US20020117022A1

US20020117022A1 - High purity iron, method of manufacturing thereof, and high purity iron targets

Info

Publication number: US20020117022A1
Application number: US09/966,425
Authority: US
Inventors: Masahito Uchikoshi; Norio Yokoyama; Tamas Kekesi; Minoru Isshiki
Original assignee: Individual
Current assignee: Sony Corp
Priority date: 2000-09-29
Filing date: 2001-09-28
Publication date: 2002-08-29
Also published as: KR100813816B1; KR20070108502A; JP4323078B2; US20030206822A1; KR100854264B1; JP2002105598A; KR20020025752A

Abstract

High purity iron with a very few content of impurities such as copper, a method of manufacturing thereof, and high purity iron targets are provided. The iron containing impurities such as copper is dissolved in a hydrochloric acid solution, and the concentration of the hydrochloric acid of the aqueous solution of iron chloride is adjusted to 0.1 kmol/m³to 6 kmol/m³. Then, iron is added in the aqueous solution of iron chloride, and an inert gas is injected into the solution with agitating, in order to convert the trivalent iron ions and divalent copper ions contained in the aqueous solution of iron chloride respectively to divalent iron ions and monovalent copper ions. Then, the aqueous solution of iron chloride is fed into a column filled up with the anion exchange resins. The divalent iron ions are not absorbed on the anion exchange resins although the monovalent copper ions are absorbed on the anion exchange resins. Therefore, copper can be separated from the aqueous solution of iron chloride. And then, the aqueous solution of iron chloride is evaporated to dryness, oxidized and heated in a hydrogen atmosphere to generate iron.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to high purity iron in which contents of impurities such as copper are reduced, a method of manufacturing thereof, and high purity iron targets.

2. Description of the Related Art

Semiconductor devices such as VLSI (very large scale integrated circuit) and ULSI (ultra LSI) have a structure where various thin metal films are deposited on, for example, a silicon (Si) wafer. Although the idea of using iron (Fe) as a material of magnetic random access memory (MRAM) has been considered in recent years, the accompanying injurious impurities in the iron may result in malfunction or deterioration of the semiconductor device, which is undesirable. For example, copper (Cu) may cause a short circuit because of high diffusion rate inside silicon, and radioactive elements such as uranium (U) and thorium (Th) will cause incorrect operations, and alkaline metals and alkaline-earth metals may cause degradation of the device properties.

Furthermore, environmental semiconductor materials such as iron silicide (FeSi ₂) have been proposed in order to build new technologies dealing with future problems in environment and depletion of resources. Iron silicide as an environmental semiconductor material requires as few impurities as typical compound semiconductors such as gallium arsenide (GaAs), cadmium telluride (CdTe) and so on. The upper limit of impurity content in iron silicide is less than in substances of semiconductor devices of VLSI and ULSI. Small amounts of impurities form impurity level that causes degradation of the semiconductor properties. Thus, iron as a semiconductor material needs high purity.

While levels in purity of the crude iron traded globally and presently are about 98% to 99.8%, such crude iron contains various impurities, for example, transition metals such as nickel (Ni), cobalt (Co), and chromium (Cr), gas elements such as oxygen (O), nitrogen (N), and sulfur (S). Therefore, in order to use iron as materials of semiconductor devices and environment semiconductors, it is necessary to remove these impurities from the crude iron and achieve higher purification. Moreover, iron appears favorable as materials of devices such as magnetic recording mediums and magnetic recording heads, as well as semiconductor devices, because of bearing properties typical of ferromagnetic metals. A higher purification of iron is indispensable to the use of iron as materials of these devices.

Various methods of removing impurities from crude iron, for example, wet processing such as solvent extraction, ion exchange, and electrolytic refining for separation of metallic elements, and dryness hydrogen gas (H ₂) processing for removal of gas elements such as oxygen and nitrogen, and floating zone melting refining method, have been studied.

SUMMARY OF THE INVENTION

However, there is a problem with the solvent extraction. It is difficult to control extraction and reverse extraction and to refine iron surely in industrial processes. And, although nearly all of metal impurities can be separated by the ion exchange, copper contents before and after refining by the ion exchange may not change, that is, it is difficult to remove copper, which is a problem with the ion exchange. In addition, there are problems with the electrolytic refining that pH control of electrolytic solutions is required, and it is difficult to remove nickel and copper. The floating zone melting refining method is intended to further raise the purity levels of metals purified to some extent, and in practice, it is reported that the floating zone melting refining method has large effects on purification (Yukio Ishikawa, Koji Mimura, Minoru Isshiki, Bulletin of the Institute for Advanced Materials Processing Tohoku University 51 (1995), pp.10-18). However, it is difficult to apply the floating zone melting refining method to large scale and the method may not always produce high purity metals surely, that is, it is difficult to produce a large amount of high purity iron at a low price with the floating zone melting refining method. Therefore, a need exists for methods of purifying iron easily, surely, and highly, and particularly for the development of methods of removing copper.

The present invention has been achieved in view of the above problems. It is an object of the invention to provide high purity iron and high purity iron targets in which contents of impurities such as copper are reduced.

It is another object of the invention to provide a method of easily and surely manufacturing high purity iron.

The invention provides high purity iron with 99.99 mass % or more in purity wherein a copper impurity content is 50 mass ppb or less.

In another aspect, the invention provides high purity iron wherein a residual resistivity ratio thereof is 3000 or more, and a copper impurity content is 50 mass ppb or less.

A method of manufacturing high purity iron according to the invention comprises the steps of; converting trivalent iron ions and impurity divalent copper ions contained in an aqueous solution of iron chloride respectively to divalent iron ions and monovalent copper ions; adjusting a concentration of hydrochloric acid in a range of 0.1 kmol/m ³to 6 kmol/m³; and separating the monovalent copper ions from the aqueous solution of iron chloride by using the ion exchange resins.

In another aspect, a method of manufacturing high purity iron according to the invention comprises: converting trivalent iron ions in an aqueous solution of iron chloride to divalent iron ions; adjusting a concentration of hydrochloric acid in a range of 0.1 kmol/m ³to 6 kmol/m³; and separating impurities of at least one selected from the group consisting of zinc, gallium, niobium, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rbenium, osmium, iridium, platinum, gold, mercury, thallium, lead, and bismuth from the aqueous solution of iron chloride by using the anion exchange resins.

The invention provides high purity iron targets with 99.99 mass % or more in purity wherein a copper impurity content is 50 mass ppb or less.

In another aspect, the invention provides high purity iron targets wherein a residual resistivity ratio is 3000 or more, and a copper impurity content is 50 mass ppb or less.

In the high purity iron and the high purity iron targets according to the invention, a concentration of copper is reduced to 50 mass ppb or less to achieve high purification.

The method of manufacturing the high purity iron according to the invention includes the steps of converting trivalent iron ions and divalent copper ions respectively to divalent iron ions and monovalent copper ions, and adjusting a concentration of hydrochloric acid. These steps allow monovalent copper ions to be absorbed on the anion exchange resins, and divalent iron ions not to be absorbed thereon. Thus the copper can be separated easily and surely from the aqueous solution of iron chloride.

Another method of manufacturing high purity iron according to the invention includes the steps of converting trivalent iron ions in an aqueous solution of iron chloride to divalent iron ions and adjusting a concentration of hydrochloric acid. These steps allow at least one of impurities selected from the group consisting of zinc, gallium, niobium, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, and bismuth to be absorbed on the anion exchange resins, and divalent iron ions not to be absorbed thereon. Thus the impurities can be separated easily and surely from the aqueous solution of iron chloride.

Other and further objects, features and advantages of the invention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a manufacturing process of high purity iron and high purity iron targets according to one embodiment of the invention. [0021]
FIG. 2 is a flow chart illustrating the manufacturing process following FIG. 1. [0022]
FIG. 3 is a diagram explaining one step of the manufacturing process shown in FIG. 1. [0023]
FIG. 4 is a diagram explaining another step of the manufacturing processes shown in FIG. 1. [0024]
FIG. 5 is a graph illustrating changes of the concentrations of metal ions in the effluent of the anion exchange resins. [0025]
FIG. 6 is another graph illustrating changes of the concentrations of metal ions in the effluent of the anion exchange resins.[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. [0027]
In accordance with one embodiment of the invention, high purity iron and high purity iron targets have 99.99 mass % or more in purity, preferably 99.999 mass % or more, or the residual resistivity ratios thereof are 3000 or more and copper impurity content thereof is 50 mass ppb or less. [0028]
The term “purity” (namely, chemical purity) used herein means values obtained by one minus all concentrations of impurities possible to be determined by using present analysis apparatus and methods (Minoru Isshiki, Koji Mimura, Bulletin of the Japan Institute of Metals, 31 (1992), 880-887). For example, the values can be obtained by one minus the concentrations of impurities of 70 or more elements determined by Glow Discharge Mass Spectroscopy. The concentrations of gas elements such as oxygen, nitrogen, and hydrogen, if required, can be determined by appropriate methods such as a non-dispersive infrared absorption method, a thermal conductivity method, and a heat conduction measurement of such gas elements separated with a column after being fused in an inert gas. [0029]
And, residual resistivity ratios provide one index showing purities of highly purified metals, and as shown in the formula I, the residual resistivity ratio is the ratio of resistivity at 298K to resistivity at 4.2K. The formula II shows a relationship between resistivity and resistance (electric resistance). Therefore, the formula I expressing the residual resistivity ratio can be transformed into the formula III, and if volume. changes by temperature are negligible, the formula I can be approximated by the ratio of the resistance at 298K to the resistance at 4.2K. It should be noted that iron is a ferromagnetic metal and factors such as geomagnetism, demagnetization conditions, and magnetic fields by measurement currents can affect the resistance measurements. Thus, it is necessary to apply vertical magnetic field that is preferably about 60 kA/m in measuring the resistance in order to suppress these influences (Seiichi Takagi, Materia Japan, 33 (1994), 6-10).[0030]
RRR=ρ _298K/ρ_4.2K (I)
RRR; residual resistivity ratio [0031]
ρ[0032] _{298 K}; resistivity at 298K (Ωm)
ρ[0033] _4.2K; resistivity at 4.2K (Ωm)
ρ=R×(S/L) (II)
ρ; resistivity (Ωm) [0034]
R; resistance (Ω) [0035]
S; cross-section area perpendicular to the direction of current (m[0036] ²)
L; length (m) [0037] $\begin{matrix} RRR = \frac{R_{298 K} \times \frac{S_{298 K}}{L_{298 K}}}{R_{4.2 K} \times \frac{S_{4.2 K}}{L_{4.2 K}}} \approx \frac{R_{298 K}}{R_{4.2 K}} & (III) \end{matrix}$
RRR; residual resistivity ratio [0038]
R[0039] _298K, S_298K, and L_298K; respectively, resistance, cross-section area, length at 298K
R[0040] _4.2K, S_4.2K, and L_4.2K; respectively resistance, cross-section area, length at 4.2K
The high purity iron and the high purity iron targets may be used as materials of devices, for example, semiconductor devices, magnetic recording mediums, magnetic recording heads, and devices with environmental semiconductors. The term “environmental semiconductor” used herein means a semiconductor substance that exists abundantly on the earth and consists of an eco-friendly material, for example, iron silicide (FeSi[0041] ₂) and calcium silicide (Ca₂Si) (See the website of Society of Kankyo Semiconductors (http://kan.engjm.saitama-u.ac.jp/SKS/index2.html)).
Such high purity iron and such high purity iron targets can be manufactured as follows. [0042]
FIGS. 1 and 2 show the manufacturing process of the high purity iron according to the embodiment. First, the iron containing impurities such as copper is dissolved in a hydrochloric acid solution in order to prepare an aqueous solution of iron chloride (FeCl[0043] ₂or FeCl₃) (Step S101). The concentration of the hydrochloric acid is adjusted in a range of 0.1 kmol/m³to 6 kmol/m³.
And, as shown in FIG. 3, the aqueous solution of iron chloride M is poured into a [0044] container 12 with a metal 11 such as iron. Then, the aqueous solution of iron chloride M is sufficiently contacted with the metal 11 by agitating with a device such as a stirrer 14, while injecting an inert gas 13 such as nitrogen gas (N₂) or argon gas (Ar) into the aqueous solution of iron chloride M (Step S102). Thus, the copper contained in the aqueous solution of iron chloride M will react with the metal 11, for example, as shown in the following chemical formula 1, converting the divalent copper ions to monovalent copper ions or metallic copper. In addition, the iron contained in the aqueous solution of iron chloride M will react with the metal 11, for example, as shown in the following chemical formula 2, converting the trivalent iron ions to divalent iron ions. It should be noted that the reaction of the chemical formula 1 may not completely proceed to the right-hand side and a small amount of the monovalent copper ions may remain in the aqueous solution of iron chloride.
[CuCl₂]⁰+Fe (solid)→[FeCl₂]⁰+Cu (solid) (1)
2[FeCl₆]³⁻+Fe (solid)→3[FeCl₄]²⁻ (2)
Dissolved oxygen can prevent reactions such as the above chemical formulas 1 and 2. Therefore, injecting the [0045] inert gas 13 into the aqueous solution of iron chloride M intends to remove oxygen dissolved in the aqueous solution of iron chloride M, in order to carry out the reactions. The inert gas 13 may be injected with agitating the aqueous solution of iron chloride M containing the metal 11, or before the metal 11 is added into the aqueous solution of iron chloride M.
Preferably, the [0046] metal 11 has large surface area such as powder, which can contact more effectively with the aqueous solution of iron chloride M and react sufficiently with the copper ions and iron ions. Substances other than iron can also be used for the metal 11. It is preferred to use iron for the metal 11 in order to avoid other impurities from contaminating the aqueous solution of iron chloride M as much as possible.
The trivalent iron ions and divalent copper ions in the aqueous solution of iron chloride M may be converted respectively to the divalent iron ions and the monovalent copper ions by contacting with the [0047] metal 11 after adjusting the concentration of hydrochloric acid in the aqueous solution of iron chloride M as described above, or before adjusting the concentration of hydrochloric acid in the aqueous solution of iron chloride.
Then, as shown in FIG. 4, a [0048] column 22 is filled up with the anion exchange resins 21, the aqueous solution of iron chloride M is fed into the column 22 from a storage tank 23, and is contacted with the anion exchange resins 21 sufficiently (Step S103). The flow rate of the aqueous solution of iron chloride M is determined effectively to contact the aqueous solution of iron chloride M with the anion exchange resins 21 sufficiently, and is preferably 1 bed volume(s)/hour. The divalent copper ions converted to the monovalent copper ions will be absorbed on the anion exchange resins 21, and the trivalent iron ions converted to divalent iron ions will be eluted from the column 22 without being absorbed on the anion exchange resins 21. FIG. 5 shows changes of the concentrations of metal ions in the effluent (elution curve). In FIG. 5, the abscissa represents the effluent volumes and the ordinate represents the concentrations standardized by the maximum concentrations of the metal ions. As shown in FIG. 5, there is no range to which the peaks of the elution curves of the divalent iron ions and the monovalent copper ions overlap, which shows that the copper can be completely separated from the aqueous solution of iron chloride. That is, the aqueous solution of iron chloride M from which copper is separated is collected into a recovery tank 24.
In addition, when at least one of impurities selected from the group consisting of zinc (Zn), gallium (Ga), niobium (Nb), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), antimony (Sb), tellurium (Te), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), thallium (Tl), lead (Pb), and bismuth (Bi) is contained in the aqueous solution of iron chloride M, as well as zinc and tin as shown in FIG. 5, in the Step S[0049] 103, these impurities can be absorbed on the anion exchange resins 21 with monovalent copper ions and can be also separated from the aqueous solution of iron chloride M.
When at least one of impurities selected from the group consisting of lithium (Li), beryllium (Be), sodium (Na), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), potassium (K), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), rubidium (Rb), strontium (Sr), yttrium (Y), zirconium (Zr), cesium (Cs), barium (Ba), lanthanoids, hafnium (Hf), francium (Fr), radium (Ra), and actinoids, is contained in the aqueous solution of iron chloride M after separating the copper, an oxidizing agent such as a hydrogen peroxide solution as may be added to the aqueous solution of iron chloride M to convert the divalent iron ions to trivalent iron ions (Step S[0050] 104). Or without such oxidation reaction the iron may be oxidized if the aqueous solution of iron chloride M is allowed to stand.
Then, the concentration of hydrochloric acid of aqueous solution of iron chloride M is adjusted in a range of 2 kmol/m[0051] ³to 11 kmol/m³and, as shown in FIG. 4, the aqueous solution of iron chloride M is sufficiently contacted with the anion exchange resins 21 (Step S105). Thus, the trivalent iron ions will be absorbed on the anion exchange resins 21, and the impurities such as lithium, beryllium, sodium, magnesium, aluminum, silicon, phosphorus, potassium, calcium, scandium, titanium, vanadium, chromium, manganese, cobalt, nickel, rubidium, strontium, yttrium, zirconium, cesium, barium, lanthanoids, hafnium, francium, radium, and actinoids will not be absorbed on the anion exchange resins 21 and be eluted.
FIG. 6 shows changes of the concentrations of metal ions in the effluent (elution curve). The changes of the concentrations of some typical impurities, that is, aluminum, silicon, phosphorus, titanium, manganese, cobalt, and chromium, are shown in the FIG. 6 for comparison with the iron. In FIG. 6, the abscissa and the ordinate represent respectively the equivalents in the FIG. 5. As shown in FIG. 6, there is no range to which the peaks of the elution curves of the trivalent iron ions and these impurities overlap, which shows that these impurities can be completely separated from the aqueous solution of iron chloride. [0052]
Moreover, when at least one of impurities selected from the group consisting of zinc, gallium, niobium, molybdenum (Mo), technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, bismuth and polonium (Po) is contained in the aqueous solution of iron chloride M, these impurities can be absorbed on the anion exchange resins [0053] 21 as well as the iron in the Step S105.
In such a case, after absorbing the iron on the anion exchange resins [0054] 21, 0.1 kmol/m³to 2 kmol/m³of hydrochloric acid solution is passed through the column 22 to elute the iron from the column filled up with the anion exchange resins 21 and separate the iron from the impurities absorbed on the anion exchange resins 21 such as zinc, gallium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, bismuth and polonium (Step S106). Changes of the concentrations of metal ions in the effluent in the Step S106 are also shown in the FIG. 6. Especially, in the FIG. 6, the changes of the concentrations of some typical impurities, that is, molybdenum and zinc are shown for comparison with the iron. As shown in FIG. 6, there is no range to which the peaks of the elution curves of the trivalent iron ions and these impurities overlap, which shows that these impurities can be completely separated from the iron.
It should be noted that molybdenum and polonium will be mainly separated from the iron in the Step S[0055] 106, because zinc, gallium, niobium, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, and bismuth have already been separated from the aqueous solution of iron chloride M with the copper in the Step S103.
After eluting the iron, the obtained aqueous solution of iron chloride M is evaporated to dryness and is oxidized in order to obtain iron oxide (Step S[0056] 107). Then, the obtained iron oxide is heated from 500 K to less than 1800 K in a hydrogen atmosphere (Step S108). It is preferred to heat to 1000 k or above for rapid reduction. Thus, the iron oxide will react as shown in the following chemical formula 3 to obtain iron.
3Fe₂O₃+H₂=2Fe₃O₄+H₂O
Fe₃O₄+H₂=3FeO+H₂O
Fe₃O₄+4H₂=3Fe+4H₂O
FeO+H₂=F+H₂O (3)
After reacting of the iron oxide, the obtained iron is molten with plasma arc using a plasma generation gas containing active hydrogen, in order to remove at least one of impurities selected from the group consisting of oxygen, nitrogen, carbon (C), sulfur, halogen, alkaline metals, and alkaline-earth metals (Step S[0057] 109). Thus, the steps described above can provide the high purity iron and the high purity iron targets according to the embodiment.
As described above, in the high purity iron and the high purity iron targets according to the invention, the contents of copper may be reduced to 50 mass ppb or less. Therefore, the high purity iron or the iron targets according to the invention may not be responsible for short circuit of devices such as semiconductor devices and can be applied to the semiconductor devices for the enhancement of properties. Moreover, the high purity iron and the high purity iron targets can be used for devices such as magnetic recording mediums and magnetic recording heads for the enhancement of properties. In addition, the high purity iron and the high purity iron targets used as materials of compound semiconductors such as iron silicide may not cause unwanted impurity level formed by small amounts of impurities responsible for property degradation and will provide good semiconductor properties. [0058]
Moreover, according to the method of manufacturing the high purity iron, the trivalent iron ions and the divalent copper ions are converted respectively to the divalent iron ions and the monovalent copper ions, the concentration of the hydrochloric acid is adjusted from 0.1 kmol/m[0059] ³to 6 kmol/m³, and the aqueous solution of iron chloride is contacted with the anion exchange resins. Therefore, the copper may be separated from the aqueous solution of iron chloride easily and the high purity iron and the high purity iron targets with low concentrations of copper can be obtained easily and surely.
Furthermore, converting the trivalent iron ions to the divalent iron ions allows at least one of impurities selected from the group consisting of zinc, gallium, niobium, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, and bismuth to be separated easily from the aqueous solution of iron chloride M as well as the copper. Thus, the high purity iron and the high purity iron targets can be obtained easily and surely. [0060]
The invention will be further described in detail by reference to FIGS. [0061] 1 to 6. In the following examples, the same reference numbers and signs will be used for equivalents of the substances in the above embodiments.

EXAMPLE

First, in order to prepare an aqueous solution of iron chloride (FeCl[0062] ₃) M, scrap iron used as a material was dissolved into 2 kmol/m³of hydrochloric acid solution until the concentration of the iron reached 0.179 kmol/m³(10 g/dm³) (Step S101). Then, as shown in FIG. 3, powdered iron 11 was added to the aqueous solution of iron chloride M, and inert gas was injected into the solution M with agitating to convert divalent copper ions and trivalent iron ions respectively to monovalent copper ions and divalent iron ions (Step S102). Then, as shown in FIG. 4, the aqueous solution of iron chloride M was contacted with the anion exchange resins 21 to absorb the monovalent copper ions and separate the copper ions from the aqueous solution of iron chloride M (Step S103).
After separating the copper, a hydrogen peroxide solution was added to the aqueous solution of iron chloride M to convert the divalent iron ions to trivalent iron ions (Step S[0063] 104). Then, the concentration of hydrochloric acid of the aqueous solution of iron chloride M was adjusted to 5 kmol/m³, and the aqueous solution of iron chloride M was contacted with the anion exchange resins 21 to absorb the trivalent iron ions and separate impurities such as lithium (Step S105). Then, the iron was eluted from the column filled up with the anion exchange resins 21 with 1 kmol/m³of hydrochloric acid solution to separate impurities such as molybdenum (Step S106).
After eluting the iron from the column filled up with the anion exchange resins [0064] 21, the obtained aqueous solution of iron chloride M was evaporated to dryness and oxidized to obtain iron oxide (Step S107). And, the obtained iron oxide was heated to 1073 K (800° C.) in a hydrogen atmosphere to obtain iron (Step S108). The iron obtained in the Step S108 was molten with plasma arc containing active hydrogen to remove impurities such as oxygen (Step S109) to obtain high purity iron.

Quantities of purities contained in the obtained high purity iron were determined by Glow Discharge Mass Spectroscopy, and a value of purity and residual resistivity ratio was calculated. Table 1 shows the results. As shown in Table 1, the copper concentration was as very low as 50 mass ppb or less, and the value of purity was as very high as 99.9997%, and the residual resistivity ratio was as very high as 5500.

TABLE 1


	Concentration		Concentration		Concentration
Element	(mass ppm)	Element	(mass ppm)	Element	(mass ppm)

Concentration	Al	0.380	Co	0.035	Rh	<0.010
of impurities	As	<0.050	Ga	0.050	Ru	<0.010
	B	<0.010	Hf	<0.010	Sb	<0.020
	Ba	<0.010	In	<0.020	Si	0.060
	Be	<0.010	K	0.015	Sn	0.270
	Bi	0.012	Li	<0.010	Th	0.001
	Ca	0.110	Mg	<0.010	Ti	0.150
	Cd	0.120	Mn	<0.050	U	0.002
	Cl	<0.050	Mo	<0.050	V	1.000
	Cr	<0.020	Na	<0.010	Zn	0.050
	Cu	<0.020	Ni	<0.020	Zr	0.016
	F	<0.050	P	0.740	Pb	0.014

Purity	99.9997%
Residual	5500
resistivity ratio

It is found that due to converting trivalent iron ions and divalent copper ions respectively to divalent iron ions and monovalent copper ions and adjusting the concentration of hydrochloric acid from 0.1 kmol/m[0066] ³to 6 kmol/m³, copper could be easily separated from the aqueous solution of iron chloride, and the high purity iron having the concentration of copper reduced to 50 mass ppb or less could be obtained easily.
As described above, the invention is explained by the embodiments and examples. These embodiments and examples are not meant to limit the scope of the invention and variations within the concepts of the invention are apparent. For example, as described in the embodiments and examples, after converting the trivalent iron ions and the divalent copper ions respectively to the divalent iron ions and the monovalent copper ions, adjusting the concentrations of hydrochloric acid and the aqueous solution of iron chloride, and contacting the aqueous solution of iron chloride with the anion exchange resins, the copper may be absorbed on the anion exchange resins and be separated from the iron. After adjusting the valencies of iron and copper and absorbing iron and copper on the anion exchange resins, iron may be eluted with 0.1 kmol/m[0067] ³to 6 kmol/m³of hydrochloric acid solution in order to separate the copper from the aqueous solution of iron chloride.
Moreover, impurities other than copper may be removed by the methods as described in the above embodiments and examples, or by other conventional methods. Furthermore, the copper may be separated as well as the impurities such as zinc from the aqueous solution of iron chloride after converting the trivalent iron ions to divalent iron ions as described above, or may be separated by other methods. [0068]
As described above, in the high purity iron and the high purity iron targets according to the invention, the contents of copper which causes influences such as a short circuit may be reduced to 50 mass ppb or less. Therefore, the high purity iron or the high purity iron targets according to the invention applied to semiconductor devices may not be responsible for short circuit of devices such as semiconductor devices and can provide the enhancement of properties of the semiconductor devices. Moreover, the high purity iron and the high purity iron targets can use for devices such as magnetic recording mediums and magnetic recording heads for the enhancement of properties. In addition, the high purity iron and the high purity iron targets used as materials of compound semiconductors such as iron silicide may not cause unwanted impurity level formed by small amounts of impurities responsible for property degradation and will provide good semiconductor properties. [0069]
Moreover, according to the method of manufacturing the high purity iron of the invention, the trivalent iron ions and the divalent copper ions are converted respectively to the divalent iron ions and the monovalent copper ions and the concentration of the hydrochloric acid is adjusted from 0.1 kmol/m[0070] ³to 6 kmol/m³. Therefore, the copper may be absorbed on the anion exchange resins and be separated from the aqueous solution of iron chloride easily. In addition, the high purity iron and the high purity iron targets with low concentration of copper can be obtained easily and surely.
Furthermore, in another aspect, according to the method of manufacturing the high purity iron of the invention, the trivalent iron ions are converted to the divalent iron ions and the concentration of the hydrochloric acid is adjusted from 0.1 kmol/m[0071] ³to 6 kmol/m³. Therefore, the impurities such as zinc may be absorbed on the anion exchange resins and be separated from the aqueous solution of iron chloride easily. In addition, the high purity iron and the high purity iron targets can be obtained easily and surely.
Obviously many modifications and variation of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. [0072]

Claims

What is claimed is:

1. High purity iron with 99.99 mass % or more in purity wherein a copper impurity content is 50 mass ppb or less.

2. High purity iron wherein a residual resistivity ratio thereof is 3000 or more, and a copper impurity content is 50 mass ppb or less.

3. A method of manufacturing high purity iron comprising the steps of;

converting trivalent iron ions and impurity divalent copper ions contained in an aqueous solution of iron chloride respectively to divalent iron ions and monovalent copper ions;

adjusting a concentration of hydrochloric acid in a range of 0.1 kmol/m³to 6 kmol/m³; and

separating the monovalent copper ions from the aqueous solution of iron chloride by using ion exchange resins.

4. A method of manufacturing high purity iron according to claim 3, comprising the steps of;

adjusting a concentration of hydrochloric acid in the aqueous solution of iron chloride in a range of 0.1 kmol/m³to 6 kmol/m³; and

contacting the aqueous solution of iron chloride with anion exchange resins to separate the monovalent copper ions from the aqueous solution of iron chloride after the steps of converting the trivalent iron ions and the divalent copper ions respectively to the divalent iron ions and the monovalent copper ions and adjusting the concentration of hydrochloric acid.

5. A method of manufacturing high purity iron according to claim 3, wherein the converting step comprises the steps of;

injecting an inert gas into the aqueous solution of iron chloride; and

converting trivalent iron ions and divalent copper ions contained in an aqueous solution of iron chloride respectively to divalent iron ions and monovalent copper ions by contacting the aqueous solution of iron chloride with iron.

6. A method of manufacturing high purity iron according to claim 3, wherein at least one of impurities selected from the group consisting of zinc, gallium, niobium, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, and bismuth is separated from the aqueous solution of iron chloride in the step of separating the copper.

7. A method of manufacturing high purity iron according to claim 3, further comprising the steps of;

adjusting the concentration of hydrochloric acid in the aqueous solution of iron chloride in a range of 2 kmol/m³to 11 kmol/m³;

contacting the aqueous solution of iron chloride with the anion exchange resins to absorb the iron of trivalent ions thereon and separate at least one of impurities selected from the group consisting of lithium, beryllium, sodium, magnesium, aluminum, silicon, phosphorus, potassium, calcium, scandium, titanium, vanadium, chromium, manganese, cobalt, nickel, rubidium, strontium, yttrium, zirconium, cesium, barium, lanthanoids, hafnium, francium, radium and actinoids contained in the aqueous solution of iron chloride, from the aqueous solution of iron chloride; and

eluting the iron from the anion exchange resins with a hydrochloric acid solution.

8. A method of manufacturing high purity iron according to claim 7, wherein a hydrochloric acid solution having a concentration of 0.1 kmol/m³to 2 kmol/m³is used for eluting the iron from the anion exchange resins in order to separate the iron from at least one of impurities selected from the group consisting of zinc, gallium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, bismuth and polonium absorbed on the anion exchange resins.

9. A method of manufacturing high purity iron according to claim 3, further comprising the steps of;

obtaining iron oxide from the aqueous solution of iron chloride which the impurity copper are separated therefrom; and

heating the iron oxide in a hydrogen atmosphere to obtain iron.

10. A method of manufacturing high purity iron according to claim 9, further comprising the step of melting the iron obtained in the heating step with plasma arc using a plasma generation gas containing active hydrogen in order to remove at least one of impurities selected from the group consisting of oxygen, nitrogen, carbon, sulfur, halogen, alkaline metals, and alkaline-earth metals.

11. A method of manufacturing high purity iron comprising the steps of;

converting trivalent iron ions in an aqueous solution of iron chloride to divalent iron ions;

separating at least one of impurities selected from the group consisting of zinc, gallium, niobium, technetium, ruthenium, rhodium, palladium, silver, cadmium, indium, tin, antimony, tellurium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, and bismuth from the aqueous solution of iron chloride by using the anion exchange resins.

12. High purity iron targets with 99.99 mass % or more in purity wherein a copper impurity content is 50 mass ppb or less.

13. High purity iron targets wherein a residual resistivity ratio is 3000 or more, and a copper impurity content is 50 mass ppb or less.