Digital Lithography Research Articles

Chaos-enhanced self-adaptive particle swarm optimization with simulated annealing for digital lithography mask optimization

In this paper, an efficient approach to mask optimization for digital micromirror device lithography is proposed, leveraging an enhanced particle swarm optimization algorithm, which significantly elevates the resolution and precision of lithography. Initially, chaos mapping is applied to the initial population to enhance particle diversity, thereby improving the optimization efficiency of the algorithm. Subsequently, self-adaptive parameter adjustments and simulated annealing are integrated to effectively avoid premature convergence and escape local optima. Numerical simulation results demonstrate a substantial reduction in pattern errors between the printed and the target images by 95.2%, 95.4%, and 89.2%. The proposed algorithm markedly surpasses conventional optimization methods, notably bolstered in optimization efficiency and pattern accuracy.

Block-based inverse lithography technology with adaptive level-set algorithm

Inverse lithography technology (ILT) is a key computational lithography approach aimed at inversely optimizing the photomask pattern to compensate for the image distortion in advanced optical lithography process. Traditional ILT algorithms, despite their capacity of significantly enhancing the image quality, bring challenges to the computational efficiency and mask manufacturability. To overcome those problems, this paper proposes a novel block-based ILT method driven by the level-set algorithm. This method leverages overlapped basis blocks with a level-set support area for mask representation, thus reducing the mask complexity. To circumvent the slow convergence rate dictated by the conventional Euler time step of the Courant-Friedrichs-Lewy condition, this research adopts the Barzilai-Borwein algorithm to update level set function using adaptive time step, which accelerates the optimization process. In addition, a testbed of digital lithography system is established to verify the proposed ILT method with a calibrated imaging model. It shows that the proposed method is superior over the widely-used and state-of-the-art ILT methods in terms of convergence speed and mask manufacturability.

Enhanced corner sharpness in DMD-based scanning maskless lithography using optical proximity correction and genetic algorithm

An optical proximity correction (OPC) method is proposed to enhance the UV patterning quality in a DMD-based scanning-type maskless lithography system with an oblique scanning and step-strobe lighting (OS3 L) scheme. The system setup, software programming, and image processing procedures are detailed. A simulation model is also introduced to predict the patterning results for a given DMD mask. Utilizing this model, a genetic algorithm (GA) is developed to optimize the mask pattern for OPC. The GA-OPC method reduces the corner-rounding effect in metal patterns fabricated using digital maskless lithography and metal lift-off processes. Optical images of the metal patterns show that the proposed GA-OPC method effectively mitigates the corner-rounding effect and improves the patterning fidelity. The work presented in this study lays the foundation for further enhancing the patterning capabilities and quality of DMD-based maskless lithography.

3D OPC method for GLV parallel scanning lithography microstructure topography control based on SinCUT.

A 3D optical proximity correction (OPC) optimization method based on single image contrastive unpaired translation (SinCUT) is proposed for the precise fabrication of 3D microstructures in GLV parallel scanning digital 3D lithography. This method is applied to the optimized fabrication of hyperbolic micro-convex lens arrays. Its fabrication accuracy is demonstrated, showing a significant reduction in the mean square error (MSE) of the morphology. When the lens height is 8.5 µm, the average height error of the lens shape is less than 5%, and the MSE is reduced from 0.727 to 0.0329, resulting in a reduction rate of 92.79%.

DMD digital lithography optimization based on a hybrid genetic algorithm and improved exposure model.

An efficient method to optimize digital micromirror device (DMD) lithography was proposed using a hybrid genetic algorithm integrated with an improved exposure model. The improved exposure model significantly refines traditional approaches by incorporating advanced parameters not previously considered, including the cross-transfer coefficient, detailed light source functions, and impulse response functions. These enhancements provide a comprehensive assessment of the entire optical imaging system's impact on lithography quality and more accurately simulate the interactions of light with the photoresist. The hybrid method combines the robust optimization capabilities of genetic algorithms (GA) with this sophisticated exposure model, facilitating precise micromirror configurations and optimizing light distribution for specific lithographic patterns. This integration results in substantial improvements in lithographic precision, with improvements of up to 84% for hexagonal star patterns, 83% for arrow patterns, and 85% for embedded figure patterns. These advancements enhance imaging quality, reduce optical proximity distortions, and improve overall lithography performance, offering crucial insights into the precision and efficiency improvement of microelectronics fabrication processes.

Edge smoothness enhancement of digital lithography based on the DMDs collaborative modulation

The rough saw-tooth edge caused by the inherent microstructures of digital micromirror device (DMD) will reduce the quality of the lithography pattern. Comprehensively considering the manufacturing efficiency, precision and cost, we propose a DMDs collaborative modulation lithography method to improve the smoothness of the lithography pattern edge. Through combining two misaligned DMDs to collaboratively modulate exposure dose, the better edge smoothness can be achieved. Collaborative exposure with 1/2 DMD pixel misalignment and 1/4 DMD pixel misalignment are both implemented to form the step-shape lithography patterns. The experimental results show that the saw-tooth edge can approximate to a straight line when increasing the number of times of the collaborative exposure. Further error analysis indicates it is effective to improve the edge smoothness while ensuring the lithography quality by using the collaborative modulation lithography. These results indicate that the DMDs collaborative modulation lithography is a promising technique for fabrication of microstructures, which may be a solution for balancing the fabrication precision, efficiency and cost.

Simple visual focusing and alignment technology for digital lithography

A simple visual focusing and alignment technology for digital lithography, which requires only one imaging system to capture both focusing and alignment information, is proposed. Firstly, the Brenner function and the global search method were chosen among the various sharpness evaluation functions, achieving visual precision focusing. Then, the mutual mapping relationship between DMD plane and CCD plane was established by image alignment technique, realizing the visualized precision alignment. Finally, a digital lithography system based on the proposed method was built and experimentally verified, by which the preparation of a grating with a line width of 1.35 μm was achieved, reaching the limit of the system resolution, and the alignment accuracy of the method reached 0.2 μm. Moreover, the mapping exposure experiments showed that the pre-exposure patterns could be converted between DMD and CCD planes, and the visualization of microstructure preparation was truly realized. This method improves the convenience of microstructure preparation and can greatly meet the needs of material scientists regarding microstructure preparation.

Alignment Control of Ferrite-Decorated Nanocarbon Material for 3D Printing.

This paper demonstrates the potential of anisotropic 3D printing for alignable carbon nanomaterials. The ferrite-decorated nanocarbon material was synthesized via a sodium solvation process using epichlorohydrin as the coupling agent. Employing a one-pot synthesis approach, the novel material was incorporated into a 3D photopolymer, manipulated, and printed using a low-cost microscale 3D printer, equipped with digital micromirror lithography, monitoring optics, and magnetic actuators. This technique highlights the ability to control the microstructure of 3D-printed objects with sub-micron precision for applications such as microelectrode sensors and microrobot fabrication.

Optofluidic chip with directly printed polymer optical waveguide Mach-Zehnder interferometer sensors for label-free biodetection

Optofluidic devices hold great promise in biomedical diagnostics and testing because of their advantages of miniaturization, high sensitivity, high throughput, and high scalability. However, conventional silicon-based photonic chips suffer from complicated fabrication processes and less flexibility in functionalization, thus hindering their development of cost-effective biomedical diagnostic devices for daily tests and massive applications in responding to public health crises. In this paper, we present an optofluidic chip based on directly printed polymer optical waveguide Mach-Zehnder interferometer (MZI) sensors for label-free biomarker detection. With digital ultraviolet lithography technology, high-sensitivity asymmetric MZI microsensors based on a width-tailored optical waveguide are directly printed and vertically integrated with a microfluidic layer to make an optofluidic chip. Experimental results show that the sensitivity of the directly printed polymer optical waveguide MZI sensor is about 1695.95 nm/RIU. After being modified with capture molecules, i.e., goat anti-human immunoglobulin G (IgG), the polymer optical waveguide MZI sensors can on-chip detect human IgG at the concentration level of 1.78 pM. Such a polymer optical waveguide-based optofluidic chip has the advantages of miniaturization, cost-effectiveness, high sensitivity, and ease in functionalization and thus has great potential in the development of daily available point-of-care diagnostic and testing devices.

DMD maskless lithography optimization based on an improved genetic algorithm

In this paper, we propose an effective method for optimizing mask design using an enhanced genetic algorithm (GA), significantly boosting digital micromirror device (DMD) maskless lithography performance. After a thorough evaluation of various optimization techniques, we determined that the simulated annealing-enhanced GA (SA-GA) offers superior improvements in lithography simulations, thus optimizing mask design more effectively. Our findings reveal that this method achieves up to 88% and 75% enhancement in simulation accuracy for circular and heart-shaped patterns, respectively, surpassing the results of conventional Hopkins lithography simulations. The remarkable effect of improved GA in enhancing the quality of DMD digital lithography shows that it will have great potential in micro-fabrication applications, and paves the way for the realization of high-fidelity and efficient DMD digital lithography technology, which has excellent versatility and adaptability in the field of microelectronics manufacturing.

Digital inverse patterning solutions for fabrication of high-fidelity microstructures in spatial light modulator (SLM)-based projection lithography.

Digital mask projection lithography (DMPL) technology is gaining significant attention due to its characteristics of free-mask, flexibility, and low cost. However, when dealing with target layouts featuring sizes smaller than the wavelength scale, accurately producing resist patterns that closely match the target layout using conventional methods to design the modulation coefficients of digital masks produced by spatial light modulators (SLM) becomes challenging. Here, we present digital inversion lithography technology (DILT), which offers what we believe to be a novel approach to reverse engineer the modulation coefficients of digital masks. In the case of binary amplitude modulation, DILT achieves a remarkable reduction in pattern errors (PE), reaching the original 0.26. At the same time, in the case of the gray amplitude modulation, the PE can be reduced to the original 0.05, which greatly improves the high-fidelity transfer of the target layout. This significant improvement enhances the accuracy of target design transfer. By leveraging the capabilities of DILT, DMPL can now attain higher precision and reliability, paving the way for more advanced applications in the field of micro-nano device manufacturing.

Edge smoothing optimization method in DMD digital lithography system based on dynamic blur matching pixel overlap technique.

Due to digital micromirrors device (DMD) digital lithography limited by non-integer pixel errors, the edge smoothness of the exposed image is low and the sawtooth defects are obvious. To improve the image edge smoothness, an optimized pixel overlay method was proposed, which called the DMD digital lithography based on dynamic blur effect matching pixel overlay technology. The core of this method is that motion blur effect is cleverly introduced in the process of pixel overlap to carry out the lithography optimization experiment. The simulation and experimental results showed that the sawtooth edge was reduced from 1.666 µm to 0.27 µm by adopting the 1/2 dynamic blur effect to match pixel displacement superposition, which is far less than half of the sawtooth edge before optimization. The results indicated that the proposed method can efficiently improve the edge smoothness of lithographic patterns. We believe that the proposed optimization method can provide great help for high fidelity and efficient DMD digital lithography microfabrication.

DMD maskless digital lithography based on stepwise rotary stitching

Diffractive optical elements (DOEs) with rotationally symmetric phase distribution are mainly produced by laser direct writing technique in a polar coordinate system, which has slow processing speed and limited fabrication area. In this paper, we propose a digital micro-mirror device maskless digital lithography technique based on stepwise rotary stitching. DOEs with rotationally symmetric phase distribution are fabricated by exposure of stitching units and rotation of rotary tables. Then, different stitching units are designed to compensate for the errors caused by the accuracy of the rotary table. Finally, the high quality DOEs are produced by the double-exposure method. When increasing the fabrication area, significantly improves the saw-tooth of the lithography pattern edge while reducing misalignment and overlap of stitching caused by residual errors. The diameter of the fabricated Fresnel zone plate was increased from 5.25 mm to 11.40 mm, and the fabrication area was 4.72 times larger than conventional lithography. The stitching error of 18.95 μm has been eliminated after optimization, and the pixelization has been smoothed. The diffraction results show that the method not only can produce large area and high-quality diffraction elements but also greatly reduce the processing cost.

Digital Mask를 이용한 STED Lithography 기술의 분석적 검증

In this study, a digital mask-based STED lithography technique was proposed, and the effective resolution of the proposed system was calculated analytically. The proposed STED lithography system uses two spatial light modulators to modulate the phase of an excitation beam and a depletion beam, respectively. The excitation spatial light modulator acts as a digital mask to form the patterning image, while the depletion spatial light modulator creates an image surrounding the projected excitation image. Thus, photopolymerization is suppressed by stimulated emission occurring in the depletion focus region surrounding the excitation focus, thereby improving lithographic resolution. Electromagnetic field and intensity distribution were calculated, and the resolution of the proposed STED lithography was simulated based on vectorial diffraction theory. An effective resolution of 72 nm was calculated under the condition of ISUBs/SUB 0.1, which is similar to the resolution of conventional STED lithography at 70 nm. These results analytically confirmed that the proposed STED lithography system could pattern a two-dimensional region simultaneously without the loss of resolution compared to conventional STED lithography.

An efficient and low-cost compensation method for exposure uniformity based on digital oblique scanning lithography

We proposed an efficient and low-cost compensation method for improving exposure uniformity. A flexible designed uniformity grayscale template compensation strategy based on digital micromirror device oblique scanning lithography was developed, which can effectively improve exposure region uniformity. In order to avoid the asynchronous error of the exposure process, the light-source synchronization control based on the pulse width modulation strategy was introduced in the lithography system. The experimental results showed that the maximum dimensional difference is decreased from 20.7% to 3.3% by the above strategy. The presented method will have a broad application prospect in the printed circuit board manufacturing field.

Bubble-based microrobots enable digital assembly of heterogeneous microtissue modules

The specific spatial distribution of tissue generates a heterogeneous micromechanical environment that provides ideal conditions for diverse functions such as regeneration and angiogenesis. However, to manufacture microscale multicellular heterogeneous tissue modules in vitro and then assemble them into specific functional units is still a challenging task. In this study, a novel method for the digital assembly of heterogeneous microtissue modules is proposed. This technique utilizes the flexibility of digital micromirror device-based optical projection lithography and the manipulability of bubble-based microrobots in a liquid environment. The results indicate that multicellular microstructures can be fabricated by increasing the inlets of the microfluidic chip. Upon altering the exposure time, the Young’s modulus of the entire module and different regions of each module can be fine-tuned to mimic normal tissue. The surface morphology, mechanical properties, and internal structure of the constructed bionic peritoneum were similar to those of the real peritoneum. Overall, this work demonstrates the potential of this system to produce and control the posture of modules and simulate peritoneal metastasis using reconfigurable manipulation.

Customized construction of microscale multi-component biostructures for cellular applications

In vitro biofabrication is employed in fields such as biomedicine and those using biomimetic materials. However, it suffers from drawbacks such as low resolution, applicability on a limited range of components, and difficulty in purposefully depositing specific cells in three-dimensional space. Hence, this paper proposes a digital micromirror device-based optical projection lithography (DOPL) system for producing multi-component microstructures with resolutions of tens of microns and explores the behavior of cells with these structures. The printability and mechanical properties of these microstructures were investigated to assess their reproduction quality and the ability to control their structural characteristics. The results show that when DOPL is used with polyethylene glycol dimethacrylate (PEGDMA) hydrogel, an array of micropits can be fabricated within a few minutes. Furthermore, uniform cell spheroids form rapidly with high throughput when they are seeded into the micropits. Additionally, PEGDMA and gelatin methacryloyl (GelMA) were used to construct multi-component microstructures, and it was demonstrated that cells with various morphologies selectively adhere to the heterogeneous interface. In addition, DOPL could enable deposition of various cells for constructing microenvironments and for drug screening. Finally, a biomimetic peritoneal model was constructed. Overall, this work demonstrates the versatility of this system and its potential in cellular applications such as cell behavior research, drug screening, and tissue engineering.

Deep Learning Based Method for Automatic Focus Detection in Digital Lithography

Deep Learning Based Method for Automatic Focus Detection in Digital Lithography

Fabrication of Polymer Optical Waveguides by Digital Ultraviolet Lithography

We present the design, fabrication and characterization of polymer optical waveguides using a digital ultraviolet (UV) lithography. Grayscale optical exposure with a nonlinear compensation in quadratic form is applied to minimize the stitching loss of the transition zone between two adjacent subpatterns. Proximity effects in lithography process are compensated based on an exposure dose-map that is calculated under the approximation of scattered light pixel with a Gaussian distribution. The bending loss and propagation loss of the fabricated polymer waveguides are experimentally characterized to be around 0.1 dB/90°-bend and 0.238 dB/mm, respectively. Moreover, 1 × 2 multimode-interference power splitter, 1 × 2 Y-branch power splitter and microring resonator are demonstrated to show the feasibility of the lithography technology on rapid fabrication of waveguides. Such a UV lithography technology flexibly manipulates huge-number light pixels for all-digital grayscale and dynamic optical exposure and thus can enable the fabrication of novel optical waveguide-based devices and sensors, such as 2.5D waveguides for multimode crossing and polymer waveguide devices for biosensing.

Rapid trapping and tagging of microparticles in controlled flow by in situ digital projection lithography.

Real-time and fast trapping and tagging of microfeatures, such as microparticles and cells, are of great significance for biomedical research. In this work, we propose a novel in situ digital projection lithography technology that integrates real-time, in situ generation of digital masks for particle processing and fluid control into conventional DMD-based projection lithography. With the help of image recognition technology, we rapidly resolve the information of the microparticle profile or channel location, combining the selection of existing masks of different shapes, thus enabling in situ generation of user-customized micro-trap arrays and microfilter arrays for particle trapping and tagging. The success in trapping and filtering single particles, particle arrays, and cells has indicated the promising prospects of this novel technology for broad applications in microfluidics, single-cell analysis, and early-stage disease diagnostics.