JP2771601B2 - Optical recording medium and manufacturing method thereof - Google Patents

Description

The present invention relates to a novel optical recording medium, more specifically, a metal layer that reflects light having high reflectance and excellent chemical stability, The present invention relates to an optical recording medium having good contrast and sensitivity and excellent environmental resistance and a method for producing the same.

2. Description of the Related Art In recent years, an optical disc has been attracting attention as a central player of a recording medium in an advanced information society, and has been 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. The information is reproduced using the reflected light from.

Among the optical discs, the read-only type has the simplest structure, and the role of the medium is only to reflect light.
In a normal compact disk, aluminum which is high in productivity and inexpensive is used.

On the other hand, in the write-once type and rewritable type, a recording layer is provided on a substrate in order to record information, and the recording layer is formed by irradiating a laser beam to form a hole according to the information. A type and a phase transformation type in which information is recorded by changing optical characteristics by laser beam irradiation are known. In an optical disc of this type, the contrast and impression related to the reflectance between the portion recorded by the laser beam and the unrecorded portion are increased or the reflectance is adjusted for the purpose of adjusting the reflectance. It is common to provide a reflective layer, and aluminum is usually used as a material of the reflective layer for the same reason as described above.

However, although this aluminum has a high reflectance, it is susceptible to chemical changes such as oxidation, and its optical constant changes over time, which may degrade the performance as an optical recording medium. Furthermore, aluminum used in optical recording media is often a thin film formed by vapor deposition, sputtering, or the like, and tends to transition to a more bulky and stable state with time. Such a phenomenon is remarkable particularly in a high-temperature or high-humidity environment, and unless this problem is solved, the use of the optical recording medium is inevitably greatly restricted.

Problems to be Solved by the Invention According to the present invention, in the optical recording medium having the recording layer and the reflective layer provided on the substrate, the contrast and sensitivity are good, and the environment resistance is excellent, and the performance deteriorates with time. The purpose of the present invention is to provide an optical recording medium that does not have any problem.

Means for Solving the Problems The present inventors have conducted intensive studies to develop an optical recording medium having the above preferable properties, and as a result, as a reflective layer,
It has been found that the object can be achieved by using a metal layer that reflects light at a specific ratio of aluminum and oxygen, and the present invention has been completed based on this finding.

That is, the present invention provides an optical recording medium having a recording layer and a metal layer that reflects light on a substrate, wherein the metal layer is composed of aluminum and oxygen, and the content of oxygen in the metal layer is reduced to the atomic ratio. An optical recording medium characterized in that the content is 0.5 to 20% based on the above.

The optical recording medium of the present invention is obtained by mixing a light-reflecting metal layer provided on the optical recording medium by co-evaporation, co-sputtering, or reactive sputtering with 0.5 to 20% oxygen based on the atomic ratio of aluminum. It can be manufactured by forming.

In the optical recording medium of the present invention, a metal layer that reflects light is provided, and it is necessary to use a material made of aluminum and oxygen as the material of the metal layer.
The aluminum film immediately after the formation of the thin film is not necessarily in a stable crystalline state, but by mixing oxygen, aluminum oxide is formed at the crystal grain boundaries, the structure immediately after the formation of the thin film is fixed, and the structure of the aluminum becomes physical. It is presumed that it is changed.

The oxygen in the metal layer is preferably mixed by a co-evaporation method, a co-sputtering method, or a reactive sputtering method.

The oxygen content in the metal layer is based on the atomic ratio.
It is necessary to choose between 0.5 and 20%. If the content is less than 0.5%, the stabilizing effect is not sufficiently exhibited, and 2
If it exceeds 0%, a large amount of Al ₂ O ₃ is formed, and since Al ₂ O ₃ and aluminum metal have completely different optical constants, the original advantage of aluminum such as high reflectance is lost.

In addition, for the purpose of enhancing the chemical stability,
If desired, a metal element other than aluminum may be added. As the metal element added as desired, an element capable of forming a stable oxide by itself, for example, vanadium, chromium, cobalt, nickel, in the sense of preventing oxygen from penetrating into the crystal grains of aluminum, is used. ,
Examples include copper, zinc, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, and gold. One of these metal elements may be used alone, or two or more of them may be used in combination. The amount of the metal element is preferably selected in the range of 0.1 to 10% based on the atomic ratio. If the addition amount is less than 0.1%, the effect of addition is not sufficiently exhibited, and if it exceeds 10%, the optical constant of aluminum may greatly change, which is not preferable.

The physical stability of the metal layer is related to the grain size of the crystal. If the grain size of the crystal is too large, voids are generated between the crystal grains and cause structural change over time. If the particle size is too small, the amount of oxide required to stabilize the interface increases, and it becomes difficult to improve only the stability without changing the optical constant of aluminum. Therefore, the crystal grain size is desirably in the range of 5 to 50 nm.

FIG. 1 is a cross-sectional view showing each example of the optical recording medium of the present invention, which may be either a write-once type or a rewritable type. ) And (c). FIGS. 1 (b) and 1 (c) show a write-once type or a rewritable type. FIG. 1 (b) has a structure in which a recording layer 3 is provided on a substrate 1 and a metal layer 2 is further provided thereon. On the other hand, (c) has a structure in which the recording layer 3, the interference layer 4, and the metal layer 2 are sequentially laminated on the substrate 1. The optical recording medium of the present invention may have any of these structures.

There is no particular limitation on the recording layer in the above configuration,
For example, in the case of a write-once type, an aperture type or a phase change type may be used, or an organic dye may be used,
In the case of a rewritable type, a magneto-optical type or a phase change type may be used. Further, as the substrate material, for example, plastics such as acrylic resin, epoxy resin, polycarbonate resin and the like are used as well as glass.

The method for forming the metal layer is not particularly limited, and an oxide may be mixed into the metal by a method conventionally used for forming a reflective layer, for example, a co-evaporation method or a co-sputtering method, or a reactive sputtering method. Depending on the method, a small amount of oxygen may be mixed into the metal. When an additional element is added, a vapor deposition source for the additional element may be added or an alloy sputtering target of the additional element and aluminum may be used in the above method.

Although any of the above methods can be used for forming the metal layer, it is important to pay sufficient attention to the residual gas in the apparatus for forming the metal layer. Most of the residual gas is water. If the metal layer is formed in a state where the pressure is high, aluminum hydroxide may be formed in the thin film and a desired effect may not be obtained. Therefore, the residual gas pressure in the apparatus for forming the metal layer is 0.1 mPa or more, preferably 0.08 mPa
It is desirable to keep below. The thickness of the metal layer thus formed is usually selected in the range of 10 to 200 nm.

Further, in the optical recording medium of the present invention, if necessary, a protective layer may be provided on the substrate or on the uppermost layer in order to prevent oxidation and corrosion of the metal layer and the recording layer.

FIG. 2 is a cross-sectional view showing an example in which the protective layer 5 is provided on the substrate 1.

Effect of the Invention The optical recording medium of the present invention has a high reflectance, has good chemical stability, and is provided with a metal layer that reflects light having excellent environmental resistance, and has high contrast and sensitivity. It has excellent characteristics such as good performance and no performance degradation over time, especially in high-temperature environments.

Examples Next, the present invention will be described in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

Reference Example 1 A thin film having a thickness of 80 nm was formed on a clean polycarbonate substrate by DC magnetron sputtering using an Al target. At this time, as a sputtering gas, a mixed gas of argon and oxygen is used, and by changing this mixing ratio,
The amount of oxygen mixed into the aluminum was varied. FIG. 3 is a graph showing the relationship between the reflectance at a wavelength of 830 nm and the amount of mixed oxygen. From FIG. 3, it can be seen that when the amount of mixed oxygen exceeds 20% on the basis of the number of atoms, the reflectance sharply decreases.

Next, these were adhered to another polycarbonate substrate with a hot-melt adhesive and left in an accelerated test environment of 80 ° C. and 90% RH. FIG. 4 is a graph showing the relationship between the test time and the reflectance in this case. In this graph, the solid line A indicates the case where the oxygen amount is 0.5% (based on the number of atoms), the solid line B indicates the case where the oxygen amount is 20.0% (based on the number of atoms), and the broken line indicates the case where oxygen is not mixed.

From FIG. 4, it has been clarified that the stability can be improved while maintaining the high reflectance of aluminum by setting the proportion of the mixed oxygen amount to 0.5 to 20% based on the number of atoms.

Reference Example 2 A thin film having a thickness of 5 nm was formed on a glass substrate by RF magnetron sputtering using an Al ₉₇ Cr ₃ target.
At this time, a mixed gas of argon and oxygen was used as a sputtering gas, and the mixing ratio was adjusted so that the mixed amount of oxygen was 2% based on the number of atoms. Also, for comparison,
Aluminum thin films of the same thickness were formed on the same substrate.

Next, these were left in an accelerated test environment of 80 ° C. and 90% RH, and the transmittance change at a wavelength of 830 nm was measured, and the results are shown in the graph of FIG. In FIG. 5, the solid line is the case of the reference example, and the broken line is the case of the comparative example.

As can be seen from FIG. 5, the transmittance is increased in the comparative example, whereas no change is observed in the reference example even after 400 hours. In addition, when observed with an optical microscope, pinholes presumed to be caused by corrosion or structural change of aluminum occurred in the comparative example.

From these results, it can be seen that by mixing oxygen, the physical and chemical stability of the thin film is improved.

Example In the structure shown in FIG. 2, a SiN thin film (protective layer) 5 and Tb ₂₀ Fe were formed on a polycarbonate substrate 1 on which a guide groove was formed.
₇₀ Co ₁₀ alloy thin film (recording layer) 3 and SiN thin film (interference layer) 4
Are sequentially formed so as to have a thickness of 90 nm, 25 nm and 30 nm, respectively, and a 50 nm-thick metal layer 2 is formed on the uppermost layer by RF magnetron sputtering using an Al ₉₇ Cr ₃ target.
Was formed. At this time, a mixed gas of argon and oxygen was used as a sputtering gas, and the mixture ratio was adjusted so that the oxygen content in the metal layer was 5% based on the number of atoms.

The two magneto-optical disks were bonded to each other with a hot-melt adhesive to form a double-sided disk, and then left in a test environment of 80 ° C. and 90% RH. The bit error rate (BE
The change in R) is shown by a solid line graph in FIG.

For comparison, the same procedure was performed except that the metal layer was formed of aluminum containing no oxygen. The change of the BER at this time is shown by a broken line graph in FIG.

FIG. 6 shows that the BER increases in the comparative example, but does not increase even after 400 hours have elapsed in the example. In the comparative example, the cause of the increase in BER is
It is presumed to be due to the pinhole observed in Reference Example 2.

[Brief description of the drawings]

1 and 2 are cross-sectional views showing different examples of the optical recording medium of the present invention. FIG. 3 is a graph showing the relationship between the reflectance of the recording medium of Reference Example 1 and the amount of mixed oxygen. 5 is a graph showing the environmental resistance of the recording medium of the reference example, and FIG. 6 is a graph showing the relationship between the BER and the test time of the recording medium of the example. In the figure, reference numeral 1 denotes a substrate, 2 denotes a metal layer, 3 denotes a recording layer, 4 denotes an interference layer, and 5 denotes a protective layer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 7/24 C23C 14/00-14/58

Claims (3)

(57) [Claims] 1. An optical recording medium having a recording layer and a metal layer for reflecting light on a substrate, wherein the metal layer is composed of aluminum and oxygen, and the content of oxygen in the metal layer is based on the atomic ratio. An optical recording medium having a content of 0.5 to 20%. 2. A light reflecting metal layer is formed by mixing 0.5 to 20% of oxygen based on the atomic ratio into aluminum by co-evaporation, co-sputtering or reactive sputtering. Item 7. A method for producing an optical recording medium according to Item 1. 3. The method for manufacturing an optical recording medium according to claim 2, wherein the residual gas pressure in the apparatus for forming the light reflecting metal layer is maintained at 0.1 mPa or less.