JPH07129999A - Optical information recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical information recording medium capable of high-density recording / erasing / reproduction repeatedly, having high reliability, and having excellent mass production efficiency. [Structure] A first protective layer, a recording layer, and
It has a structure in which a second protective layer, a reflection / heat dissipation layer, and a third protective layer are sequentially stacked, and records information by irradiating a laser beam.
In the optical information recording medium capable of erasing / reproducing,
An optical information recording medium, wherein the total stress S of the protective layer, the recording layer, the second protective layer, the reflection / heat dissipation layer and the third protective layer satisfies the following general formula. [Equation 1] (However, θ: incident angle of the laser beam on the substrate which enables the focus servo and / or the tracking servo E: Young's modulus of the substrate b: thickness of the substrate 1: (outer diameter of substrate-hole diameter of substrate) × 1 / 2ν: Poisson's ratio of the substrate)

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium, and more particularly to a phase change type optical information recording medium, in which a phase change is caused in a recording layer material by irradiating a light beam to record information.
The present invention relates to a rewritable and rewritable optical information recording medium, and is applied to an optical memory open device.

[0002]

2. Description of the Related Art As one of optical information recording media capable of recording, reproducing and erasing information by irradiation of electromagnetic waves, particularly laser beams, so-called transition utilizing a crystal-amorphous phase or a crystal-crystal phase is called. Phase change recording media are well known. This phase-change recording medium can be overwritten with a single beam, which is difficult for magneto-optical recording, and the optical system on the drive side can be simplified. There is. As a typical example thereof, as disclosed in US Pat. No. 3,530,441, Ge-Te, Ge-Te-Sn,
Ge-Te-S, Ge-Se-S, Ge-Se-Sb,
Ge-As-Se, In-Te, Se-Te, Se-A
Examples include so-called chalcogen-based alloy materials such as s.
In addition, for the purpose of improving stability and high-speed crystallization, Ge-T
Au (Japanese Patent Laid-Open No. 61-219692), Sn and A
u (JP-A-61-270190), Pd (JP-A-62-270190)
19490) and the like, for the purpose of proposing a material including added and improving repeatability of recording / erasing, Ge-Te-Se-Sb,
A material for which the composition ratio of Ge-Te-Sb is specified (Japanese Patent Laid-Open No. Sho 62-62).
-73438 and Japanese Patent Laid-Open No. 63-228433) have also been proposed. However, none of them can satisfy all of the characteristics required for a phase change rewritable optical information recording medium. In particular, improvement of recording sensitivity and erasing sensitivity, prevention of reduction of erasing ratio due to unerased portion during overwriting, and extension of life of recorded and unrecorded areas are the most important issues to be solved. For the next-generation optical information recording medium, improvement of recording density is also an important issue. In addition, the development of more efficient mass production technology is also an issue.

As a method for achieving high density in an optical information recording medium, 1) decreasing the beam diameter, 2) decreasing the track pitch, etc. are considered, and the respective technical problems have been studied.

Considering a method for achieving high density by reducing the beam diameter, the beam diameter D in optical information recording is D = K × (λ / NA) (1) (however, K: constant, λ: wavelength, NA: aperture ratio of lens). Therefore, in order to reduce the beam diameter, a method of reducing the wavelength λ can be considered, and actually,
A shorter wavelength is being studied. On the other hand, the numerical aperture NA of the lens
It can be seen that the beam diameter D is also reduced by increasing the. However, when the NA is increased, the coma aberration is greatly affected by the disc tilt. The coma aberration coefficient Wc is expressed as Wc ∞ θt (NA) ³ (2) (where θ is the incident angle of the laser beam on the substrate, t is the substrate thickness, and Wc is the coma aberration coefficient). From this equation (2), it is understood that the disc substrate thickness should be reduced in order to increase the aperture ratio and not increase Wc. 0.6mm compared to 1.2mm thickness
It has been shown that the influence of the disc tilt is smaller on the thicker substrate (Ishida et al., Proc. Of the 53rd Academic Meeting of the Applied Physics Society, p. 927 (1992)). However, when the substrate becomes thin, there arises a problem that focus servo and tracking servo are not applied due to deformation of the disk due to internal stress and thermal stress due to the dielectric layer, recording layer, and heat dissipation layer formed thereon.

On the other hand, the mass production technology of optical information recording media has a problem that the film forming conditions are made common to the substrate size. Currently used optical discs have substrate outer diameters of 2.5 inches, 3.5 inches, 5.25 inches, 1
There are various types such as 20 mm and 300 mm. Also, various substrate thicknesses of 1.2 mm, 0.8 mm, and 0.6 mm are being studied. These differences in substrate size cause differences in substrate deformation due to the film to be produced. Therefore, there are individual recording medium manufacturing conditions according to the substrate size, and it is not possible to manufacture recording media having different substrate sizes in the same manner, which deteriorates mass production efficiency. Further, an ultraviolet curable resin is generally used for the environmental protection film. However, since the UV-curable resin film is formed by a spin coater, it is of a leaf type, and a large number of spin coaters must be prepared when the amount changes. Therefore,
There were problems such as an increase in equipment cost and an increase in floor area. Further, since ultraviolet rays are irradiated to cure the resin, ozone is generated, and equipment for excluding the ozone is required. further,
At the time of spin coating, it was also necessary to collect the ultraviolet curable ray curable resin liquid scattered outside the substrate.

[0005]

In view of the above circumstances, an object of the present invention is optical information capable of high-density recording / erasing / reproduction repeatedly, having high reliability, and being excellent in mass production efficiency. To provide a recording medium.

[0006]

In order to solve the above problems, according to the present invention, a first protective layer, a protective layer, a second protective layer, a reflective heat layer and a third protective layer are sequentially laminated on a plastic substrate. In the optical information recording medium having the above-mentioned structure and capable of recording / erasing / reproducing information by irradiating a laser beam, in the first protective layer, the recording layer, the second protective layer, the reflection heat dissipation layer and the third protective layer, There is provided an optical information recording medium characterized in that the total stress S satisfies the following general formula.

[Equation 1] (However, θ: incident angle of a laser beam on a substrate that enables focus servo and / or tracking servo E: Young's modulus of substrate b: thickness of substrate l: (outer diameter of substrate-hole diameter of substrate) × 1 / 2 ν: Poisson's ratio of substrate) Further, according to the present invention, there is provided an optical information recording medium characterized in that the third protective layer has a tensile stress in the above-mentioned constitution. Further, according to the present invention, there is provided an optical information recording medium having the above-mentioned structure, wherein the third protective layer is manufactured by a dry process. In the above description, θ is a value required by the drive to enable focusing and tracking of the optical information recording medium, and it is uniquely determined by the drive although it varies slightly depending on the type of the drive.

The optical information recording medium of the present invention will be described in detail below. As shown in FIG. 1, the optical information recording medium of the present invention has a basic structure of a plastic substrate / first protective layer / recording layer / second protective layer / reflection heat dissipation layer / third protective layer. The total stress S, that is, the stress of the first protective layer (S
₁ p) + stress of recording layer (Sr) + stress of second protective layer (S ₂
p) + the stress of the reflective heat dissipation layer (Sm) + the deformation of the plastic substrate caused by the stress of the third protective layer (S ₃ p) enables focus servo and tracking servo when recording, reproducing and erasing optical information. It is adjusted to the range to be.

Generally, the stress Sf of a thin film is the internal stress (σ
It is given as the sum of the i) component and the thermal stress (σt) component (equation 3). Further, it is known that the stress Sf of the thin film and the substrate deformation amount δ shown in FIG. 2 have the relationship of Expression (4). Sf = (σi + σt) d (3) δ = {3 (1-ν) l ² / Eb ² } Sf (4) (where Sf: total stress of thin film σi: internal stress of thin film σt: thermal stress of thin film d : Thickness of the thin film δ: Deformation amount of the substrate ν: Poisson's ratio of the substrate l: Length of the substrate ((outer diameter of substrate-hole diameter of substrate) × 1 /
2) E: Young's modulus of the substrate b: Thickness of the substrate. ) Now, in FIG. 2, if the amount of deformation of the substrate is sufficiently small, it can be expressed as δ = l'sin θ = l sin θ (5). Therefore, the expression (4) becomes sin θ = {3 (1-ν) l / Eb ² } Sf (6). Here, Sf = S = S ₁ p + Sr + S ₂ p + Sm +
If the deformation limit that enables S ₃ p, focus servo, and tracking servo is ± θ, the following relational expression holds.

[Equation 2] Becomes The present invention is to adjust the total stress S so as to satisfy the expression (7).

The purpose of the third protective layer used in the present invention is to 1) balance the stress of the recording medium, 2) improve the passivation ability, and 3) form an environmental protective layer such as an ultraviolet curable resin by a dry process. It is possible to use it. For the purposes of 1) and 2), a film made of an ultraviolet curable resin may be provided on the third protective layer. For the purpose of 3), the environmental protection layer is not required and the third protection layer exhibits its function.

Generally, the optical recording medium is manufactured by the sputtering method. However, each layer of the conventional recording medium produced by the sputtering method, that is, the first protective layer / recording layer / second protective layer /
The stress acting on the reflection / heat dissipation layer is generally a compressive stress. Therefore, in order to balance the stress, it is effective that tensile stress acts on the third protective layer. The film having tensile stress can be produced by a sol-gel method or a plasma CVD method. The stress of the SiNx plasma CVD film or the SiON plasma CVD film can be relatively arbitrarily controlled from the compression type to the tension type depending on the manufacturing conditions. Also, the stress can be controlled by the thickness of these films as expressed by the equation (3).

The third protective layer formed to improve the passivation ability plays a role of supplementing the role of the ultraviolet curable resin film provided in the conventional recording medium for protecting it from the external environment. Optical information recording media are often protected against changes in the environment such as temperature, humidity, and illuminance with a film made of only an ultraviolet curable resin, which is not sufficient. For this purpose, it is desirable to use inorganic materials such as SiO ₂ , Si ₃ N ₄ . The passivation ability of SiO ₂ and Si ₃ N ₄ films is
Much better, for example, H ₂ O has a permeability of 1
It can be suppressed to about 1/00.

As described above, the conventional UV-curable resin film formation on a recording medium is a spin coating process for each leaf, and therefore the mass production efficiency is not sufficient. Moreover, problems such as generation of ozone and recovery of resin also occurred. Further, due to the improvement in recording density, the track pitch becomes smaller, and it is difficult to sufficiently cover the groove structure with the spin coat film. A method for producing the environmental protection layer by a dry process is effective for these measures. Among dry processes such as vacuum deposition, sputtering, photo CVD, plasma CVD, and low temperature CVD, film formation by plasma CVD is advantageous in terms of thickening the film and treating a large amount of a large area. In the dry process, it is also possible to continuously form the third protective layer while maintaining the vacuum after the film formation of the recording medium.

FIG. 3 shows a plasma CVD apparatus that can be used to form the third protective film of the recording medium of the present invention.
In this plasma CVD apparatus, an optical disk substrate is installed on a tray that can be revolved around its axis, the tray is provided with a tray moving mechanism that can move between front and rear film forming chambers, and an RF electrode is provided to enable film formation on both sides of the tray. There are two. Drying the production of the environmental protection layer does not require an environment with high cleanliness required for spin coating of the ultraviolet curable resin. Therefore, the degree of freedom in the layout of each film forming apparatus, the transfer line, etc. is increased, and the mass production factory can be efficiently used. In FIG. 3, 11 is an optical disc substrate, 12 is a substrate rotation unit, 13 and 13 'are Rf electrodes, 14 is a tray moving mechanism, 15 and 15' are matching circuits, 16 and 16 'are Rf power supplies, and 17 is a phase. It is a matcher. As described above, the third protective layer has various purposes, but in any case, the stress is adjusted so as to satisfy the expression (7).

The optical information recording medium of the present invention basically comprises, as shown in FIG. 1, a first protective layer 2, a recording layer 3, a second protective layer 4 and a reflected heat radiation on a plastic substrate 1 with a groove. Although the layer 5 / third protective layer 6 is provided and configured, an ultraviolet curable resin film may be further provided as an environmental protection layer on the third protective layer 6 as necessary.

Next, each layer of the optical information recording medium of the present invention will be described. Substrate materials are usually glass, ceramics,
Alternatively, it is a resin, and a resin substrate is preferable in terms of moldability and cost. Typical examples of the resin are polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin,
Examples thereof include acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin, and the like, but polycarbonate resin and acrylic resin are preferable in terms of processability and optical characteristics. . The shape of the substrate may be disk-shaped, card-shaped or sheet-shaped.

Materials for the protective layer include SiO and Si.
O ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In
₂ O ₃ , metal oxides such as MgO and ZrO ₂ , Si ₃ N ₄ ,
AlN, TiN, BN, nitrides such as ZrN, ZnS,
In ₂ S ₃ , TaS ₄ and other sulfides, SiC, TaC, B ₄
Examples thereof include carbides such as C, WC, TiC, and ZrC, diamond-like carbon, and mixtures thereof. Especially, the thermal conductivity of AlN, BN, SiC, C, etc. is 1 W / cm.
・ A protective layer of K or higher is suitable. It is extremely difficult to measure the thermal conductivity of a thin film of the order of μm or less, particularly an insulating thin film itself used for a protective layer. Therefore, the thermal conductivity described in this specification is a value measured by the vertical direction direct method or the laser flash method, with the parc state of the same substance being measured. Further, the protective layer may contain impurities as necessary. However, the melting point of the protective layer needs to be higher than the melting point of the recording layer. Further, the protective layer may be multi-layered if necessary. Such a protective layer can be formed by various vapor deposition methods such as a vacuum vapor deposition method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method and an electron beam vapor deposition method. The thickness of the protective layer is 100 to 5000 Å, preferably 200 to 3000 Å. 200 protective layer
When the thickness is less than Å, the substrate is thermally damaged, and when the thickness is more than 5000 Å, the sensitivity is lowered and the interfacial peeling is likely to occur.

As the recording layer, GeSbTe, AgIn
A phase change material represented by SbTe can be used.
Further, the present invention is not limited to the phase change type optical information recording medium,
Although it can be applied to magneto-optical recording media such as TbCo,
The phase change type optical information recording medium using the AgInSbTe recording film has excellent characteristics such as sensitivity and erasing characteristics and is particularly effective. Above all, an information recording medium in which AgSbTe ₂ having a stoichiometric composition in the erased and initialized state is present in the recording layer is effective. It is AgSbT
Since e ₂ has a cubic crystal structure that is an isotropic crystal structure,
This is because, for example, when the amorphous phase is rapidly cooled from a high temperature by a laser beam and becomes an amorphous phase (transition to recording-metastable state), a uniform phase change occurs at a high speed, and the amorphous phase has little physical or chemical variation. . It is difficult to analyze the fine structure of this amorphous phase, and the details are unknown. For example, the stoichiometric composition of the amorphous phase or a combination of AgSbTe ₂ and the amorphous phase InSb close to it, or a completely different single amorphous phase, etc. It is thought that it has become. The composition of AgInSbTe is determined by fluorescent X-rays, ICP and the like. Fluorescence X in the description
It uses the values obtained from the line.

The recording layer of the present invention may be formed by various vapor deposition methods such as vacuum vapor deposition, sputtering, plasma CVD,
It can be formed by a photo CVD method, an ion plating method, an electron beam evaporation method, or the like. In addition to the vapor phase growth method, a wet process such as a sol-gel method can also be used. The film thickness of the recording layer is 100 to 10000Å, preferably 200 to
It is good to set it to 3000Å. When the thickness is less than 100Å, the light absorption ability is remarkably lowered and the recording layer cannot serve as a recording layer. If it is thicker than 10000Å, uniform phase change at high speed is difficult to occur.

For the reflection / heat dissipation layer, a metal material such as Al, Au, Ag, or an alloy thereof can be used. The reflection / heat dissipation layer is not always necessary, but it is desirable to provide it in order to release excess heat and reduce the heat load on the recording medium itself. Such a reflective heat dissipation layer may be formed by various vapor deposition methods such as vacuum deposition method, sputtering method, plasma CVD method, photo CVD method, ion plating method,
It can be formed by an electron beam evaporation method or the like.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples. However, these examples do not limit the present invention.

Example 1 120 mmφ, 0.6 mm thickness, Young's modulus 200 kgf /
mm ^2, Poisson's ratio of 0.3, a groove with polycarbonate substrate length 52.5mm substrate, 2000 Å thickness Z
_{nS · SiO 2 (75:25),} Ag 0. 10 In 0. 15 S
_{d 0. 46 Te 0. 29} (380Å), AlN (300Å), A
g (700Å) was laminated by a sputtering method. At this stage, the substrate had a compressive stress having a convex film surface. Then, as the third protective layer, a SiNx film was formed by the plasma CVD method using the apparatus of FIG. The conditions for producing this SiNx film are as follows: discharge frequency 13.56 MHz, power 0.3 W
/ Cm ² , and the pressure was 0.1 torr (SiH ₄ + NH ₃ ). Next, an ultraviolet curable resin was formed as an environmental protection layer on the SiNx film to obtain an optical disk according to the present invention. The total stress of the optical disc thus manufactured was 10 Pa · m. The incident angle of the laser beam on the optical disk is 0.
Since it was 1 degree, in the case of this medium configuration, the total stress S is −
Servo is possible in the range of 32 Pa · m to +32 Pa · m, but the optical disk of this embodiment satisfies this condition. In addition, NA0.
6, a linear velocity of 1.
2 m / s, recording frequency 720 KHz, 200 KHz (5
Overwriting was performed at 0% duty. As a result, a C / N of 52 dB and an erasing ratio of -35 dB were obtained.

Example 2 5 1/4 inch, 0.6 mm thickness, Young's modulus 200 kgf /
mm ^2, Poisson's ratio of 0.3, a groove with polycarbonate substrate length 57.5mm substrate, 1500 Å thickness Z
_{nS · SiO 2 (80:20),} Ag 0. 10 In 0. 15 S
_{d 0. 46 Te 0. 29} (250Å), AlN (350Å), A
g (800 Å) and SiO ₂ (700 Å) were laminated by a sputtering method. Next, an ultraviolet curable resin was formed on SiO ₂ as an environmental protection layer to obtain an optical disk according to the present invention. The total stress of this optical disk was −20 Pa · m. In the case of this medium structure, the total stress of the medium that enables the laser beam servo is −30 Pa · m to +30 Pa · m.
However, the total stress of the optical disk of this example satisfies this condition. At that time, the incident angle of the laser beam on the optical disk was 0.2 degree. For the optical disc manufactured in this manner, NA 0.6,
Using a pickup with a wavelength of 780 nm, a linear velocity of 1.2 m
/ S, recording frequency 720 KHz, 200 KHz (50%
Duty) was used for overwriting. As a result, 5
A C / N of 0 dB and an erase ratio of -35 dB were obtained. In addition, this optical disk was exposed to 100 ppm H ₂ S atmosphere at 50
Corrosion of Ag did not occur even after standing for 0 hour, and the same recording characteristics as in the initial stage were obtained.

Example 3 5 1/4 inch, 0.6 mm thickness, Young's modulus 200 kgf /
mm ^2, Poisson's ratio of 0.3, a groove with polycarbonate substrate length 57.5mm substrate, 1500 Å thickness Z
_{nS · SiO 2 (85:15) /} Ag 0. 10 In 0. 15 S
_{b 0. 46 Te 0. 29} (200Å) / SiNx (300Å) /
Al (700Å) was laminated by a sputtering method. Next, as the third protective layer, a carbon film having a thickness of 1.0 μm was formed by the plasma CVD apparatus shown in FIG. 3 to obtain an optical disc according to the present invention. The manufacturing conditions of the third protective layer were as follows. Discharge frequency 13.56 MHz Electric power 0.2 W / cm ² Pressure 0.1 torr (CH ₄ ) However, before forming the third protective layer, the Al surface was treated with H ₂ plasma. It was found from FTIR absorption that the third protective layer contained C and H as main components and contained H at 35 atom%. Since the third protective layer contains a large amount of hydrogen as compared with the normal hard carbon film, the internal stress was small at -10 MPa. The theoretical value of the total stress of the medium that enables the servo of this optical disk is -30 Pa · m ~
Although it was +30 Pa · m, the total stress of the optical disk of this example was −25 Pa · m, which satisfied the above condition. The incident angle of the laser beam on the optical disk was 0.2 degree. When the optical disc manufactured in this manner was overwritten at a linear velocity of 7 m / s using a pickup having a NA of 0.6 and a wavelength of 780 nm, a C / N of 52 dB and an erasing ratio of -35 dB were obtained. Was given. In this optical disc, since the third protective layer also serves as the environmental protection layer, the process of forming the ultraviolet curable resin can be omitted, so that the mass production efficiency can be improved.

Example 4 In Example 3, the third protective layer (also serves as an environmental protection layer)
As an example, an optical disk was prepared in the same manner except that a plasma CVD film using tetraethoxysilane Si (O—C ₂ H ₅ ) ₄ and O ₂ as starting materials was used. FTIR has revealed that the plasma CVD film of tetraethoxysilane mainly contains Si and O and partially contains Si—H, Si—OC ₂ H ₅ and Si—OH. By leaving these decomposed residues in the film, the internal stress of the film decreased and the total stress became −15 Pa · m. Therefore, this optical disk was a focus servo and a tracking servo. When the optical disk thus manufactured was evaluated in the same manner as in Example 3, the C / N of 50 dB and the value of −35 dB were obtained.
The erase ratio of was obtained. Since this optical disk can be continuously formed into a film by a dry process, it is possible to improve mass production efficiency.

[0025]

According to the present invention, since the deformation of the substrate due to the thinning of the plastic substrate can be avoided by the balance of the film stress, high density recording can be realized. Also,
By forming the stress-controlled third protective layer, moisture resistance, gas resistance and the like are improved. Further, a third protective layer which replaces the UV-curable resin film as prepared by a dry process, the improvement of production efficiency, effective use of clean room, O ₃
The advantage of avoiding generation is obtained.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a layer structure of an optical information recording medium according to the present invention.

FIG. 2 is an explanatory diagram of substrate deformation.

FIG. 3 is a diagram showing an example of an apparatus for producing a third protective layer.

[Explanation of symbols]

 1 Plastic Substrate 2 First Protective Layer 3 Recording Layer 4 Second Protective Layer 5 Heat Dissipation Reflective Layer 6 Third Protective Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masato Haritani 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Company (72) Inventor Osamu Nonoyama 1-3-6 Nakamagome, Ota-ku, Tokyo Shares Inside the Ricoh Company (72) Inventor Masaetsu Takahashi 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Company Ltd. (72) Inventor Koji Deguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Company ( 72) Inventor Hiroko Iwasaki 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A structure in which a first protective layer, a recording layer, a second protective layer, a reflective heat dissipation layer and a third protective layer are sequentially laminated on a plastic substrate, and information is recorded / erased / irradiated by laser beam irradiation. In an optical information recording medium that enables reproduction,
First protective layer, recording layer, second protective layer, reflective heat dissipation layer and third
An optical information recording medium, wherein the total stress S of the protective layer satisfies the following general formula. [Equation 1] (However, θ: incident angle of a laser beam on a substrate that enables focus servo and / or tracking servo E: Young's modulus of substrate b: thickness of substrate l: (outer diameter of substrate-hole diameter of substrate) × 1 / 2ν: Poisson's ratio of the substrate) 2. The optical information recording medium according to claim 1, wherein the third protective layer has a tensile stress. 3. The optical information recording medium according to claim 1, wherein the third protective layer is manufactured by a dry process.