Enhanced Suppression of the Formation of Porous Silicon Based on Secondary Knocked-On Effect in FIB

In this paper, we report a novel porous silicon (PSi) process to realize controllable micro-to-nano scale features after FIB treatment. It is interested to notice that a "shielding area", where the etching is enhancedly suppressed, exists around the patterns treated by FIB. This shielding area is ascribed to the secondary knocked-on effect during the FIB process. The diameter of shielding area has positive correlation to the voltage used in the FIB step. Also, the diameter of shielding area decreases when the resistivity of the silicon substrate declines. We achieved a shielding area with width of approximately 4um on PSi. Typically, a circular feature of PSi with a diameter as large as 10um is demonstrated for the first time, inside of which dramatically no pore appears at all while outside shielding area remains.