Optical recording medium

[0001] [Technical field to which the invention belongs] The present invention relates to a photomagnetic recording medium. [0002] [Conventional technology] The optical recording medium is a recording medium in which a signal recording layer is irradiated with laser light by a recording / reproducing device to record and / or reproduce a recording signal. As the optical recording medium, a reproduction-only digital audio disc (so-called compact disc), an optical video disc (so-called laser disc), a magneto-optical disc, a phase change type optical disc, and the like are known. [0003] As an example of such an optical recording medium, a multilayer structure in which a first dielectric layer, a signal recording layer, a second dielectric layer, and a metal reflection layer are sequentially laminated on a transparent substrate made of, for example, polycarbonate. Examples thereof include an optical magnetic recording medium. In such an optical recording medium, a signal is recorded or a recorded signal is reproduced on a signal recording layer along a recording track, and a groove is formed along the recording track on a transparent substrate. Is formed, and it is desired to realize a recording medium having a larger capacity by improving the recording density. [0004] For example, MD (Mini Disc), which is one of the standards for optical magnetic recording media, has a magnetic recording layer formed of a magnetic thin film having an easy magnetization axis in the direction perpendicular to the substrate surface and having a large magneto-optical effect. The magnetic recording layer, the metal reflective layer, and the dielectric layer are laminated to form a recording unit having a laminated structure on a transparent substrate, and the recording unit is made of, for example, an ultraviolet curable resin. It has a structure in which protective layers are laminated. [0005] In such a minidisc (MD), the pitch of a recording track is conventionally set to 1.6 [μm], and a music signal of 60 [minutes] or 74 [minutes] can be recorded, or the pitch of a recording track is set. Further narrowing the recording density to 1.5 [μm] has been realized, and a music signal of 80 [minutes] can be recorded. [0006] [Problems to be Solved by the Invention] However, as described above, when the pitch of the recording track is narrowed in order to increase the recording capacity, the allowable amount for the defocus of the laser beam irradiated for recording / reproduction (hereinafter referred to as defocus). The problem arises that the tolerance) becomes smaller. If the defocus tolerance becomes small in this way, it may cause crosstalk or the like during recording / playback, and depending on the type of recording / playback device when recording or playing back using different types of recording / playback devices. May cause problems such as inconvenience and difficulty in obtaining compatibility, and may reduce the reliability of the optical recording medium. [0007] On the other hand, in recent years, the walls on both sides of the groove formed on the transparent substrate constituting the optical recording medium have been wobbled into independent shapes (formed in a meandering shape, hereinafter simply referred to as wobble). A so-called ADIP (address-in-pre-groove) type optical recording medium, in which an address can be obtained by this wobble, has been put into practical use. Even in such an optical recording medium, in order to increase the capacity of the signal, it is necessary to narrow the space between the grooves, which causes the above-mentioned problems. [0008] Therefore, the present inventors sufficiently secure the defocus tolerance of the laser beam to be irradiated even when the track pitch of the optical recording medium for decoding the address is narrowed by ADIP (Address in Pregroove). By doing so, it was decided to provide a highly reliable optical recording medium that is sufficiently compatible with high recording densities. [0009] [Means for solving problems] The optical recording medium of the present invention is formed by forming grooves along a recording track on a transparent substrate, and the walls on both sides of the grooves are wobbled into independent shapes, and the width of the grooves is wide. When W is, the relationship of 0.470 W / φ 0.610 is established, and when the depth of the groove is D, the relationship of 0.120 D / (λ / n) 0.142 is established, and the wall surface of the groove is It is assumed that the angle θ is 150 ° ± 10 °.<u style="single">Further, it is assumed that the track pitch of the recording track is approximately 1.5 [μm], and the difference between the defocus tolerance on the Far side and the defocus tolerance on the Near side on the transparent substrate is 4.411 μm or more.</u>However, φ is the spot diameter of the laser light to be irradiated, λ is the wavelength of the laser light in vacuum, and n is the refractive index of the transparent substrate. [0010] According to the optical recording medium of the present invention, the relationship between the width of the groove, the depth of the groove, the spot diameter φ of the laser beam irradiating the angle of the wall surface of the groove, and the wavelength λ is defined as described above. Even when the track pitch is narrowly formed, the defocus tolerance of the laser beam for recording or reproducing the signal can be sufficiently secured, and the optical recording medium having excellent reliability can be obtained. [0011] BEST MODE FOR CARRYING OUT THE INVENTION The optical magnetic recording medium of the present invention is formed by forming grooves (grooves) along a recording track on a transparent substrate such as polycarbonate, and the walls on both sides of the grooves are wobbled into independent shapes. When the width of the groove is W, the relationship of 0.470 W / φ 0.610 holds, and when the depth of the groove is D, 0.120 D / (λ / n) It is assumed that the relationship of 0.142 holds and the angle θ of the wall surface of the groove is 150 ° ± 10 °. (However, φ is the spot diameter of the irradiated laser beam, λ is the wavelength of the laser beam in vacuum, and n is the refractive index of the transparent substrate.) [0012] Hereinafter, as an example of the optical recording medium of the present invention, the optical magnetic recording medium will be described with reference to the drawings, but the optical recording medium of the present invention is not limited to the following examples. That is, the optical recording medium of the present invention is formed by forming grooves (grooves) along the recording track, and the walls on both sides of the grooves are formed in a wobble shape in an independent shape. For example, it can be applied to an optical recording medium that irradiates laser light to perform at least one of recording and reproduction. For example, reproduction in which a predetermined fine uneven pattern corresponding to a recording signal is formed on the signal recording layer. It may be a dedicated optical recording medium, and can be applied to various optical recording media such as a phase change type optical disk having a signal recording layer formed of a phase change material. [0013] FIG. 1 shows a schematic perspective view of a state in which a part of the optical recording medium 10 of the present invention is cut out, and FIG. 2 shows a schematic perspective view for showing the layer structure of the optical recording medium 10. The optical recording medium 10 of the present invention can record and reproduce a recording signal a plurality of times. For example, the optical recording medium 10 is housed in a disc cartridge (not shown) and is a recording / reproducing device (not shown). It is used detachably. [0014] As shown in FIG. 2, the photomagnetic recording medium 10 of the present invention has a first dielectric layer 3, a signal recording layer 4, and a second dielectric on a transparent substrate 2 made of a thermoplastic resin such as a polycarbonate resin. It has a structure in which a body layer 5, a reflective layer 6, and a protective layer 7 are sequentially laminated. [0015] When recording a signal from the optical recording medium 10 shown in FIGS. 1 and 2, a laser beam having a predetermined wavelength, for example, a laser beam having a wavelength of 780 nm is objectively directed from the transparent substrate 2 forming surface 2f side. This is performed by condensing and irradiating with a lens and applying a predetermined magnetic field with a recording magnetic head of a recording / reproducing device. [0016] At this time, in the optical recording medium 10, the signal recording layer 4 is heated by the laser beam and the coercive force is reduced. Therefore, the magnetic domain applied by the recording magnetic head causes the magnetic domain corresponding to the recording signal to be the signal recording layer. Recorded in 4. [0017] Further, when the recorded signal recorded on the signal recording layer 4 is reproduced, a laser beam having a weaker output than the laser beam used for signal recording is irradiated. At this time, in the optical recording medium 10, the return light reflected by the laser beam on the signal recording layer 4 is polarized by the Kerr effect, the Faraday effect, and the magneto-optical effect. The recording / reproducing device detects the direction of the magnetic field of the magnetic domain recorded in the signal recording layer 4 by detecting the polarization direction of the return light, thereby reproducing the recorded signal. [0018] The transparent substrate 2 is formed in a substantially disk shape by a hard material having transparency to laser light. As the material for forming the transparent substrate 2, for example, various resin materials such as polycarbonate resin, acrylic resin, polyolefin resin, and epoxy resin, quartz glass, and the like can be used. Further, on the transparent substrate 2, groove-shaped grooves 2b are formed in a spiral shape in the circumferential direction. The optical recording medium 10 is configured to record and reproduce a signal with respect to the signal recording layer 4 along the groove 2b. That is, in the optical recording medium 10, a recording track is formed along the groove 2b. [0019] Further, in the optical recording medium 10 of the present invention, as shown in FIG. 3, the groove 2b is formed by meandering with a minute width at a constant period in the radial direction, that is, the walls on both sides of the groove 2a. 21 and 22 are formed in a wobble shape in an independent shape. [0020] The optical recording medium 10 has a configuration in which the meandering cycle of the groove 2b can be read by the recording / reproducing device when recording or reproducing by the laser beam. As a result, the recording / reproducing device can always keep the rotation speed of the optical recording medium 10 stable based on the groove 2b meandering at a constant cycle. [0021] [0021] Further, the groove 2b is used as a positioning reference when recording or reproducing the recorded signal with respect to the signal recording layer 4 by the recording / reproducing device, and has a function of indicating the recording position, that is, the address of the recorded signal in the optical recording medium 10. Have. As a result, the recording / reproducing device can perform quick and accurate positioning when recording / reproducing with respect to the optical recording medium 10. [0022] FIG. 4 shows a simplified cross-sectional view of the layer structure of the optical recording medium 10 of the present invention. In this case, the description of the first dielectric layer 4, the second dielectric layer 5, and the reflective layer 6 will be omitted. In the optical recording medium 10 of the present invention, when the width of the groove 2a is W, 0.470 W / φ 0.610, and when the depth of the groove 2a is D, 0.120 D / (λ / n). It is assumed that 0.142 and the angle θ of the wall surface of the groove 2a is 150 ° ± 10 °. However, φ is the spot diameter of the laser beam to be irradiated, λ is the wavelength of the laser beam L in vacuum, and n is the refractive index of the transparent substrate. [0023] Further, the track pitch TP of the recording track of the optical recording medium 10 of the present invention is set to be approximately 1.5 [μm]. [0024] Also, when the width of groove 2a is W and the depth of groove 2a is D, It is formed so that 0.200 {(D / (λ / n)) / (W / φ)} 0.330. However, φ is the spot diameter of the laser light to be irradiated, λ is the wavelength of the laser light in vacuum, and n is the refractive index of the transparent substrate. [0025] The first dielectric layer 3 and the second dielectric layer 5 improve the C / N characteristics and prevent corrosion of the signal recording layer 4. That is, since the transparent substrate 2 and the protective layer 7 often contain components that corrode metals such as chloride ions, the first dielectric layer 3 and the second dielectric layer 5 are used. By forming the signal recording layer 4 so as to be sandwiched in the middle, it is possible to avoid being directly affected by the components that corrode the metal. [0026] The first dielectric layer 3 and the second dielectric layer 5 need to be formed of a material having a low absorption capacity with respect to the applicable wavelength of the laser beam L for recording / reproduction. For example, Si₃N₄, SiN, AlN, Al₂O₃, AlSiNO, HfO₂, ZnS, ZrO₂, Y₂O₃, MgO, SiO₂, MgF₂, LiF, etc. are used to form a thin film on the transparent substrate 2 by thin film forming techniques such as various sputtering methods. However, the material forming the first dielectric layer 3 has translucency with respect to the laser beam L incident to record or reproduce the recorded signal, and allows oxygen and water molecules to pass through. It is desirable to use a material that does not contain oxygen, SiN, Si₃N₄, Or AlN is preferably used. [0027] In this case, the signal recording layer 4 constituting the optical recording medium 10 of the present invention includes an optical magnetic recording layer in its configuration, and is formed in a thin film shape on the first dielectric layer 3 shape. There is. This photomagnetic recording layer is formed of a material having magneto-optical characteristics such as the Kerr effect and the Faraday effect, while the coercive force decreases due to the temperature rise exceeding the Curie temperature and the magnetization is reversed in the direction of the external magnetic field. For example, it is formed of rare earth / transition metal alloys such as TbFeCo, TbFeCoCr, and GdFeCo. [0028] The signal recording layer 4 may be formed of a single layer only by the optical magnetic recording layer, and has been proposed by, for example, a CAD (Center Aperture Ditector) disk, an MSR (Magnetic ally induced Super Resolution) disk, or the like. As described above, it may be formed in a multi-layer structure in which a dielectric layer or the like is further laminated. [0029] Further, the uneven shape of the groove 2a of the transparent substrate 2 is transferred to the signal recording layer 4. In the optical recording medium 10, a recording track on which the recording signal is recorded and reproduced is formed on the signal recording layer 4 along the groove 2a. Further, in the optical recording medium 10, the track pitch of the recording track is configured to be approximately 1.5 [μm] and 1.5 ± 0.01 [μm] in consideration of the error range. As a result, the optical recording medium 10 can improve the recording density as compared with the conventional optical recording medium having a track pitch of 1.6 [μm], for example. Therefore, the optical recording medium 10 can have a large recording capacity while maintaining the same outer diameter as that of the conventional optical recording medium. Further, in the optical recording medium of the present invention, the width of the groove 2a, the depth of the groove 2a, the spot diameter φ of the laser beam irradiating the angle of the wall surface of the groove, and the wavelength λ are numerically defined. As a result, even when the track pitch is formed narrower than in the conventional case, the defocus tolerance of the laser beam for recording or reproducing the signal can be sufficiently secured, and high reliability can be maintained. [0030] The reflective layer 6 constituting the optical recording medium 10 is formed in a thin film shape on the second dielectric layer 5. The reflection layer 6 has a function of reflecting the laser beam L transmitted through the signal recording layer 4 and the second dielectric layer 5, and the signal recording layer 4 is generated by the laser beam emitted toward the signal recording layer 4. It has a function as a heat sink that prevents heat from being accumulated in the laser. [0031] Since the reflective layer 6 of the optical recording medium 10 has a function of reflecting the laser beam, it is possible to improve the utilization efficiency of the laser beam L during recording / reproduction. As the material for forming the reflective layer 6, it is desirable to use a non-magnetic metal element or a compound thereof, which is a thermally good conductor, alone or in combination, and it is formed of, for example, Au, Al or the like. [0032] The protective layer 7 is formed in a thin film on the reflective layer 6 by, for example, curing an ultraviolet curable resin applied with a spin coater or the like. By providing the protective layer 7 in the optical recording medium 10, it is possible to prevent the signal recording layer 4 and the reflection layer 6 from being deteriorated by oxidation or the like. In addition, it is possible to prevent scratches from occurring in each layer formed on the transparent substrate 2. [0033] The protective layer 7 may be internally impregnated with various lubricants, or may be coated with various lubricants on its surface. As a result, when the recording magnetic head of the recording / reproducing device is slid on the forming surface of the protective layer 7, the optical recording medium 10 avoids wear and heat generation of the recording magnetic head and the protective layer 7. be able to. [0034] Next, the optical recording medium of the present invention will be described with reference to specific [Examples] and [Comparative Examples], but the present invention is not limited to the examples shown below. In each of the examples shown below, a magneto-optical disk (MD) will be described as the optical recording medium of the present invention. [0035] [Example 1] As an optical recording medium 10 having the structure shown in FIG. 1, a magneto-optical disk in which each layer is sequentially formed on a transparent substrate 2 having a disk shape with a diameter of 64 mm was produced as follows. The materials used to form each layer are shown below. Transparent substrate 2: Polycarbonate resin First Dielectric Layer 3: SiN Signal recording layer 4: TbFeCo Second Dielectric Layer 5: SiN Reflective layer 6: Al Protective layer 7 : UV curable resin The thickness of each layer was formed according to a known MD standard, and the track pitch of the recording track was formed to 1.5 [μm]. Further, the magneto-optical disk of [Example 1] has the following features. When the width of groove 2a is W, W / φ = 0.5411. When the depth of groove 2a is D, D / (λ / n) = 0.1385. The angle θ of the wall surface of the groove 2a is 142.9 ° at the minimum value and 155.4 ° at the maximum value. When the width of groove 2a is W and the depth of the groove is D, {(D / (λ / n)) / (W / φ)} = 0.25597. (However, φ is the spot diameter of the irradiated laser beam, λ is the wavelength of the laser beam in vacuum, and n is the refractive index of the transparent substrate.) [0036] [Example 2] to [Example 10] A magneto-optical disk in which each layer was formed on a transparent substrate was produced according to the MD standard by the same film configuration as in [Example 1] above. For these as well, the track pitch of the recording track was formed to 1.5 [μm]. Each magneto-optical disk of [Example 2] to [Example 10] has the above-mentioned W / φ, D / (λ / n), the minimum and maximum values of the angle θ of the wall surface of the groove 2a, and {(D / The values of (λ / n)) / (W / φ)} were changed so that they would be different from each other. However, in any of the magneto-optical disks of [Example 2] to [Example 10], 0.470 W / φ 0.610 and 0.120 D / (λ / n) 0.142, and the wall surface of the groove. It is assumed that the angle θ is 150 ° ± 10 ° and 0.200 {(D / (λ / n)) / (W / φ)} 0.330. [0037] [Comparative Example 1] A magneto-optical disk in which each layer was formed on a transparent substrate was produced according to the MD standard by the same film configuration as in [Example 1] above. For these as well, the track pitch of the recording track was formed to 1.5 [μm]. The magneto-optical disk of [Comparative Example 1] has the following features. When the width of groove 2a is W, W / φ = 0.5022. When the depth of groove 2a is D, D / (λ / n) = 0.1479. The angle θ of the wall surface of the groove 2a is 155.2 ° at the minimum value and 161.2 ° at the maximum value. When the width of groove 2a is W and the depth of the groove is D, {(D / (λ / n)) / (W / φ)} = 0.29446. [0038] [Comparative Example 2] A magneto-optical disk in which each layer was formed on a transparent substrate was produced according to the MD standard by the same film configuration as in [Example 1] above. For these as well, the track pitch of the recording track was formed to 1.5 [μm]. The magneto-optical disk of [Comparative Example 2] has the following features. When the width of groove 2a is W, W / φ = 0.6123. When the depth of groove 2a is D, D / (λ / n) = 0.1145. The angle θ of the wall surface of the groove 2a is 154.2 ° at the minimum value and 160.5 ° at the maximum value. When the width of groove 2a is W and the depth of the groove is D, {(D / (λ / n)) / (W / φ)} = 0.18694. [0039] [Comparative Example 3] A magneto-optical disk in which each layer was formed on a transparent substrate was produced according to the MD standard by the same film configuration as in [Example 1] above. For these as well, the track pitch of the recording track was formed to 1.5 [μm]. The magneto-optical disk of [Comparative Example 3] has the following features. When the width of groove 2a is W, W / φ = 0.4215. When the depth of groove 2a is D, D / (λ / n) = 0.1444. The angle θ of the wall surface of the groove 2a is 154.8 ° at the minimum value and 161.0 ° at the maximum value. When the width of groove 2a is W and the depth of the groove is D, {(D / (λ / n)) / (W / φ)} = 0.34261. [0040] W / φ, D / (λ / n), and the wall surface of the groove 2a of the magneto-optical disks of [Example 1] to [Example 10] and [Comparative Example 1] to [Comparative Example 3] described above. The values of the angles θ and {(D / (λ / n)) / (W / φ)} are shown in [Table 1] below. [0041] [table 1]<img file="JP4333003B2_D0001.tif" />[0042] [Characteristic evaluation] For each magneto-optical disk of [Example 1] to [Example 10] and [Comparative Example 1] to [Comparative Example 3] produced as described above, an optical system conforming to the MD standard was used. By irradiating the recording track with laser light and changing the defocus amount of the laser light in each magneto-optical disk, the defocus amount and the W / φ, D / (respectively of the above-mentioned magneto-optical disk, respectively. The relationship between λ / n), the angle θ of the wall surface of groove 2a, and the values of {(D / (λ / n)) / (W / φ)} was investigated. The measurement conditions at this time are shown below. Linear disk speed of magneto-optical disk: 1.2 ~ 1.4 [m / s] Laser beam wavelength λ: 780 [nm] Numerical aperture of objective lens NA: 0.45 [0043] The amount of defocus [μm] of the laser beam in the magneto-optical disks of the above [Example 1] to [Example 10] and [Comparative Example 1] to [Comparative Example 3] is changed, and the Near side and the Far side are used. The amount of defocus [μm] at the moment when three or more address errors that this laser beam reads from the groove of each magneto-optical disk occurs when each value is gradually increased is shown in [Table 1] above. Shown. [0044] Further, FIG. 5 shows the defocus amounts of the magneto-optical disks of [Example 1] to [Example 10] and [Comparative Example 1] to [Comparative Example 3], and the (W / φ) of each magneto-optical disk. Relationship with, Fig. 6 shows the relationship between the defocus amount of the magneto-optical disk and (D / (λ / n)) of each magneto-optical disk, and Fig. 7 shows the defocus amount of the magneto-optical disk. The relationship with {(D / (λ / n)) / (W / φ)} of the magneto-optical disk is shown. [0045] In addition, in FIGS. 5 to 7, the mark indicates that the magneto-optical disks of [Example 1] to [Example 10] have three or more address errors that the laser beam reads from the groove of each magneto-optical disk on the Near side. The amount of defocus [μm] at the moment of occurrence is shown, and the mark indicates the address error that the laser beam reads from the groove of each magneto-optical disk on the Far side in the magneto-optical disks of [Example 1] to [Example 10]. Indicates the amount of defocus [μm] at the moment when 3 or more are generated. In addition, the x mark indicates the amount of defocus at the moment when three or more address errors that the laser beam reads from the groove of each magneto-optical disk occur on the Near side in the magneto-optical disks of [Comparative Example 1] to [Comparative Example 3]. [Μm] is indicated, and the + mark indicates the moment when three or more address errors occur in the magneto-optical disks of [Comparative Example 1] to [Comparative Example 3] in which the laser beam reads from the groove of each magneto-optical disk on the Far side. Defocus amount [μm] is shown. [0046] In FIGS. 5 to 7, the alternate long and short dash line indicates the defocus tolerance (1.032 [μm]) of the limit value on the Far side where the occurrence of an error is allowed in the MD standard, and the broken line indicates the occurrence of an error in the MD standard. The allowable defocus tolerance on the Near side (-2.153 [μm]) is shown. [0047] Further, in FIGS. 5 to 7, as the defocus amount shown on the vertical axis increases in the positive direction, the focal position of the laser beam moves toward the back of the signal recording surface, and the absolute value of the value in the negative direction. The larger the value, the closer the focal position of the laser beam is toward the signal recording surface. [0048] That is, in FIGS. 5 to 7, if there is a plot inside the alternate long and short dash line, that is, in the area surrounded by the alternate long and short dash line, an address error frequently occurs even with a small amount of defocus. It is shown that. On the other hand, in FIGS. 5 to 7, when there is a plot in the region outside the alternate long and short dash line, the laser beam can follow the recording track even when the defocus amount is large. Shown. Further, in FIGS. 5 to 7, the larger the difference between the defocus tolerance on the Far side and the defocus tolerance on the Near side, that is, the larger the gap between the plots, the larger the defocus margin. Shown. [0049] As shown in FIGS. 5 and 6, when the track pitch of the recording track is manufactured to be 1.5 [μm], when the width of the groove is W, 0.470 W / φ 0.610, which is 0.470 W / φ 0.610. When the depth is D, 0.120 D / (λ / n) 0.142, and the angle θ of the wall surface of the groove is 150 ° ± 10 °. For magnetic disks, both plots have a limit defocus tolerance (1.032 [μm]) on the Far side and a limit defocus tolerance (-2.153 [μm]) on the Near side, where errors are allowed to occur in the MD standard. ]) Was exceeded, and the defocus margin could be increased. [0050] Further, as shown in FIG. 7, when the track pitch of the recording track is manufactured to be 1.5 [μm], when the width of the groove is W and the depth of the groove is D, 0.200 {( In the magneto-optical disks of [Example 1] to [Example 10], where D / (λ / n)) / (W / φ)} 0.330, all plots have errors in the MD standard. It exceeds the limit defocus tolerance (1.032 [μm]) on the Far side and the limit defocus tolerance (-2.153 [μm]) on the Near side, which are allowed to occur, and the defocus margin can be increased. did it. [0051] On the other hand, when the depth of groove 2a is D, the value of D / (λ / n) is 0.1479, which exceeds 0.142. In the magneto-optical disk of [Comparative Example 1], as is clear from FIG. Although the defocus tolerance of the limit value on the Far side and the defocus tolerance of the limit value on the Near side, which are allowed to generate errors in the MD standard, were achieved, the above-mentioned [Example 1] to [Implementation] It was found that the defocus margin was smaller than that of the magneto-optical disk in Example 10]. [0052] When the width of the groove is W, the value of W / φ exceeds 0.610, and when the depth of the groove is D, the value of D / (λ / n) is less than 0.120, and {(D / The magneto-optical disk of [Comparative Example 2] in which the value of (λ / n)) / (W / φ)} is less than 0.200, and the value of D / (λ / n) in which the value of W / φ is less than 0.470. In the magneto-optical disk of [Comparative Example 3] where the value exceeds 0.142 and the value of {(D / (λ / n)) / (W / φ)} exceeds 0.330, Fig. 5 to Fig. As is clear from 7, at least one of the limit defocus tolerance on the Far side and the limit defocus tolerance on the Near side, which are allowed to generate errors in the MD standard, cannot be achieved, as described above. It was found that the defocus margin was smaller than that of the magneto-optical disks of [Example 1] to [Example 10]. [0053] As described above, when a groove is formed on the transparent substrate along the recording track, the walls on both sides of the groove are wobbled into independent shapes, and the width of the groove is W. When the relationship of 0.470 W / φ 0.610 is established and the depth of the groove is D, the relationship of 0.120 D / (λ / n) 0.142 is established and 0.200 {(D / (λ / n)). ) / (W / φ)} 0.330, and the groove wall angle θ is 150 ° ± 10 °. In an optical recording medium, the track pitch of the recording track is narrower than before 1.5. It was found that a large defocus margin can be obtained even when the value is set to [μm]. [0054] [Effect of the invention] According to the optical recording medium of the present invention, the width W of the groove, the depth D of the groove, and the angle θ of the wall surface of the groove are 0.470 W in relation to the spot diameter φ of the laser beam to be irradiated and the wavelength λ. / φ 0.610, 0.120 D / (λ / n) 0.142, 0.200 {(D / (λ / n)) / (W / φ)} 0.330, and θ = 150 ° ± 10 ° As a result, even when the track pitch of the recording track is set to 1.5 [μm], which is narrower than before, the defocus tolerance of the laser beam for recording or reproducing the signal can be ensured to a sufficient magnitude, and the reliability is high. It was possible to use an excellent optical recording medium. [Simple explanation of drawings] FIG. 1 shows a schematic cross-sectional view of an example of the optical recording medium of the present invention. FIG. 2 shows a schematic perspective view showing a cross-sectional layer structure in which a part of the optical recording medium of the present invention is cut out. FIG. 3 shows a schematic view of the shape of the groove of the optical recording medium of the present invention. FIG. 4 shows a schematic cross-sectional view of the optical recording medium of the present invention. FIG. 5 shows the relationship between the defocus amount of the magneto-optical disk of the present invention and the (W / φ) of the magneto-optical disk. FIG. 6 shows the relationship between the defocus amount of the magneto-optical disk of the present invention and (D / (λ / n)) of the magneto-optical disk. FIG. 7 shows the relationship between the defocus amount of the magneto-optical disk of the present invention and {(D / (λ / n)) / (W / φ)} of the magneto-optical disk. [Explanation of symbols] 2 Transparent substrate, 2a groove, 2f Transparent substrate forming surface, 3 First dielectric layer, 4 Signal recording layer layer, 5 Second dielectric layer, 6 Reflective layer, 7 Protective layer, 10 Optical recording medium, 21, 22 Groove wall