JP2002056576A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain good recording characteristics which hardly cause cross erasion in an optical recording medium in which recording is carried out both in land tracks and groove tracks and the average distance between the centers of adjacent tracks (track pitch) is <=0.7×d (d is the laser beam diameter on the recording surface). SOLUTION: The medium is a phase change type optical recording medium in which recording is performed both in land tracks and groove tracks formed in the substrate and the average distance between centers of adjacent tracks (track pitch) is <=0.7×d. The medium has at least a first dielectric layer, recording layer, second dielectric layer and reflection layer in this order on the substrate, and the value of Wl/Wg (Wl and Wg are the average land width and average groove width in the position at the half depth of the groove depth, respectively) is <=0.95.

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 capable of recording, erasing and reproducing information by irradiating a laser beam. In particular, the present invention relates to a rewritable phase-change optical recording medium such as an optical disk having an erasing and rewriting function of recorded information and capable of recording an information signal at high speed and high density.

[0002]

2. Description of the Related Art A rewritable phase-change optical recording medium has a recording layer containing tellurium or the like as a main component. At the time of recording, a laser beam pulse focused on the crystalline recording layer is irradiated for a short time.
The recording layer is partially melted. The melted portion is quenched by thermal diffusion and solidified to form an amorphous recording mark. The light reflectance of this recording mark is lower than that of the crystalline state and can be reproduced optically as a recording signal. At the time of erasing, the recording mark is irradiated with a laser beam and heated to a temperature below the melting point of the recording layer and above the crystallization temperature to crystallize the amorphous recording mark and return to the original unrecorded state. . Ge ₂ Sb ₂ is used as a material for the recording layer of these rewritable phase-change optical recording media.
Alloy, such as Te ₅ (N.Yamada et al.Proc.Int.Symp.on O
ptical Memory 1987 p61-66) is known.

[0003] These optical recording media using a Te alloy as a recording layer have a high crystallization speed, and high-speed overwriting with a single circular beam is possible only by modulating the irradiation power. In an optical recording medium using these recording layers, usually, a heat-resistant and light-transmitting dielectric layer is provided on each side of the recording layer to prevent deformation and opening of the recording layer during recording. I'm preventing. Further, a technique is known in which a metal reflective layer such as light reflective Al is laminated on the dielectric layer on the opposite side to the light beam incident direction to improve the signal contrast during reproduction by an optical interference effect. I have.

In such an optical recording medium, it is desired that more information can be recorded. As a rewritable large-capacity optical recording medium, there is a DVD-RAM having a user capacity of 2.6 GB per side. In a land / groove structure using both lands and grooves as recording tracks, the land width and the groove width are almost equal, and the track pitch is 0.74 μm. In recent years, the need for recording moving image data for a long time has led to a demand for a further increase in capacity, and the recording density has been increased to the limit. However, when the track width is narrowed to increase the recording density, the signal recorded on the adjacent track affects the reproduced signal (crosstalk), or the quality of the signal recorded on the adjacent track during recording is reduced. (Cross erasure) is a major problem. In particular, the track width is 0.7 with respect to the laser beam diameter d on the recording surface.
This problem becomes more serious when the value is xd or less.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to focus on the problems of the prior art described above, perform recording on both land tracks and groove tracks, and calculate the average value of the distance between the centers of adjacent tracks (track The pitch is 0.7 × d (d
(Refers to a laser beam diameter on a recording surface) or less.

[0006]

That is, according to the present invention, information can be recorded, erased, and reproduced by irradiating a laser beam, and information recording and erasing can be performed between an amorphous phase and a crystalline phase. Recording is performed on both land tracks and groove tracks formed on the substrate by a reversible phase change, and the average value (track pitch) between the centers of adjacent tracks is 0.7 × d or less. An optical recording medium, comprising at least a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer on a substrate in this order, and Wl / Wg (Wl, Wl
g is 0.95 for the average value of the land width and the average value of the groove width at half the groove depth.
An optical recording medium characterized by the following. In addition,
d is the laser beam diameter on the recording surface, where λ is the wavelength of the laser beam and NA is the numerical aperture of the lens,
d = 0.82 × λ / NA, where λ is 380-820
nm and the numerical aperture NA of the lens are in the range of 0.4 to 1.2.

The deterioration of signal quality due to cross erasure, which is a problem to be solved by the present invention, is caused by the fact that a beam protruding from a track is irradiated on a recording mark of an adjacent track,
It is considered that heat generated at the time of recording is diffused to an adjacent track, thereby lowering the recording signal amplitude of the adjacent track. The deterioration of the groove signal when recorded on the adjacent land track after recording on the groove track was compared with the deterioration of the land signal when recorded on the adjacent groove track after recording on the land track. In such cases, the former is often more markedly degraded. That is, cross erasure is more likely to occur in the groove. It is considered that this is partly because the manner of heat diffusion differs between the land and the groove, and heat is more easily diffused to adjacent tracks when recorded on the land.

The present inventors have conducted intensive research,
To find that wider track width leads to a reduction in cross erasure, and to design the groove shape of the substrate so that groove tracks where cross erasure is likely to occur are wider and land tracks where cross erasure is less likely to occur are narrower. As a result, it has been found that an optical recording medium with less cross erasure can be obtained without reducing the recording density, and the above problem has been solved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The optical recording medium of the present invention is capable of recording, erasing, and reproducing information by irradiating a laser beam. The recording is performed on both the land track and the groove track formed on the substrate, and the average value (track pitch) between the centers of adjacent tracks is 0.7 × d ( d is the laser beam diameter on the recording surface, d = 0.82 × λ / NA, the wavelength λ of the laser light is 380-820 nm, and the numerical aperture NA of the lens is 0.4-1.2. There is).

Here, a substrate used for an optical recording medium for performing land-groove recording is usually formed so that the land width and the groove width are substantially equal. This is to make the optical characteristics of the land and the groove equivalent. However, when the track pitch is reduced for higher density, cross erasure in the groove is remarkable as described above, causing an increase in the error rate. The substrate used for the optical recording medium of the present invention is formed such that the ratio of the land width to the groove width is changed so that the groove width where cross erasure easily occurs is wide and the land width where cross erasure hardly occurs is narrow. It has special features. This makes it possible to suppress an increase in cross erasure even when the track pitch is reduced. That is, Wl / Wg (Wl,
Wg is 0.9 (the average value of the land width and the average value of the groove width) at the position of one half of the groove depth.
It is necessary to be 5 or less. In order to sufficiently obtain the effect of reducing the cross erasure without significantly changing the optical characteristics of the land and the groove, the value of Wl / Wg must be 0.7.
0 to 0.85.

As a material of the substrate, a resin such as polycarbonate, PMMA, acrylic, polyolefin, epoxy or the like or glass is used.

A preferred material for the first dielectric layer of the present invention is a film made of a mixture of ZnS and SiO ₂ .
Since this material has a small residual stress, burst deterioration due to repeated overwriting is unlikely to occur. Also, Z
The mixture of nS, SiO _2, and carbon has a smaller residual stress in the film, and is less likely to deteriorate in recording sensitivity, carrier-to-noise ratio (C / N), erasure rate, etc. even when recording and erasing are repeated. Is also particularly preferred. The thickness of the film is determined by optical conditions, but is preferably from 5 to 500 nm. If the thickness is larger than this, cracks and the like may occur. If the thickness is smaller than this, the substrate is easily damaged by heat due to repetition of overwriting, and the repetition characteristics are likely to deteriorate. A particularly preferred range of the film thickness is 50 to 200 nm.
It is.

Although the recording layer of the present invention is not particularly limited, a Ge—Sb—Te alloy is short in erasing time and capable of repeating recording and erasing many times.
It is preferable because it has excellent recording characteristics such as a carrier-to-noise ratio (C / N) and an erasing ratio. In particular, the linear velocity at which laser light for recording, erasing, or reproducing is irradiated is 7.5 × 1 per second.
0 ⁶ × not less than d, performs fast as the length in the laser moving direction of the shortest mark among the record marks recorded by the mark edge method by the laser beam is not more than 0.55 × d, the high-density recording in the case of the optical recording medium is represented by the following formula composition of the recording layer in the _{{(Ge 0.5 Te 0.5) x} (Sb 0.4 Te 0.6) 1-x} 1-y Sb y, 0.5 ≦ x ≦ 0.95, It is preferable that the composition range is 0 ≦ y ≦ 0.08. If x <0.5, the change in reflectivity due to the phase change of the recording layer is small, so that a sufficient signal intensity may not be obtained. The characteristics may be deteriorated, and the overwrite characteristics may be deteriorated. If y> 0.08, the initial erasure characteristics may be poor, or the overwrite characteristics after long-term storage may be poor. Further, in order to improve long-term storage stability, elements belonging to Groups 3A to 6B in the second to sixth periods in the periodic table of elements except for Ge, Sb, and Te, namely, Al, Si, Sc, Ti, and V ,
Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga,
Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, C
d, In, Sn, La, Hf, Ta, W, Re, Ir,
At least one element selected from Pt, Au, Tl, and Pb may be added.

The recording layer of the present invention has a thickness of 5 to 40.
It is preferably within the range of nm. In particular, in the optical recording medium for performing the above-described high-speed and high-density recording, it is preferable that the thickness be in the range of 7 to 15 nm from the viewpoint of optical design.

The material of the second dielectric layer of the present invention may be the same as the material given for the first dielectric layer,
Different materials may be used. The thickness of the second dielectric layer has a great influence on the cooling of the recording layer, and in order to obtain better recording, erasing characteristics and repetition durability, it is necessary to adjust the thickness to an optimum thickness in the range of 2 to 50 nm. preferable.

Examples of the material of the reflection layer of the present invention include light-reflective metals, alloys, and mixtures of metals and metal compounds. Specifically, Al, Au, Ag, C
high-reflectivity metals such as u, alloys containing it as a main component,
Metal compounds such as nitrides, oxides, and chalcogenides such as Al and Si are preferable. Metals such as Al, Au, and Ag, and alloys containing these as main components are particularly preferable because of their high light reflectivity and high thermal conductivity.
In particular, since the price of the material can be reduced, Al or A
An alloy containing g as a main component is preferable. The thickness of the reflective layer is usually about 30 to 300 nm.

In the present invention, it is preferable that the boundary layer is provided above and / or below the recording layer and in contact with the recording layer. By providing the boundary layer, deterioration of characteristics due to repeated overwriting can be prevented. It is considered that this is because these layers play a role of a barrier layer for preventing diffusion of atoms from the dielectric layer to the recording layer. In addition, the provision of the boundary layer improves overwrite characteristics. This is considered to be because the crystallization speed is increased by the boundary layer, and the erasing characteristics are improved. For this reason, the linear velocity at which the laser beam for recording, erasing, or reproducing is irradiated is 7.5 × 10 ⁶ × d or more per second, and the shortest mark among the recording marks recorded by the laser beam in the mark edge method is used. When performing high-speed, high-density recording such that the length in the laser traveling direction is 0.55 × d or less, it is particularly preferable to provide a boundary layer. Furthermore, by providing the boundary layer, storage durability, that is, reproduction characteristics and overwrite characteristics after long-term storage can be improved. This is presumed to be due to a change in the state of the recording layer such as an atomic arrangement and a reaction between the dielectric layer and the recording layer can be prevented even after being left for a long time.

The boundary layer is preferably composed of a layer mainly composed of carbon or a layer mainly composed of at least one selected from carbides, oxides and nitrides. Here, the main component means that 50 wt% or more is contained in the formed boundary layer. As the carbides, oxides and nitrides, carbides, oxides and nitrides with elements belonging to groups 3A to 6B in the sixth period of the periodic table can be used.
1, Si, Sc, Ti, V, Cr, Mn, Fe, Co,
Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, M
o, Ru, Rh, Pd, Ag, Cd, In, Sn, L
a, Hf, Ta, W, Re, Ir, Pt, Au, Tl,
Carbides, oxides, and nitrides of metals selected from Pb are preferably used, and more preferably, Si, Ge, Ti,
Zr, Ta, Nb, Hf, Al, Y, Cr, W, Zn,
A carbide, oxide, or nitride of a metal selected from In and Sn is used. From the viewpoint of storage stability, it is particularly preferable to use a material containing carbon as a main component. When the boundary layers are provided on both sides of the recording layer, they may be the same material or different materials.

The thickness of the boundary layer is preferably in the range of 0.5 to 10 nm from the viewpoint of difficulty in peeling and optical conditions. If the thickness exceeds 10 nm, there is a tendency that it is easy to peel off from the first dielectric layer and the recording layer. Also, 0.5 nm
If the thickness is less than the above range, it is difficult to deposit the film to a uniform thickness, and the effect of providing the boundary layer may not be obtained.

In the present invention, the absorption correction layer may be provided between the second dielectric layer and the reflection layer. By providing the absorption correction layer, the light absorption of the recording layer in the amorphous state is reduced,
This is because the difference in the amount of light absorption from the crystalline state can be reduced, and further, can be made smaller than the crystalline state. Due to the effect of the absorption correction, the difference between the temperature rising states during recording of the crystalline portion and the amorphous portion is reduced, and the shape of the recording mark is disturbed.
Since the displacement of the formation position can be reduced, the overwrite erasing characteristics are improved, and the jitter characteristics at the time of overwriting can be improved. Further, it is effective in reducing cross erasing and improving durability against repeated irradiation of the reproduction light. The absorption correction effect is determined by the thickness and the optical constants (refractive index and extinction coefficient) of each constituent layer, but greatly depends on the optical constant of the absorption correction layer. It is necessary that the refractive index and the extinction coefficient of the absorption amount correction layer are appropriately large, and the refractive index at the wavelength of the laser beam for performing recording and reproduction is 1.0 to 4.0.
And the extinction coefficient is preferably in the range of 0.5 to 3.0.

Preferred materials for the absorption correction layer include solid solution alloys, intermetallic compounds, oxides, carbides, and nitrides containing at least one of silicon, germanium, titanium, zirconium, tungsten, chromium, molybdenum, and aluminum. For example, a material mainly containing at least one selected from materials such as In particular, those obtained by combining aluminum or chromium with oxygen or nitrogen are preferable because the optical constant can be easily controlled.

The optimum thickness of the absorption correction layer varies depending on the optical constant of the absorption correction layer, but is preferably in the range of about 10 to 100 nm.

The optical recording medium of the present invention has a very high density because the track pitch is 0.7 × d or less. However, in order to further increase the density and speed, the recording mark recorded by the mark edge method is used. The recording frequency is set to a high recording frequency such that the length of the shortest mark in the laser traveling direction is 0.55 × d or less, and the linear velocity at which the laser beam is irradiated is 7.
It is particularly preferred to be 5 × 10 ⁶ × d or more. By providing the above-described boundary layer, good recording characteristics can be obtained even when performing such high-speed, high-density recording. Further, if the above-mentioned absorption correction layer is also provided, it is possible to obtain better recording characteristics.

Next, a method for manufacturing the optical recording medium of the present invention will be described. As a method for forming the first dielectric layer, the recording layer, the second dielectric layer, the reflective layer, and the like on the substrate, a thin film forming method in a vacuum, for example, a vacuum deposition method, an ion plating method, a sputtering method, and the like are used. can give. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled. Control of the thickness of the recording layer to be formed
It can be easily performed by monitoring the deposition state with a quartz crystal film thickness meter or the like.

Further, after forming the reflective layer, a dielectric layer of ZnS, SiO ₂ , ZnS—SiO ₂ , or the like, or ultraviolet curing may be used after the formation of the reflective layer within a range that does not significantly impair the effects of the present invention. A protective layer such as a resin may be provided as necessary.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. (Analysis and measurement method) The composition of the reflective layer and the recording layer is determined by dissolving the sample thin film with an acid, using an ICP emission spectrometer (manufactured by Seiko Instruments) to determine the adhesion amount of each element, and converting it to the atomic ratio. did. The composition of the absorption correction layer was confirmed by Rutherford backscattering analysis using a backscattering measuring device (manufactured by Nisshin High Voltage Co., Ltd.). Recording layer, dielectric layer,
The film thickness during the formation of the reflective layer was monitored with a quartz crystal film thickness meter. The thickness of each layer was measured by observing the cross section with a scanning or transmission electron microscope. For the land width, groove width and groove depth of the substrate, refer to AF
M.

In the optical recording medium formed by sputtering, the recording layer on the entire surface of the disk was crystallized and initialized with a beam of a semiconductor laser having a wavelength of 830 nm before recording. The recording characteristic evaluation apparatus uses a numerical aperture of the objective lens of 0.1.
6. Equipped with an optical head having a semiconductor laser wavelength of 660 nm (laser beam diameter 0.9 μm) and a linear velocity of 8.2.
Mark edge recording was performed by the 8-16 modulation method at a recording frequency of m / sec and the shortest mark length, that is, the length of the 3T mark was 0.42 μm. The recording laser waveform at that time was a general multi-pulse, and a pattern adaptive recording compensation method in which the edge position of the recording pulse was changed according to the length of the recording mark and the length of the space before and after the recording mark was used. The recording power and the erasing power were optimized for each land and groove of each disk.

The cross erasure was evaluated as follows. First, record a random pattern 100 times on the measurement track,
Jitter was measured by a time interval analyzer. Subsequently, a random pattern is recorded 10 or 1000 times on tracks on both sides adjacent to the measurement track,
In this state, the jitter of the measurement track was measured again. At this time, the durability of cross erasure was evaluated based on the degree of increase in jitter.

(Example 1) thickness 0.6 mm, diameter 12c
m, a track pitch of 0.615 μm, a land width Wl of 0.55 μm, a groove width Wg of 0.68 μm, that is, a groove-shaped polycarbonate substrate having a groove depth of 68 nm with Wl / Wg = 0.81 per minute. Sputtering was performed while rotating at 40 rotations. First, the inside of the vacuum vessel was evacuated to 1 × 10 ⁻⁴ Pa, and then a ZnS target to which 20 mol% of SiO ₂ was added was sputtered in an atmosphere of 0.2 Pa of argon gas to form a film having a thickness of 1 nm on the substrate.
A 60 nm first dielectric layer was formed. Next, a carbon target is sputtered, and a carbon layer is formed as a first boundary layer by 2n.
m was formed. Subsequently, an alloy target made of Ge, Sb, and Te is sputtered to a thickness of 12 nm and a composition of G
e _28.6 Sb _17.8 Te _{53 .6} [i.e. {(Ge _0.5 T
e _0.5 ) _0.579 (Sb _0.4 Te _0.6 ) _0.421 ｝ _0.989 Sb _0
.011 ] was obtained. Further, as a second boundary layer, a germanium nitride layer formed by sputtering a germanium target with a mixed gas of argon and nitrogen was formed to a thickness of 2 nm. Subsequently, the same Z as the first dielectric layer is used as the second dielectric layer.
by sputtering nS-SiO ₂ target to form a second dielectric layer having a thickness of 17 nm. Then Al _97.5 C
by sputtering a r _2.5 alloy, to form a reflective layer having a thickness of 200 nm. After taking out the disk from the vacuum container, an acrylic ultraviolet curable resin (SD-101 manufactured by Dainippon Ink and Chemicals, Inc.) is spin-coated on the reflective layer, and cured by ultraviolet irradiation to form a resin layer having a thickness of 3 μm. Then, a slow-acting ultraviolet curable resin was applied using a screen printing machine, and after irradiating with ultraviolet rays, two disks produced in the same manner were adhered to obtain an optical recording medium of the present invention.

The jitter when recording 100 times on only one track was 8.4% for the land and 7.6% for the groove. The jitter when recording 10 times on adjacent tracks on both sides is 8.9% for lands and 8.6% for grooves.
Met. The jitter was 9.3% for the land and 9.2% for the groove when recorded on adjacent tracks on both sides 1000 times. As described above, the rise of the jitter due to the cross erasure was suppressed to be low in both the land and groove tracks.

(Embodiment 2) Land width Wl is 0.59 μm
m, the groove width Wg is 0.64 μm, that is, Wl / W
Using the same substrate as in Example 1 except that g = 0.92,
An optical recording medium having the same film configuration as in Example 1 was manufactured.

The jitter when recording 100 times on only one track was 8.2% for the land and 7.8% for the groove. The jitter when recording 10 times on adjacent tracks on both sides is 8.8% for the land and 8.9% for the groove.
Met. The jitter was 8.8% for the land and 9.8% for the groove when recorded on adjacent tracks on both sides 1000 times. As described above, in the groove, although the rise of the jitter due to the cross erasure is slightly large, the influence of the cross erasure is suppressed to such an extent that there is no practical problem.

Example 3 The same groove-shaped substrate as in Example 2 was used, and an absorption correction layer made of aluminum oxide (AlOx x = 0.4) was provided between the second dielectric layer and the reflective layer. Otherwise, an optical recording medium was manufactured by forming a film on a substrate in the same film configuration as in Example 1. However, the thicknesses of the first dielectric layer, the first boundary layer, the recording layer, the second boundary layer, the second dielectric layer, the absorption correction layer, and the reflection layer are set to be optically optimal. 120nm, 2nm, 9nm, 2nm, 30n
m, 70 nm, and 90 nm.

The jitter when recording 100 times on only one track was 8.5% for the land and 7.8% for the groove. The jitter when recording 10 times on adjacent tracks on both sides is 8.8% for lands and 8.8% for grooves.
Met. The jitter was 8.8% for the land and 9.1% for the groove when recorded on adjacent tracks on both sides 1000 times. As described above, the rise of the jitter due to the cross erasure was suppressed to be low in both the land and groove tracks.

(Comparative Example 1) Land width Wl is 0.61 μm
m, the groove width Wg is 0.62 μm, ie, Wl / W
Using the same substrate as in Example 1 except that g = 0.98,
An optical recording medium having the same film configuration as in Example 1 was manufactured.

The jitter when recording 100 times only on one track was 7.7% for the land and 7.8% for the groove. The jitter when recording 10 times on adjacent tracks on both sides is 8.0% for lands and 9.5% for grooves.
Met. The jitter when recording 1000 times on adjacent tracks on both sides was 8.0% for the land and 10.5% for the groove. As described above, in the groove, the rise in jitter due to cross erasure was remarkable.

(Comparative Example 2) Land width Wl is 0.50 μm
m, the groove width Wg is 0.73 μm, ie, Wl / W
Using the same substrate as in Example 1 except that g = 0.68,
An optical recording medium having the same film configuration as in Example 1 was manufactured.

Since the land width is small, the amplitude of the signal recorded on the land is smaller than that of the groove, making it difficult to perform good land-groove recording.

[0039]

According to the optical recording medium of the present invention, when the track pitch is 0.7 × d or less, (land width / groove width)
Is 0.95 or less, it is possible to obtain good recording characteristics in which cross erasure hardly occurs.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D029 MA03 NA23 WB11 WB14 WC05 WC06 WD10 WD30 5D090 AA01 BB05 CC14 FF15 GG07

Claims (4)

[Claims] 1. Irradiation with a laser beam enables recording, erasing, and reproducing of information, and recording and erasing of information are performed by a reversible phase change between an amorphous phase and a crystalline phase. Recording is performed on both land tracks and groove tracks formed on the substrate, and the average distance (track pitch) between the centers of adjacent tracks is 0.7 × d (d is the laser beam diameter on the recording surface. When the wavelength of the laser beam is λ and the numerical aperture of the lens is NA, d = 0.
82 × λ / NA, where λ is 380 to 820 nm, and the numerical aperture NA of the lens is 0.4 to 1.2) or less. A body layer, a recording layer, a second dielectric layer, and a reflection layer are provided in this order, and Wl / Wg (Wl and Wg are the average value of the land width and the average value of the groove width at a position one half of the groove depth, respectively) ) Is 0.95 or less. 2. A recording medium according to claim 1, wherein a boundary layer mainly composed of at least one selected from carbon, carbide, oxide and nitride is provided at an upper portion and / or a lower portion of the recording layer in contact with the recording layer. Item 2. The optical recording medium according to Item 1. 3. The optical recording medium according to claim 1, wherein an absorption correction layer is provided between the second dielectric layer and the reflection layer. 4. The laser beam irradiation linear velocity is 7.5 per second.
× 10 ⁶ × not less than d, claim 1, wherein the length in the laser moving direction of the shortest mark among the record marks recorded by the mark edge method by the laser beam is not more than 0.55 × d The optical recording medium according to the above.