JPH087330A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain an optical recording medium showing a characteristic suit able for edge recording, by letting a dielectric layer adjacent to one side of an optical recording layer contain C, Al and Si, and forming the dielectric layer of an amorphous nitride coupled with H. CONSTITUTION:A first dielectric layer 2 is formed on a substrate 1 having a guide on a surface thereof, on which a recording layer 3, a second dielectric layer 4, a metallic reflecting layer 5 and an organic protecting layer 6 are sequentially layered. An AlSiN film is formed to be 110nm thick as the first dielectric layer 2. The recording layer 3 is formed to be 25nm thick by DC sputtering. Thereafter, the second dielectric layer 4 is obtained by forming a film off AlSiCN:H of 40nm thickness on a C chip on an AlSi target, and the metallic reflecting layer 5 is formed to be 60nm thick by using AlAuTi alloy as a target. In this manner, when the AlSiCN:H film which is a dielectric body of a low thermal conductivity is used, a dependency of a recording sensitivity on a rotating speed of a disc is decreased, and therefore bits fit for cast laser lights are easily formed. Accordingly, an optical recording medium having a characteristic suitable for edge recording is obtained.

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 for recording, reproducing and erasing information by using light from a laser or the like. Specifically, it has good sensitivity to the recording laser power,
Enables the use of low power and even short wavelength lasers,
The present invention relates to an optical recording medium using a dielectric film having a low thermal conductivity.

[0002]

2. Description of the Related Art Various researches and developments have been made on optical recording media as information recording media of high density and large capacity. In particular, a magneto-optical recording type or phase change type optical recording medium capable of rewriting information has a wide range of application fields, and various materials and systems have been announced and have been attracting attention.

The basic structure is a four-layer structure of transparent substrate / first dielectric layer / recording layer / second dielectric layer / metal reflective layer. As a recording layer therefor, in a magneto-optical recording medium, a rare earth-transition metal amorphous alloy magnetic film having an easy axis of magnetization in a direction perpendicular to the film surface is used. Alternatively, InSbTe or the like is used in the phase change type optical recording medium.

Here, the dielectric used for the optical recording medium plays a role of enhancing the Kerr effect, improving the thermal efficiency, and particularly protecting the magnetic layer in the magneto-optical recording medium. And as a material for that, SiN, AlN, nitride such as BN, Si
Examples thereof include oxides such as O ₂ , Al ₂ O ₃ and Ta ₂ O ₅ , sulfides such as ZnS, and mixtures thereof. However, among oxides and sulfides, nitrides are mainly used among them in view of oxidation of the recording layer and low refractive index.

Further, the dielectric material must have a refractive index n ≧ 1.6 in order to enhance the Kerr effect enhancement, and further preferably n ≧ 1.8. A nitride-based dielectric material containing Al and Si as main constituent elements (hereinafter referred to as AlSiN) can have a refractive index of n ≧ 2.0 and is excellent in Kerr effect enhancement. AlSiN also has excellent corrosion resistance, and by adjusting the composition ratio of Al and Si appropriately, the weakness of strength characteristics such as cracks in AlN simple substance or SiN simple substance is complemented, and desired mechanical strength characteristic can be obtained. It is a substance that is particularly effective as a dielectric for an optical recording medium.

[0006]

However, in these dielectric layers, the sensitivity to recording laser power (hereinafter referred to as recording sensitivity) greatly depends on the linear velocity of the medium. Therefore, in a disk-shaped optical recording medium,
There is a large difference between the recording sensitivity of the inner peripheral portion and the recording sensitivity of the outer peripheral portion.

Further, in consideration of the reduction of recording marks due to the shortening of the wavelength of laser light used, thermal interference between marks and adjacent tracks, and also the correspondence to mark length recording in which information is provided at both ends of the recording marks. However, sufficient characteristics cannot be obtained with these dielectrics.

Therefore, as a method of satisfying the above characteristics, there is a method of reducing the thermal conductivity of the dielectric film and increasing the thermal efficiency of the irradiation laser. Since the dielectric film having a low thermal conductivity suppresses thermal diffusion in the film, it is possible to more efficiently consume the heat energy supplied by the irradiation laser to raise the temperature of the recording layer.

Generally, if the rotation speed of the disk becomes faster,
The relative amount of thermal energy applied to the same area at the same time decreases. However, in a medium having high thermal efficiency, the difference in laser irradiation time required to raise the recording layer to the required temperature is shortened. As a result, the dependence of the recording sensitivity on the disc rotation speed is reduced.

That is, the magneto-optical recording medium using the dielectric film having a low thermal conductivity reduces the laser power required for recording to improve the recording sensitivity, and reduces the dependency of the recording sensitivity on the disc rotation speed. . Further, a medium having a small thermal diffusion easily forms a bit suitable for an irradiation laser and exhibits characteristics suitable for edge recording.

AlN-based and SiN-based nitrides, which have been widely used as dielectrics for magneto-optical recording media, are excellent in corrosion resistance and Kerr effect enhancement, but it is difficult to reduce thermal conductivity. was there.

The present invention solves the above problems and obtains an optical recording medium that reduces the dependence of recording sensitivity on the disk rotation speed, easily forms a bit suitable for an irradiation laser, and exhibits characteristics suitable for edge recording. The purpose is to

[0013]

The optical recording medium of the present invention comprises:
The dielectric layer adjacent to at least one of the optical recording layers is C
It is characterized by being made of an amorphous nitride containing Al and Si and having a bond with H.

That is, reducing the thermal conductivity of AlSiN, which is an amorphous nitride containing Al and Si, while maintaining the characteristics required for an optical recording medium is a means for solving the above problems. . The dielectric according to the present invention has a lower thermal conductivity than the AlSiCN dielectric, which has been studied as a low thermal conductivity dielectric, and the utilization efficiency of the recording laser is further improved. AlSiN having a bond with C and H is represented by AlSiCN: H, and a method of forming a bond with C and H in the film of the present invention and its characteristics will be described in detail below.

The AlSiCN: H film is formed by a known sputtering method in a mixed atmosphere of a hydrocarbon gas, an inert gas and a nitrogen gas by using an AlSi alloy target or a composite target in which an Al chip is placed on a Si target. It can be obtained by forming a film. Or Si and Al in these atmospheres
The target may be co-sputtered. Alternatively, AlSi
Sputtering may be performed using a C alloy target in a mixed atmosphere of hydrogen gas and an inert gas.

At this time, in order to adjust the refractive index of the dielectric film, reduce the linear velocity dependence of the optical recording medium, and improve the recording sensitivity, the gas composition at the time of sputtering should be adjusted to the desired values.
The flow rate, pressure and input power can be selected.

In the embodiments of the present invention described later,
Although CH ₄ gas is used as the hydrocarbon gas, the same effect can be expected with other hydrocarbons. The flow rate of each gas is Ar: 24 to 54 ccm, N ₂ : 3 to 9 ccm,
When CH ₄ : 10 to 30 ccm, total pressure 1.1 to 1.6 Pa, and input power of 300 to 600 W, the AlSiCN: H film obtained under these conditions is amorphous. ,
Confirmed by X-ray measurement.

When the AlSiCN: H-based dielectric is formed by the above method, its refractive index can be 1.6 to 2.5.
However, in consideration of the film density and optical characteristics related to durability, the refractive index is preferably 1.8 to 2.5.
Further, it is preferable that the absorption coefficient of AlSiCN: H is 0.04 or less from the transmittance measurement, and further 0.02 or less for the magneto-optical recording medium.

It is more preferable to satisfy the following conditions. (A) A reduction in the nitrogen content is required in order to avoid a decrease in film strength due to an excessive increase in N—H bonds and to promote Si—H bonds. (B) A nitrogen content is required that is capable of maintaining transparency due to the bonding of nitrogen and metal, suppressing the absorption coefficient to 0.02 or less, and maintaining the denseness of the film as a nitride.

Therefore, in order to satisfy (a) and (b),
The ratio of nitrogen in AlSiCN is preferably 15% or more and 55% or less in terms of atomic percentage ratio. That dielectric layer in atomic percentage ratio _{(C x Al y Si z N} 100-xyz) 100-a
When expressed as H _a , 15 ≦ (100−x−y−z) ≦
It is preferably 55.

Further, if the amount of hydrogen taken into the film is too large, the compactness is lowered, the protective function is not sufficient, and excessive bond termination by hydrogen reduces the strength of the film.
Therefore, the ratio of hydrogen is 0 <a ≤ in the above composition formula.
Preferably it is 40.

In order to obtain the effect of the present invention more,
More preferably, the ratio of carbon, aluminum, and silicon in the above composition formula is 0 <x ≦ 40, 18 ≦ 1.8 y ≦ z.

When manufacturing a magneto-optical recording medium using such a dielectric, the following materials are preferable for each layer. First, as the organic resin used for the substrate material, polycarbonate resin, acrylic resin, epoxy resin, 2-methylpentene resin, polyolefin resin,
Alternatively, a copolymer thereof or the like can be used. Among them, the polycarbonate resin is preferable in terms of mechanical strength, weather resistance, heat resistance, moisture permeability, and low price. From the viewpoint of productivity, it is preferable to form the entire substrate material using this polycarbonate resin.

The material for the magneto-optical recording layer may be any material capable of recording, reproducing and erasing by the magneto-optical effect.
More specifically, it has an easy magnetization direction perpendicular to the film surface,
Any magnetic thin film capable of recording, reproducing, and erasing information by the magneto-optical effect by forming an arbitrary reversed magnetic domain may be used.

For example, TbFe, TbFeCo, GdTbFe, NdDyFeC
o, NdDyTbFeCo, NdFe, PrFe, CeFe and other rare earth elements and transition metal elements, amorphous alloy thin films, their two-layer films using exchange coupling, artificial lattice multilayer films such as Co / Pt, Co / Pd, Co
A Pt-based alloy or the like can be used. Further, in the recording layer having such a constitution, as long as the perpendicular magnetic anisotropy is not lost, there is no problem even if other elements are added up to 10 atomic%. For example, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, T
c, Re, Ru, Os, Ir, Si, Ge, Bi, Pd, Au, Ag, Cu, Pt
One or more elements other than rare earths, Fe, and Co may be contained. In particular, in order to prevent corrosion of the recording layer itself due to oxidation, it is preferable to add Ti, Zr, Hf, Ta, Cr and Re.

Further, the metal reflective layer is preferably made of a material having a higher reflectance than the recording layer with respect to the laser light of the drive head used for the evaluation of C / N for improving the C / N. Specifically, the refractive index n and the extinction coefficient k, which are the optical constants at the laser light wavelength used, are n ≦ 3.5 and k ≧ 3.
It is preferable to choose a material such as 5. More preferably, n ≦ 2.5 and 4.5 ≦ k ≦ 8.5. In the medium manufactured under these conditions, the Kerr effect enhancement is improved by the improvement of the reflectance of the metal reflection layer, and the C / N can be further improved.

As a material satisfying such conditions, Al
Alternatively, an alloy in which Au is added to Ag, that is, an AlAu alloy or an AgAu alloy can be used. The decrease in reflectance is caused by Al or
The Au content is preferably 0.5 to 15 atom%, and more preferably 0.5 to 10 atom% in order to suppress the C / N reduction within 2% of that of the Ag single film.

By the way, reducing the Au content is important also from the viewpoint of reducing the cost of the target and the medium. And from the viewpoint of minimizing the Au content, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re, R
It is preferable to supplementarily add one or more specific elements such as u, Os and Ir.

The addition amount of such a specific element is 5.0 atomic%.
It should be kept within the above range, and if it is more than this range, the reflectance of the metal reflection film is lowered and the C / N is also lowered. Within 5.0 atomic%, the decrease in reflectance at the wavelength of 830 nm, which is the wavelength of the semiconductor laser used in the magneto-optical recording / reproducing apparatus, is within 2%. On the other hand, if less than 0.3 atom%,
It is not possible to compensate for the increase in thermal conductivity due to the saving of Au. Therefore, if the added amount of Au is in the range of 0.5 to 10 atomic% by adding the specific element, the reflectance of the reflective film is Al.
Alternatively, it can be suppressed within 2% compared to the Ag single film, and the cost reduction of Au can also be reduced.

Among the above-mentioned specific element groups, Ti, Zr, Hf, and T are included in order to enhance the durability of the metal reflective film itself.
Preferred are a, Cr and Re. The film thickness range of these metal reflective layers is 10 to 500 nm, but in order to suppress the C / N reduction due to the reduction of reflectance and to enable recording with a laser power of 10 mW, preferably 30 to 200 nm. , Particularly preferably 40
~ 100 nm.

As the organic protective layer, light and / or thermosetting resin, thermoplastic resin or the like can be applied and can be formed by a coating method or the like. The back surface protective layer provided on the opposite side of the recording layer from the substrate is preferably provided so as to cover at least the side surface of the recording layer.

As a method for manufacturing the above-mentioned transparent dielectric layer, recording layer, and inorganic thin film of the metal reflection layer, various thin film forming methods such as a known vacuum deposition method, PVD method such as sputtering method, or CVD method are applied. it can. However, the magneto-optical recording medium is preferably manufactured under the condition that the adhesiveness to the polymer substrate is particularly large in order not to cause the peeling that occurs in the high temperature and high humidity environment resistance test. For this purpose, the sputtering method is preferable.

The dielectric film of the present invention is preferably used for a magneto-optical recording medium in which a magnetic film having an easy axis of magnetization in a direction perpendicular to the film surface is used as a recording layer. Due to its characteristics, it can be applied to a phase change type optical recording medium.

[0034]

Examples and Comparative Examples FIG. 1 shows the construction of a magneto-optical recording medium according to an example of the present invention. In the figure, 1 is a substrate on which a guide is formed, 2 is a first dielectric layer, 3 is a recording layer,
Reference numeral 4 is a second dielectric layer, 5 is a metal reflective layer, and 6 is an organic protective layer. In particular, the second dielectric layer has a role of suppressing heat diffusion to the metal reflection film. Therefore, the second dielectric film layer is made of AlSiC.
In the embodiment of the present invention, a medium having an N: H film is used, and AlSiN, AlSi
A medium having a CN film was manufactured as a comparative example as follows, and the characteristics were compared.

First, a substrate 1 of polycarbonate resin (PC) having a spiral groove of a diameter of 130 mm and a thickness of 1.2 mm and a pitch of 1.6 μm and a spiral groove was mounted on a 3-target high frequency magnetron sputtering device (SPF manufactured by Anerva).
(-430H type), and evacuate to 53 μPa. The substrate 1 was rotated at 15 rpm during film formation.

Then, an AlSiN film was formed as the first dielectric layer 2. That is, the target has a diameter of 100 mm,
Using a disc-shaped AlSi (30:70) sintered body with a thickness of 5 mm,
Ar / N ₂ mixed gas (N ₂ 30 vol%) was introduced into the vacuum chamber, and the gas flow rate was adjusted so that the pressure became 0.6 Pa. High-frequency sputtering was performed at a discharge power of 400 W and a discharge frequency of 13.56 MHz, and an AlSiN film of 110 n was formed as the first dielectric layer 2.
m deposited.

Next, the recording layer 3 was formed. The target was changed to a disk of TbFeCo alloy that is a magneto-optical recording film, the sputtering gas was pure Ar (purity 99.999%), and the gas pressure was 0.2 Pa.
, TbFeC, a rare earth / transition metal alloy with a discharge power of 200 W
o The recording layer 3 made of a film is formed by DC sputtering 25
nm deposited.

Subsequently, the second dielectric layer 4 was formed on the recording layer. Therefore, first, the target was returned to the above-mentioned AlSi sintered target. When forming a film of AlSiCN: H, Ar gas, Ar / N ₂ mixed gas (N ₂ 30vol
%) And CH ₄ gas while changing the flow rate ratio of each sample, and high frequency sputtering was performed at a gas pressure of 0.6 Pa and a discharge power of 400 W. Comparative examples AlSiN, AlSi
When forming a CN film, the sputtering gas is also Ar / N
_The mixed gas was returned to ₂ mixed gas (N ₂ 30 vol%), and the same discharge condition as that of the first dielectric layer 2 was used. However, during AlSiCN film formation
A C chip was placed on the AlSi target to form a film. Thus, the second dielectric layer 4 having a film thickness of 40 nm was formed.

Further, a target is used as the metal reflection layer 5.
Switch to AlAuTi alloy target, return the sputtering gas to pure Ar (purity 99.999%), pressure 0.2Pa, discharge power 10
An Al alloy film of 60 nm was deposited at 0 W.

The sample thus obtained was taken out of the sputtering apparatus and attached to a spin coater. Then, while rotating the disk at 3000 rpm, apply UV curable phenol novolac epoxy acrylate resin, then pass through the UV irradiation device to cure the resin,
A 20 μm organic protective layer 6 was provided. In this case, about 20 μm
In order to set a thick film thickness, it was diluted with butyl alcohol and applied with a viscosity of about 500 cP.

With respect to the thus obtained magneto-optical recording medium having the structure shown in FIG. 1, the writing laser power (hereinafter referred to as Pth) and the disk rotation speed required to obtain a C / N value of 10 dB were 3600 rpm. Time and Pth at 1800 rpm
The difference (hereinafter referred to as ΔPth) is compared. For recording / reproducing of magneto-optical disk, DDU manufactured by Pulstec Industrial Co., Ltd.
Using -1000, the measurement was performed under the following conditions.

Recording conditions: disk rotation speed = 1800 rpm,
3600 rpm, recording track position = radius 30 mm, recording frequency = 3.7 MHz, 7.4 MHz (corresponding to 1800 rpm and 3600 rpm, respectively), applied magnetic field during recording = 250 Oe, recording laser power = 2 to 9 mW. Playback condition: Disc rotation speed = 1800rp
m, 3600 rpm, reproducing laser power = 1.5 mW.

For each medium sample thus obtained, each gas flow rate at the time of sputtering the second dielectric layer (provided that the gas was calibrated with Ar gas), the refractive index of the dielectric, and C and Al determined by AES measurement , Si composition ratio (however, C / (C + Al + Si), Al /
(C + Al + Si) and Si / (C + Al + Si) ratio), and the measurement results of Pth and ΔPth at 3600 rpm,
It shows in Table 1.

[0044]

[Table 1]

[0045]

As described in detail above, the present invention reduces the dependence of the recording sensitivity on the disk rotation speed by using an AlSiCN: H film, which is a low thermal conductivity dielectric, so that a bit suitable for an irradiation laser can be obtained. It is possible to obtain an optical recording medium that is easy to form and has characteristics suitable for edge recording.

[Brief description of drawings]

FIG. 1 is a medium laminated structure of Examples and Comparative Examples.

[Explanation of symbols]

 1 substrate with guide formed on the surface 2 first dielectric layer 3 recording layer 4 second dielectric layer 5 metal reflective layer 6 organic protective layer

Claims (3)

[Claims] 1. An optical recording medium, wherein a dielectric layer adjacent to at least one of the optical recording layers is made of an amorphous nitride containing C, Al and Si and having a bond with H. 2. A represented when expressed dielectric layer in atomic percentage ratio _{(C x Al y Si z N} 10 0-xyz) 100-a · H a, the composition is 0 <x ≦ 40,18 ≤ 1.8 y ≤ z, 15 ≤ (10
The optical recording medium according to claim 1, wherein 0−x−y−z) ≦ 55 and 0 <a ≦ 40. 3. The optical recording medium according to claim 1, wherein a magnetic film having an easy axis of magnetization in a direction perpendicular to the film surface is used as the recording layer.