JP2000030296A - Optical information recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical information recording medium which is superior in repetitive overwriting characteristics and data preservability by forming a dielectric protective layer contg. zinc, cerium, sulfur and oxygen and having a specified Zn to Ce molar ratio. SOLUTION: This optical information recording medium has at least a lower dielectric protective layer, a phase change recording layer, an upper dielectric protective layer and a reflecting layer on the substrate. At least one of the dielectric protective layers contains zinc, cerium, sulfur and oxygen and has a Zn to Ce molar ratio larger than 0 but 2.0 or smaller. This compsn. gives a compressive stress smaller than that of a pure oxide or nitride by one digit and hardly causes the peeling of a film. The desirable thickness for the lower dielectric protective layer is 50-300 nm and that for the upper dielectric protective layer is 0.1-300 nm, and then good disk characteristics are ensured.

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 high density by irradiation with a laser beam or the like.

[0002]

2. Description of the Related Art A phase change type optical information recording medium in which information is recorded or reproduced by a phase change between a crystalline state and an amorphous state is known. In a general phase change type optical information recording medium, a protective layer made of a dielectric material is provided above or below a recording layer on which recording and reproduction are performed by a phase change. Generally, in a rewritable phase change recording medium, two different laser beam powers are used to realize different crystal states. Taking this method as an example, 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 amorphization is performed by heating the recording layer to a temperature higher than the melting point. This is done by quenching. in this case,
The protective layer has a function as a heat radiation layer for obtaining a sufficient cooling rate (supercooling rate).

[0003] The material of such a protective layer is to be optically transparent to an irradiated laser beam.
It is selected from the viewpoints of high melting point, softening point, decomposition temperature, easy formation, and appropriate thermal conductivity. Further, as described above, deformation of the recording layer due to volume change accompanying melting and phase change in the process of forming an amorphous mark is suppressed, thermal damage to a plastic substrate is prevented, and deterioration of the recording layer due to moisture is prevented. In order to prevent this, the protective layer is important.

[0004] In the heating / rapid cooling process at the time of overwriting, the surface in contact with the melting region of the recording layer is set to the highest temperature inside the protective layer, and the surface in contact with the substrate or the reflective layer is set to low temperature. 100n temperature change over 100 ° C
Since it is formed instantaneously in less than sec, rapid thermal expansion deformation occurs in the direction in which the recording layer is to be pushed away. It is also necessary to withstand such rapid thermal expansion deformation of the protective layer itself.
As described above, dielectric materials such as metal oxides and nitrides are known as materials for protective layers that are chemically stable and have sufficient heat resistance and mechanical strength even at high temperatures. However, these dielectric thin films and the plastic substrate generally differ greatly in coefficient of thermal expansion and elastic properties, and thus peel off from the substrate during repeated recording and erasure, causing pinholes and cracks.

In particular, oxides, nitrides, carbides, fluorides and the like of typical amorphous dielectrics such as silicon, tantalum and rare earth elements have excellent heat resistance in a static high temperature state. In addition, since it has high hardness and shows brittleness, there is a disadvantage that microscopic defects tend to grow as cracks and become burst defects with respect to the rapid and local temperature change as described above. Further, since a plastic substrate is likely to be warped by humidity, such a dielectric protective layer easily generates stress at an interface with the substrate and the recording layer, and easily peels off.

Furthermore, these dielectric protective layers have poor adhesion to chalcogen elements commonly used as phase change recording layers, and thus are more easily peeled off. On the other hand, it is also known to use a composite dielectric in which a plurality of dielectrics are mixed as a protective layer in order to express unique physical properties that cannot be achieved by a single dielectric as described above. As such a composite dielectric, oxides such as ZnS, ZnSe, PbS, and CdS, which are compounds containing a chalcogenide-based element,
Numerous proposals have been made for a mixture of nitride, fluoride, carbide and the like. In particular, ZnS as a main component,
A material in which SiO ₂ , Y ₂ O _3, or the like is mixed therein has been proposed as a protective layer capable of realizing repetitive overwriting up to 1 million times in mark position recording.

[0007] These composite dielectric protective layers are made of GeTeS.
The adhesion to a chalcogenide-based alloy thin film such as b is superior to a pure oxide or nitride dielectric protection layer. In addition, since the growth of burst defects due to the propagation of cracks is hardly characteristic of ZnS itself, repeated overwrite durability of the medium is improved, film peeling in an accelerated test is small, and high reliability is obtained. However, when mark length recording is adopted for higher density and the mark length is shorter than about 0.5 μm, the repetition durability is significantly deteriorated. This is because a slight increase in noise or a change in reflectance, which is missed in the mark position recording, is not allowed.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical information recording medium which suppresses a decrease in reflectance and an increase in noise, suppresses mass transfer, and has excellent repetitive overwrite characteristics, and a method for producing the same. With the goal. Typical (Zn
The S) ₈₀ (SiO ₂ ) ₂₀ composite film has a relatively soft hardness and a Vickers hardness of about 350. Therefore, it has been clarified by the present inventors that microscopic plastic deformation accumulates to increase noise and decrease reflectivity.
Therefore, the present inventors have attempted to increase the durability of deformation due to repeated overwriting by changing the oxide from SiO ₂ to CeO ₂ , which has a higher hardness and is also used as an abrasive, and increases the hardness. .

On the other hand, a protective layer made of a mixture of ZnS and CeO ₂ is described in JP-A-3-125344. According to the example of this known document, CeO ₂
There is a description that the repetition characteristics are improved by mixing up to 30 mol% of the compound. However, according to this document, the mixing ratio between ZnS and CeO ₂ is determined only by controlling the sputtering power, and the actual film composition is not measured. As described later, in particular, ZnS—CeO
_{In the two} systems, the composition of the target often differs greatly from the composition of the film, and the degree varies depending on the sputtering conditions. Therefore, even in the above-mentioned literature, the film composition is actually unclear. Further, it is found that this document is not enough for further improvement of the characteristics, and that the noise increases and the C / N deteriorates due to the repetition.

[0010]

Means for Solving the Problems The present inventors have found that Zn, Ce, S, and O are important as the composition of the protective layer, and that the Zn to Ce ratio is important. It has been found that the above object can be achieved by adding Ce in a larger amount than the amount of Ce described in (1), and the present invention has been completed. The gist of the present invention is to provide an optical information recording medium having a dielectric protective layer and a phase change recording layer on a substrate, wherein the dielectric protective layer contains zinc, cerium, sulfur, and oxygen, and its Zn / An optical information recording medium characterized in that the molar ratio of Ce is 2.0 or less.

[0011]

The present inventors have focused on the fact that it is effective to include zinc, cerium and sulfur. ZnS and Ce
Since all the combinations of O ₂ have exactly the same crystal system in Cubic, they are considered to be particularly easily mixed uniformly, and are effective in preventing the propagation of cracks. Also,
CeO ₂ is a high-hardness substance that is also used as an abrasive, and is necessary for suppressing plastic deformation in a relatively low-temperature region. Also, CeO ₂ is inexpensive and is preferable as a target material.

The mechanism for preventing deterioration during overwriting by the protective layer in the present invention is based on the conventional ZnS-SiO
It is considered different from the _two films. In other words, the hardness of the recording layer is low at the time of melting and re-solidification where the volume change is remarkable, and the deformation energy is absorbed by microscopic plastic deformation. It is considered that the plastic deformation due to the volume change accompanying the phase change at the time of recrystallization of the quality mark) is suppressed. The ZnS bond easily causes slip deformation, and the microscopic plastic deformation at high temperature absorbs the energy of crack propagation, thereby suppressing the occurrence of burst cracks from microscopic defects. On the other hand, as a result of a sudden increase in hardness during cooling due to the contribution of a strong Co-O bond, plastic deformation can be suppressed from progressing more than necessary, mass transfer can be suppressed, and deformation due to volume change in the solid phase can be suppressed. Suppress.

In fact, the Nuev hardness at room temperature is ZnS and Si.
The film made of a mixture with O ₂ has a hardness of about 300, while the composite film of the present invention has a high hardness of about 600 to 800. On the other hand, cracks are less likely to grow than metals such as tantalum oxide and silicon dioxide and oxides and nitrides of semiconductors, even if they have high hardness. Further, the composition of the protective layer used in the present invention has a compressive stress which is smaller by one digit than the stress of these pure oxides and nitrides, and the film is hardly peeled. It is also important that the protective film contains sulfur in order to enhance the adhesion to the recording layer. In particular, when Te is contained in the recording layer, inclusion of a chalcogen of the same family particularly improves the adhesion to the recording layer.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The protective layer in the present invention comprises zinc,
The composition contains cerium, sulfur and oxygen, and the molar ratio of zinc / cerium in the composition is more than 0 and 2.0 or less. As a result, good disk characteristics can be obtained. The preferred lower limit of the Zn / Ce ratio is 0.01, particularly 0.1, and more preferably 0.1.
3, and the upper limit is 1.5. Specifically, 0.1
The most preferable range is 1.5 or less. When the molar ratio of Zn / Ce is too small, that is, when the content of Ce is extremely large, it is difficult to achieve this content only by controlling the sputtering conditions, and it is necessary to increase the content of Ce in the target containing Ce. However, the composite target having a large amount of the mixture is easily broken and difficult to produce, has a high risk of cracking even during film formation, and may have a problem in practical use. This is a problem especially for large targets of 5 inches or more. Furthermore, a target having too high a Ce content has a low sputtering rate when forming a film, which is not desirable in forming a thin film. When this thin film is used as a protective film and made into a disc, the sensitivity decreases and a high-output laser is required for recording.
Not preferred.

On the other hand, if the molar ratio of Zn / Ce is too large, the hardness is reduced, and the deformation and deterioration at the time of overwriting tend to occur. Specifically, a Knoop hardness of 60 at room temperature
It is preferably 0 or more, so that the Zn / Ce ratio is 2.0 or less. Further, according to the findings of the present inventors, it has been found that ordinary Ar
During sputtering using a gas, Ce atoms tend to be distributed just above the target and Zn atoms tend to spread throughout the chamber in the chamber. Therefore, from the viewpoint of increasing the production efficiency by shortening the distance between the target and the substrate,
It is not preferable to make a sputtered film rich in Zn,
It is desirable that the ratio of Zn / Ce is 2.0 or less.

The protective layer further contains sulfur. Sulfur has a strong bond with the recording layer, especially with the chalcogenide element therein, so that the adhesion between the recording layer and the dielectric protective layer can be maintained more firmly. However, in the released state, diffusion from the dielectric protective layer to the recording layer occurs, which may cause deterioration of segregation. Therefore, an optimal amount is required. The above protective layer is usually formed by sputtering. As the target material for forming the protective layer, various materials can be used as long as the above-mentioned composition can be realized, and one or more of various targets including zinc, cerium, sulfur, oxygen and the like are used. be able to. For example, cerium oxide, cerium sulfide, zinc oxide,
Zinc sulfide and composite oxides thereof are used in appropriate combination. A plurality of targets may be used, or one composite dielectric target may be used. However, when a composite dielectric target is used, composition control can be performed more stably. When co-sputtering is performed using two or more targets, a plurality of RF power sources are required, so that the size of the apparatus is increased and the composition is likely to be shifted. A preferred target is a composite dielectric target of CeO ₂ and ZnS. Zinc sulfide is chemically stable, has excellent heat resistance and low toxicity. Also, the sputtering rate is high.
Cerium sulfide is also inexpensive.

According to the findings of the present inventors, CeO ₂ and Z
In a composite dielectric target with nS, there is a problem that when the ratio of cerium oxide increases, the target is susceptible to thermal change and easily cracked. However, in this system, the target composition and the film composition are significantly different. In particular,
As mentioned above, the cerium atom is located just above the target,
Since zinc atoms tend to be distributed throughout the chamber,
By reducing the distance between the target and the substrate, it is possible to increase the content of cerium in the composition of the film compared to the composition of the target. Therefore, by selecting the sputtering conditions, it is possible to manufacture a film having a relatively high cerium ratio to some extent, using a target that is difficult to crack.

The molar ratio of zinc / cerium in the CeO ₂ and ZnS composite dielectric target is usually more than 0 to 2.5
It is as follows. If the amount of cerium is too large, the target is easily broken and is not practical. On the other hand, if the content of cerium is too small, it becomes difficult for the cerium content in the formed protective layer to fall within the range specified in the present invention, so it is preferably at least 0.1, more preferably at least 0.3, Preferably it is one or more.

In the case of a composite dielectric target of Ce ₂ S ₃ and ZnO, it tends to be difficult to manufacture the target with good reproducibility. As a method for manufacturing the composite dielectric target, the following method can be used. The target manufacturing method is important in determining the state of a film formed by sputtering. The powders having the required compositions are weighed and mixed well, and the mixed powders are put into a carbon punch and a die coated with BN (boron nitride) so that the target does not adhere to the surface, and then sintered by a hot press method. Tie. At that time, from 600 ° C to 800 ° C
Until the temperature reaches the level, the carbon is sintered in vacuum to blow impurities adhering to the carbon. . The sintering temperature is set to be lower than the melting point of the powder and a target having the highest possible density can be produced. The target density here affects the sputtering rate. A high-density target is preferable because the sputtering rate is high.

Usually, during the sintering process, the purpose is merely to change the physical state, that is, to solidify the powder into a stone. However, on the other hand, by heating and applying pressure, a solid-phase reaction can be caused to change to another substance, which can be used as a target. Specifically, for example, in a powder of rare earth sulfide and ZnO, the rare earth sulfide is decomposed by heat to cause a reaction, and becomes a rare earth oxide and ZnS by a solid phase reaction. The product of this reaction changes depending on the molar ratio of the powder to be mixed, and ZnO or the like may remain. In addition, sintering temperature conditions, sintering time,
The condition of the product can also change because the reaction conditions change depending on the pressure conditions.

When a target formed by any of the methods is used, a thin film is formed by ordinary polishing, pre-sputtering, etc., followed by sputtering. The sputtering conditions are usually as follows. Even if the target is the same, the composition of the film greatly varies depending on the sputtering conditions, and therefore, it is necessary to appropriately select the conditions for sputtering. The gas used is usually Ne, A
Although an inert gas such as r, Kr, or Xe is used, it is preferable to use Ar in view of cost and the like. The pressure for film formation is usually 1 Pa or less. If the discharge can be performed stably, it is preferable to perform sputtering at a low pressure because the film density increases. R
The frequency of the F sputter is usually 10 MHz or more. As described above, the distance between the target and the substrate greatly affects the Zn / Ce ratio of the film. The cerium concentration increases as the distance decreases, and the zinc concentration increases as the distance increases. Since a target having a high cerium ratio is easily broken, the distance between the target and the substrate is preferably short, and is usually 30 cm or less, preferably 20 cm or less. Further, it is actually 0.1 cm or more. The shorter the distance, the better in order to reduce the loss of film formation and increase the sputtering efficiency, and to eliminate the non-uniformity of the film formation distribution. During sputtering, the substrate or target
It can be rotated (rotated about the center of gravity) and / or revolved (the center of gravity rotates on a predetermined circumference). These rotation speeds are usually about 1-100 rpm. When the substrate or the target revolves, sputtering proceeds while the distance between the substrate and the target changes.
Preferably, the minimum distance is 0.1 cm or more.

The protective layer used in the present invention is usually provided in contact with the phase change recording layer, but may be provided on either side. In a normal phase-change optical recording medium, the protective layer is provided on both sides of the recording layer. In this case, the protective layer may be one or both. In the present invention, the protective layer provided on the substrate side of the recording layer is referred to as a lower protective layer (or lower dielectric protective layer), and the protective layer provided on the opposite side is referred to as an upper protective layer (or upper dielectric protective layer). Sometimes. When the above-mentioned protective layer is used as an upper (or lower) protective layer, another dielectric upper or lower dielectric protective layer may be provided. In this case, upper (or lower)
The dielectric protection layer has a multilayer structure. In the case of such a multilayer structure, the protective layer having the composition used in the present invention can be provided on the side in contact with the recording layer, and the film thickness in that case is usually 5 to 50 nm.

The thickness of the dielectric protective layer is usually 50 nm or more and 300 nm or less as the lower protective layer. If the film is too thin, there is a problem that the substrate deformation due to heat at the time of recording cannot be suppressed.If it is too thick, there is a problem that the film tends to crack, and it takes too much time to form the film during manufacturing. Not a target. When used for the upper protective layer, the thickness is preferably 0.1 nm or more and 300 nm or less.

In particular, the lower dielectric protective layer has a thickness of 50-2.
A film having a composition of a mixture of chalcogenide and SiO ₂ having a thickness of 50 nm is used.
It is very effective to use the protective layer having the composition defined in the present invention as m. Because chalcogenide and S
This is because the film having the specific Zn / Ce ratio tends to have a lower deposition rate than the film made of iO _2, and thus the above-described layer configuration is excellent in productivity.

Next, the general structure of the optical information recording medium of the present invention will be described with reference to FIG. FIG. 1 is a schematic sectional view showing an example of the layer configuration of the optical information recording medium of the present invention. The medium shown in FIG. 1 includes a substrate 1, a lower dielectric protection layer 2, a phase change recording layer 3, an upper dielectric protection layer 4, a reflective layer 5, and a protective coat layer 6. As the substrate 1, a transparent resin such as polycarbonate, acrylic, polyolefin, and photocurable resin or glass can be used.
From the viewpoint of productivity, a transparent resin is preferable, and a polycarbonate resin is particularly preferable because it has excellent water absorption, optical properties, adhesion to a protective layer, and the like.

The phase change recording layer 3, the dielectric protective layers 2, 4, and the reflective layer 5 are usually formed by a sputtering method, a vapor deposition method, or the like. It is desirable to form a layer using an in-line apparatus in which a target for the recording layer, a target for the protective layer, and a target for the reflective layer are installed in the same vacuum chamber, in order to prevent oxidation and contamination between the layers. In this case, the target used for each layer may be either co-sputtering using a plurality of targets or using a composite material target.

For the protective coat layer 6, an ultraviolet-curing or thermosetting resin having high hardness is usually used. Generally, the thickness of the 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, it is still difficult to obtain optical contrast, and cracks are likely to occur. In particular, recently developed rewritable compact discs (CDs
-RW), it is preferably 10 nm or more and 30 nm or less in order to obtain a contrast compatible with a CD (for example, a modulation degree of 50% or more) or a contrast compatible with a rewritable DVD that will appear in the future.
If the thickness is less than 10 nm, the reflectance becomes too low, and if the thickness is more than 30 nm, the heat capacity tends to be large and the recording sensitivity tends to be poor.

As a material of the recording layer, for example, GeSbT
e, InSbTe, AgSbTe, AgInSbTe
Which alloy to use. These are overwritable materials
It is. Specifically, ｛(Sb_TwoTe_Three)_1-x(GeT
e)_x｝_1-ySb_yAlloy (however, 0.2 ≦ x ≦ 0.
9, 0 ≦ y ≦ 0.1), and 10 atomic% in the ternary alloy
Up to about In, Ga, Zn, Sn, Si, Cu, A
u, Ag, Pd, Pt, Pb, Cr, Co, O, S, S
alloy containing at least one of e, Ta, Nb, and V
can give. Note that Sb_TwoTe_ThreeAnd GeTe
Ge in the composition on the line _TwoSb_TwoTe_FiveIntermetallic compound group
If the linear velocity is around 10 m / s or more
Is possible.

Further, SbTe near the eutectic point of Sb ₇₀ Te ₃₀
MSbTe alloy containing an alloy as a main component (where M is I
n, Ga, Zn, Ge, Sn, Si, Cu, Au, A
g, Pd, Pt, Pb, Cr, Co, O, S, Se, T
a, Nb, and V) are also preferable as a material capable of overwriting at high speed. More preferably, the above alloy has a range of M _w (Sb _z Te _1-z ) _1-w (where 0 ≦ w ≦ 0.20, 0.6 ≦ z ≦ 0.8). Linear velocity 2.4 m / s or more and 11.2 m / s or less (CD
Good overwriting is possible over a wide range of linear velocities in which the ratio between the maximum linear velocity and the minimum linear velocity is 2 or more at a linear velocity of 2 to 8 times the linear velocity).

In the alloy thin film near the eutectic point of Sb ₇₀ Te _{30, the} crystallization speed tends to increase as the Sb / Te ratio increases, so that the linear velocity dependency is determined by the Sb / Te ratio. The recording layer at the time of film formation is usually amorphous, and is used after the entire recording layer is crystallized to be in an initialized state (unrecorded state). The initialization is achieved by flash lamp annealing or instantaneously heating the recording layer to a temperature higher than the crystallization temperature with a laser beam focused to about 100 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, a light beam (gas laser or semiconductor laser beam) focused to a diameter of about 10 to several hundred μm or a long axis of 50 to 100 μm and a short axis of 1 to 10 μm
It is locally heated using a light beam condensed in a degree elliptical shape, and is melted only at the center of the beam. 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. The lower dielectric protective layer and the upper dielectric protective layer are provided to prevent deformation of the substrate and the recording layer due to high temperature during recording. At least one of the above-mentioned films having the specific Zn / Ce ratio is used, but the material of the other protective layer when only one of the films is used can be selected from the following viewpoints.

In general, the material of the dielectric protective layer is determined in consideration of the refractive index, thermal conductivity, chemical stability, mechanical strength, adhesion, etc., but usually has high transparency and high melting point. Oxides, sulfides, nitrides and Ca, M of metals and semiconductors
g, a fluoride such as Li is used. Further, at the time of overwriting, since the recording layer is repeatedly heated from several hundred degrees Celsius to about 1000 degrees Celsius, its melting point or decomposition point needs to be 1000 degrees Celsius or more. Furthermore, it must be substantially transparent to the laser beam wavelength used for recording and reproduction. The wavelength used is usually 600 to 800 nm, but it is expected that the wavelength will be shortened to about 400 nm in the future. It is needless to say that it is not necessary to be transparent to all the wavelengths of 400 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 generally less than 0.2.

In the case of a composite dielectric protective layer composed of a plurality of dielectrics, each dielectric must satisfy the above conditions. The film density of the dielectric protective layer is preferably 80% or more of the bulk density (bulk density) from the viewpoint of mechanical strength (This Solid Films, No. 27).
8, pp. 8 (1996). 74-81). The bulk density of the composite dielectric composed of a plurality of dielectrics uses the theoretical density of equation (1).

[0035]

Ρ = Σm _i ρ _i (1)

(However, the molar concentration of each component i is m _i , and the bulk density of each component is ρ _i )

For the reflective layer, Au, Ag, Al and their alloys are used, and a substance having a high heat radiation effect and a high thermal conductivity is desirable. When actually used, it is preferable that the thickness be 1000 nm or less from the viewpoint of production cost. Usually, it is 0.1 to 100 nm.

[0038]

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 the following examples, the Zn / Ce composition ratio is XPS
(ESI-5500MC manufactured by PHI, X-ray source: monochromatic AlKα ray, extraction angle: 65 °, pass energy: 29.35 eV), and the peak area of Zn _{2p3 / 2} and Ce _3d was corrected for sensitivity. It was determined from the corrected value.

(Example 1) ZnS: CeO_Two= 60: 4
0 (mol%), and after sufficiently stirring the powder,
Pressed at 1150 ° C and 20 tons by hot press method
It was left for 2 hours and sintered. After sufficient polishing,
Bonding of the upper and lower dielectric layers to the
Created a target for. 1.2mm thick polycarbonate
Lower dielectric protection layer / recording layer / upper dielectric protection
Protective layer / reflective layer by sputtering as follows.
Then, a phase change type optical disk was prepared by stacking. Thickness of each layer
Indicates that the lower dielectric protective layer is 110 nm, the recording layer is 30 nm,
The conductor protection layer was 30 nm, and the reflection layer was 100 nm. Recording layer
Is Ge_22.2Sb _22.2Te_55.6The reflective layer is made of Al alloy
It was used. When sputtering each layer,
Moves the substrate around a predetermined circumference and moves the target close to the circumference.
Fixed next to it. Maximum distance between substrate and target is 23
cm.

The upper and lower dielectric layers are each filled with 50% Ar gas.
The composite target was formed by high-frequency sputtering (13.56 MHz) under a pressure of 0.4 Pa at a flow rate of sccm. The film density was 5.5 g / cm ³ , 96% of the theoretical density. JIS Knoop hardness is 608,
The film stress was 9.7E + 8 dyn / cm ² in tensile stress. The refractive index of this film was 2.3 at a wavelength of 780 nm as measured by an ellipsometer. The film composition at this time contains zinc, cerium, sulfur and oxygen.
The molar ratio of Ce was 0.77.

The recording layer and the reflective layer were formed under an Ar gas pressure of 0.4.
The film was formed by direct current sputtering at Pa. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided. After the disk was initialized using an LD bulk eraser having a wavelength of 810 nm, that is, the recording layer was crystallized, dynamic characteristics of the disk were evaluated under the following conditions. While rotating the disk at a linear speed of 10 m / s, a wavelength of 4 MHz and a duty of 50% 7
Using an LD of 80 nm and NA of 0.55 as pulse light,
Overwriting was repeatedly performed with a recording power of 14.5 mW, a base power of 7.5 mW, and a reproduction power of 0.8 mW, and C
/ N was measured. Was subjected to 10 ⁵ times or more repetitive overwriting, C / N is lowered 2% compared to the first,
The noise rise was 0.1%. 80 ℃
It was left under 85% RH high temperature and high humidity condition for 500 hours,
No peeling occurred, and the disk characteristics did not change.

Example 2 As a target material for the upper and lower dielectric protection layers, ZnS: CeO ₂ = 50: 50 (m
ol%), a recording power of 14 mW and a base power of 8.5 mW.
A phase change optical recording medium was prepared and evaluated in the same manner as in Example 1. At this time, the film density of the upper and lower protective layers was 6.2 g.
/ Cm ^3, which is 93% of the theoretical density. Also, J
The IS Knoop hardness was 645, and the film stress was 8.7E + 8 dyn / cm ² in tensile stress. The refractive index of this film was 2.3 at a wavelength of 780 nm as measured by an ellipsometer. The film composition at this time contains zinc, cerium, sulfur and oxygen, and the molar ratio of Zn / Ce is 0.1.
55. Was subjected to 10 ⁵ times or more repetitive overwriting, reduced C / N is 3% compared to the initial, noise rise was 0.6%. 85% at 80 ℃
When left for 500 hours under RH high temperature and high humidity conditions, no peeling or the like occurred, and the disc characteristics did not change.

Comparative Example 1 As a target material for the upper and lower dielectric protection layers, ZnS: CeO ₂ = 80: 20 (m
ol%), and a phase change medium was prepared and evaluated in the same manner as in Example 1 except that the recording power was set to 12 mW. In this case, the film density of the upper and lower protective layers was 4.8 g / cm ³ , which was 99% of the theoretical density.
Met. The JIS Knoop hardness was 492, and the film stress was 3.7E + 8 dyn / cm ² in tensile stress. The refractive index of this film was 2.3 at a wavelength of 780 nm as measured by an ellipsometer. The film composition at this time contained zinc, cerium, sulfur and oxygen, and the molar ratio of Zn / Ce was 2.1. Was subjected to 10 ⁵ times or more repetitive overwriting, first C / N is lowered by 7% as compared to the noise rise was 1.3%. 8 this disk
After leaving for 500 hours under the condition of 0 ° C. and 85% RH at high temperature and high humidity, there was no peeling or the like, and the disc characteristics did not change.

Comparative Example 2 Example 1 except that CeO ₂ was used as the target material for the upper and lower dielectric protection layers.
A phase change type optical recording medium was prepared in the same manner as described above. In addition,
At this time, the film density of the upper and lower protective layers was 5.8 g / cm ³ , which was 81% of the theoretical density. The JIS Knoop hardness is 710, and the film stress is 7.5E +
It was 9 dyn / cm ² . The refractive index of this film was 2.2 at a wavelength of 780 nm as measured by an ellipsometer. The disk was initialized using an LD bulk eraser having a wavelength of 810 nm, that is, the recording layer was crystallized, and then left at room temperature to cause delamination,
The dynamic characteristics could not be evaluated.

[0045]

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. Further, it is possible to obtain an optical information recording medium having excellent adhesion and stability over time. Furthermore, according to the present invention,
Such a medium can be stably manufactured with high productivity.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of an optical information recording medium according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower dielectric protective layer 3 Phase change recording layer 4 Upper dielectric protective layer 5 Reflective layer 6 Protective coat layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K029 AA11 BA64 BB02 BC07 BD00 CA05 5D029 JB18 JC18 LA11 LA14 LA15 LA19 LB01 LB04 LB07 5D121 AA04 EE03 EE09 EE19

Claims (8)

[Claims] 1. An optical information recording medium having a dielectric protective layer and a phase change recording layer on a substrate, wherein the dielectric protective layer contains zinc, cerium, sulfur and oxygen, and has a Zn
An optical information recording medium, wherein the molar ratio of / Ce is 2.0 or less. 2. A dielectric protection layer is provided above and below a phase change recording layer, at least one of which contains zinc, cerium, sulfur and oxygen, and whose Zn / Ce molar ratio is 2.0 or less. The optical information recording medium according to claim 1. 3. An optical information recording medium having at least a lower dielectric protective layer, a phase change recording layer, an upper dielectric protective layer, and a reflective layer on a substrate, wherein the upper dielectric protective layer comprises zinc and cerium. 3. The optical information recording medium according to claim 2, comprising: sulfur, oxygen, and a Zn / Ce molar ratio of 2.0 or less. 4. The thickness of the upper dielectric protection layer is 10-50 nm.
, And the have a mixed composition of the lower dielectric protective layer and a chalcogen compound and SiO _2, the optical information recording medium according to claim 3 thickness is 50-250Nm. 5. The optical information recording medium according to claim 1, wherein the layer containing zinc and cerium is a thin film formed by sputtering. 6. The optical information recording medium according to claim 5, wherein a composite dielectric target is used as a target for sputtering. 7. The optical information recording medium according to claim 6, wherein a Zn / Ce ratio of the composite dielectric target is 1 to 2.5. 8. The method for manufacturing an optical information recording medium according to claim 1, wherein the medium comprises zinc, cerium, sulfur, and oxygen, and has a Zn / Ce ratio of 1 A method for producing an optical information recording medium, wherein a dielectric protective layer is formed by sputtering using a composite dielectric target of not less than 2.5 and a distance between a substrate and a target of not more than 30 cm.