JP2002100076A - Optical recording medium and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase change type optical recording medium capable of writing at a low linear velocity and having high durability. SOLUTION: The phase change type optical information recording medium is obtained by successively stacking a first dielectric layer 2, a recording layer (phase change recording layer) 3, a second dielectric layer 4, a reflecting layer 5 and a protective layer 6 on a transparent substrate 1. The second dielectric layer 4 is formed with a dielectric material adaptable to a desired writing linear velocity and this layer 4 is used as a writing linear velocity controlling layer. In an embodiment, an optical disk is produced by stacking the layers on a polycarbonate substrate using a magnetron sputtering apparatus. In this case, the first dielectric layer, the recording layer, the second dielectric layer and the reflecting layer are formed of ZnS.SiO2, Ag2In5Sb71Te20Ge2, TaOx.AlOx.SiO2 and Ag97In3, respectively.

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 and a method of manufacturing the same, and more particularly, to a dielectric material layer (dielectric layer) formed on a substrate in an optical recording medium rewritable with a phase-change recording material. ) Relates to an optical recording medium adapted to cope with various writing linear velocities. The present invention can be applied to devices that control the temperature by heat transfer.

[0002]

2. Description of the Related Art In recent years, optical recording media that can be repeatedly recorded and reproduced have been spotlighted as removable media. Among them, phase-change optical disks using phase-change materials as recording materials can secure higher recording densities than magneto-optical recording systems, and have the potential to become the mainstream of rewritable removable media in the future. I have. In order to shorten the recording / reproducing time corresponding to a high recording density, such a phase change type optical disc has a higher disk rotation speed at the time of recording / reproducing in an optical disc drive, and calls / retrieves data at a high linear velocity. It is made to record.

[0003] By the way, various linear velocities are set for the write linear velocity at the time of writing information on the optical disk for each application. As a technique for coping with these various set linear velocities, a method of introducing a predetermined additive into a phase change material for forming a recording layer (Japanese Patent Laid-Open No. 10-106025) has been proposed.

However, phase-change rewritable media (linear speed of approximately 1.2 to 1.4 m / s), digital video disks (linear speed of approximately 4.0 m / s), optical disks for photo cameras (linear Speeds of about 6.0-14.0 m / s)
One important area.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical recording medium which can be written at a low linear velocity and has high durability.

[0006]

Means for Solving the Problems In order to obtain a medium capable of writing at a low linear velocity, the present inventors have studied a dielectric material compatible with a low linear velocity and its structure, and have reached the present invention. is there. That is, when a recording layer material (phase change material) corresponding to a high linear velocity is used at a low linear velocity, an excessively heavy laser power is usually applied, so that the durability of the recording layer material is easily deteriorated. According to the dielectric material for linear velocity control (writing linear velocity control layer, that is, linear velocity control layer) according to the present invention, the number of times of rewriting can be reduced at a low speed, and at the same time, the durability is improved as compared with the prior art. Durable media can be manufactured.

An optical recording medium according to claim 1 is a phase-change optical information recording medium in which a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer are sequentially laminated on a transparent substrate, At least the second dielectric layer is formed of a dielectric material capable of coping with a desired writing linear velocity to form a writing linear velocity control layer (hereinafter, a linear velocity control layer).

[0008] The optical recording medium according to the second aspect is the first aspect.
Wherein the second dielectric layer is formed by laminating two or more linear velocity control layers having different write linear velocities.

The optical recording medium according to the third aspect is the first aspect.
(2) In the second aspect, the second dielectric layer is characterized in that a corresponding write linear velocity is in a range of 1.2 m / s to 14 m / s.

[0010] The optical recording medium according to the fourth aspect is the first aspect.
Or wherein the thermal conductivity of the dielectric material forming the linear velocity control layer is less than 0.28 W / mK.

The optical recording medium according to the fifth aspect is the second aspect.
, Wherein the corresponding write linear velocity is set by adjusting the ratio of the film thickness of each linear velocity control layer forming the second dielectric layer.

The optical recording medium according to the sixth aspect is the fourth aspect.
In the fifth or fifth aspect, the dielectric material forming the linear velocity control layer is an oxide of each of Ta, Ti, Zr, Al, Si, and Ge, or a mixture thereof.

[0013] The optical recording medium according to the seventh aspect is the fourth aspect.
In 5 or 5, the dielectric material forming the linear velocity control layer is any one of nitrides of Ta, Zr, Al, Si and Ge, ZnO alone, a mixed oxide of ZnO and Al ₂ O ₃ , or , A mixture prepared by arbitrarily selecting from these nitrides, ZnO alone, and mixed oxides.

The optical recording medium according to the eighth aspect is the sixth aspect of the present invention.
Or 7, wherein said reflective layer is made of Ag or 70 wt.
% Of Ag, and a portion of the second dielectric layer that contacts the reflective layer is formed of a dielectric material having low reactivity with Ag.

An optical recording medium according to a ninth aspect is the optical recording medium according to the sixth aspect.
Or 7, wherein at least Ag, I
It is characterized by being formed of an alloy containing four elements of n, Sb and Te.

According to a tenth aspect of the present invention, there is provided a method of manufacturing an optical recording medium according to the sixth or seventh aspect, wherein the linear velocity control layer is formed of a metal target or a low-resistance sintered body. It is characterized by being formed by direct current sputtering film formation in which a reactive gas is introduced from a body target.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The optical recording medium of the present invention controls a writing linear velocity by a dielectric layer. When the dielectric material for linear velocity control is provided at least on the second dielectric layer disposed between the recording layer and the reflective layer (claim 1), the linear velocity control function can be exhibited. In the optical recording medium of the present invention, the second dielectric layer has a laminated structure of two or more layers, and at least one of the dielectric layers forming the laminated structure is a linear velocity control layer (claim Item 2). Furthermore, the write linear speed that can be supported is 1.2 to 1
The range is 4 m / s (claim 3).

The thermal conductivity of the dielectric material to be used may be in a range (less than 0.28 W / mK) which does not prevent the recording material of the phase change material from becoming amorphous.
When a material having a thermal conductivity of 0.28 W / mK or more is used, the manufactured optical recording medium has an extremely quenched structure, and the recording material layer is heated to a temperature sufficient to make the phase change material amorphous. Can no longer be heated,
The recording operation cannot be performed on the optical recording medium.
In addition, by adjusting the ratio of the film thickness of each linear velocity control layer forming the dielectric layer (claim 5), it is possible to cope with various writing linear velocities.

As the dielectric material for forming the linear velocity control layer, those described in claims 6 and 7 can be used. In addition, any material that can satisfy the characteristics described in claim 4 can be similarly used. Such materials can be selected from all types of metal oxides, nitrides, sulfides, carbides, or mixtures thereof.

Further, the material for forming the reflection layer can be selected from all metals.
An alloy containing 0 wt% or more of Ag is particularly preferable in terms of durability. However, a chalcogenide-based substance, particularly a dielectric material composed of sulfide, has a problem with the reactivity with Ag, and therefore the Ag side has low reactivity with the Ag (more preferably, no reactivity at all). ) It is necessary to use a dielectric material (claim 8). The recording layer is made of an alloy containing at least Ag, In, Sb, and Te as a main component (claim 9), for example, having a composition ratio (atomic%) of 0.3.
≦ Ag <6, 2 ≦ In ≦ 20, 35 ≦ Sb <75, 20
≦ Te ≦ 35.

In order to manufacture such an optical recording medium, DC sputter deposition is more advantageous than RF sputter deposition in terms of deposition rate and substrate incident heat.
A film is formed by a DC sputtering process while introducing a reactive gas from a metal target or a low-resistance sintered body target. According to this, a film formation rate 1.4 to 2 times as high as that of the high frequency sputtering film formation can be obtained.

[0022]

FIG. 1 is a sectional view showing a laminated structure of an optical recording medium according to the first embodiment, and FIG. 2 is a sectional view showing a laminated structure of an optical recording medium according to the second, fourth and fifth embodiments. is there. The optical recording medium of FIG.
A first dielectric layer 2 on a transparent substrate (plastic substrate) 1;
It has a structure in which a recording layer (phase change recording layer) 3, a second dielectric layer 4, a reflective layer (reflective heat dissipation layer) 5, and a protective layer 6 are laminated in this order, and the second dielectric layer 4 is a single layer. ing. On the other hand, in the optical recording medium of FIG. 2, the second dielectric layer 4 is formed by laminating a first linear velocity control layer (dielectric layer) 4a and a second linear velocity control layer (dielectric layer) 4b. It is formed by doing. Other configurations are the same as those in FIG.

In the following examples, a polycarbonate substrate having a thickness of 0.6 mm or 1.2 mm is used as a plastic substrate, ZnS.SiO ₂ is 50 to 250 nm as a first dielectric layer, and Ag2In5Sb71 is used as a recording layer.
8 to 30 nm for Te20Ge2 (the number is atomic%), 10 to 30 nm for the second dielectric layer, and 100 to 200 n for the reflective layer
An example in which a film is formed for each of m will be described. The thickness of each layer is described with a width since it is finely adjusted by optimizing the optical and thermal characteristics.

Example 1 (Regular structure: see FIG. 1) On a polycarbonate substrate having a thickness of 0.6 mm,
By laminating each layer using Ron sputtering equipment,
An optical recording medium (optical disk) was manufactured. The first dielectric layer
Low thermal conductivity, ZnS / SiO_TwoAnd The composition is ZnS
Is 80 mol%, SiO_TwoIs 20 mol%. this
ZnS / SiO_TwoHas a thermal conductivity of 0.04 W / mK,
The thickness is 70 nm. Next, the recording layer (phase change recording layer)
Ag2In5Sb71Te20Ge2 with a thickness of 20 n
m. The recording film of this composition has a medium crystallization rate,
Suitable for mid-speed recording. The second dielectric layer is TaOx · A
10x ・ SiO_TwoAnd Composition is 2 mol of TaOx
%, AlOx is 15.5 mol%, SiOx is 82.5%
In mol%, the film thickness was 20 nm. ZnS / SiO _Two
To the first dielectric layer, TaOx.AlOx.SiO_TwoThe second
The optical recording medium used as the dielectric layer depends on the composition of the recording layer.
Can correspond to a linear velocity of 4.0 m / s. On the other hand, the reflective layer (anti
The radiation layer is Ag97In3 (atomic%) and has a thickness of
It was 140 nm. The thermal conductivity of this Ag alloy is about 4 W /
mK.

This optical disk is subjected to initial crystallization using a high-power laser, and then to a 650 nm NA
Evaluation was made with a drive having an optical pickup of 0.6. Linear recording density 0.267 μm / bit, track pitch 0.
The signal was 74 μm, the recording linear velocity was 8.5 m / s, and the signal was 8/16 modulated. The initial jitter of this optical disk was 6%. Even after rewriting 10,000 times, it was as good as 8% or less.

Example 2 (two-layer structure of second dielectric layer: see FIG. 2) An optical disk was manufactured by laminating each layer on a 0.6 mm-thick polycarbonate substrate using a magnetron sputtering apparatus. The first dielectric layer has low thermal conductivity, Z
nS · SiO ₂ . The composition is ZnS 80 mol%,
SiO ₂ is 20 mol%. This ZnS / SiO ₂
Has a thermal conductivity of 0.04 W / mK and a thickness of 65 nm. The recording layer (phase change recording layer) is made of Ag2In3Sb73.
Te20Ge2 (atomic%) and a film thickness of 20 nm.

The second dielectric layer is made of ZnS.S having a thickness of 5 nm.
a first linear velocity control layer (recording layer side) made of iO ₂ and a film thickness of 1
0 nm TaNx 2% AlNx 15.5% SiNx
It was formed by a second linear velocity control layer (reflection layer side) of 82.5% (the ratio was mol%). Reflective layer (reflective heat dissipation layer)
Is Ag97In3at%, and the film thickness is 140 nm.
The thermal conductivity of this Ag alloy is about 4 W / mK.

Initial crystallization of this optical disk was performed using a high-power laser, and then 650 nm, NA
Evaluation was made with a drive having an optical pickup of 0.6. Linear recording density 0.267 μm / bit, track pitch 0.
At 74 μm, the linear velocity (recording linear velocity) was 6.0 m / s, and the signal was 8/16 modulated. The recording power is 14 mW peak and the erasing power is 7 mW. The initial jitter of this disk was 6%. Even after rewriting 10,000 times, it was as good as 8% or less.

[0029] The second dielectric layer in Example 3-1 (see FIG. 1), only the mixed film with a thickness of 20nm made of TaOx · AlOx · SiO _2, in the optical disc (Fig. 1) fabricated Al as the reflective layer , The linear velocity that can be supported is 4
m / s.

Example 3-2 (Adjustment of Film Thickness Ratio in Stacked Second Dielectric Layer: See FIG. 2) On the other hand, ZnO.SiO ₂ was 5 nm thick, and TaOx.
In 15nm and AlOx · SiO _2, in the optical disc to form a second dielectric layer was deposited, respectively, the linear velocity can respond became 6 m / s. Further, the total film thickness is set to 20 nm, and the ZnS.SiO ₂ film thickness and TaOx.AlOx.S
When the ratio with the iO ₂ film thickness is changed, ZnS · SiO ₂
When the ratio of the film thickness increases, the linear velocity of 8.5 m / s of ZnS.SiO ₂ alone becomes TaOx.AlOx.SiO _2.
When the ratio of the film thickness is increased, TaOx.AlOx.SiO
The linear velocity was close to 4 m / s in the case of ₂ units.

[0031] In this case, even if the ZnS · SiO ₂ on the recording layer side, the linear velocity even when the TaOx · AlOx · SiO ₂ in the recording layer side opposite to the result was the same. The initial jitter of this optical disk was 6%, and the jitter was as good as 8% or less even after rewriting 10,000 times. Such a result was obtained because the reflective layer material Al and the linear velocity control layer material (ZnS.SiO ₂ or TaOx.
This is because no chemical reaction occurs with AlOx.SiO ₂ ). Therefore, the material of the linear velocity control layer in contact with the Al reflecting layer is ZnS.SiO ₂ , TaOx.AlOx.Si
In any case of O ₂ , durability is ensured. However, unlike Example 4, which will be described later, it does not have a quenched structure, and as a result of the thermal history stress applied to the recording layer, the rewriting durability becomes about 10,000 times as described above.

Example 4 (Evaluation of durability in case of Ag reflective layer: see FIG. 2) A reflective layer of Ag was formed. In the second dielectric layer, Zn
Other fixing the S · SiO ₂ recording layer side dielectric material (first line speed control layer), as TaOx · AlOx of · SiO ₂ and Ag reflective layer side dielectric material (second line speed control layer) An optical disk was manufactured with the same configuration as in Example 3-2. As a result, both the linear velocity that can be handled and the linear velocity when the film thickness ratio was changed were the same as those of the optical disk of Example 3-2.
In durability, the initial jitter of the optical disk was 6%. Also, the jitter was as good as 8% or less even after rewriting 40000 times. Since the Ag reflection layer has higher thermal conductivity than the Al reflection layer, it has a rapid cooling structure. That is, after being heated by the laser, heat is not stored around the recording layer and is radiated to the Ag reflection layer. Since there is little residual heat, deterioration of the thermal history of the recording layer due to stress is less likely to occur, and as a result, the rewriting characteristic is longer than that of Al and extended about 40,000 times.

Example 5 (Other Materials) In Example 1, an optical disk was manufactured using TiO ₂ for the second dielectric layer. The corresponding linear velocity was 4.5 m / s. The jitter of this optical disk after 50,000 times was 10% or less. The same result was obtained using ZrO ₂ .

Example 6 (Other Materials) In Example 1, ZnO.Al ₂ O ₃ was used for the second dielectric layer.
(98 mol% of ZnO and 2 mol% of Al ₂ O ₃ ) were used to produce an optical disk. Corresponding linear velocity is 8.0
m / s. The jitter of this optical disk after 100000 times was 7% or less.

Example 7 (Other Materials) In Example 1, an optical disk was manufactured using ZrN for the second dielectric layer. The corresponding linear velocity was 8.2 nm / s. The jitter of this optical disk after 100000 times was 8% or less.

Comparative Example 1 (Defect at Low Linear Velocity: See FIG. 1) By laminating each layer on a polycarbonate substrate having a thickness of 0.6 mm using a magnetron sputtering apparatus,
An optical recording medium (optical disk) was manufactured (FIG. 1). Both the first dielectric layer and the second dielectric layer have low thermal conductivity, ZnS
- was SiO _2. The composition is ZnS 80 mol%, Si
O ₂ is 20 mol%. The thermal conductivity of this ZnS.SiO ₂ is 0.04 W / mK. The thickness of the first dielectric layer is 70 nm, and the thickness of the second dielectric layer is 20 nm. The recording layer was made of Ag2In5Sb71Te20Ge2 (at a ratio of atomic%). The thickness is 20 nm. The recording film having this composition has a medium crystallization speed and is suitable for medium linear velocity recording. Z
An optical disc using nS · SiO ₂ as the first and second dielectric layers sandwiching the recording layer can support a linear velocity of 8.5 m / s. On the other hand, the reflection layer is made of Ag97In3 (the ratio is atomic%).
Then, the film thickness was set to 140 nm. The thermal conductivity of this Ag alloy is about 4 W / mK.

This optical disk was initially crystallized with a high-power laser, and thereafter, 650 nm, NA0.
Evaluation was made with a drive having 6 optical pickups. Linear recording density 0.267 μm / bit, track pitch 0.74
The signal was 8/16 modulated at μm and a recording linear velocity of 8.5 m / s. The initial jitter of this optical disk was 6%.
Also, the jitter was as good as 8% or less even after rewriting 10,000 times. The disk has a linear velocity (recording linear velocity) of 4
In order to record at m / s, a method of converting the output of laser power and the number of pulses at the time of normal recording in accordance with the linear velocity is used. However, when the writing speed is reduced, the cooling speed is reduced. A problem that formation becomes unstable occurs.

Comparative Example 2 (Problem When Thermal Conductivity Is Excessive) An optical disk using a dielectric material having a thermal conductivity of 0.28 W / mK or more was manufactured. In this case, the thermal conductivity is 0.28
A linear velocity control layer made of a TiNx film of 5 W / mK was formed with a thickness of 19 nm above the recording layer. As a result, 13 to 15 m by a semiconductor laser having a central emission wavelength of 660 nm.
At a recording power of W, the recording layer could not be made amorphous.

Comparative Example 3 (In the case of an Al reflective layer) A device was manufactured in the same manner as in Example 1. In this case, the reflection layer
1Ti (1 wt% Ti) alloy was used. However, the initial jitter was poor and was 10%. Also, the jitter after 5,000 rewrites reached 16%. This is presumably because the heat conduction of the reflective layer deteriorated, the temperature of the recording film increased, and a defect such as film flow occurred early.

Comparative Example 4 (Defect caused by reaction between Ag and ZnS: see FIG. 2) In the structure of the dielectric of Example 4, TaOx.AlOx was used.
-SiO ₂ as a dielectric material on the recording layer side (first linear velocity control layer)
Then, ZnS.SiO ₂ was fixed as a dielectric material (second linear velocity control layer) on the Ag reflection layer side. In this case, the chalcogen component (ZnS) interacts with Ag, and Ag
Since the reflective film was sulfurized (deteriorated), reading and writing of the optical disk became impossible.

As described above, when the reflective layer is made of Ag and the second dielectric layer has a laminated structure composed of a plurality of layers, the order of the lamination, that is, the second linear velocity control layer which is in contact with the Ag reflective film is formed. Depends on what kind of material
There may be a problem in durability of the Ag reflection film. Therefore, as a layer configuration, it is necessary to set the lamination position of the layer containing the chalcogen compound on the recording layer side.

[0042]

As is apparent from the above description, claim 1
The phase change type optical recording medium according to the invention, the first dielectric layer, the recording layer, the second dielectric layer, the reflective layer is sequentially laminated on a transparent substrate, at least the second dielectric layer, the desired writing The linear velocity control layer is formed by using a dielectric material that can cope with the linear velocity. As described above, by using a dielectric material suitable for the linear writing speed in the second dielectric layer, stable pit formation can be performed at a low speed without using a phase change material having a special composition, and durability can be improved. And an optical recording medium rich in

According to the second aspect of the present invention, since the second dielectric layer is formed by laminating two or more linear velocity control layers that can correspond to each other with different linear velocity, the applicable linear velocity range is widened. As a material system for forming the dielectric layer, various types can be used.

According to the third aspect of the present invention, since the write linear velocity which can be handled by the second dielectric layer is in the range of 1.2 m / s to 14 m / s, it can sufficiently cope with the current optical recording medium.

According to the fourth aspect of the present invention, since the thermal conductivity of the dielectric material forming the linear velocity control layer is less than 0.28 W / mK, the recording layer material (phase change material) is surely made amorphous. be able to. If the thermal conductivity of the dielectric material is too high, an excessively quenched structure is formed, so that the recording layer material cannot be made amorphous.

According to the fifth aspect of the present invention, the corresponding write linear velocity is set by adjusting the ratio of the thickness of each linear velocity control layer forming the second dielectric layer. The degree of freedom is improved.

According to the sixth aspect of the present invention, the dielectric material forming the linear velocity control layer is made of Ta, Ti, Zr, Al, Si, Ge.
Each oxide, or a mixture thereof,
Since these have low thermal conductivity, an optical recording medium for a lower linear velocity can be obtained as compared with the original linear velocity corresponding to the recording layer material.

According to the seventh aspect of the present invention, the thermal conductivity of the predetermined dielectric material forming the linear velocity control layer is higher than that of the dielectric material of the sixth aspect. Thus, an optical recording medium for a medium linear velocity can be provided.

According to the invention of claim 8, the reflective layer is made of Ag or
While being formed with an alloy containing 70 wt% or more of Ag,
The portion of the second dielectric layer that contacts the reflective layer is formed of a dielectric material having low reactivity with Ag. In this optical recording medium, the thermal conductivity of the reflection layer is better than that of the other metal reflection layers, so that the repetitive recording resistance is improved. In addition, since a dielectric material that does not easily react with Ag is provided in the adjacent layer, the durability against repetition is improved.

According to the ninth aspect of the present invention, since the recording layer is formed of an alloy containing at least four elements of Ag, In, Sb, and Te, it is possible to provide an optical recording medium having remarkably improved repetitive recording characteristics.

According to a tenth aspect of the present invention, in the method of manufacturing an optical recording medium according to the sixth or seventh aspect, the linear velocity control layer is formed of a metal target or a low-resistance sintered body target. Since the film is formed by direct current sputtering film formation in which a reactive gas is introduced from the substrate, the film formation speed is improved, and the substrate incident heat energy is reduced, so that an optical recording medium in which the plastic substrate has very little thermal deformation can be obtained. .

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical recording medium according to a first aspect.

FIG. 2 is a sectional view of an optical recording medium according to claims 2, 4, and 5;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transparent substrate 2 first dielectric layer 3 recording layer 4 second dielectric layer 4 a first linear velocity control layer 4 b second linear velocity control layer 5 reflective layer 6 protective layer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G11B 7/24 534 G11B 7/24 534M 534N 538 538E 7/0045 7/0045 Z 7/26 531 7/26 531 F term (Reference) 5D029 JA01 LA14 LA16 LB07 LB11 LC17 MA13 5D090 AA01 BB05 CC01 HH01 5D121 AA04 EE03 EE09

Claims (10)

[Claims] 1. A phase-change optical information recording medium comprising a transparent substrate, on which a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer are sequentially laminated, wherein at least the second dielectric layer is a desired one. An optical recording medium comprising a writing linear velocity control layer (hereinafter referred to as a linear velocity control layer) formed of a dielectric material capable of coping with the above-mentioned linear writing velocity. 2. The optical recording medium according to claim 1, wherein the second dielectric layer is formed by laminating two or more linear velocity control layers that can correspond to each other with different linear velocity. . 3. The optical recording medium according to claim 1, wherein the second dielectric layer has a corresponding write linear velocity in a range of 1.2 m / s to 14 m / s. 4. The optical recording medium according to claim 1, wherein a thermal conductivity of a dielectric material forming the linear velocity control layer is less than 0.28 W / mK. 5. The apparatus according to claim 2, wherein the corresponding write linear velocity is set by adjusting a ratio of a film thickness of each linear velocity control layer forming the second dielectric layer. Optical recording medium. 6. The dielectric material forming the linear velocity control layer is an oxide of each of Ta, Ti, Zr, Al, Si, and Ge, or a mixture thereof. Or the optical recording medium according to 5. 7. The dielectric material forming the linear velocity control layer may be any one of nitrides of Ta, Zr, Al, Si, and Ge, ZnO alone, and a mixed oxide of ZnO and Al ₂ O ₃ , The optical recording medium according to claim 4, wherein the optical recording medium is a mixture prepared by arbitrarily selecting from nitride, ZnO alone, and mixed oxide. 8. A dielectric material having low reactivity with Ag, wherein the reflective layer is formed of Ag or an alloy containing 70% by weight or more of Ag, and a portion of the second dielectric layer which contacts the reflective layer is low in Ag reactivity. The optical recording medium according to claim 6, wherein the optical recording medium is formed by: 9. The recording layer is made of at least Ag, In, S
8. The optical recording medium according to claim 6, wherein the optical recording medium is formed of an alloy containing four elements b and Te. 10. The method for producing an optical recording medium according to claim 6, wherein the linear velocity control layer is formed by direct current sputtering in which a reactive gas is introduced from a metal target or a low-resistance sintered body target. A method for producing an optical recording medium, comprising forming a film.