An ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing method and apparatus

Abstract

This invention belongs to the field of ultra-precision polishing technology and discloses an ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing method, comprising: mixing a basic polishing abrasive, a piezoelectric material, and a photocatalyst, and performing calcination and grinding treatment to obtain a modified abrasive; preparing a polishing slurry containing both piezoelectric and photocatalytic carriers; and completing the polishing process through a chain of "mechanical stress → piezoelectric electric field → efficient carrier separation → more active species participating in the reaction". This invention also discloses a matching polishing apparatus. Compared with existing technologies, this invention not only more effectively improves material removal rate and reduces polishing time, but also helps to further improve surface quality and reduce subsurface damage. Furthermore, it allows the use of a more environmentally friendly polishing slurry, reducing waste liquid treatment costs and protecting the environment. Therefore, it is particularly suitable for polishing applications requiring low-damage, ultra-smooth surfaces for various high-hardness materials.

Description

Technical Field

[0001] This invention belongs to the field of ultra-precision polishing technology, and more specifically, relates to an ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing method and apparatus. Background Technology

[0002] Chemical mechanical polishing (CMP) is a machining technique that relies on the synergistic effect of chemicals and machinery to remove material from the surface of a workpiece. It is currently the only ultra-precision machining method capable of achieving localized or even global planarization. However, CMP alone has low material removal efficiency when polishing superhard materials, often requiring a long processing time to achieve the desired material removal effect. Furthermore, traditional polishing slurries often use strong acids, strong alkalis, and strong oxidants, which does not align with the principles of green manufacturing.

[0003] Therefore, existing technologies have proposed adding energy field assistance to improve the removal efficiency of the processed material and enhance the surface quality after polishing. For example, ultrasonic vibration-assisted polishing (UVAP) utilizes ultrasound to induce minute vibrations on the material surface, thereby increasing the number of contacts between the processed surface and abrasive grains and thus improving polishing efficiency. This method can reduce processing damage to some extent, but at high frequencies and high amplitudes, it can lead to microcracks and uneven removal effects in the processed material.

[0004] Existing technologies have proposed photocatalytically assisted polishing (UV-CMP), which utilizes the dual oxidation effect of ultraviolet light and oxidants on the workpiece to form an oxide layer on the workpiece surface, which is then removed by mechanical action. While this method helps improve the surface quality of crystalline materials, the electrons and holes generated during polishing are often not stable enough, and the oxide layer formation rate is relatively low, affecting the material removal rate.

[0005] Accordingly, there is an urgent need in this field to develop a new, green, stable and efficient chemical mechanical polishing method in order to better solve the problem of ultra-precision polishing of various high-hardness materials. Summary of the Invention

[0006] To address one or more of the above-mentioned deficiencies or needs of existing technologies, this invention provides an ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing method and apparatus. By simultaneously introducing multiple energy fields such as acoustic, electrical, and optical fields for assistance, and redesigning the process route, reaction mechanism, and supporting equipment for the chemical mechanical polishing process, this invention not only more effectively improves material removal rate and reduces polishing time compared to existing technologies, but also helps to further improve surface quality and reduce subsurface damage. Furthermore, it allows the use of more environmentally friendly polishing fluids, reducing waste liquid treatment costs and protecting the environment. Therefore, it is particularly suitable for polishing applications requiring low-damage, ultra-smooth surfaces for various high-hardness materials.

[0007] To achieve the above objectives, according to one aspect of the present invention, an ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing method is provided, the method comprising the following steps: Step 1: Processing of modified abrasives Modified abrasives are obtained by mixing basic polishing abrasives, piezoelectric materials and photocatalysts, followed by calcination and grinding. The basic polishing abrasive is selected from diamond, silicon carbide, alumina, zirconium oxide or cerium oxide; the piezoelectric material is selected from particles of tetragonal barium titanate, zinc oxide or molybdenum disulfide; and the photocatalyst is selected from titanium oxide or zinc oxide. Step 2: Preparation of polishing slurry The modified abrasive obtained in step one is placed in deionized water, ultrasonically cleaned, and then magnetically stirred to obtain a polishing slurry containing both piezoelectric and photocatalytic carriers. During this process, the modified abrasive initially acquires a piezoelectric catalytic effect under various mechanical stresses, that is, it generates an internal electric field (IEF) to drive e - and h + The migration towards the modified abrasive surface simultaneously triggers redox reactions to form hydroxyl radicals (•OH) and superoxide anion radicals (•O2). - Active oxides such as ) Step 3: Chemical Mechanical Polishing The polishing slurry prepared in step two is delivered to the processing area, and ultrasonic vibration is used to further enhance the piezoelectric catalytic effect of the modified abrasive. At the same time, the modified abrasive obtains a photocatalytic effect under external ultraviolet light irradiation, that is, it excites strong oxidizing holes and reducing electrons, and reacts with surface hydroxyl (-OH) and water molecules to generate active oxide species such as hydroxyl radicals (•OH). In this way, the piezoelectric catalytic effect and the photocatalytic effect are coupled together. Under the condition of enhancing the oxidation effect on the workpiece surface, the modified abrasive further performs mechanical micro-removal on the workpiece surface material, thereby achieving a low-damage and ultra-smooth workpiece surface.

[0008] As a further preferred embodiment of the present invention, in step one, the average particle size of the basic polishing abrasive is preferably 0.05 micrometers to 1.0 micrometers; the particle size of the piezoelectric material is less than 1.0 micrometers, more preferably 50 nanometers to 400 nanometers; and the photocatalyst is preferably nanoparticles.

[0009] As a further preferred embodiment of the present invention, in step one, the basic polishing abrasive, piezoelectric material, and photocatalyst are mixed and then anhydrous ethanol is added to form a solution. The solution is then ultrasonically treated at room temperature for more than 30 minutes and allowed to stand to form a precipitate. Next, the filtered wet powder is washed with deionized water and placed in a muffle furnace and calcined at a temperature of 500°C to 800°C for 3 to 6 hours. After sintering, a dry powder raw material is obtained. Finally, the dry powder raw material is ball-milled for 10 to 100 hours, wherein the mass ratio of grinding balls to dry powder raw material is between 10:1 and 20:1, thereby obtaining the modified abrasive.

[0010] As a further preferred embodiment of the present invention, in step two, a dispersant and / or a pH adjuster may preferably be added to the polishing liquid, wherein the dispersant is selected from xanthan gum, sodium citrate, sodium carboxymethyl cellulose or sorbitol; and the pH adjuster is selected from citric acid, tartaric acid, malic acid, sodium carbonate, baking soda or betaine.

[0011] As a further preferred embodiment of the present invention, in step two, the various mechanical stresses include one or a combination of stresses such as ultrasound, stirring, water flow, friction, and compression.

[0012] As a further preferred embodiment of the present invention, in step three, an ultrasonic vibrating head is preferably used to further enhance the piezoelectric catalytic effect of the modified abrasive.

[0013] As a further preferred embodiment of the present invention, zinc oxide is preferably used as both the piezoelectric material and the photocatalyst, and the piezoelectric catalytic effect and the photocatalytic effect are obtained and coupled together.

[0014] As a further preferred embodiment of the present invention, the built-in electric field (IEF) can drive the transport of photoinduced charges in the bulk and on the surface of the modified abrasive, thereby promoting the active separation of electron-hole pairs and inhibiting recombination, and enhancing the utilization rate of the modified abrasive for ultraviolet light.

[0015] According to another aspect of the present invention, a corresponding ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing apparatus is also provided, the apparatus comprising: The polishing unit has a shell-like structure and includes a housing, a waste liquid tank, a polishing pad, a polishing disc, and a polishing disc motor housed within it. The bottom of the housing is connected to feet for supporting the entire polishing unit. The waste liquid tank is located inside the housing and is used to collect polishing waste liquid and discharge it through a waste liquid pipe. The polishing disc motor is fixed above the bottom plate of the waste liquid tank and is used to rotate the polishing disc. The polishing pad is attached and fixed to the top of the polishing disc to receive the polishing liquid delivered thereto. The liquid supply unit includes a magnetic stirrer, a peristaltic pump, a container, and a magnetic element. The container is used to hold the polishing liquid and is placed on the magnetic stirrer. The magnetic element is placed in the polishing liquid, thereby achieving stirring of the polishing liquid through the interaction of the magnetic stirrer and the magnetic element. The peristaltic pump is used to controllably deliver the polishing liquid to the polishing pad through a conduit. The side panel unit includes a vertical plate, a motion guide rail, and a lifting plate. The vertical plate is vertically mounted on the upper side of the housing, and the lifting plate is horizontally mounted on the vertical plate and can be raised and lowered along the motion guide rail. In addition, a rotary motor is provided on the lifting plate. An ultrasonic polishing head unit includes an ultrasonic vibrating head, an electric slip ring, a screw, and a square bearing. The electric slip ring is fixed to a wall hole on a lifting plate by screws. The ultrasonic vibrating head passes through the electric slip ring and is connected to the square bearing. The screw connects and fixes the square bearing to the lifting plate. The bottom end face of the ultrasonic vibrating head is used to connect a polishing fixture, thereby fixing the workpiece to be polished. In addition, a rotary motor is connected to the ultrasonic vibrating head via a V-belt, thereby providing the ultrasonic polishing head with a certain rotational speed. A photocatalytic unit, comprising an ultraviolet lamp, is used to provide ultraviolet light irradiation to the polishing slurry during the polishing process.

[0016] As a further preferred embodiment of the present invention, the photocatalytic unit preferably provides ultraviolet light with a wavelength of 365 nm.

[0017] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. This invention addresses the various shortcomings of existing chemical mechanical polishing processes by simultaneously introducing multi-energy fields such as sound, electricity, and light, and redesigning the entire process route and reaction mechanism. Compared with existing technologies, this invention not only more effectively improves material removal rate and reduces polishing time, but also helps to further improve surface quality and reduce subsurface damage. In addition, it allows the use of more environmentally friendly polishing fluids, reducing waste liquid treatment costs and protecting the environment. 2. This invention further makes targeted improvements to several key parameters in the polishing process, which can better ensure the smooth progress of the chain of "mechanical stress → piezoelectric field → efficient separation of charge carriers → more active species participating in the reaction", breaking through the limitation of fast carrier recombination in traditional photocatalysis and realizing the synergistic utilization of light and mechanical energy; 3. The present invention further makes targeted improvements to the supporting polishing device in terms of its specific composition and setting method, so as to complete the entire chemical mechanical polishing process in a convenient and efficient manner. 4. The process method and supporting device of the present invention can catalytically oxidize the workpiece in situ while mechanically grinding and removing the workpiece, reduce the brittleness of the material surface, improve the plastic removal effect of abrasive, and fully combine ultrasonic-piezoelectric-optical. Therefore, as a green, stable and efficient technical solution, it is especially suitable for polishing applications of various high-hardness materials to achieve low-damage and ultra-smooth surfaces. Attached Figure Description

[0018] Figure 1 This is a detailed process flow diagram of the ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing method according to a preferred embodiment of the present invention; Figure 2 This is a schematic diagram of the overall structure of the supporting device according to a preferred embodiment of the present invention; Figure 3 This shows a more detailed schematic diagram of the polishing unit's structure; Figure 4 This shows a more detailed structural schematic diagram of the liquid supply unit; Figure 5a and 5b These are structural schematic diagrams showing the different components of the side panel unit in more detail; Figure 6 This is a more detailed structural schematic diagram of the ultrasonic polishing head unit; Figure 7 This shows a more detailed schematic diagram of the photocatalytic unit. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] Figure 1This is a detailed process flow diagram of the ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing method according to a preferred embodiment of the present invention, which will be referred to below. Figure 1 The process method of the present invention will be explained in more detail below.

[0021] Step 1: Processing of modified abrasive.

[0022] In this step, a base polishing abrasive, a piezoelectric material, and a photocatalyst are mixed, and then calcined and ground to obtain a novel modified abrasive capable of mechanical grinding while also exhibiting the piezoelectric and photocatalytic effects, which will be explained in detail later. The base polishing abrasive is selected from diamond, silicon carbide, alumina, zirconium oxide, or cerium oxide; the piezoelectric material is selected from particles of tetragonal barium titanate, zinc oxide, or molybdenum disulfide; and the photocatalyst is selected from titanium oxide or zinc oxide.

[0023] According to a preferred embodiment of the present invention, the base polishing abrasive is a traditional polishing abrasive, and its average particle size is preferably 0.05 micrometers to 1.0 micrometers. For example, for materials with moderate hardness such as fused silica, single-crystal silicon, and zinc sulfide, zirconium oxide, silicon oxide, and cerium oxide can be selected as abrasives; for high-hardness materials, diamond and alumina abrasives can be selected. The particle size of the piezoelectric material is less than 1.0 micrometer, more preferably 50 nanometers to 400 nanometers; the photocatalyst is preferably a nanoparticle.

[0024] More specifically, the basic polishing abrasive, piezoelectric material, and photocatalyst are mixed and then added to anhydrous ethanol to form a solution (the mass ratio can be set between 1:3 and 1:5). The solution is then ultrasonically treated at room temperature (25°C) for more than 30 minutes and allowed to stand to form a precipitate. The filtered wet powder is then washed with deionized water (for example, three times) and placed in a muffle furnace to be calcined at 500°C to 800°C for 3 to 6 hours. After sintering, a dry powder raw material is obtained. Finally, the dry powder raw material is ball-milled for 10 to 100 hours. The grinding media can be high-hardness, high-toughness spherical media such as zirconium oxide, tungsten carbide, or cemented carbide, and the mass ratio of the grinding media to the dry powder raw material is between 10:1 and 20:1. The modified abrasive is thus obtained.

[0025] Step two, preparation of polishing slurry.

[0026] In this step, the modified abrasive obtained from the previous processing is placed in deionized water, ultrasonically cleaned, and then magnetically stirred to obtain a polishing slurry containing both piezoelectric and photocatalytic carriers. During this process, the modified abrasive initially acquires a piezoelectric catalytic effect under various mechanical stresses, that is, it generates an internal electric field (IEF) to drive e - and h +The migration towards the modified abrasive surface simultaneously triggers redox reactions to form hydroxyl radicals (•OH) and superoxide anion radicals (•O2). - Active oxide species such as ).

[0027] More specifically, the modified abrasive can be slowly added to a beaker containing 200 mL of deionized water and ultrasonicated for 30 minutes using an ultrasonic cleaner. The beaker is then removed and stirred using a magnetic stirrer at a speed of 1000-1500 rpm. A certain amount of dispersant is added to improve the stability of the abrasive particles in the polishing slurry. Food-grade additives such as xanthan gum, sodium citrate, sodium carboxymethyl cellulose, and sorbitol can be selected as dispersants. Deionized water is then added to the 500 mL mark on the beaker. A pH adjuster is selected based on the characteristics of the workpiece to adjust the pH of the polishing slurry. pH adjusters are mainly weak acid and acid-base green additives, including citric acid, tartaric acid, malic acid, sodium carbonate, baking soda, and betaine. At this point, the polishing slurry contains both piezoelectric and photocatalytic carriers. The magnetic stirring action initially creates a piezoelectric field in the polishing slurry, resulting in a piezoelectric catalytic effect.

[0028] Step 3: Chemical mechanical polishing.

[0029] In this step, the previously prepared polishing slurry is delivered to the processing area, and ultrasonic vibration is used to further enhance the piezoelectric catalytic effect of the modified abrasive. Simultaneously, the modified abrasive acquires a photocatalytic effect under external ultraviolet light irradiation, that is, it excites strong oxidizing holes and reducing electrons, and reacts with surface hydroxyl groups (-OH) and water molecules to generate active oxide species such as hydroxyl radicals (•OH). In this way, the piezoelectric catalytic effect and the photocatalytic effect are coupled with each other. Under the condition of enhancing the oxidation effect on the workpiece surface, the modified abrasive further performs mechanical removal of the workpiece surface material, thereby achieving a low-damage and ultra-smooth workpiece surface.

[0030] More specifically, after the polishing slurry is delivered to the processing area, the piezoelectric catalytic effect of the modified abrasive can be further enhanced by the stimulation of components such as ultrasonic vibrators, high load pressure, and mechanical friction. Under the action of various mechanical stresses, the modified abrasive continues to generate an internal electric field, driving e - and h + Migration to the modified abrasive surface triggers redox reactions to form hydroxyl radicals (•OH) and superoxide anion radicals (•O2). -The polishing slurry is stimulated by light field through the introduction of an external photocatalytic unit. Under the influence of light, the photocatalyst stimulates the polishing slurry to generate more oxide species such as hydroxyl radicals (•OH). This piezoelectric-photocatalytic coupling further enhances the polishing slurry's ability to oxidize the workpiece and strengthens the oxidation effect on the workpiece surface. The soft oxide layer is eventually removed by the modified abrasive through mechanical grinding, making it easy to achieve high-efficiency material removal.

[0031] The piezoelectric catalytic effect, which is one of the key reaction mechanisms of this invention, is explained in more detail below.

[0032] The research group of this invention discovered that piezoelectric materials, under various mechanical stresses (including but not limited to ultrasound, stirring, water flow, friction, and extrusion), can generate an internal electric field (IEF) that drives e - and h + Migration to the surface of piezoelectric materials can also trigger redox reactions to form active oxide species. Furthermore, combining piezoelectric materials with photocatalysts allows the IEF (internal energy flow) generated under strain to drive the transport of photoinduced charges in the bulk and on the photocatalyst surface, thereby promoting their active separation and inhibiting their recombination. Photocatalytic and piezoelectric properties can coexist in a single material, thus simultaneously generating piezoelectricity and photoinduced charges. - and h + It can be generated not only under light, but also under strain-induced polarized electric fields to promote charge separation and enhance surface reduction and oxidation effects.

[0033] Accordingly, in the process of this invention, the piezoelectric-photocatalytic effect of the modified abrasive is achieved through a chain of "mechanical stress → piezoelectric field → efficient carrier separation → more active species participating in the reaction," breaking through the limitation of fast carrier recombination in traditional photocatalysis and realizing the synergistic utilization of mechanical, optical, and chemical energy. In this way, the workpiece can be catalytically oxidized in situ while being mechanically ground to remove it, reducing the brittleness of the material surface and improving the plastic removal effect of the abrasive.

[0034] Figure 2 This is a schematic diagram of the overall structure of the supporting device according to a preferred embodiment of the present invention. See below for further details. Figure 2 The polishing apparatus of the present invention will be explained in more detail below.

[0035] like Figure 2 As shown, the ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing device mainly includes a polishing unit 1, a liquid supply unit 2, a side plate unit 3, a rotary motor 4, an ultrasonic polishing head unit 6, and a photocatalytic unit 7, which will be described in detail below.

[0036] You can view them at the same time. Figure 3The polishing unit 1 has a shell-like structure and includes a housing 12 and a waste liquid tank 13, a polishing pad 14, a polishing disc 15, and a polishing disc motor 16 placed inside it. The bottom of the housing 12 is connected to a foot 11 to support the entire polishing unit. The waste liquid tank 13 is cylindrical and is located inside the housing 12 to collect polishing waste liquid and discharge it through a waste liquid pipe 18. The polishing disc motor 16 is vertically fixed above the bottom plate 17 of the waste liquid tank 13 to rotate the polishing disc 15, and its top is vertically connected to the polishing disc 15. The polishing pad 14 is attached to the top of the polishing disc 15 to receive the polishing liquid delivered thereto.

[0037] More specifically, the waste liquid tank 13, the polishing disc 15 and the rotary motor are axially aligned and have the same coaxiality; one end of the waste liquid pipe 18 can pass through the housing 12 to connect to the waste liquid tank 13, and the other end is placed outside the waste liquid tank 12, thereby discharging the polishing waste liquid collected in the waste liquid tank 13.

[0038] You can refer to this at the same time. Figure 4 The liquid supply unit 2 includes a magnetic stirrer 21, a peristaltic pump 22, a container 24 (e.g., a beaker), and a magnetic stirrer 26. The container 24 is used to hold the polishing liquid and is placed on the magnetic stirrer 21. The magnetic stirrer 26 is placed in the polishing liquid 25, thereby achieving stirring of the polishing liquid through the interaction of the magnetic stirrer 21 and the magnetic stirrer 26. The peristaltic pump 22 is used to controllably deliver the polishing liquid 25 to the polishing pad 14 through a conduit 23.

[0039] More specifically, after the magnetic stirrer 26 is placed in the container 24, it will sink to the bottom of the container 24 due to gravity. When the power of the magnetic stirrer 21 is turned on and the rotation speed of the magnetic stirrer 26 is adjusted, the polishing slurry 25 can be stirred. During this process, the appropriate stirring speed can be selected according to the dispersion characteristics of the abrasive in the polishing slurry, the viscosity of the polishing slurry, and the stability of the chemical reagents. The peristaltic pump 22 can be connected to two conduits 23. One end of the pump is immersed in the polishing slurry, and the other end is suspended above the polishing pad 14. During operation, the peristaltic pump 22 delivers the polishing slurry 25 to the polishing pad 14 through the conduits. The flow rate of the polishing slurry can be adjusted at any time through the peristaltic pump 22, thereby achieving a good liquid supply effect.

[0040] You can view them at the same time. Figure 5a and 5bThe side plate unit 3 includes a vertical plate 31, a motion guide rail 32, and a lifting plate 33. The vertical plate 31 is vertically mounted on the upper side of the housing 12, and the lifting plate 33 is horizontally mounted on the vertical plate 31 and can be raised and lowered along the motion guide rail 32. In addition, a rotary motor 4 is provided on the lifting plate 33. The rotary motor 4 can be connected to the ultrasonic polishing head unit 6 via a V-belt 5, thereby giving the ultrasonic polishing head, which will be described below, a certain rotation speed.

[0041] You can view them at the same time. Figure 6 The ultrasonic polishing head unit 6 includes an ultrasonic vibrating head 61, an electric slip ring 62, a screw 64, and a square bearing 66. The electric slip ring 62 is fixed to the wall hole 34 on the lifting plate 33 by a screw 63. The ultrasonic vibrating head 61 passes through the electric slip ring 62 and is connected to the square bearing 66. The screw 64 connects and fixes the square bearing 66 to the lifting plate 33. The bottom end face of the ultrasonic vibrating head 61 is used to connect to the polishing fixture 66, thereby fixing the workpiece 67 to be polished. In addition, the rotary motor 4 is connected to the ultrasonic vibrating head 61 through a V-belt 5, thereby providing the ultrasonic polishing head 61 with a certain rotation speed.

[0042] You can view them at the same time. Figure 7 The photocatalytic unit 7 includes an ultraviolet lamp and is used to provide ultraviolet light irradiation to the polishing slurry during the polishing process.

[0043] More specifically, the photocatalytic unit 7 is used to provide ultraviolet light with a wavelength of 365nm and an adjustable power range of 0-60W, thereby providing light stimulation for the chemical reactions required in the polishing process.

[0044] When performing polishing, the polishing unit 1 is started, the polishing disc 15 is adjusted to rotate clockwise, and the height of the ultrasonic polishing head unit 6 is adjusted by the motion guide rail 32 so that the workpiece 67 fixed at the bottom of the polishing fixture 66 contacts the polishing pad 14 and has a certain pressure. Next, the rotary motor 4 is started, and the workpiece 67 fixed at the bottom of the polishing fixture 66 rotates counterclockwise. When the ultrasonic polishing head 6 is working, the workpiece 67 vibrates longitudinally. The polishing liquid 25 in the container 24 initially gains mechanical energy through the magnetic stirrer 21. The polishing liquid 25 is then transported to the polishing pad 14 by the peristaltic pump 22. At this time, the polishing liquid 25 is subjected to centrifugal force and flows between the workpiece 67 and the polishing pad 14. The polishing unit 7 is turned on and the light power is adjusted to vertically irradiate the contact area between the polishing liquid 25 and the workpiece 67. At this time, the modified abrasive in the polishing liquid 25 is subjected to friction between the workpiece and the polishing pad and the piezoelectric field generated by ultrasonic excitation, as well as light stimulation from the ultraviolet lamp. Through the ultrasonic-piezoelectric-photocatalytic coupling effect, the modified abrasive can efficiently and with low damage remove materials, achieving an ultra-smooth workpiece surface.

[0045] After polishing for the appropriate time, turn off the power to all devices, remove the workpiece from the bottom of the polishing head, rinse it with deionized water, and then gently wipe the surface of the workpiece with a non-woven cloth soaked in anhydrous ethanol. The entire processing is clean, efficient, simple and safe to operate.

[0046] In summary, the ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing scheme of the present invention introduces multiple energy fields such as sound, electricity, and light for assistance. Compared with the prior art, it can not only more effectively improve the material removal rate and reduce polishing time, but also help to further improve surface quality and reduce subsurface damage. In addition, it can use more environmentally friendly polishing fluid, reduce waste liquid treatment costs and protect the environment. Therefore, it is particularly suitable for polishing applications of various high-hardness materials to achieve low-damage and ultra-smooth surfaces, and has good practical value and application prospects.

[0047] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ultrasonic-piezoelectric-photocatalytic assisted chemical mechanical polishing method, characterized by, The method includes the following steps: Step 1: Processing of modified abrasives; Modified abrasives are obtained by mixing basic polishing abrasives, piezoelectric materials and photocatalysts, followed by calcination and grinding. The basic polishing abrasive is selected from diamond, silicon carbide, alumina, zirconium oxide or cerium oxide; the piezoelectric material is selected from particles of tetragonal barium titanate, zinc oxide or molybdenum disulfide; and the photocatalyst is selected from titanium oxide or zinc oxide. Step 2: Preparation of polishing slurry; The modified abrasive obtained in step one is placed in deionized water, ultrasonically cleaned, and then magnetically stirred to obtain a polishing slurry containing both piezoelectric and photocatalytic carriers. In this process, the modified abrasive initially obtains piezoelectric catalytic effect under the action of various mechanical stresses, that is, generates internal electric field (IEF) to drive e and h + Migrate to the surface of the modified abrasive, while triggering redox reactions to form hydroxyl radicals (•OH) and superoxide anion radicals (•O2 - ); Step 3: Chemical mechanical polishing treatment; The polishing slurry prepared in step two is delivered to the processing area, and ultrasonic vibration is used to further enhance the piezoelectric catalytic effect of the modified abrasive. At the same time, the modified abrasive obtains a photocatalytic effect under external ultraviolet light irradiation, that is, it excites strong oxidizing holes and reducing electrons, and reacts with surface hydroxyl (-OH) and water molecules to generate hydroxyl radicals (•OH). In this way, the piezoelectric catalytic effect and the photocatalytic effect are coupled together, and under the condition of enhancing the oxidation effect on the workpiece surface, the modified abrasive further performs mechanical micro-removal on the workpiece surface material, thereby achieving a low-damage and ultra-smooth workpiece surface.

2. The method as described in claim 1, characterized in that, In step one, the average particle size of the basic polishing abrasive is 0.05 micrometers to 1.0 micrometers; the particle size of the piezoelectric material is less than 1.0 micrometers; and the photocatalyst is nanopowder.

3. The method as described in claim 2, characterized in that, In step one, the basic polishing abrasive, piezoelectric material, and photocatalyst are mixed and then anhydrous ethanol is added to form a solution. The solution is then ultrasonically treated at room temperature for more than 30 minutes and allowed to stand to form a precipitate. Next, the filtered wet powder is washed with deionized water and placed in a muffle furnace and calcined at 500℃~800℃ for 3 hours~6 hours. After sintering, a dry powder raw material is obtained. Finally, the dry powder raw material is ball-milled for 10 hours~100 hours, wherein the mass ratio of grinding balls to dry powder raw material is between 10:1 and 20:1, thereby obtaining the modified abrasive.

4. The method according to any one of claims 1-3, characterized in that, In step two, a dispersant and / or pH adjuster are also added to the polishing liquid, wherein the dispersant is selected from xanthan gum, sodium citrate, sodium carboxymethyl cellulose, or sorbitol; and the pH adjuster is selected from citric acid, tartaric acid, malic acid, sodium carbonate, baking soda, or betaine.

5. The method as described in claim 4, characterized in that, In step two, the various mechanical stresses include one or a combination of ultrasonic, stirring, water flow, friction and extrusion stresses.

6. The method as described in claim 5, characterized in that, In step three, an ultrasonic vibrating head is used to further enhance the piezoelectric catalytic effect of the modified abrasive.

7. The method as described in claim 6, characterized in that, Zinc oxide is used as both the piezoelectric material and the photocatalyst, and the piezoelectric catalytic effect and the photocatalytic effect are obtained and coupled together.

8. The method as described in claim 7, characterized in that, The built-in electric field (IEF) drives the transport of photoinduced charges on the surface of the modified abrasive, thereby promoting the active separation of electron-hole pairs and inhibiting recombination, and enhancing the utilization rate of ultraviolet light by the modified abrasive.

9. An apparatus for performing the method as described in any one of claims 1-8, characterized in that, The device includes: The polishing unit (1) has a shell-like structure and includes a shell (12) and a waste liquid tank (13), a polishing pad (14), a polishing disc (15), and a polishing disc motor (16) placed inside it. The bottom of the shell (12) is connected to feet (11) to support the entire polishing unit. The waste liquid tank (13) is located inside the shell (12) and is used to collect polishing waste liquid and discharge it through a waste liquid pipe (18). The polishing disc motor (16) is fixed above the bottom plate (17) of the waste liquid tank (13) and is used to rotate the polishing disc (15). The polishing pad (14) is attached to the top of the polishing disc (15) and is used to receive the polishing liquid delivered thereto. The liquid supply unit (2) includes a magnetic stirrer (21), a peristaltic pump (22), a container (24), and a magnetic element (26). The container (24) is used to hold the polishing liquid and is placed on the magnetic stirrer (21). The magnetic element (26) is placed in the polishing liquid, thereby achieving stirring of the polishing liquid through the interaction of the magnetic stirrer (21) and the magnetic element (26). The peristaltic pump (22) is used to controllably deliver the polishing liquid to the polishing pad (14) through a conduit (23). The side plate unit (3) includes a vertical plate (31), a motion guide rail (32) and a lifting plate (33), wherein the vertical plate (31) is vertically mounted on the upper side of the housing (12), and the lifting plate (33) is horizontally mounted on the vertical plate (31) and can be raised and lowered along the motion guide rail (32); in addition, a rotary motor (4) is provided on the lifting plate (33). An ultrasonic polishing head unit (6) includes an ultrasonic vibrating head (61), an electric slip ring (62), a screw (64), and a square bearing (65). The electric slip ring (62) is fixed to a wall hole (34) on a lifting plate (33) by a screw (63). The ultrasonic vibrating head (61) passes through the electric slip ring (62) and is connected to the square bearing (65). The screw (64) connects and fixes the square bearing (65) to the lifting plate (33). The bottom end face of the ultrasonic vibrating head (61) is used to connect a polishing fixture (66), thereby fixing the workpiece (67) to be polished. In addition, the rotary motor (4) is connected to the ultrasonic vibrating head (61) via a V-belt (5), thereby providing the ultrasonic vibrating head (61) with a certain rotation speed. The photocatalytic unit (7) includes an ultraviolet lamp and is used to provide ultraviolet light irradiation to the polishing slurry during the polishing process.

10. The apparatus as claimed in claim 9, characterized in that, The photocatalytic unit (7) provides ultraviolet light with a wavelength of 365 nm.

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