JP2007265593A - Optical disk, optical disk substrate, optical master disk and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a land/groove recording optical disk of a high recording capacity that hardly causes crosstalk. <P>SOLUTION: The optical disk is obtained by forming a recording layer film or the like on an optical disk substrate in a predetermined form. In the optical disk substrate, land tracks and groove tracks are formed spirally, and on the bottom surface 12a of the groove track 12, a curved and projecting track 13 lower than the land track 11 is formed along the groove track 12, wherein the top part 13a of the projecting track 13 is lower than the top part 11a of the land track 11 (H2>H1). Recording layers are formed on the land tracks and the groove tracks of the optical disk substrate. In this case, the film thickness of the recording layer of a corner part of the bottom surface 12a of the groove track is thinner than the film thickness of the recording layer on the land mark. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc, an optical disc substrate, an optical disc master, and a manufacturing method thereof, and more particularly, for land / groove recording that realizes reduction of crosstalk and improvement of signal characteristics such as jitter when the track pitch is narrowed. It relates to optical discs.

Conventionally, for example, the following steps have been adopted as a method for manufacturing an optical disc master (master for optical disc: master), a method for manufacturing a stamper using this optical disc master, and a method for manufacturing an optical disc using this stamper.
A photoresist layer is formed on a glass substrate that has been precisely polished and cleaned to form a photoresist layer, and the photoresist layer is exposed with a laser exposure beam that is light-modulated according to a predetermined format to guide grooves. A latent image is formed. By developing and washing the photoresist layer on which the latent image is formed, guide grooves and the like are formed in the photoresist layer. Thus, an optical disc master is obtained.
Next, the optical disk master is subjected to sputtering treatment to form a nickel sputtered film. A nickel layer is formed by performing nickel electroforming on this nickel sputtered film, and then the nickel layer is peeled off from the glass substrate and the photoresist layer, and the back surface where no groove pattern is formed is polished to produce a stamper for an optical disk. To do.
Further, an optical disk substrate is produced by an injection molding method using this stamper. For example, a first dielectric layer, a recording layer, a second dielectric layer, a reflective layer, and a protective layer are formed on the surface of the optical disk substrate on which the groove that is the guide groove and the land that is the convex portion are provided. Are stacked in this order to obtain an optical disc.

However, in order to meet the recent demand for an increase in the recording capacity of the optical disc, it is necessary to reduce the track pitch of the optical disc.
FIG. 8 is a plan view showing a main part structure of an optical disc in which a recording mark 101A is formed on a groove track 101 having a narrow track pitch. As is apparent from this figure, when the recording mark 101A is large, the recording marks are very close to each other, which may adversely affect the writing / erasing of information between them. Reference numeral 102 denotes a land track.

  As a method for increasing the recording capacity of an optical disc, there is a method of recording in grooves and lands. However, in this method, the recording marks on the adjacent groove tracks and the recording marks on the land tracks are close to each other. Therefore, as in the case of FIG. This is accompanied by problems such as erasure of marks on adjacent tracks.

  By the way, as a prior art for obtaining an optical disc with improved recording density, those disclosed in Patent Document 1 and Patent Document 2 below are known.

The invention described in Patent Document 1 discloses an optical recording medium capable of forming a concavo-convex pattern having a complicated shape with a protrusion serving as a physical barrier between a land and a groove in order to improve the recording density of an optical disc. A manufacturing method of a master for manufacturing, an exposure apparatus, a master for manufacturing an optical recording medium, and an optical recording medium are provided.
As a means for achieving this object, an exposure apparatus equipped with a tracking mechanism is used to cause the laser light to follow the first concavo-convex pattern formed on the first resist layer, and to the second resist layer. A second uneven pattern is formed. By performing the exposure process twice, a complex uneven pattern combining the first and second uneven patterns is formed on the glass master.

  However, in the master production method described in Patent Document 1, the master exposure process needs to be performed twice. For this reason, the number of processes increases, leading to an increase in cost. Further, since the master exposure machine requires a tracking mechanism that is not provided in a normal apparatus, there is a problem that a special master exposure machine or a modification of the master exposure machine is required. Furthermore, if the pattern is miniaturized and densified by the photolithography technique, a technique with high process cost and apparatus cost such as an electron beam exposure apparatus is required.

  On the other hand, the invention related to the optical disk master manufacturing method and the optical disk manufacturing method described in Patent Document 2 described above can realize further higher storage capacity of the optical disk by using an existing exposure apparatus. An object of the present invention is to provide a method for manufacturing an optical disc master and a method for manufacturing an optical disc.

In order to achieve this object, a fine pattern forming method by thermal lithography is used as a method replacing the photolithography technique. Specifically, the light absorption layer is heated by laser exposure, and the structure of the resist formed on the light absorption layer is changed by this heat. After the exposure, a fine pattern is formed by removing a portion whose structure has been changed by the developing solution (or etching solution) or a portion which has not changed. According to this thermal lithography, since the thermal alteration of the resist has a certain threshold value, a pattern finer than that of optical lithography can be formed. In the embodiment according to the invention of Patent Document 2, the layer configuration of the optical disc master is substrate / intermediate layer / resist, and the material of the intermediate layer is preferably a-Si, SiO ₂ , or SiN having a low thermal conductivity. It is said. The resist is a transition metal non-oxide, and W and Mo are particularly preferable. In the embodiment, exposure is performed with an exposure wavelength of 405 nm and an objective lens NA of 0.9.

  However, in the invention of Patent Document 2, when the exposure light source is shortened for the purpose of further miniaturization of the pattern, for example, when deep ultraviolet light having a wavelength of 257 nm is used as the light source, the resist material described in Patent Document 2 However, since light absorption occurs by itself, there is a problem that a fine pattern cannot be formed. This is considered to be due to the following reasons.

  When the resist layer is a material transparent to the exposure wavelength, heat is generated by light absorption in the light absorption layer, and the heat is transmitted to the resist layer with a certain threshold value. For this reason, since only the high temperature region at the center of the exposure beam is transmitted to the resist layer, a pattern smaller than the exposure beam diameter can be formed. However, when light absorption occurs in the resist layer, heat spreads in the resist layer, and there is a problem that a fine pattern having an exposure beam diameter or less cannot be formed.

  Further, as conventional techniques for solving the problem of crosstalk, those disclosed in the following Patent Documents 3 and 4 are known.

  Among them, the invention described in Patent Document 3 aims to eliminate the adverse effect of narrow track pitch in a land / groove recording type phase change optical disc. As a specific means, the groove depth is λ / (3.78 n) or more when the wavelength of light is λ and the refractive index of the substrate is n. Further, the groove depth is set to any one of the values near λ / (3n), {λ / (3n) + λ / (2n)}, and {λ / (6n) + λ / (2n)}. It was. Furthermore, the rough width of the groove side wall is suppressed to 50 nm or less or 20 nm or less. Further, the taper angle of the groove sidewall is set to 60 degrees or more, 80 degrees or more, or 84 degrees or more.

Further, the invention described in Patent Document 4 provides an optical disc substrate having excellent crosstalk and cross erase characteristics in a land / groove recording optical disc substrate in which grooves having a depth of λ / (4n) or more are formed. It is the purpose. As a specific means, the groove depth D is limited to a value satisfying the following expression.
D = 0.4022-0.4574 · A + 0.6458 · A ²
Here, A = ((NA · TP) / λ) · (1 / sin ² θ), D = (physical groove depth) · (n / λ), TP: track pitch, θ: groove wall surface The taper angle.

  However, when crosstalk is calculated by diffraction simulation for several track pitches, it is possible to reduce crosstalk without forming a deep groove of depth λ / (4n) or more disclosed in the prior art. all right. It was found that, depending on the track pitch, the crosstalk was smaller in the shallower groove. In addition, when a large number of substrates on which grooves having a depth of λ / (4n) or more are duplicated by an injection molding method or the like, the grooves are deep and the grooves are caught at the time of mold release, which tends to cause transfer defects. is there. Further, in order to ensure good transferability, the molding time is set long. For this reason, the manufacturing tact time is longer than that of the conventional substrate, and the cost of the disk is increased.

JP 2003-59121 A JP 2004-152465 A Japanese Patent Laid-Open No. 10-320835 JP 2000-285522 A

The present invention has been made in view of the above-described problems of the prior art, and its ultimate purpose is to manufacture recording marks in an optical disc manufacturing technique in which recording capacity is increased by performing recording on groove tracks and land tracks. By suppressing the spread in the radial direction, the problem of crosstalk is solved.
That is, a first object of the present invention is to provide a land / groove recording optical disc (which realizes a narrow track pitch) having a high recording capacity in which crosstalk hardly occurs.
The second object of the present invention is to provide an optical disk substrate, an optical disk master for manufacturing such an optical disk, and a manufacturing method thereof.

According to the first aspect of the present invention, in the optical disk substrate in which the land track and the groove track are spirally formed on the substrate, a convex track lower than the land track is formed along the groove track on the bottom surface of the groove track. The top of the convex track is an optical disk substrate characterized by being lower than the top of the land track (see FIGS. 1, 2, 4, and 5).
The invention according to claim 2 is the optical disk substrate according to claim 1, wherein the convex track has a curved shape (see FIGS. 2 and 4).

The invention according to claim 3 is the land / groove recording optical disk in which the land track and the groove track are formed in a spiral shape, and the recording layer is formed on the land track and the groove track. An optical disc comprising a substrate.
The invention according to claim 4 is the optical disk according to claim 3, wherein the recording layer film thickness at the corner portion of the bottom surface of the groove track is formed thinner than the recording layer film thickness at the land track flat portion. (See FIG. 2 (1)).
The invention according to claim 5 is the optical disk according to claim 3 or 4, wherein a recording layer is not formed at a corner portion on the bottom surface of the groove track (see FIG. 2 (2)). ).

The invention according to claim 6 is an optical disk master production method for manufacturing a stamper for producing the disk substrate according to claim 1 or 2,
A film forming process for producing a resist master by laminating at least a light absorption layer and an upper resist layer on the substrate, and condensing two laser beams on the resist master, An exposure process for forming a latent image on the resist layer according to the pattern and an etching process (development process) for etching the resist master after exposure to form a pattern. _2. An optical disc master production method comprising one or a plurality of fluorine compounds arbitrarily selected from ₂ , CaF ₂ , LiF and BaF ₂ (see FIGS. 5 and 6).

The invention according to claim 7 is the optical disk master production method according to claim 6, wherein SiO ₂ is added to the resist layer.
The invention according to claim 8 is the optical disc master manufacturing method according to claim 6 or 7, wherein the light absorption layer has lower transmission performance at the exposure wavelength used in the exposure step than the resist layer. This is a master production method.
The invention according to claim 9 is the optical disc master manufacturing method according to claim 8, wherein the light absorption layer is made of any material of SbTe, GeSbTe, InSbTe, BiSbTe, GaSbTe, and AgInSbTe. This is a master production method.
The invention according to claim 10 is the optical disc master manufacturing method according to any one of claims 6 to 9, wherein the material different from both the material of the light absorption layer and the material of the resist layer between the substrate and the light absorption layer. An optical disk master production method characterized in that a protective layer is formed (see FIG. 7).
According to an eleventh aspect of the present invention, there is provided the optical disc master manufacturing method according to the tenth aspect, wherein the material of the protective layer is ZnS.

An invention according to claim 12 is an optical disc master produced by the method for producing an optical disc master according to any one of claims 6 to 11.
A thirteenth aspect of the present invention is a method of manufacturing an optical disk substrate, wherein the optical disk substrate is formed using a stamper obtained by the optical disk master according to the twelfth aspect.
The invention according to claim 14 is an optical disc manufacturing method using the optical disc substrate obtained by the manufacturing method according to claim 13.

The invention according to claims 15 and 16 is to provide an optical disc having an optical disc substrate that can reduce the influence of crosstalk when the groove depth is λ / (4n) or less.
That is, the invention according to claim 15 is an optical disc having an optical disc substrate in which land tracks and groove tracks are formed on the substrate at regular intervals, and information is recorded on each of the land tracks and groove tracks. When the wavelength of light is λ (nm), the refractive index of the optical disk substrate is n, and the distance between the land track and the groove track is TP (nm), the step D1 between the top of the groove track and the top of the land track is The optical disk satisfies the following expression (1).
(−8 × 10 ⁻⁷ · TP ² −0.0006 · TP + 0.38) · (n / λ) ≦ D1 ≦ (−3 × 10 ⁻⁶ · TP ² −0.0007 · TP + 0.22) · (n / λ) (1)
A sixteenth aspect of the present invention is the optical disk having the optical disk substrate according to the first or second aspect, wherein information is recorded on each of the land track and the groove track, and the wavelength of the reproduction light is λ (nm), and the optical disk When the refractive index of the substrate is n and the distance between the land track and the groove track is TP (nm), the step D2 from the top of the convex track to the top of the land track satisfies the following equation (2). An optical disc characterized by the above.
(−8 × 10 ⁻⁷ · TP ² −0.0006 · TP + 0.38) · (n / λ) ≦ D2 ≦ (−3 × 10 ⁻⁶ · TP ² −0.0007 · TP + 0.22) · (n / λ) (2)

(1) Operation and Effect Corresponding to Invention of Claim 3 In the optical disk having the disk substrate according to claim 1, since the recording mark can be prevented from spreading in the radial direction by a predetermined configuration, no crosstalk occurs. An optical disk for land / groove recording having a high recording capacity is provided.
In the optical disk having the disk substrate according to claim 2, since the groove track bottom surface is formed to be convexly curved so that the recording layer is formed discontinuously at the corner portion of the groove track, the recording mark is in the radial direction. Thus, a land / groove recording optical disc having a high recording capacity that can prevent the crosstalk from occurring is provided.

(2) Operational effects corresponding to inventions of claims 4 and 5 In the optical disks of claims 4 and 5, the recording mark can be prevented from spreading in the radial direction by a predetermined configuration, so that the narrow track pitch The recording capacity can be increased.

(3) Operation and Effect Corresponding to Invention of Claim 6 In the optical disk master production method according to claim 6, a material having a high transmittance with respect to the exposure wavelength is used for the resist layer, and two lasers having different powers are used. Since the first land track and the second land track are exposed by the beam, a fine pattern can be formed even by deep ultraviolet laser light, and land tracks having different heights can be easily formed.

(4) Operational effect corresponding to invention of claim 7 In the optical disk master production method of claim 7, SiO2 is added to the resist layer to increase the difference in etching rate between the exposed part and the unexposed part. Therefore, it is possible to form an uneven pattern with high contrast.
(5) Operational effects corresponding to inventions of claims 8 and 9 In the optical disc master manufacturing method according to claims 8 and 9, the light absorption layer is efficiently heated by using a material having low light transmission performance for the light absorption layer. Therefore, the uneven pattern can be formed on the resist layer without requiring a high-power laser.
(6) Operational effects corresponding to inventions of claims 10 and 11 In the method for producing an optical disc master according to claims 10 and 11, the light absorption layer and the resist layer material are between the substrate and the light absorption layer. Since the protective layers of different materials are provided, it is possible to prevent the occurrence of defects such as cracks in the light absorption layer and the resist layer.

(7) Operational effects corresponding to inventions of claims 12 to 14 An optical disk master according to claims 12 to 14, a method of manufacturing an optical disk substrate, and a method of manufacturing an optical disk are the optical disks according to any of claims 6 to 11. Since it is based on the master production method, the effects of the master production methods according to claims 6 to 11 are brought about.

(8) Operational effect corresponding to inventions of claims 15 and 16 In the optical disk substrate of claims 15 and 16, the groove depth at which the crosstalk is near the minimum value is set according to the track pitch. The recording density can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The optical disk of this embodiment is characterized by the cross-sectional shape of the substrate (optical disk substrate).
FIG. 1 (1) shows an enlarged plan view of the optical disk substrate 10 of the present invention, and FIG. As shown in FIG. 1A, land tracks 11 and groove tracks 12 are formed on the surface of the optical disk substrate 10, and convex tracks 13 are formed along the groove tracks 12 on the bottom surface of the groove tracks 12. . As shown in FIG. 1 (2), the top portion 13a of the convex track 13 having a distance H2 from the groove bottom surface 12a is formed lower than the top portion 11a of the land track 11 having a distance H1 from the groove bottom surface 12a. This is a feature of the optical disk substrate 10.

FIG. 2A is a cross-sectional view when the recording layer 21 is formed on the substrate 10 of FIG. As shown in FIG. 2 (1), since the groove corner portion 22 is thin, the recording layer of this portion includes the film thickness of the recording layer 31A on the land track top portion 11a and the recording layer on the convex track top portion 13a. It becomes thinner than any of the 31B film thickness.
Depending on the shape (corner shape) of the groove corner portion 22, a recording layer may not be formed on the groove corner portion 22 as shown in FIG. This point will be described later.

  Thus, in the case of the optical disc shown in FIG. 2A using the substrate having the cross-sectional structure shown in FIG. 1, when recording is performed on the groove track 12, as shown in FIG. 3, the groove bottom surface 12a, the convex track 13 and Since the recording layer at the boundary is thin or interrupted, it is possible to prevent the recording mark 31b formed on the convex track 13 from spreading in the radial direction. In FIG. 3, reference numeral 31 a is a recording mark on the land track 11.

  FIG. 4 shows an enlarged cross-sectional view of the optical disk substrate 10 in which the groove bottom surface 12a is curved in a convex shape. The feature of this substrate is that the groove corner portion 22 which is the boundary between the groove wall surface 12b and the groove bottom surface 12a is thin. FIG. 2B is an enlarged cross-sectional view when a recording layer is formed on the optical disk substrate shown in FIG. Similar to FIG. 2A, the film thickness of the recording layer in the groove corner portion 22 is thinner than the central portion of the groove bottom surface 12a. With this effect, it is possible to prevent the recording marks formed on the groove track 12 from spreading in the radial direction.

Next, an optical disk manufacturing method of the present invention will be described with reference to FIG.
(1) Film forming process (FIG. 5 (1))
A light absorbing layer 52 and a resist layer 53 are sequentially formed on the polished and cleaned substrate 51 to produce a resist master 50. In this case, a material whose light absorption layer 52 has lower transmission performance at the exposure wavelength than the resist layer 53 is used. Thereby, since the resist layer 53 is heated mainly by the heat generated in the light absorption layer 52, the region to be thermally altered becomes equal to or smaller than the exposure beam spot diameter, and a fine pattern can be formed. The substrate 51 may be a glass substrate, a Si wafer, a plastic substrate, or the like.
(2) Exposure process (FIG. 5 (2))
The resist master 50 in the film forming step (1) is exposed with two laser beams (laser beams LB1 and LB2) having different laser powers.
(3) Etching process (FIG. 5 (3))
The resist master after the exposure is etched with a hydrofluoric acid aqueous solution to remove the resist layer in the unexposed area, and an uneven pattern is formed to obtain the optical disc master 60. In FIG. 5C, reference numeral 61 denotes a land track, 62 denotes a groove track, and 63 denotes a convex track.
(4) Electroforming process (Fig. 5 (4))
After forming a conductive film on the optical disc master 60, Ni electroforming is performed. In FIG. 5 (4), reference numeral 64 denotes a Ni layer.
(5) Peeling and outer diameter processing step (Fig. 5 (5))
The master after the electroforming process is peeled off into a glass master and a Ni electroformed layer, and then back surface polishing and outer diameter processing are performed. Thereby, a stamper (optical disc stamper) 70 is obtained.

A plastic optical disk substrate is manufactured by a known injection molding method, 2P transfer method or the like using the stamper manufactured by the above process as a mold, and further a recording layer, a reflective layer, and a protective layer necessary for the recording optical disk are formed on the substrate. Etc. are formed to produce an optical disc.
As an example (not shown) of such an optical disk, there is a structure in which a first dielectric, a recording layer, a second dielectric, a reflective layer, and a protective layer are laminated in this order on a land track and a groove track.

  Next, FIG. 9 shows the result of calculation regarding the relationship between crosstalk and groove depth. Here, calculation is performed for the cases where the track pitch (TP) is 200, 240, 280, and 320 nm, respectively. The optical system used for the calculation has a reproducing light wavelength of 405 nm, the objective lens has an NA of 0.85, and the reproducing light is incident from the film surface. Further, the definition of the track pitch and the groove depth will be described with reference to an enlarged plan view of the optical disk substrate 200 shown in FIG. 10A and an enlarged sectional view shown in FIG. The track pitch is the distance between the center of the land track 202 and the center of the groove track 201, and the groove depth is the level difference between the land track 202 and the groove track 201.

Crosstalk was calculated by the following method.
(S11) A reproduction signal amplitude when reproducing a groove track in which a mark and a space having a length of 600 nm are repeatedly recorded is calculated. At this time, nothing is recorded on the adjacent land track.
(S12) A mark and space having a length of 600 nm are repeatedly recorded on the land track, and the reproduction signal amplitude when the adjacent groove track is reproduced is calculated. At this time, nothing is recorded on the groove track.
(S13) The ratio of the reproduction signal amplitudes of (S11) and (S12) was calculated and used as crosstalk.

FIG. 11 is a graph obtained by plotting the groove depth at which the crosstalk becomes the minimum value and the groove depth at which the degradation is 3 dB from the minimum value in the range where the groove depth is λ / 4 or less from the calculation result shown in FIG. The 3 dB degradation of CNR (Carrier to Noise ratio) due to crosstalk is a level that does not affect the bit error rate. The groove depth at which the crosstalk is near the minimum value varies depending on the track pitch, and the range thereof is approximate expression 1 (groove depth y = −3 × 10 ⁻⁶ · TP ² −0.0007 · TP + 0. 22) and approximate expression 2 (groove depth y = −8 × 10 ⁻⁷ · TP ² −0.0006 · TP + 0.38). Accordingly, the groove depth (step difference between the groove track top and the land track top) D1 at which the crosstalk is near the minimum value can be expressed by the following formula (1) in consideration of the refractive index n of the substrate. .
(−8 × 10 ⁻⁷ · TP ² −0.0006 · TP + 0.38) · (n / λ) ≦ D1 ≦ (−3 × 10 ⁻⁶ · TP ² −0.0007 · TP + 0.22) · (n / λ) (1)

When the disk substrate having the cross-sectional shape shown in FIGS. 1 and 4 is used, the groove depth (step from the top of the convex track to the top of the land track) D2 where the crosstalk is near the minimum value is Considering the refractive index n of the substrate, it can be expressed by the following formula (2).
(−8 × 10 ⁻⁷ · TP ² −0.0006 · TP + 0.38) · (n / λ) ≦ D2 ≦ (−3 × 10 ⁻⁶ · TP ² −0.0007 · TP + 0.22) · (n / λ) (2)

  If the groove depth is set in the above range, the groove depth is λ / (4n) or less, so that an optical disk with a crosstalk near the minimum value, which is easy to produce a substrate, can be obtained.

The present invention will be described more specifically with reference to examples.
[Example 1]
After the polished glass substrate 51 was washed, GeSbTe was formed as a light absorption layer 52 by a sputtering method to a thickness of 10 nm, and MgF ₂ was deposited as a resist layer 53 by a thickness of 100 nm by a vacuum deposition method to produce a glass master disc 50. (See FIG. 5 (1)). In FIG. 5 (3), the height of the land track 61 is set by the film thickness of the resist layer, so that the film thickness corresponding to the required height is formed according to the recording / reproducing system to be applied.

The material of the light absorption layer 52 may be any material as long as it has a function of absorbing light and generating heat and has a light transmittance lower than that of the resist layer 53. A semiconductor material such as Si, Ge, or GaAs can be used. An intermetallic compound material containing a low melting point metal such as Bi, Ga, In, or Sn can be used. Materials such as BiTe, BiIn, GaSb, GaP, InP, InSb, and InTe can be used. Carbide materials such as C and SiC can be used. An oxide material such as V ₂ O ₅ , Cr ₂ O ₃ , Mn ₃ O ₄ , Fe ₂ O ₃ , Co ₃ O ₄ , or CuO can be used. A nitride material such as AlN or GaN can be used. Binary phase change materials such as SbTe, ternary phase change materials such as GeSbTe, InSbTe, BiSbTe, and GaSbTe, and quaternary phase change materials such as AgInSbTe can be used.

  The film thickness of the light absorption layer 52 is set in the range of 3 to 20 nm. By reducing the thickness of the light absorption layer 52, the spread of heat in the layer can be suppressed, and a fine cylinder can be formed.

  As the substrate 51, glass, quartz or the like can be used. In addition, a substrate used for manufacturing a semiconductor such as Si, SOI (silicon on insulator) can be used. In addition, a substrate for HDD (hard disk) such as Al or opaque glass substrate can also be used. In addition, a resin substrate such as polycarbonate, acrylic resin, polyolefin, epoxy resin, polyvinyl ester, PET (polyethylene terephthalate), or ultraviolet curable resin can be used.

FIG. 6 shows a schematic diagram of the master exposure machine used in the above embodiment. This master exposure machine includes a laser light source 81 that emits a laser beam, a beam splitter 82 that separates the laser beam, mirrors M1, M2, and M3 that reflect the laser beam, and modulation from a control device of the master exposure machine (not shown). The optical modulators OM1 and OM2 that modulate the laser beam according to the signal, the beam expanders BE1 and BE2, a polarization beam splitter (PBS) that synthesizes the two laser beams, and the glass master 50 are assembled with the laser beam. An optical head 83 having a light objective lens and a focus unit, a turntable 84 for holding a glass master, and a motor 85 for rotating the optical head 83 are provided (see FIG. 5 (2)).
The optical head 83 is installed on an optical moving table, and a helical latent image is formed on the glass master 50 by moving the optical moving table as the turntable 84 rotates.

  The laser light source 81 is deep ultraviolet laser light having a wavelength of 257 nm. The laser beam emitted from the laser light source 81 is separated into a laser beam LB1 and a laser beam LB2 by a beam splitter 82. The laser beam LB1 passes through the optical modulator OM1, is reflected by the mirror M1, and then enters the PBS. On the other hand, the laser beam LB2 that has passed through the beam splitter 82 and the mirror M2 passes through the optical modulator OM2, and then enters the PBS. The laser beams LB1 and LB2 synthesized by the PBS are reflected by the mirror M3, pass through the optical head 83, and are condensed on the glass master 50. The condensing positions of the laser beam LB1 and the laser beam LB2 on the glass master 50 can be easily adjusted by adjusting the incident angle to the objective lens.

  In the condensing step, the first land track is exposed with the laser beam LB1, and the second land track is exposed with the laser beam LB2. The laser power of the laser beam LB1 is set higher than that of the laser beam LB2.

Next, the exposed glass master is immersed in a hydrofluoric acid aqueous solution, and the resist layer in the unexposed area is removed (see FIG. 5 (3)). The portion exposed by the high-power laser beam LB1 undergoes thermal alteration up to the resist layer surface, so that the resist layer remains as it is. On the other hand, in the exposed portion of the low-power laser beam LB2, only the resist layer near the interface with the light absorption layer undergoes thermal alteration, so the surface of the resist layer is removed by etching. In this way, a convex track lower than the land track is formed along the bottom surface of the groove track. The height of the convex track can be set by the exposure laser power. When the power of the laser beam LB2 is increased, the height of the convex track is increased.
In this embodiment, the height H2 of the convex track is 40 nm, and the height H1 of the land track is 100 nm, which is equal to the resist layer thickness.

A conductive film such as a Ni thin film is formed on the optical disc master on which two types of tracks having different heights (land track 61 and convex track 63) are formed as described above, and electroforming with Ni or the like is performed. After the electroformed film is peeled off from the glass master, the outer diameter is processed to obtain a Ni stamper (see FIGS. 5 (3) to 5 (5)).
Further, a resin substrate is manufactured by an injection molding method using this Ni stamper as a mold, and a dielectric film made of ZnS—SiO ₂ , a recording film made of AgInSbTe, a reflective film made of Al, and ZnS—SiO ₂ are formed on this substrate. An optical disk was manufactured by sequentially stacking the dielectric films.
From the photograph of the cross-sectional shape of the optical disk substrate after film formation, it was confirmed that the recording layer thickness at the groove edge portion (groove corner portion) was thinner than the recording layer thickness on the land track.

According to the optical disk master manufacturing method described above, land tracks and convex tracks along the bottom surface of the groove track can be formed in one exposure process.
In the case where CaF ₂ , LiF, or BaF ₂ was used for the resist layer 53, an uneven pattern could be formed similarly. On the other hand, when ZnS-SiO ₂ having low transmission performance in the exposure wavelength region was used for the resist layer 53, the uneven pattern was not formed. From this result, the material of the resist layer is preferably a material having high transmission performance in the exposure wavelength region.

[Example 2]
A method for forming a groove having a groove bottom surface 12 curved in a convex shape as shown in FIG. 4 will be described. The groove forming method in this case follows the same process as that of the first embodiment except for the setting of the master exposure machine. The difference is the setting of the beam expander BE2 shown in FIG. The beam expander BE2 can change the focused beam diameter of the laser beam LB2. As the condensed beam diameter of the laser beam LB2 is increased, the cross-sectional shape of the second land track can be changed from a rectangle to a trapezoid and from a trapezoid to a semicircle. The second land track has a semicircular shape, that is, a shape in which the groove bottom surface is convexly curved. When the stamper is peeled off from the master disk or when the stamper is peeled off from the resin substrate, the second land track is not caught. The uneven pattern can be accurately transferred.

[Example 3]
Using a disk tester (LM330 manufactured by Shibasoku Co., Ltd.) having a recording / reproducing light wavelength of 405 nm and an objective lens NA of 0.85, the jitter values of the optical disk manufactured in Example 1 and a conventional optical disk were compared. The interval between the grooves of the optical disk was 0.30 μm, and random data of 1-7 modulation (minimum mark length: 0.16 μm) was recorded on the groove track, and the jitter value at this time was evaluated. While the jitter value of the conventional optical disk was 7.5%, the jitter value of the optical disk of the present invention was 6.4%.

Next, random data of 1-7 modulation was recorded on the land track and the groove track, and the recording marks at this time were observed with a transmission electron microscope (TEM). In the conventional optical disc, the recording mark extends to the adjacent track, whereas in the optical disc of the present invention, the recording mark is contained in each recording track. According to the optical disk of the present invention, since the recording mark can be prevented from spreading in the radial direction, recording / reproduction can be performed at a narrower track pitch defined by the exposure wavelength and the NA of the objective lens.
In addition, it was confirmed that the same effect was obtained with an optical disc having a curved groove bottom surface.

Furthermore, the cross light characteristics were measured by the following procedure.
(S21) A 150-nm mark and space are repeatedly recorded on the groove track, and the CNR of the reproduced signal is measured. The recording power at this time is set to a power that maximizes the CNR.
(S22) A 600 nm long mark and space are repeatedly recorded on adjacent land tracks on both sides of (S21). The recording power at this time is equal to that in the case of (S21).
(S23) The groove track of (S21) is reproduced again, and its CNR is measured.
(S24) The steps (S22) and (S23) are performed while changing the recording power, and the change in CNR is measured.

  When the recording power for recording on the land track is increased, the protrusion of the mark recorded on the land track to the adjacent groove track increases, and the CNR of the groove track deteriorates. If the recording power at which the CNR begins to deteriorate is high, it can be determined that there is a cross-write suppression effect.

  FIG. 12 shows the measurement results of the cross light characteristics of the optical disk of this example and a disk with a flat groove (an optical disk manufactured from the substrate of FIG. 10 (referred to as Comparative Example 3)). The recording power at which the CNR is maximized is P0, which was 4.0 mW for these optical discs. In the optical disk of Comparative Example 3, the CNR of the groove track starts to decrease from 1.2P0, whereas in the optical disk on which the convex track of the present example is formed, there is no influence by the cross-write until 1.5P0. It was confirmed that the light characteristics were improved.

[Example 4]
A glass master in which the resist layer of Example 1 is changed from MF ₂ to MF ₂ —SiO ₂ (MF ₂ : SiO ₂ = 80: 20) is formed, and the same uneven pattern as in Example 1 is formed, and after etching The concavo-convex pattern was compared between MF ₂ and MF ₂ —SiO ₂ . MF ₂ —SiO ₂ had a steeper cross-sectional shape and a high-contrast uneven pattern. It is considered that the difference in the etching rate between the exposed part and the unexposed part is increased by adding SiO ₂ to the resist layer. Similar effects were obtained when the resist layer was made of CaF ₂ —SiO ₂ , LiF—SiO ₂ , BaF ₂ —SiO ₂ .

[Example 5]
When the optical disc master is exposed, a crack is generated in the light absorption layer due to expansion and contraction during melting and solidification, and an etching solution may enter from the crack in the etching process. Then, even the substrate is etched by the etchant, and the light absorption layer may be peeled off due to the penetration of the etchant.

  Therefore, by forming a protective layer resistant to the etching solution between the substrate and the light absorption layer, defects in the etching process can be reduced. The protective layer not only reduces defects in the etching process, but also has an effect of improving the adhesion of the light absorption layer.

[Example 6]
A resist master having a laminated structure shown in FIG. 7 was prepared. In this optical disk master, after forming ZnS as a protective layer 92 with a thickness of 20 nm on a substrate 91, GeSbTe as a light absorption layer 93 with a thickness of 10 nm is formed by sputtering, and then MF ₂ is vacuum-deposited as a resist layer 94. A film having a thickness of 100 nm was formed by the method. With this configuration, the above-described defects in the etching process could be reduced.

[Example 7]
The cross-sectional shape of the disk substrate is as shown in FIG. 10 (2), the track pitch is 240 nm, the groove depth is 50 nm (equivalent to 0.12λ), 65 nm (equivalent to 0.16λ), 80 nm (0.20λ). Equivalent) and 130 nm (equivalent to 0.32λ) disk substrates, ZnS—SiO ₂ as a protective layer having a thickness of 10 nm on these disk substrates, AgInSbTe as a light absorption layer thereon having a thickness of 20 nm, An optical disk was produced by forming a ZnS-SiO ₂ film as a thermal reaction layer thereon by a sputtering method so as to have a film thickness of 40 nm. This optical disk was recorded / reproduced from the film surface using a disk tester (LM330 manufactured by Shibasoku) having a recording / reproducing light wavelength of 405 nm and an objective lens NA of 0.85, and crosstalk was measured.

Crosstalk was measured by the following procedure.
(S31) A 2T mark (mark length 150 nm) is recorded on the groove track.
(S32) The 2T mark of (S31) is reproduced and the CNR of the reproduction signal is measured.
(S33) An 8T mark (mark length 600 nm) is recorded on both land tracks adjacent to the groove track of (S31).
(S34) The CNR of the reproduction signal of the groove track of (S31) is measured.
(S35) The difference in CNR measured in (S32) and (S34) is defined as crosstalk.

  The measurement results are shown in FIG. At a track pitch of 240 nm, crosstalk is minimized near the groove depth of 0.22λ. In addition, the crosstalk can be reduced when the groove depth limited by the present invention is used rather than the groove depth disclosed in the prior art.

  The same results were obtained for the disk substrates whose disk substrate had the cross-sectional shape of FIGS. 1 (2) and 2 (2). The groove depth at this time is a step between the land track top and the convex track top. With this cross-sectional shape, cross light and cross talk characteristics can be improved.

1 is a plan view showing the surface structure of the optical disk substrate of the present invention, and FIG. 2 is a cross-sectional view of (1). (1) and (2) are cross-sectional views showing a state when a recording layer is formed on the optical disk substrate of the present invention. In particular, (2) shows a state when a recording layer is formed on the optical disk substrate shown in FIG. It is sectional drawing. It is a top view which shows the form of the recording mark formed in the recording layer of the optical disk based on this invention. It is sectional drawing of the optical disk board | substrate with which the groove bottom face curved to convex shape. FIG. 4 is a cross-sectional view (process diagram from resist master production to stamper production) showing a production process of an optical disk substrate molding master according to the present invention and an optical disk substrate production stamper using the same. It is the schematic of the master exposure machine used in the Example of this invention. It is sectional drawing which shows the laminated structure of the resist original disc produced in the Example of this invention. It is a top view which concerns on the problem of a prior art, and shows the form of the recording mark formed in the recording layer of the optical disk. It is a figure which shows the result of having calculated the groove depth dependence of the crosstalk in an optical disk. 1 shows a configuration of an optical disk substrate, (1) is a plan view showing a surface structure thereof, and (2) is a sectional view of (1). FIG. 10 is a diagram in which the groove depth at which crosstalk is minimized corresponding to the track pitch is plotted based on the calculation result of FIG. 9. It is a figure which shows the measurement result of the crosslight characteristic in Example 3. FIG. It is a figure which shows the crosstalk measurement result of Example 7.

Explanation of symbols

10,200 Optical disk substrate (substrate)
11, 101, 201 Land track 11a Land track top portion 12, 102, 202 Groove track 12a Groove bottom surface 12b Groove wall surface 13 Convex track 13a Top portion of convex track 21 Recording layer 22 Groove corner portion 31A Recording layer 31a On land track Recording mark 31B Recording layer 31b Recording mark on convex track 50 Resist master disk 51 Substrate 52 Light absorbing layer 53 Resist layer 60 Optical disk master 61 Land track 62 Groove track 63 Convex track 64 Ni layer 70 Optical disk stamper 81 Laser light source 82 Beam splitter 83 Optical head 84 Turntable 85 Motor 90 Resist master 91 Substrate 92 Protective layer 93 Light absorption layer 94 Resist layer BE1, BE2 Beam expander H1 La Height LB1 of height H2 convex tracks de track, LB2 laser beam M1~M3 mirror OM1, OM2 optical modulator PBS polarizing beam splitter

Claims (16)

  In an optical disk substrate in which land tracks and groove tracks are spirally formed on the substrate, a convex track lower than the land track is formed along the groove track on the bottom surface of the groove track, and the top of the convex track is the land track. An optical disk substrate characterized by being lower than the top of the optical disk substrate.   2. The optical disk substrate according to claim 1, wherein the convex track has a curved shape.   A land / groove recording optical disk in which a land track and a groove track are formed in a spiral shape and a recording layer is formed on the land track and the groove track, having the optical disk substrate according to claim 1 or 2. optical disk.   4. The optical disc according to claim 3, wherein the recording layer thickness at the corner portion of the bottom surface of the groove track is formed thinner than the recording layer thickness at the land track flat portion.   5. The optical disc according to claim 3, wherein a recording layer is not formed at a corner portion on the bottom surface of the groove track. In the method for producing an optical disc master for producing a stamper for producing the disc substrate according to claim 1,
A film forming process for producing a resist master by laminating at least a light absorption layer and a resist layer higher than this on a substrate;
An exposure step of condensing two laser beams on the resist master and forming a latent image on the resist layer according to a predetermined pattern by the laser beams;
An etching step of forming a pattern by etching the resist master after exposure, and
The method for manufacturing an optical disc master, wherein the resist layer includes one or more kinds of fluorine compounds arbitrarily selected from MgF ₂ , CaF ₂ , LiF and BaF ₂ . In the optical disc master manufacturing method according to claim 6, the optical disc master manufacturing method in the resist layer is characterized in that SiO ₂ is added.   8. The optical disc master production method according to claim 6 or 7, wherein the light absorption layer has lower transmission performance at the exposure wavelength used in the exposure step than the resist layer.   9. The optical disc master manufacturing method according to claim 8, wherein the light absorption layer is made of any one of SbTe, GeSbTe, InSbTe, BiSbTe, GaSbTe, and AgInSbTe.   10. The method for manufacturing an optical disc master according to claim 6, wherein a protective layer made of a material different from any of a light absorbing layer material and a resist layer material is formed between the substrate and the light absorbing layer. An optical disk master production method characterized by the above.   11. The optical disk master production method according to claim 10, wherein the material of the protective layer is ZnS.   An optical disc master produced by the method for producing an optical disc master according to claim 6.   An optical disk substrate manufacturing method, comprising: molding an optical disk substrate using a stamper obtained by the optical disk master according to claim 12.   An optical disk manufacturing method using the optical disk substrate obtained by the manufacturing method according to claim 13. In an optical disc having an optical disc substrate in which a land track and a groove track are formed on the substrate at regular intervals, and information is recorded on each of the land track and the groove track,
When the wavelength of the reproduction light is λ (nm), the refractive index of the optical disk substrate is n, and the distance between the land track and the groove track is TP (nm),
An optical disc characterized in that a step D1 between the groove track top and the land track top satisfies the following expression (1).
(−8 × 10 ⁻⁷ · TP ² −0.0006 · TP + 0.38) · (n / λ) ≦ D1 ≦ (−3 × 10 ⁻⁶ · TP ² −0.0007 · TP + 0.22) · (n / λ) (1) An optical disc comprising the optical disc substrate according to claim 1 or 2, wherein information is recorded on each of the land track and the groove track.
When the wavelength of the reproduction light is λ (nm), the refractive index of the optical disk substrate is n, and the distance between the land track and the groove track is TP (nm),
An optical disc characterized in that a step D2 from the top of the convex track to the top of the land track satisfies the following formula (2).
(−8 × 10 ⁻⁷ · TP ² −0.0006 · TP + 0.38) · (n / λ) ≦ D2 ≦ (−3 × 10 ⁻⁶ · TP ² −0.0007 · TP + 0.22) · (n / λ) (2)

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