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WO2008126573A1 - Support d'enregistrement optique, cible de pulvérisation et son procédé de fabrication - Google Patents

Support d'enregistrement optique, cible de pulvérisation et son procédé de fabrication Download PDF

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Publication number
WO2008126573A1
WO2008126573A1 PCT/JP2008/054420 JP2008054420W WO2008126573A1 WO 2008126573 A1 WO2008126573 A1 WO 2008126573A1 JP 2008054420 W JP2008054420 W JP 2008054420W WO 2008126573 A1 WO2008126573 A1 WO 2008126573A1
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WIPO (PCT)
Prior art keywords
recording
layer
oxide
recording medium
optical recording
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Ceased
Application number
PCT/JP2008/054420
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English (en)
Inventor
Noboru Sasa
Yoshitaka Hayashi
Toshishige Fujii
Toshihide Sasaki
Hiroyoshi Sekiguchi
Masayuki Fujiwara
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Ricoh Co Ltd
Original Assignee
Ricoh Co Ltd
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Priority claimed from JP2007229432A external-priority patent/JP5169081B2/ja
Application filed by Ricoh Co Ltd filed Critical Ricoh Co Ltd
Priority to US12/521,197 priority Critical patent/US8124211B2/en
Publication of WO2008126573A1 publication Critical patent/WO2008126573A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B7/2437—Non-metallic elements
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • 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
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/34—Sputtering
    • C23C14/3407—Cathode assembly for sputtering apparatus, e.g. Target
    • C23C14/3414—Metallurgical or chemical aspects of target preparation, e.g. casting, powder metallurgy
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B7/2433—Metals or elements of Groups 13, 14, 15 or 16 of the Periodic Table, e.g. B, Si, Ge, As, Sb, Bi, Se or Te
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/26—Apparatus or processes specially adapted for the manufacture of record carriers
    • G11B7/266—Sputtering or spin-coating layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24302—Metals or metalloids
    • G11B2007/24314—Metals or metalloids group 15 elements (e.g. Sb, Bi)
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24318—Non-metallic elements
    • G11B2007/2432—Oxygen
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24318—Non-metallic elements
    • G11B2007/24322—Nitrogen
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24318—Non-metallic elements
    • G11B2007/24328—Carbon

Definitions

  • the present invention relates to a WORM (Write Once Read Many) optical recording medium that is capable of high density recording using laser light in the blue wavelength region, and has excellent recording and reproducing properties, particularly an excellent recording sensitivity, and to a sputtering target for forming the recording layer of the optical recording medium, and a method for manufacturing the sputtering target.
  • WORM Write Once Read Many
  • a recording layer including an organic material is irradiated with laser light to cause a change in refractive index mainly due to decomposition or transformation of the organic material to form recording pits, and the optical constant and decomposition behavior of the organic material used in the recording layer are important factors for forming good recording pits.
  • a material that has optical properties and decomposition behavior suitable for a blue laser needs to be selected as the organic material used in the recording layer of a blue laser compatible WORM optical recording medium.
  • Conventional WORM optical recording media having high to low polarity are so configured that high reflectance is ensured during non-recorded state and that the organic material is decomposed by laser irradiation to cause a large change in refractive index, thereby a large degree of modulation is obtained, so that the recording and reproducing wavelength is selected to be located at the end of a large absorption band on the long wavelength side.
  • the end of the large absorption band of the organic material on the long wavelength side is a wavelength region that has a moderate absorption coefficient and provides a large refractive index.
  • organic dye materials have a poorer stability than inorganic materials, so that they have problems in the storage property and light resistance. Then, the use of an inorganic material in the recording layer is studied for WORM optical recording media compatible with a blue laser.
  • Patent Literature 1 As a recording layer for a WORM optical recording medium compatible with a blue laser, for example, one using a phase change material similar to that of a rewritable optical recording medium is proposed in Patent Literature 1, but a WORM optical recording medium requires long period storage, and the phase change material has an insufficient storage property.
  • Patent Literature 2 A method, in which a plurality of layers of inorganic material are laminated and their reaction is used for recording, is also proposed in Patent Literature 2, but one using reaction of a plurality of layers is not suitable for long period storage, because the reaction proceeds with time.
  • Patent Literatures 7 and 8 as technologies that are similar to the above previous applications of the present inventors- a recording layer in which Te, O, and further another element are added is disclosed in Patent Literature 7; and one using an incomplete oxide of transition metal is disclosed in Patent Literature 8.
  • Patent Literature 8 although it is assumed that one including an element other than transition metal is also included, however, no specific element other than Al is described, the definition of transition metal is unclear because Zn, Y, and the like may or may not be included, and no detail description other than W and Mo is provided. Further, there is no specific description of a problem to be solved by the invention, that is, higher sensitivity, in these Patent Literatures 7 and 8.
  • a WORM optical recording medium using oxide for a recording layer is suitable for higher density, because the heat conductivity of the recording layer is low, so that heat interference between recording marks can be suppressed.
  • oxide When oxide is used for the recording layer, decreasing the degree of oxidation of oxide (increasing the amount of oxygen deficiency) is proposed as a method for further improving the recording property.
  • Technologies using a material, in which the amount of oxygen is smaller than that of the stoichiometric composition, in the red and infrared wavelength regions include, for example, one using TeOx (0 ⁇ x ⁇ 2) (see Patent Literature 9), one including at least one selected from TeOx, GeOx, SnOx, BiOx, SbOx, and TlOx, and at least one of S and Se (see Patent Literature 10), one containing Te and Sb in low oxide GeOx or containing Te and Ge in SbOx (see Patent Literature 11), one using Ni-low oxide expressed by NiOx (see Patent Literature 12), an information recording mode in which In-low oxide is irradiated with laser light to form an image (see Patent Literature 13), and the like.
  • Patent Literature 14 an invention that relates to low oxide in the red wavelength region and in which an element selected from Sn, In, Bi, Zn, Al, Cu, Ge, and Sb is added to TeOx is disclosed in Patent Literature 14.
  • BiOx an element selected from Sn, In, Bi, Zn, Al, Cu, Ge, and Sb is added to TeOx.
  • this Patent Literature 14 is an invention using a so-called blackening phenomenon in which the transmittance of light is changed by light irradiation, and an invention of a film having reversibility in which the transmittance of one recorded by blackening is returned to the original transmittance again by light irradiation.
  • the present inventors propose a WORM optical recording medium including a recording layer including at least Bi oxide and an oxide of M (M is at least one element selected from Mg, Al, Zn, Li, Si, Hf, Sn, Y, and B) as main components on a substrate, wherein the oxygen content in the oxide is smaller than that of the stoichiometric composition (see Patent Literature 15).
  • M is at least one element selected from Mg, Al, Zn, Li, Si, Hf, Sn, Y, and B
  • Patent Literature 16 discloses in Patent Literature 16 and the like that a WORM optical recording medium having a recording layer including Bi, B, and O (oxygen) exhibits good properties, and it can be confirmed to exhibit very excellent recording and reproducing properties.
  • WORM optical recording medium having a recording layer including Bi oxide as a main component is also disclosed in Patent Literature 17, however, a system to which carbon and nitrogen are added is not discussed.
  • Patent Literatures 18 to 19 Although an information recording medium using a recording layer including metal nitride and metal carbide is disclosed in Patent Literatures 18 to 19, it includes metal nitride as a main component, and decomposition of metal nitride is the recording principle, so that it is not reference for the present invention including Bi and O (oxygen) as main components.
  • Patent Literature 17 aims at an improvement in recording and reproducing properties and reliability (reproduction stability, storage stability, and the like), and does not discuss high speed recording. Further, it discusses materials in which various elements X are added to bismuth oxide, but C and N are not included in X, and no specific example in which two or more elements are added to bismuth oxide is illustrated.
  • the present inventors propose a target including Bi and Fe as a sputtering target for forming a recording layer including Bi oxide as a main component in a WORM optical recording medium that is capable of high density recording with laser light in the blue wavelength region (350 nm to 500 nm) (see Patent Literature 20).
  • the sputtering method is widely known as one of gas-phase formation methods for a thin film and is also used in industrial thin film manufacture.
  • a film is formed by preparing a target material including the same component as the component of the intended film, and usually, colliding Ar (argon) gas ions generated by glow discharge against this target material to knock out the constituent atoms of the target material to deposit the atoms on a substrate.
  • oxide generally has a high melting point, so that a method, such as a vapor deposition method, is not preferable, and high frequency sputtering in which high frequency is applied is often used.
  • the sputtering method is actually often used in the manufacture process and is also advantageous in throughput.
  • the composition of the target and the composition of the film are often not the same, so that the composition of the target needs to be studied.
  • the structure and nature of the film often differ depending on the form of a compound constituting the target, so that this point also needs to be studied. From the viewpoint of the production cost, a further improvement in the speed of film deposition is also necessary. For an improvement in the speed of film deposition, larger electric power needs to be input, and also in that case, an improvement in the strength of the target is necessary such that the target is not broken.
  • Patent Literature 21 but it differs from the present invention including
  • an optical recording medium In an optical recording medium, a highly sensitive recording property in which recording is possible at a low recording power is required in terms of the limit of the power of laser light, durability, power saving performance, and the like. Also, high linear velocity recording for an improvement in the speed of information transfer, with high density recording, are required, but in that case, high linear velocity recording requires a further improvement in recording sensitivity, compared with low linear velocity recording. Also, for compatibility, the optical recording medium needs to be compatible with the entire range of recording linear velocity from low linear velocity to high linear velocity.
  • Patent Literature l Japanese Patent Application Laid Open (JP-A) No. 09-286174
  • Patent Literature 2 Japanese Patent Application LaidOpen
  • Patent Literature 3 Japanese Patent Application LaidOpen (JP-A) No. 2005-161831
  • Patent Literature 4 Japanese Patent Application Laid-Open (JP-A) No. 2005-108396
  • Patent Literature 5 Japanese Patent Application Laid Open (JP-A) No. 2003-48375
  • Patent Literature 6 Japanese Patent Application LaidOpen (JP-A) No. 2006-116948
  • Patent Literature 7 Japanese Patent Application Laid Open (JP-A) No. 2002 133712
  • Patent Literature 8 Japanese Patent Application Laid-Open (JP A) No. 2003-237242
  • Patent Literature 9 Japanese Patent Application Laid-Open
  • Patent Literature l ⁇ Japanese Patent (JP-B) No. 1444471
  • Patent Literature 11 Japanese Patent (JP B) No. 1849839
  • Patent Literature 12 Japanese Patent (JP-B) No. 2656296
  • Patent Literature 13 Japanese Patent Application Laid-Open
  • Patent Literature 14 Japanese Patent Application Publication (JP B) No. 7-25209
  • Patent Literature 15 Japanese Patent Application Laid-Open (JP-A) No. 2006-248177
  • Patent Literature 16 Japanese Patent Application Laid-Open (JP-A) No. 2006-247897
  • Patent Literature 17 Japanese Patent (JP-B) No. 3802040
  • Patent Literature 18 Japanese Patent Application Laid-Open (JP-A) No. 2006-182030
  • Patent Literature 19 Japanese Patent (JP-B) No. 3810076
  • Patent Literature 20 Japanese Patent Application Laid Open
  • Patent Literature 21 Japanese Patent (JP B) No. 1480945
  • An optical recording medium including: a substrate; and a recording layer over the substrate, the recording layer capable of recording and reproduction of information using laser light in a blue wavelength region, wherein the recording layer comprises Bi and O as main components, comprises at least any of C and N, and does not comprise Fe.
  • the recording layer further comprises at least one element X selected from B, Li, Sn, Ge, Sr, Mg, Ba, Ca, Mo, W, Co, Si, In, Ti, Mn, Ga, Zr, Cr,
  • An optical recording medium including- a substrate; and a recording layer over the substrate, the recording layer comprising as main components Bi oxide and a simple substance of each of one or more elements M (except Bi, C, and N) that enhance a light absorption function for a recording and reproducing laser light, wherein the optical recording medium can record and reproduce information using laser light in a blue wavelength region.
  • the recording layer further comprises an oxide of the element M.
  • the sputtering target according to ⁇ 8> further including at least one element X selected from B, Li, Sn, Ge, Sr, Mg, Ba, Ca, Mo, W, Co, Si, In, Ti, Mn, Ga, Zr, Cr, Hf, K, Na, Zn, Ni, Cu, Pd, Ag, P, Ta, Y, Nb, Al, V, Sb, Te, and La series elements.
  • element X is B.
  • a sputtering target including: Bi oxide > ' and a simple substance of each of one or more elements M (except Bi, C, and N) that enhance a light absorption function for a recording and reproducing laser light of an optical recording medium, wherein the Bi oxide and the simple substance are main components.
  • ⁇ 12> The sputtering target according to ⁇ 11>, further including an oxide of the element M.
  • FIG. 1 is a graph showing the result of evaluation in Example A- 16.
  • FIG. 2 shows one example of a layer configuration of HD DVD-R, including, in order, a substrate 1, a lower protective layer 5, a recording layer 4, an upper protective layer 3, and a reflective layer 2.
  • FIG. 3 shows one example of a layer configuration of BD R, including in order, a substrate 1, a reflective layer 2, an upper protective layer 3, a recording layer 4, a lower protective layer 5, and a cover layer 6.
  • the optical recording medium of the present invention in a first embodiment, has at least a recording layer over a substrate, and the recording layer includes Bi (bismuth) and O (oxygen) as main components, further includes C (carbon) and/or N (nitrogen), and does not include Fe.
  • the main components herein mean that the content (atomic%) of Bi and oxygen combined is highest in the recording layer.
  • the expression "include Bi and oxygen” is used, because while the content of
  • Bi oxide is highest, metal Bi other than Bi oxide may be included in the recording layer.
  • Example A- 16 which will be described later, when the light absorptivity, which is one of the optical properties of the recording layer, was examined, it was clear that variations were large when Fe was included, and that variations were small when Fe was not included.
  • the embodiment of the recording layer is of three types: (l) an embodiment including Bi, O, and C; (2) an embodiment including Bi, O, and N; and (3) an embodiment including Bi, O, C, and N.
  • the proportion of oxygen in the recording layer is about 30 atomic% to 65 atomic%, preferably 45 atomic% to 62 atomic%, and more preferably about 47 atomic% to 59 atomic%. If the amount of oxygen is large, the stability improves, and the recording property also improves, but the sensitivity worsens. If the amount of oxygen is small, the sensitivity is good, but the reliability, such as storage stability, degrades.
  • the proportion of Bi is particularly preferably in a range of 20 atomic% to 38 atomic%.
  • amount of Bi since Bi and Bi oxide are essential for recording, if the amount of Bi is small, formation of recording marks is difficult, and the recording property worsens. If the amount of Bi is large, the sensitivity improves, but the reliability, such as storage property, worsens.
  • the content of C (carbon) is preferably about 1.5 atomic% to 49 atomic%, and the proportion of N (nitrogen) is preferably about 1.5 atomic% to 21 atomic%.
  • Bi and oxygen in Bi oxide are separated by irradiation with laser light to precipitate Bi, so that the optical properties change to perform recording.
  • a change in oxygen bonding state, a change in light absorptivity, and the like can be controlled, so that an improvement in sensitivity can be intended.
  • the melting point also changes, so that an improvement in sensitivity can be intended.
  • Carbon is contained in a recording layer in the form of a simple substance or a compound, or in the form of a mixture thereof.
  • a method for containing carbon in a recording layer carbon can be introduced into a recording layer by mixing a simple substance of carbon or carbide in a target and forming a film using the target. It is also possible to introduce carbon into a recording film by mixing a gas including carbon, such as CO2 or CH4, into an Ar gas and forming a film by sputtering. Also, an embodiment including carbon as an organic compound in a recording layer may be used.
  • Nitrogen is contained in a recording layer in the form of a simple substance or a compound, or in the form of a mixture thereof.
  • nitrogen can be introduced into a recording layer by mixing nitride in a target and forming a film using the target. It is also possible to introduce nitrogen into a recording film by mixing a nitrogen gas into an Ar gas and forming a film by sputtering.
  • the recording layer preferably further contains at least one element X selected from B, Li, Sn, Ge, Sr, Mg, Ba, Ca, Mo, W, Co, Si, In, Ti, Mn, Ga, Zr, Cr, Hf, K, Na, Zn, Ni, Cu, Pd, Ag, P, Ta, Y, Nb, Al, V, Sb, Te, and La series elements.
  • element X selected from B, Li, Sn, Ge, Sr, Mg, Ba, Ca, Mo, W, Co, Si, In, Ti, Mn, Ga, Zr, Cr, Hf, K, Na, Zn, Ni, Cu, Pd, Ag, P, Ta, Y, Nb, Al, V, Sb, Te, and La series elements.
  • the effect is large when about 1.5 atomic% to 18 atomic% of these elements X are included.
  • the amount of Bi nitride is preferably small, and more preferably small to the extent of being almost undetectable.
  • Preferable embodiments of the recording layer are an embodiment including Bi oxide, X oxide, and X nitride, and an embodiment including Bi oxide, X oxide, and X carbide.
  • Elements such as B, Li, Na, Mg, K, Ca, and P, have the nature of being easily vitrified by coexisting with bismuth oxide. The mechanism is not clear, but it is possible that the easiness of vitrification is related to an improvement in sensitivity.
  • elements that are relatively not easily oxidized such as Cu,
  • Bi and elements such as Cu, Ag, and Pd, exist as a simple substance metal, so that the sensitivity improves.
  • the recording layer preferably includes Bi, B, O, and C.
  • a preferable proportion of each element has been as described above. Since carbide has a high light absorption, it easily absorbs a recording light by existing in the recording layer, so that the sensitivity further improves. Also, by adding B, the phenomenon that Bi is bonded to oxygen, and releases oxygen by recording, occurs more surely.
  • a preferable embodiment of the recording layer is an embodiment including three kinds of compounds : Bi oxide; B oxide; and B carbide.
  • the recording layer preferably includes Bi, B, O, and N.
  • a preferable proportion of each element is as described above. Also, by adding B, the phenomenon that Bi is bonded to oxygen, and releases oxygen by recording, occurs more surely.
  • a preferable embodiment of the recording layer is an embodiment including Bi oxide, B oxide, and B nitride.
  • the effects of adding carbon the following (l) to (3) are considered.
  • a preferable range of the carbon content is about 1.5 atomic% to 49 atomic% of the entire recording layer.
  • WORM optical recording media were manufactured as in Example A 2 described later, except that a composite target including Bi2 ⁇ 3 and C (carbon) was used and the amount (atomic% with respect to the entire recording layer) of C was changed as shown in Table IA to form a recording layer, and the reproducing light stability was examined.
  • WORM optical recording media were manufactured as in Example A-I described later, except that a composite target, in which C (carbon) was added to a mixture of Bi2U3 and B2O3 having a molar ratio of 8 ⁇ 1, was used to form a recording layer. Carbon was added, with its amount changed according to the amount (atomic% with respect to the entire recording layer) of C shown in Table 2A.
  • Example A-I For these WORM optical recording media, the optimum recording power was examined as in Example A-I. The value of the optimum recording power was examined before and after a storage test in an environment of a temperature of 80 0 C and a humidity of 85% RH for 500-hours.
  • nitrogen also has the role that, when bismuth oxide is phase separated into Bi and bismuth oxide by recording, Bi and bismuth oxide are finely divided without aggregation. In other words, it is considered that crystals in the recording marks are finely divided by addition of nitrogen, showing a good recording property.
  • a preferable range of the nitrogen content is about 1.5 atomic% to 21 atomic% of the entire recording layer, as seen from the results in Table 3A below. It is not preferable that the amount of nitrogen is too large because the sensitivity decreases.
  • WORM optical recording media were manufactured as in Example A- 3 described later, except that a composite target, in which BN was added to a mixture of Bi2 ⁇ 3 and B2O3 having a molar ratio of 13 : 5, was used to form a recording layer. BN was added, with its amount changed according to the amount (atomic% with respect to the entire recording layer material) of N shown in Table 3A.
  • Example A For these WORM optical recording media, the optimum recording power was examined as in Example A"3. The values of the optimum recording power were examined before and after a storage test in an environment of a temperature of 8O 0 C and a humidity of 85% for
  • the thickness of the recording layer is preferably set in a range of
  • the thickness is less than 5 nm, a sufficient recording sensitivity is not easily obtained even in a recording layer in which the light absorption function at a recording and reproducing wavelength is improved by the configuration of the present invention as described above. If the thickness is more than 30 nm, the reflectance of the WORM optical recording medium decreases sharply, so that the recording and reproducing properties degrade. Both cases are not preferable.
  • Bi oxide absorbs light in the blue wavelength region well, among oxides, good recording is easily performed, but a further improvement in recording sensitivity is necessary for higher speed that is predicted in the future.
  • the points of higher sensitivity in a WORM optical recording medium using Bi oxide for a recording layer are the following two points- (1)
  • the oxygen content in Bi oxide is made smaller than that of its stoichiometric composition
  • Bi oxide A simple substance of each of one or more elements M (except Bi, C, and N) that enhance a light absorption function for a recording and reproducing laser light is contained in Bi oxide.
  • JP-B Japanese Patent (JP-B) No. 2656296 confirms that the recording sensitivity can be improved using a method for making the oxygen content in Bi oxide smaller than that of its stoichiometric composition, but if the oxygen content in Bi oxide is made far smaller than that of its stoichiometric composition, that is, if the content of metal Bi is increased over a certain level, conversely, the recording and reproducing properties, such as recording sensitivity, may worsen.
  • the cause of this is related to the recording principle in the WORM optical recording medium using Bi oxide for its recording layer.
  • phase separation of metal Bi and Bi oxide occurs. Even if the oxygen content of Bi oxide is made smaller than that of the stoichiometric composition, the recording principle is similar to the above, but the absorption coefficient of the recording layer for a recording light can be increased by the presence of metal Bi, so that the recording sensitivity is improved.
  • metal Bi is melted by recording, so that phase separation of metal Bi and Bi oxide does not occur easily.
  • the heat conductivity of metal Bi is much higher than that of Bi oxide, so that if the content of metal Bi is over a certain level, the recording and reproducing properties worsen, for example, the recording sensitivity worsens, and the degree of modulation decreases.
  • the oxygen content in Bi oxide is made smaller than that of the stoichiometric composition for increased content of metal Bi, it is important that, using Bi oxide for a matrix, metal Bi be dispersed in the matrix or that metal Bi and Bi oxide be uniformly mixed. It is not preferable that there are points where metal Bi is not uniform and exists locally in a large amount, because a melting mode will be the main part of the recording principle in the places. Also, it is not preferable that there are points where metal Bi is not uniform and exists locally in a large amount, because even irradiation with a reproducing light can cause melting in the places, so that the reproduction stability may decrease significantly.
  • a method for making the oxygen content in Bi oxide still smaller than that of its stoichiometric composition includes a method for adding an added element to Bi oxide, and in Bi oxide, an oxide of another element should be contained, as shown in Japanese Patent Application LaidOpen (JP-A) No. 2006-248177.
  • the oxygen content in Bi oxide is made smaller than that of the stoichiometric composition in the case where the recording layer is formed only of Bi oxide, the proportion of metal Bi increases so that an improvement in recording sensitivity can be expected.
  • Bi oxide which is the matrix, decreases so that metal Bi particles aggregate easily, and a melting mode will be the main part of the recording principle, thereby degrading the recording and reproducing properties.
  • a method for adding in Bi oxide an oxide of another element is effective so as to prevent aggregation of particles of metal Bi even if the proportion of metal Bi has increased. That is, a decreased amount of Bi oxide, which is the matrix, due to an increased proportion of metal Bi is compensated by addition of an oxide of another element.
  • the oxygen content in Bi oxide can be made still smaller than that of the stoichiometric composition, as compared with the case where the recording layer includes only Bi oxide, which is effective for improved sensitivity.
  • Bi oxide an oxide of another element is added to suppress an increase in the amount of crystals precipitated, formation of small marks is good, and higher density is easily achieved. Also, by adding an oxide of another element, the recording marks are stabilized, so that the storage stability improves.
  • Bi oxide is decomposed by heat due to irradiation with a recording light to produce metal Bi.
  • phase separation of metal Bi, and Bi oxide and/or another oxide occurs.
  • the optical recording medium of the second embodiment of the present invention in Bi oxide, a simple substance of each of one or more elements M (except Bi, C, and N) that enhance a light absorption function for a recording and reproducing laser light is contained in the recording layer to further improve the recording sensitivity, compared with the above related art.
  • Bi oxide NiOx, which is oxide, is added in the above Patent No. 2656296, the present invention differs largely in that with respect to Bi oxide, element M exists as a simple substance in the recording layer. Also, element M does not include Bi, because the present invention is the same as the related art if element M is Bi.
  • element M does not include C (carbon) and N (nitrogen) to avoid that the present invention is identical to the inventions of other applications of the applicant. Then, by selecting element M from elements having such a melting point that the elements are not melted by heat due to irradiation with a recording light, and also selecting an element having a large absorption coefficient for a recording and reproducing laser light, an improvement in recording sensitivity can be intended without changing the main part of the recording mode to the melting mode.
  • a light-heat conversion function in related art is performed by Bi oxide in the case of a WORM optical recording medium using Bi oxide, having an oxygen content close to the stoichiometric composition, for a recording layer, and is performed by metal Bi and Bi oxide in the case of a WORM optical recording medium using Bi oxide, having an oxygen content smaller than that of the stoichiometric composition, for a recording layer, but in the above recording layer, a light-heat conversion function is performed by a simple substance of element M, metal Bi, and Bi oxide, so that the absorption function of the recording layer for a recording light can be improved significantly.
  • the ratio of the presence of metal Bi when the ratio of the presence of metal Bi is increased, as is done conventionally, to increase the absorption coefficient of the recording layer, degradation of recording and reproducing properties easily occurs. But in the present invention, the ratio of the presence of metal Bi, which is a cause of degradation of recording and reproducing properties, need not be increased, both the recording sensitivity and the recording and reproducing properties can be intended.
  • the optical recording medium of the second embodiment of the present invention includes the following first optical recording medium and second optical recording medium.
  • the first optical recording medium of the present invention has a recording layer that contains, as main components, Bi oxide, and a simple substance of each of one or more elements M (except Bi, C, and N) that enhance a light absorption function for a recording and reproducing laser light.
  • the recording sensitivity when using laser light in the blue wavelength region (350 nm to 500 nm), can be improved, compared with conventional WORM optical recording media using Bi oxide for a recording layer.
  • the main components herein mean that the content (mole %) of combined Bi oxide and a simple substance of each of one or more elements M that enhances a light absorption function for a recording and reproducing laser light is highest in the recording layer.
  • a simple substance of element M refers to a state of being not chemically bonded to an element other than element M.
  • the light absorption function (a light-heat conversion function) is eliminated from Bi oxide, which is the base of the recording principle, or alleviation of the light absorption function is intended, and a simple substance of each of one or more elements M that enhances a light absorption function for a recording and reproducing laser light is added as a component that newly performs the light absorption function.
  • Bi oxide performs both functions of obtaining the recording and reproducing properties represent by jitter, PRSNR, error rate, the degree of modulation, reproduction stability, storage reliability, and the like, and of improving the recording sensitivity, so that a significant improvement in recording sensitivity, with the recording and reproducing properties being obtained, cannot be desired.
  • separate components have the function of obtaining the recording and reproducing properties and the function of improving the recording sensitivity, respectively, so that both of these functions are possible.
  • Element M added is not particularly largely limited, but an element having a relatively high melting point (for example, 400 0 C or more) is preferable in terms of the easiness of making a sputtering target, durability, and the like.
  • the second optical recording medium of the present invention has a recording layer that contains, as main components, Bi oxide, a simple substance of each of one or more elements M (except Bi, C, and N) that enhance a light absorption function for a recording and reproducing laser light, and an oxide of the element M.
  • Bi oxide a simple substance of each of one or more elements M (except Bi, C, and N) that enhance a light absorption function for a recording and reproducing laser light
  • an oxide of the element M an oxide of the element M.
  • the main components herein mean that the content (mole %) of combined Bi oxide, a simple substance of each of one or more elements M that enhances a light absorption function for a recording and reproducing laser light, and an oxide of the element M is highest in the recording layer.
  • the difference between the first optical recording medium and the second optical recording medium of the present invention is that an oxide of element M is contained in the recording layer.
  • An improvement in recording sensitivity is provided by a simple substance of each of one or more elements M that enhances a light absorption function for a recording and reproducing laser bight, but depending on the amount of element M and the type of element M, if element M exists only as a simple substance, the heat conductivity of the recording layer increases too much, so that adverse effects that the sensitivity worsens and that the degree of modulation decreases can occur. But, if an oxide of element M is contained in the recording layer, as in the second optical recording medium of the present invention, an improvement in recording sensitivity can be intended without impairing the recording and reproducing properties.
  • Element M added is not particularly largely limited, but an element having a relatively high melting point (for example, 400°C or more) is preferable in terms of the easiness of making a sputtering target, durability, and the like.
  • a relatively high melting point for example, 400°C or more
  • element M in the first and second optical recording media of the present invention an element having a value of imaginary part of complex refractive index of 3.0 or more, when its crystal or thin film is irradiated with a recording and reproducing laser light, is used.
  • the element M such a value of the imaginary part of the complex refractive index is not defined, because if element M exists as a simple substance, it has a light absorption function equal to or higher than that of Bi oxide, in almost all solid elements.
  • an element having a value of imaginary part of complex refractive index of 3.0 or more, when its crystal or thin film is irradiated with a recording and reproducing laser light, is preferable as element M. If the value of the imaginary part of the complex refractive index of element M added is 3.0 or more, high sensitivity can be achieved without depending on the wavelength of the recording and reproducing laser light.
  • Such an element is not particularly largely limited, but an element having a relatively high melting point (for example, 400 0 C or more) is preferable in terms of the easiness of making a sputtering target, durability, and the like.
  • B boron
  • Boron is an element that has a light absorption function (a value of imaginary part of complex refractive index) equal to or higher than that of Bi oxide, in the form of a simple substance, and provides a remarkable improvement in recording sensitivity in a small addition amount.
  • boron With boron, a sputtering target is relatively easily made, and boron has an excellent durability, therefore, it is a preferable added element. Also, a sputtering target to which boron is added has the advantages of having a very high sputtering rate and an excellent productivity.
  • At least one selected from Zn, Mg, Ru, Sb, Cr, Be, Co, Pd, V, Te, Ir, Mo, Os, and Ph is used as an element having a value of imaginary part of complex refractive index of 3.0 or more.
  • These elements are a group of elements that have a light absorption function (a value of imaginary part of complex refractive index) equal to or higher than that of Bi oxide, in the form of a simple substance, and provide a remarkable improvement in recording sensitivity in a small addition amount. Also, the melting point is relatively high, a sputtering target is relatively easily made, and the durability is excellent, therefore, they are a preferable group of added elements. If the recording and reproducing wavelength is more than 420 nm, the value of the imaginary part of the complex refractive index of the group of elements listed can be less than 3.0, so that these elements are preferably used when the recording and reproducing wavelength is 420 nm or less.
  • M/Bi is preferably 0.20 to 0.70.
  • the ratio of the number of atoms herein is simply the ratio of the number of atoms of element M to Bi, and element M and Bi include element M and Bi that exist as a simple substance and element M and Bi that exist as an oxide.
  • the above range is preferable, because both the recording and reproducing properties and the recording sensitivity can be surely achieved. If element M/Bi is less than 0.20, the effect of an improvement in sensitivity decreases. Also, if element M/Bi is more than 0.70, the reflectance often decreases significantly, and degradation of the recording and reproducing properties is often remarkable.
  • the oxygen content of Bi oxide is preferably smaller than that of the stoichiometric composition.
  • an improvement in recording sensitivity is provided by containing in the recording layer, Bi oxide and a simple substance of each of one or more elements M that enhances a light absorption function for a recording and reproducing laser light, and further, it is preferable that an improvement in sensitivity is intended also by making the oxygen content in Bi oxide smaller than that of the stoichiometric composition.
  • the ratio of an element and oxygen combined is determined, and it is called a stoichiometric composition.
  • the stoichiometric composition differs according to an element that is combined with oxygen, and for example, oxides, such as MgO, Al 2 O 3 , ZnO, Li 2 O, SiO 2 , HfO 2 , SnO 2 , Y 2 O 3 , B 2 O 3 , Fe 2 O 3 , Co 2 O 3 , V 2 O 5 , VO 2 , V 2 O 3 , and WO 3 , are formed.
  • oxides such as MgO, Al 2 O 3 , ZnO, Li 2 O, SiO 2 , HfO 2 , SnO 2 , Y 2 O 3 , B 2 O 3 , Fe 2 O 3 , Co 2 O 3 , V 2 O 5 , VO 2 , V 2 O 3 , and WO 3 .
  • the case where the oxygen content is smaller than that of the stoichiometric composition refers to the case where, for Bi 2 O 3 , 0 ⁇ x ⁇ 1.5 holds in BiOx as Bi oxide.
  • Bi oxide may be of any compound form, is not limited to an oxide of Bi alone, such as Bi 2 O 3 , and may be, for example, a composite oxide of three elements, such as BiBO 3 .
  • the value of the imaginary part of the complex refractive index is 0.30 or more, and the value of the real part is 2.20 or more, when the recording layer is irradiated with a recording and reproducing laser light.
  • the transmittance of recording layers through which a recording and reproducing light is transmitted (recording layers other than the recording layer that is located farthest from the recording and reproducing light) can be increased, and the recording and reproducing properties of the recording layer on the far side can be improved. Also, if the value of the complex refractive index of a recording layer is in the above range, high sensitivity can be achieved without depending on the wavelength of a recording and reproducing laser light.
  • the recording layer that satisfies the above numeric value limitation can be implemented by the recording layer in the optical recording medium of the present invention.
  • the thickness of the recording layer is preferably in a range of 5 nm to 30 nm, and more preferably 5 nm to 15 nm. If the thickness is less than 5 nm, a sufficient recording sensitivity may not easily be obtained even in the recording layer of the present invention in which a light absorption function for a recording and reproducing laser light is improved. If the thickness is more than 30 nm, the reflectance of the medium decreases sharply, and also the heat conductivity of the media is too high, so that the recording and reproducing properties may degrade.
  • a protective layer (an upper protective layer or a lower protective layer) is provided on both surfaces of the recording layer.
  • These protective layers have functions of suppressing the deformation or breakage of the recording layer and accepting the melting, compositional change, and diffusion of the recording layer.
  • these protective layers usually preferably pass through light with a wavelength for recording and reproducing for increased reflectance, but can also be provided with a light absorption function for the recording and reproducing wavelength, to some extent, to adjust the recording sensitivity.
  • the influences on deformation of recording marks can be made much smaller than in conventional optical recording media, and also a drastic increase in the influence on such deformation due to increased recording power in high linear velocity recording can be prevented, so that this is effective for improving the high linear velocity recording property. This is also effective for improving the storage stability.
  • Sulfide is preferable as the materials for the upper and lower protective layers.
  • the reason for this is not clear, but it is considered that by sulfide and the recording layer material being mixed or reacted, and diffused into each other, formation of recording marks is easy and good and is performed at a higher speed, so that the recording sensitivity improves. Also, it is considered that since many sulfides are relatively soft, stress due to deformation of the recording layer that occurs during recording is easily relaxed.
  • preferable examples are materials including ZnS Si ⁇ 2 as a main component. Also, Si ⁇ 2, Zr ⁇ 2, Ta2 ⁇ s, and
  • Sn ⁇ 2 are preferably included as main components to obtain a sufficient heat insulating effect.
  • Materials that are relatively hard and low reactive such as oxide, nitride, and carbide, can also be used as the upper and lower protective layer materials, and are preferable, because after recording marks are formed, their deformation and compositional change do not easily occur, and the heat of the recording layer does not cause decomposition, sublimation, cavitation, or the like.
  • oxides such as composite oxides of the above oxides, and silicate type oxides, such as 2MgO SiO 2 , MgO SiO 2 , CaO SiO 2 , ZrO 2 SiO 2 , 3Al 2 O 3 -2SiO 2 , 2MgO-2Al 2 O 3 -5SiO 2 , and Li 2 O Al 2 O 3 -4SiO 2 ; nitride type materials, such as silicon nitride, aluminum nitride, BN, and TiN; carbide type materials, such as SiC, B4C, TiC, WC, and amorphous carbon; and composite compounds, such as SiON, AlON, SiAlON
  • organic materials such as dyes and resins
  • the dyes include, for example, polymethine dyes, naphthalocyanine dyes, phthalocyanine dyes, squarylium dyes, chroconium dyes, pyrylium dyes, naphthoquinone dyes, anthraquinone (indanthrene) dyes, xanthene dyes, triphenylmethane dyes, azulene dyes, tetrahydrocholine dyes, phenanthrene dyes, triphenothiazine dyes, azo dyes, formazan dyes, or metal complex compounds thereof.
  • the resins include, for example, polyvinylalcohol resins, polyvinylpyrrolidone resins, nitrocellulose, cellulose acetate, ketone resins, acrylic resins, polystyrene resins, urethane resins, polyvinylbutyral resins, polycarbonate resins, polyolefin resins, and the like. One of these may be used alone, or two or more of these may be used in combination.
  • Formation of the first and lower protective layers can be performed by a normal way, for example, by vapor deposition, sputtering, CVD, or coating.
  • the organic material and the like should be dissolved in an organic solvent and applied using a general coating method, such as spraying, roller coating, dipping, or spin coating.
  • An organic solvent that is used for the application method is not particularly limited, can be selected appropriately according to the purpose, and includes, for example, alcohols, such as methanol, ethanol, and isopropanoL ' ketones, such as acetone, methyl ethyl ketone, and cyclohexanone, " amides such as N,N dimethylacetamide and N,N-dimethylformamide; sulfoxides such as dimethylsulfoxide; ethers, such as tetrahydrofuran, dioxane, diethyl ether, and ethylene glycol monomethyl ether J esters, such as methyl acetate and ethyl acetate; aliphatic halogenated carbons, such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride, and trichloroe thane; Aromatic compounds, such as benzene, xylene, monochlorobenzene, and dichloro
  • the upper protective layer is a layer that is provided between the recording layer and the reflective layer, and mainly performs the function of controlling the recording sensitivity and the reflective layer. If the thickness of the upper protective layer is too thin, heat generated in the recording layer is released more than necessary, so that the thickness is preferably set to 10 nm or more. Also, if the thickness of the upper protective layer is thick, heat generated in the recording layer is not easily released, and heat interference between the recording marks increases, so that the thickness is preferably set to 100 nm or less.
  • the lower protective layer is provided to obtain the storage reliability of the recording layer. That is, the lower protective layer serves to protect the recording layer from the oxygen, moisture, and other gases that permeate the substrate and the cover layer. Therefore, the thickness is preferably 10 nm or more to sufficiently protect the recording layer. However, in terms of productivity, the thickness is preferably set to 100 nm or less.
  • the optical recording media of the first and second embodiments of the present invention have a layer configuration in which at least a lower protective layer, a recording layer, an upper protective layer, and a reflective layer are sequentially laminated over the substrate.
  • a layer configuration in which at least a lower protective layer, a recording layer, an upper protective layer, and a reflective layer are sequentially laminated over the substrate.
  • FIG. 2 shows one example of a layer configuration of HD DVD-R, including, in order, a substrate 1, a lower protective layer 5, a recording layer 4, an upper protective layer 3, and a reflective layer 2.
  • a layer configuration in which at least a reflective layer, an upper protective layer, a recording layer, a lower protective layer, and a cover layer are sequentially laminated over the substrate is made.
  • an optical recording medium in accordance with BD-R specifications that has a good sensitivity and is capable of high linear velocity recording can be implemented.
  • recording and reproducing are performed from the cover layer side.
  • FIG. 3 shows one example of a layer configuration of BD R, including in order, a substrate 1, a reflective layer 2, an upper protective layer 3, a recording layer 4, a lower protective layer 5, and a cover layer 6.
  • each protective layer may have a lamination configuration including two or more layers.
  • a combination of having a lower protective layer as a two-layer configuration, using a material that includes sulfide for a layer adjacent to the recording layer, and using a layer that does not include sulfide for a layer adjacent to the reflective layer is preferable in terms of sensitivity and storage property.
  • the optical recording media according to the first and second embodiments of the present invention can record and reproduce with laser light in the blue wavelength region (350 nm to 500 nm), and laser light having a wavelength of 450 nm or less is preferable. Recording and reproducing is possible even by laser light in a wavelength region of more than 500 nm.
  • Materials of the substrate and the cover layer are not particularly limited, as long as they have excellent thermal and mechanical properties, and also have an excellent light transmission property when recording and reproducing are performed from the substrate side (through the substrate).
  • polycarbonate methyl poly me thacry late
  • amorphous polyolefin cellulose acetate, polyethylene terephthalate, and the like
  • polycarbonate and amorphous polyolefin are preferable.
  • the thickness of the substrate differs according to applications and is not particularly limited.
  • the thickness of a portion through which a reproducing light is transmitted needs to be decreased. This is because, with higher NA, the allowable amount of aberration caused by an angle at which the disc surface is displaced from the vertical with respect to the optical axis of the optical pickup (so-called a tilt angle, proportional to the square of the product of the reciprocal of the wavelength of the bight source and the numerical aperture of the objective lens) decreases, and this tilt angle is subject to the effect of aberration due to the thickness of the substrate.
  • the effect of aberration on the tilt angle is made as small as possible by providing a cover layer that is thinner than a normal substrate, and performing recording and reproducing from the cover layer side. Thereby, higher recording density that exceeds BD R specifications can be intended.
  • a thin layer of about several nm to several tens nm is used as the cover layer. This layer is preferable for high density recording, because when it has a high refractive index, light does not spread, and reaches the recording layer, remaining as a small spot.
  • a material that is hard and has good abrasion resistance and sliding property is preferably used, and preferable examples include silicon nitride, diamond-like carbon, and the like.
  • metal such as Al, Al-Ti, Al In, Al-Nb, Au, Ag, and Cu, semimetal, and alloys thereof can be used. These substances may be used alone or in combination of two or more. In terms of heat conductivity and reflectance, a simple substance metal, such as Ag, Cu, and Al, and alloys thereof are preferably used.
  • Methods for forming a reflective layer using these materials include, for example, a sputtering method, an ion plating method, a chemical vapor deposition method, a vacuum deposition method, and the like.
  • the reflective layer can be made by a sputtering method using the alloy for a target material, and in addition, the reflective layer can also be made by a chip-orrtarget method (for example, a film is formed with a Cu chip on an Ag target), a co-sputtering method (for example, an Ag target and a Cu target are used).
  • a chip-orrtarget method for example, a film is formed with a Cu chip on an Ag target
  • a co-sputtering method for example, an Ag target and a Cu target are used.
  • the thickness of the reflective layer is preferably in a range of 20 nm to 200 nm, and more preferably in a range of 30 nm to 160 nm. But when the reflective layer is applied to a multi layer optical recording medium, the lower limit of the reflective layer thickness it not limited to this. If the thickness is thinner than 20 nm, the problems that the desired reflectance is not obtained and that the reflectance decreases during storage, and further the problem that the sufficient recording amplitude is not obtained may arise. If the thickness is thicker than 200 nm, the film deposition surface may be rough, and the reflectance may decrease. This is also not preferable in terms of productivity.
  • the reflective layer includes Ag
  • a material including S is used for the protective layer
  • a sulfurization preventing layer for preventing reaction of Ag and S needs to be provided between the reflective layer and the protective layer.
  • oxide, nitride, carbide, and the like, that have a low light absorption are preferable, for example, nitride including SiN as a main component, oxide, such as Ti ⁇ 2, and carbide, such as SiC.
  • the thickness of the sulfurization preventing layer is preferably about 2 nm to 7 nm. If the thickness is thinner than 2 nm, the effect of prevention is not provided due to nonuniformity of the film. If the thickness is thicker than 7 nm, the reflectance and the recording sensitivity may decrease.
  • a thick environment protection layer is preferably formed on the reflective layer.
  • the material of the environment protection layer is not particularly limited as long as it protects the reflective layer from external force, and it can be selected appropriately according to the purpose and includes, for example, organic materials, inorganic materials, and the like.
  • the organic materials include, for example, thermoplastic resins, thermosetting resins, electron beam curable resins, ultraviolet ray curable resins, and the like.
  • the inorganic materials include, for example, Si ⁇ 2, SisN4, MgF2, Sn ⁇ 2, and the hike.
  • a spin coating method and a casting method As a method for forming an environment protection layer, application methods, such as a spin coating method and a casting method, ' a sputtering method, a chemical vapor deposition method, and the like are used, and a spin coating method is preferable among them.
  • thermoplastic resin or thermosetting resin When a thermoplastic resin or thermosetting resin is used for the environment protection layer, it is usually dissolved in a suitable solvent, applied, and dried to form a layer.
  • an ultraviolet ray curable resin When an ultraviolet ray curable resin is used for the environment protection layer, it is usually applied as it is or dissolved in a suitable solvent, and irradiated with ultraviolet rays to be hardened to form a layer.
  • the ultraviolet ray curable resin for example, acrylate type resins, such as urethane acrylate, epoxy acrylate, and polyester acrylate, and the like can be used.
  • the thickness of the environment protection layer is preferably
  • a substrate may further be attached to the reflective layer or the light transmitting layer surface, or the reflective layer and the light transmitting layer surface may be opposed to each other as inner surfaces to attach two optical recording media.
  • An ultraviolet ray curing resin layer, an inorganic type layer, and the like may be formed on the substrate mirror- surface side for surface protection and preventing attachment of dust and the like.
  • the light transmitting layer (the cover layer) is necessary when a high NA lens is used to intend higher density.
  • the thickness of a portion through which a reproducing light is transmitted needs to be decreased. This is because, with higher NA, the allowable amount of aberration caused by an angle at which the disc surface is displaced from the vertical with respect to the optical axis of the optical pickup (so-called a tilt angle, proportional to the square of the product of the reciprocal of the wavelength of the light source and the numerical aperture of the objective lens) decreases, and this tilt angle is subject to the effect of aberration due to the thickness of the substrate. Therefore, it is necessary that the thickness of the substrate is decreased to make the effect of aberration on the tilt angle as small as possible.
  • the optical recording medium is compatible with a higher NA of the objective lens by thinning the light transmitting layer.
  • a still higher recording density can be intended by providing a thin light transmitting layer, and recording and reproducing from this light transmitting layer side.
  • Such a light transmitting layer is generally formed by a polycarbonate substrate and an ultraviolet ray curable resin.
  • a layer for boding the light transmitting layer may be included in the light transmitting layer mentioned in the present invention.
  • optical recording media of the first and second embodiments of the present invention can also have the following configurations other than the above-described layer configurations, but configurations are not limited to these, and, for example, the lower protective layer and the upper protective layer may include a plurality of layers.
  • a multi layer configuration may be made based on the above configurations (a) to (d). For example, when a two layer configuration is made based on configuration (a), a configuration of a substrate/a recording layer/an upper protective layer/a reflective layer (a translucent layerVan adhesive layer/a recording layer/an upper protective layer/a reflective layer/a substrate can be made.
  • a configuration of a substrate/a recording layer/an upper protective layer/a reflective layer a translucent layerVan adhesive layer/a recording layer/an upper protective layer/a reflective layer/a substrate can be made.
  • Sputtering targets of a first embodiment of the present invention include the following first sputtering target and second sputtering target.
  • the first sputtering target of the present invention includes Bi (bismuth) and O (oxygen) as main components, further includes C (carbon), and does not include Fe.
  • the second sputtering target of the present invention includes Bi (bismuth) and O (oxygen) as main components, further includes N (nitrogen), and does not include Fe.
  • the main components herein mean that the content (atomic%) of Bi and oxygen combined, is highest.
  • the expression "include Bi and oxygen” is used, because while the content of Bi oxide is highest, metal Bi other than Bi oxide may be included.
  • Fe is not included, because a sputtering target including Fe has a relatively low strength and may be broken during film deposition. It is considered that the cause is that while Fe, which is relatively easily oxidized, easily forms oxides, such as F ⁇ 2 ⁇ 3, the coefficient of thermal expansion of these oxides is 10 (1O '6 /°C), relatively high.
  • the coefficients of thermal expansion of carbon, SiC, and BN are 1.5 ⁇ lO G /°C, 4.3 ⁇ lO G /°C, and 3.6 ⁇ lO 6 /°C respectively, and it is considered that those including carbon and nitrogen have a relatively low coefficient of thermal expansion, and have a high durability against a temperature change during film deposition.
  • a Bi B C O target used in Example A- 7 and a Bi-B-N-O target used in Example A-8 are not broken during film deposition, but an Bi B Fe O target that is made under similar sintering conditions may be broken under the same film deposition conditions, so that film deposition needs to be performed while lowering the applied electric power during film deposition from 1.2 kW to 0.8 kW. In this way, when Fe is included, the productivity is adversely affected.
  • the proportion of oxygen in a sputtering target is about 30 atomic% to 65 atomic%, preferably 45 atomic% to 62 atomic%, and more preferably about 47 atomic% to 59 atomic%. If the amount of oxygen is large, the composition of the recording layer formed is relatively stable, and the recording property also improves, but the recording sensitivity worsens. If the amount of oxygen is small, an optical recording medium having a good recording sensitivity can be manufactured, but the strength of the target tends to be relatively weak.
  • the proportion of Bi is particularly preferably in a range of 20 atomic% to 38 atomic%.
  • amount of Bi since Bi and Bi oxide are essential for recording, if the amount of Bi is small, formation of recording marks is difficult, and the recording property worsens. If the amount of Bi is large, the sensitivity improves, but the reliability, such as storage property, worsens.
  • the proportion of C (carbon) is preferably about 1.5 atomic% to 49 atomic%, and the proportion of N (nitrogen) is preferably about 1.5 atomic% to 21 atomic%.
  • Bi and oxygen substantially Bi oxide
  • Carbon is contained in the sputtering target in the form of a simple substance or a compound, or in the form of a mixture thereof.
  • carbide By containing carbide, the stability in sintering the target increases, and the productivity of the sputtering target improves.
  • Nitrogen is contained in the sputtering target in the form of a compound. Nitride can also have the function of an additive for increasing the strength of the target.
  • the first and second sputtering targets of the present invention preferably further contain at least one element X selected from B, Li, Sn, Ge, Sr, Mg, Ba, Ca, Mo, W, Co, Si, In, Ti, Mn, Ga, Zr, Cr, Hf, K, Na, Zn, Ni, Cu, Pd, Ag, P, Ta, Y, Nb, Al, V, Sb, Te, and La series elements, and more preferably contain at least one element selected from B, Mg, Ba, Ca, Mo, W, Si, Ti, Zr, Cr, Hf, Cu, Ta, Y, Nb, Al, and V.
  • Bi carbide and Bi nitride are unstable, and decompose in sintering so that the amount of Bi carbide and Bi nitride is often small to the extent of being almost undetectable. The amount of
  • Bi carbide and Bi nitride is preferably small for improving the strength of the target, and more preferably small to the extent of being almost undetectable.
  • Preferable embodiments are an embodiment including Bi oxide, X oxide, X nitride, and an embodiment including Bi oxide, X oxide, and X carbide, and an embodiment including Bi oxide and X carbide.
  • carbide and nitride are often used as a sintering aid and an additive for an improvement in strength, and largely related to the strength of the target.
  • B, Si, Ti, and Nb have a large effect on an improvement in the strength of the target.
  • the first sputtering target of the present invention preferably includes Bi, B, O, and C.
  • a preferable proportion of each element is as described above. Since B4C has a high stability, if B4C is included, the strength of the target improves, so that the effect is large. A recording layer that is formed using this target easily absorbs a recording light due to carbide having a high light absorption existing in the recording layer, so that the sensitivity further improves. Also, by adding B, the phenomenon that Bi is bonded to oxygen, and releases oxygen by recording, occurs more surely.
  • a preferable embodiment of the first target of the present invention is an embodiment including three kinds of compounds : Bi oxide; B oxide; and B carbide.
  • the second sputtering target of the present invention preferably includes Bi, B, O, and N.
  • a preferable proportion of each element is as described above. It is effective that B and N are included in the state of BN, because the strength of the target is high.
  • a preferable embodiment of the second target of the present invention is an embodiment including Bi oxide, B oxide, and B nitride.
  • the content of C is set to 1.5 atomic% to 49 atomic% of the total. If C is more than 1.5 atomic%, the recording layer formed is effective for an improvement in sensitivity, because carbon absorbs light. If carbon is more than 49 atomic%, the proportion of bismuth oxide, which is related to recording, decreases, so that the contrast between recorded portions and unrecorded portions is not easily obtained, thereby the recording property degrades. If the amount of carbon is too large, the target is not easily manufactured, and the packing density of the target does not easily improve, so that a target having a good productivity and a high strength cannot be implemented.
  • the first sputtering target of the present invention is characterized by that direct current sputtering is possible. Direct current sputtering is possible, because the resistivity decreases, particularly when carbon or carbide is contained. It is preferable that direct current sputtering is possible, because the cost of film deposition decreases.
  • the packing density (relative density) of the first and second sputtering targets of the present invention is 90% or more. Up to a packing density of about 95%, the film deposition rate and the strength of the target improve, with an improvement in packing density. But, at about 95% or more, the strength of the target gradually decreases.
  • the packing density herein refers to the ratio (%) of a density actually measured to a theoretical density when it is assumed that mixed raw materials are mixed in a predetermined ratio.
  • a method for manufacturing the first sputtering target of the present invention is a method for manufacturing a sputtering target that includes Bi and O as main components, further includes C, and does not includes Fe, the method including the steps of mixing and sintering a bismuth oxide powder and a carbon powder.
  • a bismuth oxide powder and a powder of carbide of at least one element selected from Al, B, Ca, Cr, Hf, Mo, Nb, Si, Ta, Ti, V, W, and Zr are mixed and sintered.
  • carbide carbon can be mixed with good stability. Also, since carbon has a high electrical conductivity but also has a high reduction property, Bi oxide can be reduced during sintering, but by mixing stable carbide, manufacture with good reproducibility is possible.
  • a sintering method such as a hot press method, is effective, because a mold for molding a target is made of carbon, so that carbon reaches an equilibrium state and does not escape easily.
  • a film is formed by using a sputtering target including Bi, B, and O, and mixing a gas including carbon, such as hydrocarbon, with Ar. If a target that does not contain oxygen is used, a recording layer including Bi and oxygen as main components is not obtained. If a film is deposited using a gas in which oxygen is mixed for supplement of oxygen, mixed hydrocarbon is oxidized to become carbon dioxide and water, therefore, oxygen cannot be mixed.
  • a film is formed in a mixed gas of nitrogen and Ar, using a sputtering target including Bi, B, and O. If a target that does not contain oxygen is used, a recording layer including Bi and oxygen as main components is not obtained. Then, it is possible to form a film using a gas in which oxygen is mixed for supplement of oxygen, but formation of Bi nitride is not preferable, therefore, conditions in which nitride is not formed are preferably used. Also, it is considered that by forming a film in a mixed gas of nitrogen and Ar, separation of Bi and oxygen easily occurs, so that formation of recording marks easily occurs during recording, which is effective for an improvement in recording sensitivity.
  • Sputtering targets of a second embodiment of the present invention include the following third sputtering target and fourth sputtering target.
  • the third sputtering target of the present invention contains, as main components, Bi oxide, and a simple substance of each of one or more elements M (except Bi, C, and N) that enhance the light absorption function of a WORM optical recording medium for a recording and reproducing laser light, and using this, the recording layer of the first optical recording medium of the present invention can be manufactured.
  • the third sputtering target of the present invention contains, as main components, Bi oxide, a simple substance of each of one or more elements M (except Bi, C, and N) that enhance the light absorption function of a WORM optical recording medium for a recording and reproducing laser light, and an oxide of the element M, and using this, the recording layer of the second optical recording medium of the present invention can be manufactured.
  • the element M is preferably an element having a value of imaginary part of complex refractive index of 3.0 or more when its crystal or thin film is irradiated with a recording and reproducing laser light.
  • the element having a value of imaginary part of complex refractive index of 3.0 or more is at least one selected from Zn, Mg, Ru, Sb, Cr, Be, Co, Pd, V, Te, Ir, Mo, Os, and Ph.
  • element M is preferably B.
  • the ratio of the number of atoms of the element M to Bi is preferably 0.20 to 0.70.
  • the oxygen content of Bi oxide is preferably smaller than that of the stoichiometric composition.
  • an optical recording medium that is capable of recording and reproducing by laser bight in the blue wavelength region (350 nm to 500 nm) and is also suitable for recording with high sensitivity and in a wide range of linear velocity from low linear velocity to high linear velocity, and a method for manufacturing the same, as well as a sputtering target for forming the recording layer of the optical recording medium, and a method for manufacturing the same can be provided.
  • a WORM optical recording medium that exhibits good recording and reproducing properties with laser light in the blue wavelength region (350 nm to 500 nm), particularly laser light having a wavelength near 405 nm, is capable of high density recording, and has a recording layer having a recording sensitivity higher than conventional articles, and a sputtering target for forming the recording layer can be provided.
  • the present invention will further specifically be described below by way of Examples and Comparative Examples, however, the present invention is not limited to these Examples. While examples using laser light having a wavelength of 405 nm are illustrated as Examples, in the recording layer of the present invention, the complex refractive index indicates normal dispersion, and no sharp change in complex refractive index occurs, in the range of 350 nm to 500 nm, so that recording and reproducing can be performed similarly. In other words, when the recording and reproducing wavelength changes in a range of 350 nm to 500 nm, the reflectance and recording sensitivity of the WORM optical recording medium change, but the recording principle does not change, so that similar recording and reproducing are possible. (Example A-I)
  • An AgBi alloy (Bi- 0.5 atomic%) layer having a thickness of 60 nm, a SiN film having a thickness of 4 nm, a ZnS SiO2 (80 mole %-20 mole %) layer having a thickness of 15 nm, a Bi-B-C-O layer having a thickness of 16 nm, and a ZnS SiO2 (80 mole %-20 mole %) layer having a thickness of 75 nm were provided in the order by a sputtering method employing a multilayer sputtering solution DVD SPRINTER produced by Oerlikon on a polycarbonate substrate having a thickness of 1.1 mm and a diameter of 120 mm and having a guide groove (groove depth: 21 nm, average groove width : 155 nm, track pitch: 0.32 ⁇ m) (product name : ST3000, Teijin-Bayer Polytec Ltd).
  • a polycarbonate substrate having a thickness of 75 ⁇ m (TEIJIN CHEMICALS LTD., PURE-ACE) was attached on the ZnS-Si ⁇ 2 layer as a cover layer (a light transmitting layer) to manufacture a WORM optical recording medium having a thickness of about 1.2 mm.
  • the Bi BOO layer was formed using a composite target of Bi2 ⁇ 3-B2 ⁇ 3"C (molar ratio: 8:l:i). Sputtering was performed in an Ar gas.
  • Example A-I were low for jitter and high for sensitivity, compared with those for WORM optical recording media in Comparative Example A-I and Comparative Example A- 2 that will be described later. (Example A-2)
  • a WORM optical recording medium was manufactured as in Example A l, except that the Bi-B-C-O layer was changed to a Bi C O layer, and that a composite target for film deposition was Bi2 ⁇ 3"C (molar ratio- i:i).
  • Example A-2 were low for jitter and high for sensitivity, compared with those for WORM optical recording media in Comparative Example A-I and Comparative Example A- 2 that will be described later.
  • a WORM optical recording medium was manufactured as in Example A-I, except that the Bi-B-C O layer was changed to a Bi-O layer, and that a composite target for film deposition was Bi2 ⁇ 3.
  • a WORM optical recording medium was manufactured as in Example A-I, except that the Bi-B-C-O layer was changed to a Bi-B-O layer, and that a composite target for film deposition was Bi2 ⁇ 3"B2 ⁇ 3 (molar ratio- 6 ⁇ 4).
  • Example A-I When recording was performed as in Example A-I at 4x linear velocity, a jitter value of 6.7% was obtained at an optimum recording power of 9.8 mW.
  • Example A- 3 A WORM optical recording medium was manufactured as in
  • Example A l except that the Bi B CO layer was changed to a Bi B N-O layer, and that a composite target for film deposition was Bi2 ⁇ 3 B2 ⁇ 3"BN (molar ratio: 13:5:2).
  • Example A-4 When recording was performed as in Example A-I at 4x linear velocity, a jitter value of 5.6% was obtained at an optimum recording power of 8.7 mW. These values obtained in Example A-3 were low for jitter and high for sensitivity compared with those for WORM optical recording media in Comparative Example A-I and Comparative Example A-2. (Example A 4) A WORM optical recording medium was manufactured as in
  • Example A-I except that a recording layer (a Bi-C-NO layer) was formed in a mixed gas of Ar and nitrogen (the flow rate ratio of Ar to nitrogen is 40-10), using a composite target for film deposition including Bi2 ⁇ 3"C (molar ratio: ⁇ :i).
  • a jitter value of 4.8% was obtained at an optimum recording power of 4.4 mW.
  • Example A 4 were low for jitter and high for sensitivity, compared with those for WORM optical recording media in Comparative Example A-I and Comparative Example A-2.
  • Example A- 5 A WORM optical recording medium was manufactured as in
  • Example A-I except that a recording layer (a Bi-N-O layer) was formed in a mixed gas of Ar and nitrogen (the flow rate ratio of Ar to nitrogen is 40U0), using a target including Bi2 ⁇ 3.
  • Example A-5 were low for jitter and high for sensitivity, compared with those for WORM optical recording media in Comparative Example A-I and Comparative Example A"2.
  • Example A-6 Using a sputtering method that employs a multilayer sputtering solution DVD SPRINTER produced by Oerlikon, a ZnS SiO 2 layer (80:20 mole %) having a thickness of 60 nm, a Bi-B-C O layer having a thickness of 15 nm, a ZnS SiO 2 layer (80:20 mole %) having a thickness of 20 nm, and an AgBi alloy layer (Bi: 0.5 atomic%) having a thickness of 80 nm were laminated sequentially on a polycarbonate substrate having a thickness of 0.6 mm and having a guide groove (groove depth: 26 nm, average groove width: 200 nm, track pitch: 0.4 ⁇ m).
  • the BrB-C-O layer was formed using a composite target of Bi 2 Os B 2 Os-C (molar ratio: 8:i:i). Sputtering was performed in an Ar gas. Then, an organic protective layer including an ultraviolet ray curable resin (made by SAN NOPCO LIMITED: Nopcocure 134) and having a thickness of about 5 ⁇ m was provided on the AgBi alloy layer by a spin coating method, and a dummy substrate having a thickness of 0.6 mm was attached on the organic protective layer with the ultraviolet ray curable resin to manufacture a WORM optical recording medium.
  • an ultraviolet ray curable resin made by SAN NOPCO LIMITED: Nopcocure 1344
  • a dummy substrate having a thickness of 0.6 mm was attached on the organic protective layer with the ultraviolet ray curable resin to manufacture a WORM optical recording medium.
  • optical disc evaluation unit ODTJ- 1000 Wavelength- 405 nm, NA- 0.65) manufactured by Pulstec Industrial Co., Ltd., at a recording density in accordance with HD DVD R specifications (DVD Specifications for High Density Recordable Disc (HD DVD-R) Version 1.0), and at Ix (lx speed) linear velocity.
  • Example A-6 except that the Bi-B-C O layer was changed to a Bi-B-O layer, and that a composite target for film deposition was Bi2 ⁇ 3"B2 ⁇ 3 (molar ratio : 6 : 4).
  • Example A-7 when recording was performed as in Example A-6, with the linear velocity during recording set to 4x (quadruple-speed), the value of PRSNR was 19.8 at an optimum recording power of 17.6 mW.
  • Powders of Bi2 ⁇ 3, B2O3, and B4C were weighed in a molar ratio of 76.4-11.8:11.8 in such a condition that no moisture adsorption occur, mixed, further dry mixed in a ball mill for one hour, and fired at 500°C for one hour.
  • this mixed powder was pressure molded at 150 MPa, and hot press fired in the atmosphere at 650 0 C for five hours to manufacture a sputtering target.
  • the target had a diameter of 200 mm and a thickness of 6 mm.
  • This target was bonded to a backing plate of oxygen-free copper by bonding using a low melting point metal to obtain a sputtering target.
  • the packing density of this target was 84%.
  • Powders of Bi2 ⁇ 3, B2O3, and BN were weighed in a molar ratio of 65 ⁇ 25 ⁇ 10 in such a condition that no moisture adsorption occur, mixed, further dry mixed in a ball mill for one hour, and fired at 500 0 C for one hour.
  • this mixed powder was pressure molded at 150 MPa, and hot press fired in the atmosphere at 650 0 C for five hours to manufacture a sputtering target.
  • the target had a diameter of 200 mm and a thickness of 6 mm.
  • This target was bonded to a backing plate of oxygen-free copper by bonding using a low melting point metal to obtain a sputtering target.
  • the packing density of this target was 88%.
  • Powders of Bi2U3 and SiC were weighed in such a condition that no moisture adsorption occur, mixed such that the molar ratio of Bi2 ⁇ 3 to SiC was 2-1, then, dry mixed in a ball mill for one hour, and fired at 700 0 C for one hour.
  • this mixed powder was pressure molded at 150 MPa, and hot press fired in the atmosphere at 750°C for five hours to manufacture a sputtering target.
  • the target had a diameter of 200 mm and a thickness of 6 mm.
  • This target was bonded to a backing plate of oxygen-free copper by bonding using a low melting point metal to obtain a sputtering target.
  • the packing density of this target was 97%.
  • Powders of Bi2U3 and TiC were weighed in such a condition that no moisture adsorption occur, mixed such that the molar ratio of Bi2U3 to TiC was 2-1, then, dry mixed in a ball mill for one hour, and fired at 700 0 C for one hour.
  • this mixed powder was pressure-molded at 150 MPa, and hot press-fired in the atmosphere at 750 0 C for five hours to manufacture a sputtering target.
  • the target had a diameter of 200 mm and a thickness of 6 mm.
  • This target was bonded to a backing plate of oxygen-free copper by bonding using a low melting point metal to obtain a sputtering target.
  • the packing density of this target was 94%.
  • Powders of Bi2U3 and NbC were weighed in such a condition that no moisture adsorption occur, mixed such that the molar ratio of Bi2U3 to NbC was 2-1, then, dry mixed in a ball mill for one hour, and fired at 700°C for one hour.
  • this mixed powder was pressure molded at 150 MPa, and hot press fired in the atmosphere at 750°C for five hours to manufacture a sputtering target.
  • the target had a diameter of 200 mm and a thickness of 6 mm.
  • This target was bonded to a backing plate of oxygen-free copper by bonding using a low melting point metal to obtain a sputtering target.
  • the packing density of this target was 86%.
  • a WORM optical recording medium having a thickness of about 1.2 mm was manufactured as in Example A-I, except that a Bi B C- O layer was formed using the sputtering target manufactured in Example A-7.
  • Example A- 13 A WORM optical recording medium was manufactured as in Example A-I, except that a Bi-Si C O layer was formed using the sputtering target manufactured in Example A-9.
  • Example A- 14 When recording was performed as in Example A l at 4x linear velocity, a jitter value of 5.8% was obtained at an optimum recording power of 7.3 mW.
  • a WORM optical recording medium was manufactured as in Example A-I, except that a Bi-Ti-C-O layer was formed using the sputtering target manufactured in Example A- 10.
  • Example A- 15 When recording was performed as in Example A-I at 4x linear velocity, a jitter value of 6.3% was obtained at an optimum recording power of 6.3 mW.
  • a WORM optical recording medium was manufactured as in Example A-I, except that a Bi-Nb C-O layer was formed using the sputtering target manufactured in Example A-Il.
  • Example A- 16 When recording was performed as in Example A l at 4x linear velocity, a jitter value of 6.4% was obtained at an optimum recording power of 5.9 mW.
  • Variations in light absorptivity were compared for recording layers that were formed in an Ar gas, using sputtering targets having compositions of Bi C O, Bi-B-C O, Bi B-N O, Bi Si C O, and Bi B Fe O (control), respectively.
  • the wavelength of light was 405 nm, and as samples measured, those in which a recording layer having a thickness of 13 nm was formed on a polycarbonate substrate with no groove and in which a ZnSSiO2 film having a thickness of 20 nm was formed on the recording layer were used.
  • Film deposition was performed under the same conditions, except that the time from placement in a vacuum chamber for film deposition until the start of formation of a recording layer was randomly selected and set from 0 second to 60 seconds.
  • the Bi-B-CO target was one used in Example A-7, the Bi B-N-O target was one used in Example A"8, the Bi-Si-CO target was one used in Example A 9, and as the Bi-C O target and the Bi-B Fe O target, those manufactured as follows were used. ⁇ Bi-C O Target>
  • Powders of Bi2 ⁇ 3 and C (carbon) were weighed in a molar ratio of 1 ⁇ 1 in such a condition that no moisture adsorption occur, mixed, further dry mixed in a ball mill for one hour, and fired at 750 0 C for one hour.
  • this mixed powder was pressure molded at 150 MPa, and hot press fired in the atmosphere at 780 0 C for five hours to manufacture a sputtering target.
  • the target had a diameter of 200 mm and a thickness of 6 mm.
  • This target was bonded to a backing plate of oxygen-free copper by bonding using a low melting point metal to obtain a sputtering target.
  • Example B-I A sputtering target was obtained as in Example A 7, except that powders of Bi2U3, B2O3, and Fe2U3 were used in a molar ratio of 65:30:5.
  • a lower protective layer including ZnS-Si ⁇ 2 (80 mole %:20 mole %) and having a thickness of 60 nm, a recording layer having a thickness of 10 nm, and an upper protective layer including ZnS SiO2 (80:20 mole %) and having a thickness of 20 nm were laminated sequentially on a polycarbonate substrate having a guide groove (groove depth: 28 nm, track pitch: 0.40 ⁇ m, average groove width: 0.20 ⁇ m).
  • the recording layer was formed using a sputtering target in which Bi2 ⁇ 3, B2O3, and B (boron) were mixed in a ratio of 54.7:19.0:26.3 (mole %) and fired.
  • This sputtering target was a sputtering target that satisfied the conditions of the present invention.
  • an Ag reflective layer having a thickness of 60 nm was provided by a sputtering method, and an organic protective layer including an ultraviolet ray curable resin (made by SAN NOPCO LIMITED, Nopcocure 134) and having a thickness of about 5 ⁇ m was further provided by a spin coating method to manufacture a WORM optical recording medium in Example B-I.
  • the recording layer was a recording layer that satisfied the conditions of the present invention in which boron was added to Bi oxide as an element that enhanced a light absorption function for a recording and reproducing laser light. Also, the ratio of the number of atoms of B to Bi (B/Bi) was about
  • the recording layer was a recording layer that satisfied the conditions of the present invention.
  • composition of the recording layer in the thickness direction was quantitatively analyzed by XPS (X-ray Photoelectron Spectroscopy), it was confirmed that Bi existed as oxide and metal Bi.
  • the oxygen content of Bi oxide was smaller than that of the stoichiometric composition, so that the conditions of the present invention were satisfied.
  • High Density Recordable Disc (HD DVD-R) Version 1.0) was performed on the above WORM optical recording medium, using optical disc evaluation unit ODU-1000 (wavelength- 405 nm, NA: 0.65) manufactured by Pulstec Industrial Co., Ltd. The recording speed was 6.61 m/s.
  • a WORM optical recording medium was manufactured as in Example B l, except that a recording layer was formed using a sputtering target in which Bi2 ⁇ 3 and B2O3 were mixed in a ratio of 2 ⁇ 1 (molar ratio) and fired (that is, a target in which B did not exist as a simple substance), and recording in accordance with HD DVD R specifications was performed as in Example B l.
  • an Ag reflective layer having a thickness of 60 nm, an upper protective layer including ZnS SiO 2 (80 mole %:20 mole %) and having a thickness of 20 nm, a recording layer having a thickness of 10 nm, and a lower protective layer including ZnS-Si ⁇ 2 (80 mole %:20 mole %) and having a thickness of 60 nm were laminated sequentially on a polycarbonate substrate having a guide groove (groove depth- 20 nm, track pitch- 0.32 ⁇ m, average groove width: 0.155 ⁇ m).
  • the recording layer was formed using a sputtering target in which Bi 2 O 3 , B 2 O3, and B were mixed in a ratio of 54.7:19.0:26.3 (mole %) and fired.
  • This sputtering target was a sputtering target that satisfied the conditions of the present invention.
  • a cover layer including an ultraviolet ray curing resin and having a thickness of 0.1 mm was formed on the lower protective layer by a spin coating method to obtain a WORM optical recording medium.
  • this recording layer was quantitatively analyzed by the
  • the recording layer was a recording layer that satisfied the conditions of the present invention in which boron was added to Bi oxide as an element that enhanced a light absorption function for a recording and reproducing laser light.
  • the ratio of the number of atoms of B to Bi was about 0.59, so that the recording layer was a recording layer that satisfied the conditions of the present invention. Further, when the composition of the recording layer in the thickness direction was quantitatively analyzed by X-ray Photoelectron Spectroscopy, it was confirmed that Bi existed as oxide and metal Bi.
  • the oxygen content of Bi oxide was smaller than that of the stoichiometric composition, so that the conditions of the present invention were satisfied.
  • the real part was 2.35, and the imaginary part was 0.40, so that the recording layer of this example satisfied the conditions of the present invention.
  • a WORM optical recording medium was manufactured as in Example B 2, except that a recording layer was formed using a sputtering target in which Bi2 ⁇ 3 and B2O3 were mixed in a ratio of 2 ⁇ 1 (molar ratio) and fired (that is, a target in which B did not exist as a simple substance), and recording in accordance with BD R specifications was performed as in Example B 2.
  • a lower protective layer including ZnS"SiO2 (80 mole %:20 mole %), a recording layer, and an upper protective layer including ZnS SiO2 (80 mole %-20 mole %) and having a thickness of 20 nm were laminated sequentially on a polycarbonate substrate having a guide groove (groove depth: 28 nm, track pitch: 0.40 ⁇ m, average groove width: 0.20 ⁇ m).
  • the thickness of the lower protective layer and the recording layer was adjusted such that the reflectance of the WORM optical recording medium was 14% to 18%.
  • the variation range of the thickness of the lower protective layer was 40 to 60 nm.
  • the recording layer was formed using a sputtering target in which in a mixture of Bi2U3 and an oxide of element M listed in Table IB being constant in 2 : 1 (molar ratio), added element M listed in Table IB was further mixed in a range of 1 ⁇ 1 to 2-1 (molar ratio) and the mixture was fired.
  • These sputtering targets were sputtering targets that satisfied the conditions of the present invention.
  • an Ag reflective layer having a thickness of 60 nm was provided by a sputtering method, and an organic protective layer including an ultraviolet ray curable resin (made by SAN NOPCO LIMITED, Nopcocure 134) and having a thickness of about 5 ⁇ m was further provided by a spin coating method to obtain WORM optical recording media in Examples B-3 to B- 12.
  • the recording layers were recording layers that satisfied the conditions of the present invention in which an element in Table 1 was added to Bi oxide as an element that enhanced a light absorption function for a recording and reproducing laser light. Also, every ratio of the number of atoms of added element M in
  • the oxygen content of Bi oxide was smaller than that of the stoichiometric composition, so that the conditions of the present invention were satisfied.
  • WORM optical recording media were manufactured as in Examples B 3 to B- 12, except that a recording layer was formed using a target in which Bi2 ⁇ 3 and an oxide of element M listed in the above Table IB were mixed in a ratio of 2 ⁇ 1 (molar ratio) and fired (that is, a sputtering target in which added element M did not exist as a simple substance).
  • a recording layer was formed using a target in which Bi2 ⁇ 3 and an oxide of element M listed in the above Table IB were mixed in a ratio of 2 ⁇ 1 (molar ratio) and fired (that is, a sputtering target in which added element M did not exist as a simple substance).
  • Comparative Examples B-3 to B- 12 and Examples B-3 to B- 12 can be compared and contrasted, because recording layers in a comparative example and an example having the same number include the same element. Recording in accordance with HD DVD-R specifications was performed on the above each WORM optical recording medium as in Example B-I.
  • a WORM optical recording medium was manufactured as in Example B-2, except that a recording layer was formed using a target in which Bi2 ⁇ 3 and Cu were mixed in a ratio of 1-1 (molar ratio) and fired, and recording in accordance with BD-R specifications was performed as in Example B-2.
  • the value of the imaginary part of the complex refractive index of the Cu crystal near a wavelength of 405 nm was 2.21, not satisfying the conditions of the present invention 3, but that for the values of the complex refractive index of the recording layer near a wavelength of 405 nm, the real part was 2.90, and the imaginary part was 0.40, satisfying the conditions of the present invention.
  • the optical recording medium of the present invention has a good sensitivity at a blue laser wavelength or lower, is compatible with high linear velocity recording, and is particularly suitable as a WORM optical recording medium.
  • a sputtering target and a method for manufacturing a sputtering target according to the present invention can improve the film deposition rate for an improvement in productivity, can increase the packing density, providing a high strength during film deposition, and are used suitably in the manufacture of the recording layer of the optical recording medium of the present invention.

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Abstract

L'objet de la présente invention est un support d'enregistrement optique incluant un substrat et, sur le substrat, au moins une couche d'enregistrement qui peut enregistrer et reproduire au moyen de la lumière laser dans une région de longueur d'onde bleue, laquelle couche d'enregistrement inclut Bi et O en tant que principaux composants, et inclut en outre au moins C ou N, et n'inclut pas Fe ; ou un support d'enregistrement optique incluant un substrat et, sur le substrat, au moins une couche d'enregistrement qui contient, en tant que principaux composants, un oxyde de Bi, et une substance simple pour chacun du ou des éléments M (à l'exception de Bi, C et N) qui améliore une fonction d'absorption optique pour une lumière laser d'enregistrement et de reproduction, lequel support d'enregistrement optique peut enregistrer et reproduire au moyen de la lumière laser dans une région de longueur d'onde bleue.
PCT/JP2008/054420 2007-03-28 2008-03-05 Support d'enregistrement optique, cible de pulvérisation et son procédé de fabrication Ceased WO2008126573A1 (fr)

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* Cited by examiner, † Cited by third party
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JP2010111048A (ja) * 2008-11-07 2010-05-20 Ricoh Co Ltd 追記型光記録媒体
CN112543973A (zh) * 2018-08-09 2021-03-23 松下知识产权经营株式会社 信息记录介质及其制造方法

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WO2004027770A1 (fr) * 2002-09-18 2004-04-01 Matsushita Electric Industrial Co., Ltd. Support d'enregistrement optiques d'informations et procede de fabrication
JP2005161831A (ja) * 2003-04-16 2005-06-23 Ricoh Co Ltd 追記型光記録媒体とその記録再生方法
JP2006247897A (ja) * 2005-03-08 2006-09-21 Ricoh Co Ltd 追記型光記録媒体

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WO2004027770A1 (fr) * 2002-09-18 2004-04-01 Matsushita Electric Industrial Co., Ltd. Support d'enregistrement optiques d'informations et procede de fabrication
JP2005161831A (ja) * 2003-04-16 2005-06-23 Ricoh Co Ltd 追記型光記録媒体とその記録再生方法
JP2006247897A (ja) * 2005-03-08 2006-09-21 Ricoh Co Ltd 追記型光記録媒体

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2010111048A (ja) * 2008-11-07 2010-05-20 Ricoh Co Ltd 追記型光記録媒体
CN112543973A (zh) * 2018-08-09 2021-03-23 松下知识产权经营株式会社 信息记录介质及其制造方法
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