Preparation method for densification forming of high-purity cobalt target material

Abstract

The invention discloses a preparation method for densification forming of a high-purity cobalt target material, and relates to the technical field of semiconductor material preparation, and the preparation method comprises the following steps: S1, surface in-situ reconstruction pretreatment of high-purity cobalt powder, that is, reduction treatment is performed on the high-purity cobalt powder in an inert atmosphere, and reactive gas is introduced to grow a nanoscale coating layer on the surface of the cobalt powder in situ; s2, filling and pre-pressing are conducted, specifically, the cobalt powder treated in the step S1 is loaded into a graphite mold, and initial pressure is applied to conduct pre-compaction; s3, multi-field coupling dynamic sintering is conducted, specifically, the mold is placed in a sintering furnace, direct-current pulse current is applied in a vacuum environment for heating, and meanwhile dynamic axial pressure and an external magnetic field are synchronously applied in the sintering process; and S4, magnetic field induced texturing cooling is conducted, and the mode of an external magnetic field is adjusted in the cooling stage after sintering heat preservation is finished. According to the method, a traditional large-deformation rolling process is thoroughly abandoned, and high-density, grain-refining and strong-texture integrated in-situ near-net forming of the high-purity cobalt target material is achieved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material preparation technology, and in particular to a method for densifying high-purity cobalt target material. Background Technology

[0002] High-purity cobalt sputtering targets are core materials for the fabrication of copper interconnect barrier layers and magnetic recording thin films in advanced semiconductor processes. As integrated circuit nodes evolve towards 3nm and below, the industry has placed extreme demands on the purity, density, grain uniformity, and crystal texture of sputtering targets. Mainstream fabrication processes often employ either "cold isostatic pressing of high-purity cobalt powder combined with hot isostatic pressing (HIP) sintering" or "vacuum melting followed by multi-pass hot rolling annealing." Among these, powder metallurgy is widely used due to its advantages in impurity control. Its typical process involves pressing cobalt powder under an inert atmosphere, densifying it through high-temperature, high-pressure, and long-term sintering, supplemented with trace amounts of grain refiners, and finally adjusting the grain orientation through intense plastic deformation processing to meet the stringent standards for thin film microstructure in sputtering processes.

[0003] Existing technologies still face challenges in synergistically optimizing "ultra-high densification" and "specific strong texture". Traditional sintering processes rely on high-temperature thermal activation to eliminate porosity, but this easily induces abnormal grain growth, leading to uneven microstructure. If heat input is reduced to maintain fine grains, it is difficult to eliminate micropores, and residual defects can easily cause sputtering nodules. More importantly, the grain orientation of billets obtained by conventional sintering is random, lacking the preferred orientation of the (002) plane that is conducive to electromigration performance. It is necessary to rely on subsequent large deformation rolling to induce texture. The stepwise strategy of "densification first, deformation later" is not only lengthy and costly, but also introduces residual stress and microcracks in the severe plastic deformation, making the target material prone to warping and cracking during welding or use, making it difficult to achieve integrated in-situ construction of high density, fine grains and ideal texture. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a method for preparing high-purity cobalt target material densification molding, which solves the problem that the existing technology is difficult to balance ultra-high density and fine grain structure under the step-by-step strategy of "densification first and deformation later", and is unable to directly construct strong (002) preferred texture in situ without introducing residual stress.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a high-purity cobalt target material densification molding, which includes: S1: surface in-situ reconstruction pretreatment of high-purity cobalt powder, that is, reducing high-purity cobalt powder under an inert atmosphere and introducing reactive gas to grow a nanoscale coating layer in-situ on the surface of cobalt powder. S2: Filling and pre-compressing: The cobalt powder treated in S1 is loaded into the graphite mold and pre-compressed by applying initial pressure; S3: Multi-field coupled dynamic sintering, the mold is placed in the sintering furnace and heated by DC pulse current in a vacuum environment, while dynamic axial pressure and external magnetic field are applied simultaneously during the sintering process; S4: Magnetic field-induced texturing cooling. During the cooling stage after sintering and holding, the mode of the external magnetic field is adjusted to induce the preferential orientation growth of cobalt grains. S5: Stress-relief annealing and finishing: Vacuum stress-relief heat treatment is performed on the sintered cobalt billet, followed by machining and surface polishing to obtain high-purity cobalt target material.

[0007] In a preferred embodiment of the method for preparing the high-purity cobalt target densification molding of the present invention, in step S1, the high-purity cobalt powder has a purity ≥99.999% and an average particle size of 10-30 μm; the in-situ surface reconstruction pretreatment specifically includes: First, put the cobalt powder in Reduce the mixture at 350-450℃ for 1-3 hours in a mixed atmosphere; Subsequently, while maintaining a reducing atmosphere, a trace amount of carbon- or boron-containing precursor gas is introduced, and the reaction temperature is controlled at 450-550℃, with a reaction time of 30-60 minutes, so that an amorphous carbon layer or boron carbide layer with a thickness of 2-10nm is generated in situ on the surface of the cobalt powder as a grain boundary pinning agent.

[0008] Furthermore, in step S1, high-purity cobalt powder with a purity ≥99.999% and an average particle size controlled within 10-30 μm is strictly selected as the matrix, and a two-stage in-situ surface reconstruction pretreatment is implemented. First, the surface oxide film is removed by deep reduction at 350-450℃ using an Ar+H2 mixed atmosphere. Then, a trace amount of carbon- or boron-containing precursor gas is introduced to induce a surface chemical reaction at 450-550℃, generating an amorphous carbon layer or boron carbide layer with a precisely controllable thickness (2-10 nm) in situ. This nanoscale coating layer acts as an efficient grain boundary pinning agent, laying the microstructural foundation for suppressing abnormal grain growth during subsequent high-temperature sintering.

[0009] As a preferred embodiment of the method for preparing high-purity cobalt target densification forming according to the present invention, wherein: in S3, the multi-field coupled dynamic sintering adopts pulsed electromagnetic field assisted discharge plasma sintering (PEF-SPS) process; The sintering process is divided into four stages: The first stage is the low-temperature degassing and activation period: the temperature is raised from room temperature to 600℃ at a rate of 40-60℃ / min, the pressure is maintained at 5-15 MPa, only DC pulse current is applied, and the external magnetic field is not turned on. The second stage is the phase transformation and plastic compaction period: the temperature is increased from 600℃ to 900-950℃ at a rate of 20-40℃ / min. Within this range, the axial pressure is linearly increased to the peak pressure of 70-100 MPa, and a high-frequency alternating magnetic field with a frequency of 10-50 kHz and an intensity of 0.1-0.3 T is activated. The third stage is the high-temperature heat preservation and locking period: heat preservation at 950-1050℃ for 5-15 minutes, reducing the axial pressure to 40-60 MPa, and keeping the high-frequency alternating magnetic field on. The fourth stage is the initial cooling phase: rapidly cooling from the insulation temperature to 600℃ at a cooling rate ≥80℃ / min, while maintaining constant pressure.

[0010] Furthermore, in step S3, an innovative pulsed electromagnetic field assisted discharge plasma sintering (PEF-SPS) process is adopted, which is finely divided into four dynamic control stages. The first stage involves rapid heating to 600℃ at 40-60℃ / min for low-temperature degassing activation, with only a low pressure of 5-15 MPa and a DC pulse current applied. In the second stage, in the critical phase transformation zone of 600-950℃, a simultaneous heating of 20-40℃ / min is implemented, the axial pressure linearly climbs to a peak value of 70-100 MPa, and a high-frequency alternating magnetic field of 10-50 kHz / 0.1-0.3 T is activated to promote densification by utilizing the superplasticity of phase transformation and magnetostrictive vibration. In the third stage, the microstructure is locked at 950-1050℃, the pressure is reduced to 40-60 MPa, and the alternating magnetic field is maintained. In the fourth stage, the microstructure is locked at ≥80℃ / min, and the microstructure is frozen at 600℃, effectively freezing the fine-grained structure and preventing grain coarsening.

[0011] As a preferred embodiment of the method for densifying the high-purity cobalt target material according to the present invention, the specific operation of the magnetic field-induced texturing cooling is as follows: When the sintering temperature drops from the high temperature to the range of 550-650℃, the high-frequency alternating magnetic field is turned off, and then a constant DC magnetic field with an intensity of 0.5-1.2 T is turned on, and the direction of the constant DC magnetic field is perpendicular to the pressure surface of the target material. Under the action of a constant DC magnetic field, the temperature is slowly cooled to 400℃ at a rate of 10-30℃ / min, and the (002) crystal planes are preferentially aligned along the magnetic field direction by utilizing the magnetic anisotropy of cobalt. Once the temperature drops below 400℃, turn off the magnetic field and allow it to cool naturally to room temperature, finally removing the axial pressure.

[0012] Furthermore, during the magnetic field-induced texturing cooling process in step S4, an intelligent switching strategy for the magnetic field mode is implemented. When the sintering temperature drops to the critical range of magnetic order transformation of 550-650℃, the high-frequency alternating magnetic field is decisively shut off, and a constant DC magnetic field with an intensity of 0.5-1.2 T and a direction perpendicular to the pressure surface of the target material is immediately applied. Under the drive of this strong constant magnetic field, the temperature is controlled to drop to 400℃ at a slow cooling rate of 10-30℃ / min. By utilizing the inherent magnetocrystalline anisotropy of cobalt crystals, the grains are forced to rotate and the (002) crystal planes are preferentially aligned along the magnetic field direction (i.e., the normal direction of the target material). After the magnetic domains are locked below 400℃, the magnetic field is shut off and the pressure is released, thereby directly obtaining a strong textured structure without relying on plastic deformation.

[0013] As a preferred embodiment of the method for preparing high-purity cobalt target densification molding according to the present invention, wherein: in the second stage of S3, the timing of applying the peak pressure is matched with the allotropic transformation temperature range of cobalt; The shrinkage rate of the sample is monitored in real time by a displacement sensor. When the shrinkage rate changes abruptly, it is determined that the sample has entered the active phase transition region. At this time, a pressure ramp loading strategy is implemented with a loading rate of 5-10 MPa / min to promote pore closure by utilizing the superplasticity of phase transition.

[0014] Furthermore, in the second stage of phase transformation and plastic compaction in step S3, an intelligent pressure loading mechanism based on real-time displacement feedback is introduced; the axial shrinkage rate of the billet is continuously monitored by a high-precision displacement sensor to accurately capture the cobalt allotropic transformation (HCP). The shrinkage rate abrupt change point of FCC is used to determine the entry into the active phase transformation region. Then, a pressure ramp loading strategy with a rate of 5-10 MPa / min is initiated to precisely apply the maximum external mechanical work to the phase transformation window period when the material has the best plasticity. This fully utilizes the superplastic effect of phase transformation to accelerate pore closure and grain boundary slip, thereby maximizing densification efficiency.

[0015] As a preferred embodiment of the preparation method for densification molding of high-purity cobalt target material according to the present invention, in S2, the inner wall of the graphite mold is pre-sprayed with hexagonal boron nitride (h-BN) release agent or laid with high-density graphite paper. The powder loading process is completed in an inert atmosphere glove box with an oxygen content ≤0.1 ppm and a water content ≤0.1 ppm; After pre-pressing, the mold is quickly transferred to the sintering furnace cavity, and the vacuum level in the furnace cavity is evacuated to [value missing] within 10 minutes. the following.

[0016] Furthermore, in step S2, during the filling and pre-compression stage, a comprehensive ultra-low oxygen water environment control system is constructed. The inner wall of the graphite mold is pre-coated with hexagonal boron nitride (h-BN) release agent or laid with high-density graphite paper to reduce interfacial friction. All powder filling operations are completed in an inert atmosphere glove box with both oxygen and water content ≤0.1 ppm. After pre-compression molding, the mold must be rapidly transferred to the sintering furnace within 10 minutes and evacuated to a vacuum state. The following measures are taken to minimize secondary oxidation of the powder surface before high temperature, ensuring the extremely low oxygen content of the final target material.

[0017] As a preferred embodiment of the method for preparing the high-purity cobalt target material densification forming according to the present invention, wherein: in S5, the stress-relief annealing process specifically comprises: The sintered cobalt billet is placed in a high-vacuum annealing furnace with a vacuum level better than Pa. Heat to 500-600℃, hold for 2-4 hours, then cool with the furnace or control the cooling rate to ≤50℃ / min until below 200℃ before unloading. The finishing process includes removing the surface contamination layer using diamond tools, and achieving a surface roughness Ra ≤ 0.4 μm for the target material through precision grinding and polishing.

[0018] Furthermore, in step S5, the stress-relief annealing and finishing stage, a combination of high-vacuum heat treatment and ultra-precision surface treatment is implemented. The sintered billet is placed in an annealing furnace with a vacuum level better than 5×10-45×10-4 Pa, heated to 500-600℃ and held for 2-4 hours to eliminate internal residual stress, and then cooled at a controlled rate of ≤50℃ / min. In the machining stage, diamond tools are used to remove the surface contamination layer, and multiple passes of precision grinding and polishing are performed to make the working surface of the target material reach the mirror roughness standard of Ra≤0.4μm, which meets the stringent flatness requirements of advanced processes for the sputtering source surface.

[0019] As a preferred embodiment of the method for preparing high-purity cobalt target material densification forming according to the present invention, the method further includes step S6: backplate welding; The high-purity cobalt target material treated with S5 is combined with the oxygen-free copper backing plate through diffusion welding or brazing process. The welding interface uses titanium, nickel or indium as an intermediate transition layer, and the welding temperature is controlled at 300-500℃. After bonding, it is inspected by ultrasonic scanning microscope (C-SAM) and the bonding rate is required to be ≥98% and there are no unbonded areas with a diameter greater than 0.5mm.

[0020] Furthermore, in the newly added step S6 backplate welding process, low-temperature diffusion welding or brazing technology is used to achieve a reliable connection between the target material and the oxygen-free copper backplate; titanium, nickel, or indium are selected as intermediate transition layers to alleviate the mismatch of thermal expansion coefficients; the welding temperature is strictly controlled at 300-500℃ to avoid damaging the microstructure of the target material; after welding, full-area inspection is carried out using ultrasonic scanning microscopy (C-SAM) to ensure that the bonding rate is ≥98% and there are no unbonded defect areas with a diameter greater than 0.5mm, thus ensuring the heat dissipation stability and structural integrity of the target material under high-power sputtering.

[0021] As a preferred embodiment of the method for preparing high-purity cobalt target material densification molding according to the present invention, the high-purity cobalt target material prepared by the above method has a relative density ≥99.8%, an oxygen content ≤10 ppm, and an average grain size of 10-30 μm. Furthermore, X-ray diffraction (XRD) pole figure analysis showed that the texture coefficient of the (002) crystal plane of the target working surface was ≥0.85, the grain orientation was uniform, and there was no macroscopic segregation.

[0022] Furthermore, the high-purity cobalt target material prepared through the above-mentioned optimized process exhibits excellent microstructure and performance indicators; its relative density is stable at ≥99.8%, oxygen content is controlled at ≤10 ppm, and the average grain size is uniformly distributed in the range of 10-30 μm; particularly noteworthy is that X-ray diffraction (XRD) pole figure analysis confirms that the texture coefficient of the (002) crystal plane of the target material working surface is as high as ≥0.85, the grain orientation is highly consistent and there is no macroscopic segregation, which directly meets the extreme requirements of high-end semiconductor interconnect layers for low resistivity and high electromigration resistance.

[0023] As a preferred embodiment of the method for preparing high-purity cobalt target densification molding according to the present invention, the method is based on powder metallurgy theory and the physical properties of ferromagnetic materials, utilizing the HCP-FCC phase transformation plasticity mechanism of cobalt at high temperature, combined with the regulatory effect of an external electromagnetic field on atomic diffusion and grain boundary migration. In S1, the nano-coating layer acts as a second-phase particle pinning grain boundaries, inhibiting abnormal grain growth at high temperatures; in S3, the alternating magnetic field generates micro-mechanical vibrations through magnetostriction, reducing the sintering activation energy; and in S4, the constant magnetic field utilizes the principle of minimizing magnetocrystalline anisotropy to drive grain rotation to achieve the spontaneous formation of a specific texture, thereby directly obtaining high-performance high-purity cobalt sputtering targets without relying on large-deformation rolling processes.

[0024] Furthermore, this method deeply integrates the principles of powder metallurgy dynamics and ferromagnetic material physics, constructing a three-in-one synergistic control mechanism of "nanopining-phase transformation superplasticity-magnetic texture". Specifically, the nano-coating layer generated in S1 effectively pins grain boundaries as second-phase particles to suppress coarsening, the high-frequency alternating magnetic field in S3 induces micro-mechanical vibration through magnetostriction to reduce sintering activation energy and promote mass transport, and the constant DC magnetic field in S4 drives spontaneous grain rotation and orientation by minimizing magnetocrystalline anisotropy. Thus, the traditional large deformation rolling process is completely abandoned, and the integrated in-situ near-net-shape forming of high-purity cobalt target material with high density, fine grains and strong texture is achieved.

[0025] The beneficial effects of this invention are as follows: Through the in-situ reconstruction pretreatment step of high-purity cobalt powder, a reactive gas is introduced to grow a nanoscale amorphous coating layer in situ on the basis of inert atmosphere reduction, which achieves effective pinning of grain boundaries and deep removal of surface oxides. This suppresses abnormal grain growth and reduces oxygen content during subsequent high-temperature sintering, laying the foundation for a high-purity fine-grained microstructure. Furthermore, by combining multi-field coupled dynamic sintering and magnetic field-induced texturing cooling steps, the synergistic effect of pulsed current, dynamic axial pressure, and alternating magnetic field is used to stimulate the allotropic phase transition superplasticity of cobalt to accelerate pore closure, and switching occurs in the cooling critical region. By using a constant DC magnetic field and utilizing magnetocrystalline anisotropy to drive the spontaneous rotation of the grains, the (002) crystal planes are preferentially aligned along the normal of the target material. This achieves the integrated in-situ completion of densification and strong texture construction, completely eliminating the lengthy process of traditional rolling-induced texture based on large deformation. Ultimately, it achieves the beneficial effect of directly preparing high-performance cobalt targets with ultra-high relative density, extremely low oxygen content, uniform fine grain structure, and high strength with specific preferred orientation without introducing residual stress and microcracks. This improves the sputtering stability, thin film uniformity, and anti-electromigration ability of the target material in advanced semiconductor processes. Attached Figure Description

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

[0027] Figure 1 A flowchart of a method for densifying high-purity cobalt sputtering targets. Detailed Implementation

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0031] Reference Figure 1 This is one embodiment of the present invention, which provides a method for preparing a high-purity cobalt target material through densification, comprising the following steps: Step S1: Surface in-situ reconstruction pretreatment High-purity cobalt powder with a purity of 99.999% and an average particle size of 15 μm was selected. First, it was placed in a tube furnace, and an Ar+H2 (volume ratio 95:5) mixed atmosphere was introduced. The mixture was kept at 400℃ for 2 hours to remove the surface oxide film. Subsequently, while maintaining the reducing atmosphere, a trace amount of diborane (B2H6) was introduced as a boron-containing precursor gas, and the reaction temperature was controlled to rise to 500℃ for 45 minutes. At this point, an amorphous boron carbide (B4C) nano-coating layer with a thickness of approximately 5 nm was formed in situ on the surface of the cobalt powder, serving as a grain boundary pinning agent for subsequent sintering.

[0032] Step S2: Filling and Pre-compression In an inert atmosphere glove box with oxygen and water content both ≤0.1 ppm, the treated cobalt powder was loaded into a graphite mold whose inner wall was sprayed with hexagonal boron nitride (h-BN) release agent. An initial pressure of 20 MPa was applied for pre-compaction. After pre-compaction, the mold was quickly transferred to the spark plasma sintering (SPS) furnace chamber, and the vacuum was evacuated to Pa within 8 minutes.

[0033] Step S3: Multi-field Coupled Dynamic Sintering (PEF-SPS) A four-stage sintering process is adopted: Low-temperature degassing activation period: The temperature is increased to 600℃ at 50℃ / min, the pressure is maintained at 10 MPa, and only a DC pulse current is applied.

[0034] Phase transformation plastic compaction stage: The temperature is increased from 600℃ to 920℃ at a rate of 30℃ / min. During this process, the shrinkage rate is monitored in real time by a displacement sensor. When a sudden change in the shrinkage rate is detected (indicating entry into the HCP-FCC phase transformation active region), a pressure ramp loading strategy is initiated to linearly increase the axial pressure to 85 MPa at a rate of 8 MPa / min; at the same time, a high-frequency alternating magnetic field with a frequency of 30 kHz and an intensity of 0.2 T is activated.

[0035] High-temperature insulation lock-in period: Keep at 1000℃ for 10 minutes, then reduce the pressure to 50 MPa and keep the high-frequency alternating magnetic field on.

[0036] Initial cooling phase: rapidly cool to 600°C at a rate of 100°C / min while maintaining constant pressure.

[0037] Step S4: Magnetic field-induced texturing cooling When the temperature drops to 600℃, the high-frequency alternating magnetic field is turned off, and a constant DC magnetic field with an intensity of 0.8 T and a direction perpendicular to the pressure surface of the target material is immediately turned on. Under the action of this magnetic field, the material is slowly cooled to 400℃ at a rate of 20℃ / min, and the (002) crystal planes are preferentially aligned along the normal direction by utilizing magnetocrystalline anisotropy. After the temperature drops below 400℃, the magnetic field is turned off, and the material is allowed to cool naturally to room temperature and the pressure is released.

[0038] Step S5: Stress-relief annealing and finishing The sintered blank is placed in a vacuum with a degree of superiority. In a Pa annealing furnace, the temperature is raised to 550℃ and held for 3 hours, then cooled to below 200℃ at a rate of 40℃ / min before being removed from the furnace. The surface contamination layer is removed using a diamond tool, and the surface is then precision ground and polished to achieve a surface roughness Ra of 0.3μm.

[0039] Step S6: Backplate welding Titanium (Ti) was used as an intermediate transition layer, and the target material was bonded to the oxygen-free copper backing plate by diffusion welding at 400℃. C-SAM testing showed a bonding rate of 99.2%, with no unbonded areas larger than 0.5 mm.

[0040] Results Analysis: The cobalt target material prepared in this embodiment has a relative density of 99.85%, an oxygen content of 8 ppm, and an average grain size of 18 μm. XRD pole figure analysis shows that the texture index of the (002) crystal plane is as high as 0.88, the grain orientation is uniform, and there is no macroscopic segregation.

[0041] Example 2: A rapid densification scheme based on amorphous carbon layer coating and high-frequency strong magnetic field assistance This embodiment focuses on demonstrating a process route that utilizes carbon-containing precursors to generate amorphous carbon layers and employs a high-frequency alternating magnetic field and a fast heating rate to achieve efficient and dense formation.

[0042] Step S1: Surface in-situ reconstruction pretreatment High-purity cobalt powder with a purity of 99.999% and an average particle size of 25 μm was selected. It was reduced at 380 °C for 1.5 hours in an Ar+H2 (volume ratio 90:10) atmosphere. Subsequently, methane (CH4) was introduced as a carbon-containing precursor, and the reaction was carried out at 480 °C for 50 minutes, resulting in the in-situ formation of an amorphous carbon layer with a thickness of approximately 3 nm on the surface of the cobalt powder.

[0043] Step S2: Filling and Pre-compression The operation was conducted in a glove box with an ultra-low oxygen water environment (≤0.1 ppm), and the inner wall of the graphite mold was lined with high-density graphite paper. The pre-compression pressure was set to 15 MPa. After the mold was transferred to the furnace cavity, the vacuum level was evacuated to [value missing] within 10 minutes. Pa.

[0044] Step S3: Multi-field Coupled Dynamic Sintering (PEF-SPS) Low-temperature degassing activation period: rapidly increase the temperature to 600℃ at 60℃ / min, maintain the pressure at 5 MPa, and have no external magnetic field.

[0045] Phase transformation and plastic compaction stage: The temperature is increased from 600℃ to 950℃ at a rate of 40℃ / min. The phase transformation zone is determined based on the point of abrupt change in shrinkage rate, and the pressure is increased to 95 MPa at a rate of 10 MPa / min. Simultaneously, a high-frequency alternating magnetic field with a frequency of 50 kHz and an intensity of 0.3 T is activated to violently disturb the grain boundaries using the strong magnetostrictive effect.

[0046] High-temperature heat preservation and locking period: heat preservation at 1050℃ for 5 minutes, pressure reduced to 40 MPa, maintaining magnetic field.

[0047] Initial cooling phase: rapidly cool to 600℃ at a rate of 120℃ / min.

[0048] Step S4: Magnetic field-induced texturing cooling When the temperature drops to 550℃, a vertical constant DC magnetic field of intensity 1.0 T is switched on. The temperature is then slowly cooled to 400℃ at a rate of 15℃ / min to drive the grain rotation. Below 400℃, the field is turned off for cooling and pressure relief.

[0049] Step S5: Stress-relief annealing and finishing exist Under vacuum of Pa, the furnace was held at 500℃ for 2 hours and then cooled in the furnace. After finishing, the surface roughness Ra was controlled at 0.35μm.

[0050] Step S6: Backplate welding Indium (In) was used as an intermediate transition layer, and brazing was performed at 350°C. The bonding rate, as measured by C-SAM, was 98.5%, meeting high standards.

[0051] Results Analysis: The cobalt target material prepared in this embodiment has a relative density of 99.82%, an oxygen content of 9 ppm, and an average grain size of 22 μm. XRD testing shows that the (002) crystal plane texture index is 0.86, indicating excellent potential for thin film deposition uniformity.

[0052] Example 3: Low-stress fabrication scheme based on fine grain control and strong magnetic field directional growth This embodiment focuses on demonstrating a process route for obtaining finer grains and stronger texture by using a lower sintering temperature and a stronger constant magnetic field for powders with smaller particle sizes.

[0053] Step S1: Surface in-situ reconstruction pretreatment High-purity cobalt powder with a purity of 99.999% and an average particle size of 12 μm was selected. It was reduced at 450 °C for 3 hours in an Ar+H2 (volume ratio 98:2) atmosphere to ensure deep reduction. Subsequently, acetylene (C2H2) was introduced as a precursor, and the reaction was carried out at 550 °C for 30 minutes to generate a relatively thick amorphous carbon layer of approximately 8 nm to enhance the grain boundary pinning effect at high temperatures.

[0054] Step S2: Filling and Pre-compression The powder is loaded into a strictly controlled inert atmosphere (oxygen / water ≤ 0.1 ppm), and the inner wall of the mold is sprayed with h-BN. The pre-compression pressure is 25 MPa. After transfer, a vacuum is quickly evacuated. .

[0055] Step S3: Multi-field Coupled Dynamic Sintering (PEF-SPS) Low-temperature degassing activation period: heating to 600℃ at 40℃ / min, pressure 15 MPa.

[0056] Phase transformation and plastic compaction period: The temperature was increased from 600℃ to 900℃ at a rate of 20℃ / min (slightly lower temperature to suppress grain growth). After the phase transformation abrupt change point was detected, the pressure was increased to 75 MPa at a gentle rate of 5 MPa / min; an alternating magnetic field with a frequency of 10 kHz and an intensity of 0.15 T was turned on to provide moderate micro-vibration to assist compaction.

[0057] High-temperature heat preservation and locking period: heat preservation at 950℃ for 15 minutes (slightly longer heat preservation to eliminate micropores but rely on carbon layer to inhibit coarsening), pressure maintained at 60 MPa, and magnetic field maintained.

[0058] Initial cooling phase: Cool to 600℃ at 80℃ / min.

[0059] Step S4: Magnetic field-induced texturing cooling When the temperature drops to 650℃, a strong vertical constant DC magnetic field of intensity 1.2 T is switched on. The temperature is then slowly cooled to 400℃ at an extremely slow rate of 10℃ / min, allowing sufficient time for the grains to rotate and form a perfect texture. Cooling is then performed with the field turned off below 400℃.

[0060] Step S5: Stress-relief annealing and finishing exist Under vacuum of Pa, the surface is held at 600℃ for 4 hours to fully release stress, with the cooling rate controlled at ≤50℃ / min. After finishing, the surface roughness Ra reaches 0.25μm.

[0061] Step S6: Backplate welding Nickel (Ni) was used as an intermediate transition layer, and diffusion bonding was performed at 450°C. C-SAM testing showed a bonding rate of up to 99.5%, indicating extremely strong interfacial bonding.

[0062] Results Analysis: The cobalt target material prepared in this embodiment has a relative density of 99.88%, an oxygen content as low as 6 ppm, and an average grain size refined to 14 μm. XRD pole figure analysis shows that the texture factor of the (002) crystal plane reaches 0.91, exhibiting extremely preferred orientation characteristics, which is particularly suitable for advanced process nodes of 3nm and below with extremely high requirements for grain size and texture.

[0063] In summary, this invention, through an in-situ surface reconstruction pretreatment step using high-purity cobalt powder, introduces a reactive gas to grow a nanoscale amorphous coating layer in situ on top of inert atmosphere reduction. This achieves effective grain boundary pinning and deep removal of surface oxides, thereby suppressing abnormal grain growth and reducing oxygen content during subsequent high-temperature sintering, laying the foundation for a high-purity, fine-grained microstructure. Furthermore, by combining multi-field coupled dynamic sintering with magnetic field-induced texturing cooling, the synergistic effect of pulsed current, dynamic axial pressure, and alternating magnetic field is used to stimulate the allotropic phase transition superplasticity of cobalt to accelerate pore closure, and then switches to a more stable state in the cooling critical region. A constant DC magnetic field is used to drive the spontaneous rotation of the grains by magnetocrystalline anisotropy, so that the (002) crystal plane is preferentially aligned along the normal of the target material. This achieves the integrated in-situ completion of densification and strong texture construction, completely eliminating the lengthy process of traditional rolling-induced texture with large deformation. Ultimately, it achieves the beneficial effect of directly preparing high-performance cobalt targets with ultra-high relative density, extremely low oxygen content, uniform fine grain structure and high strength with specific preferred orientation without introducing residual stress and microcracks. This improves the sputtering stability, thin film uniformity and anti-electromigration ability of the target material in advanced semiconductor processes.

[0064] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a high-purity cobalt target material through densification molding, characterized in that: include, S1: In-situ surface reconstruction pretreatment of high-purity cobalt powder, that is, reducing high-purity cobalt powder under an inert atmosphere and introducing reactive gas to grow a nanoscale coating layer in situ on the surface of cobalt powder. S2: Filling and pre-compressing: The cobalt powder treated in S1 is loaded into the graphite mold and pre-compressed by applying initial pressure; S3: Multi-field coupled dynamic sintering, the mold is placed in the sintering furnace and heated by DC pulse current in a vacuum environment, while dynamic axial pressure and external magnetic field are applied simultaneously during the sintering process; S4: Magnetic field-induced texturing cooling. During the cooling stage after sintering and holding, the mode of the external magnetic field is adjusted to induce the preferential orientation growth of cobalt grains. S5: Stress-relief annealing and finishing: Vacuum stress-relief heat treatment is performed on the sintered cobalt billet, followed by machining and surface polishing to obtain high-purity cobalt target material.

2. The method for preparing high-purity cobalt target material through densification as described in claim 1, characterized in that: In S1, the high-purity cobalt powder has a purity of ≥99.999% and an average particle size of 10-30 μm; The in-situ surface reconstruction preprocessing specifically includes: First, put the cobalt powder in Reduce the mixture at 350-450℃ for 1-3 hours in a mixed atmosphere; Subsequently, while maintaining a reducing atmosphere, a trace amount of carbon- or boron-containing precursor gas is introduced, and the reaction temperature is controlled at 450-550℃, with a reaction time of 30-60 minutes, so that an amorphous carbon layer or boron carbide layer with a thickness of 2-10nm is generated in situ on the surface of the cobalt powder as a grain boundary pinning agent.

3. The method for preparing high-purity cobalt target material densification as described in claim 2, characterized in that: In S3, the multi-field coupled dynamic sintering adopts pulsed electromagnetic field assisted discharge plasma sintering (PEF-SPS) process; The sintering process is divided into four stages: The first stage is the low-temperature degassing and activation period: the temperature is raised from room temperature to 600℃ at a rate of 40-60℃ / min, the pressure is maintained at 5-15 MPa, only DC pulse current is applied, and the external magnetic field is not turned on. The second stage is the phase transformation and plastic compaction period: the temperature is increased from 600℃ to 900-950℃ at a rate of 20-40℃ / min. Within this range, the axial pressure is linearly increased to the peak pressure of 70-100 MPa, and a high-frequency alternating magnetic field with a frequency of 10-50 kHz and an intensity of 0.1-0.3 T is activated. The third stage is the high-temperature insulation and locking period: keep it at 950-1050℃ for 5-15 minutes, reduce the axial pressure to 40-60MPa, and keep the high-frequency alternating magnetic field on. The fourth stage is the initial cooling phase: rapidly cooling from the insulation temperature to 600℃ at a cooling rate ≥80℃ / min, while maintaining constant pressure.

4. The method for preparing high-purity cobalt target material densification as described in claim 3, characterized in that: In S4, the specific operation of the magnetic field-induced texturing cooling is as follows: When the sintering temperature drops from the high temperature to the range of 550-650℃, the high-frequency alternating magnetic field is turned off, and then a constant DC magnetic field with an intensity of 0.5-1.2 T is turned on, and the direction of the constant DC magnetic field is perpendicular to the pressure surface of the target material. Under the action of a constant DC magnetic field, the temperature is slowly cooled to 400℃ at a rate of 10-30℃ / min, and the (002) crystal planes are preferentially aligned along the magnetic field direction by utilizing the magnetic anisotropy of cobalt. Once the temperature drops below 400℃, turn off the magnetic field and allow it to cool naturally to room temperature, finally removing the axial pressure.

5. The method for preparing high-purity cobalt target material densification as described in claim 4, characterized in that: In the second stage of S3, the timing of the application of the peak pressure is matched with the allotropic transformation temperature range of cobalt. The shrinkage rate of the sample is monitored in real time by a displacement sensor. When the shrinkage rate changes abruptly, it is determined that the sample has entered the active phase transition region. At this time, a pressure ramp loading strategy is implemented with a loading rate of 5-10 MPa / min to promote pore closure by utilizing the superplasticity of phase transition.

6. The method for preparing high-purity cobalt target material densification as described in claim 5, characterized in that: In S2, the inner wall of the graphite mold is pre-sprayed with hexagonal boron nitride (h-BN) release agent or laid with high-density graphite paper; The powder loading process is completed in an inert atmosphere glove box with an oxygen content ≤0.1 ppm and a water content ≤0.1 ppm; After pre-pressing, the mold is quickly transferred to the sintering furnace cavity, and the vacuum level in the furnace cavity is evacuated to a certain value within 10 minutes. the following.

7. The method for preparing high-purity cobalt target material densification as described in claim 6, characterized in that: In S5, the stress-relief annealing process specifically includes: The sintered cobalt billet is placed in a high-vacuum annealing furnace with a vacuum level better than Pa. Heat to 500-600℃, hold for 2-4 hours, then cool with the furnace or control the cooling rate to ≤50℃ / min until below 200℃ before unloading. The finishing process includes removing the surface contamination layer using diamond tools, and achieving a surface roughness Ra ≤ 0.4 μm for the target material through precision grinding and polishing.

8. The method for preparing high-purity cobalt target material densification as described in claim 7, characterized in that: The method also includes step S6: backplate welding; The high-purity cobalt target material treated with S5 is combined with the oxygen-free copper backing plate through diffusion welding or brazing process. The welding interface uses titanium, nickel or indium as an intermediate transition layer, and the welding temperature is controlled at 300-500℃. After bonding, it is inspected by ultrasonic scanning microscope (C-SAM) and the bonding rate is required to be ≥98% and there are no unbonded areas with a diameter greater than 0.5mm.

9. The method for preparing high-purity cobalt target material densification as described in claim 8, characterized in that: The high-purity cobalt target material prepared by the above method has a relative density ≥99.8%, an oxygen content ≤10 ppm, and an average grain size of 10-30 μm; Furthermore, X-ray diffraction (XRD) pole figure analysis showed that the texture coefficient of the (002) crystal plane of the target working surface was ≥0.85, the grain orientation was uniform, and there was no macroscopic segregation.

10. The method for preparing high-purity cobalt target material densification as described in claim 9, characterized in that: This method is based on powder metallurgy theory and the physical properties of ferromagnetic materials. It utilizes the HCP-FCC phase transformation plasticity mechanism of cobalt at high temperatures, combined with the regulation effect of an external electromagnetic field on atomic diffusion and grain boundary migration. In S1, the nano-coating layer acts as a second-phase particle pinning grain boundaries, inhibiting abnormal grain growth at high temperatures; in S3, the alternating magnetic field generates micro-mechanical vibrations through magnetostriction, reducing the sintering activation energy; and in S4, the constant magnetic field utilizes the principle of minimizing magnetocrystalline anisotropy to drive grain rotation to achieve the spontaneous formation of a specific texture, thereby directly obtaining high-performance high-purity cobalt sputtering targets without relying on large-deformation rolling processes.

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