JP2007287291A - Multilayer optical recording medium and method for initializing multilayer optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To initialize a rewritable multilayer optical recording medium even when it has three or more information recording layers by expanding the margin of the initialization conditions of the recording medium. <P>SOLUTION: The rewritable multilayer optical recording medium has two or more information recording layers composed of a phase change material on a substrate, and an initialization assistance layer between the information recording layers. The initialization assistance layer shows low transmittance when initializing the information recording layers arranged on the side on which the laser beam of the initialization assistance layer is made incident by using the laser beam. When initializing the information recording layer arranged opposite to the side on which the laser beam of the initialization assistance layer is made incident by using the laser beam, the transmittance of the initialization assistance layer is increased by using the laser beam. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical recording medium for recording, reproducing, and erasing information by light irradiation and heating, and an initialization method thereof.

  2. Description of the Related Art Conventionally, optical recording media have been widely used in the field of audio visual due to their portability and ease of handling by non-contact recording / reproduction, and in recent years, they are being applied as recording media for recording various information in the field of computers. In the audio visual field, the amount of information is steadily increasing due to the digitization and high quality of video and audio, and the recording capacity required for optical recording media is increasing accordingly. In addition, with the spread of small computers and the diversification of information, small and large-capacity optical recording media are required.

  There are several types of optical recording media, but it can be broadly divided into a read-only type that can only read information, a write-once type that can only record and reproduce, and information recording, reproduction, and erasure. Rewrite type.

  Of these, discs on which the user can record information are the write-once type and the rewritable type. Among them, the rewritable type is suitable not only for recording and reproducing information but also for erasing and re-recording, so that it can be rewritten repeatedly.

  As the information recording layer of the rewritable optical recording medium, a phase change material is used.

  A rewritable optical recording medium utilizes the fact that a phase change material reversibly changes its state between an amorphous and a crystal (or between a crystal and a crystal having a different structure) by laser light irradiation. is doing. The rewritable optical recording medium uses an information recording layer utilizing the fact that a phase change material is irradiated with laser light and at least one of a refractive index and an extinction coefficient of the phase change material changes. Information is written / erased. In the phase change type optical recording medium, the amplitude of the transmitted light or reflected light of the laser light irradiated to the recorded portion changes, and as a result, the transmitted light amount or reflected light amount reaching the detection system changes. Is detected and the signal is reproduced.

  In general, in a rewritable optical recording medium, the phase change type material constituting the information recording layer is in a crystalline state, and the information recording layer material is in an amorphous state. The information recording layer is made into an unrecorded state by irradiating a rewritable optical recording medium in which the information recording layer material is in an amorphous state with a laser beam power lower than that during recording and making the information recording layer in a crystalline state again. Can do.

  In general, chalcogen compounds are often used as phase change materials. Since the information recording layer made of a chalcogen compound is formed in an amorphous state, the manufactured optical recording medium needs to be unrecorded (crystallized) as a whole once. This operation is called initialization. It is known that the energy for initialization is higher than the energy for crystallizing (erasing) the recorded state (amorphous).

  The initialization process is incorporated in a part of the disk manufacturing process, and the information recording layer is made into a crystalline state using a laser beam or a flash light source. When laser light is used, the entire disk surface is initialized by irradiating the laser light while rotating the disk, focusing on the information recording layer, and shifting the position of the optical head in the radial direction of the disk. ing.

  As initialization conditions, conditions such as laser power, linear velocity, defocus amount, and feed pitch of the laser light are determined so as to satisfy the following conditions. In general, the initialization condition is that the entire initialization area is uniformly crystallized without remaining an amorphous state, and the information is overwritten multiple times (several tens of times) from the first recording. The signal quality is determined to be constant.

  From the viewpoint of increasing the recording capacity of the optical recording medium per unit area, research and development of multilayered optical recording media are being conducted. The optical recording medium having a multilayer structure includes a method for recording / reproducing information from both sides of the optical recording medium and a method for recording / reproducing information from one side of the optical recording medium.

  When recording / reproducing information from both sides of the optical recording medium, the information recording layer is provided on both sides of the optical recording medium, and when recording / reproducing information from one side of the optical recording medium, Two or more recording layers are provided on one side of the optical recording medium.

  The information recording layer is composed of two layers on one side of the optical recording medium, and a laser beam is incident on the two-layer information recording medium from one side of the optical recording medium to record and reproduce information on the two information recording layers. The technique which performs is disclosed by patent document 1 and 2 grade | etc.,.

The single-sided dual-layer optical recording medium uses a laser beam that has passed through a first information recording layer disposed in front of the laser beam incident side, and is disposed on the back side of the laser beam incident side. Recording / reproduction of the information recording layer is performed. For this reason, the first information recording layer is devised such as reducing the thickness of the information recording layer to increase the transmittance. However, as the information recording layer becomes thinner, the number of crystal nuclei formed when the information recording layer is crystallized decreases, and the distance that atoms can move is shortened. For this reason, the thinner the information recording layer, the harder the crystal phase is formed, that is, the crystallization speed is reduced. Therefore, in the first information recording layer in which the information recording layer is thin, the information recording layer is formed of a material having a higher crystallization ability, or an interface layer having a high crystallization promoting effect is provided in contact with the information recording layer. Etc. are made.
JP 2000-36130 A JP 2002-144736

  However, in the case of a multilayer optical recording medium, the information recording layer located on the laser beam incident side has a high transmittance, so that there is a problem that the information recording layer may not be sufficiently initialized.

  In order to solve this problem, there is an example in which high power is applied to the information recording layer on the near side as viewed from the laser beam incident side so that the initialization is sufficiently performed. In this case, there is also a problem that the information recording layer on the back side is affected and the recording / reproducing characteristics may be deteriorated.

  The present invention provides a method for solving such problems. When the information recording layer is multi-layered from the viewpoint of increasing the recording capacity of the optical recording medium per unit area, for example, in the case of an optical recording medium having two information recording layers, it is possible to expand the margin of the initialization condition. . Further, in the case of an optical recording medium having three or more information recording layers, it is possible to provide an optical recording medium that can be initialized for each information recording layer.

  The above object is achieved by the following optical recording medium.

  The present invention is a rewritable multilayer optical recording medium having two or more information recording layers made of a phase change material on a substrate, and an initialization auxiliary layer between the information recording layers, the initialization auxiliary A rewritable multi-layer characterized in that the layer is a film whose transmittance increases before and after the information recording layer disposed on the laser beam incident side of the initialization auxiliary layer is initialized by the laser beam It is an optical recording medium.

Further, a rewritable multilayer optical recording medium having two or more information recording layers made of a phase change material on a substrate and an initialization auxiliary layer between the information recording layers is provided on one side of the multilayer optical recording medium. A method for initializing a rewritable multi-layer optical recording medium that performs laser beam irradiation from the information recording layer in order from the information recording layer disposed on the side closer to the laser beam irradiation side,
The first initialization step of initializing the information recording layer disposed on the laser beam incident side of the initialization auxiliary layer with the laser beam includes a step of increasing the transmittance of the initialization auxiliary layer. An initialization method for a multilayer optical recording medium characterized by the above.

  According to the present invention, in the rewritable multilayer optical recording medium in which the information recording layer is multilayered from the viewpoint of increasing the recording capacity of the optical recording medium per unit area, for example, in an optical recording medium having two information recording layers. The margin for initialization conditions can be expanded. Further, in the case of an optical recording medium having three or more information recording layers, it is possible to provide an optical recording medium that can be initialized for a plurality of information recording layers.

  The present invention is a multilayer optical recording medium having two or more information recording layers, in which an initialization auxiliary layer is provided between the information recording media. The initialization auxiliary layer is a film having a low light transmittance in the initial state. When initializing the first recording layer on the light incident side of the initialization auxiliary layer, the initialization auxiliary layer has a high light transmittance from a low light transmittance state (50% <with respect to incident light). It changes to a state (50%> with respect to incident light). For this reason, the energy of the light for initializing the first recording layer can be efficiently used for the initialization of the first recording layer, and the second recording on the side opposite to the incident side of the initialization auxiliary layer. It becomes possible to suppress the influence on the layer.

  On the other hand, when the light for initializing the second recording layer is incident, the initialization auxiliary layer has a high transmittance, so that it does not become an obstacle when initializing the second recording layer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing an embodiment of an optical recording medium according to the present invention. On one main surface of the substrate 1001, the first information recording layer 1002, the first intermediate layer 1003, the first initialization auxiliary layer 1004, the second information recording layer 1005, the second intermediate layer 1006, and the second initialization auxiliary. A layer 1007, a third information recording layer 1008, a third intermediate layer 1009, a third initialization auxiliary layer 1010, a fourth information recording layer 1011 and a protective layer 1012 are sequentially stacked.

  On one main surface of the substrate 1001 on the side where each layer (from the first information recording layer 1002 to the protective layer 1012) is formed, a concavo-convex portion serving as a guide groove for guiding an optical spot when information is recorded / reproduced ( (Not shown) is formed. The thickness of the substrate 1001 is determined by the standard of the optical recording medium. The current CD is 1.2 mm, the DVD and HD DVD (High Definition DVD) is 0.6 mm, and the Blu-ray Disk (hereinafter referred to as BD). 1.1 mm.

  The material used for the substrate 1001 is preferably a material having a high transmittance at the wavelength of laser light used for recording / reproduction. For example, a plastic material such as polycarbonate resin, polyolefin resin, or acrylic resin, or glass is used. It is done.

  The first intermediate layer 1003, the second intermediate layer 1006, and the third intermediate layer 1009 are formed by dissolving an acrylic or epoxy ultraviolet curable resin in a solvent to prepare a resin solution, and by spin coating or the like. be able to. On one main surface of each intermediate layer on the protective layer 1012 side, an uneven portion (not shown) serving as a guide groove for guiding an optical spot when information is recorded / reproduced is formed. The concavo-convex portion can be formed by forming a resin layer made of, for example, an ultraviolet component resin and then forming the resin layer by 2P method (Photo-Polymerization method).

  The thickness of each intermediate layer may be set to an optimum value by optical design as appropriate, and is not particularly limited. However, when the information recording layer of the present embodiment has four layers, for example, the first intermediate layer is 15 μm, the second intermediate layer is 20 μm and the third intermediate layer can be 10 μm.

  The protective layer 1012 includes a light-transmitting sheet (film) having a planar annular shape and an adhesive layer (both not shown) for bonding the light-transmitting sheet to the fourth information recording layer 1011. The For the adhesive layer, for example, an ultraviolet curable resin or a pressure-sensitive adhesive can be used.

  The light transmissive sheet serving as the protective layer 1012 is preferably made of a material having a low absorptivity with respect to laser light used for recording / reproduction, and more preferably a material having a transmittance of 90% or more. As the material, for example, a polycarbonate resin material or a polyolefin resin is preferable.

When polycarbonate (PC) is used as the material of the light transmissive sheet, a material having a thermal expansion coefficient of about 7.0 × 10 ⁻⁵ (1 / ° C.) and a flexural modulus of about 2.4 × 10 ⁴ (MPa). Is often used. Further, when a polyolefin resin (for example, ZEONEX (registered trademark)) is used as the material of the light transmissive sheet, the thermal expansion coefficient is about 6.0 × 10 ⁻⁵ (1 / ° C.), and the flexural modulus is 2.3. × 10 ⁴ (MPa) about is often used material.

  In the case of BD, the thickness of the light-transmitting sheet serving as the protective layer 1012 is selected from the range of 3 to 100 μm, and the total thickness of each of the intermediate layers and the adhesive layer is 100 μm. It has been decided. High density recording is realized by combining such a thin protective layer 1012, a blue laser having a wavelength of 405 nm, and an objective lens having a high NA of about 0.85.

  The light-transmitting sheet according to the present embodiment uses, for example, a plurality of cooling rolls by charging a material such as polycarbonate resin into an extruder and melting it at a temperature of 250 to 300 ° C. using a heater (not shown). To form a sheet. Then, it cuts into the shape match | combined with the board | substrate 1001, and it forms.

  Further, a protective layer made of an organic or inorganic material may be further formed for the purpose of preventing dust from adhering to the surface of the protective layer 1012 or scratching. In this case as well, a material that has almost no absorption capability for the wavelength of the laser that performs recording and reproduction is desirable.

  FIG. 2 is a schematic cross-sectional view showing the first information recording layer 1002 according to the present embodiment. In this aspect, a first reflective layer 2001, a first lower dielectric layer 2002, a first information recording layer 2003, and a second upper dielectric layer 2004 are laminated in order from the substrate 1001 side.

The material of the first reflective layer 2001 is selected in consideration of, for example, the reflection function and heat conduction. That is, it has reflectivity with respect to the wavelength of the laser beam used for recording and reproduction, and the thermal conductivity is, for example, 4.0 × 10 ^{−2 to} 4.5 × 10 ² J / m · K · s (4. 0 × 10 ^{−4 to} 4.5 × 10 ⁻⁴ J / cm · K · s) is selected from metal elements, metalloid elements, and compounds or mixtures thereof. Specific examples include simple substances such as Al, Ag, Au, Ni, Cr, Ti, Pd, Co, Si, Ta, W, Mo, and Ge, and alloys containing these simple substances as a main component. Of these, Al-based, Ag-based, Au-based, Si-based, or Ge-based materials are preferable. When an alloy is used as the material of the first reflective layer 2001, for example, AlCu, AlTi, AlCr, AlCo, AlSi, AlMgSi, AgPdCu, AgPdTi, AgCuTi, AgPdCa, AgPdMg, AgPdFe, Ag, or SiB are preferable.

  The thickness of the first reflective layer 2001 is preferably selected from 80 nm to 140 nm, for example, 100 nm. If the thickness of the first reflective layer 2001 is less than 80 nm, the heat generated in the first information recording layer 2003 cannot be sufficiently diffused, the heat cooling becomes insufficient, and the jitter characteristics are degraded by the reproduction power during reproduction. Resulting in. On the other hand, even if the thickness of the first reflective layer 2001 is larger than 140 nm, there is no difference in thermal characteristics and optical characteristics, and there is not much meaning in practical use.

  The first lower dielectric layer 2002 and the first upper dielectric layer 2004 are configured by stacking a plurality of dielectric layers. The laminated dielectric layer is preferably made of a material that has a low absorption capacity for recording / reproducing laser light, and is made of a material that satisfies the relationship 0 <k ≦ 3.

  FIG. 3 shows an example of the configuration of the first lower dielectric layer 2002 and the first upper dielectric layer 2004. In the first lower dielectric layer 2002, the twelfth lower dielectric layer 3001, and the material constituting the twelfth lower dielectric layer react with the material constituting the first information recording layer 2003 and the first reflective layer 2001. The eleventh lower dielectric layer 3002 and the thirteenth lower dielectric layer 3003 are configured to prevent this. The first upper dielectric layer 2004 is an eleventh layer for preventing the twelfth upper dielectric layer 3004 and the material constituting the twelfth upper dielectric layer from reacting with the material constituting the first information recording layer 2003. It is composed of an upper dielectric layer 3005.

The eleventh lower dielectric layer 3002, the thirteenth lower dielectric layer 3003, and the eleventh upper dielectric layer 3005 are, for example, Si-N, Al-N, Zr-N, Ti-N, Ge-N, Ta-N. Such nitrides or nitride oxides containing them can be used. A carbide such as C or SiC can also be used. The twelfth lower dielectric layer 3001 and the twelfth upper dielectric layer 3004 are preferably, for example, a ZnS—SiO ₂ mixture. As the mixture, for example, a ZnS—SiO ₂ mixture having a molar ratio of about 4: 1 is selected.

  The thickness of the thirteenth lower dielectric layer 3003 is preferably selected from 4 nm to 10 nm, for example, 5 nm. If the thickness of the thirteenth lower dielectric layer 3003 is less than 4 nm, sulfur (S) that is a material constituting the twelfth lower dielectric layer 3001 diffuses, and the first reflective layer 2001 is corroded. On the other hand, if the thickness of the thirteenth lower dielectric layer 3003 is larger than 10 nm, the reflectivity is reduced and desired signal characteristics cannot be obtained.

  The thickness of the twelfth lower dielectric layer 3001 is preferably selected from 4 nm to 25 nm, for example, 10 nm. If the thickness of the twelfth dielectric layer 3001 is less than 4 nm, it becomes difficult to form the twelfth lower dielectric layer 3001 having a uniform thickness. On the other hand, if it is larger than 25 nm, the reflectivity is reduced and desired signal characteristics cannot be obtained.

  The thickness of the twelfth upper dielectric layer 3004 is preferably selected from 4 nm to 60 nm, for example, 45 nm. If the thickness of the twelfth upper dielectric layer 3004 is less than 4 nm, it becomes difficult to form the twelfth upper dielectric layer 3004 having a uniform thickness. On the other hand, if the thickness of the twelfth upper dielectric layer 3004 is greater than 60 nm, heat is likely to be stored in the first information recording layer 2003, leading to deterioration in reproduction stability.

  The thicknesses of the eleventh lower dielectric layer 3002 and the eleventh upper dielectric layer 3005 are preferably selected from 4 nm to 10 nm, for example, 5 nm. When the thickness of the eleventh lower dielectric layer 3002 and the eleventh upper dielectric layer 3005 is less than 4 nm, sulfur (S) which is a material constituting the twelfth lower dielectric layer 3001 and the twelfth upper dielectric layer 3004 ) Diffuses, the first information recording layer 2003 is corroded. On the other hand, if the thicknesses of the eleventh lower dielectric layer 3002 and the eleventh upper dielectric layer 3005 are greater than 10 nm, the reflectivity decreases and desired signal characteristics cannot be obtained.

  The first information recording layer 2003 is a phase change information recording layer that records an information signal using a crystal-amorphous structural phase change. As the material of the first information recording layer 2003, a chalcogen compound is preferably selected, and an SbTe alloy material is more preferably selected. As this SbTe-based alloy material, Ge, Sb, or Te is preferably selected. In this case, preferably, the Ge content is 2 atomic percent or more and 8 atomic percent or less, and the ratio of Sb to Te is 3.4 times or more and 4.0 times or less. More preferably, the Ge content is 2 atomic percent or more and 8 atomic percent or less, and the ratio of Sb to Te is 4.2 times or more and 4.8 times or less.

  The thickness of the first information recording layer 2003 is preferably selected from 6 nm to 16 nm, for example, 10 nm. If the thickness of the first information recording layer 2003 is selected to be less than 6 nm, it becomes difficult to obtain sufficient reproduction durability. On the other hand, if it is larger than 16 nm, the recording sensitivity is deteriorated, so that it is difficult to record the information signal.

  FIG. 4 is a schematic cross-sectional view showing the second information recording layer 1005, the third information recording layer 1008, and the fourth information recording layer 1011 according to the present embodiment. In this embodiment, a high refractive index layer 4001, a second reflective layer 4002, a second lower dielectric layer 4003, a second information recording layer 4004, and a second upper dielectric layer 4005 are sequentially provided from the side closer to the substrate 1001. Are stacked. Here, the materials constituting the second reflective layer 4002, the second lower dielectric layer 4003, and the second upper dielectric layer 4005 are the first reflective layer 2001, the first lower dielectric layer 2002, and the first It may be the same as that of the upper dielectric layer 2004. However, the film thickness of each layer may be set to a desired value by optical design as appropriate, and is not particularly limited.

  The constituent material of the second information recording layer 4004 is made of the same material as that of the first information recording layer 2003 except that Ge is partially replaced with Sn as a device for enhancing the crystallization ability.

The high refractive index layer 4001 is an important layer for increasing the transmittance in each information recording layer, and is preferably formed of a material having a high refractive index, for example, a material having a refractive index of 2.3 or more. For example, a material such as TeO ₂ , ZnO, Ta ₂ O ₅ , ZrO ₂ , or TiO ₂ is suitable, and TiO ₂ is particularly preferable. The presence of the high refractive index layer 4001 increases the transmittance by 5 to 10% in absolute value.

FIG. 5 is a schematic cross-sectional view showing the initialization auxiliary layer (first initialization auxiliary layer 1004, second initialization auxiliary layer 1007, and third initialization auxiliary layer 1010) according to the present embodiment. The initialization auxiliary layer has a structure in which a first reaction layer 5001 and a second reaction layer 5002 are stacked. The first reaction layer 5001 is disposed on the front side when viewed from the incident laser beam, and the second reaction layer 5002 is disposed on the back side when viewed from the incident laser beam. Here, the first reaction layer 5001 is mainly composed of SiN, SiC, or SiO ₂ and contains hydrogen, and the second reaction layer 5002 is mainly composed of a rare earth element of Tb or La.

  A preferred combination of the main component of the first reaction layer 5001 and the main component of the second reaction layer 5002 is SiNH / Tb. Further, the first reaction layer 5001 includes Mg, Ti, Cr, Ni, Al, Si, in addition to the above-mentioned main component, from the viewpoint of improving the stability against oxidation or sulfurization except during recording. Ga, Ge, etc. may be added.

  The thickness of each initialization auxiliary layer is not particularly limited as long as the portion of each initialization auxiliary layer that has been irradiated with the laser beam during initialization can form a hydride of a rare earth metal quickly. Further, the film thickness ratio between the first reaction layer 5001 and the second reaction layer 5002 is not particularly limited, but the second reaction layer 5002 has a low transmittance of each information recording layer before the initialization process. Therefore, the thickness is preferably 10 nm or more.

  The initialization auxiliary layer is provided in contact with the side of the information recording layer to be initialized facing the surface of the incident laser beam, but between the information recording layer to be initialized and the information recording layer to be initialized next. It may be placed anywhere if there is.

  Next, an example of a method for producing the rewritable multilayer optical recording medium will be described.

  Each information recording layer and each initialization layer arranged on the substrate 1001 can be formed by a vapor phase growth method using chemical species including constituent elements of each layer. Examples of such a vapor phase growth method include a vacuum deposition method, a sputtering method, a plasma CVD method, and the like.

  In addition to the above-described light-transmitting sheet, the protective layer 1012 may be formed by, for example, preparing a resin solution by dissolving an acrylic or epoxy-based ultraviolet curable resin in a solvent, and performing spin coating or the like. Is possible.

  In addition, the manufacturing method of the said rewritable optical recording medium is not specifically limited to the said manufacturing method, The manufacturing technique employ | adopted for manufacture of a well-known optical recording medium can be used.

  Next, an initialization method for the rewritable optical recording medium will be described.

  First, as shown in FIG. 1, a laser beam 1013 having a predetermined output is incident on the rewritable optical recording medium from the protective layer 1012 side, and is irradiated to the fourth information recording layer 1011. Then, in the fourth information recording layer, the information recording layer formed in an amorphous state transitions to a crystallization state. At the same time, in the third initialization auxiliary layer 1010, dissociation / detachment of the hydrogen element occurs from the first reaction layer 5001 and changes to a dielectric film not containing hydrogen. On the other hand, in the second reaction layer 5002, a hydrogenation reaction occurs between hydrogen released from the first reaction layer 5001 and the rare earth metal, thereby forming a rare earth metal hydride film. As a result, the second reaction layer becomes substantially transparent, and the transmittance of the third initialization auxiliary layer increases after the initialization process.

Also, the dielectric film near the stoichiometric composition formed in the initialization auxiliary layer and the rare earth metal hydride have excellent thermal stability, and the change in transmittance of the initialization auxiliary layer is an irreversible phenomenon. It becomes.
(Second Embodiment)
In the second embodiment according to the present invention, each of the initialization auxiliary layers has the same configuration as that of the first embodiment except that the initialization auxiliary layer is a thermochromic film made of a thermochromic material whose optical characteristics change with temperature. Yes. However, the arrangement position of the initialization auxiliary layer in the second embodiment is limited to an arrangement adjacent to each information recording layer and in contact with each intermediate layer as viewed from the incident laser beam.

  Examples of the material for the thermochromic film include an electron-donating color developing compound and an electron-accepting color developer, a mixed system of polar compounds, or a mixture of an electron-donating color developing compound and a phenol color developer. Examples of the electron donating color-forming compound include a fluorane compound, a spiropyran compound, a phthalide compound, and a lactam compound.

  As the polar compound, for example, alcohols are used, and can be selected from n-octyl alcohol, n-decyl alcohol, n-lauryl alcohol, n-myristyl alcohol, n-cetyl alcohol, n-stearyl alcohol and the like.

  Further, the rewritable multilayer optical recording medium manufacturing method and initialization method of this embodiment are substantially the same as those of the first embodiment described above, but the reaction mechanism in the initialization auxiliary layer is the first embodiment. Is different. In other words, the material constituting the thermochromic layer diffuses into the resin layer that forms the intermediate layer due to the heat during the initialization process, so that the molecules are separated by a distance that does not interact with each other. Even if it becomes low, it does not re-color.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the first and second embodiments.

  For example, the case where the initialization auxiliary layer has a two-layer structure in which the first reaction layer and the second reaction layer each consist of one layer has been described. However, at least one first reaction layer is in contact with the initialization reaction auxiliary layer. As long as it has at least one second reaction layer, it may be an initialization auxiliary layer composed of two or more layers. For example, an initialization auxiliary layer having a three-layer structure including two second reaction layers and one first reaction layer disposed between the two second reaction layers may be provided.

<Example>
Hereinafter, the present invention will be described in detail with specific examples, but the present invention is not limited to the following examples without departing from the gist thereof.

Example 1
After a polycarbonate substrate with tracking guide grooves formed is fixed to a substrate holder in a plasma CVD and magnetron sputter mixing device having DC, RF, and microwave power sources, a high vacuum of 2 × 10 −5 Pa or less is obtained. The chamber was evacuated with a cryopump. Thereafter, a process gas or a material gas was introduced into the chamber while being evacuated, and each layer was formed by sputtering the target or using plasma CVD while rotating the substrate. When forming the ZnS-SiO ₂ mixture, sputtering was performed by introducing O 2 gas in addition to Ar gas. The first reaction layer 5001 was formed using a microwave plasma CVD method by introducing SiH 4 gas, Ar gas, and N 2 gas. In addition, when O ₂ gas and N ₂ gas are mixed during the formation of the second reaction layer 5002, oxidation and nitridation are likely to occur, and the hydrogenation characteristics are affected. This layer was formed in a separate chamber.

  First, the first information recording layer 1002 was formed on the substrate 1001.

Ar gas was allowed to flow into the chamber, the pressure was adjusted to a desired value by adjusting conductance, and an AgNdCu layer of 80 nm was formed as the first reflective layer 2001. Thereafter, the substrate is transferred to another chamber, Ar gas and N 2 gas are allowed to flow into the chamber, and the pressure is set to a desired value by conductance adjustment. Thereafter, a 5 nm SiN layer was formed as the twelfth lower dielectric layer 3002. Thereafter, an eleventh lower dielectric layer 3001 made of a ZnS—SiO ₂ mixture was formed to a thickness of 10 nm in another chamber.

When N2 gas is mixed during the formation of the phase change film, nitriding occurs and the crystallization characteristics are affected. Therefore, the dielectric layer and the other phase change layers were formed in separate chambers. After the formation of the eleventh lower dielectric layer, the substrate is transferred to another chamber, Ar gas is introduced into the chamber, the pressure is set to a desired value by adjusting the conductance, and a GeSbTe layer is formed as a first information recording layer 2003 with a thickness of 10 nm. Filmed. Thereafter, an eleventh upper dielectric layer 3003 made of a ZnS—SiO ₂ mixture was sequentially formed to a film thickness of 45 nm, and a twelfth upper dielectric layer 3004 made of SiN was sequentially formed to a film thickness of 5 nm.

  The substrate 1001 has a diameter of 120 mm and a thickness of 1.1 mm. Concavities and convexities called grooves and lands are formed on one main surface on the side on which the first information recording layer 1002 is formed, and the repetition width (track pitch) of the concavities and convexities is 0.32 μm. Further, the Nd content in the first reflective layer 2001 was 0.4 at%, and the Cu content was 0.6 at%.

  The first intermediate layer 1003 was formed by removing the substrate from the film forming machine, dissolving an epoxy-based ultraviolet curable resin in a solvent to prepare a resin solution, and forming the resin layer with a thickness of 15 μm by spin coating. On one main surface of the first intermediate layer 1003, an unevenness was simultaneously formed as a guide groove for tracking by a 2P method (Photo-Polymerization method) using an ultraviolet component resin.

  After the formation of the first intermediate layer 1003, the disk was returned to the film forming apparatus again, and the inside of the chamber was evacuated with a cryopump until a high vacuum of 2 × 10 −5 Pa or less was reached. Thereafter, a first initialization auxiliary layer 1004 was formed on the first intermediate layer 1003.

First, Ar gas was introduced to obtain a desired pressure by adjusting conductance, and a Tb layer having a thickness of 20 nm was formed as the second reaction layer 5002. Thereafter, in another chamber, SiH4 gas is flowed into the chamber at 200 sccm and N2 gas is flowed into the 500 sccm chamber, the pressure is set to a desired value (4 to 13 Pa) by adjusting the conductance, and plasma CVD is used at a power of 1.5 kW. A hydrogen-containing SiN layer having a thickness of 20 nm was formed as one reaction layer 5001. The hydrogen content of this layer was 2.1 × 10 ²² atoms / cm ³ and the film stress was −1.0 kg / mm ² (compressive stress state).

  Thereafter, the substrate was transferred to another chamber, and the second information recording layer 1005 was formed.

First, Ar gas and O ₂ gas were introduced into the chamber to obtain a desired pressure by adjusting conductance, and 20 nm of TiO ₂ was formed as the high refractive index layer 4001. Next, an Ag alloy film having a thickness of 10 nm was formed as the second reflective layer 4002 with Ar gas in another chamber. Thereafter, a SiN layer of 5 nm and a ZnS—SiO ₂ mixture of 30 nm were formed as the second lower dielectric layer 4003, respectively. After the formation of the second lower dielectric layer 4003, a GeSnSbTe layer of 8 nm was formed as the second information recording layer 4004. Thereafter, a second upper dielectric layer 4005 composed of a ZnS—SiO ₂ mixture of 45 nm and a SiN film of 5 nm was sequentially formed.

  Thereafter, the steps from the first intermediate layer 1003 to the second information recording layer 1005 described above are repeated twice to form the second intermediate layer 1006 to the fourth information recording layer 1011, and the information recording layer is formed. Four layers were laminated.

The third information recording layer is
High refractive index layer: TiO ₂ of 15 nm,
Reflective layer: Ag alloy 8 nm,
Lower dielectric layer: SiN layer 5 nm, ZnS-SiO ₂ mixture 30 nm,
Information recording layer: GeSnSbTe layer 8 nm,
Upper dielectric layer: ZnS—SiO ₂ mixture 45 nm and SiN film 5 nm were formed.

The fourth information recording layer is
High refractive index layer: TiO ₂ 10 nm,
Reflective layer: Ag alloy 6 nm,
Lower dielectric layer: SiN layer 5 nm, ZnS-SiO ₂ mixture 30 nm,
Information recording layer: GeSnSbTe layer 6 nm,
Upper dielectric layer: ZnS—SiO ₂ mixture 45 nm and SiN film 5 nm were formed.

  Since it is difficult to measure the transmittance / reflectance of each layer after forming the multilayer optical recording medium, the optical properties (reflectance and transmittance) of each layer shown in Table 1 are the information recording layer single layer. Or, it is a measured value of each information recording layer + each initialization auxiliary layer alone. After completion of the optical recording medium, all the four information recording layers had a reflectance of 4 to 6%.

  Finally, a light-transmitting cover layer was laminated as a protective layer 1012 on the fourth information recording layer 1011 to complete the optical recording medium in this example.

  The optical recording medium manufactured in this way is irradiated with laser light from the protection 1012 side, and the information recording layers are initialized under general conditions in order from the fourth information recording layer 1011. Went. Here, the wavelength λ of the irradiation light was 810 nm, the spot diameter was 96 × 192 μm, and the linear velocity was 3 m / s. The laser output is 1 W when each layer is independent, 1 W for the fourth information recording layer, 1.2 W for the third information recording layer, 1.5 W for the second information recording layer, The information recording layer was 2W.

  As a result, in all four information recording layers, the SUM signal level, that is, the reflectivity of the disc has increased as compared to As-depo, and has reached the high level in the modulation degree during signal recording. It was confirmed that crystallization was performed by the crystallization process.

  The optical recording medium in the present embodiment is a so-called High to Low type disk in which the reflectance of the disk is reduced by recording.

(Example 2)
As the first reaction layer 5001, an optical recording medium having the same configuration as in Example 1 was produced except that SiC was used. The hydrogen content of this layer was 3.0 × 10 ²² atoms / cm ³ and the film stress was −1.5 kg / mm 2 (compressive stress state). The film forming conditions of the plasma CVD apparatus are as follows. SiH ₄ gas was 200 sccm, C ₂ H ₂ gas was 200 sccm, gas pressure was 4 to 13 Pa, and input power was 1.5 kw.

  The optical recording medium produced in this way is irradiated with laser light from the protection 1012 side in the same manner as in Example 1, and each of the fourth information recording layer 1011 is sequentially ordered under general conditions. The information recording layer was initialized.

  As a result, the SUM signal level, that is, the reflectivity of the disc increases in comparison with As-depo in all the four information recording layers as in the first embodiment, and reaches a high level in the modulation degree during signal recording. It was confirmed that crystallization was performed in the initialization process.

(Example 3)
As the first reaction layer 5001, an optical recording medium having the same configuration as in Example 1 was produced except that SiO ₂ was used. The hydrogen content of this layer was 2.6 × 10 ²² atoms / cm ³ , and the film stress was −0.5 kg / mm ² (compressive stress state). The film forming conditions of the plasma CVD apparatus are as follows. SiH ₄ gas was 200 sccm, O ₂ gas was 500 sccm, gas pressure was 4 to 13 Pa, and input power was 1.5 kW.

  The optical recording medium produced in this way is irradiated with laser light from the protection 1012 side in the same manner as in Example 1, and each of the fourth information recording layer 1011 is sequentially ordered under general conditions. The information recording layer was initialized.

  As a result, the SUM signal level, that is, the reflectivity of the disc increases in comparison with As-depo in all the four information recording layers as in the first embodiment, and reaches a high level in the modulation degree during signal recording. It was confirmed that crystallization was performed in the initialization process.

Example 4
An optical recording medium having the same configuration as in Example 1 was produced except that La was changed to 20 nm as the second reaction layer 5002.

  The optical recording medium produced in this way is irradiated with laser light from the protection 1012 side in the same manner as in Example 1, and each of the fourth information recording layer 1011 is sequentially ordered under general conditions. The information recording layer was initialized.

  As a result, the SUM signal level, that is, the reflectivity of the disc increases in comparison with As-depo in all the four information recording layers as in the first embodiment, and reaches a high level in the modulation degree during signal recording. It was confirmed that crystallization was performed in the initialization process.

(Example 5)
As the first initialization auxiliary layer 1004, the second initialization auxiliary layer 1007, and the third initialization auxiliary layer 1010, a leuco dye GN2 (manufactured by Yamamoto Kasei Co., Ltd.) is 20 nm, and a bisphenol compound BHPE (1,1- An optical recording medium having the same configuration as that of Example 1 was produced except that bis (4-hydroxyphenyl) ethane was formed by a 40 nm vacuum heating deposition method.

  The optical recording medium produced in this way is irradiated with laser light from the protection 1012 side in the same manner as in Example 1, and each of the fourth information recording layer 1011 is sequentially ordered under general conditions. The information recording layer was initialized.

  As a result, the SUM signal level, that is, the reflectivity of the disc increases in comparison with As-depo in all the four information recording layers as in the first embodiment, and reaches a high level in the modulation degree during signal recording. It was confirmed that crystallization was performed in the initialization process.

(Comparative Example 1)
A sample was prepared in the same manner as in Example 1 except that the first initialization auxiliary layer 1004, the second initialization auxiliary layer 1007, and the third initialization auxiliary layer 1010 were not provided.

  The optical recording medium produced in this way is irradiated with laser light from the protection 1012 side in the same manner as in Example 1, and each of the fourth information recording layer 1011 is sequentially ordered under general conditions. The information recording layer was initialized.

  As a result, in the first information recording layer 1002 and the second information recording layer 1005, the SUM signal level, that is, the reflectance of the disc is increased as compared with the As-depo, as in the first embodiment, and It was found that the level of modulation during signal recording increased to a high level. However, in the third information recording layer 1008 and the fourth information recording layer 1011, the SUM signal level, that is, the reflectivity of the disc is hardly changed as compared with As-depo, and the crystal of the film formed by the initialization process. It was found that the conversion was insufficient.

  As described above in detail using the examples and comparative examples, according to the optical recording medium of the present invention, the information recording layer was multilayered to increase the recording capacity of the optical recording medium per unit area. Even in this case, it is possible to provide an optical recording medium that can appropriately initialize each information recording layer.

  The SUM signal level was measured by reproduction on the evaluator. When the reproduction power is aligned, the SUM signal level and the reflectance correspond linearly. The criterion was compared with the increase in SUM signal level seen when initializing with a single layer.

1 is a schematic cross-sectional view showing a first embodiment of an optical recording medium according to the present invention. It is a schematic cross section which shows the 1st information recording layer in the 1st Embodiment of this invention. It is a schematic cross section which shows the 1st lower dielectric layer and the 1st upper dielectric layer in the 1st Embodiment of this invention. It is a schematic cross section which shows the 2nd information recording layer in the 1st Embodiment of this invention, the 3rd information recording layer, and the 4th information recording layer. It is a schematic cross section which shows the initialization auxiliary | assistant layer in the 1st Embodiment of this invention.

Explanation of symbols

1001 Substrate 1002 First information recording layer 1003 First intermediate layer 1004 First initialization auxiliary layer 1005 Second information recording layer 1006 Second intermediate layer 1007 Second initialization auxiliary layer 1008 Third information recording layer 1009 Third Intermediate layer 1010 Third initialization auxiliary layer 1011 Fourth information recording layer 1012 Protective layer 1013 Laser light 2001 First reflective layer 2002 First lower dielectric layer 2003 First information recording layer 2004 First upper dielectric layer 3001 12th Lower dielectric layer 3002 eleventh lower dielectric layer 3003 thirteenth lower dielectric layer 3004 twelfth upper dielectric layer 3005 eleventh upper dielectric layer 4001 high refractive index layer 4002 second reflective layer 4003 second lower dielectric layer 4004 Second information recording layer 4005 Second upper dielectric layer 5001 First reaction layer 5002 Second reaction layer

Claims (10)

A rewritable multilayer optical recording medium having two or more information recording layers made of a phase change material on a substrate and an initialization auxiliary layer between the information recording layers,
The initialization auxiliary layer is a film whose transmittance increases before and after the information recording layer disposed on the laser incident side of the initialization auxiliary layer is initialized by the laser light. A rewritable multilayer optical recording medium. The initialization assisting layer includes a first reaction layer made of a dielectric containing SiN, SiC, or SiO ₂ as a main component and containing hydrogen;
A second reaction layer made of a rare earth metal mainly composed of Tb or La, which is in contact with the first reaction layer and is hydrogenated by hydrogen contained in the first reaction layer at the time of initialization. The rewritable multilayer optical recording medium according to claim 1.   4. The rewritable multilayer optical recording according to claim 3, wherein in the initialization auxiliary layer, the first reaction layer is disposed closer to the incident laser beam than the second reaction layer. Medium.   3. The rewritable multilayer according to claim 2, wherein the initialization auxiliary layer is provided in contact with the information recording layer disposed on the laser beam incident side of the initialization auxiliary layer. Optical recording medium. Having an intermediate layer between the two or more information recording layers;
The initialization auxiliary layer is disposed in contact with the intermediate layer;
2. The rewritable multilayer optical recording medium according to claim 1, wherein the initialization auxiliary layer comprises a thermochromic film mainly composed of an electron donating color developing compound and an electron accepting developer. A rewritable multilayer optical recording medium having two or more information recording layers made of a phase change material on a substrate and an initialization auxiliary layer between the information recording layers is provided with a laser from one side of the multilayer optical recording medium. An initialization method for a rewritable multilayer optical recording medium that performs light initialization and sequentially initializes from the information recording layer disposed on the side closer to the laser light irradiation side,
The first initialization step of initializing the information recording layer disposed on the laser beam incident side of the initialization auxiliary layer with the laser beam includes a step of increasing the transmittance of the initialization auxiliary layer. A method for initializing a multilayer optical recording medium.   T1 <50% and T2> 50%, where T1 is the transmittance before the initialization step of the initialization auxiliary layer and T2 is the transmittance after the initialization step. The initialization method for a rewritable multilayer optical recording medium according to claim 6. The initialization assisting layer includes a first reaction layer made of a dielectric containing SiN, SiC, or SiO ₂ as a main component and containing hydrogen;
A second reaction layer made of a rare earth metal mainly composed of Tb or La, which is in contact with the first reaction layer and is hydrogenated by hydrogen contained in the first reaction layer at the time of initialization. 6. A method for initializing a rewritable multilayer optical recording medium according to claim 5, wherein:   The rewritable multilayer light according to claim 6, wherein in the initialization auxiliary layer, the first reaction layer is disposed closer to the incident laser beam than the second reaction layer. A method for initializing the recording medium.   6. The rewritable multilayer optical recording medium according to claim 5, wherein the initialization auxiliary layer comprises a thermochromic film mainly composed of an electron donating color developing compound and an electron accepting developer. Initialization method.

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