JPH0375301A - Manufacture of low oxygen metal powder - Google Patents

Abstract

PURPOSE:To manufacture a low oxygen metal powder by executing heat treatment to metal powder containing the oxygen while bringing into contact with halogen-containing gas under fluidized condition. CONSTITUTION:By heating the high m.p. powder of molybdenum, tungsten, tantalum or titanium etc., while bringing into contact with the halogen series gas of hydrogen chloride, chlorine, bromine, fluorine, iodine, etc., both is reacted. By this method, the low oxygen metal powder can be manufactured.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for producing metal powder with a reduced oxygen content, and particularly relates to a method for producing a metal powder with a reduced oxygen content, particularly for the production of high melting point materials for semiconductor electrodes. The present invention relates to a method for reducing the oxygen content of a high-melting point metal powder suitable as a raw material for a target when producing metal silicides by sputtering.

(Prior art and its problems) Conventionally, a method is known in which a silicide of a high-melting point metal such as tungsten, molybdenum, or titanium is used as a wiring or gate electrode material for VLSI. When forming C, V,
D method or sputtering method is used. Usually, this sputtering target made of a high melting point metal silicide is manufactured by a powder metallurgy method, and it is preferable that the oxygen content in the high melting point metal powder used as the raw material is as low as possible. When oxygen is present in the metal powder, it reacts with silicon, which has a high affinity for oxygen, to form high-resistance silicon oxide, which is difficult to remove in subsequent steps. There is a problem in that the specific resistance value of the silicide film remaining in the target and formed on the Si substrate after sputtering increases. Furthermore, even in applications other than the above, for example, when manufacturing high-melting point metal products, it is desirable that the amount of oxygen in the raw metal powder be small.

Conventionally, methods for reducing oxygen in metal powders as described above include:
A re-reduction method using hydrogen gas or a method in which oxides are scattered by heating in a high vacuum have been proposed.

In the heating method described above, it varies depending on the particle size of the powder, the heat treatment temperature, etc., but for example, in the case of tungsten (W) powder with a particle size of 1.5 μm, it is heated to 950 μm in hydrogen.
The amount of residual oxygen is 400pp even if the rotation rate is 1 hour at a temperature of ℃.
It is difficult to lower the temperature to less than m, and if the temperature is increased further, the powders will conversely bond with each other (sintering phenomenon), which will seriously impede the subsequent powder metallurgy process.

On the other hand, a method has also been proposed in which the silicide presintered body is exposed to Si vapor in a vacuum or an oxygen-free atmosphere to convert the contained SiO2 into SiO with a low boiling point and volatilize it (Japanese Patent Publication No. 58794/1982). However, this method also
Reactions are required at high temperatures, and the process requires complicated processes such as the need to create a high vacuum in the processing atmosphere. Normally, when molybdenum and silicon are reacted at a temperature high enough to melt them (e.g. by electron beam, vacuum arc melting, etc.), the formed oxide evaporates.
Although silicide with very low oxygen content can be obtained, it is difficult to grind the obtained silicide mass without contamination, and the problem of recontamination inevitably arises. Furthermore, in the above method, there is a new problem in that silicon easily evaporates during melting, making it difficult to adjust the Mo:Si ratio.

The present invention is directed to solving the problems of the prior art described above, and aims to provide a method for easily and efficiently removing oxygen contained in metal powder.

[Structure of the invention]

(Means and effects for solving the problems) Summary of the invention The method for producing a low-oxygen metal powder of the present invention includes heat treatment while bringing the metal powder into contact with a halogen-containing gas when removing oxygen contained in the metal powder. It is characterized by

DETAILED DESCRIPTION OF THE INVENTION As a result of extensive research into methods for solving the above-mentioned drawbacks of the prior art, the present inventors have discovered that halogen-containing gases such as hydrogen chloride can be used at relatively high temperatures to It was discovered that volatile halides or oxyhalides are formed by reacting with oxides of melting point metals, and by utilizing this reaction, oxygen contained in metal powders can be effectively removed without re-contamination. I found out that it is possible. The present invention has been made based on the above findings.

In this case, in order to quickly remove the halides or oxyhalides generated by the reaction with the halogen-containing gas from the system, the reaction between the halogen-containing gas and the metal powder to be treated must be carried out under a fluidized state such as in a rotary furnace. It is preferable to carry out the process in a stream of non-oxidizing gas such as hydrogen or an inert gas.

The metal powder to be treated in the present invention is not particularly limited, but it can be suitably applied to a raw material metal of high melting point metal silicide conventionally used as a sputtering target. Specifically, molybdenum (Mo), tungsten (W), tantalum (Ta) or titanium (
Refractory metal powders such as Ti) can be used.

In the method of the present invention, the metal powder as described above is brought into contact with a halogen-containing gas and heated, thereby causing the two to react. As the halogen gas in this case, halogen-based gases such as hydrogen chloride, chlorine, bromine, fluorine, and iodine are used. Therefore, in the present invention, halogen gas includes not only halogen gas but also halogen compounds such as hydrogen halide. According to the research conducted by the present inventors, among the above gases, hydrogen chloride gas or chlorine gas is particularly preferably used. Further, these halogen-containing gases can appropriately contain a reducing or non-oxidizing gas such as hydrogen, argon, helium, or nitrogen as a carrier gas.

Heating in the above atmosphere depends on the type of target metal and the gas used, but the higher the heating temperature, the more oxygen is reduced, so the higher the heating temperature, the better. Specifically, the temperature is preferably 600°C or higher. As for the upper limit, since sintering will occur in the metal powder if carried out at too high a temperature, it is preferable to carry out at a temperature within a range in which sintering does not occur. It depends on the melting point of the target metal, but generally the temperature is 10
When the temperature exceeds 00°C, the sintering phenomenon of the powder progresses. For example, in the case of W or Mo powder, the preliminary sintering temperature of the green compact of these metals (approximately 1400 to 1500°C) is considered to be the practical upper limit. However, even if the metal powder is sintered to some extent, it is possible to heat-treat it at a temperature higher than the temperature at which sintering occurs, if it is possible to grind it using a high-purity feed material.

According to the method according to the present invention, when removing oxygen contained in metal powder, which is usually present in the form of oxide, halogen gas first reacts with metal oxide to generate volatile halides or oxyhalides. However, in this form, the contained oxygen is removed by volatilization from the metal. In this case, halogen gas (especially hydrogen chloride) hardly reacts with metals, so
It becomes possible to efficiently remove only the oxygen in the metal.

Further, the generated volatile halides must be promptly discharged from the system. Furthermore, water is produced in the above-mentioned oxyhalide production reaction, and this water also needs to be removed.

For example, when chlorine is used as a halogen gas and tungsten is purified by chlorine, WO2C12 produced by the reaction between chlorine and tungsten undergoes the following decomposition reaction at a temperature of 140° C. or higher.

WO2CI 2→WO3+WOCl4 The WO3 thus generated further reacts with chlorine and becomes WO2C again.
There is a tendency to generate 12. If such re-decomposition and by-product reactions are left unattended, the oxygen-containing components generated by the decomposition and by-products will gather on the surface of the metal powder to be treated, thereby inhibiting the oxygen component removal reaction. Therefore, as mentioned above, in the present invention, in order to quickly remove the generated halide or oxyhalide from the system,
The reaction between the halogen-containing gas and the metal powder to be treated is preferably carried out in a fluidized state, for example, in a flow of non-oxidizing gas such as hydrogen or an inert gas, or while the halogen-containing gas itself is flowing. It is preferable to do so.

Specifically, the heat treatment is performed while flowing an atmospheric gas or a carrier gas, and the generated halide or oxyhalide is rapidly removed from the system.

Focusing on this point, the mixing ratio of the halogen-containing gas and the atmospheric gas or carrier gas, as well as the flow rate of the atmospheric gas or carrier gas, are important factors for increasing the removal efficiency.

According to the findings of the present inventors, the concentration of halogen in the halogen-containing gas used is preferably in the range of 0.5% to 60%, more preferably 2 to 26% by volume.

Furthermore, the flow rate of the halogen-containing gas to be made to flow is 5 degrees/
It is preferable that the time is longer than seconds. As mentioned above, it should be noted that when the flow rate is slow, it becomes difficult for the halides produced by the reaction to be discharged from the system, and conversely, they are deposited on the surface of the metal powder, reducing the deoxidizing effect. .

In this way, according to the method of the present invention, although it varies depending on the type of metal, the amount of oxygen contained in the metal powder can be reduced to below the lower limit of the conventional method, specifically to 300 ppm or less. becomes possible. Generally, when producing a high melting point metal silicide target, it is preferable that the metal powder contains as little oxygen as possible for the reasons mentioned above. However, commercially available metal powders usually contain 700 to 1
It is normal for it to contain about 500 ppm of oxygen. In addition, especially for sputter targets, uranium,
High-purity raw material powder is used that has been specially purified to remove impurity metal components such as thorium, alkali metals, or iron, but since these reductions are usually carried out by hydrogen reduction, the amount of oxygen contained is There is no big difference from that of the commercially available products mentioned above. Therefore, considering this point,
The present invention, which can reduce the amount of oxygen content to 300 ppm or less under relatively low temperature conditions, has excellent effects.

(Example) Example 1 First, a quartz tube (total length 600 mm) with an inner diameter of 23 mm was
It was set in a Matsufuru furnace (total length 350 mm) capable of temperature adjustment up to 100°C, hydrogen chloride gas and carrier gas were supplied from one side, and an air washing bottle containing sodium hydroxide solution was attached to the discharge side.

For hydrogen chloride gas, put 500 ml of hydrochloric acid in an oxygen-free container, drop 50 ml of concentrated sulfuric acid per hour into it, remove the generated hydrogen chloride gas with a carrier gas, and wash it with anhydrous sulfuric acid. I used the one I made. On the other hand, the metal powder that is the object to be processed is processed in a porcelain boat (
Total length 10 (J.

It was loaded to an internal volume of 4 m1) and placed in the quartz tube #C.

In this example, first, the oxygen content was 710 ppm.
, tungsten metal powder (7 g) with an average particle size of 1.5 μm
was used as the metal powder to be treated, and as the atmospheric gas, in addition to the above hydrogen chloride gas, hydrogen gas (flow rate 1.4 liters /
minutes) and further hydrogen as a carrier gas (0,
700 to 11.00" while flowing
Heat treatment was performed for 1 hour in the range of C. After that, the supply of hydrogen chloride gas was stopped, and after heating for another 5 minutes,
The treated material was rapidly cooled to prevent oxidation due to minute amounts of oxygen and moisture in the hydrogen. The oxygen content in the obtained tungsten powder was as follows.

Table 1 Before treatment 710ppm 700℃ 444ppm 900℃ 325ppm 950℃ 292ppm 1000℃ 300ppm 1100℃ 290ppm Example 2 The above procedure was carried out using molybdenum powder (5 g) with an oxygen content of 525 ppm and an average particle size of 4.1 μm as the metal powder to be treated. Contained oxygen was removed under the same conditions as in Example 1. The oxygen content in the obtained molybdenum powder was as follows.

Table 2 Before treatment 525ppm 700℃ 358ppm 900℃ 260ppm 950℃ 250ppm 1000℃ 250ppm 1100℃ 250ppm Example 3 Using the same tungsten powder as in Example 1, argon (dew point -70℃) as atmospheric gas at 300 m1/min, While flowing argon gas at a rate of 150 ml/min as a carrier gas for hydrogen chloride gas, heat treatment was performed in the range of 900 to 110° C. for 1 hour each. Thereafter, the supply of hydrogen chloride gas was stopped, and after further heating for 5 minutes, the treated material was rapidly cooled to prevent oxidation due to minute amounts of oxygen and moisture in argon. The oxygen content in the obtained tungsten powder was as follows.

Table 3 Before treatment 710ppm 900℃ 310ppm 950℃ 294ppm 1000℃ 285ppm 1100℃ 285ppm Example 4 Oxygen-containing f1525 ppm, average particle size 4.1μm
molybdenum powder (5g) as the metal powder to be treated,
Contained oxygen was removed under the same conditions as in Example 3 above.

The oxygen content in the obtained molybdenum powder was as follows.

Table 4 Before treatment 525ppm 900℃ 185ppm 950℃ 170ppm 1000℃ 170ppm 1100℃ 160ppm Comparative example 1 Tungsten powder (7g) with an oxygen content of 710ppm and an average particle size of 1.5μm was used as the metal powder to be treated, and the dew point -
Re-reduction was performed at 950°C for 1 hour while passing hydrogen at 65°C, but the oxygen content in the metal powder after re-reduction was 457.
It was ppm.

Comparative Example 2 Molybdenum powder (5 g) with an oxygen content of 525 ppm and an average particle size of 4.1 μm was used as the metal powder to be treated, and the dew point was -6.
Re-reduction was performed at 950°C for 1 hour while passing hydrogen at 5°C, but the amount of residual oxygen in the metal powder after re-reduction was 322p.
It was pm. In addition, the metal powder had already started sintering, and the surface of the powder had become somewhat hard.

Example 5 A quartz tube (total length 600 mm) with an inner diameter of 23 mm was
Matsufuru furnace (total length 3
50mm), a mixed gas of chlorine and argon is supplied from one side via a flow meter, and a cleaning tower containing sodium hydroxide solution is connected to the discharge side via a trap. prepared. In order to make the entire system an oxygen-free atmosphere, an inert gas (such as Ar) was also connected to the chlorine supply side to perform oxygen purging. On the other hand, the metal powder samples were placed on a porcelain board (full length 10, internal volume approximately 4 m1), and charged with approximately 13 g of tungsten and approximately 8 g of molybdenum.

In this example, first, the oxygen content was 710 ppm.
, tungsten powder with an average particle size of 1.5 μm was used as the metal powder to be processed, and after inserting a porcelain board charged with the tungsten powder into a quartz tube, argon gas was flowed at a flow rate of 400 m1/min for 30 minutes to make the inside of the device oxygen-free. After the temperature reached 700°C, the supply of argon was stopped, chlorine gas was flowed for 12 minutes at a flow rate of 18 ml/min, and the temperature was maintained at 700°C.

After stopping the supply of chlorine, the mixture was cooled while heating was continued for 5 minutes. In this case, the oxygen content in the tungsten powder after the chlorine treatment alone was 440 ppm.

Example 6 Oxygen-containing ff1 was added to the quartz tube of the device used in Example 5.
After inserting a porcelain board charged with 710 ppm tungsten powder with an average particle size of 1.5 μm, argon gas was flowed at a flow rate of 400 m1/min for 30 minutes to make the inside of the device oxygen-free, and the temperature was then heated to 630°C. And so. Then,
200 m1/min of argon gas (400 m1/min for the second time)
chlorine gas was supplied at a flow rate of 18 ml/min for 12 minutes, and the temperature was maintained at 630° C. during this time.

After stopping the chlorine supply, heating was continued for 5 minutes and then cooled. The oxygen content in the tungsten powder heat-treated in this way was as follows:
m1/min), it is 240 ppm, and for the second time (argon flow rate = 400 ml/min), it is 200 ppm.
It was m.

Example 7 Oxygen content 6301) I) m1 in the same manner as Example 6
Molybdenum powder with an average particle size of 4.1 μm was heat treated. In this example, the argon flow rate is 100 m1/min, 200 m1/min.
The treatment was carried out by varying the flow rates: m1/min, 400 m1/min, and 800 m1/min.

The oxygen content in the powder after treatment is as shown in Table 5 below.

Table 52 Ar flow rate (ml/min) 00 00 00 Oxygen content after treatment 50 ppm with yellow oxide layer formed on the surface 80 ppm In the above case, the gas in the furnace core tube when the Ar flow rate is 100 m1/min The flow rate of the body (mixed gas of Ar and CI 2) is 4. It was 7 tam/sec. Also, the Ar flow rate is 200
．． 400. The flow rate of the gas in the case of 800 m1/min is 8.8 when Ar 200 m1 + CI 218 m1, respectively.
mm/sec, Ar 400ml + CI218ml 16.8mm/sec, Ar 800ml + CI
2 When the volume was 18 ml, the speed was 32.1 mm/sec.

Example 8 Oxygen content was 101,000 p using the same method as in Example 5.
Tungsten powder with a p-average particle size of 1.5 μm was heat treated. Argon flow ff1600m1/min, chlorine flow ji18m
Heat treatment was performed for 12 minutes each at a temperature of 950° C. and 1050° C. under the conditions of 1/min. Post-treatment was also carried out in the same manner as in Example 5. The oxygen content of the obtained powder is 110 ppm at a temperature of 950°C, and 1050 ppm.
In the case of ℃, it was 50 ppm. This powder was highly active, and when left in air for one week, the amount of oxygen increased more than 20 times.

Example 9 Oxygen-containing ffi750ppmS molybdenum powder having an average particle size of 4.0 μm was treated. The treatment conditions and results are shown in Table 6 (for a temperature of 950°C) and Table 7 (for a temperature of 1050°C) below.

Table 6 (Temperature 950℃) Ar (m17 min) Chlorine (m17 min) Result 200
70 + 6 minutes 290ppm800
70 + 6 minutes 235pp■900 7
0 + 6 minutes 2EfOpp II Table 7 (Temperature 1 Chlorine (m17 minutes) 70 + 6 minutes 1, 8 + 12 minutes 70 + 6 minutes 18 + 12 minutes 050°C) Result 2:'8ppm 150p1) 91ppm 34ppm As is clear from the results of the above examples According to the method of the present invention, the oxygen content in the molybdenum powder is reduced to 300pp.
m or less.

〔Effect of the invention〕

In the present invention, since the metal powder containing oxygen is heat-treated while being brought into fluid contact with the halogen-containing gas, the excellent effect of easily and efficiently removing the oxygen contained in the metal powder is achieved. .

Claims (1)

[Scope of Claims] 1. A method for producing a low-oxygen metal powder, which comprises heat-treating the metal powder while bringing it into contact with a halogen-containing gas when removing oxygen contained in the metal powder. 2. The method according to claim 1, wherein the heat treatment is performed in a non-oxidizing gas stream. 3. The method according to claim 1, wherein the halogen-containing gas is a gas containing hydrogen chloride or chlorine. 4. Claim 1, wherein the metal powder is a high melting point metal powder.
The method described in.