Projection Lithography Research Articles

Micropattern of Core-shell Ag@MCS/PEGDA Nanoparticles Fabricated by Femtosecond Laser Maskless Optical Projection Lithography

Micropattern of Core-shell Ag@MCS/PEGDA Nanoparticles Fabricated by Femtosecond Laser Maskless Optical Projection Lithography

Parallel 3D projection lithography of massive tunable nanopillars for functional structures

Parallel 3D projection lithography of massive tunable nanopillars for functional structures

Fiber-integrated hybrid achromatic microlenses by combined femtosecond laser 3D printing

Compact achromats for visible wavelengths are crucial for miniaturized and lightweight full-color endoscopes. Emerging femtosecond laser 3D printing technology offers new possibilities for enhancing the optical performance of miniature imaging lenses on fibers. In this work, we combine refractive and diffractive elements with complementary dispersive properties to create thin, high-performance hybrid achromatic lenses within the visible spectrum, avoiding the use of different optical materials. Using a fiber-integrated hybrid achromatic lens array, clear images are captured across different wavelengths. The fabrication process is carried out using femtosecond laser direct writing (DLW) assisted by femtosecond projection lithography based on a digital micromirror device (DMD). Our work is expected to significantly contribute to the advancement of integrated and miniaturized biomedical imaging devices.

Empowering Advanced Photovoltaic Pioneers: A Bilateral Italy-USA Project

The sun bathes our planet with far more energy than humankind will possibly ever need (> 8,000 times the current demand). Yet, sustainable energy provision is among the most pressing challenges faced today. In order to unlock the vast potential of clean solar energy, we need disruptive technologies capable of efficiently harvesting sunlight, while being deployable at unprecedented scales. Available commercial photovoltaics (PV) can hardly cope sustainably with the sheer scale of this challenge. Silicon solar panels are the major commercial PV, they are based on a very Earth-abundant element, but their fabrication is extremely energy intensive. Conversely, thin film solar panels based on CdTe and Cu(In,Ga)Se2 require far less energy to produce, but some of their constituent elements are quite rare on the Earth’s crust. Hence, in both cases, the short term economic and ecologic sustainabilities are dubious. Recently, an advanced PV concept, called microconcentrator PV [1], has been conceived, which is free from raw materials availability constraints and is based on sunlight absorbers requiring low energy to grow. To demonstrate microconcentrator PV at laboratory scale, research groups have been using optical projection lithography (OPL), generating arrays of Cu(In,Ga)Se2 circles with tens of micrometer diameter. However, OPL cannot be scaled credibly to terawatt deployment. Industrial uptake of microconcentrator PV is only possible with a technique that ensures both high semiconductor quality, and high throughput at capital expenditure comparable or lower than currently available PVs. Inspired by the research of the US partner Gary Friedman [2], the Italian PI D. Colombara has patented a disrupting microfabrication technique [3] that could be scaled economically to deploy terawatts of microconcentrator PV. Our intent in this project is to leverage our complementary know-how to empower young PV pioneers and establish a lasting cooperation in this new promising field. Acknowledgements This work was supported in part by the Italian Ministry of Foreign Affairs and International Cooperation, grant number US23GR17. REMAP has received funding from the European Commission PathFinder Open programme under grant agreement No. 101046909. Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Innovation Council and SME Executive Agency (EISMEA). Neither the European Union nor the granting authority can be held responsible for them.

Intradermal Delivery of Cell Vaccine via Ice Microneedles for Cancer Treatment.

The living tumor cell vaccine (TCV) holds a promise for cancer immunotherapy. Microneedle arrays provide a tool to improve the immune response of vaccines by the intradermal administration in a painless manner. However, it remains challenges for microneedle arrays to deliver the living TCV intradermally. Here, an ice microneedle array delivered living TCVsis shown with sustained granulocyte-macrophage colony-stimulating factor (GM-CSF) secretion for cancer treatment. The ice microneedle array is composed of ice microneedles and a matching polymer holder, which are customized fabricated by a static optical projection lithography (SOPL) technique. The living TCV consisted ofirradiated melanoma cells transfected with nanoparticle-mediated GM-CSF plasmids. After the living TCV is readily loaded into the ice microneedle via a cryopreservation process, it couldbe efficiently delivered into the dermis by the microneedle device. Compared to the subcutaneous injection, intradermal administration led to the recruitment of more dendritic cells at the vaccination site and the increased infiltration of CD8+ T cells in the tumor. The ice microneedle array deliveres intradermal TCVssignificantly inhibited melanoma growth and effectively prevented melanoma recurrence without obvious side effects. This work demonstrates a promising TCVs for melanoma treatment, which will inspire the future of cancer immunotherapy.

Ultra-pixel precision correction method for maskless lithography projection distortion.

Distortion is a common issue in projection lens imaging, leading to image distortion and edge deformation, which significantly affects the quality of the projected pattern. Conventional methods for distortion correction are typically constrained by the precision of the projection pixel size. In this work, we propose an ultra-pixel precision correction method for projection distortion in projection lithography systems. By fitting the position error between the projected pattern and the calibration pattern, and combining the overlapping lithography method with the digital correction method to reduce quantization error, we have overcome the limitation of pixel size on correction precision, thereby achieving ultra-pixel precision calibration of the projected pattern. The resulting position error of the final exposed pattern can be reduced to approximately 1µm (with a projection pixel side length of 5.4µm). The zone plate fabricated using this method exhibits extremely high ring band position accuracy, and the diffraction test patterns are highly consistent with the simulation results. Our ultra-pixel precision correction method, based on a calibration substrate, is characterized by its simplicity of operation, cost-effectiveness, and wide adaptability. It plays a pivotal role in enhancing the quality of lithographic patterns within lithography systems.

Iterative control decoupling tuning for precision MIMO motion systems: A matrix update method

Control decoupling is the basic control step for precision MIMO (Multi-Input-Multi-Output) motion systems. After decoupling, the MIMO logical controlled plant can be diagonal dominant so that the control design for each DOF (Degree of Freedom) can be separately treated. However, due to the manufacturing tolerances and the assembling errors, the actual CoG (Center of Gravity) and actuator positions are inconsistent with the designed values. The nominal static control decoupling matrix is inaccurate, which significantly deteriorates the decoupling performance. To address the problem, this paper develops a matrix update based iterative control decoupling tuning method. Tuning with feedback control signals to achieve accurate tuning is its first distinct feature. By employing rigid-body model information to construct more accurate basis functions, fast tuning can also be achieved, especially for relatively low control bandwidth occasions. Differing from the feedforward compensation based iterative control decoupling tuning method, the matrix update method improves the dynamics of the logical controlled plant, does not increase the control complexity and is more robust to the inaccuracy of the model information. Experimental results on the short-stroke module of a precision motion stage which is the key subsystem of the lithographic projection lens testing system present significant control decoupling performance improvement (for example the peak value of the Rx-DOF servo error caused by the Z-DOF movement is reduced from 1.29 ×10−5 m to 3.19 ×10−6 m) after just two trials.

Formation of laser beams with a structured polarization distribution for the fabrication of spiral microreliefs in thin films of chalcogenide glasses

We propose a method of the formation of spiral-shaped microreliefs in thin films of chalcogenide glasses. The method is based on projection lithography using laser beams with a structured polarization distribution. To control the polarization of the initial laser beam, a spatial light modulator HOLOEYE LC 2012 is used. It is shown that changing the contrast of the mask images displayed on the modulator display affects the convexity/concavity of the formed profiles. This approach can be effectively used for the direct laser fabrication of more complex nano-/microelements, as well as their arrays.

Stiffness-Tunable Substrate Fabrication by DMD-Based Optical Projection Lithography for Cancer Cell Invasion Studies.

Cancer cell invasion is a critical cause of fatality in cancer patients. Physiologically relevant tumor models play a key role in revealing the mechanisms underlying the invasive behavior of cancer cells. However, most existing models only consider interactions between cells and extracellular matrix (ECM) components while neglecting the role of matrix stiffness in tumor invasion. Here, we propose an effective approach that can construct stiffness-tunable substrates using digital mirror device (DMD)-based optical projection lithography to explore the invasion behavior of cancer cells. The printability, mechanical properties, and cell viability of three-dimensional (3D) models can be tuned by the concentration of prepolymer and the exposure time. The invasion trajectories of gastric cancer cells in tumor models of different stiffness were automatically detected and tracked in real-time using a deep learning algorithm. The results show that tumor models of different mechanical stiffness can yield distinct regulatory effects. Moreover, owing to the biophysical characteristics of the 3D in vitro model, different cellular substructures of cancer cells were induced. The proposed tunable substrate construction method can be used to build various microstructures to achieve simulation of cancer invasion and antitumor screening, which has great potential in promoting personalized therapy.

Patterned microsphere-lens projection lithography using an electrohydrodynamic-jet-printing-assisted assembly

Microlens arrays have been widely used in the fields of micro-optics and micro- and nanofabrication. Traditional preparation methods utilize commercial photoresists and thermosetting materials, thereby restricting the optical properties of microlenses. In recent years, significant advancements have been achieved in near-field super-resolution imaging by utilizing microspheres and forming arrays of microsphere lenses via self-assembly. However, self-assembly approaches lack flexibility in terms of pattern selection. This study proposes a method that utilizes electrohydrodynamic jet (E-jet) printing to code ultraviolet (UV)-curable adhesives and assist in the assembly of patterned microsphere-lens arrays. Simulation results demonstrate that the UV-curable adhesive has little impact on the optical properties of the microsphere lens. Moreover, the microsphere lens exhibits a superior imaging resolution compared with traditional microlenses. A projection-lithography system is developed to achieve an accurate alignment between the focal plane of the microsphere lenses and the plane of the photoresist, facilitating the fabrication of patterned nanostructures. The lithographic nanostructures have a minimum feature size of 850 nm. This method enables the fabrication of arrays of microsphere lenses with arbitrary patterns and presents an inexpensive and simple strategy for fabricating micro- and nanostructure arrays with submicrometer features.

Design of Holographic Condenser Lens for Visible Light Lithography

Photolithography with visible light at λ = 405 nm utilizing the concept of nonlinear saturable absorption effect where the size of the spot is diminished to the nanometer scale as proposed by several researchers is an alluring proposition for cost-effective projection lithography. Costly conventional condenser lenses can be replaced by monochromatic aberration-free and cost-effective volume phase holographic lenses for visible light photolithography with enhanced resolution utilizing the concept of off-axis illumination. However, the diffraction efficiency of holographic lenses depends on the wavelength of illuminating light and the angle of illumination. Angular and spectral characteristics of volume phase holograms can be controlled by optimizing processing parameters. The results on the theoretical optimization of three important processing parameters, namely fringe spacing ( ∧ ), thickness of the film ( d ), and refractive index modulation ( Δ n ) in the light of coupled wave theory for recording holographic lenses of high diffraction efficiency at λ = 405 nm are presented. It is pointed out that a properly designed single holographic lens can be used for off-axis illumination of a photomask with a parallel beam of light, whereas a system of two identical holographic lenses cemented together has to be used to realize a condenser lens similar to a converging lens.

Stress, reflectance, and stability of Ru/Be multilayer coatings with Mo interlayers near the 11 nm wavelength.

The stress, reflectance, and temporal stability of Ru/Be multilayer mirrors, both with and without Mo interlayers, were studied. A Ru/Be MLM was found to have zero stress at a Ru layer thickness-to-period ratio of γ ∼ 0.4. By adding Mo interlayers to both interfaces, it is possible to achieve a record-high reflectance (R > 71%) at a wavelength close to 11 nm while maintaining near-zero stress levels. A Ru/Be MLM with Mo interlayers at both interfaces also demonstrates high temporal reflectance stability. Ru/Be MLMs may be of interest for the next-generation projection lithography at a wavelength of 11.2 nm.

Super-resolution Microscopy and Photo-lithography: How can one inspire the other

The principles of microscopy and lithography projection techniques are similar. To improve the resolution of the microscope or further reduce the image projection, both techniques face similar limitations, diffraction limits. The diffraction limit is a limitation of physical optics. In the development process of microscopes, to improve optical microscopy technology, researchers have proposed the idea of reducing the wavelength of light sources and increasing the numerical aperture based on the principle of diffraction limit generation. Modern scientists have proposed techniques to break through the diffraction limit and gradually increase the resolution of microscopes to further improve resolution. These breakthroughs also provide ideas for lithography technology, and researchers have invented techniques such as immersion lithography, multi-exposure, and two-photon direct writing. This article introduces the development process of super-resolution microscopy and lithography technology and analyzes the inspiration and influence of microscopy technology on lithography technology, that is, providing ideas for improving the accuracy of lithography technology.

Femtosecond Laser Maskless Optical Projection Lithography of Cartilage PCM Inspired 3D Protein Matrix to Chondrocyte Phenotype.

Hydrogels containing chondrocytes have exhibited excellent potential in regenerating hyaline cartilage. However, chondrocytes are vulnerable to dedifferentiation during in vitro culture, leading to fibrosis and mechanical degradation of newly formed cartilage. It is proposed to modulate cartilage formation via the developed chondrocyte pericellular matrix (PCM) -like scaffolds for the first time, in which the S, M, and L-sized scaffolds are fabricated by femtosecond laser maskless optical projection lithography (FL-MOPL) of bovine serum albumin-glyceryl methacrylate hydrogel. Chondrocytes on the M PCM-like scaffold can maintain round morphology and synthesize extracellular matrix (ECM) to induce regeneration of hyaline cartilage microtissues by geometrical restriction. A series of M PCM-like scaffolds is fabricated with different stiffness and those with a high Young's modulus are more effective in maintaining the chondrocyte phenotype. The proposed PCM-like scaffolds are effective in modulating cartilage formation influenced by pore size, depth, and stiffness, which will pave the way for a better understanding of the geometric cues of mechanotransduction interactions in regulating cell fate and open up new avenues for tissue engineering.

Structured polarized laser beams for controlled spiral-shaped mass transfer in azopolymer thin films

We present an approach for the realization of controlled spiral-shaped mass transfer in azopolymer thin films and the fabrication of spiral microreliefs. For such laser processing, we propose to use light fields with structured polarization distributions generated by a transmissive spatial light modulator. The projection lithography approach is utilized, transferring the pattern directly to the surface of azopolymer thin films. The shaped polarization distributions with different dependencies of the polarization vector orientation on the azimuthal angle allow us to drive surface waves on the sample along a spiral trajectory. Additionally, the ability to control the concavity of the formed microreliefs is demonstrated. This approach can be effectively modified for the direct laser fabrication of more complex nano-/micro-elements as well as their arrays.

Flexible nanoimprint lithography enables high-throughput manufacturing of bioinspired microstructures on warped substrates for efficient III-nitride optoelectronic devices

III-nitride materials are of great importance in the development of modern optoelectronics, but they have been limited over years by low light utilization rate and high dislocation densities in heteroepitaxial films grown on foreign substrate with limited refractive index contrast and large lattice mismatches. Here, we demonstrate a paradigm of high-throughput manufacturing bioinspired microstructures on warped substrates by flexible nanoimprint lithography for promoting the light extraction capability. We design a flexible nanoimprinting mold of copolymer and a two-step etching process that enable high-efficiency fabrication of nanoimprinted compound-eye-like Al2O3 microstructure (NCAM) and nanoimprinted compound-eye-like SiO2 microstructure (NCSM) template, achieving a 6.4-fold increase in throughput and 25% savings in economic costs over stepper projection lithography. Compared to NCAM template, we find that the NCSM template can not only improve the light extraction capability, but also modulate the morphology of AlN nucleation layer and reduce the formation of misoriented GaN grains on the inclined sidewall of microstructures, which suppresses the dislocations generated during coalescence, resulting in 40% reduction in dislocation density. This study provides a low-cost, high-quality, and high-throughput solution for manufacturing microstructures on warped surfaces of III-nitride optoelectronic devices.

Multipatterned Chondrocytes' Scaffolds by FL-MOPL with a BSA-GMA Hydrogel to Regulate Chondrocytes' Morphology.

Repairing articular cartilage damage is challenging due to its low regenerative capacity. In vitro, cartilage regeneration is a potential strategy for the functional reconstruction of cartilage defects. A hydrogel is an advanced material for mimicking the extracellular matrix (ECM) due to its hydrophilicity and biocompatibility, which is known as an ideal scaffold for cartilage regeneration. However, chondrocyte culture in vitro tends to dedifferentiate, leading to fibrosis and reduced mechanical properties of the newly formed cartilage tissue. Therefore, it is necessary to understand the mechanism of modulating the chondrocytes' morphology. In this study, we synthesize photo-cross-linkable bovine serum albumin-glycidyl methacrylate (BSA-GMA) with 65% methacrylation. The scaffolds are found to be suitable for chondrocyte growth, which are fabricated by homemade femtosecond laser maskless optical projection lithography (FL-MOPL). The large-area chondrocyte scaffolds have holes with interior angles of triangle (T), quadrilateral (Q), pentagon (P), hexagonal (H), and round (R). The FL-MOPL polymerization mechanism, swelling, degradation, and biocompatibility of the BSA-GMA hydrogel have been investigated. Furthermore, cytoskeleton and nucleus staining reveals that the R-scaffold with larger interior angle is more effective in maintaining chondrocyte morphology and preventing dedifferentiation. The scaffold's ability to maintain the chondrocytes' morphology improves as its shape matches that of the chondrocytes. These results suggest that the BSA-GMA scaffold is a suitable candidate for preventing chondrocyte differentiation and supporting cartilage tissue repair and regeneration. The proposed method for chondrocyte in vitro culture by developing biocompatible materials and flexible fabrication techniques would broaden the potential application of chondrocyte transplants as a viable treatment for cartilage-related diseases.

Distortion measurement of a lithography projection lens based on multichannel grating lateral shearing interferometry.

The optical distortion of the lithographic projection lens can reduce imaging quality and cause overlay errors in lithography, thus preventing the miniaturization of printed patterns. In this paper, we propose a technique to measure the optical distortion of a lithographic projection lens by sensing the wavefront aberrations of the lens. A multichannel dual-grating lateral shearing interferometer is used to measure the wavefront aberrations at several field points in the pupil plane simultaneously. Then, the distortion at these field points is derived according to the proportional relationship between the Z 2 and Z 3 Zernike terms (the tilt terms) and the image position shifts. Without the need for additional devices, our approach can simultaneously retrieve both the wavefront aberrations and the image distortion information. Consequently, it improves not only measurement speed and accuracy but also enables accounting for displacement stage positioning error. Experiments were conducted on a lithographic projection lens with a numerical aperture of 0.57 to verify the feasibility of the proposed method.

Distortions of parabolic mirror optics for stereophonic lithography and prospects of compensations

The distortions of parabolic mirror optics used for stereophonic projection lithography were investigated. It has already been demonstrated that resist patterns are replicable on gently curved surfaces using mirror optics composed of faced paraboloids of revolution. However, it was found that replicated resist patterns were somewhat distorted from the original patterns. The distortions were caused by characteristics of projection optics. For this reason, the distortions were first calculated by tracing light rays. The calculation procedures are explained in detail. The calculated distortions almost coincide with the ones obtained by experiments. Next, the influences of distortions on the distributions of image intensity and replicated pattern widths were investigated. The maximum distortions reached 29% of the original size at the right-side corners of a 12 mm square, and the light intensity was lowered by 30%. For this reason, printed 200 μm pattern widths reached more than 500 μm on the right side. This was considered to be unfavorable for applying the method universally in various uses. For this reason, methods for compensating or modifying the optics distortions were investigated, and light intensity distributions were discussed.

Linearized EUV mask optimization based on the adjoint method

Mask optimization, a compensation method for the thick mask effect and the optical proximity effect in projection lithography, is essential for advanced EUV-enabled production nodes. However, owing to high computation costs and the absence of gradient calculations, it is challenging to optimize EUV masks under rigorous consideration of the thick mask effect. In this work, a linearized EUV mask optimization method based on the adjoint method is proposed to provide fast and effective optimizations. The adjoint method is introduced to calculate the gradient of the EUV mask model. Additionally, a linearized gradient is proposed to quickly compensate for wafer pattern distortion caused by the prominent thick mask effect. Two examples of the EUV mask optimization implemented with a two-step strategy were provided, from which it was observed that the linearized gradient can improve the efficiency by about 40% in the coarse optimization step. The proposed method is promising for accurate full-chip EUV mask optimization.