JP2002161359A - Sintered sputtering target material for forming protective layer of light media, showing superior fracture resistance under high-power sputtering condition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a target material for forming a protective layer of light media, which shows a superior fracture resistance even when a high power condition for sputtering is employed in order to form the layer at high speed. SOLUTION: The target material for forming the protective layer of light media comprises a compact sintered with hot press consisting of mixed powder having a composition of 4-30% silicon oxide, 7-35% indium oxide, and zinc sulfide as a remainder, by mass%, and a structure in which indium oxide substantially composes a continuous reticulated phase, and a zinc sulfide phase and a silicon oxide phase bury the rest of the above reticulated continuous phase as a dispersed phase each, when the structure is observed with a scanning electron microscope.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a protective layer, which is a constituent layer of an optical recording medium such as an optical disk, on which information is recorded, reproduced, and erased by using a light beam such as a semiconductor laser by a sputtering method. The present invention relates to a sputtering target sintered material (hereinafter, referred to as a target material) used for the sputtering.

[0002]

2. Description of the Related Art Generally, an optical recording medium such as the above-mentioned optical disk is basically composed of, for example, a polycarbonate substrate, and a lower protective layer formed on the surface thereof by a high-frequency magnetron sputtering method or a DC magnetron sputtering method. It is known that the recording layer is composed of constituent layers of a recording layer, an upper protective layer, and a reflective layer. When the above-mentioned optical recording medium is formed by using, for example, a high-frequency magnetron sputtering apparatus shown in a schematic longitudinal sectional view in FIG. 3, first, a predetermined amount is provided on a backing plate cooled by cooling water circulating inside. After attaching the target material with the composition and evacuating the inside of the device with a vacuum exhaust device,
Ar gas is introduced and maintained at a predetermined sputter gas pressure,
In this state, a high-frequency power is applied to the target material by a high-frequency power source installed through a matching box, and thereby, the target material is opposed to the target material and arranged at a predetermined interval, for example, a polycarbonate substrate. It is also known that plasma is generated during this time, Ar ions in the plasma are made to collide with the surface of the target material and sputtered, and sputtered particles are deposited as constituent layers on the substrate surface.

Further, when the protective layers (lower protective layer and upper protective layer), which are constituent layers of the above-mentioned optical recording medium, are formed by using, for example, a high-frequency magnetron sputtering apparatus, Japanese Patent Application Laid-Open No. 6-65725 discloses, for example. As described, as raw material powder, silicon oxide (hereinafter, referred to as SiO ₂ ) powder and zinc sulfide (hereinafter, referred to as ZnS) each having an average particle size of 10 μm or less and a purity of 99.9 mass% or more. Using these raw material powders,
In (hereinafter,% represents mass%), SiO _2: 4 to 30
%, ZnS: remaining, blended, mixed, and then hot-pressed and sintered, and the structure was observed by a scanning electron microscope, as shown in FIG. More ZnS forms the base, 4-30%
It is also known that a target material having a structure in which SiO ₂ having a relatively low content of SiO ₂ is dispersed in the base material is used.

[0004]

On the other hand, there is a strong demand for improvement in productivity of optical recording media such as the above-mentioned optical discs in recent years, and accordingly, the film forming speed of the constituent layers tends to be increased. In order to perform high-speed film formation, it is necessary to increase the power applied to the target material to achieve high-output sputtering conditions. In particular, when forming the protective layer using the above-described conventional target material, the high-speed film formation is performed. If the sputtering conditions are set to the high-power sputtering conditions for the purpose of performing the above, cracks are likely to occur in the target material, and the service life is currently reached in a relatively short time.

[0005]

Means for Solving the Problems Therefore, the present inventors have proposed:
In view of the above, the present inventors focused on the above-mentioned conventional target material for forming the optical recording medium protective layer, and conducted research to improve the crack resistance thereof. The reason that cracks are apt to occur due to the high sputter power applied for the purpose of the above is that ZnS constituting the base material is extremely brittle against high sputter impact. That is, the high sputtering impact applied to the surface of the target material by the application of high sputtering power causes countless fine cracks to be formed in the ZnS constituting the base material, and these fine cracks become large cracks over time because the ZnS forms the base material. The cracks will lead to a service life.

(B) ZnS powder and SiO ₂ conventionally used as raw material powders in the production of the above-mentioned target material
The powder was further mixed with indium oxide (hereinafter, referred to as In ₂ O ₃ ) powder, and the hot-press sintered body (target material) was found to have substantially In ₂ O ₃ by microscopic observation with a scanning electron microscope. Assuming that a network-like continuous phase is formed and a ZnS phase and a SiO ₂ phase are each present as a disperse phase in a portion where the network of the network-like continuous phase is buried, the ZnS phase is finely divided by high sputtering impact. Even if a large crack is generated, substantially no crack is generated in the network-like continuous phase having high strength, and the growth of the crack generated in the ZnS phase is suppressed by the network-like continuous phase. The cracks do not develop into large cracks that cause the target material to break.

(C) In the target material of (b), the mixing ratio of In ₂ O ₃ constituting the network continuous phase is 35.
% Or less, the characteristics of the protective layers (lower protective layer and upper protective layer), which are constituent layers of the optical recording medium, are not adversely affected.

(D) On the other hand, the production of a target material in which In ₂ O ₃ constitutes a network-like continuous phase in the above (b) requires a normal production method, that is, as a raw material powder, ZnS having a normal particle size is used. Powder and SiO ₂ powder, and further In ₂
The method of mixing and sintering O ₃ powder is not possible. In this case, it is inevitable that the mixed powder has a simple mixed phase structure.
₂ powder and In ₂ O ₃ powder, that is, relatively coarse Zn
S powder and SiO ₂ powder, fine In ₂ O ₃ powder, preferably ZnS powder and SiO ₂ powder having an average particle diameter of 1 to 10 μm measured by a laser diffraction / scattering method;
Using In ₂ O ₃ powder 5~200nm an average particle diameter measured by "the measuring method of the specific surface area by gas adsorption BET method for fine ceramics powder" in S · R1626, these raw material powders, the fine In ₂ When a target powder is manufactured by sintering the mixed powder in a hot press using the mixed powder in which O ₃ powder is relatively dusted on the surfaces of relatively coarse ZnS powder and SiO ₂ powder, The manufactured target material is observed under a scanning electron microscope for microstructure.
As illustrated in FIG. 1, substantially In ₂ O ₃ forms a network-like continuous phase, and a ZnS phase and a SiO ₂ phase are each present as a dispersed phase in a portion where the network of the network-like continuous phase is filled. Even if fine cracks are generated in the ZnS phase by high sputter impact due to this structure,
Since the growth of cracks and the propagation of cracks are sufficiently suppressed by the mesh-like continuous phase, there is no formation of breakage over service life, and excellent performance is exhibited over a long period of time. The research results shown in (a) to (d) above were obtained.

The present invention has been made on the basis of the above-mentioned research results, and is based on SiO ₂ : 4 to 30%, In
A hot-pressed sintered body of a mixed powder having a composition of ₂ O ₃ : 7 to 35% and ZnS: remaining is formed, and the structure is observed to be substantially In ₂ O ₃ by scanning electron microscopy. Forming a continuous phase and having a structure in which ZnS phase and SiO ₂ phase are each present as a dispersed phase in a portion where the network of the network-like continuous phase is buried, exhibits excellent breakage resistance under high power sputtering conditions. The target material for forming an optical recording medium protective layer is characterized in that:

Next, the reason why the composition of the target material for forming an optical recording medium protective layer of the present invention is limited as described above will be described. (1) SiO ₂ ZnS is used as a main component of an optical recording medium protective layer because it has high optical refractive index and light transmittance required for the optical recording medium protective layer and further has heat resistance. On the other hand, Z
For example, when the protective layer of the optical disk is formed by nS alone,
A protective layer having a high internal stress is formed, and when laser irradiation for recording is performed on the optical disk in this state, the protective layer is liable to crack due to rapid heating and rapid cooling accompanying the laser irradiation. Therefore, in the optical recording medium protection layer, ZnS is made to contain SiO ₂ to reduce the residual internal stress in the protection layer. Therefore, when the mixing ratio of SiO _{2 in} the target material is less than 4%, the content ratio of the optical recording medium protective layer is also less than 4%,
The action of suppressing the generation of internal stress in the protective layer becomes insufficient. On the other hand, if the compounding ratio exceeds 30%, the content of the optical recording medium protective layer also increases to over 30%, and ZnS Since the resulting properties tend to decrease, the mixing ratio is set to 4 to 30%, preferably 10 to 15%.

(2) In ₂ O ₃ As described above, the In ₂ O ₃ component forms a network-like continuous phase having a high strength and has an effect of improving the breakage resistance of the target material. If it is less than 7%, it is difficult to form a sufficient network-like continuous phase, and it is not possible to secure desired excellent breakage resistance. On the other hand, if the compounding ratio exceeds 35%, the optical recording medium protective layer 35% each
, And the above-mentioned properties of the protective layer provided by ZnS are impaired.
The compounding ratio was determined to be 7 to 35%, preferably 15 to 25%. The target material of the present invention is suitable for use in forming an optical recording medium protective layer by a DC magnetron sputtering method because In ₂ O ₃ forming the network continuous phase has conductivity.

[0012]

Next, the target material for forming an optical recording medium protective layer of the present invention will be described in detail with reference to examples. As the raw material powder, the average particle diameters shown in Tables 1 and ₂ (the average particle diameter of ZnS powder and SiO ₂ powder are laser diffraction / scattering method, and the average particle diameter of In ₂ O ₃ powder is JIS.
R1626 "Gas adsorption B of fine ceramic powder"
ZnS powder and SiO ₂ powder having a purity of 99.9% or more, and In ₂ O ₃ having a purity of 99% or more.
Powder was prepared. First, of these raw material powders, In ₂
The O ₃ powder was weighed into a mixture having the composition shown in Table 1 and placed in a polyethylene pot.
Twice the amount of hexane was added, and the mixture was stirred and dispersed for 5 minutes, and ZnS powder and SiO ₂ powder were added thereto in the same proportion as shown in Table 1, and hexane was added thereto to further reduce the total powder. Hexane ratio is 1 by volume
2 times, add 10 kg of zirconia balls to this and add 2
This mixed powder was sufficiently dried in the air, and the surface of the ZnS powder and the SiO ₂ powder was coated with the In ₂ O ₃
The mixed powder in a powdered state was filled in a graphite mold and charged into a hot press apparatus, in a vacuum of 1.3 Pa or less, temperature: 1273 K, pressure: 34.3 MPa, holding time: 6 By sintering under the conditions of time, target materials 1 to 12 of the present invention made of a hot-press sintered body having a composition substantially equal to the compounding ratio and having a size of diameter: 125 mm × thickness: 5 mm Target materials 1 and 2 were manufactured, respectively. The comparative target materials 1 and 2 are those in which the mixing ratio of In ₂ O ₃ , which is a component of the hot-press sintered body constituting the target materials, is out of the range of the present invention.

The structures of the various target materials obtained as a result were examined with a scanning electron microscope (magnification: 3000).
As a result, the structure of each of the target materials was the same as that shown in the mimic diagram of the structure of the target material 4 of the present invention shown in FIG. 1, that is, In ₂ O ₃ formed a network-like continuous phase. A structure in which the ZnS phase and the SiO ₂ phase each existed as a dispersed phase with the network of the continuous phase being filled was shown.

Next, with respect to the target materials 1 to 12 of the present invention and the comparative target materials 1 and 2 obtained as a result,
The effect on the light refractive index and light transmittance, which are the criteria for evaluating the characteristics of the optical recording medium protective layer, was examined. That is, the above-described target materials 1 to 12 of the present invention and comparative target materials 1 and 2
Are mounted on a DC magnetron sputtering apparatus having a pulsed DC power supply as a DC power supply in a state of being soldered to a water-cooled backing plate made of oxygen-free copper. First, the inside of the apparatus is 6.7 × 10 ^{− 5} P
a, the atmosphere in the apparatus is set to a sputtering gas pressure of 1.0 Pa, and subsequently, a DC sputtering power of 1500 W is applied to the target material by a pulse superimposed DC power supply to thereby obtain the target material. Diameter: 3 which is opposed to and arranged in parallel with an interval of 50 mm
Plasma is generated between a glass substrate of 0 mm × thickness: 0.5 mm and the target material, and Ar ions in the plasma are caused to collide with the surface of the target material to sputter the target material. An optical recording medium protective layer having a thickness of 90 nm was formed by vapor deposition. For the purpose of evaluating the light refractive index and light transmittance of the optical recording medium protective layer formed as a result, the refractive index and the extinction coefficient were measured using laser light having a wavelength of 650 nm.
The measurement results are shown in Table 1.

Further, in order to evaluate the crack resistance of the target material, the conditions for applying the sputtering power to the target material are increased by 100 W from the above 1500 W, and during this period, the sputter power is maintained for 10 minutes for each increased sputtering power. Except for the conditions, sputtering is performed under the same conditions as those for forming the optical recording medium protective layer described above, and the applied sputtering power at the time when a crack occurs in the target material (critical cracking sputter power).
Was measured. The measurement results are also shown in Table 1. Table 1
Also shows the theoretical density ratio of the target material.

[0016]

[Table 1]

[0017]

From the results shown in Table 1, the target materials 1 to 12 of the present invention have the same structure as the structure of the target material 4 of the present invention shown in FIG. 1, that is, In ₂ O ₃
Have a structure forming a network-like continuous phase, whereby
All of them have not only excellent breakage resistance, but also the conductivity provided by this enables formation of an optical recording medium protective layer by a DC magnetron sputtering method. required refractive index and the refractive index of 1.90 to 2.20 is the extinction coefficient and the extinction coefficient of 0.003 to 0.007 equivalent refractive index and indicates the extinction coefficient, which is the in ₂ It is shown that if the blending ratio of O ₃ is 7 to 35%, the properties of the protective layer are not adversely affected, while the blending ratio of In ₂ O ₃ is in accordance with the present invention as seen in Comparative Target Materials 1 and _2. If the ratio is out of the lower range, the target material cannot have the desired excellent fracture resistance. On the other hand, if the proportion is out of the range of the present invention, the properties of the protective layer, especially Coefficient suddenly Obviously, it will deteriorate. As described above, the target material of the present invention has the same characteristics as those of the conventional optical recording medium protective layer because the generation of cracks is suppressed even by the load of high-power spatter, and it exhibits excellent breakage resistance. This enables the high-speed deposition of the protective layer and contributes to an improvement in productivity.

[Brief description of the drawings]

FIG. 1 is a micrograph of the structure of a target material 4 of the present invention, taken by a scanning electron microscope (magnification: 3000 times).

FIG. 2 shows a scanning electron microscope (magnification:
FIG. 4 is a tissue replication diagram by (3000 times).

FIG. 3 is a schematic longitudinal sectional view illustrating a high-frequency magnetron sputtering apparatus.

Continued on the front page (72) Inventor Rie Mori 1-297 Kitabukuro-cho, Omiya-shi, Saitama F-term in Mitsubishi Materials Corporation Research Laboratory (reference) 4G030 AA34 AA37 AA56 BA01 BA18 CA01 GA29 4K029 BA50 BD12 CA05 DC09 5D029 LA14 LA15 LA17 LA19 5D121 AA04 EE03 EE11 EE14

Claims (1)

[Claims] 1. A hot-press sintered body of a mixed powder having a composition composition of: silicon oxide: 4 to 30%, indium oxide: 7 to 35%, zinc sulfide: remaining Microscopic observation by electron microscopy shows that indium oxide substantially constitutes a network-like continuous phase, and a zinc sulfide phase and a silicon oxide phase each exist as a dispersed phase in a portion where the network of the network-like continuous phase is filled. A sintered sintered target for forming a protective layer of an optical recording medium, which exhibits excellent breakage resistance under high-power sputtering conditions.