Ultrasonic cavitation magneto-rheological chemical mechanical polishing device and GaN efficient polishing method

Abstract

The invention discloses an ultrasonic cavitation magneto-rheological chemical mechanical polishing device which comprises an operation table. A polishing groove is formed in the top of the operation table and used for containing magneto-rheological polishing liquid. A clamping driving mechanism is arranged in the polishing groove and used for clamping a workpiece to be polished and driving the workpiece to rotate. An ultrasonic transducer is arranged at the position, located above the clamping driving mechanism, in the polishing groove; the ultrasonic transducer comprises a rear cover plate, a piezoelectric ceramic piece and a front cover plate which are arranged in sequence; the rear cover plate and the front cover plate are locked through a pre-tightening bolt; the front cover plate is made of a magnetic material and faces the clamping driving mechanism; the clamping driving mechanism and the ultrasonic transducer are electrically connected with the controller. Correspondingly, the invention further provides an efficient GaN polishing method, the ultrasonic cavitation magneto-rheological chemical mechanical polishing device is used for polishing GaN, the material removal efficiency is high, the stress defect on the GaN surface can be avoided, and the polishing quality is good.

Description

Technical Field

[0001] The invention relates to the technical field of GaN polishing, and in particular to an ultrasonic cavitation magnetorheological mechanical polishing device and a GaN efficient polishing method. Background Art

[0002] As the first generation of semiconductor materials reached their theoretical limits, researchers began to explore new semiconductor materials in order to improve the performance of semiconductor devices under high pressure and high temperature. Among them, GaN began to be sought after for its excellent mechanical, electrical, thermal, and optical properties. With the continuous development of GaN devices, the requirements for it are getting higher and higher, especially in some applications in the field of ultra-precision machining, which require its surface accuracy to reach the nanometer level. Therefore, efficient atomic-level control of the GaN surface is the key to its large-scale promotion and application.

[0003] Ultra-precision polishing technology is an effective way to obtain GaN nano-scale surfaces and non-destructive sub-surfaces. Chemical mechanical polishing is currently a more mature processing technology for GaN polishing; it combines chemical and mechanical methods to remove uneven parts of the material surface to make the surface highly flat. During the polishing process, the chemical reagents in the polishing liquid will react chemically with the surface of the material to be polished to form a reaction product layer that is easily worn away and then removed by the polishing pad. However, in traditional chemical mechanical polishing, the abrasive particles are squeezed on the workpiece under the action of the polishing pad to remove the raised parts of the material surface. During the polishing process, stress and defects may be introduced, affecting the performance of the workpiece, and it is difficult to ensure the uniformity of the squeezing force of each part for complex structures. In addition, the viscosity of traditional chemical mechanical polishing liquid is too low, making it difficult to control the entire polishing area, which limits the polishing efficiency. Summary of the invention

[0004] The present invention provides an ultrasonic cavitation magnetorheological mechanical polishing device to overcome the above-mentioned problems existing in the prior art. The ultrasonic cavitation magnetorheological mechanical polishing device of the present invention adopts magnetorheological polishing liquid instead of traditional chemical mechanical polishing liquid to play the role of a polishing pad, and an ultrasonic transducer is provided to perform high-frequency vibration during the polishing process to produce a cavitation effect, drive the abrasive particles in the polishing liquid to impact the surface of the workpiece, generate a chemical mechanical reaction, and realize the polishing of the workpiece; it combines the three technologies of ultrasonic cavitation, magnetorheological polishing, and chemical mechanical polishing, improves the polishing efficiency, reduces the mechanical damage of the workpiece during polishing, and is suitable for polishing workpieces with complex structures. Correspondingly, the present invention also provides a GaN efficient polishing method, using the ultrasonic cavitation magnetorheological mechanical polishing device of the present application to polish GaN, with high material removal efficiency, and can avoid stress defects on the GaN surface, and has good polishing quality.

[0005] For the polishing device, the technical solution of this application is:

[0006] An ultrasonic cavitation magnetorheological mechanical polishing device comprises an operating table; a polishing tank is provided on the top of the operating table for containing magnetorheological polishing liquid; a clamping drive mechanism is provided in the polishing tank for clamping a workpiece to be polished and driving the workpiece to rotate; an ultrasonic transducer is provided inside the polishing tank, located above the clamping drive mechanism; the ultrasonic transducer comprises a rear cover plate, a piezoelectric ceramic sheet and a front cover plate which are arranged in sequence; the rear cover plate and the front cover plate are locked by pre-tightening bolts; the front cover plate is made of magnetic material and faces the clamping drive mechanism; the clamping drive mechanism and the ultrasonic transducer are electrically connected to a controller respectively.

[0007] Compared with the prior art, the ultrasonic cavitation magnetorheological polishing device of the present application combines the three technologies of ultrasonic cavitation, magnetorheological polishing and chemical mechanical polishing, thereby improving the polishing efficiency, reducing the mechanical damage of the workpiece during polishing, and is suitable for polishing workpieces with complex structures. Specifically:

[0008] (1) Magnetorheological polishing fluid is used instead of traditional chemical mechanical polishing fluid to play the role of polishing pad. Magnetic fluid can correct different shapes within a certain range, so that chemical mechanical polishing is no longer limited to plane polishing, but can also achieve flexible polishing of complex structures and micro-grooves workpieces, with a wide range of applications;

[0009] (2) By setting an ultrasonic transducer, high-frequency vibration is continuously performed during the polishing process to produce a cavitation effect, provide a normal force during the polishing process, drive the abrasive particles in the magnetorheological polishing fluid to impact the workpiece surface, so as to cause a chemical mechanical reaction and achieve polishing of the workpiece, thereby effectively avoiding the stress defects caused by continuous squeezing of local protrusions when using traditional polishing pads;

[0010] (3) The front cover of the ultrasonic transducer is made of magnetic material. When polishing complex curved surfaces, the magnetically sensitive particles in the magnetorheological polishing fluid will be bound by the magnetic field and will approach the front cover, generating magnetic buoyancy. The non-magnetic abrasive particles will approach the workpiece surface under the action of ultrasonic cavitation and react chemically with the workpiece in an OH- environment, generating chemical products on the workpiece surface that are easier to remove. The abrasive is then used to remove the oxide layer, making material removal easier.

[0011] (4) During the polishing process, the ultrasonic transducer continuously vibrates at a high frequency, and the magnetic fluid has to withstand 10 times the gravity acceleration to separate from the front cover plate, which can effectively prevent the magnetic fluid from solidifying at the front end of the front cover plate due to water evaporation during long-term use, making it easier to update the magnetic fluid; and the ultrasonic cavitation effect will decompose the water in the magnetorheological polishing fluid to produce more OH-, thereby promoting the chemical mechanical reaction and improving the polishing efficiency.

[0012] As an optimization, in the aforementioned ultrasonic cavitation magnetorheological mechanical polishing device, a polishing liquid delivery pipe is also provided above the clamping drive mechanism; the polishing liquid delivery pipe is connected to the polishing liquid supply system. In this case, it is more convenient to add magnetorheological polishing liquid, and it can also avoid the magnetorheological polishing liquid splashing out during the filling process, causing environmental pollution.

[0013] As an optimization, in the aforementioned ultrasonic cavitation magnetorheological mechanical polishing device, the clamping drive mechanism includes a vacuum suction cup; a group of ventilation grooves are provided on the circumferential direction of the vacuum suction cup, and a rotating shaft connected to the driving motor is provided at the bottom of the vacuum suction cup; an air suction port is also provided on the vacuum suction cup, and a rotary joint is provided at the air suction port; the rotary joint is connected to the vacuum pump through a vacuum pipeline. Compared with directly pressing or squeezing the workpiece, the workpiece is fixed by vacuum adsorption, which makes the workpiece less likely to be damaged and can guarantee the integrity and safety of the workpiece to the greatest extent.

[0014] As an optimization, in the aforementioned ultrasonic cavitation magnetorheological mechanical polishing device, the ultrasonic transducer is clamped and fixed by a fixture; the fixture is fixed to the bottom of the polishing groove. In this case, the structure is simple, the assembly is convenient, and it is easy to implement.

[0015] As an optimization, in the aforementioned ultrasonic cavitation magnetorheological mechanical polishing device, the radiation surface of the front cover plate is an arc-shaped surface, and the radius of curvature of the radiation surface is 75-85 mm. At this time, the axial sound pressure of the ultrasonic transducer in the magnetorheological polishing fluid is generally high.

[0016] As an optimization, in the aforementioned ultrasonic cavitation magnetorheological mechanical polishing device, the piezoelectric ceramic piece is a PZT-4 annular piezoelectric ceramic piece; its piezoelectric properties are stable and the price is cheap, which is conducive to controlling manufacturing costs.

[0017] As an optimization, in the aforementioned ultrasonic cavitation magnetorheological mechanical polishing device, the polishing liquid supply system and the controller are integrated in the operating table, which is beneficial to reducing the occupied space.

[0018] For the polishing method, the technical solution of this application is as follows:

[0019] A GaN efficient polishing method, which uses the aforementioned ultrasonic cavitation magnetorheological mechanical polishing device of the present application to polish GaN; the specific steps are as follows:

[0020] S1, placing the GaN to be processed on a vacuum chuck, and starting the vacuum pump to adsorb the GaN; then feeding the magnetorheological polishing liquid into the polishing tank through the polishing liquid delivery pipe; the magnetorheological polishing liquid includes H 2 O 2solution, magnetorheological fluid and abrasive particles, wherein the magnetorheological fluid includes a water base, magnetically sensitive particles and a stabilizer, and the abrasive particles are aluminum oxide; S2, starting the driving motor to drive the vacuum suction cup to rotate, so as to drive the GaN to rotate; at the same time, starting the ultrasonic transducer; at this time, the magnetically sensitive particles in the polishing liquid will generate magnetic buoyancy under the magnetic effect of the front cover plate of the ultrasonic transducer, and the non-magnetic aluminum oxide abrasive particles will impact the GaN surface under the cavitation effect of the ultrasonic transducer, causing a chemical mechanical reaction to achieve the polishing of the GaN.

[0021] Compared with the prior art, the GaN efficient polishing method of the present application combines ultrasonic cavitation, magnetorheological polishing, and chemical mechanical polishing to polish GaN, with high polishing efficiency and good quality. In this method, magnetorheological polishing fluid is used, and chemical mechanical polishing is adopted to replace the hard-polishing-hard-polishing mode of traditional magnetic fluid polishing. At the same time, aluminum oxide with lower hardness is selected as abrasive, and the impact force generated by the ultrasonic cavitation effect is used to drive the abrasive to contact with the GaN surface, and chemically react with GaN in an OH- environment to produce softer chemical products, so that the GaN surface will not leave processing stress after polishing, and the polishing quality is good. In addition, the ultrasonic cavitation effect will decompose water to produce more OH-, thereby promoting the chemical mechanical reaction and improving the polishing efficiency.

[0022] As an optimization, in the aforementioned GaN efficient polishing method, the surface of the magnetic sensitive particles is coated with epoxy resin; 2 O 2 The concentration is 20% to 30%; in step S2, the rotation speed of the vacuum chuck is 300 rpm; the aluminum oxide abrasive particles impact the GaN surface at a speed of 60 m / s. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of the ultrasonic cavitation magnetorheological mechanical polishing device of the present application;

[0024] Figure 2 is a schematic diagram of the structure of an ultrasonic transducer in an embodiment of the present application;

[0025] Figure 3 is an equivalent circuit diagram of an ultrasonic transducer in an embodiment of the present application;

[0026] Figure 4 is the vibration form of the ultrasonic transducer in the embodiment of the present application;

[0027] Figure 5 This is a polishing principle diagram when polishing is performed using the polishing method of the present application;

[0028] Figure 6 is a graph showing the relationship between polishing time and workpiece surface roughness when polishing is performed using the polishing method of the present application;

[0029] Figure 7 It is a comparison diagram of the surface morphology of a GaN workpiece after polishing using a conventional chemical mechanical polishing method and the polishing method of the present application.

[0030] The markings in the attached drawings are: 1-operating table, 101-polishing tank; 2-clamping drive mechanism; 3-ultrasonic transducer, 31-rear cover plate, 32-piezoelectric ceramic sheet, 33-front cover plate; 4-polishing liquid delivery pipe; 5-clamp. DETAILED DESCRIPTION

[0031] The present application is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present application.

[0032] Example ( Figure 1-Figure 4 ):

[0033] See also Figure 1 and Figure 2 The ultrasonic cavitation magnetorheological mechanical polishing device in this embodiment includes an operating table 1; a polishing tank 101 is provided on the top of the operating table 1 for containing magnetorheological polishing liquid; a clamping drive mechanism 2 is provided in the polishing tank 101 for clamping the workpiece to be polished and driving the workpiece to rotate; an ultrasonic transducer 3 is provided inside the polishing tank 101, located above the clamping drive mechanism 2; the ultrasonic transducer 3 includes a rear cover plate 31, a piezoelectric ceramic sheet 32 ​​and a front cover plate 33 arranged in sequence; the rear cover plate 31 and the front cover plate 33 are locked by pre-tightening bolts; the front cover plate 33 is made of magnetic material and faces the clamping drive mechanism 2; the clamping drive mechanism 2 and the ultrasonic transducer 3 are electrically connected to the controller respectively; a polishing liquid delivery pipe 4 is also provided above the clamping drive mechanism 2; the polishing liquid delivery pipe 4 is connected to the polishing liquid supply system. The polishing liquid delivery pipe 4 is provided to make it more convenient to add the magnetorheological polishing liquid, and avoid splashing of the magnetorheological polishing liquid during the filling process to cause environmental pollution.

[0034] The ultrasonic cavitation magnetorheological mechanical polishing device of the present invention combines three technologies: ultrasonic cavitation, magnetorheological polishing, and chemical mechanical polishing. It uses magnetorheological polishing liquid to play the role of a polishing pad, and by setting an ultrasonic transducer, high-frequency vibration is performed during the polishing process to produce a cavitation effect, so as to drive the abrasive particles in the polishing liquid to impact the surface of the workpiece, and a chemical mechanical reaction occurs, thereby achieving polishing of the workpiece with high polishing efficiency and good quality. In addition, the cavitation effect of the ultrasonic transducer 3 can also decompose water to produce more OH-, thereby promoting the progress of the chemical mechanical reaction and further improving the polishing efficiency.

[0035] In this embodiment, the clamping drive mechanism 2 includes an annular vacuum suction cup; a group of ventilation grooves are provided on the circumferential direction of the vacuum suction cup (the workpiece is placed above the ventilation grooves), and a rotating shaft connected to the drive motor is provided at the bottom of the vacuum suction cup (the rotating shaft and the vacuum suction cup are integrally formed); the vacuum suction cup is also provided with an air suction port, and a rotary joint (a rotating joint with a bearing, the outer ring is fixed and the inner ring rotates) is provided at the air suction port; the rotary joint is connected to the vacuum pump through a vacuum pipeline. Compared with directly pressing or squeezing the workpiece, the workpiece is fixed by vacuum adsorption, so that the workpiece is not easily damaged, and the integrity and safety of the workpiece can be guaranteed to the greatest extent. Furthermore, the flatness of the vacuum suction cup is controlled within 10μm to reduce the rotation deviation caused by processing errors; the maximum speed of the vacuum suction cup is 800rpm.

[0036] In this embodiment, the ultrasonic transducer 3 is clamped and fixed by a clamp 5; the clamp 5 is fixed to the bottom of the polishing groove 101. The ultrasonic transducer 3 adopts a longitudinal-bending vibration multi-frequency transducer with a frequency of 23-41kHz; wherein the piezoelectric ceramic sheet 32 ​​adopts a PZT-4 annular piezoelectric ceramic sheet with a thickness of 5mm, an inner diameter of 15mm, and an outer diameter of 40mm; the length of the rear cover plate 31 is 18mm, and the M10*1.0-6H thread design is selected, and the diameter of the internal thread round head is 10.4mm and the height is 10mm; the length of the front cover plate 33 is 21mm, and its radiation surface is an arc surface, and the radius of curvature of the radiation surface is 80mm (the front cover plate 33 is specifically a rectangular thin plate with an arc, and the vibration is approximately the bending vibration of the thin plate). The equivalent circuit diagram of the entire ultrasonic transducer 3 is shown as follows. Figure 3 As shown, the vibration principle is as follows Figure 4 The applicant tested the processed ultrasonic transducer 3 using a ZX70A-500K impedance analyzer (Zhixin Precision Co., Ltd.), and found that its resonant frequencies were 24.565kHz, 33.205kHz, and 35.815kHz. In addition, the axial sound pressure of the ultrasonic transducer 3 at a frequency of 25.322kHz in the magnetorheological polishing fluid was generally high, and the sound pressure value at 1mm near the surface of the front cover plate 33 was the highest, which was 5.3bar.

[0037] In this embodiment, the polishing liquid supply system and the controller are integrated in the operating table 1, which is beneficial to reducing the occupied space.

[0038] Implementation Cases:

[0039] This case uses the ultrasonic cavitation magnetorheological mechanical polishing device of the present application to polish GaN; the specific steps of the GaN efficient polishing method are as follows.

[0040] S1, place the GaN to be processed on the vacuum chuck, the distance between it and the bottom of the ultrasonic transducer 3 is 1mm, and start the vacuum pump to adsorb the GaN; then input the magnetorheological polishing liquid into the polishing tank 101 through the polishing liquid delivery pipe 4 (the polishing liquid supply system is 100mm 3 / min) to the polishing area to immerse the GaN; the magnetorheological polishing fluid comprises a base liquid and abrasive particles; the abrasive particles are 1000 mesh aluminum oxide abrasive particles with a concentration of 30%; the base liquid is H 2 O 2 The solution is mixed with the magnetorheological fluid in a ratio of 1:4, wherein the H 2 O 2 The concentration is 20%, the magnetorheological fluid includes a water base, magnetically sensitive particles and a stabilizer, and the surface of the magnetically sensitive particles is coated with epoxy resin (in this embodiment, the magnetically sensitive particles are ferroferric oxide, which is easily corroded in the acidic environment generated by hydrogen peroxide, so the magnetically sensitive particles need to be coated first to isolate them from the acidic environment).

[0041] S2, start the drive motor to drive the vacuum chuck to rotate, so as to drive the GaN to rotate, the speed is 300 rpm; at the same time, start the ultrasonic transducer 3; at this time, the magnetic sensitive particles in the magnetorheological polishing liquid will generate magnetic buoyancy under the magnetic effect of the front cover plate 33 of the ultrasonic transducer, and the non-magnetic aluminum oxide abrasive particles will impact the GaN surface under the cavitation effect of the ultrasonic transducer 3 (impact speed is 60m / s); the ultrasonic cavitation effect adds hydroxyl groups to Al atoms and Ga atoms in the OH- environment to form a bond bridge Al-O-Ga-N; the bond bridge will break under the shear stress of the magnetic fluid to form Al-O-Ga-OH and Al-O-Ga-H (see Figure 5 ), its strength is much lower than that of GaN; while the strength of alumina is lower than that of GaN, but higher than that of the mechanochemical products Al-O-Ga-OH and Al-O-Ga-H. Therefore, during each polishing, alumina only removes the mechanochemical products (to achieve polishing of the workpiece surface) without damaging GaN, thereby avoiding residual stress on the surface of the GaN workpiece.

[0042] Among them, the influence of polishing time on the surface roughness of GaN workpiece is as follows: Figure 6 As shown; the longer the polishing time, the lower the surface roughness, and as the polishing time increases, the decreasing trend of the surface roughness tends to be gentle; in this embodiment, the surface roughness of the GaN workpiece with an initial roughness of 10nm is polished for 60min, and the surface roughness of the GaN workpiece reaches 1.047nm.

[0043] In order to verify that the polishing method of the present application has higher material removal efficiency and processing uniformity, the applicant used a traditional chemical mechanical polishing method to polish GaN with an initial roughness of 10 nm as a comparison.

[0044] Among them, in the traditional chemical mechanical polishing method, the polishing liquid includes H 2 O 2 solution and 1000 mesh aluminum oxide abrasive; polishing was performed at a pressure of 12×10 4 Pa, polishing disc speed is 100 r / min, H 2 O 2 The polishing is carried out under the conditions of a hydrogen peroxide concentration of 20% and an aluminum oxide abrasive concentration of 30%; the polishing principle is: in a hydrogen peroxide environment, the aluminum oxide abrasive reacts chemically with the GaN surface to soften the high-hardness GaN and generate reactants; then, the aluminum oxide abrasive removes the reactants under the pressure of the polishing pad to achieve polishing.

[0045] Then, the surface roughness of GaN was 1.166nm after 1h of polishing using the conventional chemical mechanical polishing method (see Figure 7 a), while after polishing for 1 h using the polishing method of the present application, the surface roughness of GaN is 1.047 nm (see Figure 7 b); It can be seen that the material removal rate of the polishing method of the present application is better; In addition, from Figure 7 It can be seen that the surface of the GaN workpiece polished by the chemical mechanical polishing method still has the deeper scratches before polishing, while the surface consistency of the GaN workpiece polished by the polishing method of the present application is higher; this proves that when the workpiece is polished by the polishing method of the present invention, the efficiency is higher and the quality is better.

[0046] The above general description of the invention involved in this application and the description of its specific implementation methods should not be understood as limiting the technical solutions of the invention. Based on the disclosure of this application, those skilled in the art can, without violating the constituent elements of the invention involved, add, reduce or combine the disclosed technical features in the above general description or / and specific implementation methods (including examples) to form other technical solutions within the scope of protection of this application.

Claims

1. Ultrasonic cavitation magnetorheological mechanical polishing device, characterized in that: The invention comprises an operating table (1); a polishing groove (101) is provided on the top of the operating table (1) for containing magnetorheological polishing liquid; a clamping drive mechanism (2) is provided in the polishing groove (101) for clamping a workpiece to be polished and driving the workpiece to rotate; an ultrasonic transducer (3) is provided inside the polishing groove (101) and located above the clamping drive mechanism (2); the ultrasonic transducer (3) comprises a rear cover plate (31), a piezoelectric ceramic sheet (32) and a front cover plate (33) which are arranged in sequence; the rear cover plate (31) and the front cover plate (33) are locked by means of pre-tightening bolts; the front cover plate (33) is made of magnetic material and faces the clamping drive mechanism (2); the clamping drive mechanism (2) and the ultrasonic transducer (3) are respectively electrically connected to a controller.

2. The ultrasonic cavitation magnetorheological mechanical polishing device according to claim 1, characterized in that: A polishing liquid delivery pipe (4) is also provided above the clamping drive mechanism (2); the polishing liquid delivery pipe (4) is connected to a polishing liquid supply system.

3. The ultrasonic cavitation magnetorheological mechanical polishing device according to claim 1, characterized in that: The clamping drive mechanism (2) comprises a vacuum suction cup; a group of ventilation grooves are provided on the vacuum suction cup along the circumference, and a rotating shaft connected to the driving motor is provided at the bottom of the vacuum suction cup; an air suction port is also provided on the vacuum suction cup, and a rotary joint is provided at the air suction port; the rotary joint is connected to the vacuum pump via a vacuum pipeline.

4. The ultrasonic cavitation magnetorheological mechanical polishing device according to claim 1, characterized in that: The radiation surface of the front cover plate (33) is an arc-shaped surface, and the radius of curvature of the radiation surface is 75-85 mm.

5. The ultrasonic cavitation magnetorheological mechanical polishing device according to claim 1, characterized in that: The ultrasonic transducer (3) is clamped and fixed by a clamp (5); the clamp (5) is fixed to the bottom of the polishing groove (101).

6. The ultrasonic cavitation magnetorheological mechanical polishing device according to claim 1, characterized in that: The piezoelectric ceramic piece (32) is a PZT-4 annular piezoelectric ceramic piece.

7. The ultrasonic cavitation magnetorheological mechanical polishing device according to claim 2, characterized in that: The polishing liquid supply system and the controller are integrated into the operating table (1). 8.GaN efficient polishing method, characterized in that: The method uses the ultrasonic cavitation magnetorheological mechanical polishing device described in claim 3 to polish GaN; the specific steps are as follows: S1, placing the GaN to be processed on a vacuum chuck, and starting a vacuum pump to adsorb the GaN; then, feeding a magnetorheological polishing liquid into a polishing tank (101) through a polishing liquid delivery pipe (4); the magnetorheological polishing liquid comprises an H2O2 solution, a magnetorheological fluid and abrasive particles, and the magnetorheological fluid comprises a water base, magnetically sensitive particles and a stabilizer; and the abrasive particles are aluminum oxide; S2, start the driving motor to drive the vacuum suction cup to rotate, so as to drive the GaN to rotate; at the same time, start the ultrasonic transducer (3); at this time, the magnetic sensitive particles in the magnetorheological polishing liquid will generate magnetic buoyancy under the magnetic effect of the front cover plate (33) of the ultrasonic transducer, and the non-magnetic aluminum oxide abrasive particles will impact the GaN surface under the cavitation effect of the ultrasonic transducer (3), causing a chemical mechanical reaction, thereby achieving polishing of the GaN.

9. The GaN efficient polishing method according to claim 8, characterized in that: The surface of the magnetically sensitive particles is coated with epoxy resin; the concentration of H2O2 is 20% to 30%.

10. The GaN efficient polishing method according to claim 8, characterized in that: In the step S2, the rotation speed of the vacuum chuck is 300 rpm; the aluminum oxide abrasive particles impact the GaN surface at a speed of 60 m / s.

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