JPH11232698A - Medium for optical information recording and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medium for optical information recording displaying extremely excellent repetitive overwrite characteristics and having superior data retaining stability and improved reliability. SOLUTION: The medium for optical information recording has at least a recording layer and a protective layer on a substrate, and the relationship of HVr-HVh>=50 holds in the Vickers hardness HVr of the protective layer at room temperature and the Vickers hardness HVh of the protective layer at the time of heating recording in the medium, through which light beams are applied and by which recording is conducted by heating the recording layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium capable of recording, erasing, and reproducing information at high speed and with high density by irradiation with a laser beam or the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, an optical recording medium that performs recording using a laser beam has been developed as a recording medium that meets the demands for increasing the amount of information and increasing the density and speed of recording and reproduction.
Optical recording media include a write-once type, which allows recording only once, and a rewritable type, which allows recording and erasing as many times as possible. Examples of the rewritable medium include a magneto-optical medium such as a magneto-optical disk utilizing a magneto-optical effect, and a phase-change medium such as a phase change disk utilizing a reversible change in crystalline state.

[0003] The phase change medium does not require an external magnetic field, and can be recorded / erased only by changing the power of the laser beam. Furthermore, there is an advantage that one-beam overwriting in which erasing and re-recording are performed simultaneously with a single beam is possible. Further, a write-once type can be realized by crystallizing an irreversible phase change, particularly, an amorphous. In the phase change recording method capable of one-beam overwriting, it is general that a recording mark is formed by amorphizing a recording layer and erasing is performed by crystallization. As a recording layer material used in such a phase change recording method, a chalcogen-based alloy thin film is often used. For example, Ge-Te system, Ge-Te-Sb system, In-Sb
-Te-based and Ge-Sn-Te-based alloy thin films.

[0004] A write-once type phase change medium can be realized with almost the same material and layer structure as the rewritable type. In this case, information can be recorded and stored for a longer period because there is no reversibility, and almost semi-permanent storage is possible in principle. When a phase-change medium is used as a write-once type, unlike a perforated type, there is no ridge called a rim around the mark, so the signal quality is excellent, and there is no need for a gap above the recording layer, so it is necessary to use an air sandwich structure. There is no advantage.

[0005] There are various types of phase change media, such as those that record in a crystalline state and an amorphous state, and those that record in a different crystalline state. In a rewritable phase change medium that is usually used, the crystalline state is erased. The initial state and the amorphous state are used as recording marks to realize different crystal states by two kinds of laser beam powers. Crystallization is performed by heating the recording layer to a temperature sufficiently higher than the crystallization temperature of the recording layer and lower than the melting point, and in this case, the cooling rate is reduced to such an extent that crystallization is sufficient, thus protecting the recording layer. The layers are sandwiched, and an elliptical beam that is long in the beam moving direction is used.

On the other hand, the amorphization is performed by heating the recording layer to a temperature higher than the melting point and rapidly cooling the recording layer. At this time, the protective layer functions as a heat radiation layer for obtaining a sufficient cooling rate (supercooling rate). Therefore, the protective layer is made of a material that is optically transparent to the laser beam, has a high melting point, softening point, and decomposition temperature, is easy to form, and has an appropriate thermal conductivity. Select.

Further, the protective layer suppresses deformation of the recording layer due to volume change accompanying melting and phase change in the process of forming an amorphous mark, prevents thermal damage to a plastic substrate, and prevents the recording layer from being moistened. It also has the function of preventing deterioration.

[0008]

As described above, various substances have been studied as protective layers which are chemically stable and have sufficient heat resistance and mechanical strength even at high temperatures. Among them, dielectrics are excellent in chemical stability, heat resistance, mechanical strength, etc. and are suitable as protective layers, especially mixed multiple dielectrics to express unique physical properties that can not be achieved with a single dielectric It has been practiced to use a composite dielectric as a protective layer.

For example, many proposals have been made on a protective layer in which an oxide, a nitride, a fluoride, a carbide, or the like is mixed with a compound containing a chalcogenide element such as ZnS, ZnSe, PbS, and CdS. In particular, those containing ZnS as a main component mixed with SiO2 or Y2O3,
For example, (ZnS) ₈₀ (SiO ₂ ) ₂₀
Overwriting (rewriting) from 00 to 10000 times
Is used as a protective layer capable of realizing

However, it is not sufficient for use as an external storage device of a computer, and a larger number of rewrites has been required. In the present invention, while elucidating the cause of the increase in the number of rewrites in the conventional optical recording medium, a new protective layer is proposed based on this, and an optical information recording medium having excellent repetitive overwrite characteristics is provided. The purpose is to provide.

[0011]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a medium which has at least a recording layer and a protective layer on a substrate and which performs recording by irradiating a light beam to heat the recording layer. Wherein the Vickers hardness Hvr of the protective layer and the Vickers hardness Hvh of the protective layer during the heating recording have a relationship of Hvr-Hvh ≧ 50.

That is, by using such a protective layer showing a change in hardness depending on the temperature, the rewriting characteristics of the optical recording medium can be greatly improved. The present invention also provides a method for manufacturing such a medium, wherein a protective layer is formed by sputtering using a composite target composed of a plurality of dielectrics.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The optical information recording medium of the present invention comprises at least a recording layer and a protective layer on a substrate,
A medium for recording by heating the recording layer by irradiating a light beam. The heating temperature varies depending on the type of the recording layer. In the case of a magneto-optical recording layer, the heating is generally performed to the Curie point, and in the case of the phase change recording layer, the heating is performed to a temperature at which a phase change occurs, for example, to the vicinity of the melting point.

The protective layer not only protects the recording layer from the external environment but also plays many roles optically and thermally, and is provided on one or both sides of the recording layer. The material must have excellent optical properties, moderate thermal conductivity and chemical stability, as well as sufficient heat resistance and mechanical strength at high temperatures.
Since a heating temperature is generally high in a phase change medium, heat resistance and mechanical strength particularly in a high temperature range are important.

Dielectrics have such properties and are widely used as protective layer materials. For example, oxides, sulfides, nitrides and C of metals and semiconductors having high transparency and high melting point
a, Mg, and a fluoride such as Li. However, metal oxides and nitrides differ greatly in thermal expansion coefficient and elastic properties from plastics often used as substrates of optical discs, and have poor adhesion to chalcogen-based elements commonly used as phase change recording layers. Therefore, the pinholes and cracks are likely to be generated from the substrate while recording and erasing are repeated. Further, since the plastic substrate is likely to warp due to humidity, stress is generated at the interface between the protective layer and the substrate or the recording layer, and the plastic substrate is further easily peeled.

On the other hand, oxides such as Si, Ta and rare earth elements, nitrides, carbides, fluorides and the like are excellent in heat resistance in a static state, but have high hardness and show brittleness. For rapid and local temperature changes, microscopic defects tend to grow as cracks and become burst defects. Therefore, in order to obtain better characteristics, a plurality of dielectrics are mixed to form a composite dielectric.

As the composite dielectric protective layer, ZnS, Zn
Compounds containing a chalcogenide-based element such as Se, PbS, CdS, etc. mixed with oxides, nitrides, fluorides, carbides, etc., for example, ZnS as a main component and SiO ₂ or Y ₂ O ₃
And the like have been proposed. These composite dielectric protective layers have excellent adhesion to a chalcogenide-based recording layer such as GeTeSb, have little growth of burst defects due to the propagation of cracks, and improve the repetitive overwrite durability of the medium. Little peeling.

As a result of the present inventors' examination on this point,
The composite dielectric protective layer containing ZnS or the like as a main component is generally used.
Oxide and nitride or their composite dielectric protective layer
Microscopic crack propagation mechanism with lower hardness than
Turned out to be different. When the hardness was measured,
Typical oxide Ta_TwoO_FiveHas a Vickers hardness of about 520
On the other hand, a typical ZnS-based composite dielectric (ZZ
nS)₈₀(SiO _Two)₂₀The composite membrane has a Vickers hardness of 35
It turned out that it is comparatively low about 0. This is the main component
This is due to the characteristics of ZnS.

That is, since Ta ₂ O ₅ has high hardness and exhibits brittleness, microscopic defects grow as cracks and suddenly become burst defects with respect to a rapid and local temperature change.
It is thought that the ZnS-based composite dielectric has low hardness and dissipates the fracture energy of volume change due to melting and phase change of the recording layer by microscopic plastic deformation inside the protective layer, thereby suppressing the growth of burst defects. Can be

On the other hand, if the hardness is low and the plastic deformation is remarkable, plastic deformation is accumulated or mass transfer is promoted during repeated recording, so that the optical film thickness of the recording layer and the protective layer changes, and the reflectance increases. , Or light tends to be scattered at the deformed portion, and noise tends to increase. In fact, (ZnS) ₈₀ (S
This phenomenon is remarkable in the iO ₂ ) ₂₀ composite protective layer,
This was the main reason that the number of repeated overwrites did not increase beyond a certain level.

The present inventors have studied to overcome both the problems of burst defects due to cracks and mass transfer due to plastic deformation, and to improve the repetitive recording characteristics of an optical recording medium. As a result, the Vickers hardness Hvr at room temperature and the Vickers hardness Hvh during heating recording were Hvr−Hvh ≧
The present invention has been achieved by using a protective layer having a relationship of 50, that is, a protective layer showing a substantial change in hardness with temperature.

A conventionally used dielectric protective layer has almost no temperature dependence of hardness. For example, the above-mentioned Ta ₂ O ₅
Has almost constant Vickers hardness of about 520, (ZnS)
_{The 80} (SiO ₂ ) ₂₀ composite film was almost constant at a Vickers hardness of about 350. Therefore, only at a high temperature where the volume change of the recording layer is large, the protective film is softened and plastically deformed, so that the breaking energy of the volume change is properly released. In particular, a phase change medium utilizing the phase transition of the recording layer is effective because the volume change during recording is large.

This mechanism is considered as follows. During recording on a phase change medium, as described above, the hardness of the protective layer is low during melting and re-solidification when the volume change of the recording layer is remarkable, while absorbing the deformation energy by microscopic plastic deformation,
It is considered that the hardness immediately increases upon cooling, and plastic deformation due to mass transfer or volume change in the solid phase (volume change accompanying crystallization when erasing an amorphous mark) is suppressed.

In the medium of the present invention, the microscopic plastic deformation of the protective layer at a high temperature absorbs the energy of crack propagation, so that the occurrence of burst cracks from microscopic defects can be suppressed. On the other hand, since the hardness of the protective layer increases with cooling, plastic deformation can be prevented from progressing more than necessary, mass transfer is suppressed, and deformation due to volume change in the solid phase is suppressed.

Alternatively, another mechanism is also conceivable. The high-temperature portion of the protective layer, which is in direct contact with the melting area of the recording layer, has a low hardness, and steep temporal and spatial stresses can be relaxed by microscopic plastic deformation, causing burst defect growth due to cracks and melting of the recording layer. In the inside of the protective layer, the peripheral region slightly separated from the molten region (on the order of 10 to 100 nm) has a relatively high hardness at a relatively low temperature, and can suppress the expansion of plastic deformation in the high-temperature portion.

Regardless of the mechanism, it can be said that the hardness change of the protective layer preferably occurs rapidly at high temperatures. According to the medium of the present invention, when a protective layer having a high hardness such as an oxide of Si, Ta, a rare earth element or the like is used, the disadvantage that cracks are apt to occur due to a rapid temperature change or thermal expansion is compensated for, and a slight Since the plastic deformation easily accumulates and the mass transfer of the molten recording layer cannot be suppressed, the defect of the low hardness protective layer mainly composed of crystallized chalcogen such as (ZnS) ₈₀ (SiO ₂ ) ₂₀ can be compensated. is there.

In the present invention, it is necessary that the Vickers hardness Hvh during heating recording is substantially smaller than the Vickers hardness Hvr at room temperature, that is, Hvr-Hvh must be 50 or more. More preferably, Hvr-Hvh is set to 200 or more. More preferably, it is set to 300 or more. In particular, a phase change medium that performs heat melting recording is preferable because a large volume change occurs when erasing the recording. In the case of heat melting recording, the Vickers hardness of the protective layer near the melting point of the recording layer is Hvh.

In the present invention, the protective layer may be formed using a single material whose hardness changes with temperature. However, in order to obtain a larger change in hardness, compatibility with other functions as the protective layer is also required. For this purpose, two or more materials may be used. For example, a composite protective layer made of a material whose hardness changes with temperature and a material whose hardness does not change with temperature is used.
In particular, the hardness does not change depending on the temperature and the hardness differs from each other.
A composite protective layer comprising at least one kind of material and at least one material whose hardness changes with temperature is effective for obtaining a large change in hardness.

Conversely, simply mixing a material having a high hardness and a material having a low hardness can form a film having an intermediate hardness such as (ZnS) ₈₀ (SiO ₂ ) ₂₀ and the like. I can't. In the present invention, the hardness itself of the protective layer should be appropriately designed according to the recording method and the type of the recording layer.

Generally, in a phase change medium in which heat melting recording is performed, it is desirable that the Vickers hardness of the protective layer near the melting point of the recording layer be 150 or more and 400 or less. If it is less than 150, it is preferable to release the energy of plastic deformation, but the protective layer itself is easily deformed. If it exceeds 400, it is difficult to escape the energy of plastic deformation, and cracks are easily generated. On the other hand, the Vickers hardness Hvr of the protective layer at room temperature is preferably 400 or more. If it is less than 400, it is difficult to suppress plastic deformation and mass transfer of the recording layer.

In order to obtain such a protective layer, for example, a material A having a Vickers hardness of 150 or more and 400 or less and substantially no temperature change, and a material B having a Vickers hardness of 400 or more and substantially no temperature change are used. It is effective to mix the material C whose Vickers hardness changes with temperature. The material C whose hardness changes is important for giving the protective layer the property of hardness change with temperature.
Zinc oxide ZnO is mentioned. Vickers hardness of ZnO is 620 at room temperature (20 ° C.) and 520, 80 at 500 ° C.
It changes considerably to 440 at 0 ° C. Although it is crystalline and somewhat brittle, it has a melting point of 1975 ° C. and is excellent in stability over time because it is a chemically stable oxide. The sputtering rate during sputtering film formation is also good.

Examples of the low hardness material A include a crystalline chalcogen compound. Preferably ZnS, Zn
Zinc chalcogenide such as Se. Zinc chalcogenide is chemically stable, and ZnS has a melting point of 183.
It is excellent in heat resistance at 0 ° C. and low in toxicity, and is most preferable. Also,
ZnS is also a substance that has a very high sputtering rate during sputtering film formation, and is thus preferable. When ZnS is contained in the dielectric target, the film formation rate is improved as compared with a substance before the ZnS is contained.

Furthermore, since these chalcogenides are of the same family as Te generally contained in the phase change recording layer, they have excellent adhesion to the recording layer. As the high hardness material B, for example, a rare earth oxide ROα (R is a rare earth element) is preferable. Rare earth oxides include CeO ₂ , HfO ₂ , ZrO ₂ , Y ₂ O
₃ , Nd ₂ O _{3 and the} like. The range of α of ROα is not particularly limited.

In particular, since CeO ₂ is a high-hardness substance used as an abrasive, it is highly effective in suppressing plastic deformation in a low-temperature region. By the way, the crystalline oxide CeO ₂
Cubic structure and Zn, a crystalline chalcogenide
In the cubic structure of S, a crystal peak appears at exactly the same position in X-ray diffraction. A composite dielectric obtained by combining these two components is preferable because it is homogeneously mixed and the film quality is extremely smooth. Even if the material itself is crystalline, a microcrystalline or amorphous thin film that has been refined so that no peak can be found by X-ray diffraction as a whole can be obtained.

When the ratio of the chalcogenide zinc to the rare earth oxide is increased, there is an advantage that the sputter rate is increased and the sensitivity is improved, but the overwrite characteristics are almost stable over the above composition range. Characteristics are obtained. This can be said to be excellent in manufacturing stability. Such a composite protective layer is preferably formed by sputtering using a composite target composed of a plurality of materials. It is easy to control the film composition, and it is easy to suppress the composition fluctuation over the entire surface of the sputtered film. In addition, the configuration of the sputtering apparatus can be simplified.

The method of manufacturing the protective layer, including the method of manufacturing the target and forming the film, is extremely important in determining the state of the protective layer. For example, if the substrate temperature at the time of sputtering is high, it tends to be crystalline. Further, depending on the method of manufacturing the target, the film is easily crystallized or amorphous. Hereinafter, a general manufacturing method will be described using a composite target of ZnS, ROα, and ZnO as an example.

The above three kinds of powders were weighed and mixed well, and the powder mixed before was put into a carbon punch and a die coated with BN so that the target did not adhere to the surface of the die. Tie. then,
Until the temperature reaches 600 ° C. to 800 ° C., vacuum is applied to remove impurities adhering to the carbon. At the subsequent temperature, Ar is used to make the temperature in the tank uniform and increase the sintering efficiency.
The atmosphere is replaced and sintered.

The sintering temperature is set to be lower than the melting point of the powder, and a target having a density as high as possible can be produced. The target density here affects the film formation rate at the time of sputtering film formation. A high-density target is preferable because the sputtering rate is high. As described above, ZnS, R
A composite target of Oα and ZnO is manufactured. Generally,
The purpose of this sintering process is to merely change the physical state of solidifying the powder into a stone, but by heating and applying pressure, a solid-phase reaction occurs to change to another substance. Sometimes it is used as a target.

For example, when the powder of the rare earth sulfide RSα and ZnO is sintered, the rare earth sulfide is decomposed by heat and causes a solid-phase reaction to be converted into a rare earth oxide and ZnS. Adjusting the molar ratio of the powder to be mixed changes the composition of the reaction product,
ZnO remains and becomes a composite target of ZnS, ROα, and ZnO. In addition, the reaction condition changes depending on the sintering temperature condition, sintering time, and pressurizing condition, so that the state of the product may change.

When using a target formed by any of the methods, polishing, pre-sputtering, etc.
Sputter to form a thin film. Zn by the former method
When a film is formed by sputtering using an S, ROα, or ZnO target, the film tends to be amorphous, but when a target manufactured by the latter method is used, the film tends to be a microcrystalline film.

The above are the important characteristics of the protective layer in the present invention. Other characteristics are also described. The protective layer must be substantially transparent to the laser beam wavelength used for recording and reproduction. The wavelength used is usually 600
８００800 nm. It is considered that the wavelength will be reduced to about 400 nm in the future. Of course, 400
It is not necessary to be transparent to all wavelengths of up to 800 nm, but it is sufficient if it is transparent to the laser beam used therein. Substantially transparent means that the absorption coefficient, which is the imaginary part of the complex refractive index for that wavelength, is approximately 0.5.
Is less than.

In the case of a phase change medium in which heat melting recording is performed, since the protective layer is sometimes repeatedly heated from several hundreds to about 1000 ° C., the melting point or decomposition point of the material is 1 point.
It needs to be at least 000 ° C. Further, in terms of mechanical strength, it is desirable that the film density of the protective layer be 80% or more of the bulk density (bulk density) of the material. In addition, the theoretical density of the equation (1) is used for the bulk density of the composite film composed of a plurality of materials.

[0043] (However, the molar concentration of each component i m _i, and the [rho _i alone bulk density) medium of the present invention has at least a recording layer and a protective layer on the substrate, optionally reflective layer, a protective coat A layer or the like is provided. For example, it has a layer configuration such as a substrate, a protective layer, a recording layer, a protective layer, a reflective layer, and a protective coat layer.

As the substrate of the medium of the present invention, a general substrate generally used for an optical recording medium can be used, and a transparent resin such as polycarbonate, acrylic, polyolefin, photocurable resin, glass, or the like can be used.
Polycarbonate resins are preferable because of their excellent water absorption, optical properties, adhesion to the protective layer, and the like. The recording layer, the protective layer, and the reflective layer are formed by a sputtering method, an evaporation method,
It is desirable to form a layer using an in-line apparatus in which the target for the recording layer, the target for the protective layer, and the target for the reflective layer are installed in the same vacuum chamber, from the viewpoint of preventing oxidation and contamination between the respective layers.

The protective coat layer is usually provided by spin coating or the like using a high-hardness ultraviolet or thermosetting resin. As the recording layer, a magneto-optical recording layer, a phase change recording layer, or the like is used. Generally, as a phase change recording layer,
GeSbTe, InSbTe, AgSbTe, AgIn
Chalcogenide alloys such as SbTe may be used, for example, _{{(Sb 2 Te 3) 1} -x (GeTe) x} 1-y Sb y alloy (wherein, 0.2 ≦ x ≦ 0.9,0 ≦ y ≦ 0 .1) and up to about 10 atomic% of In, Ga, Z
n, Sn, Si, Cu, Au, Ag, Pd, Pt, P
Alloys containing at least one of b, Cr, Co, O, S, Se, Ta, Nb, and V are listed.

If the composition on the line connecting Sb ₂ Te ₃ and GeTe is close to the composition of the Ge ₂ Sb ₂ Te ₅ intermetallic compound, overwriting can be performed even at a linear velocity of 10 m / s or more. In addition, an MSbTe alloy mainly containing a SbTe alloy near the eutectic point of Sb ₇₀ Te ₃₀ (where M is In,
Ga, Zn, Ge, Sn, Si, Cu, Au, Ag, P
d, Pt, Pb, Cr, Co, O, S, Se, Ta, N
b and V) are also preferable as a material capable of overwriting at high speed.

More preferably, M _w (S
b _z Te _1-z ) _1-w (where 0 ≦ w ≦ 0.15, 0.6
≦ z ≦ 0.8). Linear velocity 2.4m / s or more1
At 1.2 m / s or less (2 to 8 times the CD linear velocity), good overwriting is possible at a wide range of linear velocity where the ratio between the maximum linear velocity and the minimum linear velocity is 2 or more. Generally, the thickness of the phase change recording layer is preferably in the range of 10 nm to 100 nm. If the thickness of the recording layer is thinner than 10 nm, it is difficult to obtain a sufficient contrast, and the crystallization speed tends to be slow. On the other hand, if it exceeds 100 nm, optical contrast is still difficult to be obtained, and cracks are likely to occur.

In particular, a rewritable compact disc (CD
-RW) to ensure compatibility with CDs.
The thickness is preferably 30 nm or more and 30 nm or less. If it is less than 10 nm, the reflectance is too low, and if it is more than 30 nm, the heat capacity becomes large and the recording sensitivity is deteriorated. The phase-change recording layer at the time of film formation is usually amorphous. In this case, it is necessary to use the phase-change recording layer after crystallizing the entire recording layer in an initialized state (unrecorded state). Initialization is flash lamp annealing, or 10
This is achieved by instantaneously heating the recording layer to a temperature higher than the crystallization temperature with a laser beam focused to about 0 μm.

Melt initialization is effective as one method for shortening the time required for initialization and surely performing initialization by one light beam irradiation. For example, 10 to several hundred μm in diameter
Heat locally using a focused light beam (gas laser or semiconductor laser beam) or an elliptical light beam with a major axis of 50-100 μm and a minor axis of 1-10 μm, limited to the center of the beam And melt.
At this time, since the periphery of the beam is also heated at the same time, the molten portion is preheated, the cooling rate is reduced, and good recrystallization is performed.

As a result, the conventional solid-phase crystallization is reduced by 1%.
The initialization time can be reduced to 1/0, the productivity can be significantly reduced, and the change in crystallinity during erasure after overwriting can be prevented.

[0051]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is applicable as long as it does not exceed the gist. In this example, a TS-1 device manufactured by Nikon Corporation was used for measurement of Vickers hardness. (Example 1) Ce ₂ S ₃ : Z was used as the material of the upper and lower dielectric layers.
After sufficiently mixing the powder mixed with nO = 20: 80 (mol%), the mixture was allowed to stand for 2 hours while being pressed at 1150 ° C. and 20 tons by a hot press method, and sintered. After sufficient polishing, a target was prepared by bonding the Cu plate with In solder.

When this target was analyzed by X-ray, Ce
Peaks indicating crystals of O ₂ , ZnS, and ZnO were confirmed. A phase change optical disk was prepared by sequentially laminating a lower dielectric layer / recording layer / upper dielectric layer / reflective layer on a 1.2 mm thick polycarbonate substrate. The thickness of each layer is the lower dielectric layer 16
0 nm, the recording layer was 30 nm, the upper dielectric layer was 30 nm, and the reflection layer was 100 nm. The recording layer is Ge _22.2 Sb _22.2 Te _55.6
And the reflection layer was an Al alloy.

The upper and lower dielectric layers were formed by high-frequency sputtering (13.56 MHz) of the composite target under a pressure of 0.4 Pa while flowing Ar gas at 50 sccm. The film density is 5.1 g / cm ³ and the theoretical density is 96 g / cm ^3.
%Met. The film stress is 4.0E +
It was 8 dyn / cm ² . The refractive index of this film was 2.3 as measured by an ellipsometer.

Using the above-mentioned composite target, a dielectric layer of 1 μm was formed on a Si (111) wafer substrate under the same conditions.
A film having a thickness of m was formed to prepare a hardness sample. FIG. 1 shows the measurement results of the temperature change of the Vickers hardness of this sample. The recording layer and the reflective layer were formed by DC sputtering at an Ar gas pressure of 0.4 Pa. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided.

After the recording layer of the optical disk was initialized using an LD bulk eraser having a wavelength of 810 nm, the dynamic characteristics of the disk were evaluated under the following conditions. 10 disks
While rotating at a linear velocity of m / s, overwriting is repeatedly performed at a recording power of 14.5 mW, a base power of 7.5 mW, and a reproduction power of 0.8 mW with a pulse light of 4 MHz and a duty of 50%, and the C / N and erasing ratio Was measured. As a result, it did not occur at all deterioration be carried out 10 ⁵ times more repetitive overwriting.

The disk was left under the conditions of high temperature and high humidity of 80 ° C. and 85% RH for 500 hours, but no peeling occurred and the characteristics of the disk did not change. Comparative Example 1 The conditions were the same as in Example 1 except that the upper and lower dielectric layers were ZnS: SiO ₂ . As a material for the upper and lower dielectric layers, a powder obtained by mixing ZnS: SiO ₂ = 80: 20 (mol%) was sufficiently stirred, and then mixed by hot pressing.
It was left for 2 hours in a state of being pressed at 200 ° C. and 20 tons for sintering. After sufficient polishing, a target was prepared by bonding the Cu plate with In solder.

The target was analyzed by X-ray.
Peaks indicating crystals of S and SiO ₂ were confirmed. 1.2
lower dielectric layer / recording layer /
An upper dielectric layer / reflective layer was sequentially laminated to produce a phase change optical disk. The thickness of each layer is 160 nm for the lower dielectric layer, 30 nm for the recording layer, 30 nm for the upper dielectric layer, and 100 nm for the reflective layer.
And The recording layer was Ge _22.2 Sb _22.2 Te _55.6 , and the reflective layer was an Al alloy.

The upper and lower dielectric layers were formed by high frequency sputtering (13.56 MHz) of the above composite target under a pressure of 0.4 Pa while flowing Ar gas at 50 sccm. The film density was 3.5 g / cm ³ and the theoretical density was 94 g / cm ^3.
%Met. The film stress is a tensile stress of 1.1E +
It was 9 dyn / cm ² . The refractive index of this film was 2.1 as measured by an ellipsometer. The composition ratio of the composite target and the sputtered film was almost the same. X-ray diffraction of this sputtered thin film did not show a clear crystalline peak.

Using the above composite target, a dielectric layer of 1 μm was formed on a Si (111) wafer substrate under the same conditions.
A film having a thickness of m was formed to prepare a hardness sample. FIG. 1 shows the measurement results of the temperature change of the Vickers hardness of this sample. The recording layer and the reflective layer were formed by DC sputtering at an Ar gas pressure of 0.4 Pa. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided.

The disk was initialized and evaluated for dynamic characteristics in the same manner as in Example 1. As a result, after 104 times, the amplitude of the reproduced signal decreased. Comparative Example 2 The same conditions as in Example 1 were used except that the upper and lower dielectric layers were Ta ₂ O ₅ . A phase change optical disk was prepared by sequentially laminating a lower dielectric layer / recording layer / upper dielectric layer / reflective layer on a 1.2 mm thick polycarbonate substrate. The thickness of each layer was 170 nm for the lower dielectric layer, 30 nm for the recording layer, 30 nm for the upper dielectric layer, and 100 nm for the reflective layer. The recording layer is Ge
_22.2 Sb _22.2 Te _55.6 , and the reflective layer was an Al alloy.

For the upper and lower dielectric layers, Ar gas was flowed at 50 sccm, and high-frequency sputtering (1
(3.56 MHz). The film density is 8.1 g /
cm ³ , which was 93% of the theoretical density. The film stress was 3.1E + 9 dyn / cm ² in tensile stress. The refractive index of this film was measured by an ellipsometer.
It was 4.

Under the same conditions, a 1 μm-thick dielectric layer was formed on a Si (111) wafer substrate to prepare a hardness sample. FIG. 1 shows the measurement results of the temperature change of the Vickers hardness of this sample. The recording layer and the reflective layer were formed by DC sputtering at an Ar gas pressure of 0.4 Pa. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided.

The disk was initialized and evaluated for dynamic characteristics in the same manner as in Example 1. As a result, 10 ⁴ times after noise rise erase ratio is lowered.

[0064]

According to the present invention, it is possible to obtain an optical information recording medium which exhibits extremely excellent repetitive overwriting characteristics, has excellent data storage stability and has improved reliability.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temperature change of Vickers hardness of a protective layer according to an example of the present invention.

Claims (18)

[Claims] 1. A recording medium having at least a recording layer and a protective layer on a substrate and performing recording by heating the recording layer by irradiating a light beam, wherein the Vickers hardness of the protective layer is Hv at room temperature.
r, the Vickers hardness Hvh of the protective layer during the heating recording is H
An optical information recording medium, wherein vr-Hvh ≧ 50. 2. The optical information recording medium according to claim 1, wherein the recording layer is a phase change recording layer. 3. The medium according to claim 1, wherein at least a protective layer, a phase change recording layer, and a protective layer are sequentially provided on the substrate, and the recording layer is heated and melted by irradiating a light beam to perform recording. The Vickers hardness of the protective layer at room temperature is Hvr, and the Vickers hardness of the protective layer near the melting point of the recording layer is Hvh.
Optical information recording medium. 4. The method according to claim 1, wherein Hvr−Hvh ≧ 200.
4. The optical information recording medium according to any one of items 3 to 3. 5. The protective layer according to claim 1, wherein the protective layer comprises a plurality of materials, and at least one material whose temperature does not change in Vickers hardness and at least one material whose temperature changes in Vickers hardness. 5. The optical information recording medium according to any one of 1 to 4. 6. The light according to claim 5, wherein the protective layer is made of two or more materials whose Vickers hardness does not change with temperature and which have different Vickers hardness, and at least one material whose Vickers hardness changes with temperature. recoding media. 7. The protective layer has a Vickers hardness of 150.
A material A having a temperature of not less than 400 and substantially no change in temperature
7. The optical information recording medium according to claim 6, comprising: a material B having a Vickers hardness of 400 or more and substantially not accompanied by a temperature change; and a material C having a Vickers hardness changed by a temperature. 8. The optical information recording medium according to claim 7, wherein said material C is ZnO. 9. The optical information recording medium according to claim 7, wherein the material A is zinc chalcogenide. 10. The material B is a rare earth oxide ROα (R
Is a rare earth element). The optical information recording medium according to any one of claims 7 to 9, wherein 11. The optical information recording medium according to claim 10, wherein the rare earth oxide ROα is CeO ₂ . 12. The optical information recording medium according to claim 1, wherein the protective layer is formed by sputtering using a composite target composed of a plurality of materials. 13. The composite target according to claim 1, wherein the material A has a Vickers hardness of 150 or more and 400 or less and substantially does not involve a temperature change, and the material B has a Vickers hardness of 400 or more and does not substantially involve a temperature change. 13. The optical information recording medium according to claim 12, comprising a material C having a Vickers hardness. 14. The optical information recording medium according to claim 13, wherein said composite target is made of zinc chalcogenide, ROα (R is a rare earth element), and ZnO. 15. The method for manufacturing an optical information recording medium according to claim 1, wherein a protective layer is formed by sputtering using a composite target composed of a plurality of dielectrics. A method for producing an optical information recording medium, comprising: 16. The composite target is composed of ZnS, Z
The method for producing an optical information recording medium according to claim 15, wherein the method is composed of nO and ROα (R is a rare earth element). 17. The composite target is obtained by mixing a powder of a rare earth sulfide RSα (R is a rare earth element) and a powder of ZnO in the same mole number or more as the rare earth sulfide and sintering at a high temperature. 17. The method for manufacturing an optical information recording medium according to claim 16, wherein: 18. The composite target comprises a mixture of a powder of a rare earth sulfide RSα (R is a rare earth element) and a powder of ZnO in the same mole number or more as the rare earth sulfide, and sintered at a high temperature. Of rare earth sulfide RSα by sulfur and Zn
17. The method for producing an optical information recording medium according to claim 16, which is obtained by substituting a part of oxygen of O.