JPH06124481A - Optical information recording medium - Google Patents

Abstract

(57) [Summary] [Object] To provide an optical information recording medium having a phase transition type optical recording layer capable of recording, erasing and reproducing information at high speed and high density by irradiation with laser light or the like. A dielectric protective layer and a phase transition type optical recording layer are provided on a substrate, and the dielectric protective layer is a mixture of zinc sulfide and tantalum oxide having a tantalum oxide content of 30 to 91 mol%. A product that has a specific density and a specific compressive stress.

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 having a phase transition type optical recording layer capable of recording, erasing and reproducing information at high speed and high density by irradiation with laser light or the like.

[0002]

2. Description of the Related Art In recent years, an optical disk using a laser beam has been developed as a recording medium that meets the demands for increasing the amount of information and increasing the recording and reproducing density and speed. There are two types of optical disks: a write-once type that allows recording only once and a rewritable type that allows recording / erasing as many times as desired. Examples of the rewritable optical disk include a magneto-optical recording medium that utilizes the magneto-optical effect and a phase change medium that utilizes reversible change in crystal state.

The phase change medium does not require an external magnetic field, and recording / erasing can be performed only by modulating the power of laser light. Further, there is an advantage that it is possible to perform one-beam overwriting in which erasing and re-recording are simultaneously performed with a single beam. In the one-beam overwritable phase change recording method, it is general that the recording film is made amorphous to form a recording bit and is crystallized to erase. 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 system, Ge-Sn-Te system alloy thin film, and the like.

A write-once type phase change medium can be realized by using almost the same material and layer structure as the rewritable type of the phase change recording system. In this case, since there is no reversibility, information can be recorded and stored for a longer period of time, and in principle, it can be stored almost permanently. When a phase change medium is used as the write-once type, unlike the punched type, there is no rise around the bit called the rim, resulting in excellent signal quality. Also, since there is no space above the recording layer, an air sandwich structure is required. There is an advantage that there is no.

Generally, in a rewritable phase change recording medium,
Two different laser light powers are used to achieve different crystalline states. This system will be described by taking as an example a case where recording / erasing is performed in an erased / initial state where an amorphous bit is crystallized. 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 cooling layer is sandwiched between dielectric layers or a long elliptical beam is used in the moving direction of the beam so that the crystallization is sufficiently slow.

On the other hand, the amorphization is performed by heating the recording layer to a temperature higher than the melting point and quenching it. in this case,
The dielectric layer also has a function as a heat dissipation layer for obtaining a sufficient cooling rate (supercooling rate). In addition, in order to prevent deformation of the recording layer due to melting and volume change in the heating / cooling process, thermal damage to the plastic substrate, and deterioration of the recording layer due to moisture as described above, A protective layer consisting of a body layer is important. The material of the protective layer material is optically transparent to laser light,
It is selected from the viewpoints of high melting point / softening point / decomposition temperature, easy formation, and proper thermal conductivity.

[0007]

When the heat resistance and mechanical strength of the protective layer and the adhesion to the substrate, recording layer, etc. are not sufficient, deterioration of the characteristics of the disk due to repeated recording and erasing and storage stability It becomes a cause of inferiority. If the heat resistance and mechanical strength are not sufficient, the protective layer is deformed by repeated recording and erasing, and the disc characteristics are deteriorated. Regarding the adhesiveness, since the coefficient of thermal expansion and the elastic property of the dielectric thin film and the plastic substrate are large, they become detached from the substrate to cause pinholes and cracks during repeated recording and erasing.

Further, although the plastic substrate is liable to warp due to humidity, peeling of the protective film may also occur, which satisfies heat resistance, mechanical strength, adhesion to the substrate, recording layer and the like. Obtaining a protective layer is not easy. The present inventors have studied the above protective film using various materials, and have found that it is possible to produce a disk with little deterioration in characteristics due to repeated recording and erasing and having excellent storage stability. Reached

[0009]

The gist of the present invention is to provide an optical information recording medium having at least a dielectric protective layer and a phase transition type optical recording layer on a substrate, wherein the dielectric protective layer is made of tantalum oxide. A dielectric containing zinc sulphide and tantalum oxide of ˜91 mol% and having a density of 0.90 ×
(4.102 × (100−X) /100+8.735×
X / 100) g / cm ³ (X is mol% of tantalum oxide)
Value) or more, and a compressive stress of 4.0 × 10 ⁹ dyn / cm ² or less, the optical information recording medium.

The protective layer is a dielectric containing zinc sulfide and tantalum oxide, and the content of the tantalum oxide is 30 to 30.
The protective layer is set to 91 mol%, that is, for example, (ZnS) _100-X (Ta ₂ O ₅ ) _X, where (30 <X <9
By using the protective layer represented by 1), the filling factor of atoms, which is considered to affect the mechanical strength, is increased as compared to the case of the film of Ta ₂ O ₅ alone, and it is considered that the adhesion is affected inside. The stress can be made lower than in the case of the film of Ta ₂ O ₅ alone, and the insufficient adhesion can be improved in the film of ZnS alone. The content of tantalum oxide is preferably 50 to 80 mol%.

When a film of ZnS alone is formed as the protective layer by the RF sputtering method, the film is inferior in adhesion and peeling occurs at the film interface at the time of initialization of the disk, and excellent recording characteristics cannot be obtained. Further, when a film made of tantalum oxide alone by the RF sputtering method is used as the protective layer, it is difficult to obtain a film having a filling rate of 90% or more of the bulk density, which is considered to affect the mechanical strength. Oxygen in the formed film is insufficient, and excellent characteristics cannot be obtained.

Further, in the case of the above single film, the internal stress becomes large depending on the film forming conditions, the film peels off under a high temperature and high humidity environment, and the characteristics are deteriorated even by repeating recording and erasing. If the film forming conditions are such that the internal stress decreases, the filling factor of the film further decreases, and the characteristics are likely to deteriorate due to repeated recording and erasing.

On the other hand, in the case of a mixture of zinc sulfide and tantalum oxide, by selecting the sputtering conditions, it is possible to provide sufficient adhesion, mechanical strength and composition stability, which could not be obtained by a single film. Ie Ta ₂ O ₅ and Z
By mixing and using nS, a film having a high density (a density close to the density calculated as a simple mixture from the density and composition ratio of the bulk of each element) can be relatively easily obtained. Although the atomic structure of the film is not clear, it can be understood that excellent disk characteristics can be obtained because a dense film with few voids is formed. The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio is 0.90 or more, which is practically preferable, and preferably 0.92 or more and 1.05 or less. good.

It is considered that by mixing ZnS and Ta ₂ O ₅ , the internal stress becomes smaller than that of Ta ₂ O ₅ alone, and the adhesion is also improved. The internal stress affects the stability (adhesion) of the high temperature and high humidity environment test, but if the compressive stress is 0 or more and 4.0 × 10 ⁹ dyn / cm ² or less, the internal stress affects the stability of the high temperature and high humidity environment test. I found it to be excellent. It is possible to reduce the compressive stress and further the tensile stress by increasing the pressure at the time of sputtering. However, at this time, the density of the film may be reduced, so care must be taken. That is, the tantalum oxide content, density,
It is necessary to satisfy all stress conditions.

Further, SiNx, SiOx, AlOx, B
A small amount of another dielectric such as N may be mixed. According to the present invention, it is possible to provide an optical information recording medium having sufficient durability against repeated recording / erasing and excellent in storage stability. The substrate of the recording medium in the present invention may be any one of glass, plastic, glass having a curable resin provided thereon, etc., but the protective layer used in the present invention has excellent heat resistance and heat of the substrate. It is possible to use a polycarbonate resin substrate which is generally used as a substrate for optical discs because it has an effect of preventing mechanical deformation.

In the present invention, the protective layer, that is, for example, (ZnS) _100-X (Ta ₂ O ₅ ) _X, where (30 <X <91)
By providing the protective layer represented by (3) between the substrate and the recording layer, thermal deformation of the substrate is prevented, and pinholes and cracks are also prevented because of good adhesion to the substrate. The thickness of the protective layer is preferably in the range of 100 to 5000Å. If the thickness is less than 100 Å, the effect of preventing deformation of the substrate and the recording film is insufficient, and it does not serve as a protective layer. On the other hand, in the case of using a plastic substrate, if it exceeds 5000 Å, (ZnS) _100-X (Ta ₂ O
₅ ) _X However, the internal stress of the protective layer consisting of (30 <X <91) and the difference in elastic properties from the substrate become remarkable, and cracks are likely to occur.

The phase change optical recording layer is GeSbTe system, InS
A bTe-based material is used, and Sn, In, for improving crystallization speed, easiness of amorphization, crystal grain size, storage stability, etc.
Ge, Pb, As, Se, Si, Bi, Au, Ti, C
You may add u, Ag, Pt, Pd, Co, Ni, etc.
The thickness is generally selected in the range of 100 to 1000Å. If the thickness of the recording layer is less than 100Å, sufficient contrast cannot be obtained, while if it exceeds 1000Å, cracks are likely to occur. The recording layer is usually sandwiched by the protective layers, that is, it is preferable that the recording layer has a structure of substrate / protective layer / recording layer / protective layer. Further, a reflective layer, an ultraviolet curable resin layer, etc. may be provided.

The recording layer, the protective layer and the reflective layer are formed by a sputtering method or the like. It is desirable to perform film formation by an in-line apparatus in which the target for recording film, the target for protective film, and the target for reflective layer material, if necessary, are installed in the same vacuum chamber in order to prevent oxidation and contamination between the layers. It is also excellent in terms of productivity.

[0019]

The present invention will be described in detail with reference to the following examples.
It Example 1 (ZnS) on a polycarbonate resin substrate₃₁(Ta
₂O_Five)₆₉Protective film, Ge₁₂Sb₃₆Te₅₂Recording film, (Zn
S)₃₁(Ta₂O_Five)₆₉Protective film and Al alloy reflective film
1100Å, 200Å, 200Å, 2000Å film thickness
Were sequentially formed by the sputtering method. (ZnS)₃₁
(Ta₂O_Five)₆₉The protective film is (ZnS)₅₀(Ta ₂O_Five)₅₀
The target having the composition of Ar is sputtered at a pressure of 0.28.
RF sputtering with Pa and input power of 500W
Formed by. DC sputtering for recording film and reflective film
It was produced by the method. Furthermore, an ultraviolet curable resin layer is provided on the reflective layer.
Was set up.

Since the recording layer of the disk manufactured as described above is in an amorphous state, it is crystallized by an Ar laser and initialized, and then the wavelength is 780 nm and the NA is 0.50.
The dynamic characteristics of the disc were evaluated by the evaluation device using the laser pickup of. When the disc was rotated at a linear velocity of 1.4 m / s and the EFM random signal was overwritten 10 times and 10000 times with a recording power of 14 mW and an erasing power of 6.5 mW, the 3T jitter was measured to be 21 nsec and 31 nsec, respectively. It was Next, place this disc in an environment of temperature 85 ° C and humidity 85% RH for 50
When the disc was observed with an optical microscope after standing for 0 hour, no defect such as film peeling was observed, and the 3T jitter of the previously recorded signal at 10 times overwriting was 23 nsec.

Next, on the glass substrate, (ZnS) ₃₁ (Ta
_{2. A} film of ₂ O ₅ ) ₆₉ was formed under the same film-forming conditions as above at 3500 liters, and the density of the film was measured from the weight change before and after film formation.
It was 03 g / cm ³ . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio, 7.03 / (4.102 × (100−X) /
The value of 100 + 8.735 × X / 100) (X is the value of mol% of tantalum oxide) was 0.96. Further, a (ZnS) ₃₁ (Ta ₂ O ₅ ) ₆₉ film was provided on a Si substrate having a thickness of 330 μm with the (1,1,1) surface as the surface under the same film forming conditions as above for 3500 Å, and the warp of the substrate before and after film formation The internal stress was determined from the result, and it was found to be a compressive stress of 2.9 × 10 ⁹ dyn / cm ² . Internal stress is measured by a wafer stress gauge (Model No. 3011, manufactured by Ionic Systems, Inc., USA).
Using 4), the Si substrate was placed with a knife edge interval of 3 inches, and the stress was calculated from the measurement result of the central warp height.

Example 2 As a protective film, a (ZnS) ₉ (Ta ₂ O ₅ ) ₉₁ film obtained by sputtering a target having a composition of (ZnS) ₃₀ (Ta ₂ O ₅ ) _{70 in} the same manner as in Example 1 A disk was manufactured in the same manner as in Example 1 except that the recording power was 14 mW, and the erasing power was 6.5 mW.
3 when overwriting 10 times and 10000 times
The T jitters were 21 nsec and 35 nsec, respectively. Next, when a high temperature and high humidity environment test was performed under the same conditions as in Example 1 and the disc was observed with an optical microscope, no defects such as film peeling were observed. (ZnS) ₉ (Ta ₂ O ₅ ) was formed on a glass and Si substrate in the same manner as in Example 1.
_{The 91} film was provided under 3400 Å under the same conditions as above and the density and stress were measured. The density was 7.57 g / cm ³ , and the compressive stress was 3.65 × 10 ⁹ dyn / cm ² . The density of the film and
The ratio of the bulk density of each simple substance and the density calculated as a simple mixture from the composition ratio of 7.57 / (4.102 ×
The value of (100−X) /100+8.735×X/100) was 0.91.

Example 3 As a protective film, a (ZnS) ₅₆ (Ta ₂ O ₅ ) ₄₄ film was obtained by sputtering a target having a composition of (ZnS) ₇₀ (Ta ₂ O ₅ ) _{30 in} the same manner as in Example 1. A disc was prepared in the same manner as in Example 1 except that the recording power was 13.5 m.
When the same evaluation was performed with W and erase power of 5.5 mW, the 3T jitters when overwriting 10 times and 10000 times were 22 nsec and 37 nse, respectively.
It was c. Next, when a high temperature and high humidity environment test was performed under the same conditions as in Example 1 and the disc was observed with an optical microscope, no defects such as film peeling were observed. In the same manner as in Example 1, (ZnS) ₅₆ (Ta
_{A 2} O ₅ ) ₄₄ film was provided under the same conditions as above for 3200 liters, and the density and stress were measured. As a result, the density was 6.22 g / cm ³ and the compressive stress was 2.34 × 10 ⁹ dyn / cm ² . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio of 6.22 / (4.10)
2x (100-X) /100+8.735xX/10
The value of 0) was 1.01.

Example 4 As a protective film, a (ZnS) ₇₀ (Ta ₂ O ₅ ) ₃₀ film obtained by sputtering a target having a composition of (ZnS) ₈₀ (Ta ₂ O ₅ ) _{20 in} the same manner as in Example 1. A disc was prepared in the same manner as in Example 1 except that the recording power was 13.5 m.
When the same evaluation was performed with W and erasing power of 6.5 mW, 3T jitter when overwriting 10 times and 10000 times was 22 nsec and 44 nse, respectively.
It was c. Next, when a high temperature and high humidity environment test was performed under the same conditions as in Example 1 and the disc was observed with an optical microscope, no defects such as film peeling were observed. In the same manner as in Example 1, (ZnS) ₇₀ (Ta
_{A 2} O ₅ ) ₃₀ film was provided under the same conditions as above for 3700 liters, and the density and stress were measured. The density was 5.61 g / cm ³ , and the compressive stress was 2.86 × 10 ⁹ dyn / cm ² . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio of 5.61 / (4.10)
2x (100-X) /100+8.735xX/10
The value of 0) was 1.03.

Comparative Example 1 A (ZnS) ₂ (Ta ₂ O ₅ ) ₉₈ film obtained by sputtering a target having a composition of (ZnS) ₁₀ (Ta ₂ O ₅ ) _{90 in} the same manner as in Example 1 as a protective film. A disk was manufactured in the same manner as in Example 1 except that the recording power was 15 mW and the erasing power was 5.5 mW.
The 3T jitter when overwriting 10 times is 21n
Although it was sec, 3 after overwriting 10,000 times
T jitter increased to 63 nsec. Next, Example 1
When a high-temperature and high-humidity environment test was conducted under the same conditions as above and the disc was observed with an optical microscope, film peeling was observed. In the same manner as in Example 1, (Zn
S) ₂ (Ta ₂ O ₅ ) ₉₈ film under the same conditions as above for 3400Å
It was provided and the density and stress were measured and the density was 7.54 g /
cm ³ , and the compressive stress was 4.01 × 10 ⁹ dyn / cm ² . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio of 7.54
/(4.102 x (100-X) /100+8.735
The value of (XX / 100) was 0.873.

Comparative Example 2 As a protective film, a (ZnS) ₈₄ (Ta ₂ O ₅ ) ₁₆ film obtained by sputtering a target having a composition of (ZnS) ₉₀ (Ta ₂ O ₅ ) _{10 in} the same manner as in Example 1. A disc was prepared in the same manner as in Example 1 except that the above was used, and the same evaluation was performed with a recording power of 12 mW and an erasing power of 5.5 mW.
The 3T jitter when overwriting 10 times is 20n
Although it was sec, overwriting was not possible 10,000 times. Next, when a high temperature and high humidity environment test was performed under the same conditions as in Example 1 and the disc was observed with an optical microscope, no defects such as film peeling were observed. In the same manner as in Example 1, (ZnS) ₈₄ (Ta
_A 2O ₅ ) ₁₆ film was provided under the same conditions as above for 4200Å and the density and stress were measured. As a result, the density was 4.98 g / cm ³ and the compressive stress was 2.10 × 10 ⁹ dyn / cm ² . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio of 4.98 / (4.10).
2x (100-X) /100+8.735xX/10
The value of 0) was 1.03.

Comparative Example 3 A disk was prepared and recorded in the same manner as in Example 1 except that a Ta ₂ O ₅ target obtained by sputtering a Ta ₂ O ₅ target in the same manner as in Example 1 was used as the protective film. Power 14.
When the same evaluation was carried out at 5 mW and an erasing power of 6.0 mW, the 3T jitter when overwriting 10 times was 24 nsec, but overwriting was not possible 10,000 times. Next, when a high temperature and high humidity environment test was performed under the same conditions as in Example 1 and the disc was observed with an optical microscope, film peeling was observed. In the same manner as in Example 1, a Ta ₂ O ₅ film was provided on a glass substrate and a Si substrate under the same conditions as above for 2900Å, and the density and stress were measured. The density was 7.950 g / cm ³ , and the compressive stress was 7.21. × 10 ⁹
It was dyn / cm ² . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio 7.950 / (4.102 × (100-X)
The value of /100+8.735×X/100) was 0.91.

Comparative Example 4 A disk was prepared in the same manner as in Example 1 except that a ZnS film obtained by sputtering a ZnS target in the same manner as in Example 1 was used as the protective film, and initialization was performed using an optical microscope. When the disc was observed, film peeling was observed. A ZnS film was provided on a glass substrate in the same manner as in Example 1 under the same conditions as above for 5800Å, and the density was measured to be 4.00 g / cm ³ . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio 4.00 / (4.102 × (100−
The value of (X) /100+8.735×X/100) is 0.9
It was 7.

Comparative Example 5 A protective film was prepared by RF sputtering a target having a composition of (ZnS) ₃₀ (Ta ₂ O ₅ ) _{70 at} an Ar sputtering pressure of 0.8 Pa and an input power of 500 W. The protective film formed had a composition of (ZnS) ₉ (Ta ₂ O ₅ ) ₉₁ . A disk was prepared in the same manner as in Example 1 except for the above.
Example 1 with a recording power of 13.5 mW and an erasing power of 6 mW
When the same evaluation as the above was performed, the 3T jitter after overwriting 10 times was 23 nsec.
Overwriting was not possible 10,000 times. Next, when a high temperature and high humidity environment test was performed under the same conditions as in Example 1 and the disc was observed with an optical microscope, no defects such as film peeling were observed. A (ZnS) ₉ (Ta ₂ O ₅ ) ₉₁ film was provided on a glass substrate and a Si substrate in the same manner as in Example 1 under the same conditions as above for 3100 Å, and the density and stress were measured to find that the density was 6.60 g / cm ^3. , Compressive stress is 2.51 ×
It was 10 ⁹ dyn / cm ² . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio of 6.60 / (4.102 × (100−
The value of (X) /100+8.735×X/100) is 0.7
It was 9.

Comparative Example 6 A protective film was prepared by RF sputtering a target having a composition of (ZnS) ₃₀ (Ta ₂ O ₅ ) _{70 at} an Ar sputtering pressure of 0.1 Pa and an applied power of 500 W. The protective film formed had a composition of (ZnS) ₉ (Ta ₂ O ₅ ) ₉₁ . A disk was prepared in the same manner as in Example 1 except for the above.
Example 1 with a recording power of 13.5 mW and an erasing power of 6 mW
When the same evaluation as the above was performed, the 3T jitter when overwriting 10 times was 21 nsec.
3T jitter after overwriting 10,000 times is 51ns
It rose to ec. Next, when a high temperature and high humidity environment test was performed under the same conditions as in Example 1 and the disc was observed with an optical microscope, film peeling was observed. In the same manner as in Example 1, 3600Å of (ZnS) ₉ (Ta ₂ O ₅ ) ₉₁ film was provided on the glass substrate and Si substrate, and the density and stress were measured. The density was 7.77 g / cm ³ , and the compressive stress was 4. 12 x 10 ⁹ dyn
Was / cm ² . The ratio of the density of the film to the density of the bulk of each element and the density calculated as a simple mixture from the composition ratio 7.77 / (4.102 × (100−X) / 100
The value of + 8.735 × X / 100) was 0.93.

[0031]

By using a mixture of zinc sulfide and tantalum oxide for the protective layer and selecting appropriate sputtering conditions, it is possible to increase the atomic packing rate and lower the internal stress as compared with the case of using tantalum oxide alone. , Repeated recording because it can increase the adhesive force compared with zinc sulfide only.
It has become possible to provide an optical information recording medium having sufficient durability against erasure and excellent in storage stability.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Natsuko Suzuki 1000 Kamoshida-cho, Midori-ku, Yokohama, Kanagawa Sanryoh Kasei Co., Ltd. (72) Kenichi Takada 1000 Kamoshida-cho, Midori-ku, Yokohama Ryokasei Co., Ltd.

Claims (1)

[Claims] 1. A medium for optical information recording having at least a dielectric protective layer and a phase transition type optical recording layer on a substrate, wherein the dielectric protective layer comprises zinc sulfide and tantalum oxide having a tantalum oxide content of 30 to 91 mol%. A dielectric containing
Density is 0.90 x (4.102 x (100-X) / 10
0 + 8.735 × X / 100) g / cm ³ (X is a value of mol% of tantalum oxide) or more, and the compressive stress is 4.0 × 10
An optical information recording medium, characterized by comprising ⁹ dyn / cm ² or less.