Abstract
Micro- and nanostructures with three-dimensional (3D) shapes are needed for a variety of applications in optics and fluidics where structures with both smooth and sharp features enhance the performance and functionality. We present a novel method for the generation of true 3D surfaces based on thermally activated selective topography equilibration (TASTE). This technique allows generating almost arbitrary sloped, convex and concave profiles in the same polymer film with dimensions in micro- and nanometer scale. We describe its principal mechanism exemplified by pre-patterned poly (methyl methacrylate) resist which is exposed to high energy electrons prior to a thermal annealing step enabling the selective transformation of stepped contours into smooth surfaces. From this we conclude, that TASTE not only offers an enormous degree of freedom for future process variations, but also will advance the patterning capabilities of current standard 3D micro- and nanofabrication methods.
Highlights
Current applications in micro- and nanotechnology mainly use binary surface topographies provided by state-of-the-art planar fabrication processes
By implementing the thermally activated selective topography equilibration (TASTE) method, we demonstrate the possibility to generate truly 3D shaped topographies with decreased technical effort while the geometrical diversity is enhanced at the same time
1.1 Background: Fundamental working principle As fundamental aspect of TASTE, we have previously identified the local variations of viscosity in the electronbeam exposed poly(methyl methacrylate) resist (PMMA) resist during the heating step, which originates from the dose dependent reduction in molecular weight Weight-averaged molecular weight (Mw) and glass transition temperature Tg of the polymer
Summary
Current applications in micro- and nanotechnology mainly use binary (i.e. two-level) surface topographies provided by state-of-the-art planar fabrication processes. 3D topographies are often approximated by steps with adapted widths and heights which resemble provisional and quasi-3D contours In this case, viable pattern fidelity is connected to high process complexity since non-continuous multilevel features need multiple lithographic and etching [5] or electroplating steps [6]. Aiming for a versatile and robust process, our investigations were focused on defining thresholds which enhance the selectivity in reflow behavior for a range of surface topographies, i.e. a selective transformation of structures into defined contours while others remain unaltered. For this we have analyzed the specific correlation between Mw and resulting Tg of the exemplary PMMA resist used in this work
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