JP2001266408A - Optical recording medium and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical recording medium excellent in reliability for a long period of time. SOLUTION: This optical recording medium has at least the first protection layer, a recording layer, the second protection layer and a reflection layer laminated on a substrate in this order. In the medium, information can be recorded, deleted or reproduced by irradiating the recording layer with light. The information is recorded and deleted by making the phase transition between the amorphous phase and the crystal phase. Each of the first and second protection layers has such a structure that two or more layers consisting of chalcogen compound and metal oxide and two or more layers consisting of carbon are laminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of recording high-density information at a high speed by irradiating a laser and a method of manufacturing the same.

[0003]

2. Description of the Related Art An optical recording medium is provided with an optical recording / reproducing information recording section on a molded substrate, and is used as a disk for files such as documents and data. While rotating the optical recording medium at a high speed, a laser beam narrowed down to about 1 μm is irradiated to read data from the recording layer or record data on the recording layer while performing focus adjustment and position detection.

An example of a specific recording / reproducing method for a phase change type optical recording medium will be described below. During recording, a focused laser pulse is applied to the crystalline recording layer for a short time to partially melt the recording layer. The melted portion is quenched by thermal diffusion and solidified to form an amorphous recording mark. If the reflectance of the recording mark is set lower than, for example, the crystalline state, information can be optically reproduced using the reflectance difference. Further, at the time of erasing, the recording mark portion is irradiated with laser light, and the recording mark in the amorphous state is crystallized by heating to a temperature lower than the melting point of the recording layer and higher than the crystallization temperature,
Return to the original unrecorded state.

As a conventional protective layer of an optical recording medium, a dielectric layer in which a chalcogen compound such as ZnS and an oxide such as SiO ₂ are mixed has been preferably used because of its high function of protecting the recording film.

However, the long-term reliability of the optical recording medium has been insufficient. That is, as a test for accelerating reliability, when the optical recording medium is read and written after storing the optical recording medium in a high-temperature, high-humidity environment, there is a problem that the byte error rate is significantly increased. Even if the characteristics immediately after production are good, if the long-term reliability is poor, the characteristics of the optical recording medium deteriorate during long-term use, which is a problem.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical recording medium having good long-term reliability.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide at least a first protective layer, a recording layer, a second protective layer and a reflective layer which are laminated on a substrate in this order, and irradiates the recording layer with light. By doing so, it is possible to record, erase, and reproduce information,
An optical recording medium in which recording and erasing of information is performed in a phase change between an amorphous phase and a crystalline phase, wherein the first protective layer or the second protective layer is a layer comprising a chalcogen compound-containing layer and a layer comprising carbon. Is achieved by an optical recording medium having a structure in which at least two layers are laminated.

Another object of the present invention is to provide a method for manufacturing an optical recording medium comprising: laminating a first protective layer, a recording layer, a second protective layer and a reflective layer on a substrate in this order by sputtering. In the step of sputtering the first protective layer and / or the second protective layer, a substrate is attached to a rotatable substrate tray, and a sputtering target containing a chalcogen compound and a sputtering target made of carbon are placed at different positions, Is achieved by performing a sputtering while rotating the optical recording medium.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical recording medium according to the present invention has a structure in which at least a first protective layer, a recording layer, a second protective layer, and a reflective layer are laminated in this order on a substrate. Preferably, for example, a laminated structure in which a first layer (first protective layer) / second layer (recording layer) / third layer (second protective layer) / fourth layer (reflective layer) is provided in this order on a substrate, Or the first layer (first protective layer) /
A second layer (recording layer) / third layer (second protective layer) / fourth layer (light absorbing layer) / fifth layer (reflective layer) and the like.

The effects of the first and second protective layers are as follows: prevention of corrosion of the recording layer, prevention of deterioration of recording characteristics caused by heat deformation of the substrate and the recording layer during recording, and signal contrast at the time of reproduction due to an optical interference effect. Has the effect of improving. The preferred thickness of the first protective layer in this case is usually 50 nm to 40 nm.
0 nm. The thickness of the second protective layer is 10 nm to 100 n
m is preferable since it is excellent in that deterioration of recording characteristics due to repetition of rewriting is small and a power margin of erasing power is wide.

As such a protective layer, a chalcogen compound such as ZnS, a metal oxide such as SiO ₂ , Ta ₂ O ₅ , ITO, or a mixed film thereof can be used.
Among these, those containing a chalcogen compound are preferable, and those containing ZnS are more preferable. Especially ZnS and S
An iO ₂ mixed film is preferable because it has excellent reliability and further suppresses deterioration at the time of recording / erasing. Further, those obtained by mixing carbon or a fluoride such as MgF _{2 with} these are also preferable because the residual stress of the film is small.

An optical recording medium according to the present invention has a first
At least one of the protective layer and the second protective layer is made of ZnS
And a layer (layered) structure of a layer containing a chalcogen compound and a layer made of carbon.

In the conventional protective layer, the chalcogen compound, particularly the Zn component or the S component diffuses into the recording layer, so that the optical constant of the recording layer changes and the amplitude of the reproduced signal may decrease. Further, the internal stress of the protective layer due to the repetition of recording and erasing causes mechanical destruction of the recording layer, causing burst defects.

In the present invention, the carbon layer can prevent the chalcogen compound from penetrating into the recording layer by forming the protective layer into the above-described laminated structure. In addition, such a laminated structure reduces the stress of the protective layer and suppresses the occurrence of burst. Accordingly, deterioration of the recording layer is suppressed, and long-term reliability can be ensured.

The number of layers may be any number as long as it is at least two layers each of a layer containing a chalcogen compound and a layer made of carbon. It is preferable because it exerts a greater effect.

It is more preferable that both the first protective layer and the second protective layer have the above-mentioned laminated structure, because the effect is even higher.

As the recording layer, it is preferable to use an alloy containing at least three elements of Ge, Sb, and Te as constituent elements from the viewpoint that overwriting can be performed at high speed. Further, the composition is preferably within the range represented by the following formula, from the viewpoint of excellent thermal stability and repetition stability. M _z (Sb _x Te _1-x ) _1-yz (Ge _0.5 Te _0.5 ) _y 0.35 ≦ x ≦ 0.5 0.2 ≦ y ≦ 0.5 0.0005 ≦ z ≦ 0.01 M represents at least one metal selected from palladium, niobium, platinum, silver, gold, and cobalt. Also,
x, y, z, and a number represent the number of atoms of each element (the number of moles of each element). In particular, palladium and niobium preferably contain at least one kind.

The light reflecting layer formed on the second protective layer or the light absorbing layer has an optical interference effect to improve the signal contrast during reproduction, and a cooling effect to provide an amorphous recording mark. Facilitates the formation of the
The effect of improving the repetition characteristics is expected. The thickness of the recording layer is preferably from 10 to 100 nm.

As a material of the reflection layer, a metal such as Al or Au having light reflectivity, or a material containing these as a main component,
alloys containing additional elements such as i, Cr, Hf and Al,
Examples include a mixture of a metal such as Au and a metal compound such as a metal nitride such as Al and Si, a metal oxide, and a metal chalcogenide. Metals such as Al and Au and alloys containing these as main components are preferable because of high light reflectivity and high heat conductivity. Examples of the aforementioned alloys include Al, Si, Mg, Cu, Pd, Ti, Cr,
At least one element such as Hf, Ta, Nb, Mn or the like added in a total of 5 at% or less and 1 at% or more, or at least one of Au, Cr, Ag, Cu, Pd, Pt, Ni, etc. Element total 20 atomic% or less 1 atomic%
These are the ones added above. In particular, an alloy containing Al as a main component is preferable because the price of the material can be reduced, and particularly, Ti and C are added to Al because of good corrosion resistance.
at least one metal selected from the group consisting of r, Ta, Hf, Zr, Mn, and Pd in a total of 5 atomic% or less and 0.5 atomic%.
The alloys added above are preferred. In particular, because corrosion resistance is good and hillocks do not easily occur,
Containing a total of 0.5 atomic% or more and less than 3 atomic% of additional elements,
Al-Hf-Pd alloy, Al-Hf alloy, Al-Ti alloy, Al-Ti-Hf alloy, Al-Cr alloy, Al-T
An alloy containing Al as a main component, such as an alloy a, an Al—Ti—Cr alloy, or an Al—Si—Mn alloy, is preferable as the material of the reflective layer.

As a substrate for a recording medium, it is preferable to use a material through which a laser beam is well transmitted in order to perform recording / reproduction from the substrate side. For example, polymethyl methacrylate resin, polycarbonate resin, polyolefin resin, epoxy resin, etc. Organic polymer resins, mixtures thereof, copolymers and the like can be used. Among them, a polycarbonate resin can be most preferably used from the viewpoint of optical characteristics and heat resistance.

Using this thermoplastic resin, a disk-shaped substrate is produced by, for example, injection molding or injection compression molding. At the time of molding the substrate, a stamper having a predetermined groove or pit male mold formed on the surface is mounted in a mold, and a substrate having a desired track formed on the surface by transfer from the stamper is molded.

The size of the substrate needs to conform to the standard required by the optical recording medium drive. For example, the diameter is 80 mm, 90 mm, 120 mm or 130 mm
Substrates are defined. As the thickness, both 1.2 mm and 0.6 mm can be used.

Next, a method for manufacturing the optical recording medium of the present invention will be described.

As a method for forming a reflective layer, a protective layer, a recording layer, and the like on a substrate, a method of forming a thin film in a vacuum, for example, a vacuum deposition method, an ion plating method, a sputtering method and the like can be mentioned. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled during film formation.

In order to form the protective layer into a laminated structure as described above, in the step of sputtering the protective layer, a substrate is attached to a rotatable substrate tray, and a sputtering target containing a chalcogen compound is different from a sputtering target made of carbon. And sputtering is performed while rotating the substrate tray.

The sputtering target containing a chalcogen compound and the sputtering target consisting of carbon are:
Installed at different positions in the sputtering chamber. When installed at the same position, or when using an integrated sputtering target in which the chalcogen compound and carbon are integrated, it becomes a protective layer in which the chalcogen compound and carbon are uniformly mixed, and the laminated layer as in the present invention. No structure is obtained. Each sputtering target,
It is preferable to install at a position 90 degrees or more away from the rotation axis of the substrate tray (on the opposite side of the sputtering chamber with the rotation axis of the substrate tray therebetween). Further, it is more preferable to set at a position of 150 to 180 degrees with respect to the rotation axis of the substrate tray.

Conventionally, in order to make the protective layer uniform, the distance between the sputtering target and the substrate has been set to some extent in the sputtering step.
However, in the present invention, it is important that the protective layer has a laminated structure, and since the effect is not exhibited even if the protective layer is uniform, it is important to reduce the distance between the sputtering target and the substrate, unlike the related art. is there. The distance between the sputtering target and the substrate is 10 mm to 150 m
m is preferable, and 20 mm to 100 mm is more preferable.
In the embodiment of the present invention, by setting the distance to about 60 mm, a good laminated structure was obtained. However, since the electric field distribution of the magnetic field differs depending on the device, the preferable distance between the sputtering target and the substrate is , It is preferable to determine the optimum distance.

The thickness of each layer to be formed is controlled by monitoring the deposition state using a quartz crystal film thickness meter or the like.
Easy to do. The formation of the recording layer or the like may be performed while the substrate is fixed, or may be moved or rotated.

After the formation of the reflective layer and the like, a UV-curable resin or the like may be provided as necessary to prevent scratches and deformation, as long as the effects of the present invention are not significantly impaired. After the formation of the reflection layer or the like, or after the formation of the above-mentioned resin protective layer, the two substrates may be bonded to each other with an adhesive.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Example 1 In a first sputtering chamber of a sputtering apparatus capable of simultaneously sputtering a plurality of sputtering targets, a target made of ZnS and SiO ₂ and a carbon target were placed 180 ° apart from the chamber, and the distance between each target and the substrate was set. Was set to be 60 mm.

When the pressure inside the chamber reaches 3 to 6e ^-5 pa, the disk substrate (120 mm DVD-R
The disk tray on which the AM standard, made of polycarbonate and having a thickness of 0.6 mm) was set was moved to a position facing the sputtering target in the first sputtering chamber, and the disk substrate was revolved at 10 rpm. Then A
r gas was introduced, and the pressure was set to 0.2 Pa. The electric power applied to each target was controlled, and ZnS was used as a first protective layer on the substrate by RF sputtering to form a 60 mol% ZnS,
One dielectric layer of 30 mol% of iO _{2 and} 10 mol% of carbon
00 nm was formed. The dielectric layer is made of ZnS and SiO ₂
And a layer made of carbon were alternately and innumerably laminated.

Next, the disk tray was moved to the second sputtering chamber, and a recording layer made of upper Ge ₁₉ Sb ₂₆ Te ₅₅ was formed on the first protective layer at an Ar gas pressure of 0.3 Pa to a thickness of 25 nm.

Next, the disk tray was moved to the third sputtering chamber, and ZnS was applied as a second protective layer on the recording layer in the same manner as in the first sputtering chamber.
A dielectric layer of 20 mol%, 30 mol% of SiO _{2 and} 10 mol% of carbon was formed to a thickness of 20 nm. The dielectric layer had a laminated structure in which layers composed of ZnS and SiO ₂ and layers composed of carbon were alternately laminated innumerably.

Further, the disk tray was moved to the fourth sputtering chamber, and a reflective layer made of Al was formed to a thickness of 80 nm at an Ar gas pressure of 0.3 Pa. Thus, the substrate / ZnS + SiO ₂ + carbon (laminated structure) / recording layer / Zn
An S + SiO ₂ + carbon (laminated structure) / reflection layer was formed, and a single-sided medium having an ultraviolet curable resin provided on the reflection layer at 5 μm was obtained. Further, a cationic UV-curable adhesive was provided thereon with a thickness of 30 μm, and two single-sided media were bonded together by a press such that the reflective layer side was opposed, thereby completing the optical recording medium of the present invention.

The measured byte error rate of the optical recording medium was 1 × e ^-4 . Further, after the optical recording medium was placed in a wet heat environment of 90 ° C. × 80%, a wet heat reliability evaluation for measuring a byte error rate was performed.
There was no change in the byte error rate from 0 hours to 1000 hours, and it was 1 × e ^-4 .

Comparative Example 1 An optical recording medium was obtained in the same manner as in Example 1 except that no carbon target was set in the first and third sputtering chamber chambers.

When the evaluation was performed in the same manner as in Example 1, the byte error rate immediately after the manufacture was 1 × e ⁻⁴ , but when it exceeded 300 hours in the wet heat reliability evaluation, the byte error rate was 1 × e ^−4. Degraded to ^-1 . Comparative Example 2 An optical recording medium was obtained in the same manner as in Example 1 except that the distance between the sputtering target and the substrate was set to 180 mm in the first and third sputtering chamber chambers. The first protective layer and the second protective layer are made of Zn
S, SiO ₂ and carbon were in a uniformly mixed layer.

When the evaluation was performed in the same manner as in Example 1, the byte error rate immediately after the manufacture was 1 × e ⁻⁴ , but it gradually deteriorated after 200 hours in the wet heat reliability evaluation. If exceeded, the byte error rate will be 1 ×
e- ¹ .

[0040]

According to the present invention, an optical recording medium having good long-term reliability can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/26 531 B41M 5/26 X

Claims (9)

[Claims] At least a first protective layer, a recording layer, a second protective layer, and a reflective layer are laminated in this order on a substrate, and information is recorded, erased, and reproduced by irradiating the recording layer with light. Wherein the recording and erasing of information is performed in a phase change between an amorphous phase and a crystalline phase, wherein the first protective layer or the second protective layer contains a chalcogen compound. An optical recording medium characterized in that the optical recording medium has a structure in which two or more layers each of which is made of carbon and carbon. 2. The optical recording according to claim 1, wherein both the first protective layer and the second protective layer have a structure in which two or more layers each of a layer containing a chalcogen compound and a layer made of carbon are laminated. Medium. 3. The optical recording medium according to claim 1, wherein the first protective layer and / or the second protective layer comprises a chalcogen compound and a metal oxide. 4. The optical recording medium according to claim 3, wherein the chalcogen compound is ZnS and the metal oxide is SiO ₂ . 5. A method for manufacturing an optical recording medium, comprising: laminating at least a first protective layer, a recording layer, a second protective layer, and a reflective layer on a substrate in this order by sputtering. Alternatively, in the step of sputtering the second protective layer, a substrate is attached to a rotatable substrate tray, a sputtering target containing a chalcogen compound and a sputtering target made of carbon are installed at different positions, and sputtering is performed while rotating the substrate tray. A method for manufacturing an optical recording medium. 6. The method according to claim 5, wherein the sputtering target containing the chalcogen compound comprises a chalcogen compound and a metal oxide. 7. The method according to claim 6, wherein the chalcogen compound is ZnS and the metal oxide is SiO ₂ . 8. The method according to claim 1, wherein each sputtering target is
6. The method for manufacturing an optical recording medium according to claim 5, wherein the optical recording medium is installed at a position separated from the rotation axis of the substrate tray by 90 degrees or more. 9. The method according to claim 5, wherein a distance between the sputtering target and the substrate is 10 mm to 150 mm.