JP4719172B2 - Multilayer optical recording medium - Google Patents

Description

  The present invention provides a multilayer optical recording medium (hereinafter referred to as “multilayer phase”) having a plurality of recording layers capable of recording and reproducing information by causing optical changes in the recording layer material by irradiating a light beam. Changeable optical recording medium ”,“ multilayer optical information recording medium ”, and“ multilayer optical disc ”).

A recordable optical disk such as DVD + R / RW generally has a structure in which a recording layer is provided on a plastic substrate, and a reflective layer having a thermal diffusion effect is provided on the recording layer. Information is recorded and reproduced by irradiating a laser beam from the substrate surface side.
For the purpose of preventing oxidation, transpiration or deformation of the recording layer caused by heating by light irradiation, usually a lower protective layer (hereinafter sometimes referred to as “lower dielectric layer”) between the substrate and the recording layer, and An upper protective layer (hereinafter also referred to as “upper dielectric layer”) is provided between the recording layer and the reflective layer. These protective layers have a function of adjusting the optical characteristics of the optical recording medium by adjusting the thickness thereof, and the lower protective layer has a function of preventing the substrate from being softened by heat during recording on the recording layer. It has both.

In recent years, as the amount of information handled by computers and the like has increased, the signal recording capacity of recordable optical discs such as DVD-RAM, DVD-R / RW, and DVD + R / RW has increased, and the density of signal information has increased. It is out. Although DVD is about 4.7 GB, 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.
Shorten the laser wavelength used to the blue region, or increase the numerical aperture (NA) of the objective lens used in the pickup for recording / reproducing, thereby reducing the spot size of the laser light irradiated on the optical recording medium. It has been proposed, research and development has been carried out, and has been put to practical use.
As a method of improving the recording capacity by improving the optical recording medium itself, it is produced by stacking at least two information layers consisting of a recording layer and a reflective layer on one side of the substrate and bonding these information layers with an ultraviolet curable resin or the like. Various optical recording media capable of two-layer recording have been proposed. A separation layer (hereinafter also referred to as an “intermediate layer”) which is an adhesion portion between these information layers has a function of optically separating the two information layers, and a laser beam used for recording and reproduction is as much as possible. Since it is necessary to reach the information layer on the back side, it is made of a material that absorbs as little light as possible.

Many problems still exist for such an optical recording medium capable of two-layer recording. 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.
Therefore, since the light transmittance and the heat dissipation effect cannot be obtained, it is necessary to form a heat diffusion layer in contact with the translucent reflective layer to supplement the light transmittance and the heat dissipation effect. In addition, since the layer structure of the first information layer is a structure in which heat does not easily escape, there is no need to use any recording material in terms of storage stability, and it is necessary to limit the recording layer material and its composition. .

  For example, Patent Documents 1 to 6 disclose a two-layer phase change type optical recording medium using laser light having a wavelength of 360 nm to 420 nm, and the thermal diffusion layer includes In oxide, Sn oxide, Sb oxide, And a material containing at least one of Zn oxide has been proposed.

  However, the light transmittance of each information layer other than the farthest side when viewed from the laser beam irradiation side is increased so that stable recording / reproduction can be performed in each information layer, excellent in repeated durability, and excellent storage stability. A multilayer optical recording medium having the properties is not provided, and the present situation is that further improvement and development are desired.

JP 2004-005920 A JP 2004-047034 A JP 2004-047038 A JP-A-2005-004943 JP-A-2005-004944 International Publication No. 02/029787 Pamphlet

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, the present invention increases the light transmittance of each information layer other than the innermost side when viewed from the laser beam irradiation side, enables stable recording and reproduction in each information layer, has excellent repeated durability, and An object of the present invention is to provide a multilayer optical recording medium having excellent storage stability.

Means for solving the problems are as follows. That is,
<1> A plurality of information layers having at least a recording layer are provided via an intermediate layer between the first substrate on the near side as viewed from the side irradiated with the laser beam having the wavelength λ and the second substrate on the back side. ,
The substrate has a spiral guide groove meandering on the recording surface side,
As viewed from the first substrate side, each information layer other than the innermost information layer has at least a lower protective layer, a recording layer, an upper protective layer, an adjustment layer, a translucent reflective layer, and a thermal diffusion layer. ,
The innermost information layer has at least a lower protective layer, a recording layer, an upper protective layer, and a reflective layer,
The multilayer optical recording medium is characterized in that the grain size of the adjustment layer is smaller than the grain size of the translucent reflective layer.
<2> The multilayer optical recording according to <1>, wherein the grain size A (μm) of the adjustment layer and the grain size B (μm) of the translucent reflective layer satisfy the following formula: B-A> 0.05 μm It is a medium.
<3> The multilayer optical recording medium according to any one of <1> to <2>, wherein the crystal occupancy of the adjustment layer is 40% or more.
<4> The multilayer optical recording medium according to any one of <1> to <3>, wherein the adjustment layer is made of the same material as the translucent reflective layer.
<5> The translucent reflective layer contains either Ag or Cu, and the content of either Ag or Cu is 95% by mass or more, according to any one of <1> to <4>. It is a multilayer optical recording medium.
<6> When the thermal diffusion layer contains In oxide, Zn oxide, Sn oxide, and Si oxide, and the respective contents [mol%] are a, b, c, and d, the following formula The multilayer optical recording medium according to any one of <1> to <5>, wherein 3 ≦ a ≦ 20, 0 ≦ d ≦ 30, and a + b + c + d = 100.
<7> When the recording layer is composed of at least Ge, Sb, and Te, and the respective composition ratios [atomic%] are α, β, and γ, the following formulas, 2 ≦ α ≦ 20, 60 ≦ β ≦ 75, The multilayer optical recording medium according to any one of <1> to <6>, wherein 6 ≦ γ ≦ 30 and α + β + γ = 100 are satisfied.
<8> When viewed from the first substrate side, the upper protective layer of each information layer other than the innermost side contains In oxide, Zn oxide, Sn oxide, and (Si oxide or Ta oxide) When the content [mol%] is e, f, g, and h, the following formulas, 3 ≦ e ≦ 20, 50 ≦ (f or g) ≦ 90, 0 ≦ h ≦ 20, e + f + g + h = 100 The multilayer optical recording medium according to any one of <1> to <7>, wherein
<9> lower protective layer in each information layer is a multilayer optical recording medium according the consisting of ZnS and SiO ₂ to any one of <1> to <8>.
<10> From the above <1> that satisfies the following formula, λ / (15 × n) ≦ H ≦ λ / (11.5 × n), where n is the refractive index of the substrate and H is the depth of the guide groove <9> A multilayer optical recording medium according to any one of <9>.

  According to the present invention, conventional problems can be solved, the light transmittance of each information layer other than the innermost side is increased, and recording / reproduction can be performed on each information layer with stable tracking accuracy. Thus, it is possible to provide a multi-layer phase change optical recording medium having excellent repeated durability and excellent storage stability.

The multilayer optical recording medium of the present invention has an information layer having at least a recording layer interposed between the first substrate on the near side and the second substrate on the back side when viewed from the side irradiated with the laser beam having the wavelength λ. Have multiple,
The first substrate and the second substrate have spiral guide grooves meandering on the recording surface side,
As viewed from the first substrate side, each information layer other than the innermost information layer has at least a lower protective layer, a recording layer, an upper protective layer, an adjustment layer, a translucent reflective layer, and a thermal diffusion layer. In addition, other layers are provided as necessary.
The innermost information layer includes at least a lower protective layer, a phase change recording layer, an upper protective layer, and a reflective layer, and further includes other layers as necessary.

Here, as the multilayer optical recording medium, a two-layer optical recording medium having a first information layer and a second information layer from the side irradiated with the laser beam is particularly preferably used. In the following, a two-layer optical recording medium will be described as a representative example.
FIG. 1 is a schematic cross-sectional view of a two-layer optical recording medium according to an embodiment of the present invention. This two-layer optical recording medium is formed by laminating a first information layer 1, an intermediate layer 4, a second information layer 2, and a second substrate 5 in this order on a first substrate 3, and further if necessary. And other layers.

The first information layer 1 includes a first lower protective layer 11, a first recording layer 12, a first upper protective layer 13, an adjustment layer 14, a first translucent reflective layer 15, and a thermal diffusion layer 16. .
The second information layer 2 includes a second lower protective layer 21, a second recording layer 22, a second upper protective layer 23, and a second reflective layer 25.
A barrier layer may be provided between the first upper protective layer 13 and the first translucent reflective layer 15 and between the second upper protective layer 23 and the second reflective layer 25.

-Adjustment layer-
If the adjustment layer has crystallinity, it can be easily estimated that the first translucent reflective layer formed on the adjustment layer is affected. However, the crystallinity can be estimated by sputtering or the like without adding temperature. It is not easy to have Therefore, high-quality thin film formation (high density, dense structure, good crystallinity, ultra-smooth surface, good quality by forming an adjustment layer by electron cyclotron resonance (ECR) microwave plasma method or ion plating method It was found that excellent adhesion and low residual stress) can be obtained.
In addition, by forming an adjustment layer with high crystallinity made of the same material as the first translucent reflective layer on the base, in the case of Cu, (111), (511), and (100) appear. The (111) direction is 18.8% in the normal sputtering method, 60.3% in the ECR method, and 48% in the ion plating method, and the ratio of the crystal orientation is high. The first information layer (L0 layer) ) Was improved by 1.2% by the ECR method and by 0.8% by the ion plating method. For comparison, the first information layer (L0 layer) formed by the RF sputtering method (the same adjustment layer thickness as that of Example 1 was formed by the ion plating method.
When the transmittance of the first information layer (L0 layer) is increased, the recording sensitivity of the recording layer of the second information layer (L1 layer) (the layer on the back side with respect to light incidence in the case of two layers) is improved. In the case of a rewritable DVD, an improvement in recording sensitivity of 2 mW or more can be expected with a 1% improvement in transmittance. In the case of Ag as well, Cu grows in the (011) direction.

Therefore, in the present invention, the grain size of the adjustment layer is smaller than the grain size of the first translucent reflection layer, and the grain size A (μm) of the adjustment layer and the first translucent reflection layer Grain size B (μm) preferably satisfies the following formula, B−A> 0.05 μm, and more preferably B−A> 0.1 μm.
Since the grain size of the adjustment layer is smaller than the grain size of the first translucent reflective layer, the crystal occupancy is increased, the transmittance of the first information layer (L0) is improved, and the second information layer ( The recording sensitivity of L1) is improved. When the grain size of the adjustment layer is larger than the grain size of the first translucent reflective layer, the crystal directions of the first translucent reflective layer are not aligned, and the transmittance of the first information layer (L0) is improved. As a result, the amount of light incident on the second information layer (L1) does not increase, so that good recording sensitivity of the second information layer (L1) may not be obtained.
Here, the grain size means the size of a region where crystal orientations are aligned. The grain size of the adjustment layer is preferably 0.09 μm to 0.12 μm. The grain size of the first translucent reflective layer is preferably 0.19 μm to 0.25 μm.
The grain size of the adjustment layer and the first translucent reflective layer is measured by taking several photographs with, for example, a high-resolution analytical electron microscope (HRTEM), actually measuring the grain portion on the photographed image, and converting the magnification. Can do.

The crystal occupancy (ratio of crystal orientation) of the adjustment layer is preferably 40% or more, and more preferably 50% to 65%. When the crystal occupancy is less than 40%, the transmittance of the first information layer (L0) is hardly improved, and the recording sensitivity of the second information layer (L1) may not be improved. When the transmittance of L0 is increased, the recording sensitivity of the second information layer (L1) is improved, and in the case of a DVD rewritable medium, an improvement in sensitivity of 2 mW or more can be expected at 1%.
Here, the crystal occupancy can be measured and calculated by, for example, a high resolution analytical electron microscope (HRTEM).

The adjustment layer is made of the same material as the first translucent reflective layer, and details thereof will be described later.
The adjustment layer is formed by an ion plating method, an electron cyclotron resonance (ECR) microwave plasma method, or the like, and the ECR method is particularly preferable because it can be performed at a low temperature, is a low damage process, and can increase crystallinity.
The electron cyclotron resonance (ECR) microwave plasma generates high-density and highly active plasma by a plasma generation method using an interaction between an electric field and a magnetic field, called electron cyclotron resonance. By utilizing this plasma, ion assist from the plasma can be effectively performed during the cleaning of the substrate and the deposition of the thin film.
Unlike the conventional sputtering method, plasma generation is performed independently of the voltage application to the target, so that low voltage sputtering and a wide range of process parameter control are possible. In addition, since the atoms sputtered from the target scrape into the high-density plasma and reach the substrate, the ionization rate of the flying atoms is high, and an ion-plated thin film can be formed.
The thickness of the adjustment layer is preferably 3 nm to 6 nm.

-First translucent reflective layer-
The first translucent reflective layer contains Ag or Cu as a main component. Thereby, it is possible to improve the recording characteristics and the storage characteristics in the first recording layer. Here, the main component means that 95% by mass or more of Cu or Ag is contained. The reason why the first translucent reflective layer containing Cu or Ag as a main component is suitable will be described below. Examples of components other than Cu or Ag include Mo, Ta, Nb, Cr, Zr, Ni, Ge, Au, and the like.

As shown in FIG. 1, in a phase change optical recording medium having two recording layers, it is preferable to transmit laser light for recording / reproduction as much as possible to the second information layer. Therefore, it is preferable to use a material in which laser light is not easily absorbed and easily transmitted for the first translucent reflective layer.
Therefore, the present inventors performed optical measurement at various wavelengths of 660 nm for various reflective layers. 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. As a result, it came to show in FIG. From the results shown in FIG. 2, Pt, Pd, and Ti have low transmittance and high absorptance, and thus are not preferable for the first translucent reflective layer.
Next, when Cu and Ag having a relatively high transmittance and a relatively low absorptance were investigated by varying (changing) the thickness, results such as FIG. 3 (Cu) and FIG. 4 (Ag) were obtained. It was. That is, it was found that the change due to the thickness was larger in Ag. This indicates that Cu is more excellent in the stability of the optical constant with respect to the thickness when the film is formed. Furthermore, the measurement result of the spectral transmittance is shown in FIG. 5, and it was found that the transmittances of Ag and Cu intersect in the wavelength region of about 450 nm. Accordingly, Cu has a higher transmittance in a wavelength region longer than the wavelength region of about 450 nm, and it is particularly preferable to use Cu as the first translucent reflective layer for laser light near 660 nm. I found that there was.
Further, for each recording medium using Cu, Ag, and Au for the first translucent reflective layer, a 3T single pattern was recorded on the first recording layer at a wavelength of 660 nm, and its C / N was measured. The result was as follows. That is, the highest C / N was obtained when Cu was used. Thus, it was found that Cu is preferable from the viewpoint of recording characteristics. Each plot in FIG. 6 is obtained by arranging a plurality of experimental data horizontally.

The first translucent reflective layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is superior in terms of mass productivity, film quality, and the like.
The thickness of the first translucent reflective layer is preferably 2 nm to 5 nm.

-First substrate and second substrate-
The first substrate needs to sufficiently transmit light irradiated for recording / reproduction, and those conventionally known in the technical field are applied. As the material, glass, ceramics, or resin is usually used, 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, silicone resin, fluorine resin, ABS resin, and urethane resin. Among these, acrylic resins such as polycarbonate resin and polymethyl methacrylate (PMMA), which are excellent in terms of moldability, optical characteristics, and cost, are particularly preferable.

On the surface side (recording surface side) on which the information layers of the first substrate and the second substrate are formed, there are helical or concentric meandering grooves for laser light tracking, which are called land portions and groove portions. An uneven pattern is formed. In this case, the groove is transferred by a stamper mounted in a mold, such as an injection molding method or a photopolymer method, and the substrate is molded. The thickness of the first substrate is preferably about 10 μm to 590 μm.
Further, 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 are different from those of the first substrate. May be. The thickness of the second substrate is not particularly limited and can be appropriately selected according to the purpose. The thickness of the second substrate is selected so that the total thickness with the first substrate is 1.2 mm. Is preferred. The depth of the groove is the same as that of the first substrate.

By defining the groove depth, a phase difference is generated in the reflected light from each of the concave and convex portions of the groove (generally called concave: land, convex: groove), and the difference in the amount of reflected light is detected. By doing so, recording and reproduction of a two-layer optical recording medium having a low light reflectance can be performed under stable tracking. Further, the first information is obtained by configuring the thermal diffusion layer of each information layer other than the innermost side when viewed from the laser beam irradiation side with a material made of In oxide, Zn oxide, Sn oxide, and Si oxide. The light transmittance of the layer can be increased. Therefore, the reflectance of light from the second information layer can be increased, and information can be recorded and reproduced under stable tracking.
Due to the eccentricity between the center hole of the optical recording medium and the center of the track, axial blurring, etc., an eccentricity of the order of several tens of micrometers occurs. In particular, the amount of eccentricity is more conspicuous in the information layer far from the optical pickup as in the multilayer recording medium than in the front side. For this reason, in order to accurately follow the track of each information layer of the multilayer optical recording medium, the tracking error is detected by an optical pickup, and the tracking actuator is driven by a servo circuit to control the minute position of the objective lens. It is necessary to always scan the laser light spot accurately on the information track. Therefore, the design of the groove depth of the substrate is particularly important for a medium having a low reflectance such as a multilayer phase change optical recording medium. A typical example of the tracking error signal is a push-pull signal.

The push-pull signal is obtained by taking reflected light from a disk having a guide groove with a track pitch p with an objective lens and detecting with a divided photodiode behind. The periodically arranged guide grooves form a kind of diffraction grating, and the reflected light generates 0th order light traveling straight and ± 1st order light diffracted at an angle θ. Here, θ is expressed as sin ⁻¹ (λ / p). The reflected light to the objective lens takes in a part of ± first order light in addition to zero order light. In the region where the 0th-order and 1st-order diffracted light overlaps, light interference occurs, and the light intensity changes depending on the beam track shift. The two-divided (or four-divided) photodiode individually detects the overlapping portion of the 0th-order light and the ± 1st-order light, and takes the differential to generate a tracking error signal. FIG. 15 shows the intensity distribution of the reflected light. When the beam center coincides with the guide groove (groove), the reflected light intensity distribution is a symmetrical distribution, and each output of the photodiode is X = Y. When tracking deviation occurs, the intensity distribution becomes asymmetric and X> Y.
When the tracking error signal Z is Z = X−Y, Z = 4 (S1) (E0) (E1) sin (φ1) sin (2πΔp / p). Where S1 is the area where the 0th and 1st order diffracted light overlaps on the detector, E0 and E1 are the amplitudes of the 0th and 1st lights, respectively, φ1 is the phase difference between the 0th and 1st lights, and p is the track Pitch and Δp are track deviation amounts. Z is an amount dependent on the track deviation Δp, and becomes an odd function, so that it can be seen in which direction the deviation is.

  FIG. 16 shows the relationship between the groove of the optical disk and the tracking error. The tracking error signal becomes 0 when the beam center coincides with the groove center, or coincides with the land center, and the sign is reversed before and after that, and the amount and direction of the track deviation are known and used as a servo signal. The tracking error signal Z has a maximum amplitude when sin (φ1) is maximum. When the groove shape is rectangular, φ1 = π / 2 and the maximum amplitude when the groove depth is λ / (8n) (n: the refractive index of the substrate). For this reason, the depth of the guide groove of the optical disk is often around λ / (8n) (see FIG. 17). However, since the recording characteristics change depending on the groove depth due to the optical characteristics and thermal characteristics due to the layer structure of the optical recording medium, the groove of the substrate combined with the layer structure of the two-layer phase change optical recording medium of the present invention. The depth H is preferably λ / (15 × n) ≦ H ≦ λ / (11.5 × n). In the pamphlet of International Publication No. 02/029787, it is 0 to λ / 4n. However, when the groove depth is set to all values within this range, it is difficult to achieve both good recording characteristics and stable tracking accuracy. . The higher the push-pull signal amplitude, the better. However, considering the balance with the recording characteristics, it may not be too high, and it is necessary to design the groove depth considering both characteristics. The Push-Pull signal in Table 2 is obtained by measuring [(Ia + Ib) − (Ic + Id)] / [Ia + Ib + Ic + Id] in the photodetector shown in FIG.

-Thermal diffusion layer-
The heat diffusion layer is a conventional ITO (In ₂ O ₃ (main component) -SnO ₂ ) mixed with In oxide and Sn oxide, or a mixture of In oxide and Zn oxide as a heat diffusion layer of an optical disk. A technique using IZO (In ₂ O ₃ (main component) —ZnO ₂ ) is disclosed. However, In oxide-rich materials are very expensive, and there are problems in terms of cost for production. Furthermore, it has been found during the development process that the light transmittance of the first information layer cannot be obtained sufficiently. Therefore, in order to increase the light transmittance of the first information layer, increase the light reflectance of the second information layer, and improve the tracking accuracy, it is different from ITO and IZO conventionally used for the heat diffusion layer. Therefore, it is necessary to find a material that has a high sputtering rate and can secure recording characteristics and light transmittance.

When viewed from the first substrate side, the thermal diffusion layer of each information layer other than the innermost side contains In oxide, Zn oxide, Sn oxide, and Si oxide, and each content rate [mol% ] Is a, b, c, and d, it is preferable to satisfy the following expressions: 3 ≦ a ≦ 20, 0 ≦ d ≦ 30, and a + b + c + d = 100.
When the In oxide content is less than 3 mol%, sufficient thermal conductivity may not be obtained, and the conductivity is lowered, so that sputtering becomes difficult. If it exceeds 20 mol%, the light transmittance cannot be secured and the cost increases. The Si oxide is preferably in this range since the repeated recording durability of the first information layer can be improved. Although the preferable composition range of Zn oxide and Sn oxide is not specifically limited, it exists in the tendency for a sputtering rate to become high, so that the content rate of either one is high. Since (In + Zn + Sn + Si) oxide has high conductivity and can be subjected to DC sputtering (direct current sputtering), it contains an In oxide that can be formed in a short time when a thermal diffusion layer having a thickness of about 60 nm is formed. The light transmittance can be improved by reducing the rate (see FIG. 12). In oxide, Zn oxide, Sn oxide, and Si oxide are all materials that do not promote deterioration of the reflective layer.

The thermal diffusion layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is particularly preferable from the viewpoints of mass productivity and film quality.
The thickness of the thermal diffusion layer is preferably 40 nm to 80 nm. If the thickness is less than 40 nm, the heat dissipation may deteriorate and repeated recording durability may deteriorate, and if it exceeds 80 nm, the light transmittance may decrease.

-Intermediate layer-
The intermediate layer preferably has low light absorption at the wavelength of light irradiated for recording / reproduction, and the material is preferably a resin in terms of moldability and cost, and is an ultraviolet curable (UV) resin, slow-acting. Resin, thermoplastic resin, etc. can be used.
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 performing recording and reproduction, and the thickness is preferably 10 μm to 70 μm. When the thickness is less than 10 μm, crosstalk between information layers may occur. When the thickness exceeds 70 μm, spherical aberration occurs when recording / reproducing the second recording layer, and recording / reproduction tends to be difficult. .

-First recording layer and second recording layer-
There are roughly two types of conventional recording layer material development. That is, the write-once recording layer materials GeTe and BiCu, the reversible Sb and Te alloy Sb2Te3, and the GeSbTe ternary alloy born from the solid solution or eutectic composition of these two materials The recording layer material consisting of is one flow. Another flow is a recording layer material in which a trace element is added to SbTe, which is an alloy of Sb and Te, but has a Sb content of about 70%, which is a eutectic composition of Sb and Sb2Te3.
In an optical recording medium having two recording layers, the information layer on the near side as viewed from the laser light irradiation side is required to have a 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. As the thickness of the recording layer is reduced, the crystallization speed decreases, so it is advantageous to make the recording layer material itself have a high crystallization speed. Therefore, in the flow of the above 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, when the amount of Sb is increased in order to increase the crystallization speed, that is, in order to increase the corresponding linear speed, the crystallization temperature is lowered and stored. It was found that the characteristics deteriorated.
In the two-layer optical recording medium, when the information layer on the back side as viewed from the laser light irradiation side is reproduced, the reflectance is low due to absorption by the information layer on the near side, and the amplitude of the reproduction signal is small. There is. Considering this, a higher reproducing light power is required than when reproducing with an optical recording medium having a single recording layer.
In the phase change type SbTe system, the amount of Sb may be increased in order to increase the crystallization speed, but this tends to lower the crystallization temperature. Therefore, when the SbTe system is used for the information layer on the front side, if a high reproduction light power is used, there arises a problem that the amorphous mark is recrystallized and cannot be reproduced. At the same time, lowering the crystallization temperature is not preferable because the storage state becomes unstable. Therefore, by adding the third element Ge to the SbTe system, the crystallization temperature is 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.
Further, other materials may be added to the GeSbTe three-element system. As the additive element, Ag, In, or the like is preferable, which is used for improving the storage characteristics. The total composition ratio of the additive elements is preferably 8 atomic% or less. If it exceeds 8 atomic%, the storage characteristics are good, but the crystallization speed of the recording layer becomes slow, and it becomes difficult to record at high speed. Further, it is not preferable because the stability of the recording state with respect to the reproduction light deteriorates.

When the amount of Sb (β) is in the range of 60 ≦ β ≦ 75 (atomic%), stable recording and reproduction can be performed as a phase change recording material. If the Sb content is less than 60 atomic%, stable recording cannot be performed, and a recording layer that is not suitable for high-speed recording as a multilayer phase change optical recording medium. If the Sb content exceeds 75 atomic%, the crystallization speed is improved, but the crystallization temperature starts to decrease, making it difficult to reproduce with high reproduction light power, and the storage state becomes unstable.
Te promotes amorphization and improves the crystallization temperature, but is effective. However, when only Te is combined with Sb alone, the crystallization speed can be adjusted by utilizing the action of promoting amorphization, but the crystallization temperature is not sufficiently increased, which improves the stability of the amorphous phase. Therefore, the recorded amorphous mark may be lost by long-term storage or high-temperature storage. On the other hand, when Te is used in combination with Ge, there is an advantage that the stability of the amorphous phase is ensured by Ge and the stability of the crystal phase is further improved. The crystal state is generally a highly stable state. However, in the case of a high-speed recording material as described here, since the crystallization proceeds at a high speed at the time of initialization or recording, the formed crystal state is not necessarily It's not stable. For this reason, when recording is performed again after long-term storage or after high-temperature storage, there arises a problem that recording characteristics and recording conditions are changed from those before storage. This is presumably because the crystal state changed due to storage compared to before storage. However, when Te is added, the deviation in recording characteristics and recording conditions due to such storage can be reduced.
In order to obtain the effect of reducing the deviation in recording characteristics and recording conditions before and after storage by improving the stability of the crystal in this way, it is preferable to add Te at least 6 atomic% (6 ≦ γ). However, if the amount is too large, the crystallization speed becomes too slow, and high-speed repeated recording cannot be performed. When used in at least the first recording layer of the two-layer phase change optical recording medium, it is preferable that the amount of Te is within 30 atomic% (γ ≦ 30).
Further, when the Ge amount (α) is in the range of 2 ≦ α ≦ 20 (atomic%), reproduction with high power is possible, and the storage state can be improved. If the amount of Ge is less than 2 atomic%, the effect of adding Ge does not appear and the storage state is not good. Further, when the Ge content is more than 20 atomic%, the crystallization temperature can be increased, so that the stability of the reproduction light and the storage characteristics are improved, but the recording sensitivity is deteriorated due to the high melting point of Ge itself. The trouble that it ends up occurs.

The first recording layer and the second recording layer can be formed by various vapor deposition methods, for example, vacuum deposition method, sputtering method, plasma CVD method, photo CVD method, ion plating method, electron beam deposition method, etc. Among these, the sputtering method is particularly preferable because it is excellent in mass productivity and film quality.
The thickness of the first recording layer is preferably 4 nm to 10 nm. If the thickness is less than 4 nm, the reflectivity becomes too low and the signal quality is deteriorated, and repeated recording characteristics may be deteriorated. If the thickness exceeds 10 nm, the light transmittance may be lowered. is there.
The thickness of the second recording layer is preferably 10 nm to 20 nm. When the thickness is less than 10 nm, the repeated recording characteristics may be deteriorated, and when it exceeds 20 nm, the recording sensitivity may be deteriorated.

-Upper protective layer-
The material used for the upper protective layer in the conventional 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. The mixing ratio in this case is ZnS: SiO ₂ = 80: 20 (molar ratio). ) Is known to be most preferred.
However, in the case of a two-layer phase change type optical recording medium, when recording is performed on the first recording layer, the first reflective layer is thin, so that heat dissipation becomes poor and recording becomes difficult. Therefore, it is better to use a material having as good thermal conductivity as possible for the first upper protective layer. When ZnS-SiO ₂ is used for the first upper protective layer, the thermal conductivity is low, so that the recording characteristics are deteriorated, and the storage stability after recording is poor. Therefore, the first upper portion of the two-layer phase change optical recording medium is used. Not suitable for protective layer (see FIG. 7). Therefore, it is preferable to use Zn oxide or Sn oxide having higher heat dissipation than ZnS—SiO ₂ . When Zn oxide or Sn oxide is a simple substance, excellent storage stability cannot be obtained, and therefore it is preferable to contain In oxide, Si oxide or Ta oxide. Since these metal oxides are transparent to light and have high thermal conductivity, when used in the first information layer of a two-layer phase change optical recording medium, light transmittance, recording characteristics, and storage stability can be improved. . Since the first upper protective layer using these oxides can secure a sufficient degree of modulation and reflectance in a thin film of about 5 nm, (In, Zn, Sn) oxides that can be sputtered by RF sputtering. It is possible to use + Ta oxide, or (In, Zn, Sn) oxide + Si oxide that can be sputtered by RF sputtering or DC sputtering. When there are a lot of Sn oxide and Zn oxide in the first upper protective layer, the recording speed can be increased because the crystallization speed of the recording layer is accelerated.

When viewed from the first substrate side, the upper protective layer of each information layer other than the innermost side contains In oxide, Zn oxide, Sn oxide, and (Si oxide or Ta oxide), When the content ratio [mol%] is e, f, g, and h, it is preferable that 3 ≦ e ≦ 20, 50 ≦ (f or g) ≦ 90, 0 ≦ h ≦ 20, and e + f + g + h = 100.
The content of 50 mol% or more is preferable because the recording speed can be improved by promoting crystallization of the recording layer. The crystallization speed of the recording layer includes a transition linear velocity as an alternative characteristic. The transition linear velocity is a linear velocity at which the reflectance after continuous light irradiation is monitored by the linear velocity and the reflectance starts to change. In FIG. 9, the transition linear velocity is 21 m / s. Generally, the higher the transition linear velocity, the higher the recording speed. Here, the continuous optical power is 15 mW. When the content is 50 mol% or more, the jitter is good when recording at high speed (see FIG. 11). Moreover, it is preferable to make Sn oxide or Zn oxide 90 mol% or less because storage stability is improved. If it exceeds 90 mol%, excellent storage reliability cannot be obtained (see FIG. 10).

Note that the second upper protective layer, may be used as usual ZnS-SiO _2. 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. However, when ZnS—SiO ₂ is used for the upper protective layer and Ag is used for the second reflective layer, an interface layer such as TiC—TiO ₂ is inserted between the second upper protective layer and the second reflective layer. It is preferable.
The thickness of the first upper protective layer is preferably 2 nm to 15 nm. If the thickness is less than 2 nm, the reflectivity becomes too high and the degree of modulation may be reduced. If the thickness exceeds 15 nm, the light transmittance is lowered, which is not preferable, and heat is difficult to escape, so that the recording characteristics are deteriorated. .
The thickness of the second upper protective layer is preferably 3 nm to 30 nm. When the thickness is less than 3 nm, the recording sensitivity is deteriorated. When the thickness is more than 30 nm, heat is easily generated and the recording characteristics are deteriorated.

-Second reflective layer-
The second reflective layer need not be translucent like the first translucent reflective layer.
The thickness of the second reflective layer is preferably in the range of 100 nm to 200 nm. If the thickness is less than 100 nm, sufficient heat dissipation cannot be obtained and the recording characteristics are deteriorated repeatedly. If the thickness is more than 200 nm, a wasteful thickness is formed even though the heat dissipation does not change. The characteristics deteriorate.
The second reflective layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is excellent in terms of mass productivity and film quality.

-Lower protective layer-
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, and ZrO _2, and nitriding such as Si ₃ N ₄ , AlN, TiN, BN, and ZrN , Sulfides such as ZnS, In ₂ S ₃ , TaS ₄ , carbides such as SiC, TaC, B ₄ C, WC, TiC, ZrC, diamond-like carbon, or a mixture thereof. These materials can be used alone as a protective film, but may also be a mixture of each other. Moreover, you may contain an impurity as needed. For example, a mixture of ZnS and SiO _{2 or} a mixture of Ta ₂ O ₅ and SiO ₂ can be used. In particular, ZnS—SiO ₂ is often used. In this case, the mixing ratio is most preferably ZnS: SiO ₂ = 80: 20 (molar ratio). 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 can be reduced. Since it can be moderately suppressed, the temperature of the recording layer can be raised to a melting temperature.

The thickness of the first lower protective layer is preferably in the range of 40 nm to 80 nm. If it is thinner than 40 nm, the repeated recording durability is deteriorated, the recording characteristics are deteriorated, and the light transmittance is lowered, which is not preferable. If it is thicker than 80 nm, the light transmittance decreases, which is not preferable.
The thickness of the second lower protective layer is preferably in the range of 110 nm to 160 nm. If the thickness is less than 110 nm, the reflectance of light from the second information layer is lowered, the reproduction signal quality is deteriorated, and the repeated recording durability is deteriorated. When it is thicker than 160 nm, the reflectance of light from the second information layer is lowered, the reproduction signal quality is deteriorated, and the mechanical characteristics of the recording medium itself are deteriorated.
The first and second upper protective layers and the first and second lower protective layers as described above are formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating. Or by electron beam evaporation. Among these, the sputtering method is superior in terms of mass productivity, film quality, and the like.

<Method for producing multilayer optical recording medium>
The multilayer optical recording medium of the present invention is not particularly limited and can be appropriately selected depending on the purpose, but 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.

  As the film forming step, in FIG. 1, 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 various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Of these, the sputtering method is superior in terms of mass productivity and film quality. In the sputtering method, film formation is generally performed while flowing an inert gas such as argon. At this time, reactive sputtering may be performed while oxygen, nitrogen, or the like is mixed.

  As an 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.

  As 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.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples. As an evaluation apparatus, ODU1000 manufactured by Pulstec Industrial Co., Ltd. is used. The laser wavelength irradiated when recording on the recording layer is 660 nm, and the numerical aperture (NA) of the objective lens is 0.65. Further, the recording linear velocity at the time of recording was 9.2 m / s, and the reproducing light power was 1.2 mW. MSG3A manufactured by Pulstec Industrial Co., Ltd. was used as the optical waveform generator. In the recording method, a 1T periodic recording strategy was used for the first information layer (L0 layer) on the front side, and a 2T periodic recording strategy was used for the second information layer (L1 layer) on the back side. The recording strategy parameters used in the experiments are shown in Tables A and B. The description of the parameters is shown in FIGS. Ε1 in Table A and Table B represents the ratio of (erasing power Pe / recording power Pw).

Example 1
It has a 12 cm diameter, 0.575 mm thickness, and has a tracking guide irregularity (groove depth is 27.0 nm) with meandering continuous grooves with a track pitch of 0.74 μm on one side, and the width of the convex part (groove) is 0.25 μm. A first substrate made of polycarbonate resin was prepared.
A first lower protective layer made of ZnS (80 mol%)-SiO ₂ (20 mol%) and having a thickness of 70 nm is formed on the first substrate by RF magnetron sputtering under a sputtering power of 4 kW and an Ar flow rate of 15 sccm. did.
Next, a first recording layer having a thickness of 7.5 nm made of Ag _0.2 In _3.5 Ge ₇ Sb _68.7 Te _20.6 under a sputtering power of 0.4 kW and an Ar flow rate of 35 sccm was applied to the DC magnetron sputtering method. The film was formed.
Next, In ₂ O ₃ (7.5 mol%)-ZnO (22.5 mol%)-SnO ₂ (60 mol%)-Ta ₂ O ₅ (10 mol) under a sputtering power of 1 kW and an Ar flow rate of 15 sccm. %) And a first upper protective layer having a thickness of 5 nm was formed by RF magnetron sputtering.
Next, as the adjustment layer, an adjustment layer having a thickness of 4 nm made of Cu—Mo (Mo content = 1.1 mass%) was formed by an ECR method under a sputtering power of 1 kW and an Ar flow rate of 20 sccm.
Next, a first transflective layer having a thickness of 4 nm made of Cu—Mo (Mo content = 1.1 mass%) was formed by RF magnetron sputtering under a sputtering power of 0.5 kW and an Ar flow rate of 20 sccm. .
Next, In ₂ O ₃ (8.8 mol%)-ZnO (41.7 mol%)-SnO ₂ (35.2 mol%)-SiO ₂ (14. under a sputtering power of 2 kW and an Ar flow rate of 15 sccm. A thermal diffusion layer having a thickness of 65 nm composed of 3 mol% was formed by DC magnetron sputtering. Thus, the first information layer (L0 layer) was produced.

In addition, it has irregularities (groove depth is 27.0 nm) of the tracking guide by a continuous groove having a diameter of 12 cm and a thickness of 0.6 mm, and a meandering groove having a track pitch of 0.74 μm on one side, and the width of the convex portion (groove) is 0. A second reflective layer made of Ag and having a thickness of 140 nm was formed by DC magnetron sputtering on a second substrate made of polycarbonate resin having a thickness of .24 μm under a sputtering power of 3 kW and an Ar flow rate of 15 sccm.
Next, an interface layer having a thickness of 4 nm made of TiC (70 mol%)-TiO ₂ (30 mol%) was formed by a DC magnetron sputtering method under a sputtering power of 2 kW and an Ar flow rate of 15 sccm.
Next, a second upper protective layer made of ZnS (80 mol%)-SiO ₂ (20 mol%) with a sputtering power of 1.5 kW and an Ar flow rate of 15 sccm was formed by RF magnetron sputtering.
Next, a 15 nm thick second recording layer made of Ag _0.2 In _3.5 Sb _71.4 Te _21.4 Ge _3.5 under a sputtering power of 0.4 kW and an Ar flow rate of 35 sccm was applied to the DC magnetron sputtering method. The film was formed.
Next, with a sputtering power 4 kW, under ZnS (80 mol%) of the Ar flow rate 15 sccm - and the second lower protective layer having a thickness of 140nm composed of _SiO 2 (20 mol%) was deposited by RF magnetron sputtering. Thus, the second information layer (L1 layer) was produced.
The sputtering apparatus used was a DVD sprinter manufactured by Unaxis.

  Next, an ultraviolet curable resin (Kayarad DVD802, manufactured by Nippon Kayaku Co., Ltd.) is applied on the film surface side of the first information layer, and the second information layer surface side of the second substrate is spin-coated and bonded to the first information layer. A two-layer phase change optical recording medium having two information layers shown in FIG. 1 was prepared by irradiating with ultraviolet rays from the substrate side and curing to form an intermediate layer having a thickness of 50 μm.

Next, the initialization process was performed by irradiating laser light in the order of the second information layer and the first information layer.
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). The initialization condition of the second recording layer was rotated in the CLV (constant linear velocity) mode, and the linear velocity was 7 m / s, the feed amount was 40 μm / rotation, the radial position was 22 mm to 59 mm, and the initialization power was 2,000 mW. The initialization conditions of the first recording layer were rotated in the CLV (constant linear velocity) mode, and the linear velocity was 6 m / s, the feed amount was 60 μm / rotation, the radial position was 22 mm to 59 mm, and the initialization power was 1100 mW.
The crystalline reflectivity after initialization was 6.2% for the L0 layer and 6.0% for the L1 layer, and was a balanced two-layer phase change optical recording medium.

  With respect to the obtained two-layer phase change optical recording medium, the grain size of the adjustment layer and the first transflective layer and the crystal occupancy of the adjustment layer were measured as follows. The results are shown in Table 1-1 to Table 1-3.

<Measurement of grain size of adjustment layer and first transflective layer>
The grain size of the adjustment layer and the first transflective layer was obtained by taking several photographs with a high-resolution analytical electron microscope (HRTEM), measuring the grain portion on the photographed photographs, and converting the magnification.

<Measurement of crystal occupancy ratio of adjustment layer>
The crystal occupancy of the adjustment layer was measured and calculated with a high resolution analytical electron microscope (HRTEM).

(Examples 2-6 and Comparative Examples 1-2)
In Example 1, Examples 2 to 6 and Comparative Examples 1 and 2 were the same as Example 1 except that the adjustment layer and the transflective layer were changed as shown in Table 1-1 and Table 1-2. Each two-layer phase change optical recording medium was prepared. The total thickness of the adjustment layer thickness and the semi-transmissive layer thickness was fixed at 8 nm.
For each of the obtained two-layer phase change optical recording media, the grain size of the adjustment layer and the transflective layer and the crystal occupancy of the adjustment layer were measured in the same manner as in Example 1. The results are shown in Table 1-1 to Table 1-3.

(Examples 7-12 and Comparative Examples 1-3)
In Example 1, Examples 7 to 12 and Comparative Examples 1 to 3 are the same as Example 1 except that the depths of the guide grooves of the first and second substrates are changed to the values shown in Table 2. Each two-layer phase change optical recording medium was prepared.
Each of the two-layer phase change optical recording media of Examples 7 to 12 and Comparative Examples 1 to 3 was evaluated. The results are summarized in Table 1.

As shown in Table 2, when the groove depth becomes shallower than the lower limit, the push-pull signal decreases, and stable tracking accuracy cannot be obtained. When the groove depth is deeper than the upper limit, jitter becomes worse. Evaluation was performed by repeatedly recording 10 times on 3 adjacent tracks of the recording layer and reproducing the middle track. The characteristic evaluation was jitter when 3T to 11T and 14T marks and spaces were randomly recorded. Jitter represents the time lag between the boundary and the clock when the reflectance level of the mark and space is binarized at the slice level. The lower this value, the better the recording characteristics. Jitter of 9% or less is a pass criterion. When the degree of modulation after recording was measured, both the L0 layer and the L1 layer were 63%. The recording power Pw at that time was 36 mW for the L0 layer and 38 mW for the L1 layer. The degree of modulation is expressed by (Rtop−Rbot) / Rtop, where Rtop is the reflectance of the crystalline phase and Rbot is the reflectance of the amorphous phase.
One of the signals for evaluating the tracking accuracy is a push-pull signal. The Push-Pull signal in Table 2 is obtained by measuring [(Ia + Ib) − (Ic + Id)] / [Ia + Ib + Ic + Id] in the photodetector shown in FIG. The measurement was filtered with a low-pass filter having a cutoff frequency of 30 kHz (−3 dB) so that meandering wobble frequency components (about 820 kHz) and other noise components were not mixed during the measurement. The push-pull signal has a pass criterion of 0.28 or more.

(Examples 13-22 and Comparative Examples 4-6)
In Example 1, each of the two-layer phase change optical recording media of Examples 13 to 22 and Comparative Examples 4 to 6 was made in the same manner as Example 1 except that the heat diffusion layer material composition was changed to the composition shown in Table 3. Produced.
The acceptance criterion for the light transmittance of the first information layer was 42%, and the jitter after 500 repeated recordings (DOW500 jitter) was evaluated in order to determine whether the repeated recording durability was good or bad. The acceptance criterion was 10%. When the amount of In oxide is less than 3 mol%, the transmittance is good, but the DOW 500 jitter is deteriorated. When the amount of In oxide is more than 20 mol%, the DOW500 jitter is good, but the transmittance tends to decrease. Moreover, when there is more Si oxide than 30 mol%, it exists in the tendency for a sputtering rate to fall.

(Examples 23 to 31 and Comparative Examples 7 to 11)
In Example 1, each of the two-layer phase change optical recording media of Examples 23 to 31 and Comparative Examples 7 to 11 was prepared in the same manner as in Example 1 except that the recording layer material composition was changed to the composition shown in Table 4. did.
Experiments were conducted to confirm the recording characteristics and storage stability. The jitter (DOW10 jitter) after 10 repeated recordings at a recording linear velocity of 9.2 m / s was measured. Furthermore, the case where the amount of jitter change after 300 hours at 80 ° C. was less than 2% was marked as “◯”, and the case where it was 2% or more was marked as “X”. In the storage test, the two-layer phase change optical recording medium was stored for 300 hours in a constant temperature bath at 80 ° C. and 85%. When Ge is less than 2%, the storage stability is poor because the crystallization temperature is low. When Ge is more than 20%, the crystallization temperature is sufficiently high, but the repeated recording characteristics are poor. When Sb is less than 60%, it is considered that high-speed recording cannot be performed because the transition linear velocity of the recording layer is low. When Sb is more than 75%, the transition linear velocity is too fast to perform recording, and the crystallization temperature is lowered, so that the storage stability is poor. If Te is less than 6%, initialization is difficult and jitter is poor. When Te is more than 30%, the transition linear velocity becomes slow and the recording characteristics are poor.

(Examples 32-39)
In Example 1, each of the two-layer phase change optical recording media of Examples 32-39 was produced in the same manner as in Example 1 except that the composition of the first upper protective layer was changed to the composition shown in Table 5.
The transition linear velocity of the first information layer and the jitter after repeated recording were evaluated 10 times. The sputtering rate is substantially the same, but when either one of ZnO and SnO ₂ is contained in an amount of 50 mol% or more, the transition linear velocity is improved and the recording characteristics are good.

(Examples 40 to 51 and Comparative Example 12)
In Example 1, each of the two-layer phase change optical recording media of Examples 40 to 51 and Comparative Example 12 is the same as Example 1 except that the first translucent reflective layer material is changed to the material shown in Table 6. Was made.
The amount of jitter change after 300 hours at 80 ° C. and 85% RH was evaluated. The case where the amount of change was less than 1% was regarded as acceptable.

  The multilayer optical recording medium of the present invention increases the light transmittance of each information layer other than the innermost side when viewed from the laser light irradiation side, enables stable recording / reproduction in each information layer, and ensures repeated durability. Since it has excellent storage stability, it is suitable for various multilayer optical recording media having a phase change recording layer such as DVD + RW, DVD-RW, BD-RE, HD DVD RW and the like.

FIG. 1 is a diagram showing the layer structure of the two-layer phase change optical recording medium of the present invention. FIG. 2 is a diagram showing the absorptance, reflectance, and transmittance of the reflective layer material. FIG. 3 is a diagram showing the thickness dependency of Cu absorptance, reflectance, and transmittance at 660 nm. FIG. 4 is a diagram showing the thickness dependence of Ag absorptance, reflectance, and transmittance at 660 nm. FIG. 5 is a diagram showing the wavelength dependence of the transmittance of Cu and Ag. FIG. 6 is a diagram showing the recording characteristics of the first recording layer when the first reflective layer is Cu, Ag, or Au. FIG. 7 is a diagram comparing storage-stable upper protective layer materials. FIG. 8 is a diagram showing a photodetector. FIG. 9 is an explanatory diagram of the transition linear velocity. FIG. 10 is a diagram showing storage stability and dependence on Sn oxide contained in the first upper protective layer. FIG. 11 is a diagram illustrating the relationship between the Zn oxide or Sn oxide content, transition linear velocity, and jitter contained in the first upper protective layer. FIG. 12 is a diagram comparing the conventional light diffusion layer material of light transmittance with the heat diffusion layer material of the present invention. FIG. 13 is a diagram showing a 1T period recording strategy for recording the first information layer (L0 layer). FIG. 14 is a diagram showing a 2T periodic recording strategy for recording the second information layer (L1 layer). FIG. 15 is a diagram illustrating the reflected light intensity distribution. FIG. 16 is a diagram showing groove irregularities and tracking error signals. FIG. 17 is a diagram illustrating the groove depth and the tracking error signal amplitude.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st information layer 2 2nd information layer 3 1st board | substrate 4 Intermediate layer 5 2nd board | substrate 11 1st lower protective layer 12 1st recording layer 13 1st upper protective layer 14 Adjustment layer 15 1st semi-transparent reflective layer 16 Heat Diffusion layer 21 Second lower protective layer 22 Second recording layer 23 Second upper protective layer 25 Second reflective layer A Absorbance R Reflectance T Transmittance

Claims (10)

Between the first substrate on the near side as viewed from the laser light irradiation side of the wavelength λ and the second substrate on the back side, it has a plurality of information layers having at least a recording layer through an intermediate layer,
The substrate has a spiral guide groove meandering on the recording surface side,
As viewed from the first substrate side, each information layer other than the innermost information layer has at least a lower protective layer, a recording layer, an upper protective layer, an adjustment layer, a translucent reflective layer, and a thermal diffusion layer. ,
The innermost information layer has at least a lower protective layer, a recording layer, an upper protective layer, and a reflective layer,
The adjustment layer is made of the same material as the translucent reflective layer,
The adjustment layer and the translucent reflective layer each contain either Ag or Cu, and the content of either Ag or Cu is 95% by mass or more,
A multilayer optical recording medium, wherein the grain size of the adjustment layer is smaller than the grain size of the translucent reflective layer.   The multilayer optical recording medium according to claim 1, wherein the grain size A (μm) of the adjustment layer and the grain size B (μm) of the translucent reflective layer satisfy the following formula: B−A> 0.05 μm.   The multilayer optical recording medium according to claim 1, wherein the crystal occupancy of the adjustment layer is 40% or more. The multilayer optical recording medium according to any one of claims 1 to 3, wherein the adjustment layer and the translucent reflective layer each contain Cu, and the content of Cu is 95% by mass or more. The multilayer optical recording medium according to any one of claims 1 to 4, wherein the adjustment layer and the translucent reflective layer further contain any one of Mo, Ta, Nb, Cr, Zr, Ni, Ge, and Au.   When the thermal diffusion layer contains In oxide, Zn oxide, Sn oxide, and Si oxide, and the respective contents [mol%] are a, b, c, and d, the following formulas, 3 ≦ The multilayer optical recording medium according to claim 1, wherein a ≦ 20, 0 ≦ d ≦ 30, and a + b + c + d = 100 are satisfied.   When the recording layer is made of at least Ge, Sb, and Te, and the respective composition ratios [atomic%] are α, β, and γ, the following formulas 2 ≦ α ≦ 20, 60 ≦ β ≦ 75, 6 ≦ γ The multilayer optical recording medium according to claim 1, wherein ≦ 30 and α + β + γ = 100 are satisfied.   When viewed from the first substrate side, the upper protective layer of each information layer other than the innermost side contains In oxide, Zn oxide, Sn oxide, and (Si oxide or Ta oxide), When the content ratio [mol%] is e, f, g, and h, the following formula is satisfied: 3 ≦ e ≦ 20, 50 ≦ (f or g) ≦ 90, 0 ≦ h ≦ 20, e + f + g + h = 100 Item 8. The multilayer optical recording medium according to any one of Items 1 to 7. The multilayer optical recording medium according to claim 1, wherein the lower protective layer in each information layer is made of ZnS and SiO ₂ . 10. The device according to claim 1, wherein n is a refractive index of the substrate and H is a depth of the guide groove, and the following equation is satisfied: λ / (15 × n) ≦ H ≦ λ / (11.5 × n) The multilayer optical recording medium described in 1.