JP2002319185A - Silver alloy for optical recording disk reflective film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silver alloy for a reflection film which has high thermal conductivity and can secure high data reliability and is suitable for an optical recording disk corresponding to a high recording density. . SOLUTION: The silver alloy for the reflection film has Ag as a main component,
Cr, Zr, La, Ce, Eu, Ca, Sr, Ba, R
It contains 0.001 to 0.1% by weight of at least one first additive element selected from u, Ni, and W. This silver alloy for a reflective film contains Zn, Mg,
At least one second additive element selected from Au and Pd can be contained in an amount of 0.1 to 5% by weight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silver alloy used as a reflection film of various optical recording disks.

[0002]

2. Description of the Related Art As a medium for recording computer information, video information or music information, a CD, a CD-R, a CD-R,
RW, DVD, DVD-RW, DVD-RAM, MO
Various types of optical recording disks (hereinafter, referred to as optical disks) such as D and MD are used.

[0003] These optical discs have different structures depending on the system, but all have a substrate made of a transparent plastic disk such as polycarbonate, on which thin films having various functions such as a reflective film and a protective film are formed in layers. Have been.

The reflective film of such an optical disc has a function of reflecting laser light used for reading and writing of recording and a function of releasing heat caused by the laser light, and is used for any type of optical disc. ing. As the material of the reflection film, Al, Au, Ag, or an alloy thereof is mainly used.

[0005] These reflective films are made of Al, Au, A
It is formed by a normal sputtering method or the like using a target made of g or an alloy thereof.

[0006]

In recent years, as the recording density of optical discs has increased, the demand for reflective films having high thermal conductivity has increased. However, it has been clarified that the required characteristics of the Al reflective film cannot be satisfied due to the low thermal conductivity. In addition, although the reflective film of Au has a possibility of satisfying the required characteristics relating to high thermal conductivity, it is difficult to use it on a commercially available optical disk because of its extremely high price.

[0007] On the other hand, although the Ag reflective film satisfies the thermal conductivity, the characteristics are greatly deteriorated due to data rewriting and storage in a high-temperature and high-humidity environment, and it is difficult to secure the reliability of the data. Have a point. For this reason, a reflective film that completely satisfies the required characteristics of thermal conductivity while ensuring data reliability has not been obtained.

In view of the above circumstances, the present invention provides a silver alloy for a reflective film, which has high thermal conductivity at the same time while ensuring high data reliability, and is suitable for an optical disk corresponding to a high recording density. The purpose is to do.

[0009]

In order to achieve the above-mentioned object, a silver alloy for a reflective film of an optical recording disk provided by the present invention contains Ag as a main component, and contains Cr, Zr, La, Ce, and E.
at least one additive element selected from the group consisting of u, Ca, Sr, Ba, Ru, Ni, and W is 0.001 to 0.1.
% By weight, with the balance being unavoidable impurities.

Further, in the silver alloy for an optical recording disk reflective film of the present invention, in addition to the above-mentioned additional elements, Zn,
At least one selected from the group consisting of Mg, Au, and Pd
The seed second additive element may comprise 0.1-5% by weight.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present inventors have studied various reasons why a conventional reflective film of an optical disk made of pure Ag is inferior in data reliability. As a result, the main cause is that crystal grains are coarsened or the film is corroded. It was confirmed that alloying by adding various elements was effective as a countermeasure.

That is, in the silver alloy for a reflective film of the optical disk of the present invention, Cr, Zr,
La, Ce, Eu, Ca, Sr, Ba, Ru, Ni, W
At least one additive element selected from
It contains 0.1% by weight. These additional elements serve to suppress the coarsening of the crystal grains in the reflective film by improving the heat resistance of the silver alloy, and at the same time, to stably obtain a high reflectance by making the crystal grains finer. . In addition, by including these additional elements, the crystal grain size of the target is also reduced, and an effect of making the sputtering rate uniform can be obtained.

The total amount of these elements added is 0.001.
If the content is less than 0.001% by weight, the concentration is too low to obtain a sufficient effect of addition, and if it exceeds 0.1% by weight, the corrosion resistance of the alloy is reduced, and This is because the characteristics of the disk are degraded due to the above factors. Desirable characteristics can be achieved even when two or more of these additional elements are added in combination. However, in general, it is more effective to add one of these elements alone. growing.

In a second embodiment of the silver alloy for a reflective film of the optical disk of the present invention, in addition to the first additive element, at least one selected from the group consisting of Zn, Mg, Au and Pd is provided. 0.1 to 5% by weight of the second additive element
Can be included. These second additive elements have an effect of improving corrosion resistance, and are particularly effective in the case of an optical disc having a protective film containing ZnS.

The amount of the second additive element is 0.1 to 0.1.
If the content is less than 0.1% by weight, the concentration is too low and the effect of improving the corrosion resistance is not sufficient. On the other hand, if it exceeds 5% by weight, the thermal conductivity of the alloy decreases, and the high recording capacity of the optical disc is increased. This is because it becomes impossible to cope with the density increase.

In the present invention, the composition of the Ag alloy constituting the reflection film is specified, and the composition of the sputtering target used for forming the reflection film can be similarly specified.

The reflection film of the present invention is not only for an optical disk, but also for a reflection mirror which is required to have corrosion resistance and high reflectance, a reflection film for a lighting fixture, a reflection film for a sign, and a reflector. Applications such as reflective films for LCDs, or reflective films such as liquid crystal displays (LCD), plasma displays (PDP), and electroluminescence (EL) displays, for which heat dissipation is important. The present invention can also be applied to various wiring materials that need to be small.

[0018]

EXAMPLES Ag, Cr, Zr, La, Ce, Eu, Ca, S having a purity of 99.9-99.999% as raw materials.
Using lump or powder of r, Ba, Ru, Ni, W, Zn, Mg, Au, and Pd, a target of each sample is prepared by a melting casting method using a vacuum melting furnace or a powder metallurgy method using a hot press. did. Table 1 below shows the composition of the target in each of the obtained samples.

[0019]

[Table 1]

Using each of these targets, a thin film for evaluation of characteristics having a thickness of 3000 mm was formed on a glass substrate by magnetron sputtering. It was confirmed by chemical analysis that the composition of the formed thin film was almost the same as the target composition used.

The reflectance, thermal conductivity, and crystal grain stability were evaluated using the obtained thin film. That is, regarding the thermal conductivity, it was difficult to directly measure the thermal conductivity of the thin film.
It was determined by calculation using the mann-Franz rule, and the results are shown in Table 2 below. The reflectance was measured using a spectrophotometer at wavelengths of 400, 650, and 780 nm.
, And the results are shown in Table 3.

[0022]

[Table 2]

[0023]

[Table 3]

Further, as an index indicating the difficulty of crystal grain coarsening, the change in crystal grain size before and after heat treatment at 150 ° C. for 48 hours in a high vacuum was examined. Table 4 below shows the results obtained by evaluating the crystal grain size before and after the heat treatment from the half-width of the X-ray diffraction peak and the results of evaluation by the surface roughness (center line surface roughness Ra) measured by an atomic force microscope. The results are shown in Table 5 below. In the case of Table 5, it is considered that the larger the surface roughness, the larger the crystal grain size.

[0025]

[Table 4]

[0026]

[Table 5]

From the above results, by using the silver alloy of the present invention, it is possible to obtain a reflective film having a high reflectivity and a high thermal conductivity, and hardly causing the crystal grains to become coarse even when subjected to heat. It is understood that it can be done.

Next, disk characteristics when the reflective film of the present invention was used for an optical disk were evaluated. That is, as the substrate 1, a CD substrate having a thickness of 1.2 mm, a diameter of 120 mm, a groove (track) pitch of 1.6 μm, and a groove depth of 50 nm;
Thickness 0.6mm, diameter 120mm, groove pitch 0.8
Two types of polycarbonate substrates, a DVD substrate having a thickness of 35 μm and a groove depth of 35 nm, were used.

The evaluation disk for CD is formed by sputtering a lower protective film, a recording film, an upper protective film,
After sequentially forming a diffusion prevention film and a reflection film, an overcoat layer of an ultraviolet curable resin was formed to a thickness of 5 μm. Similarly, on the DVD evaluation disk, a lower protective film, a recording film, an upper protective film, a diffusion prevention film, a reflective film, and an overcoat layer having a thickness of 4 μm are sequentially formed on the substrate 2 and then formed thereon. 0.6mm thick, 120mm diameter
Was produced by laminating a polycarbonate substrate of the above with an ultraviolet curing resin. Table 6 below shows the sputtering conditions used for film formation together with the materials of the above-mentioned respective films, Table 7 below showing the structure of each disk sample produced, and Table 8 below showing the thickness of each film.

[0030]

[Table 6]

[0031]

[Table 7]

[0032]

[Table 8]

As evaluation of each disk obtained as described above, a carrier-to-noise ratio (CNR), a jitter and a modulation were measured. In the case of a CD evaluation disc, the wavelength is 780.
laser light of 1 nm through a lens of NA 0.55
The measurement was performed by irradiating with a spot diameter of m. The linear velocities were set at three levels of 2.0, 5.0 and 10.0 m / sec. In the case of a DVD evaluation disc, a wavelength of 6
A laser beam of 33 nm is passed through a lens having an NA of 0.6 to produce a laser beam of 0.3 nm.
The measurement was performed by irradiating with a spot diameter of 5 μm. The linear velocity was set at two levels of 7.0 and 15.0 m / sec.

In each case, the laser power (Pe: erase power, Pw: write power) is P
When e / Pw was fixed at 0.5 and Pw was changed to 8 to 16 mW, the measurement was performed under the condition that the CNR was large and the jitter was small. The reading laser power was 0.9 mW. Although the recording film after film formation was amorphous, it was used for the test with the entire surface of the disk crystallized by 10 mW DC light.

Further, for the purpose of confirming the reliability of the disk, the disk was stored in a high-temperature and high-humidity bath at 80 ° C. and 85% RH for 500 hours, and the disk characteristics were measured in the same manner as described above. Disk characteristics before and after storage at high temperature and high humidity, namely CN
Table 9 below shows the measurement results of R, jitter, and modulation factor.

[0036]

[Table 9]

As is clear from Table 9, the reflection film using the silver alloy of the present invention has not only good initial characteristics but also little deterioration in CNR, jitter and modulation even after storage at high temperature and high humidity. It can be seen that a highly reliable disk can be obtained. On the other hand, the discs of Samples 33 to 37, which are comparative examples, do not have good initial characteristics, or one of CRN, jitter, and modulation is significantly deteriorated after storage at high temperature and high humidity. It turns out that the nature cannot be secured.

From the above results, it can be seen that the Ag alloy of the present invention is suitable as a reflective film for an optical disk, particularly for a next-generation optical disk that will be required in the future. In the above embodiment, the reflection film was formed by the sputtering method.
Various vacuum deposition methods, ion plating methods, various CVs
It can also be formed by various film forming techniques such as the D method and the plating method.

[0039]

According to the present invention, high thermal conductivity and high data reliability can be secured at the same time.
It is possible to provide a silver alloy for a reflection film suitable for an optical recording disk compatible with a high recording density.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsukasa Nakai 1-6-1, Suehirocho, Ome-shi, Tokyo Sumitomo Metal Mining Co., Ltd. Electronics Business Unit (72) Inventor Nobuaki Onagi Shinagawa-cho, Tsuzuki-ku, Yokohama-shi, Kanagawa No. 16-1 Ricoh Central Research Laboratory Co., Ltd. (72) Inventor Kazunori Ito 16-1 Shineicho, Tsuzuki-ku, Yokohama-shi, Kanagawa Prefecture Ricoh Central Research Laboratory F-term (reference) 5D029 MA13 MA14

Claims (2)

[Claims] 1. The method according to claim 1, wherein Ag is a main component, and Cr, Zr, La,
At least one additive element selected from the group consisting of Ce, Eu, Ca, Sr, Ba, Ru, Ni, and W is added to 0.00.
A silver alloy for an optical recording disk reflective film, comprising 1 to 0.1% by weight, with the balance being unavoidable impurities. 2. In addition to the additive element, Zn, Mg, A
at least one second selected from the group consisting of u and Pd
Characterized in that it contains 0.1 to 5% by weight of an additional element of
The silver alloy for an optical recording disk reflection film according to claim 1.