Preparation method of fine-grain high-density high-purity tungsten target material

Abstract

The invention discloses a preparation method of a fine-grain high-density high-purity tungsten target material, which belongs to the technical field of target material preparation, and comprises the following steps: pressing tungsten powder into a blank; the blank is placed on a hollowed-out supporting plate, the blank is sintered into the tungsten porous part under the hydrogen atmosphere which is continuously supplied in a flowing mode, the blank is located on the upstream side of the supporting plate in the hydrogen supply direction and partially covers the hollowed-out through holes, and upstream hydrogen penetrates through the supporting plate from the uncovered through holes to circulate; sleeved hot isostatic pressing treatment is carried out on the tungsten porous part to obtain the tungsten target material, a sheath is provided with a contact layer making contact with a treated workpiece, and the material of the contact layer contains tantalum. Compared with the prior art, the tungsten target material can be sintered in the hydrogen atmosphere in the sintering process, the oxygen impurity content in the tungsten target material is reduced, and the purity of the tungsten target material is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal target material, more particularly to a preparation method of fine-grain high-density high-purity tungsten target material. BACKGROUND

[0002] Particle bombardment sputtering target material makes target particles deposited on the substrate surface to form a functional thin film, which is a key thin film preparation method and is widely used in high-precision electronics, optics, energy field, especially in the field of semiconductor chip integrated circuit. With the miniaturization and high integration of semiconductor circuits, the uniformity of thin films is required to be higher. The increase of impurities (non-metallic elements, especially oxygen and carbon) in the raw material (i.e. target material) for sputtering will increase the local resistance value, resulting in insufficient uniformity of the target material and large fluctuation of the resistance value of the thin film, which will adversely affect the performance of the thin film. In particular, metal oxide impurities not only increase the local resistance value, but also produce abnormal discharge during sputtering, which may eventually lead to device failure.

[0003] Tungsten target material is a common target material. Tungsten material is easy to be oxidized by oxygen in the air, but the existing technology sintering tungsten powder compact in air atmosphere to prepare target material will form tungsten oxide on the surface of the compact, and the purity of the prepared tungsten target material is insufficient, the resistance fluctuation caused by impurities is large, and it is difficult to meet the increasing purity requirements of the semiconductor industry.

[0004] Therefore, how to provide a new tungsten target material preparation method to reduce metal oxidation during sintering and thus reduce metal oxide impurities in the target material has become a problem to be solved by those skilled in the art. SUMMARY

[0005] The present application aims to provide a preparation method of fine-grain high-density high-purity tungsten target material to solve the above technical problems.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: A preparation method of fine-grain high-density high-purity tungsten target material, comprising the following steps: pressing tungsten powder into a compact; placing the compact on a hollow tray in a sintering device, sintering the compact into a tungsten porous piece in a continuously flowing hydrogen atmosphere, along the hydrogen supply direction, the compact is located on the upstream side of the tray, covering part of the hollow perforations, and the upstream hydrogen penetrates the tray from the remaining hollow perforations of the tray; carrying out canning hot isostatic pressing treatment on the tungsten porous piece to obtain a tungsten target material, the canning is provided with a contact layer in contact with the treated workpiece, and the contact layer is made of tantalum.

[0007] Preferably, before the tungsten powder is pressed into the blank, a pretreatment step of the tungsten powder is further included, specifically comprising the following steps: The tungsten powder is heat treated in a vacuum environment.

[0008] Preferably, the tungsten powder is heat treated in a vacuum environment until the oxygen content in the tungsten powder is reduced to below 50 ppm, the carbon content is reduced to below 20 ppm, and the nitrogen content is reduced to below 10 ppm.

[0009] Preferably, the heating rate of the heat treatment of the tungsten powder in the vacuum environment is 2-10 ℃ / min.

[0010] Preferably, the pressing of the tungsten powder into the blank comprises the following steps: The tungsten powder is placed in a mold for cold isostatic pressing, the tungsten powder is cold isostatic pressed, and the tungsten powder is pressed into the blank.

[0011] Preferably, the sintering of the blank into the tungsten porous piece comprises the following steps: The blank is sintered at a first preset temperature; The blank is sintered at a second preset temperature, and the first preset temperature is less than the second preset temperature.

[0012] Preferably, the blank is sintered at a first preset temperature for a first preset time length, the first preset temperature is 1000-1300 ℃, and the first preset time length is 3-5 h; The blank is sintered at a second preset temperature for a second preset time length, the second preset temperature is 1300-1500 ℃, and the second preset time length is 3-5 h.

[0013] Preferably, the tungsten porous piece is subjected to a canned hot isostatic pressing to obtain the tungsten target material, the hot isostatic pressing temperature is 1700-2000 ℃, and the pressure is 100-150 MPa.

[0014] Preferably, along the supply direction of the hydrogen gas, a preset cavity is arranged downstream of the supporting plate to allow the hydrogen gas to flow through, a straight line along the thickness direction of the supporting plate is arranged as an axis, the supporting plate is provided with two or more first arc-shaped holes and two or more radial holes which are circumferentially distributed around the axis, one end of the radial hole is close to the axis of the supporting plate, and the other end extends outward perpendicularly to the axis of the supporting plate, all the first arc-shaped holes each correspond to at least one radial hole, and the arc-shaped outer side of the first arc-shaped hole protrudes beyond the outer edge of the blank on the supporting plate as viewed along the supply direction of the hydrogen gas.

[0015] Preferably, along the direction of the hydrogen supply, the plurality of first arc-shaped holes distributed in the circumferential direction are located in the first annular region, and the support plate is further provided with a second through hole located in the closed region of the first inner annular region, and the first arc-shaped hole and the radial hole are both spaced apart from the second through hole.

[0016] Compared with the prior art, the present application continuously supplies flowing hydrogen to the sintering environment throughout the high-temperature sintering process. The blank is sintered in a flowing hydrogen atmosphere, which has the following beneficial effects: (1) the tungsten material cannot be oxidized during the sintering process by contacting the air outside the blank; (2) the tungsten powder is easy to be oxidized and is inevitably oxidized when exposed to air before sintering. Hydrogen can contact the oxide on the surface of the blank, contact the oxide through the gaps between the tungsten powder particles, react with the tungsten oxide and some oxide impurities at high temperature to reduce them to tungsten, and carry away the water produced by the reaction through the continuous flow of gas and high temperature. The present application not only reduces the oxidation of metal during sintering, but also reduces the tungsten oxide and oxide to tungsten, which can reduce the impurity elements C, O and N in the target material and improve the purity of the tungsten target material. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which are part of this application, serve to further understand the present application, and the illustrative embodiments of the present application and their descriptions serve to explain the present application but do not constitute an improper limitation on the present application. Obviously, the drawings described below are only some embodiments, and other drawings can be obtained from these drawings by those of ordinary skill in the art without creative labor. In the drawings: Figure 1 A perspective view of the connection between the support plate, the stand and the base provided by the present application is shown; Figure 2 An installation structure diagram of the blank placed on the support plate provided by the present application is shown; Figure 1 An installation structure diagram of the blank placed on the support plate provided by the present application is shown; Figure 3 A top view of the embodiment is shown; Figure 2 A top view of the embodiment is shown; Figure 4 A bottom view of the embodiment is shown; Figure 2 A bottom view of the embodiment is shown; Figure 5 An installation structure diagram of the blank placed on the support plate provided by the present application is shown; Figure 1 An installation structure diagram of the blank placed on the support plate provided by the present application is shown; Figure 6 A metallographic diagram of the tungsten porous piece after sintering is shown; Figure 7 A metallographic diagram of the tungsten target material after hot isostatic pressing is shown; Figure 8 A metallographic diagram of the conventional target tungsten material is shown.

[0018] Reference numerals: 100, supporting plate; 110, first arc-shaped hole; 120, radial hole; 130, second arc-shaped hole; 200, stand; 300, bottom plate; 310, air outlet; 400, blank. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, not all.

[0020] The present application provides a preparation method of fine-grain high-density high-purity tungsten target material, comprising the following steps: The tungsten powder is pressed into a blank 400; The blank 400 is placed on the hollow supporting plate 100 in the sintering environment of the sintering equipment, and the blank 400 is sintered into a tungsten porous piece under the continuous flow supply of hydrogen atmosphere. The blank 400 is placed on the supporting plate 100, which means that it is placed above the supporting plate 100 in the direction of gravity, and the blank 400 is supported by the supporting plate 100 below. It also means that it is placed at the upstream end of the supporting plate 100 in the direction of hydrogen supply. Regarding the circulation of hydrogen, in one case, the blank 400 partially covers the hollow perforations of the supporting plate, and the upstream hydrogen passes through the supporting plate from the uncovered hollow perforations on the side of the blank 400 (as shown in the Figure 2 embodiment). The downstream hydrogen can also pass through the covered hollow perforations to contact the lower end of the blank 400. Alternatively, the blank 400 covers all the hollow perforations of the supporting plate 100 (as shown in the Figure 5 embodiment), and the lower end of the blank 400 is partially suspended, and the upstream hydrogen penetrates the blank 400 from the pores of the blank 400 to the hollow perforations of the supporting plate 100 below. The former is preferred.

[0021] Preferably, along the hydrogen supply direction: a preset cavity is provided downstream of the tray 100 for hydrogen flow; the tray 100 has a straight line along its thickness direction as its axis (in the context of the hydrogen supply direction, this means that the straight line is in the middle of the tray 100, extends along the thickness direction of the tray 100 and along the hydrogen supply direction, with the axis direction consistent with the hydrogen direction and the axial direction consistent with the plate thickness direction); and the direction perpendicular to this axis is defined as the radial direction of the tray 100; the tray 100 has two or more first arc-shaped holes 110 distributed circumferentially around the axis; and the tray 100 also has two or more second arc-shaped holes 130 distributed circumferentially around the axis as the second arc-shaped holes 140. Two perforations (in the context of hydrogen supply direction, "having a hole" means that the hole penetrates the support plate 100 along the hydrogen supply direction, that is, the first and second arc-shaped holes 130 penetrate the support plate 100 along the thickness direction). The circumference of the first arc-shaped hole 110 (the circumference of multiple first arc-shaped holes 110 distributed circumferentially) is fitted outside the circumference of the second arc-shaped hole 130 (same as above). The support plate 100 also has a radial hole 120 (in the context of hydrogen supply direction, "having a hole" means that the hole penetrates the support plate 100 along the hydrogen supply direction, that is, the radial hole 120 penetrates the support plate 100 along the thickness direction). "Radial" in radial hole 120 means that the hole extends in a straight line along the radial direction of the support plate 100, and is a long straight hole. One end of the radial hole 120 extends outward in a straight line from the axis (perpendicular to the axis). Along the surface direction of the pallet 100, the first arc-shaped hole 110 and the radial hole 120 are each provided with a preset distance from the second arc-shaped hole 130 (the preset distance between holes means that the holes are spaced apart and not connected to each other), and the arc-shaped middle part of each of the first arc-shaped holes 110 is connected to one end of the outer extension of a radial hole 120. Viewed along the axial direction of the pallet 100, the outer edge of the first arc-shaped hole 110 (relative to the axis of the pallet 100) protrudes beyond the outer edge of the blank 400 (relative to the axis of the pallet 100). Tungsten porous parts are subjected to encased hot isostatic pressing to obtain tungsten targets. The encasing is provided with a contact layer that contacts the workpiece being treated. The contact layer is made of tantalum, preferably pure tantalum metal or tantalum alloy.

[0022] Compared with the prior art, the present invention continuously supplies flowing hydrogen to the sintering environment throughout the high-temperature sintering process. The billet 400 is sintered in a flowing hydrogen atmosphere, which has the following beneficial effects: (1) the tungsten material will not be oxidized by contact with the air on the surface of the billet 400 during the sintering process; (2) tungsten powder is easily oxidized, and it will inevitably be oxidized when exposed to air before sintering. Hydrogen can contact the oxide on the surface of the billet 400, and contact the oxide through the gaps between the tungsten powder particles. It reacts with the tungsten oxide at high temperature to reduce it to tungsten, and the water produced by the reaction is carried away by the continuous flow of gas and high temperature. This application can not only reduce metal oxidation during the sintering process, but also reduce the original tungsten oxide to tungsten, which can reduce metal oxide impurities in the target material and improve the purity of the tungsten target material.

[0023] Furthermore, the traditional view is that the purpose of high-temperature sintering is to densify the billet 400 and maintain its physical stability. This involves sintering the billet 400 to the densest state achievable by the sintering process. Even in this densest state, micro-cracks that cannot be eliminated by sintering still exist, requiring subsequent hot isostatic pressing. Therefore, high-temperature sintering processes are designed around this core objective of densification. For example, a solid bottom support plate is deliberately used. The airflow impact force compresses the upstream tungsten material, and the combined support force, gravity, and airflow impact force of the solid support surface compress the downstream tungsten material at the bottom, causing them to become denser. This application breaks through this technical bias and takes the opposite approach, taking preliminary impurity removal as the core purpose of high-temperature sintering. It believes that necessary porosity is more conducive to the connection between deep impurities in the billet 400 and the external environment, which is beneficial to the purity improvement of the tungsten target material. The support structure is set as a hollow support plate 100 to minimize the compression of the billet 400 by the support structure, and to retain as much of the deep attached gas or reaction-generated gas in the billet 400 as possible to escape from the pore channels of the billet 400. The hydrogen flow rate is appropriately reduced to weaken the impact force of the air flow. Instead of imitating the existing technology to pursue densification, it purposefully retains porosity to sinter the billet 400 into a tungsten porous part.

[0024] This application argues that the powder pressing process aims to achieve dense forming, but the gaps between the originally loose tungsten particles cannot be completely eliminated by the pressing process. The formed blank 400 inevitably contains particle gaps and encapsulated micro-air masses deep within its interior. These gaps connect to the external environment via pore channels. The purpose of high-temperature sintering is preliminary impurity removal. Specifically, this removal involves using hydrogen to reduce tungsten oxide to tungsten through contact with the surface material of the blank 400 as much as possible, and to penetrate deep into the blank 400 through the aforementioned pore channels, thereby removing gaseous impurities from the tungsten and improving the purity of the blank 400. It also involves the activation of deep micro-air masses at high temperatures, their migration outward through the aforementioned pore channels, and their removal by airflow. Furthermore, it involves the oxidation of deep tungsten material by deep micro-air masses at high temperatures, their activation and outward migration until they come into contact with hydrogen and are reduced to tungsten and water. The evaporated water molecules are then removed by the flowing airflow and high temperature. The specific principles are described below. In this design concept, the high-temperature sintering step should not only not pursue excessive densification, but should instead suppress excessive densification and retain porosity during the sintering process. Regarding the requirement for the density and continuity of the tungsten target material in the sputtering process, this application proposes a cladding hot isostatic pressing process to close the pores of the tungsten porous component, thereby reducing the risk of collapse and peeling that may occur when bombarding the pores of the target material during sputtering, and even the risk of generating micron-sized tungsten particles adhering to the substrate (semiconductor wafer), thus avoiding short circuits or other performance defects in the chip.

[0025] The hot isostatic pressing (HIP) process of this application has two objectives: (1) densification; and (2) impurity removal. Regarding impurity removal, this application employs a sheathed HIP process, and selects a sheath with an internal contact layer material containing tantalum metal. As is well known, the sheathed HIP process involves installing the workpiece (the tungsten porous part of this application) inside a sealed sheath. The sheath has a first opening that is sealed and connected to a vacuum device. The vacuum device is used to evacuate the sealed internal environment of the sheath, and the first opening is sealed. The sheath containing the workpiece is placed in a hot isostatic pressing furnace, and the temperature and pressure are increased according to a preset process. The internal and external pressure difference causes the sheath to stretch and deform, wrapping and tightly pressing the internal workpiece, thus densifying the workpiece. During the hot isostatic pressing process of this application, under high temperature and high pressure, the movement of micro-gas clusters (oxygen, nitrogen, and CO formed by the high-temperature reaction of carbon impurities and oxygen) becomes more active, and they can escape from the billet 400 through the aforementioned pore channels. The principle is the same as that of high-temperature sintering. The tantalum metal adsorbs the escaped carbon (CO decomposes into [C] and [O], Ta + [C] → TaC), nitrogen (2Ta + N2 → 2TaN), and oxygen (2Ta + O2 → 2TaO or 4Ta + 5O2 → 2Ta2O5), which will not be elaborated here. On the other hand, the tungsten deep in the workpiece will expel oxygen under extreme high temperature. The expelled oxygen or the oxygen in the original micro-gas clusters will also thermally dissociate into active oxygen atoms [O] under extreme high temperature. The high temperature makes the atomic vibration of the tungsten lattice more intense, which greatly weakens the binding energy of the metal-oxygen bond. The binding force of the bond to the active oxygen atoms is weakened, allowing the active oxygen atoms to shuttle and diffuse freely in the interatomic gaps inside the tungsten lattice. The adsorption of tantalum metal under high pressure creates a chemical potential gradient (the oxygen concentration inside the workpiece is higher than on the surface because surface oxygen is adsorbed by the tantalum coating), driving oxygen atoms to migrate from the inside to the surface. This migration creates lattice defect sites for oxygen vacancies, which in turn activate surrounding oxygen atoms, further enhancing outward migration. Oxygen atoms migrate to the outermost layer and come into contact with tantalum metal. Tantalum's binding affinity for oxygen is stronger than tungsten, leading to the adsorption of oxygen impurities (Ta+[O]→TaO or 2Ta+5[O]→Ta2O5). Alternatively, they migrate to the outermost layer and are reduced to oxygen, which is then adsorbed by tantalum metal. Nitrogen gas thermally decomposes into active nitrogen atoms, and carbon impurities exist as active carbon atoms at high temperatures. Both can migrate outward through the aforementioned mechanism and be adsorbed by tantalum metal (Ta+[N]→TaN, Ta+[C]→TaC). The macroscopic diffusion of micro-clusters and the shuttle diffusion of active atoms complement each other and transform into one another to migrate outward in accordance with the concentration gradient of internal and external impurities, so as to capture and adsorb as many carbon, nitrogen and oxygen impurities as possible with tantalum, thereby improving the purity of the tungsten target material obtained after hot isostatic pressing.

[0026] It is this multifunctional synergy that enables the technology to produce high-purity tungsten semiconductor sputtering targets that are difficult to achieve with traditional powder metallurgy methods, possessing both ultra-high purity and full densification. This application can maintain stable low resistance in the sputtering target, suppress device defects caused by abnormal discharge in the sputtering target, and reduce the oxygen content in the sputtering target. In particular, the reduction in oxygen content can potentially achieve very low oxygen content values, from the traditional tens of ppm to 5 ppm or less.

[0027] In one possible implementation, this application does not specifically limit the number or relative number of radial holes 120 and first arc-shaped holes 110, as long as each first arc-shaped hole 110 can communicate with at least one radial hole 120 and extend inward. Preferably, the arc-shaped middle portion of each first arc-shaped hole 110 is connected to a radial hole 120, and one arc-shaped end of some of the first arc-shaped holes 110 is connected to a radial hole 120. Figure 1 As shown, the pallet 100 has a portion of radial holes 120 that are not directly connected to the first arc-shaped hole 110. Instead, one end of the radial holes 120 (which are connected to the first arc-shaped hole 110) is connected to the axis of the pallet 100. When viewed along the hydrogen supply direction, the outer end of these radial holes 120 is also located within the first arc and protrudes from the outer edge of the billet 400.

[0028] In one possible implementation, a base is provided at the downstream end of the preset cavity along the hydrogen supply direction to seal and close the hydrogen channel at the downstream end of the preset cavity. The base is provided with an outlet 310 (in the context of the hydrogen supply direction, this means that the outlet 310 is formed by penetrating the base along the hydrogen supply direction, that is, the penetration direction of the outlet 310 is consistent with the axial direction and thickness direction of the support plate 100, and the penetration direction of the first arc-shaped hole 110, the second arc-shaped hole 130 and the radial hole 120).

[0029] Optionally, the base has several gas outlets 310. Two or more identical gas outlets 310 are distributed circumferentially around the axis of the support plate 100. "Identical" means that they are completely identical in shape, size, and cross-section. The remaining gas outlets 310 are either grouped together and distributed circumferentially around the axis of the support plate 100, or they are positioned with the axis as their own opening axis, and the gas outlets 310 are spaced apart and do not communicate with each other. Along the hydrogen supply direction, the gas outlet structure formed by the gas outlets 310 of the base is symmetrical about the axis of the support plate 100. Preferably, the gas outlets 310 are equipped with valves with adjustable opening. Optionally, along the hydrogen supply direction, the side of the base facing upstream is flat and parallel to the surface of the support plate 100.

[0030] This application provides a specific embodiment of this implementation: the support plate 100 is a circular plate, and the aforementioned axis of the support plate 100 coincides with the cylindrical axis of the circular plate. The base is a bottom plate 300, which is set parallel to the support plate 100. The support plate 100 is not directly connected to the inner wall of the sintering equipment, but is connected to the bottom plate 300 through a column 200, which isolates a preset cavity for hydrogen flow. There are two or more columns, grouped together and circumferentially distributed around the axis of the support plate. The outer edge of the bottom plate 300 is sealed to the inner wall of the sintering environment of the sintering equipment to seal the hydrogen flow channel upstream and downstream of the bottom plate 300 along the hydrogen supply direction. The bottom plate 300 has N+1 gas outlets 310, where N≥2. The N gas outlets 310 are circumferentially distributed around the axis of the support plate 100, and the remaining gas outlet 310 is a circular hole with its opening axis being the axis of the support plate 100. N=6.

[0031] In another embodiment, six identical gas outlets 310 are circumferentially distributed around the axis of the support plate 100. During the sintering process, the purity and atmosphere of the hydrogen are controlled to ensure that the gas passes evenly through the surface and interior of the material. This results in a very uniform microstructure in all parts of the sintered tungsten target. Specifically, the bottom plate 300 of the sintering furnace is changed from a single gas outlet to six evenly distributed gas outlets 310. At the same time, a support plate 100 with multiple annular holes is added above the gas outlet. The target is placed on the support plate 100 to ensure that the hydrogen passes evenly through the material. In order to obtain a uniform tungsten target, the furnace temperature is also strictly controlled. The charging height is kept consistent each time to ensure that the furnace temperature at that position is consistent, with an error of no more than 50°C. This results in a tungsten target with a uniform and fine microstructure.

[0032] In one possible implementation, a vacuum tube is sealed and welded to the first opening for sealed communication with the vacuum equipment; the vacuum tube is also made of tantalum. The sheath has one or more first openings, with one or more vacuum tubes welded to them. Under the high temperature of HIP, the high temperature and pressure cause the tungsten workpiece to bond firmly through mechanisms such as plastic flow and diffusion creep, closing the pores of the porous material and achieving a density close to 99% of its theoretical density. The aforementioned vacuum equipment is a high-vacuum pump unit, such as a molecular pump.

[0033] In one possible implementation, the heating rate during sintering is as slow as possible, at 3-8°C / min, preferably 5°C / min, and the cooling rate is 3-8°C / min, preferably 5°C / min. The hot isostatic pressing temperature is 1700-2000°C, preferably 1800°C or 1900°C, the pressure is 100-150 MPa, preferably 110 MPa, 120 MPa, 130 MPa, or 140 MPa, and the duration is 3-5 hours, preferably 3.5 hours, 4 hours, or 4.5 hours. The heating and cooling rates are 5-15°C / min, preferably 8°C / min, 10°C / min, or 12°C / min, and the pressure rates are preferably 5-10 MPa / min, preferably 6 MPa / min, 7.5 MPa / min, or 8 MPa / min. Preferably, the pressure increase and heating are performed simultaneously, with the pressure increase rate slightly faster than the heating rate, to avoid premature compression of the pores by the cladding. The cladding is a tantalum cladding or a tantalum alloy cladding.

[0034] In one possible implementation, sintering the blank 400 into a tungsten porous part includes the following steps: The blank is sintered at a first preset temperature for a first preset time of 400°C. The billet is sintered at a second preset temperature for a second preset time of 400 seconds, while the first preset temperature is lower than the second preset temperature.

[0035] Optionally, the sintering step is high-temperature sintering. First, sintering is performed at a first preset temperature (relative to the second), the first preset temperature being 1000-1300℃, preferably 1200℃, and the first preset time being 3h-5h, preferably 3.5h; then, sintering is performed at a second preset temperature (relative to the first preset temperature and the hot isostatic pressing temperature), the second preset temperature being 1300-1500℃, preferably 1400℃, and the second preset time being 3h-5h, preferably 3.5h, 4h, or 4.5h.

[0036] In one possible implementation, pressing tungsten powder into a billet 400 specifically includes the following steps: cold isostatic pressing to press the tungsten powder into a billet 400.

[0037] In one possible implementation, a pretreatment step for the tungsten powder is included before pressing it into a blank 400. The pretreatment of the tungsten powder includes the following steps: heat-treating the tungsten powder in a vacuum environment at a third preset temperature.

[0038] This invention involves performing a vacuum heat treatment before sintering the powder compact, thereby reducing the content of gaseous elements in the powder and preventing the sintering process from prematurely ending due to impurities. This also increases the material's density. The vacuum heat treatment specifically includes the following steps: first, tungsten powder is placed in a vacuum heat treatment environment; then, a vacuum is drawn and the temperature is raised to a third preset temperature and held for a third preset time; finally, the temperature is lowered, and a sample is taken for compaction. It is important to note that the vacuum level must be <10.-2 Pa, preferably 0.8 x 10 -2 Pa. On the other hand, the layer thickness should not be too thick during powder loading, as this will hinder impurity removal. It should be controlled below 50mm, nor too thin, as this will limit the amount of powder loaded per furnace, increasing costs. The layer thickness should be controlled between 30-40mm, preferably 35mm. The above methods can effectively remove gaseous impurities from the powder. During vacuum heat treatment, the temperature needs to be raised and lowered slowly, approximately 3℃ / min, to prevent material agglomeration and clumping. Preferably, vacuum heat treatment is performed at a third preset temperature of 1000-1300℃ (preferably 1200℃) for 3-5 hours (preferably 3.5 hours, 4 hours, or 4.5 hours), or at a third preset temperature of 1300-1500℃ (preferably 1400℃) for 3-5 hours (preferably 3.5 hours, 4 hours, or 4.5 hours).

[0039] Optionally, the tungsten powder is heat-treated in a vacuum environment at a third preset temperature until the oxygen content in the tungsten powder drops below 50 ppm, the carbon content drops below 20 ppm, and the nitrogen content drops below 10 ppm.

[0040] The tungsten powder used before pretreatment is high-purity tungsten powder with a purity of ≥99.95% and a particle size of 2.0-2.5μm, preferably 2.3μm. The purpose of using finer tungsten powder is to obtain a high-density sintered blank. The oxygen content in the powder is required to be below 200ppm, the carbon content is below 50ppm, and the nitrogen content is below 20ppm.

[0041] In one specific embodiment, a method for preparing a fine-grained, high-density, high-purity tungsten target material includes the following steps: Powder preparation. High-purity tungsten powder with a purity of ≥99.95%, oxygen content below 200ppm, carbon content below 50ppm, nitrogen content below 20ppm, and particle size of 2.5μm is used.

[0042] Vacuum heat treatment. The layup thickness is controlled at approximately 35 mm, and the vacuum degree is 0.9 x 10⁻⁶. -2 Pa, heated to 1200℃ at a rate of 3℃ / min, vacuum heat-treated at 1200℃ for 4 hours, and then cooled to room temperature at a rate of 3℃ / min. The tungsten powder layer was then removed from the equipment.

[0043] Compression molding. Tungsten powder is loaded into a flexible rubber mold, sealed, and then cold isostatically pressed into a cylindrical blank (400) with a diameter of 500 mm and a thickness of 7 mm. The cold isostatic pressure is 180 MPa, and the time is approximately 15 minutes.

[0044] The high-temperature sintered billet 400 is a porous tungsten part. Sintering is carried out in a high-temperature sintering furnace under a hydrogen atmosphere, requiring a hydrogen purity of ≥99.999%, a dew point controlled below -70℃, and a gas supply rate of 2L / min. The pressure is increased to 0.2MPa and held, then sintered at 1200℃ for 6 hours, followed by sintering at 1600℃ for 9 hours. The heating and cooling rates are both 5℃ / min, and the pressure increase / decrease rate is 0.05MPa / min. A schematic diagram of the tooling supporting billet 400 is shown below. Figure 1 As shown: A 30mm thick tungsten plate is used as the aforementioned base. The base has holes in the center and circumference (the center hole and the six circumferential holes are all identical except for their position, and the valve openings at the outlets are consistent) to ensure uniform hydrogen discharge. A tungsten column 200 is used as a support upstream of the base. A 20mm thick tungsten plate is fixedly supported on top of the column 200 as a support plate 100. The support plate 100 has annular vent holes. The outer diameter of the first arc-shaped hole 110 is larger than the diameter of the cylindrical target material, being 520mm. A tungsten target material is then placed on the support plate 100 (the two are coaxial, and the installation structure is as follows). Figure 2 (As shown in the embodiment). The purpose of this is to ensure the uniformity of the atmosphere in each part of the tungsten plate by using the annular holes of the upper plate for airflow. The column 200 in the middle effectively buffers the atmosphere, and then the air flows evenly through the base. The gas outlet 310 of the base is equipped with a flow control valve to ensure that the amount of hydrogen gas discharged from each hole is consistent, thereby controlling the temperature and atmosphere. The tungsten porous part obtained after low-temperature sintering and medium-temperature sintering has a size of φ500 x 7mm and a relative density of 75%, i.e., 14.3g / cm³. 3 The microstructure of tungsten porous components is as follows: Figure 6 As shown in the figure, the scale bar in the lower right corner is 50 μm. The figure indicates that the porous material has a grain number of approximately 7000 per mm. 2 The material has a relatively uniform and fine structure, but the pores are not completely closed, resulting in a large number of voids.

[0045] Tungsten targets were obtained by hot isostatic pressing (HIP) with a cladding on porous tungsten parts. The high-temperature sintered porous tungsten parts were then encased in a cladding made of pure Ta metal and protected in an inert gas atmosphere. Simultaneously, the porous tungsten parts were subjected to HIP at 1800℃ and 140MPa for 4.5 hours, with a heating / cooling rate of 10℃ / min and a pressure / cooling rate of 8 MPa / min. This process was used to remove impurities and completely close any remaining isolated pores within the material, achieving a target density ≥99% of the theoretical density. The final target density was 19.1 g / cm³. 3 High-purity tungsten sputtering targets were used. The performance of the tungsten sputtering targets was measured, with a purity ≥99.999%, C, O, and N impurity content controlled below 5 ppm, and a density ≥19.1 g / cm³. 3 Microstructure was measured and observed: the number of tungsten target grains after heat treatment was 5000 / mm. 2The grain size is greater than grade 10. See attached metallographic image. Figure 7 As shown, Figure 7 The image shown is a 500X metallographic image, with a scale bar of 50 μm in the lower right corner. A metallographic image of a standard tungsten sputtering target is also attached. Figure 8 As shown, Figure 8 It is also a 500X metallographic image, with a scale bar of 50μm in the lower right corner.

[0046] Machining. The tungsten sputtering target is ground or milled according to requirements to obtain the final tungsten sputtering target.

[0047] Depend on Figure 7 and Figure 8 It can be seen that the microstructure of conventional tungsten sputtering targets (4N) is relatively uniform, but the grain size is relatively large, with a grain number of 1000 / mm. 2 The high-purity tungsten target (5N) of this invention has a uniform and fine microstructure with a grain number of 5000 / mm. 2 Conventional tungsten sputtering targets exhibit varying degrees of impurity segregation at grain boundaries, which are the weakest points and increase the risk of material cracking. In contrast, the high-purity tungsten sputtering target provided by this invention (…) Figure 7 The grain boundaries are uniform, with few impurities and almost no impurity aggregation. The impurities are evenly distributed within the grain boundaries, which also proves that this invention effectively controls the impurity content. This mutual restraint between grains during subsequent use will significantly improve the lifespan.

[0048] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a fine-grained, high-density, high-purity tungsten target, characterized in that, Includes the following steps: Tungsten powder is pressed into blanks; The billet is placed on a perforated tray in a sintering equipment. Under a continuously flowing hydrogen atmosphere, the billet is sintered into a tungsten porous part. Along the hydrogen supply direction, the billet is located on the upstream side of the tray, covering part of its perforated holes. Upstream hydrogen penetrates the tray through the remaining perforated holes. The tungsten porous part is subjected to encased hot isostatic pressing to obtain a tungsten target material. The encasing is provided with a contact layer that contacts the workpiece being treated, and the contact layer is made of tantalum.

2. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 1, characterized in that, Before pressing the tungsten powder into a blank, a pretreatment step for the tungsten powder is also included, specifically including the following steps: Tungsten powder is heat-treated in a vacuum environment.

3. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 2, characterized in that, Tungsten powder is heat-treated in a vacuum environment until the oxygen content, carbon content, and nitrogen content in the tungsten powder are reduced to below 50 ppm, below 20 ppm, and below 10 ppm.

4. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 2, characterized in that, The heating rate for heat treatment of tungsten powder in a vacuum environment is 2-10℃ / min.

5. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 1, characterized in that, Pressing the tungsten powder into a blank includes the following steps: Tungsten powder is placed in a mold for cold isostatic pressing and then cold isostatically pressed to form a blank.

6. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 1, characterized in that, Sintering the blank into a porous tungsten part includes the following steps: The blank is sintered at a first preset temperature; The blank is sintered at a second preset temperature, wherein the first preset temperature is lower than the second preset temperature.

7. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 6, characterized in that, The billet is sintered at a first preset temperature for a first preset time, wherein the first preset temperature is 1000-1300℃ and the first preset time is 3-5h. The billet is sintered at a second preset temperature for a second preset time, wherein the second preset temperature is 1300-1500℃ and the second preset time is 3-5h.

8. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 1, characterized in that, The tungsten porous part is subjected to encased hot isostatic pressing (HIP) to obtain a tungsten target material. The HIP temperature is 1700-2000℃, the HIP pressure is 100-150MPa, and the HIP duration is 3-5h.

9. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 1, characterized in that, Along the hydrogen supply direction, a preset cavity is provided downstream of the pallet for hydrogen flow. The pallet has a straight line along its thickness as its axis in the middle. The pallet has two or more first arc-shaped holes and two or more radial holes distributed circumferentially around the axis. One end of each radial hole is close to the pallet axis, and the other end extends outward in a straight line perpendicular to the pallet axis. All the first arc-shaped holes are connected to at least one of the radial holes at their respective outer ends. When viewed along the hydrogen supply direction, the outer arc of the first arc-shaped hole protrudes from the outer edge of the billet on the pallet.

10. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 9, characterized in that, Along the hydrogen supply direction, a plurality of first arc-shaped holes distributed circumferentially are located in the annular region of the first ring. The tray is also provided with a second through hole, which is located in the closed region of the inner circle of the first ring. The first arc-shaped holes and the radial holes are spaced apart from the second through hole.

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