KR20170044343A

KR20170044343A - Preparation method of reuse tungsten target and the reuse tungsten target prepared thereby

Info

Publication number: KR20170044343A
Application number: KR1020150143915A
Authority: KR
Inventors: 이효원; 홍길수; 양승호; 윤원규
Original assignee: 희성금속 주식회사
Priority date: 2015-10-15
Filing date: 2015-10-15
Publication date: 2017-04-25

Abstract

The present invention relates to a preparation method of a reuse tungsten target and a reuse tungsten target prepared thereby, wherein the reuse tungsten target has high density, high purity, and a fine crystal grain with a tungsten waste target used in a sputtering process.

Description

TECHNICAL FIELD The present invention relates to a method of manufacturing a recycled tungsten target and a recycled tungsten target produced therefrom. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reclaimed tungsten target,

The present invention relates to a method for manufacturing a recycled tungsten target using a tungsten waste target consumed in excess of 30%.

A target made of tungsten (hereinafter, referred to as a "tungsten target") is mainly used for forming gate electrodes and circuits of ICs and LSIs. Such a tungsten target is required to have properties such as low resistance, fine grain size, inhibition of particle generation, high purity and high density for thermal and chemical stability.

Conventional tungsten targets are manufactured by a method of hot rolling an ingot manufactured by an electron beam melting method, a method of pressing hot sintering of tungsten powder followed by a hot hydrostatic pressing, or a method of hot rolling a tungsten powder after pressure sintering.

However, the tungsten target produced by the above methods has disadvantages such as particle defects and grain boundary coarsening, and it is difficult to form a uniform film due to deformation of the structure after rolling. Therefore, there is a demand for the development of a tungsten target having a high density and a high purity with crystal grains becoming finer.

On the other hand, when a tungsten target consumes about 30% in a sputtering process, a protrusion called a shed is formed at the boundary defined by the erosion and around the tungsten target. If the sputtering process is continued with the Erosion or the tungsten target in which the sintered material is formed, the formation of particles is increased, which results in deterioration of the physical properties of the thin film. Therefore, when the tungsten target is consumed by about 30%, it is discarded and the use efficiency thereof is very low.

Accordingly, there is a demand for recycling tungsten waste targets that have been used for the purpose of reducing the manufacturing cost of the tungsten target and shortening the process L / T.

Korean Patent Publication No. 2010-0139152

In order to solve the above problems, it is an object of the present invention to provide a method for manufacturing a recycled tungsten target having high density, high purity and fine crystal grains by using a used tungsten waste target.

It is another object of the present invention to provide a recycled tungsten target produced by the above method.

According to an aspect of the present invention, there is provided a method of manufacturing a tungsten waste target, comprising the steps of: (a) separating a backing plate from a tungsten waste target to obtain a tungsten sintered body having a consumable part; (b) removing impurities present in the tungsten sintered body; (c) securing a tungsten powder having the same composition as the tungsten sintered body; (d) filling the tungsten powder into a consumable portion of the tungsten sintered body, and pressing and sintering to prepare a preliminary sintered body; (e) heat treating the preliminary sintered body in a reducing atmosphere or a vacuum atmosphere; (f) pressing the heat-treated pre-sintered body under hot isostatic pressure to produce a sintered body; And (g) recrystallizing the sintered body. The present invention also provides a method of manufacturing a recycled tungsten target.

The present invention also provides a recycled tungsten target produced by the above-described method.

The present invention is characterized in that a tungsten sintered body obtained from a used tungsten waste target is filled with high purity tungsten powder and then subjected to pressure sintering, heat treatment, hot isostatic pressing and recrystallization to produce a recycled tungsten target, It is possible to provide a recycled tungsten target that is controlled to a specific range and exhibits high purity and high density.

In addition, the production method of the present invention reduces the manufacturing cost of the tungsten target because the amount of tungsten powder used is smaller than that of the method of producing a new tungsten target by sintering the tungsten powder, resulting in economical, shortening of the manufacturing time, It is eco-friendly.

1 is a flowchart illustrating a manufacturing process of a recycled tungsten target according to an embodiment of the present invention.
2 is an image (crystal grains: 20 μm or less) of the crystal grains of the recycled tungsten target produced in Example 1 of the present invention.

Hereinafter, the present invention will be described in detail.

<Recycled tungsten Target Manufacturing method>

Disclosure of the Invention The present invention aims at reducing the L / T of the target and reducing the manufacturing cost by recycling the tungsten waste target that has been used in the sputtering process, and at the same time improving the physical properties (high density, high purity and low cost) of the new tungsten target produced by sintering the tungsten powder (Low) gas content) of the recycled tungsten target.

Particularly, when the tungsten waste target is recycled by the conventional method, the purity and the crystal grain can be controlled by controlling the process conditions. However, the remainder portion (tungsten sintered body) of the tungsten waste target and the portion filled with the new raw material powder ) Is different from that of the tungsten target, so that it is not easy to control the crystal grains at the interface between the remainder portion of the tungsten waste target and the filled portion.

However, the present invention provides a recycled tungsten target having a high degree of uniformity and fine crystal grains by easily controlling the grain growth at the interface between the remainder portion of the tungsten waste target and the filled portion by manufacturing the recycled tungsten target by the novel manufacturing method . Therefore, when a thin film is formed using the recycled tungsten target of the present invention, a thin film having a high uniformity and a low sheet resistance can be formed without a significant difference according to positions between the remainder portion and the filled portion of the tungsten waste target.

In the method of the present invention, a tungsten sintered body obtained from a used tungsten waste target is surface-cleaned to remove impurities such as oxides and carbides and then mixed with a purified tungsten sintered body and a high purity tungsten powder (5N grade) And a pressurizing and sintering process, a heat treatment process, a hot isostatic pressing process, and a recrystallization process are successively carried out through HP, and will be described in detail with reference to FIG.

(a) Tungsten In the lung target Backing Separate the plate (Backing Plate) to obtain a tungsten sintered body having a consumable part ( S10 ).

The tungsten waste target is not particularly limited as long as it is used in the sputtering process. For example, the tungsten target may be a tungsten target that is used (consumed) at least 20%, preferably at least 30 to 35%. A method for separating the backing plate from the tungsten waste target is not particularly limited, and examples thereof include a method of debonding using a lathe and a machining M / C. At this time, the rpm of the processing equipment is in the range of 100 to 200, and the infeed amount per one step is preferably 0.1 or more. This is because the backing plate can be separated without crack formation of the tungsten sintered body by separating the backing plate under the above processing conditions.

(b) removing impurities existing in the tungsten sintered body ( S20 ).

Impurities such as oxides, carbides and the like may be present on the surface of the tungsten sintered body obtained above. Since the present invention is for the purpose of recycling a tungsten waste target, it is preferable to maintain a surface state free from impurities. Accordingly, a process of removing surface impurities present in the tungsten sintered body is performed at least once through a conventional impurity removing method known in the art. At this time, there is no particular limitation on the method for removing the impurities, but examples thereof include a cleaning method such as cleaning using an acid, alcohol and / or distilled water, ultrasonic cleaning, plasma surface cleaning, and the like. In addition, there is also a method of carving the surface of a workpiece into a diameter of about 0.5 mm (preferably 0.1 to 0.5 mm) such as CNC, MCT, and a grinder.

Specifically, the tungsten sintered body is put into nitric acid or aqua regia and maintained at about 100 ° C. for about 1 hour. Then, whether or not the impurities present on the surface are removed is visually confirmed, and finally the impurities are removed can do. At this time, the removal of the impurities can be performed at room temperature, but since the removal time can be reduced by adding the temperature, it is preferable to carry out the removal by appropriately changing the temperature. If the impurities are not completely removed through the above process, it is preferable that the nitric acid treatment or the water treatment treatment is repeated at least once for about 30 minutes.

On the other hand, in order to confirm whether or not the impurities are removed, a specimen of the tungsten sintered body having been cleaned may be sampled and GDMS (Glow Discharge Mass Spectrometry) analysis may be performed. The purity of the tungsten sintered body from which the impurities are removed is preferably 99.995 wt% or more. Therefore, if the analysis value is 99.995 wt% or more, the next step is performed, and if it is less than 99.995 wt%, the impurity removal step is preferably repeated one or more times.

(c) securing a tungsten powder having the same components as the tungsten sintered body ( S30 ).

A tungsten powder having high purity to be sintered together with the tungsten sintered body from which the impurities have been removed is obtained as the tungsten powder having the same components as the tungsten sintered body. The tungsten powder is preferably a high-purity powder having a purity of 99.995 wt% or more. If the purity of the tungsten powder is less than 99.995 wt%, it is difficult to satisfy the customer's specifications or needs, and particles may be generated from the surface of the target during the sputtering process, thereby deteriorating the physical properties of the thin film. Here, the purity of the tungsten powder can be analyzed using GDMS (Glow Discharge Mass Spectrometry).

In order to ensure the uniformity of the thin film, it is important to control the density, purity, grain refinement of the target, and gas content such as C and O. Therefore, it is preferable that the gas content contained in the tungsten powder is controlled to a specific range. Specifically, the tungsten powder preferably has an oxygen content of not more than 500 ppm, a carbon content of not more than 100 ppm, and a nitrogen, hydrogen, and sulfur content of less than 50 ppm, respectively. Here, O, N, H, C, S analysis can be used to verify the gas content contained in the tungsten powder.

Further, the particle size of the tungsten powder is measured through particle size analysis, and it is preferable to use the one having an average particle size controlled to 5 μm or less.

(d) adding the tungsten powder to a consumable portion of the tungsten sintered body To fill Pressurized gas Thereby preparing a preliminary sintered body ( S40 ).

After the tungsten sintered body is put into a mold, tungsten powder having the same composition as that of the sintered body of tungsten is filled and pressure sintered to produce a preliminary sintered body. The mold (for example, carbon mold) is preferably coated with a mold release material commonly known in the art. At this time, if the amount of the releasing material applied is large, the material reacts with the charged tungsten powder to act as a contaminant. If the amount of the releasing material applied is small, cracks may occur during separation of the preliminary sintering material. The applied release material can then be removed using a wiper blade.

Meanwhile, a method of pressing and sintering the tungsten sintered body filled with tungsten powder is not particularly limited, but it is preferable to use a hot press. Specifically, a mold into which a tungsten sintered body and a tungsten powder are charged is charged into a hot press chamber, and a vacuum pump is used to carry out the pressure reduction, followed by the pressure sintering. At this time, it is preferable that the reduced pressure is made up to 5.0 × 10 ^-5 torr or less. The pressure sintering is preferably performed at a pressure of 15 to 20 MPa and a temperature range of 1500 to 2000 ° C for 3 to 5 hours. According to the pressure sintering as described above, the present invention can secure a foundation stone for manufacturing a recycled tungsten target.

On the other hand, when the temperature of the chamber is lower than 100 캜 after completion of the pressure sintering, the preliminary sintered body is taken out and the relative density is analyzed. When the relative density of the preliminary sintered body is analyzed to be 98.0% or more, the next step is performed. If the relative density is less than 98.0%, particles may be formed at the time of thin film formation, Do.

(e) the preliminary sintered body is subjected to a heat treatment in a reducing atmosphere or a vacuum atmosphere ( S50 ).

In order to control the gas content of the pre-sintered body prepared above, heat treatment is carried out under a reducing atmosphere or a vacuum atmosphere. At this time, it is preferable to arrange the preliminary sintered body on a ceramic plate or a similar tungsten plate (W plate) in order to prevent the incorporation of carbon.

The heat treatment is preferably performed in a vacuum atmosphere for 3 to 8 hours at a temperature range of 1700 to 2000 ° C. If the heat treatment temperature is less than 1700 캜, it is difficult to obtain the required relative density and the effect of reducing the gas content may be deteriorated. If the temperature exceeds 2000 캜, the carbon content may be increased due to the carbon heater.

On the other hand, the preliminary sintered body having completed the heat treatment preferably has a relative density of 98.8% or more. When the relative density of the preliminary sintered body is 98.8% or more, a sintered body having a relative density of 99.6% or more can be obtained through the hot isostatic pressing step described below. For high purity, the content of oxygen and carbon in the preliminary sintered body is preferably 50 ppm or less, respectively.

(f) Heat-treated The preliminary sintered body is pressurized by hot isostatic pressing to produce a sintered body ( S60 ).

After the heat-treated pre-sintered body is wrapped with a canning material, hot isostatic pressing is performed under high temperature and high pressure conditions using an inert gas such as nitrogen or argon as a medium. When the hot hydrostatic pressure is applied in this way, since the equal pressure is generated by the gas as the pressure medium, the inner pores are removed within the range in which the shape of the preliminary sintered body is not changed, so that the sintered body having high density can be manufactured.

The hot isostatic pressing is preferably performed at a temperature of 1520 to 1720 캜, a pressure of 100 to 200 MPa, and a working vacuum degree of 10 ^-4 to 10 ^-5 Torr for 2 to 5 hours. If the hot pressing temperature is less than 1520 deg. C, it is difficult to secure a high density sintered body and the effect of reducing the gas content may be deteriorated. If the temperature exceeds 1720 deg. C, the crystal grains may coarsen and the carbon content may be increased.

On the other hand, it is preferable that the relative density of the obtained sintered body obtained by hot isostatic pressing is 99.6% or more, the crystal grain is 20 m or less, and the content of oxygen and carbon is 50 ppm or less, respectively.

(g) The sintered body is recrystallized ( S70 )

In the above, the sintered body subjected to hot isostatic pressing is subjected to recrystallization treatment for stress relief (annealing treatment) and grain refining. It is preferable that the recrystallization treatment is performed for 2 to 6 hours at a temperature range of 1500 to 1650 캜. If the temperature for recrystallization treatment is less than 1500 ° C, recrystallization of the sintered body may not occur. If the temperature exceeds 1650 ° C, the crystal grains of the sintered body may be coarsened or the gas content may be increased and the purity may be lowered.

The sintered body thus recrystallized has a relative density of 99.7% or more and a purity of 5N or more, exhibiting high purity. Also, the content of oxygen and carbon in the sintered body is 50 ppm or less, respectively, and the average size of crystal grains is 20 탆 or less.

Due to the recrystallization treatment, the stress of the sintered body is removed and the microcrystallization is performed, so that the efficiency of forming the thin film can be increased.

The sintered body thus produced is then commercialized through diffusion bonding and final processing commonly known in the art. Specifically, the sintered body is subjected to a backing plate and diffusion bonding to secure a bonding rate of 99.5% or more. Then, processing is performed to the final target thickness using a processing machine, and bead and arc spray treatment are performed on the backing plate surface To obtain a final product (recycled tungsten target). At this time, it is preferable to adjust the surface roughness of the sintered body to a level of 0.5 탆 in order to improve film forming characteristics.

<Recycled tungsten target >

The present invention provides a recycled tungsten target produced by the above-described manufacturing method. The recycled tungsten target of the present invention has high purity, high density, and fine crystal grains as produced by the above-described production method. Specifically, the recycled tungsten target (i.e., sintered body) of the present invention has a relative density of 99.7% or more, a purity of 5N or more, and an average grain size of 20 占 퐉 or less.

On the other hand, the recycled tungsten target obtained by the conventional method has a problem in that the crystal grains of the remainder of the tungsten waste target (the tungsten sintered body in which the consumable part exists) are larger than the crystal grains in the portion filled with the new tungsten powder. However, since the recycled tungsten target of the present invention is manufactured by the above manufacturing method, the crystal grain growth at the interface between the remainder portion and the filled portion of the tungsten waste target is adjusted to 20% or less of the crystal grains of the remaining portion, Separation phenomenon due to the difference in crystal grain size between the exposed portions is prevented, and thus it can be stably used in the sputtering process.

Specifically, the recycled tungsten target of the present invention comprises: a tungsten sintered body separated from a tungsten waste target; A filling part filled in the consumable part of the tungsten sintered body and made of the same component as the tungsten sintered body; And an interfacial portion existing therebetween, wherein the sheet resistances of the tungsten sintered body, the interface portion and the filled portion are 2.5 to 3.0 Ω / ㅁ Spec. And the uniformity may be in the range of 1.0 to 1.35%. The uniformity means uniformity of the resistance of the thin film according to positions in the target (for example, a tungsten sintered body, an interface portion and a filling portion).

Such a recycled tungsten target of the present invention can be used in various fields, and can be particularly useful for forming gate electrodes and wirings of IC and LSI. It may be used to manufacture a compound or to produce a curing material, an electrical contact material, a resistance material, a catalyst material, a photosensitive material or an anti-cancer material.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples and Comparative Examples are merely illustrative of the present invention, and the scope of the present invention is not limited by the following Examples and Comparative Examples.

[ Example One]

After obtaining the tungsten waste target, the backing plate was separated from the processing equipment to obtain a tungsten sintered body having a consumable part. Subsequently, impurities present in the tungsten sintered body were removed at 100 DEG C for about 1 hour by using nitric acid or aqua regia.

Thereafter, tungsten powder was filled in the consumed portion of the tungsten sintered body, and pressed sintering was performed using HP to prepare a pre-sintered body having a relative density of 98.2%. At this time, the tungsten powder used had an oxygen (O) content of 470 ppm, a carbon (C) content of 50 ppm, a particle size of 3 to 4 탆, and a purity of 5N. The pressure sintering was carried out at a pressure of 18 MPa and a temperature of 1800 캜 for about 3 hours.

Next, heat treatment was performed in a vacuum atmosphere to control the density and gas content of the prepared preliminary sintered body, and the relative density of the preliminary sintered body was increased to 98.7%, wherein the heat treatment was performed at a temperature of 1850 ° C for 5 hours.

Then, the heat-treated preliminary sintered body was pressurized with hot isostatic pressure to produce a sintered body having a relative density of 99.6% or more. The hot hydrostatic pressure was performed at a temperature of 1690 캜, a pressure of 150 MPa, and a working vacuum of 10 ^-5 Torr for 4 hours.

Thereafter, the sintered body thus produced was recrystallized to obtain a sintered body having a grain size of 20 탆 or less (see FIG. 2). At this time, the recrystallization treatment was carried out at a temperature of 1600 캜 for 4 hours.

[ Comparative Example One]

The tungsten powder used in Example 1 was pressed and sintered using HP to produce a sintered body having the same size as that of the sintered body of Example 1. At this time, the pressure sintering was performed at a pressure of 20 MPa and a temperature of 2000 캜 for about 5 hours.

[ Comparative Example 2]

The tungsten powder used in Example 1 was molded, CIP, vacuum heat treatment, and hot isostatic pressing to produce a sintered body having the same size as that of the sintered body of Example 1.

Specifically, the tungsten powder was put into a mold and molded at a pressure of 40 MPa for 60 seconds to prepare a molded body. The molded body was put into a rubber container and CIP was conducted at a pressure of 300 MPa for 30 minutes. Thereafter, the formed body was subjected to vacuum heat treatment at a temperature of 1800 캜 for 3 hours, and hot hydrostatic pressure was applied at a temperature of 1850 캜 and a pressure of 150 MPa for 5 hours.

[ Evaluation example 1. Evaluation of physical properties]

The physical properties of the sintered bodies of Example 1 and Comparative Examples 1 and 2 were evaluated by the following methods. The results are shown in Table 1 below.

(1) Relative density: Relative density was measured using Archimedes' principle. When the theoretical density 19.3 was applied to obtain a relative density of 99.5% or more, it was judged to have a high density.

(2) Gas content: Gas content was analyzed by OHN analyzer and CS analyzer. It was judged that the gas content was low when the O content was 50 ppm or less and the C content was 50 ppm or less.

(3) Crystal grains: After mounting the SPL, the average value was calculated by polishing (# 2000) and etching and measuring 30EA by an optical microscope (200 magnification). When the crystal grains were 20 mu m or less, it was judged that the crystal grains were fine.

division Relative density (%) Gas Content (ppm) Grain size (탆) O C Example 99.7 22 125 17 Comparative Example 1 98.4 95 154 96 Comparative Example 2 99.4 25 42 25

Referring to Table 1, it was found that the relative density, the gas content, and the grain size were superior to those of Comparative Example 1 in Example 1 of the present invention. And the same or higher level of the result of Comparative Example 2 was obtained. Therefore, the present invention proves that the tungsten waste target can be recycled while obtaining the same or better effect as compared with the conventional method.

[ Evaluation example 2. Evaluation of physical properties of thin film]

The sintered bodies of Example 1 and Comparative Examples 1 and 2 were each bonded to a backing plate to prepare a tungsten target. The prepared tungsten target was sputtered under the following conditions to form a thin film, and physical properties of the thin film were evaluated by the following methods. The results are shown in Table 2 below.

** Thin film forming conditions **

Tungsten target size: D318

Substrate temperature: room temperature (about 21-25 ° C)

Sputtering power: 2.2kw

Ar gas: 75 sccm

Wafer size: 8inch

Film Thickness: 500 Å

(1) Surface resistance: Measured using MCP-T610 (MITSUBISHI CHEMICAL COPOLATION).

(2) Uniformity: The uniformity of sheet resistance was measured by applying the following equation.

division Sheet resistance (Ω / ㅁ) Uniformity (%) Example 1 Filling part 2.6 1.17 Interface 2.6 1.23 The sintered body of the waste target 2.8 1.43 Comparative Example 1 3.3 2.39 Comparative Example 2 2.9 1.27

Referring to Table 2, it can be seen that the sheet resistance of Example 1 of the present invention is lower than that of Comparative Example 1 and is superior in uniformity. In addition, the results were comparable to those of Comparative Example 2 or higher. Therefore, it has been found through the present invention that even if the tungsten waste target is recycled, the characteristics of the thin film according to the positions are similar, and it is also proved that the same properties as those of the new tungsten target can be secured.

Claims

(a) separating a backing plate from a tungsten waste target to obtain a tungsten sintered body having a consumable part;
(b) removing impurities present in the tungsten sintered body;
(c) securing a tungsten powder having the same composition as the tungsten sintered body;
(d) filling the tungsten powder into a consumable portion of the tungsten sintered body, and pressing and sintering to prepare a preliminary sintered body;
(e) heat treating the preliminary sintered body in a reducing atmosphere or a vacuum atmosphere;
(f) pressing the heat-treated pre-sintered body under hot isostatic pressure to produce a sintered body; And
(g) subjecting the sintered body to recrystallization treatment.

The method according to claim 1,
Wherein the purity of the tungsten powder of step (c) is at least 99.995 wt%, the powder has an oxygen content of less than 500 ppm, a carbon content of less than 100 ppm, a nitrogen, hydrogen, and sulfur content of less than 50 ppm, Lt; / RTI > or less. &Lt; RTI ID = 0.0 > 8. < / RTI >

The method according to claim 1,
Wherein the step (d) comprises pressure sintering at a pressure of 15 to 20 MPa and a temperature of 1500 to 2000 占 폚 for 3 to 5 hours.

The method according to claim 1,
Wherein the step (e) is a heat treatment in a vacuum atmosphere for 3 to 8 hours at a temperature range of 1700 to 2000 占 폚.

The method according to claim 1,
Wherein the step (f) is performed under a hot hydrostatic pressure for 2 to 5 hours at a temperature of 1520 to 1720 캜, a pressure of 100 to 200 MPa, and a working vacuum degree of 10 ^-4 to 10 ^-5 Torr. Tungsten target.

The method according to claim 1,
Wherein the step (g) comprises recrystallization for 2 to 6 hours in a temperature range of 1500 to 1650 占 폚.

A recycled tungsten target produced by the method of any one of claims 1 to 6.

8. The method of claim 7,
A density of 99.7% or more, a purity of 5N or more,
Wherein the content of oxygen and carbon in the target is 50 ppm or less, respectively.

8. The method of claim 7,
Wherein the average size of the crystal grains in the target is 20 mu m or less.

8. The method of claim 7,
Wherein the recycled tungsten target is used for forming a wiring, forming an electrode, or both.