Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1999-03-15
2001-09-11
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S277000, C428S064100
Reexamination Certificate
active
06288998
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk having concavities such as pits and grooves and a manufacturing method of an original optical disk for producing such optical disks.
2. Description of Related Art
An optical disk is a recording medium in which information is recorded by pits and phase-change marks which can be read by irradiating a light beam. Such optical disk is drawing much attention as a storage medium having a high density and large capacity memory for use in various information processing systems, including personal computers, and as a recording medium for recording audio and video signals. Presently, research and development to further increase the density and capacity of the optical disks are being actively conducted.
Generally, optical disks are manufactured by creating a stamper from an original disk via a plating step; the steps of duplicating a large number of disk substrates from the stamper by injection molding; and forming a reflection film (such as an aluminum film) or a recording film (such as a phase-change film or a magneto-optic film) on the disk substrate. The original disk is normally created by the steps of: applying a photoresist film on a glass substrate; irradiating an exposing light beam on the photoresist film while being focused by an objective lens; and developing it. Here, pits corresponding to information are formed on the original disk by modulating the intensity of the exposing light beam corresponding to signals of the information to be recorded, and grooves are created on the original disk by irradiating the exposing light beam whose intensity is uniform.
The optical disk, the replica, on which the information is recorded, in the form of pits, may be obtained by creating the stamper from the original disk having the aforementioned pits and by injection molding the reflection film on the disk substrate after transferring the pits on the disk substrate, which made of resin, by using the stamper.
Meanwhile, the replica optical disk having grooves on the recording film for tracking-guiding the light beam may be obtained by creating the grooves on the original disk and by creating the recording film on the disk substrate. In this case, information may be recorded as marks such as phase-change marks on the recording film along the grooves.
The information may be reproduced from the optical disk in which such information is recorded by obtaining reproduced signals by irradiating a reproducing light beam to the optical disk and by detecting reflected lights from the pits and marks by a photodetector.
To increase the density of the optical disk in order to respond to the demand of increased capacity of the optical disk, it is essential that, pits on the optical disk be micronized and the width of a groove be minimized to reduce the track pitch. As for the micronization of pits and groove width in the original optical disk, a micro-processing technology of forming pits and grooves of about 0.2 &mgr;m in width is now being developed by shortening a wavelength of the exposing light beam or by using a technology of exposing using an electron beam.
A micro-pit creating technology using a dry-etching technology is also being developed because very small pitches and marks can be read while suppressing cross talk between the adjacent tracks by sharpening inclination of wall faces of pits and grooves.
FIGS. 6 and 7
show sectional profiles of a pit of an optical disk, in the track width direction, created by an original optical disk produced according to prior art methods. The pit in
FIG. 6
has side walls along the track direction which are relatively mildly inclined, i.e., which are normally tapered (having an inclination by which the closer the bottom side, the narrower the width of an opening becomes). Meanwhile, the pit in
FIG. 7
is normally tapered while having sidewalls along the track direction sharply inclined. The taper having such sharp inclination, as in
FIG. 7
, may be achieved by using dry-etching in developing the photoresist film.
However, when the pits are micronized in order to densify the optical disk, it becomes difficult to mold the optical disk substrate because the fine pits on the original optical disk must be transferred to the optical disk substrate, i.e., a replica, via the stamper. In particular, it causes problems in mass-producing the replicas by injection molding since resin cannot fully enter within the pits when the inclination of the pit side wall is as sharp as shown in FIG.
7
. Thus, not only is the transferability deteriorated but the releaseability of the optical disk substrate from the stamper after the transfer is also adversely affected. These problems apply also to the case of the optical disk whose groove width is reduced.
Furthermore, when a multi-layered recording film is to be formed on this optical disk substrate according to the above-mentioned methods, it becomes difficult for the recording film material to enter within the pits or the grooves to form the recording film when the width of the pit and the groove is narrow and/or the inclination of the side wall is sharp.
As described above, the prior art technology has had the problems of the deterioration of the transferability and the releaseability of the optical disk substrate with respect to the stamper when: pits and grooves are micronized in order to densify the optical disk; the inclination of the side wall of the pit and the groove is sharpened along the side wall; and forming a recording film when the optical disk is a rewritable optical disk; the recording film is a multi-layered film in particular.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a manufacturing method of an optical disk and an original optical disk suitable for mass-producing such optical disks which facilitates the densification of the optical disks by improving the transferability and the releaseability of an optical disk substrate with respect to a stamper.
A first aspect of an inventive optical disk comprises concavities, which constitute pits or grooves, along tracks and which include side walls, along the track direction of the concavity, having inclinations relative a plane parallel to the base of the concavities so that the closer to the bottom side, the narrower a width of an opening in the track width direction of the concavity becomes, and so that the closer to the bottom side, the sharper the inclination becomes and closer the opening edge side, the milder it becomes.
A second aspect of an inventive optical disk comprises concavities which constitute pits or grooves along tracks and which include side walls, along the track direction of the concavity, having inclinations such that the closer to the bottom side, the narrower a width of an opening in the track width direction of the concavity becomes and such that the inclination is composed of a sharper first inclined portion positioned on the bottom side and a second inclined portion whose inclination is milder than that of the first inclined portion and positioned on the opening edge side.
Preferred embodiments of the present invention with respect to the above-mentioned aspects are as follows:
(1) A depth of the first inclined portion and a depth d
2
of the second inclined portion have a relationship of d
1
>d
2
,
(2) A depth d
1
of the first inclined portion and a depth d
2
of the second inclined portion have a relationship of d
1
>2(d
2
).
(3) A depth d
1
of the first inclined portion has a relationship of d
1
=&lgr;(4n), where &lgr; is wavelength of reproducing light beam and n is refractive index of a disk substrate.
(4) The second inclined portion has a curved portion.
A first aspect of an inventive manufacturing method of an original optical disk for manufacturing optical disks in which concavities which constitute pits or grooves along tracks are created comprises steps of forming a photoresist film on a substrate; exposing the photoresist film; creating a first concavity by develop
Kabushiki Kaisha Toshiba
Neyzari Ali
Pillsbury & Winthrop LLP
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