JP2000067465A - Optical recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an optical recording medium have practical durability against contact and sliding between a medium and a head, and to make reproducible signals (reproducing compatibility) by a driving device which uses about 410 nm blue laser light in future in an optical recording medium having a reflection film between the substrate and the recording film for a method with light entering the medium face. SOLUTION: The optical recording medium has a basic structure consisting of a substrate, reflection layer, lower dielectric layer, recording layer and upper dielectric layer. Further, a DLC film (diamond-like carbon film) having >=1300 kg/mm2 plastic deformation hardness, <=2.7 refractive index (n) for light at 410 nm wavelength, and <=0.4 extinction coefft. (k) is formed on the upper dielectric layer (namely, as an uppermost layer of the medium facing to a head).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium on which information is recorded and reproduced using light. In particular, the present invention relates to an optical recording medium of a type that performs recording and reproduction by irradiating a laser beam from the recording film surface side without passing through a plastic substrate, and further relates to a phase change recording medium.

[0002]

2. Description of the Related Art At present, all optical recording media commonly used are substrate-incident type optical disks in which a recording film is irradiated with a laser beam through a transparent substrate. In contrast, in recent years, attention has been paid to a film-surface incident type optical recording in which laser light is irradiated from the film surface side without passing through the substrate (see the magazine "Electronics", May 1996, pp. 87-91).

It is anticipated that this film surface incidence type medium will be capable of higher density recording than conventional media. As a recording method of the medium, a magneto-optical recording medium and a phase change recording medium are considered.

In a magneto-optical recording medium, the temperature of a recording film is increased by light irradiation, mainly laser light irradiation, the coercive force of the film is reduced, and recording / erasing is performed by reversing the magnetization direction by an external magnetic field. Things. The temperature of the recording film rises to about 200 ° C.

A phase change recording medium uses a reversible structural change (phase change) between an amorphous state and a crystalline state of a substance caused by light irradiation, mainly laser light irradiation, for recording and erasing information. We are using. The temperature of the recording film is about 600 at the time of recording.
° C, and about 170 ° C during erasing. Such a phase change recording medium has a large recording capacity in addition to a high-speed information processing capability. Also, there is an advantage that the price of the drive is lower than that of the magneto-optical recording drive because its structure is simpler.

A typical structure of the magneto-optical recording medium and the phase change recording medium is a laminate of an inorganic thin film formed by vapor deposition or sputtering on a transparent disk made of polycarbonate (PC). Commercially available normal media are PC / first dielectric / recording film / second dielectric / reflective film / organic resin protective layer,
It is a structure called. The recording layer of the magneto-optical recording medium is TbFe
Rare earth / transition metal alloys such as Co and chalcogen alloys such as GeSbTe and AgInSbTe are used for the recording layer of the phase change recording medium. The dielectric of the magneto-optical recording medium is S
The nitride of the nitride film such as iN and the dielectric of the phase change recording medium are ZnS
A ZnS-based film such as SiO ₂ is used.

In a phase change recording medium, the erasing state of information is usually set to the crystalline state of the recording film, and the recording state is usually set to the amorphous state generated by melting and quenching of the film with high laser power. Further, the recording layer of the phase change recording medium is in an amorphous state immediately after the sputter deposition, and is used after being subjected to an overall annealing treatment to be in a crystalline state, that is, an erased state.
The entire surface is annealed, for example, at about 1 watt,
This is performed by irradiating a laser beam having a width of 2 μm and a length of about 100 μm. This step is called initialization (initial crystallization).

[0008] Even in the case of a magneto-optical recording medium, the direction of the magnetization immediately after the sputter deposition of the recording film is random, and a process of aligning this magnetization direction to a fixed (corresponding to the erased state) is often adopted. It is called bulk erasing, but the coercive force is reduced by heating to near the Curie temperature of the recording film with a laser beam, as in the case of bulk erasing with a strong external magnet and the initialization of the phase change recording medium. In such a state, a weak magnetic field may be applied to perform bulk erasure.

For these current commercial ordinary media,
It is a common idea to reverse the stacking order of thin films from a substrate in a film-surface incident type medium for which research has begun. That is, research is being conducted on the basic structure of a substrate / reflective film / lower dielectric / recording film / upper dielectric. Note that a heat insulating layer is often required between the substrate and the reflective film. In particular, in a phase change recording medium, the temperature rise of the recording film is large, it is necessary to reduce thermal damage to the PC substrate, and the need for a heat insulating layer is great.

The optical head (pickup) used is
A structure similar to that of a hard disk has been proposed because the medium surface and the objective lens of the optical head need to be close to each other. That is, research is being conducted using a flying head having an objective lens mounted on a slider. Therefore, a film having high hardness is used as the upper dielectric so as to withstand contact with the slider. A typical example of such a film is a nitrided film of Si or Al, which has been frequently used as a dielectric of a magneto-optical recording medium.

[0011]

In the case of the film surface incidence type medium, a flying head (floating head) having a known structure for an HD (hard disk) equipped with an objective lens or an SIL (solid immersion lens) is used. The flying height is about 0.35μm ~ 0.5μm for early development products
Flying heads are planned. By using the flying head, unlike the conventional substrate incident type optical recording medium, there is a risk of contact between the disk and the head. In higher density recording, the flying height is further reduced, so that the frequency of contact and sliding between the head and the disk increases. In other words, it is necessary to consider from now on that even the media in the early stage of development can be played back with a higher density drive in the future (playback compatibility), and a media design that can provide sufficient contact and sliding durability must be considered. is necessary. A blue laser of about 410 nm will be used for recording and reproduction in future high-density recording drives, and it is necessary to consider that even with current media, recorded discs can be reproduced by such drives (reproduction compatibility). It is necessary to keep.

That is, according to the present invention, in the development of the above-mentioned film-incidence type optical recording medium having a reflection film between a substrate and a recording film, contact durability and sliding durability are considered in consideration of an interface with a head. An object is to obtain an excellent optical recording medium. A further object of the present invention is to obtain an optical recording medium which is also compatible with a drive using a blue laser in the future.

[0013]

The optical recording medium of the present invention comprises:
In an optical recording medium for recording / reproducing information utilizing a change in physical characteristics of a recording layer caused by light irradiation, a substrate,
It has a basic structure including a reflective layer, a lower dielectric layer, a recording layer, and an upper dielectric layer. Further, on the outer layer side of the upper dielectric layer, a plastic deformation hardness ≧ 1300 kg / mm ² , and a refractive index (410 nm light) n) ≦ 2.7 and the extinction coefficient (k) ≦ 0.
4 is characterized by having a DLC film (diamond-like carbon film).

That is, by forming a DLC film having a predetermined hardness and a low friction coefficient on the outer layer side of the upper dielectric layer, the contact durability with the head was improved. The DLC film has a sufficient light transmittance for reproducing the recorded data even with respect to the blue laser light.

In the present invention, the optical recording medium is preferably a phase-change recording medium that records and reproduces information by utilizing a change in the structural characteristics of the recording layer caused by light irradiation. That is, in the phase change recording medium, the temperature of the recording film greatly increases, and the present invention capable of reducing the thermal damage to the substrate is preferable.

Further, it is more preferable that the upper dielectric layer is formed of a metal nitride film having a high hardness, since more sufficient contact and sliding durability can be obtained by the effect of the lubrication performance with the DLC film. Furthermore, since the DLC film is added in a state where hydrogen atoms are bonded to carbon atoms in the film,
It is more preferable because the frictional force can be reduced.

In manufacturing such an optical recording medium of the present invention, a carbon target is subjected to high-frequency sputtering in an argon gas atmosphere containing hydrogen or a hydrocarbon gas to obtain a DLC.
By forming a film, an optical recording medium having the characteristics required in the present invention can be manufactured with high productivity.

Alternatively, when the optical recording medium of the present invention is manufactured, a DLC film is formed by a hot filament DC plasma CVD method using benzene or toluene as a raw material. An optical recording medium can be manufactured with high productivity.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical recording medium of the present invention has a thickness of 0.6 m.
m, a reflective layer, a lower dielectric layer, a recording layer,
This is a film-surface incident type optical recording medium having a basic configuration of an upper dielectric layer and further having a DLC film formed on the upper dielectric layer. There may be an adhesive layer between the substrate and the reflective layer. Further, when the substrate is a plastic substrate having a low heat-resistant temperature, it is preferable to have a heat insulating layer for preventing an adverse effect of heat.
Further, the dielectric layer may be a laminate of two or more transparent dielectric films. When the upper dielectric layer has a two-layer structure, a layer close to the recording layer is called a first upper dielectric layer, and a layer in contact with the DLC film is called a second upper dielectric layer. The second upper dielectric layer is preferably a metal nitride film having high hardness. Further, the liquid lubricant may be thinly applied on the DLC film.

Further, the dielectric layer may be a DLC film. When the upper dielectric layer is a DLC film, the upper part of the recording layer becomes a single DLC film, and the light transmittance of the DLC film at this time needs to be higher. Furthermore, one layer of DLC
A film having a characteristic difference in the film thickness direction such that a portion close to the recording layer has high light transmittance even at the expense of hardness and a surface portion close to the head has high hardness even if hardness is sacrificed (such as a gradient composition film). ). In addition, a high heat-resistant temperature is required when contacting the phase change recording film. Further, a DLC is provided between the upper dielectric layer (or the second upper dielectric layer) and the DLC film.
An adhesive layer may be provided for the purpose of improving the adhesiveness of the LC film.

The DLC film may be manufactured by a sputtering method, a plasma CVD method or the like. The DLC (diamond-like carbon) film referred to here is an amorphous carbon film, but a film in which a mixture of ^two bonding modes of carbon atoms, SP ² bond and SP ³ bond, is observed in a Raman scattering spectrum. is there. It is most preferable to add a hydrogen atom to the film in a state where the hydrogen atom is bonded to the carbon atom because the frictional force is reduced. In the sputtering method, a film is formed in a gas atmosphere in which H ₂ (hydrogen) or CH ₄ (methane) is added to Ar (argon) using a C (graphite) target. By using H ₂ (hydrogen) or CH ₄ (methane) gas, a DLC film to which H (hydrogen) is added can be manufactured. In the sputtering method, it is preferable to use a radio frequency (RF) discharge from the viewpoint of increasing the plasma density and preventing arc discharge. Plasma CVD (Plasma
Chemical Vapor Deposition
In the n) method, CH ₄ (methane), C ₆ H ₆ (benzene),
A DLC film is deposited on a substrate (optical recording medium in the present invention) by decomposing a source gas such as C ₆ H ₅ CH ₃ (toluene) in plasma generated by high-frequency discharge or DC discharge. In DC discharge, to increase the plasma density,
A hot filament DC plasma CVD method in which thermoelectrons are generated using a filament and a direct current voltage is applied between the filament and an anode electrode provided near the filament to discharge the filament is preferable. The high-frequency sputtering method is an industrially established method. Since various thin films constituting an optical recording medium are produced by the sputtering method, the DLC in the final step is performed.
This is a preferable method because it can be industrialized most easily because the film can be continuously formed following the previous recording film preparation. In the hot filament DC plasma CVD method, a thin and excellent hydrogenated DLC film having good film quality can be obtained. In addition, since DC discharge is used, there are great industrial advantages such as a low price of a power supply and a strict control of a discharge start time, thereby shortening a production tact time.

The hydrogenated D prepared by the above method
LC film (hereinafter referred to as DLC film) satisfies the following characteristics
As such, the film forming conditions must be selected.
First, the plastic deformation hardness of the DLC film is 1300 kg / mm^TwoLess than
The upper layer must be hard and not easily deformed plastically. Simply ya
The object of the present invention is to increase the elastic modulus (elastic deformation hardness)
Cannot be used for the upper dielectric layer. `` Plasticity of thin film
"Deformation hardness" is a magazine "Monthly Tribology", September 1997
As described on pages 20-21 of the monthly issue, Erio Co., Ltd.
Nanox Indentation Tester (Type
e ENT-1100). "Plasticity
In the measurement method, the "deformation hardness" is the tune at the time of unloading.
Find the tangent at the maximum displacement of the line,
To determine the hardness equivalent to Vickers hardness
It is something. Actual Vicker due to indenter shape etc.
Value is slightly different. Formula: HV = 3.7926 × 0.0
1 × Pmax / (hr × hr) (where Pmax is the maximum
Large load, hr is the tangent at the maximum displacement of the curve when unloading
(Displacement when load = 0). Plastic deformation
Form hardness is 1300kg / mm^TwoFor the following membranes,
Rider) and the medium have poor durability when sliding
there were. Plastic deformation hardness is 1300kg / mm ^TwoAnd water
In the present invention, a DLC film doped with element is necessary. Further
In addition, in the present invention, a high plastic deformation hardness is used as a base of the DLC film.
A metal nitride film is preferably used. Such nitriding
SiN, AlN, AlSiN, GeN, Ge
CrN and the like can be raised. Upper dielectric layer (also
Means that the second upper dielectric layer) has high hardness (plastic deformation hardness is about 1).
700 kg / mm^TwoAbove, that is, in some cases, DLC film
Higher hardness), the lubrication performance of the DLC film and
Can be more durable by combining
You. The "plastic deformation hardness" was measured on a single crystal Si substrate.
Was measured for a film having a thickness of about 100 nm prepared in the above. You
That is, unlike the actual medium, the Si substrate is formed under the same film forming conditions.
The measurement is performed on the film prepared above.

Furthermore, the DLC film of the present invention must have a high transmittance to 410 nm light, which does not hinder reading of a recording mark using 410 nm light.
The thickness of the DLC film of high hardness is approximately 10 nm to 20 n
m. When the thickness is less than 10 nm, sufficient lubrication performance is not obtained. When the thickness is more than 20 nm, problems such as peeling are likely to occur due to internal stress of the film. In order for the DLC film having a film thickness in the range of 10 nm to 20 nm to have a sufficient value of the light transmittance at 410 nm, the refractive index (n) of the DLC film is 2.7 or less and the extinction coefficient (k) is 0.5. Must be 4 or less. Preferably, the extinction coefficient (k) when the refractive index (n) is 2.2 to 2.7 or less is 0.2 or less, and the extinction coefficient (k) when the refractive index (n) is 2.2 or less. ) Is preferably 0.4 or less.

The substrate of the present invention is not particularly limited to resin, glass, Al, etc., but the thickness is 0.6 mm to 3.0 m typified by polycarbonate which is inexpensive in raw material and easy to mold.
A thermoplastic resin disc having a diameter of about 45 mm and a diameter of 45 mm to 130 mm is preferably used. The reflective film is usually made of T
An Al alloy film containing several atomic% of i, Ta, Cr, Au or the like is used. As the lower dielectric and the upper dielectric, a dielectric film having a refractive index of about 1.8 to 2.5 which is transparent to light having a used wavelength is used. Examples of the dielectric film include a ZnS.SiO ₂ film, a ZnS film, and an Al ₂ film formed by a sputtering method.
O ₃ film, SiO ₂ film, Ta ₂ O ₅ film, TiO ₂ film, Y ₂ O
_Three layers, chalcogenides such as a SiN film, an AlN film, and an AlSiN film, an oxide, a nitride film, and a layer containing a mixture thereof can be used. As the recording layer, a conventionally known recording film is used. The recording layer of the magneto-optical recording medium is TbFeC
A rare earth / transition metal alloy film such as o, and a chalcogen alloy film such as GeSbTe or AgInSbTe are used for the recording layer of the phase change recording medium. In particular, GeSbT
The e-film is more preferable because it has high repetitive overwrite performance and enables high-speed erase. The thickness of the recording layer is 10 to 40
nm is preferred. If it is thinner than 10 nm, the repetition durability deteriorates. If the thickness is more than 40 nm, the recording sensitivity becomes poor,
Also, the signal-to-noise ratio (S / N) becomes worse.

The present invention is particularly preferably applied to a phase change recording medium. The phase change recording medium does not require a magnetic field at the time of recording unlike the magneto-optical recording method, so that the structure of the head is simple and mounting on a flying head is easy.
Also, a rare earth / transition metal alloy film (TbF
eCo) has a disadvantage that at a wavelength of about 410 nm, the Kerr rotation angle becomes small and a sufficient reproduction signal cannot be obtained. 4
When a wavelength of the order of 10 nm is used, a phase change recording medium is advantageous.

[0026]

Embodiment 1 A heat insulating layer, a reflective layer, a lower dielectric layer,
Recording layer, first upper dielectric layer, second upper dielectric layer, DLC
A film surface incident type phase change optical recording medium having a film structure was manufactured. Here, the plastic substrate has 12
A substrate made of polycarbonate having a center hole having a diameter of 0 mm and an inner diameter of 15 mm was used. Spiral groove (groove) for continuous servo with radius 24m by injection molding of substrate
It is formed in the range of m to 58 mm. Groove depth is 70n
m, and the track pitch is 1.10 μm. The groove width and the land width are both about 0.55 μm.
On the recording surface (groove surface) of the substrate, a film surface incident type phase change recording medium was produced. As a heat insulating layer, a lower dielectric layer, and a first upper dielectric layer, a ZnS—SiO ₂ film (ZnS: S
A film obtained by sputtering a target with iO ₂ = 80: 20 mol%) was used. The recording layer is made of a GeSbTe alloy film (Ge: Sb: Te = 2: 2: 5 at%, film thickness 20 n)
m). The reflective layer is made of an AlCr alloy film (Al: Cr =
97: 3 atomic% and a film thickness of 150 nm). These inorganic thin films were formed by magnetron sputtering. The sputtering apparatus used was ANELVA Corp.
Is an in-line sputtering apparatus (ILC3102 type), the target is 8 inches in diameter, and the substrate is formed while revolving around its own axis. The film thickness was adjusted by the sputtering time. The thickness of the heat-insulating layer was set to a thickness capable of preventing deformation of the substrate during initialization. The thickness of the reflective film was determined from the viewpoints of recording sensitivity and repeated overwrite durability. The thickness of each layer whose thickness is related to the optical characteristics is set so that the reflectance (reflectance after initial crystallization) when light of 650 nm is irradiated from the film surface is about 20 to 40%. The thickness was adjusted. Specifically, ZnS-S
The refractive index of the iO ₂ film is 2.18, and the thickness of the heat insulating layer is 1
The thickness of the lower dielectric layer is 50 nm, and the thickness of the first upper dielectric layer is 20 nm. As described above, the thickness of the recording layer is 20 nm, and the thickness of the reflection layer is 150 n.
m.

The second upper dielectric layer was a SiN film. That is, a film was formed by sputtering using metal Si as a target and a gas having a mixture ratio of 70:30 of Ar gas and nitrogen gas.
The thickness was 70 nm and the refractive index was 1.95. The plastic deformation hardness was 4500 (kg / mm ² ).

The sample formed up to the second upper dielectric layer was separated from the sample by another vacuum device (SPF-A manufactured by Anelvac Corp.).
(430H sputtering apparatus), and a DLC film having a thickness of 15 nm was formed on the second upper dielectric layer. That is, a 4 inch C (graphite) target was formed by high frequency sputtering using a mixed gas of Ar gas and CH ₄ (methane) gas. The flow rate of Ar gas during sputtering is 63 SCC
The flow rate of M, CH ₄ (methane) gas is 7 SCCM,
The gas pressure is 0.67 Pa. High frequency power is 500W
Att the deposition rate was 4.15 nm / min. The plastic deformation hardness of this hydrogenated DLC film is 1500 (kg /
mm ² ). Refractive index (n) at 410 nm light
Was 2.20 and the extinction coefficient (k) was 0.19.

As described above, a heat insulating layer, a reflective layer, a lower dielectric layer, a phase change recording layer, a first upper dielectric layer, and a second upper dielectric layer are sequentially arranged on one side of a plastic substrate having a thickness of 1.2 mm from the substrate surface. A phase change optical recording medium of a film surface incidence type having a configuration including a body layer and a DLC film was completed. First, the optical characteristics were evaluated. The optical characteristics of the portion having no groove inside the radius of 24 mm were evaluated, and then the optical characteristics after the initialization of the phase change recording layer were evaluated. That is, the difference between the reflectance when the recording film corresponding to the erasing state is in the crystalline state and the reflectance when the recording film is in the amorphous state corresponding to the recording state is 26% for the light of 650 nm, and 26% for the light of 410 nm. It was found that a sufficient reproduction output was obtained at either wavelength.

Next, the durability was evaluated. While rotating the phase change optical recording medium at 1800 rpm, Al ₂ O ₃ .TiC
A CSS test (constant start / stop test) was performed with a flying head having a slider made of (alumina titanium carbide). No remarkable scratches were found on the medium surface even after 30,000 CSS repetitions.

From the above results, it can be seen that the phase change optical recording medium of the film surface incidence type of Example 1 has sufficient sliding durability and 410 nm
It has been found that a sufficient reproduction signal can be obtained for the light of the above.

[0032]

Embodiment 2 In the same manner as in Embodiment 1, the sample prepared from the substrate to the second upper dielectric layer (SiN film) was transferred to another vacuum apparatus (plasma CVD apparatus), and the second upper dielectric layer was formed. A DLC film having a thickness of 15 nm was formed thereon. That it is, was formed a DLC film toluene (C6H ₅ CH ₃₎ to be added 2.7 nm / minute hydrogen at hot filament DC plasma CVD method as a raw material was 15nm thick. A current of 24 A (ampere) is passed through the filament (power is 2
30 volts), 44 volts were applied between the anode and the anode placed near the filament, and a current of 230 mA was passed to generate plasma. In addition, 240 m from the plasma source
A 7 mm pitch mesh electrode (grid) is installed near the substrate installed at a distance of -1350 volts.
Was applied to accelerate the positive particles to deposit them on the substrate.

The plastic deformation hardness of this DLC film is 2200
(Kg / mm ² ). The refractive index (n) at 410 nm light was 2.42, and the extinction coefficient (k) was 0.13.

As described above, a heat insulating layer, a reflective layer, a lower dielectric layer, a phase change recording layer, a first upper dielectric layer, and a second upper dielectric layer are sequentially formed on one surface of a plastic substrate having a thickness of 1.2 mm from the substrate surface. A phase change optical recording medium of a film surface incidence type having a configuration including a body layer and a DLC film was completed. As in Example 1, first, the optical characteristics were evaluated. The optical characteristics of the portion having no groove inside the radius of 24 mm were evaluated, and then the optical characteristics after the initialization of the phase change recording layer were evaluated. That is, the difference between the reflectance when the recording film corresponding to the erased state is in a crystalline state and the reflectance when the recording film is in an amorphous state corresponding to the recorded state is 22% for light of 650 nm, and 22% for light of 410 nm. It was found that sufficient reproduction output was obtained at either wavelength.

Next, the durability was evaluated in the same manner as in Example 1. While rotating the phase-change optical recording medium at 1800 rpm, a CSS test (constant start-stop test) was performed with a flying head having a slider made of Al ₂ O ₃ .TiC (alumina titanium carbide). No remarkable scratches were found on the medium surface even after 30,000 CSS repetitions.

From the above results, the phase change optical recording medium of the film surface incidence type of Example 2 has sufficient sliding durability and 410 nm.
It has been found that a sufficient reproduction signal can be obtained for the light of the above.

[0037]

Comparative Example In the same manner as in Example 1, a phase change recording medium from the substrate to the second upper dielectric layer (SiN film) was manufactured.
However, the thickness of the SiN film was 850 nm. That is, a heat insulating layer, a reflective layer, a lower dielectric layer, a recording layer,
A film incident type phase change optical recording medium having a configuration including a first upper dielectric layer and a second upper dielectric layer was manufactured.
Here, a polycarbonate substrate having a center hole having a diameter of 120 mm and an inner diameter of 15 mm was used as the plastic substrate. A spiral groove (groove) for continuous servo is formed in a range of a radius of 24 mm to 58 mm by injection molding of the substrate. The groove depth is 70 nm, and the track pitch is 1.10 μm. The groove width and the land width are both about 0.55 μm. On the recording surface (groove surface) of the substrate, a film surface incident type phase change recording medium was produced. ZnS—SiO ₂ film (ZnS: SiO ₂ = 80: 2) as a heat insulating layer, a lower dielectric layer, and a first upper dielectric layer
A film obtained by sputtering a 0 mol% target) was used. The recording layer was a GeSbTe alloy film (Ge: Sb:
Te = 2: 2: 5 atomic%, film thickness 20 nm). The reflective layer is made of an AlCr alloy film (Al: Cr = 97: 3 atomic%,
(Film thickness 150 nm). These inorganic thin films were formed by magnetron sputtering. The sputtering apparatus used was ANELVA Corp. Inline Sputtering System (ILC3102 type) with a target of 8
With an inch diameter, the substrate is formed while revolving around its axis. The film thickness was adjusted by the sputtering time. The thickness of the heat-insulating layer was set to a thickness capable of preventing deformation of the substrate during initialization. The thickness of the reflective film was determined from the viewpoints of recording sensitivity and repeated overwrite durability. The thickness of the layer whose thickness is related to the optical characteristics is 6
The film thickness of each layer was adjusted so that the reflectance when irradiated with 50 nm light (reflectance after initial crystallization) was about 20 to 40%. Specifically, the refractive index of the ZnS—SiO ₂ film is 2.18, the thickness of the heat insulating layer is 150 nm, the thickness of the lower dielectric layer is 15 nm, and the thickness of the first upper dielectric layer is 20.
nm. Further, as described above, the thickness of the recording layer is 20 n
m, and the thickness of the reflective layer is 150 nm.

The second upper dielectric layer was a SiN film. That is, a film was formed by sputtering using metal Si as a target and a gas having a mixture ratio of 70:30 of Ar gas and nitrogen gas.
The film thickness was 850 nm, and the refractive index was 1.95.
The plastic deformation hardness was 4500 (kg / mm ² ).

As described above, a heat insulating layer, a reflective layer, a lower dielectric layer, a phase change recording layer, a first upper dielectric layer, and a second upper dielectric Thus, a film incident type phase change optical recording medium having a structure composed of a body layer has been completed. As in Example 1, first, the optical characteristics were evaluated. The optical characteristics of the portion having no groove inside the radius of 24 mm were evaluated, and then the optical characteristics after the initialization of the phase change recording layer were evaluated. That is, the difference between the reflectance when the recording film corresponding to the erased state is in the crystalline state and the reflectance when the recording film corresponding to the recorded state is in the amorphous state is 650.
It was 18% for light of nm and 26% for light of 410 nm, and it was found that a sufficient reproduction output was obtained at either wavelength.

Next, the durability was evaluated in the same manner as in Example 1. A CSS test (constant start / stop test) was performed using a flying head having a slider made of Al ₂ O ₃ .TiC (alumina titanium carbide) while rotating the phase change optical recording medium at 1800 rpm.
Significant scratches were found on the media surface after 10,000 CSS repetitions.

From the above results, it was found that the sliding durability of the film incidence type phase change optical recording medium of the comparative example did not satisfy the practical level.

The above embodiment and comparative example relate to the initialization of a film incident type phase change recording medium. However, the present invention is applicable to a film incident type magneto-optical recording medium if a flying head is used. It is valid.

[0043]

According to the optical recording medium of the present invention, by using the DLC film of the present invention as the uppermost layer, a practical level of sliding durability was obtained in a recording / reproducing system using a flying head. In addition, backward compatibility (playback compatibility) with a drive using light of about 410 nm in the future could be achieved.
As described above, a film surface incidence type optical recording medium can be put to practical use.

Claims (6)

[Claims] 1. An optical recording medium for recording / reproducing information by utilizing a change in physical characteristics of a recording layer caused by light irradiation, a substrate, a reflective layer, a lower dielectric layer, a recording layer, and an upper dielectric layer. And a plastic deformation hardness ≧ 1300 kg / mm ² , 41 on the outer layer side of the upper dielectric layer.
An optical recording medium comprising a DLC film (diamond-like carbon film) having a refractive index (n) of 2.7 nm and an extinction coefficient (k) of 0.4 at 0 nm light. 2. The optical recording medium according to claim 1, wherein the optical recording medium is a phase change recording medium that records and reproduces information by utilizing a change in the structural characteristics of a recording layer caused by irradiation of light. recoding media. 3. The optical recording medium according to claim 1, wherein the upper dielectric layer is a metal nitride film. 4. The optical recording medium according to claim 1, wherein the DLC film is added in a state where hydrogen atoms are bonded to carbon atoms in the film. 5. The optical recording medium according to claim 1, wherein the DLC film is produced by subjecting a carbon target to high-frequency sputtering in an argon gas atmosphere containing hydrogen or a hydrocarbon gas. Manufacturing method. 6. The method for manufacturing an optical recording medium according to claim 1, wherein the DLC film is manufactured by a hot filament DC plasma CVD method using benzene or toluene as a raw material.