Nanoporous SiN membranes patterned by wafer-scale nanosphere lithography

Nanoporous SiN membranes are interesting for a number of applications, e.g. stenciling, filtration, or tissue engineering [1-3]. The patterning of the pores requires a high resolution lithographic tool. Focused ion beam milling or e-beam lithography fulfills this requirement. However, they are slow, serial writing techniques and thus wafer-scale writing of nanodot arrays becomes time-consuming and expensive. Alternative parallel, fast and inexpensive tools are, for example, nanoimprint-lithography, interference lithography, block copolymer lithography, or nanosphere lithography (NSL) [4]. For applications where no long-range array order is needed, we show here that NSL using polystyrene (PS) beads provides a fast and efficient tool with sub-μm patterning resolution for the fabrication of large nanoporous membranes. Another advantage is the process flexibility. The size of the PS beads determines the later pore size. It can be changed after the deposition of the beads onto the substrate. The pore density can be controlled by choosing a different original bead size. Thus, within a certain range, the pore size and pore density can be tuned independently of each other.