Low-energy focused-ion-beam shape observation and its noise reduction for nanofabrication

Two types of noise from the variable landing-energy focused-ion-beam (FIB) system appeared when FIB was line-scanned on an n-GaAs wafer and implantation-induced damage was estimated by using selective etching and secondary electron microscope (SEM) observation. The first had a rough surface with small craters away from implanted lines and the second had clearly observable scratchiness along implanted lines. Cathode luminescence measurement and auger analysis were performed to estimate beam-tail spreading. Both the long-beam-tail and the scratchy noise probably originated from unintentionally scattered beams in the ion-beam lens column and/or neutral particles emitted from the liquid metal ion source. As a result, these noises could be greatly reduced by locating a new aperture at an appropriate position. Using this refined FIB system, low landing-energy-ion-beams should be able to be applied to fabricate high-quality mesoscopic devices.