JPH073486A - High-purity cobalt and production of thereof - Google Patents

Abstract

PURPOSE:To develop a technology for production of high-purity cobalt of a level above a 5N level contg. just a min. of impurities, such as nickel, iron, etc., used for a target material, etc. CONSTITUTION:This process for production of the high-purity cobalt consists of stepwise refining of the cobalt by using electrolytic cells 1, 2, 3. An electrolyte is intermittently or continuously passed from the final stage toward a first stage and the electrolyte from the electrolytic cell 1 of the first stage is circulated to the final stage after mainly the nickel is removed therefrom by solvent extraction 4. Crude cobalt metal is used for an anode A1 of the first stage and cathodes C1, C2 obtd. in the previous stages are used for anodes A2, A3 of the respective stages after second and subsequent stages. The electrolyte is intermittently or continuously withdrawn and mainly the iron is removed therefrom by solvent extraction 6 in the final stage. the cathode C3 of the final stage is recovered and the recovered cathode C3 is subjected to vacuum dissolution. Heavy metals and radioactive elements are removed by the electrolysis and the solvent extraction effect and volatile alkaline metals are removed by the vacuum dissolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-purity cobalt and a method for producing the same, and in particular, a cobalt sputtering target material for producing a semiconductor device by combining a multi-step electrolytic refining method and a solvent extraction method. And an electrolytic refining method for producing high-purity cobalt having a purity of 5 N or more. The high-purity cobalt purified according to the present invention is suitable for use as a cobalt / sputtering target material for semiconductor device production, since the amount of metal impurities harmful to semiconductor devices including iron and nickel is reduced to a required amount or less.

[0002]

2. Description of the Related Art Conventionally, silicon has been mainly used as an electrode material in semiconductor devices, but it has been replaced with silicide such as molybdenum and tungsten with the high integration of LSI, and more recently, titanium and cobalt. There is growing interest in the utilization of silicide. In addition, attempts are being made to use cobalt as a wiring material in place of aluminum and aluminum alloys that have been conventionally used. Such cobalt and cobalt silicide electrodes and wirings are typically formed by sputtering a cobalt target in argon together with a silicon target as necessary.

It is important that the semiconductor device member produced after sputtering contains a minimum amount of metal impurities harmful to the semiconductor device in order to ensure reliable semiconductor operation performance. For that purpose, it is essential to ensure the purity of the cobalt target, that is, to increase the purity of the target raw material itself. Impurities harmful to semiconductor devices are mainly (1) alkali metals such as Na, K and Li, (2) radioactive metals such as U and Th, and (3) heavy metals such as Fe and Ni. Alkali metals such as Na, K and Li easily move in the gate insulating film, and M
This causes deterioration of the OS-LSI interface characteristics. Radioactive metals such as U and Th cause a soft error of the device due to the α rays emitted from them. Heavy metals such as Fe and Ni cause a leak phenomenon at the interface joint.

According to current standards, it is required that the alkali metal content is 0.1 ppm or less, the radioactive element content is 0.1 ppb or less, and the heavy metal content is 10 ppm or less.

Commonly available cobalt, so-called crude cobalt agglomerates, contains several ppm to several tens of ppm of iron and several hundreds of p.
It contains pm of nickel and other impurities. As a method for producing high-purity cobalt, low-purity cobalt is electrochemically dissolved, impurities are removed from the cobalt aqueous solution by using an ion exchange method, the solution is concentrated, and further high-purity electrolytic cobalt is obtained by electrowinning. The method for producing the compound is described in, for example, Bourahla, Acad. Sci, Ser,
C. 278 (10) 679-680 (1974). However, this method has a problem that it is a batch method, and therefore it is suitable for small-scale production, has many steps, and is expensive.

The electrowinning is a method in which a solution containing a target metal is used as an electrolytic solution and the electrolytic solution is electrolyzed using an insoluble anode to deposit the target metal on the cathode. Therefore, for example, in the electrowinning method of cobalt from an aqueous solution of cobalt sulfate, an overvoltage is required for oxygen gas generation in the anode, and an electrolytic refining method in which the target metal is electrolyzed as a soluble anode to deposit the target metal on the cathode. In comparison, in addition to the above problems, there were various problems such that the cell voltage became higher by about 2 V, and the cobalt concentration and pH had to be adjusted.

On the other hand, although the electrolytic refining method can be considered, it has been considered difficult to achieve high purification by the electrolytic refining method because the standard electrode potentials of impurities nickel and iron and cobalt are very close to each other. .

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide 5N (99.999%, hereinafter simply referred to as 5N) containing a minimum amount of impurities such as nickel and iron suitable for a target application.
It is to develop a high-purity cobalt manufacturing technology of a level higher than the above level.

[0009]

Means for Solving the Problems The inventors of the present invention used a plurality of electrolytic cells for electrolytically depositing purified cobalt metal from the anode to the cathode using an aqueous solution of cobalt sulfate as an electrolytic solution. Based on stepwise purification, the anode of each stage uses the cathode obtained in the preceding stage, and the electrolyte is intermittently or continuously flowed from the final stage to the first stage, The electrolytic solution from the first-stage electrolytic cell was circulated to the final stage after removing nickel mainly by solvent extraction, and the electrolytic solution was recovered from the final stage by removing mainly iron by solvent extraction in the final stage. It has been found that by vacuum melting the cathode, it is possible to easily produce high-purity cobalt at a level of 5N level or higher, which contains impurities such as nickel and iron at a minimum.

Based on this knowledge, the present invention provides (1) a plurality of electrolytic cells for electrodepositing purified cobalt metal from an anode to a cathode using an aqueous solution of cobalt sulfate as an electrolytic solution, from a first stage to a final stage. In the method for producing high-purity cobalt by stepwise purification, the electrolytic solution is made to flow intermittently or continuously from the final stage to the first stage, and the electrolytic solution from the electrolytic bath at the first stage is mainly extracted by nickel extraction. To the final stage after the removal of hydrogen, the anode of the first stage uses crude cobalt metal and the anode of each stage after the second stage uses the cathode obtained in the preceding stage, and in the final stage (2) A method for producing high-purity cobalt, characterized in that the electrolytic solution is extracted intermittently or continuously, iron is mainly removed by solvent extraction, and the final stage cathode is recovered. A method for producing high-purity cobalt by stepwise refining cobalt by using a plurality of electrolytic cells for electrodepositing purified cobalt metal from an anode to a cathode using an aqueous solution of lithium as an electrolytic solution from the first stage to the final stage. Run from the last stage to the first stage intermittently or continuously,
The electrolytic solution from the first-stage electrolytic cell is circulated to the final stage after removing nickel mainly by solvent extraction, the crude cobalt metal is used as the first-stage anode, and the anode of each stage after the second stage is Using the cathode obtained in the previous stage, and intermittently or continuously withdrawing the electrolyte in the final stage to remove mainly iron by solvent extraction, recovering the final stage cathode, and recovering the recovered cathode. A method for producing high-purity cobalt characterized by vacuum melting, and (3) an alkali metal content of 0.1 ppm or less, a radioactive element content of 0.1 ppb or less, and a heavy metal content of 1
High-purity cobalt characterized by being 0 ppm or less,
Is provided.

[0011]

Function: The electrolytic solution is intermittently or continuously flowed from the final stage to the first stage, and the electrodeposited cobalt is used as the anode of the electrolytic cell having a low impurity concentration in the electrolytic solution of the next stage depending on the purity. The electrolytic solution from the first-stage electrolytic cell is circulated to the final stage after removing nickel mainly by solvent extraction, and in the final stage the electrolytic solution is mainly solvent-extracting iron to remove heavy metals by electrolytic action and solvent extraction action. And radioactive elements are removed, and the volatile alkali metal is removed by vacuum melting the recovered cathode in the final stage.

FIG. 1 shows a method for producing high-purity cobalt by stepwise refining cobalt by using three-stage electrolytic cells 1, 2, and 3 in which purified cobalt metal is electrodeposited from an anode to a cathode using an aqueous solution of cobalt sulfate as an electrolytic solution. 2 is a flowchart showing The material of the electrolytic cell is preferably vinyl chloride, polypropylene, polyethylene or the like, which hardly elutes impurities. The electrolytic solution is intermittently or continuously flowed from the final stage, the third stage, to the first stage. Therefore, the concentration of impurities in the electrolytic solution increases as it goes downstream. The electrolytic solution containing a large amount of impurities from the first-stage electrolytic cell is circulated to the final stage after nickel is removed mainly by solvent extraction in the solvent extraction stage 4 after supplementing cobalt as necessary. In the first-stage electrolytic cell 1, electrolytic refining is carried out between a cathode C1 having a crude cobalt ingot having a purity of about 3N charged in an anode box as an anode A1 and cobalt, titanium or the like as a seed plate. When cobalt is used as the seed plate, a cobalt plate having a predetermined purity manufactured in advance by this method or the like may be used (the same applies hereinafter). Cobalt is cathode C
Electrodeposit on 1. In the second-stage electrolytic cell 2, the electrodeposited cathode C1 is used as the anode A2, and electrodeposition is similarly performed on the cathode C2. In the third-stage electrolytic cell 3, the second-stage electrodeposited cathode C2 is used as the anode A3 to perform electrodeposition on the cathode C3. In the third stage, the diaphragm 5 is used to partition the electrolytic cell into anolyte and catholyte.
And the cathode C3 are arranged respectively. The electrolytic solution from anolyte is subjected to solvent extraction in the solvent extraction stage 6 to remove mainly iron, and then circulated to catholyte. Then, the final electrodeposition cathode C3 is recovered.

The electrolytic solution used in the present invention is an aqueous solution of cobalt sulfate acidified with sulfuric acid. The optimum cobalt concentration in the electrolytic solution is generally 40 to 140 g / l, and more preferably 70 to 120 g / l. If it is less than 40 g / l, the amount of hydrogen generated is large, so that the current efficiency is very poor and the impurity concentration in the electrodeposited cobalt is also increased, which is not preferable. When it exceeds 140 g / l, cobalt sulfate is precipitated and adversely affects the electrodeposition state, which is not preferable.

The optimum pH range of the electrolytic solution is generally 0.5.
˜3, and more preferably 1.5 to 2.5. p
If it is less than H0.5, the amount of hydrogen generated is large and the current efficiency is greatly reduced, which is not preferable. Above pH 3,
The content of impurities, especially nickel, in the electrodeposited cobalt is rapidly increased, which is not preferable.

The range of the optimum cathode current density is 0.001.
Is about 1 A / cm ² . If it is less than 0.001 A / cm ² , productivity is lowered and it is not efficient. On the other hand, 1A / c
When it exceeds m ² , the impurity concentration in the electrodeposited cobalt increases and the current efficiency also decreases, which is not preferable.

The electrolysis temperature is preferably in the range of 10 to 65 ° C, more preferably 35 to 55 ° C. If it is lower than 10 ° C, the current efficiency is lowered, which is not preferable. If it exceeds 65 ° C., the amount of evaporation of the electrolytic solution increases, the cobalt concentration in the electrolytic solution fluctuates, and cobalt sulfate precipitates, which is not preferable.

It was found that the impurity concentration in the electrolytic solution used under the above electrolysis conditions had an unexpectedly strong effect on the content of impurities in the electrodeposited cobalt. FIG. 2 is a graph showing the relationship between the average nickel concentration in the electrolytic solution and the nickel concentration in the electrodeposited cobalt. The relational expression between the average nickel concentration in the liquid (the average concentration is the average of the concentrations at the start and end of electrolysis) and the nickel content in the electrodeposited cobalt was calculated to be Y = 0.78X. It turned out that From this, in order to achieve 5N or more, the nickel content in the electrodeposited cobalt must be less than 10 ppm, and in consideration of safety, it should be 1 ppm or less. In this case, the average concentration of nickel in the electrolytic solution is 1.3 mg / It can be seen that it must be 1 or less.

In the solvent extraction stage 4, a mixed system of alkyl phosphoric acid and a non-chelate type alkyl oxime is optimal as a solvent for preferentially extracting impurities containing nickel as a main component with respect to cobalt. As alkyl phosphoric acid, D2
EHPA etc. can be mentioned. Examples of non-chelating alkyl oximes include 2 ethylhexanal oxime (EHO) and 3,5,5-trimethylhexanal oxime (TMHO). As the diluent, normal paraffin, xylene or the like can be used. When only the extractant and the diluent are used, problems such as phase separation of the organic phase, precipitation of an organic metal salt, formation of an emulsion, and increase in viscosity may occur during extraction and back extraction.
In such a case, the above problems may be solved by adding an adjusting agent. A typical regulator is tridecanol. After this solvent extraction operation, the oil in the liquid is removed by using activated carbon or the like and used as an electrolytic solution.

The usable composition range of the extractant for preferentially extracting nickel-based impurities from cobalt is as follows: Alkyl phosphoric acid: 0.2 to 2 mol / l Alkyl oxime: 0 0.5 to 4 mol / l Regulator: 0.5 to 4% by volume Diluent: balance And, in order to reduce Ni concentration in the electrolytic solution by extracting Ni from the electrolytic solution containing Ni, a known method is used. The pH of the electrolyte, the O / A ratio, the number of extraction stages, etc. may be determined. For example, in the case of an electrolyte solution having a Ni concentration of 80 mg / l, pH = 2,
If O / A = 2 and the number of extraction stages is 6, the Ni concentration can be 0.1 mg / l. For the back extraction of Ni, for example, sulfuric acid may be used.

In the solvent extraction stage 6, iron is mainly removed. Since iron in the raw material migrates as it is and is electrodeposited, in the present invention, in order to mainly remove iron in the final stage, the electrolyte solution of anolyte is extracted and solvent extraction is performed using an extractant such as alkylphosphoric acid. If necessary, the oil is removed with activated carbon or the like and then circulated through the catholyte. As alkylphosphoric acid, D2EHPA, PC88
A is a typical example.

The usable composition range of the extractant for preferentially extracting impurities mainly composed of iron with respect to cobalt is as follows: Alkyl phosphoric acid: 0.2 to 2 mol / l Modifier: 0 0.5 to 4% by volume Diluent: balance And, in order to extract Fe from the electrolytic solution containing Fe and reduce the Fe concentration in the electrolytic solution, the pH of the electrolytic solution, the O / A ratio, It suffices to determine the number of extraction stages. For example, in the case of an electrolyte solution having a Fe concentration of 0.04 mg / l, pH =
2, O / A = 1, and if the number of extraction stages is 1, Fe
The concentration can be 0.01 mg / l or less. For the back extraction of Fe, for example, sulfuric acid, hydrochloric acid, oxalic acid or the like may be used.

The Ni impurity concentration in the first-stage electrolytic cell is, for example, about 40 to 50 mg / l on average, and in this case, the Ni content of the electrodeposited cobalt is about 30 to 40 ppm. The Ni impurity concentration in the second-stage electrolytic cell is, for example, about 4 to 5 mg / l on average, and in this case, the Ni content of the electrodeposited cobalt is about 3 to 4 pp.
m. The Ni impurity concentration in the third-stage electrolytic cell is, for example, about 0.5 to 1 mg / l on average, and in this case, the Ni content of the electrodeposited cobalt recovered is about 1 ppm or less. In addition,
In this operation, the liquid in each electrolytic cell may be continuously flowed, but in consideration of the necessity of controlling the flow rate of the electrolytic solution and the like, when the production amount is small, the batch type (intermittent) operation is performed. Is convenient.

In the electrodeposited cobalt produced under the above electrolysis conditions, impurities, particularly radioactive elements, are reduced to 0.1 ppb or less, and nickel and iron contents are reduced to 10 ppm or less, particularly 0.5 ppm or less.

The recovered electrodeposition cathode C3 is melted by a vacuum melting method such as electron beam melting, and volatile elements such as Na and K contained therein are removed. Electron beam melting is a method in which an electrode (here, electrodeposited Co) is first prepared and then remelted to obtain a high-purity ingot. During melting of the electrode at high temperature, volatile components evaporate. For example, electron beam melting is performed under the following conditions: Current: 0.7 A Voltage: 20 V Vacuum degree: 10 ⁻⁵ mmHg Melting amount: 5 kg Time: 2 hr

[0025]

EXAMPLES Examples of the present invention will be presented below.

(Embodiment 1) The number of stages is 2 and the flow rate of the electrolyte is 9
An example of the case where the batch method is performed with 0 liter is shown. Crude cobalt agglomerates having the purities shown in Table 1 were charged into the anode box in the first-stage electrolytic cell. 2m thick as cathode seed plate
A cobalt plate of m × width 200 mm × length 300 mm was used. The average Ni concentration in the first-stage electrolytic cell was 15 mg / l. The Co concentration in the electrolytic solution was about 100 g / l. The electrolysis was carried out at a temperature of about 50 ° C., a pH of 2 and a cathode current density of 0.02 A / cm ² . The electrodeposited cobalt cathode thus obtained was charged into the anolyte of the second-stage electrolytic cell partitioned into anolyte and catholyte by a diaphragm. As the cathode of the catholyte, the thickness of the cathode seed plate is 2 mm × width 200 mm × length 3 as in the first stage.
A 00 mm cobalt plate was used. The electrolysis conditions in the second-stage electrolytic cell were the same as those in the first stage. After the electrolysis from the first-stage electrolyzer, D2EHPA was 0.5 mol / l and EHO was 2 mol.
Solvent extraction (p / mol), tridecanol 2 vol% and the rest normal n-paraffin
H = 2, O / A = 2, number of extraction stages = 6)
After removal, the oil was removed with activated carbon and used as the second-stage electrolyte. In the second-stage electrolytic cell, the electrolytic solution was continuously extracted from the anolyte and D2EHPA was added at 0.5 mol / min.
l, solvent extraction (pH = 2, pH = 2, tridecanol 2 vol% and the rest normal n-paraffin)
O / A = 1, the number of extraction stages = 1), after mainly removing Fe (Fe <0.01 mg / l), the oil was removed with activated carbon, and then the mixture was circulated through catholyte. The Ni concentration in the second-stage electrolytic cell was 0.64 mg / l on average, and the Fe concentration was 0.01 mg / l on average.
It was less than 1. The amount of Co electrodeposited was 8.7 kg. Table 1 shows the impurity content of electrodeposited cobalt in the second stage.
Shown in. Table 1 also shows the content of impurities after the electron beam melting of the electrodeposited cathode recovered from the second-stage electrolytic cell.

[0027]

[Table 1]

(Embodiment 2) The number of stages is 3 and the flow rate of the electrolyte is 9
An example of the case where the batch method is performed with 0 liter is shown. Example 1
A crude cobalt ingot of the same purity as was charged into the anode box in the first stage electrolyzer. As the cathode seed plate, a cobalt plate having a thickness of 2 mm, a width of 200 mm and a length of 300 mm was used. The Ni concentration in the first-stage electrolytic cell was 43 mg / l on average. The Co concentration in the electrolytic solution was about 100 g / l. The electrolysis was carried out at a temperature of about 50 ° C., a pH of 2 and a cathode current density of 0.02 A / cm ² . The electrodeposited cathode obtained in the first-stage electrolyzer was used as the anode in the second-stage electrolyzer, and a cobalt seed plate was used to make the first electrode.
Further electrolysis was carried out in the second-stage electrolyzer under the same electrolysis conditions as the stage.
The Ni concentration in the second-stage electrolytic cell was 5 mg / l on average. The electrodeposited cobalt cathode thus obtained was charged into the anolyte of the third stage electrolytic cell which was partitioned into anolyte and catholyte by a diaphragm. As the cathode of catholyte, the thickness of the cathode seed plate is 2 mm and the width is 200 mm, as in the first stage.
B. A cobalt plate having a length of 300 mm was used. The electrolysis conditions in the third-stage electrolytic cell were the same as those in the first stage. The average Ni concentration in the third-stage electrolyzer was 0.6 mg / l, and the average Fe concentration was 0.0.
It was less than 1 mg / l. The post-electrolysis solution from the first-stage electrolyzer was 0.5 mol / l for D2EHPA and 2 mo for EHO.
1 / l, 2 vol% tridecanol and the rest normal n-paraffin solvent extraction (pH =
2, O / A = 2, the number of extraction stages = 6), after mainly removing Ni (Ni = 0.1 mg / l), the oil was removed by activated carbon, and the electrolyte was used as the third stage electrolyte. In the third-stage electrolyzer, the electrolyte solution was continuously extracted from the anolyte and the D2E
HPA 0.5 mol / l, tridecanol 2 vol
% And solvent extraction using normal paraffin for the rest (pH = 2, O / A = 1, number of extraction stages = 1 stage)
After mainly removing Fe (Fe <0.01 mg / l),
After removing the oil with activated carbon, it was circulated through catholyte. Table 2 shows the impurity contents of the crude cobalt and the electrodeposited cobalt obtained in the first, second and third stages. The amount of Co electrodeposited was 23.4 kg. Table 2 also shows the content of impurities after electron beam melting of the electrodeposited cathode recovered from the third-stage electrolytic cell.

[0029]

[Table 2]

[0030]

EFFECT OF THE INVENTION High-purity cobalt having a content of 5 N or more, particularly reduced nickel and iron, can be easily obtained by electrolytic refining, and the obtained high-purity cobalt is suitable as a target material for semiconductor device production. is there. Since the electrolyte is recirculated, the amount of waste liquid is small, the current efficiency is high, the throughput can be increased, and the product can be manufactured according to the purity depending on the number of stages.

[Brief description of drawings]

FIG. 1 is a flow chart of the method of the present invention using a three-stage electrolytic cell.

FIG. 2 is a graph showing the relationship between the average nickel impurity concentration in an electrolytic solution and the nickel content in electrodeposited cobalt.

[Explanation of symbols]

 1, 2 and 3 Electrolyzer 4 Solvent extraction stage 5 Diaphragm 6 Solvent extraction stage A1, C1 1st stage electrolytic cell anode, cathode A2, C2 2nd stage electrolytic cell anode, cathode A3, C3 3rd stage electrolytic cell anode, cathode

Claims (3)

[Claims] 1. A method for producing high-purity cobalt by stepwise refining cobalt by using a plurality of electrolytic cells for electrodepositing purified cobalt metal from an anode to a cathode using an aqueous cobalt sulfate solution as an electrolytic solution from the first stage to the final stage. Therefore, the electrolytic solution intermittently or continuously flows from the final stage to the first stage, and the electrolytic solution from the electrolytic bath of the first stage is circulated to the final stage after removing nickel mainly by solvent extraction. The first stage anode uses crude cobalt metal and the second and subsequent stage anodes use the cathode obtained in the previous stage, and the electrolyte is withdrawn intermittently or continuously in the final stage. A method for producing high-purity cobalt, characterized in that mainly iron is removed by solvent extraction and the cathode in the final stage is recovered. 2. A method for producing high-purity cobalt by stepwise refining cobalt by using a plurality of electrolytic cells for electrodepositing purified cobalt metal from an anode to a cathode using an aqueous solution of cobalt sulfate as an electrolytic solution from a first stage to a final stage. Therefore, the electrolytic solution intermittently or continuously flows from the final stage to the first stage, and the electrolytic solution from the electrolytic bath of the first stage is circulated to the final stage after removing nickel mainly by solvent extraction. The first stage anode uses crude cobalt metal and the second and subsequent stage anodes use the cathode obtained in the previous stage, and the electrolyte is withdrawn intermittently or continuously in the final stage. A method for producing high-purity cobalt, characterized in that mainly iron is removed by solvent extraction, the cathode in the final stage is recovered, and the recovered cathode is vacuum-melted. 3. A high-purity cobalt having an alkali metal content of 0.1 ppm or less, a radioactive element content of 0.1 ppb or less, and a heavy metal content of 10 ppm or less.