CN-122013117-A - Preparation method for densification forming of high-purity cobalt target

CN122013117ACN 122013117 ACN122013117 ACN 122013117ACN-122013117-A

Abstract

The invention discloses a preparation method of high-purity cobalt target densification forming, which relates to the technical field of semiconductor material preparation and comprises the following steps of S1, carrying out in-situ reconstruction pretreatment on the surface of high-purity cobalt powder, namely carrying out reduction treatment on the high-purity cobalt powder under inert atmosphere, introducing reactive gas to grow a nanoscale coating layer on the surface of the cobalt powder in situ, S2, filling and prepressing, filling the cobalt powder treated by S1 into a graphite mold, applying initial pressure to carry out precompaction, S3, carrying out multi-field coupling dynamic sintering, placing the mold into a sintering furnace, applying direct current pulse current to carry out heating in a vacuum environment, synchronously applying dynamic axial pressure and an external magnetic field in the sintering process, S4, carrying out magnetic field induced texturing cooling, and adjusting the mode of the external magnetic field in a cooling stage after sintering and heat preservation. The invention thoroughly eliminates the traditional large-deformation rolling process and realizes the integrated in-situ near-net forming of high-density, fine crystallization and strong texture of the high-purity cobalt target.

Inventors

WANG DI
CHE YIFAN
YE FANGXIA
XUE YUNA
WANG YU
YANG ZHEN
YIN ZHIFU

Assignees

西安文理学院

Dates

Publication Date: 20260512
Application Date: 20260327

Claims (10)

1. A preparation method for densification forming of a high-purity cobalt target material is characterized by comprising the steps of, S1, carrying out in-situ reconstruction pretreatment on the surface of high-purity cobalt powder, namely carrying out reduction treatment on the high-purity cobalt powder in an inert atmosphere, and introducing reactive gas to grow a nanoscale coating layer on the surface of the cobalt powder in situ; S2, filling and pre-compacting, namely filling the cobalt powder treated in the S1 into a graphite die, and applying initial pressure to pre-compact; S3, multi-field coupling dynamic sintering, namely placing the die in a sintering furnace, applying direct current pulse current under a vacuum environment for heating, and synchronously applying dynamic axial pressure and an external magnetic field in the sintering process; S4, performing magnetic field induced texturing cooling, adjusting the mode of an external magnetic field in a cooling stage after sintering and heat preservation are finished, and using the magnetic field to induce cobalt grains to grow in a preferred orientation; And S5, performing stress relief annealing and finish machining, performing vacuum stress relief heat treatment on the sintered cobalt blank, and then performing mechanical machining and surface polishing to obtain a high-purity cobalt target finished product.
2. The method for preparing the high-purity cobalt target material by densification molding according to claim 1, wherein in S1, the purity of the high-purity cobalt powder is more than or equal to 99.999%, the average particle size is 10-30 μm, and the surface in-situ reconstruction pretreatment specifically comprises: firstly, cobalt powder is added in Preserving heat and reducing for 1-3 hours at the temperature of 350-450 ℃ in the mixed atmosphere; then, on the basis of keeping the reducing atmosphere, a trace of precursor gas containing carbon or boron is introduced, the reaction temperature is controlled to be 450-550 ℃, and the reaction time is controlled to be 30-60 minutes, so that an amorphous carbon layer or a boron carbide layer with the thickness of 2-10nm is generated on the surface of cobalt powder in situ and is used as a grain boundary pinning agent.
3. The method for preparing the high-purity cobalt target material by densification forming of claim 2, wherein in S3, the multi-field coupling dynamic sintering adopts a pulse electromagnetic field assisted spark plasma sintering (PEF-SPS) process; The sintering process is divided into four stages: The first stage is a low-temperature degassing activation period, namely, the temperature is raised to 600 ℃ from room temperature, the temperature raising rate is 40-60 ℃ per minute, the pressure is kept at 5-15 MPa, only direct current pulse current is applied, and an external magnetic field is not started; The second phase is a phase change plastic densification phase, namely, heating from 600 ℃ to 900-950 ℃ at a heating rate of 20-40 ℃ per minute, linearly lifting the axial pressure to a peak pressure of 70-100 MPa in the interval, and starting a high-frequency alternating magnetic field with a frequency of 10-50 kHz and a strength of 0.1-0.3T; The third stage is a high-temperature heat-preserving locking period, namely, heat preservation is carried out for 5-15 minutes at 950-1050 ℃, the axial pressure is reduced to 40-60 MPa, and the high-frequency alternating magnetic field is kept to be started; the fourth stage is the initial cooling stage, which is to cool the product from the heat preservation temperature to 600 ℃ rapidly, the cooling rate is more than or equal to 80 ℃ per minute, and the pressure is kept unchanged.
4. The method for preparing high-purity cobalt target densification according to claim 3, wherein in S4, the specific operation of the magnetic field induced texturing cooling is as follows: When the sintering temperature is reduced to 550-650 ℃, the high-frequency alternating magnetic field is closed, and then a constant direct current magnetic field with the intensity of 0.5-1.2T is opened, wherein the direction of the constant direct current magnetic field is perpendicular to the pressed surface of the target; Under the action of a constant direct current magnetic field, slowly cooling to 400 ℃ at the speed of 10-30 ℃ per minute, and utilizing the magnetic anisotropy of cobalt to induce the preferential arrangement of (002) crystal faces along the magnetic field direction; And after the temperature is lower than 400 ℃, closing the magnetic field, naturally cooling to room temperature, and finally removing the axial pressure.
5. The method for preparing high purity cobalt target densification forming according to claim 4, wherein in the second stage of S3, the application timing of the peak pressure is matched with the isomeric transformation temperature interval of cobalt; And monitoring the shrinkage rate of the sample in real time through a displacement sensor, judging that the sample enters the phase change active region when a sudden change point appears in the shrinkage rate, and executing a pressure slope loading strategy at the moment, wherein the loading rate is 5-10 MPa/min so as to promote pore closure by utilizing phase change superplasticity.
6. The method for preparing the high-purity cobalt target material by densification forming of claim 5, wherein in S2, hexagonal boron nitride (h-BN) release agent is sprayed on the inner wall of the graphite mold in advance or high-density graphite paper is paved; The powder filling process is completed in an inert atmosphere glove box with the oxygen content less than or equal to 0.1 ppm and the water content less than or equal to 0.1 ppm; After the prepressing is completed, the die is quickly transferred to a sintering furnace chamber, and the vacuum degree of the furnace chamber is pumped to within 10 minutes The following is given.
7. The method for preparing high purity cobalt target densification according to claim 6, wherein in S5, the stress relief annealing process specifically comprises: placing the sintered cobalt blank in a high vacuum annealing furnace, wherein the vacuum degree is superior to Pa; Heating to 500-600 ℃, preserving heat for 2-4 hours, and then cooling along with a furnace or controlling the cooling rate to be less than or equal to 50 ℃ per minute to below 200 ℃ and discharging from the furnace; The finishing comprises removing a surface pollution layer by using a diamond cutter, and enabling the surface roughness Ra of the target to be less than or equal to 0.4 mu m through precise grinding and polishing.
8. The method for preparing the high-purity cobalt target material by densification forming of claim 7, further comprising the step S6 of welding a back plate; Combining the high-purity cobalt target material treated by the S5 with an oxygen-free copper backboard through a diffusion welding or brazing process; The welding interface adopts titanium, nickel or indium as an intermediate transition layer, the welding temperature is controlled to be 300-500 ℃, after the welding, the welding is detected by an ultrasonic scanning microscope (C-SAM), and an unbonded area with the bonding rate of more than or equal to 98% and the diameter of more than 0.5mm is required.
9. The method for preparing the high-purity cobalt target by densification molding according to claim 8, wherein the high-purity cobalt target prepared by the method has a relative density of 99.8% or more, an oxygen content of 10 ppm% or less and an average grain size of 10-30 μm; And the texture coefficient of the (002) crystal face of the working surface of the target material is more than or equal to 0.85, and the grain orientation is uniformly distributed without macrosegregation as measured by X-ray diffraction (XRD) polar diagram analysis.
10. The method for preparing the high-purity cobalt target material by densification forming is characterized in that the method utilizes a HCP-FCC phase transformation plasticity mechanism of cobalt at high temperature based on a powder metallurgy theory and the physical characteristics of ferromagnetic materials, and combines the regulation and control effects of an external electromagnetic field on atomic diffusion and grain boundary migration; The method comprises the steps of S1, wherein a nano coating layer is used as a second phase particle pinning grain boundary to inhibit abnormal growth of high Wen Jingli, S3, an alternating magnetic field is used for generating micro mechanical vibration through a magnetostriction effect to reduce sintering activation energy, S4, and S4, a constant magnetic field is used for driving grains to rotate by utilizing a magnetocrystalline anisotropy energy minimization principle to realize spontaneous formation of a specific texture, so that a high-purity cobalt target material for high-performance sputtering is directly obtained on the premise of not depending on a large deformation rolling process.

Description

Preparation method for densification forming of high-purity cobalt target Technical Field The invention relates to the technical field of semiconductor material preparation, in particular to a preparation method for densification forming of a high-purity cobalt target. Background The high-purity cobalt target is a core key material for preparing a copper interconnection barrier layer and a magnetic recording film in the semiconductor advanced process, an integrated circuit node evolves to 3nm and below, the industry has extremely high requirements on the purity, the compactness, the grain uniformity and the crystal texture of the target, and the main stream preparation process mainly adopts a route of 'high-purity cobalt powder cold isostatic pressing combined Hot Isostatic Pressing (HIP) sintering' or 'vacuum melting plus multi-pass hot rolling annealing'. The powder metallurgy method has wide application due to the advantages of impurity control, and the typical process is to press cobalt powder under inert atmosphere, sinter and densify the cobalt powder at high temperature and high pressure for a long time, and assist with a micro refiner, and finally adjust the grain orientation through severe plastic deformation processing so as to meet the severe standard of a sputtering process on a film microstructure. The prior art still faces challenges in co-optimizing "ultra-high densification" and "specific strong texture". The traditional sintering process relies on high-temperature heat activation to eliminate pores, but the abnormal growth of crystal grains is extremely easy to induce uneven tissues, and if the heat input is reduced for keeping fine grains, micropores are difficult to eliminate, and sputtering nodulation is easy to cause residual defects. More critical is that the blank obtained by conventional sintering has random grain orientation, lacks the preferred orientation of (002) surface favorable for electromigration performance, and has to rely on subsequent large deformation rolling to induce texture, so that the step strategy of 'densification before deformation' is long and high in cost, and residual stress and microcracks are introduced in severe plastic deformation, so that the target is easy to warp and crack in welding or use, and the integrated in-situ construction of high densification, fine crystals and ideal texture is difficult to realize. Disclosure of Invention The present invention has been made in view of the above-described problems occurring in the prior art. Therefore, the invention provides a preparation method for densification forming of a high-purity cobalt target, which solves the problems that the prior art is difficult to consider ultra-high density and fine grain structure under the step strategy of densification before deformation, and cannot directly construct an integrated forming of a strong (002) preferred texture in situ on the premise of not introducing residual stress. In order to solve the technical problems, the invention provides the following technical scheme: In a first aspect, the invention provides a preparation method for densification forming of a high-purity cobalt target, comprising the steps of S1, carrying out in-situ reconstruction pretreatment on the surface of high-purity cobalt powder, namely, carrying out reduction treatment on the high-purity cobalt powder in an inert atmosphere, and introducing reactive gas to grow a nanoscale coating layer on the surface of the cobalt powder in situ; S2, filling and pre-compacting, namely filling the cobalt powder treated in the S1 into a graphite die, and applying initial pressure to pre-compact; S3, multi-field coupling dynamic sintering, namely placing the die in a sintering furnace, applying direct current pulse current under a vacuum environment for heating, and synchronously applying dynamic axial pressure and an external magnetic field in the sintering process; S4, performing magnetic field induced texturing cooling, adjusting the mode of an external magnetic field in a cooling stage after sintering and heat preservation are finished, and using the magnetic field to induce cobalt grains to grow in a preferred orientation; And S5, performing stress relief annealing and finish machining, performing vacuum stress relief heat treatment on the sintered cobalt blank, and then performing mechanical machining and surface polishing to obtain a high-purity cobalt target finished product. As a preferable scheme of the preparation method for densification forming of the high-purity cobalt target material, in S1, the purity of the high-purity cobalt powder is more than or equal to 99.999%, the average particle size is 10-30 mu m, and the surface in-situ reconstruction pretreatment specifically comprises: firstly, cobalt powder is added in Preserving heat and reducing for 1-3 hours at the temperature of 350-450 ℃ in the mixed atmosphere; then, on the basis of keeping the reducing atmosphere, a trace of precursor