KR20080048816A - Fabrication of a precious metal target using a spark plasma sintering - Google Patents

Abstract

A method that can manufacture a target having fine grains and a density close to the theoretic specific gravity in an inexpensive and prompt manner by a spark plasma sintering process as compared with conventional melting and casting process and powder sintering process is provided. A method for manufacturing a precious metal target by a spark plasma sintering process comprises: a step(S1) of performing crushing and drying of a prepared powder; a step(S2) of preparing a carbon sheet on a mold for spark plasma sintering; a step(S3) of filling a powder of a target into the mold to prepare a mold set, and setting the mold set within a spark plasma sintering equipment chamber; a step(S4) of reducing pressure of the chamber by a vacuum device, pressurizing the pressure-reduced chamber, and injecting an electric current to the pressurized chamber to increase the temperature of the chamber; a step(S5) of pressurizing the chamber at a temperature near a final sintering temperature, maintaining the chamber for dozens of minutes, and cooling the chamber in a furnace; and a step(S6) of removing the carbon sheet adhered to a sintered body.

Description

Fabrication of a precious metal target using a spark plasma sintering

1 is an overall flowchart of the production of a noble metal target using the discharge plasma sintering method of the present invention.

2 is a schematic diagram of an apparatus used to make a noble metal target of the present invention.

BACKGROUND OF THE INVENTION The present invention relates to a thin film of precious metal (Pt) for electrodes on wafers or glass, which are recently used in connection with semiconductor memories (RAM, MRAM, FeRAM), heads (MR, GMR, TMR) and capacitors. , Ir, Ru, Pd, Rh, etc.), and a method for manufacturing the precious metal target material using a new sintering method. will be.

The discharge plasma sintering method according to the present invention is a method of applying a direct current pulse current in a direction parallel to the pressing direction while sintering the powder in one axis, and injecting pressure, a low voltage and a large current into the gap between the powder particles, It is a sintering method in which high energy of plasma generated by a spark is applied to electric field diffusion and thermal diffusion. Compared to the conventional hot press method, the sintering temperature is 200 to 500 ° C lower, and the sintering can be completed in a short time including the temperature raising and holding time, which greatly reduces the power consumption, and the handling is easy. Inexpensive, skilled in the sintering technique is not required, and can be applied to materials that are difficult to process at high temperatures and sintering materials.

Conventional methods of manufacturing precious metal target materials include welding by plasma or arc after casting by melting (plasma arc melting, arc melting, high frequency induction melting, etc.), and post-processing (hot rolling, Cold rolling, heat treatment, etc.), or after grinding using a powder sintering method (Hot Press (HP), Hot Isostatic Press (HIP)).

However, in the case of the target produced by the dissolution method, since partial melting is performed due to the characteristics of the material, welding is performed so that a post-process for the production of a uniform shape is added, and a processing structure is added to the grain control to control the grain. There is a disadvantage to use it by recrystallization.

In the case of using the powder sintering method, it is difficult to increase the density by containing a large amount of gas. Particles are easily generated when a thin film is formed by using a target containing these gases, and such particles adversely affect post-processing. (Pin hole generation, etc. due to particle dropping), it is difficult to obtain a healthy precious metal thin film.

As described above, in order to produce a noble metal target by a conventionally known method (dissolution method, powder sintering method) requires a high cost by a complicated process, or difficult to secure a high-density target, the present invention to overcome these problems The present invention aims to provide a method for producing a precious metal target material having a simple process, a high density close to theoretical density, and excellent physical properties by discharging the powder into a mold of a desired shape and then discharging the plasma by a plasma sintering method. do.

In order to solve the above technical problem, the present invention comprises the steps of pulverizing and drying the powder of the prepared target target, preparing a carbon sheet (carbon sheet) in the discharge plasma sintering mold, the powder of the target target After filling the mold of the mold set to prepare a set (set) in the discharge plasma chamber sintering apparatus (chamber), the step of heating the chamber by depressurization and pressurization and current input after depressurizing the chamber by a vacuum apparatus, It is composed of a step of cooling in the furnace after pressurizing and maintaining for several tens of minutes near the final sintering temperature, and removing the carbon sheet adhered to the sintered body.

Hereinafter, the process of the present invention will be described in detail with reference to FIG. 1.

First, the powder of the target target is ground and dried (S1).

Grinding is carried out through a ball mill, an attritor mill, a planetary mill, or the like, which is generally performed, followed by drying at 200 ° C. or less for 1 hour to remove moisture and the like. In this process, since the size or shape of the powder may not be uniform in the initially prepared powder, fine and uniform powder is prepared through pulverization and drying, and the same conditions are maintained even during the sintering of the plasma discharged in the subsequent process. To do this.

Next, a carbon sheet is prepared in a mold for discharging plasma to be filled with powder (S2).

Inside the mold, a carbon sheet having a thickness of about 0.2 mm, which is generally available, is inserted into the mold. The carbon sheet is intended to avoid contact between powder, upper and lower punches and dies during the discharge plasma sintering. When the carbon sheet is not used, the carbon sheet rises to a high temperature due to the high load and current applied during the discharge plasma sintering and is fixed between the mold and the sintered body. There arises a problem, and there is a fear that expensive mold is broken when it is separated. On the other hand, when the carbon sheet is used, the carbon sheet is easily separated from the sintered body and the mold, and the carbon sheet is removed by polishing, so that a healthy sintered body can be obtained simply. If the sintering temperature is higher, even when a carbon sheet is used, a reaction may occur between the mold and the sintered body. In this case, the reaction may be suppressed by additionally using ultra high temperature BN.

After the final powder is filled in the mold to prepare a mold set and set in the discharge plasma sintering chamber (S3).

In order to prevent the damage of the mold due to the load biased to one side during the discharge plasma sintering, the height of the upper and lower punches which come out of the sintering die after preparing the mold set is adjusted to the same level. In addition, the set is protected at the center of the electrode to protect the mold even when the discharge plasma is set inside the sintering apparatus.

After the chamber is decompressed by the vacuum apparatus, the chamber is heated by pressurization and current injection (S4).

In the present invention, the pressure reduction was performed using a vacuum device such as a rotary pump (RP), a booster pump (BP), and a diffusion pump (DP), and the noble metal materials have a high sintering temperature of 1000 ° C. or higher, and are used only at high temperatures. Atmosphere control for the use of carbon molds that can maintain high strength. In addition, the high temperature sintered material which is easily volatilized in the vacuum atmosphere can be sintered by adjusting the atmosphere (N 2, Ar, etc.).

When the pressure is reduced to a certain level, it is preferable to apply a load and raise the current by raising the current at the same width for a predetermined time. At this time, the pressure is applied to 20 ~ 80MPa, the temperature increase rate is adjusted to 50 ~ 200 ℃ / min level. In the case of pressure, sintering may be insufficient when the pressure is 20 MPa or less, and 80 MPa is the highest strength of the commercially available carbon mold.

Since the applied current is different depending on the size and mold size of each equipment, it is easy to control the temperature, but if the temperature rise rate is low, the sintering time can be long, if it is high, rapid sintering proceeds, it is difficult to accurately predict the sintering temperature.

Cooling is performed in a furnace after pressurization and tens of minutes is maintained near the sintering temperature (S5).

The sintering end temperature refers to a temperature (temperature without change in height) in which the powder no longer contracts upon pressurization and temperature increase, which may vary depending on the type of powder, the size, shape and purity of the powder.

While discharge plasma sintering is a process that takes place in a short time, the material covered in the present invention is a precious metal with a very high sintering temperature, so that the sintering is completed as described above to obtain a high-density sintered body to complete sintering to the center part. After dozens of minutes. Grain growth may occur by increasing the sintering time, but there is no large grain growth because the entire process time is within several hours including the temperature raising and cooling processes.

After the completion of the discharge plasma sintering process, it should be cooled in the furnace to 100 ° C or lower while continuously reducing the pressure to protect the carbon mold.

Since the coolant is connected to the upper and lower electrodes, rapid cooling is possible by contacting the electrode with the mold while applying a minimum load. This method can be applied to metal materials with high thermal conductivity. On the other hand, ceramic materials with low thermal conductivity should be refrained due to the risk of cracking due to the rapid expansion of the inside and outside due to the rapid temperature gradient during cooling. .

The carbon sheet fixed to the sintered body is removed (S6).

This is also a step in adjusting the final target thickness. In the case of platinum target, there is no reaction with oxygen until high temperature, carbon sheet is easily removed by high temperature heat treatment in the air, and in case of ruthenium and iridium, reaction with oxygen occurs, causing discoloration and toxic oxides to be volatilized. It should be avoided, and it is desirable to control the thickness of other precious metal targets by mechanical polishing to secure the surface roughness.

Example 1 Platinum Target Preparation

In order to produce a platinum target having a thickness of 6 mm having a diameter of 4 inches, 1,061 g of purity 4N grade platinum powder was prepared in consideration of the amount removed by polishing after finishing sintering.

The prepared powder is pulverized through a planetary mill and then dried. The size of the powder after pulverization and drying was in the range of 1 to 20 µm, and the central particle size was about 8 µm. The prepared powder is filled into a mold having an outer diameter of 200 mm and an inner diameter of 102 mm, and then the mold set is set inside the discharge plasma sintering apparatus chamber. After setting, reduce the pressure to 1Pa or below by using a vacuum apparatus, pressurize to 33ton (about 40MPa in terms of conversion), and apply a current at 1000A / min to adjust the temperature increase rate to 100 ° C / min. After the shrinkage, it was terminated after holding for about 30 minutes at a temperature (near 1000 to 1100 ° C.) where the height did not change, and the upper and lower electrodes were attached to the mold with a minimum load and cooled. After cooling below 100 ℃, the vacuum is released, and the sintered compact in which the mold and the carbon sheet are fixed are separated, and the carbon sheet is removed and the thickness is adjusted by polishing. Finally, a healthy platinum target having a thickness of 6 mm and a 4 inch diameter can be obtained. .

Example 2 Preparation of Iridium Target

To prepare an iridium target having the same size as in Example 1, 1,109 g of 3N5 grade pulverized and dried iridium powder was prepared. The size of the powder is 0.05 ~ 14㎛ level, the central particle size is about 6㎛. The prepared powder was processed in the same manner as in Example 1 to prepare a final iridium target.

Example 3 Ruthenium Target Preparation

To prepare a ruthenium target of the same size as in Example 1, 612 g of 3N5 grade pulverized and dried ruthenium powder was prepared. The powder size ranged from 1 to 15 µm and the median particle size was about 4.7 µm. The prepared powder was processed in the same manner as in Example 1 to prepare a final ruthenium target.

Comparative Example 1 Platinum Target Preparation

Using a platinum powder of the same size used in Example 1 to prepare a platinum target by the dissolution method. The target manufacturing method produces a rod-shaped ingot after melting by a high frequency induction melting method which is a conventional manufacturing method. The manufactured ingot is subjected to hot forging at 1000 ° C. or more in order to break the cast structure and change it into a rectangular shape, and control the final thickness to 6 mm by cold rolling after face-to-face making a recrystallized structure through heat treatment. The heat-treated plate was obtained by using a wire cutter and a polishing machine to obtain a 4 inch platinum target.

Comparative Example 2 Preparation of Iridium Target

An iridium target was prepared by dissolution using the same size powder used in Example 2. In the target manufacturing method, four ingots were manufactured by using vacuum arc melting after being manufactured into a pseudo-molded body by pressing. The manufactured ingot was welded into one shape by using a plasma welding machine, and foreign substances on the surface were removed by pickling. The removed ingot was hot plated and rolled at 1300 ° C. to produce a plate, and after controlling the grain through final heat treatment, an iridium target having a size of 4 inches was obtained by using a wire cutter and a polishing machine.

Comparative Example 3 Ruthenium Target Preparation

A ruthenium target was prepared by a dissolution method using the same size powder used in Example 3. In the target manufacturing method, the ingot is manufactured by using vacuum arc melting after being manufactured into a pseudo-molded body by pressing. The ingot thus made is difficult to weld or other operations due to the ruthenium properties, and the upper and lower surfaces are ground and plated, and a final ruthenium target is obtained by using a wire cutter and a polishing machine.

Table 1, Table 2 and Table 3 below shows the relative specific gravity, hardness, grain size and manufacturing time for the precious metal targets produced by the discharge plasma sintering and dissolution method.

The precious metal target material produced by the discharge plasma sintering method shows a relative specific gravity close to the theoretical specific gravity, and exhibits excellent properties such as high hardness, fine grains, and shorter manufacturing time than the dissolution method. From these results, by the discharge plasma sintering method of the embodiment, it is possible to produce a precious metal target superior to the conventional and in a short time.

Platinum Target Relative weight Hardness (Hv) Crystal grain size (㎛) Manufacture time Example 1 100% 50 5 3 Comparative Example 1 100% 35 50 15

Iridium Target Relative weight Hardness (Hv) Crystal grain size (㎛) Manufacture time Example 2 99.7% 610 10 4 Comparative Example 2 99.8% 340 2200 18

Ruthenium Target Relative weight Hardness (Hv) Crystal grain size (㎛) Manufacture time Example 3 99.5% 590 15 4 Comparative Example 3 99.7% 280 1500 12

A schematic diagram of the discharge plasma sintering apparatus used to manufacture the precious metal target material of the present invention is shown in FIG. 2.

The discharge plasma sintering apparatus is composed of a main body of a sintering machine having a pressurizing mechanism on a vertical axis, a special energization mechanism with a built-in water cooling unit, a water cooling vacuum chamber, an atmosphere control mechanism (control of vacuum, Ar and N _2, etc.), a vacuum exhaust device, and an SPS DC power supply. It consists of a supply apparatus, a control apparatus, etc.

As described above, the production of a noble metal target by the conventional method requires a complicated process, a poor working environment, and a costly sintering method. However, in the present invention, the size of the final crystal powder is uniformly controlled by pulverizing and drying the powder of the target target, and the production method is simple by using the discharge plasma sintering method, has a high density close to the theoretical density, and excellent physical properties. Production of the noble metal sputtering target material which has is possible. The precious metal targets thus manufactured can be provided as thin metal materials for noble metals in various industries, such as semiconductors. In particular, wafers and glasses used in connection with semiconductor memories (RAM, MRAM, FeRAM), heads (MR, GMR, TMR) and capacitors It can be used as a sputtering material of a thin noble metal applied for phase electrodes.

Claims (7)

In the method for producing a noble metal target using the discharge plasma sintering method, Pulverizing and drying the prepared powder, Preparing a carbon sheet in a mold for discharge plasma sintering; Filling the mold with a target target powder, preparing a mold set, and then setting the mold set in a discharge plasma sintering chamber; Heating the chamber by depressurizing the chamber by applying pressure and a current after decompression; Pressing in the vicinity of the final sintering temperature and holding for several tens of minutes, then cooling in a furnace; Method of producing a noble metal target using the discharge plasma sintering method, characterized in that the step consisting of removing the carbon sheet fixed to the sintered body. The method of claim 1, The noble metal is platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), Rh (rhodium) any one of the manufacturing method of the noble metal target using the discharge plasma sintering method. The method of claim 1, The pressure applied during the discharge plasma sintering method of the noble metal target using the discharge plasma sintering method, characterized in that 20 to 80MPa. The method of claim 1, The method of manufacturing a noble metal target using the discharge plasma sintering method, characterized in that the discharge plasma sintering in a vacuum atmosphere or inert atmosphere (Ar, N ₂ ). The method of claim 1, Method for producing a noble metal target using the discharge plasma sintering method, characterized in that the temperature rise rate during the discharge plasma sintering range 50 ~ 200 ℃ / min. In the sputtering target material made of a noble metal, Sputtering target material manufactured by discharge plasma sintering method. The method of claim 6, The precious metal is any one of platinum (Pt), ruthenium (Ru), iridium (Ir), palladium (Pd), and Rh (rhodium).

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