CN110677972A - Plasma generator for SiC optical mirror processing and application method thereof - Google Patents

Abstract

The invention discloses a plasma generator for SiC optical mirror processing and an application method thereof, wherein the plasma generator comprises a shell and a combined torch tube, the combined torch tube comprises an outer tube, a middle tube and an inner tube which are sequentially nested, and an inductive coupling coil is sleeved outside the outer tube; the application method comprises the steps that a plasma generator is installed on a numerical control motion platform with a three-axis linkage function, the surface of a SiC workpiece is linearly scanned by using plasma to obtain the material removal amount of a removal function, and a removal function experimental model is obtained by extracting and fitting the cross section shape of a material removal amount groove; and calculating residence time distribution according to the removal function experimental model, and setting a processing path to carry out iterative processing on the surface of the SiC workpiece. The invention can reduce the maintenance difficulty in the ICP plasma processing process, improve the processing efficiency and long-time stability of the SiC optical mirror surface, and has the advantages of high processing efficiency, simple structure, low cost, convenient maintenance and high long-time stability.

Description

Plasma generator for SiC optical mirror processing and application method thereof

technical field

The invention relates to the field of optical material manufacturing, in particular to a plasma generator used for SiC optical mirror processing and an application method thereof.

Background technique

SiC optical materials have good characteristics such as high chemical stability, low density, high strength and elastic modulus, strong radiation resistance, high specific stiffness, small thermal deformation coefficient, and high reflectivity coating. Therefore, SiC mirrors are more and more widely used in space astronomical optics, satellite remote sensing technology and large-scale ground-based optical systems. As the application fields of SiC mirrors become more and more extensive, its increasing demand has brought new challenges to the efficient processing of SiC mirrors. At present, the traditional processing flow of SiC mirror is rough grinding, grinding, modification, polishing and other processes. Before the modification is the processing of the SiC matrix, and after the modification is the processing of the modified layer. Grinding and grinding of the substrate before modification accounted for more than half of the entire processing cycle. In addition, the hardness of SiC material is high, and the traditional mechanical grinding and polishing method is very low in material removal efficiency and long in processing cycle.

In view of the characteristics of high hardness and low processing efficiency of SiC materials, ultrasonic vibration grinding and atmospheric plasma processing have been studied at home and abroad. Although ultrasonic vibration grinding can improve the processing efficiency to a certain extent, there is the problem of grinding wheel wear. However, the atmospheric plasma processing method utilizes the chemical reaction between the highly active reactive atoms excited by the plasma and the surface atoms of the workpiece to be processed to generate highly volatile gaseous products, thereby realizing the processing method of removing the workpiece material at the atomic level. Taking the processing of SiC materials as an example, the reactive gases NF3, CF4, O2 or SF6 are excited into various active free radicals and excited F* or O* atoms, free radicals and F* atoms or O in the plasma atmosphere. *Diffusion to the surface of the SiC material, reacting to generate gaseous CO2, SiF4 and other gaseous products escaping from the surface of the workpiece to achieve the purpose of efficient removal of the surface material of the SiC material. Atmospheric plasma machining is a controllable chemical reaction process, the removal function is stable, and there are no problems such as traditional machining grinding wheel wear and grinding head wear, and it is a non-destructive machining method. At the same time, it was found through research that atmospheric plasma processing also has the ability to remove damage, which can effectively remove the residual surface and sub-surface damage after machining. Therefore, in recent years, the atmospheric plasma processing technologies studied by countries around the world include: the plasma chemical vaporization processing technology (PCVM) of Osaka University, Japan, the atmospheric plasma polishing method (APPP) of Harbin Institute of Technology, and the reactive atom of the Lawrence Livermore laboratory in the United States. Plasma Polishing Technology (RAPT) and National University of Defense Technology announced a SiC optical material processing equipment with patent number CN103456610. Commonly used plasma generator types can be divided into capacitively coupled plasma (CCP) and inductively coupled plasma (ICP). Among them, PCVM and APPP both use the CCP plasma generation method to generate plasma that can be used for processing, and have developed corresponding plasma generators and processing equipment, while the SiC optical material processing equipment of RAPT and National University of Defense Technology uses ordinary ICP A plasma generator produces plasma.

At present, in terms of plasma processing efficiency, the ordinary ICP plasma processing method can use higher power, so the plasma ionization degree is higher, the concentration of active particles is higher, and the processing efficiency is higher than that of the CCP plasma. At the same time, the absence of electrodes can prevent the corrosion of electrodes from contaminating the processing materials; however, for high-hardness materials such as SiC, the processing efficiency of ordinary ICP plasma is still low. In terms of the structure of the ICP plasma generator, the common ICP plasma generator adopts an integrated quartz torch; the integrated quartz torch will be scrapped due to the heat accumulation during ICP plasma processing, which will cause the torch to burst easily, and it is difficult to adapt to long-term Time processing, and maintenance is difficult and costly.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention: in view of the above-mentioned problems of the prior art, a plasma generator for SiC optical mirror surface processing and an application method thereof are provided. The present invention can reduce the maintenance difficulty of the ICP plasma processing process and improve the The optical mirror surface processing efficiency and long-term stability have the advantages of high processing efficiency, simple structure, low cost, easy maintenance, and high long-term stability.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

The invention provides a plasma generator for SiC optical mirror processing, comprising a casing and a combined torch mounted in the casing, the combined torch comprising an outer tube, a middle tube nested in sequence at the inlet end of the outer tube, and In the inner tube, an inductive coupling coil is sleeved on the outer wall of the middle part of the outer tube, the outlet end of the outer tube is provided with a Laval nozzle, the gap between the outer tube and the middle tube forms a cooling gas inflow channel, the The space between the middle tube and the inner tube forms an inflow channel of excitation gas, and the inner cavity of the inner tube forms an inflow channel of reaction gas.

Optionally, a torch mounting plate is sleeved and fixed on the outer wall of the combined torch, the outer pipe, the middle pipe, and the inner pipe are respectively mounted and fixed on the torch mounting plate, and the combined torch passes through the torch. The tube mounting plate is mounted on the central axis of the inner cavity of the housing.

Optionally, the inductively coupled coil is a copper tube with a first water-cooling circulation channel inside, and is mounted on the periphery of the outlet end of the combined torch through a torch mounting plate with a thermal insulation gap therebetween.

Optionally, the Laval nozzle is made of copper material.

Optionally, a nozzle housing is provided on the outer side of the Laval nozzle, a nozzle mounting plate is fixed on the nozzle housing, and the Laval nozzle is fixed on the central axis of the inner cavity of the nozzle housing through the nozzle mounting plate, and passes through the nozzle. The mounting plate is sealingly connected to the housing and maintains a central axis co-linear with the modular torch.

Optionally, a cooling cavity is formed between the outer wall of the Laval nozzle and the inner wall of the nozzle shell, the shell is provided with a shell cavity, and the shell cavity and the cooling cavity are connected to form a second water cooling cycle aisle.

Optionally, the outer wall of the outer pipe is further provided with a first ventilation inlet, the first ventilation inlet forms a cooling gas inflow channel, and the outer wall of the middle pipe is further provided with a second ventilation inlet, the second ventilation inlet is The ventilation inlet forms an inflow channel for excitation gas, and a third ventilation inlet is further provided on the outer wall of the inner tube, and the third ventilation inlet forms an inflow channel for reaction gas.

The present invention also provides an application method of the aforementioned plasma generator for SiC optical mirror processing, the implementation steps comprising:

1) The plasma generator used for SiC optical mirror processing is installed on a numerically controlled motion platform with three-axis linkage function, and the surface of the SiC workpiece is scanned linearly by the plasma to obtain the material removal amount of the removal function. The experimental model of the removal function was obtained by combining the material removal amount and the groove section shape;

2) Calculate the residence time distribution according to the experimental model of the removal function, and set the processing path;

3) Iteratively process the surface of the SiC workpiece by the plasma generator for SiC optical mirror machining.

Optionally, the detailed steps for obtaining the experimental model of the removal function in step 1) include:

1.1) A groove is processed by linear scanning along the Y-axis direction of the surface of the SiC workpiece at a specified motion speed v by the plasma generator used for SiC optical mirror processing, and the measurement groove is obtained by a vertical interferometer. Section shape data;

1.2) Fitting formula (4) on the basis of the obtained groove cross-sectional shape data to obtain the groove cross-sectional shape depth A _x , the value of the Gaussian distribution parameter σ _x of the removal function experimental model, and then according to formula (5) to obtain The experimental model of the removal function under the motion speed v;

In formula (4), G(x) is the shape function of the groove section in the X-axis direction, _Ax is the depth of the groove section shape, σx is the Gaussian distribution parameter of the experimental model of the removal function, and _x is the coordinate (x, y) ) at the abscissa;

In formula (5), R(x,y) represents the material removal amount at the coordinate (x,y), _Ax is the depth of the groove cross-sectional shape, v is the moving speed of the plasma generator, σx _is the removal function experiment Gaussian distribution parameters for the model.

Optionally, calculating the residence time distribution according to the removal function experimental model in step 2) specifically refers to using the pulse iteration method to calculate the residence time distribution τ(x, y), and using the pulse iteration method to calculate the residence time distribution τ(x). ,y) The detailed steps include:

2.1) According to the material removal amount distribution of the known surface shape of the SiC workpiece, a material removal amount matrix R is established, and the removal function matrix G and the removal function intensity B _r are determined on the basis of obtaining the removal function experimental model;

其中，R为材料去除量矩阵，B_r为去除函数强度，G为去除函数矩阵；2.2) Set the value of the initial dwell time T ₀ as R/B _r and the residual as the value of E ₀

Among them, R is the material removal amount matrix, B _r is the removal function strength, and G is the removal function matrix;

2.3) Calculate the value of the dwell time correction Δk of the _k dwell points as E _k /B _r ; wherein, E _k is the residual matrix of the k dwell points, and B _r is the removal function strength;

2.4) The value of the dwell time T _k+1 of the correction k+1 dwell points is T _k +ζ·Δ _k ; where T _k is the dwell time of k dwell points, ζ is the relaxation factor, Δ _k is the dwell time correction amount of k dwell points;

其中，E_k+1为k+1个驻留点的残差矩阵，B_r为去除函数强度，R为材料去除量矩阵，T_k+1为k+1个驻留点的驻留时间，G为去除函数矩阵；2.5) Calculate the value of the residual matrix E _k+1 as

Among them, E _k+1 is the residual matrix of k+1 dwell points, B _r is the strength of the removal function, R is the material removal matrix, T _k+1 is the dwell time of k+1 dwell points, G is the removal function matrix;

2.6) Determine whether the dwell time T _k+1 of k+1 dwell points and the residual matrix E _k+1 meet the requirements, if not, repeat step 2.3); otherwise, the iteration ends, and the dwell of all dwell points is obtained The dwell time distribution τ(x,y) formed by time.

The plasma generator used for SiC optical mirror processing of the present invention has the following advantages: the plasma generator of the present invention includes a casing and a combined torch installed in the casing, and the combined torch includes an outer tube and is sequentially nested in the outer casing. The middle tube and inner tube at the inlet end of the tube, an inductive coupling coil is set on the outer wall of the middle part of the outer tube, and a Laval nozzle is arranged at the outlet end of the outer tube, which can form arc-enhanced plasma at the Laval nozzle, which can reduce the ICP plasma The maintenance difficulty of the processing process improves the processing efficiency and long-term stability of the SiC optical mirror surface, and has the advantages of high processing efficiency, simple structure, low cost, easy maintenance, and high long-term stability.

The application method of the plasma generator for SiC optical mirror processing of the present invention has the following advantages: the application method of the plasma generator for SiC optical mirror processing of the present invention is characterized in that an arc can be generated when applied to SiC optical mirror processing Enhanced plasma, high peak removal rate and small full width at half maximum removal function are obtained. The method uses the linear scanning experimental method to obtain the experimental model of the removal function, uses the pulse iteration method to calculate the precise residence time distribution, and then sets the machining path to improve the single machining convergence ratio, thereby improving the efficiency of the entire iterative machining process.

Description of drawings

FIG. 1 is a schematic diagram of the principle structure of a plasma generator according to an embodiment of the present invention.

FIG. 2 is a schematic three-dimensional structure diagram of a plasma generator according to an embodiment of the present invention.

FIG. 3 is a schematic front view of the structure of a plasma generator according to an embodiment of the present invention.

FIG. 4 is a schematic view of the cross-sectional structure taken along the line A-A of FIG. 3 .

FIG. 5 is a schematic three-dimensional structure diagram of a combined torch in an embodiment of the present invention.

FIG. 6 is the material removal amount obtained by the conventional ICP plasma linear scanning experiment in the prior art.

FIG. 7 shows the removal depth (cross-sectional groove) obtained by the conventional ICP plasma linear scanning experiment of the prior art.

FIG. 8 is the material removal amount obtained by the linear scanning of the plasma generator according to the embodiment of the present invention.

FIG. 9 is the removal depth (cross-sectional groove) obtained by linear scanning of the plasma generator according to the embodiment of the present invention.

FIG. 10 is an experimental model of the removal function obtained in the embodiment of the present invention.

FIG. 11 is the residence time distribution obtained in the embodiment of the present invention.

Fig. 12 shows the conventional ordinary grating processing path.

FIG. 13 is the inner-nested grating processing path in the embodiment of the present invention.

FIG. 14 is the initial surface shape of the SiC optical mirror surface processed by conventional ICP plasma processing.

FIG. 15 is the surface shape of the SiC optical mirror surface processed by the conventional ICP plasma.

FIG. 16 is the initial surface shape of the arc-enhanced plasma processing of the SiC optical mirror surface in the embodiment of the present invention.

FIG. 17 is the surface shape of the SiC optical mirror surface after arc-enhanced plasma processing in the embodiment of the present invention.

Legend description: 1. Housing; 11. Housing cavity; 2. Combined torch; 20. Torch mounting plate; 21. Outer tube; 211, First vent inlet; 22, Middle tube; Inlet; 23, inner pipe; 231, third ventilation inlet; 24, inductively coupled coil; 25, Laval nozzle; 26, nozzle housing; 261, nozzle mounting plate; 262, cooling cavity; 3, RF power supply; 4, power matcher.

Detailed ways

As shown in FIG. 1 , FIG. 2 , FIG. 3 and FIG. 4 , this embodiment provides a plasma generator for SiC optical mirror processing, including a housing 1 and a combined torch 2 installed in the housing 1 . The type torch 2 includes an outer tube 21, a middle tube 22 and an inner tube 23 nested in sequence at the inlet end of the outer tube 21, an inductive coupling coil 24 is sleeved on the middle outer wall of the outer tube 21, and a Laval is provided at the outlet end of the outer tube 21. Nozzle 25, the gap between the outer tube 21 and the middle tube 22 forms the cooling gas inflow channel (shown in a in FIG. 1), and the gap between the middle tube 22 and the inner tube 23 forms the excitation gas inflow channel (b in FIG. 1). shown), the inner cavity of the inner tube 23 forms a reaction gas inflow channel (shown in c in FIG. 1 ). This embodiment provides that the plasma generator used for SiC optical mirror processing can form arc-enhanced plasma at the Laval nozzle 25. (shown in d in Figure 1).

In this embodiment, the housing 1 is made of aluminum material, and is configured as a cavity structure.

As shown in FIG. 4 , a torch mounting plate 20 is sleeved and fixed on the outer wall of the combined torch 2 , and the outer pipe 21 , the middle pipe 22 and the inner pipe 23 are respectively installed and fixed on the torch mounting plate 20 . The combined torch 2. It is installed on the central axis of the inner cavity of the casing 1 through the torch mounting plate 20, which is simple and convenient, easy to assemble and disassemble, and is convenient for the separate replacement and maintenance of the outer tube 21, the middle tube 22, and the inner tube 23.

In this embodiment, the outer tube 21 is made of quartz material, which has a good high temperature resistance effect and improves the stability of the combined torch 2 in high temperature processing. The middle pipe 22 is made of stainless steel, and the lower end opening is arranged in a trumpet shape, so as to increase the airflow velocity inside the pipe, thereby making the excited gas easier to ionize. When the plasma beam contacts the surface of the SiC workpiece, the stainless steel middle tube 22 and the SiC optical mirror will form electrodes, resulting in a discharge phenomenon, and the discharge makes the Si-C bond of the SiC material easier to break, and the Si-F bond is easier to form, reducing the The energy required for the reaction is reduced, which makes the reaction easier to carry out, thereby increasing the material removal rate, thereby improving the processing efficiency. Experiments show that this discharge phenomenon can greatly improve the efficiency of plasma processing. Under the same conditions, the efficiency of arc-enhanced plasma processing is several times higher than that of ordinary plasma processing. As shown in Figures 6 to 9, the same Under the processing conditions, the removal depth of the ordinary plasma ICP plasma linear scanning experiment is 89.5 nm, the full width at half maximum is 15.73 mm, and the removal efficiency is 0.27 μ/min; while the arc-enhanced plasma linear scanning experiment The removal depth is 604.7 nm, and the half peak is 604.7 nm. The full width is 5.27mm, and the volume removal rate is 5.36μ/min; therefore, the arc-enhanced plasma generated by the device of this embodiment can realize more efficient processing of SiC optical mirror surface than ordinary plasma ICP plasma. In this embodiment, the inner tube 23 is made of corundum material, and corundum does not react with active F*, which improves the corrosion resistance of the inner tube against F*.

In this embodiment, the inductive coupling coil 24 is a copper tube with a first water-cooling circulation channel inside, and is installed on the periphery of the outlet end of the combined torch 2 through the torch mounting plate 20 with a thermal insulation gap therebetween. The first water cooling circulation channel is used to cool the RF power coupled to generate heat, which can prevent the combined torch 2 from bursting, improve the stability of the arc and enhance the plasma processing, and prolong the service life of the torch, which can inhibit the accumulation of heat during the plasma processing. , reduce the plasma temperature and prevent the stability of plasma processing from being affected by excessive temperature; the inductive coupling coil 24 is installed on the periphery of the outlet end of the combined torch 2 through the torch mounting plate 20 and there is a thermal insulation gap between the two, which can The heat generated by the operation of the inductive coupling coil 24 is prevented from being directly conducted to the outer tube 21 to cause explosion.

In this embodiment, the Laval nozzle 25 is made of copper material, which can prevent the excited plasma from being extinguished due to the coupling of the RF electromagnetic field power to the Laval nozzle 25, thereby improving the stability of plasma processing.

As shown in FIG. 4 , the outer side of the Laval nozzle 25 is provided with a nozzle housing 26 , a nozzle mounting plate 261 is fixed on the nozzle housing 26 , and the Laval nozzle 25 is fixed on the central axis of the inner cavity of the nozzle housing 26 through the nozzle mounting plate 261 , And the nozzle mounting plate 261 is sealed with the casing 1 and kept in line with the central axis of the combined torch 2 .

In this embodiment, the nozzle housing 26 is made of aluminum material.

As shown in FIG. 4 , a cooling cavity 262 is formed between the outer wall of the Laval nozzle 25 and the inner wall of the nozzle casing 26 , the casing 1 is provided with a casing cavity 11 , and the casing cavity 11 and the cooling cavity 262 communicate with each other to form a first Two water cooling circulation channels. The second water cooling circulation channel is used to cool the overall heat generation of the plasma generator, which can suppress the accumulation of heat during the plasma processing, reduce the plasma temperature, and prevent the stability of the plasma processing from being affected by excessive temperature. As an optional implementation example, in this embodiment, the housing cavity 11 and the cooling cavity 262 are kept in communication through a plastic tube.

As shown in FIG. 5 , the outer wall of the outer pipe 21 is further provided with a first ventilation inlet 211, the first ventilation inlet 211 forms a cooling gas inflow channel, and the outer wall of the middle pipe 22 is also provided with a second ventilation inlet 221, the second ventilation The inlet 221 forms the excitation gas inflow channel, and the outer wall of the inner tube 23 is also provided with a third ventilation inlet 231, which forms the reaction gas inflow channel. The above structure can increase the ventilation volume and improve the processing performance. In this embodiment, the gap between the outer tube 21, the middle tube 22 and the first ventilation inlet 211 together form a cooling gas inflow channel, and a large flow of cooling gas Ar is introduced into the outer tube 21, so that the heat generated by the plasma increases with the The air flow is discharged; the gap between the middle pipe 22, the inner pipe 23 and the second ventilation inlet 221 together form an excitation gas inflow channel, and a small flow of plasma excitation gas Ar is introduced into the middle pipe 22; the third ventilation inlet 231 and the inner pipe The inner cavity 6 of 23 is fed into the inner tube 23 with the reaction gas SF ₆ mixed with a small flow of Ar.

In this embodiment, the inductive coupling coil 24 is connected with an excitation unit, and the excitation unit further includes a radio frequency power supply 3 and a power matcher 4 . When the system is working, the power matcher 4 matches the output power of the radio frequency power supply 3 to the inductive coupling coil 24, and then the inductive coupling coil 24 generates a high-frequency induced electromagnetic field so that the excitation gas Ar excites the reactive gas _SF6 to generate stable plasma.

The implementation steps of the above-mentioned application method of the plasma generator for SiC optical mirror processing in this embodiment include:

1) The plasma generator used for SiC optical mirror processing is installed on a numerically controlled motion platform with three-axis linkage function, and the surface of the SiC workpiece is scanned linearly by the plasma to obtain the material removal amount of the removal function. The experimental model of the removal function was obtained by combining the material removal amount and the groove section shape;

2) Calculate the residence time distribution according to the experimental model of the removal function, and set the processing path;

3) Iterative machining of the surface of the SiC workpiece by a plasma generator for SiC optical mirror machining.

The plasma generator used for SiC optical mirror processing in this embodiment can be installed on a CNC motion platform with three-axis linkage function to complete XYZ three-axis linkage processing, and the arc enhancement is generated when processing SiC optical mirror surfaces based on the plasma generator. The high-efficiency removal function is obtained, the residence time is calculated, and the processing path is set to realize the high-efficiency processing of SiC optical mirror arc-enhanced plasma.

In the present embodiment, the detailed steps of obtaining the experimental model of the removal function in step 1) include:

1.1) A groove is processed by linear scanning along the Y-axis direction of the surface of the SiC workpiece at a specified motion speed v by the plasma generator used for SiC optical mirror processing, and the measurement groove is obtained by a vertical interferometer. The cross-sectional shape data is shown in Figure 5; in this embodiment, the specified movement speed v is specifically 50 mm/min.

Referring to FIG. 8 and FIG. 9 , it can be seen that in this embodiment, the material removal amount and the removal depth obtained by linearly scanning and machining a groove along the Y-axis direction of the surface of the SiC workpiece by the plasma generator at a specified moving speed v. For comparison, Fig. 6 shows the material removal amount obtained by the ordinary ICP plasma linear scanning experiment, and Fig. 7 is the removal depth obtained by the ordinary ICP plasma linear scanning experiment. Comparing FIGS. 6 and 7 with FIGS. 8 and 9 , it can be seen that, in this embodiment, the removal function generated by the plasma generator on the SiC optical mirror surface has a high peak removal efficiency and a small full width at half maximum.

1.2) Fitting formula (4) on the basis of the obtained groove cross-sectional shape data to obtain the groove cross-sectional shape depth A _x , the value of the Gaussian distribution parameter σ _x of the removal function experimental model, and then according to formula (5) to obtain The experimental model of the removal function under the motion speed v;

In formula (4), G(x) is the shape function of the groove section in the X-axis direction, _Ax is the depth of the groove section shape, σx is the Gaussian distribution parameter of the experimental model of the removal function, and _x is the coordinate (x, y) ) at the abscissa;

In formula (5), R(x,y) represents the material removal amount at the coordinate (x,y), _Ax is the depth of the groove cross-sectional shape, v is the moving speed of the plasma generator, σx _is the removal function experiment Gaussian distribution parameters for the model.

The theoretical model of the groove cross-sectional shape function G(x) in the X-axis direction of the SiC workpiece can be described as formula (1);

In formula (1), R(x, y) represents the material removal amount at the coordinates (x, y), and v is the moving speed of the plasma generator.

The typical Gaussian-shaped removal function can be described as formula (2);

In formula (2), R(x, y) represents the material removal amount at the coordinate (x, y), A is the peak removal rate, and σ is the Gaussian distribution parameter of the removal function. Substitute formula (3) into formula (1) to have formula (3);

The parameters in formula (3) can be found in formula (1) and formula (2).

Therefore, the groove cross-sectional shape function G(x) is Gaussian fitted to Equation (4).

In the present embodiment, the groove cross-sectional shape function G(x) obtained by fitting the groove cross-sectional shape data according to the formula (4) after obtaining the measurement groove cross-sectional shape data by the vertical interferometer is:

That is, the value of the groove cross-sectional shape depth A _x is 0.604, and the value of the Gaussian distribution parameter σ _x of the removal function experimental model is 2.24. On this basis, according to formula (5), the experimental model of the removal function under the motion speed v can be obtained as:

The experimental model of the removal function at the above motion speed v is shown in Figure 10.

As shown in Fig. 6 to Fig. 9 , the peak removal efficiency of the removal function generated by the plasmon generator on the SiC optical mirror in the present invention is high, and the full width at half maximum is small. Therefore, the pulse iteration method can be used to calculate the residence time distribution. τ(x,y). In this embodiment, calculating the dwell time distribution according to the experimental model of the removal function in step 2) specifically refers to using the pulse iteration method to calculate the dwell time distribution τ(x,y), and using the pulse iteration method to calculate the dwell time distribution τ( The detailed steps of x,y) include:

2.1) According to the material removal amount distribution of the known surface shape of the SiC workpiece (determined according to the initial surface shape as shown in Figure 16), the material removal amount matrix R is established, and the removal function matrix G and remove function strength B _r ;

2.2) Set the value of the initial dwell time T ₀ as R/B _r and the residual as the value of E ₀ Among them, R is the material removal amount matrix, B _r is the removal function strength, and G is the removal function matrix;

2.3) Calculate the value of the dwell time correction Δk of the _k dwelling points as E _k /B _r ; wherein, E _k is the residual matrix of the k dwelling points, and B _r is the removal function strength;

2.4) The value of the dwell time T _k+1 of the correction k+1 dwell points is T _k +ζ·Δ _k ; where T _k is the dwell time of k dwell points, ζ is the relaxation factor, Δ _k is the dwell time correction of k dwell points; the relaxation factor ζ is used to control the rate of residual error convergence, the larger the relaxation factor ζ, the faster the residual error convergence, otherwise the residual error convergence is slower, the relaxation factor generally takes ζ ≤1.

其中，E_k+1为k+1个驻留点的残差矩阵，B_r为去除函数强度，R为材料去除量矩阵，T_k+1为k+1个驻留点的驻留时间，G为去除函数矩阵；2.5) Calculate the value of the residual matrix E _k+1 as

Among them, E _k+1 is the residual matrix of k+1 dwell points, B _r is the strength of the removal function, R is the material removal matrix, T _k+1 is the dwell time of k+1 dwell points, G is the removal function matrix;

2.6) Determine whether the dwell time T _k+1 of k+1 dwell points and the residual matrix E _k+1 meet the requirements, if not, repeat step 2.3); otherwise, the iteration ends, and the dwell of all dwell points is obtained The dwell time distribution τ(x,y) formed by time. The dwell time finally calculated in this embodiment is shown in FIG. 11 .

In order to realize the efficient processing of arc-enhanced plasma reaction of SiC optical mirror, in addition to solving the accurate residence time distribution τ(x, y), it is also necessary to reasonably plan the processing path to improve the stability of the plasma efficient processing method. In the high-efficiency processing of arc-enhanced plasma, the temperature has a great influence on the processing efficiency. For the traditional grating path, as shown in Figure 12, the grating pitch between the paths of the ordinary grating processing path is very small. As the processing time goes on, the processing temperature gradually increases. increases, resulting in an increase in the processing efficiency of the removal function. On the other hand, as the machining time increases, the temperature of the SiC workpiece itself increases, which in turn affects the stability of the machining efficiency of the removal function during the machining process. therefore. In order to solve this problem, the method of this embodiment adopts a nested raster scanning path. As shown in FIG. 13 , the raster pitch between adjacent paths in the nested raster processing path in this embodiment can be adjusted according to the size of the actual workpiece to be processed. , in order to balance the heat production of processing, balance the temperature distribution of the mirror surface during processing, and then improve the stability of the processing efficiency of the arc-enhanced plasma removal function.

普通等离子体经过10分钟加工，如图15所示，加工后面形为：PV 72nm,RMS 15.2nm，因此加工面形28.5nm RMS到15.2nm RMS，收敛比为1.87。如图16所示，SiC工件的初始面形为：PV 220nm,RMS 58nm,

用本实施例方法经过8分钟加工，如图17所示，加工后面形为：PV 166nm,RMS 19nm，面形从68nm RMS到19nm RMS，收敛比为3.58，面形不仅实现了快速收敛，而且收敛比提高了将近1倍。如果加工面形不收敛或者没有达到加工要求，再次设定材料去除量，计算驻留时间，设置光栅路径，进行迭代加工，直至加工结果满足加工要求。In this embodiment, the calculated dwell time and the set grating path are finally converted into CNC numerical control codes, and then SiC optical mirror processing is performed. According to the surface shape convergence after processing, as shown in Figure 14, the initial surface shape of the SiC workpiece is: PV 108.5nm, RMS 28.5nm,

After 10 minutes of ordinary plasma processing, as shown in Figure 15, the shape after processing is: PV 72nm, RMS 15.2nm, so the processing surface shape is 28.5nm RMS to 15.2nm RMS, and the convergence ratio is 1.87. As shown in Figure 16, the initial surface shape of the SiC workpiece is: PV 220nm, RMS 58nm,

After 8 minutes of processing by the method of this embodiment, as shown in Figure 17, the shape after processing is: PV 166nm, RMS 19nm, the surface shape is from 68nm RMS to 19nm RMS, the convergence ratio is 3.58, the surface shape not only achieves rapid convergence, but also The convergence ratio is nearly doubled. If the processing surface shape does not converge or does not meet the processing requirements, set the material removal amount again, calculate the dwell time, set the grating path, and perform iterative processing until the processing results meet the processing requirements.

The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims (10)

1. A plasma generator for SiC optical mirror finishing, characterized by: including shell (1) and install combined torch pipe (2) in shell (1), combined torch pipe (2) include outer tube (21) and nest in proper order well pipe (22) and inner tube (23) at outer tube (21) entry end, the cover is equipped with inductance coupling coil (24) on the middle part outer wall of outer tube (21), the exit end of outer tube (21) is equipped with laval nozzle (25), the space between outer tube (21), well pipe (22) forms cooling gas inflow channel, the space between well pipe (22), inner tube (23) forms and stimulates gaseous inflow channel, the inner chamber of inner tube (23) forms reaction gas inflow channel.

2. The plasma generator for SiC optical mirror finishing as claimed in claim 1, characterized in that: the combined type torch tube is characterized in that a torch tube mounting plate (20) is fixedly sleeved on the outer wall of the combined type torch tube (2), the outer tube (21), the middle tube (22) and the inner tube (23) are respectively fixedly mounted on the torch tube mounting plate (20), and the combined type torch tube (2) is mounted on an inner cavity central axis of the shell (1) through the torch tube mounting plate (20).

3. The plasma generator for SiC optical mirror finishing as claimed in claim 2, characterized in that: the inductive coupling coil (24) is a copper pipe with a first water-cooling circulation channel inside, and is arranged at the periphery of the outlet end of the combined torch tube (2) through a torch tube mounting plate (20) with a heat insulation gap left between the two.

4. The plasma generator for SiC optical mirror finishing as claimed in claim 1, characterized in that: the Laval nozzle (25) is made of copper materials.

5. The plasma generator for SiC optical mirror finishing as claimed in claim 1, characterized in that: the outer side of the laval nozzle (25) is provided with a nozzle shell (26), a nozzle mounting plate (261) is fixed on the nozzle shell (26), and the laval nozzle (25) is fixed on the central axis of the inner cavity of the nozzle shell (26) through the nozzle mounting plate (261), hermetically connected with the shell (1) through the nozzle mounting plate (261) and kept in the central axis collineation with the combined torch pipe (2).

6. The plasma generator for SiC optical mirror finishing as claimed in claim 5, characterized in that: a cooling cavity (262) is formed between the outer wall of the Laval nozzle (25) and the inner wall of the nozzle shell (26), a shell cavity (11) is arranged in the shell (1), and the shell cavity (11) and the cooling cavity (262) are communicated to form a second water-cooling circulation channel.

7. The plasma generator for SiC optical mirror finishing as claimed in claim 1, characterized in that: still be equipped with first inlet (211) of ventilating on the outer wall of outer tube (21), first inlet (211) of ventilating forms the cooling gas and flows in the passageway, still be equipped with second inlet (221) of ventilating on the outer wall of well pipe (22), second inlet (221) of ventilating forms and stimulates gaseous inflow channel, still be equipped with third inlet (231) of ventilating on the outer wall of inner tube (23), third inlet (231) of ventilating forms reaction gas inflow channel.

8. A method of using the plasma generator for SiC optical mirror finishing as defined in any one of claims 1 to 7, characterized by comprising the steps of:

1) the plasma generator for SiC optical mirror surface processing is arranged on a numerical control motion platform with a three-axis linkage function, the surface of a SiC workpiece is linearly scanned by using plasma to obtain the material removal amount of a removal function, and a removal function experimental model is obtained by extracting and fitting the sectional shape of a groove of the material removal amount;

2) calculating residence time distribution according to the removal function experimental model, and setting a processing path;

3) and performing iterative processing on the surface of the SiC workpiece by the plasma generator for SiC optical mirror processing.

9. The method of using a plasma generator for SiC optical mirror finishing as claimed in claim 8, wherein the detailed step of obtaining the experimental model of the removal function in step 1) comprises:

1.1) a groove is processed by the plasma generator for SiC optical mirror processing in a linear scanning mode along the Y-axis direction of the surface of the SiC workpiece at a specified motion speed v, and the sectional shape data of the measured groove is obtained by a vertical interferometer;

1.2) obtaining the depth A of the cross-sectional shape of the groove by fitting the formula (4) on the basis of the obtained data of the cross-sectional shape of the groove_xRemoving Gaussian distribution parameter sigma of function experimental model_xThen obtaining a removal function experimental model under the motion speed v according to the formula (5);

in the formula (4), G (X) is a function of the sectional shape of the groove in the X-axis direction, A_xDepth of cross-sectional shape of trench, σ_xTo remove the gaussian distribution parameters of the functional experimental model, x is the abscissa at coordinate (x, y);

in formula (5), R (x, y) represents the amount of material removed at coordinates (x, y), A_xIs the depth of the cross-sectional shape of the groove, v is the moving speed of the plasma generator, σ_xTo remove the gaussian distribution parameters of the functional experimental model.

10. The method as claimed in claim 8, wherein the step of calculating the distribution of residence time according to the experimental model of removal function in step 2) is a step of calculating the distribution of residence time τ (x, y) by using a pulse iteration method, and the detailed step of calculating the distribution of residence time τ (x, y) by using a pulse iteration method comprises:

2.1) establishing a material removal matrix R according to the material removal distribution of the known surface shape of the SiC workpiece, and determining a removal function matrix G and a removal function intensity B on the basis of obtaining a removal function experimental model_r；

2.2) setting the initial residence time T₀Has a value of R/B_rResidual error of E₀Has a value of

Wherein R is a material removal matrix, B_rFor removing function intensity, G is a removing function matrix;

2.3) calculating the dwell time correction amount Δ for k dwell points_kHas a value of E_k/B_r(ii) a Wherein E is_kResidual matrix of k dwell points, B_rTo remove the function intensity;

2.4) correction of the dwell time T of k +1 dwell points_k+1Has a value of T_k+ζ·Δ_k(ii) a Wherein, T_kDwell time for k dwell points, ζ is the relaxation factor, Δ_kDwell time correction amounts for k dwell points;

2.5) computing the residual matrix E_k+1Has a value of

Wherein E is_k+1Residual matrix of k +1 dwell points, B_rFor intensity of removal function, R is a matrix of material removal, T_k+1The residence time of k +1 residence points, G is a removal function matrix;

2.6) determining the residence time T of k +1 residence points_k+1And residual matrix E_k+1Whether the requirements are met or not, if not, repeating the step 2.3); otherwise, ending the iteration, and obtaining the residence time distribution tau (x, y) formed by the residence times of all the residence points.

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