JP2002123972A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information recording medium that reduces a crosstalk caused when a signal is recorded to both a groove and a land of the recording medium or reduces a difference of the quality of a reproduced signal from the both. SOLUTION: The optical information recording medium has a recording layer 3 where both the groove 7 and the land 8 adjacent to the groove 7 formed on the surface of a substrate 1 are used for a signal recording track and which reversibly records a signal through the reception of an emitted laser beam 6. The depth D of the groove 7 holds a relation of λ/(8n)<D<λ/(4n) (λ is a wavelength of a regenerated light and n is a refractive index of the substrate), a relation of 0<=R2/R1<=0.2 holds, where R1 is a higher reflectance of the recording layer and R2 is the lower reflectance, and a relation of 2mπ<ϕ1-ϕ2<(1+2m)π (m is an integer) or (2m-1)π<ϕ1-ϕ2<2mπ (m is an integer) holds, where ϕ1 is a phase of a reflected light when the reflectance of the recording layer is high and ϕ2 is a phase of the reflected light when the reflectance of the recording layer is low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium for recording and reproducing information at high speed and high density by using light, heat, etc., and more particularly to an optical disk.

[0002]

2. Description of the Related Art When a laser beam is converged by a lens system, a light spot whose diameter is small on the order of the wavelength of the light can be formed. Therefore, a light spot having a high energy density per unit area can be formed even from a light source having a small output. Therefore, it is possible to change a minute region of the substance, and it is also possible to read the change of the minute region. An optical information recording medium is used for recording and reproducing information. Hereinafter, it is described as “optical recording medium” or “recording medium”.

[0003] Phase change recording, in which one of optical recording media changes the optical constant by changing the state of a recording film material by irradiating a laser beam, detects a change in the amount of reflected light accompanying the change, and records / reproduces a signal. There is a medium. In a phase change recording medium, signals are recorded / reproduced by utilizing the fact that optical constants generally differ between an amorphous state and a crystalline state.

The reason why the amount of reflected light reaching the detection system changes is that the reflectance of the minute recording area is different from its surroundings, and that the phase of the reflected light is different between the minute recording area and its surroundings, causing diffraction. There is.

[0005] The phase change recording medium is generally designed so that a signal is reproduced by a difference in reflectance between a crystalline state and an amorphous state. Japanese Patent Application No. 63-227
No. 015) and a proposal utilizing both the reflectance difference and the phase difference (Japanese Patent Application No. 3-175001).

[0006] Phase change recording media can record signals without deforming the recording film, and can rewrite signals by reversibly changing the state of the recording film material. Is being promoted.

As a phase change recording material, a chalcogen alloy is well known, for example, GeSbTe, InSb
There are Te type, GeSnTe type, InSe type, SbTe type, and the like. These materials are melted by laser irradiation with relatively strong power and then cooled to be in an amorphous state, and the amorphous region reaches a crystallization temperature or higher by laser irradiation with relatively weak power to be in a crystalline state. Therefore, for example, a signal can be recorded by associating the amorphous state with the signal 1 and the crystalline state with the signal 0.

One of the features of the phase change optical disk is that one-beam overwriting is possible. That is, a new signal can be recorded while erasing an old signal only by passing a laser spot on a signal track once while modulating between a recording power and an erasing power with a recording signal. For details of the one-beam overwriting technique, see, for example, Japanese Journal Applied Physics Vol. 26, Supplement, page 61 (JJAP,
Vol. 26 (1987) Supplement 26
-4, P61).

On the other hand, development for high-density recording is also under way. For example, a signal is not only provided on a guide groove for signal recording of an optical disk but also between a guide groove (hereinafter referred to as a groove) and a guide groove (hereinafter referred to as a land). A method of increasing the recording density by recording (hereinafter referred to as a land and groove recording method) has been proposed (Japanese Patent Publication No. 63-57859).

Further, in this case, if the groove shape such as groove depth and groove width is limited, adjacent tracks (signals are recorded on both the groove and the land, so both are recording tracks.
(Hereinafter simply referred to as a track) can be made extremely small (Japanese Patent Application No. 4-79483).

[0011]

SUMMARY OF THE INVENTION On a substrate provided with a groove for signal recording and a land for signal recording, a recording layer which changes at least between a high reflectance state and a low reflectance state by irradiation with a laser beam or the like is provided. It has been found that the following problems, which have not been seen in the conventional optical disk that records a signal only on one of a groove and a land, may occur in the optical disk.

1) The size of crosstalk from an adjacent track (crosstalk from an adjacent groove in a land, and crosstalk from an adjacent land in a groove) greatly differs depending on not only the groove shape of the substrate but also the thin film configuration. In some cases, the crosstalk is too large to be practical.

2) The quality of the reproduced signal, that is, the reproduced signal amplitude, the signal-to-noise ratio (CNR) and the like may be different between the case of recording on a groove and the case of recording on a land. If the quality of the reproduced signal is significantly different, there arises an inconvenience that the signal processing means after reproduction needs to be changed between the land and the groove.

3) The reproduction signal quality of the groove and the land is the same at the time of initial recording, but the signal deterioration of the land may be larger when overwriting is repeated.

The land and the groove in this specification are defined as a groove that is convex toward the laser beam input side and a land that is convex on the opposite side. Laser light is usually irradiated through the substrate,
Even in the case of irradiation from the side opposite to the substrate, the contents described herein are included in the present invention according to this definition.

[0016]

According to the present invention, at least a first dielectric layer and a laser are formed on a substrate having both a groove-like groove formed on the surface with irregularities and a land between the adjacent groove and a signal recording track. An optical information recording medium provided with a recording layer, a second dielectric layer, and a reflective layer that reversibly change at least between a high-reflectance state and a low-reflectance state by irradiation with light or the like. λ and the refractive index of the substrate is n, the depth D of the groove is λ /
(8n) <D <λ / (4n), and the higher reflectivity of the recording layer is R1, the lower reflectivity is R2, and the reflected light with respect to the incident light when the recording layer has a high reflectivity. Is the phase of φ1 and the phase of the reflected light with respect to the incident light in the state where the reflectance is low is φ2, the film thicknesses of the first dielectric layer, the recording layer, the second dielectric layer, and the reflective layer By adjusting the reflectance ratio R2 / R1 and the phase difference φ1−φ2 of the reflected light, the difference between the amplitude of the signal reproduced from the groove and the amplitude of the signal reproduced from the land is within 3 dB. It is characterized by being designed to be.

By limiting the groove depth of the substrate and the reflectivity of the recording medium as described above, crosstalk can be reduced even in the land & groove recording method. Further, by limiting the phase difference, it is possible to compensate for the difference in signal quality between the land and the groove due to the groove shape and noise level of the substrate, and the signal quality deterioration in the land due to the cycle.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view of an example of an optical disk used in the present invention. Reference numeral 1 denotes a substrate, on the surface of which a groove 7 and a land 8 are provided as signal recording tracks.

As a material of the substrate, generally, transparent glass, quartz, polycarbonate, polymethyl methacrylate, or the like is used, and a laser beam is applied from the side opposite to the signal track surface of the substrate.

On the substrate, a first dielectric layer 2, a recording layer 3,
The second dielectric layer 4 and the reflection layer 5 are laminated in this order. If necessary, a protective cover 9 is provided to protect the thin film layer.
May be provided.

The recording layer 3 is made of a material that changes reversibly between optically identifiable states by irradiation with a laser beam or the like. For example, a material generally known as a phase change substance can be used.

The phase change material is an alloy such as Te, Se, Sb, In, Ge or the like which causes a state change between an amorphous state and a crystal state or between a crystal state and a different crystal state. Since the optical constant changes and the reflectance changes, the state can be optically identified by irradiation with laser light or the like. Specifically, for example, GeSbTe, InSbTe, InSbTeAg, Ga
Alloys such as Sb, InGaSb, GeSnTe, and AgSbTe are applied.

First dielectric layer 2 and second dielectric layer 4
Is preferably a transparent and thermally stable substance, for example, oxides, nitrides, chalcogenides, fluorides, carbides, and the like of metals and metalloids, and mixtures thereof. Specifically, for example, SiO ₂ , SiO, Al ₂ O ₃ , GeO ₂ , In
₂ O ₃ , Ta ₂ O ₅ , TeO ₂ , TiO ₂ , MoO ₃ , WO ₃ ,
ZrO ₂ , Si ₃ N ₄ , AlN, BN, TiN, ZnS,
CdS, CdSe, ZnSe, ZnTe, AgF, Pb
It is a simple substance such as F ₂ , MnF ₂ , NiF ₂ , SiC or a mixture thereof.

The reflection layer 5 is made of a metal film, and may be made of, for example, Au, Al, Ti, Ni, Cu, Cr, etc., or an alloy thereof.

It should be noted that the first dielectric layer 2, the recording layer 3, the second
By appropriately designing the thickness of the dielectric layer 4 described above, it is also possible to adopt a structure without using the reflective layer 5.

In the case where a signal is reproduced by a change in reflectivity as in a phase change optical disk, even if a signal is recorded on both the land and the groove as shown in FIG. 1, crosstalk is limited by limiting the groove depth. Japanese Patent Application No. 4
-79483, in which:
In order to reduce the amount of crosstalk to -20 dB or less, the groove depth D is set to the wavelength of the reproduction light, and the refractive index of the substrate is set to n.
In this case, it is sufficient to set such that λ / (7n) ≦ D ≦ 5λ / (14n) is satisfied, and further, if approximately λ / (5n) or approximately 3λ / (10n), the crosstalk is minimized. Is disclosed.

Although the geometric depth of the groove is constant, if the wavelength λ of the reproducing light and the refractive index n of the substrate change, the optical depth of the groove changes. D is all limited by optical depth.

Based on the above reference, the inventors reversibly change the state between the amorphous phase and the crystalline phase on the substrate by changing the groove depth while maintaining the land and groove widths substantially the same. A phase change optical disk which causes the above-mentioned phenomenon was manufactured, and as a result of repeated studies on recording / reproducing characteristics and crosstalk characteristics, it was found that there was a problem peculiar to land & groove recording as described above.

The present inventors have examined the above problems in detail, and found that the causes of problems 1 and 2 are a phase difference between reflected light in an amorphous state and a crystalline state, a difference in width between a groove and a land,
It was found that there was a noise difference between the groove and the land.

Although the cause of the problem 3 is not clear, it is considered that the difference is caused by a difference in thermal condition between the land and the groove. That is, for example, the groove is convex on the laser light input side, whereas the land is convex on the opposite side to the laser light input side and the geometric structure is different. It is considered that the process of raising the temperature of the recording film and the heat radiation process are also different.

The present invention has been made to address such a new problem, and the configuration of the recording medium is limited as follows.

That is, in an optical information recording medium provided with a recording layer that reversibly changes between a high reflectivity state and a low reflectivity state, if the wavelength of the reproduction light is λ and the refractive index of the substrate is n, the groove is Is λ / (8n) <D <λ /
When (4n) is satisfied and the higher reflectance of the recording layer is R1 and the lower reflectance is R2, 0 ≦ R2 /
R1 ≦ 0.2 is satisfied.

It has been found that by limiting in this way, crosstalk from an adjacent track can be suppressed to -20 dB or less. Further, it was also found that the amplitude difference between the land reproduction signal and the groove reproduction signal can be suppressed to a small value.

In the case of R2 / R1> 0.2, the case where the crosstalk exceeds -20 dB appears. However, this is because when the reflectivity (lower reflectivity) in the recording mark increases, the crosstalk from the recording mark increases. It is considered that the interference between the reflected light and the reflected light of the adjacent track increases, and the presence or absence of the recording mark can be detected from the adjacent track depending on the phase of the reflected light from the recording mark.

The difference in signal quality between the land and the groove and the deterioration in the quality of the land signal due to the cycle are caused by the difference between the phase φ1 of the reflected light in the state of high reflectance and the phase φ2 of the reflected light in the state of low reflectance. That is, it was found that control could be performed by controlling φ1−φ2 (hereinafter Δφ12).

For example, 2mπ <Δφ12 <(1 + 2m)
By designing the thin film configuration so as to satisfy π (where m is an integer), when the land width and the groove width are the same, the land amplitude becomes larger than the groove amplitude (Japanese Patent Application No. 3-1).
No. 75001).

This phenomenon is also caused by interference between reflected light from a recording mark and reflected light from an adjacent track.
The present invention utilizes this phenomenon to solve the problem of land & groove recording. That is, if Δφ12 is selected in the above range, the signal quality is lower in the land than in the groove, for example, (1) when the land width of the substrate is smaller than the groove width, or (2) when the noise level of the substrate is lower than the groove. In the case where the signal is higher, it is found that, by emphasizing the amplitude of the land, the signal quality between the land and the groove can be made equal and good, and the recording medium can be suitable for land and groove recording.

The limitation of Δφ12 is based on the problem 3 described above.
It is also effective in compensating for the signal deterioration of the land when the overwriting is repeated. That is, in the land & groove recording, the CNR of the groove and the land is used.
Are the same at the time of initial recording, but when overwriting is repeated, the CNR of the reproduced signal accompanying the increase in noise
In some cases, the degradation of the land is faster in the land, that is, the signal degradation of the land is greater. In this case, the cycle life is determined by the decrease in the land CNR.

Therefore, Δφ12 is limited to the above range, and the land amplitude is designed to be slightly larger than the groove amplitude in the initial recording stage. With this configuration, it was found that although the initial CNR in the groove was slightly reduced, the initial CNR of the land was increased by increasing the land amplitude, and the CNR reduction due to the cycle was also reduced. That is, it is possible to design so that the signal quality of the land and the groove becomes equal after many cycles, and as a result, a recording medium having a long cycle life can be supplied to both the land and the groove.

Also, (2m-1) π <Δφ12 <2m
If the thin film configuration is designed to satisfy π (where m is an integer), when the land width and the groove width are the same, the amplitude of the groove becomes larger than the amplitude of the land. If Δφ12 is selected in this range, if the signal quality of the groove is inferior to that of the land, for example, (1) the groove width of the substrate is narrower than the land width, or (2) the noise level of the substrate is lower than that of the land. When it is high, for example, by emphasizing the amplitude of the groove, the signal quality of the land and the groove can be made equal, and the recording medium suitable for land and groove recording can be obtained.

Here, how to determine the reflectance and the phase difference between the amorphous state and the crystalline state of the recording medium will be described.

A method of calculating the reflectivity of light rays and the phase of reflected light in the thin film laminated structure as shown in FIG. 1 is known, for example, as a matrix method. In the present invention, the matrix method is used based on the complex refractive index and film thickness of each layer. (For example,
Hiroshi Kubota, “Hado Optics”, Iwanami Shoten, 1971, Chapter 3).

The substrate 1 and the protective cover 9 are regarded as having an infinite film thickness (ignoring the effects of the substrate-air interface and the adhesion protective layer-air interface). The phase was determined based on the phase at the interface between the substrate 1 and the first dielectric layer 2.

The complex refractive index of the recording layer is, for example, Ge
In the case of the SbTe ternary system, the complex refractive index in the amorphous state when a film is formed on a glass substrate by a sputtering method, and the complex refractive index when the sample is heat-treated at 300 ° C. for 5 minutes in an inert gas and crystallized. Adopted rate.

Whether the substrate noise is high in the groove or the land is largely due to the manufacturing process of the substrate. The level of the board noise is an important factor related to the present invention,
This will be described in detail here, and the definition of the noise level in the present invention will be described.

The disk substrate is generally formed by an injection method (injection molding method) from a stamper provided with a groove in advance.
Alternatively, it is replicated by the 2P method (photo polymarization method).

In the method of manufacturing a stamper, first, a glass source plate 61 sufficiently polished as shown in FIG. 6 is prepared. A photoresist 62 is applied thereon, grooves are recorded by a laser beam 63, and grooves 64 having irregularities are formed by a developing process to obtain a glass master.

After a conductive film 65 is formed on the entire surface by, for example, electroless plating or sputtering, a stamper 66 made of nickel or the like is formed by an electroforming process.

The disk substrate is duplicated on the basis of the stamper 66. At this time, the groove of the substrate is formed by the glass source disk 6
The land corresponds to the transfer surface of the photoresist 62 surface, and the land corresponds to the transfer surface of the glass surface. The glass surface is a mirror surface because it is sufficiently polished, but the photoresist 62 surface may have some irregularities on the surface. As a result, although the groove surface of the substrate is a mirror surface, the land surface has irregularities, which may cause noise in signal reproduction.

In the above stamper manufacturing method, only one stamper can be obtained from the glass source plate 61.
There is also a method of obtaining a plurality of stampers by repeating the electroforming process based on the stamper 66, and the groove of the finally manufactured disk substrate may correspond to the photoresist surface. In this case, Groove noise is higher than land noise.

When a disk substrate is manufactured by the injection method, noise may be generated on the land. The injection method is a method in which a molten resin is injected under high pressure into a mold including a stamper of a disk and solidified. At this time, if the flow of the resin to the concave portion of the stamper is insufficient and the shape cannot be completely transferred, the shape of the land portion of the duplicated substrate is disturbed, resulting in noise when a signal is reproduced.

In particular, since the substrate used for land and groove recording has a deeper groove than the conventional optical disk substrate, land noise is likely to increase due to poor transfer.

As described above, the noise level between the land and the groove may differ depending on the substrate manufacturing method. Even in such a case, by setting Δφ12 such that the signal amplitude of the higher noise level becomes larger, The signal quality of the grooves can be equal.

The noise between the land and the groove of the substrate was compared by setting the disk substrate before forming the thin film in a signal recording / reproducing apparatus, rotating at the same speed as that for reproducing the signal, and applying focus and tracking control. This can be performed by scanning the land or groove while guiding the reproduced signal at that time to a spectrum analyzer and measuring the noise level in the recording signal band.

In the recording signal band, the noise level of both the land and the groove changes to broad, so that the noise comparison between the land and the groove selects one frequency included in the recording signal band and compares the noise level at that frequency. This can be done simply. For example, the frequency in the case of a recording mark length of 1 μm (mark pitch 2 μm) is generally included in the recording signal band of the optical disk.
/ S), it is expressed in V / 2 (MHz). Therefore, it is possible to determine the noise level difference between the land and the groove by measuring the noise level at this frequency.

Next, a specific embodiment in which the groove depth of the substrate, the reflectance ratio between the unrecorded portion and the recorded portion, and the phase difference of the reflected light are limited to the above ranges will be described in detail.

(Embodiment 1) FIG.
Is the same as As the substrates, three types of injection substrates made of polycarbonate and having different groove depths were prepared. Groove depth 62nm, 71nm, 99nm
Which is the refractive index n = 1.5 of polycarbonate.
8. When the laser wavelength λ = 780 nm, λ /
(8n), λ / (7n), and λ / (5n).

The evaluation of the produced optical disk was performed by a recording / reproducing apparatus using a semiconductor laser having a wavelength of λ = 780 nm as a light source. Therefore, the following refractive index and the like are shown at λ = 780 nm unless otherwise specified. The groove width and the land width are equal, each being 0.8 μm.

As the dielectric layer material, a composite material obtained by adding 20 mol% of SiO ₂ to ZnS was used. Refractive index is 2.1
It is. As a recording material, a ternary system of GeSbTe was used. The complex refractive index is 4.41-i in the amorphous state.
1.34, and the crystalline state was 5.52-i4.00.
As the reflection layer, both Au and Al were used. As for the complex refractive index, Au is 0.18-i4.64 and Al is 2.18-
i 6.80.

The first dielectric layer, the recording layer, the second dielectric layer, and the reflective layer are formed on the three kinds of substrates by changing the thickness of the first dielectric layer, the recording layer, the second dielectric layer, and the reflection layer. Various optical disks having different reflectivity ratios with respect to (crystal) and a phase difference of reflected light were produced.

Table 1 shows the thin film configurations of the manufactured samples, the reflectance ratio R2 / R1 of the amorphous state and the crystalline state obtained by the matrix method for each thin film configuration, and the phase difference Δφ12 of the reflected light. Show. Note that the land-to-groove amplitude ratio and crosstalk are the absolute values of the reflectances R1 and R1.
The value is shown because it depends on the ratio R2 / R1 instead of 2.

Here, the phase difference Δφ12 indicates the phase difference of the reflected light from the crystalline state with reference to the phase of the reflected light from the amorphous state. The sign is positive when the phase of the reflected light from the crystal state is advanced, and negative when the phase is delayed. Since the phases are equivalent with a period of 2π, they are shown in the range from -π to + π.

Since the recording layer was in an amorphous state immediately after the film formation, the entire surface of the optical disk was crystallized by previously irradiating a laser beam and initialized.

[0065]

[Table 1]

Using a recording / reproducing apparatus having a wavelength of 780 nm and a numerical aperture (NA) of an objective lens of 0.55, the reproduction amplitude difference and crosstalk when recording on the land and the groove were measured.

The signal recording / reproducing evaluation was performed in the following procedure. The optical disk is set in the recording / reproducing apparatus, the spindle motor is rotated to set the linear velocity to 5 m / s, and the light beam from the semiconductor laser is irradiated to the recording thin film layer as a minute light spot by the optical system, and focus and tracking control is performed. First, the laser spot is tracked on the groove.

By driving the laser drive circuit at a single frequency of 3 MHz, the laser light is power-modulated between a peak power (recording power) and a bias power (erasing power), so that the laser light is modulated on two continuous grooves. Record the signal at Since the recording sensitivity differs depending on the thin film configuration, the peak power is set to a value at which the reproduction amplitude is saturated, and the bias power is set to a value at which the overwrite erasure rate is maximized for each optical disk.

Next, by inverting the tracking polarity,
The laser spot is tracked on the land between the two grooves on which the signals are recorded, and a 2.5 MHz signal is recorded. Then, the reproduction amplitude of the 2.5 MHz signal on the land and the 3 MHz crosstalk from the adjacent grooves are measured.

Subsequently, 3MH is placed on two continuous lands.
A single frequency of z is recorded, the tracking polarity is reversed again, and a laser spot is tracked on a groove between the two lands where the signal is recorded, and a 2.5 MHz signal is recorded. Then, the reproduction amplitude of the 2.5 MHz signal on the groove and the 3 MHz crosstalk from the adjacent grooves are measured.

As described above, the difference between the reproduction amplitude of the land and the groove and the amount of crosstalk are examined for all the thin film structures, and the reflectance ratio R2 / R1 and the phase difference Δφ12
2 to 4 show the relationship.

FIG. 2 shows that the groove depth of the substrate is 62 nm,
FIG. 3 shows the case of 71 nm, and FIG. 4 shows the case of 99 nm. Here, the reproduction amplitude difference ΔAmp (dB) is a value obtained by subtracting the groove amplitude from the land amplitude. Therefore, a positive sign indicates that the land amplitude is large, and a negative sign indicates that the groove amplitude is large. In addition, the crosstalk was different between the land and the groove due to the influence of the phase difference Δφ12 between the amorphous and the crystal, but the larger value (the worse value) is shown in FIGS. When Δφ12 was positive, the crosstalk in the groove was large, and when Δφ12 was negative, the crosstalk in the land was large.)

2 to 4, both ΔAmp and crosstalk depend on the reflectance ratio R2 / R1, the phase difference Δφ12, and the groove depth. Depending on the thin film configuration, land &
When considered as a recording medium for groove recording, it can be seen that crosstalk is too large or the amplitude difference ΔAmp is too large to be inappropriate. However, the groove depths of this embodiment are 62 nm, 71 nm, and 99 n.
m, Δφ1 if 0 ≦ R2 / R1 ≦ 0.2
2, the crosstalk is -20 dB or less,
And the magnitude of ΔAmp can be reduced to 3 dB or less,
It can be seen that the medium has good characteristics as a land and groove recording medium.

In particular, when R2 / R1 = 0, that is, when R2 = 0, the crosstalk is small, and the amplitude can be made equal between the land and the groove.

Further, a groove depth of 71 nm (λ / (7
n)) and 99 nm (λ / (5n)), the crosstalk is small, and if it is selected in the range of 0 ≦ R2 / R1 ≦ 0.2, even if the value of Δφ12 changes, it can be reduced to −25 dB or less. I understand.

Next, by controlling the value of Δφ12, ΔA
It was found that mp can be controlled, and by using this, it is possible to suppress the difference in signal quality between lands and grooves, which is a problem of land and groove recording, and the degradation of land signal quality due to cycles. Hereinafter, specific embodiments will be described.

(Embodiment 2) Two types of substrates A and B made of polycarbonate and having a groove depth of 65 nm were prepared. In the substrate A, the glass surface of the glass source plate corresponds to the groove surface and the photoresist surface corresponds to the land surface in the manufacturing process. Conversely, for the substrate B, the glass surface corresponds to the land surface and the photoresist surface corresponds to the land surface. This corresponds to the groove surface. The groove width and the land width are equally 0.8 μm, respectively.

The noise levels of the substrates A and B were measured. The substrate was set in the recording / reproducing apparatus used in the first embodiment, the relative speed between the reproducing laser spot and the substrate was rotated at 5 m / s, and the noise level at a frequency of 5/2 = 2.5 MHz was measured. As a result, the noise level of the land was higher by 1.5 dB on the substrate A, and the noise level of the groove was higher by 1.2 dB on the substrate B.

The thin films 17 and 12 of the first embodiment were formed on the substrates A and B, respectively, to produce four optical disks. As can be seen from Table 1 and FIGS. 2 to 4, the thin film configuration 17 has a positive Δφ12 and the reproduction amplitude is larger in the land than the groove, and the thin film configuration 12 has a negative Δφ12 and the reproduction amplitude is larger in the groove. Configuration.

Table 2 shows the evaluation results when a 2.5 MHz signal was recorded and reproduced on these optical disks. In the optical disk in which the thin film structure 17 is provided on the substrate A, the amplitude of the land is 2.1 dB larger than that of the groove to compensate for the high noise of the land.
NR was obtained. Similarly, in the optical disk in which the thin film structure 12 is provided on the substrate B, the amplitude of the groove is 1.9 d from the land.
B large, compensate for the high noise of the groove,
The same CNR is obtained for the land and the groove.

When the thin film structure 12 is provided on the substrate A, the noise level is high and the amplitude is small in the land, so the CNR of the land is small. Conversely, when the thin film structure 17 is provided on the substrate B, the groove is , The noise level of the groove is high and the amplitude is small.
Since the NR is small, the signal quality differs between the land and the groove, and as a result, the recording density and the like as a land and groove recording medium are limited by the poorer signal quality.

From the above, when the substrate noise is higher in the land than in the groove, 2mπ <Δφ12 <(1 + 2
m) (where m is an integer) (the value of (Table 1) corresponds to m = 0), and when the substrate noise is higher in the groove than in the land, (2m-1) π <Δφ12 <
By designing the thin film configuration so that 2mπ (the value in Table 1 corresponds to m = 0), the signal quality of the land and the groove can be made equal, and a medium suitable for land & groove recording can be provided. it can.

The substrates A and B are considered to be caused by the glass master at the time of manufacturing the substrate. However, land noise may increase due to poor transfer from the stamper at the time of injection. Also in this case, by designing the thin film configuration so that 2mπ <Δφ12 <(1 + 2m) π as in the present embodiment, the signal quality of land and groove can be made equal, and a medium suitable for land and groove recording can be obtained. It goes without saying that it can be provided.

[0084]

[Table 2]

The signal quality difference between the land and the groove also occurs due to the difference in the width between the land and the groove. This is because the width of the recording mark is prevented from further expanding in the horizontal direction due to the step between the land and the groove. As a result, the wider the track width, the wider the recording mark width and a large amplitude is obtained. Even when the land and the groove have different widths, the signal quality of the land and the groove can be made equal by controlling Δφ12 of the optical disc.
The embodiment will be described below.

(Embodiment 3) A substrate C made of polycarbonate and having a groove depth of 65 nm was prepared. Substrate C is
The land width and the groove width are changed depending on the zone. The zone 1 has a groove width of 0.6 μm, the land width is 1.0 μm, and the zone 2 has a groove width of 1.0 μm.
m, and the land width is 0.6 μm.

As in the case of the second embodiment, thin films having the thin film structures 17 and 12 of the first embodiment were formed on the substrate C, and two optical disks were manufactured. Table 3 shows the evaluation results when a 2.5 MHz signal was recorded and reproduced on these optical disks. In a region where the thin film structure 12 is provided in the zone 1 and in a region where the thin film structure 17 is provided in the zone 2, the amplitude of the land and the groove is almost equal, and the difference in signal quality due to the difference in the width between the land and the groove is reduced. It can be seen that the compensation is made by

From the above, when the groove width is wider than the land width, 2mπ <Δφ12 <(1 + 2m) π (where,
m is an integer) (the value of (Table 1) corresponds to m = 0), and when the land width is larger than the groove width, (2
m-1) By designing the thin film configuration so that π <Δφ12 <2mπ (where m is an integer) (the value of (Table 1) corresponds to m = 0), the amplitude of the land and the groove can be made equal. And a medium suitable for land and groove recording.

[0089]

[Table 3]

An optical disc is required to have a rewriting performance many times depending on its use. In land and groove recording on a phase-change optical disc, as described above, it has been found that a phenomenon in which the CNR is more greatly reduced in a land than in a groove with a cycle may appear.

In order to solve this problem, Δφ12
It was found that by controlling the signal quality, the signal quality of the land and the groove was made equal after many cycles, and as a result, the cycle life could be extended. The embodiment will be described below.

(Embodiment 4) A substrate made of polycarbonate and having a groove depth of 71 nm was prepared. The groove width and the land width are equal, each being 0.8 μm. In this substrate, the noise level of the land and the groove was almost the same. On this substrate, the thin film structure 17 of the first embodiment is provided.
And 23, two optical disks were produced.

As can be seen from Table 1 and FIGS. 2 to 4, the thin film configuration 17 has a positive Δφ12, the reproduction amplitude is larger in the land than in the groove, and the thin film configuration 23 is the Δφ12
Is slightly negative, and the reproduction amplitude is substantially equal between the groove and the land.

These optical disks were rotated at 5 m / s to alternately overwrite signals of 3 MHz and 1.25 MHz, and the CNR of a reproduced signal of 3 MHz was measured and plotted against the overwrite cycle. 5
(The upper part is a thin film configuration 23 and the lower part is a thin film configuration 17).

In the optical disk having the thin film configuration 23, the initial CN
R is equal to about 54 dB for both land and groove,
As the number of overwrites increases, the CNR of the land decreases, and falls below 50 dB in about 30,000 overwrites.
Here, for example, assuming that the number of cycles in which the CNR is less than 50 dB is the cycle life, in the optical disk having the thin film configuration 23, the cycle life as the land & groove recording medium is determined by the cycle performance of the land, and is about 30,000 times. Become.

However, in the optical disk having the thin film configuration 17, since the reproduction amplitude of the land was larger, the land had a CNR of about 55.5 dB and a groove of about 53 dB, and the CNR of the land was larger. When the overwriting is repeated, the CNR of the land decreases as in the case of the thin film configuration 23, and the CNR of the groove is reduced by about 300,000 times of overwriting.
, But both are above 50 dB at that time. That is, in the optical disk having the thin film configuration 17, the cycle life as a land and groove recording medium is 300,000 times or more.

As described above, the problem in land & groove recording that the signal quality may be greatly reduced with the cycle in the land than in the groove is 2mπ <Δ
φ12 <(1 + 2m) π (where m is an integer) ((Table 1)
(The value of m corresponds to m = 0) can be suppressed by designing the thin film configuration, and the cycle life of the land and groove recording medium can be extended.

Next, the groove depth of the substrate applicable to the land & groove recording medium of the present invention was examined in more detail. The embodiment will be described below.

(Embodiment 5) Two types of injection substrates made of polycarbonate and having a groove depth of 41 nm and 110 nm were prepared. This corresponds to λ / (12n) and λ / (4.5n) at a wavelength of 780 nm, respectively. The groove width and the land width are each 0.8 μm as in the first embodiment.

An optical disk was formed on these substrates by using the same thin film constitutions 1 to 33 as in the first embodiment, and the crosstalk was measured by the same method as in the first embodiment. As a result, an optical disk having a groove depth of 41 nm has a small effect of reducing crosstalk due to a small groove depth,
Crosstalk was greater than -20 dB for all thin film configurations.

In the case of a substrate having a groove depth of 110 nm, the crosstalk was small and good, but it was found that the noise level of the land was about 5 dB higher than that of the groove. This is probably because the groove was too deep and the resin flow during the injection was not sufficient, and the irregularities on the surface of the stamper were not completely transferred.

Judging from both the fifth embodiment and the first embodiment, the land & groove recording medium of the present invention has a groove depth D which can reduce crosstalk.
Is in the range of λ / (8n) <D <λ / (4n), where λ is the wavelength of the reproduction light and n is the refractive index of the substrate.
Further, considering the ease of substrate formation, λ / (8n) <D
≦ λ / (5n) is good. Further, in order to sufficiently reduce the crosstalk, the range of λ / (7n) ≦ D ≦ λ / (5n) is preferable.

[0103]

As described above in detail, according to the present invention, at least a first groove is formed on a substrate in which both a groove having irregularities on the surface and a land between adjacent grooves are used as signal recording tracks. An optical information recording medium provided with a recording layer, a second dielectric layer, and a reflective layer that reversibly change at least between a high reflectivity state and a low reflectivity state by irradiation with a dielectric layer, a laser beam, or the like. Assuming that the wavelength of the reproduction light is λ and the refractive index of the substrate is n, the depth D of the groove satisfies λ / (8n) <D <λ / (4n) and the higher of the recording layer. Is the reflectance of R1, the reflectance of the lower one is R2, the phase of the reflected light with respect to the incident light in the state where the reflectance of the recording layer is high is φ1, and the phase of the reflected light with respect to the incident light in the state where the reflectance is low is φ2. When the first dielectric layer, the By designing the thicknesses of the recording layer, the second dielectric layer, and the reflective layer, the reflectance ratio R2 / R1 and the phase difference φ1−φ2 of the reflected light are adjusted, and the signal reproduced from the groove is adjusted. The reflectance ratio R2 / R1 and the phase difference φ1−φ2 of the reflected light so that the difference between the amplitude and the amplitude of the signal reproduced from the land is within 3 dB.
The present invention provides an optical recording medium and a recording apparatus suitable for land and groove recording, which can suppress crosstalk from adjacent tracks even if signals are recorded on both lands and grooves. And high-density optical recording can be realized.

Further, by limiting the difference between the phase of the reflected light from the crystalline state and the phase of the reflected light from the amorphous state, the signal quality of the land and the groove due to the shape of the groove and the land and the noise level of the substrate is reduced. By compensating for the difference, the same and good reproduction signal quality can be obtained in the land and the groove.

In addition, by limiting the difference between the phase of the reflected light from the crystalline state and the phase of the reflected light from the amorphous state and raising the signal quality of the land in the initial state from the groove, overwriting can be performed many times. When they are overlapped, the problem that the signal quality deteriorates more in the land than in the groove can be suppressed, and as a result, the cycle life can be extended.

[Brief description of the drawings]

FIG. 1 is a sectional view for explaining an embodiment of a recording medium according to the present invention.

FIG. 2 shows a groove depth of λ / according to an embodiment of the present invention.
The figure which shows the relationship between a disc characteristic, a reflectance difference, and a phase difference in the case of (8n).

FIG. 3 shows a groove depth of λ / according to an embodiment of the present invention.
The figure which shows the relationship between a disc characteristic, a reflectance difference, and a phase difference in the case of (7n).

FIG. 4 shows a groove depth of λ / according to an embodiment of the present invention.
The figure which shows the relationship between a disc characteristic, a reflectance difference, and a phase difference in the case of (5n).

FIG. 5 is a diagram showing a state of change due to an overwrite cycle of the CNR according to the embodiment of the present invention.

FIG. 6 is a diagram showing a general manufacturing method of a stamper according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 1st dielectric layer 3 Recording layer 4 2nd dielectric layer 5 Reflection layer 6 Laser beam 7 Groove 8 Land 9 Protection cover

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) G11B 7/004 G11B 7/004 Z (72) Inventor Yoshitaka Sakagami 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Kazuhisa Ide 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Naoyasu Miyakawa 1006 Odaka Makoto Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Nobuo Akahira Inventor 1006 Kadoma, Kadoma, Osaka Prefecture F-term (reference) Matsushita Electric Industrial Co., Ltd. 5D029 JC02 WB17 WD16 5D090 AA01 CC14 FF15 FF45 GG07

Claims (6)

[Claims] An irradiation of at least a first dielectric layer, a laser beam, etc., on a substrate having both a groove-shaped groove formed by unevenness on the surface and a land between the groove and an adjacent groove as a signal recording track. An optical information recording medium provided with a recording layer, a second dielectric layer, and a reflective layer that reversibly change at least between a high reflectivity state and a low reflectivity state, wherein the wavelength of the reproduction light is λ, Assuming that the refractive index of the substrate is n, the depth D of the groove is λ / (8n) <D <λ
/ (4n), the higher reflectance of the recording layer is R1, the lower reflectance is R2, the phase of the reflected light with respect to the incident light in the state where the reflectance of the recording layer is high is φ1,
When the phase of the reflected light with respect to the incident light in the state where the reflectance is low is φ2, the first dielectric layer, the recording layer,
By designing the thicknesses of the second dielectric layer and the reflective layer, the reflectance ratio R2 / R1 and the phase difference φ1−φ2 of the reflected light can be obtained.
Is adjusted so that the difference between the amplitude of the signal reproduced from the groove and the amplitude of the signal reproduced from the land is 3 dB.
An optical information recording medium characterized by being designed to be within. 2. The reflectance ratio R2 / R1 is 0 ≦ R2 / R1.
2. The optical information recording medium according to claim 1, wherein satisfies .ltoreq.0.2. 3. An optical information recording medium according to claim 2, wherein said lower reflectivity R2 satisfies R2 = 0. 4. The groove depth D is λ / (8n) <D ≦
2. The optical information recording medium according to claim 1, wherein λ / (5n) is satisfied. 5. The depth D of the groove is λ / (7n) ≦ D ≦
The optical information recording medium according to claim 4, wherein λ / (5n) is satisfied. 6. The optical information recording medium according to claim 1, wherein the recording layer is made of a phase change recording material that reversibly changes between an amorphous state and a crystalline state.