JP4397905B2 - Double-layer optical information recording medium - Google Patents

Description

  The present invention relates to a double-layer optical information recording medium having excellent recording characteristics in a wavelength range of 453 nm or more, particularly in a red wavelength (655 ± 5 nm) used in a DVD.

Optical discs such as CD-R (Compact Disc-Recordable) and CD-RW (Compact Disc-Rewritable) are recorded along the circumferential direction on a circular substrate made of plastic such as polycarbonate or a recording layer provided thereon. Further, a signal such as characters and images is recorded, and a reflective layer is formed on the surface by vapor deposition or sputtering of a metal such as aluminum, gold or silver. In this case, signal recording and reproduction are performed by irradiating a laser beam from the substrate surface side of the optical disk.
In recent years, the amount of information handled by computer memory, memory for image and sound files, optical cards, etc. has increased rapidly, so that the signal recording capacity and signal information of optical disks such as DVD + RW, DVD-RW, and DVD-RAM have increased. Densification is progressing. Currently, the recording capacity of a CD is about 650 MB, and the capacity of a DVD is about 4.7 GB. However, a higher recording density is required. As a method for increasing the recording density, in the optical system, it has been studied to shorten the wavelength of the semiconductor laser light source used and increase the numerical aperture NA (Numerical Aperture) of the objective lens. Furthermore, not only the improvement of the recording density in the two-dimensional direction, but also a method for accumulating information records by multilayering the recording layer in the thickness direction of the recording medium has been studied.

As a means for obtaining a large-capacity optical recording medium, when a multilayer recording layer is provided in the light incident direction and the laser to be used has a blue wavelength, there are the following problems.
For example, when the recording layer has a two-layer configuration, the first recording on the light incident side is performed in order to improve the light irradiation rate to the second recording layer on the light incident back side and to improve the transmittance of the irradiation return light. It is necessary to ensure the light transmittance of the layer. For this purpose, it is important to select the material and film thickness of the layer that causes light absorption. In particular, although the recording layer material is a problem, Patent Document 1 discloses that when the film thickness is reduced in order to reduce absorption, the crystallization speed tends to decrease relatively. Means for improving the crystallization speed is disclosed in Patent Document 2, and means for improving the crystallization of the recording layer material itself is also used. This method is disclosed in Patent Document 3. If the recording layer is made very thin, the light transmission increases, but the laser power absorbed by the first recording layer is reduced by the amount of light transmitted, and the recording signal difference sufficient for signal reading is reduced. Is difficult to obtain. As described above, there is a technically difficult problem in realizing the multilayer structure.

On the other hand, from the viewpoint of the recording layer material, there are two types of material development flows.
That is, it is composed of GeTe which is a write-once recording layer material, Sb ₂ Te ₃ which is an alloy of Sb and Te which can reversibly change phase, and a ternary alloy of GeSbTe from the solid solution or eutectic composition of these two materials. The recording layer material is one flow. Another flow is a recording layer material in which a trace element is added to SbTe having an eutectic composition of Sb and Sb ₂ Te ₃ and an Sb content of around 70%, which is an alloy of Sb and Te. .
The former ternary alloy-based material is necessary for recording by stabilizing Te amorphous phase by adding Ge to Te as the main component and capable of reversible phase change and mixing with Sb ₂ Te _3. Patent Documents 4 to 8 disclose that information can be recorded, erased, and rewritten at high speed by reducing the light energy and setting the mixing ratio to an optimum range. Among these, Patent Documents 5, 6, and 8 are those having a multilayer recording layer.
Regarding the latter alloy of Sb and Te, in Patent Document 9, as a recording material of the first information recording portion, Sb and Te are the main components, and the atomic ratio is 2.3 <Sb / Te ≦ 4.0. An example using a phase change recording material is disclosed. This phase change recording material is described as being capable of stable recording / reproduction and rewriting at a high transfer rate because of its high crystallization speed.

However, in the recording material system composed of the composition on the line connecting GeTe and Sb ₂ Te ₃ shown in Patent Documents 5, 6, and 8 described above, rewriting is performed because each has a high melting point and a high crystallization temperature. In order to improve the linear velocity because the speed is not sufficient, a configuration in which a crystallization auxiliary layer made of a metal alloy is laminated above and below the recording layer or a configuration in which an interface layer such as GeN is provided is generally used. It has been. The interface layer such as GeN is disclosed in Patent Document 2 and Non-Patent Document 1. Here, since the layer used for improving the linear velocity has a little light absorption, it can be said that it is a negative factor for the first recording layer that requires light transmission. Therefore, a material that can be recorded without requiring high power as the first recording layer and that can be formed with a simple layer structure is desired. Furthermore, in the case of a composition on a line connecting GeTe and Sb ₂ Te ₃ , a C / N ratio (Carrier to Noise Ratio) is as small as 30 dB, and a rewritable optical disk system which is said to be required to be at least 45 dB or more is required. It is difficult to build a stable system.

Next, a metal or an alloy is used as the reflective layer of the optical information recording medium. For example, as disclosed in Patent Document 11, Ag or an Ag alloy is often used because of its good thermal conductivity and excellent light reflection characteristics. However, Ag alone has a problem in storage characteristics, and it is necessary to provide a barrier layer or an intermediate layer for inhibiting the reaction between Ag and other substances. Since carbide or metal is used for the material of the barrier layer or intermediate layer, absorption of light energy by the reflective layer, barrier layer, and intermediate layer is disadvantageous from the viewpoint of efficient use of light energy for a configuration having a multilayer recording layer. It becomes.
As an example of the device relating to the Ag reflection layer material, there is an attempt to improve the trade-off relationship of ensuring durability and reflectivity by using an additive in addition to alloying (Patent Document 12, etc.).
Examples other than Ag or an Ag alloy include those using Cu (Patent Documents 13 to 16) and those using Au (Patent Document 17).
However, Patent Document 14 relates to a read-only ROM medium and is not related to a recordable medium. Further, although Patent Document 15 uses Cu for the reflective layer, only the AgPdCu alloy is shown as an example, and there is no specific description regarding the reflective layer containing Cu as a main component. Further, in Patent Document 16, there is a description that Cu is a main component, but in fact, it is an Ag-based disclosure, and there is no detailed description about Cu.
Further, Patent Document 18 discloses an optical information medium having a multi-layered recording layer, and the metal reflective layer mainly contains Cu and has a thickness selected from a range of 2 to 10 nm. Although described, only examples using only Cu are described in the examples, and there is no description at all regarding additive components other than Cu. In addition, the examples describe that the storage reliability can be ensured only by Cu without using other additive components. However, according to the research results of the present inventors, it has been clarified that Cu alone has characteristic deterioration after storage. Furthermore, even when an additive was added, it became clear that there was no effect depending on the type of additive.

JP 2002-144736 JP 2002-293025 A JP 2003-16687 A Japanese Patent No. 2692654 Japanese Patent No. 0216794 JP-A-10-116441 Japanese Patent Publication No. 8-032482 JP 2001-143322 A JP 2002-288876 A JP 2002-123977 A JP 2002-140838 A JP 2004-39146 A International Publication No. 02/021524 Pamphlet Japanese Patent Laid-Open No. 2003-331381 JP 2000-215516 A JP 2002-25115 A Japanese Patent No. 3087433 JP 2005-524922 Gazette Proceedings of the 10th Phase Change Symposium, pages 85-90 (1998)

  In the present invention, even in the information layer with high transparency on the front side of the laser light irradiation of the two information layers, sufficient recording characteristics are obtained in the wavelength range of 453 nm or more, particularly in the red wavelength (655 ± 5 nm) used in DVD. Another object of the present invention is to provide a two-layer optical information recording medium that can be obtained and can record / reproduce sufficient data signals from the information layer on the back side.

The above problems are solved by the following inventions 1) to 11 ).
1) In a two-layer optical information recording medium having a first substrate, a first information layer, a second information layer, and a second substrate in this order from the light incident side, the first substrate is at least a first lower portion in order from the light irradiation side. It has a dielectric layer, a first recording layer, a first upper dielectric layer, a first reflective layer, and an inorganic dielectric layer, and the second information layer is at least a second lower dielectric layer and a second recording layer in order from the light irradiation side. Layer, a second upper dielectric layer, a second reflective layer, the first reflective layer comprising 99.8-95.0 wt% Cu and Ta, Cu and 0.3-1.0 wt% Zr Cu and 0.2 to 0.8 wt% Ge, Cu and 1.1 wt% Mo, Cu and 1.1 wt% Nb, Cu and 0.7 wt% Ni, Cu and 0.6 wt% of Cr, consists either of Cu and 2.2 wt% of Au, the thickness of the first reflective layer is Ri 4~12nm der, recording and reproduction possible at the wavelength of 660nm light Dual-layer optical information recording medium, characterized in that there.
2) The two-layer optical information recording medium according to 1), wherein the first information layer and the second information layer are laminated at an optically separable interval and can be recorded by light irradiation from the same direction.
3) The two-layer optical information recording medium according to 1) or 2), wherein the first substrate is transparent.
4) The two-layer optical information recording medium according to any one of 1) to 3), wherein the first reflective layer is composed of 99.8 to 97.0% by weight of Cu and Ta .
5) The two-layer optical information recording medium according to any one of 1) to 4), wherein the first reflective layer has a thickness of 6 to 12 nm.
6) The double-layer optical information recording medium according to any one of 1) to 5), wherein the first recording layer and / or the second recording layer is made of a phase change recording material containing at least In, Sb, and Ge.
7) Any of 1) to 5), wherein the first recording layer and / or the second recording layer is composed of a phase change recording material containing at least Sb, Te, and Ge, and Ge <Te <Sb. The two-layer optical information recording medium according to claim 1.
8) The dual-layer optical information recording medium according to 6) or 7), wherein the content of Ge in the recording layer is 3.5 to 10 atomic%.
9) The two-layer optical information recording medium according to any one of 1) to 8), wherein the thickness of the first recording layer is 4 to 16 nm.
10) The two-layer optical information recording medium according to any one of 1) to 9), wherein the first upper dielectric layer contains at least an oxide of Sn and an oxide of Ta.
11) The two-layer optical information recording medium according to any one of 1) to 10), wherein the first lower dielectric layer and the second lower dielectric layer contain a mixture of ZnS and SiO ₂ .

Hereinafter, the present invention will be described in detail.
In order to solve the above problems, the present inventors first calculate the light absorption amount of the first information layer by simulation (here, the simulation means used is MULTILAYER, March 2001, manufactured by MM Research, Inc.). I tried to. ZnSSiO ₂ (ZnS: SiO ₂ = 80: 20 mol%) for the first lower dielectric layer, Ge ₅ Sb ₈₆ Te ₉ (atomic%) for the first recording layer, and the first lower dielectric layer for the first lower dielectric layer The calculation was performed for the same ZnSSiO ₂ as the dielectric layer, pure Ag for the first reflective layer, and In ₂ O ₃ for the inorganic dielectric layer. The result is shown in FIG. 2, and it was confirmed that light absorption occurred in the recording layer and the reflective layer. Since the light absorption of the recording layer is indispensable for recording and reproduction, it cannot be deleted, but the light absorption of the reflective layer is not related to the recording and reproduction characteristics. Just lose.

Next, RTA (R: reflectance, T: transmittance, A: absorption rate) data at a wavelength of 660 nm was measured for various metal films. As the measurement sample, a metal film having a thickness of 10 nm was formed on a polycarbonate substrate having a thickness of 0.6 mm. The result is shown in FIG. From these results, it was predicted that Pt, Pd, and Ti are not preferable as the reflective layer of the first information layer because of their low transmittance and high absorption rate.
Next, when Ag and Cu having a relatively high transmittance and a low absorptance were examined by varying (changing) the film thickness, the results shown in FIGS. 4 and 5 were obtained. That is, it was found that the Ag film has a larger change due to the film thickness. This indicates that Cu is superior in process stability. Furthermore, the measurement results of the spectral transmittance are shown in FIG. 6. The transmittance of Ag and Cu intersects at a wavelength λ = 453 nm, and Ag is more suitable at a wavelength shorter than 453 nm, but a wavelength longer than 453 nm. Then, it turns out that Cu is more suitable.
Next, when C / N (the ratio of carrier to noise) in 3T of Ag, Cu, and Au was measured at a wavelength of 660 nm used in DVD media, the result shown in FIG. 7 was obtained, and Cu reflection was also observed in terms of recording characteristics. It has been found that the layer is suitable for recording and reproduction at 660 nm.

As a material for the first reflective layer, a material composed of 99.8 to 95.0% by weight of Cu and an additive metal is used in order to compensate for the weak point of pure Cu. When the ratio of Cu exceeds 99.8% by weight, the effect of adding a metal cannot be obtained, and only a result equivalent to pure Cu can be obtained. On the other hand, if it is less than 95.0% by weight, there is an adverse effect of adding metal, which impairs the characteristics of pure Cu, that is, the transmittance characteristics at a wavelength of 660 nm and the C / N characteristics when signals are recorded. It will be.
As the additive metal, at least one metal selected from Ta, Nb, Zr, Ni, Cr, Ge, Au, and Mo is used. Ta and Nb are metals having strong affinity with oxygen and nitrogen, and are sometimes used as getter materials for oxygen and nitrogen. Originally, the deterioration of the reflective layer is often chemically oxidized, and the reactant known as patina particularly in the case of Cu is an oxide. From this point, Ta and Nb are effective against Cu deterioration. Next, regarding Zr, Ni, Cr, Ge, Au, and Mo, by adding these metals, an alloy with Cu is deposited on the film surface and the crystal grain boundary of copper during recrystallization. By suppressing the grain boundary diffusion of Cu by this, Cu migration is prevented and it functions to prevent deterioration.

  The reflective layer is usually made of a metal such as Al, Au, Ag, Pt, Cu, Ni, Cr, Ti, or Si, or a single metal or an alloy thereof. In order to form a recording mark, it is preferable to use a rapid cooling structure, so a material having high thermal conductivity is used, and Ag or an Ag alloy having particularly high thermal conductivity is often used. The reason is that, in addition to high thermal conductivity, high reflectivity can be obtained. However, there is a problem that sulfidation easily occurs due to contact with sulfides, and a sulfidation-resistant barrier layer or intermediate layer is required. This layer structure may be used in the case of the second reflective layer on the laser beam irradiation back side, but it is not preferable in the case of the first reflection layer on the laser beam irradiation front side. Therefore, the present inventors have focused on Cu as described above. Table 1 shows the thermal conductivity values of some metallic materials in the bulk state. Cu is the material having the highest thermal conductivity next to Ag. In addition to thermal conductivity, Cu has higher transmittance than other metals such as Ag, and the decrease in transmittance is small compared to the film, so that the information layer on the front side of the laser irradiation of the two-layer optical information recording medium Suitable for a reflective layer. Furthermore, with regard to storage characteristics, Cu has an ionization tendency that is more easily ionized than Ag. However, since the self-diffusion coefficient is small, migration is unlikely to occur, and storage reliability is ensured by a few additive elements. Is possible. The addition amount of the additive element is preferably 5% by weight or less. More preferably, it is 3% by weight or less.

第一反射層の膜厚は、第一情報層の反射率や、Ｃ/Ｎ、ジッターなどの記録特性について問題のない値が得られ、かつ、第二情報層の記録が行なえる程度の膜厚であることが要求される。即ち、下限は第一情報層の記録特性により制限され、上限は第一記録層の透過率により決定される。通常は４〜１２ｎｍ程度とし、好ましくは６〜９ｎｍとする。
また、第二反射層の膜厚は、第一反射層とは異なり、光透過性が要求されることは無く、記録特性が得られる程度の膜厚があれば良いので、第二基板の変形を起こさない程度に厚くても構わない。通常は１００〜１４０ｎｍ程度とする。

The film thickness of the first reflective layer is such that the values of the reflectance of the first information layer and the recording characteristics such as C / N and jitter can be obtained without problems and the second information layer can be recorded. It is required to be thick. That is, the lower limit is limited by the recording characteristics of the first information layer, and the upper limit is determined by the transmittance of the first recording layer. Usually, it is about 4 to 12 nm, preferably 6 to 9 nm.
In addition, unlike the first reflective layer, the second reflective layer is not required to have optical transparency, and it is sufficient if the film thickness is sufficient to obtain recording characteristics. It may be as thick as possible. Usually, it is about 100 to 140 nm.

From the viewpoint of materials, the recording layer has two systems of material development as described above, but in the two-layer optical information recording medium, the information layer (first information layer) on the front side of the laser beam irradiation is particularly For recording / reproduction of the recording layer (second recording layer) on the back side, it is required that the transmittance is good. For this reason, in parallel with efforts to reduce the absorption rate of the reflection layer, the recording layer on the front side (first recording layer) It is required to further reduce the thickness of the recording layer. Since it is known that the crystallization speed decreases as the recording layer is made thinner, it is advantageous to use a recording layer having a high crystallization speed as the first information layer. Therefore, among the above-described two systems, the latter SbTe eutectic composition having a Sb content of about 70% is preferable.
However, as a result of studies by the present inventors, if the amount of Sb is increased in order to increase the crystallization speed, that is, to increase the corresponding linear speed, the crystallization temperature decreases and the storage characteristics deteriorate. I found out that Accordingly, when a material system having a high crystallization speed with a small amount of Sb, that is, a material system capable of dealing with a high linear speed, was examined, it was found that the InSb system can improve the linear speed with a small amount of Sb. Therefore, it is preferable to use InSb as the first recording layer material that requires a thin recording layer. Among them, an InSb (Ge) system to which Ge is added is preferable. FIG. 8 shows the results of comparing the corresponding linear velocities for the InSb (Ge) system, the SbTe (Ge) system in which Ge is added to SbTe, and the GaSb system. However, the evaluation results in FIG. 8 are for the case where the information layer has a single layer structure.

Next, for the SbTe eutectic composition containing Ge and having an Sb content of around 70 atomic%, the present inventors have a structure in which the transition linear velocity at the same level as that of the InSb (Ge) system is obtained in the vicinity of 70 atomic% of Sb. Reexamined about. The results are shown in FIG. 10, and the SbTe eutectic composition containing Ge and having an Sb content of around 70 atomic% can also be used as a recording material for the first information layer that requires a high crystallization speed. I found out. This recording material contains at least Sb, Te, and Ge and has a composition that satisfies Ge <Te <Sb. If the Sb content is around 70 atomic%, it can be said that the storage reliability is not deteriorated.
Moreover, Ag and In can be selected as a material added to SbTe (Ge). It has been conventionally known that the reflectance and the ease of initialization can be adjusted by adding Ag and In.

Although various changes can be considered as the composition ratio of the constituent elements of InSb (Ge) and SbTe (Ge), the recording linear velocity that can be dealt with can be changed depending on the amount of Sb as shown in FIGS. . In the case of a two-layer optical information recording medium, the first recording layer needs to be thinned to obtain the transmittance, and since the recording linear velocity changes in the slow direction when it becomes thin, the Sb amount can be increased or decreased by taking this into consideration. That's fine. Regarding the amount of Ge, as the function of Ge, particularly when the amount of Sb is equal to or greater than the amount of the eutectic alloy, excessive Sb tends to deteriorate the storage characteristics, so that it works to suppress the deterioration of storage stability. . Usually, it is preferably 3.5 to 10 atomic%. 3.5-6 atomic% is more preferable.
The film thickness of the first recording layer for recording while transmitting laser light is 4 to 16 nm, more preferably 6 to 10 nm. If the thickness is less than 4 nm, the reproducibility of the film thickness upon film formation is unstable. If the thickness exceeds 16 nm, the transmittance is less than 20%, so that the recording / reproducing characteristics of the second recording layer are significantly deteriorated. If the wavelength range of the laser beam to be used is 453 nm or more, the superiority of the Cu reflection layer can be maintained, but from the viewpoint of merchantability, the wavelength of DVD of 660 nm is also applicable, which is preferable.
Unlike the first recording layer, the thickness of the second recording layer does not require light transmission. Therefore, the thickness of the second recording layer is the same as that of an ordinary optical information recording medium having one recording layer, that is, about 12 to 20 nm. To do.

For the first and second upper dielectric layers, usually ZnSSiO ₂ (ZnS: SiO ₂ = 80: 20 mol%) is used. However, since ZnSSiO ₂ contains sulfur, the reflective layer is deteriorated due to sulfidation, and therefore a dielectric layer or metal layer called a barrier layer or an intermediate layer is disposed. However, if these barrier layers or intermediate layers have light absorption, a problem arises in recording / reproduction of the laser light irradiation back information layer. Furthermore, in the first information layer, since the first reflective layer must be made thin, it is difficult to obtain a rapid cooling structure during recording, and it is difficult to obtain jitter characteristics during recording. Therefore, at least the first upper dielectric layer is preferably made of a material that requires a certain degree of thermal conductivity, that is, conductivity, and that does not deteriorate the reflective layer.
As such a material, a material containing at least an oxide of Sn and an oxide of Ta can be given. Each oxide is a material that does not promote deterioration with respect to the reflective layer material, and the composition ratio may be selected according to the production process, cost, allowable production time, and the like. When there are many Sn oxides, the power required for recording tends to increase. The Ta oxide is a material that does not decrease the deposition rate, but the first information layer is less likely to exhibit characteristics, and is preferably less than 20 mol%. By comprising a layer containing at least Sn oxide and Ta oxide, heat dissipation can be improved and recording sensitivity can be improved, and a high degree of modulation can be achieved even with relatively low recording power.
As other dielectric materials that can be added, materials that can ensure transparency without impairing thermal conductivity, that is, conductivity are suitable. For example, In oxide or Zn oxide used as a material for the transparent conductive film is preferable. With such a material system, since the light transmittance of the first information layer can be increased, the recording sensitivity of the second information layer can also be increased.
On the other hand, it is preferable to contain 50 mol% or more of Sn oxide. If it is less than 50 mol%, it will be difficult to obtain a sufficient crystallization speed in the first recording layer, it will be difficult to record at a high speed of about 10 m / s in the first information layer, and the jitter of repeated recording will also deteriorate.

An example of the layer structure of the two-layer optical information recording medium of the present invention is shown in FIG. In this example, a first lower dielectric layer 2, a first recording layer 3, a first upper dielectric layer 4, a first reflective layer 5, an inorganic dielectric layer 6, a first environmental protection on a first transparent substrate 1. A first information layer 10 comprising a layer 7, a second environmental protection layer 71, a second lower dielectric layer 21, a second recording layer 31, a second upper dielectric layer 41, a second reflective layer 51, and a second substrate ( The second information layer 20 composed of the bonded substrate 9) has a structure in which the adhesive layer 8 is stacked therebetween.
However, in the case where the first information layer 10 and the second information layer 20 are formed almost simultaneously, it is not necessary to provide an environmental protection layer if they are bonded together immediately. It can be omitted by setting the thicknesses of the environmental protection layer 7 and the second environmental protection layer 71 to the combined thickness.

The constituent materials and film thicknesses of the above layers will be described, but the points already described are omitted.
Examples of the first transparent substrate include glass, ceramics, and resin. A resin substrate is 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, silicone resin, fluorine resin, ABS resin, and urethane resin. Polycarbonate resins and acrylic resins that are excellent in terms of moldability, optical characteristics, and cost are preferred. In general, a transparent substrate made of polycarbonate resin in which predetermined grooves are formed by an injection molding method is often used as a substrate for CD and DVD.
The same material as the first substrate can be used for the second substrate, but a material that is not transparent may be used because it is a side on which light does not enter.

Materials for the first or second lower dielectric layer include oxides such as SiO, SiO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, and ZrO ₂ ; Si ₃ N ₄ Nitrides such as AlN, TiN, BN, and ZrN; sulfides such as ZnS and TaS ₄ ; carbides such as SiC, TaC, B ₄ C, WC, TiC, and ZrC; diamond-like carbon; or a mixture thereof . Among these, materials composed of ZnS and SiO ₂ such as ZnS—SiO ₂ (85:15 mol%), ZnS—SiO ₂ (80:20 mol%), ZnS—SiO ₂ (75:25 mol%) are preferable, and especially heat As the first dielectric layer located between the recording layer and the substrate with thermal damage due to expansion change and high temperature / room temperature change, ZnS-SiO ₂ (80 with optimized optical constant, thermal expansion coefficient and elastic modulus) is used. : 20 mol%) is often used because of the importance of thermal characteristics, optical characteristics and productivity (speed of film formation).

Since the film thickness of the first lower dielectric layer and the first upper dielectric layer greatly affects the reflectivity, the degree of modulation, and the recording sensitivity, it is desirable to select a film thickness at which the medium reflectivity is near the minimum value. In this film thickness region, the recording sensitivity is good, recording is possible with a power with less heat damage, and the overwriting performance is improved. In particular, in the case of a double-layer optical information recording medium, since the recording layer is often set with a larger recording power than that of a single optical information recording medium, a film that does not undergo deformation of the substrate even when a large power is applied. Thickness.
Specifically, the thickness of the first lower dielectric layer is about 40 to 80 nm or about 180 to 240 nm, and the thickness of the first upper dielectric layer is about 10 to 25 nm.
The film thickness of the second lower dielectric layer is about 60 to 180 nm, and the film thickness of the second upper dielectric layer is about 10 to 25 nm.

In the inorganic dielectric layer, In ₂ O ₃ , SnO ₂ , ITO (mixed composition of In ₂ O ₃ and SnO ₂ ), ZnO, a mixture thereof, or 20 mol%, which is generally used as a transparent conductive film, is used. The material etc. which added the following trace additives, such as a metal or an oxide, can be used.
The film thickness of the inorganic dielectric layer is about 40 to 80 nm or 120 to 160 nm.
As the environmental protection layer or adhesive layer material, an ultraviolet curable resin or a thermosetting resin can be used. Since the use of a thermosetting resin may affect the tilt of the substrate, an ultraviolet curable resin produced by a spin coating method is generally preferable. For example, a material containing an epoxy di (meth) acrylate, CH ₂ = COOR (R is an alicyclic hydrocarbon residue having 6 to 12 carbon atoms), an ethylenically unsaturated group other than the above components, and a photopolymerization initiator. , Epoxy di (meth) acrylate obtained by reacting bisphenol-type epoxy resin with a total chlorine content of 1500 ppm or less and (meth) acrylic acid using a tertiary amine as a catalyst, materials containing other acrylates, and UV-curable materials 2-methyl-1- (4-methylthiophenyl) -2-morpholino-propane having a pH value of 4.5 to 6.8 in a 1% by mass methanol solution of the composition (resin) and a photopolymerization initiator An ultraviolet curable composition containing 0.1 to 3% by mass of -1-one can be used.

Examples of the material for the first and second environmental protection layers include Overcoat Agent SD-318 manufactured by Dainippon Ink and Chemical INCORPORATED, NopcoCure Series nopco134 manufactured by San Nopco.
3-15 micrometers is suitable for the film thickness of a 1st, 2nd environmental protection layer, respectively. If the thickness is less than 3 μm, an increase in error may be observed when only one information layer is formed and left to stand. On the other hand, if it is thicker than 15 μm, the internal stress increases, which greatly affects the mechanical properties of the medium. In the case of a two-layer optical information recording medium, an optically separable distance is required between the first recording layer and the second recording layer, and the first environmental protection layer, the second environmental protection layer, and the adhesive In the case of a red wavelength of 660 nm as the total sum of the layers, it is preferable to set it to about 55 ± 15 μm.
The first and second environmental protection layers are formed in consideration of the possibility of leaving after the first information layer is formed on the first substrate or after the second information layer is formed on the second substrate. However, in the case where the first information layer of the first substrate and the second information layer of the second substrate are formed and bonded almost simultaneously, if the film thickness of about 55 ± 15 μm is secured, bonding with an ultraviolet curable resin or the like It may be a single layer.

  According to the present invention, even a highly transparent information layer on the front side of the laser light irradiation of the two information layers has sufficient recording in the wavelength range of 453 nm or more, particularly in the red wavelength (655 ± 5 nm) used in DVD. It is possible to provide a two-layer optical information recording medium that can obtain characteristics and can record / reproduce a sufficient data signal from the information layer on the back side.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples. Further, in the following description, a standard evaluation method / standard for a phase change type rewritable DVD double-layer medium is used, but the medium of the present invention is not necessarily limited to a medium of a specific format.

Example 1
First, a recording layer (referred to as a first information recording layer) that hits the front side when viewed from the laser irradiation direction was manufactured by the following procedure.
A first lower dielectric layer (thickness 220 nm) and a first phase change on a continuous groove surface of a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.6 mm and having a tracking guide unevenness by a continuous groove of 0.74 μm on one side A mold recording layer (film thickness 8 nm), a first upper dielectric layer (film thickness 12.5 nm), a first reflective layer (film thickness 8 nm), and an inorganic dielectric layer (film thickness 140 nm) were sequentially formed.
ZnS—SiO ₂ (80:20 mol%) is used for the first lower dielectric layer, In ₁₅ Sb ₈₀ Ge ₅ is used for the first phase change recording layer, and Ta ₂ O is used for the first upper dielectric layer. ₅ : Al ₂ O ₃ : SnO ₂ = 4: 16: 80 (mol%), Cu: Mo = 98.9: 1.1 (atomic%) for the reflective layer, and IZO for the inorganic dielectric layer Using [In ₂ O ₃ : ZnO = 90: 10 (mol%)], it was formed by sputtering using Ar gas as the sputtering gas with a single wafer sputtering apparatus (8 chambers) manufactured by Balzers (currently Unaxis). . However, the composition ratio of each element or compound indicates the ratio of the composition charged in the target.
When the inorganic dielectric layer was formed, the transmittance was measured and found to be 39.6%.
Next, a first environmental protection layer was provided thereon using a spin coater to produce a first information layer. The first environmental protection layer material is an ultraviolet curable resin, containing epoxy di (meth) acrylate, CH ₂ = COOR (where R is an alicyclic hydrocarbon residue having 6 to 12 carbon atoms) and ethylenically unsaturated groups other than the above components. And a material containing a photopolymerization initiator (Diabeam NH-7617N manufactured by Mitsubishi Rayon Co., Ltd.), and the film thickness after curing was 4 μm.
This first information layer was initialized by adjusting the focal position to the position of the first phase change recording layer with an initialization device (phase change optical disk initialization device: POP120-3Ra manufactured by Hitachi Computer). As an initialization apparatus, a pickup (NA 0.55, spot size is about 1 μm × 96 ± 5 μm) having a size of a semiconductor laser (emission wavelength 810 ± 10 nm) of about 1 μm × (75 ± 5) μm was used. Initialization conditions were such that the recording medium was rotated by CLV (Constant Linear Velocity), the linear velocity was 3 m / s, the feed amount was 36 μm / rotation, the radial position was 23 to 58 mm, and the initialization power was 700 mW.

Next, a second information layer that hits the back side when viewed from the laser irradiation direction was manufactured in the following procedure.
On a continuous groove surface of a polycarbonate substrate having a diameter of 120 mm and a thickness of 0.6 mm and having a tracking guide unevenness by a continuous groove of 0.74 μm on one side, a second reflective layer (film thickness 140 nm), a second upper dielectric layer ( Each layer of a film thickness of 20 nm), a second phase change recording layer (film thickness of 15 nm), and a second lower dielectric layer (film thickness of 120 nm) was sequentially formed.
ZnS—SiO ₂ (80:20 mol%) is used for the second lower dielectric layer, and Ag _0.45 In _4.98 Sb _68.61 Te _23.95 Ge _2.01 is used for the second phase change recording layer. For the second upper dielectric layer, and a mixture of Ta ₂ O ₅ : Al ₂ O ₃ : SnO ₂ = 4: 16: 80 (mol%), and Ag ₉₈ Pd ₁ Cu ₁ (wt%) for the reflective layer. Was formed by sputtering using Ar gas as a sputtering gas by a single wafer sputtering apparatus (8 chambers) manufactured by Balzers (currently Unaxis).
The composition ratio of each element of the second phase change recording layer material is a result of analysis in the target state by ICP emission spectroscopy (Inductively Coupled Plasma Emission Spectrometry). On top of that, the same material as the first environmental protection layer was spin coated to provide a second environmental protection layer, and a second information layer was produced.
For initialization of the second information layer, the same initialization device as that of the first information layer was used. However, since the position of the recording layer on the substrate is different, the focus position was corrected using a 0.6 mm spacer corresponding to the displacement. Initialization conditions were such that the recording medium was rotated by CLV (Constant Linear Velocity), the linear velocity was 2.0 m / s, the feed amount was 36 μm / rotation, the radial position was similarly 23 to 58 mm, and the initialization power was 600 mW.
Next, the first information layer and the second information layer were bonded together with an ultraviolet curable resin (DVD003 manufactured by Nippon Kayaku Co., Ltd.) to produce a two-layer optical information recording medium. After bonding, the coating amount and coating conditions of the ultraviolet curable resin were set so that the total thickness of the first environmental protection layer, the second environmental protection layer, and the adhesive layer was in the range of 55 μm ± 15 μm.

An optical disk evaluation device (Pultec DDU1000, laser wavelength 660 nm, NA 0.65) having a pickup equipped with a semiconductor laser having the following specifications is recorded on the manufactured double-layer optical information recording medium under the following conditions. Was evaluated.
Line speed: 3.5 to 8.4 m / s (CAV)
Recording power (Pw): 40 mW
Erase power (Pe): 16mW
Reading power (Pr): 1.4mW
3T pattern was recorded with an optimized pulse strategy, and the C / N ratio after storage for 300 hours under the condition of 80 ° C. and 85% RH was measured at the initial stage. The initial value was 53 to 56 dB, after storage for 300 hours. 50-53 dB, a change of 3 dB. In addition, the film was not lifted, the film was peeled off, or the appearance of spot-like discoloration considered to be abnormal was not observed.
The reflectance was 7.2% (however, the signal level of the photodiode when the reflectance of 140 nm pure Ag formed on the glass was read with the same measurement system was set to a reflectance of 87.7%, and the ratio was Based on the measured value).
Next, measurement was performed with a CAV (Constant Angular Velocity) with a linear velocity of 3.49 m / s at a point of a radial position of 40 mm. 8T multitrack recording was performed under the recording conditions of Pw = 36 mW and Pe = 14 mW.
When reproduction was performed at Pr = 1.4 mW and 3.49 m / s and jitter was measured, σ / T = 7.5% was obtained in the central track. The jitter of this track after storage for 300 hours under the conditions of 80 ° C. and 85% RH was good at 8.2%.

(Examples 2 to 10)
A two-layer optical information recording medium was manufactured in the same manner as in Example 1 except that the additive metal and the additive amount of the first reflective layer were changed, and the initial C / N characteristics of the first information layer and after storage for 300 hours. Was evaluated.
The results are shown in Table 2 together with Example 1. From the results of Table 2, it can be seen that the two-layer optical information recording medium of the present invention has an excellent C / N ratio before and after storage of 45 dB or more.

(Comparative Example 1)
A two-layer optical information recording medium was manufactured in the same manner as in Example 1 except that the first reflective layer material was changed to pure Ag. When the inorganic dielectric layer was formed, the transmittance was measured and found to be 34%.
Next, the first information layer was evaluated in the same manner as in Example 1. Except that the reading power was changed to 1.0 mW, 3T pattern recording was performed in the same manner as in Example 1. As a result, the initial value was 47 dB, and after storage for 300 hours, it was 40 dB, which was changed by 7 dB. The results are shown in Table 2.
The reflectance was 1% higher than that of Example 1.

(Comparative Example 2)
A two-layer optical information recording medium was manufactured in the same manner as in Example 1 except that the first reflective layer material was changed to pure Au. When the inorganic dielectric layer was formed, the transmittance was measured and found to be 40%.
Next, when the first information layer was evaluated in the same manner as in Comparative Example 1, the initial C / N of the 3T pattern was 45 to 48 dB, 30 to 33 dB after storage for 300 hours, and decreased by 15 dB. The results are shown in Table 2.

(Examples 11 to 21)
A double-layer optical information recording medium was prepared in exactly the same manner as in Example 1 except that the material of the first reflective layer was changed to Cu-Ta and the amount of Ta was changed from 0.2 wt% to 5 wt%. The initial jitter and the jitter after storage for 300 hours were evaluated.
Initial jitter and jitter change after storage for 300 hours were in the 9% range, and there was no problem in characteristics. The change in jitter after storage for 300 hours with a low addition amount is considered to be a change in the first reflective layer. Further, it is considered that the initial jitter increase of 3% by weight or more is due to a decrease in the thermal conductivity of the first reflective layer.
Furthermore, in order to evaluate the transmittance | permeability of a film | membrane, the single film of 8 nm was formed on glass, and the transmittance | permeability was measured. The results are summarized in Table 3, and the transmittance did not change to the transmittance of the single membrane up to 3% by weight, and the transmittance gradually increased when the added amount exceeded 3% by weight.

(Comparative Example 3)
A two-layer optical information recording medium was produced in the same manner as in Example 1 except that the additive metal was not added to Cu in the first reflective layer, and the same evaluation as in Examples 11 to 21 was performed. The results are shown in Table 3.
In this comparative example, there was no change in the transmittance of the single film and the initial jitter was as good as 6.5%, but the jitter after storage was 9.5% (increase of 3%) at 100 hours and 300 hours. Then, it changed greatly with 10.8% (an increase of 4.3%).

(Comparative Examples 4-6)
Except for the point that the material of the first reflective layer is Cu-Ta and the amount of Ta added is 5.5 wt% (Comparative Example 4), 6 wt% (Comparative Example 5), and 7 wt% (Comparative Example 6). A double-layer optical information recording medium was manufactured in exactly the same manner as in Example 1, and the same evaluation as in Examples 11 to 21 was performed. The results are shown in Table 3.
As can be seen from Table 3, when the addition amount exceeded 5% by weight, the transmittance of the single film increased with the addition amount, and the initial jitter changed greatly. However, the change in jitter after storage for 300 hours was small.

(Examples 22 to 26, Comparative Examples 7 to 9)
A first information layer having the same configuration and the same material as in Example 1 except that the thickness of the first reflective layer is changed is manufactured, and the second information layer having the same configuration as that in Example 1 is bonded to the first information layer. Double-layer optical information recording media of Examples 22 to 26 and Comparative Examples 7 to 9 were manufactured.
The thickness of the first reflective layer of each double-layer optical information recording medium is 3 nm (Comparative Example 7), 4 nm (Example 22), 6 nm (Example 23), 8 nm (Example 24), 10 nm (Example 25). ), 12 nm (Example 26), 13 nm (Comparative Example 8), and 15 nm (Comparative Example 9).
For these two-layer optical information recording media, an 8T signal was recorded at a linear velocity of 7 m / s and an erasing power of 16 mW and then erased (the ratio of the amplitude of the recording signal before and after erasing was expressed in decibels). Measured).
The results are shown in FIG. 9. When the film thickness is 6 nm or more, the erasure ratio does not change greatly at about -40 dB, and the erasure ratio starts to slightly decrease at the film thickness of 4 nm. It was an acceptable range. However, when the film thickness is 3 nm, only an erasure ratio of −20 dB is obtained, and unerased data before erasure occurs.
Next, for each of the two-layer optical information recording media, an 8T signal was recorded on the second information layer with a single track through the first information layer, reproduced, and jitter was measured.
The results are shown in FIG. 9, and a good jitter of 9% or less was obtained when the thickness of the first reflective layer was 12 nm or less. However, when the film thickness was 13 nm and 15 nm, the jitter exceeded 9%.
From the above results, it was found that the thickness of the first reflective layer is preferably in the range of 4 to 12 nm.

(Comparative Examples 10-13)
The material of the first reflective layer is Cu—Al <Al addition amount 2.1 wt%> (Comparative Example 10), Cu—Si <Si addition amount 2.1 wt%> (Comparative Example 11), Cu—Zn <Zn. Double-layer optical information in exactly the same manner as in Example 1 except that the amount added was 2.1 wt%> (Comparative Example 12) and Cu—Pd <Ti amount added 2.1 wt%> (Comparative Example 13). A recording medium was manufactured, and after recording a 3T pattern in the same manner as in Example 1, the C / N change after storage for 300 hours was measured.
The results are shown in Table 4. From this result, the amount of change in C / N varies greatly depending on the additive element. In general, the metal used as the reflective layer material or additive element of the optical information recording medium can be used as the additive element of Cu. It turns out that there is something inappropriate.

(Example 27)
The film thickness of the first lower dielectric layer of the first information layer is 60 nm, the material of the first phase change recording layer is Ag _0.2 In _3.5 Sb _69.2 Te _21.1 Ge ₆ , and the film thickness. 7.5 nm, the material of the first upper dielectric layer is Ta ₂ O ₅ : SnO ₂ = 20: 80 (mol%), the film thickness is 5 nm, and the film thickness of the inorganic dielectric layer is changed to 60 nm. A double-layer optical information recording medium was manufactured in the same manner as in Example 1.
When the recording characteristics of the first information layer were evaluated in the same manner as in Example 1 for this two-layer optical information recording medium, it was stored for 300 hours under the initial C / N of 3T pattern and 85 ° C. and 85% RH conditions. As for the subsequent C / N change, the initial C / N was 53 dB, the C / N change after 300 hours storage was 3 dB, and both the initial and after 300 hours were good. Neither floating of the film, peeling of the film, or appearance of spot-like discoloration that seemed to be abnormal was observed. Further, the reflectance was 6.5%.
Next, 8T multi-track recording was performed at a point of a radial position of 40 mm, playback was performed at Pr = 1.4 mW, 3.49 m / s, and jitter was measured. 0.0% was obtained. The jitter of this track after storage for 300 hours under conditions of 80 ° C. and 85% RH was as good as 8.0%.
Further, the transition linear velocity of the first information layer was measured. Here, the transition linear velocity is a line where the reflectance starts to change when the track in the crystalline state by the initialization process is irradiated with continuous light (power is 15 mW) while changing the linear velocity of the recording medium. Say fast.
The transition linear velocity in the first information layer structure of the recording layer of this example is 18 m / s. The transition linear velocity is a value obtained by substituting the crystallization speed of the recording layer, and is an important design standard for achieving the target recording speed.

(Examples 28 to 30)
An optical recording medium was manufactured in the same manner as in Example 27 except that the recording layer material having the composition shown in the column of Examples 28 to 30 in Table 5 was used for the first recording layer. The recording characteristics of the first information layer were evaluated.
Each transition linear velocity, initial jitter at the time of 8T matching track recording, and jitter after storage for 300 hours under the conditions of 80 ° C. and 85% RH are shown in Table 5, but this recording layer composition also shows initial jitter after storage for 300 hours. A value with no problem with jitter was obtained.
Regarding the transition linear velocity, the case of Example 27 (■ in the figure) is plotted together with the data of FIG. 8 and is shown as FIG. 10, but even in the case of the SbTe (Ge) system, the first information of the two-layer configuration is used. In the case of the layer (L0), the information layer is shifted to the left as indicated by an arrow in comparison with the case of a single layer structure (□ in the figure), and shows a transition linear velocity equivalent to that of the InSb (Ge) system. I understand.

(Comparative Example 14)
An optical recording medium was manufactured in the same manner as in Example 27 except that the recording layer material (GeSbTe) having the composition shown in the column of Comparative Example 14 in Table 5 was used for the first recording layer. Thus, the recording characteristics of the first information layer were evaluated.
As can be seen from the results shown in Table 5, the change after storage for 300 hours under the condition of 85% RH was not large, but the initial jitter was 16%, and satisfactory initial characteristics could not be obtained.
The transition linear velocity could not be measured by the same method as in Example 27.

The figure which shows an example of the layer structure of the two-layer optical information recording medium of this invention. The figure of the simulation result of a 1st recording layer. The figure which shows RTA data of various reflective layer materials (wavelength 660nm). The figure which shows RTA (R: reflectance, T: transmittance | permeability, A: absorptance) of Cu metal film by this invention. The figure which shows RTA (R: reflectance, T: transmittance | permeability, A: absorption factor) of Ag alloy type metal film. The figure of the spectral transmittance of Ag system and Cu system metal film. The figure which compared C / N of Ag, Au, and Cu. FIG. 3 is a diagram showing a comparison of linear speeds of three types of recording layers. The figure which shows the measurement result of the erasure | elimination ratio and 8T jitter of Examples 22-26 and Comparative Examples 7-9. The figure which added the case of Example 27 to FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st transparent substrate 2 1st lower dielectric layer 3 1st recording layer 4 1st upper dielectric layer 5 1st reflection layer 6 Inorganic dielectric film layer 7 1st environmental protection layer 8 Adhesive layer 9 2nd substrate ( Bonded substrate)
DESCRIPTION OF SYMBOLS 10 1st information layer 20 2nd information layer 21 2nd lower dielectric layer 31 2nd recording layer 41 2nd upper dielectric layer 51 2nd reflective layer 71 2nd environmental protection layer R reflectance T transmittance | permeability A absorption LV Transition linear velocity L0 configuration Layer configuration of the first information layer (see Fig. 10)

Claims (11)

In a two-layer optical information recording medium having a first substrate, a first information layer, a second information layer, and a second substrate in this order from the light incident side, the first substrate is at least a first lower dielectric in order from the light irradiation side Layer, first recording layer, first upper dielectric layer, first reflective layer, inorganic dielectric layer, the second information layer is at least a second lower dielectric layer, a second recording layer in order from the light irradiation side, The second reflective layer has a second upper dielectric layer and a second reflective layer, the first reflective layer comprising 99.8 to 95.0 wt% Cu and Ta, Cu and 0.3 to 1.0 wt% Zr, Cu 0.2 to 0.8 wt% Ge, Cu and 1.1 wt% Mo, Cu and 1.1 wt% Nb, Cu and 0.7 wt% Ni, Cu and 0.6 wt% of Cr, consists either of Cu and 2.2 wt% of Au, the thickness of the first reflective layer is Ri 4~12nm der, it can be recorded and reproduced by the wavelength of 660nm light Dual-layer optical information recording medium characterized and.   The two-layer optical information recording medium according to claim 1, wherein the first information layer and the second information layer are laminated at an optically separable interval and can be recorded by light irradiation from the same direction.   The double-layer optical information recording medium according to claim 1 or 2, wherein the first substrate is transparent. The double-layer optical information recording medium according to any one of claims 1 to 3, wherein the first reflective layer is composed of 99.8 to 97.0 wt% of Cu and Ta .   The double-layer optical information recording medium according to any one of claims 1 to 4, wherein the thickness of the first reflective layer is 6 to 12 nm.   The double-layer optical information recording medium according to any one of claims 1 to 5, wherein the first recording layer and / or the second recording layer is made of a phase change recording material containing at least In, Sb, and Ge.   The first recording layer and / or the second recording layer is composed of a phase change recording material containing at least Sb, Te and Ge, and Ge <Te <Sb. The two-layer optical information recording medium described. The double-layer optical information recording medium according to claim 6 or 7, wherein the content of Ge in the recording layer is 3.5 to 10 atomic%.   The double-layer optical information recording medium according to any one of claims 1 to 8, wherein the thickness of the first recording layer is 4 to 16 nm.   The double-layer optical information recording medium according to any one of claims 1 to 9, wherein the first upper dielectric layer contains at least an oxide of Sn and an oxide of Ta. The double-layer optical information recording medium according to claim 1, wherein the first lower dielectric layer and the second lower dielectric layer contain a mixture of ZnS and SiO ₂ .

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