manufacturing method of optical recording medium - Google Patents

Abstract

(57) [Problem] To provide a warp amount of an optical disc after lamination within an allowable range even when manufacturing conditions of one substrate are relaxed in order to extend the life of a substrate manufacturing apparatus. Is possible, and the productivity is excellent. SOLUTION: A first substrate manufacturing step of manufacturing a first substrate having a signal surface by injection molding polycarbonate,
The second having a dummy surface by injection molding polycarbonate
A second substrate manufacturing step of manufacturing the first substrate and the first substrate and the second substrate, with the signal surface side of the first substrate and the dummy surface side of the second substrate facing each other. And a laminating step of laminating, wherein the conditions at the time of injection molding in the first substrate manufacturing step are set to be more relaxed than the conditions at the time of injection molding in the second substrate manufacturing step. The warp amount A of the second substrate is set to -0.4 °
≦ A ≦ + 0.4 °.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical recording medium comprising two substrates bonded together.

[0002]

2. Description of the Related Art Conventionally, as an optical recording medium using light for recording and reproduction, an optical disk using a substrate formed by molding a synthetic resin such as polycarbonate is known. The optical disc includes a read-only type in which a pre-recorded signal is reproduced, a write-once type in which recording can be performed only once, and a rewritable type in which recording can be performed a plurality of times.

In particular, for rewritable optical disks,
There is an increasing demand for a further increase in capacity so that it can be used as an external recording medium of a computer or used for recording digital television broadcasts, which will be in full swing in several years.

In order to improve the recording density of such an optical disk, it is necessary to reduce the diameter of a beam spot emitted from a light source to the optical disk. In order to reduce the beam spot diameter, it is necessary to shorten the wavelength of the semiconductor laser used as the light source and increase the numerical aperture (NA) of the objective lens as measures against the optical pickup.

[0005] Among the measures for reducing the beam spot diameter, regarding the shortening of the wavelength of the semiconductor laser, the current CD
(Compact Disk: registered trademark) has a wavelength of 780 nm.
Near-infrared light, DVD (Digital Versatile Dis
k: registered trademark) has already adopted a wavelength of 650 nm. Further, it is certain that a GaN-based blue-violet laser having a wavelength of about 410 nm is employed. As described above, the wavelength of semiconductor lasers has been rapidly reduced.

[0006] Among the measures for reducing the beam spot diameter, increasing the numerical aperture of the objective lens is a problem.
As a result, the margin for the warpage of the optical disk is surely reduced. Specifically, as the numerical aperture of the objective lens mounted on the optical pickup is increased for the purpose of increasing the recording density of the optical disk, the larger the numerical aperture of the objective lens is, the more the optical disk is warped. The allowable value of the angle (tilt angle) formed by the axes of the optical system becomes smaller. The coma caused by the tilt angle is proportional to the cube of the numerical aperture, and the astigmatism is proportional to the square of the numerical aperture. In addition, considering the diffraction limit of the objective lens, such an aberration is 0.07 which is Marachal's allowable value.
There is a strict requirement that λ should not be exceeded.

[0007] In recent years, there has been proposed an optical disk formed by bonding two thin transparent substrates. For example, DV
D has a thickness of 1.2 mm, which is the same as a conventional CD, by bonding a 0.6 mm substrate, which is half the thickness of the CD substrate, with the recording layer inside. DVD
By using a thin substrate of 0.6 mm, the absolute value of the optical path length passing through the substrate can be reduced, and the influence of the tilt angle can be suppressed. In addition, a DVD is formed by bonding two thin substrates to a thickness of 1.2 mm so that
The VD itself can be provided with sufficient mechanical strength, and can be compatible with a conventional CD recording / reproducing apparatus.

By the way, there is a DVD capable of so-called double-sided recording / reproduction in which both of the two bonded substrates are used for recording / reproduction. Such a double-sided recording / reproducing D
VD is produced as follows. First, a mold apparatus is prepared in which a stamper having a predetermined uneven shape is attached to a surface constituting a cavity of the mold. Then, a resin such as polycarbonate is injection-molded in the cavity of the mold apparatus, thereby obtaining a transparent substrate on which the concave and convex shape of the stamper has been transferred to one main surface.

Next, various functional layers such as a reflective layer, a phase change type recording layer, an organic dye type recording layer, and a dielectric layer are formed on one main surface of the substrate having the uneven shape according to the purpose of use. Film. Further, a protective layer is formed over the functional layer.

[0010] Then, the substrate on which the functional layer and the protective layer are formed is attached to each other with an adhesive or the like with the sides on which the functional layer and the protective layer are formed facing each other, whereby a double-sided recording / reproducing DVD is formed. Complete.

The two substrates used in the above-mentioned double-sided recording / reproducing DVD have one main surface provided with an uneven shape such as a groove and a land. Clear transfer of the concave and convex shape of the stamper and reduction of the load on the mold apparatus conflict with each other, so that optimal manufacturing conditions are naturally set.
As a result, the manufacturing conditions for the two substrates are substantially the same. Therefore, the warp directions and the warp amounts of the two substrates manufactured under substantially the same conditions are also substantially the same.

When these substrates are bonded to each other, since the two substrates are warped almost plane-symmetrically, the stress that causes the warpage of each substrate, that is, the internal stress is canceled out, and as a result, an optical disk with less warpage is completed. Will do.
Therefore, in a double-sided recording / reproducing DVD, even if the amount of warpage of the substrate is large at the time of molding the substrate, the warpage is offset by bonding the two substrates, and the amount of warpage of the disc after bonding is reduced. It fell within the acceptable range and did not matter much.

It is noted that the amount of warpage of, for example, an optical disk having a diameter of 120 mm is preferably in the range of not less than -0.35 ° and not more than + 0.35 °. But the substrate is
It has the property that the amount of warpage increases with time. Therefore, in order to maintain high flatness over a long period of time, the amount of warpage of the substrate immediately after molding the substrate is −0.25 ° or more and + 0.05 °.
It needs to be in the range of 25 ° or less.

In recent years, not only large-capacity recording media,
There is an increasing demand from users for recording media having various variations of recording capacities. In order to meet such a user's request, a so-called single-sided recording / reproducing DVD capable of recording / reproducing a signal on only one side has been put to practical use. In this single-sided recording / reproducing DVD, one of the substrates is provided with a highly accurate concave / convex shape such as a groove or a servo pattern on one principal surface as a signal surface. Further, the other substrate is provided with a groove shape which is not involved in recording / reproducing a signal on one principal surface for the purpose of improving mechanical strength, and serves as a dummy surface.

As described above, since the groove shape of the substrate having the dummy surface does not contribute to the recording and reproduction of signals, the substrate having the dummy surface is not required to be as precise as the substrate having the signal surface. Therefore, when manufacturing a substrate having a dummy surface, the temperature of the mold and the mold clamping pressure of the mold in the injection molding step can be relatively relaxed as compared with the condition of the substrate having the signal surface. Therefore, the life of a stamper used for manufacturing a substrate having a dummy surface can be extended.

[0016]

However, as described above, in order to extend the life of a stamper for manufacturing a substrate having a dummy surface, the conditions for manufacturing the substrate having a dummy surface are intentionally changed to those of a substrate having a signal surface. If the manufacturing conditions are relaxed, the manufacturing conditions for the two substrates will be different. As a result, the direction of warpage and the amount of warpage differ between the substrate having the dummy surface and the substrate having the signal surface.

When substrates manufactured under such different conditions are bonded to each other, the two substrates are warped asymmetrically, and therefore the warp remains on the optical disk without canceling each other. There is a risk that the warpage of the two substrates will be synergistic to give a larger warp to the optical disc. As a result, the warp amount of the optical disk is within the allowable range of -0.25.
There is a problem that the range exceeds + 0.25 °.

In the conventional DVD production process, the amount of warpage of an optical disk after two substrates are bonded is measured, and if the amount of warpage of the optical disk falls within an allowable range, a non-defective optical disk is warped. Those exceeding the allowable range were determined to be defective. However, in such a method, various functional layers and protective layers are formed on a defective substrate that generates a defective product after bonding, similarly to a non-defective product. Further, when the amount of warpage is determined after bonding, it is impossible to feed back to the molding process, so that a substrate in a good state is bonded to a defective substrate, thereby causing a decrease in productivity.

Accordingly, the present invention has been proposed in view of such a conventional situation, and even if the manufacturing conditions of one substrate are relaxed in order to extend the life of the substrate manufacturing apparatus, the present invention is not limited to this. It is an object of the present invention to provide a method for manufacturing an optical recording medium that allows the amount of warpage of an optical disc after alignment to be within an allowable range and that is excellent in productivity.

[0020]

In order to achieve the above-mentioned object, a method for manufacturing an optical recording medium according to the present invention comprises a first method for manufacturing a first substrate having a signal surface by injection molding polycarbonate. A second step of manufacturing a second substrate having a dummy surface by injection molding polycarbonate.
And a bonding step of bonding the first substrate and the second substrate with the signal surface side of the first substrate and the dummy surface side of the second substrate facing each other. The conditions at the time of injection molding in the first substrate manufacturing step are set to be more relaxed than the conditions at the time of injection molding in the second substrate manufacturing step, and the amount of warpage of the first substrate and the second substrate A is characterized by being in the range of −0.4 ° ≦ A ≦ + 0.4 °.

In the method for manufacturing an optical recording medium configured as described above, the conditions during injection molding in the second substrate manufacturing step are made more relaxed than the conditions during injection molding in the first substrate manufacturing step. However, by defining the amount of warpage of each substrate, the warp of the first substrate and the warp of the second substrate can be canceled in a well-balanced manner. Further, by measuring the amount of warpage of the substrate immediately after injection molding, it is possible to determine a defective substrate that causes a large warp in the bonded optical recording medium.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of a method for manufacturing an optical recording medium according to the present invention will be described in detail with reference to the drawings.

First, as shown in FIG. 1, a first substrate 1 having a signal surface on one principal surface and a second substrate 2 having a non-signal surface, ie, a dummy surface on one principal surface, are formed of an adhesive. An optical disk bonded through the adhesive layer 3 will be described. This optical disk is a so-called single-sided recording / reproduction type optical disk in which recording / reproduction is performed only on the first substrate 1 having a signal surface.

The first substrate 1 and the second substrate 2 are made of polycarbonate which is a resin having transparency, and have a diameter of about 120 mm ± 0.2 mm by an injection molding method as described later.
It is formed in a disk shape of 3 mm and a thickness of about 0.6 mm ± 0.05 mm.

On the signal surface side of the first substrate 1, that is, on one main surface on the side facing the second substrate 2, grooves 10 and lands 11 formed between the grooves 10 as shown in FIG. Are formed concentrically or spirally.
In addition, the second substrate 2 is provided on one principal surface which is a dummy surface side,
Grooves not involved in signal recording / reproduction are formed.

The groove 10 and the land 1 of the first substrate 1
The first functional layer 4 is formed on the surface on which 1 is formed. When the phase change recording method is applied to an optical disc, the first substrate 1 having a signal surface is provided with a first functional layer 4
For example, a first dielectric layer, a recording layer, a second dielectric layer, and a reflective heat dissipation layer are sequentially laminated. Further, a first protective layer 5 is formed on the uppermost layer of the functional layers of the first substrate 1. The second substrate 2 has a second main surface on one main surface.
A reflective heat radiation layer is formed as the functional layer 6, and a second protective layer 7 is formed on the reflection heat radiation layer.

The single-sided recording / reproducing type optical disk having the above-described configuration records and reproduces signals as described below. The recording of the signal of the optical disc is performed by the first
By irradiating the track with laser light having a power to cause a reversible phase change in the recording layer from the substrate 1 side of
The reproduction of the signal from the optical disk is performed by irradiating the track with a weak laser beam and detecting a change in the intensity of the reflected light.

More specifically, signal recording is performed by irradiating a laser beam having an optimum power for recording to heat the recording layer of the portion irradiated with the laser beam to a melting point or higher, and to heat the recording layer to the melting point or higher. This is performed by rapidly cooling the heated portion to an amorphous state. Also, signal erasure is
By irradiating the recording layer with laser light, the recording layer is heated to a temperature equal to or higher than the crystallization temperature and equal to or lower than the melting point, so that the relevant portion of the recording layer is brought into a crystalline state.

Next, a method of manufacturing the optical disk having the above-described configuration will be described.

First, a method for manufacturing the first substrate 1 by injection molding using a mold apparatus as shown in FIG. 3 will be described. This mold device includes a fixed mold 21, a movable mold 22, and an outer peripheral mold 23.
1. It has a cavity formed by abutting the movable mold 22 and the outer peripheral mold 23. In this mold apparatus, the movable mold 22 moves in the direction approaching the fixed mold 21, and the outer mold 23 attached to the movable mold 22 comes into contact with the fixed mold 21 to form a cavity. It is formed. In this mold apparatus, the first substrate 1 is molded by filling molten polycarbonate into a cavity which is a molding space.

The fixed mold 21 is fixedly mounted on a fixed platen 24, and a stamper 25 is mounted on a surface constituting a cavity. An inner peripheral side stamper holder 26 for attaching a stamper 25 is
In addition, an outer stamper holder 27 is provided. The inner peripheral side stamper holder 26 has a projection formed to project into the cavity. The protrusion formed on the inner peripheral side stamper holder 26 is formed in an annular shape having a diameter slightly larger than the diameter of the center hole of the stamper 25. Further, the outer peripheral side stamper holder 27 is formed in a ring shape having a center hole slightly larger than the outer diameter of the cavity and slightly smaller than the outer diameter of the stamper 25. The outer peripheral side stamper holder 27 is assembled to the fixed mold 21 by mounting screws or the like.

The stamper 25 is formed in a ring shape having a center hole, has a region where a pit pattern or groove 10 is formed on one main surface, and is fixed with one main surface facing the cavity. It is attached to the mold 21. When attaching the stamper 25 to the fixed mold 21, the center hole of the stamper 25 is relatively engaged with the protrusion of the inner peripheral side stamper holder 26, and the outer peripheral part of the stamper 25 is fixed to the outer peripheral side stamper holder 27 with the stationary mold 21. 21.

The fixed mold 21 is provided with a fixed-side temperature adjusting flow path 29 to which high-pressure water is supplied between the fixed mold 21 and the fixed platen 24. The fixed-side temperature adjustment flow path 29 is connected to a water supply device (not shown), and can supply water to adjust the fixed mold 21 and the inside of the cavity to desired temperatures.

Further, a sprue bush 30 serving as a supply path for supplying the molten polycarbonate into the cavity is formed substantially in the center of the fixed mold 21. The sprue bush 30 is connected to a material supply device (not shown) at an end opposite to an end which is connected to the cavity. The sprue bush 30 serves as a supply path when molten polycarbonate is supplied from the material supply device into the cavity.

On the other hand, the movable mold 22 is disposed so as to face the fixed mold 21, and is movable toward and away from the fixed mold 21 by guide means and driving means (not shown). The movable mold 22 has a punch 31 that cuts the center of the formed first substrate 1 at the approximate center thereof.
And a push pin 32 for pushing out a central portion cut by the punch 31 and an eject pin 33 for releasing the formed substrate from the movable mold 22.

The punch 31 is provided with a sprue bush 30
It cuts a runner portion or the like from the solidified polycarbonate supplied into the cavity from above, and has an outer diameter substantially the same as the center hole of the first substrate 1 to be molded. The punch 31 can be moved in a direction to protrude into the cavity by a guide unit or a driving unit (not shown). Therefore, after the polycarbonate filled in the cavity is solidified, the punch 31 cuts the runner portion and the like to form a center hole.

The push-out pin 32 is formed in a rod shape and is disposed at the center of the punch 31. This push pin 32
Can be moved in the direction of protruding into the cavity by guide means and drive means (not shown).
The part cut by 1 is removed. Therefore, after the polycarbonate filled in the cavity is solidified, the pushing pin 32 is pushed out,
The runner part and the sprue, that is, the runner part and the polycarbonate accumulated in the supply path of the sprue bush 30 can be removed.

The eject pin 33 has a cylindrical shape having an inner diameter substantially the same as the outer diameter of the punch 31, and is disposed so as to surround the punch 31. The eject pin 33 can be moved in a direction in which the eject pin 33 protrudes into the cavity by guide means or drive means (not shown). Therefore, after the cavity is filled with polycarbonate and the center hole of the first substrate 1 is formed as described above, the eject pins 33 press the inner peripheral side of the first substrate 1 to move the movable mold 22. Then, the first substrate 1 is released from the mold.

The movable mold 22 is provided with a movable-side temperature-adjusting flow path 34 formed in a ring shape and located immediately below a surface constituting the cavity. The movable-side temperature adjusting flow path 34 is connected to a water supply device in the same manner as the fixed mold 21 described above, and the movable mold 22 and the cavity can be adjusted to desired temperatures by supplying water. .

On the other hand, the outer peripheral mold 23 is formed in an annular shape,
The movable mold 22 is attached so as to be fitted on the outer peripheral side of the surface constituting the cavity. This outer peripheral mold 23 is
In conjunction with the movable mold 22 that moves closer to and away from the fixed mold 21, it moves closer to and away from the fixed mold 21.

In the mold apparatus configured as described above, when forming the first substrate 1, first, the movable mold 22 and the outer peripheral mold 23 are moved in a direction approaching the fixed mold 21. , Fixed mold 21, movable mold 22, and outer peripheral mold 23
Are formed to form a cavity.

Next, the molten polycarbonate is filled in the cavity. The polycarbonate is heated and melted in the material supply device, and supplied into the cavity using the sprue bush 30 as a supply path.

Next, the polycarbonate filled in the cavity is cooled and hardened, and the polycarbonate is clamped. When cooling the polycarbonate, water is supplied to the fixed-side temperature adjustment channel 29 and the movable-side temperature adjustment channel 34. The polycarbonate filled in the cavity is cooled by water. Further, when performing mold clamping on the polycarbonate, the movable mold 22 is moved in a direction closer to the fixed mold 21. For this reason, the polycarbonate filled in the cavity is pressurized, and the stamper 2 is pressed.
The shape of one main surface facing the cavity side of No. 5 is reliably transferred.

Next, after the polycarbonate is sufficiently cooled and hardened, the punch 31 is moved in a direction approaching the fixed mold 21, that is, in a direction protruding into the cavity. By moving the punch 31 in the direction of protruding into the cavity, the runner portion and the sprue portion of the solidified polycarbonate can be cut.
As a result, after the polycarbonate filled in the cavity is solidified, a center hole is formed.

Next, the movable mold 22 is moved in a direction in which the movable mold 22 is separated from the fixed mold 21. As a result, the cured first substrate 1 is separated from the stamper 25 attached to the fixed mold 21, and one main surface is exposed to the outside. That is, the first substrate 1 includes the movable mold 2
It is fitted in the space defined by the outer mold 2 and the outer peripheral mold 23 with one main surface exposed.

At this time, in the mold apparatus, the portion cut by the punch 31 described above is removed by moving the push pin 32 in a direction to protrude into the cavity. In other words, when the push-out pins 32 are pushed out, the runner part and the sprue, that is, the runner part and the polycarbonate accumulated in the supply passage of the sprue bush 30 can be removed.

Next, the first substrate 1 filled in the space formed by the movable mold 22 and the outer mold 23 is taken out. At this time, in the mold apparatus, the eject pin 33 is moved in a direction to protrude into the cavity, thereby pressing the inner peripheral side of the first substrate 1 to form a space formed by the movable mold 22 and the outer peripheral mold 23. Is released from the first substrate 1. As described above, the groove 10 and the land 11
Is obtained.

Next, the second substrate 2 having a dummy surface
Is manufactured by an injection molding method using a mold apparatus as shown in FIG. 3 as in the case of the first substrate 1 described above. However, since the second substrate 2 is formed with grooves that do not contribute to the recording and reproduction of signals, instead of the concave and convex shapes of the grooves 10 and the lands 11, the second substrate 2 is attached to the surface of the fixed mold 21 that forms the cavity. A stamper having a shape corresponding to the groove is used.

By the way, the mold clamping pressure of the mold device required to mold the polycarbonate into a predetermined shape is very large, and therefore the load on the stamper 25 is also large. For this reason, the stamper 25 attached to the mold device is used.
However, the surface of the mold attached to the mold device becomes uneven with the long-term use, and eventually becomes unusable. Therefore, in the present invention, in order to extend the service life of the stamper used when manufacturing the second substrate 2 having the dummy, the production of the mold temperature, the mold clamping pressure, and the like for manufacturing the second substrate 2 is performed. The conditions are relatively relaxed as compared with the conditions for manufacturing the first substrate 1 having the signal surface. For this reason, the burden on the stamper used when manufacturing the second substrate 2 can be relatively reduced, and the life of the stamper used when manufacturing the second substrate 2 can be extended.

The specific manufacturing conditions for keeping the warp amount A of the first substrate 1 and the second substrate 2 within the above range will be described later in detail.

Next, the first produced as described above.
A first dielectric layer, a recording layer, a second dielectric layer, a reflective heat dissipation layer, and a first protective layer 5 are formed as a first functional layer 4 on the substrate 1.

First, the first substrate 1 is placed on the signal surface side, that is, on the surface on which the grooves 10 and the lands 11 are formed.
Is formed by a sputtering method or the like. First
Examples of the material used for the dielectric layer include Al, S
A nitride, an oxide, a sulfide, or the like of a metal element such as i or Zn and a metalloid element is used.

Next, a recording layer is formed on the first dielectric layer formed on the first substrate 1 by a sputtering method or the like. Materials used for the recording layer include Ag, In,
A quaternary system including Sb and Te, and a quaternary system including Ge, Sb and Te
A general phase change material mainly composed of an original phase change material can be used.

Next, a second dielectric layer is formed on the recording layer by a sputtering method or the like. For the second dielectric layer, a material similar to the material used for the above-described first dielectric layer is used.

Next, a reflective heat radiation layer made of an Al alloy or the like is formed on the second dielectric layer by a sputtering method or the like.

Next, an ultraviolet curable resin is applied on the first functional layer 4 having an uneven shape corresponding to the uneven pattern of the first substrate 1 by a spin coating method or the like, and the first protective layer 5 is formed. Form a film. One main surface of the first protective layer 5 on the first substrate 1 side is formed so as to cover the uneven pattern of the reflective heat dissipation layer which is the uppermost layer of the first functional layer 4, while the first protective layer 5 5
The other main surface on the side facing the second substrate 2 is flat.

The second substrate 2 has a second surface
A reflective heat radiation layer made of an Al alloy or the like is formed as a functional layer 6 by a sputtering method or the like. Next, an ultraviolet curable resin is applied on the reflective heat dissipation layer by spin coating or the like, and the second
Is formed.

Finally, the first substrate 1 and the second substrate 2 manufactured as described above are combined with the signal surface side of the first substrate 1 and
The second substrate 2 is bonded to the dummy surface side with an adhesive so as to face the dummy surface side to form one optical disk. As the adhesive used at this time, a hot melt resin, an ultraviolet curable resin, an adhesive tape, or the like is used.

Here, the amount of warpage A ₁ of the first substrate ₁ will be described with reference to FIG. Warpage amount A _{1 of} first substrate ₁
Is a virtual plane C passing through the center 1a of the first substrate 1 and orthogonal to the laser beam irradiated on the first substrate 1, as shown in FIG. Represents an angle between the tangent and an arbitrary point at Put the above corner first
Is measured every 4 mm from the 25 mm radius of the substrate 1 in the outer peripheral direction, and the value that is the maximum angle is taken. Also, the amount of warpage A2 of the _second substrate 2 is measured in the same manner as the amount of warpage A1 of the _first substrate 1. In addition, regarding the warp directions of the first substrate and the second substrate,
The warpage when convex on the side to be bonded is represented by “−”, and the warpage when concave on the side to be bonded is represented by “+”.

The warp B of the optical disk will be described with reference to FIG. Here, the warp amount B of the optical disk 101 is defined as a value obtained by dividing a virtual plane C ′ passing through the center 101 a of the optical disk 101 and orthogonal to the laser beam irradiated on the optical disk 101 with a tangent at an arbitrary point on the surface of the optical disk 101. The angle to be formed is measured every 4 mm from the radius of 25 mm of the optical disc 101 in the outer peripheral direction, and the value that is the largest angle among them is assumed. With respect to the warp direction of the optical disk, the warp when concave on the side irradiated with laser light is represented by “−”, and the warp when convex on the side irradiated with laser light is represented by “+”.

Here, in the present invention, the warping amount A ₁ of the _first substrate 1 and the warping amount A 2 of the second substrate ₂ (hereinafter simply referred to as the “first”) manufactured under different manufacturing conditions as described above. (The amount of warpage of the first substrate 1 and the amount of warpage A of the second substrate 2 will be referred to as “A.”)
Are in the range of −0.4 ° ≦ A ≦ + 0.4 °, respectively. Thereby, the warp amount B of the optical disk after the first substrate 1 and the second substrate 2 are bonded to each other is determined by the following equation: -0.25 ° ≦ B ≦ +
It can be within the range of 0.25 °. The fact that the warp amount B of the optical disk is within the above range indicates that the warp amount B of the optical disk is small. Therefore, the optical disk can sufficiently cope with an increase in the numerical aperture of the objective lens and a shorter wavelength of the light source, and is suitable for a high recording density.

The manufacturing conditions of the second substrate 2 having the dummy are made more relaxed than the manufacturing conditions of the first substrate 1, so that the first substrate 1 and the second substrate 2 having different warping directions and warpage amounts are different. Even when the first substrate 1 and the second substrate 2 are bonded to each other, -0.4 ° ≦ A ≦
By setting it within the range of + 0.4 °, each warp is
When they are stuck together, they are offset in a well-balanced manner.
As a result, the amount of warpage B of the optical disc after bonding is-
Within the range of 0.25 ° ≦ B ≦ + 0.25 °, an optical disk with extremely high flatness can be obtained.

Further, the first substrate 1 and the second substrate
By measuring the amount of warpage A of the substrate 2, the amount of warpage B of the bonded optical disk is within an allowable range, ie, −.
It is possible to predict whether or not the range is 0.25 ° ≦ B ≦ + 0.25 °. In other words, the warpage amount A is A <−0.
A substrate having 4 ° or A> + 0.4 ° can cause the optical disc to have a large warp, and thus can be removed from the manufacturing process before a functional layer is formed on the substrate. Therefore,
A substrate that causes a large warp in the optical disc can be determined at an early stage of the manufacturing process, feedback to the molding process can be accelerated, and productivity can be improved.

Incidentally, the first substrate 1 having the signal surface is formed by an injection molding method so that the warpage A ₁ of the first substrate 1 is in the range of −0.25 ° ≦ A ₁ ≦ + 0.25 °. Mold 2 with the stamper 25 attached.
1, the temperature is in the range of 126 ° C. or more and 132 ° C. or less,
The mold clamping pressure of the mold device should be 60 kgf / cm ² or more, 8
It is preferable to set the range to 0 kgf / cm ² or less. At the same time, the warpage amount A ₂ of the second substrate 2 having the dummy
When the second substrate 2 is manufactured by the injection molding method, the temperature of the fixed mold 21 to which the stamper 25 is attached is set to be within the range of −0.25 ° ≦ A ₂ ≦ + 0.25 °. The temperature should be in the range of 126 ° C. or more and 132 ° C. or less, and the mold clamping pressure of the mold device should be 40 kgf / cm ² or more and 60 kgf or more.
/ Cm ² or less.

When manufacturing the first substrate 1, as described above, the stamper 25 having the concave and convex shapes corresponding to the shapes of the groove 10 and the land 11 is attached to the fixed mold 21, and the stamper 25 is The polycarbonate is filled in the cavity with the irregularities facing the cavity, and the polycarbonate is pressurized at a predetermined fixed mold temperature and a predetermined mold clamping pressure. Thereby, the first molded
The groove 10 obtained by transferring the shape of the stamper 25 is reliably transferred onto the substrate 1. If the temperature of the fixed mold to which the stamper 25 is attached is set to less than 126 ° C., a huge clamping pressure is required to clearly transfer the shapes of the grooves 10 and the lands 11.
The burden on 5 increases. On the other hand, if the temperature of the fixed mold 21 to which the stamper 25 is attached is higher than 132 ° C., the amount of warpage A ₁ of the first substrate 1 increases. Further, if the mold clamping pressure of the mold apparatus is less than 60 kgf / cm ² , the transfer of the concave and convex shape of the stamper 25 becomes insufficient, and the clear groove 10 and land 11 are formed on the first substrate 1.
May not be formed. On the other hand, if the mold-clamping pressure of the mold device is larger than 80 kgf / cm ² , the mold-clamping pressure is too strong, which may increase the amount of warpage A ₁ of the first substrate 1.

When manufacturing the second substrate 2, as described above, the flat stamper is attached to the fixed mold 21, and the flat surface of the stamper 25 faces the cavity. Then, the polycarbonate is filled in the cavity, and the polycarbonate is pressurized at a predetermined fixed mold temperature and a predetermined mold clamping pressure. Thereby, the flat plate-shaped second substrate 2 having a flat surface is formed. With it,
Since the second substrate 2 is manufactured under conditions that are more relaxed than the conditions for manufacturing the first substrate 1, the life of a stamper used when manufacturing the second substrate 2 can be relatively extended.

The temperature of the fixed mold with the stamper attached
If the temperature is lower than 126 ° C., the optical disc immediately after the bonding is performed.
Even if the warp amount B of the workpiece is within the allowable range,
The amount of increase in the warpage of the second substrate 2 depends on the amount of the warp of the first substrate 1.
It will be significantly different from the increase. As a result,
May not be able to maintain good flatness for a long time
is there. On the other hand, the temperature of the fixed mold with the stamper
If the temperature is higher than 132 ° C., the warpage A of the second substrate 2_TwoTo
Will increase. Further, the mold clamping pressure of the mold apparatus is set to 40.
kgf / cm^TwoIf it is less than, the amount of warpage A_TwoIncreases
At the same time, there is a possibility that uneven thickness may occur. Meanwhile, gold
The mold clamping pressure of the mold device is 60 kgf / cm ^TwoThen the type
Since the tightening pressure is too strong, the warp amount A of the first substrate 1₁
And the second substrate 2 is manufactured.
Therefore, the life of the stamper may be insufficient.

As described above, even if the manufacturing conditions of the second substrate 2 are relatively relaxed in order to extend the life of the stamper, the warpage A of the substrate immediately after injection molding is measured. By using only the substrate having the warpage amount A in the range of −0.4 ° ≦ A ≦ + 0.4 °, an optical disk with extremely high flatness can be obtained for a long period of time. And because it can maintain extremely high flatness for a long time,
The optical disk has a shorter wavelength light source and a higher N.D.
A. This is suitable for a high-density recording system, which is increasingly used.
In addition, before forming a functional layer and a protective layer on a substrate, a defective substrate that causes a defective product can be removed from a manufacturing process, so that productivity can be improved.

In the above description, a rewritable optical disk using a phase-change material as a recording layer is taken as an example of an optical recording medium, but the present invention is not limited to this. The present invention can be applied to, for example, an optical disk using an organic dye material for a recording layer or an optical disk employing a magneto-optical recording method.

In the above description, a rewritable optical disk is taken as an example, but the present invention is not limited to this. The present invention can be applied to a read-only optical disk and a write-once optical disk.

In the above description, the case where the substrate of the optical disk is manufactured by using the mold apparatus in which the stamper 25 is attached to the fixed mold 21 has been described as an example, but the present invention is not limited to this. is not. According to the present invention, for example, a substrate of an optical disk can be manufactured using a mold device in which a stamper 25 is attached to a movable mold 22.

[0072]

EXAMPLES Specific examples to which the present invention is applied will be described below based on experimental results.

<Experiment 1> First, the relationship between the mold clamping pressure of the mold apparatus and the life of the stamper attached to the mold apparatus was examined.

As the mold device, a groove width of 640 n
A mold device as shown in FIG. 3 was used, in which a stamper having a m-shaped groove with a depth of 60 nm was mounted on a fixed mold. Injecting polycarbonate having a glass transition point of 138 ° C. into the cavity of such a mold device,
The mold clamping pressure was set to 40 kgf / cm ² , the temperature of the fixed mold was set to 130 ° C., and a substrate having a signal surface with groove and land irregularities was formed.

Then, injection molding is continuously performed at the above mold clamping pressure and temperature until the stamper becomes unusable.
A substrate for evaluation was produced. The evaluation of the life of the stamper was performed as described below.

First, a first functional layer was formed on the evaluation substrate manufactured as described above. Specifically, ZnS-Si is formed on the surface of the evaluation substrate on which the uneven shape is formed.
A first dielectric layer made of O _2, a recording layer made of Ge ₂ Sb ₂ Te _{5, a second} dielectric layer made of ZnS—SiO ₂ , and a reflective heat dissipation layer made of AlCu are formed in this order. did. Then, a first protective layer was formed by applying an ultraviolet curable resin on the reflective heat dissipation layer.

Further, as a substrate having a dummy, AlC
A flat substrate having a reflective heat radiation layer made of u and a protective layer made of an ultraviolet curable resin was formed. Then, an evaluation substrate and a substrate having a dummy surface were bonded to each other with an adhesive in such a manner that the surfaces on which the functional layer and the protective layer were formed faced each other, thereby producing an optical disk. If the tracking error signal of the obtained optical disc includes noise due to irregularities generated on the surface of the stamper attached to the fixed mold, the stamper is determined to be unusable, and the number of substrates formed at that time is determined. The stamper life was set. In addition, 1
The molding of one substrate was counted as one shot.

Further, the mold clamping pressure of the mold apparatus is set to 50 kgf.
/ Cm ² , 60 kgf / cm ² and 70 kgf / cm ² , the life of the stamper was measured in the same manner. FIG. 6 shows the relationship between the mold clamping pressure of the mold apparatus and the life of the stamper.

As is apparent from FIG. 6, it was found that as the mold clamping pressure was reduced, the load on the stamper was reduced, and the life of the stamper was extended. Specifically, when the mold clamping pressure is 40 kgf / cm ² , the life of the stamper is about 650,000 shots, and the mold clamping pressure is 50
stamper life when formed into a kgf / cm ² is about 600,000 shots stamper life when the clamping pressure and 60 kgf / cm ² is about 470,000 shots were the clamping pressure and 70 kgf / cm ² The stamper life at that time was about 350,000 shots.

<Experiment 2> Next, a first substrate having a signal surface and a second substrate having a dummy surface, which were manufactured using a mold apparatus as shown in FIG. 3, were bonded to each other. After that, the warp amount B of the optical disk was examined.

First, by using a mold apparatus similar to the mold apparatus used in Experiment 1, polycarbonate was injection-molded to form a groove and land irregularities on one main surface, and to reduce the amount of warping A ₁ . 0.8 °, -0.4 °, +0.4
A plurality of first substrates having an angle of + 0.8 ° were manufactured.

Here, the amount of warpage A ₁ of the first substrate 1 is
As shown in FIG. 4, the first substrate 1 passes through the center and the first
Of the imaginary plane C orthogonal to the laser beam irradiated on the substrate 1 of the first substrate 1 and a tangent at an arbitrary point on the surface of the first substrate 1. The above-mentioned angle is measured every 4 mm from the radius of 25 mm of the first substrate 1 in the outer peripheral direction, and the value is the largest angle among them. Note that, regarding the warping direction of the first substrate, the warpage when it is convex on the side to be bonded to the second substrate is represented by “−”, and the warpage when it is concave on the side to be bonded is represented by “+”.

Next, a first functional layer was formed on a plurality of first substrates having different amounts of warping A ₁ . Specifically, the first
ZnS-SiO on the surface of the substrate of FIG.
_2, a recording layer made of Ge ₂ Sb ₂ Te ₅ , a _second dielectric layer made of ZnS—SiO ₂ , and a reflective heat dissipation layer made of AlCu were formed in this order. . Then, a first protective layer was formed by applying an ultraviolet curable resin on the reflective heat dissipation layer.

The polycarbonate is injection-molded by using a mold apparatus having a fixed mold and a plate-shaped stamper mounted thereon, so that the plate is plate-shaped and the warpage amount A ₂ is −0.8.
°, -0.4 °, + 0.4 °, + 0.8 ° for the second
Were prepared.

Next, a reflective heat radiation layer made of AlCu was formed on the second flat plate. Then, a second protective layer was formed by applying an ultraviolet curing resin on the reflective heat dissipation layer.

Next, a first substrate on which a first functional layer and a first protective layer are formed, and a second substrate on which a reflective heat radiation layer and a second protective layer are formed as second functional layers Were bonded in a combination of the warpage amounts A as shown in Table 1 below to obtain one optical disk.

Then, the amount of warpage B was measured for the completed optical disk. Here, the warp amount B of the optical disk is a virtual plane C ′ that passes through the center of the optical disk and is orthogonal to the laser beam irradiated on the optical disk.
An angle formed by a tangent at an arbitrary point on the surface of the optical disk is measured every 4 mm from the radius of the optical disk from 25 mm to the outer circumference, and the value that is the largest angle among them is assumed. With respect to the warp direction of the optical disk, the warp when the laser beam is irradiated to the concave side is represented by "-", and the warp when the laser beam is irradiated to the convex side is represented by "+". Note that the measurement of the warpage B of the optical disk was performed immediately after the first substrate and the second substrate were bonded.

The warp amount B of the optical disk is -0.25 ° ≦
When B was less than + 0.25 °, the result was indicated by ○, and the warp amount B of the optical disk was B <−0.25 ° or B> +0.25.
What was ° was represented as x. Table 1 shows the results.

[0089]

[Table 1]

[0090] As apparent from the results shown in Table 1, when the amount of warpage of the first substrate A ₁ and the warping amount A ₂ of the second substrate is the same, even if the first substrate and the second substrate The amount of warpage A is-
Even if it is large like 0.8 ° or + 0.8 °,
The warpage was well balanced and an optical disk with high flatness was obtained.

By the way, the warp amount A ₁ of the _first substrate and the second substrate
If the warp amount A ₂ substrates are different, for example, -0.4 °
When bonding the second substrate having a first substrate and + 0.4 ° warpage amount A ₂ having a warping amount A ₁ of the warpage B of the obtained optical disc subside within the allowable range,
An optical disk with high flatness was obtained.

However, for example, the warpage A1 of the _first substrate is -0.8 °, and the warpage A2 of the _second substrate is + 0.4 °.
In the case of °, the warpage of the first substrate and the second substrate was insufficiently offset from each other, and the obtained optical disk caused a large warp.

Therefore, according to the result of Experiment 2, when the amount of warpage A1 of the _first substrate is different from the amount of warpage A2 of the _second substrate, each amount of warping A is set to -0.4 ° ≦ A ≦ + 0. .4 °
It was found that it was necessary to be within the range.

<Experiment 3> Next, the amount of warpage A1 of the _first substrate having the signal surface was found to be -0.4 in Experiment 2.
The conditions for satisfying the range of ° ≦ A ₁ ≦ + 0.4 ° were examined.

As a mold device, a mold device as shown in FIG. 3 was used, in which a stamper having an uneven shape with a groove width of 640 nm and a groove depth of 60 nm was attached to a fixed mold, as in Experiment 1. Was. Polycarbonate was injected into the cavity of such a mold apparatus, and the first substrate was molded at a predetermined mold clamping pressure and a fixed mold temperature. The mold clamping pressure and the temperature of the fixed mold were set as shown in Tables 2 and 3 below. Further, the temperature of the movable mold was set to a temperature lower than the temperature of the fixed mold.

Then, the amount of warpage A ₁ was measured for the manufactured first substrate. In Table 2, the warpage amount A ₁ of the first substrate was ○ what was in the range of _{-0.4 ° ≦ A 1 ≦ + 0.4} °. Further, the warp amount A1 of the _first substrate is -0.0.
The case where 8 ° ≦ A ₁ <−0.4 ° or the case where the warp amount A ₁ of the first substrate was + 0.4 ° <A ₁ ≦ + 0.8 ° was defined as Δ. Also, the warpage amount A ₁ of the first substrate is A ₁ <−
The case where the angle was 0.8 ° or the case where the amount of warpage A ₁ of the first substrate was A ₁ > + 0.8 ° was represented as x. Table 2 shows the results.

[0097]

[Table 2]

The transferability of the grooves and lands formed on the manufactured first substrate was evaluated. In Table 3, the first substrate on which the concave and convex shapes of the groove and the land were satisfactorily transferred was evaluated as 基板, and the first substrate on which the transfer of the concave and convex shape of the groove and the land was unclear was evaluated as x. Table 3 shows the results.

[0099]

[Table 3]

Table 2 shows the warpage amount A1 of the _first substrate.
As is clear from the results, it was found that the region shown in the upper left direction in Table 2, that is, the condition of low mold temperature and low mold clamping pressure was preferable.

On the other hand, as to the transferability of the first substrate, as is clear from the results in Table 3, the region shown in the lower right direction in Table 3, that is, the conditions of high mold temperature and high mold clamping pressure are preferable. I understand.

Therefore, in order to achieve both the amount of warpage A ₁ of the first substrate and the transferability, specifically, the mold temperature is set to a range from 126 ° C. to 132 ° C. and the mold clamping is performed. It became clear that the pressure is preferably in the range of 60 kgf / cm ² or more and 80 kgf / cm ² or less.

<Experiment 4> Next, a second method having a dummy surface
The amount of warpage A ₂ of the substrate was determined in Experiment 2 to be −0.
The conditions for satisfying 4 ° ≦ A ₂ ≦ + 0.4 ° were examined.

As the mold device, a mold device as shown in FIG. 3 in which a flat stamper was attached to a fixed mold was used. Polycarbonate was injected into the cavity of such a mold apparatus, and a second substrate was molded at a predetermined mold clamping pressure and a fixed mold temperature. In addition, the mold clamping pressure and the temperature of the fixed mold were set as shown in Table 4 below. Further, the temperature of the movable mold was set to a temperature lower than the temperature of the fixed mold.

Then, the amount of warpage A ₂ was measured for the manufactured second substrate. In Table 4, the warpage amount A ₂ of the second substrate was ○ what was in the range of _{-0.4 ° ≦ A 2 ≦ + 0.4} °. Further, the amount of warpage A ₂ of the second substrate is −0.0.
The case where 8 ° ≦ A ₂ <−0.4 ° or the case where the warpage A ₂ of the second substrate was + 0.4 ° <A ₂ ≦ + 0.8 ° was defined as Δ. Also, the amount of warpage A ₂ of the second substrate is A ₂ <−
The case where the angle was 0.8 ° or the case where the amount of warpage A ₂ of the second substrate was A ₂ > + 0.8 ° was represented as x. Table 4 shows the results.

[0106]

[Table 4]

Table 4 shows the amount of warpage A ₂ of the second substrate.
From the results, it was found that the conditions of low mold temperature and high mold clamping pressure are preferable. However, as is clear from the results of Experiment 1, increasing the mold clamping pressure shortens the life of the stamper. In addition, when the mold temperature at the time of molding the second substrate is significantly different from the mold temperature at the time of molding the first substrate, the time-dependent change in the amount of warpage of the second substrate after the bonding is the first temperature. This is significantly different from the change with time of the substrate, and the amount of warpage B of the optical disk is significantly increased.

Therefore, in order to achieve both the amount of warpage A ₂ of the second substrate having the dummy surface and the life of the stamper,
The mold temperature is in the range of 126 ° C. or more and 132 ° C. or less, and the mold clamping pressure is 40 kgf / cm ² or more and 60 kgf.
/ Cm ² or less is preferable.

[0109]

As is clear from the above description, in the method of manufacturing an optical recording medium according to the present invention, the second substrate having the dummy surface is formed under a condition that is more relaxed than the first substrate having the signal surface. However, the warpage of the first substrate and the warp of the second substrate are well-balanced, and the amount of warpage of the optical recording medium can be kept within an allowable range. For this reason, the burden on an apparatus for manufacturing the second substrate is reduced,
The life of an apparatus for manufacturing a substrate can be extended. In addition, since a defective substrate that causes a large warp in the optical recording medium can be determined immediately after the first substrate and the second substrate are injection-molded, a functional layer may be formed on the defective substrate, Manufacturing waste such as bonding a substrate with less warpage to a defective substrate is prevented. Therefore, according to the present invention, it is possible to manufacture an optical recording medium having high flatness and capable of stably recording and reproducing signals with high productivity.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing an example of a configuration of an optical disc manufactured by applying the present invention.

FIG. 2 is a schematic cross-sectional view of a main part for explaining grooves and lands formed on a first substrate.

FIG. 3 is a cross-sectional view of a main part of a mold apparatus used for manufacturing a substrate.

4 is a main part schematic cross-sectional view for explaining a first substrate measuring method warping amount A ₁ of.

FIG. 5 is a schematic cross-sectional view of a main part for describing a method of measuring the amount of warpage B of the optical disc.

FIG. 6 is a characteristic diagram for explaining the correlation between the mold clamping pressure of the mold apparatus and the life of the stamper.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 first substrate, 2 second substrate, 3 adhesive layer, 4 first functional layer, 5 first protective layer, 6 second functional layer, 7
Second protective layer

Claims (4)

[Claims] 1. A first substrate manufacturing process for manufacturing a first substrate having a signal surface by injection molding polycarbonate, and a second substrate having a dummy surface by injection molding polycarbonate.
A second substrate manufacturing step of manufacturing the first substrate and the first substrate and the second substrate, with the signal surface side of the first substrate and the dummy surface side of the second substrate facing each other. A laminating step of laminating, wherein conditions for injection molding in the first substrate manufacturing step are:
The warping amount A of the first substrate and the second substrate is set to be less than the condition at the time of injection molding in the second substrate manufacturing step, and the warp amount A of the first substrate and the second substrate is each in a range of −0.4 ° A ≦ + 0.4 ° A method for manufacturing an optical recording medium, comprising: 2. The thickness of the first substrate and the second substrate is 0.6 mm ± 0.05 mm, and the diameter of the first substrate and the second substrate is 120 m.
2. The method for manufacturing an optical recording medium according to claim 1, wherein m ± 0.3 mm. 3. The method according to claim 1, wherein in the first substrate manufacturing step and the second substrate manufacturing step, a mold apparatus having at least a pair of molds and a stamper attached to one of the molds is used. The method for manufacturing an optical recording medium according to claim 1. 4. In the first substrate manufacturing step, the temperature of the mold on the side on which the stamper is mounted is set to a range of 126 ° C. or more and 132 ° C. or less, and the mold clamping pressure of the mold apparatus is set to 60 kgf / cm. ² to 80 kgf / cm ² , and in the second substrate manufacturing step, the temperature of the mold on the side where the stamper is attached is in the range of 126 ° C. to 132 ° C. Tightening pressure is 40kgf / c
m ² or more, and 60 kgf / cm ² or less in the range of the clamping pressure in the first substrate preparation step, according to claim 3, wherein a greater than clamping pressure in the second substrate preparing step A method for manufacturing an optical recording medium.