JPH10340489A - Phase transition type optical disk and production of phase transition type optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the volume changes when a recording layer is heated for overwriting and to prevent exothermic reaction accompanied by crystallization of the recording layer, by forming the recording layer by sputtering a target comprising Ge, Sb and Te in a mixture atmosphere of Ar gas, nitrogen gas and oxygen gas. SOLUTION: A substrate 1 is set in a vacuum film forming device, and a first dielectric layer 2, a phase transition type recording layer 3, a second dielectric layer 4 and a reflection layer 5 are successively formed. The recording layer 3 is formed by sputtering a target comprising Ge-Sb-Te in an atmosphere of Ar and a mixture gas of nitrogen and oxygen. The proportion of the pressure of the mixture gas to the Ar gas is 0.3 to 5%. Thereby, decrease in the reproducing amplitude due to the movement of substances which constitute the recording layer 3 during repeated rewriting can be suppressed, and rewriting performances can be improved when a conventional material and device are used.

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, reproducing, and erasing information, and a method of manufacturing the phase change type optical disk.

[0002]

2. Description of the Related Art A phase change type optical disk has a recording layer mainly composed of chalcogen such as Te, Se, etc., a first dielectric layer and a second dielectric layer sandwiching the recording layer from both sides, and a laser beam. And a protective layer provided on the opposite side of the light incident side.

A laser beam is locally applied to an optical disk whose entire surface has been brought into a crystalline state with high reflectivity by initialization, so that the recording layer is melted and quenched to change its phase to an amorphous state. The complex refractive index of the recording layer changes with the phase change to record information. The reproduction is performed by irradiating a weak laser beam to detect a reflectance difference or a phase difference between a crystalline state and an amorphous state in the recording layer. Rewriting is performed by irradiating a laser beam with a recording peak power that is superimposed on a bias power with a low energy enough to cause crystallization of the amorphous recording layer. Rewrite (overwrite).

At the time of this overwriting, the recording layer is heated to a high temperature, melted, rapidly cooled, and a new recording mark is written. When a Ge-Sb-Te (germanium-antimony-tellurium) phase change material is used for the recording layer, 6
Since the recording layer is heated to at least 00 ° C., expansion due to melting of the recording layer, deformation of the dielectric layer and the reflective layer, mass transfer of the recording layer, and the like occur. There was a problem.

In order to solve this problem, the following methods (1) and (2) have conventionally been used. (1) A first protective layer (first dielectric layer), GeTe, Sb2Te3, and Sb are formed on a substrate to suppress a mass transfer phenomenon in which a recording layer material pulsates and moves along a guide groove.
A recording layer made of a material containing nitrogen in a mixture of the following, a second protective layer (a second dielectric layer), and a reflective layer, wherein the second dielectric layer is a first dielectric layer There has been an optical recording medium which is thinner and has a thickness of 30 nm or less.
No. 9). (2) It has a recording layer made of a material containing nitrogen in a ternary eutectic composition of Ge, Sb, and Te, has a good repetition life of recording and erasing, has a high crystallization temperature, and can perform high-speed erasing. There has been an optical information recording medium (for example, see JP-A-06-1712).
No. 34).

[0006]

However, in the above-mentioned method (1), information is recorded and erased by utilizing a change in reflectance accompanying a phase change between amorphous and crystal. Since the arrangement of atoms changes over a long distance, there is a problem that the volume change is large, and if a phase change is repeatedly generated, the recording layer material moves and the signal quality deteriorates. In the method (2) described above, crystallization is observed by thermal analysis of a recording material in which nitrogen is contained in a ternary system of Ge, Sb, and Te. In other words, in the ternary recording material of nitrogen-containing Ge, Sb, and Te, information is recorded and erased by using a reflectance change accompanying a phase change between an amorphous phase and a crystal phase. Therefore, the volume change is large, and if the phase change is repeatedly generated, the material of the recording layer moves, and the signal quality is degraded. In addition, there is a problem that the crystallization temperature rises remarkably and the recording sensitivity is greatly reduced, so that a high-output laser is required. According to the present invention, even if the recording layer is heated during overwriting, the arrangement of atoms does not change over a long distance, so that the volume change can be reduced and the exothermic reaction accompanying the crystallization of the recording layer at this time. It is an object of the present invention to provide a phase change type optical disk having a recording layer in which no crack occurs and a method for manufacturing the phase change type optical disk.

[0007]

In order to solve the above-mentioned problems, the present invention provides a phase change type optical disk having the following constitutions (1) to (4) and a method of manufacturing the phase change type optical disk.

(1) As shown in FIG.
Is a method of manufacturing a phase-change optical disc A in which a recording layer 3 made of Ge, Sb, and Te whose reflectivity changes reversibly due to irradiation of atoms is formed on the substrate 1, wherein argon gas is used. On the other hand, the recording layer 3 is formed on the substrate 1 by sputtering a target composed of Ge, Sb, and Te in an atmosphere in which at least a mixed gas of nitrogen gas and oxygen gas is mixed. A method for manufacturing a changeable optical disk.

(2) The method for manufacturing a phase-change optical disk according to (1), wherein the mixed gas is air.

(3) The phase according to (1) or (2), wherein the gas pressure of the mixed gas or the air is in the range of 0.3% to 5% of the gas pressure of the argon gas. A method for manufacturing a changeable optical disk.

(4) A phase-change optical disk having a recording layer made of Ge, Sb, and Te and containing at least Ge oxide and Sb oxide.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A phase change optical disk and a method of manufacturing a phase change optical disk according to the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. FIG. 1 is a diagram for explaining the configuration of an embodiment of a phase change optical disc according to the present invention, and FIG. 2 illustrates that rewriting is performed 100,000 times using the phase change optical disc according to the present invention shown in FIG. FIG.

As shown in FIG. 1, a phase change type optical disc A of the present invention has a first dielectric layer 2, a phase change type recording layer (recording layer) 3 on a substrate 1 on which a laser beam L is incident. , A second dielectric layer 4, a reflective layer 5, and a protective film 6 are sequentially laminated.

The above-mentioned substrate 1 is a light-transmitting substrate through which a laser beam L for recording and reproduction can pass, provided with a pre-groove or a pre-pit for guiding the laser beam L (not shown),
A plastic substrate such as polycarbonate, polyolefin, or acrylic, or a glass substrate is used. Laser light L
Pre-grooves and pre-pits are directly injection molded or 2P method (photopolymer method) on a smooth substrate
Is formed. Also, CAV (constant angular veloc)
ity or CLV (constant linear velocity)
Linear velocity) or ZCAV (zone constant angu)
lar velocity) and ZCLV (zone constant linear vel)
Ocity), a pre-groove and a pre-pit are formed, and an address signal is recorded in advance as an emboss pit at the head of each sector. The information area used by the user is composed of empty grooves, and when recording on lands and grooves, the land and groove widths are set so that the reproduction signals and overwrite performance of the lands and grooves are the same. I do.

The substrate 1 is placed in a vacuum film forming apparatus (not shown), and a first dielectric layer 2, a phase-change recording layer 3, a second dielectric layer 4, and a reflective layer 5 are sequentially laminated. I do. Each layer 2-5
As the film forming method, DC or AC sputtering, reactive sputtering, ion beam sputtering, ion plating or the like is used. The degree of vacuum before film formation is 1 × 1
It is preferable to set the pressure to 0 ^-6 Torr or less.

The first dielectric layer 2 is made of a metal oxide, nitride, sulfide, carbide, boride, or a mixture containing a plurality of these. For example, ZnS
—SiO ₂ , ZnS, GeS ₂ , SiO ₂ , Ta
₂ O ₅ , Si ₃ N ₄ , AlN, Al ₂ O ₃ , AlSiO
N, ZrO ₂ , TiO ₂ , CeO ₂ , SiC, TiC,
A simple substance such as BN or a mixture thereof is used.
The film thickness is in the range from 10 to 300 nm. Although the optimum film thickness varies depending on the wavelength of the laser beam L used, it is preferably 50 to 200 nm in order to increase the reproduction signal. Further, in order to reduce the influence of heat conduction on the substrate 1, the thickness is preferably 80 nm or more.

The phase-change recording layer 3 is made of a Ge-Sb-Te phase-change material utilizing a change in reflectance or a change in refractive index between amorphous and crystal. A fourth element may be contained for improving storage stability and reliability. The recording layer 3 is made of Ge in an atmosphere in which at least nitrogen gas and oxygen gas are mixed with argon gas which is an inert gas.
A target made of -Sb-Te is formed by DC sputtering. The gas mixture of nitrogen gas and oxygen gas is
High-purity nitrogen gas and oxygen gas may be separately introduced into the vacuum chamber through the flow control device, or simply air may be introduced as it is. In a single-wafer sputtering apparatus,
The recording layer made of Ge, Sb, and Te is effectively formed on the substrate by forming the film while reducing the degree of vacuum positively without exhausting the vacuum degree of the vacuum chamber for sputtering the recording layer 3 to a high vacuum. It can also be formed. The ratio of the gas pressure of the mixed gas of nitrogen and oxygen to the argon gas is from 0.3% to 5%
In the range. If the content is 0.3% or less, mass transfer in which the recording layer 3 flows and the film thickness decreases when overwriting is repeatedly performed cannot be suppressed. 5%
Above this, the recording sensitivity is reduced and the refractive index n and the absorption coefficient k of the recording layer 3 are changed, so that the optically optimum configuration of the laminated film is shifted and good C / N cannot be obtained. The volume fraction of the mixed gas nitrogen and oxygen is as follows.
Preferably, air can be used. When sputtering is performed with a target made of Ge, Sb, and Te in an atmosphere in which a mixed gas of at least nitrogen gas and oxygen gas is mixed with argon gas, 0.1 at% or less of Ge oxide and Sb oxide Is generated, which suppresses a change in volume of the recording layer 3. The thickness of the recording layer 3 is 10 to 10
0 nm, preferably 2 to increase the playback signal.
The thickness is preferably 0 to 60 nm.

The same material as that of the first dielectric layer 2 is used for the second dielectric layer 4 described above. The second dielectric layer 4 is thinner than the first dielectric layer 2 and has a so-called quenching structure,
In order to reduce thermal damage, the film thickness is preferably set to 2 to 50 nm.

The reflective layer 5 is made of a metal having high heat conductivity,
Alternatively, a thin film such as a semiconductor is used. Al, Au, A
Metals such as g, Cu, Ni, In, Ti, Cr, Pt and Ta, or alloys thereof are mainly used. The film thickness is desirably 50 to 300 nm.

The protective film 6 is formed by taking out the formed disk into the atmosphere and applying an ultraviolet curing resin on the reflective layer 5. The film thickness is 1 to 20 μm. As a coating method, a spin coating method, a spray 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.

The phase-change optical disk A shown in FIG.
A first dielectric layer 2, a phase-change recording layer (recording layer) 3, a second dielectric layer 4, a reflective layer 5, and a protective film 6 on a substrate 1.
Are sequentially laminated, but the phase change optical disc of the present invention is not limited to this configuration,
It also includes the configuration of one embodiment. One of the disks is a phase-change type optical disk having a configuration in which one transparent substrate similar to the substrate 1 is bonded via an adhesive layer on the protective film 6 of the disk having the configuration shown in FIG. That is, on the substrate 1, the first dielectric layer 2, the phase change recording layer 3, the second dielectric layer 4, the reflective layer 5, the protective film 6, the adhesive layer, and the substrate 1 are sequentially laminated. This is a phase change optical disk. Further, another disk is placed on the protective film 6 of the disk having the configuration shown in FIG.
This is a phase-change type optical disk having a configuration in which another disk having the configuration shown in FIG. 1 is bonded via an adhesive layer. That is, a first dielectric layer 2, a phase-change recording layer 3, a second dielectric layer 4, a reflective layer 5, a protective film 6, an adhesive layer, a reflective layer 5, a second dielectric layer This is a phase change optical disc having a configuration in which a body layer 4, a phase change recording layer 3, a first dielectric layer 2, and a substrate 1 are sequentially laminated. In this case, the laser light enters from both the substrates 1 side.

The optical disk thus manufactured is irradiated with a laser beam, a flash lamp, or the like to heat the phase-change type recording layer 3 as a recording layer to a temperature higher than a crystallization temperature, thereby performing an initialization process. Practically, the initialization laser beam applied to the optical disk has a beam diameter (spot diameter) larger than the track width, preferably longer in the radial direction, and simultaneously initializes a plurality of tracks while rotating the disk. I do.

Next, a method of manufacturing the above-described phase change optical disk and evaluation of overwriting will be described with reference to Examples 1-4 and Comparative Examples 1 and 2, as shown in FIG. Hereinafter, for convenience of explanation, a case will be described in which the phase-change optical disc A having the configuration shown in FIG. 1 is used.

<Example 1-4, Comparative Example 1-2> A first dielectric layer 2 was formed on a polycarbonate substrate 1 provided with a pregroove having a track pitch of 1.6 μm and a groove depth of 80 nm.
The phase change recording layer 3, the second dielectric layer 4, and the reflection layer 5 were formed by sputtering.

First, after evacuating to a degree of vacuum of 3.2 × 10 ⁻⁷ Torr, ZnS—SiO ₂ (80:20 mol%) is subjected to high frequency sputtering with argon (Ar) gas to provide 90 nm as the first dielectric layer 2. Was. Ar gas pressure is 1.6m
Torr, the deposition rate of the first dielectric layer 2 is 0.25 nm / s.

Next, Ge 22 Sb is used as the phase-change recording layer 3.
22 Te56 was formed to a thickness of 20 nm by a DC sputtering method.
At this time, air was introduced into Ar gas. The amount of air introduced was such that the air pressure / Ar gas pressure was 0.3% without air introduction.
0%, 0.69%, 3.1%, 5.0%, and 12.5% were produced. The Ar gas pressure is 1.6 mTorr, and the deposition rate of the recording layer 3 is 0.1 nm / s. On this, ZnS—SiO ₂ (80:20 mol) is used as the second dielectric layer 4.
%) Was formed to a thickness of 18 nm by a high frequency sputtering method. A
The r gas pressure is 1.6 mTorr, and the deposition rate of the second dielectric layer 4 is 0.05 nm / s.

Next, Al-Cr (9
7.5: 2.5 at%) by DC sputtering.
0 nm was provided. The film forming speed of the reflective layer 5 is 0.2 nm / s
It is. After removing the disc from the vacuum chamber,
As the protective layer 6, an ultraviolet curable resin (XR1 manufactured by Sumitomo Chemical Co., Ltd.)
1) was spin-coated on the reflective layer 5 and cured by irradiating ultraviolet rays to form a protective film 6 having a thickness of 5 μm. Thus, the above-described phase change optical disk A can be manufactured.

Next, overwriting of the phase-change type optical disk A thus manufactured was evaluated. First, an initialization laser beam was irradiated from the substrate 1 side while rotating the disk A to initialize the phase change recording layer 3 by changing its phase from a low reflectance state to a high reflectance state. Next, recording was performed on the lands between the guide grooves of the phase change recording layer 3 by irradiating a laser beam L as a recording laser beam from the substrate 1 side. Rand is
It is concave when viewed from the incident direction of the laser beam L (the direction of the arrow in FIG. 1).

The recording conditions are as follows. The linear velocity for rotating the disk A is 6.0 m / s, the wavelength of the recording laser (of the laser beam L) is 684 nm, and the NA of the objective lens is 0.
6, peak power 11.0 mW, bias power 4.5
mW. The 8-16 modulated signal was recorded, and the level I14 of the recording mark portion having a reproduction amplitude of 14T, which is a signal obtained by reproducing the longest hit length among the reproduction signals, was measured with respect to the number of rewrites. When rewriting is repeated, mass transfer occurs, the film thickness becomes thinner, and the level I14 decreases.

FIG. 2 shows the state after rewriting 100,000 times using the phase change type optical disc A of the present invention shown in FIG. 1, specifically, the level I14 after rewriting 100,000 times. It is a figure showing the value divided by the first level I14.
As is clear from the first to fourth embodiments, the decrease in the level I14 is suppressed as the amount of introduced air increases. Air pressure / Ar gas pressure is 0.30%, 0.69%, 3.1
% And 5.0%, the disc produced by sputtering the recording layer 3 can suppress the reduction of the level I14 in the range of 0.817 to 0.969 even after rewriting 100,000 times. Unless air is introduced as in Comparative Example 1, the decrease in level I14 due to mass transfer cannot be suppressed. On the other hand, as in Comparative Example 2, when the amount of air introduced is excessively 12.5%, the recording sensitivity is lowered, and recording cannot be performed. As described above, as in Examples 1 to 4, the reduction of the level I14 is suppressed when the air pressure / Ar gas pressure is 0.3% to 5.0%. A changing optical disk is obtained.

A thermal analysis was performed on the laminated film having the same configuration as that of the disk A by a differential scanning calorimeter (DSC). As the temperature is increased from room temperature at a rate of 10 ° C./min, the G of the recording layer 3 is increased.
The eSbTe mixture crystallizes and generates heat. The crystallization temperature is shown in FIG. When the ratio of air pressure / Ar gas pressure was 3.1% or more (Example 3), no exothermic peak was observed. No X-ray diffraction peak was observed, and the sample was in an amorphous state, but optically changed from a low reflectance to a high reflectance. Unbonded hands of recording material (dangling bond)
Is presumed to be bonded to nitrogen or oxygen to hinder crystallization. However, what can be said from this phenomenon is that since the movement of the atoms of the recording material constituting the recording layer 3 is a short distance since the amorphous state is maintained even after the heating, the volume change is small and the phase change is repeatedly caused. It is clear that the signal quality is less deteriorated.

[0032]

According to the phase change type optical disk and the method for manufacturing the phase change type optical disk of the present invention having the above-described structure, the following effects can be obtained. (1) A gas mixture of a nitrogen gas and an oxygen gas with respect to an argon gas without substantially changing the conventional manufacturing method;
Alternatively, by merely setting the gas pressure of the air within a predetermined range, it is possible to suppress a decrease in the reproduction amplitude due to mass transfer of the recording layer at the time of repeated rewriting. Rewriting performance can be improved using conventional materials and equipment. (2) A highly reliable phase-change optical disc can be easily obtained by introducing air or sputtering without increasing the degree of vacuum without using a specially high-purity gas.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining that rewriting is performed 100,000 times using the phase change optical disc of the present invention shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 1st dielectric layer 3 Phase change recording layer, recording layer 4 2nd dielectric layer 5 Reflection layer 6 Protective film A Phase change optical disk L Laser beam

Claims (4)

[Claims] 1. A method for manufacturing a phase change optical disk, comprising forming a recording layer made of Ge, Sb, and Te on a substrate, the arrangement of atoms changing reversibly by irradiating a laser beam. Ge, Sb, and Te are mixed in an atmosphere in which a mixed gas of at least nitrogen gas and oxygen gas is mixed with argon gas.
Forming the recording layer on a substrate by sputtering a target made of a phase change optical disk. 2. The method according to claim 1, wherein the mixed gas is air. 3. The manufacturing method according to claim 1, wherein the gas pressure of the mixed gas or the air is in a range of 0.3% to 5% of the gas pressure of the argon gas. Method. 4. A phase-change optical disk having a recording layer made of Ge, Sb, and Te and containing at least Ge oxide and Sb oxide.