Weak-rigidity free-form surface single-crystal silicon mirror and processing method thereof

Abstract

The application discloses a weak-rigidity free-form surface monocrystal silicon reflecting mirror piece and a processing method thereof, and the method comprises the following steps: obtaining a monocrystal silicon block; cutting the block; performing line cutting by using a diamond; performing precise grinding on the back surface; cutting the piece; adsorbing the mirror piece by using a free-form surface chuck; performing precise grinding on the front surface to form a cylindrical surface; performing magnetorheological elastomer polishing; releasing the mirror piece; adsorbing the mirror piece by using a cylindrical surface chuck; performing precise grinding on the back surface to thin the mirror piece; releasing the mirror piece; cutting the edge and performing wet etching on the back surface; and performing ion beam shaping processing to reach the final free-form surface shape precision. The X-ray reflecting mirror piece processing method is based on clamping the weak-rigidity free-form surface reflecting mirror into a cylindrical surface for processing, the whole process is ultra-precise grinding and polishing of the cylindrical surface, the processing method is simple and mature, the manufacturing cost is extremely low, the dependence on the ultra-high-precision multi-axis linkage machine tool is completely eliminated, the processing efficiency is greatly improved, and the method is suitable for mass production of the reflecting mirror.

Description

Technical Field

[0001] This invention belongs to the field of optical lens technology, specifically relating to a weakly rigid freeform surface monocrystalline silicon reflective lens and its processing method. Background Technology

[0002] X-ray telescopes are key high-end equipment for spacecraft's fully autonomous navigation and communication in deep space, as well as for deep space exploration. Grazing incidence X-ray reflectors are the core components for deep space exploration X-ray telescopes to achieve focused imaging.

[0003] Generally, the technology for constructing a high-performance segmented X-ray telescope using thin mirrors can be divided into the following steps: (1) manufacturing precision mirror substrates, including manufacturing precise substrates and stress-free polishing; (2) sputtering a metal coating onto the surface of the substrate mirror to enhance its X-ray reflectivity; (3) precisely aligning and assembling the thin-walled mirrors without introducing additional deformation; and (4) aligning the modules or shells and integrating them into a complete telescope. The performance of an X-ray telescope depends on the quality of its mirrors; therefore, the first step in manufacturing a high-performance X-ray telescope is to prepare high-performance X-ray reflecting mirrors.

[0004] Currently, through investigation and analysis of the manufacturing processes of X-ray telescope lenses at home and abroad, it has been found that the mirrors of traditional deep space exploration X-ray telescopes are mainly prepared using four conventional technologies: direct processing of microcrystalline glass, electroforming nickel-cobalt replication technology, epoxy replication technology, and hot glass forming technology.

[0005] The direct processing technology of microcrystalline glass uses microcrystalline glass as the substrate material for X-ray mirrors. By directly processing microcrystalline glass through processes such as hole drilling, ultra-precision machining of inner and outer surfaces, polishing and shaping of inner surfaces, and coating, a cylindrical mirror with a high surface accuracy and ultra-smooth surface can be obtained. Although this technology can produce mirrors with high surface accuracy and high surface integrity, it is difficult to achieve the processing of ultra-thin-walled mirrors. Currently, the wall thickness of single-layer mirrors is relatively large, resulting in a small number of nested layers of mirrors and severely limiting the light-gathering area of ​​the telescope.

[0006] Electroforming nickel-cobalt replication technology involves depositing a reflective film and a nickel-cobalt alloy substrate onto a high-precision, ultra-smooth mandrel surface, followed by cooling and demolding to separate the substrate and reflective film from the mandrel. This process can produce thin-walled cylindrical mirrors with a wall thickness of <1 mm and a roughness Ra <0.5 nm. However, X-ray mirrors manufactured using this method are prone to deformation due to difficulties in controlling stress distribution changes on the mirror surface during electroforming and cooling demolding, making it difficult to guarantee surface accuracy. Consequently, X-ray telescopes manufactured using this method have poor angular resolution (>10″), directly affecting their focusing performance for deep-space X-rays.

[0007] Epoxy replication technology uses aluminum, which has high strength and low density, as the matrix material, which can build X-ray observatories that are lightweight, low cost and have a large effective area. However, the accuracy of the lenses produced by the replication process is greatly limited. In addition, the complex assembly of thousands of image fragments limits the angular resolution of the manufactured X-ray telescope. Therefore, this technology minimizes cost and weight at the expense of angular resolution while maximizing the effective area.

[0008] Thermoforming technology uses molten silica as the forming core. After the glass sheet is thermoformed, it is cut into the required final shape. The reflective mirrors manufactured by this technology have a small wall thickness (<0.5mm) and can have more than 100 nested layers. However, the optical components are greatly affected by temperature, and the accuracy of the replicated mirrors depends heavily on the accuracy of the core. Their surface accuracy is low, which ultimately results in X-ray telescopes having a relatively moderate angular resolution.

[0009] Telescopes typically consist of multiple nested thin-walled X-ray mirrors and receiving imaging devices. However, the new generation of X-ray telescopes consists of more than 30,000 nested weakly rigid single-crystal silicon mirrors. The extremely high service performance requirements are to achieve sub-nanometer-level surface roughness, sub-micron-level surface accuracy, and extremely small slope deviation on hyperbolic cylindrical and parabolic cylindrical mirrors with a thickness of less than 1 mm.

[0010] However, existing X-ray mirror manufacturing processes still have the following problems: 1) The ultra-low surface shape error of freeform surface mirrors poses a great challenge to the precision and rigidity of machine tools. Machine tools need to achieve sub-micron level high-precision linkage across three or even more axes, while also requiring extremely high rigidity and precision retention. 2) Using high-precision multi-axis linkage machine tools and manufacturing according to freeform surface processing technology cannot meet the cost and efficiency requirements for manufacturing tens of thousands of mirrors. Therefore, to meet the requirements of lightweight, high sensitivity, and high resolution for next-generation X-ray telescopes, it is urgent to develop efficient and high-precision X-ray mirror processing technology. Summary of the Invention

[0011] In view of the problems existing in the manufacturing methods of next-generation X-ray reflective lenses, such as difficulty in controlling surface accuracy, stringent requirements for machine tools and equipment, and low processing efficiency, this invention provides a weakly rigid freeform surface monocrystalline silicon reflective lens and its processing method.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A method for fabricating a weakly rigid freeform surface monocrystalline silicon reflective mirror includes the following steps:

[0014] 1) Single-crystal silicon ingots are cut into single-crystal silicon blocks using a diamond wire saw;

[0015] 2) The monocrystalline silicon block is processed by using a diamond wire saw to cut the arc, thereby obtaining the outer cylindrical surface profile of the reflector;

[0016] 3) On a two-axis linkage CNC grinding machine or a three-axis CNC machine tool, a circular arc diamond rigid grinding wheel is used to perform ultra-precision grinding to shape the cylindrical surface of the back of the reflector, wherein the concave surface of the reflector is the front and the convex surface is the back.

[0017] 4) The monocrystalline silicon block processed in step 3 is sliced ​​using a diamond wire saw to obtain a thin-walled reflective lens with a cylindrical profile on both the front and back sides.

[0018] 5) Using a free-form porous ceramic chuck with high surface accuracy as the clamping reference, the suction force of the chuck is used to achieve the clamping deformation of the back of the thin-walled, weak-rigid reflective lens cylinder and to completely fit the surface of the chuck.

[0019] 6) On a two-axis linkage CNC grinding machine or a three-axis CNC machine tool, use a circular arc diamond rigid grinding wheel and a circular arc diamond elastic grinding wheel to perform high-precision grinding on the front of the reflector according to the cylindrical surface shape;

[0020] 7) On a two-axis cylindrical grinding and polishing machine, use a polyurethane polishing pad or magnetorheological elastomer to perform rough polishing on the front of the reflector, and use magnetorheological shear hardening adhesive to perform fine polishing with high surface integrity.

[0021] 8) The suction cup provides air cushioning and releases the reflective lens. The front surface of the lens, which was originally cylindrical, deforms into a free-form surface after the elastic stress is released.

[0022] 9) Using a high-precision cylindrical porous ceramic chuck as the clamping reference, the suction force of the chuck is used to achieve the front-side clamping deformation of the thin-walled, weak-rigid reflective lens and complete fit with the chuck surface shape, while the back side of the reflective lens is deformed into a free-form surface.

[0023] 10) On a two-axis linkage CNC grinding machine or a three-axis CNC machine tool, use a circular arc diamond rigid grinding wheel to perform ultra-precision grinding and thinning on the back of the reflector according to the cylindrical surface shape, so that the thickness of the reflector is uniform and reaches the design value of <1mm.

[0024] 11) The suction cup blows air to cushion and release the reflective lens, and both the front and back of the lens elastically return to their free-form surfaces;

[0025] 12) Based on the actual working dimensions of the reflective lens, trim the edges and perform wet etching on the back side to eliminate damage caused by grinding and trimming;

[0026] 13) The front surface of the polished reflective lens is subjected to high-precision reshaping processing using ion beam polishing method to achieve the final freeform surface accuracy.

[0027] A further improvement of this invention lies in the specific implementation method of step 3), which includes: bonding a cylindrical silicon block to a flat plate using paraffin wax; fixing it to the machine tool using a chuck table of a two-axis CNC grinding machine or a three-axis CNC machine tool; achieving high-precision tool setting based on a dial indicator or laser displacement sensor; programming a grinding CNC trajectory according to the radius of the cylindrical surface and the corresponding central angle of the arc surface to achieve deterministic grinding and shaping of the arc diamond grinding wheel; and continuously compensating for the surface shape based on offline and in-situ surface shape detection equipment until the requirements are met, with rough grinding... For semi-finish grinding, use #325 / 400 metal-bonded diamond wheels or ceramic-bonded diamond wheels with a single feed depth of 20–30 μm. For semi-finish grinding, use #800 metal-bonded diamond wheels or ceramic-bonded diamond wheels with a single feed depth of 5–10 μm. For finish grinding, use D7 resin-bonded diamond wheels with a single feed depth of 0.5–2 μm. The resulting mirror profile error PV < 1 μm and surface roughness Ra < 20 nm.

[0028] A further improvement of this invention is that the specific implementation method of step 5) includes: designing and manufacturing a free-form porous ceramic suction cup based on the theoretical free-form surface shape. When not adsorbed and deformed, the surface shape of the suction cup is S0, and the cylindrical surfaces of the front and back sides of the reflecting mirror are both S1. After the reflecting mirror is adsorbed and clamped, the back surface shape is adsorbed and deformed to completely fit the suction cup surface shape S0, and the front surface shape also elastically deforms to S0. At this time, the elastic deformation of both the front and back sides of the reflecting mirror is ΔS = S0 - S1. Subsequently, the front side of the reflecting mirror is ultra-precision ground into a cylindrical surface S1. After releasing the reflecting mirror, the elastic deformation of the back side returns to S0 - ΔS = S1, that is, the back side returns to the cylindrical surface shape S1, and the reflecting mirror... The front side should elastically deform to restore the theoretical freeform surface shape S2, i.e., S1-ΔS=S2. Therefore, the freeform surface shape of the suction cup S2=2*S1-S0. Subsequently, the suction cup is manufactured until the surface shape accuracy is below 1μm. The minimum vacuum degree is determined, a vacuum pump is selected, and the vacuum adsorption gas path and circuit are built to realize the adsorption and blowing buffer functions. The repeat adsorption accuracy of the suction cup is tested to meet the experimental requirements. At the same time, the entire adsorption deformation process is simulated and experimentally verified to ensure that the cylindrical back of the reflective lens can be clamped and deformed to completely fit the surface shape of the suction cup, and that the adsorption force and friction force provided by the suction cup can fully meet the effect of the grinding force on the reflective lens during the actual grinding process.

[0029] A further improvement of this invention is that the specific implementation method of step 6) includes: fixing the reflective lens, which is clamped by a free-form porous ceramic chuck, on a two-axis linkage CNC grinding machine or a three-axis CNC machine tool; achieving high-precision tool setting based on a dial indicator or laser displacement sensor; programming the grinding CNC trajectory according to the radius of the cylindrical surface and the corresponding central angle of the arc surface; realizing deterministic forming grinding of the arc diamond grinding wheel; continuously compensating for the surface shape based on offline and in-situ surface shape detection equipment until the requirements are met; and using #325 / 400 metal bonding for rough grinding. For semi-finishing, use a #800 metal-bonded diamond wheel or ceramic-bonded diamond wheel with a single feed depth of 20–30 μm. For semi-finishing, use a #800 metal-bonded diamond wheel or ceramic-bonded diamond wheel with a single feed depth of 5–10 μm. Then, use a D7 resin-bonded diamond wheel or elastic grinding wheel to finish the X-ray mirror with a single feed depth of 0.5–2 μm. The resulting mirror profile error PV < 1 μm and surface roughness Ra < 20 nm.

[0030] A further improvement of this invention is that the specific implementation method of step 7) includes: polishing the full-diameter mirror with a polyurethane polishing pad or a magnetron shear hardening polishing pad on a two-axis cylindrical grinding and polishing machine; the polishing head is a section of cylindrical surface with a magnetron polishing pad or polyurethane polishing pad with a thickness of 1-5mm bonded to the surface; the movement of the two vertical axes is controlled based on a dual-rotor model; an optimized Halbach magnet arrangement is used to provide a uniform magnetic field to the polishing interface, achieving uniform removal of the central area of ​​the mirror and completing the manufacturing of the mirror with a surface shape error PV < 1μm; during the polishing process, a polyurethane polishing pad or magnetorheological elastomer is first used with a 10-15% cerium oxide polishing slurry for efficient polishing; then, a magnetorheological shear hardening adhesive is used as a polishing pad with an 8-12% silicon solution to smooth the high-frequency errors on the mirror surface and preserve the low-frequency surface shape; the mirror is kept immersed in the polishing slurry during the process, ultimately achieving a surface roughness Ra < 0.5nm, a surface shape error PV < 1μm, and ultra-precision manufacturing of a weakly rigid freeform surface mirror.

[0031] A further improvement of the present invention is that the specific implementation method of step 9) includes: designing and manufacturing an outer cylindrical porous ceramic chuck based on the cylindrical surface shape, wherein the cylindrical radius of the outer cylindrical chuck is the cylindrical radius corresponding to the best fitting cylindrical surface of the theoretical front surface shape of the freeform surface reflector, continuously detecting and correcting the chuck surface shape until a surface shape accuracy of less than 1μm is achieved, and then using the adsorption force applied by the vacuum adsorption system to achieve adsorption deformation of the front surface of the reflector and complete adhesion to the surface of the chuck, thereby completing the positioning and clamping.

[0032] A further improvement of this invention is that the specific implementation method of step 10) includes: fixing the reflective mirror clamped by the porous ceramic chuck on the outer cylindrical surface onto a two-axis linkage CNC grinding machine or a three-axis CNC machine tool; achieving high-precision tool setting based on a dial indicator or laser displacement sensor; programming the grinding CNC trajectory according to the radius of the cylindrical surface and the corresponding central angle of the arc surface; achieving deterministic grinding and shaping of the arc diamond wheel; continuously compensating for the surface shape based on offline and in-situ surface shape detection equipment until the requirements are met; using a #800 metal-bonded diamond wheel or a ceramic-bonded diamond wheel for semi-finishing, with a single feed grinding depth of 5-10 μm; using a D7 resin-bonded diamond wheel for finish grinding, with a single feed grinding depth of 0.5-1 μm; and achieving a surface shape error PV < 1 μm and a surface roughness Ra < 20 nm for the processed reflective mirror.

[0033] A further improvement of the present invention is that the specific implementation method of step 12) includes: using a diamond wire cutting machine to remove the edges of the processed reflective lens, retaining the actual required reflective lens area, using an etching solution to perform wet etching on the back side to eliminate stress and damage, while protecting the front side to avoid contact with the etching solution.

[0034] A further improvement of the present invention is that the specific implementation method of step 13) includes: cleaning the reflective lens, detecting the surface shape with high precision, obtaining the surface shape data of the reflective lens, using an ion beam polishing machine, setting parameters to perform high-precision reshaping processing on the reflective lens, and finally achieving the required sub-nanometer-level surface roughness and sub-micron-level surface shape accuracy.

[0035] A weakly rigid freeform surface monocrystalline silicon reflective lens is manufactured using the aforementioned weakly rigid freeform surface monocrystalline silicon reflective lens manufacturing method.

[0036] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0037] 1. High efficiency and low cost in mirror processing. The X-ray mirror processing method proposed in this invention is based on clamping and transforming a free-form, weakly rigid mirror into a cylindrical surface for processing. The entire process involves ultra-precision grinding and polishing of the cylindrical surface. The processing method is simple and mature, with extremely low manufacturing costs. It completely eliminates the dependence on ultra-high precision multi-axis linkage machine tools, greatly improves processing efficiency, and is suitable for the mass production of tens of thousands of mirrors.

[0038] 2. High surface precision of the reflector. This invention employs mature ultra-precision grinding technology for cylindrical surfaces and high-precision polishing and shaping methods to obtain a weakly rigid reflective lens with high surface precision and high surface quality.

[0039] 3. The invention proposes using a porous ceramic curved suction cup as the clamping base for a weakly rigid reflector. The clamping and disassembly are very simple, and the repeated clamping and positioning accuracy is high. This solves the clamping problem of weakly rigid reflectors and improves the processing efficiency and safety compared with traditional adhesive technology.

[0040] 4. The processing technology proposed in this invention, which pre-deforms a free-form surface into a cylindrical surface, solves the problem of difficult processing of free-form surfaces. The process is simple. By utilizing the weak rigidity of the reflector, the complex curved surface is pre-deformed, adsorbed and clamped, and processed according to the best-fit cylindrical surface. After releasing the stress, the free-form surface can be realized. The processing method is safe and reliable. Attached Figure Description

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 This is a diagram illustrating the design process of the free-form porous ceramic suction cup surface shape when the reflective lens is adsorbed and clamped on the back side as described in this invention.

[0043] Figure 2 This is a flowchart of the high-efficiency and high-precision processing technology for the weakly rigid freeform surface monocrystalline silicon reflective lens described in this invention.

[0044] Figure 3 This is a schematic diagram of the efficient processing method for weakly rigid freeform surface monocrystalline silicon reflective lenses described in this invention. Detailed Implementation

[0045] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0046] When used, the terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0047] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0048] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0049] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0050] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0051] To address the problem of ultra-precision machining of thin-walled, weakly rigid freeform monocrystalline silicon reflective lenses, this invention proposes an efficient machining method for weakly rigid freeform monocrystalline silicon reflective lenses, employing the following steps: "diamond wire saw cutting silicon ingots into silicon blocks → diamond wire saw circular arc cutting of the cylindrical surface of the monocrystalline silicon block → ultra-precision grinding of the cylindrical surface of the monocrystalline silicon block → diamond wire saw circular arc cutting of the thin-walled, weakly rigid monocrystalline silicon reflective lens → freeform surface chuck adsorbing the lens back (convex surface) for deformation → ultra-precision grinding of the reflective lens front (concave surface) into a cylindrical surface → ultra-precision polishing of the reflective lens front → chuck releases the lens to restore deformation → cylindrical surface chuck adsorbs the lens front for deformation → ultra-precision grinding and thinning of the reflective lens back → chuck releases the lens to restore deformation → reflective lens edge trimming and back wet etching → reflective lens front ion beam shaping."

[0052] Example 1

[0053] This invention provides a method for processing a weakly rigid freeform surface monocrystalline silicon reflective mirror, comprising the following steps:

[0054] 1) Single-crystal silicon ingots are cut into single-crystal silicon blocks using a diamond wire saw;

[0055] 2) The monocrystalline silicon block is processed by using a diamond wire saw to cut the arc, thereby obtaining the outer cylindrical surface profile of the reflector;

[0056] 3) On a two-axis linkage CNC grinding machine or a three-axis CNC machine tool, a circular arc diamond rigid grinding wheel is used to perform ultra-precision grinding to shape the cylindrical surface of the back of the reflector, wherein the concave surface of the reflector is the front and the convex surface is the back.

[0057] 4) The monocrystalline silicon block processed in step 3 is sliced ​​using a diamond wire saw to obtain a thin-walled reflective lens with a cylindrical profile on both the front and back sides.

[0058] 5) Using a free-form porous ceramic chuck with high surface accuracy as the clamping reference, the suction force of the chuck is used to achieve the clamping deformation of the back of the thin-walled, weak-rigid reflective lens cylinder and to completely fit the surface of the chuck.

[0059] 6) On a two-axis linkage CNC grinding machine or a three-axis CNC machine tool, use a circular arc diamond rigid grinding wheel and a circular arc diamond elastic grinding wheel to perform high-precision grinding on the front of the reflector according to the cylindrical surface shape;

[0060] 7) On a two-axis cylindrical grinding and polishing machine, use a polyurethane polishing pad or magnetorheological elastomer to perform rough polishing on the front of the reflector, and use magnetorheological shear hardening adhesive to perform fine polishing with high surface integrity.

[0061] 8) The suction cup provides air cushioning and releases the reflective lens. The front surface of the lens, which was originally cylindrical, deforms into a free-form surface after the elastic stress is released.

[0062] 9) Using a high-precision cylindrical porous ceramic chuck as the clamping reference, the suction force of the chuck is used to achieve the front-side clamping deformation of the thin-walled, weak-rigid reflective lens and complete fit with the chuck surface shape, while the back side of the reflective lens is deformed into a free-form surface.

[0063] 10) On a two-axis linkage CNC grinding machine or a three-axis CNC machine tool, use a circular arc diamond rigid grinding wheel to perform ultra-precision grinding and thinning on the back of the reflector according to the cylindrical surface shape, so that the thickness of the reflector is uniform and reaches the design value of <1mm.

[0064] 11) The suction cup blows air to cushion and release the reflective lens, and both the front and back of the lens elastically return to their free-form surfaces;

[0065] 12) Based on the actual working dimensions of the reflective lens, trim the edges and perform wet etching on the back side to eliminate damage caused by grinding and trimming;

[0066] 13) The front surface of the polished reflective lens is subjected to high-precision reshaping processing using ion beam polishing method to achieve the final freeform surface accuracy.

[0067] Example 2

[0068] This invention provides a method for processing a weakly rigid freeform surface monocrystalline silicon reflective mirror, comprising the following steps:

[0069] 1) Cutting a monocrystalline silicon ingot into a monocrystalline silicon block using a diamond wire saw, specifically including fixing the monocrystalline silicon ingot on the worktable of the wire saw and cutting out a rectangular block of monocrystalline silicon of the required size;

[0070] 2) The single-crystal silicon block is processed by using a diamond wire saw to cut the arc to obtain the outer cylindrical surface profile of the reflector. Specifically, this includes writing the cutting CNC trajectory based on the radius of the required cylindrical surface and the central angle corresponding to the arc surface, inputting it into the CNC system, and setting the cutting parameters to complete the cutting of the outer cylindrical surface of the reflector.

[0071] 3) On a two-axis CNC grinding machine or a three-axis CNC machine tool, a circular arc diamond rigid grinding wheel is used to perform ultra-precision grinding of the cylindrical surface of the back of the reflector (where the concave surface of the reflector is the front and the convex surface is the back). Specifically, this involves bonding a cylindrical silicon block to a high-precision plate using paraffin wax, fixing it to the machine tool using a chuck table, achieving high-precision tool setting based on a dial indicator or laser displacement sensor, and programming a grinding CNC trajectory based on the radius of the cylindrical surface and the corresponding central angle of the arc surface to achieve deterministic grinding of the circular arc diamond grinding wheel. The line and in-situ surface shape detection equipment continuously compensate for the surface shape until the requirements are met. Rough grinding uses #325 / 400 metal-bonded diamond grinding wheels or ceramic-bonded diamond grinding wheels, with a single feed depth of 20-30μm. Semi-finish grinding uses #800 metal-bonded diamond grinding wheels or ceramic-bonded diamond grinding wheels, with a single feed depth of 5-10μm. Finish grinding uses D7 resin-bonded diamond grinding wheels, with a single feed depth of 0.5-2μm. The surface shape error of the processed reflector is PV<1μm, and the surface roughness Ra<20nm.

[0072] 4) The monocrystalline silicon block processed in step 3 is sliced ​​using a diamond wire saw to obtain a thin-walled reflective lens with a cylindrical profile on both the front and back sides. Specifically, this involves writing a cutting CNC trajectory based on the radius of the required cylindrical shape and the central angle corresponding to the arc surface, inputting it into the CNC system, and setting the cutting parameters to complete the cutting of the cylindrical front side of the reflective lens.

[0073] 5) Using a high-precision freeform porous ceramic chuck as the clamping reference, the suction force of the chuck is utilized to deform and perfectly fit the back of the thin-walled, weakly rigid cylindrical reflective lens. This involves designing and manufacturing the freeform porous ceramic chuck based on theoretical freeform surface shapes. The surface design process of the freeform chuck is as follows: Figure 1As shown, when the mirror is not adsorbed and deformed, let the surface shape of the suction cup be S0, and the cylindrical surfaces of both the front and back sides of the reflective mirror be S1. After the reflective mirror is adsorbed and clamped, the back surface deforms and completely conforms to the suction cup surface shape S0, and the front surface also elastically deforms to S0. At this time, the elastic deformation of both the front and back sides of the reflective mirror is ΔS = S0 - S1. Subsequently, the front side of the reflective mirror is precision ground into a cylindrical surface S1. After the reflective mirror is released, the elastic deformation of the back side recovers to S0 - ΔS = S1, that is, the back side recovers to the cylindrical surface shape S1. The front side of the reflective mirror should elastically deform back to the theoretical freeform surface shape S2, that is, S1 - ΔS = S2. Therefore, the surface shape of the freeform chuck is S2 = 2*S1 - S0. The chuck is then manufactured until the surface shape accuracy is below 1μm. The minimum vacuum level is determined, a suitable vacuum pump is selected, and the vacuum adsorption gas path and circuit are built to realize the adsorption and blowing buffer functions. The repeat adsorption accuracy of the chuck is tested to meet the experimental requirements. At the same time, the entire adsorption deformation process is simulated and experimentally verified to ensure that the cylindrical back of the reflective lens is clamped and deformed and can completely fit the surface shape of the chuck. The adsorption force and friction force provided by the chuck can fully meet the effect of the grinding force on the reflective lens during the actual grinding process, so as to avoid it falling off or shifting.

[0074] 6) On a two-axis CNC grinding machine or a three-axis CNC machine tool, a circular arc diamond rigid grinding wheel and a circular arc diamond elastic grinding wheel are used to perform efficient and high-precision grinding of the front surface of the reflector according to the cylindrical surface shape. Specifically, this includes fixing the reflector with a free-form surface porous ceramic chuck on the two-axis CNC grinding machine or a three-axis CNC machine tool, achieving high-precision tool setting based on a dial indicator or laser displacement sensor, programming the grinding CNC trajectory according to the radius of the cylindrical surface and the corresponding central angle of the arc surface, realizing deterministic shaping grinding of the circular arc diamond grinding wheel, and continuously compensating for the surface shape based on offline and in-situ surface shape detection equipment until... To meet the requirements, rough grinding uses a #325 / 400 metal-bonded diamond wheel or a ceramic-bonded diamond wheel with a single feed depth of 20–30 μm. Semi-finish grinding uses a #800 metal-bonded diamond wheel or a ceramic-bonded diamond wheel with a single feed depth of 5–10 μm. Subsequently, fine grinding of the X-ray reflector is achieved using a D7 resin-bonded diamond wheel or an elastic grinding wheel with a single feed depth of 0.5–2 μm. The resulting reflector has a profile surface error PV < 1 μm and a surface roughness Ra < 20 nm.

[0075] 7) On a two-axis cylindrical grinding and polishing machine, a polyurethane polishing pad or a magnetorheological elastomer is used to perform efficient rough polishing on the front surface of the reflector, and a magnetorheological shear hardening adhesive is used for fine polishing with high surface integrity. Specifically, on a two-axis cylindrical grinding and polishing machine, a polyurethane polishing pad or a magnetron shear hardening polishing pad is used to polish the full diameter of the reflector. The polishing head is a section of cylindrical surface with a magnetron polishing pad or polyurethane polishing pad with a thickness of 1-5mm bonded to the surface. The movement of the two vertical axes is controlled based on a dual-rotor model, and an optimized Halbach magnet arrangement is used to provide a uniform magnetic field to the polishing interface, so as to achieve uniform removal of the central area of ​​the reflector and complete the manufacturing of the reflector with a surface shape error PV < 1μm. During the polishing process, polyurethane polishing pads or magnetorheological elastomers are first used with 10-15% cerium oxide polishing slurry for efficient polishing. Then, magnetorheological shear hardening adhesive is used as a polishing pad with 8-12% silicon solution to smooth high-frequency errors on the surface of the mirror and preserve the low-frequency surface shape. During the process, the mirror is kept immersed in the polishing slurry. Finally, the surface roughness Ra < 0.5 nm and the surface shape error PV < 1 μm are achieved, resulting in the efficient and ultra-precision manufacturing of a weakly rigid freeform surface mirror.

[0076] 8) The suction cup blows air to buffer and release the reflective lens. The front of the lens is deformed from a cylindrical surface to a free-form surface after the elastic stress is released. Specifically, the vacuum pump is turned off and compressed air is introduced to release the silicon wafer, the prestress is released, the elastic deformation is restored, and the front of the lens is deformed into a free-form surface.

[0077] 9) Using a high-precision cylindrical porous ceramic chuck as the clamping reference, the suction force of the chuck is used to achieve the front-side clamping deformation of the thin-walled, weak-rigid reflective lens and complete fit with the chuck surface. The back side of the reflective lens is deformed into a free-form surface. Specifically, this involves designing and manufacturing an outer cylindrical porous ceramic chuck based on the cylindrical surface shape. The cylindrical radius of the outer cylindrical chuck is the cylindrical radius corresponding to the best-fit cylindrical surface of the theoretical front surface shape of the free-form reflective lens. The chuck surface shape is continuously detected and corrected until a surface shape accuracy of less than 1μm is achieved. Then, the suction force applied by the vacuum adsorption system is used to achieve the front-side adsorption deformation of the reflective lens and complete fit with the surface of the chuck, thus completing the positioning and clamping.

[0078] 10) On a two-axis CNC grinding machine or a three-axis CNC machine tool, use a circular arc diamond rigid grinding wheel to perform ultra-precision grinding and thinning on the back of the reflector according to the cylindrical surface shape, so that the reflector thickness is uniform and reaches the design value of <1mm. Specifically, this includes fixing the reflector with a multi-hole ceramic chuck on the outer cylindrical surface on the two-axis CNC grinding machine or a three-axis CNC machine tool, achieving high-precision tool setting based on a dial indicator or laser displacement sensor, and programming the grinding CNC trajectory according to the radius of the cylindrical surface and the corresponding central angle of the arc surface. This method achieves deterministic grinding of circular arc diamond wheels. Based on offline and in-situ surface shape detection equipment, the surface shape is continuously compensated until the requirements are met. Semi-finish grinding uses #800 metal-bonded diamond wheels or ceramic-bonded diamond wheels with a single feed depth of 5-10 μm. Finish grinding uses D7 resin-bonded diamond wheels with a single feed depth of 0.5-1 μm. The surface shape error of the processed mirror profile is PV<1μm, and the surface roughness Ra<20nm.

[0079] 11) The suction cup blows air to buffer and release the reflective mirror. Both the front and back sides of the mirror elastically recover to free-form surfaces. Specifically, this includes turning off the vacuum pump and introducing compressed air to release the silicon wafer, releasing the prestress, and restoring the elastic deformation. At this time, both the front and back sides of the reflective mirror are free-form surfaces.

[0080] 12) According to the actual working size of the reflective lens, trim the edges and perform wet etching on the back side to eliminate the damage caused by grinding and trimming. Specifically, this includes using a diamond wire cutter to remove the edges of the processed reflective lens, retaining the actual required reflective mirror area, using an etching solution to perform wet etching on the back side to eliminate stress and damage, and protecting the front side to avoid contact with the etching solution.

[0081] 13) The ion beam polishing method is used to perform high-precision reshaping of the front surface of the polished reflective lens to achieve the final freeform surface accuracy. Specifically, this includes cleaning the reflective lens, high-precision detection of the surface shape to obtain the surface shape data of the reflective lens, and using an ion beam polishing machine to perform high-precision reshaping of the reflective lens by setting parameters, so as to finally achieve the required sub-nanometer level surface roughness and sub-micron level surface accuracy.

[0082] Example 3

[0083] The present invention provides a weakly rigid freeform surface monocrystalline silicon reflective lens, which is manufactured by the weakly rigid freeform surface monocrystalline silicon reflective lens processing method described in Example 1 or 2.

[0084] The inventive points protected by this invention are:

[0085] 1. The technology and approach based on clamping and transforming a free-form, weakly rigid reflector into a cylindrical surface for machining;

[0086] 2. A combined polishing technology that uses polyurethane polishing pads or magnetorheological elastomers for efficient rough polishing and magnetorheological shear hardening adhesives for high surface integrity fine polishing, including the design of the polishing head and the polishing pads, movement patterns, and magnetic field arrangement during the polishing process;

[0087] 3. A system for achieving high-precision and high-repeatability clamping and positioning of weakly rigid reflectors and implementing adsorption prestress based on curved surface suction cup adsorption, with a design concept for the surface shape of the free-form surface suction cup.

[0088] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0089] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for processing a weakly rigid free-form single-crystal silicon mirror lens, characterized in that, The method comprises the following steps: 1) cutting a single crystal silicon ingot to obtain a single crystal silicon block by using a diamond wire saw; 2) processing the single crystal silicon block by using a diamond wire saw arc cutting method to obtain a mirror outer cylindrical surface profile; 3) on a two-axis linkage numerical control grinding machine or a three-axis numerical control machine tool, using a circular arc diamond rigid grinding wheel to perform ultra-precision grinding forming on the cylindrical surface profile of the back surface of the mirror, wherein the inner concave surface of the mirror is the front surface, and the outer convex surface is the back surface; 4) slicing the single crystal silicon block processed in step 3 by using the diamond wire saw arc cutting method to obtain a thin-walled mirror piece with a cylindrical profile on the front surface and the back surface; 5) using a high-surface profile accuracy free-form surface porous ceramic chuck as a clamping reference, and realizing clamping deformation and complete adhesion of the cylindrical back surface of the thin-walled mirror piece to the surface profile of the chuck by using the chuck suction force, comprising: designing and manufacturing a free-form surface porous ceramic chuck based on a theoretical free-form surface profile, when not being adsorbed and deformed, the surface profile of the chuck is S0, and the cylindrical surface profiles of the front surface and the back surface of the mirror piece are S1; when the mirror piece is adsorbed and clamped, the back surface profile is adsorbed and deformed and completely adheres to the chuck surface profile S0, and the front surface profile is also elastically deformed to S0, at this time, the elastic deformation amounts of the front surface and the back surface of the mirror piece are ΔS=S0-S1; subsequently, the front surface of the mirror is ultra-precision ground to a cylindrical surface S1; after the mirror piece is released, the back surface elastically deforms to recover to S0-ΔS=S1, that is, the back surface recovers to the cylindrical surface profile S1, and the front surface of the mirror should elastically deform to recover to the theoretical free-form surface profile S2, that is, S1-ΔS=S2, therefore, the free-form surface chuck profile S2=2S1-S0, subsequently, the chuck is manufactured until the surface profile accuracy is below 1 μm, the minimum vacuum degree is determined, a vacuum pump is selected, the vacuum adsorption gas circuit and the electric circuit are built, the adsorption and air blowing buffer functions are realized, the chuck repeated adsorption accuracy is detected, the experimental requirements are met, the adsorption deformation process is simulated and experimentally verified, and it is ensured that the cylindrical back surface of the mirror piece can be clamped and deformed and completely adhere to the chuck surface profile, and the adsorption force and the friction force provided by the chuck can completely meet the grinding force acting on the mirror piece in the actual grinding process; 6) on a two-axis linkage numerical control grinding machine or a three-axis numerical control machine tool, using a circular arc diamond rigid grinding wheel and a circular arc diamond elastic grinding wheel to perform high-precision grinding forming on the front surface of the mirror according to the cylindrical surface profile; 7) on a two-axis cylindrical grinding and polishing machine tool, using a polyurethane polishing pad or a magnetorheological elastomer to perform rough polishing on the front surface of the mirror, and using a magnetorheological shear hardening glue to perform high-surface integrity fine polishing; 8) the chuck blows air to buffer and releases the mirror piece, and the front surface of the mirror is deformed to a free-form surface after the cylindrical surface profile is released by elastic stress; 9) Using the cylindrical porous ceramic chuck with high surface accuracy as the clamping reference, the thin-walled and weakly rigid mirror is clamped and deformed on the front surface by the suction force of the chuck, and the front surface of the mirror is completely attached to the surface of the chuck. The back surface of the mirror is deformed into a free-form surface, including: designing and manufacturing an outer cylindrical porous ceramic chuck based on the cylindrical surface shape, the cylindrical radius of the outer cylindrical chuck is the corresponding cylindrical radius of the best fitting cylindrical surface of the theoretical surface shape of the front surface of the free-form surface mirror. The surface shape of the chuck is continuously detected and corrected until the surface accuracy is below 1 μm. Then, the suction force of the vacuum suction system is used to realize the suction deformation of the front surface of the mirror and completely attach to the surface of the chuck, and the positioning and clamping are completed; 10) On a two-axis linkage numerical control grinding machine or a three-axis numerical control machine tool, the back surface of the mirror is thinned by super-precision grinding according to the cylindrical surface shape using a circular arc diamond rigid grinding wheel, so that the thickness of the mirror is uniform and reaches the design value of <1 mm, including: the mirror clamped by the outer cylindrical porous ceramic chuck is fixed on the two-axis linkage numerical control grinding machine or the three-axis numerical control machine tool, the tool is measured with high accuracy based on the micrometer or laser displacement sensor, the grinding numerical control track is programmed according to the radius of the cylindrical surface and the corresponding central angle of the curved surface, the deterministic grinding forming of the circular arc diamond grinding wheel is realized, the surface shape is continuously compensated based on the off-line and in-situ surface shape detection equipment until the requirements are met. The semi-fine grinding uses a #800 metal bond diamond grinding wheel or a ceramic bond diamond grinding wheel, the single feed grinding depth is 5-10 μm, the fine grinding uses a D7 resin bond diamond grinding wheel, the single feed grinding depth is 0.5-1 μm, the profile surface error PV of the processed mirror is <1 μm, and the surface roughness Ra is <20 nm; 11) The chuck is blown and the mirror is released, and the front and back surfaces of the mirror are elastically restored to free-form surfaces; 12) According to the actual working size of the mirror, the edge is cut and the back surface is etched by wet etching to eliminate the damage caused by grinding and cutting; 13) The front surface of the mirror after polishing is processed by ion beam polishing method to achieve the final free-form surface accuracy.

2. The method of claim 1, wherein the weak-rigid free-form single-crystal silicon mirror is processed by a method comprising: The specific implementation method of step 3) includes: bonding the cylindrical silicon block on the flat plate with paraffin wax, fixing the chuck table of the two-axis linkage numerical control grinding machine or the three-axis numerical control machine tool on the machine tool, realizing high-precision tool setting based on the micrometer or the laser displacement sensor, writing the grinding numerical control track according to the radius of the cylindrical surface and the corresponding central angle of the arc surface, realizing the deterministic grinding forming of the arc diamond grinding wheel, continuously compensating the surface shape based on the offline and in-situ surface shape detection equipment until the requirement is met, using the metal bond diamond grinding wheel or the ceramic bond diamond grinding wheel with #325 / 400 for rough grinding, the grinding depth of single feeding is 20-30 μm, using the metal bond diamond grinding wheel or the ceramic bond diamond grinding wheel with #800 for semi-fine grinding, the grinding depth of single feeding is 5-10 μm, using the resin bond diamond grinding wheel with D7 granularity for fine grinding, the grinding depth of single feeding is 0.5-2 μm, the profile surface error PV of the processed mirror is less than 1 μm, and the surface roughness Ra is less than 20 nm. ​ 3. The method of claim 1, wherein the weak-rigid free-form single-crystal silicon mirror is processed by a method comprising: The specific implementation method of step 6) includes: fixing the mirror piece clamped by the free-form surface porous ceramic chuck on the two-axis linkage numerical control grinding machine or the three-axis numerical control machine tool, realizing high-precision tool setting based on the micrometer or the laser displacement sensor, writing the grinding numerical control track according to the radius of the cylindrical surface and the corresponding central angle of the arc surface, realizing the deterministic forming grinding of the arc diamond grinding wheel, continuously compensating the surface shape based on the offline and in-situ surface shape detection equipment until the requirement is met, using the metal bond diamond grinding wheel or the ceramic bond diamond grinding wheel with #325 / 400 for rough grinding, the grinding depth of single feeding is 20-30 μm, using the metal bond diamond grinding wheel or the ceramic bond diamond grinding wheel with #800 for semi-fine grinding, the grinding depth of single feeding is 5-10 μm, then using the resin bond diamond grinding wheel with D7 granularity or the elastic grinding tool for fine grinding of the X-ray mirror piece, the grinding depth of single feeding is 0.5-2 μm, the profile surface error PV of the processed mirror is less than 1 μm, and the surface roughness Ra is less than 20 nm. ​ 4. The method of claim 1, wherein the weak-rigid free-form single-crystal silicon mirror is processed by a method comprising: The specific implementation method of step 7) includes: polishing the mirror on the two-axis cylindrical polishing machine tool by using the polyurethane polishing pad or the magnetic control shear hardening polishing pad; the polishing head adopted is a section of cylindrical surface, the surface is bonded with the magnetic control polishing pad or the polyurethane polishing pad with a thickness of 1-5 mm, the two vertical axis movements are controlled based on the double-rotor model, the polishing interface is provided with uniform magnetic field by using the optimized Halbach magnet arrangement, the uniform removal of the central region of the mirror piece is realized, and the manufacturing requirement of the profile surface error PV of the mirror piece less than 1 μm is completed; during the polishing process, the polyurethane polishing pad or the magnetorheological elastomer is first used for efficient polishing with the polishing liquid containing 10-15% cerium oxide, then the magnetorheological shear hardening glue is used as the polishing pad to smooth the medium-high frequency error of the mirror surface with the polishing liquid containing 8-12% silicon solution, the low-frequency surface shape is preserved, the mirror piece is kept immersed in the polishing liquid during the process, and finally the surface roughness Ra less than 0.5 nm and the profile surface error PV less than 1 μm of the weak-rigidity free-form surface mirror are realized. ​ 5. The method of claim 1, wherein the method further comprises: The specific implementation method of step 12) includes: using a diamond wire cutting machine to remove the edge of the processed mirror piece, retaining the actual required mirror area, using an etching liquid to wet etch the back surface to eliminate stress and damage, and at the same time protecting the front surface from contacting the etching liquid.

6. The method of claim 1, wherein the method further comprises: The specific implementation method of step 13) includes: cleaning the mirror piece, high-precision detecting the surface shape to obtain the surface shape data of the mirror piece, using an ion beam polisher to set parameters to perform high-precision shaping processing on the mirror piece, and finally achieving the required sub-nanometer surface roughness and sub-micron surface shape precision.

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