Method for rapidly obtaining super-smooth surface by combination of plasma and tooling process

Abstract

The application discloses a method for rapidly obtaining an ultra-smooth surface by combining a plasma and a tool, which comprises the following steps: firstly, performing plasma polishing on fused quartz glass which is cut into a shape and coarsely polished; adopting a total residence time segmented superposition process to realize rapid removal of fused quartz surface material and to inhibit the thickness of a polymer deposition layer; using a polyurethane polishing pad in the middle; after removing the surface polymer, adjusting plasma process parameters and converging the fused quartz surface figure error RMS to below 13 nm without subsurface damage; and after cleaning, using a pitch disc tool in cooperation with cerium oxide abrasive to realize surface smoothing of the fused quartz. The application can significantly shorten the processing time of a lossless fused quartz ultra-smooth surface, realize common convergence of surface figure error and roughness, and finally obtain a lossless ultra-smooth surface with a roughness Ra of less than 0.20 nm.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of processing, and particularly relates to a method for rapidly obtaining an ultrasmooth surface by combining a plasma with a small tool. BACKGROUND

[0002] At present, the demand for high-quality optical elements is increasing at home and abroad, and optical manufacturing technology is also rapidly developing. Fused quartz is widely used in aerospace, telescopes and photolithography machines due to its high chemical stability and excellent optical transparency. Fused quartz glass needs to be processed by grinding forming, polishing shaping, smoothing and other processes using traditional processing methods. In the polishing shaping process, the surface shape and roughness need to be iteratively converged, and it takes more than tens of hours to achieve a surface shape error of less than 13 nm and a surface roughness of less than 0.2 nm. Surface and subsurface defects are difficult to control.

[0003] For ground fused quartz workpieces, common processing methods include chemical etching, ion beam etching, plasma etching, etc. Chemical etching uses HF acid to etch the element, but the etching process can cause rapid deterioration of surface roughness, and it is difficult to control the etching process precisely, and the etching amount is not stable. Ion beam etching has high requirements for the initial surface quality, and there are problems of ion implantation and surface quality deterioration. Inductively coupled plasma (ICP) method has the advantages of high removal efficiency and no surface and subsurface damage. The possible polymer deposition pollution problem can be effectively inhibited by the three-equal-time method, and the hardness of the polymer is lower than that of the fused quartz substrate, so the polymer can be preferentially removed by using a small tool for smoothing. The present application can fully utilize the advantages of plasma fast and non-destructive shaping, shorten the processing time, and further use the pitch disc small tool to reduce the surface roughness while maintaining the surface shape, and improve the manufacturing efficiency of non-destructive ultrasmooth surface. SUMMARY

[0004] To solve the above technical problems, the application provides a method for rapidly obtaining an ultra-smooth surface by combining plasma and small tool processing, which can rapidly process fused quartz glass after cutting, forming and rough grinding into a lossless ultra-smooth surface. First, the fused quartz glass after cutting, forming and rough grinding is subjected to plasma polishing, a total residence time segmented superposition process is adopted to realize rapid removal of fused quartz surface material and inhibit the thickness of the polymer deposition layer, a polyurethane polishing pad is used in the middle, after removing the surface polymer, the plasma process parameters are adjusted and the fused quartz surface form error RMS is converged to below 12 nm without subsurface damage, after cleaning, pitch disc small tool is used in combination with cerium oxide abrasive to realize the smoothing of the fused quartz surface. The application can significantly shorten the processing time of the lossless fused quartz ultra-smooth surface, realize the convergence of the surface form error and roughness, and finally obtain a lossless ultra-smooth surface with a roughness Ra of less than 0.20 nm.

[0005] Small tool polishing refers to a process of using small polishing tools to finish the surface of a workpiece, which is a special term.

[0006] To achieve the above purpose, the application adopts the following technical solutions:

[0007] A method for rapidly obtaining an ultra-smooth surface by combining plasma and small tool processing, comprising the following steps:

[0008] Step 1: plasma processing of the ground and formed fused quartz workpiece;

[0009] Step 2: calculate the residence time T of each point in the grating track by the removal function of plasma and the volume to be removed;

[0010] Step 3: use a polyurethane polishing pad in combination with 2 μm cerium oxide abrasive to remove the surface polymer deposition layer;

[0011] Step 4: enter the shaping stage, adjust the plasma process parameters, reduce the removal amount, and realize fine shaping to finally obtain a lossless ultra-smooth surface with a surface form error RMS of less than 13 nm;

[0012] Step 5: cleaning, then deionized water rinsing, and finally drying on a super-clean workbench to obtain a fused quartz element after plasma processing and ultrasonic cleaning;

[0013] Step 6: smoothing by pitch disc small tool in combination with cerium oxide abrasive, 3 times of processing are performed by using gradient pressure;

[0014] Step 7: cleaning again, then deionized water rinsing, and drying on a super-clean workbench, finally observing the subsurface damage by using a transmission electron microscope and measuring the surface roughness by using a white light interferometer, and finally obtaining a lossless ultra-smooth surface with a surface roughness better than 0.20 nm.

[0015] Further, in the step 1, the plasma used is generated by an inductively coupled plasma device, and the rough surface of the fused quartz workpiece after the grinding forming process is formed.

[0016] Further, in the step 1, the processing parameters of the plasma are set as follows: the power is 350 W, the gas flow is 15 sccm, and the processing distance is 12 mm.

[0017] Further, in the step 2, the residence time trisection method is to trisect the residence time of each point to generate three processing tracks, so as to suppress the influence of temperature accumulation change on the deposition thickness of the plasma processing polymer in the processing process, and remove the surface and subsurface damage generated in the previous process.

[0018] Further, in the step 3, a Φ10 mm polyurethane polishing pad with a cross groove is used, which is beneficial to the storage and update of abrasive particles in the polishing process, improves the stability of material removal, the polishing pressure is 25 N, the revolution speed is 120 rad / min, the rotation speed is 100 rad / min, the eccentricity is 3 mm, and one pass is processed.

[0019] Further, in the step 4, the power of the plasma is 320 W, the gas flow is 18, and the processing distance is 15.

[0020] Further, in the step 5, the revolution speed, rotation speed and eccentricity used are process parameters obtained after optimization.

[0021] Further, in the step 6, a pitch disc tool with a diameter of 10 mm is selected, the revolution speed is 110 rad / min, the rotation speed is 50 rad / min, and the eccentricity is 3 mm.

[0022] Further, in the step 6, a cerium oxide polishing liquid with an average particle size of 200-300 nm is used, the processing track is also a grating track, and gradient pressure is adopted for 3 times of processing, and the pressure load is 8 N, 6 N and 4 N in turn.

[0023] Further, in the step 7, the cleaning process needs to use an isopropyl alcohol jet to clean the surface of the workpiece.

[0024] The beneficial effects of the present application are as follows:

[0025] The present application is based on the problems that the fine control of the etching process is difficult and the stability of the etching amount is poor in the chemical etching method, and the problems of ion implantation and surface quality deterioration exist in ion beam etching. The inductively coupled plasma (ICP) method has the advantages of high removal efficiency and no surface and subsurface damage. For the possible polymer deposition pollution problem, it can be effectively inhibited by the three equal division method of residence time. And because the hardness of the polymer is lower than that of the fused quartz substrate, the polymer can be preferentially removed by using small tools for smoothing process. The present application can fully exert the advantages of plasma rapid and non-destructive shaping, shorten the processing time, and cooperate with the pitch disc small tool to realize the maintenance of the surface shape and the reduction of the surface roughness, and improve the manufacturing efficiency of non-destructive super-smooth surface. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A flow chart of a method for rapidly obtaining a super-smooth surface by a plasma and tool combination process of the present application;

[0027] Figure 2 A schematic diagram of the principle of ICP plasma obtaining a non-destructive surface;

[0028] Figure 3 A schematic diagram of pitch disc tool processing equipment and material removal mechanism;

[0029] Figure 4 A detection result graph of the abrasive particle size distribution used in the smoothing process;

[0030] Figure 5 A surface change real object graph during the processing process; wherein, 1 is the initial grinding and shaping surface, 2 is the surface after plasma processing, 3 is the surface after removing the polymer deposition of polyurethane, and 4 is the surface after fine shaping and smoothing;

[0031] Figure 6 The results of surface shape error and roughness measured by laser interferometer and white light interferometer respectively;

[0032] Figure 7 The results of subsurface damage detected by transmission electron microscope. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0034] As Figure 1As shown, the present application provides a method for quickly obtaining an ultra-smooth surface by combining plasma and small tools, comprising the following steps:

[0035] Step 1: Plasma processing is performed on the ground and shaped fused quartz workpiece. Since the ground surface is rough and has deep subsurface damage, a large amount of removal is required.

[0036] Preferably, the plasma processing parameters are set as follows: power 350 W, gas flow rate 15 sccm, and processing distance 12 mm.

[0037] Step 2: Calculate the residence time T of each point in the grating track by the plasma removal function and the required removal volume.

[0038] Step 3: Since the polymer deposition of the plasma will affect the further removal of the material on the surface of the workpiece, a polyurethane polishing pad is used to remove the polymer deposition layer on the surface with 2 μm cerium oxide abrasive.

[0039] Step 4: Enter the shaping stage, adjust the plasma process parameters, and reduce the removal amount to achieve fine shaping.

[0040] Preferably, the plasma power is 320 W, the gas flow rate is 18, and the processing distance is 15, and finally a lossless ultra-smooth surface with a surface shape error RMS less than 13 nm is obtained.

[0041] Step 5: Perform cleaning, then rinse with deionized water, and finally place on a clean bench to dry to obtain a fused quartz component after plasma processing and ultrasonic cleaning.

[0042] Preferably, the cleaning is ultrasonic cleaning in anhydrous ethanol at 20C° for 3-5 minutes.

[0043] Step 6: Smooth with pitch pan small tools and cerium oxide abrasive.

[0044] Step 7: Clean again, then rinse with deionized water, and place on a clean bench to dry, finally observe the subsurface damage using a transmission electron microscope, and measure the surface roughness using a white light interferometer, and finally obtain a lossless ultra-smooth surface with a surface roughness better than 0.20 nm.

[0045] Preferably, the cleaning is ultrasonic cleaning in anhydrous ethanol at 20C° for 3-5 minutes.

[0046] Further, in step 1, the plasma used is an inductively coupled plasma (ICP) device, and the previous process of the fused quartz workpiece is the rough surface after grinding and shaping.

[0047] Further, in step 2, the residence time trisection method is to trisect the residence time of each point to generate three passes of processing tracks to suppress the influence of temperature accumulation change on the deposition thickness of the plasma-processed polymer and remove the surface and subsurface damage generated in the previous process.

[0048] Preferably, since excessive residence time of the plasma single point will generate polymer deposition on the fused quartz surface, affecting the surface quality, by trisecting the residence time of the residence point, i.e. keeping the total residence time unchanged, walking three passes of grating tracks, the residence time of each pass is 1 / 3 T, the thickness of the polymer can be obviously suppressed.

[0049] Further, in step 3, the Φ10 mm polyurethane polishing pad with cross grooves is used, which is beneficial to the storage and update of abrasive particles during polishing, improves the stability of material removal, the polishing pressure is 25 N, the revolution speed is 120 rad / min, the rotation speed is 100 rad / min, the eccentricity is 3 mm, and one pass can be processed.

[0050] Further, in step 6, the revolution speed and eccentricity used are process parameters obtained after optimization, since the relative speed of the center position of the rotation axis during the rotation of the small tool is 0, material removal cannot be achieved, so the relative speed needs to be increased by revolution and promote abrasive particle update.

[0051] Preferably, a diameter of 10 mm of asphalt disc small tool is selected, the revolution speed is 110 rad / min, the rotation speed is 50 rad / min, the eccentricity is 3 mm, the average particle size of the cerium oxide polishing liquid is 200-300 nm, the processing track is also a grating track, and gradient pressure is used for 3 times of processing, and the pressure load is 8 N, 6 N, and 4 N in turn.

[0052] The average particle size of the cerium oxide polishing liquid used is 200-300 nm, which is measured by a Malvern particle size analyzer. The cerium oxide abrasive particle is an irregular polyhedron, and there are relatively sharp corners, which can easily damage the surface. Therefore, cerium oxide abrasive particles with small particle size and concentrated distribution are needed.

[0053] In step 6, the pressure gradient processing method can remove the possible polymer deposition on the surface when the first pass pressure is large, and the subsequent pressure decreases to reduce the average load of the effective abrasive particles in the polishing liquid, promote the abrasive particles to realize material removal in the way of mechanical induction chemical bond rupture, and can improve the processing efficiency while obtaining a damage-free super-smooth surface.

[0054] Further, in step 7, the cleaning process needs to use an isopropyl alcohol jet to clean the surface of the workpiece, because in the cerium oxide abrasive, in order to improve the dispersion and stability of the abrasive particles, a chemical additive needs to be used, and the isopropyl alcohol can remove the organic solvent that may be left on the surface, and then use anhydrous ethanol and deionized water for cleaning, and finally dry it.

[0055] Embodiment:

[0056] The embodiment of the application provides a method for rapidly obtaining an ultra-smooth surface by combining a plasma and a small tool, comprising the following steps:

[0057] Step 1: using an inductively coupled plasma (ICP) device to process a Φ50*5mm fused quartz workpiece ground into a shape, the material removal process is as shown in the figure Figure 2 The conventional optical element processing process needs to go through the processes of rough grinding, fine grinding, rough polishing and fine polishing from a blank to a finished product. Because the surface of the ground blank is rough and there is a deep subsurface damage, a large amount of removal is needed. The processing parameters of the plasma are set, the power is 350W, the gas flow is 15sccm, the processing distance is 12mm, and the workpiece is fixed on the workbench. Under the action of the plasma, the subsurface damage such as cracks will first go through a crack opening process, and plasma etching pits will gradually appear on the surface. With the accumulation of time, the etching pits are continuously extended and merged until the damage layer is completely removed, and finally a damage-free surface is obtained.

[0058] Step 2: the total residence time of the grating track is 60min by calculating the removal function of the plasma and the volume to be removed. By equally dividing the residence time of the residence point, that is, under the condition that the total residence time remains unchanged, walking through the grating track three times, the residence time of each time is 20min, which can obviously inhibit the thickness of the polymer and remove the surface and subsurface damage generated in the previous process;

[0059] Step 3: because the polymer deposition of the plasma will affect the further removal of the material on the surface of the workpiece, a polyurethane polishing pad is used to remove the polymer deposition layer on the surface. The Φ10mm polyurethane polishing pad used has a cross groove, which is beneficial to the storage and updating of abrasive particles in the polishing process, improves the stability of material removal, the polishing pressure is 25N, the revolution speed is 120rad / min, the rotation speed is 100rad / min, the eccentric distance is 3mm, and the processing time is 40min.

[0060] Step 4: Enter the fine shaping stage, adjust the plasma process parameters, reduce the removal amount, and achieve fine shaping. The power is 320 W, the gas flow is 18, the processing distance is 15, the processing program is regenerated according to the surface shape after each processing, and the iteration is 3 times, each processing for 10 min, a total of 30 min. Finally, a lossless super-smooth surface with a surface shape error RMS less than 13 nm is obtained;

[0061] Step 5: Ultrasonic cleaning in anhydrous ethanol at 20C° for 3-5 minutes, followed by deionized water rinsing, and finally drying on a super-clean workbench to obtain a fused quartz component after ultrasonic cleaning after plasma processing;

[0062] Step 6: Smooth with pitch disc tool and cerium oxide abrasive, processing equipment and material removal mechanism as shown in Figure 3 , the fused quartz workpiece is fixed to the workbench, the pitch disc tool acts on the surface of the fused quartz workpiece with a certain load while rotating and revolving, and since the hardness of the polymer deposit generated by the plasma is less than that of the fused quartz, the abrasive on the polishing interface preferentially removes the surface polymer deposit and ultimately achieves super-smooth processing to obtain a super-smooth surface.

[0063] Select a pitch disc tool with a diameter of 10 mm, the revolving speed is 110 rad / min, the rotating speed is 50 rad / min, the eccentric distance is 3 mm, and the average particle size of the cerium oxide polishing liquid is 200-300 nm. The detection result of the particle size distribution is shown in Figure 4 , the average particle size is 236.4 nm, the processing track is also a grating track, and gradient pressure is used for 3 times of processing, the pressure load is 8 N, 6 N, and 4 N in turn. The first pass with higher pressure can remove the possible polymer deposit on the surface, and the subsequent pressure decreases to reduce the average load of the effective abrasive in the polishing liquid, promoting the abrasive to achieve material removal in the form of mechanical-induced chemical bond breakage. This can improve the overall processing efficiency while obtaining a lossless super-smooth surface. Each processing time is 40 min;

[0064] Step 7: Clean again, use 25C° isopropyl alcohol jet to clean the additive residue in the polishing liquid, then ultrasonic cleaning in anhydrous ethanol at 20C° for 3-5 minutes, followed by deionized water rinsing, and drying on a super-clean workbench. The surface change during processing is shown in Figure 5 , where Figure 5 1 is the initial ground and shaped surface, Figure 5 2 is the surface after plasma processing, Figure 5 3 is the surface after removing the polymer deposit with polyurethane, Figure 5 4 is the surface after fine shaping and smoothing;

[0065] It can be obviously found that the surface of fused silica workpiece changes from initial rough surface to bright surface, and finally the surface profile error and roughness are measured by laser interferometer and white light interferometer respectively, as shown in Figure 6 Although the profile error is slightly deteriorated by 10.7%, the roughness is reduced by 89.8%, and the subsurface damage is observed by transmission electron microscope, and the detection results are shown in Figure 7 .

[0066] Compared with the traditional processing process, the entire processing process only needs about 250 min to process the Φ50*5 mm fused silica workpiece from the rough surface formed by grinding to the non-destructive ultra-smooth surface with a profile error less than 13 nm and a surface roughness better than 0.20 nm, which reduces the time cost and realizes the efficient processing of the fused silica ultra-smooth surface.

Claims

1. A method for rapidly obtaining an ultra-smooth surface by combining a plasma process with a tooling process, characterized in that, The method comprises the following steps: Step 1: plasma processing of a ground and shaped fused quartz workpiece; Step 2: calculating the residence time T of each point in the grating track according to the removal function of the plasma and the volume to be removed, and using a residence time tripartition method to calculate the residence time T, wherein the residence time tripartition method is to tripartition the residence time of each point to generate three processing tracks, so as to inhibit the influence of temperature accumulation change in the processing process on the deposition thickness of the polymer processed by the plasma and remove the surface and subsurface damage generated in the previous process; Step 3: removing the surface polymer deposition layer using a polyurethane polishing pad combined with 2 μm cerium oxide abrasive; Step 4: entering the shaping stage, adjusting the plasma process parameters, reducing the removal amount, and realizing fine shaping to finally obtain a lossless super-smooth surface with a surface form error RMS less than 13 nm; Step 5: cleaning, then rinsing with deionized water, and finally drying on an ultra-clean workbench to obtain a fused quartz element after plasma processing and ultrasonic cleaning; Step 6: smoothing using a pitch disc tool combined with cerium oxide abrasive, and performing 3 times of processing using gradient pressure; Step 7: cleaning again, then rinsing with deionized water, and drying on an ultra-clean workbench, finally observing the subsurface damage using a transmission electron microscope and measuring the surface roughness using a white light interferometer, and finally obtaining a lossless super-smooth surface with a surface roughness better than 0.20 nm.

2. The method of claim 1, wherein the method further comprises: In the step 1, the plasma used is generated by an inductively coupled plasma device, and the previous process of the fused quartz workpiece to be processed forms a rough surface after grinding and shaping.

3. The method of claim 1, wherein the method further comprises: In the step 1, the processing parameters of the plasma are set as follows: power 350 W, gas flow rate 15 sccm, and processing distance 12 mm.

4. The method of claim 1, wherein the method is characterized by: In the step 3, a Φ10 mm polyurethane polishing pad with a cross groove is used, which is beneficial to abrasive storage and renewal in the polishing process and improves the stability of material removal, the polishing pressure is 25 N, the revolution speed is 120 rad / min, the rotation speed is 100 rad / min, and the eccentricity is 3 mm.

5. The method of claim 1, wherein the method further comprises: In the step 4, the power of the plasma is 320 W, the gas flow rate is 18 sccm, and the processing distance is 15 mm.

6. The method of claim 1, wherein the method further comprises: In the step 5, the revolution speed, rotation speed and eccentricity used are the optimized process parameters.

7. The method of claim 1, wherein the method further comprises the step of: 7-1) applying a small tool to the substrate to obtain a super-smooth surface. In the step 6, a pitch disc tool with a diameter of 10 mm is selected, the revolution speed is 110 rad / min, the rotation speed is 50 rad / min, and the eccentricity is 3 mm.

8. The method of claim 1, wherein the method is performed in a plasma and tool integration process to rapidly obtain an ultra-smooth surface. In the step 6, an average particle size of 200-300 nm of cerium oxide polishing liquid is used, the processing track is also a grating track, and 3 times of processing is performed using gradient pressure, and the pressure load is 8 N, 6 N and 4 N in turn.

9. The method for rapidly obtaining an ultra-smooth surface using a combination of plasma and small tools according to claim 1, characterized in that, In the step 7, the cleaning process needs to use an isopropyl alcohol jet to clean the surface of the workpiece.

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