Surface cleaning method for magnetic target material

Abstract

The invention relates to the field of semiconductor manufacturing, in particular to a surface cleaning method for a magnetic target material. The method comprises the following steps: under the action of an alternating magnetic field and an ultrasonic cavitation field, spraying a magnetic target material by adopting a cleaning solution containing a surfactant; and under the action of a gradient magnetic field, carrying out directional adsorption on the magnetic particles desorbed from the surface of the magnetic target material. According to the cleaning method for strongly-adsorbed magnetic particles on the surface of the magnetic target material, particle pollution on the surface of the magnetic target material can be effectively reduced; the problems that a traditional cleaning technology cannot thoroughly remove 5-10 microns magnetic particles and the surface is prone to being damaged are solved, the particle removal rate is larger than or equal to 95%, the surface roughness fluctuation is smaller than or equal to + / -0.02 microns, the sputtering particle pollution incidence rate is reduced by 85% or above, and the method is suitable for the high-end manufacturing field of semiconductors, magnetic memories and the like.

Description

Technical Field

[0001] This invention relates to the field of magnetron sputtering target surface treatment technology, and in particular to a method for cleaning the surface of magnetic targets. Background Technology

[0002] Magnetic sputtering targets are widely used in thin film deposition processes, especially cobalt targets, which are of great value in magnetic storage, semiconductors, and optical thin films. However, particulate contamination (PA) on the surface of magnetic sputtering targets has always been a critical issue affecting film quality. During the processing of sputtering targets, especially after surface treatments such as sanding and grinding, a large number of tiny particles are generated on the surface due to the inherent properties of magnetic materials. These particles are firmly adsorbed onto the target surface through magnetic dipole interactions and van der Waals forces, forming a contamination source that is difficult to remove. These particles adsorbed on the target surface will participate in sputtering during the sputtering deposition process, causing arc discharge and further generating foreign matter that splashes onto the substrate or the film, reducing the quality of the deposition.

[0003] Currently, the surface cleaning of magnetic targets mainly employs a combination of physical and chemical methods. CN112267099A discloses a surface cleaning method for targets, which includes a multi-stage cleaning process such as water washing, ultrasonic vibration cleaning, jet cleaning, and purging drying, effectively removing contaminants, oil, and dust from the target surface. CN116809521A proposes a cleaning process for thin substrates of strongly vortex magnetic ferrite, achieving efficient and non-destructive cleaning of magnetic substrates by controlling the flow of the scouring solution in different directions and combining ultrasonic cleaning and high-pressure steam cleaning. In the field of magnetron sputtering, CN107267916A introduces a method for depositing WN hard films by DC magnetron sputtering, which uses low-energy, high-density plasma to clean and etch the substrate, effectively removing oxide scale and loose layers from the substrate surface, and optimizing the magnetic field control and coating process of the target, improving the uniformity and overall performance of the film. CN113493895A discloses a method for preparing a γ′-Fe4N magnetic porous film, in which Fe target material is used for magnetron sputtering deposition, and a magnetic film layer with a specific structure is formed by subsequent magnetic annealing.

[0004] However, existing technologies still face the following problems when cleaning magnetic targets, especially cobalt targets: First, traditional cleaning methods have limited effectiveness in removing magnetically adsorbed particles. Because magnetic particles on the surface of cobalt targets are firmly adsorbed through magnetic dipole interactions and van der Waals forces, conventional ultrasonic cleaning and chemical solvent cleaning methods are insufficient to completely desorb these particles. Even high-pressure water rinsing cannot overcome the magnetic adsorption force, resulting in unsatisfactory cleaning results. Second, existing cleaning processes may damage the target surface or alter its magnetic properties. Overly aggressive physical cleaning methods can lead to a deterioration in the target surface roughness (Ra fluctuation > ±0.05 μm), while some chemical cleaning agents may react with the target surface, altering its magnetic properties. These changes directly affect the quality and performance of the film during subsequent sputtering. Third, there is a high risk of secondary contamination from desorbed particles. Even if some particles are successfully desorbed during cleaning, they are easily suspended in the cleaning solution and re-adsorbed onto the target surface after cleaning. Existing technologies lack effective particle collection and directional removal mechanisms, failing to completely solve the problem of secondary contamination. Finally, existing technologies fail to fully utilize the modulating effect of magnetic fields on magnetic particles. While some studies have explored the application of magnetic fields in material preparation, the integration of magnetic field technology with cleaning processes has not yet been effectively achieved. Therefore, there is an urgent need to develop an efficient cleaning method for magnetic targets, particularly cobalt targets, to remove magnetically adsorbed particles from their surfaces. This method should fully utilize magnetic field technology to thoroughly remove magnetically adsorbed particles without damaging the target surface, effectively preventing secondary contamination and thus improving the quality and performance of sputtered films. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a surface cleaning method for magnetic targets. The cleaning method for magnetic targets with strong adsorption of magnetic particles, combined with magnetic field control and ultrasonic cavitation technology, effectively removes particulate contaminants from the surface of the magnetic target. This solves the problems of incomplete removal of 5-10μm magnetic particles and easy surface damage associated with traditional cleaning techniques. The particle removal rate is ≥95%, surface roughness fluctuation is ≤±0.02μm, and the sputtering particle contamination rate is reduced by more than 85%. This method is suitable for high-end manufacturing fields such as semiconductors and magnetic storage devices.

[0006] In a first aspect, this invention provides a method for cleaning the surface of a magnetic target, comprising: spraying a cleaning solution containing a surfactant onto the magnetic target under the action of an alternating magnetic field and an ultrasonic cavitation field; and directionally adsorbing the magnetic particles detached from the surface of the magnetic target under the action of a gradient magnetic field. This invention utilizes the synergistic effect of alternating magnetic field-induced particle vibration desorption and ultrasonic cavitation hydraulic stripping to clean the target surface. By spraying a cleaning solution containing a surfactant under the synergistic effect of alternating magnetic field and ultrasonic cavitation, the magnetic particles adsorbed on the target surface are stripped, and the detached particles are directionally adsorbed onto a magnetic filter screen by a gradient magnetic field. This method effectively removes particulate contaminants from the surface of the magnetic target, solving the problems of incomplete removal of 5-10μm magnetic particles and easy surface damage caused by traditional cleaning techniques. The particle removal rate is ≥95%, the surface roughness fluctuation is ≤±0.02μm, and the sputtering particle contamination rate is reduced by more than 85%.

[0007] Preferably, the surface cleaning method for the magnetic target material includes the following steps: 1) Target fixing and cleaning: The magnetic target is fixed at an angle, and deionized water is sprayed onto the surface of the magnetic target; the magnetic target includes a magnetic cobalt target.

[0008] 2) DC magnetic field polarization: The magnetic target material processed in step 1) is subjected to DC magnetic field polarization.

[0009] 3) Synergistic effect of alternating magnetic field vibration and ultrasonic cavitation: Under the action of alternating magnetic field and ultrasonic cavitation field, the magnetic target material after step 2) is sprayed with a cleaning solution containing surfactant.

[0010] 4) Gradient magnetic field treatment: The magnetic target and cleaning solution after step 3) are passed through a gradient magnetic field to drive the detached magnetic particles to migrate in a directional manner and capture them.

[0011] In this invention, the target material to be cleaned is fixed on a support and tilted at a certain angle to optimize the scouring effect of the liquid flow. A DC magnetic field is applied to the magnetic target material, causing the magnetic moments of the magnetic particles on the target surface to align in a direction along the magnetic field, reducing the random coupling between the particles and the magnetic domains on the target surface, and lowering the subsequent desorption resistance. In ferromagnetic materials, there is coupling between magnetic moments, and cobalt targets are ferromagnetic materials. When an external DC magnetic field is applied, the originally disordered magnetic moments of the magnetic particles on the target surface will overcome interference such as thermal fluctuations under the action of the magnetic field, gradually turning and aligning with the direction of the magnetic field. This directional alignment transforms the coupling between the particle magnetic moments and the magnetic domains on the target surface from a random state to an ordered state, weakening the magnetic adsorption strength between the particles and the target material, and creating more favorable conditions for subsequent particle desorption under the action of alternating magnetic field and ultrasonic cavitation.

[0012] Preferably, in step 1), the tilt angle of the magnetic target is 15°-30°; for example, 16°, 28°, 20°, 22°, 25°, 28°, 30°, etc.

[0013] Preferably, the flow rate of the deionized water is 5-10 L / min. For example, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, etc.

[0014] In this invention, the surface cleaning method is particularly suitable for solving the problem of micron-sized particle contamination on the surface of magnetic cobalt targets after grinding and polishing, which is difficult to remove due to magnetic dipole interaction. The target tilt angle is set to 15°-30°, and gravity-assisted directional flow of the cleaning fluid is used to better prevent desorbed particles from remaining in low-lying areas of the target surface during the cleaning process. At the same time, deionized water is sprayed onto the target surface through pre-spraying to better remove loose particles on the surface. The flow rate of deionized water is set to 5-10 L / min, and the shear force of the liquid flow removes loose particles that have not formed strong magnetic adsorption, laying a better foundation for subsequent deep cleaning.

[0015] Preferably, in step 2), the intensity of the DC magnetic field is 0.3-0.8T, for example, 0.3T, 0.4T, 0.6T, 0.8T, etc., and the duration is 30-60s, for example, 30s, 40s, 50s, 60s, etc. Preferably, the direction of the DC magnetic field is perpendicular to the surface of the magnetic target. By optimizing the DC magnetic field parameters, the magnetic particles on the target surface and the magnetic domain structure of the target itself are arranged in an orderly manner. If the magnetic field intensity is too low (<0.3T), it cannot drive the magnetic moment of the particles to orient, and if it is too high (>0.8T), it is easy to cause fluctuations in the magnetic properties of the target. The duration of 30-60s can ensure that the magnetic moments of the particles are completely aligned, which is more conducive to subsequent cleaning processes.

[0016] Preferably, the frequency of the alternating magnetic field is 100-200Hz, for example, 100Hz, 150Hz, 200Hz, etc., and the amplitude is 0.1-0.3T, for example, 0.1T, 0.2T, 0.3T, etc.

[0017] Preferably, the frequency of the ultrasonic cavitation field is 20-40 kHz, such as 20 kHz, 30 kHz, 40 kHz, etc., and the power density is 0.5-1 W / cm². 2 For example, 0.5 W / cm 2 0.8 W / cm 2 1 W / cm 2 .

[0018] Preferably, the surfactant is sodium dodecyl sulfate and / or polyethylene glycol.

[0019] Preferably, the surface tension of the cleaning fluid is ≤30mN / m.

[0020] Preferably, the cleaning solution is deionized water containing 0.1%-0.5% surfactant.

[0021] In the synergistic effect of alternating magnetic field vibration and ultrasonic cavitation in this invention, switching to an alternating magnetic field induces periodic magnetostrictive vibrations in the magnetic particles. Because the particles and the target material are tightly adsorbed through magnetic dipole interactions, this vibration continuously impacts and disrupts the magnetic dipole connection between the particles and the target surface, reducing the adsorption stability of the particles. Simultaneously, ultrasonic cavitation generates numerous microbubbles in the cleaning fluid. These bubbles, during rapid expansion and collapse, form high-speed microjets and strong shock waves that directly act on the particles, detaching them from the target surface. The addition of surfactants significantly reduces the surface tension of the cleaning fluid to ≤30 mN / m. The steric hindrance effect inhibits secondary agglomeration of the desorbed particles. Surfactant molecules form a protective film around the desorbed particles through steric hindrance, preventing re-agglomeration due to van der Waals forces and other forces, and also preventing them from re-adsorbing onto the target surface.

[0022] Preferably, in the setting of the gradient magnetic field, the magnetic field strength gradually changes from 0.1T to 0.5T, with a change rate of 0.02-0.05T / mm.

[0023] Further preferably, after the gradient magnetic field treatment, the particle capture efficiency is ≥99% and the secondary adsorption rate is ≤2%.

[0024] In this invention, when the cleaning fluid carrying desorbed magnetic particles flows through a spatial gradient magnetic field, the magnetic particles are subjected to a non-uniform magnetic force due to the gradient change in magnetic field strength. According to magnetic principles, magnetic particles tend to move towards areas with higher magnetic field strength. In particular, by optimizing the magnetic field strength and rate of change in the gradient magnetic field setting, this specific magnetic field gradient can generate sufficient magnetic force to drive the particles to overcome the fluid resistance in the cleaning fluid, allowing them to migrate more effectively towards areas with higher magnetic field strength. Ultimately, they are captured by capture devices such as magnetic filters placed in these areas, thus more effectively avoiding the risk of particles suspending in the cleaning fluid and re-adsorbing onto the target surface.

[0025] Further preferably, the surface cleaning method further includes secondary cleaning: purging the surface of the magnetic target material after gradient magnetic field treatment with an inert gas, wherein the dew point of the inert gas is ≤-40℃; preferably, the inert gas is high-purity nitrogen gas with a pressure of 0.1-0.3 MPa.

[0026] Further optimization shows that the residual moisture content on the surface of the magnetic target after purging is ≤0.1 μg / cm³. 2 .

[0027] In this invention, purging the target surface with high-purity nitrogen can quickly replace residual moisture, preventing the deposition of residual ions or particles after moisture evaporation, ensuring surface cleanliness after cleaning, and thus reducing film defects caused by residual particles during subsequent magnetron sputtering. In particular, purging the target surface with a pressure of 0.1-0.3 MPa, with a dew point ≤-40℃, can rapidly displace residual moisture. During natural evaporation, moisture may dissolve some impurity ions or carry tiny particles; these impurities and particles remain on the target surface after the moisture evaporates. Purging with high-purity nitrogen removes these impurities before evaporation, ensuring the cleanliness of the target surface. In subsequent magnetron sputtering, a clean target surface effectively reduces film defects caused by residual particles, improving film quality and performance.

[0028] Further preferably, the surface cleaning of the magnetic target material is carried out at a surface charge density ≤ 5 μC / m 2 It is carried out in an antistatic environment.

[0029] The beneficial effects of this invention are at least as follows: 1) Significant reduction in particulate pollution: Through the combined effects of alternating magnetic field and ultrasonic cavitation, the removal rate of 5-10μm particles reaches over 95%, and the particle reduction can reach 83.8-91 particles / cm. 2 Residual amount ≤1.2 particles / cm 2 Traditional ultrasonic cleaning methods achieve a particle removal rate of only 78.0%, with a particle reduction of only 66.3 particles / cm². 2 The residual amount reached 18.7 cells / cm³. 2 .

[0030] 2) Non-destructive to the target surface: After cleaning, the surface roughness Ra of the target surface fluctuated by only +2.5%, while the surface roughness Ra fluctuated by +39.2% after cleaning by the traditional method, proving that the method does not cause significant damage or corrosion to the target surface.

[0031] 3) Significantly reduced particle contamination rate during sputtering: In sputtering tests, the particle (PA) contamination rate (i.e., the frequency of particle defects on the film surface caused by residual particles on the target surface during magnetron sputtering, measured in times / h) was reduced by 26.6-29.9 times / h, a reduction of 83%-86% compared to before cleaning; while the PA rate reduction of the traditional method was only 12.8 times / h, a reduction of only 40% compared to before cleaning, effectively improving film quality and stability.

[0032] 4) Environmentally friendly and efficient: The gradient magnetic field collection system enables the recycling of cleaning fluid (recovery rate ≥95%) and the secondary adsorption rate of particles ≤2%, which meets the requirements of green manufacturing.

[0033] 5) Simplified process: It reduces multiple steps in traditional cleaning methods, enabling the cleaning process to be completed in a shorter time and improving production efficiency. Attached Figure Description

[0034] 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.

[0035] Figure 1 This is a schematic diagram of the cleaning method provided in an embodiment of the present invention. Detailed Implementation

[0036] 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. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0038] Unless otherwise specified, the techniques or conditions described in the literature of this invention shall apply, or the product instructions shall be followed. Devices, instruments, reagents, etc., whose manufacturers are not specified, are all conventional products that can be purchased from legitimate channels. All experimental reagents and raw materials involved are commercially available, and all reagents are analytical grade products.

[0039] Example 1 This embodiment provides a surface cleaning method for reducing magnetic target material particles, such as... Figure 1 This includes the following steps: a) Target fixing and cleaning: A cobalt target with a diameter of 200mm × 3mm (purity 99.999%) was selected. After sanding, the density of cobalt-based particles attached to the surface was 85 particles / cm³. 2The target material, with 5-10μm particles comprising 60%, was fixed at a 20° angle to an insulating PTFE support. Deionized water was pre-sprayed onto the target surface at a flow rate of 8L / min for 30 seconds to initially remove loosely attached particles. Testing showed that the surface particle density decreased to 42 particles / cm³ after pre-cleaning. 2 .

[0040] b) DC magnetic field polarization: A uniform magnetic field of 0.5T is generated by a DC excitation coil, with the magnetic field direction strictly perpendicular to the target surface, and the duration is 45s. This magnetic field strength and duration are sufficient to allow the magnetic particles on the target surface and the magnetic domain structure of the target itself to form an orderly arrangement, preparing for the subsequent cleaning steps.

[0041] c) Synergistic effect of alternating magnetic field and ultrasonic cavitation: The magnetic field is switched to an alternating magnetic field with a frequency of 100Hz and an amplitude of 0.2T, while the ultrasonic cavitation device is activated at a frequency of 30kHz and a power density of 0.8W / cm². 2 Simultaneously, deionized water containing 0.3% sodium dodecyl sulfate (SDS) surfactant was sprayed onto the target surface. The surface tension of the cleaning solution was 28 mN / m, and the process lasted for 2 minutes. The alternating magnetic field caused the magnetic particles to vibrate, and the microjets generated by ultrasonic cavitation worked synergistically with the surfactant to effectively peel off and disperse the magnetic particles on the target surface. The surfactant molecules encapsulated the desorbed particles through steric hindrance, inhibiting their initial re-adsorption onto the target surface.

[0042] d) Gradient magnetic field collection: The cleaning fluid carrying desorbed particles flows into the bottom collection tank, where a spatial gradient magnetic field is set up. The magnetic field strength linearly changes from 0.1T to 0.5T, with a change rate of 0.03T / mm. The gradient magnetic field force drives the particles to migrate directionally to the magnetic filter at the end of the collection tank, achieving a particle capture efficiency of 99.5%. Simultaneously, a simulated test piece with the same material and surface condition as the target material is placed in the collection tank to monitor the secondary adsorption of desorbed particles.

[0043] e) Secondary cleaning: The target surface was purged with high-purity nitrogen gas (dew point) at -45℃ and 0.2MPa for 60 seconds. The residual moisture content on the target surface was measured to be 0.08 μg / cm³. 2 .

[0044] After treatment using the above method, the surface of the cobalt target was tested: the residual amount of 5-10μm particles was 1.2 particles / cm. 2The particle removal rate reached 98.6%; the surface roughness Ra was 0.081 μm, with a fluctuation of only +2.5% compared to before cleaning (Ra=0.079 μm); during magnetron sputtering testing, the particle contamination (PA) rate on the film surface decreased from the initial 32 times / h to 5.4 times / h, a reduction of 26.6 times / h, which is 83% lower than before cleaning. Total desorbed particles = Initial particle count - Residual particle count = 85 - 1.2 = 83.8 particles / cm² 2 The number of newly adsorbed particles on the simulated sample and target surface was 1.5 particles / cm². 2 Secondary adsorption rate = (1.5 ÷ 83.8) × 100% ≈ 1.8% (≤ 2%). The cleaning solution recovery rate reaches 96% and can be directly recycled.

[0045] Example 2 This embodiment provides a surface cleaning method for reducing magnetic target particles, including the following steps: a) Target fixing and cleaning: A cobalt target material with a diameter of 300mm × 3mm (purity 99.999%) was selected. After sanding treatment, the density of cobalt-based particles attached to the surface was 92 particles / cm³. 2 The target material contained 70% particles of 5-10μm size. The target was fixed at a 25° angle to an insulating support made of polytetrafluoroethylene (PTFE). The target surface was pre-sprayed with deionized water at a flow rate of 10L / min for 40 seconds to initially remove loosely attached particles. Testing showed that the surface particle density decreased to 45 particles / cm³ after pre-cleaning. 2 .

[0046] b) DC magnetic field polarization: A uniform magnetic field of 0.7T is generated by a DC excitation coil, with the magnetic field direction strictly perpendicular to the target surface, and the duration is 50s. This magnetic field strength and duration are sufficient to allow the magnetic particles on the target surface and the magnetic domain structure of the target itself to form an orderly arrangement, preparing for subsequent cleaning steps.

[0047] c) Synergistic effect of alternating magnetic field and ultrasonic cavitation: The magnetic field is switched to an alternating magnetic field with a frequency of 150 Hz and an amplitude of 0.25 T, while the ultrasonic cavitation device is activated at a frequency of 35 kHz and a power density of 1.0 W / cm². 2 Simultaneously, deionized water containing 0.5% polyethylene glycol (PEG) surfactant was sprayed onto the target surface. The surface tension of the cleaning solution was 26 mN / m, and the process lasted for 2.5 minutes. The alternating magnetic field caused the magnetic particles to vibrate, and the microjets generated by ultrasonic cavitation, in synergy with the surfactant, effectively peeled off and dispersed the magnetic particles on the target surface. The steric hindrance layer formed by PEG molecules prevented the agglomeration and secondary adsorption of the desorbed particles.

[0048] d) Gradient magnetic field collection: The cleaning fluid carries the desorbed particles into the bottom collection tank. A spatial gradient magnetic field is set in the collection tank, with the magnetic field strength linearly changing from 0.1T to 0.5T, with a change rate of 0.04T / mm. The particles are driven to migrate directionally to the magnetic filter at the end of the collection tank by the gradient magnetic field force, and the particle capture efficiency reaches 99.3%. Simultaneously, a simulated test piece with the same material and surface condition as the target material is set in the collection tank to monitor the secondary adsorption of desorbed particles.

[0049] e) Secondary cleaning: The target surface was purged with high-purity nitrogen gas at a dew point of -50℃ and a pressure of 0.25MPa for 90 seconds. The residual moisture content on the target surface was measured to be 0.07μg / cm³. 2 .

[0050] After treatment using the above method, the surface of the cobalt target was tested: the residual amount of 5-10μm particles was 1.0 particles / cm. 2 The particle removal rate reached 98.9%; the surface roughness Ra was 0.083 μm, with a fluctuation of only +2.5% compared to before cleaning (Ra=0.081 μm); during magnetron sputtering testing, the particle contamination (PA) incidence rate on the film surface decreased from the initial 35 times / h to 5.1 times / h, a reduction of 29.9 times / h, which is 85% lower than before cleaning. The total number of desorbed particles = 92 - 1.0 = 91 particles / cm². 2 The number of secondary adsorbed particles was 1.7 per cm³. 2 Secondary adsorption rate = (1.7 ÷ 91) × 100% ≈ 1.9% (≤ 2%); Cleaning solution recovery rate reaches 97%, which can be directly recycled.

[0051] Example 3 This embodiment provides a surface cleaning method for reducing magnetic target particles, including the following steps: a) Target fixation and cleaning: A cobalt target with a diameter of 200mm × 3mm (purity 99.999%) was selected. After sanding, the density of cobalt-based particles attached to the surface was 80 particles / cm³. 2 The target material contained 65% particles of 5-10μm. The target was fixed at a 15° angle to an insulating support made of polytetrafluoroethylene. The target surface was pre-sprayed with deionized water at a flow rate of 6L / min for 35 seconds. After pre-cleaning, the surface particle density decreased to 38 particles / cm³. 2 .

[0052] b) DC magnetic field polarization: A uniform magnetic field of 0.3T is generated by a DC excitation coil, with the magnetic field direction perpendicular to the target surface and the duration being 30s.

[0053] c) Synergistic effect of alternating magnetic field and ultrasonic cavitation: The magnetic field is switched to an alternating magnetic field with a frequency of 200 Hz and an amplitude of 0.3 T, while the ultrasonic cavitation device is activated at a frequency of 40 kHz and a power density of 0.7 W / cm². 2 Simultaneously, deionized water containing 0.2% SDS + 0.2% PEG was sprayed onto the target surface. The surface tension of the cleaning solution was 27 mN / m, and the action was continued for 1.5 min.

[0054] d) Gradient magnetic field collection: The washing liquid carries the desorbed particles into the bottom collection tank. A spatial gradient magnetic field is set in the collection tank. The magnetic field strength gradually changes from 0.1T to 0.5T, with a change rate of 0.02T / mm. The particle capture efficiency reaches 99.1%.

[0055] e) Secondary cleaning: The target surface was purged with high-purity nitrogen gas at a dew point of -42℃ and a pressure of 0.15MPa for 70 seconds, resulting in a residual moisture content of 0.09μg / cm³. 2 .

[0056] After treatment using the above method, the surface of the cobalt target was tested: the residual amount of 5-10μm particles was 1.1 particles / cm. 2 The particle removal rate was approximately 98.6% (80-1.1) / 80×100%; the surface roughness Ra was 0.080μm, fluctuating by +2.6% compared to before cleaning (Ra=0.078μm); in the magnetron sputtering test, the PA occurrence rate decreased from an initial 30 times / h to 5.1 times / h, a reduction of 24.9 times / h, which is 83% lower than before cleaning; the total number of desorbed particles was 80-1.1=78.9 particles / cm². 2 The number of secondary adsorbed particles was 1.4 per cm³. 2 Secondary adsorption rate ≈ 1.8%; cleaning solution recovery rate reaches 95%.

[0057] Example 4 This embodiment provides a surface cleaning method for reducing magnetic target particles, including the following steps: a) Target fixing and cleaning: A cobalt target with a diameter of 250mm × 3mm (purity 99.999%) was selected. After sanding, the density of cobalt-based particles attached to the surface was 88 particles / cm³. 2 The target material had 58% particles in the 5-10μm range. The target was fixed at a 30° angle to an insulating support made of polytetrafluoroethylene. The target surface was pre-sprayed with deionized water at a flow rate of 10L / min for 45 seconds. After pre-cleaning, the surface particle density decreased to 41 particles / cm³. 2 .

[0058] b) DC magnetic field polarization: A uniform magnetic field of 0.8T is generated by a DC excitation coil, with the magnetic field direction perpendicular to the target surface and the duration being 60s.

[0059] c) Synergistic effect of alternating magnetic field and ultrasonic cavitation: The magnetic field is switched to an alternating magnetic field with a frequency of 100Hz and an amplitude of 0.1T, while the ultrasonic cavitation device is activated at a frequency of 30kHz and a power density of 1.0W / cm². 2 Simultaneously, deionized water containing 0.1% PEG was sprayed onto the target surface. The surface tension of the cleaning solution was 29 mN / m, and the action lasted for 3 minutes.

[0060] d) Gradient magnetic field collection: The washing liquid carries the desorbed particles into the bottom collection tank. A spatial gradient magnetic field is set in the collection tank. The magnetic field strength gradually changes from 0.1T to 0.5T, with a change rate of 0.05T / mm. The particle capture efficiency reaches 99.6%.

[0061] e) Secondary cleaning: The target surface was purged with high-purity nitrogen gas at a dew point of -48℃ and a pressure of 0.3MPa for 80 seconds, resulting in a residual moisture content of 0.06μg / cm³. 2 .

[0062] After treatment using the above method, the surface of the cobalt target was tested: the residual amount of 5-10μm particles was 1.2 particles / cm. 2 The particle removal rate was approximately 98.6% (88-1.2) / 88×100%; the surface roughness Ra was 0.082μm, fluctuating by +2.5% compared to before cleaning (Ra=0.080μm); in the magnetron sputtering test, the PA occurrence rate decreased from the initial 33 times / h to 5.6 times / h, a reduction of 27.4 times / h, which is 83% lower than before cleaning; the total number of desorbed particles was 88-1.2=86.8 particles / cm². 2 The number of secondary adsorbed particles was 1.6 per cm³. 2 Secondary adsorption rate ≈ 1.8%; cleaning solution recovery rate reaches 97%.

[0063] Comparative Example 1 This comparative example uses a traditional ultrasonic cleaning method, without magnetic field control or surfactant assistance, to treat a magnetic cobalt target material, including the following steps: a) Target fixing and cleaning: A cobalt target with the same dimensions as in Example 1 (Φ200mm×3mm, purity 99.999%) was selected. After sanding, the density of cobalt-based particles attached to the surface was 85 particles / cm³. 2The target material had 60% particles in the 5-10μm range. The target was horizontally fixed on an insulating support made of polytetrafluoroethylene (PTFE). The target surface was pre-sprayed with deionized water at a flow rate of 8 L / min for 30 seconds. After pre-cleaning, the surface particle density decreased to 43 particles / cm³. 2 .

[0064] b) Ultrasonic cleaning: The target material is placed in an ultrasonic cleaning tank, using deionized water without surfactants as the cleaning solution. The ultrasonic frequency is 30kHz, and the power density is 0.8W / cm³. 2 The washing process was continued for 5 minutes. Simultaneously, a simulated sample with the same material and surface condition as the target was placed in the collection tank to monitor the secondary adsorption of desorbed particles.

[0065] c) Cleaning and drying: After removing the target material, rinse it with deionized water for 2 minutes, and then dry it by purging with high-purity nitrogen gas with the same parameters as in Example 1.

[0066] Testing revealed that the residual 5-10μm particles on the surface of the treated target material was 18.7 particles / cm². 2 The particle removal rate was only 78.0%; the surface roughness Ra increased to 0.11 μm, a fluctuation of +39.2% compared to before cleaning (Ra=0.079 μm); in the magnetron sputtering test, the occurrence rate of particulate contamination (PA) on the film surface decreased from the initial 32 times / h to 19.2 times / h, a reduction of only 12.8 times / h, and only 40% lower than before cleaning. Secondary adsorption rate detection: total number of desorbed particles = 85 - 18.7 = 66.3 particles / cm². 2 The number of secondary adsorbed particles was 9.945 / cm³. 2 The secondary adsorption rate reaches 15%, making it impossible to directly recycle the cleaning solution. Furthermore, due to the lack of a particle-directed collection mechanism, the secondary adsorption rate of suspended particles in the cleaning solution reaches 15%, preventing direct recycling of the cleaning solution.

[0067] All embodiments and comparative examples of this invention have a surface charge density ≤3μC / m 2 The process is carried out in an antistatic environment. A comparison between the embodiments of the present invention and the comparative examples shows that the method of the present invention exhibits significant advantages in particle removal rate, surface roughness control, reduction of particulate contamination (PA) incidence on the film surface, and recycling of the cleaning solution, fully verifying its effectiveness in efficiently removing magnetic particles, protecting target material performance, and promoting green manufacturing.

[0068] 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 of surface cleaning of a magnetic target material, characterized by, The application relates to a method for cleaning a magnetic target material, comprising the following steps: Under the action of an alternating magnetic field and an ultrasonic cavitation field, a cleaning liquid containing a surfactant is sprayed on the magnetic target material; under the action of a gradient magnetic field, the magnetic particles desorbed from the surface of the magnetic target material are subjected to directional adsorption.

2. The surface cleaning method of a magnetic target material according to claim 1, characterized by, The method comprises the following steps: 1) Target material fixing and cleaning: the magnetic target material is fixed in an inclined manner, and deionized water is sprayed on the surface of the magnetic target material; the magnetic target material comprises a magnetic cobalt target material; 2) Direct-current magnetic field polarization: the magnetic target material treated in step 1) is subjected to direct-current magnetic field polarization; 3) Alternating magnetic field vibration and ultrasonic cavitation synergistic effect: under the action of an alternating magnetic field and an ultrasonic cavitation field, a cleaning liquid containing a surfactant is sprayed on the magnetic target material treated in step 2); 4) Gradient magnetic field treatment: the magnetic target material and the cleaning liquid treated in step 3) are subjected to gradient magnetic field treatment, so that the desorbed magnetic particles are driven to migrate in a directional manner and are captured.

3. The surface cleaning method of claim 2, wherein, In step 1), the inclination angle of the magnetic target material is 15-30 degrees; and / or the flow rate of the deionized water is 5-10 L / min.

4. The surface cleaning method of claim 2 or 3, wherein, In step 2), the strength of the direct-current magnetic field is 0.3-0.8 T, and the duration is 30-60 seconds; preferably, the magnetic field direction of the direct-current magnetic field is perpendicular to the surface of the magnetic target material.

5. The surface cleaning method of any of claims 1-4, wherein, The frequency of the alternating magnetic field is 100-200 Hz, and the amplitude is 0.1-0.3 T.

6. The surface cleaning method of any one of claims 1-5, wherein, The frequency of the ultrasonic cavitation field is 20-40 KHz, and the power density is 0.5-1 W / cm 2 .

7. The surface cleaning method of any of claims 1-6, wherein, The surfactant is sodium dodecyl sulfate and / or polyethylene glycol; and / or the surface tension of the cleaning liquid is less than or equal to 30 mN / m; and / or the cleaning liquid is deionized water containing 0.1-0.5% surfactant.

8. The surface cleaning method of any one of claims 1-7, wherein, In the setting of the gradient magnetic field, the magnetic field strength gradually changes from 0.1 T to 0.5 T, and the change rate is 0.02-0.05 T / mm.

9. The surface cleaning method of any one of claims 1-8, wherein, The method further comprises secondary cleaning: the surface of the magnetic target material treated by the gradient magnetic field is subjected to inert gas blowing, the dew point of the inert gas is less than or equal to -40 DEG C; the inert gas is preferably high-purity nitrogen, and the pressure is 0.1-0.3 MPa.

10. The surface cleaning method of any of claims 1-9, wherein, The surface cleaning of the magnetic target material is carried out in an antistatic environment with a surface charge density ≤ 5 μC / m 2 .

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