JP2003237237A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium which realizes recording of image data with a sufficient degree of modulation, even when a phase change recording layer at a high crystallization rate is formed. <P>SOLUTION: This optical recording medium has a first protecting layer 3, a phase change recording layer 4, a second protecting layer 5 and a reflective heat-radiating layer 6 formed on a substrate 2 by lamination. In addition, the medium records and regenerates image data using a reversible phase change between an amorphous phase and a crystalline phase of the phase change recording layer 4 under an exposure of a laser beam with a wavelength of λ from the area side where the, first protecting layer 3 is formed. The composition of the phase change recording layer 4 is such that In or Ga, or a mixture of In and Ga and at least one kind of element for setting the crystallization temperature of an SbTe alloy higher are added to the SbTe alloy. Further, the reflective heat-radiating layer 6 is composed of a metal whose index of refraction (n+ik) at the wavelength of λ shows that n is 1 or less and k is 5 or less. <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 Conventional phase change type optical recording media are disclosed in Japanese Patent Application Laid-Open Nos. 2000-79761 and 2000-2000.
No. 313170, No. 11-238253, No. 7-161071, and No. 2000-1.
It is disclosed in Japanese Patent No. 82277.

In Japanese Patent Laid-Open No. 2000-97761, the composition of the recording layer is XαGaβMχSbδTeε, (X: A
g, Au, Pd, Zn), (M: Sn, Ge, Si, P
d), (0.0 ≦ α ≦ 0.1, 0.01 ≦ χ ≦ 0.1
5, 0.03 ≤ β + χ ≤ 0.25) is disclosed.

Japanese Patent Laid-Open No. 2000-313170 discloses that
The composition of the recording layer is ((Sb _x Te _{1 -x} ) _y G
e _1-y ) _z M _1-z , (M: In, Ga), (0.7
There is disclosed an optical recording medium in which ≦ x ≦ 0.9, 0.8 ≦ y ≦ 1, 0.88 ≦ z ≦ 1).

Further, in Japanese Patent Laid-Open No. 11-238253, an intermediate layer is provided between a reflective layer made of Ag and an upper protective layer containing S, and the composition of the intermediate layer is T on the reflective layer side.
a, Ni, Co, Cr, Si, W, V is contained, and the protective layer side is Al, Si,
Ge, Ta, becomes Ni, Co, Cr, W, a material containing at least one and V, the composition of the recording layer, _{M y}
(Sb _x Te _1-x ) _{1 −y} (0.5 ≦ x ≦ 0.9, 0
≦ y ≦ 0.3), (M: In, Zn, Ge, Sn, S
i, Cu, Au, Ag, Pd, Pt, Pb, Cr, C
o, O, N, S, Se, Ta, Nb, V, Bi, Zr,
The optical recording medium is disclosed as being Ti, Mn, Mo, Rh, rare earth).

Japanese Unexamined Patent Publication No. 7-161071 discloses an optical recording medium having a structure of substrate / dielectric layer / recording layer / dielectric layer / high refractive index layer / light absorbing layer, which is a high refractive index layer. Is made of at least one of Ge, Si and GeSi, and the light absorption layer is made of Ti, Zr, Hf, Cr, Ta, Mo,
Mn, W, Nb, Rh, NiCr alloy, FeCr alloy,
A Monel alloy having at least one of the constitutions is disclosed.

Japanese Unexamined Patent Publication No. 2000-182277 discloses an optical recording medium comprising a substrate / dielectric layer / recording layer / absorption amount correction layer / reflection layer, wherein the absorption amount correction layer is Si,
It consists of a compound of one or more of Ge and one or more of Ti, Zr, W, Cr and Mo, and n and k of the absorption correction layer are:
2 ≦ n ≦ 5.5, 1 ≦ k ≦ 4, and the recording layer is Sb and T
It is disclosed that the phase change recording layer including e and a boundary layer containing no sulfide is formed on one side or both sides of the phase change recording layer.

The optical recording media described in JP 2000-79761 A and JP 2000-313170 A have an Sb ₇₀ Te ₃₀ eutectic composition.
Ga, Ge and the like are added to b-Te for the purpose of improving stability over time. The recording linear velocity is about 6 times that of a CD (7.2
˜8.4 m / s), and the recording density is assumed to be about CD.

On the other hand, in recent years, it has a recording density equal to or higher than that of DVD, and is five times as high as DVD (17.5 m /
s) There is a demand for an optical recording medium that achieves good recording characteristics at a high linear velocity up to a considerable extent.

The optical recording medium described in Japanese Patent Laid-Open No. 11-238253 has a wide range of linear velocities, specifically C
2-4 times faster than D (2.4-5.6 m / s), 1 for DVD
In order to enable recording at a double speed (3.5 to 7 m / s), Ag is used for the reflective layer, and an intermediate layer is provided to improve the storage stability at this time. In addition, it is said that the linear velocity dependence can be improved by making the upper protective layer as thick as 30 to 60 nm and combining a reflective film (Ag) having high thermal conductivity, instead of using a quenching structure as the layer structure.

On the other hand, in the future, there is a demand for an optical recording medium capable of good recording by maintaining a sufficient temperature rise of the recording layer and having a more rapid cooling structure.

Further, in Japanese Patent Laid-Open Nos. 7-161071 and 2000-182277, the difference in absorptance when the recording layer is crystalline and amorphous is reduced to reduce mark distortion at the time of overwriting. A Si layer or the like is provided on the upper part of the recording layer as an absorptance correction, and in order to obtain an absorptance correction effect, the film thickness is 20 to 50 nm (Japanese Patent Laid-Open No. Hei 7 (1999) -58242)
-161071), 20 to 100 nm (JP-A-20
No. 00-182277), an optical recording medium formed relatively thickly is disclosed. Similarly, while maintaining a sufficient temperature rise of the recording layer, a more rapid cooling structure is more preferable. It is desired to make a good record.

[0013]

In view of the above points,
It is desired to provide an optical recording medium having a recording density equal to or higher than that of a DVD and suitable for high linear velocity recording up to about 5 times the DVD speed (17.5 m / s).

Further, for an optical recording medium capable of recording, reproducing and erasing information by irradiation with a semiconductor laser beam, a magneto-optical recording system in which magnetization is reversed to record and erase, and a reversible phase of crystalline and amorphous. There is a phase change recording method that uses changes to record and erase. The latter is capable of overwriting with a single beam and is characterized by a simpler optical system on the drive side, and is applied as an optical recording medium for computers and audiovisual.

In the phase-change type optical recording medium, the recording layer is heated by irradiating the recording layer thin film on the substrate with a laser beam, and the reflectance is changed by changing the phase of the recording layer structure between crystalline and amorphous. The information is changed and recorded and erased. Normally, the recorded state is an amorphous phase and the erased state is a crystalline phase.

In a region where recording (change from crystal to amorphous) is desired, high power laser light is irradiated to heat the recording layer to the melting point or higher. The heated recording layer is melted and then cooled with a certain temperature profile as the laser beam passes. By making this cooling rate equal to or higher than the crystallization rate of the phase change recording layer material, the phase change recording layer becomes amorphous.

On the other hand, in a region to be erased (changed from amorphous to crystalline), a laser beam with an intermediate power is irradiated and the temperature is kept above the temperature at which 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.

As the recording layer material, a material centering on chalcogenide is used because it tends to form an amorphous material and composition segregation hardly occurs even after repeated recording. GeT has been put to practical use.
There is a system in which Ag or In is added to a composition near Sb ₇ Te _{3 in} which the molar ratio of Sb to Te is 7: 3, and a mixture of e and Sb ₂ Te ₃ . In particular, the latter is known as a material having a high crystal growth rate, the amorphous portion has a clear outline, and is suitable for high density and high linear velocity recording.

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

However, if a recording layer having a high crystallization rate is used, the recording mark tends to be thin, and it is difficult to perform recording with a sufficient degree of modulation. If the degree of modulation is small, 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 recording due to the high crystallization speed, and the formed amorphous region becomes small. In order to reduce the recrystallized region, the upper protective layer may be thinned to have a rapid cooling structure. However, if the upper protective layer is simply thinned, heat may be easily lost by the rapid cooling, and the recording layer of the recording layer may be removed. Since the absorptivity also decreases, the recording layer is not sufficiently heated and the melted region becomes smaller, and even if the recrystallized region can be made smaller, the amorphous region that is formed will eventually become smaller and a sufficient degree of modulation will be obtained. Recording cannot be performed.

In view of the above problems, the present invention provides an optical recording medium capable of recording with a sufficient degree of modulation even when a phase change recording layer having a high crystallization rate is used. And

[0022]

According to a first aspect of the invention, at least a first protective layer, a phase change recording layer, a second protective layer, and a reflective heat dissipation layer are laminated on a substrate, An optical recording medium for performing recording and reproduction by irradiating a laser beam having a wavelength λ from the first protective layer forming surface side and utilizing reversible phase change between an amorphous phase and a crystalline phase of the phase change recording layer. The composition of the phase-change recording layer is represented by the following [Chemical formula 2], and the reflection heat dissipation layer has a refractive index (n
There is provided an optical recording medium made of a metal in which n of + ik) is 1 or less and k is 5 or less.

[0023]

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

However, X is In or Ga, or I
n is a mixture of Ga and Y is (Sb _γ Te _1-γ ).
Is one or more elements that increase the crystallization temperature of
β and γ represent atomic ratios and are in the following numerical range. 0.01 ≦ α ≦ 0.1 0 ≦ β ≦ 0.1 0.65 ≦ γ ≦ 0.85

According to a second aspect of the present invention, there is provided an optical recording medium having a reflection and heat dissipation layer mainly composed of at least one of Ag, Au and Cu.

According to a third aspect of the present invention, there is provided an optical recording medium having a reflection and heat dissipation layer mainly composed of Ag.

According to a fourth aspect of the present invention, there is provided an optical recording medium having a structure in which the thickness of the reflection / heat dissipation layer is 90 nm or more.

According to a fifth aspect of the invention, there is provided an optical recording medium having a structure in which the second protective layer is made of a mixture of ZnS and SiO ₂ .

According to a sixth aspect of the invention, there is provided an optical recording medium having a structure in which the film thickness of the second protective layer is 3 to 20 nm.

In the invention according to claim 7, the reflection and heat dissipation layer is mainly composed of Ag, and the second protection layer is Zn.
A mixture of S and SiO ₂ is formed, and a sulfuration prevention interface layer having a function of preventing sulfurization of the reflection heat dissipation layer is formed between the reflection heat dissipation layer and the second protective layer in a thickness of 3 nm or more. An optical recording medium having the above structure is provided.

According to an eighth aspect of the present invention, there is provided an optical recording medium in which the sulfidation-preventing interface layer is mainly composed of SiC.

According to a ninth aspect of the present invention, there is provided an optical recording medium in which the sulfidation prevention interface layer contains Si as a main component.

According to a tenth aspect of the invention, there is provided an optical recording medium having a structure in which the phase change recording layer contains at least Ge.

According to an eleventh aspect of the invention, there is provided an optical recording medium having a structure in which the phase change recording layer contains at least Ag.

According to the invention of claim 1, it is possible to obtain an optical recording medium capable of recording with a sufficient degree of modulation even when a phase change recording layer having a high crystallization rate is used. Claim 2
According to the invention of (1), it is possible to obtain an optical recording medium having a high light absorptance of the recording layer and having high heat dissipation characteristics. According to the invention of claim 3, it is possible to obtain an optical recording medium which is low in cost and excellent in stability with time against oxidation. According to the invention of claim 4, an optical recording medium with high light utilization efficiency can be obtained. According to the invention of claim 5, an optical recording medium excellent in recording characteristics and storage reliability can be obtained. According to the invention of claim 6, an optical recording medium having excellent reproduction light stability can be obtained.

According to the invention of claim 7, 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. An optical recording medium that is excellent in stability of the reflection / heat dissipation layer against sulfidation can be obtained. According to the invention of claim 8, it is possible to perform recording 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 sulfuration is particularly excellent. It is possible to obtain an optical recording medium in which the cooling rate can be increased while maintaining the high light absorption rate. According to the invention of claim 9,
Since it is even more advantageous to increase the cooling rate while keeping the light absorption of the phase change recording layer high, it is possible to record with sufficient modulation even if a phase change recording layer with a faster crystallization rate is used. An optical recording medium can be obtained. According to the invention of claim 10, it is possible to obtain an optical recording medium in which the storage reliability of the amorphous mark of the phase change recording layer composition is improved. According to the invention of claim 11, an optical recording medium having excellent uniformity of reflectance after initial crystallization can be obtained.

[0037]

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 for protecting the surface 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].

[0041]

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

However, X is In or Ga, or I
n is a mixture of Ga and Y is (Sb _γ Te _1-γ ).
Is one or more elements that increase the crystallization temperature of
β and γ represent atomic ratios and are in the following ranges. 0.01 ≦ α ≦ 0.1 0 ≦ β ≦ 0.1 0.65 ≦ γ ≦ 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 ≦ γ ≦ 0.85 in the above formula).

However, the stability of the amorphous phase is poor with only 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 was set to 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%.

Furthermore, the present inventors have found that Ga is In as shown in Japanese Patent Application Laid-Open No. 12-289128.
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.
%, The effects of increasing the crystallization rate of the phase change recording layer and improving the storage characteristics cannot be obtained (from the above, 0.01 ≦ α ≦ 0.
1).

From the above, from the alloy Sb ₇ Te ₃ alloy composition SbTe containing about 1 to 10% of Ga or In, or a mixture thereof, the crystallization rate is high and the storage reliability is high. It is a phase change recording material with excellent properties.

Further, by adding Ge or Ag to the above phase change recording material, the characteristics can be further improved. Both Ge and Ag have the effect of increasing the crystallization temperature of the phase change recording material, and contribute to the improvement of storage reliability of the optical recording medium. Ge is particularly effective for improving storage reliability. On the other hand, Ag has the effect of facilitating the initial crystallization of the phase change recording material. In addition to Ge and Ag, the above phase change recording materials include Mg, Al, Si, Ca and C.
You may add r, Mn, Cu, Zn, Se, Sn, Dy, Bi etc. as needed. Each of these elements has the effect of increasing the crystallization temperature of the phase change recording material and contributing to the improvement of storage reliability. In addition to this effect, the crystallization speed is increased and the initial crystallinity is increased. It has the effect of facilitating conversion.

However, X-Sb-Te (X: Ga
Or In, or a mixture thereof) G added
If the addition amount of e or Ag is too large, the recording sensitivity and the overwrite characteristic are deteriorated.
It is necessary that m% or less (where 0 ≦ β ≦
0.1).

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, in the optical recording medium in which the phase change recording layer 4 is formed of a material having a high crystallization rate and Al is used as the reflection / heat dissipation layer 6, the recording mark is likely to be thin, and recording with sufficient modulation is performed. Things could be difficult. 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, but the second protective layer 5 is simply used.
If only the thickness of the film is thinned, the heat is easily removed by the rapid cooling and the absorptivity of the phase change recording layer is also reduced.
The phase change recording layer 4 cannot be heated sufficiently and, as a result, the melted region becomes small, and even if the recrystallized region can be made small, the formed amorphous region is small in the end. There is a drawback that

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 light absorption rate of the phase change recording layer 4 (crystal phase) when the substrate side is irradiated with laser light having a wavelength of 660 nm is shown in FIG. It is a result obtained by optical simulation when the value of the refractive index of 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 value of the light absorption rate 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 light absorptivity 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, the wavelength λ
By using a metal having a refractive index (n + ik) of n of 1 or less and k of 5 or less, the light absorptivity of the phase change recording layer is improved as compared with the case of using an Al alloy.

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.

[0062]

[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 k is 0 for the relationship between n and the degree of modulation of the reflective heat dissipation layer. 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 are less likely to oxidize as compared with similarly inexpensive Cu and Cu alloys. It is possible to form an optical recording medium having excellent stability over time and is suitable as a material for forming a reflection / heat dissipation layer. However, since these are easily sulfided,
In particular, when S is contained as a material for forming the second protective layer 5, in order to prevent sulfuration of the reflective heat dissipation layer, the sulfuration is prevented between the reflective heat dissipation layer 6 and the second protective layer 5. It is effective to form a so-called sulfidation prevention interface layer (not shown) having the function of

FIG. 4 shows the calculated values of the reflectance and the transmittance of the irradiation laser beam in the optical recording medium manufactured by using Ag as the reflection / heat dissipation layer 6 and changing the film thickness. It can be seen from FIG. 4 that when 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 5 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,
It is required to have the property of low thermal conductivity. Various oxide films, nitride films, and sulfide films have been proposed as materials having such properties, and well-known materials include ZnS and SiO with a molar ratio of about 8: 2.
A mixture of ₂ may be mentioned.

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
Mixture of (ZnS-SiO_Two) Showed no crystallinity
Therefore, it has an advantageous effect on the stabilization of the amorphous mark.
Considered to be Therefore, as the second protective layer 5, Z
nS and SiO_TwoIt is desirable to apply a mixture of

If the thickness of the second protective layer 5 is too thin, the temperature of the phase change recording layer 4 will be insufficiently heated, and it will not be possible to form a sufficiently large mark. 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.

As the reflection / heat dissipation layer 6, the 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.

The properties required for the material of the sulfidation preventive interface layer include that it does not contain S and that it does not permeate S. The present inventors formed various oxide films, nitride films, and the like as interface layers and evaluated the recording characteristics and storage reliability, and found that SiC and Si have excellent functions as sulfurization prevention interface layers. 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.

[0075]

[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 above-mentioned sulfurization preventing interface layer was 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, the first protective layer 3 and the phase change recording layer are provided on the polycarbonate disc-shaped 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. 4, the second protective layer 5, the sulfidation prevention 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 on the reflection heat dissipation layer 6 by spin coating. 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.

The following Table 3 shows Examples 1 to 1 in which the layer structure was changed.
6, the constitutional conditions of the optical recording media of Comparative Examples 1 to 4 are shown.
In all cases of these optical recording media, ZnS—SiO ₂ (molar ratio ZnS /
SiO ₂ = 8: 2) is 76 nm, the phase change recording layer 4 is Ga ₃ Ge ₃ Sb ₇₅ Te ₁₉ 16 nm, and the second protective layer 5 is the same as the first protective layer 3 under the conditions of 20 nm. The reflection and heat dissipation layer 6 is formed with a thickness of 140 nm.

[0080]

[Table 3]

The recording characteristics and the storage characteristics were evaluated using the forming layer items shown in Table 3 above as parameters.
The recording characteristics were evaluated by laser light wavelength: 660 nm, N.P.
A. : 0.65 pick-up head, linear density 0.267 μm / bit, EFM + modulation method. Recording was performed at a linear velocity of 14 m / s, a recording power of 16 mW, a bias power of 0.2 mW, and an erasing power of 8.5 mW, and the recording strategy was optimized according to each optical recording medium. All reproduction was performed at a linear velocity of 3.5 m / s and a power of 0.7 mW.

FIG. 6 shows Examples 1 to 6 and Comparative Examples 1 and 2.
7 shows the relationship between the number of times of recording by overwriting and the jitter, and FIG. 7 shows the relationship between the number of times of recording by overwriting and the modulation degree in Examples 1 to 6 and Comparative Examples 1 and 2. As shown in FIGS. 6 and 7, for the optical recording media of Examples 1 to 6, the overwrite 1000 was used in all cases.
The jitter up to the first time is 10% or less, and the modulation degree is 60.
%, It was found that the recording characteristics were good.

Comparative Example 1 is an example in which Al is used as the material for forming the reflection / heat dissipation layer 6 and the second protective layer is formed relatively thick as 20 nm, but the modulation degree is small and the jitter is 10% or less. I couldn't. This is because the phase change recording layer 4 is made of a material having a high crystallization rate, so that the recrystallization region becomes large.

In Comparative Example 2, when Al is used for the reflective 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 1, and the jitter was worse. This is because when the second protective layer 5 is simply thinned to have a rapid cooling structure, a large mark cannot be formed because the temperature change of the phase change recording layer 4 is insufficient and the melting region is small.

Regarding storage characteristics, changes in jitter and modulation after storage for 1000 hours at 70 ° C. and 85% RH were examined. In each of Examples 1 to 6 and Comparative Examples 1 and 2, the increase in jitter was 1% or less in the first recording and 2% or less even after 1000 times of overwriting, as compared with before the storage. The change in modulation is within 2% in each case,
It showed good storage characteristics. Further, in any case, no disc defect occurred.

Comparative Examples 3 and 4 are examples of optical recording media in which the sulfidation-preventing interface layer was formed to be extremely thin, and 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 can be confirmed by the fact that a portion where the film thickness of the sulfidation preventing interface layer is thin is formed due to the film thickness distribution in the disk, and the Ag reflection heat dissipation layer in the thinned part is sulfided and becomes a defect. .

[0087]

According to the invention of claim 1, an optical recording medium in which the phase change recording layer has a high light absorptivity can be obtained. According to the invention of claim 2, an optical recording medium having a high light absorptance of the phase change recording layer and an excellent heat dissipation characteristic was obtained.
According to the invention of claim 3, an optical recording medium having a high light absorptance of the phase-change recording layer, an excellent heat dissipation property, a low cost, and an excellent stability over time against oxidation can be obtained.
According to the invention of claim 4, an optical recording medium having a high light absorptance of the phase change recording layer and a high light utilization efficiency is obtained.
According to the invention of claim 5, an optical recording medium having a high light absorptance of the phase change recording layer and excellent recording characteristics and storage reliability can be obtained. According to the invention of claim 6, an optical recording medium having a high light absorptance of the phase-change recording layer and excellent reproduction light stability was obtained. According to the invention of claim 7, the phase change recording layer has a high light absorptivity, an excellent heat dissipation property, a low cost, an excellent stability against oxidation with time, and an excellent stability against sulfurization with time. An optical recording medium was obtained.
According to the invention of claim 8, the phase change recording layer has a high light absorptivity, an excellent heat dissipation property, a low cost, an excellent stability with time against oxidation, and an excellent stability with time against sulfurization. An optical recording medium capable of recording with a sufficient degree of modulation even if a material having a high crystallization rate is used for the phase change recording layer because a rapid cooling structure can be formed while maintaining a high light absorption rate of the phase change recording layer. Could be formed. According to the invention of claim 9, it is possible to form an optical recording medium that is more advantageous for forming a rapid cooling structure while maintaining a high light absorptance of the phase change recording layer. According to the invention of claim 10, the optical recording medium is capable of recording with a sufficient degree of modulation even when a phase change recording layer having a high crystallization rate is used, and has excellent storage reliability of amorphous marks. The optical recording medium could be formed. According to the invention of claim 11, there is provided an optical recording medium capable of recording with a sufficient degree of modulation even when a phase change recording layer having a high crystallization rate is used, and the optical recording medium has a reflectivity after initial crystallization. An optical recording medium excellent in uniformity could be formed.

[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 the jitter during overwriting.

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

[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 10 Optical recording medium

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 7/24 535 G11B 7/24 535H 538C 538 538E 538F B41M 5/26 X (72) Inventor Hajime Yuzuru Tokyo Yuko Miura, Yuji Miura, Tokyo, Ota-ku, Tokyo (72) Inventor, Hiroko Tashiro, 1-3-3, Nakamagome, Ota-ku, Tokyo Hiroko Tashiro 1-3-6 Magome In Ricoh Co., Ltd. (72) Inventor Mirai Mizutani 1-3-6 Nakamagome, Ota-ku, Tokyo In-house (72) Mikiko Abe 1-3-3 Nakamagome, Ota-ku, Tokyo No. 6 F-term in Ricoh Co., Ltd. (reference) 2H111 EA04 EA23 FA11 FA12 FA14 FA23 FA24 FA25 FA27 FB05 FB09 FB12 FB17 FB21 FB30 5D029 JA01 JB18 LA13 LA17 LB07 LB11 MA13 MA14 MA17

Claims (11)

[Claims] 1. A substrate having at least a first protective layer, a phase change recording layer, a second protective layer, and a reflection / heat dissipation layer laminated thereon, and a wavelength λ from the first protective layer forming surface side. An optical recording medium for performing recording / reproducing by irradiating the laser beam of (1) and utilizing the reversible phase change between the amorphous phase and the crystalline phase of the phase change recording layer, the composition of the phase change recording layer Is represented by the following [Chemical formula 1], and the reflection heat dissipation layer has a refractive index (n + i) at a wavelength λ.
An optical recording medium, wherein n in k) is made of a metal having a value of 1 or less and a value of k of 5 or less. Embedded image X _α Y _β (Sb _γ Te _1-γ ) _1-α-β where X is In or Ga, or a mixture of In and Ga, and Y is (Sb _γ Te _1-γ ). Is one or more kinds of elements that raise the crystallization temperature, and α, β, and γ represent atomic ratios, and are in the following ranges. 0.01 ≦ α ≦ 0.1 0 ≦ β ≦ 0.1 0.65 ≦ γ ≦ 0.85 2. The optical recording medium according to claim 1, wherein the reflection and heat dissipation layer contains at least one of Ag, Au, and Cu as a main component. 3. The optical recording medium according to claim 1, wherein the reflection / heat dissipation layer contains Ag as a main component. 4. The optical recording medium according to claim 1, wherein the thickness of the reflection / heat dissipation layer is 90 nm or more. 5. The second protective layer comprises ZnS and SiO _2.
The optical recording medium according to claim 1, which is composed of a mixture of 6. The film thickness of the second protective layer is 3 to 20 n.
The optical recording medium according to claim 1, wherein the optical recording medium is m. 7. The reflective heat dissipation layer contains Ag as a main component, the second protective layer is made of a mixture of ZnS and SiO ₂ , and between the reflective heat dissipation layer and the second protective layer, The optical recording medium according to claim 1, wherein the sulfidation prevention interface layer having a function of preventing sulfidation of the reflection / heat dissipation layer is formed to have a film thickness of 3 nm or more. 8. The optical recording medium according to claim 7, wherein the sulfidation prevention interface layer contains SiC as a main component. 9. The optical recording medium according to claim 7, wherein the sulfuration prevention interface layer contains Si as a main component. 10. The phase change recording layer is at least Ge.
The optical recording medium according to claim 1, which comprises: 11. The phase change recording layer comprises at least Ag.
The optical recording medium according to claim 1, which comprises: