Fundamental limits of Marangoni-driven patterning

Abstract

We predict the maximum aspect ratio and minimum feature pitch for equal line-space Marangoni-driven patterning (MDP) using analytical and numerical techniques and compare the predicted upper/lower bounds to prior experimental results. MDP is a novel technique that harnesses surface tension gradients to apply topography to thin polymer films. MDP operates by first exposing a polymer film to UV light though a photomask, causing a chemical reaction and a change in surface energy in the exposed regions. By heating the film above its glass transition temperature, surface tension gradients give rise to Marangoni forces, which cause the polymer to flow into the higher surface tension regions and form hill-and-valley topography. This topography could be used either as an etch mask for traditional device fabrication or as a functional coating for improved optical performance, improved adhesion, or antifouling purposes. To understand the full scope of applications for MDP, it is necessary to know the maximum aspect ratio (AR) and minimum feature pitch achievable by this technique, as densely packed, high aspect ratio features are often desirable. To determine these previously unknown limits for equal line-space patterning, we present a model for MDP and solve it analytically and numerically. Using limiting values of physical parameters and engineering constraints, we determine an upper bound for feature aspect ratio and a lower bound on feature pitch. These results are then compared to prior experimental results, showing that the AR can be significantly increased and the pitch can be significantly decreased for MDP. We conclude on the barriers and potential strategies for improving MDP.