JPH11328730A - Optical information recording medium and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Problem] It is excellent in data preservation, and can record many repetitions.
Provided is an optical information recording medium that can be erased and can be efficiently produced. The present invention relates to a 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 protective layer is formed of a chalcogen compound, a rare earth oxide. An optical information recording medium comprising three or more compounds including a substance and zinc oxide.

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 irradiating a light beam such as a laser beam.

[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 any number of times. Examples of the rewritable medium include a magneto-optical recording 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. The phase change type medium does not require an external magnetic field, and can perform recording / erasing only by changing the power of laser light. 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 type recording system capable of one-beam overwriting, it is general that a recording bit is formed by amorphizing a recording film and erasing is performed by crystallization. As a material of a recording layer 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-based, In-Sb-Te-based, Ge-Sn-Te-based alloy thin films and the like. Also, a write-once type phase change medium can be realized with almost the same material and layer configuration 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 type medium is used as a write-once type, unlike a perforated type, there is no ridge called a rim around the bit, so that the signal quality is excellent, and since an air gap is not required above the recording layer, an air sandwich structure is used. There is an advantage that there is no need.

[0004] Phase-change media include those that record in a crystalline state and an amorphous state and those that record in a different crystalline state. In a normally used rewritable phase-change medium, different crystalline states are used. To achieve this, two different laser light powers are used. This method will be described by taking a case where the amorphous state is used as a recording mark and the crystalline state is used as an erased / initial state as an example.

[0005] The 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. In this case, the recording layer is sandwiched by a protective layer made of a dielectric, and an elliptical beam long in the beam moving direction is used so that the cooling rate becomes slow enough to sufficiently crystallize. 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. In this case, the protective layer also has a function as a heat radiation layer for obtaining a sufficient cooling rate (supercooling rate).

Accordingly, the material of the protective layer is to be optically transparent to laser light, to have a high melting point, softening point, and decomposition temperature, to be easily formed, and to have a suitable thermal conductivity. Is selected from the viewpoint of Further, as described above, deformation due to volume change accompanying melting and phase change of the recording layer in the heating / cooling process, to prevent thermal damage to the plastic substrate, and to prevent deterioration of the recording layer due to moisture. , The protective layer is important.

As described above, various studies have been made on a protective layer which is chemically stable and has sufficient heat resistance and mechanical strength. Above all, dielectrics such as metal oxides and nitrides are suitable as the protective layer in the above point and are generally used. However, since the protective layer made of these dielectrics and the plastic substrate have significantly different coefficients of thermal expansion and elastic properties, they repeatedly peel off from the substrate during repeated recording and erasure, causing pinholes and cracks. There is. Further, the plastic substrate is likely to be warped due to humidity, and this may also cause peeling between the protective layer and the substrate.

On the other hand, as a new dielectric protection layer, ZnS
The main component has been proposed in which SiO ₂ , Y ₂ O ₃ or the like is mixed. These composite compounds have better adhesion to a chalcogenide-based alloy thin film such as GeTeSb, which is often used as a recording layer, than a pure oxide or nitride dielectric. Therefore, in addition to durability against repeated overwriting, film peeling in an accelerated test is small, and the reliability of the phase change medium is further improved.

[0009]

Conventionally, as described above,
ZnS, Zn, which are compounds containing chalcogenide elements
Many proposals have been made for a protective layer composed of a composite film in which an oxide, a nitride, a fluoride, a carbide, or the like is mixed with Se, PbS, CdS, or the like. However, these films have relatively low hardness (Knoop hardness of about 200), and microscopic deformation due to plastic deformation accumulates with repeated overwriting, resulting in a substantial change in optical film thickness. There has been a problem that the reflectance decreases and noise increases. Furthermore, in the above composite film, only the optimum composition range is described in some prior art documents, and even if a mixture of the composition is used, it is not necessarily better than the original protective layer composed of a pure compound alone. Characteristics were not obtained.
This is presumably because the physical properties of the composite were different from those of the compounds constituting the composites, and thus the change in the physical properties due to the production method and the like was unpredictable.

For example, a sputtering method is widely used in forming a protective layer composed of the above-mentioned composite film. However, a composite compound obtained when a composite compound target is used and when a simultaneous sputtering is performed using individual compound targets. The physical properties of the compound protective film may be different. Further, even with the same manufacturing method, physical properties may change due to pressure during sputtering and the like. In the presence of such variations in the physical properties of the protective film, it has been a problem how to find a composite compound protective film suitable for an optical information recording medium and improve the reliability of the medium.

[0011]

According to the study of the present inventors, a crystalline chalcogenide compound such as ZnS has good adhesion to a recording layer usually containing a group VIb chalcogen element or a group Vb element. Therefore, it has the property of not easily causing a change in film thickness due to separation or mass transfer, and is more flexible than the covalent bond of an oxide or the ionic bond of a fluoride. It also has the property that the growth of berths and defects can be suppressed by absorbing by visual plastic deformation. However, it has been found that the use of such a chalcogenated compound alone is not sufficient for crack propagation at the crystal grain boundaries. Further, a composite film of two kinds of compounds such as a composite film of ZnS and ZnO, a composite film of ZnS and a rare earth oxide, and a composite film of ZnS and a rare earth sulfide are also known. It is not clear since the physical properties of the composite membrane often differ from the physical properties of the individual compounds.

The present invention has been made in order to solve the above-mentioned problems. By combining three or more specific compounds, data storage stability is excellent, and a large number of repeated recording / reproduction can be performed. The medium can be manufactured with high productivity. The gist of the present invention is a medium that has at least a recording layer and a protective layer above a substrate, and performs recording by heating the recording layer by irradiating a light beam, wherein the protective layer is formed of chalcogenide. An optical information recording medium comprising at least three compounds including a compound, a rare earth oxide and zinc oxide.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical information recording medium according to the present invention has at least a recording layer and a protective layer above a substrate, and performs recording by irradiating a light beam to heat the recording layer. It is. 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. One side or both sides of the recording layer, preferably both sides (that is, above and below the recording layer). Is provided. 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. In a phase change medium, since the heating temperature is generally high, heat resistance and mechanical strength particularly in a high temperature range are important. The medium of the present invention can have one or more recording layers and one or more protective layers, and can also have other layers.

Hereinafter, an example of the structure of a phase change medium that can be suitably used in the present invention will be described. The phase change medium usually includes a substrate and a phase change type recording layer provided above the substrate,
And a protective layer provided on at least one surface of the recording layer. Preferably, as shown in FIG. 1, it has a structure of a substrate / lower protective layer / recording layer / upper protective layer / reflective layer, and more preferably is coated (protected) with a UV-curable or thermosetting resin. (Coat layer). In FIG. 1, for the substrate 1, a transparent resin such as a polycarbonate-based resin, an acrylic-based resin, or a polyolefin-based resin, or glass can be used. Among them, transparent resins, especially polycarbonate resins, are the most widely used in CDs and are most preferable because they are inexpensive. Also,
The case where a protective layer is provided in contact with the substrate is also preferable in terms of suppressing peeling of the protective layer.

In FIG. 1, a recording layer 3 is a phase change type recording layer, and its thickness is generally 10 nm to 100 n.
The range of m is preferred. 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. Further, in order to obtain a large difference in reflectance before and after recording, that is, a contrast so as to be compatible with a CD, it is practically preferable that the thickness be 10 nm or more and 30 nm or less. If the thickness is less than 10 nm, the reflectance is too low. If the thickness is more than 30 nm, contrast tends to be hardly obtained, and the heat capacity tends to be large, resulting in poor recording sensitivity.

As the recording layer 3, Ge, Sb, Te, I
A simple substance or an alloy of various metals including n, Ag, Ga, Al, Sn, Zn and the like is used. Among them, preferably G
eSbTe, InSbTe, AgSbTe, AgInS
A compound such as bTe is selected. More preferably, {(Sb ₂ Te ₃ ) _1-x (GeTe) _x ｝ _1-y Sb
_y (0.2 ≦ x ≦ 0.9, 0 ≦ y ≦ 0.1) alloy and 10 atomic% or less of In, Ga, Zn, S
n, Si, Cu, Au, Ag, Pd, Pt, Pb, C
An alloy thin film containing at least one of r, Co, O, S, Se, Ta, Nb, and V can be given. In addition, Sb ₇₀ T
a main component e ₃₀ eutectic point near the SbTe alloy, comprising the following elements M about 20 atomic%, MSbTe (where, M = 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 materials that can be overwritten at high speed, and are thus preferable.

At least twice as fast as the CD linear velocity (2.4 to
2.8m / s) to 8x speed (9.6m / s-11.2m)
/ S), a good overwriteable phase change medium
The body recording layer will be described. The recording layer composition used
It is preferable that the crystallization speed is fast enough to erase sufficiently at the maximum speed.
Good. The above ｛(Sb_TwoTe_Three)_1-x(GeTe)_x｝
_1-ySb_y(0.2 ≦ x ≦ 0.9, 0 ≦ y ≦ 0.1)
In the base alloy recording layer, Sb_TwoTe_Three-GeTe
If you deviate from the line connecting
And the composition on this line and Ge_TwoSb_TwoTe_FiveBetween metal
By setting it near the compound composition, even at 10 m / s or more,
A bar writable medium is obtained. On the other hand, Sb₇₀Te₃₀
In alloy thin films near the eutectic point, linear velocity dependence is the main component
Determined by Sb and Te, the larger the Sb / Te ratio,
The crystallization rate tends to increase. That is, Sb₇₀T
e₃₀Based on the eutectic point composition, the linear velocity is determined by the Sb / Te ratio.
Dependency depends. Therefore, the composition of the recording layer is
M_W(Sb_zTe_1-z)_1-w(0 ≦ w ≦ 0.2, 0.6
≦ z ≦ 0.8, M = In, Ga, Zn, Ge, Sn, S
i, Cu, Au, Ag, Pd, Pt, Pb, Cr, C
at least one of o, O, S, Se, Ta, Nb, and V
Species).

As a material of the reflection layer 5, Au, Ag, A
1 and alloys thereof are used, but a substance having a high heat radiation effect and a high thermal conductivity is desirable. The thickness is preferably 50 nm or more in order to enhance the heat radiation effect.
The thickness is preferably 1000 nm or less from the viewpoint of production cost. The recording medium of the present invention is usually amorphous after film formation. Therefore, usually, the entire surface of the formed recording layer is crystallized to be in an initialized state (unrecorded state). And
The initialized recording layer is locally heated to a temperature equal to or higher than the melting point, and re-solidified by rapid cooling through the protective layer to form an amorphous recording bit. Erasing is accomplished by heating the recording layer to just above the crystallization temperature and just below the melting point, and in some cases, just above the melting point to cause recrystallization. Heating below the melting point is recrystallization in the solid phase. When heating to just above the melting point, recrystallization is performed by slow cooling so as not to exceed the critical cooling rate for forming an amorphous phase. Slow cooling can be realized by controlling the pattern of the irradiation laser beam.

Initialization is performed instantaneously by flash lamp annealing or laser light focused to about 100 μm.
This is achieved by heating the recording layer above the crystallization temperature.
Melt initialization is effective as one method for shortening the time required for initialization and surely performing initialization by one light beam irradiation. In the case of the above-described layer configuration, the recording medium is not immediately destroyed just because it is melted.
For example, a light beam (gas laser or semiconductor laser) focused to a diameter of about 10 to several hundred μm or an elliptical light beam having a major axis of 50 to several hundred μm and a short axis of about 1 to 10 μm is locally used. And melted only at the center of the beam. At this time, the periphery of the beam is also heated at the same time, so that the melted portion is preheated, so that the cooling rate is reduced, and good recrystallization is performed. By using this method, for example, the initialization time can be reduced to one tenth of that of the conventional solid-phase crystallization, the productivity can be significantly reduced, and the change in crystallinity at the time of erasing after overwriting can be reduced. Can be prevented. To prevent deformation due to high temperature during recording,
In general, a lower protective layer 2 is provided in contact with the recording layer and the substrate, and an upper protective layer 4 is provided in contact with the opposite side of the recording layer. As the material of the protective layer, the refractive index,
It is determined in consideration of thermal conductivity, chemical stability, mechanical strength, adhesion, and the like.

One of the features of the present invention is that a composite compound obtained by mixing the above-mentioned three or more kinds of dielectric compounds is used as a material of the protective layer. When a plurality of protective layers are provided, at least one of the layers may contain the above-mentioned three kinds of compounds. In particular, when protective layers are provided on both sides of the recording layer, both of the above-mentioned three kinds of compounds are used. It is preferred to have the effect of the invention is remarkable. The recording layer is usually several hundred degrees Celsius to 10
Since these compounds are repeatedly heated to about 00 ° C., these three compounds preferably have melting points or decomposition points of 1000 ° C. or higher. Further, it is preferable that the material is substantially transparent to a laser beam wavelength (usually about 800 to 400 nm) used for recording and reproduction. Of course,
It is not necessary to be transparent to all 800 to 400 nm, but it is sufficient if it is transparent to the laser beam used therein. Being substantially transparent requires that the absorption coefficient, which is the imaginary part of the complex refractive index for that wavelength, be less than about 0.5.

Examples of the chalcogenizing compound to be used include zinc chalcogenides such as ZnS and ZnSe, and Cd.
II-V compounds such as S and CdSe, La ₂ S ₃ , Ce ₂
Rare earth sulfides such as S ₃ , TaS ₂ , MgS, CaS and the like can be mentioned. These alone become crystalline thin films. Zinc chalcogenides are chemically stable, and especially Z
nS has the lowest toxicity and is most preferable. Moreover, ZnS is a substance having a very high sputtering rate when performing sputtering. When ZnS is contained in the dielectric target, the film formation rate is improved as compared with the material before the ZnS is made.

In the present invention, zinc oxide is also used. Zinc oxide ZnO has excellent stability and is useful for improving the film formation rate. Note that zinc oxide is distinguished from the chalcogen compound. Furthermore, a rare earth oxide is used. La ₂ O ₃ , CeO ₂ , P
rO ₂ , Nd ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , GdO
_{2, Gd 2 O 3, Tb} 4 O 7, Dy 2 O 3, Ho
₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Lu ₂
O ₃ and Y ₂ O ₃ are used. Among them, CeO ₂ , HfO ₂ , ZrO ₂ , Y ₂ O _{3 and the} like are preferable. Among them, the crystal peaks appear at exactly the same position in the X-ray diffraction of the Cubic structure of CeO _{2 and} the Cubic structure of ZnS. The composite dielectric obtained by combining the two has an extremely smooth film quality. Even when used as a medium, the overwrite characteristics are extremely good, and noise hardly occurs. By further adding ZnO here, the sputtering rate during film formation is further improved. in this way,
By combining the three types, it was possible to achieve extremely good disk characteristics and a high deposition rate, which could not be realized by a single product, and to obtain a composite dielectric excellent in productivity. In the composite dielectric film, there may be a substance further contained in addition to these three types. In addition, a plurality of chalcogenide compounds and rare earth oxides may be used, respectively.

By using such a protective layer, it is possible to greatly contribute to the practical use of a rewritable medium having excellent data storage stability and capable of recording and erasing a large number of times. As the composition range of the protective layer, when the molar ratio of the chalcogenated compound, the rare earth oxide and the zinc oxide at the time of charging the powder of the target and at the time of the molded target is a, b and c, respectively, 0.1 ≦ a ≦ 0.9,
0.1 ≦ b ≦ 0.9, 0.01 ≦ c ≦ 0.4 (a
+ B + c = 1) is desirable. More preferably, the content of ZnO is 1 mol% or more and less than 30 mol%.

If the amount of ZnS is too small, there is a problem in the adhesion to the recording layer material, which is undesirable. If the amount is too large, the film becomes too soft, so that mass transfer cannot be suppressed. In addition, when the amount of the oxide is too large, the film may be easily cracked, so that an appropriate range is required. In particular, attention must be paid to the amount of ZnO added. The thickness of the protective layer is generally about 0.1 to 500 nm, but the thickness of the lower protective layer is preferably 50 nm or more and 300 nm or less. If it is too thin, there is a problem that the substrate deformation due to heat during recording cannot be suppressed, and if it is too thick, there is a problem that the film tends to crack and it takes too much filming time during manufacturing, Not realistic. If it is used for the upper protective layer, it is 0.
It is desirable that the thickness be 1 nm or more and 300 nm or less.

The film density of the protective layer is preferably 80% or more of the bulk state from the viewpoint of mechanical strength (Thin).
Solid Films, Vol. 278 (1996),
74-81). When a mixture dielectric thin film is used, the theoretical density of the following equation is used as the bulk density. When the molar concentration of each component i is m _i , and the bulk density of a single component is ρ _i ,

[0027]

Ρ = Σm _i ρ _i (1)

In the above description, the description has been made centering on the phase change type optical information recording medium having the layer structure as shown in FIG. 1, but the substrate, the recording layer, the reflective layer, the protective layer, etc. Is applicable to the case of another layer configuration. Further, the layer configuration of the medium of the present invention is not limited to the one described in FIG. 1, but another layer configuration may be adopted or another layer may be provided between each layer or the outermost layer. It is also possible. When the medium of the present invention is a phase change medium, as shown in FIG. 1, a lower protective layer, a recording layer,
It is preferable to adopt a configuration in which the phase change recording layer, the upper protective layer, and the reflective layer are sequentially stacked in a state of being in contact with each other. The recording layer may be a recording layer other than the phase change type, for example, a magneto-optical type.

The medium of the present invention can be produced by laminating other layers such as a protective layer and a recording layer provided above the substrate and, if necessary, a reflective layer by sputtering. In this case, a method in which each layer is formed by an in-line apparatus in which targets corresponding to the respective raw materials are installed in the same vacuum chamber is preferable from the viewpoint of preventing oxidation and contamination between the layers. As a target for forming the protective layer defined in the present invention, a plurality of targets each composed of the above three compounds can be used, but a composite compound containing a plurality of compounds constituting the protective layer The method of using a target consisting of is preferred in terms of controlling the composition.

[0030]

EXAMPLE 1 A powder mixed in a molar ratio of ZnS: ZnO: CeO ₂ = 50: 5: 45 was sufficiently stirred, and then heated under a pressure of 1150 ° C. and 20 tons by a hot press method. It was left for a time and sintered. After polishing this sufficiently, I
By bonding with n solder, a composite compound target for a protective layer was prepared. The lower protective layer / recording layer / upper protective layer / reflective layer were sequentially laminated on a 1.2 mm thick disc-shaped polycarbonate substrate by sputtering to produce a phase change optical disk. The thickness of each layer is 110 nm for the lower protective layer, 30
nm, the upper protective layer was 30 nm, and the reflective layer was 100 nm.
The recording layer was Ge _22.2 Sb _22.2 Te _55.6 , and the reflective layer was A
1 alloy was used.

The upper and lower protective layers are made of Ar gas of 5
The film was formed at a flow rate of 0 sccm under a pressure of 0.4 Pa by high frequency (13.56 MHz) sputtering of the above target. The deposition rate was 77 ° / min. The film density was 4.9 g / cm ³ , 82% of the theoretical density. The JIS Knoop hardness was 614, and the film stress was 2.78E + 8 dyn / cm ² by tensile. The optical constant of this film was 780 nm as measured by an ellipsometer.
2.2-0i for 650nm and 2.2- for 650nm
It was 0.05i. The recording layer and the reflective layer were formed by DC sputtering at an Ar gas pressure of 0.7 Pa.
Further, an ultraviolet curable resin layer having a thickness of about 5 μm was provided on the uppermost layer.

After the disk was initialized using an LD bulk eraser having a wavelength of 810 nm, ie, the recording layer was crystallized, the dynamic characteristics of the disk were evaluated under the following conditions.
4MHz, dut while rotating at a linear velocity of 10m / s
Overwriting was repeatedly performed with a recording power of 13 mW, a base power of 8.5 mW, and a reproduction power of 0.8 mW under the condition of a wavelength of 780 nm using pulse light of y50%, and the C / N and the erasing ratio were measured. As a result, no increase in noise was observed even after overwriting 100,000 times. This disk was left under the conditions of 80 ° C., 85% RH, high temperature and high humidity for 500 hours, but no peeling or the like occurred and the disk characteristics did not change.

Example 2 ZnS: CeO ₂ : ZnO = 45: 45: 10 (mol
%) Was sufficiently stirred and then left for 2 hours in a state of being pressurized at 1150 ° C. and 20 tons by a hot press method for sintering. After this was sufficiently polished, it was bonded to a Cu plate with In solder to prepare a composite compound target for a protective film. The lower protective layer / recording layer / upper protective layer / reflective layer were sequentially laminated on a 1.2 mm thick disc-shaped polycarbonate substrate by sputtering to produce a phase change optical disk. The thickness of each layer was 110 nm for the lower protective layer, 30 nm for the recording layer, 30 nm for the upper protective layer, and 100 nm for the reflective layer. 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 protective layers are made of Ar gas of 5
A film was formed at a flow rate of 0 sccm under a pressure of 0.4 Pa by high-frequency sputtering (13.56 MHz) of the above target. The film formation rate was 73 ° / min. The film density was 5.4 g / cm ³ , 88% of the theoretical density. The JIS Knoop hardness was 516, and the film stress was 1.90E + 9 dyn / cm ² in tensile stress. The optical constant of this film was 2.3-0i at a wavelength of 780 nm as measured by an ellipsometer.

The recording layer and the reflective layer are formed under an Ar gas pressure of 0.1.
The film was formed by DC sputtering at 4 Pa. Further, an ultraviolet curable resin layer having a thickness of about 5 μm was provided on the uppermost layer. The disk was initialized using an 810 mm LD bulk eraser, ie, the recording layer was crystallized, and the dynamic characteristics of the disk were evaluated under the following conditions. 10m disc
/ MHz while rotating at a linear speed of 4 MHz, duty 50
%, The overwriting was repeatedly performed at a recording power of 13.0 mW, a base power of 8.5 mW, and a reproduction power of 0.8 mW, and the C / N and the erasing ratio were measured. 10 ⁵ times even after deterioration in the reproduction signal was observed.

Comparative Example 1 A phase change type recording medium was manufactured and evaluated in the same manner as in Example 1 except that the composition of the protective layer was a composite compound of ZnS and SiO ₂ . That is, ZnS: SiO ₂ = 80: 20
(Mol%) was sufficiently stirred, and then left for 2 hours in a state of being pressurized at 1200 ° C. and 20 tons by a hot press method for sintering. After polishing this sufficiently, Cu
A composite compound target for a protective film was formed by bonding to the plate with In solder.

The lower protective layer / recording layer / upper protective layer / reflective layer were sequentially laminated on a 1.2 mm thick disc-shaped polycarbonate substrate by sputtering to produce a phase change optical disk. The thickness of each layer was 160 nm for the lower protective layer, 30 nm for the recording layer, 30 nm for the upper protective layer, and 100 nm for the reflective layer. 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 protective layers are made of Ar gas of 5
A film was formed at a flow rate of 0 sccm under a pressure of 0.4 Pa by high-frequency sputtering (13.56 MHz) of the above target. The film density was 3.5 g / cm ³ , 94% of the theoretical density. The JIS Knoop hardness is 280, and the film stress is 1.1E + 9dyn / c in tensile stress.
m ² . The optical constant of this film was 2.1-0i at a wavelength of 780 nm as measured by an ellipsometer. The composition ratio of the composite target and the sputtered film was almost the same. 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 layer having a thickness of about 5 μm was provided on the uppermost layer.

After the disk was initialized using an LD bulk eraser having a wavelength of 810 nm, that is, the recording layer was crystallized, the dynamic characteristics of the disk were evaluated under the following conditions.
4 MH while rotating the disk at a linear speed of 10 m / s
z, duty 50% pulse light, recording power 1
4.5 mW, base power 7.5 mW, reproduction power 0.
Perform repetitive overwriting at 8 mW, was measured for C / N and erase ratio, 10 ⁴ times after reproduction signal amplitude has been reduced. In addition, about 10 times of overwriting, a decrease in the CN ratio due to an increase in noise started. Although the decrease of the CN ratio itself was less than 3 dB, many local burst defects occurred.

Comparative Example 2 A phase change type recording medium was manufactured and evaluated in the same manner as in Example 1 except that the composition of the protective layer was a composite compound of ZnS and ZnO. That is, ZnS: ZnO = 50: 50 (mo
1%), and the mixture was sufficiently agitated, and then left for 2 hours in a state of being pressurized at 1200 ° C. and 20 tons by a hot press method to be sintered. After this was sufficiently polished, it was bonded to a Cu plate with In solder to prepare a composite compound target for a protective film. The lower protective layer / recording layer / upper protective layer / reflective layer were sequentially laminated on a 1.2 mm thick disc-shaped polycarbonate substrate by sputtering to produce a phase change optical disk. The thickness of each layer was 110 nm for the lower protective layer, 30 nm for the recording layer, 30 nm for the upper protective layer, and 100 nm for the reflective layer. The recording layer was Ge _22.2 Sb _22.2 Te _55.6 , and the reflective layer was an Al alloy.

For the upper and lower protective layers, Ar gas
A film was formed at a flow rate of 0 sccm under a pressure of 0.4 Pa by high-frequency sputtering (13.56 MHz) of the above target. The film density was 4.5 g / cm ³ , 94% of the theoretical density. The JIS Knoop hardness is 534, and the film stress is 2.2E + 9dyn / c in tensile stress.
m ² . The optical constant of this film was 2.2-0i at a wavelength of 780 nm as measured by an ellipsometer.

The recording layer and the reflective layer are formed under an Ar gas pressure of 0.1.
The film was formed by DC sputtering at 4 Pa. Further, an ultraviolet curable resin layer having a thickness of about 5 μm was provided on the uppermost layer. When this disk was initialized using an 810 mm LD bulk eraser, that is, when the recording layer was crystallized, cracks occurred in the film, and large cracks that could be visually observed entered the film. Even if this can be overcome by improving the initialization method, it is considered that cracks due to repetitive overwriting and peeling due to aging are inevitable.

Comparative Example 3 A phase change type recording medium was manufactured and evaluated in the same manner as in Example 1 except that the composition of the protective layer was a composite compound of ZnS and CeO ₂ . That is, ZnS: CeO ₂ = 50: 50 (m
ol%) was sufficiently stirred, and then heated at 1150 ° C. and 20 tons under a hot press method.
It was left for a time and sintered. After this was sufficiently polished, it was bonded to a Cu plate with In solder to prepare a composite compound target for a protective film. The lower protective layer / recording layer / upper protective layer / reflective layer were sequentially laminated on a 1.2 mm thick disc-shaped polycarbonate substrate by sputtering to produce a phase change optical disk. The thickness of each layer is 110 nm for the lower protective layer, 30 nm for the recording layer, 30 nm for the upper protective 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.

For the upper and lower protective layers, Ar gas
A film was formed at a flow rate of 0 sccm under a pressure of 0.4 Pa by high-frequency sputtering (13.56 MHz) of the above target. The deposition rate was as low as 67 ° / min. The film density was 5.6 g / cm ³ , which was 93% of the theoretical density. The JIS Knoop hardness was 645, and the film stress was 8.65E + 8 dyn / cm ² in tensile stress. The optical constant of this film was 2.3-0i at a wavelength of 780 nm as measured by an ellipsometer.

The recording layer and the reflective layer were formed under an Ar gas pressure of 0.2.
The film was formed by DC sputtering at 4 Pa. Further, an ultraviolet curable resin layer having a thickness of about 5 μm was provided on the uppermost layer. The disk was initialized using an 810 mm LD bulk eraser, ie, the recording layer was crystallized, and the dynamic characteristics of the disk were evaluated under the following conditions. 10m disc
/ MHz while rotating at a linear speed of 4 MHz, duty 50
%, The overwriting was repeatedly performed at a recording power of 14.0 mW, a base power of 8.5 mW, and a reproduction power of 0.8 mW, and the C / N and the erasing ratio were measured.
10 ⁵ times even after deterioration in the reproduction signal was observed. However, as described above, it can be seen that the film formation rate is small and the productivity is poor. In addition, even if the film formation rate is numerically small, the thickness of the protective film is 100 nm.
(= 1000 °), and a large amount of media is produced, so the difference is extremely large in total.

[0046]

The optical information recording medium of the present invention has excellent data storage stability and can perform a large number of repeated recording / erasing operations. Further, the information recording medium of the present invention can be manufactured at a high rate.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of an optical information recording medium according to the present invention.

[Explanation of symbols]

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

Claims (15)

[Claims] 1. A medium for recording by heating a recording layer by irradiating a light beam thereon, said recording medium comprising at least a recording layer and a protective layer above a substrate, wherein said protective layer is a chalcogenated compound. An optical information recording medium comprising three or more compounds including a rare earth oxide and zinc oxide. 2. A protective layer is provided above and below a recording layer provided above a substrate, and at least one of the protective layers is made of at least three compounds including a chalcogen compound, a rare earth oxide and zinc oxide. An optical information recording medium, comprising: 3. The optical information recording medium according to claim 2, wherein the protective layers provided above and below the recording layer are each composed of three or more compounds including a chalcogenated compound, a rare earth oxide and zinc oxide. . 4. The optical information recording medium according to claim 1, wherein the recording layer is a phase change recording layer. 5. At least a lower protective layer above the substrate,
The optical information recording medium according to any one of claims 1 to 4, further comprising a phase change recording layer, an upper protective layer, and a reflective layer. 6. The optical information recording medium according to claim 1, wherein the chalcogenated compound contains zinc chalcogenide. 7. The optical information recording medium according to claim 6, wherein the zinc chalcogenide contains ZnS. 8. The method of claim 1, wherein the rare earth oxide includes CeO _2.
8. The optical information recording medium according to any one of items 1 to 7. 9. The optical information recording medium according to claim 1, wherein the protective layer is obtained by sputtering. 10. When the molar ratio of a chalcogenide compound, a rare earth oxide and zinc oxide in a sputtering target is a, b and c, respectively, a = 0.1
-0.9, b = 0.1-0.9, c = 0.01-0.4
10. The optical information recording medium according to claim 9, wherein (a + b + c = 1). 11. The optical information recording medium according to claim 9, wherein the sputtering target is a composite compound target containing a chalcogenated compound, a rare earth oxide, and zinc oxide. 12. The film density of the protective layer is 80% of the theoretical density.
The optical information recording medium according to any one of claims 1 to 11, which is as described above. 13. The optical information recording medium according to claim 1, wherein the substrate is made of a transparent resin. 14. The optical information recording medium according to claim 13, wherein the transparent resin includes a polycarbonate resin. 15. A method for producing an optical information recording medium comprising laminating a recording layer and a protective layer above a substrate by sputtering, wherein the protective layer contains a chalcogenide compound, a rare earth oxide and zinc oxide. A method for producing an optical information recording medium, comprising three or more compounds.