Axial parallel laser direct writing photoetching method and system for programmable phase regulation and control

Abstract

The invention discloses a programmable phase regulation axial parallel laser direct writing photoetching method and a programmable phase regulation axial parallel laser direct writing photoetching system, which are characterized in that an effective illumination area of a spatial light modulator is divided into a plurality of concentric rings by utilizing a constructed ring-phase mapping relation and a ring boundary index table; the method comprises the following steps of: constructing a fitness function, enabling 0 or phase corresponding to each concentric ring to correspond to an SLM to obtain SLM pupil plane phase distribution, associating a genetic algorithm with a phase pattern loaded to the SLM, efficiently converting a genetic algorithm optimization result into a phase pattern, and then constructing a fitness function on the basis of the constructed fitness function. SLM pupil plane phase distribution corresponding to a plurality of axially generated light focuses with uniform intensity, good side lobe suppression and high resolution can be efficiently obtained by utilizing a genetic algorithm, so that axial parallel laser direct writing photoetching is realized, simultaneous generation of multiple focuses is ensured, and the stability of the system is improved. And engineering-available balance can be obtained among strength balance, side lobe control and processing robustness.

Description

Technical Field

[0001] This invention belongs to the field of laser direct-write lithography, and particularly relates to a programmable phase-controlled axial parallel laser direct-write lithography method and system. Background Technology

[0002] Laser-direct-write lithography (LDL) involves localized exposure of photoresist or polymerizable materials using a focused beam. As a maskless, flexible, and efficient lithography technique, it has demonstrated immense application potential in micro / nano device development, photonic chip manufacturing, and biomedicine. Traditional LDL schemes largely rely on single-focus scanning, requiring multiple focusing and layer-by-layer exposures when writing multi-layer structures. This results in inherent bottlenecks of low processing efficiency and high system stability requirements. Current research has proposed axial multi-focus schemes based on diffractive optical elements or fixed phase plates. However, once these static optical elements are fabricated, their optical functions are fixed, making it impossible to flexibly adjust the number, position, and intensity distribution of focal points. This also increases the overall system debugging complexity, making it difficult to adapt to complex processing requirements.

[0003] Patent application CN115598833A discloses a high-throughput three-dimensional laser direct writing method and system based on square multimode fibers. This invention uses an array of multiple square multimode fibers as the laser direct writing head. Each square multimode fiber utilizes a spatial light modulator to modulate the light field incident on the fiber according to a pre-calculated phase map, achieving focusing at the exit surface. The focused laser then performs three-dimensional laser direct writing on the object to be processed. The pre-calculated phase map for each square multimode fiber is obtained by optimizing the focal position using a closed-loop iterative genetic algorithm. The focal position of the laser emitted from each square multimode fiber is set according to the processing error during fiber array arrangement. Utilizing the compact arrangement of square multimode fibers, the system can be expanded to multiple channels, enabling multi-channel parallel direct writing and further improving writing efficiency, thus solving the problems of slow writing speed and low resolution in existing laser direct writing systems. However, the scheme disclosed in this patent application cannot achieve axial parallel laser direct writing lithography.

[0004] Patent application CN115598833A discloses a method for generating ultra-resolution optical needles with long focal depth and a high aspect ratio laser direct writing system. It utilizes multi-focal stitching to extend the focal depth and combines a genetic algorithm to overcome the contradiction between numerical aperture and focal depth in traditional lenses. By controlling the incident light field through a super-oscillating lens, a long focal depth light field under high numerical aperture is achieved, resulting in an ultra-long focal depth ultra-resolution optical needle light field that exceeds the diffraction limit. This ultra-long focal depth ultra-resolution optical needle light field, exceeding the diffraction limit, is then used to achieve high aspect ratio laser direct writing processing, enabling the fabrication of micro / nano structures with linewidths smaller than the diffraction limit and specific processing depth requirements. However, this patent application cannot generate multiple uniform intensity, well-suppressed side lobes, and high-resolution optical focal points along the axis.

[0005] While the SLM (Sequencing Linear Modulation) approach offers the possibility of programmable control of the optical field, how to accurately optimize the pupil phase using algorithms to generate multiple axially uniform, well-suppressed, and high-resolution optical focal points remains a pressing technical challenge under high numerical aperture (NA) objectives. Therefore, developing an axial multifocal direct-writing method centered on programmable phase for focusing high NA objectives is of great significance. Summary of the Invention

[0006] This invention provides a programmable phase-controlled axial parallel laser direct-write lithography method, which can generate multiple light focal points with uniform intensity, good sidelobe suppression, and high resolution in axial parallel.

[0007] This invention provides a programmable phase-controlled axial parallel laser direct-write lithography method, comprising: (1) Divide the effective illumination area of ​​the SLM into n concentric rings according to the effective illumination diameter and pixel size of the SLM, and construct a ring boundary index table based on the mapping relationship between the concentric ring radius and the concentric ring; (2) Use a random number generator to generate multiple individuals constructed from n binary numbers corresponding to concentric rings to obtain an initial population. Decode each individual in the initial population to obtain n 0 or π phases, thereby obtaining the ring-phase mapping relationship. Based on the ring-phase mapping relationship and the ring boundary index table, form the SLM pupil surface phase distribution and complete a regularization repair. Call the light field evaluation module to calculate and evaluate the axial light field and transverse light field corresponding to each individual in the set sampling area, and obtain the light field energy distribution and full width at half maximum (FWHM) of each individual in the target window area. (3) Based on the optimization objective and constraint terms that can achieve uniform focal energy, a fitness function is constructed. Based on the light field energy distribution and full width at half maximum of each individual, the fitness value of each individual is obtained through the fitness function. Based on the fitness value of each individual, a tournament selection mechanism is used to select parent individuals from the current population. (4) Perform crossover and mutation operations on the selected parent individuals to generate new offspring individuals, and merge the new offspring individuals with the selected parent individuals to form a new population; (5) Determine whether the preset maximum number of iterations has been reached, or whether the fitness difference is lower than the preset threshold. If so, stop the iteration and obtain the SLM pupil phase distribution corresponding to the individual with the highest fitness value. Otherwise, repeat steps (2)-(4). (6) Quantize and encode the SLM pupil phase distribution obtained in step (5) to generate a phase map that matches the SLM driving mode, and load the phase map into the SLM to realize axial parallel laser direct writing lithography.

[0008] Preferably, the SLM pupil plane phase distribution is formed based on the ring-phase mapping relationship and the ring boundary index table, including: The inner radius, outer radius, and ring width of each concentric ring are determined by the ring boundary index table, and the pixel position covered by the corresponding concentric ring in the SLM pixel array is determined based on the inner radius, outer radius, and ring width. Based on the ring-phase mapping relationship, the corresponding phase value is assigned to each pixel in the concentric ring, thereby constructing the SLM pupil plane phase distribution.

[0009] Preferably, after obtaining the phase distribution of the SLM pupil plane, regularization repair is required; The regularization repair includes: performing continuity and manufacturability constraints on the phase distribution of the SLM pupil plane, eliminating discontinuous or abrupt phase boundaries by limiting phase abrupt changes between adjacent concentric rings; merging or correcting isolated phase regions smaller than the preset minimum ring width to ensure that the phase structure meets the pixel resolution and manufacturing requirements of the spatial light modulator; and smoothing isolated phase points or isolated phase regions that introduce abnormal diffraction effects in the phase distribution to reduce high-frequency components.

[0010] Preferably, after obtaining the light field energy distribution and full width at half maximum (FWHM) of each individual within the target window region, the light field energy distribution and FWHM of each individual within the target window region are normalized, and the normalized values ​​are input into the fitness function to obtain the fitness value of each individual.

[0011] Preferably, the fitness value is constructed by the basic cost function and the total penalty term, wherein the basic cost function is obtained by weighted summation of the performance indicators of multiple optimization objectives; The basic cost function includes the following three performance indicators for optimization objectives: The performance indicator for the first optimization objective is the average of the sum of the reciprocals of the actual energy proportions of each target focus within the target window region, used to suppress energy imbalance between focuses; the performance indicator for the second optimization objective is the sum of the absolute values ​​of the differences between the actual energy proportion and the desired energy proportion of each target focus within the target window region, used to constrain the focus energy distribution to be close to the desired proportion; the performance indicator for the third optimization objective is the average of the ratio of the full width at half maximum (FWHM) of the optical field profile at the corresponding axial position of each target focus within the target window region to the working wavelength, used to improve lateral focusing resolution; The total penalty term is obtained by weighted summation of the penalty values ​​corresponding to each constraint. Each penalty value is a non-negative quantity and the smaller the value, the higher the degree of constraint satisfaction. The fitness value is obtained by monotonically transforming the basic cost function and the total penalty term, so that a larger fitness value indicates a better overall performance of the individual.

[0012] Preferably, the constraints include the following: ,in, For the first The evaluation range is pre-defined in the axial direction, with the center position of the target focus as the center, and is used to limit the axial target window of the target focus; Indicates the direction along the optical axis Normalized axial light intensity distribution at the location; For the first The actual energy percentage of each target focus; The number of target focal points; For the first Normalized peak value within each target focus; Indicates the first The expected energy percentage corresponding to each target focus; For the first The radial ring spacing between adjacent concentric rings; This is the minimum permissible ring spacing pre-defined based on the spatial light modulator pixel size and system manufacturing capabilities.

[0013] Preferably, the three optimization objectives are as follows: ,in, The number of target focal points; For the first The actual energy percentage of each target focus; For the first The expected energy percentage of each target focus; For the first The full width at half maximum (FWHM) of the transverse profile of the light field at the corresponding axial position of each target focus; This is the operating wavelength.

[0014] Preferably, after generating new offspring individuals, a crossover strategy that maintains the phase block structure is adopted, and a manufacturability repair rule is executed immediately after the mutation operation to ensure the feasibility of the offspring individuals, wherein: The crossover strategy that can maintain the phase block structure includes: using a phase block composed of concentric rings or several adjacent concentric rings as the smallest genetic unit, selecting one or more complete phase blocks in the parent individual as crossover segments, and exchanging them as a whole at the corresponding positions, thereby avoiding random crossover of individual pixels or individual ring elements and ensuring the continuity of the phase structure in the radial direction. The manufacturability repair rules include: detecting the phase structure generated after crossover and mutation; merging or adjusting the phase structure when the spacing between adjacent concentric rings is less than the preset minimum allowable ring width; correcting or smoothing isolated phase blocks or abnormal phase regions introduced by crossover or mutation to reduce high-frequency phase components; and performing a consistency check on the repaired phase structure to ensure that it meets the requirements of spatial light modulator pixel resolution and system stability.

[0015] Preferably, before dividing the effective illumination area of ​​the SLM into n concentric rings, the obtained optical parameters include the incident wavelength. The determined operational constraints include the photoresist refractive index n, objective lens numerical aperture NA, and focal length f, as well as the SLM effective illumination diameter, SLM pixel size and spacing. The axial target focus set is then defined. The number of target focus points is , No. The center position of each focus is Adjacent spacing and window half-width .

[0016] The present invention also provides an axial parallel laser direct-write lithography system for the programmable phase-controlled axial parallel laser direct-write lithography method, comprising: A laser is a laser source used to provide a preset direct-write laser wavelength. The first 4f system is used to reduce the laser beam to a preset multiple; The exposure switch module is used to modulate the polarization angle of the compressed laser beam, and then perform the exposure switch function in laser direct writing through the acousto-optic modulator. It then corrects the polarization direction of the first-order diffraction light emitted from the acousto-optic modulator, blocks other orders of diffraction light, and transmits the first-order diffraction light. The system comprises a polarization beam splitter, a second 4f system, and a spatial modulator. The first-order diffracted light passes through the polarization beam splitter and the second 4f system and then illuminates the spatial modulator. The spatial modulator is subjected to phase modulation of the incident laser beam by using an axially parallel laser direct-write lithography method with programmable phase control as described in any one of claims 1-9 to obtain the SLM pupil plane phase distribution. The third 4f system, the galvanometer scanning system, is used to illuminate the phase-modulated laser beam onto the galvanometer scanning system, and the galvanometer scanning system is used to deflect and scan the laser beam based on control commands. The direct-write module is used to expand the laser beam after polarization scanning and focus the expanded laser beam onto the sample to be written on the displacement platform, thereby realizing axial parallel laser direct-write lithography.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes a constructed ring-phase mapping relationship and a ring boundary index table to divide the effective illumination area of ​​the spatial light modulator into multiple concentric rings, and assigns 0 or 0 to the corresponding ring of each concentric ring. The phase is mapped onto the SLM to obtain the SLM pupil phase distribution, thus associating the genetic algorithm with the phase pattern loaded onto the SLM. This allows for the efficient conversion of the genetic algorithm's optimization results into a phase pattern. Then, based on the constructed fitness function, the genetic algorithm can efficiently obtain the SLM pupil phase distribution corresponding to multiple axially generated light focal points with uniform intensity, good sidelobe suppression, and high resolution. This enables axially parallel laser direct-write lithography, ensuring simultaneous generation of multiple focal points while achieving an engineering-usable balance between intensity balance, sidelobe control, and processing robustness. Attached Figure Description

[0018] Figure 1 A flowchart of a programmable phase-controlled axial parallel laser direct-write lithography method provided in a specific embodiment of the present invention; Figure 2 A schematic diagram of the axial parallel laser direct-write lithography system provided in an embodiment of the present invention; Figure 3 (a) is a normalized intensity distribution diagram of the axial multifocal YZ plane simulation results of a specific embodiment of the present invention; Figure 3 (b) is the axial optical field intensity distribution curve of the simulation results of a specific embodiment of the present invention; Figure 4 (a) shows the lateral light field intensity distribution curves at each focal position in the simulation results of a specific embodiment of the present invention; Figure 4 (b) is a comparison diagram of the horizontal half-height and full width of each focal point in the simulation results of a specific embodiment of the present invention. Detailed Implementation

[0019] To make the specific details of the technical solution of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. The present invention may also be implemented in other ways different from the following embodiments; therefore, the present invention is not limited to the specific embodiments described below.

[0020] This invention provides a programmable phase-controlled axial parallel laser direct-write lithography method. This method optimizes the design of the phase mask for the laser lithography machine (SLM) using a multi-objective genetic algorithm, achieving multiple focused spots distributed along the optical axis z under a high numerical aperture objective lens, significantly improving the efficiency of laser direct-write processing. The specific steps are as follows: Figure 1 As shown: Step 1: Determine the necessary optical parameters: incident wavelength λ, photoresist refractive index n, objective lens numerical aperture NA, and focal length f. Determine workpiece movement constraints: SLM effective illumination diameter, SLM pixel size, and spacing. Set the axial target focus set. (Number of target focus points is) , No. The center position of each focus is Adjacent spacing and window half-width Determine the optimization objective and corresponding constraints of the multi-objective genetic algorithm, and adjust the algorithm scale.

[0021] Step 2: Divide the effective illumination area of ​​the SLM into n concentric rings based on the effective illumination diameter and pixel size of the SLM. Construct a ring boundary index table based on the mapping relationship between the concentric ring radius and the concentric ring. The corresponding concentric ring can be found in the ring boundary index table based on the center point and radius, which prepares for the efficient loading of 0 or π phase directly onto the concentric ring. At the same time, the coordinates of the micromirrors contained in the concentric ring can be obtained by obtaining the radius and width of the concentric ring.

[0022] A unified data management structure is initialized for centralized management of relevant parameters during the optimization process. These parameters include: design target parameters for constructing the fitness function, manufacturing constraint parameters determined by factors such as the spatial light modulator pixel size and minimum achievable ring width, robustness scenarios for evaluating the stability of the phase scheme under parameter perturbation conditions, and axial and lateral evaluation grids for light field calculation. Simultaneously, fitness changes and optimal individual information are recorded during the optimization process to form an optimization process log.

[0023] In addition, a light field evaluation module is pre-built to calculate the corresponding axial and transverse light fields based on the phase distribution of the SLM pupil plane. Fixed calculation parameters and lookup tables that are independent of system parameters in this module are pre-calculated and cached, and memory allocation is completed. This reduces redundant calculations during the iteration of the genetic algorithm and improves the overall optimization efficiency.

[0024] Step 3: Use a random number generator to generate multiple individuals constructed from n binary numbers corresponding to concentric rings to obtain the initial population. It can be understood that the binary representation of the individuals, i.e., 0 or 1, corresponds to a phase of 0 or π. To improve the quality and diversity of the population, pre-designed heuristic individuals are injected. These heuristic individuals are artificially added individuals with high fitness values.

[0025] Step 4: Decode each individual in the initial population to obtain n 0 or π phases, thus obtaining the ring-phase mapping relationship. Based on the ring-phase mapping relationship and the ring boundary index table, form the SLM pupil phase distribution and complete a regularization repair. Call the light field evaluation module to evaluate the axial and transverse light fields of each individual within the set sampling area, obtain the light field energy distribution and full width at half maximum (FWHM) of each individual within the preset target window area, normalize the light field energy distribution and FWHM of each individual within the target window area, input the normalized values ​​into the fitness function to obtain the fitness value of each individual, and use a caching mechanism to avoid redundant calculations and improve optimization efficiency. The target window area provided in this embodiment is a set of multiple axial intervals pre-defined according to the expected axial focal position, used to limit the evaluation range of light field energy during the optimization process.

[0026] Specifically, the ring-phase mapping relationship is constructed, including: establishing a correlation matrix with the radius of the concentric ring as the horizontal axis and the phase value of each element in the individual as the vertical axis, to obtain the ring-phase mapping relationship. Since there is a correspondence between the ring and the micromirror coordinates, the correspondence between the phase and the micromirror coordinates is found, thus obtaining the phase distribution of the SLM pupil plane.

[0027] The specific embodiments of the present invention provide a method for forming the SLM pupil plane phase distribution based on the ring-phase mapping relationship and the ring boundary index table, including: The inner radius, outer radius, and ring width of each concentric ring are obtained through a ring boundary index table. Based on the pixel positions covered by the concentric rings corresponding to these inner and outer radii and ring widths in the SLM pixel array, and based on the ring-phase mapping relationship, the corresponding phase values ​​are assigned to each pixel within the concentric rings, thereby constructing the SLM pupil plane phase distribution. The advantages of constructing the SLM pupil plane phase distribution using the above method are: using concentric rings as the basic phase assignment units, the continuity and symmetry of the phase distribution in the radial direction can be maintained, avoiding high-frequency phase disturbances introduced by pixel-level random assignment; at the same time, the ring-phase mapping relationship establishes a clear correspondence between the discrete optimization variables in the genetic algorithm and the physical coordinates in the SLM pixel array, which is beneficial for stably and accurately mapping the optimized phase codes onto the spatial light modulator, thereby improving the stability and controllability of axial light field modulation.

[0028] In one specific embodiment, after obtaining the SLM pupil phase distribution, regularization repair is performed, including: checking the continuity of the phase distribution between adjacent concentric rings; when there are abrupt phase boundaries introduced by discrete coding, the phase distribution is locally adjusted to eliminate discontinuities or abnormal jumps; merging or correcting small ring structures or isolated phase regions in the phase distribution that do not meet the preset minimum ring width requirement to ensure that the phase structure meets the pixel resolution and manufacturability constraints of the spatial light modulator; smoothing isolated phase points or isolated phase blocks that may introduce abnormal diffraction effects to reduce high-frequency spatial components; through the above regularization repair, the obtained SLM pupil phase distribution maintains the designed optical function while possessing good numerical stability and engineering feasibility.

[0029] Step 5: Construct a fitness function based on the optimization objective and constraints that enable uniform focal energy. Obtain the fitness value of each individual based on the light field energy distribution and full width at half maximum (FWHM) of each individual. Based on the fitness value of each individual, the parent individuals are selected from the current population using a tournament selection mechanism through fast non-dominated sorting.

[0030] The fitness value provided in the specific embodiments of the present invention is constructed by the basic cost function and the total penalty term. The basic cost function is obtained by weighted summation of the performance indicators of multiple optimization objectives, and the smaller each performance indicator is, the better the performance.

[0031] The basic cost function provided in this specific embodiment of the invention includes the performance metrics of the following three optimization objectives: the first optimization objective provided in this embodiment. The performance index is the average of the sum of the reciprocals of the actual energy percentages of each target focus within the target window area. It is used to balance the energy of each focus and enhance the weakest focus, i.e., to enhance the weakest focus.

[0032] The performance index of the second optimization objective provided in this embodiment It is half the sum of the absolute values ​​of the differences between the actual energy proportion and the expected energy proportion of each target focus within the target window area, used to make the focus intensity distribution conform to expectations, i.e., focus uniformity.

[0033] The third optimization objective provided in this embodiment The performance index is the ratio of the average half-width at half-maximum (FWHM) of the optical field profile at the corresponding axial position of each target focal point within the target window area to the working wavelength, which is used to improve lateral resolution.

[0034] The three optimization objectives provided in the specific embodiments of the present invention are as follows: Where M is the number of target focal points, Let be the actual energy percentage of the m-th target focus. Let m be the expected energy percentage of the m-th target focus. Let be the full width at half maximum (FWHM) of the transverse profile of the light field at the corresponding axial position of the m-th target focal point. This is the operating wavelength.

[0035] The total penalty value provided in this specific embodiment of the invention is obtained by weighted summation of the penalty values ​​corresponding to each constraint condition. Each penalty value is a non-negative quantity, and the smaller the value, the higher the degree of constraint satisfaction. The constraints include axial sidelobe strength threshold constraints, out-of-window energy leakage constraints, minimum coverage constraints, superpeak constraints, peak range constraints of each focal point, lateral sidelobe constraints, and minimum ring width manufacturability constraints. The penalty values ​​of the constraint terms are synthesized into a total penalty value by weighted summation. The smaller the total penalty value, the higher the degree of individual satisfaction with the constraints. During the optimization process, the total penalty value and the basic cost function corresponding to the aforementioned optimization objective jointly construct the evaluation index of the individual, and form a fitness value through monotonic transformation. The larger the fitness value, the better the overall performance of the individual. Thus, the individual with the highest fitness value is selected during the genetic algorithm iteration process.

[0036] Specifically, the constraints provided in this embodiment include the following: ,in, For the first The evaluation range is pre-defined in the axial direction, with the center position of the target focus as the center, and is used to limit the axial target window of the target focus; Indicates the direction along the optical axis Normalized axial light intensity distribution at the location; For the first The actual energy percentage of each target focus; The number of target focal points; For the first Normalized peak value within each target focus; Indicates the first The expected energy percentage corresponding to each target focus; For the first The radial ring spacing between adjacent concentric rings; This is the minimum permissible ring spacing pre-defined based on the spatial light modulator pixel size and system manufacturing capabilities.

[0037] The six constraints are: axial sidelobe overthreshold penalty, out-of-window energy leakage penalty, minimum coverage insufficiency penalty, superpeak over-limit penalty, peak range over-limit penalty for each focal point, and lateral sidelobe overthreshold penalty; the seventh constraint is a manufacturability rule, which adds a minimum ring width constraint. When robustness assessment is enabled, the worst-case indicators for multiple scenarios are used to calculate the penalties.

[0038] Step 6: Perform crossover and mutation operations on the selected parent individuals to generate new offspring individuals. Merge the new offspring individuals with the selected parent individuals to form a new population. In the genetic operations, a crossover strategy that maintains the phase block structure is adopted, and the manufacturability repair rule is invoked immediately after mutation to ensure the feasibility of the offspring individuals. Merge the offspring with the best contemporary individuals retained according to the elitist strategy to form a new generation population.

[0039] In one specific embodiment, after generating new offspring individuals, a crossover strategy that can maintain the phase block structure is adopted, and a manufacturability repair rule is invoked immediately after mutation to ensure the feasibility of the offspring individuals. This includes: in the crossover operation, using concentric rings or phase blocks composed of several adjacent concentric rings as the smallest genetic unit, selecting one or more complete phase blocks from the parent individuals as crossover segments, and performing overall exchange at the corresponding positions to avoid random crossover at a single micromirror or pixel level, thereby maintaining the continuity and consistency of the phase structure in the radial direction. After the mutation operation is completed, the manufacturability repair rules are immediately executed on the generated offspring individuals. Abnormal phase structures that may be introduced by crossover or mutation are detected and processed. When there are adjacent concentric rings with a spacing smaller than the preset minimum allowable ring width, isolated phase blocks, or abnormal phase regions, the phase structure is repaired by merging, adjusting, or smoothing to ensure that the obtained phase distribution meets the pixel resolution and manufacturability requirements of the spatial light modulator. Through the aforementioned crossover and repair process, the generated offspring individuals retain phase block structure characteristics while possessing good engineering feasibility, thereby forming a new generation population for the next generation of evolution.

[0040] Step 7: Determine whether the iteration number Gen has reached the preset maximum iteration number, or whether the fitness difference is lower than the preset threshold. If so, stop the iteration, obtain the SLM pupil phase distribution corresponding to the individual with the highest fitness value, and then output the optimal phase mask. Otherwise, repeat steps (2)-(7), i.e., Gen=Gen+1.

[0041] Step 8: Output the globally optimal binary ring phase code, and save it together with the fitness history, decomposition index, robustness and manufacturing compliance report, so as to obtain the phase map that can generate target axial multi-focuses adapted to this model of SLM. Load the SLM pupil plane phase distribution obtained in step (5) onto the SLM to realize axial parallel laser direct writing lithography.

[0042] This invention successfully solves the technical challenge of generating axial multifocals under high numerical aperture objectives by organically combining a multi-objective genetic algorithm with programmable phase control. This method not only improves the efficiency of direct-write lithography through a parallel exposure mechanism, but also effectively suppresses lateral sidelobe interference and ensures the overall quality of the focused light field by achieving precise control and uniform distribution of the intensity of each focal point through carefully designed optimization objectives and constraints. Particularly noteworthy is the manufacturability constraint and robustness evaluation mechanism incorporated into the optimization process, which ensures the reliable loading of the phase pattern in a practical SLM system and enhances its adaptability to fluctuations in the working environment. This makes the method highly programmable while possessing excellent engineering practical value, providing a feasible technical approach for the rapid and high-precision fabrication of three-dimensional micro / nano structures.

[0043] The present invention also provides an axial parallel laser direct-write lithography system for the above-described programmable phase-controlled axial parallel laser direct-write lithography method, such as... Figure 2 As shown, the system includes a laser 1, a first 4f system including lenses 2 and 3, an exposure switch module including a half-wave plate 4, an acousto-optic modulator (AOM) 5, a half-wave plate 6, and a filter aperture 7, a polarization beam splitter (PBS) 8, a second 4f system including lenses 9, filter aperture 10, and lenses 11, a spatial modulator (SLM) 12, a mirror 13, a third 4f system including lenses 14 and 15, a galvanometer scanning system 17, a mirror 18, a direct writing module including lenses 19 and 20, a beam splitter (BS) 21, an objective lens 22, a precision displacement stage 23, and a computer 24.

[0044] The laser 1 provided in this embodiment provides a laser source with a preset wavelength for direct writing processing.

[0045] In this embodiment, lens 2 and lens 3 form a 4f system, which is used to reduce the laser beam to a preset magnification. The half-wave plate 4 provided in this embodiment is used to modulate the polarization angle of the laser beam so that its polarization direction is adapted to the working requirements of the AOM, thereby ensuring that the AOM obtains the highest diffraction efficiency. The acousto-optic modulator (AOM) 5 provided in this embodiment is used to perform the exposure switching function in laser direct writing processing; The half-wave plate 6 provided in this embodiment is used to correct the polarization direction of the first-order diffracted light emitted from the AOM, so that its polarization state matches the working requirements of the downstream PBS. The filter aperture 7 provided in this embodiment is used to select and transmit the first-order diffracted light emitted from the AOM, while blocking diffracted light of other orders. The polarization beam splitter (PBS) 8 provided in this embodiment is used to reflect S-polarized light and simultaneously deflect the overall optical path; In this embodiment, lens 9 and lens 11 form a 4f system, which is used to expand the laser beam to a preset multiple. At the same time, the filter aperture 10 is located at the focal point of lens 9 and serves as a spatial filter to improve the quality of the light spot. The reflector 13 provided in this embodiment is used to deflect the optical path of the expanded laser beam so that it is transmitted at a specific incident angle required by the spatial light modulator (SLM). The spatial light modulator (SLM) 12 provided in this embodiment is used to load a binary phase map generated according to the method described in the claim 12 and to perform programmable phase modulation on the incident laser wavefront. The lens 14 and lens 15 provided in this embodiment form a 4f system, which is used to reduce the laser beam modulated by SLM to a preset multiple and extend the optical path in space to adapt to the system layout. The reflectors 16 and 18 provided in this embodiment are used for optical path folding and guidance of the compressed laser beam.

[0046] The galvanometer scanning system 17 provided in this embodiment is used to deflect and scan the laser beam according to control commands during the processing.

[0047] The lens 19 and lens 20 provided in this embodiment form a 4f system, which is used to expand the laser beam to a preset magnification to match the entrance pupil size of the subsequent objective lens and assist in the planning and construction of the subsequent system.

[0048] The beam splitter (BS) 21 provided in this embodiment is used to combine the laser processing optical path with the visible light observation optical path.

[0049] The objective lens 22 provided in this embodiment is used to focus the combined laser beam with a high numerical aperture to realize the core writing function of laser direct writing.

[0050] The precision displacement platform 23 provided in this embodiment is used to support the sample to be inscribed and to achieve its precision displacement in a two-dimensional plane.

[0051] The computer 24 provided in this embodiment serves as the control unit of the system. It is connected to the SLM12, the galvanometer scanning system 17, and the precision displacement platform 23 via signals. It is used to load phase maps into the SLM, send coordinated control commands to the galvanometer and the displacement platform, and process image acquisition data.

[0052] In this specific embodiment, the semiconductor laser 1 operates at a wavelength of 517 nm. The spatial light modulator (SLM) 12 is a liquid crystal phase modulator with an effective aperture of 3 mm and a pixel size of 12.5 μm. The objective lens 22 has a numerical aperture of 1.45 and a focal length of 1.8 mm, is applied using an oil immersion method, and has a matching medium refractive index of 1.52. In this specific embodiment, the optimization target is five consecutive focal points before and after the original objective lens focal point along the axis, and the target focal point set {f_m} is {-1.2,-0.6,0,0.6,1.2} (μm).

[0053] like Figure 3 As shown, after the optimized phase mask is loaded onto the SLM, multiple focused spots distributed along the optical axis are successfully generated in the focal domain of the objective lens. Figure 3 (a) The YZ plane intensity distribution diagram clearly shows that five focal points with uniform intensity are arranged along the optical axis; Figure 3 (b) The axial light field intensity distribution curves further confirm the accuracy and intensity consistency of each focal position, and the peak-to-sidelobe ratio is better than the design requirements. Figure 4 (a) and (b) show the contrast of the full width at half maximum (FWHM) of each focal point. The lateral dimensions of all focal points are controlled at around 0.45λ, achieving parallel processing capability with super-diffraction limit resolution.

[0054] The innovation of this embodiment lies in combining a multi-objective genetic algorithm with programmable phase control, solving the technical challenge of generating axial multifocal points under high numerical aperture conditions. While maintaining the simplicity of the optical system, it achieves efficient and high-quality laser direct-write processing. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

Claims

1. A programmable phase-controlled axial parallel laser direct-write lithography method, characterized in that, include: (1) Divide the effective illumination area of ​​the SLM into n concentric rings according to the effective illumination diameter and pixel size of the SLM, and construct a ring boundary index table based on the mapping relationship between the concentric ring radius and the concentric ring; (2) Use a random number generator to generate multiple individuals constructed from n binary numbers corresponding to concentric rings to obtain an initial population. Decode each individual in the initial population to obtain n 0 or π phases, thereby obtaining the ring-phase mapping relationship. Based on the ring-phase mapping relationship and the ring boundary index table, form the SLM pupil surface phase distribution and complete a regularization repair. Call the light field evaluation module to calculate and evaluate the axial light field and transverse light field corresponding to each individual in the set sampling area, and obtain the light field energy distribution and full width at half maximum (FWHM) of each individual in the target window area. (3) Based on the optimization objective and constraint terms that can achieve uniform focal energy, a fitness function is constructed. Based on the light field energy distribution and full width at half maximum of each individual, the fitness value of each individual is obtained through the fitness function. Based on the fitness value of each individual, a tournament selection mechanism is used to select parent individuals from the current population. (4) Perform crossover and mutation operations on the selected parent individuals to generate new offspring individuals, and merge the new offspring individuals with the selected parent individuals to form a new population; (5) Determine whether the preset maximum number of iterations has been reached, or whether the fitness difference is lower than the preset threshold. If so, stop the iteration and obtain the SLM pupil phase distribution corresponding to the individual with the highest fitness value. Otherwise, repeat steps (2)-(4). (6) Quantize and encode the SLM pupil phase distribution obtained in step (5) to generate a phase map that matches the SLM driving mode, and load the phase map into the SLM to realize axial parallel laser direct writing lithography.

2. The programmable phase-controlled axial parallel laser direct-write lithography method according to claim 1, characterized in that, The SLM pupil plane phase distribution is formed based on the ring-phase mapping relationship and the ring boundary index table, including: The inner radius, outer radius, and ring width of each concentric ring are determined by the ring boundary index table, and the pixel position covered by the corresponding concentric ring in the SLM pixel array is determined based on the inner radius, outer radius, and ring width. Based on the ring-phase mapping relationship, the corresponding phase value is assigned to each pixel in the concentric ring, thereby constructing the SLM pupil plane phase distribution.

3. The programmable phase-controlled axial parallel laser direct-write lithography method according to claim 1, characterized in that, After obtaining the phase distribution of the SLM pupil plane, regularization repair is required. The regularization repair includes: performing continuity and manufacturability constraints on the phase distribution of the SLM pupil plane, eliminating discontinuous or abrupt phase boundaries by limiting phase abrupt changes between adjacent concentric rings; merging or correcting isolated phase regions smaller than the preset minimum ring width to ensure that the phase structure meets the pixel resolution and manufacturing requirements of the spatial light modulator; and smoothing isolated phase points or isolated phase regions that introduce abnormal diffraction effects in the phase distribution to reduce high-frequency components.

4. The programmable phase-controlled axial parallel laser direct-write lithography method according to claim 1, characterized in that, After obtaining the light field energy distribution and full width at half maximum (FWHM) of each individual within the target window region, the light field energy distribution and FWHM of each individual within the target window region are normalized. The normalized values ​​are then input into the fitness function to obtain the fitness value of each individual.

5. The programmable phase-controlled axial parallel laser direct-write lithography method according to claim 1, characterized in that, The fitness value is constructed by the basic cost function and the total penalty term, wherein the basic cost function is obtained by weighted summation of the performance indicators of multiple optimization objectives; The basic cost function includes the performance indicators of the following three optimization objectives: The performance indicator of the first optimization objective is the average of the sum of the reciprocals of the actual energy proportions of each target focus within the target window area, which is used to suppress energy imbalance between focuses; The performance index of the second optimization objective is the sum of the absolute values ​​of the differences between the actual energy ratio and the expected energy ratio of each target focus within the target window area, used to constrain the focus energy distribution to be close to the expected ratio; the performance index of the third optimization objective is the average ratio of the half-width at half-maximum to the working wavelength of the optical field transverse profile at the corresponding axial position of each target focus within the target window area, used to improve the transverse focusing resolution. The total penalty term is obtained by weighted summation of the penalty values ​​corresponding to each constraint. Each penalty value is a non-negative quantity and the smaller the value, the higher the degree of constraint satisfaction. The fitness value is obtained by monotonically transforming the basic cost function and the total penalty term, so that a larger fitness value indicates a better overall performance of the individual.

6. The programmable phase-controlled axial parallel laser direct-write lithography method according to claim 5, characterized in that, The constraints include the following: ,in, For the first The evaluation range is pre-defined in the axial direction, with the center position of the target focus as the center, and is used to limit the axial target window of the target focus; Indicates the direction along the optical axis Normalized axial light intensity distribution at the location; For the first The actual energy percentage of each target focus; The number of target focal points; For the first Normalized peak value within each target focus; Indicates the first The expected energy percentage corresponding to each target focus; For the first The radial ring spacing between adjacent concentric rings; This is the minimum permissible ring spacing pre-defined based on the spatial light modulator pixel size and system manufacturing capabilities.

7. The programmable phase-controlled axial parallel laser direct-write lithography method according to claim 5, characterized in that, The three optimization objectives are as follows: ,in, The number of target focal points; For the first The actual energy percentage of each target focus; For the first The expected energy percentage of each target focus; For the first The full width at half maximum (FWHM) of the transverse profile of the light field at the corresponding axial position of each target focus; This is the operating wavelength.

8. The programmable phase-controlled axial parallel laser direct-write lithography method according to claim 1, characterized in that, After generating new offspring individuals, a crossover strategy that maintains the phase block structure is adopted, and a manufacturability repair rule is executed immediately after the mutation operation to ensure the feasibility of the offspring individuals, wherein: The crossover strategy that can maintain the phase block structure includes: using a phase block composed of concentric rings or several adjacent concentric rings as the smallest genetic unit, selecting one or more complete phase blocks in the parent individual as crossover segments, and exchanging them as a whole at the corresponding positions, thereby avoiding random crossover of individual pixels or individual ring elements and ensuring the continuity of the phase structure in the radial direction. The manufacturability repair rules include: detecting the phase structure generated after crossover and mutation; merging or adjusting the phase structure when the spacing between adjacent concentric rings is less than the preset minimum allowable ring width; correcting or smoothing isolated phase blocks or abnormal phase regions introduced by crossover or mutation to reduce high-frequency phase components; and performing a consistency check on the repaired phase structure to ensure that it meets the requirements of spatial light modulator pixel resolution and system stability.

9. The programmable phase-controlled axial parallel laser direct-write lithography method according to claim 1, characterized in that, Before dividing the effective illumination area of ​​the SLM into n concentric rings, the obtained optical parameters include the incident wavelength. The determined operational constraints include the photoresist refractive index n, objective lens numerical aperture NA, and focal length f, as well as the SLM effective illumination diameter, SLM pixel size and spacing. The axial target focus set is then defined. The number of target focus points is , No. The center position of each focus is Adjacent spacing and window half-width .

10. An axial parallel laser direct-write lithography system for a programmable phase-controlled axial parallel laser direct-write lithography method according to any one of claims 1-9, characterized in that, include: A laser is a laser source used to provide a preset direct-write laser wavelength. The first 4f system is used to reduce the laser beam to a preset multiple; The exposure switch module is used to modulate the polarization angle of the compressed laser beam, and then perform the exposure switch function in laser direct writing through the acousto-optic modulator. It then corrects the polarization direction of the first-order diffraction light emitted from the acousto-optic modulator, blocks other orders of diffraction light, and transmits the first-order diffraction light. The system comprises a polarization beam splitter, a second 4f system, and a spatial modulator. The first-order diffracted light passes through the polarization beam splitter and the second 4f system and then illuminates the spatial modulator. The spatial modulator is subjected to phase modulation of the incident laser beam by using an axially parallel laser direct-write lithography method with programmable phase control as described in any one of claims 1-9 to obtain the SLM pupil plane phase distribution. The third 4f system, the galvanometer scanning system, is used to illuminate the phase-modulated laser beam onto the galvanometer scanning system, and the galvanometer scanning system is used to deflect and scan the laser beam based on control commands. The direct-write module is used to expand the laser beam after polarization scanning and focus the expanded laser beam onto the sample to be written on the displacement platform, thereby realizing axial parallel laser direct-write lithography.

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