JP4835973B2 - Method for producing refractory metal powder and method for producing target material - Google Patents

Description

  The present invention relates to a method for producing a refractory metal powder and a method for producing a target material for producing a refractory metal sintered body used for a sputtering target material or the like.

Currently, refractory metal films such as Mo with low electrical resistance are used for thin film electrodes and thin film wirings of flat display devices such as liquid crystal displays (hereinafter referred to as LCDs), and the metal thin films are formed. As a material for this purpose, sputtering target materials are widely used. In recent years, with the rapid expansion of the market for flat display devices, the demand for refractory metals including Mo is rapidly increasing, and the supply of raw material powder for sintering for producing a target material is insufficient. .
Under the circumstances described above, a method for reusing a used target material is currently being studied. For example, a chemical wet separation method in which a used target material is dissolved in a solution and chemically separated to regenerate a metal powder, or a method for producing a highly purified ingot by refining by electron beam melting has been proposed. However, the chemical method has a problem that the cost is high, and the method of manufacturing a melting ingot by electron beam melting has a problem that it is difficult to apply industrially because the processing of the ingot is difficult. is there. In addition, a method of producing a powder raw material that pulverizes a used target material and passes the obtained powder through thermal plasma to make it a spheroidized and highly purified fine powder (for example, Patent Documents). 1).
JP 2001-342506 A

  The above-mentioned Patent Document 1 has found that mechanically pulverized low-purity powder can be introduced into thermal plasma to spheroidize, reduce oxygen and increase the purity of refractory metal and noble metal powders. However, since the thermal plasma apparatus is used, there is a problem in that the production of powder from the used target material has a high cost.

  The object of the present invention is to easily and inexpensively stabilize a refractory metal powder from a used refractory metal target material without using an expensive method such as a chemical method or melting refining by thermal plasma. It is to provide a method of manufacturing.

  As a result of studying various methods for producing a refractory metal powder from a used refractory metal target material, the inventor of the present invention cuts the used target material into a dairy powder to produce a micro powder inside the dairy powder. In addition to improving crackability by introducing cracks and combining heat treatment to remove impurities such as oxygen introduced during cutting and grinding, it has the same level of purity as used refractory metal target materials The present inventors have found that it is possible to produce a refractory metal powder and have reached the present invention.

That is, the present invention is a dairy powder in which microcracks are generated by scraping a refractory metal target material having a component composition containing 50% or less of an alloy element in used Mo metal or Mo, This is a method for producing a refractory metal powder in which dairy powder is pulverized into a fine powder and then heat-treated in a reducing atmosphere.
Further, the present invention provides a dairy powder in which microcracks are generated by machining a refractory metal target material having a component composition containing 50% or less of an alloy element in used Mo metal or Mo, This is a method for producing a refractory metal-based powder, which is obtained by heat-treating Dalai powder in a reducing atmosphere and further pulverizing it into a fine powder.

Preferably, the cutting process is a method for producing a refractory metal powder using a milling cutter.
Also preferably, the pulverizing treatment of the Dalai powder is a method for producing a refractory metal powder that is impact pulverization.
Preferably, the heat treatment in the reducing atmosphere is a method for producing a refractory metal powder having a hydrogen-containing atmosphere.
Preferably, the heat treatment in the reducing atmosphere is a method for producing a refractory metal powder having a reduced pressure atmosphere of 100 Pa or less.
Preferably, the method is a method for producing a refractory metal powder having a fine particle diameter of 20 to 1000 μm with an average particle diameter by the pulverization treatment.
Preferably, the high melting point metal is a method for producing a high melting point metal powder in which pure Mo is pure Mo.
Moreover, this invention is a manufacturing method of the target material which sinters the high melting point metal type powder obtained by said manufacturing method.

  According to the present invention, it becomes possible to easily and inexpensively produce a refractory metal powder from a used refractory metal target material, and stably produce a refractory metal target material at a low cost. Therefore, the industrial utility value is high.

  The most important feature of the present invention is that the bulk body of the used high-melting-point metal target material is cut into a certain shape to produce a dairy powder in which microcracks are generated inside the metal structure. It is in the point which discovered that micronization became possible easily.

Generally, in the production of refractory metal-based target materials, the melting temperature is high, making it difficult to produce by the melt casting method, and the powder sintering method that sinters the raw material powder into a bulk body is used. Has been. Therefore, in order to recycle the used target material, it is necessary to process it into a powder that can be a raw material for sintering.
According to the study by the present inventors, from the refractory metal material, which is a composition system in which ductility is hardly recognized at room temperature, when mechanical stress is forcibly applied by a cutting process to produce a dairy powder, It was found that it is possible to introduce microcracks locally in Dalai powder. This is presumed that, in a composition system having poor ductility at room temperature, microcracks were locally generated because the original ductility was exceeded by applying a forced stress for a short time by cutting. The presence of local microcracks introduced into the Dalai powder makes it possible to easily obtain a fine powder from a high-density refractory metal-based bulk material that is difficult to grind.

  In addition, typical examples of refractory metal systems in which ductility is hardly recognized at room temperature include, in particular, metal compositions of Cr, Mo, W and components containing alloy elements in a range of 50% or less in Cr, Mo, W Composition. In the ductility test using a thermo-star, for example, Mo does not exhibit ductility up to about 150 ° C., and further, ductility is not recognized in these compositions, for example, W does not exhibit ductility unless the temperature is higher than Mo at higher melting point W. Therefore, since it is considered that microcracks are likely to be introduced by cutting, this component composition is suitable for producing powder by the production method of the present invention.

Below, the manufacturing method of the refractory metal powder of the present invention will be explained in order.
In the present invention, first, a used refractory metal-based target material is cut out to produce a dairy powder. The reason why the dairy powder is produced by the scraping process is to introduce a microcrack into the dairy powder as described above to improve the pulverization property.
As a result of investigation by the inventors of the present invention on the correlation between the dairy powder produced by cutting and the occurrence of microcracks in the dairy powder, the presence of microcracks at both ends of the dairy powder was confirmed when the thickness of the dairy powder exceeded 2 mm. However, since it does not penetrate the thickness and the tendency of the cracks to close and be integrated in the middle becomes remarkable, subsequent pulverization may be difficult. Further, in the cutting with a milling machine or the like, the resistance at the time of cutting increases, which is not preferable in terms of equipment. Moreover, if the thickness of the dairy powder is less than 30 μm, microcracks can be sufficiently introduced into the dairy powder, but the efficiency of producing the dairy powder is inferior and it becomes flaky and pulverizable. May decrease. Therefore, in consideration of the pulverization property of the dairy powder, the thickness of the dairy powder is desirably about 30 μm to 2 mm.

  Moreover, what can extract | collect a daray powder by cutting, such as a lathe, a drill, and a milling machine, can be used for cutting. In obtaining Dalai powder by cutting, it is desirable to suitably set the equipment to be used and the cutting conditions according to the composition of the used high-melting point metal-based target material. Of these lathes, drills and milling machines, milling is the most desirable. This is because, according to the milling cutter, it is possible to fix a used target material, which is generally a flat and large workpiece, and to perform cutting with high production efficiency.

Next, the obtained dairy powder is pulverized into fine powder. Since microcracks are locally introduced into the inside of the Dalai powder by the cutting process, it is much easier to make the powder finer than directly making the bulk into a fine powder.
Ball mill, vibration mill, jaw crusher, impact crusher, hammer mill, impact mill, and the like can be used as a method for crushing Dalai powder. It is desirable that the method be able to.

  In the pulverization process, it is necessary to consider mass productivity as well as avoid mixing impurities. In the pulverization method using a frictional force such as a ball mill or a vibration mill as a main stress, the amount of ultrafine powder increases and particle size control is difficult, and the fine powder tends to be oxidized. Moreover, since a pot is used, mass productivity is lacking, and the amount of impurities tends to increase due to contamination. Also, the crushing method that uses compressive force and shear force as the main stress, such as roll crusher, or the crushing method combined with friction force, tends to make it difficult to mix impurities and control particle size due to contact with the crushing tool. There is. Therefore, pulverization processing by impact pulverization using an impact force as a main stress such as a hammer mill or impact mill that can further suppress contact with the pulverization tool or liner is most desirable. The use of a hammer mill or an impact mill is desirable from the standpoint of mass productivity because it enables continuous feeding of pulverized raw material Dalai powder.

Further, the dairy powder or fine powder is heat-treated in a reducing atmosphere. This heat treatment is necessary in order to reduce the introduced oxygen to a level equivalent to that of the used refractory metal-based target material in the cutting process or pulverization process.
In addition, it is desirable to set suitable conditions for this heat treatment for reducing oxygen depending on the component composition of the dairy powder or fine powder. For example, when the component composition is Mo or W, it is desirable to have a reducing atmosphere into which hydrogen having an excellent effect as a reducing medium is introduced. In addition, in the case of MoTi alloy or MoNb alloy, in which Nb, Ti, etc. tend to occlude hydrogen and it is not desirable to have an atmosphere in which hydrogen is introduced, a method of reducing oxygen by a reducing action in a reduced pressure atmosphere of 100 Pa or less Is preferred. Although depending on the amount of oxygen adhering to the surface of the Dalai powder or fine powder, it is possible to remove oxygen more efficiently if the suction force of a general rotary pump is secured.

Further, the temperature condition of the heat treatment in the reducing atmosphere is preferably about 500 to 1500 ° C., although there are some differences depending on the composition of the dairy powder and fine powder. This is because the effect of reducing oxygen is very small at 500 ° C. or lower, whereas when the temperature exceeds 1500 ° C., the contact portion between the pulverized refractory metal powders starts diffusion bonding, so that it is difficult to crush again. It is to become. Moreover, more preferable temperature conditions are 600-1300 degreeC, More preferably, it is 800-1200 degreeC.
In addition, when the fine powder is heat-treated in a reducing atmosphere, depending on the temperature conditions, the fine powder may be lightly bonded to each other. The fine powder may be subjected to a heat treatment at a lower temperature than the heat treatment before crushing to reduce oxygen.

  In addition, when the refractory metal powder produced according to the present invention is used as a raw powder for pressure sintering, the average particle size is 20 in consideration of the filling property to the pressurized container and the production efficiency. It is desirable that the thickness be ˜1000 μm. That is, if the average particle size is less than 20 μm, it may be difficult to improve the packing density of the pressurized container. Therefore, the pulverization treatment up to the above average particle size below 20 μm is not efficient. It is. In addition, when a coarse powder having an average particle size exceeding 1000 μm is included, the packing density may not increase due to a bridging phenomenon between the powders.

Further, it is more desirable to add a step of washing the dairy powder in order to remove impurities such as carbon, oxygen, hydrogen and the like adhering to the dairy powder when the used refractory metal target material is cut out.
For this washing process, hot water of 40 ° C. or higher, acetone, ethanol, etc. can be used. However, in order to further promote safety and removal of the impurities, after washing with warm water, an alkaline industrial water-soluble cleaner and pure water are used. A method of rinsing is more desirable.
When cutting, cutting oil may be used in consideration of workability efficiency. In such a case, in order to remove the cutting oil, a hydrocarbon solvent is used. It is desirable to clean the dairy powder. As the hydrocarbon solvent, paraffinic or naphthenic “third petroleum” is desirable in consideration of environmental aspects and risk of fire explosion.

  Further, since the refractory metal powder obtained by the present invention has the same level of purity as the used refractory metal target material, a target material with high purity can be easily obtained by sintering this powder. Therefore, it is suitable as a method for producing a target material.

Examples of the present invention will be described below.
The used Mo target material was cut out by a mill using a chip made of carbide WC while applying cutting oil, and dairy powder having a thickness of about 50 μm was collected. FIG. 1 schematically shows the appearance of the Mo Dalai powder, and FIG. 2 shows a microscopic photograph taken with an optical microscope. From FIG. 2, it can be seen that microcracks are present along the grain boundaries of the Mo Dalai powder by cutting.
Thereafter, the cutting oil adhering to the collected Mo Dalai powder was removed by a centrifugal separator, immersed in a hydrocarbon solvent, washed with rocking and ultrasonic waves in combination, and dried. In addition, when the oil content adhering to this Mo dalai powder was measured with the oil concentration meter, the oil content after washing and drying was 1 mg / 50 g or less.

Mo fine powder was obtained by pulverizing the Mo Dalai powder after washing and drying by impact pulverization using an impact mill of carbide WC specification. When the particle size distribution of the obtained Mo fine powder was measured using a laser diffraction particle size distribution analyzer (Mastersizer 2000 manufactured by Malvern), the average particle size (D ₅₀ ) was 198 μm.
Subsequently, the Mo fine powder is subjected to a heat treatment in which a hydrogen pressure in the furnace is reduced to 0.115 MPa and held at 1200 ° C. for 2 hours to remove impurities such as oxygen introduced during the pulverization process. went.

  In addition, the amount of impurities in the used Mo target material, the Mo Dalai powder after the cutting process with the attached cutting oil, the Mo Dalai powder after the cleaning and drying, the Mo fine powder after the pulverization process, and the Mo fine powder after the heat treatment The analytical measurement results are shown in Table 1. Each impurity amount was analyzed and measured by Fe: atomic absorption method, C: combustion-infrared absorption method, O: inert gas dissolution-infrared absorption method, and N and H: inert gas dissolution-thermal conductivity method. .

  From Table 1, it can be seen that the Mo fine powder after the heat treatment has an impurity amount equal to or lower than that of the used Mo target material, and in particular, the oxygen amount can be greatly reduced. In addition, according to the present invention, the amount of oxygen can be greatly reduced as compared with a used target material, and therefore, it is particularly preferable as a powder raw material for producing a target material by powder sintering that has a limit in reducing the amount of oxygen. I understand.

The heat-dried Mo Dalai powder obtained by the same method as in Example 1 is subjected to a heat treatment that is held at 1200 ° C. for 2 hours in a reducing atmosphere in which the hydrogen pressure in the furnace is 0.115 MPa. A treatment for removing impurities such as oxygen was performed. The Mo Dalai powder after this heat treatment was subjected to a pulverization process by impact pulverization using an impact mill with a carbide WC specification to obtain a Mo fine powder. When the particle size distribution of the obtained fine Mo powder was measured using a laser diffraction particle size distribution analyzer (Malvern Mastersizer 2000) in the same manner as in Example 1, the average particle size (D ₅₀ ) was 198 μm. It was.
Using the same analytical measurement method as in Example 1, the used Mo target material, the Mo dalai powder after the cutting process with the attached cutting oil, the Mo dalai powder after washing and drying, and the Mo dalai powder after heat treatment in a reducing atmosphere Table 2 shows the results of analyzing and measuring the amount of impurities in the Mo fine powder after the pulverization treatment.

  Table 2 also shows that the Mo fine powder obtained by the production method of the present invention has an impurity amount equal to or lower than that of the used Mo target material, and particularly the oxygen amount can be greatly reduced. In addition, according to the present invention, the amount of oxygen can be greatly reduced as compared with a used target material, and therefore, it is particularly preferable as a powder raw material for producing a target material by powder sintering that has a limit in reducing the amount of oxygen. I understand.

2 is a diagram schematically showing the appearance of Mo Dalai powder collected in Example 1. FIG. 2 is a microstructural photograph of an Mo Dalai powder collected in Example 1 using an optical microscope.

Claims (9)

A refractory metal target material having a component composition containing used Mo metal or an alloy element of 50% or less in Mo is cut into a dairy powder that is microcracked , and the dairy powder is pulverized. A method for producing a refractory metal powder characterized in that after making into a fine powder, heat treatment is further performed in a reducing atmosphere. A refractory metal target material having a component composition containing used Mo metal or an alloy element of 50% or less in Mo is cut into a dairy powder that has been microcracked , and the dairy powder is reduced in a reducing atmosphere. A method for producing a refractory metal powder, characterized in that after the heat treatment in step 1, the powder is further pulverized into a fine powder.   The method for producing a refractory metal powder according to claim 1 or 2, characterized in that a milling is used in the cutting process.   The method for producing a refractory metal powder according to any one of claims 1 to 3, wherein the pulverization treatment of the Dalai powder is impact pulverization.   The method for producing a refractory metal powder according to any one of claims 1 to 4, wherein the heat treatment in the reducing atmosphere is a hydrogen-containing atmosphere.   The method for producing a refractory metal powder according to any one of claims 1 to 5, wherein the heat treatment in the reducing atmosphere is a reduced pressure atmosphere of 100 Pa or less.   The method for producing a refractory metal powder according to any one of claims 1 to 6, wherein the fine powder having an average particle diameter of 20 to 1000 µm is obtained by the pulverization treatment.   The method for producing a refractory metal powder according to claim 1, wherein the refractory metal is pure Mo.   A method for producing a target material, comprising sintering a refractory metal powder obtained by the method for producing a refractory metal powder according to any one of claims 1 to 8.