Influence of shank shape of field ion emitter on gas molecule capture area

Now a day, focused ion beam (FIB) systems equipped with a gallium liquid metal ion source (Ga-LMIS) have been used in the wide areas, e.g., photo-mask repair for semiconductor devices, micro-fabrication for MEMS, sample preparation for TEM and so on. However, contaminations by the irradiated gallium ions are severe problems in these applications, thus for an FIB system in the next generation, a development of a noble gas field ion source (GFIS) with higher angular current density (dl/dOmega) are expected. Recently, the helium ion microscope by adopting a built-up W(111) emitter tip was developed as a powerful apparatus for surface analysis. To obtain an excellent emission properties, the shape of emitter tip having a microscopic protrusion which terminated by a single atom or trimer has been actively researched so far. On the other hand, the shank shape of emitter remains a matter of research for obtaining an ion beam with higher brightness. To improve a dl/dOmega of GFIS, we investigated the relationship between an ion current and a taper angle of emitter shank.