JPH09198712A - Optical information recording medium and manufacturing method thereof - Google Patents

Abstract

(57) Abstract: A dielectric layer is made of a mixture of ZnS and silicon oxynitride in which nitrogen is bonded to silicon in the film, whereby mechanical strength is increased and overwrite cycle characteristics are improved. Provided is a phase change type optical information recording medium. At least a first dielectric layer (2) on a substrate (1)
A recording layer (3) made of a material that undergoes a reversible change between optically distinguishable states upon irradiation with a laser beam, and a second dielectric layer (4) are laminated, and at least the first dielectric layer (2) and the above One of the second dielectric layers 4 is a mixture of ZnS and silicon oxynitride. This dielectric layer consists of ZnS and SiO
_A sputtering target is formed from a target composed of a mixture of ₂ and Si ₃ N ₄ in a mixed gas atmosphere of rare gas and nitrogen, and the amount of ZnS in the dielectric is 40 mol% or more and 95 mol% or less, and Si ₃ N ₄ and S
The molar ratio of iO ₂ (Si ₃ N ₄ / SiO ₂ ) is preferably in the range of 0.05 or more and 1 or less.

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 for recording, reproducing and rewriting information at high density and high speed by using an optical means such as a laser beam and a method for manufacturing the same.

[0002]

2. Description of the Related Art A technique for recording and reproducing high-density information on an optical disk by using a laser beam or the like is known, and currently applied to a document file, a still image file, an external memory for a computer, and the like. . Further, research and development of a rewritable type information recording system are also in progress, and one of them is a phase change optical disk. A phase-change optical disk records a signal by utilizing the fact that the recording film undergoes a reversible state change between amorphous and crystal (or between crystals of a structure different from that of the crystal) by irradiation of a laser beam, and a signal is recorded between the amorphous and crystal. The signal is reproduced by optically detecting the difference in reflectance.

The phase change optical disk has a great merit that an overwrite for recording a new signal while erasing an old signal can be performed by only passing a laser spot once on a signal track. That is, when the power of laser light is modulated and irradiated between the recording level and the erasing level according to the signal, the area irradiated at the recording level is cooled after the recording film is melted regardless of the presence of an old signal. The region irradiated with the erasing level becomes amorphous and becomes a crystal regardless of the previous state because the region irradiated with the erasing level is heated above the crystallization temperature.

The structure of a phase change optical disk is generally a three-layer structure in which a recording layer is sandwiched between dielectric layers and provided on a substrate, and a four-layer structure in which a reflective film is further provided thereon.
The role of the dielectric layer is 1) increase the laser light absorptance of the recording layer, 2) increase the reflectance change between the amorphous state and the crystalline state to increase the reproduction signal amplitude, and 3) protect the substrate from thermal damage. Etc.

In the case of a phase change optical disc, at the time of signal recording
Melt by raising the temperature of the recording film above its melting point (eg 600 ° C)
The dielectric layer is subject to large thermal stress due to
receive. Therefore, the internal stress is small and it is thermally stable.
ZnS and SiO as various dielectric materials _TwoMixed materials (hereinafter ZnS-Si
O_Two) Has been developed (35th Joint Lecture on Applied Physics)
Proceedings 28P-ZQ-3, P839 (1988)). This material has a refractive index
Because it is large, it increases the absorption rate of laser light and
It is also suitable for increasing the reflectance change of the glass and crystal.
You.

It has been confirmed that ZnS crystals of several tens of angstroms (several nm) are dispersed in amorphous SiO ₂ in the fine structure of the mixed material of ZnS-SiO ₂ . The dielectric layer is generally formed by the sputtering method, but ZnS formed by the sputtering method is polycrystalline, and the crystal grain size changes and the recording characteristics change due to the effect of heating due to repeated recording. Or
Leads to thermal destruction of the thin film prevents the crystal growth of ZnS by dispersing Zn _S in SiO _2, it is considered that a stable dielectric material.

Further, it is proposed that when ZnS-SiO _{2 is formed} by a sputtering method, if N ₂ gas is added in a small amount in addition to Ar gas, the thermal stability is further increased and the signal overwrite cycle is improved. (JP-A-3-232133).

[0008]

However, the above-mentioned conventional technique is not suitable for forming ZnS-SiO ₂ by sputtering.
When the film is formed in an Ar + N ₂ atmosphere, the overwrite cycle is improved, but if the amount of N ₂ added is too large, the recording and erasing characteristics change and the thermal stability of the recording signal after the overwrite cycle decreases. I found it to appear. The cause is that the excessively added N ₂ gas is taken into the dielectric without binding to the elements that make up the dielectric, so it moves into the recording film when heated by the overwrite cycle, and It is considered that this is because the properties of the recording film are changed by combining with the constituent elements.

In order to solve the above-mentioned conventional problems, it is an object of the present invention to provide a highly reliable optical information recording medium having a good overwrite cycle characteristic of the phase change type optical information recording medium. .

[0010]

In order to achieve the above object, an optical information recording medium of the present invention has a state in which at least a first dielectric layer and a laser beam are optically distinguishable from each other on a substrate. An optical information recording medium comprising a recording layer made of a material that causes a reversible change between two layers and a second dielectric layer, wherein at least the first dielectric layer and the second dielectric layer. One of them is characterized by being composed of a mixture of ZnS and silicon oxynitride.

In the above structure, Zn in the dielectric is
It is preferable that the amount of S is 40 mol% or more and 95 mol% or less, and the molar ratio of Si ₃ N ₄ and SiO ₂ (Si ₃ N ₄ / SiO ₂ ) is 0.05 or more and 1 or less.

Next, the first method of manufacturing the optical information recording medium of the present invention is such that at least the first dielectric layer on the substrate is reversible between the optically distinguishable state by the irradiation of the laser beam. A recording layer made of a material that causes a change, and a second
A method for manufacturing an optical information recording medium, which comprises laminating dielectric layers of at least one of the first dielectric layer and the second dielectric layer.
Of one of the dielectric layers of ZnS and silicon oxynitride, and the dielectric layer using a target of a mixture of ZnS, SiO ₂ and Si ₃ N ₄ , mixed rare gas and nitrogen. It is characterized in that the film is formed by a sputtering method in a gas atmosphere.

Next, the second method of manufacturing the optical information recording medium of the present invention is reversible between at least the first dielectric layer and the optically distinguishable state by irradiation of the laser beam on the substrate. A recording layer made of a material that causes a change, and a second
A method for manufacturing an optical information recording medium, which comprises laminating dielectric layers of at least one of the first dielectric layer and the second dielectric layer.
One of the dielectric layers of ZnS and silicon oxynitride is used, and the dielectric layer is formed by using a target of a mixture of ZnS and silicon oxide SiO _x (0 ≦ x ≦ 1.95). It is characterized in that the film is formed by a sputtering method in a mixed gas atmosphere of gas and nitrogen or in a mixed gas atmosphere of rare gas, nitrogen and oxygen.

In the first to second manufacturing methods,
ZnS content in the dielectric is 40 mol% or more and 95 mol% or less,
And the molar ratio of Si ₃ N ₄ and SiO ₂ (Si ₃ N ₄ / SiO ₂ ) is 0.05.
It is preferable to form the film so that the range is 1 or less.

According to the above-mentioned constitution of the present invention, the dielectric layer is made of a mixture of ZnS and silicon oxynitride in which nitrogen is bonded to silicon in the film, whereby the mechanical strength is increased and the overwrite cycle is increased. improves. Since nitrogen is bonded to the element in the film, it does not move into the recording film even when it is heated by the overwrite cycle, and the recording characteristics do not change.

Further, according to the first to second manufacturing methods of the present invention, the dielectric layer can be formed from one target with good reproducibility, stability, efficiency and rational deposition.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Various heat resistant protective layers have been researched in order to reach a high temperature in a phase change optical disk by a recording operation. One solution is a ZnS-SiO ₂ film. ZnS-SiO ₂
Because of its low internal stress and thermal stability, the overwrite cycle was greatly improved compared to the dielectric materials that were considered good. Furthermore, Zn
When S-SiO ₂ is sputtered in Ar + N ₂ atmosphere to form a film, the overwrite cycle is further improved.

However, it has been found that there is an upper limit to the amount of N ₂ added when forming a film of ZnS-SiO ₂ in an Ar + N ₂ atmosphere. That is, when the amount of N ₂ added is too large, the phenomenon that the recording / erasing characteristics are changed or the thermal stability of the recording signal after the overwrite cycle is deteriorated appears. According to further research by the inventors, the cause is that the N ₂ gas added in a trace amount is bonded to the element that constitutes the dielectric, for example, silicon, but the N ₂ gas added in excess is a dielectric in the dielectric. It was found that they were incorporated without binding to the elements that make up.

Whether nitrogen is bound to an element in the film or simply incorporated into the film can be verified by, for example, thermal desorption spectroscopy (TDS). TDS detects elements released by heating a sample piece in a vacuum. In the case of a ZnS-SiO ₂ film formed in an Ar + N ₂ atmosphere, if the amount of N ₂ added is small, About 700 ℃ -900 ℃
The emission peak of N ₂ appeared over time, but when the amount of N ₂ added increased, a new peak appeared over about 300 ° C to 500 ° C. Of these two peaks, the low-temperature side peak is the release of nitrogen taken in without being bound to the element in the film, while the high-temperature side peak is bound to the film element such as silicon. It is considered that nitrogen was dissociated and released.

ZnS-Si in which only the peak on the high temperature side appears
It was found that the optical disc formed with the O ₂ film has excellent overwrite characteristics, but the optical disc formed with the ZnS-SiO ₂ film having a large peak at the low temperature side has a conversely deteriorated overwrite characteristic. When overwriting, the first peak appears 3
It is considered that the nitrogen in the dielectric moves to the recording film to reach a temperature higher than 00 ° C. to 500 ° C. and combines with the elements of the recording film to affect the recording characteristics.

Next, the nitrogen concentration in the dielectric is measured by secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES).
As a result of the analysis, when a ZnS-SiO ₂ film was formed from a mixed target of ZnS and SiO _{2 in} an Ar + N ₂ atmosphere, the nitrogen concentration was assumed to be all bonded to silicon and the Si ₃ N ₄ content was determined. When the molar ratio of Si ₃ N ₄ / SiO ₂ is less than 0.05, the high temperature side peak is dominant, while the dielectric film added more than that has the same high temperature side peak but low temperature side peak. Was found to grow and become dominant.

Therefore, the low temperature side peak does not appear,
That is, if it was possible to increase the amount of nitrogen bound to the elements in the film without including the nitrogen not bound to the elements in the film, the inventors considered that the overwrite characteristics would be further improved, and conducted extensive studies.
As a result, the following was found. (1) The amount of ZnS must be 40 mol% or more and 95 mol% or less in the film. If it exceeds 95 mol%, good overwrite cycle characteristics cannot be obtained. This is because it does not contain silicon oxynitride enough to sufficiently disperse the ZnS crystals, so the ZnS crystal growth proceeds due to the temperature rise during recording, the recording characteristics change, or the dielectric film is destroyed. It is thought to be easier. On the other hand, if it is less than 40 mol%, the noise increase with the cycle becomes large and the cycle characteristics are rather deteriorated. Further, the refractive index of the dielectric film becomes small, the reflectance change between amorphous and crystalline becomes small, or the film forming rate at the time of sputtering becomes slow, which is not preferable. (2) The molar ratio of Si ₃ N ₄ to SiO ₂ is preferably 0.05 or more and 1 or less. When it is less than 0.05, the cycle characteristics are improved as compared with the ZnS-SiO ₂ film, but it is not sufficient. Conversely 1
With the above, the cycle characteristics are rather deteriorated. This is Si ₃ N
_Although the mechanical strength of the film increases with the addition of ₄ , it is presumed that it may be because the film becomes hard and brittle. Incidentally, in the conventional film formation of a mixed target of ZnS and SiO ₂ in an Ar + N ₂ atmosphere, if it is made to be 0.05 or more, the nitrogen which does not combine with the elements in the film increases, so the cycle characteristics deteriorate rather.

A good overwrite cycle can be obtained if the composition of the dielectric is within the range that simultaneously satisfies the above (1) and (2). The dielectric film is considered to be a mixture of ZnS and silicon oxynitride, and the combination of Si, O, and N elements is Si.
-O, Si-N, ON is considered to be mixed, but in the present invention, this is represented as a mixture of ZnS, SiO ₂ and Si ₃ N ₄ (this expression is almost the case when the dielectric is transparent). I confirmed that the method is possible).

Next, a manufacturing method for easily and stably forming a dielectric layer made of a mixed material of ZnS and silicon oxynitride, which contains a large amount of nitrogen combined with elements in the film, will be described. One is a method of forming a film from a mixture target of ZnS, SiO ₂ and Si ₃ N ₄ by a sputtering method in a rare gas (for example, argon) atmosphere. In this case, it was observed that the cycle characteristics could be improved by adding a trace amount of N ₂ to the rare gas. It is speculated that this is because nitrogen atoms are bonded to dangling bonds of silicon or the like, and the strength of the film is increased. However, also in this case, if the amount of nitrogen added was too large, the cycle characteristics deteriorated sharply. It is considered that this is because unbound nitrogen is incorporated into the film.

Furthermore, ZnS and silicon oxide SiO _x (0 ≦ x ≦ 1.
Using a target composed of the mixture of (95), a film is formed by a sputtering method in a mixed gas atmosphere of a rare gas and nitrogen or a mixed gas atmosphere of a rare gas, nitrogen and oxygen. Since the target silicon oxide is not sufficiently oxidized, a large amount of nitrogen combined with the elements in the film is introduced into the film by the reactive sputtering.

FIG. 1 shows an example of the structure of the optical information recording medium according to the present invention. A first dielectric layer 2, a recording layer 3, a second dielectric layer 4, and a reflective layer 5 are laminated in this order on a substrate 1. Although glass, resin, etc. can be used as the substrate 1, transparent glass, quartz, polycarbonate resin, polymethylmethacrylate resin, polyolefin resin, etc. are generally used. The recording layer 3 is a phase change medium,
An alloy such as Te, Se, Sb, In, Ge that causes a state change between an amorphous and a crystal, or a crystal and a different crystal, for example, GeSbTe, InSbTe, GaSb, InGaSb, GeSnTe, AgSbTe.
And so on. The reflective layer 5 is composed of a simple substance such as Au, Al, Ti, Ni, Cr or an alloy. The first dielectric layer 2 and / or the second dielectric layer 4 are composed of a mixed material of ZnS and silicon oxynitride.

FIG. 1 shows a four-layer structure having a reflective layer,
The dielectric layer of the present invention is also effective for a three-layer structure having no reflective layer or other laminated structures.

[0028]

The present invention will be described more specifically with reference to the following examples.

[0029]

Example 1 As a substrate, a polycarbonate substrate having a diameter of 120 mm with a signal recording track previously provided therein, a ternary material made of GeSbTe as a recording layer, an Al alloy as a reflective layer, and ZnS, SiO ₂ and Si ₃ as upper and lower dielectric layers. An optical disc was produced using a mixed material of N ₄ . Note that a resin coat was applied on the reflective layer to protect the thin film layer of the optical disc. Here, a plurality of optical discs were manufactured by changing only the composition ratio of the dielectrics while setting the thickness of each layer and the composition of the recording layer and the reflection layer to be the same, and the composition of the dielectrics and the overwrite cycle characteristics were investigated.

The thickness of each layer is 140 n for the first dielectric layer.
m, the recording layer is 25 nm, the second dielectric layer is 30 nm, and the reflective layer is 150 nm. Each layer was formed by the sputtering method, but the dielectric layer was made of Zn in order to change its composition ratio.
Films were formed by co-sputtering in an argon atmosphere using S, SiO ₂ and Si ₃ N ₄ targets. Each composition in the dielectric layer was determined by SIMS and AES.

The produced optical disk has a laser wavelength of 780.
5MHz and 3M while rotating at 10m / s by a signal evaluation device having an optical system of nm and numerical aperture (NA) of 0.55.
The CNR (signal-to-noise ratio) of the signal of 5 MHz was measured while alternately overwriting Hz to determine the cycle characteristics. Although the CNR decreases with the overwrite cycle, the overwrite cycle that is 3 dB lower than the initial CNR is defined as the cycle life of the optical disk.

Table 1 shows the relationship between the composition of the dielectric and the cycle life. It is confirmed that the composition range of the dielectric material that can obtain a good cycle life of 500,000 times or more is that the amount of ZnS is 40 mol% or more and 95 mol% or less and that Si ₃ N ₄ / SiO ₂ is 0.05 or more and 1 or less. did it.

[0033]

[Table 1]

[0034]

Example 2 An optical disk having the same structure as in Example 1 was prepared by producing a target made of a mixed material of ZnS, SiO ₂ and Si ₃ N ₄ . The composition ratio of the target is ZnS: 70mol%, SiO ₂ : 2
4 mol%, Si ₃ N ₄ : 6 mol% (Si ₃ N ₄ / SiO ₂ = 0.25). The dielectric layer was formed using this target in an argon atmosphere (optical disk A) and in a mixed gas atmosphere of argon and nitrogen (optical disk B). The amount of nitrogen added in the optical disk B was set to 2% of the total pressure.

When the cycle life of the optical discs A and B was measured by the same method as in Example 1, it was 1 for the optical disc A.
It was, 000,000 times, and with optical disk B, it was 1.5 million times. That is, it can be seen that good cycle characteristics can be obtained even when a film is formed from a single target made of a mixed material of ZnS, SiO ₂ and Si ₃ N ₄ . The cycle characteristics were further improved by the addition of nitrogen, which was also confirmed with targets composed of other composition ratios of ZnS, SiO ₂ and Si ₃ N ₄ . However, the concentration of nitrogen added, which improves cycle characteristics, was 0.5% or more and 10% or less in terms of partial pressure. On the other hand, at 10% or more, the number of cycles decreased, but this is probably because unbound nitrogen was incorporated into the film.

[0036]

Example 3 A target made of a mixture of ZnS and silicon oxide SiO _x (x = 1.1) was prepared to prepare an optical disk having the same structure as that of Example 1. The composition ratio of the target is ZnS: 70mol
%, SiO _x : 30 mol%. The dielectric layer was formed using this target in a mixed atmosphere of argon, nitrogen and oxygen (optical disk C). The amount of nitrogen added is 10 relative to the total pressure.
%, And the amount of oxygen added was 15% of the total pressure. The dielectric film formed under these conditions is colorless and transparent, and its composition was analyzed. ZnS: 72 mol%, SiO ₂ : 23 mol%, Si ₃ N ₄ : 5 m
was _{ol% (Si 3 N 4 /} SiO 2 = 0.22).

When the cycle life of the optical disk C was measured by the same method as in Example 1, it was 1.4 million times, and good cycle characteristics were obtained. It was found that when the value of x of SiO _x is 0 or more and 1.95 or less, the film formation by the method of this example is effective and good cycle characteristics can be obtained. x is 1.95
If it exceeds, even if film formation is performed in a mixed gas atmosphere of argon and nitrogen, the effect of improving cycle characteristics is small.

[0038]

As described above, according to the present invention, the dielectric layer is made of a mixture of ZnS and silicon oxynitride in which nitrogen is combined with silicon in the film, whereby the mechanical strength is increased, The write cycle is improved. Since nitrogen is bonded to the element in the film, it does not move into the recording film even when it is heated by the overwrite cycle, and the recording characteristics do not change. As a result, the overwrite cycle characteristics of the phase change type optical information recording medium are particularly good,
It is possible to provide a highly reliable optical information recording medium.

Further, according to the first to second manufacturing methods of the present invention, the dielectric layer can be formed from one target with good reproducibility, stability, efficiency, and rational deposition. further,
According to the optical information recording medium and the method for manufacturing the same according to the present invention, an optical disc having good cycle characteristics and high reliability can be obtained.
It can be supplied with the same device as the conventional manufacturing method.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an optical information recording medium according to an embodiment of the present invention.

[Explanation of symbols]

 1 Substrate 2 First Dielectric Layer 3 Recording Layer 4 Second Dielectric Layer 5 Reflective Layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Isomura 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A substrate having at least a first dielectric layer, a recording layer made of a material that undergoes a reversible change between optically distinguishable states upon irradiation with a laser beam, and a second dielectric layer on a substrate.
An optical information recording medium having laminated dielectric layers, wherein at least one of the first dielectric layer and the second dielectric layer comprises a mixture of ZnS and silicon oxynitride. An optical information recording medium characterized by: 2. The amount of ZnS in the dielectric is 40 mol%
Above 95 mol% and the molar ratio of Si ₃ N ₄ and SiO ₂ (Si ₃ N ₄ / S
The optical information recording medium according to claim 1, wherein iO ₂ ) is in the range of 0.05 or more and 1 or less. 3. A substrate, at least a first dielectric layer, a recording layer made of a material that causes a reversible change between optically distinguishable states upon irradiation with a laser beam, and a second dielectric layer on a substrate.
A method for manufacturing an optical information recording medium, which comprises laminating dielectric layers of at least one of the first dielectric layer and the second dielectric layer.
Of one of the dielectric layers of ZnS and silicon oxynitride, and the dielectric layer using a target of a mixture of ZnS, SiO ₂ and Si ₃ N ₄ , mixed rare gas and nitrogen. A method for manufacturing an optical information recording medium, which comprises forming a film by a sputtering method in a gas atmosphere. 4. A substrate on which at least a first dielectric layer, a recording layer made of a material that reversibly changes between optically distinguishable states upon irradiation with a laser beam, and a second dielectric layer are provided.
A method for manufacturing an optical information recording medium, which comprises laminating dielectric layers of at least one of the first dielectric layer and the second dielectric layer.
One of the dielectric layers of ZnS and silicon oxynitride is used, and the dielectric layer is formed by using a target of a mixture of ZnS and silicon oxide SiO _x (0 ≦ x ≦ 1.95). A method for producing an optical information recording medium, which comprises forming a film by a sputtering method in a mixed gas atmosphere of gas and nitrogen or a mixed gas atmosphere of rare gas, nitrogen and oxygen. 5. The amount of ZnS in the dielectric is 40 mol%
Above 95 mol% and the molar ratio of Si ₃ N ₄ and SiO ₂ (Si ₃ N ₄ / S
The method for producing an optical information recording medium according to claim 3, wherein the film is formed so that iO ₂ ) is in the range of 0.05 or more and 1 or less.