Fabrication and characterization of polymeric microfiltration membranes using aperture array lithography

An ion beam aperture array lithography process was employed to fabricate highly ordered polymeric microfiltration membranes with pores that were nearly cylindrical and uniform in size. In this process, a stencil mask, containing a periodic array of circular openings (the aperture array) was irradiated by a broad beam of energetic (30 keV) helium ions. The ions passing through the openings exposed a resist on a substrate that was placed in close proximity thereby faithfully replicating the mask pattern. Over one hundred filters with either 200 or 350 nm diameter pore and pore densities varying from 2.5 × 107 to 4 × 108 #/cm2 were fabricated during the course of this study. Electron microscopy revealed that they all had highly uniform and equally spaced pores without any that overlapped. Additionally, the coefficient of variation of the pore diameter was less than 7% for all samples investigated revealing a very narrow pore size distribution in these membranes as well as a high degree of control of the lithography process. The effective filtration area of individual membranes manufactured in this study was only 0.25 cm2. However, we also show that our current manufacturing process can be scaled-up to fabricate larger areas at high throughput by employing larger masks.