Index of content:
Volume 34, Issue 6, November 2016
- 60th International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication
- Nanoimprint Lithography
34(2016); http://dx.doi.org/10.1116/1.4961250View Description Hide Description
A two-step replication process chain is developed for a microlens array structure with deep three dimensional (3D) reliefs and sharp features enabling the transfer of a photocured acrylic resist patterns into thermoplastic poly-methyl methacrylate (PMMA) with the same structural polarity via an intermediate stamp. By using ultraviolet (UV)-curable polydimethyl siloxane (PDMS), high fidelity negatives were cast from the original microstructures made by two-photon-polymerization and subsequently replicated into PMMA using thermal imprint. The mechanical properties of the new UV-PDMS (X-34-4184, Shin-Etsu Chemical Company, Ltd.), along with its nearly zero process shrinkage, proved to be highly suitable to replicate both 50 μm high concave features and sharp tips with an apex diameter of 500 nm. The results prove that silicone rubber, despite its elasticity, has specific advantages in thermal imprint in structures where both tall microstructures and submicron surface structures have to be replicated. This way, high fidelity PMMA structures with low defects could be prepared by the optimized processing found in this work to have a replication of 3D masters for further upscaling.
- Optical and Extreme UV (EUV) Lithography
Biases and uncertainties in the use of autocovariance and height–height covariance functions to characterize roughness34(2016); http://dx.doi.org/10.1116/1.4961445View Description Hide Description
Measuring the frequency response of roughness is necessary in many applications, leading to the common use of the power spectral density (PSD) of the roughness. But biases and random uncertainties in the PSD have led some to explore the use of the autocovariance function (ACF) and the height–height covariance function (HHCF) instead. These functions also entail systematic biases and random uncertainties when applied to measured roughness, requiring detailed characterization. A combination of analytical derivations and simulations of rough edges have led to a thorough characterization of these biases and uncertainties for the measurement of line-edge and linewidth roughness of lithographically produced features. The results show that ACF estimation is problematic, but that HHCF estimation is a reasonable alternative to PSD analysis under conditions typical of linewidth roughness measurement in the semiconductor industry.
Nanoimprint-assisted shear exfoliation plus transfer printing for producing transition metal dichalcogenide heterostructures34(2016); http://dx.doi.org/10.1116/1.4961384View Description Hide Description
The authors present a nanofabrication technology capable of producing arrays of transition metal dichalcogenide heterostructures that are needed for a broad range of nanoelectronic and optoelectronic device applications. This nanofabrication approach uniquely combines nanoimprint-assisted shear exfoliation (NASE) and transfer printing (TP). Using this NASE + TP method, the authors have demonstrated production of WSe2/MoS2 heterostructure arrays with a high uniformity in feature thicknesses (relative standard deviation <12%). The authors have also created photodiode devices based on such WSe2/MoS2 heterostructures, which exhibit significantly enhanced degrees of current rectification as well as photovoltaic responses in comparison with pure WSe2 devices. Such results indicate that a sizable built-in potential is formed at the pristine WSe2/MoS2 interface. This work advances the top-down approaches for manufacturing high-quality functional heterostructures based on emerging layered semiconductors.
- Nanofabrication & Biology
Design, fabrication, and characterization of polymer-based cantilever probes for atomic force microscopes34(2016); http://dx.doi.org/10.1116/1.4960726View Description Hide Description
Micromachined polymer-based cantilever probes have been proposed for atomic force microscopes (AFMs) in order to enable noninvasive, rapid high-resolution topography imaging and mechanical measurements of live biological samples. Polymer-based probes developed to date still consist of a rather stiff cantilever with a relatively high spring constant prone to causing deformation and/or distortion of biological sample surfaces during scanning and a rather blunt tip that limits high-resolution topography imaging. This paper reports the design, fabrication, and characterization of soft polymer-based AFM probes. The proposed probe design and fabrication process utilize an acrylic polymer as the structural material, sequential depositions of low and high viscosity acrylic polymers, and a properly patterned optical reflection coating in order to achieve low effective spring constants (less than 0.01 N/m), relatively small tip radii (as small as 40 nm), and relatively low strain gradient (around 10−4/μm). The fabricated polymer AFM probes are calibrated and characterized through experiments and used to obtain AFM height and deflection images of a live mammalian cell in liquid. Experimental results show that the above design specifications have been successfully achieved.