Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2000-09-29
2003-01-21
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C428S064400
Reexamination Certificate
active
06510129
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical recording medium adopting a land and groove recording system and a manufacturing method of a master disk of the optical recording medium which is used to produce a substrate of the medium, and to a cutting device used in the manufacturing method.
BACKGROUND OF THE INVENTION
Conventionally, a magneto-optical disk of a magneto-optical recording system has been used in practical applications as a re-writable optical recording medium. The magneto-optical disk in general has a groove area (area of a guide groove) and a land area (area between the guide grooves) which are formed into a spiral or a concentric circle on a disk substrate, and either of which includes a recording track. Additionally, a light beam emitted from a semiconductor laser is converged and projected onto the recording track, thereby causing a local rise in temperature of the recording track and recording or erasing information. Further, a light beam whose intensity is such that the information is not erased is converged and projected on the recording track, and by recognizing the polarization state of reflected light, the information is reproduced.
Further, among methods of obtaining address information in the magneto-optical disk, a method employing a pit series is commonly adopted. In this method, the pit series is formed continuously on the recording track of the magneto-optical disk, and address information is obtained by reproducing change in quantity of the reflected light from the pit series.
Meanwhile, lively studies and developments with respect to magnetic super resolution reproduction using a multilayer magnetic film have largely been improving a reproducing resolution of the magneto-optical disk of a super resolution magneto-optical recording system, and active research on a system of recording information on both of the groove and land areas (land and groove recording system) has been carried out.
Incidentally, in the land and groove recording system, since the recording track is formed for each of the land and groove areas, address pits which correspond to the respective areas are required.
FIG. 14
is an explanatory drawing showing a structure of a magneto-optical disk substrate disclosed in Japanese Unexamined Patent Publication No. 161077/1995 (Tokukaihei 7-161077 published on Jun. 23,1995). As shown in
FIG. 14
, in this magneto-optical disk substrate, address pits P
1
and P
2
are formed for a spirally formed groove area G and land area L, respectively, which have the same depth from surfaces of the respective areas G and L, thereby obtaining the respective address information of the groove area G and land area L.
Further,
FIG. 15
is an explanatory drawing showing a structure of a magneto-optical disk substrate disclosed in Japanese Unexamined Patent Publication No. 28729/1994 (Tokukaihei 6-28729 published on Feb. 4,1994). In this magneto-optical disk substrate, a series of address pits P
1
having the same depth as that of the groove area G is formed on the groove area G having a spiral shape. On the other hand, on a portion of the land area L away from the portion where the series of address pits P
1
are provided, a series of address pits P
2
having the same depth as that of the groove area G are formed.
By thus forming the series of address pits P
1
and P
2
at separate positions, crosstalk caused by an adjacent address pit can be reduced, thereby obtaining accurate address information.
However, a technique disclosed in the above Publication (Tokukaihei 7-161077) requires two or three types of photoresist having different photosensitivities, and an intermediate layer in a complicated exposing and developing process in order to create the groove and address pits in the magneto-optical disk substrate.
Further, the magneto-optical disk substrate disclosed in the publication (Tokukaihei 6-28729) raises such a problem that, since the address pit and groove have the same depth, a reproduced signal from the address pit becomes small, and address information cannot be reproduced accurately.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical recording medium which is easily manufactured and can accurately reproduce address information, and a manufacturing method of an optical recording medium master disk which is used to produce a substrate (optical recording medium substrate) to be used for the foregoing medium, and a cutting device used in the manufacturing method.
In order to attain the foregoing object, an optical recording medium of the present invention (present recording medium) includes a groove having a first address pit and a land having a second address pit, in which a groove depth d
G
, a first address pit depth d
P1
and a second address pit depth d
P2
are set to satisfy
d
G
<d
P1
≈d
P2
(a).
The present recording medium is an optical recording medium, including an optical disk and a magneto-optical disk such as CD (Compact Disc), for recording and reproducing information by the exposure of a light beam. Moreover, as explained, the present recording medium includes the address pits in both of the groove and land, thereby being an optical recording medium of a land and groove recording system in which both groove and land have the recording tracks.
Particularly, in the present recording medium, as indicated by equation (a) above, the first address pit provided in the groove and the second address pit provided in the land are made deeper than the groove depth. This enables a reproduced signal from these address pits to be intense, thereby reproducing address information accurately and stably.
Further, in the present recording medium, as indicated by equation (a) above, the depth (from the surface of the land) of the first and second address pits are set at values substantially equal to each other. Consequently, these two kinds of address pit can be manufactured by a single manufacturing process, and thus the present recording medium can be manufactured by a relatively facile process.
In order to attain the foregoing object, a manufacturing method (present manufacturing method) of an optical recording medium master disk in which address pits are provided in both of the land and groove, includes the steps of: (a) applying a resist over a master disk substrate; (b) performing exposure and development with respect to the substrate so as to partially maintain the resist in a groove forming area, while avoiding remaining the resist in a pit forming area; (c) etching a surface of the substrate which is uncovered in the pit forming area; (d) uncovering the surface of the substrate in the groove forming area; and (e) etching the surface of the substrate in both of the groove and pit forming areas.
The present manufacturing method is for manufacture of an optical recording medium master disk (hereafter simply referred to as master disk) which is used to manufacture a substrate used in the optical recording medium. Namely, the foregoing substrate of the optical recording medium is manufactured by injection molding of a substrate material such as resin, in which a stamper obtained from the master disk is used as a mold.
Consequently, the master disk has the same arrangement as that of the substrate of the optical recording medium (including a groove, land and address pit, etc.).
Further, as explained, the present manufacturing method is set to manufacture the master disk having the address pits in both of the groove and land. Therefore, the substrate of the optical recording medium which is manufactured from this master disk is to be adopted in an optical recording medium of a land and groove recording system.
Further, the foregoing groove forming area refers to a portion of a master disk substrate (substrate to be the master disk) where the groove is formed, and likewise, the pit forming area refers to a portion of the master disk substrate where the address pit is formed.
Meanwhile, in the present manufacturing method, the step (b) is set such that the resist partially r
Hirokane Junji
Iwata Noboru
Conlin David G.
Dike Bronstein Roberts & Cushman
Dinh Tan
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