Maskless Lithography System Research Articles

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.

Poisson Effect‐Assisted Replication Lithography for Rapid Fabrication of Three‐Dimensional Microstructures

Demands for micro‐ and nano‐fabrication techniques have been increasing over recent decades due to their foundational importance in fields such as electronics, sensors, displays, biotechnologies, and energy technologies. Still, the rapid and efficient fabrication of complex 3D microstructures has long been a challenge due to the inherent limitations of conventional imprint lithography and the slow fabrication speed of maskless lithography systems using femtosecond lasers. This study introduces a novel lithographic replication method for the rapid replication of intricate 3D microstructures with closed‐loops by leveraging the Poisson effect‐driven lateral deformation of soft molds. Specifically, the suggested technique employs an elastomeric soft mold, engraved with negative cavity parts of the target structure separated by intentional gaps. Lateral deformation of the material allows the separated cavities to assemble for replication of target microstructure and defectless release from the soft mold. In addition to the experimental demonstrations of the proposed method using well‐known materials like polydimethysliloxane (PDMS) for the soft mold and UV‐curable polyurethane acrylate (PUA) for replication, essential considerations such as material selection and master mold design are discussed. The presented method not only broadens the capabilities of imprint lithographic techniques but also holds promise for the large scale, continuous fabrication of complex 3D microstructures.

TPP-Based Microfluidic Chip Design and Fabrication Method for Optimized Nerve Cells Directed Growth

Microfluidic chips offer high customizability and excellent biocompatibility, holding important promise for the precise control of biological growth at the microscale. However, the microfluidic chips employed in the studies of regulating cell growth are typically fabricated through 2D photolithography. This approach partially restricts the diversity of cell growth platform designs and manufacturing efficiency. This paper presents a method for designing and manufacturing neural cell culture microfluidic chips (NCMC) using two-photon polymerization (TPP), where the discrete and directional cell growth is optimized through studying the associated geometric parameters of on-chip microchannels. This study involves simulations and discussions regarding the effects of different hatching distances on the mold surface topography and printing time in the Describe print preview module, which determines the appropriate printing accuracy corresponding to the desired mold structure. With the assistance of the 3D maskless lithography system, micron-level rapid printing of target molds with different dimensions were achieved. For NCMC with different geometric parameters, COMSOL software was used to simulate the local flow velocity and shear stress characteristics within the microchannels. SH-SY5Y cells were selected for directional differentiation experiments on NCMC with different geometric parameters. The results demonstrate that the TPP-based manufacturing method efficiently constructs neural microfluidic chips with high precision, optimizing the discrete and directional cell growth. We anticipate that our method for designing and manufacturing NCMC will hold great promise in construction and application of microscale 3D drug models.

Agile-X: A Structured-ASIC Created With a Mask-Less Lithography System Enabling Low-Cost and Agile Chip Fabrication

Agile-X: A Structured-ASIC Created With a Mask-Less Lithography System Enabling Low-Cost and Agile Chip Fabrication

Maskless direct write lithography for 3D wafer-level-system-integration

This publication presents lithography results for 3D wafer-level system integration applications using a reticle free maskless lithography system VPG+ 400 from Heidelberg Instruments. The focus is on high density Cu redistribution layer (RDL) formation with <2µm L/S used in polymer RDL stacks, overlay accuracy determination better than ±150nm and hybrid bond interconnect formation for 2µm interconnects, all processed on 300mm wafer size substrates.

Maskless lithography for large area patterning of three-dimensional microstructures with application on a light guiding plate.

This paper presents a maskless lithography system that can perform three-dimensional (3D) ultraviolet (UV) patterning on a photoresist (PR) layer. After PR developing processes, patterned 3D PR microstructures over a large area are obtained. This maskless lithography system utilizes an UV light source, a digital micromirror device (DMD), and an image projection lens to project a digital UV image on the PR layer. The projected UV image is then mechanically scanned over the PR layer. An UV patterning scheme based on the idea of obliquely scanning and step strobe lighting (OS3L) is developed to precisely control the spatial distribution of projected UV dose, such that desired 3D PR microstructures can be obtained after PR development. Two types of concave microstructures with truncated conical and nuzzle-shaped cross-sectional profiles are experimentally obtained over a patterning area of 160 ×115 mm2. These patterned microstructures are then used for replicating nickel molds and for mass-production of light-guiding plates used in back-lighting and display industry. Potential improvements and advancements of the proposed 3D maskless lithography technique for future applications will be addressed.

SmartPrint Single-Mode Flexible Polymer Optical Interconnect for High Density Integrated Photonics

This paper reports on the demonstration of a single-mode flexible polymer optical interconnect for efficiently and conveniently connecting integrated photonics chips to one another (chip-to-chip) and to optical printed circuit boards (chip-to-board). The interconnect uses a low-loss partially fluorinated refractive index contrast (RIC) polymer, referred to as poly(F-SBOC), that provides for direct patterning of the desired refractive index profiles into a slab waveguide consisting of poly(F-SBOC) and a flexible fluoropolymer film (Tefzel). Using a maskless lithography system, interconnects consisting of s-bends and tapers can be printed in situ into the poly(F-SBOC) material with no need for mechanical alignment. We demonstrate the efficacy of this approach by connecting two separate ion-exchange (IOX) glass waveguide chips, achieving fiber-to-fiber total insertion losses below 6dB in some cases, through the use of grayscale tapers that are written directly into the poly(F-SBOC) material.

Method for improving the speed and pattern quality of a DMD maskless lithography system using a pulse exposure method.

Maskless lithography based on a digital micromirror device (DMD) has the advantages of high process flexibility and a low production cost. However, due to the trade-off relationship between the pixel size and exposure area, it is challenging to achieve high resolutions and high patterning speeds at the same time, which hinders the wider application of this technology in micro- and nano-fabrication processes. In addition, micromirrors in DMDs create pixelated edges that limit the pattern quality. In this paper, we propose a novel DMD maskless lithography method to improve the pattern quality during high-speed continuous patterning by means of pulse exposure and oblique scanning processes. A unique criterion, the pixel occupancy, was devised to determine the parameters related to the pulse exposure and oblique scanning optimally. We also studied how the duty cycle of the pulse exposure affects the pattern quality. As a result, we were able to increase the scanning speed up to the speed limit considering the damage threshold of the DMD and improve the pattern quality by resolving the pixelation problem. We anticipate that this method can be used in various microfabrication fields with short product life cycles or in those that require custom designs, such as the manufacturing of PCBs, MEMS devices, and micro-optics devices, among others.

Maskless lithography for versatile and low cost fabrication of polymer based micro optical structures

For applications in optical communication, sensing or information projection in automotive lighting, polymer based optical devices are of keen interest. Optical structures such as waveguides and gratings are basic blocks for these devices. We report on a simple, versatile, and yet low-cost fabrication method suited for both binary and multilevel diffractive microstructures as well as multimode optical waveguides in polymers. The fabrication of the diffractive structures, i.e. gratings, with two and multiple levels, is achieved by using a maskless optical lithography system employing a spatial light modulator. With the same system, waveguide cladding structures are realized by stitching of multiple single exposure patterns. For replication of these structures on polymer, e.g. polymethyl methacrylate (PMMA), a lab-made hot embossing machine is used. We then employ UV curable material and doctor blading to realize the waveguide cores. The created diffractive and waveguide structures are characterized in terms of diffraction efficiency and optical propagation loss, respectively, showing good optical quality and performance. With our fabrication system we have demonstrated a diffraction efficiency of 71% for multilevel grating structure and a propagation loss for stitched waveguides of 2.07 dB/cm at a wavelength of 638 nm. These basic elements will be employed to realize entire optical measurement systems for applications in sensing and integrated photonics in the next step.

Multi-layer lithography using focal plane changing for SU-8 microstructures

In this paper, we report on a type of SU-8 microstructure with vertical sidewalls used for polydimethydiloxane (PDMS) microchannels. Multi-layer lithography using focal plane changing approach is proposed to expose the SU-8 photoresist based on a digital micromirror device (DMD) maskless lithography system. We used a light-emitting diode source with a wavelength of 405 nm. The thickness of the SU-8 is divided into multi-layers according to the depth of focus. Each layer corresponds to a depth of focus, and then, a virtual mask is designed for the layer. Finally, each layer is exposed to changes in the focal plane. The results indicate that the actual profile of the SU-8 mold shows good agreement with the design profile without any T-profiles. Additionally, there is better linewidth in the proposed method compared with multi-exposure by a single fixed focal plane. The PDMS microchannels result also demonstrate the stability of the SU-8 mold.

Research on Maskless Lithography System Based on Digital Oblique Scanning Strategy

Research on Maskless Lithography System Based on Digital Oblique Scanning Strategy

Modular and Customized Fabrication of 3D Functional Microgels for Bottom‐Up Tissue Engineering and Drug Screening

AbstractCustomized generation of 3D functional building blocks is crucial for bottom‐up tissue engineering. Currently, high throughput production, high survival rates, and well‐controlled shapes are considered as three major challenges in fabricating microgels. Here, an optofluidic maskless lithography system that combines digital micromirror device based 3D printing and microfluidic technologies for fabricating 3D functional microgels, is presented. With this system, 3D microgels can be custom designed online and manufactured modularly in a microfluidic device. The fabrication process is based on shadowed light, highly flexible, and requires no physical masks. Furthermore, cells in microgels exhibit features that are more similar to the complex in vivo conditions, including morphology, proliferation, and drug resistance.

Three Dimensional Maskless Ultraviolet Exposure System Based on Digital Light Processing

This paper reports the development of a three dimension maskless photolithography system with an oblique scanning method based on digital light processing technology. The system consists of a UV light source, a digital micromirror device (DMD), a microlens/pinhole array, two optical projection lenses, and a three-axis (xyz) servo-controlled stage. The optical system can form a rectangular array of UV spots with a diameter of few μm directly on the surface of a sample sitting on the stage. A photoresist (PR) layer is coated on the sample surface. Using an oblique scanning approach, the whole area of PR layer can be exposed by this UV exposure system in a maskless manner. Since the energy intensity of each UV spot can be independently modulated by a corresponding group of micromirrors in the DMD, and a three-dimensional (3D) UV dosage distribution can be achieved through computer programming on the DMD and the xyz stage. After developing processes, 3D PR microstructures with arbitrary patterns and/or surface profiles can be readily formed by this maskless lithography system. Experimental results will be addressed as well as potential applications for 2D and 3D microfabrication.

A high-speed exposure method for digital micromirror device based scanning maskless lithography system

During the process of scanning maskless lithography, exposure speed determines the efficiency and productivity of lithography fabrication. In this paper, a novel Digital Micromirror Device(DMD) based high-speed exposure method is proposed to optimize the exposure process and improve speed of scanning maskless lithography system. At first, structure and working principle of the DMD based maskless exposure system is presented. Then, fundamental principle of the proposed method is proposed. Exposure process of the proposed method and each module in the process including in scan stride pretreatment module, scan stride data storage module, high-speed real-time exposure image processing module and micromirror arrays control module are designed. Finally, the proposed method is implemented in the exposure experiment with TI DMD based scanning maskless lithography system and the results demonstrated the effectiveness of the proposed method.

Maskless lithography based on digital micromirror device (DMD) and double sided microlens and spatial filter array

A new type of maskless lithography system based on digital mirror device (DMD) is proposed, constructed, and experimentally demonstrated. It includes a pin-hole array sandwiched by two microlens arrays on each side, known as double-sided microlens/spatial-filter array (D-MSFA), and aligned with a DMD. Ultraviolet (UV) light reflected by DMD is first collected by the first microlens array, filtered through the pin-hole array, and then re-focused by the second microlens array into a UV spot array. Along with an obliquely scanning method, this D-MSFA/DMD-based maskless lithography system can perform not only 2D but also 3D UV patterning. Experimental testing successfully generates complicated patterns with a minimum line-width of 3.36 μm. Direct 3D patterning and 3D microfabrication are also experimentally demonstrated on a photoresist layer. Excellent profile accuracy and surface structure qualities are observed with great potentials for future 2D and 3D microfabrication in a maskless manner.

Fabrication of high fill-factor aspheric microlens array by dose-modulated lithography and low temperature thermal reflow

A cost-effective fabrication method for high quality and high fill-factor aspheric microlens arrays (MLAs) is developed. In this method, the complex shape of aspheric microlens is pre-modeled via dose modulation in a digital micromirror device (DMD) based maskless projection lithography system. Digital masks for several bottom layers are replaced from circle to hexagon for the purpose of enhancing the fill-factor of MLAs, then a low temperature thermal reflow process is conducted, after which the average surface roughness of microlens is improved to ~ 0.427 nm while the pre-modeled profile keeps unchanged. Experimental results show that the fabricated aspheric MLAs have almost 100% fill-factor, high shape accuracy and high surface quality. The presented method may provide a promising approach for rapidly fabricating high quality and high fill-factor aspheric microlens in a simple and low-cost way.

An integrated micro-millifluidic processing system.

The development of integrated microfluidic systems/platforms concerns many fields. Current remarkable integrated systems based on stacking multi-layer polydimethylsiloxane (PDMS) require complicated fabrication and operation and still remain challenging. We propose a novel micro-millifluidic processing system (MPS) comprising three core modules: a motherboard, a control panel and microfluidic chips. Fluids are handled in sub-millichannels in a motherboard and functional operations occur in microchannels in microfluidic chips. A motherboard with versatile functional units for fluid handling was monolithically fabricated via multimaterial 3D printing, which avoids multi-layer structures, and the major disadvantage of current 3D printing, i.e. low resolution, has been overcome by integrating novel microfluidic chips based on our developed maskless lithography platform. Both numerical and experimental studies were conducted to validate our system. Potential applications such as droplet generation and distribution, microfluidic mixing and simple bacterial resistance tests have been demonstrated via our MPS.

Maskless Lithography Based on Digital Micro-Mirror Device (DMD) with Double Sided Microlens and Spatial Filter Array

A ultra-violet (UV) maskless lithography system is developed for arbitrary UV patterning. The system consists of an UV illumination system, a digital micro-mirror device (DMD), a projection system, and a double-sided microlens and spatial filter array (D-MSFA). The DMD acts as a virtual mask for generating arbitrary patterns by individually turning on or off of each micro-mirror. The projection lens projects the image of DMD onto the D-MSFA, which consists subsquently the fisrt microlens array (MLA1), the pinholes array, and the second microlens array (MLA2). The MLA1 focus the light from DMD to its corresponding pinhole, and the MLA2 projects the image of pinhole array onto a substrate to form a point array of UV light. The profiles of microlenses are designed optimized to chieve smallest focused spot size. A method has been developed to fabricate the D-MSFA and to ensure high microlens profile accuracy and excellent alignment between microlens arrays and pinhole array. The obatined UV spot sizze is 10 μm measured at FHMW level, and the system can generate arbitrary patterns with a minimum linewidth of 5.2 μm.

Simulation of the effect of incline incident angle in DMD Maskless Lithography

The aim of this study is to provide a simulation method for investigation of the intensity fluctuation caused by the inclined incident angle in DMD (digital micromirror device) maskless lithography. The simulation consists of eight main processes involving the simplification of the DMD aperture function and light propagation utilizing the non-parallel angular spectrum method. These processes provide a possibility of co-simulation in the spatial frequency domain, which combines the microlens array and DMD in the maskless lithography system. The simulation provided the spot shape and illumination distribution. These two parameters are crucial in determining the exposure dose in the existing maskless lithography system.

A study of fabrication micro bump for TSP testing using maskless lithography system.

A study of fabrication micro bump for TSP testing using maskless lithography system.