JP2002235130A - Silver alloy for optical disk reflection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a silver alloy which has high reflectivity and high thermal conductivity, simultaneously exhibits good corrosion resistance, and is used as a reflection film for an optical disk corresponding to high recording density. SOLUTION: A silver alloy having a composition (1) containing 1 to 20 mass% Zn, and the balance Ag with inevitable impurities, or a composition (2) containing 1 to 20 mass% Zn and one or more kinds selected from Pd and Au by 0.1 to 15 mass%, and the balance Ag with inevitable impurities is used as a target to deposit an optical disk reflection film.

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, CD, CD-R, CD
-RW, DVD, DVD-RW, DVD + RW, DVD
-Various optical recording disks (hereinafter, optical disks) such as RAM, MOD, and MD are used.

The structures of these optical disks differ depending on the recording / reproducing method, but thin films having various functions are formed in layers on a transparent plastic substrate, typically a lower protective layer and a recording layer. , Upper protective layer,
The fact that the reflective heat dissipation layer and the overcoat layer are formed has a common laminated cross-sectional structure. This reflective heat dissipation layer is a reflective film to which the present invention is applied.

[0004] The reflection film has a function of reflecting a laser beam used for reading and writing of recording, and is mainly composed of Al, Au,
A thin film made of Ag or an alloy thereof is used.

[0005] The reflective film is required to have characteristics such as high reflectivity, high thermal conductivity, and high corrosion resistance.
In particular, the demand for a reflective film having both high reflectance and high thermal conductivity has been increasing in response to the increase in the recording density of optical disks.

However, Al has a problem that both reflectance and thermal conductivity are low, and Au has a problem that its price is very high and it is difficult to apply it to mass-produced products. Further, Ag has high reflectance and thermal conductivity, but has low corrosion resistance to oxidation and sulfidation, and has a problem of deterioration of disk characteristics due to rewriting, and completely satisfies required characteristics. No reflective film was obtained.

[0007]

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a reflective film for an optical disk having a high reflectance and a high thermal conductivity, exhibiting good corrosion resistance, and supporting a high recording density. An object of the present invention is to provide a silver alloy used as a silver alloy.

[0008]

In order to achieve the above object, a silver alloy for an optical disk reflective film according to the present invention comprises (1) Z
n in an amount of 1 to 20% by mass and the balance of Ag and inevitable impurities, or (2) Zn in an amount of 1 to 20% by mass and Pd
And at least one kind of Au in an amount of 0.1 to 15% by mass, with the balance being Ag and unavoidable impurities.

The optical disk reflection film of the present invention is preferably formed using the silver alloy as a target.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the components of the present invention will be described in detail.

The present inventors have conducted various studies, and as a result,
It has been found that various properties can be maintained in a suitable range by adding Zn to Ag.

(1) Zn is contained in an amount of 1 to 20% by mass, and the balance consists of Ag and inevitable impurities;
20% by mass, and at least one of Pd and Au is 0.1 to
An optical disk reflective film is formed using a silver alloy containing 15% by mass and the balance being Ag and unavoidable impurities as a target.

If the amount of Zn is less than 1% by mass, the concentration is too low and the effect of improving the corrosion resistance is small, so that the characteristics of the optical disc are degraded due to rewriting. If the content exceeds 20% by mass, the reflectivity and the thermal conductivity of the silver alloy decrease, and it is impossible to cope with an increase in the recording density of the optical disk.

Further, at least one of Pd and Au is added to 0.1%.
Although Pd and Au may be contained in an amount of 1 to 15% by mass, Pd and Au are elements having an effect of further improving corrosion resistance, and inclusion of these elements is particularly effective in an optical disk using a protective film containing ZnS. It is.

[0015] The amount of one or more of Pd and Au added is 0.
If it is less than 1% by mass, the concentration is too low and the effect of improving corrosion resistance is small. If the content exceeds 15% by mass, the thermal conductivity of the silver alloy is reduced, and it is impossible to cope with an increase in the recording density of the optical disk.

There are the following methods for forming the reflection heat radiation layer.

(1) On a pure Ag target, for example, 5
A method (on-chip method) in which chips of the added element of × 5 × 0.5 [mm] are selected and arranged in a quantity and position according to a target concentration, and sputtered (on-chip method).

(2) A target in which a pellet of the target alloy element is embedded in a pure Ag target (composite target)
Sputtering method using

(3) Ag powder and metal powder to be alloyed are mixed, and sputtering is performed using a target (hereinafter, referred to as a mixed sintered body target) manufactured by a hot press method or the like. Method.

(4) Sputtering method using an alloy target produced by a melting method. The dissolution method is a method of dissolving in the air, dissolving in a vacuum, and dissolving in an argon gas atmosphere depending on an element to be added.

In the on-chip method (1) and the method using the composite target (2), the substrate is rotated, or the substrate is rotated and revolved. In other cases (3) and (4),
Let the substrate stand still.

In the method using the on-chip method (1) and the method using the composite target (2), 99.99% by mass (4N) of pure Ag target, additional element chips and alloy element pellets are used. Use pure one.
In the method (3), the Ag powder and the metal powder to be used as the alloy also have a purity of 99.99% by mass (4N). According to the method (4), the shots of the raw material Ag metal and the additive element or the raw material powder are also 99.9% each.
A material having a purity of 9% by mass (4N) is used.

When the range of the composition of the sputtering target for forming the reflection film is specified, the composition of the reflection film formed using the sputtering target is as follows.
Although slightly different from the above range, both are included in the present invention. That is, according to the experiments performed by the present inventors, the silver alloy used for forming the reflective heat dissipation layer has a target composition even when the substrate is stationary when an alloy target manufactured by a melting method or a mixed sintered body target is used. It was found that there was almost no composition deviation between the film composition and the film composition, and that the composition uniformity in the substrate was good. When these alloy targets and mixed sintered body targets were used, the film formation rate was high and stable, so that they were suitable as sputtering targets.

A method for measuring various characteristics of the silver alloy for a reflective film of the optical disk of the present invention will be described below.

[0025] Measurement of thermal conductivity of the thermal conductivity of the reflective heat dissipation layer is very difficult when the film thickness is thin. In conventional patent publications and various papers, the thermal conductivity of a film is determined from the measured electrical resistivity by Wiedeman.
It has been evaluated that estimation is performed using the n-Franz rule. However, in order to use this method, it is necessary to thoroughly examine the sample to be measured, but in some cases it is not always sufficient. Therefore, the present inventors evaluated by the following two methods, and examined their validity sufficiently.

The first method is a method of measuring the electrical resistivity (electrical conductivity) of a film by a DC four-terminal method and obtaining the thermal conductivity according to the formula (1) according to the Wiedemann-Franz rule.

Λ · ρ / T = L ₀ = 2.43 × 10 ⁻⁸ [W · Ω / K ² ] (1)

Here, λ is the thermal conductivity of the film [W / m ·
K] and ρ are electrical resistivity [Ω · cm], T is (absolute) temperature [K], and L ₀ is Lorentz number [W · Ω / K ² ]. Note that the electric resistivity ρ may be measured by a four probe method or a Van der Pauw method.

In the second method, the thermal diffusivity of the film is measured by the AC calorimetry method, the specific heat of the film is measured by the DSC (differential scanning calorimeter), and the density of the film is measured. This is a method obtained by the expression 2).

Λ = α · Cp · ρ _d (2)

Here, λ is the thermal conductivity of the film [W / m ·
K], α are thermal diffusivity [cm ² / sec], Cp is specific heat [J / g · K], and ρ _d is density [g / cm ³ ]. All measurements were performed at room temperature (25 [° C.]) and in vacuum.

From the measured value of the electric resistivity (electric conductivity) ρ
The first method for determining the thermal conductivity λ using the Wiedemann-Franz rule is a measured value of the thermal diffusivity α by the AC calorimetry method, a measured value of the specific heat Cp by the DSC, and the density ρ _{d of the} film.
Is very simple as compared with the second method of obtaining the thermal conductivity λ from the measured value of

The reflectance of the reflective heat dissipation layer was measured by applying a film formed on a glass substrate to a spectrophotometer.

The present inventors conducted a test for the deterioration of the reflective heat dissipation layer by sulfurization by the following method and measured it.

(1) First, a silver alloy thin film is formed on a glass substrate. The film thickness was, for example, 3000 [Å].

(2) ZnS powder, which is a raw material powder for the ZnS + SiO ₂ target, contains several mass% of free S (sulfur). This is analyzed, and a silver alloy thin film formed on a glass substrate is injected into ZnS powder with free S (sulfur) of, for example, 1% by mass for a certain period of time (for example, 24 [h]). The change in rate was measured.

The rate of change of the reflectance is obtained by subtracting the reflectance of the sample after the addition from the reflectance of the sample before the addition, dividing the reflectance by the reflectance of the sample before the addition, and taking the absolute value.
Was multiplied to make the unit [%].

The tests were carried out of the measurement of the disk characteristics of disc properties in the following way.

In the case of a CD type optical disk, a wavelength of 780 [n
m] was passed through a lens with an NA of 0.55, focused on the medium surface to a spot diameter of 1 [μm], and irradiated from the substrate side.

For a DVD-based optical disk, the wavelength 633
The semiconductor laser light of [nm] was narrowed down to a spot diameter of 0.5 [μm] on the medium surface through a lens of NA 0.6 and irradiated from the substrate side.

The entire surface of the disk is sufficiently crystallized to be in an initial (unrecorded) state. At each linear velocity, the laser power is set to Pe / Pw = 0.5, and the laser power Pw at the time of recording is set to 8-16. [MW], and by selecting conditions under which the CNR (carrier-to-noise ratio) was large and the jitter was small, the CNR, jitter and modulation factor (before the test) at that time were measured. Here, Pe is the laser power at the time of erasing.

Thereafter, each optical disk was heated to 80 ° C. and 85% R
After leaving for 500 hours in a high temperature and high humidity state of H, at each linear speed,
Similarly, CNR, jitter, and modulation (after the test) were measured. This test is called a high-temperature high-humidity storage test.

(Examples) Hereinafter, the specific constitution of the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

(Examples 1, 2, 4, 6, 10 to 12, 1
5. Comparative Examples 1 and 4) CD-type optical disks were produced as follows.

Pitch 1.6 [μm], Depth 50 [nm]
1.2 mm thick and 120 mm diameter with grooves
Was produced by injection molding, and a lower protective layer, a recording layer, and an upper protective layer were sequentially formed thereon by sputtering under the conditions shown in Table 2, and a sputtering target having a target composition shown in Table 1 was obtained. The reflective heat dissipation layer used was formed, and an ultraviolet curable resin (UV curable resin) was applied thereon by spin coating, and was cured by irradiating ultraviolet rays, and 5 [μm] was laminated as an overcoat layer. A CD-type optical disk was manufactured.

The lower protective layer and the upper protective layer are made of Zn: S
= 1: 1 (Zn
S) ₈₀ (SiO ₂ ) ₂₀ film was used. Therefore, (Zn
S) A sputtering target prepared by hot pressing a sintered body target of ₈₀ (SiO ₂ ) ₂₀ was used.

The recording layer is made of Ag ₅ In ₆ Sb ₆₀ Te ₂₉
It was a membrane. Therefore, a sputtering target prepared by hot-pressing an Ag ₅ In ₆ Sb ₆₀ Te ₂₉ alloy target was used.

The reflective heat dissipation layer was a silver alloy film, and was produced by the melting method of the above four methods with the target compositions shown in Table 1.

In forming each layer, pre-sputtering was performed at least 1.5 [kWh] or more, and the ultimate vacuum in the chamber before the start of sputtering was 6.0 × 10 ⁻⁵ [Pa] or less.

(Examples 3, 5, 7 to 9, 13, and 14 and Comparative Examples 2 and 3) A DVD-type optical disk was manufactured as follows.

Pitch 0.8 [μm], Depth 30 [nm]
0.6 [mm] with a groove of 120 mm [diameter]
Was produced by injection molding, and a lower protective layer, a recording layer, and an upper protective layer were sequentially formed thereon by sputtering under the conditions shown in Table 2, and a sputtering target having a target composition shown in Table 1 was obtained. The reflective heat dissipation layer used was formed, and an ultraviolet-curable resin (UV-curable resin) was applied thereon by spin coating, cured by irradiating ultraviolet rays, and laminated as an overcoat layer of 4 [μm]. 0.6 [m] with nothing formed
m], and a polycarbonate substrate (so-called blank disk) having a diameter of 120 [mm] was bonded using an ultraviolet-curable resin to produce respective DVD-type optical disks.

The composition and forming method of the lower protective layer, the recording layer, the upper protective layer, and the reflective heat dissipation layer were the same as described above.

In Examples 1 to 15 and Comparative Examples 1 to 4, the composition of the reflective heat radiation layer and the thickness of each layer were measured. The result
The results are shown in Tables 1 and 3.

The composition of the reflective heat dissipation layer was determined by preparing each film on a glass substrate and using EPMA (Electron Probe Micro A).
analysis).

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

As can be seen from the target composition and the composition of the reflective heat radiation layer in Table 1, the change in the Zn content was within several percent.

For Examples 1 to 15 and Comparative Examples 1 to 4, the thermal conductivity of the reflective heat radiation layer, the reflectance of the reflective heat radiation layer, the rate of change of the reflectance, and the disk characteristics were measured. The results are shown in Tables 4 and 5.

The sample for measuring the electric resistivity ρ in the first method was formed into a film on a cover glass of 20 × 70 × 0.8 [mm], cut out to 3 × 6 [mm], and measured. The film thickness is 3000 [Å].

The sample for measuring the thermal diffusivity α in the second method was formed into a film on the same cover glass.
[Mm] was cut out and measured. The film thickness is 3000
[Å].

The measurement of the specific heat Cp by DSC was performed by stripping a sample formed on the same cover glass by a necessary mass and setting the sample in a sample container.

Prior to the preparation of each measurement sample,
Each composition sample was prepared in advance and subjected to X-ray diffraction to confirm its crystallinity. Further, as a sample for measuring the electric resistivity ρ and the thermal diffusivity α, a sample prepared under the condition that the number of defects in the film was very small was used.

As described above, since the measurement conditions were sufficiently examined, the estimated value of the thermal conductivity λ obtained from the measured value of the electric conductivity ρ using the Wiedemann-Franz rule and the measurement of the thermal diffusivity α by the AC calorimetry method Conductivity, λ obtained from the measured value of specific heat Cp by DSC and the measured value of film density ρ _d
And the estimated value were consistent within the measurement accuracy.

The reflectance of the reflective heat dissipation layer is determined by measuring the film formed on the glass substrate with a spectrophotometer at a wavelength of 400 to 900 [n].
m]. Each of the film thicknesses is 3000 [測定] as in the measurement of the electric resistivity ρ and the thermal diffusivity α.

[0066]

[Table 4]

In the sulfide deterioration test, the time of introducing each Ag-containing film into ZnS powder containing 1% free sulfur was set to 24 hours.
The thickness of the Ag alloy formed on the glass substrate is 3000
[Å].

Table 4 shows the rate of change before and after introduction.

In addition to the sulfide deterioration test, the surface condition was observed with a metal microscope.

The evaluation of the disk characteristics was carried out on a CD optical disk and a DVD optical disk under the above-mentioned conditions.

Although the recording layer after film formation was amorphous, the disk surface was first sufficiently crystallized with 10 [mW] DC light on the medium surface when measuring the disk characteristics.

At this time, the linear velocity of the optical disk is 2.0, 5.0, 10.0 [m
/ Sec], and two levels of 7.0 and 15.0 [m / sec] for DVD-type optical discs.
The reading power Pr was set to 0.9 [mW].

Thereafter, a high-temperature and high-humidity storage test was performed, and CNR, jitter and modulation were measured before and after the test.
Table 5 shows the results.

Table 5 shows the data of the worst linear velocity selected as a representative among the linear velocities in the embodiment of the present invention. In the comparative example, the data was almost the same at all linear velocities, but data of the best linear velocity among the linear velocities was selected and shown as a representative.

[0075]

[Table 5]

(Evaluation) Thermal conductivity As can be seen from the thermal conductivity λ in Table 4, the thermal conductivity λ generally decreases with an increase in the amount of the added element.
The amount of change varies depending on the element to be added.

In the optical disk, the required thermal conductivity λ of the reflective heat dissipation layer is different depending on the film configuration (composition, film thickness, etc.). The fact that the conductivity λ can be varied widely indicates that the silver alloy of the present invention can be widely used, and is very desirable.

As in Comparative Examples 2 to 4, when the amount of the additional element is increased beyond the range of the present invention, the thermal conductivity λ can be further varied. It is not desirable because it becomes smaller and also lowers the reflectance, which will be described below, and does not play the role of reflection.

[0079] As can be seen from the reflectance of the reflectance Table 4, silver alloys of the present invention, in a wide wavelength range, high reflectivity. Further, as described above, since the thermal conductivity λ can be varied widely, it is most suitable as an optical disk reflective heat dissipation film.

As can be seen from the reflectance change rate in Table 4,
The silver alloy of the present invention can keep the reactivity with S (sulfur) low. Therefore, the corrosion resistance to S (sulfur) could be improved.

As in Comparative Example 1, when the amount of Zn added is too small, the rate of change of the reflectance is too large, and the corrosion resistance is low, making it impractical.

As in Comparative Examples 2 to 4, the corrosion resistance can be further improved by increasing the amount of the added element beyond the range of the present invention. In addition, since the thermal conductivity is too low and the reflectance is lowered, it does not function as a reflective heat radiation layer, which is not desirable.

According to the result of observing the surface state with a metallographic microscope or the like, the cause of the decrease in reflectance is due to the Ag ₂ S phase formed on the surface of the silver alloy, and the contact time with S (sulfur) is relatively short. Is short, black dots are scattered, but when this exceeds a certain time, it reaches the entire film surface. In this process, the reflectance gradually decreases. The cause of this reaction is that silver and S (sulfur) are easily bonded, but the silver alloy of the present invention can significantly suppress this.

[0084] As can be seen from the disk characteristic table 5, the use of the silver alloy of the present invention to the reflective heat dissipation layer, it is possible to produce an optical disc having a good initial characteristics, and, after storage test high temperature and high humidity, CNR,
There was almost no change in both jitter and modulation.

This indicates that the silver alloy of the present invention has high corrosion resistance to sulfurization and also has high corrosion resistance to corrosion by moisture, that is, oxidation. Therefore, there is no fear of corrosion due to sulfurization, for example, SiN-based, Al
Protective film of various nitrides such as N-based and ZrN-based, Ta ₂ O
_{Even when} a protective film of various oxides such as a _5- system, an Al ₂ O ₃ system, a ZrO ₂ system, and a MgO system, and a protective film of a SiC-based carbide are used, a ZnS + SiO ₂ system or ZnS
When using a system, even when using a barrier layer or a diffusion prevention layer between the upper protective film and the reflective heat dissipation layer, the use of the reflective heat dissipation layer of the present invention improves the reliability of the disc. Considered useful.

On the other hand, in the optical disk of Comparative Example 1, the CNR, the jitter and the degree of modulation significantly changed after the high-temperature and high-humidity storage test. It was difficult for the optical disks of Comparative Examples 2 to 4 to have good disk characteristics in the initial characteristics.

Various analyzes of the optical disk after the high-temperature and high-humidity storage test showed that the results as in Comparative Example 1 were affected by the sulfuration of the silver alloy as the reflective heat dissipation layer. It is considered that the results as Comparative Examples 2 to 4 are mainly due to the low thermal conductivity and the low reflectance of the silver alloy of the reflective heat dissipation layer.

As can be easily understood from these results, the silver alloy of the present invention has a high reflectance and a high corrosion resistance to sulfuration. Further, it has a feature that the thermal conductivity of the reflective heat dissipation layer can be largely changed depending on the concentration of the added element. This makes it possible to manufacture an optical disc that maintains good characteristics from the initial characteristics to after the high-temperature and high-humidity storage test.

The silver alloy of the present invention can be used in applications where corrosion resistance is required and a high reflectance is required, for example, in a reflection mirror where corrosion resistance is required, in addition to the embodiments of the present invention such as an optical disk and a magneto-optical disk. It is considered that the present invention can be applied to a reflective film, a reflective film of a lighting fixture, a reflective film for a sign, and a reflective film for a reflector.

In the present invention, an example in which a film is formed by a sputtering method is shown. However, the reflective film of the present invention can be formed by various film forming techniques such as various vacuum deposition methods, ion plating methods, various CVD methods, and plating methods. Can also be produced.

[0091]

As described in detail above, the silver alloy of the present invention has high reflectance and high thermal conductivity, and at the same time shows good corrosion resistance.

The silver alloy of the present invention can be used for a liquid crystal display (LCD), a plasma display (PDP),
It is considered to be very useful for reflectors, such as (electroluminescence) displays, where heat dissipation is also important.
Of course, a high thermal conductivity indicates a high electrical conductivity, and thus it is considered to be useful for various wiring materials that require various corrosion resistances and require a low electrical resistivity.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/26 531 G11B 7/26 531 F-term (Reference) 4K029 AA11 BA22 BB02 BD09 BD12 CA05 DC04 DC08 5D029 MA13 MA17 5D121 AA05 EE14

Claims (4)

[Claims] 1. A composition containing 1 to 20% by mass of Zn and the balance of Ag
And a silver alloy for an optical disk reflective film, comprising a silver alloy. 2. A composition containing 1 to 20% by mass of Zn, 0.1 to 15% by mass of at least one of Pd and Au, and the balance of Ag
And a silver alloy for an optical disk reflective film, comprising a silver alloy. 3. A sputtering target comprising the silver alloy according to claim 1. 4. An optical disk reflection film comprising the silver alloy according to claim 1.