JP7447815B2 - optical recording medium - Google Patents

Description

TECHNICAL FIELD This disclosure relates to optical recording media .

In recent years, development of write-once optical recording media that exceeds the data capacity (maximum 128 GB) of Blu-ray Discs (BDs) has been underway. As a new optical recording medium that has achieved such a large capacity, an optical recording medium called an archive disk (AD) has been put into practical use, and each optical recording medium has a data capacity of 300 GB. .

In the technical field of write-once optical recording media, various inorganic recording materials are being studied in order to realize large capacity. For example, in Patent Documents 1 and 2, Mn oxide is proposed as an inorganic recording material.

One method of increasing the capacity of an optical recording medium is to increase the track density (the number of tracks that can be accommodated in a unit length in the radial direction of the disk). The track density can be increased as the track pitch (interval between tracks) becomes narrower. In BD, the track pitch is 0.32 μm, whereas in AD, the track pitch is narrower than that of BD, and is 0.225 μm. Further, in AD, there is a demand for further increase in capacity, and it has come to be desired that the track pitch be less than 0.225 μm.

Patent No. 6308128 Japanese Patent Application Publication No. 2012-139876

As the track pitch becomes narrower as described above, it is desired to narrow down the recording/reproducing beam to reduce the spot diameter, but it has become technically difficult to further narrow down the beam from the recording/reproducing optical system of the BD. If the track pitch is narrowed without focusing the recording/reproducing beam, crosstalk and crosswrite will occur. When the track pitch is made narrower than 0.225 μm, the occurrence of crosstalk and crosswrite becomes particularly noticeable.

Note that "crosstalk" refers to the fact that while a certain track is being played back, the signal from an adjacent track leaks in and disturbs the signal that is to be played back. "Cross write" refers to the fact that when a signal is recorded on one track and then recorded on the next track, the previously recorded signal area is partially destroyed when the next track is recorded, resulting in degraded playback signals. say.

An object of the present disclosure is to provide an optical recording medium that can suppress crosstalk and crosswrite.

In order to solve the above problems, the first disclosure is as follows:
comprising at least one recording layer,
The recording layer includes an oxide of Mn and a metal oxide other than the oxide of Mn,
At least a part of the Mn oxide exists as +4-valent Mn,
The metal oxide other than the Mn oxide contains at least one selected from the group consisting of Hf, Nb, Ta, Si, Sn and Sb oxides,
The proportion of Hf oxide in metal oxides other than Mn oxide is 8.3 at % or more and 62.4 at % or less,
The proportion of the Nb oxide in the metal oxide other than the Mn oxide is 19.5 atomic % or more and 100 atomic % or less,
The proportion of Ta oxide in the metal oxide other than Mn oxide is 7.2 at% or more and 81.1 at% or less,
The proportion of the Si oxide in the metal oxide other than the Mn oxide is 15.2 atomic % or more and 100 atomic % or less,
The proportion of Sn oxide in the metal oxide other than Mn oxide is greater than 16.6 atomic % and less than 100 atomic %,
The proportion of the Sb oxide in the metal oxide other than the Mn oxide is 14.4 atomic % or more and 100 atomic % or less,
The optical recording medium has a track pitch of 0.225 μm or less.

FIG. 1A is a perspective view showing an example of the appearance of an optical recording medium according to a first embodiment of the present disclosure. FIG. 1B is a cross-sectional view showing an example of the configuration of an optical recording medium according to the first embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of each information signal layer shown in FIG. FIG. 3 is a cross-sectional view showing a configuration example of an optical recording medium according to a second embodiment of the present disclosure. FIG. 4 is a schematic cross-sectional view showing a modification of the recording layer. FIG. 5 is a schematic diagram showing the configuration of a disk drive type evaluation device. FIG. 6A is a graph showing the relationship between the composition of the recording layer, the thickness of the recording layer, the thickness of the protective layer, and the reflectance of the recording layer. FIG. 6B is a graph showing the relationship between the composition of the recording layer, the thickness of the recording layer, the thickness of the protective layer, and the transmittance of the recording layer. FIG. 7A is a graph showing the relationship between the composition of the recording layer, the thickness of the recording layer, the thickness of the protective layer, and the crosstalk amplitude ratio. FIG. 7B is a graph showing the relationship between the composition of the recording layer, the thickness of the recording layer, the thickness of the protective layer, and CNR. FIG. 8 is a graph showing the relationship between the type of additive element added to the recording layer and the crosstalk amplitude ratio. FIG. 9A is a graph showing the relationship between the Hf oxide content and the crosstalk amplitude ratio. FIG. 9B is a graph showing the relationship between the Nb oxide content and the crosstalk amplitude ratio. FIG. 10A is a graph showing the relationship between the Ta oxide content and the crosstalk amplitude ratio. FIG. 10B is a graph showing the relationship between the Si oxide content and the crosstalk amplitude ratio. FIG. 11A is a graph showing the relationship between the Sn oxide content and the crosstalk amplitude ratio. FIG. 11B is a graph showing the relationship between the Sb oxide content and the crosstalk amplitude ratio.

In the present disclosure, it is preferable that at least one recording layer is provided on the substrate, and that a cover layer is provided on the at least one recording layer. The thickness of this cover layer is not particularly limited, but since a high-NA (Numerical Aperture) objective lens is used in high-density optical recording media, the cover layer may be a thin light-transmitting layer such as a sheet or coating layer. It is preferable to record and reproduce information signals by employing a layer and irradiating light from the side of the light-transmitting layer. In this case, it is also possible to use an opaque substrate as the substrate. The light incident surface for recording or reproducing information signals is appropriately set on at least one of the cover layer side and the substrate side surface depending on the format of the optical recording medium.

In the present disclosure, from the viewpoint of improving storage reliability, the optical recording medium preferably further includes a protective layer on at least one surface of the recording layer, and more preferably includes a protective layer on both surfaces of the recording layer. . From the viewpoint of simplifying the layer structure and manufacturing equipment, it is preferable to use the recording layer alone without providing a protective layer on any surface of the recording layer.

In the present disclosure, when an optical recording medium includes a plurality of information signal layers including a recording layer and a protective layer provided on at least one surface side of the recording layer, from the viewpoint of productivity, it is difficult to obtain a plurality of information signal layers. Preferably, all signal layers have the same layer configuration. When a plurality of information signal layers have the same layer configuration including a first protective layer, a recording layer, and a second protective layer, from the viewpoint of productivity, the first protective layer, the recording layer, and the second protective layer are Preferably, each of the two protective layers contains the same type of material in all information signal layers.

Embodiments of the present disclosure will be described in the following order.
1 First embodiment 1.1 Structure of optical recording medium 1.2 Recording principle of optical recording medium 1.3 Sputtering target 1.4 Method of manufacturing optical recording medium 1.5 Effect 2 Second embodiment 2.1 Structure of optical recording medium 2.2 Method of manufacturing optical recording medium 2.3 Effect 3 Modification example

<1 First embodiment>
[1.1 Configuration of optical recording medium]
As shown in FIG. 1A, the optical recording medium 1 according to the first embodiment of the present disclosure has a disk shape with an opening (hereinafter referred to as a center hole) provided in the center. Note that the shape of the optical recording medium 1 is not limited to this example, and may also be shaped like a card, for example.

As shown in FIG. 1B, the optical recording medium 1 is a so-called multilayer write-once optical recording medium (for example, AD (Archival Disc)), and includes a first disk 10, a second disk 20, and a bonding layer 30 provided between the two disks 10 and 20. The optical recording medium 1 is an optical recording medium of a method (hereinafter referred to as "land/groove recording method") in which data is recorded on both groove tracks and land tracks.

The first disk 10 includes an information signal layer L0, a spacer layer S1, an information signal layer L1, . It has a laminated structure on the main surface. In the second disk 20, an information signal layer L0, a spacer layer S1, an information signal layer L1, . It has a laminated structure on the main surface. However, n and m are each independently an integer of 1 or more, and from the viewpoint of improving the recording capacity, preferably an integer of 2 or more, more preferably an integer of 3 or more, and even more preferably an integer of 4 or more. be. In the following description, the information signal layers L0 to Ln and L0 to Lm are referred to as the information signal layer L unless they are particularly distinguished.

The optical recording medium 1 has light irradiation surfaces on both sides that are irradiated with laser light for recording or reproducing information signals. More specifically, the first light irradiation surface C1 is irradiated with a laser beam for recording or reproducing information signals on the first disk 10, and the first light irradiation surface C1 is irradiated with a laser beam for recording or reproducing information signals on the first disk 20. It has a second light irradiation surface C2 that is irradiated with laser light for the purpose of irradiation.

In the first disc 10, the information signal layer L0 is located at the innermost position with respect to the first light irradiation surface C1, and the information signal layers L1 to Ln are located in front of it. Therefore, the information signal layers L1 to Ln are configured to allow laser light used for recording or reproduction to pass therethrough. On the other hand, in the second disc 20, the information signal layer L0 is located at the innermost position with respect to the second light irradiation surface C2, and the information signal layers L1 to Lm are located in front of it. Therefore, the information signal layers L1 to Lm are configured to allow laser light used for recording or reproduction to pass therethrough. Although not shown, the optical recording medium 1 may further include a hard coat layer on the surfaces of the light transmission layers 12 and 22 (ie, the first and second light irradiation surfaces C1 and C2).

In the optical recording medium 1, recording or reproduction of information signals on the first disk 10 is performed as follows. That is, by irradiating each information signal layer L0 to Ln included in the first disc 10 with laser light from the first light irradiation surface C1 on the light transmission layer 12 side, the information signal of the first disc 10 is Recording or playback takes place. For example, a laser beam having a wavelength in the range of 350 nm or more and 410 nm or less is focused by an objective lens having a numerical aperture in the range of 0.84 or more and 0.95 or less, and is directed from the light transmission layer 12 side to the first disk. By irradiating each information signal layer L0 to Ln included in 10, information signals are recorded or reproduced.

On the other hand, recording or reproduction of information signals on the second disc 20 is performed as follows. That is, by irradiating each information signal layer L0 to Lm included in the second disc 20 with laser light from the second light irradiation surface C2 on the light transmission layer 22 side, the information signal of the second disc 20 is Recording or playback takes place. For example, a laser beam having a wavelength in the range of 350 nm or more and 410 nm or less is condensed by an objective lens having a numerical aperture in the range of 0.84 or more and 0.95 or less, and is directed from the light transmission layer 22 side to the second disk. By irradiating each information signal layer L0 to Lm included in 20, information signals are recorded or reproduced.

Hereinafter, the substrates 11 and 21, the bonding layer 30, the information signal layers L0 to Ln, L0 to Lm, the spacer layers S1 to Sn, S1 to Sm, the light transmission layers 12 and 22, and the hard coat layer that constitute the optical recording medium 1 will be described. will be explained in order.

(substrate)
The substrates 11 and 21 have, for example, a disk shape with a center hole provided in the center. One main surface of the substrates 11 and 21 is, for example, an uneven surface, and the information signal layer L0 is formed on this uneven surface. Hereinafter, the concave portions of the uneven surface will be referred to as lands Ld, and the convex portions will be referred to as grooves Gv.

Examples of the shapes of the lands Ld and the grooves Gv include various shapes such as a spiral shape and a concentric circle shape. Further, the land Ld and/or the groove Gv may be wobbled for stabilizing linear velocity, adding address information, etc.

Note that the spiral directions of the first disk 10 and the second disk 20 may be reversed. In this case, simultaneous recording and playback of the optical recording medium (double-sided disk) 1 made by pasting together the first disk 10 and the second disk 20 becomes possible, which approximately doubles the data transfer speed during recording and playback. be able to.

The outer diameter (diameter) of the substrates 11 and 21 is selected to be, for example, 120 mm. The inner diameter (diameter) of the substrates 11 and 21 is selected to be, for example, 15 mm. The thickness of the substrate 11 is selected in consideration of rigidity, and is preferably 0.3 mm or more and 0.545 mm or less, more preferably 0.445 mm or more and 0.545 mm or less.

As the material for the substrates 11 and 21, for example, a plastic material or glass can be used, and from the viewpoint of moldability, it is preferable to use a plastic material. As the plastic material, for example, polycarbonate resin, polyolefin resin, or acrylic resin can be used, and from the viewpoint of cost, it is preferable to use polycarbonate resin.

(Lamination layer)
The bonding layer 30 is made of a cured ultraviolet curing resin. The first disk 10 and the second disk 20 are bonded together by this bonding layer 30. More specifically, the substrate 11 of the first disk 10 and the substrate 21 of the second disk substrate are bonded together so that the light-transmitting layers 12 and 22 are on the front side, respectively.

The thickness of the bonding layer 30 is, for example, 0.01 mm or more and 0.22 mm or less. The ultraviolet curing resin is, for example, a radical polymerization ultraviolet curing resin.

(information signal layer)
The information signal layer L has concave tracks (hereinafter referred to as "land tracks") and convex tracks (hereinafter referred to as "groove tracks"). The optical recording medium 1 according to the first embodiment is configured to be able to record information signals on both land tracks and groove tracks. From the viewpoint of high recording density, the track pitch Tp between the land track and the groove track is preferably 0.225 μm or less, more preferably less than 0.225 μm. The lower limit value of the track pitch Tp is not particularly limited, but is, for example, 0.12 μm or more.

As shown in FIG. 2, the information signal layers L0 to Ln include an inorganic recording layer (hereinafter simply referred to as "recording layer") 13 having an upper surface (first principal surface) and a lower surface (second principal surface); The recording layer 13 includes a protective layer 14 provided adjacent to the upper surface of the recording layer 13 and a protective layer 15 provided adjacent to the lower surface of the recording layer 13. With such a configuration, the durability of the recording layer 13 can be improved. Here, the upper surface refers to the main surface of the recording layer 13 that is irradiated with laser light for recording or reproducing information signals, and the lower surface refers to the main surface that is irradiated with the laser light for recording or reproducing information signals. This refers to the main surface on the opposite side to the side facing the substrate, that is, the main surface on the substrate 11 side. Note that the configurations of the information signal layers L0 to Lm can be the same as those of the information signal layers L0 to Ln, so a description thereof will be omitted.

(recording layer)
The recording layer 13 contains an oxide of Mn and a metal oxide other than the oxide of Mn in a mixed state or in a composite oxide state. Here, metal is defined to include semimetals such as Si and Sb. The metal oxide other than the Mn oxide includes at least one selected from the group consisting of oxides of Hf, Nb, Ta, Si, Sn, and Sb. At least a portion of the Mn oxide exists in the recording layer 13 as +4-valent Mn (ie, MnO ₂ ). The recording layer 13 may contain an oxide of Mn other than MnO ₂ (for example, Mn ₂ O ₃ , Mn ₃ O _{4 ,} etc.). By including the Mn oxide and a metal oxide other than the Mn oxide, the recording layer 13 can suppress crosstalk and crosswrite while ensuring SNR (Signal to Noise Ratio). . The metal oxide other than the Mn oxide may further contain at least one of a W oxide, a Zn oxide, and the like, if necessary. In this way, the metal oxide other than the Mn oxide contains at least one of the W oxide, the Zn oxide, etc., thereby adjusting the optical constants, ensuring recording performance, and ensuring storage performance. be able to.

From the viewpoint of suppressing crosstalk and crosswriting, the content of the Hf oxide in the metal oxide other than the Mn oxide is preferably greater than 0 atomic % and 75 atomic % or less, more preferably 8.3 atomic %. The content is at least 16.6 at % and no more than 41.6 at %, even more preferably at least 16.6 at % and no more than 41.6 at %.

From the viewpoint of suppressing crosstalk and crosswriting, the content of the Nb oxide in the metal oxide other than the Mn oxide is preferably greater than 0 atomic % and 100 atomic % or less, more preferably 19.5 atomic %. The content is at least 100 at %, more preferably at least 34.2 at % and no more than 78.5 at %.

From the viewpoint of suppressing crosstalk and crosswriting, the content of Ta oxide in metal oxides other than Mn oxide is preferably greater than 0 atomic % and 100 atomic % or less, more preferably 7.2 atomic %. The content is at least 81.1 at %, even more preferably at least 22.2 at % and no more than 72 at %, particularly preferably at least 37.9 at % and no more than 66 at %.

From the viewpoint of suppressing crosstalk and crosswriting, the content of Si oxide in metal oxides other than Mn oxide is preferably greater than 0 atomic % and 100 atomic % or less, more preferably 15.2 atomic %. The content is at least 100 at%, even more preferably at least 39.2 at% and no more than 100 at%, particularly preferably at least 60.1 at% and no more than 100 at%.

From the viewpoint of suppressing crosstalk and crosswrite, the content of Sn oxide in metal oxides other than Mn oxide is preferably greater than 0 atomic % and 100 atomic % or less, more preferably 16.6 atomic %. The content is at least 100 atom %, and even more preferably at least 41.6 atom % and no more than 100 atom %.

From the viewpoint of suppressing crosstalk and crosswriting, the content of the Sb oxide in the metal oxide other than the Mn oxide is preferably greater than 0 atomic % and 100 atomic % or less, more preferably 14.4 atomic %. The content is at least 100 at%, even more preferably at least 37.6 atom% and at most 100 atom%, particularly preferably at least 80.8 atom% and at most 100 atom%.

(protective layer)
The protective layers 14 and 15 function as oxygen barrier layers. Thereby, the durability of the recording layer 13 can be improved. Furthermore, the protective layers 14 and 15 have a function of suppressing escape of oxygen from the recording layer 13. Thereby, changes in the film quality of the recording layer 13 (mainly detected as a decrease in reflectance) can be suppressed, and a preferable film quality for the recording layer 13 can be ensured. Furthermore, the protective layers 14 and 15 also have the function of improving recording characteristics. This function occurs when the thermal diffusion of the laser light incident on the recording layer 13 is properly controlled, and the shape change in the recording area becomes too large, or the decomposition of Mn oxide progresses too much, causing the changed shape to collapse. This is thought to be because such problems can be suppressed and shape changes during recording can be made better.

Protective layers 14 and 15 include dielectrics. The dielectric includes, for example, at least one selected from the group consisting of oxides, nitrides, sulfides, carbides, and fluorides. The protective layers 14 and 15 may be made of the same or different materials. Examples of the oxide include oxides of one or more elements selected from the group consisting of In, Zn, Sn, Al, Si, Ge, Ti, Ga, Ta, Nb, Hf, Zr, Cr, Bi, and Mg. can be mentioned. Examples of the nitride include nitrides of one or more elements selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Nb, Mo, Ti, Nb, Mo, Ti, W, Ta, and Zn. , preferably a nitride of one or more elements selected from the group consisting of Si, Ge, and Ti. Examples of the sulfide include Zn sulfide. Examples of the carbide include carbides of one or more elements selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Ti, Zr, Ta and W, preferably from the group consisting of Si, Ti and W. Examples include carbides of one or more selected elements. Examples of the fluoride include fluorides of one or more elements selected from the group consisting of Si, Al, Mg, Ca, and La. Specific examples of these mixtures include ZnS-SiO ₂ , SiO ₂ -In ₂ O ₃ -ZrO ₂ (SIZ), SiO ₂ -Cr ₂ O ₃ -ZrO ₂ (SCZ), In ₂ O ₃ -SnO ₂ ( ITO), In ₂ O ₃ -CeO ₂ (ICO), In ₂ O ₃ -Ga ₂ O ₃ (IGO), In ₂ O ₃ -Ga ₂ O ₃ -ZnO (IGZO), Sn ₂ O ₃ -Ta ₂ O ₅ (TTO), TiO ₂ --SiO ₂ , Al ₂ O ₃ --ZnO, Al ₂ O ₃ --BaO, and the like.

The thickness of the protective layer 15 is preferably in the range of 2 nm or more and 30 nm or less. When the thickness of the protective layer 15 is 2 nm or more, a good barrier effect can be obtained. On the other hand, when the thickness of the protective layer 15 is 30 nm or less, a decrease in the recording power margin can be suppressed.

The thickness of the protective layer 14 is preferably in the range of 2 nm or more and 50 nm or less. When the thickness of the protective layer 14 is 2 nm or more, a good barrier effect can be obtained. On the other hand, when the thickness of the protective layer 14 is 50 nm or less, a decrease in the recording power margin can be suppressed.

(Spacer layer)
The spacer layers S1 to Sn and S1 to Sm have the role of separating the information signal layers L0 to Ln and L0 to Lm by a sufficient physical and optical distance, respectively, and have uneven surfaces on their surfaces. There is. The uneven surface forms, for example, a concentric or spiral land Ld and groove Gv. The thickness of the spacer layers S1 to Sn and S1 to Sm is preferably 9 μm or more and 50 μm or less. Although the material of the spacer layers S1 to Sn and S1 to Sm is not particularly limited, it is preferable to use an ultraviolet curable acrylic resin. Furthermore, since the spacer layers S1 to Sn and S1 to Sm serve as optical paths for laser beams for recording and reproducing data in the deep layers, they preferably have sufficiently high light transmittance.

(light transmission layer)
The light transmitting layers 12 and 22 are, for example, resin layers formed by curing a photosensitive resin such as an ultraviolet curing resin. Examples of the material for this resin layer include ultraviolet curing acrylic resin. Alternatively, the light transmitting layers 12 and 22 may be constructed from a light transmitting sheet having an annular shape and an adhesive layer for bonding the light transmitting sheet to the information signal layers Ln and Lm. . The light-transmitting sheet is preferably made of a material that has a low absorption ability for laser light used for recording and reproduction, and specifically, it is preferably made of a material that has a transmittance of 90% or more. As the material for the light-transmitting sheet, for example, polycarbonate resin or polyolefin resin (eg, Zeonex (registered trademark)) can be used. As a material for the adhesive layer, for example, an ultraviolet curing resin or a pressure sensitive adhesive (PSA) can be used.

The thickness of the light transmitting layers 12 and 22 is preferably selected from a range of 10 μm or more and 177 μm or less, for example, 57 μm. High-density recording can be achieved by combining such thin light-transmitting layers 12 and 22 with an objective lens having a high NA (numerical aperture) of, for example, about 0.85.

(Hard coat layer)
The hard coat layer is for imparting scratch resistance and the like to the first and second light irradiation surfaces C1 and C2. As the material for the hard coat layer, for example, acrylic resin, silicone resin, fluorine resin, or organic-inorganic hybrid resin can be used. The hard coat layer may contain fine silica powder to improve mechanical strength.

[1.2 Recording principle of optical recording medium]
In the optical recording medium 1 having the above-described configuration, when a recording operation is performed as the optical recording medium 1 by irradiating the information signal layer L with light such as a laser beam having a center wavelength of about 405 nm, MnO ₂ separates oxygen. At the same time as O ₂ is generated, Mn itself changes into an oxide with a lower valence. It is believed that the light irradiation area structurally swells due to the generation of O ₂ , and a recording mark accompanied by a change in volume and a change in optical constant is formed.

Changes in the volume and optical constants of the recording material due to recording are affected by the components of the recording material. For example, volume change can be considered as expansion in the direction perpendicular to the surface of the recording layer 13 and expansion in the in-plane direction of the recording layer 13, but the degree of expansion in the vertical direction and in-plane direction differs depending on the material components. coming out. The amount of change in optical constants also differs depending on the composition of the recording material.

[1.3 Sputtering target]
The sputtering target for forming the recording layer of the optical recording medium 1 contains Mn and a metal other than Mn as an alloy or metal oxide. Hereinafter, the "sputtering target" will be simply referred to as "target." The metal other than Mn includes at least one selected from the group consisting of Hf, Nb, Ta, Si, Sn, and Sb. The metal other than Mn may further contain at least one of W, Zn, etc., if necessary.

More specifically, the target is an alloy target containing Mn and at least one member selected from the group consisting of Hf, Nb, Ta, Si, Sn, and Sb, or an oxide of Mn, an oxide of Hf, A metal oxide target containing at least one member selected from the group consisting of Nb oxide, Ta oxide, Si oxide, Sn oxide, and Sb oxide. The alloy target may further contain at least one of W, Zn, etc., if necessary. The metal oxide target may further contain at least one of a W oxide, a Zn oxide, and the like, if necessary.

The Mn oxide is contained in the target as, for example, Mn ₂ O ₃ or Mn ₃ O ₄ . Since the MnO ₂ that is desired to be present in the recording layer 13 is decomposed by heat during target production, it is difficult to produce a target containing MnO ₂ . Furthermore, even if a target containing MnO ₂ can be produced, it is difficult to include MnO ₂ in the recording layer 13 because MnO ₂ is decomposed by the energy during sputtering. Therefore, in the first embodiment, an alloy target containing Mn as an Mn alloy or a metal oxide target containing Mn as a Mn oxide such as Mn ₂ O ₃ or Mn ₃ O ₄ is used, and oxygen assist is applied during sputtering. By doing this, MnO ₂ is included in the recording layer 13.

Preferably, the target is an alloy target. When the target is an alloy target in this way, a DC sputtering device can be used as the sputtering device used to form the recording layer 13. Since DC sputtering equipment is cheaper than RF sputtering equipment, manufacturing costs can be reduced. However, since DC sputtering equipment is prone to abnormal discharge and target damage during sputtering, it is important to consider the balance between manufacturing cost and performance and decide whether to include the constituent material of the target in a metallic state or a metal oxide state. It is preferable to select.

When the target is an alloy target, from the viewpoint of suppressing crosstalk and crosswriting, the content of Hf in the metal other than Mn is preferably greater than 0 atomic % and 75 atomic % or less, more preferably 8.3 atomic %. The content is at least 16.6 at % and no more than 41.6 at %, even more preferably at least 16.6 at % and no more than 41.6 at %.

When the target is an alloy target, from the viewpoint of suppressing crosstalk and crosswrite, the content of Nb in the metal other than Mn is preferably greater than 0 atomic % and less than 100 atomic %, more preferably 19.5 atomic %. The content is at least 100 at %, more preferably at least 34.2 at % and no more than 78.5 at %.

When the target is an alloy target, from the viewpoint of suppressing crosstalk and crosswrite, the content of Ta in the metal other than Mn is preferably greater than 0 atomic % and less than 100 atomic %, more preferably 7.2 atomic %. The content is at least 81.1 at %, even more preferably at least 22.2 at % and no more than 72 at %, particularly preferably at least 37.9 at % and no more than 66 at %.

When the target is an alloy target, from the viewpoint of suppressing crosstalk and crosswrite, the content of Si in the metal other than Mn is preferably greater than 0 atomic % and less than 100 atomic %, more preferably 15.2 The content is at least 100 at%, even more preferably at least 39.2 atom% and at most 100 atom%, particularly preferably at least 60.1 atom% and at most 100 atom%.

When the target is an alloy target, from the viewpoint of suppressing crosstalk and crosslight, the content of Sn in the metal other than Mn is preferably greater than 0 atomic % and less than 100 atomic %, more preferably 16.6 atomic %. The content is at least 100 atom %, and even more preferably at least 41.6 atom % and no more than 100 atom %.

When the target is an alloy target, from the viewpoint of suppressing crosstalk and crosswriting, the content of Sb in the metal other than Mn is preferably greater than 0 atomic % and less than 100 atomic %, more preferably 14.4 atomic %. The content is at least 100 at%, even more preferably at least 37.6 atom% and at most 100 atom%, particularly preferably at least 80.8 atom% and at most 100 atom%.

When the target is a metal oxide target, from the viewpoint of suppressing crosstalk and crosswrite, the content of the Hf oxide in the metal oxide other than the Mn oxide is preferably greater than 0 at% and 75 At % or less, more preferably 8.3 atomic % or more and 62.4 atomic % or less, and even more preferably 16.6 atomic % or more and 41.6 atomic % or less.

When the target is a metal oxide target, from the viewpoint of suppressing crosstalk and crosswrite, the content of the Nb oxide in the metal oxide other than the Mn oxide is preferably greater than 0 atomic % and 100 atomic %. At % or less, more preferably 19.5 atomic % or more and 100 atomic % or less, still more preferably 34.2 atomic % or more and 78.5 atomic % or less.

When the target is a metal oxide target, from the viewpoint of suppressing crosstalk and crosswrite, the content of the Ta oxide in the metal oxide other than the Mn oxide is preferably greater than 0 atomic % and 100 atomic %. atomic % or less, more preferably 7.2 atomic % or more and 81.1 atomic % or less, even more preferably 22.2 atomic % or more and 72 atomic % or less, particularly preferably 37.9 atomic % or more and 66 atomic % or less .

When the target is a metal oxide target, from the viewpoint of suppressing crosstalk and crosswrite, the content of the Si oxide in the metal oxide other than the Mn oxide is preferably greater than 0 atomic % and 100 atomic %. At % or less, more preferably 15.2 atomic % or more and 100 atomic % or less, still more preferably 39.2 atomic % or more and 100 atomic % or less, particularly preferably 60.1 atomic % or more and 100 atomic % or less.

When the target is a metal oxide target, from the viewpoint of suppressing crosstalk and crosswrite, the content of the Sn oxide in the metal oxide other than the Mn oxide is preferably greater than 0 atomic % and 100 atomic %. At % or less, more preferably 16.6 atomic % or more and 100 atomic % or less, even more preferably 41.6 atomic % or more and 100 atomic % or less.

When the target is a metal oxide target, from the viewpoint of suppressing crosstalk and crosswrite, the content of the Sb oxide in the metal oxide other than the Mn oxide is preferably greater than 0 atomic % and 100 atomic %. The content is atomic % or less, more preferably 14.4 atomic % or more and 100 atomic % or less, even more preferably 37.6 atomic % or more and 100 atomic % or less, particularly preferably 80.8 atomic % or more and 100 atomic % or less.

[1.4 Method for manufacturing optical recording medium]
Next, an example of a method for manufacturing the optical recording medium 1 according to the first embodiment of the present disclosure will be described.

(First disk manufacturing process)
The first disk 10 is manufactured as follows.

(Substrate molding process)
First, a substrate 11 having an uneven surface formed on one principal surface is molded. As a method for molding the substrate 11, for example, an injection molding method, a photopolymer method (2P method: Photo Polymerization), or the like can be used.

(Formation process of information signal layer)
Next, the information signal layer L0 is formed by sequentially laminating the protective layer 15, the recording layer 13, and the protective layer 14 on the substrate 11 by, for example, sputtering. Below, the formation process of the protective layer 15, the recording layer 13, and the protective layer 14 will be specifically explained.

(Formation process of protective layer)
First, the substrate 11 is transported into a vacuum chamber equipped with a target for forming a protective layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure. Thereafter, the target is sputtered to form the protective layer 15 on the substrate 11 while introducing a process gas such as Ar gas or O ₂ gas into the vacuum chamber. As the sputtering method, for example, a radio frequency (RF) sputtering method or a direct current (DC) sputtering method can be used, and the DC sputtering method is particularly preferred. This is because the direct current sputtering method uses less expensive equipment and has a higher film formation rate than the high frequency sputtering method, so that manufacturing costs can be reduced and productivity can be improved.

(Recording layer formation process)
Next, the substrate 11 is transported into a vacuum chamber equipped with a target for forming a recording layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure. Thereafter, the recording layer 13 is formed on the protective layer 15 by sputtering the target while introducing a process gas such as Ar gas or O ₂ gas into the vacuum chamber.

When the target for forming the recording layer is an alloy target, by sputtering the target while performing oxygen assist to form the recording layer 13, Mn can be changed to MnO ₂ , M ₂ O ₃ , or Mn depending on the oxygen concentration in the vacuum chamber. Forms oxides such _{as 3O4} . Furthermore, at least one metal selected from the group consisting of Hf, Nb, Ta, Si, Sn, and Sb forms a stable oxide. It is known that MnO ₂ and Mn ₂ O ₃ decompose upon heating and release oxygen, and the decomposition temperatures are 535° C. and 1080° C., respectively. Furthermore, as is known, MnO ₂ is black and has light absorption ability.

When the target for forming the recording layer is a metal oxide target, by sputtering the target while performing oxygen assist to form the recording layer 13, the Mn oxide can be converted into MnO ₂ or M ₂ according to the oxygen concentration in the vacuum chamber. Oxides such as O ₃ and Mn ₃ O ₄ are formed. Further, at least one metal oxide selected from the group consisting of Hf, Nb, Ta, Si, Sn, and Sb forms a stable oxide.

(Formation process of protective layer)
Next, the substrate 11 is transported into a vacuum chamber equipped with a target for forming a protective layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure. Thereafter, the target is sputtered to form the protective layer 14 on the recording layer 13 while introducing a process gas such as Ar gas or O ₂ gas into the vacuum chamber. As the sputtering method, for example, a radio frequency (RF) sputtering method or a direct current (DC) sputtering method can be used, and the DC sputtering method is particularly preferred. This is because, as described above, using the DC sputtering method can reduce manufacturing costs and improve productivity.
Through the above steps, the information signal layer L0 is formed on the substrate 11.

(Spacer layer formation process)
Next, an ultraviolet curing resin is uniformly applied onto the information signal layer L0 by, for example, a spin coating method. Thereafter, the uneven pattern of the stamper is pressed against the ultraviolet curable resin uniformly applied on the information signal layer L0, and after the ultraviolet rays are irradiated onto the ultraviolet curable resin to cure it, the stamper is peeled off. As a result, the uneven pattern of the stamper is transferred to the ultraviolet curing resin, and a spacer layer S1 provided with, for example, lands Ld and grooves Gv is formed on the information signal layer L0.

(Information signal layer formation process and spacer layer formation process)
Next, the information signal layer L1, the spacer layer S2, the information signal layer L3, . . . , the spacer layer Sn, the information signal The layers Ln are laminated in this order on the spacer layer S1.

(Formation process of light transmitting layer)
Next, a photosensitive resin such as an ultraviolet curing resin (UV resin) is spin-coated onto the information signal layer Ln by, for example, a spin coating method, and then the photosensitive resin is irradiated with light such as ultraviolet rays and cured. As a result, the light transmission layer 12 is formed on the information signal layer Ln. Through the above steps, the first disk 10 is manufactured.

(Second disk manufacturing process)
The "second disc manufacturing process" is the same as the above-mentioned "first disc manufacturing process", so a description thereof will be omitted.

(Lamination process)
Next, in the following manner, an ultraviolet curing resin as an adhesive is stretched between the first and second disks 10 and 20 produced as described above, for example, by a spin coating method. First, an ultraviolet curing resin is applied in a ring shape to the main surface of the second disk 20 on the opposite side from the second light irradiation surface C2 along the periphery of the center hole. Next, the main surface of the first disk 10 opposite to the first light irradiation surface C1 and the second light irradiation surface C2 of the second disk 20 are The first disk 10 is pressed against the second disk 20 via the ultraviolet curing resin so that the main surface on the opposite side faces the disk.

Next, the first and second disks 10 and 20 are rotated to stretch the ultraviolet curing resin in the radial direction of the first and second disks 10 and 20 between the first and second disks 10 and 20. do. At this time, the thickness of the ultraviolet curing resin is adjusted to a predetermined thickness by adjusting the rotation speed. Thereby, the ultraviolet curable resin is spread between the first and second disks 10 and 20 from the inner circumference to the outer circumference of the first and second disks 10 and 20. Through the above steps, the optical recording medium 1 having the bonding layer 30 in an uncured state is obtained.

In the above-mentioned stretching step of the ultraviolet curable resin, it is preferable to irradiate the outer periphery of the first and second disks 10 and 20 with ultraviolet rays to temporarily cure the ultraviolet curable resin that has been stretched to the outer periphery. Thereby, it is possible to suppress the occurrence of opening in the outer peripheral portions of the first and second disks 10 and 20.

Next, the bonding layer 30 is cured by irradiating ultraviolet rays from both sides of the optical recording medium 1 using an ultraviolet lamp. As a result, the desired optical recording medium 1 is obtained.

[1.5 Effect]
The optical recording medium 1 according to the first embodiment described above includes a plurality of recording layers 13, and the plurality of recording layers 13 are made of oxides of Mn and oxides of Hf, Nb, Ta, Si, Sn, and Sb. At least a portion of the Mn oxide exists as +4-valent Mn (ie, MnO ₂ ). Thereby, it is possible to suppress the recording mark from spreading in the in-plane direction of the recording layer 13 while maintaining the signal level, so that crosstalk and cross-writing can be suppressed while maintaining the signal level. Therefore, it becomes possible to narrow the track pitch (for example, narrow the track pitch Tp to 0.225 μm or less or less than 0.225 μm), and the track density of the optical recording medium 1 can be increased. Therefore, it is possible to increase the capacity of the optical recording medium 1.

Furthermore, by including at least one kind of oxide in the recording layer 13, it is possible to increase the capacity of the optical recording medium 1. 1 large capacity can be achieved.

<2 Second embodiment>
[2.1 Configuration of optical recording medium]
As shown in FIG. 3, the optical recording medium 1A according to the second embodiment of the present disclosure is a so-called multilayer write-once optical recording medium, including an information signal layer L0, a spacer layer S1, an information signal layer L1, etc. - The spacer layer Sn, the information signal layer Ln, and the light transmitting layer 12 which is a cover layer are laminated in this order on one main surface of the substrate 11A. Note that in the second embodiment, the same parts as in the first embodiment are given the same reference numerals, and the description thereof will be omitted.

The optical recording medium 1A has a light irradiation surface C on one side, which is irradiated with light for recording or reproducing information signals. The information signal layer L0 is located at the innermost position with respect to the light irradiation surface C, and the information signal layers L1 to Ln are located in front of it. Therefore, the information signal layers L1 to Ln are configured to allow laser light used for recording or reproduction to pass therethrough.

In the optical recording medium 1A according to the second embodiment, information signals are recorded or reproduced by irradiating each information signal layer L0 to Ln with laser light from the light irradiation surface C on the light transmission layer 12 side. . For example, a laser beam having a wavelength in the range of 400 nm or more and 410 nm or less is condensed by an objective lens having a numerical aperture in the range of 0.84 or more and 0.86 or less, and from the light transmission layer 12 side, each information signal layer L0 By irradiating .about.Ln, information signals are recorded or reproduced. An example of such an optical recording medium 1A is a multilayer Blu-ray Disc (BD: Blu-ray (registered trademark) Disc).

The optical recording medium 1A is typically a groove recording type optical recording medium, but may also be a land/groove recording type optical recording medium.

The diameter of the substrate 11A is selected to be, for example, 120 mm. The thickness of the substrate 11 is selected in consideration of rigidity, and is preferably 0.3 mm or more and 1.3 mm or less, more preferably 0.6 mm or more and 1.3 mm or less, for example, 1.1 mm. Further, the diameter of the center hole is selected to be, for example, 15 mm. The material of the substrate 11A is the same as that of the substrate 11 in the first embodiment described above.

[2.2 Method for manufacturing optical recording medium]
The method for manufacturing the optical recording medium 1A according to the second embodiment of the present disclosure is similar to the "first disk manufacturing process" in the first embodiment described above.

[2.3 Effect]
In the optical recording medium 1A according to the second embodiment described above, crosstalk and crosswrite can be suppressed similarly to the optical recording medium 1 according to the first embodiment. Therefore, it is possible to increase the track density of the optical recording medium 1A and increase the capacity of the optical recording medium 1A.

<3 Modification>
In the first and second embodiments described above, a case has been described in which the information signal layer L includes the recording layer 13 having a single layer structure, but the configuration of the information signal layer L is not limited to this. For example, as shown in FIG. 4, the information signal layer L has a laminated structure consisting of a first layer 16 ₁ , . . . , an n-th layer 16 _n (n is an integer of 2 or more) having different compositions. The recording layer 16 may also be provided. In this case, at least one of the first layers 16 ₁ , . . . _, the n-th layer 16 _n has the same composition as the recording layer 13 in the first embodiment. From the viewpoint of suppressing crosstalk and _crosswriting , all the layers of the first layer 16 ₁ , . . . It is preferable to have the following composition.

Further, in the first and second embodiments described above, the information signal layer L includes the recording layer 13, the protective layer 14 provided adjacent to the upper surface of the recording layer 13, and the protective layer 14 adjacent to the lower surface of the recording layer 13. Although a configuration including a protective layer 15 provided as a wafer has been described, the configuration of the information signal layer L is not limited to this. For example, a protective layer may be provided only on either the upper surface or the lower surface of the recording layer 13. Further, the information signal layer L may be composed of only a single recording layer 13. With such a simple configuration, the cost of the optical recording media 1, 1A can be reduced and the productivity thereof can be improved. This effect becomes more pronounced as the medium has more information signal layers L.

Furthermore, in the first and second embodiments described above, the case where all the multilayer information signal layers L have the same layer structure (three-layer structure) has been described, but the characteristics required for each information signal layer L ( For example, the layer structure may be changed depending on optical properties, durability, etc.). However, from the viewpoint of productivity, it is preferable that all the information signal layers L have the same layer configuration.

Furthermore, optical recording media to which the present disclosure can be applied are not limited to those having the configurations in the first and second embodiments. For example, a substrate has a structure in which multiple information signal layers and a protective layer are laminated in this order, and information signals can be recorded or reproduced by irradiating the multiple information signal layers with laser light from the substrate side. It has a configuration in which multiple information signal layers are provided between an optical recording medium (for example, a CD (Compact Disc)) or two substrates, and a laser beam is applied to the multiple layers from at least one substrate side. The present disclosure is also applicable to optical recording media (for example, DVDs (Digital Versatile Discs)) in which information signals are recorded or reproduced by irradiating the information signal layer.

Furthermore, in the case of a multilayer recording layer configuration, the recording layer of the present disclosure may be combined with a recording layer other than a write-once type. Further, the present disclosure is also applicable to an optical recording medium in which a recording area is partially provided with read-only pits or the like.

EXAMPLES Hereinafter, the present disclosure will be specifically described with reference to Examples, but the present disclosure is not limited to these Examples.

(Evaluation device)
In this example, the optical disc was evaluated using a BD evaluation device. Furthermore, in this embodiment, since the verification of the characteristics of the recording material is the key, an optical disc having only one information recording layer (a so-called single-layer disc) was used as the optical disc.

FIG. 5 shows the configuration of a disk drive type evaluation device. Hereinafter, with reference to FIG. 5, the operation and procedure from mounting the optical disc 1A to be evaluated in the disc drive type evaluation apparatus to performing signal evaluation will be described.

First, the optical disk 1A is attached to the spindle motor section 41 and rotated. Next, the recording/reproducing optical system 42 causes the laser diode 51 to emit light, and the laser beam L is made to enter the mirror 54 via the collimator lens 52 and the beam splitter 53. The laser beam L reflected by the mirror 54 is condensed onto the recording layer of the optical disc 1A through the objective lens 55, and then reflected onto the recording layer.

Next, the objective lens 55 is moved up and down in a direction (optical axis direction) perpendicular to the light irradiation surface of the optical disc 1A, so that the focal point of the laser beam L crosses the recording layer of the optical disc 1A. At this time, the laser beam L reflected by the recording layer of the optical disc 1A returns along the path it has traveled, and part or all of the laser beam L is reflected by the beam splitter 53 of the recording/reproducing optical system 42, and the laser beam L is reflected by the condenser lens. The light is incident on a photodetector 57 via 56. The light received by the photodetector 57 is converted into an electrical signal and supplied to the signal analysis device 44. The signal analysis device 44 generates a focus servo error signal, a tracking servo error signal, an RF signal, etc. based on the electric signal supplied from the photodetector 57, and performs servo control etc. based on these generated signals. For example, in focus servo control, a focus error signal is used to control the focus servo so that the laser beam is always focused on the recording layer. In tracking servo control, a tracking error signal is used to control the laser beam so that it is focused on grooves (convex portions) and lands (concave portions) on the recording layer. With the processing up to this point, preparations for information recording are complete. Note that if the information signal has already been recorded on the optical disc 1A, the information signal can be read (reproduced) from the optical disc 1A.

Information signals are recorded on the optical disc 1A in the following manner. A signal generator 43 controls laser emission from the laser diode 51 based on an information signal recorded on the optical disc 1A. Thereby, the emission waveform of the laser beam L emitted from the laser diode 51 is controlled, and the recording layer of the optical disc 1A is irradiated with the waveform. The recording layer irradiated with the laser beam L changes depending on the laser energy. In the recording layer of this example, MnO ₂ is decomposed by laser energy and O ₂ is generated, causing a change in the refractive index and physical volume expansion of the recording layer. The laser beam L can supply sufficient energy to the recording layer to cause this change.

Reproduction of information signals on the optical disc 1A is performed as follows. To reproduce the information signal, the power is low enough that the recording layer of the optical disc 1A will not change even if the same part is reproduced 1 million times by laser beam irradiation, and the recorded information signal can be read with a sufficient S/N. It is done with the power that can be produced. The laser light set in this way is called reproduction light, and the laser power of this reproduction light is called reproduction power. The reproduction light irradiated onto the recording layer of the optical disc 1A travels backward through the recording and reproduction optical system and is detected by the photodetector 57. When information is recorded on the recording layer of the optical disc 1A, for example, the light from the recording section returns with a reduced amount of light compared to the amount of light returning from the unrecorded section. Furthermore, there are optical discs designed so that the amount of light returned from the recorded portion is higher than the amount of light returned from the unrecorded portion. The former is called a High to Low record, and the latter a Low to High record.

The optical disc 1A of this embodiment is a high-to-low recording medium, and this recording method is used in CDs (Compact Discs), DVDs (Digital Versatile Discs), and BDs. The light detected by the photodetector 57 is supplied to the signal analyzer 44, where the signal quality is evaluated.

(Evaluation method of signal characteristics)
Using the above-mentioned BD evaluation apparatus, the signal characteristics of the optical disc 1A were evaluated using the amount of crosstalk CT and CNR (Carrier to Noise Ratio) as evaluation indicators.

The measurement conditions of the evaluation device for BD are shown below.
The channel clock used when recording data on the optical disc 1A was 132 MHz, and one cycle of this clock was 1T. Further, the recording linear velocity was 4.48 m/sec, the wavelength λ of the recording/reproducing laser beam was 405 nm, and the NA of the objective lens used for laser focusing was 0.85.

In this embodiment, as a data recording method, a so-called land/groove recording method is adopted in which data is recorded on both a convex groove track and a concave land track toward the light incident side as recording tracks. In the land/groove recording method, the track next to the groove track becomes a land track. The track pitch Tp means the interval between the centers of the land track and the groove track. In this example, the track pitch Tp was set to 0.16 μm.

The amount of crosstalk CT was measured as follows by measuring the amount of leakage into the land track adjacent to the groove track where the signal was recorded. A signal with a mark length/space length of 12T was recorded on the groove track, and this was used as a 12T monocarrier signal. When recording a 12T monocarrier signal, a method was used in which the laser emission waveform was fixed and the power level was uniformly adjusted.

The amplitude modulation degree of the 12T monocarrier signal was fixed at 50%. A land track adjacent to this signal was irradiated with reproduction light, and the amplitude of the signal leaking from the groove track was observed with an oscilloscope, and was obtained as an amplitude voltage value Vpp. Further, the land track was irradiated with reproduction light at a place where neither the groove track nor the land track was recorded, and the signal level Iv at the time of unrecording was obtained as a voltage level. The amount of crosstalk (amount of leakage) CT was determined using the following formula.
Crosstalk amount CT [%] = (Vpp/Iv) x 100

Further, CNR was measured as follows. The groove track on which the above signal was recorded was irradiated with reproduction light, and the CNR was measured using a spectrum analyzer. In this embodiment, the modulation degree is defined as 50%, and the material composition does not change significantly, so the carrier level does not change much. When a difference in CNR is observed, the main reason is that the noise level changes due to recording.

Examples of the present disclosure will be described in the following order.
i Examination of the influence of the composition of the recording layer on the amount of crosstalk CT and CNR
ii Consideration of the types of additive elements to be added to the recording layer
iii Consideration of the amount of additive elements added to the recording layer

<i Examination of the influence of the composition of the recording layer on the amount of crosstalk CT and CNR>
Using oxides of Mn, W, and Zn as materials for the recording layer, the influence of the composition and thickness of the recording layer on the amount of crosstalk CT and CNR was investigated. Furthermore, the influence of the thickness of the protective layer on the amount of crosstalk CT and CNR was also investigated.

[Reference examples 1-1 to 1-4]
First, a polycarbonate substrate with a thickness of 1.1 mm was molded by injection molding. At this time, one main surface of the polycarbonate substrate was made into an uneven surface consisting of spiral lands and grooves. Further, the track pitch Tp between land and groove was set to 0.16 μm. Next, a first protective layer, a recording layer, and a second protective layer were sequentially laminated on the uneven surface of the polycarbonate substrate by sputtering. Specifically, the configuration of each layer was as follows.

A specific configuration of the information signal layer (L0 layer) is shown below.
Second protective layer (light transmitting layer side)
Material: SIZ (SiO ₂ : In ₂ O ₃ : ZrO ₂ = 20:50:30 (mol%)), thickness: 15 nm
Recording layer Material: MnO _x -WZnO _y , Thickness: 30 nm
First protective layer (substrate side)
Material: SIZ (SiO ₂ : In ₂ O ₃ : ZrO ₂ = 20:50:30 (mol%)), thickness: 15 nm

In the process of forming the recording layer, three targets, an Mn target, a WZnO (W:Zn=4:6 (mol ratio)) target, and a W target, were used to change the material composition of the recording layer. Performed cost sputtering. At this time, the sputtering conditions were adjusted so that the contents of MnO _x and WZnO _y in terms of film thickness (content in terms of film thickness) were the values shown in Table 1.

Next, an ultraviolet curable resin was uniformly applied onto the second protective layer by a spin coating method, and was cured by irradiating ultraviolet rays to form a light transmitting layer having a thickness of 100 μm. Through the above steps, the desired optical disc was obtained.

[Reference examples 2-1, 2-2]
An optical disk was obtained in the same manner as in Reference Example 1-3, except that the sputtering conditions were adjusted so that the thickness of the recording layer and the MnO _x content in terms of film thickness became the values shown in Table 1. .

[Reference examples 3-1, 3-2]
Instead of WZnO (W:Zn=4:6 (mol ratio)) target, WZnO (W:Zn=3:7 (mol ratio)) target, WZnO (W:Zn=7:3 (mol ratio)) target An optical disc was obtained in the same manner as in Reference Example 1-3 except that .

[Reference examples 4-1, 4-2]
Reference example except that the sputtering conditions were adjusted so that the recording layer thickness, the MnO _x content in terms of film thickness, and the WZnO _y content in film thickness equivalent were the values shown in Table 1. An optical disc was obtained in the same manner as in 1-3.

[Reference Examples 5-1 to 5-3]
An optical disk was obtained in the same manner as in Reference Example 1-3, except that the sputtering conditions were adjusted so that the thickness of the recording layer and the content of WZnO _y in terms of film thickness became the values shown in Table 1. .

[Reference Examples 6-1, 6-2]
An optical disk was obtained in the same manner as in Reference Example 1-3, except that the thicknesses of the first protective layer (on the substrate side) and the second protective layer (on the light-transmitting layer side) were 5 nm and 20 nm.

(Evaluation of optical discs)
The optical disc obtained as described above was evaluated as follows.

(Evaluation of optical properties)
The reflectance and transmittance of the recording layer of the optical disc were measured using the reflectance and transmittance measuring function of a spectrophotometer. The results are shown in FIGS. 6A and 6B.

(Evaluation of crosstalk amount CT)
The amount of crosstalk (amount of leakage) CT was measured using the above-mentioned "method for evaluating signal characteristics." The results are shown in FIG. 7A.

(CNR evaluation)
The CNR of the 12T mark was measured using the above-mentioned "method for evaluating signal characteristics." The results are shown in FIG. 7B.

(Optical disc configuration)
Table 1 shows the configurations of the optical discs of Reference Examples 1-1 to 6-2. Note that, as described above, since the recording layer was formed by co-sputtering, Table 1 shows the contents of MnO _x and WZnO _y in terms of film thickness ratio (volume ratio).

(Evaluation results of crosstalk amount CT and CNR)
Table 2 shows the evaluation results of the optical discs of Reference Examples 1-1 to 6-2.

The following can be seen from FIGS. 6A and 6B.
As with the optical discs of Reference Examples 1-1 to 6-2, even if the composition and thickness of the recording layer and the thickness of the protective layer are changed, there is no significant change in the optical properties (reflectance and transmittance). Recognize.

The following can be seen from FIGS. 6A, 6B, and Table 2.
Even if the ratio of MnO _x and WZnO _y is changed under the condition that the thickness of the recording layer is fixed, there is almost no effect on the CNR and the amount of crosstalk CT (Reference Examples 1-1 to 1-4).
Even if the amount of WZnO _y is changed under the condition that the amount of MnOx is fixed, there is almost no effect on the CNR and the amount of crosstalk CT (Reference Examples 5-1 to 5-3, 1-3).

<ii Examination of the types of additive elements added to the recording layer>
Based on the above evaluation results, an additive element capable of reducing crosstalk was studied by fixing the thickness of the recording layer and the amount of MnO _x and replacing part of WZnO _y with an oxide of another element.

[Examples 1-1 to 6-3, Comparative Examples 1-1 to 14-3]
In the formation process of the recording layer, in order to change the material composition of the recording layer, a Mn target, a WZnO (W:Zn=4:6 (mol ratio)) target, a metal M target (where M=Mg, Ti, Zr) were used. , Hf, V, Nb, Ta, Cr, Mo, Ru, Cu, Ag, Al, Ga, Si, Ge, Sn, Sb, Bi, Te), three-source co-sputtering was performed. Ta. At this time, the sputtering conditions were adjusted so that the contents of MnO _x , WZnO _y and MO _z in terms of film thickness became the values shown in Table 3. An optical disc was obtained in the same manner as in Reference Example 1-3 except for the above.

(Evaluation of crosstalk amount CT)
For the optical discs of Examples 1-1 to 6-3 and Comparative Examples 1-1 to 14-3 obtained as described above, the crosstalk amount CT was evaluated in the same manner as Reference Examples 6-1 to 6-2. did. The results are shown in FIG. In addition, in FIG. 8, "metal M" is written on the horizontal axis instead of "MO _z ". For example, "Mg" is written on the horizontal axis instead of "MgO _z ".

(Optical disc configuration)
Table 3 shows the configurations of the optical discs of Examples 1-1 to 6-3 and Comparative Examples 1-1 to 14-3.

From FIG. 8, in the optical disks (Examples 1-1 to 6-3) in which oxides of Hf, Nb, Ta, Si, Sn, or Sb were added to the recording layer as the additive material MO _z , the additive material MO _z was added to the recording layer. It can be seen that the amount of crosstalk CT can be reduced compared to the optical disc (Reference Example 1-3) in which no additive is added. In addition, an optical disk in which an oxide of Mg, Ti, Zr, V, Cr, Mo, Ru, Cu, Ag, Al, Ga, Ge, Bi, or Te was added to the recording layer as the additive material _MOz (Comparative Example 1-1 It can be seen that the crosstalk amount CT can be reduced compared to 14-3).
Therefore, from the viewpoint of reducing the crosstalk amount CT, it is found that it is preferable to use at least one of the oxides of Hf, Nb, Ta, Si, Sn, or Sb as the additive material _MOz .

<iii Study on the amount of additive elements added to the recording layer>
Regarding the additive elements (Hf, Nb, Ta, Si, Sn, and Sb) that were confirmed to have a particularly high effect of reducing the amount of crosstalk CT in the above study, the amounts of these additive elements were investigated.

[Examples 7-1 to 7-5, 8-3 to 8-7, 9-1 to 9-6, 10-2 to 10-7, 11-2 to 11-5, 12-2 to 12-7 , Reference Examples 8-1, 8-2, 9-7, 10-1, 11-1, 12-1 ]
In the formation process of the recording layer, in order to change the material composition of the recording layer, a Mn target, a WZnO (W:Zn=4:6 (mol ratio)) target, a metal M target (where M=Hf, Nb, Ta) were used. Three-source co-sputtering was performed using three targets: , Si, Sn, or Sb). At this time, the sputtering conditions were adjusted so that the content of oxides of additive elements other than MnO _x (ie, WZnO _y and MO _z ) became the values shown in Table 4. An optical disc was obtained in the same manner as in Reference Example 1-3 except for the above.

(Evaluation of crosstalk amount CT)
Examples 7-1 to 7-5, 8-3 to 8-7, 9-1 to 9-6, 10-2 to 10-7, 11-2 to 11-5, obtained as described above, 12-2 to 12-7, Reference Examples 8-1, 8-2, 9-7, 10-1 , 11-1, and 12-1 in the same manner as Reference Examples 6-1 to 6-2. The crosstalk amount CT was evaluated. The results are shown in FIGS. 9A to 11B.

(Optical disc configuration)
Table 4 shows Examples 7-1 to 7-5, 8-3 to 8-7, 9-1 to 9-6, 10-2 to 10-7, 11-2 to 11-5, 12-2 to 12-7, and the configurations of optical discs of Reference Examples 8-1, 8-2, 9-7, 10-1, 11-1, and 12-1 are shown. The contents (atomic %) of WZnO _y and MO _z (where M=Hf, Nb, Ta, Si, Sn or Sb) shown in Table 4 are based on the contents (atomic %) of the metal oxides contained in the recording layer. The content is shown when the remaining components excluding the Mn oxide (that is, the total amount of WZnO _y and MO _z ) is taken as 100 atomic %.

The following can be seen from FIGS. 9A to 11B.
From the viewpoint of reducing the amount of crosstalk, the Hf oxide content a is preferably 0 [atomic %]<a≦75 [atomic %], more preferably 8.3 [atomic %]≦a≦62. 4 [atomic %], and even more preferably 16.6 [atomic %]≦a≦41.6 [atomic %].

From the viewpoint of reducing the amount of crosstalk, the Nb oxide content b is preferably 0 [atomic %]<b≦100 [atomic %], more preferably 19.5 [atomic %]≦b≦100 [atomic %]. atomic %], and even more preferably 34.2 [atomic %]≦b≦78.5 [atomic %].

From the viewpoint of reducing the amount of crosstalk, the Ta oxide content c is preferably 0 [atomic %]<c≦100 [atomic %], more preferably 7.2 [atomic %]≦c≦81. 1 [atomic %], even more preferably 22.2 [atomic %]≦c≦72 [atomic %], particularly preferably 37.9 [atomic %]≦c≦66 [atomic %].

From the viewpoint of reducing the amount of crosstalk, the Si oxide content d is preferably 0 [atomic %]<d≦100 [atomic %], more preferably 15.2 [atomic %]≦d≦100 [atomic %]. atomic %], even more preferably 39.2 [atomic %]≦d≦100 [atomic %], particularly preferably 60.1 [atomic %]≦d≦100 [atomic %].

From the viewpoint of reducing the amount of crosstalk, the Sn oxide content e is preferably 0 [atomic %]<e≦100 [atomic %], more preferably 16.6 [atomic %]≦e≦100 [atomic %]. atomic %], and even more preferably 41.6 [atomic %]≦e≦100 [atomic %].

From the viewpoint of reducing the amount of crosstalk, the Sb oxide content f is preferably 0 [atomic %]<f≦100 [atomic %], more preferably 14.4 [atomic %]≦f≦100 [atomic %]. atomic %], even more preferably 37.6 [atomic %]≦f≦100 [atomic %], particularly preferably 80.8 [atomic %]≦f≦100 [atomic %].

Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments, and various modifications based on the technical idea of the present disclosure are possible.

For example, the configurations, methods, processes, shapes, materials, numerical values, etc. mentioned in the above-mentioned embodiments are merely examples, and different configurations, methods, processes, shapes, materials, numerical values, etc. may be used as necessary. Good too.

Moreover, the configurations, methods, processes, shapes, materials, numerical values, etc. of the above-described embodiments can be combined with each other without departing from the gist of the present disclosure.

In the numerical ranges described in stages in the above-described embodiments, the upper limit or lower limit of the numerical range of one stage may be replaced with the upper limit or lower limit of the numerical range of another stage. The materials exemplified in the above embodiments can be used alone or in combination of two or more, unless otherwise specified.

Further, the present disclosure can also adopt the following configuration.
(1)
comprising at least one recording layer,
The recording layer includes an oxide of Mn and a metal oxide other than the oxide of Mn,
At least a part of the Mn oxide exists as +4-valent Mn,
The metal oxide other than the Mn oxide contains at least one selected from the group consisting of Hf, Nb, Ta, Si, Sn and Sb oxides,
An optical recording medium having a track pitch of 0.225 μm or less.
(2)
a first protective layer provided on the first surface side of the recording layer;
The optical recording medium according to (1), further comprising: a second protective layer provided on the second surface side of the recording layer.
(3)
The recording layer includes two or more layers having different compositions,
The optical recording medium according to (1) or (2), wherein at least one layer of the two or more layers includes the Mn oxide and a metal oxide other than the Mn oxide.
(4)
The metal oxide other than the Mn oxide includes at least an Hf oxide,
The optical recording medium according to any one of (1) to (3), wherein the proportion of the Hf oxide in the metal oxide other than the Mn oxide is greater than 0 atomic % and 75 atomic % or less.
(5)
The optical recording medium according to (4), wherein the proportion of the Hf oxide in the metal oxide other than the Mn oxide is 8.3 atomic % or more and 62.4 atomic % or less.
(6)
The metal oxide other than the Mn oxide includes at least an Nb oxide,
The optical recording medium according to any one of (1) to (3), wherein the proportion of the Nb oxide in the metal oxide other than the Mn oxide is greater than 0 atom % and less than 100 atom %.
(7)
The optical recording medium according to (6), wherein the proportion of the Nb oxide in the metal oxide other than the Mn oxide is 19.5 atomic % or more and 100 atomic % or less.
(8)
The metal oxide other than the Mn oxide includes at least a Ta oxide,
The optical recording medium according to any one of (1) to (3), wherein the proportion of the Ta oxide in the metal oxide other than the Mn oxide is greater than 0 atomic % and 100 atomic % or less.
(9)
The optical recording medium according to (8), wherein the proportion of the Ta oxide in the metal oxide other than the Mn oxide is 7.2 atomic % or more and 81.1 atomic % or less.
(10)
The metal oxide other than the Mn oxide includes at least an Si oxide,
The optical recording medium according to any one of (1) to (3), wherein the proportion of the Si oxide in the metal oxide other than the Mn oxide is greater than 0 atom % and less than 100 atom %.
(11)
The optical recording medium according to (10), wherein the proportion of the Si oxide in the metal oxide other than the Mn oxide is 15.2 atomic % or more and 100 atomic % or less.
(12)
The metal oxide other than the Mn oxide includes at least an Sn oxide,
The optical recording medium according to any one of (1) to (3), wherein the proportion of the Sn oxide in the metal oxide other than the Mn oxide is 0 atomic % or more and 100 atomic % or less.
(13)
The optical recording medium according to (12), wherein the proportion of the Sn oxide in the metal oxide other than the Mn oxide is greater than 16.6 atomic % and 100 atomic % or less.
(14)
The metal oxide other than the Mn oxide includes at least an Sb oxide,
The optical recording medium according to any one of (1) to (3), wherein the proportion of the Sb oxide in the at least one oxide is greater than 0 atom % and less than 100 atom %.
(15)
The optical recording medium according to (14), wherein the proportion of the Sb oxide in the metal oxide other than the Mn oxide is 14.4 atomic % or more and 100 atomic % or less.
(16)
An oxide of Mn and a metal oxide other than the oxide of Mn,
At least a part of the Mn oxide exists as +4-valent Mn,
A recording layer of an optical recording medium, wherein the metal oxide includes at least one selected from the group consisting of oxides of Hf, Nb, Ta, Si, Sn, and Sb.
(17)
Contains Mn and a metal other than Mn as an alloy or metal oxide,
A sputtering target for forming a recording layer of an optical recording medium, wherein the metal other than Mn is at least one selected from the group consisting of Hf, Nb, Ta, Si, Sn, and Sb.

1, 1A Optical recording medium 10 First disk 20 Second disk 30 Laminating layer 11, 11A, 21 Substrate 12, 22 Light transmission layer 13, 16 Recording layer 14, 15 Protective layer 16 ₁ to 16 _nth 1 to Nth layer L0~Ln, L0~Lm Information signal layer S1~Sn, S1~Sm Spacer layer C Light irradiation surface C1 First light irradiation surface C2 Second light irradiation surface Gv Groove Ld Land Tp Track pitch

Claims (3)

comprising at least one recording layer,
The recording layer includes an oxide of Mn and a metal oxide other than the oxide of Mn,
At least a part of the Mn oxide exists as +4-valent Mn,
The metal oxide other than the Mn oxide contains at least one selected from the group consisting of Hf, Nb, Ta, Si, Sn and Sb oxides,
The proportion of the Hf oxide in the metal oxide other than the Mn oxide is 8.3 atomic % or more and 62.4 atomic % or less,
The proportion of the Nb oxide in the metal oxide other than the Mn oxide is 19.5 atomic % or more and 100 atomic % or less,
The proportion of the Ta oxide in the metal oxide other than the Mn oxide is 7.2 atomic % or more and 81.1 atomic % or less,
The proportion of the Si oxide in the metal oxide other than the Mn oxide is 15.2 atomic % or more and 100 atomic % or less,
The proportion of the Sn oxide in the metal oxide other than the Mn oxide is greater than 16.6 atomic % and 100 atomic % or less,
The proportion of the Sb oxide in the metal oxide other than the Mn oxide is 14.4 atomic % or more and 100 atomic % or less,
An optical recording medium having a track pitch of 0.225 μm or less. a first protective layer provided on the first surface side of the recording layer;
The optical recording medium according to claim 1, further comprising: a second protective layer provided on the second surface side of the recording layer. The recording layer includes two or more layers having different compositions,
The optical recording medium according to claim 1, wherein at least one layer of the two or more layers includes the Mn oxide and a metal oxide other than the Mn oxide.

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