Atmospheric plasma etching of polymers: A palette of applications in cleaning/ashing, pattern formation, nanotexturing and superhydrophobic surface fabrication

Abstract

Atmospheric Pressure Plasmas (APPs) are promising alternatives to their low-pressure counterparts for material surface treatment due to their potential for cost-effective continuous processing. Here we present for the first time to our knowledge a palette of applications of polymer etching showing the potential of APPs for cleaning/ashing, nanopattern formation, nanotexturing, and hierarchical superhydrophobic surface fabrication using the same plasma source configuration. First, we used a dielectric barrier discharge (DBD) plasma source to study etching/cleaning/ashing of different polymers such as PMMA films and AZ photoresist with lithographic patterns using He/O2 mixtures. We achieved high-rate, uniform etching, indicating the source potential for cleaning/ashing even in ambient air conditions. We have noticed that thick photoresist films are damaged after prolonged etching in air plasmas, a phenomenon resembling photoresist damage observed during low-pressure plasma etching. Second, we applied colloidal lithography with polystyrene (PS) nanoparticles followed by isotropic APP etching in order to form nanopatterns on both Silicon and Polymers. We observed that APP induces “cauliflower-like” nanotexturing of the PS spheres. This nanotexturing in combination with plasma etching of the underlying polymer and the spheres allow the fabrication of hierarchical surfaces. Optimization of plasma etching duration (i.e. hierarchical topography) followed by low-pressure plasma deposition of a low surface energy fluorocarbon (hydrophobic) coating led to the preparation of superhydrophobic surfaces with water contact angle 158° and hysteresis 9° (roll-off behavior).