Nanoimprint lithography (NIL) is a patterning technique that has emerged as one of the most promising technologies for high-throughput nanoscale replication. [1,2] Several applications in electronics, photonics, magnetic devices, and the biological field have been developed using this simple, low-cost, and high-resolution technique. In the biological field, DNA, [3] proteins, [4][5][6] and guides for molecular motors have been patterned; [7] nanowire arrays have been fabricated for electronic applications; [8] new magnetic devices, such as patterned magnetic media [9,10] and high density quantized magnetic discs, [11] have been engineered; and wire grid polarizers, [12,13] lightemitting diodes, [14,15] and diffractive optical elements [16] have been developed for photonics. The success of NIL as a next generation lithographic technique strongly depends on the research for new materials that are better suited as the nanoimprint resist. Because imprint lithography makes a conformal replica of surface relief patterns by mechanical embossing, the resist materials used in imprinting should be deformed easily under an applied pressure. The most commonly used materials in the original NIL scheme are thermal plastic polymers, which become viscous fluids when heated above their glass transition temperatures (T g ). However the viscosity of the heated polymers is typically high and thus the imprinting process requires significant pressure. In addition, these thermal plastic resists normally have a high tendency to stick to the mold because of non-optimized chemistry and orientation of the polymer backbone structures, which seriously affects the fidelity and quality of the pattern definition. Furthermore they do not offer the necessary etch resistance. Therefore, a nanoimprint resist system with combined mold-release and etch-resistance properties that allows fast and precise nanopatterning is highly desirable.Thermally curable monomers are very attractive materials for nanoimprint applications because they present in the liquid state, making it possible for them to be imprinted in a short period of time under low pressure and temperature, in sharp contrast to thermal plastic polymers. As one of these materials, poly(dimethylsiloxane) (PDMS) has previously been used by several research groups for micropatterning, mainly in the context of soft lithography, [17][18][19][20][21] and has found numerous applications in fields as diverse as microelectrochemical systems (MEMS), biotechnology, photonics, and nanoelectronics. In addition to its well known transparency to UV and visible light along with its good biocompatibility, it has a low surface energy (18-21 mN m -1 ) [22] that allows easy mold release without causing any structural damage to the imprinted structures; moreover, it posses a high resistance to oxygen plasma because of a higher silicon content. However, the PDMS material made from commercial Sylgard 184 as precursor is not suitable for nanoimprint applications because of two significant drawbacks. Firstly, its cur...
Epoxysilsesquioxane (SSQ)-based materials have been developed as patterning layers for large-area and high-resolution nanoimprinting. The SSQ polymers, poly(methyl-co-3-glycidoxypropyl) silsesquioxanes (T(Me)T(Ep)), poly(phenyl-co-3-glycidoxypropyl) silsesquioxanes (T(Ph)T(Ep)), and poly(phenyl-co-3-glycidoxypropyl-co-perfluorooctyl) silsesquioxanes (T(Ph)T(Ep)T(Fluo)), were precisely designed and synthesized by incorporating the necessary functional groups onto the SSQ backbone. The materials possess a variety of characteristics desirable for NIL, such as great coatability, high modulus, good mold release, and excellent dry etch resistance. In particular, the presence of epoxy functional groups allows the resists to be solidified within seconds under UV exposure at room temperature, and the presence of the fluoroalkyl groups in the SSQ resins greatly facilitate mold release after the imprint process. In addition, the absence of metal in the resins makes the materials highly compatible with applications involving Si CMOS integrated circuits fabrication.
In this study, we report a new method to fabricate a wire grid polarizer (WGP) that greatly relaxes the requirement on patterning and etching, and can be easily applied to produce flexible WGPs. The technique is to pattern a high aspect ratio and narrow linewidth grating by nanoimprint lithography followed by two angled aluminum depositions in opposite directions to produce the narrow spacing between the aluminum lines required for a visible band WGP. Anisotropic reactive ion etching is used to remove the aluminum deposited at the top of the grating but leave the aluminum layer on the grating sidewalls, thereby forming a metal wire grid with much smaller spacings than a lithographically defined grating. As a result, the fabricated WGP showed good performance in a wide range of visible wavelength.
Recently, a technique for calibrating the modulation transfer function (MTF) of a broad variety of metrology instrumentation has been demonstrated. This technique is based on test samples structured as one-dimensional binary pseudo-random (BPR) sequences and two-dimensional BPR arrays (BPRAs). The inherent power spectral density of BPR gratings (sequences) and arrays has a deterministic white-noise-like character that allows direct determination of the MTF with uniform sensitivity over the entire spatial frequency range and field-of-view of an instrument. As such, the BPR samples satisfy the characteristics of a test standard: functionality, ease of specification and fabrication, reproducibility, and low sensitivity to manufacturing error. Here we discuss our recent developments directed to the optimization of the sample design, fabrication, application, and data processing procedures, suitable for thorough characterization of large aperture optical interferometers. Compared with the previous coded-aperture based design, the improved, 'highly randomized' BPRA pattern of the new test standard provides better accuracy and reliability of instrument MTF and aberration characterization, and enables operation optimization of large aperture optical interferometers. We describe the pattern generation algorithm and tests to verify the compliance to desired BPRA topography. The data acquisition and analysis procedures for different applications of the technique are also discussed.
A novel and robust route for high-throughput, high-performance nanophotonics-based direct imprint of high refractive index and low visible wavelength absorption materials is presented. Sub-10 nm TiO2 nanostructures are fabricated by low-pressure UV-imprinting of an organic-inorganic resist material. Post-imprint thermal annealing allows optical property tuning over a wide range of values. For instance, a refractive index higher than 2.0 and an extinction coefficient close to zero can be achieved in the visible wavelength range. Furthermore, the imprint resist material permits fabrication of crack-free nanopatterned films over large areas and is compatible for fabricating printable photonic structures.
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