Preliminary Investigation of a Sacrificial Process for Fabrication of Polymer Membranes with Sub-Micron Thickness

Here we present a single mask sacrificial molding process that allows ultrathin 2-dimensional membranes to be fabricated using biocompatible polymeric materials. For initial investigations, polycaprolactone (PCL) was chosen as a model material. The process is capable of creating 250-500 nm thin, through-hole PCL membranes with various geometries, pore-sizes and spatial features approaching 2.5 micrometers using contact photolithography. The technique uses a mold created from two layers of lift-off resist (LOR). The upper layer is patterned, while the lower layer acts as a sacrificial release layer for the polymer membrane. For mold fabrication, photoresist on top of the layers of lift-off resist is patterned using conventional photolithography. During development the mask pattern is transferred onto the first LOR layer and the photoresist is removed using acetone, leaving behind a thin mold. The mold is filled with a solution of the desired polymer. Subsequently, both the patterned and lower LOR layers are dissolved by immersion in an alkaline solution. The membrane can be mounted onto support structures pre-release to facilitate handling.