UV Lithography Process Research Articles

Foundry-fabricated grating coupler demultiplexer inverse-designed via fast integral methods

Silicon photonics is an emerging technology which, enabling nanoscale manipulation of light on chips, impacts areas as diverse as communications, computing, and sensing. Wavelength division multiplexing is commonly used to maximize throughput over a single optical channel by modulating multiple data streams on different wavelengths concurrently. Traditionally, wavelength (de)multiplexers are implemented as monolithic devices, separate from the grating coupler, used to couple light into the chip. This paper describes the design and measurement of a grating coupler demultiplexer—a single device which combines both light coupling and demultiplexing capabilities. The device was designed by means of a custom inverse design algorithm which leverages boundary integral Maxwell solvers of extremely rapid convergence as the mesh is refined. To the best of our knowledge, the fabricated device enjoys the lowest insertion loss reported for grating demultiplexers, small size, high splitting ratio, and low coupling-efficiency imbalance between ports, while meeting the fabricability constraints of a standard UV lithography process.

Three-Dimensional Micropatterning Deters Early Bacterial Adherence and Can Eliminate Colonization.

Developing strategies to prevent bacterial infections that do not rely on the use of drugs is regarded globally as an important means to stem the tide of antimicrobial resistance, as argued by the World Health Organization (WHO) (Mendelson, M.; Matsoso, M. P. The World Health Organization Global Action Plan for Antimicrobial Resistance. S. Afr. Med. J. 2015, 105 (5), 325-325. DOI: 10.7196/SAMJ.9644). Given that many antimicrobial-resistant infections are caused by the bacterial colonization of indwelling medical devices such as catheters and ventilators, the use of microengineered surfaces to prevent the initial attachment of microbes to these devices is a promising solution. In this work, it is demonstrated that 3D engineered surfaces can inhibit the initial phases of surface colonization for Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa, representing the three most common catheter-associated urinary tract bacterial infections, identified by the WHO as urgent threats. A variety of designs including 11 different topographies and configurations that exhibited random distributions, sharp protrusions, and/or curvilinear shapes with dimensions ranging between 500 nm and 2 μm were tested to better understand the initial stages of surface colonization and how to optimize the design of fabricated surfaces for improved inhibition. These topographies were fabricated in two configurations to obtain either a standard 2D cross section or a 3D engineered topography using a novel UV lithography process enabling cost-efficient high-throughput manufacturing. Evaluating both the number of adhered bacteria and microcolonies formed by all three bacterial pathogens on the different surfaces provides insight into the initial colonization phase of bacterial growth on the various surfaces. The results demonstrate that both initial attachment and subsequent colonization can be significantly reduced on concrete 3D engineered patterns when compared to flat substrates and standard 2D micropatterns. Thus, this technology has great potential to reduce the colonization of bacteria on surfaces in clinical settings without the need for chemical treatments that might enhance antimicrobial resistance.

High-Throughput Synthesis of Liposome Using an Injection-Molded Plastic Micro-Fluidic Device.

For mass production of liposomes, we designed a plastic micro-channel device on the basis of 5 μm of micro-nozzle array forming T-junction with 100 μm depth of micro-channel. A micro-channel unit for synthesizing liposomes consisted of two micro-nozzle arrays for mixing two solutions as well as delivery and recovery channels for supplying solutions and collecting liposome suspension. The number of micro-nozzles was approximately 2400 for a micro-channel unit, and seven units were applied independently on a micro-channel plate. The plastic micro-channel plate was injection-molded for mass production using a micro-channel stamper previously fabricated by UV lithography and nickel electroforming process. A plastic cover plate with seven pairs of inlet and outlet ports was machined by mechanical milling and drilling and was assembled with a micro-channel plate using a holder to form a liposome synthesizing device. Flow and mixing of solutions in the micro-channels were tested using colored water to check the micro-fluidic characteristics of the device. Finally, a L-α-phosphatidylcholine (SOY PC) liposome was synthesized using EtOH solution of SOY PC (95%) and saline (0.85% NaOH solution) to find that the liposomes were around 230 and 260 nm in diameter, depending on the flow rate of the lipid solution.

Focus on lasers, imaging, and microscopy

Focus on lasers, imaging, and microscopy

Synthesis Based on a Preceramic Polymer and Alumina Nanoparticles via UV Lithography for High Temperature Applications.

Because of the increased demand for preceramic polymers in high-tech applications, there has been growing interest in the synthesis of preceramic polymers, including polysiloxanes and alumina. These polymers are preferred because of their low thermal expansion, conformability to surfaces over large areas, and flexibility. The primary objective was to evaluate the aspects of polymer-derived ceramic routs, focusing on the UV lithography process of preceramic polymers and the pyrolyzing properties of the final ceramics. We found that the p(DMS-co-AMS) copolymer was effective in scattering the hydrophilic Al2O3 nanoparticles into the exceedingly hydrophobic solvent. The physico-chemical behavior of characterized copolymers was explored during their pyrolytic transformation into amorphous silicon-based ceramics. The results indicate that an increase of the pyrolysis temperature degraded the Si–O network through the carbothermic reaction of silicon. We also found a rapid elimination of copolymer pores and densification when the temperature increased (1100 to 1200 °C). At different but specific temperature ranges, there are different distinct rearrangement reactions in the conversion of polymer to ceramic; reductions of the melting point (Tm) of the total heat of melting (ΔHm) of the pyrolysis process resulted in the crystallization of ceramic materials; hence, lithography based on pyrolysis properties of preceramic polymers is a critical method in the conversation of polymers.

Micro-Faraday cup array structures fabrication in silicon using deep reactive ion etching

Micro-Faraday cup array (MFCA) detectors are used for the detection and analysis of incident ion particles with greater stability and precision. New and simple micro FCA structures have been designed and fabricated considering the application in mass spectrometry and laser plasma techniques. MFCA structures were fabricated using UV lithography followed by deep reactive ion etching (DRIE). The UV lithography process was utilised for fabrication of micro-Faraday cup array structure in photoresist (AZ4903) deposited on n-type silicon substrate. After that DRIE process was used for creating array pattern in silicon. Ultimately 1 × 16 arrays having 25 μm widths with 125 μm spacing were fabricated. Maximum depth achieved with DRIE process was 16 μm. Exposure time of lithography was found to be reduced by 110% using UV-LED source for these structures. Effects of etch cycle time on cup depth and sidewall angle have also been discussed.

Monolithic chip-scale structural color filters fabricated with simple UV lithography.

We demonstrate an improved approach to integrate various color filters on a chip-scale by using stepwise metal-insulator-metal FP cavities. The cavity is composed of a thick silver mirror, an SU8 gap layer of controlled thickness, and a thin nickel layer. Reflective colors from red to blue can be generated from these filters through a simple UV lithography process. The filters were also fabricated on a flexible substrate which could be incorporated into wearable devices. This method can realize large-scale filter arrays with simple processing and may facilitate the use of structural color filters in displays and sensing.

Deep UV Lithography Process in Generic InP Integration for Arrayed Waveguide Gratings

Low-excess-loss arrayed waveguide gratings are enabled by unique application of deep UV lithography in InP integrated photonics through reduced feature sizes and, more specifically, well-resolved inter-waveguide gap dimensions. Submicrometer wafer-flatness is shown to be required to achieve the critical dimension uniformity better than 10 nm on 3-in substrates. Arrayed waveguide grating devices were fabricated and the effect of inter-waveguide gap scaling on the excess losses was measured and compared to simulations. Excess losses down to 0.15 dB were demonstrated to be lower than predicted with the 2-D simulations. The tapering of the etch depth inside the gaps due to the lag effect of the etch process may explain the improvements.

Channel resolution enhancement through scalability of nano/micro-scale thickness and width of SU-8 polymer based optical channels using UV lithography

This paper reports on an approach for fabrication of micro-channels with nanometer thickness achieved by optimization of UV lithography processes. Rectangular micro-channels with a staple edge are fabricated over the surface of a silicon wafer substrate in which a sub-micron layer of diluted SU-8 thin film has been coated. The optimization of the process parameters includes the duration of a two-step pre- and post-baking process, UV exposure dosage, and finally chemical developing time with constant agitation. This produces recipe produces micro-channels with high contrast edges and thickness below 100 nm. The dimensions achieved using this approach has potential applications in sub-micron optical waveguides and nanoelectromechanical (NEMS) devices.

(110)シリコンの高温下のすべりと破壊に及ぼす引張軸方位の影響

Tensile testing of single crystal silicon microstructures was performed along tensile axes of <110> and <111> at 500 °C in a vacuum to investigate crystallographic effects on their slip occurrences and fracture behaviors at the high temperature. Specimens with parallel portions 120 μm long, 2 μm wide, and 5 μm thick, were designed along the two tensile axes on (110) wafers, and were fabricated from SOI (silicon-on-insulator) wafer using UV lithography and deep RIE (reactive ion etching) processes. The specimens were subjected to tensile testing at 500 °C in a vacuum, which exhibited linear stress increments until their fractures at 3.2 GPa on <110> and at 4.0 GPa on <111>. Contrary to the obtained linear nominal stress increments, fractured specimens possessed surface steps due to slip along {111}. The fracture surfaces exhibited large planes oriented mostly along {111} indicating cleavage fracture behaviors. Stress concentration around the surface step was analyzed employing finite element method to discuss effect on the surface step on decrease in nominal tensile strength at a high temperature, and criteria for slip were discussed based on maximum shear stress along the slip system.

Transferable Integrated Optical SU8 Devices: From Micronic Waveguides to 1D-Nanostructures

We report on optical components for integrated optics applications at the micro- and nanoscale. Versatile shapes and dimensions are achievable due to the liquid phase processability of SU8 resist. On the one hand, by adjusting the UV-lithography process, waveguiding structures are patterned and released from their original substrate. They can be replaced on any other substrate and also immerged in liquid wherein they still show off efficient light confinement. On the other hand, filled and hollow 1D-nanostructures are achievable by the wetting template method. By exploiting the large range of available SU8 viscosities, nanowires of diameter ranging between 50 nm and 240 nm, as well as nanotubes of controllable wall thickness are presented. Optical injection, propagation, and coupling in such nanostructures are relevant for highly integrated devices.

Highly Uniform Trilayer Molybdenum Disulfide for Wafer‐Scale Device Fabrication

Molybdenum disulfide (MoS2) is a layered semiconducting material with a tunable bandgap that is promising for the next generation nanoelectronics as a substitute for graphene or silicon. Despite recent progress, the synthesis of high‐quality and highly uniform MoS2 on a large scale is still a challenge. In this work, a temperature‐dependent synthesis study of large‐area MoS2 by direct sulfurization of evaporated Mo thin films on SiO2 is presented. A variety of physical characterization techniques is employed to investigate the structural quality of the material. The film quality is shown to be similar to geological MoS2, if synthesized at sufficiently high temperatures (1050 °C). In addition, a highly uniform growth of trilayer MoS2 with an unprecedented uniformity of ±0.07 nm over a large area (&gt; 10 cm2) is achieved. These films are used to fabricate field‐effect transistors following a straightforward wafer‐scale UV lithography process. The intrinsic field‐effect mobility is estimated to be about cm2 V–1 s–1 and compared to previous studies. These results represent a significant step towards application of MoS2 in nanoelectronics and sensing.

Fabrication of multi-scale structures with multiple X-ray masks and synchrotron hard X-ray irradiations

Synchrotron hard X-ray irradiation can be utilized in lithography processes to manufacture precise structures. Due to the difficulty of precise X-ray mask fabrication in hard X-ray lithography, this X-ray process has been used mainly to fabricate precise microstructures. In this study, a technology is proposed for fabricating novel multi-scale patterns that include submicron-scale structures using hard X-rays. The required X-ray masks for submicron-sized patterning are fabricated by a simple UV lithography process and sidewall metal deposition. Above all, thanks to the high penetration capability of hard X-rays with sub-nanometer wavelengths, it is possible to employ multiple masks to fabricate a variety of patterns. By combining each sub-micron X-ray mask with typical micro-sized X-ray masks, a unique X-ray lithography is performed, and various multi-scale structures are fabricated. The usefulness of the proposed technology is demonstrated by the realization of these structures.

Fabrication and application of a stacked carbon electrode set including a suspended mesh made of nanowires and a substrate-bound planar electrode toward for an electrochemical/biosensor platform

Herein, we present a novel electrochemical sensing platform that consists of a set of suspended carbon nanowire-based mesh electrode with deliberately controlled shapes (hexagonal or diamond), and a substrate-bound planar carbon electrode. These electrodes overlapped one another with a pre-defined gap which was precisely controlled by using a polymerization-stop layer. By recycling the redox reactions between the electrodes with a 2.1-μm-gap, the redox current of Fe(CN)64−/Fe(CN)63− could be amplified approximately 37 times. This high current amplifying capability enabled dopamine detection down to 5μM using cycling voltammetry. The complex morphology of the stacked carbon structures was obtained by simply using multiple UV-lithography processes and a single pyrolysis process that allowed pre-defined polymer structures to shrink into sub-micrometer-scale carbon structures. The suspended carbon mesh structures confined the mass-transfer near the electrode overlap region, and hence, the electrode set operated as a “sandwich” electrode enclosed within a microchannel. This effect was studied by simulating the mass transfer of the redox species, and confirmed by electrochemical measurements.

Manufacture of μ-PIM gear mold by electroforming of Fe–Ni and Fe–Ni–W alloys

The micro gear mold for powder injection molding was made by electroforming process of Fe–Ni and Fe–Ni–W alloys using UV-lithography process. Kinetics and activation energies in electroplating of both alloys were investigated to determine the best process conditions. Fe content within electrodeposited Fe–Ni alloys increased with the increase of rotating disk speed and the decrease of temperature and it is considered from the calculated activation energy of iron content that the rate determining step is controlled by mass transfer. Iron content in Fe–Ni electrodeposit varied from 58.33% to 70.45% by increasing current density from 2 to 6 A/dm2. Also, iron content in Fe–Ni–W electrodeposit increased from 59.32% to 70.15%, nickel content decreased from 27.86% to 17.07% and the content of tungsten was almost consistent in the range of 12.78%–12.82% although the current density increases from 1.5 to 5 A/dm2. For the electroforming of micro gear mold, SU–8 mandrel with 550 μm in diameter and 400 μm in height was prepared by UV-lithography processing. Subsequently, Fe–36Ni and Fe–20Ni–13W alloys micro gear molds were electroformed successfully. Surface hardness values of the electroformed micro molds were measured to be HV490 and HV645, respectively.

Semiellipsoid microlens fabrication method using UV proximity printing

We present a new semiellipsoid microlens fabrication method that controls the printing gap in the UV lithography process without thermal reflow. The UV proximity printing method can precisely control the curvature radius ratio of the semiellipsoid microlens in the fabrication process. The proposed fabrication method facilitates mass production to achieve a high-yield and high-coupling semiellipsoid microlens that is suitable to be used in commercial fiber transmission systems. A semiellipsoid microlens can be tipped on a single-mode fiber end to improve power coupling efficiency from laser diodes. The semiellipsoid microlens allows increasing the fiber spot size and numerical aperture. It is very important to control the geometric parameters in the assembly procedure to increase the optical coupling efficiency between the laser diode and single-mode fiber. Wide misalignment tolerance, low loss, and low manufacturing cost could be achieved by the proposed fabrication method. The theoretical model is first developed to predict the optical coupling efficiency for various microstructure geometries of semiellipsoid microlens and assembly parameters in this study. Then, the Taguchi method is applied to obtain the optimal geometric parameters setting. The results show that optical coupling efficiency could be significantly improved by using the optimal geometric parameters setting.

A three-dimensional microstructuring technique exploiting the positive photoresist property

The present paper describes a three-dimensional (3D) thick-photoresist microstructuring technique that exploits the effect of exposure wavelength on dissolution rate distributions in a thick-film diazonaphthoquinone (DNQ) photoresist. In fabricating 3D microstructure with specific applications, it is important to control the spatial dissolution rate distribution in the photoresist layer, since the lithographic performance for 3D microstructuring is largely determined by the details of the dissolution property. To achieve this goal, the effect of exposure wavelength on dissolution rate distributions was applied for 3D microstructuring. The parametric experimental results demonstrated (1) the advantages of the fabrication technique for 3D microstructuring and (2) the necessity of a dedicated simulation approach based on the measured thick-photoresist property for further verification. Thus, a simple and practical photolithography simulation model that makes use of the Fresnel diffraction theory and an empirically characterized DNQ photoresist property was adopted. Simulations revealed good quantitative agreement between the photoresist development profiles of the standard photolithography and the moving-mask UV lithography process. The simulation and experimental results conclude that the g-line (λ = 436 nm) process can reduce the dimensional limitation or complexity of the photolithography process for the 3D microstructuring which leads to nanoscale microstructuring.

Refractive Index Sensor Based on a 1D Photonic Crystal in a Microfluidic Channel

A refractive index sensor has been fabricated in silicon oxynitride by standard UV lithography and dry etching processes. The refractive index sensor consists of a 1D photonic crystal (PhC) embedded in a microfluidic channel addressed by fiber-terminated planar waveguides. Experimental demonstrations performed with several ethanol solutions ranging from a purity of 96.00% (n = 1.36356) to 95.04% (n = 1.36377) yielded a sensitivity (Δλ/Δn) of 836 nm/RIU and a limit of detection (LOD) of 6 × 10−5 RIU, which is, however, still one order of magnitude higher than the theoretical lower limit of the limit of detection 1.3 × 10−6 RIU.

Towards organic light-emitting diode microdisplays with sub-pixel patterning

We report on solution processed top-emitting organic light-emitting diodes (TEOLEDs) that are compatible with TFT- and CMOS-substrates, thus being applicable in full-color microdisplays. In this device geometry TEOLEDs offer highly tunable and controllable color-coordinates. Compared to the standard sRGB-colorspace the color gamut is increased by 18%. The CIE ( Commission internationale de l’éclairage) color coordinates are more saturated in the red and green spectral region and comparable in the blue region. Brightness levels of 1000 cd/m 2 are reached at voltages below 7 V for all colors which is within the operating voltage range of CMOS-backplanes. The polymeric emitters are crosslinkable and can be patterned in a UV-lithography process. The achieved minimum feature size is suitable for high resolution microdisplays.

Magnetic Nanocrystals Modified Epoxy Photoresist for Microfabrication of AFM probes

A novel magnetic nanocomposite based on a negative tone epoxy photoresist and magnetic colloidal Fe2O3 nanocrystals (NCs) has been manufactured. The magnetic properties and the UV-photostructurability of the nanocomposite have been investigated. After the incorporation, the Fe2O3 NCs preserve their magnetism which is conveyed to the photoresist and retained after the UV-lithography process. High aspect ratio 3D microstructures have been fabricated by processing the nanocomposite with conditions comparable to those used for the pure photoresist. AFM probes on the Fe2O3 NC modified photoresist have been fabricated to confirm suitability and applicability of the preparation procedure and of the novel nanocomposite.