JP2003217171A - Optical recording medium and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium wherein an influence of the difference in groove levels on recording/reproducing characteristics can be reduced. <P>SOLUTION: In the optical recording medium which is provided with a reflection layer 12, a recording layer 13 and a covering layer 14 on one surface side of a substrate 11 and wherein recording/reproduction are performed to the recording layer 13 by irradiating the recording layer with a laser beam from the side of the covering layer 14, a smoothing layer 20 filling up at least a groove part 18 of a tracking guide groove 16 formed in the substrate 11 for performing tracking is provided to smooth the formed surface of the recording layer 13. <P>COPYRIGHT: (C)2003,JPO

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 capable of recording / reproducing with a laser beam having a relatively short wavelength, and more particularly to an optical recording medium using an organic dye in a recording layer.

[0002]

2. Description of the Related Art In recent years, not only computer information but also information such as voices, still images and moving images have been digitized, and the amount of information to be handled has become extremely large. Along with this, it has become necessary to increase the capacity of optical recording media for storing such information. In response to this, optical recording media such as DVD-RAM and DVD-RW having a capacity seven times or more that of conventional CD-R and CD-RW have been commercialized. As a means for achieving high density, the recording / reproducing laser spot diameter can be reduced by using a technique such as decreasing the laser wavelength (λ) or increasing the numerical aperture NA of the lens. DVD-RAM
The commercialization of DVD-RW and DVD-RW was realized.

However, the amount of information tends to increase further in the future. For example, a medium having a CD size of 12 cm and a capacity of 25 GB or more is desired in order to record high-quality image information for two hours or more. To meet this demand, a blue laser having a laser wavelength λ of 405 nm is used, and the objective lens NA is increased to 0.85 to reduce the laser spot diameter, thereby providing an optical recording medium for recording higher density information. Proposed (Jpn.J.Appl.Phys.Vo
l.39 (2000) pp.756-761, Part1, No.2B, Feb.2000). This optical recording medium is usually a rewritable optical recording medium using an alloy phase change material for the recording layer, and has a structure in which a reflective layer, a recording layer, and a cover layer are sequentially provided on a substrate. This is because the lens numerical aperture NA is made larger than the conventional one, so that the focal length is shortened, and it is impossible to irradiate the recording layer with laser light from the substrate side to record / reproduce as in the conventional case. That is, the film surface incidence method is used in which recording / reproduction is performed by irradiating a laser beam from the surface opposite to the conventional one. Further, as such a film surface incidence type optical recording medium, a write-once type optical recording medium using a dye material in a recording layer has also been developed.

[0004]

However, the above-mentioned film surface incidence type optical recording medium has the following problems. That is, when a recording layer made of a phase change material, a pigment material, or the like is formed on a substrate having a groove step for obtaining a servo signal, that is, a substrate having a tracking guide groove, the groove portion (recess forming the tracking guide groove) There is a problem that a recording characteristic difference occurs in the land portion (the convex portion existing between adjacent tracking guide grooves) (hereinafter, the “tracking guide groove” may be simply referred to as “guide groove”).

In an optical recording medium using a phase change material, generally, an alloy thin film is formed by a vacuum film forming apparatus such as sputtering and used as a recording layer. Therefore, sputtered particles flying from an alloy target for forming a recording film are used. Tend to be thick in the land portion and thin in the groove portion. When a difference in film thickness occurs between the land portion and the groove portion as described above, a characteristic difference occurs in recording / reproducing characteristics. In the optical recording medium using the phase change material, the recording sensitivity of the land portion is increased, the recording power margin is widened, and the signal amplitude tends to be high.
The characteristics of the land part are superior. Due to such a characteristic difference, in the rewritable optical recording medium using the phase change material, recording / writing
It has been proposed to use the land part for regeneration (2001 /
4 ODS Symposium Digest P139-141 "In Groove Recordi
ng for a Capacity of over 24GB '').

On the other hand, in the optical recording medium using the dye material,
Usually, in order to form a thin film of the recording layer by applying a solution containing an organic dye on the substrate by spin coating or the like,
The groove portion tends to be thick and the land portion tends to be thin. As a result, the recording sensitivity of the land portion tends to be lower than that of the groove portion. Further, the groove portion has a wider recording power margin than the land portion, and the signal amplitude tends to be higher. Therefore, the optical recording medium using the dye material has excellent recording characteristics in the groove portion. Then,
In the write-once type optical recording medium, although it is an optical recording medium of the same format as the rewritable type optical recording medium described above, the groove portion is used due to the above characteristics.

Further, in an optical recording medium using a substrate having a groove step, when the groove portion is used for recording / reproducing, the beam shape of the laser beam applied to the groove portion is diffracted at the shoulder portion of the land portion. In this respect, the characteristics of the land portion are superior because they are deformed under the influence of a vector wave or the like. Therefore, due to the above-mentioned characteristics, when the groove portion is used for recording / reproducing in the optical recording medium using the dye material, there is a problem that the beam shape of the laser light cannot be made into an ideal state. It will happen. An object of the present invention made in consideration of the above points is to provide an optical recording medium or the like that can reduce the influence of the recording / reproducing characteristics due to the influence of the groove step.

[0008]

Based on the above object, the optical recording medium of the present invention is an optical recording medium in which a reflective layer and a recording layer are sequentially laminated on a substrate having a tracking guide groove on the surface. And a smoothing layer that is formed so as to be interposed between the reflective layer and the recording layer and that smoothes the surface on which the recording layer is formed by closing the tracking guide groove. Here, the smoothing layer may cover at least the concave portion formed on the substrate by the tracking guide groove, but may be configured to further cover the convex portion adjacent to the concave portion. By thus smoothing the surface on which the recording layer is formed, the difference in film thickness of the recording layer due to the groove step is reduced,
The difference in recording characteristics between the land portion and the groove portion can be reduced. Here, the "recording layer forming surface" means the surface of the layer provided in contact with the interface of the recording layer on the substrate side. For example, when the recording layer is provided on the smoothing layer, the surface of the smoothing layer is "recording surface". When the recording layer is formed after the optional layer is provided on the smoothing layer, the surface of the optional layer corresponds to the “formed surface of the recording layer”. At this time, the recording layer may contain an organic dye. Further, the smoothing layer preferably has a light transmittance of 80% or more at a laser light wavelength used for recording / reproducing data to / from the recording layer.

By the way, in general, it is ideal that both the groove forming surface for applying the tracking servo and the recording layer for recording / reproducing data are both within the focal depth of the laser beam. However, in the above layer structure, the optimum surface for applying the tracking servo is the reflective layer surface corresponding to the groove surface on the substrate, and the optimum surface for recording / reproducing is the recording layer. In the above layer structure, since the smoothing layer is formed on the reflective layer and the recording layer is formed thereon, the two optimum surfaces are separated by the thickness of the smoothing layer. Therefore, it is preferable that the maximum film thickness of the smoothing layer is 2λ / Nc (Nc: refractive index of the smoothing layer) or less with respect to the laser wavelength λ used for recording / reproducing data on / from the recording layer. Here, Nc is the refractive index at the wavelength λ. The “maximum film thickness” means the film thickness of the thickest part of the smoothing layer in one optical recording medium.
The film thickness of the smoothing layer can be determined by a method such as observing a cross section with an SEM (scanning electron microscope).

Usually, the focal plane of the light beam is made to coincide with the surface of the recording layer in order to emphasize the recording / reproducing characteristics. At this time, the focus of the light beam is defocused from the surface of the reflective layer (defocus), which may cause a decrease in the tracking servo signal. As described above, within a range where it is possible to apply a sufficiently stable tracking servo, that is, 2λ / N
If the thickness of the smoothing layer is set to be c or less, a structure that achieves the object of the present invention can be obtained. Further, FIG. 4 shows the thickness of the smoothing layer and the tracking error signal when the focus servo is applied to the recording layer formed on the smoothing layer having the same refractive index as that of FIG. The (TES) relationship is shown.
The smoothing layer was formed by using an ultraviolet curable resin having a light transmittance of 80% or more at the recording / reproducing light wavelength. Although the amplitude of the tracking error signal decreases as the thickness of the smoothing layer increases, tracking servo is applied even with a thickness of about 300 nm. From the viewpoint of stabilizing recording / reproduction, it is desirable to set the thickness of the smoothing layer so that the reduction of the tracking servo amplitude is 10% or less, more preferably 5% or less.

In the optical recording medium of the present invention, the surface on which the recording layer is formed is smoothed by providing the above-mentioned smoothing layer, which is caused by groove steps (lands of the tracking guide groove and unevenness of the groove) on the substrate. The difference in film thickness of the recording layer is reduced, and the difference in recording characteristics between the land portion and the groove portion is reduced. Further, since the recording layer is formed on such a smoothed surface, the recording layer surface is also smooth. Corresponding to the guide groove on the substrate, a concave portion generated on the surface of the smoothing layer (hereinafter, "a concave portion on the surface of the smoothing layer"
It is preferable that the depth of (referred to as) is less than or equal to 1/2 of the depth of the tracking guide groove, that is, the step between the concave portion formed by the tracking guide groove and the convex portion adjacent thereto.
Here, the reason for defining the depth of the recess on the surface of the smoothing layer is
The depth after flattening is 1 / the depth of the tracking guide groove
This is because if it exceeds 2, it may be difficult to sufficiently reduce the influence of the groove step left on the surface of the smoothing layer. The smaller the step, the smaller the difference in recording characteristics between the land portion and the groove portion, which is preferable.

In the present invention, the depth D of the tracking guide groove is λ / (15Nc) ≤ D ≤ λ / (5Nc) (where λ is the wavelength of the recording / reproducing laser beam, Nc:
The refractive index of the smoothing layer) is desirable. The signal amplitude of the tracking error signal becomes maximum when the depth D is D = (2n + 1) λ / (8 · Nc) and minimum when D = (2n) λ / (8 · Nc). Therefore, the depth D is typically λ /
It is selected from the range of more than 0 and less than λ / (4 · Nc) centered on (8 · Nc), but among them, λ / (15 ·
The optimum range is Nc) or more and λ / (5 · Nc) or less. It should be noted that, even if D = 3λ / (8 · Nc) at which the tracking error signal becomes the next maximum in the range of D> (2n) · λ / (8 · Nc), it can be used according to the above theory. Since the groove becomes deep, it may be difficult to form a step.

Further, this recording layer has a wavelength λ of 500 n.
Data can be recorded / reproduced by irradiating a laser beam of m or less. The optical recording medium of the present invention comprises a substrate,
The reflective layer and the recording layer have a basic structure, but usually also have a cover layer that covers the recording layer. Further, any layer may be provided between the above layers as long as the performance of the optical recording medium of the present invention is not impaired. For example, by forming a separate layer between the recording layer and the cover layer, when the recording layer contains an organic dye, the dye forms a cover layer resin (the cover layer is formed by applying a resin composition. It is preferable) because it can prevent the cover layer from admixing with an adhesive that adheres to the recording layer.

In order to manufacture the above optical recording medium,
After forming a reflective layer on a substrate having a tracking guide groove on the surface and filling the unevenness formed by the tracking guide groove with a filler to form a substantially smooth surface on the reflective layer, the substantially smooth surface is formed. A recording layer forming material containing an organic dye may be applied thereon to form a recording layer, and then a cover layer covering the recording layer may be formed.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the accompanying drawings. FIG. 1 is a sectional view for explaining the configuration of the optical recording medium in this embodiment. The optical recording medium of the present invention may or may not have any other layer as long as it has a substrate, a reflective layer, and a recording layer, which are basic components, It is not limited to the layer structure of FIG. 1 to be described. The optical recording medium is basically disc-shaped, and a reflective layer 12, a recording layer 13, and a cover layer 14 are formed on one surface side of the substrate 11, and a separate layer is provided between the recording layer 13 and the cover layer 14. The layer 15 is formed, and the reflective layer 12 and the recording layer 13 are formed.
And the smoothing layer 20 is formed between them. That is, on one surface side of the substrate 11, the reflective layer 12, the smoothing layer 20, the recording layer 13, the separate layer 15, and the cover layer 1.
Each layer is laminated in the order of 4.

The substrate 11 has, for example, a diameter of 120 mm and a thickness of 1.1 mm, and the tracking guide groove 16 is provided on one side thereof.
Are formed. The tracking guide groove 16 is formed, for example, in a spiral shape that is continuous from the center side of the substrate 11 to the outer peripheral side. It should be noted that disc identification information, address information and the like are pre-recorded on the substrate 11 by wobbles and prepits of the tracking guide groove 16. The tracking guide groove 16 and the pre-pits are preferably provided at the time of molding the substrate 11, but may be formed on the substrate 11 by using an ultraviolet curable resin layer. When the tracking guide groove 16 has a spiral shape, the groove pitch is usually formed to be about 0.3 to 0.8 μm. The material of the substrate 11 is not particularly limited as long as it has required strength and durability. Conventionally used as a substrate material, for example, acrylic resin, methacrylic resin, polycarbonate resin, polyolefin resin (particularly amorphous polyolefin), polyester resin, polystyrene resin, epoxy resin or other resin, glass It is possible to use any of the above-mentioned materials, those having a resin layer made of a radiation-curable resin such as a photo-curable resin on glass, and the like. Injection-molded polycarbonate is preferable in terms of high productivity, cost, moisture absorption resistance, and the like. From the viewpoint of chemical resistance, moisture absorption resistance, etc., amorphous polyolefin is preferable. A glass substrate is preferable from the viewpoint of mechanical stability during high speed rotation. Since the substrate 11 does not need to be transparent at the wavelengths of the recording light and the reproducing light, in order to prevent vibration during high speed rotation, a resin such as polycarbonate may be filled with a filler such as carbon fiber to increase the rigidity. .

Lands 17 and grooves 18 are alternately formed on the substrate 11 in the radial direction of the substrate 11 by the tracking guide grooves 16. The cross-sectional shapes of the land portion 17 and the groove portion 18 are substantially trapezoidal in FIG. 1, but the shape is not necessarily limited to this.
Other cross-sectional shapes, such as a rectangular shape and a V shape, are possible. In the present embodiment, the land portion 17 and the groove portion 18 have, for example, a step D = 40 nm and a track pitch W.
= 0.32 μm and the groove width WG = 0.15 μm.

Here, the land portion 17 and the groove portion 1
It is preferable that the step difference (depth of the tracking guide groove 16) D of 8 is λ / (15 · Nc) ≦ D ≦ λ / (5 · Nc) (where λ: recording / reproducing laser wavelength, Nc : Refractive index of the smoothing layer). The signal amplitude of the tracking error signal is maximum when the step D is D 2 = (2n + 1) · λ / (8 · Nc), and is minimum when D 2 = (2n) · λ / (8 · Nc). Therefore, the value of the step D is λ / (8 ·
Nc) is the center, and is usually selected from the range of 0 <D <λ / (4 · Nc). In addition, D> (2n) · λ / (8 ·
A step D D = 3λ / (8 · Nc) that maximizes the tracking error signal next in the range Nc) can also be used according to the above theory, but the groove depth (step D) becomes deeper. It may be difficult to form a step.

The reflective layer 12 is formed by depositing, for example, a metal or an alloy on the surface of the substrate 11 by sputtering. The reflective layer 12 is preferably made of a metal or an alloy, particularly an alloy that has good corrosion resistance and is inexpensive. Specifically, for example, Au, Al, Ag, Cu, Ti, Cr, Ni, Pt, Ta, Cr
It is possible to use the metals Pd and Pd alone or as an alloy. Among these, Au, Al and Ag have high reflectance and are suitable as materials for the reflective layer. In addition to the main components other than these, the following may be included. For example, Mg, S
e, Hf, V, Nb, Ru, W, Mn, Re, Fe, Co, Rh, Ir, C
Metals and semimetals such as u, Zn, Cd, Ga, In, Si, Ge, Te, Pb, Po, Sn and Bi can be mentioned. Among them, those containing Ag as a main component are preferable from the viewpoints of low cost, high reflectance, and the like, and AgZn alloys are particularly preferable. Here, the main component means one having a content rate of 50% or more. It is also possible to stack the low refractive index thin film and the high refractive index thin film alternately with a material other than metal to form a multilayer film and use it as the reflective layer 12.

Further, the recording layer 13 in the optical recording medium of the present embodiment is not particularly limited, and as described above, even if the recording layer 13 made of an alloy (formed of a phase change material), the organic dye is used. The recording layer 13 containing (containing a dye material) may be used, but the recording layer 13 containing an organic dye is preferable because the effect is particularly remarkable. The recording layer 13 containing an organic dye is formed to have a thickness of 0.2 (absorbance measured at a wavelength of 360 nm with air as a reference), for example. Examples of organic dyes used in the recording layer 13 include benzophenone dyes, phthalocyanine dyes, naphthalocyanine dyes, cyanine dyes, azo dyes, squarylium dyes, metal-containing azo dyes, metal-containing indoaniline dyes, and thoria. A reel methane dye, a merocyanine dye, an azurenium dye, a naphthoquinone dye, an anthraquinone dye, an indophenol dye, a xanthene dye, an oxazine dye, a pyrylium dye and the like can be used. Above all, it is particularly preferable to use a benzophenone dye in the recording layer 13. The recording layer 13 includes a transition metal chelate compound (eg, acetylacetonate chelate, bisphenyldithiol, salicylaldehyde oxime, bisdithio-α-diketone) as a singlet oxygen quencher in order to improve the stability and light resistance of the layer. Etc.) or a recording sensitivity improving agent such as a metal compound for improving recording sensitivity. Here, the metal-based compound means that a metal such as a transition metal is contained in the compound in the form of an atom, an ion, a cluster, etc., for example, an ethylenediamine-based complex, an azomethine-based complex, a phenylhydroxyamine-based complex, a phenanthroline-based complex, Dihydroxyazobenzene-based complex,
Dioxime complex, nitrosoaminophenol complex,
Examples thereof include organometallic compounds such as pyridyltriazine-based complexes, acetylacetonate-based complexes, metallocene-based complexes, and porphyrin-based complexes. The metal atom is not particularly limited, but a transition metal is preferable. further,
If necessary, a wavelength of 77, which is usually used for CD-R
A near-infrared laser having a wavelength of 0 to 830 nm, a red laser having a wavelength of 620 to 690 nm, which is used for DVD-R, and the like, are used in combination with a recording light having a plurality of wavelengths, each dye being suitable for recording. Thus, the recording layer 13 corresponding to recording with laser light in a plurality of wavelength ranges can be formed. Further, if necessary, a binder, a leveling agent, a defoaming agent, etc. can be used in combination. Preferred binders include polyvinyl alcohol, polyvinylpyrrolidone, nitrocellulose, cellulose acetate, ketone resins, acrylic resins, polystyrene resins, urethane resins, polyvinyl butyral, polycarbonate, polyolefins and the like. The organic dye, the various additives, the binder resin, and the like, which are materials for forming the recording layer 13, may be collectively referred to as a "dye material". The film thickness of the recording layer 13 is not particularly limited because a suitable value varies depending on the recording method and the like, but is usually 5 nm to 1 μm.
m, preferably 10 nm to 100 nm.

The cover layer 14 is necessary for protecting the reflective layer 12 from external force and for recording / reproducing, and its film thickness is strictly defined by the use of the lens used. For example, wavelength 405 nm, NA 0.85, 100
In a lens designed to cover the cover layer 14 having a thickness of μm, the thickness of the cover layer 14 is preferably controlled within 100 μm ± 2 μm. The material of the cover layer 14 is not particularly limited as long as it protects the reflective layer 12 from external force and allows the laser beam used for recording / reproduction to pass therethrough.
Examples of the material of the organic substance include a thermoplastic resin, a thermosetting resin, an electron beam curable resin, an ultraviolet curable resin and the like. As the ultraviolet curable resin, for example, an acrylate resin such as urethane acrylate, epoxy acrylate, polyester acrylate can be used. These materials may be used alone or as a mixture, and may be used not only as one layer but also as a multilayer film. The cover layer 14 can also be provided by adhering a thin film or sheet-like film made of the above resin with an adhesive. As the adhesive, various types such as a room temperature curable adhesive, a thermosetting adhesive, an electron beam curable adhesive, and an ultraviolet curable adhesive can be used.

The separate layer 15 diffuses the dye from the recording layer 13 to the cover layer 14 when the cover layer 14 is formed, permeates the coating liquid for forming the cover layer into the recording layer 13, or adheres the cover layer 14. This is to prevent a mixing phenomenon such as diffusion and permeation of the adhesive component into the recording layer 13 at the time. For example, in the case of the recording layer 13 containing an organic dye,
When the film- or sheet-shaped cover layer 14 is attached to the recording layer 13 in the manufacturing process of this optical recording medium, the adhesive may attack the recording layer 13 and deteriorate the recording / reproducing characteristics. Further, even when the cover layer 14 is provided on the recording layer 13 by using a coating liquid, the recording / reproducing characteristics may be deteriorated because the coating liquid invades the recording layer 13 like the adhesive. On the other hand, the separate layer 15
Is provided between the recording layer 13 and the cover layer 14 to prevent these problems. As a result, the formed cover layer 14 does not affect the recording layer 13 and the recording / reproducing characteristics of the optical recording medium are improved. The cover layer 14 side of the separate layer 15
(Recording / reproducing light incidence side) Arithmetic surface roughness Ra of the interface is 50 n
By setting m or less, scattering of laser light is prevented,
Recording / reproducing characteristics are improved.

The material forming the separate layer 15 is not particularly limited as long as it has the above-mentioned function, but is not particularly limited. For example, silicon oxide, particularly silicon dioxide, oxides such as zinc oxide, cerium oxide, yttrium oxide; Examples thereof include sulfides such as zinc and yttrium sulfide; nitrides such as silicon nitride; silicon carbide; a mixture of oxide and sulfur; and alloys described later. Among them, silicon oxide, zinc sulfide, zinc oxide, silicon nitride, silicon carbide, cerium oxide, yttrium oxide,
And at least one selected from the mixture of oxide and sulfur is preferable. Further, a mixture of silicon oxide and zinc sulfide in a ratio of about 30:70 to 90:10 (weight ratio) is also suitable. Further, a mixture of zinc oxide mixture of sulfur and yttrium dioxide _{(Y 2 O 2 S-ZnO} ) is also suitable. As the alloy, an alloy containing silver as a main component and 0.1 to 15 atom% of at least one element selected from the group consisting of titanium, zinc, copper, palladium, and gold is preferable. Further, those containing silver as a main component and containing at least one kind of rare earth element in an amount of 0.1 to 15 atomic% are also preferable. As the rare earth, neodymium, praseodymium, cerium and the like are suitable. In addition to the above-mentioned inorganic compounds, as the separate layer 15, resins such as polyvinyl alcohol, vinyl acetate resin, vinyl chloride resin, and polydimethylsiloxane, and organic substances such as sucrose, tartaric acid, and paraffin are used. May be. Among these, it is preferable to use a hydrophilic resin such as polyvinyl alcohol. The thickness of the separate layer 15 may be adjusted so that the thicknesses of the cover layer 14 and the separate layer 15 are the design values of the objective lens in the optical pickup. Specifically, when formed by a dry process such as sputtering, the total film thickness of the cover layer 14 and the separate layer 15 is 10 to 100 μm, and when formed by a wet process such as spin coating, it is about 0.1 to 10 μm. Is preferred.

The smoothing layer 20 is formed on the land portion 17 of the substrate 11.
It is formed so as to absorb the step of the reflective layer 12 caused by the step D of the groove portion 18 and smooth the recording layer 13 (the surface on which the recording layer 13 is formed), and transmits the laser light used for recording / reproduction. Therefore, the smoothing layer 20 is the recording layer 1
It is desirable to form the upper surface 20a, which is the formation surface of 3, as a surface that is as smooth as possible. However, if the required characteristics can be obtained at the time of recording / reproducing in the recording layer 13, it is not necessary to be a completely smooth surface. . In this embodiment, the land portion 1
7 is that the groove step (depth of the concavo-convex, concave portion) S of the smoothing layer 20 caused by the step D between the groove portion 18 and the groove portion 18 is 1/2 or less of the step D between the land portion 17 and the groove portion 18. preferable. The depth of the concave portion formed on the surface of the smoothing layer 20 can be obtained by observing the medium cross section using an AFM (atomic force microscope) or SEM (scanning electron microscope). Further, the thickness t of the smoothing layer 20 on the land portion 17 is
Is preferably as thin as possible, for example, t = 50 nm
It can be a degree. That is, as long as the thickness t of the smoothing layer 20 on the land portion 17 can be set to 0, the material (filler) that forms the smoothing layer 20 is, for example, an ultraviolet curable resin. Although it is sufficient to fill only in the land portion 17, it is difficult to set the thickness t of the smoothing layer 20 on the land portion 17 to 0 and to reliably fill the groove portion 18 with the material in the actual manufacturing process. For,
It is preferable to set the thickness as described above. By the way, the smoothing layer 20 as described above may be a layer mainly having another function. In this case, although it is a layer mainly having another function, the land portion 17 of the substrate 11 is formed.
If the level difference of the reflection layer 12 caused by the level difference D of the groove portion 18 is absorbed and the recording layer 13 (the surface on which the recording layer 13 is formed) is smoothed, it may be said that such a layer is the smoothing layer 20. Absent.

Although the material of the smoothing layer 20 is not particularly limited,
It is preferable to use a resin because it is easy to fill the groove portion 18 with the tracking guide groove 16. Examples of such a resin include various resins such as a thermoplastic resin, a thermosetting resin, and an ultraviolet curable resin, but the amount of the solvent used may be small, or a solvent may not be used, UV curable resins are preferred.

By the way, as shown in FIG. 2, the focus of the light beam is normally focused on the recording layer 1 in order to emphasize the recording / reproducing characteristics.
Match the 3rd side. At this time, there is a concern that the intensity of the tracking servo signal may decrease because the light beam is defocused (defocused) from the surface of the reflective layer 12 (particularly the groove portion 18 portion). If the thickness t of the smoothing layer 20 is increased, this problem is more likely to be manifested. Therefore, in order to determine the allowable thickness t of the smoothing layer 20, the defocusing is performed. The relationship between the signal quality (jitter value) and the tracking signal amplitude when the amount was changed was investigated. The laser light wavelength in the used optical system is 405.
nm, the numerical aperture NA of the objective lens is 0.85. The result is shown in FIG. From this result, from the position of defocus = 0 where the jitter value becomes the minimum, the groove forming surface 12
Even if a is separated by ± 100 nm, the reduction of the tracking error signal amplitude is 10% or less, and it can be seen that a sufficiently stable tracking servo can be performed. Therefore, it is preferable to set the thickness of the smoothing layer 20 within this range. Further, FIG. 4 shows the relationship of the tracking error signal (TES) when the thickness t of the smoothing layer 20 is changed and the focus servo is applied to the recording layer 13 formed thereon. Although the amplitude of the tracking error signal decreases as the thickness t of the smoothing layer 20 increases, tracking servo is applied even with a thickness of about 300 nm. From the viewpoint of stabilizing recording / reproduction, it is desirable that the reduction of the tracking servo amplitude is 5% or less. Therefore, it is preferable to set the thickness t of the smoothing layer 20 so as to satisfy this condition. As described above, in order to secure the recording / reproducing characteristics on the recording layer 13 and the sufficient strength of the tracking servo signal, the smoothing layer 2
The light transmittance at a recording / reproducing laser light wavelength of 0 is 80
% Or more is preferable.

The single-sided recording type optical recording medium having the reflective layer 12 and the recording layer 13 on one side of the substrate 11 has been described above, but the present invention is not limited to this.
The tracking guide groove 16 may be provided on both surfaces of the above, and the reflective layer 12 and the recording layer 13 may be provided on each surface. Further, by bonding two optical recording media having the reflective layer 12 and the recording layer 13 on one side, with each layer facing outward,
It is also possible to configure an optical recording medium capable of double-sided recording.

The optical recording medium as described above records / reproduces data on / from the recording layer 13 while performing tracking by irradiating the reflection layer 12 in the groove portion 18 with laser light. Recording on the optical recording medium of the present invention obtained as described above is performed by irradiating the recording layer 13 provided on both sides or one side of the substrate with a laser beam focused to 1 μm or less. In the portion irradiated with the laser light, thermal deformation of the recording layer 13 such as decomposition, heat generation, and dissolution occurs due to absorption of the laser light energy, and the optical characteristics change. The recorded information is reproduced by reading the difference in reflectance between the portion where the change in optical characteristics has occurred and the portion where the change in optical characteristics has not occurred, by the laser light.

Now, the above optical recording medium can be manufactured by the following manufacturing method. First, the substrate 11 is manufactured. Usually, the substrate 11 is formed by injection molding of a resin as a material, and a tracking guide groove 16 having a predetermined pitch and a groove depth is formed on the surface thereof. Further, the disc recognition information, the address information and the like are pre-recorded on the substrate 11 by the wobble of the groove. These pieces of information can also be formed by prepits. When a glass substrate is used as the substrate 11, the tracking guide groove 16 may be formed on the glass substrate using a resin, or the tracking guide groove 16 may be provided by cutting the surface of the glass substrate by etching or the like. Next, the above-described various alloys and the like are deposited on the surface of the substrate 11 by the sputtering method to form the reflective layer 12. Further, a publicly known inorganic or organic intermediate layer, an adhesive layer or the like may be provided on the substrate 11 or under the reflective layer 12 in order to improve reflectance, recording characteristics, adhesion, and the like. . At this time, the thickness of the reflective layer 12 is 5
The thickness is preferably about 0 to 200 nm.

Subsequently, the substrate 11 on which the reflective layer 12 is formed
After the various resins described above are formed on the above by a known coating method such as a spin coating method, the smoothing layer 20 is formed to a predetermined thickness by curing the resin by a method suitable for the material such as ultraviolet irradiation and heating. Form.

Further, on the smoothing layer 20, a predetermined absorbance
The recording layer 13 is formed to have a thickness indicating (absorbance measured at a wavelength of 360 nm with air as a reference). Examples of the method of forming the recording layer 13 include a vacuum vapor deposition method and a spin coating method, but the spin coating method is preferable in terms of mass productivity and cost. Depending on the material of the recording layer 13, the vacuum deposition method may be preferable to the coating method. Also,
The coating solvent for forming the recording layer 13 by a coating method such as a spin coating method is not particularly limited as long as it is a solvent that does not attack the substrate 11. For example, ketone alcohol solvents such as diacetone alcohol and 3-hydroxy-3-methyl-2-butanone; cellosolve solvents such as methyl cellosolve and ethyl cellosolve; n-hexane and n-
Chain hydrocarbon solvents such as octane; cyclohexane, methylcyclohexane, ethylcyclohexane, dimethylcyclohexane, n-butylcyclohexane, tert.
-Cyclic hydrocarbon solvents such as butylcyclohexane and cyclooctane; Fluoroalkyl alcohol solvents such as tetrafluoropropanol, octafluoropentanol, and hexafluorobutanol; hydroxycarboxylic acids such as methyl lactate, ethyl lactate, and methyl 2-hydroxyisobutyrate. Examples thereof include acid ester solvents. In the case of the vacuum deposition method, the recording layer 13 is formed by evaporating the components of the material forming the recording layer 13 by resistance heating or heating with an electron beam and depositing it on the substrate 11.

After the recording layer 13 is formed in this way,
A separate layer 15 is formed on the recording layer 13. When forming the separate layer 15 using the above-mentioned inorganic material, a well-known inorganic material thin film forming method such as various dry processes such as a sputtering method can be used. When a hydrophilic resin is used, a film is formed by a known coating method (wet process) such as spin coating using water or a solvent that does not dissolve the material of the recording layer 13 previously formed. The separate layer 15 can be formed by drying this.

Thereafter, the cover layer 14 is formed to a thickness of 0.1 mm, for example, by applying a thermoplastic resin, a thermosetting resin, an ultraviolet curable resin or the like on the formed separate layer 15. Here, the thermoplastic resin, the thermosetting resin and the like can be formed by dissolving them in a suitable solvent, applying a coating solution, and drying. The UV-curable resin can be formed by preparing a coating solution as it is or by dissolving it in an appropriate solvent, applying the coating solution, and then irradiating it with ultraviolet light to cure it. As a method of forming the cover layer 14 by coating, a coating method such as a spin coating method or a casting method is used as in the case of the recording layer 13, and the spin coating method is preferable among them.

[0034]

EXAMPLE In the optical recording medium manufactured by the above manufacturing method, the substrate 11 made of injection molded polycarbonate has a diameter of 120 mm and a thickness of 1.1 mm, and the tracking guide groove 16 is formed on the surface thereof, and the groove step is formed. D = 40n
m, track pitch W = 0.32 μm, groove width WG = 0.
It was formed with a thickness of 15 μm. Furthermore, the reflective layer 12 formed on the surface of the substrate 11 was formed by a sputtering method using a target made of an AgZn alloy, and its thickness was set to 100 nm. Then, on the substrate 11 on which the reflective layer 12 is formed, 2
An ultraviolet curable resin having a viscosity of 0 cps was formed by spin coating and then cured by irradiation with ultraviolet rays to form a smoothing layer 20 having a maximum film thickness t = 50 nm.
By forming the smoothing layer 20, the groove step D on the substrate 11 was 40 nm, while the depth (groove step) S of the recess on the surface of the smoothing layer 20 was 4 nm or less. . Further, a solution containing a benzophenone dye is spin-coated on the smoothing layer 20 and dried to give a recording layer 13 having a thickness of 2.0 (absorbance measured at a wavelength of 360 nm with air as a reference). Was formed. Next, an aqueous solution containing 4-morpholine-2,5-dibutoxydiazonium trifluoromethanesulfonate and polyvinylpyrrolidone was spin-coated on the recording layer 13 and dried to give a 200 nm-thick layer. The separate layer 15 was formed.
Further, an ultraviolet curable resin was spin-coated and cured by irradiation with ultraviolet rays to form a cover layer 14 having a thickness of 0.1 mm.

For the above optical recording medium, a commercially available recording tester having an objective lens with a recording / reproducing laser beam wavelength of 405 nm and an NA of 0.85 is used, and the focus position is set on the recording surface, that is, the recording layer 13. When the focus servo was applied to the groove and the tracking servo was applied to the groove convex portion, that is, the land portion 17, a stable servo following the disc surface deviation and the eccentricity of the optical recording medium was obtained.
It should be noted that FIG. 3 shows the signal quality (jitter value) and tracking error with respect to the focus offset (defocus amount) evaluated using the optical recording medium prepared in the same manner as described above except that the thickness of the smoothing layer 20 is variously changed. It shows the relationship of signals. Compared to the case where the focus position is aligned with the groove surface, that is, the groove portion 18, the signal amplitude of the tracking error signal decreases by 2% at the focus offset value that minimizes the jitter, but it is sufficient for stable tracking servo. A large amplitude value is secured.

Next, when the noise of the optical recording medium was measured in the unrecorded state, the optical recording medium in which the groove step was not flattened
The noise was 1.5 dB lower than that of (= disc formed in the same manner as above except that the smoothing layer 20 was not provided). In addition, the shortest mark length of 0.173 μm was 1-
When a 7-modulation random pattern was recorded on the land portion 17 and the jitter was measured, it was 7% for an optical recording medium without flattening.
On the other hand, in the optical recording medium in which the smoothing layer 20 is provided and flattened, the jitter of 6.2% was obtained.

As described above, the tracking guide groove 16
Of the optical recording medium having at least the groove portion 1
By providing the smoothing layer 20 that fills 8 the formation surface of the recording layer 13 can be substantially smoothed, and as a result,
The thickness of the recording layer 13 can be averaged in the land portion 17 and the groove portion 18. As a result, in the optical recording medium of the type in which recording / reproduction is performed by making laser light incident from the cover layer 14 side, recording / reproduction is performed on the substantially smooth recording layer 13 while performing tracking with the tracking guide groove 16. It becomes possible to obtain good tracking characteristics and recording / reproducing characteristics.

[0038]

As described above, according to the present invention,
It is possible to obtain good tracking characteristics and recording / reproducing characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of an optical recording medium according to the present embodiment.

FIG. 2 is a diagram showing a state in which an optical recording medium is irradiated with laser light.

FIG. 3 is a diagram showing a relationship between a jitter value and a tracking error signal with respect to a defocus amount of laser light.

FIG. 4 is a diagram showing a relationship between a film thickness of a smoothing layer and a tracking error signal.

[Explanation of symbols]

11 ... Substrate, 12 ... Reflective layer, 13 ... Recording layer, 14 ... Cover layer, 15 ... Separate layer, 16 ... Tracking guide groove, 17 ... Land portion, 18 ... Groove portion, 20 ... Smoothing layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshihiro Noda             1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa             Within Mitsubishi Chemical Corporation (72) Inventor Hideki Nagano             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F-term (reference) 5D029 HA06 NA01 NA11 WB17 WC04                       WC05 WD10                 5D121 AA01 AA03 AA05 EE27 GG30

Claims (10)

[Claims] 1. An optical recording medium in which a reflective layer and a recording layer are sequentially laminated on a substrate having a tracking guide groove on the surface, the optical recording medium being formed so as to be interposed between the reflective layer and the recording layer,
An optical recording medium comprising a smoothing layer that smoothes a surface on which the recording layer is formed by closing the tracking guide groove. 2. The maximum film thickness of the smoothing layer is 2λ / Nc (Nc: refractive index of the smoothing layer) or less with respect to a wavelength λ of a laser beam used for recording / reproducing data on / from the recording layer. The optical recording medium according to claim 1, wherein the optical recording medium is present. 3. The optical recording medium according to claim 1, wherein the depth of the recess formed on the surface of the smoothing layer is ½ or less of the depth of the tracking guide groove. . 4. The optical recording medium according to claim 1, wherein the recording layer contains an organic dye. 5. The smoothing layer according to claim 1, wherein the smoothing layer has a light transmittance of 80% or more for a laser light wavelength used for recording / reproducing data to / from the recording layer. The optical recording medium described. 6. The optical recording medium according to claim 1, further comprising a cover layer that covers the recording layer. 7. The depth D of the tracking guide groove is λ / (15 · Nc) ≦ D ≦≦ λ / (5 · Nc) (where λ: wavelength of laser light for recording / reproducing, Nc:
7. The optical recording medium according to claim 1, wherein the refractive index of the smoothing layer). 8. The method according to claim 6, further comprising a separate layer formed between the cover layer and the recording layer to prevent an influence of a material forming the cover layer from affecting the recording layer. Optical recording medium. 9. The light according to claim 1, wherein the recording layer is capable of recording / reproducing data by being irradiated with a laser beam having a wavelength λ of 500 nm or less. recoding media. 10. A step of forming a reflective layer on a substrate having a tracking guide groove on the surface thereof, and a step of filling the irregularities formed by the tracking guide groove with a filler to form a substantially smooth surface on the reflective layer. A step of forming, a step of applying a recording layer forming material containing an organic dye on the substantially smooth surface to form a recording layer, and a step of forming a cover layer covering the recording layer on the recording layer And a method for manufacturing an optical recording medium.