JPH11296910A - Optical recording medium and optical recording medium manufacturing master disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase further recording density by forming a first groove and a second groove along a recording track so as to plot a double spiral and forming so that the phase depth of the first groove and the phase depth of the second groove satisfy a specified relation. SOLUTION: A magneto-optical disk 1 is formed so that a wobbling groove and a straight groove are formed on a disk substrate 2 so as to plot the double spiral. When the phase depth of a deeper side groove between them is made X, and the phase depth of a shallower side groove is made Y, the wobbling groove and the straight groove are formed so as to satisfy the relations: X>=0.3950-0.831Y+2.932Y<2> , Y>=2.010-9.661X+11.77X<2> , Y<=0.8480-2.450X+1.880X<2> . Thus, a signal required for a tracking servo and a seek is obtained in a sufficient level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical recording medium having grooves formed along recording tracks. The present invention also relates to an optical recording medium manufacturing master used when manufacturing such an optical recording medium.

[0002]

2. Description of the Related Art As an optical recording medium, an optical disk formed in a disk shape and optically recorded and / or reproduced has been put to practical use. Such optical discs include a read-only optical disc in which embossed pits corresponding to data are formed in advance on a disc substrate, a magneto-optical disc for recording data using a magneto-optical effect, and a phase change of a recording film. There is a phase change type optical disk for recording data by utilizing the same.

[0003] Of these optical disks, writable optical disks such as magneto-optical disks and phase-change optical disks usually have grooves along recording tracks formed on the disk substrate. Here, the groove is a so-called guide groove formed along a recording track in order to mainly perform tracking servo. The portion between the grooves is called a land.

[0004] In an optical disk having a groove formed thereon, tracking servo is usually performed based on a push-pull signal obtained from light reflected and diffracted by the groove. Here, the push-pull signal is obtained by detecting the light reflected and diffracted by the groove by two photodetectors arranged symmetrically with respect to the track center, and taking the difference between the outputs from the two photodetectors. Is obtained by

By the way, conventionally, in these optical disks, a high recording density has been achieved by improving the reproduction resolution of an optical pickup mounted on a reproduction apparatus. The improvement of the reproduction resolution of the optical pickup is mainly attained by shortening the wavelength λ of the laser light used for reproducing the data, or by increasing the numerical aperture N of the objective lens for condensing the laser light on the optical disk.
It has been realized by increasing A.

Here, CD, MD, MDData2, D
For VD + RW, DVD-ROM, wavelength λ of laser beam used for data reproduction, numerical aperture NA of objective lens,
The track pitch values are shown in Table 1 (CD, MD, MDD
ata2, DVD + RW and DVD-ROM are all trademarks of optical disks. ).

[0007]

[Table 1]

As shown in Table 1, in the conventional optical disk, narrowing the track is realized by shortening the wavelength λ of the laser beam or increasing the numerical aperture NA of the objective lens. Higher recording density has been achieved.

Incidentally, in the conventional optical disk, the track pitch is about 1/2 to 2/3 of the cutoff frequency of the optical pickup of the reproducing apparatus. here,
The cut-off frequency is a frequency at which the amplitude of a reproduced signal becomes substantially zero, the wavelength of a laser beam used for reproducing data is λ, and the numerical aperture of an objective lens for condensing the laser beam on an optical disk is NA. Is represented by 2NA / λ.

The reason why the track pitch is set to about 1/2 to 2/3 of the cut-off frequency is to realize stable tracking servo and track seek.
This is because it is necessary to obtain signals necessary for tracking servo and seek at a sufficient level.

For example, a push-pull signal is used as a tracking error signal in a recent high-density optical disk. To stably perform tracking servo, the amplitude ratio of the push-pull signal needs to be about 0.15 or more. is there. In addition, the cross track signal is used for traverse counting at the time of seek and detection of the radial position of the track,
In order to perform seek stably, the cross-track signal amplitude needs to be about 0.06 or more. In the conventional optical disc, in order to set the push-pull signal amplitude ratio to 0.15 or more and the cross-track signal amplitude to 0.06 or more, the track pitch must be set to 1/2 of the cutoff frequency.
It was necessary to be about ２.

The push-pull signal detects the light reflected and diffracted by the groove by two photodetectors A and B arranged symmetrically with respect to the track center as shown in FIG. Difference between the outputs from the two photodetectors A and B (A
-B). The cross track signal is obtained by taking the sum (A + B) of the outputs from the two photodetectors A and B.

The amplitude ratio of the push-pull signal is shown in FIG.
As shown in (1), when the maximum amplitude of the push-pull signal is C, it is represented by C / Mmax. The cross-track signal amplitude ratio is represented by D / Mmax, where D is the maximum amplitude of the cross-track signal as shown in FIG. Here, Mmax represents the sum signal from the two photodetectors A and B as M
Indicates the maximum value of the sum signal M, that is, the value of the sum signal M on the disk mirror surface.

[0014]

By the way, the demand for a higher recording density of an optical recording medium never stops, and a further higher recording density is desired for an optical recording medium such as an optical disk. In order to increase the recording density of the optical recording medium, for example, the interval between adjacent grooves may be reduced, and the track pitch may be reduced. However, in the conventional optical recording medium, if the track pitch is too narrow, signals required for tracking servo and seek cannot be obtained at a sufficient level, and tracking servo and seek cannot be performed stably. There was a problem that it would.

For example, in MDData2, the track pitch is 0.95 μm and the push-pull signal amplitude ratio is about 0.30. In this case, the push-pull signal amplitude ratio is sufficiently large, and stable tracking servo can be realized. However, in a configuration similar to MDData2, if the track pitch is set to 0.75 μm, the push-pull signal amplitude ratio decreases to about 0.07. In this case, the amplitude ratio of the push-pull signal is too small, and stable tracking servo cannot be realized.

As described above, in the conventional optical recording medium, if the track pitch is too narrow, a signal necessary for tracking servo and seek cannot be obtained at a sufficient level, and tracking servo and seek can be performed stably. There was a problem that it became impossible to do. For this reason, it has been difficult to further increase the recording density of the conventional optical recording medium.

The present invention has been proposed in view of the above-mentioned conventional circumstances. Even if the track pitch is extremely narrow, tracking servo and seek can be performed stably, and higher recording can be achieved. It is an object of the present invention to provide an optical recording medium capable of increasing the density. Another object of the present invention is to provide an optical recording medium manufacturing master disc capable of manufacturing such an optical recording medium.

[0018]

SUMMARY OF THE INVENTION An optical recording medium according to the present invention is an optical recording medium on which a groove is formed along a recording track and which is irradiated with light having a predetermined wavelength λ to perform recording and / or reproduction. The first groove and the second groove are formed so as to draw a double spiral. Here, the refractive index of the medium ranging from the light incident surface to the first groove and n _x, the depth of the first groove when the x, first grooves represented by _x × n x / λ Is the phase depth of X. Further, the refractive index of the medium reaching the second groove from the light incident surface and n _y, the depth of the second groove when the y, the second grooves represented by _y × n y / λ Let Y be the phase depth. The optical recording medium according to the present invention is characterized in that the first groove and the second groove are formed so as to satisfy the following expressions (1), (2) and (3). .

X ≧ 0.3950−0.831Y + 2.932Y ² (1) Y ≧ 2.010-9.661X + 1.77X ² (2) Y ≦ 0.8480-2.450X + 1.880X ² (3) In the optical recording medium according to the present invention as described above, the first groove and the second groove satisfy the equations (1), (2) and (3). Since it is formed, signals necessary for tracking servo and seek can be obtained at a sufficient level even if the track pitch is narrowed.

In the above-mentioned optical recording medium, it is preferable that at least one of the first groove and the second groove is a wobbling groove formed so that at least a part thereof meanders. By making the groove meander as described above to form a wobbling groove, it is possible to add address information to the groove itself.

The master for manufacturing an optical recording medium according to the present invention manufactures an optical recording medium on which recording and / or reproduction is performed by forming a groove along a recording track and irradiating light of a predetermined wavelength λ. This is a master for producing an optical recording medium used at the time. The first groove pattern and the second groove pattern are formed so as to draw a double spiral as an uneven pattern corresponding to the groove. Here, the refractive index of the medium reaching the first groove from the light incident surface of the optical recording medium and n _x, a depth of the first groove pattern 'when _{a, x' x × n x /} λ The first represented by
Let X 'be the phase depth of the groove pattern. Further, the refractive index of the medium reaching the second groove from the light incident surface of the optical recording medium and n _y, the depth of the second groove pattern 'is taken as, y' y in × n _y / λ The phase depth of the represented second groove pattern is Y ′. In the master for manufacturing an optical recording medium according to the present invention, the first groove pattern and the second groove pattern are formed so as to satisfy the following equations (4), (5) and (6). It is characterized by the following.

X ′ ≧ 0.3950−0.831Y ′ + 2.932Y ′ ² (4) Y ′ ≧ 2.010-9.661X ′ + 11.77X ′ ² (5) Y ′ ≦ 0.8480-2.450X ′ + 1.880X ′ ² (6) In the master for producing an optical recording medium according to the present invention as described above,
Since the first groove pattern and the second groove pattern are formed so as to satisfy the above equations (4), (5) and (6), by using this master for producing an optical recording medium, Equations (1), (2) and (3) above
An optical recording medium having a first groove and a second groove satisfying the above conditions can be manufactured. Therefore, according to this master for producing an optical recording medium, it is possible to produce an optical recording medium capable of obtaining signals required for tracking servo and seek at a sufficient level even if the track pitch is narrowed.

In the above-mentioned master for producing an optical recording medium, at least one of the first groove pattern and the second groove pattern is a concavo-convex pattern corresponding to a wobbling groove formed so that at least a part thereof is meandering. It is preferred that According to such a master for manufacturing an optical recording medium, an optical recording medium having a wobbling groove can be manufactured. Then, by making the groove meander and forming a wobbling groove, it is possible to add address information to the groove itself. Therefore, at least one of the first groove pattern and the second groove pattern is formed with irregularities corresponding to the wobbling groove. According to the above-described master for producing an optical recording medium having a pattern, an optical recording medium in which address information is added to the groove itself can be produced.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, a meandering groove is called wobbling, and a groove formed so as to wobble is called a wobbling groove. Also, a groove formed without meandering with respect to the wobbling groove is called a straight groove.

<Magneto-Optical Disk> FIG. 1 is an enlarged cross-sectional view of a main part of a magneto-optical disk to which the present invention is applied.

The magneto-optical disk 1 is formed in a disk shape, and data is recorded using a magneto-optical effect. The magneto-optical disk 1 is made of polymethyl methacrylate (PMMA) or polycarbonate (PC).
A recording layer 3 on which magneto-optical recording is performed and a protective layer 4 for protecting the recording layer 3 are formed on a disk substrate 2 made of the same. Here, the recording layer 3 is formed by laminating, for example, a dielectric film made of SiN or the like, a perpendicular magnetic recording film made of a TeFeCo alloy or the like, a dielectric film made of SiN or the like, and a reflective film made of Al or the like. Become. The protective layer 4 is formed by, for example, spin-coating an ultraviolet curable resin on the recording layer 3. In the present invention, the recording layer 3 and the protective layer 4
Is arbitrary and is not limited to this example.

The magneto-optical disk 1 has a wobbling groove 6 and a straight groove 7 formed in a double spiral on the disk substrate 2 as shown in FIG. The data is recorded on the land between the wobbling groove 6 and the straight groove 7 by magneto-optical recording.

That is, the portion between the wobbling groove 6 and the straight groove 7 and the straight groove 7 on the inner circumferential side of the disk becomes the first recording track TrackA where the information signal is recorded, and The portion between the wobbling groove 6 and the straight groove 7 and the portion on the inner peripheral side of the disc serving as the wobbling groove 6 is the second portion where the information signal is recorded.
Recording track TrackB.

Here, the wobbling groove 6 is ± 1.
It is formed so as to meander at a constant cycle with an amplitude of 0 nm. That is, in this magneto-optical disk 1, one of the grooves (that is, the wobbling groove 6) is set to ± 10.
By wobbling with an amplitude of nm, address information is added to the groove.

Here, the two grooves formed in a double spiral shape are the wobbling grooves 6.
In the optical recording medium according to the present invention, both of these two grooves may be straight grooves, or both may be wobbling grooves. . However, when the groove is wobbled, there is an advantage that the address information can be added to the groove itself. Moreover, when one groove is used as a wobbling groove and the other groove is used as a straight groove as in this example, it is easier to narrow the track than when both grooves are used as wobbling grooves. Higher recording density can be realized.

Then, in this magneto-optical disk 1,
The track pitch TPitch is set to 0.50 μm. Here, the track pitch TPitch corresponds to an interval between the center positions of the wobbling groove 6 and the straight groove 7. That is, in the magneto-optical disk 1, the interval between the center positions of the wobbling groove 6 and the straight groove 7 is 0.50 μm.

In the following description, the interval between the center positions of the adjacent straight grooves 7 is referred to as a track period TPeriod. The track period TPeriod is equivalent to twice the track pitch TPitch. In this magneto-optical disk 1, the track period TPeriod is:
1.00 μm.

In the magneto-optical disk 1 to which the present invention is applied, the wobbling groove 6 and the straight groove 7 are formed so that their depths are different. Specifically, the phase depth of the deeper groove of the wobbling groove 6 and the straight groove 7 is set to X.
When the phase depth of the shallower groove is Y, the wobbling groove 6 and the straight groove 7 satisfy the following expressions (1-1), (1-2), and (1-3). Is formed.

X ≧ 0.3950−0.831Y + 2.932Y ² (1-1) Y ≧ 2.010-9.661X + 1.77X ² (1-2) Y ≦ 0.8480-2 .450X + 1.880X ² (1-3) The phase depth X of the deeper groove is represented by λ, where λ is the wavelength of a laser beam used for recording and reproduction on the magneto-optical disk 1. of the refractive index of the medium leading to the groove from the light incident surface and n _x, the depth of the groove is taken as x, represented by _x × n x / λ. Also,
The phase depth Y of the shallower groove depends on the wavelength of the laser light used for recording / reproducing on the magneto-optical disk 1 by λ.
And then, the refractive index of the medium ranging from the light incident surface of the magneto-optical disc 1 to the groove and n _y, the depth of the groove 7 when the y, represented by _y × n y / λ.

The medium from the light incident surface of the magneto-optical disk 1 to the wobbling groove 6 and the medium from the light incident surface of the magneto-optical disk 1 to the straight groove 7 are:
Each is a disk substrate 2. Therefore, if the refractive index of the disk substrate 2 is n, then _nx = _ny = n.

In the magneto-optical disk 1 as described above, as can be seen from the experimental results described later, the wobbling groove 6 and the straight groove 7 correspond to the above equations (1-1), (1-2) and (1-1). Since it is formed so as to satisfy 3), signals necessary for tracking servo and seek can be obtained at a sufficient level.

<Laser Cutting Apparatus> When the above-described magneto-optical disk 1 is manufactured, a laser cutting apparatus is used for manufacturing an optical recording medium manufacturing master as the master of the magneto-optical disk 1. Hereinafter, an example of a laser cutting device used for manufacturing an optical recording medium manufacturing master will be described in detail with reference to FIG.

The laser cutting device 10 shown in FIG.
Is the photoresist 1 applied on the glass substrate 11
Exposure No. 2 to form a latent image. When a latent image is formed on the photoresist 12 by the laser cutting device 10, the glass substrate 11 coated with the photoresist 12 is attached to a rotary driving device provided on a movable optical table. When exposing the photoresist 12, the glass substrate 11 is driven to rotate by a rotation driving device as shown by an arrow A <b> 1 in the drawing so that exposure with a desired pattern is performed over the entire surface of the photoresist 12. Is translated by the moving optical table.

The laser cutting apparatus 10 is capable of exposing the photoresist 12 with two exposure beams, and forms a latent image corresponding to the wobbling groove 6 and a latent image corresponding to the straight groove 7. It is formed by each exposure beam. That is,
In the laser cutting apparatus 10, a latent image corresponding to the wobbling groove 6 is formed by the first exposure beam, and the straight groove 7 is formed by the second exposure beam.
Is formed.

The laser cutting device 10 includes a light source 13 for emitting laser light and an electro-optic modulator (EO) for adjusting the light intensity of the laser light emitted from the light source 13.
M: Electro Optical Modulator 14, an analyzer 15 arranged on the optical axis of the laser light emitted from the electro-optic modulator 14, and the laser light transmitted through the analyzer 15 into reflected light and transmitted light. First beam splitter 17 for splitting
A second beam splitter 18 that divides the laser light transmitted through the first beam splitter 17 into reflected light and transmitted light, and a photodetector (PD) that detects the laser light transmitted through the second beam splitter 18 : Photo De
tector) 19 and an auto power controller (AP) that applies a signal electric field to the electro-optic modulator 14 to adjust the intensity of laser light emitted from the electro-optic modulator 14.
C: Auto Power Controller) 20.

In the laser cutting device 10, the laser light emitted from the light source 13 is first given a predetermined light intensity by an electro-optic modulator 14 driven by a signal electric field applied from an auto power controller 20. And enters the analyzer 15. Here, analyzer 1
Reference numeral 5 denotes an analyzer that transmits only S-polarized light.
The laser beam transmitted through 5 becomes S-polarized light.

Although any light source can be used as the light source 13, a light source which emits a laser beam having a relatively short wavelength is preferable. Specifically, for example, the wavelength λ is 351 nm.
Kr laser that emits laser light of a wavelength of 442n
A He—Cd laser that emits m laser light is suitable as the light source 13.

The S-polarized laser light transmitted through the analyzer 15 is first split into reflected light and transmitted light by the first beam splitter 17, and further transmitted through the first beam splitter 17. The light is split by the second beam splitter 18 into reflected light and transmitted light.
In this laser cutting device 10, the laser beam reflected by the first beam splitter 17
And the laser beam reflected by the second beam splitter 18 becomes a second exposure beam.

The light intensity of the laser light transmitted through the second beam splitter 18 is detected by a photodetector 19, and a signal corresponding to the light intensity is transmitted from the photodetector 19 to an auto power controller 20.
Then, in response to the signal sent from the photodetector 19, the auto power controller 20 applies the light to the electro-optic modulator 14 so that the light intensity detected by the photodetector 19 becomes constant at a predetermined level. Adjust the signal electric field. As a result, automatic power control (APC: Auto Power Control) is performed so that the light intensity of the laser light emitted from the electro-optic modulator 14 becomes constant, and a stable laser light with less noise is obtained.

The laser cutting device 10
Is a first modulation optical system 22 for modulating the light intensity of the laser light reflected by the first beam splitter 17.
And a second modulation optical system 23 for modulating the light intensity of the laser beam reflected by the second beam splitter 18.
And an optical system 24 for recombining the respective laser beams subjected to the light intensity modulation by the first and second modulation optical systems 22 and 23 and condensing them on the photoresist 12.

Then, the first exposure beam reflected by the first beam splitter 17 is guided to the first modulation optical system 22, and is subjected to light intensity modulation by the first modulation optical system 22. Similarly, the second beam splitter 1
The second exposure beam reflected by 8 is guided to a second modulation optical system 23, where the light intensity is modulated by the second modulation optical system 23.

That is, the first exposure beam that has entered the first modulation optical system 22 is condensed by the condenser lens 29 and then enters the acousto-optic modulator 30. The light intensity is modulated so as to correspond to a desired exposure pattern. Here, as the acousto-optic element used for the acousto-optic modulator 30, for example, an acousto-optic element made of tellurium oxide (TeO ₂ ) is suitable. The first light intensity modulated by the acousto-optic modulator 30
Is collimated by the collimator lens 31 and then emitted from the first modulation optical system 22.

Here, a driving driver 32 for driving the acousto-optic modulator 30 is provided in the acousto-optic modulator 30.
Is attached. At the time of exposing the photoresist, a signal S1 corresponding to a desired exposure pattern is input to the driving driver 32, and the acousto-optic modulator 30 is driven by the driving driver 32 according to the signal S1, and the second exposure Light intensity modulation is performed on the beam.

More specifically, for example, when a latent image having a groove pattern corresponding to the wobbling groove 6 having a constant depth is formed in the photoresist 12, a DC signal having a constant level is transmitted to the driving driver 32. The acousto-optic modulator 30 is driven by the driving driver 32 according to the input DC signal. Thus, light intensity modulation is performed on the first exposure beam so as to correspond to a desired groove pattern.

The second exposure beam incident on the second modulation optical system 23 is condensed by a condenser lens 33 and then incident on an acousto-optic modulator 34, which The light intensity is modulated so as to correspond to a desired exposure pattern. Here, as the acousto-optic element used for the acousto-optic modulator 34, for example, tellurium oxide (T
An acousto-optic device made of eO ₂ ) is preferred. And
The second exposure beam, the light intensity of which has been modulated by the acousto-optic modulator 34, is collimated by the collimating lens 35 and transmitted through the λ / 2 wavelength plate 36, so that the polarization direction is rotated by 90 °. Then, the light is emitted from the second modulation optical system 23.

Here, a driving driver 37 for driving the acousto-optic modulator 34 is provided in the acousto-optic modulator 34.
Is attached. Then, when exposing the photoresist 12, a signal S2 corresponding to a desired exposure pattern is input to the driving driver 37, and the acousto-optic modulator 34 is driven by the driving driver 37 according to the signal S2, and the second Light intensity modulation is performed on the exposure beam.

More specifically, for example, when a latent image having a groove pattern corresponding to the straight groove 7 having a certain depth is formed in the photoresist 12, a DC signal of a certain level is supplied to the driving driver 37. Input and the D
The acousto-optic modulator 34 is driven by the driving driver 37 according to the C signal. Thereby, light intensity modulation is performed on the second exposure beam so as to correspond to a desired groove pattern.

As described above, the first exposure beam is subjected to light intensity modulation by the first modulation optical system 22,
Is subjected to light intensity modulation by the second modulation optical system 23. At this time, the first exposure beam emitted from the first modulation optical system 22 remains S-polarized light, but the second exposure beam emitted from the second modulation optical system 23 has a wavelength of λ / 2 wavelength. Since the polarization direction is rotated by 90 ° by passing through the plate 36, the polarization is P-polarized.

Then, the first exposure beam emitted from the first modulation optical system 22 is reflected by the mirror 41, guided horizontally and parallel on the moving optical table, and enters the deflection optical system 46. And the first exposure beam is
After being optically deflected by the deflecting optical system 46, the light is reflected by the mirror 44 and its traveling direction is bent by 90 ° before being incident on the polarization beam splitter 45. On the other hand, the second
The second exposure beam emitted from the modulation optical system 32 of
The light is reflected by the mirror 42 and is guided horizontally and parallel on the moving optical table, and the polarization beam splitter 4
5 is incident.

Here, the deflection optical system 46 is for performing optical deflection on the first exposure beam so as to correspond to wobbling of the wobbling groove. That is, the light emitted from the first modulation optical system 22 and the deflection optical system 4
The first exposure beam incident on the wedge prism 4
7 through an acousto-optic deflector (AOD: Acousto Optical
Deflector) 48 and is subjected to optical deflection by the acousto-optic deflector 48 so as to correspond to a desired exposure pattern. Here, as an acousto-optic element used for the acousto-optic deflector 48, for example, tellurium oxide (TeO
_The acousto-optic element consisting of ₂ ) is preferred. The first exposure beam that has been optically deflected by the acousto-optic deflector 48 passes through the wedge prism 49 to the deflection optical system 4.
6 is emitted.

Here, the acousto-optic deflector 48 includes a driving driver 50 for driving the acousto-optic deflector 48.
Is attached, and the driving driver 50 includes:
Voltage Controlled Oscilla (VCO)
tor) 51 is FM-modulated by a control signal S3 including address information and supplied. When the photoresist 12 is exposed, a signal corresponding to a desired exposure pattern is input from the voltage controlled oscillator 51 to the driving driver 50, and the driving driver 5
The acousto-optic deflector 48 is driven by 0, whereby the first exposure beam is optically deflected.

Specifically, for example, a frequency of 84.672
By wobbling the groove at kHz,
In a case where address information is added to a groove, for example, a high frequency signal having a center frequency of 224 MHz
The signal FM-modulated by the control signal of 4.672 kHz is
It is supplied from the voltage controlled oscillator 51 to the driving driver 50. In response to this signal, the driving driver 50 drives the acousto-optic deflector 48 to change the Bragg angle of the acousto-optic element of the acousto-optic deflector 48, thereby supporting wobbling at a frequency of 84.672 kHz. Optical deflection is performed on the first exposure beam.

The first exposure beam optically deflected by the deflection optical system 46 so as to correspond to the wobbling of the wobbling groove 6 is reflected by the mirror 44 and travels in the traveling direction as described above. Is 9
After being bent by 0 °, the light enters the polarization beam splitter 45.

Here, the polarization beam splitter 45
It reflects the polarized light and transmits the P-polarized light.
Then, the first exposure beam emitted from the first modulation optical system 22 and subjected to optical deflection by the deflection optical system 46 is:
The second exposure beam emitted from the second modulation optical system 23 is S-polarized light and is P-polarized light. Therefore,
The first exposure beam is reflected by the polarization beam splitter 45, and the second exposure beam passes through the polarization beam splitter 45. Thus, the first exposure beam emitted from the first modulation optical system 22 and optically deflected by the deflection optical system 46 and the second exposure beam emitted from the second modulation optical system 23 Re-combination is performed so that the traveling directions are the same.

The first and second exposure beams recombined so that the traveling directions are the same and emitted from the polarizing beam splitter 45 are adjusted to a predetermined beam diameter by the magnifying lens 52, and then the mirror 53 The light is reflected by the objective lens 54 and guided to the objective lens 54, and is focused on the photoresist 12 by the objective lens 54. This allows
The photoresist 12 is exposed, and a latent image is formed on the photoresist 12. At this time, as described above, the glass substrate 11 on which the photoresist 12 is applied is rotated by a rotary driving device as shown by an arrow A1 in the figure so that the entire surface of the photoresist 12 is exposed in a desired pattern. , And is translated by a moving optical table. As a result, a latent image corresponding to the irradiation locus of the first and second exposure beams is formed over the entire surface of the photoresist 12.

The objective lens 54 for condensing the exposure beam on the photoresist 12 has a numerical aperture N in order to form a finer groove pattern.
It is preferable that A is large, and specifically, an objective lens having a numerical aperture NA of about 0.9 is suitable.

When irradiating the photoresist 12 with the first and second exposure beams, the beam diameters of the first and second exposure beams are changed by the magnifying lens 52 as necessary. The effective numerical aperture for the objective lens 54 is adjusted. Thereby, the spot diameters of the first and second exposure beams focused on the surface of the photoresist 12 can be changed.

Incidentally, the first exposure beam that has entered the polarization beam splitter 45 is combined with the second exposure beam on the reflection surface of the polarization beam splitter 45. Here, the polarization beam splitter 45 is arranged such that the reflection surface of the deflection beam splitter forms an appropriate reflection angle with respect to the traveling direction of the light synthesized and emitted by the reflection surface.

More specifically, the reflection angle of the reflection surface of the polarizing beam splitter 54 is such that the spot corresponding to the first exposure beam and the spot corresponding to the second exposure beam in the radial direction of the glass substrate 11. The interval is the track pitch
Set to correspond to TPitch. This makes it possible to expose the portion corresponding to the wobbling groove 6 with the first exposure beam, and at the same time, to expose the portion corresponding to the straight groove 7 with the second exposure beam.

The laser cutting apparatus 10 as described above
Then, an optical system corresponding to a first exposure beam for forming a latent image corresponding to the wobbling groove 6 and an optical system corresponding to a second exposure beam for forming a latent image corresponding to the straight groove 7 Therefore, the latent image corresponding to the wobbling groove 6 and the latent image corresponding to the straight groove 7 can be collectively formed only by the laser cutting device 10. Moreover,
In the laser cutting apparatus 10, the irradiation position of the first exposure beam and the second exposure beam are adjusted by adjusting the direction of the deflection beam splitter 45 for synthesizing the first exposure beam and the second exposure beam. Can be easily adjusted.

<Method of Manufacturing Magneto-Optical Disk> Next, a method of manufacturing the magneto-optical disk 1 shown in FIGS. 1 and 2 will be described in detail with a specific example.

When manufacturing the magneto-optical disk 1, first,
As a mastering step, an optical recording medium manufacturing master having an uneven pattern corresponding to the wobbling groove 6 and the straight groove 7 is manufactured.

In this mastering step, first, a disk-shaped glass substrate 11 whose surface has been polished is washed and dried, and then a photoresist 12 as a photosensitive material is applied onto the glass substrate 11. Next, the photoresist 12 is exposed by the laser cutting device 10 to form a latent image corresponding to the wobbling groove 6 and the straight groove 7 on the photoresist 12.

When manufacturing a magneto-optical disk for evaluation, which will be described later, a Kr laser that emits a laser beam having a wavelength λ of 351 nm is used as the light source 13 of the laser cutting device 10, and the first and second exposures are performed. The objective lens 54 for condensing the beam on the photoresist 12 has a numerical aperture NA of 0.9. A lens having a focal length of 70 mm was used as the magnifying lens.

When the photoresist 12 is exposed by the laser cutting device 10, the first and second
The latent image corresponding to the wobbling groove 6 and the straight groove 7 is formed on the photoresist 12 by exposing the photoresist 12 with the exposure beam.

Here, when a latent image corresponding to the wobbling groove 6 is formed on the photoresist 12 by exposing the photoresist 12 with the first exposure beam, the first exposure beam is applied to the first exposure beam. Modulation optical system 2
2 and the optical deflection is performed by the optical deflection system 46.

More specifically, first, a DC signal of a fixed level is input to the driving driver 32, and the acousto-optic modulator 30 is driven by the driving driver 32 based on the DC signal. The light intensity modulation is performed on the first exposure beam so as to correspond to the pattern (1). Here, since the wobbling groove 6 is a continuous groove having a constant depth, while the latent image corresponding to the wobbling groove 6 is being formed, light is emitted so that the light intensity of the first exposure beam is constant. Apply intensity modulation.

Next, the first exposure beam subjected to the light intensity modulation by the first modulation optical system 22 is optically deflected by the deflection optical system 46. Specifically, a high frequency signal is FM-modulated from the voltage controlled oscillator 51 by a control signal and supplied to the driving driver 50, and the driving driver 50 drives the acousto-optical deflector 48 based on this signal, and The Bragg angle of the acousto-optic element of the acousto-optic deflector 48 is changed, and thereby the first exposure beam is optically deflected.

When a magneto-optical disk for evaluation described later is manufactured, a high-frequency signal having a center frequency of 224 MHz is FM-modulated by a control signal having a frequency of 84.672 kHz.
The voltage-controlled oscillator 51 supplied the driving driver 50. Then, based on this signal, the driving driver 50
Drives the acousto-optic deflector 48 to change the Bragg angle of the acousto-optic element of the acousto-optic deflector 48, whereby the position of the light spot of the first exposure beam focused on the photoresist 12 is changed. , Frequency 84.672 kHz
Optical deflection was performed so as to vibrate in the radial direction of the glass substrate 11 at z and amplitude ± 10 nm.

Then, the first exposure beam subjected to the light intensity modulation and the optical deflection as described above is condensed on the photoresist 12 by the objective lens 54, thereby exposing the photoresist 12 to the wobbling groove 6. A corresponding latent image is formed on the photoresist 12.

Further, the photoresist 12 is exposed by the second exposure beam at the same time as the photoresist 12 is exposed by the first exposure beam, so that a latent image corresponding to the straight groove 7 is formed on the photoresist 12. I do.

When a latent image corresponding to the straight groove 7 is formed on the photoresist 12 by exposing the photoresist 12 with the second exposure beam, the second
Is subjected to light intensity modulation by the second modulation optical system 23.

Specifically, a constant level DC signal is input to the driving driver 37, and the acousto-optic modulator 34 is driven by the driving driver 37 based on the DC signal.
As a result, light intensity modulation is performed on the second exposure beam so as to correspond to the pattern of the straight groove 7. Here, since the straight groove 7 is a continuous groove having a constant depth, while the latent image corresponding to the straight groove 7 is being formed, light is emitted so that the light intensity of the second exposure beam is constant. Apply intensity modulation.

Then, the second exposure beam subjected to the light intensity modulation as described above is condensed on the photoresist 12 by the objective lens 54, so that the photoresist 12
Is exposed to form a latent image corresponding to the straight groove 7 on the photoresist 12.

When the photoresist 12 is thus exposed to form latent images corresponding to the wobbling groove 6 and the straight groove 7, the photoresist 1 is exposed.
The glass substrate 11 coated with 2 is rotationally driven at a predetermined rotation speed and is translated at a predetermined speed.

More specifically, when producing a magneto-optical disk for evaluation, which will be described later, the rotation speed of the glass substrate 11 is controlled by the relative moving speed between the light spot by the first and second exposure beams and the photoresist 12. Was set to a linear velocity of 1.0 m / sec. Then, the glass substrate 11 was translated in the radial direction of the glass substrate 11 by 1.00 μm (that is, the track period TPeriod) for each rotation by a moving optical table.

By exposing the photoresist 12 with the first and second exposure beams as described above, the latent image corresponding to the wobbling groove 6 and the latent image corresponding to the straight groove 7 are formed into a double spiral. Formed on photoresist 12.

When the photoresist 12 is exposed by the first and second exposure beams as described above, the level of the DC signal input to the drive drivers 32 and 37 is adjusted to adjust the level of the second exposure beam. The power is set to be different from the power of the third exposure beam. As a result, the depth of the latent image corresponding to the wobbling groove 6 is different from the depth of the latent image corresponding to the straight groove 7.

In the laser cutting apparatus 10, the distance between the light spot of the first exposure beam and the light spot of the second exposure beam in the radial direction of the glass substrate 11 corresponds to the track pitch TPitch. The reflection angle of the reflection surface of the polarization beam splitter 45 is set in advance.

By setting the reflection angle of the reflection surface of the polarizing beam splitter 45 in this way, a latent image corresponding to the wobbling groove 6 is formed by the first exposure boom, and the latent image adjacent to the wobbling groove 6 is formed. A latent image corresponding to the straight groove 7 thus formed is formed by the second exposure beam. This means
In other words, the relative positioning between the wobbling groove 6 and the straight groove 7 can be realized by adjusting the direction of the deflection beam splitter 45.

After the latent image is formed on the photoresist 12 as described above, the glass substrate 11 is placed on a turntable of a developing machine such that the surface on which the photoresist 12 is coated is the upper surface. I do. Then, while rotating the glass substrate 11 by rotating the turntable, a developing solution was dropped on the photoresist 12 to perform a developing process, and the wobbling groove 6 and the straight groove 7 were formed on the glass substrate 11. An uneven pattern is formed.

Next, a conductive film made of Ni or the like is formed on the concave / convex pattern by electroless plating, and thereafter, the glass substrate 11 on which the conductive film is formed is attached to an electroforming apparatus, and the electroplating is performed. A plating layer made of Ni or the like is formed on the conductive film so as to have a thickness of about 300 ± 5 μm. Thereafter, the plating layer is peeled off, and the peeled plating is washed with acetone or the like to remove the photoresist 12 remaining on the surface to which the uneven pattern has been transferred.

Through the above steps, an original master for manufacturing an optical recording medium, ie, an uneven pattern corresponding to the wobbling groove 6 and the straight groove 7, is formed by plating the uneven pattern formed on the glass substrate 11 and transferred. The master for manufacturing an optical recording medium is completed.

The master for producing an optical recording medium is a master for producing an optical recording medium to which the present invention is applied. In other words, the master for producing an optical recording medium includes a wobbling groove 6 and a straight groove 7 along a recording track.
Is a master for manufacturing an optical recording medium used when manufacturing the magneto-optical disk 1 on which is formed the first groove pattern which is a concavo-convex pattern corresponding to the wobbling groove 6 and the straight groove 7. The second groove pattern, which is an uneven pattern, is formed in a double spiral shape. The first groove pattern and the second groove pattern are formed so that their depths are different from each other.

Next, as a transfer step, a disk substrate on which the surface shape of the master for producing an optical recording medium is transferred is manufactured by using a photopolymer method (so-called 2P method).

More specifically, first, a photopolymer is applied smoothly on the surface of the master for producing an optical recording medium on which the concave / convex pattern is formed to form a photopolymer layer. And garbage,
The base plate is brought into close contact with the photopolymer layer. Here, as the base plate, for example, a base plate made of polymethyl methacrylate (refractive index: 1.49) having a thickness of 1.2 mm is used.

Thereafter, the photopolymer is cured by irradiating ultraviolet rays, and then the master disc for producing an optical recording medium is peeled off, thereby producing a disk substrate 2 on which the surface shape of the master disc for producing an optical recording medium is transferred. .

Here, an example has been described in which the disk substrate 2 is manufactured using the 2P method so that the concavo-convex pattern formed on the optical recording medium manufacturing master is more accurately transferred to the disk substrate 2. Needless to say, when the disk substrate 2 is mass-produced, the disk substrate 2 may be manufactured by injection molding using a transparent resin such as polymethyl methacrylate or polycarbonate.

Next, as a film forming step, the recording layer 3 and the protective layer 4 are formed on the disk substrate 2 on which the surface shape of the optical recording medium manufacturing master has been transferred. Specifically, for example,
First, a first dielectric film made of SiN or the like and a TeFeCo
A perpendicular magnetic recording film made of an alloy or the like and a second dielectric film made of SiN or the like are sequentially formed by sputtering,
Further, by forming a light reflecting film made of Al or the like on the second dielectric film by vapor deposition, the light reflecting film comprises a first dielectric film, a perpendicular magnetic recording film, a second dielectric film, and a light reflecting film. The recording layer 3 is formed. Thereafter, an ultraviolet curable resin is applied on the recording layer 3 by a spin coating method, and the ultraviolet curable resin is irradiated with ultraviolet light to be cured, thereby forming the protective layer 4.

Through the above steps, the magneto-optical disk 1 is completed.

<Evaluation of Magneto-Optical Disk> Next, a plurality of evaluation magneto-optical disks having different depths of the wobbling groove 6 and the straight groove 7 are manufactured by the above-described manufacturing method, and the evaluation is performed. The results will be described.

Here, the depths of the wobbling groove 6 and the straight groove 7 were controlled by controlling the powers of the first exposure beam and the second exposure beam.

That is, when evaluating the evaluation magneto-optical disk, first, the power of the first exposure beam for forming a latent image corresponding to the wobbling groove 6 or the latent image corresponding to the straight groove 7 is used. A plurality of masters for producing an optical recording medium are manufactured by changing the power of the second exposure beam for forming, and then a magneto-optical disc for evaluation is manufactured by the 2P method using the masters for manufacturing an optical recording medium. Produced. In addition, polymethyl methacrylate having a refractive index of 1.49 was used as a material of the disk substrate of these evaluation magneto-optical disks.

The push-pull signal and the cross-track signal were measured for a plurality of evaluation magneto-optical disks having different depths of the wobbling groove 6 and the straight groove 7 manufactured as described above. Here, in measuring the push-pull signal and the cross-track signal, the wavelength λ of the laser beam is 650 nm and the numerical aperture NA of the objective lens is
Was 0.52.

The wobbling groove 6 and the straight groove 7 when the push-pull signal amplitude ratio is 0.15 or more and the cross-track signal amplitude ratio is 0.06 or more are used for these evaluation magneto-optical disks.
I checked the depth.

As a result, points a, b, c, d,
It was found that within the region surrounded by e, f, g, h, i, and j, the push-pull signal amplitude ratio was 0.15 or more and the cross-track signal amplitude ratio was 0.06 or more.

In FIG. 4, the vertical axis indicates the phase depth Y of the shallower groove of the wobbling groove 6 and the straight groove 7. The horizontal axis shows the phase depth X of the deeper groove of the wobbling groove 6 and the straight groove 7.

Here, an approximate straight line L1 connecting the points a, b, c, d, and e is represented by the following equation (2-1), and the points e, f, g, and
The approximate straight line L2 connecting the points h, i, j, and a is represented by the following equation (2-3).
It was represented by

X = 0.3950−0.831Y + 2.932Y ² (2-1) Y = 2.010-9.661X + 1.77X ² (2-2) Y = 0.8480-2 .450X + 1.880X ² (2-3) Therefore, the points a, b, c, d, e, f, g, h, i,
The area surrounded by j is the following equation (3-1) and equation (3-2)
And a region satisfying the expression (3-3).

X ≧ 0.3950−0.831Y + 2.932Y ² (3-1) Y ≧ 2.010−9.661X + 11.77X ² (3-2) Y ≦ 0.8480-2 .450X + 1.880X ² (3-3) In other words, of the wobbling groove 6 and the straight groove 7, the phase depth of the deeper groove is X, and the phase depth of the shallower groove is X. Assuming that Y is Y, the wobbling groove 6 and the straight groove 7 are expressed by the above equations (3-1), (3-2), and (3-
If it is formed so as to satisfy 3), the push-pull signal amplitude ratio becomes 0.15 or more and the cross-track signal amplitude ratio becomes 0.06 or more, which means that stable tracking servo and seek are possible. .

Here, the wavelength λ of the laser beam is 650 nm,
Since the numerical aperture NA of the objective lens is 0.52, the cutoff frequency 2NA / λ of the optical pickup is 1600 mm
It is ^-1 . On the other hand, since the track pitch TPitch of the evaluation magneto-optical disk is 0.50 μm, its spatial frequency is 2000 mm ⁻¹ . As described above, in the magneto-optical disk for evaluation, the spatial frequency of the track pitch TPitch is higher than the cutoff frequency 2NA / λ of the optical pickup.

Conventionally, the track pitch TPitch
If the spatial frequency is higher than the cutoff frequency 2NA / λ of the optical pickup, a sufficient level of push-pull signal or cross-track signal cannot be obtained, and stable tracking servo and seek cannot be performed. .

However, in the magneto-optical disk 1 to which the present invention is applied, as can be seen from the above experimental results, the wobbling groove 6 and the straight groove 7 are replaced by the above equations (3-1), (3-2) and (3-2). By forming so as to satisfy (3-3), the spatial frequency of the track pitch TPitch is made higher than the cutoff frequency 2NA / λ of the optical pickup while securing a sufficient level of push-pull signal and cross-track signal. It has become possible. That is, by applying the present invention, it is possible to reduce the track pitch TPitch and significantly improve the recording density while securing a sufficient level of push-pull signal and cross-track signal.

The present invention can be widely applied to an optical recording medium having a groove formed along a recording track, and an optical recording medium manufacturing master used for manufacturing the same. The optical recording medium to be used may be, for example, any one of a read-only optical recording medium, an optical recording medium in which data can be repeatedly written, and an optical recording medium in which data can be additionally written but cannot be erased.

The method of recording data is not particularly limited. Examples of the optical recording medium to which the present invention is applied include a read-only optical recording medium in which data is written in advance by emboss pits or the like, Either a magneto-optical recording medium for recording data using an optical effect or a phase-change optical recording medium for recording data using a phase change of a recording layer may be used.

The present invention can be widely applied to an optical recording medium in which a groove is formed in at least a part of a recording area, and an optical recording medium manufacturing master used for manufacturing the optical recording medium. That is, for example, a groove may be formed in the entire recording area, or an area in which data is recorded by embossed pits without forming a groove may exist in the recording area. .

[0112]

As is apparent from the above description, according to the present invention, an optical recording medium capable of performing tracking servo and seek stably even when the track pitch is extremely narrow, and such an optical recording medium. An optical recording medium manufacturing master capable of manufacturing an optical recording medium can be provided. Therefore, according to the present invention, the track can be further narrowed, and the recording density of the optical recording medium can be further increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an enlarged main part of an example of a magneto-optical disk to which the present invention is applied.

FIG. 2 is an enlarged view showing a part of a recording area of an example of a magneto-optical disk to which the present invention is applied.

FIG. 3 is a diagram showing an outline of an optical system of an example of a laser cutting device used when producing an optical recording medium and a master for producing an optical recording medium according to the present invention.

FIG. 4 is a diagram showing the relationship between the depth of a wobbling groove and a straight groove and a push-pull signal and a cross-track signal.

FIG. 5 is a diagram for explaining a method of detecting a push-pull signal and a cross-track signal.

FIG. 6 is a diagram for explaining a push-pull signal amplitude ratio and a cross-track signal amplitude ratio.

[Explanation of symbols]

Reference Signs List 1 magneto-optical disk, 2 disk substrate, 3 recording layer, 4 protective layer, 6 wobbling groove, 7
Straight groove

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[Procedure amendment]

[Submission date] August 18, 1998

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 6

[Correction method] Change

[Correction contents]

FIG. 6

Claims (5)

[Claims] 1. An optical recording medium in which a groove is formed along a recording track and irradiated with light having a predetermined wavelength λ to perform recording and / or reproduction, wherein the first groove and the second groove are used as the groove. 2 grooves are formed so as to draw a double spiral, and the refractive index of the medium from the light incident surface to the first groove is n _x
And when the depth of the first groove is x, x × n
_Let X be the phase depth of the first groove expressed by _x / λ, and let n _{y be} the refractive index of the medium from the light incident surface to the second groove.
And when the depth of the second groove is y, y × n
_When the phase depth of the second groove represented by _y / λ is Y, the first groove and the second groove are represented by the following formulas (1) and (2).
An optical recording medium formed to satisfy Expressions (2) and (3). X ≧ 0.3950−0.831Y + 2.932Y ² (1) Y ≧ 2.010−9.661X + 11.77X ² (2) Y ≦ 0.8480-2.450X + 1.880X ^2.・ (3) 2. An optical recording apparatus according to claim 1, wherein at least one of said first groove and said second groove is a wobbling groove formed so that at least a part thereof meanders. Medium. 3. When the numerical aperture of an objective lens used for recording and / or reproduction is NA and the wavelength of light is λ, 2 × N
2. The optical recording medium according to claim 1, wherein the spatial frequency of the track pitch is higher than the cutoff frequency represented by A / λ. 4. An optical recording medium manufacturing master used for manufacturing an optical recording medium on which a groove is formed along a recording track and irradiated with light having a predetermined wavelength λ to perform recording and / or reproduction. A first groove pattern and a second groove pattern are formed so as to draw a double spiral as an uneven pattern corresponding to the groove, and the first groove is formed from the light incident surface of the optical recording medium to the first groove. the refractive index of the medium leading to the n _x, a depth of the first groove pattern 'is taken as, x' x of the phase depth of the first groove pattern represented by × n _x / λ _X ' between, and the refractive index of the medium reaching the second groove from the light incident surface of the optical recording medium and n _y, the depth of the second groove pattern 'when _{a, y' y × n y /} λ Assuming that the phase depth of the represented second groove pattern is Y ′ , The first groove pattern and a second groove pattern is represented by the following formula (4), (5) and the optical recording medium manufacturing master, characterized in that is formed so as to satisfy the equation (6). X ′ ≧ 0.3950−0.831Y ′ + 2.932Y ′ ² (4) Y ′ ≧ 2.010-9.661X ′ + 11.77X ′ ² (5) Y ′ ≦ 0.8480 ^{-2.450X '+ 1.880X' 2 ··· (} 6) 5. The first groove pattern and the second groove pattern.
5. The master for producing an optical recording medium according to claim 4, wherein at least one of the groove patterns is an uneven pattern corresponding to a wobbling groove formed so that at least a part thereof is meandering.