Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2001-05-31
2002-11-26
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C423S139000, C420S590000, C205S591000, C205S593000, C205S594000
Reexamination Certificate
active
06485542
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an Ni—Fe sputtering target for forming magnetic thin films, and specifically to an Ni—Fe sputtering target for forming ferromagnetic thin films.
BACKGROUND OF THE INVENTION
In recent years, magnetic recording devices for computers, such as hard disks, have rapidly been downsized, and their capacities have been increased. The recording density of such devices is estimated to reach 20 Gb/in
2
in a few years. Therefore, conventional induction-type heads used as playing heads have approached their limit, and alternatively, magneto-resistance-effect-type (MR) heads have begun to be used. Use of the MR heads is expected to grow rapidly in the future in a worldwide scale accompanying the growth of the personal computer market. In coming years, the practical use of giant magneto-resistance-effect-type (GMR) heads, expected for their further higher density, will be realized.
Ni—Fe alloys have been studied for use as a ferromagnetic film of the spin-valve film used in GMR heads.
Ni—Fe alloys are normally produced by sintering or melting. However, conventional Ni—Fe alloys release a large amount of gases, produce a large number of particles during sputtering, and have the problem of corrosion resistance. Also, their magnetic properties are not found to be satisfactory.
OBJECT OF THE INVENTION
It is an object of the present invention to provide means for forming a ferromagnetic film which releases less gases, produces fewer particles during sputtering, and has good magnetic properties.
SUMMARY OF THE INVENTION
In order to solve the above problems, the inventors of the present invention repeated studies, and discovered that impurity elements, in particular, oxygen, sulfur, carbon, nitrogen, and hydrogen increased the release of gases and the production of particles, and that such impurities were the cause of lowered corrosion resistance. In addition to the above, the inventors discovered that the magnetic properties depended mainly on the crystalline structure of the thin film, and that the magnetic properties were improved when the crystals were large columnar crystals.
According to the present invention, and based on the above stated findings, an Ni—Fe alloy sputtering target for forming magnetic thin films is provided such that it has an oxygen content of 50 ppm or less, a sulfur content of 10 ppm or less, a carbon content of 50 ppm or less, and a content of total metal impurities other than the alloy components of 50 ppm or less. Preferably, the content of oxygen is 10 ppm or less, the content of sulfur is 1 ppm or less, the content of carbon is 10 ppm or less, and the content of total metal impurities other than the alloy components is 10 ppm or less.
In addition, the Ni—Fe alloy sputtering target has a nitrogen content of 10 ppm or less and a hydrogen content of 1 ppm or less. Preferably, the content of nitrogen is 1 ppm or less, and the content of hydrogen is 0.5 ppm or less.
According to another aspect of the present invention, a magnetic thin film formed by sputtering an Ni—Fe alloy target as described above is also disclosed.
According to yet another aspect of the present invention, a method of manufacturing the above discussed Ni—Fe alloy sputtering target is provided. The method includes the step of alloying by: melting high-purity Ni and high-purity Fe obtained by dissolving material Ni and Fe in hydrochloric acid to form an aqueous solution of chlorides; removing impurity metal ions by allowing the aqueous solution of chlorides to contact an ion exchange resin; evaporating to dryness or concentrating the obtained solution; dissolving it in water to form an aqueous solution of chloride having pH between 0 and 3; removing organic matters in the solution using activated charcoal; and conducting electrolytic refining of the aqueous solution as an electrolytic solution. The method also includes the step of casting the obtained alloy.
In addition, the method of manufacturing an Ni—Fe alloy sputtering target can include obtaining Ni or Fe by electrolytic refining and subjecting it to degassing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An Ni—Fe alloy sputtering target for forming magnetic thin films according to the present invention comprises an Ni—Fe alloy containing 70% by weight or more Ni. Although typical examples are two-component alloys of Ni and Fe, the examples further include alloys also containing Co, Cr, Rh, Nb, or Ta.
In the Ni—Fe alloy sputtering target according to the present invention, the contents of impurities, i.e., elements other than Ni and Fe, are reduced. In particular, the contents of oxygen, sulfur, carbon, nitrogen, and hydrogen are reduced as much as possible, because such elements lower the corrosion resistance of the target, cause particles to occur, and deteriorate magnetic properties. Among these elements, oxygen and sulfur especially lower the corrosion resistance. Furthermore, since oxygen makes crystals finer and nitrogen deviates crystal orientation, both cause the deterioration of magnetic properties. Carbon also causes particles to occur. Therefore, the content of oxygen should be 50 ppm or below, preferably 10 ppm or below; the content of sulfur should be 10 ppm or below, preferably 1 ppm or below; and the content of carbon should be 50 ppm or below, preferably 10 ppm or below.
Furthermore, the content of nitrogen should be 10 ppm or below, preferably 1 ppm or below; and the content of hydrogen should be 1 ppm or below, preferably 0.5 ppm or below.
Exceeding the above contents is not preferred because of increase in occurrence of particles, significant lowering of corrosion resistance, and marked deterioration of magnetic properties.
The inventor of the present invention found that the impurities in the Ni—Fe alloy were originated from electrolytic Ni and Fe materials. The inventor carried out the high purification of each of the Ni and Fe materials.
By the combination of ion exchange and electrolytic refining, activated charcoal treatment, and degassing as required in the method for high purification of Ni and Fe materials, extremely high-purity Ni and Fe can be obtained.
For example, the following method can be used.
High-purity Ni and high-purity Fe can be obtained by: dissolving material Ni and Fe in hydrochloric acid to form an aqueous solution of chlorides; removing impurity metal ions by allowing the aqueous solution of chlorides to contact an ion exchange resin; evaporating to dryness or concentrating the obtained solution; dissolving the concentrated solution in water to form an aqueous solution of chloride having pH between 0 and 3; removing organic matters in the solution using activated charcoal; and conducting electrolytic refining of the aqueous solution as an electrolytic solution.
Although the purity of the Ni and Fe utilized are not particularly limited, those of three-nine purity (99.9%) which are normally marketed are sufficient.
The above Ni material, or Fe material, is charged in a vessel and dissolved in hydrochloric acid. The type of hydrochloric acid utilized is not particularly limited, for instance, industrial low purity hydrochloric acid may be used. This is because impurities contained in hydrochloric acid can also be removed by practicing the present invention.
Equipment for dissolving Ni or Fe is preferably provided by a cooling tower for the effective use of hydrochloric acid and a hydrogen chloride gas recovering unit. The material of the equipment is preferably quartz, graphite, Teflon, or polyethylene.
The dissolving temperature is 10 to 100° C. If the temperature is less than 10° C., the dissolving rate decreases, and if the temperature is more than 100° C., evaporation becomes vigorous and loss of the aqueous solution increases.
When Ni is highly purified, the Ni solution is extracted, concentrated, and adjusted to have a hydrochloric acid concentration of 5 to 12N by adding hydrochloric acid. A hydrochloric concentration of less than 5N, or more than 12N, is not preferred because Co is not absorbed and removed by the ion exchange resin.
The ab
Shindo Yuichiro
Suzuki Tsuneo
Howson and Howson
Japan Energy Corporation
King Roy
McGuthry-Banks Tima
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