JP2002180244A - Sputtering target sintered material for forming photorecording medium protective layer exhibiting excellent cracking damage resistance in high output sputtering condition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a target material for forming a photorecording medium protective layer which is consisting of a hot press sintered body of a powdery mixture having a blended composition consisting of 6 to 40% SiO2 and 1 to 6% MgO, and the balance ZnS and exhibits excellent cracking damage resistance in a high output sputtering condition. SOLUTION: The target material for forming a photorecording medium protective layer is consisting of a hot press sintered body of a powdery mixture having a blended composition consisting of, by mol, 6 to 40% silicon oxide and 1 to 6% magnesium oxide, and the balance zinc sulfide.

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 sintering 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, a recording layer, an upper protective layer, and a lower protective layer all formed on the surface of the substrate by a sputtering method. It is known that the reflective layer comprises a constituent layer. In addition, the above-mentioned optical recording medium uses, for example, a high-frequency magnetron sputtering apparatus shown in a schematic longitudinal sectional view in FIG. 1, and firstly a target material having a predetermined composition is formed on a backing plate cooled by cooling water circulating inside. After the inside of the apparatus is evacuated by a vacuum evacuation apparatus, Ar gas is introduced and maintained at a predetermined sputter gas pressure, and in this state, high-frequency power is applied to the target material by a high-frequency power supply installed through a matching box. Applied, thereby generating a plasma between the target material and the substrate, for example, a polycarbonate substrate opposed to the target material and arranged at a predetermined interval,
It is also known that Ar ions in the plasma collide against the surface of the target material to be sputtered, and sputtered particles are formed on the substrate surface by vapor deposition as constituent layers.

Further, as described in JP-A-6-65725, for example, as a raw material powder, a protective layer (a lower protective layer and an upper protective layer) as a constituent layer of the optical recording medium is formed. Each of them has a silicon oxide (hereinafter, referred to as SiO ₂ ) powder having an average particle diameter of 10 μm or less and a purity of 99.9 mass% or more, and zinc sulfide (hereinafter, referred to as SiO ₂ ).
These raw material powders are represented by mol%
In (hereinafter,% indicates the _{mol%), SiO 2: 6~40%} , ZnS: rest, formulated in proportions, after mixing, the target material is used which is produced by hot press sintering It is also known that

[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. Cracks are likely to occur due to the high sputtering power applied for the purpose of carrying out the process, because ZnS, which is a component, has an extremely brittle property against high sputtering impact as compared with SiO ₂ which is also a component. There is. That is, countless fine cracks are generated in ZnS due to high sputter impact applied to the target material surface by application of high sputtering power, and these fine cracks develop into large cracks over time, and the cracks extend the service life.

(B) The above-mentioned conventional target material contains magnesium oxide (hereinafter referred to as MgO),
And if, in addition to SiO ₂ to tissue MgO coexist, the MgO is alleviated significantly higher sputtering shock experienced by the ZnS, which occurrence of fine cracks in the ZnS is suppressed by excellent also possessed MgO itself and the SiO ₂ In combination with the sputtering resistance, the resulting target material exhibits excellent cracking resistance under high-power sputtering conditions. In this case, the content of MgO in the target material is 6% by weight. % Or less, it has no adverse effect on the characteristics of the protective layers (lower protective layer and upper protective layer) that are constituent layers of the optical recording medium. The research results shown in (a) and (b) above were obtained.

[0007] This invention was made based on the above _{findings, SiO 2: 6~40%, MgO} :
1 to 6%, ZnS: for forming an optical recording medium protective layer exhibiting excellent breakage resistance under high-power sputtering conditions, comprising a hot-pressed sintered body of a mixed powder having a compounding composition of the remainder. The target material has characteristics.

In the target material for forming the protective layer of the optical recording medium, the content ratio of SiO ₂ is 6 to 40
The percentage is set for the following reason. That is, Z
nS is used as a main component of the optical recording medium protective layer because it has a high light refractive index and light transmittance required for the optical recording medium protective layer and further has heat resistance.
For example, when a protective layer of an optical disk is formed by S alone, it becomes a protective layer having a high internal stress, and when laser irradiation for recording is performed on the optical disk in this state, rapid heating and quenching accompanying the laser irradiation cause Cracking is likely to occur in the protective layer. Therefore, in the optical recording medium protective layer, ZnS is made to contain SiO ₂ to reduce the residual internal stress in the protective layer. Therefore, when the content of SiO _{2 in} the target material is less than 6%, the content of the optical recording medium protective layer is also less than 6%, and the effect of suppressing the generation of internal stress in the protective layer becomes insufficient. On the other hand, if the content exceeds 40%, the content of the optical recording medium protective layer also becomes higher than 40%, and the above-mentioned characteristics brought by ZnS tend to decrease. The mixing ratio was determined to be 6 to 40%, desirably 15 to 30%.

Furthermore, the reason why the mixing ratio of MgO in the target material is set to 1 to 6% is that if the mixing ratio is less than 1%, the effect of alleviating sputtering impact on ZnS cannot be sufficiently exhibited as described above. , While its proportion is 6%
Is more than 6%, the content ratio of the protective layer of the optical recording medium becomes higher than 6%, and the above-mentioned characteristics brought by ZnS tend to decrease. It is good to do.

[0010]

Next, the target material for forming an optical recording medium protective layer according to the present invention will be described in detail with reference to examples. Purity having an average particle size of 3 μm as raw material powder:
99.99% or more ZnS powder, purity having an average particle size of 2.5 μm: SiO ₂ powder of 99.9% or more, and MgO powder having an average particle size of 0.1 μm: 99.9% or more Was prepared, and these raw material powders were mixed in the mixing ratio shown in Table 1, and mixed in a ball mill in the presence of hexane for 4 hours. After mixing, the mixture was dried on a hot plate at a temperature of 80 ° C., and further mixed at 400 ° C. In a state where the mixed powder after drying is filled in a graphite mold, it is charged into a hot press apparatus, and the atmosphere pressure is 1.3 Pa in a vacuum and the temperature is 1373.
K, pressure: 34.3 MPa, holding time: 6 hours. Hot press sintering having substantially the same composition as the composition by sintering for 6 hours, and having dimensions of diameter: 125 mm x thickness: 5 mm. Inventive target materials 1 to 9 each comprising a body were produced, respectively.

Next, the effects of the resulting target materials 1 to 9 of the present invention and the conventional target materials 1 to 5 on the light refractive index and light transmittance, which are criteria for evaluating the characteristics of the protective layer of the optical recording medium, were examined. . That is, the above-described target materials 1 to 9 of the present invention and the conventional target materials 1 to 5 were soldered to a water-cooled backing plate made of oxygen-free copper, and then applied to a high-frequency magnetron sputtering apparatus having a structure shown in FIG. At first, the inside of the apparatus was set to a vacuum atmosphere of 6.7 × 10 ⁻⁵ Pa by a vacuum exhaust device, and then the atmosphere in the apparatus was changed to 0.2 Pa by introducing Ar gas.
Then, a sputtering power of 1000 W is applied to the target material from a high-frequency power source through a matching box from a high-frequency power supply, and the diameter of the target material is 30 mm, opposed to the target material and arranged in parallel at a distance of 50 mm.
X Thickness: Plasma is generated between a glass substrate having a thickness of 0.5 mm and the target material, and Ar ions in the plasma 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 a laser beam having a wavelength of 633 nm. The measurement results are shown in Table 1.

Next, in order to evaluate the crack resistance of the various target materials, the conditions for applying the sputtering power to the target material are increased by 200 W from the above-mentioned 1000 W in increments of 200 W. Sputtering was performed under the same conditions as those for forming the optical recording medium protective layer except that the conditions were maintained, and the applied sputter power (crack generation critical sputter power) at the time when the target material cracked was measured. Table 1 also shows the measurement results. Table 1 also shows the theoretical density ratio of the target material.

[0013]

[Table 1]

[0014]

According to the results shown in Table 1, all of the target materials 1 to 9 of the present invention have MgO content due to the inclusion of MgO.
It shows a significantly higher critical sputtering power value for crack generation as compared with the conventional target materials 1 to 5 containing no O, which suppresses the occurrence of breakage even when the sputtering conditions are set to high-power sputtering conditions, and enables high-speed deposition of the protective layer. And the refractive index and extinction coefficient of the optical recording medium protective layer formed using the target materials 1 to 9 of the present invention and the conventional target materials 1 to 5 There was almost no change between the measured values and the results, indicating that the characteristics of the optical recording medium protective layer were not impaired by the inclusion of MgO. 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 schematic longitudinal sectional view illustrating a high-frequency magnetron sputtering apparatus.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Rie Mori 1-297 Kitabukuro-cho, Omiya-shi, Saitama F-term in Mitsubishi Materials Research Laboratory (reference) 4G030 AA07 AA37 AA56 BA01 GA29 4K029 AA11 BA41 BA43 BA46 BA64 BB02 BC08 BD12 CA05 DC05 DC09 5D029 LA17 5D121 AA04 EE09 EE11

Claims (1)

[Claims] 1. A hot-press sintered body of a mixed powder having a composition of mol%, silicon oxide: 6 to 40%, magnesium oxide: 1 to 6%, zinc sulfide: remaining, Characterized by a sputtering target sintered material for forming an optical recording medium protective layer, which exhibits excellent crack resistance under high output sputtering conditions.