JPH05135409A - Optical recording medium and production of the same - Google Patents

Abstract

PURPOSE:To improve protection of a recording layer and consequently to improve is weatherability and long-term stability by forming 1st an 2nd protective film layers to have boron nitride films contg. boron nitride respectively varying in crystal structure. CONSTITUTION:A 1st layer 12 has a boron nitride film layer contg. boron nitride h-BN resembling hexagonal graphite and a 2nd protective film 14 has the boron nitride film layer contg. boron nitride c-BN having the sphalerite crystal structure of a cubic crystal system, respectively. The boron nitride film layers are chemically excellent in stability and therefore excellent in the protective property of the recording layer. The function to protect the recording layer is thus improved and the weatherability and stability are improved as well. The c-BN has a high thermal conductivity, and therefore diffuses heat within the protective film layer 14. An amorphous state of a small recording spot size is easily obtd. and C/N is improved. Generation of imperfect erasing is simultaneously obviated and the erasing ratio is improved.

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 recording medium capable of recording, erasing and reproducing information by irradiating light to heat a recording layer and a method for manufacturing the same. is there.

[0002]

2. Description of the Related Art With the demand for higher density of information, an optical recording medium which can take a large recording density in a non-contact manner has been researched and developed in place of the magnetic recording medium used conventionally. There are several types of this optical recording medium, but information can be recorded, reproduced, and erased compared to the read-only type that can only read information and the write-once type that can only record and reproduce. The rewritable type has a wide range of applications and is most expected to be put into practical use.

This rewritable optical recording medium is mainly classified into a magneto-optical type and a phase change type. In the former, when a magnetic film is irradiated with laser light and the temperature of the irradiated part rises and the coercive force decreases. Information is recorded or erased by utilizing the fact that magnetization is easily reversed, and information is reproduced by linearly polarizing light and rotating the polarization plane that occurs when reflected and transmitted on the surface of the magnetic film, that is, Kerr effect or It uses the Faraday effect.

On the other hand, in the phase change type, for example, when a material containing a chalcogen element as a main component is irradiated with a laser beam and heated to a temperature equal to or higher than the melting point and rapidly cooled, it becomes an amorphous state and has a crystallization temperature. Information is recorded / erased by utilizing the fact that it becomes a crystalline state when heated to a temperature between the melting point and the melting point, and information is reproduced by utilizing the difference in reflectance between the two.

Among the rewritable optical recording media, the phase change type is generally ZnS ₂ , ZrO ₂ or SiO ₂ on a substrate such as polycarbonate (PC), epoxy resin, acrylic resin (PMMA) or the like. A first protective layer is formed, a recording layer is formed on the first protective layer, and a second protective layer made of the same material as the first protective layer is further formed on the first protective layer (the second protective layer is further formed). In some cases, an organic protective layer is laminated on the layer).

The material used for the recording layer is required to be a substance that is rapidly crystallized, the amorphous state is stable for a long period of time, and the operation characteristics are stable even if the number of times of rewriting is increased. , In-Sn system, Ge-Sb-Te system, Ge-Te system, Sn-Te
The system or Te-O-Sn-Ge system is used. Further, the protective layer is preferably one having a large heat insulating effect so as to improve weather resistance such as oxidation resistance of the recording layer, ensure long-term stability, and efficiently heat the recording layer.
S ₂ , ZrO ₂ or SiO ₂ is used.

[0007]

However, since the protective layer has a heat insulating effect, quenching of the recording layer is often insufficient, so that the recording layer is changed from a crystallized state to an amorphous state. , The write signal level is lowered, the recording spot size is increased, and information cannot be sufficiently erased.

Further, due to the heat generated by the laser beam, the
When writing is repeated, the substrate is deformed, which causes a problem that the long-term stability of the optical recording medium is deteriorated. Therefore, the first protective layer and the second protective layer are made of materials having good thermal conductivity, or a reflective cooling layer made of Al or the like is provided on the second protective layer to improve the cooling ability of the recording layer. Attempts have been made to improve it.

However, if the cooling capacity of the recording layer is too large, the sensitivity to the laser power decreases, so that the problem arises that the laser power must be increased. Therefore, an object of the present invention is to increase the crystallization rate of the recording layer without lowering the sensitivity to laser power and increase the cooling rate when changing to an amorphous state.
Moreover, it is an object of the present invention to provide an optical recording medium capable of preventing the substrate from being deformed by heat even when repeatedly recording, erasing and writing, and a manufacturing method thereof.

[0010]

An optical recording medium according to claim 1 comprises a substrate, on which a first protective layer, a recording layer, a second protective layer, and a reflective cooling layer are sequentially formed, and the recording layer is a substrate. In an optical recording medium in which laser light is incident from the side to cause a reversible phase change, the first protective layer mainly has a boron nitride film layer containing boron nitride having a crystal structure similar to hexagonal graphite. The second protective layer mainly has a boron nitride film layer containing boron nitride having a cubic zinc blende type crystal structure.

The method of manufacturing an optical recording medium according to a second aspect is the method of manufacturing an optical recording medium according to the first aspect, wherein the boron nitride film layer is formed by vacuum vapor deposition or sputtering on the layer formation surface. And the deposition of boron at the same time, alternately or after the deposition of boron, by irradiating the layer-forming surface with ions containing nitrogen ions, and mixing the nitrogen ions with an inert gas, etc. By controlling the number ratio of boron atoms and nitrogen atoms, the acceleration energy of ions, and the like, the first protective layer mainly contains boron nitride having a crystal structure similar to that of hexagonal graphite, and the second protective layer contains It is characterized in that it mainly contains boron nitride having a cubic zinc blende type crystal structure.

[0012]

According to the optical recording medium of claim 1, as shown in FIG. 1, a first protective layer 12, a recording layer 13, a second protective layer 14 and a reflective cooling layer 15 are sequentially formed on a substrate 11. Has been done. 16 is a surface protective layer. In this case, the first protective layer is mainly boron nitride having a crystal structure similar to that of hexagonal graphite (hereinafter referred to as h-BN).
The second protective layer mainly has a boron nitride film layer containing boron nitride having a cubic zinc blende type crystal structure (hereinafter referred to as c-BN). Since these boron nitride film layers are excellent in chemical stability, they are excellent in function as a protective layer of the recording layer, weather resistance is improved, and long-term stability of the optical recording medium is secured. Also c-
Since BN has a high thermal conductivity, the heat applied to the recording layer is
Since it is diffused in the protective layer, the temperature rise region where the recording layer is irradiated with the laser beam during writing is limited,
An amorphous state with a small recording spot size diameter is obtained in the recording layer to improve the C / N ratio (carrier-to-noise ratio), and
Since the cooling rate of the recording layer at the time of erasing is improved and the recording spot size diameter is made smaller than the irradiation diameter of the laser beam, the problem of remaining unerased can be solved. It is possible to improve. In addition, the thermal effect on the substrate is mitigated and the substrate can be prevented from being deformed by heat, so that stable and good repeating characteristics can be obtained. Furthermore h-
Since BN is included in the first protective layer, it is possible to adjust the cooling capacity of the optical recording medium and prevent a decrease in sensitivity to laser power.

According to a second aspect of the present invention, there is provided a method for producing an optical recording medium, which comprises depositing boron on the surface of a base material on which a layer is formed by vacuum vapor deposition or sputtering, and simultaneously, alternately or after depositing boron. A boron nitride film layer is formed by irradiating the layer formation surface with ions including nitrogen ions.
An example of this apparatus is shown in FIG. That is, 1 is a substrate, 2 is a holder for supporting the substrate 1, 3 is an evaporation source for evaporating a substance containing a boron element, 4 is an ion source for irradiating ions, and 5 is a layer of a base material such as the substrate 1. A film thickness monitor for measuring the number of boron vapor-deposited on the formation surface and its film thickness, for example, a crystal vibration type film thickness meter, 6 for measuring the number of ions irradiated on the layer formation surface , An ion current measuring device such as a Faraday cup equipped with a secondary electron suppressing electrode. These are housed in a vacuum container (not shown).

In carrying out this manufacturing method, the substrate 1 is first supported by the holder 2 and then the inside of the vacuum container is set to 1 × 10.
Evacuate to a high vacuum of ^-5 Torr or less. In this case, the substrate 11 itself is held by the holder 2 when the first protective layer 12 is formed on the substrate 1, and the substrate 1 is held when the second protective layer 14 is formed.
A holder 2 holds the first protective layer 12 and the recording layer 13 formed on the holder 1.

Then, the evaporation source 3 is driven to vacuum-deposit the substance 3'containing the boron element on the substrate 1. On this occasion,
As the substance containing the boron element, simple substance of boron, oxide of boron element, nitride, or the like is selected. Also,
The method of the evaporation source 3 is not particularly limited, and for example, a method using means such as an electron beam (EB), laser or high frequency is appropriately selected.

Further, the substance 3'containing elemental boron is
A film may be formed on the substrate 1 by sputtering. At this time, the method of sputtering is not particularly limited, and the ion beam is used.
It is sputtered by means such as a magnet, magnetron or high frequency. At the same time as, or alternately with, one of the vacuum deposition and the sputtering of the substance 3 ′ containing the boron element, or after the completion of the vacuum deposition / sputtering, the ion source 4
Ions 4'containing more nitrogen ions are irradiated onto the surface to be vapor-deposited. As the ions 4 ', nitrogen ions or a mixture of nitrogen ions with inert gas ions or hydrogen ions is selected. Also, the type of the ion source 4 is not particularly limited, and for example, a Kauffman type, a bucket type or the like is selected.

As a result, boron nitride (B
A thin film containing N) is formed, and the atoms forming the layer and the mixed layer thereof are formed at the interface between the substrate 1 etc. and the boron nitride film layer by collision and recoil of the vapor deposition substance and the ions. A boron nitride film layer having excellent adhesion is formed on the layer forming surface. At this time, the acceleration energy of the irradiated ions is preferably 10 KeV or less per ion. When it exceeds 10 KeV, damage to the substrate 1 by irradiation ions becomes excessive, which is not preferable.

Further, the evaporation amount of the boron-containing substance during the film formation and the nitrogen ions are adjusted so that the atomic ratio of boron and nitrogen (B / N composition ratio) contained in the boron nitride film layer becomes 20 or less. It is necessary to appropriately adjust the irradiation dose of the contained ions.
This is because when the B / N composition ratio of the boron nitride film layer exceeds 20, the amount of boron nitride contained in the layer decreases.
This is because there is a risk that the properties of boron nitride will not be fully extracted. The film thickness monitor 5 is used to adjust the B / N composition ratio.
And the ion current measuring device 6.

As described above, by the method of depositing boron on the layer-forming surface by any one of vacuum deposition and sputtering, and simultaneously, alternately or after depositing boron, the method of irradiating with ions containing nitrogen ions is performed. Not only is boron nitride (h-BN) having a hexagonal crystal system having a chemical structure similar to that of graphite, which is soft, but having high chemical stability, not only contained in the boron nitride film layer, but also ion and boron atoms to be vapor-deposited. Since boron atoms that are vapor-deposited etc. are excited by the collision of Cu, a thin film of c-BN having a cubic zincblende crystal structure with high chemical stability and high thermal conductivity is synthesized under a non-thermal equilibrium process. It becomes possible with.

Further, by cooling the holder 2 supporting the substrate 1 with water, it is possible to cool the substrate 1 during formation of the boron nitride film layer, thereby further preventing damage due to heat during film formation. Is possible. During film formation,
It has been confirmed that the adhesion between the boron nitride film layer and the substrate 1 and the content of c-BN do not change even when the substrate 1 is cooled.

Then, for example, when forming the first protective layer 12, nitrogen is used as an ionic species, and the second protective layer 1 is used.
When 4 is formed, a mixture of nitrogen and an inert gas is used as an ionic species. As a result, the first protective layer 12
Mainly consists of h-BN, and the second protective layer mainly consists of c-BN. Further, in the first protective layer 12, the irradiation energy of ions is set to 2 KeV or less, and the number of boron atoms and nitrogen ions reaching the substrate during film formation (B / N transport ratio).
Is adjusted between 2 and 4, h-B in the boron nitride film
Not only N but also c-BN comes to be contained. Therefore, for the first protective layer 12, the optimum mixture ratio of h-BN and c-BN may be determined from the C / N ratio when writing to the optical recording medium. The second protective layer 14 is formed under the condition of B / N transport ratio = 1 using Ar as an inert gas in the acceleration energy of ions of 2 KeV or less, for example. As a result, the second protective layer becomes a layer mainly composed of c-BN.

According to this manufacturing method, c-BN can be synthesized at a low temperature by utilizing the exciting action due to the collision between the vaporized atoms and the ions, so that the substrate 11 and the recording layer 13 in the manufacturing process are manufactured. It is possible to avoid the heat influence on. Since high temperature is required when synthesizing this c-BN by another method, for example, the CVD method, the substrate 11 and the recording layer 13 are likely to be thermally damaged, and the substrate 11 is coated with a thin film. Was difficult. Further, when the boron nitride film layer is formed, by controlling the mixing amount for mixing an inert gas or the like with nitrogen ions, the number ratio of boron atoms and nitrogen atoms in the layer, and the acceleration energy of ions, B
Since the crystal structure of N can be changed to h-BN or c-BN, it is relatively easy to manufacture the protective layer having the effect described in claim 1. Further, due to the collision between the vaporized atoms and the ion irradiation, a mixed layer composed of the constituent atoms of both is formed between the boron nitride film layer and the base material thereof, so that a layer having excellent adhesion is formed.

[0023]

EXAMPLE The optical recording medium of FIG. 1 is manufactured. That is, the substrate 11 is a polycarbonate (PC) substrate on which a number of tracking grooves (not shown) are formed, on which a first protective layer 12 of 30 nm and a recording layer 1 of Ge-Sb-Te system of 60 nm are formed.
A second protective layer 14 having a thickness of 3,200 nm, a reflective cooling layer 15 made of Al having a thickness of 100 nm, and a surface protective layer 16 made of UV resin having a thickness of 10 nm are sequentially laminated.

In this optical recording medium, the first protective layer 1
2 was prepared by the apparatus shown in FIG. 2 using nitrogen ions having an acceleration energy of 500 ev while adjusting the B / N transport ratio so that the B / N composition ratio was 2.
Is a mixed ion of nitrogen ions and Ar ions with an acceleration energy of 2 KeV (created so that the gas pressure ratio of Ar gas / nitrogen gas when introduced into the ion source is 30%),
It was prepared while adjusting the B / N transport ratio so that the B / N composition ratio = 1.

When writing on this optical recording medium (the recording layer is in a crystallized state in advance), the rise of the laser power is 16 mW, C / N ratio = 22 dB, and C / N when 25 mW.
The ratio was 55 dB. Also, write a 3.7MHz, duty33% signal with a power ratio of 23 / 10mW, and then write 2.22MHz to the same place.
, Duty20% signal was overwritten under the same power condition, the write C / N ratio was 50dB and the erase ratio was 27dB.
Met.

As Comparative Example 1, in the optical recording medium of FIG. 1, both the first protective layer and the second protective layer formed of a SiO ₂ layer without a boron nitride film layer, a laser for writing was used. Power rises at 16mW and C / N
The C / N ratio when the ratio was 22 dB and 25 mW was 55 dB. In addition, when the 3.7MHz, duty33% signal was written at a power ratio of 23 / 10mW, and then the 2.22MHz, duty20% signal was overwritten at the same location under the same power condition, the C / N ratio for writing was It was 45 dB and the erasure ratio was 20 dB.

As Comparative Example 2, in the optical recording medium of FIG. 1, both the first protective layer 12 and the second protective layer 14 are c.
-Use is made of a boron nitride film layer mainly composed of BN.
The rise of the laser power at the time of writing in this comparative example 2 is 20 mW, C / N ratio = 16 dB, and C at 25 mW.
The / N ratio was 45 dB. Also, as in the first embodiment,
3.7MHz, duty33% signal was written at 23 / 10mW power ratio, then 2.22MHz, duty20% signal was overwritten at the same power condition at the same power condition. The C / N ratio of writing was 50dB, The erase ratio was 27 dB.

As described above, the one according to the present invention has an excellent erasing ratio and the like as compared with the protective layer using only the one having the heat insulating effect as in Comparative Example 1, and the first protective layer 12 and the second protective layer. C-B having excellent thermal conductivity for both protective layers 14 of
It can be seen that the laser power sensitivity is superior to that of Comparative Example 2 in which the boron nitride film layer containing N is used.

In the present invention, the recording layer, the reflection cooling layer and the surface protection layer, the type of substrate and the film thickness of each layer are not particularly limited. Further, the entire first protective layer and the second protective layer may be formed by the boron nitride film layer, or the boron nitride film layer may be formed on a part of the first protective layer and the second protective layer. It may be a thing.

[0030]

According to the optical recording medium of the first aspect, in the optical recording medium in which the first protective layer, the recording layer, the second protective layer, and the reflection cooling layer are sequentially formed on the substrate, the first recording layer is formed. The protective layer has a boron nitride film layer containing mainly boron nitride having a crystal structure similar to that of hexagonal graphite, and the second protective layer is mainly a cubic boron-blende-type boron nitride crystal structure. Since it has a boron nitride film layer containing (c-BN), the protective layer has an excellent function of protecting the recording layer by the boron nitride film having excellent chemical stability, and thus the weather resistance of the recording layer is improved and The long-term stability of the recording medium is secured. Further, since the heat conductivity of c-BN is high, the heat applied to the recording layer is diffused in the second protective layer, so that the temperature rising region where the recording layer is irradiated with the laser beam during writing is limited. As a result, an amorphous state with a small recording spot size diameter is obtained in the recording layer, the CN ratio (carrier-to-noise) ratio is improved, and the cooling speed of the recording layer at the time of erasing is improved, and the recording spot size diameter is reduced. By making the irradiation diameter of the laser light smaller, it is possible to solve the problem of remaining unerased and improve the erasing ratio. In addition, the thermal effect on the substrate is mitigated and the substrate can be prevented from being deformed by heat, so that stable and good repeating characteristics can be obtained. Furthermore, h-BN is the first
With the protective layer, the cooling capacity of the optical recording medium is adjusted, and it is possible to prevent a decrease in sensitivity to laser power.

According to the method of manufacturing an optical recording medium of claim 2, the layer is formed on the layer-forming surface by deposition of boron by either vacuum deposition or sputtering, and simultaneously, alternately and after the deposition of boron. Since the boron nitride film layer is formed by irradiating the surface with ions including nitrogen ions, c-BN can be synthesized at a low temperature at which thermal influence on the substrate and the recording layer can be avoided. Further, when forming a boron nitride film layer, by controlling the amount of nitrogen gas mixed with an inert gas, the number ratio of boron atoms and nitrogen atoms in the layer, and the acceleration energy of ions, the BN crystal structure can be obtained. Since it can be changed to one having a structure similar to hexagonal graphite or one having a cubic zinc blende type crystal structure, it is relatively easy to manufacture a protective layer having the effect of claim 1. Further, the collision between the vaporized atoms and the ion irradiation forms a mixed layer composed of the constituent atoms of the boron nitride film layer and the underlying material, so that a layer having excellent adhesion is formed. There is.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a layer structure of an optical recording medium.

FIG. 2 is a schematic explanatory view of an apparatus for carrying out the manufacturing method of the present invention.

[Explanation of symbols]

 11 substrate 12 first protective layer 13 recording layer 14 second protective layer 15 reflective cooling layer

Front page continuation (72) Inventor Akinori Ebe 47 Umezu Takaunecho, Ukyo-ku, Kyoto City Nissin Electric Co., Ltd.

Claims (2)

[Claims] 1. A first protective layer, a recording layer, a second protective layer, and a reflective cooling layer are sequentially formed on a substrate, and the recording layer is reversible when laser light is incident from the substrate side. In the phase change optical recording medium, the first protective layer mainly has a boron nitride film layer containing boron nitride having a crystal structure similar to hexagonal graphite, and the second protective layer is mainly cubic. An optical recording medium having a boron nitride film layer containing boron nitride having a crystallized zinc blende type crystal structure. 2. The method of manufacturing an optical recording medium according to claim 1, wherein the boron nitride film layer is deposited on the layer-forming surface by vacuum vapor deposition or sputtering by at least one of: Alternately or after deposition of the boron, formed by irradiating ions containing nitrogen ions on the layer forming surface, and the nitrogen ions mixed amount of an inert gas or the like,
By controlling the number ratio of boron atoms and nitrogen atoms in the layer, the acceleration energy of ions, and the like, the first protective layer mainly contains boron nitride having a crystal structure similar to hexagonal graphite, 2. A method for producing an optical recording medium, characterized in that the protective layer 2 contains mainly boron nitride having a cubic zinc blende type crystal structure.