JP4238284B2 - Optical recording medium - Google Patents

Description

  The present invention relates to an optical recording medium, and more particularly to a disk-shaped optical disk used for reproducing information.

  Examples of conventional optical recording media include optical disks such as CD-ROM and DVD-ROM. In these optical disks, pit rows made of irregularities are formed on a transparent substrate made of polycarbonate or the like, and a metal reflective film made of Al or the like is formed thereon. Information is reproduced by irradiating a light beam to the metal reflection film serving as the information recording surface from the surface side opposite to the surface on which the metal reflection film is formed.

  In addition, optical recording media that record and reproduce information by irradiating a light beam are widely used, and there are high expectations for improvement in the recording density in the future. In recent years, various optical discs capable of reproducing large-capacity image / audio data and digital data have been developed. For example, a high-density read-only optical disc that increases the storage capacity of an optical disc having a diameter of 12 cm to 23.3 to 30 GB. Research and development is ongoing.

  On the other hand, in a DVD read-only recording medium, a technique for preventing unauthorized use and unauthorized copying of recorded information, a so-called security technique, is an area in which medium identification information capable of individually identifying each recording medium is overwritten with a barcode pattern. A BCA (Burst Cutting Area) area is provided. In the BCA area, medium identification information different for each optical recording medium is recorded at the time of manufacturing the optical recording medium, and an encryption key and a decryption key are recorded as necessary.

For example, media identification to prevent unauthorized use and unauthorized copying by partially removing the metal reflective film of the optical disk with pit rows as main data by laser trimming and recording the modulated data individually Information is recorded (for example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 10-233019

  However, in order to achieve high density as described above, the track pitch is narrowed or the shortest pit length is miniaturized, so data of 23.3 GB or more was recorded on a 12 cm diameter disk. It has been found that when a metal reflective film made of an Al alloy having a film thickness of 50 to 70 nm used for DVD reproduction-dedicated optical disks is formed on a high-density optical disk substrate, the quality of the reproduced signal is deteriorated.

  This is presumably because the metal reflection film is difficult to be formed at the bottom of a minute pit of about 0.2 μm, and the smaller the pit, the deeper the pit depth and the smaller the pit size. Therefore, the metal reflection film used in the DVD reproduction-dedicated optical disk cannot be directly used as the metal reflection film of the high-density reproduction-dedicated optical disk.

  In the manufacture of a DVD read-only optical disk, medium identification information is recorded using a medium identification information recording apparatus equipped with a YAG (Yttrium Aluminum Garnet) laser. However, using this medium identification information recording device, the medium identification information is displayed on the area where the pits of the high density read-only optical disc are not formed or on the pit row recorded at the same track pitch 0.74 μm as the DVD read-only optical disc. Even if recording is performed with a code pattern, the pattern cannot be formed, or the reproduction noise of the medium identification information becomes high, so that a sufficient defocus margin cannot be secured.

  This is because the high-density read-only optical disk has a thinner metal reflection film than the DVD read-only optical disk, and the metal reflection film material used is different, so the heat capacity until the metal reflection film reaches the melting point is high. This is thought to be because it is very different. Therefore, a medium identification information recording apparatus equipped with a conventional YAG laser cannot be used for manufacturing a high-density read-only optical disk as it is.

  An object of the present invention is to record medium identification information capable of recording data at a higher density than a DVD read-only optical disk and capable of securing a sufficient defocus margin using a conventional medium identification information recording apparatus. It is to provide an optical recording medium that can be used.

  An optical recording medium according to the present invention includes a main information area in which a metal reflection film is formed on a substrate on which pit rows are formed as main data, and a plurality of reflection film removal areas by partially removing the metal reflection film. An optical recording medium that reproduces information by irradiating the metal reflective film with a light beam having a sub-information area in which medium identification information for individually identifying the optical recording medium is recorded. In the sub information area, pit rows or guide grooves are formed on the substrate, and a track pitch of the pit rows or guide grooves is 0.24 μm or more and 0.45 μm or less.

  The reflectance of the metal reflective film is preferably 35% or more and 70% or less for a light beam having a wavelength of 405 nm.

  The metal reflective film is made of Ag or an Ag alloy material, and the thickness of the metal reflective film is preferably 25 nm or more and 70 nm or less.

  The metal reflective film may be made of Al or an Al alloy material, and the metal reflective film may have a thickness of 15 nm to 40 nm.

  When the wavelength of the light source of the light beam is λ and the refractive index of the resin layer formed on the metal reflective film is n, the depth of the pit row or guide groove formed on the substrate in the sub information area The length D preferably satisfies the relational expression of λ / (6 × n) ≦ D ≦ λ / (3 × n).

  It is preferable that the depth of the pit row formed on the substrate in the main information region is equal to the depth of the pit row or guide groove formed on the substrate in the sub information region.

  The track pitch of the pit rows formed on the substrate in the main information region is 0.24 μm or more and 0.43 μm or less, and the shortest pit length of the pit rows formed on the substrate in the main information region is 0. It is preferable that they are 12 micrometers or more and 0.21 micrometers or less.

  The track pitch of the pit rows formed on the substrate in the main information area is preferably equal to the track pitch of the pit rows or guide grooves formed on the substrate in the sub information area.

  According to the present invention, a pit row or guide groove is formed in the sub-information area on the substrate, and the track pitch of the pit row or guide groove is set to 0.24 μm or more and 0.45 μm or less, so that a shorter wavelength can be obtained. Using a reproducing light beam and an optical system with a higher numerical aperture, it is possible to record data at a higher density than an optical disk dedicated for DVD reproduction, and the thermal conductivity and melting point, which are eigenvalues of the metal reflective film, are different. However, it is possible to record medium identification information that can ensure a sufficient defocus margin using a conventional medium identification information recording apparatus.

  Hereinafter, a ROM type optical disk will be described as an example of an optical disk according to an embodiment of the present invention. The optical recording medium to which the present invention is applied is not particularly limited to this example. For example, the present invention is applied to various optical recording media having fine irregularities in the information recording layer, such as a magneto-optical disk and a phase change disk. The same can be applied.

  This ROM-type optical disc has a main information area in which a metal reflection film is formed on a substrate on which pit rows consisting of unevenness are formed as main data, and a plurality of reflection film removal areas are formed by partially removing the metal reflection film. By doing so, it has a sub-information area in which medium identification information for individually identifying the optical disk is recorded, and information is reproduced by irradiating the metal reflection film with a light beam.

  Generally, to increase the density of ROM type optical discs, it is necessary to narrow the track pitch and make the shortest pit length (shortest mark length) fine. However, if the track pitch is made too narrow, crosstalk in the RF signal characteristics may occur. If the shortest pit length is too small, the resolution of the reproduced signal is lowered and the jitter value of the reproduced signal is deteriorated.

  For this reason, the optimum track pitch was repeatedly investigated using an information reproducing apparatus in which the wavelength λ of the light source of the reproducing light beam was 405 nm and the numerical aperture NA of the objective lens was 0.85. As a result of the examination, the measurement results shown in the table below were obtained, and it was found that if the track pitch is 0.24 μm or more, the crosstalk signal does not cause a practical problem with respect to the main signal.

  In addition, as a result of investigating the optimum shortest pit length using the above information reproducing apparatus and investigating the resolution with which a good reproduction signal can be obtained, the measurement results shown in the table below are obtained, and the shortest pit length is 0.12 μm. From the above, it has been found that the resolution of the reproduction signal can be sufficiently secured.

  In consideration of various margins of the optical disk and the drive, the jitter value indicating the characteristics of the optical disk needs to be 6.5% or less.

Here, in order to reproduce an optical disk having a diameter of 12 cm using the above information reproducing apparatus so that the storage capacity of the optical disk is 23.3 GB or more, (shortest pit length) × (track pitch) ≦ 0.0512 μm ² Must satisfy the relational expression. For example, when the recording capacity is 23.3 GB and the shortest pit length is 0.12 μm, the upper limit of the track pitch is about 0.43 μm. Similarly, when the recording capacity is 23.3 GB and the track pitch is 0.24 μm, the upper limit of the shortest pit length is about 0.21 μm.

  Next, a method for manufacturing an optical disk having a recording capacity of 23.3 GB or more and having a diameter of 12 cm will be described. As described above, in order to produce an optical disk having a recording capacity of 23.3 GB or more and a diameter of 12 cm, the track pitch is 0.24 μm or more and 0.43 μm or less, and the shortest pit length is 0.12 μm or more and 0.21 μm or less. It is necessary to use a certain substrate.

  For example, in order to produce an optical disk having a recording capacity of 25 GB and a diameter of 12 cm, first, a substrate on which a pit row having a shortest pit length of 0.149 μm and a track pitch of 0.32 μm was formed was prepared. As this substrate, for example, a substrate made of a polycarbonate material produced by an injection molding machine can be used.

  Next, a metal reflective film was formed on this substrate by a film forming apparatus. As the film forming apparatus, a magnetron sputtering apparatus, a vapor deposition apparatus, or the like that can form a metal reflective film uniformly can be used. For example, by using a magnetron sputtering apparatus and changing the film forming time, the film of the metal reflective film can be used. Thickness can be controlled. The material and film thickness of the metal reflective film will be described later.

  Next, the optical disk was placed on a spin coater so that the metal reflective film was on top, an ultraviolet curable resin was dropped, and a 88 μm thick transparent sheet made of polycarbonate was placed thereon. While rotating the optical disk with the spin coater in this state, the ultraviolet curable resin is irradiated with ultraviolet rays, and the spin coater rotation speed is controlled so that the cured thickness of the ultraviolet curable resin becomes 12 μm. A transparent resin layer having a thickness of 100 μm was formed. As this ultraviolet curable resin, for example, an acrylic resin can be used.

  As described above, a metal reflective film was formed on a substrate on which a pit row having a minimum pit length of 0.149 μm and a track pitch of 0.32 μm was formed, and a resin layer having a thickness of 100 μm was formed thereon. An optical disc was manufactured.

  Next, with respect to the optical disc manufactured as described above, the pit depth with respect to the quality of the reproduction signal, the material and film thickness of the metal reflection film, etc. were examined. Specifically, the manufactured optical disk is set in the information reproducing apparatus, and a light beam is incident on the metal reflection film through the resin layer having a thickness of 100 μm by the information reproducing apparatus, and the reproduction signal obtained from the optical disk is evaluated. did.

  First, the dependence of playback signal quality on pit depth was examined. The jitter value representing the variation in the reproduction signal was measured by changing the pit depth of the optical disk manufactured as described above. FIG. 1 is a diagram showing the measurement result of the jitter value with respect to the pit depth. The horizontal axis represents the pit depth (nm), and the vertical axis represents the jitter value (%). In FIG. 1, a metal reflective film made of an Al alloy having a thickness of 25 nm and a purity of 99 wt% is used, but a metal reflective film made of Ag98Pd1Cu1 (wt%) (hereinafter referred to as an AgPdCu alloy) is used. The same results as below were obtained.

  Generally, in order to ensure a sufficient system margin, it is necessary to make the jitter value 6.5% or less. From FIG. 1, when the pit depth is 44 nm or more and 88 nm or less, the jitter value is 6.5%. I found that I can do the following: Since the refractive index n of the prepared resin layer is 1.53 and the wavelength λ of the light beam is 405 nm, from the above measurement results, the pit depth D at which a good reproduction signal can be obtained is λ / (6 × n) was found to be λ / (3 × n) or less.

  This is considered to be due to the following reasons. That is, the pit depth affects the amplitude of the reproduction signal. In optical calculation, the amplitude is maximum when the pit depth is λ / (4 × n), and the refractive index n of the resin layer is 1.53. When the wavelength λ of the light beam is 405 nm, the pit depth becomes maximum at around 66 nm, but the jitter value of the reproduced signal is almost unchanged even if the amplitude is slightly reduced. However, when the pit depth is shallower than λ / (6 × n) or deeper than λ / (3 × n), a sufficient signal-to-noise ratio (hereinafter referred to as S / N ratio) is obtained. This is because the jitter value of the reproduction signal deteriorates.

  Next, an appropriate film thickness of the metal reflective film was examined. First, a substrate having a pit depth of λ / (4 × n) is prepared. As a metal reflection film, a metal reflection film made of an AgPdCu alloy and a metal reflection film made of an Al alloy having a purity of 99 wt% are used. The jitter value was measured while changing the thickness. FIG. 2 is a diagram showing the measurement result of the jitter value with respect to the film thickness of the metal reflection film made of AgPdCu alloy, and FIG. 3 is a diagram showing the measurement result of the jitter value with respect to the film thickness of the metal reflection film made of Al alloy. The horizontal axis represents the film thickness (nm) of the metal reflection film, and the vertical axis represents the jitter value (%).

  In the case of the metal reflection film of AgPdCu alloy from FIG. 2, when the film thickness is 25 nm or more and 70 nm or less, the jitter value can be 6.5% or less, and in the case of the metal reflection film of Al alloy from FIG. It was found that the jitter value could be 6.5% or less when the wavelength was 15 nm or more and 40 nm or less. The material of the metal reflective film is not particularly limited to the above example, and other materials may be used as long as a high reflectance is obtained and the film can be uniformly formed on the substrate by a film forming apparatus. In order to improve the corrosion resistance, a small amount of a rare earth metal element such as Nd or a transition metal element such as Ti or Cr may be added to the Ag or Al reflective film material.

  Next, the reflectance of the metal reflective film was examined. When the metal reflection film is thin, the amount of reflected light is small. When the amount of reflected light is small, the medium noise is also proportionally reduced, so the S / N ratio does not change. On the other hand, system noise and laser noise do not depend on the amount of reflected light. If the system noise and laser noise are low enough to be ignored compared to medium noise, the quality of the reproduced signal will not be affected even if the amount of reflected light is reduced. .

  However, when the amount of reflected light is reduced and the system noise and laser noise are approximately the same as the medium noise, the reduction in the amount of reflected light deteriorates the quality of the reproduction signal. Further, when the metal reflection film has the same film thickness, when the material is different, the reflectance is different, so the film thickness at which the signal quality is deteriorated is different. Furthermore, when the thickness of the metal reflective film is increased, the reproduction signal is deteriorated. For example, in a magnetron sputtering apparatus, metal atoms on a target knocked out by Ar ions fly onto a substrate to form a metal reflection film, and the size of the metal atoms depends on the structure of the film forming apparatus and the conditions for film formation. However, it tends to be difficult to form a film on the bottom of the shortest pit.

  FIG. 4 is a cross-sectional view of an optical disc in which a 100 nm-thick metal reflective film made of an AgPdCu alloy is formed on a substrate on which pits are formed. As shown in FIG. 4, when the shortest pit 11 and the long pit 12 longer than the shortest pit 11 are formed on the substrate 1, the metal reflective film 2 is formed on the bottom of the shortest pit 11 than the long pit 12. Since it is difficult to form a film, in the shortest pit 11, the pit shape after the metal reflective film 2 is formed is smaller than the pit shape on the substrate 1, and the pit depth is deepened.

  In anticipation of this phenomenon, if the recording power is increased to record the shortest pit 11 greatly, the signal quality of the shortest pit 11 is improved. However, by increasing the recording power, the width of the long pit 12 is increased and the adjacent pit 11 is increased. Crosstalk from the track increases and the jitter value deteriorates. As a result of producing a substrate suitable for the metal reflective film of Al alloy and AgPdCu alloy in consideration of the deterioration factors of both signal quality, the maximum film thickness of the metal reflective film of Al alloy that does not deteriorate the jitter value is 40 nm, and AgPdCu The maximum film thickness of the metal reflective film of the alloy was 70 nm.

  Based on the above examination, the reflectance with respect to each film thickness of the metal reflective film of the AgPdCu alloy shown in FIG. 2 and the metal reflective film of the Al alloy shown in FIG. 3 was measured. FIG. 5 is a diagram showing the measurement result of the reflectance with respect to the film thickness of the metal reflection film made of AgPdCu alloy, and FIG. 6 is a diagram showing the measurement result of the reflectance with respect to the film thickness of the metal reflection film made of Al alloy. The horizontal axis represents the film thickness (nm) of the metal reflective film, and the vertical axis represents the reflectance (%). The refractive index n of the resin layer used for the measurement is 1.53, and the wavelength λ of the light beam is 405 nm.

  In the case of the metal reflection film of AgPdCu alloy from FIG. 5, the reflectance is 35% to 70% with respect to the film thickness range of 25 nm to 70 nm where a good jitter value is obtained. The reflectance was 35% to 70% with respect to the film thickness range of 15 nm to 40 nm where a good jitter value was obtained. As a result, it was found that the reflectance of the metal reflective film that can guarantee the quality of each reproduction signal is 35% or more and 70% or less.

  Next, details of the medium identification information formed in the sub information area of the optical disc in which the pit string composed of irregularities is formed as the main data in the main information area so that a reproduction signal having a good jitter value as described above can be obtained. Explained. FIG. 7 is a diagram illustrating an example of the main information area and the sub information area of the optical disc.

  In the example shown in FIG. 7, a main information area 21 (hatched portion in the figure) is set on the outer periphery of the optical disc, and a BCA area 22 (2 indicated by a broken line in the figure) is a sub-information area in an annular portion inside thereof. Area between two circles) is set, and medium identification information 23 is recorded in the BCA area 22 in a barcode pattern. The medium identification information 23 is obtained by forming a transparent resin layer such as polycarbonate on the metal reflection film and then irradiating the metal reflection film at a depth of 0.1 mm from the surface of the optical disk with a pulse laser (for example, YAG laser). Recorded. At this time, it is considered that a phenomenon occurs in which the metal reflective film melts and accumulates at the boundary portions on both sides due to surface tension. In this way, a BCA area in which medium identification information for individually identifying an optical disc is recorded is created by partially removing the metal reflection film and forming a plurality of reflection film removal areas.

  Next, a method for recording the medium identification information in the BCA area of the optical disc will be described in detail. In the following example, a recording method of the BCA area for a metal reflective film made of Ag98Pd1Cu1 (wt%) or Al99Cr1 (wt%) will be described as a metal reflective film. However, if the same effect is obtained, other metal reflective The present invention can be similarly applied to a film, a phase change film, or a magneto-optical recording film.

  FIG. 8 is a block diagram showing a configuration of a medium identification information recording apparatus that records medium identification information in the BCA area. The medium identification information recording apparatus shown in FIG. 8 is a BCA pattern recording apparatus used for creating a BCA area on a DVD-ROM, and includes a motor 101, a rotation control unit 102, an optical pickup 103, a laser driving unit 104, A waveform setting unit 105, a BCA signal generation unit 106, a focus control unit 107, a preamplifier 108, and a system control unit 109 are provided.

  The rotation control unit 102 controls the rotation of the motor 101. The motor 101 rotates the optical disc 100 at a predetermined rotational speed. The BCA signal generator 106 modulates the medium identification information recorded on the optical disc 100 to create a BCA signal. The waveform setting unit 105 shapes a laser modulation waveform based on the BCA signal. The laser driver 104 drives the high-power laser in the optical pickup 103 according to the laser modulation waveform. The optical pickup 103 condenses the light beam generated from the high-power laser onto the optical disc 100 through an internal optical system. The preamplifier 108 amplifies the reproduction signal from the optical pickup 103 and outputs it to the focus control unit 107. The focus control unit 107 controls the objective lens in the optical pickup 103 using the amplified signal from the preamplifier 108 in order to focus the light beam on the metal reflective film of the optical disc 100. The system control unit 109 comprehensively controls the operations of the rotation control unit 102, the laser drive unit 104, the waveform setting unit 105, the BCA signal generation unit 106, and the focus control unit 107.

  Next, the recording operation of the medium identification information recording apparatus configured as described above will be described. First, based on an instruction from the system control unit 109, the rotation control unit 102 drives the motor 101 to rotate the optical disc 100. The laser driving unit 104 drives a high output laser as a light source, and a light beam emitted from the high output laser is irradiated onto the optical disc 100 from the optical pickup 103. At this time, focus control is performed by the focus control unit 107, and the light beam emitted from the high-power laser is condensed on the metal reflection film of the optical disc 100.

  Here, the reflected light from the optical disc 100 is detected by a photodetector in the optical pickup 103, and a reproduction signal is output as an electrical signal from the photodetector. This reproduction signal is amplified through the preamplifier 108 and input to the focus control unit 107. The focus control unit 107 drives the objective lens of the optical pickup 103 according to the amplified reproduction signal and finely moves it in the focus direction of the optical disc 100 so that the light beam is condensed on the metal reflection film of the optical disc 100. The optical pickup 103 is controlled.

  Next, the system control unit 109 detects the position of the optical pickup 103 in the tracking direction by a position detector (not shown), and determines that the optical pickup 103 is at the sub information recording start position based on the detected position information. recognize. Next, the system control unit 109 instructs the BCA signal generation unit 106 to generate the BCA signal, the BCA signal is output from the waveform setting unit 105, the BCA recording sequence is started, and the medium identification information is stored in the BCA area. To be recorded.

  Using the above-described medium identification information recording apparatus, recording of a BCA pattern (barcode pattern) is attempted on a portion of the optical disk on which a 50 nm-thick metal reflective film made of an AgPdCu alloy is formed and where no pit row or guide groove is formed. It was. However, even if the output power of the laser is increased, the reflection film removal region from which the metal reflection film is removed cannot be produced.

  This is because the melting point of Al is 660 ° C., whereas the melting point of Ag is as high as 960 ° C., so that the metal reflective film of the AgPdCu alloy melts and requires a large amount of energy. In addition, while the thermal conductivity of Al is 237 W / (m · K), the thermal conductivity of Ag is as high as 427 W / (m · K), so the metal reflective film of AgPdCu alloy is irradiated with laser light. This is because the amount of heat that diffuses to the surroundings due to heat conduction is large. In general, in order to lower the melting point of a metal, a different metal can be mixed to lower the melting point. However, for the purpose of ensuring sufficient reflectivity and preventing corrosion, Ag in the metal reflective film can be reduced. The wt% cannot be lowered to 97% or less.

  Next, on an optical disc on which a 50 nm-thick metal reflective film made of an AgPdCu alloy is formed, a pit row is formed with a track pitch of 0.74 μm used in the BCA region of a DVD-ROM, and a BCA pattern is recorded on that portion. did. At this time, the information could not be reproduced because the BCA pattern could not be recorded with the desired width, but a part of the metal reflective film of the AgPdCu alloy melted to form a small reflective film removal portion. We were able to. This is because the metal reflective film tends to be difficult to be formed on the inclined surface on the substrate with the unevenness, and thus the thickness of the metal reflective film on the pit inclined surface portion is locally reduced, thereby hindering heat conduction.

  FIG. 9 is a cross-sectional view of an optical disk in which a metal reflection film is formed on a substrate on which pits are formed, and a resin layer is further formed on the metal reflection film. As shown in FIG. 9, when the metal reflective film 2 is formed on the substrate 1 on which the pits 12 are formed and the resin layer 3 is further formed on the metal reflective film 2, the metal reflective film 2 formed on the slope portion 4 Since the film thickness is thinner than the film thickness of the metal reflective film 2 formed on the pit bottom 5 and the flat plate part 6, heat conduction to the surroundings is reduced. For this reason, the smaller the track pitch of the pit row and the larger the area of the slope portion 4, the greater the heat conduction to the surroundings. Further, since the unit volume of the metal reflection film 2 is smaller in the slope portion 4 than in other places, the heat capacity until reaching the melting point is reduced, and the melting point is reached with low irradiation power.

  Based on the above knowledge, an optical disk was prepared in which a metal reflective film made of AgPdCu alloy and having a thickness of 50 nm was formed on a substrate on which pit rows were formed at various track pitches, and a BCA pattern was recorded. FIG. 10 is a diagram showing the measurement result of the defocus margin of the BCA recording power with respect to the track pitch of the pit row formed on the optical disc having a 50 nm metal reflection film made of an AgPdCu alloy, and the horizontal axis is the track of the pit row. The pitch (μm), and the vertical axis represents the defocus margin (%).

  As shown in FIG. 10, in the area where the pit row was formed with a track pitch of 0.54 μm or less, the BCA pattern could be recorded and the medium identification information could be reproduced, but the track exceeding 0.54 μm A defocus margin could not be secured in the area where the pit rows were formed at the pitch. Here, the determination that the BCA pattern could be recorded was made based on whether or not the medium identification information recorded in the BCA area can be accurately reproduced by setting the created optical disk on the evaluator and reproducing it. As the evaluation machine, a reproducing apparatus having a reproducing light beam wavelength λ of 405 nm and an objective lens numerical aperture NA of 0.85 was used.

  Here, when considering the mass productivity of the optical disk, the thickness of the metal reflection film may vary, the BCA recording power may vary, and so on. From FIG. 10, it was found that the track pitch at which a defocus margin of 20% or more is obtained is 0.24 μm or more and 0.45 μm or less. As described above, a sufficient defocus margin can be ensured when the track pitch of the pit row recorded in the BCA area is 0.24 μm or more and 0.45 μm or less, and the reason why the medium identification information can be recorded is as follows. Is estimated as follows.

  That is, when the track pitch of the pit row recorded in the BCA area exceeds 0.45 μm, the number of pits occupying the unit area is small, so the area of the slope of the pit is also reduced, and the heat conduction is sufficiently cut off. Absent. For this reason, if the heat capacity absorbed by the metal reflective film due to defocusing varies, a BCA pattern with low noise cannot be recorded.

  On the other hand, when the track pitch is narrower than 0.24 μm, the pits are too close to each other, the land portion between the pits is not sufficiently formed, and the angle of the slope portion of the pit is reduced. For this reason, it is easy to form a metal reflective film also on the slope portion of the pit, and the heat conduction blocking effect due to the formation of the pit is reduced. In FIG. 10, the BCA pattern could be recorded and reproduced up to a track pitch of 0.22 μm, but the BCA pattern could not be recorded at a track pitch narrower than 0.22 μm. A dotted line of 0.22 μm or less is an expected line.

  FIG. 10 shows the track pitch dependence of the defocus margin in an optical disc on which a 50 nm-thick metal reflective film made of an AgPdCu alloy is formed. However, an optical disc that can obtain a good jitter value is made of Ag or an Ag alloy. When the thickness of the metal reflective film is 25 nm or more and 70 nm or less, a defocus margin similar to the above can be obtained in the range where the track pitch of the pit row recorded in the BCA region is 0.24 μm or more and 0.45 μm or less. I was able to.

  Similarly, an experiment similar to that described above was performed on an optical disc in which a guide groove was formed instead of a pit row. However, even in the case of a guide groove, the tendency that a metal reflection film is difficult to be formed on the slope portion of the guide groove is the same as that in the pit row. Therefore, a defocus margin similar to the above could be obtained when the track pitch of the guide groove recorded in the BCA area was in the range of 0.24 μm to 0.45 μm.

  Therefore, in the optical disk that can obtain a good jitter value, when the film thickness of the metal reflection film made of Ag or Ag alloy is 25 nm or more and 70 nm or less, the track pitch of the pit row or guide groove recorded in the BCA portion is 0.24 μm or more and 0 If it is less than .45 μm, a sufficient defocus margin can be secured.

  Next, an optical disc produced using a metal reflective film (hereinafter referred to as an Al reflective film) made of Al99Cr1 (wt%) as the metal reflective film will be described. First, an optical disk on which an Al reflective film having a thickness of 30 nm was formed was prepared, and recording of a BCA pattern was attempted on a portion where no pit row or guide groove was formed using the above-described medium identification information recording apparatus. In this case, a portion from which the Al reflective film was removed could be formed, and the medium identification information recorded as a BCA pattern could also be reproduced. However, since the film thickness of the Al reflective film is thinner than the film thickness (50 to 70 nm) used for DVD-ROM, a sufficient defocus margin cannot be obtained. In addition, in the optical disk on which an Al reflective film having a film thickness of 30 nm was formed, a BCA pattern was recorded in a region where a pit row was formed with a track pitch of 0.74 μm used in the BCA region of a DVD-ROM. It was a result.

  For this reason, an optical disk in which an Al reflective film having a film thickness of 30 nm was formed on a substrate on which pit rows were formed at various track pitches was prepared, and a BCA pattern was recorded. FIG. 11 is a diagram showing the measurement result of the defocus margin of the BCA recording power with respect to the track pitch of the pit row formed on the optical disk having an Al reflective film with a film thickness of 30 nm, and the horizontal axis represents the track pitch of the pit row ( μm), and the vertical axis represents the defocus margin (%).

  Even in the case of the Al reflective film, the defocus margin at the time of BCA recording is required to be 20% or more in the same manner as described above. Therefore, the track pitch at which a defocus margin of 20% or more can be obtained is 0.24 μm or more from FIG. It was found to be less than 45 μm. Thus, even with an optical disk on which an Al reflective film having a thickness smaller than that of a DVD-ROM is formed, a sufficient defocus margin can be obtained when the track pitch of pits recorded in the BCA area is 0.24 μm or more and 0.45 μm or less. The reason why the medium identification information can be recorded is estimated as follows.

  That is, when the track pitch of the pit row recorded in the BCA area exceeds 0.45 μm, the heat capacity to reach the melting point becomes extremely small because the Al reflective film is thin, and the edge portion of the BCA pattern is formed well. This is because the noise of the BCA reproduction signal becomes high.

  On the other hand, when pit rows are formed with a track pitch of 0.45 μm or less, the probability that pits are formed at the edge portion of the BCA pattern increases as the track pitch decreases, and pits are formed in the molten Al reflective film. The flow is suppressed where it is. For this reason, the noise of the BCA pattern is smaller in a region where pits are formed with a small track pitch. As a result, when a pit row is formed with a track pitch of 0.45 μm or less, a BCA pattern capable of realizing a sufficient defocus margin can be recorded.

  However, if the track pitch is narrower than 0.24 μm, the angle of the slope of the formed pit is reduced, the force that hinders the flow of the Al reflecting film is weakened, and a sufficient defocus margin cannot be obtained.

  Therefore, by forming pit rows on the substrate with a track pitch of 0.24 μm or more and 0.45 μm or less, thermal control is easy even with a thin Al reflective film, and the Al reflective film is almost completely removed. And a good BCA pattern could be recorded.

  FIG. 11 shows the track pitch dependence of the defocus margin in an optical disk on which a metal reflective film made of Al99Cr1 (wt%) having a thickness of 30 nm is formed. However, in an optical disk capable of obtaining a good jitter value, Al or Al If the film thickness of the metal reflective film made of an alloy is 15 nm or more and 40 nm or less, the defocus margin is the same as the above in the range where the track pitch of the pit row recorded in the BCA region is 0.24 μm or more and 0.45 μm or less. Could get.

  Similarly, an experiment similar to that described above was performed on an optical disk in which guide grooves were formed instead of pit rows. However, since the same effect occurs in the case of guide grooves, the track pitch of the guide grooves recorded in the BCA area is In the range of 0.24 μm to 0.45 μm, the same defocus margin could be obtained.

  Next, a multilayer optical disk that is a multilayer optical recording medium formed by laminating a plurality of metal reflective films as an information recording layer will be described. For example, a 45 nm thick first metal reflective film made of Al is formed on the first polycarbonate substrate having a thickness of 1.1 mm on which a pit row is formed by the above-described magnetron sputtering apparatus, and pits are formed thereon. The second polycarbonate substrate having a thickness of 15 μm is bonded so that the side of the substrate on which the pits are not formed is in contact. For this adhesion, for example, a photo-curing resin having strong adhesion can be used. Further, a 28 nm-thick metal reflective film made of AgPdCu is formed on the second polycarbonate substrate bonded as described above, and a transparent resin layer having a thickness of 70 μm is adhered thereon. For this adhesion, for example, a pressure-sensitive adhesive sheet or the like can be used.

  Even in the two-layer optical disc produced as described above, if the track pitch of the pit row recorded in the BCA area is 0.24 μm or more and 0.45 μm or less, the two-layer optical disc is adjusted by focusing on the BCA recording. A BCA pattern could be recorded on either of them, and a defocus margin comparable to the above could be obtained.

  The method for producing the multilayer optical disc is not particularly limited to the above example, and the optical disc may be multilayered by forming a plurality of substrates before the transparent resin layer is bonded. In this case, a BCA pattern can be recorded on a desired layer by focusing on the BCA recording even if the optical disk is multilayered. Further, instead of a photocurable resin and a pressure-sensitive adhesive sheet, a transparent medium having adhesiveness such as a dry photopolymer may be used for laminating a transparent resin layer and adhering a polycarbonate substrate, or Alternatively, the transparent resin layer may be formed with only the pressure-sensitive adhesive sheet or the photocurable resin without bonding the transparent resin layer.

  As described above, in this multilayer optical disc, the recording density can be improved by laminating a plurality of layers, and the track pitch of the pit rows or guide grooves formed in the BCA area is 0.24 μm or more and 0.45 μm. By setting as follows, the laser beam is focused at the time of recording the BCA pattern, and an appropriate laser power is applied by focusing on the metal reflecting film on which the pit row or the guide groove is formed. The pattern could be recorded.

  In the read-only optical disc, the cost can be reduced as the recording time of the optical disc is shorter. Therefore, in each of the above examples, the pit row or guide groove in the BCA area and the pit row in the main information area are formed simultaneously. It is desirable. In addition, if the track pitch of the pit row or guide groove in the BCA area and the track pitch of the pit row in the main information area are greatly different, the disc rotation speed at the time of manufacturing the master disc can be changed discontinuously and greatly. Since the area and the BCA area are adjacent to each other, the rotational speed of the disc must be controlled to the desired rotational speed in as short a time as possible, so that the linear velocity is always constant, It is preferable that the track pitch and the track pitch of the pit row or guide groove in the BCA area are equal.

  The optical recording medium according to the present invention is capable of recording data at a higher density than a DVD read-only optical disc, and records medium identification information capable of ensuring a sufficient defocus margin using a conventional medium identification information recording apparatus. Therefore, it is useful as a disk-shaped optical disk used for information reproduction.

It is a figure which shows the measurement result of the jitter value with respect to pit depth. It is a figure which shows the measurement result of the jitter value with respect to the film thickness of the metal reflecting film which consists of AgPdCu alloys. It is a figure which shows the measurement result of the jitter value with respect to the film thickness of the metal reflective film which consists of Al alloys. It is sectional drawing of the optical disk which formed the metal reflective film with a film thickness of 100 nm which consists of AgPdCu alloy on the board | substrate in which the pit was formed. It is a figure which shows the measurement result of the reflectance with respect to the film thickness of the metal reflecting film which consists of AgPdCu alloys. It is a figure which shows the measurement result of the reflectance with respect to the film thickness of the metal reflective film which consists of Al alloys. It is a figure which shows an example of the main information area | region and sub-information area | region of an optical disk. It is a block diagram which shows the structure of the medium identification information recording device which records medium identification information in a BCA area | region. FIG. 3 is a cross-sectional view of an optical disc in which a metal reflective film is formed on a substrate on which pits are formed, and a resin layer is further formed on the metal reflective film. It is a figure which shows the measurement result of the defocus margin of BCA recording power with respect to the track pitch of the pit row | line | column formed in the optical disk which has a 50-nm metal reflective film which consists of AgPdCu alloys. It is a figure which shows the measurement result of the defocus margin of BCA recording power with respect to the track pitch of the pit row | line | column formed in the optical disk which has a 30-nm-thick Al reflective film.

Explanation of symbols

1 Substrate 2 Metal reflective film 3 Resin layer 4 Slope 5 Pit bottom 6 Flat plate 11 Shortest pit 12 Long pit

Claims (2)

An optical recording medium having a substrate and a metal reflective film formed on the substrate, and reproducing information by irradiating the metal reflective film with a light beam having a wavelength of about 405 nm,
A main information area in which a pit row is formed as main data;
A sub-information area in which medium identification information for individually identifying an optical recording medium is recorded by partially removing the metal reflection film with a laser to form a plurality of reflection film removal areas. ,
In the sub information area, pit rows or guide grooves are formed on the substrate, and a track pitch of the pit rows or guide grooves is 0.24 μm or more and 0.45 μm or less,
An optical recording characterized in that the track pitch of the pit row formed in the main information area is 0.24 μm or more and the shortest pit length of the pit row formed in the main information area is 0.21 μm or less. Medium. An information reproducing method for reproducing the optical recording medium according to claim 1,
An optical recording comprising reproducing a main information area in which the pit row is formed and a sub information area in which the medium identification information is recorded by irradiating the metal reflective film with a light beam having a wavelength of 405 nm. A method for reproducing information on a medium.

Images