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Significance statement
Combined grayscale patterning and polymer reflow is an emerging lithography technique for, e.g., micro-nano-structures in optical and fluidic applications. In a recent publication [1], we described the thermoplastic polymer reflow as a creep-like process being governed by surface-energy imbalances. This paper presents a novel, fast and precise modeling approach of the reflow. The huge benefit of our approach is the minimum of required material properties and computational resources. To enhance the understanding of our method, supplemental material (free simulation codes, video) is provided with the journal article [2].
[1] R. Kirchner, A. Schleunitz, H. Schift, Energy-based thermal reflow simulation for 3D polymer shape prediction using Surface Evolver, J. Micromech. Microeng. 24 (2014), 055010 (7pp) [2] With Journal access: ftp://ftp.aip.org/epaps/journ_vac_scitech_b/E-JVTBD9-32-312406/
Vac. Sci. Technol. B32, 06F701(2014);
Robert Kirchner , Helmut Schift.
Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
Abstract
This work demonstrates implementation of the main effects of viscoelastic thermal polymer reflow in an efficient energy and mobility based simulation. The concept is based on a finite-element, soap-film method using the free software SURFACE EVOLVER. Properties of a homogeneous 3D volume are thereby represented by a corresponding 2D surface. The simulation only requires the contact angle between polymer and substrate for infinite long reflow times, obtained from fingerprint experiments, and a mobility value as input. The mobility value is a measure for the polymer-chain mobility and is directly linked to the polymer viscosity. This concept allows for an accurate and fast treatment of the thermomechanically complex polymer behavior close to the glass transition. The simulation time scale is linearly related to the experimental time scale allowing for accelerated-time simulations. Simulation and experiment showed a very good agreement. As a generalized concept, the approach presented here can be used for fast and full 3D shape computation during any complex, energy driven geometry optimization process like polymer reflow, viscoelastic wetting or dewetting and droplet coagulation. This simulation may facilitate a faster uptake of grayscale reflow technologies for industrial processes. Supplementary material supports a quick grasp of the simulation approach.
© 2014 American Vacuum Society
