Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-10-14
2004-03-02
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S945000, C369S275200, C369S288000, C369S286000, C428S064500
Reexamination Certificate
active
06699637
ABSTRACT:
TECHNICAL FIELD
The present invention relates to phase change optical information recording mediums having a recording layer of changing phase between a crystalline state and an amorphous state in accordance with the intensity of an irradiation beam, and in particular, it relates to a method for producing an optical information recording medium capable of making an initialization process unnecessary.
BACKGROUND ART
Recently, optical information recording mediums have been extensively studied and developed as means for recording, reading and erasing an immense quantity of information. Especially, a so-called phase change optical disk which records/erases information, using the fact that the phase of the recording layer changes reversibly between a crystalline state and an amorphous state, has the advantage that only by changing the laser beam power, old information is erased while new information is being recorded simultaneously (hereinafter referred to as “overwrite”). Thus, such optical disk is regarded as being full of promise.
As the recording materials of such overwritable phase change optical disk, chalcogen alloys are mainly used which include In—Se alloys (see “Appl. Phys. Lett. Vol. 50, p. 667, 1987”), In—Sb—Te alloys (see “Appl. Phys. Lett. Vol. 50, p.16, 1987”), and Ge—Te—Sb alloys (see Japanese Patent Laid-Open Publication Sho No. 62-53886), which have a low melting point and a high absorption efficiency for a laser beam.
When information is actually recorded/erased on/from such optical disk of a chalcogen alloy, at least one kind of dielectric layer of a material selected from the group consisting of metal or semi-metal oxides, carbides, fluorides, sulfides, and nitrides is generally formed directly above and/or under the recording layer in order to prevent the substrate from being deformed due to heat produced on recording/erasing, to prevent the recording layer from being oxidized, and/or to prevent the substances from moving along the guide grooves or from being deformed.
Optical disks having a three- or four-layered structure which includes a recording layer of a chalcogen alloy, a dielectric layer provided directly under and/or above the recording layer, a reflective layer which also acts as a cooling layer (for example, Al-alloy) provided on an opposite side of a transparent substrate from the recording layer, provided on the substrate, are the mainstream of the phase change optical disks because they are preferable in terms of the recording/erasing characteristics.
In general phase change optical disks, when the recording layer is irradiated with a laser beam having a recording power to heat it up to its melting point and is then rapidly cooled, the recording layer material is produced amorphous to thereby form a recording mark. Then, when the recording layer is irradiated with a laser beam having an erasing power to be heated to more than the crystallizing temperature and then gradually cooled, the recording layer material is crystallized to thereby erase the recording mark.
Such phase change optical disks are each produced by sequentially forming thin layers as the respective layers on the substrate by sputtering/evaporation. Since the recording layer present immediately after its layer formation is amorphous, it is irradiated with a laser beam to be wholly crystallized, which is generally referred to as “initialization process”, and the optical disks, thus obtained, are then shipped.
However, this initialization process takes a time of a little less than one minute to initialize the whole optical disk having a diameter of 120 mm even with the use of the most-efficient laser beam irradiation, which leads to an increase in the manufacturing cost of the optical disks. For the time required for processing one optical disk in each manufacturing substep (cycle time), the time required for the initialization process is long compared to the substrate molding step or the layer forming step. Thus, in order to eliminate a time loss taken to pass to the initialization process when the cycle time for the layer forming step is 8 seconds, the six or seven very expensive initializing devices are required. As a result, by performing the initialization process, the manufacturing cost of the optical disks is increased.
In order to reduce the time required for the initialization process, for example, Japanese Patent Laid-Open Publication Hei No. 5-342629 discloses providing an auxiliary layer of an easily crystallizable continuous film or discontinuous island-like film adjacent to the recording layer. As the components of the auxiliary layer, compounds are named which include tellurium (Te), Selenium (Se) or Te—Se compounds.
However, according to this method, the time required for initializing the recording layer is reduced, but the initialization process cannot be eliminated as a rule, excluding the case where both of the auxiliary layer and the recording layer are comprised of extremely easily crystal-growing substances.
It is therefore an object of the present invention to provide an optical information recording medium which eliminates the necessity for the initialization process.
DISCLOSURE OF THE INVENTION
The present invention provides a method for producing an optical information recording medium which has on one side of a substrate a recording layer whose main components comprise germanium (Ge), antimony (Sb) and tellurium (Te) (hereinafter referred to as “Ge—Te—Sb alloy ”), comprising the steps of forming a crystallization assisting layer of materials having a face-centered cubic lattice system crystal structure on one side of the substrate, and forming a recording layer directly above the crystallization assisting layer. According to this method, the recording layer immediately after its formation is crystallized.
The Ge—Te—Sb alloys take two types of crystal phases: namely, a face-centered cubic lattice system crystal structure and a hexagonal system crystal structure. It is known that as the temperature of this alloy is raised from its amorphous state, its phase changes from a face-centered cubic lattice crystal structure to a hexagonal structure. In the present invention, the recording layer is easily crystallized when its layer is formed due to the presence of the crystallization assisting layer having the same face-centered cubic lattice system crystal structure as the recording layer.
The face-centered cubic lattice system crystal structures include face-centered cubic lattices, and face-centered tetragonal lattice; diamond-shape structures: CuAu—, CuPt—, Ni
2
Cr—, Cu
3
Au—, Ni
4
Mo—, Ag
3
Mg—, Ni
3
V—, Cu
3
Pd—, and Au
3
Mn-type superlattices; NaCl—, NaTl—, ZnS—, CaF
2
—, FeS
2
—, cristobalite high-temperature-, Laves phase MgCu
2
—, Cu
3
Au—, Al
3
Ti—, Cu
2
AlMn—, Al
2
MgO
4
—, and Bi
2
Te
3
-type structures; and their interstitial and substitutional solid solutions.
The present invention also provides a method for producing an optical information recording medium having on one side of a substrate a recording layer whose main components comprise germanium (Ge), antimony (Sb) and tellurium (Te), comprising the steps of forming on one side of a substrate a crystallization assisting layer of a tellurium (Te)-free material having a crystal structure of a rhombohedral lattice system, and forming a recording layer directly over the crystallization assisting layer. According to this method, the recording layer becomes crystallized immediately after its formation.
In the present invention, the absolute value of a lattice unconformity between the crystal structure of the crystallization assisting layer and that of the recording layer is preferably not more than 8%. The lattice unconformity is represented by:
Lattice unconformity (%)=((
B−A
)/
A
)×100 (a)
A: When the recording layer is of a face-centered cubic lattice system crystal, an atomic interval in a direction <110> of the crystal;
B: A particular one of the atomic intervals of a crystallized crystallization assisting layer such that the difference between A and the partic
Fujii Atsushi
Ogawa Shuichiro
Takeguchi Keigo
Angebranndt Martin
Asahi Kasei Kabushiki Kaisha
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
LandOfFree
Process for producing optical information recording medium... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing optical information recording medium..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing optical information recording medium... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3247265