Development of Micro-aperture for Annular Pupil on Electron Optics by Focused Ion Beam Technique

Micro-apertures for annular pupil on electron optics have been developed using a focused ion beam technique to realize an increase in the depth of focus, aberration-free imaging and separation of amplitude and phase images under scanning transmission electron microscopy (STEM). A tantalum plate 30 μm thick was used as the annular pupil material in the present experiment. The apertures were designed with various outer diameters from φ120 μm to φ60 μm and at inner diameter of 80% outer diameter. Fabricated apertures were characterized by a scanning ion-beam microscope and a scanning electron microscope. Apertures were successfully obtained at the designed size, although the slits of the pupils were slightly tapered by the ion-beam etching process. These annular pupils were loaded on a STEM and confirmed to display no charge-up phenomenon by observation of the projection image on a scintillator using a CCD camera.