JPH09227967A - Production of high-purity cobalt and high-purity cobalt sputtering target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process capable of stably and easily producing high- purity cobalt of >=5N level which is suitable for applications, such as targets, and contains alkaline metal elements, radioactive elements, transition metal elements and impurities, such as gaseous components only to the min. possible extent. SOLUTION: An aq. cobalt chloride soln. which contains impurities including at least Fe and/or Ni and has a hydrochloric acid concn. of 7 to 12N is brought into contact with an anion exchange resin to have the cobalt adsorbed thereon and, thereafter, the cobalt is eluted by using the hydrochloric acid of 1 to 6N. After the resulted eluate is evaporated to be dried up or is thickened, the aq. soln. of the high-purity cobalt chloride of pH=0 to 6 is obtd. Further, the org. matter in the soln. is removed by active carbon and the electrodeposited cobalt is obtd. by electrolytic refining using the aq. soln. as an electrolyte. The org. matter in the soln. derived from the anion exchange resin is removed by the active carbon.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing high-purity cobalt and a high-purity cobalt sputtering target produced using the method. The high-purity cobalt produced according to the present invention is an extremely high-purity cobalt containing not only alkali metal elements, radioactive elements, and transition metal elements, but also impurities such as gas components to a minimum. It can be suitably used as a target material for formation and the like.

[0002]

2. Description of the Related Art Conventionally, polysilicon has been mainly used as an electrode material in semiconductor devices, but with the high integration of LSI, its use for silicide such as molybdenum and tungsten has been advanced, and further titanium and cobalt silicide have been used. There is a growing interest in the use of. Further, attempts are being made to use cobalt as a wiring material in place of Al and Al alloys that have been conventionally used. Such electrodes and wirings are typically formed by sputtering a cobalt target in argon.

The semiconductor member formed after sputtering is required to ensure reliable semiconductor operation performance.
It is important that semiconductor devices contain minimal harmful metal impurities. That is, (1) alkali metals such as Na and K, (2) radioactive elements such as U and Th, (3) transition metals such as Fe, Ni, and Cr (4) gas components such as C and O. Alkali metals such as Na and K easily move in the gate insulating film and cause deterioration of MOS-LSI interface characteristics. Then, radioactive elements such as U and Th cause a soft error of the element due to α rays emitted from the element. On the other hand, heavy metals such as Fe, Ni, and Cr also cause troubles at the interface joint. Further, gas components such as C and O are also considered to be unfavorable because they cause the generation of particles during sputtering.

Commonly available cobalt, so-called crude cobalt agglomerates, contains tens of ppm Fe and hundreds of ppm Ni.
Contains as an impurity. As a method for producing high-purity cobalt in the future, first, an electrolytic refining method can be considered.
However, in electrolytic refining, impurities Ni and Fe
Since the standard electrode potentials of cobalt and cobalt are very close to each other, it is difficult to achieve high purification by a simple electrolytic refining method. Therefore, in order to perform high purification by the electrolytic refining method, impurities in the electrolytic solution are removed by a solvent extraction method or the like, that is, when the cobalt concentration is 40 to 60 g / L, for example, Ni concentration should be 1.3 mg / L or less and Fe concentration should be 0.1 mg / L or less.
Requires very tight control. In addition, removal of Ni by solvent extraction requires a special solvent such as an alkyl oxime, and since cobalt is also co-extracted, a complicated operation is required. Furthermore, this extraction solvent is dissolved in the electrolytic solution. However, there is also the problem of becoming a loss.

Therefore, the present inventors have filed Japanese Patent Application No. 7-8083.
In No. 1, a cobalt chloride aqueous solution having a hydrochloric acid concentration of 7 to 12 N is brought into contact with an anion exchange resin to adsorb cobalt, and then the cobalt is eluted using 1 to 6 N hydrochloric acid, and the resulting aqueous solution is evaporated to dryness. After solidification or concentration, pH = 0
A high-purity cobalt chloride aqueous solution of No. 6 was prepared, and a method for producing high-purity cobalt by electrolytically refining the aqueous electrolyte solution was proposed. With these methods, it has become possible to produce high-purity cobalt containing only a minimum amount of impurities such as Ni and Fe.

[0006]

However, in the above invention, there is a case where the deposited cobalt is exfoliated during the electrolytic refining. It was also pointed out that it may be difficult to reduce the content of gas components such as carbon and oxygen (collectively referred to as gasifiable components) in high-purity cobalt.

The object of the present invention is to provide 5N (99.999%, 5N, 99.999%, which is suitable for use as a target, etc., containing not only alkali metal elements, radioactive elements and transition metal elements but also impurities such as gas components to a minimum. It is to develop a method capable of stably and easily producing high-purity cobalt having a level of 5 N or more).

[0008]

Means for Solving the Problems As a result of diligent investigations by the present inventors to stably produce high-purity cobalt,
Anion exchange method-A certain organic substance flows out little by little from the anion exchange resin used in the electrolytic refining method during electrolytic refining and is mixed in the electrolytic solution to be mixed into the target as a gas component such as carbon and oxygen. I found that there is a possibility. Then, by combining activated carbon treatment with anion exchange method-electrolytic refining method, and further performing a vacuum dissolution method as necessary, an alkali metal as an impurity, a radioactive element,
It has been found that high-purity cobalt for sputtering targets, which has reduced not only transition metals but also gas components such as carbon and oxygen, can be stably and easily mass-produced at low cost.

Based on this, in the present invention, (1) an aqueous cobalt chloride solution containing at least Fe and / or Ni as impurities and having a hydrochloric acid concentration of 7 to 12 N was brought into contact with an anion exchange resin to adsorb cobalt. After that, cobalt was eluted with hydrochloric acid of 1 to 6 N, the obtained eluent was evaporated to dryness or concentrated, and then a high-purity cobalt chloride aqueous solution of pH = 0 to 6 was obtained. Removed,
A method for producing high-purity cobalt, characterized in that electrolytic cobalt is obtained by electrolytic refining using the aqueous solution as an electrolytic solution,
(2) A cobalt chloride aqueous solution containing at least Fe and / or Ni, an alkali metal containing Na and K, and a radioactive metal containing U and Th as impurities, and having a hydrochloric acid concentration of 7 to 12 N as an anion exchange resin. Contact and Co and F
After adsorbing e and U, Co was added using 1-6N hydrochloric acid.
And the eluent obtained was evaporated to dryness or concentrated,
A high-purity cobalt chloride aqueous solution having a pH of 0 to 6, further removing organic substances in the liquid derived from the anion exchange resin with activated carbon, and using the aqueous solution as an electrolytic solution to obtain electrodeposited cobalt. (3) In electrolytic refining, the anode and the cathode are separated by a diaphragm or anion exchange membrane, and a high-purity cobalt chloride aqueous solution is at least intermittently added to the cathode side, and at least intermittent anolyte is used. The method for producing high-purity cobalt according to the above (1) or (2), wherein (4) the extracted anolyte has a hydrochloric acid concentration of 7 to 12 N, and then contacted with an anion exchange resin. (2) The method for producing high-purity cobalt as described in (2) above, and (5) the electrodeposited cobalt is further melted under vacuum. Serial (1) to (4) The method of producing high purity cobalt of any one, and (6) above, wherein the treatment with pre-acid activated carbon (1) to (2)
A method for producing the described high-purity cobalt is provided.

The present invention also provides (A) a sodium content of 0.05 ppm or less, a potassium content of 0.05 ppm or less, an iron, nickel or chromium element content of 1 ppm or less, a uranium content of 0.01 ppb or less, and thorium. Content 0.01 ppb or less, carbon content 50 ppm or less, oxygen content 100 ppm or less; high-purity cobalt sputtering target characterized by the balance being cobalt and other unavoidable impurities, and (B) sodium content 0.05 ppm Hereinafter, the content of potassium is 0.05 ppm or less, the content of each element of iron, nickel and chromium is 1 ppm or less, the content of uranium is 0.01 ppb or less, the content of thorium is 0.01 ppb or less, the carbon content is 10 ppm or less, and the oxygen content is 100 ppm. Below; balance is cobalt and other unavoidable impurities Providing a high purity cobalt sputter target, wherein the door.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous solution of cobalt chloride used in the present invention is not particularly limited, but it is usually commercially available, that is, so-called several tens of ppm of Fe and several hundreds of ppm of N.
Crude cobalt containing i as an impurity dissolved in hydrochloric acid is used. On the other hand, the hydrochloric acid used for dissolving the crude cobalt is not particularly limited, but may be industrial low-purity hydrochloric acid. The reason for this is that impurities contained in hydrochloric acid can also be removed by carrying out the present invention.

The apparatus for dissolving cobalt is preferably equipped with a cooling cylinder and a hydrogen chloride gas recovery apparatus in order to effectively utilize hydrochloric acid. The material is preferably quartz, graphite, Teflon, a poly container or the like. The melting temperature is 50 to 1
The temperature is 00 ° C, preferably 80 to 95 ° C. If it is less than 50 ° C, the dissolution rate is slow, and if it exceeds 100 ° C,
Evaporation is severe and the loss of the aqueous solution is large. The final concentration of hydrochloric acid in the cobalt chloride aqueous solution is preferably 7 to 12N. If it is less than 7 N or more than 12 N, cobalt is hardly adsorbed during ion exchange. The cobalt concentration is preferably 10 to 70 g / L. Cobalt concentration is 1
If it is less than 0 g / L, a large amount of hydrochloric acid is required, which causes an increase in cost. On the other hand, when it exceeds 70 g / L, in a solution having a high hydrochloric acid concentration, cobalt chloride is precipitated at room temperature, that is, about 20 ° C., which is not preferable.

In the anion exchange, the cobalt chloride is adsorbed using the above cobalt chloride aqueous solution. In the present invention, the resin used is not particularly limited as long as it is an anion exchange resin, but DOWEX 1 × 8, DO
WEX2 × 8 (Muromachi Chemical Co., Ltd.), Diaion SA
10A etc. are illustrated. Cobalt forms a chloride complex in high-concentration hydrochloric acid, and since it exists as an anion, it is adsorbed on the resin. Fe and U also behave similarly to cobalt and are adsorbed on the anion exchange resin, but N, which is a major impurity,
Since i and alkali metals such as Na and K and Th do not form a chloride complex, they do not adsorb and flow out from the column.

Further, in order to remove impurities remaining in the column, the column is washed with 7 to 12N hydrochloric acid. Outside this range, the bond between cobalt and the anion exchange resin is weak, and cobalt is eluted, which is not preferable.

Next, in order to elute only the cobalt adsorbed on the anion exchange resin, 1 to 6N, preferably 3N to 4N.
N hydrochloric acid is used. When it is less than 1N, Fe and U adsorbed as impurities are also eluted, which is not preferable. 6
If it exceeds N, it becomes difficult to elute cobalt from the resin and the amount of hydrochloric acid used increases, which is not preferable.

The Fe and U adsorbed on the anion exchange resin after elution of cobalt can be easily eluted by using hydrochloric acid of less than 1N. Therefore, the anion-exchange resin can be regenerated by taking into consideration the adsorption capacity of the anion-exchange resin and the like and eluting Fe and U at an appropriate time.

By the above operation, impurities Ni, F
Heavy metals such as e, alkali metals such as Na and Ka, and U and T
It is possible to separate cobalt from radioactive elements such as h.

Since the eluted cobalt chloride aqueous solution has a high hydrochloric acid concentration, it cannot be used as it is for electrolytic refining. Therefore, in the present invention, the eluted cobalt chloride aqueous solution is evaporated to dryness or concentrated, and then water is added to form a high-purity cobalt aqueous solution having a pH of 0 to 6, and the aqueous solution is used as an electrolytic solution.

The method of evaporating to dryness or concentration may be carried out by using a rotary evaporation device or the like. The temperature for evaporation to dryness or concentration is 80 ° C or higher, preferably 100 ° C.
℃ or above. When the temperature is lower than 80 ° C, it takes time to evaporate to dryness or concentrate. Further, at that time, if the treatment is carried out under a slightly reduced pressure with an aspirator or the like, the time for evaporation to dryness or concentration can be shortened. Quartz, graphite, Teflon, or the like is preferable as a material for the apparatus for evaporation to dryness or concentration. The hydrochloric acid gas generated at this time is cooled and condensed to dissolve cobalt,
Alternatively, it can be reused for hydrochloric acid or the like used in the anion exchange.

Further, organic substances (styrene, divinylbenzene, amines, etc.) in the ion exchange resin start to flow little by little and may be mixed in the liquid. Activated carbon treatment is performed to remove such organic substances. Since activated carbon may contain a large amount of impurities such as Fe, it is preferable to use it after performing an acid treatment of washing and removing it with hydrochloric acid or the like. The activated carbon may be granular, fibrous, powdery, or the like, but it is preferable that activated carbon does not contain impurities Fe and the like, but when it is large, it is necessary to remove it with hydrochloric acid or the like as described above. In the activated carbon treatment, the eluted cobalt chloride aqueous solution is usually evaporated to dryness or concentrated, and water is added to adjust the pH to 0.
Although it is performed after adjusting to 6, the order does not necessarily have to be in this order, and may be performed anywhere between the elution of cobalt chloride and the electrolytic refining.

The pH of the electrolytic solution made of the high-purity aqueous cobalt solution thus produced is 0 to 6, preferably 1 to
4 is assumed. When the pH is less than 0, the amount of hydrogen generated increases and the current efficiency decreases, which is not preferable. When the pH exceeds 6, cobalt is converted to cobalt hydroxide and precipitates, which is not preferable.

The concentration of cobalt in the electrolytic solution in electrolytic refining is 10 to 160 g / L, preferably 30 to 130 g / L.
L. If it is less than 10 g / L, the amount of hydrogen generated is large, so that the current efficiency is lowered and the concentration of impurities in the electrodeposited cobalt is increased, which is not preferable. When it exceeds 160 g / L, cobalt chloride is precipitated and adversely affects the electrodeposition state, which is not preferable.

The range of current density is 0.001 to 0.1 A
/ Cm ² . If it is less than 0.001 A / cm ² , productivity is lowered and it is not efficient. If it exceeds 0.1 A / cm ² , the impurity concentration increases and the current efficiency also decreases, which is not preferable. The electrolysis temperature is 10 to 90 ° C., preferably 35 to 5
5 ° C. If the temperature is lower than 10 ° C, the current efficiency decreases, while if it exceeds 90 ° C, the amount of evaporation of the electrolytic solution increases, which is not preferable. Crude cobalt is used as the anode. As the cathode, cobalt, titanium plate, or the like is used. The material of the electrolytic cell is preferably vinyl chloride, polypropylene, polyethylene or the like.

In the electrolytic refining, the cathode and the anode are separated by a diaphragm or anion exchange membrane, and the cathode side is purified by anion exchange so that impurities eluted from the anode do not enter the cathode side. It is preferable that anolyte having a high impurity concentration is extracted at least intermittently from the anode side. The amount of catholyte added at this time is preferably at least equal to or more than the amount of anolyte to be extracted. In the present invention, the septum or anion exchange membrane that can be used is not particularly limited, but examples of the septum include filter cloths PP-2020 and PP-100.
(Azumi Filter Paper Co., Ltd.), Teviron 1010, and anion exchange membranes include Ionac MA-3475 (Muromachi Chemical Co., Ltd.) and the like.

The extracted anolyte can be recycled by circulating it by bringing it into contact with an anion exchange resin after adjusting the hydrochloric acid concentration to 7 to 12 N, whereby electrolytic refining can be continuously carried out. . In the present invention, at least intermittent means continuous or intermittent.

By electrolytic refining, a small amount of radioactive elements such as U and Th remaining in the electrolytic solution can be separated from cobalt.

The recovered electrodeposited cobalt is, if necessary,
It can be dissolved by a vacuum melting method such as electron beam melting to remove a trace amount of volatile elements such as Na and K contained therein. Electron beam melting is a method in which an electrode (here, electrodeposited cobalt) is first prepared and then remelted to obtain a high-purity ingot. Volatile components evaporate during melting of the electrode under high temperature and high vacuum. For example, when the melting amount is 5 kg, electron beam melting is performed under the following conditions: current: 0.7 A, voltage: 20 KV, vacuum degree: 10 ⁻⁵ mm
Hg, time: 2 hr.

The high-purity cobalt produced by the above operation has a small amount of impurities and is preferable as a target material for semiconductor production. Sodium content 0.05
ppm or less, potassium content 0.05 ppm or less, iron,
The content of each element of nickel and chromium is 1 ppm or less, the uranium content is 0.01 ppb or less, and the thorium content is 0.01.
ppb or less, carbon content 50 ppm or less, preferably 1
It is possible to obtain a high-purity cobalt sputtering target characterized in that 0 ppm or less and oxygen content 100 ppm or less; the balance is cobalt and other unavoidable impurities.

[0029]

EXAMPLES Examples of the present invention will be presented below, but the present invention is not limited thereto.

Example 1 600 g of crude cobalt ingot having the purity shown in Table 1 was charged into a container of about 12.5 L of 11.6 N hydrochloric acid aqueous solution. Then, the temperature was raised to 95 ° C. and 12 hours later, an aqueous cobalt chloride solution having a hydrochloric acid concentration of 9 N and a cobalt concentration of 50 g / L was obtained. 12 L of this liquid was used as a polypropylene column (150 mmφ × 12) filled with 12 L of anion exchange resin (Muromachi Kagaku: DOWEX, 2 × 8).
00mmL) and after adsorbing cobalt, 9N
It was washed with 12 L of hydrochloric acid. The resin used at this time was
It was new.

Next, 18 L of 4N hydrochloric acid was passed in to elute cobalt. The obtained purified cobalt chloride aqueous solution was heated at a temperature of 11 using a rotary evaporation device.
Evaporated to dryness at 0 ° C. Evaporated dry matter is CoCl ₂ · 2
It was H ₂ O and obtained 600 g in terms of Co. This was dissolved in pure water to make 10 L. The cobalt concentration at this time is 60
g / L. Then, after adjusting the pH to 2, organic matter was removed by activated carbon, 5 L of this high-purity cobalt solution was put in an electrolytic cell, and the remaining 5 L was used as a supply liquid for catholyte. The activated carbon was washed with 6N hydrochloric acid before use to sufficiently remove impurities such as Fe.

Next, electrolytic purification was carried out with a current density of 0.02 A / cm ² and a temperature of 50 ° C. and using a crude cobalt plate as a cathode. At this time, the anode side and the cathode side were separated by a diaphragm (PP2020, manufactured by Azumi Filter Paper Co., Ltd.). A high-purity cobalt chloride aqueous solution is supplied to the cathode side at a feeding rate of 12
It was supplied at 0 mL / hr and withdrawn at the same rate from the anode side. After 40 hours, the obtained electrodeposit was 83 g, and the yield was 95%. The electrodeposited state was smooth with no surface irregularities, and no peeling of the electrodeposited cobalt occurred.

Further, the obtained electrodeposited cobalt was subjected to electron beam melting and processed into a sputtering target. Table 1 shows the content of impurities after electrodeposited cobalt and electron beam melting.

Reference Example An operation was performed in the same manner as in Example 1 except that activated carbon which had not been subjected to acid treatment was used. The purity of the electrodeposited cobalt obtained by this operation is shown in Table 1. It can be seen that the content of the impurity Fe is high.
However, there is no problem if activated carbon having a low Fe content is used.

(Comparative Example) The same operation as in Example 1 was carried out except that activated carbon was not used. The purity of the electrodeposited cobalt obtained by this operation is shown in Table 1. It can be seen that the carbon and gas component contents are high. Further, the electrodeposited state was a surface state with irregularities, and a part was peeled off from the cathode plate, which was very brittle.

[0036]

[Table 1]

(Sputtering Test Data) Sputtering was carried out using the targets produced in Example 1, Reference Example and Comparative Example, and impurities in the film were analyzed by GDMS. The results were as follows. (Gas components cannot be analyzed)

[0038]

[Table 2]

The above film was subjected to SIMS analysis to find C, O,
Qualitative analysis was performed on N and H. Although the absolute amount of each is not known, all the components showed the lowest values in the case of the examples. The relative strength when the strength of the example was 1 was as follows.

[0040]

[Table 3]

The results of measuring the electric resistance of the above film are shown below. (Film thickness 30 nm)

[0042]

[Table 4]

[0043]

【The invention's effect】

(1) High-purity cobalt of 5N or more is anion exchange-
Combining electrolytic purification method (or electrolytic collection method) with activated carbon treatment,
Further, by carrying out a vacuum melting method as required, it is possible to obtain an extremely low impurity content, stable quality, easy operation, and low cost. (2) The obtained high-purity cobalt is suitably used as a target material for manufacturing a semiconductor device.

Claims (8)

[Claims] 1. A cobalt chloride aqueous solution containing at least Fe and / or Ni as impurities and having a hydrochloric acid concentration of 7 to 12 N is contacted with an anion exchange resin to adsorb cobalt, and then 1 to 6 N hydrochloric acid is used. To elute cobalt and evaporate the resulting eluent to dryness or concentration, and then pH = 0 to 6
The method for producing high-purity cobalt, characterized in that the high-purity cobalt chloride aqueous solution is further removed, organic matter in the solution is removed by activated carbon, and the aqueous solution is used as an electrolytic solution to obtain electrodeposited cobalt by electrolytic refining. 2. At least Fe and / or Ni, and N
An aqueous solution of cobalt chloride containing an alkali metal containing a, K and a radioactive metal containing U, Th as impurities and having a hydrochloric acid concentration of 7 to 12 N is brought into contact with an anion exchange resin to form Co.
After adsorbing Fe and U, Co was eluted with hydrochloric acid of 1 to 6 N, and the obtained eluent was evaporated to dryness or concentrated to obtain a high-purity cobalt chloride aqueous solution having a pH of 0 to 6, Furthermore, a method for producing high-purity cobalt, characterized in that organic matter in the liquid derived from the anion exchange resin is removed by activated carbon, and electrolytically refined cobalt is obtained by using the aqueous solution as an electrolytic solution. 3. In electrolytic refining, the anode and the cathode are partitioned by a diaphragm or anion exchange membrane, and a high-purity cobalt chloride aqueous solution is at least intermittently introduced into the cathode side, and at least intermittently withdrawing anolyte. The method for producing high-purity cobalt according to claim 1 or 2. 4. The hydrochloric acid concentration of the extracted anolyte is 7 to 7.
The method for producing high-purity cobalt according to claim 3, wherein the method is brought into contact with an anion exchange resin after having been adjusted to 12N. 5. The method for producing high-purity cobalt according to claim 1, wherein the electrodeposited cobalt is further melted in vacuum. 6. The method for producing high-purity cobalt according to claim 1, wherein the activated carbon is previously treated with an acid. 7. A sodium content of 0.05 ppm or less,
The content of potassium is 0.05 ppm or less, the content of each element of iron, nickel and chromium is 1 ppm or less, and the content of uranium is 0.
01 ppb or less, thorium content 0.01 ppb or less,
Carbon content 50 ppm or less, oxygen content 100 ppm or less; the balance is cobalt and other unavoidable impurities, a high-purity cobalt sputtering target. 8. A sodium content of 0.05 ppm or less,
The content of potassium is 0.05 ppm or less, the content of each element of iron, nickel and chromium is 1 ppm or less, and the content of uranium is 0.
01 ppb or less, thorium content 0.01 ppb or less,
Carbon content 10 ppm or less, oxygen content 100 ppm or less; the balance is cobalt and other unavoidable impurities, a high-purity cobalt sputtering target.