A method and device for plasma polishing a workpiece

Abstract

The present invention relates to the technical field of plasma polishing, and more specifically, to a method and apparatus for plasma polishing a workpiece. The method for plasma polishing a workpiece includes the following steps: placing the workpiece to be polished on a workpiece holder in a polishing vacuum chamber, and evacuating the polishing vacuum chamber; introducing an inert gas into the vacuum chamber until the air pressure in the vacuum chamber reaches a set value; performing plasma heating on the workpiece to be polished; after completing the plasma heating, introducing a fluorine-containing gas into the vacuum chamber until the air pressure in the vacuum chamber reaches a set value; turning on the ion source and energizing the grid to immerse the workpiece to be polished in the plasma for polishing; turning off the ion source and simultaneously de-energizing the grid, thereby completing the polishing of the workpiece; through the effective cooperation of the ion source, high-frequency electric field, electromagnetic field, and grid, effective control of the plasma is achieved, and immersion polishing is realized; the present invention can achieve plasma conformal shaping of the workpiece and realize polishing of complex-shaped surfaces and flat surfaces.

Description

Technical Field

[0001] The present invention relates to the technical field of plasma polishing, and more specifically, to a method and device for plasma polishing workpieces. Background Art

[0002] Polishing is a fine processing technology for the surface of materials. In order to achieve a smooth surface of the workpiece to meet the actual industrial production requirements, contact and non-contact polishing technologies are often used to remove materials on the surface. Simple mechanical polishing and numerical control grinding and polishing are mostly contact polishing technologies, which are likely to cause surface and subsurface damage to the material, and it is difficult to achieve a nanoscale smooth surface. The processing efficiency is low, the accuracy is insufficient, and the quality is difficult to control. In order to further improve the polishing quality and the refinement degree of polishing, people have developed non-contact polishing technologies, such as magnetorheological polishing technology, ion beam polishing technology, etc., which can achieve nanoscale and sub-nanoscale roughness surfaces. Magnetorheological polishing is not suitable for processing concave surfaces and surfaces with complex shapes. The ion beam polishing technology can only achieve further fine processing on the basis of pre-stage polishing, and the processing efficiency is extremely low. It cannot effectively remove the surface and subsurface damage in the pre-stage polishing, affecting the performance of the polished surface.

[0003] Plasma polishing is to introduce fluorine-containing gas during the ion beam polishing process. The fluorine-containing active particle groups react with the substances on the workpiece surface to generate gaseous reactants, realizing the removal of materials. The plasma polishing process has the property of isotropic etching, which can effectively eliminate microcracks and pits on the material surface and achieve surface flattening.

[0004] There is a kind of existing plasma polishing equipment, including a plasma generating device, a magnetic field device, a high-energy charged ion confinement cavity, and a processing and polishing vacuum cavity. The magnetic field generated by the magnetic field device confines and isolates the high-energy charged ions generated by the plasma generating device in the high-energy charged ion confinement cavity outside the polishing area in the processing and polishing vacuum cavity. The free radical plasma active groups generated by the plasma generating device enter the polishing area in the processing and polishing vacuum cavity to achieve polishing.

[0005] The above-mentioned existing plasma polishing equipment will release a large amount of heat during the processing, causing its temperature to rise rapidly when processing hard and brittle materials, and at the same time, it will also affect the roughness of the polished surface. Moreover, the above-mentioned existing plasma polishing equipment can only polish workpieces in a small area in the vacuum chamber, and it is difficult to efficiently process workpieces with a large surface area. Summary of the Invention

[0006] The present invention aims to overcome the problems that the polishing effect of the above-mentioned existing plasma polishing method is poor and it is difficult to perform plasma polishing on workpieces with a large surface area, and provides a method and device for plasma polishing workpieces.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for plasma polishing a workpiece, comprising the following steps:

[0009] S1. Place the workpiece to be polished on a rotating rack in a polishing vacuum chamber, and evacuate the polishing vacuum chamber until the vacuum degree in the polishing vacuum chamber reaches a set value;

[0010] S2. Introduce an inert gas into the polishing vacuum chamber until the air pressure in the vacuum chamber reaches a set value P1;

[0011] S3. Connect the rotating rack to a negative bias voltage to excite plasma and perform plasma heating on the workpiece to be polished, and the heating time is T1;

[0012] S4. After completing the plasma heating, introduce a fluorine-containing gas into the polishing vacuum chamber until the air pressure in the polishing vacuum chamber reaches a set value P2;

[0013] S5. Turn on the ion source and energize the grid. The grid has a positive voltage to weaken the directionality of the plasma, and immerse the workpiece to be polished in the plasma for a time T2;

[0014] S6. Turn off the ion source and at the same time cut off the power supply to the grid. After the workpiece to be polished cools down, the polishing of the workpiece to be polished is completed.

[0015] The present invention realizes the immersion polishing of the workpiece to be polished through the setting of the ion source and the negative bias voltage. In step S2, an inert gas is used, and in step S4, a fluorine-containing gas is used to combine plasma polishing and plasma-assisted chemical polishing. The grid with a positive voltage attracts electrons and can weaken the directionality of the plasma, so that the plasma region evenly fills the entire vacuum cavity, and all surfaces of the workpiece placed in the polishing vacuum chamber can be polished, thereby realizing the processing of workpieces with a relatively large surface area.

[0016] Further, in the step S1, the vacuum degree in the polishing vacuum chamber is greater than or equal to 9×10 -3 Pa.

[0017] Further, in the step S2, the inert gas is argon, which is the most economical and efficient inert gas in the field of plasma processing.

[0018] Further, in the step S2, P1 is 0.5 to 2 Pa.

[0019] Further, the step S3 is as follows:

[0020] Turn on the DC pulsed bias power supply. The turntable is electrically connected to the DC pulsed bias power supply to perform plasma heating on the workpiece to be polished. The negative voltage ranges from 30 to 100 V, the frequency ranges from 80 to 350 KHz, the duty cycle ranges from 5 to 40%, and the heating time is T1, where T1 is 30 to 120 min.

[0021] Further, in the step S4, the fluorine-containing gas is a mixed gas of two or more of carbon tetrafluoride, nitrogen trifluoride, and sulfur hexafluoride; P2 is 0.5 to 5 Pa. The introduction of the fluorine-containing gas can achieve the polishing form of plasma-assisted chemical polishing.

[0022] Further, the step S5 is as follows:

[0023] Turn on the ion source. The negative bias voltage is maintained at 400 to 1200 V, the frequency is 80 to 350 KHz, and the duty cycle is 5 to 10%; energize the grid, and the positive voltage is 50 to 100 V; immerse the workpiece to be polished in the plasma for T2 time. By controlling the voltage for generating the plasma to be below 1000 V, the plasma energy is relatively low, and thus the thermal effect is weak, controlling the heat during the plasma polishing process, greatly reducing the heat released during the polishing process, and avoiding poor polishing effect of the workpiece to be polished due to excessive heat generated by the plasma. Further, the step S5 is as follows:

[0024] Turn on the ion source. The negative bias voltage is maintained at 400 to 1200 V, the frequency is 80 to 350 KHz, and the duty cycle is 5 to 10%; energize the grid, and the positive voltage is 50 to 100 V. Immerse the workpiece to be polished in the plasma for T2 time, and at the same time rotate the workpiece to be polished at a speed of 1 to 5 rpm.

[0025] Further, T2 is 30 to 240 min.

[0026] The present invention also provides a plasma polishing device, including a vacuum chamber, a turntable for placing the workpiece to be polished, an ion source, an electromagnetic coil, a vacuum pump, an anode, and a grid; the turntable is rotatably arranged in the vacuum chamber; the ion source is strip-shaped, the anode and the ion source are symmetrically arranged on the inner wall of the vacuum chamber with the turntable as the axis of symmetry, the electromagnetic coil is arranged at the outer top and outer bottom of the vacuum chamber, the grid is arranged around the turntable in the vacuum chamber, and the grid is located between the turntable and the anode and the ion source; the vacuum pump is communicated with the vacuum chamber.

[0027] The plasma polishing device of the present invention has a strip-shaped ion source, which helps to achieve immersion plasma polishing rather than focused ion beam polishing; the positively charged grid attracts electrons and can weaken the directionality of the plasma, making the plasma region evenly cover the entire vacuum chamber, so that all surfaces of the workpiece placed in the polishing vacuum chamber can be polished, thereby enabling the processing of workpieces with a larger surface area.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. Through the effective cooperation of the ion source, high-frequency electric field, electromagnetic field and grid, the device realizes the effective control of the plasma and achieves immersion polishing; different from the form of focused ion beam polishing, the present invention can achieve the conformal shaping of the plasma to the workpiece and polish complex-shaped surfaces and flat surfaces.

[0030] 2. By combining plasma polishing with plasma-assisted chemical polishing, the present invention can achieve better and more precise polishing effects.

[0031] 3. By controlling the voltage for generating the plasma to be below 1000V, the plasma energy is relatively low, resulting in a weaker thermal effect, controlling the heat during the plasma chemical polishing process, greatly reducing the heat released during the polishing process, and avoiding poor polishing effects caused by excessive heat generated by the plasma on the workpiece to be polished.

[0032] 4. The plasma region covers the entire vacuum chamber, so that all surfaces of the workpiece placed in the polishing vacuum chamber can be polished, and workpieces with a larger surface area can be polished. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the overall structure of an embodiment of the device for polishing a workpiece by plasma of the present invention.

[0034] Figure 2 It is a schematic diagram of the internal structure of an embodiment of the device for polishing a workpiece by plasma of the present invention;

[0035] Figure 3 It is a schematic diagram of the internal structure of another angle of an embodiment of the device for polishing a workpiece by plasma of the present invention;

[0036] Figure 4 It is an AFM topography map of the surface of the Si wafer in the polishing effect detection test of Example 1;

[0037] Figure 5 It is an AFM topography map of the surface of the Si wafer in the polishing effect detection test of Example 2;

[0038] Figure 6It is the AFM topography map of the Si wafer surface in the polishing effect detection test of Example 3;

[0039] Figure 7 It is the AFM topography map of the Si wafer surface in the polishing effect detection test of Comparative Example 1;

[0040] Figure 8 It is the AFM topography map of the Si wafer surface in the polishing effect detection test of Comparative Example 2;

[0041] Figure 9 It is the AFM topography map of the quartz wafer surface in the polishing effect detection test of Comparative Example 3.

[0042] In the attached drawings: 1. Polishing vacuum chamber; 2. Rotating frame; 3. Ion source; 4. Electromagnetic coil; 5. Vacuum pump; 6. Anode; 7. Grid; 8. Motor; 9. Workpiece. Detailed implementation manners

[0043] The attached drawings are only for illustrative purposes and cannot be construed as a limitation of this patent; for better illustration of this embodiment, some components in the attached drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the attached drawings may be omitted. The positional relationships described in the attached drawings are only for illustrative purposes and cannot be construed as a limitation of this patent.

[0044] In the attached drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "long", "short", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the attached drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the attached drawings are only for illustrative purposes and cannot be construed as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0045] The technical solutions of the present invention will be further specifically described below through specific embodiments and in combination with the attached drawings:

[0046] Example 1

[0047] Refer to Figures 1 to 3, which is Embodiment 1 of a device for plasma polishing workpieces according to the present invention, includes a polishing vacuum chamber 1, a turntable 2 for placing the workpiece 9 to be polished, an ion source 3, an electromagnetic coil 4, a vacuum pump 5, an anode 6 and a grid 7. The turntable 2 is rotatably arranged in the polishing vacuum chamber 1. A motor 8 is provided on the outer bottom wall of the polishing vacuum chamber 1. The output end of the motor 8 is welded to the bottom of the turntable 2. By starting the motor 8, the motor 8 can drive the turntable 2 to rotate. The ion source 3 is strip-shaped. The anode 6 and the ion source 3 are symmetrically arranged on the inner wall of the polishing vacuum chamber 1 with the turntable 2 as the axis of symmetry. The electromagnetic coil 4 is arranged on the outer top and outer bottom of the polishing vacuum chamber 1. The grid 7 is arranged around the turntable 2 in the polishing vacuum chamber 1, and the grid 7 is located between the turntable 2 and the anode 6 and the ion source 3. The vacuum pump 5 is connected to the polishing vacuum chamber 1.

[0048] The method for plasma polishing the workpiece 9 in this embodiment is as follows:

[0049] S1. Clamp the workpiece 9 on the turntable 2, and then use the vacuum pump 5 to evacuate the polishing vacuum chamber 1. The vacuum degree in the polishing vacuum chamber 1 is 5×10 -4 Pa;

[0050] S2. Introduce argon into the polishing vacuum chamber 1 until the air pressure in the polishing vacuum chamber 1 reaches 1 Pa;

[0051] S3. Turn on the DC pulse bias power supply to perform plasma heating on the workpiece 9 to be polished. The negative voltage is 80 V, the frequency is 300 KHz, the duty cycle is 20%, and the heating time is 80 min;

[0052] S4. After completing the plasma heating, introduce a mixed gas of carbon tetrafluoride, nitrogen trifluoride and sulfur hexafluoride into the vacuum chamber until the air pressure in the vacuum chamber reaches 3 Pa;

[0053] S5. Turn on the ion source 3, keep the negative bias voltage at 800 V, the frequency at 300 KHz, and the duty cycle at 8%; energize the grid 7, and the positive voltage is 80 V; immerse the workpiece 9 to be polished in the plasma for 180 min, and at the same time rotate the turntable 2 at a speed of 3 rpm;

[0054] S6. Turn off the ion source 3, and at the same time cut off the power supply of the grid 7. Wait for the workpiece 9 to cool to 25 °C, and the polishing of the workpiece 9 is completed.

[0055] In the polishing effect detection test of this embodiment, the AFM morphology diagram of the Si wafer surface is as Figure 4 shown.

[0056] Embodiment 2

[0057] The difference between this embodiment and Embodiment 1 lies in the method for plasma polishing the workpiece 9, which specifically includes the following steps:

[0058] S1. Place the workpiece 9 on the turntable 2, and then use the vacuum pump 5 to evacuate the polishing vacuum chamber 1. The vacuum degree in the polishing vacuum chamber 1 is 9×10 -3 Pa;

[0059] S2. Introduce argon gas into the polishing vacuum chamber 1 until the air pressure in the vacuum chamber reaches 0.5 Pa;

[0060] S3. Turn on the DC pulse bias power supply to perform plasma heating on the workpiece 9 to be polished. The negative voltage is 30 V, the frequency is 80 KHz, the duty cycle is 5%, and the heating time is 30 min;

[0061] S4. After the plasma heating is completed, introduce a mixed gas of nitrogen trifluoride and sulfur hexafluoride into the polishing vacuum chamber 1 until the air pressure in the vacuum chamber reaches 0.5 Pa;

[0062] S5. Turn on the ion source 3, keep the negative bias voltage at 400 V, the frequency at 80 KHz, and the duty cycle at 5%; energize the grid 7, and the positive voltage is 50 V; immerse the workpiece 9 to be polished in the plasma for 30 min, and at the same time rotate the turntable 2 at a speed of 1 rpm;

[0063] S6. Turn off the ion source 3, and at the same time cut off the power supply of the grid 7. Wait for the workpiece 9 to cool down to 25 °C, and the polishing of the workpiece 9 is completed.

[0064] In the polishing effect detection test of this embodiment, the AFM topography map of the Si wafer surface is as Figure 5 shown.

[0065] Example 3

[0066] The difference between this embodiment and Example 1 lies in the method of plasma polishing the workpiece 9, which specifically includes the following steps:

[0067] S1. Place the workpiece 9 on the turntable 2, and then use the vacuum pump 5 to evacuate the polishing vacuum chamber 1. The vacuum degree in the polishing vacuum chamber 1 is 1×10 -3 Pa;

[0068] S2. Introduce argon gas into the polishing vacuum chamber 1 until the air pressure in the vacuum chamber reaches 2 Pa;

[0069] S3. Turn on the DC pulse bias power supply to perform plasma heating on the workpiece 9 to be polished. The negative voltage is 100 V, the frequency is 350 KHz, the duty cycle is 40%, and the heating time is 120 min;

[0070] S4. After the plasma heating is completed, introduce a mixed gas of carbon tetrafluoride and nitrogen trifluoride into the polishing vacuum chamber 1 until the air pressure in the vacuum chamber reaches 5 Pa;

[0071] S5. Turn on the ion source 3, keep the negative bias voltage at 1200V, the frequency at 350KHz, and the duty cycle at 10%; energize the grid 7 with a positive voltage of 100V; immerse the workpiece 9 to be polished in the plasma for 240 min, and at the same time rotate the turntable 2 at a speed of 5 rpm;

[0072] S6. Turn off the ion source 3, and at the same time cut off the power supply to the grid 7. Wait for the workpiece 9 to cool down to 25°C, then the polishing of the workpiece 9 is completed.

[0073] In the polishing effect detection test of this embodiment, the AFM topography of the Si wafer surface is as Figure 6 shown.

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 1 lies in the method of plasma polishing the workpiece, which specifically includes the following steps:

[0076] S1. Place the workpiece on the turntable, and then use a vacuum pump to evacuate the polishing vacuum chamber. The vacuum degree in the polishing vacuum chamber is 10×10 p3 Pa;

[0077] S2. Introduce argon gas into the vacuum chamber until the air pressure in the polishing vacuum chamber reaches 1 Pa;

[0078] S3. Turn on the DC pulse bias power supply to heat the workpiece to be polished by plasma. The negative voltage is 80V, the frequency is 300KHz, the duty cycle is 30%, and the heating time is 80 min;

[0079] S4. After the plasma heating is completed, introduce a mixed gas of carbon tetrafluoride, nitrogen trifluoride and sulfur hexafluoride into the polishing vacuum chamber until the air pressure in the vacuum chamber reaches 3 Pa;

[0080] S5. Turn on the ion source, keep the negative bias voltage at 1200V, the frequency at 300KHz, and the duty cycle at 8%; energize the grid with a positive voltage of 200V; immerse the workpiece to be polished in the plasma for 180 min, and at the same time rotate the turntable at a speed of 3 rpm;

[0081] S6. Turn off the ion source, and at the same time cut off the power supply to the grid. Wait for the workpiece to cool down to 25°C, then the polishing of the workpiece is completed.

[0082] In the polishing effect detection test of this comparative example, the AFM topography of the Si wafer surface is as Figure 7 shown.

[0083] Comparative Example 2

[0084] The difference between this comparative example and Example 1 lies in the method of plasma polishing the workpiece, which specifically includes the following steps:

[0085] S1. Place the workpiece on the turntable, and then use a vacuum pump to evacuate the polishing vacuum chamber to form a vacuum chamber with a vacuum degree of 10×10 -3 Pa;

[0086] S2. Introduce argon into the vacuum chamber until the air pressure in the vacuum chamber reaches 1 Pa;

[0087] S3. Turn on the DC pulse bias power supply to perform plasma heating on the workpiece to be polished, with a negative voltage of 200 V, a frequency of 300 KHz, a duty cycle of 30%, and a heating time of 80 min;

[0088] S4. After completing the plasma heating, introduce a mixed gas of carbon tetrafluoride, nitrogen trifluoride, and sulfur hexafluoride into the vacuum chamber until the air pressure in the vacuum chamber reaches 3 Pa;

[0089] S5. Turn on the ion source, keep the negative bias voltage at 800 V, the frequency at 300 KHz, and the duty cycle at 8%; energize the grid, with a positive voltage of 80 V; immerse the workpiece to be polished in the plasma for 180 min, and at the same time rotate the turntable at a speed of 3 rpm;

[0090] S6. Turn off the ion source, and at the same time cut off the power supply of the grid. Wait for the workpiece to cool down to 25 °C, and the polishing of the workpiece is completed.

[0091] In the polishing effect detection test of this comparative example, the AFM morphology map of the Si wafer surface is as Figure 8 shown.

[0092] Comparative Example 3

[0093] This comparative example uses a large-scale radio frequency ion source polishing and etching process debugging platform developed by the Southwestern Institute of Physics, Nuclear Industry. This equipment platform includes a linear ion source, a control system, a workbench, and a vacuum pumping system. It generates a magnetic field through a high-frequency (13.56 MHz) current coil, and then an electric field is induced by the alternating magnetic field to generate a low-pressure, high-density, and plasma with a certain energy, which then impacts the surface of the workpiece to achieve surface polishing. In the polishing effect detection test of this comparative example, the AFM morphology map of the Si wafer surface is as Figure 9 shown.

[0094] Polishing effect detection test

[0095] Prepare fifty Si wafers to be polished, divided into five groups, with ten wafers in each group. The first to third groups are polished using the plasma polishing devices and methods of Examples 1 to 3 respectively, and the fourth to fifth groups are polished using the devices and methods of Comparative Examples 1 to 2 respectively. After polishing, measure the average surface roughness of all Si wafers, then record the surface roughness of all Si wafers in each group, and calculate the average value. The test data is shown in Table 1, and the test results are referred to Figures 4 to 8。The sixth group is the polishing result of the quartz wafer in Comparative Example 3, and the test results are referred to Figure 9 。

[0096] Table 1

[0097]

[0098] As can be seen from the above table, for the workpieces polished by the method and device of the present invention, compared with the workpieces polished by the existing radio frequency ion source polishing and etching process debugging platform, the surface roughness is significantly reduced. In particular, for the workpieces polished by the method in Example 2, compared with the workpieces polished by the prior art, the surface roughness is reduced by 5 times. It can be seen that the method and device for plasma polishing workpieces of the present invention have significant advantages.

[0099] At the same time, the surface roughness of the workpieces in the first group, the second group and the third group in the above table is significantly lower than that of the workpieces in the fourth group and the fifth group. It can be seen that the method of the present invention can achieve a better polishing effect by using a lower voltage. Since the voltage is lower, the plasma energy is lower, and thus the thermal effect is weaker, controlling the heat in the plasma polishing process, greatly reducing the heat released during the polishing process, and avoiding poor polishing effect caused by excessive heat generated by the plasma on the workpiece to be polished.

[0100] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for plasma polishing a workpiece, characterized in that, It includes the following steps: S1. Place the workpiece (9) to be polished on the turntable (2) inside the polishing vacuum chamber (1), and evacuate the polishing vacuum chamber (1) until the vacuum degree inside the polishing vacuum chamber (1) reaches the set value. Electromagnetic coils (4) are provided on the outer top and outer bottom of the vacuum chamber (1); S2. Introduce an inert gas into the polishing vacuum chamber (1) until the air pressure inside the vacuum chamber reaches the set value P1; S3. Connect the turntable (2) to a negative bias voltage to excite plasma and perform plasma heating on the workpiece (9) to be polished. The heating time is T1; S4. After completing the plasma heating, introduce a fluorine-containing gas into the polishing vacuum chamber (1) until the air pressure inside the polishing vacuum chamber (1) reaches the set value P2; S5. Turn on the ion source (3), energize the grid (7), and the grid is positively charged to weaken the directionality of the plasma, so that the workpiece (9) to be polished is immersed in the plasma for T2 time; S6. Turn off the ion source (3), and at the same time cut off the power supply of the grid (7). After the workpiece (9) to be polished cools down, the polishing of the workpiece (9) to be polished is completed; The step S3 is: Turn on the DC pulse bias power supply. The turntable (2) is electrically connected to the DC pulse bias power supply to perform plasma heating on the workpiece (9) to be polished. The negative voltage range is 30-100V, the frequency is 80-350KHz, the duty cycle is 5-40%, the heating time is T1, and the T1 is 30-120min; The step S5 is: Turn on the ion source (3), the negative bias voltage is maintained at 400-1200V, the frequency is 80-350KHz, and the duty cycle is 5-10%; energize the grid (7), and the positive voltage is 50-100V, so that the workpiece (9) to be polished is immersed in the plasma for T2 time, and at the same time the workpiece (9) to be polished rotates at a speed of 1-5rpm.

2. The method for plasma polishing a workpiece according to claim 1, characterized in that, In the step S1, the vacuum degree in the polishing vacuum chamber (1) is greater than or equal to 9×10 -3 Pa.

3. The method for plasma polishing a workpiece according to claim 1, wherein In the step S2, the inert gas is argon.

4. The method for plasma polishing a workpiece according to claim 1, wherein In the step S2, P1 is 0.5-2Pa.

5. The method for plasma polishing a workpiece according to claim 1, wherein In the step S4, the fluorine-containing gas is a mixed gas of two or more of carbon tetrafluoride, nitrogen trifluoride and sulfur hexafluoride; the P2 is 0.5-5Pa.

6. The method for plasma polishing a workpiece according to claim 1, wherein The T2 is 30-240min.

7. A plasma polishing apparatus for applying the method of plasma polishing a workpiece according to any one of claims 1-6, characterized in that, It includes a polishing vacuum chamber (1), a turntable (2) for placing the workpiece (9) to be polished, an ion source (3), electromagnetic coils (4), a vacuum pump (5), an anode (6), a grid (7) and a motor (8); the turntable (2) is rotatably arranged inside the polishing vacuum chamber (1), the motor (8) is arranged at the bottom of the polishing vacuum chamber (1), and the output end of the motor (8) is connected to the bottom end of the turntable (2); the anode (6) and the ion source (3) are symmetrically arranged on the inner wall of the polishing vacuum chamber (1) with the turntable (2) as the axis of symmetry, the electromagnetic coils (4) are arranged on the outer top and outer bottom of the polishing vacuum chamber (1), the grid (7) is arranged around the turntable (2) inside the polishing vacuum chamber (1), and the grid (7) is located between the turntable (2) and the anode (6) and the ion source (3); the vacuum pump (5) is communicated with the polishing vacuum chamber (1).

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