JPH0729206A - Optical recording medium - Google Patents

Abstract

PURPOSE:To convert recorded spots formed in a recording layer into minute spots and to increase recording density by reducing the spot diameter of laser light by the lens effect of a recording assisting layer whose volume and refractive index have been varied by irradiation with laser light. CONSTITUTION:A 1st dielectric layer 2 is formed on the surface of a transparent disk substrate 1 and plural layers including a recording assisting layer 7 and a recording layer 3 are formed on the layer 2. The assisting layer 7 is made of a Pb-Te alloy or an In-Sb alloy having a high coefft. of thermal expansion and high temp. dependency of its refractive index. When the resulting optical recording medium is irradiated with laser light from the assisting layer 7 side, the surface shape and optical thickness distribution of the layer 7 are varied by the heat of the laser light, the spot diameter of laser light is reduced by the produced convex lens effect of the layer 7 and recorded spots formed in the recording layer 3 are made minute. Recording density is increased, a reproduced signal detecting region is limited and minute recorded spots can be reproduced.

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 used in the fields of home appliances and file memories for computers, and more particularly to high density optical recording medium.

[0002]

2. Description of the Related Art A partial sectional view of a conventional magneto-optical recording medium is shown in FIG. 1 and its manufacturing method will be described. A transparent disk-shaped substrate 1 having an optical head guide groove and a concavo-convex pattern such as pits indicating addresses and sector marks or recording information on the surface is placed in a sputtering apparatus equipped with a ternary target source at a distance of 10 cm from the target. It was set and rotated.

In an argon-nitrogen mixed gas having a nitrogen concentration of 10%, a sputtering gas pressure of 5 mTorr was applied from the first target.
i is reactively sputtered to form Si ₃ N ₄ as the first dielectric layer 2.
The film was formed to a thickness of 70 nm. Next, in argon, Tb was applied from the second alloy target at a sputtering gas pressure of 5 mTorr.
-Fe-Co alloy is sputtered, film thickness is 30 nm, Curie temperature is about 200 ° C, compensation temperature is about 100 ° C, coercive force Hc ₁
The first magnetic layer 3 having a composition of Tb ₂₇ Fe ₆₆ Co ₇ was formed at 15 kOe 2. Next, in the argon-nitrogen mixed gas having a nitrogen concentration of 10%, the sputtering gas pressure was 5
Si was reactively sputtered at mTorr to form a Si ₃ N ₄ film as the second dielectric layer 4 with a thickness of 20 nm. Finally, an Al-Ti film having a thickness of 50 nm was provided as a metal layer 5 from a fourth target in argon with a sputtering gas pressure of 5 mTorr. Further, a resin layer 6 having a thickness of about 10 μm was formed on the surface.

The optical recording medium is a high-density and large-capacity memory for recording and reproducing information using laser light.
It is used as a file memory for computers or a memory for recording music information and image information. The optical recording medium is formed by forming a first dielectric layer on a transparent substrate by a normal sputtering method, laminating a recording layer, and further laminating a second dielectric layer. The recording layer of the optical recording medium is, for example, TbFe, TbFeCo, TbDyF.
An amorphous magnetic film composed of a transition metal and a rare earth such as eCo, GdTbFeCo, or GdTbFe, or GeTe,
An amorphous film made of a nonmetal and a semimetal such as GeSbTe, SnSbTe, SnTeSe is used.

The first and second dielectric layers are S for the purpose of improving the magneto-optical effect or preventing the oxidation of the recording film.
A dielectric such as i ₃ N ₄ is used. Information is recorded or reproduced by irradiating the recording layer with laser light from the substrate side of the optical recording medium or the side opposite to the substrate. Thereby, when the recording film is irradiated with the laser beam, a recording point having a shape corresponding to the diameter of the laser beam on the surface of the recording film is formed.

[0006]

In the prior art, recording / recording of information by irradiating the recording layer with a laser beam and physically changing it is performed.
Play. That is, in recording / reproducing information, the recording film formed on the surface of the substrate is irradiated with laser light, and the irradiated portion is magnetized or crystallized or amorphized to form a minute recording point. Car rotation due to optical effects and the amount of reflected light are used as information bearers. Therefore,
In order to increase the density of the optical disc, the diameter of the laser spot irradiated on the medium surface may be reduced.

To reduce the diameter of the laser spot,
There is a method of shortening the wavelength of the laser or using a short wavelength of the second harmonic (SHG) generated by the resonance of light. However, the output is small. Further, a method of increasing the NA (numerical aperture) of the lens for narrowing down the laser light can be considered. However, there is a problem that aberrations are likely to occur even if the disc is slightly tilted, and the shapes of recording points irradiated with laser light under the same conditions are different.

An object of the present invention is to provide an optical recording medium capable of forming a high density and large capacity memory by forming minute recording points without shortening the wavelength of a laser or increasing the NA of a lens. To do.

[0009]

The above object is to form a dielectric layer on the surface of a transparent substrate and then have a plurality of thin films including at least one recording auxiliary layer and a recording layer. It is achieved by irradiating a laser beam from the recording auxiliary layer. That is, the recording auxiliary layer is provided on the surface of the dielectric layer in close proximity to the recording layer. At this time, the recording auxiliary layer is provided on the side on which the laser light is incident. The recording auxiliary layer may have its volume expanded and / or its refractive index changed by the irradiation of the incident laser beam. As a result, the shape of the surface and / or the interface of the recording auxiliary layer and the distribution of the optical film thickness are changed, and the diameter of the laser beam spot is reduced by the effect of the convex lens, and the laser beam spot is formed in the adjacent recording layer. The recording point can be reduced.

Therefore, a material having a high coefficient of thermal expansion and / or a material having a high temperature dependence of the refractive index may be used for the recording auxiliary layer. The rate of change of the refractive index of the recording auxiliary layer before and after irradiation with laser light is preferably in the range of 1.1 or more and 2.0 or less. Further, the film thickness is preferably in the range of 5 nm to 200 nm.

The film thickness of the recording auxiliary layer varies somewhat depending on the rate of change of the refractive index, but can be arbitrarily controlled by the material used for the recording auxiliary layer. If the film thickness of the recording auxiliary layer is 5 nm or less, the effect of reducing the diameter of the laser beam is small even if a material having a large rate of change in refractive index is used. Further, when the film thickness is 200 nm or more, the laser light is absorbed by the recording auxiliary layer and the amount of light is reduced, so that recording points cannot be formed on the recording layer.

Further, the extinction coefficient corresponding to the amount of light absorption for generating heat in the recording auxiliary layer upon irradiation with laser light is
The range of 0.1 or more and 1 or less is preferable. When the extinction coefficient is 0.1 or less, heat is less likely to be generated, while when it is 1.0 or more, the amount of light passing through the recording auxiliary layer and reaching the recording layer is reduced, so that recording points cannot be formed on the recording layer. The recording auxiliary layer is Pb-
A material containing a material having a composition close to that of a Te alloy, an In-Sb alloy, an In-Sb-Se alloy, or the like is used.

In addition to the nitride such as Si ₃ N ₄ , the dielectric layer may be a compound thin film such as sulfide, selenide, fluoride and carbide. Materials containing nitrides, sulfides, selenides, fluorides or carbides as main components are Sb ₂ S ₃ , S
b ₂ Se ₃ , GeS, GeSe, GeS ₂ , GeSe ₂ , S
nS, SnSe, SnS ₂ , SnSe ₂ , PbS, PbSe,
In ₂ S ₃ , In ₂ Se ₃ , Cu ₂ S, Ag ₂ S, ZnS, Z
nSe, CdS, CdSe, Si ₃ N ₄ , AlN, TiN, Z
At least one selected from materials having compositions close to rN, BN, and C or a mixed material thereof is used. More preferably, ZnS, Si ₃ N ₄ or AlN
A material having a composition close to each of the above is used as the main component.

Only the protective layer on one side of the recording film may be made of these materials, but it is more preferable if the protective layers on both sides are made of these materials.

When a magnetic film is used for the recording layer, an oxide compound thin film may be used for the dielectric layer on the side far from the recording layer. Materials whose main component is oxide are CaO and ZrO.
₂ , MgO, Y ₂ O ₃ , B ₂ O ₃ , SiO, SiO ₂ , TiO
₂ , Al ₂ O ₃ , Ta ₂ O ₅ , SnO ₂ , MnO and Sb ₂
At least one selected from materials having a composition close to that of O ₃ or a mixed material thereof is used. More preferably, a material containing a material having a composition close to ZnS, Si ₃ N ₄ or AlN as a main component is used.

The recording layer is an amorphous film composed of a rare earth and a transition metal, or a thin film that changes phase between amorphous-crystalline, crystalline-crystalline, and amorphous-amorphous. Alternatively, it is preferable to use a thin film that utilizes the reaction between the upper and lower layers.
For example, amorphous film materials composed of rare earths and transition metals are Tb-Fe-Co, Gd-Dy-Fe-Co, Gd.
-Tb-Fe, Tb-Fe, Tb-Dy-Fe-Co,
Gd-Tb-Fe-Co and the like are preferable. Ge-Sb-Te, Sn-Sb-Te, Sn-S are thin-film materials that change phases.
b-Se is preferred. In addition, the Pt / Co multilayer film may be 10 to
A 20-layer structure is preferable.

[0017]

After the first dielectric layer is formed, a recording auxiliary layer having a large temperature dependence of a volume change and / or a refractive index change and a recording layer adjacent to the recording auxiliary layer are formed. Recording points smaller than the diameter of the light spot can be formed on the recording layer. That is, the recording auxiliary layer generates heat due to the irradiation of the laser beam, the volume expands and / or the refractive index changes, and changes to a convex shape toward the recording layer side and / or the first dielectric layer side. As a result, the recording auxiliary layer produces an optical lens effect, and the diameter of the laser beam spot on the recording layer adjacent to the recording auxiliary layer becomes smaller than the diameter when the recording auxiliary layer is irradiated. Therefore, the recording points formed on the recording layer can be reduced by providing the recording auxiliary layer, which has a large temperature dependency of the volume change, close to the laser beam incident side of the recording layer.

Further, the shape of the recording point can be further reduced by the mutual time delay between when the lens effect of the recording auxiliary layer is generated and when the recording film is irradiated with light. Further, at the time of reproducing the recording signal, an optical mask is formed due to the difference in the refractive index due to the temperature distribution of the recording auxiliary layer, and the region for detecting the reproducing signal is limited. As a result, a small recording point can be reproduced.

[0019]

【Example】

(Embodiment 1) A partial sectional view of an optical recording medium of the present invention according to this embodiment is shown in FIG. This optical recording medium was manufactured as follows.

A transparent disk-shaped substrate 1 is placed 10 cm from the target in a sputtering apparatus equipped with a quaternary target source.
I set it to the distance of and rotated it. Next, Si is reactively sputtered from a first target in an argon-nitrogen mixed gas having a nitrogen concentration of 10% at a sputtering gas pressure of 5 mTorr to form a Si ₃ N ₄ film as a first dielectric layer 2 to a thickness of 70 nm. did. Next, Pb-Te was sputtered with a second target in argon gas at a sputtering gas pressure of 5 mTorr to obtain a film thickness of 2
A 0 nm recording auxiliary layer 7 was formed. Next, nitrogen concentration 10%
Si was reactively sputtered at a sputtering gas pressure of 5 mTorr from the first target in a mixed gas of argon and nitrogen to form a Si ₃ N ₄ film as the second dielectric layer 8 to a thickness of 10 μm. Further, a Tb-Fe-Co alloy was sputtered in argon with a sputtering gas pressure of 5 mTorr from a third alloy target, and the film thickness was 30 nm, the Curie temperature was about 200 ° C., the compensation temperature was about 100 ° C., and the coercive force was Hc ₁ 15 kOe. Composition is T
The first magnetic layer 3 of b ₂₇ Fe ₆₆ Co ₇ was formed. Next, as in the case of the first dielectric layer 2, a sputtering gas pressure of 5% was applied from the first target in an argon-nitrogen mixed gas having a nitrogen concentration of 10%.
Si was reactively sputtered at mTorr to form a Si ₃ N ₄ film as the third dielectric layer 4 with a thickness of 20 nm. Finally, an Al-Ti film having a thickness of 50 nm was provided as a metal layer 5 from a fourth target in argon with a sputtering gas pressure of 5 mTorr. Further, a resin layer 6 having a thickness of about 10 μm was formed on the surface.

(Embodiment 2) A disk A manufactured by the procedure of a conventional example and a recording auxiliary layer d = 20 nm are used in Embodiment 1
The recording / reproducing characteristics of the disk B manufactured in 1. were measured. First, at a linear velocity of 4.2 m / s, a magnetic field (300 Oe) opposite to that at the time of recording was applied in the direction perpendicular to the film surface, and 6.7 m
The magnetization direction was aligned in one direction by irradiating DC light of W 2. Next, while the applied magnetic field was reversed, recording was performed while sequentially changing the laser power with a signal of 1 MHz, and the C / N (carrier-to-noise ratio) of the fundamental wave and the second harmonic was measured.

Here, the optimum recording power is the laser power that minimizes the second harmonic component. This is because the lengths of the recorded portion and the unrecorded portion are the same in both discs A and B when recording is performed with laser power that minimizes the second harmonic component.

By using this optimum recording power, the disk A
And the shape and size of the recording point of the disk B were compared. In the disk A, at the optimum recording power of 8.2 mW, the shape of the recording point was 800 nm in length and width. Disc B has a length and width of 600 nm at 9.0 mW,
The size of the recording point became about 75% of that of the disk A, and the length and width of the recording point could be reduced. As a result, the recording density could be improved about twice.

At this time, the C / N of the disks A and B were equal to 54 dB, respectively.

Pb-Te used for the recording auxiliary layer of this embodiment
When the film thickness was changed, the shape of the recording point and the C / N changed as shown in Table 1. Here, the optimum power is slightly different for each film thickness.

[0026]

[Table 1] The reason why the C / N does not change when the film thickness of the recording auxiliary layer is 100 nm or more is that the laser power at the time of reproduction is changed to form an optical mask to limit the region for detecting a reproduction signal. This is the effect. That is, in the Pb-Te film used as the recording auxiliary layer here, the refractive index changes in accordance with the temperature distribution, and the light intensity distribution is generated in the laser light spot correspondingly, and an optical mask is formed. The area for detecting the reproduction signal is limited. This substantially increases the ratio of the area of the laser light spot for detecting the reproduction signal and the area of the recording point, and as a result, a reproduction signal of a small recording point is obtained.

When the film thickness of the recording auxiliary layer is 250 nm or more, the laser beam necessary for recording is insufficient, and the recording point cannot be formed. This is because the light absorption of the recording auxiliary layer is large.
Therefore, the laser power may be increased, or the wavelength of the laser light may be changed, and the composition of the recording auxiliary layer suitable for optimum light absorption may be obtained. P used for the recording auxiliary layer here
Since the b-Te film has different optimum powers depending on the film thickness, the refractive index also changes. Further, the shape of the recording point can be further reduced by the mutual time delay between when the lens effect of the recording auxiliary layer is generated and when the recording film is irradiated with light. Further, at the time of reproducing the recording signal, an optical mask is formed due to the difference in refractive index due to the temperature distribution of the recording auxiliary layer,
Since the area for detecting the reproduction signal is limited, a small recording point can be reproduced as a result. Similar results were obtained even when the recording auxiliary layer was made of a material other than the Pb-Te alloy and having a composition similar to In-Sb alloy or In-Sb-Se alloy.

(Embodiment 3) A partial sectional view of an optical recording medium of the present invention according to this embodiment is shown in FIG. This optical recording medium was manufactured as follows.

A transparent disk-shaped substrate 1 is placed 10 cm from the target in a sputtering apparatus equipped with a quaternary target source.
It was set to the distance of and rotated. Next, Si is reactively sputtered from a first target in an argon-nitrogen mixed gas having a nitrogen concentration of 10% at a sputtering gas pressure of 5 mTorr to form a Si ₃ N ₄ film as a first dielectric layer 2 to a thickness of 70 nm. did.
Next, Pb-Te is sputtered with a second target in argon gas at a sputtering gas pressure of 5 mTorr to obtain a film thickness of 100
A recording auxiliary layer 9 having a thickness of nm was formed. Furthermore, the sputtering gas pressure is 5 mTorr from the third alloy target in argon.
Tb-Fe-Co alloy is sputtered with
The Curie temperature was about 200 ° C., the compensation temperature was about 100 ° C., the coercive force was Hc ₁ 15 kOe, and the first magnetic layer 3 having a composition of Tb ₂₇ Fe ₆₆ Co ₇ was formed. Next, similarly to the first dielectric layer 2, Si is reactively sputtered from a first target in an argon-nitrogen mixed gas with a nitrogen concentration of 10% at a sputtering gas pressure of 5 mTorr to form Si as the second dielectric layer 4. _{A 3} N ₄ film was provided to a thickness of 20 nm. Finally, sputter gas pressure 5 in argon
From the fourth target at mTorr, Al-as the metal layer 5 is formed.
A Ti film was provided with a thickness of 50 nm. Furthermore, about 1 on the surface
The resin layer 6 having a thickness of 0 μm was formed.

Recording and reproducing characteristics were measured using this disk. First, under a linear velocity of 4.2 m / s, a magnetic field (300 Oe) opposite to that at the time of recording was applied in the direction perpendicular to the film surface,
The magnetization direction was aligned in one direction by irradiating DC light of 6.7 mW. Next, while the applied magnetic field was reversed, recording was performed while sequentially changing the laser power with a signal of 1 MHz, and the C / N (carrier-to-noise ratio) of the fundamental wave and the second harmonic was measured.

Here, the optimum recording power is the laser power that minimizes the second harmonic component. This is because the lengths of the recorded portion and the unrecorded portion become equal when recording is performed with laser power that minimizes the second harmonic component.

Using this optimum recording power, the shape and size of the recording point were measured. At 9.0 mW, the length and width were 600 nm, the size of the recording point was about 75% of that of the disk A shown in Example 2, and the length and width of the recording point could be reduced. As a result, the recording density could be improved about twice.

Further, P used in the recording auxiliary layer of this embodiment
In the b-Te film, when the film thickness was changed, the shape of the recording point and the C / N changed as shown in Table 2. Here, the optimum power is slightly different for each film thickness.

[0034]

[Table 2]

[0035]

According to the present invention, the diameter of the spot of the laser light which has passed through the recording auxiliary layer, whose volume and / or refractive index has been changed by irradiating the laser light, is determined by the optical lens effect. It is smaller than the diameter when irradiated to. Thereby, high density recording is possible. Further, by reproducing by utilizing the same effect, an optical mask is formed, the region for detecting a reproduced signal can be limited, and a small recording point can be reproduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a portion of a manufactured magneto-optical recording medium of a conventional example.

FIG. 2 is a sectional view showing a portion of a magneto-optical recording medium manufactured according to Examples 1 and 2.

FIG. 3 is a sectional view showing a part of a magneto-optical recording medium manufactured according to Example 3.

FIG. 4 is a cross-sectional view showing a portion of a magneto-optical recording medium manufactured according to Example 4.

[Explanation of symbols]

1 ... Disc-shaped substrate, 2 ... First dielectric layer, 3 ... Recording layer,
4 ... Second dielectric layer, 5 ... Metal layer, 6 ... Protective layer, 7 ... Recording auxiliary layer, 8 ... Third dielectric layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Jiichi Miyamoto 1-280 Higashi Koikeku, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Toshio Niihara 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory

Claims (4)

[Claims] 1. An optical recording medium for recording / reproducing information by utilizing the phenomenon of being optically changed by irradiation of laser light, having a plurality of thin films including a recording layer and a recording auxiliary layer on a substrate, An optical recording medium, wherein the recording auxiliary layer changes shape and / or refractive index by irradiating the laser beam from the recording auxiliary layer side. 2. The laser beam is radiated through the recording auxiliary layer on the substrate side of the recording layer or on the side opposite to the substrate, and the average diameter of the laser beam near the interface of the recording layer is An optical recording medium having optical characteristics smaller than the average diameter before entering the recording auxiliary layer. 3. The laser light is irradiated through the recording auxiliary layer on the substrate side of the recording layer or on the side opposite to the substrate, and the portion of the recording auxiliary layer irradiated with the laser light is the recording auxiliary layer. An optical recording medium made of a material having a volume change and / or a refractive index change. 4. The recording auxiliary layer according to claim 1, wherein the recording auxiliary layer on the substrate side of the recording layer or on the side opposite to the substrate is irradiated with laser light, and the recording auxiliary layer serves as a heat absorption layer. An optical recording medium having a two-layer structure of a thermal expansion change layer and having an optical characteristic that an average diameter of the laser light near an interface with the recording layer is smaller than an average diameter before being incident on the recording auxiliary layer.