Combining nanoimprint lithography and a molecular weight selective thermal reflow for the generation of mixed 3D structures

Abstract

Sloped and stepped 3D structures were added to surface-patterned resists using grey-scale electron beam lithography and thermal reflow. A poly(methyl methacrylate) resist with moderate initial molecular weight of 120 kg/mol was chosen, which enabled processing with both nanoimprint and electron beam lithography. Using proper exposure doses, a molecular weight distribution was generated that allowed a selective thermal postprocessing of the exposed steps while the imprinted gratings on top of the resist were preserved. This allows fabricating mixed structures of microprisms surrounded by large-area nanogratings in the same resist layer. Working stamps were casted from the template pattern and subsequently replicated using thermal nanoimprint. As a possible application, backlight devices with arrays of light outcoupling prisms can be seen. V

Mogul‐Patterned Elastomeric Substrate for Stretchable Electronics

“…Fabrication of Mogul Pattern by Double Photolithography : First, positive PR (ma‐P 1275 HV, Micro Resist Technology GmbH, Germany) was coated on a Si wafer and patterned to reticulated bumps using the first photomask (Section 2 and 3 and Figure S1a, Supporting Information). The patterned positive PR was then reflowed by thermal heating . Second, this pattern was duplicated to the inverse pattern of Ormostamp (Micro Resist Technology GmbH, Germany) on a positive PR surface according to the surface treatments of the antiadhesion and the adhesive treatment on a glass substrate (Taewon Scientific, Korea) for Ormostamp.…”

Selective Surface Smoothening of Polymer Microlenses by Depth Confined Softening

“…This process is termed the “TASTE” process. It opens up lithography‐based reflow to a lot of new 3D contours that were not possible without material contrast . For reducing the surface roughness without modifying the contour of a homogeneous material, one needs a surface sensitive exposure followed by reflow.…”

Complex 3D structures via hybrid processing of SU-8

“…Block-copolymer lithography was combined with wrinkling of grapheme to provide hierarchical structures [8]. Nanoimprint was combined with molecular weight selective thermal reflow to prepare sloped structures, again in PMMA [4]. The preparation of stamps for nanoimprint in SU-8 was demonstrated by combining thermal and UV nanoimprint [9] and by combining thermal nanoimprint with conventional photolithography [10].…”

“…Examples are the embodiment of colors via surface topography (e.g. the famous morpho blue [3]), absorber structures for light harvesting or light management with solar cells or light emitting diodes and out-coupling structures for backlight devices [4]. Typically, such 3D structures comprise combinations of micro-and nano-geometries often realized by a single technique like electron beam lithography (EBL) or focused ion beam exposure (FIB) [5].…”