JP2781421B2 - Manufacturing method of optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a novel optical recording medium manufacturing method. More specifically, the present invention relates to a method for manufacturing a low-noise optical recording medium that eliminates structural discontinuities that cause non-uniform light reflection.

<Prior Art> In recent years, optical recording media represented by optical discs have been attracting attention as players who play a central role in recording media in the advanced information society, and are being actively studied.

There are three types of optical disks: a read-only type represented by a compact disk, a write-once type capable of recording and reproducing information, and a rewritable type capable of recording, erasing and reproducing information. Information is reproduced using light reflected from the surface.

For this reason, in any of the above optical disks, it is common to provide a reflection layer in some form.

The simplest type is a read-only type. In this case, the reflective layer only needs to have a high reflectance, and usually, aluminum which has high productivity and is inexpensive is used.

On the other hand, in the case of the write-once type or the rewritable type, the role of the reflection layer is to increase the optical contrast and adjust the reflectance.

In this case as well, regarding the optical characteristics, the reflective layer may be made of aluminum. It is more advantageous to do so.

Such materials include, for example, indium, tin,
Examples include antimony, tellurium, bismuth, and lead.

By the way, since the above-mentioned materials all have a crystallization temperature near room temperature, they tend to be non-uniform crystals at least partially left in an amorphous state at least immediately after formation. Since the optical constants are significantly different between the amorphous state and the crystalline state, such a non-uniform structure results in uneven reflectance and increases noise during reproduction.

In particular, the thickness of the reflective layer used in the optical recording medium is often selected from 20 nm to 100 nm in order to achieve both the reflectance and the thermal conductivity. This is particularly inconvenient because it is similar to the recording bit and directly leads to an increase in noise.

<Problems to be Solved by the Invention> It is an object of the present invention to provide a reflective layer that prevents an increase in noise due to non-uniform structure as described above, and has good optical characteristics and sensitivity.

<Means for Solving the Problems> The present inventors have conducted intensive studies to solve the above problems, and as a result, have found means for resolving the non-uniformity of the structure. That is, the present invention provides a method for producing a phase change optical recording medium having at least a substrate, a phase change recording and a reflection layer, wherein a eutectic alloy comprising two or more elements of the reflection layer or a substance having a composition in the vicinity thereof is used. A phase-change optical recording medium characterized by forming a film into a reflective layer in an amorphous state. Further, the reflective layer is a eutectic alloy selected from the group consisting of germanium-antimony, gallium-antimony, indium-antimony, lead antimony, antimony-tellurium, germanium-tellurium, and tin-tellurium. It is a preferred embodiment of the present invention that a film is formed using a material having a composition in the vicinity of the film to form an amorphous reflective layer.

 Hereinafter, the present invention will be described in detail.

As long as a crystalline substance is used for the reflective layer, it is not possible to strictly avoid uneven optical constants due to non-uniform crystallinity and crystal grain size.

On the other hand, the function of the present invention is to make the reflection layer amorphous, thereby making the optical constants uniform and preventing an increase in noise.

According to this method, the thin film forming conditions at the time of forming the reflective layer,
Good reproduction characteristics can be realized irrespective of the configuration of the applied optical recording medium.

In order to form a reflective layer in an amorphous state, a eutectic alloy of two or more components or a composition in the vicinity thereof is used.

Specifically, when using an alloy having a eutectic composition of two or more elements selected from silicon, gallium, germanium, selenium, indium, tin, antimony, tellurium, thallium, bismuth, and lead, or a composition in the vicinity thereof Good.

For example, alloy systems such as germanium-antimony system, gallium-antimony system, indium-antimony system, lead-antimony system, antimony-tellurium system, germanium-tellurium system, and tin-tellurium system can be easily formed by vapor deposition or sputtering. It is suitable as a material for a reflective layer of an optical recording medium in that it has advantages such as appropriate thermal conductivity and optical constant and relatively low cost.

In addition, these alloys also have an advantage that when the crystallization temperature needs to be adjusted as described later, the crystallization temperature can be easily changed by the composition.

Hereinafter, the present invention will be described in more detail by taking a germanium-antimony system as an example.

The eutectic composition of this alloy system is Ge ₁₃ Sb ₈₇ based on the number of atoms, and an amorphous alloy can be obtained near this composition.

If the ratio of germanium is less than 5%, crystals of antimony alone crystallize out, so that it does not become amorphous. If the ratio exceeds 35%, the reflectance decreases. Therefore, the ratio of germanium is preferably 5% or more and 35% or less. .

Which composition is optimal in this range slightly varies depending on the type and configuration of the optical recording medium to be applied.

FIGS. 1 (b) and 1 (c) show an example of the configuration of an optical recording medium manufactured according to the present invention. As shown in FIG. When a heat insulating layer is inserted, the temperature of the reflective layer does not rise when the optical recording medium is used.
It is better to choose below.

On the other hand, when the thickness of the interference layer or the heat insulating layer is small, or when the reflective layer is in direct contact with the recording layer as shown in FIG. Rises to about the same level as the recording layer due to heat conduction.

Therefore, in order to maintain the amorphous state of the reflective layer even when performing a recording / erasing operation, the crystallization temperature must be higher than the operating temperature of the recording layer.

For example, in the case of a magneto-optical recording medium, the recording layer temperature is close to its Curie temperature, often about 100 ° C. to 200 ° C., so that the germanium ratio is preferably selected from 7% to 30%.

In the case of a phase-change recording medium, the temperature of the reflective layer rises depending on the phase-change temperature of the recording layer to be used. For example, if the phase-change temperature is from 150 ° C. to 200 ° C., the germanium ratio should be 10% or more. %, The desired effect can be obtained.

A transition metal such as titanium, vanadium, chromium, cobalt, nickel, zirconium, niobium, tantalum, or molybdenum may be added to the reflective layer formed in the present invention for the purpose of enhancing stability.

The amount of addition should be such that it does not affect the optical constant and crystallization temperature of the reflective layer, and is preferably 5% or less based on the number of atoms.

As a substrate material, besides plastics such as acrylic, polycarbonate, polyolefin and epoxy, glass and the like can be used.

Further, by providing a protective layer composed of a dielectric between the substrate and the recording layer or on the reflective layer, the stability of the optical recording medium can be dramatically improved.

As the derivative material, it is preferable to use oxides such as magnesium, aluminum, silicon, zinc, germanium, titanium, and tantalum, nitrides, oxynitrides, sulfides, fluorides, and the like, or composites and laminates thereof. .

<Examples> Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

REFERENCE EXAMPLE GeSb alloy thin films of various compositions having a thickness of 80 nm were formed on a cover glass for a microscope by co-sputtering, and the crystallization temperatures were measured.

Since the optical constant of the GeSb alloy changes discontinuously in the amorphous crystalline state, the temperature at which the reflectance changes rapidly when the sample is heated is defined as the crystallization temperature.

 The measurement wavelength was 830 nm.

FIG. 2 shows the relationship between the crystallization temperature and the composition of the alloy thin film.

In the case of a thin film having a Ge content of 0%, that is, only Sb, the above-mentioned rapid change in reflectance does not appear.

This is presumably because the crystallization temperature of Sb is other than room temperature, and the crystal has already grown immediately after the film formation.

As the sample is heated, the reflectance gradually increases as the crystal grows.

This indicates that the crystals immediately after film formation are still non-uniform.

Therefore, when this thin film is used as a reflection layer of an optical recording medium, noise is expected to occur due to optical unevenness.

As Ge is added thereto, the crystallization temperature gradually rises from room temperature, and becomes 200 ° C. or more at 35% Ge.

As a result of X-ray diffraction, it was confirmed that the sample immediately after the film formation was amorphous in the sample containing 5% or more of Ge.

This result suggests that adding 5% or more of Ge to the Sb reflection layer forms an optically uniform reflection layer, thereby obtaining an optical recording medium with less noise.

Example 1 As shown in FIG. 3, Sb ₁₈ Te ₅₂ Ge ₃₀ was used as a recording layer 2 on a polycarbonate substrate 1 for an optical disk having a diameter of 130 nm.
A 30 nm thick alloy film, a 50 nm thick GeSb alloy film as the reflective layer 3 and a 20 nm thick SiO thin film as the protective layer 4 were formed by sputtering.

The recording layer is formed of a compound target having the above composition, and the reflective layer is formed of a protective layer formed by co-sputtering using Ge and Sb targets.
The reflective layer was formed by reactive sputtering using a Si target, and in particular, the reflective layer was changed in the ratio of Ge from 0% to 37.5% based on the number of atoms by adjusting the ratio of the input power to each target.

In order to investigate the recording characteristics of this disc,
m, radius position R = 30mm, frequency 1.0MHz, duty ratio 50
Was recorded (recording bit length 2.8 μm), and the carrier level and noise bell were measured.

 FIG. 4 shows the results.

In this figure, the horizontal axis represents the composition of the reflective layer in terms of Ge atom%.
The vertical axis indicates the carrier-to-noise ratio (CNR) and the noise bell.

The noise level is about -61 dB in the case of Sb only, but Ge
Ratio starts to decrease from 3% to 5%, and becomes constant at about -76 dB above 10%.

In the case of only Sb, the reason why the noise is high is that crystals of about several μm are grown irregularly.

In order to prevent this, it is effective to add only 5% of Ge. However, in the case of a phase change type recording medium as in this embodiment, the crystallization temperature of the reflective layer is set higher than the crystallization temperature of the recording layer. It is more preferable to keep this in order to prevent noise rise due to crystallization of the reflective layer during recording.

Since the crystallization temperature of the recording layer of this embodiment is about 160 ° C., it is preferable that the addition amount of Ge is 10% or more based on the number of atoms in consideration of the results of the reference example.

Due to the above-mentioned effects, the CNR increases with a decrease in noise. However, the CNR starts to decrease when the amount of Ge exceeds 25%, and sharply decreases when the amount of Ge exceeds 35%.

This is not due to an increase in noise, but to a decrease in carrier.

It is considered that the reason for this is that the change in the optical constant of the reflective layer due to the addition of Ge cannot be ignored, and the contrast of the recording signal has decreased.

From the above results, it has become clear that it is effective to configure the reflective layer with a GeSb alloy in order to prevent an increase in noise due to crystallization of the reflective layer.

The composition of the GeSb alloy is most suitably selected from the range of 5% or more, more preferably 10% or more, in order to prevent an increase in noise, and 35% or less in the sense of preventing contrast reduction.

Example 2 In the optical disk of Example 1, the reflective layer 3 was formed of Ge ₁₂ S
The nozzle level was measured when the same signal as in Example 1 was recorded, composed of b ₈₈ , In ₃₀ Sb ₇₀ , Sb ₁₉ Pb ₈₁ , Sb ₈₅ Te ₁₅ , and alloy thin films.

Further, in order to examine the structure of each alloy thin film, only the reflection layer was formed on a microscope slide glass, and the X-ray diffraction pattern was measured.

Deposition sputtering with compound target only Ga ₁₂ Sb _88, the other was carried out by co-sputtering by the target of each component element.

The composition used here is the eutectic composition of each alloy system or the composition in the vicinity thereof. Table 1 shows the results.

In each of the alloy systems, the noise level is reduced by 13 to 15 dB as compared with the case where the reflective layer is formed only of Sb.

This indicates that the optical unevenness of each alloy is significantly lower than that of Sb alone.

In addition, all the alloy thin films were amorphous, and it became clear that uniform structure was effective in reducing noise.

<Effect of the Invention> According to the manufacturing method of the present invention, it is possible to provide an optical recording medium with low noise without optical unevenness due to structural nonuniformity of the crystalline reflective layer.

[Brief description of the drawings]

1 and 3 are views showing an example of the configuration of an optical recording medium manufactured by the present invention, wherein 1 is a substrate, 2 is a recording layer, 3 is a reflective layer, 4 is a protective layer, an interference layer, and heat insulation. A dielectric layer used as a layer or the like. FIG. 2 is a diagram showing the crystallization temperature of the reflection layer of the optical recording medium used in the present invention. FIG. 4 is a graph showing the reproduction characteristics of the optical recording medium manufactured according to the present invention. In FIG. 4, the solid line indicates the carrier-to-noise ratio, and the dashed line indicates the noise level.

Claims (2)

(57) [Claims] 1. A method for manufacturing a phase change optical recording medium having at least a substrate, a phase change recording layer and a reflection layer, wherein the reflection layer is made of a eutectic alloy comprising two or more components or a material having a composition in the vicinity thereof. A method for manufacturing a phase-change optical recording medium, comprising forming a film into a reflective layer in an amorphous state. 2. The eutectic alloy or a substance having a composition in the vicinity of the eutectic alloy includes germanium-antimony, gallium-antimony, indium-antimony, lead-antimony,
2. The method according to claim 1, wherein the phase change optical recording medium is selected from the group consisting of antimony-tellurium, germanium-tellurium, and tin-tellurium.