Method and apparatus for fabricating single-crystal silicon reflectors

Abstract

This application discloses a method and apparatus for fabricating a monocrystalline silicon reflector. The method includes: providing a monocrystalline silicon reflector to be fabricated; performing a first type of polishing on the monocrystalline silicon reflector based on magnetorheological polishing technology; and performing a second type of polishing on the monocrystalline silicon reflector after the first type of polishing based on magnetorheological polishing technology to obtain a monocrystalline silicon reflector that meets the requirements; wherein the particle size of the polishing slurry corresponding to the first type of polishing is larger than the particle size of the polishing slurry corresponding to the second type of polishing. This method not only meets the precision requirements of monocrystalline silicon reflectors but also significantly reduces production costs while improving polishing efficiency.

Description

Technical Field

[0001] This application relates to the field of mirror technology, and in particular to a method and apparatus for fabricating a single-crystal silicon mirror. Background Technology

[0002] Synchrotron radiation sources possess unique properties such as high throughput, high brightness, and wide spectrum, and are widely used in many cutting-edge scientific fields, yielding a series of significant scientific research results. Synchrotron radiation sources typically employ optical modulation processes such as collimation, monochromaticity, and focusing to obtain millimeter- to nanometer-scale fine beams that are then transmitted to experimental stations for user use.

[0003] The development of synchrotron radiation optics technology has placed higher precision demands on single-crystal silicon mirrors. While related combined polishing techniques can achieve high-precision machining of mirrors, they limit their processing efficiency and have significant limitations. Summary of the Invention

[0004] The method and apparatus for preparing monocrystalline silicon reflectors provided in this application not only meet the precision requirements of monocrystalline silicon reflectors, but also significantly reduce production costs while improving polishing efficiency.

[0005] To address the aforementioned technical problems, this application provides a method for fabricating a monocrystalline silicon mirror. The method includes: providing a monocrystalline silicon mirror to be fabricated; performing a first type of polishing on the monocrystalline silicon mirror to be fabricated using magnetorheological polishing technology; and performing a second type of polishing on the monocrystalline silicon mirror to be fabricated after the first type of polishing using magnetorheological polishing technology to obtain a monocrystalline silicon mirror that meets the requirements. The particle size of the polishing slurry corresponding to the first type of polishing is larger than the particle size of the polishing slurry corresponding to the second type of polishing.

[0006] The process of performing a first type of polishing on the monocrystalline silicon mirror to be prepared based on magnetorheological polishing technology includes: obtaining the target surface shape of the monocrystalline silicon mirror to be prepared; determining the polishing process parameters based on the target surface shape; and performing a first type of polishing on the monocrystalline silicon mirror to be prepared using magnetorheological polishing technology based on the process parameters.

[0007] The process parameters include immersion depth, rotation speed, and / or moisture content; in response to a target surface being cylindrical, the immersion depth is 0.2 mm, the rotation speed is 80 rpm, and / or the moisture content is 17%.

[0008] The polishing process parameters for the first type of polishing and the second type of polishing are the same.

[0009] The process involves performing a second type of polishing on the monocrystalline silicon mirror to be prepared after completing the first type of polishing using magnetorheological polishing technology to obtain a monocrystalline silicon mirror that meets the requirements. This includes: performing a second type of polishing on the monocrystalline silicon mirror to be prepared after completing the first type of polishing using magnetorheological polishing technology; performing surface quality inspection on the monocrystalline silicon mirror to be prepared after completing the second type of polishing; and obtaining a monocrystalline silicon mirror that meets the requirements based on the quality inspection results.

[0010] Among them, the surface quality inspection of the single-crystal silicon mirror to be prepared after the second type of polishing is carried out, including: the root mean square of surface residuals, wavefront gradient, roughness and cross-sectional curve consistency inspection of the single-crystal silicon mirror to be prepared after the second type of polishing is carried out.

[0011] In this process, the edges of the monocrystalline silicon mirror to be prepared are equipped with baffles to control the trajectory of the polishing equipment during polishing, thereby reducing edge defects in the monocrystalline silicon mirror to be prepared.

[0012] The polishing time for the second type of polishing is 1-2 hours.

[0013] Among them, the polishing slurry corresponding to the second type of polishing is a cerium oxide polishing slurry with a particle size of 50nm.

[0014] To address the aforementioned technical problems, this application also provides an apparatus for fabricating a monocrystalline silicon mirror. The apparatus includes: a support component for supporting the monocrystalline silicon mirror to be fabricated; and a polishing device for polishing the monocrystalline silicon mirror to be fabricated using the fabrication method provided above, thereby obtaining a monocrystalline silicon mirror that meets the requirements.

[0015] The method and apparatus for fabricating a monocrystalline silicon reflector provided in this application involve performing a first type of polishing on the monocrystalline silicon reflector to be fabricated using magnetorheological polishing technology; and then performing a second type of polishing on the monocrystalline silicon reflector to be fabricated after the first type of polishing using magnetorheological polishing technology to obtain a monocrystalline silicon reflector that meets the requirements. The particle size of the polishing slurry corresponding to the first type of polishing is larger than that of the polishing slurry corresponding to the second type of polishing, which not only meets the precision requirements of the monocrystalline silicon reflector but also significantly reduces the production cost while improving the polishing efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1This is a schematic flowchart of an embodiment of the method for fabricating a single-crystal silicon reflector provided in this application;

[0018] Figure 2 This is a schematic flowchart of another embodiment of the method for fabricating a single-crystal silicon reflector provided in this application;

[0019] Figure 3 This is a schematic flowchart of another embodiment of the method for fabricating a single-crystal silicon reflector provided in this application;

[0020] Figure 4 This is a schematic diagram of an embodiment of the fabrication apparatus for a single-crystal silicon reflector provided in this application;

[0021] Figure 5 This is a schematic diagram of the test results of hardness testing on the back surface, the surface after CNC polishing, and the surface after magnetorheological polishing of monocrystalline silicon provided in this application;

[0022] Figure 6 This application provides Figure 5 A diagram showing the comparison of test results;

[0023] Figure 7 This is a schematic diagram showing the effect of immersion depth, rotation speed, and water content on contact pressure provided in this application;

[0024] Figure 8 This is a schematic diagram of the actual force curves measured at different rotational speeds provided in this application;

[0025] Figure 9 This is a schematic diagram of the theoretical surface shape of the aperture of the single-crystal silicon mirror provided in this application;

[0026] Figure 10 This is a comparative schematic diagram showing the positions of the three cross sections provided in this application and the cross section curves at positions 1, 2 and 3. Detailed Implementation

[0027] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0028] In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. The terms "first," "second," and "third" in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movements between components in a specific orientation (as shown in the figures). If the specific orientation changes, the directional indication will also change accordingly. The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to these processes, methods, products, or devices.

[0029] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0030] Synchrotron radiation sources possess unique properties such as high throughput, high brightness, and wide spectrum, and are widely used in many cutting-edge scientific fields, yielding a series of significant scientific research results. Synchrotron radiation sources typically employ optical modulation processes such as collimation, monochromaticity, and focusing to obtain millimeter- to nanometer-scale fine beams that are then transmitted to experimental stations for user use.

[0031] The development of synchrotron radiation optics technology has placed higher precision demands on single-crystal silicon mirrors. While related combined polishing techniques can achieve high-precision machining of mirrors, they limit their processing efficiency and have significant limitations.

[0032] Based on this, this application proposes a first type of polishing based on magnetorheological polishing technology for the preparation of a single-crystal silicon reflector; and a second type of polishing based on magnetorheological polishing technology for the single-crystal silicon reflector after the first type of polishing, to obtain a single-crystal silicon reflector that meets the requirements. The particle size of the polishing slurry corresponding to the first type of polishing is larger than that corresponding to the second type of polishing, which not only meets the precision requirements of the single-crystal silicon reflector but also significantly reduces production costs while improving polishing efficiency. See any of the following embodiments for details.

[0033] See Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the method for fabricating a single-crystal silicon reflector provided in this application. The method includes:

[0034] Step 11: Provide the single-crystal silicon mirror to be prepared.

[0035] In some embodiments, the single-crystal silicon mirror to be prepared can be used to prepare a single-crystal silicon X-ray mirror.

[0036] Step 12: Perform the first type of polishing on the single-crystal silicon mirror to be prepared based on magnetorheological polishing technology.

[0037] Magnetorheological finishing (MRF) is an ultra-precision machining method that utilizes the rheological properties of magnetorheological polishing fluid in a magnetic field for polishing. The magnetorheological fluid mainly consists of discrete micron-sized magnetic particles, a carrier liquid, and surface surfactants. It possesses characteristics such as magnetic properties, rheological properties, and stability.

[0038] Without an external magnetic field, the magnetic particles are randomly distributed, and the magnetorheological fluid is a flowable liquid. However, under the action of an external magnetic field, the magnetic particles are distributed in a chain-like manner, and their rheological properties change drastically (on the order of milliseconds), exhibiting properties similar to those of a solid. After the magnetic field is removed, the original liquid properties are immediately restored.

[0039] Specifically, magnetorheological polishing technology utilizes the rapid relative movement between a flexible "small grinding head" with viscoplastic behavior formed by the rheological change of the magnetorheological polishing slurry in a gradient magnetic field and the workpiece, which causes the workpiece surface to be subjected to a large shear force, thereby removing the material from the workpiece surface.

[0040] Magnetorheological polishing technology is a polishing method that falls between contact polishing and non-contact polishing. Compared with traditional polishing methods, it has advantages such as high polishing precision, no tool wear or clogging, high removal rate and no introduction of subsurface damage, and can achieve near-zero subsurface damage and nanometer-level precision polishing.

[0041] Step 13: Perform a second type of polishing on the monocrystalline silicon mirror to be prepared after the first type of polishing is completed using magnetorheological polishing technology to obtain a monocrystalline silicon mirror that meets the requirements.

[0042] Among them, the particle size of the polishing slurry corresponding to the first type of polishing is larger than that of the polishing slurry corresponding to the second type of polishing.

[0043] After the first type of polishing of the monocrystalline silicon mirror to be fabricated, the surface shape of the mirror may meet the requirements, but the surface roughness may not. Therefore, based on magnetorheological polishing technology, a second type of polishing is performed on the monocrystalline silicon mirror after the first type of polishing using a polishing slurry with a smaller particle size, resulting in a monocrystalline silicon mirror that meets the requirements. Using a polishing slurry with a smaller particle size can achieve rapid convergence of surface roughness while avoiding damage to the processed surface shape.

[0044] In some embodiments, the polishing method described above can exhibit edge effects. Therefore, employing an edge extension approach—that is, installing blocks of equal height at the edges of the monocrystalline silicon mirror to be fabricated and controlling the trajectory of the polishing equipment during the polishing process—can effectively avoid edge effects. In other words, blocks are installed at the edges of the monocrystalline silicon mirror to be fabricated, and the trajectory of the polishing equipment is controlled during the polishing process to reduce edge defects in the monocrystalline silicon mirror.

[0045] In some embodiments, using a polishing slurry with a smaller particle size can accelerate the polishing efficiency; therefore, the polishing time for the second type of polishing can be 1-2 hours.

[0046] In some embodiments, the polishing slurry corresponding to the second type of polishing is a cerium oxide polishing slurry with a particle size of 50 nm.

[0047] In this embodiment, a first type of polishing is performed on the monocrystalline silicon mirror to be prepared based on magnetorheological polishing technology; a second type of polishing is then performed on the monocrystalline silicon mirror to be prepared after the first type of polishing based on magnetorheological polishing technology to obtain a monocrystalline silicon mirror that meets the requirements; wherein, the particle size of the polishing slurry corresponding to the first type of polishing is larger than the particle size of the polishing slurry corresponding to the second type of polishing, which not only meets the precision requirements of the monocrystalline silicon mirror, but also significantly reduces the production cost while improving the polishing efficiency.

[0048] See Figure 2 , Figure 2 This is a schematic flowchart of another embodiment of the method for fabricating a single-crystal silicon reflector provided in this application. The method includes:

[0049] Step 21: Provide the single-crystal silicon mirror to be prepared.

[0050] Step 22: Obtain the target surface shape of the single-crystal silicon mirror to be fabricated.

[0051] In some embodiments, different monocrystalline silicon mirrors have different surface shape requirements during fabrication. These surface shapes include cylindrical surfaces, elliptical cylindrical surfaces, ellipsoids, hyperboloids, etc.

[0052] Step 23: Determine the polishing process parameters based on the target surface shape.

[0053] The process parameters include immersion depth, rotation speed, and / or moisture content. It can be understood that the corresponding process parameters can be determined based on the specific surface shape.

[0054] For example, in response to a target surface being cylindrical, an immersion depth of 0.2 mm, a rotation speed of 80 rpm, and / or a moisture content of 17%.

[0055] Step 24: According to the process parameters, use magnetorheological polishing technology to perform the first type of polishing on the single crystal silicon mirror to be prepared.

[0056] The polishing equipment and polishing slurry were controlled according to the corresponding process parameters. Then, magnetorheological polishing technology was used to perform the first type of polishing on the monocrystalline silicon mirror to be prepared.

[0057] Step 25: Perform a second type of polishing on the monocrystalline silicon mirror to be prepared after the first type of polishing is completed using magnetorheological polishing technology to obtain a monocrystalline silicon mirror that meets the requirements.

[0058] In some embodiments, the polishing process parameters corresponding to the first type of polishing and the second type of polishing are the same.

[0059] Among them, the particle size of the polishing slurry corresponding to the first type of polishing is larger than that of the polishing slurry corresponding to the second type of polishing.

[0060] After the first type of polishing of the monocrystalline silicon mirror to be fabricated, the surface shape of the mirror may meet the requirements, but the surface roughness may not. Therefore, based on magnetorheological polishing technology, a second type of polishing is performed on the monocrystalline silicon mirror after the first type of polishing using a polishing slurry with a smaller particle size, resulting in a monocrystalline silicon mirror that meets the requirements. Using a polishing slurry with a smaller particle size can achieve rapid convergence of surface roughness while avoiding damage to the processed surface shape.

[0061] In some embodiments, the polishing method described above can exhibit edge effects. Therefore, employing an edge extension approach—that is, installing blocks of equal height at the edges of the monocrystalline silicon mirror to be fabricated and controlling the trajectory of the polishing equipment during the polishing process—can effectively avoid edge effects. In other words, blocks are installed at the edges of the monocrystalline silicon mirror to be fabricated, and the trajectory of the polishing equipment is controlled during the polishing process to reduce edge defects in the monocrystalline silicon mirror.

[0062] In some embodiments, using a polishing slurry with a smaller particle size can accelerate the polishing efficiency; therefore, the polishing time for the second type of polishing can be 1-2 hours.

[0063] In some embodiments, the polishing slurry corresponding to the second type of polishing is a cerium oxide polishing slurry with a particle size of 50 nm.

[0064] In this embodiment, a first type of polishing is performed on the monocrystalline silicon mirror to be prepared based on magnetorheological polishing technology; a second type of polishing is then performed on the monocrystalline silicon mirror to be prepared after the first type of polishing based on magnetorheological polishing technology to obtain a monocrystalline silicon mirror that meets the requirements; wherein, the particle size of the polishing slurry corresponding to the first type of polishing is larger than the particle size of the polishing slurry corresponding to the second type of polishing, which not only meets the precision requirements of the monocrystalline silicon mirror, but also significantly reduces the production cost while improving the polishing efficiency.

[0065] See Figure 3 , Figure 3 This is a schematic flowchart of another embodiment of the method for fabricating a single-crystal silicon reflector provided in this application. The method includes:

[0066] Step 31: Provide the single-crystal silicon mirror to be prepared.

[0067] Step 32: Perform the first type of polishing on the single-crystal silicon mirror to be prepared based on magnetorheological polishing technology.

[0068] Step 33: Perform second-type polishing on the single-crystal silicon mirror to be prepared after completing the first type of polishing based on magnetorheological polishing technology.

[0069] Steps 31 to 33 have the same or similar technical solutions as any embodiment of this application, and will not be described in detail here.

[0070] Step 34: Perform surface quality inspection on the single-crystal silicon mirror to be prepared after completing the second type of polishing.

[0071] In some embodiments, appropriate testing equipment is used to perform surface residual root mean square, wavefront gradient, roughness, and cross-sectional curve consistency tests on the single-crystal silicon mirror to be prepared after the second type of polishing.

[0072] Step 35: Obtain a single-crystal silicon reflector that meets the requirements based on the quality inspection results.

[0073] In some embodiments, the requirements are: root mean square surface residual less than 10 nm, wavefront gradient less than 0.5 μrad, roughness less than 0.5 nm, and cross-sectional curve consistency less than 4%.

[0074] Among them, the particle size of the polishing slurry corresponding to the first type of polishing is larger than that of the polishing slurry corresponding to the second type of polishing.

[0075] After the first type of polishing of the monocrystalline silicon mirror to be fabricated, the surface shape of the mirror may meet the requirements, but the surface roughness may not. Therefore, based on magnetorheological polishing technology, a second type of polishing is performed on the monocrystalline silicon mirror after the first type of polishing using a polishing slurry with a smaller particle size, resulting in a monocrystalline silicon mirror that meets the requirements. Using a polishing slurry with a smaller particle size can achieve rapid convergence of surface roughness while avoiding damage to the processed surface shape.

[0076] In some embodiments, the polishing method described above can exhibit edge effects. Therefore, employing an edge extension approach—that is, installing blocks of equal height at the edges of the monocrystalline silicon mirror to be fabricated and controlling the trajectory of the polishing equipment during the polishing process—can effectively avoid edge effects. In other words, blocks are installed at the edges of the monocrystalline silicon mirror to be fabricated, and the trajectory of the polishing equipment is controlled during the polishing process to reduce edge defects in the monocrystalline silicon mirror.

[0077] In some embodiments, using a polishing slurry with a smaller particle size can accelerate the polishing efficiency; therefore, the polishing time for the second type of polishing can be 1-2 hours.

[0078] In some embodiments, the polishing slurry corresponding to the second type of polishing is a cerium oxide polishing slurry with a particle size of 50 nm.

[0079] In this embodiment, a first type of polishing is performed on the monocrystalline silicon mirror to be prepared based on magnetorheological polishing technology; a second type of polishing is then performed on the monocrystalline silicon mirror to be prepared after the first type of polishing based on magnetorheological polishing technology to obtain a monocrystalline silicon mirror that meets the requirements; wherein, the particle size of the polishing slurry corresponding to the first type of polishing is larger than the particle size of the polishing slurry corresponding to the second type of polishing, which not only meets the precision requirements of the monocrystalline silicon mirror, but also significantly reduces the production cost while improving the polishing efficiency.

[0080] See Figure 4 , Figure 4 This is a schematic diagram of an embodiment of the fabrication apparatus for a single-crystal silicon mirror provided in this application. The fabrication apparatus 100 includes a support component 10 and a polishing device 20.

[0081] The support component 10 is used to support the monocrystalline silicon mirror to be fabricated.

[0082] The polishing equipment 20 is used to polish the monocrystalline silicon mirror to be prepared using the preparation method provided in any of the above embodiments, so as to obtain a monocrystalline silicon mirror that meets the requirements.

[0083] The polishing equipment 20 may include a corresponding polishing wheel and components that work together to implement magnetorheological technology.

[0084] In one application scenario, the fabrication of a single-crystal silicon X-ray mirror will be used as an example for illustration:

[0085] Synchrotron radiation sources possess unique properties such as high throughput, high brightness, and wide spectrum, and are widely used in many cutting-edge scientific fields, yielding a series of significant scientific achievements. Synchrotron radiation sources typically use optical modulation processes such as collimation, monochromaticity, and focusing to obtain millimeter- to nanometer-scale fine beams for transmission to experimental stations for user use. As the most important band of synchrotron radiation, X-rays, due to their low refractive index and strong absorption characteristics in various materials, often employ a grazing incidence total internal reflection focusing mode. Therefore, high-quality X-ray mirrors are the most widely used optical components in synchrotron radiation and are crucial for the construction of synchrotron radiation sources. In recent years, with the construction of hard X-ray free-electron laser facilities, higher surface accuracy requirements and a greater demand for high-precision X-ray mirrors have been placed on their surface shape.

[0086] The different applications make X-ray mirrors different from ordinary mirrors. First, to obtain a sufficient receiving angle, the X-ray mirror surface needs to be very long in the direction of light incidence (i.e., the meridional direction). Therefore, X-ray mirrors are usually elongated strips that are narrow laterally but very long axially. Second, because they also need to achieve focusing, these optical elements are usually complex aspherical surfaces, with shapes including cylindrical, elliptical cylindrical, ellipsoidal, and hyperboloid surfaces, and the radii of curvature in the meridional and sagittal directions of the reflecting surface differ greatly. Therefore, the manufacturing technology of such optical elements is extremely difficult. Furthermore, considering the high energy of synchrotron radiation beams, both rapid heat dissipation and a small coefficient of thermal expansion are required. To precisely control the mechanical and thermal deformation of the element, X-ray mirrors are usually made of single-crystal silicon.

[0087] There are two main types of manufacturing processes for high-quality X-ray mirrors.

[0088] The first type focuses on CCP and IBF as the core technologies. While refining the surface shape errors in the lower frequency band, a smoothing process is added to suppress mid-frequency ripple errors, and an ultra-smooth process is used to reduce high-frequency roughness errors. Through multiple iterations, these three technologies enable the fabrication of ultra-high precision X-ray mirrors.

[0089] The second category involves a combined processing technique that integrates plasma chemical vaporization polishing (PVCM) and elastic emission polishing (EEM). In the rough polishing stage, PVCM simultaneously brightens the surface and corrects surface shape errors with spatial wavelengths greater than 5 mm. In the fine surface correction stage, EEM is used to progressively improve processing resolution and accuracy, achieving an ultra-smooth surface while simultaneously correcting surface shape errors greater than 0.3 mm at the atomic level.

[0090] In addition, research was conducted on the processing and measurement of focusing mirrors using ion beam polishing technology and nano-optical measurement machine (NOM). Through the processing experiment of a 100mm silicon planar mirror, the surface shape error slope PV was obtained as 327marcscc and RMS as 74marcscc, which is equivalent to an error height of 0.35nm, which is nearly 3 times more convergent than the initial surface shape.

[0091] In summary, although the relevant X-ray mirror processing technology can meet the high precision requirements, the use of combined processes will significantly reduce the processing efficiency of the mirrors. Furthermore, some processing methods, such as ion beam polishing, are costly, resulting in the X-ray mirror processing technology not being universally applicable and unable to meet the needs of mass production.

[0092] This application considers that magnetorheological polishing, with its advantages of high determinism, fast convergence of surface errors, and no introduction of subsurface defects, is widely used in the production of optical components. However, research on using this method to process X-ray mirrors is almost nonexistent. Therefore, creatively using magnetorheological polishing to replace related combined processing techniques for X-ray mirror processing is undoubtedly a new attempt. This method can meet the precision requirements of mirrors and significantly reduce production costs while improving processing efficiency.

[0093] Specifically, for single-crystal silicon X-ray cylindrical mirrors, a corresponding combined processing strategy was proposed by combining a highly deterministic magnetorheological polishing method, and corresponding experimental verification was carried out, ultimately obtaining a high-quality optical surface.

[0094] Fused silica is an amorphous (glassy) state of silicon dioxide with a long-range disordered atomic structure. Its high operating temperature and low coefficient of thermal expansion, achieved through three-dimensional cross-linking, result in a Mohs hardness of 7.0. Due to its excellent physicochemical properties, it is widely used in high-tech fields such as military, aerospace, optical communication, and laser technology. Monocrystalline silicon, on the other hand, is a crystal with a basically complete lattice structure. The atomic arrangement of the entire crystal is regular and periodic, with a consistent crystallization direction. It is brittle and easily cracked, with a Mohs hardness of 6.5. Compared to fused silica, it is softer. Therefore, existing mature processes for processing fused silica components are not suitable for the high-precision processing of monocrystalline silicon. Corresponding processing strategies need to be developed to meet its precision requirements.

[0095] To better reflect the surface accuracy of X-ray mirrors and their impact on beamline quality, synchrotron radiation optics typically employs multiple evaluation metrics to assess the surface quality of X-ray mirrors. For cylindrical single-crystal silicon mirrors, four metrics are used to comprehensively consider the surface quality of the single-crystal silicon mirror after magnetorheological polishing: RMS of surface residuals (R-RMS), wavefront gradient GRMS, roughness Ra, and cross-sectional curve consistency δ. The table below shows the required values ​​for these four metrics for X-ray mirrors under synchrotron radiation conditions.

[0096] Table 1. Requirements for Evaluation Criteria of X-ray Mirrors

[0097] Evaluationindexes R-RMS GRMS Ra δ Requirements 10nm 0.5 μrad 0.5nm 4％

[0098] Based on existing processing experience, a significant issue has emerged: the surface hardness of monocrystalline silicon undergoes changes after pretreatment processes such as CNC polishing. Furthermore, if magnetorheological polishing is performed using common process parameters, the resulting surface forces inevitably produce scratches, pitting, and other defects, leading to poor surface quality. Therefore, experiments were conducted to verify the changes in hardness of monocrystalline silicon surfaces after different treatments in order to develop appropriate processing strategies. Square planar monocrystalline silicon samples were used. Their surfaces were first pretreated with CNC polishing, followed by magnetorheological polishing of a selected central area. A nanoindenter was used to test the hardness of the post-polished, CNC-polished, and magnetorheologically polished surfaces.

[0099] like Figure 5 As shown, the test results for different detection areas are presented. Figure 5 (a) in the figure corresponds to the hardness test results of the back surface of monocrystalline silicon. Figure 5 (b) in the figure corresponds to the hardness test results of the surface of monocrystalline silicon after CNC polishing. Figure 5 (c) corresponds to the hardness test results of the surface of monocrystalline silicon after magnetorheological polishing. Based on this, the data were integrated and compared to obtain the following results: Figure 6 The curves shown represent a comparison of the surface hardness of monocrystalline silicon devices after different treatments.

[0100] Since the amount of material removed in a single magnetorheological polishing cycle typically does not exceed 1 micrometer, data obtained from different measurement areas when the indentation depth is less than 1 micrometer are of significant reference value. Only data with indentation depths less than 1 micrometer are selected for comparative analysis; this assumption applies to all subsequent conclusions. Figure 6It is evident that the surface hardness of unprocessed monocrystalline silicon is significantly higher (original hardness). After the preceding process (CNC polishing), the surface hardness decreases substantially (after pre-polishing). However, after magnetorheological polishing on top of pre-polishing, the surface hardness of the device remains largely unchanged (after magnerorheological finishing). This indicates that magnetorheological polishing does not affect the surface properties of monocrystalline silicon devices, allowing for multiple iterations of processing with the same parameters. Conversely, the preceding process significantly alters the surface hardness of monocrystalline silicon devices, necessitating adjustments to the magnetorheological polishing process parameters. In summary, appropriate parameter adjustments are necessary during magnetorheological polishing to generate minimal force, preventing scratches and other defects while improving surface roughness.

[0101] Magnetorheological polishing (MRP) offers high determinism, as it allows for the creation of flexible polishing spots with varying sizes and characteristics through the selection of process parameters. This makes it feasible to fabricate high-precision cylindrical mirrors using MRP. In the fine polishing stage (Type I polishing), by controlling the process parameters, including immersion depth and moisture content, the interaction force between the polishing spot and the component surface can be reduced. This results in a surface shape that closely matches the theoretical surface shape and minimizes surface defects. Furthermore, the edge effects often observed in sub-aperture polishing methods are unavoidable in MRP. Therefore, employing an edge extension approach—installing stops of equal height at the component edges and controlling the polishing equipment's trajectory during processing—can effectively prevent edge effects.

[0102] After fine polishing, the surface shape of the component has reached the required precision, but while the surface roughness has reached a high level, it still cannot achieve the required precision. At this point, the processed monocrystalline silicon mirror should proceed to the next process, namely ultra-smooth processing (type II polishing). Compared with fine polishing, the process parameters for ultra-smooth processing are the same; the only change is the particle size of the polishing slurry. Using a self-developed small-particle-size (50nm) polishing slurry can achieve rapid surface roughness convergence while avoiding damage to the processed surface shape. In addition, ultra-smooth processing can be completed in a very short iteration time (1-2 hours).

[0103] Furthermore, to elucidate the influence of process parameters on the force exerted by the polishing equipment on the component surface, an in-depth analysis of the relative forces during the magnetorheological polishing process was conducted.

[0104] The corresponding formulas indicate that contact pressure is primarily influenced by film thickness, relative velocity, and viscosity, a fact verified experimentally. In actual processing, these three factors are often controlled by selecting appropriate immersion depths, rotational speeds, and moisture content.

[0105] Therefore, the contact pressure between the component and the polishing spot was simulated and analyzed using the controlled variable method, focusing on immersion depth, rotation speed, and moisture content, aiming to derive the optimal process parameters for low-force processing. Commonly used immersion depths in processing are 0.2mm, 0.3mm, and 0.4mm. Similarly, rotation speeds are typically selected within the range of 80rpm, 90rpm, and 100rpm, which can be used as the basis for assigning values ​​to variables in the simulation process. The moisture content, which affects the viscosity of the polishing slurry, is usually controlled within the range of 13% to 17%. This is mainly because too low a moisture content makes the polishing slurry too viscous, difficult to flow, and hard to control surface quality, while a high moisture content results in a thin slurry with greater fluidity on the surface of the high-speed rotating polishing wheel, easily causing side leakage. The moisture contents selected in the simulation calculations were 13%, 15%, and 17%, which are within a controllable range. Figure 7 The effects of immersion depth, rotation speed, and moisture content on contact pressure are presented in the figures. It is worth noting that the pressure data in the pressure curves are derived from the pressure of each polishing point on the central cross-section of the polishing spot, rather than the combined pressure of the entire polishing spot. Figure 7 The horizontal axis in the figure is X-Normalized, which is obtained by normalizing the length (X direction) of each polishing spot obtained from theoretical simulation, to facilitate data comparison and analysis.

[0106] The contact pressure at the polishing point on the central cross-section increases with both rotational speed and immersion depth. Conversely, increasing the water content of the polishing slurry leads to a gradual decrease in the contact pressure at the polishing point on the central cross-section.

[0107] This indicates that in order to obtain lower contact pressure during the polishing process, it is necessary to select a lower rotation speed and immersion depth, as well as a higher moisture content, within a controllable range.

[0108] Furthermore, to verify the correctness of the above simulation results and conclusions, a high-resolution three-directional force gauge was used to test the interaction force between the polishing spot and the component under different rotational speeds multiple times. To avoid signal interference from the electromagnetic field inside the polishing wheel to the force gauge, a non-magnetic backplate was used to fix the component below it. Since the material removal process in magnetorheological polishing is dominated by shear force, it is only necessary to analyze the evolution curve of the shear force. Figure 8 The force curves obtained from the test are presented.

[0109] As the polishing wheel's rotational speed increases, the applied force shows a continuous upward trend, which is consistent with the simulation results. This indicates that the simulation results and conclusions obtained above have high accuracy and can be used as a basis for selecting process parameters. Therefore, the optimal selection of process parameters in actual processing is an immersion depth of 0.2 mm, a rotational speed of 80 rpm, and a moisture content of 17%.

[0110] Furthermore, to verify the deterministic combined processing strategy based on magnetorheological polishing proposed in this application, a verification experiment was conducted on a planar single-crystal silicon mirror with a light-transmitting aperture of 30mm × 20mm. The light-transmitting aperture needs to be processed into a cylindrical surface with a diameter of 100 meters through magnetorheological polishing, with a theoretical surface shape as shown. Figure 9 As shown.

[0111] In the cylindrical shaping stage, high moisture content, low immersion depth, and low rotation speed are used to reduce the force exerted on the component surface by the polishing mold formed by the magnetorheological fluid. Non-contact positioning and mounting ensure the accuracy of the component's surface shape processing, and edge extension is used to control edge defects. In the ultra-smooth processing stage (second type polishing), a cerium oxide polishing slurry with a particle size of 50nm is used to smooth the shaped surface. After processing, a high-precision optical interferometer and a Nano Cam SQ dynamic optical profilometer are used to inspect the surface shape and roughness of the single-crystal silicon mirror.

[0112] To measure the surface quality of a single-crystal silicon mirror, the residual distribution of the surface shape is obtained by subtracting the theoretical surface shape from the actual surface shape. The RMS value of the residual is 7.2 nm, which meets the accuracy requirements.

[0113] The wavefront gradient of the component was obtained by low-pass filtering the processed surface data (cutoff frequency of 10 nm), with a GRMS value of 0.42 μrad. The surface roughness Ra measured under a 50x optical lens was 0.28 nm. Both the wavefront gradient and surface roughness meet the accuracy requirements.

[0114] Three random locations were selected within the light-transmitting aperture of a single-crystal silicon mirror to analyze the degree of agreement between the actual and theoretical cross-sectional curves of the element at different locations. The actual cross-sectional curve was fitted using the least squares method to obtain the fitting radius at that location, and the proportion of its deviation from the theoretical radius was used as the interface curve consistency index δ at that location. Figure 10 As shown, the section curve consistency at positions 1, 2, and 3 are 0.1335%, 0.0398%, and 0.0768%, respectively. These values ​​are far lower than the required accuracy for the cylindrical single-crystal silicon mirror used in this experiment. Figure 10 (a) in the figure represents the location of the three cross sections. Figure 10(b) in the figure represents the cross-sectional curve at position 1. Figure 10 (c) in the figure represents the cross-sectional curve at position 2. Figure 10 (d) in the figure represents the cross-sectional curve at position 3.

[0115] Table 2 shows a comparison of the various evaluation indicators of the processed cylindrical monocrystalline silicon mirror with the required precision. All indicators meet the precision requirements, indicating that the magnetorheological polishing-based combined processing strategy proposed in this paper can be applied to the high-precision processing of cylindrical monocrystalline silicon mirrors. Furthermore, this strategy not only breaks through the limitations of traditional combined methods but also significantly improves production efficiency while ensuring precision.

[0116] Table 2. Comparison of Actual Values ​​and Evaluation Index Requirements

[0117]

[0118] In summary, the method and apparatus for fabricating a monocrystalline silicon reflector provided in this application perform a first type of polishing on the monocrystalline silicon reflector to be fabricated based on magnetorheological polishing technology; and then perform a second type of polishing on the monocrystalline silicon reflector to be fabricated after the first type of polishing based on magnetorheological polishing technology to obtain a monocrystalline silicon reflector that meets the requirements. The particle size of the polishing slurry corresponding to the first type of polishing is larger than that corresponding to the second type of polishing, which not only meets the precision requirements of the monocrystalline silicon reflector but also significantly reduces production costs while improving polishing efficiency.

[0119] In the several embodiments provided in this application, it should be understood that the disclosed methods and devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed.

[0120] If the integrated units in the other embodiments described above are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0121] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. Any equivalent device or equivalent process transformation made based on the content of this application specification and drawings, or direct or indirect application in other related technical fields, are similarly included in the patent protection scope of this application.

Claims

1. A method for fabricating a single-crystal silicon X-ray mirror, characterized in that, The method includes: Provide a single-crystal silicon X-ray reflector to be fabricated; The single-crystal silicon X-ray mirror to be prepared is polished using magnetorheological polishing technology of the first type. The magnetorheological polishing technology is used to perform a second type of polishing on the single-crystal silicon X-ray mirror to be prepared, which has completed the first type of polishing; the polishing process parameters corresponding to the first type of polishing and the second type of polishing are the same; the polishing process parameters include immersion depth, rotation speed and / or moisture content. The surface residual root mean square (RMS), wavefront gradient, roughness, and cross-sectional curve consistency of the single-crystal silicon X-ray mirror to be prepared after the second type of polishing are tested; wherein, the requirements for surface residual root mean square (RMS) are less than 10 nm, the requirements for wavefront gradient are 0.5 μrad, the requirements for roughness are less than 0.5 nm, and the requirements for cross-sectional curve consistency are less than 4%; Based on the quality inspection results, a single-crystal silicon X-ray reflector that meets the requirements is obtained; wherein, the particle size of the polishing slurry corresponding to the first type of polishing is greater than the particle size of the polishing slurry corresponding to the second type of polishing.

2. The method according to claim 1, characterized in that, The first type of polishing of the single-crystal silicon X-ray mirror to be prepared based on magnetorheological polishing technology includes: Obtain the target surface shape of the single-crystal silicon X-ray mirror to be fabricated; Determine the polishing process parameters based on the target surface shape; According to the process parameters, the magnetorheological polishing technology is used to perform the first type of polishing on the single-crystal silicon X-ray mirror to be prepared.

3. The method according to claim 2, characterized in that, In response to the target surface being cylindrical, the immersion depth being 0.2 mm, the rotation speed being 80 rpm, and / or the moisture content being 17%.

4. The method according to any one of claims 1-3, characterized in that, The edge of the single-crystal silicon X-ray mirror to be prepared is equipped with a stop to control the trajectory of the polishing equipment during the polishing process, thereby reducing edge defects of the single-crystal silicon X-ray mirror to be prepared.

5. The method according to any one of claims 1-3, characterized in that, The polishing time for the second type of polishing is 1-2 hours.

6. The method according to any one of claims 1-3, characterized in that, The polishing solution corresponding to the second type of polishing is a cerium oxide polishing solution with a particle size of 50nm.

7. An apparatus for fabricating a single-crystal silicon X-ray mirror, characterized in that, The preparation apparatus includes: Supporting components are used to support the single-crystal silicon X-ray mirror to be fabricated. Polishing equipment for polishing a single-crystal silicon X-ray mirror to be prepared using the preparation method as described in any one of claims 1-6, to obtain a single-crystal silicon X-ray mirror that meets the requirements.

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