Laser interference lithography is a low-cost method for the exposure of large surfaces with regular patterns. Using this method, microsieves with a pore size of 65 nm and a pitch of 200 nm have been fabricated. The pores are formed by inverting a square array of photoresist posts with a chromium lift-off process and by subsequent reactive-ion etching using the chromium as an etch mask. The method has wider process latitude than direct formation of holes in the resist layer and the chromium mask allows for etching of pores with vertical sidewalls.
Kuiper, S., van Wolferen, H. A. G. M., van Rijn, C. J. M., Nijdam, W., Krijnen, G. J. M., & Elwenspoek, M. C. (2001). Fabrication of microsieves with sub-micron pore size by laser interference lithography. Journal of micromechanics and microengineering, 11(1), 33-37. https://doi.org/10.1088/0960-1317/11/1/306