JPH10124925A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable recording of >=3 values by irradiating a recording layer which is formed on a substrate and contains either of Te or Se with light to enable recording, erasing and reproducing of information and executing the recording and erasing of the information by the phase transition between an amorphous phase and two kinds of different crystalline phases. SOLUTION: After the inside of a vacuum vessel is evacuated to 1×10<-5> Pa, a target consisting of Pd, Nb, Sb, Te is sputtered on a glass substrate in a gaseous Ar 98%-N2 2% atmosphere kept under 2×10<-1> P. A dielectric layer is formed on the recording layer of 300nm film thickness formed in such a manner by sputtering ZnS added with 20mol% SiO2 in a gaseous Ar atmosphere of kept under 2×10<-1> P. This substrate is heat treated for 30 minutes at 150 deg.C and is thereafter heat treated further for 30 minutes at 300 deg.C. The reflectivity is divvied to three stages by having differences of 5 to 10% within a range of 400 to 700nm from the results obtd. by using the spectral reflectivity of this sample. As a result, the three-values recording is made possible and the recording density is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to
The present invention relates to an optical information recording medium capable of recording, erasing, and reproducing information. In particular, the present invention provides a method for erasing recorded information,
The present invention relates to a rewritable phase-change optical recording medium such as an optical disk having a rewritable function and capable of recording an information signal at high speed and at high density.

[0002]

2. Description of the Related Art The technology of a conventional rewritable phase-change optical recording medium is as follows. These optical recording media have a recording layer mainly composed of tellurium or the like, and during recording, a laser beam pulse focused on the crystalline recording layer is irradiated for a short time to partially melt the recording layer. I do. The melted portion is quenched by thermal diffusion and solidified to form an amorphous recording mark. The light reflectance of this recording mark is lower than that of the crystalline state and can be optically reproduced as a binary recording signal.

At the time of erasing, a recording mark portion is irradiated with a laser beam and heated to a temperature lower than the melting point of the recording layer and higher than the crystallization temperature, thereby crystallizing the recording mark in an amorphous state and leaving the original unrecorded portion. Return to condition.

As a material for the recording layer of these rewritable phase change optical recording media, alloys such as Ge ₂ Sb ₂ Te ₅ (N.Ya) are used.
mada et al, Proc.Int.Symp. on Optical Memory 198
7 p61-66) are known.

[0005] These optical recording media using a Te alloy as a recording layer have a high crystallization speed, and high-speed overwriting with a single circular beam is possible only by modulating the irradiation power. In an optical recording medium using these recording layers, usually, a dielectric layer having heat resistance and light transmissivity is provided on both sides of the recording layer to prevent the recording layer from being deformed or having an opening during recording. Further, a metal reflective layer such as light-reflective Al is provided on the dielectric layer on the side opposite to the light beam incident direction to improve the signal contrast at the time of reproduction by an optical interference effect. There is known a technique which facilitates formation of a recording mark in a crystalline state and improves erasing characteristics and repetition characteristics.

[0006]

Various attempts have been made to increase the recording density of an optical recording medium. However, the two-dimensional recording density is naturally limited. 2
One of the methods for improving the recording density without changing the dimensional recording density is multi-valued recording of three or more values.

However, in the conventional phase-change type optical recording medium, binary recording is performed between two states of amorphous and crystalline. Therefore, except for providing two or more recording layers, recording of three or more values is required. It is impossible to do. Providing two or more recording layers increases the cost of the recording medium because the number of layers increases. Also, in the recording / reproducing apparatus, it is necessary to provide a mechanism capable of switching the focus between different layers at the time of recording / reproducing, which causes a cost increase.

An object of the present invention is to solve the above-mentioned problems of the conventional optical recording medium and to provide an optical recording medium capable of easily and inexpensively recording three or more values.

[0009]

According to the present invention, information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light.
An optical recording medium characterized by being performed by a phase change between an amorphous phase and two different crystal phases.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The first and second dielectric layers of the present invention are provided with a heat-insulating substrate and a recording layer, for example, in order to prevent the substrate and the recording layer from being deformed by heat during recording to prevent the recording characteristics from deteriorating. There is an effect of improving the signal contrast at the time of reproduction by an effect of protecting from a signal and an optical interference effect.

[0011] The thickness d1 of the first dielectric layer is usually 50 nm or more and 400 nm or less because it is difficult to peel off from the substrate or the recording layer and hardly cause defects such as cracks. In order to increase the carrier-to-noise ratio (C / N) by increasing the contrast of the recording / reproducing signal, it is more preferable that d1
Is 0.25λ / wavelength λ of light used for recording and reproduction.
n1 ≦ d1 ≦ 0.70λ / n1. n1 is the real part of the refractive index of the first dielectric layer.

As the first dielectric layer and the second dielectric layer, there are inorganic thin films such as ZnS, SiO ₂ , silicon nitride, and aluminum oxide. Especially ZnS thin film, Si, G
e, a thin film of a metal oxide such as Al, Ti, Zr, Ta, and Ce; a thin film of a nitride such as Si and Al;
A thin film of a carbide such as Hf and a film of a mixture of these compounds are preferable because of high heat resistance. Further, those obtained by mixing carbon or a fluoride such as MgF _{2 with} these are also preferable because the residual stress of the film is small. Especially ZnS and S
The mixed film of iO ₂ or the mixed film of ZnS, SiO ₂ and carbon has a recording sensitivity,
It is preferable because deterioration such as C / N and the erasing rate does not easily occur, and a mixed film of ZnS, SiO ₂ and carbon is particularly preferable.
The molar ratio between ZnS and SiO ₂ is ZnS / SiO ₂ = 85 /
A 15~65 / 35, (ZnS + SiO 2) molar ratio of C is _{(ZnS + SiO 2) / C} = 99 / 1~80 /
It is preferably 20.

Particularly, since the recording sensitivity is high, one-beam overwriting is possible at high speed, and the erasing rate is large and the erasing characteristics are good, the main part of the optical recording medium can be constituted as follows. preferable.

As a material of the reflection layer, a metal such as Al or Au having light reflectivity, or a material containing these as a main component,
Alloys containing additional elements such as i, Cr, Hf and Al, A
Examples thereof include a mixture of a metal such as u and a metal compound such as a metal nitride such as Al and Si, a metal oxide, and a metal chalcogenide. Metals such as Al and Au and alloys containing these as main components are preferable because of their high light reflectivity and high thermal conductivity. As an example of the above-mentioned alloy, Al, Si, Mg, Cu, Pd, Ti, Cr, H
At least one element such as f, Ta, Nb, Mn and the like added in a total of 5 at% or less and 1 at% or more, or at least one of Au, Cr, Ag, Cu, Pd, Pt, and Ni Element total 20 atomic% or less 1 atomic%
These are the ones added above. Particularly, an alloy containing Al as a main component is preferable because the price of the material can be reduced.
at least one metal selected from the group consisting of r, Ta, Hf, Zr, Mn, and Pd in a total of 5 atomic% or less and 0.5 atomic%.
The alloys added above are preferred. In particular, because corrosion resistance is good and hillocks do not easily occur,
Al-Hf-Pd alloy, Al-Hf alloy, Al containing a reflective layer containing a total of 0.5 to 3 atomic% of additional elements
-Ti alloy, Al-Ti-Hf alloy, Al-Cr alloy,
Al-Ta alloy, Al-Ti-Cr alloy, Al-Si-
It is preferable to use any one of the Mn alloys mainly containing Al.

The recording layer in the present invention has two or more different crystal phases. A phase change can be made between an amorphous phase and two or more different crystal phases or a mixture of at least three phases having different optical constants. This enables recording of three or more values.

The recording layer is not particularly limited, but a recording layer containing at least one of Te and Se is preferable in that the erasing time can be shortened.
d-Ge-Sb-Te alloy, Nb-Ge-Sb-Te alloy, Pd-Nb-Ge-Sb-Te alloy, Pt-Ge-
Sb-Te alloy, Ge-Sb-Te alloy, Co-Ge-
Sb-Te alloy, In-Sb-Te alloy, Ag-In-
There are an Sb-Te alloy, an In-Se alloy and the like. Since the recording can be rewritten many times, Pd-Ge-S
b-Te alloy, Nb-Ge-Sb-Te alloy, Pd-N
A b-Ge-Sb-Te alloy and a Ge-Sb-Te alloy are more preferable.

In particular, Pd-Ge-Sb-Te alloy, Nb-
Ge-Sb-Te alloy, Pd-Nb-Ge-Sb-Te
Alloys are preferable because they have a short erasing time, can be repeatedly recorded and erased many times, and have excellent recording characteristics such as C / N and erasing rate. Also, for these alloys,
Further, it may contain 10 atomic% or less of nitrogen.

The composition of the recording layer other than nitrogen is more preferably in the range represented by the following formula. M _z (Sb _x Te _1-x ) _1-yz (Ge _0.5 Te _0.5 ) _y 0.35 ≦ x ≦ 0.5 0.2 ≦ y ≦ 0.5 0.0005 ≦ z ≦ 0.01 M represents at least one metal selected from palladium, niobium, platinum, silver, gold, and cobalt. Also,
x, y, z, and numbers represent the number of atoms of each element (the number of moles of each element).

In the present invention, the wavelength of light used for recording and reproduction is λ, the thickness of the first dielectric layer is d 1, the refractive index (real part) is n 1, the thickness of the recording layer is dr, and The thickness of the two dielectric layers is d2, the refractive index (real part) is n2, and the thickness of the reflective layer is d.
Assuming that f, the following equation: 0.25λ / n1 ≦ d1 ≦ 0.70λ / n1 10 ≦ dr ≦ 40 (unit nm) 10 ≦ d2 ≦ 60 (unit nm) 40 ≦ df ≦ 200 2 ≦ n1 ≦ 2.5 The layer thickness is preferably set so as to satisfy 2 ≦ n2 ≦ 2.5.

As the material of the substrate of the present invention, various transparent synthetic resins, transparent glass and the like can be used. In order to avoid the effects of dust and scratches on the substrate, it is preferable to use a transparent substrate and perform recording from the substrate side with a focused light beam, and such transparent substrate materials include glass, polycarbonate, polymethyl methacrylate, Polyolefin resin, epoxy resin, polyimide resin and the like can be mentioned. In particular, a polycarbonate resin and an amorphous polyolefin resin are preferable because they have low optical birefringence, low hygroscopicity, and are easy to mold.

The thickness of the substrate is not particularly limited, but is practically 0.01 mm to 5 mm. 0.01m
If it is less than m, even when recording with a light beam focused from the substrate side, it is susceptible to dust, and if it is 5 mm or more,
It becomes difficult to increase the numerical aperture of the objective lens, and the spot size of the irradiation light beam becomes large, so that it becomes difficult to increase the recording density. The substrate may be flexible or rigid. The flexible substrate is used in the form of a tape, a sheet, or a card. The rigid substrate is used in the form of a card or a disk. In addition, these substrates may be formed into an air sandwich structure, an air incident structure, or a close bonding structure by using two substrates after forming a recording layer or the like.

The light source used for recording on the optical recording medium of the present invention is a high-intensity light source such as a laser beam or a strobe light. Particularly, a semiconductor laser beam has a small light source, low power consumption, Is preferred because of the simplicity.

The recording is performed by irradiating a laser beam pulse or the like to the recording layer in a crystalline state to form an amorphous recording mark. Alternatively, a recording mark in a crystalline state may be formed on a recording layer in an amorphous state. Erasing can be performed by irradiating a laser beam to crystallize an amorphous recording mark or to make a crystalline recording mark amorphous. Since the recording speed can be increased and the recording layer is hardly deformed, it is preferable to form an amorphous recording mark during recording and crystallize during erasing.

Further, when forming a recording mark, the light intensity is high.
One-beam overwriting, in which erasing is slightly weakened and rewriting is performed by one light beam irradiation, is preferable because the time required for rewriting is reduced.

Next, a method for manufacturing the optical recording medium of the present invention will be described. Examples of a method for forming a reflective layer, a recording layer, and the like on a substrate include a known thin film forming method in a vacuum, for example, a vacuum deposition method, an ion plating method, and a sputtering method. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled. The thickness of the recording layer or the like to be formed can be easily controlled by monitoring the deposited state with a quartz crystal film thickness meter or the like.

The formation of the recording layer or the like may be performed while the substrate is fixed, or may be moved or rotated. Since the in-plane uniformity of the film thickness is excellent, the substrate may be rotated or revolved.

Further, after forming a reflective layer and the like within a range that does not significantly impair the effects of the present invention, a dielectric layer such as ZnS or SiO ₂ or a resin protection such as an ultraviolet curable resin is used to prevent scratches and deformation. Layers and the like may be provided as necessary. After the formation of the reflection layer or the like, or after the formation of the above-mentioned resin protective layer, the two substrates may be opposed to each other and bonded with an adhesive. Further, a resin hard coat layer may be provided on the substrate surface on which the laser is incident, and this layer may be formed before the formation of the first dielectric layer or the like or after the formation of the reflection layer or the like.

Before the actual recording, the recording layer is preferably irradiated with a laser beam or a light such as a xenon flash lamp to be crystallized in advance.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. (Analysis and Measurement Method) The compositions of the reflective layer and the recording layer were confirmed by ICP emission analysis (manufactured by Seiko Instruments Inc.).
The reflectance is measured by a spectrophotometer (CM2002 manufactured by Minolta Co., Ltd.).
Was measured by The amount of nitrogen in the recording layer was analyzed by a nuclear reaction method. The film thickness during formation of the recording layer, the dielectric layer, and the reflective layer is:
It was monitored by a quartz crystal thickness meter.

Example 1 After evacuating the vacuum chamber to 1 × 10 ⁻⁵ Pa, 2 × 10
Pd, on a glass substrate by DC magnetron sputtering in an atmosphere of Ar 98% -N ₂ 2% gas of ^-1 Pa.
Nb, Ge, Sb, by sputtering a target composed of _{Te, Nb 0.00 6 Pd 0.001 Ge} 0.173 Sb 0.26 Te
A recording layer having a thickness of _{0.56 and} a thickness of 300 nm was formed. Then 2x
Z in which 20 mol% of SiO ₂ was added by high frequency magnetron sputtering in an Ar gas atmosphere of 10 ^-1 Pa.
nS was sputtered to form a dielectric layer.

After measuring the spectral reflectance and X-ray diffraction pattern of this sample, it was heat-treated at 150 ° C. for 30 minutes, and the spectral reflectance and X-ray diffraction pattern were measured again. Further, after that, heat treatment was performed at 300 ° C. for 30 minutes, and the spectral reflectance and the X-ray diffraction pattern were measured again.

From the X-ray diffraction pattern of FIG. 1, the unheated sample was amorphous, the sample heat-treated at 150 ° C. for 30 minutes had a face-centered cubic structure, and the sample heat-treated at 300 ° C. It can be seen that the structure is a mixture of the face-centered cubic structure.

From the measurement result of the spectral reflectance of FIG.
In the range of nm to 700 nm, the reflectance is 5 to 1
With a difference of 0%, it was divided into three stages, indicating that ternary recording was possible.

Example 2 A sample was prepared in the same manner as in Example 1 except that the atmosphere during the production of the recording layer was a gas of 98% Ar-4% N ₂ .

After measuring the spectral reflectance and X-ray diffraction pattern of this sample, it was heat-treated at 200 ° C. for 30 minutes, and the spectral reflectance and X-ray diffraction pattern were measured again. Further, after that, heat treatment was performed at 300 ° C., and the spectral reflectance and the X-ray diffraction pattern were measured again.

From the X-ray diffraction pattern of FIG. 3, the unheated sample is amorphous, the sample heat-treated at 200 ° C. for 30 minutes has a face-centered cubic structure, and the sample heat-treated at 300 ° C. for 30 minutes is It can be seen that the face-centered cubic structure is mixed with the rhombohedral structure.

From the measurement result of the spectral reflectance of FIG.
In the range of nm to 700 nm, the reflectance is 5 to 1
With a difference of 0%, it was divided into three stages, indicating that ternary recording was possible.

The amount of nitrogen atoms in the recording layer formed on a quartz substrate under the same conditions was 1.55 atomic%.

Example 3 A sample was prepared in the same manner as in Example 1 except that the atmosphere during the production of the recording layer was a gas of 98% Ar-6% N ₂ .

After measuring the spectral reflectance and X-ray diffraction pattern of this sample, it was heat-treated at 250 ° C. for 30 minutes, and the spectral reflectance and X-ray diffraction pattern were measured again. Further, after that, heat treatment was performed at 300 ° C., and the spectral reflectance and the X-ray diffraction pattern were measured again.

From the X-ray diffraction pattern in FIG. 5, the unheated sample is amorphous, the sample heat-treated at 250 ° C. for 30 minutes has a face-centered cubic structure, and the sample heat-treated at 300 ° C. for 30 minutes is It can be seen that the face-centered cubic structure is mixed with the rhombohedral structure.

From the measurement result of the spectral reflectance shown in FIG.
In the range of nm to 700 nm, the reflectance is 5 to 1
With a difference of 0%, it was divided into three stages, indicating that ternary recording was possible.

The amount of nitrogen atoms in the recording layer formed on the quartz substrate under the same conditions was 2.70 atomic%.

Example 4 After evacuating the vacuum vessel to 1 × 10 ⁻⁵ Pa, 2 × 10
^In a Ar gas atmosphere of ^-1 Pa, a SiO
_A first dielectric layer having a thickness of 165 nm was formed on the substrate by sputtering ZnS to which ₂ mol% was added. Next, 2
× 10 ^-1 Pa in an atmosphere of Ar 98% -N ₂ 2% gas,
On a glass substrate, by DC magnetron sputtering,
A target composed of Pd, Nb, Ge, Sb, and Te was sputtered to obtain Nb _0.006 Pd _0.001 Ge _0.173 Sb _0.26
A recording layer of Te _{0.56 having} a thickness of 25 nm was formed. Next, similarly to the first dielectric layer, 20 mol of SiO ₂ was added.
% ZnS by sputtering was added to form a second dielectric layer having a film thickness of 30 nm, then to form a reflective layer having a thickness of 100nm of Pd _{0. 001} Hf _0.02 Al _0.979 alloy.

After measuring the spectral reflectance of this sample,
Heat treatment was performed at 0 ° C. for 30 minutes, and the spectral reflectance was measured again.
Further, after that, heat treatment was performed at 300 ° C. for 30 minutes, and the spectral reflectance was measured again.

From the measurement result of the spectral reflectance of FIG.
In the range from nm to 700 nm, the reflectance was divided into three levels, indicating that ternary recording was possible.

Example 5 A sample was prepared in the same manner as in Example 4 except that the thickness of the first dielectric layer was 80 nm, and the gas for sputtering the recording layer was 96% Ar-4% N ₂ .

After measuring the spectral reflectance of this sample,
Heat treatment was performed at 0 ° C. for 30 minutes, and the spectral reflectance was measured again.
Further, after that, heat treatment was performed at 300 ° C. for 30 minutes, and the spectral reflectance was measured again.

From the measurement result of the spectral reflectance shown in FIG.
In the range from nm to 700 nm, the reflectance was divided into three levels, indicating that ternary recording was possible.

[0050]

According to the optical recording medium of the phase change type, recording of three or more values can be performed, and even at the same surface recording density, higher density recording can be performed than ordinary binary recording.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction pattern of an unheated sample in Example 1.

FIG. 2 is an X-ray diffraction pattern of a heat-treated sample at 150 ° C. in Example 1.

FIG. 3 is an X-ray diffraction pattern of a heat-treated sample at 300 ° C. in Example 1.

FIG. 4 shows a result of measurement of spectral reflectance in Example 1.

FIG. 5 is an X-ray diffraction pattern of an unheated sample in Example 2.

FIG. 6 is an X-ray diffraction pattern of a heat-treated sample at 200 ° C. in Example 2.

FIG. 7 is an X-ray diffraction pattern of a heat-treated sample at 300 ° C. in Example 2.

FIG. 8 shows a result of measurement of spectral reflectance in Example 2.

FIG. 9 is an X-ray diffraction pattern of an unheated sample in Example 3.

FIG. 10 shows X of the heat-treated sample at 250 ° C. in Example 3.
Line diffraction pattern

FIG. 11 shows X of the heat-treated sample at 300 ° C. in Example 3.
Line diffraction pattern

FIG. 12 shows a result of measurement of spectral reflectance in Example 3.

FIG. 13 shows a result of measurement of spectral reflectance in Example 4.

FIG. 14 shows a result of measurement of spectral reflectance in Example 5.

Claims (6)

[Claims] A recording layer formed on a substrate is irradiated with light so that information can be recorded, erased, and reproduced. The information recording and erasing can be performed in an amorphous phase and two different types of crystals. An optical recording medium that is effected by a phase change between phases. 2. The optical recording medium according to claim 1, wherein the recording layer contains at least one of Te and Se. 3. The optical recording medium according to claim 1, wherein one of the two different crystal phases is a face-centered cubic system. 4. The optical recording medium according to claim 1, wherein one of the two different crystal phases has a rhombohedral symmetry. 5. The optical recording medium according to claim 1, wherein the two different crystal phases are composed of a face-centered cubic system and a rhombohedral system, or a mixture thereof. 6. The optical recording medium according to claim 1, wherein the optical recording medium has a structure in which at least a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer are laminated in this order on a transparent substrate.