JP6317636B2 - Sputtering target for magnetic recording media - Google Patents

Description

  The present invention relates to a sputtering target for a magnetic recording medium, and more particularly to a sputtering target for a magnetic recording medium of a hard disk that employs a perpendicular magnetic recording method.

A Co-based ferromagnetic material having a hexagonal crystal structure is used for the recording layer of the perpendicular magnetic recording medium. In order to reduce medium noise, to achieve a nanometer-order microstructure in which ferromagnetic crystal grains having an in-plane grain size of about 5 to 8 nm are magnetically isolated in a 10 to 20 nm thick thin film Is essential. For this reason, in a perpendicular magnetic recording medium, a CoPtCr—SiO ₂ composite material in which SiO ₂ is mixed as a phase separation material has been put to practical use as a recording layer material (Non-patent Document 1).

The recording layer of the perpendicular magnetic recording medium is manufactured by sputtering a sputtering target having the same component composition and forming a magnetic film on the substrate. In order to form a CoPtCr—SiO ₂ composite material as a recording layer, an oxide-dispersed sputtering target in which SiO ₂ that is nonmagnetic inorganic particles for magnetically separating a CoPtCr alloy phase is dispersed is used. .

However, since SiO ₂ which is a non-magnetic inorganic particle tends to aggregate and segregate easily, abnormal discharge is likely to occur during sputtering, and there is a problem of generating particles destroyed by abnormal discharge. Various methods have been proposed to solve the problem of particle generation.

The CoPtCr—SiO ₂ -based sputtering target can be produced by a powder sintering method in which metal particles or alloy particles as raw materials and SiO ₂ particles are mixed and sintered. During sintering, SiO ₂ is crystallized to form cristobalite, which causes particles to be generated during sputtering. Therefore, the sintering temperature is set to 1120 ° C. or lower to suppress cristobalite formation during sintering. It has been proposed to make SiO ₂ exist in a sputtering target (Patent Document 1), or to suppress the formation of cristobalite by using quartz as a raw material for SiO ₂ (Patent Document 2). In the method described in Patent Document 1, it is necessary to maintain the sintering temperature at 1120 ° C. or lower. Since voids remain in the sintered structure at a low sintering temperature, the relative density of the sputtering target is low, and as a result, the generation of particles during sputtering increases. In Patent Document 2, in order to solve the problem of relative density that could not be solved by the method described in Patent Document 1, quartz is used as a raw material to suppress cristobalite formation without lowering the sintering temperature.

  However, the method described in Patent Document 2 has a restriction that quartz is used as a raw material.

In addition, in order to obtain a non-magnetic material particle-dispersed magnetic material sputtering target with reduced arcing, stable discharge, high density and low particle generation, Cr powder, Pt powder, Co powder, SiO ₂ powder and Cr ₂ O ₃ powder is mixed and hot pressed in a vacuum atmosphere at 1150 ° C. to disperse the SiO ₂ oxide phase having an average area of 2.0 μm ² or less in the CrPtCo alloy phase, and within the SiO ₂ oxide phase or its There has been proposed a method of obtaining a target containing 0.3 mol% or more and less than 1.0 mol% of Cr ₂ O ₃ on the surface (Patent Document 3). Patent Document 3 describes that when the Cr ₂ O ₃ powder is not added, each particle of the SiO ₂ oxide phase grows large and the generation of particles cannot be suppressed.

Japanese Patent No. 5032706 Japanese Patent No. 5009447 Japanese Patent No. 4837801

Takahashi, et al., “Sputtering Targets for Functional Thin Film Formation -Technical Issues and Guidelines for the Future-" J. Vac. Soc. Jpn. Vol. 50, no. 1, 2007, p. 22-27

The purpose of the present invention is to suppress the generation of particles during sputtering even if cristobalite is included at a high sintering temperature of 1200 ° C. or higher without extending the burn-in time without extending the raw material SiO ₂ . It is an object of the present invention to provide a sputtering target for a CoPtCr—SiO ₂ magnetic recording medium that can achieve a high relative density.

As a result of diligent research to solve the above problems, the present inventors have dispersed an oxide phase containing CrTi ₂ O ₅ in addition to SiO ₂ in a metal phase, so that microcracks and particles can be formed even if cristobalite is present. As a result, it was found that a sputtering target for a magnetic recording medium with a small amount of generation was obtained, and the present invention was completed. Specifically, the present invention includes the following aspects.
[1] Cr: more than 0 mol% to 10 mol%, Pt: more than 11 mol% to 25 mol% or less, the remainder of the metal phase consisting of Co and inevitable impurities 80 mol% to less than 100 mol%, CrTi ₂ O ₅ and SiO ₂ The sputtering target for magnetic recording media characterized by including the oxide phase containing 0 mol% and 20 mol% or less.
[2] The sputtering target for magnetic recording media according to [1], wherein SiO ₂ is cristobalite.
[3] The sputtering target for a magnetic recording medium according to [1], wherein the content of CrTi ₂ O ₅ is more than 0 mol% and 10 mol% or less.
[4] The oxide phase further includes one or more selected from TiO ₂ , Cr ₂ O ₃ , B ₂ O ₃ , CoO, and Co ₃ O ₄ [1] to [3] The sputtering target for magnetic recording media as described in any of the above.
[5] The sputtering target for magnetic recording media according to any one of [1] to [4], wherein the relative density is 97% or more.

  The sputtering target for a magnetic recording medium of the present invention generates less particles even when cristobalite is present. Therefore, it is not necessary to suppress the formation of cristobalite by maintaining the sintering temperature at 1120 ° C. or lower, and the relative density of the sputtering target can be increased.

Further, since cristobalite is allowed to exist in the target, any of amorphous, cristobalite, and quartz can be used as the raw material SiO ₂ .

The sputtering target for a magnetic recording medium of the present invention can provide a stable discharge because the ionization effect of the inert gas efficiently proceeds when sputtering with a magnetron sputtering apparatus. Further, it is possible to suppress the generation of particles during sputtering queuing can be suppressed aggregation of SiO _2, it is possible to produce a magnetic thin film at a low cost.

It is the X-ray diffraction spectrum which extracted only the oxide phase of the sample cut out from the sputtering target created in Example 1, and performed the XRD analysis. It is the X-ray diffraction spectrum which extracted only the oxide phase of the sample cut out from the sputtering target produced in the comparative example 1, and performed the XRD analysis.

Preferred embodiment

According to the present invention, Cr: more than 0 mol% and 10 mol%, Pt: more than 11 mol% and less than or equal to 25 mol%, and the remainder of the metal phase consisting of Co and unavoidable impurities 80 mol% or more and less than 100 mol%, CrTi ₂ O ₅ And an oxide phase containing SiO ₂ in excess of 0 mol% and 20 mol% or less. A sputtering target for a magnetic recording medium is provided.

The metal phase functions as a magnetic phase, and is preferably an alloy phase composed of Cr: more than 0 mol% and 10 mol%, Pt: more than 11 mol% and not more than 25 mol%, with the remainder being Co and inevitable impurities. It is preferable that inevitable impurities are not included as much as possible, considering that impurities contained in Cr, Pt, Co as raw materials, and impurities formed during mixing or sintering will inevitably remain. It is a thing. It goes without saying that it is preferable to eliminate inevitable impurities as much as possible by using a high-purity raw material and controlling the sintering atmosphere and conditions.

The oxide phase has a function of magnetically separating the metal phase. As long as the oxide phase contains CrTi ₂ O ₅ and SiO ₂ , it may further contain other oxides. As the other oxide, one or more selected from TiO ₂ , Cr ₂ O ₃ , B ₂ O ₃ , CoO, and Co ₃ O ₄ can be preferably used. Moreover, it is not limited to the case where CrTi ₂ O ₅ is added as a raw material as an oxide phase, but includes a case where it is formed in the manufacturing process even if it is not added as a raw material. For example, even when TiO ₂ and SiO ₂ are used as raw materials for the oxide phase, CrTi ₂ O ₅ is formed depending on the manufacturing conditions. The content of CrTi ₂ O ₅ is preferably more than 0 mol% and 10 mol% or less in the sputtering target for magnetic recording media. If the CrTi ₂ O ₅ does not exist can not suppress aggregation of SiO _2, the CrTi ₂ O ₅ is present beyond 10 mol%, sputtering relative density of the target becomes low, and the magnetic characteristics change sputtering This makes it difficult to form a desired magnetic film.

In the present invention, since the oxide phase contains a CrTi ₂ O ₅ and SiO _2, it is possible to prevent the SiO ₂ to aggregate by CrTi ₂ O ₅ is interposed. Therefore, SiO ₂ may be quartz, amorphous, or cristobalite, but the effect of the present invention is more exhibited when cristobalite is easily pulverized. Cristobalite has poor wettability with metals, and the adhesion strength is extremely low even if the metal phase and the oxide phase are adjacent to each other. On the other hand, CrTi ₂ O ₅ has good wettability with metal and high adhesion strength with the metal phase.

  The ratio of the metal phase to the oxide phase is such that the metal phase is 80 mol% or more and less than 100 mol%, the oxide phase is more than 0 mol% and 20 mol% or less, the metal phase is 84 mol% or more and 92 mol% or less, and the oxide The phase is preferably 8 mol% or more and 16 mol% or less.

  The sputtering target for magnetic recording media of the present invention can achieve a relative density of 97% or more, preferably 98% or more.

  In the sputtering target for magnetic recording medium of the present invention, Cr, Pt and Co metal powders as raw materials are weighed so as to have a predetermined blending ratio, alloy bath water is prepared, and gas atomization is performed to prepare alloy atomized powder. Then, the oxide powder can be mixed and dispersed in the alloy atomized powder to prepare a mixed powder and sintered.

As the oxide powder, at least SiO ₂ and TiO ₂ , at least SiO ₂ , TiO ₂ and CoO or Co ₃ O ₄ , or at least SiO ₂ and CrTi ₂ O ₅ are used, based on the desired composition of the sputtering target for the magnetic recording medium. Add another oxide powder. As will be described later in Examples, the presence of CrTi ₂ O ₅ was confirmed in the sputtering target as the final product by adding the combination of the above oxides.

Although the exact reaction mechanism has not been elucidated, the Cr-based alloy powder and TiO ₂ and CoO or Co ₃ O ₄ are mixed, so that CrTi ₂ O ₅ is formed in the sintering process as shown in the following formula 1 or 2. It is thought that it was formed.

Also, when a small amount of oxygen is present during sintering, it is considered that CrTi ₂ O ₅ is formed as shown in the following formula 3 without adding Co oxide such as CoO or Co ₃ O _4. It is done.

Therefore, it is sufficient that CrTi ₂ O ₅ is present in the sputtering target as the final product, and it is not necessary to include CrTi ₂ O ₅ as the raw material oxide powder. The raw material SiO ₂ may be amorphous, cristobalite, or quartz.

  The sintering temperature is not particularly limited as long as the relative density can achieve 97% or more, and can be a high temperature exceeding 1120 ° C. However, the preferred range of the sintering temperature is 1120 ° C from the viewpoint of cost effectiveness. It is over 1300 ° C.

  The sintering atmosphere is a vacuum or an inert gas atmosphere in order to prevent oxidation of the metal constituting the metal phase. Sintering can be performed by a known method such as vacuum hot pressing, plasma discharge sintering, hot isostatic pressing.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

[material]
The raw materials used in the examples are as follows.

As the metal raw material, an electrolytic Co ingot having a purity of 99% or more, an electrolytic Cr ingot having a purity of 99% or more, and a Pt ingot having a purity of 99.5% or more are used, and the oxide is an amorphous type having an average particle diameter of 1.0 μm. SiO ₂ powder, escorite-type Cr ₂ O ₃ powder having an average particle diameter of 1 μm, rutile-type TiO ₂ powder having an average particle diameter of 0.1 μm, and CoO powder having an average particle diameter of 1 μm were used.

[Component analysis of oxide phase]
A part of the sputtering target for magnetic recording media produced in the examples was cut out, hydrochloric acid was added and dissolved by heating, further nitric acid was added and dissolved by heating, and the residue obtained by filtration was washed thoroughly to remove the acid. After washing away, it was dried in a drying oven at 80 ° C. and then air-cooled to extract only the oxide. Next, XRD analysis (SmartLab manufactured by Rigaku Corporation) of the extracted oxide was performed, and components were identified from the obtained X-ray diffraction spectrum.

  The X-ray diffraction spectrum measurement conditions were tube voltage 40 kV, tube current 30 mA, scan speed 4 ° / min, step 0.02 °, and measurement range 2θ = 15 ° -60 °.

[Relative density]
It is most reliable to use the density measured by the Archimedes method, but as a simple measurement method, the absolute density can be calculated by measuring the dimensions and weight of the sputtering target. The relative density can be calculated by dividing the absolute density thus measured by the theoretical density calculated by assuming that each molecule is mixed in the composition ratio.

[Leakage magnetic flux]
ASTM F2086-1
[Example 1]
Each metal raw material was weighed so that Co: 80.38 at%, Cr: 7.93 at%, and Pt: 11.72 at%, and heated to 1700 ° C. to form a molten alloy, followed by gas atomization. A 7.93Cr-11.72Pt alloy powder was prepared. The prepared atomized alloy powder was classified with a 150-mesh sieve to obtain a post-classification atomized alloy powder with a particle size of φ106 μm or less.

Then, classification after atomized alloy _{powder: 87mol%, SiO 2: 5mol} %, TiO 2: 4mol%, Cr 2 O 3: 2mol%, CoO: weighed such that 2 mol%, were mixed with Zr ball mill After classification, a mixed powder in which oxide particles were dispersed in an atomized alloy powder was obtained.

This mixed powder was hot-pressed under the conditions of sintering temperature: 1250 ° C., pressure: 24.5 MPa, holding time: 180 minutes, vacuum atmosphere: 5 × 10 ⁻² Pa or less, φ165.1 mm × thickness 4. A 0 mm sputtering target was prepared. The relative density of the produced sputtering target was 98.1%.

A sample is cut out from the sputtering target, and hydrochloric acid is added and dissolved by heating. Further, nitric acid is added and dissolved by heating, and the residue obtained by filtration is thoroughly washed to wash away the acid, and then placed in a drying oven at 80 ° C. After drying, air cooling, and extracting only the oxide phase, X-ray diffraction analysis is performed to confirm that the oxide is cristobalite type SiO ₂ , escorite type Cr ₂ O ₃ and CrTi ₂ O ₅ (FIG. 1).

The sample for analysis was cut out from the produced sputtering target, the sample for analysis was dissolved using hydrochloric acid and nitric acid, and then filtered to separate the filtrate and the residue. The residue was made into a solution by an alkali dissolution method, and the mixed solution was mixed again with the filtrate, and analyzed by an ICP analyzer. Since the oxide by XRD analysis has been confirmed to be a _SiO 2, CrTi ₂ O ₅ and _Cr 2 _{O 3,} and oxides of the raw materials of Si and Ti by ICP analysis as SiO ₂ and CrTi ₂ O _5, respectively Cr ₂ O ₃ was quantified from the amount of oxygen, and the final composition was 91 (Co-5.38Cr-11.21Pt) -5SiO ₂ -2CrTi ₂ O ₅ -2Cr ₂ O ₃ , or 75.9Co-4.9Cr- It was confirmed that it was 10.2Pt-5SiO ₂ -2CrTi ₂ O ₅ -2Cr ₂ O ₃ .

[Comparative Example 1]
A sputtering target of φ165.1 mm × thickness 4.0 mm was produced in the same manner as in Example 1 except that the sintering temperature was 1050 ° C. and the holding time was 60 minutes. The relative density of the produced sputtering target was 97.1%.

An oxide was extracted from the obtained sputtering target in the same manner as in Example 1, and component analysis was performed by X-ray diffraction. As a result, amorphous SiO ₂ and escorite Cr ₂ O ₃ were confirmed (FIG. 2). However, CrTi ₂ O ₅ and rutile TiO ₂ could not be clearly confirmed.

  The sputtering target of the present invention can be used for film formation of a magnetic thin film of a magnetic recording medium, particularly a granular magnetic recording phase of a hard disk employing a perpendicular magnetic recording method.

Claims (5)

Cr: more than 0 mol% to 10 mol%, Pt: more than 11 mol% to 25 mol% or less, the rest of the metal phase consisting of Co and inevitable impurities 80 mol% to less than 100 mol%, and oxidation including CrTi ₂ O ₅ and SiO ₂ A sputtering target for a magnetic recording medium, comprising a physical phase exceeding 0 mol% and not exceeding 20 mol%. The sputtering target for magnetic recording media according to claim 1, wherein SiO ₂ is cristobalite. _{2. The} sputtering target for a magnetic recording medium according to claim 1, wherein the content of CrTi ₂ O ₅ is more than 0 mol% and 10 mol% or less. The oxide phase _is, according to any of claims 1 to 3, further comprising one or more selected _{TiO 2, Cr 2 O 3,} B 2 O 3, CoO, from _Co 3 _{O 4} Sputtering target for magnetic recording media.   5. The sputtering target for a magnetic recording medium according to claim 1, wherein the relative density is 97% or more.