Christian Neuber

Fast diffusion-limited lyotropic phase transitions studied in situ using continuous flow microfluidics/microfocus-SAXS.

Fast concentration-induced diffusion-limited lyotropic phase transitions can be studied in situ with millisecond time resolution using continuous flow microfluidics in combination with microfocus small-angle X-ray scattering. The method was applied to follow a classical self-assembly sequence where amphiphiles assemble into micelles, which subsequently assemble into an ordered lattice via a disorder/order transition. As a model system we selected the self-assembly of an amphiphilic block copolymer induced by the addition of a nonsolvent. Using microchannel hydrodynamic flow-focusing, large concentration gradients can be generated, leading to a deep quench from the miscible to the microphase-separated state. Within milliseconds the block copolymers assembly via a spinodal microphase separation into micelles, followed by a disorder/order transition into an FCC liquid-crystalline phase with late-stage domain growth and shear-induced domain orientation into a mesocrystal. A comparison with a slow macroscopic near-equilibrium kinetic experiment shows that the fast structural transitions follow a direct pathway to the equilibrium structure without the trapping of metastable states.

Combinatorial Optimization of a Molecular Glass Photoresist System for Electron Beam Lithography

Electron beam lithography is a powerful technique for the production of nanostructures but pattern quality depends on numerous interacting process variables. Orthogonal gradients of resist composition, baking temperatures, and development time as well as dose variations inside writing fields are used to prepare ternary combinatorial libraries for an efficient stepwise optimization of a molecular glass negative tone resist system.

Combinatorial preparation and characterization of thin-film multilayer electro-optical devices

In this article we present a setup for the combinatorial vapor deposition of thin-film multilayer devices as well as methods for the fast and efficient analytic screening of the libraries obtained. The preparation setup is based on a commercially available evaporation chamber equipped with various evaporation sources for both organic and metallic materials. The combinatorial approach is realized by the combination of a rotation stage for the substrate, a five-mask sampler, and an additional mask whose position can be deliberately varied along one axis during the evaporation process. The latter is used to evaporate linear as well as step gradients by continuous or stepwise movement of a shutter mask. The mask sampler allows to define the sectors of the library and to evaporate more complex structures, e.g., an electrode layout. Finally, the simultaneous evaporation of two or more materials enables us to produce layers of varying composition ratio in general and doped materials, in particular. For the control of the evaporation process we have developed an automation software, which is particularly helpful for complex library designs and which grants excellent repeatability of experiments. Efficient and fast characterization of the obtained libraries is realized by (i) a purely optical setup and (ii) an electro-optical setup. (i) The UV/vis reader FLASHScan 530 permits to map out the UV/vis absorbance or fluorescence of the whole library. The UV/vis absorbance is primarily used to determine layer thicknesses and to confirm thickness uniformity across larger regions. The fluorescence measurements are used to determine the composition of layers containing fluorescent dyes. (ii) For a detailed short- and long-term electro-optical analysis we have developed an automated measurement system, which allows the characterization of 8x8 optoelectronic devices and to study their degradation behavior. Both solar cells and organic light-emitting diodes can be tested. Finally, we have developed a data analysis software to extract characteristic values from the huge amount of data and with this facilitate the finding of systematic dependencies.

Tailored star-shaped statistical teroligomers viaATRP for lithographic applications

A series of five star-shaped teroligomers consisting of a saccharose core, and arms, composed of α-gamma butyrolactone methacrylate (GBLMA), methyl adamantyl methacrylate (MAMA) and hydroxyl adamantyl methacrylate (HAMA) with defined arm length and number of arms were prepared via the core-first atom transfer radical polymerization (ATRP) route. The saccharose core was modified with ATRP initiating sites and non-reactive sites, enabling the synthesis of star polymers with a smaller arm number but identical core. Star teroligomers were synthesized with narrow molecular weight distributions with low polydispersity indices (PDIs 50%. The absence of side reaction and the precise achievement of the target molecular weight indicated excellent control over the reaction. A selected star-shaped teroligomer was investigated for the first time as a photoresist material. The delicate conditions of the lithographic process were optimized by a combinatorial approach. The obtained low line edge and line width roughness of the observed pattern demonstrate the potential of the star architecture for this application.

Athermal Azobenzene‐Based Nanoimprint Lithography

A novel nanoimprint lithography technique based on the photofluidization effect of azobenzene materials is presented. The tunable process allows for imprinting under ambient conditions without crosslinking reactions, so that shrinkage of the resist is avoided. Patterning of surfaces in the regime from micrometers down to 100 nm is demonstrated.

Tailored Star Block Copolymer Architecture for High Performance Chemically Amplified Resists

Star block copolymers are demonstrated for their application as a high-performance resist material. This new resist material shows advanced progress in sensitivity and solubility contrast and is finally combinatorially optimized to achieve a 66 nm line/space pattern. The tailored molecular architecture of the star block copolymer is synthesized via core-first atom transfer radical polymerization (ATRP) and shows narrow polydispersity indices below 1.2.

Tailored molecular glass resists for scanning probe lithography

In the presented work solvent-free film preparation from tailored molecular glass resists, their thermal analysis, the characterization of etch resistance for plasma etching transfer processes, and the evaluation of the patterning performance using scanning probe lithography (SPL) tools, in particular electric field and thermal based SPL, are demonstrated. Therefore a series of fully aromatic spiro-based and tris-substituted twisted resist materials were systematically investigated. The materials feature very high glass transition temperatures of up to 173 °C, which allows solvent-free thin film preparation by physical vapor deposition (PVD) due to their high thermal stability. The PVD prepared films offer distinct advantages compared to spin coated films such as no pinholes, defects, or residual solvent domains, which can locally affect the film properties. In addition, PVD prepared films do not need a post apply bake (PAB) and can be precisely prepared in the nanometer range layer thickness. An observed sufficient plasma etching resistance is promising for an efficient pattern transfer even by utilizing only 10 nm thin resist films. Their lithographic resolution potential is demonstrated by a positive and a negative tone patterning using electric field, current controlled scanning probe lithography (EF-CC-SPL) at the Technical University of Ilmenau or thermal scanning probe lithography (tSPL) investigations at the IBM Research - Zurich. High resolution tSPL prepared patterns of 11 nm half pitch and at 4 nm patterning depth are demonstrated.

Synthesis and Properties of Lyotropic para-Linked Aromatic Poly(amic ethyl ester)s

The paper describes the synthesis and structure-property relations of para-linked aromatic poly(amic ethyl ester)s with the intention to realize lyotropic precursor solutions for rigid-rod polyimides. As compared to the commonly used flexible precursors, these preorganized precursors should be superior to obtain perfectly oriented polyimide films, orientation layers, and fibers. The poly(amic ethyl ester)s were synthesized by polycondensation of 2,5-diethylbis-(ethoxycarbonyl)terephthaloyl acid dichloride and several para-functionalized diamines bearing fluoro substituents, bulky side groups, or non-coplanar structures. Certain introduced structural modifications improve the solubility in NMP to concentrations up to 50 wt.-% and lyotropic nematic solutions could be obtained. Polymers without fluoro atoms in the ortho position to the polyamide bond have a strong tendency to form a birefringent gel at room temperature which turns into a shearable lyotropic phase above 50°C. This transformation was studied by temperature dependent FTIR spectroscopy and WAXS. However when the ortho position is fluorinated the precursors form a lyotropic phase at room temperature under shear. The macroscopic surface morphology of the dried gels of concentrated solutions is dramatically affected by the chain stiffness, para-Poly-(amic ester)s show a distinct wormlike morphology, indicating molecular order within the gel, whereas the corresponding flexible meta-poly(amic ester)s show a structureless, smooth surface.

Electric field scanning probe lithography on molecular glass resists using self-actuating, self-sensing cantilever

Within last two years, we have shown the positive-tone, development-less patterning of calixarene molecular glass resists using highly confined electric field, current-controlled scanning probe lithography scheme. Herein, we give a more detailed view insight describing the applied Scanning Probe Lithography (SPL) technology platform applying selfactuating, self-sensing cantilever. The experimental results are supported by first preliminary simulation results estimating the local electric field strength, the electron trajectories, and the current density distribution at the sample surface. In addition, the diameter of Fowler-Nordheim electron beam, emitted from SPL-tip, was calculated as function of the bias voltage for different current set-points and tip radii. In experimental part we show the reproducible writing of meander line patterns as well as the patterning of individual features using specially developed pattern generator software tool.

Combinatorial methods for the optimization of the vapor deposition of polyimide monomers and their polymerization

A combinatorial study on the synthesis and in situ orientation of thin films of aromatic polyimides on different aligning surfaces was carried out. Monomer and polyimide libraries prepared by using a combinatorial approach consisting of step gradients with different thicknesses, sectors with different compositions, and sectors with or without alignment layers were investigated. As aligning surfaces, friction deposited layers of PTFE, rubbed polyimide films, and highly oriented polyimide layers prepared by a shearing technique were used. In addition to 3,3′,4,4′-biphenyldianhydride (BPDA), only para-linked dianhydrides and diamines with different aspect ratios were utilized. Vapor deposition was performed first with individual monomers, then sequentially or by coevaporation of two or more monomers. By using this combinatorial approach, the monomer and polyimide orientation can be optimized by variation of monomer composition, film thickness, and deposition sequence. The resulting films were characterized regarding their thickness and the achieved degree of orientation by polarized FTIR and UV–vis spectroscopy. The highest degree of orientation indicated by a dichroic ratio of nine to ten was observed for 4,4″-diamino-p-terphenyl on PTFE surfaces. For other monomers, dichroic ratios of around two were determined irrespective of the aligning surface, indicating low orientation. It was found that coevaporation of both monomers yields isotropic polyimide films in good quality, whereas sequential evaporation of monomer pairs yields polyimide films with anisotropic properties.