JP2000228032A - Optical information medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical information recording medium having high performance and excellent in aging stability by forming a metallic reflecting layer with an Ag alloy obtained by incorporating a specified amount of Cu into Ag and then disposing a sulfur-free organic or inorganic protective layer or an adhesive layer on the metallic reflecting layer. SOLUTION: The optical information medium, which is not a magneto-optical recording medium, has a metallic reflecting layer comprising an Ag alloy obtained by incorporating 0.5-30 at.% Cu into Ag and has an organic or inorganic protective layer not substantially containing elemental sulfur or an adhesive layer on the metallic reflecting layer. When the reflecting layer comprises an Ag alloy obtained by incorporating 0.5-30 at.% Cu and 0.5-12 at.% at least one of Ta and Ti into Ag, considerably enhanced recording sensitivity and corrosion resistance are ensured. The metallic reflecting layer is preferably applied to a phase change type optical recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information medium having a metal reflective layer for reproducing, recording, and erasing information with light from a laser or the like. In particular, regarding a disk-shaped medium, more specifically, a reversible structural change (phase change) between an amorphous state and a crystalline state of a substance caused by irradiation of a focused laser beam is used for recording and erasing information. And a phase change type optical recording medium. Furthermore, the present invention relates to a film-surface incident type optical information medium, which has been researched and developed in recent years.

[0002]

2. Description of the Related Art Various optical information media (optical disks) have been put to practical use. CD (compact disc) and CD-ROM discs are well-known as read-only types, CD-R discs can be written only once, and magneto-optical discs and phase-change recording discs are recordable / erasable types. is there. As phase change disks, CD-RW disks, PD disks, and DVD-RAM disks are commercially available. In particular, in recent years, phase-change optical recording media have attracted attention as large-capacity rewritable media such as DVD-RWs, and have become the most important media as large-capacity moving-image recording media in place of future video tapes.

A phase-change optical recording medium has a reversible structural change between an amorphous state and a crystalline state of a recording layer induced by a difference in heat history of heating and cooling by light irradiation (laser light irradiation). (Phase change) is used for recording / erasing information.
That is, the recording layer is heated and melted and rapidly cooled to make the recording layer amorphous, thereby performing the recording. Further, the recording layer is kept at a temperature higher than the crystallization temperature for a certain time to be crystallized and erased. The temperature of the recording layer (typical GeSbTe film) is about 600 ° C. during recording.
It is estimated that the temperature will be about 170 ° C. at the time of erasing.
Reproduction of a signal is performed using a difference in reflectance between an amorphous state and a crystalline state. Such a phase-change optical recording medium has a large recording capacity in addition to a high-speed information processing capability. In addition, since the structure of the drive (such as an optical head) is simpler than that of a magneto-optical recording drive, there is an advantage that the cost can be reduced. In such a phase-change optical recording medium, usually, the crystal state of the recording film is set to an erasing state of information, and the film is melted by high laser power.
An amorphous state (amorphous mark) generated by rapid cooling is defined as a recording state.

Technical report of the Institute of Electronics, Information and Communication Engineers [Electronic parts and materials] CPM90-35, pp43-48
The "rapid cooling structure phase change optical information medium using a ZnS-SiO ₂ dielectric" (July 27, 1990) has the structure of a typical phase-change disk which is practically the current is shown. Its structure is a polycarbonate substrate (usually 0.6
mm or 1.2 mm thickness) / Lower dielectric layer (ZnS · S
iO ₂ film) / recording layer (GeSbTe film) / the upper dielectric layer (ZnS · SiO ₂ film) / reflective layer (Al alloy) / adhesive layer is.

[0005] It is a common idea to reverse the stacking order of thin films from a substrate in a film-incidence type medium, which has been studied, with respect to these current commercially available normal media.
That is, research has been conducted on the configuration of a substrate / reflective film / lower dielectric / recording film / upper dielectric. As an optical head (pickup) to be used, a structure similar to a hard disk has been proposed because an objective lens needs to be brought close to a medium surface. That is, utilization of a flying head having an objective lens mounted on a slider is being studied.

As can be seen from the above-mentioned literature, a chalcogen alloy such as GeSbTe or AgInSbTe is used for a recording layer of a phase change type optical recording medium. Zn for the dielectric film
A ZnS-based film such as S.SiO ₂ is used. As the reflective layer, an Al alloy film, an Au film, an Ag film, or the like has been practically used.
For Al alloys, AlTi containing several percent of Ti or Cr
Films and AlCr films are frequently used. In a medium (such as a CD-R disc) having an organic dye as a recording layer, an Au film or an Ag film is used as a reflective layer. In a read-only CD (compact disk), an Al film is generally used.

[0007]

The above-mentioned practically used Al alloy film, Au film and Ag film have the following problems. A
The alloy film is formed by a sputtering method using a target made of the alloy. However, the alloy target must be made of an alloy of two kinds of metals having greatly different melting points. Due to the low yield, there are disadvantages such as a low film deposition rate of sputtering and a relatively low reflectance (reflectance of the film alone) of 80 to 85%. The Ag film has a reflectance of nearly 100%, but has a disadvantage that corrosion resistance is not good. Au films are stable but very expensive. That is, at present, the search for a reflective layer that simultaneously satisfies all of performance, price, production speed, and the like is continued.

The present inventors have previously described AgCuTi alloy, A
A reflective layer of gCuTa alloy was proposed. At that time, the alloy film was applied to a magneto-optical recording medium and achieved a certain result. However, there were cases where there was a problem in applying the alloy film to a medium other than the magneto-optical recording medium, and a satisfactory result was not obtained. In particular, in a phase-change optical recording medium, a ZnS.SiO ₂ film is used as a dielectric layer. When the dielectric film is formed on the reflective layer of an Ag-based alloy by sputtering, Ag is sulfurized and the reflectance is reduced. There was a problem to do.

The present invention has been made in view of the above-mentioned circumstances. By specifying a reflective layer having high reflectivity, excellent corrosion resistance and good productivity, and a protective layer thereon, a high-performance and inexpensive optical information can be obtained. It is an object of the present invention to provide a medium, particularly a phase change type optical recording medium.

[0010]

Means for Solving the Problems As described above, the present inventors have intensively studied the improvement of the metal reflection layer which simultaneously satisfies all of the performance, price, production speed, and the like, and as a result, the metal reflection layer was made of AgCu alloy. By forming an organic or inorganic protective layer or an adhesive layer containing no S (sulfur) on the metal reflective layer, the optical information has high performance, is inexpensive, has excellent productivity, and has excellent stability over time. It has been found that a medium can be obtained.

That is, according to the present invention, in an optical information medium other than a magneto-optical recording medium having a metal reflection layer, the metal reflection layer contains Ag (silver) containing 0.5 to 30 atomic% of Cu (copper). An optical information medium comprising an Ag alloy and having an organic or inorganic protective layer or an adhesive layer substantially free of S element formed on the metal reflective layer. Further, the present invention provides a reflective layer comprising an Ag alloy containing 0.5 to 30 atomic% of Cu in Ag and further containing 0.5 to 12 atomic% of at least one of Ta (tantalum) and Ti (titanium). Optical information medium. Further, the metal reflection layer of the present invention is preferably applied to a phase change type optical recording medium.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have focused on an Ag film having a high reflectance for the purpose of improving the reproduction signal noise ratio (C / N).
Ag is a material having poor corrosion resistance, and is not practical with only an Ag film. Therefore, when the addition of another metal was examined as an improvement, Cu formed on the slide glass was reduced by 0.5%.
The AgCu alloy film doped with ３０30 atomic% has a high reflectivity, and 80 ° C.8 which is a standard accelerated deterioration test condition of an optical information medium.
It was found that the reflectance did not decrease even when left in an atmosphere of 5% relative humidity for 72 hours or more, and that the sample had durability. Note that Cu
Even if the content of is less than 0.5 atomic% or more than 30 atomic%, the reflectance dropped to 90% or less of the initial value within 24 hours. As described above, the AgCu alloy film has a high reflectance (for example, Ag ₈₅ Cu ₁₅ (subscript is an atomic% composition) alloy film of 780 n).
(reflectance of 98% at a wavelength of m), and the durability is not bad.
However, it has been further found that the AgCu film has a high thermal conductivity, so that the recording sensitivity is reduced in a phase-change optical recording medium using the AgCu film as a reflection film.

The present inventors have further improved this point in the third.
Focusing on the addition of elements, as a result of intensive research, the AgCu film
It has been found that when at least one of a and Ti is added in an amount of 0.5 to 12 atomic%, recording sensitivity and corrosion resistance are greatly improved. If the content of Ta or Ti is less than this range, there is no effect of improving the recording sensitivity, and if the content is too large, the reflection is reduced and the C / N is deteriorated. Further, in the phase-change optical recording medium, the contents of Ta and Ti are set to 1.5 because the effect of improving sensitivity is large and the effect of improving C / N is not impaired.
-10 at% is more preferred. In order to further improve the stability over time, other elements such as Cr, Nb, and Re may be added in small amounts.

The thickness of the metal reflective layer is preferably 3 to 200 nm. In a phase-change optical recording medium, when the medium configuration (recording film configuration) is used as the medium configuration (recording film configuration), the absorbance correction configuration that makes the light absorption rate when the recording layer is in a crystalline state larger than the light absorption rate when the recording layer is in an amorphous state A reflective layer is used.

In the present invention, it is necessary to form an organic or inorganic protective layer or an adhesive layer substantially containing no S element on the Ag alloy reflecting layer. As described above, the AgCu alloy exhibited sufficient durability in an oxidizing atmosphere such as an atmosphere at 80 ° C. and 85% relative humidity, but easily blackened in an atmosphere containing an S element (H ₂ S gas atmosphere, etc.). It has become.
In order to prevent this, it is necessary to form an organic or inorganic protective layer or an adhesive layer. As the organic protective layer, an ultraviolet curable acrylic resin or the like is used.

When two sheets of a medium having a thickness of 0.6 mm are bonded to each other to form a double-sided medium, an adhesive sheet, a hot melt adhesive, or an ultraviolet curable adhesive is used. As a protective layer of the inorganic thin film not containing the S element, a nitride film such as SiN or GeN is preferable. ZnS · SiO ₂ film which are widely used in phase-change optical recording medium is not formed on the reflective layer of the AgCu system to form a reflective layer of AgCu alloy ZnS · SiO ₂ film on the opposite It is possible.

As a method for forming the metal reflection layer, known vacuum evaporation, sputtering, ion beam sputtering, CVD, etc., can be considered. Adhesion with the underlayer, controllability of alloy composition, composition distribution, etc. For example, a sputtering method is preferable. Film forming conditions such as a film deposition rate and a sputtering gas pressure are appropriately selected in consideration of productivity and film stress.

When the optical information medium of the present invention is a phase-change optical recording medium, the recording layer is made of a chalcogen alloy such as GeSbTe or AgInSbTe. In particular, a Ge ₂ Sb ₂ Te ₅ (Ge: Sb: Te = about 22.2: 22.2: 55.6 at%) thin film having a composition ratio of about 2: 2: 5 has a high repetitive overwrite performance, and Since high-speed erasing is possible, it is preferably used in the present invention.

The dielectric layer used in the phase-change type optical recording medium is required to exhibit effects such as a heat insulating effect and an optical interference effect according to the purpose, and preferably has a certain degree of hardness and a high refractive index. . Further, it is necessary that the transparent dielectric layer is transparent to the laser beam to be used. As the transparent dielectric layer, metal oxides, nitrides, sulfides, carbides, fluorides or composites thereof can be applied as is well known. Specifically, silicon oxide, titanium oxide, indium oxide, tantalum oxide, aluminum oxide, silicon nitride, germanium nitride, tantalum nitride, aluminum nitride, titanium nitride, zinc sulfide, magnesium fluoride, aluminum fluoride, Needless to say, it includes, but is not limited to, silicon carbide and composites thereof. The optimum thickness of these transparent dielectric layers varies depending on the medium configuration and the refractive index, and cannot be determined uniquely.
A thickness of about nm to 150 nm is preferably used. These transparent electric layers are formed by the same method as that for forming the metal reflection layer due to the continuity of production.

As the substrate, glass, acrylic resin, polycarbonate resin, epoxy resin, polyolefin resin, and their modified products are preferably used.
Polycarbonate resins are preferred in terms of mechanical strength, price, weather resistance, heat resistance, and moisture permeability. As the substrate used for the phase-change type optical recording medium, a polycarbonate disk having a thickness of about 0.6 mm to 2.0 mm and a diameter of about 60 mm to 120 mm produced by injection molding is preferably used.

The structure of the phase-change type optical recording medium mainly described above is as follows: substrate / lower dielectric layer / recording layer / upper dielectric layer / reflective layer (AgCu alloy) / organic or inorganic protective layer or adhesive It is a structure called a layer. On the other hand, a phase change type optical recording medium of the film surface incidence type has a basic structure of a reflective layer / lower dielectric layer / recording layer / upper dielectric layer on one or both surfaces of a plastic substrate in order from the substrate surface. Has,
Recording and reproduction are performed from the thin film laminate side without passing through the substrate. An adhesive layer may be provided between the substrate and the reflective layer, or a heat insulating layer for preventing the adverse effect of heat on a plastic substrate whose substrate has a low heat-resistant temperature. Such a film-surface incident type phase change optical recording medium is expected to have a remarkably excellent recording capacity, so that the reflective layer is also required to have excellent properties such as high reflectance, thermal conductivity, and durability. The metal reflection layer of the present invention is more preferably applied. In this film surface incident type phase change optical recording medium, the protective layer on the AgCu alloy reflective layer is a layer corresponding to the lower dielectric layer. Therefore, the lower dielectric layer must not (substantially) contain the S element above the impurity level. Such a lower dielectric layer is preferably the aforementioned nitride.

The metal reflective layer of the AgCu alloy of the present invention can be used not only in a phase-change optical recording medium but also in all optical information media having a metal reflective layer (excluding magneto-optical recording media).
A CD-R disc manufactured by applying a light-absorbing organic dye such as a cyanine dye on a polycarbonate substrate, forming a metal reflective film on the dye film, and further coating a protective layer on the metal reflective film. Also, the present invention can be applied to a metal reflection layer of a DVD-R disc. Further, it can be used as a reflection layer of a read-only disk such as a CD. The AgCu alloy is more expensive than the Al alloy, but has the same performance even if it is thin because of its high reflectivity. Can be made cheaper than the Al alloy film.

[0023]

Examples 1 to 5, Comparative Examples 1 and 2 1.2 mm thick, 12
On one surface of a polycarbonate optical disc plastic substrate having a center hole with a diameter of 0 mm and an inner diameter of 15 mm, 95 nm ZnS.SiO ₂
Lower dielectric layer, 20 nm GeSbTe recording layer, 16 n
m ZnS.SiO ₂ upper dielectric layer, 150 nm Ag
Phase-change optical recording media (Examples 1 to 5) having a configuration including a CuTi reflection layer and an ultraviolet-curable organic resin protective layer were produced. Examples 1 to 5 used AgCuT as described in Table 1.
This is a medium in which the Ti content of the i-reflection film is changed. The medium of Comparative Example 1 has the same configuration, except that only the reflective layer is an Ag film.
The medium of Comparative Example 2 had the same configuration but only the reflective layer was made of AlTi.
It is a medium that is a film. A spiral groove (groove) for continuous servo has a radius of 24 mm to 58 m on the substrate by injection molding.
m. The groove depth is 80 nm,
The track pitch is 1.20 μm, and both the groove width and the land width are about 0.60 μm.

The sputtering apparatus used was a high-frequency magnetron sputtering apparatus (SPF manufactured by Anelva Co., Ltd.) in which the substrate holder was modified so that an optical disk substrate could be mounted.
-430H type). In this apparatus, three targets are set in one vacuum chamber, and three types of films can be formed continuously. The target used was 101 mm in diameter and 5 m in thickness
m: ZnS and SiO ₂ are 80:20 mo
ZnS.SiO ₂ target mixed and sintered at a ratio of 1%, Ge: Sb: Te = GeSb having an atomic ratio of about 2: 2: 5
A Te alloy target, an AgCu (Cu: 10 atomic%) alloy target, and an AlTi (Ti: 2.0 atomic%) alloy target. When producing AgCuTi film, use AgC
A 1 mm thick, 5 mm square Ti metal tip was placed on the u target and sputtered. The number of Ti chips and the arrangement on the target were adjusted so that the Ti content shown in Table 1 was obtained. The distance between the target and the substrate is about 120 mm,
Sputter deposition was performed while the substrate was rotated (rotated) at 20 rpm about a position about 100 mm away from the center of the target as the center of rotation.

The substrate is placed in a vacuum chamber of this apparatus,
Evacuation was performed until the pressure reached 10 ⁻⁵ Pa, and then Ar gas was introduced into the vacuum chamber at a flow rate of 75 SCCM, and the orifice on the main valve was adjusted to a pressure of 0.8 Pa. Input power is Z
High frequency power of 500 Watt during sputtering of nS.SiO ₂ sintered body, 50 W under sputtering of GeSbTe target
att DC power was used. 200 Watt DC power was used for AgCu target sputtering, and 400 Watt DC power was used for AlTi target sputtering. The deposition rate of each film was 2 for ZnS.SiO ₂ film.
3.3 nm / min. , AlTi film is 10.2 nm / m
in. , AgCu film and AgCuTi film are 17.3 nm /
min. And a GeSbTe film of 20.5 nm / mi
n. Met. The deposition rate of the AgCuTi film of the present invention is:
The electric power was half and the deposition rate was 1.7 times that of an Al alloy film such as an AlTi film which is frequently used at present. When compared at the same power, the deposition rate was 3.4 times higher, and the productivity was found to be extremely good.

Further, an ultraviolet-curable phenol novolak epoxy acrylate resin containing no S (sulfur element) is applied on the AlCr reflective layer by a spin coater, and cured by irradiation with ultraviolet light to form an organic protective layer of about 11 μm. A changeable optical recording medium was used.

The initialization apparatus used for the initialization (annealing crystallization) is a bulk eraser apparatus (LK, manufactured by Shibasoku Co., Ltd.).
101A type). However, the optical head used had a maximum laser beam intensity of about 1 watt on the disk surface, a wavelength of 810 nm, and an NA (objective lens numerical aperture) of 0.3.
4. Spot size = 125 μm (long axis length) × 1.2
7 μm (short axis length) was used with the beam major axis inclined at 30 ° from the disk radial direction. Initialization is
While rotating the disk at a constant linear velocity of 5 m / sec,
While feeding the optical head at a feed speed of 86 μm / rotation (the speed at which the optical head advances 86 μm in the radial direction during one rotation of the disk), the laser power is increased to 65% of the maximum value (ie, about 65%).
0 mW).

The electrical characteristics of the medium were evaluated at a wavelength of 780 nm.
The measurement was performed using a DDU-1000 type electrical characteristic evaluation device manufactured by Pulstec Industrial Co., Ltd. having an optical head having a numerical aperture NA = 0.55 of the objective lens. Disk rotation speed 2030
rpm, radius of 26 mm, writing frequency 4 MHz,
Recording was performed at a single frequency with a pulse width of 62 nsec with a constant bias power of 4.5 mWatt and a variable recording peak power, and a signal reproduced at a reproduction power of 1 mWatt was measured for CNR (signal noise ratio) with a spectrum analyzer. In the rising curve of CNR when the recording peak power was sequentially increased, CNR = 30 dB
The recording peak power at the time of was set as the evaluation value of the recording sensitivity. When the recording sensitivity is too high (recording is performed with too low power), the durability of repeated overwriting is deteriorated, and when the sensitivity is low, excessive power is required and the load on the drive increases. The recording sensitivity is preferably about 8 to 12 mWatt. The larger the value of CNR, the better. Table 1 shows the evaluation results.

From the above examples, it was found that the recording sensitivity was too low with the Ag-only reflective film, and that the CNR was not sufficient with the AlTi reflective film.
Turned out to be low. In addition, these samples
When an accelerated deterioration test was performed for 1000 hours under the conditions of a temperature of 80 ° C. and a humidity of 85%, 30 or more pinholes were generated only in Comparative Example 1, but no change was observed in other samples.

Further, the same sample was prepared again up to the point where the reflective layer was formed by sputtering, and this time (without coating the organic protective layer), a ZnS.SiO ₂ film was formed on the reflective layer by 20 nm by sputtering. However, although the medium of the AlTi reflective layer showed the same performance as the above, other Ag reflective layers and A
The discoloration of the surface of the medium of the gCuTi reflection layer was already observed immediately after the sputtering of ZnS.SiO ₂ , and it was presumed that silver sulfide was generated. In addition, the CNR also deteriorated to about 46 dB. Furthermore, instead of ZnS · SiO ₂ on the reflective layer,
When a GeN (germanium nitride) film was formed by sputtering, no change was observed in any of the samples, and the characteristics were satisfactory.

[0031]

Examples 6 to 8 The same as Examples 1 to 5 except that a Ta chip was placed on an AgCu target instead of Ti and the metal reflective layer was made of an AgCuTa alloy shown in Table 2. Produce a phase change optical disk with the configuration
Evaluation was performed in the same manner. Table 2 shows the results.

From this example, it can be seen that the AgCuTa
The same effect as the CuTi film was confirmed. Further, when the samples (Examples 6, 7, and 8) coated with an organic protective layer were subjected to an accelerated deterioration test for 1000 hours at a temperature of 80 ° C. and a humidity of 85%, no change was observed in all the samples. Good environmental durability.

As shown in the above embodiments, the Cu
Containing Ag and at least one of Ta and Ti
With a phase change optical recording medium having a metal reflective film made of an alloy, an optical information medium having excellent CNR and sensitivity and high durability can be obtained. In particular, when the content of Ta and Ti is 1.5
In the range of at least atomic%, the reduction of the optimum recording laser power, that is, the improvement of the recording sensitivity is remarkable, and the CNR is much better than the well-known phase change type optical disk using, for example, an AlTi alloy film as a reflection film. T in terms of such effects
The content of a and Ti is particularly preferably 1.5 to 10 atomic%.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

As described above, according to the optical information medium of the present invention, A
gCu alloy, AgCuTi alloy, or AgCuTa
By employing an alloy as the reflective layer, it has become possible to manufacture a medium that is inexpensive, has good performance, and has excellent environmental resistance with good productivity.

Claims (5)

[Claims] In an optical information medium excluding a magneto-optical recording medium having a metal reflection layer, the metal reflection layer is formed by adding Ag to Cu in an amount of 0.1 to 0.1%.
An optical information medium comprising an Ag alloy containing 5 to 30 atomic% and a protective layer or an adhesive layer substantially free of S (sulfur) element formed on the metal reflective layer. 2. The method according to claim 1, wherein the metal reflection layer is formed by adding 0.5 to 30 Cu to Ag.
2. The optical information medium according to claim 1, wherein the optical information medium is made of an Ag alloy containing at least one of Ta and Ti in an amount of 0.5 to 12 at%. 3. The optical information medium according to claim 2, wherein the optical information medium is a phase change type optical recording medium. 4. An optical information medium having a structure in which at least one recording layer is formed on a substrate, and reads (reproduces) information and / or writes (records) information by using a laser beam.
The optical information medium according to any one of claims 1 to 3, wherein the optical information medium is of a film surface incident type in which the light is incident from the recording layer side without passing through the substrate. 5. The recording layer of an optical information medium is made of Ge, Sb, Te.
The optical information medium according to any one of claims 3 to 4, wherein the optical information medium has a thickness of 10 to 40 nm.