JP2001195785A - Optical recording medium and its recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical recording medium having low noise and high CNR of recording signal. SOLUTION: The optical recording medium is formed by providing an information layer containing at least a recording layer on a substrate having groove parts and inter-groove parts each placed between the adjacent groove parts to each other, the cross-section of substrate vertical to the extended direction of the groove is shaped so that a recessed curved surface and a projecting curved surface are alternately continued and when the interval of the center of the grooves adjacent to each other is expressed by TP as a groove pitch and the sum total of the length of a set of the groove part and a flat part of the inter-groove part adjacent to each other is expressed by F as the flat part, the flat part F is <=45% of the groove pitch TP.

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 used for recording information and a recording / reproducing method thereof.

[0002]

2. Description of the Related Art An optical recording medium represented by an optical disk such as a magneto-optical disk, a phase change disk, an inorganic perforated disk, and a dye disk is a large-capacity information recording medium that can be recorded by a user, and is an external storage device of a computer. Widely used as a medium for Music, photos, images,
It is also rapidly spreading as a medium used for recording and reproducing devices such as music players, digital cameras, videos, and set-top boxes for recording information such as moving images.

As a magneto-optical disk, a 3.5-inch type 640 MB product, a 230 MB product, a 128 MB product,
1.3GB product, 5.25 inch type 650MB-4.
An 8 GB product, a mini disk, and the like are known. As the phase change disk, a CD-RW, a DVD-RAM, and the like have been commercialized, and a DVD + RW, a DVD-RW, and the like have been developed. Dye disks include CD-R, DVD-
Products such as R are known.

A recording track is generally provided on these optical recording media, and a recording / reproducing system such as an optical head of a recording / reproducing apparatus moves (tracks) along the track and irradiates the recording / reproducing light with the above-mentioned recording track. Various information (data)
Is recorded on a recording track and reproduced or erased.
Tracking is usually performed by relying on an uneven groove or an uneven pit provided on the optical recording medium.

Many recordable optical disks are provided with spiral or concentric concave and convex grooves, and recording tracks are formed along the grooves. This includes grooves (recesses in the substrate)
A land recording type in which recording is performed by using a groove recording type in which recording is performed as a recording track, a land recording type in which recording is performed by using an inter-groove portion (a convex portion of a substrate) located between adjacent grooves, as a recording track & Groove recording (L
& G record) type.

Generally, such concave and convex grooves are provided on a substrate, and thin films such as a recording layer, a protective layer, and a reflective layer are formed on the substrate. For forming each layer, a vacuum process such as sputtering or vacuum deposition, or a coating method by spin coating is used. In the following, a layer that actually stores information (hereinafter, referred to as a recording layer) and a layer including thin films such as a protective layer and a reflective layer provided before and after the layer are collectively referred to as an information layer.

When an inorganic material-based information layer such as a magneto-optical disk or a phase change disk is used, a sputtering method or a vacuum evaporation method (electron beam evaporation, thermal evaporation, etc.) is usually used. Since a dense and good film quality is obtained, a sputtering method is often used.

[0008]

In recent years, a groove recording type optical disk has been used in addition to a land recording type optical disk which has been mainly used in the past. In addition, land and groove recording types have also been put into practical use. Land & groove recording can make the recording track pitch extremely high, and is useful for high-density recording.

However, a medium on which information is recorded by using the groove as a recording track has a problem that the information layer is difficult to uniformly adhere to the inside of the groove. Hereinafter, description will be made with reference to the drawings. FIG. 2A is a diagram showing a relationship between a groove shape of a substrate of a conventional optical recording medium and obliquely incident particles during film formation.
(B) is a diagram showing a film adhesion state after film formation.

Conventionally, V-shaped and rectangular shapes are known as the shape of the groove. When the groove portion is used as a recording track, the rectangular shape may be used in order to obtain a high reproduction signal or in terms of tracking characteristics. Many. Here, the rectangular type is also called a U-shaped type, and includes a trapezoidal type. As shown in FIG. 2 (a), a conventional groove recording type optical disk has an optical disk substrate 1 in which a groove portion 2, an inter-groove portion 3 and a groove wall surface 6 connecting them are formed.
A rectangular groove is formed.

When the information layer 5 is formed on the substrate 1 by a sputtering method or a vacuum evaporation method, the film-forming particles fly toward the substrate from various angles. Normally incident particles (not shown) which fly vertically from just above the substrate uniformly adhere to the groove portion 2, the inter-groove portion 3, and the groove wall surface 6. However, the particles (obliquely incident particles) 4 flying obliquely toward the substrate are partially part of the bottom of the groove and one of the groove wall surfaces due to shadowing in which the arrival of the obliquely incident film-forming particles is prevented by the influence of the groove wall surface. Section (shadowing area) 7 cannot be reached. Therefore, as shown in FIG. 2B, the thickness of the information layer 5 is significantly smaller in the groove 2 than in the inter-groove 3. Therefore, if the shadowing is too large, there is a problem that the film thickness of the groove becomes insufficient and good recording cannot be performed.

Further, the film-forming particles, which are blocked from reaching the groove bottom by shadowing, adhere to the upper portion of the groove wall surface as it is, so that the film thickness at that portion increases, and as the film formation proceeds, the groove width becomes smaller. Narrowing down. Further, since the film adhesion to the groove bottom is smaller than that between the grooves, the groove depth becomes deeper, and the recording sensitivity and the characteristics are different in land and groove recording. Since the influence of shadowing is stronger near the wall than at the center of the groove, the shape of the groove after film formation is particularly deep at a portion near the wall. That is, a narrow concave portion is formed along the wall surface. Since it is difficult to reproduce a signal from the narrow recess, the signal from the groove deteriorates more greatly than the signal between the grooves.

Further, according to the study of the present inventor, it has been found that shadowing also causes an increase in noise of a reproduced signal. Usually, a certain degree of roughness (fine irregularities) is present on the substrate surface, but the roughness of the groove wall surface, that is, a change in the angle of the slope, changes the state of shadowing and changes the film formation speed, so that film formation proceeds. In accordance with this, the roughness of the wall surface is remarkably emphasized. As a result, it was found that the groove width and the groove depth were locally changed, and this caused fluctuations in the reproduction signal, and as a result, large noise was generated.

The recording / reproducing method for an optical recording medium includes a substrate surface incidence method in which recording / reproducing light enters through a substrate to perform recording / reproducing, and a recording / reproducing light enters (from the recording layer side) without passing through the substrate. There is a film surface incidence method, but in an optical recording medium of the film surface incidence method, deterioration of characteristics due to shadowing becomes a greater problem. In general, the layer configuration of an optical recording medium of the substrate incident type is substrate / first dielectric layer / recording layer / second dielectric layer (/ reflective layer), and the layer configuration of the optical recording medium of the film incident type. Indicates a substrate (/ reflection layer) / first dielectric layer / recording layer / second dielectric layer.

In either system, the reproduction light is reflected on the surface of the recording layer, and this light is detected by a detector to become a reproduction signal. That is, in the substrate surface incidence method, the reproduction light is reflected at the interface between the first dielectric layer and the recording layer, and in the film surface incidence method, the reproduction light is reflected at the recording layer / second dielectric layer interface. Here, amplification of groove wall roughness due to shadowing,
Since the deformation increases as the film formation proceeds, the deformation becomes more remarkable on the surface of the film farther from the substrate. In the film surface incidence method, the reproduction light is reflected by the film surface having a larger deformation, so that the noise tends to increase.

As described above, the deformation of the groove shape on the film surface, which becomes narrower and deeper as the film is formed, becomes larger as the film surface becomes more distant from the substrate. However, the problem of the characteristic difference between the groove portion and the inter-groove portion is also larger in the film surface incidence method. In order to reduce shadowing, the distance between the substrate and the target (or deposition source) is increased (long throw), or only particles that fly vertically between the substrate and the target (or deposition source) reach the substrate. There is a method of inserting a cylindrical grid (collimator) to make it work.

However, in any of the methods, the use efficiency of the target and the vapor deposition source is remarkably reduced, so that the production cost is increased. Further, since the film forming speed is reduced, the time required for manufacturing is also increased. If the depth of the groove is made very shallow, shadowing can be reduced. However, in this case, a signal for tracking the track (referred to as a tracking signal, a groove signal, etc.) is significantly reduced, so that the tracking cannot be performed satisfactorily.

In particular, the land and groove recording type uses a technique of reducing crosstalk (leakage signal from an adjacent recording track) by an optical interference effect in order to increase a reproduction signal. Is too shallow, crosstalk is increased and the reproduction signal characteristics are degraded. Alternatively, as a method for improving noise in a magneto-optical recording medium by improving the groove shape, Japanese Patent Application Laid-Open No. H11-213470 describes a method in which an edge portion of a groove is curved. It is stated that this eliminates disturbance of the magnetic anisotropy of the magneto-optical recording layer and reduces noise. However, in this method, since only the edge portion is a curved surface, shadowing by the groove wall surface still exists, and the above-mentioned problem could not be solved.

An object of the present invention is to provide an optical recording medium having a low noise and a high CNR of a reproduction signal and a recording / reproducing method for the same by reducing the difference in film thickness between the groove and the groove by greatly reducing shadowing. To provide. In addition, it is another object of the present invention to provide a land and groove recording type optical recording medium having a small difference in signal characteristics between lands and grooves, and a recording / reproducing method suitable therefor.

[0020]

The first gist of the present invention is as follows.
An optical recording medium in which an information layer including at least a recording layer is provided on a substrate having a groove portion and an inter-groove portion located between adjacent groove portions, wherein the information recording medium has at least an information layer including a recording layer. The groove shape of the cross section is a shape in which the concave curved surface and the convex curved surface are alternately continuous, and the interval between the centers of adjacent groove portions is a groove pitch TP, and a pair of adjacent groove portions and grooves When the total length of the flat portion of the portion is defined as a flat portion F, the flat portion F has a shape of 45% or less of the groove pitch TP.

A second gist of the present invention is an optical recording medium comprising an information layer including at least a recording layer provided on a substrate having a groove and an inter-groove located between adjacent grooves. The cross-sectional shape of the substrate perpendicular to the direction in which the grooves extend is such that the distance between the centers of adjacent groove portions is equal to the groove pitch T.
P, and the sum of the lengths of the flat portions of the pair of adjacent groove portions and inter-groove portions is referred to as a flat portion F, where the flat portion F is 45% or less of the groove pitch TP, and An optical recording medium characterized by having a shape in which an intervening portion is joined by a curved surface.

The third gist of the present invention is that the medium
The present invention resides in a recording / reproducing method for an optical recording medium, wherein recording and / or reproduction is performed using at least a groove as a recording track. A fourth gist of the present invention resides in a recording / reproducing method for an optical recording medium, characterized in that recording and / or reproducing are performed on the medium using both the groove and the groove as recording tracks.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS That is, in a conventional optical recording medium, in particular, a magneto-optical recording medium or a phase-change recording medium, a portion where information is recorded is flat, which is good for obtaining a high reproduction signal. It had been. On the other hand, as a result of the study, the present inventor has found that by using a substrate in which both the groove portion including the portion for recording information and the inter-groove portion are mostly curved surfaces, shadowing can be significantly reduced, and the groove portion and the inter-groove portion can be reduced. It has been found that it is possible to reduce the difference in film thickness and to reduce noise caused by shadowing.

Here, the definition of the groove shape in the present invention will be described with reference to FIG. The interval between the center of the groove and the center of the adjacent groove is defined as a groove pitch TP. The sum of the flat portions of the set of groove portions and the inter-groove portions is referred to as a flat portion F. The groove depth d is the vertical distance between the deepest portion of the groove and the highest portion of the groove between the adjacent groove portions and the groove cross-sectional shape of the groove portion. The groove width w is the width of the groove connecting the positions where the groove depth is d / 2. Note that a line connecting the positions where the groove depth is d / 2 is set as a reference line.

In the optical recording medium of the present invention (claim 1), the cross-sectional groove shape of the substrate is such that a concave curved surface and a convex curved surface are alternately continuous, and the flat portion F is 45% of the groove pitch TP. It has the following shape. That is, as shown in FIG. 3, the concave curved surface and the convex curved surface are continuous with respect to the reference line. here,
Although a continuous state is shown for only one TP, much more irregularities are continuous in an actual medium. The total of the flat portion of the groove portion and the flat portion of the inter-groove portion is as small as 45% or less of the groove pitch TP.

The concave curved surface means a mostly concave curved surface, and the convex curved surface means a mostly convex curved surface.
Any of them may include a flat portion F if it is a little (see FIG. 3). Here, the flat portion is a flat region substantially parallel to the surface of the region where the groove is not formed in the substrate. More strictly, the height variation of the substrate surface is one of the groove depths.
% Can be regarded as a flat portion. However, fluctuations due to minute surface roughness or protrusions are not regarded as height fluctuations.

The groove shape can be measured, for example, by an atomic force microscope (AFM). That is, the present invention is characterized in that both the groove portion and the inter-groove portion of the substrate are mostly constituted by curved surfaces. And the cross-sectional groove shape is smooth with almost no edges or steep groove wall surfaces. Hereinafter, such a groove having a groove shape is also referred to as a “wavy groove”.

By using such a corrugated groove, shadowing of film-forming particles by edges and groove wall surfaces can be significantly reduced. Therefore, the film is uniformly formed on both the groove portion and the inter-groove portion, so that the difference in film thickness between the groove portion and the inter-groove portion can be made very small, and uniform characteristics can be obtained in both. In addition, since the film is formed uniformly, the microscopic and macroscopic deformation of the groove shape after film formation as in the related art is small, and the groove shape after film formation is similar to the substrate groove shape. Noise during playback can be reduced.

This will be described in more detail with reference to the drawings. FIG. 2A is a diagram showing a relationship between a groove shape of a substrate of a conventional optical recording medium and obliquely incident particles during film formation. The groove shape is a groove shape having a cross section perpendicular to the extending direction of the groove. Note that the actual film-forming particles fly from various angles.
In (a), only obliquely incident particles in one direction are described for convenience.

FIG. 2B is a view showing the state of film adhesion after film formation. If the conventional cross section has a groove shape close to a trapezoid, the depth of the groove becomes large because a film is difficult to be formed at the bottom of the groove due to shadowing. Further, since the shadowed particles adhere to the wall surface, the groove width is reduced. Further, the groove depth is the deepest in a portion close to the wall surface of the groove bottom. Therefore, the groove shape after film formation is considerably different from the original shape of the substrate.
Such a change in the groove shape due to shadowing causes a change in the characteristics of the groove portion and the portion between the grooves, and noise has been generated due to local variations.

That is, in the case of an optical recording medium such as a phase-change medium, a dye-type medium, and an inorganic write-once medium, which performs reproduction by detecting a change in the reflectance of reproduction light, a change in groove shape causes a change in reflectance. , Causing noise. In the case of a magneto-optical recording medium, the signal intensity is determined by the reflectance, the Kerr rotation angle, and the ellipticity. Each reflected light from the groove and the inter-groove has a phase difference due to a difference in the optical path length. Thus, the overall ellipticity is determined by their combination. When the groove width and the depth change, the ellipticity of the reflected light changes, and a large noise is generated in combination with the change in the reflectance.

As described above, in the case of the magneto-optical recording medium, both the change in the reflectance and the change in the ellipticity generate noise, so that the noise accompanying the shadowing is larger than that of the other types of optical recording medium. On the other hand, FIG. 1A is a diagram showing the relationship between the groove shape of the substrate of the optical recording medium of one embodiment of the present invention and obliquely incident particles during film formation. The groove shape is a groove shape having a cross section perpendicular to the extending direction of the groove. Although actual film-forming particles fly from various angles, FIG. 1A shows only obliquely incident particles in one direction for convenience.

According to the wavy groove of the present invention, since there is almost no edge or a steep groove wall surface, shadowing of film-forming particles by the groove wall surface is significantly reduced as shown in FIG. By using such a wavy groove,
The groove shape after film formation is very similar to the original substrate groove shape as shown in FIG. As a result, the difference in film thickness between the groove portion and the inter-groove portion becomes very small, and uniform characteristics can be obtained. In addition, since there is no unevenness in the film thickness in the groove, the characteristics of the reproduced signal from the groove are greatly improved. Further, since both microscopic and macroscopic deformations of the groove shape due to shadowing are small, noise can be reduced.

In the present invention, in order to reduce shadowing, the flat portion F is preferably as small as possible, and is set to 45% or less of the groove pitch TP. More preferably, the flat portion F is set to 30% or less of the groove pitch TP, and still more preferably 20%.
% Or less. Most preferably, in the present invention, the flat portion F does not exist, and the groove portion and the inter-groove portion are all formed of curved surfaces. As a result, in land and groove recording, it is possible to substantially eliminate the difference in characteristics between the groove and the groove.

The wavy groove of the present invention can be considered as follows. That is, the optical recording medium of the present invention (Claim 10)
Indicates that the cross-sectional groove shape of the substrate is such that the flat portion F has a groove pitch TP of 4
5% or less, and adjacent grooves and inter-grooves are joined by curved surfaces. As shown in FIG. 3, the sum of the flat portion of the groove portion and the flat portion of the inter-groove portion is
It is as small as 45% or less of the groove pitch TP. Then, the adjacent groove portion and the inter-groove portion are smoothly connected by a curved surface. Here, the groove portion has a concave curved surface, and the inter-groove portion has a convex curved surface.

By using such a corrugated groove, shadowing of film-forming particles by edges and groove wall surfaces can be significantly reduced. Therefore, the film is uniformly formed on both the groove portion and the inter-groove portion, so that the difference in film thickness between the groove portion and the inter-groove portion can be made very small, and uniform characteristics can be obtained in both. In addition, since the film is formed uniformly, the microscopic and macroscopic deformation of the groove shape after film formation as in the related art is small, and the groove shape after film formation is similar to the substrate groove shape. Noise during playback can be reduced.

In the above-described wavy groove, to reduce shadowing, the flat portion F is preferably as small as possible, and is set to 45% or less of the groove pitch TP. More preferably, the flat portion F is set to 30% or less of the groove pitch TP, and further preferably 20% or less. Most preferably, the flat portion F does not exist, and the groove portion and the inter-groove portion are all constituted by curved surfaces. As a result, in land and groove recording, it is possible to substantially eliminate the difference in characteristics between the groove and the groove.

Note that the groove shape is intended to reduce noise in an area where recording and reproduction are performed. Therefore, the groove shape does not necessarily have to be a curved surface in an area that is not used by a user for recording. For example, the cross-sectional shape of the pit in the area where the address information and the like are recorded by the uneven pits on the substrate may not be a curved surface. According to the present invention, the CNR is greatly improved particularly at the groove, and it is preferable to perform recording and reproduction using the groove of the present medium as a recording track because noise is low and CNR is high.

In addition, the reproduction signals of the land and the groove can both be improved, and the difference in signal characteristics between the two can be reduced.
The effect is great when applied to an optical recording medium for performing recording and reproduction on both lands and grooves. Also, as described above, the film surface incidence type medium is easily affected by shadowing.
When the present invention is applied to a film-incidence type medium, especially CNR
Is greatly improved, and very high-density information recording can be performed.

Furthermore, the information layer can be formed by a sputtering method or a vacuum evaporation method. In these methods, however, the particles reach the substrate linearly from the evaporation source, so that the influence of shadowing is strong. The improvement effect by applying the present invention is great. However, besides the above, for example, even in the spin coating method, there has conventionally been a problem that the coating liquid is accumulated in the groove portion and is applied thicker than the inter-groove portion. However, it can be improved by applying the present invention.

The optical recording medium having the wavy grooves will be described in more detail. The substrate of an optical recording medium is generally manufactured by first preparing a precise mold called a stamper and transferring the surface shape of the stamper to a resin. The stamper exposes the glass plate coated with the photoresist with a laser and develops it to obtain a glass master (master).
It can be manufactured by copying the unevenness of the resist on the surface from a glass master onto a metal surface such as Ni. To this stamper,
In general, a substrate is produced by performing injection molding with a resin such as polycarbonate.

In order to form the wavy grooves in the present invention, there are a method of forming the stamper at the time of manufacturing, and a method of forming the substrate by performing some processing after the manufacturing. First, as a method of forming the stamper at the time of manufacturing, the following method can be used. For example, a wavy groove can be formed by using, as the above-mentioned photoresist, a photoresist having a so-called low γ value in which the photosensitive characteristic changes relatively slowly with respect to the amount of irradiation, and exposing and developing it with a laser. Alternatively, even when the laser beam spot is not completely focused on the photoresist at the time of laser exposure and is exposed in a somewhat blurred state, a wavy groove can be formed.

Alternatively, after a groove having a conventional shape is formed in the photoresist by exposure and development, the groove shape may be changed by some means to form a wavy groove. According to this method, it is only necessary to perform the steps up to the formation of the groove by the conventional method without greatly changing the conventional manufacturing method, and then to add the groove shape changing step. For example,
The photoresist in which the groove is formed is subjected to a heat treatment up to around its softening point to soften the photoresist and obtain a curved surface by surface tension.

There is also a method of irradiating energy rays such as ultraviolet rays. As the ultraviolet light source, a low-pressure mercury lamp or an excimer lamp can be used. According to this principle, it is considered that the etching is performed by decomposing the resin surface by ultraviolet rays and generating excited oxygen atoms to oxidize the decomposed resin. By this processing, the corner of the groove wall surface is shaved and a curved surface can be obtained. The use of an excimer lamp is preferred because the processing time is shorter than that of a low-pressure mercury lamp. For example, a lamp having a wavelength of 172 nm can be used.

In the case of heat treatment, the groove depth tends to be shallower than before the treatment. On the other hand, in the case of the UV treatment, the groove depth once becomes deeper than before the treatment, and tends to become smaller as the treatment proceeds. Therefore, it is preferable to adjust the groove shape before processing so as to obtain an optimal shape after processing. Next, as an example of a method of forming a wavy groove by performing some kind of groove shape change processing after manufacturing a substrate, a heat treatment may also be performed up to around its softening point. In addition, wet etching in which a substrate is immersed in a liquid that causes a chemical reaction with a substrate and dissolved therein, or dry etching in which a reactive gas is used for etching can also be used.

In the case of a resin substrate, a method of irradiating energy rays such as ultraviolet rays can also be used. This principle is the same as described above. Comparing the processing in the stamper manufacturing stage with the processing in the substrate, by performing the processing in the stamper manufacturing stage, it is possible to manufacture a large amount of the substrate without processing by injection molding or the like using the stamper, so the substrate is processed. The process is simpler than the above and is very preferable.

The shape of the concave and convex pits in which distribution information or address information to the user, information on recording and reproduction of the medium, and the like are recorded in advance is preferably optimized in consideration of the shape change due to processing. .
More specifically, since pits generally become larger due to the processing, it is preferable to prepare pits smaller than the optimum value in advance.

Alternatively, it is also preferable to form a pit having an optimum size and then mask the area where the uneven pit is formed by any method so as not to change the shape of the uneven pit. For example, when etching with ultraviolet light, a mask plate for locally cutting off ultraviolet light may be inserted between the ultraviolet lamp and the substrate. Next, an information layer is formed on the substrate provided with the wavy grooves manufactured by any of the above methods.

For film formation, a sputtering method or a vacuum evaporation method can be used. In these methods, since the particles reach the substrate linearly from the evaporation source, the influence of shadowing is strong, and the improvement effect by applying the present invention is large.
However, besides the above, for example, even in the spin coating method, there has conventionally been a problem that the coating liquid is accumulated in the groove portion and is applied thicker than the inter-groove portion. However, it can be improved by applying the present invention.

Next, an optical recording medium to which the present invention can be applied will be described. The present invention is applicable to an optical recording medium on which a user can record. That is, various types of recording layers can be used. For example, a magneto-optical recording layer, a phase change recording layer, a dye recording layer, and an inorganic write-once recording layer are used. In addition, various layer configurations can be adopted.

As the magneto-optical recording layer, for example, TbFe,
TbFeCo, TbCo, GdFeCo, DyTbFe
Amorphous magnetic layer of rare earth such as Co and transition metal, MnB
i, a polycrystalline perpendicular magnetization layer such as MnCuBi, a Pt / Co multilayer film or the like is used. The magneto-optical recording layer may be a single layer, or two or more magnetic layers such as GdTbFe / TbFe may be used in order to enable overwriting or MSR (magnetic super-resolution).

As the phase change type recording layer, for example, GeSb
Te, InSbTe, InGeSbTe, AgSbT
Compounds such as e and AgInSbTe can be used. Preferably, {(Sb ₂ Te ₃ ) _1-x (GeTe) _x }
_{1-y Sb y (0.2 <} x <0.9,0 ≦ y <0.1) alloy, and In of up to about 10 atomic% to the ternary alloy, G
a, Zn, Sn, Si, Cu, Au, Ag, Pd, P
t, Pb, Cr, Co, O, S, Se, Ta, Nb, V
Alloy thin film containing at least one of the above.

Alternatively, as a material that can be overwritten at high speed, MSbTe (M = In, Ga, Zn, MSbTe) mainly containing an SbTe alloy near the eutectic point of Sb ₇₀ Te ₃₀ .
Ge, Sn, Si, Cu, Au, Ag, Pd, Pt, P
b, Cr, Co, O, S, Se, Ta, Nb and V). The inorganic write-once type recording layer may be made of TeSe or the like, and the dye type recording layer may be made of a cyanine dye, a phthalocyanine dye, a metal-containing azo dye, or a mixture thereof.

The upper and / or lower portions of the recording layer have weather resistance,
A transparent intermediate layer having properties such as high hardness and high lubricity is provided. The material of the intermediate layer is selected in consideration of these properties. A dielectric is preferable in terms of weather resistance and high hardness. As the dielectric, metal oxide, nitride, chalcogenide, carbide, fluoride, a mixture thereof, and the like are used.

As the metal oxide, Al ₂ O ₃ , Ta ₂ O
₅ , metal oxides such as SiO ₂ , SiO, and TiO ₂ alone or a mixture thereof, or a composite oxide of Al—Ta—O. Examples of the metal nitride include silicon nitride and aluminum nitride. Examples of chalcogenides include zinc chalcogenides such as ZnS and ZnSe, CdS,
II-V group compound such as _{CdSe, La 2 S 3, Ce} 2 S
Rare earth sulfides such as ₃ , TaS ₂ , MgS, CaS and the like. Zinc chalcogenide is chemically stable, and among them, ZnS is particularly preferable because of its low toxicity.

Further, a reflective layer made of a metal or an alloy having high reflectivity may be provided. Al, A as the reflective layer material
g, Au, Pt, or an alloy thereof, or an alloy containing one or more of these as a main component is used. In the present invention, the various layers described above are collectively referred to as an information layer. As described above, since the increase in noise due to shadowing is particularly large in the magneto-optical recording medium, the noise reduction effect by applying the present invention is remarkable.

Further, since the sputtering method and the vacuum evaporation method are greatly affected by shadowing, they are highly effective when used for a medium on which at least a part of the information layer is formed by the sputtering method or the vacuum evaporation method. In the above description, the film surface incidence method in which light is incident on the recording layer without passing through the substrate has been mainly described. However, the operation of the present invention is the same in the substrate surface incidence method in which light is incident through the substrate. This is because, even in the substrate surface incidence method, shadowing of the transparent intermediate layer formed first is involved. However, as described above, the use of the medium of the film surface incidence type has a greater noise reduction effect.

The present invention has a remarkable effect when used for a medium of the type in which information is recorded using the groove as a recording track. In particular, when used for a land and groove recording medium in which recording is performed in both the groove portion and the groove portion, the difference in characteristics between the groove portion and the groove portion is preferably small. In this case, it is desirable that the corrugated grooves have the same shape in which the convex groove portions and the concave groove portions are substantially inverted.

Hereinafter, a more preferable groove shape in the present invention will be described. As described above, if the groove is extremely shallow, the influence of shadowing is small. But,
If the groove is too shallow, it will be difficult to obtain a sufficient track following signal during recording and reproduction. Further, the shallow groove reduces the distance that heat is transmitted between adjacent tracks, so that there is a high possibility that heating at the time of recording or erasing will interfere with the adjacent track. That is, the allowable range of the optical power for recording and erasing tends to be narrow.

Further, in land and groove recording, by setting the groove depth to an appropriate range, crosstalk is reduced by optical interference between reflected light from the groove and light reflected from the inter-groove. Is used. Generally, in order to achieve this effect, a groove depth of at least λ / 6 is required for a wavelength λ of light incident on the groove. However, it is preferably λ / 3 or less. Here, in the case of the film surface incidence method, λ is the wavelength in the air, and in the case of the substrate surface incidence method, λ is the wavelength in the substrate.

Conventionally, when the groove depth is increased, the influence of shadowing increases, so that an optimum groove shape cannot always be obtained in both the groove recording method and the land & groove recording method. Was. According to the present invention, since the shadowing can be reduced, the groove shape can be optimized in consideration of only the above points.

The preferred groove depth has a lower limit of λ / 20 or more, more preferably λ / 15 or more. The upper limit is λ / 4 or less, more preferably λ / 5 or less.
Further, an optical recording medium having a narrow groove width such as a groove width of 0.7 μm or less is greatly affected by shadowing, so that the effect of the present invention is particularly high. If the ratio (aspect ratio) between the groove depth and the groove width is large, it is difficult for the reproduction light to enter the groove, and the reproduction signal tends to decrease. Therefore, the relationship between the groove depth d and the groove width w is

[0063]

It is preferable that d / w <0.3. More preferably,

[0064]

## EQU2 ## d / w <0.2. In the case of the land & groove recording medium, the groove width w is preferably 35% or more of the groove pitch TP,
More preferably, it is at least 40%. However, it is preferably 65% or less, more preferably 60% or less. With this range, it is possible to obtain a medium having good and well-balanced recording and reproducing characteristics in both the land and the groove (groove).

In order to keep the relationship between the groove width w and the groove depth d in this range, the ultraviolet treatment and the heat treatment of the substrate and the stamper are controlled to an appropriate time and strength. Further, according to the present invention, fluctuations in groove shape due to film formation can be suppressed,
In particular, the effect is high when used in the film surface incidence method. In this method, since there is no occurrence of aberration associated with the substrate, a lens having a higher numerical aperture than the substrate surface incidence method can be used. Further, since the objective lens can be brought close to the film surface, a SIL (Solid Immersion Lens) having a large numerical aperture exceeding 1 can be used.

As a recording / reproducing method for bringing the objective lens close to the film surface, for example, there is a method of mounting the objective lens on a floating head. According to the present invention, it is possible to greatly improve the CNR of such a film-surface incident type medium, so that extremely high-density information recording becomes possible. The present invention is directed to a medium having a thick recording layer, such as a light modulation overwrite medium, a magnetic super resolution (MSR) medium, etc., which is a type of magneto-optical recording medium, since the groove shape fluctuation due to shadowing increases as the film thickness increases. Preferred for use. The thickness of the recording layer produced by sputtering or vacuum evaporation is 100 n
The effect of application to media of m or more is high. Further, the effect of application to a medium having a recording layer having a thickness of 200 nm or more is high.

In the case where the adhesion efficiency of the film at the time of film formation is low but does not cause a serious problem, a combination of a wavy groove and long slow sputtering or a collimator is used.
Shadowing can be further reduced.

[0068]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention. The disks manufactured in the following examples and comparative examples are all magneto-optical disks used for land & groove recording. (Examples 1 to 6, Comparative Example 1) A plurality of polycarbonate substrates each having a spiral groove formed thereon and having a thickness of 1.2 mm and a diameter of 130 mm were prepared. The refractive index of polycarbonate is 1.58
It is. In each case, the groove shape in a cross section perpendicular to the direction in which the groove extends was a substantially trapezoid having a groove width of 0.67 μm and a groove depth of 60 nm. The groove pitch TP was 1.4 μm, the flat portions between the groove portions and the inter-groove portions were each 0.6 μm, and the total flat portions were 1.2 μm, which was 86% of the groove pitch.

With respect to these substrates, except for one, an output of 20
Ultraviolet irradiation was performed with an excimer lamp (manufactured by Ushio Inc.) having a wavelength of 0 W and a wavelength of 172 nm. The distance between the board and the lamp is 3m
m. After irradiating each substrate with ultraviolet light for 1 minute, 1 minute 30 seconds, 2 minutes, 3 minutes, 5 minutes, and 10 minutes, the groove shape was observed by AFM (atomic force microscope). The results are shown in Table 1.

[0070]

[Table 1]

The flat portion decreased with irradiation, and the groove shape of the present invention was obtained by irradiation for 1 minute or more. The irradiation for 2 minutes only slightly left a flat portion in the inter-groove portion, which was reduced to 12% of TP. With irradiation for 3 minutes or more, the entire surface was substantially composed of a curved surface without a flat portion. The case where the irradiation time was 3 minutes was such that the groove portion and the inter-groove portion had the same shape which was substantially inverted from each other (Example 4).

However, when the irradiation time was 10 minutes, the groove width was widened as the inter-groove portion was reduced, and the flat portion in the groove was increased. Next, 70 nm thick Ta oxide and 100 nm thick Tb21 (Fe80
Co20) 89 and an 80 nm-thick Si nitride film were formed to produce a magneto-optical disk. Ta oxide and Si nitride were formed by DC reactive sputtering, and TbFeCo was formed by DC sputtering.

Wavelength 680 nm, numerical aperture NA of the objective lens
= 0.55 with these discs at a linear velocity of 8 m / s
The evaluation was performed by both the film surface incidence method and the substrate surface incidence method while rotating at. In each case, a sufficient track following signal (tracking signal) was obtained. In addition,
Since the objective lens of the evaluator was designed so as to be optimized to be used through a 1.2 mm substrate, during evaluation by the film surface incidence method, 1.
A 2 mm glass plate was inserted.

Each was recorded with a mark length of 1.52 μm,
Table 1 shows the reproduced signal characteristics CNR (dB). CN
R is preferably obtained at least 40 dB, more preferably at least 45 dB. Further, it is preferable that the difference between the groove portion and the inter-groove portion is smaller. In all of Examples 1 to 6 in which the flat portion F is 45% or less of the groove pitch TP, CNR of 40 dB or more is obtained in both the groove portion and the inter-groove portion, and Examples 2 to 6 in which F / TP is 30% or less. Is approximately 45 dB.
However, in Example 6, the CNR in the inter-groove portion was reduced because the inter-groove portion was reduced by long-time ultraviolet irradiation.

Next, with respect to the disks of Example 4 and Comparative Example 1, the noise at the gap between the grooves was measured by the film surface incidence method. FIG. 6 shows a noise spectrum from 0 to 20 MHz in both erased states. In the fourth embodiment, noise is improved by up to 7 dB over the frequency band of 0 to 12 MHz as compared with the first comparative example. (Examples 7 to 10, Comparative Example 2) A plurality of polycarbonate substrates each having a spiral groove and a thickness of 1.2 mm and a diameter of 130 mm were prepared. In any case, the groove shape having a cross section perpendicular to the direction in which the groove extends has a groove width of 0.68 μm and a groove depth of 91 μm.
It was substantially trapezoidal in nm. The groove pitch TP is 1.2 μ
m, the flat portion of the groove portion was 0.6 μm, and the flat portion of the inter-groove portion was 0.1 μm.
4 μm, the total flat portion is 1.0 μm, and the groove pitch is 8
3%.

Except for one of these substrates, 135
Heating was performed in a heating oven set to ° C. Each board
After heating for 1.5 hours, 3 hours, 5 hours, and 7 hours, respectively, the groove shape was observed with an AFM (atomic force microscope).
Table 2 shows the results.

[0077]

[Table 2]

The flat portion decreases with heating.
After heating for 5 hours, the groove shape of the present invention was obtained. After heating for 3 hours, only a flat portion remains slightly.
%. Next, a 70 nm-thick Ta oxide film and a 100 nm-thick T
b21 (Fe80Co20) 89 and a 80 nm-thick Si nitride film were formed to produce a magneto-optical disk. Ta oxide and Si nitride
Was formed by DC reactive sputtering, and TbFeCo was formed by DC sputtering.

680 nm wavelength, numerical aperture NA of objective lens
= 0.55 with these discs at a linear velocity of 8 m / s
The evaluation was performed by both the film surface incidence method and the substrate surface incidence method while rotating at. In each case, a sufficient track following signal (tracking signal) was obtained. In addition,
Since the objective lens of the evaluator was designed so as to be optimized to be used through a 1.2 mm substrate, during evaluation by the film surface incidence method, 1.
A 2 mm glass plate was inserted.

Each was recorded with a mark length of 1.52 μm,
Table 2 shows the reproduced signal characteristics CNR (dB). CN
R is preferably obtained at least 40 dB, more preferably at least 45 dB. Further, it is preferable that the difference between the groove portion and the inter-groove portion is smaller. In all of Examples 7 to 10 in which the flat portion F is 45% or less of the groove pitch TP, the effect of improving the CNR is obtained in both the groove portion and the inter-groove portion with respect to Comparative Example 2, and F / TP Is less than 30%,
Almost 45 dB has been obtained. However, in Example 10, since the groove was reduced by the long-time ultraviolet irradiation, the CN of the groove was reduced.
R is decreasing.

[0081]

According to the present invention, the difference in film thickness between the groove and the groove can be reduced by greatly reducing shadowing, noise can be reduced, and a reproduced signal having a high CNR can be obtained. In particular, since the CNR is greatly improved in the groove, it is preferable to perform recording and reproduction using the groove of the present medium as a recording track because noise is low and CNR is high.

In addition, it is possible to provide a land-and-groove recording type optical recording medium in which both the reproduction signal of the land and the groove are improved and the difference in signal characteristics between the land and the groove is small.
In addition, when the present invention is applied to a film-surface incident type medium, the CNR can be particularly greatly improved, so that extremely high-density information recording becomes possible.

[Brief description of the drawings]

FIG. 1A is a diagram showing a relationship between a groove shape of a substrate of an optical recording medium according to an embodiment of the present invention and obliquely incident particles during film formation, and FIG. It is a figure showing an adhesion state.

FIG. 2A shows a groove shape of a substrate of a conventional optical recording medium,
It is a figure which shows the relationship with the oblique incidence particle during film formation, (b)
FIG. 4 is a diagram showing a film adhesion state after film formation.

FIG. 3 is an explanatory diagram showing definitions of parameters of a groove shape.

FIG. 4 is a diagram showing noise spectra in Example 4 and Comparative Example 1.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 groove portion 3 groove portion 4 obliquely incident particle 5 information layer 6 groove wall surface 7 shadowing region

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/105 521 G11B 11/105 521E

Claims (21)

[Claims] 1. An optical recording medium comprising: a substrate having a groove portion and an inter-groove portion located between adjacent groove portions; and an information layer including at least a recording layer provided on the substrate. The groove shape having a cross section perpendicular to the extending direction is a shape in which concave curved surfaces and convex curved surfaces are alternately continuous, and a distance between centers of adjacent groove portions is defined as a groove pitch TP,
When the sum of the lengths of the flat portions of a pair of adjacent groove portions and inter-groove portions is defined as a flat portion F, the flat portion F is 4 times the groove pitch TP.
An optical recording medium having a shape of 5% or less. 2. The optical recording medium according to claim 1, wherein the flat portion F is 30% or less of the groove pitch TP. 3. The optical recording medium according to claim 1, wherein the flat portion F does not exist. 4. The optical recording medium according to claim 1, wherein the medium is a medium for performing recording and reproduction by irradiating a recording layer with recording and reproduction light without passing through a substrate. 5. The optical recording medium according to claim 1, wherein at least a part of the information layer is formed by a sputtering method or a vacuum evaporation method. 6. The optical recording medium according to claim 1, wherein the medium is a medium for recording information using at least a groove as a recording track. 7. The optical recording medium according to claim 1, wherein the medium is a medium for recording information using both the groove and the groove as recording tracks. 8. The groove width w is 35% or more of the groove pitch TP and 65 or more.
%. 9. The optical recording medium according to claim 1, wherein the recording layer is a magneto-optical recording layer. 10. An optical recording medium comprising an information layer including at least a recording layer provided on a substrate having a groove portion and an inter-groove portion located between adjacent groove portions. The groove shape of the cross section perpendicular to the existing direction is defined as a groove pitch TP, which is the distance between the centers of adjacent groove portions.
When the sum of the lengths of the flat portions of a pair of adjacent groove portions and inter-groove portions is defined as a flat portion F, the flat portion F is 4 times the groove pitch TP.
An optical recording medium characterized by being 5% or less and having a shape in which adjacent groove portions and inter-groove portions are joined by a curved surface. 11. The optical recording medium according to claim 10, wherein the flat portion F is 30% or less of the groove pitch TP. 12. The optical recording medium according to claim 10, wherein the groove has a shape in which all of a groove and an inter-groove have curved surfaces. 13. The optical recording medium according to claim 10, wherein, in the groove shape, a groove portion is concave and an inter-groove portion is convex. 14. The optical recording medium according to claim 10, wherein the medium is a medium for performing recording and reproduction by irradiating a recording layer with recording / reproduction light without passing through a substrate. 15. The information layer according to claim 1, wherein at least a part of the information layer is formed by a sputtering method or a vacuum evaporation method.
15. The optical recording medium according to any one of 0 to 14. 16. The medium for recording information using at least a groove as a recording track.
16. The optical recording medium according to any one of 0 to 15. 17. The optical recording medium according to claim 10, wherein the medium is a medium for recording information using both the groove and the groove as recording tracks. 18. The groove width w is 35% or more of the groove pitch TP.
The optical recording medium according to claim 17, wherein the content is 5% or less. 19. The recording layer according to claim 1, wherein the recording layer is a magneto-optical recording layer.
19. The optical recording medium according to any one of 0 to 18. 20. A recording / reproducing method for an optical recording medium, comprising: performing recording and / or reproduction on the optical recording medium according to claim 1 using at least a groove as a recording track. 21. The optical recording medium according to claim 1, wherein both of the groove and the space between the grooves are recorded as recording tracks.
Or, a recording / reproducing method for an optical recording medium, comprising performing reproduction.