JP3444037B2 - Optical information recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium having a phase change type optical recording layer. More specifically, 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. 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 modulating 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 system, Ge-Te-Sb
System, In-Sb-Te system, Ge-Sn-Te system alloy thin film and the like. [0005] A write-once type phase change medium can be realized with almost the same material and layer structure as the rewritable type. In this case, information can be recorded and stored for a longer period because there is no reversibility, and almost semi-permanent storage is possible in principle. When a phase-change medium is used as a write-once type, unlike a perforated type, there is no ridge called a rim around the bit, so that the signal quality is excellent. There is no advantage. 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 where an amorphous bit has been 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 radiation layer for obtaining a sufficient cooling rate (supercooling rate). [0008] Further, in order to prevent the recording layer from being deformed due to melting and volume change 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 protective layer made of the dielectric layer is important. The material of the protective layer material is selected from the viewpoints of being optically transparent to laser light, high melting point, softening point, high decomposition temperature, easy formation, and moderate thermal conductivity. Is done. The protective layer having sufficient heat resistance and mechanical strength includes a dielectric thin film such as a metal oxide or nitride. Since the dielectric thin film and the plastic substrate have significantly different coefficients of thermal expansion and elastic properties, they repeatedly separate from the substrate and cause pinholes and cracks during recording and erasing. [0010] Further, the plastic substrate is liable to be warped due to humidity, but this may also cause peeling of the protective film. On the other hand, as a new dielectric protection layer,
There has been proposed a material containing ZnS as a main component and mixed with SiO ₂ , Y ₂ O _{3 and the} like. 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. [0011] 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, many proposals have been made for protective films in which oxides, nitrides, fluorides, carbides and the like are mixed with ZnS, ZnSe, etc., which are compounds containing chalcogenide elements, but some of them have been proposed. Only the optimum composition range is described, and even if a mixture of the composition is used, characteristics superior to those of the original protective layer composed of a pure compound alone cannot be obtained. [0013] This is because the physical properties of the above-mentioned composite material are significantly different from those of the compound constituting the composite material, so that a change in physical properties due to the production method or the like cannot be predicted. For example, a sputtering method is widely used in forming a protective layer made of the above-described composite compound. However, when a composite target is used and when a simultaneous sputtering is performed using individual compound targets, a composite compound protection is naturally obtained. The physical properties of the film differ. 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. In the presence of such variations in physical properties of the protective film, it has been a problem how to find a protective film suitable for a phase change medium. [0015] Means for Solving the Problems An optical information recording medium of the present invention, at least the phase transition type optical recording layer on a substrate, the optical information recording medium having a dielectric layer, dielectric body
Optics layers, characterized in that it consists essentially LaB ₆
Information recording medium . DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an optical recording medium according to the present invention will be described. The optical recording medium of the present invention has at least a phase-change optical recording layer and a dielectric layer on a substrate. Usually, it has a configuration of substrate / dielectric layer / recording layer / dielectric layer / reflection layer. The substrate can be made of a transparent resin such as polycarbonate, acrylic, or polyolefin, or glass. A dielectric layer satisfying the above characteristics is provided on the substrate surface, usually in a thickness of 10 to 500 nm.
If 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 the dielectric layer tends not to serve as a protective layer. If the thickness exceeds 500 nm, the internal stress of the dielectric layer itself and the difference in elastic properties between the dielectric layer and the substrate become remarkable, and cracks are easily generated. The dielectric layer contains at least lanthanum (La) and boron (B). In particular, since LaB ₆ has a large wavelength dependence of the absorption coefficient and the extinction coefficient,
This is effective in controlling the absorption and the reflectance when designing the thickness configuration of the multilayer film using the light interference effect. The present invention is not limited to the above two elements. La
If the main component is boron and boron, another dielectric may be mixed. Other dielectrics include SiO ₂ , Y ₂ O ₃ , Z
rO ₂ , BaO, B ₂ O ₃ , Ta ₂ O ₅ , NdF ₃ , ZnS,
Si ₃ N ₄ , SiC and the like can be mentioned. When another dielectric is mixed with the dielectric, it is preferable that the dielectric has a heat resistance of 1000 ° C. or higher and is optically transparent. Preferably, the dielectric layer is provided by using a composite sputtering target composed of a plurality of elements constituting the dielectric. This is generally the case in which a sputtering method is widely used to form a dielectric layer made of the above-mentioned substances.However, using a composite target, compared to simultaneous sputtering using individual single targets,
This is because the uniformity of the constituent elements of the obtained compound protective film is superior, and the characteristics as the protective film are also excellent. The dielectric layer has a film density of 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 about 0.8 to 0.1 Pa. Further, a small amount of oxygen or nitrogen gas may be mixed with Ar gas which is usually preferably used in sputter discharge. The recording layer of the medium of the present invention is a phase change type recording layer, and its thickness is preferably in the range of 10 nm to 100 nm. If the thickness of the recording layer is less than 10 nm, it is difficult to obtain a sufficient contrast. In addition, the crystallization speed tends to be slow, and it is difficult to erase data in a short time. On the other hand 10
If it exceeds 0 nm, optical contrast is still difficult to be obtained, and cracks are likely to occur. The thicknesses of the recording layer and the dielectric layer are adjusted so that the laser beam absorption efficiency is high and the amplitude of the recording signal, that is, the contrast between the recorded state and the unrecorded state is increased in consideration of the interference effect associated with the multilayer structure. Is chosen. For the recording layer, a ternary compound such as GeSbTe or InSbTe is selected as a material capable of overwriting. These ternary compounds are added in an amount of 0.1 to 10 atomic%.
Of Sn, In, Pb, As, Se, Si, Bi, Au,
One or more elements are added from among Ti, Cu, Ag, Pt, Pd, Co, Ni and the like, and the crystallization rate is increased.
It is also effective to improve the optical constant and oxidation resistance. An optical reflection layer and a hard coat layer for preventing thermal deformation are provided on the protective layer. The optical reflection layer is preferably made of a substance having a high reflectance, and Au, Ag, Cu, Al, or the like is used. This reflective layer has the effect of promoting the diffusion of the thermal energy absorbed by the recording layer, so that Ta, Ti, Cr, Mo, Mg, V, Nb, Zr
May be added in small amounts. 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. The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. Example 1 A dielectric layer / recording layer / dielectric layer / reflective layer was formed on a polycarbonate resin substrate using a sintered target obtained by hot pressing LaB ₆ powder as a dielectric layer material.
A recording medium having a layer structure was prepared. The thickness of each layer is as follows: lower dielectric layer 180 nm, recording layer 30 nm, upper dielectric layer 30 n
m, and the reflective layer was 100 nm. The composition of the recording layer is Ge _22.2 Sb _22.2 Te _55.6
It is. The reflection layer used an Al-Ta alloy. The dielectric layer was formed by high frequency (13.56 MHz) sputtering at an Ar gas pressure of 0.7 Pa and an oxygen gas pressure of 15 mPa. The film density was 4.1 g / cc, which was 87% of the theoretical density. The recording layer and the reflective layer were formed by DC sputtering at an Ar gas pressure of 0.7 Pa. About 4μ thick
m of an ultraviolet curable resin. After the disk was initialized using an Ar ion laser, ie, the recording layer was crystallized, the dynamic characteristics of the disk were evaluated under the following conditions. 4MHz, 50% duty while rotating at a linear speed of 10m / s
Overwriting was repeatedly performed at a recording power of 16.5 mW and a base power of 9 mW, and the C / N ratio and the erasing ratio were measured each time a predetermined number of times was reached. As shown in FIG. 1, the C / N was reduced by about 2 dB in the 1,000 repetitions compared to the first repetition, and the erasing ratio was equivalent to the first repetition even in 10,000 repetitions. Comparative Example 1 A disk was prepared in the same manner as in the example except that the molar ratio of ZnS and TiO ₂ was 80:20 as the dielectric layer material, and the same dynamic characteristics were evaluated. The results are shown in FIG. As is clear from the graph of FIG. 2, the reduction in C / N is about 12 dB after 2,000 repetitions compared to the first repetition, and the erasing ratio is about 15 dB lower than the first repetition after 2,000 repetitions. did. By using the optical recording medium of the present invention, recording and erasing can be performed a number of times repeatedly, and this type of medium which can be repeatedly recorded and erased is very effective for practical use.

[Brief description of the drawings] FIG. 1 is a graph of C / N and an erasing ratio in an example. FIG. 2 is a graph of C / N and erase ratio in a comparative example. [Explanation of symbols] 1 C / N ratio 2 Elimination ratio

Claims (1)

(57) Patent Claims 1, wherein at least the phase transition type optical recording layer on a substrate, the optical information recording medium having a dielectric layer, dielectric
Light body layer, characterized in that consists essentially of LaB ₆
For recording scientific information.