JP2003228884A - Information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium which has a phase transition type recording layer and has a good recording sensitivity, high density and high amplitude (high modulation) in correspondence to high-speed recording. <P>SOLUTION: The optical recording medium is formed by laminating a reflection layer 2, a first protective layer 3, the recording layer 4 and a second protective layer 5 in this order on a substrate 1, in which the second protective layer 5 consists of a mixture composed of ZnS and SiO<SB>2</SB>; the recording layer consists of Ge, Sb and Te as chief component elements; the reflection layer consists of Al alloy, an adhesive layer and a cover layer 6 are formed on the second protective layer 5, the first protective layer 3 consists of two layers; the mixture layer composed of the ZnS and SiO<SB>2</SB>and the AlN layer is formed on the reflection layer side. <P>COPYRIGHT: (C)2003,JPO

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 record binary signals and detect tracking signals by utilizing the reflectance change caused by the interference of reflected light from the bottoms of concave pits and the mirror surface. ing. 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. Further, a system DVR having a capacity of 20 GB or more has been proposed in which the recording / reproducing wavelength is shortened to 390 nm to 420 nm, the numerical aperture and NA (Numerical Aperture) are increased, while the capacity of DVD is 4.7 GB. See Patent Document 1.).

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 type recording layer, an upper protective layer, and a reflective layer are provided on a substrate, and the multiple interference of these layers is used to determine the reflectance difference and the phase difference. It can be controlled and made compatible with CDs and DVDs. In CD-RW, the reflectance is 15 to
Within the range of 25%, compatibility between the CD and the recording signal and groove signal can be ensured, and reproduction is possible with a CD drive equipped with an amplification system that covers low reflectance.

Since the phase-change recording medium can perform the erasing and re-recording processes only by intensity modulation of one focused light beam, the recording is performed in the phase-change recording medium such as CD-RW and rewritable DVD. And includes overwrite recording in which recording and erasing are performed 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 rewritable phase change recording currently in practical use. The medium is generally recorded by forming a non-recorded / erased state into a crystalline state and forming an amorphous mark. A chalcogen element, that is, a chalcogenide alloy containing S, Se, and Te is often used as the material of the recording layer.

[0005] For example, GeTe-Sb2Te3 pseudo-binary alloy as a main component GeSbTe system, InTe-Sb2T
In3SbTe based on e3 pseudo binary alloy, Sb
Examples include AgInSbTe-based alloys and GeSnTe-based alloys whose main component is 0.7Te3.3. Of these, GeTe
-Sb2Te3 pseudo binary alloy system with excess Sb added,
In particular, compositions near the intermetallic compound such as Ge1Sb2Te4 or Ge2Sb2Te5 have been mainly put into practical use.

[0006] These compositions are characterized by crystallization not accompanied by phase separation 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 a practically overwrite characteristic from the past (see Non-Patent Document 2).

Further, conventionally, 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 (Patent Documents 1 to 4).
reference. ). 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.

[0008]

[Patent Document 1] Japanese Patent Laid-Open No. 61-258787 (claims)

[Patent Document 2] Japanese Patent Laid-Open No. 62-152786 (claims)

[Patent Document 3] Japanese Patent Laid-Open No. 1-63195 (Claims)

[Patent Document 4] Japanese Unexamined Patent Publication No. 1-211249 (Claims)

[Non-Patent Document 1]: ISOM Technical Digest'00 (2000),
210

[Non-Patent Document 2] SPIE, Vol. 2514 (1995), pp294-3
01

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the circumstances as described above.
In such an optical recording medium for high density recording having a rewritable phase change recording layer such as DVR, the recording sensitivity is good (role of ZnSSiO ₂ ) corresponding to high-speed recording, and the rapid cooling structure (AlN and heat dissipation layer). Role) to make it a medium. Secondly, in such an optical recording medium,
By limiting the ratio of the film thickness of TaO _{2 and} the film thickness of ZnSSiO _{2 in} the rapid cooling structure, the recording sensitivity is not deteriorated and the rapid cooling structure is adopted to achieve high-speed recording at high speed. Thirdly, in such an optical recording medium, the film thickness of AlN having a rapid cooling structure is limited so that the recording sensitivity is not deteriorated and a rapid cooling structure is provided for high-speed recording at high density. And fourth,
In such an optical recording medium, not only is the warp of the substrate corrected, but dust can be wiped off and scratches are less likely to occur. Furthermore, the fifth
In addition, 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 scratches are less likely to occur. Furthermore, sixthly, by optimizing the groove width for the substrate, Ge, Sb, T
It is to obtain high amplitude and high amplitude (high modulation) in the phase change recording layer containing e as a main constituent element.

[0010]

In order to achieve the above-mentioned object, the present invention firstly provides an optical recording medium utilizing a phase transition phenomenon of crystal and amorphous by light irradiation, wherein the optical recording medium is on a substrate. A reflective layer, a first protective layer, a recording layer, a second layer
The protective layers of the above are laminated in this order, and the first and second protective layers are formed.
The 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 layer is a recording medium made of an Al alloy. A ZnSSiO ₂ layer having a relatively high thermal conductivity was formed to improve the temperature, and AlN was formed between ZnSSiO ₂ and the heat dissipation layer to form a quenching structure for high-speed recording.

Secondly, in the first optical recording medium, the recording sensitivity is deteriorated by setting the film thickness ratio of AlN and ZnSSiO _{2 in} the quenching structure to 1/2 or less and 1/5 or more. Instead, a rapid cooling structure was used for high-speed recording and high-density recording.

Thirdly, in the first or second optical recording medium, recording is performed by setting the film thickness of AlN in the quenching structure to 0.20 times or more and 0.80 times or less the film thickness of the reflecting layer. A high-speed recording was performed with a rapid cooling structure without deteriorating the sensitivity.

Fourthly, by forming a hard coat, not only the warp of the substrate is corrected but also dust can be wiped and scratches are less likely to occur when dust or the like is attached.

Fifth, the thickness of the hard coat is set to 1 μm.
By forming the film with a thickness of m or more and less than 5 μm, not only the warp of the substrate can be corrected, but also dust or the like can be wiped off to prevent scratches.

Further, sixthly, by setting the average groove width of the substrate to 0.3 to 0.5 of the track pitch, Ge, S
It is intended to obtain high amplitude and high amplitude (high modulation) in the phase change recording layer containing b and Te as main constituent elements.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a recording portion of an optical recording medium of the present invention. The substrate (1) / reflection layer (2) / first protective layer (3) / recording layer (4 ) / Second protective layer (5) /. On top of that (second
The protective layer (5) of (1) is coated with an ultraviolet or thermosetting resin (protective coating layer (6)) (which will be described later) or is bonded by an adhesive layer (6). A cover layer (7) is provided. The hard coat is formed by coating the cover layer (7) with an ultraviolet ray or thermosetting resin. 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), transparent resin such as polycarbonate, acryl, polyolefin, or transparent glass can be used. Among them, the polycarbonate resin is most preferable because it has a track record of being most widely used in CD and is inexpensive. Grooves having a pitch of 0.8 μm or less for guiding the recording / reproducing light are provided on the substrate (1), but the grooves do not necessarily have to be geometrically rectangular or trapezoidal grooves. The grooves may be optically formed by forming a waveguide having different refractive indexes.

Next, the recording layer (4) of the present invention will be described. The recording layer (4) of the optical recording medium of the present invention is a phase change type recording layer, and its thickness is generally 5 nm to 100 n.
A range of m is preferred. When the thickness of the recording layer is less than 5 nm, it is difficult to obtain sufficient contrast, and the crystallization speed tends to be slow, which makes it difficult to erase in a short time. On the other hand, when the thickness exceeds 100 nm, it becomes difficult to obtain optical contrast and cracks easily occur.
Further, it is necessary to obtain a contrast that is compatible with a read-only disc such as a DVD, and 5 is required for high-density recording in which the shortest mark length is 0.5 μm or less.
The thickness is preferably 25 nm or more and 25 nm or less. If it is less than 5 nm, the reflectance becomes too low, and the non-uniform composition at the initial stage of film growth,
The effect of a sparse film is likely to appear, which is not preferable.

On the other hand, if the thickness is more 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 be high. 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 sputtering film forming method, the density of the recording layer (4) is set by lowering the pressure of the sputtering gas (rare gas such as Ar) at the time of film formation, or by arranging the substrate close to the front surface of the target. It is necessary to increase the amount of high energy Ar irradiated on the recording layer. The high-energy Ar is the one in which Ar ions irradiated on the target for the sputtering are partially repelled and reach the substrate side, or A in the plasma.
Either the r ions are accelerated by the sheath voltage on the entire surface of the substrate to reach the substrate. The irradiation effect of such a high-energy rare gas is called the atomic peening effect. Atomic peeni is used for sputtering with commonly used Ar gas.
Due to the ng effect, Ar is mixed in the sputtered film. The atomic peening effect can be estimated by the amount of Ar in the film. 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
However, the Ar taken into the film becomes void during repeated overwriting and precipitates, deteriorating the repeated durability. A suitable amount of Ar in the recording layer film is 0.1 atom% or more and 1.5 atom% or less. 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 the present invention, the recording layer is composed of a thin film containing an alloy containing Ge, Sb, and Te as the main constituent elements having the above-mentioned composition as a main component. That is, Ge in the recording layer,
It suffices that the ratio of the amount of each element of Sb and Te is within the above composition range, and other elements may be added to the recording layer up to a total of about 10 atom% if necessary. Further, O, N,
The optical constant of the recording layer can be finely adjusted by adding at least one element selected from S and S to 0.1 at% or more and 5 at% or less. However, the addition of more than 5 atomic% is not preferable because it lowers the crystallization rate and deteriorates the erasing performance.

Further, 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 SbTe is 15 in total.
It is preferably at most atomic%. If included in excess, S
It induces phase separation other than b. 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 have the same four coordination network as Ge.

Addition of 8 atomic% or less of Al, Ga, and In has the effect of increasing the crystallization temperature and at the same time reducing jitter and improving recording sensitivity, but segregation is likely to occur, so that 6 atoms are included. % Or less is preferable. The content of Ge and Ge is preferably 15 atomic% or less, and more preferably 13% or less. The addition of 8 atomic% or less of Ag is also effective in improving the recording sensitivity, and is particularly effective when used when the Ge atomic weight exceeds 5 atomic%. However, the addition of more than 8 atomic% is not preferable because it increases the jitter and impairs the stability of the amorphous mark, and the addition amount together with Ge is 15
If it exceeds atomic%, segregation is likely to occur, which is not preferable.
The most preferable content of Ag is 5 atomic% or less.

The recording layer (4) of the recording medium of the present invention.
The state after film formation is usually amorphous. Therefore, it is necessary to crystallize the entire surface of the recording layer after the film formation so that the recording layer is initialized (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, in the recording layer (4) of the present invention, the crystal due to the melt recrystallization and the crystal due to the annealing in the solid phase have different reflectances, and if they coexist, they cause noise. In 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. It is desirable to scan at a linear velocity of 10 m / s. Even with the same focused light, if it is close to a circle, the melted region is too wide, re-amorphization is likely to occur, and damage to the multilayer structure and the substrate is large, which is not preferable.

It can be confirmed as follows that the initialization was performed by the melt recrystallization. That is, the recording power (P) for melting the recording layer focused on the spot diameter smaller than about 1.5 μm in the initialized medium is set.
The recording light of w) is radiated direct current at a constant linear velocity. When 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 (P
e) If the reflectance in the erased state obtained by direct-currently irradiating the erase light of (≦ Pw) is almost the same as the reflectance in the unrecorded initial state, the initialized state is the melt recrystallized state. Can be confirmed. 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. Note that the reflectance Rini in the initialized state and the reflectance in the melt recrystallized state Rcry are almost the same (Rini-R
It means that the difference between the reflectances defined by cry) / {(Rini + Rcry) / 2} 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, the recording layer (4) of the present invention has a first protective layer (3) and a second protective layer (5).
It is sandwiched between them and provided on the surface (groove formation surface) of the substrate (1). Here, the first protective layer (3) is mainly effective in preventing deformation of the surface of the substrate (1) due to high temperature during recording. The second protective layer (5) prevents mutual diffusion of the recording layer (4) and the reflective layer (2) and suppresses deformation of the recording layer (4), while efficiently heating the reflective layer (2). It also has the function of missing.

The materials for the protective layers (3) and (5) are:
It is determined by paying attention to the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion and the like. Generally, oxides, sulfides, nitrides, and carbides of metals and semiconductors having high transparency and high melting point and fluorides such as Ca, Mg, and Li can be used. As a result of consideration of the above, it is considered that a mixture of ZnS and SiO ₂ is the most preferable in view of the above viewpoint and compatibility with the material constituting the recording layer (4) of the present invention. Not limited to this material, the above oxide,
Sulfides, nitrides, carbides, and fluorides do not necessarily have to have a stoichiometric composition, and it is also effective to control the composition or mix them for controlling the refractive index and the like.

The function and the like of the protective layer will be described in more detail. The layer structure of the present invention 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 film thickness of the second protective layer (5) is set to 5 nm or more and 30 nm or less. 5
If the thickness is less than 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 invention is
It greatly affects the durability in repeated overwriting,
In particular, it is important in suppressing the deterioration of jitter. When the film thickness is thicker than 30 nm, the temperature difference between the recording side of the second protective layer (5) and the reflective layer (2) side becomes large at the time of recording, and the thermal expansion difference between both sides of the protective layer causes The protective layer itself is likely to be asymmetrically deformed. 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. However, according to the study by the present inventors, in order to realize high density recording When a short wavelength laser diode (for example, a wavelength of 410 nm or less) is used, further attention needs to be paid to the layer structure of the quenching structure. In particular, in studying 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, flattening the temperature distribution in the mark width direction is effective for high erasing ratio and erasing. It has been found to be important for achieving a wide power margin.

This tendency is due to wavelengths of 390 to 420 nm and N
The same applies to the DVR compatible optical system using the optical system of A = 0.85 or so. In the high density mark length modulation recording using such an optical system, one having particularly low heat conduction characteristics is used as the second protective layer (5). The film thickness is preferably 7 nm or more and 25 nm or less. In any case, by providing a protective layer with high thermal conductivity on it,
High-speed recording is possible because heat does not escape rapidly during high-speed recording and a thermal gradient is created.

The erasing ratio and erasing power margin can be improved by using a material having a high thermal conductivity for the reflective layer (2). According to the study, in order to exert the good erasing characteristics of the recording layer of the present invention in a wide erasing power range, not only the temperature distribution in the film thickness direction and the time change,
It is preferable to use a layer structure that can flatten the temperature distribution in the film surface direction (direction perpendicular to the recording beam scanning direction) as much as possible.

The present inventor also flattens the temperature distribution in the cross-track direction in the medium by appropriately designing the layer structure of the optical recording medium, so that the medium is melted and re-amorphized. Without doing so, an attempt was made to widen the recrystallizable width and widen the erase ratio and erase power margin.

On the other hand, in order to promote heat dissipation from the recording layer (4) to the reflection layer (2) having an extremely high thermal conductivity, the first protective layer (3) having a low thermal conductivity and a very thin first layer is used. It was found that the temperature distribution in the recording layer became flat by using two protective layers (3). Even if the thermal conductivity of the second protective layer (5) is increased, the heat dissipation effect is promoted, but if the heat dissipation is promoted too much, the irradiation power required for recording will increase, that is, the recording sensitivity will decrease significantly. Will end up.

In the present invention, the first protective layer (3) is 2
It is preferable to use a protective layer having a low thermal conductivity on the recording layer (4) side. By using a thin protective layer having a low thermal conductivity, several nsec to several tens of times when the recording power irradiation is started.
In nsec, the heat conduction from the recording layer (4) to the reflective layer (2) can be delayed in time, and then the heat radiation to the reflective layer (2) can be promoted. Does not reduce sensitivity. Conventionally known SiO ₂ , Ta ₂ O ₅ , Al ₂ O ₃ , AlN, Si
The protective layer material containing N or the like as the main component is too high in thermal conductivity and is not preferable to be used as a single substance. However, of the two layers of the first protective layer, this heat is applied to the reflective layer side. Recording can be performed at high speed by forming AlN because of its high conductivity and compatibility with the Ag alloy as the heat dissipation layer.

First, during recording, a ZnSSiO ₂ low thermal conductivity layer is used for recording, and when heat is released, the heat is rapidly cooled by using an AlN layer having a high thermal conductivity as a thermal gradient layer instead of directly using a metal. Therefore, a recording medium capable of high-speed recording can be manufactured without deteriorating the recording sensitivity.

In FIG. 3, the film thickness ratio (AlN film thickness / ZnSS
The iO ₂ film thickness), the linear velocity at which recording is possible, and the recording sensitivity are shown. When the modulation is 50% or more, the difference between the reflectances of the crystal and the amorphous can be drastically increased, and the allowable range of the recording / reproducing characteristics is good (a region where the error is 10 ⁶ units). Also, the recording power was set to NA = 0.85 for a blue-violet LD and the beam diameter (1 / e ² ) was set to 0.4 μm.
In the vicinity of the medium surface, the maximum emission power is about 8 mW of pulse. Therefore, it is necessary that the recording sensitivity is 8 mW or less and the modulation is 50% or more, so that a large difference between crystal and amorphous can be obtained.

A linear velocity (recording power of 8 mW or less, modulation of 50% or more) that can be recorded at a film thickness ratio (AlN film thickness / ZnSSiO ₂ film thickness) of 1/5 (0.2) or more can be recorded rapidly at a high speed. Moreover, the recording linear velocity is approximately twice as fast as that of the medium on which AlN is not formed. The film thickness ratio (AlN film thickness / ZnSSiO ₂ film thickness)
Is 1/2 (0.5) or more, the recording sensitivity sharply deteriorates,
The recording linear velocity drastically decreased despite inputting the recording power.

That is, the film thickness ratio of the two layers of the first protective layer (AlN film thickness / ZnSSiO ₂ film thickness) is 1/5 or more 1 /
The range of 2 or less was a range where the recording sensitivity was good (8 mW or less) and the linear velocity could be recorded rapidly. On the other hand, heat dissipation in the reflective layer can be achieved by increasing the thickness of the reflective layer, but when the thickness of the reflective layer exceeds 300 nm, heat conduction in the film thickness direction becomes more remarkable than in the film surface direction of the recording layer, and the film The effect of improving the temperature distribution in the plane direction cannot be obtained. Further, the heat capacity of the reflective layer itself becomes large, and it takes time to cool the reflective layer and eventually the recording layer, which hinders the formation of amorphous marks.

Most preferably, a reflective layer having a high thermal conductivity is thinly provided to selectively promote heat radiation in the lateral direction. The quenching structure used in the past focuses only on the one-dimensional escape of heat in the film thickness direction, and is intended only to quickly escape the heat from the recording layer to the reflective layer. Not enough attention was paid to flattening.

The so-called "super-quenching structure in which the heat conduction delay effect in the first protective layer is taken into consideration" of the present invention, when applied to the recording layer of the present invention, is a conventional GeTe-Sb ₂ Te.
It is more effective than the _three recording layers. This is because, in the recording layer of the present invention, the crystal growth during resolidification near Tm is the rate-determining factor for recrystallization. The ultra-quenching structure is effective for maximizing the immediate cooling rate in the vicinity of Tm to ensure the formation of the amorphous marks and the edges thereof, and the temperature distribution in the film surface direction. With the flattening, the high-speed erasing that was originally possible in the vicinity of Tm can surely secure the erasing by recrystallization up to a higher erasing power.

In the present invention, it is desirable that the material of the second protective layer (5) has a 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. Examples of the material for the second protective layer having a low thermal conductivity that gives favorable results include ZnS and Zn.
A composite dielectric containing at least one of O, TaS _{2, and} rare earth sulfides in an amount of 50 mol% to 90 mol% and a heat-resistant compound having a melting point or a decomposition point of 1000 ° C. or more is desirable.

More specifically, a composite dielectric containing a rare earth sulfide such as La, Ce, Nd or Y in an amount of 60 mol% to 90 mol% is desirable. Alternatively, the composition range of ZnS, ZnO or rare earth sulfide is 70 to 90 mol%.
Is desirable.

Examples of the heat-resistant compound material having a melting point or decomposition point of 1000 ° C. or more to be mixed with these are Mg and C
a, Sr, Y, La, Ce, Ho, Er, Yb, Ti,
Zr, Hf, V, Nb, Ta, Zn, Al, Si, G
e, Pb and other oxides, nitrides, carbides, Ca, Mg, L
Fluorides such as i can be used.

Especially as a material to be mixed with ZnS
Is SiO_TwoIs desirable, and this combination is the best in the present invention.
I think it is suitable. The first protective layer (3) is made of Zn
SSiO_TwoIt is better to have two layers of
If the thickness of the protective layer is thicker than 30 nm, the temperature in the mark width direction
30 nm because a sufficient flattening effect of the degree distribution cannot be obtained.
Below. It is preferably 25 nm or less. 5nm not yet
When full, the effect of delaying heat conduction in the first protective layer is insufficient.
However, the recording sensitivity is significantly lowered, which is not preferable. First insurance
The thickness of the protective layer is such that the wavelength of the recording laser light is 600 to 700.
nm is preferably 15 nm to 25 nm, and the wavelength is 350
In the range of ~ 600 nm, 5 ~ 20 nm is preferable, and more preferable.
The width is 5 to 15 nm. In the present invention,
As described above, both the first and second protective layers are ZnS and SiO. _TwoTo
It is supposed to be mixed, but make the same material like this
Also, it is advantageous in terms of manufacturing cost reduction.

Next, the reflective layer (2) will be described. The present invention is characterized in that a thin reflective 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.

The thermal conductivity of the reflective layer (2) can be measured directly in order to define the reflective layer (2) of high thermal conductivity which exhibits good characteristics in the present invention. The quality can be estimated by using the electric resistance. 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 the measurement region. Volume resistivity and area resistivity can be measured by the ordinary 4-probe method, and JIS K
7194. This method provides much simpler and more reproducible data than actually measuring the thermal conductivity of the thin film itself.

In the present invention, the preferable characteristic of the reflective layer (2) is that the volume resistivity is 20 nΩ · m or more and 150 nΩ.
· M or less, more preferably 20 nΩ · m or more and 10
It is 0 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. Volume resistivity 15
Even if the volume resistivity is larger than 0 nΩ · m, for example, 3
The sheet resistivity can be reduced by using a thick film having a thickness of more than 00 nm. However, according to the study by the present inventor, a sufficient heat dissipation effect can be obtained even if only the sheet resistivity is lowered with such a high volume resistivity material. I couldn't do it. 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 film thickness 30
A low volume resistivity material that obtains an area resistivity of 0.2 to 0.9Ω / □ at 0 nm or less is used. 0.5Ω /
□ is the most preferable. The preferable thickness of the reflective layer of Al alloy is 100 to 300 nm.

Materials suitable for the present invention are as follows. For example, it is an Ag-Cu alloy containing Cu in an amount of 0.3% by weight or more and 5.0% by weight or less. Especially ZnS and Si
O ₂ is mixed, and Cu is used for the two protective layers of AlN.
Ag-C containing 0.5% by weight or more and 4.0% by weight or less
A u-based alloy is desirable as a reflective layer that satisfies all of corrosion resistance, adhesion, and high thermal conductivity in good balance. Also, Si
It is also effective to use an Ag-Pd-Cu based alloy containing 0.3 to 0.8 wt% of Pd and 0.3 to 1.2 wt% of Pd. Although an Al alloy has good thermal conductivity, the surface property after film formation is poor and the Ag alloy is more suitable for high density recording. In addition, Cu is 0.5 atom% or more and 0.8 atom% or less with respect to the first protective layer (3) which is composed mainly of a mixture of ZnS and SiO _{2 and} has two layers of AlN. AgCu alloy is desirable as a reflective layer that satisfies all of corrosion resistance, adhesion, and high thermal conductivity in good balance. When the Ag alloy is used as the reflective layer, the preferable film thickness is 150 nm or more and 300 nm or less. If it is less than 150 nm, the heat dissipation effect is insufficient even with pure Ag. 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 layer itself is large, and the cooling rate of the recording layer slows down. In addition, the microscopic flatness of the film surface also deteriorates.

Further, Ag, Ti, V, Ta, Nb,
W, Co, Cr, Si, Ge, Sn, Sc, Hf, P
An Ag alloy containing 0.2 atomic% or more and 5 atomic% or less of d, Rh, Au, Pt, Mg, Zr, Mo, or Mn is also desirable. When importance is attached to stability over time, Pd is preferable as an additive component. When the Ag alloy is used as the reflective layer, the preferable film thickness is 30 nm or more and 200 nm or less. If it is less than 30 nm, the heat dissipation 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 present inventor has found that the additive element to the above Al, Ag
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 layer is usually formed by a sputtering method or a vacuum evaporation method, but the total amount of impurities is 2 atomic% including not only the amount of impurities in the target and the evaporation material itself but also the amount of water and oxygen mixed during film formation. Must be: For this reason, it is desirable that the ultimate vacuum of the process chamber is 1 × 10 ⁻³ Pa or less. Further, if the film is formed at an ultimate vacuum degree lower than 10 ⁻⁴ Pa, it is desirable to prevent impurities from being taken in by setting the film formation rate to 1 nm / sec or more, preferably 10 nm / sec or more.

Alternatively, when the intentional additive element is contained in an amount of more than 1 atomic%, it is desirable that the film formation rate is 10 nm / sec or more to prevent the addition of additional impurities as much as possible. The film forming conditions may affect the crystal grain size regardless of the amount of impurities. For example, in an alloy film in which Ag is mixed with about 2 atomic% of Cu, 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 also depends on the manufacturing method of the alloy target used for sputtering and the sputtering gas (Ar, Ne, Xe, etc.). As described above, the volume resistivity in a 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.

It is also effective to make the reflective layer multi-layered in order to obtain higher thermal conductivity and higher reliability. 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 layer film thickness,
The other layers are configured to contribute to the improvement of corrosion resistance, adhesion to the protective layer, and 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, and tends to deteriorate a little when repeatedly overwritten. In addition, corrosion tends to occur in an accelerated test environment of high temperature and high humidity. Therefore, it is also effective to use Ag and Ag alloy as the low volume resistivity material and to provide an alloy layer containing Al as a main component between 1 nm and 100 nm inclusive as an interface layer with the upper protective layer. When the thickness is 5 nm or more, the layer does not have an island structure and is easily formed uniformly.

Further, when an Ag alloy reflection layer is used, Ag
Are relatively easy to diffuse into each other, so Ag
It is more preferable to oxidize the surface to a thickness of more than 1 nm to provide an interfacial oxide layer. Interfacial oxide layer is 5 nm, especially 10 n
If it exceeds m, it becomes a thermal resistance, and the function as a reflecting layer having an extremely high heat dissipation property, which is the original purpose, is impaired, which is not preferable. The multilayer structure of the reflective 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 reflective layer is a multilayer reflective layer composed of a plurality of metal films, the total thickness is 40 nm or more and 300 nm or less, and 50% or more of the thickness of the multilayer reflective layer is a metal thin film layer having a volume resistivity of 20 nΩ · m or more and 150 nΩ · m or less. (It may be multi-layered).

When an Ag alloy is used for the reflective layer, AlN is formed between ZnSSiO ₂ and therefore, if ZnS is directly sulphidized, it has an effect on reliability. As shown in FIG. 4, ZnSSiO ₂ which is a protective layer and a protective layer has an intermediate coefficient of thermal conductivity and a higher transmittance than that of the reflective layer, which is more effective than a simple heat dissipation layer. Able to take
N is formed between the reflective layer and the recording layer, and the film thickness ratio (AlN film thickness / reflective layer film thickness), the linear velocity (Pw ≦ 8 mW & modulation ≧ 50%) and the recording sensitivity (50 As shown in FIG. 4, when the recording power (mW) at which the% modulation is obtained is a reflective layer / AlN film thickness ratio of 0.2 or more, the linear velocity that can be recorded is as high as almost twice or more than 0.1 or less. Can be recorded on. This effect means that by limiting the AlN film thickness with good thermal conductivity, the heat conduction can be successfully processed to Al alloy or Ag alloy, which is a metal with higher thermal conductivity. Further, the film thickness ratio is set to 0.
When it is larger than 8, the recording sensitivity is rapidly deteriorated and the modulation cannot be obtained. From the above, the reflective layer and Al
By setting the film thickness ratio of N to 0.2 to 0.8, a recording medium having good recording sensitivity and capable of high-speed recording can be obtained.

Structure in which the cover layer (7) is provided (see FIG. 1)
In the case of using a high NA objective lens, a thickness of 0.3 mm or less, more preferably 0.06 to 0.20 mm is required, and thus 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, etc. Polycarbonate resin and acrylic resin, which are excellent in properties and cost, are preferable. 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.

The hard coat is made of an ultraviolet curable resin to adjust the hardness such that the pencil hardness is H or more and is not scratched, and the mechanical characteristics such as surface deflection and tilt of the disc.
to form a thickness of less than μm An ultraviolet curable resin is used as the ultraviolet curable resin. For example, MH7617 manufactured by Mitsubishi Rayon Co., Ltd.
By forming N (product name) to 1 μm, it is resistant to dust and scratches. The film thickness of the hard coat usually formed by MO or the like is 5 μm or more. If the film thickness is increased to this extent, film thickness unevenness is likely to occur. Therefore, in the present invention, the film thickness unevenness is formed by forming the film thickness less than 5 μm. Was formed and the surface hardness was maintained and mechanical characteristics were formed with a film thickness that does not deteriorate surface runout and tilt.

Table 1 shows the hard coat film thickness and the disc jitter characteristics (inner circumference, middle circumference, and outer circumference). Since the hard coat is applied by spin coating, the film thickness becomes thicker at the outermost circumference, so that when the thickness of the hard coat is 6 μm (setting), the jitter characteristic on the outer circumference becomes worse than 9% (clock-data). Hard coat of 5 μm (setting) has 9% jitter property
It is the limit below. How to apply the hard coat depends on the viscosity, but it is 70c to apply 5μm or less uniformly.
It is necessary to apply about ps. The lower limit is 0.
It was found that when the thickness is 5 μm or less, the hard coat film lacks mechanical strength and does not function.

[0060]

[Table 1] Measurement position: inner circumference (r24mm), middle circumference (r40mm),
Outer circumference (r58mm)

FIG. 2 shows that, in place of the protective substrate (7) of FIG. 1, another optical recording medium is laminated via a protective coat layer (6) so as to have a mirror image relationship with the optical recording medium below. It is a thing. Corresponding to the substrate (1), the reflective layer (2), the first protective layer (3), the recording layer (4) and the second protective layer (5) of the lower optical recording medium, the substrate (1 ') , A reflective layer (2 '), a first protective layer (3'), a recording layer (4 ') and a second protective layer (5'), and the materials and the thickness of each layer are the same. By doing so, not only can the optical recording medium be protected, but the recording capacity can be doubled.

Next, another feature of the present invention will be described. FIG. 5 shows a value obtained by dividing the average groove width by the track pitch, with a high speed recording of 13 m / s and a minimum mark length of 0.160 μm.
The modulation when recorded in m is shown. The track pitch is 0.33 μm for groove recording. When the ratio (value obtained by dividing the average groove width by the track pitch) is 0.3 or more, the modulation exceeds 50%. When the ratio is 0.3 or more, the modulation rapidly increases. Modulation is 5
When 0% or more is obtained, the difference between the reflectances of the crystal and the amorphous can be drastically increased, and the range is within a permissible range with good recording / reproducing characteristics (a region where the error is 10 ⁶ units). Further, if the ratio (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 the tracking did not become unstable. Therefore, in the present invention, the ratio (value obtained by dividing the average groove width by the track pitch) is set to 0.3 or more and 0.5 or less for stable tracking, and the modulation is 50% or more. was gotten.

[0063]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 The track pitch was 0.32 μm, and the ratio (average groove width 0.15 divided by the track pitch 0.32) was 0.46.
On a disc-shaped polycarbonate substrate having a thickness of 1.1 mm and a diameter of 120 mm, a reflective layer (AgCu) of 120 nm, a first layer
As a protective layer, AlN is 5 nm and (ZnS-SiO ₂ ) is 1 nm.
2nm thick, a recording layer (AglIn3Sb70Te23Ge3) 12nm thick, a second protective layer (ZnS · SiO ₂₎ 12
The film thickness was sequentially formed with a single-wafer sputter device with a thickness of 0 nm, and further modified acrylic adhesive (manufactured by Nitto Denko Corporation, trade name: DA8
310-A50) with a 60 μ polycarbonate cover layer and a hard coat on the incident side of the disc (Mitsubishi Rayon Co., Ltd., trade name: MH7617N).
Was formed to a thickness of 1 μm, and a phase change type optical disk according to the present invention having a final thickness of 1.2 mm was produced. Figure 1 shows the media structure
As shown in. Evaluation is 15 m / s, linear density is 0.1
Evaluation was performed at 3 μm / bit, 405 nm, NA = 0.85. Recording was performed with multi-pulses at a recording power of 6 mW and an erasing power of 3 mW (leading pulse width 0.3T, multi-pulse width 0.3T, off-pulse 0.8T). The multi-pulse off pulse was cooled to a bottom power of 0.2 mW. As a result, good characteristics of 65% modulation and 6.9% jitter were shown.

Comparative Example 1 The track pitch was 0.32 μm, and the ratio (the average groove width 0.15 divided by the track pitch 0.32) was 0.46.
A disc-shaped polycarbonate substrate having a thickness of 1.1 mm and a diameter of 120 mm, a reflective layer (AgCu) of 140 nm, a first layer
As the protective layer, (ZnS—SiO ₂ ) is 12 nm thick, and the recording layer (Ag ₁ In ₃ Sb ₇₀ Te ₂₃ Ge ₃ ) is 12 nm thick.
Thickness of the second protective layer (ZnS · SiO ₂ ) is 120 nm
Thick film is sequentially formed by a single-wafer sputtering apparatus, and further modified acrylic adhesive (manufactured by Nitto Denko Corporation, trade name: DA8310)
-A50), a 60 μ polycarbonate cover layer is provided, and 1 μ of a hard coat (made by Mitsubishi Rayon Co., Ltd., trade name: MH7617N) is provided on the incident side of the disc.
A phase-change type optical disc having a final thickness of 1.2 mm was formed with a thickness of m. Recording was attempted under the same conditions as in the example, but recording was not possible at 15 m / s.

[0065]

As is apparent from the detailed and specific description above, in the optical recording medium according to the first aspect of the present invention, AlN is used to form the quenching structure of the protective layer between the reflective layer and the recording layer. By adopting a two-layered structure of ZnSSiO ₂ , there is an effect that high-speed recording is possible without deteriorating the recording sensitivity. Further, in the optical recording medium according to claim 2 of the present invention, since the film thickness ratio of the two-layer protective layer between the reflective layer and the recording layer is 1/2 or less and 1/5 or more, the recording sensitivity is deteriorated. It has an effect that a high-speed recording can be performed with a high-speed recording without a quenching structure. In the optical recording medium according to claim 3 of the present invention, the thickness of AlN, which is one of the protective layers between the reflective layer and the recording layer, is 0.20 times or more and 0.80 times or less the thickness of the reflecting layer. Thus, there is an effect that high-speed recording can be performed at high speed with a rapid cooling structure without deteriorating the recording sensitivity. Further, in the optical recording medium according to claim 4 of the present invention, by forming a hard coat, it is possible not only to correct the warp of the substrate, but also to prevent dust from adhering and to prevent scratches when dust or the like is attached. There is an effect. Further, in the optical recording medium according to claim 5 of the present invention, the film thickness of the hard coat is 5 μm.
By forming the thickness less than m, not only the warp of the substrate can be corrected, but also the thickness of the hard coat itself can be reduced, and when dust or the like is attached, dust can be wiped out and scratches are less likely to occur. Further, in the optical recording medium according to claim 6 of the present invention, by setting the average groove width of the substrate to 0.3 or more and 0.6 or less of the track pitch, Ge, Sb, T
The phase change recording layer containing e as a main constituent element has an effect of enabling high speed and high density recording.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a layer structure of an optical recording medium applied to the present invention.

FIG. 2 is a cross-sectional view showing another example of the layer structure of the optical recording medium applied to the present invention.

FIG. 3 is a diagram showing a relationship between a film thickness ratio, a recordable speed, and recording sensitivity.

FIG. 4 is another diagram showing the relationship between the film thickness ratio, the recordable speed, and the recording sensitivity.

FIG. 5 is a diagram showing modulation with respect to average groove width.

[Explanation of symbols]

1 substrate 1'substrate 2 reflective layer 2'reflection layer 3 First protective layer 3'first protective layer 4 recording layers 4'recording layer 5 Second protective layer 5'second protective layer 6 Protective coating layer or adhesive layer 7 cover layer

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI theme code (reference) G11B 7/24 538 G11B 7/24 538E 561 561N G03C 1/725 503 G03C 1/725 503

Claims (6)

[Claims] 1. An optical recording medium utilizing a crystal-amorphous phase transition phenomenon by light irradiation, wherein the optical recording medium comprises a reflective layer, a first protective layer, a recording layer and a second protective layer on a substrate. The second protective layer is composed of a mixture of ZnS and SiO ₂ , and the recording layer is G
e, Sb, and Te as main constituent elements, and the reflective layer is Al
The second protective layer comprises an adhesive layer and a cover layer, and the first protective layer is a mixture layer of ZnS and SiO ₂ and A.
An optical recording medium comprising an AlN layer formed of two 1N layers on the reflective layer side. 2. The film thickness of the AlN layer of the first protective layer is ⅕ of the film thickness of the mixture layer of ZnS and SiO ₂ of the first protective layer.
The optical recording medium according to claim 1, wherein the optical recording medium is 1/2 or less. 3. The light according to claim 1, wherein the thickness of the AlN layer of the first protective layer is 0.20 times or more and 0.80 times or less the thickness of the reflection layer. recoding media. 4. The optical recording medium according to claim 1, wherein a hard coat is formed on the cover layer. 5. The film thickness of the hard coat is 1 μm or more,
The optical recording medium according to claim 4, wherein the optical recording medium has a thickness of less than 5 μm. 6. The optical recording according to claim 1, wherein the substrate has a groove shape having an average groove width of 0.3 or more and 0.5 or less of a track pitch. Medium.