Fabrication of nanoporous silicon dioxide/silicon nitride membranes using etched ion track technique

Abstract

A robust method of fabricating freestanding nanoporous silicon dioxide/silicon nitride membrane on a silicon holder using etched ion track technique was demonstrated in this paper. The basic track etching parameters of silicon dioxide and silicon nitride were studied and appropriate irradiation conditions were obtained. The freestanding membranes were obtained by standard silicon fabrication procedures. The multilayer composite silicon/silicon dioxide/silicon nitride was irradiated by Br ions with fluence of 108–1010cm−2. The latent ion tracks in silicon dioxide were then etched to the silicon nitride layer by aqueous HF solution (4%) to produce conical nanopores. Subsequently, these nanopores in silicon dioxide layer, acting as a mask, were transferred into the silicon nitride layer by reactive ion etching (RIE). Finally, with an extra HF wet etching step, the nanoporous silicon dioxide/silicon nitride membrane can be thinned to nanoporous silicon nitride membrane. The diameter of the nanopores in silicon nitride can be varied by varying the HF wet etching time. Via this method, nanoporous silicon dioxide/silicon nitride membrane with designed pore density and pore diameter of sub 100nm can be achieved.