JPH0954986A - Two-layered optical disk, its recording method and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the characteristics of the reproducing light from respective recording layers the same by forming the information pits of the optical disk on the side upon which the reproducing light is made incident to the size different from the size of the information pits of another optical disk. SOLUTION: The two-layered disk 10 records the information by the information pits P1 of a width W1 on a substrate 1 and records the information by the information pits p2 of a width W2 larger than the width W1 on a substrate 5. A reflection film 2 having reflectivity of about 30 to 50% is formed on the substrate 1 and a reflection layer 4 having reflectivity of about 70 to 100% is formed on the substrate 5 and thereafter, the substrates 11, 12 are adhered by an adhesive. The irradiation of both recording layers with a laser beam is executed from the same direction in order to read out the information from the disk 10. In such a case, the width W2 of the pits p2 is so formed as to be effectively equaled to the width W1 of the pits p1. As a result, the asymmetric characteristics of the reproduced signals and the characteristics of the servo signals formed from the reproduced signals are approximated and the control of the reproducing device is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual-layer optical disc having two recording layers in which information is recorded by information pits, a recording method thereof and a manufacturing method thereof.

[0002]

2. Description of the Related Art An optical disc in which a circular information track is provided on a transparent substrate, and information pits are formed on the information track to record information, and the information is optically read by a reproducing optical head. There is. Then, in order to increase the amount of information on this optical disc, information is recorded 2
Two optical disks are attached to each other to have two recording layers,
In addition, in order to improve operability, a two-layer optical disc has been proposed in which information of the two recording layers is read from the same direction by laser light.

FIG. 5 is a diagram showing an example of a conventional two-layer optical disc. In FIG. 5, the two-layer optical disc 20 has a first
The optical disc and the second optical disc are adhered substantially in parallel with each other with an adhesive layer 3 for protection and adhesion. Therefore, the two-layer optical disc 20 has two recording layers, and information is recorded on each recording layer by concentric and concavo-convex information pits, respectively. This figure is a cross-sectional view of a two-layer optical disc cut in the radial direction. The first optical disc arranged on the reproduction light side is composed of the first substrate 1 and the first reflection layer 2, and is arranged on the opposite side. The second optical disc is composed of a second substrate 5 and a second reflective layer 4. Then, the first substrate 1, the first reflective layer 2,
The adhesive layer 3, the second reflective layer 4, and the second substrate 5 are laminated in this order from the bottom of the drawing.

On the first substrate 1, information is recorded on a circular information track by information pits p1.
Information is recorded on the substrate 5 by information pits p2 in a circular information track, and both substrates are made of a photopolymer.
It is adhered by an adhesive made of resin or the like. First
The reflective layer 2 is a layer having a reflectance of 30 to 50%, and the second reflective layer 4 is a layer having a reflectance of 70 to 100%. To read information from the two-layer optical disc 20, the laser light emitted from the reproducing optical head is focused and irradiated from the lower side of the drawing,
This is performed by detecting the reflected light with a photodiode. In reading from any of the recording layers, laser light irradiation is performed from the same side.

In the laminated two-layer optical disc shown in FIG. 5, the information pits are formed similarly on the first substrate and the second substrate. That is, the width q1 of the information pits on the first substrate and the width q2 of the information pits on the second substrate are formed to be equal. By the way, when reproducing the two-layer optical disc 20, the laser beam is irradiated from below as shown in the figure, and the effective width of the information pit at this time is affected by the second reflection layer. For example, if the film thickness of the first reflective layer 2 is t1 and the film thickness of the second reflective layer 4 is t2, the effective width of the information pits of the first optical disk remains q1, but the information pits of the information pits of the second optical disk are the same. The effective width q4 is smaller than q2 and becomes q2-2 * t2.

As described above, the effective widths of the information pits on the two substrates are different. This is because when reproducing the information pits of the read side substrate (first substrate), the reproduction light incident from the first substrate is focused on the information pits p1 as in the single-layer read optical system. The information is read out by using the photodiode of the reading optical head by being reflected by the boundary surface between the pit and the first reflective layer 2. On the other hand, when reproducing the information pits q2 on the opposite substrate (second substrate), the reproduction light incident from the first substrate is partly at the boundary surface between the information pits p1 on the first substrate and the first reflective layer 2. The reflected light and the remaining light are condensed and reflected on the surface of the second reflective layer formed in the information pit q2 of the second substrate, and the information is read using the photodiode of the reading optical head.

That is, the reflective surface of the information pits on the first substrate is the boundary surface between the information pits p1 recorded on the substrate and the first reflective layer, whereas the reflective surface of the information pits on the second substrate is: It is the surface of the second reflective layer attached to the information pits recorded on the substrate. Since the effective size of the information pits during reproduction is not defined by the size of the information pits themselves formed on the substrate by the uneven shape, but by the reflective surface, the information pits of both layers are formed with the same size. In this case, the effective width of the information pits in the laminated double-layer optical disc is different between the two layers. Then, the asymmetry characteristic of the reproduction signal read by the reproduction optical head and the servo signal (focus error signal etc.) generated from the reproduction signal.
In some cases, the characteristics and the like differ between the two optical discs, making it difficult to control the playback device.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and in reproduction of a laminated double-layer optical disk, the asymmetry characteristics of the reproduction signal, the servo signal characteristics obtained from the reproduction signal, etc. The purpose is to prevent dispersion between both optical disks.

[0009]

In order to achieve the above-mentioned object, the present invention attaches a first substrate on which information pits are formed and a second substrate on which information pits are formed so as to be substantially parallel to each other, A two-layer optical disc in which reproducing light is emitted from one direction to read information, and the size of the information pit formed on the first substrate and the size of the information pit formed on the second substrate are different. Is characterized by.

Further, in the optical disc of the present invention, in the above-mentioned two-layer optical disc, the pit width or length of the information pit of the first substrate on the reading side is W1, and the reflective layer of the second substrate on the other side is formed. The width or length of the previous information pit is W2,
The angle formed between the information pit wall surface of the second substrate and the second substrate is θ, the film thickness of the second reflective layer on the second substrate side is t, and a correction coefficient unique to the reflective layer deposition apparatus and reflective layer deposition conditions Is defined as α, and the value of W2 is W2 = W1 + β * 2t * tan (θ / 2) * (cos
The size of the information pit on the second substrate is determined by the calculation of θ + α) / (1 + α). Here, the correction coefficient β is given by O.5 to 2.0.

In addition, according to the present invention, the general formula W2 can be obtained from the above-described formula, which is a general value of the angle of the wall of the information pit and a general value of the correction coefficient α related to the amount of the reflection layer adhered to the wall of the information pit during film formation. = W1 + 0.75 * β * t allows the size of the information pits of the second substrate to be simply corrected with respect to the first substrate.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A two-layer optical disc of the present invention comprises a first optical disc having a first reflective layer formed on a first substrate having information pits p1 formed thereon and a second substrate having information pits p2 formed thereon. A second optical disc having a second reflective layer formed on
What is claimed is: 1. A two-layer optical disc, which is adhered so as to be substantially parallel to each other by an adhesive layer and reads out information by irradiating reproduction light from one direction, the size of information pits formed on a first substrate, and a second substrate. The size of the information pit formed in the above is different. An embodiment of the double-layer optical disc of the present invention will be described below with reference to FIG. FIG.
FIG. 2 is a cross-sectional view showing an embodiment of a two-layer optical disc of the present invention, in which two optical discs are stuck together, 2
Since the main part of the configuration, such as the point having two recording layers, is substantially the same as that of the conventional example shown in FIG. 5, the corresponding parts are designated by the same reference numerals.

In FIG. 1, a two-layer optical disc 10 is composed of a first optical disc, a second optical disc, and an adhesive layer 3, and therefore has two recording layers, each recording layer being concentric or spiral. The information is recorded on each of the information tracks by the uneven information pits.
The two-layer optical disc 10 is configured by laminating a first substrate 1, a first reflective layer 2, an adhesive layer 3, a second reflective layer 4, and a second substrate 5 in this order from the bottom of the drawing. On the first substrate 1,
Information is recorded by the information pits p1 on the circular information track, information is recorded by the information pits p2 on the circular information track on the second substrate 5, and both substrates are made of photopolymer resin or the like. It is adhered by an adhesive. The first reflective layer 2 is a layer having a reflectance of 30 to 50%, and the second reflective layer 4 is a layer having a reflectance of 70 to 100%.

To read information from the double-layer optical disk 10, the laser light emitted from a reproducing optical head (not shown) is focused and irradiated from the lower side of the drawing, and the reflected light is detected by the photodiode of the reproducing optical head. Is done by doing. Irradiation of the laser beam on any of the recording layers is performed from the direction shown in the figure. The formation of the information pits of the double-layer optical disc 10 is such that the size of the information pits is larger on the side of the second optical disc than on the side of the first optical disc. That is,
To compare the size of the information pits before the formation of the reflective layer, the width W2 of the information pits p2 on the second substrate 5 is determined by the first substrate 1
Of the information pit p1 is formed so as to be larger than the width W1 of the information pit p1.

The size of the information pits in the double-layer optical disc of the present invention will be described below with reference to FIG. FIG.
[Fig. 4] is an enlarged view of information pits on the second substrate. In FIG. 2, W1 is the width of the information pit p1 formed on the first substrate,
W2 is the width of the information pit p2 to be formed on the second substrate,
t represents the film thickness of the second reflective layer, and θ represents the angle between the wall surface of the information pit p2 and the second substrate 5. The width of the information pit is shown where the dimension in the depth direction of the pit is 1/2 when the wall surface of the information pit is not vertical.

As described in the conventional example, also in the two-layer optical disc 10, the width of the information pit before the formation of the reflective layer and the effective width at the time of reproduction are different on the second substrate side. That is, on the first substrate side, the width W1 of the information pit before the formation of the reflective layer is equal to the effective width at the time of reproduction, and on the second substrate side, the width of the information pit is W2 before the formation of the reflective layer. , The effective width at the time of reproduction decreases, so this should be W1. By thus making the effective widths of the information pits of the two substrates equal, the characteristics of the reproduction signal read from both recording layers become substantially the same, and the asymmetry characteristics of the reproduction signal and the servo signal generated from the reproduction signal are obtained. The characteristics of are also close.

In FIG. 2, the information pit p on the second substrate side
The width W2 of 2 is set to a value obtained by correcting the information pit width W1 according to the film thickness t of the second reflective layer and the angle θ. (B) of the same figure is an enlarged view of a part of (A) of the same figure. In (B) of the figure, angle BAC = angle D
AC = θ / 2. Further, d is (W2-W1) / 2. Thus, when the relationship between W2 and W1 is obtained, d
Becomes t * tan (θ / 2), and the effective size at the time of reproducing the information pit is reduced by 2t * tan (θ / 2). However, the amount of the adhesion of the reflective layer to the wall surface of the information pit changes depending on the film forming apparatus and the film forming conditions, and the above-mentioned geometrical expressions cannot express the influence of the reflective layer on the size of the information pit. I found out.

Therefore, an equation for correcting this is experimentally obtained,
In the above geometrical equation, as a correction coefficient for film formation (cos
It was found that a substantially satisfactory condition can be derived by multiplying θ + α) / (1 + α). Here, α is a value determined by the film forming apparatus and film forming conditions, and can be experimentally obtained from the optimum correction amount when the wall surface of the information pit is perpendicular to the disk substrate. Normally, α is about 0.2. Further, in consideration of variations in pit formation on the inner and outer circumferences of the two-layer optical disc and variations in the thickness of the reflective layer, the above correction equation 2t
If correction is performed by multiplying * tan (θ / 2) * (cos θ + α) / (1 + α) by a correction coefficient β (0.5 ≦ β ≦ 2),
It was found that the optimum correction amount was obtained. As a result, W2 = W1 + β * 2t * tan (θ / 2) * (cos θ
By setting + α) / (1 + α), a reproduction signal having the same characteristics can be obtained from the information pits on either substrate side.

[0019]

EXAMPLES Next, a recording method and a recording apparatus for a double-layer optical disk according to the present invention will be described with reference to FIG. FIG. 3 is a diagram showing an example of a cutting optical system in a recording device for a two-layer optical disc of the present invention. In FIG. 3, gas (A
r) The noise of the cutting beam emitted from the laser light source 11 is removed by the noise removal device 12, modulated by the recording signal by the E / O modulator 14, and then incident on the recording optical head 30. In the recording optical head 30,
The beam width is adjusted by the slit 17, and the light is focused by the objective lens 21 on the cutting glass master 23 coated with the photoresist. Focus control of the objective lens 21 is performed by an actuator 22. The photoresist is photo-reacted by the condensed laser light (cutting light) to be deteriorated, and only the portion exposed to the cutting light is removed in the developing process after the cutting, and that portion becomes an information pit. Usually, the thickness of the resist corresponds to the depth of the information pit.

At this time, it is the resist sensitivity and the size that affect the size of the finished information pit on the first substrate.
Recording conditions such as the resist thickness, the wavelength of the cutting light, the cutting power, the NA of the objective lens, the slit width, and the duty correction amount of the recording signal. Further, in the second substrate, the size of the surface of the second reflective layer formed on the information pits is the effective size of the information pits. Therefore, the effective size of the information pits on the second substrate is the above cutting conditions. In addition, it depends on the film thickness t of the second reflective layer and the film forming conditions of the reflective layer.

There are factors other than the above-mentioned factors that determine the effective size of the information pit. In practice, the cutting conditions are determined by considering all the factors, but here, for the sake of simplicity of explanation, the cutting conditions are The explanation will be limited. Hereinafter, a method of adjusting the size of the information pit using the width of the slit as a parameter will be described. FIG. 4 is a diagram showing the relationship between the slit width and the laser beam half-value width. As shown in FIG. 4, when the slit width of the slit 17 is changed, the beam half-width changes, so that the size of the information pit can be controlled. In the case of this embodiment, the slits 17 are arranged so that the width direction of the information pits changes.

First, the cutting condition is that the slit width in cutting in the first substrate 1 is 4 mm,
Other cutting conditions are fixed parameters. The film thickness of the first reflective layer 2 is fixed to 70 nm. The correction coefficient α for the reflective layer film forming apparatus and the reflective layer film forming conditions is obtained in advance by experiments as described below. In order to obtain the above α, first, the cutting power is set to be high with respect to the first optical disc so that the information pit wall surface becomes substantially vertical,
By recording a single frequency and then recording a single frequency on the second optical disc while changing the cutting power while maintaining the condition that the information pit wall surface is almost vertical, several types of different information pit sizes can be obtained. Have a band. Then, a reflection layer having a film thickness t (70 nm in this case) is formed on each of the first substrate and the second substrate by the reflection layer forming apparatus and the reflection layer forming conditions, and both the optical discs thus formed are bonded to each other by the adhesive layer 3 And stick them in parallel.

This is reproduced by irradiating it with laser light from the side of the first optical disk, and a cutting band from which a reproduction signal equivalent to that at the time of reproducing information pits of the first optical disk is obtained is selected from the second optical disk. At this time, assuming that the pit width of the first optical disc is W1 and the pit width of the second optical disc before the formation of the reflective layer of the selected band is W2, β = 1, and W2 = W1 + 2t * tan (π / 4) * (Cos (π
/ 2) + α) / (1 + α) can be obtained as follows: α = (W2- W1) / (2t- (W2- W
1)) In this example, α is about 0.2.

The information pits of the first substrate recorded under the cutting conditions determined as described above had a width of 300 nm and a wall surface angle of about 60 degrees by microscopic observation. At this time, W2 is 300 + 2 * 70 * tan (30deg)
* (cos (60deg) + 0.2) / (1 + 0.2) about 347.
2 nm, and when forming information pits on the second substrate,
The cutting conditions may be set so as to be about 16% larger than the size of the information pits on the first substrate. That is, FIG.
Since the slit width in the cutting of the first substrate is set to 4 mm from the slit width vs. the half width shown in (4), if the slit width in the cutting of the second substrate is set to 3.5 mm, the beam half width increases by about 14%. Almost satisfies the calculation conditions.

More simply, from the general formula W2 = W1 + 0.75 * β * t, assuming β is 1, W2 = 300 + 0.75 * 70 = 352.5 nm. Therefore, the slit width is set to the same as the above result. If you set it, you can get almost satisfactory results. Actually, the cutting condition is set by multiplying the whole by the correction coefficient β (0.5 ≦ β ≦ 2) in consideration of the film thickness distribution of the reflective layer, the deformation of the information pit due to molding, and the difference between the inner and outer circumferences. .

In the embodiment, in order to change the pit width,
As an example, the description has been made by changing the slit width of the recording optical system.
Although the control accuracy is lower than that of the present embodiment, the recording power may be changed without changing the recording optical system and the recording signal. Also,
In the above description, the width has been described as the size of the information pit, but it goes without saying that the same applies to the length direction of the pit, and the correction of the size of the information pit is performed in the width direction and the length direction. You may do it for both. Further, as a method for changing the pit length in the time axis direction, there is a known technique of a recording signal duty correction method for changing the pulse width of a recording electric signal. It is easy to change the pit length in the time axis direction by using this duty correction method.

In the above description, as the pit width of the information pit, it is adopted for convenience that the depth of the information pit is halved. However, depending on the relationship between the resist sensitivity curve and the cutting beam intensity curve, Since the relationship of the pit width is not uniquely determined, it is defined for convenience. When setting the actual cutting conditions, the relationship between the cutting condition and the pit width is defined in consideration of the relationship between the resist sensitivity curve and the cutting beam intensity curve.

Further, in the description of the present invention, the portion formed by irradiating the resist with the cutting beam at the time of cutting is referred to as an information pit, following the normal optical disk manufacturing process. Depending on the situation, the opposite may occur. In this case, it is clear that the size relationship between the information pits on the first substrate and the information pits on the second substrate is reversed. (W1 and W2 in the correction formula are opposite)

[0029]

As described above, according to the optical disc, the optical disc recording method, and the optical disc manufacturing method of the present invention, two optical discs in which information pits are recorded are bonded together to have two recording layers. When the reproduced two-layer optical disc is reproduced, the reproduction signals read from both optical discs have the same characteristics, and the asymmetry characteristics of the reproduction signal and the characteristics of the servo signal (focus error signal etc.) generated from the reproduction signal. Became very similar on both sides,
This has the effect of facilitating control of the playback device.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a two-layer optical disc of the present invention.

FIG. 2 is an enlarged view of information pits on a second substrate.

FIG. 3 is a diagram showing an example of a cutting optical system in a recording apparatus for a two-layer optical disc of the present invention.

FIG. 4 is a diagram showing a relationship between a slit width and a laser beam half width.

FIG. 5 is a diagram showing an example of a conventional dual-layer optical disc.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st board | substrate 2 1st reflective layer 3 Adhesive layer 4 2nd reflective layer 5 2nd substrate 10 Two-layer optical disk 13 of this invention 13,18 Miller 15 Beam splitter 20 Conventional two-layer optical disk 30 Recording optical head t Film thickness of the reflective layer on the second substrate side W1 Width of information pits on the first substrate side W2 Width of information pits on the second substrate side θ Angle between the wall surface of the information pits on the second substrate side and the substrate

Claims (3)

[Claims] 1. A two-layer optical disc in which two optical discs in which information pits carrying information are recorded are adhered to each other and reproduction light is emitted from a single direction, and the size of the information pits of both optical discs. A dual-layer optical disc characterized in that 2. A recording method for a two-layer optical disc, wherein two optical discs on which information pits carrying information are recorded are adhered to each other and reproducing light is emitted from a single direction.
A recording method for a dual-layer optical disc, wherein information is recorded by changing the size of information pits of both discs. 3. A method of manufacturing a two-layer optical disc, wherein two optical discs having information pits for carrying information recorded thereon are bonded to each other and reproducing light is emitted from a single direction.
A recording method for a dual-layer optical disc, wherein the information pits are formed so that the information pits on both discs have different sizes.