JP2001081507A - High purity cobalt powder and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of stably and easily producing high purity cobalt powder in which not only alkali metal elements, radioactive elements, Fe and Ni but also impurities such as gaseous components are reduced as possible and to provide high purity cobalt powder effective, e.g. for a sputtering target in which the formation of contaminants caused by the mutual diffusion of materials composing a laminated thin film is suppressed, and particles and an abnormal discharging phenomenon thereby do not caused. SOLUTION: As for the method for producing high purity cobalt powder, a cobalt raw material containing impurities is dissolved with hydrochloric acid, an aqueous solution of cobalt chloride having a hydrochloric acid concentration of 7 to 12 N is brought into contact with an anion exchange resin to adsorb cobalt, thereafter, cobalt is eluted with hydrochloric acid of 1 to 6N, the obtained eluted solution is evaporated and solidified or is neutralized with ammonium hydroxide to form into the chloride or hydroxide of cobalt and is moreover subjected to hydrogen reduction at >=600 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity cobalt powder and a method for producing the same, wherein the high-purity cobalt powder produced according to the present invention comprises an alkali metal element, a radioactive element, Fe
The present invention relates to a high-purity cobalt powder having a small amount of impurities such as a gas component (including a gasifying component) as well as Ni and is useful as a target material for forming a VLSI electrode and a wiring, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a variety of electronic devices have been born starting from the dramatic progress of semiconductors, and their performance has been improved and new devices have been developed every day. Under such circumstances, there is a tendency that the size of electronic devices and device devices is further reduced and the degree of integration is increased. Many thin films are formed in many of these manufacturing processes. Cobalt is used for forming many electronic device thin films as a cobalt film, its alloy film, cobalt silicide film, etc. due to its unique metallic properties. I have. Conventionally, polysilicon has been mainly used as an electrode material in semiconductor devices, but with the increasing integration of LSIs, the use of silicides such as molybdenum and tungsten has advanced, and titanium and cobalt silicides have been used. It has become. In addition, the conventionally used A
Proposals have also been made to use cobalt as a wiring material instead of l and Al alloys. Such electrodes and wirings are often formed by sputtering a cobalt target in argon.

A method of forming a thin film by sputtering is a method in which positive ions such as Ar + physically collide with a target placed on a cathode to release metal atoms constituting the target with the collision energy. Alternatively, it is formed by sputtering using an alloy or a target such as cobalt silicide in an argon gas atmosphere.

On the other hand, when forming such a thin film of cobalt (including alloys and compounds), care must be taken that the amount of metal impurities harmful to the semiconductor device is extremely small, that is, the semiconductor device itself requires extremely high purity. It is to be. That is, in order to ensure reliable semiconductor operation performance of electrodes or wirings formed after sputtering, the following is necessary. (1) Alkali metal elements such as Na and K. (2) Radioactive elements such as U and Th. (3) Fe and Ni. (4) Minimizing the inclusion of impurities such as gas components such as C and O. The alkali metals such as Na and K easily move in the gate insulating film and cause deterioration of MOS-LSI interface characteristics.
Radioactive elements such as U and Th cause α-rays emitted from the elements to cause soft errors in the element. On the other hand, Fe and Ni cause trouble at the interface joint. Also, C,
Gas components such as O are also not preferable because they cause particles to be generated during sputtering, as described later.

[0005] Commonly available cobalt raw materials, so-called crude cobalt lumps, contain tens of ppm of Fe and hundreds of ppm of N
i as an impurity. As a method for producing high-purity cobalt from such a raw material, first, an electrolytic refining method can be considered. However, since the standard electrode potentials of Ni and Fe, which are impurities, and cobalt are very close in electrolytic refining, it is difficult to achieve high purity by simple electrolytic refining. Therefore, in order to perform high purification by electrolytic refining, while removing impurities in the electrolytic solution by a solvent extraction method or the like, that is, for example, when the cobalt concentration is 40 to 60 g / L, It must be performed while keeping the Ni concentration at 1.3 mg / L or less on average and the Fe concentration at 0.1 mg / L or less on average, and requires very strict control. In addition, removal of Ni by solvent extraction requires a special solvent such as an alkyl oxime, and also coextracts cobalt, which requires complicated operations, and the extraction solvent is dissolved in the electrolytic solution. However, there is also a problem that loss occurs.

[0006] Thin films used in semiconductor devices and the like tend to be thinner and shorter, and the distance between the thin films is extremely small and the integration density is improved. The problem arises that impurities to be diffused into the adjacent thin film. As a result, the balance between the constituent materials of the self-film and the adjacent film is lost, and a major problem occurs in that the function of the film that must be originally possessed is reduced. In the process of manufacturing such a thin film, the thin film may be heated to several hundred degrees, and the temperature may increase during use of an electronic device incorporating the semiconductor device. Such a temperature increase further increases the diffusion coefficient of the substance (impurity), and causes a serious problem in that the function of the electronic device is deteriorated due to the diffusion.

In forming a sputtering film,
If impurities are present in the cobalt (alloy / compound) target, coarse particles floating in the sputtering chamber adhere to the substrate and cause a short circuit in the thin film circuit or cause protrusions of the thin film. If the amount of generated particles increases and a large amount of gas components such as oxygen, carbon, hydrogen, and nitrogen are present, an abnormal discharge, which is considered to be caused by the sudden occurrence of gas during sputtering, occurs, and a uniform film is not formed. Occurs.

[0008] From these facts, the conventional impurity F
It has been desired to produce high-purity cobalt having reduced gas components such as e and Ni, alkali metal elements, radioactive elements, and oxygen. However, according to these usual methods, alkali metal elements, Fe and Ni, radioactive elements,
Since other metal elements are contained in a large amount and the content of oxygen is high, stable high-purity of true cobalt at a low cost on an industrial scale has not been realized.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and particularly, to an alkali metal element, a radioactive element, Fe
And a method capable of stably and easily producing high-purity cobalt powder of 5N (99.999%, hereinafter simply referred to as 5N) or higher, in which impurities such as gas components and the like are reduced as much as possible. An object of the present invention is to provide a high-purity cobalt powder which is effective for a sputtering target or the like which suppresses contaminants caused by mutual diffusion of substances constituting a laminated thin film and does not cause particles or abnormal discharge phenomenon.

[0010]

Technical means for solving the above problems include treatment with strictly controlled hydrochloric acid,
It has been found that impurities can be controlled by an anion exchange method and a hydrogen reduction treatment, and high-purity cobalt powder that can be used for applications such as a sputtering target can be obtained. Based on this finding, the present invention is characterized by: 1) a high-purity cobalt powder characterized in that each content of Fe and Ni is 10 ppm or less; 2) a feature characterized in that each content of Fe and Ni is 1 ppm or less. High purity cobalt powder 3) Each content of alkali metal elements such as Na and K is 0.1
ppm or less and each content of radioactive elements such as U and Th is 0.1 ppb or less 4) High purity cobalt powder according to 1) or 2) 4) Each content of gas components such as oxygen and carbon Amount is 1000pp
m or less, and the high-purity cobalt powder according to each of 1) to 3) is provided.

The present invention also provides: 5) a cobalt raw material containing impurities such as Fe and Ni, a radioactive element, an alkali metal element and the like as an impurity by dissolving with hydrochloric acid, and adding an aqueous solution of cobalt chloride having a hydrochloric acid concentration of 7 to 12 N to an anion exchange resin. 1-6N after adsorbing cobalt by contact with
Elute cobalt with hydrochloric acid, evaporate the resulting eluate to dryness or neutralize with ammonium hydroxide to form cobalt chloride or hydroxide, and further reduce the hydrogen at a temperature of 600 ° C or higher. 6) A cobalt raw material containing Fe and Ni, a radioactive element, an alkali metal element, and the like as impurities is dissolved in hydrochloric acid, and an aqueous solution of cobalt chloride having a hydrochloric acid concentration of 7 to 12 N is added to a negative electrode. After contacting with an ion exchange resin to adsorb cobalt, iron and uranium, cobalt is eluted with 1 to 6N hydrochloric acid, and the obtained eluate is evaporated to dryness or neutralized with ammonium hydroxide to remove cobalt. Chloride or hydroxide, further 600 °
Method for producing high-purity cobalt powder characterized by hydrogen reduction at a temperature not lower than C 7) High-purity cobalt powder according to 5) or 6), wherein each content of Fe and Ni is 10 ppm or less. 8) The method for producing high-purity cobalt powder according to 5) or 6), wherein each content of Fe and Ni is 1 ppm or less. 9) Each content of alkali metal elements such as Na and K. Is 0.1
ppm or less, and each content of radioactive elements such as U and Th is 0.1 ppb or less 5) to 8)
10) Each content of gas components such as oxygen and carbon is 1000 p
pm or less, the method for producing a high-purity cobalt powder according to any one of 5) to 9), wherein

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Cobalt raw materials used in the present invention are generally commercially available on the order of tens of ppm of Fe and hundreds of pp.
The crude cobalt containing m impurities such as Ni is dissolved in hydrochloric acid and used. However, the present invention is not limited to this. . The hydrochloric acid used for dissolving the crude cobalt is not particularly limited, but low-purity hydrochloric acid for industrial use can be used. This is because impurities contained in hydrochloric acid can also be removed by the production method of the present invention.

The apparatus used for dissolving cobalt is:
In order to use hydrochloric acid effectively, it is desirable to provide a cooling cylinder and a device for collecting hydrogen chloride gas. As a material, quartz, graphite, Teflon, a poly container or the like can be used.
The melting temperature is 50 to 100 ° C, preferably 80 to 9 ° C.
5 ° C. If the temperature is lower than 50 ° C., the dissolution rate is low, and if the temperature exceeds 100 ° C., evaporation is severe and loss of the aqueous solution is large. The concentration of hydrochloric acid in the aqueous cobalt chloride solution is preferably finally 7 to 12N. If less than 7N or more than 12N, cobalt is hardly adsorbed during ion exchange. Cobalt concentration is 10
~ 70 g / L is preferred. If the cobalt concentration is less than 10 g / L, a large amount of hydrochloric acid is required, which leads to an increase in cost. On the other hand, if the cobalt concentration exceeds 70 g / L, cobalt chloride at room temperature, that is, about 20 ° C. This is not preferable because of precipitation.

In anion exchange, cobalt is adsorbed using the above-mentioned aqueous solution of cobalt chloride. The resin used in the present invention is not particularly limited as long as it is an anion exchange resin, but DOWEX (Dowex) 1 × 8, DOWEX
X2 × 8 (Muromachi Chemical Co., Ltd.), Diaion SA10
A or the like can be used. Cobalt forms a chloride complex in high-concentration hydrochloric acid and adsorbs to the resin because it exists as an anion. Fe and U also behave similarly to cobalt and adsorb to the anion exchange resin, but the main impurities Ni and alkali metals such as Na and K and radioactive elements such as Th do not form chloride complexes, so that they are adsorbed. Elute from the column without washing.

Further, to remove impurities remaining in the column, the column is washed with 7 to 12N hydrochloric acid. Outside this range, the binding between cobalt and the anion exchange resin is weak, and cobalt is eluted, which is not preferable. Therefore, cleaning is performed within the above range. Next, in order to elute only the cobalt adsorbed on the anion exchange resin, 1-6N,
Preferably, 3N to 4N hydrochloric acid is used. If it is less than 1N, Fe and U adsorbed as impurities are also eluted, which is not preferable. If it exceeds 6 N, it becomes difficult to elute cobalt from the resin, and the amount of hydrochloric acid used is undesirably increased.

The Fe and U adsorbed on the anion exchange resin after the elution of cobalt can be easily eluted by using hydrochloric acid of less than 1N. Therefore, by taking into account the adsorption capacity of the anion exchange resin and the like and eluting Fe and U at an appropriate time, the anion exchange resin can be regenerated. By the above operation,
Transition metal elements such as Ni and Fe as impurities, Na and Ka
And a radioactive element such as U and Th, and cobalt can be separated, and high-purity cobalt can be obtained.

Next, the eluted aqueous cobalt chloride solution is evaporated to dryness or neutralized with ammonium hydroxide to form a cobalt chloride or hydroxide, and further reduced with hydrogen at a temperature of 600 ° C. or more to obtain high purity cobalt. Produce flour.
The method of evaporating to dryness is preferably performed using a rotary evaporator or the like. The temperature to evaporate to dryness is 80 ℃
Above, preferably 100 ° C. or higher. If the temperature is lower than 80 ° C., it takes time to evaporate to dryness. In this case, the evaporation and drying can be shortened by performing the treatment while slightly reducing the pressure with an aspirator or the like. The material of the apparatus for evaporating to dryness is preferably quartz, graphite, Teflon or the like. The hydrochloric acid gas generated at this time can be cooled and condensed and reused as hydrochloric acid used for dissolving cobalt or anion exchange.

Further, there is a possibility that organic substances (styrene, divinylbenzene, amines, etc.) in the ion-exchange resin gradually flow out and get mixed in the liquid. Activated carbon treatment can be performed to remove such organic matter. Activated carbon may contain a large amount of impurities such as Fe. Therefore, it is preferable to use the activated carbon after performing an acid treatment for washing and removing it with hydrochloric acid or the like. Activated carbon is in the form of granules, fibers, powder, etc., but preferably does not contain impurities such as Fe, but when it is large, it needs to be removed with hydrochloric acid or the like as described above. This activated carbon treatment can be performed after the elution of cobalt chloride

The high-purity cobalt powder produced by the above operation is sintered to obtain a sputtering target. The cobalt target thus produced has a low impurity content, and a material suitable for a target for semiconductor production and the like can be obtained. That is, the total content of Fe and Ni is 10 ppm or less, the total content of alkali metal elements such as Na and K is 0.1 ppm or less, and the total content of radioactive elements such as U and Th is 0.1 ppb or less. And a high-purity cobalt powder having a total content of gas components such as carbon of 1000 ppm or less. Usually, for example, the Na content is 0.05 ppm or less, the K content is 0.05 ppm or less, the content of each element of Fe and Ni is 1 ppm or less, the U content is 0.01 ppb or less, the Th content is 0.01 ppb or less, and the C content is An amount of 10 ppm or less, an O content of 100 ppm or less; a high-purity cobalt powder whose balance is Co and other unavoidable impurities is obtained.

A cobalt film formed by sputtering using a target manufactured from this cobalt powder moves in the gate insulating film to reduce alkali metals such as Na and K which cause deterioration of MOS-LSI interface characteristics. The soft error of the element due to α rays of radioactive elements such as U and Th
Trouble at the interface joint due to Fe and Ni is also reduced.
Further, the problem that the substance constituting the thin film or the impurities contained in the thin film diffuses into the adjacent thin film is eliminated, and the balance between the constituent materials of the self-film and the adjacent film is not lost, and the function of the film originally owned is deteriorated. The problem of doing so is also gone. Therefore, a reliable semiconductor operability of an electrode, a wiring, or the like formed after sputtering can be sufficiently ensured. Furthermore, when the sputtering film is formed, impurities in the cobalt (alloy / compound) target, particularly, gas components such as oxygen, carbon, hydrogen, and nitrogen are reduced, so that coarse particles floating in the sputtering chamber are formed. No longer causes short-circuiting of the thin-film circuit due to adhesion on the substrate, reduces the amount of particles that cause thin-film projections, and causes abnormal discharge that may be caused by gas burst during sputtering. Will not occur.

[0021]

Next, an embodiment of the present invention will be described. This embodiment is merely an example, and the present invention is not limited to this example. That is, the present invention encompasses all aspects and modifications other than the present embodiment included in the technical concept of the present invention.

Example 1 A cobalt raw material as shown in Table 1, that is, 600 g of crude cobalt ingot having a purity of about 12.
It was charged to a container of 5 L of 11.6 N aqueous hydrochloric acid. The temperature was raised to 95 ° C., and after 12 hours, an aqueous solution of cobalt chloride having a hydrochloric acid concentration of 9 N and a cobalt concentration of 50 g / L was obtained. 12 L of this solution is applied to an anion exchange resin (Muromachi Chemical: DOWE)
X, 2 × 8) The solution was passed through a polypropylene column (150 mmφ × 1200 mmL) packed with 12 L, adsorbed cobalt, and washed with 12 L of 9N hydrochloric acid.

Next, 4N hydrochloric acid was used to elute cobalt.
18 L of liquid was passed. The obtained purified cobalt chloride aqueous solution
After removing organic substances with activated carbon in advance,
Evaporate to dryness at 110 ° C using an evaporator
I let it. Evaporated and dried product is CoCl ₂・ 2H₂O and Co
600 g was obtained in conversion. Activated carbon is 6N before use
It was washed with hydrochloric acid to sufficiently remove impurities such as Fe. next,
High purity edge by reducing hydrogen at 800 ° C
Rt powder was obtained. The analytical results of the cobalt powder thus obtained were
The results are shown in Table 1. As shown in Table 1, in the first embodiment,
Degree of cobalt powder was obtained.

[0024]

[Table 1]

[0025]

Example 2 A cobalt raw material having the same components as in Example 1 was dissolved in hydrochloric acid in the same manner as described above, and the solution was passed through an anion exchange resin under the same conditions to adsorb cobalt. Washed with 12L. Then 4 to elute cobalt
18 L of N hydrochloric acid was passed. The obtained purified aqueous solution of cobalt chloride is subjected to neutralization with ammonium hydroxide after removing organic substances in advance with activated carbon, and then cobalt hydroxide (Co (O (O
H) ₂ ) was obtained in an amount of 600 g in terms of Co. The activated carbon was washed with 6N hydrochloric acid before use to sufficiently remove impurities such as Fe. Next, high-purity cobalt powder was obtained by hydrogen reduction at a temperature of 1000 ° C. Table 1 shows the analysis results of the cobalt powder thus obtained. As shown in Table 1,
In Example 2, high-purity cobalt powder was obtained.

[0026]

Comparative Example As a comparative example, a commercially available cobalt powder was used. As shown in Table 1, commercially available cobalt powder has Fe770 pp
m, Ni950ppm, Na20ppm, K50pp
m, U10ppb, Th10ppb, C190ppm,
It contains 5000 ppm of O and 100 ppm of N, and both have high impurity concentrations.

Next, using the cobalt powders of Examples 1 and 2 and the comparative example and high-purity silicon powder, a further 120
Hot pressing was performed at 0 ° C. for 3 hours to obtain a high-purity cobalt silicide sputtering target. Using these targets, the electrical resistance of the film formed by sputtering and the number of generated particles were compared. Table 2 shows the results. As is apparent from Table 2, the electric resistance of the comparative example is 15 μΩ · cm, whereas the electric resistances of Examples 1 and 2 of the present invention are 5 μΩ · c, respectively.
m, 5.1 μΩ · cm, which were all low. In the comparative example, the number of generated particles was 100 pieces / wafer, which was extremely large.
In this case, the numbers are 8 / wafer and 10 / wafer, respectively, which are low and the present invention is superior. It can be seen that the improvement in the purity of the present invention results in a decrease in electric resistance and a remarkable decrease in the number of particles generated during sputtering.

[0028]

[Table 2]

[0029]

As described above, the sputtering film using the cobalt powder of the present invention moves in the gate insulating film and
Alkali metals such as Na and K, which cause deterioration of the S-LSI interface characteristics, are reduced, soft errors of the element due to α rays of radioactive elements such as U and Th are increased, and troubles of the interface junction due to Fe and Ni are also caused. Decrease. In addition, the problem that the material constituting the thin film or the impurities contained in the thin film diffuses into the adjacent thin film is eliminated, and the balance of the constituent materials of the self-film and the adjacent film is not lost, and the function of the film originally owned is deteriorated. In addition, there is no problem that an electrode or a wiring formed after sputtering can sufficiently guarantee reliable semiconductor operability. Furthermore, when the sputtering film is formed, impurities in the cobalt (alloy / compound) target are reduced, and in particular, oxygen, carbon, hydrogen, nitrogen, etc., which are gas components, are reduced, so that coarse particles floating in the sputtering chamber are formed. It is possible to prevent the deposited particles from adhering to the substrate to short-circuit the thin film circuit, and to reduce the amount of particles that cause protrusions of the thin film. Further, during sputtering, abnormal discharge, which is considered to be caused by the sudden occurrence of gas, does not occur, and the electric resistance of the cobalt film is small.

Claims (10)

[Claims] 1. A high-purity cobalt powder, wherein each content of Fe and Ni is 10 ppm or less. 2. A high-purity cobalt powder, wherein each content of Fe and Ni is 1 ppm or less. 3. The content of each of alkali metal elements such as Na and K is 0.1 ppm or less, and each content of radioactive elements such as U and Th is 0.1 ppb or less. 3. The high-purity cobalt powder according to 1 or 2. 4. Each content of gas components such as oxygen and carbon is 1
3,000 ppm or less.
High-purity cobalt powder described in each of the above. 5. A cobalt raw material containing Fe and Ni, a radioactive element, an alkali metal element and the like as impurities is dissolved in hydrochloric acid, and an aqueous solution of cobalt chloride having a hydrochloric acid concentration of 7 to 12N is brought into contact with an anion exchange resin to remove cobalt. After the adsorption, cobalt was eluted with 1-6N hydrochloric acid, and the obtained eluate was evaporated to dryness or neutralized with ammonium hydroxide to obtain a chloride or hydroxide of cobalt.
A method for producing high-purity cobalt powder, comprising reducing hydrogen at the above temperature. 6. A cobalt raw material containing Fe and Ni, a radioactive element, an alkali metal element and the like as impurities is dissolved in hydrochloric acid, and an aqueous solution of cobalt chloride having a hydrochloric acid concentration of 7 to 12 N is brought into contact with an anion exchange resin to obtain cobalt. After adsorbing iron and uranium, cobalt is eluted with 1-6N hydrochloric acid, and the obtained eluate is evaporated to dryness or neutralized with ammonium hydroxide to form a chloride or hydroxide of cobalt, A method for producing high-purity cobalt powder, further comprising reducing hydrogen at a temperature of 600 ° C. or higher. 7. The method for producing a high-purity cobalt powder according to claim 5, wherein each content of Fe and Ni is 10 ppm or less. 8. The method for producing a high-purity cobalt powder according to claim 5, wherein each content of Fe and Ni is 1 ppm or less. 9. The content of each of alkali metal elements such as Na and K is 0.1 ppm or less, and each content of radioactive elements such as U and Th is 0.1 ppb or less. 9. The method for producing a high-purity cobalt powder according to any one of 5 to 8. 10. The method according to claim 5, wherein each content of gas components such as oxygen and carbon is 1000 ppm or less.
9. The method for producing a high-purity cobalt powder according to 9 above.