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

Abstract

The application discloses a preparation method of fine-grain high-density high-purity tungsten target material and belongs to the technical field of target material preparation. The method comprises the following steps: tungsten powder is pressed into a blank; the blank is placed on a hollow supporting plate, and the blank is sintered into a tungsten porous piece under a continuously flowing hydrogen atmosphere; the blank is located on the upstream side of the supporting plate along the hydrogen supply direction and partially covers the hollow perforations; upstream hydrogen penetrates the supporting plate through the uncovered perforations; a tungsten target material is obtained by performing a hot isostatic pressing treatment on the tungsten porous piece; a sleeve is provided with a contact layer in contact with the treated workpiece, and the contact layer is made of tantalum. Compared with the prior art, the application can sinter the tungsten target material in a hydrogen atmosphere during the sintering process, reduces the oxygen impurity content in the tungsten target material, and improves the purity of the tungsten target material.

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 the thin film 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 tungsten target material prepared 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:

[0007] A preparation method of fine-grain high-density high-purity tungsten target material, comprising the following steps:

[0008] Pressing tungsten powder into a compact;

[0009] Placing the compact on a hollow supporting plate 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 supporting plate, covering part of the hollow perforations, and the upstream hydrogen penetrates the supporting plate from the remaining hollow perforations of the supporting plate;

[0010] 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.

[0011] Preferably, before the tungsten powder is pressed into the blank, a pre-treatment step of the tungsten powder is further included, specifically comprising the following steps:

[0012] The tungsten powder is heat treated in a vacuum environment.

[0013] 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.

[0014] Preferably, the heating rate of the heat treatment of the tungsten powder in the vacuum environment is 2-10 ℃ / min.

[0015] Preferably, the pressing of the tungsten powder into the blank comprises the following steps:

[0016] 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.

[0017] Preferably, the sintering of the blank into the tungsten porous piece comprises the following steps:

[0018] The blank is sintered at a first preset temperature;

[0019] The blank is sintered at a second preset temperature, and the first preset temperature is less than the second preset temperature.

[0020] Preferably, the blank is sintered at a first preset temperature for a first preset time, the first preset temperature is 1000-1300 ℃, and the first preset time is 3-5 h;

[0021] The blank is sintered at a second preset temperature for a second preset time, the second preset temperature is 1300-1500 ℃, and the second preset time is 3-5 h.

[0022] Preferably, the tungsten porous piece is subjected to a canned hot isostatic pressing to obtain a tungsten target material, the hot isostatic pressing temperature is 1700-2000 ℃, and the pressure is 100-150 MPa.

[0023] Preferably, along the supply direction of the hydrogen gas, a preset cavity is arranged downstream of the support plate for the flow of hydrogen gas, a straight line along the thickness direction of the support plate is arranged as an axis, the support plate is provided with two or more first arc-shaped holes and two or more radial holes that are circumferentially distributed around the axis, one end of the radial hole is close to the axis of the support plate, and the other end extends outward perpendicular to the axis of the support 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 support plate as viewed along the supply direction of the hydrogen gas.

[0024] 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 inner circle of the first annulus, and the first arc-shaped hole and the radial hole are both spaced from the second through hole.

[0025] 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. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which are part of this application, serve to further understand the present application, 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 in the following description 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:

[0027] Figure 1 A perspective view of the connection between the support plate, the stand and the base provided by the present application is shown;

[0028] 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;

[0029] Figure 3 A top view of the embodiment is shown; Figure 2 A top view of the embodiment is shown;

[0030] Figure 4 A bottom view of the embodiment is shown; Figure 2 A bottom view of the embodiment is shown;

[0031] 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;

[0032] Figure 6 A metallographic diagram of the sintered tungsten porous part is shown;

[0033] Figure 7A metallographic diagram of a tungsten target material after hot isostatic pressing treatment;

[0034] Figure 8 A metallographic diagram of a conventional tungsten target material.

[0035] The drawings show: 100, a support plate; 110, a first arc-shaped hole; 120, a radial hole; 130, a second arc-shaped hole; 200, a stand; 300, a base plate; 310, an air outlet; 400, a blank. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, not all.

[0037] The present application provides a preparation method of fine-grain high-density high-purity tungsten target material, comprising the following steps:

[0038] The tungsten powder is pressed into a blank 400;

[0039] The blank 400 is placed on the hollow support 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 support plate 100, which means that it is placed above the support plate 100 in the direction of gravity, and the blank 400 is supported by the lower support plate 100; it also means that it is placed at the upstream end of the support 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 support plate, and the upstream hydrogen passes through the support plate from the uncovered hollow perforations on the side of the blank 400 (as shown in the Figure 2 embodiment), and 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 support 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 lower support plate 100. The former is preferred.

[0040] 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).

[0041] 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.

[0042] Compared with the prior art, the application continuously supplies flowing hydrogen to the sintering environment throughout the high-temperature sintering process. The blank 400 is sintered in a flowing hydrogen atmosphere, which has the following beneficial effects: (1) the tungsten material will not be oxidized during the sintering process by contacting the air outside the blank 400; (2) tungsten powder is easy to oxidize and will inevitably be oxidized before sintering when exposed to air. Hydrogen can contact the oxide on the surface of the blank 400, contact the oxide through the gaps between the tungsten powder particles, react with tungsten oxide at high temperatures to reduce it to tungsten, and carry away the water produced by the reaction through the continuous flow of gas and high temperature. The application not only reduces metal oxidation during sintering, but also reduces tungsten oxide to tungsten, both of which can reduce metal oxide impurities in the target material and improve the purity of the tungsten target.

[0043] In addition, the conventional concept generally considers that the purpose of high-temperature sintering is to densify the blank 400 and maintain the physical stability of the blank 400, and the blank 400 is sintered to the most dense state that the sintering process can achieve, and the most dense state after processing still has small cracks that cannot be eliminated by sintering, and then a hot isostatic pressing process is performed after sintering. Therefore, the high-temperature sintering process is designed around the core purpose of densification, such as deliberately using a solid bottom support plate, and the gas flow impact force forces the upstream tungsten material to be dense, and the support force of the solid support surface, gravity and gas flow impact force cooperate to force the bottom downstream tungsten material to be dense by mutual extrusion. The application breaks through this technical prejudice and reverses it, taking preliminary impurity removal as the core purpose of high-temperature sintering, considering that necessary pores are more conducive to the connection between deep impurities in the blank 400 and the external environment, and are conducive to the improvement of the purity of the tungsten target, and the support structure is set to a hollow tray 100 to reduce the extrusion of the support structure on the blank 400 as much as possible, as many as possible. Pore channels for deep-attached gas groups or reaction-generated gas groups in the blank 400 to escape from the blank 400, and appropriately reducing the hydrogen flow rate to weaken the gas flow impact force, not only do not imitate the existing technology to blindly pursue densification, but also purposefully retain pores to sinter the blank 400 into a tungsten porous piece.

[0044] The application considers that the powder compacting process is to compact the tungsten particles. The gaps between the tungsten particles cannot be completely eliminated by the compacting process. The gaps between the tungsten particles exist in the deep layer of the compacted blank 400. The gaps are connected to the outer environment through the pore channels. The purpose of the high-temperature sintering is to remove impurities. The impurities are removed by hydrogen to reduce tungsten oxide to tungsten as much as possible, to penetrate into the deep layer of the blank 400 through the pore channels as much as possible, to remove the gas impurities in the tungsten, and to improve the purity of the blank 400. The deep layer of the micro gas group is activated at high temperature, and the deep layer of the micro gas group is removed outward through the pore channels. The deep layer of the micro gas group is removed outward by the gas flow. The deep layer of the micro gas group is oxidized at high temperature. The deep layer of the tungsten material is activated outward, and is reduced to tungsten and water by hydrogen. The evaporated water molecules are removed by the flowing gas and high temperature. The specific principle is described below. In this design concept, the high-temperature sintering step should not only pursue densification, but also should inhibit excessive densification in the sintering process, and should retain pores. Regarding the requirement of the sputtering process for the continuity of the tungsten target material, the application sets a sleeved hot isostatic pressing process to close the pores of the tungsten porous part, thereby reducing the risk of collapse and peeling of the sputtering process, and even the risk of micron-sized tungsten particles adhering to the substrate (semiconductor wafer), avoiding short circuit or other performance defects of the chip.

[0045] The hot isostatic pressing process of the present application has two goals: (1) densification; (2) impurity removal. Regarding impurity removal, the present application adopts a hot isostatic pressing process with a can, and the can is made of a material containing tantalum metal. As is known, the hot isostatic pressing step with a can is that the workpiece (the tungsten porous piece of the present application) to be processed is installed in a sealed can, the can is provided with a first opening in sealed communication with a vacuum device, the vacuum device is used to evacuate the sealed internal environment of the can, and the first opening is sealed. The can containing the workpiece is placed in a hot isostatic pressing furnace, and the temperature and pressure are raised according to the preset process. The internal and external pressure difference causes the can to stretch and deform, wrapping and tightly fitting the workpiece inside, so that the workpiece is densified. In the hot isostatic pressing process of the present application, under high temperature and high pressure, the micro gas clusters (oxygen, nitrogen, carbon impurities and oxygen react to form CO at high temperature) move more actively, and can more easily escape from the blank 400 through the aforementioned pore channels. The principle is consistent with high-temperature sintering. The tantalum metal adsorbs the escaped carbon (CO is decomposed into [C] and [O], Ta + [C] → TaC), nitrogen (2Ta + N2→ 2TaN), and oxygen (2Ta + O2→ 2TaO or 4Ta + 5O2→ 2Ta2O5), which will not be described here. On the other hand, the tungsten deep in the workpiece will exclude oxygen at extremely high temperatures. The excluded oxygen or oxygen in the original micro gas cluster will also be thermally dissociated into active oxygen atoms [O] at extremely high temperatures. High temperature makes the atomic vibration of the tungsten lattice more violent, greatly weakening the binding energy of the metal-oxygen bond, weakening the binding force of active oxygen atoms, so that active oxygen atoms can shuttle and walk in the interatomic gaps inside the tungsten lattice, and diffuse freely. The wrapping and adsorption of tantalum metal under high pressure form a chemical potential gradient (the oxygen concentration inside the workpiece is higher than the surface, because the surface oxygen will be adsorbed by the tantalum can), which drives the oxygen atoms to migrate from the inside to the surface, and the oxygen migration forms lattice defect sites with oxygen vacancies in situ. The surrounding oxygen atoms will be in an active state due to the defect, further strengthening the outward migration of oxygen. Oxygen atoms are migrated to the outermost layer and contact with tantalum metal, and the combination ability of tantalum and oxygen is stronger than that of tungsten, so that the oxygen impurities are adsorbed (Ta + [O] → TaO or 2Ta + 5[O] → Ta2O5). Or reduced to oxygen gas and adsorbed by tantalum metal. Nitrogen gas is thermally decomposed into active nitrogen atoms, and carbon impurities exist in the form of active carbon atoms at high temperatures, which can be adsorbed by tantalum metal (Ta + [N] → TaN, Ta + [C] → TaC) through the above principle mechanism. The macroscopic diffusion of micro gas clusters and the shuttle diffusion of active atoms complement each other, and mutually transform to migrate outward in response to the internal and external impurity concentration gradient, capture and adsorb as much carbon, nitrogen and oxygen impurities as possible with tantalum, and improve the purity of the tungsten target material obtained after hot isostatic pressing.

[0046] It is this synergistic effect of multi-functionality that enables the technology to produce high purity tungsten semi-conductor sputtering targets with ultra-high purity and full densification that is unattainable by traditional powder metallurgy methods. The application can maintain stable low resistance in sputtering targets, can inhibit device failure caused by abnormal discharge of sputtering targets, and can reduce the oxygen content in sputtering targets, especially the reduction of oxygen content, which can achieve very small oxygen content values, from tens of ppm to 5 ppm or less.

[0047] In a possible implementation, the number of radial holes 120 and the number of first arc-shaped holes 110 are not specifically limited, as long as each first arc-shaped hole 110 can at least correspond to one radial hole 120 and extend inwardly. Preferably, each first arc-shaped hole 110 has a plurality of groups of arc-shaped central portions corresponding to the radial holes 120, and some of the arc-shaped ends of the first arc-shaped holes 110 each correspond to a radial hole 120. As shown in the figure, the pallet 100 has a plurality of radial holes 120 that are not directly connected to the first arc-shaped holes 110, but are connected to the radial holes 120 near the end of the axis of the pallet 100. When viewed in the direction of the hydrogen supply, the outer end of these radial holes 120 is also located in the first arc-shaped hole and protrudes from the outer edge of the blank 400. Figure 1

[0048] In a possible implementation, the bottom of the preset cavity is provided with a base at the most downstream end in the direction of the hydrogen supply, for sealing and closing the hydrogen passage at the most downstream end of the preset cavity. The base is provided with a gas outlet 310 (in the context of the direction of the hydrogen supply, it means that the gas outlet 310 penetrates the base to form a hole in the direction of the hydrogen supply, that is, the penetration direction of the gas outlet 310 is consistent with the axis direction and thickness direction of the pallet 100, and the penetration directions of the first arc-shaped hole 110, the second arc-shaped hole 130 and the radial hole 120 are consistent).

[0049] Optionally, the base is provided with a plurality of gas outlets 310, and two or more consistent gas outlets 310 are distributed around the circumference of the axis of the pallet 100. Consistent means that the shape, size, etc. are completely consistent, and the cross section is consistent. The remaining gas outlets 310 are either consistently grouped and distributed around the circumference of the axis of the pallet 100, or are spaced apart and not connected to each other with the axis as their own opening axis. In the direction of the hydrogen supply, the gas outlet structure formed by the gas outlets 310 of the base is centrally symmetric around the axis of the pallet 100. Preferably, the gas outlet 310 is provided with a valve with adjustable opening degree. Optionally, in the direction of the hydrogen supply, the side of the base facing its upstream is flat and parallel to the direction of the plate surface of the pallet 100.

[0050] ​In a specific embodiment of the implementation, the supporting plate 100 is a circular plate, and the aforementioned axis of the supporting plate 100 coincides with the cylindrical axis of the circular plate. The base is a bottom plate 300, which is arranged parallel to the supporting plate 100. The supporting plate 100 is not directly connected to the inner wall of the sintering device, but is connected to the bottom plate 300 through the stand 200, and the stand 200 separates a preset cavity for hydrogen flow. The stand is more than two, which are uniformly arranged in groups and are distributed circumferentially around the axis of the supporting plate. The outer edge of the plate surface of the bottom plate 300 is sealingly connected to the inner wall of the sintering environment of the sintering device, so as to seal the hydrogen flow channel of the bottom plate 300 along the upstream and downstream of the hydrogen supply direction. The bottom plate 300 is provided with N+1 gas outlets 310, N≥2. N gas outlets 310 are circumferentially distributed around the axis of the supporting plate 100, and the remaining one gas outlet 310 is a circular hole, which takes the axis of the supporting plate 100 as its own opening axis. N=6.

[0051] In another embodiment, six uniform gas outlets 310 are arranged circumferentially around the axis of the supporting plate 100. During the sintering process, the purity of hydrogen is controlled while the hydrogen atmosphere is controlled, so that the gas uniformly passes through the surface and interior of the material, so that the structure of the sintered tungsten target material at each position is very uniform. The specific operation method is to change the bottom plate 300 of the sintering furnace from the original single gas outlet hole to the uniformly distributed six gas outlets 310, and to increase the supporting plate 100 with multiple annular holes above the outlet gas. The target material is placed on the supporting plate 100 to ensure that the hydrogen gas uniformly passes through the material. In order to obtain uniform tungsten target material, the furnace temperature control is also strictly controlled in the present application, and the loading height is kept consistent each time to ensure that the furnace temperature at this position is consistent, and the error is not more than 50°C. In this way, tungsten target material with uniform and fine structure can be obtained.

[0052] In a possible implementation, a suction pipe is sealingly welded on the first opening to sealingly communicate with the vacuum device, and the suction pipe is also made of tantalum metal. The cladding sleeve is provided with one or more first openings, and one or more suction pipes are welded. Under the action of high temperature of HIP, the high temperature and pressure make the tungsten workpiece firmly combined through plastic flow, diffusion creep and other mechanisms, the pores of the porous material are closed, and the theoretical density of nearly 99% can be reached. The aforementioned vacuum device is a high vacuum pump set, such as a molecular pump.

[0053] In a possible implementation, the sintering has a heating rate of 3-8°C / min, preferably 5°C / min, and a cooling rate of 3-8°C / min, preferably 5°C / min. The hot isostatic pressing has a temperature of 1700-2000°C, preferably 1800°C or 1900°C, a pressure of 100-150MPa, preferably 110MPa, 120MPa, 130MPa or 140MPa, and a time length of 3-5h, preferably 3.5h, 4h or 4.5h. The heating and cooling rate is 5-15°C / min, preferably 8°C / min, 10°C / min or 12°C / min, and the pressure increasing rate is preferably 5-10MPa / min, preferably 6MPa / min, 7.5MPa / min or 8MPa / min. Preferably, the pressure increasing and the temperature increasing are performed synchronously, and the pressure increasing rate is slightly faster than the temperature increasing rate, so as to avoid the sleeve pressing the pores in advance. The sleeve is a tantalum sleeve or a tantalum alloy sleeve.

[0054] In a possible implementation, the sintering of the blank 400 into the tungsten porous piece includes the following steps:

[0055] sintering the blank 400 at a first preset temperature for a first preset time length;

[0056] sintering the blank 400 at a second preset temperature for a second preset time length, the first preset temperature being lower than the second preset temperature.

[0057] Optionally, the sintering step is high-temperature sintering. First, low-temperature sintering is performed at a first preset temperature (lower than the second preset temperature) of 1000-1300°C, preferably 1200°C, for a first preset time length of 3h-5h, preferably 3.5h. Then, medium-temperature sintering is performed at a second preset temperature (lower than the first preset temperature and the temperature of the hot isostatic pressing) of 1300-1500°C, preferably 1400°C, for a second preset time length of 3h-5h, preferably 3.5h, 4h or 4.5h.

[0058] In a possible implementation, the pressing of the tungsten powder into the blank 400 specifically includes the following step: cold isostatic pressing of the tungsten powder into the blank 400.

[0059] In a possible implementation, before the pressing of the tungsten powder into the blank 400, the method further includes a step of pretreating the tungsten powder. The pretreatment of the tungsten powder includes the following step: heat treatment of the tungsten powder at a third preset temperature in a vacuum environment.

[0060] The present application carries out a vacuum heat treatment before sintering the powder compact, reduces the content of gaseous elements in the powder in advance, so that the sintering process does not end too early due to the influence of impurity elements, and also improves the density of the material. The vacuum heat treatment specifically includes the following steps: first, lay the tungsten powder in the vacuum heat treatment environment, then vacuumize and heat to a third preset temperature for a third preset time, cool down, and take out the sample compact. On the one hand, the vacuum degree should be less than 10 -2 Pa, preferably 0.8 x 10 -2 Pa. On the other hand, when loading the powder, the layer thickness should not be too thick, otherwise the impurity removal effect will be poor, and should be controlled below 50 mm. The layer thickness should not be too thin either, otherwise the loading capacity will be limited and the cost will increase. The layer thickness is controlled to be 30-40 mm, preferably 35 mm. Through the above method, the gaseous impurity elements in the powder can be effectively removed, and during the vacuum heat treatment, the temperature needs to be slowly increased and decreased, at about 3℃ / min, to prevent the material from clumping and caking. Preferably, the vacuum heat treatment is carried out at a third preset temperature of 1000-1300℃ (preferably 1200℃) for 3-5h (preferably 3.5h, 4h or 4.5h), or at a third preset temperature of 1300-1500℃ (preferably 1400℃) for 3-5h (preferably 3.5h, 4h or 4.5h).

[0061] Alternatively, the tungsten powder is heat treated in a vacuum environment at a third preset temperature until the oxygen content in the tungsten powder is reduced to below 50ppm, the carbon content is reduced to below 20ppm, and the nitrogen content is reduced to below 10ppm.

[0062] The purity of the tungsten powder before pretreatment is ≥99.95% high-purity tungsten powder, and the particle size is 2.0-2.5μm, preferably 2.3μm. The purpose of using finer tungsten powder is to obtain a high-density sintered compact. The oxygen content in the powder should be below 200ppm, the carbon content should be below 50ppm, and the nitrogen content should be below 20ppm.

[0063] In a specific embodiment, a method for preparing a fine-grained high-density high-purity tungsten target material includes the following steps:

[0064] Powder preparation. High-purity tungsten powder with a purity of ≥99.95%, an oxygen content of below 200ppm, a carbon content of below 50ppm, an N content of below 20ppm, and a particle size of 2.5μm is used.

[0065] Vacuum heat treatment. The layer thickness is controlled to be about 35mm, the vacuum degree is 0.9 x 10 -2 Pa, the temperature is increased to 1200℃ at a rate of 3℃ / min, the vacuum heat treatment is carried out at 1200℃ for 4h, and the temperature is decreased to room temperature at a rate of 3℃ / min. Open the equipment and take out the tungsten powder layer.

[0066] Press forming. The tungsten powder was loaded into a flexible rubber mold, and after sealing, cold isostatic pressing was performed to form a cylindrical blank 400 with a diameter of 500 mm and a thickness of 7 mm. The cold isostatic pressure was 180 MPa, and the time was about 15 min.

[0067] The high-temperature sintered blank 400 was a tungsten porous piece. Sintering was performed in a hydrogen atmosphere in a high-temperature sintering furnace, which required a hydrogen purity of more than 99.999% and a dew point control of less than -70°C, and the gas supply rate was 2 L / min. The pressure was raised to 0.2 MPa, and sintering was first performed at 1200°C for 6 h. Subsequently, sintering was performed at 1600°C for 9 h. The heating and cooling rates were both 5°C / min, and the pressure raising and lowering rates were both 0.05 MPa / min. The schematic diagram of the workpiece supporting the blank 400 is shown in Figure 1 The tungsten plate with a thickness of 30 mm was set as the aforementioned base, and the base was perforated in the middle and the circumferential direction (all the positions were consistent except for one hole in the middle and six holes in the circumferential direction, and the valve opening degree of the gas outlet was consistent), to ensure uniform hydrogen discharge. The column 200 upstream of the base was supported by a tungsten material, and the upper layer of the column 200 was fixedly supported by a tungsten plate with a thickness of 20 mm as a supporting plate 100. The supporting plate 100 was processed with a ring-shaped gas hole, and the outer diameter of the first arc-shaped hole 110 was greater than the diameter of the cylindrical target material, which was 520 mm. The tungsten target material was placed on the supporting plate 100 (both were coaxial, and the installation structure is shown in Figure 2 the embodiment). The purpose of this was to use the ring-shaped hole of the upper plate to pass through the gas flow, to ensure the uniformity of the atmosphere of each part of the tungsten plate, to effectively buffer the atmosphere by the middle column 200, and then to pass through the base uniformly. The base gas outlet 310 was provided with a flow control valve to ensure that the hydrogen discharge amount of each hole was consistent, thereby controlling the temperature and atmosphere. The tungsten porous piece obtained after low-temperature sintering and medium-temperature sintering had a specification of φ500 x 7 mm, and a relative density of 75%, i.e., 14.3 g / cm 3 . The microstructure of the tungsten porous piece is shown in Figure 6 the lower right corner of the figure, and the scale is 50 μm. As can be seen from the figure, the number of grains of the porous material was 7000 / mm 2 , and the structure was relatively uniform and small. The material pores were not completely closed, and there were many holes.

[0068] The tungsten porous piece was subjected to a canning hot isostatic pressing treatment to obtain a tungsten target material. The high-temperature sintered tungsten porous piece was loaded into a canning made of pure Ta metal, and the canning was protected in an inert gas atmosphere. At the same time, the tungsten porous piece was subjected to a canning hot isostatic pressing treatment at a high temperature of 1800°C and a high pressure of 140 MPa for 4.5 h, with a temperature raising and lowering rate of 10°C / min and a pressure raising and lowering rate of 8 MPa / min, to remove impurities and completely close the residual isolated pores in the material, so that the target material density reached ≥99% of the theoretical density. Finally, the density of the target material was 19.1 g / cm 3High-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. 2 The 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.

[0069] Machining. The tungsten sputtering target is ground or milled according to requirements to obtain the final tungsten sputtering target.

[0070] 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.

[0071] 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 placed in a mold for cold isostatic pressing, and the tungsten powder is cold isostatically pressed to form a blank. The billet is placed on a perforated tray in a sintering apparatus. Under a continuously supplied hydrogen atmosphere, the billet is sintered at a first preset temperature for a first preset time, and at a second preset temperature for a second preset time, thereby sintering the billet into a tungsten porous part. The first preset temperature is 1000-1300℃, the first preset time is 3-5h, the second preset temperature is 1300-1500℃, and the second preset time is 3-5h. 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 (HIP) treatment 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. 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, 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.

6. The method for preparing fine-grained, high-density, high-purity tungsten target material according to claim 5, 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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