A tungsten target and its preparation method

Abstract

This invention provides a tungsten sputtering target and its preparation method, relating to the field of magnetron sputtering target preparation technology. The preparation method includes first loading tungsten powder into a casing; then performing vacuum hot pressing sintering on the casing filled with tungsten powder. During vacuum hot pressing sintering, the casing isolates the tungsten powder from the carbon atmosphere, preventing the introduction of impurity elements, and simultaneously achieving degassing, sealing, and sintering of the tungsten powder in the casing; followed by hot isostatic pressing. The casing is made of a metal with a melting point higher than 2000℃ that does not chemically react with tungsten. Before vacuum hot pressing sintering, this invention uses a metal casing to fill the tungsten powder, which not only improves the initial density and uniformity of the tungsten powder and increases the contact area between powder particles, thus improving sintering activity; it also prevents carbon elements from intruding into the blank, reducing carbon inclusions, improving the purity of the target material, lowering the sintering temperature and pressure, improving production efficiency, reducing energy consumption, and extending the service life of the mold.

Description

Technical Field

[0001] This invention relates to the field of magnetron sputtering target preparation technology, and in particular to a tungsten target and its preparation method. Background Technology

[0002] High-purity tungsten sputtering targets are key materials for fabricating advanced memory chips, flat panel displays, and solar cells. They are primarily used to deposit W / WN films in the gate metal stack layer using magnetron sputtering technology to maintain a low gate stack resistivity. Due to its high melting point (over 3400℃), high hardness, and high brittleness, tungsten metal is difficult to densify sufficiently through traditional plastic deformation. Low-density targets are prone to arc discharge and particulate phenomena during sputtering, severely affecting film yield and leading to device failure.

[0003] Currently, the preparation of high-purity tungsten target blanks mainly employs powder metallurgy technology, which promotes powder densification through the combined effects of high temperature and high pressure. However, high-temperature and high-pressure treatment can easily lead to abnormal grain growth, and coarse grains can affect the uniformity of coating thickness and deposition rate. Tungsten targets used in high-end processes require a purity ≥99.999% (5N), a density ≥99.5%, and a grain size ≤100μm. This places higher demands on the preparation process, especially on the control of carbon impurities and grain size.

[0004] Therefore, based on the one-step sintering forming technology of powder metallurgy, various improved technologies have been derived. For example, CN103567444B discloses a method for manufacturing tungsten targets, including: providing tungsten powder; placing the tungsten powder in a casing and evacuating it; performing a first densification treatment using a cold isostatic pressing process to form a first tungsten target blank; after removing the casing, performing a second densification treatment using an induction sintering process to form a second tungsten target blank; and finally, performing a third densification treatment using a hot isostatic pressing process to form the final tungsten target. However, this method does not isolate the carbon element environment during the hot pressing sintering process. Due to the carbon-rich characteristics of the hot pressing sintering environment, the graphite mold, as a carbon source, transports carbon atoms to the tungsten blank through gas-phase reaction and solid-phase diffusion under high temperature and pressure, forming carbides. The carbon impurities introduced in this process become scattering centers for charge carriers during sputtering, significantly increasing the resistivity of the thin film, thereby affecting the electrical performance and reliability of the device, and failing to meet the stringent requirements of high-end semiconductor processes for tungsten targets. Summary of the Invention

[0005] This invention provides a tungsten target material and its preparation method, which can obtain a high-purity tungsten target material with low carbon content, high density, and fine and uniform composition.

[0006] This invention provides a method for preparing a tungsten target material. First, tungsten powder is loaded into a casing. Then, the casing filled with the tungsten powder is subjected to vacuum hot pressing sintering. During the vacuum hot pressing sintering, the casing isolates the tungsten powder from the carbon atmosphere, preventing the introduction of impurity elements, and simultaneously achieving degassing, sealing, and sintering of the tungsten powder in the casing. Finally, hot isostatic pressing is performed. The casing is made of a metal with a melting point higher than 2000℃ that does not chemically react with tungsten.

[0007] Before vacuum hot pressing sintering of tungsten powder, this invention uses a metal casing to fill the tungsten powder. The casing acts as an intermediate container, pre-treating the tungsten powder to improve its initial density and uniformity, increase the contact area between powder particles, and enhance sintering activity. During sintering, the casing effectively prevents the billet from being directly exposed to the carbon environment, preventing carbon intrusion, reducing carbon inclusions, and improving the purity of the target material. Furthermore, the use of the casing, by improving the initial density and uniformity of the tungsten powder in the early stages, effectively reduces the density requirements of the billet during subsequent hot pressing and hot isostatic pressing, thereby lowering the sintering temperature and pressure, improving production efficiency, reducing energy consumption, and extending the service life of the mold.

[0008] Since the processing of tungsten targets involves temperatures above 1000°C for most of the time, and the cladding made of a material with a low melting point cannot undergo subsequent vacuum hot pressing sintering with the tungsten powder, a cladding material with a melting point of 2000°C or less will significantly reduce the structural strength of the cladding and increase the risk of breakage.

[0009] Furthermore, the coating has a purity ≥3N5, a thickness of 0.2~3mm, and a relative density ≥99%. When the performance of the coating meets the above range, it can achieve a better effect in improving the purity and density of the target material.

[0010] Preferably, the cover includes a lower cover and a cover top disposed above the lower cover.

[0011] Furthermore, when filling the tungsten powder using the packaging, the tungsten powder is first loaded into the lower packaging, the tungsten powder is compacted by vibration, and then the upper cover of the packaging is placed on top of the powder layer formed.

[0012] Furthermore, a dense layer is formed on the surface of the blank after vacuum hot pressing sintering. During the vacuum hot pressing sintering process, the sleeve is bonded to the surface of the blank, forming a dense layer on the surface of the blank. In the subsequent hot isostatic pressing treatment, this dense layer can be used to block the entry of external high-pressure gas, concentrate the force during sintering on the blank, and further increase the density of the blank.

[0013] Preferably, the relative density of the dense layer is ≥99.5%, and the thickness is 0.2~3mm. When the performance of the dense layer is controlled within the above range, a better effect can be achieved in increasing the density of the target material.

[0014] Preferably, the relative density of the blank after vacuum hot pressing sintering is 70%~85%, and the grain size is ≤5μm.

[0015] Furthermore, the parameters of the vacuum hot pressing sintering include: sintering pressure of 10~30 MPa, sintering temperature of 1000~1800℃, and sintering time of 1~3 h.

[0016] Preferably, the sintering temperature is 1200~1400℃.

[0017] In this invention, during vacuum hot pressing sintering, tungsten powder is first placed inside a metal sleeve. This sleeve can improve the initial density and uniformity of the tungsten powder, allowing the billet to be sintered at a relatively low temperature (1200~1400℃) and pressure. This reduces the temperature and pressure during vacuum hot pressing sintering, improves production efficiency, and extends the service life of the mold. In addition, the reduction in sintering pressure and temperature can effectively inhibit grain growth, making it easier to obtain high-purity tungsten targets with low carbon content, high density, and fine and uniform composition.

[0018] Furthermore, the purity of the tungsten powder is ≥5N, and the carbon content is ≤10ppm. Controlling the purity and carbon content of the tungsten powder within the above range can further improve the purity of the tungsten target material.

[0019] Preferably, the average particle size of the tungsten powder is 1~5μm.

[0020] Furthermore, the parameters of the hot isostatic pressing (HIP) include: a sintering pressure of 120-150 MPa, a sintering temperature of 1600-1800 °C, and a sintering time of 2-4 h. Controlling the HIP parameters within the above range can further increase the density of the billet and obtain a high-purity, high-density tungsten target material.

[0021] Preferably, the hot isostatic pressing is performed under an inert atmosphere.

[0022] Furthermore, the hot isostatic pressing process includes a machining step, which includes removing the outer sheath of the billet obtained by hot isostatic pressing.

[0023] A tungsten target material is prepared using the method described above.

[0024] Furthermore, the tungsten target material has at least one of the following characteristics: a. Purity ≥ 5N; b. C content ≤15ppm; c. Relative density ≥ 99.5%; d. The microstructure is uniform with no obvious orientation, and the grain size is ≤10μm.

[0025] This invention provides a tungsten sputtering target and its preparation method. Before vacuum hot pressing sintering, the method involves pre-treating the tungsten powder in a metal casing, improving its initial density and uniformity, increasing the contact area between powder particles, and enhancing sintering activity. This casing is then introduced into the vacuum hot pressing sintering process. During sintering, it effectively blocks the migration path of carbon elements, preventing carbon intrusion into the blank, reducing the carbon content in the tungsten sputtering target, and improving its purity. Furthermore, it reduces the density requirements of the blank in vacuum hot pressing and hot isostatic pressing processes, lowers the sintering temperature and pressure, improves production efficiency, and extends the mold's service life. This yields a high-purity tungsten sputtering target with low carbon content, high density, and a fine and uniform microstructure, achieving synergistic control of fine grains, high density, and low impurities, meeting the stringent requirements of sputtering for tungsten sputtering targets in high-end semiconductor processes. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a structural diagram of the casing used in the embodiment.

[0028] Figure label: 1: Lower packaging; 2: Top cover of the packaging; 3: Powder layer. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0031] Example 1 This embodiment provides a method for preparing a tungsten target, the steps of which are as follows: (1) High-purity tungsten powder with a purity of 5N, a carbon content of 10ppm, and an average particle size of 5μm was used as raw material; a cladding made of tungsten material with a purity of 3N5, a carbon content of 80ppm, and a wall thickness of 0.6mm was selected (structure as follows). Figure 1 As shown), the relative density of the casing is 99.2%. The tungsten powder is evenly filled into the lower casing, and the casing is transferred to a vibrating table by a hoisting device to compact the powder. Then the top cover of the casing is placed flat on the surface of the powder layer.

[0032] (2) The package filled with tungsten powder was placed into a graphite mold, and the package was degassed using the vacuum system of a hot press sintering furnace. The vacuum level was reduced to 8×10 at room temperature. -1 After Pa, hot pressing sintering is performed at a pressure of 25 MPa, a temperature of 1600℃, and a time of 2 hours to obtain a primary sintered billet. The primary sintered billet has a relative density of 75%, an average grain size of 3.6 μm, and a dense layer with a thickness of 0.6 mm and a relative density of ≥99% is formed on its surface.

[0033] (3) After machining to remove excess flash from the cladding, the cladding is placed in a graphite fixture and subjected to hot isostatic pressing (HIP) under an argon atmosphere to achieve secondary densification. The sintering pressure is 150 MPa, the sintering temperature is 1600℃, and the sintering time is 2 hours. Subsequently, a 1mm layer is removed from the surface of the sintered billet using a grinding machine and wire cutting. After machining, the billet is processed again to the required dimensions to obtain a high-purity tungsten target.

[0034] Example 2 This embodiment is basically the same as Embodiment 1, except that the cladding in step (1) is made of molybdenum and the sintering temperature in step (2) is 1000℃. The specific steps are as follows: (1) High-purity tungsten powder with a purity of 5N, a carbon content of 10ppm, and an average particle size of 5μm was used as raw material; a cladding made of molybdenum material with a purity of 3N5, a carbon content of 80ppm, and a wall thickness of 0.6mm was selected (structure as follows). Figure 1 As shown), the relative density of the casing is 99.2%. The tungsten powder is evenly filled into the lower casing, and the casing is transferred to a vibrating table by a hoisting device to compact the powder. Then the top cover of the casing is placed flat on the surface of the powder layer.

[0035] (2) The package filled with tungsten powder was placed into a graphite mold, and the package was degassed using the vacuum system of a hot press sintering furnace. The vacuum level was reduced to 8×10 at room temperature. -1After Pa, hot pressing sintering is performed at a pressure of 25 MPa, a temperature of 1000℃, and a time of 2 hours to obtain a primary sintered billet. The primary sintered billet has a relative density of 60%, an average grain size of 3 μm, and a dense layer with a thickness of 0.6 mm and a relative density of ≥99% is formed on its surface.

[0036] (3) After machining to remove excess flash from the cladding, the cladding is placed in a graphite fixture and subjected to hot isostatic pressing (HIP) under an argon atmosphere to achieve secondary densification. The sintering pressure is 150 MPa, the sintering temperature is 1800℃, and the sintering time is 4 hours. Subsequently, a 1mm layer is removed from the surface of the sintered billet using a grinder and wire cutter. After machining, the billet is processed again to the required dimensions to obtain a high-purity tungsten target.

[0037] Example 3 This embodiment is basically the same as Embodiment 1, except that the sintering temperature in step (2) is 1200℃. The specific steps are as follows: (1) High-purity tungsten powder with a purity of 5N, a carbon content of 10ppm, and an average particle size of 5μm was used as raw material; a cladding made of tungsten material with a purity of 3N5, a carbon content of 80ppm, and a wall thickness of 0.6mm was selected (structure as follows). Figure 1 As shown), the relative density of the casing is 99.2%. The tungsten powder is evenly filled into the lower casing, and the casing is transferred to a vibrating table by a hoisting device to compact the powder. Then the top cover of the casing is placed flat on the surface of the powder layer.

[0038] (2) The package filled with tungsten powder was placed into a graphite mold, and the package was degassed using the vacuum system of a hot press sintering furnace. The vacuum level was reduced to 8×10 at room temperature. -1 After Pa, hot pressing sintering is performed at a pressure of 25 MPa, a temperature of 1200℃, and a time of 2 hours to obtain a primary sintered billet. The primary sintered billet has a relative density of 68%, an average grain size of 3.4 μm, and a dense layer with a thickness of 0.6 mm and a relative density of ≥99% is formed on its surface.

[0039] (3) After machining to remove excess flash from the cladding, the cladding is placed in a graphite fixture and subjected to hot isostatic pressing (HIP) under an argon atmosphere to achieve secondary densification. The sintering pressure is 150 MPa, the sintering temperature is 1600℃, and the sintering time is 2 hours. Subsequently, a 1mm layer is removed from the surface of the sintered billet using a grinding machine and wire cutting. After machining, the billet is processed again to the required dimensions to obtain a high-purity tungsten target.

[0040] Comparative Example 1 This comparative example provides a method for preparing a tungsten target, the steps of which are as follows: (1) High-purity tungsten powder with the same 5N purity as in Example 1 was used as raw material.

[0041] (2) High-purity tungsten powder is evenly loaded into a graphite mold, and then drawn to 8×10 at room temperature. -1 After Pa, hot pressing sintering was carried out at a pressure of 25 MPa, a sintering temperature of 1600℃, and a sintering time of 2 hours to obtain a tungsten billet with a relative density of 75%, and no dense layer was formed on its surface.

[0042] (3) The billet is placed in a graphite fixture and subjected to hot isostatic pressing (HIP) sintering under an argon atmosphere. The sintering pressure is 150 MPa, the sintering temperature is 1600 °C, and the sintering time is 2 h. Subsequently, the surface 1 mm portion of the sintered billet is removed using equipment such as a grinder and wire cutter. After machining, the high-purity tungsten target material is obtained by machining it again to the required dimensions.

[0043] The performance of the tungsten targets prepared in the examples and comparative examples of this invention was tested. The C content was determined using LECO assay, the relative density was measured using the water displacement method, and the grain size was obtained statistically based on observations using a metallographic microscope. The results are shown in Table 1. Table 1 Performance test results of tungsten sputtering targets in the examples and comparative examples

[0044] As shown in Table 1, the main purpose of adding the cladding during the sintering process is to form a dense layer on the surface of the billet. This dense layer can effectively isolate the billet from the high-carbon environment of the sintering furnace. In Comparative Example 1, with the process unchanged, after removing the cladding, the carbon content in the sintered billet can increase from less than 10 ppm of high-purity tungsten powder to more than 80 ppm. In addition, after hot isostatic pressing sintering, the billet without a dense layer cannot be densified, resulting in a relative density difference of more than 20% between the billet density and that described in Example 1.

[0045] The vacuum hot pressing sintering temperature of Examples 2 and 3 is lower than that of Examples 1 and Comparative Example 1, resulting in a lower density of the sintered billet. However, since a dense layer is formed on the surface of Examples 2 and 3, even with a low-density billet, the requirements for subsequent hot isostatic pressing can still be met. As a result, the relative density of the high-purity tungsten target material obtained after hot isostatic pressing of Examples 2 and 3 is not significantly different from that of Example 1, but is significantly higher than that of Comparative Example 1.

[0046] Based on the above analysis, it can be seen that the method of the present invention can not only effectively reduce the sintering temperature and the carbon content in the tungsten target, but also increase its relative density, thereby obtaining a high-density, high-purity tungsten target.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a tungsten target, characterized in that, First, tungsten powder is loaded into a casing; then, the casing filled with the tungsten powder is vacuum hot-pressed and sintered. During the vacuum hot-pressing and sintering, the casing isolates the tungsten powder from the carbon atmosphere, preventing the introduction of impurity elements, and simultaneously achieving degassing, sealing, and sintering of the tungsten powder in the casing; then, hot isostatic pressing is performed; the casing is made of a metal with a melting point higher than 2000℃ that does not chemically react with tungsten.

2. The method for preparing the tungsten target material according to claim 1, characterized in that, The sheath has a purity ≥3N5, a thickness of 0.2~3mm, and a relative density ≥99%; Preferably, the cover includes a lower cover and a cover top disposed above the lower cover.

3. The method for preparing the tungsten target material according to claim 2, characterized in that, When filling the tungsten powder using the aforementioned packaging, the tungsten powder is first loaded into the lower packaging, the tungsten powder is then compacted by vibration, and the upper cover of the packaging is placed on top of the formed powder layer.

4. The method for preparing the tungsten target material according to any one of claims 1-3, characterized in that, A dense layer is formed on the surface of the blank after vacuum hot pressing and sintering. Preferably, the dense layer has a relative density ≥99% and a thickness of 0.2~3mm; Preferably, the relative density of the blank after vacuum hot pressing sintering is 60%~85%, and the grain size is ≤5μm.

5. The method for preparing the tungsten target material according to any one of claims 1-4, characterized in that, The parameters for the vacuum hot pressing sintering include: sintering pressure of 10~30 MPa, sintering temperature of 1000~1800℃, and sintering time of 1~3 h; Preferably, the sintering temperature is 1200~1400℃.

6. The method for preparing the tungsten target material according to any one of claims 1-5, characterized in that, The tungsten powder has a purity ≥5N, a C content ≤10ppm, and an average particle size of 1~5μm.

7. The method for preparing the tungsten target material according to any one of claims 1-6, characterized in that, The parameters of the hot isostatic pressing include: sintering pressure of 120~150MPa, sintering temperature of 1600~1800℃, and sintering time of 2~4h. Preferably, the hot isostatic pressing is performed under an inert atmosphere.

8. The method for preparing the tungsten target material according to any one of claims 1-7, characterized in that, The hot isostatic pressing process is followed by a machining step, which includes removing the outer sheath of the billet obtained by hot isostatic pressing.

9. A tungsten target material, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The tungsten sputtering target according to claim 9, characterized in that, The tungsten target material has at least one of the following characteristics: a. Purity ≥ 5N; b. C content ≤15ppm; c. Relative density ≥ 99.5%; d. The microstructure is uniform with no obvious orientation, and the grain size is ≤10μm.

Images