JP2003115129A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high speed recording without impairing recording sensitivity. SOLUTION: In the optical recording medium wherein a reflective heat dissipation on layer 2, a first protective layer 3, a recording layer 4 and a second protective layer 5 are layered in this order on a substrate 1 having grooves formed thereon, the second protective layer 5 consists of a mixture of ZnS and SiO2 , the recording layer 4 has Ge, Sb and Te as main constituent elements, the reflective heat dissipation layer 2 consists of Ag alloy and the first protective layer 3 consists of two layers of a mixture layer of ZnS and SiO2 and an Al2 O3 layer and the Al2 O3 layer having higher heat conductivity is positioned on the side of the reflective heat dissipation layer 2.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rewritable DV.
The present invention relates to an optical recording medium for high density recording having a phase change recording layer such as R.

[0002]

2. Description of the Related Art Generally, compact discs (CDs) and DVDs perform binary signal recording and tracking signal detection by utilizing the reflectance change caused by the interference of the reflected light from the bottom and the mirror surface of the concave pit. It is being appreciated. CD in recent years
As a medium compatible with, a phase change type rewritable compact disc (CD-RW, CD-Rewrita)
ble) is being widely used. As for the DVD, various phase change type rewritable DVDs have been proposed. In addition, the recording / reproducing wavelength is shortened to 390 nm to 420 nm for the DVD capacity of 4.7 GB, and the numerical aperture and NA are set.
(Numerical Aperture) has been raised to propose a system DVR with a capacity of 20 GB or more (: ISOM Technical Di
gest'00 (2000), 210).

These phase change type rewritable CDs and DVs
The D and DVR detect the recorded information signal by utilizing the reflectance difference and the phase difference change caused by the refractive index difference between the amorphous state and the crystalline state. An ordinary phase-change medium has a structure in which a lower protective layer, a phase-change recording layer, an upper protective layer, and a reflective layer are provided on a substrate. Can be controlled to be compatible with CD and DVD. In CD-RW, the reflectance is 15
The compatibility between the CD and the recording signal and the groove signal can be ensured within the range reduced to -25%, and the CD drive equipped with an amplification system that covers the low reflectance can be reproduced.
Since the phase-change recording medium can perform erasing and re-recording processes only by intensity modulation of one focused light beam, recording in a phase-change recording medium such as a CD-RW or a rewritable DVD is Includes overwrite recording that records and erases simultaneously. For recording information using phase change, crystalline, amorphous, or a mixed state thereof can be used, and a plurality of crystalline phases can be used, but the rewritable phase change currently in practical use. It is general that a non-recorded / erased state of a mold recording medium is a crystalline state, and an amorphous mark is formed for recording. A chalcogen element, that is, a chalcogenide alloy containing S, Se, and Te is often used as the material of the recording layer.

For example, GeTe-Sb2 Te3, a GeSbTe system containing a pseudo binary alloy as a main component, InTe-Sb2.
In3SbTe based on Te3 pseudo binary alloy, S
AgInSbT mainly composed of eutectic system of b0.7 Te0.3
Examples include e-based alloys and GeSnTe-based alloys. Of these, Ge
Te-Sb2 Te3 pseudo-binary alloy with excess Sb added, especially Ge1 Sb2 Te4 or Ge2 Sb
Compositions in the vicinity of intermetallic compounds such as 2Te5 have been mainly put to practical use. These compositions are characterized by crystallization without phase separation, which is peculiar to intermetallic compounds, and have a high crystal growth rate. Therefore, initialization is easy and recrystallization rate during erasing is fast. Therefore, a pseudo binary alloy system or a composition in the vicinity of an intermetallic compound has been attracting attention as a recording layer exhibiting practical overwrite characteristics (Reference Jpn.J.Appl.Phys., Vol.69 (1991). ) ， P2
849, or SPIE, Vol.2514 (1995), pp294-301
etc). Further, there have been reports on the ternary composition of GeSbTe, or the composition of the recording layer containing the additive element with the ternary composition as a matrix (JP-A-61-2587).
No. 87, No. 62-53886, No. 62-15.
2786, JP-A-1-63195, JP-A 1-211249, JP-A 1-277338). However, application of the material having such a composition to an optical recording medium for high-density recording such as a rewritable DVR has just begun development, and there are many problems to be solved.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and the first object thereof is to provide a high density recording medium having a phase change recording layer such as a rewritable DVR. An optical recording medium for recording has a high recording sensitivity (role of ZnS and SiO ₂ ) corresponding to high-speed recording and has a rapid cooling structure (role of Al ₂ O ₃ layer and heat dissipation layer). Secondly, in such an optical recording medium, the film thickness of the Al ₂ O ₃ layer having a quenching structure and ZnS-Si
By limiting the film thickness ratio of O2, it is possible to realize a high-speed recording with a rapid cooling structure without deteriorating the recording sensitivity. Thirdly, in such an optical recording medium, by limiting the film thickness of the Al ₂ O ₃ layer having a rapid cooling structure, a rapid cooling structure can be formed without deteriorating the recording sensitivity so that high-speed recording can be performed at high density. Especially. Fourthly, in such an optical recording medium, not only is the warp of the substrate corrected, but also dust and the like can be wiped off and scratched less easily. Sixth, by optimizing the groove width of the substrate, Ge, Sb, Te
In order to obtain a high density and high amplitude (high modulation) in the phase change recording layer containing as a main constituent element.

[0006]

In order to achieve the above-mentioned object, the invention according to claim 1 provides an optical recording medium utilizing a phase transition phenomenon of crystal and amorphous by light irradiation,
A reflective heat dissipation layer, a first protective layer, a recording layer, and a second protective layer are laminated in this order on a grooved substrate, and the second protective layer is made of a mixture of ZnS and SiO ₂ . The recording layer has Ge, Sb, and Te as main constituent elements, and the reflective heat dissipation layer is a recording medium made of an Ag alloy, and an adhesive layer and a cover layer are formed on the second protective layer, The protective layer is composed of two layers of a mixture layer of ZnS and SiO ₂ and an Al ₂ O ₃ layer, and the Al ₂ O ₃ layer is located on the reflection and heat dissipation layer side.

According to a second aspect of the invention, in the optical recording medium according to the first aspect, the thickness of the Al ₂ O ₃ layer of the first protective layer is a mixture layer of ZnS and SiO ₂ of the first protective layer. The film thickness is 1/5 or more and 1/2 or less of the film thickness.

According to the invention of claim 3, claim 1 or 2
The optical recording medium as described above, wherein the first protective layer comprises Al ₂ O ₃
The thickness of the layer is 0.20 or more of the thickness of the reflection / heat dissipation layer,
The configuration is such that it is 0.80 or less.

According to a fourth aspect of the present invention, the first to third aspects are provided.
In the optical recording medium according to any one of 1 to 3, a hard coat is formed on the cover layer.

According to a fifth aspect of the invention, in the optical recording medium according to the fourth aspect, the hard coat has a film thickness of 1 μm.
As described above, the thickness is less than 5 μm.

According to a sixth aspect of the present invention, the first to fifth aspects are provided.
In the optical recording medium according to any one of items 1 to 5, the average groove width in the groove shape of the substrate is 0.
The structure is 3 or more and 0.5 or less.

[0012]

DETAILED DESCRIPTION OF THE INVENTION A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a recording portion of an optical recording medium according to the present embodiment. The optical recording medium includes a substrate 1, a reflection / heat dissipation layer 2, a first protective layer 3, and a recording layer. It has a layer 4 and a second protective layer 5. Further, an adhesive layer (protective layer) 6 made of an ultraviolet ray or thermosetting resin is formed on the second protective layer 5, and the cover layer 7
Are glued together. The hard coat is coated on the cover layer 7 with an ultraviolet ray or thermosetting resin (this will be described later). The order of the layers as shown in FIG. 1 is suitable when a focused light beam for recording and reproduction, for example, a laser beam is applied to the recording layer through the transparent substrate.

First, the substrate 1 will be described. For the substrate 1, a transparent resin such as polycarbonate, acrylic, or polyolefin, or transparent glass can be used. Among them, the polycarbonate resin is the most preferable because it has a track record of being most widely used in CD and is inexpensive. The substrate 1 is provided with a groove having a pitch of 0.8 μm or less for guiding the recording / reproducing light, but the groove does not necessarily have to be a geometrically rectangular or trapezoidal groove. The grooves may be optically formed by forming a waveguide having a different index. Next, the recording layer 4 will be described. The recording layer 4 is a phase-change recording layer, and its thickness is generally preferably in the range of 5 nm to 100 nm. The thickness of the recording layer 4 is 5 nm
If it is thinner, it is difficult to obtain a sufficient contrast, and the crystallization speed tends to be slow, which makes it difficult to erase in a short time. On the other hand, if it exceeds 100 nm, it becomes difficult to obtain optical contrast, and cracks are likely to occur.

Further, it is necessary to obtain a contrast enough to be compatible with a read-only disc such as a DVD, and for high density recording such that the shortest mark length is 0.5 μm or less, 5 nm or more and 25 nm or less is preferable. 5 nm
If it is less than the above range, the reflectance becomes too low, and a nonuniform composition in the initial stage of film growth and the influence of a sparse film are likely to appear, which is not preferable. On the other hand, if it is thicker than 25 nm, the heat capacity becomes large, the recording sensitivity becomes poor, and the crystal growth becomes three-dimensional, so that the edges of the amorphous marks are disturbed and the jitter tends to increase. Furthermore, the volume change due to the phase change of the recording layer becomes remarkable, and the repeated overwrite durability deteriorates, which is not preferable. From the viewpoints of mark edge jitter and repeated overwrite durability, the thickness is more preferably 20 nm or less. The density of the recording layer is preferably 80% or more of the bulk density, more preferably 90% or more. In the sputter film formation method, the density of the recording layer is irradiated to the recording layer by lowering the pressure of the sputter gas (rare gas such as Ar) at the time of film formation or by disposing the substrate close to the front of the target. It is necessary to increase the amount of high energy Ar. The high-energy Ar is whether the Ar ions irradiated on the target for sputtering are partially repelled and reach the substrate side, or the Ar ions in the plasma are accelerated by the sheath voltage on the entire surface of the substrate and reach the substrate. Is one of.

The effect of irradiating such a high-energy noble gas is controlled by atomic peening.
ng) effect. Sputtering with Ar gas, which is generally used, has an atomic peening effect.
Ar is mixed in the sputtered film. Depending on the amount of Ar in the film,
The atomic peening effect can be estimated. That is, if the amount of Ar is small, high energy A
This means that the r irradiation effect is small, and a film having a low density is likely to be formed. On the other hand, if the amount of Ar is large, high energy Ar
Although the irradiation of Ar is intense and the density is high, the Ar incorporated in the film is repeatedly voided during overwriting.
d) and precipitates, deteriorating the durability of repetition. An appropriate Ar content in the recording layer film is 0.1 atomic% or more, 1.5
It is at most atomic%. Furthermore, it is preferable to use high-frequency sputtering rather than direct-current sputtering because the amount of Ar in the film can be reduced and a high-density film can be obtained. In this embodiment, the recording layer 4 includes Ge, Sb, and
It is composed of a thin film containing an alloy containing Te as a main constituent element as a main component. That is, it suffices that the ratio of the amount of each element of Ge, Sb, and Te in the recording layer is within the above composition range, and if necessary, other elements may be added up to a total of about 10 atomic%. Good. The recording layer further contains at least one element selected from O, N, and S in an amount of 0.1 atom% or more and 5 atom% or more.
By adding below, the optical constant of the recording layer can be finely adjusted. However, the addition of more than 5 atomic% is not preferable because it lowers the crystallization rate and deteriorates the erasing performance.

In order to increase the stability over time without decreasing the crystallization rate during overwriting, V, Nb, T
at least one of a, Cr, Co, Pt, and Zr is 8
It is preferable to add at most atomic%. More preferably,
Add 0.1 atom% or more and 5 atom% or less. The total addition amount of these additional elements and Ge to Sb and Te is 1 in total.
It is preferably 5 atomic% or less. If it is contained excessively, phase separation other than Sb will be induced. In particular, when the Ge content is 3 atomic% or more and 5 atomic% or less, the addition effect is large. To improve stability over time and finely adjust the refractive index, S
It is preferable to add at least one of i, Sn, and Pb in an amount of 5 atomic% or less. The total content of these additional elements and Ge is preferably 15 atomic% or less. These elements are Ge
It has the same 4-coordination network as. Addition of 8 atomic% or less of Al, Ga, and In has the effect of raising the crystallization temperature and at the same time reducing jitter and improving recording sensitivity, but segregation tends to occur, so 6 atomic% or less Is preferred. Also, the content including Ge is 15
It is desirable that the content be atomic% or less, preferably 13% or less. Addition of 8 atomic% or less of Ag is also effective in improving the recording sensitivity, and especially when the Ge atomic weight is 5 atomic%.
If it is used in a case of exceeding, the effect is remarkable. But 8
Addition of more than atomic% is not preferable because it increases jitter and impairs stability of the amorphous mark, and addition of more than 15 atomic% together with Ge is not preferable because segregation easily occurs. The most preferable content of Ag is 5 atomic% or less.

Now, the recording layer 4 of the optical recording medium of the present embodiment.
In general, the state after film formation is amorphous. Therefore, after the film formation, it is necessary to crystallize the entire surface of the recording layer to the initialized state (unrecorded state). As the initialization method, initialization by solid phase annealing is possible, but initialization by melt recrystallization in which the recording layer is once melted and gradually cooled during resolidification to be crystallized is desirable. This recording layer has almost no crystal growth nuclei immediately after film formation, and it is difficult to crystallize in the solid phase.However, by melt recrystallization, a small number of crystal nuclei are formed and then melted. , The crystal growth is the main, and the recrystallization proceeds at high speed. Further, since the recording layer 4 has different reflectances from the crystal obtained by melt recrystallization and the crystal obtained by annealing in the solid phase, if mixed, it causes noise. During actual overwrite recording, the erased portion becomes crystals due to melt recrystallization, so it is preferable that the initialization is also performed by melt recrystallization.

At this time, the recording layer is melted locally and only for a short time of about 1 millisecond or less. This is because if the melting region is wide, or if the melting time or cooling time is too long, each layer is destroyed by heat and the surface of the plastic substrate is deformed. In order to give such a thermal history, high-power semiconductor laser light having a wavelength of about 600 to 1000 nm is focused and irradiated on the long axis of 100 to 300 μm and the short axis of 1 to 3 μm, and the short axis direction is set as the scanning axis. -10m
It is desirable to scan at a linear velocity of / s. Even with the same focused light, if it is close to a circle, the melted region is too wide and re-amorphization tends to occur, and the multilayer structure and the substrate are greatly damaged, which is not preferable. It can be confirmed as follows that the initialization was performed by melt recrystallization. That is, the recording medium having the recording power Pw for melting the recording layer, which is focused to a spot diameter smaller than about 1.5 μm, is irradiated to the medium after the initialization at a constant linear velocity. If there is a guide groove, the tracking servo and the focus servo are applied to the groove or the track formed between the grooves. After that, the erase power Pe (≦ P
If the reflectance in the erased state obtained by irradiating the erasing light of w) with a direct current is almost the same as the reflectance in the completely unrecorded initial state, the initialized state can be confirmed to be a crystalline state upon melting. This is because the recording layer is once melted by the irradiation of the recording light, and the state in which it is completely recrystallized by the irradiation of the erasing light undergoes the process of melting by the recording light and recrystallization by the erasing light. This is because it is in a simplified state.

The fact that the reflectance Rini in the initialized state and the reflectance in the melt recrystallized state Rcry are almost the same is (R
ini-Rcry) / {(Rini + Rcry) / 2} means that the reflectance difference between the two is 20% or less. Usually, the reflectance difference is larger than 20% only by solid phase crystallization such as annealing. As shown in FIG. 1, such a recording layer 4 is provided on the surface (groove forming surface) of the substrate 1 so as to be sandwiched between the first protective layer 3 and the second protective layer 5. Here, the first protective layer 3 is mainly effective in preventing the deformation of the surface of the substrate 1 due to the high temperature during recording. The second protective layer 5 also has a function of preventing mutual diffusion of the recording layer 4 and the reflection / heat dissipation layer 2, suppressing deformation of the recording layer 4, and efficiently releasing heat to the reflection / heat dissipation layer 2. . The material of the protective layers 3 and 5 is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesiveness and the like. In general, metal or semiconductor oxides, sulfides, nitrides, carbides and fluorides such as Ca, Mg, and Li having high transparency and high melting point can be used. As a result of investigating the materials, ZnS and SiO ₂ are taken into consideration in view of the above point and compatibility with the material forming the recording layer 4 of the present invention.
Is believed to be the most preferred. Not limited to this material, the above oxides, sulfides, nitrides, carbides, and fluorides do not necessarily have to have a stoichiometric composition, and the composition can be controlled or mixed to control the refractive index. It is also effective to use.

The functions of the first protective layer 3 and the second protective layer 5 will be described in more detail. The layer structure of this embodiment is
It belongs to a type of layer structure called a quench structure. The rapid cooling structure adopts a layer structure that promotes heat dissipation and increases the cooling rate during resolidification of the recording layer, thus avoiding the problem of recrystallization during the formation of amorphous marks and achieving high temperature crystallization. Achieve an erase ratio. Therefore, the thickness of the second protective layer 5 is 5 nm.
It is set to 30 nm or less. If the thickness is less than 5 nm, the recording layer is apt to be destroyed by deformation when melted, and the heat dissipation effect is too large, and the power required for recording unnecessarily increases. The film thickness of the first protective layer 3 of the present embodiment has a great influence on the durability in repeated overwriting, and is particularly important for suppressing the deterioration of jitter. Film thickness is 30
When the thickness is larger than nm, the temperature difference between the recording side and the reflecting layer side of the second protective layer 5 becomes large at the time of recording, and the protective layer itself is asymmetrically deformed due to the difference in thermal expansion between the both sides of the protective layer. It will be easier. Repeating this is not preferable because it causes microscopic plastic deformation to accumulate inside the protective layer, resulting in increased noise.
When the recording layer material of the present invention as described above is used, low jitter can be realized in high density recording with a shortest mark length of 0.3 μm or less, but according to the study by the present inventors, high density recording is realized. Short wavelength laser diode (eg
When a wavelength of 410 nm or less) is used, further attention must be paid to the layer structure of the quenching structure. In particular,
In the study of the one-beam overwrite characteristic using a small focused light beam having a wavelength of 500 nm or less and a numerical aperture NA of 0.55 or more, it is possible to flatten the temperature distribution in the mark width direction to obtain a high erase ratio and an erase power margin. Has been found to be important for taking widespread.

This tendency is due to wavelengths of 390 to 420 nm and N
DVR compatible optics using an optical system with A = 0.85.
The same applies to the system. Higher with such an optical system
Especially in density mark length modulation recording, low thermal conductivity characteristics
An element is used as the second protective layer 5. Preferably that
The film thickness is 7 nm or more and 25 nm or less. In any case
Also, to provide a protective layer with high thermal conductivity on it
So, at high speed recording, the heat does not escape rapidly and there is a heat gradient
High-speed recording is possible because of the presence. The reflective heat dissipation layer 2
By using a material with high thermal conductivity, the erasure ratio and
The erase power margin can be improved. Wide examination
Within the erasing power range, the recording layer 4 of this embodiment has
To achieve good erasing characteristics, simply use the temperature in the film thickness direction.
Not only the distribution and time change but also the film surface direction (recording beam scan
Temperature distribution in the vertical direction) can be made as flat as possible
It is preferable to use such a layer structure. In addition, the present inventors
By properly designing the layer structure of the optical recording medium,
To flatten the temperature distribution across the track in the medium
Re-crystallize without melting and re-amorphizing
The width that can be extended, the erase rate and the erase power margin
Tried to spread. On the other hand, the thermal conductivity is low and very thin
Extremely high heat transfer from the recording layer 4 through the first protective layer 3.
In order to promote heat dissipation to the reflective heat dissipation layer 2 of conductivity, FIG.
As shown in FIG._Twoof
Mixture layer and Al_TwoO_Three2 layers, Al _TwoO_ThreeReflective layers
It was positioned on the heat dissipation layer 2 side. As a result, the recording layer 4
Temperature distribution becomes flat.

Even if the thermal conductivity of the second protective layer 5 is increased, the heat dissipation effect is promoted, but if heat dissipation is promoted too much, the irradiation power required for recording will increase. That is, since the recording sensitivity is remarkably lowered, the film thickness of the Al ₂ O ₃ layer having high thermal conductivity among the two layers of the first protective layer 3 is set to ZnS-SiO ₂
It is 1/2 or less of the film thickness of the layer, and if it is 1/5 or more, recording can be performed at high speed, high density and high sensitivity. In the present embodiment, it is preferable that the first protective layer 3 has two layers and that the recording layer 4 side has a low thermal conductivity protective layer. By using a thin protective layer having a low thermal conductivity, heat conduction from the recording layer 4 to the reflection / heat dissipation layer 2 is delayed in time from several nsec to several tens of nanoseconds at the start of irradiation of recording power, and then the reflection / heat dissipation layer is provided. Since it is possible to accelerate the heat radiation to No. 2, the recording sensitivity will not be lowered more than necessary due to the heat radiation.

Conventionally known SiO ₂ , Ta
_The protective layer material containing ₂ O ₅ , Al ₂ O ₃ , AlN, SiN or the like as its main component has too high thermal conductivity and is not preferable to use alone, but the first protective layer 5 Of these two layers, the reflective heat dissipation layer 2 side has high thermal conductivity, and as a heat dissipation layer, compatibility with Al alloy and stability in sputtering and R
By forming an Al ₂ O ₃ layer capable of F film formation, recording can be performed at high speed. First, when recording, a ZnS-SiO ₂ low thermal conductivity layer is used for recording, and when heat is released, the heat is rapidly cooled by using an Al ₂ O ₃ layer having a high thermal conductivity as a thermal gradient layer instead of a direct metal. Therefore, a recording medium capable of high-speed recording can be manufactured without deteriorating the recording sensitivity.

FIG. 3 shows the thickness ratio (Al ₂ O ₃ layer thickness / ZnS-SiO ₂
The film thickness), the linear velocity at which recording is possible, and the recording sensitivity are shown. When the modulation is 50% or more, the recording / reproducing characteristics are in an allowable range (for example, the jitter is 10% or less and the error is 10 ⁶ ). Recording power is blue-violet LD
When NA = 0.85 and the beam diameter (1 / e ² ) is around 0.4 μm, the maximum output power is about 8 mW of pulse on the medium surface, so the recording sensitivity should be 8 mW or less and the modulation should be 50% or more. Becomes Thickness ratio (Al ₂ O ₃ layer thickness / Zn
For media that can record at a linear velocity (recording power of 8 mW or less, modulation of 50% or more) that can be recorded at a S-SiO ₂ film thickness of 1/5 (0.2) or more, and that does not form an Al ₂ O ₃ layer. The recording linear velocity is approximately twice as fast as the recording speed. Also, when the film thickness ratio (Al ₂ O ₃ layer film thickness / ZnS-SiO ₂ film thickness) exceeds 1/2 (0.5), the recording sensitivity sharply deteriorates, and the recording line The speed decreased sharply. That is, the film thickness ratio of the two layers of the first protective layer 3 (Al ₂ O ₃ layer film thickness / ZnS-SiO ₂ film thickness) is 1/5 or more 1/2
The following is the range where the recording sensitivity is good (8 mW or less) and the linear velocity can be recorded rapidly.

On the other hand, heat dissipation in the reflection heat dissipation layer 2 can be achieved by increasing the thickness of the reflection heat dissipation layer 2, but when the thickness of the reflection heat dissipation layer 2 exceeds 300 nm, the film thickness becomes larger than that in the film surface direction of the recording layer 4. The heat conduction in the direction becomes remarkable, and the effect of improving the temperature distribution in the film surface direction cannot be obtained. In addition, the heat capacity of the reflective heat dissipation layer 2 itself becomes large, and it takes time to cool the reflective heat dissipation layer 2 and eventually the recording layer 4, which hinders the formation of amorphous marks. Most preferably, the reflective heat dissipation layer 5 having a high thermal conductivity is thinly provided to selectively promote heat dissipation in the lateral direction. The conventionally used quenching structure focuses only on the one-dimensional escape of heat in the film thickness direction, and is intended only to quickly release the heat from the recording layer 4 to the reflective heat dissipation layer 2. Not enough attention was paid to the flattening of the temperature distribution. The so-called "super-quenching structure in which the heat conduction delay effect in the first protective layer 3 is taken into consideration" of the present embodiment is applied to the recording layer 4 according to the present embodiment, and the conventional GeTe-
It is more effective than the Sb ₂ Te ₃ recording layer. This is because, in the recording layer 4 of the present embodiment, the crystal growth during resolidification near Tm is the rate-determining factor for recrystallization. Tm
The ultra-quenching structure is effective for maximizing the immediate cooling speed in the vicinity to ensure the formation of the amorphous marks and their edges reliably and clearly. This is because, by the flattening, what was originally capable of high-speed erasing in the vicinity of Tm was able to reliably ensure erasing by recrystallization up to a higher erasing power.

In the present embodiment, it is desirable that the material of the second protective layer 5 has low thermal conductivity, but the standard is 1 × 10 ⁻³ pJ / (μm · K · nsec).
However, it is difficult to directly measure the thermal conductivity of such a low thermal conductivity material in a thin film state, and instead, a guide can be obtained from thermal simulation and actual measurement results of recording sensitivity. As the material of the second protective layer 5 having a low thermal conductivity which gives preferable results, ZnS, ZnO,
5 at least one of TaS ₂ or rare earth sulfide
A composite dielectric containing 0 mol% or more and 90 mol% or less and a heat-resistant compound having a melting point or a decomposition point of 1000 ° C. or more is desirable. More specifically, La, Ce, Nd, Y
It is desirable to use a composite dielectric containing a rare earth sulfide such as 60 mol% or more and 90 mol% or less. Alternatively, ZnS, Zn
The composition range of O or rare earth sulfide is 70 to 90mo
It is preferably set to 1%. To be mixed with these,
Examples of the heat-resistant compound material having a melting point or a decomposition point of 1000 ° C. or higher include Mg, Ca, Sr, Y, La, Ce, Ho and E.
r, Yb, Ti, Zr, Hf, V, Nb, Ta, Zn,
Oxides such as Al, Si, Ge and Pb, nitrides, carbides and fluorides such as Ca, Mg and Li can be used.

Particularly, SiO ₂ is desirable as a material to be mixed with ZnS, and this combination is considered to be optimal in this embodiment. The first protective layer 3 is ZnS
-It is preferable to use _two layers of SiO ₂ layer and Al ₂ O ₃ layer. First
If the thickness of the protective layer 3 is more than 30 nm, a sufficient flattening effect of the temperature distribution in the mark width direction cannot be obtained.
m or less. It is preferably 25 nm or less. 5 nm
When the amount is less than 1, the effect of delaying the heat conduction in the first protective layer 3 is insufficient and the recording sensitivity is significantly lowered, which is not preferable. The thickness of the first protective layer 3 is such that the wavelength of the recording laser light is 600 to 7
In the case of 00 nm, 15 nm to 25 nm is preferable, and the wavelength is 3
When it is 50 to 600 nm, it is preferably 5 to 20 nm, more preferably 5 to 15 nm. In the present embodiment, as described above, ZnS and S are used for both the first and second protective layers.
Although a mixture of iO ₂ is used, using the same material in this way is also advantageous from the viewpoint of manufacturing cost reduction.

Next, the reflection / heat dissipation layer 2 will be described. The present embodiment is characterized in that the thin heat dissipation layer 2 having a very high thermal conductivity and 300 nm or less is used to promote the heat dissipation effect in the lateral direction. In general, the thermal conductivity of a thin film differs greatly from the thermal conductivity in the bulk state and is usually small. In particular, in the case of a thin film having a thickness of less than 40 nm, the thermal conductivity may decrease by one digit or more due to the influence of the island structure at the initial stage of growth, which is not preferable. Furthermore, the crystallinity and the amount of impurities differ depending on the film forming conditions, which causes the difference in thermal conductivity even with the same composition. In order to define the reflective heat dissipation layer 2 having a high thermal conductivity and exhibiting good characteristics in the present embodiment, the thermal conductivity of the reflective heat dissipation layer 2 can be directly measured. You can estimate using. This is because the thermal conductivity and the electrical conductivity have a good proportional relationship in a material such as a metal film in which electrons mainly control heat or electrical conductivity. The electric resistance of a thin film is represented by a resistivity value standardized by the film thickness and the area of a measurement region. Volume resistivity and area resistivity can be measured by the ordinary 4-probe method.
K 7194. By this method,
Data that is much simpler and has better reproducibility can be obtained than when actually measuring the thermal conductivity of the thin film itself.

The preferred reflective heat dissipation layer 2 in this embodiment
The characteristic is that the volume resistivity is 20 nΩ · m or more 150
nΩ · m or less, and more preferably 20 nΩ · m or more and 100 nΩ · m or less. A material having a volume resistivity of less than 20 nΩ · m is practically difficult to obtain in a thin film state. Even if the volume resistivity is larger than 150 nΩ · m, the sheet resistivity can be reduced by using a thick film having a thickness of more than 300 nm. However, according to the study by the present inventors, such a high volume resistivity is obtained. A sufficient heat dissipation effect could not be obtained even if only the sheet resistivity was lowered with the rate material. It is considered that the thick film increases the heat capacity per unit area. Further, such a thick film is not preferable from the viewpoint of manufacturing cost because it takes time to form the film and the material cost increases. Further, the microscopic flatness of the film surface is also deteriorated. Preferably, the area resistivity is 0.2 or more and 0.9 Ω / □ at a film thickness of 300 nm or less.
A low volume resistivity material is used such that:
0.5Ω / □ is the most preferable.

Materials suitable for this embodiment are as follows. For example, 0.3 wt% or more of Cu and 5.0 wt%
It is an Al-Cu based alloy contained below. In particular, an Al—Cu alloy containing a mixture of ZnS and SiO ₂ and containing Cu in an amount of 0.5 wt% or more and 4.0 wt% or less with respect to the first protective layer 3 having two layers of Al ₂ O _3. However, it is desirable as the reflection heat dissipation layer 2 which satisfies all of corrosion resistance, adhesion, and high thermal conductivity in a good balance. In addition, Si is 0.3% by weight or more and 0.8% by weight
Hereinafter, an Al-Mg-Si based alloy containing 0.3 wt% or more and 1.2 wt% or less of Mg is also effective. Furthermore, Al
Ta, Ti, Co, Cr, Si, Sc, Hf, Pd,
An Al alloy containing Pt, Mg, Zr, Mo, or Mn in an amount of 0.2 atomic% or more and 2 atomic% or less increases the volume resistivity in proportion to the concentration of the additive element and improves the hillock resistance.
It can be used in consideration of durability, volume resistivity, film formation rate, and the like. Regarding Al alloys, if the amount of added impurities is less than 0.2 atom%, the hillock resistance is often insufficient depending on the film forming conditions. If it is more than 2 atomic%, it is difficult to obtain the above low resistivity. When importance is attached to stability over time, Ta is preferable as an additive component.

Further, for the first protective layer 3 mainly composed of a mixture of ZnS and SiO _{2 and} having two layers of Al ₂ O ₃ , Ta is 0.5 atomic% or more, 0.8 An AlTa alloy with an atomic percentage of less than or equal to is desirable for the reflective heat dissipation layer 2 that satisfies all of corrosion resistance, adhesion, and high thermal conductivity in a well-balanced manner. Further, in the case of Ta, addition of only 0.5 atomic% brings about a preferable manufacturing effect that the film formation rate during sputtering is increased by 30 to 40% as compared with pure Al or Al-Mg-Si alloy. When the above Al alloy is used as the reflection / heat dissipation layer 2, the preferable film thickness is 150 nm or more and 300 n.
m or less. If it is less than 150 nm, the heat radiation effect is insufficient even with pure Al. When it exceeds 300 nm, heat escapes in the vertical direction from the horizontal direction, does not contribute to the improvement of the heat distribution in the horizontal direction, the heat capacity of the reflective heat dissipation layer 2 itself is large, and the cooling rate of the recording layer slows down. In addition, the microscopic flatness of the film surface also deteriorates. Furthermore, Ag on Ti,
V, Ta, Nb, W, Co, Cr, Si, Ge, Sn,
Sc, Hf, Pd, Rh, Au, Pt, Mg, Zr, M
Ag containing O or Mn of 0.2 atomic% or more and 5 atomic% or less
Alloys are also desirable. When more importance is attached to stability over time, Ti and Mg are preferable as additive components. When the Ag alloy is used as the reflection / heat dissipation layer, the preferable film thickness is 30 nm.
It is 200 nm or less. If it is less than 30 nm, the heat radiation effect is insufficient even with pure Ag. When it exceeds 200 nm, heat escapes in the vertical direction from the horizontal direction, does not contribute to the improvement of the heat distribution in the horizontal direction, and unnecessary thick films reduce the productivity. In addition, the microscopic flatness of the film surface also deteriorates.

The inventors of the present invention added Ag, an additive element to the above Al.
It has been confirmed that the volume resistivity of the element added to the element increases in proportion to the concentration of the element added. By the way, it is considered that addition of impurities generally reduces the crystal grain size, increases electron scattering at grain boundaries, and lowers thermal conductivity. It is necessary to adjust the amount of added impurities in order to obtain the original high thermal conductivity of the material by increasing the crystal grain size. The reflective heat dissipation layer is usually formed by a sputtering method or a vacuum evaporation method, but the total amount of impurities, including the amount of water and oxygen mixed during film formation as well as the amount of impurities in the target and the evaporation material itself, is 2 atoms. It must be less than or equal to%. For this reason, it is desirable that the ultimate vacuum of the process chamber is 1 × 10 ⁻³ Pa or less. In addition, if the film is formed at an ultimate vacuum degree lower than 10 ⁻⁴ Pa, the film formation rate is 1 nm / sec or more,
It is desirable to prevent impurities from being taken in, preferably at 10 nm / sec or more. Alternatively, when the intentional additive element is contained in an amount of more than 1 atomic%, the film formation rate is 10n.
It is desirable to prevent the addition of additional impurities as much as possible at m / sec or more. The film forming conditions may affect the crystal grain size regardless of the amount of impurities. For example, in an alloy film in which about 2 atomic% of Ta is mixed with Al, an amorphous phase is mixed between crystal grains, but the ratio of the crystal phase and the amorphous phase depends on the film forming conditions. Further, as the sputtering is performed at a lower pressure, the proportion of crystal parts increases, the volume resistivity decreases, and the thermal conductivity increases. The impurity composition or crystallinity in the film is determined by the method of manufacturing the alloy target used for sputtering and the sputtering gas (Ar, Ne, Xe, etc.).
Also depends on.

As described above, the volume resistivity in the thin film state is not determined only by the metal material and composition. In order to obtain high thermal conductivity, it is desirable to reduce the amount of impurities as described above, but on the other hand, pure metals such as Al and Ag tend to be inferior in corrosion resistance and hillock resistance. The optimum composition is determined in consideration. In order to obtain higher heat conduction and higher reliability, it is also effective to form the reflection / heat dissipation layer 2 in multiple layers. At this time, at least one layer substantially controls the heat dissipation effect as the low volume resistivity material having a film thickness of 50% or more of the total reflection heat dissipation layer film thickness, and the other layers have corrosion resistance and adhesion to the protective layer, It is configured to contribute to the improvement of hillock resistance. More specifically, Ag, which has the highest thermal conductivity and the lowest volume resistivity among metals, has poor compatibility with the protective layer containing S,
Deterioration tends to be rather fast when repeatedly overwritten. In addition, corrosion tends to occur in an accelerated test environment of high temperature and high humidity. Therefore, Ag and Ag alloy are used as the low volume resistivity material, and an alloy layer containing Al as a main component as an interface layer between the upper protective layer and the upper protective layer is 1 nm or more and 100 n or more.
It is also effective to provide m or less. When the thickness is 5 nm or more, the layer does not have an island structure and is easily formed uniformly.

As the Al alloy, as described above, for example, T
a, Ti, Co, Cr, Si, Sc, Hf, Pd, P
t, Mg, Zr, Mo, or Mn is 0.2 atomic% or more 2
An Al alloy containing at most atomic% can be used. If the thickness of the interface layer is less than 1 nm, the protective effect is insufficient, and if it exceeds 100 nm, the heat dissipation effect is sacrificed. The use of the interface layer is particularly effective when the reflection / heat dissipation layer is Ag or an Ag alloy. Furthermore, when an Ag alloy reflective layer and an Al alloy interface layer are used, Ag and Al are a combination that relatively easily diffuses each other.
It is more preferable to oxidize the Al surface to a thickness of more than 1 nm to provide an interfacial oxide layer. Interfacial oxide layer is 5 nm, especially 1
If it exceeds 0 nm, it becomes a thermal resistance, and the function as a reflection and heat dissipation layer having an extremely high heat dissipation property, which is the original purpose, is impaired, which is not preferable. The multilayered reflection / heat dissipation layer is also effective for obtaining a desired sheet resistivity with a desired film thickness by combining a high volume resistivity material and a low volume resistivity material. The adjustment of the volume resistivity by alloying can simplify the sputtering process by using the alloy target, but it also increases the manufacturing cost of the target and eventually the raw material ratio of the medium. Therefore, it is also effective to obtain a desired volume resistivity by forming a multi-layer of a thin film of pure Al or pure Ag and a thin film of the additive element itself. If the number of layers is up to about 3, the initial device cost may increase, but the individual medium cost may be suppressed rather. The reflection and heat dissipation layer 2 is a multilayer reflection and heat dissipation layer composed of a plurality of metal films, and the total film thickness is 40 nm or more 30
It is preferable that the thickness is 0 nm or less, and 50% or more of the thickness of the multilayer reflection / heat dissipation layer is a metal thin film layer (may be a multilayer) having a volume resistivity of 20 nΩ · m or more and 150 nΩ · m or less.

It is more effective than just a multi-layered heat dissipation layer
As shown in FIG. 4, the reflective heat dissipation layer 2 and the protective layer ZnS-
SiO₂Has an intermediate thermal conductivity and a higher transmittance than the reflective heat dissipation layer 2.
Al_TwoO₃Be formed between the reflective heat dissipation layer 2 and the recording layer 4.
And. Moreover, the film thickness ratio (Al _TwoO₃Thickness / reflection heat dissipation layer
Recordable linear velocity (Pw ≦ 8mW & modulation)
≥50%) and recording sensitivity (recording level that gives 50% modulation)
As can be seen from the relationship of power (mW), the reflective heat dissipation layer and Al_Two
O₃If the film thickness ratio is 0.2 or more, the linear velocity that can be recorded is
It is possible to record at high speed, which is more than 0.1 times or more. This effect is heat
Al with good conductivity_TwoO₃By limiting the film thickness of
The heat of the Al alloy and Ag alloy, which are metals with high thermal conductivity,
It means that conduction can be handled well. Also the film thickness
If the ratio is larger than 0.8, the recording sensitivity will not deteriorate rapidly.
Therefore, the modulation cannot be taken.

From the above, by setting the film thickness ratio of the reflection / heat dissipation layer 2 to the Al ₂ O ₃ layer to 0.2 to 0.8, a medium having good recording sensitivity and capable of high-speed recording can be obtained. When a high NA objective lens is used in the configuration (FIG. 1) in which the cover layer 7 is provided,
The thickness is 0.3 mm or less, more preferably 0.06 to 0.
Since a thickness of 20 mm is required, a sheet shape is preferable. Examples of the material include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, and the like.
Polycarbonate resin with excellent optical properties and cost,
Acrylic resins are preferred. Examples of the method for forming a thin substrate using the transparent sheet include a method of attaching the transparent sheet via an ultraviolet curable resin or a transparent double-sided adhesive sheet. Alternatively, an ultraviolet curable resin may be applied onto the protective layer and cured to form a thin substrate. Hard coat is usually 5μ in order to adjust the mechanical properties such as surface wobbling and tilt of the disc, which is a UV-curable resin and has a pencil hardness of H or higher that is not scratched.
m to 10 μm. One example is an ultraviolet curable resin. For example, MH76 made by Mitsubishi Rayon
By forming 17 μm (trade name) to 1 μm, it is resistant to dust and scratches. Normally, the film thickness of the hard coat formed by MO or the like is 5 μm or more, but as a result of the inventor's earnest study, the recording medium of the present embodiment has a film thickness unevenness of 5 μm or more, which causes jitter. It was found that the characteristics deteriorate.

Table 1 shows the results of examining the jitter characteristics (inner circumference, middle circumference, outer circumference) of the disks having different hard coat film thicknesses.

[0038]

[Table 1]

Since the hard coat is applied by spin coating, the film thickness becomes thicker at the outermost circumference. Therefore, when the thickness of the hard coat is 6 μm (setting), the jitter characteristic at the outer circumference is 9% or more (clock-data), which is bad. Become. If the jitter is 9% or less, an error does not occur even under the worst condition of the inclination of the medium and the pickup, the inclination in the radial direction of ± 0.7 degrees, and the inclination in the groove direction of ± 0.5 degrees. If the jitter is 9% or more, an uncorrectable error will occur when the media and drive (pickup) are in the worst combination, so the jitter must be 9% or less. The limit of the hard coat of 5 μm (setting) is 9% or less in the jitter characteristic. That is, in the present invention, 5 μm
It can be seen that it is necessary to set the value less than the above in order to satisfy the jitter characteristic. Although the coating method of the hard coat varies depending on the viscosity, it is necessary to apply an ultraviolet curable resin having a viscosity of about 70 cps to uniformly coat the hard coat of 5 μm or less. In addition,
Although it is the lower limit, it has been found that when the thickness is 0.5 μm or less, the hard coat film has insufficient mechanical strength and does not function. next,
Other features of the optical recording medium of the present embodiment will be described.
FIG. 5 shows the modulation when high-speed recording was performed at 15 m / s and the minimum mark length was 0.16 μm with respect to the value obtained by dividing the average groove width by the track pitch. The track pitch is 0.35 μm and groove recording is performed. When the ratio (the average groove width divided by the track pitch) exceeds 0.2, the modulation sharply increases, and at 0.3 or more, the modulation is 50%.
And the recording / reproducing characteristics are improved. When the ratio is 0.3 or more, the modulation becomes sharply large. When the modulation is 50% or more, the recording / reproducing characteristics are in an acceptable range (for example, the jitter is 10% or less and the error is 10 ⁶ ). Further, when the ratio (the value obtained by dividing the average groove width by the track pitch) is 0.6 or more, the width of the land becomes narrow, and the land width fluctuates greatly when forming the stamper, and tracking is unstable. Therefore, in the present embodiment, stable tracking is performed by setting the ratio (the value obtained by dividing the average groove width by the track pitch) to 0.3 or more and 0.5 or less, and the modulation is also 50% or more, so that the recording / reproducing characteristics are excellent. was gotten.

Example 1 A track pitch of 0.33 μm, a ratio (average groove width 0.15 divided by track pitch 0.33) of 0.45, thickness 1.1 m
m, a disk-shaped polycarbonate substrate having a diameter of 120 mm, a reflective heat dissipation layer (AgPdCu) 140 nm, a first protective layer of Al ₂ O ₃ of 5 nm, a layer of (ZnS-SiO ₂ ) of 12 nm, and a recording layer of Ag1In3Sb70Te23Ge3 of 12 nm.
A second protective layer (ZnS.SiO ₂ ) having a thickness of 120 nm is sequentially formed by a single-wafer sputtering apparatus, and a modified acrylic adhesive ((Nitto Denko Corp .: trade name: (DA8310-
A50)) with a 70μ polycarbonate cover layer, and a hard coat (made by Mitsubishi Rayon Co., Ltd .: trade name (MH7617N)) on the incident side of the disc.
A phase change type optical disc according to the present embodiment having a final thickness of 1.2 mm was formed with a thickness of μm. Figure 1 shows the media structure
As shown in. Evaluation is 15m / s, minimum mark length 0.16
It was evaluated at μm / bit, 405 nm, and NA = 0.85. The recording power was 6 mW and the erasing power was 3 mW, and recording was performed by multi-pulse. (Start pulse width 0.4T, multi pulse width 0.4T, off pulse 0.5T). Multi-pulse off pulse has bottom power of 0.
Cooled to 2 mW. As a result, modulation 63%,
It showed good characteristics with a jitter of 6.8%.

Comparative Example 1 A track pitch of 0.33 μm and a ratio (average groove width 0.15 divided by track pitch 0.33) of 0.45 and a thickness of 1.1 m
m, disk-shaped polycarbonate substrate with a diameter of 120 mm, reflective heat dissipation layer (AgPdCu) 140 nm, (ZnS-SiO ₂ ) 12 nm thick as the first protective layer, recording layer (Ag1In3S).
b70Te23Ge3) having a thickness of 12 nm and a second protective layer (ZnS.SiO ₂ ) having a thickness of 120 nm are sequentially formed with a single-wafer sputtering apparatus, and a modified acrylic adhesive ((Nitto Denko Corp .: trade name: ( DA8310-A5
0)), a 70 μ polycarbonate cover layer is provided, and a hard coat (made by Mitsubishi Rayon Co., Ltd .: trade name (MH7617N)) is formed to a thickness of 1 μm on the incident side of the disk, and a final thickness of 1.2 mm is obtained according to the present invention. A phase change type optical disk was manufactured. Attempts were made to record under the same conditions as in the example, but recording was not possible at 15 m / s.

Next, a second embodiment will be described with reference to FIG. FIG. 6 shows a protective coat layer 6 instead of the cover layer 7 of FIG.
Another optical recording medium is bonded to the optical recording medium below so as to have a mirror image relationship with each other. Corresponding to the substrate 1, the reflection / heat dissipation layer 2, the first protective layer 3, the recording layer 4, and the second protection layer 5 of the optical recording medium below, the substrate 1 ′, the reflection / heat dissipation layer 2 ′, the first Protective layer 3 ', recording layer 4', second protective layer 5 '
The materials and the thickness of each layer are made the same. This way, not only can you protect the optical recording medium,
The recording capacity can be doubled.

[0043]

According to the first aspect of the present invention, in an optical recording medium utilizing the phase transition phenomenon of crystal and amorphous due to light irradiation, a reflection heat dissipation layer is formed on a substrate in which a groove is formed.
The protective layer, the recording layer, and the second protective layer are laminated in this order, the second protective layer is made of a mixture of ZnS and SiO ₂ , and the recording layer is mainly composed of Ge, Sb, and Te. The reflection heat dissipation layer is a recording medium made of an Ag alloy, and an adhesive layer and a cover layer are formed on the second protective layer,
The first protective layer is a mixture layer of ZnS and SiO ₂ and Al ₂ O.
_{Since the} Al ₂ O ₃ layer is composed of two layers, and the Al ₂ O ₃ layer is located on the reflection heat dissipation layer side, in such an optical recording medium, the protective layer between the reflection heat dissipation layer and the recording layer is rapidly cooled. In order to do so, by making Al ₂ O ₃ a two-layer structure of ZnS—SiO 2, high-speed recording is possible without deteriorating the recording sensitivity.

According to a second aspect of the invention, in the optical recording medium of the first aspect, the thickness of the Al ₂ O ₃ layer of the first protective layer is ZnS and SiO ₂ of the first protective layer. Since the thickness is 1/5 or more and 1/2 or less of the film thickness of the mixture layer, in such an optical recording medium, high-speed recording can be performed with a rapid cooling structure without deteriorating the recording sensitivity.

According to the invention of claim 3, in the optical recording medium of claim 1 or 2, Al _{2 of} the first protective layer is formed.
Since the film thickness of the O ₃ layer is set to 0.20 or more and 0.80 or less of the film thickness of the reflection / heat dissipation layer, such an optical recording medium has a rapid cooling structure without deteriorating the recording sensitivity. High-speed recording enables high-density recording.

According to the fourth aspect of the invention, in the optical recording medium according to any one of the first to third aspects, since the hard coat is formed on the cover layer, only the warp of the substrate is corrected. Not only that, when dust or the like adheres, the dust can be wiped off and scratches are less likely to occur.

According to the invention of claim 5, in the optical recording medium of claim 4, the film thickness of the hard coat is 1
Since the thickness of the optical recording medium is not less than μm and less than 5 μm, not only the warp of the substrate is corrected but also the thickness of the hard coat itself is reduced, and dust is adhered when dust or the like adheres. It can be wiped and scratch-resistant.

According to a sixth aspect of the invention, in the optical recording medium according to any one of the first to fifth aspects, the average groove width in the groove shape of the substrate is 0.3 or more of the track pitch and 0. Since the constitution is 0.5 or less, in such an optical recording medium, high-speed and high-density recording can be performed by the phase change recording layer containing Ge, Sb, and Te as main constituent elements.

[Brief description of drawings]

FIG. 1 is a sectional view of essential parts of an optical recording medium according to a first embodiment of the present invention.

FIG. 2 is a main-portion cross-sectional view showing a positional relationship between a first protective layer and a reflection / heat dissipation layer.

FIG. 3 is a graph showing the relationship between the film thickness ratio (Al ₂ O ₃ layer film thickness / ZnS—SiO ₂ film thickness) and the recordable linear velocity and recording sensitivity.

[FIG. 4] Film thickness ratio (film thickness of Al ₂ O ₃ / reflection heat dissipation layer film thickness), recordable linear velocity (Pw ≦ 8 mW & modulation ≧ 50%) and recording sensitivity (recording power (50% modulation can be obtained)) m
It is a graph which shows the relationship of W)).

FIG. 5 is a graph showing the relationship between the average groove width and the modulation.

FIG. 6 is a cross-sectional view of essential parts of an optical recording medium according to a second embodiment.

[Explanation of symbols]

1 substrate 2 Reflective heat dissipation layer 3 First protective layer 4 recording layers 5 Second protective layer 6 Adhesive layer 7 cover layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ identification code FI theme code (reference) G11B 7/24 535 G11B 7/24 535G 538 538E 538F 561 561N B41M 5/26 B41M 5/26 X

Claims (6)

[Claims] 1. An optical recording medium utilizing a phase transition phenomenon of a crystal and an amorphous by light irradiation, wherein a reflection and heat dissipation layer, a first protective layer, a recording layer and a second protective layer are formed on a grooved substrate. The second protective layer is made of a mixture of ZnS and SiO ₂ , the recording layer has Ge, Sb, and Te as main constituent elements, and the reflective heat dissipation layer is a recording medium made of Ag alloy. there, constitutes an adhesive layer and a cover layer on the second protective layer, said first protective layer comprises two layers of mixture layer and the Al ₂ O ₃ layer of ZnS and SiO _2, the Al ₂ O ₃ An optical recording medium, wherein a layer is located on the side of the reflection / heat dissipation layer. 2. The optical recording medium according to claim 1, wherein the thickness of the Al ₂ O ₃ layer of the first protective layer is 1 / the thickness of the mixture layer of ZnS and SiO ₂ of the first protective layer. 5 or more, 1 /
An optical recording medium characterized by being 2 or less. 3. The optical recording medium according to claim 1, wherein the thickness of the Al ₂ O ₃ layer of the first protective layer is 0.20 or more and 0.80 or less of the thickness of the reflection / heat dissipation layer. An optical recording medium characterized by: 4. The optical recording medium according to claim 1, wherein a hard coat is formed on the cover layer. 5. The optical recording medium according to claim 4, wherein the thickness of the hard coat is 1 μm or more and less than 5 μm. 6. The optical recording medium according to claim 1, wherein the average groove width in the groove shape of the substrate is 0.3 or more and 0.5 or less of a track pitch. And an optical recording medium.