We present the inscription and characterization of fiber Bragg gratings (FBGs) in polypropylene coreless cylindrical fibers. Polypropylene material offers several advantages, such as strong chemical resistance, biocompatibility, and high tensibility. Therefore, polypropylene FBGs can be useful for sensing in chemically aggressive environments and in biomedical applications. The coreless, cylindrical polypropylene waveguides used in these experiments had a diameter of 150 μm, typical length up to 20 cm, and a refractive index of 1.49. The inscription was performed in the 1550 nm transparency window by using a phase mask technique and 193 nm excimer laser radiation. Inscribed FBGs demonstrated complex multi-peak reflection spectra due to highly multi-mode nature of the polypropylene waveguides. Due to a high attenuation of the polypropylene, the maximum waveguide FBG interrogation length -in reflection- was 6 cm. Gratings characterization demonstrated a strain sensitivity of 0.9 pm/με, a temperature sensitivity of -60.4 pm/°C and humidity-insensitive behavior.
High quality poly(methyl methacrylate) (PMMA) thin nanocomposite films doped with different concentration of silver (Ag) nanoparticles are demonstrated. SEM and TEM confirmed the presence of Ag-PMMA nanocomposites with excellent dispersion of Ag nanoparticles into the PMMA matrix and nanoparticles with an average size of 9 nm. By using a direct Laser writing system with a continuous wave 405 nm diode Laser source the films were exposed, allowing the formation of hole-like or linear patterns in the sub 200nm regime, using a 280nm FWHM sized laser spot, demonstrating, for the first time, the potential for sub-diffraction limit laser processing in such 2-material composite systems.
Polymeric materials with an imaging chemistry based on the main chain cleavage under the influence of photogenerated acid are a promising resist platform for EUV lithography. Backbone scission resist materials are, in principle, capable of creating very small structures due to the fact that the removing parts can have dimensions in the order of the monomers that they consist of. Nevertheless, in the case of the commonly used non-chemically amplified materials of this type, issues like sensitivity and poor etch resistance limit their applications, whereas inadequate etch resistance and non-satisfactory process reliability are the usual problems encountered in acid-catalyzed materials based on main chain scission. In this work, we report on optimization of the formulation of new high-sensitive polymeric materials for EUV lithography by tuning the ratio between the photoacid generator (PAG) and the base quencher. In our material design, the acid-catalyzed chain cleavable polymers contain very sensitive acid-labile bonds in their backbone while they remain intact in alkaline ambient. These photoresists were evaluated with several PAG and base quencher (BQ) loadings. The PAG ratio spans from 4% to 7% with respect to polymer weights, whereas the BQ ratio tuned to 5%, 10%, and 15% with respect to PAG weight. High-performance patterning capabilities were achieved for linesspaces down to 22 nm half-pitch using EUV interference lithography. We report linewidth roughness versus dose-to-size for 25 nm and 22 nm half-pitch for different PAG and BQ loadings and provide a comparison.
The main target of the current work was to develop new sensitive polymeric materials for lithographic applications, focusing in particular to EUV lithography, the main chain of which is cleaved under the influence of photogenerated acid. Resist materials based on the cleavage of polymer main chain are in principle capable to create very small structures, to the dimensions of the monomers that they consist of. Nevertheless, in the case of the commonly used nonchemically amplified materials of this type issues like sensitivity and poor etch resistance limit their areas of application, whereas inadequate etch resistance and non- satisfactory process reliability are the usual problems encountered in acid catalysed materials based on main chain scission. In our material design the acid catalyzed chain cleavable polymers contain very sensitive moieties in their backbone while they remain intact in alkaline ambient. These newly synthesized polymers bear in addition suitable functional groups for the achievement of desirable lithographic characteristics (thermal stability, acceptable glass transition temperature, etch resistance, proper dissolution behavior, adhesion to the substrate). Our approach for achieving acceptable etch resistance, a main drawback in other main chain cleavable resists, is based on the introduction of polyaromatic hydrocarbons in the polymeric backbone, whereas the incorporation of an inorganic component further enhances the etch resistance. Single component systems can also be designed following the proposed approach by the incorporation of suitable PAGs and base quencher molecules in the main chain. Resist formulations based on a random copolymer designed according to the described rules evaluated in EUV exhibit ultrahigh sensitivity, capability for high resolution patterning and overall processing characteristics that make them strong candidates for industrial use upon further optimization.
In this work, direct-write, high-resolution multiphoton photolithography using doped random methacrylic co-polymer thin films is demonstrated, using a continuous wave ultraviolet (UV) 375 nm diode laser source. The random copolymers are specifically designed for enhancing resolution and addressing issues arising from laser ablation processes, such as the berm-formation around the created holes in the film, which can be accessed by tuning the polymeric material properties including Tg, surface adhesion etc. The methacrylic copolymer is composed of monomers, each of them especially selected to improve individual properties. The material formulations comprise perylene molecules absorbing at the exposure wavelength where the polymeric matrix is transparent. It was found that if the radiation intensity exceeds a certain threshold, the perylene molecules transfer the absorbed light energy to the acrylate polymer matrix leading to polymer degradation and ablation of the exposed areas. The non-linear nature of the light absorption and energy transfer processes resulted in the creation of holes with critical dimensions well below the used wavelength reaching the sub 50 nm domain. Arrays of holes having various dimensions were fabricated in the laser ablation experiments using a directwrite laser system developed specifically for the purposes of this project.
The main target of the current work was to develop new polymeric materials for lithographic applications, the main chain of which is cleaved under the influence of photogenerated acid. Acetals have been chosen as functional groups in the main polymer chain since they can be cleaved in the presence of an acid while they remain untouched in alkaline ambient. The synthesized polymers were designed to bear in addition suitable functional groups for the achievement of desirable lithographic characteristics (thermal stability, acceptable glass transition temperature, etch resistance, proper dissolution behaviour). The synthesis was carried out via polyaddition of a vinyloxyl compound and a diol compound to produce novel polymers with acetal repeating units in their backbone. We chose polyaromatic hydrocarbons as diol units to achieve increased etch resistance. In addition, the polyaromatic units allow exposure at 193 nm as well, where the absorption of simple aromatics is prohibitively high. Good solubility and increased surface adhesion were achieved by choosing cycloaliphatic vinyloxyl ethers as the second component for the polyaddition. In addition, the same route can be followed to incorporate chromophores that can tune the resist absorbance in different spectral regions. Furthermore, single component systems can be designed following this approach by the incorporation of suitable PAGs in the main chain.
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