JP3246350B2 - Optical information recording medium - Google Patents

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 In recent years, an optical disk using a laser beam has been developed as a recording medium that meets the demand for an increase in the amount of information and a high density and high speed of recording and reproduction. Optical discs include a write-once type, which allows recording only once, and a rewritable type, which allows recording / erasing any number of times.

Examples of the rewritable optical disk include a magneto-optical recording medium utilizing a magneto-optical effect and a phase change medium utilizing a reversible change in crystalline state. The phase change medium is
Recording and erasing are possible only by changing the power of the laser beam without the need for an external magnetic field. Furthermore, there is an advantage that one-beam overwriting in which erasing and re-recording are performed simultaneously with a single beam is possible.

In the phase change recording method 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 recording layer material used in such a phase change recording method, a chalcogen-based alloy thin film is often used.

For example, Ge-Te type, Ge-Te-Sb
System, In-Sb-Te system, Ge-Sn-Te system alloy thin film and the like. It should be noted that 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 medium is used as a write-once type, unlike a perforated type, there is no swelling called a rim around the bit, so that the signal quality is excellent. Further, since no air gap is required above the recording layer, an air sandwich structure is used. There is an advantage that there is no need to do this. Generally, in a rewritable phase change recording medium, two different laser beam powers are used to realize different crystal states.

This method will be described by taking as an example a case where recording / erasing is performed in an erased / initial state in which an amorphous bit is crystallized. 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 between dielectric layers, or 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 dielectric layer also has a function as a heat dissipation layer for obtaining a sufficient cooling rate (supercooling rate). Further, in order to prevent deformation due to melting and volume change of the recording layer in the heating / cooling process as described above, to prevent thermal damage to the plastic substrate, and to prevent deterioration of the recording layer due to moisture, the dielectric layer is used. The protective layer consisting of the body layer is important.

The material of the protective layer material is such that it is optically transparent to laser light, has a high melting point, softening point, high decomposition temperature, is easy to form, and has a suitable thermal conductivity. Selected from a viewpoint. The protective layer having sufficient heat resistance and mechanical strength includes a dielectric thin film such as a metal oxide or nitride.

[0010] Since these dielectric thin films and plastic substrates have greatly different coefficients of thermal expansion and elastic properties, they repeatedly peel off from the substrate and cause pinholes and cracks during recording and erasure. In addition, the plastic substrate is likely to be warped due to humidity, and this may also cause peeling of the protective film.

On the other hand, as a new dielectric protective layer, ZnS
The main component has been proposed in which SiO ₂ , Y ₂ O ₃ or the like is mixed. These composite compound protective films have better adhesion to chalcogenide-based alloy thin films such as GeTeSb, which are often used as recording layers, than pure oxide or nitride dielectric films.

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.

[0013]

However, composite compounds do not necessarily exhibit good properties simply by mixing. Depending on the composition range and the physical properties of the composite film, the reliability may be reduced rather than the case where individual pure compounds are used.

Conventionally, oxides, nitrides, fluorides, etc. are added to chalcogenide-based compounds such as ZnS and ZnSe.
Numerous proposals have been made for a protective film in which a carbide or the like is mixed. However, these films have relatively low hardness, and there is a problem that microscopic deformation due to plastic deformation accumulates due to repeated overwriting, which substantially changes the optical film thickness and lowers the reflectance. .

Further, in the above composite film, only the optimum composition range is described in part, 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 because the physical properties of the above-described composite are significantly different from those of the compounds constituting the composite, so that changes in the physical properties due to the production method and the like were unpredictable.

For example, a sputtering method is widely used in forming a protective layer made of the above-mentioned composite compound.
Obviously, the physical properties of the obtained composite compound protective film differ between the case of using the composite target and the case of simultaneous sputtering using individual compound targets. Further, it is a well-known fact that even in the same manufacturing method, the physical properties change due to the pressure during sputtering and the like. Given such variations in physical properties of the protective film, there has been a problem how to find a composite protective film suitable for a phase change medium.

[0017]

The optical information recording medium of the present invention In order to achieve the above object, according to the substrate, at least the phase transition type optical recording layer, 及
In the optical information recording medium having a fine dielectric layer, dielectric material layer is, (1) disulfide, tantalum diselenide, tantalum disulfide, zirconium and tungsten disulfide Tona
And (2) a heat-resistant compound having a melting point or a decomposition temperature of 1000 ° C. or more (wherein the dielectric layer is tantalum disulfide).
And tantalum oxide) .

[0018]

DETAILED DESCRIPTION OF THE INVENTION At least one substance (1) selected from the group consisting of tantalum disulfide, tantalum diselenide, zirconium disulfide and tungsten disulfide is
It is known as a material having a two-dimensional layered structure, and exhibits high hardness against compression of the upper part, but relatively easily generates slip deformation between layers against shear stress in two-dimensional planes, Absorbs stress.

Therefore, there is an effect that a stress caused by a volume change and thermal expansion during recording of the phase change medium is released, and the occurrence of microscopic cracks is prevented. However, since it is easy to crystallize by itself and the above-mentioned shear deformation between the layers easily progresses to a macroscopic level, it is necessary to keep the deformation at a microscopic level by mixing and dispersing oxides and the like.

Since the substance (1) contains a chalcogen element, the substance (1) has good adhesion to chalcogen mainly contained in the phase change type recording layer and its peripheral elements. As the compound (2), that is, the heat-resistant compound having a melting point or a decomposition temperature of 1000 ° C. or more, for example, an oxide is mentioned. Specific examples of the oxide include silicon dioxide, yttrium oxide, zirconium oxide, barium oxide, At least one selected from the group consisting of tantalum oxide, tungsten oxide and boron oxide is used.

The heat-resistant compound to be mixed is required to have a heat resistance of 1000 ° C. or higher and to be sufficiently optically transparent. 10
The heat resistance of 00 ° C. or higher means that the melting point is maintained at 1000 ° C. or higher and no decomposition occurs even when heated to 1000 ° C. Further, it is referred to as being sufficiently optically transparent in a wavelength region having a thickness of about 50 nm and a light absorption coefficient of about 600 nm or more.
5 or less.

In order to obtain this optical transparency, it is preferable to use a mixed gas of Ar and nitrogen and / or oxygen at the time of film formation by sputtering. The content of the total amount of the substances (1) and (2) in the dielectric layer of the dielectric containing at least the substances (1) and (2) is preferably 50 mol% or more, and more preferably 80 mol%.

When the content is less than 50 mol%, the effect of preventing deformation of the substrate or the recording film is insufficient, and the content tends not to function as a protective layer. The content of the substance (1) is at least 10 mol% and 90 mol% of the whole dielectric layer.
% Or less is preferable. If it is less than 10 mol%, the desired properties are not exhibited.

On the other hand, if it exceeds 90 mol%, the optical absorption coefficient increases, which is not preferable, and more preferably 60 mol%.
1% or less. The content of the heat-resistant compound (2) is preferably 10 mol% or more and 90 mol% or less, more preferably 40 mol% or more of the whole dielectric layer.
In other ranges, desired characteristics may not be obtained.

The content of the heat-resistant compound (2) is preferably higher than that of the substance (1). Among the substances (1), TaS ₂ and TaSe ₂ are particularly preferable because they have a high decomposition temperature and improve the overwrite durability in a rewritable medium. Zirconium disulfide and tungsten disulfide are desirable for improving the recording sensitivity of the write-once medium.

The above substances (1) and (2) are added to the dielectric layer.
A mixture of different compounds is used, but substances (1) and
The total amount of (2) is the main component (50 mol% or more, preferably
80 mol% or more), other dielectrics and non-metals
Substances may be mixed. Other dielectric and non-metallic materials
Are ZnS, ZnSe, CaS, La_TwoS_Three, Mg
F_Two, LaF_Three, NdF_Three, TbF_Three, SiC, Si_ThreeN_Four,
C, BN, AlN, B _FourC and the like.

The film density of the dielectric layer is 80% of the theoretical density.
It is preferable that it is above. Here, the theoretical density of the film is represented by the following formula, and is an integrated value obtained by multiplying the density of each constituent compound in a bulk state by the molar content of the constituent compound. Theoretical density = {(density of constituent compound bulk state) × (molar content of constituent compound)} By setting the density of the mixture dielectric layer in this way, the durability against repeated recording and aging can be significantly improved. it can.

The film density can be controlled by adjusting the degree of vacuum during sputtering. To increase the film density, the degree of vacuum is reduced (the argon gas pressure is reduced).
The degree of vacuum is usually 1 Pa or less, preferably 0.3 to 0.8 Pa. The thus obtained dielectric layer of the present invention has a higher mechanical strength than a known composite film containing ZnS or ZnSe as a main component, has a hardness close to that of an oxide, and prevents cracks due to microscopic shear change. The effect to be obtained is obtained.

Further, since the compressive stress is smaller than that of the oxide itself, peeling hardly occurs. The dielectric layer is preferably provided using a composite sputtering target composed of a mixture of a plurality of compounds constituting the film. In forming a dielectric composed of the above-described composite compound, a sputtering method is generally widely used.However, a composite target is obtained compared to simultaneous sputtering using individual compound targets. It is preferable because the uniformity of the constituent elements of the composite compound protective film is superior and the characteristics as the protective film are also excellent.

Next, the configuration of the optical recording medium according to the present invention will be described. The optical recording medium of the present invention is usually
It has at least the structure of substrate / dielectric layer / recording layer / dielectric layer / reflective layer, and a transparent resin such as polycarbonate, acrylic, or polyolefin, or glass can be used for the substrate. On the substrate surface, a dielectric material satisfying the above characteristics is usually provided with a thickness of 10 to 500 nm.

When the thickness of the dielectric layer is less than 10 nm,
The effect of preventing deformation of the substrate or the recording film is insufficient, and tends not to serve as a protective layer. If the thickness exceeds 500 nm, the internal stress of the dielectric itself and the difference in elastic characteristics with the substrate become remarkable, and cracks are easily generated. The recording layer of the medium of the present invention is a phase change type recording layer, and its thickness is 10n.
The range from m to 100 nm is preferred.

If the thickness of the recording layer is less than 10 nm, it is difficult to obtain a sufficient contrast, and the crystallization speed tends to be slow.
On the other hand, if it exceeds 100 nm, optical contrast is still difficult to obtain, and cracks tend to occur, which is not preferable. The thicknesses of the recording layer and the dielectric layer are selected in consideration of the interference effect associated with the multilayer structure, so that the laser light absorption efficiency is good and the amplitude of the recording signal, that is, the contrast between the recorded state and the unrecorded state is increased. .

As the recording layer, a known phase-change optical recording layer can be used. For example, GeSbTe, InSbTe, AgS
Compounds such as bTe and AgInSbTe are selected as overwritable materials. These compounds have 0.
1 to 10 atomic% of Sn, In, Pb, As, Se, S
i, Bi, Au, Ti, Cu, Ag, Pt, Pd, C
It is also effective to improve the crystallization speed, optical constant and oxidation resistance by adding one or more elements from among o, Ni and the like.

On the outer protective layer (protective layer not on the substrate side), an optical reflection layer and a hard coat layer for preventing thermal deformation may be provided. The optical reflection layer is preferably made of a material having a high reflectivity, such as Au, Ag, Cu, or Al, particularly usually Al.
And its alloys are used. Since the reflective layer of Al or the like has an effect of promoting the diffusion of the thermal energy absorbed by the recording layer, Ta, Ti, Cr, M is used for controlling the thermal conductivity.
o, Mg, V, Nb, Zr, etc. at 0.5 to 5 at. % Should be added.

The recording layer, the dielectric layer, and the reflection layer are formed by a sputtering method or the like. It is desirable to form a film using an in-line apparatus in which a target for a recording film, a target for a protective film, and if necessary, a target for a reflective layer material are installed in the same vacuum chamber, from the viewpoint of preventing oxidation and contamination between layers. It is also excellent in productivity.

[0036]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the examples unless it exceeds the gist. Example 1 TaS ₂ as a substance (1) as a dielectric layer material and Y ₂ O ₃ powder as a substance (2) (oxide) in a molar ratio of 20 were used.
The mixture was adjusted and mixed so as to be 80, and a composite sintered body target was obtained by a hot press method.

On the polycarbonate resin substrate, a dielectric layer /
A recording layer / dielectric layer / reflection layer was provided to prepare a recording medium having a four-layer structure. The thickness of each layer is the lower (substrate side) dielectric layer 1
The thickness was 50 nm, the recording layer was 30 nm, the upper dielectric layer was 30 nm, and the reflection layer was 100 nm. The composition of the recording layer is Ge (22.2) Sb
(22.2) Te (55.6), and the reflective layer was made of Ta at 2.5 at.
% Al alloy was used.

An Ar gas is flowed at 50 sccm through the dielectric layer, the pressure is 0.7 Pa, and a high frequency (13.56 MHz) is used.
z) A film was formed by sputtering. The theoretical density of this film was 5.40 g / cm ³ , the measured value was 5.20 g / cm ³ , and the film density was 96% of the theoretical density. The JIS Knoop hardness is 640 and the compressive stress is -1.0 × 10 ⁸ dy
n / cm ² .

The recording layer and the reflective layer were formed under an Ar gas pressure of 0.7 P.
a) A film was formed by DC sputtering. Further, an ultraviolet curable resin having a thickness of about 5 μm was provided. After the disk was further initialized using an Ar ion laser, ie, the recording layer was crystallized, the dynamic characteristics of the disk were evaluated under the following conditions.

4M while rotating at a linear speed of 10 m / s
Overwriting was repeatedly performed at a recording power of 18.5 mW and a base power of 8.5 mW using a pulse light of 50 Hz and a duty of 50%, and the C / N ratio and the erasing ratio were measured each time a predetermined number of times was reached. The results are shown in FIG. As is clear from FIG. 1, the reduction in the C / N ratio was about 10 dB after 100,000 repetitions. The erasure ratio showed a value almost equal to that of the first time even after 200,000 repetitions. The melting point of Y ₂ O ₃ is about 2400 ° C., the Knoop hardness is 800, and the compressive stress is 2
× 10 ⁹ dyn / cm ² .

Example 2 TaS having a molar ratio of 20:80 was used as a dielectric layer material._TwoPassing
And Ta_TwoO_FiveExcept for using the same method as in Example 1,
A disk was prepared and similar dynamic characteristics were evaluated. Figure the result
It is shown in FIG. After 100,000 repetitions, the C / N ratio drops for the first time
It was about 5 dB as compared with the case of. The erasure ratio is repeated 10
The number of times increased by about 5 dB from the first time. This dielectric thin
The Knoop hardness of the film is 440 and the compressive stress is 1 × 10⁹d
yn / cm^TwoMet. Note that Ta_TwoO_FiveHas a melting point of about 190
0 ° C., Knoop hardness of 420, compressive stress of 5 × 10
⁹dyn / cm^TwoMet. The theoretical density of this film is
8.48 g / cm ^Three, Measured value is 7.60 g / cm^ThreeOk
The film density was 90% of the theoretical density.

Example 3 ZrS ₂ and Ta ₂ O ₅ having a molar ratio of 20:80 were used as the dielectric layer materials, and the thickness of each layer was changed to a lower (substrate side) dielectric layer 140 nm, a recording layer 20 nm, and an upper dielectric layer. The body layer was 20 nm and the reflective layer was 200 nm.
A disc was prepared in the same manner as in Example 1 except that n (15) Sb (60) Sn (25) was used.

This disc is used as a write-once optical disc.
Using a pulse light of 4 MHz and a duty of 50% while rotating at a linear velocity of 9.5 m / s, a recording power of 10 mW
After writing the signal, the temperature is 80 ° C and the humidity is 80%
After 500 hours of storage in a high-temperature and high-humidity bath, the film was taken out and observed with an optical microscope, and no physical damage such as swelling or cracks was found. Also, there was no change in the signal characteristics of the disk such as the C / N ratio and jitter. The Knoop hardness of this film is 440 and the compressive stress is 0.8 × 10 ⁹ d.
yn / cm ² . The theoretical density is 8.31 g / c.
The measured value was 6.99 g / cm ^{3 with} respect to m ³ , and thus the film density was 84% of the theoretical density.

Comparative Example 1 A disk was prepared in the same manner as in Example 1 except that Ta ₂ O ₅ was used as a dielectric layer material, and similar dynamic characteristics were evaluated. The results are shown in FIG. After 20,000 repetitions, the C / N ratio and the erasing ratio decreased by about 11 dB respectively compared to the first repetition.
And about 25 dB. The Knoop hardness of this film is 50
0, and the compressive stress was 3.1 × 10 ⁹ dyn / cm ² .
In addition, the theoretical density was 8.70 g / cm ^3, whereas the measured value was 8.07 g / cm ³ , and the film density was 93% of the theoretical density.
Met.

Comparative Example 2 A disk was prepared in the same manner as in Example 1 except that ZnS and TiO ₂ having a molar ratio of 80:20 were used as a dielectric layer material, and similar dynamic characteristics were evaluated. Fig. 4 shows the results.
Shown in After 2,000 repetitions, the C / N ratio and the erasure ratio decreased by about 11 dB and about 16 dB, respectively, as compared with the first cycle. The Knoop hardness of this dielectric thin film was 400 and the compressive stress was 2 × 10 ⁹ dyn / cm ² . The measured value is 3.79 g / c ³ against the theoretical density of 4.10 g / cm ^3.
m ³ , and thus the film density was 92% of the theoretical density. It is known that thermal decomposition of TiO ₂ starts at around 600 ° C., oxygen atoms are released, and the TiO ₂ turns black.

Comparative Example 3 A disk was prepared in the same manner as in Example 1 except that ZnS and MoS ₂ having a molar ratio of 80:20 were used as a dielectric layer material, and similar dynamic characteristics were evaluated. Fig. 5 shows the results.
Shown in After 1,000 repetitions, the C / N ratio and the erasure ratio decreased by about 9 dB and about 16 dB, respectively, as compared with the first cycle. The Knoop hardness of this dielectric thin film was 230, and the compressive stress was 1 × 10 ⁹ dyn / cm ² . The measured value is 4.16 g / c ³ against the theoretical density of 4.30 g / cm ^3.
m ³ , and thus the film density was 97% of the theoretical density. It is known that MoS ₂ becomes thermally unstable around 350 ° C. and easily forms an alloy.

Example 4 TaSe ₂ having a molar ratio of 20:80 was used as a dielectric layer material.
And except that using the Ta ₂ O ₅ in the same manner as in Example 1 to create the disk was subjected to the same dynamic characteristics evaluation. FIG. 6 shows the results. After 100,000 repetitions, the decrease in the C / N ratio was 12 dB as compared with the first time. The erasing ratio was increased by about 5 dB from the first time at 100,000 times. This dielectric thin film has a Knoop hardness of 480 and a compressive stress of 4 × 10 ⁹ dyn.
/ Cm ² . The measured value was 7.26 g / cm ³ against the theoretical density of 8.70 g / cm ³ , and thus the film density was 84% of the theoretical density.

Example 5 As a dielectric layer material, TaSe ₂ having a molar ratio of 40:60 was used.
And except that using the Ta ₂ O ₅ in the same manner as in Example 1 to create the disk was subjected to the same dynamic characteristics evaluation. FIG. 6 shows the results. After 100,000 repetitions, the decrease in C / N ratio was 6 dB as compared with the first time. The erasure ratio was increased by about 1 dB from the first time at 100,000 repetitions. This dielectric thin film has a Knoop hardness of 390 and a compressive stress of 3 × 10 ⁹ dyn /
cm ² . Also, the theoretical density of 8.67 g / cm ^3, measured value 7.18 g / cm ^3, thus film density was 83% of theoretical density.

[0049]

The use of the optical recording medium of the present invention is effective for practical use of a write-once medium excellent in data storage stability and a rewritable medium capable of repeatedly recording / erasing many times. .

[Brief description of the drawings]

FIG. 1 is a graph showing measurement results of a C / N ratio and an erasing ratio in Example 1.

FIG. 2 is a graph showing measurement results of a C / N ratio and an erase ratio in Example 2.

FIG. 3 is a graph showing measurement results of a C / N ratio and an erase ratio in Comparative Example 1.

FIG. 4 is a graph showing measurement results of a C / N ratio and an erasing ratio in Comparative Example 2.

FIG. 5 is a graph showing measurement results of a C / N ratio and an erase ratio in Comparative Example 3.

FIG. 6 is a graph showing the measurement results of the C / N ratio and the erase ratio in Examples 4 and 5.

[Explanation of symbols]

 Graph showing 1 C / N ratio. 2 A graph showing an erasing ratio.

Continuation of the front page (56) References JP-A-63-164041 (JP, A) JP-A-4-186537 (JP, A) JP-A-4-251452 (JP, A) JP-A-5-89519 (JP) JP-A-3-173684 (JP, A) JP-A-62-285738 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/24

Claims (5)

(57) [Claims] 1. An optical information recording medium comprising at least a phase-change optical recording layer and a dielectric layer on a substrate, wherein the dielectric layer comprises: (1) tantalum disulfide, tantalum diselenide, Zirconium disulfide and tungsten disulfide
Selected from the group consisting of the at least one and (2) the melting point or the optical information recording medium in which the decomposition temperature is characterized by containing a heat-resistant compound above 1000 ° C. (provided that the
The dielectric layer contains tantalum disulfide and tantalum oxide
Unless otherwise specified) . 2. The dielectric layer according to claim 1, wherein the dielectric layer contains (1) tantalum disulfide and / or tantalum diselenide and (2) a heat-resistant compound having a melting point or decomposition temperature of 1000 ° C. or higher. The optical information recording medium according to the above. 3. The heat-resistant compound is silicon dioxide, yttrium oxide, zirconium oxide, barium oxide, tantalum oxide, tungsten oxide, boron oxide, zinc sulfide, zinc selenide, calcium sulfide, La ₂ S ₃ , MgF ₂ , LaF ₃ ,
The optical information recording medium according to claim 1, wherein the medium is at least one selected from the group consisting of NdF ₃ , TbF ₃ , SiC, Si ₃ N ₄ , BN, AlN, and B ₄ C. 4. The optical information recording medium according to claim 1, wherein the film density of the dielectric layer is 80% or more of the theoretical density. 5. The dielectric layer formed by sputtering using a composite sputtering target composed of a plurality of compounds constituting a dielectric.
The optical information recording medium according to any one of the above.