JP2001014726A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain sufficient recording and reproducing characteristics while making possible higher recording density by forming thin-film layers which are recorded in both of land parts and groove parts and are formed with lands and grooves to flatten the surface on a light incident side. SOLUTION: The light reflection film 4, the dielectric film 5, the phase transition film 6 and the dielectric film 7 are laminated and formed on a disk substrate 3 formed with the lands L and grooves G along recording tracks. The surface of the dielectric film 7 which is the thin-film layer existing on the extreme surface of this phase transition optical disk 1 is flattened. Then, the appearance of the rugged patterns of the lands L and grooves G on the surface thereof does not occur and the surface of the optical disk 1 is made nearly flat. Since the surface of the dielectric film 7 which is the thin-film layer existing on the medium surface is flattened, the evanescent light from the lens end face of a solid immersion lens 2 successively intrudes into the phase transition type optical disk 1. The good recording and reproducing characteristics are thus obtained, even if the difference in level D of the lands L and the grooves G is large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium on which recording and / or reproduction is performed by irradiating light condensed under a condition that the numerical aperture is 1 or more.

[0002]

2. Description of the Related Art Recording and reproduction are performed on an optical recording medium in a non-contact manner by irradiating light condensed by an objective lens. For example, in a read-only optical disk in which information is recorded in advance by embossed pits or a phase-change optical disk in which information is written by changing the phase of a recording layer, the light condensed by an objective lens is irradiated and the reflectance of the reflected light is reflected. The recorded information is reproduced by detecting the change. Also, for example, in a magneto-optical disk that records and reproduces information by using a magneto-optical effect, the light condensed by an objective lens is irradiated, and a change in the Kerr rotation angle of the reflected light is detected, thereby obtaining a magnetic field. By detecting the magnetization direction of the domain,
Play the recorded information.

As described above, when condensing light with an objective lens and irradiating the light on an optical recording medium, the size of a light spot on the optical recording medium is determined by setting the numerical aperture of the objective lens to NA and the light wavelength to λ. Then, it is approximately λ / NA. Since the smaller the light spot, the higher the resolution, it is desirable to increase the numerical aperture NA of the objective lens in order to increase the recording density of the optical recording medium.

[0004] Here, assuming that the refractive index of the medium is n and the angle of the marginal ray of the objective lens is θ, the numerical aperture NA = ns
inθ. Therefore, when the medium is air (n
= 1), the numerical aperture NA cannot exceed 1. Therefore, as a technology exceeding this limit, a technology for recording and reproducing data on an optical recording medium using a so-called solid immersion lens as an objective lens is disclosed in, for example, "BDTerris et al.," Near Field Opti.
cal data storage, "Appl. Phys. Lett. 68 (2), 1996"
And so on.

For example, as shown in FIG. 15, recording on a phase change type optical disk 106 in which a light reflection film 102, a dielectric film 103, a phase change film 104, and a dielectric film 105 are laminated on a disk substrate 101. When reproduction is performed using the solid immersion lens 107, the solid immersion lens 107 is brought close to the surface of the phase-change optical disk 106. Then, the light for recording and reproduction is transmitted through the solid immersion lens 107 to the phase-change optical disk 10.
Focus on 6

At this time, the solid immersion lens 1
If the distance between the lens end surface of the lens 07 and the surface of the phase-change optical disk 106 is sufficiently narrower than the wavelength of light, the evanescent light from the lens end surface of the solid immersion lens 107 is coupled to the phase-change optical disk 106. Then, the light is taken out of the lens, and recording and reproduction using the evanescent light can be performed.

As described above, the numerical aperture NA is n · sin
where n is the refractive index of the solid immersion lens when a solid immersion lens is used. Therefore, by using a solid immersion lens, the numerical aperture NA can be set to 1 or more. As a result, it is possible to increase the resolution by reducing the light spot and increase the recording density of the optical recording medium.

When recording and reproduction are performed using a solid immersion lens with a numerical aperture NA of 1 or more, it is preferable from an optical point of view that there is no gap between the solid immersion lens and the optical recording medium. . However, since it is necessary to rotate the optical recording medium at the time of recording and reproduction, a slight gap is required between the solid immersion lens and the optical recording medium.

In a system having such a gap, the numerical aperture N
In order to set A to be 1 or more, the lens end face of the solid immersion lens may be brought sufficiently close to the optical recording medium so that the evanescent light from the lens end face of the solid immersion lens is coupled to the optical recording medium. Here, the evanescent light decays exponentially from the interface. Therefore, even if a gap is provided between the solid immersion lens and the optical recording medium, the gap needs to be sufficiently narrowed.

[0010] For example, "K. Saito et al.," MTF ca
lculation of M0 readout using solid immertion len
s, "Digest of MORIS '99, PD-03", if the gap between the solid immersion lens and the optical recording medium is about 1/10 of the wavelength of light used for recording and reproduction, the solid immersion lens It has been reported that a good reproduction signal can be obtained under the condition that the numerical aperture NA is 1 or more, even if there is a gap between the optical recording medium and the optical recording medium.

Meanwhile, as a technique for increasing the recording density of an optical recording medium, a so-called land-groove recording technique has been devised. For land / groove records,
For example, "N. Miyagawa et a1.," Land and Groove Recordi
ng for High Track Densityon Phase-Change 0ptical D
Isks, "Jpn. J. Appl. Phys. Vol. 32 (1993)".

In land-groove recording, an optical recording medium
Lands and grooves are formed along the recording tracks.
Here, the groove is a groove formed spirally or concentrically along the recording track, and is also referred to as a guide groove.
The land on the hill between the grooves becomes the land.

These lands and grooves are formed mainly for stably performing tracking servo. In other words, the lands and grooves are for enabling the generation of a tracking error signal indicating the deviation of the light spot from the recording track. At the time of recording and reproduction, the light spot is recorded based on the tracking error signal. It is controlled to follow the track.

In many conventional optical recording media, only land portions are used as recording tracks, or only groove portions are used as recording tracks. On the contrary,
In land / groove recording, recording is performed on both the land portion and the groove portion using both the land portion and the groove portion as recording tracks. Therefore, by employing land-groove recording, the track density can be almost doubled as compared with a conventional optical recording medium in which only the groove portion or the land portion is used as a recording track.

The refractive index of the portion where the groove is formed is denoted by n, the physical step between the land and the groove is denoted by D,
When the wavelength of light used for recording and reproduction is λ, n × Dｎ
In the case of λ / 6, crosstalk from an adjacent recording track is minimized. In other words, in land / groove recording, the optical depth of the groove is set to 1/6 of the wavelength of light used for recording / reproducing, so that the signal recorded on the land portion is reproduced from the adjacent groove when reproducing the signal. Signal leakage and signal leakage from adjacent lands when a signal recorded in a groove portion is reproduced are minimized.

[0016]

A technique in which recording / reproducing is performed using a solid immersion lens with a numerical aperture NA of 1 or more and a land / groove recording technique are combined to use each technique independently. It is expected that the recording density can be further increased as compared with. However, if these techniques are simply combined, sufficient recording / reproducing characteristics cannot be obtained. The result of verifying this with a specific example will be described below.

Here, a phase change optical disk 110 as shown in FIG. 16 will be described as an example. The phase-change optical disk 110 is an optical recording medium on which land-groove recording is performed by laser light condensed using a solid immersion lens 111 under the condition that the numerical aperture NA is 1 or more.
The disk substrate 112 includes lands L and grooves G formed along recording tracks. Then, on the disk substrate 112, a light reflection film 113, a dielectric film 114, a phase change film 115, and a dielectric film 116 are laminated and formed.

The phase change optical disk 110 is a rewritable optical recording medium, and has a phase change film 115 as a layer for retaining information. This phase change optical disk 110
Is irradiated with the laser light, the temperature of the phase change film 115 at the portion irradiated with the laser light rises, and that portion is melted.
Thereafter, when the light spot moves and the position of the light spot shifts, the temperature of the melted portion decreases.

At this time, if the laser beam is irradiated so as to have a very high temperature, the temperature drops rapidly, and the portion becomes amorphous because there is no time for crystallization. On the other hand, when the laser beam is irradiated so as to have a relatively low temperature, the temperature gradually decreases, so that portion is crystallized.

As described above, the phase change optical disk 110
Records information by setting the phase change film 115 to an amorphous state or a crystalline state. Here, the phase change film 1
Reference numeral 15 is formed of a material having a different refractive index between a crystalline state and an amorphous state. Reproduction of the recorded information is performed by detecting a difference in reflectance caused by a difference in refractive index of the phase change film 115 as a change in intensity of reflected light.

Incidentally, such a phase change type optical disk 11
For recording and reproducing 0, for example, an optical system as shown in FIG. 17 is used. In this optical system, the laser light from the laser diode 121 is converted into parallel light by the collimator lens 122, and the parallel light is converted into the polarization beam splitters 123 and 1 /.
A two-group objective lens 12 composed of a convex lens 125 and a solid immersion lens 111 via a four-wavelength plate 124
6 and is focused on the phase-change optical disk 110 by the second group objective lens 126. The light condensed on the phase change optical disk 110 is
It is reflected by 10. The return light reflected and returned by the phase-change optical disk 110 enters the polarization beam splitter 123 via the second-group objective lens 126 and the quarter-wave plate 124. Then, the return light that has entered the polarization beam splitter 123 is reflected and extracted by the polarization beam splitter 123, and is detected by the photodetector 127. Here, for the sake of simplicity, optical systems for focus servo and tracking servo are omitted.

In the case where the recording / reproducing of the phase change optical disk 110 is performed by the above optical system,
The reproduction characteristics were calculated. Here, the disk substrate 112
Has a refractive index of 1.55. The light reflecting film 113 is
The film thickness was 200 nm, and the refractive index was 1.0 + 6.0i. The dielectric film 114 has a thickness of 20 nm and a refractive index of 2.1. The phase change film 115
It is assumed that the film thickness is 20 nm, the refractive index in the crystalline state is 4.2 + 3.5i, and the refractive index in the amorphous state is 4.0 + 1.8i. The dielectric film 116 has a thickness of 120 nm and a refractive index of 2.1.

FIGS. 18 and 19 show models used for calculating the reproduction characteristics. FIG. 18 shows a model in which a recording mark is formed in a land portion, and FIG. 19 shows a model in which a recording mark is formed in a groove portion.
In FIGS. 18 and 19, the correspondence between the lands and the grooves and the light spots is shown in an easily understandable manner.
Illustration of the solid immersion lens and the like is omitted. In FIGS. 18 and 19, cross-hatched portions indicate recording marks formed on the phase change film 115. The recording mark portion is in an amorphous state, and the others are in a crystalline state.

In the models of FIGS. 18 and 19, the carrier level of the reproduced signal can be calculated by calculating the amplitude of the reproduced signal when the light spot moves along the arrow a in the figure. Further, by calculating the reproduction signal when the light spot moves along the arrow b in the figure, it is possible to calculate signal leakage from an adjacent recording track, that is, crosstalk.

Therefore, in the model of FIG. 18, the reproduction signal from the land portion, which is convex when viewed from the light incident side, and the crosstalk from the groove portion, which is concave when viewed from the light incident side, are calculated. did. In the model of FIG. 19, the reproduction signal from the groove portion, which is a concave portion as viewed from the light incident side, and the crosstalk from the land portion, which is a convex portion as viewed from the light incident side, were calculated. Here, the numerical aperture NA when condensing the laser light is 1.5, the wavelength λ of the laser light used for recording and reproduction is 600 nm, the pitch Py of the recording marks is 200 nm, and the track pitch is 24.
It was set to 0 nm. In addition, the solid immersion lens 11
The refractive index of 1 was 2.0, and the gap between the solid immersion lens 111 and the phase change optical disk 110 was 50 nm on the land.

In the above model, how the carrier level and the crosstalk of the reproduced signal change when the depth of the groove is changed and the step D between the land and the groove is changed is calculated. The results are shown in FIG. 20 and FIG.
It is shown in FIG.

FIG. 20 shows the land and groove steps D as parameters for the carrier level of the reproduced signal calculated using the model of FIG. 18 and the crosstalk calculated using the model of FIG. I have. Here, the step D between the land and the groove is standardized by the wavelength λ of the laser beam used for recording and reproduction. The crosstalk is standardized by the carrier level of the reproduced signal calculated using the model of FIG.

FIG. 21 shows, as parameters, the land and groove steps D for the carrier level of the reproduced signal calculated using the model of FIG. 19 and the crosstalk calculated using the model of FIG. I have. Here, the step D between the land and the groove is standardized by the wavelength λ of the laser beam used for recording and reproduction. The crosstalk is normalized by the carrier level of the reproduced signal calculated using the model of FIG.

As described above, when land-groove recording is performed using an ordinary optical system, the optical depth of the groove is set to 1/6 of the wavelength of the laser beam used for recording and reproduction. , Crosstalk can be suppressed. However, as can be seen from FIGS. 20 and 21, when the numerical aperture NA is set to 1 or more using a solid immersion lens, even if the optical depth of the groove is set to 1/6 of the laser light wavelength. However, the crosstalk becomes very large.

As can be seen from FIGS. 20 and 21, when the numerical aperture NA is set to 1 or more using a solid immersion lens, as the step D between the land and the groove increases, the data is recorded in the groove portion. When the signal is reproduced, the carrier level of the reproduced signal is extremely deteriorated.

As described above, if the technology for recording / reproducing with a numerical aperture NA of 1 or more using a solid immersion lens and the technology for land / groove recording are simply combined, sufficient recording / reproducing characteristics are obtained. It was not obtained and practical application was difficult.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and has been developed by combining a technique for recording / reproducing with a numerical aperture NA of 1 or more and a technique for land / groove recording. It is an object of the present invention to provide an optical recording medium capable of obtaining sufficient recording and reproducing characteristics while increasing recording density.

[0033]

An optical recording medium according to the present invention is an optical recording medium on which recording and / or reproduction is performed by irradiating light condensed under a condition that the numerical aperture is 1 or more. Then, lands and grooves are formed along the recording tracks, recording is performed on both the lands and grooves, and one or more thin film layers are formed on the surface on which the lands and grooves are formed. The surface on the side is flattened.

In this optical recording medium, since the surface on the light incident side is flattened, land-groove recording may be performed by irradiating light condensed under the condition that the numerical aperture is 1 or more. And sufficient recording / reproducing characteristics can be obtained.

In the optical recording medium, for example, after forming one or more thin film layers on the surface on which the lands and grooves are formed, the surface of the thin film layer is polished.
The surface on the light incident side is flattened. Alternatively, for example, a light incident side surface is flattened by forming a thin film layer having a thickness equal to or larger than the step between the land and the groove on the surface on which the land and the groove are formed. Alternatively, for example, a protective film made of a resin material is formed on the outermost surface on the light incident side to flatten the surface on the light incident side.

When a protective film made of a resin material is formed on the outermost surface on the light incident side to flatten the surface on the light incident side, it is preferable to satisfy the following expression (1). .

D <t <48.5 × λ × (n / NA) ² (1) where λ is the wavelength of light irradiated during recording and / or reproduction, and NA is the light condensed. , D is the step between the land and the groove, n is the refractive index of the protective film, and t is the average film thickness of the protective film.

[0038]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, a phase-change type optical disc is taken as an example of an optical recording medium to which the present invention is applied. The present invention is also applicable to optical recording media other than optical discs.

FIG. 1 shows an example of a phase change type optical disk to which the present invention is applied. The phase-change type optical disc 1 is an optical recording medium on which land-groove recording is performed by laser light condensed using a solid immersion lens 2 with a numerical aperture NA of 1 or more.

The phase-change type optical disk 1 has a light reflection film 4 made of Al, Ag, etc., on a disk substrate 3 on which lands L and grooves G are formed along recording tracks, and a Zns-SiO ₂ film. A dielectric film 5 made of AlN or SiN, a phase change film 6 made of GeSbTe, or the like;
It is formed by laminating a dielectric film 7 made of SiO ₂ , SiN or the like.

In the phase change type optical disc 1, the dielectric film 7, which is a thin film layer located on the outermost surface, has a flat surface. Therefore, this phase change optical disk 1
Then, no uneven pattern of the land L or the groove G appears on the surface, and the surface of the phase-change optical disc 1 is almost flat.

It should be noted that, here, 4
An example is shown in which thin films of layers are stacked, but in the present invention, the stacked structure of these thin films is arbitrary. That is,
In the present invention, the surface of the thin film layer located on the outermost surface on the light incident side only needs to be flattened, and the number of stacked thin films formed on the surface on which the lands L and the grooves G are formed, the material, etc. are arbitrary. It is.

The phase change optical disk 1 shown in FIG. 1 is a rewritable optical recording medium, and has a phase change film 6 as a layer for holding information. When the phase-change optical disc 1 is irradiated with a laser beam, the temperature of the phase-change film 6 at the portion irradiated with the laser beam rises, and that portion is melted. afterwards,
When the light spot moves and the position of the light spot shifts,
The temperature of the melted portion falls.

At this time, if the laser beam has been irradiated so as to have a very high temperature, the temperature drops sharply, and that portion has no time to crystallize, so that it becomes amorphous. On the other hand, when the laser beam is irradiated so as to have a relatively low temperature, the temperature gradually decreases, so that portion is crystallized.

As described above, the phase change type optical disc 1 records information by setting the phase change film 6 in an amorphous state or a crystalline state. Here, the phase change film 6 is formed of a material (GeSbTe in this example) having a different refractive index between the crystalline state and the amorphous state. Then, the recorded information is reproduced by detecting a difference in reflectance caused by a difference in refractive index of the phase change film 6 as a change in intensity of reflected light.

The recording / reproducing of this phase change type optical disc 1
For example, using a solid immersion lens 2 with an optical system as shown in FIG. In order for the numerical aperture NA to be 1 or more using the solid immersion lens 2, it is necessary that evanescent light from the lens end face of the solid immersion lens 2 enters the phase change optical disc 1.

Conventionally, as shown in FIGS. 20 and 21, as the step D between the land L and the groove G increases, the evanescent light does not enter the medium well, and the signal recorded in the groove is reproduced. The carrier level of the reproduced signal has deteriorated extremely. This is because an uneven pattern of lands L and grooves G appeared on the medium surface.

On the other hand, in the phase-change optical disk 1 to which the present invention is applied, since the surface of the dielectric film 7 which is a thin film layer located on the surface of the medium is flattened, the lens end surface of the solid immersion lens 2 Evanescent light from the optical disc enters the phase change optical disc 1 successfully. Therefore, in the phase change type optical disc 1, even if the step D between the land L and the groove G is large, good recording / reproducing characteristics can be obtained.

When the recording and reproduction of the phase-change optical disk 1 as described above were performed using the solid immersion lens 2 under the condition that the numerical aperture NA was 1 or more, the reproduction characteristics were calculated. The calculation results are shown in FIGS.

Here, the refractive index of the disk substrate 3 is 1.5
It was assumed to be 5. The light reflection film 4 had a thickness of 200 nm and a refractive index of 1.0 + 6.0i. The dielectric film 5 had a thickness of 20 nm and a refractive index of 2.1. The phase change film 6 was assumed to have a thickness of 20 nm, a refractive index of 4.2 + 3.5i in a crystalline state, and 4.0 + 1.8i in an amorphous state.
The dielectric film 7 was assumed to have a refractive index of 2.1. The surface of the dielectric film 7 is flattened. Here, it is assumed that the average value of the thickness of the dielectric film 7 at the groove portion and the thickness at the land portion is 120 nm. Also, the solid immersion lens 2 has a refractive index of 2.0,
The distance between the solid immersion lens 2 and the disk surface was 50 nm. The calculation of the reproduction characteristic was performed based on a model as shown in FIGS. 18 and 19, similarly to the calculation of the reproduction characteristic of the conventional phase change optical disk described above.

FIG. 2 shows the steps D of the land L and the groove G as parameters for the carrier level of the reproduced signal calculated using the model of FIG. 18 and the crosstalk calculated using the model of FIG. I have. Here, the step D between the land L and the groove G is standardized by the wavelength λ of the laser beam used for recording and reproduction. The crosstalk is standardized by the carrier level of the reproduced signal calculated using the model of FIG.

FIG. 3 shows the carrier level of the reproduced signal calculated using the model of FIG. 19 and the crosstalk calculated using the model of FIG. 18 using the step D between the land L and the groove G as a parameter. Is shown. Here, the step D between the land L and the groove G is standardized by the wavelength λ of the laser beam used for recording and reproduction. The crosstalk is normalized by the carrier level of the reproduced signal calculated using the model of FIG.

As shown in FIGS. 20 and 21, conventionally, as the level difference D between the land L and the groove G increases, the carrier level of the reproduced signal when reproducing the signal recorded in the groove portion becomes extremely high. Had deteriorated. On the other hand, as can be seen from FIGS. 2 and 3, in the phase change optical disc 1 to which the present invention is applied, even if the step D between the land L and the groove G is increased, the carrier level of the reproduced signal is extremely deteriorated. No good reproduction characteristics are obtained.

As can be seen from FIGS. 2 and 3, in the phase-change optical disc 1 to which the present invention is applied, crosstalk is greatly reduced by appropriately setting the step D between the land L and the groove G. be able to.

Specifically, as shown in FIG.
In the case where the step D between the groove and the groove G (value standardized by the wavelength λ of the laser beam) is about 0.125, the crosstalk in the model of FIG. 19 is minimized. Further, as shown in FIG. 3, when the step D between the land L and the groove G (value standardized by the wavelength λ of the laser beam) is about 0.167, the crosstalk in the model of FIG. 18 is minimized. .

Accordingly, the step D between the land L and the groove G (a value standardized by the wavelength λ of the laser beam) is set to about 0.5.
By setting it within the range of 125 to 0.167, crosstalk when reproducing the signal recorded on the land L and crosstalk when reproducing the signal recorded on the groove G can be reduced. .

Therefore, in the phase change type optical disk 1 to which the present invention is applied, the step D between the land L and the groove G
Is preferably set such that the value normalized by the wavelength λ of the laser beam used for recording and reproduction is about 0.125 to 0.167. In other words, in the phase change optical disc 1 to which the present invention is applied, the step D between the land L and the groove G is about λ / 8 to λ / 6, where λ is the wavelength of the laser beam used for recording and reproduction. Is preferred.

Next, a method for manufacturing the above-described phase change optical disk 1 will be described.

When manufacturing the phase-change type optical disc 1, first, as a master process, an optical recording medium manufacturing master (stamper) having an uneven pattern corresponding to the lands L and grooves G formed on the disk substrate 3 is manufactured. I do.

In the mastering step, first, a disk-shaped glass substrate having a polished surface is washed and dried, and then a photoresist as a photosensitive material is applied onto the glass substrate. Next, the photoresist applied on the glass substrate is heat-treated at a temperature of about 70 ° C., and thereafter, as shown in FIG. A latent image corresponding to the land L and the groove G to be formed is formed.

After the latent image is formed on the photoresist, the glass substrate is placed on a turntable of a developing machine so that the surface on which the photoresist is applied is the upper surface. Then, while rotating the glass substrate by rotating the turntable, a developing solution composed of an alkaline solution is dropped on the photoresist to perform a developing process. Thereby, as shown in FIG. 4B, a concavo-convex pattern corresponding to the land L and the groove G is formed on the glass substrate.

Next, a conductive film made of Ni or the like is formed on the uneven pattern by an electroless plating method, and then the glass substrate on which the conductive film is formed is attached to an electroforming apparatus.
A plating layer made of Ni or the like is formed on the conductive film by electrolytic plating so as to have a thickness of about 300 ± 5 μm.

Thereafter, as shown in FIG. 4 (c), the plating layer is peeled off, so that an optical recording medium manufacturing master (so-called stamper) made of plating to which a concave / convex pattern formed on a glass substrate is transferred. ) Is completed. The master for producing an optical recording medium serves as a mold of the disk substrate 3, and has an uneven pattern corresponding to the lands L and the grooves G formed on the disk substrate 3.

Next, as a transfer step, a disk substrate 3 on which the surface shape of the master for producing an optical recording medium is transferred by injection molding is manufactured. That is, the master for manufacturing an optical recording medium is mounted on a mold of an injection molding apparatus, and injection molding is performed using a transparent resin such as polymethyl methacrylate or polycarbonate to produce a disk substrate 3.
Thereby, as shown in FIG. 4D, the disk substrate 3 on which the uneven pattern of the land L and the groove G is formed is obtained.

Next, as a film forming step, as shown in FIG. 4E, a light reflecting film 4 and a dielectric film are formed on a disk substrate 3 on which the surface shape of an optical recording medium manufacturing master has been transferred. 5,
A phase change film 6 and a dielectric film 7 are formed. More specifically, for example, a light reflection film 4 made of Al, Ag, or the like, and a Zns-Si
A dielectric film 5 made of O ₂ , SiN, or the like, a phase change film 6 made of GeSbTe, or the like, and a dielectric film 7 made of Zns—SiO ₂ , SiN, or the like are stacked in this order by a sputtering method or the like.

At this time, the dielectric film 7, which is the thin film layer located on the outermost surface, is formed to be slightly thicker than the finally desired thickness. After the formation of the dielectric film 7, FIG.
The surface is polished and flattened as shown in FIG.
As a result, the phase-change optical disc 1 having a flat surface is obtained so that the uneven pattern of the lands L and the grooves G does not appear on the surface.

In the above-described manufacturing method, the dielectric film 7, which is the thin film layer located on the outermost surface, is formed to be relatively thick, and the surface is polished after the formation, so that the disk surface is flattened. I have. However, the method of flattening the disk surface is not limited to this.

For example, even if a thin film layer having a thickness sufficiently larger than the step D between the land L and the groove G is formed on the surface on which the land L and the groove G are formed, the disk surface is flattened. be able to. FIG. 5 shows an example of such a phase change optical disk.

The phase-change type optical disk 10 shown in FIG. 5 is, like the phase-change type optical disk 1, landed by laser light condensed using the solid immersion lens 2 under the condition that the numerical aperture NA is 1 or more. An optical recording medium on which groove recording is performed, and includes a disk substrate 11 on which lands L and grooves G are formed along recording tracks. Here, the step D between the land L and the groove G is set to about several tens nm to several hundreds nm.

In the phase-change optical disk 10, a light reflection film 12 made of, for example, Al or Ag, a dielectric film 13 made of Zns-SiO ₂ , SiN, etc., and a GeSbTe And a dielectric film 15 made of Zns-SiO ₂ , SiN, or the like. The dielectric film 15, which is a thin film layer located on the outermost surface, is The thickness is made sufficiently thicker than the step D of the groove G.

In such a phase change type optical disk 10,
The thickness of the dielectric film 15 which is the thin film layer located on the outermost surface is
Since it is sufficiently thicker than the step D between the land L and the groove G, even if the disk surface is not polished, no uneven pattern of the land L or the groove G appears on the disk surface, and the disk surface becomes almost flat.

When the recording / reproducing of the phase change optical disk 10 was performed using the solid immersion lens 2 under the condition that the numerical aperture NA was 1 or more, the reproducing characteristics were calculated. 6 and 7 show the calculation results.

Here, the refractive index of the disk substrate 11 is 1.
55. The light reflection film 12 has a thickness of 200 nm.
And the refractive index was assumed to be 1.0 + 6.0i. The dielectric film 13 had a thickness of 20 nm and a refractive index of 2.1. The phase change film 14 is assumed to have a thickness of 20 nm, a refractive index of 4.2 + 3.5i in a crystalline state, and a refractive index of 4.0 + 1.8i in an amorphous state. The dielectric film 15 has a refractive index of 2.1. The dielectric film 15 was formed sufficiently thick so that the surface became flat, and the average value of the thickness at the groove portion and the thickness at the land portion was 1000 nm. The refractive index of the solid immersion lens 2 was 2.0, and the distance between the solid immersion lens 2 and the disk surface was 50 nm. The calculation of the reproduction characteristic was performed based on a model as shown in FIGS. 18 and 19, similarly to the calculation of the reproduction characteristic of the conventional phase change optical disk described above.

FIG. 6 shows, as parameters, the step D between the land L and the groove G for the carrier level of the reproduced signal calculated using the model of FIG. 18 and the crosstalk calculated using the model of FIG. I have. Here, the step D between the land L and the groove G is standardized by the wavelength λ of the laser beam used for recording and reproduction. The crosstalk is standardized by the carrier level of the reproduced signal calculated using the model of FIG.

FIG. 7 shows the steps of the land L and the groove G as parameters for the carrier level of the reproduced signal calculated using the model of FIG. 19 and the crosstalk calculated using the model of FIG. ing. Here, the step between the land L and the groove G is standardized by the wavelength λ of the laser beam used for recording and reproduction. The crosstalk is normalized by the carrier level of the reproduced signal calculated using the model of FIG.

Dielectric film 1 which is a thin film layer located on the outermost surface
As shown in FIGS. 6 and 7, even in the phase-change optical disk 10 in which the unevenness pattern of the lands L and the grooves G is prevented from appearing on the disk surface by forming the layer 5 thickly,
As in the case of the phase change type optical disc 1, even if the step D between the land L and the groove G is increased, the carrier level of the reproduction signal does not extremely deteriorate, and good reproduction characteristics can be obtained. I have. Also, as can be seen from FIGS. 6 and 7, in this phase-change optical disc 10, as in the case of the above-described phase-change optical disc 1, by appropriately setting the step D between the land L and the groove G, crosstalk is greatly reduced. Can be reduced.

Incidentally, in the phase change type optical disc 1 shown in FIG. 1, the dielectric film 7 formed on the phase change
It was exposed on the disk surface. Similarly, in the phase change optical disk 10 shown in FIG. 5, the dielectric film 15 formed on the phase change film 14 was exposed on the disk surface. However, in the present invention, a protective film made of a resin material may be formed on the outermost surface on the light incident side, and by setting the thickness of the protective film to be sufficiently large, it is possible to flatten the disk surface. Can be.

That is, even if a protective film made of a resin material, which is sufficiently thicker than the step D between the land L and the groove G, is formed on the surface on which the land L and the groove G are formed, The surface can be flattened.
FIG. 8 shows an example of such a phase change optical disk.

The phase-change type optical disc 20 shown in FIG. 8 is, like the phase-change type optical discs 1 and 10, formed by a solid immersion lens 2 and condensed by laser light having a numerical aperture NA of 1 or more. And an optical recording medium on which land-groove recording is performed, and includes a disk substrate 21 on which lands L and grooves G are formed along recording tracks. Here, the step between the land L and the groove G is several tens nm.
To about several hundred nm.

In the phase-change optical disk 20, a light reflecting film 22 made of, for example, Al or Ag, a dielectric film 23 made of Zns-SiO ₂ , SiN, etc., and a GeSbTe And a dielectric film 25 made of Zns-SiO ₂ , SiN or the like, and a protective film 26 made of a resin material is formed on the dielectric film 25.

Here, the protective film 26 is formed, for example, by applying an ultraviolet curable resin on the dielectric film 25 by a spin coating method, and then irradiating the ultraviolet curable resin with ultraviolet rays to cure the resin. I do. At this time, the protective film 2
6 is sufficiently larger than the step D between the land L and the groove G, the surface of the protective film 26 becomes flat,
The appearance of the uneven pattern of the lands L and the grooves G on the disk surface is eliminated.

When the protective film 26 made of a resin material is formed by the spin coating method, it is difficult to make the thickness of the protective film 26 completely uniform, and a slight change in thickness occurs. FIG. 9 shows the average film thickness per rotation of the disk at a certain disk radius position and the variation of the film thickness at several disk radius positions with respect to the film thickness of the protective film 26 formed by the spin coating method. The results are shown. As can be seen from FIG. 9, when the protective film 26 having a thickness of 100 μm is formed, a variation of about ± 1 μm occurs in the thickness. That is, when the protective film 26 is formed, the film thickness varies about 1/100 of the average film thickness.

Such a variation of the protective film 26 causes a defocus when the laser beam is focused. That is, if the thickness of the protective film 26 has a variation of ± 1 μm, a defocus of ± 1 μm occurs. Here, when the wavelength of the laser light is λ, the numerical aperture when condensing the laser light is NA, the refractive index of the protective film 26 is n, and the defocus amount is Δz, the generated wavefront aberration W ₂₀ is represented by the following equation (2).

W ₂₀ = {(1 / √3) (1/4) (NA / n) ² (Δz / λ)} λ (2) Specifically, for example, NA = 1.5, λ In the case of = 650 nm, when defocus of 1 μm occurs, the wavefront aberration W ₂₀ becomes 0.124λ. This is larger than the criterion of Martial (0.07λ) which is a standard of the diffraction-limited performance, and it is difficult to put it to practical use. In other words, when the protective film 26 is formed, defocus occurs due to the variation in the film thickness of the protective film 26, and the wavefront aberration caused by the defocus is set to 0.07λ or less. There is a need.

As described above, when the protective film 26 made of a resin material is formed by the spin coating method, the variation in the film thickness of the protective film 26 is 1/10 of the average film thickness.
It is about 0. Therefore, the average thickness of the protective film 26 is set to t.
, The defocus amount Δz is Δz = t / 100
It can be expressed as. Then, when Δz = t / 100 and the condition that the wavefront aberration is 0.07λ or less is obtained from the above equation (2), the following equation (3) is obtained.

T <48.5 × λ × (n / NA) ² (3) That is, if the above expression (3) is satisfied, the protective film 26 made of a resin material is formed by spin coating. Even
The generation amount of the wavefront aberration due to the variation in the thickness of the protective film 26 is 0.07λ or less, which satisfies the criterion of Martial, which is the reference of the diffraction limit performance.

When the protective film 26 is formed on the disk surface, the thickness of the protective film 26 should be at least equal to that of the land L so that the uneven pattern of the land L or the groove G does not appear on the disk surface. It is made larger than the step D of the groove G. That is, when the step between the land L and the groove G is D, the average thickness t of the protective film 26 is set to satisfy the following expression (4).

D <t <48.5 × λ × (n / NA) ² (4) By setting the average thickness t of the protective film 26 so as to satisfy the above expression (4), the disk surface Land L and groove G
And the amount of wavefront aberration can be reduced to less than the critical criterion of Malay, and good recording / reproducing characteristics can be obtained.

In an optical system using a solid immersion lens, in order to keep the gap between the solid immersion lens and the optical recording medium very small, for example, the technology of a slider in which a magnetic head is mounted in a hard disk drive is used. In this case, a solid immersion lens is mounted on the slider. When the optical recording medium is stopped, the slider on which the solid immersion lens is mounted is moved to a predetermined CSS (contact standard) on the optical recording medium.
(art stop). When the optical recording medium is driven to rotate, the slider on which the solid immersion lens is mounted is placed on the optical recording medium by several tens of n.
so as to float in the order of m.

However, when a solid immersion lens is mounted on the slider, if the surface of the optical recording medium is too flat, the slider may be attracted to the surface of the optical recording medium. Therefore, when the surface of the optical recording medium is flattened by applying the present invention, it is preferable that the surface of the CSS region of the optical recording medium is textured after the flattening process. The texture process is a process for roughening the surface on the order of several nm. By performing such a texture process, it is possible to prevent the slider from being attracted to the surface of the optical recording medium.

By the way, in an optical recording medium having a dielectric film formed on the surface, by appropriately setting the thickness of the dielectric film, a gap between the disk surface and the lens end surface of the solid immersion lens (hereinafter, referred to as a solid immersion lens) can be obtained. , An air gap).

For example, on a disk substrate on which lands and grooves are formed, a light reflection film made of Al having a thickness of 165 nm, a first dielectric film made of ZnS + SiO ₂ having a thickness of 20 nm, and a film having a thickness of 20 nm. A phase change film made of GeSbTe having a thickness of 20 nm, a second dielectric film made of ZnS + SiO ₂ having a thickness of 83 nm, a third dielectric film made of SiO ₂ having a thickness of 15 nm, and a SiN film having a thickness of 50 nm A fourth dielectric film made of and a fifth dielectric film made of SiO ₂ are laminated to form a phase change optical disk. Here, the step between the land and the groove is about 100 nm.
The fifth dielectric film is formed sufficiently thicker than the step between the land and the groove, and the surface is polished and flattened after the film formation.

In such a phase change type optical disk,
By changing the thickness of the fifth dielectric film, the air gap becomes 0n.
For each of m, 50 nm, 100 nm, 150 nm, and 200 nm, the relationship between the numerical aperture NA of light condensed on the disk surface and the MTF was examined. The results are shown in FIGS. 10 shows the case where the average thickness of the fifth dielectric film is 150 nm, FIG. 11 shows the case where the average film thickness of the fifth dielectric film is 200 nm, and FIG. 12 shows the average film thickness of the fifth dielectric film. 13 shows the case where the average thickness of the fifth dielectric film is 300 nm, and FIG. 14 shows the case where the average thickness of the fifth dielectric film is 350 nm.

As can be seen from FIGS. 10 to 14, the fifth
By setting the average film thickness of the dielectric film to about 200 to 300 nm, the deterioration of the MTF with respect to the fluctuation of the air gap is reduced. As can be seen from this, in an optical recording medium having a dielectric film formed on the surface, setting the thickness of the dielectric film to about 200 to 300 nm makes it less susceptible to air gap fluctuations. Stable recording and reproduction can be performed.

[0095]

As described in detail above, in the optical recording medium according to the present invention, lands and grooves are formed along recording tracks, and recording is performed on both the land portions and the groove portions. One or more thin film layers are formed on the surface on which the grooves are formed, and the light incident side surface is flattened.

With such a configuration of the optical recording medium, it is possible to achieve a high recording density by combining a technique for recording / reproducing under the condition that the numerical aperture NA is 1 or more and a technique for land / groove recording. It is possible to obtain excellent recording and reproduction characteristics. Therefore, according to the present invention, it is possible to further increase the recording density of the optical recording medium.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view of an essential part showing an example of a phase-change optical disc to which the present invention is applied, and a solid immersion lens used for recording and reproduction of the phase-change optical disc.

FIG. 2 is a diagram showing reproduction characteristics when reproducing a recording mark recorded on a land portion of the phase change optical disk shown in FIG.

FIG. 3 is a view showing a reproduction characteristic when a recording mark recorded in a groove portion of the phase change optical disc shown in FIG. 1 is reproduced.

FIG. 4 is a diagram schematically showing a manufacturing process of the phase change optical disc shown in FIG.

FIG. 5 is an enlarged sectional view of a main part showing another example of the phase change type optical disc to which the present invention is applied, and a solid immersion lens used for recording and reproduction of the phase change type optical disc.

FIG. 6 is a diagram showing reproduction characteristics when reproducing a recording mark recorded on a land portion of the phase change optical disk shown in FIG. 5;

FIG. 7 is a diagram showing reproduction characteristics when reproducing a recording mark recorded in a groove portion of the phase change optical disk shown in FIG. 5;

FIG. 8 is an enlarged sectional view of a main part showing another example of a phase change optical disk to which the present invention is applied, and a solid immersion lens used for recording and reproduction of the phase change optical disk.

FIG. 9 is a diagram showing a result of measuring a variation in the thickness of a protective film formed by a spin coating method.

FIG. 10 shows that the average thickness of the dielectric film on the disk surface is 150
FIG. 9 is a diagram showing a result of calculating MTF with the air gap as a parameter for nm.

FIG. 11 shows that the average thickness of the dielectric film on the disk surface is 200.
FIG. 9 is a diagram showing a result of calculating MTF with the air gap as a parameter for nm.

FIG. 12 shows that the average thickness of the dielectric film on the disk surface is 250.
FIG. 9 is a diagram showing a result of calculating MTF with the air gap as a parameter for nm.

FIG. 13 shows that the average thickness of the dielectric film on the disk surface is 300.
FIG. 9 is a diagram showing a result of calculating MTF with the air gap as a parameter for nm.

FIG. 14 shows that the average thickness of the dielectric film on the disk surface is 350
FIG. 9 is a diagram showing a result of calculating MTF with the air gap as a parameter for nm.

FIG. 15 is a diagram for explaining a technique for performing recording and reproduction using a solid immersion lens under the condition that the numerical aperture NA is 1 or more.

FIG. 16 is an enlarged cross-sectional view of a main part showing an example of a conventional phase change optical disk and a solid immersion lens used for recording / reproduction of the phase change optical disk.

FIG. 17 is a diagram illustrating an example of an optical system in the case where recording and reproduction are performed using a solid immersion lens with a numerical aperture NA of 1 or more.

FIG. 18 is a diagram for describing a model used for calculating the reproduction characteristics of the optical recording medium, and is a diagram illustrating a model in which a recording mark is formed on a land portion.

FIG. 19 is a diagram for explaining a model used for calculating the reproduction characteristics of the optical recording medium, and is a diagram showing a model in which a recording mark is formed in a groove portion.

FIG. 20 is a diagram showing reproduction characteristics when reproducing a recording mark recorded on a land portion of the phase-change optical disc shown in FIG. 16;

FIG. 21 is a diagram showing reproduction characteristics when reproducing a recording mark recorded in a groove portion of the phase change optical disc shown in FIG. 16;

[Explanation of symbols]

1 phase change type optical disk, 2 solid immersion lens, 3 disk substrate, 4 light reflection film, 5
Dielectric film, 6 Phase change film, 7 Dielectric film, L land, G groove

Claims (5)

[Claims] An optical recording medium on which recording and / or reproduction is performed by irradiating light condensed under a condition that the numerical aperture is 1 or more, lands and grooves are formed along recording tracks,
Recording is performed on both the land portion and the groove portion, and one or more thin film layers are formed on the surface on which the land and the groove are formed, and the surface on the light incident side is flattened. Optical recording medium. 2. Forming at least one thin film layer on a surface on which lands and grooves are formed, and then polishing the surface of the thin film layer to make sure that the surface on the light incident side is flattened. The optical recording medium according to claim 1, wherein: 3. A light incident side surface is flattened by forming a thin film layer having a thickness equal to or larger than a step between the land and the groove on the surface on which the land and the groove are formed. The optical recording medium according to claim 1, wherein 4. The optical recording medium according to claim 1, wherein the surface on the light incident side is flattened by forming a protective film made of a resin material on the outermost surface on the light incident side. 5. The wavelength of light irradiated at the time of recording and / or reproduction is λ, the numerical aperture when condensing the light is NA, the step between land and groove is D, and the refractive index of the protective film is 5. The optical recording medium according to claim 4, wherein D <t <48.5 × λ × (n / NA) ² where n is an average thickness of the protective film.