JP2006247855A - Optical recording medium of multilayer phase changing-type - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the optical recording medium of a multilayer phase changing-type which can simultaneously satisfy requirements of high linear velocity recording, regenerative light stability and shelf stability. <P>SOLUTION: This optical recording medium of a multilayer phase changing type comprises a plurality of information layers including a phase changing recording layer which can record information by giving rise to a phase change with laser light irradiation, and further, and each information layer excepting those on an innermost side as viewed from the side where a laser light is emitted comprises at least a lower protecting layer, a phase changing recording layer, an upper protecting layer, a reflective layer and a heat diffusion layer. The phase changing-recording layer comprises three elements such as In, Sb and Ge, and when the composition ratio is α, β and γ[atomic%], the requirements of 10≤α≤20, 65≤β≤85 and 2≤γ≤20, are met. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multilayer in which a plurality of information layers including a phase change recording layer capable of recording and reproducing information by irradiating a light beam to cause an optical change in a recording layer material and rewriting the information. The present invention relates to a phase change optical recording medium.

Phase-change optical discs (phase-change optical recording media) such as CD-RW are generally provided with a recording layer made of a phase-change material on a plastic substrate, on which a light absorption rate of the recording layer is improved. In addition, a structure in which a reflective layer having a thermal diffusion effect is formed is used as a basic configuration, and information is recorded and reproduced by irradiating a laser beam from the substrate surface side.
Phase change recording materials change between a crystalline state and an amorphous state by heating with laser light irradiation and subsequent cooling, become amorphous when rapidly cooled after rapid heating, and crystallize when slowly cooled. The type optical recording medium applies this property to information recording and reproduction.
Furthermore, for the purpose of preventing oxidation, transpiration or deformation of the recording layer caused by heating by light irradiation, a lower protective layer (also referred to as a lower dielectric layer), a recording layer and a reflective layer are usually provided between the substrate and the recording layer. An upper protective layer (also referred to as an upper dielectric layer) is provided therebetween. Furthermore, these protective layers have a function of adjusting the optical characteristics of the recording medium by adjusting the thickness thereof, and the lower protective layer softens the substrate by heat during recording on the recording layer. It also has a function to prevent this.

In recent years, as the amount of information handled by computers and the like has increased, the signal recording capacity of rewritable optical discs such as DVD-RAM, DVD-RW, and DVD + RW has increased, and the density of signal information has been increasing. The current recording capacity of CDs is about 650 MB, and DVDs are about 4.7 GB. However, it is expected that the demand for higher recording density will increase in the future. In addition, it is considered that an improvement in recording speed is required as the amount of information increases. Currently, DVD rewritable discs have been developed that are capable of 8 × speed recording with a single layer.
As a method for increasing the recording density using such a phase change type optical recording medium, for example, the laser wavelength used is shortened to the blue region, or the numerical aperture NA of an objective lens used for a pickup for recording / reproducing is used. It has been proposed to reduce the spot size of the laser beam irradiated to the optical recording medium, and research and development have been carried out, and it has come to be put to practical use.

On the other hand, as a method of improving the recording capacity by improving the optical recording medium itself, at least two information layers consisting of a recording layer and a reflective layer are stacked on one side of the substrate, and these information layers are bonded with an ultraviolet curable resin or the like. Various types of two-layer phase change optical recording media have been proposed. The separation layer (referred to as an intermediate layer in the present invention) that is an adhesive portion between the information layers has a function of optically separating the two information layers, and the information layer on the back side has as much laser light as possible for recording and reproduction. Therefore, it is made of a material that does not absorb laser light as much as possible.
However, many problems still exist for this two-layer phase change optical recording medium. For example, if the laser beam is not sufficiently transmitted through the information layer (first information layer) on the front side when viewed from the laser beam irradiation side, information is recorded on the recording layer of the information layer (second information layer) on the back side. Since recording and reproduction cannot be performed, the reflective layer constituting the first information layer must be an extremely thin translucent reflective layer.
In addition to the flow of increasing the recording capacity, it is also required to improve the recording speed. An example of a method for increasing the recording speed is to increase the crystallization speed of the phase change recording material. As a result, the information can be easily erased in a short time. Further, when recording, it is necessary to heat and cool the laser beam in an extremely short time.

  Recording on the phase change type optical recording medium is performed by irradiating the phase change type material of the recording layer with laser light and rapidly cooling it to change the crystal to amorphous to form a mark. In the case of a semi-transparent reflective layer having a small thickness, the heat dissipation effect is reduced, and it becomes difficult to form an amorphous mark. In particular, an SbTe eutectic recording material, which is one of materials generally used for phase-change optical recording media such as CD-RW and DVD + RW, has an excellent erasure ratio compared to a GeSbTe compound-based recording material. Further, it is known as an excellent one in that the outline of the amorphous part of the recording mark is clear because of its high sensitivity. However, since the SbTe eutectic recording material has a higher crystallization speed than the GeSbTe compound recording material, it must be rapidly cooled in order to become amorphous, and a rapid cooling structure is required. Material.

A phase change type optical recording medium generally has Sb as a base material, and in order to cope with a high recording linear velocity, a method of increasing the crystallization speed of the material by increasing the amount of Sb is taken. Even in the SbTe eutectic recording material known for its high crystallization speed, the crystallization speed can be controlled by manipulating the Sb amount. However, if the Sb amount increases to some extent, the crystallization temperature of the material decreases. The problem of end up occurs. For this reason, the amorphous mark is recrystallized only by irradiating the reproduction light, and there is a problem that the information cannot be read, and that the information storage state at room temperature is deteriorated.
Known documents relating to the multilayer phase change optical recording medium include those using SbTe-based materials for the recording layer (Patent Documents 1 to 6), those using GeBiSbTe-based materials (Patent Document 9), and GeSbTe-based materials. There are no descriptions regarding the composition of the InSbGe system used in the present invention.

JP-A-2005-004943 JP 2004-259382 A JP 2004-110913 A JP 2004-047038 A JP 2003-045085 A JP 2003-296966 A JP 2001-243655 A JP 2001-215516 A JP 2004-311011 A

In a multilayer phase change optical recording medium, it is necessary to allow light to reach the second information layer through the first information layer, so that the reproduction light is about twice as much as that of a single layer phase change optical recording medium. I need. Therefore, in order to simultaneously solve a plurality of problems of high linear velocity recording, reproduction light stability and storage stability, crystallization is possible even if the Sb content of the first recording layer material contained in the first information layer is relatively small. It is necessary to cope with a recording material that can secure a high speed.
It is an object of the present invention to provide a multilayer phase change optical recording medium using a recording material that satisfies such requirements.

The above problems are solved by the following inventions 1) to 6) (hereinafter referred to as the present inventions 1 to 6).
1) A plurality of information layers including a phase change recording layer capable of recording information by causing a phase change by laser light irradiation, and each information layer other than the innermost side when viewed from the laser light irradiation side Is composed of at least a lower protective layer, a phase change recording layer, an upper protective layer, a reflective layer, and a heat diffusion layer, and when the composition of the phase change recording layer is InαSbβGeγ (α, β, and γ are atomic%), A multilayer phase change optical recording medium characterized by satisfying the above requirements.
10 ≦ α ≦ 20
65 ≦ β ≦ 85
2 ≦ γ ≦ 20
2) The reflection layer other than the innermost side when viewed from the side irradiated with the laser beam is Cu or at least one metal of Mo, Ta, Nb, Cr, Zr, Ni, and Ge with respect to Cu. The multilayer phase change optical recording medium according to 1), comprising a material to which 0.6 to 2.0% by weight of an element is added.
3) The multilayer phase change optical recording medium according to 1) or 2), wherein the upper protective layer other than the innermost side when viewed from the side irradiated with the laser beam contains an oxide of Sn.
4) The multilayer phase change optical recording medium according to any one of 1) to 3), wherein the thermal diffusion layer contains an oxide of In.
5) The multilayer phase change optical recording medium according to 4), wherein a Zn oxide is mixed in the thermal diffusion layer.
6) The multilayer phase change optical recording medium according to 4), wherein an oxide of Sn is mixed in the thermal diffusion layer.

Hereinafter, the present invention will be described in detail.
There are roughly two types of conventional recording layer material development. That is, from the write-once recording layer material GeTe, the reversible Sb and Te alloy Sb ₂ Te ₃ , and the GeSbTe ternary alloy developed from the solid solution or eutectic composition of these two materials. The recording layer material is one flow. Another flow is an alloy of Sb and Te, which is a recording layer material in which a trace element is added to SbTe whose Sb content is about 70%, which is a eutectic composition of Sb and Sb ₂ Te _3. is there.
In the optical recording medium having a two-layer recording layer, the information layer on the near side as viewed from the laser light irradiation side is required to have high transmittance in consideration of recording and reproduction of the information layer on the back side, For this purpose, it is required to make the recording layer thinner in parallel with efforts to reduce the absorption rate of the metal layer. Since it is known that the crystallization speed decreases when the recording layer is made thinner, it is advantageous to make the recording material itself have a high crystallization speed. Therefore, in the flow of this material series, the latter SbTe eutectic composition in which the Sb content is about 70% is preferable.

However, according to a study by the present inventors, if the amount of Sb is increased in order to increase the crystallization speed, that is, to increase the linear speed that can be handled, the crystallization temperature is lowered and the storage is continued. It was found that the characteristics deteriorated. Therefore, when a material system that has a high crystallization speed with a small amount of Sb, that is, a high linear speed that can be dealt with, compared to the GeSbTe system or the SbTe system, it was found that the linear speed can be improved with a small amount of Sb in the InSb system. It was. Therefore, it is preferable to use InSb as the recording layer material of the first information layer that requires a thin recording layer thickness. For example, FIG. 1 compares the transition linear velocity (LV) of an InSb-based single layer structure with that of an SbTe system and a GaSb system. As can be seen from this figure, the InSb system can have a high crystallization rate with a small amount of Sb.
Here, the transition linear velocity is a substitute characteristic of the crystallization speed of the phase change recording layer. When the linear velocity dependence R (v) of the reflectance obtained by irradiating with continuous light (DC light) having a power capable of heating the recording layer to the melting point or higher is taken, the crystal level changes to the amorphous level. The linear speed that changes. The reason for substituting the physical quantity of transition linear velocity is that it is difficult to know the absolute value of the crystallization speed of the phase change recording layer.

In a two-layer phase change optical recording medium, when reproducing the information layer on the back side as viewed from the laser beam irradiation side, the reflectivity is low and the amplitude of the reproduction signal is low due to absorption by the information layer on the near side. There is a problem of being small. Considering this, a higher reproducing light power is required than when reproducing with an optical recording medium having a single recording layer. Here, in the phase change type optical recording medium having a single layer structure, the reproducing light power Pr is about 0.7 mW. In a two-layer phase change optical recording medium, at least a reproducing light power larger than this is required. In the InSb system, in order to increase the crystallization speed, the amount of Sb may be increased, but this tends to lower the crystallization temperature. For this reason, when an InSb binary system is used for the information layer in the foreground, if a high reproducing light power is used, the amorphous mark recrystallizes and cannot be reproduced. At the same time, lowering the crystallization temperature is not preferable because the storage state becomes unstable. However, when the third element Ge is added to the InSb system, the crystallization temperature can be kept high. As a result, the amorphous mark is not recrystallized even when reproduced with high reproduction light power, and the storage state can be stabilized.
As described above, in the phase change recording layer of the multilayer phase change type optical recording medium, the phase change recording layer material that can be recorded at high speed, can be reproduced even with high reproduction light power, and can be stably stored. What consists of at least ternary system of InSbGe is preferable.

Next, the layer configuration of the optical recording medium and the characteristics of each layer will be described with reference to the example of FIG. 2 having two information layers including a phase change recording layer.
In the present invention 1, when the Sb amount (β) is in the above specified range, stable recording and reproduction can be performed as a recording material using phase change. If the amount of Sb is less than 65 atomic%, stable recording cannot be performed, and a recording layer that is not suitable for high-speed recording becomes a multilayer phase change optical recording medium. If the amount of Sb is more than 85 atomic%, the crystallization speed can be improved, but the crystallization temperature starts to decrease, making it difficult to reproduce with high reproduction light power and the storage state is unstable.

When the amount of In (α) is in the specified range, a high crystallization speed can be maintained even if the amount of Sb is relatively small, and the recording characteristics can be improved even in high linear velocity recording. it can. Since In promotes amorphization, it becomes possible to adjust the crystallization speed suitable for the desired recording linear velocity according to the addition amount. At the same time, the crystallization temperature can be increased according to the amount added, and the storage stability of the amorphous phase is improved. Further, the initialization is easy and the recording sensitivity is improved. If the amount of In is less than 10%, the storage characteristics in the amorphous state are deteriorated. If the amount of In is more than 20%, the effect of slowing down the crystallization speed becomes strong, making it unsuitable for high-speed recording.
When the Ge amount (γ) is in the above-described range, reproduction with high power is possible, and the storage state can be improved. If the amount of Ge is less than 2%, the effect of Ge does not appear and the storage state is not good. On the other hand, if the amount of Ge is more than 20%, the crystallization speed becomes slow and it becomes impossible to cope with high-speed recording, and furthermore, the melting point of Ge itself is high so that the recording sensitivity is deteriorated.

Here, preferable thicknesses of the lower protective layer, the phase change recording layer, the upper protective layer, the reflective layer, and the thermal diffusion layer that constitute each information layer other than the innermost side when viewed from the side irradiated with the laser beam explain.
The thickness of the lower protective layer is preferably in the range of 20 to 250 nm. When the thickness is less than 20 nm, the reflectance variation with respect to the film thickness is large, so that it is difficult to produce stably. When the thickness is more than 250 nm, the light transmittance is low and it is difficult to transmit light to the information layer at the back, and the film formation time is reduced. This increases the productivity of optical recording media.
The film thickness of the phase change recording layer made of InSbGe defined by the composition range of the present invention 1 is preferably in the range of 4 to 14 nm. If it is thinner than 4 nm, it is difficult to form a uniform film, which is not preferable. When it is thicker than 14 nm, the light transmittance is low and it is difficult to transmit light to the information layer in the back.

The thickness of the upper protective layer is preferably in the range of 5 to 30 nm. When the thickness is less than 5 nm, the reflectance variation with respect to the film thickness is large, so that it is difficult to produce the film stably. Further, it is difficult to generate heat and it is difficult to secure the degree of modulation. If it is thicker than 30 nm, the light transmittance is low and it becomes difficult to transmit light to the information layer in the back, and the film formation time is lengthened and the productivity of the optical recording medium is lowered. Also, there is a problem that the recording characteristics deteriorate due to excessive heat.
The thickness of the reflective layer is preferably in the range of 5 to 15 nm. If it is thinner than 5 nm, it is difficult to form a uniform film, and it is difficult to obtain a heat dissipation effect, which is not preferable. If it is thicker than 15 nm, the light absorption by the reflective layer increases and the light transmittance decreases, making it difficult to transmit light to the information layer in the back.
The thickness of the thermal diffusion layer is preferably in the range of 40 to 250 nm. If it is thinner than 40 nm, it is difficult to record because it cannot play the role of supplementing the heat dissipation effect of the ultra-thin reflective layer. If it is thicker than 250 nm, the heat dissipation effect is obtained, but the light transmittance is low, and it is difficult to transmit light to the information layer in the back.

According to the second aspect of the present invention, it is possible to improve the recording characteristics and the storage characteristics in the first recording layer. The reason why the first reflective (heat radiation) layer made of Cu is suitable will be described below.
As shown in FIG. 2, in a phase change optical recording medium including two recording layers, it is necessary to transmit as much laser light for recording / reproduction as possible to the second information layer. Therefore, as a matter to be considered when considering the first reflective layer, a material that is difficult to be absorbed and easily transmitted by the first reflective layer is preferable. Therefore, the present inventors performed optical measurement at various wavelengths of 660 nm for various reflective films. Here, data of A (absorbance), R (reflectance), and T (transmittance) were measured. As a measurement sample, a metal film having a thickness of 10 nm was formed on a 0.6 mm polycarbonate substrate. The result is shown in FIG. From FIG. 3, it is expected that Pt, Pd, and Ti are not preferable as the first reflective layer because they have low transmittance and high absorption.

Next, when Ag and Cu having a relatively high transmittance and a relatively low absorptance were investigated by varying (changing) the film thickness, results as shown in FIGS. 4 and 5 were obtained. That is, it has been found that Ag has a larger change due to the film thickness. This indicates that the stability of the optical constant with respect to the film thickness when Cu is formed is excellent.
Furthermore, although the measurement result of spectral transmittance is shown in FIG. 6, it turned out that the transmittance | permeability of Ag and Cu cross | intersects in the wavelength range of about 450 nm. Accordingly, Cu has higher transmittance in a wavelength region longer than the wavelength region of about 450 nm, and it is preferable to use Cu as the first reflective layer for laser light in the vicinity of 660 nm. I understand.
Furthermore, when the 3T single pattern was recorded on the first recording layer at a wavelength of 660 nm and the C / N was measured with respect to the three recording media in which the first reflective layer was Ag, Cu, and Au, as shown in FIG. As a result. When the first reflective layer was made of Cu, the highest C / N was obtained, and it was found that Cu was preferable from the viewpoint of recording characteristics.

In order to further improve the storage characteristics, a reflective layer in which a trace amount of metal element of about 0.6 to 2.0% by weight is added to Cu may be used. The trace metal element is preferably at least one selected from Mo, Ta, Nb, Cr, Zr, Ni, and Ge. Thereby, the storage characteristics can be improved without deteriorating the recording characteristics as compared with the case of Cu alone.
Ta and Nb are metals having strong affinity for oxygen and nitrogen, and are sometimes used as getter materials for oxygen and nitrogen. Originally, deterioration of a metal layer is often chemically oxidized, and in the case of Cu in particular, a reactant known as patina is an oxide. From this point, Ta and Nb are effective against Cu deterioration.
Next, regarding Mo, Zr, Cr, Ni, and Ge, when these metals are added, an alloy with Cu precipitates on the film surface or the copper grain boundary during recrystallization, and Cu grain boundary diffusion occurs. Therefore, Cu migration is prevented and deterioration is prevented.
The second reflective layer does not need to be translucent like the first reflective layer. The first reflective layer and the second reflective layer as described above are formed by various vapor deposition methods such as vacuum vapor deposition, sputtering, plasma CVD, photo CVD, ion plating, electron beam vapor deposition, and the like. it can. Among these, the sputtering method is excellent in mass productivity and film quality.

In the third aspect of the present invention, Sn oxide is contained in the upper protective layer other than the innermost side when viewed from the side irradiated with the laser beam.
The material used for the upper protective layer in the single-layer phase change optical recording medium is preferably made of a material that is transparent, allows light to pass through, and has a higher melting point than the recording layer, and prevents deterioration and deterioration of the recording layer. In particular, ZnS—SiO ₂ is often used, and ZnS: SiO ₂ = 80: 20 (mol%) is most preferable.
However, in the case of a multilayer phase change type optical recording medium, when information is recorded on the first recording layer, the film thickness of the first reflective layer is so thin that heat dissipation becomes poor and recording becomes difficult. Therefore, it is better to use a material having as good a thermal conductivity as possible for the first upper protective layer. Therefore, it is preferable to use an oxide of Sn that has higher heat dissipation than ZnS—SiO ₂ . Further, the Sn oxide may contain a metal-based oxide (for example, Ta oxide or Al oxide).
By using the Sn oxide, it is easy to form an amorphous mark on the first recording layer even if the first reflective layer is relatively thin. Sn oxide, Ta oxide, and Al oxide are materials that do not promote deterioration with respect to the reflective layer, and the composition ratio may be selected according to the production process, cost, allowable production time, and the like. However, when there are many Sn oxides, the power required for recording tends to increase. When there are many Ta oxides, although it is a material which does not reduce the film-forming speed | rate, it becomes difficult to show a recording characteristic in a 1st information layer. When the amount of Al oxide is large, the deposition rate tends to decrease.
For the second upper protective layer, ZnS—SiO ₂ may be used as usual, or Sn oxide may be used. The reason is that when recording on the second recording layer, the second reflective layer can be formed sufficiently thick, so that sufficient heat dissipation is obtained.

The first lower protective layer and the second lower protective layer are preferably made of a material that is transparent, allows light to pass through, and has a melting point higher than that of the recording layer, prevents deterioration and deterioration of the recording layer, and increases the adhesive strength with the recording layer. The metal oxide, nitride, sulfide, carbide, etc. are mainly used. Examples include metal oxides such as SiO, SiO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ , Si ₃ N ₄ , AlN, TiN, BN, ZrN, etc. Examples thereof include nitrides, sulfides such as ZnS, In ₂ S ₃ and TaS ₄ , carbides such as SiC, TaC, B ₄ C, WC, TiC and ZrC, and diamond-like carbon. These materials can be used alone as a protective film, but they may be mixed with each other. Further, impurities may be included as necessary. For example, _Ta 2 _O 5 -SiO a mixture of ZnS and _ZnS-SiO 2 mixed with SiO _{2, Ta} 2 _{O 5} and SiO2 and the like. In particular, ZnS—SiO is often used, but ZnS: SiO ₂ = 80: 20 (mol%) is most preferable. Since this material has a high refractive index n and an extinction coefficient k of almost zero, the light absorption efficiency of the recording layer can be increased, and since the thermal conductivity is small, the diffusion of heat generated by light absorption is moderate. Therefore, the temperature of the recording layer can be raised to a melting temperature.
The first upper protective layer, the second upper protective layer, the first lower protective layer, and the second lower protective layer as described above may be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, and photo CVD. It can be formed by a method, an ion plating method, an electron beam evaporation method or the like. Among these, the sputtering method is excellent in mass productivity and film quality.

In the present invention 4, an oxide of In is used for the thermal diffusion layer.
As the thermal diffusion layer, it is desirable that the thermal conductivity is high in order to quench the first recording layer irradiated with the laser. It is also desirable that the absorption rate at the laser wavelength is small so that the second information layer on the back side can be recorded and reproduced. From the above, it is preferable that at least one of nitride, oxide, sulfide, carbide and fluoride is included. Examples thereof include AlN, Al ₂ O ₃ , SiC, SiN, IZO (indium oxide-zinc oxide), ITO (indium oxide-tin oxide), DLC (diamond-like carbon), and BN. Among them, IZO (corresponding to the present invention 5) or ITO (corresponding to the present invention 6) is most preferable.
First, it is preferable that 1 to 10% by weight of tin oxide contained in ITO (indium oxide-tin oxide) is contained. If it is less than or greater than this range, the thermal conductivity and transmittance will be reduced. Further, other elements may be added for the purpose of improving storage stability. These elements can be added within a range that does not affect the optical properties, and are preferably contained in an amount of 0.1 to 5% by weight. If the amount is less than 0.1% by weight, the effect cannot be obtained. If the amount is more than 5% by weight, the light absorption increases and the transmittance decreases. In addition, at the wavelength of the laser beam used for recording / reproducing information, the absorption coefficient is preferably 1.0 or less, and more preferably 0.5 or less. If it is greater than 1.0, the absorptance in the first information layer increases, and recording / reproduction of the second information layer becomes difficult.
In addition, when IZO (indium oxide-zinc oxide) is used instead of ITO (indium oxide-tin oxide), the internal stress in the optical recording medium is reduced, so that a very small change in film thickness hardly occurs. preferable.
The thermal diffusion layer as described above can be formed by various vapor phase growth methods such as vacuum vapor deposition, sputtering, plasma CVD, photo CVD, ion plating, electron beam vapor deposition and the like. Among these, the sputtering method is excellent in mass productivity and film quality.

The first substrate is required to be sufficiently transparent to the light irradiated for recording / reproduction, and one known in the art is used. As the material, usually glass, ceramics, resin, or the like can be given, and resin is particularly preferable in terms of moldability and cost.
Examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicon resin, fluorine resin, ABS resin, and urethane resin. Acrylic resins such as polycarbonate resin and polymethyl methacrylate (PMMA), which are excellent in terms of moldability, optical characteristics, and cost, are preferable.
On the surface on which the information layer on the first substrate is formed, a spiral or concentric groove for tracking the laser beam is formed as necessary, and a concave / convex pattern usually referred to as a groove portion or a land portion is formed. It may be formed by an injection molding method or a photopolymer method. The thickness of the first substrate is preferably about 10 to 600 μm.
As the material of the second substrate, the same material as that of the first substrate may be used, but a material opaque to the recording / reproducing light may be used, and the material and groove shape may be different from those of the first substrate. Good. The thickness of the second substrate is not particularly limited, but it is preferable to select the thickness so that the total thickness of the second substrate is 1.2 mm.

  The intermediate layer preferably has low light absorption at the wavelength of light irradiated for recording / reproduction, and as the material, a resin is preferable in terms of moldability and cost, and an ultraviolet curable resin, a slow-acting resin, A plastic resin or the like can be used. The second substrate and the intermediate layer may be provided with uneven patterns such as grooves and guide grooves formed by an injection molding method or a photopolymer method, similar to the first substrate. The intermediate layer is a layer that enables the pickup to discriminate between the first information layer and the second information layer and perform optical separation when recording / reproducing, and the thickness is preferably 10 to 70 μm. If it is thinner than 10 μm, crosstalk between information layers occurs. On the other hand, when the thickness is larger than 70 μm, spherical aberration occurs when recording / reproducing the second recording layer, and recording / reproduction tends to be difficult.

The two-layer phase change optical recording medium of the present invention is preferably produced as follows. The manufacturing method includes a film forming process, an initialization process, and an adhesion process, and each process is basically performed in this order.
In the film forming step, in FIG. 2, the first information layer is formed on the surface of the first substrate on which the groove is provided, and the second information layer is formed on the surface of the second substrate on which the groove is provided. The first information layer and the second information layer can be formed by the various vapor deposition methods described above. Among them, the sputtering method excellent in mass productivity, film quality and the like is generally performed while flowing an inert gas such as argon, and at that time, reactive sputtering may be performed while mixing oxygen, nitrogen and the like.
In the initialization step, the entire surface is initialized by irradiating the first information layer and the second information layer with energy light such as laser light, that is, the recording layer is crystallized. If there is a possibility that the film may float due to laser light energy during the initialization process, before the initialization process, spin coat UV resin or the like on the first information layer and the second information layer, It may be cured by irradiating with ultraviolet rays, and an overcoat may be applied. Moreover, after performing the next contact | adherence process previously, you may initialize a 1st information layer and a 2nd information layer from the 1st board | substrate side.
In the adhesion process, the first substrate and the second substrate are bonded to each other through the intermediate layer while the first information layer and the second information layer face each other. For example, UV resin can be applied to any one of the film surfaces, the film surfaces face each other, both substrates can be pressed and adhered, and the resin can be cured by irradiation with ultraviolet rays.

  According to the present invention, it is possible to provide a multilayer phase change type optical recording medium that simultaneously satisfies high linear velocity recording, reproduction light stability, and storage stability.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples. The two-layer phase change optical recording medium prepared in the example has a configuration as shown in FIG. As the sputtering apparatus, an 8-chamber single wafer sputtering apparatus manufactured by Balzers was used. The evaluation apparatus used was DVDTester LM330A (laser wavelength 660 nm irradiated during recording, numerical aperture NA = 0.65 of the objective lens) manufactured by ShibaSoku. The reproducing light power was 1.4 mW.

Example 1
ZnS (80 mol%)-SiO ₂ (20 mol%) is formed on a first substrate made of a polycarbonate resin having a diameter of 12 cm and a thickness of 0.6 mm and having a tracking guide irregularity with a continuous groove having a track pitch of 0.74 μm on one side. ), A first lower protective layer having a thickness of 220 nm, a first recording layer having a thickness of 8 nm, made of In ₂ 0Sb ₆₅ Ge _15, and a film made of SnO ₂ (90 mol%)-Ta ₂ O ₅ (10 mol%). A first upper protective layer having a thickness of 12.5 nm, a first reflective layer having a thickness of 8 nm made of Cu, and a thermal diffusion layer having a thickness of 140 nm made of In ₂ O ₃ (90 mol%)-ZnO (10 mol%). A film was formed by a sputtering method in an Ar gas atmosphere.
On the other hand, using the same substrate as the first substrate as the second substrate, a second reflective layer made of Ag having a thickness of 140 nm, SnO ₂ (80 mol%)-Ta ₂ O ₅ (4 mol%)- A second upper protective layer having a thickness of 11 nm made of Al ₂ O ₃ (16 mol%) and a second recording having a thickness of 14 nm made of Ag _0.2 In _3.5 Sb _71.4 Te _21.4 Ge _3.5 The layers and the second lower protective layer having a thickness of 120 nm made of ZnS (80 mol%)-SiO ₂ (20 mol%) were formed in this order by a sputtering method in an Ar gas atmosphere.
Next, the first information layer and the second information layer were irradiated with laser light from the first substrate side and the second information layer film surface side, respectively, and an initialization process was performed. Initialization was performed by condensing the laser beam emitted from the semiconductor laser (emission wavelength 810 ± 10 nm) with an optical pickup (NA = 0.55). Initialization conditions were such that the optical recording medium was rotated in the CLV (constant linear velocity) mode, the linear velocity was 3 m / s, the feed amount was 36 μm / rotation, the radial position was 23 mm to 58 mm, and the initialization power was 700 mW.
Next, an ultraviolet curable resin (Nippon Kayaku Kayrad DVD576M) is applied on the film surface side of the first information layer, the second information layer surface side of the second substrate is bonded and spin-coated, and from the first substrate side. A two-layer phase change optical recording medium having two information layers was prepared by irradiating ultraviolet light to cure the ultraviolet curable resin as an intermediate layer. The thickness of the intermediate layer was 45 μm.
The recording linear velocity when recording on the first recording layer was 7 m / s.

(Examples 2 to 10, Comparative Examples 1 to 4)
Except that the composition of the first recording layer was changed to that shown in Table 1, the two-layer phase change optical recording media of Examples 2 to 10 and Comparative Examples 1 to 4 were prepared in the same manner as Example 1. did. Table 1 shows the recording linear velocity when recording on the first recording layer.

The characteristics of the two-layer phase change optical recording media of Examples 1 to 10 and Comparative Examples 1 to 4 were evaluated. The evaluation criteria are a case where the C / N ratio at the time of 8T single pattern recording is 45 dB or more, a case where it is less than 45 dB, and a case where the erase ratio when overwriting the 3T single pattern is -30 dB or less, The case where it exceeded -30 dB was made disqualified. In the storage test, after storing for 100 hours under the condition of 80 ° C. and 85% RH, the case where the decrease in C / N ratio is less than 3 dB is “◯”, and the case where it is 3 dB or more is “x”.
The results are summarized in Table 1, but if the composition of the first recording layer is outside the range of the present invention, the C / N ratio at the time of 8T single pattern recording becomes unacceptable and the storage characteristics become x. I understand.

(Examples 11-17, Comparative Examples 5-7)
Except that the composition of the first recording layer was changed to In ₁₅ Sb ₈₀ Ge ₅ and the first reflective layer was changed to Cu added with the metals shown in Table 2 in the proportions shown in Table 2 with respect to Cu. In the same manner as in Example 1, Examples 11 to 17 and Comparative Examples 5 to 7 were prepared as two-layer phase change optical recording media.
The storage characteristics of these media were examined in the same manner as in Example 1.
The evaluation criteria are passed after storage at 80 ° C. and 85% RH for 100 hours, and when the C / N ratio decrease is 1.5 dB or less (change amount is −1.5 dB or less), it is rejected when 1.5 dB or more. It was.
The results are shown in Table 2, and it can be seen that the amount of change exceeds -1.5 dB in the comparative example.
For each of the above media, 8T single pattern recording was performed before the storage test in the same manner as in Example 1. As a result, a C / N ratio of 50 dB or more was obtained.

The figure showing the transition linear velocity of the crystallization speed in case a recording layer is a single layer structure. The figure showing the layer structure of the two-layer phase change type optical recording medium. The figure showing the absorptivity, reflectance, and transmittance of the reflective layer material. The figure showing the film thickness dependence of the absorptivity, reflectance, and transmittance of Cu at 660 nm. The figure showing the film thickness dependence of the absorptivity, reflectance, and transmittance of Ag at 660 nm. The figure showing the wavelength dependence of the transmittance | permeability of Cu and Ag. The figure showing the recording characteristic of the 1st recording layer in case the 1st reflective layer is Cu, Ag, and Au.

Explanation of symbols

LV transition linear velocity R reflectivity T transmittance A absorptance

Claims (6)

A plurality of information layers including a phase change recording layer capable of recording information by causing a phase change by laser light irradiation, each information layer other than the innermost side when viewed from the side irradiated with laser light, When at least a lower protective layer, a phase change recording layer, an upper protective layer, a reflective layer, and a heat diffusion layer are used, and the composition of the phase change recording layer is InαSbβGeγ (α, β, and γ are atomic%), the following requirements Multilayer phase change optical recording medium characterized by satisfying
10 ≦ α ≦ 20
65 ≦ β ≦ 85
2 ≦ γ ≦ 20   The reflective layer other than the innermost side when viewed from the side irradiated with the laser beam is Cu, or at least one metal element of Mo, Ta, Nb, Cr, Zr, Ni, and Ge with respect to Cu. 2. The multilayer phase change optical recording medium according to claim 1, comprising a material added in an amount of 0.6 to 2.0% by weight.   3. The multilayer phase change optical recording medium according to claim 1, wherein the upper protective layer other than the innermost side when viewed from the side irradiated with the laser beam contains an oxide of Sn.   4. The multilayer phase change optical recording medium according to claim 1, wherein the heat diffusion layer contains an oxide of In.   5. The multilayer phase change optical recording medium according to claim 4, wherein Zn oxide is mixed in the thermal diffusion layer. 5. The multilayer phase change optical recording medium according to claim 4, wherein an Sn oxide is mixed in the thermal diffusion layer.

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