Stamps For Nanoimprint Lithography Research Articles

Integration of Multi-Lithography Technologies for the Fabrication of Flexible Optical Link

The advancement in demand for high bandwidth energy-efficient communication in the data centre and edge cloud servers needs a viable optical interconnection solution to cope with the demands. Therefore, the presented study describes the concept of flexible multi-mode waveguides (MMWGs) as an optical link for co-packaged optics. It evaluates three lithography technologies; UV-lithography, 2 photon polymerization direct laser writing process (2PP-DLW), and nano-imprint lithography (NIL) for the fabrication of flexible MM-WGs. The UV-lithography and 2PP-DLW process were evaluated for the fabrication of MM-WGs and micro-mirrors, respectively, for the master pattern of the NIL stamp. The NIL evaluates the imprinting of the MM-WGs with micro-mirrors at either end on the flexible and transparent PEN substrates with a low-loss OrmoClad lower cladding layer. There are five different crosssections from 10x10 μm2 to 50x50 μm2 of MM-WGs with micromirrors were imprinted. Additionally, it presents the importance of integrating multi-lithography technologies to fabricate flexible optical links where a 2PP-DLW process shows the best results for printing μm-scale optical components. On the other side, UV-lithography with SU-8 gives the foremost definition of the master for the polymeric MM-WGs. Furthermore, NIL offers the industrial mass-production option alongside prototyping.

Fabrication and Characterization of Nano-Structured ZnS:Cu LED

A wide range of Light Emitting Diodes (LEDs) applications, from general lighting to transmission sources of the Visual Light Communication (VLC) system, makes the LEDs very important to be developed. This research focuses on comparing LED performance due to the variation in surface size and shape of the LED. The research method is carried out with a simulation and an experimental approach. Before the experiment, the LED was simulated with nanopattern variations to determine the best fabrication parameter. The simulation method is carried out using Ansys Lumerical FDTD 2021. The experiment method used to fabricate nanopatterns on the surface of a semiconductor LED layer uses the nanoimprint lithography method. Stamps for nanoimprint lithography are made using Polydimethylsiloxane (PDMS), and the nanopattern sources are obtained from DVD and Blu-ray grating patterns. The characterization of nanoscale patterns was carried out using a Scanning Electron Microscope (SEM). The light emission intensity is measured using a lux meter at a series of emission angles. The results obtained from this research are that the smaller the width and the periodicity of the grating nanopattern, the light produced will be distributed at a wider angle, but the light intensity will decrease; conversely, for a planar surface without a grating nanopattern, level of focus and intensity of light will be higher. In addition, the thicker the ZnS:Cu layer, the better the intensity of the light produced.

Mastering of NIL Stamps with Undercut T-Shaped Features from Single Layer to Multilayer Stamps.

Biomimetic structures such as structural colors demand a fabrication technology of complex three-dimensional nanostructures on large areas. Nanoimprint lithography (NIL) is capable of large area replication of three-dimensional structures, but the master stamp fabrication is often a bottleneck. We have demonstrated different approaches allowing for the generation of sophisticated undercut T-shaped masters for NIL replication. With a layer-stack of phase transition material (PTM) on poly-Si, we have demonstrated the successful fabrication of a single layer undercut T-shaped structure. With a multilayer-stack of silicon oxide on silicon, we have shown the successful fabrication of a multilayer undercut T-shaped structures. For patterning optical lithography, electron beam lithography and nanoimprint lithography have been compared and have yielded structures from 10 µm down to 300 nm. The multilayer undercut T-shaped structures closely resemble the geometry of the surface of a Morpho butterfly, and may be used in future to replicate structural colors on artificial surfaces.

Optimal Design of Narrow Line‐Width Front Contact Grid Pattern for Silicon Solar Cells and Low‐Cost Fabrication of Electroless Nickel Plated Imprint Lithography Hard Stamp

Herein, a systematic investigation on the design and development of a cost‐effective nickel hard stamp suitable for fabrication of a new front‐side metallization pattern to reduce the shadow losses in solar cells is demonstrated. Finite element analysis (FEA)–based simulations indicate an optimal finger width of ≈20 μm with interfinger spacing of 1000 μm which can effectively enhance solar cell efficiency by ≈1% due to reduced shadow loss. The optimal grid design is further patterned by means of nanoimprint lithography (NIL) followed by an electroless deposition method. A cost‐effective, electroless deposited nickel hard template is developed for NIL patterning using UV pattern transfer. To avoid the physical damages during the imprinting process and improve the durability of the NIL stamp, silane‐based antiadhesive coating is used which can withstand up to 18 cycles of imprinting process. The nickel hard stamp exhibits improved hardness of 5.63 GPa and roughness of 8 nm and is used to transfer the narrow‐line width patterns during the imprinting process. The proposed industry‐ready technology overcomes the limitations of the existing screen printing process pertaining to the formation of high‐aspect‐ratio narrow line‐width finger grid patterns.

Multiphysics modelling of manufacturing processes: A review

Numerical modelling is increasingly supporting the analysis and optimization of manufacturing processes in the production industry. Even if being mostly applied to multistep processes, single process steps may be so complex by nature that the needed models to describe them must include multiphysics. On the other hand, processes which inherently may seem multiphysical by nature might sometimes be modelled by considerably simpler models if the problem at hand can be somehow adequately simplified. In the present article, examples of this will be presented. The cases are chosen with the aim of showing the diversity in the field of modelling of manufacturing processes as regards process, materials, generic disciplines as well as length scales: (1) modelling of tape casting for thin ceramic layers, (2) modelling the flow of polymers in extrusion, (3) modelling the deformation process of flexible stamps for nanoimprint lithography, (4) modelling manufacturing of composite parts and (5) modelling the selective la...

Polymerization related deformations in multilayer soft stamps for nanoimprint

This paper presents a study concerning the macroscale deformation of soft stamps for nanoimprint lithography. Composite stamps consisting of two or three layers were prepared with varying process parameters, and the bow of the stamps was investigated with an optical profilometer. Deflection measurements were compared with results from a mechanical model in order to prove its validity. The composite stamps were prepared from polydimethylsiloxane (S-PDMS) and OrmoStamp® layers on different substrate materials (silicon or AF-32-glass). The influence of selected preparation parameters on the deformation was investigated, such as layer thickness, curing, and hardbake temperatures, as well as UV-exposure intensities. It is discussed how an appropriate choice of preparation parameters can reduce the deformation, too. By decreasing the curing intensity of a thin OrmoStamp layer, coated on top of a silicon wafer, from 200 mW/cm2 to 2 mW/cm2, the deformation was reduced from 6 μm to 0. It is shown that the mechanical model is capable of predicting the deformation of composite stamps consisting of OrmoStamp layers on top of a silicon substrate. Further on, deformation results for S-PDMS top layers are presented and discussed. As a promising process option for the reduction of stamp deformations, a new, room temperature curable PDMS recipe is introduced. For composite stamps prepared with this material, the deformation value was reduced below 10 μm, compared to values ranging from 10 μm up to 127 μm for thermally cured S-PDMS (50 °C or 70 °C). Finally, different two-layer stamps were coated with an additional third layer and measured again, in order to investigate the deflection for tri-layered cases. The research is of high relevance for the fabrication and application of substrate conformal imprint lithography stamps with minimized deflection.

Synthesis and characterization of surface patterned nanoimprinted in1–xCrxP/P(VDF‐TrFE) nanocomposite films for solar cell application potential

Nanoimprinted nanocomposites based on the inclusion of semiconductor quantum dots (QDs) into ferroelectric polymer matrix have shown a paramount encouragement owing to their versatile applications, such as field effect transistors, lasers, LEDs, bio‐probes, metal ion sensors, and photovoltaic devices. Here, we have developed a novel approach to fabricate nanoimprinted In1–xCrxP/P(VDF‐TrFE) nanocomposite films based on the nanoimprint lithography stamp technique for the first time. In1–xCrxP QDs have been prepared by colloidal technique at various contents of Cr ions from 1 at% to 9 at%. These QDs were doped into P(VDF‐TrFE). The prepared nanocomposite films were characterized by X‐ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, Fourier transform spectroscopy, and atomic force microscopy. The thermal properties were investigated by thermogravimetric and differential scanning calorimetry. The inclusion of the In1–xCrxP QDs into the P(VDF‐TrFE) nanocomposites resulted in an enhancement of the thermal stability, an increase of the melting temperature and decrease of the Curie temperature. The nanoimprinted In0.91Cr0.09P/P(VDF‐TrFE) nanocomposite film showed high photocurrent response. The generated electromotive force, emf, in the nanoimprinted films was five times greater than the flat deposited film. Therefore, the developed surface pattern nanocomposite film based on In1–xCrxP/P(VDF‐TrFE) nanocomposite will open a new avenue for the flexible solar cell application potential. POLYM. COMPOS., 40:E136–E145, 2019. © 2017 Society of Plastics Engineers

Fast fabrication of TiO2 hard stamps for nanoimprint lithography

The fabrication of imprinting stamps plays a vital role in the nanoimprinting lithography. In this work, we proposed a facile method to fabricate TiO2 hard stamp by patterning sol-gel films. A polydimethysiloxane (PDMS) soft stamp with highly ordered micropit array was used as an original stamp to imprint the TiO2 sol which was spin coated on a quartz wafer. The nano-hardness and Young’s modulus of TiO2 hard stamp are in the range of 7.7–10.0GPa and 118.9–130.0GPa, which is much higher than the conventional PDMS material. Afterwards the TiO2 hard stamps are demonstrated in both UV and hot embossing lithography with a promising life cycle. The proposed stamp can be extended to other metal oxides, which possesses a promising prospective for large scale patterning because of the low cost and excellent mechanical durability.

Model for large-area monolayer coverage of polystyrene nanospheres by spin coating

Nanosphere lithography, an inexpensive and high throughput technique capable of producing nanostructure (below 100 nm feature size) arrays, relies on the formation of a monolayer of self-assembled nanospheres, followed by custom-etching to produce nanometre size features on large-area substrates. A theoretical model underpinning the self-ordering process by centrifugation is proposed to describe the interplay between the spin speed and solution concentration. The model describes the deposition of a dense and uniform monolayer by the implicit contribution of gravity, centrifugal force and surface tension, which can be accounted for using only the spin speed and the solid/liquid volume ratio. We demonstrate that the spin recipe for the monolayer formation can be represented as a pathway on a 2D phase plane. The model accounts for the ratio of polystyrene nanospheres (300 nm), water, methanol and surfactant in the solution, crucial for large area uniform and periodic monolayer deposition. The monolayer is exploited to create arrays of nanoscale features using ‘short’ or ‘extended’ reactive ion etching to produce 30–60 nm (diameter) nanodots or 100–200 nm (diameter) nanoholes over the entire substrate, respectively. The nanostructures were subsequently utilized to create master stamps for nanoimprint lithography.

Nanoscale silicon substrate patterns from self-assembly of cylinder forming poly(styrene)-block-poly(dimethylsiloxane) block copolymer on silane functionalized surfaces

Poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) is an excellent block copolymer (BCP) system for self-assembly and inorganic template fabrication because of its high Flory–Huggins parameter (χ ∼ 0.26) at room temperature in comparison to other BCPs, and high selective etch contrast between PS and PDMS block for nanopatterning. In this work, self-assembly in PS-b-PDMS BCP is achieved by combining hydroxyl-terminated poly(dimethylsiloxane) (PDMS-OH) brush surfaces with solvent vapor annealing. As an alternative to standard brush chemistry, we report a simple method based on the use of surfaces functionalized with silane-based self-assembled monolayers (SAMs). A solution-based approach to SAM formation was adopted in this investigation. The influence of the SAM-modified surfaces upon BCP films was compared with polymer brush-based surfaces. The cylinder forming PS-b-PDMS BCP and PDMS-OH polymer brush were synthesized by sequential living anionic polymerization. It was observed that silane SAMs provided the appropriate surface chemistry which, when combined with solvent annealing, led to microphase segregation in the BCP. It was also demonstrated that orientation of the PDMS cylinders may be controlled by judicious choice of the appropriate silane. The PDMS patterns were successfully used as an on-chip etch mask to transfer the BCP pattern to underlying silicon substrate with sub-25 nm silicon nanoscale features. This alternative SAM/BCP approach to nanopattern formation shows promising results, pertinent in the field of nanotechnology, and with much potential for application, such as in the fabrication of nanoimprint lithography stamps, nanofluidic devices or in narrow and multilevel interconnected lines.

Soft Graphoepitaxy for Large Area Directed Self‐Assembly of Polystyrene‐block‐Poly(dimethylsiloxane) Block Copolymer on Nanopatterned POSS Substrates Fabricated by Nanoimprint Lithography

Polyhedral oligomeric silsequioxane (POSS) derivatives have been successfully employed as substrates for graphoepitaxial directed self‐assembly (DSA) of block copolymers (BCPs). Tailored POSS materials of tuned surface chemistry are subject to nanoimprint lithography (NIL) resulting in topographically patterned substrates with dimensions commensurate with the BCP block length. A cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) BCP is synthesized by sequential living anionic polymerization of styrene and hexamethylcyclotrisiloxane. The patterned POSS materials provide a surface chemistry and topography for DSA of this BCP and after solvent annealing the BCP shows well‐ordered microphase segregation. The orientation of the PDMS cylinders to the substrate plane could be controlled within the trench walls by the choice of the POSS materials. The BCP patterns are successfully used as on‐chip etch mask to transfer the pattern to underlying silicon substrate. This soft graphoepitaxy method shows highly promising results as a means to generate lithographic quality patterns by nonconventional methods and could be applied to both hard and soft substrates. The methodology might have application in several fields including device and interconnect fabrication, nanoimprint lithography stamp production, nanofluidic devices, lab‐on‐chip, or in other technologies requiring simple nanodimensional patterns.

Modeling and simulation of the deformation process of PTFE flexible stamps for nanoimprint lithography on curved surfaces

In the presented work, simulations of the deformation process of flexible stamps used for nanoimprint lithography on curved surfaces are presented. The material used for the flexible stamps was polytetrafluoroethylene (PTFE) whose material behavior was found to be viscoelastic–viscoplastic. This behavior was described in a temperature dependent constitutive model consisting of a Zenerbody for the viscoelastic deformation and the Johnson–Cook model for the description of the viscoplastic deformation. The constitutive model was implemented in the general purpose finite element software ABAQUS through a user material subroutine. In order to take the large strains and deformations during the imprinting manufacturing process into account, non-linear geometry was applied in the simulations. The model was first verified through a series of experiments, where nanoimprint lithography on a curved tool insert for injection molding were performed with various process parameters such as temperature, imprinting pressure and flexible stamp thickness. Good agreement between simulations and experimental results was found. The optimum process parameters were then used in the final application, where nanoimprint of a nanostructure giving a color effect was performed numerically and experimentally. Both experiment and simulation showed a mismatch between the defined and measured nanostructures as a result of stretching of the flexible stamp. The model was shown to predict the stretch of the nanostructures with a maximum error of 0.5%, indicating that the model is able to capture the physics of this manufacturing process and can be used to give an insight into the nanoimprinting procedure on curved surfaces.

Focused ion beam induced Ga-contamination—An obstacle for UV-nanoimprint stamp repair?

Ultravoilet (UV)-nanoimprint lithography (NIL) master stamps are subject to wear due to the mechanical nature of the imprint process. To extend the useful lifespan of expensive NIL master stamps, a focused ion beam repair process is highly desirable. Due to the inevitable Ga-staining induced by the focused ion beam processing the transmissivity of repaired NIL stamps is locally degraded. In this work, the authors investigate the impact of Ga-induced transmission losses on the imprint process. Experimental results indicate that the reduced transparency mainly impacts the amplitude of bow deformations in the imprint. These deformations are strongly enhanced by Ga-staining of the master stamp. The authors present a method for quantification of such bow-deformations. The introduced bowing-factor allows to make a qualified decision on whether the occurring deformation is acceptable for the target application. The authors have achieved control over the extent of the Ga-induced bow-deformation by tuning the UV-dose applied during NIL resist exposure. The bowing-factor provides excellent guidance for adapting the required exposure-dose of the NIL resist to reduce the bow-deformation to an acceptable level. With the presented approach, the mitigation of Ga-staining induced defects in the imprint is successfully achieved.

Modeling the constitutive and frictional behavior of PTFE flexible stamps for nanoimprint lithography

In the present work, the deformation on micro-scale of PTFE flexible stamps for nanoimprint lithography is modeled. This is achieved via a combination of proper models for the constitutive behavior as well as the frictional conditions between the deforming PTFE stamp and the steel tool. The model was verified through an experiment, where a PTFE sheet was deformed by a steel sphere mounted in a tensile test machine. Good agreement between simulations and experimental results is found, both regarding force–displacement and corresponding principal strain measurements. As expected, applying the correct frictional behavior between PTFE and steel on micro-scale is shown to be of major importance in order to accurately simulate the strain field in the deformed PTFE stamp.

Fabrication of Single Gold Particle Arrays with Pattern Directed Electrochemical Deposition

A simple and efficient method for fabricating gold nanoparticle (AuNP) arrays is developed. With this method, the AuNP arrays are fabricated by taking an electrochemical deposition (ECD) process on the ITO substrate, which is initially patterned with nanoimprint lithography (NIL). The stamp for NIL is fabricated by the cost-efficient nanosphere lithography (NSL). The size of the AuNPs can be adjusted by varying the potential and duration of ECD. In this work, the diameters of AuNPs are varied from 130 to 420 nm. The AuNP arrays can be readily extended to other conductive substrates, which may be applied for detecting and sensing.

Optimization of 3D patterning by Ga implantation and reactive ion etching (RIE) for nanoimprint lithography (NIL) stamp fabrication

Nanoimprint lithography (NIL) has the unique capability to replicate 3D patterns in one single step. However, to exploit this feature high quality, 3D patterned NIL stamps are required. While grayscale electron-beam lithography suffers from resolution limitations due to proximity effects, focused ion beam (FIB) milling and gas assisted etching is inherently slow. We introduce a new 3D patterning process based on FIB implantation and subsequent reactive ion etching (RIE) for NIL stamp fabrication. The presented process is more than 100 times faster than FIB milling. We demonstrate NIL stamps with complex 3D patterns and resolutions down to 50nm fabricated with this process.

Printed Functionalized Capacitors for Water-Induced Label-Free Detection of DNA Hybridization

In the last decade, new device concepts based on novel fabrication methods have emerged as a powerful and general class of supersensitive sensors for the direct detection of biological and chemical targets. Pushed by the opportunity to activate the physical-chemical phenomena at the nanoscale, novel patterning paradigms have gained nanofabrication accuracy accompanied by the fast development of bottom-up strategies. In this frenetic framework, the combination of some heterogeneous techniques-basically nano-imprint lithography, grafting of functional molecules, and synthesis of new ligands and probes to capture specific biological targets-have gained strong attention as enabling emerging technological mixture to fabricate ultra dense array of specialized sensors. Within the scope of this technological convergence, the paper is basically devoted to describe the processes involved in the production of stamps for nanoimprint lithography, the fabrication of printed array of silicon sensors on the micrometer and sub-micrometer resolution, the subsequent covalent biofunctionalization with single strand DNA and some preliminary electrical detection of the hybridization events via water modulating ac resistance. Among the possible choices, focus was given to planar functionalized capacitors for their intrinsic simple configuration and also because they appeared to be the most promising candidates for mass production in printed device architecture. The paper is based on original results but contains also data and achievements taken from the literature to make the discussion self-contained. © 2011 American Scientific Publishers.

Nanoimprint lithography from CHARPAN Tool exposed master stamps with 12.5 nm hp

The use of working stamps for nanoimprint lithography is highly interesting due to a number of reasons. We present results of such a master stamp – working stamp – imprint process where we achieved a resolution of 12.5nm half pitch. To fabricate master stamps for nanoimprint lithography we use massively parallel ion beam lithography provided by the CHARPAN Tool. Exposed and developed hydrogen silsesquioxane (HSQ) on Si is directly used as a master to fabricate working stamps from UV-curable polymers, which are then used for UV-based nanoimprint lithography.

Focused ion beam–based nanoimprint stamp for replicating micro/nanostructures under low temperature

Focused ion beam (FIB) was employed to fabricate nanoimprint lithography stamps. Complex micro/nanopatterns were fabricated in the stamp, including curved nanograting structures. These micro/nanostructures were then replicated to SU-8 2000.1 resist, with an imprint temperature of 95 °C, which is lower than for conventional imprint polymers. Atomic force microscopy was used to characterize the surface profiles of stamp and replica's and the replication fidelity as well. The results show that nanoimprint with the FIB fabricated stamp can successfully replicate complex micro/nanostructures under low temperature in SU-8.

Eliminating the undercut phenomenon in interference lithography for the fabrication of nano-imprint lithography stamp

We show an easy method to eliminate the undercut profile of photoresist by fabricating periodic nano-patterns on a substrate using interference lithography. An undercut phenomenon occurs frequently on the sidewall of photoresist patterns because of the 3-dimensional intensity distribution generated when two beams are merged to make an interferogram. This is mainly caused by the vertical interference between the incident beam and the one reflected from the surface of a substrate, and bottom-anti-reflection-coating (BARC) material is usually used to prevent beams from being reflected onto the substrate. We propose a simple post-process which helps researchers fabricate well-defined patterns without using BARC material. We developed this process to fabricate stamps for nano-imprint lithography at low cost, and show the results of our nano-imprint process which transfers patterns on a stamp directly through thermal resist.