A two-step zeta potential-controlled chemical mechanical polishing method for polycrystalline diamond

Abstract

This invention provides a two-step zeta potential-controlled chemical mechanical polishing (CMP) method for polycrystalline diamond, relating to the field of ultra-precision machining of superhard materials. The method includes mechanical polishing, rough polishing with zeta potential control during CMP, fine polishing with zeta potential control during CMP, and cleaning, ultimately yielding polycrystalline diamond with a low-damage, high-quality surface. By controlling the zeta potential of the polishing slurry during the rough and fine polishing processes, this invention can reduce the mechanical damage to the polycrystalline diamond caused by the abrasive in the polishing slurry and improve the surface quality of the polished polycrystalline diamond, thereby achieving low-damage, high-quality machining of polycrystalline diamond.

Description

Technical Field

[0001] This invention relates to the field of ultra-precision machining technology for superhard materials, and in particular to a chemical mechanical polishing method for polycrystalline diamond based on two-step zeta potential control. Background Technology

[0002] Diamond, with its excellent optical, mechanical, and thermal properties, is of great significance for the development of optical windows / radomes, heat dissipation substrates for high-power devices such as TR components and lasers used in airborne, missile-borne, and shipborne infrared search and tracking systems, as well as tool coatings in cutting and machining. However, the high brittleness, high hardness, and chemical stability of diamond greatly increase the difficulty of subsequent processing, especially for large-size polycrystalline diamond wafers, where the complex polycrystalline orientation characteristics make surface processing control even more difficult. The stress, deformation, and subsurface damage defects that occur during diamond processing are also problems that urgently need to be solved. Currently, ultra-precision machining of large-size diamonds has become a bottleneck in many diamond application fields, and breakthroughs must be made to overcome this key obstacle hindering the application of diamond materials.

[0003] To address the ultra-precision machining of diamond, researchers have employed methods such as laser polishing, ion beam polishing, and plasma-assisted polishing, which are based on direct or assisted polishing using energy beams. However, these novel ultra-precision machining methods suffer from high costs, small sample sizes, and complex operations. Currently, chemical mechanical polishing (CMP) remains the most effective technique for ultra-precision diamond polishing. During CMP, polishing process parameters, the composition and ratio of the polishing slurry, and the type of polishing pad all significantly influence the surface quality. Existing technologies disclose polishing slurries for single-crystal diamond CMP and their preparation methods. These slurries possess high oxidation capacity and removal rates, achieving high-quality and efficient diamond machining. Existing technologies also disclose a double-sided CMP method for single-crystal diamond wafers. By preparing a polishing slurry with environmentally friendly reagents such as ursolic acid, iodine, and kerosene as main components, coarse and fine polishing of single-crystal diamond wafers is performed, solving the problems of numerous scratches and large damage layers inherent in traditional mechanical grinding. Both of these methods achieve high-quality diamond machining by improving the composition of the polishing slurry, but they cannot control or completely remove surface damage during the polishing process. Therefore, it is necessary to propose a new chemical mechanical polishing method to obtain high-quality polycrystalline diamond with low / no damage. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention provides the following technical solution:

[0005] A two-step zeta potential-controlled chemical mechanical polishing method for polycrystalline diamond includes:

[0006] Step S1: Mechanical polishing

[0007] The polycrystalline diamond film is fixed on a quartz plate. First, a diamond liquid with a particle size of 10-20μm is prepared for rough polishing, and then a diamond liquid with a particle size of 1-5μm is used for fine polishing.

[0008] Step S2, coarse polishing with zeta potential control

[0009] Prepare polishing slurry A and adjust its zeta potential so that the difference between its zeta potential and that of the polycrystalline diamond film is within the range of -80 to -110 mV (i.e., the zeta potential of the diamond film minus the zeta potential of polishing slurry A). Place the mechanically polished polycrystalline diamond film on a polyurethane polishing pad for polishing. By controlling a larger potential difference, the hard abrasive and the surface of the diamond film can be repelled, thereby reducing the damage of the hard abrasive to the surface of the diamond film.

[0010] Step S3: Fine polishing with zeta potential control

[0011] Prepare polishing slurry B and adjust its zeta potential so that the difference between its zeta potential and that of the polycrystalline diamond film is within the range of -5 to -30 mV (i.e., the zeta potential of the diamond film minus the zeta potential of polishing slurry B). Place the coarsely polished polycrystalline diamond film on a velvet polishing pad and continue fine polishing the polycrystalline diamond film. By controlling a small potential difference, the repulsion between the soft abrasive and the diamond film surface can be reduced, thereby enhancing the polishing effect of the soft abrasive on the diamond film surface.

[0012] Step S4, Cleaning

[0013] The polished polycrystalline diamond film was cleaned sequentially with acetone, alcohol, and deionized water.

[0014] In step S2, the larger zeta potential difference between polishing slurry A and the polycrystalline diamond film is to ensure a greater electrostatic repulsion between them, reducing the damage to the polycrystalline diamond film surface caused by the hard abrasives in polishing slurry A. In step S3, the smaller zeta potential difference between polishing slurry B and the polycrystalline diamond film is to ensure a smaller electrostatic repulsion between them, increasing the polishing effect of the soft abrasives in polishing slurry B on the polycrystalline diamond film surface, resulting in a polycrystalline diamond film with better surface quality.

[0015] Preferably, the polishing disc used for mechanical polishing in step S1 is a cast iron disc, and the rotation speed of the cast iron disc is 30-200 r / min, the load pressure is 0.5-3 MPa, and the grinding time is 30-120 min during rough polishing and fine polishing.

[0016] Preferably, in step S2, the polishing fluid A comprises K2FeO4, H2O2, CH3COOH, single-crystal diamond powder (abrasive), and deionized water, wherein the K2FeO4 content is 30-50 g / L, the H2O2 content is 20-60 g / L, the CH3COOH content is 15-30 g / L, and the single-crystal diamond powder has a particle size of 50-100 nm and a content of 70-100 g / L.

[0017] Preferably, in step S2, the zeta potential of polishing solution A is adjusted by changing the pH value of polishing solution A. The pH value of polishing solution A is adjusted by NaOH and / or HCl solution. The pH value of polishing solution A is 4-9, and the corresponding zeta potential value of polishing solution A is -15 to -40 mV. The DLS particle size distribution of single crystal diamond in polishing solution is 150-200 nm (diamond powder will agglomerate in solution), and the zeta potential value of diamond film surface is -5 to -150 mV.

[0018] Preferably, in step S2, the polishing disc rotation speed is 50-200 r / min, the polishing pressure is 100-800 kPa, the polishing fluid flow rate is 2-10 ml / min, and the polishing time is 40-180 min.

[0019] Preferably, in step S3, the polishing solution B comprises SiO2 (abrasive), sodium methylene bis(naphthalene) sulfonate, polyethylene glycol, and deionized water, wherein the SiO2 powder has a particle size of 10-60 nm and a content of 20-40 g / L, the sodium methylene bis(naphthalene) sulfonate content is 1-5 g / L, and the polyethylene glycol content is 30-60 g / L. The compositions of polishing solutions A and B in this invention are specifically designed to suit the polishing system of this invention, particularly for polishing with hard and soft abrasives respectively, and can further improve the polishing effect of this invention.

[0020] Preferably, in step S3, the zeta potential of polishing solution B is adjusted by changing the pH value of polishing solution B. The pH value of polishing solution B is adjusted using NaOH and / or HCl solution, and the pH value of polishing solution B is 2-10. The corresponding zeta potential value of polishing solution A is 0 to -50 mV, the DLS particle size distribution of SiO2 in the polishing solution is 40-100 nm (SiO2 will agglomerate in the solution), and the zeta potential value of the diamond film surface is -5 to -150 mV. In this invention, the process conditions of steps S2 and S3 were selected by comprehensively considering cost and polishing effect.

[0021] Preferably, in step S3, the polishing disc rotation speed is 30-100 r / min, the polishing pressure is 50-300 kPa, the polishing fluid flow rate is 2-10 ml / min, and the polishing time is 30-120 min.

[0022] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0023] This invention is the first to apply zeta potential control to the polishing of diamond films. In the chemical mechanical polishing (CMP) process, polycrystalline diamond films have a large negative zeta potential, which leads to electrostatic attraction between the polycrystalline diamond film and the abrasive in a liquid environment. In the zeta potential-controlled rough polishing process, the diamond abrasive in polishing solution A, with a negative zeta potential, has the same zeta potential sign as the polycrystalline diamond film. By adjusting the zeta potential, a larger electrostatic repulsion can be achieved between them, reducing mechanical damage to the polycrystalline diamond film from the diamond abrasive, thus achieving low-damage, high-efficiency processing with superhard abrasives. In the zeta potential-controlled fine polishing process, although the SiO2 abrasive in polishing solution B has the same zeta potential sign as the polycrystalline diamond film, adjusting the zeta potential can achieve a smaller electrostatic repulsion between them, enhancing the adsorption behavior of the SiO2 abrasive and strengthening the mechanical energy field effect, thus achieving high-quality processing with soft abrasives. In summary, the two-step zeta potential-controlled polycrystalline diamond CMP process can achieve low-damage, high-efficiency, and high-quality processing of polycrystalline diamond films. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a process flow diagram of the present invention;

[0026] Figure 2(a) shows the surface morphology of the polycrystalline diamond film after mechanical polishing in the comparative example;

[0027] Figure 2(b) shows the surface morphology of the polycrystalline diamond film after chemical mechanical polishing in Example 2;

[0028] Figure 2(c) shows the surface contour of the polished samples in the comparative example and Example 2;

[0029] Figure 3 This is a SEM image of the surface of the polycrystalline diamond film after chemical mechanical polishing in Example 2. Detailed Implementation

[0030] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0031] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0032] In this embodiment of the invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent. Similarly, the terms "of," "corresponding," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent.

[0033] In this embodiment of the invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0034] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] A two-step zeta potential-controlled chemical mechanical polishing method for polycrystalline diamond, the specific process of which is as follows: Figure 1 As shown, it includes the following steps:

[0037] S1 Mechanical Polishing: The polycrystalline diamond film is fixed onto a quartz plate with paraffin wax and placed in a fixture. A cast iron disc is used as the polishing disc. First, a diamond liquid with a particle size of 10μm is prepared for rough polishing. During rough polishing, the rotation speed of the cast iron disc is 200r / min, the load pressure is 2MPa, and the polishing time is 120min. Then, a diamond liquid with a particle size of 2μm is used for fine polishing. During fine polishing, the rotation speed of the cast iron disc is 100r / min, the load pressure is 1MPa, and the polishing time is 60min.

[0038] S2 zeta potential controlled coarse polishing: Prepare polishing solution A, place the mechanically polished polycrystalline diamond film on a polyurethane polishing pad for polishing. Polishing solution A contains 30 g / L K2FeO4, 20 g / L H2O2, and 15 g / L CH3COOH. The single-crystal diamond powder has a particle size of 50 nm and a content of 70 g / L. The zeta potential of polishing solution A is adjusted by changing the pH value of the solution. The pH value of polishing solution A is 6, and the corresponding zeta potential value of polishing solution A is -20 mV. The DLS particle size distribution of the single-crystal diamond in the polishing solution is 174 nm. The zeta potential value range of the diamond film surface is -100 mV. The polishing disc rotation speed is 150 r / min, the polishing pressure is 600 kPa, the polishing solution flow rate is 5 ml / min, and the polishing time is 100 min.

[0039] S3 Zeta Potential Controlled Fine Polishing: Prepare polishing solution B, replace the polyurethane polishing pad used in coarse polishing with a cloth polishing pad, and continue fine polishing of the polycrystalline diamond film. The particle size of SiO2 powder in polishing solution B is 30nm and the content is 20g / L, the content of sodium methylene bis(naphthalene) sulfonate is 1g / L, and the content of polyethylene glycol is 30g / L. The zeta potential value of polishing solution B is adjusted by changing the pH value of the solution. The pH value of polishing solution B is 3, and the corresponding zeta potential value of polishing solution B is 0mV. The DLS particle size distribution of SiO2 in the polishing solution is 45nm, the zeta potential value of the diamond film surface is -5mV, the polishing disc speed is 50r / min, the polishing pressure is 100kPa, the polishing solution flow rate is 5ml / min, and the polishing time is 60min.

[0040] S4 Cleaning: Clean the polished polycrystalline diamond film sequentially with acetone, alcohol, and deionized water.

[0041] Example 2

[0042] A two-step zeta potential-controlled chemical mechanical polishing method for polycrystalline diamond includes the following steps:

[0043] S1 Mechanical Polishing: The polycrystalline diamond film is fixed onto a quartz plate with paraffin wax and placed in a fixture. A cast iron disc is used as the polishing disc. First, a diamond liquid with a particle size of 15μm is prepared for rough polishing. During rough polishing, the cast iron disc rotates at 200 r / min, the load pressure is 2.5 MPa, and the polishing time is 120 min. Then, a diamond liquid with a particle size of 1μm is used for fine polishing. During fine polishing, the cast iron disc rotates at 50 r / min, the load pressure is 1 MPa, and the polishing time is 60 min.

[0044] S2 zeta potential controlled coarse polishing: Prepare polishing solution A, place the mechanically polished polycrystalline diamond film on a polyurethane polishing pad for polishing. Polishing solution A contains 40 g / L K2FeO4, 40 g / L H2O2, and 20 g / L CH3COOH. The single-crystal diamond powder has a particle size of 70 nm and a content of 80 g / L. The zeta potential of polishing solution A is adjusted by changing the pH value of the solution. The pH value of polishing solution A is 8, and the corresponding zeta potential value of polishing solution A is -30 mV. The DLS particle size distribution of single-crystal diamond in the polishing solution is 170 nm. The zeta potential value range of the diamond film surface is -120 mV. The polishing disc rotation speed is 180 r / min, the polishing pressure is 700 kPa, the polishing solution flow rate is 6 ml / min, and the polishing time is 150 min.

[0045] S3 Zeta Potential Controlled Fine Polishing: Prepare polishing solution B, replace the polyurethane polishing pad used in coarse polishing with a cloth polishing pad, and continue fine polishing of the polycrystalline diamond film. The particle size of SiO2 powder in polishing solution B is 50nm and the content is 30g / L, the content of sodium methylene bis(naphthalene) sulfonate is 1g / L, and the content of polyethylene glycol is 40g / L. The zeta potential value of polishing solution B is adjusted by changing the pH value of the solution. The pH value of polishing solution B is 4, and the corresponding zeta potential value of polishing solution B is -15mV. The DLS particle size distribution of SiO2 in the polishing solution is 42nm, the zeta potential value of the diamond film surface is -20mV, the polishing disc speed is 70r / min, the polishing pressure is 200kPa, the polishing solution flow rate is 6ml / min, and the polishing time is 60min.

[0046] S4 Cleaning: Clean the polished polycrystalline diamond film sequentially with acetone, alcohol, and deionized water.

[0047] From Figure 2(a), Figure 2(b), Figure 2(c) and Figure 3 It can be seen that the surface roughness of the diamond film polished by the polishing method of the present invention is significantly better than that of the diamond film polished by mechanical polishing.

[0048] Example 3

[0049] A two-step zeta potential-controlled chemical mechanical polishing method for polycrystalline diamond includes the following steps:

[0050] S1 Mechanical Polishing: The polycrystalline diamond film is fixed onto a quartz plate with paraffin wax and placed in a fixture. A cast iron disc is used as the polishing disc. First, a diamond liquid with a particle size of 20μm is prepared for rough polishing. During rough polishing, the rotation speed of the cast iron disc is 200r / min, the load pressure is 3MPa, and the polishing time is 120min. Then, a diamond liquid with a particle size of 1μm is used for fine polishing. During fine polishing, the rotation speed of the cast iron disc is 50r / min, the load pressure is 2MPa, and the polishing time is 60min.

[0051] S2 zeta potential controlled coarse polishing: Prepare polishing solution A, place the mechanically polished polycrystalline diamond film on a polyurethane polishing pad for polishing. Polishing solution A contains 50 g / L K2FeO4, 60 g / L H2O2, and 30 g / L CH3COOH. The single-crystal diamond powder has a particle size of 80 nm and a content of 100 g / L. The zeta potential of polishing solution A is adjusted by changing the pH value of the solution. The pH value of polishing solution A is 9, and the corresponding zeta potential value of polishing solution A is -20 mV. The DLS particle size distribution of single-crystal diamond in the polishing solution is 180 nm. The zeta potential value range of the diamond film surface is -130 mV. The polishing disc rotation speed is 200 r / min, the polishing pressure is 800 kPa, the polishing solution flow rate is 8 ml / min, and the polishing time is 150 min.

[0052] S3 Zeta Potential Controlled Fine Polishing: Prepare polishing solution B, replace the polyurethane polishing pad used in coarse polishing with a cloth polishing pad, and continue fine polishing of the polycrystalline diamond film. The particle size of SiO2 powder in polishing solution B is 60nm and the content is 40g / L, the content of sodium methylene bis(naphthalene)sulfonate is 1g / L, and the content of polyethylene glycol is 50g / L. The zeta potential value of polishing solution B is adjusted by changing the pH value of the solution. The pH value of polishing solution B is 5, and the corresponding zeta potential value of polishing solution B is -55mV. The DLS particle size distribution of SiO2 in the polishing solution is 50nm, the zeta potential value of the diamond film surface is -75mV, the polishing disc speed is 90r / min, the polishing pressure is 300kPa, the polishing solution flow rate is 7ml / min, and the polishing time is 60min.

[0053] S4 Cleaning: Clean the polished polycrystalline diamond film sequentially with acetone, alcohol, and deionized water.

[0054] Comparative Example 1

[0055] The polycrystalline diamond film was fixed onto a quartz plate using paraffin wax and placed in a fixture. A cast iron disc was used as the polishing disc. First, a diamond solution with a particle size of 15 μm was prepared for rough polishing. During rough polishing, the cast iron disc rotated at 200 r / min, the load pressure was 2.5 MPa, and the polishing time was 120 min. Then, a diamond solution with a particle size of 1 μm was used for fine polishing. During fine polishing, the cast iron disc rotated at 50 r / min, the load pressure was 1 MPa, and the polishing time was 60 min.

[0056] Comparative Example 2

[0057] A two-step zeta potential-controlled chemical mechanical polishing method for polycrystalline diamond includes the following steps:

[0058] S1 Mechanical Polishing: The polycrystalline diamond film is fixed onto a quartz plate with paraffin wax and placed in a fixture. A cast iron disc is used as the polishing disc. First, a diamond liquid with a particle size of 15μm is prepared for rough polishing. During rough polishing, the cast iron disc rotates at 200 r / min, the load pressure is 2.5 MPa, and the polishing time is 120 min. Then, a diamond liquid with a particle size of 1μm is used for fine polishing. During fine polishing, the cast iron disc rotates at 50 r / min, the load pressure is 1 MPa, and the polishing time is 60 min.

[0059] S2 zeta potential controlled coarse polishing: Prepare polishing solution A, place the mechanically polished polycrystalline diamond film on a polyurethane polishing pad for polishing. Polishing solution A contains 40 g / L K2FeO4, 40 g / L H2O2, and 20 g / L CH3COOH. The single-crystal diamond powder has a particle size of 70 nm and a content of 80 g / L. The zeta potential of polishing solution A is adjusted by changing the pH value of the solution. The pH value of polishing solution A is 8, and the corresponding zeta potential value of polishing solution A is -30 mV. The DLS particle size distribution of single-crystal diamond in the polishing solution is 170 nm. The zeta potential value range of the diamond film surface is -120 mV. The polishing disc rotation speed is 180 r / min, the polishing pressure is 700 kPa, the polishing solution flow rate is 6 ml / min, and the polishing time is 150 min.

[0060] S3 Cleaning: Clean the polished polycrystalline diamond film sequentially with acetone, alcohol, and deionized water.

[0061] Performance testing:

[0062] The roughness of the polycrystalline diamond films obtained by polishing in Examples 1-3 and the comparative example was tested, and compared with...

[0063] The specific results regarding polishing quality are shown in Table 1:

[0064] Table 1

[0065]

[0066] Results Analysis: Comparative examples and comparative examples show that the present invention achieves a surface roughness Ra of 0.56 nm for the polycrystalline diamond film by first mechanically polishing it and then performing a two-step zeta potential-controlled chemical mechanical polishing, thus obtaining a polycrystalline diamond film with a high-quality surface. Furthermore, if the zeta potential is not within the range defined by the present invention, it is impossible to obtain the polycrystalline diamond film with the high-quality surface of the present invention.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A two-step zeta potential-controlled chemical mechanical polishing method for polycrystalline diamond, characterized in that, include: Step S1, Mechanical polishing The polycrystalline diamond film is fixed on a quartz plate. First, a diamond liquid with a particle size of 10-20μm is prepared for rough polishing, and then a diamond liquid with a particle size of 1-5μm is used for fine polishing. Step S2, coarse polishing with zeta potential control Prepare polishing slurry A containing hard abrasive and adjust the zeta potential of polishing slurry A so that the difference between its zeta potential and that of the polycrystalline diamond film is in the range of -80 to -110 mV. Place the mechanically polished polycrystalline diamond film on a polyurethane polishing pad for polishing. Step S3: Fine polishing with zeta potential control Prepare polishing slurry B containing soft abrasive and adjust the zeta potential of polishing slurry B so that the difference between its zeta potential and that of the polycrystalline diamond film is in the range of -5 to -30mV. Place the coarsely polished polycrystalline diamond film on a velvet polishing pad and continue to finely polish the polycrystalline diamond film. Step S4, Cleaning The polished polycrystalline diamond film was cleaned sequentially with acetone, alcohol, and deionized water. In step S2, the polishing slurry A comprises K2FeO4, H2O2, CH3COOH, single-crystal diamond powder, and deionized water, wherein the K2FeO4 content is 30-50 g / L, the H2O2 content is 20-60 g / L, the CH3COOH content is 15-30 g / L, and the single-crystal diamond powder has a particle size of 50-100 nm and a content of 70-100 g / L. In step S3, the polishing solution B consists of SiO2, sodium methylene bis(naphthalene) sulfonate, polyethylene glycol, and deionized water. The SiO2 powder has a particle size of 10-60 nm and a content of 20-40 g / L, the sodium methylene bis(naphthalene) sulfonate content is 1-5 g / L, and the polyethylene glycol content is 30-60 g / L.

2. The method according to claim 1, characterized in that, In step S1, the polishing disc used for mechanical polishing is a cast iron disc. During rough polishing and fine polishing, the rotation speed of the cast iron disc is 30-200 r / min, the load pressure is 0.5-3 MPa, and the grinding time is 30-120 min.

3. The method according to claim 1, characterized in that, In step S2, the zeta potential of polishing solution A is adjusted by changing the pH value of polishing solution A. The pH value of polishing solution A is adjusted by NaOH and / or HCl solution. The pH value of polishing solution A is 4-9, and the corresponding zeta potential value of polishing solution A is -15 to -40mV. The DLS particle size distribution of single crystal diamond in polishing solution is 150-200nm, and the zeta potential value of diamond surface is -5 to -150mV.

4. The method according to claim 1, characterized in that, In step S2, the polishing disc rotation speed is 50-200 r / min, the polishing pressure is 100-800 kPa, the polishing fluid flow rate is 2-10 ml / min, and the polishing time is 40-180 min.

5. The method according to claim 1, characterized in that, In step S3, the zeta potential of polishing solution B is adjusted by changing the pH value of polishing solution B. The pH value of polishing solution B is adjusted by NaOH and / or HCl solution. The pH value of polishing solution B is 2-10, and the corresponding zeta potential value of polishing solution B is 0~-50mV. The DLS particle size distribution of SiO2 in polishing solution is 40-100nm, and the zeta potential value of diamond film surface is -5~-150mV.

6. The method according to claim 1, characterized in that, In step S3, the polishing disc rotation speed is 30-100 r / min, the polishing pressure is 50-300 kPa, the polishing fluid flow rate is 2-10 ml / min, and the polishing time is 30-120 min.

7. A low-damage, high-quality surface polycrystalline diamond prepared by a two-step zeta potential-controlled chemical mechanical polishing method for polycrystalline diamond according to any one of claims 1-6.

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