A method and apparatus for lithographically patterning a circular ring microstructure array on a curved surface

Abstract

A method and device for photolithography of annular microstructure arrays on curved surfaces belong to the technical field of laser direct writing exposure machines. The present invention addresses the problems of processing difficulties and low efficiency when existing methods are used to manufacture metasurfaces, frequency selective surfaces, metal grids, etc. composed of annular microstructures on the surface of a curved substrate such as a sphere, and proposes an exposure method and a corresponding photolithography device. The optical path structure of the device of the present invention consists of a hollow annular beam generating part and a hollow annular beam shrinking part, which modulates the incident collimated light beam into a hollow annular beam for exposure. The exposure beam modulated by the exposure method of the present invention has the advantages of a thinner ring width, a longer focal depth, and a longer working distance, reduces the influence of substrate height changes on the exposure ring, reduces the demand for positioning errors of the mechanical translation stage, and the pulsed laser beam can directly expose a complete single ring, greatly improving the exposure efficiency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of laser direct writing exposure machine, and particularly relates to a direct writing exposure method and a corresponding device for photolithography of a circular ring microstructure array on a curved surface. The prepared circular ring microstructure array can be used as a basic structural unit for applications such as metasurfaces, frequency selective surfaces, and electromagnetic shielding metal mesh. BACKGROUND

[0002] In today's era, the research and development process of various electronic products increasingly emphasizes electromagnetic wave compatibility, shielding, and protection. Electromagnetic functional devices such as electromagnetic shielding metal mesh, frequency selective surface, and electromagnetic metasurface composed of microstructure arrays have increasingly highlighted their application value due to their functions of electromagnetic wave shielding and protection, electromagnetic wave regulation, etc. However, in the current research status at home and abroad, electromagnetic wave functional devices composed of such microstructure arrays are mostly in the form of planar substrates, while research on curved substrates is relatively less. In practical applications, devices and equipment with curved outer contours account for a high proportion, especially electromagnetic shielding light windows with spherical substrates, which inherently have more advantages in applications. In terms of optical imaging, spherical light windows can allow the use of larger field angle lenses for internal cameras, expanding the imaging range and reducing image distortion. In terms of mechanical properties, spherical and streamline curved surfaces can withstand greater pressure and have contours that conform to aerodynamic characteristics, reducing the drag of high-speed aircraft and enhancing aerodynamic performance. Covering microstructure arrays on spherical light windows, electromagnetic functional devices can match the outer contour of the applied equipment to adapt to various angle of incidence conditions of electromagnetic waves. In addition, research on microstructure units shows that for transparent electromagnetic shielding metal mesh, using circular ring symmetric microstructure as its basic unit can effectively reduce the influence of high-order diffraction spots on imaging. In addition, applying such microstructure units to metasurfaces can effectively improve the electromagnetic wave polarization mode insensitivity of the device. Therefore, electromagnetic wave functional devices combining circular ring symmetric microstructures with curved substrates have extremely high application value. However, there are still great difficulties in processing and preparing circular ring microstructures on curved optically transparent substrates.

[0003] Although there are some cases of using laser direct writing method to prepare microstructures on spherical surfaces, the practicality of related achievements is still low. The technical difficulties and problems mainly lie in the following three aspects: first, the spherical surface is a three-dimensional structure. The multiple rotating shafts and displacement tables equipped in the exposure device increase the sources of positioning errors in the equipment. The accumulation of errors will be obviously reflected in the defocus distance of the lithography system, resulting in blurred light spot and reduced lithography quality. Second, the light path of the conventional laser direct writing lithography equipment uses a microscope objective to reduce the spot size of the exposure beam. In order to obtain smaller line width, a high magnification microscope objective is usually used, which has a large numerical aperture and a short working distance. During the movement, the objective lens is prone to collide with the surface of the substrate. Third, the conventional spherical laser direct writing equipment generates a single point exposure spot. The continuous uniform motion of the multi-axis displacement table connects the single point into a line, which has low exposure efficiency. The above difficulties widely exist in the laser direct writing equipment for exposing microstructures on spherical substrates, not to mention on the surface of a more complex streamline curved surface.

[0004] At present, among the methods and devices for processing microstructures such as gratings, optical gratings, and frequency selective surfaces on spherical substrates by laser direct writing, the representative achievements and patents are as follows:

[0005] Patent publication number: CN1101722362A "Laser direct writing method for deep concave spherical weft intersection grid pattern", patent publication number: CN1488997A "A concave spherical photoetching machine", patent publication number: CN216990334U "A warp and weft spherical laser processing machine", patent publication number: CN113172335A "A method for etching non-developable FSS curved surface by multi-axis precision laser processing machine tool", and papers such as "Implementation of constant exposure amount laser direct writing control for deep concave spherical grid", "Research on curved surface grid writing technology", "Research on curved surface laser direct writing system and key technology", "Convex spherical grid laser direct writing technology", "Research on curved surface laser direct writing system and key technology", etc. The multi-axis displacement table is used to drive the sample to move continuously, so that a single point spot is exposed to a line. This exposure method affects the line width consistency and has low exposure efficiency. Moreover, the short working distance of the microscope objective leads to a conflict in space structure, which limits the application of the technology.

[0006] The paper "Research on key technology of high-efficiency curved surface laser direct writing lithography" uses a nonlinear optical lever structure to change the focal length of the optical system in real time according to the height of the spherical sample surface, which improves the height range of the spherical surface that can be exposed. However, this technology still cannot avoid the problems of low single-point exposure efficiency of laser and short working distance of microscope objective. Moreover, for the positions with large edge slope of the spherical sample, there is also a problem of decreased exposure quality.

[0007] The paper "Laser-lithography on Non-planar Surfaces" is based on a commercial laser direct writing machine, and the equipment platform is modified by adding a mechanical structure that can drive the substrate to rotate. However, this achievement is limited by the original equipment hardware, and the exposure angle in the inclined area is limited. Moreover, it still uses the method of direct writing in different areas, which is easy to produce more graph splicing marks.

[0008] Patent publication number: CN111077741B "Curved surface lithography method using DMD and liquid crystal modulation" can theoretically realize general maskless lithography on curved surfaces. However, due to the use of DMD and liquid crystal spatial light modulator, the cost is high, the structure complexity is high, and the projection objective lens used still has the problem of high positioning accuracy requirement and easy collision with the substrate.

[0009] Patent publication number: CN102097296A "Preparation method of semiconductor nanometer circular ring" generates a circular ring light spot by the principle of diffraction Poisson light spot, which is different from the method used in this invention. SUMMARY

[0010] The present invention aims to overcome the difficulties in the preparation of spherical microstructure in the prior art, especially the microstructure represented by laser direct writing metal mesh, which has the problems of difficult line width improvement, poor line width consistency, low manufacturing efficiency, equipment structure conflict, etc. A method and corresponding lithography device for lithography circular ring microstructure array on spherical and complex curved surfaces are proposed, which has the advantages of finer line width, good line width consistency, large tolerance to defocus, high processing efficiency, and high cost performance of equipment. It can also meet the processing needs of metal mesh and metasurface, frequency selective surface and other applications.

[0011] The technical solution adopted by the present invention is: a method and device for lithography circular ring microstructure array on curved surfaces, characterized by: the lithography device is composed of a laser light source, a hollow circular ring beam generating part, a hollow circular ring beam micro-shrinking part, a curved surface sample, and a numerical control multi-axis displacement table. The surface of the curved surface sample is coated with photoresist. By exposing in sequence, circular ring microstructure units arranged on the surface of the curved surface sample are generated, forming a circular ring microstructure array. Before exposing each circular ring microstructure unit, the numerical control multi-axis displacement table adjusts the rotation angle and coordinates of the curved surface sample, so that the surface of the curved surface sample enters the set exposure position. A collimated light beam is emitted from the laser light source, a hollow circular ring beam with fixed ring width is generated through the hollow circular ring beam generating part, and a micro-shrinking hollow circular ring beam is generated through the hollow circular ring beam micro-shrinking part. The micro-shrinking hollow circular ring beam gradually shrinks in ring width during propagation, and the micro-shrinking hollow circular ring beam with a ring width of 0.1-10 microns is formed at a working distance Z WThe transition of the to-be-exposed region of the hollow circular ring light beam is a circular ring light spot for photoetching, the circular ring light spot exposes the photoresist coated on the surface of the curved sample, and a single circular ring microstructure unit is generated; after each circular ring microstructure unit is exposed, the curved sample is rotated and moved to the next to-be-exposed region by the numerical control multi-axis displacement table, and the above exposure step is repeated until the exposure of the circular ring microstructure array arranged on the surface of the curved sample is completed.

[0012] In the technical solution of the above summary: the hollow circular ring light beam generating part is composed of a hollow conical light beam diffusing element and a hollow conical light beam converging element; the spacing between the hollow conical light beam diffusing element and the hollow conical light beam converging element is Z A , Z A is proportional to the diameter of the hollow circular ring light beam; the hollow circular ring light beam generating part adopts any one of the following two combinations: the first combination is two convex conical lenses, and the second combination is a concave conical lens and a convex conical lens.

[0013] In the technical solution of the above summary: the hollow circular ring light beam micro-shrinking part is composed of a front positive lens group and a rear positive lens group, the focal length f1 of the front positive lens group is greater than the focal length f2 of the rear positive lens group, the spherical aberration of the rear positive lens group is greater than the spherical aberration of the front positive lens group, and the hollow circular ring light beam micro-shrinking part relies on the spherical aberration of the internal optical elements to converge the light rays of different radial heights before reaching the focal point of the rear positive lens group, so as to be modulated into a circular ring light spot; the spacing Z C between the front positive lens group and the rear positive lens group is used to adjust the divergence of the outgoing light beam, Z C is less than f1+f2; the circular ring light spot has a ring width of micrometer or sub-micrometer level; and the hollow circular ring light beam micro-shrinking part has a focal depth of hundreds of micrometers, and the circular ring microstructure unit with a surface height fluctuation range less than the focal depth length of the curved sample is exposed.

[0014] In the technical solution of the above summary: the optical element types used by the hollow circular ring light beam generating part and the hollow circular ring light beam micro-shrinking part include solid lenses made of optical glass, diffractive optical elements, holograms loaded on reflective and transmissive spatial light modulators, and super surface lenses.

[0015] In the technical solution of the above summary: the optical elements of the hollow circular ring light beam generating part and the hollow circular ring light beam micro-shrinking part are installed on a linear displacement table, and the spacing Z A and Z C between the elements is changed by an upper computer control during the exposure process, so as to adjust the exposure size of the circular ring light spot.

[0016] In the technical solution of the above summary: achromatic cemented lenses and single lens combinations with achromatic function are combined in the front positive lens group and the rear positive lens group.

[0017] The components in the laser light source include a laser, a shutter, a beam collimator, and a beam expander.

[0018] The adjustable light shielding plate is arranged between the hollow annular light beam generating part and the hollow annular light beam shrinking part, the part of light rays of the hollow annular light beam is shielded, and the modulated annular light spot becomes an annular ring with a notch.

[0019] The method is suitable for the following types of photoetching: ultraviolet photoetching using conventional positive photoresist and negative photoresist, additive manufacturing using a photo-curing principle, and ablation or denaturation of a material coated on a curved surface of a sample by using a high-power laser.

[0020] The innovation and good effect of the present application are as follows:

[0021] 1. In the present application, the spherical aberration in the aberration characteristics of the spherical convex lens is used as a dominant factor for causing the annular light beam to converge, compared with the conventional photoetching method using a microscopic objective lens to scale the light beam, the converging angle of the light beam is reduced, which can produce two advantages. On the one hand, the exposure light beam avoids the limitation of the numerical aperture of the objective lens, greatly improving the focal depth range of the optical system; this advantage not only prevents the annular structure exposed from being deteriorated due to the defocusing of the objective lens, and improves the tolerance range of the device, but also utilizes the focal depth range to ignore the fluctuation of the surface profile of the curved surface, and realizes the preparation of the annular structure on the complex curved surface. On the other hand, the reduced converging angle of the light beam can provide a longer working distance. For the concave spherical surface and the curved surface structure with a block at the edge, the extension of the working distance can effectively avoid the spatial conflict between the objective lens and the curved surface, and prevent collision.

[0022] 2. The optical system of the device of the present application causes the light rays with different radial heights in the incident light beam to be deflected due to spherical aberration, the light rays extend linearly along the propagation direction after exiting and cross in turn near the image plane, and converge into an annular light spot with a narrow ring width, which can reach the micron and sub-micron level; the conventional photoetching device using a microscopic objective lens follows the principle of imaging optics, and the limit of the spot size is the product of the incident light beam size and the vertical magnification of the optical system.

[0023] 3. The device of the present application can adjust the diameter of the annular ring or the position and width of the notch of the annular ring during the exposure process by adjusting the linear displacement table position of the optical element and the opening size of the light shielding plate, so that the device of the present application can be suitable for the unit structure requirements of various gratings, metasurfaces and other applications.

[0024] 4、The exposure method of the application is specially designed for circular ring microstructure, and a complete circular ring can be generated at one time, and the curved surface sample and the direct writing head do not need to be moved in the middle of exposure, that is, the formation of the circular ring line no longer depends on mechanical movement, so that the exposure efficiency is higher, the continuity of mechanical movement avoids affecting the uniformity of the line width, and the exposure quality is improved.

[0025] 5、The tolerance of the defocus error of the application is large, and the single exposure position is fixed, so that the precision requirement of other components such as displacement table and focusing system in the device can be reduced, the cost is reduced, and the production and manufacturing are more suitable.

[0026] In summary, the application fully utilizes the spherical aberration characteristics of the spherical lens to generate a circular ring light beam, which can be used for photoetching a circular ring microstructure on a curved surface substrate, and has the characteristics of large focal depth, thin and uniform ring width. The circular ring line generated by the method has high quality, low precision requirement for other components of the device, good economy and practicability. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0028] Figure 1 It is a schematic diagram of function division of internal elements of a device for photoetching circular ring microstructure array on curved surface.

[0029] Figure 2 It is a schematic diagram of setting elements of a device for photoetching circular ring microstructure array on curved surface according to specific embodiment 1.

[0030] Figure 3 It is a schematic diagram of converging light beam by spherical aberration of the last spherical convex lens of the device in specific embodiment 1.

[0031] Figure 4 It is a circular ring light spot intensity distribution diagram simulated according to the optical elements used in specific embodiment 1.

[0032] Figure 5 It is an intensity profile diagram of the circular ring light spot using specific embodiment 1.

[0033] Figure 6 It is a circular ring microstructure obtained by exposing a sample coated with photoresist using a prototype of specific embodiment 1.

[0034] Figure 7Fig. 2 and Fig. 3 are the radial height distribution diagrams of the light rays at the image plane position of the optical elements used in Example 1 and Example 2, respectively, calculated by using the ray tracing method. The abscissa is the image plane position of the light path along the optical axis, and the ordinate is the height along the optical axis section. The straight lines in the diagrams are the propagation trajectories of the light rays of different wavelengths at the position.

[0035] Part No. in the diagram: 1. Laser light source; 2. Hollow circular ring light beam generating part; 3. Hollow circular ring light beam minifying part; 4. Curved surface sample; 5. Numerical control multi-axis displacement table; 6. Circular ring light spot for photoetching; 7. Collimated light beam emitted by the light source; 8. Hollow circular ring light beam with fixed ring width; 9. Minified hollow circular ring light beam; 10. Focal depth range of the circular ring light beam for exposure; 11. First conical lens; 12. Second conical lens; 13. First convex lens; 14. Second convex lens; 21. Hollow circular conical light beam diffusing element; 22. Hollow circular conical light beam converging element; 31. Front group of positive lens; 32. Rear group of positive lens; Z A . Distance between the hollow circular conical light beam diffusing element and the hollow circular conical light beam converging element; Z C . Distance between the front group and the rear group of positive lens; Z W . Working distance of the objective lens. DETAILED DESCRIPTION

[0036] The present application is further described below with reference to the accompanying drawings and preferred embodiments:

[0037] The purpose of the present application is achieved in that the optical path system in the present application is the core of the device for realizing circular ring microstructure photoetching, Figure 2 is a most basic implementation form of a method and device for photoetching circular ring microstructure array on a curved surface, and the parameters of the optical elements are as shown in the specific Example 1. In the example, two convex conical lenses are used as the hollow circular ring light beam generating part, and two spherical plano-convex lenses are used as the hollow circular ring light beam minifying part.

[0038] The laser light source emits a collimated light beam, which, after passing through the first conical lens, is deflected along the central symmetry axis, converges and then diverges, forming a hollow conical light beam. The second conical lens reshapes the hollow conical light beam, and the light beam converges again in the propagation direction, forming a hollow cylindrical light beam. After passing through the hollow circular ring light beam generating part composed of conical lenses, the light beam then enters the hollow circular ring light beam shrinking part. In principle, for a spherical convex lens, the incident light beam will cause the light rays near the lens axis to focus at a position slightly away from the lens, while the light rays near the lens edge will focus at a position slightly close to the lens, and there is an area where the light rays intersect. The present application utilizes this principle, using a spherical plano-convex lens with large spherical aberration (small focal length) as the positive lens rear group. Before the circular ring light beam reaches the focal point, the light rays near the inner diameter and outer diameter of the circular ring will converge due to spherical aberration, and the ring width of the light beam in a certain area during propagation is relatively thin, which can be used for photolithography exposure. In addition, another spherical plano-convex lens with large focal length (small spherical aberration) is used as the positive lens front group. By using two plano-convex lenses in combination and adjusting the distance between the two plano-convex lenses, the light ray tracing cross-sectional view of the hollow circular ring light beam formed at the end is shown in Figure 3 This structure is similar to the reversed telescope type optical path, which can proportionally reduce the overall size of the incident light beam to the target set diameter, and the scaling ratio is related to the focal length of the two plano-convex lenses; the difference is that the distance between the two plano-convex lenses is less than the sum of the focal lengths of the two plano-convex lenses, so that the diameter of the outgoing light beam remains stable in the area where the ring width is relatively thin. The present application generates a thin circular ring light spot by spherical aberration convergence, and the convergence process of the light beam is slower, so it has a longer focal depth and working distance than the traditional objective lens focusing method. Therefore, the present device does not use a traditional objective lens, avoiding the problem that the advantages of spot size, focal depth, and working distance cannot coexist.

[0039] Based on the above-mentioned circular ring light beam modulation method, a multi-axis displacement stage with translation and rotation functions is configured, and a curved sample coated with photoresist is fixed on the displacement stage. Before each exposure, the numerical control multi-axis displacement stage moves the position of the curved sample to be exposed to the area of the thin circular ring light spot generated by the light path. After each circular ring light spot is exposed, the multi-axis displacement stage will move to the next position to be exposed, and the above process will be repeated until all circular ring unit photolithography is completed. The device relies on the above working principle, which not only avoids the problem of exposure quality degradation caused by the change of defocus distance due to the positioning error of the displacement stage, but also allows the surface profile of the curved sample to change within the focal depth range, and is compatible with more shapes of curved surfaces.

[0040] The above two advantages enable the surface of the curved sample coated with photoresist to be successfully exposed to a circular ring microstructure array. The following will explain the innovation and role played by the present application by perfecting the parameters of the specific embodiments.

[0041] Example 1:

[0042] According to one embodiment 1 of the method and device for curved surface lithography of circular ring microstructure array, the parameters of the components are as follows: the wavelength of the laser is 405 nm; the first conical lens is made of quartz, the base angle a is 10°, and the diameter d is 12.5 mm; the second conical lens is made of quartz, the base angle a is 10°, and the diameter d is 25 mm; the first plano-convex lens is made of N-BK7, the focal length f is 500 mm, the diameter d is 25.4 mm, and the radius of curvature R is 258.4 mm; the second plano-convex lens is made of N-BK7, the focal length f is 20 mm, the diameter d is 6.3 mm, and the radius of curvature R is 10.36 mm. According to Snell's law n1sinθ1=n2sinθ2, ray tracing calculation is performed, and the corresponding optical path is built on the experimental equipment. It can be seen that when the diameter of the target circular ring is 0.8 mm, the distance between the two conical lenses Z A is 124.8 mm; the distance between the two plano-convex lenses Z C is 525.6 mm; and the working distance of the second plano-convex lens Z W is 31.8 mm.

[0043] The test method in the laboratory of this embodiment is as follows: a CMOS camera is installed on a multi-axis displacement table, the distance between the sensor of the camera and the center of the last surface of the second plano-convex lens is adjusted to the working distance Z W , and the circular ring spot energy intensity distribution photo in Figure 4 can be captured. The energy intensity values in the horizontal and vertical directions are taken through the center of the circular ring, and the normalized energy intensity distribution profile in Figure 5 can be obtained. It can be seen from the two graphs that the energy distribution of the circular ring spot is sharp and smooth at the edge, and the ring width is relatively uniform. By controlling the output power and exposure time of the exposure light source through the upper computer, the sample coated with photoresist is exposed, and the circular ring structure height map shown in Figure 6 can be obtained after the surface topography of the photoresist is collected by the laser confocal microscope. It can be seen from the measurement of the laser confocal microscope that when the diameter of the circular ring is 0.8 mm, the ring width can be kept at 3 μm-4 μm. The perpendicularity of the exposed area and the non-exposed area is good, which is conducive to the subsequent metal deposition process and the like.

[0044] Embodiment 2:

[0045] One embodiment 2 of the method and device for lithography of the circular ring microstructure array on the curved surface is based on embodiment 1, wherein the plano-convex lens of the positive lens rear group is replaced by a doublet achromatic lens. The parameters of the doublet achromatic lens are as follows: the first surface curvature radius R1 is 12.363 mm, the second surface curvature radius R2 is -8.703 mm, the third surface curvature radius R3 is -24.846 mm, the material of the doublet lens is H-K9, the material of the meniscus lens is H-ZF2, the focal length f is 20 mm, and the diameter d is 6 mm. The other lens parameters remain unchanged.

[0046] The theoretical calculation result by using the light path tracing method is shown in FIG. 6. Figure 7 The laser with the central wavelength of 405 nm is targeted at the circular ring with the modulation radial height of 0.3 mm. When the laser wavelength has a frequency width of ±2 nm, the spot width caused by the dispersion at the image plane position of embodiment 1 is 4.5 μm, and the spot width after using the achromatic optical element of embodiment 2 is 3.7 μm, that is, the ring width caused by the chromatic aberration can be reduced by 17.8% in theory. It can be seen that by adding the chromatic aberration correction lens made of flint glass in the positive lens front group and the positive lens rear group of the hollow circular ring beam micro-shrinking part, the chromatic aberration of the light path in the present application can be effectively controlled, and the quality of the circular ring spot can be improved.

[0047] The above cases prove that the present application has high advantages and practicability. Obviously, for those skilled in the art, after understanding the content and principle of the present application, various modifications and changes in form and details can be made without departing from the principle and structure of the present application, but these modifications and changes based on the idea of the present application are still within the protection scope of the claims of the present application.

Claims

1. A method for photolithographically forming a circular microstructure array on a curved surface, characterized in that: The invention is applied to a photolithography device, which is composed of a laser light source (1), a hollow ring beam generating part (2), a hollow ring beam miniaturization part (3), a curved surface sample (4) and a numerical control multi-axis displacement stage (5). The method comprises: emitting a collimated light beam (7) from the laser light source (1), generating a hollow ring beam (8) with a fixed ring width through the hollow ring beam generating part (2), and then generating a miniaturized hollow ring beam (9) through the hollow ring beam miniaturization part (3), wherein the ring width of the miniaturized hollow ring beam (9) gradually decreases during propagation and the collimated light beam (9) is disposed at a working distance Z. W The area to be exposed is transformed into a circular light spot (6) for photolithography, and the circular light spot (6) exposes the photoresist coated on the surface of the curved sample (4) to produce a single circular microstructure unit; the hollow circular light beam generating part (2) is composed of a hollow conical light beam diffusion element (21) and a hollow conical light beam focusing element (22); the distance between the hollow conical light beam diffusion element (21) and the hollow conical light beam focusing element (22) is Z A , adjust Z A The diameter of the hollow annular beam (8) is adjusted by the distance; the hollow annular beam micro-contraction part (3) is composed of a positive lens front group (31) and a positive lens rear group (32); the focal length f1 of the positive lens front group (31) is greater than the focal length f2 of the positive lens rear group (32); the spherical aberration of the positive lens rear group (32) is greater than the spherical aberration of the positive lens front group (31); the hollow annular beam micro-contraction part (3) relies on the spherical aberration of the internal optical elements to make the light of different radial heights converge before reaching the focus of the positive lens rear group (32), thereby modulating into an annular light spot (6) with a narrowed annular width; the distance Z between the positive lens front group (31) and the positive lens rear group (32) is C Used to adjust the divergence of the outgoing beam, Z C Less than f1+f2; the surface of the curved surface sample (4) is pre-coated with photoresist, and circular microstructure units arranged on the surface of the curved surface sample (4) are generated by sequential exposure to form a circular microstructure array; before each circular microstructure unit is exposed, the numerically controlled multi-axis displacement stage (5) adjusts the rotation angle and coordinates of the curved surface sample (4) so ​​that the surface area to be exposed of the curved surface sample (4) enters the set exposure position; after each circular microstructure unit is exposed, the numerically controlled multi-axis displacement stage (5) rotates and moves the curved surface sample (4) to the next area to be exposed, and repeats the above exposure steps until the exposure of the circular microstructure array arranged on the surface of the curved surface sample (4) is completed.

2. The method for photolithographically forming a circular microstructure array on a curved surface according to claim 1, wherein: The hollow ring light beam generating part (2) adopts any one of the following two combinations: the first is two convex cone lenses, and the second is one concave cone lens and one convex cone lens.

3. The method for photolithographically forming a circular microstructure array on a curved surface according to claim 1, wherein: The circular light spot (6) has a ring width of the order of micrometers or submicrometers; the light beam (9) generated by the micro-contraction part (3) of the hollow circular light beam has a focal depth of the order of hundreds of micrometers, and exposes a photoresist layer with a height fluctuation smaller than the focal depth range on the surface of the curved sample (4), thereby generating a circular microstructure unit.

4. The method for photolithographically forming a circular microstructure array on a curved surface according to claim 1, wherein: The optical elements used in the hollow ring beam generating part (2) and the hollow ring beam miniaturizing part (3) include solid lenses made of optical glass, diffraction optical elements, holograms loaded on reflective and transmissive spatial light modulators, and metasurface lenses.

5. The method for photolithographically forming a circular microstructure array on a curved surface according to claim 1, wherein: The optical elements of the hollow ring beam generating part (2) and the hollow ring beam miniaturizing part (3) are mounted on a linear displacement stage, and the distance Z between the elements is changed by the host computer during the exposure process. A and Z C , continuously adjust the exposure size of the annular spot (6).

6. The method for photolithographically forming a circular microstructure array on a curved surface according to claim 1, wherein: A combination of an achromatic cemented lens and a single lens with an achromatic function is used in the positive lens front group (31) and the positive lens rear group (32).

7. The method for photolithographically forming a circular microstructure array on a curved surface according to claim 1, wherein: The components in the laser light source (1) include a laser, a shutter, a beam collimator, and a beam expander.

8. The method for photolithographically forming a circular microstructure array on a curved surface according to claim 1, wherein: An adjustable light shielding plate is provided between the hollow ring light beam generating portion (2) and the hollow ring light beam miniaturization portion (3) to shield part of the light of the hollow ring light beam (8), so that the modulated ring light spot (6) becomes a ring with a notch.

9. The method for photolithographically etching a circular microstructure array on a curved surface according to claim 1, wherein: The photolithography types applicable to the method include: ultraviolet photolithography using conventional positive photoresist and negative photoresist, additive manufacturing using the principle of photocuring, and ablation or denaturation of the material coated on the surface of the curved sample (4) using a high-power laser.

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