WO2022186117A1 - 光記録媒体およびその製造方法、光記録媒体用の記録材料ならびに光記録媒体用のスパッタリングターゲット - Google Patents
光記録媒体およびその製造方法、光記録媒体用の記録材料ならびに光記録媒体用のスパッタリングターゲット Download PDFInfo
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- oxide
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- C—CHEMISTRY; METALLURGY
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
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Definitions
- the present disclosure relates to an optical recording medium and its manufacturing method, a recording material for the optical recording medium, and a sputtering target for the optical recording medium.
- Optical disc systems are also used as cold archives, and in optical disc systems, there is a demand for systems and optical discs with a lower bit unit price (an index that converts the price of the optical disc and its system per unit of information).
- low-priced Mn-based oxides have been proposed as recording materials for the above applications in place of expensive Pd-based oxides, and cost reduction has been promoted (see Patent Documents 1 and 2, for example).
- Mn-based oxides take a long time to form a film, which is disadvantageous in terms of tact time. Therefore, a recording material capable of shortening the tact time is desired.
- An object of the present disclosure is to provide an optical recording medium capable of shortening the tact time, a method for manufacturing the same, a recording material for the optical recording medium, and a sputtering target for the optical recording medium.
- the first disclosure is comprising at least one recording layer,
- the recording layer is an optical recording medium containing oxides of Bi.
- the second disclosure is forming a recording layer by sputtering a target while introducing a process gas; the target comprises an oxide of Bi;
- the process gas contains noble gases and oxygen,
- a method for manufacturing an optical recording medium wherein the flow rate ratio of oxygen to the rare gas (oxygen flow rate/rare gas flow rate) is 0.15 or more.
- a third disclosure is: A recording material for an optical recording medium, It is a recording material containing an oxide of Bi.
- a fourth disclosure is: A sputtering target for an optical recording medium, comprising: A sputtering target containing an oxide of Bi.
- At least one recording layer is provided on the substrate, and a cover layer is provided on the at least one recording layer.
- the thickness of the cover layer is not particularly limited, but high-density optical recording media use objective lenses with a high NA (Numerical Aperture). It is preferable to employ a layer and to record and reproduce information signals by irradiating light from the side of this light transmission layer. In this case, it is possible to adopt a substrate having opacity.
- the incident surface of light for recording or reproducing information signals is appropriately set to at least one of the surfaces on the cover layer side and the substrate side according to the format of the optical recording medium.
- the optical recording medium preferably further comprises a protective layer on at least one surface of the recording layer, and more preferably comprises a protective layer on both surfaces of the recording layer. . From the viewpoint of layer structure and simplification of manufacturing equipment, it is preferable to use the recording layer alone without providing a protective layer on any surface of the recording layer.
- the optical recording medium when the optical recording medium includes a plurality of information signal layers each including a recording layer and a protective layer provided on at least one side of the recording layer, from the viewpoint of productivity, a plurality of information
- the signal layers all have the same layer structure.
- a plurality of information signal layers have the same layer structure including a first protective layer, a recording layer, and a second protective layer, from the viewpoint of productivity, the first protective layer, the recording layer, and the second protective layer
- Each of the two protective layers preferably contains the same type of material in all the information signal layers.
- FIG. 1A is a perspective view showing an example of the appearance of an optical recording medium according to an embodiment of the present disclosure.
- FIG. 1B is a schematic cross-sectional view showing an example configuration of an optical recording medium according to an embodiment of the present disclosure.
- FIG. 2A is a schematic diagram showing a first configuration example of each information signal layer.
- FIG. 2B is a schematic diagram showing a second configuration example of each information signal layer.
- FIG. 3A is a schematic diagram showing a third configuration example of each information signal layer.
- FIG. 3B is a schematic diagram showing a fourth configuration example of each information signal layer.
- FIG. 4 is a schematic cross-sectional view showing an example of the configuration of an optical recording medium according to a modification.
- FIG. 1A is a perspective view showing an example of the appearance of an optical recording medium according to an embodiment of the present disclosure.
- FIG. 1B is a schematic cross-sectional view showing an example configuration of an optical recording medium according to an embodiment of the present disclosure.
- FIG. 5 is a schematic diagram showing the configuration of a disk drive type evaluation device.
- FIG. 6 is a graph showing crosstalk-CNR characteristics.
- 7A, 7B, and 7C are graphs showing crosstalk-CNR characteristics, respectively.
- 8A, 8B, and 8C are graphs showing crosstalk-CNR characteristics, respectively.
- 9A, 9B, and 9C are graphs showing crosstalk-CNR characteristics, respectively.
- 10A and 10B are graphs showing crosstalk-CNR characteristics, respectively.
- FIG. 11 is a graph showing crosstalk-CNR characteristics.
- FIG. 12 is a graph showing crosstalk-CNR characteristics.
- FIG. 13A is a schematic diagram of a cross-sectional TEM image of an optical disc in an unrecorded state.
- FIG. 13A is a schematic diagram of a cross-sectional TEM image of an optical disc in an unrecorded state.
- FIG. 13A is a schematic diagram of a cross-sectional TEM image of an
- 13B is a schematic diagram of a cross-sectional TEM image of the optical disc in the recorded state.
- 14A, 14B, and 14C are graphs showing the relationship between the volume ratio of the metal oxide and the reflectance, respectively.
- 15A, 15B, and 15C are graphs showing the relationship between the volume ratio of metal oxide and the reflectance, respectively.
- Embodiments and examples of the present disclosure will be described in the following order.
- Embodiment 1-1 Configuration of Optical Recording Medium 1-2. Recording Principle of Optical Recording Medium 1-3. Sputtering target 1-4. Manufacturing method of optical recording medium 1-5. Action and effect 1-6. Modification 2.
- Example 2-1 Evaluation apparatus and evaluation method for signal characteristics 2-2. Metal oxide to replace Mn-based oxide 2-3. Influence of additive elements on recording/reproducing signal quality 2-4. Bi-based oxide sputtering gas conditions 2-5. Amount of oxide of Bi for ensuring good recording/reproducing signal characteristics
- FIG. 1A is a perspective view showing an example of the appearance of an optical recording medium 10 according to an embodiment of the present disclosure.
- the optical recording medium 10 has a disk shape with an opening (hereinafter referred to as "center hole") in the center. It should be noted that the shape of the optical recording medium 10 is not limited to this example, and a card shape or the like is also possible.
- FIG. 1B is a schematic cross-sectional view showing an example of the configuration of the optical recording medium 10 according to one embodiment of the present disclosure.
- This optical recording medium 10 is a so-called multi-layer write-once optical recording medium, and as shown in FIG.
- An information signal layer Ln and a light transmission layer 12 as a cover layer are provided in this order.
- the information signal layers L0 to Ln may be referred to as the information signal layer L when the information signal layers L0 to Ln are not particularly distinguished.
- information signals are recorded or reproduced by irradiating the information signal layers L0 to Ln with laser light from the surface C on the light transmission layer 12 side.
- a laser beam having a wavelength in the range of 400 nm or more and 410 nm or less is condensed by an objective lens having a numerical aperture of 0.84 or more and 0.86 or less.
- Information signals are recorded or reproduced by irradiating .about.Ln.
- Such an optical recording medium 10 is, for example, a multi-layer BD-R.
- the above wavelength and numerical aperture ranges are examples, and the wavelength of the laser light and the numerical aperture of the objective lens are not limited to the above wavelength and numerical aperture ranges. good.
- the substrate 11 the information signal layers L0 to Ln, the intermediate layers S1 to Sn, and the light transmission layer 12, which constitute the optical recording medium 10, will be sequentially described below.
- the substrate 11 has, for example, a disc shape with a center hole provided in the center.
- One main surface of the substrate 11 is, for example, an uneven surface, and the information signal layer L0 is formed on this uneven surface.
- concave portions of the uneven surface are referred to as lands Gin, and convex portions are referred to as grooves Gon.
- the shapes of the land Gin and groove Gon include, for example, various shapes such as spiral and concentric circles. Also, the land Gin and/or the groove Gon may be wobbled (meandering) for stabilizing the linear velocity, adding address information, and the like.
- the diameter (diameter) of the substrate 11 is selected to be 120 mm, for example.
- the thickness of the substrate 11 is selected in consideration of rigidity, preferably 0.3 mm or more and 1.3 mm or less, more preferably 0.6 mm or more and 1.3 mm or less, for example 1.1 mm.
- the diameter of the center hole is selected to be 15 mm, for example.
- a plastic material or glass can be used as the material of the substrate 11, and it is preferable to use a plastic material from the viewpoint of cost.
- a plastic material for example, a polycarbonate-based resin, a polyolefin-based resin, an acrylic-based resin, or the like can be used.
- the information signal layers L0 to Ln include at least a recording layer configured to record information signals by irradiation with laser light.
- the information signal layers L0 to Ln have a recording capacity of 25 GB or more for a wavelength of 405 nm and a numerical aperture NA of 0.85 of the condenser lens.
- the information signal layers L0 to Ln preferably further include a protective layer on at least one surface of the recording layer, more preferably on both surfaces of the recording layer.
- the layer structure of the information signal layers L0 to Ln may be the same for all layers, and the layer structure may be changed according to the properties (eg, optical properties, durability, etc.) required for each of the information signal layers L0 to Ln.
- the information signal layers L0 to Ln may be composed of a single recording layer. With such a simple configuration, the cost of the optical recording medium 10 can be reduced and the productivity can be improved. Such an effect becomes more pronounced in a medium having a larger number of information signal layers L0 to Ln.
- FIG. 2A is a schematic diagram showing a first configuration example of each information signal layer L.
- the information signal layers L0 to Ln are adjacent to the recording layer 21 having an upper surface (second principal surface) and a lower surface (first principal surface) and the upper surface of the recording layer 21. and a protective layer 22 provided on the substrate. With such a configuration, the durability of the recording layer 21 can be improved.
- FIG. 2B is a schematic diagram showing a second configuration example of each information signal layer L.
- the information signal layers L0 to Ln are adjacent to the recording layer 21 having a top surface (second principal surface) and a bottom surface (first principal surface) and the bottom surface of the recording layer 21. and a protective layer 23 provided on the substrate. With such a configuration, the durability of the recording layer 21 can be improved.
- FIG. 3A is a schematic diagram showing a third configuration example of each information signal layer L.
- the information signal layers L0 to Ln are adjacent to the recording layer 21 having a top surface (second principal surface) and a bottom surface (first principal surface) and the bottom surface of the recording layer 21. and a protective layer 22 provided adjacent to the upper surface of the recording layer 21 .
- the durability of the recording layer 21 can be improved as compared with the first and second configuration examples.
- FIG. 3B is a schematic diagram showing a fourth configuration example of each information signal layer L.
- the information signal layers L0 to Ln have, for example, a two-layer structure in which a recording layer 21a and a recording layer 21b are laminated.
- the recording layer 21a and the recording layer 21b have different material compositions, for example.
- the recording layer 21 contains Bi oxide as a recording material.
- the recording layer 21 may further contain an oxide of metal M other than Bi.
- Bi and metal M may form a composite oxide.
- the metal M is, for example, Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Ru, Pd, Ag, At least one selected from the group consisting of In, Sn, Sb, Te, Hf, Ta, W and Pb is included.
- the metal M preferably contains at least one selected from the group consisting of Cu, Zr, Nb, Sn, Ta, W, Ge, In, Sb and Mo. More preferably, it contains at least one selected from the group consisting of Ga and Zn.
- the thickness of the recording layer 21 is, for example, 10 nm or more and 100 nm or less. It is preferable that the content of Bi oxide in the recording layer 21 is 10 nm or more in terms of the thickness of the thin film. If the content of Bi oxide in the recording layer 21 is 10 nm or more in terms of the thickness of the thin film, the light energy absorption capability required for recording can be ensured.
- the content of the Al oxide in the recording layer 21 is preferably 15 vol% or more and 50 vol% or less, more preferably 17 vol% or more and 50 vol% or less.
- the reproduced signal quality can be improved.
- desirable optical characteristics (reflectance, transmittance, etc.) of the recording layer 21 of the information signal layers L0 to Ln can be obtained.
- the content of Ga oxide in the recording layer 21 is preferably 17 vol% or more and 67 vol% or less, more preferably 33 vol% or more and 67 vol% or less.
- the reproduced signal quality can be improved.
- desirable optical characteristics (reflectance, transmittance, etc.) of the recording layer 21 of the information signal layers L0 to Ln can be obtained.
- the content of Zn oxide in the recording layer 21 is preferably 17 vol% or more and 55 vol% or less, more preferably 17 vol% or more and 50 vol% or less.
- the content of Zn oxide in the recording layer 21 is 17 vol % or more and 55 vol % or less, the reproduced signal quality can be improved.
- desirable optical characteristics (reflectance, transmittance, etc.) of the recording layer 21 of the information signal layers L0 to Ln can be obtained.
- volume ratio the content of the oxide of metal M in the recording layer 21 is indicated by volume ratio (vol %).
- the contents of materials in the recording layer 21 are often expressed in terms of molar ratios. Since the number of moles varies greatly, the volume ratio is adopted.
- the oxide of Bi is Bi 2 O 3
- the amount of Bi 2 O 3 in the recording layer 21 is T (BiOx) in terms of film thickness
- the amount of oxide of metal M is T in terms of film thickness.
- the contents of materials in the recording layer 21 are generally expressed in terms of molar ratios.
- the conversion method from volume ratio to molar ratio is as follows.
- the densities of Bi oxide (Bi 2 O 3 ) and metal M oxide (MOx) are ⁇ (BiOx) and ⁇ (MOx), respectively, and the chemical formula weights are MW(BiOx) and MW(MOx), respectively.
- the number of moles of each metal oxide is proportional to T ⁇ /MW.
- the relative mole numbers Mol(BiOx) and Mol(MOx) of each metal oxide are determined by the following equations.
- Mol(BiOx) T(BiOx) ⁇ (BiOx)/MW(BiOx)
- Mol(MOx) T(MOx) ⁇ (MOx)/MW(mOx)
- the molar ratio of the oxide of metal M is determined by the following formula.
- Molar ratio (mol%) of oxide of metal M Mol (MOx) / [Mol (MOx) + Mol (BiOx)] ⁇ 100
- the molar ratio of oxides of Bi is determined by the following formula.
- Bi 2 O 3 molar ratio (mol%) Mol (BiOx) / [Mol (MOx) + Mol (BiOx)] ⁇ 100
- the recording layer 21 preferably does not contain Mn. From the viewpoint of reducing the manufacturing cost of the optical recording medium 10, the recording layer 21 preferably does not contain Pd. From the viewpoint of reducing the manufacturing cost of the optical recording medium 10 and shortening the tact time in the manufacturing process of the optical recording medium 10, the recording layer 21 preferably does not contain Mn and Pd.
- the recording layer 21, for example, is not limited to a single layer structure, and may have a laminated structure of multiple layers with different compositions.
- the recording layer 21 is mainly composed of, for example, a complex oxide containing Bi.
- each layer constituting the recording layer 21 contains composite oxides having different material compositions as main components. At least one of them contains a Bi-containing composite oxide as a main component.
- the protective layers 22 and 23 are protective layers that protect the recording layer 21 .
- Protective layer 22 and protective layer 23 may have a function as a gas barrier layer.
- the durability of the recording layer 21 can be improved by the protective layer 22 and the protective layer 23 functioning as gas barrier layers.
- changes in film quality of the recording layer 21 mainly detected as a decrease in reflectance
- Film quality can be ensured.
- Protective layer 22 and protective layer 23 contain, for example, at least one selected from the group consisting of oxides, nitrides, sulfides, carbides and fluorides.
- the protective layer 22 and the protective layer 23 may be made of the same material, or may be made of different materials.
- oxide for example, oxidation of at least one element selected from the group consisting of In, Zn, Sn, Al, Si, Ge, Ti, Ga, Ta, Nb, Hf, Zr, Cr, Bi and Mg. things are mentioned.
- Nitrides include, for example, nitriding of at least one element selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Nb, Mo, Ti, Nb, Mo, Ti, W, Ta and Zn.
- Sulfides include, for example, Zn sulfides.
- Carbides include, for example, carbides of at least one element selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Ti, Zr, Ta and W, preferably Si, Ti and W. Carbide of at least one element selected from the group can be mentioned.
- fluorides include fluorides of at least one element selected from the group consisting of Si, Al, Mg, Ca and La.
- Mixtures thereof include, for example, ZnS—SiO 2 , SiO 2 —In 2 O 3 —ZrO 2 (SIZ), SiO 2 —Cr 2 O 3 —ZrO 2 (SCZ), In 2 O 3 —SnO 2 (ITO ), In 2 O 3 —CeO 2 (ICO), In 2 O 3 —Ga 2 O 3 (IGO), In 2 O 3 —Ga 2 O 3 —ZnO (IGZO), Sn 2 O 3 —Ta 2 O 5 (TTO), TiO 2 —SiO 2 , Al 2 O 3 —ZnO, Al 2 O 3 —BaO and the like.
- the intermediate layers S1 to Sn play a role of physically and optically separating the information signal layers L0 to Ln with a sufficient distance, and have uneven surfaces on their surfaces.
- the uneven surface forms, for example, concentric or spiral grooves (land Gin and groove Gon).
- the thickness of the intermediate layers S1 to Sn is preferably set to 9 ⁇ m or more and 50 ⁇ m or less.
- the material of the intermediate layers S1 to Sn is not particularly limited, it is preferable to use an ultraviolet curable acrylic resin.
- the intermediate layers S1 to Sn preferably have sufficiently high light transmittance because they serve as optical paths for laser light for recording or reproducing information signals in the inner layers.
- the light transmission layer 12 is, for example, a resin layer formed by curing a photosensitive resin such as an ultraviolet curable resin. As a material of this resin layer, for example, an ultraviolet curable acrylic resin can be used.
- the light-transmitting layer 12 may be composed of a ring-shaped light-transmitting sheet and an adhesive layer for bonding the light-transmitting sheet to the substrate 11 .
- the light-transmitting sheet is preferably made of a material having a low absorption ability for the laser light used for recording and reproduction, and specifically preferably made of a material having a transmittance of 90% or more.
- a material for the light-transmissive sheet for example, a polycarbonate resin material, a polyolefin-based resin (for example, Zeonex (registered trademark)), or the like can be used.
- a material for the adhesive layer for example, an ultraviolet curable resin, a pressure sensitive adhesive (PSA), or the like can be used.
- the thickness of the light transmission layer 12 is preferably selected from the range of 10 ⁇ m or more and 177 ⁇ m or less, for example, 100 ⁇ m. High-density recording can be realized by combining such a thin light transmission layer 12 with an objective lens having a high NA (numerical aperture) of about 0.85, for example.
- the optical recording medium 10 may have a hard coat layer on the surface C of the light transmission layer 12 .
- the optical recording medium 10 can be protected from mechanical impacts and scratches.
- the adhesion of dust, fingerprints, etc. to the surface C of the light transmission layer 12 can be suppressed, and the recording/reproducing quality of information signals can be ensured.
- the hard coat layer may contain silica fine powder in order to improve mechanical strength.
- a solvent type or non-solvent type UV curable resin can be used as the resin composition for forming the hard coat layer.
- the thickness of the hard coat layer is preferably about 1 ⁇ m to several ⁇ m.
- the recording layer 21 containing Bi oxide absorbs the laser beam and reacts with the laser beam. and expands in volume. The inside of the volume-expanded recording layer 21 becomes bubble-like.
- the recording layer 21 is a so-called optical thin film from an optical point of view.
- the light reflectance of an optical thin film changes depending on the refractive index and thickness of the thin film.
- the recording layer 21 changes both the refractive index and the thickness by irradiation with recording light.
- Regarding the change in refractive index it is considered that in addition to the decrease in density due to expansion, the change in refractive index also occurs due to the thermal reaction of the recording material.
- the recording layer 21 is irradiated with recording light, a volume change and an optical constant change occur to form a recording mark.
- a difference in reflectance with respect to reproduction light occurs between the recorded marks (recorded portions) and the unrecorded portions. This makes it possible to read the information of the recording marks by irradiating the reproduction light.
- volume change can be divided into expansion in the film thickness direction and expansion in the in-plane direction of the recording layer.
- the amount of change in the optical constant also varies depending on the components of the recording material.
- a sputtering target for forming the recording layer of the optical recording medium 10 contains Bi or an oxide of Bi.
- the target may further include a metal M other than Bi or an oxide of a metal M other than Bi.
- Bi and metal M may form a composite oxide.
- the metal M is as described as the material of the recording layer 21 .
- the content of Al oxide in the target is preferably 15 vol% or more and 50 vol% or less.
- the content of Ga oxide in the target is preferably 17 vol % or more and 67 vol % or less.
- the content of Zn oxide in the target is preferably 17 vol % or more and 55 vol % or less.
- a substrate 11 having an uneven surface formed on one main surface is formed.
- a method for molding the substrate 11 for example, an injection molding method, a photopolymer method (2P method: Photo Polymerization), or the like can be used.
- the information signal layer L0 is formed on the substrate 11 by, for example, sputtering.
- a specific formation process of the information signal layer L0 differs depending on the configuration of the information signal layer L0. Below, the formation process of the information signal layer L0 in the case of adopting the third configuration example (see FIG. 3A) as the configuration of the information signal layer L0 will be specifically described.
- Step of forming protective layer First, the substrate 11 is transferred into a vacuum chamber provided with a target for forming a protective layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure. After that, the protective layer 23 is formed on the substrate 11 by sputtering the target while introducing a process gas such as rare gas or O 2 gas into the vacuum chamber.
- a process gas such as rare gas or O 2 gas
- the sputtering method for example, a radio frequency (RF) sputtering method or a direct current (DC) sputtering method can be used, and the direct current sputtering method is particularly preferable.
- the direct-current sputtering method can lower the manufacturing cost and improve the productivity because the equipment is cheaper and the film-forming rate is higher than that of the high-frequency sputtering method.
- At least one selected from the group consisting of Ar, Kr and Xe can be used as the rare gas in the film forming process of the protective layer 23 .
- the substrate 11 is transported into a vacuum chamber provided with a target for forming the recording layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure.
- the recording layer 21 is formed on the protective layer 23 by sputtering the target while introducing a process gas such as rare gas or O 2 gas into the vacuum chamber.
- the target the above target for forming the recording layer is used.
- the recording layer 21 is formed by sputtering with oxygen assist, thereby forming a thin film in which Bi and the oxide of the metal M are mixed at the compound level.
- the flow rate ratio of oxygen to the rare gas is preferably 0.15 or more.
- the recording layer 21 can contain oxides of Bi having a good light absorption capability.
- At least one selected from the group consisting of Ar, Kr and Xe can be used as the rare gas in the film forming process of the recording layer 21 .
- Step of forming protective layer the substrate 11 is transferred into a vacuum chamber provided with a target for forming a protective layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure.
- the protective layer 22 is formed on the recording layer 21 by sputtering the target while introducing a process gas such as rare gas or O 2 gas into the vacuum chamber.
- a process gas such as rare gas or O 2 gas
- the sputtering method for example, a radio frequency (RF) sputtering method or a direct current (DC) sputtering method can be used, and the direct current sputtering method is particularly preferable.
- the information signal layer L0 is formed on the substrate 11 .
- an ultraviolet curable resin is uniformly applied on the information signal layer L0 by spin coating, for example.
- the uneven pattern of the stamper is pressed against the UV curable resin uniformly applied on the information signal layer L0, and the UV curable resin is irradiated with UV rays to be cured, and then the stamper is peeled off.
- the uneven pattern of the stamper is transferred to the ultraviolet curable resin, and the intermediate layer S1 provided with, for example, lands Gin and grooves Gon is formed on the information signal layer L0.
- an information signal layer L1 an intermediate layer S2, an information signal layer L2, .
- a layer Sn and an information signal layer Ln are stacked in this order on the intermediate layer S1.
- a photosensitive resin such as an ultraviolet curable resin is spin-coated on the information signal layer Ln by, for example, a spin coating method, and then the photosensitive resin is cured by irradiating light such as ultraviolet rays. Thereby, the light transmission layer 12 is formed on the information signal layer Ln.
- the intended optical recording medium 10 is obtained.
- the recording layer 21 contains oxides of Bi, so the film formation time of the recording layer 21 can be shortened. As a result, the production tact time can be shortened. That is, the time required for mass production can be shortened. Therefore, the bit unit price can be reduced.
- the production cycle of the recording layer 21 can be shortened without providing a plurality of film forming apparatuses. Therefore, it is possible to reduce the number of film forming apparatuses. From this point of view as well, a reduction in the bit unit price can be expected.
- the recording layer 21 contains at least one selected from the group consisting of Al metal oxide, Ga metal oxide, and Zn metal oxide, high reproduced signal quality can be obtained.
- the upper limit or lower limit of the numerical range at one stage may be replaced with the upper limit or lower limit of the numerical range at another stage.
- the optical recording medium 10 has been described as having multiple information signal layers L, but as shown in FIG. 4, it may have a single information signal layer L0.
- a plurality of information signal layers and light transmission layers are laminated in this order on the substrate, and information is obtained by irradiating the information signal layer with a laser beam from the light transmission layer side.
- the present disclosure is also applicable to optical recording media (for example, CDs (Compact Discs)) on which signals are recorded or reproduced.
- CDs Compact Discs
- It has a structure in which one or more information signal layers are provided between two substrates, and an information signal is generated by irradiating one or more information signal layers with a laser beam from one substrate side.
- the present disclosure can also be applied to an optical recording medium (for example, DVD (Digital Versatile Disc)) on which recording or reproduction is performed.
- the present disclosure can also be applied to an optical recording medium (for example, AD (Archival Disc)) in which information signals are recorded or reproduced on a second disc by irradiating a laser beam from the disc-side surface of the second disc.
- the first disc and the second disc may have the same layer structure as the optical recording medium 10 according to the above embodiment.
- the recording layer of the present disclosure may be combined with a recording layer other than the write-once type, such as a ROM layer or a rewritable recording layer.
- the present disclosure can also be applied to an optical recording medium partially provided with a recording area such as read-only pits.
- the present disclosure can also employ the following configuration.
- (1) comprising at least one recording layer, The optical recording medium, wherein the recording layer contains an oxide of Bi.
- the recording layer includes Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Se, Y, Zr, Nb, Mo, Ru, Pd, Ag, In , Sn, Sb, Te, Hf, Ta, W and Pb oxides.
- the optical recording medium according to (1), wherein the recording layer further contains at least one selected from the group consisting of Cu, Zr, Nb, Sn, Ta, W, Ge, In, Sb and Mo oxides.
- the recording layer further contains at least one selected from the group consisting of oxides of Al, Ga and Zn.
- the recording layer further includes an Al oxide, The optical recording medium according to (1), wherein the content of the Al oxide in the recording layer is 15 vol % or more and 50 vol % or less.
- the recording layer further includes an oxide of Ga, The optical recording medium according to (1), wherein the content of the Ga oxide in the recording layer is 17 vol % or more and 67 vol % or less.
- the recording layer further includes a Zn oxide; The optical recording medium according to (1), wherein the content of the Zn oxide in the recording layer is 17 vol % or more and 55 vol % or less.
- a recording layer by sputtering a target while introducing a process gas includes an oxide of Bi, the process gas comprises a noble gas and oxygen;
- a method for producing an optical recording medium wherein the flow rate ratio of oxygen to the rare gas (oxygen flow rate/rare gas flow rate) is 0.15 or more.
- a recording material for an optical recording medium A recording material containing an oxide of Bi.
- a sputtering target for an optical recording medium comprising: A sputtering target containing an oxide of Bi.
- FIG. 5 shows the configuration of a disk drive type evaluation device.
- the operation and procedure from the time when the optical disk 30 to be evaluated is mounted on the disk drive type evaluation apparatus to the time when the signal is evaluated will be described.
- the optical disk 30 is attached to the spindle motor unit 31 and rotated.
- the recording/reproducing optical system 32 causes the laser diode 41 to emit light, and the laser light L is incident on the mirror 44 via the collimator lens 42 and the beam splitter 43 .
- the laser light L reflected by the mirror 44 is incident on the recording layer of the optical disc 30 via the objective lens 45 while being condensed.
- the objective lens 45 is vertically moved in a direction (optical axis direction) perpendicular to the light irradiation surface of the optical disc 30 to focus the laser light L on the recording layer of the optical disc 30 .
- the laser beam L reflected by the recording layer of the optical disc 30 returns along the path it traveled, and part or all of the laser beam L is reflected by the beam splitter 43 of the recording/reproducing optical system 32, and is reflected by the condenser lens. It is incident on a photodetector 47 via 46 . Light received by the photodetector 47 is converted into an electrical signal and supplied to the signal analyzer 34 .
- the signal analyzer 34 generates a focus servo error signal, a tracking servo error signal, an RF signal, and the like based on the electrical signal supplied from the photodetector 47, and performs servo control and the like based on these generated signals.
- a focus error signal is used to operate the focus servo so that the focus of the laser beam is always positioned on the recording layer.
- the tracking error signal is used to control so that the focus of the laser beam is positioned on the convex portion (Gon) of the guide groove on the recording layer.
- a signal generator 33 controls laser emission of a laser diode 41 based on an information signal to be recorded on the optical disc 30 .
- the emission waveform of the laser light L emitted from the laser diode 41 is controlled, and the recording layer of the optical disc 30 is irradiated.
- the recording layer irradiated with the laser light L changes due to this laser energy.
- the laser energy decomposes the metal oxide (BiOx, for example) to generate O 2 , causing a change in the refractive index and physical volume expansion of the recording layer. It is assumed that the laser light L supplies sufficient energy to the recording layer to cause this change.
- the reproduction of information signals from the optical disk 30 is performed as follows.
- the information signal is reproduced with a sufficiently low power that does not change even if the same portion of the recording layer of the optical disk 30 is reproduced one million times by laser light irradiation, and the recorded information signal is read with a sufficient S/N. It is done with the power that can be put out.
- the laser light set in this manner is called reproduction light, and the laser power at that time is called reproduction power.
- the reproduction light irradiated onto the recording layer of the optical disk 30 travels backward through the recording/reproduction optical system and is detected by the photodetector 47 .
- the optical disc 30 has a system in which the amount of light returned from the recorded area is lower than the amount of light returned from the unrecorded area, and a system in which the amount of returned light from the recorded area is higher than the amount of light returned from the unrecorded area.
- the former is called a high-to-low recording method, and the latter is called a low-to-high recording method.
- the optical disc 30 of this embodiment is a medium for high-to-low recording, and is used for CDs, DVDs, and BDs.
- the light detected by the photodetector 47 is supplied to the signal analysis device 34, and the signal quality is evaluated by the signal analysis device 34.
- An object of the present embodiment is to provide a recording material with high reproduction signal quality in addition to reducing the disc production bit cost.
- a general SNR Signal to Noise Ratio
- a CNR Carrier to Noise Ratio
- the signal level of the reproduced track used in the case of an optical disc are used.
- evaluation indexes such as crosstalk, which use the signal level at which recording signals from adjacent tracks leak as an evaluation index.
- a method for evaluating CNR and crosstalk will be described.
- the recording/reproducing signal evaluation of the optical disk was performed as follows using the evaluation device for BD described above.
- a channel clock used for recording data on an optical disc is set to 132 MHz, and one period of this clock is set to 1T.
- the recording linear velocity was set to 4.48 m/sec.
- the wavelength ⁇ of the recording/reproducing laser beam was set to 405 nm.
- the NA of the objective lens used for laser focusing was set to 0.85.
- As a recording method a so-called land/groove recording method was used in which data is recorded in both convex grooves and concave lands on the light incident side. A land was formed on the track next to the groove.
- the track pitch was the interval between the center of the groove and the land.
- Crosstalk was evaluated as follows. The amount of leakage into the track: land next to the signal recorded in the groove was evaluated. A signal with a mark length/space length of 12T was recorded in the groove. This was used as a 12T monocarrier signal. In recording the 12T monocarrier signal, a method was used in which the laser emission waveform was fixed and the power level was uniformly adjusted. The amplitude modulation degree of the 12T monocarrier signal was fixed at 50%. A reproduction beam was arranged on the land adjacent to this signal, and the amplitude of the signal leaking from the groove was observed with an oscilloscope and obtained as an amplitude voltage value Vpp. On the other hand, the reproducing beam was placed on the land where neither the groove nor the land was recorded, and the signal level Iv at the time of non-recording was obtained as a voltage level. The amount of leakage CT was defined as Vpp/Iv.
- CNR was evaluated as follows.
- a single-frequency signal monocarrier was recorded in the groove. No signal was recorded on the lands of adjacent tracks.
- the carrier level and noise level of the monocarrier reproduced signal were measured with a spectrum analyzer using the reproduced signal obtained from the photodetector 47 .
- the degree of modulation of the signal from the photodetector 47 detected by direct current (DC) the value obtained by normalizing the signal amplitude by the signal level at the time of non-recording is set constant.
- DC direct current
- the degree of modulation was fixed at 50%.
- the noise components are known to be media noise caused by the recording surface of the optical disk, laser noise, shot noise caused by light hitting the photodetector 47, and thermal noise of the reproduction signal circuit system, but media noise is the main component. Therefore, it is desirable to select an appropriate monocarrier frequency and laser power, fix them, and make comparisons between optical discs.
- a 12T monocarrier signal is used.
- the carrier level C (dBm) of the monocarrier reproduction signal and the media noise N (dBm) in the vicinity of that frequency are measured.
- Example 1-1 Reference Examples 1-1 to 1-17
- a silicon wafer sample was produced by forming a recording layer with a thickness of 30 nm on a silicon wafer by a sputtering method. At this time, the film formation time required to form a recording layer with a thickness of 30 nm was measured. Table 1 shows the results.
- As materials for the recording layer 18 kinds of metal oxides (Mn, V, Cr, Bi, Te, Cu, Ag, W, Zn, Sn, Zr, Ge, Mg, Mo, Ti, Sb , Nb or Ta) was used.
- Table 1 shows the evaluation results of the optical constants and the measurement results of the film formation time. However, the optical constants are values at a wavelength of 405 nm.
- an optical disc was produced as follows.
- Example 2-1 Reference Examples 2-1 to 2-5
- a polycarbonate substrate having a thickness of 1.1 mm was molded by injection molding.
- a recording track was formed in a spiral shape with projections and depressions.
- a convex spiral track is defined as a groove
- a concave spiral track is defined as a land.
- a first protective layer, a recording layer, and a second protective layer were sequentially laminated on the uneven surface of the polycarbonate substrate by a sputtering method.
- Second protective layer (light transmission layer side) Material: SIZ composite oxide (Si:In:Zr 20:50:30 (mol% ratio)) Thickness: 10nm
- Second protective layer (light transmission layer side) Material: SIZ composite oxide (Si:In:Zr 20:50:30 (mol% ratio)) Thickness: 10nm
- recording materials metal oxides (MnOx, VOx, CrOx, BiOx, CuOx, AgOx) shown in Table 2 were used. The process gas conditions (Ar+O 2 ) were adjusted so that tetravalent Mn was generated in the Mn-based oxide in the film formation process by the sputtering method. In addition, an excessive amount of O 2 was introduced to oxidize the metal element, and an oxide film was formed by reactive sputtering. Thickness: 30nm
- First protective layer (substrate side) Material: SIZ composite oxide (Si:In:Zr 20:50:30 (mol% ratio)) Thickness: 10nm
- an ultraviolet curable resin was uniformly coated on the second protective layer by a spin coating method and cured by irradiating ultraviolet rays to form a light transmission layer having a thickness of 100 ⁇ m. As described above, the intended optical disc was obtained.
- a reproduction signal of the optical disk was obtained using an optical disk inspection apparatus, and the reproduction signal level was converted into a reflectance R.
- FIG. 1 A reproduction signal of the optical disk was obtained using an optical disk inspection apparatus, and the reproduction signal level was converted into a reflectance R.
- Transmittance T was calculated from comparison with the standard value of the transmittance reference sample.
- An ellipsometer was used as a measuring device.
- sputter rate For MOx, VOx, CrOx, BiOx, CuOx, and AgOx, using the film formation time data and the extinction coefficient k in Table 1, the film formation speed at a film formation power of 1 kW: sputtering rate (hereinafter referred to as “sputter rate (1 )”), and the sputtering rate (hereinafter referred to as “sputtering rate (2)”) on the assumption that a layer having the same light absorption is formed with the same deposition power as a relative value with respect to Mn oxide. digitized. Table 2 shows the results.
- Sputter rate (1) in Table 2 was calculated by the following formula using the data in Table 1.
- Sputter rate (nm/kW/sec) (thickness 30 nm)/deposition time (sec)/deposition power (W) ⁇ 1000
- Sputter rate (2) in Table 2 was calculated using the data in Table 2 by the following formula.
- Sputter rate (normalized by Mn) (1-RT) x (nm/kW/sec)/[(1-RT) of MnOx x (nm/kW/sec)]
- Table 2 shows evaluation results of reflectance R, transmittance T, absorptance (1-RT), recording/reproducing signal quality and sputtering rate.
- the evaluation results for BiOx (Bi 2 O 3 ) (sputter rate (1)) are those for an optical disc on which a recording layer was formed by RF sputtering, and the evaluation results for metal oxides other than BiOx are , an optical disc having a recording layer formed by DC sputtering. It is known that when RF sputtering and DC sputtering are performed at the same power to form a thin film, the RF sputtering rate is half the DC sputtering rate. Therefore, when the correction is incorporated, the order of sputtering rate of each metal oxide is as follows. Ag oxide>Bi oxide>Cu oxide>Cr oxide>Mn oxide>V oxide They were 19.1 times, 8.0 times and 4.6 times.
- Figure 6 shows the evaluation results of CNR and CT.
- a decrease (deterioration) of CNR of 7.5 dB is offset by a decrease (improvement) of CT of 10 dB.
- the straight line graph in FIG. 6 is a line drawn with a CNR/CT slope of 7.5 dB/10 dB based on the evaluation result (plot) of Mn oxide, and the evaluation result (plot ) has better CT-CNR performance than Mn oxide.
- recording materials with better CT-CNR performance than Mn oxides are Cr and Bi oxides.
- Cr oxide is a recording material inferior in sputtering rate to Mn oxide, and therefore Bi oxide is preferable as a recording material.
- the recording layer was formed from the composite oxide of )).
- the volume ratio of the oxide of Bi (BiOx) and the oxide of metal M (MOx) in the recording layer was set to the value shown in Table 3 by adjusting the film formation conditions.
- An optical disc was obtained in the same manner as in Example 1-1 except for the above.
- FIGS. 7A to 10B show evaluation results of optical discs using composite oxides of BiOx and MOx as recording materials.
- FIG. 11 shows evaluation results of an optical disk using a composite oxide of CuOx and MOx as a recording material.
- the straight lines shown in FIGS. 7A to 10B and 11 are straight lines drawn so that the CNR/CT slope is 7.5 dB/10 dB based on the data of Mn-based oxides.
- Bi-based oxides whose evaluation results (plots) are located on the upper side have better CT-CNR performance than Mn-based oxides.
- "%" described in Figs. 7A to 10B and Table 4 means "vol%".
- a recording material using an oxide of Bi contains an oxide of Bi with a high valence, and oxygen generated by recording energy expands the volume of the recording layer to obtain a difference in reflectance between a recorded portion and an unrecorded portion. It is characterized. In the following, we show that sputtering in oxygen-rich conditions is preferred.
- Examples 14-1 to 14-5) A silicon wafer sample was produced by forming a recording layer with a thickness of 30 nm on a silicon wafer by a sputtering method.
- Bi 2 O 3 (Bi-based oxide) having a stoichiometric composition was used as a recording layer deposition material (target material), and Ar gas and O 2 gas were used as process gases.
- the flow ratio of Ar gas and O 2 gas was adjusted as shown in Table 5 for each sample. Also, the input power for film formation was fixed.
- Example 15-1 to 15-5 An optical disc was obtained in the same manner as in Example 2-1 except that the recording layer was formed under the same film forming conditions as in Examples 14-1 to 14-5.
- optical constants (refractive index n, extinction coefficient k) of the recording layer of the silicon wafer sample obtained as described above were measured with an ellipsometer.
- Cross-sectional TEM images of the optical disk obtained as described above were obtained in the unrecorded state and the recorded state.
- Table 5 shows the evaluation results of the optical constants of the recording layer. However, the optical constants are values at a wavelength of 405 nm.
- FIG. 12 shows the evaluation results of the signal characteristics of the optical disk.
- the data of Mn-based oxides are marked with "x" as in FIGS. 7A to 10B.
- straight lines similar to those in FIGS. 7A to 10B and the like are shown. From FIG. 12, it can be seen that increasing the amount of oxygen significantly reduces the CT value and improves the CT-CNR performance.
- the flow rate ratio (O 2 gas flow rate/Ar gas flow rate) of Ar gas and O 2 gas in sputtering is 0.15 or more in order to ensure the recording/reproducing signal characteristics (O 2 flow rate/Ar flow rate). is preferably
- FIG. 13A A schematic diagram of a cross-sectional TEM image of an unrecorded state is shown in FIG. 13A.
- FIG. 13B A schematic diagram of a cross-sectional TEM image in a recorded state is shown in FIG. 13B.
- the film thickness increases from the viewpoint of the optical film, and the material density in the space decreases due to the expansion, so the refractive index also decreases.
- the recording material undergoes a chemical change such as thermal reaction or thermal decomposition due to recording, and this chemical change is also included in the refractive index change.
- a change in the amount of reflected light with respect to the information reproducing light occurs between the recorded portion and the unrecorded portion.
- the oxide of Bi is preferably formed under conditions of excess oxygen, and that the oxide of Bi is a useful recording material as a detonator.
- Bi Oxide Amount for Ensuring Good Recording/Reproducing Signal Characteristics The amount of BiOx was estimated to secure the recording/reproducing signal characteristics and to obtain the reflectance and transmittance for use in a multilayer optical disk. Film thickness notation is used here. Since the recording mode uses the expansion of the recording material, the amount of reproduced signal depends on the amount of oxygen released from the reactant BiOx. In the case of notation of the composition ratio, the number of elements differs greatly even if the composition ratio is the same, depending on the type of other additive elements in the recording material, and the amount of oxygen released varies.
- FIGS. 14A to 14C and 15A to 15C show compositional data that ensure CT-CNR characteristics equal to or higher than those of the Mn-based recording material used as the comparison standard. From this data, it can be seen that the reflectance can be adjusted in the range of 3% to 9%, and the transmittance can be adjusted in the range of 75% to 90%. .
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Abstract
Description
少なくとも1層の記録層を備え、
記録層は、Biの酸化物を含む光記録媒体である。
プロセスガスを導入しながらターゲットをスパッタリングすることにより、記録層を形成することを含み、
ターゲットは、Biの酸化物を含み、
プロセスガスは、希ガスおよび酸素を含み、
希ガスに対する酸素の流量比(酸素流量/希ガス流量)が、0.15以上である光記録媒体の製造方法である。
光記録媒体用の記録材料であって、
Biの酸化物を含む記録材料である。
光記録媒体用のスパッタリングターゲットであって、
Biの酸化物を含むスパッタリングターゲットである。
1.実施形態
1-1.光記録媒体の構成
1-2.光記録媒体の記録原理
1-3.スパッタリングターゲット
1-4.光記録媒体の製造方法
1-5.作用効果
1-6.変形例
2.実施例
2-1.信号特性の評価装置および評価方法
2-2.Mn系酸化物に代わる金属酸化物
2-3.記録再生信号品質に対する添加元素の影響
2-4.Bi系酸化物のスパッタリングガス条件
2-5.良好な記録再生信号特性を確保するためのBiの酸化物量
[1-1.光記録媒体の構成]
図1Aは、本開示の一実施形態に係る光記録媒体10の外観の一例を示す斜視図である。光記録媒体10は、中央に開口(以下「センターホール」という。)が設けられた円盤形状を有する。なお、光記録媒体10の形状はこの例に限定されるものではなく、カード状等とすることも可能である。
基板11は、例えば、中央にセンターホールが設けられた円盤形状を有する。この基板11の一主面は、例えば、凹凸面となっており、この凹凸面上に情報信号層L0が成膜される。以下では、凹凸面のうち凹部をランドGin、凸部をグルーブGonと称する。
情報信号層L0~Lnは、レーザー光の照射により情報信号を記録可能に構成された記録層を少なくとも備える。情報信号層L0~Lnは、例えば、波長405nm、集光レンズの開口数NA0.85に対して25GB以上の記録容量を有する。情報信号層L0~Lnは、保存信頼性向上の観点からすると、記録層の少なくとも一方の表面に保護層をさらに備えることが好ましく、記録層の両方の表面に保護層を備えることがより好ましい。情報信号層L0~Lnの層構成は、全ての層で同一の構成としてもよく、情報信号層L0~Lnごとに求められる特性(例えば光学特性や耐久性等)に応じて層構成を変えるようにしてもよいが、生産性の観点からすると、全ての層で同一の層構成とすることが好ましい。情報信号層L0~Lnが、記録層単層により構成されていてもよい。このような単純な構成とすることで、光記録媒体10を低廉化し、かつ、その生産性を向上することができる。このような効果は、情報信号層L0~Lnの層数が多い媒体ほど、顕著となる。
図2Aは、各情報信号層Lの第1の構成例を示す模式図である。図2Aに示すように、情報信号層L0~Lnは、上側面(第2の主面)および下側面(第1の主面)を有する記録層21と、記録層21の上側面に隣接して設けられた保護層22とを備える。このような構成とすることで、記録層21の耐久性を向上することができる。
図2Bは、各情報信号層Lの第2の構成例を示す模式図である。図2Bに示すように、情報信号層L0~Lnは、上側面(第2の主面)および下側面(第1の主面)を有する記録層21と、記録層21の下側面に隣接して設けられた保護層23とを備える。このような構成とすることで、記録層21の耐久性を向上することができる。
図3Aは、各情報信号層Lの第3の構成例を示す模式図である。図3Aに示すように、情報信号層L0~Lnは、上側面(第2の主面)および下側面(第1の主面)を有する記録層21と、記録層21の下側面に隣接して設けられた保護層23と、記録層21の上側面に隣接して設けられた保護層22とを備える。このような構成とすることで、上記の第1および第2の構成例に比して記録層21の耐久性を向上することができる。
図3Bは、各情報信号層Lの第4の構成例を示す模式図である。図3Bに示すように、情報信号層L0~Lnは、例えば、記録層21aと記録層21bとが積層された2層構造を有する。記録層21aと記録層21bは、例えば、互いに材料組成が異なっている。
記録層21は、記録材料としてBiの酸化物を含む。記録層21は、Bi以外の金属Mの酸化物をさらに含んでもよい。記録層21が金属Mの酸化物を含む場合、Biと金属Mは複合酸化物を構成していてもよい。金属Mは、例えば、Mg、Al、Si、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、Se、Y、Zr、Nb、Mo、Ru、Pd、Ag、In、Sn、Sb、Te、Hf、Ta、WおよびPb等からなる群より選ばれた少なくとも1種を含む。金属Mは、再生信号品質の向上の観点から、Cu、Zr、Nb、Sn、Ta、W、Ge、In、SbおよびMoからなる群より選ばれた少なくとも1種を含むことが好ましく、Al、GaおよびZnからなる群より選ばれた少なくとも1種を含むことがより好ましい。
金属Mの酸化物の体積比率(vol%)=T(MOx)/[T(MOx)+T(BiOx)]
Mol(BiOx)=T(BiOx)×ρ(BiOx)/MW(BiOx)
Mol(MOx)=T(MOx)×ρ(MOx)/MW(mOx)
金属Mの酸化物のモル比率は、以下の式により求められる。
金属Mの酸化物のモル比率(mol%)=Mol(MOx)/[Mol(MOx)+Mol(BiOx)]×100
例えば、Biの酸化物のモル比は、以下の式により求められる。
Bi2O3モル比(mol%)=Mol(BiOx)/[Mol(MOx)+Mol(BiOx)]×100
保護層22および保護層23は、記録層21を保護する保護層である。保護層22および保護層23は、ガスバリア層としての機能を有していてもよい。保護層22および保護層23がガスバリア層として機能することで、記録層21の耐久性を向上することができる。また、記録層21の酸素の逃避やH2Oの侵入を抑制することで、記録層21の膜質の変化(主に反射率の低下として検出)を抑制することができ、記録層21として好ましい膜質を確保することができる。
中間層S1~Snは、情報信号層L0~Lnを物理的および光学的に十分な距離をもって離間させる役割を果たし、その表面には凹凸面が設けられている。その凹凸面は、例えば、同心円状または螺旋状のグルーブ(ランドGinおよびグルーブGon)を形成している。中間層S1~Snの厚みは、9μm以上50μm以下に設定することが好ましい。中間層S1~Snの材料は特に限定されるものではないが、紫外線硬化型のアクリル系樹脂を用いることが好ましい。また、中間層S1~Snは、奥側の層への情報信号の記録または再生のためのレーザー光の光路となることから、十分に高い光透過性を有していることが好ましい。
光透過層12は、例えば、紫外線硬化樹脂等の感光性樹脂を硬化してなる樹脂層である。この樹脂層の材料としては、例えば、紫外線硬化型のアクリル系樹脂が挙げられる。また、円環形状を有する光透過性シートと、この光透過性シートを基板11に対して貼り合わせるための接着層とから光透過層12を構成するようにしてもよい。光透過性シートは、記録および再生に用いられるレーザー光に対して、吸収能が低い材料からなることが好ましく、具体的には透過率90パーセント以上の材料からなることが好ましい。光透過性シートの材料としては、例えば、ポリカーボネート樹脂材料、ポリオレフィン系樹脂(例えばゼオネックス(登録商標))等を用いることができる。接着層の材料としては、例えば、紫外線硬化樹脂、感圧性粘着剤(PSA:Pressure Sensitive Adhesive)等を用いることができる。
光記録媒体10は、光透過層12の表面Cにハードコート層を備えていてもよい。光透過層12の表面Cにハードコート層を備えることで、機械的な衝撃や傷から光記録媒体10を保護することができる。また、光透過層12の表面Cに対する塵埃や指紋の付着等を抑制し、情報信号の記録再生品質を確保することができる。ハードコート層は、機械的強度を向上させるために、シリカの微粉末を含んでいてもよい。ハードコート層を形成するための樹脂組成物としては、例えば、溶剤タイプまたは無溶剤タイプ等の紫外線硬化樹脂を用いることができる。機械的強度、撥水性および撥油性等をハードコート層に持たせるためには、ハードコート層の厚さは、1μmから数μm程度であることが好ましい。
上記の構成を有する光記録媒体10では、例えば中心波長405nm近傍のレーザー光が情報信号層Lに照射されると、Biの酸化物を含む記録層21が、レーザー光を吸収およびレーザー光と反応し、体積膨張する。体積膨張した記録層21の内部は、バブル状になる。
光記録媒体10の記録層成膜用のスパッタリングターゲット(以下単に「ターゲット」という。)は、BiまたはBiの酸化物を含む。ターゲットは、Bi以外の金属MまたはBi以外の金属Mの酸化物をさらに含んでもよい。ターゲットが金属Mの酸化物を含む場合、Biと金属Mは複合酸化物を構成していてもよい。金属Mは、記録層21の材料として説明した通りである。
以下、本開示の一実施形態に係る光記録媒体の製造方法の一例について説明する。
まず、一主面に凹凸面が形成された基板11を成形する。基板11の成形方法としては、例えば、射出成形(インジェクション)法、フォトポリマー法(2P法:Photo Polymerization)等を用いることができる。
次に、例えばスパッタリング法により、基板11上に情報信号層L0を形成する。情報信号層L0の具体的な形成工程は、情報信号層L0の構成により異なる。以下では、情報信号層L0の構成として上記の第3の構成例(図3A参照)を採用した場合にける情報信号層L0の形成工程について具体的に説明する。
まず、基板11を、保護層成膜用のターゲットが備えられた真空チャンバー内に搬送し、真空チャンバー内を所定の圧力になるまで真空引きする。その後、真空チャンバー内に希ガスやO2ガス等のプロセスガスを導入しながら、ターゲットをスパッタリングして、基板11上に保護層23を成膜する。スパッタリング法としては、例えば高周波(RF)スパッタリング法、直流(DC)スパッタリング法を用いることができるが、特に直流スパッタリング法が好ましい。直流スパッタリング法は高周波スパッタリング法に比して装置が安価で、かつ、成膜レートが高いため、製造コストを下げ生産性を向上することができるからである。保護層23の成膜工程における希ガスとしては、Ar、KrおよびXeからなる群より選ばれた少なくとも1種を用いることができる。
次に、基板11を、記録層成膜用のターゲットが備えられた真空チャンバー内に搬送し、真空チャンバー内を所定の圧力になるまで真空引きする。その後、真空チャンバー内に希ガスやO2ガス等のプロセスガスを導入しながら、ターゲットをスパッタリングして、保護層23上に記録層21を成膜する。ターゲットとしては、上記の記録層成膜用のターゲットが用いられる。ターゲットが金属Mまたは金属Mの酸化物を含む場合、酸素アシストを行いながら記録層21をスパッタリングで成膜することで、Biと金属Mの酸化物が化合物レベルで混在した薄膜が形成される。
次に、基板11を、保護層成膜用のターゲットが備えられた真空チャンバー内に搬送し、真空チャンバー内を所定の圧力になるまで真空引きする。その後、真空チャンバー内に希ガスやO2ガス等のプロセスガスを導入しながら、ターゲットをスパッタリングして、記録層21上に保護層22を成膜する。スパッタリング法としては、例えば高周波(RF)スパッタリング法、直流(DC)スパッタリング法を用いることができるが、特に直流スパッタリング法が好ましい。
以上により、基板11上に情報信号層L0が形成される。
次に、例えばスピンコート法により紫外線硬化樹脂を情報信号層L0上に均一に塗布する。その後、情報信号層L0上に均一に塗布された紫外線硬化樹脂に対してスタンパの凹凸パターンを押し当て、紫外線を紫外線硬化樹脂に対して照射して硬化させた後、スタンパを剥離する。これにより、スタンパの凹凸パターンが紫外線硬化樹脂に転写され、例えばランドGinおよびグルーブGonが設けられた中間層S1が情報信号層L0上に形成される。
次に、上記の情報信号層L0の成膜工程および中間層S1の形成工程と同様にして、中間層S1上に、情報信号層L1、中間層S2、情報信号層L2、・・・、中間層Sn、情報信号層Lnをこの順序で中間層S1上に積層する。
次に、例えばスピンコート法により、紫外線硬化樹脂等の感光性樹脂を情報信号層Ln上にスピンコートした後、紫外線等の光を感光性樹脂に照射し硬化する。これにより、情報信号層Ln上に光透過層12が形成される。以上の工程により、目的とする光記録媒体10が得られる。
上記のように、本開示の一実施形態に係る光記録媒体10では、記録層21はBiの酸化物を含むので、記録層21の成膜時間を短縮することができる。これにより、生産タクトタイムを短縮することができる。すなわち、数量生産に要する時間を短縮することができる。したがって、ビット単価を低減することができる。
以上、本開示の実施形態について具体的に説明したが、本開示は、上記の実施形態に限定されるものではなく、本開示の技術的思想に基づく各種の変形が可能である。
(1)
少なくとも1層の記録層を備え、
前記記録層は、Biの酸化物を含む光記録媒体。
(2)
前記記録層は、Mg、Al、Si、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、Se、Y、Zr、Nb、Mo、Ru、Pd、Ag、In、Sn、Sb、Te、Hf、Ta、WおよびPbの酸化物からなる群より選ばれた少なくとも1種をさらに含む(1)に記載の光記録媒体。
(3)
前記記録層は、Cu、Zr、Nb、Sn、Ta、W、Ge、In、SbおよびMoの酸化物からなる群より選ばれた少なくとも1種をさらに含む(1)に記載の光記録媒体。
(4)
前記記録層は、Al、GaおよびZnの酸化物からなる群より選ばれた少なくとも1種をさらに含む(1)に記載の光記録媒体。
(5)
前記記録層は、Mnを含まない(1)から(4)のいずれかに記載の光記録媒体。
(6)
前記記録層は、Pdを含まない(1)から(4)のいずれかに記載の光記録媒体。
(7)
前記記録層は、MnおよびPdを含まない(1)から(4)のいずれかに記載の光記録媒体。
(8)
前記記録層は、Alの酸化物をさらに含み、
前記記録層中における前記Alの酸化物の含有量が、15vol%以上50vol%以下である(1)に記載の光記録媒体。
(9)
前記記録層は、Gaの酸化物をさらに含み、
前記記録層中における前記Gaの酸化物の含有量が、17vol%以上67vol%以下である(1)に記載の光記録媒体。
(10)
前記記録層は、Znの酸化物をさらに含み、
前記記録層中における前記Znの酸化物の含有量が、17vol%以上55vol%以下である(1)に記載の光記録媒体。
(11)
前記記録層中における前記Biの酸化物の含有量が、薄膜の膜厚換算で10nm以上である(1)から(10)のいずれかに記載の光記録媒体。
(12)
プロセスガスを導入しながらターゲットをスパッタリングすることにより、記録層を形成することを含み、
前記ターゲットは、Biの酸化物を含み、
前記プロセスガスは、希ガスおよび酸素を含み、
前記希ガスに対する前記酸素の流量比(酸素流量/希ガス流量)が、0.15以上である光記録媒体の製造方法。
(13)
光記録媒体用の記録材料であって、
Biの酸化物を含む記録材料。
(14)
光記録媒体用のスパッタリングターゲットであって、
Biの酸化物を含むスパッタリングターゲット。
以下、実施例により本開示を具体的に説明するが、本開示はこれらの実施例に限定されるものではない。
(信号特性の評価装置)
本実施例では、光ディスクの評価は、BD用の評価装置を用いて行った。また、本実施例では、記録材料の特性検証が鍵となるので、光ディスクとしては情報記録層を1層のみ備える光ディスク(いわゆる単層ディスク)を採用した。
本実施例では、ディスク生産ビットコストの低減に加えて再生信号品質の高い記録材料を提供することを目的とする。再生信号品質を示す指標には一般的なSNR(Signal to Noise Ratio)、SNRをより簡便に評価するためのCNR(Carrier to Noise Ratio)や、光ディスクの場合に用いられる再生トラックの信号レベルに対し隣接トラックの記録信号が漏れ込む信号レベルを評価指標とするクロストーク等の種々の評価指標がある。ここではCNRとクロストークの評価方法について説明する。
Mn系酸化物の代わりになる記録材料を探すために、Mn、V、Cr、Bi、Te、Cu、Ag、W、Zn、Sn、Zr、Ge、Mg、Mo、Ti、Sb、Nb、Taの酸化物の光学定数を調査した。
スパッタリング法によりシリコンウェハー上に30nm厚の記録層を形成することにより、シリコンウェハサンプルを作製した。この際、30nm厚の記録層を成膜するのに要する成膜時間を測定した。その結果を表1に示す。
上記のようにして形成された記録層の光学定数(屈折率n、消衰係数k)をエリプソメーターにより測定した。その結果を表1に示す。
表1に、光学定数の評価結果および成膜時間の測定結果を示す。但し、光学定数は、波長405nmにおける値である。
まず、射出成形により、厚さ1.1mmのポリカーボネート基板を成形した。なお、このポリカーボネート基板上には、スパイラル上に凹凸で記録トラックが形成された。凸部のスパイラル状トラックをグルーブ、凹部のスパイラル状トラックをランドと定義する。次に、次に、スパッタリング法により、ポリカーボネート基板の凹凸面上に第1の保護層、記録層、第2の保護層を順次積層した。
第2の保護層(光透過層側)
材料:SIZ複合酸化物(Si:In:Zr=20:50:30(mol%比率))
厚さ:10nm
記録層
材料:記録材料として、表2に示される金属酸化物(MnOx、VOx、CrOx、BiOx、CuOx、AgOx)が用いられた。スパッタリング法による成膜工程において、Mn系酸化物で4価のMnが生成されるように、プロセスガス条件(Ar+O2)は調整された。また、金属元素の酸化には過剰な量のO2が投入され、反応性スパッタリングによる酸化物成膜が行われた。
厚さ:30nm
第1の保護層(基板側)
材料:SIZ複合酸化物(Si:In:Zr=20:50:30(mol%比率))
厚さ:10nm
以上により、目的とする光ディスクを得た。
上記のようにして得られた光ディスクの反射率、透過率、吸収率および記録再生信号品質を評価した。また、上記の光ディスクに用いた記録材料のスパッタレートを算出した。これらの評価方法および算出方法の詳細は以下のとおりである。
光ディスク検査装置を用いて光ディスクの再生信号を取得し、この再生信号レベルを反射率Rに換算した。
透過率リファレンスサンプルの基準値との比較から透過率Tを算出した。測定装置として、エリプソメーターが用いられた。
上記の反射率Rと透過率Tを用いて、吸収率(1-R-T)を求めた。
MOx、VOx、CrOx、BiOx、CuOx、AgOxについて、表1の成膜時間データと消衰係数kを用いて、成膜パワー1kW時の成膜の速さ:スパッタレート(以下「スパッタレート(1)」という。)を求め、更に同一の光吸収を有する層を同一成膜パワーで成膜すると仮定したスパッタレート(以下「スパッタレート(2)」という。)を、Mn酸化物に対する相対値として数値化した。その結果を表2に示す。光ディスクの光学特性を設計する際、特に多層光ディスクの場合は各記録層の光透過率と記録パワー制御が重要になり、光吸収率の観点で制御することが多いため、同一光吸収量の観点でのデータを表2に示す。
表2中のスパッタレート(1)は、表1のデータを用いて次の式により算出された。
スパッタレート(nm/kW/sec)=(膜厚30nm)/成膜時間(sec)/成膜パワー(W)×1000
表2中のスパッタレート(2)は、表2のデータを用いて次の式により算出された。
スパッタレート(Mnで規格化)=(1-R-T)×(nm/kW/sec)/[MnOxの(1-R-T)×(nm/kW/sec)]
上記の[2-1.信号特性の評価装置および評価方法]に記載の方法により、光ディスクのCNRとCTを測定した。
表2に、反射率R、透過率T、吸収率(1-R-T)、記録再生信号品質およびスパッタレートの評価結果を示す。
Agの酸化物>Biの酸化物>Cuの酸化物>Crの酸化物>Mnの酸化物>Vの酸化物
Ag、Bi、Cuの酸化物のスパッタレートはそれぞれ、Mn酸化物のスパッタレートの19.1倍、8.0倍、4.6倍であった。
Biの酸化物、Cuの酸化物それぞれに金属M(添加元素)の酸化物を添加し、記録再生信号品質に対する金属Mの酸化物の影響を評価した。
表3に示すように、Biの酸化物(BiOx)と金属Mの酸化物(MOx(但し、Mは、Al、Ga、Ge、In、Mo、Nb、Sb、Sn、W、ZnまたはZrである。))の複合酸化物により記録層を形成した。この際、成膜条件を調整することにより、記録層中におけるBiの酸化物(BiOx)と金属Mの酸化物(MOx)の体積比率を表3に示す値に設定した。上記以外のことは実施例1-1と同様にして光ディスクを得た。
表4に示すように、Cuの酸化物(CuOx)と金属Mの酸化物(MOx(但し、Mは、Zr、Nb、Mo、W、Zn、Al、Ga、In、Ge、SnまたはSbである。))の複合酸化物により記録層を形成した。この際、成膜条件を調整することにより、記録層中におけるCuの酸化物(CuOx)と金属Mの酸化物(MOx)の体積比率を表4に示す値に設定した。上記以外のことは実施例1-1と同様にして光ディスクを得た。
上記の[2-1.信号特性の評価装置および評価方法]に記載の方法により、光ディスクのCNRとCTを測定した。
図7A~図10Bに、記録材料としてBiOxとMOxの複合酸化物が用いられた光ディスクの評価結果を示す。図11に、記録材料としてCuOxとMOxの複合酸化物が用いられた光ディスクの評価結果を示す。図7A~図10B、図11中には、比較のために、Mn系酸化物のデータを「×」印で記載した。図7A~図10B、図11中に記載された直線は、Mn系酸化物のデータを基準にCNR/CT傾斜が7.5dB/10dBの傾きとなるように引いた直線であり、この直線より上側に評価結果(プロット)が位置するBi系酸化物は、Mn系酸化物に比べて良好なCT-CNR性能を有することになる。図7A~図10B、表4に記載された「%」は「vol%」を意味する。
図11から、Cu系酸化物では、添加金属Mの酸化物(MOx)を用いた場合には、Mn系酸化物と同等またはそれ以下の記録再生信号品質が得られることがわかる。
Biの酸化物を用いた記録材料は、価数が高いBiの酸化物を含み、記録エネルギーよって発生する酸素によって記録層の体積膨張が起こり記録部と未記録部に反射率差を得ることを特徴とするものである。以下では、酸素過多な状態でのスパッタリングが好ましいことを示す。
スパッタリング法によりシリコンウェハー上に30nm厚の記録層を形成することにより、シリコンウェハサンプルを作製した。記録層成膜用材料(ターゲット材料)としては化学量論組成のBi2O3(Bi系酸化物)が用いられ、プロセスガスとしては、ArガスとO2ガスが用いられた。ArガスとO2ガスの流量比は、サンプル毎に表5に示すように調整された。また、時成膜の投入パワーは固定された。
実施例14-1~14-5と同様の成膜条件により記録層を形成すること以外は実施例2-1と同様にして光ディスクを得た。
上記のようにして得られたシリコンウェハサンプルの記録層の光学定数(屈折率n、消衰係数k)をエリプソメーターにより測定した。
上記のようにして得られた光ディスクのCNRとCTを上記の<2-1.信号特性の評価装置および評価方法>に記載の方法により測定した。
上記のようにして得られた光ディスクについて、未記録状態および記録状態の断面TEM像を取得した。
表5に、記録層の光学定数の評価結果を示す。但し、光学定数は、波長405nmにおける値である。
光ディスクの信号特性の評価結果を図12に示す。図12中には、比較のために、図7A~図10B等と同様にMn系酸化物のデータを「×」印で記載した。また、図7A~図10B等と同様の直線を記載した。図12から、酸素量を多くすることによりCT値が大幅に低減し、CT-CNR性能が改善することがわかる。スパッタリングにおけるArガスとO2ガスの流量比(O2ガス流量/Arガス流量)は、記録再生信号特性を確保するためには、ガス流量比(O2流量/Ar流量)は0.15以上であることが好ましい。
未記録状態の断面TEM像の模式図を図13Aに示す。記録状態の断面TEM像の模式図を図13Bに示す。なお、これらの断面TEM図は、ArガスとO2ガスの流量比が(Ar:O2)=(60:20)である実施例14-2の光ディスクのものである。上記断面TEM像の観察結果から、光ディスクの記録マークは、図13Bに示すように、記録マーク部が膨張し紡錘形になることがわかった。
記録再生信号特性を確保し、かつ、多層光ディスクに用いるための反射率、透過率を得る為のBiOx量を見積もった。ここでは膜厚表記を用いた。記録材用の膨張を利用した記録モードのため、反応剤BiOxから放出される酸素量に再生信号量が依存する。組成比表記の場合、記録材料中の別の添加元素の種類によって、同じ組成比でも元素数が大きく異なり酸素放出量が変わるため、酸素放出量に結びつく膜厚換算値を用いた。
11 基板
12 光透過層
21 記録層
22、23 保護層
L0~Ln 情報信号層
S1~Sn 中間層
Gon グルーブ(案内溝の凸部のトラック)
Gin ランド(案内溝の凹部のトラック)
C 光照射面
Claims (14)
- 少なくとも1層の記録層を備え、
前記記録層は、Biの酸化物を含む光記録媒体。 - 前記記録層は、Mg、Al、Si、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、Se、Y、Zr、Nb、Mo、Ru、Pd、Ag、In、Sn、Sb、Te、Hf、Ta、WおよびPbの酸化物からなる群より選ばれた少なくとも1種をさらに含む請求項1に記載の光記録媒体。
- 前記記録層は、Cu、Zr、Nb、Sn、Ta、W、Ge、In、SbおよびMoの酸化物からなる群より選ばれた少なくとも1種をさらに含む請求項1に記載の光記録媒体。
- 前記記録層は、Al、GaおよびZnの酸化物からなる群より選ばれた少なくとも1種をさらに含む請求項1に記載の光記録媒体。
- 前記記録層は、Mnを含まない請求項1に記載の光記録媒体。
- 前記記録層は、Pdを含まない請求項1に記載の光記録媒体。
- 前記記録層は、MnおよびPdを含まない請求項1に記載の光記録媒体。
- 前記記録層は、Alの酸化物をさらに含み、
前記記録層中における前記Alの酸化物の含有量が、15vol%以上50vol%以下である請求項1に記載の光記録媒体。 - 前記記録層は、Gaの酸化物をさらに含み、
前記記録層中における前記Gaの酸化物の含有量が、17vol%以上67vol%以下である請求項1に記載の光記録媒体。 - 前記記録層は、Znの酸化物をさらに含み、
前記記録層中における前記Znの酸化物の含有量が、17vol%以上55vol%以下である請求項1に記載の光記録媒体。 - 前記記録層中における前記Biの酸化物の含有量が、薄膜の膜厚換算で10nm以上である請求項1に記載の光記録媒体。
- プロセスガスを導入しながらターゲットをスパッタリングすることにより、記録層を形成することを含み、
前記ターゲットは、Biの酸化物を含み、
前記プロセスガスは、希ガスおよび酸素を含み、
前記希ガスに対する前記酸素の流量比(酸素流量/希ガス流量)が、0.15以上である光記録媒体の製造方法。 - 光記録媒体用の記録材料であって、
Biの酸化物を含む記録材料。 - 光記録媒体用のスパッタリングターゲットであって、
Biの酸化物を含むスパッタリングターゲット。
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