Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
  • C22C5/06—Alloys based on silver
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C5/00—Alloys based on noble metals
• • 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
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
  • C23C14/14—Metallic material, boron or silicon
• • 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
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
  • C23C14/14—Metallic material, boron or silicon
  • C23C14/18—Metallic material, boron or silicon on other inorganic substrates
  • C23C14/185—Metallic material, boron or silicon on other inorganic substrates by cathodic sputtering
• • 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
• • 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
  • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
  • G11B7/258—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of reflective layers
  • G11B7/259—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of reflective layers based on silver
• • 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
• • 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
  • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
  • G11B7/258—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of reflective layers

Definitions

• the present invention relates to a silver alloy suitable as a constituent material for a reflection coating for an optical recording medium, especially to a silver alloy for a reflection coating, which is capable of inhibiting decrease in reflectivity during a long-term service.
• Optical recording media such as CD-ROM, DVD-ROM or the like normally comprise a substrate on which a recording layer, a reflection coating layer and a protective layer (i.e. overcoat) are provided.
• a reflection coating layer an aluminum alloy has been used conventionally from the viewpoint of cost and reflectivity.
• application of materials having higher reflectivity has been demanded as the mainstream of optical recording media shifts to recordable or rewritable ones (CD-R/RW, DVD-R/RW/RAM).
• organic dye materials have been widely used as a constituent material for a recording layer in recordable or rewritable media, and organic dye materials allow extinction of a light beam to become great, so that the extinction should be compensated by improved reflectivity of a reflective layer.
• silver In terms of reflectivity, it is silver that has been applied as a material for a reflective layer in an optical recording medium. Silver is a suitable material in view of higher reflectivity and moderate price compared to gold, which also has higher reflectivity. However, silver has a disadvantage that it is poor in oxidation resistance and sulfur resistance, hence it readily corrodes due to oxydation or sulfuration and will turn black to deteriorate the reflectivity.
• optical recording media to which silver alloy is applied as a reflective layer to increase corrosion resistance while reflectivity is secured.
• Many of these media have adopted silver as a main component, to which one, two or more different additive elements should be added. Specifically, some cases have been disclosed where 5-10 at % ruthenium and 0.1-10 at % aluminum are added to silver, or 0.5-4.9 at % palladium is added. It is further disclosed that these silver alloys have good corrosion resistance and can maintain reflectivity under an operating environment, thereby being suitable as a reflective layer (See Japanese Patent Publication Laid-Open Nos. Hei 11-134715 and 2000-109943 for details of these prior art).
• red semiconductor laser (wavelength of 650 nm) is currently applied as a light source for recording, however practical use of blue laser (wavelength of 405 nm) has been in sight recently.
• Application of blue laser can insure a five- or six-fold storage capacity compared to the present optical recorders, so that it is considered blue laser-applied optical recorders will become mainstream in the next-generation ones.
• the present inventors have confirmed the reflectivity of a reflective layer will fluctuate in accordance with the wavelength of laser to be irradiated, and especially have confirmed irradiation of laser having a short-wavelength will cause deterioration in reflectivity irrespective of presence or absence of corrosion and the deterioration in reflectivity due to corrosion will be prominent more frequently than in a case of irradiation of laser having a long-wavelength.
• irradiation of laser having a short-wavelength will cause deterioration in reflectivity irrespective of presence or absence of corrosion and the deterioration in reflectivity due to corrosion will be prominent more frequently than in a case of irradiation of laser having a long-wavelength.
• the present invention has been made with the above matters as a background, and it relates to a silver alloy composing a reflective layer in an optical recording medium. It is an objective of the invention to provide a material for a reflective layer, capable of serving with the reflectivity kept not deteriorated due to a long-term use. Furthermore, the present invention provides a material having a higher reflectivity with respect to laser beams of short-wavelength.
• the present inventors determined to adopt silver as a main component as had been done in the earlier technologies, and to discover suitable materials for a reflective layer from a different viewpoint from the earlier technologies.
• the reason that silver was selected as a main component is based on consideration of the advantages (higher reflectivity and lower cost) that silver has as discussed above.
• An approach that the present inventors made in a different manner from conventional one was to address the improvement of corrosion resistance only, through adding additive elements as had been done in the earlier technologies. Specifically, corrosion (oxidation) of a reflective layer during use is inevitable in a practical sense.
• the present inventors considered such a silver alloy suitable as a material for a reflective layer if it is not deteriorated in reflectivity when oxidized, while daring to permit oxidation during use.
• the present inventors came up with the present invention through discovering a silver alloy causing no deterioration in reflectivity when oxidized, to which added are/is indium and/or tin which are preferentially oxidized over silver and do not affect the reflectivity.
• the present invention relates to a silver alloy for use in a reflection coating for an optical recording medium, which comprises silver as a main component and indium and/or tin as an additive element.
• Oxides to which indium and/or tin have/has been added as an additive element in the present invention are transparent, as it is understandable from the fact that they have been widely applied as a transparent electrode material thus far.
• the indium and/or tin are/is oxidized during use and the oxide(s) are/is transparent, thereby causing no damage to the reflectivity of the alloy.
• indium oxide and tin oxide are dispersed within the alloy, and an oxide layer composed of indium oxide and tin oxide are formed on the surface of the alloy.
• the oxide layer serves as a protective layer for the alloy against further oxidation, and inhibits the silver to be a base material against oxidation.
• a reflective layer to be formed with the alloy according to the present invention is capable of maintaining a reflectivity with the action described above.
• Some DVD-ROMs among optical recording media have a dual structure, in which the combination of a recording layer and a reflective coating layer have been made dual from the viewpoint of insuring memory capacity.
• the alloy according to the present invention is excellent in transmittance, and applicable to the reflective layers in a DVD-ROM having a dual structure.
• the content of the indium and tin as being additive elements in the present invention will be preferably both 0.1-25 wt % if maintenance of reflectivity should be taken into consideration.
• the reason is that when the added amount is less than 0.1, it is not effective in terms of maintenance of reflectivity, and when the concentration of added elements exceeds 25%, some environments and wavelengths of incident laser beams may substantially reduce the reflectivity, causing a major practical obstacle.
• Especially preferable concentration is 0.1-5.0 wt %. The reason is that, if fallen within the range, the reflectivity can be maintained at higher levels regardless of the environment and wavelength of a laser beam. It should be noted that these ranges of concentration indicate for all the additive elements, and when both indium and tin are contained, it is indicated that the total concentration of each element is within these ranges.
• the silver alloy according to the present invention is suitable as a material for use in a reflective layer for an optical recording medium, and it is enumerated a higher thermal conductivity as a preferable property if provided to a material for an reflective layer.
• the reason is that lower thermal conductivity of a reflective layer will deteriorate the sensitivity of a recording medium.
• the silver alloy according to the present invention which imparts properties preferable in terms of both maintenance of reflectivity and higher thermal conductivity, will be further preferable if it is provided with a concentration of additive elements such as indium and tin 0.1-0.5 wt %.
• the silver alloy according to the present invention can be produced through a melting and casting method. Production through the melting and casting method has no specific difficulties, and the silver alloy can be produced through a common method in which each raw material should be checkweighed, melted and mixed for casting.
• oxygen is mixed with argon gas, which is to be introduced to a sputtering apparatus used in a sputtering method, reactive sputtering is conducted to form the reflective layer while oxidizing the same, thereby forming a protective film at an earlier stage of a reflective layer formation.
• the reactive sputtering may undermine a production efficiency of a reflective layer because it needs subtle adjustment to an introduction of oxygen gas in order to regulate the degree of oxidation of a reflective layer.
• the present inventors came up with an idea that in the present alloy, a normal sputtering process without introduction of oxygen gas, which requires subtle regulation can form a protective film to a reflective layer by preliminarily oxidizing indium and tin as additive elements. That is to say, the present inventors determined to oxide partially or entirely indium and/or tin as additive elements with respect to the silver alloy according to the present invention in which silver is a main component. They discovered a thin film produced with the internally oxidized alloy employed as a target will be formed to have oxides of indium and tin uniformly dispersed compared with the one at the production stage of a thin film.
• Production of the internally oxidized silver alloy can be effected through: producing a silver alloy containing predetermined compositions of indium and/or tin; and pressurizing and heating the silver alloy in a high-pressure oxygen atmosphere to allow the indium and tin in the alloy to be oxidized partially or entirely.
• the pressurization and heating are conducted in an atmosphere of oxygen tension 0.1-1 MPa at 700-800° C. for 60-80 hours.
• the above-described silver alloy according to the present invention has preferable properties as a reflective layer, and has been inhibited from deteriorating in reflectivity during use. Further, the silver alloy shows better reflectivity and maintenance thereof compared to the conventional materials for a reflective layer even under irradiation of laser beams of short wavelength, as described later.
• a sputtering method is generally applied in producing a reflective layer for an optical recording medium.
• the sputtering target comprises of the silver alloy according to the present invention is contributive to production of an optical recording medium provided with a reflective layer having preferable properties.
• a target as a silver alloy composed of Ag, In 1.2 wt %, and Sn 0.8 wt % was produced, and a thin film was formed through sputtering with the use of this target.
• formed thin film was subjected to corrosion tests (acceleration tests) under various environments for studying variations in reflectivity of post corrosion tests.
• each metal was checkweighed to reach a predetermined concentration, and is molten and mixed in a high-frequency melting furnace to prepare an alloy. Then, it was poured into a mold to solidify for preparing an ingot, which was forged, rolled,.heat treated, and formed to produce a target.
• a substrate borosilicate glass
• a target borosilicate glass
• argon gas was introducedintroduced to a level of 5.00 ⁇ 10 ⁇ 1 Pa.
• a film was formed under sputtering conditions with 1 kW of direct-current and time period of 1 minute to make the film thickness 1000 ⁇ . Distribution of the film thickness was confirmed within ⁇ 10%.
• a corrosion test of a thin film was done with the thin film exposed to each environment described below and with the reflectivity of a tested thin film measured while a wavelength was changed with the use of a spectrophotometer, and variation in reflectivity was inspected with the reflectivity of the silver of immediately after film formation standardized.
• the thin film was placed on a hot plate, and was heated in accordance with the above prescribed temperature and duration of time.
• This test environment is for inspecting an oxidization resistance of the thin film.
• the thin film was soaked in pure water of 60° C. This test environment is for inspecting a moisture resistance of the thin film.
• the thin film was soaked in a sodium hydroxide solution of 3% (temperature 30° C.) for 10 minutes.
• This test environment is for inspecting an alkaline resistance of the thin film.
• thin films were produced from three targets composed of silver alloys, specifically of Ag-1.0 wt % Au-1.0 wt % Cu, Ag-1.0 wt % Pd-1.0 wt % Cu, and Ag-1.0 wt % Nd-1.0 wt % Cu, and corrosion tests similar to the above-described one were conducted to measure likewise variations in reflectivity.
• the results of the corrosion tests in this example will be shown in Tables 1 through 3.
• the reflectivity as shown in Tables are relative values when the reflectivity of the silver of immediately after film formation is set to 100. Each measured value represents reflectivity in the wavelengths of 400 nm, 560 nm, and 650 nm (corresponding to the wavelength of blue, yellow, and red laser, respectively.).
• the thin film produced from the silver alloy according to the present example shows higher values than any of the comparative examples in terms of reflectivity.
• the thin film according to the present example maintains the reflectivity of that of immediately after film formation with respect to one tested about corrosion under any environment.
• the comparative examples show fluctuations in reflectivity depending on the environment for the corrosion test. Therefore, it is known that the thin film according to the present invention is a more preferable one as a reflective layer than those according to the conventional technologies.
• the silver alloys produced and employed in this example were Ag—Sn alloys, and silver alloys in which the tin concentration was varied in the ranges between 2-50 wt % were examined.
• the method for producing the silver alloys in this example is the same as that in Example 1, however in terms of the corrosion test environment, a test in which the silver alloys were soaked in a 0.01% sodium sulfide solution (at the temperature of 25° C.) for 1 hour was conducted to examine sulfur resistance, in addition to the test environment of Example 1. Measurement of the reflectivity after the corrosion test was conducted in a similar manner to that in example 1.
• the concentration of the additive element should be preferably 5.0 wt % or lower.
• Example 3 the silver alloys studied in Example 3 have good reflectivity immediately after film formation, however have large variations in reflectivity due to heating in the atmosphere. It is shown a correlation between the concentration of additive elements and reflectivity, and as the concentration of additive elements becomes lower, the reflectivity after heating has a tendency to decrease.
• the acceptance criterion is set to 60, it is understood that the thin film having a concentration of additive elements of less than 0.1 wt % (i.e. 0.05 wt %) can no longer maintain the reflectivity of post-atmospheric oxidization. Therefore, it is considered appropriate to set the lower limit of the concentration of additive elements to 0.1 wt %.
• Table 10 specifically shows each thermal conductivity of three kinds of silver alloys as produced as Comparative Example of Example 1, which are of Ag-1.0 wt % Au-1.0 wt % Cu, Ag-1.0 wt % Pd-1.0 wt % Cu, and Ag-1.0 wt % Nd-1.0 wt % Cu, and the thermal conductivity of thin film of pure silver.
• the Ag—In—Sn alloy thin film according to the present example exhibits thermal conductivity which decreases in proportion to increase in the concentration of additive elements.
• an acceptance line of thermal conductivity is set to be 50% or higher of that of silver, it is considered appropriate to hold the added amount of the additive elements below 0.5 wt % in view of the thermal conductivity.
• concentration of additive elements in terms of two conditions, namely maintenance of reflectivity and high thermal conductivity, ranges 0.1 and 0.5 wt %. It was also confirmed every silver alloy thin film according to Comparative Example has thermal conductivity of less than 50% of that of silver.
• the silver alloy according to the present invention inhibits reduction of reflectivity during use through addition of elements, which generate oxide that causes no adverse effects on reflectivity when get oxidized.
• the present invention can produce a reflective layer less likely to decrease in reflectivity due to long-term use, thereby prolonging the duration of life of an optical recording medium.
• the silver alloy according to the present invention exhibits better reflectivity and maintenance thereof than the conventional materials for a reflective layer even if subjected to irradiation of laser having a short-wavelength
• the present silver alloy is applicable to recording media for optical recorders adopting a short-wavelength laser as a light source and expected to be a future mainstream.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
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• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Inorganic Chemistry (AREA)
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• Optical Record Carriers And Manufacture Thereof (AREA)
• Physical Vapour Deposition (AREA)
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• 2002
  • 2002-12-10 JP JP2002358040A patent/JP2004192702A/ja active Pending
• 2003
  • 2003-12-04 TW TW092134136A patent/TW200419000A/zh unknown
  • 2003-12-09 KR KR1020047012143A patent/KR20050086366A/ko not_active Application Discontinuation
  • 2003-12-09 CN CNB2003801002061A patent/CN1323397C/zh not_active Expired - Lifetime
  • 2003-12-09 WO PCT/JP2003/015696 patent/WO2004053861A1/ja active Application Filing
  • 2003-12-09 AU AU2003289251A patent/AU2003289251A1/en not_active Abandoned
  • 2003-12-09 EP EP03777368A patent/EP1569215A4/en not_active Withdrawn
  • 2003-12-09 US US10/501,751 patent/US20050089439A1/en not_active Abandoned

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