JPH09265665A - Phase change optical disk and method of manufacturing the same - Google Patents

Abstract

(57) [PROBLEMS] To provide a phase-change type optical disc with very few errors even if it is rewritten many times. SOLUTION: A dielectric layer 2, a recording layer 3, a dielectric layer 4, a reflective layer 5, a protective film 6 or a bonded substrate 7 are sequentially laminated on a transparent substrate 1, and a film thickness of the dielectric layer 4 is formed. In the disk in which t ₂ is smaller than the film thickness t ₁ of the dielectric layer 2, the reflective layer 5 is composed of reflective layers 51 and 52 made of the same material,
The film thickness t ₃ of the reflective layer 51 is smaller than the film thickness t ₄ of the reflective layer 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type optical disk capable of optically recording and reproducing information.

[0002]

2. Description of the Related Art FIG. 6 is a diagram for explaining the structure of a conventional phase change optical disk. The phase change type optical disc A is
As shown in FIG. 6, a first dielectric layer 2, a phase change recording layer 3, a second dielectric layer 4, a reflective layer 5, and a protective film 6 are sequentially laminated on a transparent substrate 1. It is an optical disc having a configuration. In the figure, an arrow a indicates the incident direction of the laser light with which the optical disc A is irradiated.

The above-mentioned recording layer 3 is made of Te (tellurium) or Se.
The recording layer is mainly composed of chalcogen such as (selenium). The first and second dielectric layers 2 and 4 sandwich the recording layer 3 from both sides. The reflective layer 5 and the protective film 6 are provided opposite to the laser light incident direction a.

Information is recorded, reproduced, and rewritten using the phase change type optical disc A having the above-described structure as follows.

(Recording of information) Laser light is locally irradiated onto the optical disk A whose initialization is initialized to a crystalline state with a high reflectivity on the entire surface of the disk, and the recording film on the recording layer 3 is melted and rapidly cooled to be in an amorphous state. Change the phase. With this phase change, the complex refractive index of the recording film changes, and information is recorded.

(Reproduction of information) In reproduction, a laser beam whose power is weaker than that at the time of recording of the above-mentioned information is locally applied to the optical disc A, and a crystal film and an amorphous film in the recording film on the recording layer 3 are formed. This is performed by detecting the reflectance difference or the phase difference.

(Information Rewriting) In rewriting (overwriting), laser light having a recording peak power superimposed on a low energy bias power that causes crystallization of crystals in the recording film on the recording layer 3 is recorded on the optical disc A. By irradiating the recording layer 3 locally, the recording mark already recorded is overwritten without passing through the erasing process. At the time of overwriting, the recording film is heated to a high temperature, melted and rapidly cooled, and a new recording mark is written.

By the way, Ge is recorded on the recording layer 3 of the optical disk A.
When rewriting information using SbTe phase change material, 60
Expansion due to melting of the recording layer 3 due to being heated to 0 ° C. or higher,
As a result, the dielectric layers 2 and 4 and the reflective layer 5 are deformed, the mass transfer of the recording film and the like occur, and there is a problem that the error rapidly increases when rewriting is performed many times.

In order to suppress such damage due to heat and improve the number of times of rewriting, the thickness of the second dielectric layer 4 is smaller than that of the first dielectric layer 2, and more specifically, 20 nm
It is known that it is effective to make the structure as thin as possible and to use a quenching structure in which the cooling rate is stopped.

In addition to the above, the following optical discs (1) and (2) have been proposed in order to prevent damage to the recording layer due to heat due to overwriting and improve the number of times of rewriting.

(1) An optical disk having a structure in which a dielectric layer is further provided on a reflective layer (for example, Japanese Patent Application Laid-Open No. 3-41636).
"Optical information medium" described in Japanese Patent No.

(2) An optical disk whose mechanical strength is improved by providing a metal having a high Young's modulus and a low thermal conductivity on the reflective layer (for example, "optical recording medium" described in JP-A-5-325256). .

[0013]

As described above, in order to suppress the damage of the recording layer 3 due to the heat due to the overwriting of the phase change optical disk A and to improve the number of times of rewriting, the above-mentioned (1) and (2) are described. Although the optical disc of was proposed, there were the following problems.

(A) The optical disc of (1) above is
The adhesion between the reflective layer made of metal and the overcoat layer made of a dielectric is small, and the dielectric is apt to crack, resulting in poor reliability. Further, in order to form the dielectric film, it is necessary to newly introduce a reactive gas or change the power source for sputtering, and there is a problem that the manufacturing apparatus needs to be modified.

(B) In the above optical disc of (2), since two different metal reflection layers are provided, there is a problem in adhesion, and there is a problem that the range of selection of materials is narrowed.

(C) Further, according to the experiments conducted by the present inventors, the number of times of rewriting is improved by simply providing the dielectric layer 4 or the reinforcing layer (not shown) on the reflective layer 5 of the phase-change optical disk A. I couldn't do it. Further, in the manufacturing process of the phase change optical disc A, the second dielectric layer 4
It was also found that the film formation rate of the reflective layer 5 greatly influences the number of overwrite repetitions, and the repetition performance is improved as the film formation rate is decreased. However, when the film formation speed of the entire reflective layer 5 is slowed to increase the film formation, the increase in jitter is suppressed, but this has a problem that the manufacturing time is long and the productivity is poor.

[0017]

In order to solve the above problems, the present invention provides a phase change type optical disk having the following configurations (1) to (4) and a method for manufacturing the same.

(1) As shown in FIG. 1, it is a phase change type optical disk capable of optically recording and reproducing, and a first dielectric layer 2 and a phase change type recording layer 3 are formed on a transparent substrate 1. And the second dielectric layer 4, the reflective layer 5, the protective film 6 or the bonded substrate 7 are sequentially laminated, and the film thickness t _{2 of} the second dielectric layer 4 is
Is smaller than the film thickness t _{1 of} the first dielectric layer 2 (t ₂ <
In the phase change type optical disc of t ₁ ), the reflective layer 5 is made of the same material as the first and second reflective layers 51, 52.
And the thickness t ₃ of the first reflective layer 51 is smaller than the thickness t _{4 of} the second reflective layer 52 (t ₃ <t ₄ ).
A phase change optical disc B characterized by the above.

(2) Phase change type optical disc B shown in FIG.
A method of manufacturing a phase change type optical disc, wherein the first dielectric layer 2 and the phase change type recording layer 3 are sequentially laminated on the transparent substrate 1, and then the phase change type The film formation rate of the second dielectric layer 4 laminated on the mold recording layer 3 is set lower than the film formation rate of the first dielectric layer 2, and the film thickness of the second dielectric layer 4 is set. the t ₂ as a small (t ₂ <t ₁₎ than the thickness t ₁ of the first dielectric layer 2, to form the second dielectric layer 4, then, the second dielectric layer 4 has a thickness t ₃ of the first reflective layer 51 laminated on ₄ smaller than the thickness t _{4 of} the second reflective layer 52 (t ₃ <t ₄ ), and The film forming rate is set lower than the film forming rate of the second reflective layer 52, and the first and second reflective layers 5 are formed.
1. A method for manufacturing a phase change optical disc, which comprises forming 1, 52.

(3) The first and second reflective layers 51,
In forming 52, the first and second reflective layers 5
The method for producing a phase change type optical disk according to (2) above, wherein the cathodes of 1,52 are separately formed by using a DC sputtering method.

(4) The first and second reflective layers 51,
In forming 52, the first and second reflective layers 5
The method of manufacturing a phase change type optical disk according to the above (2), wherein the cathodes of 1,52 are made the same and are formed by a DC sputtering method.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a phase change type optical disk of the present invention and a method for manufacturing the same will be described with reference to FIGS. FIG. 1 is a diagram for explaining a configuration of an embodiment of a phase change type optical disc of the present invention, FIG. 2 is a diagram for explaining rewriting evaluation of the phase change type optical disc of the present invention, FIG. 3, FIG. 4, FIG. FIG. 3 is a diagram for comparing rewriting evaluations of phase change optical disks. The same components as those described above are designated by the same reference numerals.

As shown in FIG. 1, the phase-change optical disk B of the present invention comprises a first dielectric layer 2, a phase-change recording layer 3, a second dielectric layer 4, and a first dielectric layer 2 on a transparent substrate 1. Reflective layer 5, protective film 6
Alternatively, it is an optical disc having a structure in which the bonded substrates 7 are sequentially laminated. The reflective layer 5 is the first and second reflective layers 5
1, 52. In the figure, an arrow a indicates the incident direction of the laser light with which the optical disc B is irradiated.

The above-mentioned substrate 1 is a translucent substrate capable of transmitting laser light for recording and reproduction, and is provided with pregrooves and prepits for guiding the laser light (neither is shown), such as polycarbonate, polyolefin, and acrylic. A plastic substrate or a glass substrate is used. The pre-grooves and pre-pits for guiding the laser light are directly injection-molded or formed on the smooth substrate by the 2P method (photopolymer method).

The substrate 1 is a CAV (constant angul).
ar velocity and CLV (constant linear)
velocity or ZCAV (zone constan)
t angular velocity) and ZCLV (zone constant line)
ar velocity) format, and an address signal is recorded in advance as an emboss pit at the beginning of each sector. The information area used by the user is composed of empty grooves, and when recording on the land and the groove, the widths of the land and the groove should be almost equal so that the reproduction signals of the land and the groove are equal. Has been formed.

The substrate 1 having such a structure is installed in a vacuum film forming apparatus (not shown), and the first dielectric layer 2, the phase change recording layer 3, the second dielectric layer 4 and the first reflection layer are provided. 51 and the second reflective layer 52 are sequentially laminated. As a film forming method, resistance heating type or electron beam type vacuum deposition, direct current or alternating current sputtering, reactive sputtering, ion beam sputtering, ion plating, or the like is used.

The above-mentioned first and second dielectric layers 2 and 4
For, metal oxides, nitrides, and sulfides are used. For ^{example, ZnS-SiO 2, ZnS,} SiO 2, Ta
² O ⁵ , Si ³ N ⁴ , AlN, Al ² O ³ , AlSiO
A single substance such as N, ZrO ² or TiO ² or a mixture thereof is used.

The thickness t ₁ of the first dielectric layer 2 is 10 to 20.
It is in the range of 0 nm. The optimum film thickness varies depending on the wavelength of the light source used, but it is preferably 80 to 150 nm in order to increase the reproduction signal. Moreover,
In order to reduce the influence of heat conduction on the substrate, it is preferable that the thickness be 80 nm or more.

The above-mentioned recording layer 3 is made of a phase change material which utilizes a change in reflectance or a change in refractive index between amorphous and crystalline. Ge-Sb-Te system, Ag-In-T
Examples thereof include e-Sb system. The film thickness t ₅ of the recording layer 3 is 1
0 to 100 nm, preferably 20 to 60 nm in order to increase the reproduction signal.

The same material as that of the first dielectric layer 2 is used for the second dielectric layer 4 described above. The film thickness t ₂ of the _second dielectric layer 4 is thinner than that of the first dielectric layer 2 and has a so-called quenching structure, and the film thickness is 2 to 5 in order to reduce thermal damage.
The thickness is preferably set to 0 nm. The film forming rate of the second dielectric layer 4 is slower than the film forming rate of the first dielectric layer 2 (second
Film formation rate of the dielectric layer 4) / (film formation rate of the first dielectric layer 2) is 0.05 to 0.75, preferably 0.1 to
0.5 is good). By doing this, by rewriting,
The increase in jitter is suppressed and the number of rewrites is extended.

The reflective layer 5 is composed of a first reflective layer 51 and a second reflective layer 52 which are made of the same material. As described later, the film thickness t ₃ of the first reflective layer 51 is formed thinner than the film thickness t ₄ of the second reflective layer 52. The film formation rate of the first reflective layer is slower than the film formation rate of the second reflective layer. This suppresses an increase in jitter due to rewriting and extends the number of times of rewriting.

The reflective layer 5 is made of Al, Au, Ag, Cu, N.
Metals such as i, In, Ti, Cr and Pt, or alloys or semiconductors thereof are used. The thickness t ₃ of the first reflective layer 51 is 5 to 30 nm, and the thickness t ₄ of the second reflective layer 52 is
The thickness is preferably 30 to 150 nm. The reflection layer 5 may be, for example, one cathode, which is used to sequentially stack the first reflection layer 51 and the second reflection layer 52 in the same vacuum chamber, or two cathodes may be used to form the first reflection layer in different vacuum chambers. Reflective layer 51 and second
The reflective layers 52 are sequentially laminated.

For example, the substrates 1 are conveyed one by one, and each layer 2
Using a single-wafer sputtering apparatus for depositing 5 to 5 in a plurality of vacuum chambers, the total thickness (t ₃ + t ₄ ) of the reflective layer 5 is 150 nm.
In the case of forming, the first reflective layer 51 is formed in one vacuum chamber at a film forming rate of 2 nm / s, and the second reflective layer 52 is formed in another vacuum chamber at a film forming rate of 13 nm / s. The disks B can be successively formed in a short time of 10 seconds.

The above-mentioned protective film 6 is formed by taking out the formed disk into the atmosphere and applying an ultraviolet curable resin on the reflective layer 5. The film thickness is 1 to 20 microns. As a coating method, a spin coating method, a spraying method, a dipping method, a blade coating method, a roll coating method, a screen printing method or the like is used. The ultraviolet curable resin comprises at least a prepolymer, a monofunctional acrylate monomer, a polyfunctional acrylate monomer and the like and a photopolymerization initiator. If necessary, a transparent substrate may be attached or a substrate provided with a recording layer may be attached to form a double-sided optical disc.

The optical disk B thus manufactured is irradiated with a laser beam, a flash lamp or the like to heat the phase-change recording layer 3 to a temperature above the crystallization temperature for initialization. Practically, the laser beam with which the optical disc B is irradiated has a beam diameter larger than the track width, and is preferably long in the radial direction, and simultaneously initializes a plurality of tracks while rotating the disc.

Next, a method of manufacturing the phase change type optical disc B having the above-mentioned structure will be described.

<Example 1> A polycarbonate substrate 1 provided with a pregroove having a track pitch of 1.6 µm and a groove depth of 60 nm is provided with a first dielectric layer 2, a phase change recording layer 3 and a second dielectric layer 2.
A phase change optical disc B having the dielectric layer 4 formed by sputtering is manufactured.

First, after evacuating to a degree of vacuum of 1 × 10 -6 Torr or less, ZnS-SiO 2 (80:20 mol%) was added to Ar.
The first dielectric layer 2 was provided with a thickness of 90 nm by high-frequency sputtering with gas. The Ar gas pressure is 2 mtorr and the film formation rate is 0.25 nm / s.

Then, as a phase change recording layer 3, Ge22Sb is used.
22Te56 was formed to a thickness of 20 nm by a DC sputtering method.

ZnS-SiO2 (80:20 mol%) was deposited as a second dielectric layer 4 on the phase-change recording layer 3 in a thickness of 18 nm by a high frequency sputtering method. Ar gas pressure is
2 mtorr, film formation rate is 0.05 nm / s.

Next, a reflective layer having a thickness of 150 nm was formed as a whole. First, Al—Cr (97.
5: 2.5 at%) 20 nm by DC sputtering method
Provided. The film formation rate is 0.1 nm / s. Then, using the same cathode, a second reflective layer 52 having a thickness of 130 nm was formed. The film forming rate at this time was 0.25 nm / s.

After removing the disk from the vacuum chamber, an ultraviolet curable resin (XR manufactured by Sumitomo Chemical Co., Ltd.) was used as the protective layer 6.
The film thickness of the protective film obtained by spin coating 11) on the second reflective layer 52 and irradiating it with ultraviolet rays to cure was 8 μm.

Thus, the first dielectric layer 2, the phase change recording layer 3 and the second dielectric layer 4 are formed by sputtering on the polycarbonate substrate 1 having the pregrooves having the track pitch of 1.6 μm and the groove depth of 60 nm. It was possible to manufacture the phase change type optical disc B.

Next, the disk B thus manufactured will be evaluated.

First, while rotating the disk B, laser light was emitted from the substrate 1 side to initialize the phase change recording layer 3 from an amorphous state to a crystalline state with high reflectance.

Next, recording was performed from the substrate 1 side to the land portion between the guide grooves of the phase change recording layer 3. The land has a concave shape when viewed from the incident direction a of the laser light. The recording conditions are
It is as follows. The linear velocity is 6.2 m / s, the recording laser wavelength is 684 nm, the NA of the objective lens is 0.6, the peak power is 10.5 mW, and the bias power is 4.0 mW. 8-17
The modulated signal was recorded, and the jitter, which is a value obtained by dividing the standard deviation σ by the window width Tw, was measured with respect to the number of times of rewriting.

The jitter after rewriting 100,000 times is 10.3% as shown in FIG. When the jitter after rewriting 100,000 times becomes 12% or more, it is counted as an error. Therefore, the disc manufactured under this condition shows sufficiently low jitter even after rewriting many times,
It can be said that it has excellent reliability. 2 to 5, the first dielectric layer 2 is the "first dielectric layer", the second dielectric layer 4 is the "second dielectric layer", and the first reflective layer 51 is the "first reflective layer". ",
And the 2nd reflective layer 52 is each displayed with the "2nd reflective layer."

Comparative Example 1 The film formation rate of the second dielectric layer 4 was made the same as that of the first dielectric layer, and the reflection layer 5 was set to 1
A disk having a layer (thickness: 150 nm) was made of the same material and thickness as in Example 1. The jitter after rewriting 100,000 times was measured.

The jitter after rewriting 100,000 times is 18.1% as shown in FIG. Although the material and the film thickness are the same as those in the first embodiment, the increase of jitter is remarkable and the rewriting performance is poor.

<Comparative Example 2> A disk in which the film formation rate of the second dielectric layer 4 was made the same as that of the first dielectric layer 2 and the reflective layer 5 was one layer (film thickness 150 nm) was prepared. The same material and film thickness as in Example 1 were used. The jitter after rewriting 100,000 times was measured.

The jitter after rewriting 100,000 times is 12.2% as shown in FIG. Although the material and the film thickness are the same as those in the first embodiment, the increase of jitter is remarkable and the rewriting performance is poor. In addition, the film formation time of the reflective layer 5 is 2.1 times as long as that in Example 1.

<Comparative Example 3> The film formation rate of the second dielectric layer 4 is set lower than that of the first dielectric layer 2, and the reflection layer 5 is formed.
A disc having one layer (thickness 150 nm) was manufactured with the same material and thickness as in Example 1. The jitter after rewriting 100,000 times was measured.

The jitter after rewriting 100,000 times is 15.9% as shown in FIG. Although the material and the film thickness are the same as those in the first embodiment, the increase of jitter is remarkable and the rewriting performance is poor.

As described above, the jitter (10.3%) after rewriting 100,000 times using the phase change type optical disk B according to the first embodiment of the present invention is as follows. Jitter (18.1%, 12.2%) after rewriting 100,000 times using any of the phase change type optical discs
%, 15.9%).

[0055]

According to the present invention having the above-mentioned structure, the following effects can be obtained. (1) Rewriting performance can be improved using conventional materials and devices. (2) Control of the film formation rate and dividing the reflective layer into two layers are sufficient, and this can be easily realized. (3) The manufacturing time is short and the productivity is excellent.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a configuration of an embodiment of a phase change optical disc of the present invention.

FIG. 2 is a diagram for explaining rewriting evaluation of the phase change type optical disc of the present invention.

FIG. 3 is a diagram for comparing rewrite evaluations of phase change optical disks.

FIG. 4 is a diagram for comparing rewriting evaluations of phase change optical disks.

FIG. 5 is a diagram for comparing rewrite evaluations of phase change optical disks.

FIG. 6 is a diagram for explaining the configuration of a conventional phase change optical disc.

[Explanation of symbols]

1 Translucent Substrate 2 First Dielectric Layer 3 Phase Change Recording Layer 4 Second Dielectric Layer 5 Reflective Layer 51, 52 First and Second Reflective Layer 6 Protective Film 7 Bonded Substrate A, B Phase Changeable optical discs t ₁ , t ₂ , t ₃ , t ₄ film thickness

Claims (4)

[Claims] 1. A phase change type optical disk capable of optical recording and reproduction, wherein a first dielectric layer, a phase change type recording layer, a second dielectric layer and a reflective layer are formed on a transparent substrate. In a phase-change type optical disc in which a protective film or a bonded substrate is sequentially laminated, and the film thickness of the second dielectric layer is smaller than the film thickness of the first dielectric layer, the reflective layer is made of the same material. A phase change type optical disc comprising a first and a second reflective layer, wherein the first reflective layer has a thickness smaller than that of the second reflective layer. 2. A method of manufacturing a phase-change optical disk according to claim 1, wherein the first dielectric layer and the phase-change recording layer are provided on the transparent substrate. Are sequentially laminated, and then the film formation rate of the second dielectric layer laminated on the phase-change recording layer is set lower than the film formation rate of the first dielectric layer, and the second dielectric layer is formed. The second dielectric layer is formed by making the thickness of the dielectric layer smaller than that of the first dielectric layer, and then the second dielectric layer is laminated on the second dielectric layer. The film thickness of the first reflective layer is smaller than that of the second reflective layer, and the film formation rate of the first reflective layer is smaller than that of the second reflective layer. 1. A method for manufacturing a phase change type optical disc, which comprises forming first and second reflection layers. 3. When forming the first and second reflective layers, the cathodes of the first and second reflective layers are separated from each other by D
The method for producing a phase change optical disk according to claim 2, wherein the method is a C-sputtering method. 4. When forming the first and second reflective layers, the cathodes of the first and second reflective layers are made the same and are formed by a DC sputtering method. A method for manufacturing the phase change type optical disc according to [4].