JPH0230706A - Manufacture of beta-tungsten powder - Google Patents

Abstract

PURPOSE:To efficiently manufacture beta-tungsten powder by mixing WF6 and H2 under condition of specifying mol ratio and temp. and executing reaction at the specific temp. CONSTITUTION:The tungsten hexafluoride(WF6) and the hydrogen(H2) are separately introduced into the reaction system so as to become >=4 of H2/WF6 mol ratio and after mixing at 400-1400 deg.C, the mixed material is reacted at 650-1400 deg.C. Then, at the time of making about 100Torr-1.5atm of the reaction pressure, the almost spherical shaped beta-tungsten powder having about 0.1-20mu particle size is obtd. and is available to a sputtering target, electric conductive paste material, etc.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention is directed to high purity tungsten powder useful as sputtering target or conductive paste material, especially β
- Concerning a method for producing tungsten powder.

[Prior art] Tungsten is a metal with a high melting point and low electrical resistance.
It is widely used as a material for various electronic materials in the form of simple metal or its silicide, and is particularly used as a sputtering material.In such applications, tungsten powder with low impurities, especially oxygen, is used as the raw material. A low content is required.

Furthermore, for use in conductive pastes, agglomerated powders are easily separated from the vehicle, so powders with good dispersibility are required. Furthermore, in all of these uses, it is preferable that the particles be nearly spherical.

A common method for producing tungsten powder is to reduce tungsten oxide obtained by hydrolyzing ammonium paratungstate in a hydrogen atmosphere (referred to as a wet method).

In such methods, impurities derived from raw materials and processing chemicals are mixed in, and it is desired that the sputtering target material has as low an oxygen content as possible; Oxygen removal is difficult. Furthermore, the powder obtained in this manner is in a state where the particles appear to be coagulated, and has very poor dispersibility.

Further, tungsten itself has α-form and β-form as its crystal modifications, and α-form is the stable form, and tungsten powder obtained by a conventionally well-known wet method is α-form. The β-form has a crystal structure with the same X-ray diffraction pattern as W3C and W3C, and even if tungsten powder containing β-type tungsten is obtained, the X-ray diffraction pattern cannot be distinguished from W3C and W3C. -Currently, the existence of tungsten is not generally recognized.

[Specific Means for Solving the Problem 1] In view of the problem, the inventors of the present invention have conducted intensive studies, and found that by causing a gas phase reaction of a mixed gas of tungsten hexafluoride and hydrogen under specific conditions. We discovered that it is possible to obtain highly pure, almost spherical, monodisperse tungsten powder, and have already applied for a patent for this method.
In the course of this study, it was found that when using this method, the tungsten powder obtained contains β-tungsten powder! In particular, in order to efficiently obtain β-tungsten powder, the present invention was achieved by discovering that the temperature during mixing of tungsten hexafluoride and hydrogen must be 400° C. or higher. That is, the present invention is characterized in that tungsten hexafluoride and hydrogen are mixed at a molar ratio of H2/WF of 4 or more in the range of 400 to 400°C, and the reaction is carried out at a temperature in the reaction system of 650 to 1400°C. This is a method for producing β-tungsten powder. In the present invention, the molar ratio of H2/W-F is set to 4 or more, but if the molar ratio is smaller than this, the particle size of the produced tungsten powder will be uneven, and some WF6 will remain unreacted. This is not desirable as it will be discharged as is.

In addition, if the temperature in the reaction system is lower than 650°C, and the wall surface of the reactor is sufficiently wide for the amount of raw material tungsten hexafluoride, the reaction will proceed on this wall surface, forming a tungsten film. However, if the wall surface of the reactor is not wide enough for the amount of raw material tungsten hexafluoride, most of the tungsten hexafluoride is discharged from the reaction system unreacted.

The temperature in the reaction system basically does not matter as long as it is higher than this temperature, but since the reaction rate is sufficient at about 1400° C., there is no particular advantage in increasing the temperature above this temperature.

In order to efficiently obtain β-tungsten, 6) it is necessary to set the temperature when mixing ν-tungsten and hydrogen to 400° C. or higher. Below this temperature, most of the tungsten powder obtained is only in the α-form, and the β-form is not obtained.The reason for this is not clear, but if the temperature at the beginning of the reaction is low when the raw material gases are mixed, the tungsten nuclei in the α-form are It is considered that even if the α-form tungsten that has been produced is then passed through a reaction zone at a higher temperature, it no longer transforms to the β-form and is directly obtained as α-tungsten powder. -For boat fishing, there are α and β states.
It is said that the β-state is stable and that the β-state irreversibly transitions to the α-state at 600 to 700°C.In the system used in the method of the present invention, surprisingly, the β-state selectively changes its properties at higher temperatures. It is something that can be achieved.

The oxygen content in the tungsten powder obtained in this way is extremely low at 20 ppm or less, and the present inventors found that the carbon content was also extremely low (0,1 ppm or less) and that W3C and W3C were not present. This was confirmed, and the presence of β-tungsten powder was confirmed from the X-ray diffraction pattern.

The amount of β-tungsten in the obtained tungsten powder increases as the mixing temperature of the raw material gas increases (as the mixing temperature increases, but even at the same temperature, the amount of β-tungsten tends to increase as the mixing ratio (H2/WF8) increases. For example, at a mixing temperature of 600°C , when the mixing molar ratio (H2/WF8) is 5 and the reaction temperature (the highest temperature of the reaction system) is 1000'C, the amount of β-form in the obtained tungsten powder is about 15%. When the conditions are the same except that 35, the amount of β-form is about 63%.

In order to increase the mixing temperature to 400"C or higher, it is practically necessary to introduce the raw material gases separately into the reactor. Also, hydrogen is introduced near the entrance of the reaction tube, and 62 fluoride It is preferable to introduce tungsten on the downstream side of the reaction tube. In this way, a stagnation layer of gas can be eliminated and a powder with a uniform particle size can be obtained. There is no particular restriction on the zero reaction pressure, but tungsten is produced in a reduced pressure system. There is a tendency for the tungsten particle size to become smaller, and there is also a tendency for the particle size to become slightly larger in pressurized systems, - 100T for boat fishing.
orr~1.5 at! A range of 1 is recommended, and atmospheric pressure is most preferable from the viewpoint of ease of equipment and operation. The tungsten powder thus obtained is a monodisperse particle having a particle size of about 0.1 to 20 μm, depending on the reaction conditions, and its shape is approximately spherical.

When an inert gas is added to the reaction system in addition to tungsten hexafluoride and hydrogen, the shape of the resulting tungsten powder becomes even more spherical.

There are no particular restrictions on the reactor, but a vertical reactor is advantageous because of the ease of collecting the produced tungsten powder.If you want to obtain relatively large tungsten powder with a particle size of 0, the specific gravity of tungsten should be high. A raw material gas is introduced into the upper part of the reaction tube, and is caused to react by flowing from the upper part of the reaction tube toward the bottom. Tungsten powder produced by the reaction is collected in a tungsten powder collector provided below the reaction tube.

On the other hand, if you want to obtain fine tungsten powder, introduce the raw material gas from the bottom of the reaction tube, let the gas flow from the bottom to the top to react, and collect it with a tungsten powder collector installed above the reaction tube. .

The material of the reaction tube is preferably carbon. Heat-resistant alloys can also be used, but if you want to obtain extremely high-purity tungsten powder, a trace amount of impurity will be mixed into the product tungsten due to corrosion (surface reaction) by WF and by-product HF in a reducing atmosphere. It is not appropriate for Further, since carbon does not have sufficient airtightness, it is preferable to coat the surface with tungsten. Vapor phase reactive deposition of tungsten hexafluoride and hydrogen is suitable as a means of coating.

Hereinafter, the present invention will be specifically explained with reference to Examples.

Examples 1 to 5, Comparative Examples 1 to 4 Inside diameter 50 m1.Tungsten coated on the surface by gas phase reaction of tungsten hexafluoride and hydrogen. length 1
A vertical reactor equipped with a 000 mm carbon reaction tube was used, and raw material gases were separately introduced from the upper part of the reaction tube. The method of introduction is as follows.

Hydrogen is introduced from the side of the upper end of the reaction tube, and tungsten hexafluoride and inert gas are introduced from the upper end of the reaction tube in a double tube, with tungsten hexafluoride on the inside and inert gas on the outside. I set it to approximately 1/3rd position (
The position was variable depending on the reaction conditions). The reaction was carried out using the raw material gas flow rate, mixing temperature, reaction temperature (maximum temperature in the reaction system), reaction pressure, and residence time as shown in Table 1.

The results are shown in Table 1. In addition, Example 3, Example 2
The X-ray diffraction patterns of the tungsten powder obtained in Comparative Example 4 are shown in FIGS. 1, 2, and 3, respectively. In addition, the crystal structure of the tungsten powder obtained in Example 2 and the commercially available tungsten powder obtained by the wet method (Comparative Example 1) was
8M photographs are shown in FIGS. 4 and 5, respectively.

The content of β-tungsten in the tungsten powder was measured by X-ray diffraction using Cu-Kt X-rays, 30 KI/, 20 mA, scanning speed = 4''/i+in, time constant: 10 sec, full scale: 10 Kcsp. Calculated from the peak height of β-tungsten at 2θ = 40.0' in the pattern and the peak height of α-tungsten at 2θ-40.3°.In addition, if the amount of β-tungsten is less than 20% by weight, For β-tungsten, the peak height of 2θ-43,9' was used.The primary particle diameter was determined from the scanning electron micrograph.
000 and was determined by image analysis. The secondary particle size is ■
The measurement was performed using a laser diffraction particle size analyzer manufactured by Seishin Enterprises. This ratio was defined as the degree of aggregation.

(The following are blank spaces) Figure 1 Figure 2 [Effects of the Invention] According to the present invention, it is possible to easily obtain tungsten powder with high purity, especially with extremely low oxygen content, and the obtained powder is monodisperse with no cohesion. Because they are particles and have a spherical shape, they have good sinterability when used as a sputtering target, and have very good dispersibility when used as a conductive paste. It is possible to easily obtain powder containing a large amount of .

[Brief explanation of the drawing]

Figures 1, 2, and 3 are Example 3 and Example 2, respectively.
FIG. 4 and FIG. 5 show the X-ray diffraction pattern of the tungsten powder obtained in Comparative Example 4.
and 88M of the particle structure of the tungsten powder of Comparative Example 1.
The photo is shown. 2θ Tsutomu 4 Figure 5 Figure 1: m to j7

Claims (1)

[Claims] Production of β-tungsten powder characterized by mixing tungsten hexafluoride and hydrogen at a molar ratio of H_2/WF_6 of 4 or more in the range of 400 to 1400°C, and reacting at a temperature of 650 to 1400°C in the reaction system. Law.