JP2003191638A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase-change type optical information recording medium, with which a high density recording is possible by employing a short wavelength such as a blue wavelength as a recording wavelength, and the regeneration of recording and the interchangeability of ROMs can coexist with each other. <P>SOLUTION: This optical recording medium consists of at least a first protective layer 3, a phase change recording layer 4, a second protective layer 5 and a reflection radiating layer 6 so as to record and regenerate signals by irradiating the laser light with a wavelength of λ from the formed surface side of the first protective layer 3 due to the reversible phase change between the amorphous phase and the crystal phase of the phase change recording layer 4. The specified composition of the phase change recording layer 4 is represented by X<SB>α</SB>Y<SB>β</SB>Dy<SB>γ</SB>(Sb<SB>δ</SB>Te<SB>1-δ</SB>)<SB>1-α-β-γ</SB>(wherein X is In or Ga or a mixture of In and Ga; Y is one or more kinds of elements for heightening the crystallization temperature of (Sb<SB>δ</SB>Te<SB>1-δ</SB>); and α, β and γ are atomic ratio under the following conditions: 0.01≤α≤0.07, 0.02≤β≤0.1, 0.01≤γ≤0.07 and 0.65≤δ≤0.85.). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type optical recording medium.

[0002]

2. Description of the Related Art By irradiating a semiconductor laser beam,
Optical recording media that can record, reproduce, and erase signals use the magneto-optical recording method that erases the recorded signal by reversing the magnetization, and the reversible phase change between crystalline and amorphous. Then, there is a phase change recording method for erasing the recording signal. In particular, in the phase change recording method, so-called single beam overwriting is possible, and since the optical system on the drive side is simple, it is applied as a recording medium for computers and audiovisual.

A phase change type optical recording medium is heated by irradiating a recording layer thin film formed on a substrate with laser light, and the reflectance is changed by changing the phase of the recording layer structure between crystalline and amorphous. , Recording and erasing signals. Normally, the signal recording state is the amorphous phase and the erasing state is the crystalline phase, and the medium formed by depositing the recording layer, the protective layer, etc. was further initially crystallized by irradiation with a large-diameter laser beam. Use is started in the state.

In the phase change type optical recording medium, in a region where a signal is desired to be recorded, laser light of high power is irradiated to heat it to a temperature higher than the melting point of the material forming the recording layer. The recording layer heated in this way is cooled with a certain temperature profile as the laser passes after melting. By selecting this cooling rate to be higher than the crystallization rate of the recording layer material, the recording layer can be made amorphous and signals can be recorded.

On the other hand, in the case of erasing a signal, in a region where the signal is to be erased, a laser having an intermediate power is irradiated and the temperature is maintained at a temperature higher than a temperature at which the material forming the recording layer can be crystallized. The recording layer heated at this temperature undergoes a phase change from an amorphous state to a more stable crystalline state, which erases the signal.

As a material for forming the recording layer of the phase-change type optical recording medium, a material that easily forms an amorphous state and is unlikely to cause composition segregation even after repeated recording is preferable. For example, chalcogenide is mainly used. The material can be applied.

Specific recording layer materials include a mixture of GeTe and Sb ₂ Te ₃ and a system in which Ag or In is added to a composition near Sb ₇ Te ₃ in which the molar ratio of Sb and Te is 7: 3. Is mentioned. In particular, a system in which Ag or In is added to the composition near Sb ₇ Te ₃ has a high crystal growth rate, has a clear amorphous portion outline, and is a material suitable for high density and high linear velocity recording.

The phase change type optical recording medium as described above is
It is expected that applications for high-density image recording will expand in the future,
It is necessary to realize higher speed overwrite. In Japanese Patent Application No. 12-289128, the present inventors have proposed a recording layer composition suitable for high linear velocity recording and having excellent overwrite characteristics and storage characteristics. The crystallization rate of the phase change material forming the recording layer can be adjusted by adjusting the composition ratio of the elements. In order to improve the erasing ratio even by high speed overwriting, it is advantageous that the crystallization speed is high.

[0009]

However, when the phase-change material constituting the recording layer of the phase-change type optical recording medium as described above is adjusted to have a composition that increases the crystallization rate, initial crystallization is difficult to occur, There was a drawback that the reflectance distribution after initial crystallization was difficult to be uniform.

Further, when the recording layer is formed of a phase change material having a high crystallization rate, the marks of recorded signals are likely to be thin, which makes it difficult to perform recording with a sufficient degree of modulation. In addition, if the degree of modulation is small, there is a problem that jitter is generally bad and good recording cannot be performed.

The reason for this is that the recrystallization region of the melted region becomes large at the time of signal recording due to the high crystallization speed, and the amorphous region formed becomes small. In order to reduce such a recrystallized region, it is conceivable that the thickness of the protective layer formed on the phase change recording layer is thinned and the phase change recording layer material is rapidly cooled. If the thickness of the protective layer on the phase-change recording layer is simply reduced, heat is likely to be removed by quenching,
Furthermore, since the heat absorption rate of the phase change recording layer also decreases, it is not possible to sufficiently raise the temperature of the phase change recording layer, and the melting region becomes small, and even if the recrystallization region can be made small. In the end, the formed amorphous region becomes small, and there is a problem that recording with a sufficient degree of modulation cannot be performed.

Therefore, in the present invention, a DVD (Digita
l Versatile Disc) has a recording density equal to or higher than
It is an object of the present invention to provide an optical recording medium suitable for high linear velocity recording at about 5 times the VD speed (17.5 m / s).

[0013]

According to a first aspect of the present invention, at least a first protective layer, a phase change recording layer, a second protective layer and a reflection heat dissipation layer are formed on a substrate,
A laser beam having a wavelength λ is irradiated from the side of the first protective layer formation surface to record and reproduce a signal by utilizing the reversible phase change between the amorphous phase and the crystalline phase of the phase change recording layer. An optical recording medium, wherein the composition of the phase change recording layer is represented by the following [Chemical formula 2].

[0014]

Embedded image X _α Y _β Dy _γ (Sb _δ Te _1-δ ) _1-α-β-γ

(However, X is In or Ga, or In
And Ga, where Y is (Sb _δTe_1-δ) Crystals
Α, β, γ, which are one or more elements that increase the oxidization temperature
Represents the atomic ratio and is in the following range. 0.01 ≤ α ≤ 0.07 0.02 ≦ β ≦ 0.1 0.01 ≦ γ ≦ 0.07 0.65 ≦ δ ≦ 0.85

In a second aspect of the invention, the phase change recording layer provides a phase change type optical recording medium containing at least Ge.

In the invention according to claim 3, in the reflection / heat dissipation layer, n of the refractive index (n + ik) at the wavelength λ is 1
Provided is a phase change type optical recording medium which is made of a metal having k of 5 or less.

According to a fourth aspect of the present invention, there is provided a phase change type optical recording medium, wherein the reflection / heat dissipation layer contains at least one of Ag, Au and Cu as a main component.

In a fifth aspect of the present invention, the reflection heat dissipation layer provides a phase change type optical recording medium containing Ag as a main component.

According to a sixth aspect of the invention, there is provided a phase change type optical recording medium in which the film thickness of the reflection / heat dissipation layer is 90 nm or more.

In a seventh aspect of the invention, there is provided a phase change type optical recording medium in which the second protective layer is made of a mixture of ZnS and SiO2.

According to an eighth aspect of the present invention, there is provided a phase change type optical recording medium in which the thickness of the second protective layer is 3 to 20 nm.

In the invention according to claim 9, the reflection and heat dissipation layer is mainly composed of Ag, and the second protection layer is Z.
The sulfide prevention interface layer is formed of a mixture of nS and SiO2 and has a film thickness of 3 nm or more between the reflection heat dissipation layer and the second protective layer. Provided is a phase change type optical recording medium having a function of preventing sulfidation of an element forming a reflection / heat dissipation layer.

According to the tenth aspect of the invention, there is provided a phase change type optical recording medium in which the sulfuration preventing interface layer contains SiC or Si as a main component.

According to an eleventh aspect of the present invention, there is provided a phase change type optical recording medium in which the main component of the sulfidation prevention interface layer is Si.

According to the invention of claim 1, it is possible to obtain an optical recording medium excellent in the uniformity of the reflectance distribution after the initial crystallization of the phase change recording layer. According to the invention of claim 2, it is possible to obtain an optical recording medium having excellent storage reliability of amorphous marks. According to the invention of claim 3, even when the phase change recording layer having a high crystallization rate is applied, the light absorption rate of the phase change recording layer is adjusted so as to enable signal recording having a sufficient degree of modulation. A high optical recording medium can be obtained. According to the invention of claim 4, it is possible to obtain an optical recording medium in which the phase change recording layer has a high light absorptivity and excellent heat dissipation characteristics.

According to the invention of claim 5, it is possible to obtain an optical recording medium which is excellent in stability over time with respect to oxidation and whose cost is reduced. According to the invention of claim 6,
An optical recording medium with high utilization efficiency of laser light can be obtained. According to the invention of claim 7, an optical recording medium excellent in recording characteristics and storage reliability can be obtained. According to the invention of claim 8, an optical recording medium excellent in reproduction light stability can be obtained.

According to the invention of claim 9, recording can be performed with a sufficient degree of modulation even when a phase change recording layer having a high crystallization rate is used, the cost is low, and the stability with time against oxidation is excellent. It is possible to obtain an optical recording medium having excellent stability of the reflective heat dissipation layer against sulfidation. According to the invention of claim 10, even when the phase change recording layer having a high crystallization rate is used,
It is possible to obtain an optical recording medium capable of recording with a sufficient degree of modulation, particularly excellent in stability of the reflection and heat dissipation layer against sulfidation, and capable of increasing the cooling rate while keeping the light absorption rate of the recording layer high. According to the invention of claim 11, it is possible to obtain an optical recording medium capable of recording with a sufficient degree of modulation even if a phase change recording layer having a high crystallization rate is used.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Regarding the optical recording medium of the present invention,
This will be described below with reference to the drawings. The optical recording medium of the present invention is not limited to the following examples. FIG. 1 shows a schematic configuration diagram of a phase change type optical recording medium 10 of the present invention.
This optical recording medium 10 includes a substrate 2 having a predetermined guide groove.
The first protective layer 3, the phase-change recording layer 4, the second protective layer 5, the reflection / heat radiation layer 6, and the resin layer 7 are laminated on the upper surface.

As the material for forming the substrate 2, for example, glass, polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin,
Any conventionally known material such as a silicone resin, a fluororesin, a urethane resin, an ABS resin, or the like can be applied as a material for a substrate of an optical recording medium.

The first protective layer 3 is made of SiO, SiO ₂ , Z.
nO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ ,
Oxides such as MgO and ZrO ₂ , Si ₃ N ₄ , AlN, T
nitrides such as iN, BN, and ZrN, ZnS, In ₂ S ₃ ,
Sulfides such as TaS ₄ , SiC, TaC, WC, TiC,
It can be formed by using a carbide such as ZrC, diamond-like carbon, or a mixture thereof. The first protective layer 3 can be formed by sputtering, ion plating, vacuum deposition, plasma CVD or the like.

In the optical recording medium of the present invention, the composition of the phase change recording layer 4 is represented by the following [Chemical formula 3].

[0033]

Embedded image X _α Y _β Dy _γ (Sb _δ Te _1-δ ) _1-α-β-γ

(However, X is In or Ga, or In
And Ga, where Y is (Sb _δTe_1-δ) Crystals
Α, β, γ, which are one or more elements that increase the oxidization temperature
Represents the atomic ratio and is in the following range. 0.01 ≤ α ≤ 0.07 0.02 ≦ β ≦ 0.1 0.01 ≦ γ ≦ 0.07 0.65 ≦ δ ≦ 0.85)

The material for forming the phase change recording layer 4 will be considered below. S in which the molar ratio of Sb and Te is 7: 3
The alloy having a composition in the vicinity of b ₇ Te ₃ is a phase change recording material having excellent repetitive recording characteristics. The crystallization speed can be adjusted by adjusting the compounding ratio of Sb and Te, and the crystallization speed can be increased by increasing the Sb ratio.

According to the experiments by the present inventors, Sb is 65a.
If it is at least tom%, at least CD (Compact Dis
It is possible to perform signal recording at a linear velocity (1.2 m / s) of c). When Sb is less than 65 atom%,
Even at 1.2 m / s, the increase in jitter due to overwriting was large, and good recording could not be performed. Sb
The higher the ratio of, the higher the crystallization rate and the better recording was possible at a higher linear velocity.

On the other hand, when Sb exceeds 85 atom%,
The rate of increase of the crystallization speed became sharp, and it became almost impossible to form amorphous marks. Therefore, Sb and Te
The ratio of Sb in the binary system is 65 atom% or more 8
It is preferably 5 atom% or less (that is, 0.65 ≦ δ ≦ 0.85 in the above formula).

However, the stability of the amorphous phase is poor only with the Sb-Te binary system. For example, in a high temperature environment of about 70 to 80 ° C., the amorphous mark is crystallized within about 50 hours. There is a problem. Therefore, it is preferable to add one or more kinds of the third element that can increase the crystallization temperature and enhance the stability of the amorphous phase to the material for forming the phase change recording layer. However, the higher the Sb ratio, the more the storage reliability tends to deteriorate even if the third element is added. Therefore, in such a case, the Sb content ratio cannot be made too high.

Therefore, in order to form a record having a high crystallization rate which is advantageous for high-speed overwriting, it was necessary to increase the crystallization rate without increasing the Sb ratio so much. In view of the above, it was decided to add In as an element that has a high effect of improving the storage reliability and further can increase the crystallization rate. However, this I
With respect to n, too much addition causes adverse effects such as a large increase in jitter due to overwriting.
According to the experiments by the present inventors, the amount of In added is 10
It was confirmed that the increase in jitter due to overwriting can be suppressed to a low level when the content is not more than atom%.

Further, the present inventors have found that Ga is In as described in Japanese Patent Application Laid-Open No. 12-289128 filed earlier.
It has been found that the element has a great effect of increasing the crystallization rate even in a smaller amount. Further, Ga is also superior to In in terms of the effect of improving storage reliability.
However, in this case as well, it is possible to suppress the increase in jitter due to overwriting to be low when the addition amount is 10 atom% or less of the material. Moreover, the addition amount of these is 1 atom.
If it is less than%, the effect of increasing the crystallization rate of the phase change recording layer or improving the storage characteristics cannot be obtained.

From the above, a system in which Ga or In or a mixture thereof is added in an amount of 1 to 10% to an alloy SbTe system having a composition near Sb ₇ Te ₃ has a high crystallization rate and high storage reliability. It is a phase change recording material with excellent properties.

In order to increase the crystallization rate without increasing the Sb ratio, it is effective to increase the added amounts of Ga and In. However, since Ga and In have a very high effect of increasing the crystallization temperature, if the addition amount is large, the phase change recording layer 4
However, there is a drawback in that the initial crystallization is hard to occur and the reflectance distribution after the initial crystallization becomes non-uniform because the crystallization temperature becomes high. Considering such a point of initial crystallization, G
The total amount of a and In added is 7 atom% or less (that is, 0.01 ≦ α ≦ 0.07 in the above formula), and more preferably 5 atom% or less. However, if it is 5 atom% or less, the crystallization speed is limited, and it becomes difficult to form a phase change recording layer having a high erasing rate at about 5 times the DVD speed (17.5 m / s).

If the amount of Ga or In added is reduced, the storage reliability is impaired. Therefore, it is desirable to add an element that has a lower effect of raising the crystallization temperature than Ga or In and, when added to Sb-Te, raises the crystallization temperature and has the effect of improving the storage reliability.

As an element having such an effect, Ge
Is very excellent, and even if added in a small amount, storage reliability can be dramatically improved. If the amount of addition at that time is 2 atom% or more, the effect of improving the amorphous stability of the phase change recording layer having a high crystallization rate appears,
It was confirmed by experiments that the effect increases as the added amount of Ge increases.

However, if the amount of Ge added is too large,
Since this leads to deterioration in recording sensitivity and overwrite characteristics, it is necessary to set this to 10 atom% or less (0.02 ≦ β ≦ 0.1 in the above formula). However, since Ge does not have the effect of increasing the crystallization speed, it is difficult to form a phase change recording layer having a high erasing rate at about 5 times the DVD speed (17.5 m / s).

Then, the inventors of the present invention added various elements and evaluated the crystallization temperature and the recording characteristics. As a result, Dy had the effect of increasing the crystallization speed, and the amount of Ga or In added was increased to the same degree. It was found that the crystallization temperature is lower than that of the above crystallization rate, and therefore, the excellent effect can also be obtained on the uniformity of the reflectance after the initial crystallization.

If the added amount of Dy is lower than 1 atom%,
Since the effect of increasing the crystallization speed cannot be clearly obtained, 1
Add more than atom%. On the other hand, if the addition amount of Dy is too large, the recording sensitivity and the overwrite characteristic are deteriorated. Therefore, it is desirable that the content be 7 atom% or less (0.01 ≦ γ ≦ 0.07 in the above formula).

By forming the phase change recording layer 4 by using the above-mentioned materials and adjusting the composition ratio of each, the overwrite characteristics, the storage characteristics, and the ease of initial crystallization are satisfied. At the same time, the optical recording medium 10 having a crystallization rate suitable for high linear velocity recording can be obtained.

Next, the reflection / heat dissipation layer 6 will be described. In a conventional phase change type optical recording medium, an alloy containing Al as a main component is used as a material for forming a reflection / heat dissipation layer. Al is a material having a high reflectance and a high thermal conductivity, and is also excellent in stability over time when formed into a disk. When Al is used as the material for forming the reflection / heat dissipation layer 6, the first protective layer 3, the phase change recording layer 4, the second protection layer 5, and the reflection / heat dissipation layer 6 are formed on the substrate 2 by using a resin. Layer 7
As a top coat layer, an optical recording medium excellent in recording characteristics and stability over time can be formed with a simple structure in which a conventionally known resin is overcoated.

However, depending on the crystallization rate of the material forming the phase change recording layer 4, the reflective heat dissipation layer 6 may be made of Al.
In the optical recording medium to which is applied, the recording mark is likely to be thin, and it may be difficult to perform recording with sufficient modulation. The reason for this is that when the crystallization speed of the phase change recording layer 4 is high, the recrystallized region of the melted region becomes large at the time of signal recording, and the formed amorphous region becomes small. To be

In order to reduce the recrystallized region in the melted region, the film thickness of the second protective layer 5 may be made sufficiently thin to form a so-called quenching structure. However, the second protective layer 5 is simply used.
It is not possible to sufficiently raise the temperature of the phase-change recording layer 4 by only reducing the thickness of the film, and as a result, the melting region becomes small, and even if the recrystallization region can be made small. After all, the formed amorphous region becomes small.

In view of the above points, in the present invention,
By specifying the material and the film thickness of the reflective heat dissipation layer 6 and the second protective layer as described later, a configuration in which a more rapid cooling structure is considered is realized while ensuring a sufficient temperature rise of the phase change recording layer 4. . This makes it possible to produce an optical recording medium that can perform recording with sufficient modulation even if a phase change recording layer material having a high crystallization rate is applied.

In the present invention, as a material for forming the reflection / heat dissipation layer 6, a metal having a refractive index (n + ik) at wavelength λ of n of 1 or less and k of 5 or less is applied. Thereby, the light absorption rate of the phase change recording layer 4 can be improved.

In FIG. 2, the first protective layer 3 (76) is formed on the substrate 2.
nm), the phase change recording layer 4 (16 nm), the second protective layer 5
(20 nm) and a reflective heat dissipation layer 6 (140 nm) are sequentially laminated, and the absorptance of the phase change recording layer 4 (crystal phase) when the laser light having a wavelength of 660 nm is radiated from the substrate side is shown in FIG. It is the result obtained by the optical simulation when the value of the refractive index is changed to various values.

The refractive index of the sputtered film of an alloy obtained by adding 1 wt% of Ti to Al, which has been conventionally used as the material for forming the reflection / heat dissipation layer 6, is n = 1.3 and k =
It is 6.5, and the calculated absorptance of the phase change recording layer 6 in this case is 59%.

On the other hand, when n is 1 or less and k is 5 or less, the absorptance is 60% or more, and the absorptance is improved as compared with the case of using the Al alloy. The refractive index of each of the phase-change recording layer 4, the first protective layer 3, and the second protective layer 5 changes depending on what is used, so that the absorptance values shown here also change. Whichever phase change recording layer or protective layer is used, an Al alloy is used by using a metal having a refractive index (n + ik) at wavelength λ of n of 1 or less and k of 5 or less as the reflection / heat dissipation layer 6. The absorptance of the phase change recording layer is improved as compared with the case where it is present.

Metals satisfying the above conditions include Au,
Examples thereof include Ag, Cu and alloys containing them as main elements. Table 1 shows the measured values of the refractive index of the sputtered film at λ = 660 nm and the literature values (bulk) of the thermal conductivity in the case of these pure metals.

[0058]

[Table 1]

As shown in Table 1 above, Au, Ag, Cu
At the same time, both have higher thermal conductivity than Al. Therefore, when these are used as the material for forming the reflection / heat dissipation layer 6, the light absorption rate of the phase change recording layer 4 is improved, the temperature of the phase change recording layer 4 is increased, and the melted region is enlarged. Since the cooling rate is also improved, the recrystallized region at the time of cooling becomes small, and it becomes possible to form a larger amorphous region than when an Al alloy is used.

Further, the degree of modulation is obtained from an optical simulation of the reflectance when the phase change recording layer 4 is in the crystalline phase and in the case of the amorphous phase, and the relation between n and the degree of modulation of the reflective heat radiating layer is k = 0. 3 for each case
It was shown to. As shown in FIG. 3, it can be seen that when the material having n of 1 or less and k of 5 or less is used as the reflection / heat dissipation layer 6, the optical modulation degree is simply larger than that of the case of using the Al alloy. The modulation degree of the recording mark is determined by the optical modulation degree and the size of the mark, and the optical modulation degree is large.
The larger the mark, the larger the mark. Therefore, the phase change recording layer 4
As a result, even when high linear velocity recording is performed using a material having a high crystallization rate, a large recording mark can be formed due to a large absorptivity and a high cooling rate when the above-mentioned reflective heat dissipation layer is used. Since the difference in reflectance is large, recording with a large degree of modulation becomes possible.

Among the above-mentioned three kinds of metals and alloys containing them as the main elements, Ag and Ag alloys are relatively inexpensive, and similarly, inexpensive Cu and C are also used.
Since it is less likely to be oxidized than the u alloy, it is possible to form an optical recording medium excellent in stability over time, and it is suitable as a material for forming a reflection / heat dissipation layer. However, since these are easily sulphurized, particularly when S is contained as a material for forming the second protective layer 5, a function of preventing sulphidation is provided between the reflection heat dissipation layer 6 and the second protective layer 5. It is necessary to form a so-called sulfidation preventive interface layer (not shown) having

FIG. 4 shows calculated values of reflectance and transmittance in an optical recording medium in which Ag is used as the reflection / heat dissipation layer 6 and the film thickness is changed. It can be seen from FIG. 4 that if the film thickness of the reflection / heat dissipation layer 6 is 90 nm or more, the transmittance is 1% or less, so that the laser light can be efficiently used.

Next, the second protective layer 5 will be described in detail. The second protective layer 4 is a phase change recording that prevents the phase change recording layer 4 that repeatedly melts and solidifies from changing its film thickness due to flow or the like, or from changing the film quality due to some reaction. In addition to the role of protecting the layer 4, it plays a role of increasing the temperature of the phase change recording layer 4 by delaying the time for releasing the heat absorbed by the phase change recording layer 4 to the reflection heat dissipation layer 6.

Therefore, the second protective layer 5 has heat resistance,
The property of low thermal conductivity is required. Various oxide films, nitride films, sulfide films, etc. have been proposed as materials having such properties, and as well-known materials,
There is a mixture of ZnS and SiO _{2 with} a molar ratio of around 8: 2.

We have used several types of protective layers.
Form an optical recording medium and check the recording and storage characteristics.
It was As a result, in terms of recording characteristics, ZnS and SiO_Two
There were some membranes that were superior to the mixture of
In terms of properties, ZnS and SiO _TwoA mixture of
The stability of the fass mark was excellent. ZnS and SiO_Two
The mixture of a.
It is thought that this is because it has an advantageous effect on the stabilization of the worm. Obey
As the second protective layer 5, ZnS and SiO_TwoA mixture of
It is desirable to apply the thing.

If the second protective layer 5 is too thin, the temperature of the phase-change recording layer 4 will be insufficiently heated, and a mark of a sufficient size cannot be formed. Further, if it is too thick, the cooling rate becomes insufficient and the recrystallized region becomes large, so that a mark having a sufficient size cannot be formed. When the phase change recording layer having a relatively low crystallization rate is used, if the second protective layer 5 is thickened, the jitter of the first recording is good and the modulation degree is large. However, since the temperature rises too much, film deterioration due to overwriting tends to proceed. In addition, the temperature of the reproducing light also increases significantly, and the stability of the reproducing light is poor.

The reflective heat dissipation layer 6 has a refractive index (n + ik)
When n of 1 or less and k of 5 or less are used, the light absorption rate of the phase change recording layer 4 becomes large, so that the conventional A
When recording is performed under the same recording power and linear velocity as when the 1 alloy is used, the optimum film thickness of the second protective layer 5 is thinner than when the Al alloy is used. When the film thickness of the second protective layer 5 becomes thin, the cooling rate becomes fast, so that the recrystallization region can be made small, which is more advantageous when a phase change recording layer material having a fast crystallization rate is used. Become. The optimum film thickness of the second protective layer 5 varies depending on the recording conditions, the material used for the interface layer, the film thickness, etc., but the wavelength is 660 nm.
N. A. With a pickup head of 0.6, 0.7 mW,
Considering the reproduction light stability when reproducing at 3.5 m / s, when Ag is used for the reflection / heat dissipation layer 6, the thickness is preferably 20 nm or less.

However, when Ag or an Ag alloy is used as the reflection / heat dissipation layer 6, when S is contained in the second protective layer 5 like a mixture of ZnS and SiO ₂ , Ag is sulfided to cause defects. Will occur. Therefore, it is preferable to provide a so-called sulfidation prevention interface layer (not shown) having a sulfidation prevention function between the reflection / heat dissipation layer 6 and the second protective layer 5. If the sulfidation-preventing interface layer has a thickness of 3 nm or more, the film formed by sputtering will be substantially uniform and exert a sulfidation-preventing function. If the thickness is less than 3 nm, the probability of partially causing defects suddenly increases.

Properties required for the material of the sulfidation preventing interface layer include that S is not contained and that S is not permeated. The present inventors formed various oxide films, nitride films, etc. as interface layers and evaluated recording characteristics and storage reliability, and found that SiC and Si have excellent functions as interface layers for preventing sulfidation. I understood.

In Table 2 below, SiC, Si and ZnS-
The measured value of the refractive index of the sputtered film of SiO ₂ and the literature value (bulk) of the thermal conductivity are shown. SiC and Si are ZnS
It can be seen that the thermal conductivity is higher than that of —SiO ₂ by one digit or more.

[0071]

[Table 2]

FIG. 5 shows the result of an optical simulation of the change in the absorptance of the phase-change recording layer 4 (crystal) when the film thickness of the sulfurization preventing interface layer is changed. For comparison,
The results are shown on the assumption that ZnS-SiO ₂ is formed on the second protective layer 5 in the same manner as the sulfidation prevention interface layer.

On the substrate 2, the first protective layer 3 (76n
m), phase change recording layer 4 (16 nm), second protective layer 5
(10 nm), a sulfidation prevention interface layer (2 to 20 nm), and a reflection and heat dissipation layer 6 (140 nm) are sequentially laminated, and the results are obtained when laser light having a wavelength of 660 nm is incident from the substrate 2 side. As shown in FIG. 5, SiC is ZnS-
The result is almost the same as that of SiO _2, and in the range up to 20 nm, Si has a higher absorptance with the same film thickness. When SiC or Si is used for the sulfidation prevention interface layer, the phase change recording layer has a higher thermal conductivity than the case where ZnS—SiO ₂ which is the second protective layer 5 is simply formed to have a similar thickness. The quenching structure can be achieved while maintaining the absorptivity of No. 4, and since Si has a higher absorptivity even if the film thickness is thinner, the phase change recording layer 4 can be sufficiently heated and the quenching structure can be obtained. Is advantageous to

The optical recording medium of the present invention will be described below with reference to specific examples. In any of the following examples, in each case, the first protective layer 3, the phase change recording layer 4, and the first protective layer 3, the phase change recording layer 4, on the polycarbonate disk substrate 2 with a guide groove having a diameter of 12 cm, a thickness of 0.6 mm and a track pitch of 0.74 μm. The second protective layer 5, (sulfidation-preventing interface layer), and the reflection heat dissipation layer 6 are sequentially formed by sputtering, and further, a diameter of 12 cm is provided through an organic protection film formed by spin coating on the reflection heat dissipation layer 6. A polycarbonate disc having a thickness of 0.6 mm adhered was initially crystallized by a large-diameter laser beam and used as a sample. Recording and reproduction are performed by irradiating a laser beam having a wavelength of 660 nm from the substrate side.

Example 1 As the first protective layer 3, (Z
nS) 80 mol% (SiO ₂ ) 20 mol% to 76 n
m, Ga ₃ Ge ₅ Dy ₃ Sb ₇₁ as the phase change recording layer 4
Te ₁₈ of 16 nm is used as the second protective layer 5 (ZnS).
80 mol% (SiO ₂ ) 20 mol% 20 nm, Al-1wt% Ti alloy 140 nm as the reflective heat dissipation layer 6
The disk on which was deposited was initially crystallized.

When the initial crystallization was carried out using a laser having a diameter of 1 μm × 100 μm under conditions of a feed of 36 μm and a linear velocity of 3 m / s, the power at which the reflectance was saturated after the initial crystallization was examined and found to be 780 mW. there were. Under this condition, the reflectance distribution was almost uniform. This phase-change recording layer 4 is about 18 m / s when the continuous light power applied is 9 mW and the value of the transition linear velocity evaluated by the present inventors as a substitute characteristic of the crystallization speed is equivalent to DVD5X. The composition has a high crystallization rate and is considered to be suitable for recording. The linear velocity of transition is the recording layer when the linear velocity is low when the rotational speed of the disc is changed and the reflectance is monitored by irradiating continuous light of power on the disc with a pickup head for recording. However, once melted, all the crystals are recrystallized, so that the reflectance is high, and when the linear velocity is high, the cooling rate is also high, so that the melted phase change recording layer 4 cannot be completely recrystallized and some amorphous remains and the reflectance remains. Is low, and is the linear velocity at the boundary between high reflectance and low reflectance at this time. The faster the transition linear velocity,
The crystallization rate can be regarded as fast.

A linear velocity of 17.5 m / s, a recording power of 17 mW, a bias power of 0.2 mW, and an erasing power of 8.
Recording of a 3T single pattern was performed at 5 mW and a linear density of 0.53 μm / bit.
It was stored for 00 hours and examined for changes in jitter and modulation.
The jitter was increased by about 1%, and the change in modulation was about 2%, showing good storage characteristics.

[Comparative Example 1] Ga ₆ G was added to the phase-change recording layer 4.
Initial crystallization and storage characteristics were examined using a disk having the same layer structure as in [Example 1] except that e ₅ Sb ₇₁ Te ₁₈ was used. This phase change recording layer has a transition linear velocity substantially equal to that of [Example 1], and the crystallization rate is set to [Example 1] by increasing the amount of Ga without using Dy. It's just as fast. When the feeding and the linear velocity were made the same as in [Example 1] and the power at which the reflectance was saturated was examined, it was 860 mW. At this time, the reflectance distribution had a maximum difference of about 2% in terms of reflectance difference. It is considered that this is because the output of the laser became high and the beam profile varied, and this was reflected in the reflectance distribution. If the reflectance distribution varies, it becomes noise, and it is difficult to reduce the jitter. Therefore, in order to make the reflectance distribution uniform, it is necessary to further lower the power during the initial crystallization, and for that purpose, it is necessary to take measures such as slowing the linear velocity. If the linear velocity is slow, it takes time to initialize and the manufacturing efficiency is lowered, which is not preferable. Regarding the storage characteristics, the same test as in [Example 1] was conducted, but there was no particular problem in practical use.

[Comparative Example 2] Ga ₃ Ge ₅ was used for the phase change recording layer.
Initial crystallization and storage characteristics were examined using an optical disc having the same layer structure as in [Example 1] except that Sb ₇₉ Te ₁₃ was used. This phase change recording layer has a transition linear velocity substantially equal to that of [Example 1], and the crystallization rate is set to [Example 1] by increasing the amount of Sb without using Dy. It's just as fast.
When the feed and linear velocity were made the same as in [Example 1] and the power at which the reflectance was saturated was examined, it was 740 mW, and the uniformity of the reflectance at this time was almost uniform, and there was no problem in initialization. However, when the storage characteristics were tested in the same manner as in [Example 1], it was found that after 1000 hours of storage, the amorphous part was crystallized to such an extent that jitter could not be measured, and there was a problem in practical use. .

[Examples 2 to 5] and [Comparative Examples 3 to 6] Table 3 below shows the conditions of the optical recording media of [Examples 2 to 5] and [Comparative Examples 3 to 6] having different layer structures. Indicated. In all of these cases, the first protective layer 3 is (ZnS)
80 mol% (SiO ₂ ) 20 mol% is 76 nm, and the phase change recording layer is Ga ₃ Ge ₅ Dy ₃ Sb ₇₁ Te ₁₈ 1
6 nm, and the second protective layer material is (ZnS)
20 mol% of 80 mol% (SiO ₂ ) was used, and the film thickness of the reflective heat dissipation layer 6 was 140 nm. Further, these are initially crystallized under the condition that the reflectance is saturated. Recording characteristics with the items shown in Table 3 below as parameters, and
The storage characteristics were evaluated. Recording characteristics are evaluated at wavelength 6
60 nm, N.W. A. A 0.65 pickup head was used to record a random pattern by an EFM + modulation method with a linear density of 0.267 μm / bit. Record linear velocity 1
The recording strategy was optimized for each disk at 7.5 m / s, recording power 18 mW, bias power 0.2 mW, and erasing power 8.5 mW. All reproduction was performed at a linear velocity of 3.5 m / s and a power of 0.7 mW.

[0081]

[Table 3]

FIGS. 6 and 7 show the jitter and the change in the modulation degree due to the overwriting of [Examples 2 to 5] and [Comparative Examples 3 to 4] described above. In any of Examples 2 to 5, it can be seen that the jitter up to the 1000th overwrite is 11% or less, and the modulation degree is 60% or more, showing good recording characteristics.

Comparative Example 3 is an example in which Al is used for the second protective layer 5 and the second protective layer is also relatively thick as 20 nm, but the modulation degree is small and the jitter is 11% or less. I couldn't. This is because the phase change recording layer 4 is made of a material having a high crystallization rate, and thus the recrystallized region is large.

In Comparative Example 4, when Al is used for the reflection / heat dissipation layer 6, the second protective layer 5 is thinned to have a rapid cooling structure for the purpose of reducing the recrystallized region. The degree of modulation was smaller than that of Comparative Example 3, and the jitter was worse. If the second protective layer 5 is simply thinned to have a rapid cooling structure, a large mark cannot be formed because the temperature rise of the phase change recording layer 4 is insufficient and the melting region is small.

The storage characteristics are 1 at 70 ° C. and 85% RH.
Changes in jitter and modulation after storage for 000 hours were examined. In each of Examples 2 to 5 and Comparative Examples 3 to 4, the increase in jitter was 1% or less in the first recording and 2% or less even in the 1000 times of overwriting, as compared with before the storage.
The change in modulation was within 2% in all cases, indicating good storage characteristics. Further, in any case, no disc defect occurred.

In Comparative Examples 5 and 6, although the thickness of the sulfidation-preventing interface layer was thin, only the occurrence of defects due to storage of the initially crystallized disk was examined. In both cases, after storage in an environment of 70 ° C. and 85% RH for 1000 hours, dot-like defects that could be visually recognized appeared in a part of the disk. It is considered that this is because the thickness of the sulfidation-preventing interface layer is partially thinned due to the film thickness distribution inside the disk, and the Ag reflection / heat dissipation layer in the thinned portion appears to be a defect due to sulfidation. To be

[0087]

According to the invention of claim 1, an optical recording medium having a high crystallization rate and excellent uniformity of reflectance after the initial crystallization can be obtained. According to the invention of claim 2, an optical recording medium having a high crystallization rate, excellent uniformity of reflectance after initial crystallization, and excellent storage reliability of amorphous marks was obtained. According to the invention of claim 3,
An optical recording medium having a high light absorption coefficient of the phase change recording layer was obtained. According to the invention of claim 4, an optical recording medium having excellent heat dissipation characteristics is obtained. According to the invention of claim 5, an optical recording medium having a high light absorptivity, a high heat dissipation property, a low cost, and an excellent stability over time against oxidation can be obtained. According to the invention of claim 6, an optical recording medium having high light utilization efficiency is obtained. According to the invention of claim 7, an optical recording medium having excellent recording characteristics and storage reliability can be obtained. According to the invention of claim 8, an optical recording medium excellent in reproduction light stability was obtained. According to the invention of claim 9, it is possible to record with a sufficient degree of modulation even when a phase change recording layer having a high crystallization rate is used, the cost is low, and the optical recording medium is excellent in stability with time against oxidation. Thus, an optical recording medium excellent in stability of the reflection / heat dissipation layer against sulfidation was obtained. According to the invention of claim 10, recording can be performed with a sufficient degree of modulation even when a phase change recording layer having a high crystallization rate is used, and the stability of the reflection heat dissipation layer against sulfidation is particularly excellent. An optical recording medium capable of increasing the cooling rate while maintaining a high light absorption rate was obtained. According to the invention of claim 11, it is more advantageous to increase the cooling rate while keeping the light absorption rate of the phase change recording layer high. Therefore, the phase change recording layer having a higher crystallization rate is used. Thus, an optical recording medium capable of recording with a sufficient degree of modulation was obtained. Provided.

[Brief description of drawings]

FIG. 1 shows a schematic configuration diagram of an example of an optical recording medium of the present invention.

FIG. 2 shows the relationship between the refractive index of the reflective heat dissipation layer and the light absorption rate of the phase change recording layer.

FIG. 3 shows the relationship between the refractive index and the degree of modulation of the reflective heat dissipation layer.

FIG. 4 shows the relationship between the film thickness of the reflection / heat dissipation layer and the reflectance (transmittance).

FIG. 5 shows the relationship between the film thickness of the sulfidation prevention interface layer and the light absorptance of the phase change recording layer.

FIG. 6 shows the relationship between the number of recordings and jitter.

FIG. 7 shows the relationship between the number of recordings and the degree of modulation.

[Explanation of symbols]

2 substrates 3 First protective layer 4 Phase change recording layer 5 Second protective layer 6 Reflective heat dissipation layer 7 resin layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hajime Jyohara             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Hiroko Tashiro             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Yuji Miura             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Mizutani Mirai             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh (72) Inventor Mikiko Abe             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F term (reference) 2H111 EA04 EA12 EA23 FA12 FA14                       FA23 FA25 FA27 FA29 FB05                       FB09 FB12 FB16 FB21 FB30                 5D029 JA01 LA14 LA15 LA17 LB07                       MA27 NA13

Claims (11)

[Claims] 1. At least a first protective layer, a phase, on a substrate.
A change recording layer, a second protective layer, and a reflective heat dissipation layer are formed.
Be Irradiate laser light of wavelength λ from the side of the first protective layer formation surface.
Then, the amorphous phase and the crystalline phase of the phase change recording layer are reversible.
Recording medium that records and reproduces signals using various phase changes
And The composition of the phase change recording layer is represented by the following [Chemical formula 1].
An optical recording medium characterized by: [Chemical 1] X_αY_βDy_γ(Sb_δTe_1-δ)_1-α-β-γ (However, X is In or Ga, or a mixture of In and Ga.
And Y is (Sb _δTe_1-δ) Higher crystallization temperature
One or more elements that
It is expressed in the following range. 0.01 ≤ α ≤ 0.07 0.02 ≦ β ≦ 0.1 0.01 ≦ γ ≦ 0.07 0.65 ≦ δ ≦ 0.85) 2. The optical recording medium according to claim 1, wherein the phase change recording layer contains at least Ge. 3. The optical recording medium according to claim 1, wherein the reflection / heat dissipation layer is made of a metal having a refractive index (n + ik) at wavelength λ of n of 1 or less and k of 5 or less. 4. The optical recording medium according to claim 3, wherein the reflection / heat dissipation layer contains at least one of Ag, Au, and Cu as a main component. 5. The optical recording medium according to claim 3, wherein the reflection / heat dissipation layer contains Ag as a main component. 6. The optical recording medium according to claim 3, wherein the thickness of the reflection / heat dissipation layer is 90 nm or more. 7. The second protective layer comprises ZnS and SiO ₂
The optical recording medium according to claim 1, comprising a mixture thereof with. 8. The film thickness of the second protective layer is 3 to 20 n.
The optical recording medium according to claim 3, wherein the optical recording medium is m. 9. The reflection and heat dissipation layer contains Ag as a main component,
The second protective layer is made of a mixture of ZnS and SiO _2, and a sulfuration prevention interface layer has a film thickness of 3 between the reflective heat dissipation layer and the second protective layer.
4. The optical recording medium according to claim 3, wherein the optical recording medium is formed to have a thickness of at least 1 nm, and the sulfurization preventing interface layer has a function of preventing sulfuration of an element forming the reflection and heat dissipation layer. 10. The optical recording medium according to claim 9, wherein the sulfidation prevention interface layer is mainly composed of SiC or Si. 11. The main component of the sulfurization preventing interface layer is Si
An optical recording medium characterized by: