Ion-beam Sculpting - FIB Exposure

FIB Exposure

This is the easiest of the techniques, but the least useful. After a hole is milled with an FIB, one can just image the hole (analogous to the TEM technique). The ions stimulate movement on the wafer, and also implant themselves to help close the hole. Unlike the other two methods, the holes closed in this technique are not very circular and smooth. The holes appear jagged under TEM photos. Also, it is much hard to control the size of the hole to the single nanometer regime. Another drawback to this technique is that while imaging the hole, the ion beam is continually sputtering membrane material away. If the beam scan area is large enough, the rate of atoms moving to close the hole will be greater than the rate of sputtering, so the hole will close. If the membrane is too thin or the scan area too small, then the rate of sputtering will win, and the hole will open up.

An alternative ion beam sculpting technique has been developed using a commercially available FIB system. This sculpting method can fabricate symmetrically circular nanopores with smooth edge, and, in addition, it can sculpt multiple nanopores of similar shape and size simultaneously. Dependent on the resolution and working condition of the instrument, this method can produce symmetrically shaped nanopores with diameters below 10 nm.