JPH0615681B2 - Method for producing high-purity molybdenum or tungsten powder - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to high-purity molybdenum (Mo) or tungsten.
(w) Regarding the method for producing powders, more specifically, radioactive elements such as uranium and thorium; alkali metals such as sodium and potassium; impurities such as heavy metals such as iron and nickel up to the ppb order It relates to a method for easily producing reduced extremely high purity Mo powder or W powder.

[Technical Background of the Invention and its Problems] MOS-LSI, especially the circuit conductor part of a VLSI device of 256 Kbits or more is usually formed by applying a sputtering method using a target composed of Mo or W. Is. It is essential that the target used at this time has high purity.

For example, if the target material contains impurities such as uranium and thorium, the operational reliability of the VLSI device obtained by the damage of α rays from these radioactive elements is significantly reduced. Therefore, the allowable dose of these radioactive elements is ppb.
Must be on order. Also sodium,
Alkali metal such as potassium easily migrates in the gate insulating film of the device and deteriorates the MOS interface characteristics, so the allowable amount must be on the order of tens of ppb. Furthermore, since heavy metals such as iron and nickel cause the leak phenomenon at the interface joint, the allowable amount is 10
It is required to be in ppb order.

By the way, the above-mentioned target is generally manufactured by sintering Mo or W powder. Therefore, in order to obtain a high-purity Mo target or W target with few impurities, it is inevitable that the Mo powder or W powder used as a raw material must be of an extremely high purity containing no impurities as described above. Becomes

Mo powder is typically a Mo ore is dissolved in an alkaline solution such as caustic soda, is added to a solution of nitric acid, such as resulting sodium molybdate and molybdenum oxide (MoO _3), the MoO ₃ in aqueous ammonia It is produced by a method of dissolving, decompressing and concentrating the solution while heating to precipitate crystals of paramolybdate, and then reducing the crystals with hydrogen. Also, in the case of W powder, a paratungstate is prepared in the same manner, and then it is produced by reducing it with hydrogen.

However, it is extremely difficult to remove the above-mentioned impurities to ppb order by these methods, and it is practically impossible to remove the radioactive element. As a purification treatment in the above method, a recrystallization method is applied to crystals of paramolybdate or paratungstate.

However, even when this recrystallization method is applied, since the paramolybdate and the paratungstate both have the unique property of adsorbing the impurity element, the efficiency of removing the impurities becomes low. Combined with the impracticality, the refining process requires a long time, and more complicated auxiliary equipment is required, so that the obtained Mo powder and W powder become extremely expensive.

Further, in order to increase the purity of the target plate, a method (EB melting method) of irradiating a target plate produced by sintering from Mo powder or W powder with an electron beam has been developed. According to this method, alkali metals and heavy metals can be removed relatively efficiently, but uranium and thorium are difficult to remove because their melting points and vapor pressures are close to those of Mo and W, respectively. Is not a valid solution.

[Object of the Invention] The present invention solves the above-mentioned problems, and extremely high-purity Mo or W in which the content of impurities as described above is in the order of ppb.
It is intended to provide a method for producing powder.

[Summary of the Invention] The method for producing high-purity Mo or W powder according to the present invention comprises the step of decomposing Mo or W powder with hydrogen peroxide solution (first step); the obtained aqueous solution is contacted with a cation exchange resin. Step (second)
Step); a step of heating and concentrating the aqueous solution obtained in the second step, and then reducing the concentrated solid matter with hydrogen;

First, the first step is a step of dissolving Mo powder or W powder, which is manufactured by a conventionally known method and thus contains a large amount of impurities, in hydrogen peroxide solution to decompose it.

Although the details of the decomposition reaction at this time are not always clear,
It is presumed that the reactions shown in Eq. (1) for Mo powder and Eq. (2) for W powder occur, and the impurities contained in each powder become cations.

2Mo ＋ 7H ₂ O ₂ 2HMoO ₄ ＋ 6H ₂ O ……… (1) 2W ＋ 7H ₂ O ₂ 2HWO ₄ ＋ 6H ₂ O ……… (2) That is, both Mo and W behave as some kind of complex ion, and impurities are positive. It is considered to behave as an ion.

If the particle size of the Mo powder or W powder used is too large, the time required for the above decomposition reaction becomes long, which is not preferable in terms of productivity. Conversely, if the particle size is too small, the time required for the decomposition reaction becomes short. This is preferable, however, as will be described later, the decomposition reaction proceeds rapidly, which makes the control considerably complicated.
Usually, it is 1 to 100 μm, preferably 1 to 30 μm.

Further, the hydrogen peroxide solution used has a hydrogen peroxide concentration of 5 to 5.
35 wt%, preferably 20 to 35 wt% is used. If the concentration exceeds 35% by weight, handling becomes extremely difficult, and if the concentration is lower than 5% by weight, the above-mentioned problems are solved, but the aqueous solution obtained through the second step is When heating and concentrating (part of the third step),
It is not preferable because the heat energy required for evaporation of water increases and the overall cost increases.

This first step proceeds as an exothermic reaction. When the reaction system is too high temperature oxide of Mo or W in the system, i.e. MoO _3, and at the same time such as WO ₃ starts to generate hydrogen peroxide itself is thermally decomposed (1), (2 The reaction of the formula) does not proceed smoothly. Therefore, in the first step, it is preferable that the reaction system is usually cooled and set in the temperature range of 10 to 40 ° C. Further, if Mo powder or W powder and hydrogen peroxide solution are brought into contact with each other all at once to cause a decomposition reaction, a so-called bumping phenomenon occurs, so that, for example, Mo powder or W powder is gradually added with hydrogen peroxide. It is preferred that the reaction is allowed to proceed slowly with addition and stirring of the whole.

The second step is a step of bringing the aqueous solution obtained by the first step into contact with a cation exchange resin and adsorbing impurities existing as cations to the cation exchange resin to remove it from the aqueous solution. In this process, Mo, W
(1), as shown in equation (2), respectively MoO ₄ ^-, WO ₄ ^-
Therefore, it is not adsorbed by the cation exchange resin and is eluted. Thus, in this step, only the impurities contained in the starting Mo powder or W powder are adsorbed by the cation exchange resin and almost completely removed.

The cation exchange resin used is preferably H type, and the particle size thereof may be appropriately selected depending on factors such as the amount of the aqueous solution to be treated, the purification efficiency and the liquid flow rate.
Usually, the particle size is 100 to 30 mesh. Specifically, based on a copolymer of polystyrene and divinylbenzene,
Divinylbenzene (D with a strongly acidic sulfone group as an exchanger)
VB) It is preferable to use a cation exchange resin of about 8%. Product name: Diaion SK, Amber Light (IR-
120), DOWEX 50W-8X and so on.

As a contact method, a method is suitable in which these cation exchange resins are packed in a column at an appropriate packing density to form ion exchange columns, and the aqueous solution obtained in the first step is allowed to flow therethrough. In addition, the multi-stage method in which a plurality of ion exchange columns are connected is a preferable method in terms of high purification and separation efficiency.

In the third step, the aqueous solution that has been subjected to the ion exchange treatment in the second step is heated to evaporate the water to concentrate it, and the concentrated solid obtained as a result is hydrogen-reduced to obtain the desired high-purity Mo or This is a step of obtaining W powder.

When the aqueous solution obtained in the second step, that is, the aqueous solution containing only Mo and W is heated to evaporate water, the concentrated solid product obtained is MoO ₃ or WO ₃ . This heating concentration is usually
It may be performed at 100 to 300 ° C. By heating the obtained solid matter to a temperature of 800 to 1000 ° C. in a hydrogen atmosphere by a conventional method, the solid matter is reduced to powder of Mo or W.

[Examples of the invention] Example 1 (1) First step A crude Mo powder (average particle size: 5 μm) containing the impurities shown in Table 1 in the indicated amount was used, and the inner wall was made of a tetrafluoroethylene polymer. It was put in a container, 500 ml of water was added thereto, and the whole was stirred. Then, while cooling the container with running water, 30% hydrogen peroxide solution 2.1 was added into the container at an addition rate of about 1.0 / hr.
Was added to dissolve all the crude Mo powder. At this time, the temperature of the reaction system was kept at 40 ° C or lower. Then, water was added to the whole to make a total amount of 10.

(2) Second Step First, an H-type cation exchange resin of strongly acidic polystyrene sulfonic acid (trade name, Diaion SK # 1, particle size 50 to 100 mesh: manufactured by Mitsubishi Kasei Co., Ltd.) was prepared. After 400 g of this cation exchange resin has been sufficiently swollen with water, the inner diameter is 35 mm.
3 in a 400 mm long polypropylene column
I made an ion exchange column of a book. An apparatus as shown in the figure was assembled using these three ion exchange columns.

In the figure, 1 is a sample aqueous solution obtained in the first step, 2 is a liquid-sending pump, 3 and 4 and 5 are the above-mentioned ion-exchange columns, and 6, 7, 8, 9, 10, 11, 12 is a three-way cock for changing the flow path of the sample aqueous solution. 13 shows the Mo eluate from the ion exchange column. Reference numerals 15 and 16 represent a hydrochloric acid solution and a cleaning solution for regenerating the cation exchange resin, and 14 is a three-way cock.

First, the three-way cocks 6, 7, 8, 9, 10 are opened to form a flow path through which the sample aqueous solution 1 flows through the ion exchange columns 3 and 4 sequentially by the liquid feed pump 2 and does not flow into the ion exchange columns 5. After that, the liquid feed pump 2 was operated to flow the sample aqueous solution 1. When the flow rate reaches 5, the three-way cock 10 is switched and the three-way cocks 11 and 12 are opened to form a flow path through which the sample aqueous solution 1 sequentially flows through the ion exchange columns 3, 4, and 5 to remove the Mo eluate 13. Obtained.

(3) Third step The Mo eluate obtained in the second step was placed in a container having an inner wall made of a tetrafluoroethylene polymer and heated to a temperature of 150 ° C. for evaporation and dehydration treatment. The concentrated solid obtained was heated to 900 ° C. in a hydrogen furnace for reduction to obtain 980 g of powder. yield
97%.

(4) Quantitative Analysis of Impurities The powder obtained in the third step was quantitatively analyzed to measure the quantitative value of impurity elements excluding Mo. The results are shown in Table 1. For comparison, the results of quantitative analysis of Mo powder purified by the above-mentioned conventional method (recrystallization method) are also shown. The unit is ppm.

Example 2 A purified W powder was obtained in the same manner as in Example 1 except that the crude W powder containing impurities shown in Table 2 was used. The results of the quantitative analysis are shown in Table 2.

[Effects of the Invention] As is clear from the above description, according to the method of the present invention, impurities can be reduced to about 1/100 as compared with the conventional purification method. Moreover, the apparatus used for purification is extremely simple, and its method is also simple.

The Mo powder and the W powder purified by the method of the present invention are extremely high in purity because the amount of radioactive elements is less than 0.1 ppb and alkali metals and heavy metals are less than 0.05 ppm.
It is useful as a target material for devices.

[Brief description of drawings]

The figure is a conceptual diagram showing an example of a refining apparatus used in the second step of the method of the present invention. 1 …… Sample solution 2 …… Sending pump 3,4,5 ， Ion exchange column 6,7,8,9,10,11,12 …… Three-way cock 13 …… Eluent of molybdenum or tungsten

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Tsutomu Yamashita No. 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research Institute Co., Ltd. (72) Inventor Satoru Yamaguchi 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock Company Toshiba Yokohama Metal Factory (56) Reference JP-A-57-183309 (JP, A)

Claims (1)

[Claims] 1. A step of decomposing molybdenum or tungsten powder with hydrogen peroxide solution (first step); a step of bringing the obtained aqueous solution into contact with a cation exchange resin (second step); a second step And a step of hydrogenating the concentrated solid after heating and concentrating the aqueous solution obtained in 1 .; and a method for producing a high-purity molybdenum or tungsten powder.