JP4350326B2 - Multilayer phase change optical recording medium - Google Patents

Description

【００１８】
【発明の効果】
本発明１によれば、保護膜にＡｌ、Ｓｉ、Ｎを構成元素とする材料を用いたので、保存後の特性が改善された多層相変化型光記録媒体を提供できる。
また、保護膜の材料組成を特定したので、透過率が高く、生産性に優れ、保存前後の特性がより改善された多層相変化型光記録媒体を提供できる。
また、（Ａｌ_{１００−ａ}Ｓｉ_ａ）_{１００−ｘ}Ｎ_ｘからなる上部保護膜の膜厚範囲を特定したので、記録消去の繰り返し特性の優れた多層相変化型光記録媒体を提供できる。
また、（Ａｌ_{１００−ａ}Ｓｉ_ａ）_{１００−ｘ}Ｎ_ｘからなる下部保護膜の膜厚範囲を特定したので、記録特性がよく、量産性のよい多層相変化型光記録媒体を提供できる。
本発明２によれば、記録層の構成元素を特定したので、消去比に優れ、保存前後の特性がよい多層相変化型光記録媒体を提供できる。
本発明３によれば、最も奥側に位置する情報記録層以外の情報記録層の少なくとも１層に特定の膜厚範囲の反射層を設けたので、透過率を大きく下げることなく、再生信号振幅の大きい多層相変化型光記録媒体を提供できる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係わる２層光記録媒体の概略断面図。
【図２】保存前後のジッターのＳｉ濃度依存性を示す図。
【符号の説明】
１ 第１情報記録層
２ 第２情報記録層
３ 光透過層
４ 透明層
５ 保護基板
１１ 第１下部保護膜
１２ 第１記録膜
１３ 第１上部保護膜
２１ 第２下部保護膜
２２ 第２記録膜
２３ 第２上部保護膜
２４ 反射膜[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium for recording / reproducing information by light such as a laser, and more particularly to a multilayer phase change optical recording medium.
[0002]
[Prior art]
For optical disks such as CD-R and CD-RW, a recording layer is provided on a circular substrate made of plastic such as polycarbonate, and a reflective layer is formed thereon by depositing or sputtering a metal such as aluminum, gold, or silver. The laser beam is incident from the substrate surface side to record and reproduce signals.
In recent years, since the amount of information handled by computers and the like has increased, the signal recording capacity of optical disks such as DVD-RAM and DVD-RW has increased and the density of signal information has increased. At present, the recording capacity of a CD is about 650 MB and the DVD is about 4.7 GB, but further higher recording density is required.
As a means for realizing such a high recording density medium, it has been proposed to shorten the wavelength of the laser used to the blue light region. Further, by increasing the numerical aperture of the objective lens used for the recording / reproducing pickup, the spot density of the laser beam irradiated onto the optical recording medium can be reduced, so that a high recording density can be achieved.
However, since there is a limit to the method of increasing the recording density by reducing the spot size by shortening the laser wavelength or increasing the numerical aperture of the objective lens, a technology for increasing the capacity by providing two information recording layers on one side. Is proposed in Japanese Patent No. 2702905.
[0003]
However, the two-layer phase change optical disc has many problems and has not yet been put into practical use. For example, if the recording layer positioned in front of the laser beam irradiation side cannot sufficiently transmit the laser beam, the recording layer positioned on the back side cannot be recorded / reproduced. Therefore, in order to sufficiently transmit the laser light, the reflecting film such as Ag or Al must be eliminated or made extremely thin.
In general, in phase change optical recording, an amorphous mark is formed by irradiating a recording film with laser light and rapidly cooling, but it is difficult to form a mark in a recording layer without a reflective film due to small thermal diffusion. become. In particular, the Ag-In-Sb-Te quaternary recording material used for phase change optical disks such as CD-RW has a good erasure ratio and requires a rapid cooling structure. Is even more so. In order to enhance the thermal diffusion effect, use of AlN for the protective film is proposed in Japanese Patent Laid-Open No. 2000-21016.
However, in the case of an optical disk using AlN, the sputtered film of AlN is crystal and has a large film stress, and the AlN film may be hydrolyzed to generate ammonia, and is harder and more brittle. There was also a problem that the characteristics deteriorated.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a phase change optical recording medium having a large capacity and an excellent erasing ratio.
[0005]
[Means for Solving the Problems]
The above problems are solved by the following inventions 1) to 3 ) (hereinafter referred to as the present invention 1 to 3 ).
1) In an optical recording medium having a plurality of information recording layers having a recording film on which information is recorded by a phase change between a crystalline state and an amorphous state by light irradiation and a protective film adjacent thereto, as viewed from the light incident side At least one information recording layer other than the information recording layer located on the innermost side is provided with a protective film made of a material represented by the following composition formula on the back side or the near side of the recording film when viewed from the light incident side. Have
(Al _100-a Si _a ) _100-x N _x (40 ≦ x ≦ 60, 1 ≦ a ≦ 10)
A phase change optical recording medium , wherein the thickness of the protective film on the back side is 3 to 50 nm, and the thickness of the protective film on the near side is 30 to 170 nm .
2) at least one layer other than the information recording layer located farthest side when viewed from the light incident side, 1 and having a recording film made of Ag-In-Sb-Te quaternary alloy) according Multi-layer phase change optical recording medium.
3) 1) or 2), wherein a reflective film having a thickness of 1 to 10 nm is provided on at least one of the information recording layers other than the information recording layer located on the innermost side when viewed from the light incident side. Phase change type optical recording medium.
[0006]
Hereinafter, the present invention will be described in detail.
FIG. 1 is a schematic sectional view of a two-layer optical recording medium according to an embodiment of the present invention.
The first information recording layer 1, the transparent layer 4, the second information recording layer 2, and the protective substrate 5 are sequentially laminated on the light transmission layer 3.
The first information recording layer 1 includes a first lower protective film 11, a first recording film 12, and a first upper protective film 13. The second information recording layer 2 includes a second lower protective film 21 and a second recording film 22. The second upper protective film 23 and the reflective film 24 are included.
The material of the light transmission layer 3, the transparent layer 4, and the protective substrate 5 is usually glass, ceramics, or resin, and a resin substrate is preferable in terms of moldability and cost.
Examples of the resin include polycarbonate, acrylic resin, epoxy resin, polystyrene, acrylonitrile-styrene copolymer resin, polyethylene, polypropylene, silicone resin, fluorine resin, ABS resin, urethane resin, and the like. Acrylic resins such as polycarbonate and polymethyl methacrylate (PMMA), which are excellent in terms of optical properties and cost, are preferred.
[0007]
The light transmission layer 3 or the transparent layer 4 is provided with an uneven pattern such as a guide groove by injection molding or a photopolymer method.
The thickness of the transparent layer 4 is preferably 30 to 50 μm so that the pickup can distinguish between the first information recording layer and the second information recording layer and perform optical separation when recording / reproducing is performed. When the thickness is larger than 50 μm, spherical aberration occurs when recording / reproducing the second information recording layer, and recording / reproducing becomes difficult.
As the material of the recording films 12 and 22, chalcogen-based alloy thin films such as Ge—Te, Ge—Te—Sb, Ge—Sn—Te are often used, but recording (amorphization) sensitivity / speed, In addition, an Ag—In—Sb—Te quaternary alloy thin film is preferable because the erase ratio is extremely good. Further, an alloy having the same composition may be used for the recording films 12 and 22.
Other elements and impurities can be added to these recording film materials for the purpose of further improving performance and reliability.
Examples of the method for forming a recording film using an inorganic material include 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 preferable because it is excellent in mass productivity and film quality.
[0008]
As the reflective film 24, a metal material such as Al, Au, Ag, Cu, Ta, or an alloy thereof can be used. Further, Cr, Ti, Si, Pd or the like is used as an additive element.
Such a reflective film can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, electron beam deposition, etc. It is preferable because of excellent film quality.
The thickness of the reflective film is 50 to 200 nm, preferably 80 to 150 nm.
If the thickness is less than 50 nm, the reflectance decreases, and if it is more than 200 nm, the sensitivity is lowered, which is not preferable.
Although not shown in the drawing, a reflective film 14 using the same material as described above can be provided between the first upper protective film 13 and the transparent layer 4. By providing the reflective film 14, the heat of the first recording film 12 during recording is diffused to the reflective film 14 via the first upper protective film 13, so that the cooling rate is further increased. Also, according to the optical simulation, the difference between the reflectance of the crystal part and the reflectance of the amorphous part can be increased, so that a large reproduction signal amplitude can be obtained.
However, in consideration of the amount of laser light transmitted to the second information recording layer, the thickness of the reflective film 14 is preferably 1 to 10 nm. If it is thicker than 10 nm, the transmittance is reduced, and recording / reproduction of the second information recording layer becomes difficult.
[0009]
The protective films 11, 13, 21, and 23 are provided for the purpose of preventing deterioration and deterioration of the recording films 12 and 22, increasing the adhesive strength of the recording films 12 and 22, and improving the recording characteristics. It must be higher than the recording film.
Examples of the material 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 ; Si ₃ N ₄ , AlN, TiN, BN, and ZrN. Nitrides such as ZnS, sulfides such as In ₂ S ₃ and TaS ₄ ; carbides such as SiC, TaC, B ₄ C, WC, TiC and ZrC; diamond-like carbon and the like.
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.
Such a protective film can be formed by various vapor phase growth methods, for example, vacuum deposition method, sputtering method, plasma CVD method, photo CVD method, ion plating method, electron beam deposition method and the like. Among these, the sputtering method is preferable because it is excellent in mass productivity and film quality.
[0010]
Further, among the protective films 11, 13, 21, and 23, a material having high thermal conductivity is used as the material of the first lower protective film 11 and / or the first upper protective film 13, specifically, Al, Si , N is a feature of the present invention.
As described above, it is difficult to provide a reflective film on the first information recording layer from the viewpoint of transmittance, and even if it is provided, the thickness is 1 to 10 nm, so that a sufficient thermal diffusion effect at the time of forming an amorphous mark cannot be obtained. In order to solve this problem, a material having a high thermal conductivity is used for the protective film. A dielectric having a high thermal conductivity is AlN. When the AlN protective film is formed by sputtering, it becomes a crystal film and has a large film stress. Further, there is a possibility that ammonia is generated due to hydrolysis and the recording film is deteriorated. Furthermore, there is a problem that the storage characteristics are not good due to the property of being hard and brittle.
The present inventors have found that when Si is added to AlN, the film stress is reduced and hydrolysis is less likely to occur, so that the storage characteristics are improved.
In particular, when an Ag—In—Sb—Te quaternary alloy having an excellent erasing ratio is used as a recording material, a rapid cooling structure and a structure having excellent storage stability can be realized, and the effect of the present invention is great.
[0011]
When the composition formula of the protective film material obtained by adding Si to AlN and _{(Al 100-a Si a)} 100-x N x, and 40 ≦ x ≦ 60,1 ≦ a ≦ 10.
When x is less than 40, the absorption coefficient k increases and the transmittance decreases. When x is larger than 60, the production becomes difficult and the film becomes very brittle, so that the storage characteristics are not good. On the other hand, when a is less than 1, the function of the present invention is not achieved. When a is more than 10, the thermal conductivity decreases and the jitter at high recording density increases.
The thickness of the first upper protective layer 13 including a material having the above composition is 3 to 50 nm, preferably shall be the 5 to 30 nm. If it exceeds 50 nm, the repetitive recording performance deteriorates, and if it is less than 3 nm, the function of the present invention is not achieved.
The thickness of the first lower protective layer 11 with a material of the composition shall be the 30～170Nm. If the thickness is less than 30 nm, heat may affect the substrate during recording, and the substrate may be deformed. On the other hand, when the thickness exceeds 170 nm, it becomes difficult to produce an optical recording medium (disk) having excellent mass productivity.
[0012]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited by these Examples.
[0013]
Examples 1-8, Comparative Examples 1-6
A 6 nm-thick first recording film comprising a first lower protective film and Ag ₁ In ₇ Sb ₇₀ Te ₂₂ on a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm having continuous groove-like irregularities on the surface. Then, the first upper protective film was sequentially formed to form the first information recording layer. The compositions and film thicknesses of the first lower protective film and the first upper protective film in each example and comparative example are as shown in Table 1.
Each film is formed by sputtering, and the protective film made of ZnS.SiO ₂ and the first recording film are made of (Al _100-a Si _a ) _100-x N _x in an Ar gas atmosphere. As the protective film, an Al _100-a Si _a target was used, and nitrogen gas was introduced into the Ar gas atmosphere at the time of film formation. The nitrogen concentration in the film can be changed by adjusting the amount of nitrogen gas introduced when forming the protective film.
The transmittance of the first information recording layer thus prepared was measured. The results are shown in Table 1.
Next, a 40 μm-thick transparent layer having continuous groove-shaped tracking guide irregularities was formed on the first information recording layer by a 2P (photo polymerization) method.
Furthermore, thereon, ZnS · SiO ₂ composed of thickness 40nm second lower protective layer _of, Ag ₁ In ₇ Sb 70 consists _{Te 22} film thickness 12nm second recording film, film thickness 15nm made of ZnS · SiO ₂ The second upper protective film and a 150 nm-thick reflective film made of AlTi were sequentially formed to form a second information recording layer. A method for forming each film is a sputtering method in an Ar gas atmosphere.
Subsequently, an overcoat layer was provided on the second information recording layer using a spin coater to produce a two-layer phase change optical disc.
Finally, the recording layer of the optical disk was initialized by an initialization apparatus having a large-diameter semiconductor laser.
[0014]
Each optical disk produced as described above was recorded under the following conditions, and then the jitter of the first information recording layer at a linear density of 0.20 μm / bit and the jitter after recording 100 times were measured. The results are shown in Table 1.
・ Laser wavelength = 407 nm
・ NA (aperture ratio) = 0.65
・ Linear speed = 6.5m / s
・ Track pitch = 0.40μm
Next, after each optical disk was stored in an environment of 80 ° C. and 85% RH for 100 hours, jitter was measured as an archival characteristic evaluation. The evaluation criteria are as follows. The results are shown in Table 1.
○ ... Transmittance 45% or more, Jitter less than 14% x ... Transmittance less than 45%, Jitter 14% or more Also shows the Si concentration dependence of jitter before and after storage in Examples 1 to 3 and Comparative Examples 1 and 2. FIG. 2 shows that when a (amount of Si) is less than 1, the jitter after storage deteriorates, and when it exceeds 10, the initial jitter before storage deteriorates.
When the nitrogen concentration was less than 40, the transmittance deteriorated, and when it exceeded 60, molding could not be performed.
Furthermore, it has been found that the initial jitter deteriorates when the thickness of the upper protective film made of (Al _100-a Si _a ) _100-x N _x is less than 3 nm or more than 50 nm.
Further, when the thickness of the lower protective film made of (Al _100-a Si _a ) _100-x N _x was less than 30 nm, the substrate was deformed by heat, and the initial jitter was not good.
[0015]
Examples 9-10, Comparative Example 7
A two-layer phase change type optical disc was prepared in the same manner as in Example 1 except that a reflective film made of Ag was formed on the first information recording layer, and recording and evaluation were performed in the same manner as in Example 1. It was. The results are shown in Table 1.
As can be seen from Table 1, in the disk provided with Ag having a film thickness of 10 nm or less, the transmittance was 50% or more and the jitter before and after storage was good. On the other hand, the disk with Ag having a thickness of 20 nm had a transmittance of 20%, and recording / reproduction on the second information recording layer could not be performed.
[0016]
Example 11
On a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm with continuous groove-shaped irregularities on the surface, a 150 nm-thick first lower protective film made of ZnS · SiO ₂ , Ag ₁ In ₇ Sb ₇₀ Te ₂₂ A first recording film having a thickness of 6 nm and a first upper protective film having a thickness of 40 nm made of (Al _100-a Si _a ) _100-x N _x were formed in this order to form a first recording layer.
Each film is formed by sputtering, and the protective film made of ZnS.SiO ₂ and the first recording film are made of (Al _100-a Si _a ) _100-x N _x in an Ar gas atmosphere. As the protective film, an Al _100-a Si _a target was used, and nitrogen gas was introduced into the Ar gas atmosphere at the time of film formation. The nitrogen concentration in the film can be changed by adjusting the amount of nitrogen gas introduced when forming the protective film.
Next, a 30 μm-thick transparent layer having continuous groove-shaped tracking guide irregularities was formed on the first recording layer by a 2P (photo polymerization) method.
Furthermore, a 150 nm thick second lower protective film made of ZnS · SiO _{2, a} 6 nm thick second recording film made of Ag ₁ In ₇ Sb ₇₀ Te ₂₂ , (Al _100-a Si _a ) _100- order to form a film of the second upper protective layer of thickness 40nm consisting _x N _x, to form a second recording layer. The film forming method is the same as that for the first recording layer.
Next, a 30 μm thick transparent layer having continuous groove-shaped irregularities for tracking guide was formed on the second recording layer by the 2P method.
Next, on the second lower protective layer of thickness 50nm made of ZnS · SiO _2, second recording film having a film thickness 12nm made of _{Ag 1 In 7 Sb 70 Te 22} , the film thickness made of ZnS · SiO ₂ A 15 nm second upper protective film and a 150 nm thick reflective film made of AlTi were sequentially formed to form a third recording layer.
Subsequently, an overcoat layer was provided thereon using a spin coater to produce a three-layer phase change optical disc.
Finally, the recording layer of the optical disk was initialized by an initialization apparatus having a large-diameter semiconductor laser.
[0017]
Recording and evaluation were performed on the first and second recording layers of this optical disc under the same conditions as in Example 1. The results are shown in Table 1 (jitter values are listed in the order of the first information recording layer and the second information recording layer).
As can be seen from the table, both the first information recording layer and the second information recording layer had good jitter before and after storage.
[Table 1]

[0018]
【The invention's effect】
According to the first aspect of the present invention, since the material containing Al, Si, and N as the constituent elements is used for the protective film, a multilayer phase change optical recording medium having improved characteristics after storage can be provided.
Further , since the material composition of the protective film is specified, it is possible to provide a multilayer phase change optical recording medium having high transmittance, excellent productivity, and improved properties before and after storage.
Further , since the film thickness range of the upper protective film made of (Al _100-a Si _a ) _100-x N _x is specified, it is possible to provide a multilayer phase change optical recording medium having excellent recording / erasing repetition characteristics.
In addition , since the thickness range of the lower protective film made of (Al _100-a Si _a ) _100-x N _x is specified, it is possible to provide a multilayer phase change optical recording medium with good recording characteristics and good mass productivity.
According to the second aspect of the present invention, since the constituent elements of the recording layer are specified, it is possible to provide a multilayer phase change type optical recording medium having excellent erasure ratio and good characteristics before and after storage.
According to the third aspect of the present invention, since the reflective layer having a specific film thickness range is provided in at least one of the information recording layers other than the information recording layer located on the innermost side, the reproduction signal amplitude is not greatly reduced. Can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a two-layer optical recording medium according to an embodiment of the present invention.
FIG. 2 is a graph showing the Si concentration dependence of jitter before and after storage.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st information recording layer 2 2nd information recording layer 3 Light transmission layer 4 Transparent layer 5 Protective substrate 11 1st lower protective film 12 1st recording film 13 1st upper protective film 21 2nd lower protective film 22 2nd recording film 23 Second upper protective film 24 Reflective film

Claims (3)

In an optical recording medium provided with a plurality of information recording layers having a recording film on which information is recorded by a phase change between a crystalline state and an amorphous state by light irradiation and a protective film adjacent thereto, as viewed from the light incident side, At least one information recording layer other than the information recording layer located on the side has a protective film made of a material represented by the following composition formula on the back side or the near side of the recording film when viewed from the light incident side. ,
(Al _100-a Si _a ) _100-x N _x (40 ≦ x ≦ 60, 1 ≦ a ≦ 10)
A phase change optical recording medium , wherein the thickness of the protective film on the back side is 3 to 50 nm, and the thickness of the protective film on the near side is 30 to 170 nm . At least one layer other than the information recording layer located farthest side when viewed from the light incident side, a multilayer of claim 1, wherein further comprising a recording film made of Ag-In-Sb-Te quaternary alloy Phase change type optical recording medium. 3. The phase according to claim 1, wherein a reflective film having a thickness of 1 to 10 nm is provided on at least one of the information recording layers other than the information recording layer located farthest from the light incident side. Changeable optical recording medium.

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