WO2007058377A1

WO2007058377A1 - Optical information-recording medium, substrate for optical information-recording medium, stamper, method for producing optical information-recording medium, and method for producing a stamper

Info

Publication number: WO2007058377A1
Application number: PCT/JP2006/323380
Authority: WO
Inventors: Hirokazu Hashimoto; Tomokazu Umezawa
Original assignee: Fujifilm Corporation
Priority date: 2005-11-17
Filing date: 2006-11-16
Publication date: 2007-05-24
Also published as: JP2007141340A; TW200741704A

Abstract

An optical disk (10A) includes a substrate (18) comprising a recording layer (28) and a pregroove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, wherein the pregroove (16) includes a plurality of meandering portions (40). Each of the meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of a land (36), and a second curved portion (46), which is curved toward the land (36) from a second groove (42b) disposed adjacently on the other side of the land (36). An expression, 100 nm < T1 < 200 nm, is satisfied, where T1 represents an amount of protrusion of said first curved portion (44) with respect to said first groove (42a).

Description

DESCRIPTION

OPTICAL INFORMATION-RECORDING MEDIUM, SUBSTRATE FOR OPTICAL INFORMATION-RECORDING MEDIUM, STAMPER,

METHOD FOR PRODUCING OPTICAL INFORMATION-RECORDING MEDIUM, AND METHOD FOR PRODUCING A STAMPER

Technical Field The present invention relates to a heat mode type optical information-recording medium, which is capable of writing (recording) information and reading (reproducing) information using a high energy density laser beam. The present invention also relates to a substrate for an optical information-recording medium, a stamper, a method for producing an optical information-recording medium, and a method for producing a stamper.

Background Art An optical information-recording medium (optical disk), on which information can be recorded by means of a laser beam, has hitherto been known. Known types of optical disks include disks having one information-recording layer and disks having two information-recording layers. The first type of optical disk, which has only one information-recording layer, comprises a substrate with a pregroove formed on the surface thereof, a reflective layer formed along the surface of the substrate, an information- recording layer formed on the reflective layer, and a protective layer formed on the information-recording layer.

The second type of optical disk, which has two information-recording layers, comprises a substrate with a first pregroove formed on the surface thereof, a semitransparent reflective layer formed along concave/convex portions of the surface of the substrate, a first information-recording layer formed on the semitransparent reflective layer, an intermediate layer formed on the first information-recording layer and further having concave/convex portions formed on the surface thereof, a second information-recording layer formed along the concave/convex portions on the surface of the intermediate layer, a reflective layer formed on the second information- recording layer, and a protective layer formed on the reflective layer (see, for example, Japanese Laid-Open Patent Publication No. 2005-4808, Japanese Laid-Open Patent Publication No. 10-283682, and Japanese Laid-Open Patent Publication No. 8-203125). The reflective layer is formed along concave/convex portions of the intermediate layer. Accordingly, the concave/convex portions of the reflective layer function as a second pregroove of the second information-recording layer. Address pits, which are provided to detect addresses, are formed in the pregroove of the first optical disk, as well as in the first and second pregrooves of the second optical disk. Further, servo prepits, which are provided to enable servo control of a spindle motor, tracking control of a pickup, and focusing control, also are formed in the pregrooves . The pregroove of the first optical disk, as well as the first and second pregrooves of the second optical disk, are wobbled in some cases (see, for example, Japanese Laid-Open Patent Publication No. 9-219024). When the pregrooves are subjected to wobbling, it is possible to provide sector management information, such as sector addresses, and/or it is possible to obtain rotational control information, which is used during recording by performing reproduction from the wobbled pregroove. Therefore, it is unnecessary to provide any exclusive address pits or servo prepits, and it is possible to improve data writing efficiency equivalently to the case of having the aforementioned address pits and servo prepits. Further, an advantage is also obtained in that a system such as CLV rotational control, which is effective when continuous data writing is performed, can be adopted. When information is recorded on the information- recording layer of the first optical disk, a laser beam is radiated in a direction oriented from an end surface of the substrate toward the information-recording layer, wherein the laser beam is focused on the information-recording layer in order to record information.

When information is recorded on the first information- recording layer of the second optical disk, a laser beam is radiated in a direction oriented from an end surface of the substrate toward the first information-recording layer, wherein the laser beam is focused on the first information- recording layer in order to record information. Similarly, when information is recorded on the second information- recording layer, the laser beam is radiated in a direction oriented from an end surface of the substrate toward the second information-recording layer, wherein the laser beam is focused on the second information-recording layer in order to record information.

When information is recorded on the information- recording layer of the first optical disk, and on the first information-recording layer of the second optical disk, the pregroove and the information-recording layer (first information-recording layer) are formed in this order, as viewed in a direction in which the laser beam is radiated. Therefore, when the pregroove and the first pregroove are subjected to wobbling, the wobbling shape thereof can reliably be detected by the reproducing laser beam. Similarly, when address prepits and servo prepits are formed on the pregroove and the first pregroove, such prepits can reliably be detected by the reproducing laser beam.

However, when information is recorded on the second information-recording layer of the second optical disk, the second information-recording layer and the second pregroove are formed in this order, as viewed in the direction in which the laser beam is radiated. Therefore, when the second pregroove is subjected to wobbling, an inconvenience arises in that a portion of the wobbling shape is hidden by the pits recorded on the second information-recording layer, such that the reproducing laser beam cannot reliably detect the wobbling shape. Similarly, when address prepits and servo prepits are formed on the pregroove and the first pregroove, a problem arises in that such prepits are hidden by the pits recorded on the second information-recording layer, and hence the reproducing laser beam cannot reliably detect the prepits.

Disclosure of Invention

The present invention has been made taking the foregoing problems into consideration, wherein an object of the invention is to provide an optical information-recording medium, which still includes a substrate comprising a recording layer and a groove formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein a meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer.

Another object of the present invention is to provide a substrate for an optical information-recording medium, wherein the substrate enables the optical information- recording medium to be fabricated with ease, wherein a meandering portion of a groove can reliably be detected, and information can be stably recorded on a recording layer. Still another object of the present invention is to provide a stamper that facilitates easy manufacturing of an optical information-recording medium, wherein a meandering portion of a groove can reliably be detected, and information can be stably recorded on a recording layer. Still another object of the present invention is to provide a method for producing an optical information- recording medium, as well as a method for producing a stamper, in which the optical information-recording medium can be manufactured with ease, wherein a meandering portion of a groove can reliably be detected, and information can be stably recorded on a recording layer.

According to the first embodiment of the present invention, there is provided an optical information- recording medium having a substrate comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied:

100 nm < Tl < 200 nm where Tl represents an amount of protrusion of the first curved portion with respect to the first groove.

Further, according to the second embodiment of the present invention, there is provided a optical information- recording medium having a substrate comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied: 2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nm² where Al represents an area of protrusion of the first curved portion with respect to the first groove.

In each of the optical information-recording medium according to the first and second embodiments of the present invention, the meandering portions of the groove can reliably be detected, and information can be stably recorded on the recording layer, even in cases where the optical information-recording medium includes a substrate comprising the recording layer and the groove formed in this order, as viewed in a direction in which the recording and/or reproducing laser beam is radiated.

In each of the first and second embodiments of the present invention, it is also preferable that the following expressions are satisfied: 350 nm ≤ Wg ≤ 460 nm 700 nm ≤ Lw ≤ 1,000 nm 700 nm ≤ Wp ≤ 1,000 nm where Wg represents a width of the land, Lw represents a length of the meandering portion, and Wp represents a distance from an apex of the first curved portion to an apex of the second curved portion of the meandering portion. In each of the first and second embodiments of the present invention, another substrate may be stacked on the substrate with an intermediate layer intervening therebetween, wherein the other substrate comprises a groove and a recording layer, which are formed in this order as viewed in the direction in which the laser beam is radiated.

In this arrangement, the other substrate, the intermediate layer, and the substrate may be stacked in this order, as viewed in a direction in which the laser beam is radiated. Alternatively, the optical information-recording medium may have a substrate comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied: 0.8 < T1/T2 < 2.0 where Tl represents an amount of protrusion of the first curved portion with respect to the first groove, and T2 represents an amount of protrusion of the second curved portion with respect to the land. According to the third embodiment of the present invention, there is provided a substrate for an optical information-recording medium comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions , and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied:

100 nm < Tl < 200 nm wherein Tl represents an amount of protrusion of the first curved portion with respect to the first groove.

Further, according to the fourth embodiment of the present invention, there is provided a substrate for an optical information-recording medium comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied:

2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nm² where Al represents an area of protrusion of the first curved portion with respect to the first groove. Accordingly, an optical information-recording medium can be fabricated with ease, having a substrate comprising a recording layer and a groove formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein a meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer.

Alternatively, the substrate for the optical information-recording medium may comprise a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied:

0.8 < T1/T2 < 2.0 where Tl represents an amount of protrusion of the first curved portion with respect to the first groove, and T2 represents an amount of protrusion of the second curved portion with respect to the land.

According to the fifth embodiment of the present invention, there is provided a stamper for producing a substrate for an optical information-recording medium comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied: 100 nm < Tl < 200 nm where Tl represents an amount of protrusion of the first curved portion with respect to the first groove. According to the sixth embodiment of the present invention, there is provided a stamper for producing a substrate for an optical information-recording medium comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied:

2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nm² where Al represents an area of protrusion of the first curved portion with respect to the first groove.

Accordingly, an optical information-recording medium can easily be manufactured having a substrate comprising a recording layer and a groove formed in this order as viewed in the direction in which a recording and/or reproducing laser beam is radiated, wherein a meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer.

Alternatively, the stamper for producing a substrate for an optical information-recording medium may comprise a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein the groove includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is- curved toward a first groove disposed adjacently on one side of a- land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied: 0.8 < T1/T2 < 2.0 where Tl represents an amount of protrusion of the first curved portion with respect to the first groove, and T2 represents an amount of protrusion of the second curved portion with respect to the land.

According to the seventh embodiment of the present invention, there is provided a method for producing an optical information-recording medium comprising a first substrate, an intermediate layer, and a second substrate, which are stacked in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, the method comprising the steps of manufacturing the first substrate formed with a groove and a land using a first stamper, forming a recording layer on a surface of the first substrate on which the groove and the land are formed, manufacturing the second substrate formed with a groove and a land using a second stamper, and forming a recording layer on a surface of the second substrate on which the groove and the land are formed, wherein the groove, which is formed on the second substrate when the second substrate is manufactured using the second stamper, includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of the land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied: 100 nm < Tl < 200 nm where Tl represents an amount of protrusion of the first curved portion with respect to the first groove.

Further, according to the eighth embodiment of the present invention, there is provided a method for producing an optical information-recording medium comprising a first substrate, an intermediate layer, and a second substrate, which are stacked in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, the method comprising the steps of manufacturing the first substrate formed with a groove and a land using a first stamper, forming a recording layer on a surface of the first substrate on which the groove and the land are formed, manufacturing the second substrate formed with a groove and a land using a second stamper, and forming a recording layer on a surface of the second substrate on which the groove and the land are formed, wherein the groove, which is formed on the second substrate when the second substrate is manufactured using the second stamper, includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of the land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied:

Accordingly, an optical information-recording medium can easily be manufactured, having a substrate comprising a recording layer and a groove formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein a meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer.

Alternatively, the method for producing the optical information-recording medium comprising a first substrate, an intermediate layer, and a second substrate, which are stacked in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, may comprise the steps of manufacturing the first substrate formed with a groove and a land using a first stamper, forming a recording layer on a surface of the first substrate on which the groove and the land are formed. manufacturing the second substrate formed with a groove and a land using a second stamper, and forming a recording layer on a surface of the second substrate on which the groove and the land are formed, wherein the groove, which is formed on the second substrate when the second substrate is manufactured using the second stamper, includes a plurality of meandering portions, and each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of the land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land, and wherein the following expression is satisfied: 0.8 < T1/T2 < 2.0 where Tl represents an amount of protrusion of the first curved portion with respect to the first groove, and T2 represents an amount of protrusion of the second curved portion with respect to the land.

According to the ninth embodiment of the present invention, there is provided a method for producing a stamper for manufacturing a substrate for an optical information-recording medium comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, the method comprising the steps of manufacturing the stamper having concave/convex portions formed on a surface thereof by selectively applying etching to a stamper master plate, wherein the concave/convex portions are shaped so that the groove is transferred to the substrate when the substrate is manufactured using the stamper, and wherein the groove satisfies the following features :

( 1 ) the groove includes a plurality of meandering portions ;

(2) each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land; and

(3) the following expression is satisfied: 100 nm < Tl < 200 nm where Tl represents an amount of protrusion of the first curved portion with respect to the first groove.

Further, according to the tenth embodiment of the present invention, there is provided a method for producing the stamper for manufacturing a substrate for an optical information-recording medium comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, the method comprising the step of manufacturing the stamper having concave/convex portions formed on a surface thereof by selectively applying etching to a stamper master plate, wherein the concave/convex portions are shaped so that the groove is transferred to the substrate when the substrate is manufactured using the stamper, and wherein the groove satisfies the following features:

(1) the groove includes a plurality of meandering portions ;

(3) the following expression is satisfied: 2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nm² where Al represents an area of protrusion of the first curved portion with respect to the first groove.

Accordingly, an optical information-recording medium can be easily manufactured, having a substrate comprising a recording layer and a groove formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated, wherein a meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer.

Alternatively, the method for producing the stamper for manufacturing a substrate for an optical information- recording medium comprising a recording layer and a groove, which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam is radiated. may comprise the step of manufacturing the stamper having concave/convex portions formed on a surface thereof by selectively applying etching to a stamper master plate, wherein the concave/convex portions are shaped so that the groove is transferred to the substrate when the substrate is manufactured using the stamper, and wherein the groove satisfies the following features:

(1) the groove includes a plurality of meandering portions; (2) each of the meandering portions includes a first curved portion, which is curved toward a first groove disposed adjacently on one side of a land, and a second curved portion, which is curved toward the land from a second groove disposed adjacently on the other side of the land; and

(3) the following expression is satisfied: 0.8 < T1/T2 < 2.0 where Tl represents an amount of protrusion of the first curved portion with respect to the first groove, and T2 represents an amount of protrusion of the second curved portion with respect to the land.

As explained above, according to the optical information-recording medium of the present invention, the meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer, even in cases where the optical information-recording medium includes a substrate comprising the recording layer and the groove formed in this order, as viewed in a direction in which the recording and/or reproducing laser beam is radiated.

With the substrate for the optical information- recording -medium according to the present invention, an optical information-recording medium can be easily fabricated having the substrate comprising the recording layer and the groove formed in this order, as viewed in the direction in which the recording and/or reproducing laser beam is radiated, wherein the meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer.

Further, according to the stamper of the present invention, an optical information-recording medium can be provided having the substrate comprising the recording layer and the groove formed in this order, as viewed in the direction in which the recording and/or reproducing laser beam is radiated, wherein the meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer.

Still further, in the method for producing the optical information-recording medium, as well as the method for producing the stamper, according to the present invention, an optical information-recording medium can be easily manufactured having the substrate comprising the recording layer and the groove formed in this order, as viewed in the direction in which the recording and/or reproducing laser beam is radiated, wherein the meandering portion of the groove can reliably be detected, and information can be stably recorded on the recording layer.

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.

Brief Description of Drawings

FIG. 1 is a sectional view illustrating, with partial omission, an optical disk according to a first embodiment;

FIG. 2 is a sectional view illustrating a first substrate; FIG. 3 is a sectional view illustrating a second substrate;

FIG. 4 illustrates the shape of a meandering portion formed on a second pregroove;

FIG. 5 illustrates the steps of a method for producing the optical disk according to the first embodiment;

FIG. 6 is a sectional view illustrating, with partial omission, an optical disk according to a second embodiment; FIG. 7 illustrates the steps of a method for producing the optical disk according to the second embodiment; and FIG. 8 is a table illustrating the results of an evaluation concerning the aperture ratio (AR) and a PI error (PIE), corresponding to Examples 1 through 5 and Comparative Examples 1 and 2.

Best Mode for Carrying Out the Invention

An explanation shall be given below with reference to FIGS. 1 to 8, concerning exemplary embodiments in which an optical information-recording medium, a substrate for the optical information-recording medium, a stamper, a method for producing the optical information-recording medium, and a method for producing the stamper according to the present invention, are applied to optical disks having two information-recording layers.

At first, as shown in FIG. 1, an optical disk 1OA according to a first embodiment comprises a first substrate 14, which has a first pregroove 12 formed on the surface thereof, and a second substrate 18, which has a second pregroove 16 formed on the surface thereof. The first substrate 14 and the second substrate 18 are stuck to one another, with an intermediate layer 20 intervening therebetween. That is, as shown in FIG. 2, a first information- recording layer 22 is formed on the surface of the first substrate 14 along concave/convex portions of the first pregroove 12. A semitransparent reflective layer 24 is formed on the first information-recording layer 22. As shown in FIG. 3, a reflective layer 26 is formed on the surface of the second substrate 18 along concave/convex portions of the second pregroove 16. A second information- recording layer 28 is formed on the reflective layer 26, and a barrier layer 30 is formed on the second information- recording layer 28.

When the first substrate 14 and the second substrate 18 are bonded to one another, as shown in FIG. 1, the first information-recording layer 22 formed on the first substrate 14 is opposed to the second information-recording layer 28 formed on the second substrate 18. Further, the first substrate 14 and the second substrate 18 are bonded to one another with the intermediate layer 20 intervening therebetween. Accordingly, the optical disk 1OA according to the first embodiment is constructed and completed in this manner.

When information is recorded on the first information- recording layer 22, the recording laser beam 32 is radiated in a direction oriented from the end surface 14a of the first substrate 14 toward the first information-recording layer 22, whereby the recording laser beam 32 is focused on the first information-recording layer 22 to record the information (as pits) therein. During this procedure, information is recorded in portions of the first information-recording layer 22, corresponding to the groove 34 of the first pregroove 12. A semiconductor laser beam, which has an oscillation wavelength within a range of 600 nm to 700 nm (preferably 620 to 680 nm, and more preferably 630 to 660 nm) , is used as the recording laser beam 32.

When information is recorded on the second information- recording layer 28, the recording laser beam 32 is radiated in a direction oriented from the end surface 14a of the first substrate 14 toward the second information-recording layer 28, whereby the recording laser beam 32 is focused on the second information-recording layer 28 to record the information (as pits) therein. During this procedure, information is recorded in portions of the second information-recording layer 28, corresponding to the land 36 of the second pregroove 16. Therefore, when the intermediate layer 20 intervenes between the first information-recording layer 22 and the second information-recording layer 28, it is possible to avoid interference between the information recorded on the first information-recording layer 22 and the information recorded on the second information-recording layer 28. Hence, when the information is reproduced, satisfactory recording reproduction signals can be obtained from the first information-recording layer 22 and the second information-recording layer 28. Recording of information on the first information- recording layer 22 is of a form such that the first pregroove 12 and the first information-recording layer 22 are formed in this order, as viewed in a direction in which the laser beam 32 is radiated. Therefore, when the first pregroove 12 is subjected to wobbling (i.e., when a wobbling process is performed on the first pregroove 12), the wobbling shape can reliably be detected by the reproducing laser beam (i.e., the laser beam used when reproducing information) .

On the other hand, recording of information on the second information-recording layer 28 is of a form such that the second information-recording layer 28 and the second pregroove 16 are formed in this order, as viewed in a direction in which the laser beam 32 is radiated. Therefore, if the second pregroove 16 is subjected to wobbling (i.e., if a wobbling process is performed on the second pregroove 16), a portion of the wobbling shape becomes hidden by pits recorded on the second information- recording layer 28. An inconvenience arises in some cases, such that it is impossible for the reproducing laser beam to reliably detect the wobbling shape. Accordingly, in the case of the optical disk 1OA according to the first embodiment, the shape of the second pregroove 16, which is formed on the surface of the second substrate 18, is constructed so that the wobbling shape of the second pregroove 16 can reliably be detected. Of course, the shape of the first pregroove 12 formed on the surface of the first substrate 14 may be constructed in the same manner.

That is, as shown in FIG. 4, the second pregroove 16 includes a plurality of meandering portions 40, as illustrated by a magnified portion of the second pregroove 16. FIG. 4 representatively shows one such meandering portion 40. Further, FIG. 4 shows one land 36, and a first groove 42a and a second groove 42b, which are arranged on both sides of the land 36.

Each of the meandering portions 40 (one of which is shown in FIG. 4) includes a first curved portion 44, which is curved toward the first groove 42a disposed adjacently on one side of the land 36, and a second curved portion 46, which is curved toward the land 36 from the second groove 42b disposed adjacently on the other side of the land 36.

The meandering portion 40 is formed to satisfy the following expression, where Tl represents an amount of protrusion of the first curved portion 44 with respect to the first groove 42a.

100 nm < Tl < 200 nm -..(1)

Alternatively, the meandering portion 40 may be formed to satisfy the following expression, where Al represents an area of protrusion (area indicated by hatched lines) of the first curved portion 44 with respect to the first groove 42a.

2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nm² ...(2) Of course, the meandering portion 40 may be formed to satisfy both the above expressions (1) and (2).

The meandering portion 40 may also be formed to satisfy the following expression, where Tl represents an amount of protrusion of the first curved portion 44 with respect to the first groove 42a, and T2 represents an amount of protrusion of the second curved portion 46 with respect to the land 36. 0.8 < T1/T2 < 2.0 ... (3)

In this arrangement, the meandering portion 40 may be formed such that expressions (2) and (3) are satisfied, such that expressions (1) and (3) are satisfied, or such that expressions (1), (2), and (3) are satisfied.

It is further preferable that the following expressions are satisfied, where Wg represents a width of the land 36, Lw represents a length of the meandering portion 40, and Wp represents a distance from the apex of the first curved portion 44 to the apex of the second curved portion 46 of the meandering portion 40.

350 nm ≤ Wg ≤ 460 nm ...(4)

700 nm ≤ Lw ≤ 1,000 nm ...(5)

700 nm < Wp ≤ 1,000 nm ...(6) Accordingly, the meandering portion 40 of the second pregroove 16 can reliably be detected, and information can be stably recorded on the second information-recording layer 28, even in cases where the optical disk 1OA comprises the second information-recording layer 28 and the second pregroove 16 formed in this order, as viewed in the direction in which the recording and/or reproducing laser beam 32 is radiated.

An explanation shall now be made, with reference to FIGS. 1 to 3 and FIG. 5, concerning a method for producing the optical disk 1OA according to the first embodiment.

First, referring to FIG. 5, in Step Sl, a first stamper for manufacturing the first substrate 14 is manufactured. In this procedure, the first stamper, having concave/convex portions on the surface thereof, is manufactured by selectively applying etching to a first master plate, to thereby provide the first stamper. The first stamper is manufactured, for example, such that the first master plate is subjected to highly accurate mastering by means of cutting using a DUV (deep ultraviolet light having a wavelength of not more than 330 nm) or an EB (electron beam) process . During this procedure, mastering is applied to the first master plate, in order to manufacture the first stamper. Using the first stamper, as finally produced, the first pregroove 12 is formed on the surface of the first substrate 14 when the first substrate 14 is formed by means of, for example, injection molding or extrusion molding with a resin material.

On the other hand, in Step S2 of FIG. 5, a second stamper for manufacturing the second substrate 18 is manufactured. In this procedure, the second stamper, having concave/convex portions on the surface thereof, is manufactured by selectively applying etching to a second master plate, to thereby provide the second stamper. The second stamper also is manufactured, for example, such that the second master plate is subjected to highly accurate mastering by means of cutting using a DUV (deep ultraviolet light having a wavelength of not more than 330 nm) or an EB (electron beam) process. During this procedure, mastering is applied to the second master plate, in order to manufacture the second stamper. Using the second stamper, as finally produced, the second pregroove 16 having a meandering portion 40, which satisfies at least expression (1) or (2) described above, and preferably which satisfies expressions (4) to (6) as well, is formed on the surface of the second substrate 18 when the second substrate 18 is formed by means of, for example, injection molding or extrusion molding with a resin material.

Subsequently, in Step S3 of FIG. 5, for example, a resin material such as polycarbonate is subjected to injection molding with respect to the first stamper, thereby manufacturing the first substrate 14. During this procedure, the concave/convex portions of the first stamper are transferred onto the surface of the first substrate 14, in order to form the first pregroove 12.

On the other hand, in Step S4 of FIG. 5, for example, a resin material such as polycarbonate is subjected to injection molding or extrusion molding with respect to the second stamper, thereby manufacturing the second substrate 18. During this procedure, the concave/convex portions of the second stamper are transferred onto the surface of the second substrate 18, in order to form the second pregroove 16, which satisfies at least expression (1) or (2) described above, and preferably which satisfies expressions (4) to (6) as well. In the example described above, injection molding or extrusion molding is performed with a resin material, such as polycarbonate, in order to manufacture the first substrate 14 and the second substrate 18. However, as described below, pregroove layers may be formed on the surfaces of the first substrate 14 and the second substrate 18, which are made into flat surfaces respectively, in order to form the first pregroove 12 and the second pregroove 16. As for the material for such pregroove layers , it is possible to use a mixture of a photopolymerization initiator and at least one monomer (or oligomer) from among a monoester, diester, triester, and tetraester of an acrylic acid. The pregroove layer is formed as follows, for example, in relation to the first substrate 14. Specifically, a mixed liquid, composed of an acrylic acid ester and a photopolymerization initiator, is applied onto the first stamper, and further, the first substrate 14 is placed on the applied liquid layer. Thereafter, ultraviolet light is radiated via the first substrate 14 or the first stamper, so as to cure the applied layer by the ultraviolet light, so that the first substrate 14 and the applied layer are secured to one another. Subsequently, the first substrate 14 is exfoliated from the first stamper. Accordingly, the first substrate 14 having the pregroove layer secured thereon can be obtained, wherein the first pregroove 12 is formed on the surface thereof. An equivalent procedure may be used for manufacturing the second substrate 18. Similarly, when the second stamper is used, the second substrate 18 having the pregroove layer secured thereon can be obtained, wherein the second pregroove 16 is formed on the surface thereof. Subsequently, in Step S5 of FIG. 5, the first information-recording layer 22 is formed on the surface of the first substrate 14, and then, the semitransparent reflective layer 24 is formed on the first information- recording layer 22. On the other hand, in Step S6 of FIG. 5, the reflective layer 26 is formed on the surface of the second substrate 18, and then, the second information-recording layer 28 is formed on the reflective layer 26. Further, the barrier layer 30 is formed on the second information-recording layer 28.

Subsequently, in Step S7 of FIG. 5, the first substrate 14 and the second substrate 18 are bonded to one another. In this procedure, the first information-recording layer 22 formed on the first substrate 14 is opposed to the second information-recording layer 28 formed on the second substrate 18. Further, the first substrate 14 and the second substrate 18 are bonded to one another while providing the intermediate layer 20, which intervenes between the first substrate 14 and the second substrate 18. As a result of such bonding, the optical disk 1OA, according to the first embodiment of the invention, is completed.

When the optical disk 1OA is produced using the second stamper and the second substrate 18 as described above, the optical disk 1OA according to the first embodiment, comprising the second information-recording layer 28 and the second pregroove 16 formed in this order as viewed in the direction in which the recording and/or reproducing laser beam 32 is radiated, can be easily produced, wherein the meandering portion 40 of the second pregroove 16 can reliably be detected, and information can be stably recorded on the second information-recording layer 28. Preferably, the optical disk may be used as a DVD-R or DVD+R type disk. In this arrangement, the groove is subjected to wobbling at 100 to 200 kHz in the case of a DVD-R disk, whereas the groove is subjected to wobbling at 800 to 900 kHz in the case of a DVD+R disk. Next, an explanation shall be made, with reference to

FIG. 6, concerning an optical disk 1OB according to a second embodiment .

The optical disk 1OB according to the second embodiment is constructed approximately in the same manner as the optical disk 1OA according to the first embodiment described above. However, the optical disk 1OB differs from the optical disk 1OA in that the surface of the second substrate 18 is a flat surface, the concave/convex portions are formed instead at an interface between the intermediate layer 20 and the barrier layer 30, and the concave/convex portions are reflected by the surface of the reflective layer 26 to function as the second pregroove 16 of the second information-recording layer 28. Further, the optical disk 1OB also differs from the optical disk 1OA in that an adhesive layer 48 is interposed between the reflective layer 26 -and the second substrate 18. Also; in the case of the optical disk 1OB according to the second embodiment, the optical disk still comprises the second information-recording layer 28 and the second pregroove 16 formed in this order, as viewed in the direction in which the recording and/or reproducing laser beam 32 is radiated, whereby the meandering portion 40 of the second pregroove 16 can reliably be detected, and information can be stably recorded on the second information-recording layer 28. However, in view of performance, the optical disk 1OA according to the first embodiment is considered more preferable.

An explanation shall now be made with reference to FIGS. 6 and 7, concerning the method for producing the optical disk 1OB according to the second embodiment.

First, in Step SlOl of FIG. 7, a first stamper for manufacturing the first substrate 14 is manufactured. The procedure, which is the same as or equivalent to the procedure performed in Step Sl of FIG. 5 described above, is performed in Step SlOl. Therefore, duplicate explanations thereof shall be omitted. On the other hand, in Step S102 of FIG. 7, a second stamper for manufacturing the second substrate 18 is manufactured. In this procedure, the second stamper is manufactured so that the surface of the second substrate 18 will have a flat surface when the second substrate 18 is formed, for example, by means of injection molding with a resin material utilizing the second stamper. Further, in Step S103 of FIG. 7, a third stamper, which is used to form the concave/convex portions on the surface of the intermediate layer 20, is manufactured. In this procedure, the third stamper, having concave/convex portions on the surface thereof, is manufactured by selectively applying etching to a third master plate, to thereby provide the third stamper. The third stamper is manufactured, for example, such that the third master plate is subjected to highly accurate mastering by means of cutting using a DUV (deep ultraviolet light having a wavelength of not more than 330 nm) or an EB (electron beam) process.

During this procedure, mastering is applied to the third master plate, in order to manufacture the third stamper. Using the third stamper, as finally produced, the second pregroove 16 having a meandering portion 40, which satisfies at least expression (1) or (2) described above, and preferably which satisfies expressions (4) to (6) as well, is formed on the surface of the reflective layer 26 when the concave/convex portions are formed on the surface of the intermediate layer 20, and the barrier layer 30, the second information-recording layer 28, and the reflective layer 26 are formed on the intermediate layer 20.

Subsequently, in Step S104 of FIG. 7, a resin material is subjected to injection molding or extrusion molding with respect to the first stamper, thereby manufacturing the first substrate 14. During this procedure, the concave/convex portions of the first stamper are transferred onto the surface of the first substrate 14 in order to form the first pregroove 12.

On the other hand, in Step S105 of FIG. I₁ a resin material is subjected to injection molding or extrusion molding with respect to the second stamper, thereby manufacturing the second substrate 18. During this procedure, the second substrate 18 (see FIG. 6), which has a flat surface, is manufactured.

Substantially, in Step S106 of FIG. 7, the first information-recording layer 22 is formed on the surface of the first substrate 14. Thereafter, the semitransparent reflective layer 24 is formed on the first information- recording layer 22, and the intermediate layer 20 is formed on the semitransparent reflective layer 24.

Subsequently, in Step S107 of FIG. 7, the third stamper is pressed against the intermediate layer 20 formed on the first substrate 14. During this procedure, the concave/convex portions of the third stamper are transferred onto the surface of the intermediate layer 20.

Subsequently, in Step S108 of FIG. 7, the barrier layer 30 is formed on the intermediate layer 20, and then, the second information-recording layer 28 is formed on the barrier layer 30. Further, the reflective layer 26 is formed on the second information-recording layer 28. During this procedure, the reflective layer 26 is formed while reflecting the concave/convex portions of the intermediate layer 20. The second pregroove 16 is formed, which has a meandering portion 40 satisfying at least expression (1) or (2), and preferably satisfying expressions (4) to (6) as well .

Subsequently, in Step S109 shown in FIG. 7, the adhesive layer 48 is formed on the reflective layer 26, and then, the second substrate 18 is bonded to the adhesive layer 48, whereby the optical disk 1OB according to the second embodiment is completed.

When the optical disk 1OB is produced using the third stamper as described above, the optical disk 1OB according to the second embodiment, as an optical disk comprising the second information-recording layer 28 and the second pregroove 16 formed in this order as viewed in the direction in which the recording and/or reproducing laser beam 32 is radiated, can be easily produced, wherein the meandering portion 40 of the second pregroove 16 can reliably be detected, and information can be stably recorded on the second information-recording layer 28.

Next, an explanation shall be made concerning exemplary materials utilized for the respective layers making up the optical disks 1OA and 1OB according to the first and second embodiments .

At first, various materials may arbitrarily be selected and used, which have been used as materials for substrates in conventional optical disks, as the materials for fabricating the first substrate 14 and the second substrate 18. Examples thereof are glass, acrylic resins such as polycarbonate and polymethyl methacrylate, vinyl chloride- based resins such as polyvinyl chloride and vinyl chloride copolymer, epoxy resins, amorphous polyolefin, polyester, and metals such as aluminum. These materials may be used in combination if desired.

Among the materials described above, it is preferable to use thermoplastic resins, such as amorphous polyolefin and polycarbonate, taking into consideration, for example, humidity resistance, size stability, and low price. Polycarbonate is particularly preferable.

When the aforementioned resins are used, the first substrate 14 and the second substrate 18 can be manufactured by means of injection molding.

The thickness of each of the first substrate 14 and the second substrate 18 is within a range of 0.7 to 2 mm. Such thickness is preferably within a range of 0.9 to 1.6 mm, and more preferably within a range of 1.0 to 1.3 mm.

Preferably, the upper limit value should not exceed 500 nm for the track pitch of each of the first pregroove 12, which is formed on the first substrate 14, and the second pregroove 16, which is formed on the second substrate 18. More preferably the upper limit value should not exceed 420 nm, even more preferably should not exceed 370 nm, and even more preferably should not exceed 330 nm. On the other hand, the lower limit value preferably should not be less than 50 nm, more preferably should not be less than 100 nm, even more preferably should not be less than 200 nm, and even more preferably should not be less than 260 nm.

As for the width (half value width) of each of the first pregroove 12 and the second pregroove 16, the upper limit value thereof should preferably not exceed 250 nm, more preferably should not exceed 200 nm, even more preferably should not exceed 170 nm, and even more preferably should not exceed 150 nm. On the other hand, the lower limit value preferably should not be less than 23 nm, more preferably should not be less than 50 nm, even more preferably should not be less than 80 nm, and even more preferably should not be less than 100 nm.

The upper limit value of the (groove) depth of each of the first pregroove 12 and the second pregroove 16 preferably should not exceed 150 nm, more preferably should not exceed 100 nm, even more preferably should not exceed 70 nm, and even more preferably should not exceed 50 nm. On the other hand, the lower limit value preferably should not be less than 5 nm, more preferably should not be less than 10 nm, even more preferably should not be less than 20 nm, and even more preferably should not be less than 28 nm.

The upper limit value of the angle of each of the first pregroove 12 and the second pregroove 16 preferably should not exceed 80° . more preferably should not exceed 70°, even more preferably should not exceed 60° , and even more preferably should not exceed 50°. On the other hand, the lower limit value preferably should not be less than 20°, more preferably should not be less than 30°, and even more preferably should not be less than 40°.

The aforementioned upper and lower limit values, respectively, in relation to the first pregroove 12 and the second pregroove 16, can be arbitrarily combined. The values for the first pregroove 12 and the second pregroove 16 can be measured using an AFM (atomic force microscope) .

For example, when the groove depth of the first pregroove 12 is taken to be D, with the surface of the first substrate 14 before forming the groove being taken as a standard, the angle of the first pregroove 12 is defined as an angle formed by the surface of the first substrate 14 (bottom surface of the groove) and a straight line that connects an inclined portion having a depth of D/ 10 from the surface and another inclined portion having a height of D/ 10 from the deepest portion of the groove. This definition also holds equivalently for the angle of the second pregroove 16.

When optical disks 1OA and 1OB according to the first and second embodiments are read-only optical disks, the pits representing predetermined information are formed simultaneously when the first pregroove 12 and the second pregroove 16 are formed.

It is preferable for an undercoat layer to be formed on surfaces of each of the first substrate 14 and the second substrate 18, in order to improve flatness thereof, as well as to improve the adhesive force.

Materials usable for the undercoat layer may include, for example, surface-modifying agents, such as a silane coupling agent , and high molecular weight compounds , such as polymethyl methacrylate, acrylic acid-methacrylic acid copolymers, styrene-maleic anhydride copolymers, polyvinyl alcohol, N-methylolacrylamide, styrene-vinyltoluene copolymers, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate-vinyl chloride copolymers, ethylene-vinyl acetate copolymers, polyethylene, polypropylene, and polycarbonate.

The undercoat layer may be formed by dissolving or dispersing the above-described materials in an appropriate solvent to prepare a coating liquid, and then coating the substrate surface with the coating liquid, by means of coating methods such as spin coating, dip coating, and extrusion coating. The layer thickness of the undercoat layer is generally within a range of 0.005 to 20 μm, and preferably within a range of 0.01 to 10 μm. The first information-recording layer 22 and the second information-recording layer 28 preferably are of the dye type, containing a dye as the recording substance. The recording substance, which is contained in the first information-recording layer 22 and the second information- recording layer 28, includes, for example, organic compounds such as dyes and phase-change metallic compounds. In particular, the first information-recording layer 22 and the second information-recording layer 28 are preferably of the dye type, in which information can be recorded only once by means of a laser beam. The first information- recording layer 22 and the second information-recording layer 28 of the dye type preferably contain a dye that exhibits absorption within the recording wavelength region. Such dyes include, for example, cyanine dyes, oxonol dyes, metal complex dyes, azo dyes, and phthalocyanine dyes. In particular, use of oxonol dyes is preferred. When an oxonol dye is contained within the first and second information- recording layers 22 and 28, stable maintenance of the recording and reproduction characteristics can be maintained over a long period of time.

Further explanations shall now be made concerning the oxonol dye used for the first and second information- recording layers 22 and 28.

Specific examples of oxonol dyes are described, for example, in "Heterocyclic Compounds -Cyanine Dyes and Related Compounds," by F. M. Harmer, John & Wiley & Sons, New York, London, 1964.

The oxonol dye can be synthesized by a condensation reaction with a corresponding active methylene compound and a methine source (which is a compound used in order to introduce the methine group into the methine dye).

As for details of such compounds, reference may also be made to Japanese Patent Publication Nos . 39-22069, 43-3504, 52-38056, 54-38129, 55-10059, and 58-35544, Japanese Laid- Open Patent Publication Nos. 49-99620, 52-92716, 59-16834, 63-316853, and 64-40827, British Patent No. 1133986, and United States Patent Nos. 3,247,127, 4,042,397, 4,181,225, 5,213,956, and 5,260,179. Such compounds also are described in Japanese Laid-Open Patent Publication Nos. 63-209995, 10- 309871, and 2002-249674.

A single oxonol dye may be used, or alternatively, two or more of the oxonol dyes may be used in combination. Further, alternatively, a known oxonol dye may be used in combination with dye compounds other than oxonol dyes.

Examples of dyes that may be used in combination with the oxonol dye include, for example, azo dyes (including those which form complexes with metal ions), pyrromethene dyes, and cyanine dyes . As for the dye, it is preferable to use a dye having the thermal decomposition temperature within a range of 100 ⁰C to 350 ⁰C. More preferably, the thermal decomposition temperature is within a range of 150 ⁰C to 300 ⁰C. Even more preferably, the thermal decomposition temperature is within a range of 200 ⁰C to 300 ⁰C.

Coefficients n (real part: refractive index) and k (imaginary part: extinction coefficient) of the complex refractive index preferably satisfy the expressions 2.0 ≤ n ≤ 3.0 and 0.005 ≤ k ≤ 0.30 in view of optical characteristics of an amorphous film of the dye (i.e., a "known oxonol dye" or a "known oxonol dye and another dye used in combination therewith" ) that is used for the first information-recording layer 22 and the second information- recording layer 28. More preferably, the coefficients should satisfy the expressions 2.1 ≤ n ≤ 2.7 and 0.01 ≤ k ≤ 0.15. Even more preferably, the coefficients should satisfy the expressions 2.15 ≤ n ≤ 2.50 and 0.03 ≤ k ≤ 0.10.

Various anti-fading agents may be contained in the first information-recording layer 22 and the second information-recording layer 28, in order to further improve light resistance. Representative examples of such anti- fading agents may include, for example, a metal complex, diimmonium salts, and aminium salts, represented by general formulas (III), (IV), and (V) as described in Japanese Laid- Open Patent Publication No. 3-224793, nitroso compounds as described in Japanese Laid-Open Patent Publication Nos . 2- 300287 and 2-300288, and TCNQ derivatives as described in Japanese Laid-Open Patent Publication No. 10-151861.

The first information-recording layer 22 and the second information-recording layer 28 may be formed as follows. Specifically, a known oxonol dye, and optionally a quencher and a binding agent, for example, are dissolved in a solvent to prepare a coating liquid. Subsequently, the coating liquid is applied to surfaces of the first substrate 14 and the second substrate 18, respectively, to form coating films thereon, followed by drying. The solvent for the coating liquid may be exemplified by esters such as butyl acetate, ethyl lactate, and cellosolve acetate, ketones such as methyl ethyl ketone, cyclohexanone , and methyl isobutyl ketone, chlorinated hydrocarbons such as dichloromethane, 1 , 2-dichloroethane, and chloroform, an amide such as dimethylformamide, a hydrocarbon such as cyclohexane, ethers such as tetrahydrofuran, ethyl ether, and dioxane, alcohols such as ethanol, n-propanol, isopropanol, n-butanol, and diacetone alcohol, fluorine-based solvents such as 2,2,3,3,- tetrafluoropropanol, and glycol ethers such as an ethylene glycol monomethyl ether, a ethylene glycol monoethyl ether, and a propylene glycol monomethyl ether. An individual solvent as described above may be used, or alternatively, two or more of the aforementioned solvents may be used in combination, taking into consideration the solubility of the compound to be used. Various additives including, for example, antioxidants, UV-absorbing agents, plasticizers, and lubricants, may also be added into the coating liquid depending on the object.

Examples of the binding agent are exemplified by natural organic high molecular weight substances including, for example, gelatin, cellulose derivatives, dextran, rosin, and rubber, as well as by synthetic organic high molecular weight compounds including, for example, hydrocarbon-based resins such as polyethylene, polypropylene, polystyrene, and polyisobutylene, vinyl-based resins such as polyvinyl chloride, poly(vinylidene chloride), and poly(vinyl chloride) -poly(vinyl acetate) copolymers, acrylic resins such as poly(methyl acrylate) and poly(methyl methacrylate) , and initial condensates of thermosetting resins such as polyvinyl alcohol, chlorinated polyethylene, epoxy resins, butyral resins, rubber derivatives, and phenol-formaldehyde resins .

When the binding agent is used in combination as the material for the first information-recording layer 22 and the second information-recording layer 28, the amount of binding agent used is generally within a range of 0.01 to 50 times (mass ratio), and preferably within a range of 0.1 to 5 times (mass ratio), with respect to the amount of dye, represented by a known oxonol dye, that is used. A coating liquid prepared as described above has a dye concentration, which is generally within a range of 0.01 to 10 % by mass, and preferably within a range of 0.1 to 5 % by mass.

The coating method, for example, may be any of a spray method, a spin coating method, a dip method, a roll coating method, a blade coating method, a doctor roll method, and a screen printing method. Each of the first information- recording layer 22 and the second information-recording layer 28 may be a single layer or multiple layers. The layer thickness of each of the first and second information- recording layers 22, 28 is generally within a range of 20 to 50 nm, and preferably within a range of 50 to 300 nm. Next, an explanation shall be made concerning the semitransparent reflective layer 24 and the reflective layer 26. A light-reflective substance that is used as the material for the reflective layer 26 is a substance having a high reflectance with respect to the laser beam. Examples of such light-reflective substances may include stainless steel, half metals, and metals such as Mg, Se, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Si, Ge, Te, Pb, Po, Sn, and Bi.

Among these substances, Cr, Ni, Pt, Cu, Ag, Au, Al, and stainless steel are preferred, and Ag is especially preferred. The substances described above may be used individually. Alternatively, two or more of these substances may be used in combination or as an alloy. The reflective layer 26 can be formed on each of the first information-recording layer 22, the second information- recording layer 28, and the second substrate 18, by performing, for example, vapor deposition, sputtering, or ion plating, using the reflective substances described above .

It is preferable for the layer thickness of the semitransparent reflective layer 24 to be within a range of 2 to 150 nm. The layer thickness of the reflective layer 26 is generally within a range of 10 to 300 nm, and preferably, within a range of 50 to 200 nm.

On the other hand, the barrier layer 30 is provided in order to physically and chemically protect, for example, the second information-recording layer 28. The barrier layer 30 may also be provided on portions of the first substrate 14 and the second substrate 18 where the first information- recording layer 22 and the second information-recording layer 28 are not provided, in order to enhance resistance to scratching and humidity.

The material used for the barrier layer 30 is exemplified by inorganic substances, such as SiO, SiO₂, MgF₂, SnO₂, Si₃N₄, and ZnO-Ga₂O₃, and organic substances, such as thermoplastic resins, thermosetting resins, and UV- curable resins .

The barrier layer 30 can be provided by means of a method such as vacuum vapor deposition, sputtering, and/or coating. When a thermoplastic resin or the thermosetting resin is used, the barrier layer 30 can also be formed such that the resin is first dissolved in an appropriate solvent to prepare a coating liquid, whereupon the coating liquid is applied, and then dried. In the case of a UV-curable resin, the barrier layer 30 can also be formed such that the resin is used as is, or wherein the resin is dissolved in an appropriate solvent to prepare a coating liquid, whereupon the coating liquid is applied and the resin is cured by irradiating with UV light. Further, various other additives including, for example, antistatic agents, antioxidants, and UV-absorbing agents, may be added into the coating liquid depending on the object. The layer thickness of the barrier layer 30 is generally within a range of 1 nm to 10 μm.

On the other hand, the intermediate layer 20 is provided at least between the first information-recording layer 22 and the second information-recording layer 28, as described above.

Materials useable for the intermediate layer 20 and the adhesive layer 48, for example, are thermoplastic resins, thermosetting resins, electron beam-curable resins, ultraviolet light-curable resins, pressure sensitive double- sided tape, and inorganic materials such as SiO₂. Such materials may be used singly or in combination with each other. The invention is not restricted to using a single layer only. Multilayer films may also be provided and used. The intermediate layer 20, as described above, can be formed by means of a spin coating method, a casting method, and/or a sputtering method. The thickness of the intermediate layer 20 preferably is 5 to 100 μm, and more preferably, the thickness of the intermediate layer 20 is 10 to 70 μm.

An explanation shall now be made concerning exemplary experiments, which were used to evaluate AR (aperture ratio, %) and PIE (PI error pieces), in relation to the following Examples 1 through 5 and Comparative Examples 1 and 2.

Initially, the content of Examples 1 through 5 and Comparative Examples 1 and 2 shall be described, as follows.

Example 1 A polycarbonate resin was subjected to injection molding using a first stamper, to thereby form a substrate having a thickness of 0.575 mm and a diameter of 120 mm, provided with a spiral-shaped first pregroove 12 (depth: 120 nm, groove width: 365 nm, track pitch: 0.74 μm) . This substrate was designated as a first substrate 14 for forming a first information-recording layer 22.

After that, an oxonol dye, represented by the following chemical formula (ch-1), and an oxonol dye, represented by the following chemical formula (ch-2), were mixed together at a ratio of 90:10. A coating liquid was prepared by dissolving 1.00 g of the mixed dye in 100 ml of 2,2,3,3- tetrafluoropropanol . The surface of the first substrate 14, on which the first pregroove 12 was formed, was coated with the coating liquid by means of a spin coat method in order to form the first information-recording layer 22.

(ch-1)

(ch-2)

Subsequently, an AgBiNd alloy (target composition: Ag = 99.45 at. %, Nd = 0.35 at. %, Cu = 0.20 at. %) was sputtered onto the first information-recording layer 22 in order to form a semitransparent reflective layer 24 having a layer thickness of 13 nm. Accordingly, the first substrate 14, having the first information-recording layer 22 thereon, was obtained.

On the other hand, a polycarbonate resin was subjected to injection molding using a second stamper, to thereby form a substrate having a thickness of 0.600 mm and a diameter of 120 mm, provided with a spiral-shaped second pregroove 16 (depth: 30 nm, land width: 440 nm, track pitch: 0.74 μm) . This substrate was designated as a second substrate 18 for forming a second information-recording layer 28.

In Example 1, the shape of the second pregroove 16 formed on the second substrate 18 was such that Tl in the above-described expression (1) was 120 nm, T2 in the above- described -expression (3) was 110 nm, and the length Lw of the meandering portion 40 was 800 nm (T1/T2 = about 1.091). The shape of the concave/convex portions formed on the second stamper was such that the value corresponding to Tl in the above-described expression (1) was 138 nm, and the value corresponding to T2 in the above-described expression (3) was 127 nm (T1/T2 = about 1.087).

That is. Example 1 satisfied at least expressions (1), (3), (4), and (5) described above.

Subsequently, an AgBiNd alloy (target composition: Ag = 99.45 at. %, Nd = 0.35 at. %, Cu = 0.20 at. %) was sputtered onto the surface of the second substrate 18 on which the second pregroove 16 was formed in order to form a reflective layer 26 having a layer thickness of 120 nm.

Further, 2.00 g of an oxonol dye, represented by the aforementioned chemical formula (ch-1), was dissolved in 100 ml of 2 , 2 , 3 , 3-tetrafluoropropanol in order to prepare a coating liquid. The surface of the second substrate 18 formed with the reflective layer 26 was coated with the coating liquid by means of a spin coating method in order to form a second information-recording layer 28 wherein an absorbance = 1.10 thereof was given for the longest wavelength λmax of the laser beam. Subsequently, ZnO-Ga₂O₃ (target composition: ZnO = 30 wt. %, Ga₂O₃ = 70 wt. %) was applied, by RF sputtering, onto the second information-recording layer 28 in order to protect the dye. Thus, a barrier layer 30 having a layer thickness of 5 nm was formed. Accordingly, the second substrate 18, having the second information-recording layer 28, was obtained.

Thereafter, the first substrate 14 and the second substrate 18 were bonded together using an ultraviolet light-curable resin adhesive (Daicure Clear SD 640, produced by Dainippon Ink and Chemicals, Inc.), thereby resulting in the optical disk. The adhesive layer, i.e., the intermediate layer 20, had a thickness of 50 μm.

Example 2

The shape of the second pregroove 16 formed on the second substrate 18 in Example 1 was changed, such that Tl in the aforementioned expression (1) was 150 nm, T2 in the above-described expression (3) was 100 nm, and the length Lw of the meandering portion 40 was 800 nm (T1/T2 = 1.5). The shape of the concave/convex portions formed on the second stamper was changed, such that the value corresponding to Tl in the aforementioned expression (1) was 173 nm, and the value corresponding to T2 in the above-described expression (3) was 115 nm (T1/T2 = about 1.504).

That is, Example 2 satisfied at least the expressions (1), (4), and (5) described above. Example 3

The shape of the second pregroove 16 formed on the second substrate 18 in Example 1 was changed such that Tl in the expression (1) described above was 190 nm, T2 in the above-described expression (3) was 160 nm, and the length Lw of the meandering portion 40 was 800 nm (T1/T2 = 1.186). The shape of the concave/convex portions formed on the second stamper was changed such that the value corresponding to Tl in the expression (1) described above was 219 nm, and the value corresponding to T2 in the above-described expression (3) was 184 nm (T1/T2 = about 1.190).

That is, Example 3 satisfied at least the expressions (1), (3), (4), and (5) described above.

Example 4

The shape of the second pregroove 16 formed on the second substrate 18 in Example 1 was changed, such that Tl in the aforementioned expression (1) was 150 nm, T2 in the above-described expression (3) was 130 nm, and the length Lw of the meandering portion 40 was 900 nm (T1/T2 = 1.154). The shape of the concave/convex portions formed on the second stamper was changed, such that the value corresponding to Tl in the aforementioned expression (1) was 173 nm, and the value corresponding to T2 in the above- described expression (3) was 150 nm (T1/T2 = about 1.153). That is. Example 4 satisfied at least the expressions (1), (3), (4), and (5) described above.

Example 5

The shape of the second pregroove 16 formed on the second substrate 18 in Example 1 was changed, such that Tl in the aforementioned expression (1) was 150 nm, T2 in the above-described expression (3) was 110 nm, and the length Lw of the meandering portion 40 was 1,000 nm (T1/T2 = 1.364). The shape of the concave/convex portions formed on the second stamper was changed, such that the value corresponding to Tl in the aforementioned expression (1) was 173 nm, and the value corresponding to T2 in the above- described expression (3) was 127 nm (T1/T2 = about 1.362). That is. Example 5 satisfied at least the expressions (1), (3), (4), and (5) described above.

Comparative Example 1

The shape of the second pregroove 16 formed on the second substrate 18 in Example 1 was changed, such that Tl in the aforementioned expression (1) was 80 nm, T2 in the above-described expression (3) was 70 nm, and the length Lw of the meandering portion 40 was 900 nm (T1/T2 = 1.143). The shape of the concave/convex portions formed on the second stamper was changed, such that the value corresponding to Tl in the aforementioned expression (1) was 92 nm, and the value corresponding to T2 in the above- described expression (3) was 80.5 nm (T1/T2 = about 1.143). That is. Comparative Example 1 satisfied at least the expressions (3), (4), and (5) described above.

Comparative Example 2

The shape of the second pregroove 16 formed on the second substrate 18 in Example 1 was changed, such that Tl in the aforementioned expression (1) was 220 nm, T2 in the above-described expression (3) was 200 nm, and the length Lw of the meandering portion 40 was 900 nm (T1/T2 = 1.1). The shape of the concave/convex portions formed on the second stamper was changed, such that the value corresponding to Tl in the aforementioned expression (1) was 253 nm, and the value corresponding to T2 in the above-described expression (3) was 230 nm (T1/T2 = about 1.1).

That is. Comparative Example 2 satisfied at least the expressions (3), (4), and (5) described above.

Evaluation

An 8-16 modulation signal was recorded at a linear velocity of 7.68 to 30.72 m/sec, using DDU-1000 and a multisignal generator (produced by PulseTech, laser wavelength = 659.8 nm, numerical aperture of objective lens = 0.60), in order to perform an evaluation of the push-pull signal, i.e., an evaluation of the aperture ratio (AR). The utilized light emission pattern of the recording laser (recording strategy) was optimized for each of the optical disks .

Thereafter, reproduction was performed at a linear velocity of 3.84 m/sec, using DDU-1000 (produced by

PulseTech, laser wavelength = 651.0 nm, numerical aperture of objective lens = 0.60), in order to evaluate the PI error. FIG. 8 shows results of an evaluation of the aperture ratio (AR), and the PI error, with respect to Examples 1 through 5 and Comparative Examples 1 and 2.

In Comparative Example 1, though the PI error was less than 280 pieces, as the normalized value, the aperture ratio (AR) was as excessively low as 0 % , because Comparative

Example 1 did not satisfy the expression (1) described above .

In Comparative Example 2, though the aperture ratio

(AR) was not less than 10 % of the normalized value, the PI error was as excessively much as 853 pieces, because

Comparative Example 2 did not satisfy the expression (1) described above.

In contrast, in Examples 1 through 5, which satisfied at least the expressions (1), (4) and (5), the aperture ratio (AR) was not less than 10 % of the normalized value.

Further, the PI error was less than 280 pieces, as the normalized value. According to this fact, both the AR and the PI error, which mutually are in a trade off relationship, have satisfactory values, and a satisfactory balanced relationship between AR and IP error is provided in

Examples 1 through 5. This shows that information can be stably recorded on the second information-recording layer 28. In Examples 1 through 5, the modulation degree during 2x speed recording (linear velocity: 7.68 m/sec) was not less than 0.50 and not more than 0.63.

It is a matter of course that the optical information- recording medium, the substrate for the optical information- recording medium, the stamper, the method for producing the optical information-recording medium, and the method for producing the stamper according to the present invention, are not limited by the descriptions given with respect to the embodiments and examples described above. The present invention may be embodied in other various forms, without deviating from the gist or essential characteristics of the present invention, as set forth in the appended claims.

Claims

1. An optical information-recording medium having a substrate (18) comprising a recording layer (28) and a groove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, wherein: said groove (16) includes a plurality of meandering portions (40) ; each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of a land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36); and wherein the following expression is satisfied: 100 nm < Tl < 200 nm where Tl represents an amount of protrusion of said first curved portion (44) with respect to said first groove (42a).

2. A optical information-recording medium having a substrate (18) comprising a recording layer (28) and a groove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, wherein: said groove (16) includes a plurality of meandering portions (40) , each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of a land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36); and wherein the following expression is satisfied:

2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nm² where Al represents an area of protrusion of said first curved portion (44) with respect to said first groove (42a).

3. The optical information-recording medium according to claim 1 or 2 , wherein the following expressions are satisfied: 350 nm ≤ Wg < 460 nm

700 nm ≤ Lw < 1,000 nm 700 nm ≤ Wp < 1,000 nm where Wg represents a width of said land (36), Lw represents a length of said meandering portion (40), and Wp represents a distance from an apex of said first curved portion (44) to an apex of said second curved portion (46) of said meandering portion (40).

4. The optical information-recording medium according to any one of claims 1 to 3 , wherein another substrate (14) is stacked on said substrate (18) with an intermediate layer (20) intervening therebetween, and wherein the other substrate (14) comprises a groove (12) and a recording layer (22), which are formed in this order as viewed in said direction in which said laser beam (32) is radiated.

5. The optical information-recording medium according to claim 4, wherein the other substrate (14), said intermediate layer (20), and said substrate (18) are stacked in this order as viewed in said direction in which said laser beam (32) is radiated.

6. A substrate for an optical information-recording medium comprising a recording layer (28) and a groove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, wherein: said groove (16) includes a plurality of meandering portions ( 40 ) ; each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of a land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36); and wherein the following expression is satisfied: 100 nm < Tl < 200 nm where Tl represents an amount of protrusion of said first curved portion (44) with respect to said first groove (42a).

7. A substrate for an optical information-recording medium comprising a recording layer (28) and a groove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, wherein: said groove (16) includes a plurality of meandering portions ( 40) ; each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of a land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36); and wherein the following expression is satisfied:

8. A stamper for producing a substrate for an optical information-recording medium comprising a recording layer (28) and a groove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, wherein: said groove (16) includes a plurality of meandering portions ( 40 ) ; each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of a land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36); and wherein the following expression is satisfied:

100 nm < Tl < 200 nm where Tl represents an amount of protrusion of said first curved portion (44) with respect to said first groove (42a).

9. A stamper for producing a substrate for an optical information-recording medium comprising a recording layer (28) and a groove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, wherein: said groove (16) includes a plurality of meandering portions ( 40 ) , each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of a land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36); and wherein the following expression is satisfied: 2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nm² where Al represents an area of protrusion of said first curved portion (44) with respect to said first groove (42a).

10. A method for producing an optical information- recording medium comprising a first substrate (14), an intermediate layer (20), and a second substrate (18), which are stacked in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, said method comprising the steps of: manufacturing said first substrate (14) formed with a groove (12) and a land using a first stamper,- forming a recording layer (22) on a surface of said first substrate (14) on which said groove (12) and said land are formed; manufacturing said second substrate (18) formed with a groove (16) and a land using a second stamper; and forming a recording layer (28) on a surface of said second substrate (18) on which said groove (16) and said land are formed, wherein: said groove (16), which is formed on said second substrate (18) when said second substrate (18) is manufactured using said second stamper, includes a plurality of meandering portions (40); each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove

(42a) disposed adjacently on one side of said land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36); and wherein the following expression is satisfied: 100 nm < Tl < 200 nm where Tl represents an amount of protrusion of said first curved portion (44) with respect to said first groove (42a).

11. A method for producing an optical information- recording medium comprising a first substrate (14), an intermediate layer (20), and a second substrate (18), which are stacked in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, said method comprising the steps of: manufacturing said first substrate (14) formed with a groove (12) and a land using a first stamper; forming a recording layer, (22) on a surface of said first substrate (14) on which said groove (12) and said land are formed; manufacturing said second substrate (18) formed with a groove (16) and a land using a second stamper; and forming a recording layer (28) on a surface of said second substrate (18) on which said groove (16) and said land are formed, wherein: said groove (16), which is formed on said second substrate (18) when said second substrate (18) is manufactured using said second stamper, includes a plurality of meandering portions (40); each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of said land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36), and wherein the following expression is satisfied:

2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nin² where Al represents an area of protrusion of said first curved portion (44) with respect to said first groove (42a).

12. A method for producing a stamper for manufacturing a substrate (18) for an optical information-recording medium comprising a recording layer (28) and a groove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, said method comprising the step of: manufacturing said stamper having concave/convex portions formed on a surface thereof by selectively applying etching to a stamper master plate, wherein: said concave/convex portions are shaped so that said groove (16) is transferred to said substrate (18) when said substrate (18) is manufactured using said stamper, and wherein said groove (16) satisfies the following features:

(1) said groove (16) includes a plurality of meandering portions (40); (2) each of said meandering portions (40) includes a first curved portion (44), which is curved toward a first groove (42a) disposed adjacently on one side of a land (36), and a second curved portion (46), which is curved toward said land (36) from a second groove (42b) disposed adjacently on the other side of said land (36); and

(3) the following expression is satisfied: 100 nm < Tl < 200 nm where Tl represents an amount of protrusion of said first curved portion (44) with respect to said first groove (42a).

13. A method for producing a stamper for manufacturing a substrate (18) for an optical information-recording medium comprising a recording layer (28) and a groove (16), which are formed in this order as viewed in a direction in which a recording and/or reproducing laser beam (32) is radiated, said method comprising the step of: manufacturing said stamper having concave/convex portions formed on a surface thereof by selectively applying etching to a stamper master plate, wherein: said concave/convex portions are shaped so that said groove (16) is transferred to said substrate (18) when said substrate (18) is manufactured using said stamper, and wherein said groove (16) satisfies the following features:

(3) the following expression is satisfied: 2.8 x 10⁴ nm² < Al < 1.6 x 10⁵ nm² where Al represents an area of protrusion of said first curved portion (44) with respect to said first groove (42a).