JP2998681B2 - Optical recording medium and method for producing master disk - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optically recordable and reproducible optical recording medium having pregrooves and address pits, and a method for producing a master for the same. 2. Description of the Related Art First, with reference to FIGS. 1 and 2, a conventional optical recording medium capable of recording and reproducing will be described.
1 and 2, reference numeral 1 denotes an optical recording medium (disk).
In FIG. 1, PG is a pre-groove (in FIG. 1, a concentric pre-groove, but may be a spiral pre-groove close to a circle), SC is a sector of each pre-groove PG, and AP is a pre-groove. The pre-groove PG for indicating the number of the PG and the number of the sector SC
Are address pits formed at the end of each sector SC. Note that the pitch of the pregroove PG is 2.0 μm.
m, and its width is 0.8 μm. As shown in FIG. 2, this optical recording medium 1 has a single or multi-layered low melting point metal layer (pre-groove PG) on which information is to be optically recorded on a transparent plastic substrate 2 made of acrylic or the like. A reflective metal layer 3 is formed. Here, LD is a land portion of the metal layer 3. Reference numeral 4 denotes a protective layer made of plastic and formed on the metal layer 3. In the optical recording medium 1, the laser beam from the laser light source is scanned while tracking the pre-groove PG of the metal layer 3, and the pre-groove P
Information is optically recorded in G. The recording is performed by irradiating the pre-groove PG with a laser beam, thereby changing the structure of the metal layer 3 and increasing the reflectivity thereof, thereby performing frequency modulation, phase modulation, Recording is performed so as to form a recording track as a row of optical dots by PCM or the like.
Optical dots can also be formed by melting the metal 3 with a laser beam to reduce its reflectivity, or by exposing another metal layer underneath to thereby increase the reflectivity. Next, with reference to FIG. 3, a master 1 'for manufacturing the above-mentioned optical recording medium will be described. FIG.
A is a partial top view of the master 1 ', and B is a partial sectional view thereof. Reference numeral 5 denotes, for example, a glass substrate, wherein the wavelength of the recording and reproducing beams for the optical recording medium 1 is λ, and the refractive index of the light transmitting layer through which the recording and reproducing beams transmit, that is, the transparent substrate 2 is n. When the thickness is λ / (8n)
The photoresist layer 6 is uniformly deposited so that
This is cut to reach the surface of the glass substrate 5, that is, a laser beam is radiated and developed, whereby each of the pregrooves P has a phase depth of λ / (8n).
G 'and address pits AP' are formed. Thereafter, as is well known in the art, plating is performed on the photoresist layer 6 remaining on the glass substrate 5 of the master 1 ', and a metal master is formed based on the plating to form a mother from the metal mask. create. Then, a stamper is formed from the mother, a light-transmissive resin such as acrylic is stamped using the stamper to form a transparent substrate 2, a light-reflective metal layer 3 is formed thereon, and a protective layer is formed thereon. The layer 4 is formed by deposition (see FIG. 2). In the master 1 'of the optical recording medium 1 shown in FIG. 3, the thickness of the photoresist layer 6 applied on the glass substrate 5 is 600.
In addition to the drawbacks of being extremely thin, about 800 °, having a non-uniform thickness and causing pinholes, the pre-groove P
Since both the phase depth of G ′ and the phase depth of the address pit AP ′ are λ / (8n), the following problem occurs. That is, the amount of light reflected by the metal layer 3 of the optical recording medium (disc) 1 finally formed as shown in FIGS. 1 and 2 will be described with reference to FIG. Assuming that the amount of reflected light when the light reflecting metal layer 3 is an ideal mirror surface is I _O , the metal layer 3
The amount of reflected light I _TOP on the land portion LD is substantially equal to I _O. S _AP indicates a portion where the amount of reflected light is modulated by the address pit AP, and its peak level is defined as I _PP . S _RP indicates the modulation of the amount of reflected light when an information signal is recorded in the pre-groove PG and is reproduced, and I _RP indicates its peak value. The phase depth of the pregroove PG is λ / (8n)
Therefore, the level of the tracking error signal (push-pull signal) becomes large, but on the other hand, the phase depth of the address pit AP becomes λ / similar to that of the pre-groove PG.
(8n), as can be seen from FIG. 4, the peak value of the reproduction light amount from the address pit AP is 2 of I _O.
It turns out that it is very small, 0 to 30%. Conversely, in order to increase the peak value I _{PP of the} amount of reproduced light from the address pit AP, the address pit AP
If the phase depth of both the pre-groove PG and the pre-groove PG is set to λ / (4n), the level of the tracking error signal decreases, and the degree of modulation of the pre-groove PG increases, thereby lowering the S / N of the reproduction information signal. . Therefore, in order to satisfy both requirements, at the time of manufacturing the master 1 ′, the λ / (4n)
A thick photoresist layer 6 is deposited and formed, and the light amount of the same beam is reduced by the pre-groove PG 'and the address pit AP'.
The phase depth of each pregroove PG 'is λ / (8n),
In the address pit AP ', the phase depth is λ /
(4n) may be considered. But,
In this case, the photoresist layer is formed of a pre-groove PG '.
Is exposed in halftone, the process control is difficult, and the photoresist layer exposed in halftone is not uniform due to uneven development.
When the phase depth of the address pit AP 'becomes non-uniform, recording is performed on the disk 1 made based on this, and when the address pit AP is reproduced from now on, the S of the reproduced signal is
/ N is worse. Conventionally, information is recorded in the pre-groove PG of the optical recording medium 1, so that the reproduction information signal S
/ N was small, and the possibility of dropout was high. In view of the above, the first aspect of the present invention is to provide an optical recording medium having a pre-groove and an address pit, which is optically recordable and reproducible. S /
It is an object of the present invention to provide a signal capable of reproducing an information signal having a good N, a small dropout, and a good S / N. A second aspect of the present invention is to provide a method for producing an optical recording medium master from which an optical recording medium master according to the first invention can be easily manufactured. An optical recording medium according to the present invention has a transmission layer through which recording and reproduction beams are transmitted, and is formed on one surface of the transmission layer to form an optical recording medium. An optical recording medium having a reproducible recording layer and a protective layer provided on the recording layer for protecting the recording layer, and provided with a plurality of sectors in the circumferential direction, Assuming that the wavelength of the reproducing beam is λ and the refractive index of the transmitting layer through which the recording and reproducing beams pass is n, a concentric or spiral λ is formed on the surface of the transmitting layer on which the recording layer is formed.
A pre-groove having a phase depth of / (8n) and address pits having a phase depth of λ / (4n) formed in the area sandwiched by the pre-grooves and at the end of each sector. It is. According to the present invention, in an optical recording medium having a pre-groove and an address pit and capable of optically recording and reproducing, the level of the tracking error signal is large and the S of the reproduction signal of the address pit is high. It is possible to obtain an information signal having a good S / N ratio, a small dropout, and an information signal having a good S / N ratio. As a result, according to the present invention, even in an optical recording medium having a sector structure, a sufficient degree of modulation of the address pit portion can be obtained as shown in FIG. There is no problem that a signal based on the address pit cannot be obtained accurately at the time of recording and reproduction to and from, and a correct recording or reproduction operation cannot be performed. [0015] A method for producing a master of an optical recording medium according to the present invention comprises a transmission layer for transmitting a recording and reproducing beam;
It has a recording layer that is adhered and formed on one surface side of the transmission layer and is optically recordable and reproducible, and a protection layer that is provided on the recording layer and protects the recording layer. A method for producing a master of an optical recording medium provided with a plurality of sectors, comprising: a first light beam whose beam intensity is controlled by a first modulator on a glass substrate provided with a photoresist layer; The second light beam modulated based on the address signal by the second modulator is scanned while being focused by the objective lens, and the wavelength of the recording and reproducing beam used for recording and reproducing on the optical recording medium is performed. Where λ is the refractive index of the transmission layer through which the recording and reproducing beams pass, and n is the phase depth of the concentric or spiral λ / (8n) formed by the first beam in the photoresist layer. Form pre-groove Then, in a region sandwiched by the pre-grooves, and at the end of each sector, the second beam having the beam intensity higher than the first beam intensity has λ / (4).
An address pit having a phase depth of n) is formed. According to the present invention, the master of the optical recording medium according to the present invention can be easily manufactured, and the phase depth formed in the photoresist layer by controlling the intensity of the first beam. Grooves and address pits having different sizes can be easily formed. Further, the optical recording medium manufactured based on the master obtained by the method of manufacturing the master according to the present invention can obtain a sufficient degree of modulation at the address pit portion as shown in FIG. 7 described later. Referring to FIG. 5, the structure of an optical recording medium master according to the present invention will be described below. A photoresist layer 6 is formed on a glass substrate 5 in the same manner as in FIGS. 1 and 2 described above.
(4n). Then, as will become clear from the description below, the address pit AP 'is formed by using two beams.
The photoresist layer 6 is cut by exposure and development until the photoresist layer 6 reaches the surface of the glass substrate 5, and the pregroove PG 'is λ / (8n) using a beam having a smaller amount of light than the beam forming the address pit AP'. ). Then, the master 1 'thus formed is formed.
The optical recording medium 1 as shown in FIG. That is, a pregroove PG having a phase depth of λ / (8n) on a transparent substrate 2 made of acrylic or the like,
A low melting point metal layer 3 having an address pit AP having a phase depth of λ / (4n) is formed by deposition. 4 is a protective layer. In this case, the pre-groove PG is formed on the land portion LD of the metal layer 3, the pitch is 2 μm, the interval between the pre-groove PG and the address pit AP is 1 μm, and the width of each is 0.5 μm. The information signal is recorded at the center of the land LD of the metal layer 3. It goes without saying that the beam from the co-optical system during recording and reproduction enters the metal layer 3 of the medium 1 from the transparent substrate 2 side. The amount of reflected light of the optical recording medium 1 obtained in this manner will be described with reference to FIG. 7. In FIG. 7, portions corresponding to FIG. In this case, it can be seen that the peak level I _PP due to the modulation of the reflected light amount of the address pit is 50 to 60% of I _O , which is much larger than that in FIG. The optical recording medium thus formed uses one beam, reproduces the address pits AP on the land, detects the tracking error signal, and outputs the information signal to the land LD by dots. Record. Further, detection of a tracking error, reproduction of an address pit, and recording of an information signal may be performed using three beams. Also at the time of reproduction, the same device can reproduce an information signal that has been phase-modulated or frequency-modulated and PCM-recorded on the land LD. According to the above-mentioned optical recording medium, even if the level of the tracking error signal is large and the degree of modulation of the pre-groove is slightly varied, the influence on the reproduced information signal is small, and the address pits are reduced by S / N. An information signal that can be reproduced well, has a good yield, has a good S / N, and has a low possibility of dropout can be reproduced. Also, since the tracking error signal for the address pit is zero, no disturbance is mixed into the tracking error signal by the address pit. Since no information signal is recorded in the pre-groove, its width can be reduced, which leads to an improvement in recording density. Next, with reference to FIG. 8, an apparatus for manufacturing the master of the above-mentioned optical recording medium will be described. Reference numeral 7 denotes a laser light source (for example, an Ar or He-Cd laser light source) which emits, for example, an S-polarized laser beam LB _O , which is incident on a beam splitter 8 to emit first and second beams LB ₁ , LB ₁ , separated into LB _2. The optical path of the first beam LB ₁ is deflected by 90 ° by the beam splitter 8, and the optical path of the second beam LB ₂ is deflected by 90 ° by the mirror 9 after going straight. The first and second beams LB ₁ and LB
₂ is supplied to first and second optical modulators (electro-optical conversion elements) 12 and 13 via lenses 10 and 11, respectively.
A DC voltage from a DC power supply 14 is applied to the first optical modulator 12. Pulse signal from the signal source 15 to the second optical modulator 13, i.e., is supplied with an address signal indicating a track number and sector number, the second beam LB ₂ is optically modulated. 9 and 10 show the waveforms of the beams obtained from the first and second optical modulators 12 and 13, respectively. The intensity of the beam for exposing the photoresist layer 6 can be adjusted by the voltage applied to the first and second optical modulators 12 and 13 so that the former is weaker and the latter is stronger. The first and second optical modulators 12 and 13
S and P-polarized beams LB ₁ and LB ₂ obtained from the mirrors 18 and 19 via convex lenses 16 and 17, respectively.
And its optical path is deflected by 90 °. First
Beam LB ₁ is further reflected by mirror 20 so that its optical path is 9
The light is deflected by 0 ° and is incident on the polarization beam splitter 21. The second beam LB ₂ deflected by 90 ° by the mirror 19 is also polarized beam splitter 2.
1 is incident. Then, the first and second beams LB ₁ and LB ₂ emitted from the polarizing beam splitter 21 are
After the light is incident on the mirror 23 through the mirror 2 and its optical path is deflected by 90 °, it is incident on the objective lens 24 to form a focused beam, and these beams LB ₁ and LB ₂ are spaced apart by 1 μm from the glass substrate 5 described above. Irradiation is performed on the photoresist layer 6 formed thereon, and the photoresist layer 6 is exposed. This exposed photoresist layer 6
Is developed to remove a portion exposed to light, thereby forming a pre-groove PG 'and an address pit AP' as shown in FIG. According to the optical recording medium master manufacturing apparatus described above, the optical recording medium master can be easily manufactured. By changing the polarity of the tracking servo circuit, tracking of the optical recording disk according to the present invention can be easily performed using a conventional optical recording / reproducing apparatus. The optical recording medium of the present invention is provided with a plurality of sectors in the circumferential direction. The recording and reproducing beam has a wavelength of λ, and the recording and reproducing beam has a wavelength of λ. Assuming that the refractive index of the transmitting layer to be transmitted is n, a concentric or spiral pregroove having a phase depth of λ / (8n) is formed on the surface of the light transmitting layer on which the recording layer is formed. At the same time, address pits having a phase depth of λ / (4n) are formed in the area sandwiched by the pregrooves and at the end of each sector. According to the present invention, in an optical recording medium having a pre-groove and an address pit and capable of optically recording and reproducing, the level of the tracking error signal is large and the S of the reproduction signal of the address pit is high. It is possible to reproduce an information signal having a good S / N ratio and a good S / N ratio. Further, according to the present invention, even in an optical recording medium having a sector structure, a sufficient degree of modulation of the address pit portion can be obtained as shown in FIG. Also, there is no problem that a signal based on the address pit cannot be obtained accurately at the time of reproduction, and correct recording or reproduction cannot be performed. According to the method for producing a master of an optical recording medium of the present invention, the first and second beams are set so that the intensity of the second beam is higher than that of the first beam. While scanning the photoresist layer, the wavelength of the recording and reproduction beam used for recording and reproduction of the optical recording medium is λ, when the refractive index of the transmission layer through which the recording and reproduction beam is transmitted is n, A concentric or spiral pre-groove having a phase depth of λ / (8n) is formed in the photoresist layer by the first beam, and the pre-groove having a phase depth of λ / (8n) is formed between the pre-groove and the end of each sector. An address pit having a phase depth of λ / (4n) is formed by the second beam having a higher beam intensity than the first beam. According to the present invention, the above-mentioned optical recording medium of the present invention can be easily obtained, and the phase depth formed in the photoresist layer can be reduced by controlling the intensity of the first beam. Different grooves and address pits can be easily formed. Further, the optical recording medium manufactured based on the master obtained by the method of manufacturing the master according to the present invention can sufficiently obtain the modulation degree at the address pit portion as shown in FIG. it can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a conventional optical recording medium capable of recording and reproduction. FIG. 2 is a cross-sectional view of a conventional recording / reproducing optical recording medium. FIG. 3A is a plan view showing a master of the optical recording medium of FIGS. 1 and 2; FIG. 3B is a cross-sectional view showing a master of the optical recording medium of FIGS. 1 and 2. FIG. 4 is a curve diagram showing characteristics of reflected light of a conventional optical recording medium. FIG. 5A is a plan view showing a master of an optical recording medium according to the present invention. B is a sectional view showing the master of the optical recording medium according to the present invention. 6 is a sectional view of an optical recording medium according to the present invention obtained by using the master shown in FIG. FIG. 7 is a curve diagram showing characteristics of reflected light of the optical recording medium of FIG. 6; FIG. 8 is a layout view showing an apparatus for manufacturing an optical recording medium master according to the present invention. 9 is a waveform diagram showing a waveform of an output beam of a first optical modulator of the apparatus for manufacturing a master shown in FIG. FIG. 10 is a waveform diagram showing a waveform of an output beam of a second optical modulator of the apparatus for manufacturing a master shown in FIG. 8; [Description of Signs] 1 optical recording medium, 2 transparent substrate as light transmitting layer,
3 Reflective metal layer formed thereon, 4 Protective layer formed thereon, PG pregroove, AP address pit, 7 light sources, 8 division means, 12, 13 First and second optical modulators, 24 Objective lens, 1 'master

Claims (1)

(57) [Claims] A transmission layer that transmits recording and reproduction beams, a recording layer that is formed on one surface of the transmission layer and that can be optically recorded and reproduced, and is provided on the recording layer to protect the recording layer An optical recording medium provided with a plurality of sectors in a circumferential direction, wherein the wavelength of the recording and reproducing beam is λ, and the transmitting layer transmits the recording and reproducing beam. Is defined as n, a concentric or spiral pre-groove having a phase depth of λ / (8n) is formed on the surface of the transmission layer on which the recording layer is formed. An optical recording medium, wherein address pits having a phase depth of λ / (4n) are formed in an area sandwiched by the pregrooves and at the end of each sector. 2. A transmission layer that transmits recording and reproduction beams, a recording layer that is formed on one surface side of the transmission layer, and that can be optically recorded and reproduced, and the recording layer that is provided on the recording layer. A method for producing a master of an optical recording medium having a plurality of sectors provided in a circumferential direction, comprising a protective layer for protecting, wherein a beam is formed by a first modulator on a glass substrate provided with a photoresist layer. Scanning a first light beam whose intensity is controlled and a second light beam modulated based on an address signal by a second modulator in a state of being focused by an objective lens, and When the wavelength of the recording and reproduction beam used for recording and reproduction is λ, and the refractive index of the transmission layer through which the recording and reproduction beam passes is n, the first beam is applied to the photoresist layer. Concentric or A pregroove having a phase depth of λ / (8n) is formed in a winding shape, and the intensity of the beam is higher than the intensity of the first beam in an area sandwiched between the pregrooves and at the end of each sector. Forming an address pit having a phase depth of [lambda] / (4n) by the second beam having high intensity.