Method for obtaining ultra-smooth surface by dispersing abrasive particles of polishing solution under assistance of ultrasonic vibration

Abstract

The invention discloses a method for obtaining an ultra-smooth surface by dispersing abrasive particles of a polishing solution under the assistance of ultrasonic vibration, and belongs to the technical field of machining. The method comprises the steps that S110, the abrasive particles in the polishing solution are dispersed through an ultrasonic generator; s120, the dispersed polishing solution is conveyed to the surface of the fused quartz workpiece; and S130, ultra-smooth machining of the fused quartz workpiece is conducted through the machining tool. According to the device and the method, a large number of cavitation bubbles are generated under the ultrasonic cavitation effect, transient high temperature and high pressure and micro jet flow can be generated locally during collapse, so that abrasive particles in the polishing solution are promoted to be dispersed, efficient abrasive particle depolymerization is achieved by optimizing process parameters of ultrasonic vibration, the average particle size of the abrasive particles is reduced by about 26.0%, and particle size distribution is remarkably narrowed.

Description

Technical Field

[0001] This invention belongs to the field of processing technology, specifically relating to a method for obtaining an ultra-smooth surface by dispersing abrasive particles in an ultrasonic vibration-assisted polishing slurry. Background Technology

[0002] In the field of modern cutting-edge technology, ultra-smooth surfaces have become the cornerstone determining the performance and reliability of core devices. From optical mirrors in extreme ultraviolet lithography (EUVL) systems that achieve nanoscale fabrication to gravitational wave detectors that probe ripples in spacetime, the continuous shrinking of device feature sizes and increasingly stringent performance requirements have placed extremely high demands on surface roughness at the sub-nanometer and even atomic levels. In processing methods involving polishing slurries, the dispersion state of abrasive particles, as the medium directly involved in material removal, is crucial. However, abrasive particles are prone to uncontrolled agglomeration, forming large aggregates. These aggregates are the main cause of random scratches, microscopic damage, and abnormally high local roughness on polished surfaces, severely restricting the realization of ultra-smooth surfaces and the yield of high-end devices.

[0003] Traditionally, methods such as mechanical stirring, circulating filtration, or adding chemical dispersants have been used to suppress abrasive agglomeration. However, these methods have significant limitations: mechanical shearing forces are insufficient to effectively break the strong forces between nanoparticles; and the introduction of chemical additives may contaminate the polishing slurry, disrupt the chemical-mechanical balance of CMP, and trigger side reactions.

[0004] In recent years, ultrasonic vibration technology has been introduced to improve dispersion effects. Existing ultrasonic-assisted methods mainly fall into two categories: one is applying ultrasonic vibration directly to the workpiece or polishing pad. While this can improve material removal rates, the vibration energy, after being transmitted through multiple stages, has a weak targeted effect on abrasive agglomeration in the polishing slurry, and is prone to surface quality deterioration due to improper parameters; the other is using ultrasonic atomization technology to uniformly spray the polishing slurry. While this can save on the amount of polishing slurry used, its action time is short, and its dispersion effect on abrasive agglomeration is limited and uneven. Furthermore, the ultrasonic cavitation effect itself has been attempted for direct material removal, but the extreme local conditions generated when cavitation bubbles collapse can create micron-sized pit defects on the workpiece surface, making it unsuitable for direct material surface processing. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted abrasive particle dispersion in polishing slurry. Using ultrasonic vibration to deagglomerate polishing abrasive particles can significantly reduce particle aggregation, increase the concentration of particle size distribution, and avoid damage caused by cavitation bubbles directly acting on the workpiece surface. This is an effective method for improving the efficiency of ultra-smooth polishing slurry processing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion includes the following steps:

[0008] S110 uses an ultrasonic generator to disperse the abrasive particles in the polishing fluid;

[0009] S120 delivers the dispersed polishing liquid to the surface of the fused silica workpiece;

[0010] S130 is used for ultra-smooth machining of fused silica workpieces using machining tools.

[0011] The beneficial effects of this invention are as follows:

[0012] This invention addresses the problem of surface defects such as scratches and pitting caused by abrasive particle agglomeration during three-body friction in polishing slurries. It utilizes the transient high temperature and pressure generated by the collapse of ultrasonic cavitation bubbles and the resulting microjets to break up the agglomeration of abrasive particles caused by van der Waals forces or partial chemical bonding. This promotes abrasive particle dispersion in the polishing slurry and improves the three-body friction process. The external load is then shared by the dispersed, uniformly sized abrasive particles, ensuring a more even distribution on the workpiece surface. This avoids the situation where large abrasive particle agglomerates bear the majority of the external load, causing scratches and pitting. By optimizing the ultrasonic vibration process parameters, the average abrasive particle size is significantly reduced by approximately 26.0%, and the particle size distribution is significantly narrowed. Using the ultrasonically treated polishing slurry for small tool machining reduced the surface roughness Rq of fused silica from approximately 0.821 nm to 0.145 nm, a reduction of 82.3%, and a 70.9% reduction compared to the un-ultrasonicized control group. This efficiently achieves nanoscale uniformity and low-damage ultra-smooth surface machining, improving the manufacturing efficiency of ultra-smooth surfaces. Among them, small tool processing refers to the process of using small polishing tools to perform fine processing on the surface of a workpiece, which is a specialized term. Attached Figure Description

[0013] Figure 1 This is a flowchart of a method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to the present invention;

[0014] Figure 2 A schematic diagram of a device for obtaining an ultra-smooth surface by dispersing abrasive particles in an ultrasonic vibration-assisted polishing slurry;

[0015] Figure 3 This is a schematic diagram of the dispersion of abrasive particles by ultrasonic cavitation; where (a) is the state of abrasive particle aggregation in the polishing fluid before ultrasonic vibration, (b) is the energy transfer process when ultrasonic vibration is just turned on, and (c) is the state of abrasive particle aggregation after ultrasonic vibration for 5 minutes.

[0016] Figure 4 The particle size distribution of the polishing fluid before and after ultrasonic vibration;

[0017] Figure 5 A schematic diagram of the material removal mechanism in small tool processing equipment;

[0018] Figure 6 The difference in the three-body friction process during small tool polishing before and after abrasive grain agglomeration and dispersion is shown; where (a) is the three-body friction state when abrasive grains are not dispersed, and (b) is the three-body friction state after abrasive grain agglomeration and dispersion.

[0019] Figure 7 The surface roughness was measured using a white light interferometer before and after abrasive particle agglomeration and dispersion.

[0020] Figure 8 The surface roughness was measured by atomic force microscopy before and after abrasive particle agglomeration and dispersion. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] like Figure 1 As shown, the present invention provides a method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion, comprising the following steps:

[0023] S110 uses an ultrasonic generator to disperse the abrasive particles in the polishing fluid;

[0024] S120 delivers the dispersed polishing liquid to the surface of the fused silica workpiece;

[0025] S130 is used for ultra-smooth machining of fused silica workpieces using machining tools.

[0026] Furthermore, in step S110, the polishing slurry is placed in an abrasive container. The polishing slurry used is a cerium oxide polishing slurry with a nominal particle size of ≤1.5μm and a pH of 8. The diameter of the abrasive container is ≤8mm and the abrasive depth is 10-12cm. The container diameter is controlled to avoid the impact of the shock wave generated by the ultrasound and the radial attenuation of the microjets on the abrasive particle agglomeration and dispersion effect.

[0027] The abrasive container is placed in a water-cooling tank, and the water temperature in the tank is controlled at 23-25℃ to prevent the heat generated during ultrasonic vibration from affecting the physical and chemical properties of the polishing slurry. In addition, it is ensured that the liquid level in the water-cooling tank is higher than the liquid level in the abrasive container to ensure uniform heat dissipation of the entire polishing slurry.

[0028] The combination of ultrasonic transducer and ultrasonic probe is inserted into the polishing fluid. Before being inserted into the polishing fluid, the ultrasonic probe needs to be cleaned by ultrasonic vibration in anhydrous ethanol for five minutes to avoid contaminating the polishing fluid. The probe tip is 1-2 cm away from the bottom of the abrasive container so that the circulation generated by the vibration can cover the abrasive container. The probe diameter is 6-8 mm, and the maximum output power of the ultrasonic vibration is adjusted.

[0029] Furthermore, the ultrasonic generator used produces a frequency of 20-25kHz, an output power of 260-430W, and operates at a duty cycle of 40%-60%. The ultrasonic vibration cavitation effect disperses the agglomeration of abrasive particles as follows: Figure 3 As shown, (a) is the agglomerated state of the polishing fluid before ultrasonic vibration, (b) is the energy transfer process when ultrasonic vibration is first turned on, and (c) is the state after the agglomerated particles are dispersed 5 minutes after ultrasonic vibration. Without ultrasonic vibration, the agglomerated particles agglomerate due to van der Waals forces and other effects. After ultrasonic vibration is turned on, when the amplitude of the negative half-cycle of the sound pressure exceeds the sum of the static pressure and tensile strength of the liquid at the probe end, microscopic cavities or cavitation bubbles are generated inside the liquid. These bubbles collapse rapidly within the positive half-cycle, releasing shock waves and microjets within the microsecond time and micrometer spatial scale, thus dispersing the agglomerated particles.

[0030] The particle size distribution of the polishing slurry before and after ultrasonic vibration is as follows: Figure 4 As shown, after 5 minutes of ultrasonic vibration with specified parameters, the peak particle size of the polishing slurry decreased from 893.8 nm to 420.2 nm, and the average particle size decreased from 791.1 nm to 419.6 nm, a reduction of 46.9%.

[0031] Furthermore, in step S120, a peristaltic pump is used to deliver the dispersed polishing liquid to the surface of the fused silica workpiece. The peristaltic pump is used in continuous delivery mode, and the delivery speed of the polishing liquid is 25-50 ml / min. The peristaltic pump needs to be turned on 5 minutes after the ultrasonic generator is turned on.

[0032] Furthermore, the diameter of the fused silica workpiece is 50mm, the polishing pad is a 10mm diameter asphalt disc, the polishing pressure is 5N, the eccentricity is 3mm, the revolution speed is 120r / min, and the rotation speed is 60r / min.

[0033] In step S130, the fused silica workpiece undergoes ultra-smooth machining using a robotic tool. The material removal mechanism of the tool polishing is as follows: Figure 5 As shown, material removal occurs in the region after the rough peaks of the polishing pad come into contact with and are compressed against the workpiece surface (e.g., Figure 5 (A circular area with a radius of R1, R2 or R3), and material removal is achieved through three-body friction of polishing pad-effective abrasive grains-workpiece.

[0034] The difference in the three-body friction process of small tool polishing before and after adding ultrasonic vibration is as follows: Figure 6 As shown, without ultrasonic vibration, the external load is mainly borne by the agglomerated large abrasive grains, leading to load concentration and easily causing defects such as scratches and pits on the workpiece surface. Figure 6 As shown in (a), the agglomerates of abrasive particles in the polishing slurry dispersed by ultrasonic vibration are dispersed, resulting in a more concentrated particle size distribution. Under the same external load, they are more evenly dispersed on the contact surface, as shown in (a). Figure 6 As shown in (b), it effectively avoids surface defects such as scratches and pits.

[0035] Based on the above, the overall processing device is as follows: Figure 2 As shown, the system includes an ultrasonic generator, an ultrasonic probe, a small tool polishing unit (i.e., the robotic tool mentioned above), a peristaltic pump, a water-cooling tank, an abrasive container, a polishing fluid, and a polishing pad. It also includes a transducer to convert the high-frequency electrical energy output from the ultrasonic generator into mechanical vibrations of the same frequency. This vibration is amplified by the probe and transmitted to the polishing fluid to induce cavitation. The entire process also involves process parameter control, referring to the control panel of the ultrasonic generator or an external control system, used to set and adjust the frequency, power, and duty cycle to ensure stable cavitation. A fixed fixture can also be used to hold the fused silica workpiece, ensuring its positional stability during processing and maintaining a defined relative motion relationship with the small tool polishing unit.

[0036] Furthermore, after processing, the fused silica workpiece was rinsed with deionized water, then ultrasonically cleaned in anhydrous ethanol, and finally dried on a clean bench. The surface roughness was measured using a white light interferometer and an atomic force microscope. Ultimately, a non-destructive ultra-smooth surface with a surface roughness better than Rq 0.15 nm was obtained.

[0037] The cleaning process involved rinsing with deionized water for 3 minutes, followed by ultrasonic cleaning in anhydrous ethanol for 5 minutes. Finally, the surface was dried on a clean bench at 25-40℃. After cleaning, a white light interferometer was used to measure the surface roughness of the polishing solution used for ultra-smooth machining with and without ultrasonic vibration. Figure 7 As shown, the measurement area is a circular region with a diameter of 420 μm. Before processing, the surface roughness of the two samples was basically the same. In the comparative experiment where ultrasonic vibration was the only variable, the processing time was 45 min. The surface roughness of the polishing slurry without ultrasonic vibration converged from Rq 2.254 nm to 0.424 nm, with a convergence rate of 81.2%. The surface roughness of the polishing slurry with ultrasonic vibration converged from Rq 2.395 nm to 0.247 nm, with a convergence rate of 89.7%. Compared with the result of the polishing slurry without ultrasonic vibration, the convergence rate was further reduced by 41.7%.

[0038] To further evaluate the impact of ultrasonic vibration on the morphology and roughness of polished surfaces at higher frequencies, specifically at the angstrom and sub-angstrom levels, atomic force microscopy was used to examine the surface roughness of polishing fluids applied with and without ultrasonic vibration during ultra-smooth machining. Figure 8 As shown, the measurement area was 10μm × 10μm. Before processing, the surface roughness of the two samples was basically the same. In the comparative experiment where ultrasonic vibration was the only variable, the processing time was 45 min. The surface roughness after processing with the polishing slurry without ultrasonic vibration converged from Rq 0.840nm to 0.498nm, with a convergence rate of 40.7%. However, the surface still had relatively obvious scratches and pits due to abrasive particle agglomeration. The surface roughness after processing with the polishing slurry with ultrasonic vibration converged from Rq 0.822nm to 0.145nm, with a convergence rate of 82.1%. Compared with the result after processing with the polishing slurry without ultrasonic vibration, the convergence was further reduced by 90.9%, and the surface was more uniform with no obvious scratches or other defects.

[0039] A comprehensive analysis of the particle size distribution of the polishing slurry and the test results of the surface roughness after processing shows that the addition of ultrasonic vibration can disperse abrasive agglomerates, significantly reduce the average particle size of the polishing slurry, and thus improve the three-body friction process in the polishing of small tools. This allows the external load to be applied evenly to the contact area, avoiding surface defects such as scratches and pits, and obtaining a higher quality ultra-smooth surface.

[0040] Although the invention has been described with respect to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of explaining or limiting the subject matter of the invention.

Claims

1. A method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion, characterized in that, Includes the following steps: S110 uses an ultrasonic generator to disperse the abrasive particles in the polishing fluid; S120 delivers the dispersed polishing liquid to the surface of the fused silica workpiece; S130 is used for ultra-smooth machining of fused silica workpieces using machining tools.

2. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 1, characterized in that, In step S110, the polishing slurry is placed in an abrasive container. The polishing slurry used is a cerium oxide polishing slurry with a nominal particle size of ≤1.5μm and a pH of 8. The diameter of the abrasive container is ≤8mm and the abrasive depth is 10-12cm.

3. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 2, characterized in that, The abrasive container is placed in a water-cooled pool, the water temperature of which is controlled at 23-25℃, and the liquid level in the water-cooled pool is higher than the liquid level in the abrasive container.

4. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 3, characterized in that, The ultrasonic transducer and ultrasonic probe of the ultrasonic generator are immersed in the polishing fluid. Before being immersed in the polishing fluid, the ultrasonic probe has been cleaned by ultrasonic vibration in anhydrous ethanol for five minutes. The end of the ultrasonic probe is 1-2 cm away from the bottom of the abrasive container. The diameter of the ultrasonic probe used is 6-8 mm.

5. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 1, characterized in that, The ultrasonic generator used produces a frequency of 20-25kHz, an output power of 260-430W, and operates at a duty cycle of 40%-60%.

6. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 1, characterized in that, In step S120, the dispersed polishing slurry is delivered to the surface of the fused silica workpiece using a peristaltic pump in continuous delivery mode. The delivery speed of the polishing slurry is 25-50 ml / min, and the peristaltic pump is turned on 5 minutes after the ultrasonic generator is turned on.

7. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 6, characterized in that, The diameter of the fused silica workpiece is 50mm. The polishing pad is a 10mm diameter asphalt disc. The polishing pressure is 5N, the eccentricity is 3mm, the revolution speed is 120r / min, and the rotation speed is 60r / min.

8. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 1, characterized in that, In step S130, the processing tool is a robot tool.

9. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 1, characterized in that, It also includes the following steps: After processing, the fused silica workpiece is rinsed with deionized water, then ultrasonically cleaned in anhydrous ethanol, and finally dried on a clean bench. The surface roughness is then measured using a white light interferometer and an atomic force microscope.

10. The method for obtaining an ultra-smooth surface by ultrasonic vibration-assisted polishing slurry abrasive particle dispersion according to claim 9, characterized in that, The cleaning process begins with rinsing with deionized water for 3 minutes, followed by ultrasonic cleaning in anhydrous ethanol for 5 minutes, and finally drying on a clean bench at 25-40℃.

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